One type of fusion welding is gas welding. It is widely used in the manufacture of structures made of thin carbon steel, in repair welding of cast iron products, and in welding defects in cast products made of ferrous and.
Gas welding - schematic diagram
Gases used
Natural gas, acetylene, and gasoline vapors are used as flammable gases for gas welding. All these gases burn well in air, but do not develop a high temperature sufficient for welding and are therefore burned in an oxygen stream. It is also very popular. 
The most popular is acetylene. It is formed by the interaction of water and calcium carbide. The temperature of the flame during its combustion in a stream of oxygen reaches 3200 – 3400 °C. Acetylene is produced using special devices - generators, widely produced by industry.
Oxygen reducer
Oxygen is supplied from a special cylinder painted blue or light blue. To ensure normal operation, it is necessary that oxygen be supplied to the welding torch evenly under low pressure of 3 - 4 atm. For this purpose, a reducer is used on the cylinders to regulate the gas supply.
When performing gas welding with your own hands, in order to obtain a high-quality welded joint, you must carefully prepare the edges to be welded, select the method of joining the metal, install the torch in the appropriate position and determine the necessary parameters of the torch power and the diameter of the filler wire.
The edges of the product are cleaned of scale, oil and other contaminants. The bevel of the edges is carried out using a manual or pneumatic chisel or using special machines. This operation can also be performed by mechanized or manual oxygen cutting. The resulting scale and slag are removed with a metal brush or chisel.
Before welding, tack the edges of the parts to be welded to prevent changes in their relative position during the work performed. When working with thin metal and short seams, the length of the tacks should be 5 - 7 mm, and the distance between them should be 70 - 100 mm. When working with thick metal and with seams of considerable length, the tacks should be 20 - 30 mm long, and the interval between them should be 300 - 500 mm.
Welding performance and quality largely depend on the position of the torch and the direction of movement along the seam. There are two main ways to perform gas welding: left and right. With the left method, the torch is moved from right to left with its movement over the filler rod, while the flame is directed to the still unwelded edges and warms them up, preparing them for welding. With the right method, the burner is led from left to right, moving in front of the filler rod and directing the flame to the forming seam. 
Gas welding technique, left and right methods
The right method is used when welding metal more than 5 mm thick. Welding vertical seams from bottom to top is best done using the left method. It is more convenient to weld ceiling seams using the right method. In order to prevent the flow of molten metal, it is recommended to form the weld pool with a slight distortion. 
Angles on the clone and methods of moving the torch during gas welding
During the welding process, the torch nozzle, together with the filler wire, simultaneously performs two movements: the first is along the axis of the seam, and the second is an oscillatory movement across the axis of the seam. The end of the filler rod moves in the direction opposite to the movement of the mouthpiece.
It is prohibited to perform gas welding in close proximity to flammable and flammable substances. Welding in boilers, tanks and closed, cramped spaces must be carried out with frequent breaks and access to fresh air. In semi-closed and enclosed spaces, removal of harmful substances should be carried out using local suction. When welding in tanks, the presence of a second worker is necessary - an observer located outside.
Gas welding must be performed using special safety glasses that prevent the negative effects of emerging bright rays on the blood and retina of the eyes, as well as protect against splashes of slag and metal. 
Gas welding kit
The equipment must always be in good condition. A welding station for gas welding must contain an oxygen cylinder, an acetylene generator or a flammable gas cylinder, reducers to reduce the pressure of the gas leaving the cylinder, gas torches for welding and a cutter, a set of replaceable tips, hoses (hoses) providing the supply of flammable gas and oxygen into the torch or cutter, a set of welder’s tools, a welding table, devices required for assembling products, safety glasses and welder’s clothing.
Gas cylinders must be carried on a special stretcher or carried on a trolley. Other methods of transporting cylinders are unsafe. Under no circumstances should cylinders knock against each other or fall during transportation. When transporting cylinders, they must be wearing a protective cap. It is prohibited to store oxygen cylinders at the work site. The exception is installation and construction work. They can be moved over short distances by tilting with a slight inclination. 
Transportation of cylinders
If more than 10 welding stations are used, then the gas supply must be distributed through gas pipelines from acetylene and oxygen stations. The acetylene generator must be installed strictly vertically in a well-ventilated room or in air with a temperature of at least 5°C. It is necessary to constantly monitor the required water level in the water seal. The latter must be in good working order and turned on during operation.
The burner flame must be directed in the direction opposite to the power source. If this condition cannot be met, the power source should be protected using a metal shield. Gas-conducting hoses should be located to the side of the welder during work. During the break, the burner flame should be extinguished.
In many industrial and domestic processes there is a need to join metals using gas welding. In the process of gas welding, with the help of a flammable gas substance (acetylene, propane, gasoline) and oxygen at a high combustion temperature, strong adhesion of the surfaces of contacting metals is achieved.
To ensure a reliable and safe gas welding process, you will need professional equipment:
1) Gas equipment: flammable gas cylinders, oxygen cylinders, welding powders, oxygen reducers, acetylene generators, burners of various types, rubber hoses;
2) Filler wire
3) Accessories for welding: safety glasses, steel brushes for cleaning the surface, hammer;
4) A welding table or a special device for securing parts.
Gas welding, like any technological process, has certain features, advantages and disadvantages. The advantages of gas welding include:
1. Autonomy of the work performed. Gas welding does not require a dedicated electrical power source. Modern gas welding equipment is small in size and weight, which allows it to be transported without special equipment. Gas welding can be carried out in remote locations if sufficient supplies are available.
2. Adjustable flame temperature. Melting of different metals requires a certain temperature. Gas welding makes it possible to vary the temperature not only using the torch, but also using the angle of the flame.
3. Wide range of applications. Gas welding can be used to join a wide variety of metals: carbon and alloy steel, cast iron, copper, brass, bronze. 
Let us also highlight the disadvantages when carrying out gas welding work:
1. Increased heating area. During the gas welding process, the thermal effect spreads to adjacent elements, which can lead to unexpected defects.
2. Increased danger. The need to work with flammable gases and compressed oxygen is associated with an increased danger of the gas welding process. When transporting and storing gas equipment, precautions must be taken.
Specialists without a protective mask and a suit made of durable fire-resistant fabric are not allowed to carry out welding work.
3. Low efficiency. When welding metals with a thickness of more than 5 mm, gas welding loses its effectiveness.
4. Increased requirements for the welder. Gas welding is a process that requires special training. In order to learn how to operate gas welding equipment, a professional level of training is required. 
Gas welding is indispensable in construction and installation work, the metallurgical industry, and agriculture.
Gas welding equipment makes it possible to join most existing metals. Let's look at the welding features for some of them.
Welding cast iron
By welding cast iron, casting defects and cracks are eliminated, and broken parts are reattached. It can also be used to repair or restore parts. When welding, use a small torch flame so as not to promote the formation of white cast iron grains in the weld metal.
Bronze welding
When working with bronze, a wire similar to the metal being welded is used. Due to the fact that the oxidizing nature of the flame can contribute to the burning of metals from bronze, a reducing flame is used.
Copper welding
Molten copper has increased fluidity, making gas welding difficult. When welding it, no gap is provided between the edges. Copper rod is used as an additive. It is allowed to use fluxes to remove slag and deoxidize copper.
Welding carbon steels
Carbon steels are very convenient for gas welding. They can be joined using many gas welding methods. When welding, low carbon steel wire is used. The weld seam acquires a coarse-grained structure.
This method of joining metal parts, such as gas welding, has been around for over a hundred years. During this time, this technology continues to be successfully improved, although other welding methods that use an electric arc are developing more actively and are replacing welding, which uses a gas torch.
This method of joining metals, such as gas welding, involves melting the materials being joined, resulting in the formation of a homogeneous structure. The combustion of gas, due to which the heating and melting of the metal occurs, is ensured by the introduction of pure oxygen into the gas mixture. This method of joining metals has a number of advantages.
This method also has disadvantages.
Gas welding technology involves the use of various types of gases, the choice of which depends on a number of factors.
One of the gases used for welding is oxygen. This gas is characterized by the absence of color and odor; it acts as a catalyst, activating the melting processes of the material being joined or cut.
In order to store and transport oxygen, special cylinders are used in which it is kept under constant pressure. Oxygen may ignite upon contact with industrial oil, so the possibility of such contact should be excluded. Cylinders containing oxygen must be stored indoors, protected from sources of heat and sunlight.
Welding oxygen is obtained by separating it from ordinary air, for which special devices are used. Depending on the degree of its purity, oxygen is of three types: the highest (99.5%), first (99.2%) and second (98.5%) grade.
For various manipulations with metals (welding and cutting), colorless acetylene gas C2H2 is also used. Under certain conditions (pressure exceeding 1.5 kg/cm2 and temperature exceeding 400 degrees), this gas can spontaneously explode. Acetylene is produced by the interaction of calcium carbide and water.
The advantage of using acetylene when welding metals is that its combustion temperature allows this process to be carried out without problems. Meanwhile, the use of cheaper gases (hydrogen, methane, propane, kerosene vapor) does not make it possible to obtain such a high combustion temperature.
To weld metals, in addition to gas, you also need. It is due to these materials that the welding seam is created and all its characteristics are formed. The wire used for welding must be clean, without signs of corrosion and paint on its surface. In some cases, a strip of the same metal that is being welded can be used as such wire. In order to protect the weld pool from external factors, it is necessary to use a special flux. Boric acid and borax are often used as such flux, which are applied directly to the surface of the metal being welded or to the wire used for welding. Gas welding can be done without flux, but when joining parts made of aluminum, copper, magnesium and their alloys, such protection is necessary.
Gas welding technology involves the use of certain equipment.
Water seal
A water seal is necessary to ensure protection of all equipment elements (acetylene generator, pipes) from the backdraft of fire from the burner. Such a valve, in which the water must be at a certain level, is placed between the gas burner and the acetylene generator.
A cylinder containing gasSuch cylinders are painted with different colors depending on what gas is planned to be stored in them. Meanwhile, the top part of the cylinder is not painted to prevent gas from contacting the paint components. It should also be borne in mind that cylinders in which acetylene is stored should not be fitted with copper valves, as this may lead to a gas explosion.
GearboxIt is used to reduce the pressure of the gas leaving the cylinder. Gearboxes can be direct or reverse acting, and for liquefied gas, models with fins are used, which prevent it from freezing upon exit.
Special hosesGas welding cannot be performed without the use of special hoses, through which both gas and flammable liquids can be supplied. Such hoses are divided into three categories, marked with 1) a red stripe (operate at pressures up to 6 atmospheres), 2) a yellow stripe (for supplying flammable liquids), 3) a blue stripe (operate at pressures up to 20 atm).
Mixing of gases and their combustion is ensured through the use of a burner, which can be of an injection or non-injector type. Burners are also classified according to their power, which characterizes the amount of gas passed per unit of time. So, there are burners of high, medium, low and micro-low power.
Special tableGas welding is carried out in a specially equipped place called a post. Essentially, such a place is a table, which can have a rotating or fixed top. This table, equipped with exhaust ventilation and everything necessary for storing auxiliary tools, greatly facilitates the work of the welder.
The flame parameters are adjusted using a gearbox, which allows you to change the composition of the gas mixture. Using a reducer, you can produce three main types of flame: reducing (used for welding almost all metals), oxidizing and with an increased amount of combustible gas. When welding metals in a molten pool, two processes occur simultaneously - oxidation and reduction. At the same time, when welding aluminum and magnesium, oxidative processes occur more actively.
The welding seam itself and the area adjacent to it are characterized by different parameters. Thus, the section of metal adjacent to the seam is characterized by minimal strength, and it is this area that is most prone to destruction. The metal adjacent to this zone has a structure with large grains.
To improve the quality of the seam and the area adjacent to it, additional heating or so-called thermal forging of the metal is performed.
Welding technologies for various metals have their own nuances.
Manual gas welding involves the welder holding the torch in one hand and holding the gas welding wire with the other. The welder must be provided with personal protective equipment, including special glasses.
Figure 1. Scheme of gas welding technology.
Do-it-yourself metal cutting and gas welding require mandatory compliance with safety precautions. There should be no flammable or flammable substances near the place where welding is performed. When performing gas welding indoors, the worker must periodically breathe fresh air.
The diagram of gas welding technology is shown in Fig. 1. When directing the flame of a gas torch for welding onto a material, the edges of the metal must be located in the flame zone, which is a reduction zone.
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It is impossible to definitively answer the question of which welding method is better. Mini-welding installations or conventional equipment - each has its own distinctive features. When choosing gas equipment, be sure to take gas welding methods into account.
Welding is carried out only with the help of specialized equipment. The main tool, which is equipment for gas welding, is a gas torch, which allows you to mix acetylene with oxygen in the required volumes. As a result, a flammable mixture is formed, which flows out of the mouthpiece at the required speed, while providing a stable flame.
Each type of equipment is characterized by its own technology for gas welding of metals, so when choosing, first of all, you need to start from this. Only after this they move on to studying the features inherent in this or that type of equipment.
To protect the pipeline, welding devices are provided with safety water solutions. Otherwise, there is a risk that the fire may backfire. The use of an acetylene generator in a machine used for acetylene welding involves protection against the same risk.
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The welding station is equipped with a shutter, the presence of which should ensure an appropriate level of safety for welding operations. The valve is the main part of the gas welding station; it must always be in its normal position, filled with water to the level at which the control valve is located. The shutter in the torch is located between it or the cutter and the acetylene generator.
When welding with gas, special gas cylinders must be used. They contain oxygen or other compressed gas. The balloon itself is represented by a cylindrical vessel. The neck of such a product is always equipped with a threaded hole into which the shut-off valve is screwed. Cylinders are made from alloy and carbon steel pipes. To avoid confusion between the cylinders, they are painted in the appropriate color, indicating the type of gas it contains. The upper spherical part remains unpainted, since it contains passport data.
A distinctive feature of the welding station for a gas torch is a securely mounted cylinder clamp in a vertical position. Before purchasing devices for gas welding, you should find out the requirements for the valves used in the cylinders. The production of such products is carried out only from brass, since steel has the characteristic feature of quickly corroding. For the production of acetylene valves, steel is used, but not copper, since it and alloys with its content over 70% are prohibited.
The use of a gas reducer is necessary to reduce the gas pressure coming from the cylinder. It must be maintained at an optimal level. Gearboxes for different models of welding devices have the same operating principle and are equipped with the same components. Gearboxes can be either single-chamber or double-chamber. The latter are not as prone to freezing as the former, providing a constant and constant level of pressure.
Using hoses, also called hoses, the burner is supplied with gas. The hoses must have sufficient strength, flexibility, and the ability to withstand gas pressure. For the production of sleeves, vulcanized rubber is used, supplying this device with fabric gaskets. Oxygen and acetylene pass through the hoses. For the production of hoses that allow gasoline and kerosene to pass through, gasoline-resistant rubber is used.
Various consumables can be used in the gas welding process. First of all, this is a filler wire for gas welding, which is close to the structure of the metal being welded in chemical composition, so using random types of wire is prohibited.
The surface of the wire is smooth and even. It should not have traces of oil, scale, rust, or paint. The melting temperatures of the metal and wire must be the same. It is correct if the welding wire melts evenly and the filler materials do not splash. As a result, a dense metal with a homogeneous structure is formed, free of impurities and other defects. When welding, flat cut metal sheets of the same grade as the products being welded can be used. This is typical for welding non-ferrous metals or stainless steel.
In order to protect the molten metal from oxidation during welding, fluxes are used, which are bridges or powders applied to the wire and the edge of the workpiece. When choosing a flux composition, you should rely on the properties of the metal and its type. Boric acid and borax (calcined) are also used as a flux.
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Gas press welding is carried out on the basis of installations that include a machine for upsetting during welding with mechanisms that allow clamping of parts. The device includes a burner that performs heating. The equipment includes a supply system with gases, air (for the use of pneumatic devices) and water for the purpose of the cooling process.
Gas press welding is performed using multi-nozzle torches that are water-cooled. Welding of pipes and rods is sometimes done using split torches, which include two halves that are hinged together. End heating and welding torch sheets are sometimes made one-piece.
The materials of the part undergo upset and clamping in the machine, which is determined by the size of the product, as well as the required amount of axial pressure when welding manually using pneumatic devices or mechanized, involving the use of hydraulic devices.
The implementation of the clamping and upset method depends on the magnitude of the maximum force required when performing these operations in relation to the size of the sections of the parts that are welded on this equipment. The clamping force is 2 times higher than the force for upsetting, which is influenced by the materials being welded themselves.
Certain types of machine designs are characterized by the presence of a carriage that allows the welding torch to be secured and moved. The design of the burners is determined by the shape of the parts being welded.
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Welding of gas pipelines, like other types of welding, requires specialization of mechanized installations, which is based on the specific type of design of the parts and joints being welded. The creation of a universal tool that allows mechanization of the welding process led to the development of equipment on which gas-flame welding is performed. Various types of installations used in industry for the purpose of gas-flame welding are characterized by particular difficulties in their creation. They are economical, compact and efficient. For such installations, a maximum reduction in time for carrying out work is provided.
Among the main types of equipment, one can note the presence of a cutter with valves for supplying oxidizer and fuel. This includes cylinders with oxidizer and fuel. Liquid oxygen, which acts as an oxidizing agent, is characterized by technical purity. The fuel is a gaseous hydrocarbon, which is liquefied at a pressure of 140 to 180 atmospheres. Household gas and acetylene are the most common. Due to acetylene, the flame becomes hotter, and the use of household gas is cheaper and more accessible.
