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Bearings: An Introduction

Bearings are needed whenever one part of a machine slides against another. Bearings can be classified as providing sliding or rolling contact.

A sliding bearing typically uses a lubricant to reduce friction between the sliding surfaces. A shaft and bushing bearing is known as a journal bearing. The fluid lubricant forms a film between the sliding surfaces so that there is no contact between solid components. This kind of bearings are known as fluid film bearings.

Rolling contact bearings are often referred to antifriction bearings. Antifriction bearings, as their name implies, minimize friction by removing any possible sliding between bearing surfaces and replacing all contacts with rolling interfaces. Please select "Antifriction Bearings" for a more detailed explanation.

History of Bearings

Sliding bearings have existed since the first skid-supported wheel barrow was used by primitive man. With the invention of the wheel, efficient and robust bearings became a necessity since so much force is applied to the small area of the bearing surface. Lubrication of wood bearings probably started with animal fat grease. After metals were discovered, they were soon applied to wheel bearings.

It was with the eighteenth century industrial revolution that bearings came to the forefront of engineering endeavor. Machine speeds increased dramatically and bearings were central to rotary and linear movement. In addition, accuracy and repeatability of positioning rose in emphasis. The nineteenth century advent of railroad trains sparked further development in bearing technology. Now, not only did bearings need to operate at high speed, but heat, vibration, and shock loads were greatly increased and since railroad cars were a commodity, cost was paramount. Rolling element (antifriction) bearings proliferated during this period. The introduction of the automobile further increased the volume and decreased the cost of antifriction bearings. Because an automobile is a consumer product, bearings needed to be less dependent upon maintenance and inspection.

During World War II, ball bearing factories were an important bombing target because of their pivotal role in keeping the enemies' war effort rolling. Today, bearing design continues to progress with advanced materials and new geometries enabled by computer-aided design (CAD). Computer Aided Manufacturing, such as computer numerical controlled (CNC) machining, has drastically improved the accuracy of mass produced bearings. Accurate and position-repeatable bearings, especially linear ones, have become crucial for robot implementation.