Plain bearings - also called bushings, sleeve bearings, or journal bearings - support shaft or pin loads through sliding contact rather than rolling elements. Maintenance-free plain bearings incorporate a dry lubricant layer - typically PTFE composite, sintered bronze with PTFE fill, or carbon graphite - that provides a lubricating film during operation without any external grease or oil supply. This dry operation eliminates lubrication maintenance intervals and avoids grease contamination of surrounding components and products. The fundamental operating characteristic is full contact between shaft and bearing bore - generating significantly higher friction than rolling bearings but tolerating shock loads, edge loading, and misalignment better. Load capacity per unit area (PV value) determines the service life and temperature of the bearing surface. At low speeds and oscillating motion, plain bearings often outperform rolling bearings in simplicity, cost, and service life. Available as cylindrical bushings, flanged bushings, thrust washers, and spherical plain (rod end) bearings. Materials include sintered bronze with PTFE fill (standard), PTFE-fibre composite (higher loads), and carbon graphite (extreme temperatures or where contamination must be avoided). Operating temperatures range from -200°C to +280°C for PTFE-based types. Maintenance-free plain bearings are specified in hydraulic cylinder pin joints, construction equipment pivot points, agricultural machinery joints, food processing equipment pivot assemblies where grease contamination of product is unacceptable, earthmoving machinery links, and any pivoting or oscillating joint where lubrication access is difficult, contamination is a concern, or maintenance intervals must be minimised.
