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Installation and adjustment of high-speed bearings

wallpapers News 2020-09-28
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, the following two points should be considered when considering their fit and clearance:
(1) Dimensional change and hardness change when rising from normal temperature to 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.
Thermal expansion at high temperature, or 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.
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 condition that the inner and outer ring ball groove centers are precisely aligned. 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 relatively displacing the inner and outer rings 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 easy to deform at high temperature, and the possibility of certain permanent deformation caused by multiple temperature changes from normal temperature to high temperature.
 
2. Requirements for related parts of the host
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 the shoulder of the seat hole or journal Verticality, and when considering these issues, we must also pay attention to 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.

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