Thermal effects of different kind influencing lubricated non-conformal contacts

Three steel spherical specimens with different diameters are tested against a glass disc under the same working conditions in several rolling speeds and slide-to-roll ratios. The same tests are carried out with the specimens connected to a steel shaft with and without a ceramic insert purposely designed for limiting the transfer of the heat generated by the shaft seals and bearings to the specimens, in order to evaluate the influence of the experimental apparatus on friction results. A general increase in friction is found when the ceramic insert is used probably related to a greater local lubricant viscosity inside the contact due to the reduction in the specimen surface temperature. However, the configuration of the experimental apparatus does not influence in a significant way the shape of the friction curves as a function of the entraining speed and of the slide-to-roll ratio. The analysis of the interference images of the contact shows that the thermal insulation due to the ceramic insert does not affect particularly the film thickness.