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The working principle, characteristics, and typical applications of gas bearings

Release time:

2023-01-13

Source:

Bearing Magazine

Gas bearing is a type of sliding bearing that uses gas as the lubricating medium. Its lubricating film thickness is usually between submicrons and tens of micrometers, and its load-bearing surface has diversity, such as rigid or flexible, smooth or grooved, flat or other shaped surfaces. Due to the low viscosity, good viscosity temperature characteristics, and radiation resistance of gases, gas bearings have shown excellent application prospects in special occasions such as high-speed, high-precision, low friction, low power consumption, high and low temperatures, 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 following will introduce the working principles, characteristics, and typical applications of these three types of bearings.

1. Aerostatic bearing

Gas hydrostatic bearings, also known as externally supplied gas bearings, operate as shown in Figure 1. The external gas supply system provides high-pressure gas for the bearings, and compressed gas enters the bearing gap through a throttle to form a pressure gas film, thereby achieving a load-bearing effect.

In order to ensure good performance of aerostatic bearings, a small bearing clearance is required, usually with a clearance value of 5-20 μ m. When the bearing clearance changes, the gas film pressure distribution and bearing capacity of the bearing will also change accordingly. Considering that the size of fine dust particles is similar to the size of the bearing gap, the gas source must undergo strict filtration before entering the bearing gap. The throttle design is an important part of the design of aerostatic bearings, which directly affects the performance of the bearings. According to the throttling form of aerostatic bearings, they can be divided into small hole throttling aerostatic bearings, surface throttling aerostatic bearings, narrow slot throttling aerostatic bearings, and porous throttling aerostatic bearings.

The small orifice throttling aerostatic bearing is the earliest proposed aerostatic bearing structure. It improves the throttling effect by designing different gas chambers. Usually, the gas film pressure is not affected by changes in bearing clearance and has good static stiffness. However, its stability is poor, and the throttling device is difficult to process, which is prone to blockage.

The surface throttling gas static pressure bearing generates throttling effect through surface micro grooves, which overcomes the difficulty of small hole machining and makes the bearing clearance smaller.

Slit throttling gas static pressure bearing refers to a type of bearing in which gas enters the bearing gap through the narrow slot on the bearing sleeve for throttling purposes. This bearing reduces the scattering effect of gas flow, but for smaller sized narrow slots, it is difficult to process and ensure accuracy.

The porous material is used as the bearing surface for the multi orifice throttling gas static pressure bearing, and external gas enters the bearing surface through a large number of small pores inside the porous material, forming a pressure bearing gas film. This bearing has the characteristics of high bearing capacity, high stiffness, simple structure, and good stability, but its 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, turbomachinery, food processing, and medical devices.

2. Gas dynamic bearing

Pneumatic bearings, also known as self acting bearings, no longer require an external air supply system compared to aerostatic bearings. Instead, they operate using the principle of dynamic pressure effect.

The two relative moving surfaces form a certain convergence gap, and the high-speed movement of the moving surface will have