GB1313795A - Powdered metal filter - Google Patents

Abstract

1313795 Sintered metal filters MINNESOTA MINING & MFG CO 20 April 1970 [21 April 1969 22 Jan 1970] 18782/70 Heading B1D [Also in Division C7] A filter comprises one or more layers of sintered metal powder presenting one smooth surface, which may be curved or flat, and one surface extended by corrugations, truncated pyramids or cones (Figs. 7 to 12, not shown). In making the flat discular filters of Figs. 1 to 8, the individual layers may be preformed to shape while green, either by pressing an initially flat sheet or slitting and opening out an extruded tube. In making the tubular filter of Fig. 9, the layers are separately extruded or made by bending a sheet to tubular form. The preformed layers are then wetted with a solvent which softens the organic binder therein and pressed together, dried and sintered under vacuum or in an inert atmosphere. Numerical details of pressing and sintering conditions are given. The pressing die may be cooled with liquid nitrogen, passed through a surrounding coil, or the die may be immersed in liquid nitrogen to freeze the binder so that the pressed green layers may be removed from the press for drying and sintering. Or the pressing, drying and sintering may be performed without removing the layers from the die. The filter is made of any one of a number of metals and alloys listed, including austenitic stainless steels. In some examples stainless steel and molybdenum powders are mixed together with methyl cellulose binder and glycerine to make the green layers. The layers in the final filter are metallurgically integral, but comprise powders of different grain sizes. Fig. 5 shows a coarse layer 3 sandwiched between and acting as a drainage support for fine layers 4, 5, which may act in series or parallel. In Figs. 6, 7, 8 (not shown) the coarse layer presents an extended upstream surface and the fine layers are attached to its flat downstream face. The fine layer 16 in Fig. 9 could equally well be applied to the outside of the filter. Fig. 10 (not shown) illustrates a one-layer filter whose truncated cone extensions are hollow, and Figs. 11, 12 (not shown) illustrate two-layer modifications thereof. The filters are used to filter polymers before extruding into fibres.