Gas lubrication uses a thin film of gas, commonly air, to separate moving surfaces and reduce friction and wear. Gas-lubricated bearings are used in applications where very low friction, high rotational or surface speeds, low vibration, clean operation or freedom from liquid lubricant contamination are required.
Unlike conventional oil- or grease-lubricated bearings, gas bearings operate with a gas film between the bearing surfaces. When correctly designed and operating with full film separation, this can provide extremely low friction, quiet operation and very low wear.
Gas-lubricated bearings can provide several advantages compared with conventional liquid- or solid-lubricated bearing systems:
The low viscosity of gases also means that gas bearings generally have lower load capacity and stiffness than comparable liquid-film bearings. Bearing geometry, clearance, gas-film thickness, operating speed and applied load are therefore important design considerations.
Gas and air bearings may operate using either hydrodynamic or hydrostatic principles.
Hydrodynamic gas bearings generate the supporting gas pressure through relative motion between the bearing surfaces. The geometry and movement of the bearing draw gas into the converging clearance and develop the pressure required to support the load.
Hydrostatic gas bearings, often referred to as externally pressurised air bearings, receive pressurised gas from an external supply. The gas is introduced through restrictors, orifices or porous bearing surfaces to maintain separation between the moving components.
Air bearings are used in precision machinery, measuring equipment, high-speed machinery and other applications requiring smooth, low-friction movement. Air pads use the same general principle to support and move large or heavy loads over suitable flat surfaces with very low resistance to movement.
Selection and design of a gas-lubricated bearing should consider the applied load, bearing speed, required stiffness, operating clearance, gas supply pressure and quality, temperature, surface finish and dimensional accuracy. Start-up and shutdown conditions may also be important because full gas-film separation may not exist under all operating conditions.
A gas-lubricated bearing uses a thin film of gas, commonly air, to separate the bearing surfaces. This allows very low friction and wear when adequate film separation is maintained.
A hydrodynamic gas bearing develops supporting pressure through relative movement of the bearing surfaces. A hydrostatic gas bearing uses an external pressurised gas supply to support and separate the bearing surfaces.
Air bearings can provide very low friction, low wear, smooth motion, low vibration and clean operation without conventional oil or grease lubrication. They are particularly useful for precision and high-speed applications.
Because gases have low viscosity, gas bearings generally provide lower load capacity and stiffness than comparable liquid-film bearings. They can also require accurate manufacture, small operating clearances and, for hydrostatic designs, a reliable clean gas supply.