Oil Viscosity at High Shear Rates Measured by a Floating Journal Bearing

A high shear rate, lx10⁶sec^-1, viscometer uses a commercial tool post grinder fitted with a three-bearing internal type spindle to drive a one inch (2.54 cm) diameter journal at 10,400 rpm. A 0.0005 inch (0.00127 cm) thick fluid film between the journal and a floating bearing transfers a torque to the bearing. An oil pump built into the journal minimizes temperature and oil flow problems. Torques measured with Newtonian oils provide a torque-viscosity calibration that is used to convert torques of non-Newtonian oils to viscosities. Two bearings are used; one measures viscosities from 1.6 to 5 cp, the other, 3.4 to 10 cp. Less than one hour is required to measure an oil's viscosity over the range of either bearing at temperatures up to 370°F (188°C).

This apparatus measures viscosities at the shear rate and temperatures of critical high shear sections of operating engines and hydraulic systems. The differences between ASTM D 445 kinematic viscosities and viscosities at lx10⁶sec^-1 shear rate were determined for multigraded oils formulated with a number of polymeric viscosity index improvers. At the high shear rate the percent loss of the kinematic viscosity contributed by the polymers increases as temperature decreases.