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Installation and adjustment of high-speed bearings

by:JNSN     2021-12-24
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) from normal temperature to Dimensional change and hardness change at high temperature; (2) Force system change and shape change caused by centrifugal force at high speed.   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 raceway deformation 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 combined with the under-ring lubrication method and the hydrostatic lubrication method can be adopted, and this scheme may cause the dmn value of the bearing to 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 fit interference and clearance of the bearing, it is necessary to pay attention to the characteristics of the material becoming soft and easy to deform at high temperatures, and the possibility of permanent deformation caused by multiple temperature changes from room temperature to high temperature. 2. Requirements for the relevant parts of the main engine. High-speed bearings require that the rotating system where the bearing is located be precisely balanced. The shaft and the 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 gear. The verticality of the shoulder to the seat hole or 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 taken to increase the support rigidity, and hollow shafts can be used to reduce system mass.  3. Development examples 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. It is difficult to adjust, and it is hoped that tapered roller bearings can be used to overcome 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 face 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 the tapered roller bearing of ordinary structure, the circulation route of the lubricating oil is difficult to obtain lubricating oil at the contact part of the large rib of the inner ring and the large end face of the roller, 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 lubricating oil can lubricate the contact parts of the outer ring ribs and the large end surface of the roller. It can also store some oil to avoid lean oil burns when starting. However, several oil drain holes are opened on the outer ring ribs as needed to avoid oil not having a drain channel and being retained in a certain part, causing power loss and temperature of 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 to run normally without skewing, 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 the gas turbine reducer is 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.
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