The action of lubricants under extreme pressure conditions in a modified four-ball tester

The authors present a new method for research of scuffing. It is realized on the four-ball tester and considers scuffing as a process leading to seizure, i.e. the stopping of the relative movement of a tribosystem. During a run, load increases continuously. Using the method, tribological experiments were performed employing various lubricants; viscosity improvers, AW and EP additives were added to a base oil. Mineral and synthetic base oils of different viscosity were also used. The aim was to investigate an influence of such lubricants on the scuffing propagation and wear intensity. It is shown that rheological properties of lubricants have no effect on the propagation of scuffing and wear. However, there is a significant influence of AW and EP additives. The results of surface analyses (EDS and AES) show a decisive role of chemical reactions of AW and EP additives with the steel surface as well as diffusion of sulfur, resulting in creation of a surface layer. Its good antiseizure properties mitigate the scuffing propagation and reduce wear intensity.