Thermit welding process

Thermit welding is a chemically reaction welding process. The weld joint is produced by pouring of superheated molten metal around the joint to be welded, applying with or without of pressure. Thermit welding basically called a mixture of finely divided metal oxide and a metal reducing agent as aluminium.


Thermit welding principle:


The necessary heat  for joining metal of thermit welding is obtained from chemical reaction of metal oxide and metal reducing agent. Usually iron oxide is used as a metal oxide and aliminium or magnesium is used as metal reducing agent. The strong chemical attraction of aluminium for oxygen is the basis for thermit process. First the thermit mixture is ignited by a burning magnesium ribbon. The ignited temperature of thermit is about 12000C. When ignited in one spot of mixture, the heat reaction spreads through the mass. The aluminium merging with the oxygen of metal oxide and setting free the iron, which is deposited on joint portion into the mold as a highly superheated liquid metal. If theoretical temperature is about 30000C of thermit, due to chilling effect of crucible the temperature is reduced about 25000C. So it is sufficient for welding temperature.

The thermit reaction is required about thirty second to ignite and it is non-explosive process.

Thermit welding diagram

Some chemical reaction:


3Fe3O4 + 8Al 9Fe + 4Al2O3 (719.3 Kcal)

Fe2O3 + 2Al 2Fe + Al2O3 (181.5 Kcal)

3MnO + 2Al 3Mn + Al2O3 (403 Kcal)

3CuO + 2Al 3Cu + Al2O3 (275.3 Kcal)


Thermit welding application :


It has large application in railway track repairing on the spot.

It is used in large frame like locomotive frame welding.

Thermit welding is used in crank shaft welding.





Site map

Contact Us


Gas welding

Air acetylene welding

Oxy-acetylene welding

Oxy-hydrogen welding

Pressure gas welding

Arc welding

Carbon arc welding

TIG welding

MIG welding

Submerged arc welding

Shielded metal arc welding

Plasma arc welding

Flux cored arc welding

Stud arc welding

Electro slag welding


Resistance welding

Spot welding

Seam welding

Percussion welding

High frequency welding

Projection welding

Resistance butt welding

Flash butt welding


Solid state welding

Friction welding

Cold welding

Ultrasonic welding

Hot pressure welding

Diffusion welding

Forge welding

Explosive welding


Radiant energy welding

Laser beam welding

Electron beam welding


Thermo-chemical welding

Thermit welding

Atomic welding








Thermit welding

Thermit weld principle



Classification of welding

Effect of welding speed

Welding defects

Types of welding joints

Welding position

Welding electrodes

Types of welding flame

Welding flux

Welding techniques

Welding symbol

Welding edge preparation

Advantages of welding joints

Thermal properties of metal

Welding safety

Types of welds

                                                 ©  Copyright 2010-2014  Thermit welding

     Home       Link     Link 1     Link 2     Site map       Contact Us

    Spot Welding    Seam Welding     Butt Welding     Flash Welding     TIG Welding     MIG Welding     Ultrasonic Welding

    Plasma Welding     Laser Welding     Stud Welding     Arc Welding     Oxy-acetylene Welding     Air-acetylene Welding

    Oxy-hydrogen Welding    Pressure Gas Welding     Brazing      Soldering