Patent GB-677515-A (GB)
Title: Improvements in or relating to a filter element and method of making the same
IPC: B01D29/00
Filed: 1948-10-12
Abstract: 677,515. Filtering media. STEVENS, A. H. (Cuno Engineering Corporation). Oct. 12, 1948, No. 25636/48. Class 46 [Also in Groups V and XXVIII] A filter element for depth-type filtration comprising a tubular self-supporting structure sufficiently rigid to withstand radial compression loads in excess of 50 1b. per square inch without deformation is composed of an integral resin-bonded fibrous mass having graduated porosity from the inner to the outer surface, the mass containing resin substantially uniformly dispersed therethrough in relation to the denseness of the fibres and in an amount equal to about 25 to 60 per cent of the weight of the mass, the outer surface of the structure being free from any poresealing resin film. In a method of making a thick-walled tubular filter element of graduated porosity such as the above by accretion from an aqueous suspension of fibres the fibres are impregnated with a thermo-setting resin amounting to 25 to 60 per cent of the weight of the fibres, the element is dried by subjecting it to heat below the resin-setting temperature, air heated to a resin-setting temperature is passed through the body for a period sufficient to set the resin, and the resin, is then cured. As shown, an aqueous suspension of fibres containing also resin-forming ingredients is fed to a tank 15, Fig. 3, which is provided with a motor-operated agitator 16 for maintaining the fibres in suspension, and a suction pipe 25 leading to a manifold block 24 which supports a number of formers, Fig. 4. Each former comprises a perforated tube 31 attached to a disc 27 by a bayonet fastening 32 and carrying an upper disc 29 having a woven wire disc 33<SP>1</SP> attached to its undersurface. The discs 27 are secured in their turn to the manifold block 24 by pairs of spring prongs 28. During the forming operation the progressive lessening of suction brought about by the building-up of the elements 36 results in their becoming progressively more porous from the inner to the outer layers, but this porosity may be further controlled by the degree of vacuum applied. The finished elements, each together with tube 31 and discs 27, 29 are next transferred to a drying cabinet, where they are inserted in an upper manifold and heated air drawn inwards. The resin impregnating the fibres is then set by a reverse current of heated air, in the same or another cabinet. The elements are then removed from the tubes and discs and cured in a further cabinet, and finally have the outer skin removed. For this purpose the element 36 may be mounted on a wheel 48, Fig. 8, rotated by a motor 49, and trimmed by a bandsaw 53 which may be moved relatively to the axis of the wheel 48. The fibres preferably consist of from 60 to 90 per cent by weight of wool and from 40 to 10 per cent of vegetable (preferably esparto) fibres, the amount of resin being preferably from 35 to 60 per cent of the weight of the fibres. 'The aqueous suspension (of uniform consistency) may be made by beating wool fibres in water, adding a quantity of another fibre having a diameter of the order of ten microns, continuing the beating, adjusting the consistency to the proper value, and adding a dispersion of resinforming ingredients.