GB671171A - An improved process for forming ingots of refractory metal - Google Patents

Abstract

671,171. Making ingots. METRO-CUTANIT, Ltd. (Metallwerk Plansee Ges.). May 2, 1950, No. 10816/50. Classes 83 (i), 83 (ii) and 83 (iv). [Also in Group XI] Powder metallurgy; casting.-An ingot of refractory metal is obtained by extruding into rod form a pasty mixture of a powder of the metal and a binder which decomposes and volatilizes at red heat in a hydrogen atmosphere, sintering the extruded mass to form a rod and then melting the rod in a protective atmosphere by means of an electric arc. The metal powder is of high purity obtained by known processes and the binder 1-3 per cent by weight, may comprise a starchy glue. The mixture may be first presintered to drive off the binder or may be slowly heated to the final sintering temperature, which in the case of mixtures of metals is about 10 per cent below the melting point, and held at that temperature for half an hour to two hours. In order to form a rod of the size or length required, a number of sintered rods may be joined end to end as by welding or by a screwed joint and may also be joined side by side as by welding or by clamping or tying. The melting furnace comprises a base 19 to which is clamped an air-tight casing 58 which may be evacuated by a pump 81. The sintered rod 25 is fed by insulated rolls 27, 28, operated by a hand wheel 34, between electrodes 38, 39 and into a crucible 20 resting on an insulated pad 21. The crucible is preferably slightly tapered to facilitate the removal of the cast ingot. Both the crucible and the electrodes are hollow and have cooling water circulated through them by inlet pipes 23, 40 and outlet pipes 24, 43, at least part of each pipe being of insulating material. They are also connected to a transformer 87 through insulated bolts 53, 46. In operation, the rod is lowered until it touches the bottom of the crucible and is raised as an arc is struck and is thereafter slowly fed down as the end of the rod melts into the crucible. For a molybdenum bar of 4 cms. x 4 cms. cross-section a current of 4000 to 6000 amperes under a voltage of 4 to 6 volts is suitable. The method may be used for other refractory metals such as zirconium, tantalum, columbium, and tungsten or alloys thereof.