ASTM D6821 Standard Test Method for Low Temperature Viscosity of Drive Line Lubricants in a Constant Shear Stress Viscometer
4. Summary of Test Method
4.1 A drive line fluid is preheated to 50 °C for a specified time and then cooled at a programmed rate (see Table X1.1) to the final test temperature and soaked at the final temperature for a defined period of time. At the completion of the soak time, the viscosity is measured by applying a prescribed torque and measuring rotational speed to determine the apparent viscosity of the sample.
5. Significance and Use
5.1 Viscosity of drive line lubricants at low temperature is critical for both gear lubrication and the circulation of the fluid in automatic transmissions. For gear oils (GOs), the issue is whether the fluid characteristics are such that the oil will flow into the channel dug out by the submerged gears as they begin rotating and re-lubricating them as they continue to rotate. For automatic transmission fluids, torque, and tractor fluids the issue is whether the fluid will flow into a pump and through the distribution system rapidly enough for the device to function.
5.2 The low temperature performance of drive line lubricant flow characteristics was originally evaluated by the channel test. In this test, a pan was filled to a specified depth of approximately 2.5 cm and then cooled to test temperature. The test was performed by scraping a channel through the full depth of the fluid and across the length of the pan after it had soaked at test temperature for a specified time. The time it took the fluid to cover the channel was measured and reported. The channel test was replaced by Test Method D2983 in 1971.
5.3 The results of this test procedure correlate with the viscometric measurements obtained in Test Method D2983.
The correlation obtained is:
V = 0.941 x VD2983
where:
V = the apparent viscosity measured by this test method, and
VD2983 = the apparent viscosity measured by Test Method D2983.
5.3.1 The equation was obtained by forcing the fit through zero. The coefficient of variation (R2) for this correlation is 0.9948.
