Aluminothermic Welding

The thermite reaction was discovered by Dr. Hans Goldschmidt in Germany in 1895, and it was subsequently utilized in the United States for connecting train cars. This is when the method was introduced as a welding technique to the world. Thermite welding is a fusion welding process that provides the heat necessary to melt the edges of the materials and join them together using an explosive material that generates a substantial amount of heat. Today, this welding method has been replaced in advanced countries for rail connections due to problems such as welding distortions and low fatigue life by other more advanced welding methods. However, it is still used in less developed countries due to its simplicity and cost-effectiveness.

The method of performing this type of welding is very similar to casting, where the two pieces that need to be welded are placed inside a mold. The explosive material is positioned in such a way that, after detonation, it produces the molten material necessary for joining the two pieces.

The most common combination used to generate the heat required for thermite welding is a mixture of metal oxide and aluminum powder, resulting in metal and aluminum oxide, along with heat.

Heat + Metal + Aluminum Oxide → Aluminum Powder + Metal Oxide

The process of thermite welding is as follows: a mold is formed around the area to be welded. Once the mold is in place, thermite materials are placed in a crucible and ignited using a spark. An exothermic reaction occurs in the crucible, known as the aluminothermic reaction. During the reaction, the metal oxide (iron oxide) is converted into iron and aluminum oxide is formed. A large amount of heat is produced. This generated heat melts the iron and aluminum oxide, creating molten iron and aluminum oxide slag. The molten metal is then poured into the mold, and when the molten metal reaches the sections that need to be joined, it welds with the metal pieces. After solidification, it forms a very strong weld.

Narrow Gap Welding

The central piece is the most important and sensitive component in the assembly of railway switches, playing a crucial role in guiding the rolling stock on diverging tracks. The central piece is a single unit made of Hadfield manganese steel and is produced through casting. To connect the R260 rail, which is made of high-strength pearlitic steel, we use the narrow gap welding method.

Narrow gap welding was first developed in 1963 by the Battelle Memorial Institute in the United States. In recent years, various countries around the world have made numerous efforts to advance this method. Among them, Japan has shown particular interest in this method. Narrow gap welding was first used in the rail industry between 1971 and 1985 in Japan during the construction of the New Tōkaidō Trunk Line. After the 1970s, it was employed by the German electric railways as a superior method compared to thermite welding for connecting rails.

This welding is performed using the Shielded Metal Arc Welding (SMAW) method. As the electrode approaches the rail, an electric arc is formed between the rail and the electrode, causing the metal to melt and creating a strong bond once it solidifies.

Given that the narrow gap welding process is being used for the first time to connect Hadfield steel to rail steel, there are no specific standards for this connection in relevant sources. Therefore, various references have been utilized for this connection; however, the primary source used for implementing this welding process is the instructions from ESAB and the EN standard pertaining to rail-to-rail connections. The use of this type of welding serves as a substitute for flash butt welding, providing similar mechanical properties and pressure tolerance. Consequently, the EN 14587-3 standard, which is established for testing flash butt welds, is employed for the testing of this weld.