Special lubricant systems have been developed over the years to reduce friction and prevent wear and welding between working surfaces of bearing and gear teeth when, as a result of extreme pressure, low speed, high temperatures or reduced viscosity, the film which normally completely separates moving parts becomes thin enough to permit partial metal-to-metal contact. When moving machine parts are subjected to severe conditions of load, speed and temperature, as for example, the high tooth pressures and high rubbing velocities often encountered in hypoid and spurtype gearing, base lubricating oils themselves do not have the necessary qualities to provide adequate lubrication; metal-to-metal contact would occur which results in scoring, galling and local seizure of the gear teeth; therefore it is necessary to employ lubricants which contain extreme pressure additives. Extreme pressure (EP) additives are a special class of boundary lubrication additives which chemically react with the metal surface to form compounds with lower shear strength than the metal. The resultant lowshear compound thus provides the requisite lubrication. EP oils are basically inhibited oils with added extreme pressure additives.
USPTO Backgrounds
USPTO Backgrounds