Automotive bearings are rolling-element bearings that are used in vehicles to provide smooth, low friction motion. They consist of an inner race that is a circular pathway for ball bearings, solid balls that rotate and are enclosed by the outer race and another circular pathway that holds the balls in and rotates.
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There are two main types of ball bearings that are identified by the direction of motion that they provide: radial ball bearings and thrust bearings. Radial bearings can carry radial and axial (also known as thrust) loads, whereas thrust bearings are designed solely for axial motion, which is linear. Automotive bearings may be constructed from metal or plastic; the most common materials are steel and ceramic, specifically silicon nitrate. Hybrid bearings have ceramic balls that travel in steel races. The balls are sometimes coated with chrome. There is no one type of automotive bearing; the term refers to bearings that are used in an automobile, which is quite a range and includes angular contact bearings or sealed ball bearings. Automotive bearings are used in many assemblies and parts found in cars, trucks and other vehicles. Specific applications include wheel hub unit bearings, belt tensioner units, water pump spindles, wheel bearings, clutch release bearings, propeller shaft support and centering bearings, suspension bearings and free wheel clutches.
Automotive bearings consist of three or four parts: the inner ring, the balls, the outer ring and possibly a separator that holds the balls in place and makes sure that the balls do not rub against each other, causing friction and wear. The balls make very little surface contact with the inner and outer rings, and therefore they spin with minimal friction. Other parts and equipment are attached to the bearing and benefit from the fast, smooth motion that automotive bearings permit. Preloading the bearings reduces or eliminates the clearance between the balls and the races, helping the bearing carry heavier loads. However, if the maximum load is surpassed, the bearing balls may flatten slightly and become deformed, ruining the bearing's ability to provide efficient motion. The balls are generally quite strong and are made from metal wire the thickness of the intended final diameter. The wire is given a rough shape and then processed in a stamping machine that smoothes the workpieces into spheres. Then the balls are heat-treated and receive additional finishing until they are symmetrical and perfectly identical. Precision ball bearings may undergo chemical treatments to further harden the balls. The rings are manufactured through multiple grinding stages to achieve parts that are just as exact as the balls.
