In this post, you’ll learn what is gas welding and how it is done? Its working principle, equipments, application and types of gas welding.
Gas Welding and Types
Gas welding is accomplished by melting the edges or surfaces to be joined by gas flame and allowing the molten metal to flow together, thus forming a solid continuous joint upon cooling.
This process is particularly suitable for joining metal sheets and plates having a thickness of 20 to 50 mm. The filler material of more than 15 mm thick is added to the weld as a welding rod.
Several gas combinations can be utilised for producing a hot flame for welding metals. Common mixtures of gases are oxygen and acetylene, oxygen and hydrogen, oxygen and other fuel gas, and air and acetylene.
The oxygen-acetylene mixture is used to a much greater extent than the other and has a prominent place in the welding industry. The temperature of the oxy-acetylene flame in its hottest region is about 3200°C, whereas the temperature obtained in the oxy-hydrogen flame is about 1900°C.
Gas Welding Flames Types
The accurate arrangement of the flame is necessary for reliable works. When oxygen and acetylene are supplied to the torch in nearly equal volumes, a neutral flame is produced having a maximum temperature of 3200°C.
This neutral flame is desired for most welding operations, but in certain cases a slightly oxidizing flame, in which there is an excess of oxygen or slightly carburizing flame, in which there is an excess of acetylene is needed. The condition of the flame is readily determined by its appearance.
A Neutral Flame Has Two Definite Zones
- A sharp brilliant cone extending a short distance from the tip of the touch, and
- An outer cone or envelope only faintly luminous and of a bluish colour. The first one develops heat and the second protects the molten metal from oxidation because the oxygen in the surrounding atmosphere is consumed by the gases from the flame. The neutral flame is broadly used for welding steel, cast iron, stainless steel, aluminium, copper, etc.
Carburizing Flame Has Three Zones
A carburizing flame is one in which there is an excess of acetylene; This flame has three zones:
- The sharply defined inner cone,
- An intermediate cone of whitish colour, and
- The bluish outer cone. The length of the intermediate cone is an indication of the ratio of excess acetylene in the flame.
When welding steel, this will tend to give the steel in the weld higher carbon content than the parent metal, resulting in a hard and brittle weld.
Oxidizing Flame Has Two Zones
An oxidizing flame is one in which there is an excess of oxygen. This flame has two zones:
- The small inner cone which has a purplish tinge.
- The outer cone or envelope. In the case of oxidizing flame, the inner cone is not sharply defined as that of neutral or carburizing flame. This flame is necessary for welding brass. In steel, this will result in large grain size, increased brittleness with lower strength and elongation.
Types of Gas Welding
Following are the 5 different types of gas welding:
- Oxy-acetylene gas welding
- Oxy-gasoline gas welding
- MAPP gas welding
- Butane or propane welding
- Hydrogen gas welding
1. Oxy-acetylene Welding
In this type of welding, oxy-acetylene welding applies a mixture of acetylene gas and oxygen gas to supply welding torches. Oxy-acetylene welding is the most generally used gas welding type. This gas mixture provides the highest flame temperature of available fuel gases.
Although acetylene is generally the most expensive of all fuel gases. Acetylene is a volatile gas and requires specific handling and storage procedures.
2. Oxy-gasoline Welding
The pressurized gasoline is used as welding fuel where construction costs are an issue, especially in places where acetylene canisters are not available. Gasoline torches may be more useful than acetylene for torch-cutting thick steel plates.
Gasoline can be pumped by hand from a pressure cylinder, which is a common practice by jewellery manufacturers in poor areas.
3. MAPP Gas Welding
In this, gas welding stands for Methylacetylene-propadiene-petroleum gas welding. The (MAPP) is a gas mixture that is much more inert than other gas mixtures, making it safe to use and store for beginner and recreational welders.
MAPP can also be used at extremely high pressures, it is used in high-volume cutting operations.
4. Butane or Propane Welding
These are similar gases that can be used as separate as fuel gases or combined together. Butane and propane have lower flame temperatures as compared to acetylene but are less costly and easier to transport.
Propane torches are used more often for soldering, bending, and heating. Propane needs a different type of torch tip than the injector tip because it is a heavy gas.
5. Hydrogen Welding
The hydrogen can be utilised at higher pressures than other fuel gases, making it particularly useful for underwater welding processes.
Some hydrogen welding equipment performs electrolysis by splitting the water into hydrogen and oxygen used in the welding process. Such electrolysis is often used for small torches, These are used in the jewellery making process.
Parts of a Gas Welding
Following are the main parts of a gas welding:
- Cylinder valves
- Pressure regulator
- Flashback arrester
- Flexible holes
- Non-return valves
All oxy/fuel gas processes operate in the same way. A fuel gas such as propane or acetylene is mixed with oxygen in the torch or blowpipe to produce a flame that is hot enough for this purpose.
A fuel gas such as propane or acetylene is mixed with oxygen in a blowpipe (often called a ‘torch’) to produce a flame that is hot enough for this purpose.
The main components of oxy/fuel gas equipment are:
- Cylinders of oxygen and fuel gas (propane or acetylene).
- A means to shut off or isolate the gas supply, usually the cylinder valves.
- A pressure regulator fitted to the outlet valve of the gas cylinder used to reduce and control gas pressure.
- A flashback arrester to protect cylinders from flashbacks and backfires.
- Flexible hoses to convey the gases from the cylinders to the blowpipe.
- Non-return valves to prevent oxygen reverse flow into the fuel line and fuel flow into the oxygen line.
- A blowpipe or other burner device where the fuel gas is mixed with oxygen and ignited.
Equipment Used in Gas Welding
Following are the equipment used in gas welding:
- Welding torch
- Welding hand-screen or helmet
- Protective gloves
- Welding goggles
In gas welding, the cylinders are used to store the amount of oxygen and acetylene and it is usually made of steel. The cylinder must always be safe and used in an upright position. The valve cap should always be in place when the cylinder is not being used.
2. Welding Torch
The welding torch has a mixer chamber and control values. At the other end of the torch is a nozzle where the fuel – oxygen mixture is ignited together.
3. Welding Hand-screen or Helmet
The welding hand-screen or helmet is usually made of lightweight material. The hand-screen or helmets protect the welder’s face and eyes from hazardous damage.
4. Protective Gloves
It is very necessary to wear protective gloves when you are doing gas welding to protect the hand from hazardous radiations and flame of fire.
5. Welding Goggles
It is essential to wear welding goggles while you are doing gas welding. The welding goggles protect eyes from radiation and sparks produced in welding.
What is Joint Edge Preparation
Sheet metal melts easily and does not need any special edge preparation. In welding operations including plate, joint edge preparation and proper spacing between edges are essential factors. The width of the plates determines the amount of edge preparation required.
The faces of square edges can be butted together and welded for joint on plate up to 3/16 of an inch thick. For plate 3/16 to 1/4 inch thick, a slight root opening between the parts is required to gain full penetration. Plates greater than 1/4 of an inch thick require beveled edges and an original opening of 1/16 of an inch.
For oxy-gas welding on the plate more than 1/4 of an inch thick, bevel the edges at an angle of 30 degrees to 45 degrees, making the groove included angle from 60 degrees to 90 degrees. Preparation of the edges will be done by flame cutting, shearing, flame grooving, machining, chipping, or grinding. In any case, the edge surface should remain free of oxide, scale, dirt, grease, or other foreign matter.
A plate from 3/8 to 1/2 inch thick can be welded from one side only, but thicker sections must be welded by framing the edges on both sides. Typically, butt joints prepared on both sides allow easy welding, produces less deformation and ensures better weld properties.
The heavy steel plates are rarely welded with oxy-gas unless other types of welding equipment are not available. The welding of the heavy plate is just not cost-effective because of the amount of gas consumed and the time used to complete a weld. If possible, use a form of electric arc welding because the joint can be welded faster, is cheaper, and has less heat distortion.
Precautions of Gas Welding
The following precautions will be required for gas welding:
- Work in a safe location away from other people.
- Wear protective clothing, gauntlets and eye protection.
- Shut off the blowpipe when not in use. Do not leave a burning torch on a bench or the floor as the force of the flame may cause it to move.
- Clamp the workpiece, do not hold it by hand.
- Keen hoses away from the working area to prevent contact with flames, heat, sparks or keep hoses clear of sharp edges and abrasive surfaces or where vehicles can hot spatter; keep no run over them.
- Do not allow hot metal or spatter to fall on hoses.
- Handle cylinders carefully. Keep them in an upright position and fasten them to prevent them from falling or being knocked over. For ex, chain them in a wheeled trolley or upon a wall.
- Always turn the gas supply off at the cylinder when the job is finished.
- Maintain all equipment and keep in good condition.
- Regularly check all connections and equipment for faults and leaks. Always provide enough ventilation during welding and cutting operations.
- Store gas cylinders outside whenever possible or in a well-ventilated place.
- Avoid taking gas cylinders into poorly ventilated rooms or confined spaces.
Applications of Gas Welding
Following are the applications of gas welding:
- To join most ferrous and non-ferrous metals, carbon steels, alloy steels, cast iron, aluminium and its alloys, nickel, magnesium, copper and its alloys, etc.
- To join thin metals.
- For joining metals in the aircraft industries and automotive.
- To join metals in sheet metal fabricating plants.
- To join the materials which require a relatively slow rate of heating and cooling etc.
Advantages of Gas Welding
Following are the main advantages of gas welding:
- It is the most portable and versatile process.
- This has better control over temperature.
- This weld dissimilar is suitable for metals.
- It has better control of filler-deposition rate.
- It has low maintenance and cost.
Disadvantages of Gas Welding
Following are the disadvantages of gas welding:
- It is not suitable for heavy conditions.
- Gas welding has a low working temperature of gas flame.
- It has a slow rate of heating.
- Gas welding is not suitable for reactive metals and refractory.
- Flux shielding in gas welding is not so effective.
- More problems in storage and handling of gases.
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