Study on surface film in the wear of electrographite brushes against copper commutators for variable current and humidity

In this paper studies on the wear of brushes against copper commutators were briefly reviewed. The effects of alternate current density and humidity on the wear rate of electrographite brushes were investigated and the wear mechanism was discussed in detail. SEM (scanning electron microscope) and EDS (energy dispersive X-ray analysis) were used to observe the morphology of contact surface of brushes and analyze the compositions of contact surface. The results show that the oxide layer on the contact surface becomes thick and the wear rate of brushes increases with current density. In 50% relative humidity (RH), an oxide layer can be formed on the contact surface, which can act as lubricants, and the wear rate of brushes is small. While in 10% RH, no oxide layer is formed and the wear rate is large. Under a regular condition the fatigue wear mechanism of electrographite brushes is supported in this study while in low humidity seizure mechanism is dominant.