High-Pressure Viscosity as an Explanation of Apparent Oiliness 370187
OILS from three different crudes, matched as to initial viscosity but with widely different viscosity indexes, gave markedly different values when tested in an oiliness machine. As viscosity index indicates temperature effects only, the effect of pressure on viscosity was investigated in a high-pressure viscometer. For each oil, values up to 50,000 lb. per sq. in. pressure were obtained and for three temperatures. From these data characteristic curves were plotted giving complete pressure, viscosity, and temperature (P.Z.T.) relations. Using such curves it was possible to trace the changes in viscosity which each oil underwent in its passage through the bearing and obtain an estimate for equivalent viscosity. When this investigation was made the different so-called “oiliness” effects were shown to be but the normal effect of the true viscosity actually existing in the oil film.
The paper calls attention to the need for information on the influence of pressure on viscosity as well as of temperature on viscosity when comparing or predicting the performance of oils in service bearings.