Optimisation of material erosion and welding performance by metal oxides and magnetic particles

Contact erosion, welding and low conduction are the most common failures in switching devices. Silver mixed with Metal-oxide (MeOx) and more recently with magnetic particle contact materials (pseudo-alloys) have been developed to decrease erosion and welding. In this paper, we will attempt to find a compromise to maintain the best performance of lower erosion and lower welding forces by varying the content of tin oxide in the range 0% to 14% and/or with the addition of the appropriate level of magnetic particles. There are two bench tests, one used to simulate arcing on break and subsequent contact erosion at 42 VDC and 90 A has been performed and the other has a controlled make-arc experiment being carried out to produce bounce induced arcing. Considering that a long-lived arc on break may change surface topography and structure, we have tested non-aged and aged materials. The erosion, the welding tendency, welding force and contact resistance are being investigated for materials with different tin oxide content and with two kinds of shape. It has been found that increasing the oxide percentage enhances erosion and surface degradation compared to pure silver. Cylindrically shaped samples are prepared by adding the metal oxide and appropriate magnetic particles to silver powder. It was found that changing the shape of the contacts by large size (tips), reduces the arc duration and its consequences on erosion and welding occurrence.