Thermally sprayed coatings for highly stressed sliding bearings

Sliding bearings have to fulfil various requirements depending on the operating conditions. Conventional sliding bearings, however, cannot be used for critical operating conditions such as frequent acceleration and shut-down procedures or they require the use of complex manufacturing processes and cost-intensive material solutions. For this reason, complex multilayer systems or rolling bearings are currently used for frequent start-up cycles and low relative velocities. New material systems and manufacturing processes are of particular interest in order to operate sliding bearings cost-effectively and reliably even under these increased requirements. Within the scope of this study, new material concepts are developed by thermal spraying. Thermal spraying allows the production of innovative material combinations, which cannot be produced by melting metallurgy. In addition, coatings can be applied by thermal spraying on a wide variety of geometries directly on the bearing support structure, thus achieving increased freedom of design and additional cost savings compared to conventional processes. The coating concepts are based on a cobalt or bronze matrix into which friction-reducing solid lubricants can be integrated during the coating process. One particular goal of the coating concepts is to improve the operating properties under critical conditions, such as low relative velocities and high loads. Therefore, the developed coatings are tested on a modified ring-on-disc tribometer and are compared to a reference sliding bearing material produced by conventional casting. To verify the coating capability, the most promising coating is investigated on a full-scale main bearing test bench of a wind turbine. For the first time, a thermally sprayed coating and a new conical sliding bearing design are evaluated as a substitution for currently used rolling bearings as main bearings in wind turbines. Hereby, it is demonstrated whether these new coating concepts can meet the requirements of this highly stressed bearing position.