In thermochemical welding processes, the desired heat is obtained through exothermic reactions to join metals together.
Here, we will discuss about the important thermochemical welding processes which are widely used in the industry such as:
- Atomic-hydrogen welding process
- Thermit welding process
Thermit welding process
The concept of thermit welding was discovered by Goldschmidt in 1896. His idea was that a cold mixture of metallic oxides and finely divided aluminum could be ignited in one spot.
and the reaction of this spot would provide enough heat to spread the reaction through the entire mass.
Thermit welding involves a set of welding processes in which the desired heat is achieved as a result of a chemical reaction between a mixture of metal oxide and aluminum powder.
Principle of operation
In thermit welding, mainly metal reducing agents (aluminum powder or magnesium) and metal oxides (iron oxides) are used, the reaction is an exothermic reaction. The most common reaction used in thermit welding is as follows:
- 3Fe3O4 +8Al → 9Fe + 4Al2O3 (3088 °C) 719.3 Kcal
The theoretical temperature resulting from this reaction is 3088 °C, but the loss of radiant heat and loss to the reaction vessel however reduces this temperature to approximately 2538 °C. Other additions to adjust the chemical composition of the metal and the slag for fluidity eventually reduce the temperature of the filler Weld metal to approximately 2100°C.
Other typical reactions of thermit welding are as follows:
- Fe2O3 +2Al → 2Fe +Al2O3 (2960°C) 181.5 kcal
- 3CuO +2Al → 3Cu +Al2O3 (4865°C) 275.3 kcal
- Cr2O3 +2Al →2Cr+Al2O3 (2977°C) 546.5 kcal
Working Methods of thermit welding
The heat of the Thermit reaction can be used for joining metals in a number of ways such as:
- It can heat and fuse to weld metal parts to be welded.
- The mixture also acts as a filler metal.
- The heat of the reaction may be used for the purpose of brazing also.
- It may heat the metal parts to be welded and raise them to the forging temperature when the weld faces are forced together to forge a bond of the heated parts, This process is known as pressure welding.
Thermit welding is fusion welding in which desired heat is achieved as a result of a chemical reaction between a mixture of metal oxide and aluminum powder.
To be continued…