Lubricating Additive
Lubricating additives are compounds that are added to base lubricants—such as oils and greases—to enhance the lubricity and other performance characteristics of the lubricant. These substances are usually added to the base oil or grease in small amounts to help reduce friction, prevent corrosion and protect against wear. While some lubricating oils and greases come with additives already included in the formulation, others may require the addition of an external agent, depending upon the particular application.
Lubricating additives come in different varieties and are typically classified based on their chemical structure, functions and applications. Common types of lubricating additives include anti-wear agents, viscosity index improvers, detergents, dispersants, corrosion inhibitors, extreme pressure (EP) agents, friction modifiers and pour point depressants. Each type has a different function and will affect the lubricants properties in different ways.
Anti-wear agents are typically the most commonly used type of lubricating additive and are used to reduce wear and friction. These agents tend to form a protective film on the surface of the metal, preventing contact and reducing friction. Common types of anti-wear agents include zinc dithiophosphates, molybdenum dithiophosphates, sulfide compounds, and organophosphorus esters.
Viscosity index improvers, also called viscosity modifiers, are used to reduce the rate at which a lubricant’s viscosity changes with changes in temperature. This can help maintain viscosity and lubrication under a wide range of temperatures and viscosity requirements. The most common types of viscosity modifiers include polyurea copolymers, ethylene-vinyl acetate copolymers, and ethylene-methacrylate copolymers.
Detergents are used to keep foreign particles in suspension or to react with the acid by-products that are formed due to the oxidation of lubricants. They can also absorb certain compounds that lead to deposits, in order to keep the lubricant in proper condition. Common types of detergents used in lubricants include sulfonates and phosphates.
Dispersants are used to keep dirt, sludge and other residues suspended in the lubricant and to prevent these particles from forming into gels or solids. These agents also keep the surface of the metal free of dirt and sludge, so that the lubricant can maintain its full effect. Common dispersants include carboxylates and polyisobutylenes.
Corrosion inhibitors are used to protect the metal surfaces against corrosion, which can cause friction and lead to wear and tear. Common corrosion inhibitors include amines and organic acid salts.
Extreme pressure agents are an important type of lubricating additive used to reduce wear caused by high load and shock loading, as well as to prevent cold welds from occurring. Common extreme pressure agents include sulfurized or chlorinated fatty agents and sulfur-phosphorus compounds.
Friction modifiers are used to reduce friction caused by metal-to-metal contact. These agents form a protective film on the metal surfaces, which reduces friction and wear. Common types of friction modifiers include long-chain fatty acids, organo-metallic esters, and synthetic resins.
Lastly, pour point depressants are used to reduce the temperature at which a lubricant becomes a ‘solid’ or to reduce its freezing point. Common pour point depressants include naphthenic and paraffinic alcohols and waxes.
Overall, lubricating additives are an important part of any lubrication system and can have a significant impact on the performance of the lubricant. Therefore, it is important to choose the right type and concentration of additives to match the particular application and ensure optimal performance.
