Characteristics of surface film on slipring in the low atmospheric pressure

The surface film of slipring is important for good sliding contact of brush and slipring. 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 guessed 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 slipring 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 film resistance. The wear length of the test brushes, depending upon the brush grade, was many times larger than the wear in the air.