EPEN Technology Knowledge: Analyze the working principle of oil film sliding bearing

  • The oil film sliding bearing used in the turbine compressor belongs to the dynamic pressure bearing, that is, relying on the rotation of the Journal (or thrus



The oil film sliding bearing used in the turbine compressor belongs to the dynamic pressure bearing, that is, relying on the rotation of the Journal (or thrust disc) itself, the oil is brought between the Journal (or thrust disc) and the bearing bush to form a wedge-shaped oil film, which is squeezed by the load to establish the oil film pressure to bear the load, as shown in Figure 1.




Fig. 1 principle of oil film sliding bearing


In order to illustrate the bearing capacity of the wedge-shaped oil film, take the oil wedge of the thrust bearing as an example. First, it is assumed that the pad does not tilt and remains parallel to the thrust disc. Due to the rotation of the thrust disc, of course, oil will be brought into the gap between the pad and the thrust disc to form an oil film. When the thrust disc rotates, how much oil will be brought in and how much oil will be brought out. If pressure is applied to such an oil film with the help of the thrust disc, the oil will be extruded from the gap. Of course, the oil will be extruded not only from the oil outlet, but also from the oil inlet. As a result, compared with the case without pressure, the average speed of the oil flowing in from the oil inlet is smaller than that flowing out of the oil outlet, and the amount of oil entering the gap is inversely smaller than the flow out, so this oil film cannot last. If the area of oil inlet is properly increased, it will converge with the flow direction. Under the action of load, the amount of oil inlet and oil outlet will be kept equal, so that a stable oil film can be maintained, continuous oil film pressure can be generated, and the bearing load can be borne.


From this simple analysis, we can see that in order to make the oil film stable and have bearing capacity, first, the oil gap must be wedge-shaped, with large oil inlet and small oil outlet; Second, the thrust disc (or journal) has a relative speed to the pad; Third, oil has a certain viscosity. The thrust bearing and support bearing oil film mentioned above have these characteristics, so they can play the role of bearings. The pressure at all parts of the bearing oil film is not consistent, as shown in Figure 1 (b). From the oil inlet of the oil wedge, the oil film pressure along the lower half pad gradually increases to the maximum pressure pmax, and then gradually decreases. The task of supporting the bearing is to form oil film pressure under a certain load P, speed and oil supply, bear the load P, maintain a certain minimum clearance hmin between the journal and the bearing bush, and the oil temperature should not be too high.


The formation of bearing oil film and oil film pressure are affected by shaft speed, oil viscosity, bearing clearance, bearing load and bearing structure. Generally, the higher the speed, the greater the viscosity of the oil, the more oil is brought in, the greater the oil film pressure, and the greater the load it bears. However, if the viscosity of the oil is too large, the oil will be unevenly distributed, increase friction loss, and cannot maintain good lubrication effect. Excessive bearing clearance is unfavorable to the formation of oil film and increases the consumption of oil; If it is too small, the oil quantity will be insufficient, which cannot meet the requirements of bearing cooling. If the load is too large, it will be difficult to form oil film. When the bearing capacity is exceeded, the bearing bush will be burned out. For the supporting bearing, the ratio of bearing length L and diameter d also has a great influence on the bearing capacity. The larger L/d is, the greater the bearing capacity is. However, if the L/d is too large, the lubricating oil is not easy to flow away from the shaft end, causing the bearing temperature to rise. Moreover, due to manufacturing and installation errors, the inevitable shaft deflection causes excessive edge pressure at the bearing end, causing serious wear and fatigue damage. Therefore, too large L/d is not beneficial. Generally, L/d of round pad bearing and tilting pad bearing are 0.6~1.0 and 0.4~0.6 respectively.


The first and most common bearings used in turbine compressors were round pad bearings, and later elliptical pad bearings, multi oil wedge bearings and tilting pad bearings were gradually used.


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EPEN constantly studying the latest research and development of latest technology materials and products. The companys existing main products are metal plastic composite series sliding bearings, bi-metal series bearings, single metal series sliding bearings, etc.


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