3 Types of Oxy Acetylene Gas Welding Flame (9 things to know)

types of oxy acetylene gas welding flame

There are basically 3 types of oxy acetylene gas welding flames.

  1. Neutral flame (50% oxygen and 50% acetylene)
  2. Carburizing flame or reducing flame (less oxygen)
  3. Oxidizing flame (excess oxygen)

These flames are divided into three categories on the basis of proportion of oxygen and acetylene in the mixture.

The image mentioned above shows the neutral flame, carburizing flame and oxidizing flame.

Here I have discussed each type of Oxy Acetylene gas welding flames and their applications.

3 Types of Oxy Acetylene Gas Welding Flames

Types of gas welding flames are discussed below along with the picture.

#1) Neutral flame (equal proportion)

Neutral flame

The neutral oxy acetylene flame contains equal proportion of oxygen and acetylene (i.e 50% oxygen and 50% acetylene.)

The acetylene present in the mixture is completely burned out and all the available heat is released in this type of flame.

Neutral oxy acetylene flame is mostly applicable for welding of stainless steel, cast iron, mold steel, etc.

As shown in the above picture, the neutral flame has 2 zones.

The inner zone and the outer zone.

The inner zone is white in color and the temperature of this zone is around 3100 °C, while the outer zone is blue in color and has a temperature range of around 1270 °C.

#2) Carburizing flame (less oxygen)

Carburizing flame

Carburizing flame (also known as reduction flame) contains less amount of oxygen and more amount of acetylene.

In carburizing flame, the combustion of acetylene is not completed as the supply of oxygen is less, and so the part of the combustible matter is left.

The carburizing flame is similar to the neutral flame, but it has one extra zone present in between the inner zone and outer zone.

This intermediate cone has a reddish-yellow colored flame.

The carburizing flame contains some unburned carbon which is sometimes added to the weld during the gas welding process.

Carburizing flame or reducing flame is suitable for welding high carbon steel. It is also used for carburizing the surface of mild steel or low carbon steel.

#3) Oxidizing flame (excess oxygen)

Oxidizing flame

In oxidizing flame, the amount of oxygen supply is more than the acetylene supply.

Just like the neutral flame, the oxidizing flame also contains two zones. The inner white flame and the outer blue flame.

The difference is that the inner white come is smaller than that in the neutral flame and this gives rise to higher tip temperature (around 3400 °C).

The oxidizing flame also produces loud noise due to excess amount of oxygen present in the flame.

While welding with the oxidizing flame, the oxygen is introduced into the weld and so this flame is not suitable for welding of steels.

In order to weld copper base alloys, zinc base alloys, cast iron and manganese steels, you can use slightly oxidized flame.

How hot is Oxy Acetylene flame?

How hot is Oxy Acetylene flame

The oxy acetylene flame can be divided into three zones.

The zone which is very near to the outlet of the welding torch is zone 1, where the acetylene gas burns in the presence of oxygen gas.

Zone 2 produces carbon monoxide and hydrogen gas in the ratio of 2:1 by volume.

This zone gives the highest temperature of the welding flame.

Zone 3 is the outer zone of the flame where the temperature gradually falls (see above image).

This zone converts Carbon monoxide to carbon dioxide and H2O vapors.

How does the combustion take place in Oxy acetylene gas welding process?

In oxy acetylene gas welding process, the combustion of fuel occurs in two steps.

  1. In the inner cone, the oxygen (O2) and acetylene (C2H2) burns and produces the white cone.
    The oxygen combines with the carbon of the acetylene and forms carbon monoxide (CO), and hydrogen gas (H2) is liberated.

    C2H2 + O2  —–> 2CO + H2 + heat (448 kg/mol)
  1. Further in the outer envelope, the CO obtained from the inner cone reacts with the oxygen of the atmosphere and forms Carbon dioxide (CO2). The hydrogen gas (H2) also burns in the presence of atmospheric oxygen and forms water vapors (H2O).

    4CO + 2H2 + 3H2  —–> 4CO2 + 2H2 + 812 kg/mol

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