Patent GB-1036543-A (GB)
IPC: B07B7/083
Abstract: 1,036,543. Classifiers. INSINOORITOIMISTO-ENGINEERING BUREAU R. T. HUKKI. Feb. 1, 1965, No. 4227/65. Headings B2H and B2P. Solid particles in a carrier fluid medium are classified by means of a two-step process carried out in one and the same apparatus. In the first step, the feed material is separated into two fractions under turbulent, spirally flow conditions in the lower part of the apparatus and the coarse or heavy fraction is discharged as the final underflow product. In the second step, the remaining fraction is classified in the upper part of the apparatus into two new fractions in the same medium are radially inwardly and upwardly directed, relatively their coaxial layers under the influence of controlled centrifugal force. The suspended fine or light fraction is discharged as the final overflow product while the middling fraction, consisting of particles rejected by the centrifugal force, is returned back to the lower part of the apparatus and discharged with the underflow product. The carrier fluid medium may be a gas, a liquid (e.g. tetrabromoethane) or a suspension of fine solids in a liquid (e.g. fine ferrosilicon in water). The medium may be added with the feed, separately or both ways. The medium may have a specific gravity between those of the light and heavy fractions. A hydraulic classifier, Fig. 1, comprises a vessel having conical top and bottom portions 1, 3 and a cylindrical middle portion 2. Pulp is admitted via a pipe 8 into a hollow shaft 4 rotated by a pulley 6 and provided with a conical extension 9 to which is attached a solid shaft 10. The pulp is whirled in the conical portion 3 of the vessel by vanes 19 carried by the extension 9 and by an impeller 11 mounted on the shaft 10. Additional medium is introduced through tangential pipes 13. The separated coarse fraction is discharged with same medium through a manually or automatically controlled valve 12. The remainder of the pulp travels upwards into the vessel portion 2 where it passes between conical discs 14 mounted on the rotary shaft 4. The fine fraction and the bulk of the medium are discharged via an annular space 21 and a collar 22 into a launder 23 and finally through an outlet 24. The middlings separated out by centrifugal force are urged against the wall of the portion 2 and travel downwards in helical fashion into the portion 3 from which they are finally discharged through the valve 12. In a modification, Fig. 2 (not shown), the pulp is introduced in the upper part of the conical portion 3 via a tangential inlet pipe 26. The shaft 4 is solid and the extension 9, slight 10 and impeller 11 are omitted. The vanes 19 are attached to the lower conical member 15 supporting the discs 14. In another embodiment, Fig. 3 (not shown), the apparatus is constructed for pneumatic classification. The solid shaft 10 extends throughout the hollow shaft 4 in which it is mounted on bearings 29 and is rotated by a pulley 30 at a speed different from that of the shaft 4. The shaft 10 carries a conical member 31 and an impeller 11. The portion 3 of the vessel has a cylindrical extension 28 to form an elutriation column. Feed is admitted with gaseous medium through a tangential inlet pipe 26. Additional medium is introduced via a pipe 32 to wash the settling coarse fraction in countercurrent fashion first in the utriation column and then in the conical passage between the member 31 and the wall of the conical portion 3. The overflowing gaseous suspension is collected by a covered discharge means 33. In all the above embodiments, the walls of the vessel may be lined with wear resisting material, e.g. rubber and the discs may similarly be rubber covered on one or both sides and there surfaces may have additional design features to help classification. A number of classifiers may be connected in series or parallel.