Railroad thermite welding is a common method in railroad construction. We know that there is an interface at the railroad joint between two rails. There is a problem in the railroad industry. When a train drives by, the tremendous pressure can cause shaking or even cracking. These problems will threaten the service life of the rails and the safety of the trains. Therefore, how to solve this interface is an important project for railroad technology.

With the development of manufacturing industry, there are two main methods to weld the rails. One is electric welding and the other method is thermite welding.

What is thermite welding?

Railroad thermite welding is considered to be the most efficient method to weld railway rails. Due to its high efficiency, reliable quality and adaptability, railway thermite welding has become the most popular method in railroad construction. thermite welding has a wide range of applications. It is used to weld rails in railroad construction. Seamless rails can be made by thermite welding technology.

Its working principle is easy to understand. After setting up the thermal welding machine, we preheat the rails to 600 degrees. The welded part is then placed in a crucible and the welded part is ignited. The welded part will produce steel and slag. The high temperature molten steel will melt the interface between the two rails.

Features and Benefits

The current cut-off at the weld point is equal to that of the wire.
That the weld joint is permanent and will not cause high resistance due to loosening or corrosion.
that the weld joint is like copper, but tougher than the copper itself and unaffected by corrosive products.
that the solder joint can withstand repeated multiple high inrush (fault) currents without degradation.
simple and easy-to-follow welding operation method.
Lightweight equipment, easy to carry.
welding without the need for an external power or heat source.
the quality of the weld can be verified from the appearance.
Can be used to weld copper, copper alloys, copper-plated steel, various alloy steels including stainless steel and high resistance heating heat source materials.

Thermite welding is easy to handle. crs railroads offers thermite welding kits such as welding sections, sand molds, igniters and other separate components for railroad thermite welding. How is the rail welded? What is the procedure for thermal welding?CRS Railroad has laid out a simple guide for you.
 

The process of railway thermite welding

The railway thermite welding technique has 13 steps. We can divide it into three parts. The first part is preparation, the second part is operation and the third part is inspection. First, we will describe the preparation.

Preparation

First of all, we should prepare the welding site. We need to dig a hole with a depth of 300 mm and put the crucible into the hole. Then remove the railroad fasteners and measure the temperature of the railroad track. Also, verify the railroad track model and check if the thermite is suitable for that railroad track.
Next, we should inspect the railroad track. Check whether there is oxide on the surface and check whether the position of rail end is correct. The distance between the rail end and the railroad sleeper should be more than 10cm, otherwise we need to adjust the position of the rail. 
Thirdly, this is an important step. We need to make sure that both ends of the rails are aligned. The four main parameters that need to be checked are distance, vertical alignment, horizontal alignment and twist.
The distance between the two ends of the rails should be 23 mm to 27 mm. Horizontal alignment means keeping the centerline of each rail aligned. Vertical alignment means the distance between rail sleepers should be 1.5mm.(The distance between wooden sleepers should be 3.2mm.) Twisting means keeping the rail head and rail tail aligned.

Working process

After all things are ready, we start to weld the rails.
First of all, the sand mold is placed on the rail and coated with leak-proof material. What's more, workers must keep the centerline of the sand mold and the axis of the rail in line.
The next step is preheating. The purpose of preheating is to eliminate moisture and raise the temperature of the sand mold, thus avoiding the disappearance of air bubbles and slag. The fuels are oxygen and propane. In this process, you can prepare the hot stone and crucible.
Then, workers pour the thermite into the sand mold. after 5 minutes, workers take away the waste plates and crucibles and remove the sand mold.

Inspection

Hot grinding and cold grinding are necessary steps before use. During the hot grinding process, there are a few tips to keep in mind. First, remove the wedge after 15 minutes. Secondly, the inside and outside of the weld head are flush with the sides of the rail.
The purpose of cold grinding is to eliminate geometric discontinuities due to welding. Cold grinding should be operated 1 hour after pouring.
After that, workers should clean up the welding site and mark the welds.
 
So far, we have described the railroad thermite welding method. If you are interested in this railroad technology, you can contact us for more details. crs railroad provides you with thermite welding consumables and tools.