ASTM D2273 standard test method for trace sediment in lubricating oils
8. Procedure
8.1 Measure 50 +/- 1 mL of precipitation naphtha. (Warning - Extremely flammable.) In each of two clean, dry centrifuge tubes at room temperature. Then fill each tube to the 100-mL mark with the oil sample and close tightly with a softened cork covered with a thin pliable plastic film which is resistant to petroleum products (not a rubber stopper). Shake sample well to ensure complete mixing, then invert each tube at least 20 times allowing the liquid to drain thoroughly from the tip of the tube at each inversion. If the liquid refuses to drain upon inversion, gently tap the inverted tube against the palm of the hand to jolt the liquid out of the tip. Place the tubes in a water bath at 32 to 35°C for 5 +/- 1 min. Momentarily remove the corks to relieve any pressure, and invert each tube again at least 20 times exactly as before. The success of this method depends to a large degree upon having a thoroughly homogeneous mixture which will drain completely as possible from the tip when the tube is inverted.
8.2 Balance the two centrifuge tubes or pairs of tubes with their respective trunnion cups and place them on opposite sides of the centrifuge head. Then whirl them for 10 +/- 1 min at a rate sufficient to produce a relative centrifuge force (rcf) between 600 and 700 at the tips of the whirling tubes (see 5.1). At the end of the 10-min whirling period, decant the mixture carefully, allowing the sediment to remain in the tubes. Measure another 50 +/- 1 mL of the naphtha into each of the two tubes, then add the oil sample until the total volume reaches the 100 mL mark. Then stopper the tubes, repeatedly invert, heat, and again invert as described in 8.1. Whirl the tubes in the centrifuge for 10 +/- 1 min as before, repeating the 10-min whirling operation until the volume of sediment in each tube remains constant for three consecutive readings. In general, not more than four whirlings will be required for oils having low sediment values. Record the final reading for sediment in each tube.
