The Theoretical Analysis And Experimental Research Of Vibration Frictional Of Dry Gas Seal Based On Fractal Theory

With the rapid development of modern industry,the requirements for dynamic seal of rotating shaft end were getting higher and higher.Dry gas seal,as a non-contact seal,was favored for its low leakage rate,high reliability and wide application of medium.However,engineers found that due to the influence of manufacturing level,assembly process errors and working conditions and other factors,the dry gas seal end face may have contact friction in the start-up phase,the stop phase and the operation phase in the work.At the same time,the contact friction will be accompanied by vibration,wear,noise,temperature rise and other phenomena between the end faces of the moving-ring and static-ring,the whole sealing system may be unstable or even fail.The friction vibration was a common phenomenon in the process of friction and wear,which contains a lot of information reflecting the tribological characteristics and the friction state of the system.Therefore,it was of vital significance to study the frictional vibration of the end face of the moving-ring and static-ring of dry gas seal of dry friction.In this paper,the frictional vibration of the end face of moving-ring and static-ring of dry gas seal was studied.Based on the microscopic contact mechanics of the friction interface,the contact deformation mode of the micro-convex body and the base length of the root of the micro-convex body of actual load were redefined,together with the fractal theory,the friction vibration system of normal contact stiffness and tangential contact stiffness were constructed.The friction system combined with friction system characteristic parameters of the dry gas seal end face was simplified into a two-degree-of-freedom model,so that the friction vibration system model of two-degree-of-freedom dry gas seal sliding friction interface was established.At the same time,the testing platform of friction vibration of dry gas seal was constructed to test the signal the friction vibration of the end face of the moving-ring and static-ring.Ultimately,the frictional vibration of the end face of the moving-ring and static-ring of dry gas seal was studied by the model calculation and the test.According to research about the incipient sliding problem of the non-conforming elastic bodies under tangential force and the end face morphology of dry gas seal was characterized by fractal parameters and the re-established contact deformation model of the micro-convex body,the fractal model for normal contact stiffness and tangential contact stiffness of dry gasseal were established.The rationality and correctness of the model was verified by the comparison with the related experimental data and the model,the key factors influencing the normal contact stiffness and the tangential contact stiffness were analyzed numerically,and the results showed that the normal contact stiffness increased with the increased of fractal dimension and real contact area.When the contact area was fixed,the normal contact stiffness decreased with the increased of the characteristic scale and friction coefficient.The effect of the coefficient of friction on the normal contact stiffness was relatively small compared to the fractal dimension and the characteristic scale,the tangential contact stiffness increased with the increased of fractal dimension,real contact area,and material properties factor.It decreased with the increased of the characteristic scale and friction coefficient.The effect of the coefficient of friction on the tangential contact stiffness was relatively small compared to the fractal dimension,the characteristic scale and the material properties factor.The dimensionless normal contact stiffness and the dimensionless tangential contact stiffness obtained by the above mentioned model provided a theoretical foundation for the paper study and establishment of the two-degree-of-freedom frictional vibration system model of the sliding frictional interface of dry gas seal.The microstructure and stress of the end face of the moving-ring and static-ring of dry gas seal were analyzed under dry friction condition and based on fractal theory and the dimensionless normal and tangential contact stiffness has been given,the normal displacement excitation of seal face with fractal parameters and a two-degree-of-freedom frictional vibration system model of dry gas seal in dry friction state were constructed.The influence factors of the friction vibration system model were analyzed numerically.The results show that the normal vibration displacement and velocity increase first and then decrease with the increase of fractal dimension and rotation speed.The displacement and velocity of normal vibration increase with the increase of characteristic scale and friction coefficient.The normal vibration changes with quasi-periodic high-frequency and micro-amplitude vibration law.Compared with the characteristic scale,the fractal dimension has a more significant influence on the normal vibration,while the friction coefficient is not a sensitive factor for the normal vibration.The tangential vibration displacement and velocity increase with the increase of friction coefficient,and change periodically with high-frequencyand micro-amplitude vibration.Meanwhile,the influence of friction coefficient on tangential vibration was more obvious than that on normal vibration.The above mentioned researches provide a foundation for further study of the frictional vibration with high frequency and micro-amplitude in the dry gas seal.In order to verify the friction vibration system model of two-degree-of-freedom dry gas seal sliding friction interface in this paper,a test platform of dry gas seal friction vibration was established.The friction vibration signal between the end faces of the moving ring and the stationary ring was tested by the acceleration sensor,and the friction vibration signal was analyzed and processed by the harmonic wavelet packet transform.According to different working conditions,the friction vibration parameters was calculated by using the theoretical calculation model in this paper and the friction vibration parameters was measured by the test platform of the research group.The contrastive analysis shows that when the load was constant,the calculated amplitude of the theoretical model and the measured amplitude increase with the increase of the rotational speed.When the rotational speed was constant,the calculated amplitude of the theoretical model and the measured amplitude increase with the increase of the load.Under the same condition,the calculated amplitude of the theoretical model was closer to that of the experimental test,and the calculated amplitude of the theoretical model was larger than that of the experimental test.Although the calculated amplitude of the theoretical model was deviated from the measured amplitude,especially in the normal direction,the variation law and trend were basically similar,and the frictional vibration amplitude was of the same order of magnitude.This shows that the two-degree-of-freedom frictional vibration system model of dry gas seal was reasonable and correct.