Measurement of oil film thickness in elastohydrodynamic contacts influence of various base oils and Vl-lmprovers

The objective of the research was the investigation of lubricant film formation in elastohydrodynamic contacts for oils of different origin (paraffinic, naphthenic, polyalphaolefin) and various types of VIimprovers (polymethacrylate, olefin copolymer, styrène butadiene copolymer). An essential part of the research was to find out whether VI-improvers maintain their thickening effect under contact conditions of high pressure (p > 8000 bar), temperature (o > 100 °C), high shear rate (y > 10s s'1) and short time of contact, all these conditions occurring simultaneously. A twin disk machine was used to determine mean (integral) values of film thickness as well as film profile in the contact zone for line contact. For these measurements, two electrical capacitance methods were used. Important lubricant properties both for interpretation of the electrical data and for the corresponding EHL calculations were determined. In addition to a thermal viscosity loss, high shear rate Y leads to considerably reduced film thicknesses due to non-Newtonian viscosity loss.