ASTM D4693 for low-temperature torque of grease-lubricated wheel bearings
ASTM D4693 standard test method for low-temperature torque of grease-lubricated wheel bearings
10. Procedure
10.1 Clean races of bearing cups, previously installed in the hub, and inspect for nicks or rust spots; replace cups if damaged. Apply a thin film of the test grease to races.
10.2 Stir the test grease with a spatula. Fill a half-scale grease worker with the stirred test grease and work 60 strokes as described in Test Method D1403.
10.3 Fill the bearings with the worked test grease using a Test Method D3527 bearing packer, or equivalent. The bearing packer must be clean and dry prior to use. Flushing out old grease with new test grease is not acceptable.
10.4 Withdraw the bearing, and with a spatula remove excess grease from the bore and strike off grease flush with both ends of the bearing cone. Remove remaining grease from bore with a lintless cloth or tissue. Remove grease from outer surfaces of rollers and retainer. Care must be exercised to prevent relative rotation of any part of the bearing during this part of the procedure and from this point onward.
10.5 Add or remove grease so that the inner and outer bearings contain 3.0 and 2.0 +/- 0.1 g, respectively.
10.6 Install the inner bearing on the spindle, without rotating the rollers and aligning bearing slot with spindle key or pin. Install hub. Install outer bearing on spindle, without rotating rollers and aligning keyway with key.
NOTE 8 - Bearings are supplied with keyways or slots, and spindles with corresponding keys or pins, to prevent rotation of the inner races of the bearings during the test. Assembly of the test unit can be facilitated by securing the spindle in a vertical position in a bench vise. (Warning - Do not tighten vise excessively, or else spindle bore will deform and prevent installation of test unit on drive shaft.)
10.7 Complete assembly of the test unit by installing the inner compression plate (Part 11, Fig. 3), spring (Part 8, Fig. 3), outer compression plate (Part 9, Fig. 3), compression washer (Part 10, Fig. 3), and compression nut (Part 12, Fig. 3). Place the spring gage, described in 8.3.3, between the compression plates. Tighten nut until the required 400 N load is applied. Loosen the nut slightly, just enough to slip spring gage from between compression plates.
10.8 Install the thermocouple (Part 16, Fig. 3) in the spindle (Part 1, Fig. 3) such that it bottoms in the thermocouple well.
NOTE 9 - The spindle is drilled to locate the thermocouple junction midway between the bearings, and the spindle end is drilled and tapped (1/8 NPT) to accept a fitting (Part 15, Fig. 3) to hold the thermocouple in place. The compression nut of the fitting should be tightened just enough to hold the thermocouple at its proper depth yet permit it to rotate during the test run. This can be accomplished when a TFE-fluorocarbon ferrule is used in the fitting. Use of the fitting is not required: (1) if the cold chamber is equipped with access ports to permit installation and removal of the thermocouple without opening the cold chamber door (which would change the temperature of the test unit), and (2) a means of holding the thermocouple junction in contact with the bottom of the thermocouple well is provided.
10.9 Place the assembled test unit in an oven pre-heated to 70 +/- 3°C and heat for 60 +/- 5 min. Remove test unit from oven and immediately install on drive shaft of test machine located in cold chamber pre-cooled to -40°C.
10.10 Rotate the test machine drive pulley by hand to position the torque arm slightly (not more than 3 mm) above load cell contact, but not touching. Do not position torque arm by rotating it relative to the hub. It is imperative that the bearings not be rotated after charging with the test grease. Consequently, it is advantageous to always orient the hub in the same position relative to the spindle during assembly. One way to do this is to align the hub torque arm in the same plane as the spindle key (Part 14, Fig. 3). In similar fashion, always preposition the keyway of the test machine drive shaft so that the test unit can be installed with the torque arm above the load cell. Rotate the pulley by hand or with short bursts of the drive motor to achieve proper position of the torque arm.
10.11 Cold soak test unit at -40 +/- 0.5°C for 5 +/- 0.1 h at a cooling rate described in Fig. 2(A) and Fig. 2(B).
NOTE 10 - Because of the wide variety of cold chambers, in order to satisfy the prescribed cooling rate, it may be necessary to insulate the test unit to slow the rate or to add a small fan or squirrel-cage blower to increase it. Once the suitable amount of insulation or wind velocity is established, the cooling rate should remain nearly constant from one test to the next and not require constant adjustment.
10.12 At the end of the cold soak period, prepare the instrumentation for the torque determination. Select the highest millivolt range on the recording potentiometer, or a lower range if foregained knowledge of the torque indicates its suitability. Standardize the potentiometer according to the manufacturer's instructions.
10.13 Measure and record the temperature of the test unit just before starting the drive motor. Start the chart drive of the recording potentiometer. Start the drive motor and run the test for a minimum of 3 min.
NOTE 11 - Data logging software may be used to collect this data.
10.14 Measure the pen displacement on the potentiometer record at the equivalent of 60-s running time. Also, if maximum torque occurs after 60 s, record maximum torque and its time of occurrence, as well as the 60-s torque. Due to manufacturing tolerances, some test units may give cyclic torque records at high torques. In such cases, measure pen displacement as indicated in Fig. 4.
NOTE 12 - Data logging software may be used to collect this data.
10.15 Remove test unit from apparatus and place in an oven preheated to about 70°C to preclude rusting. Do not disassemble until unit has been heated and moisture driven off. Generally, rusting can be precluded by not disassembling test unit until preparation for next test is required.
