2023 February the Third Week KYOCM Technical Knowledge: What is air bearing?

Bearing, I believe that everyone will not be unfamiliar with it. Our common rolling bearing should be the most familiar. It is an important part of modern mechanical equipment. What is air bearing?

In 1854, the French G. A. Ian put forward the idea of using gas as a lubricant. Finally, in 1896, the first air bearing came out.

Air bearing: sliding bearing with gas as lubricant. The most commonly used gas lubricant is air, and nitrogen, argon, hydrogen, helium or carbon dioxide can also be used as needed. In gas compressor, expander and circulator, the working medium is often used as lubricant.

Air bearing refers to the bearing that supports the load with the help of the pressure air film formed between the sliding pair surfaces of the bearing. When working, the sliding pair surfaces are completely separated by the air film. The air bearing belongs to the fluid sliding bearing in the sliding bearing, which is lubricated by fluid when working, and its lubricating medium is air.

According to the formation mechanism of pressure air film, air bearings are mainly divided into two types: aerodynamic bearings and aerostatic bearings.

The pressure air film of the aerodynamic bearing is formed by the mutual movement of the sliding pair to bring the air into the convergence area between the surfaces of the sliding pair. The air film is roughly wedge-shaped, as shown in Figure 1. Since aerodynamic bearings do not require external air sources, they are also called "self acting bearings".

Fig. 1 Working principle of pneumatic bearing

The pressure air film of the aerostatic bearing is formed by the external compressed air introduced between the sliding pair surfaces through the throttle, as shown in Figure 2. The aerostatic bearing needs a clean external air source.

Fig. 2 Working principle of aerostatic bearing

Air bearing features

① Very low friction

Because the viscosity of gas is much lower than that of liquid, the viscosity of air at room temperature is only one fifth of that of No. 10 machine oil, and the friction resistance of bearing is proportional to the viscosity, so the friction resistance of gas bearing is lower than that of liquid-lubricated bearing.

② Wide applicable speed range

The gas bearing has low friction resistance and low temperature rise. When the rotating speed reaches 50000 rpm, the temperature rise does not exceed 20~30 ℃, and the rotating speed even reaches 1.3 million rpm. Aerostatic bearings can also be used at extremely low speeds, even zero speeds.

③ Wide temperature range

The gas can maintain the gas state in a large temperature range, and its viscosity is slightly affected by the temperature (the viscosity increases slightly when the temperature rises, for example, the temperature rises from 20 ℃ to 100 ℃, and the air viscosity increases by 23%). Therefore, the applicable temperature range of the gas bearing can reach - 265 ℃ to 1650 ℃.

④ Low bearing capacity

The bearing capacity of the dynamic pressure bearing is proportional to the viscosity, and the bearing capacity of the gas dynamic pressure bearing is only a few thousandths of that of the liquid dynamic pressure bearing of the same size. Due to the compressibility of the gas, the bearing capacity of the gas dynamic bearing has a limit value. Generally, the load per unit projected area can only be increased to 0.36 MPa.

⑤ High machining accuracy requirements

In order to improve the bearing capacity and gas film stiffness of the gas bearing, the bearing clearance (less than 0.015mm) smaller than that of the liquid-lubricated bearing is usually used, and the part accuracy needs to be improved accordingly.

Application of air bearing

Air bearing is a new type of bearing that uses aeroelastic potential energy to support. The only lubricant used is air; Therefore, air bearing technology is ideal for workpieces or working environments that must be pollution-free.

In air bearings, the ball is replaced by an air cushion. Perhaps one of the most familiar applications of air bearings is hovercraft.

The huge fan blows the air under the hovercraft and prevents the air from escaping through the elastic rubber "skirt". The high air pressure generated under the hovercraft can support the weight of the hull, thus making it float on the hovercraft.

Since the 1950s, the application of gas bearing has become more and more extensive, and has been widely and deeply studied. At present, gas bearings can be used in textile machinery, cable machinery, instrument machine tools, gyroscopes, high-speed centrifugal separators, dental drills, refrigerators operating at low temperatures, hydrogen expanders and gas circulators operating at high temperatures.

More about KYOCM Combined Bearing：

Composite bearing is a kind of roller bearing which can bear both radial load and axial load. The structure of the combined bearing is axial and radial bearing running at 900 °, the main load is borne by the radial bearing, and the axial bearing bears the lateral thrust.

Combination bearing is used together with profile guide rail or channel steel. There are two main types of profiles, I and C profiles. The combined bearing slides into the profile guide rail to generate the required linear movement. The combined bearing is welded with the flange plate for installation according to the application requirements. The assembly is mainly used for precise heavy vertical and horizontal movement.

https://www.kyocm.com/products/Combined-Bearing/743.html