| Rubbing and breaking machine is a new type of forage processing equipment, which is developed in China in recent years. It is a new processing method which is between cutting and crushing process technologies. The rubbed straws are soft and fluffy filaments, which have appropriate length and coarseness. As a result, it is extremely beneficial for directly feeding,smashing,drying,grinding,granulating,briquetting (cake),chemical processing,biological treatment and other subsequent processing However, the rubbing and breaking machine are the same as the most rotating machines that have the disadvantages of high noise and strong vibration, which seriously impedes the further promotion and development of rubbing and breaking machine. This paper is a study of aerodynamic noise and mechanical noise, which combined with theoretical analysis, numerical simulation and experimental study on the mechanism of its noise generation and characteristics, the main contents are as follow:(1) According to national standard GB6971-86《mill test methods》and GB3768-83《noise source power level measurement method for simple》, the experiment had been conducted on five measurement points around 9R-40 rubbing and breaking machine under no-load and load conditions, The result is that aerodynamic noise is the main noise source whether it is no-loaded or loaded.(2) Based on wavelet tools package provided by MATLAB software, the main noise sources are identified using the technology of wavelet and spectrum analysis. The noise signals which are obtained on the no-load and load conditions are decomposed with db4 wavelet in the scale of 6, for the fifth measurement points.then the decomposed coefficients in seven different frequency band were obtained. According to the energy distribution of the 7 different frequency bands noise signals of the 9R-40 rubbing and breaking machine, the result is that the main signal of the rubber noise is mid-frequency noise.(3) The separation study is carried out that take deflector,toothed plat,hammer and fan and combination of them as main factors. The result obtained that is aerodynamic noise was mainly caused by rotating fan, and secondary factors were hammers.Deflector has little effect on the noise, but tooth plate has an effect of sound absorption.(4) The relationship between sound pressure level and rotating speed,the number of hammer which have great impact on the noise were obtained. The higher the speed is, the greater the noise is. And in the range of speed from 2400 r/min to 2800r/min, the optimum speed should be about 2600r/min. The numbers of hammer pieces are more related to noise size, but less related to noise frequency.(5) By vibration testing, the actual vibration frequencies of the main parts of the rubbing and breaking machine focused on the range of 100-500Hz. Besides there was seriously rotor dynamic imbalance, and the vibration energy of bearing in the three directions of x, y, z are large, which has a lot of critical effects on the life of bearings and vibration of the whole machine.(6) Based on structural mechanics and vibration theory, the natural frequency and vibration mode of the upper and lower shell of 9R-40 rubber were analyzed using the finite element analysis software ANSYS, combining with vibration test results and simulation results, the structural optimization program was purposed on the point of stiffness, which provide a theoretical reference for improving machine and performance optimization.(7) For studying principle, property and law of producing air disturbulance noise, three dimensional inner flow fields were simulated with Fluent software. Properties and state of the flow fields were showed directly. Comparing numerical simulation curves with experiment data, the maximum relative error was indicated less than 8%. The distribution of pressure and velocity of flow fields were obtained from the simulation results at 2800 r/min. By analyzing the simulation results of flow field, both rotation noise and eddy current noise were produced when low airflow from inlet was affected by high rotating rotor. In addition, a reversed flow is formed in the outlet, which can cause a block and produce noise.
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