Gas Bearing Research and Development
introduction
Replacing human labor with rotating machinery is an important invention and achievement in the history of human civilization . Every rotating machine has Rotating axis, And every shaft needs bearings, So if there is an “axis”, there is a " bearing ". Combination of bearings
Form a dynamic system (Rotor-Bearing Dynamic System). The function of the bearing is (1) to support the gravity borne by the shaft and (2) limit the movable space of the shaft and maintain the stable operation of the shaft.
The vibration problem of the moving shaft is different from that of the general structure vibration and become another dynamic system.
Bearings can be classified according to whether the shaft is in direct contact with the bearing : (1) The two are in direct contact , Rolling element bearings
(Rolling Element Bearing) including ball bearings (Ball Bearing), roller bearings (Roller Bearing) and Needle Bearing .(2) There is a gap between the shaft and the bearing with lubricants ( fluids , Gas and solid ) or without lubricants such as magnetic bearings .With liquid lubricant such as oil the oil cylindrical bearing is widely used in heavy machinery. The bearing using gas as lubricant is the subject of this article .
Characteristics of gas bearings
Gas bearings usually use surrounding air as lubricant , so they are often called air bearings . Air is available everywhere (except in a vacuum environment). Gas bearings do not require lubricant storage and delivery equipment like oil bearings. Therefore, the gas bearing can be started at any time Also known as Self -Acting Bearing. If you need to increase the load capacity, the externally-pressurized bearing can be employed.
Gas is not as easily polluted as oil. Gas bearings are suitable for harsh environments. In addition, gas bearings are mostly used in high-speed rotating machinery, such as turbines, compressors, and pumps in the aerospace and aviation industries /they are also used in biotechnology machinery such as dental drills, etc. under high speed conditions. On the other hand liquid lubricants such as oil as the temperature rises, viscositydecline , This reduces the load capacity. If the temperature reaches the boiling point, the bearing will lose operation function; Turbochargers using oil bearings may have this concern. In contrast, the viscosity of gas increases with the temperature rising so that the bearing load increases as well.
But nothing is perfect; gas bearings have a weakness. When the shaft starts and stops , That is, zero speed , The shaft surface contacts the bearing surface . There are concerns about wear and tear. In addition, starting speed so-called Lift -Off Speed is also an important issue of design. If the shaft speed does not reach this speed, the shaft cannot take off and separate from the bearing surface. In addition, the damping coefficient of the gas bearing is low. Therefore, the dynamic analysis of shaft vibration is also an important topic for designers.
In order to fully utilize the advantages of gas bearings and improve their disadvantages, different types of gas bearings with various configurations are developed.
Types of gas bearings
Gas bearings have different uses and functions. There are categorized as the following:
(1) Thrust Bearing: To bear the axial impact of the rotating shaft. Like rocket thrust. The principle is to use the relative movement of two sliders to generate pressure in the fluid between them to form load gravity. Figure 1 below shows its shape. Two opposite disks Put on the rotating shaft. The disc below is the bearing disc.