ball bearing

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bearing, machine part designed to reduce friction between moving parts or to support moving loads. There are two main kinds of bearings: the antifriction type, such as the roller bearing and the ball bearing, operating on the principle of rolling friction; and the plain, or sliding, type, such as the journal bearing and the thrust bearing, employing the principle of sliding friction. Roller bearings are either cylindrical or tapered (conical), depending upon the application; they overcome frictional resistance by a rolling contact and are suited to large, heavy assemblies. Ball bearings are usually found in light precision machinery where high speeds are maintained, friction being reduced by the rolling action of the hard steel balls. In both types the balls or rollers are caged in an angular grooved track, called a race, and the bearings are held in place by a frame, commonly called a pillow block or plummer block. Ball bearings or roller bearings reduce friction more than sliding bearings do. Other advantages of antifriction bearings include ability to operate at high speeds and easy lubrication.

A journal bearing usually consists of a split cylindrical shell of hard, strong metal held in a rigid support and an inner cylindrical part of soft metal, which holds a rotating shaft, or journal. A self-aligning journal bearing has a spherically shaped support that turns in a socket to adjust to movements of the shaft. Slight misalignment of the shaft can be accommodated in the ordinary journal bearing by wearing of the soft bearing material, often an alloy of tin or lead. Less frequently used are aluminum alloys, steel, cast iron, or a thin layer of silver covered with a thin coating of a soft bearing material. Ideally, a film of lubricant, normally oil, separates journal and bearing so that contact is prevented (see lubrication). Bearings that are not split are called bushings.

A thrust bearing supports an axial load on a shaft, i.e., a force directed along a shaft's length. It may be a plate at the end of a shaft or a plate against which the collar on the shaft pushes. Large thrust bearings, such as those used to transmit the motive force of a ship's propeller from the shaft to the hull, have blocks that are separated from the collar on the shaft by wedge-shaped spaces filled with oil. Graphite bearings are used in high-temperature situations. Certain plastics make satisfactory self-lubricating bearings for low speeds and light loads and, if additionally lubricated, work at higher speeds and carry greater loads. Rubber and a naturally oily wood, lignum vitae, are used in water-lubricated bearings. Watches and other precision instruments have glass or sapphire pivot bearings. In gas-lubricated bearings a film of gas separates the bearings from the moving machine parts. Magnetic bearings employ magnetic repulsion to separate journal from bearing, reducing friction still further.

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ball bearing

[‚bȯl ′ber·iŋ]
(mechanical engineering)
An antifriction bearing permitting free motion between moving and fixed parts by means of balls confined between outer and inner rings.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

ball bearing

1. a bearing consisting of a number of hard steel balls rolling between a metal sleeve fitted over the rotating shaft and an outer sleeve held in the bearing housing, so reducing friction between moving parts while providing support for the shaft
2. a metal ball, esp one used in such a bearing
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
References in periodicals archive ?
Police recovered the ball-bearing from inside the house.
``About six weeks ago we had a similar incident and then a steel ball-bearing went through a window and through a wooden shutter as well.''
Police have confirmed a big crackdown on West Yorkshire's streets on weapons - including air pistols and ball-bearing guns.
Police at Little Park Street police station were handed the ball-bearing gun yesterday.
Mr David Travers, prosecuting, told Coventry Magistrates' Court yesterday that a customer, Taj Sandhu, aged 25, from Coventry, only discovered the ball-bearing while eating a mouthful of ice cream.
POLICE today gave parents some stern advice: Do not let your children have ball-bearing guns this Christmas.
Police are now urging parents to make sure their children are not playing with ball-bearing guns.
Warwickshire police spokeswoman Di Houlder said a ball-bearing gun looked just like a real weapon.
A booby-trapped motorcycle loaded with nails and ball-bearings went off in a crowded bazaar Friday in Baghdad, killing at least 13 people and injuring dozens, Iraqi officials said.
"But if people are firing ball-bearings at cars on the M62 the potential for such stupidity to cause an incredibly serious collision on such a busy road is obvious.
One recent example: when Chrysler added a performance version of its PT Cruiser, it found that its ball-bearings couldn't handle the added strain, so it turned to Timken with a quick development request.
Tolerating up to 1,500 psi, the expanded series of 148 bonded Frelon-lined anodized aluminum bearings carry between 4 and 8x the load of ball-bearings, while lasting on average 4-8 times longer than ball-bearings.