When rolling bearings are operated in the mixed friction regime, there is a risk of wear, which can be minimized by the application of suitable lubricants with anti-wear (AW) additives. These lubricants form thin surface-bound additive-based tribolayers (< 150 nm) under tribological strain, which provide a separation of the steel surfaces even under severe mixed friction. The trend towards a reduction of additive concentration requires new methods of effective wear protection because tribolayers no longer form under severe conditions.
This lecture shows the possibility of an increase in wear protection in rolling bearings for different oils (with low content of AW additives and without) by suitable run-in procedures. During the run-in procedures the operation parameters (e.g. load, speed) must be specifically chosen, in order to allow tribolayers to form on the surface. Depending on the additive concentration, different parameters are needed for this effect. Furthermore, the growth rate of the layer significantly depends on the contact conditions. However, run-in procedures are time-consuming and not practical in most applications. It is shown, how run-in procedures can be replaced by thermal surface treatment. In addition to the influence on wear protection, different tribolayers show significantly different frictional properties, which determine the efficiency of the rolling bearing. The tribolayers are characterized using EPMA, FIB-TEM, and nano-indentation analyses. Based on the experiments and analyses, wear protection mechanisms are derived.