Gas Bearings

Space Electronics manufactures precision gas bearings (also called air bearings, although they can also function with nitrogen). We specialize in the manufacturing of large hemispherical and spherical gas bearings.

Typical Applications:

Providing a well defined pivot and allowing friction-free rotation, these air bearings offer ideal space simulating platforms for testing attitude control systems.

This video shows a spherical gas bearing being tested with a 1000 lb. load.

Below are two typical examples of systems we may provide to you:

Spherical Gas Bearing

(see picture above). Spherical bearings allow 360 degrees rotation about two axes (one vertical axis and one horizontal axis).

They also allow rotation about the third axis. Rotation about this third axis is limited by the shaft that goes through the center of the sphere and provides a mounting pattern for the payload. Rotation up to 30 degrees is common for these systems.

Most of these spherical bearings are custom made to clients' specifications.

Hemispherical Gas Bearing for Space Simulators

The system shown here has 360 degree rotation around the vertical axis and 5 degree tilt capability.

Most of our standard systems allow +/- 10 to 30 degrees of tilt. More tilt can be obtained with custom designs.

These hemispherical systems are mainly used to test attitude control systems. Great care must be used when mounting a payload onto a hemispherical bearing. The center of gravity of the moving assembly must be located below the center of rotation for the system to remain stable. Our air bearings can be equipped with optional tilt and uplift stops to prevent capsizing.

Highlighted Benefits

Gas bearings present a number of advantages over other types of bearings:

No friction Since the air bearing is non-contacting, the only friction is the almost un-measurably shear force in an air film. For example, a 20,000 pound balanced rotor can be turned by applying less than 1 gram force to a 10 inch moment arm. There is no "stick-slip", allowing almost perfectly smooth slow speed motion.

No wear Because they are non-contacting, air bearings never wear out.

5 micro-inch precision Air bearings can be made with a precision which is 10 or 100 times better than any other type of bearing. The motion of an air bearing follows the average of the shape of the rotor, so that the precision of motion is better than the precision of the surface of the bearing. Since there are no balls or rollers, the motion is completely smooth..

Outstanding stiffness for small deflections Most engineers visualize an air bearing as being like a hovercraft, and they erroneously conclude that a bearing which floats on air cannot be very stiff. Actually these gas bearings are many times stiffer than a ball or roller bearing. Sapphire orifices within the bearing gap control the pressure in a film of air which is only 0.0003 inches thick. As a load is applied to displace the bearing rotor or slider, the gap decreases very slightly on one side, reducing the flow of air through the adjacent sapphire orifice. This results in a pressure increase in the gap on this side which pushes the rotor back to its original position. In essence, the air bearing is a servomechanism with closed loop control, and maintains a uniform gap in spite of external forces that may be applied. This results in bearing stiffness of millions of pounds per inch for small deflections. Stiffness is linear and does not change with temperature. In contrast, ball or roller bearings have almost no stiffness unless heavily preloaded. The stiffness of a ball bearing is not linear, and varies considerably with temperature.

No bearing instability Because air bearings have closed loop control, poorly designed bearings can exhibit a form of instability known as "pneumatic hammer". Space Electronics bearings are designed for optimum stability. Our air bearings remain stable over a wide range of loads and pressures. There is no need to fine tune the gas pressure with our bearings!

Operate in dirty as well as clean environments You might think that such a high precision bearing would be sensitive to dirt or adverse environment, but just the opposite is true. The gap between rotor and stator is larger in an air bearing than it is in a ball bearing, and the flow of air constantly expels dirt from this gap. Therefore, air bearings can be operated in environments which are too dirty for a ball bearing to survive.

Not damaged by shock loads Air bearing are also more rugged than any other type of bearing. Shock loads will flatten or brinell the balls in a ball bearing, but a gas bearing has no point contact and can usually withstand loads 10 or 100 times greater than its load rating.

No damage due to loss of air Most air bearings can be damaged if air pressure is lost, because this results in metal to metal contact. Gas bearings manufactured by Space Electronics minimize this problem. We make the rotor of hard anodized aluminum (which has a hardness in the range of sapphire), and the stator is lined with a bearing material that is self lubricating. If desired, we can provide a backup emergency air tank, which supplies high pressure air during deceleration of a bearing which is spinning at high speeds.

Motor forces An improperly designed air bearing will begin spinning on its own with no torque applied externally. Space Electronics air bearings are manufactured with near perfect symmetry of air flow, so this does not occur.

No bearing noise Ball and roller bearings exhibit a vibration or "noise" when rotated. Gas bearings do not have this problem, making them ideal for use in precision machines or instruments.

More than one direction of freedom A cylindrical gas bearing can be used simultaneously for a rotating or a sliding bearing. Porous bronze sleeve bearings have this same advantage, but their friction is too great for many applications. Ball or roller bearings are not capable of multiple modes of freedom.

Corrosion resistance Air bearings are more resistant to corrosion than any other type of bearing. The constant flow of air also serves to dry the bearing.

Clean air required Air bearings require a source of clean dry air which does not contain oil. Gas bearings typically operate in a pressure range from 30 PSI to 120 PSI. Space Electronics manufactures a variety of compressor-dryers which are ideal for this application. Air bearings can also be operated from compressed dry nitrogen.

Space Electronics Gas Bearings are custom designed to meet the specific needs of each individual application.


 

Air bearings

Ball or Roller Bearings

Runout

As little as 1 micro inch

More than 50 micro inch

Small deflection stiffness

1 million lb/inch or more

Depends on preload and can be lower than 1000 lb/inch

Wear

None

Depends on unbalance, preload and speed

Resistance to dirt

Excellent

Poor

Stick-slip at very low speeds

No

Yes

Friction

Typically less than 0.01 lb-in

Varies with preload and temperature; typical spindle is between 1 lb-in and 50 lb-in

Bearing noise

Un-measurably small

Significant for critical applications

Resistance to shock load

Excellent

Poor

Sensitivity to temperature changes

Operates over wide range of temperatures

Sudden temperature changes can cause bearing to seize; radial stiffness will change dramatically due to preload change


Gas bearings are better than ball or roller bearings in every way!

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