What is an air bearing?

Bearings, I believe everyone is familiar with them. The rolling bearings that we commonly use should be the most familiar. They are important components in contemporary mechanical equipment. So what is an air bearing? In 1854, the French G.A Ian proposed the idea of ​​using gas as a lubricant, and finally in 1896, the first air bearing came out. Air bearing: A plain bearing that uses gas as a lubricant. The most commonly used gas lubricant is air, but nitrogen, argon, hydrogen, helium or carbon dioxide can also be used as required. In gas compressors, expanders and circulators, the working medium is often used as a lubricant. Air bearing refers to a bearing that supports the load by means of the pressure air film formed between the sliding surfaces of the bearing, and the sliding surfaces are completely separated by the air film during operation. The air bearing belongs to the fluid sliding bearing in the sliding bearing. It is fluid lubricated during operation, and its lubricating medium is air. According to the formation mechanism of the pressure air film, air bearings are mainly divided into two categories: 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 area of ​​convergence between the surfaces of the sliding pair. The air film is roughly wedge-shaped, see Figure 1. Since aerodynamic bearings do not require an external air source, they are also called 'self-acting bearings'. Fig. 1 Working principle of air dynamic pressure bearing The pressure air film of air static pressure bearing is formed by the introduction of external compressed air between the sliding surfaces through the restrictor, as shown in Fig. 2. Aerostatic bearings require a clean external air source. Figure 2 Working principle of air hydrostatic bearing Features of air bearing ① Extremely 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-fifth thousandth of that of No. 10 mechanical oil, while the frictional resistance and viscosity of bearing is proportional, so the frictional resistance of gas bearings is lower than that of liquid lubricated bearings. ② Applicable speed range Large gas bearing has low friction resistance 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 even reaches as high as 1.3 million rpm. Aerostatic bearings can also be used at very low speeds, even zero speeds. ③ Wide applicable temperature range The gas can maintain a gaseous state in a very large temperature range, and its viscosity is little affected by temperature (the viscosity increases slightly when the temperature rises, such as the temperature increases from 20°C to 100°C, the air viscosity increases by 23% ), therefore, the applicable temperature range of gas bearing can reach -265 ℃ to 1650 ℃. ④ Bearing capacity The bearing capacity of low dynamic pressure bearings is proportional to the viscosity, and the bearing capacity of gas dynamic pressure bearings is only a few thousandths of that of hydrodynamic bearings of the same size. Due to the compressibility of the gas, the bearing capacity of the gas dynamic pressure bearing has a limit value, and the load per unit projected area can only be added to 0.36MPa. ⑤ High machining accuracy requirements In order to improve the bearing capacity and air film stiffness of the gas bearing, the bearing clearance (less than 0.015 mm) is usually smaller than that of the liquid lubricated bearing, and the accuracy of the parts needs to be improved accordingly. Application of air bearing Air bearing is a new type of bearing that uses the elastic potential energy of air to play a supporting role. The only lubricant used is air; therefore, air bearing technology is ideal for workpieces or work environments that must be free of contamination. In an air bearing, the balls are replaced by air cushions. Perhaps one of the most well-known applications of air bearings is in hovercraft. Huge fans blow air beneath the hovercraft, preventing the air from escaping through elastic rubber 'skirts'. The high air pressure created below the hovercraft supports the weight of the hull, thus causing it to float on the air cushion. Since the 1950s, the application of gas bearings has become more and more extensive, and has been extensively and deeply studied. At present, gas bearings can be used in textile machinery, cable machinery, instrumentation machine tools, gyroscopes, high-speed centrifuges, dental drills, refrigerators operating at low temperatures, hydrogen expanders, and gas circulators operating at high temperatures. (Source: Manufacturing Principles)