Oxy-acetylene welding and equipment for it. Welding methods

Acetylene welding is a time-tested technology that allows you to make beautiful, high-quality and reliable connections of metal elements. Acetylene is a combustible gas made from water, oxygen and calcium carbide. This technology is versatile, which allows it to be used to work with metals of different refractoriness. Equipment for such welding with acetylene includes appropriate cylinders with oxygen, which is mixed with carbide during operation, which makes it possible to obtain high-quality combustible acetylene at the output.

Used equipment

In the recent past, it was difficult to provide a high-quality connection using acetylene, which was explained by the imperfection of the technologies used. However, today high-quality equipment has appeared that allows you to get a flame with even parameters at the output, and the welder has the ability to easily adjust the intensity and temperature of the burning flame of the burner. Such acetylene welding equipment includes an appropriate generator, which is charged with carbide during operation and allows you to control the level of pressure in the system. Modern installations for such welding with acetylene they are completely safe in operation, they are reliable, and easy to use.

It is also possible to use a cylinder filled with acetylene instead of oxygen and a generator, which makes it possible to significantly simplify the implementation welding work. This reduces labor costs and increases the productivity of such welding. However, it must be taken into account that the use of already filled acetylene cylinders leads to some increase in the cost of the elements being performed.

Acetylene gas welding of metal products

One of the undoubted advantages of this welding technology is its simplicity. For such work, special burners for working with acetylene will be required. Such burners are marked with indexes from 0 to 5. Equipment with index 0 has the lowest productivity and is designed to work with light alloy metals. But installations marked 5 are characterized by maximum productivity, which allows them to be used for working with refractory metals.

The key to the high-quality performance of such welding with acetylene will be right choice burner and its competent adjustment. It must also be taken into account that the number of electrodes used must correspond to the marking of the burner. In general, the choice of electrodes is not difficult. In terms of parameters, they must correspond to the indicators of the refractoriness of metals and be close to it with their alloy.

The burner is purged with combustible gas from the generator, and only after the appearance of a characteristic smell of acetylene can the burner be ignited and a small amount of oxygen added from the cylinder. By adjusting the valve on the oxygen cylinder, the welder can adjust the intensity of the flame, its temperature and saturation. The reducer pressure should be approximately 2 atmospheres for an oxygen cylinder and 2 to 4 atmospheres for a generator. In each case, these indicators should be selected depending on the characteristics of the metal elements being welded.

The surfaces of metal elements for welding with acetylene must be cleaned of paint and other contaminants. They are adjusted as close as possible to each other. Next, the flame of the burner must be directed to the seam of the joint, and the filler material must move after the burner. Such a technology of work will ensure the elasticity and strength of the connection. You can also use welding technology when the flame from the burner is directed away from the resulting seam. In this case, the filler material is introduced into the high-temperature weld pool, melts and flows into the resulting joint. The disadvantage of this technology is an increase in the heating zone, which can lead to warping of metal elements and a change in the structure of the metal.

Welding with acetylene and oxygen: advantages and disadvantages of this technology

If we talk about the advantages and disadvantages of this technology, we can note the following:

Advantages:

• Low cost of work.
• Quality burner flame.
• High welding temperature.
• Connection quality.

Flaws:

• The need for sophisticated equipment.
• Strict safety requirements.
• Difficulty in welding indoors.
• Certain difficulties when working with thin materials.

The existing advantages and disadvantages must be taken into account when choosing this welding technology, as well as be sure to follow the safety rules, which will allow you to perform a high-quality connection of metal elements.

Conclusion

Acetylene-oxygen welding is widely used today in industrial work. Using this technology, it is possible to weld various metal elements that differ in their refractoriness. This technology can significantly reduce the cost of working with metal, while there are no difficulties in performing such welding. It is essential to use high quality reliable equipment and follow the safety regulations.

Gas welding is almost always associated with acetylene, since it is this gas that gives the highest flame temperature when burned with the addition of purified oxygen. This makes it possible to economically use the same volumes of acetylene gas compared to other gas mixtures.

The widespread use and production of acetylene has declined somewhat in recent decades. This is due to the introduction of high quality electrodes for. Some industries have permanently abandoned the use of gas welding, but some repair and field work remains impossible without it.

Acetylene for welding (C2H2)

general information

Acetylene has a hydrocarbon composition with a triple carbon bond. cheap way made from calcium carbide and water has made it the most common fuel gas for welding. The high combustion temperature of acetylene results in the release of solid carbon particles, which begin to glow brightly from a yellow flame to white. This allowed the use of acetylene for flashlights.

Acetylene is transported and stored in gas cylinders white or red (for a liquefied state) color, 40 liters each under a pressure of 1.6 MPa. It is explosive when oxygen or air is added, as well as at high pressure.

Properties of acetylene

• At a temperature of minus 83.3 0 C, acetylene passes into a liquid state.
• When minus reaches more than 90 0 C, the gas solidifies.
• This gas is soluble in water, and completely soluble in organic solvents such as acetone.
• At high temperatures (500 0 C) acetylene explodes, as well as at a pressure of more than 2 atm.

Advantages and disadvantages of acetylene combustible mixture for welding

Advantages:

• highest combustion temperature.
• The possibility of obtaining acetylene from generators and the acquisition of better quality in factory cylinders.
• Compared to other combustible gases, it is the most advantageous.

Flaws:

• Increased explosion hazard and strict safety conditions.
• High gas contamination of the premises during work.
• Possible occurrence of defects: burnout and overheating of thin metals.

Equipment and materials for acetylene welding

In gas welding, acetylene is most often used as a combustible gas, but due to a number of reasons it is also replaced by other gases. In addition, acetylene is not the only gas and consumable material that is necessary to obtain a high-quality metal compound.

Consumables for gas welding

• Acetylene or alternative gas

He may be in ready-made(in a cylinder), as well as in the liquid obtained by decomposition under the action of an electric arc discharge or by decomposition of calcium carbide with water. Other substitute gases with low thermal conductivity are used for individual metals as deoxidizers. Their combustion requires different amount oxygen, but they are not economical.

• Oxygen

To ensure sufficient temperatures and rapid melting of metals, combustible gas vapors or the gas itself are burned with the addition of pure oxygen. For welding, technical oxygen of three grades is used, which is estimated by volume at atmospheric pressure:

1. top grade - frequency 99.5% + 0.5% nitrogen;
2. first grade - frequency 99.2% + nitrogen, argon;
3. second grade - frequency 98.5% + nitrogen and argon.

Liquid oxygen is not used in welding, but it is more convenient and safer for transportation in thermally insulated containers.

• Filler wire

used in accordance with chemical composition welded metals. The main criterion for its selection is the melting point, which should be slightly lower than the melting point of metals. As an exception for steel, copper, brass and lead, the wire can be replaced by cut thin strips of metal of the same grade.

• Fluxes

Welding pastes or powders, called fluxes, are used in welding with acetylene and its substitutes to protect the molten metal from oxidation and quickly remove oxide films that have already formed.

Wire and metal edges are treated with fluxes, which, when heated, form slags and float to the surface of liquid metal. The slag film protects the weld pool of liquid metal from oxidation. the choice of flux composition, as well as filler wire, depends on the type of metals being welded.

Equipment for welding

requires the same set of equipment regardless of the type of combustible gas used. The main set of a welder at a welding post is:

• Water lock. It is necessary to prevent the ignition of the acetylene-oxygen mixture in the gas channels during the so-called reverse impact. The safety seal is always connected between the torch or torch and the gas pipeline to a cylinder or an acetylene generator.

• Means of protection of the welder and the tool. Welding mask, goggles, gloves, balloon wrenches, hammer and metal brush for cleaning welds.

This whole set of equipment and Supplies is mandatory, but not minimal. For oxygen cutting, a torch-cutter is also used. Due to the danger of welding with an explosive mixture, all equipment must be regularly checked and in perfect working order.

Technological process of welding with acetylene

Acetylene is the most beneficial gas for welding thick metals, as well as the most convenient when using it in field conditions. At the same time, the technology for obtaining a welded seam is quite simple and has long been mastered, but it requires special care of the welder.

Acetylene welding technology

1. Based on the thickness of the metals to be welded, the required burner is selected (from 0 to 5). Its thickness will affect the width of the seam and the consumption of combustible gas.
2. The burner must be purged with acetylene until an odor appears and is checked for readiness for operation.
3. Combustible gas is ignited and oxygen is slowly added until a steady flame is formed. At the same time, the outlet pressure on the reducers: acetylene - 3-4 atm., oxygen - 2 atm.
4. By adjusting the burner, the necessary welding flame and its power are selected.
5. Thoroughly cleaned metal surfaces move towards each other and are slowly heated by the burner.
6. The welding process itself is carried out either left or right way.
7. The filler wire moves behind the burner.

Lets get reliable connection, and the quality of the seam depends on the skill of the welder. But it should be borne in mind that the combustion temperature of acetylene is very high, so a lot depends on the correct matching of the welding flame with the metal.

Selection of the welding flame

The composition of the combustible mixture determines the temperature, appearance and, accordingly, the power of the welding flame. By adjusting the ratio of oxygen and acetylene in the mixture, the welder can get three main types of flame:

1. Carburizing (excess acetylene). It is used when joining hard metals, as well as aluminum and magnesium alloys.
2. Normal (neutral). The most commonly used type of flame for welding "ferrous" metals. The flame has a distinct crown and consists of three color zones: the core is bright blue, the recovery zone is pale blue, and the torch is yellow. The recovery zone and the torch are the working areas of the burner flame.
3. Oxidative (excess oxygen). Used when cutting metal, welding brass and soldering together with filler wire.

The welding flame directly affects the quality and strength of the weld. Its power must correspond to the thermophysical properties of the metal and its thickness. Also wire, flux and angle selection gas burner are the defining parameters of the process of welding metals.

Metallurgical processes of acetylene welding

The use of acetylene leads to the characteristic features of the seam formation process:

• formed small bath molten metal;
• at the point of welding, a high temperature and the main concentration of heat are reached;
• the metal quickly melts and cools quickly, but not like in arc welding;
• the liquid metal of the bath has time to be intensively mixed by the gas flow of the flame and wire, which ensures the smoothness of the weld;
• chemical interaction between the molten metal and the gases of the welding flame takes place.

The main reactions of gas welding:

• Oxidation: metals that have an affinity for oxygen (magnesium, aluminum).
• Recovery: iron, nickel and so on.

The use of certain fluxes and wires depends on the type of metal and the reaction that occurs during welding.

Structural changes in welded metals

The zone of influence of the flame is a section with a width 3 times greater than the thickness of the metals being welded. Accordingly, the process of melting metals with a thickness of more than 5 mm with acetylene is difficult, and in this case, the edges must be bevelled. But the total zone of influence of the gas flame is larger than in arc welding, which allows you to connect thicker metals.

With uniform heating, the base metal layers adjacent to the weld pool acquire a coarse-grained structure. The largest and most clearly traced structure is observed in the area close to the seam itself.

This is a zone of incomplete melting of the metal, which is the most fragile and prone to the formation of defects. The zone of possible destruction is also followed by a zone of coarse-grained metal structure - a zone of non-recrystallization, which is characterized by lower melting temperatures. All subsequent zones at a distance of several millimeters from the seam do not change their fine-grained (normal) structure.

To reduce the zone of possible defects, either preheating is used directly in the welding zone, or a general heat treatment of the part, or a hot wire for the seam. All this allows the deposited weld metal to have a lower elongation and a lower viscosity coefficient compared to the base metal, which provides increased joint ductility.

Acetylene welding modes for some metals

Carbon steel

High carbon steels are not recommended for welding with acetylene. And for low-carbon steels, gas welding is applicable in any case, with the choice of any welding method. With a normal burner flame and an average power of 120 dm 3 /h, the right welding method is used. To improve the quality of the seam, mild steel wire is most often used. When heated, part of the manganese, silicon and carbon burns out, which provides a coarse-grained structure of the base metal. wire with a content of 0.17% carbon, 1.1% manganese and 0.9% silicon is used to obtain a layer of weld metal of an even structure.

Alloy steel

The thermal conductivity of alloyed steels leads to a high degree of deformation at significant temperatures, which makes it difficult to weld with acetylene.

• Low alloy steels: well welded with normal flame using appropriate fluxes.
• Chrome-nickel steels: welded with a low-power normal flame (up to 75 dm 3 / h).
• Heat resistant steels: 25% chromium and 21% nickel wire is used.
• Corrosion resistant steels: wire with 3% molybdenum, 11% nickel and 17% chromium is used.

Cast iron

Oxidizing flame adversely affects. When it is used, silicon burns out in the heating zone and grains of white cast iron are formed in the weld metal. Such a connection is not strong and pricks easily. It is possible to use a normal or carburizing flame of a gas burner to connect parts of cast iron parts.

Copper

The high coefficient of thermal conductivity of copper requires a supply from a gas burner significantly more heat than for steels. In this case, copper melts very quickly and is a superfluid material in the liquid state. Therefore, its connection must be made without a gap between the edges of the parts or using pure copper wire. To remove copper slag, special fluxes are used, which also provide deoxidation of the seam.

Brass

The brass connection is not amenable to electric arc welding, therefore gas welding is used. When forming a seam, it is necessary to use temperatures of about 900 0 C, which are sufficient for the formation of a joint, but not enough for the complete evaporation of zinc from the metal. In gas welding, the permissible percentage of evaporation of zinc from the seam and near the seam zone is 25%, which makes it possible to form a non-porous seam.

If the amount of acetylene in the burning mixture is increased to 35%, then the amount of evaporated zinc will decrease significantly. In this case, you can not do without filler brass wire and flux.

Bronze

Bronze is heavily exposed oxidative reactions, as a result of which tin, silicon and aluminum quickly evaporate from it. Therefore, all connections using gas welding must be carried out with a reducing flame of the burner. The directly connected metal is used as a filler wire, and 0.5% silicon is also added to the metal to deoxidize the weld. For bronze, fluxes of the same composition are suitable as for copper and brass.

Pros and cons of acetylene welding

First of all, any manual gas welding has great potential compared to arc welding. But this same advantage also requires more control on the part of the welder, which means it increases the possibility of errors and violations of the integrity of the joint.

Advantages:

• Ease of use in construction and installation conditions, where there is no power cable and energy source. Welding equipment is quite mobile and easy to transport.
• Possibility to combine several types of metals with different melting points using one type of equipment. Only by regulating the flame and the concentration of acetylene in the combustible mixture.
• Indispensable for, brass, copper.
• Improving the quality of the seam by using the right wire.
• The ability to adjust the heating rate of the metal when welding with acetylene.

Flaws:

• Human factor: high qualification of the welder is required for a sufficient level of productivity.
• A large heat-affected zone, which is unacceptable in mechanical engineering.
• At more than 5 mm, arc welding is more profitable in terms of costs and in terms of the speed of obtaining a joint.
• the process of gas welding cannot be mechanized and automated.
• Gas welding does not provide a high-quality connection of high-carbon steels.
• The occurrence of stresses in the metal, which leads to deformation during overlap welding.
• An economically unfavorable option compared to the use of arc welding to obtain high-quality and reliable welded joint.
• Explosiveness of the materials used, which cannot be used under certain conditions.

Features of welding with acetylene:

• Ideal for butt, not end connections.
• Welding performance is directly proportional to the purity of oxygen and acetylene.

With all the shortcomings and dangers in the use and storage of acetylene, it was and remains the main combustible gas for welding. In turn, gas welding will never completely lose ground and will not lose its popularity, since in some conditions it is simply irreplaceable and many industries can no longer do without it.

The high qualification of the welder and numerous work experience allows the acetylene welding process to become not only profitable in terms of material consumption, but also in terms of the productivity of obtaining welded joints of various parts of metal structures. Strict adherence to safety regulations and all precautions minimizes the occurrence of dangerous situations when using acetylene welding.

An old welding technology that always produces a beautiful and durable seam, acetylene welding. At the core this process lies a combustible gas - acetylene, which was always obtained by mixing water and calcium carbide. And they did it in a special container called a generator. Added to the equipment oxygen balloon, a set of hoses, a burner mounted on a special handle, on which control valves are located. With their help, the supply and consumption of acetylene and oxygen was regulated.

There has always been a lot of fuss with the gas generator. It had to be loaded with carbide and filled with water before each welding process. After the end of welding, the mixture was poured, thereby obtaining an unforeseen consumption of materials. Today, instead of whimsical generators, cylinders are used, which are factory filled with acetylene under the required pressure.

Gas welding with acetylene, or rather, its quality, depends on the burner. From its exact choice in size, from the competent supply of gases into its cavity. As for the sizes, the burners are marked from zero to five. In this case, "0" is the smallest size, respectively, "5" is the largest. Here, it mainly refers to the size of the hole. And the larger it is, the wider the welding seam will be after welding, and, accordingly, the consumption of the gas mixture will be greater.

Therefore, when starting to weld metal blanks with acetylene, you must first make sure that the tip (its number) corresponds to the nozzle through which the combustible gas mixture will be supplied.

Welding technology

Before welding acetylene, it is necessary to open the supply of acetylene gas until a sharp specific smell appears. The burner is ignited, after which it is necessary to gradually add oxygen until a stable blue flame forms. Please note that reducers are installed on each cylinder: acetylene and oxygen. So, when supplying both gases, a supply under pressure of 2-4 atm should be installed on an acetylene cylinder, and up to 2 atm on oxygen. There is no point in increasing the pressure, because this will lead to incorrect adjustment of the combustible mixture.

When welding ferrous metals, usually welders set the so-called neutral flame. It consists of three parts that are clearly visible to the naked eye:

• Inside is the core, it has a bright blue color, often with a greenish tinge.
• Next comes the restorative flame. This so-called Workspace having a pale blue color.
• And on top is a torch of flame. And he is also a worker.

In total, experts note four varieties of acetylene welding flame, but it is the neutral type that is used most often. It needs to be set up correctly. And if the setting was carried out illiterately, then welding with acetylene will not cook the metal, but cut it. It is very important not to let the burner flame be long and orange-tipped. Such a flame introduces carbon in excess into the heated metal. And this one chemical element for the welding process - not the best indicator.

Welding methods

There are two types of welding: “on yourself” and “away from you”. In the first case, the torch moves first, heating the weld pool to the required temperature, followed by the filler wire. In this case, it is necessary that the flame of the burner is fed into the welding zone at an angle of 45 °. The burner should move in circles or semi-circles along the seam, the additive should keep up with the flame and move into the weld zone.

In the second case, on the contrary, the filler rod moves in front of the burner. Usually thick metal blanks are welded in this way. Because the process of melting the base metal and the additive occurs simultaneously, and the mixed molten metal completely fills the weld pool. But the most important thing with this method of connection is to achieve uniform mixing of the two metals. If the mutual penetration is weak, then the seam will turn out to be of poor quality.

By the way, the interpenetration of metals, in a scientific way, penetration, may look purely outwardly ugly, but at the same time, the strength of the connecting seam will be as high as possible. And, conversely, a beautiful seam does not provide high quality welded joint. In this case, beauty can be deceiving. But in order for the result to be guaranteed of high quality, it is necessary to set the gap between the workpieces to a minimum, as well as to carry out preliminary tacks for the same purpose - to reduce the gap.

Features of gas welding

Oxy-acetylene welding has three main parameters that affect the quality of the final result. This is the power of the fire (flame), this is the angle at which the burner is located to the welding surface, the diameter of the filler rod used.

The power of the burner flame is selected depending on the thermophysical properties of the metal and on the thickness of the workpieces to be welded. The dependence is as follows: the thicker the parts, the higher the thermal conductivity and melting temperature of their metal, the greater the power of the burner flame should be. The latter is determined by the flow rate of the gas mixture. The higher the flow, the higher the power. For each type of metal, its own power indicator is selected. There are formulas by which it is determined. The main dependence is the thickness of the workpieces to be welded.

• For ferrous metals (steel and cast iron), the power is in the range (100-150) n, where n is the thickness of the part.
• For non-ferrous metals, for example, for copper, the range is (150-200) n.

The power of the flame, as well as the consumption of gases, has a unit of measurement - l / h.

As for the angle of inclination of the burner, it also varies depending on the thickness of the products to be joined. For example, if the thickness varies in the range from 1 to 15 mm, then the angle of inclination will vary from 10 to 80 °. And the thicker the metal, the more angle tilt. But at the very beginning of welding, it is necessary to maintain the maximum angle of inclination, even up to 90 °, because at this value the parts to be joined will heat up faster, plus the weld pool will form faster.

The diameter of the filler rod is also selected depending on the thickness of the workpieces. The definition formula is simple: half the thickness plus one millimeter. For example, if parts with a thickness of 4 mm are welded together, then an additive with a diameter of 3 mm is required to connect them.

Advantages and disadvantages

The advantages of gas welding include:

• Complete independence from electricity.
• The ability to change the temperature of the weld pool only by changing the angle of the direction of the flame, that is, the location of the burner.
• The ability to avoid burn-through by changing the distance from the welding surface to the torch.
• The apparatus and all equipment for acetylene welding is mobile.

But this technology also has its drawbacks.

• Low productivity of the welding process.
• A sufficiently large heating area, which most often negatively affects the base metal itself.
• Welding work requires a highly qualified welder.
• Rarely used commercially.

Most often, acetylene gas welding is used to join thin-walled workpieces. For example, for joining thin-walled pipes, where it is impossible to use flux or shielding gas from the inside. Be sure to check out the video tutorial, the rules for conducting acetylene welding.

One of the most popular types of gas plasma welding is acetylene welding. It gained its popularity for its simplicity and low cost of raw materials for obtaining the required acetylene and a relatively simple set of required equipment. Acetylene welding allows you to get good quality connections of even the most complex structures.

How to boil with acetylene

To obtain high-quality seams and the reliability of the resulting joint, it is necessary to observe the features of the acetylene welding technology. It is necessary to monitor the main parameters of the welding process. These options include:

• combustion intensity of the gas mixture (flame power);
• the angle of inclination of the gas burner to the surface of the fastened parts;
• nozzle diameter;
• filler rod diameter.

The first parameter is selected based on data on physical and mechanical properties welded metals. The angle of inclination is set based on the thickness of the elements to be welded. All other parameters are selected based on the internal parameters of the structures to be welded and the external welding conditions.

Before carrying out work, it is necessary to choose a welding method. This choice depends on the welding conditions. The most common and technologically advanced are the following methods:

• to myself;
• Push;
• using flux.

If welding with acetylene of selected parts requires the torch to be tilted to the surface at an angle of approximately 45 °, the first method is used. In this case, it is necessary to ensure circular movements of the burner flame in relation to the direction of the seam.

The use of the second method is most rational in oxy-fuel welding of parts made of thick steel. In this case, it is necessary to maintain a constant temperature at the point of formation of the seam.

Flux technology is quite universal way. In this case, electrodes are used which have a lower melting point than the melting point of the metals themselves. Rods made of non-ferrous metals: brass or bronze are especially widespread. The use of an appropriate flux allows degreasing the surface of the formation of the seam. This allows to significantly improve the effect of diffusion during heating and increase the so-called papillary effect. Flux carbide welding significantly improves the quality of the resulting joint.

Used equipment

Oxygen welding involves the creation of a seam by creating a flame during the combustion of a mixture of two gases, acetylene and oxygen. Therefore, it is necessary to ensure: the correct percentage of these gases, the combustion temperature, the size of the flame.

To solve these technical problems, the following equipment is used:

• oxygen storage cylinder (usually use a standard steel cylinder with a capacity of 40 liters);
• a special container for storing carbide and producing acetylene (such units are called gas generators);
• cylinders filled with acetylene can be used in industrial conditions;
• reducers for pressure control of incoming gases;
• gas supply pipes to the burner (should be designed for pressure up to 16 atmospheres);
• gas burner (the number of the burner determines its hole size: the smallest has a zero designation, the largest is fifth).

Welding with acetylene and oxygen is carried out in various conditions. For this purpose, the division of all equipment into an acetylene part and an oxygen part was carried out. For example, the acetylene supply reducer is made in black, oxygen in blue color. Threaded connections the acetylene part was performed with a left-hand direction, the oxygen part with a right-hand direction. This reduces the possibility of errors during installation, increases the reliability and safety of the assembled apparatus.

Necessary tools and materials

Oxy-acetylene welding involves the use of the following tools and materials.

The materials used are calcium carbide, which, when it enters the water, releases the necessary acetylene for welding. Oxygen filled into cylinders. Filler wire, depending on the materials of the parts to be welded. Acetylene and oxygen must meet the specified requirements.

In addition to basic equipment workplace welder must be equipped with the following tools:

• hammer;
• metal brush (for preparing the welding site);
• pliers;
• a set of special needles (they allow you to clean the gas burner nozzle);
• a set of wrenches for attaching reducers to cylinders and adapter fittings to hoses.

Advantages and disadvantages of technology

Any type of welding has its advantages and disadvantages. The advantages include the following:

• acetylene welding process does not require electrical source energy;
• the equipment necessary for carrying out the work is quite mobile and can be deployed anywhere (in the country house, garden plot, industrial facility, just on the street);
• the admissibility of a smooth change in the temperature of the gas jet due to a change in the angle of inclination of the burner with respect to the surface of the parts to be welded;
• avoid so-called burn-through of parts due to free choice distance between the burner and the seam;
• high manufacturability when welding fixed seams and a small distance to the nearest structures (for example, to a wall);
• there is no need to produce the so-called operational joint;
• perform work at different temperatures of the melt of metals or alloys from which the structures themselves are made;
• high quality of the welded joint is ensured;
• low cost of equipment and materials.

The main disadvantages include:

• low productivity of welding work;
• creation of an extensive heating area (leads to a change in the mechanical characteristics of the metal from which the welded parts are made);
• work can only be performed by a well-trained welder;
• the use of combustible gases (acetylene and oxygen) determines its high explosiveness;
• in the place of work there is a high gas content, which requires compliance with special safety conditions;
• inability to mechanize and automate welding work;
• it is impossible to obtain a high-quality connection of parts made of alloy steels and high-carbon steels;
• the impossibility of overlap welding (this will lead to uncontrolled deformation of the metal and the formation of separate sections with increased stress).

Despite the above disadvantages and high explosiveness, oxy-acetylene welding is very popular when joining thin-walled structures, non-ferrous metal parts.

The path to IT can be very thorny for everyone. For example, in my childhood I wanted to be a welder - it's so beautiful when splashes of molten metal fly around! But somehow it didn’t work out: they started to subscribe to the magazine “ Young Technician", where on last page one of the issues was told about a robot controlled by a BK-0010 computer ... But the fad remained ...

Also, someone probably remembers the program “Crazy Hands”, where various creative (as they would say now) things were made from plastic bottles.

Under the cut - I'll show you how plastic bottle, an insulin syringe, several meters of rubber hose, glue gun(where without it) and some other things that can be found in every home * make a real oxy-acetylene welding.

Theory

As a fuel, hydrocarbons are usually considered. Carbon when burned gives carbon dioxide and hydrogen is water. Water has a very high heat capacity (4.183 versus 1.4 kJ / (kg * K)), respectively, the more carbon in the fuel and the less hydrogen - the higher, in the first approximation, the potentially achievable temperature.

The best combination- for acetylene C 2 H 2, and for example for methane CH 4 and propane C 3 H 8 - this ratio is much worse.

But there are other compounds with equal amounts of carbon and hydrogen - for example, benzene, C 6 H 6. In addition to the toxicity of benzene, less energy is released during its combustion, because. in acetylene, "extra" energy is stored in an unstable triple carbon bond, which provides it with one of the highest combustion temperatures in oxygen - 3150 ° C.

This excess energy (~16%) can be released during the spontaneous detonation of compressed acetylene even without air access (the reaction product will be just benzene and vinylacetylene). Wikipedia claims that this requires a pressure of only 2 atmospheres - but I compressed acetylene in a syringe to 4-5 atmospheres and nothing happened (apparently, catalysts, shock or elevated temperature are needed). In any case, because of this effect, acetylene is not stored in a compressed form, but is dissolved in cylinders in acetone. But there is also a simpler and safer method for obtaining acetylene in small volumes - the reaction of calcium carbide with water. This is the method that will be used.

Remarkably, you can reach even higher temperatures - if you use substances that do not contain hydrogen at all as fuel: cyanogen (hello Android), (CN) 2 - burns at 4525 ° C and dicyanoacetylene C 4 N 2, burns at 4990 ° C (again due to triple carbon bonds, and a smaller relative amount of excess nitrogen). But practically for this purpose they are not used because of toxicity.

Safety

Acetylene will be generated from a small amount of calcium carbide (~100g per session), in a 0.5l bottle. Initially I wanted to use 2l so that the pressure was more even - but after looking on YouTube how a liter of acetylene explodes with oxygen- I decided to cut the sturgeon. In order not to create dangerous pressure in the generator, the acetylene outlet on the burner should never be blocked. The acetylene generator needs to be cooled - otherwise there will be a “self-acceleration” of the reaction due to heating.

Oxygen - will be generated by a medical oxygen concentrator, which is relatively safe.

There could still be a danger of pumping oxygen into the acetylene generator with subsequent popping - but for this it is necessary that the protective valve in the oxygen generator does not work, and the gas outlet from the burner is blocked (by dirt, for example).

And of course, you need to work in special glasses - not only to protect against metal splashes, but also ultraviolet radiation flame (i.e. clear plastic goggles will not work here).

In order to prevent the accumulation of an explosive concentration of acetylene in case of leaks, the fan constantly blew the workplace + all operations were carried out in the open air.

There is also the problem of "backlash": when the gas flow rate in the burner becomes too low, the flame goes inside the burner with a pop, and if there is air in the acetylene, the flame can reach the acetylene generator. Therefore, I did not ignite the acetylene immediately after the start of the reaction, but waited ~ 15-30 seconds until the air was expelled. Also this problem can be solved by adding a water valve in the acetylene path.

Design

Next - the standard acetylene torch "Baby", it has the smallest nozzle, bought in an online store (960 rubles):

My acetylene generator works as follows: water from a can standing at a height of 1-2 meters (to create pressure) through the needle of an insulin syringe drips in small drops onto calcium carbide in a bottle. As soon as the pressure rises due to the released gas, the water stops dripping until the pressure drops. Thus the system stabilizes itself. However, the generator in the bank with cold water- to avoid excessive heating:

Result

With the inclusion of oxygen, everything changes:

You can melt and set fire to steel, but there is still not enough power to cut (you need to take a thicker tip, increase the pressure):

It turned out that a flexible glass “fiber” is obtained automatically - when molten glass drips, as soon as the thickness of the neck becomes small enough, it cools very quickly and does not thin further.

You can melt glass like butter, seal capsules from glass tubes:

The task of life is completed, I hope you were interested :-)

PS. And don't repeat this at home.

Addition from a specialist (@freuser):

From the point of view of a professional welder (30 years, 11 years of experience, 2 of them are gas welding):
Good article, in general, the disclaimers are correct. It is worth adding that the work is carried out on fireproof surfaces (sparks fly about 2 meters from the wind, and metal drops, even darkened to normal colors, can burn through shoes if they are shoes.)

The design of the generator is called VK (water on carbide), there are also KV and VV (google with diagrams, the copyright is still Soviet :)).

There are no comments on the video, there is nothing special to watch (from my point of view), it is only worth adding that large glasses (or whole bottles), as well as stone / concrete / some bricks, when heated, can burst / delaminate with the formation of low-flying fragments, which are wonderful they stick and fuse into the skin (especially on the face), however, by a millimeter, no more, and are easily removed from there.

I would also like to answer specifically to habrahabr.ru/post/185720/#comment_6461342: this is not a reverse blow, or rather not what Nepherhotep warned against, but simply the burner either overheated, or, rather, from low pressure and an obstacle close to the nozzle ( or blockage inside the nozzle) the flame went towards the flow, to the injector (in this burner it is under the union nut, between it and the valves), but did not move further. And usually, a blowback is understood as the case when the flame slipped through the injector and went through the hose towards the source. There are two types of reverse blows (I saw one with my own eyes): the flame goes through an acetylene hose (normal combustion, only the end of the hose constantly burns and the flame moves evenly to the cylinder / generator) and through oxygen (everything is more beautiful here - the hose is suddenly 20-30 cm a piece flashes and turns into tatters, a second pause is the next segment, etc. until the balloon itself.) Although the second case is rare. The simplest defense- you pinch the hose in the distance, press down with your foot (do not forget about the shoes) and yell to your partner “Sanka, close the cylinders, *** !!” For more civil protection, you can make water locks - also a bottle, two tubes, one to the bottom - incoming, the second short - to the burner. Up to half filled with water and that's it, the bubbles run beautifully))

Tags:

• acetylene
• oxygen
• we burn with napalm
• cyanogen