Make arc erosion and welding in the automotive area

A make arc has been investigated using a new testing apparatus. This apparatus which includes a piezo-translator, enables controlled bouncing to be studied at make under mechanical conditions similar to those encountered in automotive relays. Material transfer and welding tendency of silver, silver alloys and silver metal oxide contact materials have been studied under inductive, resistive and lamp loads at 14 V dc and 10-70 A. With all loads, anode to cathode material transfer has been observed. AgCdO, Ag and AgNi under lamp and resistive loads show the highest material transfer, as opposed to non doped and doped AgSnO₂ under inductive loads. This well known transfer is due to the anodic arc, which occurs during bounces when the gap between the contacts is shorter than ~5 μm, at the beginning and the end of the bounce. We have demonstrated that welding occurs at the beginning of the bounce, i.e. when the contacts begin to separate under arc, and not when the contacts close under arc at the end of the bounce. It was found that welding occurs mainly with Ag, AgCdO, AgZnO, AgFeRe, and AgFeO_x contact materials, and under high inrush current produced by lamp loads