Characteristics of surface film on slip-ring in the low atmospheric pressure

The surface him of slip-ring is important for good sliding contact of brush and slip-ring. This film formation is influenced by the brush material, the atmospheric temperature, humidity and atmospheric pressure. The condition of sliding contact and surface film can be estimated by the measurement of contact voltage drops. The contact resistance is classified into constriction resistance and film resistance. From the results of this paper, in the low atmospheric pressure, the oxidized film scarcely grew on the slip-ring surface, so the contact resistance is thought to be generated mainly by the current constriction. Further, it can be found that the resistance in the low atmospheric pressure was only constriction resistance, and that the resistance in the air was composed of the constriction resistance and him resistance. The wear length of the test brushes at reduced atmospheric pressure, depending upon the brush grade, was many times larger than the wear in the air