Exploring the Failures of Deep Groove Ball Bearings Under Alternating Electric Current in the Presence of Commercial Lithium Grease

Abstract

Deep groove ball bearings are important mechanical elements in the automotive and process industries, particularly in electric motors. One of the primary reasons for their failure is lubricant degradation due to stray shaft current. Thus, the present work exhibited the failure of bearings under simulated lubricated conditions similar to those of real time bearings failing in presence of stray electric current. The test was conducted using a full bearing test rig with an applied radial load, 496 N, an alternating current, 10 A, and a rotation of 2000 rpm for 24 h. The bearings (6206 series) were greased using two commercially available ester-polyalphaolefin oil-based greases with viscosity 46–54 cSt (Grease 1) and 32–35 cSt (Grease 2, also contained aromatic oil). The optical microscopic images of the bearing raceways after the tribo test indicated the superior performance of Grease 1 compared to Grease 2, with lesser formation of white etching areas, micro-pitting, spot welds, and fluting on the surfaces of the bearings. Additionally, 80% less vibrations were recorded during the test with Grease 1, indicating a stable lubricating film of Grease 1 during the test as compared to Grease 2. Furthermore, a higher extent of Grease 2 degradation during the tribo test was also confirmed using Fourier transform infrared spectroscopy. Statistical analysis (t-test) indicated the significant variation of the vibrations produced during the test with electrified conditions. The present work indicated that the composition of the greases plays a significant role in controlling the bearing failures.