Rail Joint Thermit Welding In Low Temperature Quality Analysis And Countermeasure Research

This thesis analysis a lot of rail welding problems, points out the importance of studying them, which is in order to improve the welding process and enhance the quality of welding.First, rail failure in Changchun permanent way section have been researched and been made statistical analysis at full length, by analyzing the parts of welding defects appearing in field, two types of welding defects are defined——outer defects and inner defects. Then the concept of welding defects, the causes and the features are introduced in detail. The results show that low temperature is the major cause of rail failure in Changchun permanently way section.Second, the theory of the thermit welding is introduced, after that, the low temperature effects on the mechanical property index of welding head, microstructure and the thermit welding progress are analyzed. After further study, the mechanism for low temperature causes thermit welding quality defects is obtained. Low temperature increases the weld cooling rate and that lowers the quality. This thesis proposes two types of thermit welding, one is isothermal welding method and another is temperature compensation welding method.Then in order to check its practical feasibility, the analysis has been done with a serials of experiments. The results show that both of them have remarkable effect of improving the welding quality in low temperature. But isothermal welding not only needs more time which is limited by the time of’sky-light’but also has potential safety hazard. These make the method not implemented easily. The temperature compensation welding method needs relative less time and is not affected by the weather. This method not only ensures the thermit welding quality in low temperature but also meets the requirements of train operation, which has a great practical significance on improving the rail welding quality in winter.Last, this thesis has confirmed that thermit welding in winter has a wide serviceability internationally.The temperature compensation welding method had been applied in Changchun permanent way section. And it worked well.In order to improve the thermit welding quality, this thesis argues that welding head extensibility and equipment of thermit welding in low temperature have rooms for improvement and look forward to further developed.