History of Gas welding
As the name indicates, gas welding is a process in which, Flammable gases provide sufficient heat for fusion. The discovery of gas welding is attributed to Henri Louis Le Chatelier, who first introduced 1895, the phenomenon of combustion and the theory of chemical equilibrium, measurement of high temperatures.
He highlighted in his research on the flame of oxy-acetylene, that the flame produced by the mixture of oxygen and acetylene, producing the highest temperature known up to that time and capable of smelting the metal easily.
A practical type of gas torch was introduced in the early 1900s, and by 1903 the oxyacetylene process began to be used industrially.
Gas welding is a fusion welding process, in which the desired heat is obtained by mixing oxygen/air with flammable gas, following types of flammable gases are used in this process.
Two familiar fuel gases used in gas welding, are the most popular in the gas welding process.
• the mixture of oxygen and acetylene gas using in Air- acetylene welding.
• the mixture of oxygen and hydrogen gas using in the oxy-hydrogen welding.
Classification of gas welding
The gas welding process can be classified as follows:
• Air-acetylene Welding
• Oxyhydrogen welding
• Oxyacetylene welding,
• Pressure gas welding
In this process, acetylene is mixed with oxygen in a certain proportion in a welding torch and ignited. The flame emanating from the tip of the torch reaches a temperature of about 3200°C, this temperature capable of smelting the metal easily. When making joints of thick metals, a filler metal is often used,
This filler metal combines with the molten metal to form greater strength. There is no need to apply any pressure until the weld pool is formed and solidified.
Oxy-hydrogen gas welding
In the oxy-hydrogen process, hydrogen is used in the place of acetylene, which has a lower temperature than oxy-acetylene, which is around 2500 °C.
In other gas welding processes, flame temperatures with oxygen mixture, are as follows :
Oxygen with acetylene 3200
Oxygen with hydrogen 2500
Oxygen with propane 2500
Gas welding Equipment
The basic types of equipment, used to carry out gas welding are as follows:
• Oxygen gas cylinder
• Acetylene gas cylinder
• Acetylene pressure regulator
• Oxygen pressure regulator
• Oxygen gas Hose (Blue)
• Acetylene Hose (Red)
• Welding torch or blowpipe with a set of nozzles and gas lighter
• Trolleys for the transportation of oxygen and acetylene cylinders
• A set of keys and spanners.
• Filler rods and fluxes
• Protective clothing for the welding operator
Types of flames
The correct type of flame is essential in the gas welding process.
Flames can be classified as follows:
1. Acetylene flame
2. Reducing flame
3. Neutral flame
4. Oxidizing flame
A neutral flame is produced when approximately equal volumes of oxygen and acetylene are mixed into the welding torch and fired at the tip of the torch. The temperature of the Neutral flame is of the order of about 3260 degrees centigrade.
A neutral flame is applied in the welding of stainless steel, mild steel, cast iron aluminum, and copper.
The oxidizing flame is the second stage of the neutral flame. After established the neutral flame, the oxygen supply ratio is increased and the oxidizing flame is established. This flame is identified by a small white cone, which is smaller, bluer in color, and higher than a neutral flame.
The oxidizing flame is applied in the welding of Zinc base metals, copper base metals, and some types of ferrous metals like cast iron.
The reducing flame is established when the amount of oxygen supplied is reduced by the neutral flame. This can be identified by the acetylene feather, which is present between the inner core and the outer envelope. The outer flame envelope is longer as compared to the neutral flame and is generally brighter in color. The temperature of the reducing flame is about 3038 degrees centigrade.
As we know that the maximum temperature of the oxyacetylene flame is 3100 to 3300 degrees centigrade and the center of the heat concentration is just off the extreme tip of the white cone.
Chemistry of flame
It can be described in following stages:
When equal proportions by volume of oxygen and acetylene are mixed and burn in the inner white cone:
2C2H2 +2O2 = 4CO +2H2
When passing into outer envelope of the flame:
4CO +2H2 +3O2 = 4CO2 +2H2O
Combining equations (i)and (ii)above
2C2H2 +5O2 = 4CO2 +2H2O