Dynamics of Solid Dispersions in Oil During the Lubrication of Point Contacts, Part I—Graphite

Abstract

A Hertzian contact is lubricated with dispersed graphite in mineral oils under boundary lubrication conditions. The contacts are optically observed under pure rolling, combined rolling and sliding, and pure sliding conditions. The contact is formed with a steel ball on the flat surface of a glass disk. Photomicrographs are presented which show the distribution of the graphite in and around the contact. In addition, friction and surface damage are shown for conditions when the base oils are used alone and when graphite is added to the base oils. Under pure rolling and combined rolling and sliding conditions, it is found that, for low speeds, a graphite film can form which will separate the contacting surfaces. In contrast, under pure sliding conditions, graphite accumulates at the inlet and sweeps around the contact, but very little of graphite passes through the contact. The accumulated graphite appears to act as a barrier which reduces the supply of oil available to the contact for boundary lubrication. Friction data show no clear short-term beneficial or detrimental effect caused by addition of graphite to the base oil. However, during pure sliding, more abrasion occurs on the polished balls lubricated with the dispersion than on those lubricated with the base oil alone. All observations were for the special case of a highly polished ball on a glass surface and may not be applicable to other geometries and materials, or to rougher surfaces.

Presented at the 36th Annual Meeting in Pittsburgh, Pennsylvania, May 11–14, 1981

Notes

Presented at the 36th Annual Meeting in Pittsburgh, Pennsylvania, May 11–14, 1981