Bearing (mechanical)

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A  'bearing ' is a component used to reduce friction in a machine. Bearings may be classified broadly according to the motions they allow and according to their principle of operation.

Major types

Common motions include linear/axial and rotary/radial. A linear or thrust bearing allows motion along a straight line, for example a drawer being pulled out and pushed in. A rotary bearing allows motion about a center, such as a wheel on a shaft or a shaft through a housing. Common kinds of rotary motion include both one-direction rotation and oscillation where the motion only goes through part of a revolution. Essentially, bearings can reduce friction by shape, or by its material.  'By shape ', finds an advantage by reducing contact surface, such as using a sphere to roll anything on.  'By material ', exploits the nature of the bearing material used. An example would typically be the various plastics that have self-lubricating properties. Combinations of shape and properties, 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

There are at least six common principles of operation: sliding bearings, usually called 'bushings', 'Journal (mechanics) bearings', 'sleeve bearings', or 'plain bearings'; rolling-element bearings such as ball bearings and roller bearings; jewel bearings, in which the load is carried by rolling the axle slightly off-center; fluid bearings, in which the load is carried by a gas or liquid; magnetic bearings, in which the load is carried by a magnetic field; and flexure bearings, in which the motion is supported by a load element which bends.

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 first plain and rolling-element bearings were wood, but ceramic, sapphire or glass can be used, and steel, bronze, other metals, and plastic (e.g., nylon, polyoxymethylene, teflon, and UHMWPE) are all common today. Indeed, stone was even used in various forms. Think of the 'jewelled pocket watch', which incorporated stones to reduce frictional loads, and allow a smoother running watch. Of course, with older, mechanical timepieces, the smoother the operating properties, then the higher the accuracy and value.
Wood can still be seen today in old water mills, and the water itself had a part to play in the cooling/lubrication implications, of such natural and commonly found, bearing resources. 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 by horology John Harrison in his H3 chronometer of 1760. An early example of a wooden ball bearing (see rolling-element bearing), supporting a rotating table, was retrieved from the remains of a Roman Republic ship in Lake Nemi, Italy. The wreck was dated to 40 BC. Leonardo da Vinci is said to have described a type of ball bearing around the year 1500. One of the issues with ball bearings is that they can rub against each other, causing additional friction, but this can be prevented by enclosing the balls in a cage. The captured, or caged, ball bearing was originally described by Galileo Galilei in the 1600s. The mounting of bearings into a set was not accomplished for many years after that. The first patent for a ball race was by Philip Vaughan of Carmarthen in 1794. 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. The initials of the names'Fischers Automatische Gußstahlkugelfabrik' or 'Fischer Aktien-Gesellschaft' became a logo which was registered on 29 July, 1905. In 1962 it got the look it still has today, and it finally became an integral part of the company in 1979. The modern, self-aligning design of ball bearing is attributed to Sven Wingquist of the SKF ball-bearing manufacturer in 1907.

See also

• Hertz contact stress

External links

• How Bearings Work - Animations and functioning
  
  This article is licensed under the GNU Free Documentation License.It uses material from the Wikipedia article 'Bearing (mechanical)' (click for full Wikipedia text) Hide