Gas welding is a fusion welding process that helps to join metals using the heat generated from a gas flame. Various types of flames like xy-hydrogen, air-acetylene, and oxy-propane are used in Gas welding. It uses a mixture of gases as the heat source to melt and join metal parts. This method has been widely used for over a century and is well-known for its versatility, affordability, and portability. There are various gas welding techniques that are used for the operation, as on the thickness and position of the workpiece. Gas welding uses different flames like neutral, oxidising, and carburising, each suitable for specific metals. Advantages of gas welding include cost-effectiveness, portability, and simplicity, making it ideal for repair and light fabrication work. However, it also has disadvantages like limited welding speed, less suitability for thick sections, and safety hazards from gas cylinders and open flames.

In this article, we will provide a comprehensive overview including the history, principles, techniques, and applications. We will also discuss the pros and cons of this welding method and provide tips for safe and effective gas welding.

We have made this theoretical subject more fun to learn to help you ace your SSC JE ME and GATE ME exams. Let’s start learning!

Gas welding

Gas welding, also known as oxy-fuel welding or oxyacetylene welding, is a heat-based process used to cut and join metals together. It involves the combustion of fuel gases, such as acetylene or gasoline, with oxygen to generate heat that melts and fuses the ends of the metals. This method is one of the oldest forms of welding and is commonly used in industries such as automotive repair, metalworking, and construction. The process can be performed using different gas combinations, but the most common one is oxygen and acetylene.

What is Gas Welding?

Gas welding is a metal joining process conducted by melting the metals with the help of fuel gases like acetylene, propane, or hydrogen mixed with oxygen to produce the weld. This welding type is commonly known as ‘Oxy Acetylene Welding’. 

This is because oxygen and acetylene are the most commonly used gases in this type. Edmund Davy discovered Acetylene in 1836 and it was brought to practical use by 1900 with the development of the welding torch.

A practical example of this type is depicted in the image shown below.

The green cylinder is used to store oxygen and the red is usually for acetylene. Let us learn how this welding process works.

Technically, welding is a metal fabrication process used to join two metals by heating them above melting temperatures and fusing them by cooling them. Along with the heat, pressure is also used to produce the weld. A demonstration of welding can be seen in the GIF below.

There are different types of energy sources used for welding like gas flames, electric arcs, electron beams, laser, friction, and even ultrasound. Based on the energy used, the welding process can be categorized into gas, arc, and solid-state welding. 

Working Principle of Gas Welding

The basic principle behind most types of welding remains to melt the two metals (by heating them above their melting points), add flux, and fuse them. Let us learn the working principle of gas welding.

Fig 1: Gas Welding Process Diagrammatic Representation 

The metals are melted by the heat from the reaction of fuel gas (Acetylene, Propane, Butane, Hydrogen, etc) and oxygen. When the gases from the cylinder stored at high-pressure are released, they flow through the torch at high velocity and are mixed. 

The mixture has high temperatures with traits of carbon dioxide, and this is ignited by an external spark. The flame starts blowing from the torch. The heat from this flame can be increased by increasing the pressure of the outflow gas.

How is gas welding done?

Gas welding is a welding process that uses a flame produced by the combustion of a fuel gas mixed with oxygen to generate the heat required for welding.

Parts of Gas Welding Equipment

Let us refer to the image below while learning the parts involved in the gas welding equipment.

Fig 2: Parts of Gas Welding

(a) Regulator: It is used to adjust the required pressure at which the gas should be released for the operation.

(b) Fusible Plugs: It is a safety valve which is used when the pressure in the system goes beyond the optimum. Plugs are usually made of Tin which has a low melting point.

(c) Hose: They are simply pipes that are designed to allow the flow of various gases without reacting with them. Usually, every gas welding equipment has two hoses: One for oxygen and the other for fuel gas. In India, oxygen hose has a standard colour of black and acetylene has red.

(d) Non-return valve: These valves are essential to prevent the oxygen and fuel gas from flowing back into the cylinder, which may cause the cylinder to explode.

(e) Check valve: It is a chamber with a ball pressed against one end through a spring. The check valve is used to aid the flow in one direction.

(f) Torch: This is the working tool that the operator uses to make the weld. It is the getaway for the final output of reactions from the cylinder to the metal.

Fig 3: Gas Welding Setup

Types of Flames in Gas Welding

As we just discussed the concept of the torch, the flame coming out of the torch also plays a major role in the quality of the weld in the final output. There are three types of flames as shown in the below figure.

Fig 4: Types of Flames in Gas Welding

Carburising Flame

• The quantity of acetylene gas is more than oxygen in the carburising flame
• It is a special flame with three zones: a luminous inner zone, a feather of acetylene, and a blue outer envelope.
• It is used to weld high carbon steels (HCS) and cast iron.

Neutral Flame

• When the acetylene and oxygen are mixed in equal proportions through the torch, the neutral flame is obtained
• This flame consists of two cores: Inner core (white colour) and outer core (blue colour)
• It is used to weld stainless steel, copper, cast iron, aluminium, and mild steel.

Oxidising Flame

• The oxygen flowing through the torch is more than acetylene in the oxidizing flame
• These flames have the highest temperature and make a roaring noise
• It is used for welding alloys like brass, Iron carbide, and brazing ferrous metals.

Types of Gas Welding

Gas welding is generally classified into four types. Aspirants are advised to go through the various gas welding processes to get familiar with welding types. The flame temperature and gas used at the time of welding vary for all the processes. It is important to choose the right mixture of gas to get the desired results. For more information, candidates can refer to the table provided below. 

Gas Welding Types

Now, we have learnt about oxy acetylene welding or gas welding in common, it makes us curious about the various types: Oxy-gasoline, MAPP, Butane or Propane, and Oxy-hydrogen welding.

Oxy-Gasoline Welding

In oxy-gasoline gas welding, pressurized gasoline is employed as welding fuel for the process at places where the provision for acetylene canisters is rare. The gasoline torches have proved to be useful in welding thick plates better than acetylene.

Typical oxy-gasoline welding equipment is shown in the image below.

Fig 5: Oxy-Gasoline Gas Welding Equipment

It has a cylinder to fill gasoline and a torch attached to the top to blow a flame that is hot enough to melt thick sheet metals. 

One of its applications is in jewellery manufacturing at places where another welding we impossible to afford. This is because of the advantage of oxy-gasoline welding that it can be pumped by hand from a cylinder.

MAPP Gas Welding

MAPP stands for Methyl Acetylene Propadiene Petroleum. It is a gas safer to store at normal temperatures. Original MAPP gases are combined with oxygen for welding, brazing, and soldering. The flames from this process reach a temperature of 2900 \(^{\circ} C\) and above. 

A typical MAPP equipment is shown below. 

Fig 6: MAPP Welding Equipment

One advantage is that it can be used in high-volume operations, but the disadvantage is that the MAPP gas is costly.

Butane or Propane Welding

Butane \(C_4 H_{10}\) and Propane \(C_3 H_8\) are both organic hydrocarbons or compounds (which are gas at normal temperatures usually stored in a cylinder) used in welding for simple and economical welding processes. 

Propane and Butane can be mixed or used individually for welding as they are capable of producing flame. Generally, propane torches are used for brazing, heating, and soldering. These are available in can-like equipment with a nozzle attached to the top end as shown in the figure below.

Fig 7: Butane or Propane Gas Welding Torch

Oxy-Hydrogen Welding

In the oxy-hydrogen gas welding process, oxygen is combined with hydrogen to attain a flame temperature of 2800 \(^{\circ} C\). The amount of oxygen supplied to the welding process is always less as the combustion process is completed with the addition of atmospheric oxygen. 

This is because the welded area is exposed to the atmosphere. The addition of atmospheric oxygen develops a protective preheating flame surrounding the main flame reducing the flame temperature. Due to this, the whole process is slow compared with others.

An illustration of the process is depicted in the image below.

Fig 8: Oxy-Hydrogen Welding

Precautions for the Gas Welding Process

We learnt that the process involves some flames and gases that may affect the operator and the workpiece. In this case, there is a need for some precautions.

1. A burning torch or the torch that is not turned off should not be kept as it is on the worktable when not in use.
2. Never hold the workpiece by hand but clamp it.
3. Keep the gas cylinders in a ventilated area.
4. Hoses should be kept clean and free from sharp edges or abrasive surfaces.
5. Prevent direct contact of the hose with the welded surface.
6. Operating cylinders should be handled with care, making sure that they are held in place properly.
7. Keep in check the connections and leaks from any equipment part.
8. Turn off the supply of gas after the operations are completed.

Gas Metal Arc Welding & Gas Tungsten Arc Welding

Gas Metal Arc Welding (GMAW), also known as Metal Inert Gas (MIG) welding, is a welding process that uses a consumable electrode and a shielding gas to join metals. It is one of the most widely used welding methods due to its versatility, efficiency, and ease of operation.

Gas Tungsten Arc Welding (GTAW), also known as Tungsten Inert Gas (TIG) welding, is a welding process that uses a non-consumable tungsten electrode to create an electric arc and join metals. It is a versatile welding method that can be used to weld various metals, including stainless steel, aluminum, copper, and titanium.

Gas Welding vs. Arc Welding

Types of Gas Welding Techniques - Overview 

To get the desired results, it is important to select the correct technique for gas welding. There are various factors that determine the gas welding technique. It is important to consider the thickness of the material and the position of the workpiece. The flame direction varies for all the welding techniques. For more details on welding techniques, candidates can refer to the table below. 

Gas Welding Technique Types

Aspirants can check various techniques for gas welding below

Leftward Welding Technique (Forward)

In this technique, the flame is directed toward the direction of welding. The torch is held at 30 to 45 degrees, and the filler rod at 30 degrees on the opposite side. The technique is generally used for thin material (up to 5 mm). The forward welding technique is generally used in sheet metal, pipe welding and light fabrication work. The main advantage of of forward welding technique is that it provides a smooth and continuous weld.

Fig 9: Leftward welding technique

Rightward Welding Technique (Backward)

The flame is directed backwards and opposite to the welding direction. Righward technique in gas welding is used to weld thick materials (Above 5 mm). It required slightly higher pressure in comparison to other techniques. The technique is used basically in the construction of Structural steel, pressure vessels and heavy components.

Fig 10: Rightward welding technique

Vertical Welding Technique

This gas welding technique is used in a vertical or upright position. It involves the upward movement while controlling the molter pool. The vertical gas welding technique is generally used in Pipe joints, shipbuilding and pressure vessels.

Fig 11: Vertical welding technique

Overhead Welding Technique

This type of welding technique is performed below the joint. It required a small frame, low heat input and fast manipulation. The overhead gas welding technique is used in Maintenance welding and construction.

Fig 12: Overhead welding technique

Horizontal Welding Technique

This welding technique is performed along a horizontal surface or edge. It is easier than the vertical or overhead positions. It is important to keep the flame angle and speed consistent. Horizontal gas welding is used in the construction of frames, chassis and flat surface joints.

Fig 13: Rightward welding technique

Advantages of Gas Welding

After learning the whole concept, we are keen to know the advantages of the process.

• No need for a high-skill operator to operate on this machine or setup
• Anyone can set it up as the initial cost is low compared to arc and resistance welding machines
• One can travel with it to the site where welding needs to be done, in other words, the machine is portable
• Easy maintenance and easy to repair.

Disadvantages of Gas Welding

We learnt the valuable advantages but unlike all other processes, this also has some notable disadvantages.

• Welding speed is low due to the rate of metal joining.
• By the end of the welding process, there will be large heat-affected areas.
• Welding Titanium, Zirconium, or High-Speed steel (HSS) is not recommended for gas welding.
• It is suitable for thinner sheet metals but not thicker sheet metals.

Applications of Gas Welding

Amidst the disadvantages, the gas welding process has found its applications in a few notable industries. 

• This welding process is used for joining non-ferrous metals, cast iron, carbon steel, nickel, alloys of aluminium, etc.
• It is used to join thin metals which have as low as 1.6 mm thickness.
• It is commonly used in sheet metal industries.
• It is used to join metals with a low rate of cooling and heating.
• Sometimes, this is used to repair tools and equipment of other welding processes.
• They are used in automobile industries, shipbuilding, heavy vehicle manufacturing, and agricultural machinery manufacturing to weld thinner sections.

Theoretical concepts like these should not be taken for granted. Practice with the AE/JE Mechanical previous year’s question mock tests along with some fire-starter from our Super teachers will help you to crack the AE/JE Mechanical exam. 

You should consider these theoretically oriented concepts to help you crack the GATE ME exams and learn more through the GATE ME test series. Do all these on our website and mobile app. Download the Testbook app now!