ASTM D1478 test method for low-temperature torque of ball bearing grease
8. Procedure
8.1 Wash the selected test bearing thoroughly in Stoddard solvent and rinse it in a beaker of n-heptane. Dry the bearing for approximately 20 min in a warm oven (not over 100°C (212°F)). Permit the bearing to cool to room temperature before proceeding.
8.2 Lubricate the bearing with five drops of oil having a viscosity of 28 to 32 cSt at 100°C (135 to 150 SUS at 210°F). The bearing shall then show no roughness or catching when rotated between the fingers while applying light pressure axially and then radially. Use the dynamometer to determine the running torque at room temperature; note the average and maximum running torque peaks. The average shall not exceed 20 g•cm (2.0 mN•m), and no peak shall exceed 25 g•cm (2.5 mN•m). If torque values fall below these limits, the bearing is suitable for the grease torque test. If torque values exceed these limits, the bearing should be recleaned and retested or discarded.
8.3 Clean and dry a bearing that has been determined to be acceptable (8.2). Mount the bearing on a hand spindle (Fig. 4), fastening the inner race by means of the washer and screw. Fill the grease cup (Fig. 5) at least three-fourths full of the test grease, using a clean steel spatula. Minimize the inclusion of air.
8.4 Force the bearing down into the grease and rotate the spindle-bearing assembly slowly, first in one direction and then the other, to ensure that grease is worked into all parts of the bearing. When the bearing bottoms in the cup, slide the cylindrical cup ring off the plate and remove the spindle-bearing assembly from the cup. (The assembly may be pushed or pulled through the cup.)
8.5 Remove the bearing from the spindle. Turn the bearing end-for-end, and refasten it on the spindle.
8.6 Repack excess grease into the assembled grease cup. Again, force the bearing down into the grease, while rotating the spindle-bearing assembly slowly, first in one direction and then the other, until the bearing bottoms.
8.7 Slide the cup ring off of the plate, and remove the spindle-bearing assembly from the cup ring. Scrape the excess grease off flush with the sides of the bearing, filling any visible voids, and then remove the spindle.
NOTE 6 - Caution: Take care not to rotate the bearing at any time after striking the grease flush and prior to the measurement of starting torque.
8.8 Insert the packed bearing into the test housing and fasten the clamp cap over the bearing.
8.9 With the low-temperature box precooled to the test temperature, open the box and slide the test bearing and housing over the end of the test shaft. Fasten it with the washer and nut tightly enough to prevent slippage.
8.10 Attach the cord under the head of the screw on the periphery of the housing. Rotate the test shaft until the slack in the cord hanging from the hook on the dynamometer scale above is almost taken up. The screw on the periphery must then be at least 90 degrees down from vertical. More than 90 degrees is acceptable, provided that the cord does not slip off the periphery of the housing (Fig. 1).
NOTE 7 - Measurements can also be made from horizontal or other positions if the cord attaching point is at or beyond the point of tangency of the cord while torque is being measured. This will ensure a full 65-mm (2.56-in.) torque radius.
8.11 Close the box, and recool it to the test temperature. Maintain this temperature within +/- 0.5°C (1°F) for 2 h after the box has recovered to the test temperature.
NOTE 8 - Caution: During this time the bearing must not be disturbed or the test will be invalid.
8.11.1 It is desirable that excessive condensation of moisture from the air in the cold box be prevented, especially during humid weather. To this end and prior to the test, place shallow trays containing a desiccant in the bottom of the low temperature box.
8.12 Check the torque cord to be sure it is free of ice and not stuck to the box. A split rubber stopper can be used to close the hole in the box wall, through which the cord runs, to keep the cord and passage free of ice from moisture-laden air. Remove the stopper before the run.
8.13 To determine starting torque, start the drive motor and observe the dynamometer scale. Record the maximum reading and calculate the starting torque according to Section 9.
8.14 Continue rotation of the test shaft for 60 min while maintaining the test temperature within +/- 0.5°C (1°F). At the end of this time, observe the dynamometer reading for a period of 15 s, and record the average value and calculate the running torque according to Section 9.
8.15 When running repeat tests, the bearing shall be recleaned (see 8.1) and packed with a fresh charge of grease (see 8.3 and 8.4) between tests. Do not force out tested grease with a fresh charge of grease.
NOTE 9 - A pressure sprayer employing Stoddard Solvent can be used to facilitate the removal of grease from the bearing.
