First, the type and characteristics of gas lubricated bearings
Gas lubricated bearings are plain bearings that use gas as a lubricant. It utilizes the gas transportability (diffusion, viscosity and thermal conductivity), adsorption and compressibility to form a friction between the friction pairs, under the action of hydrodynamic pressure, static pressure and extrusion. The layer is complete with a film that has the function of supporting load and reducing friction. Gas lubricated bearings are generally classified into three types: gas dynamic pressure bearings, gas static pressure bearings and gas extrusion bearings. The lubrication state of the actual bearing often exists in the form of dynamic and static pressure, dynamic, extrusion, static, extrusion and dynamic, static and extrusion lubrication.
1. Advantages of gas lubrication
(1) High speed
The small 氦 turbo expander has reached 650 000r/min and the linear speed is 238m/s, which has reached 455x106mm·r/min according to the dn value.
(2) high precision
The gas film has an error homogenization effect, and its accuracy is two orders of magnitude higher than that of the rolling bearing, and the vibration is small and the noise is low.
(3) Small friction loss
The viscosity of the gas is only one thousandth of the viscosity of the lubricating oil, so the frictional torque caused by friction in the film is three orders of magnitude lower than that of the oil film.
(4) Wide temperature range, capable of antigenic radiation
High temperature resistance up to 300-500 ° C, temperature can be as low as 10K gas bearings can still work.
(5) No pollution
Lubricating gas is generally air or inert gas and is emitted to the atmosphere without pollution. The bearing has low vibration and low noise, and it does not pollute the environment.
(6) long life
Gas hydrostatic bearings have no metal direct contact and the theoretical life is infinite. Consider other conditions, generally should be above 104h. There is inter-metal friction at the moment of starting and stopping of the dynamic pressure gas bearing, and the service life is affected to some extent, but it is also above 3000h.
2. Disadvantages of gas lubricated bearings
(1) Low carrying capacity
Compared with similar oil-lubricated bearings, gas-lubricated bearings have a bearing capacity of about one to two orders of magnitude lower. According to the bearing capacity per unit area, oil-lubricated bearings are generally (0.5 to 2) MPa, while gas-lubricated bearings are only (0.02 to 0.04) MPa.
(2) Poor reliability
On the one hand, gas-lubricated bearings are prone to instability, and common air hammer vibrations and eddy instability occur. On the other hand, gas-lubricated bearings are stuck, hung or bitten.
(3) High manufacturing precision and expensive construction
Since the gas film is very thin, generally between a few micrometers and several tens of micrometers, the manufacturing precision of parts is required to be high, and the cost is increased. In addition, there are special process requirements such as processing spiral grooves, orifices and porous materials, which increases manufacturing difficulty and cost.
(4) demanding working conditions
Gas lubricated bearings require a high clean working environment and strict adherence to operating procedures to ensure proper bearing operation and no accidents. To this end, its widespread application and commercialization have been limited to a certain extent.
Second, the application of gas lubricated bearings
Application examples of gas lubricated bearings in machine tools
Gas lubricated bearings are mainly used for spindle support in machine tools, including workpiece axes, tool axes, grinding wheel shafts, etc. Machine tool spindle bearings generally use two types of hydrostatic bearings and hydrostatic bearings. Wave foil bearings can also be used for small high speed spindles. Gas hydrostatic bearings are the most widely used in machine tools, with small orifice throttling and toroidal throttling bearings being the most common. Porous gas hydrostatic bearings have been increasingly used in machine tool active static pressure hybrid lubrication bearings in recent years. Floating ring dynamic and static pressure gas bearings are newly developed high-speed gas-lubricated bearings in recent years, which are promising for high-speed spindle support.
Ultra-high-speed air bearing internal grinding heads are now capable of precision grinding of small holes and small holes. The use of air bearings improves the machining accuracy of the machine by 2-3 orders of magnitude, enabling precision mirror machining.
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