Thermite welding is a fusion welding process that uses a mixture of aluminum powder and iron oxide to produce superheated liquid steel without the need for an external power source or electrode. The process involves preparing a mold with the parts to be joined, preheating the parts, igniting the thermite mixture to create molten metal over 2500°C, and pouring the liquid into the mold to fuse the parts together. Thermite welding can join very large structures like rail tracks or pipes.

1. Presented By
Bhushan J.Sarise

2. KEY POINTS
•Thermite welding is a type of fusion welding
process.
•It is also known as Exothermic welding or
bonding.
•This process is used to welding a heavy and large
structures.
•It requires no electrode and power supply

3. Principle
•In this process, welding is done by pouring
superheated liquid steel around parts to be joined.
•A short molding process is to be done before welding

4. What is Thermite / Thermit?
•A mixture of fine aluminum powder and iron oxide
that produces a very high temperature on
combustion, used in welding and for incendiary
bombs.
•Thermite reaction involving aluminum is also
called Goldschmidt alumino thermic reaction.
Usually this reaction is triggered by burning
magnesium ribbon in presence of Barium peroxide.

5. •By weight, 75% of iron oxide and 25% of
fine aluminum powder (OR)
•Fine aluminum powder and iron oxide
should have a ratio of 1:3 (by weight)
•We can also use copper or chromium
instead of aluminum.

6. •The ends of parts to be joined are kept
parallel with a uniform gap between them.
•That gap is filled with wax which becomes
the pattern.
•Molding sand is rammed around wax
pattern. Pouring gate, heating gate and
risers are cut.

8. •Joints to be welded are preheated by
a flame (external source). Due to
preheat wax melts and goes out.
•After melting of wax, weld joints are
preheated due to flame.
•Then heating is stopped and heating
gate is closed.

14. •The mixture of aluminum and iron oxide is placed
in a crucible.
•Barium Peroxide is added to the crucible. Barium
peroxide arises by the reversible reaction of
O2 with barium oxide. The peroxide forms around
500°C and oxygen is released above 820°C
•Mixture is ignited using a match stick (or) small
magnesium wire. So combustion takes place in
the crucible.
•Due to combustion, thermite mixture becomes
superheated liquid within max. time of 30
seconds.

15. •That superheated liquid (pouring metal) have
temperature of 2500--3000°C (around 5000°F)
•The reduction of ferric oxide by aluminum is highly
exothermic and therefore the iron formed will be in
the molten state.
•Aluminum is chosen as metal since it has strong
affinity towards oxygen and its oxide, Al2O3 is a
highly exothermic compound.
•Reaction takes place:
Fe2O3 + 2Al --------> Al2O3 + 2Fe + heat

16. •Crucible is placed directly above the joints to be
welded.
•After preheating of joints, liquid thermite steel from
the crucible is poured into mold between the gap to
weld.
•The molten metal solidifies and weld is completed.

18. •This process is used to weld very large works like
joining of rails, pipes, broken teeth on large gears
and large frame work.
•This process is generally used for welding ferrous
metals

19. ADVANTAGES:
•Very large size structure can be easily weld
•No power supply and electrode needed
DISADVANTAGES:
•Skilled labor required
Long process