The Research On The Leakage Fault Diagnosis And Machining Process Improvement Of The High Pressure Ferrule Tube Fittings

This paper focuses on the leakage of the ferrule tube fittings used on cars and analyzes the main reasons of it by fault diagnosis methods.Through improving material,optimizing the surface heat treatment process,the manufacturing and the assembly process,the ferrule tube fittings can have a better seal capability and a lower leakage failure rate.The main contents of this dissertation are as follows:(1)Determination of the leakage fault location.According to the leakage data comparisons of hydraulic system and the application of ferrule tube fittings at home and abroad,we find the main place where leakage fault happens is at the pipe connections.(2)Leakage fault diagnosis of the ferrule tube fittings.According to the analysis of working principle and seal characteristics of ferrule tube fittings,the paper uses the subjective diagnosis method,the oil sample analysis method and the fault tree diagnosis method to confirm the reasons of the leakage in ferrule tube fittings.Three leakage elements are improper selection of materials,low manufacturing accuracy and irregular assembly process.(3)Material selection and surface heat treatment process.The paper analyzes the components of stainless steel and researches the influence of different elements.In consideration of the different environment where ferrule tube fittings are used,the paper chooses 316 stainless steel as its material and uses Carbonitriding Technology to strengthen the surface of two ferrules.The ferrules can have a better performance on wear resistance,corrosion resistance and hardness.(4)The FEA(Finite Element Analysis)of ferrule tube fittings.The paper uses ANSYS finite element software to make a three-dimensional model of ferrule tube fitting.The paper makes an analysis of ferrule tube fitting by FEA based on the load and constraints imposed during assembly.Comparing the stress distribution under different preloading forces can get the range of its preload.(5)The processing,assembly process and tests of the ferrules.The paper manufactures the new ferrules and installs them with the reasonable assembly process.After testing the new ferrule tube fittings,we find its seal characteristic is better than before,and its leakage fault rate is reduced.