Study Of Acoustic Emission On Rubbing Impact Fault Diagnosis Of Rotating Machines

The rubbing and impact between the static and dynamic components is the common typical malfunction of rotating machinery, which is great harmful to the safe and steady running. So identifying and diagnosing the rubbing and impact malfunction have heavy significance on the warranting the safe running of the rotating machinery.It is necessary to analyze the mechanism of acoustic emission signals generated from the rubbing and impact, which will make better understand of acoustic emission signal and carry out the effective identifying of rubbing impact malfunction. By analyzing the process of static and dynamic rubbing impact, the principle of static and dynamic rubbing impact is the contact of multi-micro asperity, which is proposed in this paper; based on the GW contact model, the theoretical model of acoustic emission signals which have the relationship between the rubbing impact contact forces is established. By analyzing this model, it indicates that the distribution of measured acoustic emission signals is the same as the distribution of contact micro asperity. From the full circular and local rubbing impact experimental research, it is verified that the propagation of acoustic emission energy in rotor structure is the linear attenuation.It is necessary to study the noise reduction techniques for acoustic emission signals because that the acoustic emission signal of early static dynamic rubbing impact malfunction is weak compared with background noise. So based on the characteristic of acoustic emission signals, the self adapting threshold method is employed to reduce the noise of continuous wavelet transformation coefficients and then the coefficients will be rebuilt by using inverse continuous wavelet transformation. The results indicate that this method can eliminate the noise of the signals effectively and keep the weak impulse components.By analyzing the structure of the rotor, the rubbing impact locating problem is the case of linear location for acoustic emission source. It indicates that the key techniques of allocating the malfunction position are how to obtain the arriving time and the velocity of the wave. Then the AR model is employed to get the arriving time of acoustic emission wave based on the characteristic of burst acoustic emission signals. For successive acoustic emission signals, the frequency characteristic is obtained by applying the bandpass filtration and the time delay is determined by employing the cross correlation technique to extract signals, also the spreading velocity will be identified.The blind deconvolution technique is applied to the treat the acoustic emission signals, which can identify the signals effectively and classify the signals better. This method of analyzing the effect of signals attenuating on the transmission path from detected acoustic emission signals can extract the true acoustic emission source signals possibly.The rubbing impact between the sealing pads and sealing disks experiments, the rubbing impact of journal tilting pad bearing experiments are carried out on the 600MW super-critical steam turbine-generator simulated test rig. The results indicate that the concerned method from the research above can treat the detected signals which have strong background noise and reduce the noise. The results of tilting pad bearing malfunction experiments indicate that by arranging the acoustic emission sensors on the housing reasonably, and employing the arriving time of different acoustic emissions sensors and the mean square root of acoustic emission signals, the rubbing impact position of the pads can be identified, which provides the effective way for the early diagnose of rubbing impact malfunction.