Gas welding is also known as oxy-fuel welding or oxy welding. It is the process of joining and cutting metal by using heat created from gas flame. When the gas fuel (acetylene) mixed with oxygen in a mixing chamber of welding touch. It produces a very hot heat of about 5700-5800°f which has the ability to melt metals including, cast iron, steel, copper and aluminum. These melting process leads to to fusion of like metals with close related strength of the fused metal. Addition strength is obtain if more metal of like nature is added. This process is known as oxy-acetylene welding.
Cutting operation in gas welding is slightly different from that of welding. It uses oxygen and acetylene to preheat metal to red hot and then uses pure oxygen to burn away the preheat metal. This process is achieved by oxidation which is only effective on metals that are easily oxidized such as mid steel and alloy steels. Oxy-fuel cutting can be used to cut metals with thickness of 2/8 up to 12.
Generally oxy-fuel processes are used for flame hardening, brazing, fusion welding, metalizing, soldering, stress reliving, cutting and bending but these modern days the primary uses are welding, brazing and cutting.
At the end of this article, the reader is expected to have basic understanding on the following listed below:
- Basic concept of gas welding and cutting.
- Characteristics of gas welding.
- Advantages and Disadvantages of gas welding.
- Equipments of oxy-fuel welding (gas welding).
- Safety precaution in gas welding.
Commercial fuel gas requires oxygen to support the combustion. When it comes to welding operations. If a fuel-gas is burn with oxygen, it must have high rate of flame propagation, high flame temperature, minimum chemical reaction of the flame with base and filler materials and adequate heat content.
Acetylene is a hydrocarbon just as propane and methane, but seems to be differ from those hydrocarbon because molecule is made up of two carbon atoms and two hydrogen atoms. Chemist called this process “triple bond” when the carbon atom are joined. When acetylene it kindling temperature (lowest temperature at which a substance burst into flame), this bond breaks and releases energy. When acetylene and oxygen mixes and ignited, this is when the flame reaches the temperature of 5700°f to 6300°f. This is done by triple bond.
Some characteristics of gas welding
1. Acetylene gas is obtained by mixture of calcium carbide and water and is composed of carbon and hydrogen with the chemical formula C²H²
2. Hydrocarbon burns in two stages with primary combustion zone (cone flame) and secondary combustion zone (envelope flame)
3. Natural flame temperature of 5420°f as the end of the inner cone. This can be increased to the minimum of about 5800°f by increasing oxygen strength through the torch.
Advantages of gas welding process
- It doesn’t uses electricity
- Different metals parts can easily be joined.
- It can be used for preheating, case hardening, metal cutting, soldering and annealing.
- The equipment are portable and easy to transport.
- Welder has control over the rate of heat input.
- It becomes extremely dangerous if used above 15 pounds pressure
- The welding process is slower than of electric arc welding
Equipment of oxy-acetylene (gas welding)
The following listed below are equipments used to carryout oxy-acetylene operation. They are:
- Acetylene gas cylinder
- Oxygen gas cylinder
- Oxygen pressure regulator
- Acetylene pressure regulator
- Oxygen gas hose
- Acetylene gas hose
- Welding torch or blow pipe
- Gas lighter
- Set of keys and spanners
- Filler rods and fluxes
- Protective clothing for the welder
This cylinder is usually painted maroon and the valves are screwed left handed. Acetylene cylinders are manufactured from drowned steel available in sizes of 300, 120, and 75 cubic feet. Acetylene cylinder pressure is 250 psi when filled. Acetylene is completely unstable in its pure form at pressure above 15psi which require a special porous material on the storage of acetylene. These materials can be balsa wood, charcoal, corn pith, or portland cement that is saturated with acetone to allow storage acetylene to be safe. The important of the porous materials is to prevent high-pressure gas forming in the cylinder. Acetone is a colourless, flammable liquid that is added to cylinder until about 40 percentage of the porous material is saturated.
Oxygen gas cylinder
Oxygen gas cylinder are painted green and the valves are screwed right handed. The cylinder are also made of high strength steel plate drowned to required size of 244, 122, and 80 cubic feets. Oxygen are stored within the cylinder at a pressure of 2200 psi. When the original pressure of a full oxygen cylinder drops by 10% during welding. This is to indicate that 1/10th of the cylinder content have been consumed.
Gas Welding pressure regulators
Pressure regulators are connected between the cylinder and the house that lead to the welding torch. Pressure needed for the welding torch maybe somewhere up to 35psig for oxygen and 15psig for acetylene. The pressure of the gases obtained from the cylinders is considerations higher than the gas pressure used to operate the welding torch. The primary function of the pressure Regulators is to reduce the higher pressure of the gas in the cylinder to a desired working pressure and to produce Steady flow of gas under varying cylinder pressures. The pressure regulator is fitted with two pressure gauges. One of it indicates the gas pressure in the cylinder and the shows the amount of level at which the gas is going out. Gas pressure can be classified into, Single stage regulator and two stage regulators.