GB476375A - Improvements in and relating to methods of uniting metals - Google Patents

Abstract

476,375. Making composite plates, electric fittings, &c. by soldering. BRITISH THOMSON-HOUSTON CO., Ltd. July 12, 1937, No. 19295. Convention date, July 16, 1936. Drawings to Specification.. [Classes 83 (ii) and 83 (iv)] In uniting articles consisting of metals or alloys which form amalgams with mercury, a film of mercury is applied to the clean surfaces of the parts, which are then brought into intimate contact and treated for the removal of entrapped gas and are then subjected to simultaneous heat and pressure to vaporize excess mercury and thus complete the joint. Parts of silver, copper, lead, tin, barium, bismuth, cadmium, chromium, gold, magnesium, manganese, potassium, sodium, strontium and iron may thus be united to parts of the same or the other metals. In joining parts of copper and silver, the copper may be cleaned by acid dipping or scrubbing with pumice and the mercury applied either in the form of an aqueous solution of mercuric nitrate and sodium cyanide or metallic mercury and sodium cyanide by means of a pad of chamois skin so as to avoid extraneous particles in the joint. After drying the part is polished by a dry chamois skin pad. A strip of silver, e.g. 3 mils. thick, is brushed or wiped clean and coated by immersing in a bath of metallic mercury. After brushing, it is pressed by hand on the amalgamated copper part. The parts are then either passed through rubber pressure rolls, if flat, or the silver part is patted down with a stiff wire brush to remove entrapped gas. The parts are then heated and pressed between platens heated, e.g. electrically. to a temperature below 290‹ C. and preferably between 225-250‹ C. in order to complete the joint. Prior to placing in the press, the parts may be enclosed in a cushion of compressible material, such as aluminium sheet, pressboard or heavy paper or parts of such material may be placed thereon. Irregularities of the surfaces are thus compensated for and intimate contact between the parts ensured. The pressure may vary from 500-40,000 lb. per sq. in., preferably between 1000 and 4000. If desired, the parts may again be heated in a curing oven. A rupture-free layer of an alloy of copper and silver amalgams is formed between the amalgamated surfaces of the parts. In joining two parts of copper to an intermediate strip of silver, the silver is amalgamated on both surfaces and the copper parts on their inner surfaces. Copper bars may be lap jointed by forming a 2" bevel on each part and after amalgamation inserting an amalgamated piece of silver of 0À002" thickness and applying a pressure of 40,000 lb. per sq. in. at a temperature of 110‹ C. for 5 minutes. The parts are then removed from the press and heated in an oven at 110‹ C. for 12 hours. A copper electric switch stud is united to a copper tongue by slotting the end, amalgamating both parts, inserting the tongue together with amalgamated silver foils in the slot and placing between steel blocks and the whole assembly between the heated platens of an hydraulic press.