Conveyor Belt Hand Book
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CONVEYOR BELT HAND BOOK
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This CONVEYOR CONVEYOR HANDBOOK” HANDBOOK” is provided provided by WE to allow designer designers s to select the correct specification belting for any particular installation. This is just a general guideline and final decisions are to be taken by the user based on actual working conditions. Properties of fabrics used in Polyester Nylon multi-ply belting constructions are given in detail, while the general properties and application areas of special multi-ply constructions, solid woven, Aramid and steel belting are also shown. The use use of variou various s natur natural al and synthe synthetic tic rubber rubbers s with these reinfo reinforce rcemen ments ts for handli handling ng different service conditions is set out for the designer. Design considerations affecting power demands, belt curves, transitions etc., are provided. Whilst users are vitally interested in these design considerations for conveyors, there is a special section on fault diagnosis to enable users to identify causes of troubles which may occur and correct them before belt damage either occurs or becomes extended. The layout of this manual and easy approach to belt design will be readily followed by belt design engineers.
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This CONVEYOR CONVEYOR HANDBOOK” HANDBOOK” is provided provided by WE to allow designer designers s to select the correct specification belting for any particular installation. This is just a general guideline and final decisions are to be taken by the user based on actual working conditions. Properties of fabrics used in Polyester Nylon multi-ply belting constructions are given in detail, while the general properties and application areas of special multi-ply constructions, solid woven, Aramid and steel belting are also shown. The use use of variou various s natur natural al and synthe synthetic tic rubber rubbers s with these reinfo reinforce rcemen ments ts for handli handling ng different service conditions is set out for the designer. Design considerations affecting power demands, belt curves, transitions etc., are provided. Whilst users are vitally interested in these design considerations for conveyors, there is a special section on fault diagnosis to enable users to identify causes of troubles which may occur and correct them before belt damage either occurs or becomes extended. The layout of this manual and easy approach to belt design will be readily followed by belt design engineers.
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Reinforcements Reinfor cements ………………………………………………………………………… 1 - 1 General Properties Propert ies …………………………………………………………………….. 1 - 3
Capacity Calculations Calculat ions …………………………………………………………………. 2 - 1 Properties Proper ties of Materials Materia ls …………………………………………………………………. 2 - 2
Belt Power Calculations Formulae ……………………………… …………………………………………… …………………. ……. 3 - 1 Calculation Calcula tion of Maximum Tensions ….……………………………………………….. ….……………………………………………….. 3 - 5 Graduated Graduat ed Idler Spacings ……………………………………………………………... ……………………………………………………………... 3 - 7 Feeder Belt Calculations ………………………………………………………………. 3 - 9 Acceleration and Deceleration Deceleration ……………………………… ……………………………………………… ……………………….. ……….. 3 - 10 Application of Forces …………………… …………………………………… ……………………………… …………………………… …………….. .. 3 - 14 Algebraic Signs of Conveyor Forces Forces …………………………… …………………………………………… ………………….. ….. 3 - 15 Coasting ……………………………………… …………………………………………………… …………………………… …………………………….. …………….. 3 - 16 Check List for Large Conveyor Systems ……………………………… …………………………………………... …………... 3 - 17
Belt Construction Requirements ……………………………… ……………………………………………… ………………….… ….… 4 - 1 Considerations Consider ations ….……………………………………………………………………… 4 - 1 Procedure Procedur e ………..……………………………………………………………………… 4 - 2
Considerations…………………………………………………………………………… 5 - 1 Selection……………….…………………………………………………………………..5 - 1 Pulley side cover………………………………………………………………………… 5 - 1
Parallel face face pulleys…………… pulleys…………………………… ……………………………… …………………………… ……………………….. ………….. 6 - 1 Crown face pulleys……………………………………………………………………… 6 - 2 Pulley face width………………………………………………………………………… 6 - 2
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Multiple Slope Slope and Vertical Vertical Curve Curve Conveyors Conveyors ……………………………… ……………………………………... ……... 7 - 1 Terminal Troughing Idler Arrangements ……………………………… ……………………………………………. ……………. 7 - 4 Transitions …………………………………………………………………..…………….7 - 4 Take - Up Arrangements ……………………………………………………………….. 7 - 5
Belt Mass and thickness………………………..………………………………………. Shipping dimensions and roll sizes………………………… sizes…………………………….…………… ….………………...….. …...….. Length Length of belt on a roll………… roll………………… ……………… ……………… ……………… ……………… ……………… ………...…… ...…….. Belt transport transpo rt guidelines……………………………………………………….………. guideli nes……………………………………………………….……….
8-1 8-1 8 - 2 8-3
Belt construction………………………… construction………………………………………… …………………………… …………………………… …………………. …. 9 - 1 Belt and cover thickness……………………………………………………………….. 9 - 2 Operating Operati ng temperature temperat ure range………………………………………………………….. 9 - 2 Operating factor of safety………………………………………………………………. 9 - 2 Safety Safety…… ………… ………… ………… ………… ………… ………… ………… ………… ………… ………… ………… ………… ………… ………… ………… …… 9 - 2
Genera Generall Mainte Maintenan nance ce .…… .………… ………… ……….. …..…… ………… ………… ………… ………… ………… ………… ………… ……… … Loading point considerations……………………………………………….. consider ations………………………………………………..………. ………. Random events …………………………………………………………………………. Troubleshooting Troubles hooting ………………….………………………………………….………….
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10 - 1 10 - 2 10 - 4 10 - 5
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1–0
Reinforcements ……………………………………… …………………………………………………… …………………………… …………………….. …….. 1 – 1 General Properties ……………………………………………………………………… 1 – 3 Table 1 Reinforcement Reinfor cement Fabrics ………………………………………………… Table 2A Cover Compounds Compound s ……………………………………………………... Table 2B Heat Resistant Resistan t Belts …………………………………………………… Table 2C Oil & Chemical Resistant ……………………………………………… Table 2D Fire Resistant & Anti Static Belts …………………………… …………………………………….. ………..
1 – 2 1–4 1 – 5 1 – 6 1 – 7
The composition of a conveyor belt can be considered in two parts: A. The Carcass, whether ply type (textile) or steel cord construction, which must have sufficient strength to handle the operating tensions and to support the load. B. The Covers, which must have the required physical properties and chemical resistance to protect the carcass and give the the conveyor belt an economical economical life span. The The gene genera rall prop proper erti ties es and and the the appl applic icat atio ion n usag usage e of the the more more econ econom omic ical al avail availab able le reinforcement fabrics and rubber compounds are discussed in this section. REINFORCEMENTS
Fabrics Fabrics that are commonly used as reinforcement in conveyor belts are shown in Table 1 of this Section The fabric designation indicates the material used in both warp and weft, e.g. EP signifies that the fabric has Polyester warp fibers and Nylon weft fibers. The ultimate strength of the belt in kilo newtons per metre width is shown along with the number of plies. EP1000/4 designates a belt with four plies of polyester warp, nylon weft fabric and an ultimate full-belt tensile strength of 1000 kN/m. Alternatively the belt can be often described as 4 ply EP250 where the strength of the individual plies is shown. The allowable working tensions allocated are shown in tables 1 and 2 in section 4.
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GENERAL PROPERTIES OF BELT COVERS AND GRADES The following tables give a comparison of general characteristics of polymers used in belting compounds. Special compounding can result in substantial changes to these general polymer properties. Generally conveyor belts are supplied with electrical resistance in the anti-static range and should not be used for electrical insulation. Special non-conductive grades are available on request. There are four separate tables: Belts for Mining, Quarrying and General Service Heat Resistant belts Oil and Chemical Resistant grades Fire Resistant and Anti-static belts Notes referred to in these tables are: 1. Available with extended ozone resistance capabilities on special request. 2. The low temperature performance figures given in the table are representative of general purpose compounds in each classification. Belts for operation at lower temperatures than those given are available on request. 3. The high temperature performance figures given in the table are representative of situations where the belt is subject to relatively long exposures of blanketing heat. Considerably higher temperature bulk material can often be carried in ventilated situations or where the belt surface can be shielded to some extent by a protective layer of cooled fines. 4. Resist most acids except concentrated strongly oxidising ie., Sulphuric, Nitric and their derivatives. 5. Fire resistant and anti-static grades: GRADE S meets AS4606 for UNDERGROUND COAL MINING. GRADE E, F fire resistant and anti-static - mostly for ENCLOSED ABOVE GROUND USE GRADE K fire retardant and anti-static - meets MSHA 2G and ISO433 requirements 6. Resists most oils however resistance may vary greatly depending on the type of oil. 7. May have poor resistance to oils with low aniline points.
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4. Belt Carcass Selection Belt Construction Requirements …………………………………………………
4-1
Considerations ….……………………………………………………………………… 4 - 1 Procedure ………..…………………………………………………………………
4 - 2
Table 1A Allowable Working Tensions – Standard constructions…………….. 4-3 Table 1B Allowable Working Tensions – Coal Master series………………….. 4-4 Table 2A Load support table – Standard constructions……………………….. … 4 - 5 Table 2B Load support table – Coal Master series………………………………… 4 - 6 Table 3 Belt troughability –………………………………………………………. 4 - 7
BELT CONSTRUCTION REQUIREMENTS. To select the optimum plied belt carcass, five properties must be considered: •
The belt width.
•
The service conditions under which the belt will operate.
•
The maximum operating tension (T max) – both steady state condition and peak (see table 1).
•
The minimum number of plies required to support the load (see tables 2).
•
The maximum number of plies beyond which transverse flexibility is reduced and the troughing efficiency is affected. This varies with the belt width, trough angle and the idler roll arrangement (see table 3).
CONSIDERATIONS: Operating conditions The allowable working tensions shown on Table 1 that follow are applicable for reasonably well maintained conveyors operating with moderate impact, i nfrequent starts and good loading. Peak tension – on starting or braking, should not exceed 140% of the allowable working tension. For more severe operating conditions, moderate maintenance, short time cycles, frequent DOL or loaded starts, poor loading or severe impact, hot materials handling etc., reduce the tabled figures by 15%. Tension on starting or braking should not exceed 150% of the resulting rated tension.
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For severe service conditions, poor maintenance, very hot materials, chemically aggressive environment, severe impact and short time cycles etc., reduce the tabled figures by 30%. Tension on starting or braking should not exceed 160% of the resulting rated tension. Safety factors The working tensions shown on these tables are based on the application of a safety factor of 6.7:1 on the strength of the belt at the splice or fastened join. The safety factor is increased for more difficult operating conditions with further restrictions applying for starting and braking. Starting and braking tensions A check should always be made comparing the acceleration or braking tension with the allowable peak tension for the belt, i.e. 140% of rated working tension. If the peak tension exceeds the latter figure, a stronger belt can be selected or the choice of control must be changed to reduce peak tension. Mechanical fasteners WE always recommend hot vulcanised splices for plain weave plied belting. Other constructions including the Crows Foot Weave, Double Weave and Solid Woven PVC can be successfully operated at close to vulcanized joint tensions for long periods of time whereas plain weave constructions generally operate at reduced tensions when fitted with mechanical fasteners Recommended precautions including frequent inspection and monitoring, any Local Authority restrictions and greater than normal care should always be observed when using Mechanical Fasteners. Belt cleaners should only be fitted if specifically suited to operation with mechanical fasteners If a conveyor belt is to be operated for any length of time with mechanical fasteners then the selected combination of belt and fastener should be statically tensile tested and a working tension of not more than 15% of that result. Table 1 lists WE recommendations for its common range of belts. Troughability and load support This table provides a guide to the maximum width of belt that will support the load when carrying material with the bulk density shown. This table provides a guide to the minimum width of belt that will trough satisfactorily at the trough angle shown. The widths shown above are a guide only and experience may dictate the selection of a ply more or a ply less. Some factors that may influence the choice are: • • •
Partially filled belt. Idler trough angle Convex or concave curve radius and idler pitch
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Lump size of material Installed pulley diameters
PROCEDURE: Consider the possible belt constructions. 1. Calculate working tension needed for the both steady state and peak (accelerating or braking). Required Working Tension (kN/m) =
Tmax (kN) Belt width (m)
Where: Tmax. = Peak or Steady State tension in conveyor (kN). 2. Considering operating conditions and starting and braking tensions and determine suitable belt constructions from tables 1A and 1B. Working tensions shown in tables 1A and 1B are applicable for reasonably well-maintained conveyors with moderate impact, infrequent starts and good loading and are reduced where operating conditions are less favourable - see discussion below. 3. Consider special needs and the use of special fabrics such as Crow’s foot or Double weaves. 4. Establish the various practical carcass/ ply number combinations to support the load for the conveyor working conditions under review - (Tables). Load support r equirements may dictate that the selected belt is operating at a fraction of it’s allowable working tension. 5. Check that the selected construction(s) are acceptable for troughing - (Table 3) 6. Check that the installed pulley diameters are adequate – (refer section 6) The final selection should be checked with WE since cost, availability and service criteria can be additional factors for consideration.
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Considerations…………………………………………………………………………… 5 - 1 Selection……………….………………………………………………………………….. 5 - 1 Pulley side cover………………………………………………………………………… 5 - 1 Table 1 Top Cover Thickness ………………………………………………………… 5 – 2
CONSIDERATIONS There are a number of factors that must be taken into account when selecting the belt grade or cover material, such as: • • • • • • • • • • • • • •
Fire resistance or anti-static properties Resistance to oils or chemicals Temperature of the operating environment or conveyed material Resistance to ageing, weathering and ozone. The type of material being conveyed The lump size and shape of the material being conveyed The mix of lumps and fines in the material The abrasiveness of the material The method of loading the belt The fall height of material to the belt The cycle time of the conveyor for a single revolution of the belt Performance or experience in a similar application For replacement belts – the performance of previous belts on the same installation Availability and cost
SELECTION Previous experience will always be the best guide to the optimum selection of both the type and thickness of belt cover, however if this information is not available as will be the case for new installations, the following steps should be followed. •
•
•
From table 1 – 2 select the most suitable cover types of cover or belt grades for the application. In some cases statutory requirements or the operating conditions will limit selections to one or two possibilities. Calculate the time cycle of the conveyor = (2 x L) S Where:L = conveyor centres (m) S = belt speed (m/s) Use table 1 as a guide to select the appropriate thickness of top cover. Consideration should be given to the applicable properties of the cover in making this selection.
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For difficult applications such as belt feeders, or impact belts, heavier covers may be required. PULLEY SIDE COVER As a guide, pulley side cover should generally be not less than 1/4 of carry side cover for covers up to 9mm and about 1/3 of carry cover thickness for covers heavier than 9mm. Operating conditions can dictate that heavier pulley side covers are required. For long centre, long time cycle conveyors, pulley side cover can be up to 1/2 of carry side cover.
Parallel face pulleys…………………………………………………………………….. 6 - 1 Crown face pulleys……………………………………………………………………… 6 - 2 Pulley face width………………………………………………………………………… 6 - 2 Table 1 Standard constructions – operating at over 60% of allowable working tension ………………
6-3
Table 2 Standard constructions – operating at 30 - 60% of allowable working tension ….……………
6-4
The minimum pulley diameter recommended for a particular belt depends upon three factors: •
Carcass Thickness – The wire rope diameter in the case of Steel Cord belts. - The overall thickness of all plies plus the rubber skims between plies in the case of Ply Type belts. -The overall thickness of the thick woven fabric separating the top and bottom covers in the case of Solid-woven belts.
•
Operating Tension – The relationship of the operating tension of the belt at the particular pulley to the belt’s Allowable Working Tension.
•
Carcass modulus – The relationship between elongation of the carcass and the resulting stress.
Whatever the carcass type, Steel Cord, Ply Type or Solid Woven, when the belt is bent around a small radius, tension stresses are developed in the outer fibers while compression stresses are built up in the inner fibers. At a given tension, if the radius is too small the elastic limit of the outer fibers may be exceeded and fracture, and at the same time, the compression of the inner fibers may cause severe crinkling and eventual ply separation.
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Since the elastic properties of the rubber or PVC cover material is so much greater than the carcass material, the cover thickness of the belting is not a factor in determining minimum pulley size, and may be ignored.
The tables of recommended pulley diameters in the INFINITY handbook for Ply Type belting are based on the three classes of pulleys defined in ISO 3684. viz.; •
• •
Type “A” – High tension / tight side pulleys (T1) e.g. head, drive, tripper and shuttle pulleys Type “B” – Low tension or slack side pulleys (T2) such as tail and take up pulleys Type “C" – Low tension snub or bend pulleys with wrap angle of less than 30 degrees
Two sets of Pulley Diameter tables follow: •
For belts operating at over 60% of allowable working tension Table 1 - for standard belt constructions
•
For belts operating at 30 – 60% of allowable working tension Table 2 - for standard belt constructions
For belts operating at less than 30% of the allowable working tension, the diameter of Type “A” pulleys can be reduced to the same as Type “B”. PARALLEL FACE PULLEYS With just a few special exceptions, all pulleys used with modern high strength, high modulus fabric belts should be parallel face types. It is absolutely mandatory that all pulleys used in conveyors fitted with Steel Cord belting be parallel face type. One notable exception to this rule is in the case of Bucket Elevators which, lacking any other means of tracking the belt centrally, may benefit from Crown Faced Pulleys. CROWN FACE PULLEYS A Crown Faced pulley can have the effect of centering the tracking of the belt, but only in the case where there is a long unsupported length of belt leading into the pulley, as the belt must be able to bend longitudinally along its centre line to benefit from the crown. High modulus Ply Type belts have very little ability to bend longitudinally and Steel Cord belts have virtually no ability at all. Solid Woven belts are not quite so rigid but still need an unsupported distance of something like 4 to 6 times the belt width to be able to react. Apart from not serving much purpose in troughed conveyor systems, Crowned pulleys can seriously damage the belt by severely overstressing the carcass in the centre of the belt, particularly in the case of Steel Cord belts. The few special cases where Crowned pulleys are useful include, Bucket Elevators, the Takeup pulley in long gravity Take-up arrangements and for some short centre - wide belt, reversing conveyors. In cases like this where there are no supporting idlers to train the belt, some benefit may be obtained from the installation of Crowned pulleys. It is fairly common practice to crown a pulley by machining a taper of 1 in 100 from each pulley edge
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towards the centre over a distance of 1/4 pulley face. It is more correct to relate the amount of pulley crown to the pulley diameter, not to its face width. Viz.; d = D - 0.008 x D PULLEY FACE WIDTH As all belts tend to wander a bit in operation, the overall face width of the pulleys should exceed the belt width by the following minimum amounts, if serious edge damage is to be avoided; • • •
Belts up to 650mm wide …. …. …. …. …. …. …. …. 100mm Belts 750 to 1400mm wide …. …. …. …. …. …. …. …. 150mm Belts over 1400mm wide …. …. …. …. …. …. …. …. 200mm
For conveyors built on unstable ground, as in underground coal mines and very long overland conveyors, the above allowances should be increased by 50mm.
Multiple Slope and Vertical Curve Conveyors …………………………………….. 7 - 1 Terminal Troughing Idler Arrangements ……………………………………………. 7 - 4 Transitions …………………………………………………………………..…………... 7 - 4 Take – Up Arrangements ………………………………………………………………. 7 - 5 Table 1 Table 2 Table 3 Table 4
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Average Elastic Modulus ‘E’ ……………………………….… Transition Distances for Head Pulleys ……………………… Transition Distances for Tail End Loading Points ………..… Gravity Take – Up Travel ………………………………..……
7-3 7-4 7 - 5 7 - 6
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Belt Mass and thickness………………………..………………………………,,,,,,,,,,,
8-1
Shipping dimensions and roll sizes…………………………….………………...…
8-1
Length of belt on a roll…………………………………………………………...……
8-2
Belt transport guidelines……………………………………………………….……
8-3
Table 1
Belt carcass mass and thickness – standard constructions……………………………………………… 8 - 4
Table 2
Belt carcass mass and thickness – CoalMaster series…………………………………………………… 8 - 5
Table 3
Belt carcass and cover mass factors……………………………….. 8 – 6
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Belt construction…………………………………………………………………………. 9 - 1 Belt and cover thickness……………………………………………………………….. 9 - 2 Operating temperature range………………………………………………………….. 9 - 2 Operating factor of safety………………………………………………………………. 9 - 2 Safety………………………………………………………………………………………. 9 - 2 Table 1 Belt Designations…………………………….. ….……..…………….…
11 – 2
BELT CONSTRUCTION Fenaplast conveyor belting consists of three main components: • • •
Textile Solid Woven Carcass PVC Impregnation Cover Material
THE TEXTILE CARCASS The solid-woven carcass is generally woven with nylon or polyester load bearing warp fibers and nylon or nylon/cotton weft. Synthetic binder yarns follow a complex pattern to give the carcass its solid-woven properties. Various combinations of synthetic, and natural fibers are chosen, together with the fabric design to meet the requirements of impact resistance, belt elongation, flexibility for troughing and small diameter pulleys, load support and fastener retention. The patented Fenaplast PVC impregnation method also renders the carcass impervious to attach from moisture, dirt, chemicals, bacteria, and oils. Cotton pile warp yarns may be included for improved impact resistance and special edge reinforcement can be included where these are particular problems. The Fenaplast carcass design facility enables users to choose the properties of a custom-built belt. All Fenaplast belts have a solid woven carcass where all layers of yarn are mechanically interlocked during the weaving process and bound together by a self binding warp yarn interweave, thus making subsequent delimitation impossible. High tenacity continuous filament synthetic yarns are used for the warp fie length direction), such yarns also provide most of the necessary strength in the weft (transverse/width) direction. PVC IMPREGNATION After weaving the roll of carcass is vacuum impregnated with PVC plastisol containing a careful blend of polymer, plasticizers, stabilisers, fire retardants, and special additives, with special attention being given to viscosity control in order to ensure full impregnation of the woven structure. Whilst the textile elements fix many of the belts properties such as tensile strength and elongation in service, the properties of the plastisol are equally important, and it's formulation will influence not only
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COVER MATERIAL PVC covers PVC covers to meet numerous fire resistance specifications or for other properties such as resistance to oils, chemicals, fertilizer etc., are generally available up to 3mm thick per side. They can also be compounded to give improved abrasion resistance or coefficients of friction. Rubber covers Rubber covers to a specified safety standard may be applied on one or both sides of a PVC impregnation parent belt up to a maximum of 6mm + 2mm, dependent on belt width, tensile and construction. SR wear-resistant nitrile rubber covers are also available, single or double sided, up to 6mm + 2mm maximum, dependent on belt construction. BELT AND COVER THICKNESS When considering cover thickness the user should be aware of the thick, high textile content of Fenaplast and the special solid-woven carcass properties. Consequently thinner covers may generally be chosen than normal with rubber, plied belting; the Fenaplast carcass being more substantial and providing the necessary load support and impact resistance. OPERATING TEMPERATURE RANGE Above 90 °C PVC softens and the belt properties change, therefore Fenaplast is not recommended for conveying materials above this temperature. Standard Fenaplast can be used in cold climates at minus 15°C and special cover compounds are available for operation down to minus 40 °C. Cold weather details should be supplied to ensure a belt with suitable coefficient and flexibility characteristics is supplied. OPERATING FACTOR OF SAFETY With good quality mechanical fasteners or vulcanized joints a factor of safety of 8:1 may be acceptable. SAFETY Fenaplast is used extensively in underground coal mines and as such it exhibits excellent Fire Resistant, Anti-Static properties. In Australia it is manufactured to AS 1332 and is tested to AS1334. It meets or exceeds all of the requirements of AS 4606-2000.
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BELT DESIGNATION: Belts can be produced to various tensile specifications, using either polyamide orpolyester base warp yarn. Some markets still prefer to specify belt types based on tensile strengthexpressed in Ibs/in width (the Fenaplast Belt Designation uses this terminology), whilst others opt for thepreferred ISO types expressed in kN/m. BELT WEIGHTS: The above table shows some typical figures for minimum warp and weft strengths, belt thickness and weight for a selection of belt types, based on In- PVC covers. For thicker covers, add 1.3 kg/m2/mm for PVC covers and 1.4 kg/m2/mm for rubber covers. The nominal figures quoted for thickness and weight are based on specific belt constructions and PVC covers of l mm. Alternative belt constructions may vary these figures which are only for indicative purposes and establishing shipping capacities. ALTERNATIVE CONSTRUCTIONS: Many alternative constructions are available which give values higherthan those in the table. This is particularly relevant to weft strength, where special yarns designs may be recommended for improved properties such fastener holding, load support, weft stability etc. The use of such special yarns may increase the belt weight and thickness which may be critical for shipping purposes or underground transportation. An APEX FENNER engineer should always be consulted where this information is likely to be critical. PULLEY DIAMETERS: The drum diameters are the minimum recommended without complete application details. With information regarding wrap configurations, tensions, belt speeds, jointing methods, etc., it maybe possible to accept smaller drums.
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General Maintenance .…………………..…………………………………..… 10 – 1 Loading point considerations……………………………………………….. 10 - 2 Random events ………………………………………………………………… 10 - 4 Troubleshooting ………………….…………………………………………….. 10 - 5
GENERAL MAINTENANCE
Conveyor belting represents a very significant portion of the overall plant cost and as such warrants regular inspection and maintenance to protect this investment. Broadly speaking, apart from normal wear, rubber conveyor belting fails through chemical attack or mechanical damage in one form or another. •
Chemicals such as all greases, oils, solvents and animal fats should be removed as soon as detected from belts not designed to handle these materials. Susceptible belts including all natural rubber belts should be washed down with water and detergent immediately after contamination.
•
Ozone is a common cause of premature failure in natural rubber and many synthetic and rubber belts, particularly when operating near the sea, enclosed near electrical machinery or in a salty environment. INFINITY belts are supplied with high levels of ozone resistance, and this level of protection can be increased by special request at the time of ordering for extreme conditions.
•
Mechanical damage is best prevented by clean design and erection, (no jagged edges) good path clearance, generous belt paths, frequent checking and prompt remedying of all faults.
•
Belt cleaners perform a very important role in the protection of the belt. Properly sited and fitted they protect the belt from damage through: o o o
o
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Trapping of material between return belt flight and pulley. Belt wander through running off as material forms a crown on the pulley. Damage to pulley face through belt edge slapping and grinding at the pulley face edges. Spill from the return side building up under the belt to damage both belt and return idlers. Belt cleaners must be selected carefully and deserve frequent attention.
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Idlers - All noisy idler should be looked at immediately. All jammed or broken idlers should be removed immediately. Hot idlers should be hosed down and remain under supervision whilst the conveyor is stopping and down to ambient temperature. It must be removed immediately the conveyor is stopped. A jammed idler causes increased friction resulting in excess cover wear higher power consumption and may create sufficient heat to start a fire when the belt stops. •
Pulleys - Material trapped between a pulley and the belt may cause belt wander and if hard lumps are present may rupture the belt. Plough cleaners should be fitted wherever a spill onto the return belt is carried onto a pulley. This is crucial at high tension pulleys but can lead to tracking and loading problems after the tail pulley. •
•
Take-up may be automatic or manual . The Automatic Take-up is the most desirable as properly maintained, it is able to maintain the correct tension in the belt under all normal operating conditions including starting, running, stopping and changes in belt length caused by changes in ambient and operating temperature . If for any reason the Automatic Take-up travel becomes restricted or jammed, belt slippage at the drive may occur, this will cause extreme damage to the belt. The Manual Take-Up has the advantages of compactness and low cost, however it is unable to maintain optimum tension through the normal operating conditions including starting, running, stopping and changes in belt length caused by changes in ambient and operating temperature. •
Be aware of abnormal or changed noises emanating from the conveyor as these, if left unattended could lead to a fire, gearbox or pulley / coupling failure to name just two items. The following plant items should be frequently listened to and looked at. Analyse the problem and take maintenance precautions.
LOADING POINT CONSIDERATIONS: Chutes, loading boots and skirts - These items are frequent trouble spots when fitted too closely to the belt. They can cause rapid localised cover wear and in extreme cases, slit the belt. Conversely when installed with too much clearance, material is allowed to spill over, often falling onto the return belt and building up on the tail pulley causing tracking problems in the loading boot further exacerbating the problem. If the spilled material is hard, the belt may also be punctured. Also to be considered is wedging between a chute wall and the belt. In the mildest occurrence, this will accelerate the cover wear, in more severe occurrences the belt carcass is permanently damaged. Most wear and tear on the belt takes place at the loading point. The manner of loading may influence the life expectancy of the belt and the components of the loading boot. Loading points should be arranged with particular care and the following points should be observed: •
• •
The material being conveyed should be fed onto the belt at belt speed in the running direction of the belt. The height of the drop from the feeding point onto the belt should be as small as possible. Impact idlers should be installed at the loading points.
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The following sketches show some loading point arrangements. Loading Point Arrangements
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RANDOM EVENTS AND CAUSES OF BELT DAMAGE TRAMP IRON Most rips, some continuing the entire length of the belt, are caused by tramp iron becoming wedged into the belt at loading chutes. If this hazard is prevalent, the installation of a mechanical or magnetic detector to stop the belt may be justified. Dangerous material can be magnetically extracted or some reliable rip detection/protection device may be warranted. Work practices and vigilance among all employees and contractors can also reduce this problem. MINOR REPAIRS Unless repaired, minor tears quickly become major repairs or catastrophic failure. Early detection and prompt attention is the best long-term strategy.
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INSTALLATION, JBS Kumar
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STORAGE New conveyor belt should be stored upright in the factory package until used. A cool dry room, free from sunlight, steam pipes, oil and corrosive fumes is best. Under no conditions should rolls of belt be laid flat on a concrete floor. Moisture will shrink any exposed fabric which gets damp from such storage and the belt is liable to “ bow” on one edge. Upright rolls on a dry wooden floor is recommended.
HANDLING THE ROLL Conveyor belting is customarily packaged in cylindrical reels or rolls which may be rolled from place to place. All rolls are marked with an arrow showing the direction in which they should be rolled. (Fig. 1) Rolling in a direction opposite to that of the arrow tends to loosen and telescope the belt. Reels or rolls should never be dropped from a freight car, truck, or other means of conveyance since their weight will break the packaging and may damage the belt. Reels or rolls should always be rolled or provision should be made for hoisting them. For hoisting, a bar is passed through the hole in the center of the roll. Chains or cables looped around the bar ends should be provided with a spreader above the roll to avoid damage to the belt edges.
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INSTALLATION Once the roll of belting has been transported to the point of installation it should be mounted on a suitable shaft for unrolling and threading onto the conveyor. Conveyor belting is normally rolled at the factory with the carrying side out. Consequently, in mounting the roll the belt must lead off the top of the roll if it is being pulled onto the troughing or carrying idlers but off the bottom of the roll if it is being pulled onto the return idlers. When pulling the belt onto the conveyor, the roll will turn opposite the direction indicated by the arrows on the crate. Fig. 2 illustrates a suitable method of mounting as well as leading off the top of the roll for pulling onto the troughing idlers. In some cases, such as in mines where head room does not permit maneuvering a roll, the belt may have to be pulled off the roll and reefed. (Fig. 3) Extreme care should be exercised to see that the loops have large bends to avoid kinking or placing undue strain on the belt, and no weight should ever be placed on the belt when it is in this position. Another method of handling belting under such conditions is to lay the roll on a turntable with a vertical spindle. OOTING
INSTALLATION
, MAINTENANCE & TROUBLESHOOTING
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TRAINING THE BELT Training the belt is a process of adjusting idlers, pulleys and loading conditions in a manner which will correct any tendency of the belt to run other than centrally. When all portions of a belt run off through a part of the conveyor length the cause is probably in the alignment or leveling of the conveyor structures, idlers or pulleys in that area. If one or more portions of the belt run off at all points along the conveyor the cause is more likely in the belt itself, in the splices or in the loading of the belt. When the belt is loaded off-center the center of gravity of the load tends to find the center of the troughing idlers, thus leading the belt off on its lightly loaded edge. (See Fig. 4) These are the basic rules for diagnosis of belt running ills. Combinations of these things sometimes produce cases that do not appear clear-cut as to cause but if a sufficient number of belt revolutions is observed the running pattern will become clear and the cause disclosed. The usual cases when a pattern does not emerge are those of erratic running which may be found on an unloaded belt that does not trough well or a loaded belt which is not receiving its load uniformly centered.
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FACTORS AFFECTING THE TRAINING OF A BELT Pulleys and Snubs Relatively little steering effect is obtained from the crown of conveyor pulleys. Crown is most effective when there is a long unsupported span of belting, (approximately four times belt width) approaching the pulley. As this is not possible on the conveyor carrying side, head pulley crowning is relatively ineffective and is not worth the lateral mal-distribution of tension it produces in the belt. Tail pulleys may have such an unsupported span of belt approaching them and crowning may help except when they are at points of high belt tension. The greatest advantage here is that the crown, in some degree, assists in centering the belt as it passes beneath the loading point which is necessary for good loading. Takeup pulleys are sometimes crowned to take care of any slight mis-alignment which occurs in the takeup carriage as it shifts position All pulleys should be level with their axis at 90 to the intended path of the belt. They should be kept that way and not shifted as a means of training with the exception that snub pulleys may have their axis shifted when other means of training have provided insufficient correction. Pulleys with their axes at other than 90 to the belt path will lead the belt in the direction of the edge of the belt which first contacts the mis-aligned pulley. When pulleys are not level the belt tends to run to the low side. This is contrary to the old rule of thumb statement that a belt runs to the high side of the pulley. When combinations of these two occur, the one having the stronger influence will become evident in the belt performance. °
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Carrying Idlers Training the belt with the troughing idlers is accomplished in two ways. Shifting the idler axis with respect to the path of the belt, commonly known as knocking idlers , is effective where the entire belt runs to one side along some portion of the conveyor. The belt can be centered by knocking ahead (in the direction of belt travel) the end of the idler to which the belt runs. (See Fig. 5) Shifting idlers in this way should be spread over some length of the conveyor preceding the region of the trouble. It will be recognized that a belt might be made to run straight with half the idlers knocked one way and half the other, but this would be at the expense of increased rolling friction between belt and idlers. For this reason all idlers should initially be squared with the path of the belt and only the minimum shifting of idlers used as a training means. If the belt is over-corrected by shifting idlers it should be restored by moving back the same idlers, not by shifting additional idlers in the other direction. “
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Obviously such idler shifting is effective for only one direction of belt travel. If the belt is reversed, a shifted idler, corrective in one direction, is mis-directive in the other. Hence reversing belts should have all idlers squared up and left that way. Any correction required can be provided with self aligning idlers designed for reversing operation. Not all self-aligners are of this type, as some work in one direction only. Tilting the troughing idler forward (not over two degrees) in the direction of belt travel produces a selfaligning effect. The idlers may be tilted in this manner by shimming the rear leg of the idler stand. Here again this method is not satisfactory where belts may be reversing. This method is illustrated in Fig. 6.
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Return Idlers Return idlers, being flat, provide no self-aligning influence as in the case of tilted troughing idlers. However, by shifting their axis (knocking), with respect to the path of the belt, the return roll can be used to provide a constant corrective effect in one direction. As in the case of troughing rolls, the end of the roll toward which the belt is shifting should be moved longitudinally in the direction of return belt travel to provide correction. (Fig. 5) Self-aligning return rolls should also be used. These are pivoted about a central pin. Pivoting of the roll about this pin results from an off-center belt and the idler roll axis becomes shifted with respect to the path of the belt in a self-correcting action. (Fig. 8) Some return idlers are made with two rolls forming a 10 to 20 V-trough which is effective in helping to train the return run. °
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A further aid to centering the belt as it approaches the tail pulley may be had by slightly advancing and raising the alternate ends of the return rolls nearest the tail pulley. (Fig. 9)
Assuring Effectiveness of Training Rolls Normally, extra pressure is desired on self-aligning idlers and, in some cases, on standard idlers where strong training influence is required. One way to accomplish this is to raise such idlers above the line of adjacent idlers. Idlers or bend pulleys on convex (hump) curves along the return side have extra ressure due to component of the belt tension and are therefore effective training locations. Carrying side self aligners should not be located on a convex curve since their elevated positions can promote idler juncture failure of the carcass.
Side Guide Rollers Guides of this type are not recommended for use in making belts run straight. (Fig. 10) They may be used to assist in training the belt initially to prevent it from running off the pulleys and damaging itself against the structure of the conveyor system. They may also be used to afford the same sort of protection to the belt as an emergency measure, provided that they do not touch the belt edge when it is running normally. If they bear on the belt continually, even though free to roll, they tend to wear off the belt edge and eventually cause ply separation along the edge. Side guide rollers should not be located so as to bear against the belt edge once the belt is actually on the pulley. At this point no edge pressure can move the belt laterally.
The Belt Itself A belt having extreme lateral stiffness, relative to its width, will be more difficult to train due to its lack of contact with the center roll of the carrying idler. Recognition of this fact enables the user to take extra precaution and, if necessary, load the belt during training to improve its severability. Observation of troughability design limitations will normally avoid this trouble. (Fig. 11) Some new belts may tend to run off to one side, in a certain portion or portions of their length, because of temporary lateral mal-distributions of tension. Operation of the belt under tension corrects this condition in practically all cases. Use of self-aligning idlers will aid in making the correction.
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SEQUENCE OF TRAINING OPERATIONS Initial installation of conveyor equipment should ensure good alignment of all pulleys, troughing and return idlers, i.e., they should be placed at right angles to the direction of belt travel, leveled and centered on a straight line. First movement of the belt should be slow and intermittent so that any tendency of the belt to run off may be quickly observed and the belt stopped before damage occurs. When the conveyor is a long center installation, men should be stationed at frequent intervals to observe the action of the belt. They should be provided with an effective method of communication so as to report their observations and, if necessary, cause the belt to be stopped. Initial movement of the belt will provide indication of where corrections of the types described are required. The first corrections must be those at points where the belt is in danger of being damaged. Once the belt is clear of all danger points, a sequence of training operations can be followed. The best procedure to use in starting the training sequence is probably to start with the return run and work toward the tail pulley. This assures early centering of the belt on the tail pulley so that it can be centrally loaded. If the empty belt troughs readily, so that its running tendencies are not erratic, the training can and should be completed. Should the belt tend toward stiffness and erratic running, getting some load onto the belt as soon as the return run has been straightened up and the belt centered on the tail pulley will help hold the top run. Normally, the belt can be trained properly onto the tail pulley by manipulation of return idlers and with the assistance of self-aligning return rolls. Seldom is any adjustment of snub or tail pulley necessary but the snub can be used as a supplementary training means. Training of the top run, with the belt empty, is usually no problem if the belt troughs readily. In this case self-aligners on top are not required except as insurance against damage in the region approaching the head pulley. There, two self-aligners, placed approximately 40 and 80 feet preceding the pulley, will help re-center the belt if it is ever forced off due to some temporary disturbance. It should not be necessary to use the head pulley for training purposes if it has been aligned properly. Likewise, the snub following the head pulley should not be required as a training means. It is relatively ineffective as a training device due to the strong influence of the head pulley. The take up carriage has a strong influence on the running of the belt at that point and, due to its movement as belt length changes, is subject to mis-alignment. A vertical take up carriage, hanging in a festoon of belt, must be guided in its travel so that the pulley shaft remains horizontal. The belt cannot be depended upon to center itself on the pulley and, once it moves off center, the pulley will tip out of horizontal if not guided closely on its posts. A horizontal take up carriage is subject to mis-alignment due to loose track gauge, fouled rails or even jumping off the track. V-shaped rails will hold the gauge tight and, with the apex upward, are selfcleaning. Hold-down rails above the wheels with sufficient clearance so that they do not touch under normal operation will help prevent jumping off the track. (Fig. 12)
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With the empty belt trained satisfactorily, good operation with load is usually assured. Disturbances which appear with load are usually due to off-center loading or to accumulation of material from the load on snub pulleys and return idlers. When equipment is known to be properly aligned, training action should be taken slowly and in small steps because the belt requires some time to respond to corrective measures. It should begin at some point preceding that where run-off occurs and then gradually proceed forward, in the direction of belt travel, until the run-off condition has been corrected. Under some conditions of operation where the conveyor is not level, is extremely short or too wide to be affected by permissible crowning, belts with a special guide strip have been used. This V-guide strip runs loosely in grooved pulley and idler rolls. Guide strips are not recommended or necessary for the long conveyors normally encountered in industrial use.
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CLEANING Special care must be exercised to keep the return rolls and snub pulleys clean. Buildup of material on this equipment has a destructive effect upon training with the result that the belt may run against the structure and damage itself. It is adviseable wherever possible that return idlers be suspended far enough below the structure so that any mis-alignment or dirty idlers can be easily seen. Keeping the return rolls and snubs clean requires that the belt be clean when it enters the return run. Scraping is the most common method of doing this. Rubber scrapers can be made by clamping rubber slabs 1/2 to 1 thick (not old belting) between two metal or wooden bars. Extend the rubber about twice its thickness beyond the bars and suspend the mechanism with a counter-weight to provide the pressure against the belt. (Fig. 13) Replace the rubber when it wears down near the bars. Two or three such scrapers can be used in succession. ”
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The most common steel scraper is a series of diagonally set blades mounted on the end of a leaf spring to maintain pressure against the belt. These will scrape sticky materials which rubber scrapers may ride over. (Fig. 14) Washing the belt with a water spray before wiping with a rubber scraper will do a good cleaning job on almost any material, including iron ores and mixed concrete. Dry materials can be cleaned off the belt with rotating bristle or rubber vane brushes, driven at fairly high surface speed, usually three to five times the belt speed. (Fig. 15) They wear rapidly, require considerable maintenance and are likely to fill up solid if used with wet and sticky materials. It is preferable to clean just after the head pulley and before the snub. An exception to this is that sticky material often requires scraping on the head pulley. This is because a large part of the fine material sticks to the belt and must be scraped into the chute. In some cases the best possible cleaning is insufficient and steps must be taken to compensate for the effect of a dirty belt. Snub pulleys can be kept from building up by the use of soft rubber lagging or by scraping directly against the pulley. Diagonal grooving will distort and discharge accumulations on these pulleys. Rubber disc or spiral type return rolls prevent build-up on themselves and thus save a training problem. (Fig. 16 & 17) The only cleaning required on the pulley side is removal of material, principally lumps, which may fall or bounce onto the return run, and be carried between the belt and tail pulley if not removed. (Fig. 20) Rubber faced plows immediately in front of the tail pulley are used for this purpose. (Fig. 18 & 19) they are usually held against the belt by gravity and set at an angle to the direction of belt travel.
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LOADING Receiving material off center will cause the belt to move sideways after loading as the center of the load seeks the lowest point in the troughing idlers. This can be corrected by proper chute arrangement provided, of course, that the belt is centered as it enters the loading point. (Fig. 4) The loading point of any conveyor is nearly always the critical point, the life determining point of the belt. Here the conveyor receives its major abrasion, and practically all of its impact. The “ideal condition” is to have the material pass from chute to belt at the same speed and direction of travel as the belt with a minimum amount of impact. The subject of chute design and arrangement is too broad to be discussed in detail here. In lieu of such discussion, the following suggestions are offered: The width of the receiving end of the loading chute should be great enough to accept material lying on the extreme edge of the preceding belt or feeder, and its position determined by the trajectory of the material coming into it. At no place should the chute be less than twice the size of the largest lumps, if fines are present, and 3 1/2 times the size of lumps, if uniform. The discharge width of the chute thus determined should not exceed about 2/3 of the receiving belts ’ width. (Fig. 21) The slope of the chute is determined by the nature of the material, its entering velocity and length of the chute. This value varies with each particular installation, but about 35° has been found satisfactory for most dry industrial materials such as coal and rock.
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[ An attempt to approach the above “ideal condition” should be made continually by adjusting the chute arrangement. Optimum loading and transferring through chutes still requires considerable experimental adjustment in the field. Skirt boards should be used to further center and settle the load as it leaves the loading point. The steel structure of the chute and skirts never should be placed closer to the surface of the belt than 1 ”, this distance to be made increasing in the direction of belt travel to free any material trapped between the belt surface and the skirt. (Fig. 22) Skirt boards are usually 4 or 5 times the belt width in length, but may vary considerably due to belt speed, type of material and lump size. Sample skirt board arrangements are shown in Fig. 23.
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Impact of material being loaded on the belt is often the cause of severe cuts and gouges. The degree of impact can be lessened to some extent by providing a cushion in the form of rubber covered disc type or semi-pneumatic idlers which also tend to prevent material from crowding under the skirt boards at the instant of impact. (Fig. 24) The use of a “Grizzly,” a slightly fanned row of bars, at the bottom of the transfer chute reduces wear on the belt. It distributes the impact of large lumps by allowing the fines to fall onto the belt first to act as a cushion. The fan shape of the “Grizzly” in the direction of travel prevents jamming of the lumps. (Fig. 25) A “V-slot” cut in the bottom of the chute is another very satisfactory method of allowing fines to fall on the belt before the lumps and thereby reduce belt wear at this point. (Fig. 26)
PULLEY LAGGING Lagging is recommended for drive pulleys for the following reasons: 1. Improved co-efficient of friction. This permits a belt to be driven by lower slack side tension and sometimes results in lower total tension. 2. Reduction of slippage due to wet conditions if grooved lagging is used. 3. Increased life for pulley and pulley cover of belt. Other pulleys in the system, especially those contacting the carrying side of the belt, are often lagged to prevent build-up of material. Grooving improves cleaning action on the lagging and the belt.
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TYPES OF LAGGING 1. Bolted lagging is usually fabric reinforced, the fabric being necessary to give proper bolt-holding. This type has no inner or pulley cover; where no grooving is intended, 1/8 ” top cover is the proper minimum, but if the lagging is to be grooved a minimum of 1/4 ” top cover must be used.
Bolted lagging is usually applied in two or more circumferential strips, applied under tension with the points in the different strips staggered around the pulley. (On flat-faced pulleys, one strip the width of the pulley may be used.) For open end pulleys 5/16 ” or 3/8” diameter flat head elevator bolts with nuts may be used. Alternate methods include slotted bolts with tapped holes or self tapping screws for use in welded steel pulleys. It is necessary that the bolt heads be sunk below the level of the surrounding lagging to prevent damage to the belt as it passes over the pulley. This may be accomplished by counter-sinking the holes in the pulley or, where the lagging cover is greater than about 1/8 ”, it is possible to sink the heads merely by tightening the bolts. Ends of the strips should be bolted in a dovetail joint as shown in Fig. 27. In addition, bolts should be used in rows running across the face and around the circumference of the pulleys no further than 10 ” apart in either direction. Edges of all strips should be bolted down and it is recommended that all exposed fabric edges be cemented to keep out moisture. 2. Vulcanized lagging is a sheet of rubber, usually 1/2 ” thick, bonded directly to the metal. No fabric is used because no bolt-holding reinforcement is needed. It is much longer wearing, has better and more uniform adhesion to the pulley and eliminates the hazard of serious belt damage due to a loose bolt.
This type of lagging can be applied in two different ways: Spiral method – generally used for lower tension applications. A 4 ” wide strip is recommended for ease of handling. (Fig. 28) The length of the strip may be calculated by the formula:
In application by the sheet wrap method, a beveled lateral splice is recommended. (Fig. 29) The tie gum side should contact the beveled leading edge for maximum adhesion at the splice. 3. Grooved lagging should be used on drive pulleys if they are likely to be wet. The grooves break the film of moisture between the belt and lagging thereby eliminating slippage. Either bolted or vulcanized lagging can be furnished with grooves. Either type can be grooved in the field with a tire-groover if there is sufficient rubber to prevent cutting into the fabric carcass or metal pulley. Herringbone grooving 3/16 ” deep and wide spaced 1 ” apart is recommended. (Fig. 30) 4. A modified type of bolted pulley lagging is also available which features replaceable rubber pads that slip into metal guides bolted or welded to the pulley. (Fig. 31)
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