Condition Monitoring of Water Contamination in Lubricating Grease for Tribological Contacts

The purpose of this thesis is to summarize the research carried out that led to the development of measurement techniques which measure the water content of lubricating grease. A simple and effective grease mixing method for preparing grease samples was developed and tested for repeatability. Calcium sulphonate complex (CaS-X) grease was used in all experiments. The water content of these samples were also tested with time and temperature as added variables to study if and how much water will evaporate from the samples. Additionally, two measurement techniques were investigated: optical attenuation in the visible and near-infrared (NIR) region and with a dielectric measurement method. The optical attenuation investigation found that the attenuation ratio of two wavelengths of light appear to approximate the water content of grease samples with an acceptable coefficient of determination. Additionally, aged and oxidized grease were measured as well and were not found to affect the measurement results. The dielectric method uses the temperature dependence on the dielectric properties of water-contaminated grease to approximate the water content of the grease samples. An additional parameter of incomplete fill/coverage of the sensor has been investigated as a prestudy. Both methods were found to provide measurements of water content in the prepared grease samples (ranging from 0.22% to 5.5% added water). The dielectric measurement is likely going to be better for applications requiring the possibility of measuring a larger bulk of the grease within the bearing. It shows promise for providing an accurate and robust system for monitoring grease condition as well as the amount of grease contained. The optical measurement will likely provide additional information; however, it will only measure small point samples within the bearing instead of the larger bulk. This could be of use though, because the sensors could be small (in the several millimeter scale) and could measure where water damage is determined to be most important to detect at