Lubricant Additive

Additives

Very little unadditized mineral oil is sold as a lubricant. Almost all commercial lubricants contain additives to enhance their performance in amounts ranging from less than 1 to 25% or more. By far the largest market for such additives is in the transportation field, including additives for engines and drivetrains in cars, trucks, buses, locomotives, and ships. The function of additives can be summarized as:

  • Protect metal surfaces (ring, bearings, gears, etc.)
  • Extend the range of the lubricant applicability
  • Extend lubricant life


Additive Types

Antifoamant
Purpose: Prevent lubricant from forming a persistent foam
Function: Reduce surface tension to speed collapse of foam

Antioxidant<
Purpose: Retard oxidative decomposition
Function: Decompose peroxides and terminates free-radical reactions

Antiwear and EP Agents
Purpose: Reduce friction and wear and prevent scoring and seizure
Function: Chemical reaction with metal surfaces to form a film with lower shear strength than the metal, thereby preventing metal-to-metal contact.

Corrosion and Rust Inhibitor<
Purpose: Prevent corrosion and rusting of metal parts in contact with the lubricant
Function: Preferential adsorption of polar constituent on metal surface to provide protective film, or neutralize corrosive acids.

Detergent<
Purpose: Keeps surfaces free of deposits<
Function: Chemical reaction with sludge and varnish precursors to neutralize them and keep them soluble.

Dispersants
Purpose: Keep insoluble contaminants dispersed in the lubricant
Function: Contaminants are bonded by polar attraction to dispersants molecules, prevented from agglomerating and kept in suspension due to solubility of dispersant.

Friction Modifiers
Purpose: Alter coefficient of friction<
Function: Preferential adsorption of surface-active materials

Metal Deactivator
Purpose: Reduces catalytic effect of metals on oxidation rate
Function: Form inactive film on metal surfaces by complexing with metallic ions.

Pour Point Depressants
Purpose: Enable lubricant to flow at low temperatures
Function: Modify wax crystal formation to reduce interlocking

Seal Swell Agents
Purpose: Swell elastomeric seals<
Function: Chemical reaction with elastomer to cause slight swell

Viscosity Modifier<
Purpose: Reduce the rate of viscosity change with temperature
Function: Polymers expand with increasing temperature to counteract oil thinning