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1.0 2.0

INTRODUCTION BELT DRIVES 2.1 2.2 2.3 V-Belt Design Data Design Data for Neoprene and Buna Belts Design Data for Polyurethane Belts 468 468 469 476 477 478 478 480 481 481 481 482 484 467


CHAIN DRIVES 3.1 3.2 3.3 3.4 3.5 3.6 Design Data for No. 25 Single Strand Roller Chain Drive Selection Sprocket SelectionRecommendations Selection of Center Distances Chain Drive Selections for Very Slow Speeds Lubrication



A. MISCELLANEOUS BELT AND CHAIN DRIVES 1.0 INTRODUCTION Since it is our specialty to service the users of small commercial quality drive components, we will limit ourselves to design data up to 1 H.P. capacity. This should prove most useful to the designer of businessmachines, computer equipment, instrumentation and small automatic machinery of all kinds. This write up is divided Into the following categories: Belt Drives* • Flat Belts • Synchronous Belts • V-Belts • Variable Speed Pulleys • Round Belts Chain Drives • Roller 1. Standard Size 2. Miniature • Ladder • Bead Tensioning Mechanisms 2.0 BELT DRIVES (a) Flat Belts Flat belts find considerable usage inapplications requiring small pulley diameters, high belt surface speeds, low noise levels, low weight and inertia. They cannot be used where absolute synchronization between pulleys must be maintained because they rely on friction for their proper functioning, All flat belts except the toothed type mentioned in the next data section are subject to creepage because of the relative motion betweenthe pulley surface and the adjacent belt surface which is under load deformation from the combined tension and flexural stresses. Flat belts must be kept under tension to function and therefore require tensioning devices. Fractional H.P. belts are manufactured two ways. 1. Woven and 2. Film. Woven belts are usually made from Nylon or Dacron fibers and impregnated with rubber. Sometimes they are madefrom fiberglass for high temperature applications. They can operate at pulley speeds up to 140,000 R.P.M. and pulley diameters as small as 3/8 inch. Film type belts are made from Mylar. Annular rings are die cut from a basic Mylar sheet and subsequently formed into an endless belt. Belt thickness can be as small as .0005 inches, thus enabling operation over pulley diameters as small as .050inches for tens of millions of cycles. Creep and pitch Pine variations are also small because of the thickness of the belt. Film type belts are finding considerable application in miniature and airborne tape recording equipment. (b) Synchronous Belts Synchronous belts, commonly known as timing belts, are basically flat belts with a series of evenly spaced teeth on the inside circumference, therebycombining the advantages of the flat belt with the _____________ *Reprinted with permission from Uniroyal Industrial Products Manual 181 and Browning Manufacturing Div. of Emerson Electric Co. Cat. No. 6. 468

positive grip features of chains and gears. There is no slippage or creep as with plain flat belts. Required belt tension is low, therefore producing very small bearing loads. Synchronousbelts will not stretch and require no lubrication. Speed is transmitted uniformly because there is no chordal rise and fall of the pitch line as with roller chain. The tooth profile on timing belt pulleys is an involute curve similar to a spur gear. Unlike the spur gear however, the outside diameter of a timing pulley is manufactured smaller than its pitch diameter, thus creating an imaginary pitchdiameter which is larger than the pulley itself. This is illustrated in Figure 1. Backlash between pulley and belt teeth is negligible. Synchronous timing belts are also available in double sided designs which offer an infinite number of new design possibilities on computer equipment, business machines, office equipment, textile machines and similar light duty applications. Belts with driving...
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