The Mechanical Handling and Storing of Material

16 THE MECHANICAL HANDLING OF MATERIAL In cases where it is necessary to employ large top terminal pulleys (3 ft. and over) in order to obtain delivery of a desired quantity in a given time, the bottom terminal pulley may be of smaller size, in which case the elevator legs are not parallel, but at an anole with the axis of the elevator. Fig. 8 illustrates the usual form of grain elevator. Speed and Capacity of Mineral Elevators.—As regards data for mineral elevators, it is exceedingly difficult to tabulate such information, as the speed and consequently the capacity of such elevators vary greatly with the nature of the material to be elevated, whether hard, tough, or friable. While it is usual to run coal elevators 90 to 130 ft. per minute, according to the friability of the coal coke elevatois run only Fig. 8. Usual Form of Grain Elevator. at 50 to 90 ft. per minute; while, on the other hand, minerals which do not deteriorate through breakage may be elevated at the rate of 120 to 160 ft. per minute. The capacity of such elevators depends of course on the speed of travel and on the size and pitch of the buckets. The following table gives a few particulars of the speed and capacity of coal elevators Width of Buckets. Pitch. Speed of Travel. Delivery. Inches. Inches. ■ Feet per Minute. Tons per Hour. 12 18 120 20 18 18 120 30 24 18 120 40