GB1352131A - Arc welding torches and methods - Google Patents

Abstract

1352131 Welding by fusion BRITISH OXYGEN CO Ltd 19 April 1971 [14 April- 1970] 17765/70 Heading B3R In a plasma arc welding torch a consumable electrode 2 is fed axially through a central non-consumable electrode 8. The electrode 8 comprises a water-cooled copper shank 6 on which is screwed a tip 8 of W, Ta, Mo, Zr or any alloy of these. A surrounding electrode 10 is of copper and is water-cooled. Plasma forming gas is introduced into the gap 12 between the electrodes 8, 10 and plasma guiding gas is introduced into a space 18 between the electrode 10 and a nozzle 16 of refractory and insulating material. Current sources 20, 21 are connected across respectively the electrodes 8, 10 and the electrode 8 and the workpiece 22. The shank 6 and/or electrode 8 are/is in sliding contact with the consumable electrode 2. In operation of Fig. 1, a pilot are is struck between the electrodes 8, 10 from the source 20 and thereafter transferred to the workpiece and maintained from the source 21. The consumable electrode 2 is then fed towards the workpiece, the electrode function being transferred to the electrode 2 as it emerges from the electrode 8, droplets 28 of fused electrode metal then being projected from the electrode 2 into the workpiece molten pool 26. Although the electrode 2 is shown at positive potential, it may be at a potential below that of the workpiece, with the electrode 10 at an intermediate potential. In Fig. 2, the source 20 is connected to the electrode 10 through an adjustable resistor 30 and to the workpiece through a normally closed contact IR of a relay connected between the source 21 and the workpiece. The contact IR is opened when current through the relay reaches a chosen minimum. In operation, a non-transferred are is struck between the electrodes 8, 10 from the source 20, the current value being restricted by adjusting the resistor 30. When the torch is sufficiently close to the workpiece the arc is transferred to extend between the electrode 8 and the workpiece from the source 20. The consumable electrode 2 is fed towards the workpiece and when it extends beyond the electrode 10 an arc is struck between the consumable electrode and the workpiece from the source 21, the then energized relay opening the contact IR, thereby leaving the non-transferred arc between the electrodes 8, 10 and an arc between the consumable electrode 2 and the workpiece. On cessation of the consumable electrode feed, the arc thereof lengthens and the current from the source 21 reduces to de-energize the relay and close the contact IR. The transferred arc from the source 20 may then readily be struck and used for crater filling. Source current and voltage values are specified.