The abbreviation EP stands for “Extreme Pressure” and refers to high pressures that can occur in a mechanical system between two friction partners. Under these extreme conditions, the lubricating film of a lubricating oil can break off and seizure damage to the gearbox is the result. In such cases, additions of extreme pressure additives can significantly increase the service life of transmission parts. EP additives are oil-soluble organic compounds with functional groups of sulphur, chlorine, phosphorus or carboxylene, which are able to maintain the lubricating film during operation under extreme pressure and separate the friction partners so that they do not weld together. EP additives optimise the load-bearing capacity of a lubricant and minimise wear.
Function of EP additives
If extremely high pressure occurs between two friction partners during a lubricating movement, these functional groups of the EP additives adsorb or chemisorb with the material surface or become metal salts in the boundary friction range through a chemical reaction. The reaction layers are significantly more stable than the material itself. EP additives prevent contacts of the metal surface unevenness and enable lubrication even at high loads.