Page 37 - Y-bearing-units

Selecting the bearing unit
size using the static load 1
carrying capacity
A Y-bearing or Y-bearing unit size should be
determined on the basis of the static load rating
C 0 , instead of bearing life, when one of the
following conditions exists:
• The bearing is stationary and subjected to
continuous or intermittent (shock) loads.
• The bearing makes slow oscillating or align-
ment movements under load.
• The bearing rotates under load at a very slow
speed (n < 10 r/min) and is not required to
have a long service life. In this case, the life
equation for a given equivalent load P would
give such a low requisite basic dynamic load
rating C that the bearing selected on a life
basis would be seriously overloaded in ser vice.
• The bearing rotates and, in addition to the
normal operating loads, has to sustain heavy
shock loads that act during a fraction of
a revolution.
In all these cases, the permissible load for a
Y-bearing is determined by the load that will
cause permanent deformations to the ball/race-
way contacts and is not determined by material
fatigue. Heavy loads acting on a stationary or
slowly oscillating bearing, or shock loads on
a rotating bearing, produce flattened areas on
the balls and indentations on the raceways.
The indentations may be irregularly spaced
around the raceway, or may be evenly spaced
at positions corresponding to the spacing of
the balls. If the load acts for several revolutions,
the deformation will be evenly distributed over
the whole raceway.
The extent to which this damage is detri mental
to bearing performance depends on the applica-
tion and the demands placed on the bearing.
To prevent or minimize this type of damage,
Y-bearing units with a sufficiently high static
load carrying capacity should be selected.
When determining the Y-bearing or Y-bearing
unit size based on static load carrying capacity, a
given safety factor s 0 , which represents the rela-
tionship between the basic static load rating C 0
and the equivalent static bearing load P 0 , is used
to calculate the requisite basic static load rating.

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