ASTM D4048 test method for detection of copper corrosion from lubricating grease
9. Procedure
9.1 Place about 60 mL (about 50 to 70 g, depending on its specific gravity) of grease sample into the bottom of a clean test jar (see 6.1). Bring the depth of the grease to about 80 mm (3.2 in.). Tap the grease down into the jar carefully. Smooth the top to give a relatively flat surface. Wipe excess grease off the jar walls.
9.2 To prevent touching the strip with fingers, wear impervious gloves (see Note 1) or use stainless steel forceps; and insert cleaned copper strip into the grease until it touches the bottom of the tube and is completely immersed and covered by at least 5 mm (0.2 in.) of grease.
9.3 Cover the jar(s) loosely with a beaker, crucible, watch glass, or vented cork (see 6.2).
9.4 Place the jar(s) in an oven or liquid bath so that they are supported approximately vertical. Regulate the oven or liquid bath to maintain a specified temperature for a specified period of time. Commonly used conditions are 100 more or less 1°C (212 more or less 2°F) for 24 h more or less 5 min.
9.5 At the end of the test period, remove the jar(s) from the oven or liquid bath and allow them to cool to room temperature.
9.6 Strip Examination:
9.6.1 Wearing impervious gloves (see Note 1), or using stainless steel forceps, remove the strip from the grease, and carefully remove excess grease clinging to the strip. Take care not to disturb the tarnish on the strip, and immediately immerse it in wash solvent. Withdraw the strip at once, dry with quantitative filter paper by blotting and not by wiping, and inspect for evidence of tarnishing or corrosion by comparison with the Copper Strip Corrosion Standard. Hold both the test strip and the standard strip plaque in such a manner that light reflected from them at an angle of approximately 45° will be observed.
NOTE 2 - It has been suggested that a very light grease may be blotted off the strip with filter paper or a laboratory wiper. Heavier greases may require wiping or removal with a plastic, rubber, or stainless steel spatula. However the grease is removed from the strip, exercise care not to disturb the tarnish or corrosion on the strip.
9.6.2 In handling the test strip during the inspection and comparison, the danger of marking or staining can be avoided if it is inserted in a flat tube (see Appendix X1 of Test Method D130), which can be stoppered with absorbent cotton.
10. Interpretation
10.1 Interpret the corrosiveness of the sample according to how the appearance of the test strip agrees with one of the strips of the Copper Strip Corrosion Standard.
10.1.1 When a strip is in the obvious transition state between that indicated by any two adjacent standard strips, judge the sample by the more tarnished standard strip. Should a strip appear to have a darker orange color than standard strip 1b, consider the observed strip as still belonging in this Classification 1b; however, if any evidence of red color is noticed, the observed strip belongs in Classification 2.
10.1.2 A claret red 2a strip can be mistaken for a 3a strip, if the brassy underlay of the 3a strip is completely masked by a magenta overtone. To distinguish between them, immerse the strip in acetone (Warning - see 7.1). a strip will appear as a 1b strip, while a 3a strip will not change.
10.1.3 To distinguish a 2c strip from a 3b strip, place it in a 20-mm by 150-mm test tube, and bring it to a temperature of 315 to 370°C (600 to 700°F) in four to six minutes using a hot plate. Adjust the temperature by observing an ASTM high temperature distillation thermometer inserted in a second test tube lying on the hot plate. c strip will assume the color of a 2d strip and successive stages of tarnish, while a 3b strip will take on the appearance of a 4a strip.
10.1.4 Repeat the test if blemishes due to fingerprints or due to spots from any water droplets or entrained air that may have touched the test strip during the test period are observed.
10.1.5 Repeat the test also if the sharp edges along the flat faces of the strip appear to be in a classification higher than the greater portion of the strip; in this case, it is likely that the edges were burnished during polishing.
