GB900023A - Method and apparatus for making pressure seals between metallic surfaces, more especially in electron tubes - Google Patents

Abstract

900,023. Welding by pressure. EITELMcCULLOUGH Inc. Oct. 27, 1958 [Dec. 5, 1957], No. 34315/58. Class 83 (4). [Also in Group XL (a)] A method of making articles, e.g. electron tubes, comprising parts presenting metallic sealing surfaces joined together in a pressure seal, comprises placing the parts in a vacuumtight chamber removing air from the chamber, heating the metallic sealing surfaces by inducing an electric current therein while maintaining vacuum or inert conditions in the chamber, and forcing together the metallic sealing surfaces while hot with sufficient pressure to form a permanent seal, the temperature to which the metallic sealing surfaces are heated being less than the melting temperature of said surfaces. In the arrangement shown, a double triode tube 10 comprises a plurality of ceramic rings and a plurality of metal rings, e.g. of nickel or an alloy. The ceramic rings have a molybdenummanganese metallizing coating covered by a nickel sealing surface and thin copper sealing rings (not shown) are interposed between the ceramic and metal rings. Terminal tabs arranged in two diametrically opposed rows are connected to the metal rings. The tube parts together with an elevating ring 100 and a pressure ring 102 are loaded into a cylindrical jig 94 and supported on a cylindrical stand 98 seated in a recess 45 in a base-plate 40 having apertures 43 and 44 leading to a pumping system. A coupling 72 is connected to an hydraulic system. A glass cylinder 80 and a ram 82 are held in a recess in the coupling 72 by frictional engagement of the cylinder 80 with sealing rings 77 and 78 surrounded by a cooling coil 79. The ends (not shown) of a cooled radio frequency coil 85 are supported from an insulating platform 87 clamped to the coupling 72 by a screw 88. The jig 94, stand 98, rings 100 and 102 and ram 82 are made of a dielectric material such as ceramic. In operation the cylinder 80 is raised and the stand 98, jig 94, the tube parts and rings 100 and 102 placed in position. Heater leads 108 and 109 are then clipped to the tube heater terminals and the cylinder 80 lowered to the position shown in which it engages a sealing ring 47 surrounded by a cooling coil 48, whereupon pumping is commenced. The tube parts are then outgassed and the sealing surfaces cleaned by r.f. heating current induced by the coil 85 and the cathode is formed by applying current to the leads 108 and 109. The ram 82 is then operated to form the pressure seals. The prior art of forming the metallic sealing surfaces with an optical finish is referred to.