Thermite Welding Overview

Thermite welding is a process that results from a chemical reaction that is created through heating metal to a super high temperature between two reducing agents, one of which will be a metal oxide and the other aluminum or sometimes other types of reducing agents are used. This can be done with pressure or without pressure. At this point the liquid metals will produce a filler metal.

 

The chemical reaction that is produced will give off a temperature of 4500 degrees Fahrenheit or 2482 degrees Celsius. This metal that was created with high heat is found in a crucible that is part of the weld joint. It is actually above this joint.

 

This chemical reaction or exothermic reaction as it is also called, will be slow compared to other processes; it takes about 20 or 30 seconds and it doesn't matter how many chemicals are part of the process -- it still takes about the same amount of time.

 

When the welder wants to weld two things together, the two parts are lined up equally but a gap is made between the two pieces of metal. Before the two pieces of metal are put together there is a mold that is put between them so that the hot steel can go into the mold. Because this new metal is hotter than the base metal, the base metal will melt along the edge of the pieces to be welded.

 

From the crucible, the hot metal now allows heat to be lost and this causes the metal that has been melted to become solid again and a process called coalescence happens and this completes the weld. In the event that you have larger parts that need to be welded, you may need to preheat them and this is done inside the cavity within the mold.  This is done to bring these larger pieces to the correct temperature for welding and the process also help to make sure that the mold is dry.

 

When you have smaller parts, this preheating is usually not necessary. The mode that is used for thermite welding is the automatic one which means that once the chemical reaction starts, the process continues until it is finished.

 

The process of thermite welding uses gravity to bring the metal down to the cavity between the two parts through the gap. This practice of welding is like pouring castings in foundry type businesses. The basic difference between these two processes is that in Thermite welding the temperature of melted metal is higher.

 

After the metal filler cools you may find extra filler on it and this can easily be removed by using a machine, grinding it or by using oxygen cutting. However, when the weld is finished you the finished weld surface is usually very smooth and you don't have to worry about doing any finishing.

 

Thermite Welding is used a lot at the Railroads to weld the rails together.  A couple of advantages of this type of welding is that it that it doesn't need a power source that is outside of the process because the heat is produced through the chemical reaction and you can join parts if they are larger and have heavy sections.