Gas Welding is the process where two or more parts of the metal are joined or united by melting them using the heat transmitted by flame produced by the reaction of oxygen and fuel gas.
Gas Welding is also called oxy-fuel welding. It is called oxy-fuel welding because in this process oxygen is used with burning fuel. In this process, heat is obtained combustion of fuel gases.
When fuel gas like acetylene (C2H2) mix with oxygen and burns to produce temperature in the range of 3100 degree Celcius.
In gas welding, there are two cylinders :-
i) One is of fuel gas and is of maroon colour.
ii) The second one is oxygen gas and is black colour.
Both the cylinders have pressure regulators at there top. These two cylinders are connected with welding torch via gas pipes.
The most commonly used method of gas welding is Oxyacetylene welding because in this welding the temperature of the flame is very high.
After the completion of the welding process, the flux is used to deoxidize and cleanse the weld metal. This flux solidifies and forms a slag skin on the welded metal.
Parts of Welding Torch:
Two types of gas are stored under pressure in two different steel cylinders.
These cylinders should always be used safely in an upright position.
When the cylinders are not used, the cylinders should be covered with a valve cap.
2) Pressure Regulators:
For welding, the oxygen and acetylene are required at low pressure but in the cylinders, they are filled in high pressure. So a pressure regulator is required to control the pressure of oxygen and acetylene before reaching the mixing chamber.
The torch consists of the handle Oxygen and the fuel gas valves and the mixing chamber.
Inside the handle, there are tubes through which the oxygen and fuel gas flow.
4) Mixing Chamber:
In this chamber oxygen and fuel gas are mixed. In this mixing chamber, the ratio of oxygen and fuel gas is mixed according to the type of flame required. Neutral, oxidizing or carburizing are three types of flame used in welding.
5) Control Valves:
There are two control valves available in this torch. One is for the oxygen and the second one is for fuel gas. These control valves are used to control the flow of oxygen or fuel gas to the mixing chamber.
6) Gas Hoses:
The gas hoses are used to transfer oxygen and fuel gas from the cylinder to the welding torch.
These hoses are colour coded for easy identification. This colour coding varies from country to country. For Example:- In USA the oxygen hose is green and the duel hose is red and in UK, the oxygen hose is blue and the fuel gas hose is red.
The mixture of oxygen and acetylene comes out of this nozzle. The mixture of these gases comes out in pressure from the nozzle and then is ignited by the striker.
8) Googles and gloves :
In gas welding goggles and gloves are used for the safety of the operator who does welding.
They are used to protect the hand and eyes of the welding operator from radiation and heat of the flame.
Working of Gas Welding:
At first, all the equipment of gas welding is fitted properly and carefully. After that, A regulated pressure of gas and oxygen supplied to the torch where they are properly mixed.
The mixture of fuel gas and oxygen is then ignited by the striker.
Then the flame of the torch is controlled by different valves present in the welding torch.
Based on the type of flame required, the valves are operated accordingly. If the neutral flame is required, then both the valves are opened equally. If the oxidizing flame is required then the valve of oxygen is opened more and if the carburizing flame is required then the valve of the fuel gas is opened more.
The flame is set as neutral, oxidizing, and carburizing based on the metal, its thickness, and some other welding conditions.
After that, the flame of the welding torch is moved along the line between the two metal plates.
Along with the metal plates, a filler rod is also used which is used to create a pool of molten material that will fill the gap between the two metal plates interface.
The filler rod is move along with the flame. The filler rod is kept at an angle of 30 degrees to 40 degrees according to the welding technique being used.
After moving the flame and filler rod along the line of two metal plates interface, the two metal plates join together because of the melting and solidification of metal plates interface part and the filler rod.
Types of gas welding:
1) Oxy-Acetylene Welding:
In Oxy acetylene welding, a mixture of acetylene gas and oxygen gas is used to feed the welding torch.
This acetylene and oxygen gas mixture provide the highest flame temperature of all oxygen fuel gas mixture.
2) Oxy Gasoline Welding:
Oxy Gasoline Weldings are more effective than oxy-acetylene when torch cutting of steel plates are done. The gasoline can be hand pumped from a pressure cylinder.
3) MAPP Gas Welding:
The full form of MAPP is Methylacetylene Propadiene Petroleum is a gas mixture that is more inert than other gas mixtures. As MAPP is more inert than other mixture, so it is much safer than other mixtures.
As MAPP can also be used as high pressure, so it can be used for high volume cutting operations.
4) Butane/Propane Welding:
The flame temperature of butane and propane is less than that of acetylene. These two gases are also less expensive and are easy to transport. This type of welding is more used for bending, soldering, and heating.
Propane welding requires a different type of torch tip to be used than an injector tip because propane is a heavier gas.
5) Hydrogen Welding:
Hydrogen can also be used at a higher pressure than the other types of welding discussed above. As hydrogen can be used at high pressure, so it is used in underwater welding.
Some equipment of hydrogen welding work from electrolysis by spitting water into hydrogen and oxygen to be used in the welding process.
It is also used in the jewelry making process.
Techniques of gas welding:
There are mainly 4 types of gas weldings:
1) Leftward or Forward Welding Technique:
In this welding technique, the welding is started from the right side and is proceeded towards the left side. When this technique is used then the welding torch is held in the right hand and the filler rod is held in the left hand.
The torch tips make an angle of 60 to 70 degrees and the filler rod make an angle of 30-40° with the metal plates which is to be welded.
This welding technique is used for welding unbevelled steel plates up to 3mm and bevel plates up to 6mm.
2) Rightward or Backward Welding Technique
In the rightward welding technique, the welding is started from the left side and proceeded towards the right side.
When this technique is used, the welder holds the welding torch in the right hand and filler rod in the left hand.
The torch flame makes an angle of 40-50 degree and the filler rod makes an angle of 30-40 degrees with the metal plates which are to be welded.
This welding technique is used for welding steel plates which have thickness over 6mm.
This technique produces stronger, denser, and tougher weld.
3) Vertical Welding Technique:
In the vertical welding technique, the welding is started from the bottom and is proceeded towards the top.
The metal plates to be welded are placed vertically in this technique.
The welding torch and the filler rod are given oscillating movement while using this welding technique.
The torch flame makes an angle of 25-90 degrees and the filler rod makes an angle of 30 degrees with the vertical plate.
For welding more than 5mm thick plates, two welders are required in this technique.
4) Linde Welding Technique:
Linde welding is used for butt welding of steel pipes. In this technique, excess acetylene flame is used.
The two pipes to be welded are beveled at 70 degrees and are welded together with a gap of nearly 2.5 mm. During this welding process, the pipes are rotated continuously so that seam is in the horizontal position only. In this technique, rightward welding is used to weld the pipes.
Types of Flames in Gas Welding:
1) Natural Flame or Neutral Flame:-
Most of the welding process is carried out using this flame. It is called natural flame because when we do welding with this flame no chemical reaction takes place. Also, this flame produces very little smoke.
A neutral flame has equal oxygen and gas fuel by volume. In this flame, there are two cones. The inner cone is white in colour and the outer cone is red in colour.
It is used to weld mild steel, stainless steel, cast iron, copper, aluminum, etc.
2) Carburizing Flame:-
This flame is called carburizing because when this flame is used in welding then metal carbide is formed. If a metal that absorbs carbon is welded using this flame then the properties of the metal will be changed.
This flame is more smoky and quiet. In this flame, more fuel gas is used as compared to oxygen. The ratio of fuel gas to oxygen in this flame is 3:2.
Carburizing Flame has three cones or zones, the inner cone is white in colour, the intermediate cone is red in colour and the outer cone is blue in colour.
Carburizing flame is used in medium carbon steel, nickel, etc. This flame is used in metal which does not absorb carbon or in a condition where absorption of carbon is required.
3) Oxidizing Flame:-
In this oxidizing flame, the content of oxygen is more than the content of fuel gas by volume.
It has two zones or two cones, the first one is called the inner cone and is white in colour. The inner zone is very bright. The second one is called the outer cone and is blue in colour. The size of the inner cone in the oxidizing flame is very small as compared to its size in a natural or neutral flame. It has more heat than a neutral flame.
If more heat is required to weld then we use an oxidizing flame in which the temperature of the inner cone is very high.
The oxidizing flame is used to weld copper alloys like brass, bronze, etc.
The oxidizing flame should not be used to weld metals like zinc, copper, manganese steel, cast iron, etc.
For more details about welding flames, click here.
Advantages of Gas Welding:
1) It is easily portable.
2) It is very less expensive and very affordable.
3) It can be easily maintained and repaired.
4) It is a very simple piece of equipment.
5) It is self-sufficient and does not rely on other equipment.
Disadvantages of Gas Welding:
1) The metal joining rate is very slow, so the welding speed is low.
2) A skilled operator is required to operate this machine.
3) The power density is low.
4) The heat affected zone is large.
5) Gas welding is not recommended for welding reactive and refractory metals like titanium and zirconium.
Applications of Gas Welding:
1) It is joining thin materials.
2) Used for joining ferrous and nonferrous materials.
3) Gas welding is used in sheet metal fabrication.
4) It is used in aircraft industries.