Both gas welding and gas cutting are highly sought out procedures by technicians in many industries. Although their working methodology is the same which is oxy-fuel combustion, the difference lies in the purpose. Among a wide array of resemblances, it can be difficult to figure out the dissimilarities of gas welding vs. gas cutting for average welders.
While the principle and equipment are the same, the choice of fuel remains the main difference. Also, the role of oxidation is different in the two. Gas cutting works in different stages whereas gas welding gets the job done in one continuous phase.
Have you ever seen those pictures that look exactly the same at first glance, but then they tell you there are 8 or 10 differences between the two and you have to find them? The discussion about Gas welding and gas cutting is kind of like that. Let’s not waste any more time and just get on with it.
Oxy-fuel Combustion Process
This one may seem out of context, but trust me, it is not. To know the difference between gas welding and gas cutting, first, you’ll have to know about the oxyfuel combustion process. Both gas welding and cutting work on the same principle which is oxy-fuel combustion, only the application and outcome are different.
Oxy-fuel combustion is the process of burning fuel using oxygen. The purity of oxygen is the key here. Any change in the purity results in higher fuel consumption and low heat. So naturally, the speed of the procedure declines.
There are two major applications of oxy-fuel combustion. Gas welding and gas cutting. In both processes, fuel is combusted using oxygen, then applied on a metal surface for joining or cutting purposes.
Some Important Terms You Should Know
There are few important terms that you ought to know for better comprehension of the topic. Please go through these before heading on to the differences between gas welding and gas cutting.
Carburizing Flame:A reducing flame differs slightly from a carburizing flame. Both carburizing flame and reducing flame have lower oxygen and higher acetylene than neutral flame. But the carburizing flame has more acetylene content than the reducing flame.
It is suitable for welding lead and hardening the surface by adding carbon. On the other hand, the reducing flame does not carburize the metal; instead, it ensures the absence of oxidation.
Kindling Temperature: Kindling temperature has different names such as kindling point or autoignition temperature. It is the temperature at which a substance ignites into flame without any external source of heat.
Kerf: Kerf is the width of the cut. To understand better, think of the slit that you make you run a knife through a cake or butter. That is the kerf.
Now that you know the fundamentals of oxy-fuel combustion, you will easily grasp the concept of gas welding. Before we start, you should know that although many different types of gases and fuels are used in oxy-fuel combustion, they are primarily for gas cutting. For gas welding, acetylene is the primary and choice.
When acetylene and oxygen are mixed at the right proportion, they produce an extremely high-temperature flame. The flame is directed towards the weld area. The high-temperature flame melts the faces of the two metal pieces that you are welding and forms a weld pool.
The welding technician may or may not add filler metal. Then the welder gradually removes the flame from the weld pool, giving it enough time to harden without forming slag.
Types of Gas Welding Flames
There are three types of flame concerned with oxyacetylene welding. Flame is the most important aspect of gas welding. All the equipment and material are the means of controlling the flame. The three types are oxidizing flame, reducing flame, and neutral flame. Let’s discuss each of them briefly:
Neutral Flame: In a neutral flame, the oxygen and acetylene ratio is 1:1. However, it is called neutral not because of the balance in the ratio, but because it has no chemical effect on the metals that you are welding, unlike oxidizing and reducing flame. The temperature of the neutral flame is 5900° Fahrenheit.
There are two zones in a neutral flame. The inner bluish-white cone and a light blue envelope. A neutral flame is common for welding mild steel, stainless steel, cast iron, copper, and aluminum.
Oxidizing Flame: Oxidizing flame has high oxygen content. Excess oxygen causes oxidation in most metals. That’s why oxidizing flame is unsuitable for welding in most cases. It is only used to weld copper-based alloys, zinc-based alloys, manganese steel, and cast iron.
The oxidizing flame has a smaller white cone, more bluish and pointed compared to the neutral flame. The flame burns with a signature roaring noise. The temperature of the oxidizing flame is 6300° Fahrenheit due to the increased oxygen ratio.
Reducing Flame: Reducing flame has less oxygen content than neutral flame. It has unique visual characteristics. The flame has three zones. An inner white cone, white acetylene feather, and bluish outer cone. Reducing flame has a temperature of 5500° Fahrenheit which is the lowest among the three.
Due to the reducing nature, reducing flame may add carbon and remove oxygen from the weld metal, resulting in the formation of iron carbide. Due to this same nature, this flame is suitable for welding metals that have already undergone oxidation. Reducing flame is great for welding high carbon steels and cast iron.
Although people often use the terms reducing flame and carburizing flame interchangeably, there is a slight difference. I will get into that later.
Gas welding offers a lot of convenience and flexibility to consumers. Here are some advantages of gas welding:
- Versatility: Gas welding can join ferrous and nonferrous metals. This is one of its biggest advantages.
- Inexpensive: Initial cost of gas welding is lower than other types of welding. The instruments and materials are affordable and cheap to set up.
- Easy to learn: Gas welding doesn’t require top-of-the-line mastery. That’s why it’s easy to find gas weld technicians at an affordable price.
- Portability: Gas welding equipment is lightweight and easily portable. You can easily move them from place to place and take them for welding in remote areas.
- Easy control over the procedure: The welder has precise control over the procedure, unlike other forms of welding. The weld bead size, shape, viscosity along with heat input, and temperature can be accurately controlled.
Nothing is without flaw. Gas welding has some downsides as well. There are quite a few regards where it falls short of arc welding. Followings are some disadvantages of gas welding:
- Not compatible for thick sections: Gas welding is not suitable for heavy or thick sections. Theoretically, you can weld metal pieces up to 25 mm, but practically welders use gas welding for not more than 2 mm thick metals.
- Not compatible for all types of metals: refractory and reactive metals cannot be welded by this technique.
- Inferior thermal properties than arc welding: Heating time and flame temperature of gas welding are lower than that of arc welding.
- Time-consuming: gas welding takes longer than arc welding.
- Mediocre flux shielding: Flux shielding system of gas welding is not as proficient as arc welding.
- More overall cost: Greater overall cost compared to arc welding.
Due to the low cost and is easy to learn, gas welding has many uses. Followings are some applications of gas welding:
- Gas welding is great for joining thin sections such as soldering copper tubing.
- For joining ferrous and nonferrous metals.
- To join metals where extremely high temperatures of arc welding can cause problems.
- Gas welding is great for minor repairs.
- Extensively used in the automobile industry and aircraft industry.
Gas cutting follows the same principle of the oxy-fuel combustion technique. But the difference is gas cutting uses different types of gas as fuel. So, you cannot name it oxyacetylene cutting straight up. The oxy-fuel flame is applied to heat the metal. Then a jet of oxygen cuts through the preheated metal. There are three phases of gas cutting. I will discuss them briefly below:
Preheating: In this phase, the oxy-fuel flame is applied to the metal section that is intended to be cut. The metal needs to preheat to its kindling temperature, slightly below the melting point.
Oxidation: After reaching that specific temperature, a jet of pure oxygen is applied to the heated section. The chemical process that takes place subsequently is known as oxidation. The metal reacts with oxygen and forms oxides. Rapid oxidation is known as burning and slow oxidation is known as rusting.
Cutting the Metal: The oxidation reaction releases some extra heat and burns the oxidized metal. The burned-up oxidized metal runs off as slag along with the flow of oxygen, gradually a kerf forms and cuts the metal.
Types of Fuel Gases Used in Gas Cutting
There are different types of fuels used in gas cutting to achieve different flame properties such as temperature, size of the flame, etc. Here, are some common fuel gases in gas cutting:
Acetylene is the most widely used fuel in oxy-fuel combustion. It is a hydrocarbon similar to methane, propane, butane, etc. There is a distinction in its chemical properties. Acetylene has two carbon atoms and two hydrogen atoms. The two carbon atoms bond together with a triple bond.
When acetylene reaches a specific temperature, the carbon triple bond breaks, and releases energy. Whereas in other hydrocarbons, breaking carbon bonds absorbs energy.
This release of energy is the reason acetylene produces such a high temperature which is up to 6300° Fahrenheit. Oxyacetylene flame also has a higher flame speed and calorific volume compared to propane.
MAPP is not a generic name. It is a trademark of the Linde group. It is a mixture of various hydrocarbons, chiefly methylacetylene and propadiene. MAPP is liquid at normal temperature. You can easily handle it like propane, with higher properties than propane being the closest to acetylene.
It can reach up to 5600° Fahrenheit temperature. 70 pounds of MAPP can work equal to 1500 cubic feet of acetylene. You can work at a higher pressure using MAPP compared to acetylene. That’s why it can be used for underwater welding.
Hydrogen produces lower heat than acetylene which is around 5100° Fahrenheit. For combustion, the hydrogen ratio should be anywhere between 4% to 95%. It is great for underwater welding. Oxyhydrogen flame is suitable for aluminum.
Propylene has a similar temperature to MAPP, although lower than acetylene. It releases high heat in its outer cone and has higher fuel to gas requirements.
- Natural Gas
Natural gas has the lowest property for any fuel used in gas cutting. That’s why people use it rarely. Its inner flame heat value is 1,490kJ/m3 which is significantly lower than oxy-acetylene flames. Hence, natural gas has very low piercing power.
Propane can reach up to a maximum of 5000° Fahrenheit. The flame concentration is smaller than oxyacetylene flame. As a result, the heat-affected zone (HAZ) is larger, and the piercing time is longer. To reach the maximum temperature, 3.5 times more oxygen is required in the mixture compared to acetylene.
Flame Types In Gas Cutting
Similar to gas welding, the flame types also play a role in gas cutting. As the fundamental chemistry is the same, so are the flame types. Let’s take a look at how the flame types are concerned with gas cutting:
Neutral flame: The neutral flame is where oxygen and the fuel ratio are equal as I have mentioned earlier. It does not chemically affect the workpiece, that’s why many industries use it to cut a wide range of metals.
Oxidizing flame: Oxidizing flames oxidize the metal before reaching a specific temperature. So, it is used in combination with a neutral flame. High oxidizing flame is suitable for only underwater cutting.
Reducing flame: Reducing flame adds carbon to metal so it is not suitable for cutting low carbon alloys. Technicians use reducing flame to exclusively cut metals with carbon doping such as cast iron, steel, etc.
Gas cutting is the first choice in various sectors despite having some limitations. Here are the applications of gas cutting:
- Manual severing and cutting scraps
- Cutting metals that easily undergoes oxidation and the oxides have low melting point than the metal
- Precision cutting in automatic systems
- Cutting high carbon steels
- Cutting cast iron
You cannot cut metals that resist oxidation by gas cutting.
Gas cutting remains one of the top choices for cutting metals in various industries. Followings are some advantages of gas cutting:
- Cost-effective: Equipment and the overall cost is low which makes gas cutting affordable.
- No electricity: Both oxygen gas and fuel gas flow from high pressure to low pressure area of the cylinder through the pipe. The torch does not need electricity to operate.
- Can be mechanized: Gas cutters can be used either manually or mechanized using robotic arms for more precise cutting.
- Suitable for thick sections: You can cut thick sections of metals using gas cutters. Oxy-fuel flame can pierce up to 4-inch-thick metals.
- Mobile: Gas cutting equipment are easily moveable, same as gas welding equipment.
It has some disadvantages as well. That’s why many prefer other forms of metal cutting procedures. Here are some cons of gas cutting:
- Not suitable for all metal types: Its application is limited to low alloy steels. Gas cutting is not fitting for stainless steel and aluminum.
- Slow: Gas cutting is slower and time-consuming than plasma cutting.
- Quality can differ: The skill of the technician does not alone determine the cutting quality. The condition of the torch nozzle and plate surface play a role in the end result.
- Heat affected zone: Gas cutting has a larger heat affected zone, so the properties of the surrounding metal may alter.
What’s the Difference Between Gas Welding and Gas Cutting?
Now that you know the bits and pieces of gas welding and gas cutting, I believe you can differentiate between them. To make things easy for you, here are the main differences between gas welding and gas cutting in a tabulated format:
|Joining two metal pieces together
|Cutting a piece of metal into two
|Acetylene, MAPP, propylene, propane, etc.
|Role of Oxidation
|Oxidation is dreadful in this procedure
|Oxidation plays an important role in the process
|The three types of flames play a vital role
|Flame types do not have any significant role, neutral flame is the common choice
|No separate stages
|The entire cutting procedure has three stages
|MAPP, hydrogen, acetylene
|MAPP, hydrogen, acetylene, propylene, propane, LPG, natural gas
So, the bottom line is, when it comes to gas welding vs gas cutting, their differences lie in their application. One is used to join multiple metal parts together and the other is used to cut metals. These two are quite similar in how they work. So. It is pretty normal for you to be confused.
But I hope after reading this article, you have a better understanding of the two and how they differ.