However, negative effects occur when the proportion of acids in the oil increases. There are several reasons for this:
The acid load of engine oils increases in the course of their use due to combustion products.
"Blow-by" gases enter the oil circuit. Sulfur, which stems from the fuel, adds further acidity to the oil. They all have to be neutralized and rendered harmless by the engine oils. This means that the BN of an oil in internal combustion engines, also known as the alkaline reserve, decreases during operation.
Although no acidic combustion products contaminate the oil in hydraulic oils and industrial lubricants, such lubricants also become acidic through oxidation. To neutralize used oils, more caustic potash solution is consumed in the laboratory if the oil has been aged by reaction with air-oxygen over long periods of use or by high temperature. During oil aging, the typical hydrocarbon chains become "acidic" due to the accumulation of oxygen.
Wear protection additives, often referred to as EP additives, protect the surface from localized welding and from increased wear by forming metal salts on the surface that are relatively easy to remove. The reaction products resulting from the wear mechanism also have an acidic effect.