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Railroad Tracks: How are They Welded Together?

Train railroads are joined together by a process called exothermic welding – a chemical called Thermite is lit off and then sends molten iron into a mould.

Much further advanced now than in the past, many different methods are used to merge two rails chemically to create a continuously welded rail—methods like gas-pressure welding, enclosed arc welding, flash-butt welding and, as discussed above, thermite welding.

Thermite welding is used across the globe. There are two main reasons for this. Firstly, the skill level threshold to undertake such a process is much lower compared to other processes and secondly, it does not require an electric power source so it can be carried out wherever required.

Welders must cut two adjacent tracks so there’s a specific gap {usually about an inch}, each of the rail sections are clamped and sealed through sand moulds, ensuring the two rails are aligned perfectly. The ends of these rails are then heated with gas torches to prevent bubbles.

Then, a crucible is attached {which is filled with an thermite compound – iron oxide, aluminium and alloying agent} on top of the mould and the thermite is lit off using a high-temperature magnesium sparkler.

This causes the thermite to melt, which in turn melts the plug at the bottom of the cruicle, sending the iron into the gap left between the two railtracks. The alumia slag {which is yielded from the melted thermite} flows in last because it has a lower density. Then this overflows and is gathered in catch pans on the side of the rail.

Once the metal has hardened, the moulds are removed and the welds are cleaned up with hammers, chisels and grinders.

And, that is how railroad tracks are welded together!