Prediction of Viscosity-Shear Properties for VI Improved Crankcase Oils 940819

This study evaluates the shear-thinning effects of a commercial Viscosity Index (VI) improver in a variety of mineral oil base stocks to produce a series of viscosity grades from 0W-20 to 20W-50. All of these fluids also include a DI package in addition to an olefin copolymer VI improver and base oil. The Penn State high shear capillary viscometer was used to collect the primary data at shear rates of up to 10⁶ s^-1 and at 10 to 177°C. Data are fitted to a double truncated power law model to determine the incipient non-Newtonian shear rate Υ̇₁, the power law index n, and the incipient second Newtonian shear rate Υ̇₂. These parameters are found to be smooth functions of temperature and polymer concentration in the different base stocks. Using the data obtained from OW-20, 10W-30, and 20W-50 SAE grade formulations, these parameters (Υ̇₁, Υ̇₂ and n) are correlated as functions of temperature, polymer concentration, and a viscosity temperature property of the base oil.

These correlations were then used to predict Υ̇₁, Υ̇₂ and n for 10 additional multigrade lubricants formulated with the same VI additive. These three parameters and the Newtonian viscosity of these oils at 150°C predicted high temperature-high shear values at 10⁴, 10⁵, and 10⁶ s^-1 with the same precision as direct measurement with the Penn State high temperature, high shear viscometer. Consequently, this paper presents a method of predicting blend properties from a simple calibration system for blends of a single VI polymer in a relatively homogeneous set of base oils.