GB696149A - Methods of and apparatus for size reduction of materials - Google Patents

Abstract

696,149. Grinding mills. WESTON, D. Jan. 4, 1951, No. 319/51. Class 59 In a method of reducing material to a desired particle size in a mill an original feed is prepared having a predetermined percentage of a selected plus size of relatively coarse material and having a predetermined ratio of such relativelv coarse material to the fine material thereof, the original feed is separated into relatively coarse and relatively fine parts, the parts are stored, and the parts are distributed from storage to the mill substantially in. the ratio of coarse to fine in the original feed. The predetermined percentage of the selected plus size of relatively coarse material in the original feed may be a minimum of 25 per cent plus three-inch material. The relatively fine part of the material may be dried, preferably to a value of less than 6 per cent, after preparing the original feed. The material may be thawed before preparing the original feed therefrom. The original feed may be prepared by crushing the material before separating it into relatively coarse and relatively fine parts for storage. In the apparatus shown, a skip car 11 running on a track 12 conveys dry fines and coarse material to a separator 13 through which the fine part of the material falls to form a pile of fines 14 in a bin 15. The coarse material falls off the end of the separator to form a pile 16 of relatively coarse material. The piles overlap at 17 and feeders 18, 20 and 21 are arranged below openings in the bin; the feeder 18 being located in accordance with the natural angles of repose of the separate piles and the overlapping portion therebetween. Alternatively, the material for the piles may be fed into the bin in a predetermined way. e.g., by moving the separator 13 so that the apices of the piles are located in the bin in predetermined manner in accordance with the natural angles of repose of the material therein. The separator may have a shoot 13a through which the fines pass. Material passes from the feeders to a conveyer 19 which extends into the enclosed shoot 22 having an air entry control valve mechanism 23 at the inlet opening 24. The feed material falls down the shoot 22 past the inlet opening 25 and then slides down the inclined wall 26 into an opening 'in the drum 29 of the mill 10. The drum has annular liners 31, 32. The mill receives a ball charge the volume of which is less than 5 per cent of the volume of the mill the initial ball size being about 5 inches. Air flows through the axis of the mill to a cyclone collector 37 from which a predetermined size of product is delivered at 38. The collector is connected to a fan 40 which is connected by a return line 41 to the inlet opening 25. The air preferably carries the fines directly through the mill without their being reduced. The dust and moisture content of the air passing through the mill is controlled by exhausting part of the re-circulated air to atmosphere through a dust collector 42 and by introducing fresh air into the shoot 22 through the valve mechanism 23. Specifications 632,532 and 696,137 are referred to.