Air bearings are bearings with shaft and bearing bush separated by a thin air layer. In contrast to traditional rolling element bearings this air layer allows an almost friction-free movement, even at high speeds. Additionally, the air bearing is compensating the deviations caused at the surface of the bearing component during the manufacturing process by one scale.
Compared to hydrostatic or hydrodynamic bearings, the positive thermal behaviour of air bearings is caused by a factor 1000 lower viscosity of air compared to oil. Furthermore, air is available in almost every environment and the air exhausting from the air bearing does not require further treatment.
Operating principle: Static air bearing Two types of bearings are distinguished: the static and the dynamic air bearing.
The dynamic air-bearing builds self-acting the air film through movements between the bearing parts.
For static air bearings air pressure (0.4 MPa up to 1 MPa) is fed into the bearing via restrictors. The restrictors control the air pressure in the air gap and adapt it to the changing conditions during operation (loads, movements etc.). In the air bearing industry, various types of restrictor types are popular. In practice, however, orifices, long-size drillings and porous inserts made of graphite or metal powder are common practice.
unloaded air bearing 
pressure distribution in unloaded air bearings 
loaded air bearing 
pressure distribution in loaded air bearings If a radial air bearing is not exposed to load, the air gap has the same thickness everywhere. The air bearing forms an axial-symmetric pressure field in the bearing gap. All forces are in equilibrium, with no external reaction force being generated.
An external force, torque or displacement, or the pitch during operation, lead on to an axial offset, so that the shape of the air gap changes. The pressure field in the air gap is no longer axial-symmetric, so that reaction forces and moments will be generated. The vector sum of these forces and moments adds up to a resultant force or a resultant moment which counterbalances the external load and thus keeps the entire system in equilibrium.
Possible load variants (force and torque), single or in combination.Air bearings are used, where
- a high degree of accuracy,
- a very high relative speed and acceleration,
- a very high repeatability and positioning accuracy,
- a very short travel (in the nanometre range) as well as
- nearly zero friction and slip-stick free
are of the essence of the application. Air bearings have already been used for decades in measuring machines, machine tools, in the semi-conductor industry and in many other fields of application.
The interaction between the air bearing technology and the linear motor technology opens up new perspectives. This combination allows users of both technologies to design contactless mounted and driven positioning units. Such as a machine slide without solid-state contact with the machine support. Besides, this unit has excellent control properties, while the air bearings' very good damping properties must not be forgotten, either. The so-called "squeeze-film" damping of larger oscillating amplitudes in particular will result in a dynamic behaviour that is clearly superior to that of rolling element bearings or rolling element slideways.
Advantages of air bearings at a glance:
- High relative speeds
- No oil required to eliminate the solid-state contact
- Very good damping properties as compared with rolling element bearings or rolling element slideways
- Smooth and silent motion, since there are no moving parts (balls, separator)
- The motion of the air bearings depends only indirectly on the surface finish quality
- No wear, since there is no solid-state contact
- Nearly zero friction
