Patent GB-1075995-A (GB)
Title: Improvements in, or relating to, apparatus for sifting granular materials
IPC: B07B1/38
Filed: 1965-02-22
Abstract: 1,075,995. Sifting apparatus. C. STOCKTON. Feb. 22, 1966 [Feb. 22, 1965], No. 7645/65. Heading B2H. An apparatus for sifting granular materials comprises a rigid, box-like and closed body (16), Fig. 1 (not shown), which contains a stack of alternately disposed sieve frames and transfer trays and is imparted a gyratory movement by means of a driving mechanism comprising a vertical master shaft 7, Fig. 3, having an upwardly projecting and eccentric column 13 which is journalled in, and coaxial with, the bottom of the body 16. The shaft 7 is driven through belt and pulley (10), 11, 12, or through gearing, by an electric motor (5) and is journalled in bearings 8, 9 in a housing 3. The column 13 is journalled in a bearing 14 carried by a beam 15 fixed to the body 16 and carries an arm 17 which counterbalances the body 16 and its contents statically and dynamically. The housing 3 has an L-shaped rigid extension 18 in which a slave shaft 19 is journalled in a bearing 20, the slave shaft having an eccentric column 21, of the same eccentricity as column 13, which is journalled in a bearing 22 carried by a beam 23 fixed to the body 16. The cover (23) for the body (16) is provided with a flexible tube 25 for the feeding of granular material. The bottom of the body is formed or provided with flexible tubes (26), Figs. 1 and 2 (not shown) for the discharge of the various size fractions. Each sieve frame, Figs. 4 and 5 (not shown), comprises a boundary wall (27) to which are anchored, by means of bars (29), concentric annular partitions (28) which support an outwardly and downwardly sloping screen mesh (32). The annular space between the wall (27) and the outermost partition (28) has a floor (30) provided with holes (31) one or more of which may be closed as required. Each annular space between the partitions (28) is provided with spaced circular rods or tubes (33) and resilient balls (34) are accommodated between the screen mesh (32) and the rods or tubes (33) so that the gyratory movement imparted to the body (16) causes the rods or tubes to bounce the balls against the underside of the screen to prevent blocking or chocking of the screen apertures. One form of transfer tray, Fig. 6 (not shown), comprises a boundary wall (35) and a downwardly inclined floor (38) formed with a central hole (39) and with holes (45) adapted to correspond with the holes (31) in each screen frame. Another form of transfer tray, Figs. 7 and 8 (not shown), has an outwardly and downwarly sloping plate (14) supported on an annular partition (41) spaced from a boundary wall (40) and forming therewith an annular channel having a floor provided with holes (45) adapted to correspond with the holes (31) of each screen frame. In operation, the gyratory movement imparted to the body 16 causes material fed via the flexible tube (25) on to the mesh (32) of the top screen to progress spirally towards its periphery. Material rejected by the screen is delivered to the outer annular channel between the boundary wall (27) and the outermost partition (28) and pass through a selected hole 31 and aligned holes 31, 45 or 45a in succeeding trays and screens to an outlet tube (26). Material accepted by the screen passes through the clearances between the tubes or rods (33) and is either transferred by the tray through the central hole (39) in the floor of the tray, Fig. 6 (not shown) on to the centre of the smaller apertured screen mesh of a succeeding screen, or, in the case of a tray of the type of Figs. 7 and 8 (not shown), to the outer channel thereof. By closing an aligned hole (45a) in the type of tray constructed according to Fig. 6 (not shown), the material is caused to be passed to a succeeding screen to be re-sifted. The body (16), the sieve frames and transfer trays may be rectangular instead of circular.