GB593959A - Improvements in and relating to production of molded metallic articles - Google Patents

Abstract

A method of making porous metal articles comprises mixing together metal powder, a hydrated metallic bonding compound, preferably a hydroxide of the metal in the form of a colloidal suspension and, if desired a volatilisable binder, moulding the resulting pasty mass to the desired shape, drying and then heating in a reducing atmosphere to reduce the hydroxide to the metal and to sinter the metal particles. The method is described in connection with the production of porous moulds for casting metals and of porous filter elements. In one example, iron filings, all of which passed a 40 mesh screen and 90 per cent of which was retained on a 100 mesh screen was mixed with a paste comprising 30 per cent ferric hydroxide, water and ammonium chloride solution and with granulated ammonium chloride, the proportions being 80 parts iron powder, 4 parts granulated ammonium chloride and 16 parts of the paste. The mixture had the consistency of damp moulding sand and was formed into the desired shape using ordinary foundry technique for moulding sand. The resulting moulded shape was allowed to dry and was then heated in a hydrogen atmosphere for two hours and forty-five minutes at a temperature of 2100 DEG F. In another example 75 per cent of iron powder all screened between 20 and 50 mesh, 15 per cent by weight of ferric hydroxide paste containing 30 per cent ferric hydroxide and 7 per cent by weight of dry ammonium chloride were mixed and moulded into discs four inches in diameter and half an inch thick. There were dried and heated in a reducing atmosphere for two and a half hours at 2000 DEG F. to form filters which could be further treated by hot steam to partially oxidise the exposed surfaces. Instead of using hydroxide in the form of a paste added to the iron powder, the powder may be treated with acid and then with ammonium chloride so as to form a thin coating of ferric hydroxide on the granules. The invention may also be used for the production of articles of chromium, nickel, cobalt, copper, manganese, aluminium, cadmium, magnesium, tin, zinc either alone or in admixture with each other or with iron.