Research And Simulation Analysis On Friction And Wear Of Piston Ring Of EMU Air Compressor

With the rapid development of society,railway transportation plays an increasingly important role in our national economy.Bullet trains have gradually become the first choice for people to travel because of their advantages of convenience and speed.The application of piston type oil-free air compressor in high speed train is concentrated in air conditioning system and train braking system.The core friction pair of piston air compressor is the piston ring and cylinder liner,which is very important for the sealing of the compressor.In the working process,the piston ring and cylinder liner are easy to wear,especially when there are impurities in the compressed air,the wear phenomenon is aggravated,which requires the piston and cylinder liner to have good wear resistance.This paper uses thermosetting polyimide（TPI）as the matrix material.Polyimide（TPI）,silicon nitride(Si₃N₄)and reduced graphene（r-GO）composites（TPI/r-GO/Si₃N₄）were synthesized using silane coupling agent（APS）.The mechanical properties and tribological and wear properties of the coatings were investigated.Then,Workbench analysis software was used to conduct simulation analysis of the piston ring-cylinder liner system before and after coating at 22℃and 90℃.The specific research work is as follows:（1）By analyzing the working conditions of piston ring and cylinder liner,the performance requirements of the self-lubricating layer were obtained.In this paper,TPI was used as the matrix,r-GO/Si₃N₄ was prepared as the reinforcement phase and added into the matrix,r-GO/Si₃N₄/TPI composite material was prepared as the self-lubricating coating.After various characterization of the material,it was found that r-GO/Si₃N₄/TPI,r-GO/Si₃N₄ had certain chemical bonds,rather than simple mixing,which provided a basis for the subsequent friction experiment analysis.（2）After the friction experiment of TPI composite coating composed of reinforcement phases with different loads and different percentage content,the relevant friction coefficient and wear rate were obtained and the data were analyzed.The results showed that the tribological properties of the composite coating were improved compared with that of pure TPI when r-GO and r-GO/Si₃N₄ were added as reinforcement phases respectively.The friction coefficient and wear rate of r-GO/Si₃N₄ composites are better than that of pure TPI and r-GO/TPI composites under the same load,and r-GO/Si₃N₄/TPI composites exhibit better tribological properties with greater load.The minimum friction coefficient and wear rate are both generated at 300N loading,respectively,of 0.25 and 0.6×10-8 mm³N^-1m^-1,which proves the macro-improvement effect of r-GO/Si₃N₄.（3）A series of characterization methods were used to characterize the worn surface after friction and the transfer film on the surface of the dual ring,and the friction and wear mechanism of the self-lubricating coating was analyzed.When adding different reinforcement,the relative wear morphology can be improved.When r-GO/Si₃N₄ is added,the improvement effect of the wear morphology is the best,which shows that the wear surface becomes more smooth and only a few pitting pits.It can be seen from the characterization and observation of the transfer film formed on the surface of the dual ring that the addition of r-GO/Si₃N₄ can significantly improve the quality of the transfer film formed.r-GO/Si₃N₄/TPI composite is a kind of high polymer self-lubricating material with excellent frictional properties.（4）The finite element analysis software of Workbench was used to simulate the running condition of piston rings at room temperature and high temperature by setting the comparison experiment at 22℃and 90℃under the thermodynamic coupling condition.According to the simulation results,the stress,strain,friction stress,temperature of piston ring and cylinder liner before and after adding coating are improved after a cycle of friction at the same temperature respectively.When the temperature rises from 22℃to 90℃,the working environment of piston ring and cylinder liner and coating is more severe,the stress,strain and friction stress are significantly increased.Combined with the experimental and simulation results,it can be seen that r-GO/Si₃N₄/TPI self-lubricating coating has excellent tribological properties and effectively improves the working environment of the piston ring,which also provides a reference for the application of the coating on the inner wall of the cylinder liner.