Here are some examples of how foil bearings might fit candidate applications. All loads are projected area loads (length x width for radial).
Common Uses of Foil Bearings
| Item | Lower Risk | More Challenging |
|---|---|---|
| Free-free undamped critical speeds | All well above maximum operating speed | One or more below operating speed |
| Shaft surface speed over normal operating speed range at radial bearing location for "reasonable" shaft configuration | 500 to 740 ft/s (150 to 225 m/s) | Less than 100 ft/s (30 m/s) More than 1000 ft/s (305 m/s) |
| Startup load for "reasonable" sized radial and thrust bearings | Less than 5 psi (34 kPa) | More than 5 psi (34 kPa) |
| Operating static + dynamic load for "reasonable" sized radial bearing (including off design) * | Less than 20 psi (140 kPa) | More than 50 psi (340 kPa) |
| Operating static + dynamic load for "reasonable" sized thrust bearing (including off design) * | Less than 15 psi (100 kPa) | More than 35 psi (240 kPa) |
| Available starting torque | High | Low |
| Damping required for stability and reasonable response* | Low | High |
| Bearing operating temperature | Less than 400 F (200 C) | More than 700 F(370 C) |
| Bearing compartment pressure | Near atmospheric | Sub atmospheric or very high pressure |
| Operating fluid | Reasonably clean, dry air | Very dirty air Occasional liquid present |
*Ambient air, machines that operate at higher pressures or with higher viscosity fluids can be a significant exception to these guidelines
Need more information? Contact us today to learn more about how Xdot Air and Process Gas Lubricated Foil Bearings can help you design smaller, faster, simpler, machines to meet your application’s needs.