Improvements in or relating to methods for processing filter tubes

944,319. Making filters. COMMISSARIAT A L'ENERGIE ATOMIQUE. Nov. 15, 1961 [Nov. 16, 1960], No. 40854/61. Heading B3A. [Also in Divisions B1 and F2] A method of precessing a filter tube of sintered metal comprises compacting a portion of the tube, annealing said portion in a reducing atmosphere and securing the tube by a part of said portion. An end portion 2 of a microporous sintered metal, e.g. nickel-copper powder tube 1 is supported on a mandrel, compacted, e.g. by hammering or shrinkage and annealed by high-frequency heating in a reducing atmosphere of, e.g. hydrogen. The compacted portion of the internal diameter of the tube is subsequently roughened by wire brushing, sand blasting or by spraying on an emulsion comprising grains of metallic powder, which may be coated with a nickel phosphorous alloy, suspended in a liquid cement of, e.g. a 2% aqueous solution of gum aragon and annealing at 900‹ C. to sinter the grains to the wall. The bore of the tube is finally completely coated with a microporous layer of, e.g. nickel and fitted by welding or flanging to a supporting plate 3. Two tubes may be joined by fitting one into the other and treating them as above.