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Before going to Gas welding we first discuss welding. So, Welding is defined as
It is a fabrication process that joins materials, usually metals or thermoplastics, by causing coalescence.
This is often done by melting the workpiece and adding a filler material from a pool of molten material that cools to become a strong joint, but Sometimes the pressure is used in conjunction with heat, or by itself, to produce the weld.
This is in contrast with soldering and brazing which involves melting a lower-melting-point material between the workpiece to form a bond between them, without melting the workpiece.
Another definition is,
The welding process is a material joining process which produces coalescence of Material by heating them to suitable temperature with or without application of pressure or by the application of pressure alone and with or without the use of filler materials.
Gas welding is a type of liquid state welding process, in which fuel gases burns to generate heat.
This heat is used to melt interface surfaces of welding plates which are held together to form a joint.
In this welding process, mostly oxy-acetylene gas is used as working fuel gas.
This process can be done with or without the help of filler material.
Main component or Equipment of Gas Welding:
Oxygen and acetylene are stored under pressure in a steel cylinder.
They are seized by the amount of oxygen or acetylene that they hold.
Cylinders should always be secured and used in the upright position.
When a cylinder is not being used the valve cap should always be in place.
These cylinders are made of Steel and are usually painted green. They contain compressed oxygen at presses that can be as high as 2200 PSI. All cylinders have valves and are fitted with a screw on steel cap that protects the cylinder valve when the cylinder is not in use.
These cylinders contain acetylene under pressure are painted black made of steel and have cylinder valves.
The cylinders contain a porous filler material which is fitted with acetone that allows the acetylene to be safely be contained in the cylinder at 250 PSI.
Acetylene should never be used at a pressure that exceeds 15 PSI as it becomes highly unstable which depending upon the condition could cause it to decompose and explode.
Both oxygen and fuel gases are filled in the cylinder at high pressure.
These gases cannot use at this high pressure for welding works, So a pressure regulator is used between the flow.
It supplies oxygen at a pressure about 70 – 130 Kn/m2 and gas at 7 – 103 Kn/m2 to the welding torch.
The torch assembly consists of the handle Oxygen and fuel gas valves and the mixing chamber.
Welding tips or cutting attachment can be used with the handle the allowing it to be used for welding, heating and cutting operations.
Oxygen and fuel gas flow through tubes inside the handle which blend in the mixing chamber or tip. it is at the tip that the mixed gas is ignited.
Goggles and Gloves:
These two Goggles and Gloves are used for safety purpose.
Goggles protect eyes and Gloves protects the hand from radiation and flame of fire.
Types of Flames:
Welding is generally carried out using the neutral flame sitting which has equal quantities of oxygen and acetylene.
The oxidizing flame is obtained by just increasing the oxygen flow rate.
Carburising or Reducing Flame:
The carburizing or reducing flame is achieved by increasing acetylene flow in relation to oxygen flow.
Because steel melts at a temperature of 1500 degree centigrade the mixture of Oxygen and acetylene is used as it is the only gas combination with enough heat to weld Steel.
However other gases such as propane hydrogen and coal gas can be used for joining lower melting point of metals and for brazing and silver soldering.
As the figure shows all the equipment are set carefully and now the gas cylinder and oxygen cylinder connected to the welding torch through pressure regulators.
Now the regulate pressure of gas and oxygen supplied to the torch where they properly mixed.
The flame is ignited by a striker. Take care the tip of a torch is pointing downward.
Now the flame is controlled through valves situated in the welding torch.
The flame is set at the natural flame or carburizing flame or oxidizing flame according to the welding condition.
Now the welding torch moved along the line where joint to be created.
This will melt the interface part and join them permanently.
3 Types of technique in gas welding:
The leftward technique is used almost exclusively and is Ideally suited for welding butt, fillet, and lap joints in sheet thickness up to approximately 5 mm.
The rightward technique finds an application on plate thickness above 5 mm for welding in the flat and horizontal-vertical position.
All positional rightward technique:
The all positional rightward method is a modification of the rightward technique and is ideally suited for welding steel plate and in particular pipework where positional welding (vertical and overhead) has to be carried out.
Types of Gas Welding:
Advantages, Disadvantages, and Application of Gas Welding:
- Process is versatile
- Adapted too many different jobs
- Equipment is relative to low cost
- Independent from the availability of external energy sources.
- Welders skill required in manipulating the torch, the flame, and the filler Rod.
- Flux required for most materials other than low Carbon Steel.
- Reactive or refractory metals are unsuited to gas welding.
- Slow metal joining rate.
- For joining thin materials.
- For joining most ferrous and nonferrous materials.
- Used in automatic and aircraft industries and sheet metal fabrication.
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