| Compressor rectifier is an important component of aero-engine,whose manufacturing quality directly affects the working performance and efficiency of the aero-engine.At present,the small rectifier is mostly processed by butt welding,and the paste solder used for its vacuum brazing is composed of adhesive and alloy powder in proportion.The bubbles in the paste solder after mixing will lead to the formation of porosity defects in the weld of the rectifier during brazing,which reduces the working performance and service life of the aero-engine.However,paste solder is high viscosity,poor fluidity and expensive,conventional degassing method is difficult to meet the demand.In view of the above problems,this paper proposed to use the high shear effect and vacuum negative pressure of planetary centrifugal mixer(PCM)to break the solder bubbles,and realize the uniform mixing of solder through the spiral vortex flow field of PCM at the same time.The specific research contents are as follows:(1)The influence factors of PCM on the degassing effect of solder were studied.The existing forms of bubbles in solder were analyzed,and the theoretical models of the influence of PCM vacuum environment and planetary motion on the degassing process of solder were established.The influence of PCM working parameters on solder degassing effect was studied by CFD simulation,and then the influencing factors of PCM on solder degassing effect and the degassing mechanism were analyzed.The results show that the main factors affecting the degassing effect of PCM on solder are flow field structure,vacuum degree and viscous shear stress.PCM mainly through the comprehensive action of shearing thinning,spiral vortex flow,vacuum negative pressure and viscous shear stress to break solder bubble.Finally,the degassing experiment of PCM on adhesive was carried out to verify the correctness of the research results.(2)The influence of PCM’s working parameters on the mixing effect of solder was studied,and the process parameters of PCM mixing and degassing solder were formulated.The numerical simulation model of PCM mixed solder was established,and the mixing index was defined to quantitatively characterize the mixing effect of solder.The correctness of the simulation model was verified by particle mixing experiments.The simulation model established was used to solve the flow field structures,low velocity regions and discrete particle distribution of PCM mixing solder with different working parameters.Then,the influence of working parameters on the effect of PCM mixed solder was analyzed.The results show that when the rotation speed is constant,the mixing effect of PCM on solder increases first and then decreases with the increase of revolution speed,and the greater the rotation speed,the greater the corresponding optimal revolution speed.Combined with the influence factors of PCM on the degassing effect of solder,the process parameters of PCM mixing and degassing solder were formulated as rotation 1000 r/min,revolution 1800 r/min and vacuum degree 96 k Pa.Finally,the degassing experiment of PCM on solder was carried out and compared with the results of traditional degassing methods,it was verified that PCM can achieve efficient degassing and mixing of solder under this process parameter.(3)The in-situ coating of solder was realized and the feasibility of degassing solder with PCM to remove weld porosity was verified.Aiming at the problem that the degassed solder is mixed with bubbles due to transfer,a solder in-situ coating device was designed and built.The practicability of the device was verified by coating and sintering experiments.The vacuum brazing experiment was carried out,and the weld porosity was detected by X-ray detection system.The weld X-ray image porosity detection program was compiled based on MATLAB,and the weld porosities were measured and counted.The results show that mixing and degassing solder using the PCM can reduce the average diameter of weld porosity by about37.04% and the porosity by about 86.82%,which can effectively inhibit the weld porosity defects in vacuum brazing of high viscosity solder. |
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