ASTM D4425 for oil separation from lubricating grease
ASTM D4425 standard test method for oil separation from lubricating grease by centrifuging (Koppers Method)
9. Procedure
9.1 For each grease, two centrifuge tubes are required. New tubes must be used for each test and they must be handled with care to avoid scratches.
9.1.1 Determine the total volume, V, in cubic centimetres, of each tube by filling with water and then pouring into a graduated cylinder and measuring.
9.1.2 Measure the inside diameter, d, in millimetres with a vernier caliper.
9.2 Take grease samples from the container without including any free oil found on the grease surface.
9.3 Charge each tube with approximately 0.5 g of grease for each cubic centimeter of tube capacity (example: 7 g of grease in a tube of 14 cm3) taking care that the difference in mass of each does not exceed 0.3 g to minimize centrifuge imbalance.
9.4 Place the tubes in diametrically opposite compartments if all rotor compartments are not used. Always use even numbers of tubes.
9.5 The centrifuge lid must always be closed when the rotor is turning. The rotor should never be touched while rotating.
9.6 Operate the centrifuge at a G value of 1000 for 3 min to eliminate any trapped air bubbles in the grease charge.
9.7 Measure the distance, a, in millimetres from the top of the test tube to the closest point on the grease surface as shown in Fig. 3, and calculate the grease volume as in 10.1.
9.8 Replace the tubes in the rotor head, close the lid, and bring the speed up to a relative acceleration, G, of 36000. Consult manufacturer's instructions for proper speed.
9.9 At the end of the test interval, the rotor must come to a complete stop before opening the lid.
9.10 Measure the amount of oil separated as follows:
9.10.1 Cover the mouth of the tube with a piece of hard rubber or plastic material and invert for 1 to 2 min or until all the oil flows to the top of the tube.
9.10.2 Measure the height, b, of the separated oil in millimetres, as shown in Fig. 4.
9.11 Calculate the oil volume as indicated in 10.2.
9.12 Calculate the percent of oil separated from the grease as indicated in 10.3.
9.13 If the test is to be continued, return the tubes to their respective compartments in the centrifuge rotor. When the covering over the tube mouth is removed all adhering oil must be returned to the tubes.
9.14 Measure the amount of oil separation after one or more of the following time periods: 6, 12, 24, 48, or 96 cumulative hours of testing at a G value of 36 000. No more than 72 h of interruption is acceptable between two test periods.
9.15 The normal duration of a test is 24 cumulative hours.
9.15.1 The test can be extended to 48 or 96 h if desired, but special reporting conditions prevail (see 11.4.2).
