ASTM D2596 for measurement of extreme-pressure properties of lubricating grease
ASTM D2596 for standard test method for measurement of extreme-pressure properties of lubricating grease (Four-Ball method)
9. Procedure
9.1 Bring lubricant to be tested to 27 more or less 8°C (80 more or less 15°F).
9.2 Completely fill the ball pot with the lubricating grease to be tested, avoiding the inclusion of air pockets. Imbed the three steel test balls in the grease. Place the lock ring carefully over the three balls and screw down the lock nut securely (7.2). Scrape off the excess grease pushed onto the lock nut.
NOTE 3 - Subsequent independent investigations reported in 1971 by several laboratories indicate that optimum test repeatability is obtained when the force on the lock-down nut is maintained within the range 50 more or less 5 ft•lbf (68 more or less 7 N•m), applied and measured by means of a torque wrench. Significantly lower weld points were obtained when the force applied was approximately 100 ft•lbf (136 N•m).
9.3 Press one ball into the ball chuck and mount the chuck into chuckholder.
9.4 Examine the ball chuck carefully before each run. The chuck is continually subjected to wear and seizure and should be replaced when it will not fit into the ball chuck-holder tight enough to support its own weight, or if the ball seat shows signs of seizure.
9.5 Install the ball pot assembly on the test apparatus in contact with the fourth ball. Place the mounting disk between ball pot and thrust bearing.
9.6 Place the weight tray and weights on the horizontal arm in the correct notch for a base test load of 784 N (80 kgf). Release the lever arm and gently apply (Note 4) the test load to the balls, making certain the ball pot assembly and mounting disk are centered. If the optional friction-measuring device is used, connect the calibrated arm on the ball pot to the indicator spring by means of the clip and wire, placing clip and indicator support over the numbers which correspond to the applied load.
NOTE 4 - Shock-loading should be avoided as it may deform the balls permanently.
9.7 Start the motor and run for 10 more or less 0.2 s. The time for the apparatus to "coast" to a stop is not considered.
9.8 Remove the load from the balls by raising the lever arm and locking it in raised position. If the friction-measuring device is used, remove clip and wire. Remove the ball pot assembly; remove the chuck and discard the ball.
9.9 Measure the scar diameter of test balls as follows:
9.9.1 Option A - Remove the lock nut and release the test balls. Clean the balls with Stoddard solvent and then n-heptane, and wipe dry with soft cloth. Place the individual balls on a suitable holder and by means of a microscope, measure to the nearest 0.01 mm the scar diameters both parallel (horizontal) and normal (vertical) to the striations in the scar surface of one of the three test balls.
9.9.2 Option B - Retain the balls in the ball pot. Wipe excess grease from the balls and ball pot. Wash the ball surfaces with Stoddard solvent and then n-heptane. Using a microscope, measure to the nearest 0.01 mm the scar diameters both parallel (horizontal) and normal (vertical) to the striations in the scar surface of one of the three test balls. Measurement by microscope of the scar diameters on all three balls rather than one ball as outlined in Options A or B may be made if the operator so desires.
9.10 Record (Table 1, Column 2) for the 784 N (80 kgf) load the average scar diameter by any one of the three techniques described in 9.9. Compare this average scar diameter (Table 1, Column 3). Discard the balls. If the average scar diameter is not more than 5 % from the compensation scar diameter, repeat the test at the next higher load (Table 1, Column 1), and again compare scar diameters. Continue this procedure until the last nonseizure load is determined.
9.11 If the measured scar diameter for the 784 N (80 kgf) load is more than 5 % from the compensation scar diameter, the next run is made at the next lower load (Table 1, Column 1). Continue this procedure until the last nonseizure load is determined.
NOTE 5 - When the optional friction-measuring device is used, the last nonseizure load is detected by a gradual transverse movement of the indicating pen.
9.12 Make additional runs at consecutively higher test loads (Table 1, Column 1), recording the measured scar diameter(s) and discarding test balls, until welding occurs. Make a check run at this point. If welding does not occur on the check run, then repeat the test at the next higher load until welding is verified.
9.13 Shut off the motor immediately to prevent damage to the tester. Excessive wear or seizure of the ball and ball chuck may result if caution is not observed. Welding may be detected by any or all of the following:
(1) If friction-measuring device is used, a sharp transverse movement of the indicating pen.
(2) Increased noise level of motor.
(3) Smoking from the ball pot.
(4) A sudden drop in the lever arm.
