Here, we developed a technique to assess the workability of sealed-for-life greased rolling bearings after a long-term storage. In this framework, we devised a model of equivalent transition between the conditions of natural ageing under daily and seasonally fluctuating temperature, and the conditions of accelerated thermal ageing at a constant high temperature. The tested bearings were thermally aged, and then their steady state friction and outer ring temperature were examined in a custom high-speed spindle. These results were compared to the performance of a reference new bearing tested under the same loading conditions. Our findings suggest that long-term storage can significantly degrade the performance of sealed-for-life greased rolling bearings. However, a proper running-in can substantially deter the ageing-driven degradation of the bearings.

Nanoscale fretting can be studied by using scanning probe microscopy (SPM) and a newly proposed “slip index” which provides unified approach to fretting on different scales. Various relevant issues such as production of colloidal probes and SPM calibration will be presented. Partial and gross slip nanoscale fretting tests with displacement amplitude from 5 to 500 nm and normal load from 15 to 28 μN will be described. Experiments show a substantial increase of the friction at the transition from partial to gross slip and a significant difference of damaged surfaces in the two fretting regimes.