Viscosity-Pressure-Temperature Characteristics of High Viscosity Index Mineral Base Oils and Their EHL Traction

Viscosity-pressure-temperature relations at a pressure up to 0.7 Gpa and a temperature between 30 and 90°C were determined with a falling ball type viscometer for some paraffinic mineral base oils including solvent refined oils, hydrocracked oils and the oil produced by a wax isomerization process. Then, the viscosity at a higher pressure condition than that of the viscometer was derived by applying the simplified non-Newtonian solution to the traction curves determined with a ball on disk type EHD tester. When the measured viscosity and the calculated viscosity were plotted against pressure, for the oils with higher viscosity index than 120, the viscosity derived from traction measurements followed the extrapolated curve to the high pressure region by either the Yasutomi formula or the Roelands formula using the parameters obtained with the viscometer. On the other hand, the calculated viscosity for the higher viscosity index oils deviated upwards from the extrapolated curve.