Gas Welding and Types of flames

Primary reaction:

C_2+H_2\: \to \: 2CO+H_2+\Delta H_1

Secondary Reaction:

 2CO+H_2+\frac 3 2O_2 \: \to 2 CO_2+H_2O+\Delta H_2

 C_2H_2+\frac 5 2 \:O_2 \: \to 2 CO_2+H_2O+\Delta H



  • While burning the acetylene in the presence of . Due to the exothermic reaction heat is released, which is useful for melting of the material to produce a fusion joint
  • For complete combustion of 1 mole of acetylene 2.5 moles of oxygen is required in which one mole is supplied from oxygen cylinder and 1.5 moles is consumed from atmosphere
  • By controlling the flow rates of oxygen and acetylene different flames are produced, which are used for different applications.
  • Due to primary reaction carbon monoxide is formed by releasing some amount of heat, due to which the inner cone is produced that has max temperature.
  • Due to instability, carbon monoxide will react with oxygen present in the atmospheric, which produces a stable form of carbon dioxide by releasing some heat in secondary reaction.
  • Due to this heat, outer blue flame is produced by covering more area, as it has less temperature when compared to inner core.

Types of flames:

Types flame

Neutral flame:

It is used for general purpose application for welding of mild steel, low carbon steels, alloy steels and cast iron.


This flame is used for the copper, zinc, bronze and brass.


This process is used for high carbon steel, cast iron, aluminum and nickel based alloys.

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