lubrification

Lubrification is the process of introducing a lubricant between contacting surfaces to reduce friction, wear, heat generation, and the risk of seizure. It is a central concept in mechanical engineering and is also relevant to biological joints where synovial fluid performs a similar function.

Lubricants come in several forms, with major families including mineral oils, synthetic oils, and greases. Solid lubricants such as graphite or molybdenum disulfide are used in high-temperature or vacuum environments. Lubricants differ in viscosity, volatility, chemical stability, and additive content. Additives can provide anti-wear, extreme pressure, detergency, dispersancy, antioxidants, and corrosion protection. Viscosity determines film thickness and is sensitive to temperature, so lubricants are selected for the operating conditions of a machine.

Lubrication operates through different regimes depending on film thickness and load: boundary lubrication, mixed lubrication, hydrodynamic lubrication, and elastohydrodynamic lubrication. In hydrodynamic and elastohydrodynamic regimes, a continuous film fully separates surfaces; in boundary and mixed regimes, protective films are thinner and rely more on chemical or surface treatments. Lubrication systems may be oil-lubricated with circulating oil, grease-lubricated with thickened bases, or dry/solid-lubricated in specialized cases.

Applications span engines, transmissions, bearings, gears, turbines, and sliding contacts in both industrial machinery and consumer products. Proper lubrication reduces energy losses, extends component life, lowers maintenance costs, and can improve heat transfer. Maintenance practices include regular oil or grease changes, contamination control, and compatibility checks between lubricants and materials. Environmental and safety considerations emphasize spill prevention and choice of biodegradable or low-toxicity lubricants where appropriate.