Patent GB-994280-A (GB)
Title: Grinding mill and process of grinding
IPC: B02C17/18
Filed: 1963-01-25
Abstract: 994,280. Grinding. HARDINGE CO. Inc. Jan. 25, 1963 [Jan. 29, 1962], No. 3177/63. Heading B2A. A method of grinding run-of-the-mine friable material consisting of intermixed ranges of relatively large, intermediate and fine sizes thereof by tumbling such mixture within a mill whose drum has a diameter substantially greater than its length to reduce autogenously all sizes thereof simultaneously and progressively to a predetermined range of fine sizes comprises the steps of mixing all sizes of material within the mill by imparting substantially axial movement to said material as it tumbles, progressively removing a mixture of such range of fine sizes and intermediate oversize material from the grinding zone of the mill, sizing said mixture of material by tumbling to separate said intermediate oversize material of a predetermined range of sizes from said range of fine sizes of material as said material is tumbled by the rotation of the mill, returning said separated intermediate oversize material to the grinding zone of the mill by flow thereof in a direction counter to that of the removal thereof from the grinding zone of the mill for further treatment, and discharging said range of fine sizes from the mill. The mill shown in Fig. 1 comprises a drum 10 having a segmental discharge grate 40 spaced from end wall 16 to form a chamber 68, the inner edge of the grate having adjacent thereto a ring 42 with which is contiguous an exit member 44 having a central opening 46. A sizing device 98 is connected to discharge trunnion 20 so as to be rotatable therewith. Device 98 comprises a shell 100 having a flange 102 to define an annular opening 96 and a screen 104 terminating in a flange 106. Lifting of material within chamber 68 is accomplished by radial partitions 94. The holes in the grate are of a size to pass fines and intermediate oversize which pass through opening 96. Fines are discharged through screen 104 and the oversize is returned through opening 46 to the grinding zone by means of a radial tube 108 having an inlet 112 and an exit 110. The drum liners are provided with lifter bars. In a modification, Fig. 4, the sizing means 128 comprises an inner shell 130 connected to a trommel 134 and an outer shell 138 connected to a screen 142. The coarser size ranges are returned to the grinding zone by means of a tube 150 supported by radial hollow columns 152, 154 having openings 156, 158 respectively. The return movement of the coarser size ranges is facilitated by helical blades 146. In another modification, Fig. 5, the discharge ends of segmental spaces 68 are connected to tube-like passage members 164. A cylindrical shell 170 is connected to exit trunnion 20 and comprises a deflecting cone 172 provided with spaced ribs 174. A screen 176 is connected to shell 170. Intermediate oversize is returned through spaces 166 between the members 164 to the grinding zone. In a further modification, Fig. 7, discharged material is directed to sizing means 184 by a plurality of tubes 186. An air stream 190 conveys the material through a tube 192 to a settling chamber 194. Heavier particles pass through spaces between the tubes 186 back to the grinding zone. In another modification, Fig. 8, which can be used for wet grinding, the sizing means 202 comprises tube-like passage members 204 which convey discharged material to the interior of a shell 208 from which it passes to a receptacle 210. Oversize material is returned between the members 204 to the grinding zone by means of conduits 222 having adjustable inlet openings. In a further modification, Fig. 10, primarily intended for wet grinding, the sizing means 228 comprises a cylindrical receptacle 238 having an annular end wall 240. Oversize is returned to the grinding zone by means of a radial conduit 250 having spaces 246 the size of which can be varied by means of a manually-adjustable closure plate 252. In another modification, Fig. 12, grate 268 has a number of larger apertures 270 for discharging pebbles 272. Fines, oversize and pebbles are directed from chamber 68 along the exterior of a shell 274 to a trommel 286 surrounded by a screen 288. The outer end of the trommel is adjustably closed by an arcuate segmented end plate 296. Pebbles not discharged from the trommel together with oversize are conveyed to the inside of the shell 274, and thence to the grinding zone, by means of conduits 306 and 310. In a further modification, Fig. 14, a housing 330 is connected to exit trunnion 320 and contains a screen 332 connected to a trommel 334 the outlet of which has an adjustable opening 338. Fines passing through the screen and pebbles discharged from the trommel are conveyed to a second mill 360. Pebbles not discharged from the trommel together with oversize are conveyed to a conductor 346, and thence to the grinding zone, by conduits 348, 350.