ASTM D5183 Determination of the Coefficient of Friction of Lubricants
ASTM D5183 Standard Test Method for Determination of the Coefficient of Friction of Lubricants Using the Four-Ball Wear Test Machine
4. Summary of Test Method
4.1 Three 12.7 mm (0.5 in.) diameter steel balls are clamped together and covered with 10 mL of the wear-in lubricant. A fourth 12.7 mm diameter ball, referred to as the "top ball" is pressed with a force of 392 N (40 kgf) into the cavity formed by the three clamped balls for three-point contact. The temperature of the wear-in lubricant is regulated at 75°C (167°F), and then, the top ball is rotated at 600 rpm for 60 min.
4.2 Fluid is discarded and balls cleaned. The wear scar diameter on each of the lower three balls is examined. If the wear scars average 0.67 +/- 0.03 mm, (0.026 +/- 0.001 in.) then the 10 mL of test fluid is added to the ball cup with the worn-in test balls in place. The temperature of the test lubricant is regulated at 75°C (167°F) and the top ball is rotated at 600 rpm at 98.1 N (10 kgf) for 10 min.
4.3 The load is then increased by 98.1 N (10 kgf) at the end of each successive 10 min interval up to the point where the frictional trace indicates incipient seizure. The coefficient of friction is measured at the end of each 10 min interval.
5. Significance and Use
5.1 This test method can be used to determine the coefficient of friction of lubricating fluids under the prescribed test conditions. The user of this test method should determine to his own satisfaction whether results of this test method correlate with field performance or other bench test machines.
