① Although granite is a popularly used material due to its stability and machinability, it has a fairly different coefficient of thermal expansion (CTE) compared to metals such as aluminum and steel.

② Very often, high precision machine equipment is utilized in a climatized environment.

Air bearings have some clear advantages over rolling element bearings of which the application can benefit. The main advantages are listed below.

Near zero friction and wear

Since the air film separates the moving and stationary surfaces, no static friction is present in the bearing. This yields very high repeatability in positioning and infinite resolution of the motion. In high-speed air bearing application friction losses become more prominent due to viscous shearing in the air film, although due to the low viscosity of the gas3, the frictional losses remain much lower as compared to oil lubricated systems in similar working conditions. 

③ The viscosity of air is of the order of one-thousandth of the viscosity of light machine oil.

The non-contact nature of air bearings also yields a silent and low-vibration operation, which is highly desirable in high precision applications, for instance metrology machines.

Cleanliness

Fully separated moving parts also mean theoretically zero wear, which result in a virtually infinite lifetime of the bearing component and very low particle generation. In cleanroom applications, this is a significant advantage, apart from the fact that grease or oil lubrication of mechanical bearings can be avoided by switching over to air bearings.

Dynamic properties

A well-designed air bearing will realize excellent stiffness and damping properties. The supply pressure and surface area of the air bearing film is proportional to the stiffness that can be realized. Nevertheless, the proper dimensioning of the restriction in combination with features in the bearing gap are of the utmost importance to realize a stiff bearing. The film damping in the bearing gap results in excellent dynamic performance. In squeeze film damping, the surfaces that realize the air film, move so that the gap in between expands and contracts. When the gap contracts, the gas film is squeezed between the two surfaces. In slide film damping, the motion of the air bearing parallel to the base, leads to shearing within the gas film. The motion of the system generally results in a mixture of both squeeze and slide film damping, although often one is dominant.

High speed applications

Air bearings are widely used in high-speed applications, where they exhibit lower frictional losses and better dynamic performance as compared to mechanical bearings. In high-speed spindle applications, air bearings can exceed the acceleration of mechanical spindle bearings which are prone to ball slippage above certain acceleration levels.