Wind Turbine Lubrication: Low Temperature Fretting Wear Behaviour of Four Commercial Greases

Fretting tests on four commercial greases were run on a ball-on-disc machine at 25, 7, - 20, - 40 & DEG;C. Post-test wear was measured on the ball and the chemical composition of lubricant films in the wear scar analysed by FTIR (RA-IRS), Raman and SEM-EDS. At 25 and 7 & DEG;C the greases had similar friction and wear properties. At - 20 and - 40 & DEG;C the highest base-oil viscosity grease gave an inferior friction and wear performance. RA-IRS analysis showed thickener remaining in the wear scar for most test conditions. The highest wear was linked to the absence of thickener in the scar. Better wear and friction performance at low temperatures was associated with thickener present in the lubricated contact and lowest base-oil viscosity.