Bearing

A bearing is a machine element that constrains relative motion between moving parts to either support axial and radial loads or enable smooth rotation or linear movement. Bearings are designed to handle radial loads, axial (thrust) loads, or a combination, and are selected based on speed, load, accuracy, and environment. The primary contact types are rolling contact, where rolling elements such as balls or rollers transfer load by rolling, and plain or sliding contact, where surfaces slide against each other with a lubricating film.

Common bearing types include ball bearings, cylindrical and spherical roller bearings, needle bearings, and plain bearings. Ball bearings use spherical rolling elements between inner and outer rings; roller bearings use cylindrical or tapered rollers to support higher radial loads. Plain bearings rely on a lubricating film between sliding surfaces. Bearings typically consist of inner and outer rings, rolling elements or sleeves, and a cage or retainer; lubrication (grease or oil) reduces wear and heat.

Performance depends on dynamic and static load ratings, rotational speed, temperature, lubrication, and fit. Misalignment, contamination, or inadequate lubrication can cause wear, spalling, brinelling, or fatigue. Design considerations include seals and shields, preload or clearance, mounting details, and lubrication method. Life expectancy is estimated using standard calculations based on dynamic load rating and operating conditions.

Applications span automotive wheels, industrial machinery, electric motors, turbines, aerospace, and computer storage devices. Bearings have evolved from simple bushings to highly engineered rolling-contact elements with advanced materials and sealed lubrication systems. Maintenance involves regular lubrication, seal checks, alignment verification, and contamination control to extend service life.