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Horizontal Sleeve Bearings
Key Words: Bearing; Bush; Sleeve; Horizontal; Generator;
Hydrogenerator; Turbogenerator;Tachogenerator; Induction;
Synchronous; Direct CurrentClassification: ComponentNatural
CoolingThe term natural cooling means that the area of thermal
exchange around the bearing is enough totransfer the heat generated
by viscous friction of the oil film between shaft and bearing
liner.
Figure 1 Typical assembly of a sleeve bearingThe oil is agitated
by the oil ring which in contact with the oil storaged in the
bearing compartment,
makes the oil circulate and ensure enough amount of oil to form
the oil film on the rotor shaft.The oil replacement interval
specified by manufacturers is 8000 hours.Theoretically, considering
there is no metal to metal contact between shaft and bearing liner,
bearingliner can be considered infinite.Due to that, maintenance of
these bearings consists of replacing the oil within the required
viscosity.
Fig.2 Bearing liner and oil ringWater cooled
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A water cooled system with the application of a serpentine
inside the oil compartment of the bearings isactually required when
the peripheral speed is quite high. However, lubrication is enough
and the heatgeneration is excessive or the shaft temperature is
high.For this type of cooling, plenty amount of water is required
so as to ensure proper operation of thesystem under required
conditions.The specified oil exchange interval is also 8000 hours
as this lubrication system is the same as the
natural cooling system.With independent oil cooling systemAn
independent oil cooling system (lubrication through an external oil
circulation system) is actuallyrequired when the lubrication with
the application of an oil ring can no longer be applied due
toexcessive peripheral speed or when losses cause by friction
and/or heat transfer through the shaftrequire an oil cooling
provided by an independent oil circulation system.On this type of
cooling, the oil exchange interval can be increased to 20,000 hours
as the oil is usuallyfiltered.
Figure 3 Typical hydraulic unit for oil circulation or
pressurizationHorizontal Sleeve Bearing with Oil Pressurization
System
l Low speedThe bearing usually requires an oil pressurization
system when need to operate at a quite lowspeed (below 10 rpm) or a
motor starting quite slow, affecting the oil film that protects the
motorshaft.On this case, pressure must be enough to lift the shaft
over the bearing.
l Specific pressure excessively highThis normally occurs when a
flywheel or a turbine is coupled to the motor shaft end where
thepressure on the bearing is excessively high.
Horizontal Sleeve Bearing with Axial ThrustWhen axial thrusts
are required, bearings with axial supports are used so as to
withstand such thrusts.Based on the thrust required and on the
peripheral speed, these supports vary in size and quantity.
