Patent GB-946480-A (GB)
Title: Solid-solid separating apparatus
IPC: B03B5/44
Filed: 1961-07-11
Abstract: 946,480. Separating solid materials. J. B. GREENSHIELDS, and R. A. GREENSHIELDS. July 11, 1962 [July 11, 1961 ; Oct. 10, 1961], Nos. 25039/61 and 36292/61. Heading B2H. Apparatus for separating pieces of a first solid material from a mixture of the first solid material with other solid materials of different densities, comprises a receptacle to contain a bed 2 of particulate solid material, means for supplying compressed fluid to the receptacle to fluidize the bed to a density intermediate those of the first and the other solid materials, means for supplying the mixture to an inlet zone, means for conveying the pieces constituting the mixture across the bed and outlet means positioned within the receptacle to receive only pieces of the first solid material. In the apparatus shown in Fig. 1 a mixture of two dissimilar solid materials is fed from a hopper 1 into the fluidized bed 2 of finely divided material, e.g. dry sand or sawdust. The bed is carried on an endless perforated moving belt 3 and is fluidized by a rapid sequence of air blasts from an air chest 4 fed from a compressed air source through a rotary valve (not shown). The pieces of material of the smaller density float on the bed and are caught on a grid 10, whilst the pieces of material of greater density are caught on a grid 11. The grids are made from a parallel array of spaced rods to allow the sand to pass through and the sand is recycled by a conveyer belt 12, a shoot 13, and a conveyer 14. In the apparatus shown in Fig. 2 a fluidized bed of dry sand is formed in a receptacle 20 by reciprocation of a nylon bellows 33 fitted with a flap valve 36. The air pulses from the bellows are transmitted through a perforated plate 29, a steel wire-cloth 30, and a sheet 31 of wire mesh to fluidize the bed 21. The perforations in the plate 29 are of greater density at the centre where the depth of the bed 21 is greatest to ensure even fluidization of the bed. The solids to be separated are pushed through the bed by rotation of banks 24 of tines secured to a drum 23. The tines are interleaved by grids 25, 27, 28 formed of spaced parallel rods which serve to guide the solids on passage through the apparatus. A mixture of potatoes and stones is fed from a shoot 26 on to the grids 25, 27 and rests on the tines until it enters the fluidized bed 21. The potatoes float on the bed 21 and are pushed by the tines over the grid 28, whilst the stones sink and are pushed under the grid 28. Rollers 41, 38 mounted on pivoted arms 42, 39 respectively serve to ensure removal of the potatoes and stones from the tines, and the weight of sand in the receptacle 20 is reduced by the provision of inserts 37 spaced to allow passage of the tines. The grids 25, 27, 28 may be rubber covered. Fig. 3 shows a receptacle 51 supporting a bed 52 of dry grain on a steel wire-cloth 54. The bed is fluidized by reciprocation of a piston 57 having a flap valve 58, and the air pulses are fed through a perforated plate 55 having a greater density of perforations at the centre where the depth of the bed 52 is greatest. Further a strip 56 of the plate 55 has a greatly increased density of perforations and this causes the part of the bed above the strip to be reduced in density so that currents are produced in the bed as indicated by the arrows. Two conveyers 61, 62 are disposed within the bed and these have rods 63 standing proud to carry the material. A mixture of potatoes and stones is fed from a shoot 64 to the bed 52 and the potatoes float towards the strip 56 and are caught up by the conveyer 62. The stones sink and are removed by the conveyer 61. A grid 65 prevents stones or potatoes from falling between the conveyers 61, 62. An adjustable valve (not shown) may be fitted to the air chest 53 in which the piston 57 is reciprocated to control the degree of fluidization of the bed 52. The air may be supplied by a rotary compressor or fan through a rotary valve in place of the piston 57. The bed may be divided into compartments each of which may be fluidized by air from a different part.