BEARINGS
A bearing is a machine element that constrains
relative motion between moving parts to only give the desired motion.
The design of bearing may be provide for free linear movement of the
moving parts or free rotation around a fixed axis or it may prevent
motion by controlling the vectors of normal forces that bear on the
moving parts .They are mainly used to minimize the friction between
moving parts.
The invention of the rolling bearing, within the sort
of wood rollers supporting, or bearing, associate object being affected
is of nice antiquity, and may predate the invention of the wheel. The
ball bearing was originally described by GALILEO in the 17th century.
Bearings played a significant role in technological
revolution allowing the new industrial machinery to work with
efficiency. There are various types of bearings. The most common bearing
is plain bearing which uses lubricant between the rubbing surfaces.
Types of bearings:
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Plain Bearing
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Journal bearing
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Sleeve bearing
Rolling element Bearing
Jewel Bearing
Fluid Bearing
Magnetic Bearing
Flexure Bearing
Common motions permitted by bearing are as follows
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Axial Rotation
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Linear Motion
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Spherical Rotation
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Hinge Motion
Bearings are designed on the basis of the following subjects
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Friction
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Speeds
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Loads
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Purpose
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Stiffness
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Life
Maintenance and Lubrication of a Bearing is very
important. The external factors that effect a bearing are electrical
signals, temperature,exposure to environment. To prevent bearing from
these external factors they should be frequently lubricated and
maintained properly.
Plain Bearing:
They have rubbing surfaces with lubricants between
them .Friction factor depends on the material and construction.
Stiffness is good. Life depends on application and also depends on
lubrication
Roller Bearing:
Ball or rollers are used between rotating surfaces.
This prevent and minimize the friction. Life is moderate and speed
changes according to requirements. These kind of bearings are widely
used now a days.
Jewel bearing:
Jewel bearing has an off centre bearing rolls in seating. Friction of this bearings is very low. Speed and life are low.
Fluid Bearing:
In these bearings fluid is forced between two faces
and held in by edge seal. Friction is zero at zero speed. Stiffness is
very high. Can be used for high speed applications. Life is infinite in
some applications.
Magnetic Bearing:
The two faces of bearing are kept separate by
magnets. Zero friction at zero speed but eddy currents are often
induced. Stiffness is low and there is no practical limit for speed and
life.
Flexure Bearing:
These bearings are provided with material flexes to
give any constrain movement. Friction is very low. Stiffness is low, and
speed can be very high with high life.
Reducing friction in bearings is commonly important
for efficiency. It helps to cutback the wear and tear and to facilitate
extended use at high speeds and to avoid heating and premature failure
of the bearing. Friction of a control depends on its form, material, and
fluid used between two surfaces applied on bearings. Completely
different bearing operative have different operational speed limits.
Plain bearings generally handle only lower speeds. However the gap
between the components that are separated by the bearing varies with
load. Forces working on the bearing may be radial, axial or bending
moments perpendicular to the most axis.
