GB795355A - Method and apparatus for milling and classifying materials - Google Patents

Abstract

795,355. Grinding; pneumatic separating. HARDINGE, H. June 3, 1955 [June 14, 1954], No. 15954/55. Classes 59 and 117 A process of comminuting and separating asbestos rock, coal ores and other material consists in feeding the material to a mill 10, Fig. 2, and subjecting the material discharged therefrom to a primary gaseous current adapted to entrain therein the finer comminuted particles, the coarser particles not so entrained being subjected to an auxiliary gaseous current which separates from them any finer remaining particles for entrainment in the primary current. The mill, which may be a ball or rod mill or one which discharges wholly or partially by gravity, is shown in Fig. 2 as a ball mill consisting of a rotary drum having hollow trunnions constituting the inlet 16 and exit 18 of the mill, the inlet and exit are connected in a closed conduit circuit 22, 28, 30 including a fan or blower 26, separator 20, classifier 68 and waste collector 24; valves 34, 36 in an exhaust vent 32 and inlet conduit 30, respectively, serve to regulate the air stream 48. The inlet 16 is fitted with a feed spout 38, and the outlet 18 is provided with a grate 42 for preventing the passage of the balls and large pieces of material and a helical blade 44 co-operating with a scoop 46 for returning the coarser particles of material to the mill The separator 20 consists of a throat 50, Fig. 12, connecting the exit 18 with the-lower end of the suction conduit 22, and a depending outlet 52 for the downward passage of the. coarser and heavier particles 54 from the air stream. The lower end of the outlet 52 is controlled by a counterweighted and pivoted valve 60 which is maintained open to a predetermined extent to provide an upward flow of air but can be opened further by the downward flow of coarse material. The throat 50 and outlet 52 are formed of telescopically-slidable members 72, 74, 76 which may be set to vary the crosssections of the throat and outlet independently of each other. The air stream passing up the conduit 22 contains, in addition to a substantial percentage of the fine useful products 56 (e.g. asbestos fibres), a proportion of the finer particles of waste material dependent partly upon the setting of the valve 60 and partly upon the degree of constriction of the throat and outlet provided by the members 72, 74, 76; the upward flow of air in the outlet 52 separates out from the falling coarse material 54 for discharge into the conduit 22 any fine particles of usable material and a desired range of waste particles depending upon the degree of constriction of the passages. A conveyer 80 beneath the outlet 52 takes away the coarse material. The classifier 68 is not an essential part of the apparatus and the air circulating system need not be of closed type.