Ceramic coated bearings bring benefits for VSD users

NSK says that the insulating effect of the ceramic coating prevents current transfer, which not only extends bearing service life but also avoids the potential for damage to adjacent drive components. Energy efficient VSDs are stated to be particularly economical when different power levels are required in response to variable demand. However, frequency regulation calls for bearings that fit a different set of requirements, largely because there is always a risk of parasitic current reaching the driven components via the motor shaft and bearings. This current has the potential to cause damage to the bearings from phenomena such as ripple formation and the melting of running surfaces. Further, says NSK, the function and service life of driven components can also be impaired by the passage of current. 

Design engineers are able to counteract these relatively common problems by using deep groove ball bearings with a ceramic coating on the outer ring. The insulating effect of the coating prevents current transfer and, subsequently, prevents bearing damage. Based on an extensive series of tests, NSK says that it has enhanced the ceramic coating used and that this has resulted in two prime advantages. Firstly, the insulating effect of the coating is up to 10 times greater. Secondly, the company says that the impact resistance of the normally very brittle ceramic is now more than three times that of ceramic coatings found on conventional bearings, allowing the NSK units to deliver a significantly longer service life. 

A further benefit claimed is that the optimised ceramic coating provides better dissipation of the heat generated in the bearing as rotation occurs, again contributing to extended service life. NSK’s range of ceramic-coated deep groove ball bearings is described in a new catalogue entitled ‘Bearings for Electric Motors’, which is available in print or as a PDF download here.