Aluminium Extrusions - Technical Design Guide

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ALUMINIUM EXTRUSIONS —

a technical design guide

i;c

Forfree, objectiveadviceon allmatters relating to aluminium extrusions contact: TheShapemakers Information Service Broadway House Calthorpe Road Birmingham

B151TN Tel: 021 4562276 Fax: 021 4562274

ALUMINIUM EXTRUSIONS —a

technical design guide

PUBLISHED BY THE SHAPEMAKERS —the information arm of the UK Aluminium Extruders Association

'I

©TheShapemakers Broadway House Calthorpe Road Birmingham B151TN

DISCLAIMER

This book is intended for use by technically skilled personnel. The use of the information contained herein by suchtechnicallyskilled personnel, is at the risk of the user. While all reasonable skill and care hasbeen exercised in the preparation of this book, there are no warranties, express or implied, as to the accuracy or completeness of this work,either by the author or the publisher, both ofwhom deny responsibility or liability for any results obtainedor damagescaused as a consequenceofthe usethereof .The publisher and the authorhereof grantno licence withthis book and disclaim all liability for suitability, practicability, infringement of property rights of third parties or non-conformance with anycodes, standards or regulations.

ACKNOWLEDGEMENT TO BSI Extracts from British Standards are reproduced with the permission of BSI. Complete copies ofthe Standards canbe obtained by postfromBSI Sales, Linford Wood, Milton Keynes, MK14 6LE. First published October1989 Reprinted July 1991

Printed in Great Britain by St Edmundsbury Press Ltd Bury St Edmunds, Suffolk

VI

Reprinted August 1994

PREFACE to the 1994 reprint — by Howard Spencer

Since this manual was originally published, British Standards havepublished a new aluminium structural code, BS 8118 1991, whichsupersedes BS CP118 1969: — —

Part 1: Code of Practice for Design Part 2: Specification for Materials, Workmanship and Protection

There is at presenta change-over periodwhere both design codes are valid, but at some time in the future BS CP118 will be withdrawn. This new code is intended to bring aluminium structural design into line with othermetals and also with European standard codes, which will simplify future preparation of an overall European structural code for aluminium.

I intend here to give users ofthe manual averybrief outline of how the new codes will affect the use of aluminium. It is impossible to go into too much detail. Those requiring additional information should refer to the codes themselves, available from British Standards (see address below). The New Code The new code is based around a new design approach, based on the principle of 'limitstatedesign'. Thisprinciple is concerned with ensuring that anygivenstructure cancarry the loadsand forces placed upon it withoutfailure, up to a pre-determined limit. The factored resistance of a structure must therefore never be less than the factored loading. The following equation can be applied: Y12R = Y4S

R

S

= overall resistance factor = calculated resistance = overall loading factor = maximum design load

The resistance is calculated from the effective sectional properties, the limiting stressand a material and connection factor. The loading effectisfactored fortypeof load, i.e. dead load, imposed load, wind load and temperature induced forces. The new code also covers the calculation of elastic instabilities. Aluminium sections with verywide, thinelements are susceptible to local buckling underhigh compressive stresses. The relevantcalculations have been simplified in the new code by adopting a classification system based upon a factored relationship between the width or depth of the element and the thickness. Three categories are listed for moment resistance — compact, semi-compact and slender. For compact sections,

I

no further check is required as theywill not suffer fromlocal buckling. (For example, afl the sections listed in BS 1161 "AluminiumStructural Sections" are compact.) Semi-compact resistance is obtained by using the quoted limiting stress of the material. Sections defined as slender, however, are assessed on the basis of a reduced effective wall thickness and the extent of the reduction can be obtained from a seriesofcurves. Only the compact and slender categories are allowed when calculating the axial resistance of struts. Therecommendation fordeflection levels hasnot changed, but a word of caution is included in the specification against imposing too tight a standard on aluminium structures when the particularapplication does not merit it. The section on welding has been greatly extended from that in the original code. Guidance is provided on the design of weldstaking intoaccount the strength ofthe weld metal and a partial reduction in strength in the heat affected zoneof the parent metal. The limiting stressesfor both filler and parent metal are given with factorsfor designing butt and lap joints for both traverse and longitudinal welds. Adhesively bonded joints are only recommended for secondary stressed connections. The factored resistance of a bonded joint can be calculated from an expression containing a failing standard, obtainedfromtesting, and a material connection factor for bonded joints, If validated test data is available, it can be used in the joint resistance expression.

The section on fatigue has also been greatly extended, incorporating information fromboth UK and European research. The tablesfor both welded and non-welded structures contain detailed sketches illustrating the typeof construction, direction of stress, fluctuation and possible cracklocations. Thetables are based upon BS 5400 Part 10: Bridges and give the classification for a range of structural detail. Full supporting data including mathematical formulae relevanttothe design calculationsand curvesused in the codeare setout in the appendices of the new codeand can be used to assistcomputer aided design.

All references in the manual to BS CP1 18 now apply to BS 8118 and, as the new code does not cover permissible stress levels, table 3.2 and figure 3.3 are not applicable. Tables 3.4 and 6.11 have also been modified as the standard elastic modulus for all wroughtaluminium alloysis now 70,000 N/mm2 Reviewing the worked examples given in the manual, the pedestrian balustrade (pages 113—122) results in marginal modifications to some sections whenworkedto the new code but gives similar overall results. In the case of the unloading ramp, however (pages 111—112) there could be a slight saving in the thickness of the section when meeting the new code. The column example (pages 123—125)refers to alloy2014AT6 which is no longer astandard material inthe newcode. Although it can be used, the limit statestresses would have to be established and, in this case, the sectionthicknesswould haveto be slightly increased.

VIII

Competently used, the old code should still give an acceptable level of design. It should be noted, however, that if the calculations are to be officiallyapproved then only the new code is valid. Furthermore, the up-dated information in the new code can result in a more economical structural useof the material. Codes referred to: BS 8118 Part 1: BS 8118 Part 2:

Codeof Practice for Design 1991 Specification for Materials, Workmanship and Protection 1991

These are available from:

Sales Dept, BSI, Linford Wood, Milton Keynes, MK14 6LE, or any HMSO.

ix

INTRODUCTION

Aluminium is a highly versatile, light and strongmaterial whichcanbe produced in a varietyofalloysandextruded intoan almost infinite number ofshapes. Thispowerful combination of factors enables the user to be more innovative and facilitates costeffective design. Comprising 8% of the earth's crust, aluminium is a plentiful resource. It is a modern material, first used in commercial production in 1886. Since then, the list of applications has grown immensely. Now, designers working in a whole range of different sectors, including generalengineering, construction, transport, packaging and consumer products, are reaping the benefits gained by using aluminium extrusions.

The Shapemakers was established by the Aluminium Extruders Association (AEA) in 1984 to provide independent guidance on all matters relating to extruded aluminium. Representing the UK's top extrusion companies, The Shapemakers is ableto drawupon thesecompanies' considerable resources and expertise. This technical design guide contains a wealth of information on aluminium itself, as well as giving details on the extrusion process, fabrication and finishing. Also included is a comprehensive design section, which outlinesthe important design considerations and shows a number ofworked examples.

Forreasonsofclarity, onlysix alloys have been incorporated intothemainbody of the manual. These have been carefully selected to illustrate the various uses of alloys — from general purpose to high strength. Additional alloys are listed in the appendices. For details of the availability of anyalloy listed in this manual, please contact the Shapemakers Information Service in Birmingham, Tel: 021 4562276. The AEA would like to thank The Shapemakers' technical consultant, Howard Spencer, forall his workin compiling thisdesign guide. Aspecial thanksalsogoesto TheShapemakers' members, Hugo Ravesloot, Jim Peach and Chris Forman.

Derek Phillips Chairman of The Shapemakers

CONTENTS

PRINCIPLES OF EXTRUSION

1

MATERIAL SPECIFICATIONS

25

MECHANICAL PROPERTIES

33

DURABILITY

45

SURFACE FINISHING

55

FABRICATION

63

CONDUCTIVITY

87

TEMPERATURE

93

FIRE

97

CARE AND CONTROL

101

DESIGN

105

GLOSSARY OF TERMS

127

APPENDICES

133



SECTION 1 - PRINCIPLESOF EXTRUSION

CONTENTS Title

Page No.

EXTRUSIONPROCESS Direct Extrusion IndirectExtrusion Hollow Sections

4

EXTRUDABILITY Extrusion Ratio Shape Factor

7 7 7

SIZE

8

THICKNESS

8

4 5 6

SLOTS

10

SECTION CLASSIFICATION

11

CORNERS

11

TOLERANCES

12

List of Figures Fig No.

Title

1.1

TheDirect ExtrusionProcess

1.2

TheDiffering Operating Principlesof Direct

Page No. 4

and IndirectExtrusion

5

1.3

Extrusion of a Hollow Section

6

1 .4

Thick to Thin Transitionsin Extrusion Cross Section

10

1.5

PressureHinge

10

1.6

SlotAspect Ratios

10

1.7

Standard Section Types

11

Listof Tables No.

Title

1.1

Shape Factor Value

8

1.2

A Guide to MinimumThickness

9

1.3

Toleranceson Diameter of Round Bar Intendedfor use on Automatic Lathes

12

Toleranceson Widths Across Flats of HexagonalBar forthe Manufactureof Nut & Bolts

13

Toleranceson Diameter of Round Bar in the Controlled StretchedCondition

13

1.4

1.5

Page No.

2

List of Tables (contd.) No

Title

1.6

Toleranceson Diameter or Width Across Flats of Bars for General Purposes and on Width of Solid or Hollow RegularSections

14

Angular Tolerancesfor ExtrudedRegul&Sections

15

1.8

PermittedCorner Radii

15

1 .9

Toleranceson Wall Thicknesses of ExtrudedRound Tube (classes A, B and C).

16

Toleranceson Thicknessof Bars and Regular Sections

17

Toleranceson Open End of Channelsand L Beams

18/19

1 .7

1.10

1.11

1.12

1.13

1 .14

1.15

1 .16

1 .17

Page No.

Tolerances on the Outside Diameter of All Extruded Round Tube and on the Inside Diameter of Class A and Class B Extruded Round Tube

20

Toleranceson Thicknessof Hollow Sections (classes A and B)

21

Toleranceson Straightnessfor ExtrudedBar, RegularSections and Extruded RoundTubes

22

Toleranceson Length for All Materials Suppliedin Fixed Cut Lengths

23

Tolerances on Concavity and Convexityfor Extruded Solid and Hollow Sections

23

Toleranceon Twist for Extruded Solid and Hollow Sections

24

3

EXTRUSIONPROCESS

Direct Extrusion The direct extrusion processcan be clearly seen in the schematicdiagram in Fig. 1.1. Cylindrical aluminium alloy billets of cast or extruded manufacture are heated to between4500and 500° before being loaded into a container and the billet squeezed through a die orifice using ram pressuresof up to 68OMPa. The die is supported by a series of back dies and bolsters so that the main press load is transferred to a front platen.

Ram cross head Stem

Liner

Die slide

Dummy block Platen

Container

Billet Die

Backer

Sub bolster Extruded section

Fig. 1.1 - The Direct Extrusion Process

4

On leavingthe die the temperatureof the section is more than 500°C and with heat treatable afloys the quenching, or solution heat treatment, takes place in the production line. Thiscanbe bywater bath, water spray or forced-draughtair, with the latter being particularly useful for thin sections. The approximatetemperaturedrop during the traverse of the quench box is 250°C. To avoid distortion care hasto be exercised in handling sections with extreme aspect ratios and large variations in thickness.

Afterextrusionthe section is guided downthe table by a puller on to a slatted moving belt. Modern Pullers are based on linear motor s,stemsand operateon tables up to 40 metres long. On completion of an extruded length, the section is sheared at the press end and lifted from the slatted table by eccentric pivoted arms. It is then transferred by a walking beam or multi-belttransfertable to the stretcher bay where it is given a controlled stretch to straighten and remove minor mis-alignments.The section is then taken and cut to ordered lengths on high speed tungsten carbide tipped saws.

If the material is requiredin the solution heat treated condition (T4) it is released at this stage. If the full strength aged material (T6) is required, it is given a precipitation treatment before release. In the caseof the T5 temper,there is limited cooling atthe press exit and the material goes directly to precipitationtreatment. Indirect Extrusion In the traditional direct methodof extrusion,as described above, the die is stationary and the press ram applies pressure on to the billet. In the indirect method,the ram carriesthe die and appliespressureon tothe stationarybillet, inthe oppositedirection of extrusion.There can be variationto this basic concept,but in every case the billet remains stationary in relationto the container,thereby keepingfriction loss to a bare minimum. See Fig. 1.2. Die

Extrusion Billet

Die

Extrusion

Indirect extrusion Die

Billet

Fig. 1.2 - The DifferingOperatingPrinciplesof Directand Indirect Extrusion

5

HollowSections A bridgeor 'port-holedie' is usuallyusedto makehollowsections.Asolid billet isforced, under pressure,through acompositedietoolthatfirstdividesthe metal intotwo or more separate streams which then flows down under the bridge to be pressure welded together and emerge, as an extruded section,through the orifice formed betweenthe mandrel nose and the outer section shape which hasbeen cut in the die. See Fig. 1.3. Any sample taken across the section would show an integralmaterial quality with no reductionofstrength in the weld areas. Inspectionmethodsare usually by destructive test samplingin line with that laid down by the British Standards for scaffold tubing in specificationBS 1139. Productionmethodsfor this kind of section are wellestablished and extruders will be pleased to advise on the feasibility of producing any hollow section.

Some caution must be exercised, howeverwherethin hollowsections are required in thestronger alloys,particularlyfromthebridgeorport-holeproductionmethods.Hollow sections are usually produced in these alloys by using centre mandrelsthat are not connectedtothedie but are passedthrough a boredor piercedhole inthecentre ofthe billet and eitherconnectedorsupportedby the press rod. In this type of production,the metalflow aroundthe mandrelis not interruptedandthereare no extrusionweld planes inthe section. Theremaybesome restrictionintheavailabilityofthis type ofproduction and in the range of sectionsobtainablefrom it. As the standardoftolerances may also be wider further informationand advice should be sought from the extruderforstrong alloy hollow sections.

area

Pressure

Mandrel nose

Bridge

Fig. 1.3 - Extrusionof a Hollow Section 6

EXTRUDABILITY Aluminium alloys offer a wide range of performance characteristics and important amongst these is its extrudability. Linked with modern die-making facilities and traditionalexpertisethe metal offersa virtuallyunlimitedvarietyof sectionshapes. The feasibilityof any extrusionhasboth technicaland commercialconsiderationsand most extruders use a numberof methodsto evaluateextrusioncomplexity. These methods are usually based upon a combinationof extrusiontheory and experience.

ExtrusionRatio Extrusion ratio isthe valueobtained bydividingthe cross-sectionarea ofthe extrusion billet bythe cross-sectionarea of the extrusionto be produced. It dependsvery much on the size and type of press available and is a factor that can only be considered by the extruder. Optimumextrusion ratiosfordirect extrusionare usuallybetween30 and 50.

With lowvaluesof 7or under,there isvery littleworkingofthe materialduringextrusion. This gives a correspondingdrop in mechanicalpropertiesand the possibilityof coarse grain bands. Values of 80 and above require high breakthroughpressureswhich are likely to cause die distortion and possible breakage. In some casesthe extrusionratiocanbe improvedby usinga multi-holedie. Inthecase of indirectextrusionmuch higherextrusionratios are possiblebecauseofthe relatively low frictional force developed in the system. Shape Factor

The resistanceof a sectionto extrusioncan be influencedby the shapefactor. This is the relationshipbetween the periphery and cross-sectionareaof the section being extruded. It is usualforextrudersto modifytheshapefactor value, interms of extrusion weight, by dividingthe peripheryby the cross sectional area and multiplyingby .0027. The shape factor of a proposed extrusion is usually compared with that of a similar existing extrusionto obtain a measureof extrudability. This is not a precise method, however, as any large difference in wall thickness canalter the ratio substantially. In general, the higherthe value the moredifficult the extrusion and the more limitedthe alloy choice thereby restrictingsome high strength alloys. Table 1 .1 sets out some general values which can be used for reference.

7

Table 1.1 - Shape FactorValues

SectionType

CCD mm

Thickness mm

Shape Factor

L

142

2.5

300

L

70

1.5

500

112

5.0

152

O

142

solid

15

O

70

solid

30

©

50

3.0

247

©

50

1.5

494

ltiiiiiil

210

3.0

190

210

2.0

285

140

2.0/6.0

183

40

2.0/1.5

430

I

Iii 11J II SIZE

The sizeofanextrudedshape is determinedbythediameterof thecircumscribingcircle (CCD) required to enclose the cross-section. The maximumCCD for any die size is governed by the need to keep an unbroken structural ring aroundthe die orifice.The minimumwidth ofthat ring can vary from 20 mm on an averagesize solid dieto 60 mm or more on dies for large hollow sections. Most averagesectionsfit intoCCDs below 155 mm with a medium range of 250 mm and very large sections up to 400 mm. The section, should, as far as possible, be distributedaroundthe centre of the CCD. In anyextrusion,metalflow is slowertowardsthe outsideedge ofthe dieso the placing of thicker parts of the sectionaway fromthe centre results in a more even metal flow. THICKNESS Factorsthat dictatethickness are influencedbysection shape,alloy, dieface pressure, extrusionspeed and section stability duringsolution heattreatment and post-extrusion handling. Ageneral guide to minimumthickness isgiven in Table 1.2 which is based on 6063 material.

8

Table 1.2 - A Guideto Minimum Thickness

E E

I0) 0)

r

C-)

0)

0)

200

50

250

300

C C D in mm

a)

b)

Values for 6082 should be increasedby 25% Thesethickness - GCDratios representaveragevaluesbased upongood working practice.

c) d)

The values up to 1 .25 mm thick are for small specialised presseswith very high die face pressurelevels. When ratios below those shown are required contact extruders.

The extrusionprocess will toleratevariations in sectionthicknessbut it is importantto avoid abrupt change. Acceptabletransition betweenthicknessescanbe obtained by using radii or blendingcurves, see Fig. 1 .4. Short spans of local thinning can also be

incorporatedin most sections. This is a useful methodof introducingpressurehinges in section elementswhichwillbedeformedduring subsequentfabrication,see Fig. 1 .5. 9

p p

Radius

Fig. 1.4 - Thick to Thin Transitionsin ExtrusionCross-Section

I Thin hinge

/

—

Fig. 1.5 - PressureHinge

SLOTS The formationofslots,or open boxchannels,in asection requiresafinger or box spigot to be retainedon the die. As it is not possibleto reinforcethese spigots, which actas local cantileversunder extrusion pressure,a practical limitmust be placed on the size and type of slots available. Fig. 1.6 detailsthe normal methodofcalculatingslot aspect ratios althoughwhere gaps are below 3 mm these ratiosare evenfurther reduced. The maximum ratios are 3:1. Higher valuesare possible,particularly in 6063 alloy. Screw ports and bolt slots are detailed under these headings in section 6 Fabrication.

— Gap

— Depth

___

_____ =—

—

Area Aspect Ratio =

Aspect Ratio

Gap2

Fig. 1.6 - Slot Aspect Ratios.

10

Depth

Width

Width

SECTION CLASSIFICATION There arethreestandardtypesof section - solid,semi-hollowand hollow. Thefirstand last are self-explanatory.Semi-hollowdescribesthose solid sectionswhich have open box recesseswith aspect ratios (depth/width)less than three. In general,the tooling and productioncosts increasewith section categoriesfrom solid to semi-hollowand then hollow.

Solid

Semi-hollow

Hollow

Fig. 1.7 - Standard SectionTypes CORNERS

All corners are normally broken by a radius but where absolutely necessary,sharp cornerscanbe incorporatedin asection either internallyor externallybut the life of the die and thespeedofextrusionare both markedlyreduced.Suchcorners also introduce problems where paintedfinishes are specified, introducingobvious sight lines. The breakingof the corners,even by 0.5 mm radii is helpful in overcomingthese problems but for ideal extrusion conditions, radii should be related to the overall size of the section. Table 1.8 sets out preferredvalues.

11

TOLERANCES Tolerance levels for regular sectionsare laid down in BS 1474, howeveras the bulk of extrusions are non-standardthey are not covered in the standard. The extrusion industry regards BS 1474 as a target level and is preparedto accept if for all general business,apart from verythin or complexsections which will bethe subject of special enquiry. Closertolerancescanbeobtainedfor some sectionsbut, again,this isamatter betweencustomer and extruder.

In line with most productionmethods,tolerancesare necessaryto cover variationsin the actual process and wearing of toolsand dies. Most tolerances are quoted as plus or minus around a datum value but, if required, unilateral tolerance can be obtained, either all positiveor all negative. It is essential, however, to agree this requirement before die manufacture is commenced as the dimensional datum of the die will be altered.

Alltolerancesshouldbe measuredat 160G. This isparticularlysignificantforthelength tolerancesof long bars.

There is no laid-downstandardfor the surface smoothnessor texture of mill finished extruded sections. Table 1.3 - Tolerances on Diameter of Round Bar Intended for useon AutomaticLathes Diameter Over

Up to and

including

mm 10 18

mm 18 30

30 40 60 80

40

100

Plus and minimum toleranceson diameter

+mm

60 80

100 160

±

-mm

0.10 0.13 0.14 0.20 0.30 0.40 0.5% of specifieddiameter 0.05 0.08 0.14 0.20 0.30 0.40

12

Table 1.4 - Tolerances on Width Across Flatsof Hexagonal

Barfor theManufactureof Nuts & Bolts

Width across flats Over

Up to and

Tolerance on width across flats (all minus)

Including mm

mm

-

mm 0.08 0.10 0.13 0.15 0.20

4.0

4.0

19.0

19.0 36.0

36.0

46.0

80.0

46.0

Table 1.5 - Tolerances on Diameter of Round Bar in the Controlled Stretched Condition* Diameter Over

Up to and including

Tolerances on diameter (plusand minus)

mm

mm

+mm

-mm

10 18

18

0.05 0.08 0.14 0.20 0.30 0.40

0.20 0.26 0.28 0.40 0.60 0.80

0.5% of

1.0 % of

specified

specified

diameter

diameter

30 40 60 80 100

30 40 60 80 100 180

* The controlledstretch procedurereducesthe level of any residual stressesin abar and is ideal for machining stock. SpecialTempersT6510 and T6511 refers.

13

Table 1.6 - Tolerances on Diameter or Width Across Flats of Bars for General Purposesandon Width of Solid or Hollow Regular Sections Diameter, width or

width across flats Over

Up to and including

mm

mm

-

3

3

10 18

10 18

30 40 60 80 100

120 140 160 180

200 240 280

Tolerances (see notes 1 and 2)

±mm 0.16 0.20 0.26

30

0.32

40 60

0.40 0.45 0.50 0.65

80

100 120 140

0.80

180

0.90 1.00 1.10

200 240 280 320

1.20 1.30 1.50 1.70

160

NOTE 1: Tolerances in this table apply to solid materialsother than: (a) round bar for use on automaticlathes (see table 1.4) (b) controlledstretchedbar (see table 1.6) (c) hexagonalbars for the manufactureof nuts and bolts (see table 1.5) NOTE 2: Tolerances in this table apply to hollow regular sections having awall thicknessnot less than 1.6mmor3%of the overall width, whichever is the greater. In the case of non-heat-treatedmaterial or 1.6mm or4% oftheoverall width, whicheveris the greater,in the case of heat treated material. The tolerance should be appliedto the width measuredat the corners.

14

Table 1.7 - AngularTolerances for Extruded Regular Sections Nominal thickness of Allowabledeviation from angle thinnest leg (measured at the exUp to and specified Over tremitles of thesection) including mm -

j-

mm 1.6 5.0 -

1.6 5.0

2°

1.5° 1°

Table 1.8- PermittedCorner Radii For square and rectangularsections Minor dimension Over

Up to and Including

mm -

mm 5

5

10

10

25

25 50 120

Radius on corner (max.) mm 0.4 0.8 1.6 2.5 3.0 5.0

50 120 -

I

For regular sections (e.g. angle, channel, I- and - sections) Thicknessof Radius on corner (max.) section mm

mm

Up to and including 5

0.8

Over5

1.5

15

Table 1.9 - Tolerances on Wall Thicknessof Extruded Round Tube (classes A, B and C) (see note 1) Class A

ClassB

Toleranc Wall thickness on mean atany point thickness wall oftube thickness

Class C

Nominal

Tolerano

wall

on mean

(Max.)

(Mm.)

mm

mm

±mm

1.0 1.5

1.20 1.71

2.0

0.15 0.16 0.17

2.23

0.80 1.29 1.77

0.18 0.20

2.5 3.0 4.0

0.18 0.20 0.23

2.74 3.27 4.30

2.26 2.73 3.70

0.22 0.27

5.0 6.0

0.26 0.28 0.31

4.66 5.62 6.57

0.37 0.43

7.0

5.34 6.38 7.43

8.0

0.34 0.40 0.46

8.47

10.0 12.0

10.52 12.61

7.53 9.48

14.0 16.0 18.0

0.53 0.58 0.63

20.0 22.0 25.0

0.68 0.74

NOTE 2:

NOTE3:

NOTE 4: NOTE5:

Wall thickness at any point

wall

thickness

±mm

NOTE 1:

Tolerance on mean

wall

mm

0.81

Wall thickness at any point

-

.

(Max.)

(Mm.)

mm

mm

-

-

1.74

2.27 2.80

3.36 4.42

0.31

thickness

.

(Max.)

(Mm.)

±mm

mm

mm

-

-

1.26 1.73

2.20 2.64 3.58

-

-

0.65 0.70

3.87 4.93

2.13 3.09

6.00 7.09 8.18

4.00

6.73 8.64

-

-

4.51

0.75

0.51

5.49 6.58 7.67

5.42 6.33

0.82 0.89

8.76 10.85 13.03

7.24 9.15

0.94

9.27

11.39

0.56 0.65 0.77

10.97

1.03 1.15

11.36 13.54

10.46

14.71 16.76 18.82

13.29

0.88

12.76 14.66 16.56

1.30 1.40 1.50

12.25

1.00 1.13

15.24 17.34 19.44

15.75

15.24 17.18

20.90 23.00 26.10

19.10 21.00 23.90

1.22 1.35 1.49

21.63

18.38

23.81

20.19 23.00

1.60 1.73 1.88

27.00

4.91

5.82

17.88

14.12

20.00

16.00

22.13 24.32

17.88

27.50

22.50

19.68

BStoleranceclassesA,B and C forround tube denote a descendingorder of tolerancestandard. All classesapplicable to 6063, 6063A, 6082, 6101A, 6463, Only Classes B & C are applicableto 2014A

The tolerances given in this table apply to non-heat-treatedtube ofwall thicknessnot less than 1.6mmor3% ofthe outsidediameter,whicheveris the greater and to heat treatedtube ofwall thicknessnot less than 1.6mmor4% of the outside diameter,whichever is the greater. These toleranceson wall thickness do not apply where tolerances on both outside and inside diameterare required in which case the eccentricity toleranceon the resultantwall should be agreedbetweenthe purchaserand the supplier at the time of the enquiry and order. Mean thicknessisdefinedasthe sum ofthe wall thicknessesmeasuredatthe ends ofany two diameters at right angles, divided by four. The toleranceon the wall thicknessof intermediatenominal wall thickness should be taken as those of the next lower size.

16

—4

034 036 -

032 -

180

240

320

120

180

240

Over

32

060

050

040

036

0

0 28

026

022

020

± mm

065

055

045

039

034

0 30

028

024

022

± mm

6mm up to and up to and including including 6mm 10mm thick thick

3mm

Over

070

060

050

042

0 37

0 33

030

026

-

± mm

10mm up to and including 18mm thick

Over

075

065

055

045

0 40

0 36

032

.

-

+ mm

080

070

060

048

043

0

40

085

075

065

052

50

090

080

070

057

0

-

0 45

-

-

+ mm

-

mm

-

-

-

+

+ mm

-

095

085

075

065

-

.

-

± mm

mm

100

090

082

080

-

.

-

-

105

095

090

-

-

-

-

+ mm

mm

1

10

105

100

-

-

.

-

including including including including including including including including 30mm 40mm 60mm 80mm 100mm 120mm 140mm 160mm thick thick thick thick thick thick thick thick

Over Over Over Over Over Over Over Over 18mm 30mm 40mm 60mm 80mm 100mm 120mm 140mm up to and up to and up to and up to and up to and up to and up to and up to and

NOTE:- For sectionsover 160 mm thick, the toleranceson thickness are thoseshown for comparablewidths (see Table 1.6)

0 30

0 28

80

120

0 26

24

60

80

024

022 0

30

020

018

mm

018

±

016

mm

18

18

10

mm

Over 1.6mm up to and including 3mm thick

30

10

Up

Including

Up to and Including 1.6mm to and thick

Tolerances on specifiedthickness (plus and minus)

60

-

mm

Over

Widthacross flats of bar or width of section

Table 1.10- Tolerances on Thickness of Bars and Regular Sections

mm

10

18

30

40

60

80

100

120

140

160

-

10

18

30

40

60

80

100

120

140

including

3.0 6.0 3.0 6.0 3.0

60 3.0 6.0 -

6 -

3.0

3.0 6.0

3.0

-

3 0

6.0

3.0 6.0

-

6

6 -

6

-

6

-

6

-

6

-

30

1.5

6

1.5

-

mm 1.5 3.0 -

6 0

For 0

-

-

-

-

-

-

-

0.45 0.45 0 43

0.37 0.35

037

-

-

-

-

0.65 0.62 0.59

0.57 0.54

060

0.55 0.52 0.49

0.41

047 044

0.34 0.32

038

0.28 0.26

0.31 0 29 0.28

032

mm

0.23 0 22

+

026

* mm

Up to and up to and over

1.5 3.0

mm

For 0

1.21

1.25

1.11

1.15

1.01

1.05

086

0.90

0.71 0.66

0 75

061

0.70 0 66

0.65 0.61 0 56

053 048

0.57

0.47 0 40 0.36

0.41 0.34 0.30

÷ mm

36 1.30 1

126 120

1.16 1.10

095

1.01

073

0.86 0.80

0.75 0.68

1.52 1.44

134

1,42

32 1.24 1

1.17 1.09

1.02 0.94 0.82

0,77

097 0 89

0.84 0.72

0.70 0 63

081

0 92

0.64

055 0 76

076

0.84

0.55 0.47

070

• -

-

0.68 0.62

0.56 0.46 0.41

• -

* mm

deep

deep + mm

over 40mm up to and including 60mm

ForD over 30mm up to and including 40mm

ForD

23

73 1.61 1

1.63 1,51

1.53 1.41

1.38 1.26

1.11 0.96

1

1.18 1 06 0.91

1.13 1.01 0 86

093 0 78

1.05

74 59

1.94 1.79

1.84 1.69

1

1

59 1.44 1

44 1.29 1.09 1

1.39 24 1.04 1

1 34 1.19 0.99

091

1.11

126

-

-

+ mm

deep

-

mm

For 0 over 80mm up to and including 100mm

• -

+

For 0 over 60mm up to and including 80mm deep

2.15 1.95

1.86

206

1.95 1.76

1.61

1.80

1.46 1.22

165

117

1.41

1.60

1.55 1.36 1.12

-

-

* mm

deep

For 0 over 100mm up to and Including 120mm

76

2.36 2.14

2.26 2.04

2.16 1.94

2.01 1 79

1.35

164

1.86

181 1 59 1.30

1,54 1.26

1

-

-

-'

-

-

-

-

+ mm

mm

2.57 2.31

247 221

2.37 2.11

2.22 1.96

148

2.07 1.81

2.02 1.76 1 43

-

-

-

-

-

-

+

For 0 over 120mm 140mm to and up up to and including including 140mm 160mm deep deep

For 0 over

Inlernalor exte,nai tolerance on open end dimensionfor various deplhs of opening D(pius and minus)

For 0 over 18mm including including 10mm 10mm to and up up to and deep including including 18mm 30mm deep deep

of webor flange

Minimum thickness

Up to and Over

mm

Over

Overall width Wof channelor i-beam

Table 1.11 Tolerances on Open End Channels and L Beams

2.49

2.78

2.39

265

2.58 2.29

2.14

2.43

161

1.99

2.28

-

-

-

-

-

-

+ mm


-L (0

320

280

Depth of

280

240 6

-

Open end dlmens!on

-

-

-

-

-

-

-

6

6

-

6

240

-

200

6

-

6

200

-

180

6

6

180

-

160

mm

mm

mm mm

10mm deep

Web

Flonqe

-

-

-

-

31

55 71

Open

1.91

1

151

1

141

1.45

1

1.35

2.00

180

66

160

1

150

56

2

0

14

194

1 82 1.74

1.72 1.64

1.54

1.40 1

162

146

+ mm 71

232

211

191

2 03

181

1.93

1

183

mm

2.40

229

209

2,24

214 199

1.89

204

+

deep

mm

deep +

For D over 80mm up to and including 100mm


Depth of opeeng

+ mm

mm

+ mm +


For D over

For D over 18mm 30mm to and to and up up up to and Including Including including 18mm 30mm 40mm deep deep deep

or D For D to and up to and over including IncludIng 10mm

Up

mm

Up to and Over Including

of web or flange

2.66

246

2.26

2 45

2.35 2.16

2.06

225

+ mm

deep

For D over 100mm up to and including 120mm mm

284

264

2.44

2 66

2.34

256

2.24

246

+

deep


0

3.01

281

2 87 261

277 251

241

2.67

+ mm

over 140mm up to and including 160mm deep

For

Minimum thickness internal or external tolerance on open end dimension for variousdepths of opening D (plus and minus)

Over

Overallwidth Wof channel or I-beam

Table 1.11 (continued)

0

3.19

299

3 08 279

298 269

288 259

+ mm

deep

over 160mm up to and including 180mm

For

Table 1.12 - Toleranceson the OutsideDiameter ofAll Extruded Round Tube and on the Inside Diameter of Class A and class B Extruded RoundTube (see note 1)

Outsidediameter, Over

Up to and Including

Tolerance on the actual diameter(see notes 5 and 6)

mm

mm

±mm

±mm

18

0.19 0.23

0.34 0.40 0.45

or inside diameter

12 18 30

30 40

0.25 0.30 0.36

40 50 60

50 60 80

0.45 0.54 0.60

80

300

1%of diameter

Tolerance on themean diameter(see

notes5 and 6)

0.27

314%of

diameter

NOTE 1. For detailsconcerningtheapplicabilityoftolerance class (A or B) to alloy, see 1.9. NOTE 2. The tolerancesare applicableto non-heat-treated tubing ofwallthicknessnotIessthan1.6mmor 3% ofthe outside diameter, whichever is thegreater,and to heat-treated tubing of wall thickness not less than 1.6 mm or 4 % of the outside diameter, whichever Is the greater. NOTE3. In the caseoftubing in straight lengths, the above tolerancelimits are Inclusiveof ovality. NOTE4. Whereatoleranceon wallthicknessisrequired,the toleranceson diameter areto beappliedeithertothe outside diameteror to the Inside diameter, but notto both. NOTE 5. Tolerances on the actual diameter Indicate the amountby which the diameter (inside or outside, as appropriatemeasured in anydirection maydepartfromthespecified diameter. Tolerances on the mean diameter(inside or outside, as appropriate) Indicate the amount by which the mean oftwo diametersmeasured In two directions at right angles in the same plane may depart from the specified diameter.

NOTE6. Thegiventoleranceson the actual diameter do not apply to annealed tube, coiled tube, or tube having a wall thickness less than 2.5 % of outside diameter. The tolerancesoftheseproductsandofcontrolledstretchedtube are subject to agreement between purchaserand supplier.

20

-'

N)

0.48

0.65

.

. -

180

240 320

120 180 240 -

036 041 58

-

075 095

0

0.85 1 05 1 25

0.68

1

1

20 45

0.95

00

mm

1 1

40 80

110

1

-

. 062 0 82

048 058

0.41

048

-

.

-

-

-

* mm

30mm thick

075 -

-

-

0.65

.

055

0.45

036

0.28

-

-

036 045

0.28

022

-

* mm

+ mm

including 1.6mm up to and including 3.0mm thick

Up to and Over

-

0.85 1 00

065 075 0 80

0.54

* mm

3.0mm up to and including 6.0mm thick

Over

mm

00

20 1 40 1

110

1

090 095

-

.

-

40

mm

60 1 80 2 00 1

1.50

145

1

.

-

nm

2 60

240

2.20

2 00

-

-

+

including including including 30mm 10mm 18mm thick thick thick

Over Over 10mm 18mm to and to and up to and up up

6mm

Over

NOTE 2. The tolerancesapply to non-heat-treated sections of wall thickness not less than 1.6 mm or 3% of the overal width, whichever is the greater, and to heat-treated sections of wall thickness not less than 1.6mm or 4% of the overall width, whicheveris the greater.

NOTE 1. For detailsconcerningthe applicabilityof tolerance class (A to B) to alloy, see Note 1 of Table 1,9

0,36

032

60 80 120

0.22 0.28

mm

18mm thick

032

.

+

18mm

Over

-

.

10mm

6.0mm up to and including 10mm thick

Class B

up to and up to and 1.6mm including Including thick

Over

Over

. .

* mm

* mm

30 60 80

026

0.20

+ mm

10 18 30

mm

6.0mm thick

3.0mm thick

Over Up to and Up to and Over 3.0mm Including including 1.6mm 1.6 mm up to and up to and thick including Including

Class A

Tolerances on specified thickness

10 18

mm

Over

Width or widlh across flats

Table 1.13- Tolerances on Thickness of HollowSections(classesA and B(

Table 1.14 - Tolerances on Straightness for Extruded Bar, Regular Sectionsand Extruded Round Tubes (see below) For bars, tubes Temper

Nominal length of bar, tube or section L

or sections

within a circumscribing circle

Over 100

Maximum

S from straightnessof localized kink in any 300 mm length L (metres) portion

(see below)

mm


Maximum derivation

m

mm

mm

All tempers

over 0.4

1.5 L

0.6

F

over 0.4

2.0 L

0.8

All other tempers

over 0.4

2.5 L

1.0

NOTE 1. The straightnessis measured by determining the maximum deviation from straightnessSover length1,whenthe bar, sectionortubeis supportedonaflattable such that the deviationis minimizedby Its own mass. NOTE 2. Kink Is measured using a straightedge 300 mm in length(see below). NOTE 3. Tolerances on straightnessfor annealed and controlled stretched materials should besubject toagreement between the purchaserand thesupplieratthe timeofthe enquiryand order.

Localized kink

V

7/ / /

300mm straightedge

/

Bar,tube or section ot length L

///V/ ////4// // /// // / // Maximum

deviation S

Length L

22

Section through tiatness measuring table -

Table1.15 - Tolerances on Length for All Materials Supplied in FixedCut Lengths Diameter, width Tolerances on length for givenlength (plus and minus) across flats or (see notes 1 and 2) overall width Over

Over Up to and Over 1000 mm including 300 mm up to and up to and including including 1000 mm 1500 mm

long

long

Over 1500 mm up to and including 5000 mm

Over Over Over 5000 mm 7000 mm 10000 mm up to and up to and long 7000 mm

10000 mm

long

long

long

including including

mm

mm

jmm

jmm

jmm

jmm

jmm

60

60 100 140 180 240

2.0 2.0 3.0 3.5

2.5 2.5 3.5 4.0 5.0

2.5 3.5 4.0 5.0 6.5

3.5 4.0 5.0 6.5 8.0

4.0 5.5 6.5 8.0 9.5

100 140 180

4.5

jmm 6.5 7.5 8.0 9.5 11.0

NOTE 1. Tolerances on length are measured at a temperature of 16 5 C. Theyprovide for out-of-squareness of cutto the extent of 10. NOTE 2. Total tolerances (i.e. the sum of the plus and minus limits) may be applied unilaterallyby agreement between the supplierand the purchaser.

Table 1.16 - Tolerances on Concavity and Convexityfor Extruded Solid and HollowSections Width

of section W

Maximum allowable deviationD(see figure)

mm

mm


0.125

Over25

0.l2Sper2Smm

Coocoolty

increment in width (e.g. for 150 mm width maximumdeviation D permitted is 0.75 mm)

23

Table 1.17- Tolerances on Twist for ExtrudedSolid and Hollow Sections

degrees

3

Under 20

20 up to and including40

degrees

7 5

Over 40 upto and including 80

0.5

Over 80: Lengths upto and including 8000 mm Lengths over 8000 mm

Twist T 24

3



SECTION 2- MATERIAL SPECIFICATIONS

CONTENTS

Title

Page No.

ALLOYS

27

TEMPER Solution Heat Treatment PrecipitationHeat Treatment

29 30 30

25

List of Figures Fig No. Title

Page No.

2.1

Temper Cycles

29

2.2

Solubility Diagram

31

Listof Tables No.

Title

2.1

Chemical Composition

27

2.2

Alloy Characteristicsand Uses

28

Page No.

26

ALLOYS High purity aluminium,99.00% and above, hasexcellentdurability together with high thermal and electrical conductivity.It is easily worked and afthoughit can be strengthendby cold working it remains a low stength material.

For more general use, alloying elements are introduced, producingmaterialsthat retain the general characteristicsof pure aluminium but have greater structure strength (refer to Table 2.2). In the extrusion industry, the alloys most widely used throughoutthe world are in the InternationalStandards 6000 series, to which the British Standards alloys also conform.The main alloying constituents in this series are silicon and magnesium(refer to Table 2.1). Table 2.1 - Chemical Composition

ALLOY

COMPOSITION (%)

BS 1474 SI

6063

0.200.450.60 0.35 0.10 0.10 0.90 0.10

-

0.10 0.10 0.05 0.15

REM

6063A

0.30- 0.150.600.60 0.35 0.10 0.15 0.90 0.05

-

0.15 0.10 0.05 0.15

REM

6082

0.700.40- 0.601.30 0.50 0.10 1.00 1.20 0.25

-

0.20 0.10 0.05 0.15

REM

6101A

0.300.70 0.40 0.05

-

-

-

-

0.03 0.10

REM

6463

0.200.450.60 0.15 0.20 0.05 0.90 -

-

0.05

-

0.05 0.15

REM

0.90 0.50 5.00 1.20 0.80 0.10 0.40 0.25 0.20 0.05 0.15

REM

*

0.502014A

Fe

Cu

Mn

-

Cr

Others Each Total

(1987)

Mg

0.400.90

3.90- 0.40- 0.20-

* 6101A comformsto BS 2898

** T + Zr

27

NI

Zn

TI

Al

0.15-

Table 2.2 - Alloy CharacteristIcs and Uses

BS

CHARACTERISTICS

TYPICAL USES

6063

Suitable for intricate extruded sections ofmid-strength. Forms well in T4 condition. High corrosion resistance. Good surface finish.

Themost widely usedalloy. Architectural

A stronger version of 6063 but retaining mostofthat alloy'sgood

Road and rail transport, general engineering, ladders and light structures.

6063A

surface finish and formability. 6082

The recommended alloy for

structural purposes with good strengthand generalcorrosion resistance.

members i.e. glazing bars and window frames; windscreensections, roadtransport.

Road and rail transport, scaffolding, bridges, cranes and heavy structures.

Busbar,electrical conductorsand fittings

6101A The best combination of electrical and mechanical conductor properties with conductivity of 55% of the InternationalAnnealed Copper Standard.

6463

Based on high purity (99.8%) aluminium, this alloy was developed to respond well to chemical or electro-chemical brighteningor anodizing. It has excellent formability.

2014A A high strength alloy with moderatecorrosion resistance.

Motor car trim and other applications requiringa bright finish.

Structures, aerospace,general engineering.

28

TEMPER

Thepropertiesof alloysinthe6000 and2000range canbeimprovedby heattreatments after extrusion. These alloys, although available in the F, "as manufactured", condition, are more usually produced in one of the followingthree tempers:T4

-

T5

-

precipitationtreated (artificiallyaged)

T6

-

solutionheat treatedand precipitationtreated (fully heattreated)

solution heat treated

T5 PRECIPITATION

___________

SOLUTION

HEAT TREATMENT (AGEING)

EXTRUSION_F (QUENCHING)

: F

Fig. 2.1 TemperCycles

The current procedure for producingthe T4temper is usually 'on-line". An extrusion, emerging from the die at about 500°C, is rapidly cooled by air, water spray or water immersion, depending upon the section shape and extrusion speed. The temper, although strongerthan in the F condition, is stillof relatively low strengthand, with its high elongationvalue, it is an excellent choicewheresevere forming is required. Some natural ageing or hardening will occur which will, in some alloys, curtail the time available forforming.

For thin sections a strongertemper, T5, is available. T5 is given greater strengthby carrying out precipitation treatment without any solution heat treatment. This is provided by heatingthe materialup to about 180°C and soakingfor several hoursin an oven.

29

The final and strongest temper available (without the applicationof cold work) is T6 which combines both the solution heat treatment and the precipitationtreatment. The relationship between mechanical properties and heat treatment of a range of aluminiumalloyswasfirst discoveredbyWilm in 1906. Overtheyears,theprocesshas been developed with improvementsand innovations being introduced which have helped to make the "heattreated" alloys the most widely used extrusion materials in

the world.

in recent years, much greater use has been made of reheat treatment following low temper or heat inducedfabrication operations such as bending and welding. This is a property of aluminium that is well worth considering at the design and material selection stage of fabricated components.

It is not the purpose of this manual to deal with detailed metallurgical aspects of aluminium and its alloys,but the followingsimplifiedexplanationof heat treatmentmay be of background interest:The thermal treatment consists of two phases: a)

b)

solution heat treatment precipitation heat treatment

Solution Heat Treatment Thechemical constituentsofaluminiumalloys are to agreateror lesserextent soluble in aluminium. The degreeofabsorptionvaries with the amount and typeofconstituent andtemperature. The higherthetemperature,the greaterthe amount dissolved. Fig. 2.2 shows a typical solubility diagram where, at temperaturesabove point A , (the Solvus temperature) the atoms are in solid solution and designated by the prefix "solute". These atom phases ofconstituentsare thus dissolved in solid solution and a rapid temperaturedrop,throughquenching,willpreventthe solute atomsfrom diffusing out of solution. This condition, however, is not totally stable and a natural ageing will take place, varying from several days to several weeks depending upon the alloy. Duringthe ageing processa fine dispersionof clustersofsolute atomswilloccur. The final stable condition is defined as T4 temper. PrecipitationHeat Treatment The precipitationheat treatment process, also known as artificial ageing, speeds up and greatly increases the rate of precipitationand fine dispersion of the constituent atoms,which are distributed in clusters over the whole matrix. Thealloy will nowtend to resist material dislocation, resultingin a marked improvementin both strengthand hardness, usually to a level well above that obtained by natural ageing.

30

Liquid

Liquid

- solid

0 U)

CU

0 U)

E

U) I—

Solid

5 % Constituent

Figure 2.2 - Solubility Diagram

31




SECTION 3- MECHANICAL PROPERTIES

CONTENTS

Title

Page No.

INTRODUCTION

35

STRESS Axial Loading

36 38

STIFFNESS

41

HARDNESS

43

FATIGUE

43

33

Listof Figures Page No.

Fig No.

Title

3.1

Yield Point

36

3.2

Typical Stress Strain Curves

37

PermissibleCompressive Stresses in Struts

39

RelationshipBetween Hardness Number and Tensile, Yield Strengths

42

FatigueCurves For Some Aluminium Alloys (Rotating CantileverTests)

44

3.3

3.4

3.5

List of Tables Page No.

No.

Title

3.1

Propertiesto BS 1474

35

(1987)

3.2

PermissibleStresses

38

3.3

EffectiveLengths of Struts

40

3.4

Moduli of Elasticity

41

34

INTRODUCTION

A wide range of mechanicalproperties is availablefrom aluminiumand its alloys with

the level of performancevarying withthe degreeof alloying and temper. The property range forthe more generally availablecommercial alloys is given in Table 3.1. Table 3.1 - Propertiesto BS 1474(1987) ALLOY TEMPER

MAX THICKNESS

0.2% Ps

mm

N/mm2

16

200 150 25 150

T4 15 T6

25 25 25

Fe) T4 T5

6063

6063A

Fe) T4 15

6082

%ELONGATIONb)

5.65y'

50

mm

13 16

12 14

110 160

100 130 150 195

8 8

7 7

90 160 190

150

14 8 8

12

200 230

12

7 7

200

-

150

120 230 255

110 190 270 295

13 16

8

8 7

6 20a)

T6

70

ULT. STRESS N/mm2

-

14

T6

-

170

200

10

8

T4 T6

50 50

75

6463

160

125 185

16 10

-

14 T6

20a) 20a)

230 370

370 435

11

2014A

10 6

6lOlAd)

a) b)

C)

d) e)

7

Thicker sections are possible and give higher mechanicalproperties. For details contact extruder. Theelongationisobtainedfrom atensiletestsampleon which agauge length is markedpriortotesting. Thegauge length is specified,being either 50 mm long or 5.65 cross-sectionalarea. (So) The properties of aluminiumvary with temperatureoutside an approximate rangeof-50°Cto+80°C. They willincreaseat lowtemperaturesand decrease at high temperatures. Thevalues vary with the alloy, seeTable 8.2. Alloy 6101A conformsto BS 2898. Values given for F condition are not specifiedproperties in British Standards and are given for informationonly.

/

35

STRESS Aluminiumdoes not exhibit a yield point. Stress/strainbehaviouris similar to that of a numberof othermetals,includingsome alloy steels. It is necessary,therefore,toadvise a recognisablepoint of departure from elastic to plastic behaviour. In the method chosen, the stress level registeredat 0.2%. Permanentstrain is regardedas the yield point. Theyield point can be obtainedfrom thestress/straincurve bydrawingtheoffset of O.2% strain parallel to the elastic line for the alloy under consideration. The 0.2% proofstress can be read atthe pointof intersectionofthe two lines, seeFig.3.1. Alloy curves will have a different point of departurefor each temper condition.

200

/ / 0.2

Ordinate

E E

z 0, CO

U)

/

/

/ 20

NB. for reasons of clarity the alloy curve is exaggerated

/ 0.50

0.60

% Strain

Fig. 3.1 - Yield Point

36

0.70

2014A T6

500-

Mild Steel 400

/

——

//

E

z

300-

//'7

6082 T6

/

a,

/

ci)

'—'—I

(I)

200-

100-

0

I

I

5

10

I

15 %

20

Strain

Fig. 3.2 - Typical StressStrain Curves

37

Table 3.2 - PermissibleStresses

ALLOY

TEMPER

AXIAL e)

BENDING

N/mm2

N/mm2 Pbt Pbc

SHEAR

BEARING

N/mm2

N/mm2

Pt

Pc

s

6063

15

62

69

37

117

106

6063

T6

87

96

52

139

81

6082

16

139

154

83

222

61

2014A

T4

135 124

153 142

81

239

71

2014A

16

154d)

108

278

49

20 154d) 224

Pt AXIAL TENSION Pc AXIAL COMPRESSION Pbt BENDING TENSION PbcBENDING COMPRESSION s SLENDERNESSRATIO AT EULER BLEND POINT SEE FIG. 3.3 a) b) C)

d)

e)

Permissible stress levels are laid down in BS CP1 18 TheStructural Use of Aluminium". 6063 values are applicableto 6101A and 6463. 6063A is a new alloy, not yet allocateda value but from experienceit should be slightly in excess of 6063 values (8%). Arbitrarily reducedvalues to allow for inferior crack-propagationresistance. Applies only when buckling is notthe criterion.

AxIal Loading

Foraxial loading,incolumnsand struts,the permissiblecompressivestress isobtained by inserting the appropriate slendernessratio into the alloy/tempercurves given in Fig. 3.3, and using the effective length factor from Table 3.3.

38

CM

E E

z'a CM

a) (1)

a)

>

U)

(a a)

0. E

0 0

a)

.0

0) 0) E a)

100

1

A Slenderness Ratio Fig. 3.3 - PermissibleCompressive Stressesin Struts =

K!.

K L r

= = = =

slendernessratio end fixity factor (effective length)

r

=

A

= =

whore

also

spaninmm radius of gyration of section in mm

inertia cross sectional area 39

Table 3.3 - EffectiveLengthsof Struts End Condition

Effective Length

ofStrut

Effectivelyheldin position and restrained in direction at both ends

0.7 L

Effectivelyheldin positionat both ends and restrainedin directionat one end

0.85 L

Effectivelyheldin positionat both ends, but not restrainedin direction

L

Effectivelyheldin position and restrained in direction at one end and partially restrainedin direction but not heldin position atthe other end Effectivelyheldin position and restrained in direction at one end, but not held in position or restrainedat other end

1.5 L

2.0 L

NOTE. L is the length of strut betweenpoints of lateral support.

Theextensive range of shapes and, over the last few years, the ability of the industry to producethinner extrusions hasencouragedthe use of slendersections. Because of low aspect ratios (width/depth)and high elementthickness ratios (width/thickness) of the thinner extrusions they require examination for possible modes of elastic instability. The modesoffailure listedbeloware particularlyrelevanttothin-walledopen sections of asymmetricalshape in aluminium alloys. a) b) C)

Torsional warping Lateral instability Local buckling

All thefactors are influencedbythe shapeand dimensionsofthe section and, whilst (a) and (b) are also relevantto span, (C) is not. Althoughsafe valuesare oftenquoted in simpletermsforaspect and elementthickness ratios,theyare not entirely reliableand should not be used. Ifthere is anydoubt about the robustnessof asection in theformoffailures list above,it shouldbechecked, using appendicesF, G, H and Kin BS CP 118- TheStructuralUseofAluminium".Thedesign approach uses equivalent slenderness ratios in conjunction with alloy compression curves. The strut curves in Fig. 3.3 can be used for torsional warping but will give pessimistic values for lateral instability and local buckling, where the equivalent slendernessratio falls on thestraight line partsofthegraphs: See BS CP1 18 Fig. 2 for modifiedcompression curves suitable for solving lateral instabilityand local buckling.

40

STIFFNESS The stress/strain relationshipis given by Hooke's Law which states that intensity of stress is proportionaltostrain. Thisisapplicabletoaluminiumalloys toa leveljustbelow the 0.2% proof stress, the slope ofthe line being obtained from: Table 3.4 - Modull of Elasticity E

=

ALLOY

Stress Strain

where E is the modulusof elasticity MODULUSOF ELASTICITY E N/mm2

6063 6063A 6082 6101A 6463 2014A

65,500 65,500 68,500 65,500 65,500 72,000

These values are approximately one third of that of mild steel, 210,000 N/mm2. Aluminium under elastic bending will therefore give deflectionsthree times greater than those obtained from mild steel under similar loading conditions. This is not true for self weight loadingwherethe light weightofaluminiumcounteractsthe effect ofthe lower elastic modulus of aluminium. The advantage to be obtained from a low modulus are greater impact absorption with shock loads and lower imposed stress levels from movement in static structurescaused by temperaturevariationor support settlement.The modulusof elasticitywill vary with temperature,see Table 8.2. In applicationswhere deflection is the controlling design factor, the performance of aluminium can be dramatically improvedby utilising the advantagesof the extrusion process to position materialsstrategicallyaround the section. The geometric properties can also be increasedby small additionsto section depth. This modification applies to all materials but can be more readily incorporated into extrudedaluminium sections. Examplesare given in Section 11, Design.

Therelationshipbetweenlateral and longitudinalstrain,within the elastic limit, isgiven by Poisson's Ratio which, for aluminium alloys, is usually 0.34.

41

35

30

Tensile

x E E

z

Relationshipbetween hardnessnumberand tensile strength for magnesium- silicide alloy extrusions in the artificially aged condition

25

-c

0)

c

Yield

20

)2)

(0

D

.; (0 C

a

15-

10

I-

(1/6063 T5 & T6 F

6063A

j"1

Brinell

6082 T6 •1

i'•

T6

45 055 6065 707580 85 9095100105110

Vickers Rockwell

'F' 46 51 56 61

66 71 76 82 87 92 98103 109115

54 61 67 71 76 79 82 85 87 89 91

-

'E' 68 72 77 80 83 86 88 90 92 94 96 Rockwell 'B' 47 55 62 - - -I - 12 23 32 39 45 50 55 60 63 66 Rockwell 'K' Rockwell

I

Webster

I

15253441485358826670737678 5 7 9 10 11 12 13131414—151515161616—1717

—

Hardness number HARDNESS TESTER SETTINGS Rockwell

Brinell

lOmm.Steel ball penetrator - 500kg.load Vickers Diamond penetrator - various loadings

1.6mm

Rockwell

'B'

Steel ball penetrator - lOOkg.load

'K'

3.2mm Steel

Rockwell 'F' 1.6mm Steel ball penetrator - 6Okg.load Rockwell 'E' 3.2mm, Steel ball penetrator - lOOkg.load

Webster Model

ball penetrator - l5Okg.load

'B'

Note: Asthistable shows, a hardnessvalue covers a range of stress levels and must not therefore be used to give precise measurementsof strength.

Fig. 3.4 - Relationship Between Hardness Number and Tensile, Yield Strengths 42

HARDNESS

The surfaces hardnessof aluminium alloys can be assessed by most of the general methods of measurement,Brinell, Vickers and Webster etc. The accuracy of the results canvary, particularlywith those methodsthat usemanual pressureto obtain the surface indentation. Thetrendto relatemechanicalpropertiesto hardnessvaluesis nottobe recommended as there is no accurate constant relationship. The curves shown in Fig. 3.4 are for general guidanceonly and indicatethat there are given rangesof stress levels foreach hardnessvalue. FATIGUE Aluminium is similar in its fatigue behaviourto other non-ferrous metals in that the stress/cyclecurves nevertotally flatten out. An arbitrary maximumendurancelevel is therefore imposed,. usually 50 million cycles. Curves are drawn up for alloy and temper groups against semi-rangeof stress levels (see Fig. 3.5). Fatigue curves are usuallybased upon actualtestresultsfrom Wohler typebeam machineswhich subject the specimensto sinusoidal reversedbending. Theresults are generally plotted for high cycle applications,above 1 O cycles, and any high strain/low cycle applications should be discussed with the extruder. The surface finish and geometric aspects of components, particularly joints, can influenceperformance. Shot blasting of the surface can improve fatigue resistance, whilstnotchescan reduceit. Withweldedconnections,itis usualto obtainbetter results from butt joints than those which are lapped and continuous welds give a superior performance to that of intermittent welds. Some data based upon nine different classifications of structural componentsis given in BS CP1 18.

43

300-

270-

240-

210E E

z a

180-

a

0 a

a, 150C C,,

E

120-

90-

60 -

i0

106 i07 Endurance (cycles)

108

Similar results are obtained for alloy 6082T6

Fig. 3.5- Fatigue Curvesfor Some AluminiumAlloys (Rotating CantileverTests) 44



SECTION 4- DURABILITY

CONTENTS

Page No.

Title INTRODUCTION

47

ATMOSPHERIC

47

CHEMICAL

49

MATERIALS Bi-MetaIlic

49 49 53 53 53

Wood InsulatingMaterials Concrete

45

Listof Figures Fig No.

Title

4.1

6082 T6 Alloy (Mill Finish) ExposureGraph (1)

48

6082 T6 Alloy (Mill Finish) ExposureGraph (2)

48

4.2

4.3

4.4

Page No.

Principleof Galvanic Reaction

49

Typical Bi-metallic ConnectionsBetween Aluminium and Steel

52

Listof Tables 4.1

Electro-ChemicalSeries

50

4.2

Guide to Bi-metallic Corrosion Effects at Junction of Aluminium and Other Metals

51

46

INTRODUCTION Aluminiumand its alloys have, in general,excellentdurabilityand corrosionresistance. Like most materials, however,their behaviourcan be influenced by the way in which they are used. In this section the manner in which aluminium respondsto various environments and design situations is reviewed with advice on use in specific applications. ATMOSPHERIC Aluminium's naturalaffinitywith oxygen resultsin theformation of an oxide layer when exposedto air. The resultingfilm is generally50Ang thick, extremely hard,chemically stable, corrosion resistantand adheres stronglyto the parent metal surface, producing an integrated material. Once formed, it prevents further oxidisation and, if damaged in any way, will reform, oxygen availability permitting. The only practical reason for removingthis film is to facilitate anodizingor welding. In the firstinstance, a thicker, morecontrolled deposition of the oxide layer can be carried out and in the latter case, the oxide film would be a deterrentto good metal fusion.

The behaviour under atmospheric exposure can therefore be described as selfstifling. If the surface layer is pitted by any of the air-borne pollutants usuallyfound in industrialor marine atmospheres,such as sulphuric acid and sodium chloride,the resultingchemical reaction producesa larger volume of powderedcorrosionproduct than the volumeof the original pit, thereby sealingoffthe surfaceof the aluminiumand inhibiting any further corrosive reaction. In general,the ratio of corrosion productto pit volume is 240:1. With time, existingpits, which are usuallyof ashallow hemisphericalshape,are sealed and the rate of formation of new pits is reducedso that eventuallyall reaction can be assumed to have ceased. This processcan bedescribed as weathering,forthe depth of pittingis extremelysmall. Thelevel of pollutionofcourse will determinethe general appearance,which will appear to be a soft blueish-greycolour in ruralareas and dark grey to black in industrial areas. Regular maintenanceand washing down should prevent the permanentdiscolourationfrom industrial pollutants. Anodized surfaces, however,will retain their original appearancefor a much longer period, providing that regular maintenanceis carried out. See Section 10. For the purposes of assessment,the various types of environmentalconditionsare divided into 3 categories: a)

RURAL

b)

MARINE

c)

INDUSTRIAL

47

E E

1)

D

Marine Industrial 0.

Rural

3-

6

Exposuretime

Fig. 4.1

- years

- 6082 T6 Alloy (Mill Finish) ExposureGraph (1)

The exposure trialson which Fig. 4.1 is based also provided samples for testing the mechanicalpropertiesofthematerials. As canbeseen inFig. 4.2there isvery littledrop in these properties, even afterprolonged exposure of 12 years. In both figures, the graph line isvirtually horizontaland thereforedurabilityand mechanicalpropertiescan be assumed to have reachedstable conditions.

stri:l

i::

0

6 8 Exposure time - years

10

Fig. 4.2- 6082 T6 Alloy (MillFinish) ExposureGraph (2) 48

12

CHEMICAL The behaviourof aluminium alloys in contact with a wide range of chemicals is welldocumentedarid requestsfor specific information can usually be dealt with by your material supplier. In general,corrosion of aluminiumonly occurs to anygreat degree where the ph is be'ow 3 or above 9, i.e. under strongacidic or alkalineconditions. is thereforenecessaryto knowthe concentrationofthechemical underconsiderationand also thetemperatureat which it will operate, as in some casesthetemperaturecan be the major considerationby alteringthe normal behaviourpattern.

t

MATERIALS When aluminiumwill be in contactwith other materialsunder wet or moist conditions, it is necessaryto check whether some form of protectionis required.

Bi-Metallic When dissimilar metals are coupled together in the presence of moisture, there is a likelihood of a galvanic reaction in which one metal will corrode see, (Fig. 4.3). In this situation an electrolytic couple is formed in which a current flows from the less noble metal,acting as an anode, tothe morenoble metal,acting as acathode,with corrosion concentratedon the less noble metal. This behaviouris usually consistent with the relative placings in the electro chemical series, see Table 4.1.

Corrosion Electrons

—

ri 1

+

Positive ions

2

Electrolyte Cathode

Anode

Corrosion cell

Fig. 4.3 - Principleof Galvanic Reaction

49

Base or less noble metal Noble metal

Theseverityofthe galvanicactionalso dependsonthe degreeof separation,electrical resistanceofthe metalpath, conductivityofthe solution and the arearatio betweenthe two dis-similar metals. In practice, however, reaction between the metals can be avoided by insulatingthem from each other with an electrically inert non-abosrbent barrier. An excellent exampleof this kind of connection is between the aluminium super-structure and steel decking on ships. Reference can be made to B.S. publication PD 6484 - 1984.

Table 4.1 - Electro-Chemical Series

BASE

Magnesium Zinc Aluminium Cadmium

Mild Steel Cast Iron Lead Tin

Nickel Brasses Copper Bronze Monel Silver solders (70% Ag. 30% Cu) Nickel

Stainless Steel (Type 304) Silver Titanium

NOBLE

Graphite Gold Platinum

50

PASSIVE

Table 4.2 - Guideto Bi-metallicCorrosion Effects at Junction of Aluminium and Other Metals Metals Coupled With

AluminiumOf

Bi-metallic Effect

Aluminium Alloy Gold.platinum, rhodium,silver.

Attackacceleratedin mostenvironments

Copper,copperafloys. irwnersion.silver solder

Attack acceleratedin mostatmospheres to aluminiumand itsand conditionsof total

Soldercoatingson steel orcopper

Attack acceleratedattheinterfacein severeor moderateatmospheresand underconditionsof total immersion,

Nickel,nickelalloys

Attackacceleratedin marineand industrial atmospheresand conditions of total irmtersionbutnot in mildenvironments,

—_____________

—---

Steel,castiron

Attackacceleratedin marineand industrial atmospheres and conditionsof total immersion butnot in mildenvironments.

Lead,tin

Attackacceleratedonlyin severeenvironments, such asmarineand some indiatrial.

I

These metals,and especiallythoseat thetop of thelist are generallycathodicto aluminiumand its alloys,whichtherefore suffer preferential attack when corrosion occurs.

Tin zinc plating (80/20)onsteel

Attackacceleratedonlyin severeatrrspheres and condtionsof total Immersion.

Pure aluminiumand alloysnot containing

Whenaluniniumis alloyedwith appreciableamountsof copper becomesmoe nobleand when alloyedwith appreciable amountsof zinc itbecomesless noble. Inmarineor industrial atmospheres orwhen totallyimmersed,alunnium alloysuffers acceleratedattackwhen Ingood electricalcontactwith another aluminiumalloy that containssubstantialcopper,such ax wroughtalloys2024 and 2014and castalloysLM 4-M and BS L92. Thealuminium-zincalloys,being less noble,areused ascladdingfortheprotectionof thestrongeraluminuimalloys,

Cadmium

No acceleration ofattack on cadmiumexcept infairlysevereatmospheresin contactwith an aluminiumalloy containingcopperand under conditionsof total immersion,

Zinc and zinc alloys

Attackon zinc acceleratedin severeenvironments such as marineand industrial and under conditionsof total immersion,

si,stantialadditions of copperorzinc

Magnesiumand magnesiumbase alloys

Titanium

Attackonmagnesiumacceleratedinsevere environments such asmarineand industrialand underconditionsof total immersion,

Thesemetalsare generallyanodicto aluminiumand suffer attackwhen corrosion occurs,thereby protectingthe aluminium,

Attackonalurntnium may alsobe accelerated.

Not manydata available,but attackon alurTinium is knownto beacceleratedin severemarineand industrial conditionsand when immersedin seawater.

Stainlesssteel (18 8. 18/8/2and

/

13%, Cr)

Chromiumplate

Noacceleration ofattack on aluminiumin moderate atmospheres, butattack maybeaccelerated inseveremarineand industrial atmospheres and underconditionsof total irrynertion.

—-

Noacceleration ofattack on aluminiumwhen plating is not less than 0.0025 mmthick. except insevereatmospheres; alsoprovldedthe preliminarynickelcostingus in accordancewith requirements of BS 1224.

51

These metalsform protectivefilms that tend to reduce bi-metalliceffects. Where attackoccurs thealuminiumbase materialsuffers.

Bulb plate stiffener

Aluminium

plating

between Steel bracket and 150mm mm. Steel foundation bar

A

Inside

Outside

Inside

Outside

)

Treatment as for A but with plate lapped to inside of foundation bar.

C

Steel rivets

B

Aluminium plate lapped to joggled steel flat bar. Galvanised steel bolts with insulating washers and ferrules. Treatment otherwise as for A.

C

Figure 4.4 - Typical Bi-metallicConnectionsBetween Aluminium and Steel 52

Wood In dry conditions there is usually no reaction on the aluminium but if the wood is unseasonedor in damp conditions,it should be coated with aluminiumor bituminous paint. Invery aggressive environments(immersion)anon-absorbentinsulatinggasket should be fitted as with bi-metallicjoints. Where timber is treated with preservative advice should be obtained from your aluminiumsupplier.

Insulating Materials In the unusual event of insulatingmaterials becoming saturated, some protection of the aluminium would be necessary for, apart from the possibility of attack from leached-outchemicals, some poultice corrosion could occur, activatedmainly by the reduced availabilityof oxygen. Protectioncan be afforded by using an inert barrier. Concrete Under perfectly dry conditions,aluminium buried in concrete would need no protection. In practice,however, such conditionsare rarely achievedtherefore it is recommendedthat in all cases the contact areaofthe aluminiumis coated with a bituminous paint. In no circumstancesshouldthe steel reinforcementused in concretebe allowed to come in direct contact with the aluminiumas this will result in a bi-metallicreaction which in turn could cause spalling of the concrete.

53




SECTION5- SURFACE FINISHING

CONTENTS Page No.

Title

INTRODUCTION

57

PRE-TREATMENT

57

ANODIZING SpecificationFactors for ArchitecturalType Anodizing Chromic Acid Anodizing Hard Anodizing

57

PAINTING Electrophoretic Electrostatic Paint Performance

61 61

55

59 61 61

61

62

List of Figures Fig

No.Titie

5.1

AnodizingProgramme

58

5.2

Depositionof Colouring

59

Page No.

Listof Tables 5.1

Suitabilityfor Anodizing

60

5.2

Paint Performances

62

56

INTRODUCTION One ofthe most importantconsiderationsrelatingto surfacefinish is the need to have a sound and permanent bond between any applied film or coating and the parent material. In this respectaluminiumand its alloys are particularlysuitable, providingas theydo integralbondingwith anodizingand excellentpaintkeys when suitablyetched and de-greased. PRE-TREATMENT The surfacetextures on aluminium,like those on other metals, will be visible through all but the thickest coating so it is as well to considerthis aspect before deciding on the final surfacetreatment. Where positive relief features are required, like ribbing or serrations,these can be easily incorporated into the extrusion shape. The usual cycle for pre-treatmentincorporatesa de-greasingdip, followed by a rinse and then an etch dip. The make-up and chemical concentrationof this etch can be varied to produce a range of surfacesthat will affect the final appearanceof an anodizedfinish. These canbe graded from the natural metal appearance,through a light grey satin finish to a darker grey frosted appearance. Specialisedsurface finishes can be applied,such as chemical brightening,mechanical polishing, scratch brushing and shot or vapour blasting. The special finishes extend from bright reflective polished surfaces, through to heavy peened rough textures. Aluminiumprovidesan excellentsurfacefor paint. Afterdegreasing,alight etchis used followed, when necessary,by a chemicalconversioncoatingto improvethe paint key even further. All ofthese services are available directly or indirectlythrough extrusionsuppliers. In general the level of concentrationof pre-treatmentchemicals makesthem unsuitable for manual non-dip application. ANODIZING Anodizing is a controlled surface oxidisation by immersion in an electrolyte, usually dilutesulphuricacid. A lowvoltage,high amperagedirect current is passedthroughthe metal, using the aluminium as the anode and a hard, non-corrodingoxide film builds up on the surface of the aluminium. A less dense layer is subsequentlyformed in which there are capillary pores. These pores provide the meansfor further oxidisation, building up the thickness from the base. This film is an integralpart of the metal and is not an applied coating.

57

ProTreatment

Degrease

OPTIONAL TREATMENTS Mechanically Polish

Chemically

Metallic Colour

Brighten

Organic Colour

Scratch Brush

Vapour Blast Rinse

r

r

Shot Blast Light Etch Etch

Rinse

I

I

Anodize I

Natural Finish

Seal I

FIg. 5.1 - Anodizing Programme

Afterthe actual anodizingoperation, the surface film is porous and in a conditionto accept colouring agents, if required. If a natural aluminiumfinish is desired then the material proceedsdirectly tothe final tankwhich is usuallyboilingwater. Thechemical reaction of immersion seals the pores against further moisture penetration,giving a hard, weather resistingsurface.

Wherecolour is required, thechoice lies betweenthose obtainedfrom organicdies, as used with textiles, and those obtainedfrom metallicsalts. Theformergives a rangeof primarycolours,whilstthe latterofferscolours varyingfrom greythrough umbertodark brown and black. As will be seen from Fig. 5.2the organic dies tend to remain at the top and the metallic salts at the bottom of the surface pores.

58

l7nm

25 micron (25,000nm) H Ratio d

= 1500:1

Natural

Organic dies

Metallic salts

Fig. 5.2 Deposition of Colouring SpecificationFactorsfor ArchitecturalType Anodizing British Standardslay downspecificationsto govern thequality of anodizing. BS 1615coversgeneral anodizedcoatings in aluminiumand BS3987 covers external architecturalapplications. Europeanstandardsare covered by the Qualanod quality control scheme.

The average thicknesses readily available are usually designated in AA values, the figures conformingdirectly to the film thickness in microns.

M 5

Applications Furniture and other indoor products. Also used with chemically brightened material where a thicker coating would tend to reduce reflectivity.

101 155

Internal applicationslikely to have more robust handlingsuch as hand-railingand internalpartitions.

25

All external applicationssuch as windowframes etc.

59

c)

The mostappropriateextrusion alloysfordecorativeand architectural anodizing are in the 6063 range. Other alloys canbe anodizedbutthe finish cannot be guaranteed to meet the requirements of British Standards architectural specifications.

Table 5.1 - Suitability For Anodizing

*

Alloy

Natural

Colour

Brightened

Protective

6063

V

V

G-V

V

6063A

V

V

G-V

V

6082

F

F

F

G

6463

V

V

E

V

2014A

F

F

U

G

*This also includes "hard"anodizing E = excellent V = very good G = good F = fair U = unsuitable d)

In componentanodizing,the heat affectedzone ofwelded orbrazed joints will show somecolour variationfrom that on the rest ofthesection. This can vary fromslightly darker tone to averydark grey oreven black if a siliconfiller wire is used in brazing.

e)

There can be slight variation in colour between production batches, so top and bottom colour limits should be agreed with the anodizer. This is particularlyso where cast and wrought componentsare concerned,because an exact colour match is rarely possible due to the markeddifference in the chemical composition of the two materials.

f)

Electrical contact is extremely important between the loading bars and the aluminium section during anodizing. It is obtained by jigging with nonmetallicclamps. Thecontact areas, however, do not anodizeor colour and willtherefore leavea light-colouredarea even on naturallyanodized material. Non-visible surfacesshould be shownondrawings sothat the clamps can be placed in the best possible position. If all surfacesare visible, then an extra 50 mm should be allowedat eachendofthe bar forclampings,which can be cutoff after anodizing. 60

ChromicAcid Anodizing The original commercially developed anodizing process used chromic acid as the electrolyte.The procedureis similarto that employedwith sulphuricacid but the bath temperatureis higher.The resultantfilm is softer and thinner (max. 10 microns) but for equal thicknessesitoffers morecorrosionresistancewhich makesit idealforaggressive industrialenvironmentswhere the relatively soft surface is no disadvantage.As the chromicacid is passivewithaluminium,itisalso recommendedlorfinished components where there are laps or crevices which could retainelectrolyte.

Hard Anodizing Hard anodizingis a lowtemperatureoperation,usingconsiderablyhighervoltage than other anodizingprocesses.The relatively rough surfaceproduced is extremelydense and hard and is available up to 125 micronsthick. The film is normally left unsealed but can be waxed or treated with mineraloil. In either case, the abrasion resistance is very high, comparingfavourablywith that of tooled steel and chromiumplate. Hard anodizedfilms have good electrical insulationpropertiesand their excellent corrosion resistance and durability make them ideal for use even in aggressiveenvironments. PAIN11NG

Aluminium rarely needs to be paintedfor protectionbut where colour is necessaryon aesthetic grounds a number of high-quality paints and methods of application are available.Thesurfacepresentedby aluminiumis idealforcoatingwhenthecorrect pretreatmentiscarriedout. As mostcoatingsare appliedbycommercialcoatingcompanies, the basic pre-treatmentsare usuallyvariedtosuit their particularpaintformulationsand methods of application. In general, the oxide film is removed and the material degreased,etchedand rinsed.This is adequatepreparationfor electrophoreticpaints but thereis an additionalchemicalconversioncoatingwhich isthen appliedforelectrostatic application. Electrophoretic

Thepre-treatedworkpiecesare madeanodicand dippedinto electricallychargedpaint tanks. This ensuresthat the paint is attractedto the metal surfaceand deposited in an even coating.Afterrinsing,thematerial passesthroughstoving ovensatapproximately 160°Cforadurationof 15 minutes.Duringthis operationthepaint isfused and strongly bonded to the aluminium. Electrostatic Afterpre-treatment,the workpieces are passed through an electrostatic field during which time paint, in theform of wet or powderparticles,is sprayed on to the surfaces. Theworkpiecesare then transferredto atunnel oven where they are stoved at 200°C for 10 minutes. 61

Paint Performance Comparing paint surfaces and their respective performance is always somewhat subjective,neverthelessTable5.2 attemptsto providegeneralised information.Paint and coating companies are always pleased to advise on the best system of application. For all paints and systems, sharp corners provide a challenge in that either a metal or a shadow line appears,depending upon the thickness of the paint. This can be avoided by following good extrusion design although for paint the minimum recommendedcorner radius is 1mm. Table 5.2 - Paint Performances PAINT

Acrylic

Method of

Mean Colour Thickness Range Application (Microns)

Surface Texture

Electro-

Gloss Level

Colour Fastness

Hardness Inside Groove

Post

Coating

Painting Fabrication

V. good

Good

25

White

Smooth

70%

Moderate

Hard

60-80

Wide

Slightly Textured

20%-

Good

93%

Moderate Shallow Channels

Polyphorec urethane (WetBath) Polyester

Electrostatic

Range

(Powder Spray) PVF2

Electrostatic

Excellent

Only

30-100

Small

(a)

Range

25(a)

Wide

V.good

(Powder Spray)

Fluoro- ElectroCarbon

static

Smooth

9%70%

Excellent

Moderate

Moderate

Smooth

9%90%

Good

Hard

V. good

Range

(Wet Spray) Acrylic ElectroPolyesterstatic

25

Full Range

(Wet Spray)

(a) Suitable formulti-coat applications Further information is available from: Aluminium Coating Association Broadway House Calthorpe Road Birmingham B15 1TN

62

ALUMINIUM EXTRUSIONS — a technical

design guide

SECTION6- FABRICATION

CONTENTS

Titles

Page No.

BENDING MachineTypes Alloy/Temper Shape Factors Tube Bending

65 65 67 67 69 70 70

Springback

Lubrication MACHINING

70 72 73 74

Routing Drilling

Sawing JOINING Welding

75 75 79

JointDesign

81

Screwing Crimping

82 83 85 86

Riveting Bolting

Adhesives

63

Listof Figures Fig No.

Title

Page No.

6.1 6.2

Bending Methods Routing (Profilingand

65/66 72 73 74 77 78

Facing) 6.3

6.4 6.5 6.6

6.7 6.8 6.9 6.10 6.11 6.12

Drills Types of Saw TIG Welding MIG Welding RecommendedDiameters of ScrewGrooves LongitudinalScrew Grooves Crimping Blind Rivets Self-Piercing Rivets Clench Rivets

81

82 82 83 84 84

Listof Tables No.

Title

6.1 6.2 6.3 6.4 6.5 6.6

Bending Characteristics Minimum Bend Radii (1) Minimum Bend Radii (2) Minimum Bend Radii (3) Minimum Bend Radii (4) Minimum Root Radii R in Terms of Tube Diameter Basic Saw Tool Data Process Capacity RecommendedFiller Alloys for Welding Parent Metal Combinations Edge Preparationand Fit Up forTiGand MIG Permissible Stress Levels

6.7 6.8 6.9

6.10 6.11

Page No.

64

67 68 68 69 69 71

74 76

79 80 81

BENDING There are several types of torming machinesuitablefor bending aluminium sections. Thechoicedepends uponthe class ofsection, whethersolid open or hollow;the range of support tooling available; the alloy and the temper. Machine Types Bending may be carried out by four main methods, as shown in Fig. 6.1. The three roll bender has a centralmoveablerollerwhich is graduallydepresseduntil the desired radius is obtained. The point bender has a similarmethodof operation,the load either being appliedgraduallyorimpacted. Theroll and point methodsof bendingare usually applied to robust sections. In the wrap and the mandrel benders, it is possible to provide formers and other support tools which enable tighter radii to be obtained and minimise the amount of buckling.

As the name implies,the stretchformer putsthe section into tension and then, moving laterally,wraps it arounda former: this method reducesthe likelihoodof compression failure. As well as the above basic machines, a number of specialist benders are available, such as the rotating disc, which is suitable for tube bending.

-Former

Wrap Bender

I

Clamp

Guide

Draw Mandrel Bender

Former Moves Around Section

Section Moves Around Former

Fig. 6.1 - Bending Methods 65

Section Bending Roll Fixed Position Drive Rolls

Three Roll Bender

Bending Point

Fixed Position Drive Points

Three Point Bender

L

Stretch Former

FIg.6.1 - BendingMethods(continued) 66

Alloy/Temper

Heattreated aluminium alloys in the T6 conditionhave relatively short plastic ranges with proof-stress/ultimate-stressratiosof0/86: 1 and minimumelongationvaluesof7% - 10%. Althoughthese values do notprovidethe whole pictureof ductileperformance, theygive a reliableindicationof bendability. Where bending is aprimary requirement, it is usualto use materialinthe T4 solutiontreated condition. Theplastic stress range ratios are then improvedto0.6:1 with minimumelongationvaluesof between14%and 16%. Theslowrateof natural ageing in the 6000 series alloys does not appreciably affect the bending characteristics,except in the most severe bending cases. Bending at raised temperatures is not usually recommended as the mechanical propertieswould be affected. It is possibletocarry out post-bendingheattreatmenton T4 temper materialthat will increase its propertiestowards those of the T6 condition. Care should be exercisedwith thin sections as some distortioncould occur underthis treatment. Table 6.1 - Bending Characteristics

Alloy

Temper

Bending Index

6063

T4 T6

V

6063A

G

14 T6

G

6082

T4 T6

G F

G = good

6101A

T6

G

F=fair

6463

T4 T6

G

2014A

V

V=verygood

V

G

14 T6

F

Shape Factors The complexityof shapesavailablein aluminiumalloys makes it verydifficultto provide information to cover every situation. By considering the behaviour of the various elements of the shape in relationto the bending axis it is possible to predictthe most likely modeoffailure when bent throughtoo tight a radius. In most cases,the neutral axis of the section and the bending axis almostcoincide butthis is nottrueforstretchforming where, becauseof longitudinaltension,the bending axis is assumedto move outside of the section. 67

Thefollowing tables give minimum bend radii for section elements under the various forms of bending stresses. Radii values are to the neutral axis and are given in multiplesof y.

y is the maximumdistancefrom outerfibres of the element to the neutral axis ofwhole section. t is thickness of element. Flange denotes shaded element parallelto the plane of bending. Web denotes shaded element vertical to the plane of bending.

Theuse of support tooling in the bucklingmodescan reduce the minimum radiibelow the levels shown in the tables. Theextent of the reduction depends upon the typeof tooling used. Table 6.2 - Minimum Bend Radii (1)

y t

1

2

4

8

12

Alloy

Temper

6063

T4

O.7y

0.7y

O.8y

2.Oy

3.5y

T6

O.8y

0.By

l.4y

3.Sy

7.Oy

T4

2.5y

2.5y

2.5y

3.Oy

5.Oy

T6

2.5y

2.5y

2.5y

3.5y

7.Oy

6082

=1

Table 6.3 - Minimum Bend Radii (2) y

t

2

3

4

6

Alloy

Temper

6063

T4

l.Oy

3.5y

8.Oy

20.Oy

T6

l.Oy

4.Oy

1O.Oy

20.Oy

T4

l.8y

4.Oy

1O.Oy

20.Oy

T6

l.8y

5.Oy

1O.Oy

25.Oy

6082

WEB TENSILE

L

L WEB BUCKLING

C1

68

F1

Table 6.4

- Minimum Bend Radii (3) FLANGE

FLANGEWIDTH THICKNESS

4

8

Alloy

Temper

6063

14

7.Oy

8.Oy

T6

10.Oy

lO.Oy

14

8.Oy

Boy

T6

10.Oy

lO.Oy

6082

TENSILE

Table 6.5 - Minimum Bend Radii (4) FLANGE WIDTH THICKNESS

FLANGE 4

8

J

Alloy

Temper

6063

T4

5.Oy

8.OY

T6

8.Oy

20.OY

T4

7.Oy

l2.Oy

16

8.Oy

2O.Oy

6082

N.B.

BUCKLING

Where flanges have bulbs greater than 3t thick they can be bent to radii 60%

of those shown in the table. Tube Bending The recommendedmethodsof tube bending are wrap and draw mandrel. Although threepoint bendingcan be used,there is lesscontrolparticularlywiththin-walledtubes in the stronger alloys and tempers. Aluminiumtubes can be readily bent but, like all materials,there are limitsand thekey to successfulbendingisto understandthem and take appropriateaction at both the design and fabrication stages. Failure modesare, once again,tensiletearing and compressionbuckling butthere are in-between situations where wrinkling, necking and flattening can occur without causingfracture ofthetube. To preventthese surfacedefectsor to restrictthem to an acceptable level, the tubes can be filled with sand, springs or low melting materials such as Wood's metal. 69

Theseare allestablishedmethodsofprovidinginternalsupportwhich,together withthe use of external groove formers and followers,provide the maximum level of bending control. Table 6.6 shows the minimumrootradiifor a rangeof tube sizes based upondiameter! wall thickness ratios, alloys and tempers but ignoringflattening. Sprlngback Althoughthedegreeofspringbackcanbecalculatedforaspecific sectionthathas been bent around a given radius,it involvesa lengthy process. The more usual method of establishing springback is to carry out trials prior to a production run. Generally, sectionswhich are symmetricaland havethe majorportion oftheir material awayfrom the neutral axis exhibit less springbackthan a heavy centred cruciform section or an asymmetricalT-bar.

Lubrication Frictionbetweenthesurfacesof steelformingtoolsand the natural surfaceoxideof the aluminiumcreatesthe need to lubricateboth work and tools. This helpsto reducetool wear and prevent damageto the surfacefinish ofthe formed parts. Dependingupon toolshape,sectionsize andalloy,thelubricantscommonlyusedincludemineraloil, lard oil, proprietarywater soluble compounds and waxes. MACHINING Aluminium alloys are amongst the most machinable metals and can be cut at high speeds. Two basic properties influencethe machiningoperation: a)

the high co-efficient of linear expansion of aluminium.

b)

the friction generated betweensmall tools and aluminium.

The problems associatedwith the above characteristicscan easily be overcome by using a combined lubricantand coolant. Machines normallyfound in a workshopare suitable for use on aluminium. The best results are obtained with relatively high speeds and it is frequently found that woodworkingmachinescan be employedfor machining,providingthey have sufficient power and rigidity. High speed steel tools may be used on all the aluminium alloys. Plain carbon steels may also be used for short runs buttheydo not have sufficient life for quantity production. For long productionruns tungsten carbide tips are recommended but even these toolswould require regular resharpeningparticularly when used with anodized material. A chip breaker should be used on alloy 6082 for high speed operations to avoid the formation of long spiral swart.

70

Table 6.6 - Minimum Root Radii R In Termsof TubeDiameter

MATERIAL DESIGNATION

CHARACTERISTICCURVE

AND TEMPER

WRAP

MANDREL

B B

B B

C

C

F T4 T6

B

B

C D

C D

6101A T6

C

C

6063

6082

F T4 T6

4U -

30

30

C

tr o

o

20

10

Ill S

20

-

S 15

——--———-

lEt

2D

———-

3D

4D

5

lD

50

Minimum Root RodS In Terms Of lobe Diomneter

2D

3D

71

5D

Minimum Rout Rods In Terms Of Tube Diameter

Mandrel Bend

Wrap Bends

4D

Where extensive removalof metal is to becarried out, there is alwaysthe possibilityof distortion occurring. Machining practiceswill also affect the amount of distortion that takes place. Coolingand lubricationshould be generous but even so, over-tightened chuckscould add tootherstressesoccurringthroughthermalexpansion. Ifthere is any doubt, the material suppliershould be consulted. Routing One ofthebest methodsofmachiningaluminiumis byrouting. This resemblesa milling operation, giving a good surface finish, as fine as 0.75 micron,and can be used with spindle speeds up to 24,000 rpm. The high operating speed, in conjunctionwith low loading,ensures smooth, easy controlwhich is essentialwhen followingthe contours of a complextemplate. See Fig 6.2.

Helix angle

Radial rake

Primary clearance

CUlliNG SPEED

FEED

HELIX

RADIAL

rn/mm

rn/mm

ANGLE

RAKE

Profiling 600-2100

Up to 6 Reduced

CLEARANCE

speeds

Facing:

Upto 6000

necessary with increase in work thickness

5-7°

25°

Fig. 6.2 - Routing(Profiling and Facing) 72

5-10°

Drilling As with other aluminiummachiningoperations,drilling can be carriedout atveryhigh speeds. Specialmachinesfor usewith small diameterdrills work at 80,000 rpm, most drilling operations, however, are carried out at more modest speeds. The cutting performanceot adrill is influencedby its peripheralspeedand this shouldbetaken into account when deciding upon the spindle speed for a given drill diameter. Drills should be inspectedregularly to ensure that they keep their bright finish and polishedflutes to ensure rapid chip removal and prevent build-up. When necessary, thedrills should be regroundwithcare beingtaken to ensurethatthechisel edgeretains itscorrect lengthandtheweb atthedrill point does notthicken. Shouldthickeningoccur therewill be increased end pressureon the drill with the possibilityof drill breakage. When drilling deep holes, particularlyof large diameter,excessiveheat is generated and if not dissipatedby the coolant, hole contractioncould take place.

TOOL ANGLE

DRILL ELEMENT PointAngle,H

118°

Helix AngIe

20 - 25°

ClearanceAngle, 0

12 - 20°

Flutes

Polished

Web Thickness

Thiner than that used for other metals

Fig. 6.3 - Drills

73

Sawing Modernsawsused inthefabricationofaluminiumsectionsgiveclean, virtuallyburr-free cuts providedthatthe correcttooth size and rotationspeed are used and theteeth kept sharp. This is particularlyso for tungsten carbidetipped blades which are in general useforaluminium. Thistypeofblade gives excellentresultsonthe hardsurfaceof preanodizedsections. Feedwill vary with the type of saw, section size, alloy and temper butshouldneverbebelow 0.05mm per tooth. When cuttingthin sections,itis advisable to havetwo or moreteeth engaging at the same time. Table 6.7 sets out basic tooldata. Thelower speed range is recommendedfor high speed steel blades and the higher range for tungsten carbide tipped blades. It is always advisable to use a cutting fluid. Segmental teeth High speed steel Top clearance Top clearance

Top rake

Th

Depth of

Depth of

gullet

gullet

Fig. 6.4 - Typesof Saw Table 6.7 - Basic Saw Tool Data Type of Blade Saw & Size

Teeth Cutting Pitch Gullet Speed

Blade Material

m/min

mm

Circular 250-460 dia High Speed x Steel 2.3-3.7 thick Circular 5601220 Segmental dia Inserted x Carbide 64-12.7 thick Tips

mm

Depth mm

8.5-13

1500 to 2400

Hollow to Ground 12.7

6.4

1200

coarse

to

25-50

4500

12.7breaker 57 teeth Chip-

74

Top Rake

Angles Clearances Side Top

Handfeed: 12-18° 20-30° Powerfeed: 15-24° 25-35° Handfeed: 5-12° 7-9° Powerfeed: 10-20° 5-7°

1-2°

1.2°

JOINING Aluminium alloys can beconnected in avariety ofways. Theusual methods, all wellestablished,are welding, riveting,bolting, screwing,corner crimpingand glueing (but aluminium alloys have also been explosivelybonded to other materials)..

The combination of material flexibility and the extrusion process enables mating sectionsto be manufacturedin a range coveringboth permanentand releasabletypes of sliding, rolling or straight clip connections. Detailsof this type of joining are given under Section 11, Design. Welding Aluminium welding is a widely accepted method of fabrication, with no shortage of competent personnel in the engineering and manufacturingindustries. There are several methodsavailable,the basic ones being Tungsten Inert Gas (hG) and Metal InertGas (MIG). As the titles suggest,both are inert gasshieldedsystems where the weld area is shrouded from the air to prevent the reformation of an oxide film. Preparation Cleanlinessand the removalof theoxide film are most important. The proposedweld areas has to be de-greased, using white spirit or acetone and the joints wiped dry. Adequate ventilation must be provided for any solvents used but is particularly applicableto industrialcleaning solvents, such as carbontetrachlorideetc. After degreasing the joint is deaned, using stainless steel wire brushes or a chemical etch cleanerto removethe oxide film. Welding should be carried out as soon as possible afterwards. Carborundumwheels are not recommendedas grit particlescanbecome embedded in the surfacecausing contaminationof the completed weld. Filler wire is cleaned by wiping with wire wool; pre-packed spool wire is supplied in a clean condition. Tungsten Inert Gas In the tungsten inert gas (TIG) process,the arc is struck betweenthe workpieceand

a non-consumabletungsten electrode. The filler wire is fed independently. Although mechanisedTIG is available the process is more widely used as a manual system where close controloftheweldingconditionscan be readily maintained. The resulting welds are usuallyof good appearanceand penetration,particularlywhere no backing plate is available. Fig. 6.5 shows a schematiclayout of atypical TIGsystem and Table 6.8 shows the thickness range.

75

Metal Inert Gas

In the metal inert gas (MIG) process, the arc is struck betweenthe workpieceand a consumable electrode which is constantly fed from a wire spool. The arc is selfadjusting and takes into account small movements of the torch. Penetration and appearanceare not so easyto control as in the TIG system, althoughthe addition of pulsed arc equipment will improve the penetrationand reduce the need for backing plates. Fig. 6.6shows a schematiclayoutofatypical MIGsystemand Table 6.8shows the thickness range. Small spool hand guns, sometimes called fine wire, are also available with MIG systems. These dispense with the need for long wire feed leads thereby increasingthe areaof work accessible from the base unit. Table 6.8- ProcessCapacity

PROCESS

PARENT METAL THICKNESS I Max. Mm (mm) (mm)

EQUIPMENT Item Compositeunit (350A) Transformer(350 A) H.F. orSurge Injector unit Suppressor Welding Torches

TIG 1.2

Compositeunit (250 A)

MIG 0.5 kg

1.6

MIG 5kg

NOTES:

9.5 (1)

4.8

withWire Feed unit and Welding Gun for 1 lb Spool

8.0 (2)

Compositeunit (350 A)

withWire Feed unit and Welding Gun for 10 lb spool

None

(1)

Althoughthe TIG processcanweld thicker material, for economicreasons it is not normallyused for aluminium over 9.5 mm thick.

(2)

In theory there is no upper limit for 'one-pound'MIG, but it is more economicalto use 'ten-pound MIG for material over 8.0 mm thick.

'

76

NOTES 1

CompositeTIG welding units include all the necessaryauxiliaries: argon and watershut-offvalves are usually controlledby solenoids, although they may be manuallyoperated.

2

The main power cable, fuseand torch can be air-or water-cooled.

Fig. 6.5 - TIG Welding 77

Dry Bobbin Flowmeter Pressure Reducing Valve

Pressure Gauge

Wire Feed Unit

Workpiece

4

NOTES

Voltage pick-up lead for 'one-pound' MIG.

1

The a.c. supply is 11OV for 'one pound'MIG and 220V tot 'ten-pound'

5

The main power cable and gun of 'ten-pound MIG can be watercooled.

6

Arc Voltage in MIG Welding Proceduresis measuredwitha voltmeterconnected between the contact tube and the workpiece.

MPG welding. 2

CompositeMIG welding units have the contactorand control box built in.

3

The filler wire feed unit is integral withthe gun in 'one-pound' MIG and independentof it in 'ten-pound MIG Systems.

Fig. 6.6 - MPG Welding 78

Filler Wire 6063 and 6082 alloys can be readilywelded to awide rangeofotheraluminiumalloys. Table 6.9shows the preferredweld filler wire in bold print. An alternative,where given canbe usedwhen the finished componentis to be anodizedand a close colour match is required betweenthe weld area and the parent metal. Alloy 2014A is not shown in the table as this alloy is not recommended for welding using the TIG and MIG processes.

Table 6.9 - Recommended Filler Alloys for Welding Parent Metal Combinations PARENT ALLOY

6063 6082

1050a

4043 5356

3103

4043 5356

5083

5356

5251

5356

5454

5356

6061

6063 6082

4043 5356

Alloy 2014A is Not Recommendedfor FusionWelding

Joint Design Good joint design encompassesboth the practicalitiesof thewelding processand the structuralrequirementsofthejoints in service. Theedgepreparationwill depend upon the typeofjoint, butt or lap, thickness of materialto be joined and the weldingprocess to be employed. Table 6.10 shows typical edge preparation for both TIG and MIG processes.

Thestrength of welds is covered by BS CP118 which gives permissiblestress levels for both 6063 and 6082 alloys in both butt and filled applicationssee Table 6.11. The reduction in strength from the 0.2% proof stress levels is very marked, allowing for 79

Table 6.10 - Edge Preparation and Fit Up for Tig and Mig THICKNESSt MIG

TIG

n

g

(1) NOMINAL

MAXIMUM

ROOT

GAP

GAP

(mm)

(mm)

FACE (mm)

a

-

0.8c

Nil

Nil

-

-

-

1.2c 1.6c 4.8c

Nil Nil Nil 1.6

Nil

1.6 1.6

3.2c 4.8c 3.2p 8.0

6.4c

-

Nil 1.6

0.8

3.2

1.6

60 60 60 75

2.4 4.8

0.8 1.6

2.4 3.2 6.4 2.4

Nil

g

4iit

6.4c

Nil

12.7 15.9

-

Nil Nil

0.8 0.8

1.6 1.6

90 90

-

1.6 2.4 6.4

Nil Nil Nil

Nil 0.8 1.6

-

-

6.4p

-

1.6

3.2

0.8

60

9.5

-

Nil

0.8

0.8

60

-

1.6 -

Nil

8.9

Nil Nil Nil

0.8 1.6

-

-

25.4

-

Nil Nil Nil

1.6 1.6 1.6

3.2 4.8 6.4

60 60 60

-

0.8

Nil

Nil

-

-

-

1.2c 2.4c

Nil Nil

Nil

-

-

-

1.6

Nil Nil

-

-

3.2 4.8

3.2 4.8 12.7 19.0

3.2c

1) MinimumThicknessof ParentMetal

0.8

Nil 0.8

80

DETAIL

$

4.8 1.6

4.8P -

JOINT

INCLUDED ANGLE (deg.)

jj I

HL

g

r Li

[JJ flu

n

p= PermanentBacking Plate c=TemporaryBacking Plate

g

contingenciesinthe weldingprocessand the reducedpropertylevels of theweld heat affectedzones. Themost cost effectiveway ofdesigningwelded structures,therefore, is to keepthe weldedconnectionsclearof maximumstress points, as far as possible. Table 6.11- PermissibleStressLevels BUTT WELDED JOINTS & REDUCEDHAZ.

ALLOY

FILLET JOINTS (WELD METAL)

TENSION COMPN TRANSVSL LONGITL 6063

31

19

54

31

6082

51

31

54

31

PermissibleStressesfor Table WeldedJoints in N/mm2 HAZ = Heat affected zone Screwing The ease with which aluminiumalloys canbe drilled orpunched and the incorporation of screws ports or channels in extrusions has encouragedthe useof stainless steel self-tappingscrews asthe standardmethod of joining, particularlyin the window and door industries. The stainless steel threads bite into the aluminium to give a very positiveconnection. A typical patio door will use two self-tappingscrews per kilogram of aluminium section used. Screw ports are rarely fully closed as the use of 300 degree ports, (Fig. 6.8), gives a very marked improvementin extrudabilitywith very little loss in pullout strength. The dimensional accuracy of the port diameter is very important and all extruders have standardbore dimensionsfor each screw size. It is advisableto contact extruders at the die design stage and where possibleprovide samplescrews. Screw —

—

__

1.78mm

(mm) N

..

....

\\

Size

\

6 8

60°

/ // I /

10

12 14

Screw Dia. (mm) 3.45 4.17 4.88 5.59 6.25

Screw Groove Int. Dia. (mm) 3.20 3.56 4.32 5.03 5.74

FIg 6.7 - Recommended Diameters of Screw Grooves 81

Theuse of longitudinalscrew grooves, (Fig. 6.8), is not so widespreadbut thecorrect combinationof slot width and screw size can ensure high pullout values. Some care is necessary if self-tapping screws of triangulated cross-section are used as full engagementof threads may not be possible on both sides ofthe groove. Advice from the extruder is recommended.

Li Fig. 6.8 - LongitudinalScrew Grooves Crimping

In this method of corner connection,the extrusion has a built-in channel recess and afterthe sections have been mitred,thecrimpingangle isfitted and thejointassembled and heldin a rigidjig. Two pressureprongsthen upsetthesectionflange intothe corner angle, producingavery stableframe assembly,see Fig 6.9. Most crimped corners rely onmechanicalconnections,but, if required,aslowsettingadhesivecan beusedtoseal the corners and providesome extra strength. Crimpingis most likely to befound in the door and window industrybut is applicableto anycomponent orform of constructionwhere mitredcorners are used.

Crimping flange

Fig. 6.9 - Crimping 82

Riveting Aluminiumcanberivetedwith aluminiumrivets, which are usuallydrivencold. As there is atendency for these to work hardenduringthe processtheyshould be closed with the minimumnumberofblows. It is advantageousto use a long stroke hammer,asize larger than would be used with equivalentdiameterhot steel rivets. Therivets should be drivensquare, not rolled round theedges. Largerdiameterrivets(over 12 mm.)can have pre-formedend recess points to assist initialforming. Poweroperated squeeze riveters are ideal for aluminiumas the heads are formed in a single stroke. Where aluminium is to be riveted to steel structures, the faying (contact) surfaces should betreated with azinc-chromateprimerand broughttogether whilestill wet. Hot driven steelrivets should be used but these must be given at least one coat of primer in way of the aluminium, after driving and cooling. Blind Riveting This form of joining is well established and uses rivets of tubular constructionwhich enablethe workto becarriedoutfrom one side only. This isparticularlyattractivewhere accesstothe reverseside is difficult. Only one operator is required and there is choice of setting tools - pneumatic,hydraulicor hand held. Thereare a numberof proprietary systems available,in diametersupto6.5 mm. Rivetlengthsare availableforcombined joint thickness of up to 13 mm. Furtherdetails are availablefrom rivet manufacturers.

ELE Mandrel breaks and falls free

Setting tool Clinching mandrel

Fig. 6.10 - Blind Rivets

83

Self-Piercing Riveting

This is a relatively new developmentwhich canbe usedon combined thicknesses of up to 6.5 mm.

T Max.

L = 9.5mm 1=6.5mm S = 5.0mm Countersunk

Fig. 6.11 - Self-PiercingRivets Clench Riveting

A numberofproprietaryfasteningsystemsusethegripof threadedboltswiththeclosing mechanismof clench riveting. Fig. 6.12 showsatypicalpin and collet assembly. The bolts are closedfromone side in asimilar mannerto blind riveting, althoughaccess to the non-closing side is necessary to install the rivet. The collet deforms around the threaded pinbefore the pin breaksoff atthe waistedneckunder a pre-determinedload. As well as the advantage of ease of installation, these fastenings have excellent vibration resistance.

Fig. 6.12 - Clench Rivets

84

Bolting Inthismethodoconstructionstainlesssteel,aluminiumor mildsteelboltscan be used. If stainlesssteel to 18/8 specificationis used, no extraprotectionis used andthe bolts can be used in the conventionalmanner. The best aluminiummaterials are 6082 and 2014A but the latter will need painted protection in heavy industrial and marine environments. Alloy 2011 is a widely used and available bolt material but would certainly need protection in any external application. In the case of mild steel bolts, galvanizedsteel washers MUST be fitted. All boltsare best used in close-fitting holes and the appropriate tolerance levels will be found in BS CP118. Where possib'e, controltorque levels shoudbe specifiedfor aluminium bolts and the indiscriminate use of "tommy bars' is an unacceptable practice. In line with good bolting practice, no part of the threaded portion should be within the thickness of the joint flanges. The extrusion processallowscaptive bolt head slots to be built intothe extrusion. The bolt can be positioned anywhere along the slot, thus requiring hole accuracy in one dimension only. The internal width of the slot should be dimensioned to suit the maximum width of the boithead across flats thereby locking the bolthead against turning when tightening up the nut. See Fig. 11.3

85

Adhesives This methodofjoining hasfound favour inthe high-techindustries,i.e. electronicsand aero-spacewhere product cleanlinessand close fabricationcontrol were alreadywellestablished practices. In more recent years, adhesives tolerant of imperfect joint conditions have been developed and have been taken up, particularly by transport, engineering and even structural industries. In general, bonding systems still require clean etched surfaces; some respond to unsealed,anodizedor conversioncoatedsurfaces. The range of adhesivesavailable covers cold, impact or heat curing together with single or two-part mixes. Each has its own characteristicand therefore advice on suitabilityfor any specific application should be sought from adhesive manufacturers.

86



SECTION7- CONDUCTIVITY

CONTENTS

Title

Page No.

THERMAL Thermal Barriers

89 89

ELECTRICAL

90

87

Listof Figures Fig No. Title 7.1

7.2

Page No.

MechanicallyClosed InsulatingWeb

90

Poured Resin InsulatingWeb

90

List of Tables No.

Title

7.1

Thermal Conductivity 0-100°C

90

7.2

Electrical Conductivity

91

Page No.

88

THERMAL Aluminium has a high co-efficientof conductivity. It varies withthe different alloys but the value forpure aluminium is 244 W/m0C. SeeTable 7.1. This propertyis extremely useful whendesigningheat transferproducts,such as radiatorsand electrical heat sink units. It is obviously less attractive in those applicationswhere low heat transfer is required and it is then often necessary to in-corporatecomponents to improve the thermal resistance, e.g. thermally broken window sections. Thermal Barriers This solution to the therma transfer problem has been used in the building and constructionindustriesfor nearlythirty years. During this time, design and manufacturehasbeen refined so that now two majortypes of systems are in general use. In the first, Fig. 7.1, the thermal insulatingweb, or webs, is madefrom strip material nylon, polyamide etc. - fixed into position by mechanical closing of dovetail type channelsinthe aluminiumsections. Twoseparatesections are used enablingdifferent surface finishes or colours to be used. The closing methods vary between rolling, pressingand broaching,dependinguponindividualmanufacturers.Internalbroaching, can only be used in the case of double web sections.

Thesecond systemis frequentlyreferredto as the "pour and cut" method, Fig. 7.2. A specially formulated liquid resin is poured into a semi-closedchannel in the single aluminium section. After the resin has solidified,the connecting aluminiumstrip "a" is cutaway leavingthe thermalbarrier orbarriers. Aswith thefirstsystem, a doubleweb sectioncanbeproduced,inthis case byusingeitheraproprietaryinstantaneousdouble pourmachineor by a two pass procedureon conventionalmachines. Thestructural properties of thermal barrier materials will generally be below those of aluminiumand will varynotonly betweendifferentmaterialsbut alsoover atemperature range of -20°C to +80°C. It is good design procedure,therefore,to keep the thermal barrier materialas close as possible to the neutral axis of thefinal composite section. In practice,this is not always possible and examplescanbe seen in existingwindow systems wherethethermal barrieris offset. Inthese cases it is essentialthat extensive laboratory proving tests are carried out to confirm that the composite section has sufficient strengthand stiffness as wellas thermal performance.

89

Lips Mechanically Closed On Insert Aluminium

Resin Webs

Holding Web Cut Out "a"

Solid Insulating Inserts

Mechanically Closed

Poured Resin

Fig. 7.1 - Mechanically Closed Insulating Web

Fig. 7.2 - Poured Resin Insulating Web

Table 7.1 - Thermal Conductivity

0- 1000C

ALLOY 6063 6063A 6082 2014A

TEMPER

W/m°C

T4 T6 T4 T6 14 T6 T4 T6

* InternationalAnnealed

% IACS

197

50

201

51.1

197

50

201 172

51

184 142 159

43.7 46.7 36.1

39.8

CopperStandard

ELECTRICAL Materials that are good thermal conductors are in general also good electrical conductorsand this is certainlytrueof aluminium. Thecopper/aluminiumratio values for thermal conductivity run virtually parallel to those for electrical conductivity. A special alloy hasbeen developedforelectrical use-6101 A. Thismedium strengthalloy hasexcellent electricalconductivityandgood fabricatingcharacteristics. It isavailable in the T6 temper only. Comparedwith copper, an aluminiumconductorofequal current-carryingcapacitywill have cross-sectionalarea 84% larger but will be only 54% ofthe weight of the copper bar.

90

Table 7.2 - Electrical Conductivity Electrical

Resistivity

Conductivy

ALLOY

(20°C) Microhm

(200C) %IACS

6101AT6

3.133 max.

55.1 mm.

91

Temperature Coefficientof Resistance per°C

0.00364




SECTION8- TEMPERATURE

CONTENTS Title

Page No.

EXPANSION

95

MECHANICALPROPERTIES Creep Melting Point

96 96

93

95

List of Tables No.

Title

8.1

Coefficientof Linear Expansion (200 C - 1000 C)

95

Influence of Temperature on Propertiesas % of 25° C Values

96

8.2

Page No.

94

EXPANSION Although aluminium has a relatively highco-efficientof linear expansion,24x 10-6 per degree Cin its pureform,the low modulusofelasticityenablesthetemperatureinduced stresses to be held at a low level. These are usually two thirds of those induced in a similarsteelstructure. It is still recommended,however,that all long restrained structures likely to be subjectedto temperature variation and particularly those in dark colours are checked out in the design stage. Any excessivestresses can be reduced by fitting simple expansion joints. The general effect of alloying is to reduce the coefficient of expansion and relevantvalues forthe more common aluminiumalloys are shown in Table 8.1. Table 8.1 - Coefficientof LInear Expansion (20°C - 100°C) ALLOY

TEMPER

106/0C

6063

T4 T6

24 23.5

6063A

T4 16

24

6082

T4

23

T6

23

T6 T4

23.5

16

23.5 22 22

6101A

6463 2014A

T4 T6

23.5

24

MECHANICAL PROPERTIES Variation in temperaturealso directly affects the mechanicalproperties of aluminium alloys. At low temperaturesthe structural strength and elastic modulus values are actually increased, whilst at higher temperatures they are reduced. A further important characteristicis that at low temperaturesaluminiumand its alloys show no brittleness which makes them extremely useful in cryogenic applications such as containers for low temperatures liquid gases. The more important properties are given for each of the alloys in Table 8.2. The dotted line inTable 8.2 signifies the maximumtemperatureat which itis recomendedeach alloycancontinuouslybe used. Some official codes will accept highertemperaturesin specific applications- BS5222 "Aluminium PressurePiping" sanctionstemperaturesup to 2000C. Note: special alloys have been developed for high temperatures applications, contact extruders for performancedata and availability.

95

Table 8.2 - Influence of Temperature on Properties as % of 25°C Values

Alloy Temper

Stress

606316 Ult

Temoerature -200 -100 25 100 150

130

0.2% PS 115 608216 Ult 130 0.2% PS 115

2014AT6

Ult

124

0.2% PS 125

200

110 105 110

100 100 100

95 95 95

65 20 65 I 20 70 I 40

105 108 109

100 100 100

95 85 87

44 41

10 10 10 5

L40 191

11

17

10

Modulus

of Elasticity

300

I

110

105

100

100

95

90

70

Creep

At elevated temperatures under the prolonged application of a stress of sufficient magnitude,metalwill"creep"and may eventuallyrupture.This behaviour,the progressivedeformationwithout increasein load, does notenterinto the designconsiderations for structures operating below 100°C but may require study in high temperature applications. When creep is consideredto be adesign factor, moreinformationshould be obtained from the material supplier.

Melting Point As aluminiumapproachesits melting point it does not change colour, so othermeans such as temperature sensitive crayons, must be employed if a visual check on the temperature is required. While pure aluminium has a well-defined melting point of 660°C, aluminium alloys have a meltingrange which, forthe alloys listed in the Table 8.2, varies from 570°Cto 660°C.

96



SECTION9- FIRE

CONTENTS Title

Page No.

ALUMINIUMANDFIRE

97

99

List of Tables No.

Title

9.1

BS 476 Fire Test Series

Page No.

98

99

ALUMINIUM AND FIRE ALUMINIUMDOES NOT BURN. It will not ignite. Itwill not add tothe fire load. It will not spread surface flame. Although aluminiummelts at around 620°C, it has athermal conductivityof fourtimes that of steel and a specific heat twicethatof steel. Heat isconducted away faster and therefore agreater heat inputis necessarytobring aluminiumupto agiventemperature than required for steel. In any applicationrequiringa structuralfire resistancemeasured against time, a test certificate is usually necessary. Although aluminiumcomponents have obtained approvals above 30 minutes in tests it is not possibleto make accurate predictions. It is necessary,therefore,to obtain atestapprovalfor eachtypeof application. Where highertime ratings are required, aluminium must be used in conjunction with other conventional fire-resisting materials.

The more usual fire performance requirements for aluminium extrusions can be obtained from the results of the British Standardstestsshown in Table 9.1. Table 9.1 - BS 476 Fire Test Series Part No.

Aluminium Results

Title

*4

Non-CombustibilityTest

Non-Combustible

*5

ignitibility Test

P, not easily ignited

*6

Fire PropagationTest

P. actual index will

*7

Surface Spread of FlameTest

Class 1. Painted surfaces will reduce performancerating

21 1 22 23

Time/Structural Resistance& Insulation Test

vary with thickness

** individual component testing required

99

The BritishStandardfire testsare laid down in BS 476 and define results irrespective of materials. Aluminiumand its alloys achieve the highestpossibleratingsfor parts 4, 5, 6 and 7 and are therefore widely used throughout the construction and other industries where the highest standards of performance are required. Painted surfaces could, however, reduce the levels of performance.

Tests 21, 22 and 23 are used to obtain the performanceof a component or unitfor strength, integrity and insulation, all compared to time against closely calibrated temperature levels. **

It is usualfor aluminium extrusions,in these instances,to be used in conjunction with other materials to obtain resistancetimes in excess of 30 minutes.

*

Indicated highestpossible rating.

100



SECTION 10- CARE ANDCONTROL

CONTENTS

Pag No.

Title INTRODUCTION

102

HANDLING

102

STORAGE

102

MAINTENANCE

103

101

INTRODUC11ON

In post-extrusionhandling,every care is taken by extrudersto minimisedamage. It is essential that this "good house-keeping"is continued in customers'works and warehouses. As with other high quality materials,carelessnesscan cause unnecessary rejection, resultingin higher productioncosts. HANDLING The following recommendedpractices should be followed:-

(1) Single lengths should never be pulled longitudinallyfrom the middle of a bundle of aluminium sections as the entrappedend will score adjacent sections. (2) Cleanlinessis very important,particularly with sections to be anodised. Gloves should be worn whenever dealing with this typeof section as the natural oil from the hands can cause finger print corrosion which will become apparent at the etching stage of the process. (3) When lifting by crane, double slings should be used as single slings can cause bending damage particularly with bundles of long, light sections. (4) The sectionsshould always have adequatesupportwhen liftedby a fork-lifttruck. STORAGE Although aluminiumalloys are very resistantto atmosphericcorrosion,certain simple precautionsshould be taken duringtheir storage. All materialsshould be storedaway fromexcessivedustor fumes; particularlywhen portable gas or oil heaters are used, for as wellas pollutantsthese heaters also produce moisture. Storagespacesshould be dry and well ventilated and kept at a constant temperature above 16°C. Any superficial corrosion that occurs on extrusions is usually easily removed by hand cleaning with white spirit. Even the most severe superficial corrosion responds to cleaning with finewire wool and white spirit. The moretroublesomeform of staining is water marking,caused by moisture ingress betweensections that are closely nested, e.g. angle bars. Thiscan occur directly or by condensation. In the latter case, it is possiblefor the moistureto work upwardsby capillary action. Stacking in a self-draining position is therefore no solution. It is, however, easily avoided by spacing the sections and ensuring that moisture can not bridgethe gap. Thestain canbe removedby wire-brushingand chemical treatment. Storage staining and corrosion will not usually have any detrimental effect on the mechanicalproperties of the material.

102

Vertical racks are preferred for storage. If horizontal storage is unavoidable, care should be taken not to overloadracksand to supportlight sections adequatelyto avoid local damage atthe points ot support. Timberrubbing bars should be fitted to steel racksto minimiseabrasion and to avoidspots which could cause condensationunder adverse storage conditions. Racking should be arrangedto facilitate easyinspectionwhich should be carried out at regularintervals. As mostaluminiumalloys look alike, materialsshould be stamped or colour-coded so that different alloys and tempers can easily be identified. This would not be necessary where an alloy or temper is consistentwith a special shape. It is also usefulto mark batches on arrival in store to ensure that they are used in the original delivery sequence. MAINTENANCE Aluminium alloys require little or no maintenanceto retain their original mechanical properties. Without regularcleaning,however,surfacescanbecome stained particularly under prolonged exposure on industrial sites. Mill-finishedaluminium can be cleaned by rubbing down with finewire wool and white spirit. Anodised surfaces are more resistantto staining but, nevertheless,benefit from regular washing down with soapy water. Proprietarycleaners are available for both mill finished and anodised surfaces but should they be used, it is absolutely essential that the manufacturer's instructionsare strictly adhered to.

103




SECTION 11 - DESIGN

CONTENTS Page No.

Title DESIGN PROCEDURE

107

VALUEANALYSIS

107

PRACTICALDESIGN FEATURES

109

WORKEDEXAMPLES UnloadingRamps PedestrianBalustrade

111 111

Columns

105

113 123

Listof Figures Fig No. Title

Page No.

11.1

Steel and Aluminium Beams

108

11.2

Examplesof Solid Section Aluminium

108

11.3

Built-in MechanicalFastener

110

11.4

Advantagesof Aluminium Versus Steel

110

Various Snap Fit Connections

110

11.5

106

DESIGN PROCEDURE

Indesigningasection,itisusualto haveaperformancespecificationsettingoutthetotal requirements of both section and material. This could be part of a much wider specificationfor a completefinished product ofwhich the aluminiumextrusion is only one of the components. The extentand detail requiredfor such a specificationwillvary with the applicationand also within different industries. It is good design practice to have such a "check list" providing, as it does, a target of what needs to be achieved and alogical procedurefor assessingdifferentideas. Acomprehensivelistofdesign considerations is set out in Appendix 1. Rarely will all these factors need to assessed and a moregeneral approach is given in the following flow chart. Idea Performance Specification I Material Selection

4

I

Fabrication

Appearance

I Mechanical

I••

Durability

Properties

I.

Machining

Shape

Strength

Atmospheric Electrical Conductivity

Forming

Surface Finish

Stiffness

Chemical

I

Jointing

Hardness

I.

Unit Special Requirements Cost

.1..

Availability

Unit Weight

Fatigue

VALUE ANALYSIS Although basic materialcost isimportant,itshould be balancedagainstthe overallcost of fabrication and subsequentservice performance. This is particularly relevant to aluminium extrusionswhere shapes can be produced that require little or no further fabrication and the aluminiumalloys availablehave characteristicssuitable for awide range of applications. Aluminium extrusions are usually sold by weight which tends to encouragecomparison with other materials on a straight weight/cost basis. This in unrealistic as compared with steel, allowingfor the lower elastic modulus, aluminium/steelweight ratios of 1 : 2 are easily attained to equal performancespecifications.

107

..

100

145

0L Steel 21.7 kg/M

150

Aluminium 10.6 kg/M

Ag. 11.1 - Steeland Aluminium Beams Thetwo beams in Fig. 11.1 have been designed for equal stiffnessin both xx and yy axes. The strength of the aluminiumbeam is well over twice that of mild steel if alloys 2014A 16 or 6082 T6 are used. It is importantalways to check the actualdeflectionrequirementas in many cases the steel design has been stress based and the corresponding level of deflection is automaticallyaccepted without considerationof the real level required. The economic use of aluminium alloys is not just confined to comparisonswith steel and other materials. The proficient use of extrusions can frequently result in comparisons with other aluminium profiles to obtain the optimum shape. Fig. 11.2 illustratesthe design of solid sectionsto give good strengthand stiffness in both major axes instead of a more expensivehollow section.

ii

[1

ft_

11

Fig. 11.2- Examples of Solid SectionAluminIum

108

Inothercases,the useofstandardstructuralsections is moreappropriate. Two ranges of I beams,channels,Tbars and anglesare available,namelythe speciallydesigned lipped sections conforming to BS 1161 and the range covering structural sections similar to the universalsections used in the steel industry.

in manufacture,the availabilityof sectionsthat require little or no fabrication can be a majorfactor in reducingfinal componentcosts. Thisequallyappliesto site erection

where, apartfrom light weight, the ability to use hiddenfixings can simplify procedure. PRACTICAL DESIGN FEATURES Replace several parts One extrusioncan oftendo thework ofseveral structural shapesjoined togetherand produce a neater, sounder design,at less cost.

Place metal where It is most effective Thus, bulbs,fillets and variationsin thicknesscaneasily be incorporated for structural advantage and local increasesof thicknesscan beintroduced tocounter wear and abrasion orpermittappingofscrews. The two bulbs, and root buteress improve inertia and section modulus values as well as increasing torsional resistance.

Hinge Fits Continuous hinges with built in stop bars plus screw groove forend stops.

Aslidefitwhichallowsone shapetomoveinacirculararc with respecttotheother.

109

Slots, holes and threads for mechanical fasteners can be extrudedas integralfeatures.

Adjustable locking connection.

FIg. 11.3 - Built-in Mechanical Fastener

Typical early steelframe section.

Typical aluminium frame section.

FIg. 11.4- Advantagesof AluminiumVersus Steel

Retractable Cover

Locking Cover

Fig. 11.5 - Various Snap Fit Conections 110

Adjustable Locking

WORKED EXAMPLES

UnloadingRamps Singlelengthsofchannelbar are frequentlyused intandemto unload wheeledvehicles. In the interests of good working practice, they should always be longitudinally and transversely restrained. There are severalwaysof calculatingthe size required. The followingmethodis based upon simple point load bending without any axial component. it is assumed that unloading is always controlled and no unusualdynamic loads will occur.

Slope Q in degrees

Specification. The rampsshould be a maximumweight of 50 kg each. Span 2.5 metres. Operatingangle up to 30 degrees. Maximumvehicle load2.0 tonnes equally shared on fourwheels. Maximumtyre width 200 mm with 25 mm clearance.

Theinitialchoice of sectionsize isgovernedby the final specificationrequirement,that of typewidth and clearance. Channel Section : 254 x 88 x

11

web x 14 flanges (all in mm)

Section properties: Area

5030 mm2

Modulus

Zxx

54620 mm3

Inertia

lxx

3459100 mm4-

Radius of Gyration Weight/metre Alloy

26.2 mm 13.39kg/m 6082 T6

111

Note: as section is used in this plane check with propertytables to confirm the wayx & y axes are given

Asthevehicle isunloadedit movesoutofthe horizontalwith aconsiderable shift in its neutralaxis and the loadingon thefirstsetofwheels increasing. This will be a feature of the individualvehicle. Forthe purposesofthis calculation it is assumedto be 10%, hence Loading.

Maximum individual wheel load

= 1 9640N (2 tonnes) x 1 10 = 5400N 4

100

Bending Stresses. The ramp acts as a simply supported beam and with normal wheelbasedvehicles will have a central load as the worst condition. (Load Case 2.)

M=

WL = 5400N x 2500mm 4

4

Maximum bending moment = 3375000 Nmm Maximum Stress =

3375000= 54620

fbc= 61.8N/mm2

Allowable Stress Levels. See Table 3.2 (From British Standards CP1 18) 6082 T6 alloy Bending

p,

154N/mm2

Deflection

8 =

For 6082 E = 68,900N/mm2 48El

8 =

5400x 2500 48 x 68900 x 3459100

8 =

7.45mm

The deflection/spanfactor =

336 which is well insidethe recommendedvalue of 200

Lateral Instability. It is usuallyadvisableto checkthe ramp for lateral instability. The methodforcalculatingthis canbefound in BS CP1 18. Thecross-tyingofthetwo ramps together with lateral ties will dramatically increasethe resistanceto lateral instability, but in thiscase, with thestronger axis ofthe section acting transversally,instabilitywill not occur.

112

Pedestrian Balustrade Specification. To enclosean external pavedareawithintheconfinesofan officeblock. Therailingsmustmeetthe requirementsofthe appropriateBritishStandardsandwhilst being functional should have an attractive appearance. Low maintenance is also essential. BS 3049 Pedestrianguardrail BS 6180 Protective barriers in and around buildings. In this instance BS 6180 applies. As it isa possible areaof assembly,althoughin anofficedevelopment,two categories of use are applicable. From BS 6180 Table 1 Type 4 Type 7b

Office building Placeof assembly

LOAD FACTORS Tables 2 and 3 from BS 6180 TYPE

4

7b

HORIZONTAL U.D.L. kN/M

INFILL

0.74 1.5

1.0 1.5

IJ.D.L. kN/M2

INFILL MINIMUM POINT LOAD BARRIER HEIGHT

kN 0.50 1.50

mm 1100 800

Access will be controlled and private so that type 4 will apply. Material.

Aluminium alloy 6063 T6 will meet all the requirementsof surfacefinish durability low maintenance

It is also an approved material in BS 6180 and its structuralcharacteristicsare set out in BSCP 118.

113

.r 76x50 Top rail

70x70x2.5 Posts

—30x30x2 Balusters E

—100mm Max Gap

E 0 0

50x54 1lOOmm

1500mm

1500mm

FabricationDetails Main stanchions: Theseare tobesetdirectly into concretefoundations.Thestanchion base overthe areato be bedded intothe ground is to be giventwo coats of bituminous paint.

Topandbottom rails: Theseare to be connectedtothe stanchionsusingbolted lugs. Bolts to be stainless steel to 18/8 specification. Balusters: These are to be slotted intothetop rail and intopunchedslots inthe bottom rail, then welded intoposition on both top and bottom rails. Surface finish: A natural anodized finish is required to AA 25 suitable for external application. This will necessitate the infill panels being anodized as single units. Check availabilityof suitable facilities.

114

SectionDesign Thefollowing sectionshave been drawn upto meet the requirementsof the performance specification.

76

::

70

Rad.: 70

Overallthickness 2.5mm

—I

lop rail

Stanchion

54 2mm

50

Baluster Bottom rail

STANCHION

TOP RAIL

Area

661 mm2

CCD

99mm

Shapefactor 298

Area 585 mm2 CCD 89mm Shape factor 334

BALUSTER

BOTTOMRAIL

Area

215 mm2

CCD

43mm

Area 300 mm2 CCD 74mm Shapefactor 370

Shapefactor 370 115

The CCDs are wellwithin the capacityof most medium sized presses with container diameters of 150 mm. The shape factors are slightly above average,but still acceptable. Thethicknesses have been checked out against Table 1.2 and are within the level required for 6063 material. A further check is necessaryon the top rail forboth the extrudabilityratios of the semienclosedareaand the depth/width ratio of the side channels. 59 mm x 45 mm = 2655 mm2

=

Large recess Gap Area/gap2 ratio

= 31 mm = 2.76: 1

Gap2

= 961 mm2

The section can be classed as a solid and the extrudability is acceptable. Side channels Depth Gap Depth/gapratio

17.5 mm = 3.5 mm = 5:1

This is not acceptable so it is necessary to reduce the outer flange from 20 mm to 13 mm.

The internal depth of the channel is now 10.5 mm Thedepth/gap ratio is now 3 : 1 This is now acceptable and the new top rail section details are as follows: = = =

Area CCD Shape factor

550 mm2 89mm 314

Section Properties STANCHION

-

Area Modulus Z Inertia

TOP RAIL (modified)

-

BOTTOMRAIL

-

I

Area Modulus Zy Inertia ly

Area Modulus Zy* Inertia ly * *effective area values (less slot area) 116

661 mm2 14190 mm3 496680 mm4

550 mm2 11150 mm3 423740 mm4

300 mm2 5650 mm3 152500 mm4

-

BALUSTERS

Area Modulus Z Inertia I

215 mm2 1838 mm3 27600 mm4

Loading

The load is appliedto the stanchionthrough the top rail.

STANCHIONS

740N1M x 1.5M = 111ON

Hence load RAILS

The loadfor the top and bottom rails is the same as thatfor the stanchions. Hence load

BALUSTERS

=

..WL

=

Z

=

=

8Z

=

WI.

=

8Z

Y.L.

4Z

lllONxl500mm 8 x11150mm3 Load Case

=

86.OON/mm2

lllONxl500mm

Two span, simply supported UDL =1886N/mm2

Simply supportedUDL = 36.BON/mm2

8x5650mm3

BALUSTERS f =

Cantilever

14190 mm3

BOTTOM RAIL

f

lllQNxllQOmm Load Case

- YL.

500N

Load Case

TOP RAIL

f

111ON

Central point load

STANCHIONS

f

=

Load Case

=

500N x 100mm

4x1838mm3

117

Simply supported central point load

=

68.OON/mm2

From CP 118 "StructuralUseofAluminium",the allowablestress levelsfor6063 T6 are as follows (see Tables 3.2 and 6.11) Bending

96N/mm2

Shear

52N/mm2

Welded areas Heat affected zones

Bending

31N/mm2

Shear

19N/mm2

Welds (throatarea)

31N/mm2

Assessment of bending stresses. STANCHIONS No welding. Allowablebendingstress 96N/mm2 Section acceptable TOP RAIL Heat affected zone is in maximumbending position. Allowablestress level 31N/mm2. Section acceptable. BOTTOMRAIL Heat affected zone in maximumbending position. Allowablestress level 31N/mm2. Section not acceptable - re-design BALUSTER Heat affected zone clearof maximum bending position. Allowable stress level 96N/mm2. Section acceptable. 54

Redesignof Bottom Rail.

Large bulbs placed at toesof flanges and merged into 2 mm thickness by 45 degrees fillet to ease transition.

Newextrudabilityfactors Area CCD Shape factor

= = =

350 mm2 74mm 335 118

New geometric properties (effectiveless slot area) ModulusZy Inertialy

=

6830mm3 184410 mm4

=

Re-checkbending stress

= lllONxl500mm =30.5Nfmm2

= 8Z

8 x6830

Allowablestress for heat affected zone material from Table 6.11

=

31N/mm2

New section acceptable.

Weld

Weld Strenath Baluster

Thebalustersare slottedintothetopchannelandwelded in position. They stand on the top ofthe bottomchannel web and arewelded intoposition.Thetopweldshold the balusterin the line ofthe top rail and do notdirectlytake the full load. This is also the case at the bottom ofthe balusterand itis reasonable, therefore, to consideronly the bottom rail.

Weld 25mm each side (no transversewelds)

Consideraweld leg lengthof3mm. Thecriticaldimension weld design isthe throat width. It isusual to define this dimensionas afractionof the leg length.

Throat LegI

For 90degreesangle throat factor=0.7.

Weld

Throat width = 0.7 leg length = 2.1 Effectiveweld area = length of weld x throat width

5Ommx2.1 mm=105mm2

Shear load on weld

= QQII

=

250N/mm

=

2.3NImm2

=

19N/mm2

2

Stress in weld

=

QJ

105 mm2 Allowablestress in weld material

With such ahigh safety factor,the balustercan be weldedtothe bottom rail in a similar manner to that at the top, on the longitudinalsides only. Weld strengthacceptable,topand bottomwelds resistingdownwardloadwithtopweld also resistingsideways load. 119

TIG WELDING Electrode dia.

rod dia.

Nozzle Bore

mm

mm

2.4

2.4

Filler

Alt.

Weld speed

mm

Argon flow Llmin

current A

mm/mm

9.5

5.7

110

190

Weld passes

1

No edge preparation and no gap between sections. Filler rod material - 4043 or 5356 This material would give better colour match after anodising Deflections.

STANCHIONS 6

=

Load Case

WL3

=

TOP RAIL =

Load Case WL3

=

BOTTOM RAIL =

BALUSTERS =

lllOx 1500

=

5x1110x15003

LoadCase

1.3 48E1

0.73mm

Simply supported UDL

=

3.93mm

384x65500x 184410

384EI

8

Two span, simply supported UDL

Load Case

=

15.14mm

185 x 65500 x 423740

1 85E1

8

=

1110x11003

3 x 65500 x 496680

3E1

8

Cantilever

=

500x l000

central load Simplysupported =

5.70 mm

48 x 65500x 27600

Allowable Deflection. BS6180sets out a maximumdeflectionstandardof 12 mm but calculatedon the basis of: Aoolied load + wind load

2 120

This requires a wind load assessmentto be made using BS CP3 chapter V "Wind Loading". It is necessaryto know where the installationis to be, as thewind code lays down a map of basic wind speeds related to area and on which the dynamic wind pressure is based. Birminghamand the West Midlandsare in the 44m/sec area. This value is, however,factored for there are other considerations:

Si Topography (site exposure)

i

For urban areas the value is .00. S2 Ground roughnessand height For urban areas the value is 0.56 in this case. S3 ProbabilitylevelsTheprobabilityofthe maximumdesign wind speed being exceeded. Theusualfactor is once in 50 years and the value is 1.00. Wind speed is therefore: 44 x 1.00

x 0.56 x 1.00 = 25 m/s.

Dynamic Pressure = 383N/m2 Total area per panel span of balustrading = 0.59m2 Wind load = 383

x 0.59 = 226N

The worst case is the stanchionwith an actual deflectionof 15.14 mm. Therefore considerthe stanchion. Code BS61 80 requiresthe deflectionto be consideredusing an equivalenttotal load which equals: Basic load

+ Wind load 2

121

And where the resultingdeflection should not exceed: Span between stanchions 125

Equivalentdesign load

=

111ON

+ 226N =

668N

2

Stanchion deflection with load 668N = 9.20 mm Permissibledeflection

= j.QQ =

12mm

125 Stanchion is acceptable.

It is obvious that allthe other sectionswill meet the deflectionstandard. Temperature. In hot sheltered sites thermal expansion should be considered and in general it is preferable to fit expansionjoints in long runs of balustrading. Assumed erection temperature

16°C

*Max surfacetemp. on aluminium 36°C 20°C

Temperature rise

*Thiswillvaryonthe degree of sun and wind as well as onthe colourofthe aluminium.

= 23.5 x

Thermal expansion of 6063

1 061°C

Fit expansion joints at 15 metre intervals Expansion = 23.5 x

=

10-6

x 20°C x 15000 mm

7.1 mm

Stress induced in the rails if this expansion is not relieved can be obtained from: Stress Strain

= =

E

69000M/mm2

x

7.1 mm

=

32.4N/mm2

15000mm

If expansionjoints are not fitted, the 32.4N/mm2stress will be absorbedaxially down the rail. To check the ability of the rail to withstand this stress it will be necessary to calculatethecombined bendingand axial compressionin asimilarmannerto that given 122

inthe columnexamplepage 11.20. The bottom rail, however,is performingvery close to its allowable stress level e.g. 30.5N/mm2 to 31.ON/mm2. Therefore it will not withstandthe extratemperatureinducedstress. Expansionjoints at 15 metre intervals are therefore necessary.

The above proposed design meets all the requirementsof BS 6108 and is therefore acceptable.

Columns a)

An aluminium alloy column, 1 metre long, is fixed and restrained at both ends. The cross section is a 50 mm x 50 mm x 2 mm hollow box and subjectedto a 62 kN concentric load. It is necessaryto confirmthe most appropriate alloy and temper.

Section Properties 384 mm2 5910 mm3 19.6 mm

Section Area Section Modulus Radius of gyration Actual axial stress

f

=

Load

Cross sectional area =

62000 = 161.5N/mm2 384

As the column is rigidly held at both endsthe effective length from Table 3.3

= o.7L = 700 mm X

=

Effective Lenath

Radiusof gyration

=

700 mm = 35.7 19.6 mm

Using this value in the strut curve Fig 3.3 the 35.7 vertical ordinate gives the permissible axial stress for a numberof alloys and tempers. Pc = 163N/mm2 for 2014A T6

A 50 x 50 x 2 mm box hollow in 2014A T6 is acceptable. b)

If the load in the above column is offset by 10 mm, will the column still be strong enough?

Theloadeccentricitywill inducebending stressesas well as axial stressesintothe column.

123

The simplestwayto checkistoconsiderthe axial and bendingstressesindividually and then check against the requirementsof the combined stresses.

Theaxial stressat 161 .5N/mm2 is 99% or the permissiblestress of 163N/mm2so there is obviously no allowance left for bending in the original section. Increasesection size to 70 x 70 x 2.5 mm boxalloy 2014A T6. Section properties 675 mm2 14670 mm3 27.6 mm

Section Area Section Modulus Radius of gyration =

700mm = 25.4 27.6 mm

FromFig. 3.3 25.4 ordinatefor 2014AT6 Givesthepermissiblestress = 177N/mm2 Actual axial stress from concentric load

fc fc

Load Cross sectional area =

f bc f bc

f

= bc

62,000N x 10mm 620,000 N mm Moment

Section modulus =

62.000mm 675mm2

92N/mm2

Induced bendingstress Moment = =

=

= 620.000N mm 14,670 mm3

42.3N/mm2

Permissiblecompressive bending, stress for 2014A 16 from Table 3.2 =

202N/mm2

Individuallythe bending and axial stress levels are within thepermissiblestresses laid down in BS CP 118, but the should be checked against combined stress allowances.

124

For combined bending and axial compression

I bc

+

Pc

must not exceed 1

Pbc(1-J Pe

Where

fPcc 5 bc Pbc

Pe

axial compressivestress permissibleaxial compressivestress compressivestressesdue to bending permissiblebending compressivestress Euler critical stress for buckling

where Pe =

Pe

it2

x 72.400 =

1108N!mm2

25.42

fc

Pc

5 bc Pbc Combined stresses

= = = =

92N/mm2 177N/mm2 42.3N/mm2 202N/mm2

= .52 + .23 < 1 = .75 < 1

New 70 x 70 x 2.5 mm box section in 2014A T6 is within combined stress requirementsin BS CP 118. Further modificationscould be carried out by reducingthe size of the section in order to obtain a moreefficientsolution and thereby approximatingthe combined stress ratios towards unity.

125




GLOSSARY OF TERMS Term

Definition

Ageing

Precipitationfrom solid solution resulting in a change in properties of an alloy, usually occurring slowly at room temperature (natural ageing)and morerapidlyat elevatedtemperatures(artificialageing).

Angularity

Conformity to, or deviation from, specified angular dimensions in the cross sectionof a shape or bar.

Annealing

Thermal treatment intended to soften a metal or alloy hardened by cold work or artificialageing.

Anodizing

An electrochemicalmethod of producing an integral oxide film on aluminium surfaces. See Section 5.

Anodizing

Describes material with characteristics that make it suitable for decorative anodizingaftersuitable preliminary treatment.

Quality Billet

A cast aluminiumproductsuitableforsubsequentextruding.Usually of circular cross-sectionbut also may be rectangular.

Bow

The deviation, in the form of an arc, of the longitudinal axis of a product.

Bright anodizing

A process used to obtain highly reflective and bright anodized

Buffing

A mechanical finishing operations in which fine abrasives are appliedto a metal surfaceby rotatingfabric wheels for the purpose

surfaces using alloy 6463.

of developing a lustrousfinish. Burr

Athin ridgeorroughnessleftby a cutting operationsuch as routing, punching, drilling and sawing.

Chemical brightening

Treatment to improve the reflectivity of a surface.

Circumscribing

(CCD)A circlethatwilljust containthe crosssection of an extrusion, usually designatedby its diameter. 127

circle diameter

Cold work

Plastic deformation of metal at such temperature and rate that strain hardeningoccurs.

Concavity

A concave departure from flat.

Concentricity

Conformityto acommoncentre as, for example, the inner and outer walls of round tube.

Container

A hollow cylinder in an extrusion press from which the billet is extruded.

Conversion coating

Treatment of materialwith chemicalsolutionsby dippingorspraying to increasethe surface adhesion of paint. See Section 5.

Corrosion

Thedeteriorationof a metal bychemicalor electrochemicalreaction with its environment. See Section 4.

Direct extrusion

A process in which a billet in the containeris forced under pressure through an aperture in a stationary die.

Drift test

A routine samplingtestcarried outon hollow sectionsproducedby

bridge or porthole methods, in which a tapered mandrel is driven into the end of the section until it tears or splits. Drawing

The process of pulling material through a die to reduce the size, change the cross section or shape, or work harden the material.

Etching

Theproductionof a uniform mafl finish by controlled chemical (acid or alkali), treatment.

Etching test

Thetreatment of a sample using a chemical reagentto reveal the macro-structureof the material.

Extrusion ratio

The ratio of the cross-sectionalareaof the extrusion container to that of the extrudedsection (or sections in the case of multi-cavity dies).

Fillet

A concave junction betweentwo surfaces.

Flutes

Longitudinalconcavecorrugationswith sharpcusps betweenthem used to break up the surface decoratively.

Free machining An alloy designedto give small broken chips, superiorfinish and/or alloy longer tool life. Full heat treatment

Solution treatment followed by artificial ageing. 128

Grain growth

The coarsening of the grain structure occurring under certain conditionsof heating.

Grain size

The mean size of the grain structure usuallyexpressed in terms of the numberof grains per unit area or as the mean grain diameter.

Hardness

The resistanceof a metaltoplasticdeformationusuallybycontrolled indentation.

Heat treatable

An alloy capable of being strengthenedby suitable heat treatment.

alloy

Homogenization A high temperature soaking treatment to eliminate or reduce segregationby diffusion. Indirect extrusion A process wherebya moving die locatedat the end of a hollow ram is forced against a stationary billet. Mean diameter

The sum of any two diameters at right angles divided by two.

Mean wall thickness

The sum of the wallthickness of tube measureat the ends of any two diametersat right angles, divided by four.

Mechanical properties

Those propertiesof a material that are associatedwith elastic and inelasticreactionwhenforce isapplied,orthatinvolvethe relationship between stress and strain. These properties are often incorrectly referred to as physical" properties.

Modulus of Elasticity

The ratio of stress to corresponding strain throughout the range wherethey are proportional.Also referredto as "Young'sModulus".

Modulus of Rigidity

The ratiooftheunit shearstress,inatorsion test,tothe displacement caused by it per unit length in the elastic range.

Non-heat treatable

An alloy incapable

Ovality

The departureof the cross section of a round tube, bar or wire from

Percentage

The increase in distance between two gauge marks that results from stressing the specimen in tension to fracture.

elongation Physical properties

of being strengthenedby thermal treatment.

a true circle.

The properties,other than mechanical,that pertain to the physics of a material;for example, density, electrical conductivity,thermal expansion. 129

Pitting

Localised corrosion resulting in small pits or craters in the metal surface. See Section 4.

Porthole die

An extrusion die that incorporatesa mandrelas an integral part of itsassembly. Bridgeand spider are specialforms of this typeofdie, which are used to produce extruded hollow products from solid extrusion billets.

Proof stress

The level of stress used to signify the limit of proportionality designated at the point of 0.2% strain for aluminium and it alloys.

corrosion

See Section 3. Quenching

Controlled rapidcooling of a metalfrom an elevatedtemperatureby contact with a liquid, gasor solid.

Residual stress That internalstresswhich is left in afinished productafterfabrication. Sealing

A treatment applied after anodizing to reduce the porosity of the surface.

Segregation

Non-uniform distribution or concentrationof impurities or alloying constituentsthat arises during the solidificationof a billet.

Solution heat treatment

A thermal treatment

Stabilizing

A thermal treatmentto reduce internalstresses in order to promote

Stepped extrusion

An extrudedshapewhosecross sectionchangesabruptly in areaat

Stretching

The straightening of extruded and drawn materials by imparting

Tempers

Stable levels of mechanicalpropertiesproduced in a metal or alloy by mechanical or thermal treatments.

Twist

A winding departure from flatness.

Ultimate tensile strength

The maximum stress which a material is capable of sustaining in tension under a gradual and uniformly applied load.

in which an alloy is heated to a suitable and held for sufficienttimeto allowsolubleconstituents temperature to enterintosolid solutionwheretheyare retainedinasupersaturated state after quenching. See Section 2.

dimensional and mechanical property stability. intervals along its length. sufficient permanentextensiontoremove distortion. Specificlevels of stretching (permanent set) can be imparted to relieve internal stresses.

130

Waterstains

Superficial surface oxidization due to the reaction of water films held betweenclosely adjacentmetal surfacessuch as nested angle sections. The appearancevaries from iridescentin mild cases, to white, grey or black in more severe instances.

ABBREVIATIONS *N

E = Young's modulus of elasticity G = Torsion modulus r = Radius of gyration k = End fixity co-efficient = Slendernessratio 8 = Deflection

=

Newton

= kiloaramme gravity

* P = Pascal = N/m2 = Micron P = Stress suffix - - tension c - compression * iN/mm2 = 1MPa both terms are used to define stress

t

levels

131



design guide

LISTOF APPENDICES No.

Title PageNo.

APPENDIX 1

DESIGN CONSIDERATIONS

135

APPENDIX 2

BEAM STRESSAND DEFLECTIONTABLES

139

PREVIOUS B.S. DESIGNATIONS

153

COMPARISONOF NATIONAL SPECIFICATIONS-WROUGHTALLOYS

155

CHEMICALCOMPOSITION LIMITS AND MECHANICAL PROPERTIES

159

APPENDIX 3 APPENDIX 4

APPENDIX 5

133




APPENDIX 1 - DESIGN CONSIDERATiONS

135

Thefollowing list containsmost potentialconsiderationslikelyto arise in the design of aluminium extruded products. ALLOY TEMPER MECHANICALPROPERTIES -

0.2% proof stress Ultimate stress

% elongation Compressive strength Axial loading - column length end fixing load eccentricity Shear stress Bearing stress (jointing) Surface hardness Torsion Fatigue Stiffness SECTION DESIGN

- Size, shape and thickness Production availabilityand section extrudability Geometric properties Weight Tolerance Value engineering

SURFACEFINISH

-

Mill Etched

Shot blasted Anodised - Natural Colour (organic) Colour (metallic) AAthickness Protective anodizing - Colour Paint Electrostatic(Powder Spray or Wet Spray) Electrophoretic(Wet Dip)

136

JOINING

- Welding

-

TIG Filler wire MIGJ

Gas Welding Brazing

Rivetingi Bolting

I

Screwing

-

Bearing strength Choice of fastening material Screw material and size Pull out strengths

Corner crimping Adhesives - Type Strength Applicationdetails FABRICATION

-

Bending

-

Alloy and temper Tooling Twisting Necking

Machir;ing -

Springback Routing Drilling

Sawing TEMPERATURE

- Expansion/Contraction Effect

CONDUCTIVITY

-

on mechanicalproperties

Heat transfer Electrical

DURABILITY

-

Atmospheric

-

Environment -

Chemical

-

Substance Concentration Temperature Design of Bi-metallic connections

Rural Marine Industrial

Compatibility -

FIRE

-

Melting point Non-combusibility

Non-ignitability Fire propogation Surface spread of flame Structuralresistance

137




APPENDIX 2-

BEAM STRESSAND DEFLECTIONTABLES

139

Stresses

Typeof Beam

GeneralFormulafor Stress atany Point

Case 1.- Supportedat Both Ends, TOTAL LOAD W

fjfjjfijf4

Points

Stress at centre,

UniformLoad

2

StressesatCritical

If

s=-

cross-section is

constant, this maximumstress.

2 Betweeneachsupport Stress at centre, andload,

Case 2.- SupportedatBoth Ends, Loadat Center

S= -

If

2Z

is the

-

cross-section

constant, this maximumstress.

is

is the

2

2

For segmentof length

Case 3.- SupportedatBoth Ends, Loadatany Point

a,

5=-x ZI

Stressat load - wa

If

cross-section is

For segmentof length constant, this maximumstress. b,

I

I

ab1

Case 4.- SupportedatBoth Ends, TwoSymmetricalLoads

TId w

w

-

w

S

Way

—-

Between each support andadjacentload,

s=

-z

Between loads,

w

z

140

is the

Stress at each load, andatallpointsbetween, Wa

Deflections

GeneralFormulafor Deflection atany Point

at CriticalPoints

Deflections

Maximumdeflection,at centre,

W(I-)

V3

——

24E11 '12÷x(I-x)J

El

384

Betweeneach supportandload, Maximumdeflection,atload, WI3

4BEl (312-4x2) For segmentoflength a, —

6E11

(I2--b)

For segmentoflength b,

4E7

Deflectionatload, Wa2b2

3E II Let a be the length of the shorter segment and b of the longer one. The maximum deflectionisin the longersegment,at

(12-v2-a2)

bv'jj

Betweeneach supportandadjacentload,

Maximumdeflectionat centre,

y=

=

Way

v=

Betweenloads,

"

Wa

- 6E I f3a (I a) x2)

'312-4a2)

Deflectionatloads

Wa

6E1 (3v(I-v)-a21

141

= v1, and is

(3/-4a)

Stresses

Typeof Beam

Case 5.- Both EndsOverhanging SupportsUnsymmetrically, UniformLoad

GeneralFormulafor Stressatany Point

L2ZL

Foroverhangingendof lengthd, S=

=1

C2Lx

÷d2X(!X)} 2(/-d-c)

Points

Stress at support next Foroverhangingendof endoflength c, length c, Wc2 w X(c-u)2 s— 2ZL Criticalstressbetween isat supports Betweensupports, /2÷ c2- d2 X 2/

TOTAL LOADW

w 2! ÷d-c)

Stressesat Critical

2ZL W

andis

2)

2ZL (C2- X7 Stress at supportnext

endoflengthd,

Ld2

If

2ZL

cross-section

is

constant, the greatest of these three is the maximumstress. If x,>' the stress is 2 - c2 zero at points on both sides of x =Xr

.f

Case 6..- Both EndsOverhanging

Supports, Loadatany Point

ba Between

I

(a+b=I)

Between supports: For segmentoflength a,

s=_x ZI For segmentoflength

b,

S7f

Way

Beyondsupportss=o.

142

Stress atload,

7i Wa!)

If cross-section is constant, this is the maximumstress.

Defiections

GeneralFormulafor Deflectionatany Point

Deflections

at CriticalPoints

For overhangingend of length c, Wv

Deflectionatend c,

24E1L (21(d2÷2c2)

i-6c2u-u2(4c-u)-13J

24E1L (21(d2÷ 2c2)÷3c3-13J

Betweensupports,

Deflectionatend d,

Wx (I -x) I' 24E1L x(I-9+I2--2(d2÷c2)

-

24E1L (21(c2÷ 2d2)÷3d3-131

fd÷ c2(Ix)J}

Thiscase is socomplicatedthatconvenient generalexpressionsforthe critical deflections betweensupportscannotbeobtained.

For overhangingendoflength d,

)24EILt2+2c) ÷6d2w-w2(4d-w)-13J Between supports, same as Case 3. For overhangingend oflength c,

y=

Wabu

For overhangingend oflength d,

Between supports,same asCase 3.

Deflectionatend c,

Wabc

Deflectionatendd,

+ 6EII (I a)

y = - WaLw (1÷ a)

143

Stresses

Type of Beam

General Formulafor

Stress at any Point

Case 7.- Both Ends Overhanging Supports, Single Overhanging Load

Stressesat Critical Points

Between load and Stress at support adjacent support, adjacentto load, WC

W(c - U)

-

Between supports, Wc S=

z If

cross-section is

constant, this is the (I x) maximum stress. Stress is zero at other Between unloadedend support. andadjacentsupport, s

= 0. Case 8.- Both Ends Overhanging Supports, Symmetrical Overhanging Loads

Between each load and adjacentsupport,

s=

w

w

W

Stress atsupports and at all points between,

--(c-u)

Wc

1

Between supports S= W

W

Wc

Case 9.- Fixed at One End,

If cross-section is constant, this is the maximum stress. Stress at support,

Uniform Load

W thi-2

TOTAL LOAD W

-WI

If

cross-section is

constant, this is the maximumstress.

144

Deflections

General Formulafor Deflection

Deflectionsat Critical Points

at any Point

Between load and adjacent support,

Wu

all Wcx

—y

(a + I)

Maximum upward deflection is at

Between supports,

Y=

!.1 3EI

Deflectionat load,

(3cu-u2÷2c!)

x=042265I, and

(I-x)(2I-x)

Wc12

5

15.55E1

Betweenunloadedendandadjacentsupport, Deflectionat unloaded end,

y=

Betweeneach load and adjacent support, =

WcId

Wc/w

Deflections

(3c(I + U) - u2]

Between supports,y

-W-

at loads,

Deflection at center,

2E1 (I-x)

6EI

—

(2c + 3/)

7

Wa!2

The above expressions involve the usual approximationsof the theory of flexure, and hold only for smalldeflections. Exact expressionsfor deflectionsofany magnitudeare as follows:

a

Between supports the curve is circle ofradius __________

Deflectionat centre,

/r - / 2

r=E

Wc

y = V'r2 1/412

/2 (l/2 I-

2-

y= 24E1! -'--—f2! + (2!- x)2]

Maximumdeflection,at end, WI3 8E1

145

x)2

Stresses

Type of Beam

General Formulafor Stress at any Point

Case 10. - Fixed at One End, Load

Stress at support,

at Other

s=

w

wI(

Stresses at Critical Points

W

-y (i-x)

If

cross-section is

constant, this is the maximum stress.

Case 11. - Fixed at One End, IntermediateLoad

Between support and load, S

wI

=

W

Z

Beyondload, s = o.

Case 12. - Fixed at OneEnd,

If

cross-section

is

constant, this is the maximum stress.

Maximumstress at

Supportedat the Other, Uniform Load

TOTAL LOAD W

Stress at support,

wi

point of fixture,y

r

Stress is zero at

S1)r/4Ix) 2Z1

=V4L

Greatest negative stress isatx=6/.Iand

5

9

146

WI

Deflections

General Formulafor Deflectionat any Point

(3!-x)

y

-

Deflectionsat Critical Points

Maximumdeflection,at end,

Betweensupport and load,

Y=

Deflections

(31-x)

at load,

WI3

Maximumdeflection,at end,

Between unloadedendandadjacentsupport, WI2

y=

(3v -I)

(2! ÷ 3b)

Maximumdeflection is at x = 05785I,

and is =

W2 (I -x) 48E

(31- 2x)

Y?I_ 185E

I

Deflection at center,

I

192E

Deflection at point of greatest negative stress,

147

atX=

— us

8

WI3

187E1

Stresses

Type of Beam

General Formulafor Stress at any Point


Case 13. - Fixed at One End,

Between point of Maximum stress at Supportedat the Other, Load at Center fixture and load, point offixture, 3 14'! 16 Z s= w lix) Stress is zero at w Between support and x= 3 I

-(3I-

-

load, 16

I

5

s=_T

Case 14. - Fixed at One End, Supported at the Other, Load at

32Z

Z

of

2(n-mx)

Between support and load,

Wab(/÷b) 2/2

s= a2

w[i--(sI-a)]

Greatest

-Wa 2v

2(3Ia)

positive

stress, at point offixture,

/2

V.P(J÷)

Wb

s=

n=aI(I÷b)

Wv

Between point fixture and load,

any Point

m_—(I÷a)(I+b)+a/

Greatest negative stress at center, 5 Wi

Greatest negative stress, at load, Wa2b 2Z13

(3!- a)

If a <0.5858 I, the first isthe maximumstress. If

a = 0.5858!, the two are equal and are

wa2(31-a)

5.83Z a 0.5858 I, the second is the

2I

If

maximum

stress.

Stress is zero atX

Case 15. - Fixedat Both Ends,

n

Maximum stress at WI ends,

Uniform Load TOTAL LOAD W

s=

Will x x 21

Stress is zero at x=0-78871 and at

x=O.2li31

2

=

Greatest flegativewi stress, atcentre, -

2

148

Deflections General Formulafor Deflectionat any Point

Deflections

Between support and load,

=

W2

(9!- lix)

96E

I,

at Critical Points

Maximumdeflectionisatv=0.4472 and is WI3 107.33E

I

Between supportand load, Deflectionat load, Wv

i_

768

!tV El

96E1

(312-5v2)

Between point of fixture and load,

Deflectionat load,

Wx2b

12E1/3 (3n-mx) Betweensupport and load, Wa2v

If

(3! + b)

a < 0.5858 1, maximum deflection is

between load and support, at

v=!/andis

1312b-v2(3!-a)J

12E1/3

Wa3b2 12E113

21÷b Ifa=0.58581, maximumdeflectionisatload

and is

6E1

WI3

1Oi.9E I Ifa>0.5858!,maximumdeflectionisbetween load and point of fixture, at 2n

and

Wbn3

'53EIm2I3

Maximumdeflection,at centre,

—

Wx2

24E1! (/-x)2

384E1

149

Stresses

Typeof Beam

GeneralFormulafor Stress atany Point

Case 16.- Fixedat Both Ends,


Stress at end next segmentoflength a,

Loadatany Point

Wab2

For segmentoflength a,

Wab2

Wab /2

s=

3(aI-x(I÷2a)]

r2

Stress at end next segmentoflength b, Wa2b Z12

Maximum stress is at

Forsegmentoflength end b,

Tb2(/2) Wa2(/2;f fT

next

shorter

segment.

32(bI V(I+ 2b)j

S

Stress is zero for

a!

=

I÷2b Greatest negative stress,

atload

2Wa2b2

---patCenterof Each

TOTAL LOAD ON EACH SPAN,W

J'I-j) (I/i) 2Z!

Case 18. -

ContinuousBeam,with

TwoEqualSpans, EqualLoads

atCenterofEach w

-

Maximum stress at WI pointA,

Case 17. - ContinuousBeam,with TwoEqualSpans, EqualLoads

-_____

Stress is zero at

x=4I

--

Greatest negative stressisatx=5/5! and is,_ 9 WI

Maximumstress at Between point A and 3 WI A, point load,

s=

w

j-(3I-llx)

Between point B and load,

5iT 150

5

Wv

16

Z

Stress is zero at X

3

Greatestnegative stressatcenterof span 5 WI

----r

Deflections

GeneralFormulafor Deflectionatany Point

Deflections

atCritical Points

Wa

Deflectionatload, For segmentoflength a, 2b2

(2a(I-x)÷I(a-x)]

For segmentof length b,

Letb bethe length ofthelongersegmentand aoftheshorterone. The maximum deflection is in the longer segment,at 2N

V1

= Wv2a2 (2b (I- v) + I(b - v)J

6EJ/3

and is

I(I÷ 2b)2

2Wa2b3

3E

Maximum deflectionisatx=0.5785!, and is WI3

185E1

- Wv2(I-) 48EII —

Deflectionatcenterofspan,

'3/ - 2Xi

Deflectionatpointofgreatestnegative stress, atx

BetweenpointA andload,

I £ 8

is

WI3

187E1

Maximumdeflectionis at v=0.4472!, andis

W y= -j.(9I-11x)

WI3

107.33E1

Betweenpoint Bandload, =

WI3

192EI

Deflectionatload,

wv

9J(3I 2-5v2)

151

L !! El

768



design guide

APPENDIX3- PREVIOUSBS DESIGNATIONS

153

PREVIOUS B.S. DESIGNATIONS (PROPERTIESIN IMPERIAL UNITS)

OLD

NEW

B.S. B.S. TEMPER NUMBER NUMBER OLD NEW

50 MM

ON

4.5

8.5

14

T5

7.1

9.7

7

IF

T6

10.4

12.0

7

M

F

7.5

12

TB

14

7.8

12.4

14

TF

16

16.5

19.1

7

TB

T4

HE9

TE

HE9

6063

% ELONG

12

F

HE9

ULT.

STRESS TONS/IN2 6.5

M

HE9

0.2 % PROOF STRESS TONS/IN2

-

HE3O HE3O

1 6082

HE3O

E91E

6101A

TF

T6

11.3

13.3

8

BTRE6

6463

TF

T6

10.4

12.0

9

HE15

2014A

TB

14

15.3

24.7

10

TF

T6

24.7

29

6063A

TB

T4

6.0

10.0

12

6063A

TE

15

10.4

13.3

7

6063A

IF

16

12.6

15.3

7

HE15

6

Thesedesignations andproperties areforguidanceonly. All orders are manufactured to the existing British Standards alloy numbers and tested in metric units.

154



APPENDIX 4-

COMPARISON OF NATIONALSPECIFICA11ONS

155


01

—

Al Cu 4Mg 1

2024

Si Mn

144054

Al

Cu 451 Mn

Pb

1

N61 H20 H9 H30

AIM5IS1Cu Al Mg 0.5 Si

AISi I Mg Mn

55565

6061

6082

2L95;L160;L161; L162

Al Zn 6Mg Cu

7075

DTD 5025: 5104A: 50945

7014

Hi7

DTD0I3O:5120A

7010

Al Zn 4.5 Mg

E6

6463

7020

916

6101A

6063

1452

1451

Al Mg 3.6

5454

5554

N4

Al Mg 2

5251

145

N8

Al Mg 4.5 Mn

5083

5154A

N6

51Mg 5

50565

1441.

Al Mg

142

4047

5005

N21

N31

4043

3105

N3

3.4335 3.4365

A-Z 5G U

3.2315

3.3537

3.3525

33547

3.3555

A-Z 5 G

A-SG M0.7

A-CSUC

A-G 2,5 MC

A-G 2 M

A-C 4.5 MC

A-C 0.6

A-S 12

A-S 5

3.0505

3,0515

Mn

Al Zn Mg Cu 1.5

Al Zn Mgi

1

UN13735

UN17791

UN13571

UN13569

UN16170

Granges SM 6958

144212

Mg

Zn 45Mg

1

1

0.5

Zn 6Mg Cu

Al

Si

Sil Mn Al Mg

Al

Mg 2.7 Mn

Al Mg 5

Al Mgi

Mg 21 Mn

144104

144140

144106

Al Mg 2 UN17789

UN13575

UN17790

U14l13576

UN15764

UN13568

Mg 2 Mn 0.3

Mg 4.5 Mn

Al Mg Si

Al

Al

Al

Al Mg 5

Al Mn 0.5 Mg 0,5

Al

Al

5

1318

1316

— —

2024

2017A

20145

2011

1350

V95

6063

7075

7020

7014

7010

6463

6101A

6082

6061

AD3I

55565

5554

5454

0201

5154A

5083

50585

5005

4547

4043

3105

3103

AD3

AMG3

AK4-1

26185

3103

A-U2GN

Al Mn

Al Cu 4Mg 1.5

Al

Bi

2117

UN13577

LJN13583

144338

Al Cu 6

2031

Al Cu Mg 0.5

Al Cu Mg2

UN13SO1

144355

H16

—

Cu

AlCuMgi

Al

UN16362

A-U 20 3.1305

3,1355

3.1325

3,1255

Al Cu Si Pb

E-Al99,S

A-U2N

A-U4GI

A-U4G

A-U4SG

3.1655

A-U 5 Pb Bi

E-Al

26185

1

1080A

10505

InternationalNumber

2218

Al Mn

AK8

USSR

7L25

2117

Li 10

.

A199.0

A199,5

Switcerland

1200

3.0257

A5/L

144010

144004

144007

Sweden

1199 UN13567

Italy

A4 Al99

A199 5

A99 3.0205

3.0255

WantGermany WerkstottNumber DIN Designation

2218

H12 3L86

2031

Cu 2 Mg

AICu 4Mg Si

20175

Al

H15

Al Cu 4Si Mg

2014A

2L 97, 2L 98, L 109, DTO 5100A

EC1

Al Cu 6 Di Fb

1E

2011

1350

1C

1200

A199

1

AS

IA

A199-5

1080A

1199

A5

lB

A199-S

1OSOA

Franca

FormerNF

FormarBS Designation

Alloy Type as Depicted by Old ISO Number

BS and International




APPENDIX 5-

CHEMICAL COMPOSITION LIMITS AND MECHANICAL PROPERTIES

159


a)

'1

0_to

0.35

0.20

0.40

0.35

7020

0.10

0.45-

1.001.40

0.50

0.200.60

0.450.90

0.05-

0.401.20

005

0,40-

-

090

0.601.20

090

0,50-

0.35

0,10-

0.10

-

-

025

005

035

120

0.90

0.04-

0.80-

0.401.00

075

0.10

0.15

0.05

0.35-

0.10

0.60

¾

%

Chromium

¾

Manganese Magnesium

-

0.10

-

-

-

-

-

5.00

4.00-

0,25

005

-

0.20

015

0_ia

0.25

0_is

-

%

-

Zinc

¾

Nickel

( INDIVIDUAL PERCENTAGE VALUESOF CONSTITUANTSARE MAXIMUM (2) ALL MECHANICALPROPERTIESARE TYPICAL. BARS (3) TEMPER T6510 APPLIES ONLY TO CONTROLLEDSTRETCHINGOF SOLID

5 00

3.90-

0,50

0.500.90

20i4A

060

0,20-

0.20

0.40

030-

6101A

0.15

0.50

0.70130

6082

6463

0.05

035

070

0.10

0.15-

atO

0.150.40

060

0.60

0.20-

080

0.10

¾

Coppe

0.70

030

0,40-

0.10-

060

%

%

0.30-

iron

Smlioon

0.30-

6063A

6063

6061

6060

Material designation

008-0.25 Zr Ti

0.20 Zr eTi

-

0.15

-

-

. -

0.15

0.10

0.10

0.15

0_to

¾

-

'

-

-

¾

Other restrictions Titanium

________

0.05

0.05

0.05

0.03

0.05

0,05

0.05

0.05

005

¾

Each

0.15

0,15

0,15

0.10

0.15

0.15

0.15

0.15

0.15

¾

Total

—

Rent

Rem.

Rent.

Rem.

Rem.

Rent

Rent.

Rem.

Rent.

¾

Aluminium

T4 T6

T65i0

T6

T4

T4 T6

T6

T5 T6 T65t0

20

20 75

-

25 25

200 150

20

150 200

20 75

50 50

.

190 280

230 250 250 230 370 435 420 390

150

78

170

300 340

370 435 480 465 435

370 390 390

125 185

200

(100) 190 170 270 295 310 280

-

' -

150 200 230

(100) 130 120 150 195 150

-

280

190

190

120 145

90 160 190

70 70 110 160 130

-

.

150 120 200 100 6 230 20 255 ISO 270 200 240

205 200

25

25 25

200 200 150 200 25 150 205

75 150

-

itS

iSO 240

150

Mm.

strength

Max,

5.65 'JSo (rrrin.(

On

-— -

-

-

-

-

170

-

-

-

-

-

-

140

-

-

-

12 10

7 7

7

8 8 7

ii ii

16 tO

10

8 8 S

(13) 16 13

16

8 8

14

8 8 6

(13) 16 13

15

8

16

16 8 8

N/mm' N/mm' N/mm' %

proof stress (mm.)

150 60 150 100 150 150

mm

—

20 7S

-

150

-

-

-

150

-

-

150

T4

F

0

iSO

T4 T5 T6

l,

I

150

5 -

-

-

-

-

-

mm

-

T5 T6

T4

F

0

T65i0

T6

T4

T4 T5 T6

—

(bar) or thickness (tube! section)

and mechanical properties °1 of heat-treatable Aluminium alloy bars, extruded round tube and sections

(Figures in parentheses refer to the notes at the end of this table)

Chemical composition limits

10 8

-

-

-

6

-

-

10

14 9

8

-

8 7

-

(12) 14

14

12

7 7

-

7 7

-

14

(12)

13

7

14

-

¾

(mn.)

On 50 mm


Aluminiumextrusions are used in a wide variety of engineering and architectural applications. As a strong, light, non-corrosive material which can be extruded into complex shapes, aluminium provides the solution

to a whole range of design problems.

This concise technical guide provides the reader with the

information necessary to design effectively with aluminium extrusions.

It presents brief details on the extrusion

process,

outlines aluminium's material specifications and mechanical properties and covers such design considerationsas conductivity, temperature, fabrication and finishing. The book also contains specific guidance on design procedure, including worked examples, and concludeswith an extensiveglossary.

"It's a true working manual...a

must for every

drawing office which uses or might use aluminium extrusions" Chris Rand, Industrial Technology magazine

"A valuable document...four star rating out of

fve" Andy Pye, Design Engineering magazine

"A much needed source of reference" Roy Woodwarci,Aluminium Industry magazine

Published by The Shapemakers — the information Aluminium ExfrudersAssociation

Aluminium

arm of the

UK

Aluminium Extrusions - Technical Design Guide

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