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Fitting and Adjustment of High Speed u200bu200bBearing

by:JNSN     2022-03-12
1. Fit and clearance of high-speed bearings Since high-speed bearings must meet the requirements of both high-precision bearings and high-temperature bearings, the following two points should be considered when considering their fit and clearance: (1) From room 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 a word, under the conditions of high speed and high temperature, it is difficult to maintain the accuracy and working performance of the bearing from the selection of fit and clearance. In order to ensure the small deformation of the raceway after the bearing is installed, the interference of the interference fit cannot be too large, and the centrifugal force at high speed and the thermal expansion at high temperature may offset the normal pressure of the mating surface. Or make the mating surface slack, 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 contradiction in the calculation results is too large (usually only at ultra-high speed), only the dual lubrication measures of the under-ring lubrication method and the hydrostatic lubrication method are adopted, and this solution may make the dmn value of the bearing break through. 3 million mark. When considering the clearance of high-speed bearings, not only the above factors should be considered, but also the influence of thermal elongation of the shaft on the clearance should be considered. The kind of clearance is formed when the center of the inner and outer ring ball grooves are precisely aligned. Since 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 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 temperature, and the possibility of certain permanent deformation caused by repeated temperature changes from normal temperature to high temperature. 2. Requirements for the relevant parts of the main engine. High-speed bearings require that the rotary system where the bearing is located must undergo precise dynamic balance, and the shaft and seat hole where the bearing is installed should have dimensional accuracy and shape and position accuracy higher than the general requirements, especially the coaxiality and block. The verticality of the shoulder to the seat hole or journal, and when considering these issues, it is also necessary to pay attention to the high speed factor and high temperature factor 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 the surface roughness and improving the surface strengthening can be taken to improve the support rigidity, and the hollow shaft can be used to reduce the system mass. 3. Examples of the development of ultra-high-speed bearings The development of ultra-high-speed HA-type tapered roller bearings is taken as an example. (1) Problems raised in gas turbines and some machine tools and construction machinery, high speed and large axial load, the use of ball bearings is too short, the use of short cylindrical roller bearings, the axial load capacity is insufficient, the axial clearance It is difficult to adjust, and we hope to use tapered roller bearings to overcome this problem. (2) The technical key that must be solved The technical key to improving 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 burn at high speed, which is the limit The main reason for its high speed. (3) Solution In the tapered roller bearing of ordinary structure, it is difficult to obtain lubricating oil at the contact part between the large rib of the inner ring and the large end face of the roller in the circulation route of the lubricating oil, and this part has relatively large sliding, which is precisely the most in need of lubrication. Oil. Therefore, Japan and other countries have developed HA type tapered roller bearings. This kind of bearing rib is on the outer ring, so that the circulating lubricating oil can lubricate the contact part between the outer ring rib and the large end face of the roller. It can also store some oil, avoiding the accident of poor oil burn during starting, but there are several oil drain holes on the outer ring rib as needed to avoid oil without a drain channel, and it will remain in a certain part, causing power loss and temperature of oil stirring. Raised too high. Since the inner ring has no ribs, the temperature is lowered, thus reducing the possibility of creep 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 normal operation, avoiding vibration and excessive wear, which is also conducive to high speed. (4) The effect that can be achieved The dmn value of this HA type bearing can reach 2 million, which is twice as high as that of the ordinary structure. Under the condition of load of 1000N, the oil supply of 2L/min is guaranteed to supply No. 4 turbine oil to the bearing, and its working speed can reach 60,000 rpm without causing burns.
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