What is Thermo Chemical Welding? Thermo chemical welding is a fusion welding process in which the joining of metals takes place by using the heat produced due to exothermic chemical reactions.
There are two major types of thermo chemical welding process used for joining the metals.
Let’s see both these thermo chemical welding processes one by one.
#1) Thermite welding
What is Thermite Welding? Thermite welding (also known as exothermic welding or exothermic bonding) is a fusion welding process in which the joining of metals takes place with the help of superheated molten metal and slag resulting from chemical reaction between aluminum and metal oxide.
The heat produced in thermite welding process is just because of the exothermic reaction between aluminum and the metal oxide. No external heat or current is applied during the process.
During the thermite welding process, the pressure may or may not be applied depending upon the applications.
Thermite Welding process is generally used for welding of rails. Hence the process is also referred as Thermite Rail Welding.
Thermite Welding of Rails (8 Steps)
Rail thermite welding process can be done in 8 steps as mentioned below.
Step 1: Clean the joints
Step 2: Setup the rail gap
Step 3: Align the rails and setup the clamps and mold
Step 4: Prepare the thermite mixture in a crucible
Step 5: Preheat the mold
Step 6: Ignite the thermite mixture
Step 7: Open the mold
Step 8: Finish the mold
For detailed information on Thermite welding, you can refer the main article: Thermit welding of rails (The complete process)
#2) Atomic hydrogen welding
What is Atomic Hydrogen Welding? Atomic hydrogen welding is a welding process in which the joining of metals takes place by heating them with an electric arc maintained between two tungsten electrodes in the atmosphere of hydrogen which acts as a shielding gas.
Atomic hydrogen welding process does not require any kind of flux.
Also the welding rod (or filler material) may or may not be used during the atomic hydrogen arc welding process.
Atomic Hydrogen Welding Process
The setup for Atomic hydrogen welding process is shown in the diagram above.
In atomic hydrogen welding process, the heat required for the welding operation is produced by the heat liberated from the combination of hydrogen atoms.
When the electric current is passed through the electrodes and workpiece, the electric arc is produced between them.
The high temperature of the arc dissociates the molecules of hydrogen gas (H2) into hydrogen atoms (H) and a large quantity of heat is absorbed by the hydrogen during this dissociation.
When these atoms (H) leave the arc, they recombine to form hydrogen molecules (H2) and liberate a huge amount of heat.
The average temperature of the flame reaches around 4000 °C, and this temperature is even higher than the oxyacetylene welding flame temperature.
For detailed information on atomic hydrogen welding, you can refer to the main article: What is Atomic hydrogen welding (And how does it work?)