锤片式粉碎机噪声源识别及降噪方法

为了解决锤片式饲料粉碎机工作过程中噪声大的问题,运用虚拟仪器测试技术和台架试验相结合的方法,对粉碎机的噪声信号进行采集和分析,针对影响噪声的主要因素如锤片、筛网、进料口、出料口和转子转速等进行相应的声压级和频谱测试分析,寻找粉碎机主要噪声源及其与主要影响因素之间的规律,并通过对粉碎机各部件的结构参数进行改进设计,达到降低整机噪声的目的。研究结果表明:粉碎机噪声信号主要包含48、180、200、361、893和1 263 Hz共6种频率成分;筛网、进料口和出料口对主频成分没有影响,只影响噪声频率的幅值;筛网具有降噪作用;进料口和出料口都不同程度地增强了噪声声压级;通过对主轴转速为2 400~2 800 r/min时的空载噪声频谱图分析知,当转速升高时,噪声幅值急剧升高,可见转速对粉碎机的噪声有影响;对不同锤片数量的空载噪声频谱图分析知,锤片数量只影响噪声幅值,对主要频率变化影响较小。此外,对粉碎机进料口、出料口、筛网的结构参数进行改进设计,以出料口的改进设计为例,基于有限元法对改进前后分离装置内的流场湍动能分布情况经行了模拟,将改进前后的结果进行对比分析发现:出料口改进后分离装置内气流的湍动能较小,流动较为稳定。通过台架试验表明:当选用改进后的出料口时,粉碎机整机噪声得到明显改善,噪声总声压级降低了3 d B(A),各测点噪声声压级降低1.9~3.6 d B(A),进一步粉碎试验表明使用改进后的出料口并未影响粉碎机的生产效率以及吨料电耗,研究所采用的降噪措施可行,此法可为控制粉碎机噪声提供理论依据。

Noise sources identification and noise reduction methods of hammer mill

Abstract: In order to solve the problem of big noise during the working process of the hammer mill, and search for the main noise source and noise reduction method of hammer mill, the noise signals were collected and analyzed by the virtual instrument software LabVIEW and bench test on the hammer mill. The sound pressure level of the hammer mill was tested and analyzed in no-load and load conditions, and the spectrum of the hammer mill was tested. The result of this test shows the no-load sound pressure level of the hammer mill is bigger than the load sound pressure level. The material loading or not only changes the size of the peak of the noise. Thus it can be seen the key of absorbing the noise is to reduce the no-load aeromechanic noise. The noise sources of hammer mill were superimposed, bringing about the multivariate source coupling problem. The distribution operation method was used to test the noise of the hammer, screen, feeding inlet and feeding outlet. Sound pressure level and frequency spectrum were analyzed to find the main noise sources of the hammer mill, according to the main factors of noise such as the hammers, screen, feeding inlet and feeding outlet. Noise pressure level was tested and spectrum was analyzed in the state of noise with a single factor and combination of multiple factors. The results are as follows: The noise signals contain 47, 180, 200, 361, 893 and 1263 Hz. The screen, feeding inlet and outlet have no effect on the main frequency component. The screen has the noise reduction function; the feeding inlet and outlet enhance the noise pressure in different degrees. The sound pressure level of the single rotor is very small, which reveals that the hammer has a great influence on the noise. The noise is strengthened when the hammer and the outlet work together; the noise of hammer mill is greatly reduced when it has no hammer piece. Based on the analysis of no-load noise spectrum of 2400-2800 r/min, when the speed increases, the noise amplitude increases dramatically, indicating that the effect of noise on high-speed grinder is evident. When the speed is 2400-2800 r/min, the main noise source is in good agreement with the noise base frequency and the second-harmonic frequency of the hammer mill; when the speed is lower than 2600 r/min, the broadband signal energy to noise frequency signal of grinder is larger, indicating mill noise of vortex at low speed is dominant; when the speed is higher than 2600 r/min, the discrete signal energy to noise frequency signal of hammer mill is larger, that is to say the rotating noise is dominant at high speed. In the working condition of no load and rated speed, the noise sound pressure level of the hammer mill was tested with no hammer, single row hammer, 2 row hammers, 3 row hammers and 4 row hammers respectively. It is known that the number of hammers only affects the amplitude of the noise and has little influence on the change of the main frequency by analyzing the spectrum diagram of the no-load noise with different numbers of hammer pieces. Besides, the structure of feeding inlet, outlet and screen was improved in design. Taking the outlet improvement design as an example, turbulent kinetic energy of original and improved separation device was simulated. The comparison results show that the kinetic energy of the improved outlet is less. It is proved that the improvement of the outlet is beneficial to the noise reduction in the experiment, the total sound pressure level was reduced by 3 dB(A), the sound pressure levels of test points were reduced by 1.9-3.6 dB(A), and the hammer mill production was not greatly affected. Some other methods of noise reduction were proposed. This research provides theoretical evidence for the noise reduction design of the hammer mill.