Abstract
Anode spots configuration on the molten pool in the moving GTA was discussed from observation of slag bits behaviour with varying welding condition and base metal elements.
The positions of slag bits on the pool are greatly influenced by surface flow on the pool caused by change of plasma stream direction with a little arc inclination and content level of minor elements in steels such as sulfur and oxygen. Especially, on condition that the surface flow is slow in the stationary state, the anode spot is greatly moved by a little fluctuation and irregular weld beads caused by the anode spot movement are liable to occur.
On the other hand, effect of the size of anode region dispersed on the pool on melting the back of a thin steel plate was discussed.
The anode region size is greatly influenced by arc length and arc force (shape of tungsten electrode tip) which spread the higher temperature region of plasma, and content level of the minor elements which is reported to change directions of metal flow on the pool surface.
The ratios of radius of anode region to radius of the pool in a stationary arc with arc length of 3 mm are 0.73 under the condition of the lower content level and 45 deg. conical tip, 0.64 under the condition of the same content level and truncated conical tip, and 0.61 under the condition of the higher content level and 45 deg. conical tip.
