APPARENT VISCOSITY BY CAPILLARY VISCOMETER AT HIGH TEMPERATURE HIGH SHEAR: D4624
TEST SUMMARY
This test method covers the laboratory determination of the viscosity of engine oils at 150° C and 1 x 10(6) s(-1) using capillary viscometers. Viscosities are determined directly from calibrations that have been established with Newtonian oils in the range from 2 to 7 mPa• s.
Viscosity is determined from measurements of the relationship between pressure drop and flow rate through a capillary under the desired conditions. Two types of capillary viscometers are recognized by this test method:
Constant Pressure Viscometer - in which the pressure is set to a desired shear stress and the resulting flow rate is measured.
Constant Flow-Rate Viscometer - in which the flow rate is set to give a desired shear rate and the resulting pressure drop through the capillary is measured.
For viscometers of both types, the capillary is first calibrated by establishing the relationship between viscosity and flow rate or between viscosity and pressure drop for a series of Newtonian oils by the same procedure and under the same conditions used for test oils.
This test method determines the viscosity at 150° C and a shear rate of 10(6) s(-1). For constant pressure viscometers, the viscosity at 10(6) s(-1) is determined by interpolation from viscosities measured at several shear stresses. Constant flow-rate viscometers usually can be set for a flow rate that will be at or very close to a shear rate of 10(6) s(-1). Operating procedures are highly dependent on the design of each particular viscometer.
