Research On Acoustic Emission Of Diamond-coated Mechanical Seal Wear And Health Evaluation

Mechanical seals are the key rotating machinery in industrial applications related to petrochemical,nuclear power,aerospace,and marine.Specifically,mechanical seals are widely applied in centrifugal pumps,compressors,mixers,turbines and aerospace engines,and other rotating equipment.The changes in the operating conditions of mechanical seals eventually affect their end face condition,and poor working conditions will intensify end face wear,which in turn will lead to a decline in seal performance,and even sudden failure.It will seriously endanger production safety and cause economic losses.Therefore,it is important to study the wear process,condition monitoring and health assessment methods of mechanical seals to ensure the normal operation of mechanical seals.With the development of condition monitoring technology,massive studies have focused on the monitoring and analyzing the seal face friction process,but mainly on the lubrication state of non-contact seals.With the development of coating technology,diamond-coated contact mechanical seals have received much attention due to their lower cost and good sealing performance.The wear process of contact mechanical seals is more continuous,and the wear is more frequent and complex compared to non-contact seals.Previous research has confirmed the effectiveness of acoustic emission techniques for monitoring the wear of seals.However,few researches have been carried out on acoustic emission of contact seal wear.Yet,no precise method has been proposed to assess the seal condition.In addition,there has not been sufficient research into acoustic emission signal denoising for contact mechanical seals under actual conditions.In this paper,a mechanical seal test platform and acoustic emission-based condition monitoring systems are designed based on a comprehensive analysis of the previous research.Using modern signal analysis and processing methods,experimental analysis of diamond-coated mechanical seal wear acoustic emission signals is carried out,and noise reduction methods for seal wear acoustic emission are proposed.Finally,the evaluation method of seal health status is studied.The research contents and corresponding results are as follows.(1)Based on the multi-functional friction and wear testing machine and pump sealing device,a test system was designed and constructed for the study of wear acoustic emission characteristics and continuous wear process of diamond-coated mechanical seal,and the related condition monitoring system was established,which provided a solid foundation for subsequent research.(2)The characteristics of the wear acoustic emission signal of diamond-coated contact mechanical seals operating under different working conditions are studied.Firstly,by analyzing the correlation between the acoustic emission band energy and the friction coefficient,the main frequency distribution of the wear acoustic emission was found to be in the range of 0～200k Hz;then,the wear acoustic emission was analyzed from the time domain,frequency domain and timefrequency domain of the acoustic emission signal,respectively.It was found that the increase in speed and load would aggravate the wear of the seal but would not result in the frequency shift of the wear acoustic emission.In general,the wear process was random and sudden,and the higher the wear intensity,the more complex the distribution of the acoustic emission spectrum.(3)The noise characteristics of diamond-coated contact mechanical seals are studied,and the EWT-KLD noise reduction method is proposed.The electrical noise and mechanical background noise characteristics are analyzed by rotating the test rig with bare hands and by idling the test rig without the seal installed.It was observed that the electrical noise occurs at ultra-high frequencies around 710 k Hz,while the mechanical background noise is distributed between 100 and 400 k Hz and increases with speed.In order to attenuate the effect of noise on the wear acoustic emission signal,the wear signal and the noise signal are decomposed by EWT,and the KLD of the corresponding frequency band is calculated based on the decomposed signals.Furthermore,the KLD threshold is calculated by the CUSUM algorithm to distinguish the noise band from the useful signal band,and the noise reduction is implemented by reconstructing the signal with the retained useful signal.By verifying simulation data and real experimental data,the traditional methods regarding selecting correlation coefficient bands are compared.The results show that the proposed EWT-KLD achieves satisfying and stable noise reduction performance.(4)The mechanical seal wear process was studied,and the mechanical seal tests under different working conditions was designed and conducted continuously.The results shows that the wear process of the mechanical seal conforms to the general rule of typical wear process,and the acoustic emission signals of the grinding stage,stable stage and violent stage are distinctly different.By extracting the characteristics of the original acoustic emission signals,the trend of acoustic emission characteristics of the seal wear process is analyzed.Three friction states of diamondcoated contact seals are studied,namely water-lubricated fluid friction,stable dry friction,and severe dry friction,and a CNN-based seal friction state identification model is proposed.This improves the qualitative and quantitative assessment of the health of mechanical seals.The validity of the health assessment method is verified through four sets of experimental data of continuous operation of mechanical seals under different working conditions.(5)Based on the results of theoretical research,the mechanical seal health evaluation system is designed,and all functions are implemented by software,which confirms the application value of the theoretical research in this paper.