Detection of surface defects in bearings using electromagnetic flux

Abstract

The electromagnetic flux of rotating ball bearings was measured by a gradiometer-configured inductance coil. Ball spin, and drive and slave ring frequencies are distinguishable throughout the testing. One bearing was tested for 22 h, 45 min without reaching the failure, and the second bearing test involved restarting a bearing that had already reached the failure level but showed minimal visible damage. The first test showed increased magnetization of the bearing via an increase in flux at the spin frequency by 14 dB. The second test showed a consistent level of flux at the spin frequency compared to the final level detected in the first test. As the surface of the bearing becomes damaged from skidding, an increase in the magnetic field is hypothesized to originate from the abrased ferrous surfaces. The spinning ball allows this feature to be detected easily by a simple coil of wire. [See NOISE-CON Proceedings for full paper.]