The imbalance of turbine rotor and motor main shaft is the main source of vibration. From the perspective of the structure of the turbine rotor, the reasons that affect its balance are:
1. Uneven material of the rotor (including uneven density and uneven expansion coefficient);
2. The processing errors of each component part of the turbine rotor during manufacturing, such as coaxiality, parallelism of the rotor end face, asymmetry of the rotor body, etc.;
3. Assembly quality of the rotor. For example, the upper and lower impellers of the turbine rotor are deviated due to improper assembly; the turbine rotor is not installed correctly on the motor shaft; or the pressing force is insufficient during assembly, causing looseness after high-speed operation, etc.
The above factors will cause uneven mass distribution of the turbine rotor and form a certain mass eccentricity. When the rotor rotates, an unbalanced centrifugal force will be generated, causing the molecular pump to produce harmful vibration and noise.
2. Since the speed of the turbomolecular pump is very high, preventing vibration is also an important issue. In the design of molecular pumps, the working speed should be correctly selected and the main shaft of the motor should be reasonably designed.
3. The supporting conditions of the main shaft, such as bearing accuracy, installation method, lubrication conditions, etc., will also have a greater impact on the vibration of the molecular pump.
In order to reduce the vibration of the molecular pump when the whole machine is working, the following measures should be taken during the design and manufacture of the pump:
1. When process conditions permit, the zero vibration should be increased as much as possible. Machining accuracy of components.
2. Conduct strict dynamic balancing tests on rotating parts such as motor spindles and turbine rotors.
3. In order to prevent vibration and ensure the safe operation of the pump, the pump should be designed so that the operating speed n of the main shaft is outside its critical speed at each stage. During the preliminary design of the shaft, its critical speed should be checked to make it at least about 20% different from the operating speed. Otherwise, the size or rigidity of the shaft should be changed to meet the above requirements.
4. Set a rubber damping ring on the outside of the spindle bearing. In addition to the vibration reduction and sound insulation effects, the rubber vibration damping ring is also helpful in crossing the maximum vibration zone and attenuating high-frequency vibration and noise.
5. In order to reduce the outward transmission of vibration of the molecular pump and reduce the impact of external vibration on the molecular pump, four rubber pads are installed under the four pillars of the molecular pump to act as vibration isolation.