Gas bearing is a kind of sliding bearing with gas as lubricating medium. Its lubricating film thickness is usually between sub-micron and tens of microns. surface etc. Because the gas has the characteristics of low viscosity, good viscosity-temperature characteristics and radiation resistance, the gas bearing has shown excellent application prospects in special occasions such as high speed, high precision, low friction, low power consumption, high temperature and radiation. According to its working principle, gas bearings can be divided into gas static pressure bearings, gas dynamic pressure bearings and extruded film gas bearings. The working principle, characteristics and typical applications of these three kinds of bearings will be introduced separately below. 1. Gas static pressure bearing Gas static pressure bearing is also called external pressure supply gas bearing, and its working principle is shown in Figure 1. The external gas supply system provides high-pressure gas for the bearing, and the compressed gas enters the bearing gap through the restrictor to form a pressure gas film, thereby realizing the bearing effect. Fig. 1 The principle of hydrostatic lubrication In order to ensure that the gas hydrostatic bearing obtains better characteristics, the bearing clearance is required to be small, and the clearance value is usually 5-20 μm. When the bearing clearance changes, the air film pressure distribution and bearing capacity of the bearing will also vary. change. Considering that the particle size of the fine dust is similar to the size of the bearing gap, the gas source must be strictly filtered before it can enter the bearing gap. The restrictor design is an important design part in the design of aerostatic bearing, which directly affects the performance of the bearing. According to the throttling form of the gas static pressure bearing (as shown in Figure 2), it can be divided into small hole throttle gas static pressure bearing, surface throttle gas static pressure bearing, slit throttle gas static pressure bearing and porous throttle gas bearing Hydrostatic bearings, etc. Fig. 2 Bearing throttling form Small hole throttling Gas static pressure bearing is the earliest proposed gas static pressure bearing structure. It improves the throttling effect by designing different air cavities. Usually, the air film pressure is not affected by the change of the bearing gap, and has good static stiffness, but its stability is poor, and the choke is difficult to process and prone to blockage. The surface throttling gas hydrostatic bearing produces throttling effect through the surface micro groove, which overcomes the difficulty of small hole processing and makes the bearing clearance smaller. Slit throttling gas hydrostatic bearing refers to a kind of bearing in which the gas enters the bearing gap through the slit on the bearing sleeve to play the role of throttling. The bearing reduces the scattering effect of gas flow, but it is difficult to process for small size slits. , the accuracy is difficult to guarantee. Porous throttle gas hydrostatic bearing uses porous material as the bearing surface, and the external gas enters the bearing surface through a large number of tiny pores inside the porous material to form a bearing pressure gas film. The bearing has the characteristics of large bearing capacity, high rigidity, simple structure and good stability, but the throttling performance is greatly affected by the permeability coefficient of porous materials, which is difficult to guarantee. Based on the above characteristics, aerostatic bearings are currently widely used in textiles, handling and packaging, semiconductors, measuring instruments, precision machinery spindles, turbo machinery, food processing and medical equipment. 2. Gas dynamic pressure bearing Gas dynamic pressure bearing is also known as self-acting bearing. Compared with gas static pressure bearing, it no longer needs an external air supply system, but works on the principle of dynamic pressure effect, as shown in Figure 3. Fig. 3 The principle of dynamic pressure lubrication The two relative moving surfaces form a certain convergence gap. The high-speed movement of the moving surfaces brings the viscous gas into the wedge-shaped gap to generate a pressure rise, which in turn generates the bearing capacity acting on the rotor. The bearing capacity varies with the rotational speed. increases with the increase. Wedge gap, lubricating film thickness and gas viscosity are the key conditions for the formation of dynamic pressure effect. Since the dependence on the gas source gas supply system is eliminated, the structure of the gas dynamic pressure bearing is simple and the cost is reduced. However, when the rotation speed is low and the dynamic pressure effect is weak in the start-stop phase, it is not enough to generate the supporting force acting on the rotor, resulting in the contact between the rotor and the inner wall of the bearing, resulting in serious friction and wear, which directly affects the life of the bearing. In addition, the gas dynamic pressure bearing also has the problem of poor damping characteristics and difficulty in passing the rotor critical. In response to the above problems, researchers solve this problem by developing wear-resistant coatings or designing bearings with different structural forms. Among them, the more representative gas dynamic pressure bearing structures include grooved gas dynamic pressure bearing, tilting pad gas dynamic pressure bearing, and foil gas dynamic pressure bearing, as shown in Figure 4. Figure 4 Typical gas dynamic pressure bearing structure Slotted gas dynamic pressure bearing refers to a type of gas bearing with different grooves carved on the surface of the bearing or rotor to improve the bearing characteristics and stability. The distribution and stiffness damping change, so as to obtain better bearing characteristics;