Bearing Types and Application Design, Ball Bearings, Roller Bearings, Thrust Bearings

For additional information see Bearing Application Chart & Bearing Representation Chart.

Bearings permit smooth, low-friction movement between two or more surfaces.  This movement is either rotary (shaft rotating within a mount) or linear (one surface moving along another).  Bearings , are anti-friction devices, each having different anti-friction characteristics. By far the largest number of bearings are oil-lubricated.  The oil film can be maintained through pumping by a pressurization system (pump). Or it can be maintained by a squeezing or wedging of lubricant produced by the rolling action of the bearing itself.

General Application Guidelines:

Ball bearings are the less expensive choice in the smaller sizes and under lighter loads, while roller bearings are less expensive for larger sizes and heavier loads.

Roller bearings are more satisfactory under shock or impact loading than ball bearings.

Ball-thrust bearings are for pure thrust loading only. At high speeds, a deep-groove or angular-contact ball bearing usually will be a better choice, even for pure thrust loads.

Self-aligning ball bearings and cylindrical roller bearings have very low friction coefficients.

Deep-groove ball bearings are available with seals built into the bearing so that the bearing can be pre-lubricated to operate for long periods reducing maintenance requirements.

Careful consideration of speed requirements are important for proper bearing application design. Useable speeds are influenced by bearing size, properties, lubrication and operating temperatures. The permissible speed varies inversely with mean bearing diameter.

Ball Bearing Useable Life

Ball bearings were formerly rated on the basis of the compressive stress in the most heavily loaded ball. Except for static loads, experience has shown that the actual cause of failure is fatigue. Fatigue characteristics are used for load rating and are dependent on experimental results.  Analytical methods are available to determine a particular bearings useable life.  Consult with manufacturer to determine typical bearing performance characteristics.

The life of a ball bearing is the life in hours at some known speed, or the number of revolutions, that the bearing will attain before the first evidence of fatigue appears on any of the moving elements. Experience has shown that the life of an individual ball bearing cannot be precisely predicted. Fatigue characteristics are used for load ratings.

Even if bearings are properly installed, adequately lubricated, protected from foreign matter, and are not subjected to extreme operating conditions, they can ultimately fatigue. Under ideal conditions, the repeated stresses developed in the contact areas between the balls and the raceways eventually can result in fatigue of the material which results in spalling of the bearing load carrying surfaces. In most applications, the fatigue life is the maximum useful life of a bearing.

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