Air bearings are a type of bearing that uses a thin film of pressurized air to support a load.

Bearings, as everyone knows, are important components in modern machinery. In the early forms of linear motion bearings, a row of wooden rods was placed under a row of pry boards. Modern linear motion bearings use the same working principle, but sometimes balls replace rollers. A simple rotating bearing is a sleeve bearing, which is just a bushing sandwiched between the wheel and the axle. This design was later replaced by rolling bearings, which use many cylindrical rollers instead of the original bushing, with each rolling element acting like a separate wheel. In 1854, the Frenchman G.A. Ian proposed the idea of using gas as a lubricant, and finally, in 1896, air bearings were introduced.

Today, I will introduce air bearings.

Air bearings, as the name suggests, are bearings that use gas as a lubricant, with air being the most commonly used gas lubricant. Depending on the needs, nitrogen, argon, hydrogen, helium, or carbon dioxide can also be used. In gas compressors, expanders, and circulators, the working medium often serves as a lubricant. The materials used for air bearings mainly include tool steel, bronze, tungsten-cobalt-molybdenum alloys, powder metallurgy porous materials, ceramics, and engineering plastics.

1. The mechanism of gas-lubricated bearings forming a load-bearing gas film is the same as that of liquid-lubricated bearings, and they are divided into gas dynamic pressure bearings and gas static pressure bearings. Gas dynamic pressure bearings: These use the fluid dynamic pressure generated by gas in a wedge-shaped space to support the load. Shallow threaded grooves are often made on the surface of the shaft neck or bearing shell to enhance load-bearing capacity through the pumping action of the grooves. Gas dynamic pressure thrust bearings: These are gas dynamic pressure thrust bearings with spiral grooves. Gas static pressure bearings: The supply pressure for gas static pressure bearings generally does not exceed 0.6 MPa. Gas enters the gas chamber through the supply holes, then flows through a throttle into the gap between the bearing and the shaft neck, and finally flows out from both ends of the bearing, forming a static pressure gas film that supports the load within the gap. The inner surface of gas static pressure bearings generally does not have gas cavities to increase the stiffness of the gas film and improve stability.

2. According to the direction of the load they bear, they can be divided into gas radial bearings, gas thrust bearings, and gas radial-thrust combination bearings.

① Very low friction: Since the viscosity of gas is much lower than that of liquids, the viscosity of air at room temperature is only one five-thousandth of that of No. 10 machine oil, and the friction of bearings is proportional to viscosity, so the friction of gas bearings is lower than that of liquid-lubricated bearings.

② Wide applicable speed range: Gas bearings have low friction and low temperature rise. At speeds up to 50,000 RPM, the temperature rise does not exceed 20-30°C, and speeds can even reach up to 1.3 million RPM. Gas static pressure bearings can also be used at extremely low speeds, even at zero speed.

③ Wide applicable temperature range: Gas can remain in a gaseous state over a very large temperature range, and its viscosity is minimally affected by temperature (viscosity slightly increases with temperature, for example, when the temperature rises from 20°C to 100°C, the viscosity of air increases by 23%). Therefore, the applicable temperature range of gas bearings can reach from -265°C to 1650°C.

④ Low load-bearing capacity: The load-bearing capacity of dynamic pressure bearings is proportional to viscosity, and the load-bearing capacity of gas dynamic pressure bearings is only a fraction of that of liquid dynamic pressure bearings of the same size. Due to the compressibility of gas, the load-bearing capacity of gas dynamic pressure bearings has a limit, and the load per unit projected area can generally only reach 0.36 MPa.

⑤ High processing precision requirements: To improve the load-bearing capacity and gas film stiffness of gas bearings, it is common to use bearing clearances smaller than those of liquid-lubricated bearings (less than 0.015 mm), which requires corresponding improvements in part precision.

Since the 1950s, the application of gas bearings has become increasingly widespread and has been the subject of extensive and in-depth research. Currently, gas bearings can be used in textile machinery, cable machinery, instrument machine tools, gyroscopes, high-speed centrifugal separators, dental drills, cryogenic refrigeration machines, hydrogen expanders, and high-temperature gas circulators.

Since the 1950s, the application of gas bearings has become increasingly widespread and has been extensively and deeply researched. At present, gas bearings can be used in textile machinery, cable machinery, instrument tools, gyroscopes, high-speed centrifugal separators, dental drills, low-temperature operating refrigerators, hydrogen expanders, and high-temperature operating gas circulators.