DE2422322

1453366 Welding by fusion VSES NI PROEKTNO-KONSTRUKT I TEKHNOL INST ELEKTROSVAROCH OBORUDOVANIA 9 May 1974 20609/74 Heading B3R [Also in Divisions H3-H5] A non-consumable plasma torch electrode assembly comprises a water cooled rod like electrically conductive copper holder 1, containing a refractory metal insert 2 at one end, a chamber 3 symmetrical about the longitudinal axis of the assembly being provided in the holder 1 and being bounded on one side by a central portion only of the insert 2, the chamber being filled with a substance of lower thermal conductivity than the material of the holder 1 so that the central portion of the insert 2 is cooled less than the peripheral portion which is in direct contact with the holder 1. Thus in use the arc is centred on the hotter central zone of the insert 32 and does not tend to migrate to the cooler peripheral zone. The refractory metal of the insert may be a refractory metal of groups IV, V and VI, or an alloy of these metals. Specified alloys are Ta 73%/Hf 25%/Mo 2% : Hf 99%/ Mo 1% : W 97%/La 3%. The material filling the chamber 3 may be titanium, steel, pig iron, air or argon. The plasma torch may be a d.c. transferred arc torch in which the electrode assembly is supported in a hollow water cooled nozzle by an insulating spacer provided with longitudinal channels for introduction of plasma forming gas to the end of the electrode assembly. In Fig. 4 (not shown) two plasma torches with electrode assemblies as described connected in series are supplied from a d.c. source to produce a heated plasma for surfacing an adjacent workpiece. The electrode assembly if connected to the positive pole has a gas filled chamber behind the insert and the electrode assembly connected to the negative pole has a solid filled chamber. The torch can be used for welding, surfacing, surface finishing and cutting metals.