Benutzer:Dittum/Folienlager

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Foil-air bearing
A foil-air bearing for the core rotor shaft of an aircraft turbine engine.

A foil 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.

Development

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
Foil Bearing
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.
Load capacity against rotation speed, for Gen I and Gen III bearings

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]

Applications

Turbomachinery is the most common application because foil bearings operate at high speed.[6] The main advantage of foil bearings is the elimination of the oil systems required by traditional bearing designs. Other advantages are:

  • Higher efficiency, due to a lower heat loss to friction; instead of fluid friction, the main source of heat is parasitic drag
  • Increased reliability
  • Higher speed capability
  • Quieter operation
  • Wider operating temperature range (40–2,500 K)
  • High vibration and shock load capacity
  • No scheduled maintenance
  • No external support system
  • Truly oil free where contamination is an issue
  • Capable of operating above critical speed

Areas of current research are:

  • Higher load capacity
  • Improved damping
  • Improved coatings

The main disadvantages are:

  • Lower capacity than roller or oil bearings
  • Wear during start-up and stopping
  • High speed required for operation

See also

References

Vorlage:Reflist

External links


[[Category:Bearings (mechanical)]] [[Category:Gas turbine technology]]

  1. ↑ Giri L. Agrawal: Foil Air/Gas Bearing Technology — An Overview. In: American Society of Mechanical Engineers (Hrsg.): Publication 97-GT-347. 1997.
  2. ↑ Giri L. Agrawal: Foil Bearings Cleared to Land Archiviert vom Original am 15 April 2016. 1978-1980, Nr. 120, July 1998.
  3. ↑ Scholer Bangs: Foil Bearings Help Air Passengers Keep their Cool. In: Power Transmission Design. February 1973.
  4. ↑ Application of Air Bearings to High-Speed Turbomachinery. In: Society of Automotive Engineers (Hrsg.): Technical Paper No. 700720. September 1970. 700720.
  5. ↑ Hooshang Heshmat: Major Breakthrough in Load Capacity, Speed and Operating Temperature of Foil Thrust Bearings. In: American Society of Mechanical Engineers (Hrsg.): Technical Paper No. WT2005-63712. September 2005. WT2005-63712.
  6. ↑ The Quest for Oil-Free Gas Turbine Engines. In: SAE (Hrsg.): SAE Technical Papers. 2006. 2006-01-3055.
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