Structure and principle of air bearings
Published on:
2025-06-13 10:28
Air bearings, as the name suggests, use gas as a lubricant for bearings. The most commonly used gas lubricant is air, and nitrogen, argon, hydrogen, helium or carbon dioxide can also be used as needed. In gas compressors, expanders and circulators, working media is often used as lubricants. The main materials for air bearings include tool steel, bronze, tungsten-cobalt-molybdenum alloys, powder metallurgy porous materials, ceramics and engineering plastics.
1. The mechanism of forming a load-bearing gas film in gas-lubricated bearings is the same as that in liquid-lubricated bearings, and is divided into gas dynamic pressure bearings and gas static pressure bearings. Gas dynamic pressure bearing: It uses the fluid dynamic pressure generated by gas in the wedge-shaped space to support the load. Shallow thread grooves are often made on the surface of the journal or bearing pad to improve the load-bearing capacity by using the pumping effect of the groove. Gas dynamic pressure spiral groove thrust bearing: gas dynamic pressure spiral groove thrust bearing. Gas static pressure bearing: the gas supply pressure of gas static pressure bearing generally does not exceed 0.6 MPa. The gas enters the air chamber through the air supply hole, then flows through the throttle into the gap between the bearing and the journal, and then flows out of the bearing from both ends, forming a static pressure air film in the gap to support the load. The inner hole surface of the gas static pressure bearing generally does not have an air cavity to increase the stiffness of the air film and improve stability.
2. According to the different directions of load bearing, it can be divided into gas radial bearings, gas thrust bearings and gas radial thrust combined bearings.
① Extremely low friction: Since the viscosity of gas is much lower than that of liquid, the viscosity of air at room temperature is only one five thousandth of that of No. 10 mechanical oil, and the friction of the bearing is proportional to the viscosity, so the friction of the gas bearing is lower than that of the liquid-lubricated bearing.
② Wide applicable speed range: Gas bearings have low friction and low temperature rise. When the speed is as high as 50,000 rpm, the temperature rise does not exceed 20-30℃, and the speed can even be as high as 1.3 million rpm. Gas static pressure bearings can also be used at extremely low speeds, even zero speed.
③ Wide applicable temperature range: Gas can remain in gaseous state within a wide temperature range, and its viscosity is little affected by temperature (viscosity increases slightly when temperature rises, such as when the temperature rises from 20°C to 100°C, the air viscosity increases by 23%). Therefore, the applicable temperature range of gas bearings can reach -265°C to 1650°C.
④Low load-bearing capacity: The load-bearing capacity of a hydrodynamic bearing is proportional to the viscosity, and the load-bearing capacity of a gas hydrodynamic bearing is only a few thousandths of that of a liquid hydrodynamic bearing of the same size. Due to the compressibility of gas, the load-bearing capacity of a gas hydrodynamic bearing has a limit, and the load per unit projected area can generally only be added to 0.36 MPa.
⑤ High processing precision requirements: In order to improve the load-bearing capacity and air film stiffness of gas bearings, a smaller bearing clearance (less than 0.015 mm) than that of liquid-lubricated bearings is usually used, and the part precision needs to be improved accordingly.
Since the 1950s, air bearings have been used more and more widely and have been widely and deeply studied. Currently, air bearings can be used in textile machinery, cable machinery, instrumentation machine tools, gyroscopes, high-speed centrifugal separators, dental drills, low-temperature refrigerators, hydrogen expanders, and high-temperature gas circulators.
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