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{{Short description|Type of air bearing}} |
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[[Image:Foilbearing.jpg|thumb|A foil-air bearing for the core rotor shaft of an aircraft turbine engine.| alt= Foil-air bearing ]] |
[[Image:Foilbearing.jpg|thumb|A foil-air bearing for the core rotor shaft of an aircraft turbine engine.| alt= Foil-air bearing ]] |
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''' |
A'''foil bearing''', also known asa '''foil-air bearing''', is a type of [[fluid bearing#Air bearings|air bearing]]. A shaft is supported by a compliant, spring-loaded [[foil (metal)|foil]] journal lining. Once the shaft is spinning fast enough, the working [[fluid]] (usually [[air]]) pushes the foil away from the shaft so that no contact occurs. The shaft and foil are separated by the air's high pressure, which is generated by the rotation that pulls gas into the bearing via viscosity effects. The high speed of the shaft with respect to the foil is required to initiate the air gap, and once this has been achieved, no wear occurs. Unlike aerostatic or [[hydrostatic bearings]], foil bearings require no external pressurisation system for the working fluid, so the hydrodynamic bearing is self-starting. |
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==Development== |
==Development== |
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[[Image:FoilBearing.png|right|thumb|Foil Bearing | alt= Sectional diagram of a foil bearing, showing the component parts (inner, moving outwards) of the shaft journal, a smooth top foil, the bump foil (both foils joined) and finally the bearing housing |
[[Image:FoilBearing.png|right|thumb|Foil Bearing | alt= Sectional diagram of a foil bearing, showing the component parts (inner, moving outwards) of the shaft journal, a smooth top foil, the bump foil (both foils joined) and finally the bearing housing ]] |
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[[Image:Foil Bearing Capacity.png|thumb| Load capacity against rotation speed, for Gen I and Gen III bearings | alt= Graph of load capacity against speed for first and third generation bearings |
[[Image:Foil Bearing Capacity.png|thumb| Load capacity against rotation speed, for Gen I and Gen III bearings | alt= Graph of load capacity against speed for first and third generation bearings: The load is proportional to rotation speed, bearing length, and the square of shaft diameter. Third-generation bearings carry about three times as much load as first-generation ones. ]] |
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Foil bearings were first developed in the late 1950s by AiResearch Mfg. Co. of the [[Garrett AiResearch|Garrett Corporation]] using independent [[R&D]] funds to serve military and space applications.<ref > |
Foil bearings were first developed in the late 1950s by AiResearch Mfg. Co. of the [[Garrett AiResearch|Garrett Corporation]] using independent [[R&D]] funds to serve military and space applications.<ref >{{cite journal |
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|author=Giri L. Agrawal |
|author=Giri L. Agrawal |
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|title=Foil Air/Gas Bearing Technology — An Overview |
|title=Foil Air/Gas Bearing Technology — An Overview |
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|url=http://www.rddynamics.com/foil-97-gt-347.pdf |
|url= http://www.rddynamics.com/pdfs/foil-97-gt-347.pdf |
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|publisher=[[American Society of Mechanical Engineers]] |
|publisher=[[American Society of Mechanical Engineers]] |
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|journal=Publication 97-GT-347 |
|journal=Publication 97-GT-347 |
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|year=1997 |
|year=1997 |
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}}</ref><ref >{{cite |
}}</ref><ref >{{cite magazine |
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|author=Giri L. Agrawal |
|author=Giri L. Agrawal |
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|title=Foil Bearings Cleared to Land |
|title=Foil Bearings Cleared to Land |
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|magazine=Mechanical Engineering |
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|url=http://www.rddynamics.com/Foil-Bearings-Cleared-to-Land.pdf |
|url=http://www.rddynamics.com/pdfs/Foil-Bearings-Cleared-to-Land.pdf |
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|publisher=[[memagazine]] |
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|volume=120 |
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|issue=7 |
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|date=July 1998 |
|date=July 1998 |
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|archive-url = https://web.archive.org/web/20160415030128/http://www.rddynamics.com/pdfs/Foil-Bearings-Cleared-to-Land.pdf |
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| ⚫ | |||
|archive-date=15 April 2016 |
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| ⚫ |
}}</ref> They were first tested for commercial use in [[United Airlines]] [[Boeing 727]] and [[Boeing 737]] cooling turbines in the early |
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|via=R&D Dynamics |
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| ⚫ | }}</ref> They were first tested for commercial use in [[United Airlines]] [[Boeing 727]] and [[Boeing 737]] cooling turbines in the early and mid-1960s.<ref >{{cite journal |
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|author=Scholer Bangs |
|author=Scholer Bangs |
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|title=Foil Bearings Help Air Passengers Keep their Cool |
|title=Foil Bearings Help Air Passengers Keep their Cool |
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|journal=Power Transmission Design |
|journal=Power Transmission Design |
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|date=February 1973 |
|date=February 1973 |
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}}</ref> Garrett AiResearch [[air cycle machine]] foil bearings were first installed as original equipment in 1969 in the [[DC-10]]'s [[Environmental Control System|environmental control systems]]. Garrett AiResearch foil bearings were installed on all US military aircraft to replace existing oil-lubricated rolling-contact bearings. The ability to operate at [[cryogenic]] gas temperatures |
}}</ref> Garrett AiResearch [[air cycle machine]] foil bearings were first installed as original equipment in 1969 in the [[DC-10]]'s [[Environmental Control System|environmental control systems]]. Garrett AiResearch foil bearings were installed on all US military aircraft to replace existing oil-lubricated rolling-contact bearings. The ability to operate at [[cryogenic]] gas temperatures and at very high temperatures gave foil bearings many other potential applications.<ref >{{cite journal |
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| |
|author1=M. A. Barnett |author2=A. Silver |
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|title=Application of Air Bearings to High-Speed Turbomachinery |
|title=Application of Air Bearings to High-Speed Turbomachinery |
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|publisher=[[Society of Automotive Engineers]] |
|publisher=[[Society of Automotive Engineers]] |
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|journal=Technical Paper No. 700720 |
|journal=Technical Paper No. 700720 |
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|series=SAE Technical Paper Series |
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|id=700720 |
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|date=September 1970 |
|date=September 1970 |
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| ⚫ | |||
| ⚫ |
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|doi=10.4271/700720 |
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| ⚫ | |url=http://www.sae.org/servlets/productDetail?PROD_TYP=PAPER&PROD_CD=700720 |
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}}</ref> |
}}</ref> |
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Current-generation foil bearings with advanced coatings have greatly exceeded the limitations of earlier designs. |
Current-generation foil bearings with advanced coatings have greatly exceeded the limitations of earlier designs. Antiwear coatings exist that allow over 100,000 start/stop cycles for typical applications.<ref >{{cite journal |
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|first=Hooshang |last=Heshmat |
|first=Hooshang |
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|last=Heshmat |
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| |
|author-link=Hooshang Heshmat |
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|title=Major Breakthrough in Load Capacity, Speed and Operating Temperature of Foil Thrust Bearings |
|title=Major Breakthrough in Load Capacity, Speed and Operating Temperature of Foil Thrust Bearings |
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|publisher=[[American Society of Mechanical Engineers]] |
|publisher=[[American Society of Mechanical Engineers]] |
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|date=September 2005 |
|date=September 2005 |
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|url=http://store.asme.org/product.asp?catalog_name=Conference%20Papers&category_name=%26nbsp%3b_WTC2005T-5&product_id=WTC2005-63712 |
|url=http://store.asme.org/product.asp?catalog_name=Conference%20Papers&category_name=%26nbsp%3b_WTC2005T-5&product_id=WTC2005-63712 |
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|access-date=2006-09-25 |
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| ⚫ | |||
|archive-url=https://web.archive.org/web/20080214192746/http://store.asme.org/product.asp?catalog_name=Conference%20Papers&category_name=%26nbsp%3B_WTC2005T-5&product_id=WTC2005-63712 |
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|archive-date=2008-02-14 |
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| ⚫ | |||
==Applications== |
==Applications== |
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[[Turbomachinery]] is the most common application because foil bearings operate at high speed.<ref >{{cite journal |
[[Turbomachinery]] is the most common application because foil bearings operate at high speed.<ref >{{cite journal |
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|author1=R. M. "Fred" Klaass |author2=Christopher DellaCorte |
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|title=The Quest for Oil-Free Gas Turbine Engines |
|title=The Quest for Oil-Free Gas Turbine Engines |
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|publisher=[[Society of Automobile Engineers|SAE]] |
|publisher=[[Society of Automobile Engineers|SAE]] |
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|journal=SAE Technical Papers |
|journal=SAE Technical Papers |
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|id=2006-01-3055 |
|id=2006-01-3055 |
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|year=2006 |
|year=2006 |
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|url=http://www.sae.org/technical/papers/2006-01-3055 |
|url=http://www.sae.org/technical/papers/2006-01-3055 |
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|access-date=2007-08-18 |
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}}</ref> The main advantage of foil bearings is the elimination of the [[oil]] systems required by traditional bearing designs. Other advantages are: |
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|archive-url=https://web.archive.org/web/20070930201550/http://www.sae.org/technical/papers/2006-01-3055 |
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|archive-date=2007-09-30 |
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}}</ref> |
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Commercial applications in production include microturbines,<ref >{{cite conference |
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|author=Lubell, D. |author2=DellaCorte, C. |author3=Stanford, M. |
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|book-title=Proceedings of the ASME Turbo Expo 2006: Power for Land, Sea, and Air |
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|volume=5: Marine; Microturbines and Small Turbomachinery; Oil and Gas Applications; Structures and Dynamics, Parts A and B |
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|title=Test Evolution and Oil-Free Engine Experience of a High Temperature Foil Air Bearing Coating |
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|publisher=[[American Society of Mechanical Engineers|ASME]] |
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|id=GT2006-90572 |
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|year=2006 |
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|pages=1245–1249 |
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|doi=10.1115/GT2006-90572 |
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|isbn=0-7918-4240-1 |
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}}</ref> fuel cell blowers,<ref>{{cite web | url=https://www.turbomachinerymag.com/view/compressors-with-foil-bearings-applied-in-fuel-cells | title=Compressors with foil bearings applied in fuel cells | date=13 April 2020 }}</ref> and air cycle machines. The main advantage of foil bearings is the elimination of the [[oil]] systems required by traditional bearing designs. Other advantages are: |
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* Higher efficiency, due to a lower heat loss to friction; instead of [[friction|fluid friction]], the main source of heat is [[parasitic drag]] |
* Higher efficiency, due to a lower heat loss to friction; instead of [[friction|fluid friction]], the main source of heat is [[parasitic drag]] |
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* Increased reliability |
* Increased reliability |
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==See also== |
==See also== |
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* |
* {{annotated link|Fluid bearing}} |
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* |
* {{annotated link|Tribology}} |
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==References== |
==References== |
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{{reflist| |
{{reflist| |
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<ref> Some early history is reported in Giri L. Agrawal (1997),『http://www.rddynamics.com/pdfs/foil-97-gt-347.pdf — An Overview』(PDF). Publication 97-GT-347. American Society of Mechanical Engineers.</ref> |
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}} |
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==External links== |
==External links== |
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*[http://www.nasa.gov/centers/glenn/about/fs14grc.html NASA Glenn Research Center "Creating a Turbomachinery Revolution"] |
*[http://www.nasa.gov/centers/glenn/about/fs14grc.html NASA Glenn Research Center "Creating a Turbomachinery Revolution"] {{Webarchive|url=https://web.archive.org/web/20160304105630/http://www.nasa.gov/centers/glenn/about/fs14grc.html |date=2016-03-04 }} |
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*[http://www.grc.nasa.gov/WWW/StructuresMaterials/TribMech/ NASA Tribology & Mechanical Components Branch] |
*[https://web.archive.org/web/20090413134503/http://www.grc.nasa.gov/WWW/StructuresMaterials/TribMech/ NASA Tribology & Mechanical Components Branch] |
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*[http://www.rddynamics.com R&D Dynamics Corporation Foil bearing supported high speed turbomachinery] |
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*[http://www.uta.edu/mae/turboenergy/research.html Turbomachinery and Energy System Laboratory at UTA] |
*[http://www.uta.edu/mae/turboenergy/research.html Turbomachinery and Energy System Laboratory at UTA] {{Webarchive|url=https://web.archive.org/web/20160305133258/http://www.uta.edu/mae/turboenergy/research.html |date=2016-03-05 }} |
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*[http://www. |
*[http://www.mohawkinnovative.com/products/compliant-foil-bearings/ Mohawk Innovative Technology, Inc.] |
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*[http://rotorlab.tamu.edu/ |
*[https://web.archive.org/web/20110720055621/http://rotorlab.tamu.edu/Tribgroup/ Tribology Group at Texas A&M] |
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*[http://ubisa.kist.re.kr/Teams/ubisa/afb.htm Korean Institute for Science and Technology KIST] |
*[https://web.archive.org/web/20080726082137/http://ubisa.kist.re.kr/Teams/ubisa/afb.htm Korean Institute for Science and Technology KIST] |
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*[https://web.archive.org/web/20100707181721/http://www.cerom.lsu.edu/projects_foil.htm Center for Rotating Machinery at LSU] |
*[https://web.archive.org/web/20100707181721/http://www.cerom.lsu.edu/projects_foil.htm Center for Rotating Machinery at LSU] |
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*[https://oilfreemachinery.com/bearing-tech Oil-Free Machinery, LLC] |
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Afoil bearing, also known as a foil-air bearing, is a type of air bearing. A shaft is supported by a compliant, spring-loaded foil journal lining. Once the shaft is spinning fast enough, the working fluid (usually air) pushes the foil away from the shaft so that no contact occurs. The shaft and foil are separated by the air's high pressure, which is generated by the rotation that pulls gas into the bearing via viscosity effects. The high speed of the shaft with respect to the foil is required to initiate the air gap, and once this has been achieved, no wear occurs. Unlike aerostatic or hydrostatic bearings, foil bearings require no external pressurisation system for the working fluid, so the hydrodynamic bearing is self-starting.
Foil bearings were first developed in the late 1950s by AiResearch Mfg. Co. of the Garrett Corporation using independent R&D funds to serve military and space applications.[1][2] They were first tested for commercial use in United Airlines Boeing 727 and Boeing 737 cooling turbines in the early and mid-1960s.[3] Garrett AiResearch air cycle machine foil bearings were first installed as original equipment in 1969 in the DC-10's environmental control systems. Garrett AiResearch foil bearings were installed on all US military aircraft to replace existing oil-lubricated rolling-contact bearings. The ability to operate at cryogenic gas temperatures and at very high temperatures gave foil bearings many other potential applications.[4]
Current-generation foil bearings with advanced coatings have greatly exceeded the limitations of earlier designs. Antiwear coatings exist that allow over 100,000 start/stop cycles for typical applications.[5]
Turbomachinery is the most common application because foil bearings operate at high speed.[6] Commercial applications in production include microturbines,[7] fuel cell blowers,[8] and air cycle machines. The main advantage of foil bearings is the elimination of the oil systems required by traditional bearing designs. Other advantages are:
Areas of current research are:
The main disadvantages are:
