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Encyclopedia > Bearing (mechanical)

A bearing is a device to permit constrained relative motion between two parts, typically rotation or linear movement. Bearings may be classified broadly according to the motions they allow and according to their principle of operation as well as by the directions of applied loads they can handle.

An example of a four-point contact ball bearing

## Contents

Image File history File links Download high-resolution version (2320x1760, 1134 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Bearing (mechanical) ... Image File history File links Download high-resolution version (2320x1760, 1134 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Bearing (mechanical) ... Working principle for a ball bearing. ...

## Bearing friction

Low friction bearings are often important for efficiency, to reduce wear and to facilitate high speeds. Essentially, a bearing can reduce friction by virtue of its shape, by its material, or by introducing and containing a fluid between surfaces.

• By shape, gains advantage usually by using spheres or rollers.
• By material, exploits the nature of the bearing material used. (An example would be using plastics that have low surface friction.)
• By fluid, exploits the low viscosity of a layer of fluid, such as a lubricant or as a pressurised medium to keep the two solid parts from touching.
• By fields, exploits electromagnetic fields, such as magnetic fields, to keep solid parts from touching.

Combinations of these can even be employed with the same bearing. An example of this is where the cage is made of plastic, and it separates the rollers/balls, which reduce friction by their shape and finish.

## Principles of operation

Animation of ball bearing

There are at least six common principles of operation: Image File history File links BallBearing. ... Image File history File links BallBearing. ...

Bearings vary greatly over the forces and speeds that they can support.

Forces can be radial, axial (thrust bearings) or moments perpendicular to the main axis. A thrust bearing is a particular type of bearing. ...

## Speeds

Bearings very typically involve some degree of relative movement between surfaces, and different types have limits as to the maximum relative surface speeds they can handle, and this can be specified as a speed in ft/s or m/s.

For rotational bearings generally performance is defined in terms of the product 'DN' where D is the diameter (often in mm) of the bearing and N is the rotation rate in revolutions per minute.

Generally in terms of relative speed of the moving parts there is considerable overlap between capabilities, but plain bearings can generally handle the lowest speeds while rolling element bearings are faster, followed by fluid bearings and finally magnetic bearings which have no known upper speed limit.

## Life

Fluid and magnetic bearings can potentially give indefinite life.

Rolling element bearing life is statistical, but is determined by load, temperature, maintenance, vibration, lubrication and other factors.

For plain bearings some materials give much longer life than others. Some of the John Harrison clocks still operate after hundreds of years because of the lignum vitae wood employed in their construction, whereas his metal clocks are seldom run due to potential wear. John Harrison John Harrison (March 24, 1693â€“March 24, 1776) was an English clockmaker, who designed and built the worlds first successful chronometer (maritime clock), one whose accuracy was great enough to allow the determination of longitude over long distances. ... Lignum vitae is the heartwood of species of the genus Guaiacum, the trees of which are usually called guayacan. ...

## Maintenance

Many bearings require periodic maintenance to prevent premature failure, although some such as fluid or magnetic bearings may require little maintenance.

Most bearings in high cycle operations need periodic lubrication and cleaning, and may require adjustment to minimise the effects of wear.

## History and development

An early type of linear bearing was an arrangement of tree trunks laid down under sleds. This technology may date as far back as the construction of the Pyramids of Giza, though there is no definitive evidence. Modern linear bearings use a similar principle, sometimes with balls in place of rollers. The Giza pyramid field, viewed from the southwest. ...

Rotary bearings are required for many applications, from heavy-duty use in vehicle axles and machine shafts, to precision clock parts. The simplest rotary bearing is the sleeve bearing, which is just a cylinder inserted between the wheel and its axle. This was followed by the roller bearing, in which the sleeve was replaced by a number of cylindrical rollers. Each roller behaves as an individual wheel. The first practical caged-roller bearing was invented in the mid-1740s by horologist John Harrison for his H3 marine timekeeper. This used the bearing for a very limited oscillating motion but Harrison also used a similar bearing in a truly rotary application in a contemporaneous regulator clock. For other uses, see Wheel (disambiguation). ... Horology is the study of the science and art of timekeeping devices. ... John Harrison John Harrison (March 24, 1693â€“March 24, 1776) was an English clockmaker, who designed and built the worlds first successful chronometer (maritime clock), one whose accuracy was great enough to allow the determination of longitude over long distances. ...

Friedrich Fischer's idea from the year 1883 for milling and grinding balls of equal size and exact roundness by means of a suitable production machine formed the foundation for creation of an independent bearing industry. Friedrich Fisher is considered the father of the modern ball bearing, having invented the process for milling standard bearings in 1883. ...

Tapered steering head bearings for a motorcycle

The modern, self-aligning design of ball bearing is attributed to Sven Wingquist of the SKF ball-bearing manufacturer in 1907. Image File history File links Metadata No higher resolution available. ... Image File history File links Metadata No higher resolution available. ... For other uses, see Motorcycle (disambiguation). ... Wingquist, Sven (1876-1953), industrialist, inventor, Sweden. ... SKF, Svenska Kullagerfabriken AB, later AB SKF, is a Swedish bearing company founded in 1907, supplying bearings, seals, lubrication and lubrication systems, maintenance products, mechatronics products, power transmission products, customer solutions and related services globally. ... Year 1907 (MCMVII) was a common year starting on Tuesday (link will display the full calendar) of the Gregorian calendar (or a common year starting on Monday of the 13-day-slower Julian calendar). ...

Henry Timken, a 19th century visionary and innovator in carriage manufacturing, patented the tapered roller bearing, in 1898. The following year, he formed a company to produce his innovation. Through a century, the company grew to make bearings of all types, specialty steel and an array of related products and services. This article or section does not cite its references or sources. ...

The Timken Company (Sale \$4,973.4M, 2006), The SKF company(\$6,195.1M, 2005), the Schaeffler Group (Private), the NSK company(\$5,344.5M, 2006), and the NTN Bearing company(\$3,697.8M, 2006) are now the largest bearing manufacturers in the world. The Timken Company is a major manufacturer of tapered roller bearings and specialty steels located in Canton, Ohio. ... SKF, Svenska Kullagerfabriken AB, later AB SKF, is a Swedish bearing company founded in 1907, supplying bearings, seals, lubrication and lubrication systems, maintenance products, mechatronics products, power transmission products, customer solutions and related services globally. ...

## Types

There are many number of different types of bearings.

Type Description Stiffness* Speed Life Notes
plain bearing rubbing surfaces, with lubricant Good, provided wear is low, but some slack is normally present low/moderate (often requires cooling) moderate (depends on lubrication) The simplest type of bearing, widely used, relatively high friction
Rolling element bearing Ball or rollers are used to prevent or minimise rubbing Good, but some slack is usually present moderate-high (often requires cooling) moderate (depends on lubrication, often requires maintenance) Used for higher loads than plain bearings with lower friction
jewel bearing off-center bearing rolls in seating Low due to flexing low adequate (needs cleaning and lubrication requires maintenance) Mainly used in low-load, high precision work such as clocks
fluid bearing Fluid is forced between two faces and held in by edge seal Very high Very high- speeds usually limited by seals Virtually infinite in some applications, may wear at startup/shutdown in some cases Can fail quickly due to grit or dust or other contaminants. Maintenance free in continuous use.
magnetic bearings Faces of bearing are kept separate by magnets (electromagnets or eddy currents) low Infinite Infinite Often needs considerable power. Maintenance free.
Flexure bearing Material flexes to give and constrain movement low Very high Very high or low depending on materials and strain in application Limited range of movement
• - stiffness is the amount that the gap varies when the load on the bearing changes, it is distinct from the friction of the bearing

Stiffness is the resistance of an elastic body to deflection or deformation by an applied force. ... It has been suggested that Bushing be merged into this article or section. ... ruby jewel bearings used in an Omega mechanical watch movement A jewel bearing is a bearing which allows motion by running a shaft slightly off-center so that the shaft rolls inside of the bearing rather than sliding. ... Fluid bearings are bearings which solely support the bearings loads on a thin layer of liquid or gas. ... A magnetic bearing is a bearing which supports a load using magnetic levitation. ... An electromagnet is a type of magnet in which the magnetic field is produced by the flow of an electric current. ... As the circular plate moves down through a small region of constant magnetic field directed into the page, eddy currents are induced in the plate. ... A flexure bearing is a bearing which allows motion by bending a load element. ... For other uses, see Friction (disambiguation). ...

Wikimedia Commons has media related to:
 Hinge Journal bearing Main bearing Needle roller bearing Rolamite Rolling-element bearing

Image File history File links Commons-logo. ... Working principle for a ball bearing. ... Ball splines (Ball Spline bearings) are mechanical devices that are used to provide nearly frictionless linear motion while allowing the member to transmit torque simultaneously. ... This article or section does not adequately cite its references or sources. ... A combined bearing or combination bearing includes a main body and a mating member. ... Fluid bearings are bearings which solely support the bearings loads on a thin layer of liquid or gas. ... In mechanical engineering, Hertz contact stress is a description of the stress within mating parts. ... A hinge is a type of bearing that connects two solid objects, typically allowing only a limited angle of rotation between them. ... A bogie from a railroad car. ... In a piston engine, the main bearings are the bearings on which the crankshaft rotates. ... A needle roller bearing A needle roller bearing is a bearing which uses small cylindrical rollers. ... Rolamite is a technology for very low friction bearings developed by Sandia National Laboratories in the 1960s. ... Four-point-contact radial bearings A rolling-element bearing is a bearing which carries a load by placing round elements between the two pieces. ...

Results from FactBites:

 Bearing (mechanical) - Wikipedia, the free encyclopedia (985 words) Bearings may be classified broadly according to the motions they allow and according to their principle of operation. A rotary bearing or thrust bearing allows motion about a center, such as a wheel on a shaft or a shaft through a housing. The first practical caged-roller bearing was invented in the mid-1740s by horologist John Harrison for his H3 marine timekeeper.
 ball bearing: Definition and Much More from Answers.com (2891 words) Conrad bearings have the advantage that they take both radial and axial loads, but the disadvantage they cannot be filled to a full complement and thus have reduced load-carrying capacity compared to a full-complement bearing. The angular-contact bearing is able to withstand such a combined load, as well as small misalignments which often occurs, due to the flexibility of the front fork. Hard drive bearings used to be highly spherical, and were said to be the best spherical manufactured shapes, but this is no longer true, and more and more being replaced with fluid bearings.
More results at FactBites »

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