A Study of the Arc Welding Phenomena at Reduced Gas Pressures (Report 2)

Thermal Characteristics of the Tungsten Arc in Argon Atmosphere

Abstract

The thermal characteristics of an arc with straight polarity formed between a tungsten electrode and a water-cooled copper plate in argon atmosphere of 18 to 760 mm Hg are examined in relation to the electrical characteristics mentioned in the previous report. The experiment is made under the following conditions. Pressure of atmosphere P : 18 to 760 mm Hg
Arc current I : 250, 450 A
Distance between electrodes L : 1 to 25 mm
The facts elucidated are as follows.
1. The ratio of anode power to arc power is 93-95% at L≅0 mm and decreases linearly with increasing L. At the pressure above 320 mm Hg and below 50 mm Hg athe decreasing tendency of the ratio is particularly remarkable.
2. At the pressure below 50 mm Hg, anode power decreases continuously with L. This tendency should be explained as follows: the power carried away from the cathode lone increases remarkably with increasing Lbecause the power is larger at lower pressure condition, resulting in the decrease in the transfer rate of the power to the anode, on the other hand the power of arc column increases little with increasing L.
3. The variation of cathode power with gas pressure is small and the ratio of cathode power to arc power is about 5-7%. Joule's beat of the tungsten electrode is as large as or larger than the cathode power, hence within the pressure range used in the experiment, the power generated at the cathode is made negative by the cooling action of thermally emitted electrons just as under the atmospheric pressure.