APPARENT VISCOSITY USING HTHS CAPILLARY VISCOMETERS
Several different configurations of capillary viscometers have been successfully used for measuring the viscosity of engine oils at the high shear rates and high temperatures that occur in engines. There are at least five methods available for this determination.
EXPLANATION
Viscosity is an important property of a fluid lubricant. Many common petroleum lubricants are non-Newtonian; their viscosity varies with shear rate. The viscosity of all fluids varies with temperature. The viscosity of lubricants is to be measured at or near the conditions of shear rate and temperature that they will experience in service. The conditions of shear rate and temperature of these test methods are thought to be representative of those in the bearings of automotive engines in severe service.
APPARENT VISCOSITY BY CAPILLARY VISCOMETER AT HIGH TEMPERATURE HIGH SHEAR:
ASTM 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.
ASTM D4683
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) shear rate using a tapered bearing simulator-viscometer (TBS Viscometer) equipped with a refined thermoregulator system. Older TBS units not so equipped must use Test Method D4683-87.
The Newtonian calibration oils used to establish this test method cover the range from approximately 1.5 to 5.6 cP mPa•s at 150° C. The non-Newtonian reference oil used to establish this test method has a viscosity of approximately 3.5 cP mPa•s at 150° C and a shear rate of 1 x 10(6)s(−1).
Applicability to petroleum products other than engine oils has not been determined in preparing this test method.
A motor drives a tapered rotor that is closely fitted inside a matched stator. The rotor exhibits a reactive torque response when it encounters a viscous resistance from an oil that fills the gap between the rotor and stator. Two oils, a calibration oil and non-Newtonian reference oil, are used to determine the gap distance between the rotor and stator so that a shear rate of 1 x 10(6)s(−1) is maintained. Additional calibration oils are used to establish the viscosity/torque relationship that is required for the determination of the apparent viscosity of test oils at 150° C.
ASTM D4741
TEST SUMMARY
This test method covers the laboratory determination of the viscosity of oils at 150° C and 1 x 10(6)s(−1) using Ravenfield high shear rate tapered-plug viscometer models BE or BS. This test method may readily be adapted to other conditions if required.
Newtonian calibration oils are used to adjust the working gap and for calibration of the apparatus. These calibration oils cover a range from approximately 1.8 to 5.9 cP mPa•s at 150° C. This test method should not be used for extrapolation to higher viscosities than those of the Newtonian calibration oils used for calibration of the apparatus.
