Complete Guide in Types of Welding Flames – Facts & Applications

Selecting a suitable flame for the welding process can be a headache for a newbie fabricator and can often cause problems in his work. There is a lot of science behind it and there are different requirements for each outcome. In this article, I will cover all the critical aspects of selecting the best welding flame for each process. Let’s discuss the basics first.

Different Types of Welding Flames: The Big Picture

In gas welding, the combustion of the fuel produces high energy flames and the temperature rises to thousands of degrees. This allows both metals in the joint to turn into liquids and welding is possible. It is essential to know about different types of welding flames as the weld properties are highly dependent on it and vary, respectively. So, the conditions where welding occurs has a lot to do with the composition of the burning gases. It’s up to the welder to produce the exact flame that he needs. 

The three basic types of welding flames are balanced flame, carburizing flame, and oxidizing flame. Here is an overview of those types.

  1. Neutral Flame: As the name implies, there is no chemical reaction on the metal, which is under operation.
  2. Carburizing Flame: A flame which produces iron carbide (not recommended for carbon-absorbing materials)
  3. Oxidizing Flame: It has more temperature than that of a neutral flame (Recommended for Copper or Zinc)

Neutral Flame

Also called natural flame, a neutral flame is the most common and widely used flame type out of all. This flame does not have any significant effect on the chemical properties of the metal because it gets burnt completely. The color of this flame is yellow and a bit smoky, which is a sign of complete combustion. It does not have any reaction on the metal surface because of the low tendency of a chemical reaction. So it is a practical and usable flame for light metals. 

Every flame has different zones in it. The same is the case with a neutral flame. There are two zones in it. The first one (inner) is bluish-white in color and has a temperature of about 3100°C. The other one (outer) is blue, which is an indication that it has lower temperature than the other zone. However, 1275°C is still a pretty high temperature. This considerable variation in temperature allows the welder to control it in the welding seam by adjusting the distance of the torch from the joint.

How to Produce a Neutral Flame

But how is a neutral flame produced? Well, there is no rigorous science in it because it’s just a matter of paying attention to what the flame looks like. All a welder needs to do is finding a balance on the ratio of acetylene to oxygen. Let’s assume that the acetylene is at excessive levels compared to oxygen. Inside the flame, you will notice that there is an oval-shaped layer (acetylene feather) outside the inner white colored one and inside the blue colored one. In order to calibrate the flame, the acetylene levels will have to be decreased until it starts to get burnt completely. As the acetylene levels are decreasing, you will notice that the oval-shaped layer also decreases. Once this layer disappears, the flame will be a neutral one because the composition of both gases is present in one to one ratio.

But how can we be sure if the flame is neutral or has become an oxidizing one? There is a solution to it too. The most common solution is to leave a very small zone with size from 1/16 to 1/8 inches. The excess of acetylene is slight that the flame is still considered a neutral one.

Applications of Neutral Flames

The materials that can be welded by using this type of welding flame are given below.

  • Mild Steel
  • Stainless Steel
  • Cast Iron
  • Aluminum
  • Copper

Adjustment of a flame is crucial not only for the metal welding process but also for the preheating in cutting operations. A great benefit of using this flame is that you get quite a clearer metal puddle that flows and gets removed quickly without any foaming or sparking. 

Carburizing Flame

Flame of carburization is the second most important one in the types of welding flames. The difference between the composition of carburizing flame and the neutral flame is that the acetylene and oxygen are not in equal proportions; instead, acetylene (or we can say Carbon) is supplied more to get a carburizing flame. 

Talking about the characteristics of this flame, it generally has a lower temperature than a neutral flame. You can see an extra zone in it which is present at the core of the inner zone and making an envelope inside. The inner core is light bluish and extends with its feathery edge, which is white, called acetylene feather. It is also called the central core of the carburizing flame. The outer core is light bluish and often hard to identify. The temperature at the tips of the inner cores is around 3150°C.

Producing Carburizing Flame

In neutral flame, the acetylene and oxygen are in equal volume so that they react completely, but the excess of acetylene is supplied from the blowpipe so that the combustion reaction is incomplete and the carburizing flame is produced. We get this type of flame by adjusting the flame to the neutral state and then by gradually opening the acetylene inlet to get more of it until we get to see the oval-shaped layer between the inner and outer ones.

A flame is called a 2X flame if the inner core is half of the acetylene feather. It is just a way of expressing the carbon content in the flame and is an indication of the degree of flame carburization. 

Applications of Carburizing Flame

In order to weld low carbon steel, you can use a carburizing flame to produce the welding. When a carburizing flame is used for welding, the metal under process gets boiled and cannot be seen clearly. In actuality, the steel itself is absorbing Carbon content from the flame and eventually produces heat. Therefore, the metal boils, and when it gets cold, its properties drastically change to the brittle structure, which consists of high carbon content and thus can be cracked easily. 

Backhand welding is a notable technique where a carburizing flame is used. We would recommend the welders to use this flame on a metal whose carbon content is already high or metals that are hard-faced, such as Nickel, Zinc, or Monel. One thing to keep in mind while using this flame is that it is not a good flame for soft solder operations, and only its outer core should be used for solder processes as we need low temperature in it. 

Oxidizing Flame

There is an excess of oxygen present in the oxidizing flame, and it requires critical identification to distinguish the oxidizing flame from a neutral flame. The ratio is generally 1.5:1 for oxygen and acetylene. 

How to Produce an Oxidizing Flame

The oxidizing flame can be obtained similarly as a neutral and carburizing flame. It is produced by adjusting the oxygen supply slightly more than acetylene flame. Just like carburizing the flame, the fabricator has to balance the amount of oxygen and acetylene and then increase the flow of oxygen until he notices the length of the inner core to be shortened by one-tenth. You will see a point in the inner core of purple color after that. The temperature of the inner core is around 3500°C. 

Applications of Oxidizing Flame

It is famous for its capability of oxidizing metals easily. Hence, it creates problems in various welding operations, such as excessive weld deposit and undesired change in chemical properties. Therefore, it is not so common in industrial applications for weld joints purposes. But it is still a useful type of flame for cutting operations and welding of Ironless metals. 

One distinct feature of the oxidizing flame is that it produces a noticeable hissing sound. There are many typical applications where an oxidizing flame is used for.

  • Steel (Torch Brazing)
  • Cast Iron (Torch Brazing)
  • Brass
  • Bronze

When a welder uses oxidizing flame on steel, the metal (molten) gets burnt and starts to foam and forms sparks, which is an indication of the combination of oxygen with Steel and chemical reaction between them (Combustion). It depends on case to case, and the welder has to decide the distance between flame and metal by looking at the response of the molten metal because of the flame.

Therefore, some pre-thinking must be done before using an oxidizing flame for your application. It shouldn’t be used on a metal that gets oxidized easily, such as Magnesium or Aluminum. Hence, it is not a recommended flame for most of the welding applications. Only light oxidizing flame is suitable for the implementation of torch brazing of steel and cast iron. 

Wrapping Up

I hope that you got a lot of information about the types of welding flames and their applications. It is not so much information that you couldn’t digest once, Was it? Well, still, we would love to hear about your opinions and suggestions to improve it. Please share your feedback in the comments section, and don’t forget to check other articles on this website. 

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