Effect of polarity and various contact pairing combinations of electrographite, polymer-bonded graphite and copper on the performance of sliding electrical contacts

This study focuses on the wear, friction and electrical characteristics of the newly developed, disc-disc contact design for sliding electrical contacts. Different types of graphite and copper, as the material combinations, different contact operating variables and, in particular, different directions of the electrical current, i.e., the disc polarity, were investigated under real contact conditions in a dedicated tribological test rig. The electrographite and polymer-bonded graphite were running in a self-mated contact, against copper and against each other. The polymer-bonded-graphite/polymer-bonded-graphite pair performed the best for almost all the studied parameters, while the mixed, dissimilar, polymer-bonded-graphite/electrographite combination had the worst performance. Moreover, all the pairs containing electrographite material exhibited unstable contact behaviour, and generally gave a worse overall performance. The wear of the self-mated graphite pairs was less than that of the graphite/copper pairs. The effect of the polarity on the graphite/graphite material combinations was negligible, while in the graphite/copper combinations the direction of the electrical current was found to significantly affect the wear of the discs. The wear of the positive graphite disc was up to 30% lower than the negative graphite disc, while the wear of the positive copper disc was up to 8 times more than that of the negative copper disc. Differences in the boundary contact film were observed in the graphite/copper contacts depending on the surface polarity, meaning that sliding contacts with the current flowing from the graphite disc to the copper disc saw less wear than the contacts where the current flows from the copper disc to the graphite disc.