Air bearings

Air bearings (also known as aerostatical or aerodynamical bearings) are bearings that use a thin film of pressurized air to provide an exceedingly low friction load-bearing interface between surfaces. The two surfaces do not touch. As they are contact-free, air bearings avoid the traditional bearing-related problems of friction, wear, particulates, and lubricant handling, and offer distinct advantages in precision positioning, such as lacking backlash and static friction, as well as in high-speed applications.

The fluid film of the bearing is air that flows through the bearing itself to the bearing surface. The design of the air bearing is such that, although the air constantly escapes from the bearing gap, the pressure between the faces of the bearing is enough to support the working loads. Thus, there is a differentiation that has to be made between Aerodynamical bearings, which establish the air cushion through their movement, and Aerostatical bearings, in which the pressure is being externally inserted.

Air bearings are being mainly used in precision machinery tools (measuring and processing machines) and fast running machines (highspeed spindle).

The main air bearing types fall under the following categories:

The main advantage of a hydrostatic air bearing is that even at little or no movement, there is no friction. This is what gives the bearing ultra high repeatability and indefinite lifetime. Hydrodynamic air bearings do not require any external air supply. However, they have the issue of friction and wear until sufficient velocity is attained to create the air gap.

Air bearings belong to slide bearings. Pressurized air acts as a lubricant in the gap between bearing moving parts. The air cushion carries the load without any contact between the moving parts. Normally, the compressed air is supplied by a compressor. A key goal of supplying the air pressure in the gap is that the stiffness and damping of the air cushion reaches the highest possible level. In addition, air consumption and uniformity of air supply into the gap are crucial for the behaviors of air bearings.

Supplying air to the interface between moving elements of an aerostatic bearing can be achieved in a few different methods:

There is no single best approach to feeding the air to the film. All methods have their advantages and disadvantages specific to each application.

Dead volumes refer in particular to chambers and canals existing in conventional air bearings in order to distribute the air and increase the compressed pressure within the gap. The cavity inside porous (sintered) air bearings are also attributed to dead volume.

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Wikipedia