The study of temperatures in a tungsten electrode at reverse polarity arcing

The paper considers the features of energy release in a tungsten electrode under the reverse polarity TIG welding. The study substantiates the statement that the chemical composition of an electrode does not significantly affect the transfer of anode power to it. The specific effective power of an electrode is substantiated and taken as 6 W/A. The authors analyzed the features of arcing on the flat tip of a 3 mm diameter electrode using high-speed video. The analysis identified that at limiting currents ensuring tip melting, the tip heating is uniform over the cross-section. As a design scheme, the authors selected a continuous flat heat source on the semi-infinite rod surface with surface heat transfer. The authors obtained averaged values for volumetric heat capacity сρ=3.2 J/(cm³∙°С) and heat transfer coefficient а=0.3 cm²/s. The current at which the tip melting temperature is reached was taken as a limiting current. Using the limiting current value and start time of the electrode tip melting, the authors calculated the electrode heat transfer coefficient value b. The calculated melting depth for the over-limiting current welding mode showed good coincidence with an experiment. The authors recalculated the b value for the electrodes of 4-, 5-, and 6-mm diameter and calculated limiting currents for these diameters. The design limiting currents for these diameters also showed good coincidence with experimental results. The study showed that the increase of a coefficient up to 0.4 cm²/s does not cause changes in temperature and limiting currents at simultaneous сρ adjustment according to the constant thermal and physical properties сρа^0.5. As a result, the authors obtained temperature dependencies for the electrode over time and length. Time dependence of the electrode tip heating allows calculating limiting currents with the decrease in arcing time.