Research On Induction Brazing Technology Of Brake Tube Of Heavy Freight Train

The brake tube is one of the important parts in the braking system of railway freight train.It is connected with the gate valve and brake through the joint body,and transmits the braking force when the vehicle is braking.The connection between the brake tube and the joint body is realized by an arc welding girth weld.In the process of vehicle operation,vibration caused by a variety of reasons often causes fatigue fracture at the welding toe,which poses a threat to railway transportation safety.The stress concentration at the toe of arc welding joint is an important cause of fatigue failure.It is necessary to improve the welding process to improve the anti-fatigue performance of the joint between brake tube and joint body.To solve the above problems,induction brazing is used in this paper to complete the welding of brake tube and joint body instead of arc welding.The process parameters of induction brazing are optimized by orthogonal test combined with analysis and test of joint microstructure,hardness and shear strength.Finally,the fatigue life of the joint under a given load is determined by three-point bending fatigue test,and the anti-fatigue performance of brazing joint and arc welding joint is compared and analyzed.The results show that when the assembly clearance is constant,several factors jointly affect the welding quality of brazing joint,among which the most important factor is the holding time,followed by other factors.Under the premise of ensuring the same assembly relationship between the brazing joint and the brake tube,the shear strength of the brazing sample is 396MPa,which is lower than that of the arc welding sample 452MPa,but the maximum shear load can be borne by the brazing joint is higher than that of the arc welding joint because the total lap area of the brazing joint is larger than that of the arc welding joint.When other influencing factors are the same,the shear strength of brazed joint increases with the decrease of assembly clearance,and reaches the maximum value 443MPa when the assembly clearance is 0.05mm.Under the given load P=10.18k N,the fatigue life of arc welding sample is 3.72×10~5 and that of brazing 30°angle transition sample is 4.73×10~5.The joint structure reduces the influence of stress concentration,and the fatigue resistance is improved obviously.It has been proved that the best parameters of brazing joint are:assembly gap 0.05mm,joint transition angle 30°,heating time 30s,heat holding time 70s,heating current 900A,heat preservation current 705A.