The Mechanical Handling and Storing of Material

BAND CONVEYORS 83 The belt strain caused by the application of the last weight being 1,500, is equivalent to a stress of 3T25 lb. per inch per ply. The belt being 12 in. wide and four ply, this is not far short of the manufacturer’s guarantee of 40 lb. per inch per ply as the ultimate working strength of rubber-covered cotton duck belting. The best .method of joining conveyor belts is by butt joint with ordinary belt fasteners. Conveyor belts will la'st longer if they are not strained over too small rollers or terminals, if not troughed too deeply, and if the troughing rollers are kept away from the terminals at least a distance of six times the width of the belt. Fig. 109. Diagram showing Amount of Wear of Various Materials after being subject to an Equal Abrasion. It may be noted that bands made of woven wire are sometimes used in connection with coal-washing plants. As these bands have much in common with belts of textile material, they may be handled in much the same way, and run at a high speed, nearly 10 ft. per second. To ensure a proper grip, the driving terminals must be faced with rubber, leather, or lagged with wood. Such bands are not very durable, their ten- Fig. 110. Supporting Roller for Grain Conveyor. Fig. 111. Idler Roller Bearing for Band Conveyor. dency to stretching and their relatively high price being against their more frequent adoption. Troughing of the Belt.—Not many belt conveyors are used at the present time with flat belts, on account of the larger capacity of troughed conveyors. '1 he ordinary ■conveyor belt, with uniform plies of duck across the whole surface, is naturally stiff, and, if forced to assume the shape of a deep trough, is bound to suffer, as the adherence between the plies of duck and the rubber coating are strained and distorted by the ever- repeated process of bending. This .type of belt, if otherwise suitable for the material to be conveyed, should never be bent more than into a shallow trough. For deep troughing the type of belt advocated by Robins is advantageous, as only a belt of this type can stand the strain of being continually shaped into a deep trough. This kind of belt has a natural tendency to trough, as the sides are stiffer than the middle. Idlers.—A supporting roller or idler for a grain conveyor is shown in Fig. 110.