Experiment Study On Tribological Performance Of The DLC Thin Film Micro-textured Surface With Dry Gas Seal

The end faces of dry gas seal are separated from each other and the interface is in the state of gas lubrication,during system normal operation.Under the conditions of start,stop and fluctuation conditions,the dynamic pressure effect between the in-terface is insufficient,due to the low speed,the seal ring end faces contact each other,the interface is in a state of dry friction,the seal ring end face will cause friction and wear and self-induced vibration,which affect seriously the sealing performance.In engineering practice,the friction and wear of the end face has become an important factor affecting the sealing effect and shortening the use of the sealing ring surface.Under boundary and dry friction condition,in order to improve the tribologica l performance of the sealing material,solve the poor sealing ring wear resistance and short service life.The DLC coating technology improving seal ring material perfor-mance and the surface texture changing material surface morphology and organiza-tion perspective are studied in this paper.The effects on friction performance in dry gas seal of DLC film textured face friction characteristics and vibration intensity are the research object in this study.Under simulated conditions,the tests are completed by the friction and wear test platform and data information acquisition system.The performance of friction mechanism is analyzed according to the data graph of DLC film texture surface,the vibration acceleration time-domain signal is reconstructed and decomposed by using the harmonic wavelet package and Fourier transform,then the frequency band of self-induced vibration is analyzed and the characteristic value of vibration is extracted through the spectrum curve of the friction vibration.Three-dimensional non-contact surface profilometer and scanning electron microscope（SEM）were used to measure the surface appearance and wear.The micro-textured surface was processed by the optical fiber laser marking machine,the pits are arranged circular matrix,the diame-ter of the pit includingΦ150μm,Φ200μm andΦ250μm,surface density including 5%,10%and 15%,indentation depth is10μm;Then micro-textured surfaces were coated with DLC film with film thickness of 3μm,thus 9 kinds of textured surfaces with different parameters and 16^o and 18^o SiC spiral groove sealing rings were prepared.Under simulated working conditions,the DLC textured surface sealing ring and SiC spiral groove sealing ring form a"hard-to-hard"friction pair.The friction char-acteristics were tested by the end friction and wear tester.The influence law and friction mechanism of surface texture geometric parameters and working conditions on the tribological performance of dry gas seals were analyzed through the curve of friction coefficient.The experimental results show that the structure surface changes the contact state of the friction pair and reduces friction.The friction coefficient of textured surface is much lower than that of smooth surface under the same working condition.The friction coefficient first decreases and then increases with the increase of the diameter of the pit,but the range of the friction coefficient changes gradually decreases with the increase of the diameter,the larger the diameter,the more stable the friction state is,the less particles on the sealing ring surface.With the increas ing of textured surface density,the load on per unit area increases,and the friction coef-ficient increases.However,the surface density is the larger,the dynamic pressure effect between the interfaces is the more obvious,so that the friction state becomes more stable.The research results show that the friction condition ofΦ200μm textured surface is relatively stable;The friction coefficient of 10%texture surface is low and improve the friction state of dry gas seal obviously.Under the same condition,due to the comprehensive influence of dynamic pressure effect and surfac e morphology,the friction coefficient decreases with the increase of load and rotate speed,and the fric-tion state tends to be stable.The friction vibration characteristics of the dry gas seal at the opening stage were tested,and the data of friction torque,temperature and acceleration of friction vibration were collected under the simulation condition.The textured surface of the seal ring can effectively improve the friction performance and the contact state of the end face of the dry gas seal system.Texture can not only produce dynamic pressure effect to stabilize the system operation,but also cause the collision between the in-terface and the edge of the pit,which changes in the friction force and vibration ac-celeration signal of the friction interface.Through the contrastive analysis of the ex-perimental data and the mechanism of the frictional vibration,the research shows that the dynamic pressure effect ofΦ150μm and 5%of texture surface is small,the sta-bility of the system is poor,the dynamic pressure effect ofΦ250μm and 15%surface texture is evident during running,but the end face of the impact will be worse.So pits withΦ200μm diameter and10%density can effectively improve the tribological and wear properties of interface.Frictional self-induced vibration is a weak high frequency low amplitude vibra-tion,and the time-domain signal of vibration acceleration is decomposed and recon-structed by using the harmonic wavelet packet and Fourier transform to obtain 32sub-bands.By analyzing the time domain diagram and frequency domain diagram of the vibration signal,the characteristics of the friction vibration signal are extracted,and the frequency of the self-induced vibration of the system is about 7.5 KHz.The natural frequency of vibration is 1.140 KHz,and the maximum amplitude is0.3417?10^-3 and the frequency is 19350Hz.Through the stability analysis of the self-induced vibration acceleration data and its variance and other parameters,it can be seen that the screw angle of 16^o can better improve the friction state between the end faces of the sealing ring than that of 18^o.The results will provide basis for the stability of the system,the selection of friction pair materials and the optimal design of surface texture simulation.