Laboratory Thermal Oxidation Study on Axle/Gear Lubricants

The oxidation process and mechanism of an 80W-90 axle/gear oil was studied using the laboratory modified Universal Oxidation Test (ASTM D4871). It provides useful information to better understand the oxidation behavior of a typical sulfur-phosphorus based GL-5 gear lubricant. Most importantly, the laboratory bench test provides helpful information regarding how hot is hot for the axle temperatures likely encountered during the actual field-trial driving. The testing result shows that the temperature of an axle lubricant is a decisive factor during the oxidation process. At the temperatures higher than 163°C, the viscosity and TAN increase very rapidly within a short period of time. The single FT-IR absorbance at 1715 cm^-1 provides helpful complementary information to the oxidation process of the axle lubricants. The general trend of FT-IR agrees with both the viscosity change and TAN change of oxidized axle/gear lubricant.