Effect of Lubricant Aging on the Antiwear Properties of Zinc and Molybdenum Dithiophosphates

The effect of aging on antiwear properties of lubricants based on solutions of zinc and molybdenum dithiophosphates in oils such as I-20A, PAO-6, and VHVI-6 (viscosity grade 32 by ISO) is studied. Zinc dithiophosphate is known as an antiwear and antioxidative agent, and molybdenum dithiophosphate is a high-temperature antifriction agent. Antiwear and antiscuffing properties have been estimated by GOST 9490-75 using a four-ball testing machine. During the first test, fresh lubricants are used; then they are aged by high-temperature catalytic oxidation using technique no. 42/607 dated May 10, 1983, by VNII NP, and the second test is carried out. According to comparison of the tribological test results for fresh and aged lubricants containing the DF-11 antioxidative agent, the acid number does not increase in some cases, which is caused by the introduction of antioxidation additives in such compositions.