Electric Phenomena in Relation to Lubrication

General. The effect of shaft currents passing through an oil film in a bearing is to accelerate polymerization and oxidation and cause thermal decomposition. The oil darkens in colour, sometimes increases in acidity, and generally deposits a chocolate-colour precipitate in the oil system. Arcing will also cause small particles of metal to flake off and contaminate the oil. If a shaft current is produced in anyone of the ways described below, it may, if of sufficient strength, arc through the oil film and cause pitting of the shaft and bearing. Electrolysis or galvanic action might cause currents to flow through the oil film without the presence of actual sparking or arcing.