Glossary term
Bearing
A machine element that supports relative motion between parts while carrying radial, axial, or combined loads with controlled friction and alignment.
Definition
deviceA machine element that supports relative motion between parts while carrying radial, axial, or combined loads with controlled friction and alignment.
Bearings guide motion and transmit load while limiting friction, wear, heat generation, vibration, and misalignment. Their selection affects life, efficiency, noise, precision, lubrication, maintainability, and failure risk in rotating and sliding machinery.
A bearing is a component that supports motion while carrying load between machine parts. It may support a shaft, wheel, spindle, rotor, screw, linkage, turntable, or sliding surface. The bearing’s job is not only to reduce friction but also to locate the moving part, control stiffness, manage heat, and survive repeated contact stress.
Main types
Rolling-element bearings use balls or rollers between races and are common where low starting friction, predictable catalog selection, and compact packaging are needed. Plain bearings use sliding contact, often with a lubricant film or self-lubricating material. Fluid-film bearings support load through hydrodynamic or hydrostatic pressure in a lubricant. Magnetic and air bearings are used where very low friction, cleanliness, or high speed is required.
Engineering role
Bearing selection affects load capacity, speed limit, friction, efficiency, noise, runout, vibration, service life, lubrication interval, contamination sensitivity, and maintenance strategy. The same shaft load can require very different bearing choices depending on speed, duty cycle, temperature, shock, misalignment, installation method, and required precision.
Life and load rating
Rolling bearing life is often specified with an L_{10} rating: the life at which 90 percent of a sufficiently large group of identical bearings are expected to survive under stated conditions. This is a statistical fatigue concept, not a guarantee for a single bearing. Equivalent dynamic load, static load, lubrication quality, contamination, temperature, preload, and mounting accuracy all influence real life.
Lubrication and installation
Lubrication controls friction, heat, wear, corrosion protection, and fatigue life. Viscosity must match speed, load, temperature, and bearing type. Installation quality is equally important: incorrect fits, brinelling during mounting, poor alignment, over-preload, loose housings, and contamination can destroy a properly selected bearing quickly.
Common mistakes
Common mistakes include selecting from radial load only while ignoring axial load, moment load, shock, speed, or misalignment. Another is treating catalog life as field life without checking lubrication, contamination, temperature, and installation. In rotating machinery, bearing stiffness and damping can affect rotor dynamics, so the bearing cannot always be treated as a rigid support.