GB766186A - "improvements in or relating to sintering metallic powders" - Google Patents

Abstract

766,186. Powder metallurgy. METAL-LURGIE DES POUDRES. Oct. 1, 1954 [Oct. 16,1953], No. 28645/53. Class 83 (4). In a process for sintering a metallic powder having a melting point of at least 600‹ C., the powder is mixed with an organic lubricant, the mixture is subjected to pressure to form a compact which is then treated to remove substantially all the lubricant and the compact is then sintered in a non-oxidizing atmosphere in the presence of a reacting agent which reacts with the metal to form a compound which is subsequently decomposed to deposit metal on the particles of the compact before the sintering is completed. The compression of the powders to form a compact is generally effected at a pressure of between 10 and 150 kg. per sq. mm. The lubricant is used in the proportion of up to 2 per cent by weight of the metallic powder and is preferably a stearate, such as zinc stearate, but it may be an oil or soap dissolved in a volatile solvent. The lubricant may be removed by heat alone in the presence of an inert gas at temperatures between 250‹ and 650‹ C. or by heating at similar temperatures in the presence of a gas or vapour, such as air or steam, which reacts with the lubricant. If the lubricant is removed from the compacts by heating in air, the compacts are preferably de-oxidized by heating them above 800‹ C. in an atmosphere of cracked ammonia. When the lubricant is removed by means of a solvent the compacts may be wetted with a liquid such as perchlorethylene or carbon tetrachloride, the solvent being evaporated by heating the compacts to a temperature generally below 200‹ C. The metallic compound formed in the compact is preferably liquefied before the decomposition is effected and its formation on the compact may be effected by introducing a reacting agent such as ammonium or hydrogen halide or phosphorus sulphide. The process is applicable to pure metallic powders or to powders of alloys, such as tungsten, molybdenum, copper, nickel, cobalt, aluminium, stainless steel, cast iron, iron-chromium alloys, ironsilicon alloys, iron - aluminium alloys, aluminium-nickel-iron alloys or to mixtures of powders. The powders have a particle size finer than 350 mesh (B.S.S.). The compacts may be sintered in boxes of iron partially sealed by a joint of alumina or the furnace illustrated may be used. The furnace has baffles 9 and 10 and trays 11 carry the compacts from 12 to 13. Pure hydrogen introduced at X to form an inert atmosphere in the area of the cooling jacket 6 is partly removed at Y and re-introduced at Z after having been charged with the reacting agent and the hydrogen and agent are largely removed at P; hydrogen saturated with steam for the removal of the lubricant is introduced at Q and removed at S.