Movement and Tracking of Low-Pressure Arc Cathode Spots on SS400 Surface with Oxide Layer

摘要

A remarkable characteristic of the cathode spot of alow-pressure arc is that the cathode spot moves around the metal surface. Furthermore, a cathode spot can remove the oxide layer. Cathode spots of low-pressure arcs have been used for cleaning metal oxide surfaces before thermal spraying or surface modification. However, the influence of an oxide layer on movement of a cathode spot remains unclear. As described in this paper, the cathode spot movement on the surface of oxide layer and metal surface were measured to determine the cathode spot movement of a low-pressure arc. Experiments were performed using a SS400 cathode work piece and a cylindrical copper anode. Argon was used as the ambient gas. A high-speed video camera recorded the cathode spot movement. Because of the cathode spot's high brightness, a neutral density filter was attached to it. The obtained images were analyzed using plasma image processing (PIP). The work piece surface was covered with 9.67 μm of oxide thickness. The cathode spot movement was generated mainly on the oxide layer, but sometimes on the processed surface. When the arc splits, the first arc remains at the boundary; the second arc moves on the bulk surface and reappears at a different boundary. Therefore, when the arc splits, the second arc does not appear suddenly, meaning that the split is generated continuously. The oxide layer removal process does not always have priority for cathode spots, but the oxide layer serves an important role for the cathode spot existence because of oxide layer vaporization.