GB547755A - Method for joining metallic bodies - Google Patents

Abstract

547,755. Brazing parts of vacuum tubes &c. STANDARD TELEPHONES & CABLES, Ltd. May 23, 1941, No. 6635. Convention date, July 13, 1940. [Classes 83 (ii) and 83 (iv)] In brazing together two pieces of metal, such as the copper parts of a vacuum tube of the electron discharge type prior to heating to a high temperature to effect degasifying, the pieces are first each coated with a thin film of a metal with which the brazing material has a lower rate of alloying than with the metal of the pieces, placing the coated pieces in close proximity, heating to brazing temperature and applying brazing material. The coating ensures the capillary flow of brazing material completely between the pieces instead of soaking into the pieces adjacent the point of application of the brazing material and thus renders the joint gas tight. Copper pieces may be coated with nickel or iron and the brazing material may consist of silver solder containing 70 per cent of silver and 30 per cent of copper. A pair of two inch copper discs may be electrolytically coated with nickel for five minutes at a rate of 20 amperes per sq. ft. current density. The parts are then placed together leaving a space not exceeding 0.002 inch and preferably 0.001 inch and the silver solder applied round the periphery and the parts heated for 2-5 minutes at brazing temperature which may be from 100-300‹ C. in excess of the melting point of the silver solder. Brazing may be effected in the presence of fluxes such as borax or fluorides or in an atmosphere of hydrogen. The silver solder may alternatively be deposited as one or more globules in one of the parts prior to assembly. A wire 8 of silver solder may be held at the joint between a pair of closed nickel plated copper tubes 6, 7 by a corrugated spring clip 9 consisting of a wire of an alloy which does not melt at the brazing temperature such as a nickel-chromium alloy. Two apertured discs 10, 11 to be brazed to a tube 12 have their apertures flared to leave a space to receive a wire 13 of silver solder, the parts being previously nickel plated.