Patent GB-731836-A (GB)
Title: Improvements in alternating current inert gas shielded arc welding
Inventor: MULLER ALBERT
IPC: B23K35/22
Filed: 1952-07-28
Abstract: 731,836. Welding by fusion. AIR REDUCTION CO., Inc. July 28, 1952, No. 19010/52. Class 83 (4). In gas shielded alternating current arc welding with a consumable electrode, a material is introduced into the welding zone to improve the arc stability without reacting appreciably with the weld metal, the material containing or being a control metal which is electropositive with respect to the base metal of the electrode and workpiece and being absorbed on the surface of the cathode base metal to form a surface having a thermionic emissivity higher than that of the base metal alone. The material may be on the surface of the electrode, embodied in the electrode as an alloying or mixing element, entrained in the shielding gas stream, applied directly on the workpiece or added on the surface of a filler wire. The material is preferably a metal with an ionization potential lower than that of any of the other constituents of the arc atmosphere. With a cold cathode material the arc re-ignition voltage is reduced by producing emission from the cathode exceeding the glow discharge arc transition emission, so that a low open-circuit voltage of not more than 74 volts may be employed. The material may be selected from the alkali metals lithium, sodium, potassium, rubidium, caesium and fracium; the alkaline earth metals calcium, barium, strontium and radium; lanthanum and the lanthanum series rare earth metals cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutecium; actinium and the actinium series rare earth metals thorium, protactinium, uranium, neptunium, plutonium, americium and curium; scandium and yttrium. Compounds of these elements which dissociate in the arc to liberate the elements may be used, e.g. the oxides, carbonates, borates, phosphates, nitrates, silicates or halides. Preferred materials are caesium nitrate, rubidium carbonate, caesium rubidium chloride, barium oxide or carbonate, barium strontium mixtures in the form of oxides or carbonates, lanthanum and lanthanum series metals in oxide forms, thorium oxide and potassium carbonate. The use of these materials also concentrates the arc cathode spot and improves the transfer from the electrode to the work. The workpiece and the electrode may consist of aluminium, aluminium alloys, copper, copper alloys, nickel, nickel alloys, magnesium and magnesium alloys. In an embodiment a mild steel wire is knurled in rolls and a paste of rubidium carbonate and alcohol is brushed on the surface and some is trapped therein when the wire is passed through smoothing rolls. The wire is dried and fed from a reel 23, Fig. 1, by a device 25 through a conduit 26 to a gun 27. Argon is supplied through the conduit 26 to the gun 27 to be discharged therefrom as an annular non-turbulent stream. Rubidium oxide or barium oxide may be used in place of rubidium carbonate. An aluminium alloy wire with rubidium carbonate in the surface may be used in the apparatus of Fig. 1. In another embodiment an electrode made from molten mild steel to which is added mixed metal-52 per cent cerium, 33 per cent lanthanum, 1.5 per cent iron, balance rare earth metals-is employed with argon shielding gas. In another embodiment an untreated mild steel electrode 90, Fig. 8, is fed from a reel 91 through a conduit 93 to a gun 94. Argon is supplied to the gun 94 from a cylinder 110 to flow non turbulently from a water-cooled nozzle. Steel filler wire 119 with barium oxide in its surface is fed to the arc from a reel 120 through a conduit 122. The arc is started by coating the work with an alcohol solution of stabilizing material. In a further embodiment using a gun similar to that in Fig. 8, powdered barium oxide is introduced by a vibrating powder dispenser into an organ shielding gas stream about a mild steel electrode. Helium gas may be used. In a further embodiment an untreated mild steel electrode is used in the apparatus of Fig. 1 with argon shielding gas and a slurry of rubidium carbonate and alcohol is applied by brush to the workpiece. Specifications 662,806, 684,011 and 687,666 are referred to.