Litigation of China's petroleum and chemical standards and quality talk about the noise control of screw air compressors Xu Donglai Sinopec Nanjing Engineering Co., Ltd. Nanjing, Jiangsu 211100 Xinshang screw air compressor is an air compressor promoted and applied in China in recent years. At present, many companies use this compressor as an auxiliary equipment for production: screw air compressor has better performance and higher economic efficiency than piston air compressor, but the noise generated during operation is It can not be ignored: Yiwen will measure and analyze the noise of the screw air compressor and propose a control method. The screw air compressor refers to two spiral rotors in the compressor casing. A volumetric rotary air compressor in which the transmission ratio is intermeshing and rotating to pressurize the gas. This air compressor is recognized by more and more enterprises for its small size, long life and high performance. In order to meet the needs of users and respond to the call of national environmental protection, screw air compressors must take measures to control the air during manufacturing. The noise generated by the press during operation. 1 Measurement and Analysis of Noise of Screw Air Compressor 1.1 Beep Measurement of Screw Air Compressor Due to the special structure of screw air compressor, most of the test methods for noise are not feasible. Currently, there are three main methods for measuring and analyzing noise signals: near-field measurement, spectrum analysis, and correlation analysis. The most common method used in the noise measurement of screw air compressors is near field measurement. This method is simple to operate: only the operator needs to scan the surface of the screw air compressor with the sound level meter, and the approximate position of the noise source can be found according to the indication value of the sound level meter. It should be noted that the near field measurement method has certain limitations. Since the microphone is the principle of proximity in the sound level, the microphone can only measure the noise source closest to it. In addition, the microphone may also be disturbed by the surrounding sound source during the measurement. Therefore, this method cannot provide accurate measurement values, and is generally used as a general source of noise sources and main occurrences or a rough positioning before accurate measurement. In order to identify the exact location of the noise, it is necessary to specifically grasp the distribution of the noise with the frequency, and then the spectrum analysis method can be adopted. There are many frequency inconsistent components in the noise generated by the screw air compressor, and these noise components are continuously distributed according to the frequency. At present, frequency doubling analysis and spectrum analysis based on Fourier transform are often used in China. Among them, the frequency multiplier analyzer is often used in combination with the sound level, and the Fourier transform (FFT) based spectrum analysis is the most effective spectrum analysis method. The test parameters of the spectrum method can be selected from the A-weighted assessment sound level, and the 1/3-fold frequency range analyzer is used. In order to measure the noise more accurately, the author recommends the following five tests: First, the screw air compressor is not started. Test the pressure level and spectrum of the A-weighted sound of the noise floor of each observation point. Second, run the screw air compressor to test the pressure level of the A-weighted sound of the noise of each observation point under normal working conditions. Horizontal and noise spectrum; third, open the box cover during normal operation of the air compressor, test the sound pressure level level and noise spectrum of each observation point A; fourth, only start the motor of the screw air compressor and open the box cover Test the sound pressure level and noise spectrum of each observation point A. Fifth, when the air compressor is in normal operation, open the box cover in the state where the air compressor does not inhale, and test the sound pressure of each observation point A. Level level and noise spectrum. According to the observation and analysis of each measurement point, it is possible to find out the cause of the noise exceeding the standard and take measures to control it. In addition, correlation analysis can be used to measure noise. This analysis mainly derives the characteristics of the noise source by collecting signals such as vibration and pressure of the compressor and then comparing the correlation of these signals with the noise signal. Since the pressure fluctuation of the screw air compressor and the vibration and noise of the compressor are related to each other, comprehensive analysis and comparison can better grasp the noise source law of the screw air compressor. 1.2 Noise Source Analysis of Screw Air Compressor The noise source of screw air compressor mainly has the following aspects: First, the noise generated by the cylinder when the screw air compressor works. Under normal working conditions, the periodic change of gas pressure will cause gas noise in the cylinder. At the same time, the change of air pressure will cause vibration of components such as cylinders and pistons. Second, the fluctuation of the tangential force during the operation of the screw air compressor produces noise. When the screw air compressor is turned on, the machine will shake sharply under the tangential force fluctuation, which generates noise. In addition, it also causes the bearing vibration noise of the compressor and the vibration noise of the outside of the body (such as the support structure and the base). Thirdly, the noise generated when the screw air compressor valve is opened and closed, and the airflow noise generated by the air valve chamber and the suction chamber and the exhaust chamber pipe. In the case where the exhaust pressure is increased, the pressure in the volume and the pressure difference in the exhaust port are also increased correspondingly, and the noise dividing edge is also increased. In short, the noise source of the screw air compressor changes with the load of the air compressor. In the case of heavy load, the main noise source is the exhaust artery; in the case of light load, the vibration of the rotor The rate will increase and become an important source of noise. Noise Control of W 2 Screw Air Compressor For the noise problem of screw air compressor, the manufacturer must take corresponding noise control measures, so that the appearance machinery meets the national standards and guarantee the manufacturing quality of the screw air compressor. 2.1 Controlling noise on the way of screw air compressor propagating noise to the outside world On the one hand, manufacturers can introduce advanced foreign technology and adopt a double-shell structure, which can effectively reduce the radiation and diffusion of noise to the surrounding; On the one hand, manufacturers can directly add noise enclosures outside the casing of the screw air compressor to reduce noise decibels. 2.2 Install the corresponding muffling equipment in the gas system of the screw air compressor to control the noise generated by the gas pressure pulsation. When selecting the muffler, the resistant muffler made of loose material should be selected. It should be noted that the muffler system The material should be selected from fibers and foams. Because the spiral air compressor operates, the pulsating airflow will damage the protective layer of the fiber material, and the foam plastic will age into a powder. If these fibers or powder enter the cylinder, the cylinder wall is easily damaged, thereby causing mechanical failure. 2.3 Control the noise generated by the rotor during vibration, so as to achieve the purpose of reducing noise. The specific methods are: first, change the geometric parameters of the rotor to reduce the noise caused by vibration; second, improve the assembly precision of the rotor, reduce the rotor in Vibration during exercise. For example, the manufacturer can change the tooth profile of the rotor on the basis of research to reduce the contact force of the tooth surface received by the rotor during operation, so that the screw air compressor can smoothly vibrate under various loads, thereby realizing Control noise. The manufacturer can also improve the machining accuracy of the rotor, such as changing the rotor from the original milling to grinding, which reduces the surface roughness of the rotor and reduces the medium and high frequency generated by the screw air compressor during operation. noise. In addition, it is also possible to reduce the noise of the exhaust duct by the bandage damping method, and control the noise by controlling the vibration of the air compressor body by the vibration isolation method. 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