The unit was put into operation in August 2001 and has been operating smoothly.
On May 16, 2009, after the motor was overhauled, the cooling capacity was insufficient, and the vibration was abnormal. The vibration monitoring of the compressor was carried out. The state monitoring result showed that the maximum amplitude of the unit was 2.42 mm/s, and the vibration value was acceptable, but the vibration spectrum had abnormal frequency. As shown.
It is known that the vibration frequency of the compressor is mainly the motor's 1, 2 frequency 50Hz, 100Hz and high-speed shaft frequency 160Hz, while the compressor has 733Hz, 783H frequency peak, 733Hz, 783Hz frequency is the compressor's non-integer multiple frequency. From the structure of the compressor and analysis of common faults, there may be poor gear meshing or turbulence <2>.
The meshing fault is based on the degree of malfunction of the meshing failure. There are three cases of the frequency of the meshing fault: a. A slight misalignment can arouse the fault feature with the meshing frequency as the carrier frequency.
b. Moderate meshing failure can arouse the fault characteristics of the gear self-vibration frequency as the carrier frequency.
c. Severe poor meshing can provoke fault characteristics with the self-vibration frequency of the gearbox components as the carrier frequency.
Turbulent fault turbulence is a flow phenomenon that occurs when the normal gas flow of the compressor is disturbed or blocked. The turbulent flow can generate random high-frequency vibrations, sometimes stimulating low-frequency vibration.
2 fault handling.
According to the above analysis, first adjust the flow rate of the compressor, the temperature and pressure of the inlet and outlet, and the cooling capacity of the unit is still not improved, and the turbulence phenomenon of the fluid can be eliminated. It is further determined that there is a fault in the gear meshing state of the compressor, and the compressor needs to be disassembled to check the meshing condition of the gear.
3 disintegration check situation.
On May 17, 2009, the maintenance personnel dismantled the unit and found that the main faults were as follows: 3.1 The high and low speed teeth were almost flat and could not be engaged, that is, the high speed shaft could not be rotated at all.
3.2 The main thrust surface of the high-speed bearing bush is seriously worn.
In combination with the damage of the compressor, the maintenance record is checked and it is determined that the motor is reversed, resulting in poor gear meshing and abnormal wear. (see, 4)
4 Further analysis of the cause of the failure.
4.1 Gear grinding.
Loss Cause Analysis The ideal meshing contact line of the gear is shown as 6.
During the installation process, the maintenance worker has carefully adjusted the gear rotation surface, as shown, the tooth surface is evenly stressed. Since the reverse meshing line of the gear is not adjusted, if it rotates in the reverse direction, the tooth surface will inevitably make a point contact. As shown in Fig. 6, the stress on the tooth surface is concentrated, which eventually causes serious damage to the gear, as shown in Fig. 3.
4.2 Main thrust.
The analysis of the cause of the wear of the tile is as shown in the figure. When the rotor is rotating forward, the axial force generated by the pressure difference between the high-speed shaft and the inlet and outlet of the impeller is F1, and the axial force generated by the low-speed shaft helical gear applied to the high-speed shaft is F2. The resultant force F=F1-F2 acts on the main thrust bearing bush.
As shown, when the rotor is reversed, the axial force generated by the impeller inlet and outlet pressure difference of the high-speed shaft is F1', and the axial force generated by the low-speed shaft helical teeth applied to the high-speed shaft is F2', and the two directions are the same, superimposed, and combined force ∑ F'=F1'+F2' acts on the main thrust bearing.
∑F' is significantly larger than ∑F, exceeding the bearing capacity of the bearing bush, causing severe wear of the main thrust bearing bush.
5 Conclusion.
Apply condition monitoring and fault diagnosis knowledge, analyze the causes of vibration, and carry out targeted maintenance. The gears and bushes were replaced. The compressor was started on May 25, 2009. The vibration of the unit was 1.2 mm/s and the vibration was normal.
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