Vibration analysis of journal bearings under water contaminated lubrication

Water as a common contaminant in the lubricating oil can degrade lubricant performance and cause a serious fault of the journal bearing and shorten its service life. Differing from the pure lubricating oil, the contaminated oil with water exhibits a non-Newtonian behavior and has a significant impact on the dynamic performance of the journal bearing. This paper is to establish a relationship between the water contamination and the vibration response of the journal bearing in order to achieve an online condition monitoring of the tribological behaviour of journal bearings. The research progress regarding to the effects of water contamination on the lubrication is firstly reviewed. A theoretical model is then developed for the dependence of the viscosity of the contaminated oil on the shear rate and temperature. The effects of such rheological behavior on the dynamic performance of the journal bearing are also studied. To validate the theoretical analysis, the rheological measurement for the contaminated oil with such water fraction as 0, 1, 3, 5, 7 and 10 per percent by volume, is carried out with the Malvern Bohlin Gemini HR^Nano rheometer. Those contaminated oil are then fed into the bearing housing. Through accelerometers attached on the housing, vibration responses of the journal bearing are acquired under different working condition. The results outlined that volume water ratios in lubricating oil had the different degrees of effects on the tribological behaviour of journal bearings, which allows early detection of abnormal lubricants to be implemented online vibration responses.