GB1435022A - Welded elements and methods for making such elements - Google Patents

Abstract

1435022 Welding by fusion; soldering; making composite metal tubing TEXAS INSTRUMENTS Inc 45533/73 Headings B3A and B3R A two-layer metal tubing is formed from a composite metal strip 10 comprising a layer 12 of a first metal of a selected fusing temperature and, metallurgically bonded thereto at an interface 16, a layer 14 of a second metal of a relatively lower fusing temperature, said strip being formed into a tubular configuration and longitudinally seam welded by application of heat from the first metal layer side of the strip such that the juxtaposed first metal layer edges are fused together only at a location spaced from the interface 16 and, by conduction through the first metal layer, the juxtaposed second metal layer edges are fused together, preferably throughout the thickness thereof. As shown, the composite metal strip 10 comprises a stainless steel layer 12 and a copper layer 14 bonded together as by roll bonding or pressure welding. The strip 10 is cleaned and then drawn by rolls 24 through a series of dies 26 to form a tube with the stainless steel outermost and preferably with the strip edges forced together. The seam is arc welded by a T.I.G. torch 28 (using, e.g. helium) thereby welding together the edges of the layers 12, 14 at 44, 48 respectively. A small amount of the copper layer 14 tends to be drawn by capillary action between the unfused portions of the ends of the stainless steel layer 12 so that the latter are brazed together. The copper may comprise 0À02 % phosphorous, and the stainless steel may comprise 0À08% max. carbon, 1À00% max. manganese, 1À00% max. silicon, 0À045% max. phosphorous, 0À045% max. sulphur, and 0À50% max. nickel with a titanium content five times said carbon content, 12À00% chromium and balance iron. Preferably the stainless steel and copper layers are not less than 0À020 inches thick. If desired, strip preheating and slight fusion of the layer 12 edges may be effected by an upstream torch 51. A post-weld heat treatment may be provided. In Figs. 8, 9 (not shown) additional welding heat is applied internally of the tube, simultaneously with that applied externally, to ensure complete fusion of the layer 14 edges. In Figs. 3, 4 (not shown) the layer 14 is disposed outermost and the welding is effected internally of the tube. A T.I.G. torch for the above-mentioned internal welding, Fig. 6, comprises an electrically conductive rod (56), e.g. of copper, provided with a laterally opening, shielding gas recess 62, a surrounding, e.g. press-fitted, electrically insulating sleeve 72 (e.g. of epoxy-bonded fibreglass) apertured at 74 in alignment with the recess 62, a tungsten electrode 68 adjustably screw-secured in the rod so as to extend through the recess 62, a shielding gas duct 64 extending between a flexible tube 80 and the recess 62, a flexible cable or, for rod support, rigid current feed means 75 and an elongated U-shaped passage 82 for coolant fluid (e.g. water).