A thrust bearing is a particular type of rotary bearing. Like other bearings they permanently rotate between parts, but they are designed to support a predominantly axial load.
Thrust bearings come in several varieties.
Thrust bearings are commonly used in automotive, marine, and aerospace applications. They are also used in the main and tail rotor blade grips of RC (radio controlled) helicopters.
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.
Thrust bearings are also used with radio antenna masts to reduce the load on an antenna rotator.
One kind of thrust bearing in an automobile is the clutch "throw out" bearing, sometimes called the clutch release bearing.[clarification needed]
Fluid-film thrust bearings were invented by Albert Kingsbury, who discovered the principle in the course of bearing and lubrication investigations commencing in 1888 while a student. His first experimental bearing was tested in 1904. He filed for a patent in 1907, and it was granted in 1910. The first Kingsbury bearing in hydroelectric service, one of its major applications, was installed at the Holtwood Generating Station in 1912. It remains in full use today.
Thrust bearings were independently invented by Australian engineer George Michell (pronounced Mitchell) who patented his invention in 1905.
Fluid thrust 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.
Kingsbury and Michell's invention was notably applied to the thrust block in ships. The small size (one-tenth the size of old bearing designs), low friction and long life of Kingsbury and Michell's invention made possible the development of more powerful engines and propellers. They were used extensively in ships built during World War I, and have become the standard bearing used on turbine shafts in ships and power plants worldwide. (See also Michell/Kingsbury tilting-pad fluid bearings)
Today thrust bearings continue to play an essential role in rotating equipment like expanders, pumps, and gas or steam turbines or compressors. In addition to the traditional babbitt bearings which were used since the early 20th century, new materials for the thrust pads have come into use. For example Bronze and Copper-Chromium are commonly used to improve the bearings performance.