Wear protection in rolling bearings by preconditioning of the workpiece surfaces in manufacturing

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Rolling bearings are a central machine element for the transmission of forces with simultaneous relative movement between machine components. The service life and the reduction of unplanned shutdowns is guaranteed by the use of Extreme Pressure (EP) and Anti Wear (AW) additives in the lubricant, among other things. The additives protect the rolling bearings’ surfaces against wear by forming additive-induced reaction layers on the surface. These layers prevent direct contact of the metallic surfaces in the regime of mixed friction and thus ensure wear protection. Currently used additives, e.g. zinc dialkyldithiophosphate (ZDDP), are ecotoxicologically questionable and furthermore, can negatively influence the service life of components due to their sulphur and phosphorus content. In addition, a damage-promoting effect of ZDDP on the damage phenomena white etching cracks (WEC) and micro pitting is known. Therefore, the aim is to reduce the additive concentration in the lubricant or to avoid the use of harmful additives.Preliminary work shows that the wear protection in the rolling bearing is guaranteed even without additives in the lubricant, if the formation of the reaction layer took place in a run-in process. The additives lead to an initial wear-protecting reaction layer and only have to regenerate the layer after its formation. The further development of this potential for reducing the additive concentration is the objective in this project by means of a suitable surface conditioning, so that the initial reaction layer is already produced during production process.Rolling bearings are mainly manufactured from 100Cr6 steel and are finished by grinding. The thermo-mechanical-chemical loads during grinding influence the inner boundary layer of the workpiece. In addition, high temperatures can cause chemical reactions with the surrounding media, especially the cooling lubricant, and reaction layers, i.e. an outer boundary layer, can be formed. If a boundary layer’s formation during grinding has a wear-reducing effect in the later operation of the rolling bearing is not sufficiently known. By knowing the cause-effect relationships between the process input variables during grinding and the formation of the boundary layer, the run-in phases of highly loaded rolling bearings could be reduced or substituted and lubricant additives in the later operation of the bearing could be minimized by a specific adjustment of the initial boundary layer properties by means of grinding. The goal of this cooperation project is therefore to explain the initial boundary layer formation as a function of the process input variables during grinding and their effect on the layer formation at different additive concentrations as well as on the wear behaviour of rolling bearings.