||A bearing is a mechanical device that supports the
moving parts of a machine and to guide or confine its motion, while preventing motion in the direction of applied load. Its primary purpose is to reduce
friction with a minimum loss of energy and at the same time should control the rate of wear. Bearings are made to support radial loads, thrust loads, or
combined radial-thrust loads. Bearings can be located at:
1) Between the shafts frame of the machine, or
2) Between the contact members and the frame of the machine. or
3) Between the contact members and the frame or between the contact members and linkage members.
The two most common forms of bearings are rotary bearings and linear bearings.
Linear bearings are used to permit motion in a straight line. For example, a drawer
makes use of linear bearings to help pull the drawer in and out. Rotary bearings help an object move around a central point. For example, a wheel on a
shaft rotates using rotary bearings. Rotary bearings can include one-direction rotation and oscillation. With oscillation, the rotary bearings only go through
a part of a revolution.
Within these forms of bearings are bearings that utilize differing principles of
design. One of these designs uses rolling element bearings, such as roller bearings and ball bearings. Rolling element bearings carry loads by placing a
round element between two pieces. This causes the round elements to roll, or tumble, with very little sliding.
Fluid bearings are another type of bearings. With fluid bearings, the load is carried
by a liquid or a gas. Fluid bearings are used when a process requires high speed, high loads, or high precision, because ball bearings will wear out
quickly in this application.
Magnetic bearings are used when a load is carried by a magnetic field. Magnetic bearings
are often used to in electrical meters to measure power consumption. They are also used to support trains, resulting in a lower noise level and a smoother
ride. Magnetic bearings create a very low amount of friction and can run without the use of lubrication. They can also run in a vacuum, but they are
Flexure bearings are used when the load element needs to bend. Typically, flexure
bearings are just one part that joins two other parts. A door hinge is an example of flexure bearings. Flexure bearings are simple and inexpensive. They
are usually lightweight and produce a low amount of friction, but their range of motion is limited and generally canít support high loads.
||Every form of antifriction Bearing consists of four basic parts:- An Inner Ring An Outer Ring Rolling ElementsA Cage
An Inner Ring:-This is the smaller of the two bearing rings and gets its name from the
position it holds. It has a groove on its outside diameter to form a path for the balls. The surface of this path is precision finished to extremely
tight tolerances and is honed to a very smooth, mirror-like surface finish. The inner ring is mounted on the shaft and is usually the rotating element.
An Outer Ring:-This is the larger of the two rings and, like its counterpart the inner ring, its name is derived from the position it holds.
Conversely, there is a groove on its inside diameter to form a pathway for the balls. This surface also has the same high precision finish of the
inner ring. The outer ring is normally placed into a housing and is usually held stationery.
Rolling Elements:-These are the rolling elements that separate the inner and outer ring and permit the bearing to rotate with minimal friction. The ball
radius is slightly smaller than the grooved ball track on the inner and outer rings. This allows the balls to contact the rings at a single point,
appropriately called point contact. Ball dimensions are controlled to very tight tolerances. Ball roundness, size variations, and surface finish are
very important attributes and are controlled to a micro inch level
(1 micro inch = 1/1,000,000th, or one-millionth of an inch). Rolling elements can be either Balls, Cylindrical Rollers, Spherical Rollers, Tapered Rollers and Oil
in case of Journal type of Bearings.
The Cage:-The main purpose of the cage is to separate the balls, maintaining an even and consistent spacing,
to accurately guide the balls in the paths, or raceways, during rotation, and to prevent the balls from falling out.
Cage may be of Steel, Brass, Bronze, or Phenolic composition, depending upon the type and application
of the bearings.
Bearings are designed in such a way that they offer following advantages:
Low Friction--Particularly low starting friction.The ability to support both radial and thrust load and high speeds of rotation.
Accurate performance under changing load and speed.High load carrying capacity.Operating ability under extreme conditions of speed and performance.
Practically no wear in running.Simple methods of lubrication.Inherently precision mechanisms.