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Gas Welding (GW)

Dr. Dmitri Kopeliovich

Gas Welding is a welding process utilizing heat of the flame from a welding torch. The torch mixes a fuel gas with Oxygen in the proper ratio and flow rate providing combustion process at a required temperature. The hot flame fuses the edges of the welded parts, which are joined together forming a weld after Solidification.

The flame temperature is determined by a type of the fuel gas and proportion of oxygen in the combustion mixture: 4500°F - 6300°F (2500°C - 3500°C). Depending on the proportion of the fuel gas and oxygen in the combustion mixture, the flame may be chemically neutral (stoichiometric content of the gases), oxidizing (excess of oxygen), carburizing (excess of fuel gas).

Filler rod is used when an additional supply of metal to weld is required. Shielding flux may be used if protection of weld pool is necessary.

Most of commercial metals may be welded by Gas Welding excluding reactive metals (titanium, zirconium) and refractory metals (tungsten, molybdenum).

Gas Welding equipment:

  • Fuel gas cylinder with pressure regulator;
  • Oxygen cylinder with pressure regulator;
  • Welding torch;
  • Blue oxygen hose;
  • Red fuel gas hose;
  • Trolley for transportation of the gas cylinders.

Advantages of Resistance Welding:

  • Versatile process;
  • Low cost, portable equipment;
  • Electricity supply is not required.

Disadvantages of Resistance Welding:

  • High skill operator is required;
  • Flame temperature is lower, than in arc welding;
  • Fumes evolved by shielding fluxes;
  • Some metals cannot be welded (reactive and refractory metals).

The most popular methods of Gas Welding are:

Oxyacetylene Welding (OAW)

Oxyacetylene Welding is a Gas Welding process using a combustion mixture of acetylene (C2H2) and oxygen (O2) for producing gas welding flame.

Oxyacetylene flame has a temperature of about 6000°F (3300°C). Combustion of acetylene proceeds in two stages:

1. Inner core of the flame. C2H2 + O2 = 2CO + H2

2. Outer envelope of the flame: CO + H2 + O2 = CO2 + H2O

Acetylene is safely stored at a pressure not exceeding 300 psi (2000 kPa) in special steel cylinders containing acetone. Outside of cylinder acetylene is used at a absolute pressure not exceeding 30 psi (206 kPa). Higher pressure may cause explosion.

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Oxyhydrogen Welding (OHW)

Oxyhydrogen Welding is a Gas Welding process using a combustion mixture of Hydrogen (H2) and oxygen (O2) for producing gas welding flame.

Oxyacetylene flame has a temperature of about 4500°F (2500°C).
Combustion reaction is as follows:

2H2 + O2 = 2H2O

Oxyhydrogen Welding is used for joining metals with low melting points, like aluminum, magnesium, etc.

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Pressure Gas Welding (PGW)

Pressure Gas Welding is a Gas Welding, in which the welded parts are pressed to each other when heated by a gas flame.

The process is similar to Resistance Butt Welding.
Pressure Gas Welding does not require filler material.

Pressure gas welding is used for joining pipes, rods, railroad rails.

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gas_welding_gw.txt · Last modified: 2012/06/01 by dmitri_kopeliovich
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