BELT (AS. belt, allied with OHG. balz, Lat. balteus, girdle, belt). in engineering, a flexible cord or band passing about the periphery of wheels or drums for the purpose of transmitting motion or power from one to another. (_'om monly the name 'belt' is given only to broad, flat Lands of leather. rubber, or woven fabric; ropes, chains, etc., although serving similar purposes, being elassed separately. (See l'owElt, TRANSMIS SION or.) The best leather belts are made from the back strips of all oak-tanned leather, curried with the use of cod-oil and tallow. Such belts have continued in use for thirty years when em ployed as simple driving-belts, driving a proper amount of power, and having had suitable care. To form the lengths of leather into the long end less belt, they are connected end to end by lac ing, riveting, or cementing and lacing. The strength of leather belts in the bo4ly of the belt is from '2000 to 5000 pounds per square inch; at the joints only about from 1000 pounds to 1500 pounds, for lacing, and from 1000 pounds to 2500 pounds for riveted joints; the safe working strain is taken generally at not over one-third the strength at the joint. Leather belts should be protected from steam, vapor, water, oil-drip pings, and moisture, and should not be submitted to a heat of over 110° F. They are usually run with the grain side next to the pulleys, since this side stands the wear better, and also because the flesh side is stronger and the part least subjected to wear. This arrangement gives the belt longer life and greater propelling power. Leather-chain or leather-link belting consists of short sections of leather joined by metal rivets. Rubber belts are made of two or more layers of canvas con nected together with a rubber composition, and then heated until the rubber vulcanizes. The ad vantages claimed for rubber belting are perfect uniformity in width and thickness; ability to en dure greater degrees of heat or cold safely; less danger of injury from moisture and steam vapor; great durability and strength, and gm-eater adhe sion to the pulleys than is afforded by leather belting. Grease rapidly deteriorates and destroys rubber belts. Besides leather and rubber belt ing, there are quite a variety of woven-fabric belts employed. Cotton, hair, and most of the
more common textile fibres are used for manu• faetnring them. Transmission of power by belts is more common in the United States than in European countries, but of late years there has been an increase in the use of belts outside of the United States. The great favor with which power-transmission by belting is received in the United States is due to the fact that the belt is elastic and will slip without injury to the ma chinery if unduly strained. Ordinarily, flexible belts transmit power by the friction between them and their pulleys. •he pulley which eom municates motion is the driving-pulley; that which receives, the driven pulley; that part of the belt which runs from the driven pulley to the driver is the driving part of the belt, since it is pulled by the driver, and in turn pulls on the driven pulley; the part of the belt which runs from the driver to the driven pulley is the slack belt. If the pulley is higher at one side than at the other, the belt will creep toward the highest part; for this reason the surface of the pulley is usually not made cylindrical, but of greater diameter at the centre. If this be over done, the belt does not pull, except along its central part. The pulleys usually lie in the same plane, and with their axes parallel; but this is not necessary, provided that the course of each part of the belt—the driving and the slack part alike—he in the plane of the pulley toward which that part of the belt runs; the belt being always delivered by one pulley into the plane of the other.
Belts are made in a great variety of sizes, some of them being very large. As extreme eases, may be noted: .A leather belt of the New Jersey Zinc Works, 4 thicknesses, 4S inches wide, and 102 feet long; a rubber belt in Chicago. 6-ply, 4S inches wide, and 320 feet long: a leather belt for a paper-mill in Wilmington, Del., 60 inches wide and feet long. For a summary of modern practice in the calculation, operation, and care of belts and belting, consult Kent, Mechanical Engineer's Pocket-Book (New York, 1900).