GB1453494A - Arc welding method and apparatus - Google Patents

Abstract

1453494 Welding by fusion PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 28 Oct 1974 [31 Oct 1973] 46561/74 Heading B3R In plasma-MIG arc welding wherein a consumable electrode 13 is fed coaxially through a water-cooled, copper, plasma gas nozzle 7 and a metal arc is struck between said consumable electrode and a workpiece 15 in a plasma arc between said nozzle (acting as a non-consumable electrode) and said workpiece, said plasma arc, emanates from an inner surface 37 defining an orifice 9 of the nozzle. As shown, the consumable electrode 13 is fed by adjustable speed motor driven rollers 17 through a contact tube 11 accommodated, by way of an insulating cap 12, in a housing 5 provided with the nozzle 7. The nozzle is cooled by water in chambers 27 fed via duets 29. Plasma gas, e.g. argon, is fed to the nozzle through a pipe 21 and the housing. Shielding gas, e.g. a mixture of argon and carbon dioxide, is fed to a hood 23 surrounding the nozzle. The consumable electrode and the nozzle have the same polarity and are connected to separate current sources, respectively a source 43 having a flat output characteristic and a source 47 having a drooping output characteristic. In operation, the plasma arc is spontaneously struck by striking of the metal arc by consumable electrode/workpiece contacting. Electromagnetic force derived from currents in the consumable electrode draws the plasma arc radially inwards and along so as to be attached to the inner surface 37 of the nozzle. Increased bore diameter of the nozzle upstream of the orifice and restricted axial width of the surface 37 prevents arc climbing and fusing of the contact tube.