Improving the Precision of High Temperature High Shear Rate Viscosity Measurements

Capillary viscometers provide a convenient method of measuring the viscosity of polymer containing lubricants at 150°C and 10⁶ sec^-1 shear rate as specified in ASTM D4624 Procedure. The commercial Cannon HTHS viscometer and the Penn State HTHS viscometer were used in this study.

Improved calibration of the capillaries in the commercial viscometer provided an order of magnitude improvement of the HTHS repeatable values from 4.47% to 0.39% for a typical polymer containing lubricant. The viscosities of seven polymer containing lubricants at 10⁶ sec^-1 and 150°C gave an absolute mean percentage difference of 0.62% from measurements made with both capillary viscometers used in this study. The data suggests that substantial improvements can be made in the repeatability of ASTM D4624 HTHS viscosity measurements without changing the design of the current commercial viscometer.