Belt and Chain Drives

BELT AND CHAIN DRIVES

BELT DRIVES drives that are more impor- BELT DRIVES ...... A105 tant in some applications elts, pulleys, and CHAIN DRIVES...... A109 than others are: sheaves for OEM BELT AND CHAIN DRIVES ADVERTISING...... A115 1. Endless belts usually Bhigh-volume-pro- cannot be repaired when duced products such as they break. They must be home appliances and passenger car sign, and delivery priorities prevail for replaced. engines are usually custom designed belts and sheaves for industrial ma- 2. Slippage can occur, particularly and manufactured by the thousands chines built only a few at a time. The if belt tension is not properly set for specific functions and operating same low-quantity-needs approach and checked frequently. Also, wear of conditions. The heavy expense of cus- must be taken on belt drive systems for belts, sheaves, and bearings can re- tom belt design, extensive testing, own-use machinery, rebuilt machin- duce tension, which makes retension- and special tooling are absorbed eas- ery, plant pump equipment, com- ing necessary. ily in the volume production of identi- pressed air equipment, and the full 3. Adverse service environments cal belts. Short delivery time is not ex- range of heating, ventilation, and air- (extreme temperature ranges, high pected in the mass produced product conditioning systems. It is difficult to moisture, oily or chemically filled at- until a specific production date is set. justify the expense of custom belts and mospheres, etc.) can damage belts or An entirely different set of cost, de- sheaves when only a few (and some- cause severe slipping. times a few hundred) 4. Length of endless belts cannot be of any one size are adjusted. needed. Fortunately, a Design considerations — Belt wide variety of stan- type, belt materials, belt and sheave dard sizes and types of construction, power requirements of industrial belts and the drive, speeds of driving and sheaves is readily driven sheaves, sheave diameters, available from stock at and sheave center distance are key industrial power belt drive design considerations. Ba- transmission products sic to power transmission design with distributors. Repre- belt drives is to maintain friction de- sentative standard veloped between the belt and the belts, Figure 1, in- sheave or pulley contact surface. clude flat, classical V, Belt creep and slip — All belts narrow V, double V, V- (except synchronous) creep, but creep ribbed, joined V, and must be differentiated from slip. For synchronous designs. example, a V-belt under proper ten- Advantages of belt sion creeps about 0.5% because of its drives include: elasticity and the changes in cross 1. No lubrication is- section and length taking place as a required, or desired. section of the belt moves from the 2. Maintenance is tight side to the slack side of the drive minimal and infre- and back. That cyclical stressing, plus quent. the bending action of the belt as it 3. Belts dampen travels around the sheaves, causes sudden shocks or only a slight increase in belt tempera- changes in loading. ture. Most of that heat will be dissi- 4. Quiet, smooth op- pated by the sheaves so that they will eration. be only slightly warm if touched. (Of 5. Sheaves (pulleys) course, the belt drive must be at rest are usually less ex- before an operator would dare touch pensive than chain the sheaves.) drive sprockets Slip, which is a movement greater V-ribbed and exhibit little than the 0.5% creep, can create wear over long periods enough heat to be very uncomfortable of operation. if the sheaves are touched (again, Figure 1 — Representative belt configurations. Drawbacks of belt when the drive is stopped). Another

1998 PT Design A105 way to check for slip is to touch the designed belts will belt (when it is stopped). If the belt is not run properly; uncomfortable to the touch (over 140 they may slip, vi- F), it probably needs to be tightened. brate too much, or Belt tension — Checking operating turn over in the temperatures of sheaves and belts (the grooves. touch test) is but one of several ways All torque is experienced machine operators and transmitted plant maintenance people check belt through the belts, tension without the need for compli- and torque does cated measurements and calculations. not change for a Other equally simple and useful Figure 3 — Wedging action of V-belt given horsepower and speed. This ba- belt tensioning approaches involve vi- increases force of belt against sheave sic concept is best revealed in a multi- sual and sound techniques. The bow groove and helps prevent slip. ple-belt drive. For example, a multiple or sag on the slack side of belt drives V-belt drive formerly requiring seven increases as a drive approaches full given drive. belts may need only five higher-rated load. Undulations and flutter on the f ϭ Dynamic coefficient of friction belts with the same cross section. For slack side of belts can be very infor- between belt and sheave. five belts to deliver the same horse- mative to the experienced eye. Proper ␾ ϭ Wrap angle (arc of contact on the power as seven belts, each of the five tensioning can reduce or eliminate smaller sheave in radians). new belts must carry more load. In- these conditions. K applies only to V-belt drives. A creased tension in the individual belts Tension adjustment based on belt practical tension ratio of 5 for V-belts will not overload the bearings, as some sound can be a useful technique. allows for such variations as lack of engineers may fear, because total ten- Loads such as industrial fans require rigidity of mountings, low initial tension in the drive should be exactly the peak torque at starting. If belts squeal sion, moisture, and load fluctuations. same value. Each belt has a higher as the motor comes on or at some sub- For rubber flat belt drives, a tension tension, but there are fewer belts to sequent peak load, experienced belt ratio of 2.5 is considered most efficient. transmit the tension to bearings. people say the belts should be tight- The difference between tightened until the squeal disappears. strand and slack-strand tensions is Belt types Calculating V-belt tension — effective tension, or Te ϭ T1 Ϫ T2. Ef- Figure 2 represents a belt drive ar- fective tension is the actual force that Flat belts — Most of the general rangement which can be used to study turns the driven sheave. principles of belt drive operation dis- factors affecting V-belt tensions and Stress and power ratings — The cussed earlier apply to flat belt drives. stresses. At standstill, the belt strand usable strength of a belt is the tensile In calculating tension ratios for flat tensions T1 and T2 are equal. When stress the belt withstands for a speci- belts, consult the manufacturer for load is applied to the driving pulley, fied number of stress cycles, usually typical values of the friction coeffi- tension T1 increases and T2 decreases. the equivalent of 3 years of continu- cient, f. For a flat belt drive, k = 1. ous operation, or Several useful formulas for endless about 25,000 hr. The belts follow (refer to Figure 4). For relationships of effec- belt length in an open belt drive: tive tension, T (lb), 2 e ()Dd− belt stress ratings, Sp LC=+2157. () Dd ++ (psi), and cross-sec- 0 4C tional area, A (in.2), of Belt length in a crossed belt drive: the belt are given in 2 the formula T ϭ AS . ()Dd+ e p LC=+2157. () Dd ++ For belt drive x 4C transmitted horse- Figure 2 — Effective belt tension is the power: difference between tight-strand and Where: slack-strand tensions. = TVe T1, tight side tension, divided by T2 hp slack side tension, is the tension ratio 33, 000 of a belt drive. The formula for ten- V ϭ Belt velocity, fpm ϭ 0.262DN sion ratio is as follows: D ϭ Pulley diameter, in. Where: N ϭ Pulley speed, rpm Great advancements have been T1 kfφ = e made in various materials used in V- T 2 belts in recent years. Horsepower rat- ϭ e 2.718 (the base of natural loga- ings may vary considerably from one Figure 4 — Basic dimensions for rithm). belt to another. It’s important to pro- calculating open and crossed belt k ϭ Wedging factor, from Figure 3, vide greater tension for belts carrying lengths and arc of contact on smaller which is considered constant for a higher power. Otherwise the newly pulley or sheave.

A112 1997 Power Transmission Design Where: vantage of the electrical conductivity adaptable to practically any drive, al- C ϭ Center distance, in. of metal belts to ground conveyed though sometimes they may not be d ϭ Small pulley diam., in. parts that are sensitive to static elec- optimal in terms of life-cycle cost or D ϭ Large pulley diam., in. tricity. compactness. Wrap angle or arc of contact on the Attachments, such as pins and Besides their wide availability, V- smaller pulley in degrees is: brackets, can be provided on metal belts are often used in industrial and belts to carry, position, or locate parts commercial applications because of ()Dd− φ =−180 57. 3 being transported on the belt. Perfora- their relative low cost, ease of installa- C tions in the belts enable their use in tion and maintenance, and wide range sprocket-driven applications for of sizes. The V shape obviously makes Drive system torque transmitted, greater positioning accuracy, Figure 5. it easier to keep fast-moving belts in lb-in., is: sheave grooves than it is to keep a flat belt on a pulley. Td T = e Probably the biggest opera- 2 tional advantage of a V-belt is that it is designed to wedge into One version of flat belting is an the sheave groove, Figure 3, endless woven type that is made in which multiplies the frictional seamless tubes. Materials are cotton force it produces in tension and, and synthetic yarns, both spun fila- in turn, reduces the tension re- ment and continuous filament. Belt quired to produce equivalent carcasses can be impregnated and torque. Naturally, wedging ac- coated with elastomers or synthetic tion requires adequate clear- resin. If an endless belt less than ance between the bottom of the 0.010 in. thick is needed, specify one belt and the bottom of the made of polyester film. sheave groove. The effect of the Another material used for flat belt- wedging factor, k, on the belt ing is leather. The National Indus- tension ratio is shown in the trial Belting Association (NIBA) pro- section that discusses V-belt vides information on belt speeds for tension calculations. standard pulley diameters and Figure 5 — Metal belt attachments When V-belts first appeared in in- widths. NIBA divides pulleys into transport or position parts. Perforated dustrial applications to replace wide belts are used with sprockets to improve three standard series: light duty (up flat belts, it was not unusual to use 10 accuracy. to 40 hp), medium duty (40 to 75 hp), to 15 belts between a single pair of and heavy duty (75 to 150 hp). shafts. Thus the term “multiple” belts Flat belts with tension members Endless round belts — An elas- originated, which today is referred to made of nylons and polyesters are popu- tomeric O-belt is a seamless, circular as “classical multiple” or “heavy-duty lar because they offer high strength-to- belt that features a round cross sec- conventional” belts. weight ratios and negligible permanent tion and an ability to stretch. Al- Classical V-belts and mating stretch. More favorable friction charac- though O-belts look like O-rings, they sheaves have been standardized with teristics can be achieved by laminating are designed for power transmission letter designations from A through E, nylon or polyester flat belting with a applications. The elasticity of O-belts small to large cross sections. Those friction surface of chrome leather, simplifies design problems and re- standard sizes are recognized world- polyurethane, rubber, PVC, or other duces costs. However, they are lim- wide. A and B sizes are frequently material. Laminated belts are used ited to subfractional horsepower ap- used individually but not the C, D, widely in industrial drives ranging from plications such as recorders, and E sizes because of cost and effi- fractional horsepower to more than projectors, and business machines. O- ciency penalties. Belts with cogged or 6,000 hp at belt speeds to 20,000 fpm. belt materials include natural rubber notched bases permit more severe Metal belts — Flat belts made of and four polymers — neoprene, ure- bends, which allows operation over metal offer lightweight, compact thane, ethylene-propylene-terpoly- smaller diameter sheaves. drives with little or no stretch. End- mer (EPT), and ethylene-propylene- Although classical V-belts can be less belts are made by butt welding dienemonomer. used in some applications individu- the ends with laser or electron-beam Minimum pulley diameter is 6 ally, they tend to be over designed for methods. Belts are generally avail- times the belt cross section. Pulley a number of light duty applications. able in thicknesses ranging from grooves should be semicircular with a Thus, a special category of belts has 0.002 to 0.030 in. and widths from radius 0.45 of the cross-sectional di- evolved under the description single 0.030 to 24 in. Circumferential length ameter of the belt. Manufacturers can V-belts; they are also denoted as frac- ranges from 6 in. to about 100 ft. Usu- supply charts showing the relation- tional horsepower and light duty. ally made of stainless steel, metal ship of O-belt horsepower and belt Cross-sectional size designations run belts have a high strength-to-weight speeds for various cross sections. from 2L (the smallest) to 5L (the ratio, low creep, high accuracy, and V-belts — Available from virtually largest). The 4L and 5L sections are resistance to corrosion and high tem- all power transmission components dimensionally similar to A and B clas- perature. Some applications take ad- distributors, standard V-belts are sical belts and can operate inter-

1997 Power Transmission Design A113 Table 1 — Standard dimensions of conventional duce a whipping tions denoted by a four-digit number synchronous belts action in multiple followed by the letter V. Refer to the belt systems, Adjustable-Speed Drives Product De- Pitch, in. Length, in. Width, in. which sometimes partment of this handbook for a dis- 0.080 3.6 to 20.8 1/8, 3/16, 1/4 causes belts to cussion on these drives. 1/5 6 to 26 1/4, 3/8 turn over in the Synchronous (timing) belts are 3 1 3 /8 12.4 to 60 /2, /4, 1 grooves. The basic used where input and output shafts 1/2 24 to 180 3/4, 1, 11/2, 2, 3 belt element can be must be synchronized. Trapezoidally `7/8 50.7 to 180 2, 3, 4 either classical or shaped teeth of the belt mate with 11/4 70 to 180 2, 3, 4, 5 narrow. The joined matching grooves in the pulleys to changeably on A and B sheaves. configuration avoids the need to order provide the same positive, no-slip en- Narrow V-belts are the latest step multiple belts as matched sets. Joined gagement of chain or gears. Standard in the evolution of a single-belt config- 5V and 8V belts are available with sections are designated MXL, XL, L, uration. For a given belt width, nar- aramid fiber reinforcement which of- H, XH, and XXH. Table 1 shows typi- row belts offer higher power ratings fer extremely high power capacity — cal synchronous belt dimensions. than conventional V-belts. Narrow up to 125 hp per inch of width. Because stable belt length is essen- belt size designations are standard- V-ribbed belts combine some of the tial for synchronous belts, they were ized as 3V, 5V, and 8V. They are also best features of flat belts and V-belts. originally reinforced with steel. To- available in notched designs to maxi- Tensioning requirements are not as day, glass fiber reinforcement is com- mize bending capability. high as flat belts but are about 20% mon and aramid is used if maximum Cogged, raw-edge belts have no more than V-belts. Five standard con- capacity is required. cover, thus the cross-sectional area figurations are available, with desig- Modifications of traditional trape- normally occupied by the cover is used nations H, J, K, L, and M. The M sec- zoidal tooth profiles to more circular for more load-carrying cord. Cogs on tion is capable of transmitting up to forms offer more uniform load distri- the inner surface of the belt increase 1,000 hp. The power density permits bution, increased capacity, and air flow to enhance cooler running. compact drive configurations, but the smoother, quieter action. These They also increase flexibility, en- belt is usually applied only in mass- newer synchronous belts incorporate abling the belt to operate with smaller produced products. a rounded curvilinear tooth design to sheaves. Cogged belts are available in Belts for variable-speed drives re- handle the higher torque capabilities both AX, BX, and CX Classical V quire special care in selection. Those normally associated with chain shapes plus 3VX and 5VX narrow V for fixed-pitch drives, in which the drives, Figure 6. configurations. speed ratios are changed only at Link-type V-belts consist of remov- Double sided or hexagonal belts standstill, are offered with sheaves able links that are joined by T-shaped come in AA, BB, and CC narrow V-belt for 3L through 5L, A through D classi- rivets or interlocking tabs. These cross sections. These belts transfer cal, and 5V and 8V narrow belts. belts offer application advantages power from either side in serpentine For the adjustable (while running) such as installation without disman- drive configurations where a single variable speed drives, 4L, 5L, A, or B tling drive components, reduced belt belt operates with multiple pulleys. belts can be used if power require- inventory (no need for different Joined V-belts solve special prob- ments are less than 2 hp and speed lengths), wide temperature range, lems for conventional multiple V-belt variations are limited to 4.5:1. Special and resistance to chemicals, abrasion, drives produced by pulsating loads, wide belts have been developed for and shock loads. A matrix of polyester such as those generated by internal variable-speed applications that ac- fabric and polyurethane elastomer combustion engines driving compres- commodate speed variations of up to enables link-type belts to meet the sors. The intermittent forces can pro- 9:1. There are 12 standard belt sec- horsepower ratings of classical V-

Figure 6 — Typical synchronous belt and pulley with trapezoidal teeth, left, and curvilinear- tooth, high-torque drive, right.

A114 1997 Power Transmission Design belts. They are available in 3/8 Types of chains and sprockets gle-strand roller chain are: No. 50 through 7/8-in. widths for speeds up to chain indicates a 5/8-in. pitch chain of 6,000 rpm. There is a wide variety of standard basic proportions; and No. 35 indi- and nonstandard chain and sprocket cates a 3/8-in. pitch rollerless bushed CHAIN DRIVES designs. The American National design. In multiple strand roller Standards Institute (ANSI) has set chain, 60-2 designates two strands of Power transmission chains can be standards for chain that are prefixed a No. 60 chain in parallel having com- categorized as roller chain, engineer- ANSI B29. The standards cover mon chain assembly pins, and 60-3 ing steel chain, silent chain, detach- transmission and conveyor chain as designates a triple strand. able chain, and offset sidebar chain. well as sprocket tooth dimensions, Double-pitch roller chain — Some of the advantages of chain pitch diameters, and sprocket mea- Also known as extended pitch chain, drives over belt drives are: suring procedures. The best known of double-pitch roller chain dimensions, • No slippage between chain and all chain is roller chain, the first to be which are listed in the ANSI B29.3 sprocket teeth. standardized by ANSI. standard, are the same as standard • Negligible stretch, allowing Roller chain — Flexure joints in roller chain with comparable load ca- chains to carry heavy loads. roller chain contain pins that pivot in- pacity except the pitch is doubled, • Long operating life expectancy side the roller bushings. The pins are Figure 8. Because a given length of because flexure and friction contact usually press fitted into the pin link double-pitch chain contains only half occur between hardened bearing sur- plates, and roller bushings are press as many pitches, it is lighter and less faces separated by an oil film. fitted into roller link plates, Figure 7. expensive than standard roller chain. • Operates in hostile environ- The ANSI standard for single pitch It is especially suitable for long center ments such as high temperatures, roller chain is B29.1. A free-turning distance applications. Double-pitch high moisture or oily areas, dusty, roller encircles each bushing to pro- roller chain offers essentially the dirty, and corrosive atmospheres, etc., vide rolling engagement and contact same strength characteristics as especially if high alloy metals and with sprocket teeth. B29.1 chain because all dimensions other special materials are used. The distance between flexing joints are the same except pitch. Double- • Long shelf life because metal in roller chain is the pitch, which is pitch chain designation numbers add chain ordinarily doesn’t deteriorate the basic designation for different “20” preceding what would be a stan- with age and is unaffected by sun, chain sizes. Larger pitch indicates dard roller chain number. For exam- reasonable ranges of heat, moisture, larger links with higher load ratings. ple, 2050 designates a 5/8 ϫ 2 or 11/4- and oil. Although a small pitch chain carries in. double-pitch roller chain. • Certain types can be replaced less load, it offers smoother, quieter (Multiplying 5/8 ϫ 80 ϭ 50 preceded without disturbing other components operation than a chain of larger pitch. by 20 for the double pitch.) mounted on the same shafts as Standard sizes of roller chain vary Sprockets for double-pitch roller sprockets. from 1/2 to 3-in. pitch. A nominal size chain are either single-cut (one wide- Drawbacks of chain drives that is designated by multiplying pitch by tip tooth between each pair of chain might affect drive system design are: 80. Thus, a chain with a 1/2-in. pitch is rollers) or double-cut (two teeth be- • Noise is usually higher than with No. 40. tween each pair of chain rollers). belts or gears, but silent chain drives Also included in the roller chain Silent (inverted tooth) chain — are relatively quiet. standard are two sizes that have no Quieter running and more flexible • Chain drives can elongate due to rollers but are propor- wearing of link and sprocket teeth tioned much like larger- contact surfaces. pitch roller chain. These • Chain flexibility is limited to a rollerless sizes have 1/4 single plane whereas some belt drives and 3/8-in. pitches and are not. are designated No. 25 • Usually limited to somewhat and No. 35, respectively, lower-speed applications compared to with the 5 indicating the belts or gears. rollerless design. The • Sprockets usually should be re- outside surface of each placed because of wear when worn chain link bushing con- chain is replaced. V-belt sheaves ex- tacts the sprocket teeth hibit very low wear. directly. Each link of a chain drive transmits The right-hand digit load in tension to and from sprocket in roller chain designa- teeth. Because of the positive driving tion is 0 for roller chains characteristics of a chain drive, it re- of the usual proportions, quires only a few sprocket teeth for ef- 1 for lightweight chain, fective engagement that allows higher and 5 for rollerless reduction ratios than are usually per- bushed chain. A hyphenated numeral Figure 7 — Single pitch roller chain is mitted with belts. Load capacity of 2 suffixed to the chain number de- available in pitch sizes above 3/8 in. chain drives can be increased with notes a double-strand, 3 a triple- Single and multiple-strand versions are multiple-strand chains. strand, etc. Example numbers for sin- available.

1997 Power Transmission Design A115 numbers following the 03 (which identifies the chain as 3/16-in. pitch) indicate the total number of chain links wide. Width (or thickness) of each link is approximately 1/32-in. Therefore, the number SC0314 desig- Figure 8 — Double pitch roller chain. nates a 3/16-in. pitch silent chain that is approximately 7/16-in. wide. than conventional roller chain, silent Any of several techniques can be chain, Figure 9, is available in 3/16 to used to position silent chain axially on 2-in. pitch sizes. Standards for in- sprockets. In one technique, center verted-tooth chain are ANSI B29.2 link plates ride in circumferential and B29.9. grooves in the sprocket. In another Figure 10 — Pressed steel detachable link The several different types of silent method, side link plates hold the chain, A, and malleable iron detachable chain construction prohibit mixing chain in place on the sprocket axially. link chain, B. chains in a strand, but a chain of the Detachable link chain — The correct size usually will operate on ANSI standard for detachable link or other ferrous metals with compara- sprockets from a different manufac- chain is B29.6. The major advantage ble properties, Figure 10B. Pressed- turer. Load capacity is increased by of chain with detachable links is that steel detachable chain links (ANSI widening silent chain rather than us- they can be separated at any joint B29.6) typically range in size from 0.9 ing multiple strands. without using special tools. Of course, to 2.3-in. pitch. The typical pitch For silent chain with a 3/8-in. pitch the mountings for one or both sprock- range for cast detachable chain links or greater, an SC prefix in the chain ets must be loosened and the sprock- (formerly ANSI B29.7, now with- size designation indicates confor- ets moved closer together to loosen drawn) is 0.9 to 4 in. mance to ANSI B29.2. The first one or the chain. This procedure allows posi- Detachable chain is low in cost and two digits following the SC indicate tioning adjacent links at such an an- can transmit up to 25 hp at speeds to pitch in eighths of an inch followed by gle to each other that they can be 350 fpm. It is not as smooth running the next two to three digits, which in- taken apart by sliding a pair of con- as precision chain and does not re- dicate chain width in 1/4-in. incre- necting links sideways. quire lubrication. ments. For example, SC1012 desig- Detachable link chains are fabri- Engineering steel chain — nates ANSI standard silent chain cated with one-piece elements; either Where the transmission of high power with a 11/4-in. pitch and a 3-in. width. press-formed from flat rolled steel, is the primary requirement, engineer- For silent chain with a 3/16-in. pitch, Figure 10A, or cast in malleable iron ing steel drive chains offer many useful solutions. Engineering steel chains are perhaps the most widely used, with applications mainly in industrial drives and conveyors. Stan- dards for heavy duty, offset sidebar type engineering steel roller chain, Fig. 11A, are given in ANSI B29.10. Specifications for heavy duty straight-sidebar, roller-type conveyor

Figure 11 — Heavy duty, offset sidebar engineering steel roller chain, A, and Figure 9 — Inverted tooth (silent) chain drive. These sprockets are grooved for center heavy duty, straight sidebar roller type guide chain. conveyor chain, B.

A116 1997 Power Transmission Design chain, Fig. 11B, are covered in the ANSI B29.15 standard, steel bushed rollerless chain in B29.12, welded Figure 13 — Arc of roller chain steel mill chain in B29.16, and drag engagement should chain in B29.18. not be less than Shaft center distance — In gen- 120 deg. eral, the preferred range of center distance for roller chain drives that allow adjustable center distances is 30 to 50 set sidebar chain. chain pitches, Figure 12. Roller chain Ratings for most drives with fixed centers should be power application limited to about 30 pitches. chains are based Obviously, the minimum center on life of 15,000 to distance must allow clearance be- 20,000 hr assum- tween the teeth of the two sprockets. ing alignment, lu- Other than that requirement, the arc brication, and of chain engagement should not be maintenance re- less than 120 deg, Figure 13. For ra- 7. Center distance between shafts. quirements are met. See Table 2 for tios of 3:1 or less, there will be 120 deg (If distance is adjustable, what is the maximum horsepower vs. sprocket or more of wrap. range of adjustment?) speed data. It is best to apply gener- 8. Limits on ous service factors, as high as 1.7, es- space and posi- pecially if heavy shock loading is tion of drive. anticipated. See Table 3 for recom- 9. Proposed lu- mended service factor data. brication method. Sprockets are also covered by ANSI 10. Special con- standards. Various types of sprockets ditions such as are available including cast iron, pow- drives with more dered metal, flame-cut steel plate, than two sprock- machined metal, and plastic materi- ets, use of idlers, als. Special-purpose sprockets are of- abrasive or corro- fered with shear pins, overload sive environ- clutches, and other devices to protect Figure 12 — Preferred range of center ments, extreme temperatures, and against shock or overload. distance for roller chain drives. wide variations in load and speed. Speed ratios should not exceed 10:1 These data, when used with pub- for roller or silent chain and a limit of A center distance equivalent to 80 lished chain capacity ratings, allow 6:1 for other types. If needed, use dou- pitches is usually considered a practi- the designer to select the proper drive ble-reduction drives to stay within cal maximum. Very long center dis- for each application. ANSI B29 stan- those limits. For roller chain operat- tances cause excessive tension and dards contain ca- may cause the chain to jump teeth. pacity ratings as Table 2 — Maximum hp capacity at various speeds Long chains may need to be supported do chain manufac- for 15-tooth sprockets by guides or idlers. Idlers are dis- turers’ catalogs. Maximum horsepower capacity cussed in the PT Accessories Product Standards cover- Roller chain Department of this handbook. Other ing roller chain Sprocket speed, Single Four Double Offset drive system design approaches for and inverted tooth rpm strand strand pitch sidebar extremely long center distances are to chain provide use two or more chain drives in series, horsepower-capac- 100 101 333 21.5 241 or the lighter-weight double-pitch ity tabulations for 200 188 620 21.1 290 chain may be the answer where speed a wide range of 400 297 980 8.5 270 is slow and loading is moderate. sprocket sizes and 600 140 462 6.6 140 Chain application principles — rotational speeds. 800 83.5 276 4.3 Regardless of the type or class of Standards for de- 1,000 59.7 197 chain, most of the following items are tachable chain 1,200 41.4 137 needed to design a chain drive: cover only allow- 1,400 29.5 97.4 1. Type of input power source (elec- able working 1,600 21.3 70.3 tric motor, internal combustion en- loads. Standards 1,800 17.9 59.0 gine, etc.). and some manu- 2,000 13.2 43.5 2. Type of driven load (uniform facturers’ litera- 2,200 11.4 37.6 load, moderate shock, heavy shock). ture contain both 2,400 10.0 33.0 3. Power (hp) to be transferred. allowable working 2,600 7.4 24.6 4. Full-load speed of fastest shaft. loads and horse- 2,800 6.7 22.1 5. Desired speed of slow shaft. power-capacity 3,000 6.0 19.8 6. Shaft diameters. tabulations for off-

1997 Power Transmission Design A117 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 10 30 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 11 32 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

A118 1997 Power Transmission Design Figure 14 — Roller chain pitch selection chart.

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

Roller chain drive design example

Problem: Select an electric-motor-driven roller chain drive to transmit 10 hp from a countershaft to the main shaft of a wire drawing machine. The countershaft has a 115/16-in. diam. and operates at 1,200 rpm. The main shaft Classification for this drive is listed in sprocket — Because the driver is to also has 115/16-in. diam. and must op- Table 4 as heavy shock load. The ser- operate at 1,200 rpm and the driven erate between 378 and 382 rpm. Shaft vice factor from Table 3 for heavy at a minimum of 378 rpm, the speed centers, once es- shock load and electric motor is 1.5. ratio ϭ 1,200 Ϭ 387 ϭ 3.175 mini- tablished, are Step 2. Design horsepower — mum. Therefore, the large sprocket fixed and by ini- The design horsepower is 10 ϫ 1.5 should have 20 ϫ 3.175 teeth = 63.50 tial calculations ϭ15 hp. teeth (use 63). must be approx- Step 3. Tentative chain selec- This combination of 20 and 63 teeth 3,000 4,000 5,000 imately 221/2 in. tion — On the pitch selection chart, will produce a main drive shaft speed 1.92 1.25 0.89 The load on the Figure 14, locate 15 hp under the sin- of 381 rpm, which is within the limita- 2.25 1.46 1.04 main shaft ex- gle-strand column at the left, and tion of 378 to 382 rpm. 2.59 1.68 1.20 hibits “peaks,” then follow the horizontal “horse- Step 6. Possible alternate — 2.95 1.92 1.37 which places it power” line across the chart to where Sometimes space for a sprocket is lim- 3.33 2.16 1.55 in the heavy it intersects with the vertical 1,200- ited, or higher capacity is needed from 3.72 2.42 1.73 shock load cate- rpm line for the small sprocket. This a given chain size. In this case, select 4.13 2.68 1.92 gory. All drive intersection clearly lies in the diago- a multiple-strand chain drive. For ex- 4.55 2.95 2.11 parts are pres- nal area for No. 50 roller chain. ample, a double-strand drive trans- 5.42 3.52 2.52 sure lubricated Step 4. Final selection of chain mits 1.7 times the power of a single 6.35 4.13 2.95 from a central and small sprocket — On the horse- strand drive of the same pitch. 7.33 4.76 3.41 system; there- power rating table, Table 5, for No. 50 Step 7. Chain length — Because 8.35 5.42 0 fore, the drive chain at 1,200 rpm, the computed de- 20 and 63-tooth sprockets are to be 9.42 6.12 0 will receive sign horsepower of 15 hp is realized placed in 221/2-in. centers, the calcu- 10.5 6.84 0 Type C lubrica- with a 20-tooth sprocket. Table 6 lated chain length is: 11.7 7.58 0 tion. shows that this sprocket will accept 2 12.9 8.35 0 Nn+ ()Nn− Step 1. Ser- the specified shaft. LC=+2 + vice factor — Step 5. Selection of the large 2 4π 2C

1997 Power Transmission Design A119 Table 6 — Maximum bore diameters of roller chain sprockets (with standard keyways) Chain pitch, in.

3 1 5 3 1 1 Number of teeth ⁄8 ⁄2 ⁄8 ⁄4 11⁄2 22⁄2

5 5 12 ⁄8 7/8 1 ⁄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 19/32 111/16 131/32 223/32 451/2 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 57/16 793/4

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

Where: pitches and recompute the centers: pitch roller chain. In Table 5, Type B L ϭ Chain length, pitches lubrication is indicated and the ϭ 2 2 C Shaft centers, pitches Nn+  Nn+  8()Nn− existing central lubrication N ϭ Number of teeth in large L− +− L  − system exceeds this require- 22  4π 2 ■ sprocket C = ment. n ϭ Number of teeth in small 4 sprocket C = 35. 6 pitches or 22.25 in. The sample problem appearing Substituting values for C, N, and n above is reprinted from Chains for yields L ϭ 114.8 in. Power Transmission and Material Step 8. Correction of center dis- Summary — Our final solution is Handling, edited by L.L. Faulkner and tance — Because chain is to couple at 20 and 63-tooth sprockets mounted on S.B. Menkes, pages 142-145, by cour- 5 an even number of pitches, use 114 22.25-in. centers using No. 50, ⁄8-in. tesy of Marcel Dekker, Inc., New York.

A120 1997 Power Transmission Design