Foil bearings are self-generating, compliant hydrodynamics bearings. The compliant foils conform to the shape of the mating rotating shaft. During operation the shaft is supported on a thin film of self generated cushion of air (or gas). These bearings have demonstrated high load carrying capacity and good stability characteristics. A pair of foil journal bearings provide radial support and a pair of foil thrust bearings provide axial support.

A typical foil journal bearing is shown in the figure to the left. It contains a thin layer of top foils supported on corrugated foils. There is a small amount of preload between the shaft and the bearings. For low friction during lift-off and touch-down, the foils are coated with a solid film lubricant. During lift-off, air/gas is drawn between the shaft and the bearing and locally compressed. Due to hydrodynamic action, the shaft lifts off and floats on a cushion of air/gas. The self generated pressure on top foils provides support for the shaft while the corrugated foils provide the compliant feature of the bearing. The spring rate of the corrugated segments accommodate shaft expansion, shaft excursion and housing misalignment. The corrugated foils also provide a flow path for small amount of cooling air/gas. The corrugated bump foils also support the upper smooth foils while providing whirl suppression.

Similar to foil journal bearings, there are a pair of foil thrust bearings in the rotating machinery which support axial load. A typical thrust bearing is shown to the left. Principals of R&D Dynamics have developed foil journal bearings from 0.375 inch diameter to 4.50 inch diameter. They have developed foil thrust bearings from 0.80 inch diameter to 9.00 inch diameter.


Advantages of foil air/gas bearings are:
  • Increased reliability
  • No oil contamination
  • Higher speed capability
  • Increased performance
  • Higher and lower temperature
    capability (40K to 2500K)
  • No scheduled maintenance
  • Any process fluid can be used
  • High load capacity
  • High vibration and shock load capacity
  • Quieter operation
  • Lower lifecycle cost

    Additional References:
    Foil Air/Gas Bearing Technology ~ An Overview

    Foil Air Bearing Cleared to Land ~ Mechanical Engineering Magazine

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