A thrust bearing is a particular type of rotary bearing

Bearing (mechanical)

A bearing is a device to allow constrained relative motion between two or more 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...

. Like other bearings they permit rotation between parts, but they are designed to support a high axial

Axial

Axial may mean:* Along the same line as an axis of rotation in geometry* A type of modal frame in music* One of several anatomical directions in an animal body* Axial age, the period from 800 to 200 BC in China, India and the western world...

 load while doing this.

Thrust bearings come in several varieties.

• Ball thrust bearings, composed of ball bearing
  Ball bearing
  A ball bearing is a type of rolling-element bearing that uses balls to maintain the separation between the bearing races.The purpose of a ball bearing is to reduce rotational friction and support radial and axial loads. It achieves this by using at least two races to contain the balls and transmit...
  
  s supported in a ring, can be used in low thrust applications where there is little radial load.
• Roller thrust bearings consist of small cylindrical rollers arranged flat with their axes pointing to the axis of the bearing. They give very good carrying capacity and are cheap, but tend to wear due to the differences in radial speed and friction is higher than with ball bearings.
• Tapered roller bearing
  Tapered roller bearing
  Tapered roller bearings are bearings that can take large axial forces as well as being able to sustain large radial forces.-Description:...
  
  s consist of small tapered rollers arranged so that their axes all converge at a point on the axis of the bearing. The length of the roller and the diameter of the wide and the narrow ends and the angle of rollers need to be carefully calculated to provide the correct taper so that each end of the roller rolls smoothly on the bearing face without skidding. These are the type most commonly used in automotive applications (to support the wheels of a motor car for example), where they are used in pairs to accommodate axial thrust in either direction, as well as radial loads. They can support rather larger thrust loads than the ball type due to the larger contact area, but are more expensive to manufacture.
• Fluid bearing
  Fluid bearing
  Fluid bearings are bearings which support the bearing's loads solely on a thin layer of liquid or gas.They can be broadly classified as fluid dynamic bearings or hydrostatic bearings. Hydrostatic bearings are externally pressurized fluid bearings, where the fluid is usually oil, water or air, and...
  
  s, where the axial thrust is supported on a thin layer of pressurized liquid—these give low drag.
• Magnetic bearing
  Magnetic bearing
  A magnetic bearing is a bearing which supports a load using magnetic levitation. Magnetic bearings support moving machinery without physical contact; for example, they can levitate a rotating shaft and permit relative motion with very low friction and no mechanical wear...
  
  s, where the axial thrust is supported on a magnetic field. This is used where very high speeds or very low drag is needed, for example the Zippe-type centrifuge
  Zippe-type centrifuge
  The Zippe-type centrifuge is a device designed to collect Uranium-235. It was developed in the Soviet Union by a team of 60 Austrian and German scientists captured after World War II, working in detention...
  
  .

They are commonly used in automotive, marine, and aerospace applications.

Thrust bearings are used in cars because the forward gears in modern car gearboxes use helical gears which, while aiding in smoothness and noise reduction, cause axial forces that need to be dealt with. The double helical or herringbone gear

Herringbone gear

A herringbone gear, also known as a double helical gear, is a special type of gear which is a side to side combination of two helical gears of opposite hands. Unlike helical gears they can sustain axial load smoothly...

 balances the thrust caused by normal helical gears.

One specific thrust bearing in an automobile is the clutch

Clutch

A clutch is a mechanical device which provides for the transmission of power from one component to another...

 "throw out" bearing, sometimes called the clutch release bearing.

Fluid-film thrust bearings were invented by Australian engineer George Michell

Anthony Michell

Anthony George Maldon Michell FRS was an Australian mechanical engineer of the early 20th century.-Early life:...

 who patented his invention in 1905. Michell bearings contain a number of sector-shaped pads, arranged in a circle around the shaft, and which are free to pivot. These create wedge-shaped regions of oil inside the bearing between the pads and a rotating disk, which support the applied thrust and eliminate metal-on-metal contact.

Michell's invention was notably applied to the thrust block

Thrust block

A thrust block, also known as a thrust box, is a specialised form of thrust bearing used in ships, to resist the thrust of the propellor shaft and transmit it to the hull.- Early thrust boxes :...

 in ships. The small size (one-tenth the size of old bearing designs), low friction and long life of Michell's invention made possible the development of more powerful engines and propellers. They were used extensively in ships built during World War I

World War I

World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...

, and have become the standard bearing used on turbine shafts in ships and power plants worldwide.

Thrust ball bearing

Thrust ball bearings consist of two precision chrome steel

Chrome steel

Chrome steel is one of a class of non stainless steels such as AISI 52100, En31, SUJ2, 100Cr6, 100C6, DIN 5401 which are used for applications such bearings, tools and drills.-Popular culture:...

 washer

Washer

Washer may refer to:People*Mal Washer, an Australian politician*Paul Washer, a Christian preacherOther*Washing machine*Washer *Washer Method, a mathematical formula for finding volume*Washer pitching, an outdoor game...

s (ring) and a ball

Ball (bearing)

Bearing balls are special highly spherical and smooth balls, most commonly used in ball bearings. The balls come in many different grades, as defined by the American Bearing Manufacturers Association , which defines the precision of the balls...

 complement spaced by bronze

Bronze

Bronze is a metal alloy consisting primarily of copper, usually with tin as the main additive. It is hard and brittle, and it was particularly significant in antiquity, so much so that the Bronze Age was named after the metal...

 retainer. They can be supplied with or without radius ball grooves in the rings. Thrust bearings are used under purely axial loads.

External links

• The MichellThrust Bearing: a low-friction bearing for thrust shafts (Powerhouse Museum
  Powerhouse Museum
  The Powerhouse Museum is the major branch of the Museum of Applied Arts and Sciences in Sydney, the other being the historic Sydney Observatory...
  
  website)