Assessment of Water Contamination on Grease Using the Contact Angle Approach

Abstract

Many grease-lubricated machinery components operate in wet environments, making them susceptible to water contamination. It has been reported that the presence of a mere 1% water contamination in grease reduces the life of a bearing by 90%. Yet there are only a few standards available to characterize grease performance in the presence of water, most of which are primarily qualitative, providing inconclusive information, often relative to standard samples, at a significant cost in time and materials. In this paper, a unique approach is proposed for evaluating grease capability for repelling water. The method utilizes the contact angle of a water droplet on a grease surface to quantify grease water resistance. It is hypothesized that the higher the hydrophobic nature of the grease, the greater the resistance to water and vice versa. The validation of the hypothesis is established by performing extensive contact angle measurements on seven types of commercially available greases. The efficacy of contact angle results is established by measuring the change in the yield stress values obtained using a rheometer. From the obtained results, it is shown that the proposed approach is reliable and capable of distinguishing greases as water repellent/attractive.