Formation of boundary layer during grinding - Wear protection in rolling bearings by preconditioning of the workpiece surfaces in manufacturing

 

Additives in cooling lubricants protect the surfaces of rolling bearings against wear by forming additive-induced reaction layers on the surface. However, the additives currently used are of ecotoxicological concern and furthermore, can negatively influence the service life of components due to their sulfur and phosphorus content. An appropriate surface conditioning during grinding offers the potential to reduce additive concentration in the later operation of rolling bearings so that the initial reaction layer is already produced during the production process.

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 cooling lubricant, and reaction layers, i.e. an outer boundary layer, can be formed. Whether a boundary layer’s formation during grinding has a wear-reducing effect in the later operation of the rolling bearing is not sufficiently known.

The goal of this cooperation project between the Institute for Machine Elements and Systems Engineering MSE and the Laboratory for Machine Tools and Production Engineering WZL of RWTH Aachen University 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. The influence on the wear behavior of rolling bearings will be also examined. Based on the findings, optimized grinding processes can be designed with regard to the formation of a wear-protecting reaction layer. These make it possible to minimize the concentration of harmful additives in later operations and to reduce the run-in phases of rolling bearings.