Development of a simple DC plasmatron for plasma arc metallurgy

Plasma arc metallurgy of tantalum is of considerable interest in view of its relevant role in our national development. Since a commercial high power direct current (DC) plasmatron is very expensive and has not yet been available in our laboratory, we have successfully modified a tungsten inert gas(TIG) welder for preliminary experiments. The gas-cooled cathodes are thoriated tungsten rods of diameter 1.6 and 3.2 mm for operation in the current range of 35-75 A and 60-180 A respectively. The water-cooled anode is made of copper with 4 mm inner diameter nozzle. Welding grade argon gas is used as a plasma gas. After the initial assistance from the high frequency ignitor unit, the plasma jet erupts almost instantly. The gas stabilized plasma jet consists of the inner hot zone and the cooler tail. The gas flowrate (2-14 1/min) has been found to influence the arc voltage (13.5-25 V), the power input, the hot jet length and the environmental noise. Further works will involve that plasma diagnostics development and the design of a plasma processing reactor. (author). 6 refs, 10 figs