The Influence of Water Contamination on the Extreme-Pressure Properties and Mechanical Stability of Lubricating Greases Applied to Wind Turbines

This paper reports a study on the influence of water contamination, in new and worked grease conditions, on five different commercially available wind turbine bearing greases. Among the studied greases were lithium and calcium-based soaps in combination with mineral and synthetic hydrocarbon oils of different viscosity and anti-wear additives. A series of tests using the Four Ball method for the evaluation of extreme-pressure properties of lubricating greases were performed in the samples, before and after being subjected to shear by Roll Stability test (i.e., worked condition) and water contamination, aimed to characterize the influence of these factors on the greases’ ability to reduce wear. The mechanical stability of the greases under the studied conditions was evaluated by monitoring the consistency change. The comparative analyses between the different greases made it possible to conclude, above all, that water contamination can have a great impact on a grease’s lubrication capacity, reducing from 17% to 32% its capacity to avoid wear. The changes in a grease’s properties can result in significant increase in bearing power losses and mechanical wear.