Principle of Air dynamic pressure bearing

Air dynamic pressure bearing is one of the forms of sliding bearings. Its structure and working principle are similar to those of liquid sliding bearings. The difference is that the gas (mostly air) is used as the lubricating medium.

Use air as lubricant

The most commonly used gas lubricant for bearings that use gas as a lubricant is air, and nitrogen, argon, hydrogen, helium, or carbon dioxide can also be used as needed. In gas compressors, expansion and circulation machines, the working medium are often used as a lubricant. selection of air bearing materials mainly includes tool steel, bronze, tungsten-cobalt-molybdenum alloy, powder metallurgy porous materials, ceramics and engineering plastics.

① Very low frictional resistance: Because the viscosity of gas is much lower than that of liquid, the viscosity of air at room temperature is only one-five thousandths of No. 10 mechanical oil, and the frictional resistance of the bearing is proportional to the viscosity, so the frictional resistance of the gas bearing Liquid lubricated bearings is low.

② A wide range of applicable speeds: The frictional resistance of the gas bearing is low, and the temperature rise is low. When the speed is as high as 50,000 rpm, the temperature rise does not exceed 20 to 30 ℃, and the speed can even reach as high as 1.3 million rpm. Aerostatic bearings can also be used at extremely low speeds, even zero speeds.

③ Wide applicable temperature range: gas can maintain gaseous state in a large temperature range, and its viscosity is little affected by temperature (when the temperature rises, the viscosity will increase slightly, if the temperature rises from 20℃ to 100℃, the air viscosity will increase 23%), therefore, the applicable temperature range of gas bearings can reach -265℃ to 1650℃.

④ Low load carrying capacity: The load carrying capacity of the hydrodynamic bearing is proportional to the viscosity, and the load carrying capacity of the gas hydrodynamic bearing is only a few thousandths of that of the hydrodynamic bearing of the same size. Due to the low compressibility of gas, the load-bearing capacity of the gas dynamic pressure bearing is also low.

High machining accuracy requirements: In order to improve the bearing capacity and gas film stiffness of gas bearings, bearing clearances (less than 0.015 mm) are usually smaller than those of liquid lubricated bearings, and the machining accuracy of parts needs to be improved accordingly.

The gas enters the gas chamber through the air supply hole, and then flows through the restrictor into the gap between the bearing and the journal in fractional paths, and then flows out of the bearing from both ends, forming a static pressure gas film supporting the load in the gap. The surface of the inner hole of the aerostatic bearing generally does not have an air cavity to increase the rigidity of the gas film and improve the stability.