The theory of antiwear for ZDDP at elevated temperature in boundary lubrication condition

Abstract

Abstract Based on the experimental results from mechanical and physical analyses, this paper proposes a theory of antiwear for ZDDP added to a base oil at elevated temperature in boundary lubrication condition. It is assumed that the decomposition products of ZDDP can react chemically with one or both of the rubbed surfaces. The theory is established with physical and mechanical models, instead of considering the process of the formation of chemical film. In the theory, a simplified elastic model is employed to predict the duration of run-in and the critical thickness of a chemical film that should grow to achieve the antiwear performance. In this model the hardness and roughness of the contacting surfaces are the most important characteristics which control whether or not an antiwear film can be developed or the amount of wear under rubbing action. Once a chemical film is established, the growth of the film is predicted with a diffusion model. The amount of the chemical film which is scraped off the rubbed surface can also be determined theoretically with this model. The theory also takes into account the effect of decomposition of ZDDP on the growth of chemical film. In accordance with the experimental data in hand, the theory is confirmed to be correct.