3.C] What is gas welding? Explain with neat sketch principle of operation of oxy-acetylene gas welding.
Answer:-
Gas welding is a fusion method of welding, in which a strong gas flame is used to raise the temperature of the workpieces so as to melt them. As in arc welding, a filler metal is used to fill the joint. The gases that can be used for heating are:
(i) oxygen and acetylene mixture.
(ii) oxygen and hydrogen mixture.
The oxy-acetylene gas mixture is most commonly used in
gas welding.
Oxy-Acetylene Welding
When the right proportions of oxygen and acetylene are mixed in the welding torch and then ignited, the flame produced at the nozzle tip is called as the oxy-acetylene flame.
This flame when used in welding is known Oxy-acetylene welding. The temperature attained by the oxy-acetylene flame is around 3200°C and therefore has the ability to melt all commercial metals.
Thus, there is a complete bonding of the joining metals that can be achieved during welding Equipment. The oxy-acetylene gas equipment consists of two large steel cylinders one containing oxygen at high pressure, and the other dissolved acetylene also at high pressure, rubber tubes, pressure regulators and blow torch. The oxygen and the acetylene are supplied to the blow torch separately, where both of them get mixed and come out through the nozzle of the blow torch.
Working:-
The typical oxy-acetylene welding process is shown in Figure. After the initial equipment preparation, the to-be-welded component setup and safety checks are completed, the pressure regulators fitted to the oxygen and acetylene cylinders are adjusted to draw the oxygen and acetylene gas in the required proportions from the cylinders respectively.
The pressure regulator in each of the cylinders is fitted with two gauges. One gauge indicates the gas pressure inside the cylinder and the other gauge indicates the reduced pressure at which the gas goes out. The respective gases from cylinders are carried from the pressure regulator to the welding torch using the rubber hose pipes.
Upon reaching the welding torch, these gases are allowed to mix in a mixing chamber and then are led out of the torch through the orifice of the blowpipe. The resultant flame at 3200 degrees Celsius is used to melt the workpieces.
To fill up the gap between workpieces and to add strength to the joint, filler rods (mostly of metal similarto the workpieces) are added to the molten metal pool. A Flux such as borax is used to dissolve and remove metal oxides formed during welding.
The technique used to weld can be leftward or rightward welding technique. In the leftward welding technique, the flame from the torch preheats the material yet to be welded, while in the right ward welding, the flame post-heats the weld-bead. The molten metal pool that contains the molten metal of the filler rod and the workpiece solidifies to form a welded joint.