Friction torque of cylindrical roller thrust bearings lubricated with wind turbine gear oils

Planetary gearboxes used in wind turbines very often have premature bearing and gear failures, some of them related to the lubricants used. Five fully formulated windmill gear oils with the same viscosity grade and different formulations were selected and characterized. The lubricant tribological behavior in a cylindrical roller thrust bearing was analyzed. A modified four-ball machine was used to assemble the bearings. They were submitted to an axial load and the tests were performed at velocities ranging between 150 and 1500 rpm. Experimental results for the operating temperatures and for the internal friction torque are presented.