A welding method that uses the flame generated by the mixed combustion of combustible gas and combustion-supporting gas as the heat source to melt the weldment and the welding material to achieve interatomic bonding.
What is Gas Welding?
Oxygen fuel gas welding (OFW) is a welding method that uses the flame generated by the mixed combustion of combustible gas and combustion-supporting gas as a heat source to melt the weldment and welding material to achieve interatomic bonding. The combustion-supporting gas is mainly oxygen, and the combustible gas is mainly acetylene, liquefied petroleum gas, etc. The welding materials used mainly include combustible gas, combustion-supporting gas, welding wire, gas welding flux, etc. Features The equipment is simple and does not require electricity. The equipment mainly includes oxygen cylinders, acetylene cylinders, pressure reducers, welding guns, hoses, etc. This method is one of the most dangerous of all welding methods because the gas cylinder used is a pressure vessel and the gas is flammable and explosive. The outside of the oxygen cylinder is blue metal. Gold and silver materials are the best, but they are more expensive and heavier, followed by copper, which has a weaker oxidizing property. The hydroxide of copper is blue. So, the color of the oxygen cylinder should be blue.
Gas welding is also called air welding. PMA plasma welding machine completely replaces traditional welding equipment, a new generation of welding equipment that does not require oxygen, acetylene, liquefied gas, alcohol, gasoline, and combustible gas. Using the IGBT inverter control principle, the flame is stable during welding, and the whole equipment is light and convenient, suitable for outdoor welding. The welding machine is easy to operate, and only those who know a little about the welding machine do not need special training. This product does not require flammable and explosive gases such as acetylene, and the safety performance is greatly improved, only electricity can be used. During the soldering process, gas flux can be used directly instead of the traditional manual addition of borax to improve the wettability and fluidity of soldering, and to reduce the generation of pores. Improve the tensile strength of the weld, and the surface will not be oxidized or blackened during the welding process. No need for pickling, which improves welding efficiency.
What is the Principle of Gas Welding?
A welding method that uses the flame generated by the mixture of combustible gas and combustion-supporting gas as the heat source to melt the weldment and the welding material to achieve atomic bonding. Gas welding and gas cutting are open flame operations with high temperature, high pressure, flammable, and explosive characteristics, and often deal with flammable and flammable substances and pressure vessels, so there is a greater risk of fire and explosion. Acetylene, hydrogen, coal gas, natural gas, liquefied petroleum gas, etc. used in gas welding and gas cutting are all flammable and explosive gases. Oxygen has strong combustion-supporting properties, and its chemical properties (O2) are extremely active. If you are not careful, it is easy to burn and cause explosions.
The equipment and appliances used in gas welding and gas cutting, such as acetylene generators, acetylene cylinders, liquefied petroleum gas tanks, and oxygen cylinders, are all pressurized or high-pressure containers, which themselves have greater risk factors. The flame temperature of gas welding and gas cutting is high, and the molten metal sparks splash around during the operation. If it splashes on the surrounding combustibles, it can cause smoldering and cause fire. Especially when gas cutting is performed, the temperature is higher, and the molten metal oxides are more. The splashing distance is larger, and the danger of causing a fire is more prominent. Gas welding is widely used. Thin metal containers, such as gasoline drums, gas tanks, and various metal containers, are inseparable from gas welding during maintenance. Gas welding is also used when connecting steel bars, often due to the residual gasoline in these containers. It will explode when it meets flammable gas and welding and cutting flames.
In welding and cutting construction sites, many flammable and explosive substances, as well as various pressure vessels and pipes will also be encountered. Although the equipment and energy used in gas welding and gas cutting have certain fire hazards, the occurrence of fire and explosion accidents is not mainly caused by these equipment and energy sources, but most of them are due to paralysis of thinking and improper operation in gas welding and gas cutting operations. The system is not strict, and the safety measures are not implemented effectively.
What are the Main Gases that Can be Used as a Gas Source for Gas Welding?
Gas welding does not require a gas source, only gas + combustion-supporting gas. Gas welding does not use a shielding gas, and gas welding uses a flame to protect the molten pool.
- Common gas includes acetylene gas, liquefied petroleum gas, coal gas, natural gas, hydrogen, and so on. Acetylene mixed with oxygen is called oxyacetylene.
- Common combustion-supporting gases are oxygen and air.
What are the Advantages and Disadvantages of Gas Welding?
Advantage:
- The equipment is simple, the cost is low, the movement is convenient, and the use is flexible.
- It has strong versatility and good adaptability to the welding of cast iron and some non-ferrous metals.
- Since no power supply is required, it has practical value in places without a power supply and in fieldwork.
Disadvantages:
- Low production efficiency. Gas welding flame temperature is low, heating speed is slow.
- After welding, the deformation of the workpiece and the heat-affected zone is large, the heating area is wide, the welding heat-affected zone is wide, and the welding deformation is large.
- During the welding process, the molten metal is poorly protected, and the welding quality is not easy to guarantee.
- It is difficult to realize automation.
How does Gas Welding Work?
- Right welding method:
It means that the welding torch moves from left to right during welding, the torch flame points to the welding seam, and the welding torch moves in front of the welding wire during the welding process. The disadvantage is that it is not easy to control, and the operation process has no preheating effect on the weldment, so it can only be used for welding thicker and higher melting point weldments.
- Left welding method:
It means that the welding torch moves from right to left during welding. Compared with the right welding method, the left welding method is easier to control and is widely used. The disadvantage is that the weld is easy to oxidize, cools quickly, and the heat utilization rate is low. It is suitable for welding thinner plates and low melting point metals.
Construction Conditions of Gas Welding:
- Cleaning before welding:
Before gas welding, the oxide, rust, oil, and other dirt on the surface of the weldment joint should be cleaned, otherwise, it will easily be brought into the metal molten pool, causing defects such as slag inclusion and pores in the weld. After cleaning, spot welding can be performed to fix the mutual position of the workpieces. Spot welding can be started from the middle or both sides.
- Preheating before welding:
After the point is fixed, the gas welding parts need to be preheated. Welding preheating can balance the temperature difference of each part of the joint, so that the heat distribution of the welded joint is more uniform, which can slow down the welding cooling speed, improve the welding metal structure, and make the welding seam quality. has seen an increase. When the weldment is preheated to a certain temperature, the flame is increased a little for heating, heated until the weldment is melted, a molten pool is formed, and then the welding wire is sent to the molten pool for welding.
What is the Welding Process?
- Welding process:
During the welding process, the welding tip moves forward with a slight reciprocating swing along the butt gap. The welding speed should be uniform, and the welding should be done in one breath without stopping as much as possible.
- Post-weld heat treatment and slow cooling measures:
The post-weld heat treatment is selected according to the situation. If the grains of the gas welding seam and the heat-affected zone is coarse, and the grains need to be refined, normalizing treatment is used. If it is the assembly and welding of large ordinary low carbon steel containers assembled on the construction site, a single medium temperature tempering can be used. When welding to the end, after filling the molten pool, the welding torch is slowly too high, and the external flame is used to heat and bake the joint and its surroundings to make it cool slowly. The heating and cooling of the heat treatment should not be too fast, and the inner and outer walls should be uniform.
- Welding porosity treatment:
The porosity is that during the welding process, the bubbles in the molten pool in the metal do not escape before the metal cools and solidifies, forming the bubbles in the weld. Therefore, before welding, the oil, rust, and other contaminants on the surface of the weldment should be thoroughly cleaned, and the welding speed should be adjusted appropriately so that the gas can fully escape from the molten pool.
Application of Gas Welding:
Gas welding is mainly used in the welding of thin steel plates, low melting point materials (non-ferrous metals and their alloys), iron castings, carbide tools, and other materials, as well as repair welding of worn and scrapped parts, flame correction of component deformation, etc. Applicable appliances include welding torches, pressure-reducing valves, and rubber hoses.
