What is Welding Flame?- Neutral, Carburizing & Oxidizing - Engineering Choice (2022)

Today we will learn about the types of welding flames used in gas welding. In my last post, we have discussed gas welding. In this welding process gases, fuels are burned and produce high-temperature flames which are further used to create a weld joint.

The flame plays lead role to create weld joint and the weld properties are highly depended on it. There are three types of flames natural flame, carburizing flame and oxidizing flame. Natural flame has synchronized mixture of fuel and oxygen, carburizing flame has more fuel and oxidizing flame has more oxygen. Different materials used different flames according to weld condition.

What is Welding Flame?

Welding flame is used to heat metal or thermoplastics, fusing them as they cool. Most gas welding processes use oxyfuel welding. It’s one of the oldest welding processes, first developed in 1903. With oxyfuel welding, which is also called oxyacetylene welding, you need a liquid fuel or gas, such as acetylene. The gas is combined with oxygen to increase the temperature of the flame.

The torch has hoses that connect to gas tanks. When I’m ready to start welding, I open the valves and ignite the gas as it exits the torch. I can then adjust the valves to adjust the flow of each gas, altering the gas ratio.

Each flame also has several zones called cones. The inner cone is the hottest part of the flame. It’s where acetylene and oxygen combine. The outer cone is cooler as it gets more oxygen from the surrounding air. It’s also commonly called the outer envelope or sheath.

What is Welding Flame?- Neutral, Carburizing & Oxidizing - Engineering Choice (1)

Types of Welding Flames

There are three types of flames natural flame, carburizing flame, and oxidizing flame.

(Video) Differences between Carburizing Flame and Oxidizing Flame.

  • Natural flame has a synchronized mixture of fuel and oxygen,
  • The carburizing flame has more fuel and,
  • Oxidizing flame has more oxygen..
What is Welding Flame?- Neutral, Carburizing & Oxidizing - Engineering Choice (2)

As we know there are three basic welding flames. These areas follow.

1. Natural Flame

As the name implies, this flame has an equal amount of oxygen and gases fueled by volume. This flame burns fuel completely and does not produce any chemical effect on the metal to be welded. It is mostly used for welding mild steel, stainless steel, cast iron, etc. It produces little smoke.

This flame has two zones. The inner zone has white in color and has a temperature of about 3100-degree centigrade and the outer zone has a blue color and has a temperature of about 1275 degrees centigrade.

2. Carburizing Flame

This flame has an excess of fuel gas. This flame chemically reacts with metal and form metal carbide. Due to this reason, this flame does not use with metal which absorbs carbon. It is a smoky and quiet flame. This flame has three regions.

The inner zone has white color, the intermediate zone which is red in color and the outer cone has a blue color. The inner cone temperature is about 2900 degrees centigrade. This flame is used to weld medium carbon steel, nickel, etc.

(Video) Types of Welding Flames | Neutral flame, Carburizing flame, Oxidizing flame.

3. Oxidizing Flame

When the amount of acetylene reduces from natural flame or the amount of oxygen increases, the inner cone tends to disappear and the flame obtained is known as oxidizing flame. It is hotter than natural flame and has clearly defined two zones.

The inner zone has a very bright white color and has a temperature of about 3300 degrees centigrade. The outer flame has blue in color. This flame is used to weld oxygen-free copper alloys like brass, bronze, etc.

What Type of Gas Should You Use for an Ideal Flame?

Acetylene is the most used gas for producing the types of gas welding flames discussed but it’s not the only option. MAPP and hydrogen are often listed as alternatives to acetylene. Acetylene has a “triple bond” that uniquely bonds carbon atoms.

When other gases reach their ignition temperatures, the bond breaks. The gases then absorb energy. When the bond breaks in acetylene, it releases energy. This allows acetylene to achieve higher temperatures.

Compared to other gases, acetylene also has fewer oxidizing characteristics. However, it also ignites easily. MAPP was created as a safer option. MAPP gas is a liquified petroleum gas combined with propane and acetylene. It can be shipped in smaller containers compared to standard acetylene, has a higher ignition temperature, and works with much higher pressures.

The drawback to MAPP is the temperature. The flames produced using MAPP achieve lower temperatures compared to acetylene flames. It’s not suitable for use with most steels but may work well for aluminum. Hydrogen is another gas that welds aluminum easily. As with MAPP, hydrogen flames reach lower temperatures and work with higher pressures.

(Video) Differences Between Carburizing or reducing Flame and Oxidising Flame

Unless you plan on fusing aluminum, stick with acetylene. The low temperature and withdrawal rate keep MAPP and hydrogen from properly fusing harder metals. While MAPP and hydrogen aren’t the best choices for gas welding, they’ve become popular options for gas cutting. When used with a high-pressure torch, MAPP and hydrogen provide cleaner cutting.

The lower temperatures also make MAPP and hydrogen common choices for heating, bending, and brazing.

Common Ratios for Producing Oxyacetylene Flames

Neutral gas welding flames have an equal mixture of oxygen and gas. Carburizing flames have less oxygen while oxidizing flames contain more oxygen. So how do you determine the ratio?

No matter the project, start with a neutral flame. The carburizing flame and oxidizing flame are created by increasing the release of acetylene or oxygen after achieving a neutral flame.

I created the following list to break down the typical ratio of oxygen to acetylene for each flame:

  • Carburizing flame: 0.8 to 1.0
  • Neutral flame: 0
  • Oxidizing flame: 1.0 to 2.5

As you increase the flow of acetylene, the distinct feather starts to extend from the inner cone. The feather should reach about two or three times the length of the inner cone. Preventing the gas from fully combusting also lowers its temperature.


If you need an oxidizing flame, you increase the flow of oxygen instead of increasing the flow of acetylene. The extra oxygen produces the oxidizing effect and allows the gas to combust faster, resulting in higher temperatures.

How Do You Create a Neutral Flame for Gas Welding?

As the neutral flame is the starting point for creating other flames, it’s the first flame that I learned how to produce. Start by adjusting the regulators. The oxygen cylinder and acetylene cylinder each have a regulator with two gauges. One gauge tells you the remaining pressure while the other displays the working pressure.

Adjusting the screw on the regulator adjusts the working pressure, allowing you to increase or decrease the flow of oxygen or gas. Before lighting the torch, stand away from the front of the regulators and slowly open the oxygen cylinder and then the acetylene cylinder. Turn the regulator screws to adjust the pressure settings.

With the pressure on the regulators set, you can light and adjust the torch. Open the acetylene valve a quarter turn and ignite the torch. Slowly open the oxygen valve until you see three distinct zones. You should see the inner cone, the feather-shaped acetylene cone, and the outer envelope. Continue to slowly open the oxygen valve until the feather disappears into the inner cone. You now have a neutral flame.

To create a carburizing flame, slowly open the valve on the acetylene cylinder until the feather reaches two to three times the length of the inner cone. To create an oxidizing flame, increase the flow of oxygen until the inner cone is about a quarter of its original size. You should also hear the distinct hissing sound.


What is flame in welding? ›

The flame plays lead role to create weld joint and the weld properties are highly depended on it. There are three types of flames natural flame, carburizing flame and oxidizing flame. Natural flame has synchronized mixture of fuel and oxygen, carburizing flame has more fuel and oxidizing flame has more oxygen.

What is the application of oxidizing flame neutral flame and carburizing flame? ›

A carburizing flame will produce iron carbide, causing a chemical change in steel and iron. For this reason a carburizing flame is not used on metals that absorb carbon. An oxidizing flame is hotter than a neutral flame and is often used on copper and zinc.

What is oxidizing flame in welding? ›

An oxyfuel gas flame in which there is an excess of oxygen, resulting in an oxygen-rich zone extending around and beyond the cone.

What is Carburising flame in welding? ›

A carburizing flame is produced when there is an excess of acetylene gas for the amount of oxygen being consumed in an oxy-acetylene mixture, producing an acetylene-rich gas. This kind of flame is used for welding materials that do not absorb carbon. A carburizing flame is also known as a reducing flame.

What is meant by neutral flame? ›

Definition of neutral flame

: a flame resulting from the burning of gases supplied in the proper proportions for perfect combustion (as approximately equal volumes of acetylene and oxygen)

What is a neutral flame used for? ›

A Neutral Oxy Acetylene Flame is used for Welding, Brazing and Silver Soldering most metals and is therefore the most common type of flame to use. A Neutral Flame is also used for Oxy Acetylene Cutting.

How many types of welding are there? ›

The four main types of welding are: Gas Metal Arc Welding (GMAW/MIG), Gas Tungsten Arc Welding (GTAW/TIG), Shielded Metal Arc Welding (SMAW), and Flux Cored Arc Welding (FCAW).

Which type of flame is used in gas welding? ›

Flame in Gas Welding

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.

Why is oxidizing flame used? ›

The oxidizing flame is mainly used for welding brass. It is also very suitable for the cutting operations due to nonferrous metals (brasses and bronzes) due to formation of a tenuous oxide film over the molten metal which prevents the vaporization of zinc.

What is the difference between a carburizing flame and oxidizing flame? ›

Carburizing flame is obtained when less oxygen than that is required for stoichiometrically complete combustion is supplied. Oxidizing flame is obtained when excess oxygen than that is required for stoichiometrically complete combustion is supplied.

What is a flame in chemistry? ›

A flame (from Latin flamma) is the visible, gaseous part of a fire. It is caused by a highly exothermic chemical reaction taking place in a thin zone. When flames are hot enough to have ionized gaseous components of sufficient density they are then considered plasma.

What is the carburizing process? ›

Carburising is a thermochemical process in which carbon is diffused into the surface of low carbon steels to increase the carbon content to sufficient levels so that the surface will respond to heat treatment and produce a hard, wear-resistant layer. There are three types of carburising commonly used: gas carburising.

How hot is a neutral flame? ›

Table of comparison:
CharacteristicsNeutral flameReducing flame
Inner temp in oC3250 approx2900 approx
Intermediate temp oC2100 approx2500 approx
Outermost temp in oC1300 approx1275 approx
NoiseHissing noiseNo noise
1 more row

What is the name of gas flame? ›

The LPG (propane) is a blue flame because complete combustion creates enough energy to excite and ionize the gas molecules in the flame. The exception is a gas fireplace having yellow or red flames, for a more realistic look.

How is oxidizing flame produced? ›

If the flame has too much oxygen, an oxidizing flame is produced. When the amount of oxygen increases, the flame shortens due to quicker combustion, its color becomes a more transparent blue, and it hisses/roars.

What are neutral reducing and oxidizing flames? ›

The key difference between oxidizing and reducing flame is that oxidizing flames are produced in the presence of an excessive amount of oxygen, whereas reducing flames are produced in the presence of a low level of oxygen. Oxidizing flames can oxidize metal surfaces while reducing flames can reduce molten metal.

What are the types of flame in chemistry? ›

What are the types of flame? There are three types of natural flames, which are carburized flames and oxidising flames. Natural flame has a balance fuel-oxygen combination, carburizing flame has more fuel and oxidising flame has more oxygen.

How do you make a neutral flame? ›

How to Light and Set a Neutral Flame with a Gas Torch | ESAB Elite

Which material is welding using neutral flame? ›

Statement (I): In gas welding process, neutral flame is the most common flame used for welding and cutting stainless steel.

How do you get a neutral flame? ›

How to get a neutral flame on a gas welder - YouTube

What is flame made of? ›

Most flames are made of hot gas, but some burn so hot they become plasma. The nature of a flame depends on what is being burnt. A candle flame will primarily be a mixture of hot gases (air and vaporised paraffin wax). The oxygen in the air reacts with the paraffin to produce heat, light and carbon dioxide.

What is the difference between fire and flame? ›

Based on Cambridge dictionary: Flame is a stream of hot, burning gas from something on fire: Fire (material that is in) the state of burning that produces flames that send out heat and light, and might produce smoke: It seems that the "fire" refers to the state while "flame" refers to the result of this state.

What colour is a flame? ›

Color tells us about the temperature of a candle flame. The inner core of the candle flame is light blue, with a temperature of around 1670 K (1400 °C). That is the hottest part of the flame. The color inside the flame becomes yellow, orange, and finally red.

What is the difference between combustion and flame? ›

What is the difference between combustion and flame?
1. Combustion is a chemical reaction of carbon-based material with oxygen.Flame is the visible part of the fire
2 more rows

How does a flame work? ›

Fire is the result of applying enough heat to a fuel source, when you've got a whole lot of oxygen around. As the atoms in the fuel heat up, they begin to vibrate until they break free of the bonds holding them together and are released as volatile gases. These gases react with oxygen in the surrounding atmosphere.

What is the meaning of this emoji 🔥? ›

The fire emoji is a flame that is mostly yellow with a little red on the top. It is used to signify that something is cool, awesome, exciting, or more colloquially, “on fire.” It can also convey that someone is sexy, (i.e., hot), or refer to other various metaphorical fires.

Is flame a gas? ›

Fire is a plasma, not a gas or a solid. It's a kind of transient state between being composed of the elements prior to ignition and the spent fumes (Smoke - solid particles and Gasses = Gas molecules.)

What is an example of flame? ›

The definition of a flame is burning gas, fire or blaze, or a strong passion. An example of a flame is a fire from a lighter.

What are the 4 types of fire? ›

Let's break down each of the 5 different classes of fires more thoroughly.
  • Class A Fires: “Ordinary” Fires. ...
  • Class B Fires: Liquids & Gases. ...
  • Class C Fires: Electrical Fires. ...
  • Class D Fires: Metallic Fires. ...
  • Class K Fires: Grease Fires or Cooking Fires. ...
  • Choose the Right Fire Extinguisher. ...
  • Complete Regular Training.
10 Jun 2021

What is flame in simple words? ›

Definition of flame

(Entry 1 of 2) 1 : the glowing gaseous part of a fire. 2a : a state of blazing combustion the car burst into flame. b : a condition or appearance suggesting a flame or burning: such as. (1) : burning zeal or passion.

How hot is a flame? ›

Deep red fire is about 600-800° Celsius (1112-1800° Fahrenheit), orange-yellow is around 1100° Celsius (2012° Fahrenheit), and a white flame is hotter still, ranging from 1300-1500 Celsius (2400-2700° Fahrenheit). A blue flame is the hottest one of all, ranging from 1400-1650° Celsius (2600-3000° Fahrenheit).

How hot is wood fire? ›

Under medium density and at equilibrium humidity with that of the surrounding air, the wood ignites at a temperature of about 300 degrees Celsius (572 degrees Fahrenheit). The wood does burn hot, averaging temperatures ranges from 800 to 950 degrees Celsius (1472 to 1742 degrees Fahrenheit ).

Why is my fire green? ›

A green flame, for instance, indicates the presence of copper. As copper heats up, it absorbs energy that's manifested in the form of a green flame. A pink flame, on the other hand, indicates the presence of lithium chloride.

What are the 3 types of combustion? ›

They are:
  • Rapid Combustion,
  • Spontaneous Combustion, and.
  • Explosive Combustion.
10 Mar 2022

What is the structure of a flame? ›

It is made up of a solid block of fuel with an embedded wick. A candle flame consists of three zones. Namely, the outer zone or non-luminous zone; this is the hottest zone, the middle zone or luminous zone; this zone is moderately hot, and the innermost zone or dark zone; there is no combustion in this zone.

How flame is produced? ›

Fire is the result of a chemical reaction called combustion. At a certain point in the combustion reaction, called the ignition point, flames are produced. Ordinarily, flames consist primarily of carbon dioxide, water vapor, oxygen, and nitrogen.


1. Firepower How-to: Setting a Neutral Flame - Welding Attachment
(Firepower Metal Cutting & Welding Equipment)
2. Firepower How-to: Setting a Neutral Flame - Cutting Attachment
(Firepower Metal Cutting & Welding Equipment)
3. Types of flames | Gas Welding
(The Learning Hub)
4. How to get a neutral flame on a gas welder - Quick Reference to go with the long safety/set up video
(Way of the Wrench)
5. Types of Oxy-Acetylene gas flames# Neutral flame# Oxidizing flame# Carburizing flame.
6. The Carburizing Flame for Brazing
(George Goehl)

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