How Foil Bearings Stack Up to Other Types of Bearings
| Gas/Air Foil Bearing | Oil Bearing (Sleeve, Tilting Pad) | Rolling Element Bearing | Active Magnetic Bearing | |
|---|---|---|---|---|
| Maximum Operating Speed at Bearing Surface (Bore) for Radial Bearing | Essentially unlimited, 500 to 740 ft/s (150 to 225 m/s) is fairly typical | Generally 250 to 350 ft/s or less (75 to 105 m/s) | 1,000,000 DN (bore in mm x RPM) for typical applications, 3,000,000 DN for some aerospace applications. Equal to a surface speed of 170 to 515 ft/s (52 to 157 m/s) |
590 ft/s for typical materials,650 ft/s for special alloys (180 to 200 m/s) |
| Minimum Required Operating Speed | Yes, application dependent | Yes, application dependent | None | None |
| Typical Continuous Load Capacity and Typical Projected Area Loads | Low to moderate | Potentially very high | Moderate to high | Low to moderate |
| Short term overload capability | Varies, possibly 2 to 3 times static | Substantial | Good | Limited, backup bearings generally required |
| Bearing Operating Temperature Range | Cryogenic to 1200+ F (650+ C) | Varies with construction and lubricant, but most babbitt surfaced industrial bearings operate in the range of 90 to 180 F (32 to 82 C), and alarm by 250 F (120 C) | -20 to 450 F (-30 to 230 C) | -300 to 1000 F (-180 to 540 C) claimed by developers |
| Power Loss | Radial very low Thrust moderate |
Can be significant | Generally low to moderate | Generally very low |
| Oil Free? | Yes | No | No | Yes (although backup bearings could be grease lubricated) |
| Misalignment Capability | Low to moderate | Moderate, depends on construction | Very low (highly loaded angular contact) to moderate (spherical roller) | Moderate |
| Auxiliary Systems | Source of a limited amount of low pressure "cooling" air (although the actual temperature of this air could be very high in some high temperature applications) | Pumps, coolers, filters | Nothing for grease lubricated bearings, ranging to pumps, filters, etc. for oil-jet lube at high speeds and loads | Control system electronics, auxiliary bearings, generally some amount of cooling air |
| Radial Envelope Requirement | Length in range of 0.5 to 2x shaft diameter, Bearing housing OD in range of 1.25 to 2 times diameter | Length in range of 0.5 to 2x shaft diameter, OD in range of 1.25 to 2 times diameter Plus lube oil system |
Length in range of 0.2 to 0.5x shaft diameter, OD in range of 1.5 to 2 times diameter Plus lube oil system |
Length in range of 1 to 2x shaft diameter, OD in range of 1.5 to 4 times diameter Plus electronics if external |
| Weight | Generally the lightest option | Generally heavy when pumps, filters, piping etc considered along with the actual bearings | Relatively light | Moderate including electronics |
| Stiffness | Low | Moderate to high | High | Depends on tuning, generally are tuned soft |
| Damping | Low to moderate | Generally high | Very low | Moderate to high depending on tuning and system dynamics |
| Shock Tolerance | Good | Very good | Moderate | Can be poor |
What Makes Xdot Air and Process Gas Lubricated Foil Bearings a Cut Above the Rest
At Xdot Engineering and Analysis, we take our foil bearings all the way from development, through design to production. Historically, teams who wanted to create machines using foil bearings found themselves up against prohibitive cost, manufacturing, and design challenges. We listened to their concerns and developed our unique, high-performance design to address them.
But we don't stop there. When you choose Xdot for your Air and Process Gas Lubricated Foil Bearings, you get:
Stock sizing.
We are developing a set of stock "frame" sizes that allow us to efficiently customize a bearing to meet the specific needs of new and existing machines.
Custom sizing.
If our stock sizes don't fit your needs, we can produce a custom-sized bearing. Our hardware experience is backed-up with analytical capability so that we get it right the first time, not after a costly build-and-bust development.
Rotordynamic and integration help.
We work with your team to ensure that the overall system is properly designed to work well with foil bearings.
Help developing new applications.
We can assist you with everything from performing independent assessments, to lending subject expertise as a team member, to assembling a team and leading prototype development projects. If you require a more extensive test program, we can leverage our test-rig experience and infrastructure to help ensure a healthy balance of risk versus cost.
If you are planning a new machine and want to consider foil bearings, we encourage you to contact us early in the design process. We can help your team, or subcontract designer, make the most efficient choices and save you time and money down the line.
Get in touch with us to learn more.