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 + Al 2 O 3 + 880kJ Fe 2 O 3 + 2Al  2Fe + Al 2 O 3 + 860kJ Slag Molten metal at 2400°C

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

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 placethe thermite mix should be stored in a dry place the crucible should be drythe crucible should be dry moisture should not be allowed to enter in the weld areamoisture should not be allowed to enter in the weld area preheat workpieces before weldingpreheat workpieces before welding

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