Evaporation Rate of Vacuum Arc Cathode Spot Affected by Ambient Pressure

Abstract

The high ambient pressure is important for surface treatment on the metal surface using the vacuum arc cathode spot because the cost becomes low, and the equipment becomes simple. However, the effects of ambient pressure on the physical process, surface roughness, and removal of the oxide layer remain unclear. The surface roughness might be derived from the removal area speed of oxide layer and evaporation rate. Consequently, the evaporation rate of the vacuum arc cathode spot as affected by ambient pressure is important to ascertain the removal process. This study elucidated the evaporation rate of the vacuum arc cathode spot as it is affected by ambient pressure. The mean number, split frequency, removal area speed, and mean current density were measured experimentally with changes in ambient pressure. In addition, the evaporation rate and temperature distribution are calculated using heat conduction simulation of the oxide layer, bulk, and ambient gas. Experiments were conducted using an SS400 cathode and a cylindrical copper anode. A high-speed video camera recorded the cathode spot movement. Then, the obtained images were analyzed using plasma image processing. Heat conduction was calculated using the energy conservation equation. The mean number, split frequency, removal area speed, and mean current density of cathode spots decrease concomitantly with increasing ambient pressure. The evaporation rate mostly increases concomitantly with increasing speed of the cathode spot movement, i.e., the low ambient pressure and small cathode spot area. The evaporation rate depends on the power density and the specific heat and thermal conductivity of the material. Therefore, the evaporation rate is derived from the stagnation time and the cathode spot temperature, and also from the current density and cathode spot area.