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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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