What are the extreme pressure additives in gear oil?

Extreme pressure additives, or EP additives, are lubricant additives specifically designed to protect metal surfaces under high pressure and temperature conditions. They form a protective film on metal surfaces that can withstand extreme pressure and prevent metal-to-metal contact, reducing wear and extending the life of gear components.

Some common extreme pressure additives used in gear oils include:

1. Phosphorus compounds: Phosphorus compounds, such as zinc dialkyldithiophosphate (ZDDP), are widely used as extreme pressure additives in gear oils. These compounds react chemically with the metal surface to form a protective layer that can withstand extreme pressure and reduce friction.
2. Sulfur-containing compounds: Sulfur-containing compounds, such as sulfurized olefins and sulfur-phosphorus compounds, are also used as EP additives. These compounds react with the metal surface to form a protective layer of iron sulfide that acts as a solid lubricant.
3. Chlorine-containing compounds: Chlorine-containing compounds, such as chlorinated paraffins, are used as EP additives in certain applications. These compounds react with metal surfaces to form thin layers of metal chlorides that act as solid lubricants under extreme pressure conditions.

It’s worth noting that extreme pressure additives may corrode some metals, so they should be formulated to be compatible with the specific gear and material they are lubricating. In addition, gear oils containing extreme pressure additives should be selected based on the specific application and requirements of the equipment used.