Rolling bearings are used in various machines and are often the cause of failures. In recent years, with the spread of BEVs and HEVs, the possibility of electrolytic corrosion occurring in rolling bearings in motors and leading to damage has increased. While the use of conductive grease can suppress the occurring of electrolytic corrosion, it is insufficient to ensure long-term reliability. We focused on the fact that graphite-like carbon (GLC) is generated from polyphenyl ether (PPE) oil and found that the higher the number of benzene rings in the molecular structure of PPE, the more GLC is generated through decomposition. Additionally, we added pentaphenyl ether (5P4E) with five benzene rings in the molecular structure or alkyldiphenyl ether (ADE) with two benzene rings in the molecular structure to conventional conductive grease, and conducted a 500-hour bearing life test by applying current between the inner and outer rings of the bearing filled with the modified grease. The results confirmed that adding PPE to conductive grease at a weight ratio of less than 5% achieves long-term stability of conductivity.
HIKITA et al. (Wed,) studied this question.