GAS WELDING

DEFINITION: - Gas welding is a type of fusion welding process in which heat is produced by combustion of oxygen/air and fuel gas (mainly acetylene). The heat or flame directly strikes the weld area and melts the metal surface and filler material, after cooling they join together.

  • In gas welding the combustion takes place by mixing Oxygen with fuel gas.
  • Oxygen cylinder is seamless steel cylinder.
  • Oxygen cylinder valves are made of brass.
  • Acetylene is stored in gas cylinder in liquid form.
  • Acetylene cylinder valves are made by steel.
  • Acetylene is very dangerous gas because it can explore under its own weight.
  • Acetylene is generated from Calcium carbonate (CaCo3)

NEUTRAL FLAME: - (Most Commonly used flame)

  • By volume, Oxygen: Acetylene = 1:1
  • The flame is used to weld Mild steel, Low carbon steel and Aluminium.
  • It produces Hissing sound.
  • The flame has two parts – 1. Inner white cone (3100°C – 3400 °C) and 2. Outer blue envelop (12750C).

CARBURIZING FLAME: -

  • Lots of free carbon.
  • This flame is used to weld high carbon steel and Cast Iron.
  • The ratio of Oxygen: Acetylene = 0.9:1
  • Temperature is lower than the Neutral and Oxidized flame.
  • Used to weld metal Aluminium, SS, Zn die casting, Ni.
  • It has three zones –  a) Inner white cone(2900 °C - 3200 °C), b) Acetylene red feather(2100 °C), c) Outer blue cone(1200 °C - 1300 °C).

OXIDIZING FLAME: -

Oxidizing Flame
Fig. 1 |  Oxidizing Flame



  • Hottest flame and produces roaring sound.
  • This flame is used for welding alloys of Cu and Zn [brass] and manganese steel.
  • The temperature of this flame is about 34800c.
  • The ratio of Oxygen: Acetylene = 1.5: 1
  • This flame has two zones – a) inner white cone(3300 °C - 3500 °C), b) Outer blue cone(1200°C).
  • Oxy-acetylene flame cuts metal by – intensive oxidation.
  • Mild Steel is best cut by Oxy-cutting process.