Sapa Extrusion Design Manual

Design manual D e s i g n

m a n u a l

Success with

aluminium pro�les

Cover picture: The aluminium profile on the front cover fits snugly into

the plastic casing shown above. The whole is part of the G H2 ceilingmounted lift produced by Guldmann A/S in Denmark. In use, the lift facilitates the safe handling of patients. By reducing the physical exertion demanded of care staff, it also provides a safer working environment. The lifting unit runs in rails (also aluminium profiles) and the whole assembly weighs only 8.7 kg. Its lifting capacity is 2 00 kg. Besides low weight and high strength, aluminium profiles profiles have have many other design advantages. The profile on the cover is 284 mm wide and has three compartments for housing the lift motor and batteries. The profile’s various channels are purpose-designed to guarantee the rapid and easy fitting of all t he lift’s components. Once the profile has been extruded, the only machining required is cutting to length and the milling of the holes for cables and the lift mechanism. The profile shown here here has a natural anodised finish.

Production: Sapa Profiler AB, Sapa Profiles Ltd and Jonsson & Lindén.

1st UK edition : 2000 copies, current as of May 2007. 2007. This manual can be quoted from provided that the source is clearly stated. Illustrations and pictures may only be reproduced with the consent of Sapa Profiler AB.

Design manual

Sapa Profiles Ltd is a part of an international industrial group developing, manufacturing and marketing aluminium products

with high added value. The company has operations throughout Europe and in the USA and China. The building, automotive and engineering industries are the company’s largest customer segments. For further details, see www.sapagroup.com. 1

CONTENTS

1. Aluminium profiles – the possibilities 2. Aluminium – the properties

Physical properties of some of the most commonly used metals and plastics 3. From bauxite to recycled metal

4–5 6–9 8 10 – 11

12 – 17 The environmental impact of extrusion, surface treatment and machining 13 Product examples 14 – 16 Cars 14 – 15 Underground railway carriages 15 – 16 Window frames 16 – 17 Health 17

4. Environmental impact

4.1 4.2 4.2.1 4.2.2 4.2.3 4.3

5. Aluminium profiles – the applications

Statistics – use by industry Statistics – total consumption 6. Extrusion principles

Solid profiles and hollow profiles 7. Choosing the right alloy

Alloying elements, alloy codes and types At-a-glance alloy selection Heat treatment recommendations Common construction alloys Special alloys

20 – 21 21 22 – 27 22 24 25 26 27 28 – 29

9. General design advice

30 – 34 30 31 31 31 32 32 32 – 33 33 34

35 – 73 Screw ports 35 – 36 Jointing – nuts and bolts 37 Snap-fit joints 38 – 39 Jointing profile to profile 39 – 51 Longitudinal jointing 39 – 40 Telescoping 41 – 42 Latitudinal jointing 42 – 44 Hinges 44 – 46 T-joints 47 – 48 Corner joints 49 – 51 Jointing with other materials 52 – 53 Riveting 54 – 55 End caps 55 – 56 Adhesive bonding 57 – 63 Essential knowledge 57 Joint design 58 Choice of adhesive 59 – 62 Pre-treatment operations in bonding 63 Literature 63 Fusion welding 64 – 67 Most aluminium alloys can be welded 64

10. Jointing

10.1 10.2 10.3 10.4 10.4.1 10.4.2 10.4.3 10.4.4 10.4.5 10.4.6 10.5 10.6 10.7 10.8

10.9 2

18 – 19 18 19

8. Wide profiles with tight tolerances

Recommended wall thickness – guidelines 9.1 Uniform wall thickness 9.1.1 Exceptions 9.2 Soft lines 9.3 Solid profiles if possible 9.4 Fewer cavities in hollow profiles 9.5 Profiles with deep channels 9.6 Heat sinks 9.7 Decorate!

10.10

Methods – MIG, TIG and robot welding 65 Welding economy 66 Filler metals 66 Strength 67 Profile design with regard to fusion welding 67 Friction Stir Welding 68 – 73 An established technology 68 The principle of FSW – illustrations 69 FSW welds – a comparison with MIG 70 Strength, Leakproofness, Repeatability, Corrosion resistance, Limitations 71 Strength of FSW joints, Comparison with MIG and TIG – Reference: The Royal Institute of Technology, Sweden 72 – 73

11. Profile tolerances

Tolerances on dimensions EN 755 -9 Cross-sectional dimensions Alloy groups Tolerances on dimensions other than wall thickness Tolerances on wall thickness of solid and hollow profiles Length Squareness of cut ends Tolerances on form Straightness Convexity – Concavity Contour Twist Angularity Corner and fillet radii EN 12020-2 Cross-sectional dimensions Tolerances on dimensions other than wall thickness Tolerances on wall thickness of solid and hollow profiles Length Squareness of cut ends Length offset for profiles with a thermal barrier Tolerances on form Straightness Convexity – Concavity Contour Twist Angularity Corner and fillet radii 12. Surface classes

Visible surfaces – important information Review profile design carefully The effects of surface treatment Handling and stocking Surface classes 1 – 6, Area of application, Suitable Sapa alloys 13. Thermal break profiles

Sapa’s method Single or double insulation Insulated profile design

74 – 86 75 – 78 75 75 76 77 78 78 78 – 81 79 79 80 80 81 81 82 – 86 82 82 82 83 83 83 83 – 86 83 84 84 85 85 86 87 – 89 87 88 88 88 89 90 – 91 90 90 91

CONTENTS

14. Machining

General 14.1 Stock cutting 14.1.1 Punching/cutting 14.2 Stock removal 14.2.1 Turning 14.2.2 Drilling 14.2.3 Milling 14.2.4 Cutting to length 14.3 Plastic forming 14.3.1 Draw bending 14.3.2 Roller bending 14.3.3 Stretch bending 14.3.4 Press bending 14.4 Threading 14.5 Tolerances Product examples – stock cutting, stock removal and plastic forming 14.6 Hydroforming The principle Example product

15.

Surface treatment

15.1 15.2 15.3

Profile design Mechanical surface treatment Anodising Coloured oxide layers 15.4 Painting 15.4.1 Powder coating Product examples – powder coating 15.4.2 Decoral 15.4.3 Wet painting 15.5 Sapa HM-white 15.6 Screen printing 15.7 Function-specific surfaces 15.8 At-a-glance guide for choice of surface treatments 15.9 Colour guide for anodising

16.

Corrosion

16.1 16.2 16.2.1 16.2.2 16.2.3 16.2.4 16.2.5 16.2.6 16.3 16.4 16.5 16.6 16.7 16.8 16.9 16.10 17.

Aluminium’s corrosion resistance The most common kinds of corrosion Galvanic corrosion Preventing galvanic corrosion Pitting Preventing pitting Crevice corrosion Preventing crevice corrosion Aluminium in open air Aluminium in soil Aluminium in water Corrosion at the water line Aluminium and alkaline building materials Aluminium and chemicals Aluminium and dirt Aluminium and fasteners At-a-glance guide for choosing fasteners Corrosion checklist

Cost-efficiency

17.1

How you, the designer, can influence cost-efficiency

92 – 103 92 – 93 94 94 95 – 96 95 96 96 96 97 – 98 97 97 98 98 99 99

17.2 17.3 18.

121 122 123 – 134 123 123 – 127 124 125 126 126 127 127 128 129 129 130 131 131 131 132 – 133 133 134

139 – 141 The Profile Academy 139 Further sources of knowledge 140 – 141 Sapa Technology 140 Colleges, industry organisations, etc. 141

19. Design

19.1 19.2 19.3 19.4 19.4.1 19.4.2 19.5

136 – 137 138

Knowledge banks

18.1 18.2 18.2.1 18.2.2

100 – 101 102 – 103 102 103 104 – 122 104 105 106 – 109 108 110 – 115 110 – 111 112 – 113 114 – 115 115 116 – 117 118 – 119 120

How you, the purchaser, can influence cost-efficiency Sapa’s vision

19.6 19.6.1 19.6.2 19.7 19.7.1 19.7.2 19.7.3 19.7.4 19.7.5 19.7.6 19.7.7 19.7.8 19.7.9 19.7.10 19.8 19.8.1 19.8.2 19.8.3 19.8.4 19.8.5 19.8.6 19.8.7 19.8.8 19.8.9 19.8.10 19.9 19.9.1 19.9.2 19.9.3 19.9.4 19.9.5

General Design literature Key considerations in aluminium design Cross-sectional shape Asymmetrical profiles – the shear centre Solid or hollow profiles? Design using the partial coefficient method – general Material Material values Partial coefficients Designing General Buckling Effective thickness Reinforced elements Axial force Torsional buckling and lateral-torsional buckling Bending moments Lateral buckling Transverse force Torsion Combined loads Bending instability Concentrated force and support reaction Joints General Force distribution in joints Types of failure in joints using fasteners Nuts and bolts Self-tapping screws Screw ports Open screw port Closed screw ports Tracks for nuts and bolts Rivet joints Welded joints Miscellaneous jointing methods Fatigue General Scope Fatigue load Designing for fatigue Detail types

142 – 163 142 142 142 – 143 143 – 145 143 – 144 144 – 145 145 145 – 146 145 – 146 146 146 – 151 146 146 – 147 147 – 148 148 148 – 149 149 149 – 150 149 – 150 150 150 151 151 151 – 155 151 151 152 152 – 153 153 153 – 154 153 – 154 154 154 154 154 – 155 155 155 – 163 155 155 155 155 – 156 156 – 163

135 – 138 135 – 136 3

“It is what we remember that makes us wise.” Remember to keep this manual readily to hand!

4

1. THE POSSIBILITIES

1. Aluminium profiles

– the possibilities

Aluminium profiles help designers to create unique solutions that satisfy all expectations, hopes and demands. The tooling costs are reasonable, there are few technical limitations and a whole new world of possibilities is opened up for exploration. It is at the design stage that there are so many opportunities to incorporate features that will make the profile easier to machine and easier to fit. Low weight combined with high strength, excellent corrosion resistance and superb finishes are just some of the properties the designer can fine-tune to ensure that the final product meets all specifications. On top of all this, aluminium is easy to recycle and the extrusion process is simple – applying considerable pressure, a heated billet is forced through a die. The resultant profile is shaped exactly like the aperture in the die. This manual is primarily intended for those who would like to gain further insight into success with aluminium profiles. Whenever there is a need for greater help or guidance, Sapa is happy to provide advice and expertise. Few manufacturers can match our depth of knowledge and experience. Contact us and find out for yourself!

5

2. THE PROPERTIES

2. Aluminium

– the properties

Low weight, high strength, superior

malleability, easy machining, excellent

corrosion resistance...

After iron, aluminium is now the second most widely used metal in the world. This is because aluminium has a unique combination of attractive properties. Low weight, high strength, superior malleability, easy machining, excellent corrosion resistance and good thermal and electrical conductivity are amongst aluminium’s most important properties. Aluminium is also very easy to recycle. Weight

With a density of 2.7 g/cm , aluminium is approximately one third as dense as steel. 3

Strength

Aluminium alloys commonly have tensile strengths of between 70 and 700 MPa. The range for alloys used in extrusion is 150 – 300 MPa. Unlike most steel grades, aluminium does not become brittle at low temperatures. Instead, its strength increases. At high temperatures, aluminium’s strength decreases. At temperatures continuously above 100°C, strength is affected to the extent that the weakening must be taken into account. Linear expansion

Compared with other metals, aluminium has a relatively large coefficient of linear expansion. This has to be taken into account in some designs. Malleability

Aluminium’s superior malleability is essential for extrusion. With the metal either hot or cold, this property is also exploited in the rolling of strips and foils, as well as in bending and other forming operations. Machining

Easy to

mill,

drill, cut, punch, bend, weld, bond, tape...

6

Aluminium is easily worked using most machining methods – milling, drilling, cutting, punching, bending, etc. Furthermore, the energy input during machining is low. Jointing

Features facilitating easy jointing are often incorporated into profile design. Fusion welding, Friction Stir Welding, bonding and taping are also used for jointing.

2. THE PROPERTIES

Aluminium combines low density and high strength. These properties are here being used in the decking of a bridge.

These heat sinks exploit aluminium’s high thermal conductivity.

Aluminium has superior malleability. 7

2. THE PROPERTIES

Conductivity

Aluminium is an excellent conductor of heat and electricity. An aluminium conductor weighs approximately half as much as a copper conductor having the same conductivity. Reflectivity

Aluminium is a good reflector of both visible light and radiated heat. Screening – EMC

Tight aluminium boxes can effectively exclude or screen off electromagnetic radiation. The better the conductivity of a material, the better the shielding qualities. Corrosion resistance

The oxide layer is dense and provides excellent corrosion protection.

Aluminium reacts with the oxygen in the air to form an extremely thin layer of oxide. Though it is only some hundredths of a µm thick (1 µm is one thousandth of a millimetre), this layer is dense and provides excellent corrosion protection. The layer is self-repairing if damaged. Anodising increases the thickness of the oxide layer and thus improves the strength of the natural corrosion protection. Where aluminium is used outdoors, thicknesses of between 15 and 25 µm (depending on wear and risk of corrosion) are common. Aluminium is extremely durable in neutral and slightly acid environments. In environments characterised by high acidity or high basicity, corrosion is rapid. Further details are given in chapter 16, “Corrosion”. Non-magnetic material

Aluminium is a non-magnetic (actually paramagnetic) material. To avoid interference of magnetic fields aluminium is often used in magnet X-ray devices. Zero toxicity

After oxygen and silicon, aluminium is the most common element in the Earth’s crust. Aluminium compounds also occur naturally in our food. For further details, see chapter 4, “Environmental impact”. Physical properties of some of the most commonly used metals 1) and plastics Al Density, g/cm3 Melting point,°C Thermal capacity, J/k g, °C Thermal conductivity, W/m, °C Coeff. of linear expansion, x 10 -6/°C El. conductivity, % I.A.C.S. 2) El. resistance, x 10 -9 m Modulus of elasticity, GPa

2.7 658 900 230 24 60 29 70

Fe 7.9 1 540 450 75 12 16 105 220

Cu 8.9 1 083 390 390 16 100 17 120

Zn 7.1 419 390 110 26 30 58 93

Nylon

®

Delrin

(Polyamide 6–6)

(Polyacetal)

1.1 255 1 680 0.23 70 – 100 – – 3

1.4 175 1 470 0.23 80 – 90 – – 3

Table values are for commercially pure metals. 100% I.A.C.S. (International Annealed Copper Standard) is the conductivity that, at 20 °C, corresponds to 58 m/ , mm2.

1) 2)

8

®

2. THE PROPERTIES

Aluminium is easy to work using most machining methods.

Aluminium has excellent resistance in neutral and slightly acid environments.

Weight and strength – aluminium is approximately one third as dense as steel. Aluminium alloys have tensile strengths of between 70 and 700 M Pa. 9

3. THE RAW MATERIAL

3. From bauxite to recycled metal

The Earth’s crust is 8% aluminium.

There is plenty of raw material for the production of aluminium. In a variety of forms, aluminium compounds make up a full 8% of the Earth’s crust. Bauxite

Bauxite is the main starting point in the production of aluminium. It has been estimated that, given the present rate of aluminium production, there is enough bauxite to last another 200 to 400 years. This assumes no increase in the use of recycled aluminium and no further discoveries of bauxite. Bauxite forms when certain aluminium bearing rocks decompose. Its main constituents are aluminium oxides, iron and silicon. The largest and most lucrative bauxite deposits are located around the Equator. Major producers include Australia, Brazil, Jamaica and Surinam. Alumina (Al2O3)

Normally in close proximity to the mine, bauxite is refined into alumina. The next stage, production of aluminium by molten electrolysis of the alumina, is concentrated in countries with good supplies of electricity. The production of 1 kg of aluminium requires around 2 kg of alumina. The production of 2 kg of alumina requires about 4 kg of bauxite. The metal

Due to aluminium’s chemistry, relatively large amounts of energy (primarily electricity) are required to reduce alumina to aluminium. Around 47 MJ (approx. 13 kWh) goes into the molten electrolysis of 1 kg of the metal. However, this investment gives excellent dividends. The energy expended in aluminium production is often recouped several times over. By reducing the weight of vehicles, the use of aluminium reduces fuel consumption (see also chapter 4). Similarly, energy losses in aluminium power lines are comparatively small. Recycling

Aluminium scrap – a valuable raw material.

10

Scrap aluminium is a valuable resource that is set to become even more important. In principle, all scrapped aluminium can be recycled into a new generation of products. With appropriate sorting, scrap aluminium can advantageously be recycled to produce the same sorts of products over and over again. Furthermore, recycling requires only 5% of the original energy input.

3. THE RAW MATERIAL

In today’s environment-conscious society, the recycling of used aluminium products is becoming ever more important and ever more common.

The aluminium cycle

G I N L D I U B

In the aluminium cycle, the metal can be reused for the same purposes

L E C TRI C A L A P P

E A N D

L I C A T I O N

S

MECH AN IC A L T H E R

T R O

D O A N

P S N A R

T

PRODUCTS

A P P L I

AG I N G

P A C K

CASTING

C A T I O

over and over again. Unlike

N

S

many other materials, aluminium does not lose its unique properties.

REMELTING

PRIMARY ALU MI NI UM

Al 2O3 Al 2O3

So easy to recycle: Aluminium is the perfect “eco-metal”. Very little aluminium is lost in the remelting

process. Increased recovery, dismantling and sorting of spent products has led to even greater recycling of aluminium.

11

4. THE ENVIRONMENT

4. Environmental impact All industrial activity consumes natural resources and has an impact on the environment. The aluminium industry is no exception to this. However, using aluminium in preference to other products often has a positive impact. Thus, to gain a true assessment of an aluminium product from the environmental point of view, a life cycle analysis is essential. Several examples are given later in this chapter. Absolute recyclin recycling g

Absolute recycling

– repeatable recycling with maintained quality and high yield.

Aluminium collected for recycling enters an almost never-ending “eco-circle”. This is because very little metal is lost in remelting. On average, losses through oxidation during remelting amount to a few per cent only. Furthermore, the quality of the remelted material is so high that it can be used for the same product over and over again. Hence our use of the term “absolute recycling” – repeatability with maintained quality and high yield. Extrusion

As mentioned in chapter 3, producing aluminium from bauxite requires comparatively large amounts of energy. The manufacture of aluminium profiles, on the other hand, requires relatively little energy. At the web site of EAA (the European European Aluminium Association) you can obtain obtain further information on profile manufacturing and a number of other subjects connected with the use of aluminium and profiles. The address: www.aluminium.org

The remelting works in Sjunnen, Sweden.

12

4.1 EXTRUSION – ENVIRONMENTAL IMPACT

4.1 The environmental impact of extrusion, surface treatment and machining Cutting to length is the main source of noise in factories producing aluminium profiles. This noise has been reduced by screening. Changing the lubricants used on billet end faces has not only improved the quality of air in workshops, but also given cleaner profiles that require less post-extrusion cleaning. A further measure to reduce potentially negative environmental impact is the increased use of gas nitriding nitr iding for the hardening of dies. Dies are now stored s tored with residue aluminium on them, thus minimising the need for cleaning. Similarly, the mineral oil based cooling and cutting fluids previously used in the machining of semi-finished goods have been replaced by water-based products. This has reduced the need to use organic degreasing agents. Sapa no longer uses trichloroethylene for degreasing. The alkaline water solutions used today produce a semi-stable emulsion containing droplets of grease and oil. Drawing off this emulsion extends the life of the degreasing bath and gives a product that can be recycled as, for example, a lubricant for machining operations. The etching process in anodising has been been improved by the use of “neverdump” baths. These consume minimum quantities of chemicals and produce less waste. Used etching baths are a re neutralised. This precipitates the aluminium content as a hydroxide, which is then refined into chloride. To To an increasing extent, the chloride is being used as a flocking agent in water treatment plants. Copper and cobalt salts were were previously used for dyeing profiles during anodising. Again to lessen any potentially negative impact on the environment, these have been replaced by tin salts.

Die cleaning – a closed process producing no waste water.

13

EVERYDAY USE 4.2 ENVIRONMENT – ALUMINIUM IN EVERYDAY

4.2 Product examples 4.2.1 Cars

More and more car manufacturers are using aluminium in preference to steel. It is perfectly possible to replace 182 kg of steel components with 82 kg of aluminium – 100 kg less strain on the engine. If no recycled metals are used, aluminium components require require 2,7 2,740 40 MJ more energy to produce than the steel parts they replace. However, with a typical lifetime of use, the lighter car will require 640 litres less fuel. This is the equivalent of 23,000 MJ. Furthermore, when the content of recycled metal reaches 90%, an aluminium component actually consumes less production energy than its steel counterpart. Environmental benefits

Assuming no recycled steel or aluminium is used: – During the car’s lifetime, the extra energy used in producing aluminium is recouped a good eight times t imes over. – Production of the aluminium components emits 100 100 kg more CO2 than is the case for steel. This higher impact on the environment is made good many times over during the car’s lifetime – the reduced petrol consumption reduces CO2 emissions by 1,500 kg. Total life cycle analysis

The production of a steel bonnet presents a 60% greater total load on the environment than the production of an aluminium bonnet.

Total life cycle analyses underline the energy and environmental benefits resulting from the use of aluminium. Car manufacturers make extensive use of such analyses. In this sector of industry, the Swedish EPS method1) is the most widely used analytical tool. An example is given below. A steel car bonnet is replaced by an aluminium one. This reduces the weight from 18 to 10 kg. Applying the EPS method, the total load on the environment presented by the steel bonnet is around 60% greater than the load presented by the aluminium bonnet. EPS = Environmental Priority Strategies in product design is a practical method for calculating “environmental load”. The method takes into account what happens throughout the manufacture, use and eventual disposal of a product. Calculations are based on the following formula: 1)

Environmental load index x Quantity = ELU (Environmental Load Unit)

An environmental load index is a numerical value corresponding to the load on the environment considered to be presented by a defined quantity/amount of a substance, product or activity.

14

4.2 ENVIRONMENT – ALUMINIUM IN EVERYDAY USE

Space Frame

One of the modern technologies used in the manufacture of car bodies is the Space Frame, a skeleton of aluminium profiles. Covering the frame with aluminium sheets gives weight reductions of up to 200 kg per car. This is double the saving cited on the previous page. As in other applications, replacing steel with aluminium reduces weight. Here, this leads to reductions in petrol consumption and emissions. Other plus points are improved crash-safety, reduced risk of corrosion a nd decreased environmental load. 4.2.2 Underground railway carriages Nearly all modern underground railways use carriages with bodies constructed of longitudinally welded aluminium profiles. In Japan, analyses of real energy consumption have been carried out on the Chiyoda line. The analyses compared the line’s steel-carriaged trains with those having aluminium-bodied carriages. In the latter, 9,450 kg of steel is replaced by 4,000 kg of aluminium.

Energy consumption in the production process 1)

Aluminium Steel Difference

Energy consumption during two years of operation

Steel carriages Aluminium carriages Difference

1)

No recycled metal used.

4,000 x 37.2 2) 9,450 x 9.5 2)

= 148,800 kWh 3) = 89,775 kWh 59,025 kWh 561,200 kWh 489,900 kWh 71,300 kWh

Consumption as estimated by Sapa Technology. 1 kWh = 3.6 MJ.

2) 3)

15

4.2 ENVIRONMENT – ALUMINIUM IN EVERYDAY USE

Energy savings in less than two years

Assuming no use of recycled aluminium or steel, the Chiyoda example shows that, in less than two years, aluminium carriages represent an “energy saving”. Similar real-life analyses in Atlanta (USA) and Germany have given figures of 3 and 1.6 years respectively as the times in which the extra energy used in production is recouped. When the use of recycled metals is taken into consideration, aluminium carriages are clearly more “energy-efficient” even at the production stage. The recycling of aluminium consumes far less energy than the recycling of steel. 4.2.3 Window frames

In Austria, there has been a study in 1991 of the environmental aspects of the use of various materials (aluminium, PVC coated steel, wood and aluminium clad wood) in window frames. The results obtained using the EPS method are summarised below. – Calculated over the entire life cycle of the product, aluminium clad wooden frames present the lowest load on the environment. – In the production phase, wooden frames present unquestionably the lowest environmental load. However, this is more than nullified by the need for regular maintenance/replacement. – Aluminium frames are far superior to plastic coated steel frames. – Frames of plastic coated steel present the largest load on the environment. – The possibility of recycling aluminium with very little energy consumption is a significant factor in aluminium’s good performance.

16

4.3 HEALTH ASPECTS

Conclusion

The use of aluminium in products such as window frames has clearly demonstrable benefits for the environment.

4.3 Health All normal forming and cutting of aluminium has no consequences for human health. However, if worksite ventilation is inadequate, lengthy periods of gas welding can have an effect on the respiratory organs. Before undertaking gas welding, current recommendations and regulations should be studied. Local health and safety bodies are usually able to provide help here. Friction Stir Welding (see pages 68 – 73 of this manual) does not use filler metals or shielding gases. This avoids the problem outlined above. Aluminium is non-toxic

All life on Earth is adapted to its presence – aluminium has always been a natural part of the environment. The soil contains, on average, 7% aluminium (by weight). The use of aluminium products, whether untreated or anodised, presents no health hazards. As an illustration of this, aluminium has been used for decades in kitchen pots and pans. At one time, aluminium was cited as a possible cause of Alzheimer’s disease. However, the leading medical scientists of today consider that there is no such link. It is also worth mentioning that our normal diet includes aluminium. Food and food additives account for roughly 97% of our daily intake of approximately 12 mg. The remaining 3% comes from aluminium products such as kitchen foil and cooking vessels.

Aluminium in the diet: 97% from foodstuffs,

3% from food preparation.

17

5. THE APPLICATIONS

5. Aluminium profiles

– the applications

The purpose of this manual is to give its readers an insight into optimum design using aluminium profiles. Further details and concrete advice are readily available from Sapa. Whatever the field

Whatever the field of operation, it seems that aluminium profiles have something to offer. The transport industry makes extensive use of aluminium profiles in lorries, buses, cars, trains, ships, etc. With increasing demand for lighter vehicles that consume less fuel and place less strain on the environment, the use of profiles is constantly rising. The benefits are clear. Other sectors of industry have also seen the advantages. Profiles are being used in all types of design solutions. Examples include machine parts, a wide range of products for everyday home and office use and equipment used in free time activities. In the electronics industry, aluminium profiles are used in heat sink s, casings, front plates and so on. The building industry uses aluminium profiles in, amongst other things, doors, windows, fascias and glass roofs. The list of Furniture/office Other Transport 39% sectors and applications is long. equipment 8% 10% In all sectors, the demand for recyclability is Building growing ever stronger. No structural material can 24% be more profitably recycled than aluminium. This Electronics Machine parts factor is sure to acquire increasing significance. 10% 9% Aluminium profiles will become more common End use of the aluminium profiles in all industries. In some respects, the use of produced in the Nordic countries in 2000. aluminium and extrusion has really only just begun.

18

5. THE APPLICATIONS

The advantages of aluminium and extrusion

More and more constructors and designers are realising the advantages of extrusion – the freedom it gives them to create precisely the shape that solves the problem, low tooling costs, easy machining, purpose-tailored surface treatment, etc. Furthermore, extrusion technology continues to develop and new production methods such as Friction Stir Welding and hydroforming are adding still further to the possibilities opened up by aluminium profiles. On top of all this, aluminium has a host of unique structural properties. Simply put, aluminium profiles facilitate the creation of efficient designs at competitive prices – exactly the right conditions for new products on new markets.

Profile use is increasing in line with the demand for reduced energy consumption and minimum stress on the environment.

Young metal, young industry

The electrolysis of alumina to produce aluminium was first achieved in 1886. This was the major breakthrough that eventually led to the commercial production of aluminium products. By the turn of the century, world production of primary aluminium had reached around 5,700 tons. In 2001, highlighting the importance of aluminium in modern industrial production, the figure was approximately 24.5 million tons. To give some idea of scale, 24.5 million tons is the combined weight of something over 18 million Volvo S40s. In Sweden, the first attempts to extrude aluminium were made in the middle of the 1920’s. Still in Sweden, it was in 1937 that Metallverken, a company in Finspång, started regular production of profiles. At the same time, Saab began production of aeroplanes in Linköping. Over the next few years, and reaching a peak at the end of the Second World War, Saab made extensive use of aluminium. Since the late 1940’s, the consumption of aluminium and aluminium profiles has risen steadily as shown in the graph below.

MIO Tonnes 30

25

World Production of Primary Aluminium 1950 – 2002

20

15

10

5

0

1950

2002

19

6. EXTRUSION PRINCIPLES

6. Extrusion principles Extrusion starts with aluminium alloy logs. These are cut into billets, which then go into an induction furnace for heating to the right extrusion temperature of 450 – 500°C. Next, applying considerable pressure, each heated billet is forced through a die, the profile emerging rather like toothpaste from a tube. The profile emerges at a speed of 5 – 50 metres per minute and length is normally between 25 and 45 metres. Cooling in air or water commences immediately the profile leaves the die. After cooling, the profile is stretched. This is both to relieve any stress and to give the profile the desired straightness. At the same time, all functionally important dimensions and surface quality are checked. The profile is then cut to a suitable length or to the exact length requested by the customer. The final strength of the material is controlled through natural or artificial ageing. Dies

Dies are made of tool steel (normally SIS 2242). The die aperture, which corresponds to the desired cross section of the profile, is produced by spark erosion. Sapa both makes its own dies and buys in from independent manufacturers.

Billets are heated to the right temperature in an induction furnace. 20

6. EXTRUSION PRINCIPLES

Two main classes

There are two main classes of profile – solid and hollow: Solid profiles are produced using a flat, disc-shaped die. Hollow profiles are produced using a two-part die. In hollow dies, the mandrel (the part that shapes the cavity in the profile), is supported on a bridge. During extrusion, the metal separates around the bridge. The other part of the die shapes the outer contour of the profile. Large and medium-sized profiles are pressed through a die with only one aperture. Smaller profiles can be advantageously pressed through multi-apertured dies – there may be as many as 16 apertures. Die lifetime depends on the shape and desired surface quality of the profile. The cost of replacement dies is covered in the price of the profile.

Dies for solid profiles.

A hollow die.

A profile emerging onto the cooling table.

Stretching relieves profiles of any stress or twisting. 21

7. ALLOYS

7. Choosing the right alloy Pure aluminium is relatively soft. To overcome this, the metal can be alloyed and/or cold worked. Most of the aluminium reaching the marketplace has been alloyed with at least one other element. Sapa uses a long-established international system for identifying aluminium alloys (see the table below). The first digit in the four-digit alloy code identifies the major alloying element. The European standard uses the same codes. The table below gives the broad outline of the systems.

Alloying element

Alloy code

Alloy type

None (pure aluminium)

1000 series

Not hardenable

Copper

2000 series

Hardenable

The 6000 series is by

Manganese

3000 series

Not hardenable

Silicon

4000 series

Not hardenable

far the most widely used in extrusion.

Magnesium

5000 series

Not hardenable

Magnesium + silicon

6000 series

Hardenable

Zinc

7000 series

Hardenable

Other

8000 series

As cold working is the only way to increase the strength of the alloys that cannot be hardened, most of these go for rolling. In extrusion, on the other hand, hardenable alloys are the most commonly used. The 6000 series, which has silicon and magnesium as the alloying elements, is by far the most widely used in extrusion. In Sapa’s 7021 alloy, zinc and magnesium are responsible for the hardening effect. Some alloys use manganese, zirconium or chrome to increase toughness. Iron, which is found in all commercial aluminium, can have a negative effect on toughness and finish (amongst other things) if present in high quantities.

22

7. ALLOYS

Heat treatment

Apart from 1050A, all Sapa alloys are hardenable. Their final strength is thus determined by solution heat treatment and ageing (precipitation hardening). Solution heat treatment is normally carried out during extrusion by carefully controlling the temperature of the emerging profile. Precipitation hardening, which takes a few hours, occurs afterwards in special furnaces. In some circumstances, it may be necessary for the customer to carry out heat treatment. Sapa’s recommendations in these cases are given in the table on page 25. Natural ageing is the spontaneous hardening of solution treated aluminium at room temperature (refer to the table on page 25). Choosing the right alloy

Amongst the factors affecting the choice of the right alloy for an extruded product are: – Strength, finish, suitability for decorative anodising, corrosion resistance, suitability for machining and forming, weldability and production costs. The at-a-glance table on the next page should only be used as a rough guide. In cases of doubt, contact Sapa for advice and guidance. For example, optimum cost-efficiency may sometimes be gained by choosing a comparatively lower strength alloy with higher extrudability.

In cases of doubt, contact Sapa for

advice.

Logs being prepared for extrusion. 23

7. ALLOYS

At-a-glance alloy selection

Relative grading: 3 = top mark Special alloys for Common construction alloys

Property Sapa 6060

Sapa Sapa Sapa Sapa Sapa 6063 6063A 6005 6005A 6082

s l r o a t c c i r u t d c n e l o E c

g n i s t i h d g o i r n B a

Sapa 7021

Sapa Sapa 1050A 6101

Sapa 6463

Tensile strength

1

1

1

2

2

2

3

0

1

1

Impact strength

3

3

3

1

2

2

2

3

3

3

Surface finish Suitability for decorative anodising

3

3

3

2

2

2

1

3

3

3

3

3

3

2

2

1

1

2

3

3

Corrosion resistance

3

3

3

2

2

2

1

3

3

3

Machinability: cutting forming Weldability

1 3 3

2 3 3

2 2 3

2 2 3

2 2 3

2 2 3

3 2 3

0 3 3

2 3 3

2 3 3

Price

3

3

3

2

2

2

2

3

3

3

Suitable alloys for anodising

Refer to 15.3, “Anodising”.

24

s h t n g o n i e t c r t u r s - t h s n g i o H c

7. ALLOYS

Heat treatment recommendations A A 0 A 1 6 0 0 6 3 0 6 3 0 0 5 0 5 0 8 2 0 2 6 3 0 1 0 5 6 1 6 0 6 6 6 6 0 6 7 1 6 4 a a a a a a a a a a p p p p p p p p p p S a S a S a S a S a S a S a S a S a S a Soft annealing: Rapid full through heating, followed

by approx. 30 min. at stated temperature. Cooling should be slow and, down to 250°C, preferably in a furnace. After that, free cooling.

380- 380- 380- 380- 380- 380 400- 380- 380420 420 420 420 420 420 420 450 420 a) b)

(380420) c)

Solution heat treatment: Rapid full through heating,

followed by 15 – 30 min. (depending on wall thickness) 510 at stated temperature. Forced air-cooling (fan) if wall ±10 thickness under 6 mm. Water cooling where over 6 mm. Cooling speed, 1 – 2°C per sec. Occurs spontaneously at room temperature. Temper T4 achieved in stated number of days. Natural ageing:

Artificial ageing: Heat to the stated

age hardening temperature (°C). Hold there for approx. 8 hours. After that, free cooling.

510 530 530 530 535 460 ± 10 ± 10 ± 10 ± 10 ± 10 ± 10 d)

e)

2

2

2

2

2

2

30

175 ±5

175 ±5

175 ±5

175 ±5

175 ±5

175 ±5

f) g)

– –

530 ± 10

(510 ± 10) c)

–

2

2

–

175 ±5

175 ±5

a) Cool to 220 – 230°C in a furnace. Hold at this temperature for 4 – 6 hours. After that, free cooling. b) Coarse grain structure may form (a coarse-grained structure decreases strength and gives a poorer finish after anodising). c) Sapa 6463 should not be soft annealed and subjected to solution heat treatment. This lessens the material’s suitability for bright anodising. d) To be cooled quickly (usually in water). When cooling, the material must be moved quickly from furnace to water (approx. 10 sec.). e) The cooling rate in the critical range, 400 – 200°C, should be at least 1°C per sec. It must not exceed 5°C per sec. Rates above this may cause stress corrosion. f) Artificial ageing can be 100°C (± 5°C) for 4 hours + 150°C (± 5°C) for 8 hours. g) For maximum strength, a break of at least 72 hours between solution heat treatment and artificial ageing is required.

Heat treatment alters alloy properties. The picture above shows temperature control during solution heat treatment. 25

7. ALLOYS

Common Construction Alloys

Alloy data as per EN-755-2 Alloy designations

European standards: numerical notation chemical notation 1) USA: Aluminum Association Swedish standards:

Sapa 6060

Sapa 6063

Sapa 6063A

Sapa 6005

Sapa 6005A

EN-AW-6060 AlMgSi

EN-AW-6063 AlMg0.7Si

EN-AW-6063A AlMg0.7Si(A)

EN-AW-6005 AlSiMg

EN-AW-6005A AlSiMg(A)

AA 6060

AA 6063

AA 6063A

AA 6005

AA 6005A

SS-EN-AW6060

SS-EN-AW6063

SS-EN-AW6063A

SS-EN-AW6005

SS-EN-AW6005A

Alloy data T4 2)

Temper

Tensile strength

T6

T4 2)

T66 F25

T4 2)

t  10 170

t  10 200

t  25 90

10 < t  25 160

10 < t  25 180

T6

T6

T6

T6

T6

T6

Solid Hollow Solid Hollow profile profile profile profile

3)

t = wall thickness, mm Yield strength R p0.2 , MPa, min.

t  25 60

t  3 150

t  25 65

3< t  25

140

t  10 190

t  5 225

t  5 215

t  5 225

t  5 215

10 < t  25 180

5
5
5
5
200

10 < t  2 5 200 Ultimate tensile strength Rm , MPa, min.

t  25 120

t  3 190

t  25 130

3< t  25

170

t  10 215

t  10 245

10 < t  25 195

10 < t  25 225

t  25 150

10 < t  25 200

t  10 230

t  5 270

t  5 255

t  5 270

t  5 255

10 < t  25 220

5
5
5
5
10 < t  25 250 Elongation A, % min.

t  25 16

t  25 8

t  25 14

t  25 8

t  25 8

t  25 12

t  10 7

10 < t  25 250

t  25 t  15 t  25 8 8 8

t  15 8

10 < t  25 5 Hardness

(for guidance) Webster B, approx. Vickers, approx.

5 40

10 60

5 45

12 70

13 80

7 50

13 80

14 85

14 85

14 85

14 85

at 20°, W/m,°C

190

190

190

190

190

190

190

170

170

170

170

Density, kg/dm3

2.7

2.7

2.7

2.7

2.7

2.7

2.7

2.7

2.7

2.7

2.7

Thermal conductivity

Alloys suitable for decorative anodising All alloys:

All applications requiring the highest quality finish and where strength is not the crucial factor, e.g. picture frames, exclusive furniture.

Coefficient of linear expansion: 23 x 10-6 /°C Modulus of elasticity: 70,000 MPa Modulus of rigidity: 27,000 MPa Poisson's ratio: 0.33

Temper codes: F As extruded O Annealed

26

All applications – furniture, decorative trims, etc. This alloy has good properties in most areas.

Certain load-bearing structures, e.g. sailing boat masts, ladders, etc.

Where high strength is essential, e.g. balconies, doorways, ladders, sailing boat masts.

High-strength building and structural components, e.g. profiles for lorry beds and trains. Can be anodised.

Version 7 T4 T6 T66

Hardened and naturally aged Hardened and artificially aged Hardened and artificially aged

7. ALLOYS

Special Alloys

Alloy data as per EN-755-2 Alloy designations

European standards: numerical notation chemical notation 1)

Sapa 7021

Sapa 1050A

Sapa 6101

Sapa 6463

EN-AW-7021 AlZn5.5Mg1.5

EN-AW-1050A Al99.5(A)

EN-AW-6101 AlMgSi

EN-AW-64 63 AlMg0.7Si(B)

AA 1050A

AA 6101

AA 6463

AA 6082

SS-EN-AW7021

SS-EN-AW1050A

SS-EN-AW6101

SS-EN-AW6463

SS-EN-AW6082

T6

F 4)

T6

USA: Aluminum Association Swedish standards:

Sapa 6082

EN-AW-60 82 AlSi1MgMn

Alloy data Temper Tensile strength

T4

T6

T4 2)

3)

t = wall thickness, mm Yield strength R p0,2 , MPa, min.

Ultimate tensile strength Rm , MPa, min.

310

350

t  50 170

20

t  50 200

60

Elongation A, % min. 10

t  50 8

25

t  50 75

t  50 125

t  50 14

t  50 160

t  50 195

t  50 10

t  25 110

t  25 205

t  25 14

Hardness

(for guidance) Webster B, approx. Vickers, approx.

T6

T6

Solid Hollow profile profile

16 110

t  5 250

t  5 250

5
260

5
t  5 290

t  5 290

5
310

5
t  5 8

t  5 8

5
10

5
10 60

7 50

10 60

11 65

15 95

15 95

Thermal conductivity

at 20°, W/m,°C Density, kg/dm

3

All alloys:

Coefficient of linear expansion: 23 x 10-6 /°C Modulus of elasticity: 70,000 MPa Modulus of rigidity: 27,000 MPa Poisson's ratio: 0.33

145

235

190

190

190

170

170

170

2.8

2.7

2.7

2.7

2.7

2.7

2.7

2.7

When choosing this highstrength alloy, Sapa should be contacted for further details. Applications include car bumpers and motorway safety barriers.

Good conductivity (approx. 60% I.A.C.S. at 20°C) and low mechanical strength. Applications – conductor rails, etc.

Good conductivity (approx. 55-60% I.A.C.S. at 20°C) and good mechanical strength. Applications – tubes for transformer stations, etc.

1) The designations must start with EN-AW, e.g. EN-AW-AlMgSi.

Specifically intended for chemical bright anodising, e.g. decorative trims, reflectors, etc.

High-strength building and structural components, e.g. trailer profiles for lorries and floor profiles. Unsuitable for decorative anodising. Version 7

2) Stated tensile strength is attained with a minimum of 72 hours natural ageing after extrusion. 3) Stated tensile strength applies to sections with a wall thickness of up to 25 mm. For further information, contact Sapa. 4) Sapa 1050A is a non-hardenable alloy – its mechanical properties cannot be improved by heat treatment.

27

8. PROFILE DESIGN – WIDE PROFILES WITH TIGHT TOLERANCES

8. Wide profiles with tight tolerances 3 0

0 3

300 400 500 620 28

8. PROFILE DESIGN – WIDE PROFILES WITH TIGHT TOLERANCES

The illustration shows max. profile dimensions for our largest press 1) Max width: 620 x 50 mm. Max square: 300 x 300 mm. Max round: 320 mm diam. Profile weight: max 65 kg/m.

Weight Sapa can extrude profiles weighing from as little as 0.1 kg/m to as much as 65 kg/m 1).

1) 2006, press P1, Belgium

7 , 0 0 0 0 3 0 2 5 4 2 1 2 3 3

Important We continuously develop techniques and processes and invest in new production equipment. It is therefore important to contact Sapa before finally deciding measurements and exact shape of your profile. Version 7

29

9. PROFILE DESIGN – GENERAL ADVICE

9. General design

advice

Wall thickness

When deciding how thick the walls of a profile should be, strength and optimum cost-efficiency are two of the main considerations. Profiles with a uniform wall thickness are the simplest to produce. However, where necessary, wall thickness within a profile can easily be varied. For example, a profile’s bending strength can be increased by concentrating weight/thickness away from the centre of gravity. Cost-efficient production

To optimise cost-efficiency, a profile’s design should always be as production-friendly as possible. To achieve this, the profile should: – have a uniform wall thickness – have simple, soft lines and radiused corners – be symmetrical – have a small circumscribing circle – not have deep, narrow channels. Recommended wall thickness – guidelines

Amongst the factors having an effect on wall thickness are extrusion force and speed, the choice of alloy, the shape of the profile, desired surface finish and tolerance specifications. 5 4.5 4 s 3.5 s e n k 3 c i h t l l 2.5 a w . 2 n i M 1.5

1 1 n o i s r e V

0.5 0 0

50

100

150

200

250

300

Circumscribing circle, mm 6082 hollow profiles 6005A/6063F25 hollow profiles and 6082 solid profiles 6060/6063 hollow profiles and 6005A/6063F25 solid profiles 6060/6063 solid profiles 30

350

400

9. PROFILE DESIGN – GEN ERAL ADVICE

9.1 Uniform wall thickness

It is often acceptable to have a large range of wall thicknesses within a single profile.

Here, the profile’s internal and external walls have different dimensions.

However, a profile with uniform wall thickness is easier

9.2 Soft lines

Extrusion cannot achieve razor-sharp corners.

Corners should be rounded. A radius of

A design may sometimes demand sharp internal angles, e.g. a profile to enclose a box shape.

This is easily solved by incorporating a hollow moulding.

As far as possible, sharp tips should be avoided. The tip can easily become wavy and uneven.

Tips should, therefore, also be rounded.

to extrude.

It is an advantage if internal and external walls are of the same thickness. This decreases die stress and improves productivity.

9.1.1 Exceptions

It is, of course, perfectly acceptable for a profile to have walls of different thicknesses. For example, for strength reasons, it may be best to concentrate weight/thickness away from the centre of gravity.

Following extrusion, a profile with large variations in wall thickness cools unevenly. This gives rise to a visible structural unevenness that is particularly marked after anodising.

0.5 – 1 mm is often sufficient.

Always use soft lines!

31


9.3 Solid profiles if possible

Solid profiles reduce die costs and are often easier to produce.

9.4 Fewer cavities in hollow profiles

9.5 Profiles with deep channels For profiles with pockets or channels, there is a basic rule that the width to height ratio should be approximately 1:3. This ensures that the strength of the die is not jeopardised.

By using large radii at the opening of the channel, and a full radius at the bottom, the ratio can be increased to 1:4.

NB! Where channel width is under 2

mm, or where a profile’s design is complex, permissible channel depth must be determined on a case-by-case basis. This hollow profile is extremely complex to produce.

Is it essential for this profile to have two cavities?

32

By replacing the hollow profile on the left with two telescoping profiles, the product is considerably easier to produce.

In many cases, reducing the number of cavities

in a hollow profile makes it easier to extrude. This increases die stability.

It may be possible to increase radii and opening dimensions without compromising functionality.

Here, a holder has to enclose a slide. Redesigning the holder on the left gives a more extrusion-friendly profile and improved functionality.


A profile can be extruded “open”...

9.6 Heat sinks

The use of cooling fins on profiles greatly increases the heat dissipating area. This can be further increased by giving the fins a wavy surface. Where there is forced air-cooling longitudinally along the profile, it is better to leave the fins smooth. This helps to avoid the problem of eddy formation.

... and then rolled to its final shape.

Waviness here increases the area by 10 – 15%. An undulating surface increases the heat dissipation area of fins.

The solution above gives a narrow, deep channel and an extrusion-friendly profile.

Reduced channel depth using a step. The step is removed during rolling.

This profile exemplifies technical development at Sapa: A large profile with deep channels – yet t ight tolerances are respected and there is a high quality surface fi nish.

33


9.7 Decorate!

Masking of imperfections

Decoration has several advantages: – Design – Masking of imperfections – Protection against damage during handling and machining. Design advantages

Where a profile has, for example, arms and screw ports, there may be process induced shadowing (heat zones) opposite such features.

Using decoration, the heat zones can be completely masked.

Protection against damage A decorative pattern can make a plain aluminium surface more attractive. The consistent use of a pattern on all a product’s component profiles can help make it uniquely identifiable. There are endless possibilities for c reating unique designs.

A joint can be elegantly hidden by making it part of a fluted design.

34

Well designed decoration can also protect profiles from handling and machining damage.

10.1 JOINTING – SCREW PORTS

10. Jointing 10.1 Screw ports 60°

The screw port can be threaded in the normal way for machine screws .

Here, a component is being fitted by screwing through a port at right angles to the profile . In such cases, the port should have a shoulder (see illustration).

D

t

Most commonly, screw ports are used directly for selftapping screws. In these cases, the screw ports will have projections to centre the screws.

Port diameters for self-tapping screws Closed screw ports: Where Screw no.

ST 3.5 (B6) ST 4.2 (B8) ST 4.8 (B10) ST 5.5 (B12) ST 6.3 (B14)

Port diam. D

3.1 ± 0.15 3.8 ± 0.15 4.2 ± 0.2 4.9 ± 0.2 5.6 ± 0.2

Wall thick- Screw head ness t, min. 1) clearance

1.5 1.5 1.5 2.0 2.0

the design requires a more robust screw (e.g. M8), the screw port can be closed. The port is to be dimensioned for thread cutting or for self-tapping metric screws.

4.2 5.0 5.8 6.6 7.4

For further information on wall thickness, refer to chapter 19. 1)

Placing screw ports at corners saves material. To ensure that the screw head does not protrude beyond the contours of the profile at outer corners, pay special attention to screw head diameter. 35

10.1 JOINTING – SCREW PORTS

A screw port along the length of a profile facilitates “stepless fastening”, i.e. screw joints can be made at any point along the profile. Suitable dimensions are given in the table below.

w

Solutions with special screws that fill the screw head clearance hole are common in, for example, the furniture industry.

Screw port dimensions – screws at 90° to the profile Screw no.

Channel width w

ST 3.5 (B6) ST 4.2 (B8) ST 4.8 (B10) ST 5.5 (B12) ST 6.3 (B14)

2.6 3.1 3.6 4.2 4.7

One way of avoiding step drilling and visible holes is to replace the hollow profile with two snap-fit profiles. This solution is often used in handrails.

Upper joint: A hollow profile joined to another profile via a

screw port. To avoid unwanted flexing in the joint, the screw is driven directly through the bottom of the hollow profile. A single screw is sufficient – the hollow profile’s flanges stabilise the design. After step drilling, the hole through which the screw is introduced can be hidden using a plastic plug. Lower joint: The same solution, but without a hollow profile. The U-profile has tracks for the insertion of, for example, a metal or foil laminate strip. 36

This placement of the screw ports increases bending strength.

10.2 JOINTING – NUTS AND BOLTS

10.2 Tracks for nuts or bolt heads

Continuous tracks enable stepless fastening with no need to machine the profile. Dimensions for various nuts and bolt heads are given below. Using special nuts/bolts, fastening can take place without having to slide the nut/bolt in from the end of the track. There are no accepted standards, but various solutions are available from screw and fastener manufacturers.

W G

H

Dimensions – nut/bolt tracks Size

M4 M5 M6 M8 M10 M12 M14 M16

Width, W

(ISO)

7.3 ± 8.3 ± 10.3 ± 13.4 ± 16.5 ± 18.5 ± 21.7 ± 24.7 ±

0.15 0.15 0.2 0.2 0.3 0.3 0.4 0.4

Width, W

(DIN)

17.5 ± 0.3 19.5 ± 0.3 22.7 ± 0.4

Height, Gap, H G

4.0 5.5 6.0 8.0 9.5 12.0 14.0 16.0

4.4 5.4 6.4 8.5 10.7 12.7 15.0 17.0

If a standard bolt is too long, it is not always necessary to find a shorter bolt. The track for the nut can easily be designed/extruded as shown above.

If a set c/c distance between the bolt holes is required, a flat bar with precut threads can be put in the track.

The profile can be stamped to fix fasteners longitudinally in position. 37

10.3 JOINTING – SNAP-FIT JOINTS

10.3 Snap-fit joints Aluminium’s elasticity is highly suited to snap-fit joints. These give far quicker assembly than, for example, screw or welded joints. Snap-fit joints are widely used in a range of industries.

If a design cannot accommodate hooking arms of sufficient length, the sprung part of the profile should be replaced by plastic clips or similar. The same applies if the joint is to be repeatedly opened. Aluminium’s fatigue properties do not permit frequent changes in loading.



In openable snap-fit joints, the hook angle is  = 45°. In permanent snap-fit joints, the hook angle is  = 0° (or negative). The length of the snap-fit joint has an effect on design.

If a snap-fitting is difficult to assemble/disassemble, punching a section out of the hooking arm may be the solution.

A permanent snap-fit joint.

Dimensions and tolerances must be decided on a case-by-case basis. The length of the hooking arm should not be under 15 mm. In some cases, long hooking arms may have to be extruded pre-stressed. This can eliminate the need for special tolerances. 38

Amongst other factors, the design of the joint is determined by whether or not it is to be openable. This joint can be opened using, for example, a screwdriver in the outer track.

10.4 JOINTING – PROFILE TO PROFILE

10.4 Jointing – profile to profile 10.4.1 Longitudinal jointing

Examples of snap-fit joints.

Joining with a standard flat bar.

C

A

B

Plate A has a punched, rectangular hole. Mounting profile B is pushed into the hole until a snap-fit joint is formed. Lamella profile C is then pushed into profile B to form another snap-fit joint. Exploiting the space under the plate makes it possible to have sufficiently long hooking arms. The hinge profile A (cut from a longer profile) forms a snap-fit joint with main profile B.

Reinforcement to avoid

deformation of visible surface areas.

B

c A

d

Punched hole c also provides longitudinal locking. Sufficient spring is generated in the hooking arm by springing the main profile at d.

Joining with a fluted, sprung profile in purpose-designed channels.

39


Torsionally stiff tube joint with wall reinforcement

to accommodate a thread.

Longitudinal joining via asymmetrically located screw ports and a pre-drilled spacer. The profiles are turned so that the screws do not foul each other.

A

A sprung inner section that compresses to allow assembly. For easy entry, the inner profile ( A) is bevelled and cut parallel to the m ain profiles. Tolerances are not critical in this solution. The result is a play-free joint. Longitudinal joining via longitudinal screw joints . A gap slightly longer than the length of the screw is milled in the screw port.

Anchoring joined profiles by welding – the illustration shows solutions with a solid profile and a hollow profile respectively.

40

Longitudinal jointing using the spring and friction in a snap-fit design.


10.4.2 Telescoping

Height adjustment where the outer profile has a fixed thread (blind rivet nut) and the bolt clamps the inner profile in position.

To ensure smooth and silent operation, plastic components are often used in telescoping designs. This design features stepless height adjustment using a nut (a threaded flat bar could also be used) that runs freely in its track. Tightening the fasteners locks the height and removes any play in the joint.

Height adjustment where the inner profile has a fixed thread (blind rivet nut) and the outer profile has a punched or extruded channel.

Telescope solution with stepless clamping.

Telescope solution with spring locking.

41


10.4.3 Latitudinal jointing Sapa can extrude wide profiles with tight tolerances. Larger cross-sectional areas can be economically created by joining a number of profiles together. This solution is often chosen because it is easier to machine smaller profiles individually rather than a single construction as a whole.

Where a play-free joint is essential (e.g. a single leg stand), plastic gauge blocks are used.

Mechanical joints, adhesive bonding, fusion welding and, as illustrated above, Friction Stir Welding, can all be

used for latitudinal jointing. Adhesive bonding is examined in chapter 10.8, fusion welding in 10.9 and FSW in 10.10. The examples below are of mechanical joints.

Plastic is often an excellent solution where components have to be able to slide. A plastic profile can be a part of a telescoping assembly.

Plastic wheels used as part of the fastening in the

outer profile serve as s pacers and give smooth, play-free telescoping. 42

Using a flat bar, bracket or similar to join profiles together gives good flatness.


Latitudinal jointing using screw ports.

Latitudinal jointing with a clamp.

Locking using a splined dowel pin.

Latitudinal jointing with a snap-fit.

Locking using a tubular spring pin.

Latitudinal jointing with a snap-fit.

43


10.4.4 Hinges

Jointing using an end plate that holds the sections together. A simple hinge – the ball’s diameter should never be less than 5 mm.

If the hinge has a screw port, it can be easily locked longitudinally using plastic inserts and self-tapping screws. Jointing by stamping (creates visible deformations).

Latitudinal jointing using dovetail tracks. Note the shape – to achieve acceptable precision, sharp-tipped corners must be avoided.

44

A hinge with approximately 110 degrees opening.


Up to approx. 270 degrees opening using three profiles. Two profiles with 180 degrees opening.

Self-locking with approx. 180 degrees opening.

Complex hinging for securing lorry tarpaulins. The hinge

is made from three profiles joined together.

Chamfering the ball enables hinge disassembly as

Both parts of this hinge are made from a single profile.

shown above. 45


Three-part hinge made from a single profile.

A longitudinally adjustable hinge.

Two-part hinge made from a single profile and with identical machining.

Hinges can be made from other materials than aluminium. The illustration shows a solution where a plastic or rubber profile can be used.

A pin in each end gives wide opening and a cost-efficient solution.

46


10.4.5 T-joints

To avoid flexing in the joint, the screws are driven directly through the inner wall. The outer clearance holes are plugged with standard plastic caps.

A simple T-joint using screw ports.

A strong joint with flanges to take up torsional stress .

Fitting to a wall or another profile : The end fastener is cut from a longer profile and secured with screws.

Screw ports used to join

Joining of a round tube and a transverse profile : The transverse tube comprises two profiles held together by a snap-fit joint. This fastening avoids troublesome mating of the contours.

tubular and rectangular profiles.

47


The Sapa tie, stocked by Sapa, is a simple and stable

solution for T and corner jointing of square tubes.

In the furniture and interior decoration industry, special fasteners are used where joints must be easy to take apart . The fasteners often run in a nut track and there is thus a stepless fit with the mounting profile.

Examples of other special fasteners.

Expansion locking using a wedge shape.

A simple T-joint using nut tracks, right-angled brackets

and bolts.

Expansion locking using splined pins.

48


10.4.6 Corner joints Channel for stamping Screw ports

There are various types of brackets that are extremely suitable for corner joints where the strength and rigidity requirements are high. The brackets are usually cut from long aluminium profiles. Brackets are usually designed to allow several fitting methods. The corner bracket above has both screw ports (for side screws) and channels for stamping. Fitting method can then be chosen to suit equipment, series size, etc.

In picture frames and other light constructions, the corner joint comprises two flat right-angled brackets, one of them with threaded holes.

Stamping tool (punch) This corner joint for square tubes uses self-tapping screws in the transverse screw ports.

A special machine or an excentric press is used in the stamping method of connecting profiles. The method is particularly common in long production runs.

Cast metal and plastic ties are a solution that is especially common in long runs and where jointing has to be provided in more than two directions. Various ties are available in standard formats. 49


Tie using sprung steel clips.

50

A simple corner joint using a relatively easily machined standard profile and a special profile cut at 90 degrees.

Ties are often rectangular. The main profile’s contours are, of course, immaterial as long as there is an inner, rectangular chamber.

This stable corner joint, which has precise angles and good design, involves relatively easy machining only.

A torsionally rigid joint using a single screw . As shown, one of the profiles has flanges. This type of corner joint is used in, amongst other things, TV stands.

The flanges of the corner profile are bolted to the insides of the frame profiles. The frame profiles need only be cut at 90 degrees to ensure a snug fit. Where corners are visible, a large radius (as shown by the broken line) gives an attractively rounded design.


A corner joint that can be used in, for example, a table. The plate and joint combination represents a very stable solution. These frame profiles have screw ports and, to give a snug fit, need only be cut at 90 degrees when used with the corner profile shown in the illustration. The flanges of the corner profile create channels for the fitting of an outer profile (free choice of radius). Plastic caps are used to cover the ends.

A U-section with a punched or sawn cut. The saw cut should go down into the base of the profile. This can then be folded to give a frame with slightly rounded corners . The frame is locked using a joint on either a long or a short side.

Reinforcement

Corner joint using pre-mounted bolts in two of the profiles. The bolts are tightened from above using a s pecial tool.

51

10.5 JOINTING WITH OTHER MATERIALS

10.5 Jointing with other materials

Printed circuit boards, metal sheets and other plates can be fitted in channels in the profile. A small deformation (catch) in the plate or the channel ensures good locking.

Glass and metal plates, etc. can be locked in place using a sprung, special plastic profile (the yellow profile).

A snap-fit joint can be used with formed plates.

Protrusions punched into the profile/plate ensure radial

locking.

Rattle-free locking through having the profile’s arms

actively grip the plate/sheet.

52

A standard method of glazing windows and doors: Rubber profiles, which form snap-fits with the aluminium profiles, act as spacers for the glass. This method can also be used for other plates.

10.5 JOINTING WITH OTHER MATERIALS

The “Christmas tree model” is a simple solution when jointing with wood. Short snap-fit brackets can be screwed/nailed into wood strips.

A snap-fit using a track in the wooden board.

A snap-fit joint between aluminium and plastic profiles.

Special screws with “snap-fit heads” can be used when jointing with wood or metal plates.

To deal with high local surface loads and reduce wear (e.g. from a rolling steel wheel), a steel strip can be inserted in profiles. 53

10.6 JOINTING – RIVETING

10.6 Riveting

Press nuts: These are fitted from the

back using, for example,

an excentric press.

Examples of blind rivet nuts and press nuts.

In a long profile, it is often uneconomic to build in extra thickness simply to provide longer threads.

Sliding pop riveting in a longitudinal profile channel.

Using blind rivet nuts or press nuts, all that is required is a hole.

The blind rivet nut is fitted from the outside using a special rivet gun.

54

Pop riveting at the end of a screw port.

10.7 JOINTING – END CAPS

10.7 End caps End caps are manufactured in many different ways and from many different materials. They are screwed, pressed, bonded, snapped or welded in place.

Self-punching rivets countersink and join in a single

operation.

Screws and screw ports are the most common method of securing metal or plastic end caps to box profiles.

Riveting without rivets: This method, which is highly

suitable for long runs, can join different materials of different wall thicknesses. A crimping press is used.

If the end cap and the profile have the same nominal outer dimensions, any departures from tolerance specifications are clearly visible. The places where metal has been cut become particularly prominent if the profile is surface treated. One solution is to make the end cap slightly bigger than the main profile. 55

10.7 JOINTING – END CAPS

An end cap with sprung arms – the cap is removable.

If the main profile is long, it is more cost-efficient not to have screw ports in this but in a purpose-designed end cap. Slight displacement of the holes in the main profile (relative to the screw ports) ensures that a force is set up pulling the end cap into the main profile.

This plastic end cap is held in place by stamped catches in the profile.

Cast metal or plastic end caps are suitable for long runs

This end cap wedges into t he main profile. There is a strong press-fit between the end cap’s arms and the channels in the main profile.

Channels in the main profile for the fitting of an end cap with a sprung arm.

56

where the shape of the main profile is complex or where a highly rounded end cap is required.

Two end caps can be held together using long screws or draw bars. Screw ports with adequate clearance are a suitable way of guiding the screws. The result is one end cap with no visible screws. This is a good solution in, for example, fascias.

10.8 JOINTING – ADHESIVE BONDING

10.8 Adhesive bonding After steel, aluminium is the metal that is most frequently bonded. Though, for example, far more cars are produced than aeroplanes, the adhesive bonding of aluminium in the aero-industry has attracted the most detailed research. Aeroplanes have used bonded joints since the mid 40’s. Nowadays, the bonding of aluminium is even used for load-bearing components in aircraft. Of course, there are many more down-to-earth examples of the use of bonded aluminium joints. Volvo’s roof rack rail is just one of these.

Many different adhesives, pre-treatments and bonding methods have been developed. Selecting the right one is not always easy. Nor is it risk-free to simply start bonding without adequate information. Essential knowledge

The intermolecular forces that determine whether bonding is possible exert their pull over a maximum range of 0.5 nm (one half of a millionth of a millimetre). If the surface is contaminated or is made up of low strength oxides exceeding this critical “thickness”, there will be no attraction between the adhesive and the aluminium profile. For good and consistent bonds, the joint surface must be known, reproducible and clean. The adhesive must wet the entire surface that is to be bonded. To do this, it has to have a lower surface tension than the material being bonded. Otherwise, the adhesive will form droplets rather than spread evenly over the surface. All adhesives wet aluminium. To bond aluminium to another material, the adhesive must be able to wet this material too. If the other material is a plastic, it can sometimes be difficult to find an adhesive with a lower surface tension.

For good and consistent bonds, the joint surface must be known, reproducible and clean.

57


Traditional tongue and groove.

Tongue and groove with a channel into which the “locking hook” can be hammered or rolled.

A variant of the “adhesive trap” and “locking hook” method.

Joint design

Adhesives cope best with shearing forces.

58

Adhesive bonding involves the formation of a plastic or rubber load-carrying element. The material in the cured adhesive bond is not as strong as the aluminium. This can be compensated for by designing profile solutions that provide large contact surfaces. Aluminium profiles can be easily worked into a wide range of shapes. Where tongue and groove type bonded joints are a possibility, they may be the best solution. The illustrations above give some ideas and guidance on joint design. Adhesives cope best with shearing forces. Joints subjected to tensional forces are often unsuitable for high loads. Peeling and cleaving forces concentrate stress on a small part of the joint and should be avoided whenever possible.


Choice of adhesive

Bonded joints distribute stress relatively well. However, very rarely is stress evenly distributed across the entire surface area of a bonded joint. As a rule, stress is greatest at the edges of the joint. The stiffer the chosen adhesive, the greater the concentration of any subsequent stress. This leads to (sometimes unnecessarily) high stress on the adhesive and the surface that has been bonded to. Thus, never choose an adhesive that is stiffer than necessary. Thicker bonded joints also reduce the concentration of stress at the edges of the joint. The choice of adhesive is determined by the way in which the adhesive works and what is required of the bonded joint (filling/sealing, heat resistance, toughness, etc.). To be able to mould itself to the surface structure of the profile, the adhesive must have good liquid properties. It must also harden into a material that can transfer stress in the environment where it is used. Furthermore, it is important that the adhesive has time to mould itself to the surface’s micro-profile. Fast setting, high-viscosity adhesives rarely permit this. In such cases, it may be advisable to first apply a low-viscosity primer. The change from liquid to solid is effected in three different ways.

Drying

Cooling

Curing by

Solvent or water vaporisation.

The adhesive is liquid when it is hot.

– – – – – –

Mixing Heating Exposure to moisture Illumination (UV or blue light) In the absence of oxygen Contact between adhesive and hardener (without preliminary mixing).

Stress distribution in a simple overlap joint as seen using tension spectrometry.

Never a stiffer

adhesive than is necessary.

Drying

Solvents and water vaporise. Thus, adhesives containing solvents or water are unsuitable where:

– gap filling is required – both the materials are unable to let the solvent escape. Double-sided PSA tape should be regarded as a drying adhesive that never dries. The material forming the joint is the same as that in the roll. However, if the stress is low, double-sided structural PSA tape may prove suitable for joining aluminium profiles together. Double-sided PSA structural tapes formed entirely of the adhesive substance itself are available in thicknesses from 0.1 to 6 mm. There are also double-sided PSA tapes that can be heat cured. The tape holds the components even during curing – other forms of clamping are unnecessary. Testing of a simple overlap joint has shown a strength after curing of around 10 N/mm2.

Strength data

for a structural PSA tape: Creep strength:

0.1 N/mm2 (100 kg/dm2) 1 week at 22°C. Peel strength:

90°: 2 N/mm (at 22°C).

Cooling

Some thermoplastic adhesives have good plasticity when hot. Hot-melt adhesives are the most widely used. However, the thermoplastic hot-melt adhesives usually set too quickly on aluminium. This results in poor contact with the aluminium surface. Hot-melt adhesives also have very low creep and heat strengths. Many thermoplastic hot-melt adhesives become brittle in cold environments. Moisture-curing hot-melts are applied at lower temperatures and, compared to thermoplastic hot-melts, have excellent properties after curing. They are used for, amongst other things, applying foil coatings to aluminium profiles. 59


Heat-reactivated adhesive is also used when coating aluminium profiles with

foil. An adhesive solution or a water-based adhesive is applied to the material and left to dry completely. In the bonding process, so that it wets the opposite surface, the adhesive is heated. Moisture-curing hot melts and heat-reactivated adhesives can both give strong, durable bonds. Curing Curing adhesives make up the large group of structural adhesives. They cure (often

with negligible contraction) in one of the following ways: Curing by mixing of the components

Typical of this group are the epoxy and polyurethane adhesives. They have very good gap filling properties. In principle, they can be cast. Modified acrylic adhesives are now also becoming more common. There are both stiff and elastic, 2-component, epoxy and polyurethane based adhesives. Epoxy adhesives with an elongation at fracture of up to 120% are now available. Elastic epoxy adhesives normally give a bond that is relatively heat-sensitive. Using epoxy adhesives, higher strength bonds and improved durability are achieved by curing at elevated temperatures. The curing times are also considerably reduced – the curing time halves for each 10°C rise in temperature. Two-component polyurethane elastomers give “rubber-like” joints that remain elastic even at low minus temperatures (°C). There are also 2-component silicon adhesives that cure relatively quickly at room temperature. Curing by contact between hardener and adhesive (adhesive on one surface – hardener on the other)

These types of adhesives are usually referred to as SGA adhesives. They have excellent peel and impact strengths, but are not particularly suitable where a gap filling adhesive is required. These adhesives have been largely replaced by modified acrylic adhesives, which are mixed direct from their packaging and can be used to form thick joints. Acrylic adhesives of this type that adhere to untreated polyolefines (e.g. PE and PP) are now also available. Curing by heating

Here, the most common adhesives are the 1-component epoxies. These require heat curing at a minimum of 100°C. With induction heating of aluminium profiles, curing times of approx. 60 seconds are possible. The aero-industry makes extensive use of heat-hardening adhesive films. These require at least 30 minutes to harden at a minimum of 125°C. One-component polyurethane elastomers can be heat cured at 70°C – 90°C (in 10 – 30 minutes).

60


Curing by contact with moisture

Cyanoacrylate adhesives harden very quickly in contact with moisture. A bond

between two aluminium surfaces takes longer to harden than a bond between aluminium and plastic or rubber materials. Cyanoacrylate adhesives are best suited for small joint surfaces and thin bonds. Normally, they have low peel and impact strengths. However, there are “rubber-filled” (black) cyanoacrylate adhesives with good peel and impact properties. Colourless, elastic cyanoacrylates are also available, but these are not particularly suitable as structural adhesives for metal. Cyanoacrylate adhesives may be suitable where, for example, a plastic is to be bonded to an aluminium profile. One-component polyurethane elastomers can also be cured by the humidity of the air. This type of adhesive is used in, for example, the bonding of car windows and, on a large scale, for aluminium profiles in container and vehicle body manufacturing. Curing is comparatively slow (hours) and dependant on relative air humidity and joint geometry. Heat-curing polyurethane elastomers have been mentioned above. There are also polyurethane elastomers that harden both with moisture and heat. Two-component type polyurethane elastomer adhesives are also available. As an alternative to polyurethane elastomers, there are the so-called MS polymers. These also harden with moisture. Two-component MS polymers are primarily chosen for work environment considerations. Curing in UV light

There have long been 1-component acrylate adhesives that cure in tenths of a second when exposed to UV light (wavelength approx. 350 nm) or blue light (wavelength > 400 nm). Acrylate adhesives are often limpid and very suitable for bonds between aluminium profiles and glass (most of them perform less well with transparent plastics). Epoxy adhesives that harden in UV light have also been developed. There are many types of these - limpid, filled, low-viscosity, hard, elastic, etc. Some of these adhesives can be irradiated prior to bonding and will then cure relatively quickly. Curing in the absence of oxygen

Such adhesives cure on contact with active metal ions. They are normally referred to as anaerobic adhesives (or “locking fluids”). They are not particularly suitable for aluminium. Aluminium surfaces should be regarded as passive. An activator has to be used in such cases. This gives a lower strength bond. Variants of these adhesives that do harden without an activator on aluminium surfaces are now available. Temperature limits

With many adhesives, the practical maximum temperature at which stressed bonded joints can be used is between 60 and 80°C. The highest heat-resistance (approx. 150 – 250°C) is achieved with heat-curing adhesives and heat-curing adhesive films. However, silicon adhesives can give heat-resistance of around 250°C without heat curing.

61


Long-term strength

Aluminium surface at x 25,000 magnification (the red bar is 1 µm).

Bonds to aluminium are as strong and durable as the aluminium oxides with which the bond is formed. Aluminium that has had no surface treatment has a large percentage of magnesium in its surface. Aluminium surfaces should normally always be treated in some way. Used in a dry environment, an untreated aluminium profile can give an excellent bond. The same bond outdoors in a coastal climate may have a far shorter life. Bond lifetime depends on the synergistic effects of stress, temperature and environment. Normally, the problem is not the degradation of the adhesive or the failure of adhesion, but the effects of changes in the underlying aluminium. Any good microscope will show that there are no completely flat or even surfaces. Highly viscous (slow flowing) and fast setting adhesives will, therefore, most probably only come into limited contact with the surface. This results in a bond with in-built weak points (air pockets) where the adhesive’s properties are not being exploited. In humid environments, this air will eventually be replaced by water. Where the water is salty, the need for surface treatment is even greater. Aluminium’s durability can be improved by, for example, anodising. Basic principles for long-lasting bonds

The basic principles for long-lasting bonds are well filled joints and resistant oxides. A large number of pre-treatment processes have been developed for aluminium. Some of the most common (and some of the more unusual) are presented here. Choice is determined by the environment where the aluminium is to be used, likely stresses and costs. Full details of the processes and any risks to the work environment should, of course, be obtained before starting any form of treatment. The main purpose of priming prior to the bonding of aluminium is to fill (seal) the surface when high-viscosity and/or fast setting adhesives are to be used. Priming becomes more important where the aluminium is to be used in a corrosive environment and no surface treatment that improves corrosion resistance (e.g. anodising) is contemplated. Primer also “impregnates” and strengthens porous oxides, e.g. after chromating. Requirement specification

It is advisable to draw up a requirement specification for the properties of the final bond and the use-related aspects of the adhesive. This helps crystallise the demands really being placed on the adhesive. It also makes it easier to specify exactly what is required to the adhesive manufacturer.

62


Pre-treatment operations in bonding Process

Result

Use (max.)

Cleaning/ degreasing

Minimum requirement for ensuring a clean and defined bonding surface.

For moderately stressed joints in dry surroundings.

Fine grinding/ blast cleaning

Removes weak surface layers e.g. oxides. Safer than degreasing.

Highly stressed joints in dry environments. Unstressed joints in fresh water.

Alkaline pickling

Removes weak surface layers e.g. oxides. Safer than degreasing.

Highly stressed joints in dry environments. Unstressed joints in fresh water.

Boiling water for 5 – 10 min. after pickling

Gives resistant, but moderately strong oxides.

Lightly stressed joints using flexible adhesives in humid, corrosive environments.

Phosphating/ chromating

Corrosion resistant, but weak, porous oxides.

Lightly stressed joints using elastic or very low-viscosity adhesives in corrosive environments.

Hydrochloric acid at 20°C for 30 seconds

Quick, can impart a dark-colouring to the aluminium surface.

Moderately stressed joints, even in corrosive surroundings. Relatively uncommon process.

Etching in chrome/ sulphuric acid

Thin, strong oxides. Long used in the American aero-industry.

Highly stressed joints outdoors. However, cannot withstand strongly corrosive environments.

Anodising in sulphuric acid

Thick very resistant oxide.

Lightly stressed joints in corrosive environments. Best with elastic adhesives.

Anodising in chromic acid

Medium-thick, strong oxide. Used in the European aero-industry since the 40’s.

Highly stressed joints, even in corrosive environments.

Anodising in phosphoric acid

Porous, very resistant oxide. Is used together with low-viscosity primer.

Optimum pre-treatment for highly stressed joints in corrosive environments.

Literature Limning av aluminium , Sapa Technology – 2001. Readily available publication on aluminium bonding. Includes

examples of adhesives and bonded joints (28 pages). I n Swedish. Limhandboken, Casco Nobel, Helsingborg – 1991, ISB N 91-630 0608-1. Easy-to-read introduction to bonding

(108 pages). In Swedish. Industrial Adhesives Handbook , Casco Nobel, Helsingborg – 1992, ISB N 91-630 1007-0. Easy-to-read introduc-

tion to bonding (108 pages). Adhesion in Bonded Aluminium Joints for Aircraft Construction , W. Brockman, O-D Henneman, H. Kollek and C.

Matz, International Journal of Adhesion and Adhesives, volume 6, no. 3, July 1986. Discusses the phenomena associated with stressed bonds to aluminium in corrosive environments (28 pages). Handbook of Aluminium Technology and Data , J. Dean Minford, Marcel Dekker Inc, New York, Basel, Hong

Kong, ISB N 0-8247 8817-6. Collated findings and data on aluminium bonding. Contents include 4,6 86 references (744 pages). Härdplaster , AFS 1996:4, Arbetarskyddsstyrelsens Författningssamling, Publication service, Solna. Regulates the

use of hardening plastics and adhesives in Sweden (78 pages). In Swedish. 63

10.9 JOINTING – FUSION WELDING

10.9 Fusion welding Aluminium is eminently suitable for welding. Although many welding methods are possible with aluminium, only a few are used in practice. Refinements in welding machines, equipment and materials have resulted in welding acquiring increasing importance as a jointing method. Oxide formation

When welding aluminium, the metal’s reaction with oxygen, and the oxide rapidly generated therein, have to be taken into account. The oxide is strong, has a high melting point (approx. 2,050°C) and can easily cause welding defects. The oxide is heavier than the weld pool and may form inclusions. Thus, before all welding of aluminium, it is important to remove oxides from the joint surfaces. This may suitably be done using a stainless steel wire brush. Thoroughly cleaned, oxide-free joint surfaces are a basic requirement for faultless welded joints. Weld porosity formation

The risk of void formation must also be taken into account. The hydrogen contained in moisture and contaminants on or in the welding materials, work piece or air is highly soluble in molten aluminium. It loses this solubility almost completely when the metal solidifies. As the weld pool sets, the hydrogen forms bubbles that may become trapped and form voids.

Most aluminium alloys can be welded Highly weldable alloys

Sapa

Chemical designation EN-AW

1050A

Al99.5(A)

1050A

Most of the non-hardenable alloys, e.g.

–

AlMn1 AlMg2.5 AlMg4.5Mn0.7

3103 5052 5083

Certain hardenable alloys, e.g.

6063 6063A 6005 6005A 6082 7021 6101

AlMg0.7Si AlMg0.7Si(A) AlSiMg AlSiMg(A) AlSi1MgMn AlZn5.5Mg1.5 AlMgSi

6063 6063A 6005 6005A 6082 7021 6101

All types of unalloyed aluminium, e.g.

Most aluminium alloys can be welded.

64

Swedish standard SS-EN-AW


Methods

Nowadays, gas arc welding methods, MIG and TIG in particular, dominate. Argon (Ar) and helium (He) are used as the shielding gases in the MIG and TIG welding of aluminium. Argon and helium are inert gases and do not, therefore, form chemical compounds with other substances. Where there is a high penetration requirement, e.g. in a fillet weld or when welding very thick work pieces, an argon-helium mixture can be used in MIG welding. The economic threshold for using mixed gases is a material thickness of 10 – 12 mm. As welds in aluminium are prone to the formation of oxide inclusions and voids, the shielding gas must also meet certain purity requirements. The minimum requirement is 99.5% argon or helium. Besides playing a part in the electrical processes in the arc, the gas also has the jobs of protecting the electrode and the weld pool from oxidation and of cooling the electrode. MIG welding

As a rule, MIG welding is used for material thicknesses from 1 mm upwards. In special cases, thicknesses under 1 mm can be welded using a pulsed MIG arc. Filler metal is added in the form of a wire fed through the welding torch. MIG welding can be performed in any position and for all joint types. A higher current density than in TIG welding gives higher welding speeds. The high welding speed has a positive effect on distortion and shrinkage (narrower heat-affected zone).

MIG:

From 1 mm upwards.

TIG welding

TIG welding is suitable for material thicknesses down to under 1 mm. In practice, there is an upper limit of around 10 mm, but edge preparation is then necessary. Filler metal is normally used and is introduced from the side. TIG welding can be performed in any position and, when performed correctly, gives the most fault-free welds. The welding speed is relatively high, and even higher in mechanical TIG welding. TIG welding can be recommended where the gap width varies.

TIG:

Materials under 1 mm thick.

Robot welding

Robotised MIG welding can be used with advantage in long production runs. This method noticeably increases productivity and is also advantageous from a work environment point of view. The position of the work piece is easy to control. This facilitates welding from the optimum position and gives good results. Certain problems may arise with very thin materials and uneven gap widths.

65


Welding economy

Measured on cost per length, MIG welding is normally cheaper than TIG welding. Equipment costs are identical. Filler metals

The table below gives recommendations for appropriate filler metals. AIMg5 generally gives the greatest strength. AISi5 is more stable as regards cracking and easier to use when welding hardenable alloys. If the welded assembly is to be anodised, Si alloyed filler metals cannot be used. When anodising, the silicon is precipitated and imparts a dark grey, almost black, colour. In order not to compromise weld quality, filler metals should be stored so that the risk of oxidation and the formation of other coatings is avoided.

Parent metal A Sapa

Swedish standard SS-EN AW

1090 1080A 1070A 1050A 1050A 1200 3103 5005 5251 5052 5754 5083 6060 6063 6063A 6005 6005A 6082 7021

6060 6063 6063A 6005 6005A 6082 7021


Al99.90 Al99.8(A) Al99.7(A) Al99.5(A) Al99.0 AlMn1

Recommendations for choice of filler metals Al99.8 Al99.5 Al99.5Ti Al99.5Ti AlMn1 AlMg52)

Al99.5 Al99.5Ti Al99.5Ti AlMn1 AlMn1 AlSi5 AlMg52) AlMg52) AlMg3 AlMg5

Where several filler metals are listed in the same box, any of them can be used for all the alloys in question.

AlMg1(B) AlMg2 AlMg2.5 AlMg3 AlMg4.5Mn0.7 AlMg5 2) AlMg52) AlMg52) AlMg5 AlMg4.5Mn AlMgSi AlSi5 AlSi5 AlSi5 AlMg3 AlMg0.7Si AlMg51) AlMg0.7Si(A) AlSiMg AlSiMg(A) AlSi1MgMn AlZn5.5Mg1.5 AlSi5 AlSi5 AlSi5 AlMg4.5Mn AlMg5

Parent metal B


A Swedish standard 0 0 A 9 8 0 7 SS-EN-AW 0 1 0 1 0 1 Sapa

1) Unsuitable where there is to be subsequent anodising. 66

) ) ) A ( A A ( 0 ( 9 . 8 . 7 . 5 . 0 . 9 9 9 9 9 9 l 9 l 9 l 9 l 9 l A A A A A A 0 0 5 0 0 1 2 1 A 0 5 0 1

AlMg5 AlMg4.5Mn AlMg5 AlSi51) AlMg4.5Mn AlMg3 AlMg5

AlMg4.5Mn AlMg4.5Mn AlMg5 AlSi5 AlMg5

1 n M l A

) B 5 ( . 1 2 2 3 g g g g M l M l M l M l A A A A

7 . 0 n M 5 . 4 g M l A

3 0 1 3

5 1 2 4 0 5 5 5 0 2 0 7 5 5 5 5

3 8 0 5

2) Less suitable material combinations. However, TIG welding with stated filler metal is possible.

AlMg4.5Mn AlMg5

5 ) . A ( ) n 1 i g S S A M M i 7 . 7 . ( g 5 . S 0 0 g g M 5 g g g i M M 1 n i i M M M S S S Z l l l l l l l A A A A A A A A A 0 3 3 5 5 2 6 6 6 0 0 8 0 0 0 0 0 0 6 6 6 6 6 6 A A 0 3 3 5 5 2 6 6 6 0 0 8 0 0 0 0 0 0 6 6 6 6 6 6

1 2 0 7 1 2 0 7


Strength

In welding, the heat treatment to which the material is subjected affects the structure locally around the weld. The illustration is a schematic representation of how strength and hardness vary with distance from a weld in a hardenable alloy. N/mm2 With aluminium profiles, it is easy to compensate for 300 decreased joint strength by increasing the wall thickness 200 locally. Furthermore, edge preparation can be 100 directly incorporated into the profile’s design.

Solution heat treated zone e r u d t c l u e t r W s

C ° 0 0 5

d e l a e t e f o n n n S a o z

, e y n l l o a i z C c d ° fi i 0 t r e g 0 A a 3

d e t c e , C f f ° a e 0 n n o 3 U z 1

f u

f wu r = 0,6

Profile design with regard to fusion welding

Appropriately designed profiles can greatly simplify s implify welding. Edge preparation, material compensation, in-built fastening, integral root backing and the minimisation of the number of welds required are all examples of proactive aluminium profile design. In many cases, aluminium profiles can be designed in a way that reduces reduces the required number of welds. Sometimes, welds can also be located in a low stress section of the cross-sectional area. This will mean fewer welds and improved strength.

Edge preparation integrated into profile design – the illustration also features material compensation for strength reduction in the weld zone.

Placing of welds in lower stress sections of the cross sectional area. This results in fewer welds, and butt rather than fillet welds. Permanent root backing.

In-built fastening – used in dry environments.

Number of welds reduced from 12 to 4 – butt welds rather than the weaker fillet welds (which are also harder to x-ray). Fewer components, reduced welding (consequently fewer heat-affected zones) and straightening minimised. 67

10.10 JOINTING – FRICTION STIR WELDING

10.10 Friction Stir Welding (FSW) Friction Stir Welding (FSW) exploits aluminium’s ability to withstand extreme plastic deformation at temperatures that are high, but not above the melting point. In FSW, the clean metal surfaces of the profiles that are to be joined are heated by friction generated by a rotating tool and pressed together at very high pressures. This forms a new, homogeneous structure. Compared with fusion welding, FSW gives:

Increased

strength and leakproofness. Reduced

thermal deformation.

– Increased strength. – Increased leakproofness – entirely void-free, impermeable impermeable joints of a higher strength than fusion welded joints. – Joints that are, are, in principle, flush with the surface. – Reduced thermal deformation – only low thermal stress in the material, hence the flat surfaces. – Increased repeatability – production has few variables and these are easily A heat sink panel – using FSW, profiles have controlled; the result is tight tolerances. been joined to form a flat, 530 x 1,290 mm panel.

An established established technology technology

FSW is an established technology. It was developed by The Welding Institute (TWI) in Cambridge, England. Sapa has actively participated in the process of converting theory and laboratory experimentation into full-scale production. Sapa started series production production using FSW in 1996. We We are are now the world world leaders in the use of FSW and can supply FSW joined panels up to 3 metres wide and 14.3 metres long. Several leading classification societies have, after extensive testing, approved FSW as a jointing method for demanding uses in railway and marine applications.

A cross-section of a joint – x 13 magnification.

68

The homogeneous crystal structure in the centre section of an FSW joint – x 220 magnification.


Using FSW rather than traditional fusion welding to join panels together gives, amongst much else, increased flatness and straightness. Strength is also increased (see the Royal Institute of Technology’s tests, pages 72 – 73). The Sapa panel below is 3 x 14.3 metres.

A rotating tool is pressed into the metal and moved along the line of the joint. No filler metals or shielding gases are used. FSW takes place at a temperature below the metal’s melting point. The results include very little thermal deformation, hence the flat surfaces.

The void-free weld.

The joint is, in principle, flush with the surface and the FSW weld is, to all intents and purposes, completely void-free. The strength properties are also very good.

69


The FSW weld – homogenous and void-free with no oxide inclusions

Homogenous and void-free

with no inclusions.

To paint a clearer picture of FSW, we have chosen to compare it with the most commonly used method of welding – fusion welding. At the same time, we must stress that, in our production of added-value aluminium profiles, we often use fusion welding (MIG). The old does have its place alongside the new. Fusion welding, MIG for example, uses filler metals and shielding gases. The filler metal and the parent metal are melted and produce a weld bead that has a solidification structure different from that of the rest of the metal. In MIG and TIG welding, attention has to be paid to the metal’s reaction with oxygen. The oxide rapidly formed in this reaction can cause weld failure. The oxide is heavier than the weld pool and may form inclusions. There is also a risk of void formation. FSW uses no filler metals or shielding gases. The joint is formed under the influences of friction generated heat and extreme plastic deformation. The material being joined never reaches its melting point, but the profiles weld together in a way entirely analogous to the extrusion of hollow profiles. The result is a homogenous and void-free weld with no inclusions. FSW stands out in having only a few variables. These can be easily controlled to ensure the same results from one weld to the next. Fusion welding is a more complicated process. Consequently, results often vary. MIG

Precipitation in a MIG weld.

FSW

50 µm

7.4 mm

Precipitation in an FSW weld.

50 µm

4.7 mm

The MIG weld rises above the surface. Furthermore, its chemical composition differs from that of the welded material.

The FSW weld is, in principle, flush with the welded material. No filler metals are used.

A MIG weld viewed from above.

An FSW weld viewed from above.

To give a fair comparison, the adjacent pictures are of very high quality fusion welds.

70


Strength

Experience and extensive testing have shown that an FSW weld is usually stronger than a fusion weld. The table below shows the standardised values for arc welded butt joints as per SS-EN 288-4 (see also the tests carried out by the Royal Institute of Technology, pages 72 – 73). The values given for FSW joints are based on a large number of measurements and should be regarded as guideline values. Since there are, as yet, no standards for FSW joints, the values for fusion welded joints are used in calculating the strength of standardised designs. Weld factor for the ultimate tensile strength of butt welds, ALMgSi alloys Condition of parent metal before welding

Ageing after welding

T =

Rm (w) Rm (pm)

Arc welding 1)

FSW 2)

T4

Natural ageing

0.9

0.9

T4

Artificial ageing

0.7

0.9

T5-T6

Natural ageing

0.6

0.7

T5-T6

Artificial ageing

0.7

0.8

1) For example, MIG or TIG.

Ultimate tensile strength, Rm (w), of the welded test rod normally has to satisfy the following: Rm (w) = Rm (pm) x T , where Rm (pm) is the prescribed minimum ultimate tensile strength of the parent metal and T is the joint’s weld factor.

2) Guideline values only.

Leakproofness

The pictures on the right are of heat sink units based on solid profiles that are then CNC machined by Sapa. The machined interior is closed with a cover, welded in place by FSW. Helium leak testing was used to assess leakproofness. The result was no loss of impermeability owing to weld failures. FSW joints have also been tested using the water pressure test. The results are unambiguous – FSW gives a joint that can be used in components with the severest demands for leakproofness. Repeatability

The experience Sapa has gained in series production since 1996 shows: – Very small variations from joint to joint throughout a production cycle. – Very small variations from joint to joint in repeat customer orders. This is true of all variables – the joint’s structure, its strength, leakproofness and flatness. Corrosion resistance

The chemical composition of the material in the joint is identical to that of the original material. Thus, in principle, corrosion resistance is unaltered. Limitations

FSW requires the work piece to be held securely in place. This means, amongst other things, that repair welding of finished constructions is rarely possible with FSW. Repairs can, of course, be carried out using traditional methods.

All 25,000 units passed helium testing for leakproofness.

71


Strength of FSW joints Higher fatigue strength than

MIG and TIG welds.

Comparison with MIG and TIG – Reference: The Royal Institute of Technology, Sweden FSW welds have higher fatigue strength than MIG and TIG welds. This is the finding documented by Mats Ericsson, graduate engineer, and Rolf Sandström, professor, (both of the Institution for Materials Science at Sweden’s Royal Institute of Technology) in the December 2001 research report, Influence of Welding Speed on the Fatigue of Friction Stir Welds and Comparison with MIG and TIG. Test material and test methods

This extract from the report gives values for extruded profiles in alloy SS-EN AW 6082 (AlSi1MgMn) – temper T6, material thickness 4 mm. The dimensions of the test pieces were as per SS-EN 284-4. FSW was carried out by Sapa in a plant used for series production. Test materials welded at two different speeds were included in testing. To the same high quality standards as those applying in the aero-industry, fusion welding was carried out by CSM Material Technology. TIG and pulse MIG welding were used. Vickers hardness was measured with a load of 10 kg. Fatigue testing was carried out with a stress ratio (min/max) of 0.5, the main direction of stress being across the weld. Hardness profile 110 100 ) 0 90 1 V H (

80

s s e n 70 d r a H

60

0 -40

-30

-20

-10

0

10

20

30

40

Distance from the weld centre (mm)

The graph shows the variations in Vickers hardness across a cross section of an FSW joint (green) welded at a speed of 1,400 mm/min. and across a MIG weld (grey). Comments: In both welds, hardness in the heat-affected zone decreases. This is clearly more marked in the M IG weld. Hardness is lowest (just under 60 HV) around the centre of the MIG weld. This is because fusion welding involves higher working temperatures, “foreign” filler metals and a less favourable structure in the weld. More heat is supplied in TIG welding than MIG welding. Consequently, the HAZ is a little wider. No significant difference was observed between the HAZs of the two FSW welds carried out at different speeds.

72


Mechanical properties

Fractures under the microscope

Yield strength R p0,2 (MPa)

Tensile strength R m (MPa)

Elongation A 50 mm (%)

Reference

T6, parent metal

291

317

11.3

ME, RS 1)

Min. values for profiles t < 5 mm

250

295

6

Pulsed MIG

147

221

5.2

ME, RS 1)

TIG

145

219

5.4

ME, RS 1)

FSW, speed A 2)

150

245

5.7

ME, RS 1)

FSW, speed B 2)

150

245

5.1

ME, RS 1)

SS-EN AW 6082

SS-EN 755-2

MIG weld: This SEM micrograph (x 25 magnification)

shows the fracture surface. Fatigue fracture developed at several points in the root (to the right).

1) Mats Ericsson and Rolf Sandström, averages of the results in the report in question. 2) Speed A, 700 mm/min. Speed B, 1,400 mm/min.

Fatigue strength 120 110 ) a P100 M ( e g n a r s s e r t S

Same MIG weld as above (x 2,500 magnification):

Fatigue striation in the area close to the root edge.

90 80

70 60 50 0 1 • 10 5

1 • 10 6

1 • 10 7

Number of cycles to failure

The graph above shows the results of fatigue tests on MIG welds (grey), TIG welds (blue) and FSW welds (green). Comments: The FSW weld shows the best values throughout. In the study, TIG welds gave considerably better results than MIG welds. For failure at 500,000 cycles, the stress ranges were: MIG approx. 60 MPa, TIG approx. 70 MPa, FSW approx. 90 MPa at 700 and 1,400 mm/min (a shade higher at 1,400 mm/min).

FSW: Fracture surface through the fine-grained

section of an FSW weld (root to the right). Fracture probably developed close to the root.

Literature

A. Kluken, M. Ranes, Aluminium bridge constructions – welding technology and fatigue properties, Svetsaren, vol 50, no. 3, pages 13 – 15, 1995. P.J. Haagensen, O.T. Midling, M. Ranes, Fatigue performance of friction stir butt welds in a 6000 series aluminium alloy, Computional Mechanics Publications (USA), pages 225 – 237, 1995. 73

11. PROFILE TOLERANCES

11. Profile tolerances The range of profiles that can be produced by extrusion is almost endless. For this reason, there are no general rules detailing potential solutions and applicable tolerances. Profile design, wall thickness and alloy are some of the crucial factors directly affecting tolerances. In this connection it is important to mention that tighter tolerances can affect productivity and, consequently, price. This should be borne in mind during the design stage. Some profile manufacturers have standard tolerances of their own. Others use national standards for their production. CEN, the European Committee for Standardisation, has prepared European standards. These EN norms will gradually replace the different national norms. In the dialogue between the customer and the supplier it is therefore in each case important to clarify which norm that applies. Below you find extracts of the profile norms EN 755-9 and EN 12020-2.

74

11. PROFILE TOLERANCES – EN 755-9

EN 755-9 Alloy groups, EN AW

Tolerances on dimensions

Group I

Cross-sectional dimensions

1050A, 1070A, 1200, 1350 3003, 3103 5005, 5005A 6101A, 6101B, 6005, 6005A, 6106, 6008, 6060, 6063, 6063A, 6463

General

The tolerances on the dimensions listed below (see Figure 1) are specified in the relevant Tables 1 to 7. A wall thicknesses except those enclosing the hollow spaces in hollow profiles; B wall thicknesses enclosing the hollow spaces in hollow profiles, except those between two hollow spaces; C wall thicknesses between two hollow spaces in hollow profiles; E the length of the shorter leg of profiles with open ends; H all dimensions except wall thickness.

E

Group II

2007, 2011, 2011A, 2014, 2014A, 2017A, 2024, 2030 5019 1), 5051A, 5251, 5052, 5154A, 5454, 5754, 5083, 5086 6012, 6018, 6351, 6061, 6261, 6262, 6081, 6082 7003, 7005, 7020, 7022, 7049A, 7075 1) EN AW-5019 is the new designation for EN AW-5056A.

H

E

B

B

A

C

H

H

H H

B

A

H Figure 1: Definition of dimensions A, B, C, E, H

Note: All dimensions in this chapter are in millimetres.

Version 1

75


Tolerances on dimensions other than wall thickness

The tolerances on dimensions shall be as specified in Tables 1 and 2. Table 2: Tolerances on cross-sectional dimensions of solid and hollow profiles – Alloy group II

Table 1: Tolerances on cross-sectional dimensions of solid and hollow profiles – Alloy group I

Dimension H Over

Up to and including

Tolerances on H for circumscribing circle CD

Tolerances on H for circumscribing circle CD CD

 100

100 < CD  200

200 < CD  300

300 < CD  500

500 < CD  800

CD

 100

100 < CD  200

200 < CD  300

300 < CD  500

500 < CD  800

–

10

± 0.25 ± 0.30 ± 0.35 ± 0.40 ± 0.50 ± 0.40 ± 0.50 ± 0.55 ± 0.60 ± 0.70

10

25

± 0.30 ± 0.40 ± 0.50 ± 0.60 ± 0.70 ± 0.50 ± 0.70 ± 0.80 ± 0.90 ± 1.1

25

50

± 0.50 ± 0.60 ± 0.80 ± 0.90 ± 1.0 ± 0.80 ± 0.90 ± 1.0 ± 1.2 ± 1.3

50

100

± 0.70 ± 0.90 ± 1.1 ± 1.3 ± 1.5 ± 1.0 ± 1.2 ± 1.3 ± 1.6 ± 1.8

100

150

–

± 1.1 ± 1.3 ± 1.5 ± 1.7

–

± 1.5 ± 1.7 ± 1.8 ± 2.0

150

200

–

± 1.3 ± 1.5 ± 1.8 ± 2.0

–

± 1.9 ± 2.2 ± 2.4 ± 2.7

200

300

–

–

± 1.7 ± 2.1 ± 2.4

–

–

300

450

–

–

–

± 2.8 ± 3.0

–

–

–

± 3.5 ± 3.8

450

600

–

–

–

± 3.8 ± 4.2

–

–

–

± 4.5 ± 5.0

600

800

–

–

–

–

–

–

–

± 5.0

± 2.5 ± 2.8

–

± 3.1

± 6.0

Table 3: Additions to the tolerances on cross-sectional dimensions H of solid and hollow profiles with open ends – Alloy groups I and II

Dimension E

Over

76

Up to and including

Additions to the tolerances on H in Tables 1 and 2 for dimensions across the ends of open ended profiles

–

20

–

20

30

± 0.15

30

40

± 0.25

40

60

± 0.40

60

80

± 0.50

80

100

± 0.60

100

125

± 0.80

125

150

± 1.0

150

180

± 1.2

180

210

± 1.4

210

250

± 1.6

250

–

± 1.8

Version 1


Tolerances on wall thickness of solid and hollow profiles

The tolerances on wall thickness of solid and hollow profiles shall be specified in Tables 4, 5, 6 and 7. Table 4: Tolerances on wall thickness for profiles with a circumscribing circle up to and including 300 mm – Alloy group I

Up to and including

Tolerances on wall thickness Circumscribing circle


Nominal wall thickness A, B or C Over

Table 5: Tolerances on wall thickness for profiles with a circumscribing circle over 300 mm – Alloy group I

B 1)

A

100 < CD  300

CD

 100

C

100 < CD  300

CD

 100

100 < CD  300

CD

 100

B 1)

A

300 < CD  500

C

500 < CD  800

300 < CD  500

500 < CD  800

300 < CD  500

500 < CD  800

–

–

–

–

–

–

1.5

± 0.15 ± 0.20 ± 0.20 ± 0.30 ± 0.25 ± 0.35 ± 0.25

1.5

3

± 0.15 ± 0.25 ± 0.25 ± 0.40 ± 0.30 ± 0.50 ± 0.35 ± 0.40 ± 0.60 ± 0.80 ± 0.75 ± 1.0

3

6

± 0.20 ± 0.30 ± 0.40 ± 0.60 ± 0.50 ± 0.75 ± 0.40 ± 0.50 ± 0.80 ± 1.0 ± 1.0 ± 1.2

6

10

± 0.25 ± 0.35 ± 0.60 ± 0.80 ± 0.75 ± 1.0

± 0.45 ± 0.55 ± 1.0 ± 1.2 ± 1.2 ± 1.5

10

15

± 0.30 ± 0.40 ± 0.80 ± 1.0 ± 1.0 ± 1.2

± 0.50 ± 0.60 ± 1.2 ± 1.5 ± 1.5 ± 1.9

15

20

± 0.35 ± 0.45 ± 1.2 ± 1.5 ± 1.5 ± 1.9

± 0.55 ± 0.65 ± 1.7 ± 2.0 ± 2.0 ± 2.5

20

30

± 0.40 ± 0.50 ± 1.5 ± 1.8 ± 1.9 ± 2.2

± 0.60 ± 0.70 ± 2.0 ± 2.5 ± 2.5 ± 3.0

30

40

± 0.45 ± 0.60

± 0.70 ± 0.80 ± 2.2 ± 2.7 ± 2.7 ± 3.3

40

50

–

± 0.70

–

± 2.0

–

–

–

± 2.5

–

–

± 0.80 ± 0.90

–

–

–

–

1) For seamless hollow profiles the tolerances given for wall thickness C shall apply.

Table 6: Tolerances on wall thickness for profiles with a circumscribing circle up to and including 300 mm – Alloy group II



Up to and including

Table 7: Tolerances on wall thickness for profiles with a circumscribing circle over 300 mm – Alloy group II

B 1)

A CD

 100

100 < CD  300

CD

 100

Tolerances on wall thickness Circumscribing circle C

100 < CD  300

CD

 100

B 1)

A

100 < CD  300

300 < CD  500

C

500 < CD  800

300 < CD  500

500 < CD  800

300 < CD  500

500 < CD  800

–

–

–

–

–

–

1.5

± 0.20 ± 0.25 ± 0.30 ± 0.40 ± 0.35 ± 0.50 ± 0.35

1.5

3

± 0.25 ± 0.30 ± 0.35 ± 0.50 ± 0.45 ± 0.65 ± 0.45 ± 0.50 ± 0.70 ± 0.90 ± 0.90 ± 1.2

3

6

± 0.30 ± 0.35 ± 0.55 ± 0.70 ± 0.60 ± 0.90 ± 0.60 ± 0.60 ± 0.90 ± 1.0 ± 1.2 ± 1.3

6

10

± 0.35 ± 0.45 ± 0.75 ± 1.0 ± 1.0 ± 1.3

± 0.65 ± 0.70 ± 1.2 ± 1.5 ± 1.5 ± 1.9

10

15

± 0.40 ± 0.50 ± 1.0 ± 1.3 ± 1.3 ± 1.7

± 0.70 ± 0.80 ± 1.5 ± 1.8 ± 1.9 ± 2.3

15

20

± 0.45 ± 0.55 ± 1.5 ± 1.8 ± 1.9 ± 2.2

± 0.75 ± 0.85 ± 2.0 ± 2.5 ± 2.5 ± 3.1

20

30

± 0.50 ± 0.60 ± 1.8 ± 2.2 ± 2.2 ± 2.7

± 0.80 ± 0.90 ± 2.5 ± 3.0

30

40

± 0.60 ± 0.70

40

50

–

± 0.80

– –

± 2.5 –

± 3.1 ± 3.7

–

–

± 0.90 ± 1.0 ± 3.0 ± 3.2

–

–

–

–

± 1.0 ± 1.1

–

–

–

–

1) For seamless hollow profiles the tolerances given for wall thickness C shall apply.

Version 1

77


Length

If fixed lengths are to be supplied, this shall be stated on the order. The tolerances on fixed length shall be specified in table 8. Table 8: Tolerances on fixed length

Circumscribing circle diameter

Tolerances on fixed length L

CD

Over

Up to and including

–

100

100

200

200

450

450

800

L

 2 000

+5 0 +7 0 +8 0 +9 0

2 000
5 000 10 000 15 000
+ 16 0 + 18 0 + 20 0 + 22 0

+ 22 0 + 24 0 + 28 0 + 30 0

If no fixed length is specified in the order, profiles may be delivered in random lengths. The length range and the tolerances on the random length shall be subject to agreement between purchaser and supplier. Squareness of cut ends

The squareness of cut ends shall be within half of the fixed length tolerance range specified in Table 8 for both fixed and random length, e.g. for a fixed length tolerance of + 100 mm, the squareness of cut ends shall be within 5 mm.

Tolerances on form General

Tolerances on form for O and T x 510 tempers shall be subject to agreement between purchaser and supplier.

78

Version 1


Straightness

Deviations from straightness, hs and ht , shall be measured as shown in Figure 2 with the profile placed on a horizontal baseplate so that its own mass decreases the deviation. The straightness tolerance ht shall not exceed 1.5 mm/m length. Local deviations hs from straightness shall not exceed 0.6 mm/300 mm length. m m 3 0 0

W

Key 1 Baseplate 2 Ruler

h s

2

1

1 F

Key 1 Baseplate

t

h t

1

L

F

W

1 Figure 2: Measurement of deviation from straightness

Figure 3: Measurement of convexity – concavity

Convexity – Concavity

The convexity – concavity shall be measured as shown in Figure 3. The maximum allowable deviation on convexity – concavity for solid and hollow profiles shall be as specified in Table 9 as a function of profile thickness width W and thickness t . Table 9: Convexity – concavity tolerances

Deviation F

Width W Over

Hollow profiles 1) Wall thickness t  5

Up to and including

Sold profiles

Wall thickness t  5

–

30

0.30

0.20

0.20

30

60

0.40

0.30

0.30

60

100

0.60

0.40

0.40

100

150

0.90

0.60

0.60

150

200

1.2

0.80

0.80

200

300

1.8

1.2

1.2

300

400

2.4

1.6

1.6

400

500

3.0

2.0

2.0

500

600

3.6

2.4

2.4

600

800

4.0

3.0

3.0

In the case of solid and hollow profiles with a width W of least 150 mm, the local deviation F 1 , shall not exceed 0.7 mm for any 100 mm of width W 1 .

1) If the profile has varying wall thicknesses in the measurement range, the thinnest wall thickness shall be used.

Version 1

79


Contour

Table 10: Contour tolerances

For profiles with curved cross sections, the deviation at any point of the curve from the theoretically exact line as defined by the drawing, shall not be greater than the appropriate tolerance C specified in Table 10. Considering all points on the curve, a tolerance zone shall be defined as the zone between two envelopes running tangentially to all circles of diameter C which can be drawn with their centres lying along the theoretically exact line; this is shown in Figure 4 (a and b).

Width W of the contour Over

X

C 4a

W

C

X

–

30

0.30

30

60

0.50

60

90

0.70

90

120

1.0

120

150

1.2

150

200

1.5

200

250

2.0

250

300

2.5

300

400

3.0

400

500

3.5

500

800

4.0

checked by placing a section of the profile on a 1:1 scale projection of the drawing with the contour tolerance indicated on the drawing. Another recommended method is the use of suitable gauges (min./max.).

Figure 4a and b: Definition of contour tolerances

Table 11: Twist tolerances

Twist T shall be measured as shown in Figure 5 by placing the profile on a flat baseplate the profile resting under own mass, and measuring the maximum distance at any point along the length between the bottom surface of the profile and the baseplate surface. Tolerances shall be as specified in Table 11 as a function of the width W and the length L of the profile. L

1

Key 1 Baseplate W

Up to and including

NOTE Contour tolerances can be

4b

Twist

Contour tolerance = diameter C of the tolerance circle

Twist tolerance T for length L

Width W Up to and including

Per 1 000 of length 1)

–

30

30

Over

On total profile length L Over 6 000

1.2

Over 1 000 and including 6 000 2.5

50

1.5

3.0

4.0

50

100

2.0

3.5

5.0

100

200

2.5

5.0

7.0

200

300

2.5

6.0

8.0

300

450

3.0

8.0

450

600

3.5

9.5

600

800

4.0

10.0

3.0

1.5 x L (L in metres)

1) Twist tolerances for lengths less than 1,000 mm shall be subject to agreement between purchaser and supplier.

T

Figure 5: Measurement of twist

80

Version 1


Angularity

The deviation from a specified angle shall be measured as shown in Figures 6 and 7. The angularity tolerances for right angles shall be as specified in Table 12 as a function of profile width W . The maximum allowable deviation  in an angle other than a right angle shall be ± 1°. In the case of unequal side lengths the tolerance on angularity shall apply to the shorter side of the angle, i.e. it is measured starting from the longer side. Z 

W

Figure 6: Measurement of angularity in a right angle

Table 12: Angularity tolerances for right angles

Up to and including

Maximum allowable deviation, Z from a right angle

–

30

0.4

30

50

0.7

50

80

1.0

80

120

1.4

120

180

2.0

180

240

2.6

240

300

3.1

300

400

3.5

Width W Over

Figure 7: Measurement of angularity in an angle other than a right angle

Corner and fillet radii

Sharp corners and fillets may be slightly rounded unless otherwise indicated on the drawing. The maximum allowable corner and fillet radii shall be as specified in Table 13. When a corner or fillet radius is specified, the maximum allowable deviation from this radius shall be as specified in Table 14. Table 14: Maximum allowable deviation from specified corner and fillet radii

Table 13: Maximum allowable corner and fillet radii

Maximum allowable radius

Wall thickness A, B or C 1) 5

>5

Alloy group I

0.6 1.0

Specified radius mm

Maximum allowable deviation from specified radius

0.8

5

± 0.5 mm

1.5

>5

± 10 %

Alloy group II 2)

1) Where varying wall thicknesses are involved, the maximum allowable radius in the transition zone is a function of the greater wall thickness. 2) These tolerances only apply to 6xxx series alloys in group II. The maximum allowable radii for the other alloys in group II shall be subject to agreement between purchaser and supplier.

Version 1

81


EN 12020-2 The information below applies only to the alloys EN AW-6060 and EN AW-6063. Note: All dimensions in this chapter are in millimetres. E

A

Cross-sectional dimensions General

The tolerances of the following dimensions (see Figure 1) are specified in the relevant Tables 1 and 2. A wall thicknesses except those enclosing the hollow spaces in hollow profiles; B wall thicknesses enclosing the hollow spaces in hollow profiles, except those between two hollow spaces; C wall thicknesses between two hollow spaces in hollow profiles; E the length of the shorter leg of profiles with open ends; H all dimensions except wall thickness.

The tolerances for dimension H shall be as specified in Table 1.

Over

Up to and including

Tolerances on H (open ends) E

 60

60 < E  120 1)

–

10

± 0.15

± 0.15

2)

10

15

± 0.20

± 0.20

2)

15

30

± 0.25

± 0.25

2)

30

45

± 0.30

± 0.30

± 0.45

45

60

± 0.40

± 0.40

± 0.55

60

90

± 0.45

± 0.45

± 0.65

90

120

± 0.60

± 0.60

± 0.80

120

150

± 0.80

± 0.80

± 1.0

150

180

± 1.0

± 1.0

± 1.3

180

240

± 1.2

± 1.2

± 1.5

240

300

± 1.5

± 1.5

± 1.8

1) Tolerances for values of dimension E over 120 mm shall be subject to agreement between purchaser and supplier. 2) Shall be subject to agreement between purchaser and supplier. 82

H B H

A

A

H Figure 1: Definition of dimensions A, B, C, E, H

Tolerances on wall thickness of solid and hollow profiles

Table 2: Tolerances on wall thickness

Table 1: Tolerances on cross-sectional dimensions

Tolerances on H (except open ends)

A

C

The tolerances on wall thickness (see Figure 1) of solid and hollow profiles shall be as specified in Table 2.

Tolerances on dimensions other than wall thickness

Dimension H

B

Tolerances on wall thickness A B and C


Up to and including

Circumscribing circle  100

CD

100 < CD  300

 100

CD

100 < CD  300

–

1.5

± 0.15

± 0.20

± 0.20

± 0.30

1.5

3

± 0.15

± 0.25

± 0.25

± 0.40

3

6

± 0.20

± 0.30

± 0.40

± 0.60

6

10

± 0.25

± 0.35

± 0.60

± 0.80

10

15

± 0.30

± 0.40

± 0.80

± 1.0

15

20

± 0.35

± 0.45

± 1.2

± 1.5

20

30

± 0.40

± 0.50

–

–

30

40

± 0.45

± 0.60

–

–

When, for functional reasons, tolerances are specified for both the outside and inside dimensions of hollow sections, then the deviations given in Table 2 shall not apply as a wall thickness tolerance, but as a tolerance on the difference in wall thickness. This difference shall be determined by measuring the maximum and minimum wall thickness in the same plane. Version 1


Table 3: Tolerances on fixed length

Length

If fixed lengths are to be supplied, this shall be stated on the order. The fixed length tolerances shall be as specified in Table 3. If no fixed or minimum length is specified in the order, profiles may be delivered in random lengths. The length range and the tolerances on the random lengths shall be subject to agreement between purchaser and supplier.

Circumscribing circle CD Over

Up to and including

–

100

100

200

200

300

Tolerances on fixed length L 2 000
L

 2 000

+5 0 +7 0 +8 0

L 5 000
+7 0 +9 0 + 11 0

+ 10 0 + 12 0 + 14 0

t o n t t e c m e e j b e r u g S a

Squareness of cut ends

The squareness of cut ends shall be within half of the fixed length tolerance range specified in table 3 for both fixed and random lengths, e.g. for a fixed length tolerance of mm the squareness of cut ends shall be within 5 mm. + 10 0

Length offset for profiles with a thermal barrier

Length offset K , see Figure 2, for profiles with a thermal barrier shall be within the tolerance range for the fixed length specified in Table 3, e.g. for a fixed length tolerance of + 10 mm the length offset shall be within 10 mm.

1

Key 1 Length of profile 2 Profile 1 3 Thermal barrier 4 Profile 2

2 3 4 K

Figure 2: Length of offset K

Tolerances on form

t

h

1

L

Figure 3: Measurement of deviation from straightness

Table 4: Straightness tolerances

Straightness tolerances ht for specified length L L

 1 000

0.7

Version 1

s

2

Straightness

Deviations from straightness, hs and ht , shall be measured as shown in Figure 3 with the profile placed on a horizontal baseplate so that its own mass decreases the deviation. The straightness tolerance ht shall be as specified in Table 4. The local deviation from straightness hs shall not exceed 0.3 mm per 300 mm length.

Key 1 Baseplate 2 Ruler

h

m m 3 0 0

1 000 2 000 3 000 4 000 5 000 L
1.8

2.2

2.6

3.0

3.5

83


Convexity – Concavity

Table 5: Convexity – concavity tolerances

The convexity – concavity shall be measured as shown in figure 4. The tolerances shall be as specified in Table 5.

Width W Over

Key: W = Width, F = Deviation, W 1 = 100 mm, F 1 = 0.5 mm maximum F

W

W

F

1

W 1

F

F W Figure 4: Measurement of convexity – concavity

Maximum allowable deviation

Up to and including

F

–

30

0.20

30

60

0.30

60

100

0.40

100

150

0.50

150

200

0.70

200

250

0.85

250

300

1.0

In the case of profiles with a width W of at least 200 mm, the local deviation F 1 shall not exceed 0.5 mm for any 100 mm of width, W 1 .

Contour

For profiles with curved cross sections, the deviation at any point of the curve, from the theoretically exact line as defined by the drawing shall not be greater than the appropriate tolerance C specified in Table 6. Considering all points on the curve, a tolerance zone shall be defined as the zone between two envelopes running tangentially to all circles of diameter C which can be drawn with their centres lying along the theoretically exact line ; this is shown in Figure 5 (a and b). X C 5a

Table 6: Contour tolerances

Width W of the contour Over

Contour tolerance = diameter C of the tolerance circle

Up to and including

–

30

0.30

30

60

0.50

60

90

0.70

90

120

1.0

120

150

1.2

150

200

1.5

200

250

2.0

250

300

2.5

NOTE Contour tolerances can be

checked by placing a section of the profile on a scale projection of the drawing with the contour t olerance indicated on the drawing. Another recommended method is the use of suitable gauge (min./max.).

W

C

X 5b

Figure 5a and b: Definition of contour tolerances

84

Version 1


Twist

Twist T shall be measured as shown in Figure 6 by placing the profile on a flat baseplate, the profile resting under its own mass and measuring the maximum distance at any point along the length between the bottom surface of the profile and the baseplate surface. Tolerances shall be specified in Table 7 as a function of the width W and the length L of the profile.

Key 1 Baseplate

L

1

Figure 6: Measurement of twist

T

W

Table 7: Twist tolerances

Width W Over

Twist tolerances T for specified length L

L L Up to 1 000 2 000 3 000 4 000 5 000 and
–

25

1.0

1.5

1.5

2.0

2.0

2.0

25

50

1.0

1.2

1.5

1.8

2.0

2.0

50

75

1.0

1.2

1.2

1.5

2.0

2.0

75

100

1.0

1.2

1.5

2.0

2.2

2.5

100

125

1.0

1.5

1.8

2.2

2.5

3.0

125

150

1.2

1.5

1.8

2.2

2.5

3.0

150

200

1.5

1.8

2.2

2.6

3.0

3.5

200

300

1.8

2.5

3.0

3.5

4.0

4.5

t n e m e e r g a o t t c e j b u S

Angularity

The deviation from a specified angle shall be measured as shown in Figures 7 and 8. The angulary tolerances for right angles shall be as specified in table 8 as a function of profile width W . The maximum allowable deviation  for angles other than a right shall be ± 1° (see Figure 8). In the case of unequal side lengths the tolerances on angularity shall apply to the shorter side of the angle, i.e. it is measured starting from the longer side. Z 

W

Figure 7: Measurement of angularity in a right angle

Version 1

Table 8: Angularity tolerances for right angles

Up to and including

Maximum allowable deviation, Z from a right angle

–

30

0.3

30

50

0.4

50

80

0.5

80

100

0.6

100

120

0.7

120

140

0.8

140

160

0.9

160

180

1.0

180

200

1.2

200

240

1.5

Width W Over

Figure 8: Measurement of angularity in an angle other than a right angle

85


Corner and fillet radii

Sharp corners and fillets may be slightly rounded, unless otherwise indicated on the drawing. The maximum allowable corner and fillet radii shall be as specified in Table 9. When a corner or fillet radius is specified, the maximum allowable deviation from this specified radius shall be as specified in Table 10. Table 9: Maximum allowable corner and fillet radii

Wall thickness A, B 1) or C 1) Over

Up to and including

Maximum allowable corner and fillet radii

–

3

0.5

3

6

0.6

6

10

0.8

10

20

1.0

20

40

1.5

Table 10: Maximum allowable deviation from specified corner and fillet radii

Specified radius mm

Maximum allowable deviation from specified radius

5

± 0.5 mm

>5

± 10 %

1) When varying wall thicknesses are involved, the maximum allowable radius in the transitionzone is a function of the greater wall thickness.

CEN – the European Committee for Standardisation

CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom. You can buy the complete European standard from your national CEN member. These extracts based on DS/EN 755-9:2002 and DS /EN 12020-2:2001. All rights of exploitation in any form and by any means are given by The Danish Standards Association. 86

Version 1

12. SURFACE CLASSES

12. Surface classes Surface quality The surface quality of an extruded aluminium profile depends on, amongst other things, the condition of the die, production conditions and choice of alloy. Sapa has a well proven classification system for evaluating surface quality (finish). The six classes have been devised to satisfy the standard requirements of different product groups. Always contact Sapa for advice on which class is best suited to a product. Various types of surface defects are recognised. Stripes, for example, are formed by the extrusion process itself (when the profile emerges from the die) and are always to be expected. They occur, to greater or lesser extents, in all surface classes. Sapa’s production standards minutely detail the requirements applying to each surface class. Visible surfaces – important information

Information on a profile’s visible surfaces is important. Besides being used in surface evaluation, surface specifications are also vital in the construction of dies and when preparing profiles for anodising or painting. Incorrect or incomplete information may increase production costs. Profile drawings must always indicate visible, less visible and invisible surfaces. Visible surface: Less visible surface: Invisible surface:

(no marking)

Less visible surfaces are those which are not normally exposed in the final product. Examples include the returns on door and window frames, the underneaths of table surfaces and the backs of cabinets. A profile’s surface class relates to its visible surfaces. Less visible surfaces are classed one step lower and invisible surfaces two steps lower (though never higher than surface class 5). Profiles with no visible surfaces at all are classified as surface class 6.

Surface class relates to visible surfaces.

Any changes in surface class requirement must be clearly stated when ordering. In some cases, it is impossible to achieve a higher surface class using the specified die. Always contact Sapa for advice.

87

12. SURFACE CLASSES

Review profile design carefully

Even at the design stage, it is possible to reduce the risk of surface defects. Sharp transitions between thick and thin areas of material may give rise to heat zones. These, in turn, can affect surface finish in a way that is particularly visible after anodising. A large radius also reduces the risk of surface defects. Consult Sapa for advice on profile design. Specimen profiles are not representative as regards surfaces and material properties. They should only be used for checking dimensions, etc. If possible, the profile’s area of application should be stated. This information is important not only when evaluating surface class, but also in all other production phases. The effects of surface treatment

Anodising results in a general improvement of surface quality. With chemical or mechanical treatment (grinding, brushing and/or polishing) before anodising, material supplied as surface class 2 can be brought up to surface class 1. Bright anodising emphasises any surface defects. Consequently, it lowers surface class one step compared to the untreated material as extruded. Handling and stocking

Where it is important to maintain the decorative finish of products in surface classes 1 – 5, the following should be borne in mind: – When handling aluminium that has not been surface treated, special attention should be paid to the metal’s poor scratch resistance. To protect the profile against sweat-initiated corrosion, gloves should always be worn. – Aluminium which has not been surface treated is to be stocked dry, preferably indoors, so that it is not exposed to corrosive forces.

88

12. SURFACE CLASSES

Surface class (at delivery)

Area of application, etc.

Suitable Sapa alloys

approx. 0.6 m

6060, 6063, 6463

approx. 1 m

6060, 6063, 6463

approx. 2 m

6060, 6063, 6463

approx. 3 m

approx. 5 m

approx. 8 m

1

2

Profiles with very high surface quality requirements

3

Profiles with high surface quality requirements

4

Profiles with ordinary surface quality requirements

5

Profiles with low surface quality requirements

Structural systems, balconies, roofs, doorways, awnings, railing posts, sailing boat masts, ladders, goalposts, etc. Standard sections in Sapa 6063 alloy, body sections.

6060, 6063, 6063A, 6005, 6005A, 6082, 6101, 6463

6

Profiles with no surface quality requirements

All

Furniture, fittings, radios/TVs, picture frames, ornamentation and profiles that are to be brought up t o surface class 1. Max. delivery length, 2.4 m unless otherwise agreed. Production requires individual handling and inspection as well as a large labour input in all phases. Highest surface class for bright anodising. Profiles that have visible surfaces on all sides cannot be produced in this surface class. Profiles in this class must, as a rule, be anodised. Individual packaging/protection required during transport.

Furniture, light fittings, fridge-freezers, bathroom fittings and equipment, shower cubicles and decorative trims. As a rule, profiles that have visible surfaces on all sides cannot be produced in this surface class. Profiles in this class are usually anodised.

Structural systems, facades, windows, doors, balustrades. Also products for use in public facilities: Furniture, shop fittings, showcases, shower cubicles, machine casings, heat sinks. Profiles in this surface class are usually anodised/painted.

Viewing distance Normal eyesight in normal lighting

6060, 6063, 6463

Profiles with extremely high surface quality requirements

Radios/TVs, lighting fixtures, decorative trims, ornaments. Max. delivery length, 2.4 m unless otherwise agreed. This surface class can only be achieved with material extruded as surface class 2 and then treated chemically or mechanically (grinding, brushing and/or polishing) before finally being anodised. Production requires individual handling and inspection as well as a large labour input in all phases. Profiles that have visible surfaces on all sides cannot be produced in this surface class (except where the profile is also to be ground on all sides). Individual packaging/protection required during transport.

Load-bearing structures, guide rails, conducting rails, scaffolding, components in mechanical systems, brackets, industrial railings, fencing posts. Standard profiles in Sapa 6082 alloy, trailer profiles for lorries and floor profiles. Profiles with no visible surfaces. Profiles in Sapa 7021 and Sapa 1050A alloys can only be extruded to this surface class. Version 1

89

13. THERMAL BREAK PROFILES

13. Thermal break profiles Why insulated profiles? Because aluminium’s good thermal conductivity leads heat out and lets cold in. This can be a problem in, for example, facades, windows and doors designed with uninsulated profiles. Sapa’s solution is to connect the internal and the external sections of a profile via plastic insulation strips. Sapa’s method Glass fibre reinforced polyamide (nylon) strips

In Sapa’s solution, rolling is used to join two aluminium profiles via glass fibre reinforced polyamide strips. – Insulating strip width is normally 14 – 30 mm. Sapa keeps the most common widths in stock (check with Sapa). – Rolling can be used on lengths from 4.5 – 7.5 m. – Degree of insulation depends on strip width and profile design. Produced in three steps

The production equipment is purpose-designed. The three steps are: 1. Machining (knurling) of the track to ensure durability. 2. Joining of the aluminium profiles by sliding in the polyamide strips. 3. Rolling – the aluminium channels are closed around the polyamide strips. During production, random sampling is used to check the strength of the rolling.

1. Knurling of the profile.

2. Joining of the profiles.

3. Rolling.

Single or double insulation

Two insulation strips are always recommended where lack of space does not leave single insulation as the only possibility. Strength properties and tolerances are considerably better with two strips.

90

13. THERMAL BREAK PROFILES

Insulated profile design

Besides normal design rules, the following also apply: – To provide the necessary support during rolling, the sides have to be minimum 5 mm and perpendicular to the plastic strips. – Regarding the handling of aluminium profiles in the rolling equipment, Z profiles must be modified so that they do not tilt. The rolling surfaces should be centred and at 90° to the insulation strips. A certain degree of imbalance can be handled by special supports (contact Sapa for advice). – The minimum distance between insulation strips is 16 mm. – Both insulation strips should normally be of the same width.

Examples of insulated door profiles.

91

14. MACHINING

14. Machining At the design stage, it is possible to create a profile that needs a minimum amount of post-extrusion machining. However, some form of further processing is often necessary after extrusion. Machining aluminium profiles is, comparatively speaking, inexpensive. The metal’s malleability means that die costs are, as a rule, highly competitive. The cutting speeds attainable with aluminium are far higher than those with steel. Machining can take place both before or after anodising. The choice is determined by the demands made on the product. “Protective anodising” is a good way of preventing damage to profiles during machining.

92

14. MACHINING

High-speed machining

In recent years, machines and equipment for machining aluminium have seen relatively rapid development. High machining speeds have made it possible to achieve reduced wall thicknesses and tighter tolerances. This has further increased aluminium’s competitiveness. As regards the high-speed machining of aluminium, it is cutting speeds of 3,500 m per minute and over that are most interesting. At this point, the cutting forces diminish and, with increased cutting speed, fall to a very low level. This allows feed speeds to be increased. As a result, machining times are reduced. Lower cutting forces also reduce burr formation and increase tool service life. Machines capable of exploiting these higher feed speeds require significantly improved dynamics, and considerably more efficient control systems, than conventional machines. Shorter lead times

In today’s market, there is a constant demand for ever shorter lead times. Amongst other things, this has led to the development of the “product workshop” concept of production. The demand for shorter lead times makes it highly desirable to avoid transfers of materials between independent machining centres and areas of responsibility. The solution is a concept in which operations are integrated – there is a single centre of responsibility and, very often, a single supplier. Series sizes

The size of a product series is often a crucial factor in deciding which production methods are to be used. Thus, as early as possible, it is vital that an assessment is made of the series sizes of all the necessary parts.

Scrap – a valuable raw material

For Sapa, production scrap is a valuable raw material that can be immediately exploited for transformation into new profiles. This is an important consideration. Machining methods

Machining methods are classified by the way in which they give shape to the work piece – plastic deformation, stock cutting and stock removal. The following pages examine some of the methods that are suitable for machining aluminium. 93

14.1 MACHINING – STOCK CUTTING

14.1 Stock cutting 14.1.1 Punching/cutting

Cutting using a punch and a die is commonly referred to as punching. The bottom part of the punch and the upper edges of the die present a cutting profile corresponding to the contours and cavities of the part to be cut. Usually, the punch is mobile and the die is fixed.

Punch Material Die

The punch penetrates the material. Deformation is at first elastic and then plastic. This is followed by fracture initiation, first at the punch edges and then at the die edges. Cutting is completed by these fractures propagating through the material and then joining.

94

14.2 MACHINING – STOCK REMOVAL

14.2 Stock removal Extruded aluminium is easy to cut. Thanks to high cutting speeds, and the high feed speeds this makes possible, machining costs are low and production rates are high. If care is not taken, problems such as build-up on the cutting tools, chip blockages, burr formation and difficulty in meeting tolerances can arise. The right cutting settings and tool geometry are important. Broadly speaking, cutting tools for extruded aluminium are characterised by positive cutting angles and ample space for chips. PKD tools (tools with diamond inserts) very often give good results. Sapa has, on occasions, drilled up to 500,000 holes using the same tool. Titanium coated, hard metal blades are a further example of a class of cutting tool with a long service life. In long production runs, machining can often be streamlined by, for example, having automated transport between machines and using a line system.

Up to 500,000 holes with

the same cutting tool.

14.2.1 Turning Turning in automatic lathes is only possible with alloys that produce short chips. As a rule, an alloy should be worked at its highest possible temper. Furthermore, if possible, a hardenable alloy should be chosen. With the metal in a soft condition, problems such as build-up on the blade, long chips, chip blockages, extreme burr formation and difficulty in meeting tolerances may arise.

It is important to choose the correct cutting settings (e.g. cutting speed and feed) so that, amongst other things, the chips fall away from the point of cutting. Cutting fluid (mineral oil or, in some cases, a water-based emulsion) is used to cool the cutting tool and wash chips away. Cutting tools are most usually made of hard metals or high-quality high-speed steel. To give good turning results and surface quality, the cutting tool should have high surface fineness and a good edge. In CNC lathes with several tool arms, drilling, tapping and milling can be carried out at the same time as turning. 95

14.2 MACHINING – STOCK REMOVAL

14.2.2 Drilling Drill bits suitable for extruded aluminium have a tip angle of around 130°, a spiral angle of approx. 40° and provide ample room for chips. Recommended settings for cutting

Diameter:

10 mm.

Cutting speed, v

Depth:

Feed, s

High-speed steel

Hard metal

70 – 150 m/min. 0.1 – 0.4 mm/rotation

150 – 1,000 m/min. 0.1 – 0.7 mm/rotation

30 mm. Time:

approx. 0.3 sec.

The cutting speed depends on the drill’s speed (rpm) and the speed at which the bit is fed into the material. With the right equipment and settings, a 10 mm wide, 30 mm deep hole can be drilled in 0.3 seconds. 14.2.3 Milling Extruded aluminium can be milled in everything from simple milling machines to high-speed machines. High-speed machining makes it possible to achieve very good tolerances, surface finishes and processing speeds. Sapa has high-speed machines that operate from 20,000 to 40,000 rpm.

Milling.

Cutting to length.

14.2.4 Cutting to length Circular saw speed should be around 3,000 rpm and blade diameter between 200 and 800 mm. Saws especially designed for cutting aluminium can cut the work piece so neatly that, for most purposes, there is no need for further processing of the cut. Radial saws can cut profiles that are up to 500 mm wide.

96

14.3 MACHINING – FORMING

14.3 Plastic forming 14.3.1 Draw bending

Draw bending is the most commonly used bending method. It is suitable for tight radii and has a high degree of repeatability. Using an adjustable clamping jaw, the work piece is fixed against a rotating die. The clamping jaw and the tool are shaped to reproduce the profile’s cross section. The work piece rotates with the die. This stretches the material on the outside of the profile and compresses that on the inside. To prevent scratches and clamping marks on the profile, the tools are usually made of plastic. Anodised profiles: Being hard and brittle, the oxide layer forms many fine cracks during bending. If a high quality surface is required, it is recommended that anodising is left until after bending.

Draw bending.

For high quality surfaces ,

bend before anodising.

Roller bending.

14.3.2 Roller bending Roller bending is used for forming large radii in the work piece. The work piece is rolled between two drive rollers and a pressure roller. The shape presented by the rollers corresponds to the profile’s cross section. Vertical adjustment of the upper roller (the pressure roller) alters the radius of the bend. Thus, in CNC machines, a number of different radii can easily be pressed into a single work piece. As rollers are most usually made of steel, lubrication is often required to prevent cutting and scratching of the profile.

97

14.3 MACHINING – FORMING

14.3.3 Stretch bending Stretch bending gives very high three-dimensional sha pe accuracy. The work piece is fixed between two clamping jaws and then gradually stretched over a shaping block. The shape presented by the block corresponds to the profile’s cross-section. The metal is stretched to its upper elastic limit and spring-back is thus negligible. As the tooling investment is relatively high, stretch bending is best suited to large series production.

Very high threedimensional shape accuracy.

Stretch bending.

14.3.4 Press bending Press bending (point bending) is suitable for simple bending of large series. The work piece is formed using compressive force. An upper and a lower die are contoured to give the work piece the desired shape. Pressure is applied by some form of excentric or hydraulic press. Depending on the exterior of the part to be pressed, dies can be steel or plastic.

Press bending.

98

14.4 – 5 MACHINI NG – THREADING, TOLERANCES

14.4 Threading Cutting and forming methods can both be used to make threads. When cutting using taps, a chipping angle of 35 – 40º is recommended. Cutting speed should be 30 – 40 m/min. When producing a thread by rolling, the so-called oil groove method is recommended. Speed should be 40 – 70 m/min. The milling of threads gives good results all the way down to, in some cases, M3.

14.5 Tolerances Machining is normally to ISO 2768-1 (middle), but tighter tolerances normally present no problem. In high-speed machining, channels and holes can be milled to, for example, H7. This does away with the need for subsequent reaming.

Thread milling even down to M3.

99

14. MACHINING – EXAMPLE PRODUCTS

g g, i n i n a c h n o d i s i n m N C ), a h, C a d i n g t g r e e n t o l l in g, t h y. g n l i i t r b l C u t l in g, d s s e m l a i ( m d i n g, b e n

C g, C N t h, , d r i l l in g n e , t o l l l in g in g g ( m i d i s i n g t t C u h i n i n , a n o b l y. c ) m a a d i n g s s e m a t h r e d i n g, n b e

N C g, h, C r m i l l in s i n g, t g l e n t o u o d i g t o g ( c o n g ), a n n i t C u t h i n i n r e a d i n b l y. c m a in g, t h a s s e m l d r il d i n g, e b n

g, ), r i l l in l a s t in g d , l l in g g ( b ( m i b u r r in g n d e i n i a c h s h i n g, l y. m b C u C N d b r s e m in g, g ), e n g, a s t t C u a d i n a s h i n t h r e l in e w a l k a

, i n g e n d b r a w h, d h i n g. t g l e n r u s g t o , e n d b n i t t C u c h i n g p u n

g, g. h i n r u s u n c h i n b , p e n d t h, i l l in g ) g n e g ( m t o l in g c h i n i n t t C u C m a C N

100

, g t h l e n g o t i n t in g h i n t C u t C m a c in g, fl a l in g ), l C N e b o r g, d r i . h i l l in i n g t a l h ( e m a s f a c l in e w a l k a

t h, e n g a d i n g l o t e t in g , t h r n d C u t p i n g d s ), e s i n g. m i s t a t h r e a a n o d n , e g ( t s h i n b r u

g i n i n a c h n d m C , e , C N a d i n g ) n g ), h t s t i e n g r e t o l l in g, t h g ( b l a g l n n i r ti ri C u t l in g, d d e b u r . l g i , g i ( m s h i n a s h n b r u l in e w a l k a

g, r r in u b , d e f a c e g t h ( n fl a t N C e l g o t n C i , t in g h i n i n g, n g ) C u t C m a c n o d i s e b o r i C N in g ), a ( l a t h g. g l m i l h i n i n a s h i n c e w a m l in a l k a

a g i n k a l in e n i a l m p s t a n g, n d b r u s h i a g t h d l e n n e, e n o t i t in g a c h C u t c i a l m s p e h i n g. w a s , i n g m p d i n g. a t s b e n t h, e n g p r e s s l o t g, t in g r r in C u t d e b u e n d

14. MACHINING – EXAMPLE PRODUCTS

C , , C N i l l in g h t m g , , n g g e t o l i l l in h i n n e in g n g ( d r d b r u s a l k a l i t t C u c h i n i ), e n t in g ), m a a d i n g ( b l a s t h r e u r r in g d e b h i n g. w a s

, in g ), m i ll a s t in g ( g b l ( i n i n a c h u r r in g m N C d e b in g. h, C s h i n g, r o m a t t g h u e n t o l e n d b r w h i te c in g g , , t ) t C u a d i n a s h i n g t h r e l in e w a l k a g, i l l in m , l l in g ( d r i in g ), g i n t r c h i n g, c e n a C m a d i n , C N g, t h r e h t e n g i n h s. t o l , r e a m l e n g t g g t in n g C u t e b o r i i n l o n g h l a t d i s i n a n o

i n g n g. c h i n w a s h i a C m n e C N a l k a l i , h t ), e n g n g t o l e c u t ti g t in o l C u t l in g, h l i ( m

. i n g T u r n

C ), , C N m i l l in g h t e n g t f a c e C N C . t o l ( , a g ) g t in i n g fl d i s i n g d r i l l in t u C h i n a n o in g, c m a d i n g, ( m i ll g r g in c h i n i n a m

g, r r in u b ), b l y. , d e g g t h ( m i l l in s s e m n e t o l n g g, a in g a c h i n i d i s i n t t C u C m , a n o C N c h i n g p u n

g, i l l in m ( i n g c h i n g. a C m i s i n , C N , a n o d h t e n g n g ) t o l e b o r i g n ti t h C u t c i a l l a e C p ) s , C N m i l l in g h t g n e c C e t o l a t f a , C N ). t in g i n g ( fl d i s i n g d r i l l in g t u C h i n n o c n g, a m a d i n g, ( m i l li g r in h i n i n g c m a

g, h i n c n o n g t o l ( , p u n g n g g t h . d i s i ), c u t ti , n o e n l A t h s n i n g i n g g r g t o w a s h n i l e n t h, t u t g . c u t n e l e n c h i n g s ), a l k a l i h t n g g, p u n g l e k i n l o n t e r s i n ( g n i s i n , c o u d o g A n a d i n t h r e

h, n g t , e l t o i n g t in g a c h i n a l in e t u C C m , a l k C N u r r in g d e b h i n g. w a s

101

14. MACHINING – HYDROFORMING

14.6 Hydroforming Complex parts with

very good dimensional accuracy.

Our starting point is an extruded aluminium pipe. Hydroforming allows us to shape it three-dimensionally in a single operation. The process offers as yet unexplored possibilities. All, or parts, of a profile’s cross section can be tailored using hydroforming. In a single operation, complex parts can be created with very good dimensional accuracy. In a single hydroforming operation, it is also possible to make local changes such as domes or holes. By eliminating several machining operations, lead times can be shortened. Hydroforming of aluminium profiles is a competitive choice at yearly volumes of around 20,000 units upwards. The principle

The profile is placed in a die that has an inner geometry exactly replicating the shape of the finished component. The die is locked securely in position and hydrostatic pressure is then set up in the pipe (profile). As the profile is pressed against the die, it takes up the shape of the die. The automotive industry – Research and series deliveries

Since the end of the 90’s, along with Volvo and Ford, Sapa has been involved in research projects on, and prototype production of, vehicle side beams hydroformed from extruded aluminium profiles. Today, Sapa has world-leading and unique expertise and experience in the hydroforming of long aluminium beams. In the autumn of 2001, Sapa began series deliveries to Volvo.

Simulation, using the FE method, to study the critical points in the forming process.

The shaped component. Note the cross-sectional changes throughout its length. 102

14. MACHINING – HYDROFORMING

Example product: Side beam for a Space Frame . p i p e m u i n i l u m e d a d u r t n e x m a o r f ts s t a r t io n c u P r o d

1.

h r o u g s t h e o g h e n p e t i n g. i p d h e 2. T w b e n d r a

n t. o n e p o m d c e h s fi n i T h e

Cross-sectional change so that the profile can fit into a narrow passage. In order to make a hole during the hydroforming process, a punch is included in the tooling. Punching extends process time by a few seconds only. The hole is precisely positioned and no further machining is required.

3 .

The result – very good dimensional accuracy and exactly the geometry required by the product and production.

Compared with traditional steel/plate bodies, hydroforming gives weight savings of around 50%.

Profile design, dimensions and tolerances

In discussions, Sapa has contributed advice in respect of a wide range of designs for, amongst others, the automotive, furniture, electronics and engineering industries. In design discussions, it has become clear that hydroforming opens the way to unique solutions for a wide range of design problems. Thus, it would not be easy to here give simple rules for profile design, dimensions and tolerances. Contact Sapa’s hydroforming department in Vetlanda, Sweden, for further details. 103

15. SURFACES

15. Surface treatment

Suitable surface treatment can enhance a range of attributes that are important for appearance and/or function.

Even before surface treatment, the appearance and surface quality of extruded aluminium profiles is perfectly satisfactory for many applications. Thanks to good corrosion resistance, surface treatment is rarely necessary simply to provide corrosion protection. However, there are many other reasons for treating the surfaces of profiles. Examples of attributes that can be changed by surface treatment include: – surface structure – colour – corrosion resistance – hardness – wear resistance – reflectivity – electrical insulation. The untreated surface

Surfaces do no always need treatment after extrusion. Load-bearing structures and machine parts are examples of products where the surface quality is satisfactory without any treatment.

15.1 Profile design Lines and extrusion stripes that would be noticeable on visible surfaces can easily be hidden using decoration. Such patterns or optical effects are an integral part of the profile solution created at the design stage. Refer also to “Decorate”, page 32.

Sailing boat mast – Sapa delivers profiles in 12.4 metre lengths. Seldén Mast joins these to form 20 – 25 metre high masts.

104

15.2 SURFACES – MECHANICAL SURFACE TREATMENT

15.2 Mechanical surface treatment Grinding

Grinding is one of the methods used for improving surface quality. The process leaves a fine striation in the direction of grinding. The resultant surface can be “very fine”, “medium” or “coarse”. Grinding is most commonly used for furnishing and interior design products. Ground surfaces are often anodised. Grinding before painting can further improve the surface finish. Polishing

Polishing smoothes the surface. Quality and gloss are determined by customer specifications. Polished surfaces normally go on to be anodised. To achieve a high-gloss finish, polishing is followed by bright anodising. Tumbling (barrel polishing)

Tumbling is mainly used for deburring. Determined by the polishing medium used in the drum, surfaces range all the way from matt to gloss.

Bottle openers – deburred by tumbling, anodised in short lengths and screen printed.

A

Deburring by tumbling.

B

C

Ground surfaces – A: “very fine”, B: “medium”, C: “coarse”. 105

15.3 SURFACES – ANODISING

15.3 Anodising The reasons for anodising

The advantages

of anodising.

Anodising, one of the most common surface treatments, is used to (amongst other things): – maintain a product’s “as-new” appearance. – enhance corrosion resistance. – create a dirt repellent surface that satisfies stringent hygiene requirements. – create a decorative surface with durable colour and gloss. – create a “touch-friendly” surface. – create function-specific surfaces, for example, slip surfaces, abrasion-resistant surfaces for use in machine parts, etc. – give surfaces an electrically insulating coating. – provide a base for the application of adhesives or printing inks. Recommended layer thicknesses when anodising Layer thickness

Area of application

25 µm

Where surfaces are exposed to severe stress in the form of corrosion or abrasion.

20 µm

Great or normal stress outdoors (e.g. transport and construction industries). Indoors – great stress arising from the use of chemicals (e.g. the foodstuffs industry).

15 µm

Severe abrasion, indoors and outdoors in dry and clean atmospheres.

10 µm

Normal stress indoors.

3 – 5 µm

Protective anodising before machining, short period of etching.

Choice of alloy when anodising Sapa alloy

6060

6063

6063A

6005

Decorative anodising (natural, coloured, Hx) 1)

x

x

x

x

Protective anodising (natural)

x

x

x

x

6005A

6082

7021

1050A

6101

6463 3)

x

(x)

x x

x

2)

x

1) Using the same anodising process, gloss and shade vary between different alloys. 2) Anodising should be avoided as it contaminates the process bath. 3) Specifically intended for bright anodising (prior protective anodising should be avoided).

The anodising process

There are normally four stages in the process: pre-treatment, anodising, colouring (where required) and sealing. The most frequent type of anodising is natural anodising. The electrolytic process takes place once the metal surface has received the appropriate mechanical or chemical pre-treatment and has been thoroughly cleaned. 106


The profile is connected to a direct current source and becomes the anode (hence anodising). An electrolytic cell is formed. Dilute sulphuric acid at room temperature is normally used as the electrolyte. During electrolysis, the surface of the metal is oxidised. The process continues until the desired layer thickness (usually 5 – 25 µm) is reached. Sealing

The oxide layer contains a large number of pores, approx. 1011/cm2 (i.e. around a hundred billion). The diameter of the pores is between 120 and 330 Å. To obtain an impermeable surface, the pores have to be sealed. Sealing is achieved by treating the surface in de-ionised water at 95 – 98°C. This changes the aluminium oxide into bohemite, the attendant increase in volume closing the pores. The oxide layer formed in natural anodising is transparent. Coloured oxide layers are also possible (see pages 108 and 109). Natural anodised profiles are delivered with matt or semi-matt surfaces.

Sealing.

Maintenance – cleaning

The anodic oxide layer has good corrosion resistance in most environments. With the proviso that the surface is cleaned, anodised profiles are virtually maintenance-free. The surface cleans easily in both water with a little neutral detergent and in white spirits. Although solvents do not affect aluminium, strong alkaline solutions should be avoided. Resistance to corrosion, discoloration and abrasion increases with layer thickness. Recommendations for suitable thicknesses are given in the table on the previous page. As the anodic oxide layer has poor cold formability, forming should take place before anodising. Cutting and drilling can be carried out after anodising but the exposed surfaces will, of course, be untreated. Welding is to be carried out before anodising.

Virtually maintenancefree.

Properties of anodised aluminium

Corrosion resistance is very good, especially where pH is between 4 a nd 9. In contact with strongly alkaline substances, surfaces can stain and be damaged. Thus, it has to be borne in mind that aluminium should be protected against lime, cement and gypsum (e.g. on building sites). Visible surfaces can be protected using tape. The hardness of the oxide layer depends on the anodising process used. Generally, the layer is harder than glass and as hard as corundum. The oxide layer is transparent. Whether natural or coloured, its appearance depends on the viewing angle. At temperatures above 100°C, fine cracks form in the oxide layer. From an aesthetic point of view, this may be an undesirable effect.

Very good corrosion resistance.

107


The reflectivity of bright etched aluminium is high. The gloss value is 90 units (ISO 7599, 60° viewing angle). This decreases slightly with anodising. The oxide layer is an electrical insulator. A sealed, 15 µm oxide layer has a breakdown voltage of 500 – 600 V. An anodised profile can be recycled with no pre-treatment. Before remelting, painted profiles must first have the paint removed.

Coloured oxide

layers

Dyeing

Natural anodised, unsealed aluminium can be coloured using organic or inorganic pigments (dyes). Profiles are sealed after dyeing. Electrolytic Hx colouring

Like the dyeing process, electrolytic colouring is also a separate stage after anodising. Under the influence of an alternating current, pigment is precipitated at the bottom of the oxide layer’s pores. The pigmenting agent is tin salt and the colour scale ranges from champagne to black. The colours, designated from Hx 10 to Hx 50, are highly resistant to fading. After colouring, profiles are sealed. Outdoor colourfastness

Colourfastness depends on the pigments and colouring technique

used.

108

The colourfastness of an anodised layer depends on the pigments and colouring technique used. Dyeing: Some coloured layers have limited outdoor colourfastness. Electrolytic Hx colouring: Limited choice of colours, very good lightfastness, suitable for outdoor use. Sapa’s colour designations

See the colour guide on page 122. All colours are delivered with a matt or semi-matt finish.


Colour guide

on page 122.

1

2

Reflector panels emerging from the anodising bath. This profile, produced for Infrarödteknik AB, is GD-20-l, semi-matt anodised. 2 Combined casings-heat sinks for compact modules using hybrid technology from Ericsson Components. Protective anodising before treatment, then BL-20-I, semi-matt anodising in short lengths. 1

109

15.4 SURFACES – PAINTING

15.4 Painting Painting offers a limitless choice of colours and very good colour matching (repeatability). Powder coating is now easily the most widespread method of painting aluminium profiles. GSB certification

Chrome-free ,

GSB approved alternative.

98% is used,

the rest is recycled.

Since 1994, Sapa Lackering has been certified to the German GSB standards. It is the only company in Sweden to have this certification. To qualify for certification, our products and processes must meet stringent requirements. Continued compliance is monitored by inspectors who make a number of unannounced visits every year. Besides continous checks during production, we have also undertaken to, amongst other things, carry out some 15 tests a day in shielded rooms. To ensure traceability, the tests are archived for 5 years. Pre-treatment

To ensure the right adhesion for the paint, it is important that pre-treatment, paint application and subsequent curing are all carried out correctly. As maximum adhesion and durability are prime goals, pre-treatment is of crucial importance. Pre-treatment normally comprises degreasing and pickling of the surface, followed by a chemical treatment. The chemical treatment (chrome-free or chrome-based) gives good adhesion and effective corrosion resistance. The chrome-free titanium based process is GSB approved and is now our standard method. It has undergone extensive testing. Rinse water from the chromating process is treated in efficient cleaning plants. The sludge is drawn off and sent away for appropriate disposal. Pre-treatment is the same for both powder coating and wet painting. 15.4.1 Powder coating Broadly speaking, there are absolutely no limits t o the choice of colour. Besides the RAL and NCS S colour systems, we also work to customers’ own colour definitions. Standard gloss is 77 units (ISO 2813, 60° viewing angle). Powder coatings are applied and cured without solvents. This gives a good work environment and has no negative impact on the external environment. In a wet coating plant, half the paint is lost through evaporation and the waste involved in over-spraying. In Sapa’s powder coating plant, up to 98% of the powder is used. Powder that does not adhere to the product is recirculated via a reclamation system. Powder coating qualities

The prime qualities of powder coating and powder coats are: – No risk of running or blistering. – High repeatability. – Powder coatings withstand knocks and abrasion far better than wet paint coatings. – Good formability (e.g. can be formed after coating). – Suitable for outdoor use – good resistance to UV and corrosion.

110


Coating thickness is normally 60 – 140 µm. In some designs, the thickness of the coating has to be taken into consideration when determining profile dimensions and tolerances. Structural, metallic, clear and Decoral coatings

Sapa works with all the kinds of coatings requested by customers. In addition to the traditional powder coatings, this includes structural, metallic and clear coatings. Decoral, a development of powder coating, gives patterned surfaces (see also 15.4.2).

Sapa has a number of powder coating plants, each of them specialising in different products. We also have a Decoral production unit and one for wet painting. The picture shows a vertical powder coating line – profiles up to 7 metres long are suspended vertically rather than horizontally, thereby giving a manifold increase in capacity.

Left: Powder coatings are applied via triboelectric (frict ion) or electrostatic charging.

Profiles emerging from the powder box. Right: Profiles on their way to the curing oven (temperature is approx. 180°C). Curing takes about 15 minutes, the time depending on the design of t he profile. Both these pictures are taken f rom one of our horizontal coating lines. 111


Exact colour matching easy

with paint.

Picture 1. DHL Worldwide Express, Helsinki’s Vantaa airport – powder coating in a red colour to match that specified in DHL’s manual (Pantone colour scale).

1

Picture 2. The profiles in this grille (Scania 4 series) are powder coated. Picture 3. Shower cubicle from IDO – white powder coating in a special tint to blend with IDO’s other ranges.

2

3

Picture 4. Renault roof rail – a special anthracite-grey, powder coating. Picture 5. Outdoor play equipment from Kompan – powder coated handles.

112

4

5


No risk of

running or blistering.

7

6

Picture 6. Detail of a glass facade – light-oak Decoral in combination with a powder coating.

9

Picture 7. Stockholm II folding stool, designed by Hans Ehrich of A & E Design and produced by Lectus Office – powder coated. Picture 8. Aluminium doors replacing worn out wooden doors – Decoral light-oak finish. Picture 9. Interior from the Bo01 home exhibition, Malmö – powder coated window frames.

8

10

Picture 10. Cables and leads hidden by Thorsman’s FrontLine installation system – powder coated.

113


15.4.2 Decoral A development of powder coating that gives patterned surfaces

Deep

penetration.

The technique: A special composition powder coating is first applied. The pattern is then transferred to the profile. The original pattern, most usually a photographic image of wood or stone, is copied onto a film that holds the pigments forming the decorative design. The depth of penetration is crucial for the results – a shallow pattern is subject to comparatively large stresses. The Decoral technique ensures deep penetration. The result is a surface with all the properties of a traditional powder coating (see “Powder coating qualities”, page 110).

Key properties Test

Method

Result

Thickness

ISO 2360

Min. 60 µm on visible surfaces

Adhesion

ISO 2409

Cross-cut 0 1)

Buchholz hardness

ISO 2815

Min. 80

Erichsen

ISO 1520

Min. 3 mm

Bending 2)

ISO 1519

Ø 8 mm

Kesternich (SO2)

ISO 3231 24 cycles

< 1 mm

Boiling water

Pressure cooker, 1 hour

No defects or blisters

Mortar resistance

ASTM D 3260

Meets base requirements

Damp resistance

DIN 50017, 1,000 hours

< 1 mm

Salt spray

ISO 9227

< 1 mm

Impact 2

ASTM D 2794

> 22 inch-pounds

All tests carried out on decorated plates and profiles. 1) Evaluation is on a scale of 0 – 5 where 0 is best. 2) Test carried out on 1 mm thick, AA 5005 H 24 aluminium alloy plates.

Before The Decoral system has been used in series production since 1996. This has given us a wealth of experience regarding how Decoral surfaces work in practice in, amongst other countries, Italy and Germany. Extensive testing in laboratories has also provided comprehensive documentation.

114

After


Example patterns – choose from a wide range, or create your own.

Design and construction advantages of Decoral

Without being any thicker than normal powder coatings, Decoral can add the look of solid wood to a profile's durability, “create” marble with the same density as aluminium... When it comes to patterns and colours, there are no limitations.

15.4.3 Wet painting Sapa uses many different types of paint and can, of course, offer water-based paints. Alkyd paints are often used in wet painting. However, they have low formability and cannot be used for products that are to be formed after painting. Resistance to solvents and oils is poor.

115

15.5 SURFACES – SAPA HM-WHITE

15.5 Sapa HM-white The perfect complement to both anodising and powder coating

Sapa HM-white is produced by electrophoresis (Honnystone Method). An anodised and unsealed profile is dipped into a tank where, using direct current, the paint is applied – electrophoretic deposition. The paint (an acrylic based melamine) is then hardened in an oven at around 180°C. Total coating thickness is approximately 30 µm. This method offers a range of advantages:

– – – – – –

– –

A UV-resistant white. Very good gloss retention and resistance to chemicals. Very good corrosion resistance. The coating penetrates into the pores of the anodised surface and sticks there. This gives very good adhesion. The surface is impermeable and dirt-repellent. The values for hardness, impact and abrasion resistance are almost identical to those for powder coatings. However, as regards abrasive wear, it must be borne in mind that HM-white has a surface thickness of 30 µm compared to powder coating’s 60 – 140 µm. Surface thickness is the same for the entire surface. There is no build-up of coating at the edges. This is perfect for structural profiles that have to be mated with each other and for snap-fit and telescopic designs.

Perfect for structural profiles.

HM-white coating at approx. x 20,000 magnification. One third of the coating is the anodic oxide layer, 2/3 is the paint itself. This picture was taken by a scanning electron microscope (SEM). 116

A hinge – HM-white has a great advantage here as the coating thickness is even on all profile surfaces and there is thus no build-up at the edges.

15.5 SURFACES – SAPA HM-WHITE

Good chemical resistance, very good corrosion resistance and an impermeable, dirt-repellent surface. 1

1

2

3

Pictures 1 and 2, H M-white in use. Picture 3. Coloured profiles emerging from the process bath.

Sapa HM-white – examples of the standards to which the coating is quality tested Test

Thickness Gloss Adhesion Buchholz hardness Pencil hardness – destructive/abrasive Kesternich (SO 2 ) Salt spray test Machu Boiling water Mortar resistance

Method

Result

ISO 2360 ISO 2813 (60° viewing) ISO 2409 ISO 2815 INTA 160 30 ISO 3231 ISO 3768

30 µm 85 ± 5 Cross-cut 01) > 100 5H–3H 24 cycles 1,000 hours < 0.5 mm 5 hours No adhesion

BS 4842 ASTM C 207 C, 24 hours

1) Evaluation is on a scale of 0 – 5 where 0 is best. 117

15.6 SURFACES – SCREEN PRINTING

15.6 Screen printing

Often under

EUR 100.

Screen printing (formerly silk-screen printing) is an ancient printing method. The original design is reproduced on a transparent film that is then placed on a fine-meshed screen (usually nylon nowadays). This is then exposed and developed photographically. The screen is next fitted into a frame. Either manually or automatically, a squeegee is dragged along the screen to transfer the design onto the printing surface. Initial costs (production of the nylon screen, etc.) are low – often less than EUR 100. Tampon printing

Tampon printing is a technique that makes it possible to use screen printing on both concave and convex surfaces. Natural and coloured anodising on the same profile

Using screen printing, a profile’s surfaces can combine natural anodising and colouring. Anodising is interrupted when the oxide layer has formed. The profile areas that are not to be printed are then coated with a special masking ink. After printing, the profile is sealed in the normal way. Unanodised surfaces on anodised profiles

A masking technique is also used when parts of a profile are to emerge unanodised from the anodising process. This preserves the surface’s electrica l and thermal conductivity (the anodic oxide layer is insulating).

118

15.6 SURFACES – SCREEN PRI NTING

Screen printing can also be used on painted and HM white surfaces.

119 11 9

RFACES S – FUNCTION-SPECIFIC SURFACES 15.7 SU RFACE

15.7 Function-specific surfaces We define a function-specific surface as one where certain function-related properties are of critical importance. Whatever you require of your function-specific surfaces, have a word with Sapa! Slip, friction and sealing surfaces

Here, the surface roughness (i.e. the Ra values, axially and radially) is of the utmost importance. Sapa can meet even the most severe demands. Cylinder tubes are an example. Direct from the press, we can deliver tubes where the insides have Ra values as low as 0.6 axially and 1.2 radially. The Ra values can, of course, be further improved by machining. Abrasion-resistan Abrasio n-resistantt surfaces surfaces

These surfaces have to be anodised.

Four height adjustable legs made from telescoping aluminium profiles – slip surfaces direct from the press (no machining). The product: Control cabinet lift columns from MPI.

120

15.8 SURFACES – AT-A-GLANCE GUIDE

15.8 At-a-glance guide for choice of surface treatments Process

Result

Use

Profile Design

Patterning.

Design purposes. Covering lines and extrusion stripes. Increasing friction (grip).

MECHANICAL SURFACE TREATMENT Embossing

Patterning.

Design purposes. Marking.

Grinding

Improved surface quality. Superior appearance.

Wherever an exclusive appearance at a reasonable price is the goal.

Polishing

Improved surface finish. Superior appearance.

Furnishing and interior design products. Finish and gloss as specified by the customer.

Tumbling

Smoothing of cut edges. Deburring. Matt to gloss surfaces depending on tumbling medium.

ANOD IS ING General

Primarily deburring.

Very good corrosion protection. The surface retains its “as-new” appearance, is dirt-repellent and resistant to mechanical abrasion. Colour and gloss resist fading. An electrically insulating coating.

Both indoors and outdoors. A base for application of adhesives or printing inks.

Intense gloss, high reflectivity.

Where there are high demands as regards surface finish.

Huge choice of colours, some of them with very high lightfastness.

Primarily indoors – some outdoor applications.

Hx

Limited choice of colours – champagne to black. Very high lightfastness.

Primarily outdoors.

PAINTING

Unlimited choice of colours. A range of painting systems to meet different requirements. Very good corrosion resistance.

Both indoors and outdoors.

ELECTROPHORESIS Sapa HM-white

UV-resistant colour with a more durable gloss than UV-resistant traditional paints. Very good corrosion resistance. Coating thickness the same over the entire surface.

Both indoors and outdoors.

Wide choice of colours. Limited abrasion resistance.

Design purposes. Logos.

Bright anodising Colour anodising Colouring

SCREEN PRINTING Printing on the surface

121 12 1

15.9 SURFACES – COLOUR GU IDE FOR ANODISING

15.9 Colour guide for anodising Sapa’s standard colours

Designation

Max length

Designation

(mm)

(mm)

Natural 5-25

µm

NA-5 – NA-25

12,400

Violet

LI-25-I LI-30-I

2,400 2,400

Brown olive

BO-20-I BO-35-I

2,400 2,400

SV-50-U

2,400

Hardoxal

Champagne Light amber Amber Dark amber Black

Hx-10 Hx-20 Hx-30 Hx-40 Hx-50

7,500 7,500 7,500 7,500 7,500

Gold

GD-20-I GD-30-I GD-30-U GD-40-I

7,800 7,800 7,800 7,800

YW-40-U

2,400

Orange

OR-35-I

2,400

Red

RD-15-I RD-25-U

2,400 2,400

Red cerise

RC-30-I

2,400

Green

GN-40-I

2,400

Blue

BL-20-I BL-30-U

2,400 2,400

BG-10-I BG-30-I

2,400 2,400

Yellow

Blue grey

Max length

(x) (x)

Black

(x)

Bright anodising (alloy Sapa 6463)

Nature Gold Yellow Orange Red Red cerise Green Blue Blue grey Violet Brown olive (x)

Black

NA-5-GI GD-20-GI YW-20-GI OR-35-G I RD-25-GI RC-30-GI GN-40- GI BL-20-GI BG-30-GI LI-30-GI BO-20-GI BO-35-GI SV-50-GI

2,400 2,400 2,400 2,400 2,400 2,400 2,400 2,400 2,400 2,400 2,400 2,400 2,400

(x)

(x) (x)

(x) Certain restrictions apply to colours marked (x) – see below

Explanation of RD-25-U, GD-30-I, etc. Sapa’s colour designations have three parts: Colour – intensity – properties. RD = red 25 = intensity U = outdoor use GD = gold 30 = intensity I = primarily indoor use

The intensity scale runs from 0 to 50.

122

Amongst the many factors influencing the perceived appearance of anodised surfaces are: – Profile shape – Viewing light and angle – Surface structure – Thickness of the anodising layer – Choice of alloy. Taken all together, this means that aluminium is truly a “living” material.

All colours can be delivered with a matt or semi-matt finish. Gloss finishes are also available. The table above lists the colours that can be delivered with a gloss finish. For colours marked with (x) there are some restrictions – please ask Sapa for further details. Furthermore these colours might have a greater variation than other colours.

16. CORROSION

16. Corrosion 16.1 Aluminium’s corrosion resistance

Untreated aluminium has very good corrosion resistance in most environments. This is primarily because aluminium spontaneously forms a thin but effective oxide layer that prevents further oxidation. Aluminium oxide is impermeable and, unlike the oxide layers on many other metals, it adheres strongly to the parent metal. If damaged mechanically, aluminium’s oxide layer repairs itself immediately. This oxide layer is one of the main reasons for aluminium’s good corrosion properties. The layer is stable in the general pH range 4 – 9. In strongly acid or alkaline environments, aluminium normally corrodes relatively rapidly.

Corrosion rates

– aluminium (µm/year) 2500 2000 1500 1000 500 0

Corrosion resistance in common profile alloys

Between Sapa’s most widely used alloys, there is little variation in corrosion resistance. However, alloys containing more than 0.5% copper generally have poorer resistance. Therefore, they should not be used unprotected in environments with a high chloride content (e.g. where there is road salt or near sea water).

0

2

4

6

8

10

14

The graph shows corrosion rates (i.e. the average depth of corrosion) for aluminium at different pH values (pH adjustment using hydrochloric acid and sodium hydroxide).

16.2 The most common kinds of corrosion The most common types of corrosion are: – – –

12

galvanic corrosion pitting crevice corrosion

Stress corrosion, which leads to crack formation, is a more special type of corrosion. It occurs primarily in high-strength alloys (e.g. AlZnMg alloys) where these are subjected to prolonged tensile stress in the presence of a corrosive medium. This type of corrosion does not normally occur in common AlMgSi alloys.

123

16. CORROSION

16.2.1 Galvanic corrosion

Galvanic corrosion may occur where there is both metallic contact and an electrolytic bridge between different metals. The least noble metal in the combination becomes the anode and corrodes. The most noble of the metals becomes the cathode and is protected against corrosion. In most combinations with other metals, aluminium is the least noble metal. Thus, aluminium presents a greater risk of galvanic corrosion than most other structural materials. However, the risk is less than is generally supposed. Aluminium

Steel

Steel

A small cathode surface and a large anode surface results in negligible corrosion.

Aluminium

In the reverse situation (large cathode, small anode), attack can be serious in difficult environments.

Galvanic corrosion and aluminium

Both

conditions have to be met!

Galvanic corrosion of aluminium occurs: – Only where there is contact with a more noble metal (or other electron conductor with a higher chemical potential than aluminium, e.g. graphite). – While, at the same time, there is an electrolyte (with good conductivity) between the metals. Galvanic corrosion is often attributable to unsuitable structural design. Galvanic corrosion does not occur in dry, indoor atmospheres. Nor is the risk great in rural atmospheres. However, the risk of galvanic corrosion must always be taken into account in environments with high chloride levels, e.g. areas bordering the sea. Copper, carbon steel and even stainless steel can here initiate galvanic corrosion. Problems can also occur where the metallic combination is galvanised steel and aluminium. The zinc coating of the galvanised steel will, at first, prevent the aluminium being attacked. However, this protection disappears when the s teel surface is exposed after the consumption of the zinc. As it has a thicker zinc coating than electroplated material, hot dip galvanised material gives longer protection. Thus, in combination with aluminium in aggressive environments, hot dip galvanised material should be used.

Close-up of galvanic corrosion in an aluminium rail post (25 year’s use). The rectangular hollow profile was held in place by a carbon steel bolt. The contact surfaces between the steel and the aluminium were often wet and attack was aggravated by wintertime salting. 124

16. CORROSION

16.2.2 Preventing galvanic corrosion

The risk of galvanic corrosion should not be exaggerated – corrosion does not occur in dry, indoor atmospheres and the risk is not great in rural atmospheres. Electrical insulation

Where different metals are used in combination, galvanic corrosion can be prevented by electrically insulating them from each other. The insulation has to break all contact between the metals. The illustration shows a solution for bolt joints. Insulation Aluminium

Steel

Breaking the electrolytic bridge

In large constructions, where insulation is difficult, an alternative solution is to prevent an electrolytic bridge forming between the metals. Painting is one way of doing this. Here, it is often best to coat the cathode surface (i.e. the most noble metal). A further solution is to use an insulating layer between the metals. Cathodic protection

Cathodic protection can be gained in two ways. The most common is to mount an anode of a less noble material in direct metallic contact with the aluminium object to be protected. The less noble material “sacrifices” itself (i.e. corrodes) for the aluminium. It is thus referred to as a sacrificial anode. For the above to work, there also has to be liquid contact between the surface to be protected and the sacrificial anode. Zinc or magnesium anodes are often used for aluminium. Another way of obtaining cathodic protection is to connect the aluminium object to the negative pole of an exterior DC voltage source. The illustration below shows the cathodic protection of an outboard motor.

Cathodic protection can be gained in two ways.

Sacrificial anode

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16. CORROSION

16.2.3 Pitting

For aluminium, pitting is by far the most common type of corrosion. It occurs only in the presence of an electrolyte (either water or moisture) containing dissolved salts, usually chlorides. The corrosion generally shows itself as extremely small pits that, in the open air, reach a maximum penetration of a minor fraction of the metal’s thickness. Penetration may be greater in water and soil. As the products of corrosion often cover the points of attack, visible pits are rarely evident on aluminium surfaces. 16.2.4 Preventing pitting

Rinsing with water is often sufficient.

Pitting is primarily an aesthetic problem that, practically speaking, never affects strength. Attack is, of course, more severe on untreated aluminium. Surface treatment (anodising, painting and coating with HM-white) counteracts pitting. Cleaning is necessary to maintain the treated surface’s attractive appearance and its corrosion protection. Rinsing with water is often sufficient. Alkaline detergents should be used with care. Mild alkaline detergents are now available. These are used in, amongst other areas, the industrial cleaning of aluminium. Pitting can be prevented by cathodic protection (see previous page). It is also important to design profiles so that they dry easily.

Avoid angles and pockets

126

Instead, use a shape that promotes

in which water can collect.

draining.

The risk of dirt build-up is reduced with radiused corners.

Stagnant water is avoided by suitably inclining the profile and/or providing drain holes (min. Ø 8 mm, or 6 x 20 mm, so that capillary forces do not prevent the water running off ). The ventilation of “closed” constructions reduces the risk of condensation.

16. CORROSION

16.2.5 Crevice corrosion

Crevice corrosion can occur in narrow, liquid-filled crevices. The likelihood of this type of corrosion occurring in extruded profiles is small. However, significant crevice corrosion can occur in marine atmospheres, or on the exteriors of Film of liquid vehicles. During transport and storage, water sometimes collects in the crevices between superjacent aluminium surfaces and leads to superficial corrosion (“water staining”). The source of this water is rain or condensation that, through capillary action, is sucked in between the metal surfaces. Condensation can form when cold material is taken into warm premises. The difference between night and day temperatures can also create condensation where aluminium is stored outdoors under tarpaulins that provide a tight seal.

16.2.6 Preventing crevice corrosion

Using sealing compounds or double-sided tapes before joining two components prevents water from penetrating into the gaps. In some cases, rivets or screws can be replaced by, or combined with, Sealing adhesive bonding. This counteracts compound the formation of crevices.

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16. CORROSION

16.3 Aluminium in open air Excellent durability

in normal rural atmospheres and moderately sulphurous atmospheres.

The corrosion of metals in the open air depends on the so-called time of wetness and the composition of the surface electrolytes. The time of wetness refers to the period during which a metal’s surface is sufficiently wet for corrosion to occur. The time of wetness is norma lly considered to be when relative humidity exceeds 80% and, at the same time, the temperature is above 0°C (e.g. when condensation forms). In normal rural atmospheres, and in moderately sulphurous atmospheres, aluminium’s durability is excellent. In highly sulphurous atmospheres, minor pitting may occur. However, generally speaking, the durability of aluminium is superior to that of carbon steel or galvanised steel. The presence of salts (particularly chlorides) in the air reduces aluminium’s durability, but less than is the case for most other construction materials. Maximum pit depth is generally only a fraction of the thickness of the material. Thus, in marked contrast to carbon steel, strength properties remain practically unchanged. Field exposure tests by the Swedish Corrosion Institute

Weight losses after 8 years

Marine atmosphere In a range of outdoor atmospheres, the South-west Sweden Swedish Corrosion Institute has carried out (bar chart on the right) field exposure tests on untreated metals. Al 7 g/m2 Cu 57 g/m 2 For plates that had received no surface Zn 133 g/m 2 treatment, the weight losses after eight Fe 933 g/m2 year’s exposure are given here. Urban atmosphere After the eight years, the average pit Stockholm depth in the aluminium plates was 70 µm Al 2 g/m2 (0.07 mm). Cu 31 g/m 2 The bar chart shows that aluminium’s Zn 61 g/m 2 Fe 676 g/m 2 weight loss near the sea was: – approx. 1/100th that of carbon steel (Fe). Al Cu Zn Fe – approx. 1/10th that of galvanised steel (see Zn in the bar chart). The rate of corrosion decreases rapidly with distance from the sea. Approximately 1 km from the sea, aluminium behaves more or less the same as it does in a rural atmosphere. The corrosion rate of the pits decreases with time.

The picture shows an untreated sample after 20 years off the south-west coast of Sweden. UV radiation, sulphuric acid and nitric acid in combination with chlorides have not left any deep marks. After 22 years in a marine atmosphere, examination of an untreated aluminium sample (alloy AA 6063) showed that corrosion attack was so limited (max. depth approx. 0.15 mm) that strength was not affected. 128

1,000

800

600

400

200

0

16. CORROSION

16.4 Aluminium in soil Soil is not a uniform material. Mineral composition, moisture content, pH, presence of organic materials and electrical conductivity can all vary widely from site to site. These differences make it difficult to predict a metal’s durability in soil. Furthermore, other factors (e.g. stray currents from DC voltage sources) can also affect durability. Aluminium’s corrosion properties in soil very much depend on the soil’s moisture, resistivity and pH value. Unfortunately, present knowledge about the corrosiveness of different types of soils is not comprehensive. When using aluminium in soil, some form of protective treatment, e.g. a bitumen coating, is recommended. Corrosion can also be prevented by cathodic protection.

Aluminium in soil – protection is recommended.

Bitumen coating (here of a fence post and a telephone pole) prevents corrosion.

16.5 Aluminium in water A metal’s corrosion in water is largely dependent on the composition of the water. For aluminium, it is the presence of chlorides and heavy metals that has the greatest effect on durability. In natural fresh water and drinking water, aluminium may be subject to pitting. However, with regular drying and cleaning, the risk of harmful att ack is small. Pots, pans and other household equipment can be used for decades without there being any pitting. The likelihood of harmful attack increases where water is stagnant and the material is wet for long periods.

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Pitting can however be prevented by:

– design solutions that reduce the risk of water being trapped – cathodic protection – corrosion inhibitors, e.g. used in car radiators.

d = k 3 t Pots and pans can be used for decades

without there being any pitting.

The rate of pitting in fresh water decreases strongly with time and has been proven to obey the above formula, where d is maximum pit depth, k a constant determined by the alloy and water composition and t is time. The formula indicates, for example, that a doubling of the pit depth that has developed by the end of the first three years can only be expected after a total of 24 years. In sea water, AlMg alloys with over 2.5% Mg (and AlMgSi alloys) show particularly good durability. Copper containing alloys should be avoided. Where they are used, they must be given effective corrosion protection. When correct attention has been paid to design, especially as regards use with other materials (and the risk of galvanic corrosion), aluminium is an excellent material in a marine context. One example of this is the extensive use of aluminium in many types of ships and boats. Cathodic protection against corrosion is widely used here.

Corrosion at the water line

Aluminium that is only partly submerged in water can corrode directly under the water line (so-called waterline corrosion). This type of corrosion, which only occurs in stagnant water, can be prevented by coating the area around the water line.

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16.6 Aluminium and alkaline building materials Splashes of damp alkaline building materials, e.g. mortar and concrete, leave superficial but visible stains on aluminium surfaces. As these stains are difficult to remove, visible aluminium surfaces should be protected on, for e xample, building sites. Other materials also require the same sort of protection. Aluminium cast into concrete is similarly attacked. This increases the adhesion between the materials. Once the concrete has set (dried), there is normally no corrosion. However, where moisture persists, corrosion may develop. The volume of the products generated by corrosion can give rise to cracks in the concrete. This type of corrosion can be effectively prevented by coating the aluminium with bitumen or a paint that tolerates alkaline environments. As the oxide layer is not stable in strongly alkaline environments, anodising does not improve durability here. Provided that the concrete has set, aluminium does not need to be protected in dry, indoor atmospheres.

Visible

surfaces should be protected.

16.7 Aluminium and chemicals Thanks to the protective properties of the natural oxide layer, aluminium shows good resistance to many chemicals. However, low or high pH values (less than 4 and more than 9) lead to the oxide layer dissolving and, consequently, rapid corrosion of the aluminium. Inorganic acids and strong alkaline solutions are thus very corrosive for aluminium. Exceptions to the above are concentrated nitric acid and solutions of ammonia. These do not attack aluminium. In moderately alkaline water solutions, corrosion can be hindered by using silicates as inhibitors. Such kinds of inhibitors are normally included in dishwasher detergents. Most inorganic salts are not markedly corrosive for aluminium. Heavy metal salts form an exception here. These can give rise to serious galvanic corrosion due to the reduction of heavy metals (e.g. copper and mercury) on aluminium surfaces. Aluminium has very good resistance to many organic compounds. Aluminium equipment is used in the production and storage of many chemicals.

Good resistance

to many chemicals.

16.8 Aluminium and dirt Coatings or build-ups of dirt on the metal’s surface can reduce durability to a certain extent. Very often, this is attributable to the surface now being exposed to moisture for considerable periods. Thus, depending on the degree of contamination, dirty surfaces should be cleaned once or twice a year.

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16.9 ALUMINIUM AND FASTENERS

16.9 Aluminium and fasteners When choosing fasteners for use with aluminium, special attention should be paid to avoiding galvanic corrosion and crevice corrosion (see sections 16.2.1, 16.2.2 and 16.2.5). Galvanic corrosion of aluminium occurs where there is metallic contact with a more noble metal. It should be pointed out that, indoors and in other dry atmospheres, aluminium can be in permanent contact with brass and carbon steel with no risk of galvanic corrosion. The table on page 129 shows some of the most common surface coatings for fasteners. The evaluation of the surface coatings is based on the findings of fastener and coating suppliers, as well as the experience of Sapa and its customers (primarily in the building and automotive industries). In deciding which fasteners to use, the table should be regarded as an introductory guideline. As development is rapid, Sapa also recommends that fastener and coating suppliers be contacted. The pictures below show the results of an accelerated corrosion test, the Volvo Indoor Corrosion Test (VICT). The test cycle is 12 weeks. This corresponds to five year’s use of a car in a moderately large town (Gothenburg).

Zinc/iron-coated steel nut and bolt. The fastener is completely rusted. In the aluminium, 0.43 mm deep pits have formed.

132

Dacrolit-coated steel nut and bolt. The fastener has not been attacked. No pits have formed in the aluminium.

ALUMINI UMINI UM AND FASTENERS 16.9 AL

At-a-glance guide for choosing fasteners The table below lists some of the most common materials and coatings for fasteners used with aluminium. It also gives an evaluation of corrosion resistance in different environments. Substrate material

Surface treatment

Carbon steel

Atmospheres

Comments

Marine

Industrial

Rural

Electroplated (Zn/Ni) approx. 7 – 10 µm + yellow chromating.

++

+++

+++

Used in the automotive industry. Good protection against galvanic corrosion.

Carbon steel

Electroplated (Zn/Fe) approx. 7 – 10 µm + yellow chromating.

–

+

+++

Negative results on vehicles. The Zn layer disappears relatively quickly and galvanic corrosion then sets in.

Stainless steel, 18/8

Electroplated, approx. 7 – 10 µm Zn + yellow or bright chromating.

++

+++

+++

Used primarily in the building industry. The Zn coating is principally t o reduce friction (bolt threads).

Stainless steel, 18/8

Dacrolit – Zn and Al flakes in an organic binder containing, amongst other things, chromate.

+++

+++

+++

Used primarily in the building industry. The Dacrolit coating is used to reduce friction (bolt threads) and the risk of galvanic corrosion.

Stainless steel, 2302

Electroplated (Zn/Fe) 7 – 10 µm + yellow or bright chromating.

+

+++

+++

Used primarily in the building industry.

Carbon steel

Dacrolit – Zn and Al flakes in an organic binder containing, amongst other things, chromate.

++

+++

+++

Used primarily on vehicles and, in some cases, buildings. Withstands 12 weeks VICT (Volvo Indoor Corrosion Test)

Carbon steel

Geomet – Zn and Al flakes in a matrix of Si, Zn and Al oxides. Chrome-free.

++

+++

+++

Very good corrosion resistance shown in tests in the automotive industry. Suppliers state that it withstands 1,000 hours in a neutral salt spray (ISO 92 27).

Carbon steel

Polyseal – Zn phosphating approx. 3 µm + organic protection layer (seal) + organic top coat.

–

++

+++

Used in the automotive industry, Good results in acetic acid and neutral salt spray (ISO 9 227).

Aluminium rivet with electroplated steel mandrel.

No coating.

++

+++

+++

Used in the building industry.

Stainless steel (18/8) rivet with stainless steel mandrel.

No coating.

+

++

+++

Galvanic corrosion in marine atmospheres.

Evaluations: +++ = very good; ++ =

good; + = acceptable with moderate demands as regards lifetime (up to 10 years)

and surface finish. References: 1) Korro Korrosionshärdigheten sionshärdigheten hos fästelement – marknadsinventering avseende nya produkter .

Swedish Corrosion Institute report 1983:5. In Swedish. 2) Korrosionshärdigheten 1995:7. In Swedish. Korrosionshärdigheten hos fästelement. Slutrapport. Swedish Corrosion Institute report 1995:7. 3) Discussions with Sapa customers and suppliers of fasteners and and coatings. 133

16.10 CORROSION CHECKLIST

16.10 Corrosion checklist The summary below is intended to give a picture, from the perspective of durability, of aluminium as a construction material. Used correctly, aluminium has a long life.

Environments Rural atmosphere

Aluminium has excellent durability.

Moderately sulphurous atmosphere

Aluminium has excellent durability.

Highly sulphurous and marine atmospheres

Superficial pitting can occur. Nonetheless, durability is generally superior to that of carbon steel and galvanised steel.

Corrosion problems can be overcome

134

Profile design

The design should promote drying, e.g. good drainage. Avoid having unprotected aluminium in protracted contact with stagnant water. Avoid pockets where dirt can collect and keep the material wet for protracted periods.

pH values

Low (under 4) and high (over 9) values should, in principle, be avoided.

Galvanic corrosion

In severe environments, especially those with a high chloride content, attention must be paid to the risk of galvanic corrosion. Some form of insulation between aluminium and more noble metals (e.g. carbon steel, stainless steel, copper) is recommended.

Closed systems (liquid)

In closed, liquid containing systems, inhibitors can often be used to provide corrosion protection.

Severe, wet environments

In difficult, wet environments, the use of cathodic protection should be considered.

17. COST-EFFICIENCY

17. Cost-efficiency When compared with other design solutions, aluminium profiles are almost always competitive. Though the price per kg is higher than that of, for example, steel, this is counterbalanced by advantages such as: – very great freedom in creating creating exactly the shape that solves the design problem and contributes to the high quality of the end product – aesthetically pleasing surfaces – low die costs – low machining costs – low weight weight combined with high strength – long lifetime, minimum maintenance – high recycling value. The balance sheet comes out in favour of products based on aluminium profiles!

17.1 How you, the designer, can influence cost-efficiency Through carefully considered design, designers can influence the following cost-affecting factors: alloy, shape, weight per meter, surface class, tolerances, surface treatment, machining, recycling. Alloy

A number of factors have to be taken into consideration when choosing the right alloy for an extruded product. These include strength requirements, surface quality, suitability for decorative anodising, corrosion resistance, machining (cutting or plastic), weldability and cost-efficiency. High-alloy aluminiums are relatively more expensive and more difficult to extrude. Thus, alloys with higher than necessary strength should not be chosen. It is sometimes more cost-efficient to increase dimensions and extrude the profile in a slightly softer, but more easily extruded, alloy. See also chapter 7, “Choosing the right alloy”. Shape

Exploit the potential to create a shape that reduces the need for further machining and simplifies the assembly of the final product. Simplify the cross section as much as possible. Refer back to chapters chapters 9 and 10, 10, “General design advice” and “Jointing”. Weight per meter

Carefully considered design can reduce weight per meter. This often lowers costs. See also chapter 9, “General design advice”. Surface class

The choice of surface class affects price. The finer the surface, the higher the production cost (greater monitoring of dies, lower extrusion speed, increased handling costs). Surface classes 5 and 6 are the most economical to produce. Think carefully about which surfaces really need to be classed and marked as visible (refer to chapter 12, “Surface classes”). 135

17. COST-EFFICIENCY

Tolerances

Tight tolerances decrease productivity and, consequently, increase production costs. Thus, special tolerances should be restricted to the dimensions that are most important for the profile’s functionality. See also chapter 11, “Profile tolerances”. Surface treatment

Choosing the right surface treatment has a positive impact on appearance, function and durability. See also chapter 15, “Surface treatment”. Machining

At the design stage, it is important to create a shape that requires a minimum amount of subsequent machining. Extrusion provides many possibilities for including a number of functional features (screw ports, tracks, snap-fit joints, etc.) in the profile solution. Refer to chapters 9 and 10, “General design advice” and “Jointing”. Carefully considered machining (tolerances, deburring, machining before or after surface treatment, etc.) can also have a positive impact on the product’s final price. See also chapter 14, “Machining”. Recycling

The recycling of aluminium consumes relatively little power. It must be borne in mind that bolt joints, and other solutions involving the use of materials other than aluminium, can complicate recycling. See also chapter 4, “Environmental impact”.

17.2 How you, the purchaser, can influence cost-efficiency Order volumes

Unit price for small volumes is always higher than it is for large volumes. The larger the ordered volume, the less the unit price is affected by fixed costs such as tooling-up, machine adjustments, etc. Precise budgeting

Where you yourself take charge of machining, a lot of work is involved in inviting and evaluating tenders. Besides material and machining costs, calculations should also make provision for: – inspection of incoming profile material – warm storage – production preparation – tool inspection – tool storage – tool installation – rejects – production waste – transport to and from subcontractors – loading, packing, unpacking, etc. – dealing with offers and orders – dealing with invoices. On top of all that, the cost of tied-up capital also has to be taken into consideration. 136

17. COST-EFFICIENCY

Rejects and production waste

With Sapa in charge of machining, you do not have the bother of taking care of rejects and production waste. You receive a fixed price for t he finished component. Production is tailored to minimising production waste. Sapa’s long experience ensures that there is minimal rejection. All the scrap stays at Sapa

For Sapa, rejects and production waste are a high-grade raw material that can be directly exploited and put back into production without expensive intermediaries. Shorter lead times

Our planning is made easier by the fact that we have control of the entire production chain. Should anything unexpected occur, e.g. during machining, we can rapidly bring in extra profiles. Along with reduced transport, this contributes to shorter lead times. Less tied-up capital

When you choose Sapa as your partner, you only pay: – when the finished components are delivered – for the exact number of components supplied. When you yourself take charge of machining, you have to bear the full capital cost of materials all the way through production. This includes the costs associated with what becomes scrap and waste. Reduced administration

For you, having Sapa as the single centre of responsibility, means (amongst other things): – reduced work in connection with tenders – reduced ordering and organising of transport – simplified monitoring of deliveries – simplified quality assurance – fewer invoices – minimal work in connection with claims. Simplicity itself

You have a single supplier, a single point of contact, one order, one delivery, one invoice and one telephone number to ring. It really is that simple!

I N

O U T

Having Sapa as your partner reduces the burden of administration. It also offers every possibility for increased profitability, higher productivity and improved quality.

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17. COST-EFFICIENCY

It is all about co-ordination – general and specific, large and small, chalk and cheese, s trategic and tactical. Business development, research and development, quality assurance, logistics, market analyses, materials science, mechanical engineering, assembly, production planning, product development, profile optim isation, project management, technical development, technical calculation, monitoring and inspection, training, surface treatment and much, much more.

17.3 Sapa’s vision “Sapa shall be the most sought after partner in our industry and shall be the market leader in the Nordic countries. Our focus is customer service, technical expertise, quality and delivery dependability.” Are we in a position to help you with expertise, quality and resources? Can we free resources for your company's core business? There is a reason for contacting Sapa for open discussions. Many companies have found that the closer the partnership with Sapa, the sharper the resultant competitive edge. 138

18. KNOWLEDGE BANKS

18. Knowledge banks As a construction material, aluminium is capturing an ever greater share of the market. Unfortunately, this development has escaped the attention of the formal seats of learning. Consequently, knowledge about aluminium and profile design is low in comparison with that in respect of more traditional materials and construction methods. As the market leader in Sweden, and the other Nordic countries, we see it as our duty to increase the insight of industry and educational establishments into our field of expertise. That is one of the reasons behind the publication of this manual. The Profile Academy shares the same goal.

18.1 The Profile Academy The lack of a permanent forum for sharing knowledge and findings meant that people involved in product development, design and production generally had limited awareness of aluminium profiles and the possibilities they offer. To combat this, Sapa founded the Profile Academy (for Sapa customers). Via this establishment, experts from Sapa, together with a great number of highly qualified external lecturers, give advanced courses on the construction possibilities offered by aluminium profiles. Examples of course scope

1. Materials science and corrosion. 2. Design, recycling and the environment. 3. Profile technology and design for optimal production. 4. Dimensioning and strength. 5. Surface treatment. 6. Forming. 7. Cutting. 8. Mechanical joints. 9. Welds. 10. Case studies – examples and analyses of profile solutions and total cost-efficiency. Participants’ opinions

“The Profile Academy covers a wide area – for example, materials science, profile design, jointing and machining. The course provided a good basis for further study of areas that, not least for those of us in the vehicle industry, are both interesting and essential. I have been made aware of the great possibilities offered by the material and profile technology.” “My visit to the Academy gave me interesting insights into the potential for constructing with aluminium profiles. The course covered the technology and also provided many ideas for applications. To sum up, my understanding was both widened and deepened.” “I think the Profile Academy course is very good. Efficient, concentrated and comprehensive with a good balance between theory and practical application.” Since the beginning of 1994, each participant has given a thorough evaluation of the full course. Amongst other things, the results show that over 99% would recommend it to their colleagues.

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18. KNOWLEDGE BANKS

18.2 Further sources of knowledge 18.2.1 Sapa Technology Sapa Technology (ST) is Sapa’s research and development centre. It is also a resource for customers. The centre’s specialists offer expertise on how aluminium’s properties can be tailored by the choice of alloy and production conditions. The research laboratories have advanced equipment at their disposal for measurement and scientific material examination. ST also runs development projects along with Sapa and our customers. In addition to this, much work is done in collaboration with universities, colleges and research institutes. Shorter assignments such as chemical analyses, structure investigations and strength testing form another part of ST’s operations. Advice on material selection, design, jointing, surface treatment, recycling and so on are further examples of its work in this field. Hardware and software

ST’s equipment, the hardware, is often particularly advanced – in some cases, unique.

Most important amongst its array of instruments are those for analyses, structure investigations and mechanical testing. However, “instrument time” is not the essence of what ST supplies. At heart, the most important thing ST offers is its “software” – the way it solves problems and develops potential, the expertise of its employees, etc. ST’s metallurgists, chemists, metallographers, physicists, designers, mechanics and engineering technicians all have aluminium as their speciality.

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18. KNOWLEDGE BANKS

Aluminium profiles as floor gratings in reefer vessels

FEM image of the stresses in

a loaded cross section. The finite element method (FEM) is a powerful tool in calculating and optimising strength, deformation, characteristic frequency, etc.

Fatigue testing of floor gratings

under simulated operating conditions. Sapa Technology designs and produces test equipment tailored to customer needs.

18.2.2 Colleges, industry organisations, etc. Outside Sapa, a number of institutions are involved in aluminium-related research, development and knowledge sharing. Many technical and regional colleges, high schools and private sector training companies run projects that have the goal of raising understanding of aluminium technology. Industry organisations support, at many different levels, researchers and lecturers in their aluminium-related activities. In all these initiatives, Sapa plays an active role as an institutor and implementor.

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19. DESIGN

19. Design This section was compiled by Torsten Höglund (Dr. Tech. and Professor at the Royal Institute of Technology, Stockholm, Sweden) and Peter Benson (Dr. Tech., Sapa).

19.1 General Extrusion enables the production of aluminium profiles that, to the widest possible extent, meet all a designer’s function-related demands. Profiles can have almost any cross section. Consequently, much is demanded of the designer. Furthermore, there are no standard tables to turn to for data on cross-sectional properties. This section is intended as an aid for all those interested in using aluminium profiles in load-bearing constructions. The section contains advice and views on crosssectional design as well as formulae and tables for dimensions. The section’s contents mirror those of the Swedish Building Code (BKR). In many ways, this is similar to the proposals for Eurocode 9, Design of Aluminium Structures, on which the European Committee for Standardisation, CEN, is working at present. For information on more complex structures and phenomena, refer to the literature cited in 19.2.

19.2 Design literature Boverkets handbok för st ålkonstruktioner , BSK 94,

Boverket. In Swedish. Design Regulations, BKR, of the Swedish Board

of Housing, Building and Planning, June 2000. Eurocode 9: Design of Aluminium Structures ENV 1999-1-1 , European Committee for Standardisation,

Brussels, 1999. European Recommendations for Aluminium Alloy Structures Fatigue Design, ECCS no. 68, 1992. Kapitel K18, Utdrag ur Handboken Bygg , Fritzes, 1994.

In Swedish. SBN 80 avd 2A, Bärande konstruktioner med kommentarer , Statens Planverk, 1979. In Swedish. StBK-N5, Swedish Code for Thin Gauge Steel Structures 79, Statens Stålbyggnadskommitté, 1980. TALAT – Training in Aluminium Application Technologies, F. Osterman and others, 1995.

19.3 Key considerations in aluminium design Low weight (density = 2,700 kg/m 3)

Low weight is important not only where the structure’s own weight dominates, but also in transport and assembly. Low modulus of elasticity

(E = 70,000 MPa) Where structures are subjected to compression, the goal is as little slenderness as possible. For aluminium structures, deformation requirements are often determinative as regards dimensions. Distribute mass appropriately (e.g. latticing) or use statically indeterminate designs. Relatively low fatigue resistance

Aluminium structures subjected to fatigue loading should be designed so that the cross sections where large stress variations are expected are, as far as possible, of unweakened parent metal.

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Heat induced reductions in strength

The strength of the material used in load-bearing aluminium structures is increased by cold working or heat treatment. Local strength is reduced by the heat applied in hot straightening, hot forming and, in particular, welding. If heating is necessary for technical reasons connected with structure or production, it should take place in areas where stress is low. Relatively low hardness

Hardness is relatively low. For hardness values, refer to pages 26 – 27, chapter 7, “Choosing the right alloy”. Avoid unnecessary transport and components that, because of their size and shape, are prone to deformation or surface damage. Not prone to brittle fracture at low temperatures

Aluminium does not become brittle at low temperatures. As a rule, it becomes tougher and stiffer.

High corrosion resistance

Corrosion resistance is often a determining factor in the decision to use aluminium. Can be extruded

Extrusion offers many possibilities for the production of function-tailored profiles. Formability

Especially at low tempers, aluminium is easy to form when cold. Aluminium sheets and plates can be formed in press brakes and roller presses. They can also be deep drawn. Tight cross-sectional tolerances

Extruded aluminium profiles with open cross sections are produced to tight tolerances. Furthermore, compared with rolled profiles, initial curvature is small. Low residual stress

The residual stresses in extruded aluminium profiles are low.

Low damping factor

Where oscillation may be induced by variations in interference frequencies (e.g. gusts of wind), the structure should be sufficiently stiff to place its characteristic frequency well above the largest interference frequency. Relatively high thermal expansion

The coefficient of thermal expansion is relatively high, 23 x 10-6 per °C change. The effects of temperature variations (varying operating temperatures, changes in ambient temperature, etc.) have to be taken into account if the resultant expansions and contractions can induce stress. Because of the low modulus of elasticity, the stresses induced by resistance to longitudinal expansion are moderately large. In statically indeterminate systems, attention should be paid to the stresses induced by changes in temperature. High thermal conductivity

Temperature differences between the different sides of a profile are rapidly evened out. For the relevant values, see pages 26 – 27, chapter 7, “Choosing the right alloy”.

19.4 Cross-sectional shape 19.4.1 Asymmetrical profiles – the shear centre

Functional requirements often determine a profile’s cross section. Consequently, asymmetrical profiles are common. An asymmetrical profile’s shear centre (SC) does not coincide with its centre of gravity (CG). This affects both how the profile works and its load-bearing properties. Loading a beam to the side of its shear centre induces torsion in the beam – torsion and warping stresses arise. For example, a U-profile subjected to a load directly over its web will deform (bend) in the load plane. As the shear centre lies outside the cross section, the profile will also be subjected to torsion. The position of the shear centre in relation to the load plane is of greater significance in solid profiles than it is in hollow profiles. This is because the torsional rigidity of the latter is often considerably greater. On the next page, there are some examples of the position of the shear centre for various profiles.

143

19. DESIGN

The SC of a profile with two planes lies in the point of intersection (figure 19.4.1.a-b). The SC of a hollow profile often lies inside the cross section (figure 19.4.1.c-d). For solid profiles, it often lies outside (figure 19.4.1.e-f). With large openings, the SC lies further from the profile than is the case with small openings. To prevent undesired torsion, every attempt should be made to place the SC in the load plane (figure 19.4.1.g). Alternatively, a hollow profile should be used. To calculate SC position, refer to the appropriate literature (see 19.2, “Design literature”) and the computer programmes that are now available.

= SC (Shear centre)

= CG (Centre of gravity)

19.4.2 Solid or hollow profiles? It is almost as easy to extrude a hollow profile (closed cross section) as it is a solid profile (open cross section). However, which is the right solution for the application in question? In structures where profiles are subjected to torsion, a closed cross section has the edge. The torsional rigidity of a hollow profile is considerably greater than that of the corresponding solid profile. To illustrate this, figure 19.4.2.a compares a selection of profiles having the same width, height and crosssectional area. In this example, the hollow profile is 290 times stiffer than the corresponding solid profiles. Hollow profiles can be used in structures that are subjected to direct torsion. Concentrated loading of plate structures is a different area. In figure 19.4.2.b, a plate is constructed of transversally joined hollow profiles. In principle, the joints transfer shearing forces only. To achieve torsional rigidity, the ends of the profiles are joined to support structures. When a concentrated load is applied, it is transferred to the supports by the bending and torsion between adjacent profiles.

Figure 19.4.1. a-b

t1

= SC = CG

h

K v =

7

w Figure 19.4.1. c-d

t2 h

K v = 3.4

h

K v = 1,000

w Figure 19.4.1. e-f

t2

w Figure 19.4.1.g. The shear centre and centre of gravity for

various profiles.

144

Figure 19.4.2.a. Comparison of torsional rigidity (K v ) in a selection

of solid and hollow profiles having the same width, height and cross-sectional area (w = 200 mm, h = 30 0 mm, t 1 = 17.2 mm, t 2 = 12 mm).

19. DESIGN P

a

2.6 mm

b

2.3 mm

c

1.8 mm

d

1.1 mm

design value for the structure’s resistance and is the result of characteristic strength (R k) divided by the product of the partial coefficients  m and  n . R d is also referred to as design resistance. The allowable value corresponding to that in the allowable stress method is obtained by dividing the design resistance ( R d) by the load coefficient ( f ). Design here takes into account the structure’s resistance in the serviceability limit state and in the ultimate limit state. In the serviceability limit state, i.e. the demands made on the structure in normal use, deformation may be one of the crucial factors. In the ultimate limit state, demands are put on the structure’s ultimate load-bearing capacity. This includes material fractures, instability, toppling, deformations that make the structure unusable, etc. The rules given in the following are based on the partial coefficient method.

Figure 19.4.2.b. Four examples of a plate structure constructed

from hollow aluminium profiles (profile width = 250 mm, height = 150 mm, wall thickness = 5 mm, span = 2,000 mm and load = 10 kN). In example a, the profiles are not joined. The loaded profile has to bear the entire load. In example b, the profiles are connected and have low torsional rigidity. In examples c and d, the cavities are larger and, consequently, torsional rigidity is greater. Through torsion, the load is distributed across several profiles.

19.5 Design using the partial coefficient method – general Two methods are used for designing load-bearing structures – the allowable stress method and the partial coefficient method. In the allowable stress method, strength

 

s

= allowable

where s is a safety factor providing a margin for uncertainty and allowable is the allowable stress value. This method is increasingly being dropped in favour of the partial coefficient method. When designing with the partial coefficient method, the conditions below have to be satisfied. S d  R d S d = S k  f R d =

R k

 m  n

S d is the design load, i.e. the characteristic load

multiplied by the partial coefficient  f . This latter provides a margin for load uncertainties. R d is the

19.6 Material 19.6.1 Material values The design value for strength is determined from f yd

=

f yk

 m  n

where f yk is the characteristic value at the material’s 0.2% proof strength. The design value for the material’s ultimate strength is determined from f ud

=

f uk

1.2  m  n

where f uk is the characteristic value of the material’s ultimate tensile strength. The factor 1.2 provides an additional safety margin against material fracture. In welding, the heat input affects the material nearest the weld. The result is a local reduction in strength. The design value for material affected by welding is determined from f wud

=

f wuk

1.2  m  n

where f wuk is the characteristic value of the material’s ultimate tensile strength in the heat-affected zone. The design value for the modulus of elasticity is determined from E d

E k

=   m n

where E k is the characteristic value of the modulus of elasticity. Characteristic material values are given in table 19.6.1.a (next page). Partial coefficient values are given in section 19.6.2. 145

19. DESIGN

Table 19.6.1.a. Characteristic strength values for Sapa’s structural alloys.

Certain values may differ from those given in BKR – contact Sapa for further details. Property

f yk f uk f wuk E k A5

[MPa] [MPa] [MPa] [MPa] [%]

Sapa 6060

Sapa 6063

Sapa 6063A

Sapa 6005

T6 150 190 100 70,000 12

T6 170 215 100 70,000 12

T6 200 230 100 70,000 10

T6 240 270 * 70,000 10

Sapa 6005A

T6 240 270 * 70,000 10

Sapa 6082

Sapa 7021

T6 250 290 180 70,000 8

T6 310 350 * 70,000 10 * Contact Sapa.

19.6.2 Partial coefficients When calculating the resistance of a profile based on its nominal dimensions reduced by the lower tolerance deviation limit,  m is set at 1.0. In all other cases,  m = 1.1. The coefficient  n is determined by safety class (as per 19.6.2.a).

Table 19.6.2.a. Coefficient  n Safety class

Consequence of fracture

 n

1 (Low)

Low risk of serious personal injury.

1.0

Some risk of serious personal injury.

1.1

High risk of serious personal injury.

1.2

2 (Medium) 3 (High)

When designing for the ultimate limit state, load is determined from n

F d

=

  F i=1

fi

ki

where  fi is the partial coefficient for load F ki . The values for  f can be read from table 19.6.2.b.

Table 19.6.2.b. Partial coefficient

 f

Load type

Load value F k

Partial coefficient

Permanent loads A variable load Other variable loads

G k Qk  Qk

1.0 och 0.8 1.3 1.0

 f

For permanent loads, the  f value giving the most unfavourable load condition is selected. When designing for the serviceability limit state,  f is set at 1.0. For further information on loads and load coefficients, refer to BKR.

146

19.7 Designing 19.7.1 General Unless otherwise stated, the design methods given here apply to unwelded constructions. 19.7.2 Buckling Slender parts of a cross section (“strips”) have a resistance that is greater than the buckling load of the ini tially flat plate of which they form a part. This i s because the edges of the strips are prevented from bending outwards by the adjacent strips. Figures 19.7.2.a and 19.7.2.b show the difference between a plate with two free edges ( a), and one with all four sides simply supported ( b). A plate with two free edges fails in the same way as a bar and deforms to leave a surface with a single curve. All the vertical strips are exposed to the same compressive strain and bending. Consequently, the stress is constant transversally. Under buckling, the plate simply supported on all four sides deforms to give a surface with a double curvature. As the plate buckles, the stresses to which strips on the edges are exposed are not the same as those affecting the strips in the centre. The edge strips remain straight and the compression leads to compressive strain and increased stress. The centre strips, however, bend away without there being any significant increase in compressive strain. For a plate that has little slenderness, the resistance is lower than the buckling load and failure arises through material fracture. For a plate that has a great amount of slenderness, the failure load is higher than the buckling load, see figure 19.7.2.c. Under the rules set out in BKR and StBK-N5, it is permitted to use the resistance over and above the buckling load, i.e. the real resistance. Buckling under normal loads can be taken into account by replacing the true cross section with an effective cross section. In StBK-N5, this is done by replacing the true width with an effective width, see figure 19.7.2.e. BSK , on the other hand, uses an effective thickness, see figure 19.7.2.f. With certain simplifications, this latter method is used in the following formulae.

19. DESIGN

19.7.3 Effective thickness The calculation of effective thickness uses a slenderness parameter that depends on the support conditions, stress distribution, material values and the ratio between the width and the thickness of the elements of which the cross section is composed.

Initially straight bar

Cross section with outstand Initially bent bar and plate with two free edges

 = 1.52

bk

f yk

t

E k

Figure 19.7.2.a.

Outstand

Initially flat plate Figure 19.7.3.a.

Initially buckled plate

t ef

= t if   0.67

t ef

=

1 

–

0.22

t if   0.67

 2

Flat internal elements

Figure 19.7.2.b.

Constant compressive stress

Buckling load Resistance

 = 0.526

b t

f yk E k

d a o L

Slenderness

Figure 19.7.2.c.

Figures 19.7.2.a - 19.7.2.c. Exposed to normal force, a plate with

two free edges fails in the same way as a bar (figure a). With all edges simply supported, the plate buckles, but can carry a higher load (figure b). At the same tim e, the stiffness of the plate decreases. The connection between slenderness, buckling load and resistance is particularly clear in figure c.

Figure 19.7.3.b. Variable compressive stress

 =

b

f yk

(2.67 – 0.77  ) t

E k Stress distribution for the gross cross section

Figure 19.7.2.d.

Figure 19.7.2.e.

Figure 19.7.2.f.

True stress distribution.

Stress distribution using the effective width method.

Stress distribution using the effective thickness method. Figure 19.7.3.c.

147

19. DESIGN

Alternating compressive stress

 = 0.375

bc f yk t

E k Stress distribution for the gross cross section

b

a

Figure 19.7.4.a. Profile without longitudinal reinforcement (a).

Profile with longitudinal reinforcement (b).

Figure 19.7.3.d.

In these cases:

t ef

= t if   0.6

t ef

= 0.06 +

0.85 

–

0.172  2

t if   0.6

Elements subjected to shear stress

 = 0.35

bw

f yk

t w

E k

19.7.5 Axial force For a profile subjected to axial tensile forces, resistance is determined, in most cases, by the strength of the material. Where the load consists of axial compressive forces, resistance is determined by the material’s strength and modulus of elasticity as well the profile’s cross section and length. Failure can occur as a material fracture or loss of stability, e.g. bending instability, lateral-torsional buckling or torsional buckling. The resistance of a profile subjected to axial loading is determined from N d

= f yd A gr c

where A gr is the gross surface of the cross section and c is a factor that takes the nature of the load into account. For tensile force, c is set at 1.0. For compressive force, c can be read from figure 19.7.5.c. The slenderness parameter is determined from  c =

Figure 19.7.3.e.

t ef

= 0.67 t w if   0.75

t ef

=

0.50  w

l c

f yk

 i

E k

where l c is the critical length of buckling (l c = L , see figure 19.7.5.b) and i is the radius of inertia (= I/A) for the profile.

t w if   0.75 Figure 19.7.5.a. Buckling of a bar

subjected to an axial compressive force.

19.7.4 Reinforced elements The resistance of profiles with wide, thin elements subjected to compressive or shear forces is often reduced by local buckling. One way of improving resistance is to use longitudinal reinforcement, see figure 19.7.4.a. Methods for designing reinforced internal elements are given in StBK-N5.

148

For cross sections with slender elements, i is replaced by i ef

=

I def Aef

where I def is the moment of inertia calculated for a cross section based on elements with effective thickness t def as per below. Aef is cross-sectional area based on effective elements as per 19.7.3.

19. DESIGN

The deformation is a combination of bending and torsion. When designing for torsional buckling and lateral-torsional buckling, refer to BKR or Eurocode 9.

 = 2.1

=1

 = 0.8

 = 1.2

 = 0.6

Figure 19.7.5.b.  values for simple support conditions.

For internal elements (e.g. the web of a beam): t def

= 33 t 2 / b  t Figure 19.7.5.d. Torsional buckling.

For outstands (e.g. a beam flange): t def

= 12 t 2 / b  t

c 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0

0.5

19.7.6 Bending moments The resistance of a profile subjected to a bending moment is determined from the lower of the two values

1.0

1.5

 c

2.0

Figure 19.7.5.c. Factor c as a function of  c . Curve 1 is for sym-

metrical cross sections and curve 2 for asymmetrical cross sections.

M d

= f yd W 

M d

= f ud W net

compressed edge or edge subject to tensile forces edge subject to tensile forces

where W is the profile’s flexural resistance and  is a shape factor that takes the slenderness of elements into consideration. Where the profile has compact elements,  is set at 1.0. This gives conservative results. For a more finely detailed method, refer to BKR. For profiles with slender elements,  = W ef / W , where W ef is flexural resistance for a profile composed of elements with effective thickness. W net is the flexural resistance of a profile with local weakening, e.g. a hole. Lateral buckling

Torsional buckling and lateral-torsional buckling

Torsional buckling is the type of stability failure demonstrated when a bar, under compression, twists around its longitudinal axis, see figure 19.7.5.d. Torsional buckling occurs in cross sections with point or double symmetry and limited torsional rigidity. Lateral-torsional buckling is a form of stability failure that can occur in a compressed bar where the loading falls outside the axis of the profile’s shear centre. Lateral-torsional buckling can arise when, for example, a simple or asymmetric profile is loaded along the axis of its centre of gravity, or when a symmetrical profile is subjected to an off-centre load.

Lateral buckling is a failure mode occurring i n a beam that, under the influence of a bending moment and/or transversal loading, bends away at right angles to the load plane and, at the same time, twists, see figure 19.7.6.a. Lateral buckling is a particular problem of beams that have little torsional rigidity and little flexural rigidity perpendicular to the load plane. A great deal of calculation is required to determine the design bending moment in respect of lateral buckling in beams with a cross section deviating from the common I or U-profile. Thus, designs should normally seek to eliminate lateral buckling. If the compressed flange (or the edge of the rectangular beam) is supported laterally, or if the beam is prevented from twisting throughout its length, the 149

19. DESIGN

The structure exerting the load often provides support and/or twist prevention, for example, a plate placed on the upper flange of an I beam. Lateral buckling does not normally occur in round tubes or in square tubes where the height is less than three times the width. For the design of beams in respect of lateral buckling, refer to the literature.

19.7.8 Torsion The resistance of a solid or hollow profile subjected to pure torsion is T Rd = 0.58 f yd Z v v

where Z v is torsional resistance as per the theory of plasticity, and v a reduction factor that takes shear buckling into account. For solid profiles, v = 1,0. For hollow profiles, v can be read from table 19.7.8.a. In this table,  w is determined (using the same formulae as for a plate subjected to shearing stress) for elements with maximum slenderness bw /t w . For other types of torsion, e.g. mixed torsion, refer to the literature.

Table 19.7.8.a. Reduction factor v (shear buckling in hollow

profiles subjected to torsion) as a function of  w . Fork or hinge support

 w

l i f

< 1.25

E k f yk

lateral buckling is not crucial for the design. In this formula, l is the distance between side braces and i f is the radius of inertia for a c ross section comprising the compressed flange and 1/6 th of the web.

0.67 0.435 /  w

– 0.65 0.65 – 2.37

Figure 19.7.6.a. Lateral buckling in a simply supported beam.

A common example of lateral buckling is that occurring between battens providing lateral bracing (compare this with the lateral buckling of the top bar in beam latticing). In this case, the following rule of thumb can be used. If

v

Table 19.7.8.b. Cross section properties for pure torsion.

K v

Cross section

Solid, thin wall cross section Hollow, thin wall cross section



hi t i 3

kv

3

t max

4 A2



W v

ds t

2 At min

Z v



hi t i 2

2

2 At min

19.7.7 Transverse force In a profile that acts as a beam, transverse forces are taken up by the web. This can be compared to a plate subjected to shearing stress. The transverse force capacity of a beam subjected to transverse forces only is determined from V Rcd = bw t wef f yd

where bw is the width of the web and t wef is the effective thickness value for a plate subjected to a shearing force – as per 19.7.3. When designing a girder with a stiffened web, refer to BKR or Eurocode 9.

150

Figure 19.7.8.a. Explanation of terms in t he calculation of cross

section properties. A = the area within the centre of gravity line.

19. DESIGN

19.7.9 Combined loads Bending instability

Where a bar is subjected to axial force and bending in one plane, the formulae below can be used for checking the resistance. Both conditions of the formulae have to be met. The formulae give conservative results for compact cross sections. For greater precision, refer to BKR or Eurocode 9. N Sd

0.8

+

N Rxcd N Sd

M Rd

+ 0.63

M Ryd

V Sd V Rd

V Rd

+

T Sd T Rd

2

+

E d f yd

19.8  1.00

+

N Sd N Rd

 1.38

For a profile simultaneously subjected to a bending moment, transverse force and torsion, the following condition has to be met: V Sd

2

F Rcd = 0.70 t w

0.8

M Syd

where N Sd = axial force, M Sxd = the moment around the x axis, M Syd = the moment around the y axis, N Rxcd = the design axial force in respect of buckling around the x axis, N Rycd = the design axial force in respect of buckling around the y axis, M Rxd = the design moment with regard to bending around the x axis and M Ryd = the design moment with regard to bending around the y axis. To check lateral torsional buckling for a bar subjected to normal force and a bending moment, refer to BKR or Eurocode 9. For a profile simultaneously subjected to a bending moment, transverse force and axial force, the following condition has to be met: M Sd

For beam webs without stiffeners, the design value (F Rcd ) for resistance in respect of stresses and buckling under concentrated loads is:

 1.00

M Rxd

+

N Rycd

Concentrated force and support reaction

where t w is web thickness.

M Sxd

0.8

19.7.10

M Sd 2 M Rd

Joints

19.8.1 General Aluminium profiles can be joined together using mechanical joints, welding and adhesive bonding. Mechanical joints include screw and rivet joints where a part of the joint (e.g. a screw port or nut track) is integrated into the profile. The jointing can even be completely integrated into the profile, e.g. clamp and snap-fit joints. Joints using nuts and bolts are designed in accordance with the tables in BKR. Rivet joints and joints using self-tapping screws are designed as per StBK-N5. There are types of fasteners with properties different from those discussed here and types of joint that are not taken up in this text. In these cases, characteristic strength can be determined by testing. For further information on this, refer to BKR.

19.8.2 Force distribution in joints Centric force with several identical fasteners is distributed equally between all the fasteners if L < 15d . When L > 15d , the force (F S ) on the most highly loaded fastener will be as in figure 19.8.2.a.

 1.00

where T Sd is the torsion and T Rd is the torsion capacity.

n no. of fasteners with diameter d

Where L  15d Where 15d < L  65d

F F S = n 1

F S =

1.075 – Where L > 65d

F S = 1.33

L

F n

200d

F n

Figure 19.8.2.a. Force distribution in joints.

151

19. DESIGN

19.8.3

19.8.4 Nuts and bolts The resistance of a bolt subjected to tensile force is

Types of failure in joints using fasteners

In joints made by fasteners, failure can occur in the material (the profile) or the fastener. The design methods here are in respect of the following failure modes that are themselves dependent on the type of joint and the loading:

F Rtd = t As f bud f bud =

f buk

1.2  n

where As is the bolt’s stressed area and f buk is the bolt’s characteristic ultimate tensile strength. The reduction factor t is 1.0 for pretensioned bolts in strength classes 8.8 and 10.9. For normally tightened bolts, t is 0.6. Characteristic tension resistance F Rtk is given in

Shear resistance in the fastener

Bearing resistance

F Rtd =

t F Rtk

1.2  n

In a bolt joint subjected to shearing force, resistance is determined by whichever is the lower of F Rvd (the bolt’s shear resistance) and F Rbd (the bearing resistance).

Tilting

Pull through resistance

F Rvd = 0.60 A1 f bud

where A1 is the bolt’s nominal area if the shearing plane intersects the unthreaded bolt stem. In other cases, A1 is the bolt’s stressed area. To ensure that a joint fails as a result of a bearing resistance failure, F Rvd is reduced by 25%. The bearing resistance is determined from

Punched through resistance

Tension resistance

Pulling out of the base

F Rbd = 1.2

e 1 d

– 0.5 d t f ud

where d is the bolt’s diameter, t is the thickness of the structural element transferring the force to the bolt and e 1 is the distance from the hole centre to a free edge

Figure 19.8.3.a.

Table 19.8.4.a. Characteristic ultimate tension resistance F Rtk in a bolt/screw (as per BSK ). Load in [kN]. As

Strength class

M4 M5 M6 M8 M10 M12 M14 M16 1)

152

SS 2332, SS 2343.

2)

Stainless steel 1)

Steel

(mm )

4.6

8.8

10.9

50

8.8 14.2 20.1 36.6 58 84 115 157

3.51 5.68 8.04 14.6 23.2 33.6 46.0 62.8

7.02 11.4 16.1 29.3 46.4 67.2 92.0 126.0

8.78 14.2 20.1 36.6 58.0 84.0 115.0 157.0

4.39 7.10 10.1 18.3 29.0 42.0 57.5 78.5

2

Maximum hole diameter.

80 7.02 11.4 16.1 29.3 46.4 67.2 92.0 126.0

dmax2)

(mm) 4.5 5.5 6.6 9 11 14 16 18

19. DESIGN

(or the centre of an adjacent hole) measured in the direction of the force. If e 1 > 2d , then e 1 = 2d is used. The simultaneous effect of tensile force and shearing force is F Std F Rtd

2

F Rvd

 1.00

19.8.5 Self-tapping screws Self-tapping screws can thread into drilled holes or, as in figure 19.8.5, be given a drill tip. The tip on the left can be used in thin materials. The one on the right is suitable for thicker materials. The shear resistance of a screw subjected to shearing forces is determined from

520 T  m  n

N

F Std F Rtd

where T is the characteristic ultimate tensile strength of the screw ( see table 19.8.5.a). For joints subjected to a shearing force, bearing resistance is determined from 2.8 t 3d f yd 1.6 t d f yd

if t = t 1. For 1 < t 1/t < 2.5, there is straight line interpolation between these equations ( t is the thickness of the plate nearest the screw head and t 1 is the thickness of the other plate). For joints subjected to tensile force, resistance is determined by pull through resistance and punched through resistance.

2

F Svd

+

 1.00

F Rhd

2

2

F Svd

+

 1.00

F Rvd

where F Std is the tensile force and F Svd is the shearing force.

Figure 19.8.5.a. Self-tapping screws – the screws can be given drill

tips for thin material (left) or thick material (right). Table 19.8.5.a. Self-tapping screws

– characteristic tension resistance, T , [kN].

T  2.3 x 10-3 F Rhd (kN/screw)

F Rhd = min

2

F Rgd

where F Std is the tensile force and F Svd the shearing force.

F Rvd =

F Std

2

F Svd

+

For the effects of combined loads, the following conditions are to be checked:

d (mm)

Aluminium SS 4338

Stainless steel SS 2332 SS 2333 SS 234 3

Stainless steel SS 2302 Carbon steel SS 1370 Case-hardened

4.8 5.5 6.3 8.0

4 6 8 13

7 10 13 22

8 11 15 25

19.8.6 Screw ports Open screw port d

t

F Rgd = 6.5 t f yd

(t in mm and f yd in MPa give F Rgd in N.) Figure 19.8.6. Open screw port.

pulling out of the base

F Rud = 0.65 t 1 d f yd

and tension resistance in the screw F Rtd =

800 T  m  n

Screw ports can be threaded for machine screws or used for self-tapping screws. The allowable force in respect of a screw pulling out of the base is determined from the formula F Rud = 1.6 a f yd

where a is the thread length of the port (a in mm and f yd in MPa give F Rud in N). 153

19. DESIGN

Shear strength depends on the direction of the force. With a force acting against the opening of the port, the allowable force is determined from F Rvd = ( 2t + 0.16a) f yd

where t is the thickness of the material in the screw port (t and a in mm and f yd in MPa give F Rvd in N). The formulae have been verified for screw diameters 3  d  7 mm. Where the force acts in towards the port, the screw’s strength is determinative – refer to 19.8.5, “Self-tapping screws”. With a force acting perpendicularly into the opening, resistance is determined by material thickness. F Rvd can be used as described above. Greater thickness, t , leads to increases in both pull-out and shearing force. Values can be determined by testing. Closed screw ports

Closed screw ports have to be used where strength requirements are high. The depth of engagement for metric fine-pitch screws should be 3d , where d is screw diameter. Resistance in respect of tension and shearing is determined as for the screws in table 19.8.4.a. 19.8.7 Tracks for nuts and bolts Nut and bolt tracks can be used for the rapid interconnection of profiles, or for rapidly connecting profiles with other components. Resistance in respect of tensile force is determined by the shear resistance of the profile material or by the bolt’s strength. Resistance in respect of the bolt pulling out of the base material is determined from F Rgd = 1.2d t f yd

where t is the material’s thickness and d is the size of the track opening. The latter should not be more than 10% larger than the bolt’s diameter. Tension resistance in the bolt is determined as per 19.8.4. 19.8.8 Rivet joints There are various types of rivets. The most common are those with a mandrel. For rivet connections, there are the same fracture modes as for self-tapping screws. The rivet is put into a pre-drilled hole. It is introduced and headed from one direction. Heading takes place when the mandrel is pulled out by special tongues. Where mandrel material is incorporated into the rivet at heading, the rivet has a sealing effect. 154

The following load capacity values apply to shear resistance in rivets: F Rvd =

800 S  m  n

where S is a value read from table 19.8.8.a. Bearing resistance – the same as for selftapping screws of identical diameter, d . Pull through resistance and punched through resistance (F Rgd ): 0.4 times the value for self-tapping screws. Tension resistance in the rivet: 1.5 times the value for shearing fracture. Pulling out from the base (F Rud ): 0.3 times the value for self-tapping screws. Table 19.8.8.a. Rivet with mandrel.

Characteristic shearing fracture force ( S ) in [kN]/rivet. d (mm)

4 4.8 5 6 6.4

Aluminium AA 5053 AA 5056

0.8 1.1

1.1 1.6 1.7 2.6 3.1

2.0

Steel

Monel

Stainless steel SS 1325 SS 2332 SS 2333 SS 2343

1.6 2.4 2.6

2.4 3.5

2.8 4.2 4.6

4.4

6.2

19.8.9 Welded joints Fusion welding gives very good results with alumini um. A number of methods are possible, but the most common for construction purposes are Metal Inert Gas (MIG) and Tungsten Inert Gas (TIG). When aluminium is welded, there is a lowering of strength in the heat-affected zone (HAZ). To take this into account, calculations reduce material thickness in the area 25 mm around the weld. Thickness is determined from t haz =

f wud f ud

t

If thickness is also reduced to take l ocal buckling into account (t ef ), then the lower of the values t haz and t ef is chosen. For profiles with transverse welds, f wud replaces f yd when f wud < f yd in an area of 25 mm on each side of the weld. When designing welded joints, exploit the possibilities offered by profiles. Increase material thickness locally in highly loaded areas. This will reduce stress. Use butt welds wherever possible.

19. DESIGN

Build edge preparation into your design at the drawing board stage – see figure 19.8.9.b. The calculation of forces and stresses in the weld is the same as for steel constructions. For the design of longitudinal welded beams and beams with transverse welds, see BKR. Solution heat treated zone e r u t d c l u e t r W s

d e l C ° t a e e 0 f n 0 o n n o 5 S a z

d e g C a ° y 0 l 0 l a 3 i c , fi e i t r n o A z

° d C e 0 t c 3 e 1 , f f e a n n o U z

products, offshore structures and similar structures using semi-finished products in the form of profiles, plates and drawn or forged tubes. The methods used in the recommendations are not valid for cast alloys. The operating temperature of components has an upper limit of 70°C. The environmental class is M3. Component thickness is limited to 25 mm. For thicker material, testing should be carried out. If testing is not possible, fatigue strength is to be reduced as per the instructions in ERAAS FD. The jointing method can be MIG or TIG welding, screw or rivet joints.

N/mm2

f u

300 200

f wu 100

r = 0.6 Figure 19.8.9.a. How the material is affected by heat input at

welding.

Figure 19.8.9.b. The reduction in strength can be compensated

for by increasing material thickness locally – edge preparation at the design stage.

19.8.10 Miscellaneous jointing methods There are several methods of jointing thin-walled profiles using the material itself and no extraneous agents or fasteners – see chapter 9, “General design advice”, and chapter 10, “Jointing”.

19.9

Fatigue

19.9.1 General Fatigue is often a critical design factor for aluminium structures and, in particular, welded aluminium structures. As regards the fatigue design of welded and unwelded aluminium structures, BKR refers to the ECCS document, European Recommendations for Aluminium Alloy Structures Fatigue Design (ERAAS FD). The methods given there are partially reproduced here. For fuller details, refer to ERAAS FD.

19.9.2 Scope The recommendations are for building-related structures, machine parts and components, transport

19.9.3 Fatigue load Any load that gives rise to stresses that vary during use is to be regarded as a fatigue load. Vibration, thermal fluctuation, load movement and inertial loads can cause fatigue. Dynamic load increases often have a significant effect on stress levels and must be considered in all calculations. When designing in respect of fatigue, the design load must mirror stress conditions throughout the component’s lifetime. Normally, this load is of a different type to that used when designing in respect of fracture. The stress range is determined as the largest algebraic difference between the main stresses acting in the main stress planes intersecting each other at less than 45° (minimum angle). Generally, irrespective of whether the greatest stress is positive or negative, the entire stress range is used for the calculation of fatigue load. In some cases, where the structure is built from unwelded material, a certain increase in strength can be taken into account – see ERAAS FD. The effect of the stress concentrations that build up around welds, and when making holes for bolts, screws and rivets, were taken into account in plotting the fatigue curves for the standard details in 19.9.5, The designer must also consider stress increases occasioned by other factors, e.g. the cutting of hol es, large variations in material thickness and misalignment in joint intersections. 19.9.4 Designing for fatigue The characteristic strength ( f rk ) of standard detail solutions and standard alloys is given in tables 19.9.5.a – 19.9.5.c. These tables give strength values in the load cycle range 103 < N < 108. Stress range variations have been taken into account by giving the values for standardised stress spectra as per figure 19.9.3.a.

155

19. DESIGN

The following applies to fatigue design rd < f rd f rd

=

f rk

1.1  n

where rd is the stress range determined from the largest difference between stress levels at a point in the detail. For cross sections subjected to more than uniaxial stress, rd is taken as the main stress.

19.9.5 Detail types This section includes 33 detail types used in structures. The arrows show the direction of stress. The typical crack zones are marked by red stripes. These areas have to be examined for fatigue. Each detail type has been given a designation and a characteristic fatigue strength, C (detail class), at 2 x 106 load cycles and at R = 0.5, where R is the ratio of the smallest stress in the load cycle to the corresponding largest stress.

Structural detail A1, simple profiles and machined parts in alloy 7020, detail class 130

These values are for simple profiles, e.g. flat bars or angles with as-extruded surfaces and no sharp edges. Surfaces have no obvious stress raisers.

Figure 19.9.3.a. Standardised stress spectra.

Structural detail A2, components in alloy 7020, detail class 8 5

Components of extruded products (hollow profiles and members both included therein). Surfaces are as extruded.

Structural detail A3, simple profiles and machined parts in alloy 5000/6000, detail class 95

Simple profiles, e.g. flats and angles with as-extruded surfaces and no sharp edges. Surfaces have no obvious stress raisers.

156

19. DESIGN

Structural detail A4, components in alloy 5000/6000, detail class 70

Components of extruded products (hollow profiles and members both included therein). Surfaces are as extruded. Structural detail A5, notches, holes

Structural detail B2, simple elements with transverse butt welds, detail class 50

Simple and light structural elements (e.g. flats) with full penetration, transverse butt welds made from both sides. The overfill angle is greater than 150°. Members must have edges as extruded or carefully machined/ ground in the direction of the stress. As set out in specified quality control requirements (non-destructive testing included therein), welds must be proven free of detectable discontinuities. Transverse splices in flats must be tapered (in width or in thickness) with a slope not exceeding 1:4. Structural detail B3, simple elements with transverse butt welds, detail class 45

Simple notched components with drilled and reamed holes. Fatigue strength is 90% of that of the base metal. This also applies to riveted or bolted beam-flange attachments that are not load-bearing. Structural detail B1, simple elements with transverse butt welds, detail class 55

Simple and light structural elements (e.g. flats) with full penetration, transverse butt welds made from both sides. The overfill is ground flush with the surface (finished by machining in the direction of the applied stress). Members must have edges as extruded or carefully machined/ground in the direction of stress. As set out in specified quality control requirements (non-destructive testing included therein), welds must be proven free of detectable discontinuities. Transverse splices in flats must be tapered (in width or in thickness) with a slope not exceeding 1:4.

Simple and light structural elements (e.g. flats) with full penetration, transverse butt welds made from both sides or from one side only without permanent backing. The overfill angle is greater than 130°. Members must have edges as extruded or machined/ ground in the direction of the stress. Welds must be fully fused, fully penetrated, free of cracks and inspectable from both sides. Transverse splices in flats must be tapered (in width or in thickness) with a slope not exceeding 1:4. Structural detail B4, simple elements with transverse butt welds, detail class 40

Simple profiles such as flats. Welding from one side with permanent root backing. Welds must be fully fused, fully penetrated and free of cracks. 157

19. DESIGN

Structural detail B5, profiles with transverse butt welds, detail class 45

Complex profiles with full penetration, transverse butt welds made from both sides. The overfill is ground flush with the surface (finished by machining in the direction of the applied stress). Members must have edges as extruded or carefully machined/ground in the direction of the stress. After grinding flush, and as set out in specified quality control requirements (nondestructive testing included therein), welds must be proven free of detectable discontinuities. Transverse splices in flats must be tapered (in width or in thickness) with a slope not exceeding 1:4. Structural detail B6, profiles with transverse butt welds, detail class 40

The overfill angle is greater than 130°. Members must have edges as extruded or machined/ground in the direction of the stress. Welds must be fully fused, fully penetrated and free of cracks. Full penetration must be verified by inspection from both sides. Transverse splices in flats must be tapered (in width or in thickness) with a slope not exceeding 1:4. Structural detail B8, profiles with transverse butt welds, detail class 30

Complex profiles with full penetration, transverse butt welds made from one side only without permanent backing. Welds must be fully fused, fully penetrated and free of cracks. Full penetration must be verified by inspection from the root side. Transverse splices in flats must be tapered (in width or in thickness) with a slope not exceeding 1:4. Structural detail B9, built-up components with transverse butt welds, detail class 40

Complex profiles with full penetration, transverse butt welds made from both sides or from one side only. The overfill angle is greater than 150°. Members must have edges as extruded or machined/ground in the direction of the stress. Welds must be fully fused, fully penetrated and free of cracks. Full penetration must be verified by inspection from both sides. Transverse splices in flats must be tapered (in width or in thickness) with a slope not exceeding 1:4. Structural detail B7, profiles with transverse butt welds, detail class 35

Complex profiles with full penetration, transverse butt welds made from both sides or from one side only. 158

Beams built up from several profiles joined together by full penetration, transverse butt welds made from both sides or from one side only. The transverse butt welds between the profiles being joined end to end are made and ground flush before longitudinal welding of the profiles. Before any longitudinal assembly/welding, and as set out in specified quality control requirements (non-destructive testing included therein), the transverse welds must be proven free of detectable discontinuities. Transverse splices must be tapered (in width or in thickness) with a slope not exceeding 1:4. The design stress must make allowance for misalignment induced stress raisers.

19. DESIGN

Structural detail B10, built-up components with transverse butt welds, detail class 35

Structural detail C1, longitudinal, ground flush butt welds, detail class 60

Beams built up from several profiles joined together by full penetration, transverse butt welds made from both sides. The transverse welds are made before final assembly of the beam by longitudinal web-to-flange welds. The overfill angle is greater than 150°. Welds must be fully fused, fully penetrated and free of cracks. Full penetration must be verified by inspection from both sides. Transverse splices must be tapered (in width or in thickness) with a slope not exceeding 1:4. The design stress must make allowance for misalignment induced stress raisers.

Members with continuous, full penetration, longitudinal butt welds. The overfill is ground flush with the surface (finished by machining in the direction of the applied stress). As set out in specified quality control requirements, the welds must be proven free of significant defects. The members must have edges as extruded or carefully machined/ground in the direction of stress. Structural detail C2, longitudinal butt welds, detail class 4 5

Structural detail B11, built-up components with transverse butt welds, detail class 30

Members with continuous, full penetration, longitudinal butt welds (overfill angle greater than 130°). Welding must be uninterrupted throughout the root pass and the final pass. Beams built up from several profiles joined together by full penetration, transverse butt welds made from one side only without permanent backing. The transverse welds are made before final assembly of the beam by longitudinal web to flange welds. Welds must be fully fused, fully penetrated and free of cracks. Full penetration must be verified by inspection from the root side. Transverse splices must be tapered (in width or in thickness) with a slope not exceeding 1:4. The design stress must make allowance for misalignment induced stress raisers.

Structural detail D1, longitudinal, continuous fillet welds without interruptions, detail class 45

Members with continuous longitudinal fillet welds. Welding must be uninterrupted throughout the root pass and the final pass, i.e. stop-start positions and/or tack welds are not allowed.

159

19. DESIGN

Structural detail D2, longitudinal fillet welds with interruptions, detail class 40

Structural detail E2, attachment to the web of a beam, detail class 23

Members with continuous, longitudinal fillet welds made from one or both sides. The welds are tack welds or have stop-start positions. Structural detail D3, longitudinal, intermittent fillet welds, detail class 35

Members with intermittent, longitudinal fillet welds. Welds must be free of undercut and crater cracks. This class includes beams with intermittent web-to-flange welds.

Round or rectangular shapes welded to the web and having no load-bearing function. Stress range to be calculated using principal stresses. Structural detail E3, attachment (with a transition radius) to the edge of a flange, detail class 35

Structural detail E1, attachment via transverse fillet welds, detail class 35

r

Gusset plate welded to the edge of a plate or a beam flange – transition radius  50 (mm). Smooth transition radius, r , achieved by machining the gusset plate before welding and then grinding the weld area parallel to the direction of stress. Structural detail E4, attachment (no transition radius) to the edge of a flange, detail class 18

Vertical stiffener on an extruded beam or built-up beam. Stiffener fitted by transverse fillet welds to one or both flanges. The stress range at potential crack zones must be calculated using principal stresses.

160

Gusset plate welded to the edge of a plate or a beam flange – no transition radius.

19. DESIGN

Structural detail E5, vertical attachment (with a transition radius) on flange, detail class 35

Structural detail F1, cruciform joint, transverse, toe crack failure, detail class 30

r

Details of any length fillet welded (parallel to the direction of stress) on the flange of an extruded profile – transition radius  50 (mm). Smooth transition radius, r , achieved by machining the gusset plate before welding and then grinding the weld area parallel to the direction of stress. Structural detail E6, vertical attachment (no transition radius) on flange, detail class 23

Joint between a profile and a plate using full penetration butt welds or double fillet welds. As set out in specified quality control requirements (nondestructive testing included therein), welds must be proven free of detectable discontinuities. The fatigue check is performed by determining the stress range in the load-bearing plates. The maximum allowable misalignment of the load-bearing plates i s less than 15% of the thickness of the intermediate (connecting) plate. Structural detail F2, cruciform joint, transverse, throat crack failure, detail class 25

Details of any length fillet welded (parallel to the direction of stress) on the flange of an extruded profile.

Structural detail E7, vertical attachment on flange without transition radius, detail class 18

Details of any length fillet welded (parallel to the direction of stress) on the flange of a beam built up from several profiles. Structural detail E8, vertical attachment to the flange plane, detail class 23

Details fillet welded (transverse to the direction of stress) on the flange of a beam built up from several profiles.

Joint between a profile and a plate using full penetration butt welds or double fillet welds. As set out in specified quality control requirements (nondestructive testing included therein), welds must be proven free of detectable discontinuities. The fatigue check is performed by determining the stress range in the weld throat area. The maximum allowable misalignment of the load-bearing plates i s less than 15% of the thickness of the intermediate (connecting) plate. Structural detail F3, cover plate with transverse, load-bearing fillet welds, detail class 20

End zones of cover plates on beams built up from several profiles (cover plate ends attached by transverse or longitudinal fillet welds). 161

19. DESIGN

Table 19.9.5.a. Characteristic fatigue strength

Table 19.9.5.b. Characteristic fatigue strength

for standardised stress spectra, details A1 – A4. 

162

for standardised stress spectra, details B1 – B4, C, D and F. C

log nt

 log nt

70

85

90

130

20

25

30

35

C 40

45

50

55

60

1

3 4 5 6 7

207 149 107 77 70

252 181 130 94 85

281 203 146 105 95

385 277 199 144 130

1

5/6

3 4 5 6 7 8

242 176 127 92 66 48

294 213 154 112 80 58

327 238 172 125 89 65

448 326 235 171 122 88

5/6

3 136 169 204 238 272 305 338 372 407 4 81 100 121 140 161 181 200 220 241 5 4 8 60 72 84 95 107 119 131 143 6 29 36 42 49 57 63 70 76 83 7 16 20 24 29 33 37 41 45 49 8 13 15 19 21 24 28 30 34 36

2/3

3 4 5 6 7 8

287 211 153 111 81 59

347 256 187 136 98 71

388 286 209 152 109 80

532 392 286 208 150 108

2/3

3 4 5 6 7 8

1/2

3 4 5 6 7 8

343 260 194 142 103 75

416 316 235 172 126 92

465 353 263 193 140 102

634 483 359 264 192 140

1/2

3 198 248 297 3 47 396 445 495 4 122 152 182 212 243 273 303 5 73 92 110 128 146 165 183 6 43 55 66 77 87 98 110 7 26 32 39 45 52 58 64 8 19 25 29 34 39 43 48

544 333 201 120 71 52

593 364 219 131 77 57

1/3

3 4 5 6 7 8

402 322 250 189 141 103

488 391 305 230 171 125

546 438 339 257 192 139

746 599 465 352 262 190

1/3

3 248 309 372 434 495 4 159 199 238 278 317 5 98 123 148 172 196 6 61 76 90 105 120 7 36 45 54 63 72 8 27 34 41 47 54

681 436 269 164 99 74

742 475 295 180 108 81

1/6

3 4 5 6 7 8

451 383 318 256 201 150

547 465 386 311 244 182

612 520 431 347 273 203

837 712 590 475 374 278

1/6

3 308 384 461 538 615 692 769 846 4 214 267 320 373 426 479 533 586 5 142 177 212 247 283 318 353 387 6 90 113 135 158 180 203 225 248 7 58 72 86 100 115 129 143 157 8 41 50 60 70 80 90 100 110

923 639 423 271 172 120

0

3 4 5 6 7 8

485 428 372 317 265 216

589 519 452 385 322 262

658 581 505 431 360 292

901 794 691 589 493 400

0

3 364 455 546 637 728 819 909 1000 4 273 342 410 478 546 614 682 750 5 199 248 297 347 396 445 495 544 6 140 174 209 244 278 313 348 382 7 96 120 143 167 191 214 238 262 8 66 8 2 99 115 131 147 163 179

1091 818 594 417 287 197

3 4 5 6 7

116 145 174 203 232 261 290 320 349 68 85 102 119 136 153 170 188 205 40 50 60 70 80 90 100 110 120 23 29 35 41 47 53 59 65 70 16 20 24 28 32 36 40 44 49

161 203 243 2 83 323 363 404 444 485 97 122 145 169 193 217 242 266 290 58 73 87 101 116 130 144 159 173 35 43 52 60 69 77 86 94 103 20 25 30 35 40 45 50 55 60 15 19 22 26 30 34 38 41 45

557 357 221 134 81 61

618 396 246 150 90 67

19. DESIGN

Table 19.9.5.c. Characteristic fatigue strength

for standardised stress spectra, details B5 – B11 and E1 – E8. 

C

log nt 18

23

30

35

40

45

1

3 4 5 6 7

172 87 44 22 14

219 111 56 28 18

286 145 73 37 23

334 169 85 43 27

382 193 97 49 30

429 217 109 55 34

5/6

3 4 5 6 7 8

201 102 52 27 14 10

257 130 67 33 18 13

335 170 87 44 24 16

390 199 100 52 28 19

446 227 116 58 31 22

501 254 129 66 35 24

2/3

3 4 5 6 7 8

239 124 63 33 17 12

306 158 80 42 23 15

399 205 106 54 29 20

466 240 122 63 34 23

532 274 141 71 38 26

599 308 157 81 44 30

1/2

3 4 5 6 7 8

296 156 81 42 23 15

376 198 103 53 29 20

492 259 134 69 37 26

573 302 155 81 44 30

656 344 178 92 50 35

737 387 201 103 55 38

1/3

3 4 5 6 7 8

377 2 05 110 57 31 22

482 263 139 73 39 28

628 343 182 96 52 36

733 400 211 111 61 42

837 456 243 127 69 49

942 513 273 142 77 54

1/6

3 4 5 6 7 8

494 291 164 90 50 34

631 371 209 115 65 44

8 23 483 272 149 84 57

960 1097 1234 564 645 725 317 363 408 173 199 223 97 112 126 66 75 85

0

3 4 5 6 7 8

627 411 258 156 94 59

801 525 329 200 119 75

1045 684 429 260 156 97

1219 1393 1567 798 911 1025 500 572 643 303 346 390 182 207 233 114 130 146

163

This design manual draws on the expertise Sapa has acquired through its many years of work with aluminium structures. It is emphasised that the profile solutions presented in the manual are based on general principles and theoretical calculations. Thus, the manual is not in any way intended as a substitute for the specific analyses necessary in each design project. Conditions vary from case to case and allowance has to be made for this. The information, advice and comments in this manual are based on data gathered from a number of different sources. The data was judged to be correct at the time of printing. However, Sapa accepts no liability whatsoever for the correctness and/or completeness of the details in this manual. Sapa reserves the right to alter technical specifications.

Sapa Extrusion Design Manual

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