GB892934A - Casting complex structures with foamed metal core and solid skin - Google Patents

Abstract

892,934. Metal foams. LOR CORPORATION. Jan. 1, 1960 [Jan. 5, 1959], No. 120/60. Class 82(1). [Also in Groups XIV, XXII and XXXIII] A molten metal intermixed with a substance thermally caused to form a gas at the melting point of said metal is introduced into a mould before foaming has taken place, the inner surface of the mould having a temperature sufficiently low to cause solidification of a skin of said metal which is not remelted or foamed, so as to form an article having a substantially rion-porous skin and a low density core. In one embodiment, Fig. 3, the metal container 20 is held under a pressure sufficient to repressthe foaming action, the mixture being agitated by mechanical or electromagnetic means 21. The mixture is then fed to the mould 22 under pressure or so rapidly that foaming does not occur until the pressure is fully released in the mould. Foaming agents referred to for low melting point metals such as Al, Mg, Zn, Pb &c. are metal hydrides such as Ti, Zr, Li, Li-Al and Mg, carbonates such as Na 2 CO 3 and NaHCO 3 , stable hydrates such as chromium oxide hydrate, and decomposable organic materials such as phthalocyanine and silicon products. For high melting point metals such as the ferrous metals and alloys, Ni, Co, Ti, Zr, Nb may be mixed with a lower melting point metal such as Zn, Ca, Li, Mg, the ebullition being repressed by pressure while mixing, sudden release of the pressure then causing the low melting point metal to become gas. Cu and its alloys may be formed by either of the above methods. In one example, 90% of an alloy, 33% Mg, 67% Al, is mixed with 10% zirconium hydride at a temperature of 465‹C. and the mixture then injected into a stream of molten aluminium in a ratio 1 : 9 and the metal cast into a cold sand mould before foaming commences. In another example, 1 part titanium hydride powder and 12 parts Al powder enclosed in an Al container is dumped in 200 parts of molten Al at 675-680‹C, which is then cast in a pressurised mould heated to 500‹C. In a further example 0À1 Kg of zirconium hydride mixed with 1À2 Kg of Al powder in Al tubing is introduced into violently stirred molten Al which is then cast into shell moulds. Specification 729,339 is referred to.