Greases

Greases are semisolid lubricants designed to stay in place on surfaces that require lasting lubrication. They consist of a base oil that provides liquidity and film strength, thickened by a gelling agent to form a semi-solid structure. This combination allows greases to remain on bearings, gears, and joints, even under vibration and at elevated temperatures.

Base oils can be mineral, synthetic, or biodegradable vegetable oils. The thickener, often a soap such as lithium, calcium, or aluminum complex, or a non-soap polymer such as polyurea, gives the grease its consistency and defines temperature and load performance. Additives such as anti-wear agents, extreme pressure additives, corrosion inhibitors, antioxidants, and pour-point depressants tailor greases to specific conditions.

Performance is described by properties such as NLGI grade, measured by hardness from 000 to 6; hardness correlates with consistency and applicability. Other key metrics include base oil viscosity, dropping point, and work penetration. Standards from organizations like ASTM and NLGI guide testing and classification.

Greases are chosen by load, speed, temperature, and environment. Common types include lithium-based greases for general use, calcium-based greases for high water exposure, and specialty greases for food processing (H1), extreme temperatures, or high-speed bearings. Proper grease selection also considers compatibility with seals and materials, as well as grease life and re-lubrication intervals.

Maintenance involves keeping greases clean and uncontaminated, avoiding mixing different thickeners, and ensuring proper application during re-lubrication. Storage should be cool and dry, with containers sealed to prevent moisture ingress and polymerization. Contamination and aging reduce performance and bearing life.