SETT FOR PLASMA-MIG-SVETSNING SAMT SVETSPISTOL FOR UTFORANDE AV SETTET

摘要

1340794 Welding by fusion PHILIPS GLOEILAMPENFABRIEKEN NV 30 Nov 1972 [12 July 1972] 32572/72 Heading B3R In arc welding with a plasma-MIG torch wherein a consumable electrode is guided into the plasma stream extending from a non- consumable, e.g. tungsten, electrode, an oxidizing gas stream is introduced, through at least one channel, into the plasma stream intermediate the respective ends of the consumable and non-consumable electrodes to improve arc stability and allow higher currents. The electrodes may be both positive or, as shown, both negative. The oxidizing gas stream oxidizes the end of the consumable electrode to prevent cathode root excursion in the case of a negative consumable electrode, and prevents damage to the torch nozzle or contact tube in the case of a positive consumable electrode, thus enabling a shorter set-back of the consumable electrode contact tube and, consequently, allowing the torch to be brought closer to the workpiece surface. The oxidizing gas stream may comprise up to 10%, preferably 2%, by volume, of O 2 in an inert gas, e.g. A; the plasma gas may be A; and shielding gas surrounding the plasma stream and MIG arc may be a mixture of A and CO 2 (e.g. 20% by volume CO 2 ). As shown, a consumable electrode contact tube 13 and a non-consumable electrode 9 in a holder 8 are disposed respectively coaxial with and eccentric of a constructing orifice 7 of a nozzle 5 of a housing 3. A consumable electrode 11 is fed through the contact tube by rollers 15 driven by a controllable speed motor. Plasma and shielding gases are fed respectively through ducts 19, 21. The housing 3, holder 8 and contact tube 13 are water cooled through connections 231, 2311, 251, 2511, 271, 2711. The non- consumable electrode is connected to the negative terminal of a supply 29 via an H.F. generator 31 and the consumable electrode is connected to the negative terminal of the supply 33. The oxidizing gas stream is injected through a tube 32 terminating in a radial bore 39 of the nozzle 5.