Types of Welding Flames (Neutral, Carburizing & Oxidizing)

In oxy fuel welding, commonly known as gas welding process in which flames has been produced by burning fuels and then flames are used to create a weld joint. So different types of flame play an important role in deciding properties of welding. We have three types of flames discussed below.

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3 Types of Welding Flames

Neutral or natural Flame
Carburizing Flame
Oxidizing Flame

1. Neutral or natural Flame

According to its name, in this process of welding flame neutral or equal proportion or volume of oxygen and acetylene are released and it absorbs additional oxygen from air then complete combustion process occurs .it is also known as natural flame because no chemical reaction takes place on the metal to be welded. Generally, natural flame is preferred for welding process due to its mild and fine nature.

There are two types of zones in this flame:

Inner zone
Outer zone

The temperature of the inner zone is about 3100°C – 3400 °C while the temperature of the outer zone is about 1200°C – 1300°C. The inner zone of the flame turns out luminous that is white-bluish indicating the completion of the combustion process. The outer zone of the flame is a light blue envelope or a sheath.

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We use natural flame for almost every welding operation and for pre heating in cutting procedures. While welding a steel by using neutral flame, the molten metal flows flawlessly without foaming, sparking or boiling and the metal puddle is quiet and clear without any chemical reaction. Ferrous and non-ferrous metals for example mild steel, copper, iron, stainless steel, aluminum are welded by using this neutral flame.

Neutral Welding Flame Gradient

2. Carburizing Flame

According to its name, as a chemical reaction metal carbide is produced when we use this flame for welding purpose because this flame has an excessive amount of acetylene. Due to this reason, metal that absorbs carbon is not welded because if a metal that absorb carbon is welded using this flame properties of the metal will be changed. This flame is smoky and burns with a bristly rushing noise. It has three zones.

Inner zone that is clearly white bluish in color
Intermediate zone has red color in it indicates the excessive amount of acetylene
Outer zone is a light blue outer flare envelope

The temperature of inner zone is approximately 3149 degree centigrade. For welding medium carbon steel, nickel this type of flame has been used. If the acetylene proportion is twice then the the inner zone will be long and known as a 2X flame through which excessive amount of acetylene will be expressed. This flame is formed by adjusting to neutral and then gradually opening the acetylene flow until an acetylene feather is at the end of the inner cone.

The more lengthy acetylene feather means the more high degree of flame carburization. In welding operations, this acetylene feather should not be more than half the length of the inner zone. You can also read our reviews on best 220v MIG welders.

If we use strong carburizing flame for welding, the metal will boil and not be clear. The steel, having a property of absorbing carbon from the flame, gives off heat. This will ultimately makes the metal to boil. When cold, the weld metal has the properties of high carbon steel, being brittle and can be easily cracked.

For the purpose of back-hand welding we use slight feather of acetylene. For welding high carbon steel such as non-ferrous alloys e.g. we use this type of flame.

Carburizing Welding Flame Components

3. Oxidizing Flame

According to its name, flame obtained by increasing the proportion of oxygen is known as oxidizing flame. We can say if the ratio of acetylene is one and we increase the ratio of oxygen from one to one and a half then the inner zone of the flame tends to disappear and the oxidizing flame has been produced. This flame is hotter than natural flame and has two distinct zones.

  • Inner zone: The inner zone has very bright and sharp white color
  • Outer zone: The outer zone has blue color

The temperature of inner zone is approximately 3300 degree centigrade and the temperature of outer zone is approximately 1200 degree centigrade. In the oxidizing flame inner zone is very small in diameter as compared to its diameter in a natural or neutral flame.

For the purpose of welding oxygen free copper alloy for example brass, bronze etc. we use this type of flame. If more heat is needed for welding then we use oxidizing flame in which the temperature of inner zone is very high. Oxidizing flame is not suitable for the welding of metals for example zinc, copper, manganese steel, cast iron etc.

When we weld steel by using oxidizing flame, chemical reaction takes place and it causes the molten metal to foam and gives off sparks. The excessive amount of oxygen in oxidizing flame combines with steel and causes it to burn or be porous or brittle. This flame has a clear hissing sound.

Oxidizing Welding Flame Components


So that was all about the types of welding flames. All the processes depend upon the usage and criteria of the welder and the material that is being utilized. Varieties of materials utilize various welding flame methods and techniques. Hopefully, this article has helped you with all the necessary information required to utilize the type of flames for welding. 

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Brayden Author

Brayden has been a welding enthusiast and expert for the past 7 years. He always loves to help others by guiding them as a welder expert. That’s the reason he found writing on a site “welderexpert.com” to guide other new and beginner welders.