1. THERMITE WELDING

2. Thermite welding - principle of operation

3. Thermite rail welding

4. The thermite reaction occurs between an iron oxide and Al requires the temperature of liquid steel to ignite highly exothermic - once started is self sustaining the thermite mixture can be ignited in one spot, the reaction will continue throughout the rest of the mass it is NOT explosive 3FeO + 2Al  3Fe + Al2O3 + 880kJ Fe2O3 + 2Al  2Fe + Al2O3 + 860kJ Slag Molten metal at 2400°C

5. Thermite welding typical defects 1) Inclusions 2) Incomplete fusion 3) Porosity 4) Cracks 5) Shape defects (misalignment, deviation from straight, etc.)

6. Thermite welding safety Moisture in the thermite mix, in the crucible or on the workpieces can lead to steam and violent ejection of molten metal from the crucible • the thermite mix should be stored in a dry place • the crucible should be dry • moisture should not be allowed to enter in the weld area • preheat workpieces before welding

7. Thermite welding advantages/disadvantages Advantages: Disadvantages: 1) No power supply needed  field use 1) High skill factor 2) Slag inclusions 2) Can weld complex shapes 3) Low deposition rate and operating factor 3) Simple, inexpensive equipment 4) High level of fume 5) Hydrogen control 6) Can’t weld low melting point (e.g. Pb, Sn, Zn) or reactive metals (e.g. Ti)