EXPLANATION
This test method covers the determination of the extent to which a grease retards the rotation of a slow speed ball bearing by measuring starting and running torques at low temperatures (<-20° C or 0 ° F). This test method has proved helpful in selecting greases for low powered mechanisms, such as instrument bearings used in aerospace applications. Test Method D4693 may be better suited for applications using larger bearings or greater loads. These two test methods may not give the same torque values because the apparatus and test bearings are different.
TEST SUMMARY
A No. 6204 open ball bearing is packed completely full of grease and cleaned off flush with the sides. The bearing remains stationary while ambient temperature is lowered to the test temperature and held there for 2 h. At the end of this time, the inner ring of the ball bearing is rotated at 1±0.05 r/min while the restraining force on the outer ring is measured. Torque is measured by multiplying the restraining force by the radius of the bearing housing. Both starting torque and after 60 min of rotation are determined.
TEST PRECISION
The values are percent of the mean.
This test method has no bias.