Gas welding technique is a fusion-welding technique 
In which metals are melted using heat generated from a mixture of oxygen/air and fuel gases such as acetylene, hydrogen, propane or butane.
Through this intense heat (flame) is produced, so that the metal melts and the edges of the parts are welded together.
This process is usually welded with the additional use of filler metal.


Two familiar fuel gases are used in gas welding: - 
  • A mixture of oxygen and acetylene gas - Oxidized acetylene welding process. -
  • A mixture of oxygen and hydrogen gas - oxy-hydrogen welding process


It is the most versatile and widely used gas welding process due to its higher flame temperature (up to 3500o C) than the oxy-hydrogen process (up to 2500o C).
The most essential requirement is to weld pieces of two or more metals together by
 the welding process.
 Pressure may also be employed.  Since a slight gap usually exists between the edges 
of work pieces, a 'filler metal' is used to supply additional material to fill the gap.
However, welding can also, be done without the use of filler metal.
The filler metal is melted, combines with the molten metal of the work and forms an integral part of the weld when it freezes.
An ideal joint can be made between two pieces of metal by heating the workpiece to 
the appropriate temperature.
 In other words, when heated, the material softens sufficiently so that the surface fuses together.

OXY ACETYLENE WELDING(Principle of Operation)

When acetylene is mixed with the right proportion of oxygen in a welding torch and ignited, the metal on the flame of the torch tip is melted and added to the base metal.
The oxy-acetylene flame reaches a temperature of about 3200 ° C and can  melt all commercial metals, which, during welding, actually combine together to form a 
complete bond.
 A filler metal rod is usually added to the molten metal pool.


The device consists of two large cylinders: one containing oxygen at high pressure 
and the other with acetylene gas.
 Two pressures on the respective cylinders regulate or control the pressure of the
 gas flowing from the cylinder to the welding torch according to regulatory 
 The welding torch is used to mix both oxygen and acetylene gas in the appropriate proportions and in the end the mixture is ignited.
A match stick or spark lighter may be used to ignite the mixture at the tip of the
 The resulting the flame temperature at the tip ranges from 3200 ° C - 3500 ° C and this 
heat is sufficient to melt the workpiece metal.
Filler metal is used of the same material or almost the same chemical composition 
as in workpiece materials.
The filler molten metal attaches to the molten metal of the workpiece and forms 
a piece of metal upon freezing.
Flux, if necessary, can be used during the process. It can be applied directly to 
the surface of the workpiece or to the hot end of the filler metal.

Advantage of Gas Welding 

This is possibly the most versatile process. It can be applied to a wide variety of manufacturing and maintenance situations.
In this method, the welder has considerable control over the temperature of the metal in the weld zone. 
  • The rate of heating and cooling is relatively slow.
  • The welder has control over the filler-metal deposition rate.
  • The device is versatile, low cost and usually portable.
  • The cost and maintenance of gas welding equipment is lower than some
  •  other welding processes.

The disadvantage of Gas Welding
  • Heavy classes may not be financially covered. The flame temperature is less than the arc temperature. 
  • A gas flame takes longer to heat a metal than an arc. 
  • More safety problems are associated with the handling and storage of gases. 
  • Acetylene and oxygen gases are expensive.
  • Flux shielding in gas welding is not as effective as TIG or an inert gas 
shielding in MIG welding.

Welding Technique

Depending on the methods of using the welding rod and welding torch, there are

 two common techniques of gas welding, such as: -
  • The left-wing technique or forehand welding method
  • The correct technique or backhand welding method.

Left word 

in gas welding technique

The filler rods, when used, are directed towards the welded part of the joint.

The weld is started from the right side of the seam, working on the left-hand side.
The blow or welding torch is given small sideways movements, while the filler 
rods are rapidly transferred to the seam.
GAS WELDING TECHNIQUEThe filler rod is connected using the back and forth moves of the rod, allowing the flame to melt the lower edges of the plate next to the weld plate.

Rightward  in gas welding technique

The welding torch is placed in the right-hand side of the welder and the filler rod in the left hand.
Welding begins at the left-hand end of the joint and proceeds to the right, In the technique on the right the flashlight flame is directed towards the full weld and the fire is directed 
continuously along the edges of the filler rod flame and the V ahead of the
 full weld, so no sideways movement of the welding torch is required. As a result, 
a narrow V-groove (30 ° bevel or 60 ° included angle) can be used in 
comparison to leftward welding. This provides a larger control and lower
 welding costs.

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