Types of Gas Welding Flames and Their Uses

Hello friends in this topic, we will know about types of gas welding flames and their uses and at the last also discuss some FAQ related to gas welding flame.

Gas welding is the most important type of welding process, which has already been discussed in the previous post.


In gas welding, gas welding flame plays a very most important role so before knowing the types of gas welding flames firstly we have to know what is a flame in gas welding?

Choosing the wrong flame can lead to many welding defects like porosity, cracks, slag inclusion and many more.

So, without wasting time let's know the types of gas welding flames and their uses.


What is Flame?

In gas welding, the flame produced by mixing a flammable gas and oxygen in the nozzle or tip of the blow pipe is called flame.


Mostly in gas welding, Oxy-acetylene flames are used.

Always grind the welded area after welding and re-welding if needed.

Oxy-acetylene Flame

Oxy-acetylene flame is mostly used for gas welding because of its high flame temperature (3200 °C). 

Oxygen is generated by liquefaction of air or by electrolysis of water and acetylene is produced as a result of a chemical reaction of calcium carbide in contact with water.

calcium carbide + water → oxy-acetylene + slaked lime

CaC2 + 2H2O → C2H2 + Ca (2 OH )

Various flames can be obtained by changing the respective amounts of acetylene and oxygen in the gas mixture.

In an oxy-acetylene method, metal is heated through the hot flame of a gas-fed torch which melts the metals and joins together to form a weld. 

In many cases, excess metal from a welding rod is melted into the joint and making the joint as strong as the base metal.


Parts of the Oxy-acetylene Flame


The oxy-acetylene flame consists of three main parts.

  • Inner Part (2760 °C -3,480 °C)
  • Middle Part (2090 °C -3,800 °C)
  • Outer Part (1260 °C -2100 °C )

Inner Part or Inner Cone 


The inner cone or inner part is the part where the mixture of both the gases Oxygen and Acetylene exits the tip of the blow pipe. 


It is also called the luminous cone or inner cone or inner zone. 

It is a bright white low and the size is also less.


The temperature of this part is from 2760 °C to 3,480 °C.


The front part of the inner part is the hottest part of the flame.


Middle Part or Intermediate Zone


The middle part of the flame is also known as the Intermediate zone.


It is also called the blue reducing zone of carbon monoxide and hydrogen.


Its temperature is around 2090 °C.


Outer Part or Outer Envelope


This is the outer part of the flame.


It completes its combustion process by getting oxygen from the air. 


The temperature of this part varies from 1260 °C to 2100 °C. 


Air, oxygen, and acetylene combine in different proportions to form different types of flame. 


In this zone acetylene first burns with the oxygen added inside the torch and later this burnt gas burns again in the atmospheric air.


Now, let's know how many types of gas welding flames are and their applications.


Types of Gas Welding Flames

There are the following types of gas welding flames are used.

  • Neutral Flame
  • Carburizing flame
  • Oxidizing Flame

Show in the figure types of gas welding flames which are described below in detail.


types of gas welding flame
Types of Gas Welding Flames

Neutral Flame


The neutral flame is made by mixing both oxygen and acetylene gases in equal quantities.


Its temperature is around 3,200 °C.


This flame is most commonly used.


This flame is also called a balanced flame as well as a natural flame.

There are two regions of this flame first one is the inner zone and the second one is the outer zone.


The inner region is white in color, and its temperature varies from 3,100 to 3,500 degrees centigrade and the outer region is blue in color and its temperature varies from 1275 to 1400 degrees centigrade.

You can see in the above mentioned figure.


This neutral flame has a well-defined inner zone, and it is surrounded by an outer flame envelope which is also known as the outer zone, which results from the combination of oxygen in the air and extremely hot carbon monoxide and hydrogen gases from the inner zone.

This flame is called a neutral flame because during welding there are no any type of chemical changes on the molten metal and so it’s not oxidized or carburized the metal.  


Uses of Neutral Flame

This flame is used for welding mild steel, cast iron, stainless steel, copper, and aluminum.


Chemical Reaction of Neutral flame

When molecules of oxygen mix with acetylene gas in the same proportion then neutral flame produces.


O2 + C2H2 = CO + H2 + heat



O2 = Oxygen


C2H2 = Acetylene Gas


CO = Carbon monoxide


H2 = Hydrogen


After that hydrogen and carbon monoxide again react with oxygen and developed an outer envelope or outer zone.

CO + H2 + O2 = CO2 + H2O



CO2 = Carbon dioxide


H2O = Water


Carburizing Flame


The amount of acetylene in this flame is high, it has three parts, first one is the inner zone and it also has the middle part which is called an intermediate zone.


And the last part is the outer zone.


In which the inner zone looks white in color, the intermediate zone which looks like red in color and the outer zone is look like blue in color.

You can clearly see this in the figure.


The temperature of this flame is 3,100 °C.


It is also known as reducing flame.


A reducing flame or carburizing flame can be identified by the acetylene feather which is present between the inner zone and outer zone. 


The outer cone or outer envelope is always longer as compared to the neutral flame and also much brighter in color.


A reducing flame does not fully consume the available carbon; therefore, it has a lower burning temperature, and the remaining carbon is injected into the molten metal. 

With iron and steel, it produces a very hard, brittle material called iron carbide. 

This iron carbide makes the metal unsuitable for many applications that may require bending or stretching of welds. 


Metals that absorb carbon should not be welded with a reducing flame.


Uses of Carburizing Flame

It is used for welding high carbon steel, aluminum, and alloy steel.


Oxidizing Flame

In this, the amount of oxygen in the gases coming out of the blow pipe is high, it consists of two parts, the inner part is very small and sharp with a very shiny white color, its temperature is 3,300 ° C.

An oxidizing flame can be identified only by the smaller region which is always smaller and more pointed as compared to the neutral flame.

The outer flame envelope is very small.

Oxidizing flame is hotter than neutral flame.

This is due to excess oxygen and due to which the temperature becomes higher. 

Excess oxygen combines with many metals to form hard, brittle, low strength oxides.

For these reasons, oxidizing flames are of limited use in welding.

It is not used in welding steel. 

A slightly oxidizing flame is helpful when welding most copper bases or zinc base metal.


Uses of Oxidizing Flame 

This flame is used for welding copper, zinc, cast iron, brass.


So here I discussed types of gas welding flames and their uses, applications as well as chemical reaction of these flames.

I hope you all enjoy this post.


FAQ for Types of Gas Welding Flames


Which flame is used for gas welding? 

Oxy-acetylene is the flame which is most used in gas welding.


What are the three types of flame in oxyacetylene welding?


In oxyacetylene welding the three types of flame is neutral, oxidizing and carburizing flame.


Which flame is used for Aluminium welding?

For aluminium welding mostly used neutral as well as carburizing flame.


Which flame is used for cutting operation?

For cutting operation always use neutral  flame.


Which flame is used for copper welding?

For copper welding mostly used Oxidizing flame.


Which of the following flame is harmful to steel?

The flame which is harmful to the steel is oxidizing flame due to excess of oxygen in this flame more chance to rust of steel.

Post a Comment