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Designing with Air Bearings

 

Air Bearings allow designers to push the envelope on precision and high speed applications. Unlike contact roller bearings, air bearings utilize a thin film of pressurized air to provide a ‘zero friction’ load bearing interface between surfaces that would otherwise be in contact with each other. Being non-contact, air bearings avoid the traditional bearing-related problems of friction, wear, and lubricant handling, and offer distinct advantages in precision positioning and high speed applications.

The fluid film of the bearing is achieved by supplying a flow of air through the bearing itself to the bearing surface. Unlike traditional ‘orifice’ air bearings, New Way Air Bearings deliver the air through a porous medium to ensure uniform pressure across the entire bearing area. The design of the air bearing is such that, although the air constantly dissipates from the bearing site, the continual flow of pressurized air through the bearing is sufficient to support the working loads.

Air bearings are a natural choice for applications in coordinate measuring machines, precision machine tools, semiconductor wafer processing machines, and other clean room, high speed, and precision positioning environments.


Porous Media Technology

Broadly speaking there are two techniques for achieving the compensating effect in air bearings. Orifice compensation is traditionally the most widely used method, but porous surface compensation is rapidly emerging as the method of choice due to its many advantages and increasing availability.

In traditional orifice compensation the precisely sized orifices are strategically placed on the bearing and are often combined with grooves to distribute the pressurized air evenly across the bearing face. However, if the bearing face becomes scratched across a groove or near an orifice, the volume of air that escapes may be more than the orifice can supply, causing the bearing to crash even with normal air supply pressure. Rather than the small number of orifices of conventional air bearings, porous air bearings control the airflow across the entire bearing surface through millions of holes in the porous material (see figure). Because of this they are harder to clog and will still fly even after being severely scratched.

Even under normal operations, the air in an orifice air bearing loses pressure and creates pressure gradients in the air gap as it expands away from the orifice or groove. This is not an issue for porous air bearings where the air pressure remains almost uniform across the entire surface (see figure below).

Porous carbon has been found to be one of the best materials for this purpose, producing an ideal supply of uniform air pressure across the face of the bearing while automatically restricting and damping the air flow at the same time. The carbon surface also provides greater bearing protection if there is an air supply failure, and allows the bearings to be moved during air failure without damaging the support surface.


Application and Design Guide

This design resource provides in-depth information about New Way air bearings, design and application assistance, care and maintenance guidelines, and much more. Note: This is a large file, which takes longer to download than usual. Your patience is appreciated.


History of Air Bearings

1828

Wills Publishes Earliest Known Treatise
Rev. Wills publishes a work in the Cambridge Philosophical Society entitled “On the Pressure Produced on a Flat Surface When Opposed to a Stream of Air Issuing from an Orifice in a Plane Surface.”

1897

Kingsbury’s Experiments Highlight Inherent Difficulties
A. Kingsbury experiments with a 6”diameter journal bearing supported on externally pressurized air. The practical problems of matching bore and shaft geometry and size to achieve a consistent .0005” gap all the way around were and are a manufacturing challenge. Small gaps are required when using air because the viscosity is so low. Kingsbury finds that the higher viscosity of water or oil works better with the relatively large gaps that can be manufactured at that time.

1904

Westinghouse Receives Thrust Bearing Patent
G. Westinghouse receives a patent for an air thrust bearing used in a vertical steam turbine.

1950s and 1960s

US National Labs Lead the Way
Although obscure, air bearings are an important enabling technology in meeting the exacting needs of the defense department and the nuclear power industry. US National Labs is a leader in the application of air bearings to ultra-precision machine tools.

1960s

Porous Media Air Bearings Are Developed
Porous air bearings are developed, and have their genesis inside the National Labs.

1965

Air Bearings Revolutionize the Coordinate Measuring Machine
The Check Mate is the first CMM to employ air bearing technology, using a granite guide surface. Russ Shelton — known by some as the father of the CMM — used porous carbon air bearings on machines he built 40 years ago. Some of these machines are still in use today. This is because the air bearings provide straighter, frictionless motion. The smooth, silent operation is especially evident in the resolution of scanning or measurement on the fly-type machines.

1970s

IBM Commercializes Air Bearing Technology
Air bearing technology is commercialized when IBM uses air bearing spindles to produce large hard disc drives. The hard disc drive industry still relies almost exclusively on air bearing spindles for its spin stands.

1982

Sheffield Develops Its Own Air Bearings for Its CMMs
Sheffield Corporation (now Giddings & Lewis Metrology) — a builder of CMMs — is one of the few companies to develop its own porous media air bearings. The company considers the technology an important technical advantage. Originally employed on the Apollo Machine in 1982, Giddings & Lewis Metrology continues to use porous media air bearings today.

1984

The First Standard Air Bearing Product Line Is Introduced
Aeolus Air Bearings – the predecessor to New Way Air Bearings — offers the first standard air bearing product line. For the first time, customers are able to choose from five sizes of inexpensive, readily-available, simple-to-employ air bearings.

1987

Age of the Air Bearing Ushered In As Starrett Uses Commercial Products On Its CMMs
The L.S. Starrett Co. builds a rolling-element bearing CMM when it redesigns its machines to employ the advantages of air bearing technology. They elect to purchase New Way® Porous Media™ air bearings rather than developing their own. Today they continue to purchase New Way air bearings.