Properties of water-contaminated lubricating oil: variation with temperature and small water content

Abstract

Water contamination is one of the most insidious factors in industrial applications. If the water content exceeds a certain level that the lubricating oil cannot accept, it may shorten the service of lubricating oil and damage machines gradually. Dynamic viscosity and permittivity are selected as performance indexes to study the effects of water contamination on lubricating oil. Models of water content considering both viscosity and permittivity of water in oil mixtures have been previously proposed to estimate the state of water-contaminated lubricating oil. However, temperature, which is the most significant factor for lubricating oil especially affecting the viscosity, as well as the permittivity, remains uninvestigated. Therefore, this paper investigates temperature and water content simultaneously to obtain the correlation with the viscosity and permittivity of lubricating oil, separately. The Vogel’s law is employed to express theoretical relationship between temperature and dynamic viscosity. The extended models are proposed in order to give good correlations with the viscosity and permittivity of water-contaminated lubricating oil as a function of temperature and water content. Moreover, this paper also presents the on-line monitoring system to monitor aforementioned parameters in real time. Consequently, a conclusion can be drawn that the dynamic viscosity and permittivity of lubricating oil have an approximate linear relationship with water content within small water content and a certain temperature span; the variations of used oil properties under different temperatures at a certain water content follow the same relationship as those of pure oil.