In the aluminothermic welding process, molten steel is poured into a mould surrounding the gap between the rail ends to be joined. The rail ends are connected by the liquid metal. The principle of aluminothermic welding is based on an exothermic chemical reaction of aluminium powder and iron oxide, producing sufficient heat to cause melting.
Before melting can start, the ends of the rails are cut to create a specified gap and the rails are aligned. Then a refractory mould is fastened around the gap by means of steel mould shoes. Leaks in the moulds are prevented by special luting material. After pre-heating both rail ends the exothermic reaction of the aluminium powder and iron oxide is started in a re-usable or a 'one-shot' crucible and the liquid metal flows into the mould. The metal fills the mould and the slag is discharged into slag bowls. After a cooling period the excess metal at the head of the rail is removed and grinding of the rail can commence.
As the welding quite often takes place in tracks which are in use, the speed of the welding operation and the safety of the welders are important aspects of welding on railway tracks.
In the process of theremit welding, the preheating temperature plays a decisive role in the welding quality. Improper preheating will cause poor welding. The performance of the welding heat affected zone will deteriorate, which will lead to welding failure.
The rail thermit welding timed preheating method adopts the rail top strong preheater developed in our designing. Under the constant process parameter specification, the preheating temperature of the rail end face is controlled by time to reach more than 600 ℃. At this temperature, the rail end face will not burn completely. , but it can ensure that the temperature distribution of the rail end face is uniform during pouring.
Secondly, in the design of the welding sand mould pouring system, part of the aluminothermic molten steel is used to further heat the rail end face so that it can be adjusted to a suitable welding temperature range. Since the process parameters of the strong preheater are constant, the preheating temperature and molten steel of the rail end face is stable, as well as the welding process of the rail during welding and pouring is also constant. When parameters are stabilized and the welding quality is reliable. The welding process with timed preheating greatly reduces the influence of human factors and makes the welding quality stable and reliable.
Using durable magnesia crucible and self-fusing plug automatic pouring technology. The use of durable magnesia crucible reduces the inclusion of silicon in the thermit weld, which improves the purity of the weld metal, it can adjust the silicon content in the weld as needed to improve the weld strength. The automatic pouring of self-fusing plugs simplifies the operation process, reduces the influence of human factors and makes the welding process more safer.
Combined with the current situation of China, we have developed an environmentally friendly disposable one shot crucible, which is characterized by no harmful gas generated during use, which effectively protects the physical and mental health of operators under harsh conditions. The use of one shot crucibles reduces factory welding tools and greatly simplifies operations, so it is widely welcomed by the project site.
With the increase in the type of rails in China, U74 hot-rolled rails, U71 Mn hot-rolled rails, PD2 quenched rails, PD3, hot-rolled rails, PD3 waste heat quenched rails, rare earth rails and other rails have been put into use, and the types of rail thermit portion are also increasing. Recently, we has developed thermit portion suitable for different strength grades.
In order to reduce the labor intensity of rail thermit welding, a two-way manual hydraulic shearing machine is developed, which is light in weight, easy to operate, safe and reliable, and greatly reduces the labor. Not only that, the use of the shearing machine avoids the joint caused by premature unpacking to ensure welding quality.
The developed frame type rail aligner device shorten the operation process and improve the smoothness of the joint. After the welded joint is polished and trimmed, the joint is smooth.
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