Abstract
Effects of helium gas on the maximum arc pressure and on the critical travel speed to melt a base metal were investigated in GTA welding.Results were obtained as follows;(1) The critical speed in helium (He) gas arc is much higher than in argon (Ar) gas arc. Heat input per bead length at the critical speed in He gas arc is lower than in Ar gas arc. This fact is understood because distribution of a heat source in He gas arc is more concentrative than in Ar gas arc.(2) Electrode geometry is effective on the critical speed and especially the critical speed has a maximum value at a vertex angle of 45°, when a diameter of electrode is held constant.(3) The pressure in He gas arc is much lower than in Ar gas arc and is not sensitive to electrode geometry. This fact is understood because a spreading angle of arc current in a front of an electrode tip in He gas arc is smaller than in Ar gas arc.(4) When He gas is mixed into Ar shielding gas, generally the pressure decreases, but the critical speed is held constant. This fact shows that mixed He gas has a great influence on arc phenomena in a front of electrode tip, but it has little influence on an arc column.(5) When a few litter per minute of He gas is added to an upper part of an electrode tip through a nozzle in Ar shielding gas, the pressure effectively decreases to the degree of the pressure measured in He shielding gas.
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