[Air bearings] spindles make the difference in PCB manufacturing, automotive coating, semiconductor manufacturing equipment, and many other markets where performance needs are outside the scope of conventional bearing technology.

Basically, air bearings use a thin film of pressurized air to support a load, the same way the puck on an air hockey table "floats" on air. This type of bearing is called a "fluid film" bearing. Fluid film bearings have no solid-to-solid contact under typical running conditions; instead, a film of lubricating fluid (in our case pressurized air) forms a layer between the solid machine elements and serves to transfer forces from one to the other. To compare this with ball bearings, in ball bearings the balls are in constant contact with and form a solid bridge between the machine elements.

While most people are familiar with oil fluid film bearings - for example the crankshaft journal bearings in car engines - most people have not been exposed to air bearings. Remembering our high school physics class, there are two basic types of fluids - liquids and gasses. In terms of fluid film bearings, the difference between these two is essentially the viscosity - liquids have much higher viscosity than gasses. When applied to a fluid film bearing, this difference has a number of implications.

The first question is how to generate the pressurized supply of fluid for the fag bearing. There are two ways to do this - one is using an external pressurized supply (hydrostatic) and the other is to use the relative motion of the machine components to generate the pressure internally (hydrodynamic or "self-generating"). While hydrodynamic bearings are common for oil fluid film bearings, which generate internal pressures quite easily due to the relatively high viscosity of oil, it is much rarer to see this technique used for air bearings because the pressure generated is quite low (although Nelson Air has built bearings of this type for low load, high speed rotary applications such as optical scanners).

While some configurations of air bearings are self-preloading (e.g. journal bearings) others such as flat pads and linear rectangular ntn bearings can benefit from preload. Air bearings can be used without any preload (such as a simple flat pad riding on a granite surface), however, in order to maximize the stiffness of the air bearing and help maintain constant air gap it is typical to preload it using one of four basic methods.

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