GB580414A - Improvements in porous metallic bodies - Google Patents

Abstract

580,414. Filtering liquids. CALLITE TUNGSTEN CORPORATION. Nov. 4, 1943, No. 18353. Convention date, May 13. [Class 46] [Also in Groups II and XXXIV] A porous body is made by coating broken crystalline metallic particles with a lower melting point metal and sintering into a coherent body. Preferred metals are tungsten molybdenum and ironmolybdenum - manganese alloy. In the case of tungsten an ingot is heat treated at about 2,800‹C. until formed into large crystals, then broken up to separate the crystals which are further crushed into irregular particles as by ball milling or hammering. The particles are then sorted into batches by successive passage through screens, e.g., of 40, 60, 100, 150, 200, 250, 300 and 350 mesh. Material remaining on one screen may be mixed with that from another to provide control of the degree of porosity. In the case of the alloy the brittle crystalline structure is produced by casting and chilling. The graded particles are wetted with an aqueous solution of silver-nitrate, dried, mixed with a binder of paraffin dissolved in carbon tetrachloride. In an example particles from the 350 mesh screen so treated are loaded into a die 1 and compressed by a plunger 2 to about two-thirds the original volume at 4. Material from the 200 mesh screen is added and pressed into a second layer 5 and particles from the 60 mesh screen form a third layer 6. Pressure is now increased to 30,000 lbs. per sq. in. to compact the entire mass and causes a limited amount of interpenetration at the boundaries of the layers. The compact is removed from the die and heat treated in stages (a) to volatilize the binder, (b) to reduce the silver nitrate to oxide, (c) to reduce the oxide to silver and (d) to sinter the silica coated particles into a strongly coherent porous mass. Bodies so produced are suitable for use as filters or bearings.