ASTM D5763 Standard Test Method for Oxidation and Thermal Stability Characteristics of Gear Oils Using Universal Glassware
4. Summary of Test Method
4.1 The viscosity of the gear oil being tested is determined. A100-g aliquot of the oil in a weighed apparatus is subjected to a temperature of 120°C for 312 h while dry air is passed through the aliquot at 3 L/h.
4.2 At the end of the stress period, the aliquot is cooled to room temperature. The apparatus is reweighed to determine oil loss. Filterable sludge is recovered by vacuum filtration using a 2.8-µm glass fiber filter medium. The viscosity of the filtered oil is determined. Sludge adhering to the oxidation cell and associated glassware is rinsed with heptane and the washings passed through the same filter used to filter the filterable sludge. The filter is dried in an oven to a constant weight to determine the total filterable sludge.
4.3 The apparatus is dried and weighed to determine the amount of adherent sludge. The sum of the filterable sludge and adherent sludge is reported as total sludge. The percentage change in viscosity and percent oil loss are also reported.
5. Significance and Use
5.1 Degradation of gear oils by oxidation or thermal breakdown, or both, can result in sludge buildup and render the oil unsuitable for further use as a lubricant.
5.2 This is the only test method that employs glassware to measure the amount of sludge produced during oxidation and thermal degradation. This test method is a modification of Test Method D2893 which measures the viscosity increase and precipitation number of the oil stressed at 95°C, but does not measure the amount of sludge formed.
5.3 This test method can be used to evaluate the oxidation/thermal stability of gear oils. However, the test results may not correlate with the performance of gear oils in field service.
