ASTM D4172 for wear preventive characteristics of lubricating fluid (Four-ball method)
10. Procedure
10.1 Thoroughly clean four test balls, clamping parts for upper and lower balls and the oil cup using solvent or solvents with precautions indicated in 6.2. The parts can be final wiped using a fresh (unused) lint free industrial wipe. After cleaning, all parts are only to be handled using a fresh wipe. No trace of solvent should remain when the test oil is introduced and the machine assembled.
10.2 Tighten one of the clean balls into the spindle of the test machine.
10.3 Assemble three of the clean test balls in the test-oil cup and hand tighten using the wrench supplied by the equipment manufacture which has been found to be approximately 2.8 to 5.6 N•m [25 to 50 lb•in.].
10.4 Pour the oil to be evaluated into the test-oil cup to a level at least 3 mm [1/8 in.] above the top of the balls. Observe that this oil level still exists after the test-oil fills all of the voids in the test-oil cup assembly. In the round-robin to establish this test method the effect of oil level on wear was not determined.
10.5 Install the test-oil cup/three balls in the machine and avoid shock loading by slowly applying the test load (147 or 392 N) [15 or 40 kgf].
10.6 Turn on the heaters and set controls to obtain 75 more or less 2°C [167 more or less 4°F]. Heater voltage or offset on proportional controllers should be capable of bringing stabilized temperature within the prescribed limits.
10.7 When the test temperature is reached, start the drive motor which was previously set to drive the top ball at 1200 more or less 60 rpm. Machines with automatic start using a proportional controller will start below the set temperature. The proportional band should be set narrow enough to limit the "under temperature" at start to near 2°C [4°F].
10.8 After the drive motor has been on for 60 more or less 1 min, turn off the heaters and drive motor and remove the test-oil cup and three-ball assembly.
10.9 Measure the wear scars on the three lower balls to an accuracy of6 0.01 mm by one of the following methods:
10.9.1 Option A - Drain the test oil from three-ball assembly and wipe the scar area with a tissue. Leave the three balls clamped and set the assembly on a special base of a microscope that has been designed for the purpose. Make two measurements on each of the wear scars. Take one measurement of the scar along a radial line from the center of the holder. Take the second measurement along a line 90° from the first measurement. Report the arithmetic average of the six measurements as scar diameter in millimetres.
10.9.2 Option B - Remove the three lower balls from their clamped position. Wipe the scar area. Make two measurements of each of the three scars. Make the two measurements at 90° to each other. If a scar is elliptical take one measurement with the striations and the other across the striations. Take care to ensure that the line of sight is perpendicular to the surface being measured. As in Option A, average the six readings and report as scar diameter in millimetres.
10.9.3 If the average of the two measurements on one ball varies from the average of all six readings by more than 0.04 mm, investigate the alignment of the three lower balls with the top ball.
