Thrust bearing

Family of rotary bearings designed to support axial loads

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A thrust ball bearing

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.[1]

Thrust bearings come in several varieties.

• Thrust ball bearings, composed of bearing balls supported in a ring, can be used in low-thrust applications where there is little axial load.
• Cylindrical thrust roller 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 which is higher than with ball bearings.
• Tapered roller thrust bearings 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 greater thrust loads than the ball type due to the larger contact area, but are more expensive to manufacture.

A spherical roller thrust bearing

• Spherical roller thrust bearings use asymmetrical rollers of spherical shape, rolling inside a house washer with a raceway with spherical inner shape. They can accommodate combined radial and axial loads and also accommodate misalignment of the shafts. They are often used together with radial spherical roller bearings. Spherical roller thrust bearings offer the highest load rating density of all thrust bearings.

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• Fluid bearings, where the axial thrust is supported on a thin layer of pressurized liquid&#;these give low drag.

Miba fluid film thrust bearing

• Magnetic bearings, 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.

Thrust bearings are commonly used in automotive, marine,[3] 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.[4][clarification needed]

Fluid film thrust bearings

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Exploded view of a Michell type thrust bearing. Note, each sector shaped pad can pivot on the ridges on the lower plate.

Fluid-film thrust bearings were invented by Albert Kingsbury, who discovered the principle in the course of bearing and lubrication investigations commencing in while a student. His first experimental bearing was tested in . He filed for a patent in , and it was granted in .[5] The first Kingsbury bearing in hydroelectric service, one of its major applications, was installed at the Holtwood Generating Station in . It remains in full use today.

Thrust bearings were independently invented by Australian engineer George Michell (pronounced Mitchell) who patented his invention in .

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. [6]

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Citations

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References

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• Simmons, J.E.L.; Henderson, N. (). "Developments in Naval Thrust Bearings". Journal of Naval Engineering. 32 (2): 344&#;353.

Thrust roller bearings are compact bearings designed to rotate between parts and reduce friction. They&#;re built to handle axial loads in both vertical and horizontal shafts, and help prevent shafts from drifting. Typically, they are contained in a two-piece cage which ensures that the rollers glide accurately.

In this article, we&#;ll discuss several aspects of thrust roller bearings, including their design, typical applications, and advantages.

Types of Thrust Roller Bearings

There are two major types of thrust roller bearings. The primary difference between the two is the roller element that is used in the design.

• Cylindrical Thrust Roller Bearings: As the name suggests, cylindrical thrust roller bearings feature cylindrical rollers. In general, this type of thrust bearing offers good carrying capacity, but doesn&#;t bear the load that spherical bearings do. 
• Spherical Thrust Roller Bearings: Featuring spherical rollers, this thrust bearing has the highest load rating density among thrust bearings. They&#;re self-aligning and thus accommodate misalignment. They also have a low coefficient of friction.

How Do They Work?

All thrust bearings share a similar purpose&#;to carry axial loads with minimal friction.

As previously mentioned, the rollers in thrust bearings can be spherical or cylindrical. The rolling elements are contained within cages and separated by consistently spaced pockets. When the elements roll, they are confined to raceways along a single axis. This prevents them from sliding out of position and causing bearing failure. The cages themselves don&#;t bear any load; their function is to keep the rollers in place.

Components

Thrust roller bearings are usually integrated (or unitized) and have three important components.

• Rollers: These may be cylindrical or spherical. They are most commonly made of stainless steel or ceramic.
• Cage: The cage holds the rollers. They are usually stainless steel or brass, depending on the application.
• Inner & Outer Rings: When aligned, the inner and outer rings form what&#;s called a raceway, which the rollers travel on. 

Industry Applications & Uses

Bearings in general have a wide array of industry uses. Thrust roller bearings find a lot of use in the automotive industry, but they&#;re also commonly used in marine, aerospace, agriculture, petroleum, and medical equipment industries.

Common applications for thrust roller bearings include drivetrains, machine tools, compressors, hydraulic pumps and all kinds of industrial machinery, especially machines that involve rotation. Essentially, they&#;re useful for any application that requires a compact bearing with a high axial load capacity.

Advantages

• Compact Design: The cross-section height of thrust roller bearings is similar to that of conventional thrust washers.
• Economical: The simplicity of design is favorable for mass production. It also means they&#;re readily available in a wide assortment of choices.
• Ease of Use: Integrated and cage-roller assemblies make them simple to mount in small spaces. Separable design allows the interchanging of components, such as the inner ring.
• Wear Resistance: The surface-hardened cage provides high rigidity along with wear resistance.

Order Custom Thrust Roller Bearings from Universal Bearings

Which thrust roller bearing is right for your application? If you have questions, turn to Universal Bearings. Founded in , we&#;re an ISO -, ISO -, and IATF -certified manufacturer specializing in producing custom needle roller bearings. Contact us today to learn more about our capabilities or to schedule a design consultation.