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
6. Apparatus
6.1 Low-Temperature Wheel Bearing Torque Apparatus, illustrated in Fig. 1.
NOTE 1 - Several apparatus configurations are available, differing mainly in the drive system. For example, with large cold chambers, a unitized apparatus (see Fig. 1) can be used totally within the cold chamber. With small cold chambers, the drive system can be mounted externally and only the test unit subjected to low temperature. Regardless of the exact configuration, the essential apparatus consists of a 1/3 hp electric motor connected to a gear reducer by means of a timing belt and pulleys, which drive a specially-manufactured spindle-bearings-hub assembly equipped with a spring-loading mechanism. For apparatus contained totally within the cold chamber, the drive system should be prepared by replacing the grease in the motor bearings with a suitable low-temperature grease (<1 N•m torque at -40°C), such as one meeting the requirements of Specification MIL-G-10924F or similar, and the lubricant in the gear reducer should be replaced with a suitable low-temperature (< -50°C pour point) worm-gear lubricant. In addition, if not already so-equipped, large-diameter (152 mm), narrow-width (13 mm) timing pulleys and a suitable timing belt should be used.
6.2 Torque Measuring System, consisting of a strain-gage load cell with a matching bridge-balance unit, a suitable strip-chart recorder to record the load-cell output, and a series of weights (up to 20 kg, at least) suitable for load-cell calibration.
NOTE 2 - In order to calculate torque from force measurements, the load cell should be located a known distance from the test-unit centerline; 100 mm is convenient. A convenient way to do this is to centrally drill a 1.78-mm diameter hole (No. 50 drill) in the torque arm, 100 mm from the spindle centerline; temporarily replace the load cell contact with a second contact having a 1.59-mm diameter pin (soldered in place) extending about 5 mm above the contact point; position the load cell to permit insertion of the pin in the torque-arm hole; secure the position of the load cell by tightening the clamping screws; replace pin contact with original contact before running test.
6.3 Temperature Measuring System, consisting of Type T (preferred) or Type J (acceptable), 3.18-mm diameter metal-sheathed, grounded thermocouples meeting Specifications E 585/E 585M and E 608/E 608M and conforming to the special limits of error defined in Table 1 of Specification E 230; a suitable potentiometer, satisfying the requirements for Groups B or C as described in Test Method E 220; an ASTM 73C precision thermometer meeting Specification E 1, certified (traceable to National Institute of Standards and Technology certification) or verified and calibrated according to Test Method E 77; a suitable comparator as described in Test Method E 77; and an ice bath prepared according to Practice E 563.
NOTE 3 - Other temperature-measuring instrumentation, such as a precision platinum resistance thermometer, may be used instead of thermocouples, providing the limits of error are within those defined in Specification E 230.
6.4 Test Bearing - Use LM67010-LM67048 and LM11910-LM11949 (AFBMA Standard 19) inboard and outboard tapered roller bearings, respectively.
6.5 Low-Temperature Test Chamber, equipped with internal fan, and capable of maintaining the spindle at -40 +/- 0.5°C, and with sufficient capacity to cool the spindle at the rate shown in Fig. 2(A) and Fig. 2(B).
6.6 Laboratory Oven, forced air, capable of maintaining 70 +/- 3°C.
6.7 Grease Packer, as described in Test Method D3527 or equivalent.
6.8 Ultrasonic Cleaner.
7. Reagents and Materials
7.1 Purity of Reagents - Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all reagents shall conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society where such specifications are available. Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high purity to permit its use without lessening the accuracy of the determination.
7.2 Ethylene Glycol, commercial automotive antifreeze. (Warning - Moderately toxic. Can be harmful if inhaled, swallowed or absorbed through skin. Contact can irritate eyes, or mucosa.)
7.3 Chloroform, reagent grade. (Warning - Health hazard.)
7.4 1,1,1-Trichloroethane, reagent grade. (Warning - Health hazard.)
7.4.1 For routine testing, a functionally equivalent solvent may be substituted throughout this test method wherever 1,1,1-trichloroethane is specified. However, in referee situations, 1,1,1-trichloroethane or chloroform shall be used unless contractual parties agree on the acceptability of the functionally equivalent solvent.
7.4.1.1 To be functionally equivalent, the solvent must not affect test results, must clean as effectively as 1,1,1-trichloroethane, have similar volatility characteristics, leave no residue on evaporation, and contain no water or additives.
NOTE 4 - This test method (and the precision values) was originally developed using chloroform. This was subsequently replaced by 1,1,1-trichloroethane which was declared an ozone depleting substance by the U.S. Environmental Protection Agency (EPA). Federal regulations ban the production of this material after December 31, 1995, but existing stocks may continue to be used. Currently there are no EPA restrictions on the use of chloroform, but the user should be aware of its health hazards, if it is used. No other solvent intended as a substitute for 1,1,1-trichloroethane in this test method has been cooperatively evaluated. (Warning - If the functionally equivalent solvent is flammable or a health hazard, proper precautions should be taken.)
