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Installation and adjustment of high-speed bearings

by:JNSN     2021-10-22

1. The fit and clearance of high-speed bearings. Because high-speed bearings must meet the requirements of high-precision bearings and high-temperature bearings, when considering their fit and clearance, the following two points must be considered: (1) When the temperature rises from room temperature to high temperature Dimensional changes and hardness changes; (2) Force system changes and shape changes caused by centrifugal force at high speeds. In short, under high-speed and high-temperature conditions, it is difficult to maintain the accuracy and performance of the bearing from the selection of fit and clearance. In order to ensure that the deformation of the raceway after the bearing is installed is small, the interference of the interference fit cannot be too large, and the centrifugal force at high speed and thermal expansion at high temperature may offset the normal pressure of the mating surface. Or to loosen the mating surface, so the interference must be calculated carefully under the premise of considering the above two factors. The effective interference at normal temperature and speed may be invalid for high-speed bearings. If the calculation result is too contradictory (usually only at super high speeds), only the dual lubrication measures of the under-ring lubrication method and the hydrostatic lubrication method can be adopted, and this scheme may make the dmn value of the bearing break through. The 3 million mark. When considering the clearance of high-speed bearings, not only the above factors must be considered, but also the influence of the thermal elongation of the shaft on the clearance. The bearing is required to have the best clearance under the working condition, that is, at the working temperature. This kind of clearance is formed under the state of precise alignment of the ball groove centers of the inner and outer rings. As high-speed bearings strive to reduce relative sliding and internal friction, it is best not to adjust the clearance of the ball bearing by displacing the inner and outer rings relative to each other in the axial direction. When considering the fitting interference and clearance of the bearing, it is necessary to pay attention to the characteristic that the material becomes soft and easily deformed at high temperature, and the possibility of certain permanent deformation caused by the temperature change from normal temperature to high temperature repeatedly. 2. Requirements for relevant parts of the main engine. High-speed bearings require precise dynamic balance of the rotating system where the bearing is located. The shaft and seat hole where the bearing is installed should have higher dimensional accuracy and shape and position accuracy than the general requirements, especially the coaxiality and shoulder pair The verticality of the seat hole or the journal, and when considering these issues, we must also pay attention to the high-speed factors and high-temperature factors when the bearing is running. The shaft support system requires both high rigidity and light weight as much as possible. In order to overcome this contradiction, measures such as reducing surface roughness and improving surface strengthening can be adopted to increase the support rigidity, and hollow shafts can be used to reduce system mass. 3. Examples of the development of ultra-high-speed bearings Take the development of ultra-high-speed HA tapered roller bearings as an example. (1) The problem is raised. In gas turbines and some machine tools and construction machinery, high speed and large axial load, the use of ball bearings will have a short service life, and the use of short cylindrical roller bearings will result in insufficient axial load capacity and axial clearance. Difficult to adjust, hope to use tapered roller bearings to break through this problem. (2) The key technology that must be resolved The key technology to improve the high-speed limit of tapered roller bearings is to improve the lubrication state between the large rib of the inner ring and the large end surface of the roller. This part is most prone to severe wear and burns at high speed, which is the limit. The main reason for its high speed. (3) Solution In a tapered roller bearing with a common structure, it is difficult to obtain the lubricating oil in the contact part of the large rib of the inner ring and the large end face of the roller in the circulation route of the lubricating oil, and the relative sliding of this part is large, and it is precisely that the lubrication is most needed. Oil. Therefore, Japan and other countries have developed HA type tapered roller bearings. The bearing ribs are on the outer ring, so that the circulating lubricant can lubricate the contact parts of the outer ring ribs and the large end of the roller. It can also store some oil to avoid lean oil burns during start-up. However, several oil drain holes are opened on the outer ring ribs as needed to prevent the oil from having no discharge channel and being retained in a certain part to cause the power loss and temperature of the oil stirring. Rise too high. Because the inner ring has no ribs, the temperature is reduced, which reduces the possibility of creeping between the mating surfaces between the inner ring and the shaft. The bearing of this structure adopts the outer ring guiding method for the cage, so that the cage can guide the rollers smoothly without skewing and run normally, avoiding vibration and excessive wear, which is also conducive to high speed. (4) The achievable effect The dmn value of this type of HA bearing can reach 2 million, which is twice that of the ordinary structure. For example, the bearing (model I-IA30205) for the main shaft of a gas turbine reducer is in the axial Under the condition of a load of 1000N, a 2L/min oil supply is guaranteed to circulate No. 4 turbine oil to the bearing, and its working speed can reach 60,000 rpm without burns. (end)

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