Kogellager

Kogellager, commonly translated as ball bearing in English, is a rolling-element bearing designed to constrain relative motion to a single axis. It reduces friction between moving parts and supports both radial and axial loads. A typical kogellager consists of an inner race, an outer race, a number of hardened steel balls, and a cage that spaces the balls evenly. The races are precision-ground to create raceways for the balls. Lubricants such as grease or oil are used to minimize wear and dissipate heat; seals or shields protect the lubricant from contamination.

When in operation, load is transmitted from the outer race to the balls and then to the inner race. Because the balls roll, friction is much lower than sliding contact, allowing higher rotational speeds. The contact is point-like, but the load is distributed over a small area. Common types include deep-groove ball bearings (universal radial and moderate axial loads); angular-contact ball bearings (support higher axial loads in one direction and higher stiffness); self-aligning ball bearings (accommodate misalignment with an outer spherical race); and thrust ball bearings (primarily for axial loads). Miniature and corrosion-resistant variants exist for specialized uses.

Materials typically include bearing-grade steel, with ceramic variants for high-speed or low-friction applications. Kogellager are ubiquitous in motors, gearboxes, household appliances, automobiles, and aerospace equipment. They require proper lubrication, clean housing, and occasional inspection for wear or contamination. The term kogellager is used in Dutch engineering literature to refer to ball bearings.