Belt Chan

1998 PT Design A105

BELT DRIVES

Belts, pulleys, andsheaves for OEMhigh-volume-pro-

duced products such ashome appliances and passenger carengines are usually custom designedand manufactured by the thousandsfor specific functions and operatingconditions. The heavy expense of cus-tom belt design, extensive testing,and special tooling are absorbed eas-ily in the volume production of identi-cal belts. Short delivery time is not ex-pected in the mass produced productuntil a specific production date is set.

An entirely different set of cost, de-

drives that are more impor-tant in some applicationsthan others are:

1. Endless belts usuallycannot be repaired whenthey break. They must be

replaced.2. Slippage can occur, particularly

if belt tension is not properly set and checked frequently. Also, wear ofbelts, sheaves, and bearings can re-duce tension, which makes retension-ing necessary.

3. Adverse service environments(extreme temperature ranges, highmoisture, oily or chemically filled at-mospheres, etc.) can damage belts orcause severe slipping.

4. Length of endless belts cannot beadjusted.

Design considerations — Belttype, belt materials, belt and sheaveconstruction, power requirements ofthe drive, speeds of driving anddriven sheaves, sheave diameters,and sheave center distance are keybelt drive design considerations. Ba-sic to power transmission design withbelt drives is to maintain friction de-veloped between the belt and thesheave or pulley contact surface.

Belt creep and slip — All belts(except synchronous) creep, but creepmust be differentiated from slip. Forexample, a V-belt under proper ten-sion creeps about 0.5% because of itselasticity and the changes in crosssection and length taking place as asection of the belt moves from thetight side to the slack side of the driveand back. That cyclical stressing, plusthe bending action of the belt as ittravels around the sheaves, causesonly a slight increase in belt tempera-ture. Most of that heat will be dissi-pated by the sheaves so that they willbe only slightly warm if touched. (Ofcourse, the belt drive must be at restbefore an operator would dare touchthe sheaves.)

Slip, which is a movement greaterthan the 0.5% creep, can createenough heat to be very uncomfortableif the sheaves are touched (again,when the drive is stopped). Another

sign, and delivery priorities prevail forbelts and sheaves for industrial ma-chines built only a few at a time. Thesame low-quantity-needs approachmust be taken on belt drive systems forown-use machinery, rebuilt machin-ery, plant pump equipment, com-pressed air equipment, and the fullrange of heating, ventilation, and air-conditioning systems. It is difficult tojustify the expense of custom belts andsheaves when only a few (and some-

times a few hundred)of any one size areneeded. Fortunately, awide variety of stan-dard sizes and types ofindustrial belts andsheaves is readilyavailable from stock atindustrial powertransmission productsdistributors. Repre-sentative standardbelts, Figure 1, in-clude flat, classical V,narrow V, double V, V-ribbed, joined V, andsynchronous designs.

Advantages of beltdrives include:

1. No lubrication is-required, or desired.

2. Maintenance is minimal and infre-quent.

3. Belts dampensudden shocks or changes in loading.

4. Quiet, smooth op-eration.

5. Sheaves (pulleys) are usually less ex-pensive than c h a i nd r i v e s p r o c k e t sand e x h i b i t l i t t l ewear over long periodsof operation.

Drawbacks of belt

BELT AND CHAIN DRIVESBELT DRIVES ...................................................A105CHAIN DRIVES .................................................A109BELT AND CHAIN DRIVES ADVERTISING ........A115

Figure 1 — Representative belt configurations.

V-ribbed

way to check for slip is to touch thebelt (when it is stopped). If the belt isuncomfortable to the touch (over 140F), it probably needs to be tightened.

Belt tension — Checking operatingtemperatures of sheaves and belts (thetouch test) is but one of several waysexperienced machine operators andplant maintenance people check belttension without the need for compli-cated measurements and calculations.

Other equally simple and usefulbelt tensioning approaches involve vi-sual and sound techniques. The bowor sag on the slack side of belt drivesincreases as a drive approaches fullload. Undulations and flutter on theslack side of belts can be very infor-mative to the experienced eye. Propertensioning can reduce or eliminatethese conditions.

Tension adjustment based on beltsound can be a useful technique.Loads such as industrial fans requirepeak torque at starting. If belts squealas the motor comes on or at some sub-sequent peak load, experienced beltpeople say the belts should be tight-ened until the squeal disappears.

Calculating V-belt tension —Figure 2 represents a belt drive ar-rangement which can be used to studyfactors affecting V-belt tensions andstresses. At standstill, the belt strandtensions T1 and T2 are equal. Whenload is applied to the driving pulley,tension T1 increases and T2 decreases.

T1, tight side tension, divided by T2

slack side tension, is the tension ratioof a belt drive. The formula for ten-sion ratio is as follows:Where:

e 5 2.718 (the base of natural loga-rithm).

k 5 Wedging factor, from Figure 3, which is considered constant for a

designed belts willnot run properly;they may slip, vi-brate too much, orturn over in thegrooves.

All torque ist r a n s m i t t e dthrough the belts,and torque doesnot change for a

given horsepower and speed. This ba-sic concept is best revealed in a multi-ple-belt drive. For example, a multipleV-belt drive formerly requiring sevenbelts may need only five higher-ratedbelts with the same cross section. Forfive belts to deliver the same horse-power as seven belts, each of the fivenew belts must carry more load. In-creased tension in the individual beltswill not overload the bearings, as someengineers may fear, because total ten-sion in the drive should be exactly thesame value. Each belt has a highertension, but there are fewer belts totransmit the tension to bearings.

Belt typesFlat belts — Most of the general

principles of belt drive operation dis-cussed earlier apply to flat belt drives.In calculating tension ratios for flatbelts, consult the manufacturer fortypical values of the friction coeffi-cient, f. For a flat belt drive, k = 1.Several useful formulas for endlessbelts follow (refer to Figure 4). Forbelt length in an open belt drive:

Belt length in a crossed belt drive:

given drive. f 5 Dynamic coefficient of friction

between belt and sheave.f 5 Wrap angle (arc of contact on the

smaller sheave in radians).K applies only to V-belt drives. A

practical tension ratio of 5 for V-beltsallows for such variations as lack ofrigidity of mountings, low initial ten-sion, moisture, and load fluctuations.For rubber flat belt drives, a tensionratio of 2.5 is considered most efficient.

The difference between tight-strand and slack-strand tensions iseffective tension, or Te 5 T1 2 T2. Ef-fective tension is the actual force thatturns the driven sheave.

Stress and power ratings — Theusable strength of a belt is the tensilestress the belt withstands for a speci-fied number of stress cycles, usuallythe equivalent of 3 years of continu-

ous operation, orabout 25,000 hr. Therelationships of effec-tive tension, Te (lb),belt stress ratings, Sp

(psi), and cross-sec-tional area, A (in.2), ofthe belt are given inthe formula Te 5 ASp.

For belt drivetransmitted horse-

power:Where:

V 5 Belt velocity, fpm 5 0.262DND 5 Pulley diameter, in.N 5 Pulley speed, rpm

Great advancements have beenmade in various materials used in V-belts in recent years. Horsepower rat-ings may vary considerably from onebelt to another. It’s important to pro-vide greater tension for belts carryinghigher power. Otherwise the newly

A112 1997 Power Transmission Design

Figure 2 — Effective belt tension is thedifference between tight-strand and slack-strand tensions.

TT

ekf1

2

= φ

Figure 3 — Wedging action of V-beltincreases force of belt against sheavegroove and helps prevent slip.

hpT Ve=

33 000,

Figure 4 — Basic dimensions forcalculating open and crossed beltlengths and arc of contact on smallerpulley or sheave.

L C D dD d

C0

2

2 1 574

= + +( ) +−( )

.

L C D dD d

Cx = + +( ) ++( )

2 1 574

2

.

1997 Power Transmission Design A113

Where: C 5 Center distance, in. d 5 Small pulley diam., in. D 5 Large pulley diam., in.

Wrap angle or arc of contact on thesmaller pulley in degrees is:

Drive system torque transmitted,lb-in., is:

One version of flat belting is anendless woven type that is made inseamless tubes. Materials are cottonand synthetic yarns, both spun fila-ment and continuous filament. Beltcarcasses can be impregnated andcoated with elastomers or syntheticresin. If an endless belt less than0.010 in. thick is needed, specify onemade of polyester film.

Another material used for flat belt-ing is leather. The National Indus-trial Belting Association (NIBA) pro-vides information on belt speeds forstandard pulley diameters andwidths. NIBA divides pulleys intothree standard series: light duty (upto 40 hp), medium duty (40 to 75 hp),and heavy duty (75 to 150 hp).

Flat belts with tension membersmade of nylons and polyesters are popu-lar because they offer high strength-to-weight ratios and negligible permanentstretch. More favorable friction charac-teristics can be achieved by laminatingnylon or polyester flat belting with afriction surface of chrome leather,polyurethane, rubber, PVC, or othermaterial. Laminated belts are usedwidely in industrial drives ranging fromfractional horsepower to more than6,000 hp at belt speeds to 20,000 fpm.

Metal belts — Flat belts made ofmetal offer lightweight, compactdrives with little or no stretch. End-less belts are made by butt weldingthe ends with laser or electron-beammethods. Belts are generally avail-able in thicknesses ranging from0.002 to 0.030 in. and widths from0.030 to 24 in. Circumferential lengthranges from 6 in. to about 100 ft. Usu-ally made of stainless steel, metalbelts have a high strength-to-weightratio, low creep, high accuracy, andresistance to corrosion and high tem-perature. Some applications take ad-

adaptable to practically any drive, al-though sometimes they may not beoptimal in terms of life-cycle cost orcompactness.

Besides their wide availability, V-belts are often used in industrial andcommercial applications because oftheir relative low cost, ease of installa-tion and maintenance, and wide rangeof sizes. The V shape obviously makesit easier to keep fast-moving belts in

sheave grooves than it is tokeep a flat belt on a pulley.Probably the biggest opera-tional advantage of a V-belt isthat it is designed to wedge intothe sheave groove, Figure 3,which multiplies the frictionalforce it produces in tension and,in turn, reduces the tension re-quired to produce equivalenttorque. Naturally, wedging ac-tion requires adequate clear-ance between the bottom of thebelt and the bottom of thesheave groove. The effect of thewedging factor, k, on the belttension ratio is shown in thesection that discusses V-belttension calculations.

When V-belts first appeared in in-dustrial applications to replace wideflat belts, it was not unusual to use 10to 15 belts between a single pair ofshafts. Thus the term “multiple” beltsoriginated, which today is referred toas “classical multiple” or “heavy-dutyconventional” belts.

Classical V-belts and matingsheaves have been standardized withletter designations from A through E,small to large cross sections. Thosestandard sizes are recognized world-wide. A and B sizes are frequentlyused individually but not the C, D,and E sizes because of cost and effi-ciency penalties. Belts with cogged ornotched bases permit more severebends, which allows operation oversmaller diameter sheaves.

Although classical V-belts can beused in some applications individu-ally, they tend to be over designed fora number of light duty applications.Thus, a special category of belts hasevolved under the description singleV-belts; they are also denoted as frac-tional horsepower and light duty.Cross-sectional size designations runfrom 2L (the smallest) to 5L (thelargest). The 4L and 5L sections aredimensionally similar to A and B clas-sical belts and can operate inter-

vantage of the electrical conductivityof metal belts to ground conveyedparts that are sensitive to static elec-tricity.

Attachments, such as pins andbrackets, can be provided on metalbelts to carry, position, or locate partsbeing transported on the belt. Perfora-tions in the belts enable their use insprocket-driven applications forgreater positioning accuracy, Figure 5.

Endless round belts — An elas-tomeric O-belt is a seamless, circularbelt that features a round cross sec-tion and an ability to stretch. Al-though O-belts look like O-rings, theyare designed for power transmissionapplications. The elasticity of O-beltssimplifies design problems and re-duces costs. However, they are lim-ited to subfractional horsepower ap-plications such as recorders,projectors, and business machines. O-belt materials include natural rubberand four polymers — neoprene, ure-thane, ethylene-propylene-terpoly-mer (EPT), and ethylene-propylene-dienemonomer.

Minimum pulley diameter is 6times the belt cross section. Pulleygrooves should be semicircular with aradius 0.45 of the cross-sectional di-ameter of the belt. Manufacturers cansupply charts showing the relation-ship of O-belt horsepower and beltspeeds for various cross sections.

V-belts — Available from virtuallyall power transmission componentsdistributors, standard V-belts are

φ = −−( )

180 57 3.D d

C

TT de=2

Figure 5 — Metal belt attachmentstransport or position parts. Perforatedbelts are used with sprockets to improveaccuracy.

changeably on A and B sheaves.Narrow V-belts are the latest step

in the evolution of a single-belt config-uration. For a given belt width, nar-row belts offer higher power ratingsthan conventional V-belts. Narrowbelt size designations are standard-ized as 3V, 5V, and 8V. They are alsoavailable in notched designs to maxi-mize bending capability.

Cogged, raw-edge belts have nocover, thus the cross-sectional areanormally occupied by the cover is usedfor more load-carrying cord. Cogs onthe inner surface of the belt increaseair flow to enhance cooler running.They also increase flexibility, en-abling the belt to operate with smallersheaves. Cogged belts are available inboth AX, BX, and CX Classical Vshapes plus 3VX and 5VX narrow Vconfigurations.

Double sided or hexagonal beltscome in AA, BB, and CC narrow V-beltcross sections. These belts transferpower from either side in serpentinedrive configurations where a singlebelt operates with multiple pulleys.

Joined V-belts solve special prob-lems for conventional multiple V-beltdrives produced by pulsating loads,such as those generated by internalcombustion engines driving compres-sors. The intermittent forces can pro-

tions denoted by a four-digit numberfollowed by the letter V. Refer to theAdjustable-Speed Drives Product De-partment of this handbook for a dis-cussion on these drives.

Synchronous (timing) belts areused where input and output shaftsmust be synchronized. Trapezoidallyshaped teeth of the belt mate withmatching grooves in the pulleys toprovide the same positive, no-slip en-gagement of chain or gears. Standardsections are designated MXL, XL, L,H, XH, and XXH. Table 1 shows typi-cal synchronous belt dimensions.

Because stable belt length is essen-tial for synchronous belts, they wereoriginally reinforced with steel. To-day, glass fiber reinforcement is com-mon and aramid is used if maximumcapacity is required.

Modifications of traditional trape-zoidal tooth profiles to more circularforms offer more uniform load distri-bution, increased capacity, andsmoother, quieter action. Thesenewer synchronous belts incorporatea rounded curvilinear tooth design tohandle the higher torque capabilitiesnormally associated with chaindrives, Figure 6.

Link-type V-belts consist of remov-able links that are joined by T-shapedrivets or interlocking tabs. Thesebelts offer application advantagessuch as installation without disman-tling drive components, reduced beltinventory (no need for differentlengths), wide temperature range,and resistance to chemicals, abrasion,and shock loads. A matrix of polyesterfabric and polyurethane elastomerenables link-type belts to meet thehorsepower ratings of classical V-

duce a whippingaction in multiplebelt systems,which sometimescauses belts toturn over in thegrooves. The basicbelt element can beeither classical ornarrow. The joined

configuration avoids the need to ordermultiple belts as matched sets. Joined5V and 8V belts are available witharamid fiber reinforcement which of-fer extremely high power capacity —up to 125 hp per inch of width.

V-ribbed belts combine some of thebest features of flat belts and V-belts.Tensioning requirements are not ashigh as flat belts but are about 20%more than V-belts. Five standard con-figurations are available, with desig-nations H, J, K, L, and M. The M sec-tion is capable of transmitting up to1,000 hp. The power density permitscompact drive configurations, but thebelt is usually applied only in m a s s -p r o d u c e d products.

Belts for variable-speed drives re-quire special care in selection. Thosefor fixed-pitch drives, in which thespeed ratios are changed only atstandstill, are offered with sheavesfor 3L through 5L, A through D classi-cal, and 5V and 8V narrow belts.

For the adjustable (while running)variable speed drives, 4L, 5L, A, or Bbelts can be used if power require-ments are less than 2 hp and speedvariations are limited to 4.5:1. Specialwide belts have been developed forvariable-speed applications that ac-commodate speed variations of up to9:1. There are 12 standard belt sec-


Table 1 — Standard dimensions of conventional synchronous belts

Pitch, in. Length, in. Width, in.

0.080 3.6 to 20.8 1/8, 3/16, 1/41/5 6 to 26 1/4, 3/83/8 12.4 to 60 1/2, 3/4, 11/2 24 to 180 3/4, 1, 11/2, 2, 3`7/8 50.7 to 180 2, 3, 411/4 70 to 180 2, 3, 4, 5

Figure 6 —Typicalsynchron-ous beltand pulleywithtrapezoidalteeth, left,andcurvilinear-tooth, high-torquedrive, right.


belts. They are available in 3/8

through 7/8-in. widths for speeds up to6,000 rpm.

CHAIN DRIVESPower transmission chains can be

categorized as roller chain, engineer-ing steel chain, silent chain, detach-able chain, and offset sidebar chain.Some of the advantages of chaindrives over belt drives are:

• No slippage between chain andsprocket teeth.

• Negligible stretch, allowingchains to carry heavy loads.

• Long operating life expectancybecause flexure and friction contactoccur between hardened bearing sur-faces separated by an oil film.

• Operates in hostile environ-ments such as high temperatures,high moisture or oily areas, dusty,dirty, and corrosive atmospheres, etc.,especially if high alloy metals andother special materials are used.

• Long shelf life because metalchain ordinarily doesn’t deterioratewith age and is unaffected by sun,reasonable ranges of heat, moisture,and oil.

• Certain types can be replacedwithout disturbing other componentsmounted on the same shafts assprockets.

Drawbacks of chain drives thatmight affect drive system design are:

• Noise is usually higher than withbelts or gears, but silent chain drivesare relatively quiet.

• Chain drives can elongate due towearing of link and sprocket teethcontact surfaces.

• Chain flexibility is limited to asingle plane whereas some belt drivesare not.

• Usually limited to somewhatlower-speed applications compared tobelts or gears.

• Sprockets usually should be re-placed because of wear when wornchain is replaced. V-belt sheaves ex-hibit very low wear.

Each link of a chain drive transmitsload in tension to and from sprocketteeth. Because of the positive drivingcharacteristics of a chain drive, it re-quires only a few sprocket teeth for ef-fective engagement that allows higherreduction ratios than are usually per-mitted with belts. Load capacity ofchain drives can be increased withmultiple-strand chains.

gle-strand roller chain are: No. 50chain indicates a 5/8-in. pitch chain ofbasic proportions; and No. 35 indi-cates a 3/8-in. pitch rollerless busheddesign. In multiple strand rollerchain, 60-2 designates two strands ofa No. 60 chain in parallel having com-mon chain assembly pins, and 60-3designates a triple strand.

Double-pitch roller chain —Also known as extended pitch chain,double-pitch roller chain dimensions,which are listed in the ANSI B29.3standard, are the same as standardroller chain with comparable load ca-pacity except the pitch is doubled,Figure 8. Because a given length ofdouble-pitch chain contains only halfas many pitches, it is lighter and lessexpensive than standard roller chain.It is especially suitable for long centerdistance applications. Double-pitchroller chain offers essentially thesame strength characteristics asB29.1 chain because all dimensionsare the same except pitch. Double-pitch chain designation numbers add“20” preceding what would be a stan-dard roller chain number. For exam-ple, 2050 designates a 5/8 3 2 or 11/4-in. double-pitch roller chain.(Multiplying 5/8 3 80 5 50 precededby 20 for the double pitch.)

Sprockets for double-pitch rollerchain are either single-cut (one wide-tip tooth between each pair of chainrollers) or double-cut (two teeth be-tween each pair of chain rollers).

Silent (inverted tooth) chain —Quieter running and more flexible

Types of chains and sprockets

There is a wide variety of standardand nonstandard chain and sprocketdesigns. The American NationalStandards Institute (ANSI) has setstandards for chain that are prefixedANSI B29. The standards covertransmission and conveyor chain aswell as sprocket tooth dimensions,pitch diameters, and sprocket mea-suring procedures. The best known ofall chain is roller chain, the first to bestandardized by ANSI.

Roller chain — Flexure joints inroller chain contain pins that pivot in-side the roller bushings. The pins areusually press fitted into the pin linkplates, and roller bushings are pressfitted into roller link plates, Figure 7.The ANSI standard for single pitchroller chain is B29.1. A free-turningroller encircles each bushing to pro-vide rolling engagement and contactwith sprocket teeth.

The distance between flexing jointsin roller chain is the pitch, which isthe basic designation for differentchain sizes. Larger pitch indicateslarger links with higher load ratings.Although a small pitch chain carriesless load, it offers smoother, quieteroperation than a chain of larger pitch.Standard sizes of roller chain varyfrom 1/2 to 3-in. pitch. A nominal sizeis designated by multiplying pitch by80. Thus, a chain with a 1/2-in. pitch isNo. 40.

Also included in the roller chainstandard are two sizes that have norollers but are propor-tioned much like larger-pitch roller chain. Theserollerless sizes have 1/4

and 3/8-in. pitches andare designated No. 25and No. 35, respectively,with the 5 indicating therollerless design. Theoutside surface of eachchain link bushing con-tacts the sprocket teethdirectly.

The right-hand digitin roller chain designa-tion is 0 for roller chainsof the usual proportions,1 for lightweight chain,and 5 for rollerlessbushed chain. A hyphenated numeral2 suffixed to the chain number de-notes a double-strand, 3 a triple-strand, etc. Example numbers for sin-

Figure 7 — Single pitch roller chain isavailable in pitch sizes above 3/8 in.Single and multiple-strand versions areavailable.

than conventional roller chain, silentchain, Figure 9, is available in 3/16 to2-in. pitch sizes. Standards for in-verted-tooth chain are ANSI B29.2and B29.9.

The several different types of silentchain construction prohibit mixingchains in a strand, but a chain of thecorrect size usually will operate onsprockets from a different manufac-turer. Load capacity is increased bywidening silent chain rather than us-ing multiple strands.

For silent chain with a 3/8-in. pitchor greater, an SC prefix in the chainsize designation indicates confor-mance to ANSI B29.2. The first one ortwo digits following the SC indicatepitch in eighths of an inch followed bythe next two to three digits, which in-dicate chain width in 1/4-in. incre-ments. For example, SC1012 desig-nates ANSI standard silent chainwith a 11/4-in. pitch and a 3-in. width.

For silent chain with a 3/16-in. pitch,

or other ferrous metals with compara-ble properties, Figure 10B. Pressed-steel detachable chain links (ANSIB29.6) typically range in size from 0.9to 2.3-in. pitch. The typical pitchrange for cast detachable chain links(formerly ANSI B29.7, now with-drawn) is 0.9 to 4 in.

Detachable chain is low in cost andcan transmit up to 25 hp at speeds to350 fpm. It is not as smooth runningas precision chain and does not re-quire lubrication.

Engineering steel chain —Where the transmission of high poweris the primary requirement, engineer-ing steel drive chains offer many use-ful solutions. Engineering steelchains are perhaps the most widelyused, with applications mainly in in-dustrial drives and conveyors. Stan-dards for heavy duty, offset sidebartype engineering steel roller chain,Fig. 11A, are given in ANSI B29.10.Specifications for heavy dutystraight-sidebar, roller-type conveyor

numbers following the 03 (whichidentifies the chain as 3/16-in. pitch)indicate the total number of chainlinks wide. Width (or thickness) ofeach link is approximately 1/32-in.Therefore, the number SC0314 desig-nates a 3/16-in. pitch silent chain thatis approximately 7/16-in. wide.

Any of several techniques can beused to position silent chain axially onsprockets. In one technique, centerlink plates ride in circumferentialgrooves in the sprocket. In anothermethod, side link plates hold thechain in place on the sprocket axially.

Detachable link chain — TheANSI standard for detachable linkchain is B29.6. The major advantageof chain with detachable links is thatthey can be separated at any jointwithout using special tools. Of course,the mountings for one or both sprock-ets must be loosened and the sprock-ets moved closer together to loosenthe chain. This procedure allows posi-tioning adjacent links at such an an-gle to each other that they can betaken apart by sliding a pair of con-necting links sideways.

Detachable link chains are fabri-cated with one-piece elements; eitherpress-formed from flat rolled steel,Figure 10A, or cast in malleable iron


Figure 8 — Double pitch roller chain.

Figure 9 — Inverted tooth (silent) chain drive. These sprockets are grooved for centerguide chain.

Figure 10 — Pressed steel detachable linkchain, A, and malleable iron detachablelink chain, B.

Figure 11 — Heavy duty, offset sidebarengineering steel roller chain, A, andheavy duty, straight sidebar roller typeconveyor chain, B.


chain, Fig. 11B, are covered in theANSI B29.15 standard, steel bushedrollerless chain in B29.12, weldedsteel mill chain in B29.16, and dragchain in B29.18.

Shaft center distance — In gen-eral, the preferred range of center dis-tance for roller chain drives that allowadjustable center distances is 30 to 50chain pitches, Figure 12. Roller chaindrives with fixed centers should belimited to about 30 pitches.

Obviously, the minimum centerdistance must allow clearance be-tween the teeth of the two sprockets.Other than that requirement, the arcof chain engagement should not beless than 120 deg, Figure 13. For ra-tios of 3:1 or less, there will be 120 degor more of wrap.

A center distance equivalent to 80pitches is usually considered a practi-cal maximum. Very long center dis-tances cause excessive tension andmay cause the chain to jump teeth.Long chains may need to be supportedby guides or idlers. Idlers are dis-cussed in the PT Accessories ProductDepartment of this handbook. Otherdrive system design approaches forextremely long center distances are touse two or more chain drives in series,or the lighter-weight double-pitchchain may be the answer where speedis slow and loading is moderate.

Chain application principles —Regardless of the type or class ofchain, most of the following items areneeded to design a chain drive:

1. Type of input power source (elec-tric motor, internal combustion en-gine, etc.).

2. Type of driven load (uniformload, moderate shock, heavy shock).

3. Power (hp) to be transferred.4. Full-load speed of fastest shaft.5. Desired speed of slow shaft.6. Shaft diameters.

set sidebar chain.Ratings for most

power applicationchains are basedon life of 15,000 to20,000 hr assum-ing alignment, lu-brication, andmaintenance re-

quirements are met. See Table 2 formaximum horsepower vs. sprocketspeed data. It is best to apply gener-ous service factors, as high as 1.7, es-pecially if heavy shock loading is anticipated. See Table 3 for recom-mended service factor data.

Sprockets are also covered by ANSIstandards. Various types of sprocketsare available including cast iron, pow-dered metal, flame-cut steel plate,machined metal, and plastic materi-als. Special-purpose sprockets are of-fered with shear pins, overloadclutches, and other devices to protectagainst shock or overload.

Speed ratios should not exceed 10:1for roller or silent chain and a limit of6:1 for other types. If needed, use dou-ble-reduction drives to stay withinthose limits. For roller chain operat-

7. Center distance between shafts.(If distance is adjustable, what is therange of adjustment?)

8. Limits onspace and posi-tion of drive.

9. Proposed lu-brication method.

10. Special con-ditions such asdrives with morethan two sprock-ets, use of idlers,abrasive or corro-sive environ-

ments, extreme temperatures, andwide variations in load and speed.

These data, when used with pub-lished chain capacity ratings, allowthe designer to select the proper drivefor each application. ANSI B29 stan-dards contain ca-pacity ratings asdo chain manufac-turers’ catalogs.Standards cover-ing roller chainand inverted toothc h a i n p r o v i d ehorsepower-capac-ity tabulations fora wide range ofsprocket sizes androtational speeds.Standards for de-tachable chaincover only allow-a b l e w o r k i n gloads. Standardsand some manu-facturers’ litera-ture contain bothallowable workingloads and horse-power-capacitytabulations for off-

Figure 12 — Preferred range of centerdistance for roller chain drives.

Figure 13 — Arc ofroller chainengagement shouldnot be less than 120 deg.

Table 2 — Maximum hp capacity at various speeds for 15-tooth sprockets

Maximum horsepower capacity

Sprocket Roller chainspeed, Single Four Double Offset rpm strand strand pitch sidebar

100 101 333 21.5 241200 188 620 21.1 290400 297 980 8.5 270600 140 462 6.6 140800 83.5 276 4.3

1,000 59.7 1971,200 41.4 1371,400 29.5 97.41,600 21.3 70.31,800 17.9 59.02,000 13.2 43.52,200 11.4 37.62,400 10.0 33.02,600 7.4 24.62,800 6.7 22.13,000 6.0 19.8


Table 3—Service factors

Table 4—Load classifications

Table 5 — Horsepower ratings, standard, single-strand No. 50 roller chain (5/8-in. pitch)

Number of teeth on Revolutions per minute—small sprocket

small sprocket 100 200 300 500 700 900 1,000 1,200 1,400 1,600 1,800 2,100 2,400 2,700 3,0

9 0.67 1.26 1.81 2.87 3.89 4.88 5.36 6.32 6.02 4.92 4.13 3.27 2.68 2.25 1.10 0.76 1.41 2.03 3.22 4.36 5.46 6.01 7.08 7.05 5.77 4.83 3.84 3.14 2.63 2.11 0.84 1.56 2.25 3.57 4.83 6.06 6.66 7.85 8.13 6.65 5.58 4.42 3.62 3.04 2.12 0.92 1.72 2.47 3.92 5.31 6.65 7.31 8.62 9.26 7.58 6.35 5.04 4.13 3.46 2.13 1.00 1.87 2.70 4.27 5.78 7.25 7.97 9.40 10.4 8.55 7.16 5.69 4.65 3.90 3.14 1.09 2.03 2.92 4.63 6.27 7.86 8.64 10.2 11.7 9.55 8.01 6.35 5.20 4.36 3.15 1.17 2.19 3.15 4.99 6.75 8.47 9.31 11.0 12.6 10.6 8.88 7.05 5.77 4.83 4.16 1.26 2.34 3.38 5.35 7.24 9.08 9.98 11.8 13.5 11.7 9.78 7.76 6.35 5.32 4.18 1.43 2.66 3.83 6.07 8.22 10.3 11.3 13.4 15.3 13.9 11.7 9.26 7.58 6.35 5.20 1.60 2.98 4.30 6.80 9.21 11.5 12.7 15.0 17.2 16.3 13.7 10.8 8.88 7.44 6.22 1.77 3.31 4.76 7.54 10.2 12.8 14.1 16.6 19.1 18.8 15.8 12.5 10.2 8.59 7.24 1.95 3.63 5.23 8.29 11.2 14.1 15.5 18.2 20.9 21.4 18.0 14.3 11.7 9.78 8.26 2.12 3.96 5.70 9.03 12.2 15.3 16.9 19.9 22.8 24.2 20.3 16.1 13.2 11.0 9.28 2.30 4.29 6.18 9.79 13.2 16.6 18.3 21.5 24.7 27.0 22.6 18.0 14.7 12.3 1030 2.49 4.62 6.66 10.5 14.3 17.9 19.7 23.2 26.6 30.0 25.1 19.9 16.3 13.7 1132 2.66 4.96 7.14 11.3 15.3 19.2 21.1 24.9 28.6 32.2 27.7 22.0 18.0 15.1 12

Type A Type B Type C


ing at low speed, thesmaller sprocket couldusually operate effec-tively with 12 to 17teeth. At high speeds,the smaller sprocketshould have at least 25teeth.

Roller chain drive design example

Problem: Select anelectric-motor-drivenroller chain drive totransmit 10 hp from acountershaft to themain shaft of a wiredrawing machine. Thecountershaft has a115/16-in. diam. and op-erates at 1,200 rpm. The main shaftalso has 115/16-in. diam. and must op-erate between 378 and 382 rpm. Shaft

centers, once es-tablished, arefixed and by ini-tial calculationsmust be approx-imately 221/2 in.The load on themain shaft ex-hibits “peaks,”which places itin the heavyshock load cate-gory. All driveparts are pres-sure lubricatedfrom a centralsystem; there-fore, the drivewill receiveType C lubrica-tion.

Step 1. Ser-vice factor —

sprocket — Because the driver is tooperate at 1,200 rpm and the drivenat a minimum of 378 rpm, the speedratio 5 1,200 4 387 5 3.175 mini-mum. Therefore, the large sprocketshould have 20 3 3.175 teeth = 63.50teeth (use 63).

This combination of 20 and 63 teethwill produce a main drive shaft speedof 381 rpm, which is within the limita-tion of 378 to 382 rpm.

Step 6. Possible alternate —Sometimes space for a sprocket is lim-ited, or higher capacity is needed froma given chain size. In this case, selecta multiple-strand chain drive. For ex-ample, a double-strand drive trans-mits 1.7 times the power of a singlestrand drive of the same pitch.

Step 7. Chain length — Because20 and 63-tooth sprockets are to beplaced in 221/2-in. centers, the calcu-lated chain length is:

Classification for this drive is listed inTable 4 as heavy shock load. The ser-vice factor from Table 3 for heavyshock load and electric motor is 1.5.

Step 2. Design horsepower —The design horsepower is 10 3 1.5515 hp.

Step 3. Tentative chain selec-tion — On the pitch selection chart,Figure 14, locate 15 hp under the sin-gle-strand column at the left, andthen follow the horizontal “horse-power” line across the chart to whereit intersects with the vertical 1,200-rpm line for the small sprocket. Thisintersection clearly lies in the diago-nal area for No. 50 roller chain.

Step 4. Final selection of chainand small sprocket — On the horse-power rating table, Table 5, for No. 50chain at 1,200 rpm, the computed de-sign horsepower of 15 hp is realizedwith a 20-tooth sprocket. Table 6shows that this sprocket will acceptthe specified shaft.

Step 5. Selection of the large

3,000 4,000 5,000

1.92 1.25 0.892.25 1.46 1.042.59 1.68 1.202.95 1.92 1.373.33 2.16 1.553.72 2.42 1.734.13 2.68 1.924.55 2.95 2.115.42 3.52 2.526.35 4.13 2.957.33 4.76 3.418.35 5.42 09.42 6.12 010.5 6.84 011.7 7.58 012.9 8.35 0

Figure 14 — Roller chainpitch selection chart.

L CN n N n

C= + + +

−( )2

2 4

2

2π


Where: L 5 Chain length, pitches C 5 Shaft centers, pitches N 5 Number of teeth in large

sprocket n 5 Number of teeth in small

sprocket Substituting values for C, N, and n

yields L 5 114.8 in.Step 8. Correction of center dis-

tance — Because chain is to couple atan even number of pitches, use 114

pitches and recompute the centers:

Summary — Our final solution is20 and 63-tooth sprockets mounted on22.25-in. centers using No. 50, 5⁄8-in.

pitch roller chain. In Table 5, Type Blubrication is indicated and theexisting central lubricationsystem exceeds this require-ment. ■

The sample problem appearingabove is reprinted from Chains forPower Transmission and MaterialHandling, edited by L.L. Faulkner andS.B. Menkes, pages 142-145, by cour-tesy of Marcel Dekker, Inc., New York.

C

LN n

LN n N n

=− + + − +

−−( )

2 2

8

44

2 2

2π

C = 35 6. pitches or 22.25 in.

Table 6 — Maximum bore diameters of roller chain sprockets (with standard keyways)

Chain pitch, in.

Number of teeth 3⁄8

1⁄2

5⁄8

3⁄4 1 11

⁄2 2 21⁄2

12 5⁄8 7/8 15

⁄32 19/32 125/32 23/4 35/8 423/32

14 27/32 15/32 15/16 13/4 29/32 35/16 411/16 523/32

16 31/32 19/32 111/16 131/32 223/32 4 51/2 7

18 17/32 117/32 17/8 29/32 31/8 421/32 61/4 81/8

20 19/32 125/32 21/4 211/16 31/2 57/16 7 93/4

22 17/16 115/16 27/16 215/16 37/8 57/8 83/8 107/8

24 111/16 21/4 213/16 31/4 49/16 613/16 95/8 13

Documents

Belt Chan