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Conveyor system From Wikipedia, the free encyclopedia
Jump to: navigation navigation,, search "Conveyor" redirects here. For other uses, see Conveyor (disambiguation). (disambiguation). This article is about conveyor systems. For information on conveyor belts, see conveyor belts.. For information on overhead conveyors, see overhead conveyors. belts conveyors.
An overhead chain conveyor conveys cars at Mercedes in Germany A conveyor system is a common piece of mechanical handling equipment that moves materials from one location to another. Conveyors Co nveyors are especially useful in applications involving the transportation of heavy or bulky materials. Conveyor systems allow quick and efficient transportation for a wide variety of materials, which make them v ery popular in the material handling and packaging and packaging industries. Many kinds of conveying systems are available, and are used according to the various needs of different industries.
Contents [hide hide]] •
1 Industries That Use Conveyor Systems
•
2 Care and Maintenance of Conveyor Systems
•
3 Types of Conveyor Systems ○
3.1 Pneumatic Conveyor Systems
○
3.2 Vibrating Conveyor Systems
○
3.3 Flexible Conveyor Systems
•
4 See also
•
5 References
[edit edit]] Industries That Use Conveyor Systems
A lineshaft roller conveyor conveys boxed produce at a distribution center
A Conveyor belt conveys papers at a newspaper print plant
Roller conveyor for carton transport in the apparel industry Conveyor systems are used widespread across a range o f industries due to the numerous benefits they provide. •
•
•
•
Conveyors are able to safely transport materials from one level to another, which when done by human labor would be strenuous and expensive. They can be installed almost anywhere, and are much safer than using a forklift or other machine to move materials. They can move loads of all shapes, sizes and weights. Also, many have advanced safety features that help prevent accidents. There are a variety of options available for running conveying systems, including the hydraulic, mechanical and fully automated systems, which are eq uipped to fit individual needs.
Conveyor systems are commonly used in many industries, including the automotive, agricultural, computer , electronic, food processing, aerospace, pharmaceutical, chemical, bottling and canning, print finishing and packaging. Although a wide variety of materials can be conveyed, some of the most common include food items such as beans and nuts, bottles and cans, automotive components, scrap metal, pills and powders, wood and furniture and grain and animal feed. Many factors are important in the accurate selection of a conveyor system. It is important to know how the conveyor system will be used beforehand. Some individual areas that are helpful to consider are the required conveyor operations, such as transportation, accumulation and sorting, the material sizes, weights and shapes and where the loading and pickup points need to be.
[edit] Care and Maintenance of Conveyor Systems A conveyor system is often the lifeline to a company’s ability to effectively move its product in a timely fashion. The steps that a company can take to ensure that it performs at peak capacity, include regular inspections, close monitoring of motors and reducers, keeping key parts in stock, and proper training of personnel. Increasing the service life of your conveyor system involves: choosing the right conveyor type, the right system design and paying attention to regular maintenance practices. A conveyor system that is designed properly will last a long time with proper maintenance. Here are six of the biggest problems to watch for in overhead type conveyor systems including I-beam monorails, enclosed track conveyors and power and free conveyors. Poor take-up adjustment: This is a simple adjustment on most systems yet it is often it is
overlooked. The chain take-up device ensures that the chain is pulled tight as it leaves the drive unit. As wear occurs and the chain lengthens, the take-up extends under the force of its springs. As they extend, the spring force becomes less and the take-up has less effect. Simply compress the take-up springs and your problem goes away. Failure to do this can result in chain surging, jamming, and extreme wear on the track and chain. Take-up adjustment is also important for any conveyor using belts as a means to power rollers, or belts themselves being the mover. With poor-take up on belt-driven rollers, the belt may twist into the drive unit and cause damage, or at the least a noticeable decrease or complete loss of performance may occur. In the case of belt conveyors, a poor take-up may cause drive unit damage or may let the belt slip off of the side of the chassis. Lack of lubrication: Chain bearings require lubrication in order to reduce friction. The chain
pull that the drive experiences can double if the bearings are not lubricated. This can cause the system to overload by either its mechanical or electrical overload protection. On conveyors that go through hot ovens, lubricators can be left on constantly or set to turn on every few cycles. Contamination: Paint, powder, acid or alkaline fluids, abrasives, glass bead, steel shot, etc. can
all lead to rapid deterioration of track and chain. Ask any bearing company about the leading cause of bearing failure and they will point to contamination. Once a foreign substance lands on the raceway of a bearing or on the track, pitting of the surface will occur, and once the surface is compromised, wear will accelerate. Building shrouds around your conveyors can help prevent the ingress of contaminants. Or, pressurize the contained area using a simple fan and duct arrangement. Contamination can also apply to belts (causing slippage, or in the case of some materials premature wear), and of the motors themselves. Since the motors can generate a considerable amount of heat, keeping the surface clean is an almost-free maintenance procedure that can keep heat from getting trapped by dust and grime, which may lead to motor burnout.
Product Handling: In conveyor systems that may be suited for a wide variety of products, such
as those in distribution centers, it is important that each new product be deemed acceptable for conveying before being run through the materials handling equipment. Boxes that are too small, too large, too heavy, too light, or too awkwardly shaped may not convey, or may cause many problems including jams, excess wear on conveying equipment, motor overloads, belt breakage, or other damage, and may also consume extra man-hours in terms of picking up cases that slipped between rollers, or damaged product that was not meant for materials handling. If a product such as this manages to make it through most of the system, the sortation system will most likely be the affected, causing jams and failing to properly place items where they are assigned. It should also be noted that any and all cartons handled on any conveyor should be in good shape or spills, jams, downtime, and possible accidents and injuries may result. Drive Train: Notwithstanding the above, involving take-up adjustment, other parts of the drive
train should be kept in proper shape. Broken O-rings on a Lineshaft, pneumatic parts in disrepair, and motor reducers should also be inspected. Loss of power to even one or a few rollers on a conveyor can mean the difference between effective and timely delivery, and repetitive nuances that can continually cost downtime. Bad Belt Tracking or Timing: In a system that uses precisely controlled belts, such as a sorter
system, regular inspections should be made that all belts are traveling at the proper speeds at all times. While usually a computer controls this with Pulse Position Indicators, any belt not controlled must be monitored to ensure accuracy and reduce the likelihood of problems. Timing is also important for any equipment that is instructed to precisely meter out items, such as a merge where one box pulls from all lines at one time. If one were to be mistimed, product would collide and disrupt operation. Timing is also important wherever a conveyor must "keep track" of where a box is, or improper operation will result. Since a conveyor system is a critical link in a company’s ability to move its products in a timely fashion, any disruption of its operation can be costly. Most “downtime” can be avoided by taking steps to ensure a system operates at peak performance, including regular inspections, close monitoring of motors and reducers, keeping key parts in stock, and proper training of personnel.
[edit] Types of Conveyor Systems
Belt driven roller conveyor for cartons and totes. •
Gravity roller conveyor
•
Gravity skatewheel conveyor
•
Belt conveyor
•
Wire mesh
•
Plastic belt
•
Belt Driven Live Roller
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Lineshaft roller conveyor
•
Chain conveyor
•
Screw conveyor
•
Chain driven live roller conveyor
•
Overhead conveyors
[edit] Pneumatic Conveyor Systems Every pneumatic system, makes use of pipes or ducts called transportation lines that carry mixture of materials and a stream of air. These materials are such as dry pulverised or free flowing or light powdery materials like cement, fly ash etc. These materials can be transported conveniently to various destinations by means of a stream of high velocity air through pipe lines. Products are moved through various tubes via air pressure, allowing for extra vertical versatility. Pneumatic conveyors are either carrier systems or dilute-phase systems; carrier systems simply push items from one entry point to one exit point, such as the money exchanging tubes used at a bank drive-thru window. Dillute-phase systems use push/pull pressure to guide materials through various entry and/or exit points. Three basic systems that are used to generate high velocity air stream: 1. Suction or Vacuum systems: utilizing a vacuum created in the pipeline to draw the material with the surrounding air.The system operated at a low pressure, which is practically 0.40.5 atm below atmosphere, and is utilized mainly in conveying light free flowing materials. 2. Pressure Type systems: in which a positive pressure is used to push material from one point to the next. The system is ideal for conveying material from one loading point to a number of unloading points. It operates at a pressure of 6 atm and upwards. 3. Combination systems: in which a suction system is used to convey material from a number of loading points and a pressure system is employed to deliver it to a number of unloading points.
[edit] Vibrating Conveyor Systems A Vibrating Conveyor is a machine with a solid conveying surface which is turned up on the side to form a trough. They are used extensively in food grade applications where sanitation, washdown, and low maintenance are essential. Vibrating conveyors are also suitable for harsh, very hot, dirty, or corrosive environments. They can be used to convey newly cast metal parts which may reach upwards of 1,500 °F (820 °C). Due to the fixed nature of the conveying pans vibrating conveyors can also perform tasks such as sorting, screening, classifying and orienting parts. Vibrating conveyors have been built to convey material at angles exceeding 45° from horizontal using special pan shapes. Flat pans will convey most materials at a 5° Incline from horizontal line.
[edit] Flexible Conveyor Systems
Flexible conveyor The flexible conveyor is based on a conveyor beam in aluminium or stainless steel, with low friction slide rails guiding a plastic multi-flexing chain. Products to be conv eyed travel directly on the conveyor, or on pallets/carriers.
[edit] See also •
Manufacturing
•
Moving bed heat exchanger
[edit] References Retrieved from "http://en.wikipedia.org/wiki/Conveyor_system" Categories: Commercial item transport and distribution | Packaging machinery
References 1. ^
http://www.provisioneronline.com/CDA/Articles/Feature_Article/BNP_GUID_9-52006_A_10000000000000421648
2. ^
Conveyor Maintenance - Increase the Service Life of Conveyor Systems Including Enclosed Track Conveyors http://www.provisioneronline.com/CDA/Articles/Feature_Article/BNP_GUID_9-52006_A_10000000000000421648
3. ^ 4. ^
Spec: Process Engineers Who Build
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Design procedure The Conveyor Design Procedure can be used to design a conveyor. Contact Quick Conveyor if you need assistance.
1. Determine product rate (products/min). 2. Determine product length (inches). 3. Determine product weight (lbs). 4. Calculate chain speed (feet/min): Product length (inches) x 1 ft/12 inches x product rate (bottles/min) x 1.5 = ft/min. Above formula gives speed with 1/2 product length space between each product. 5. Sketch path conveyor needs to follow. 6. Start with idle end of conveyor. You have three choices:
a. Q123 24" Idle. b. Q144 30" Flush Left Idle. c. Q198 30" Flush Right Idle. If you want to transfer product from a machine to conveyor, select either Q144 or Q198. If conveyor is free standing, select Q123. Flush side idles are free of bearings and bolt heads on the flush side. 7. Select straights required to get to first curve or drive. You have five choices: a. Q134 12" Straight. b. Q191 24" Straight. c. Q120 48" Straight. d. Q199 72" Straight. e. Q130 96" Straight. If you need length that is not an even multiple of 1 foot, then any straight can be cut to length desired. 8. Curves are available in two designs. Curve Design # 1: 18" radius friction curves. Friction curves cost less but limit conveyor length. a. Q168 15 Degree 18" Radius. b. Q190 30 Degree 18" Radius. c. Q185 45 Degree 18" Radius. d. Q124 60 Degree 18" Radius. e. Q140 90 Degree 18" Radius. The total of these curves should not exceed 180 degrees (i.e. two 90 degree curves or four 45 degree curves, etc.) If you need to exceed the 180 degree limitation, then a transfer needs to be used to break conveyor path into two conveyors. You have two choices: a. Q187 30" Right to Left Transfer. b. Q195 30" Left to Right Transfer. Curve Design # 2: 8" radius non-friction curves. Non-friction curves cost more but do not have drag. Do not count these curves when determining the 180 degree curve limitation. A conveyor with a Disk Curve is considered a straight conveyor. You have three choices: a. Q157 90 Degree 8" Radius Disk Curve. b. Q167 135 Degree 8" Radius Disk Curve. c. Q197 180 Degree 8" Radius Disk Curve. 9. Continue to select curves and straights until you complete your conveyor path. 10. Complete conveyor with a drive. You have three choices: a. Q158 24" Drive. b. Q192 30" Flush Left Drive. c. Q117 30" Flush Right Drive. Again, if you want to transfer product from a conveyor to a machine, select either Q192 or Q117. If conveyor is free standing, select Q158. Flush side drives are free of bearings and bolt heads on the flush side. 11. Now that you have completed the path and selected conveyor modules, you need to check if each conveyor is within design limits. a. To accurately determine chain pull, dowanload Rexnord's Calculation Software for Rex Tabletop Chains. Use the Tabletop Conveyor Analyzer. Select Sideflexing Conveyor Analysis. b. Ideally, each conveyor should have less than 180 degrees of friction curves. c. For additional help, contact Quick Conveyor. If you exceed the recommended length for y our configuration, revise conveyor by shortening conveyor, reducing number of 18" radius friction curves, replacing 18" radius friction curves with 8" radius disk curves or adding transfers. 12. Select gear motor based on s peed required. a. Q161 1/2 HP, 45 to 228 FPM. (FPM=Feet/Minute) b. Q162 1/4 HP, 11.5 to 32.5 FPM.
See product information pages for details. All gear motors have 230/460 three phase motors. If 115 volt single phase input is required, purchase a variable frequency controller product Q121 that has 115 volt input and 230 volt 3 phase output. If variable speed is desired, again you will need to purchase a variable frequency controller. 13. Select legs as required. Legs must be used on end of idles and drives, (two legs on transfers) and at least every 8' of conveyor. If flush drives or idles are securely bolted to a machine, those legs can be eliminated. Legs adjust in height for top of chain elevations between 36" and 41". Shorter legs can be made by cutting standard pipe support as required. Longer legs can be made by purchasing 1.5" schd. 10 stainless steel pipe and cutting to desired length. You have six choices for legs: a. Q107 Disk Curve Leg. b. Q118 Double Conveyor Leg. c. Q126 Drive/Idle Return Shoe Leg supports Q123 or Q158 20 1/2" from end of conveyor. d. Q154 installs on straight conveyor. e. Q155 18" Radius Curve Leg used on Q140. f. Q194 installs on drives, idles and transfers. 14. Order chain Q137 for conveyor. Chain is sold in 120" lengths. 2' of chain is required for every 1' of conveyor length. 15. Order wearstrip Q113 for straight conveyors. 4' of wearstrip is required for each 1' of conveyor length. Only straights require wearstrips to be installed by customer. Drives, idles, transfers and curves have wearstrip installed by Quick Conveyor. Wearstrip is s old in 240" lengths. 16. Order guide rail materials. You have two choices of molded plastic top guide rail brackets and one stainless steel top bracket: a. Q116 Short Top Guide Rail Bracket. b. Q119 Tall Top Guide Rail Bracket. c. Q128 Single Rail Top Guide Rail Bracket. Modules are supplied with bottom guide rail brackets but without top guide rail brackets. Bottom brackets are slotted vertically so they can be installed high or low. High position allows top bracket to extend over the top of chain. Low position allows product to overhang the edge of chain and not hit the bottom bracket. Guide rail Q178 has 1/2 round UHMW plastic insert. Q179 has a 1.25" flat UHMW plastic insert. They are sold in 96" lengths. With two guide rails on each side of conveyor, order 4' of guide rail for every 1' of conveyor. At each attachment point of the guide rail to the top guide rail bracket, you will require a Guide Rail Clip Kit Q100. Each top guide rail bracket requires a Carriage Bolt and Ratchet Handle Q106 to bolt top guide rail bracket to bottom guide rail bracket or carriage bolt and not Q136. The following additional parts are available if required: a. Q101 18" Radius Curve Guide Rail Kit. b. Q110 Guide Rail Splice Plate Kit. c. Q111 Guide Rail Splice Sleeve is used if you need to join two guide rails. d. Q115 Bottom Guide Rail Kit is used if you need to add additional bottom brackets. e. Q151 90 Degree Disk Curve Guide Rail Kit. f. Q152 135 Degree Disk Curve Guide Rail Kit. g. Q153 180 Degree Disk Curve Guide Rail Kit. 17. Order other accessories if required: a. Q108 Machine Interface provides parts to bolt Quick Conveyor to a machine. b. Q135 Roller Deadplate Kit - 3 1/4 Chain. c. Q164 Straight Connector Kit is used to connect two straights. 18. We also have 6' Handpack Stations Q148 and Q149. 19. We also have 42" Dia. feed and pack disks Q172, Q173, Q174, and Q175. Comments on this procedure are welcome.
1.
I NTRODUCTI ON
2.
JUSTIFICATION FOR A STANDARD
3.
PRESENT DESIGN STANDARDS
4.
PROPOSED STANDARD FORMAT 4.1 4.2 4.3 4.4 4.5
5.
Power and Tension Pulley and Shafts Selection of Belt Width and Velocity Idler Standards Drive Standards
CONCLUSION
SUMMARY This paper has been prepared with the intention of highlighting the problems faced by design engineers who are forced to undertake the design of belt conveyor systems using a multitude of design standards which have not been brought into line with modern technological advancements. To overcome some of these problems, a basic outline of a universal standard has been proposed, which can easily be adapted to suit individual needs, without reducing the efficiency of the designer and his team. 1. INTRODUCTION The design of belt conveyor systems has been one of the most common occurrences in the South African mining field for over one hundred years. Conveyors are seen on virtually all mining installations, and are the biggest problem for the plant maintenance engineer, being the cause of most plant shutdowns. Why do belt conveyors cause such problems? It must be remembered that mining houses usually have a set of design standards to conform to; standards which are claimed have been developed over many years to suit their own needs in the materials handling field. However, as I can understand the need for some aspects of a standard, others completely baffle me. It appears that having spent a great deal of time over certain requirements of a design standard, many of the fundamentals to which I am referring are of course the effects of overpowering on the whole conveyor system. Also, we know that to convey material from one point to another requires a specific amount of power using a belt designed to withstand a definite t ension, so why is it that if a conveyor design problem is set to a number of designers, they will come up with many variations on a solution, even using the same design specification. This of course comes down to the interpretation of, and the familiarity with the standard to be used. Basically I am suggesting that the standards as available to-day, leave a lot to be desired from the point of view of completeness, and ease of application. 2. JUSTIFICATION FOR A STANDARD Do we need a standard at all? and if so, what form should it take? To answer this question let us look at a typical design office set up. On any project there are three key categories of staff, the designers, his draughtsmen and a group of peripheral staff, (planners, buyers, structural, civil and electrical engineers). Thus we have a set up which looks as follows:Figure 1. Typical project Engineering Flow Sheets
The designer is given a basic specification which will include material type and quantity to be conveyed from A to B. This he must transform into drawings for manufacture and fabrication, design data for civil, electrical and structural engineers, bills of quantities for buyers and activity networks for planners. With the exception of the planning information which is only really relevant for the construction phase of the project, the designer has a problem which he will find very difficult to overcome, and that is to supply all the necessary information to each discipline on the project when they require it. Therefore having obtained a scope of work from the client in question, the designer has to quickly produce the design data, but before he is able to proceed he must obtain information from his drawing office relating to the layout of the conveyors in the system. Now the problems begin: Prior to undertaking any calculations whatsoever the designer must check the specifications to which he must conform. As virtually all clients have their own opinion on the subject of conveyor design, we can rest assured there will be some form of client input, whether it be a two volume manuscript or simply an, 'All drives shall ........' document.
The designer is confronted with conforming to the said specification, but much worse, he must ensure that his drawing office staff are aware that there is a specification to work to. Consider that the previous week they may have been working on another project and had to conform to a completely different specification. What does the designer do? Does he circulate multiple copies to his drawing office with the instruction that it must be read prior to any work being started. If so, he will possibly not meet his deadline on the supply of data to the peripheral disciplines. Does he try to check that his draughtsmen conform by 'looking over their shoulders' from time to time (which is the way mistakes are guaranteed to occur). Alternatively does he instruct his drawing office that there is a specification to work to and that it is lying around somewhere and to 'please check it i f you are not to sure of how to proceed'. In all the offices in which I have worked, the last two solutions have been applied, with the result that, almost without exception, the experienced draughtsmen who know how to make a system work will continue with very little reference to the said specification. The problem may be that on this project 'the pulleys are much bigger, the take-up length must be selected using an ill defined formula and basically we don't know how to design a conveyor anymore. If this problem is caught early enough we only have to change a quantity of drawings and are then back on the right road. However you can be sure that in practice it will be too late, and the designer has to go to the client and ask for a concession because he is not able to conform to the specification, and to make any changes to the drawings now will put him way behind schedule. Furthermore before the client will accept deviations to the proposed format, every avenue must be explored, and a report on the deviation prepared. The designer is now behind whether he likes it or not and to make up time he must neglect the one function which completes the total conveyor design, that of secondary design. By secondary design, I mean the design which comes after the conceptual or general arrangement layouts are complete. This is the design of the chutes, the location of bearings, the belt cleaning system to be employed and the access for maintenance. This is left to a draughtsman without any engineering support. However, the secondary design usually encompasses the major problems of belt conveyor system design. These are areas with very little coverage in specifications, with comments such as, 'all conveyors will have pulleys at terminal points', being the limit to such specifications. I pose the question again, do we need a design standard? Those who agree with the scenario I have set will probably say, 'Allow the designer the freedom to do the job'. However 1 feel that a standard is essential. There are very few specialist conveyor designers and thus some form of guidance must be given. However there should be only one standard, with one basic set of parameters and which can cater for the needs of every mining and process plant application. Without lessening the efficiency of the designer and his team such a standard will facilitate the efficiency the overcoming of the problems occurring in secondary design. We know this has been tried repeatedly in the past, but always in isolation from the main stream of design and usually with the statement, 'but it caters for our own individual needs', as justification. Having been confronted with conveyor design standards for a number of years, I have still to find a true specialist need, I know that some clients require less capacity on a belt, others require larger pulleys and thicker belts, requiring the use of complicated formula to arrive at a solution, but this can not be justification for devising completely individual specifications, which could more suitably be covered in a single paragraph of a comprehensive specification. 3. PRESENT DESIGN STANDARDS Let us look at at the Conveyor design standards available, and in particular the four most commonly used, C.E.M.A., GOOD YEAR, ISCOR and A.A.C. If we consider the power and tension variation predicted by using these systems, as in Table 1, we see quite a wide range of possibilities. The reason for this is in the selection of the rolling resistance factor, (coefficient of friction, resistance to flexure or other commonly used terms) which varies between 0,016 and 0,035 as used in the above standards. Table 1 Power and Tension calculations. 1(a) based on belt capacity of 500tons per hour, belt width of 900mm and a belt velocity of 2,2m/sec. Length
Lift
C.E.M.A.
GOOD YEAR
ISCOR
A.A.C.
Power
Tesn
Power
Tesn
Power
Tesn
Power
Tesn
m
m
kW
kN
kW
kN
kW
kN
kW
kN
30
0
6
9
15
16
16
19
12
18
200
60
101
65
99
64
104
66
102
66
1000 1000
0 40
81 132
40 72
89 143
43 77
113 167
54 88
104 158
50 84
1(b) based on belt capacity of 2000tons per hour, belt width of 1500mm and a belt velocity of 3m/sec. Length
m
Lift
m
C.E.M.A.
GOOD YEAR
ISCOR
A.A.C.
Power
Tesn
Power
Tesn
Power
Tesn
Power
Tesn
kW
kN
kW
kN
kW
kN
kW
kN
30 200
0 60
18 378
22 167
36 380
1000
0
1000
40
41 168
38 403
42 176
37 391
42 172
221
84
439
174
262
98
349
127
315
116
479
188
567
217
533
206
On the shorter systems this difference is quite insignificant, except that the belt length factor plays an important part. However on the now common large overland type systems, these variations are unsatisfactory to say the least. Are we able or prepared to accept such variations? Able, I will say yes, provided we take cognisance of the effects of overpowering. However I am not convinced we should be prepared to accept these variations, apart from the overpowering factor there are purely economic considerations to account for. This point is very noticeable when one becomes involved in economic evaluations (feasibility studies) of various alternative solutions to a specific materials handling problem. For instance, how competitive would a pneumatic conveying system or cable belt system be if designed to similar sets of standards as the conveyor. However as these standards are as yet, not available, the manufacturer of competitive systems has far reaching advantages over the conveyor manufacturers. I am not for one moment suggesting that the competitive systems are under designed, simply that the designer is not limited to designing within a conservative specification. Too often we see examples of conveyor systems feeding process plants, where to conform to specification the whole conveyor network is designed for a large amount of excess capacity. However, this philosophy is not transferred to the related equipment in the rest of the plant. 4. PROPOSED STANDARD FORMAT 4.1 Power and Tension With power and tension calculations there exists the possibility for a combination of all four of the above standards by utilizing a single friction factor for the shorter belts, but eliminating the belt length factor which can easily be compensated for with the overrating factor of the motor. In progressing to the longer conveyors this factor could be variable, as advocated by C.E.M.A., only now be simply a function of belt length and capacity. Then we could use a simplified formula as follows:Power (kW) =
9.81 x L.V((kX+kY(Wm+Wb)+,015Wb)+ (H.Wm)) 1000
Where 1.
L = Horizontal pulley centers (m)
2.
H = Vertical pulley centers (m)
3.
V = Belt velocity (m/sec.)
4.
Wm = Mass of ma terial per meter run (kg)
5.
Wb = Mass of belt per metre run (kg)
6.
0,015 = Return belt resistance
7.
kX = Belt slide a nd Idler rotational resistance and can be obtained from:kX = 0,00068(Wm+Wb)+0,022(rotating mass of the Idler per meter) (kg/m)
8.
kY = Resistance of the belt of flexure as it moves over the Idlers, and can be considered to be the same as the friction factors given i n all the specifications. Typical values of kY are given in table 2 below. Table 2. Selection of kY factor based on Belt length, lift and capacity. Length
Lift
kY
kY
kY
kY
m
m
500t/hr.
1000t/hr.
2000t/hr.
3000t/hr.
100
20
0,035
0,030
0,026
0,022
200
20
0,032
0,026
0,022
0,020
200 400
40 20
0,030 0,030
0,022 0,022
0,020 0,020
0,020 0,020
400
40
0,026
0,020
0,020
0,020
800
40
0,022
0,020
0,020
0,020
1000
40
0,020
0,020
0,020
0,020
To enable the client to maintain control of the outcome of the calculation, it is necessary only to specify the kY factor to be used in a simple addendum to the main specification. Belt tension calculation can be kept straightforward, provided the designer starts by considering the minimum belt tensions, at both the drive and tail pulleys, by using the following formulae :-
Tmin = 4,2x9,81/1000 si(Wb+Wm) kN Where 4,2 = Factor based on a 3% belt sag. Si = Idler spacing,m and Tslack side = Teffective / e -1 Where T effective is the installed drive effective tension and not the effective tension computed from the above power formula. The one problem that is encountered is in the selection of a coefficient of friction for the drive pulley. A standard such as given In Table 3 could be used. Table 3 Coefficient of Friction for Drive Pulleys. Type of Take Up Automatic
Manual
Plant Description
Conveyor Construction
Lagged
Unlagged
Lagged
Unlagged
Wet
Covered Uncovered
0,25 0,20
0,10 0,10
0,20 0,20
0,10 0,10
Covered Uncovered Covered Uncovered
0,30 0,25 0,35 0,30
0,20 0,15 0,22 0,18
0,25 0,22 0,25 0,25
0,18 0,13 0,20 0,15
Semi-wet Dry
Table 3 has been compiled from empirical data such as that given in Table 4. It should be noted that these values are the limiting conditions (when the belt is on the point of slipping). The actual coefficients of friction developed between surfaces are, in practically all cases where slipping does not occur, in excess of t hose listed. Therefore, the convention of using these values does not reflect what actually occurs at the drive pulley. If one considers a drive pulley under operating conditions then the higher tensioned belt section is stretched more than on the lower tensioned section, thus the belt entering the positive drive will be traveling faster than when it leaves it. The elastic recovery of the belt occurs over only a part of the total angle of contact, and it is at this point, where creep takes place, that the driving is done, whil e making full use of the coefficient of friction. By applying the classic tension formula to the whole angle of wrap a fictitious coefficient of friction is being used Table 4. Recommended Drive Coefficient of Friction of Various Standards. Condition
C.E.M.A.
STEVENS ADAMSON
BRIDGESTONE
LINATEX
REMA TIP TOP
Bare pulley Lagged
0,25 0,35
0,35 0,35
0,20 ---
--0,60
--0,45
Dry Lagged
0,35
0,35
0,35
0,60
0,45
Wet Lagged
0,35
0,35
0,25
0,80
0,35
Wet & Dirty
0,35
0,35
0,20
0,40
0,25
The advantage of working from minimum drive tension back to the maximum drive tension, can be better explained if one looks at the design of pulleys and shafts. Over the years there has been a lot written about the design of a pulley shaft, with the aim of trying to eli minate the high failure rate and the cost associated with such failures. I feel that there are only two basic reasons for pulley failure, firstly the bad manufacturing procedures, and secondly, failure owing to an inability to calculate the minimum drive tension. The latter case of incorrect design results in the counterweight mass having to be increased to overcome drive slip on startup, with the result that pulley shafts are subjected to excessive loads, producing eventual failure. By contrast, if the minimum drive tension is used as a design basis, we can overcome, failures in pulleys, caused by inaccurate design. Thus the maximum tension wil l be obtained from :Tmaximum = Tminimum +Teffective Where Teffective is computed from shaft power and not the installed power. Note that the formulae discussed above are applicable to 90% of the conveyor installations being designed to-day. However a little more analysis is required for some overland and complex systems. 4.2 Pulley and Shaft Standards There are presently two major standards used for pulley and shaft selection, these being the ISCOR and AAC systems. I know much has been written about t he high degree of oversizing adopted by both standards, but I feel that as the pulley is one of the least expensive components in a conveyor installation, we should not be over concerned on the point. Efforts should rather be directed at reducing the amount of variations there are in the selection of face width and bearing centers. At the moment both ISCOR and AAC have two sizes per belt width, all different. This should be reduced to a single
size per belt width, and this size should be as big as possible to allow easy access and hence reduce the damage to conveyor belts. A standard along the lines of table 5 based on the ISCOR specification would be t he most acceptable. Pulley and shaft diameters should be kept to a minimum of two per conveyor, with as much standardization as possible being employed on the whole conveyor system. The selection of pulleys and shafts could be from a table similar to that shown as Table 6. Table 5. Pulley Face Width and Bearing Centers Belt width mm
Face width mm
Bearing center mm
450
550
890
600
700
1140
750
900
1370
900
1050
1520
1050 1200
1200 1350
1670 1850
1350
1500
2000
1500
1700
2300
1800
2000
2630
2100
2300
2930
4.3 Selection of Belt Width and Velocity The selection of belt width and velocity is probably the most frustrating of problems facing the designer. There are a variety of factors being used, factors such as :- the belt width must be t hree times the maximum lump size, the belt width must be such that the system can cater for 66% excess capacity, and if a tripper is used the factors must be increased by a further 30% etc. This type of factor forms the basis for most standards in use to-day, and these could therefore be rationalized into a single more acceptable standard to make the designer's task easier. The first necessary step is the removal of the age old belt speed restrictions, after all speeds in excess of 4m/sec are now quite common. I am not advocating that the highest possible belt speed be used for all installations; I simply suggest that belt speeds should not be selected only on the basis of past experience, but on the basis of belt length, transfer point and economic considerations. I feel that to use the criterion I have set out will automatically result in the selection of the most suitable belt width and speed. My reasoning here is that, for inplant installations belt widths and speeds are almost al ways selected on the basis of standardization and possible transfer point problems. By contrast, the larger overland systems are selected on the basis of capital costs and the associated operating and maintenance costs, because as belt speeds increase operating and maintenance costs usually follow suit. Consider the suggested methods of selecting a belt width and speed. Firstly, the amount of material on a belt must be related to the expected transfer point problems. A flat feed point fed by a controlled system will be far easier to design than an inclined feed point fed from a crusher, where surges are very common. Therefore to suggest a similar standard for both applications is not practical. We often are told that conveyors should not be fed at angles of 8° incline feed points and very tight vertical curves, with the result that the feed point stays clean, but at the curve the belt has lifted causing spillage. I would like to suggest that a belt can be easily fed at angles of up to 16°, provided the belt width and speed are correctly selected. It may be necessary to install belts with thicker covers, but this can form the basis for a better design. Thus the type of standard that could be used is shown in Table 7 . Table 7 Implant Conveyor Load Factors Loading Point Type
Feed Type
Overload Factor
Horizontal Horizontal
Uniform Surge
1,20 1,50
Incline
Uniform
1,50
Horizontal
Surge
1,75
Tripper
.....
1,75
Shuttle
.....
1,50
The overload factor would be used to increase the design tonnage for selection purposes. For overland conveyors it is common to use horizontal loading points, and we are not confronted with the same problems. As mentioned earlier it is only necessary to consider the economics of the system, with the following limitations as given in Table 8. Table 8. Overland Conveyor Minimum Belt Widths and Maximum Speeds
Terminal Pulley Centers (m)
Belt Width (mm)
Belt Speed (m/sec)
300 to 500 500 to 1000
600 750
3,50 3,50
over 1000
900
7,00
The overload factor used should always be a minimum of 1,2 times the design tonnage. 4.4 Idler Standards 4.4.1 Introduction The introduction of the SABS Idler specification will ensure a more uniform selection of idlers. As a result the choice of type and spacing for Idlers should be on a more scientific basis. The types of Idler to be used on conveyors are; transition, troughing, impact and return idlers. At this time there is no satisfactory training idler available so t hey should be avoided. 4.4.2 Troughing Idler Spacing Two types of troughing idler are used frequently, fixed and suspended roll. There is very little difference between the two, except the training characteristics and possible cost savings associated with the suspended roll. The question of idler spacing needs be considered more carefully. The restrictive standards as applied to-day do more harm than good to a conveyor system. Idlers are the highest maintenance cost item on a conveyor installation and the biggest cause of belt damage, therefore 'the fewer the better. Idler spacing must be selected on the grounds of available belt tension, fatigue life of the idler bearings, and structural considerations. The upper spacing limit should be set at 2200mm. Account should be taken of four and five roll sets, but no significance can be attached to the claim that four and five roll idlers give better belt life. 4.5 Drive standards The standardization of drives is the key to most successful conveyor systems. The problem is however that some drives have to be drastically oversized to obtain some degree of conformity. By considering this point at an early stage in the design process. it is usually possible to overcome the problem, therefore simple cost analyses of all the possible solutions can quickly decide on the drive sizes to be adopted. Also it is at this point in time when a final selection of belts can be carried out, because there is often scope to change belt speeds to the required degree of standardization, and we should not be afraid to to this. 5. Conclusion To conclude I would like to reiterate the need for a single design standard, which could be applied to any conveyor installation. However, this standard must be such that it allows the client a small amount of individuality and flexibility. The design system as outlined in this paper can offer this flexability, by allowing the client the freedom to select the kY factor, the drive coefficient of friction and the load factor for selecting the belt width and speed. Coupled with this we can have a very efficient system especially if it is adapted to computerised calculation techniques. I know to-day that many such design programs are available, but because of the variations in standards that must be incorporated, their credibility is unjustly made suspect, forcing the designer to revert to the longwinded number crunching exercises which obviously reduce his effectiveness in the drawing office. BELT
PULLEY
HEAVY DUTY
MEDIUM DUTY
LIGHT DUTY
SHAFT BEARING SHAFT BEARING SHAFT BEARING WIDTH DIA.D
DIA.d
DIA.d1
DIA.d
DIA.d1
DIA.d
DIA.d1
BELT TYPE PLY STEEL CLASS CORE
MAXIMUM SHAFT LOAD kN
450
300 400 500 630
90 100 125 140
75 75 100 110
75 75 100 110
50 50 75 90
75 90
50 75
200 250 630 800
18 22 56 72
600
400 500 630 710
110 125 140 160
90 100 110 125
90 100 110 125
75 75 90 100
75 90 100 110
50 75 90 90
250 630 800 1250
30 75 95 150
750
400 500 630 710 800
125 140 160 180 200
100 110 125 140 160
100 125 140 160 180
75 100 110 125 140
75 90 110 125 140
50 75 90 100 110
250 630 800 ST500 1250 ST630 1250 ST1250
35 95 120 190 280
900
400 500
140 160
110 125
110 140
110 140
90 110
90 110
250 630
45 110
630 710
180 200
140 160
160 180
125 140
125 140
100 110
800 1250
ST500 ST630
145 225
All DIMENSIONS IN MILLIMETRES MAXIMUM LOAD FIGURE = PERMISSIBLE LOAD ON PULLEY = TWICE BELT TENSION HEAVY DUTY = 100% MAXIMUM LOAD MEDIUM DUTY = 60% MAXIMUM LOAD LIGHT DUTY = 30% MAXIMUM LOAD DENOTES RATING BASED UPON STEEL CORE BELT FOR ALLOWABLE LOAD ON BEARING SEE BEARING RATING TABLES BELT RATING CHART, Table 6a BELT
PULLEY
HEAVY DUTY
MEDIUM DUTY
LIGHT DUTY
BELT TYPE
SHAFT BEARING SHAFT BEARING SHAFT BEARING PLY STEEL WIDTH DIA. D DIA. d DIA. d1 DIA. d DIA. d1 DIA. d DIA. d1 CLASS CORE
MAXIMUM SHAFT LOAD kN
1050
500 630 710 800 1000 1250
180 200 220 240 250 360
140 160 180 200 220 340
140 160 180 200 220 260
110 125 140 160 180 220
110 110 125 140 160 180
75 90 100 110 125 140
630 800 ST500 1250 ST630 1250 ST1250 1600 ST1600 2000 ST3150
130 170 260 395 505 985
1200
500 630 710 800 1000 1250
180 200 220 240 260 360
140 160 180 200 220 340
140 160 180 200 220 300
110 125 140 160 180 260
110 125 140 160 180 220
90 100 110 125 140 180
630 800 ST500 1250 ST630 1250 ST1250 1600 ST1600 2000 ST3150
150 190 300 450 575 1130
1350
500 630 710 800 1000 1250 630 710 800 1000 1250 1400
200 220 240 280 300 360 240 280 300 320 360 400
160 180 200 240 260 320 200 240 260 280 320 380
180 200 220 240 260 300 200 220 240 260 280 320
140 160 180 200 220 260 160 180 200 220 240 280
140 160 180 200 220 240 140 160 180 200 220 240
110 125 140 160 180 200 110 125 140 160 180 200
630 800 1250 1250 1600 2000 800 1250 1250 1600 2000 2500
ST500 ST630 ST1250 ST1600 ST3150 ST500 ST630 ST1250 ST1600 ST3150 ST4000
170 215 340 505 650 1270 240 375 560 720 1400 1800
1800
710 800 1000 1250 1400 1500
300 320 340 380 410 430
260 280 300 340 380 400
260 280 300 320 340 360
220 240 260 280 300 320
180 200 240 260 380 300
160 180 260 220 240 260
1250 1250 1600 2000 2500
ST630 ST1250 ST1600 ST3150 ST4000 ST5000
450 670 865 1700 2100 2700
2100
710 800 1000 1250 1400 1500
300 320 340 380 410 430
260 280 300 340 380 400
260 280 300 320 340 380
220 240 260 280 300 340
180 200 240 260 280 300
160 180 200 220 240 280
1250 1250 1600 2000 2500
ST630 ST1250 ST1600 ST3150 ST4000 ST5000
525 790 1010 1900 2500 3100
1500
SEE GENERAL NOTES ON SHEET 1 BELT RATING CHART, Table 6b
