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Bearing Load In general, the
bearing pressure is obtained by dividing the max. load
imposed on the bearing by the pressure supporting area of
the bearing. The pressure supporting area is defined as the
projected loading area which contacts with the shaft,
projected in the direction of the load in cases of a
cylindrical and spherical bearings. |
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Type of load
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Velocity
The main cause of generated heat
is the work done at the friction surface of the bearing. It
is known from experience that the rise in temperature at the
friction surface is affected more by the velocity than by
the pressure. With the same PV value, the larger V value is,
the high bearing temperature will be. When used in a high
velocity operation, it is recommended that the bearings
should be designed and used in such a manner that the
co-efficient of friction be reduced by positive supply of
oil to enhance both cooling and lubricating effectiveness,
in order to take advantage of their wear resistance.
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Oscillating
Motion
The oscillating motion is considered to be one of the most
severe conditions to bearings zero velocity in each cycle of
motion. Oil film is liable to be disrupted, fatigue and wear
of material be accelerated and wear particles tend to remain
longer. The ball bearing which are designed mainly for
rotational motion have a very small contact area causing,
extreme high contact stress to develop at their pressure
supporting areas. They are, thus, unsuitable for oscillating
motion because which have large contact sleeve bearings
which have large contact area are generally considered
better for this application.
CSB self-lubricating bearings are the most adequate bearings
for oscillating motion having a very tough sliding surface
which generates little wear particles, and being an
oil-containing type which will not cause noise due to
disruption of oil film. |
Operation
intervals
Operation may either be continuous
or intermittent. Intermittent operations can be advantageous
for general type bearings because of intervals which allows
generated friction heat to cool down. This enables a PV
value to remain relatively high. The disadvantage of
intermittent operations is that frequent operational
interruptions tend to cause inadequate amount. Moreover,
resulting in increasing wear occur when restarting. The
heavy load imposed in an intermittent operation is liable to
cause boundary lubrication condition. A bearing should be
selected which safely endures friction and wear in that
condition. Oil-containing bearings self-supply lubricant oil
to the sliding surface, and exhibit excellent
lubricant-maintaining capability. CSB650# in particular has
a high load carrying capacity and displays excellent
performance in intermittent operations with high load
because of the tough film of solid lubricants covers the
sliding surface. |
Bearing
Temperature
The life of a bearing is greatly
influenced by environment temperature and friction heat that
is generated from oscillating and reciprocating motion. For
a high temperature application, the PV value of the bearing
should be limited to a small value. The heat resistance of
plastic bearings are generally inferior to that of metallic
bearings. In particular thermoplastic resins poor resistance
to heat. They also have high thermal expansion rate.
Consequently to maintain a min. Required clearance, careful
dimensional control is necessary when the bearings of these
materials are designed. |
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