Green Bearings

Description

Within the context of increasing scarcity of resources and the large number of fields of application in which mineral oil-based lubricants may not or cannot be used, dry-running and coated rolling bearings are investigated in this thesis. This involves determining a thin-film system appropriate for overrolling which compensates for the lack of friction and wear protection of a conventional lubricant to such an extent that the operation of the dry-running bearing can be achieved for a minimum duration of 10^6 revolutions. Therefore, the selection of the components to be coated of the considered deep groove ball bearing is of significant interest, which is why the resulting three variants of the sole ring or ball Coating as well as the combination of these are discussed. Based on comprehensive component tests and a detailed wear analysis, a metal-containing hydrogenated amorphous carbon film (a-C:H:Me) applied using PVD technology is identified as suitable. The longest running times are realised when the coating is applied exclusively to the balls. Detailed analyses of the individual rolling contact using two-disc tests reveal a speed-dependent threshold of the contact pressure, Above which the coating-to-coating contact negatively impacts the operating life and longer running times are achievable by coating only one contact partner.

Following the above, a contribution is made to the calculation of the operating life of dry-running coated rolling bearings, as no validated approach for amorphous carbon films exists so far. For this purpose, a friction energy wear model, originally designed for solid lubricants with layered lattice structures, is modified in various aspects. The necessity arises from the consideration of radial loads as well as the application of the coating system on the rings, especially regarding the radial force-induced non-uniform load distribution. Furthermore, the pressure- and speed-dependent non-linear wear behaviour of the a-C:H:Me coating is integrated. The validation using experimental operating lives determined by Weibull analysis shows excellent agreement, demonstrating the correct predictive capability of the modified friction energy wear approach.