A bearing is a machine element that constrains relative motion to only
the desired motion, and reduces friction between moving parts. The design of
the bearing may, for example, provide for free linear movement of the moving
parts or for free rotation around a fixed axis; or, it may prevent a motion by
controlling the vectors of normal forces that bear on the moving parts. Most
bearings facilitate the desired motion by minimizing friction. Bearings are
classified broadly according to the type of operation, the motions allowed, or
to the directions of the loads applied to the parts.
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1. Plain Bearings.
2. Rolling Element bearings.
Rolling Element Bearings are also two types.
a. Roller bearings.
b. Ball bearings
3. Jewel Bearings.
4. Fluid Bearings.
5. Magnetic Bearings.
6. Flexure Bearings.
Plain bearings are the simplest type of bearing and are composed of just
the bearing surface with no rolling elements. They have a high load-carrying
capacity, are generally the least expensive and, depending on the materials,
have much longer lives than other types.
Plain Bearings are several specific styles: such
as bushing, journal bearing, sleeve
bearing, rifle bearing, composite bearing.
Rolling-element bearing in which rolling elements placed between the
turning and stationary races prevent sliding friction.
There are two main types-
Ball bearings are extremely common because they can handle both radial
and thrust loads, but can only handle a small amount of weight. They are found
in a wide array of applications, such as roller blades and even hard drives.
Roller Bearings are designed to carry heavy loads—the primary roller is
a cylinder, which means the load is distributed over a larger area, enabling
the bearing to handle larger amounts of weight.
Jewel bearings are plain bearings with a metal
spindle that turns in a jewel-lined pivot hole. They carry loads by rolling the
axle slightly off-center and are usually used in mechanical watches or clocks.
Fluid bearings support their load using a thin
layer of gas or liquid and can be classified into two types: fluid-dynamic
bearings and hydrostatic bearings.
Fluid-dynamic
bearings use rotation to form the liquid into a lubricating wedge against the
inner surface. In hydrostatic bearings, the fluids – usually oil, water, or air
– rely on an external pump. Fluid bearings are used in high load, high speed or
high precision application.
Magnetic bearings support moving parts without
physical contact, instead relying on magnetic fields to carry the loads. They
require continuous power input to keep the load stable, thus requiring a
back-up bearing in the case of power or control system failure.
A typical flexure bearing is one part joining two others, like a hinge,
in which motion is supported by a load element that bends. These bearings
require repeated bending.