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The concept and development history of gas bearings
Source: China Bearing Network Time: 2018-03-25
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Gas bearing
Sliding bearing with gas as smoothing agent. The most commonly used gas smoothing agent is air; nitrogen, argon, hydrogen, helium or carbon dioxide can also be used according to requirements. In gas compressors, expansion machines and circulators; often working medium As a smoothing agent. Gas bearings can be used in textile machinery, cable machinery, surface machine tools, gyroscopes, high-speed centrifugal separators, dental drills, low-temperature working refrigerators, hydrogen expansion machines and high-temperature gas circulators.
As early as 1854; French G. A. Ian proposed the idea of ​​using gas as a smoothing agent. The first air bearing was introduced in 1896. The British W in 1913. J. Harrison announced the paper on fluid dynamics analysis of gas smooth bearings. Since the 1950s, the use of gas bearings has gradually expanded; and has been extensively and deeply studied.
The characteristic gas bearing has the following characteristics: 1 The friction is extremely low: because the viscosity of the gas is much lower than that of the liquid; the viscosity of the air at room temperature is only one-fifth of the mechanical oil of No. 10, and the friction of the bearing is proportional to the viscosity. Therefore, the friction of the gas bearing is lower than that of the liquid smooth bearing. 2 The applicable speed is large: the friction of the gas bearing is low; the temperature rise is low; when the speed is up to 50,000 rpm, the temperature rise does not exceed 20 to 30 ° C; And even up to 1.3 million rev / min. Gas static pressure bearings can also be used for very low speed; even zero speed. 3 Wide temperature range: gas can adhere to the gas state in a very large temperature scale; its viscosity is affected by temperature Very small (the viscosity is slightly added when the temperature rises; if the temperature is raised from 20 ° C to 100 ° C, the viscosity of the air is increased by 23%), therefore, the applicable temperature range of the gas bearing can reach -265 ° C to 1650 ° C. 4 load capacity. Low: The bearing capacity of the dynamic pressure bearing is proportional to the viscosity; the bearing of the gas dynamic pressure bearing can be as long as a few thousand of the same size hydrodynamic bearing. Because of the compressibility of the gas; the bearing of the gas dynamic bearing can have the limit value. Usually on the projected area of ​​the unit The load can only be added to 0. 36 MPa. 5 high processing precision requirements: for the bearing capacity of the improved gas bearing and the film stiffness, usually a smaller bearing clearance than the liquid smooth bearing (less than 0. 015 mm); the demand is correspondingly improved Part accuracy.
The type of gas smooth bearing constitutes the same mechanism as the liquid smooth bearing; it is also divided into a gas dynamic pressure bearing and a gas static pressure bearing. The direction of the receiving load is different; it can be divided into a gas radial bearing and a gas thrust bearing. And gas radial thrust combined bearings. Gas dynamic pressure bearings use the fluid dynamic pressure generated by the gas in the wedge space to support the load. The shallow thread groove is often made on the outer surface of the journal or the bearing shell; the pumping effect of the groove is improved. Fig. 1 [Gas dynamic pressure spiral groove thrust bearing] is a gas dynamic pressure spiral groove thrust bearing. The gas supply pressure of the gas static pressure bearing (Fig. 2 [gas static pressure bearing]) usually does not exceed 0.6 MPa. After entering the air chamber through the air supply hole; then the fractional path flows through the economizer into the gap between the bearing and the journal; then the bearing flows out from both ends; the static pressure film forming the supporting load in the gap. The inner diameter of the gas static bearing is usually not Open the air cavity; to increase the film stiffness; improve stability.
The materials for making gas bearings are tool steel, bronze, tungsten-cobalt-molybdenum alloy, powder metallurgy porous materials, ceramics and engineering plastics.
References J. W. Powell; Ding Weigang, Lin Xiangqun, etc.: "Aerostatic bearing depiction"; National Defense Industry Press, Beijing, 1978. (J. W. Powell, Desin of Aerostatic Bearins, Machinery Publ. Co., 1970.)
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