In the olden days, metals were cut by laborers manually using hand tools. The different tools involved were a hacksaw, cutters, and many more. But with the advent of better alternatives, it is easier to cut metals with newer methods. Gas cutting is one such process that allows you to cut through thick metals using an oxy-acetylene flame.
This gas cutting process is also known as oxyacetylene cutting or oxy-fuel cutting. This process of gas cutting is exactly the opposite of welding.
Types of flames in oxy-acetylene gas cutting
There are usually three main types of flames in the gas cutting process. We will explain them briefly below.
The maximum temperature of this flame is 3000 degrees centigrade. In this flame, the long white inner feather is surrounded by a transparent blue envelope. It has a distinct visible area. This flame has more fuel content than other types of flames. Carburizing flame is obtained when the ratio between oxygen and acetylene is less than 1. In this, the flame temperature reduces because acetylene decomposes into carbon and hydrogen. This flame has a low temperature and is mainly used for processes where low temperature is required like brazing and soldering.
2. Neutral flame
The maximum temperature of the neutral flame is 3200 degrees Celcius. The bright white core is surrounded by a transparent blue envelope. This flame is obtained when the ratio between oxygen and acetylene is 1. A neutral flame is mostly used for gas welding processes.
3. Oxidising flame
Oxidizing flame is the main flame used in the gas cutting process. It is the flame used to cut the metals because it oxidizes the metal while cutting it. Oxidizing flame is obtained when the ratio of oxygen and acetylene is greater than 1. The excess oxygen present in this flame reacts with carbon present in the metal. But it is generally used to weld copper and its alloys.
Oxyacetylene is made of two gases
Oxy-acetylene gas is a mixture of two gases that is oxygen and acetylene.
Oxygen(O2) is a component present in the air. Approximately 21% of oxygen is present in the air. Oxygen is mainly found naturally in the environment. It is manufactured industrially by distilling air below the freezing point. Oxygen is an accelerant everything which comes in contact with the accelerant to burn faster and hotter. This is the main reason for using oxygen in gas cutting.
Acetylene (C2H2) is used in combination with oxygen for this gas cutting process. The acetylene is stored generally in red-colored has cylinders. It is a hydrocarbon and is used as fuel. It burns ver efficiently thus producing the desired temperature and flame when mixed with oxygen.
Oxyacetylene gas cutting process and its working principle
Here we are going to explain the methodology of the flame cutting process.
In this method, metal is merely melted by the flame of the oxy-acetylene gas torch and blown away to form a gap or kerf.
• When ferrous metal is cut, actual burning of iron takes place according to one or more of the following reactions.
• Fe + O = FeO + Heat
3Fe + 2O2 = Fe3O4 + Heat
4Fe + 3O2 = 2Fe2O3 + Heat
• As these reactions can’t take place below 815°C, the oxy-acetylene flame is first used to raise the metal temperature where burning can be initiated. Then a stream of pure oxygen is added to the torch to oxidize the iron.
• The liquid iron and iron oxides are then expelled from the joint by the kinetic energy of the oxygen gas stream.
• Low rate of heat input, and need for preheating before the cut, Oxy-acetylene flame produces a relatively large heat-affected zone with an associated distortion zone.
• The process is suitable when the edge finish or tolerance is not critical. Theoretically, heat generated due to the burning of iron is sufficient to continue cutting but due to losses, additional heat supply is needed.
• Workpiece temperature of 1200°C is needed to sustain the cutting. Low carbon steel from 5 to 75 mm can be cut.
• Cast iron can’t be cut to a smooth finish as it starts melting and flowing before it can be oxidized. Similarly, other nonferrous metals behave in a similar fashion.
Oxy-acetylene cutting procedure
Here we are going to mention the standard procedure used for cutting metals using the oxy-acetylene gas cutting process.
Precautions before starting the work
- Clean the surface area of the metal to be cut and remove any flammable substance.
- Mark the area or outline of the cut to be made with chalk.
- line up the oxy-acetylene bottles and open their valves.
- Wear a safety apron, safety goggles to protect your eyes, and safety shoes before starting any work.
- Carry out a proper assessment of the surrounding area and remove any flammable material.
- Use insulated hand gloves to protect your hands from heat.
- Crack open the acetylene gas from the torch and light the torch with a lighter.
- Supply the oxygen slowly and balance the flame using oxygen and acetylene
- Supply more oxygen for cutting by pressing the lever and you can start the cutting process.
Parts of Oxy-acetylene gas cutting system
Here we are going to list some of the major parts of a gas cutting system, these make up the important components of the system.
Oxyacetylene gas cutting torch
The oxy-acetylene gas cutting torch or flame torch as many call it is the crucial component of a gas cutting process. The nozzle has tiny holes in them which allow the flame to come out in a sharp come shape. It is imperative to handle the torch safely to prevent damage to the nozzle holes. The damage especially happens when the torch is hot, fresh after a cutting process. The torch has two pipes in them allowing the oxygen and acetylene to pass separately and finally mix at the nozzle tip. The lever on the torch is used to control the flow of oxygen into the nozzle to get the desired flame. The torch also has a flame or flashback arrester fitted so that flame from the torch does not go back into the hose and prevents it from eventually ending up entering the bottle. This will prevent a potential hazard from occurring which could result in an explosion.
Oxyacetylene gas bottles
The acetylene bottle consists of a perforated honeycomb structure inside where the acetylene is stored. Acetylene is a gas dissolved with acetone. The acetylene bottle is left-handed thread and is painted red in color. The oxygen bottles are painted blue in color. Both these bottles are stored in an upright condition away from the heat source. These bottles sometimes have their own well-ventilated dedicated storage room or can be found on a bottle stand near the place of work.
Oxyacetylene gas hose
The hose of the oxyacetylene system is connected to the torch and the gas bottle using a regulator. The hoses are made of dedicated colors representing the type of gas they carry. The red color is for the acetylene gas and the blue color is for the oxygen gas. They are made of fire retardant material and can resist flame for some time.
Advantages of oxyacetylene gas cutting
- There is no need for an electrical power supply
- The gas cutting equipment is always portable and can be carried anywhere.
- Low maintenance
- More economical
- Simple to operate and need less skill
- Gases are easily available
Disadvantages of oxy-acetylene gas cutting
- There is always a danger of fire when cutting metals using flame
- The metals that are cut will be subjected to heat stresses.
- Cannot be used to cut very thick metals
- The cuts made are not accurate in the manual process.
Applications of oxy-acetylene gas cutting
Oxy-acetylene gas cutting finds its applications in a wide range of processes and industries
- It is used in domestic work shops to cut metals
- In ship building
- In factories and industries
- Automated versions of gas cutting processes are applied in manufacturing industries
Oxyfuel cutting is a combustion process using oxygen or a fuel gas flame. The heating flame warms up the material to its ignition temperature. Next, an oxygen jet of at least 99.5 percent purity is blown onto the heated spot, oxidizing the metal. Burning metal immediately turns to liquid iron oxide.
Oxy-fuel torches are normally used for cutting only ferrous metals or those containing iron, such as carbon steel. For the most part, they are not used for cutting cast iron, aluminum or stainless steel.
Oxy cutting is a method of cutting through ferrous metals using gas to produce a flame. It uses a mixture of oxygen and acetylene (or propane, natural gas, LPG) to rapidly oxidise the metal and cut through it. Oxy acetylene will only work on metal that contains iron because the cutting is done by oxidisation.