Gas welding is different. Gas welding and cutting of metals

This method of joining metal parts, like gas welding, has been around for more than a hundred years. Throughout 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 that uses a gas torch.

Pros and cons of gas welding

This method of joining metals, such as gas welding, involves the melting of the joined materials, resulting in the formation of a homogeneous structure. The combustion of gas, due to which the heating and melting of the metal is carried out, is ensured by introducing pure oxygen into the gas mixture. This method of joining metals has a number of advantages.

• This welding method does not require the use of sophisticated equipment ( welding inverter or semi-automatic).
• All Consumables for the implementation of such welding is easy to purchase.
• Gas welding(respectively, gas welding of pipes) can be carried out even without a powerful source of energy and sometimes without special protective equipment.
• The process of such welding lends itself well to regulation: you can set the required power of the burner flame, control the degree of heating of the metal.

At this method there are also disadvantages.

• The metal heats up very slowly, in contrast to the use electric arc.
• The heat zone that is formed by the gas burner is very wide.
• It is very difficult to concentrate the heat generated by a gas burner, it is more dispersed compared to the electric arc method.
• Gas welding can be attributed to rather expensive methods of joining metals, when compared with. The cost of the spent oxygen and acetylene significantly covers the price of electricity spent for welding the same type of parts.
• When welding thick metal parts, the speed of the connection is significantly reduced. This is due to the fact that the heat concentration when using a gas burner is very low.
• Gas welding is difficult to automate. Only the process of gas welding of thin-walled pipes or tanks, which is performed using a multi-flame torch, can be mechanized.

Gas welding consumables

Gas welding technology involves the use various types 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 smell, 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. Upon contact with technical oil, oxygen can ignite, so the very 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%), the first (99.2%) and the second (98.5%) grade.

For various manipulations with metals (welding and cutting) it is also used colorless gas acetylene C2H2. Under certain conditions (pressure exceeding 1.5 kg / cm2 and temperatures above 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.

Wire and flux for welding

For the implementation of welding of metals, except for gas, are also needed. It is due to these materials that a welding seam is created, 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 a wire. In order to protect the weld pool from external factors, it is necessary to use a special flux. As such a flux, boric acid and borax are often used, which are applied directly to the surface of the metal to be welded or to the wire used for welding. Without flux, gas can be performed, and when connecting parts made of aluminum, copper, magnesium and their alloys, such protection is necessary.

Gas welding equipment

Gas welding technology involves the use of certain equipment.

water lock

A water seal is necessary to ensure the protection of all elements of the equipment (acetylene generator, pipes) from the back draft of fire from the burner. Such a shutter, the water in which must be at a certain level, is placed between the gas burner and the acetylene generator.

Such cylinders are painted with different colors depending on what kind of gas is planned to be stored in them. Meanwhile, the upper part of the cylinder is not painted to prevent contact of the gas with 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 can lead to an explosion of the gas.

It is used to reduce the pressure of the gas leaving the cylinder. Reducers can be direct or reverse action, and for liquefied gas models with ribs are used, which exclude its freezing when exiting.

Gas 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 1) with a red stripe (operating at pressures up to 6 atmospheres), 2) a yellow stripe (for supplying flammable liquids), 3) a blue stripe (operating at pressures up to 20 atm).

The mixing of gases and their combustion is ensured through the use of a burner, which can be of the injection and non-injection 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 large, medium, small and micro-low power.

Gas welding is carried out in a specially equipped place, which is called a post. In fact, such a place is a table, which can be with a swivel or fixed top. This table, equipped with exhaust ventilation and everything necessary for storing auxiliary tools, greatly facilitates the work of the welder.

Features of gas welding

Adjustment of the flame parameters is carried out using a reducer, which allows you to change the composition of the gas mixture. With the help of a reducer, it is possible to obtain a flame of three main types: reduction (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 proceed more actively.

The welding seam itself and the area adjacent to it are characterized by different parameters. So, the metal section adjacent to the seam is characterized by minimal strength, it is he who 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 the so-called thermal forging of the metal is performed.

Welding technologies various metals have their own nuances.

• Gas is performed using any gas. As a filler material for welding such steels, a steel wire containing a small amount of carbon is used.
• Welding methods are selected depending on their composition. So, stainless heat-resistant steels are welded using a wire containing chromium and nickel, and some grades require the use of a filler material that additionally contains molybdenum.
• Cast iron is brewed with a carburizing flame that prevents the pyrolysis of the silicon and the formation of brittle white iron grains.
• For welding copper it is necessary to use a flame of greater power. In addition, due to the increased fluidity of copper, parts from it are welded with a minimum gap. As a filler material, copper wire is used, as well as a flux, which contributes to the deoxidation of the weld metal.
• When there is a risk of volatilization of zinc from its composition, which can lead to increased porosity of the weld metal. To avoid this, more oxygen is supplied to the burner flame, and brass wire is used as an additive.
• Welding of bronze is carried out with a reducing flame, which does not burn out tin, aluminum and silicon from this alloy. As an additive, a bronze wire of a similar composition is used, which additionally contains silicon, which contributes to the deoxidation of the weld metal.

Gas welding is a type of welding when parts need to be heated to a molten state by means of a high-temperature flame. This method is widely used in the creation of structures based on thin carbon steel, in the repair of cast iron products, and also, if necessary, welding of defects in various products obtained by casting from non-ferrous or ferrous metals.

What gases are used?

In gas welding, combustible gases are used - natural, acetylene, gasoline vapors, hydrogen. These gases are distinguished by good combustion in air, without developing a high temperature; an oxygen jet is also sufficient for combustion. Gas welding is most often carried out on the basis of acetylene, which is created on the basis of water and calcium carbide. It burns at a temperature of 3200-3400 degrees.

What are the features?

The advantages of gas welding include the following:

1. Simple technology.
2. No need for a welding power source.
3. The simplicity of the equipment on the basis of which gas welding is performed.

On the other hand, this process is not very productive. Welding is performed only manually, and the mechanical and operational properties finished products not always high quality.

oxygen reducer

When welding, oxygen comes from a special cylinder - it turns blue or blue. To ensure normal operation, oxygen must flow into the burner evenly and at low pressure. It is for these purposes that the cylinders have a reducer - it regulates the gas supply. In this case, sleeves for gas welding - acetylene and oxygen - are supplied to the burner. Oxygen is supplied to the central channel, where the jet discharges more, sucks in acetylene, which enters the burner under low pressure. The gases are mixed in the chamber, after which they exit the tip to the outside.

Technology features

When performing gas welding, it is important to obtain a quality connection, therefore great attention is given to careful preparation of the edges to be welded, the choice of the method of joining the metal, the installation of the burner in the desired position and the determination of the necessary burner power parameters. Gas welding technology assumes that the edges must be thoroughly cleaned of various contaminants. Beveling is performed using a manual or pneumatic chisel, and sometimes special machines are involved. Scale and slag can be removed with a wire brush. Tacking the edges prevents their position from changing during welding.

Welding methods

Gas welding can be carried out in several ways. The first is left hand welding, which is the most common. It is used when working with thin and fusible metals. The torch moves from right to left, and the filler wire is led ahead of the flame directed to the unwelded section of the seam. In right hand welding, the torch is driven from left to right, and the filler wire is moved behind the torch. At this method the heat of the flame is dissipated to a lesser extent, therefore the opening angle of the seam is not 90 degrees, but less - 60-70.

It is advisable to use right welding for joining metal, the thickness of which is from 3 mm and above, as well as metals with high level thermal conductivity. It is recommended to use a filler wire with a diameter equal to half the thickness of the metal to be welded.

Gas welding technology also involves a process that is carried out with a through roller. In this case, the sheets are installed vertically to the gap - it is equal in size to half the thickness of the sheet. Using a burner, the edges are melted to form a round hole. Then it is melted from all sides until the seam is welded. This method is good because the welded sheets have a tight seam without pores and slag inclusions.

Tray welding is good for welding joints and corners of metal joints that have a maximum thickness of 3 mm. As soon as a bath forms on the seam, the end of the filler wire is inserted into it, which melts slightly, then the end of the wire moves to another section of the seam. The peculiarity of this approach is in a seam of excellent quality, especially if thin sheets and pipes made of steel (low-carbon and low-alloy) were welded.

Gas welding and cutting can be carried out on the basis of multi-layer welding. This method has a number of features:

• the heating zone is small;
• the underlying layers are simply annealed during surfacing of subsequent ones;
• each seam can be forged before the next one is put on it.

This improves the quality of the seam. On the other hand, this method is characterized by low productivity, requires a high gas consumption compared to single-layer welding, so it is used when it is necessary to create responsible and high-quality products.

Features of welding various seams

To work with horizontal seams, the right method is used, which makes it possible to easily form a seam, and the bath metal itself does not flow. Welding of vertical and inclined seams is carried out in the left way, and if the metal thickness is higher than 5 mm, a double roller is used. Welding ceiling seams involves heating the edges until they melt, then a filler wire is introduced into the bath - its end quickly melts. The process itself is carried out in the right way.

What equipment?

The gas welding equipment for gas welding is a wide choice of the devices allowing to carry out a number of works. This type of welding is considered simple, and the equipment itself is quite concise and easy to operate. Depending on the type of fuel, gas welding devices are propane-oxygen or acetylene-oxygen, gasoline or kerosene-oxygen. Most often, welding is carried out on the basis of propane-oxygen and acetylene-oxygen welding, since the flame of these gases has the highest temperature.

Gas welding equipment for gas welding is also a generator, which is supplemented different types gas. Also, when working, you will need an oxygen cylinder and reducers. The most common are acetylene generators for gas welding, which allow you to get acetylene directly by mixing calcium carbide and water. This type of generator is presented in five types, which allows you to choose the best option for a particular material.

Safety locks play an important role when working with welding, their task is to ensure safety during welding. With their help, the passage of the reverse blow of the flame that occurs during welding is prevented. In addition, check valves prevent back flow of gas into rubber hoses during flame treatment of metals and work with compressed gases.

Gas cylinders

Equipment for gas welding includes cylinders and valves for them. A cylinder is a vessel with a cylindrical shape, which has a threaded hole in the neck, where a shut-off valve is screwed into. It is created from alloyed or carbon steel, and each such product has its own color depending on the gas it contains. Cylinder valves are made of brass, as steel is not resistant to corrosion.

Gearboxes: types and features

The gas reducer is a device that constantly lowers or keeps the gas pressure at a certain level. Gas welding and cutting of metals are carried out on the basis of different types of gearboxes:

1. Oxygen are used in gas welding and welding of metals. Such a gearbox is made with a blue marking. It can be used in an aggressive environment, as it is made of corrosion-resistant metals.
2. Acetylene reducers are widely used in gas welding. They are marked in white, fastening to the cylinder is carried out with a collar. This type The reducer has two pressure gauges, one of which controls the gas pressure in the cylinder, the second - the gas pressure in the working chamber.
3. Carbon dioxide reducers are widely used in industry - food, chemical. They have one or two pressure gauges and can only be connected to a vertical pressure gauge.

In argon-arc welding, argon reducers are widely used, which can also work with non-combustible gases.

Features of gas burners

Gas welding of steels is a process that requires the use of a variety of devices. Gas burners are an essential element of equipment used in various industries. By design, the products are approximately the same: each burner consists of a body. Several elements are attached to it at once: a tip, a valve that regulates the supply of fuel, and a lever that adjusts the height of the flame. The connection to the cylinder is made by a gearbox, while the burner itself can often be supplemented with piezo ignition, flame wind protection and other components.

The propane gas welding torch is safe to operate with a high flame temperature, sufficient for a wide range of jobs. Many types of welding are carried out on the basis of acetylene torches, which operate on a mixture of acetylene and oxygen.

Types of gas cutters

Gas torches come in a variety of types: acetylene, propane, and powered by gas substitutes or liquid fuels. The product design includes a handle, nipples to which gas hoses are attached, a body, an injector, a mixing chamber, a tube, a cutting torch head and a tube with a valve. Gas welding of metals and its quality depend on how well the cutter is chosen.

The essence of its work is as follows: from the cylinder, oxygen enters the reducer, the sleeve, after which it enters the body - here the cutter branches into two channels. Part of the oxygen passes through the valve and is directed to the injector. From here, the gas exits at high speed, and during this process combustible gas is sucked in. When combined with oxygen, it forms a combustible mixture, which is sent to the space between the mouthpieces and burns out. As a result, a heating flame appears. Oxygen, which was directed through the second channel, exits into the tube, due to which a cutting jet is formed. It is he who processes the metal section.

Features of pipe welding

Welding of gas pipes is carried out in several stages. First, the metal is prepared, that is, marking is carried out, pipes are cut and assembled. Due to the circular section of the pipes, cutting is done with a thermal cutter. Most of the welding work is the assembly of parts for it, when it is necessary to take into account many details - from the series of products to their diameter and other factors. Assembly is carried out with welding tacks, which prevent possible displacement of pipe sections, which affects the appearance of cracks during cooling.

The arc is ignited. It's done different ways. Then the melting of metals begins - the main and electrode. For a quality seam, it is important to pay attention to the angle of the electrode.

Gas cutting technology

Oxy-fuel cutting is carried out using metals and their alloys, which burn in a jet of commercially pure oxygen. This type of cutting is performed in two ways - separation or surface. The first method allows you to cut blanks, cut metal, cut the edges of the seam for welding. With the help of surface cutting, the surface metal is removed, grooves are cut, and surface defects are removed. This procedure is performed on the basis of special cutters.

Safety

Gas welding is a process that requires careful attention. dangerous situations may occur in several cases:

1. Welding must not be carried out near flammable and flammable materials (gasoline, kerosene, tow, shavings).
2. If welding is performed in a confined space, workers should periodically go outside for fresh air.
3. Work must be carried out in well-ventilated areas.
4. If flame treatment of metal is carried out, the room must be ventilated to remove harmful gases.
5. Cutting and welding are carried out at a distance of up to 10 m from bypass ramps, acetylene generators.
6. Load box sections must not be overfilled with carbide.
7. The body of the generator must always be filled with the right amount of water.
8. It is forbidden to work with an oxygen cylinder, the pressure of which is below normal.
9. The burner flame is directed in the direction opposite to the gas supply source.

Welding work must be carried out with maximum observance of safety rules and using only high-quality equipment. This will make the process safe, and the connection of metals reliable.

Gas welding belongs to the group of fusion welding. The gas welding method is simple, does not require sophisticated equipment and source electrical energy. The disadvantages of gas welding include a lower speed and a large heating zone than with.

Gas welding is used in the manufacture and repair of products made of sheet steel with a thickness of 1-3 mm, the installation of pipes of small and medium diameters, joints and assemblies made from thin-walled pipes, welding products from aluminum and its alloys, copper, brass and lead, welding cast iron with use as an additive of cast iron, brass and bronze bars, surfacing of hard alloys and brass on steel and cast iron parts.

Almost all metals and alloys currently used in industry can be joined by gas welding. The most widely used in construction and installation works, in agriculture and during repair work.

Welding requires that the welding flame has sufficient heat output. The power of the burner flame is determined by the amount of acetylene passing through the burner in one hour and is controlled by the burner tips. The power of the flame is selected depending on the thickness of the metal to be welded and its properties. The amount of acetylene per hour required for 1 mm of the thickness of the metal to be welded is established by practice.

Example. When welding mild steel, 100-130 dm 3 of acetylene per hour is required per 1 mm of the thickness of the metal to be welded.

For welding mild steel with a thickness of 4 mm, the minimum power of the welding torch will be 100x4=400 dm 3 /h, the highest - 130x4=520 dm 3 /h.

Gas welding of various metals requires certain kind flame - normal, oxidizing, carburizing. The gas welder adjusts and sets the type of welding flame by eye. At manual welding the welder holds a welding torch in his right hand, and a filler wire in his left. The welder directs the flame of the burner to the metal being welded so that the welded ones are in the reduction zone at a distance of 2-6 mm from the end of the core. The end of the filler must be in the reduction zone or in the weld pool.

The heating rate is controlled by changing the angle of inclination a of the mouthpiece to the surface of the metal being welded.

Figure 1 - Angle of inclination (a) and methods of moving the mouthpiece of the burner (b)

The angle value is selected depending on the thickness and type of metal being welded. The thicker the metal and the greater its thermal conductivity, the greater the angle of inclination of the burner mouthpiece to the surface of the metal being welded. At the beginning of welding, for better heating of the metal, the angle of inclination is set larger, then, as the metal being welded warms up, it is reduced to a value corresponding to a given thickness of the metal, and at the end of welding, it is gradually reduced in order to better fill and prevent overheating of the metal.

The torch handle can be located along the axis of the seam or perpendicular to it. This or that position is chosen depending on the conditions (convenience) of the work of the gas welder, so that the welder's hand is not heated by the heat radiated by the heated metal.

In the process of gas welding, the gas welder makes two movements simultaneously with the end of the mouthpiece of the burner: transverse - perpendicular to the axis of the seam and longitudinal - along the axis of the seam. The main is the longitudinal movement, the transverse one serves to uniformly heat the edges of the base and filler metal and obtain a seam of the required width.

Method 1, in which the flame is periodically diverted to the side, is not recommended for gas welding, since the oxidation of the molten metal with air oxygen is possible. Method 2 - in a spiral and method 3 - in a crescent are recommended when welding metal of medium thickness, method 4 - when welding thin sheets (Figure 1).

The filler can make the same oscillatory movements, but in the opposite direction to the movements of the end of the burner mouthpiece.

The end of the filler wire is not recommended to be removed from the weld pool and especially from the reducing zone of the flame. The movements made by the end of the torch mouthpiece and the end of the filler wire during the welding process depend on the position of the seam in space, the thickness of the metal being welded, the type of metal and the required dimensions of the weld. For welding seams in the lower position, the crescent movement is most common.

Gas flame processing of metals is a series associated with the processing of metals with a high-temperature gas flame.

Gas welding- fusion welding, in which the edges of the parts to be joined are heated by the flame of gases burned at the outlet of the gas welding torch. When gas welding the workpiece 1 and filler material 2 in the form of a rod or wire is melted with a high-temperature flame 4 gas burner 3 (picture 1).

Figure 1 - Gas welding scheme

Gas welding technology

A gas flame is most often formed as a result of combustion (oxidation) of combustible gases with commercially pure oxygen (purity not lower than 98.5%). Acetylene, hydrogen, methane, propane, propane-butane mixture, gasoline, lighting kerosene are used as combustible gases.

Figure 2 - Temperature distribution along the axis of a normal gas flame

A gas welding oxy-acetylene "normal" flame has the shape shown schematically in Figure 2.

In the inner part of the flame core 1, the gas mixture coming from the nozzle is heated to the ignition temperature. Partial decomposition of acetylene occurs in the outer shell of the nucleus. The emitted carbon particles are hot, glow brightly, clearly highlighting the outlines of the core shell (the temperature of the gases in the core is low and does not exceed 1500 0 C).

Zone 2 is the most important part of the welding flame (welding zone). The first stage of combustion of acetylene takes place in it due to oxygen entering the nozzle from the cylinder, as a result of which the maximum temperature develops here. The gases contained in the welding zone have reducing properties with respect to oxides of many metals, including iron oxides. Therefore, it can be called restorative. The carbon content in the weld metal changes insignificantly.

In zone 3 or the torch of the flame, the afterburning of gases occurs due to oxygen in the air, which reflects the composition of the gases in the torch. The gases contained in the flame and their dissociation products oxidize metals, i.e. this zone is oxidative. The type of oxy-acetylene flame depends on the ratio of oxygen and acetylene supplied to the burner in the gas mixture is called the coefficient β.

Figure 3 - Structure of an oxy-acetylene flame

At β = 1.1 ... 1.2 the flame is normal (see Figure 2). With an increase in this ratio, i.e. relative increase in oxygen content (oxidizing flame), the shape and structure of the flame change (Figure 3). In this case, the oxidation reactions are accelerated, and the core of the flame turns pale, shortens and acquires a conical pointed shape. In this case, the welding zone loses its reducing properties and acquires an oxidizing character (the carbon content in the weld metal decreases and burns out). As β decreases, i.e. with an increase in the content of acetylene in the gas mixture, the oxidation reactions slow down. The nucleus is elongated and its outlines become blurred. The amount of free carbon increases, its particles appear in the welding zone. With a large excess of acetylene, carbon particles also appear in the flame. In this case, the welding zone becomes carburizing, i.e. the carbon content in the weld metal increases.

The flame of acetylene substitutes is fundamentally similar to oxyacetylene and has three zones. Unlike hydrocarbon gases, the hydrogen-oxygen flame does not have a luminous core (there are no luminous particles of carbon).

One of the most important parameters that determine the thermal, and hence the technological properties of the flame, is its temperature. It is different in its various parts both in length along its axis (Figure 2) and in cross section. It depends on the composition of the gas mixture and the degree of purity of the gases used. highest temperature observed along the flame axis, reaching a maximum in the welding zone at a distance of 2 ... 3 mm from the end of the core. This welding zone is the main one for melting the metal. As β increases, the maximum temperature increases and shifts towards the burner mouthpiece. This is due to the increase in the combustion rate of the mixture with an excess of oxygen. With an excess of acetylene (β less than 1), on the contrary, the temperature maximum moves away from the mouthpiece and decreases in value.

Flammable substitute gases for acetylene are cheaper and not in short supply. However, they calorific value lower than acetylene. The maximum flame temperatures are also significantly lower. Therefore, they are used in limited quantities in technological processes that do not require a high-temperature flame (welding of aluminum, magnesium and their alloys, lead; welding of thin sheet steel; gas cutting, etc.). For example, when using propane and propane-butane mixtures, the maximum temperature in the flame is 2400 ... 2500 0 C. They are used when welding steel, up to 6 mm thick, welding cast iron, some non-ferrous metals and alloys, gas cutting, etc.

When using hydrogen, the maximum temperature in the flame is 2100 0 C. The heating of the metal by the flame is due to radiant and mainly convective heat exchange between the flow of hot gases and the metal surface in contact with it. In a vertical position away from the flame, its spreading flow forms a heating spot symmetrical with respect to the center on the metal surface. When the flame is tilted, the heating spot is extended in the direction of the axis and narrows from the sides. The intensity of heating in front of the core is higher than behind it.

The input of heat into the product during gas welding occurs over a larger area of ​​the heating spot. The heat source is less concentrated than with other fusion welding methods. As a result of the extensive heating area of ​​the base metal, the near-weld zone (heat-affected zone) is large, which leads to the formation of increased deformations (buckling).

During gas welding, the metal of the weld pool is actively affected by the gas phase of the entire flame and especially the welding zone, which contains mainly CO + H 2 and partially water vapor, as well as CO 2, H 2, O 2 and N 2 and a certain amount of free carbon . The composition of the gas phase is determined by the ratio of oxygen and combustible gas in the gas mixture, the temperature of the flame, and is different in its various zones. The metallurgical interactions of the gas phase with the metal of the weld pool depend on this. The main reactions in welding are oxidation and reduction. The direction of the reaction depends on the concentration of oxygen in the gas phase (oxidizing and carburizing flame), the interaction temperature, and the properties of the oxide. When welding steels, the main interaction of the gas phase occurs with iron, i.e. formation of its oxides or reduction. Elements that have a greater affinity for oxygen than iron (Al, Si, Mn, Cr, etc.) can be intensively oxidized when the oxidation reactions of iron do not take place. They are easily oxidized not only in their pure form, but also in the form of alloying additives, and the higher their content, the more intense the oxidation. Oxidation of such elements as Al, Ti, Mg, Si and some others cannot be completely excluded, and in order to reduce their waste, in addition to regulating the composition of the gas mixture, fluxes should be used.

Due to the relatively low protective and restorative effect of the flame, deoxidation of the metal in the weld pool during welding of steels is achieved by introducing manganese, silicon and other deoxidizers into it through the filler wire. Their action is based on the formation of liquid slags, which contribute to the self-fluxing of the weld pool. The slags formed on the surface of the weld pool protect the molten metal from oxygen, hydrogen and nitrogen, the gaseous environment of the flame and sucked air. The hydrogen contained in the flame can be dissolved in the molten metal of the weld pool. During the crystallization of the metal, a part of the hydrogen that did not have time to evolve can form pores. Nitrogen entering the molten metal from the air forms nitrides in it. Structural transformations in the weld metal and heat-affected zone during gas welding are of the same nature as in other fusion welding methods. However, due to slow heating and cooling, the weld metal has a more coarse-grained structure with irregularly shaped equilibrium grains. In it, when welding steels with a content of 0.15 ... 0.3 carbon, a Widmanstatt structure can form during rapid cooling. The higher the rate of cooling of the metal, the finer the grain in it and the higher mechanical properties seam metal. Therefore, welding should be done at the highest possible speed.

The heat affected zone consists of the same characteristic areas as in arc welding. However, its width is much larger (up to 30 mm when welding thick steel) and depends on the gas welding mode.

Gas welding technique

During the welding process, the base and filler metals are melted. The regulation of the degree of their melting is determined by the power of the burner, the thickness of the metal and its thermophysical properties. Gas welding is performed.

Metal up to 2 mm thick is joined end-to-end without cutting edges and without a gap, or, better, with flanging without filler metal. Metal with a thickness of 2 ... 5 mm with filler metal is welded end-to-end without cutting edges with a gap between the edges. When welding metal over 5 mm, V- or X-shaped cutting of edges is used.

Tee and lap joints are allowed only for metal up to 3 mm thick. With a large thickness, uneven heating leads to significant deformations, residual stresses and the possibility of cracking.

The edges to be welded are decontaminated by 30 ... 50 mm mechanically or with a gas flame. Before welding, the parts of the welded joint are fixed in an assembly and welding fixture or assembled using short tack seams.

Figure 4 - Gas welding methods

The direction of movement of the torch and its inclination to the metal surface has a great influence on the heating efficiency of the metal, welding performance and weld quality. There are two welding methods: right and left (Figure 4). Appearance the seam is better with the left welding method, since the welder sees the process of seam formation. With a metal thickness of up to 3 mm, the left welding method is more productive due to the preheating of the edges. However, with a large thickness of the metal during welding with edge preparation, the angle of the bevel of the edges with the right welding method is 10 ... 15 0 less than with the left one. The angle of inclination of the mouthpiece can also be 10 ... 15 0 less. As a result, welding productivity is improved. The thermal effect of the flame on the metal depends on the angle of inclination of the flame axis to the metal surface (Figure 5).

Figure 5 - Applied angles of inclination of the torch depending on the thickness of the metal

In the process of welding, the torch is subjected to oscillatory movements and the end of the mouthpiece describes a zigzag path. The welder holds the torch in his right hand. When using filler metal, the filler rod is held in the left hand. The filler rod is located at an angle of 45° to the metal surface. The melted end of the filler rod is imparted zigzag vibrations in the direction opposite to the movement of the mouthpiece (Figure 6). Gas welding can be made in the lower, vertical and overhead positions. When welding vertical seams “on the rise”, it is more convenient to carry out the process in the left way, horizontal and ceiling - in the right way.

Figure 6 - Torch and wire movements

a) when welding steel with a thickness of more than 3 mm in the lower position; b) when welding fillet welds;
1 - wire movement; 2 - burner movement; 3 - places of traffic delays

If necessary, it is applied to the edges to be welded or introduced into the weld pool with the melted end of the filler rod (sticking to it when immersed in the flux). Fluxes can also be used in gaseous form when they are supplied to the welding zone with combustible gas.

Gas welding

Gas welding

connection of parts with heating (melting) of the welding points with a gas flame obtained by burning various combustible substances in oxygen. There are hydrogen-oxygen, gasoline-oxygen, acetylene-oxygen and other types of welding. Greatest industrial application received acetylene-oxygen. Unlike an electric arc or other sources of energy, a gas flame heats the material more slowly and more smoothly. This determines the expediency of using gas welding for joining parts made of cast iron, tool steels, when heating or slow cooling is needed in the process of joining metal. Gas welding does not require complex equipment (welding torches and gas from a cylinder are used), so this welding method is often used for repair work. A variety of gas welding is gas pressure welding, produced with draft (squeezing) after heating the connected parts - pipes, rails, etc.

Encyclopedia "Technology". - M.: Rosman. 2006 .

See what "gas welding" is in other dictionaries:

gas welding- Fusion welding, in which the heat of the flame of a mixture of gases burned with a torch is used for heating. [GOST 2601 84] [Terminological dictionary for construction in 12 languages ​​(VNIIIS Gosstroy of the USSR)] gas welding Fusion welding, with ... ... Technical Translator's Handbook

Modern Encyclopedia

Gas welding- GAS WELDING, fusion welding using a flame formed by burning a mixture of combustible gas (acetylene, hydrogen, gasoline vapors, etc.) with oxygen in a welding torch. The creation of gas welding was facilitated by the use of processes ... ... Illustrated Encyclopedic Dictionary

See Welding. Technical railway dictionary. M.: State transport railway publishing house. N. N. Vasiliev, O. N. Isaakyan, N. O. Roginsky, Ya. B. Smolyansky, V. A. Sokovich, T. S. Khachaturov. 1941 ... Technical railway dictionary

Big Encyclopedic Dictionary

Gas cutter device ... Wikipedia

Gas welding- 32. Gas welding Fusion welding, in which the heat of the flame of a mixture of gases burned with a burner is used for heating. Source: GOST 2601 84: Welding of metals. Terms and definitions of the main concepts of the original document ... Dictionary-reference book of terms of normative and technical documentation

A method for welding metal products using a gas flame formed during the combustion of a mixture of combustible gas (acetylene, hydrogen, gasoline vapors, etc.) with oxygen. Used for welding thin-walled products made of steel, non-ferrous metals and alloys ... encyclopedic Dictionary

gas welding- dujinis suvirinimas statusas T sritis chemija apibrėžtis Neišardomas metalinių detalių sujungimas dujų liepsna. atitikmenys: engl. gas welding. gas welding ryšiai: sinonimas – autogeninis suvirinimas … Chemijos terminų aiskinamasis žodynas

Fusion welding, when cutting for heating, the heat of the flame of a mixture of combustible gas (acetylene, hydrogen, gasoline vapors, etc.) with oxygen, burned with a welding torch, is used. The highest temperature (approx. 3200 ° C) is acetyleno-oxygen ... Big encyclopedic polytechnic dictionary

gas welding- fusion welding, in which the surfaces to be welded are heated by a gas flame, the gas supply to the burners during gas flame welding is carried out from cylinders (O2 and C2H2) and directly from combustible gas generators. Such gases... Encyclopedic Dictionary of Metallurgy

Books

• Gas welding and cutting of metals, I. I. Sokolov. Reproduced in the original author's spelling of the 1975 edition (publishing house `Moskva`). IN…