GB722502A - Improvements in and relating to the electric welding of sheet-metal articles - Google Patents

Abstract

722,502. Making containers; welding by pressure; soldering. KREFT, H. Nov. 23, 1950 [June 29, 1950], No. 28720/50. Addition to 682,191. Classes 83 (2) and 83 (4). In the electric resistance welding of containers &c. seams wherein one or more pairs of electrodes extend the length of the seam and a single high current impulse is employed as claimed in the parent Specification a concentrated heat zone is created at the seam such that welding is effected while the temperature of the metal outside the welding zone remains below welding temperature. The resistance between the surfaces to be welded is made higher than that at the electrode contact points. If the metal is of high resistance the electrodes are silvered or nickelled or in the case of tinplate, the plating is removed only at the areas to be welded. The surfaces of the electrodes may be of tin, nickel or silver and the surfaces contacted by the electrodes may be silvered or tinned while the areas to be welded may have their resistance artificially increased. The edges of the sheets may be bent, see Fig. 5, or flanged to increase the resistance or oxide, semiconductor, lacquer or metal powder layers or metal or semi-metal in the form of thin foil or wire may be introduced between the welding areas. Coated sheet-metal, e.g. tin, silver or nickel plate may have resistance increased by roughening, perforating, knurling, scraping, &c. Oxide coated sheets may retain the oxide at the welding area while at the electrode contactpoints the oxide is removed or silvered or tinned. When welding, e.g. tinplate, with insertions for resistance increase, the insertions may fuse into the welded surfaces. Alternatively the insertions may not cover the whole overlapped area so that, e.g., tin coatings contact over part of the area and form soldered areas when welding of the middle of the area is effected. The insertions may have high resistance parts edged with solder, e.g. tin. to obtain a welded joint edged with solder. Fluxes in paste or gas form or as an integral part of the insert may be used. Small current densities are employed, obtained by using a cylindrical electrode 35, Fig. 7, or 42, Fig. 8, with coacting electrodes 38 and 41.