ABSTRACT
The primary function of lubricants is to protect the metal surface and to reduce friction. The rusting of the metal surfaces results in the formation of rust particles, which might contribute to the wear and the sludge formation. The literature also reports that the rusting of the metal surfaces could cause rapid seal and packing wear resulting in the increased leakage and the system contamination (Pirro and Wessol, 2001). The typical acidic type rust inhibitors, such as partially esterified alkylsuccinic acid (EASA), do not degrade the demulsibility properties of solvent-refined base stocks but were found effective only in lower viscosity mineral oils. The basic type rust inhibitors, such as succinic anhydride amine (SAA), were found effective in low and high viscosity mineral base stocks but degrade their demulsibility properties. The patent literature reports that a synergism between two different rust inhibitors allows obtaining the rust protection at a lower concentration of the mixture than can be obtained when using a single rust inhibitor (Pillon, Reid, and Asselin, 1995). The rust-preventive properties of lubricating oils are tested at 60°C following the ASTM D 665 method for rust-preventing characteristics of inhibited mineral oils and the evaluation pass/fail is usually used. The literature reports on the variation in the severity of rusting but the oil passes the test only if no rusting is observed, not even one rust spot (Pillon, 2007).
