Kenji Sunahara

Preliminary Measurements of Electrical Micropitting in Grease-Lubricated Point Contacts

The dielectric breakdown characteristics of three types of grease used in motors are compared by direct observations of flashes caused by the electric discharge between surfaces composed of a steel ball and a glass disc coated with chromium and indium tin oxide films. The flashes produce pitting on the steel ball and coated glass disc surfaces. It has been found that the frequency of the flash signal depends on the film thickness. It has also been found that the dielectric breakdown of greases is mainly influenced by the base oil rather than the thickener. Furthermore, it has been proved through the calculation of electrical energy brought by the flash or dielectric breakdown that the pitting is caused by melting of the steel surface due to a concentration of the electric current.