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设计方案
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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.
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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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