ASTM D1478 test method for low-temperature torque of ball bearing grease
4. Summary of Test Method
4.1 A No. 6204 open ball bearing is packed completely full of the test 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.
4.2 Torque is determined by multiplying the restraining force by the radius of the bearing housing. Both starting torque and torque after 60 min of rotation (running torque) are determined.
5. Significance and Use
5.1 This test method was developed using greases having very low torque characteristics at -54°C (-65°F). Specifications for greases of this type commonly require testing at this temperature. Specifications for greases of other types can require testing at temperatures from -75 to -20°C (-100 to 0°F).
5.2 This test method has proved helpful in the selection of greases for low-powered mechanisms, such as instrument bearings used in aerospace applications. The suitability of this test method for other applications requiring different greases, speeds, and temperatures should be determined on an individual basis.
5.3 Test Method D4693 may be better suited for applications using larger bearings or greater loads. However, greases having such characteristics that permit torque evaluations by either this test method or Test Method D4693 will not give the same values in the two test methods (even when converted to the same torque units) because the apparatus and test bearings are different.
