Bearing (mechanical)
The design of the bearing may, for example, provide for free linear movement of the moving part 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.
Bearings are classified broadly according to the type of operation, the motions allowed, or the directions of the loads (forces) applied to the parts.
The most sophisticated bearings for the most demanding applications are very precise components; their manufacture requires some of the highest standards of current technology.
A wide variety of bearing designs exists to allow the demands of the application to be correctly met for maximum efficiency, reliability, durability, and performance.
[1][2][3]: 31 The Egyptians' own drawings in the tomb of Djehutihotep show the process of moving massive stone blocks on sledges as using liquid-lubricated runners which would constitute plain bearings.
[11][12] The first patent on ball bearings was awarded to Philip Vaughan, a British inventor and ironmaster in Carmarthen in 1794.
For example, they were used for holding wheel and axle assemblies to greatly reduce friction compared to prior non-bearing designs.
The first patent for a radial-style ball bearing was awarded to Jules Suriray, a Parisian bicycle mechanic, on 3 August 1869.
[14] In 1883, Friedrich Fischer, founder of FAG, developed an approach for milling and grinding balls of equal size and exact roundness by means of a suitable production machine, which set the stage for the creation of an independent bearing industry.
The modern, self-aligning design of ball bearing is attributed to Sven Wingquist of the SKF ball-bearing manufacturer in 1907 when he was awarded Swedish patent No.
Henry Timken, a 19th-century visionary and innovator in carriage manufacturing, patented the tapered roller bearing in 1898.
Richard Stribeck's extensive research[15][16] on ball bearing steels identified the metallurgy of the commonly used 100Cr6 (AISI 52100),[17] showing coefficient of friction as a function of pressure.
Over their history, bearings have been made of many materials, including ceramic, sapphire, glass, steel, bronze, and other metals.
With suitable lubrication, plain bearings often give acceptable accuracy, life, and friction at minimal cost.
Forces can be predominately radial, axial (thrust bearings), or bending moments perpendicular to the main axis.
In contrast, a lathe may position a cutting tool to ±0.002 mm using a ball lead screw held by rotating bearings.
Some small internal combustion engines specifically contain special plastic flinger wheels which randomly scatter oil around the interior of the mechanism.
[24] For high-speed and high-power machines, a loss of lubricant can result in rapid bearing heating and damage due to friction.
[25] High-speed turbochargers also typically require a pressurized oil system to cool the bearings and keep them from burning up due to the heat from the turbine.
Composite bearings are designed with a self-lubricating polytetrafluorethylene (PTFE) liner with a laminated metal backing.
The PTFE liner offers consistent, controlled friction as well as durability, whilst the metal backing ensures the composite bearing is robust and capable of withstanding high loads and stresses throughout its long life.
Alignment factors can play a damaging role in wear and tear, yet overcome by computer aid signaling and non-rubbing bearing types, such as magnetic levitation or air field pressure.
[clarification needed] Fluid and magnetic bearings can have practically indefinite service lives.
In practice, fluid bearings support high loads in hydroelectric plants that have been in nearly continuous service since about 1900 and show no signs of wear.
[citation needed] Rolling element bearing life is determined by load, temperature, maintenance, lubrication, material defects, contamination, handling, installation and other factors.
Harris 2001 describes a bearing for a rocket motor oxygen pump that gave several hours life, far in excess of the several tens of minutes needed.
[29] Depending on the customized specifications (backing material and PTFE compounds), composite bearings can operate up to 30 years without maintenance.
From the late 1700s through the mid-1900s, industry relied on many workers called oilers to lubricate machinery frequently with oil cans.
One example is bearings in the conveyor of a rock crusher are exposed continually to hard abrasive particles.
In addition, the turbine does not always run and is subjected to different operating behavior in different weather conditions, which makes proper lubrication a challenge.
