Gas welding is the process of melting and joining metal parts by means of a gas flame. Generally pressure is not applied during the process of gas welding. Oxygen and acetylene gases are made to pass through the welding torch. These gases are mixed at the required ratio at the torch and the tip of the welding torch is ignited to produce the flame. Because of the heat generated by the flame, the edges of the metal parts are melted. Filler rod provides the additional metal required for making the joint. The flux coated on the electrodes prevents oxidation and removes impurities. This method is suitable in welding metal parts of thickness varying from 2mm to 50 mm. The temperature of the flame is around 3200°C.
Gas Welding Equipments
The following equipments are necessary for gas welding
- Gas cylinders
- Pressure gauges
- Rubber hoses
- Welding torch
- Safety goggles
- Spark lighter
- Wire brush
1. Gas Cylinders
Oxygen and acetylene gases are stored in separate cylinders and used for gas welding. The colour of oxygen cylinder is black and the acetylene gas is stored in maroon cylinders. Oxygen is stored at a pressure of 125Kg/cm2. Acetylene gas is stored at a pressure of 16 Kg/cm2. in the cylinder.
Separate regulators are fitted on both the cylinders. A regulator is used to control the working pressure of the gases. The working pressures of oxygen is 1Kg/cm2 and acetylene is 0.15Kg/cm2. Working pressure of these gases are altered according to the thickness of the metal parts of the joint.
3. Pressure Gauges
Two pressure gauges are fitted each on the oxygen cylinder and on the acetylene cylinder. One of the pressure gauges indicates the pressure of the cylinder and the other gauge indicates the working pressure of the specific gas.
Separate hoses are used to connect the two cylinders with the welding torch through regulators. The colour of the hose from the oxygen cylinder is black and the one from the acetylene cylinder is red. These hoses carry the gases to the welding torch.
5. Welding Torch
Oxygen and acetylene reach the welding torch through the passages of hoses from the respective cylinders. These gases are mixed in the mixing chamber of the welding torch. Flame is produced at the tip of the torch when the gases are ignited. There are two control valves present in the torch to control the quantity of oxygen and acetylene. By this control, the grade of the flame can be altered. The size of the flame is altered to suit the thickness of the metal parts.
Oxy acetylene flame emits ultraviolet and infrared rays. These rays are highly harmful to bare eyes. In order to protect the eyes of the welder, goggles should be used by him.
7. Welding Gloves
Protective hand gloves are used by the operator to prevent possible damages that may be caused by high temperatures and metal splashes during welding.
8. Spark Lighter
Spark lighter is used to ignite the oxy-acetylene gas at the tip of the welding torch.
9. Wire Brush
Wire brushes are useful in cleaning the weld before and after the welding process.
Filler Rods Used in Gas Welding
Filler rods used in gas welding supply the additional metal in making joints. These rods are melted by the gas flame and deposited over the parts of the joint. Generally the filler rods are made of the same metal as that of the parts of the joint.
The diameter of the filler rod depends upon the thickness of the parts to be welded. The strength of the welding joint is increased by adding Nickel or Chromium in filler rods. A thin coat of copper is provided on the filler rods to prevent the molten metal from reacting with atmospheric oxygen. Flux may be applied either in powdered form or liquid form.
Advantages of Gas Welding
- Applied for different classes of work
- Welding temperature is controlled easily
- The quantity of filler metal added in the joint can easily be controlled
- The cost of the welding unit is less
- The cost of maintenance is less
- Both welding and cutting can be done
Limitations of Gas Welding
- Intended for welding thin workpieces only
- The process of welding is slow
- The time taken by the gas flame to heat the metal is more when compared with electric arc
- The strength of the joint is less
- Great care should be taken in handling and storing gas cylinders
Differences Between Arc Welding and Gas Welding
|Arc Welding||Gas Welding|
|1. The heat is generated by the electric arc||1. The required heat is provided by the gas flame|
|2. The working temperature is about 4000°C||2. The temperature of the gas flame is about 3200°C|
|3. The filler rod is used as electrode.||3. Filler rod is used separately|
|4. Care should be taken aginst the dangers that may be caused because of electricity||4. The danger of the process is because of the gases at high pressure|
|5. The strength of the joint is more||5. The joint is not as strong as that of arc welding|
|6. Brazing and soldering cannot be performed by the electric arc||6. The processes of brazing and soldering can be done with the gas flame|
|7. The filler rod metal should be selected as the same metal as that of the parts of the joint.||7. The filler rod metal can be different from that of the parts of the joint.|