Oxy Acetylene Gas Welding Process | How it work? (Explained)

Gas welding

What is Oxy Acetylene Gas Welding?
Oxy Acetylene Gas Welding (also known as Oxy fuel Gas Welding or Gas Welding) is a type of welding process that uses the heat from the fuel gases such as acetylene in combination with oxygen, in order to melt and weld the metal parts.

The heat produced by the combustion of acetylene gas is enough to melt any metal. And hence the oxy acetylene welding process is universally accepted.

The common gases that are used in the gas welding process include acetylene, propane, butane and hydrogen gas.

Out of these, the most commonly used system is the oxygen-acetylene gas welding system.

Oxy Acetylene Gas Welding Process

Oxy acetylene gas welding

The setup for the oxy acetylene welding process is mentioned in the diagram above.

Oxy Acetylene Gas Welding Process involves following steps.

  1. Setup the gas cylinders
  2. Make sure the pressure regulator valves are turned off
  3. Take safety precautions before starting the gas welding process
  4. Adjust the hand valves for the gas flow, and ignite the torch
  5. Regulating the flame as per requirements
  6. Use filler rod to fill the weld groove
  7. Adding gas welding flux
  8. Use leftward or rightward welding technique
  9. Allow the welded part to cool down

Let me tell you few important things about each of these steps.

#1) Setup the gas cylinders

Gas welding cylinders

As shown in the above diagram, the oxygen cylinder as well as acetylene cylinder are set up on the site where gas welding is to be done.

The oxygen cylinder is painted with black colour and the acetylene cylinder is painted with maroon colour.

On the top of the cylinder, there are pressure regulator valves.

#2) Make sure the pressure regulator valves are turned off

pressure regulator valves

Both the cylinders are provided with the pressure regulator valves that need to be turned off initially.

These pressure regulator valves are also called pressure reducing valves. The main function of the pressure reducing valves is to regulate the pressure of the individual gases in the torch.

Basically, there are two types of pressure regulator valves found on the gas cylinders.

  • Single stage or
  • Two stage

The single stage regulator valve reduces the cylinder pressure to the working pressure in just a single step. (For example, it reduces the pressure from 2200 psi to 3 psi).

While in the two stage regulator valve, the pressure is reduced in two stages. In first stage, the pressure is reduced to some moderate level (about 30 psi), while the second stage reduces the pressure to the required pressure for the welding operation.

#3) Take safety precautions before starting the gas welding process

Gas welding safety precautions

Before starting the gas welding process, the welder must take safety precautions like;

  • Wearing the safety glasses for protection of eyes.
  • Wearing the fireproof apron.
  • Use welding gloves during the welding operation.
  • Wear a long sleeve shirt.
  • Fire resistant cap or shoulder covers are necessary for overhead weldings.

#4) Adjust the hand valves for the gas flow, and ignite the torch

gas welding torch

In order to ignite the gas welding torch, the pressure valves are opened slightly and the hand valves are adjusted for the supply of gas.

The gas cylinders contain two gauges, one for measuring the gas pressure inside the cylinder and another indicates the pressure of gas supplied in the hose pipe.

The welding torch has a mixing chamber in which the oxygen gas and acetylene gas are mixed and they are ignited at the tip of the torch.

One thing you should note that for extinguishing the flame, the acetylene gas supply should be turned off first followed by oxygen supply.

In cases of backfires, the oxygen supply should be turned off first in order to prevent the high temperatures and damage to the hose pipe.

The hose pipe can not handle excessive temperature. They are just designed to handle the regulated pressure of the supply gases.

The acetylene hose pipe is red in color while the oxygen hose is green in color.

Also the acetylene hose pipe has left handed threads for fitting and the oxygen hose has right handed threads for fitting.

Due to this, there is no issue of alternate connection of hose pipes.

#5) Regulating the flame as per requirements

welding flame

Flame is produced by burning of the gas mixture at the tip of the torch.

Different types of flames are produced by combination of different proportions of gases in the welding torch.

This proportion of gas is regulated by using the hand valves present on the welding torch.

There are basically 3 types of flames obtained in the oxy acetylene gas welding process.

  • Neutral flame
  • Reduction flame or carburizing flame
  • Oxidizing flame (excess oxygen)

In Neutral flame, the acetylene is completely burned and it releases all the available heat.

In Reduction flame, the supply of oxygen gas is less and so there occurs incomplete combustion.

In Oxidizing flame, the top temperature of the white flame reaches as high as 3400 °C. This flame also produces a loud noise due to excess amount of oxygen.

In gas welding process, different temperature range can be achieved by using different types of fuels.

Gas welding temperature ranges for different fuel gases are mentioned below.

Fuel gasesMaximum temperatureNeutral temperature
Acetylene3300 °C3100 °C
Hydrogen2870°C2350 °C
Propylene2860 °C2500 °C
Methane2740 °C2350 °C
Propane2700 °C2450 °C
Natural gas2400 °C2350 °C

#6) Use filler rod to fill the weld groove

filler rod

Filler material (or filler rod) is added to the weld groove and it forms the integral part of the weld after its solidification.

The filler materials generally have the same material composition as that of the parent metal which is to be welded.

#7) Adding gas welding flux

When the metal gets heated during the gas welding process, the oxygen from the atmosphere reacts with the metal and forms oxides. Because of this the quality of the weld becomes poor and its strength decreases.

The main purpose of using flux is to avoid the contamination of atmospheric oxygen.

#8) Use leftward or rightward welding technique

In gas welding process, there are two techniques used for welding.

  • Leftward technique
  • Rightward technique

Leftward technique

Forehand technique (or Leftward technique)

In Leftward technique, the welding torch is on the right side, the filler rod is on the left side, and the welding torch moves in the direction of the welding. The torch remains inclined at the angle of 65° to the surface (see diagram).

Rightward technique

Backhand technique (or Rightward technique)

In Rightward technique, the welding torch is on the right side, filler rod is on the left side and the torch is inclined at the angle of 45° to the weld surface (see diagram).

#9) Allow the welded part to cool down

After the welding process is completed, always look after that no one touches the hot welded part with bare hands.

Advantages of oxy acetylene gas welding

The advantages of oxy acetylene gas welding process are mentioned below.

  • Gas welding is suitable for welding of thin sheets or plates as the flame is not piercing as that of arc welding.
  • By using a gas welding process, better control over temperature can be achieved.
  • Deposition of filler material can also be controlled in the gas welding process.

Disadvantages of oxy acetylene gas welding

The disadvantages of oxy acetylene gas welding process are mentioned below.

  • Gas welding is a time consuming process as compared to arc welding process.
  • The Heat Affected Zone (HAZ) and distortion are larger in gas welding process, while in arc welding process, these are less.

Applications of oxy acetylene gas welding

The applications of oxy acetylene gas welding process are mentioned below.

  • Oxy acetylene gas welding process is used for welding the ferrous as well as non ferrous metals.
  • Gas welding can also be used for repairing worn-out machines or any other metal equipments.
  • Gas welding is applicable in fabrication of air conditioning ducts as well as ventilation systems.
  • It is used in various industries like shipping industries, automobile industries, etc.

External links:
Filler rod image: Image credits (Indiamart)
Oxy-acetylene gas welding diagram: Image by Cierrex, CC BY-SA 3.0, via Wikimedia Commons

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