Friction in low speed lubricated rolling and sliding contacts:Dissertation

A four-disc machine was built for friction measurements at low speed lubricated rolling and sliding contacts.The most important parameters influencing friction in these conditions turned out to be the sliding speed, the lubricant and its additive content, the disc material combination, the lubricant viscosity and the topography of the surfaces.The load, rolling speed and surface roughness had only a slight influence on friction.Values for the coefficient of friction in the range of 0.03 - 0.11 were measured.The mechanisms of lubrication in low speed rolling and sliding conditions is governed by a combination of three effects: the chemical formation of the boundary lubrication film, the creation of a hydrostatic pressure in lubricant trapped by the surface topography and the squeeze effect of lubricant in grooves formed by the surface topography.In conditions of pure rolling at low speeds the lubricant and its additive content has a considerable influence on friction because of a deforming or mangling effect of the boundary lubricant film in the inlet region of the contact.The rolling speed had a significant influence on rolling friction and a slight influence of the disc material combination could be measured.No appreciable influence of load, lubricant viscosity or surface roughness on the coefficient of rolling friction was found