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Noise and vibration control of screw refrigeration compressors


The screw refrigeration compressor is the "heart" of the screw chiller . Its importance can be seen. In actual applications, it is not uncommon to often encounter the noise generated by the screw refrigeration compressor exceeding the normal standard. In response to this problem, we will analyze the source of the screw refrigeration compressor in detail and introduce some effective measures and examples to reduce vibration and noise to help everyone understand and solve the problem as a whole.
First, the noise source of screw refrigeration compressor
1.Vibration and noise of air conditioning machinery in the machine room. Imbalance of the rotor and its fittings; impact noise caused by rotor meshing and rotor speed fluctuations; vibration and noise caused by misalignment of the motor and coupling of the open-type screw refrigeration compressor ; Bearing vibration and noise. The exterior of the machine body includes vibration and noise of the machine case, supporting structure, and base.
2, fluid-induced noise: including airflow noise and oil flow noise. If the airflow noise treasure is the suction and exhaust noise, including the gas radon, the eddy current noise formed when the exhaust cavity and the volume of the rotor cogging element are formed, the jet noise generated by the backflow and expansion during the exhaust process; Elbow vibration and noise; suction and exhaust check valve noise. Oil flow noise includes injection noise, oil flow pipe noise, oil pump cavities, etc.
3. Electrical noise: For open-type screw refrigeration compressors, the motor noise consists of ventilation noise, mechanical noise and electromagnetic noise. Generally speaking, the ventilation noise is large, the rolling bearing noise is the second among mechanical noise, and the sliding bearing noise is small. Electromagnetic noise is a noise specific to electric motors. It belongs to mechanical noise and is caused by harmonic magnetic field force waves in the air gap between the stator and rotor. When the power supply voltage is unstable, electromagnetic vibration and noise are most likely to occur.
4. Unit noise: Including vibration and noise of oil separator, evaporator and cooling system.

Second, vibration and noise reduction measures and examples
From the domestic and foreign studies on the noise and vibration of screw refrigeration compressors, there is little research on noise source identification, noise and vibration distribution, noise and vibration characteristics, and noise and vibration control. A complete research idea and R & D system is usually the key to identifying the source of vibration noise using a noise test system, and then measures to reduce vibration and reduce noise are taken. Some enterprises have adopted a series of simple and effective measures based on the common types of mechanical failures caused by abnormal vibration and noise.
1. On-site dynamic balance method reduces power frequency vibration; JZK31 5 screw refrigeration compressor in a refinery shows strong vibration after maintenance, and the vibration speed reaches 4lmm /. Measures such as strengthening the exit pipeline and adjusting the load on the site did not work. The manufacturer adopted the following measures. (1) Check the shaft bending and clearance of each part. (2) Replace the bearing. (3) Strengthen the foundation. (4) Adjust the compressor level. (5) Adjust the clearance at the discharge end of the compressor. (6) Dynamic balance of two screws, the balance accuracy is higher than the design requirements. (7) Refining the screw, put the two screws on the tumbling machine, apply red dandelion powder, check the meshing condition, and grind off the high point. (8) Clean up welding slag and dirt in the population pipeline. (9) Reinforce outlet pipes. (l0) Strictly correct each disassembly. The noise has been reduced from 106dB to 96dB, but the power frequency vibration speed is still as high as 37mm /. Later, the on-site counterweight method was adopted to reduce the vibration speed to 7mm /.
2. Correct the coaxiality of the motor shaft and the compressor shaft to reduce vibration; for example, the JZK-KFl25-100 screw air conditioner chiller used in a chemical fiber factory has a large vibration after overhaul. The vibration spectrum of the screw-type refrigeration compressor was measured by a data acquisition instrument, and the cause of the vibration was judged to be that the main axis of the compressor motor and the main axis of the compressor were not concentric. Considering the special case where the relative position of the compressor main shaft and the motor main shaft is at a certain angle, the coaxiality is adjusted so that it does not exceed 0 08mm within the limited range of the two coupling transmission cores. After restarting, the vibration is greatly reduced and the operation is stable.
3. Replace different types of flexible couplings to reduce the machine noise. The noise of the LG2OCAB screw refrigeration compressor during the test run exceeded the standard. According to the test, the noise was caused by the flexible coupling. Various debuggings were started, and the noise reduction effect was not obvious. Later, the diaphragm coupling was replaced with an elastic pin coupling, and the compressor noise was improved and reached the standard requirements.
4. Fasten parts and components, improve assembly clearance, reduce bearing vibration, and reduce machine noise. The C-650 two-stage propane screw refrigeration compressor in a certain oil field's mouth is not operating well and malfunctions. Regarding the abnormal sound of running sounds, the main reasons for judging are loosening of the compressor fastening bolts, poor alignment of the coupling between the compressor and the motor, and poor rotor operation. In addition, when disassembling the machine, it was found that the bearing shell was excessively worn, which resulted in the inability to carry the load, and the rotor pulsated and made abnormal noises. Check that the tightness of the fastening bolts reaches the specified value, adjust the centering of the coupling, replace the wearing parts, and adjust the various assembly gaps within the specified value. The machine runs normally.

In summary, although we understand the sources of noise generated by all common screw refrigeration compressors, as well as some countermeasures and examples, we still need to analyze specific problems when we encounter problems, because it is likely to occur The same failure phenomenon is caused by different problems, so you cannot memorize it, but you should understand it!



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