The Mechanical Handling and Storing of Material

BAND CONVEYORS 8r substances, as any abrasion or cut in the covering, sufficiently deep to admit the moisture to the cotton, may cause serious damage to the belt, as the rubber loosens its hold on the damp cotton, forming blisters, which soon elongate along the belt through the compression and extension of the inner parts when passing over the terminals. The number of plies of duck of which the belt is com- posed must be such as to make the belt sufficiently rigid to sup- port the maximum load between the supporting idlers without sagging. This is the only con- dition which need be observed for ordinary conveyors of medium lengths. According to Mr C. K. Baldwin, of Chicago, the num- ber of plies should be as follows : belts of 12 to 14 in. wide should be not less than three ply; belts 16 to 20 in. wide not less than four ply ■ belts 22 to 28 in. not less than five ply; while not less than six ply should be used for belts from 30 to 36 in. in width. For extra long conveyors, however, and in cases where one or more additional belts or other machinery are to be driven from the end terminal of a conveyor, the tensile strength of the belt has to be taken into consideration, and the belt so constructed that the tension is not more than 20 to 25 lb. per inch per ply, although a good belt should have a breaking strain of about 400 lb. per ply per inch. The Robins type of belt is made with a flexible central portion by stopping off some of the plies of duck at varying dis- tances from the edge, and by Fig. 10S. Coal Conveying Plant of the Berlin Anhaitische Maschinenbau Aktien-Gesellschaft.