Gas welding basics, Techniques and flames



Gas welding is fusion welding is used to join the metal by heat produced by combustion of oxygen/air and fuel gas (i.e. acetylene, propane, hydrogen and butane) Mixture.
the heat produced by combustion is used to melt the material and fuse together with or without using filler metal.gas welding equipment


  • Oxy-acetylene welding
  • Oxy-hydrogen welding
  • oxy-propane welding
  • Air-acetylene welding
in this all types the mainly used gas welding process is Oxy-acetylene welding.

working of oxy-acetylene welding

-when oxygen and acetylene is  mixed with correct proportion in the welding torch and ignited ,the created flame is used to melt the metal and join by using filler metal.
-it reaches about 3200 degree temperature.
-which is able to melt any commercial metal.

welding flames

welding flame are very important they required to create perfect fillet size,perfect size,it is required to create satisfactory welds.
type of flame to be used is based on types,thickness etc of metal.

Types of welding flames

  1. acetylene flame
  2. reducing flame
  3. neutral flame
  4. oxydising flame

*Neutral flame*

  • approximately equal volumes of oxygen and acetylene is used to create flame.
  • temperature of this flame is about 3260 degree.
  • flame colour is light  blue.
  • It is named neutral flame because it effects no chemical change in molten metal and therefore will not carburize or oxidize.

Neutral flame is used for welding of

  • mild steel
  • stainless steel
  • cast iron
  • copper
  • aluminium

*Oxidising flame*

  • for creating oxidising flame oxygen supply is increased.
  • its temperature is about 3482 degree.
  • its colour is dark blue
  • it is named oxidising flame because oxygen supply is more in this than acetylene.
  • due to excessive oxygen it will create dirty weld bead appearance so it is not used in the welding of steel.

Oxydising flame is used for welding of

  • copper base metals and
  • zinc base metals
  • mn and C.I.

*Reducing flame*/Carburising flame

opposite to the oxidising flame if the volume of the oxygen is reduced then the reducing flame or carburising flame is produced .The acetylene percentage is more than oxygen in this flame.
carburising flame contains more acetylene than reducing flame on this basis they are distinguished.

  • oxygen supply is reduced
  • its temperature is about 3038 degree
  • much brighter in colour
  • it is named reduced flame because oxygen composition is reduced.

Reducing and carburising flame applications

  • Reducing flame is used for welding of -low alloy steel and high carbon steel.
  • Carburising flame is used for welding of lead and surface hardening processes like carburising.


  1. Oxygen and Acetylene gas cylinders
  2. oxygen and acetylene pressure regulators
  3. oxygen and acetylene gas hoses
  4. welding torch
  5. trolley for transportation purpose
  6. keys and spanners set.
  7. filler rods and fluxes
  8. safety clothing for welder like welding goggles,gloves etc etc.
oxy acetylene welding equipments



In air acetylene the flame required for welding is obtained from combustion of air with acetylene so it is called air acetylene welding

principle of operation of air-acetylene welding

The acetylene flowing through the small opening called jet sucks or aspirates appropriate amount of atmospheric air required for combustion process takes place.
Acetylene is provided from cylinder and air is taken from atmosphere in order to obtain oxygen required for combustion.

air-acetylene welding

Application of air-acetylene welding

it creates less temperature than other gas welding processes hence used for
  • copper plumbing
  • welding light sections of lead.
  • refrigeration and air conditioning parts i.e. in silver brazing.


  • butt
  • lap
  • corner
  • T
  • edge
gas welding joints used


there are two commonly used welding techniques for as welding
  1. forehand welding method also known as leftward technique
  2. backhand welding method also known as rightward method.

gas welding techniques

1- Leftward technique/forehand welding method

  • welder holds torch in right hand and filler rod in left hand
  • welding flame is directed towards unwelded part of the joint and filler rod towards welded part
  • the weld is started from right hand side towards left hand hence it is called leftward technique.
  • This technique is used for welding of thin metals having thickness less than 5mm 

2- Rightward technique/backhand welding method

  • welder holds torch in right and filler rod in left hand as same as leftward technique.
  • welding flame is directed towards completed weld and if filler wire is used remains between completed weld section and flame. 
  • the weld is started from left hand side and directed towards right hand side hence it is called rightward technique.
  • this technique is used for thick metals usually more than 5mm in thickness.


  • upto 8mm thickness no bevel is required
  • for more than 8 mm thick plates where bevel is required  angle of v only 60 degree required.Hence require less filler metal hence cost saving achieved.
  • better control and higher weld speeds
  • reduces shrinkage and distortion
  • weld quality is better than leftward technique
  • lower cost of welding than leftward. 


gas welding pdf  joints used in gas welding process
gas welding process   and welding techniques
gas welding ppt
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