What you need to know about gas welding. How gas welding is done with your own hands Use gas welding

Gas welding is widely demanded in production and in the household. More and more private traders who prefer to do various work on their own are doing it using sophisticated equipment. This allows them to perform complex tasks and carry out a variety of projects.

For this reason, do-it-yourself gas welding is of interest to home craftsmen. But before picking up a burner, you need to find out what and how it is done.

Welding on gas: purpose and specifics

Gas welding is the process of melting base and filler metals on the edges of parts as a result of exposure to a burner flame. The choice of the chemical composition of filler rods depends on the physical and chemical characteristics of the base metal.

Figure 1. Gas welding technology.

The flame is maintained by supplying gas to the burner along with commercially pure oxygen (Fig. 1). The addition of the latter makes fire suitable for use in welding. Moreover, the proportion of oxygen that determines the property of fire and its practical application.

According to the ratio of gases, the flame of gas welding is divided into three types:

• restorative;
• oxidative;
• carburizing.

The flame of the first type (it is also called normal) contains equal parts of acetylene and oxygen. An oxidizing fire is formed with an excess of oxygen, and a carburizing fire is characterized by an excess of acetylene.

Unlike arc welding, gas welding provides smooth heating of metal edges.

With its help, with different methods of soldering and surfacing, steel parts with a thickness of 0.2-5 mm, various types of tool steels, as well as non-ferrous metals and cast iron are processed. All of these metals must be welded by gentle and slow heating.

What gases are used in gas welding?

The flame of a gas burner is created by the combustion of working gases under the influence of oxygen. The purity of the latter must be at least 98%.

In gas welding, several gaseous chemical elements are used as combustible gases. These are acetylene, methane, hydrogen, propane and propane-butane mixtures, vapors of lighting kerosene and gasoline. All of these substances burn well in the open air.

Figure 2. Welding methods - right and left.

The peculiarity of all the mentioned gases is that they do not by themselves generate the very high temperature necessary for the rapid melting of metal structures. To do this, they require additional oxygen flow.

The most popular among these gaseous substances today is acetylene gas. It is actively formed as a result of a chemical reaction when calcium carbide is combined with ordinary water. Interacting with an oxygen jet, acetylene at the time of combustion "gives out" a temperature of up to 3200-3400 ° C. To obtain it, special generators are used, which are currently widely produced by industry.

In a gas welding machine, the combination of acetylene with oxygen occurs in a special mixing part of the burner. Both gases are fed into this chamber through hoses separately: acetylene from the generator, and oxygen from a cylinder, which traditionally has either blue or blue color. The oxidizer is contained in the tank under pressure of 3-4 atmospheres.

It should be noted that the constituent components of the gas mixture are supplied under different pressures (it is higher for oxygen). Therefore, when oxygen enters the central supply channel of the burner, its promotion creates a strong vacuum, due to which acetylene, pumped at a lower pressure, is sucked into the channel by gravity. Here, in the mixing section, the gases are mixed, reacted and through the tip go outside, to the welding point.

Features of the preparation and welding of metals by gas welding

Figure 3. The angles of the torch mouthpiece when welding various thicknesses.

In order to properly perform welding work, it is necessary to understand the principles of welding operations and the sequence of actions of a gas welder. The technology of these works includes preparatory operations, including the processing of the welded edges of metal blanks and the choice of welding method, setting the gas burner to the proper position, as well as determining all the required parameters of the gas welding machine, including the power of the fire jet and the diameter of the wire additive.

In preparation for welding work, the metal edges of the workpiece should be cleaned of various contaminants, scale and oil. On a special machine or, if the machine is not available, using an ordinary chisel (you can also use a pneumatic version of this tool), a bevel is made on the edges, which is necessary to fill the future seam with molten welding filler.

During operation, it is very important that the position of the elements to be welded is rigidly fixed. In order to ensure the impossibility of their movement relative to each other, before the main welding, the edges of the workpieces are tacked.

If we are talking about thin metal sheets and short seams, then the tacks are made 6-7 mm long each, between them there should be non-tacked gaps about 70-100 mm long. If thick metal parts are connected, and the seams are planned to be long, the length of each tack should reach 25-30 mm at intervals between them of 300-500 mm.

Turning to welding, we note that its quality largely depends on the correct position of the burner in relation to the butt joint and on the direction of the wire along the joint. Here, right and left variants of the direction of production of welding operations are distinguished (Fig. 2).

When using the movement of the working body of the gas welding unit to the right, the wiring is carried out from left to right. In this case, the torch moves in front of the wire filler and its flame is directed towards the weld being formed.

The left method, on the contrary, involves moving the burner from right to left. With this movement, the burner is located above the additive. As a result, the fiery jet is directly directed at the metal edges that are not welded to each other. Intensive heating of the edges takes place, which are thus prepared for the subsequent high-quality welding.

It is worth noting that using the right method, metal parts with a thickness of more than 5 mm are connected, ceiling welds are made. At the same time, vertical seams are formed in the left way if welding is performed from the bottom up.

During gas welding, the torch tip and the filler rod must move relative to each other (Fig. 3) / The mouthpiece is moved along the seam and at the same time across the seam axis, and the filler rod is gradually advanced towards the movement of the mouthpiece.

Safety precautions when working with gas

Welding equipment must be in good condition. Otherwise, work is prohibited.

Transportation of gas cylinders is carried out either by special stretchers or on a specially designed trolley.

When working indoors, it is imperative to provide breaks with access to fresh air.

When working in containers, the presence of a second worker outside is mandatory.

The welder must wear protective goggles.

Observing all these rules, you can do gas welding at a high level with your own hands.

Gas welding is a type of fusion welding, in which the heating source is the heat released during the combustion of a mixture of combustible gases.

The method is suitable for joining almost all metals used in engineering. It is used in industry, agriculture, construction, when performing repair work.

GOSTs

All information related to gas welding and the materials used is set out in GOSTs, which must be followed.

Some standards:

1. Terms and Definitions: GOST R ISO 857-1-2009 - definition of the term "gas welding.
2. Welding consumables: GOST 5457-75 - technical specifications for gaseous and dissolved technical acetylene, GOST 3022-80 - technical hydrogen.
3. Gas welding and cutting: GOST 29090-91 - requirements for materials for gas welding.

Principle of operation

Acetylene is a compound of carbon and hydrogen. Colourless, flammable gas with a sharp specific odor, explosive. Working with gas requires caution and safety precautions.

Transportation of cylinders

Acetylene Substitutes

Welding of metals having a melting point below steel can be carried out using substitute gases. For example: propane, methane, hydrogen.

Propane is a technical gas that is colorless, has a pungent odor, and is heavier than air.. For welding, a propane-butane mixture containing 5-30% butane is used. The temperature of the propane-oxygen flame reaches 2400 °C.

Methane-oxygen mixture is almost odorless. The flame has a temperature of 2100-2200 ° C, so this combustible gas is used to a limited extent.

Hydrogen is a light, flammable, odorless, colorless gas.. In certain proportions with oxygen and air, it can form an explosive mixture. Therefore, it is imperative to comply with safety regulations when working with gas. Hydrogen for welding is in green steel cylinders. Has a gaseous state. The hydrogen-oxygen flame has a blue tint. The fuzzy outlines of its zones make it difficult to adjust.

Types of flames and their uses

The composition of the combustible mixture affects the appearance and temperature of the welding flame. It has 3 zones: core, reduction (middle), torch-oxidizing. The core includes a mechanical mixture of oxygen heated to a high temperature and decomposed acetylene.

Depending on the proportion of acetylene and oxygen, 3 types of flame are distinguished:

• oxidative;
• restorative;
• with a high content of combustible gas.

Oxidative

The flame is formed when the oxygen supply to the burner is increased or the amount of acetylene is reduced. For 1 volume part of acetylene, there should be 1.3 or more parts of oxygen. Character traits:

1. Shortened pointed nucleus of pale color with blurred borders.
2. Reducing the length of the middle zone and the flame.
3. Flame coloring- bluish-violet.
4. Burning is noisy.
5. Flame temperature is too high.

This type of flame is used for joining mild steel and welding brass.

Recovery (normal)

The ratio of acetylene to oxygen can range from 1:1 to 1:1.3. In the flame, carbon and hydrogen are formed, due to which the metal is deoxidized and reduced. Under such conditions, homogeneous without gas bubbles and pores is formed.

The core of the flame is light, the recovery zone and the torch have a darker shade. As the oxygen pressure increases, the nucleus elongates. The flame has a temperature well below the reduction zone. A normal flame is used for most types of welding.

With a high content of combustible gas

It has a name - carburizing or acetylene flame. It is characterized by an increase in the supply of acetylene or a decrease in oxygen. For 1 part of acetylene, 0.95 or less of a part of oxygen is taken. Characteristic signs:

• increase in the size of the combustion zone;
• vague outline of the nucleus, the appearance of a green corolla at its end;
• brightening of the recovery zone almost to its connection with the nucleus;
• flame yellowing.

The result of an excess of acetylene is its incomplete combustion, the flame smokes due to a lack of oxygen. Excess acetylene decomposes into carbon and hydrogen. Carbon is transferred to the molten metal. The result is a carburized weld metal.

A flame with a small excess of combustible gas is used for welding magnesium and aluminum alloys, cast iron.

Characteristics of gas welding methods

There are 2 ways:

• right;
• left.

Right

This is a method in which welding is performed from left to right. Direction:

• welding flame- welded section of the seam;
• filler wire- next to the burner.

The mouthpiece of the burner makes small transverse oscillations.

Compared to the left way:

• welding performance 20-25% higher e;
• better weld quality;
• gas consumption is less by 15-20%.

Flame heat dissipation is less compared to the left method, and therefore the seam opening angle is 60-70°, which helps to reduce the amount of deposited material, wire consumption and reduce warping of the product.

The method is expedient when connecting elements with high thermal conductivity and parts whose thickness exceeds 5 mm.

Left

The way is to move:

• burners from right to left;
• filler wire- in front of the flame, which is directed to the unwelded zone of the seam.

The edges of the base metal are heated before starting welding, which contributes to good mixing of the weld pool.

The left method is used to connect elements from low-melting and thin (up to 3 mm) metals.

Scheme of welding methods

Technology characteristics

There are different techniques for applying welding seams:

• multilayer;
• roller;
• baths;
• oxidizing flame.

multilayer

Application - making critical connections. Welding work is carried out by driving short sections. The condition is the mismatch of the joints of the seams in separate layers.

Before applying the next layer, the surface of the previous one is cleaned of slag and scale with a wire brush.

Advantages of the method compared to single-layer welding:

• smaller heating zone;
• ensuring annealing of underlying layers;
• forging each layer.

Disadvantage: high gas consumption.

Roller

The connected elements are installed vertically with a gap of half the thickness of the sheet. The flame melts the edges with the simultaneous formation of a round hole. Its lower section over the entire thickness of the metal is melted with filler material. The flame is transferred higher, the edge of the hole is melted at the top, and the next layer of material is applied to its lower part. The steps are repeated until the end of the formation of the weld.

If the metal has a thickness of 6-12 mm, work is simultaneously carried out on both sides by two welders.

The seam has the form of a through roller that connects. The weld metal is dense, has no defects.

Trays

The method is used when welding low-alloy and low-carbon steel up to 3 mm thick, when corner and butt joints are required. Welding wire is used.

At the moment of formation of a bath with a diameter of 4-5 mm at the seam, the end of the wire is directed into it, its small section is melted, and then transferred to the reduction zone. At the same time, the mouthpiece makes a circular motion to move to the area of ​​the new bath adjacent to the seam. It should overlap by 1/3 of the diameter of the previous bath.

To avoid oxidation, keep the end of the wire in the reduction zone. It is impossible to allow the core to be immersed in the bath in order to prevent carburization of the weld metal.

oxidizing flame

The method is used for welding mild steel. The goal is to increase the productivity of the welding process by 10-15%.

Flame composition β = 1.4. Excess oxygen during welding of steels contributes to the oxidation of the weld metal, so it turns out to be brittle and has pores. Therefore, when working with the aim of deoxidizing iron oxides in the weld pool, filler wires with an increased composition of silicon and manganese are used. For example: Sv 08G, Sv 08G2S, Sv-12GS.

Advantages and disadvantages

The positive qualities of gas welding include:

• simplicity;
• inexpensive equipment;
• the ability to control the speed of heating and cooling welded metal;
• strong and tight welds.

Flaws:

• process degradation with an increase in the thickness of the welded material;
• large heating zone;
• high cost of fuel gas compared to electricity
• complexity of mechanization and automation of the process.

Having appeared on the market, inverter welding machines have replaced the rest of the equipment used to connect metal parts and assemblies. But any experienced welder will say that oxyfuel welding is the first class in the welder's school curriculum, without which it is impossible to master the technique of welding metals and understand the welding process itself. In addition, it should be noted that this type of welding is still often used, and in some cases it is simply impossible to do without it.

Autogenous welding includes:

• Two cylinders: oxygen and acetylene.
• Two reducers, one for each cylinder.
• Flame arresters, one per cylinder.
• Set of two hoses: one for oxygen, the other for acetylene.
• A burner equipped with nozzles with holes of different diameters.

An oxygen cylinder is a metal container with a wall thickness of 6 mm, a volume of 40 liters, in which 6000 liters of oxygen are placed at a pressure of 150-200 atmospheres. The cylinder is seamless, which is why it can withstand such high pressure loads. In its upper part there is a valve to which the oxygen reducer is screwed. The main requirement for safe operation is to prevent oil and grease from getting on the valve, especially at the junction with the gearbox. Oxygen quickly interacts with oils, and an oxidation reaction occurs, which leads to an explosion.

The acetylene cylinder has a completely different design. The thing is that the compression of acetylene necessarily leads to an explosion. To prevent this from happening, it is necessary to divide this gas into small volumes. And to increase the volume itself, you need to dissolve it in acetone, which absorbs acetylene in large quantities. The absorption ratio is 1 to 360. That is, one liter of acetone absorbs 360 liters of acetylene. The breakdown of the mixture into small volumes is carried out due to the porous structure of the balloon filler. This material contains acetone. By the way, its amount is 16 liters, respectively, the amount of acetylene at a pressure of 15 atmospheres will be equal to 6000 liters.

The porous material is a symbiosis of asbestos, charcoal, diatomaceous earth and binder fillers. The wall thickness of the acetylene cylinder is 4-5 mm.

As in the case of an oxygen cylinder, an acetylene one also has a valve to which its own special reducer is attached. It should be noted that the oils and fats of this container are not terrible. The only thing to consider is to keep the acetylene cylinder in a vertical position when welding with an autogenous.

As for the gearboxes (acetylene and oxygen), their task is to reduce the pressure of gases to the required levels. Both devices have almost the same design, which is based on a spring-loaded valve. They also have two pressure gauges installed, one of which shows the pressure inside the cylinder, the second is the gas pressure after the reducer, that is, on the burner.

The pressure indicators after the reducer should be as follows:

• Oxygen - 2.5-3.0 atm.
• Acetylene - 0.3-0.7 atm.

These indicators are not absolute, because gas welding is used to connect metals of different thicknesses. And the thicker the blanks, the more gas pressure should be on the burner. In addition, metal cutting with autogenous is also carried out at elevated pressures.

Flame arresters or non-return valves are devices that protect against kickback. They are installed immediately after the gearboxes, and the hoses themselves are connected to it. What does backlash mean.

There are situations when acetylene begins to rise through the oxygen hose, reaching its reducer. If mixing of two gases occurs in this place, then this is a guarantee of a big explosion. Fire valves help to avoid this. In addition, there are certain actions of the welder himself, which ensure the safety of working with an autogenous. But more on that below.

Now for the hoses. What are the requirements for them.

• These are rubber products with a fabric cord inside.
• The color of the oxygen hose is blue, the color of the acetylene hose is red. Changing them is strictly prohibited.
• They are connected to welding equipment devices only on fittings through nipples.
• Frequently used hoses have an inner diameter of 9 or 12 mm.
• Their minimum length is 8 m, the maximum is 20 m.
• The hose set is a dual construction of acetylene and oxygen.

The torch is the most important piece of welding equipment where the two gases are mixed and where the mixture escapes at supersonic speeds. Hoses to the burner are connected by means of fittings. Above the handle are valves that regulate the flow of each gas. In this case, oxygen passes through the injector, in which acetylene pulls along with it. That is why the pressure of the acetylene reducer is set equal to atmospheric pressure or slightly higher.

Welding technique

A very important point is to properly ignite the gas mixture and turn it off. The connection is made in the following order.

• First, the oxygen valve on the burner is opened.
• Then acetylene.
• The burner is taken aside and ignited.
• In this case, the flame will have a red tint, it will be long, and it will definitely smoke.
• The oxygen supply is opened a little more and the acetylene supply is reduced. You can visually check the setting, the flame should turn bluish.

The burner is turned off in the reverse order: first the acetylene valve is closed, after 10 seconds the oxygen valve is closed. It is this procedure for shutting off the gas supply that ensures the safety of the operation of welding equipment. That is, the occurrence of the same reverse impact is prevented.

As for the conduct of the welding process, it can be carried out from left to right or vice versa. The first option is when the torch moves along the weld, and the filler wire moves behind it. The second option - the wire moves ahead of the burner. The first option is preferable, because the welding joint is first heated, and then the molten metal of the wire enters it. In this case, the flame pushes oxygen and nitrogen out of the welding zone, which adversely affect the quality of the final result.

The quality of a welded seam is not only about technology and correctly selected gas pressure parameters. This is a fairly large list of additional criteria, depending mainly on the thickness of the workpieces to be welded. Namely:

• the thickness of the wire used;
• correctly selected diameter of the burner nozzle;
• the speed of the burner along the seam;
• wire feed speed to the welding zone;
• percentage of each gas in the feed mixture.

In this case, it should be taken into account that the temperature in the welding zone when using an acetylene torch is several times lower than when welding with electrodes. Therefore, autogenous welding should be carried out more slowly. And accordingly, the process itself should be carried out more accurately. Otherwise, defects in the weld cannot be avoided. For example, an uncooked seam may form, which welders call cold. Pores, oxide-type inclusions, or undercuts may appear. Often there is a notch at the very root of the seam.

Safety

• Cylinders can only be moved by special transport.
• The distance from the cylinders to industrial and residential buildings is at least 10 m.
• They can only be stored in metal cabinets with holes, the cabinet must be installed outdoors and always be locked.
• Welding is carried out away from explosive and flammable substances.
• A fire extinguisher must always be present at the welding site.
• During operation, a constant check is made to detect gas leaks.

Autogenous technology for welding metals is simpler. A little experience, and you can already cook without looking back at the master. That is why it is considered to be a primary school for a welder.

Gas welding refers to fusion welding. The process of gas welding consists in heating the edges of the parts at the point of their connection to a molten state with the flame of a welding torch. To heat and melt the metal, a high-temperature flame is used, obtained by burning a combustible gas mixed with commercially pure oxygen. The gap between the edges is filled with molten metal of the filler wire.
Gas welding has the following advantages: the welding method is relatively simple, does not require complex and expensive equipment, as well as a source of electricity. By changing the thermal power of the flame and its position relative to the place of welding, the welder can control the rate of heating and cooling of the metal being welded over a wide range.
The disadvantages of gas welding include a lower heating rate of the metal and a large zone of heat effect on the metal than in arc welding. In gas welding, the heat concentration is less, and the warping of the parts to be welded is greater than in arc welding. However, with a correctly selected flame power, skillful regulation of its composition, the proper grade of filler metal and the appropriate qualifications of the welder, gas welding provides high-quality welded joints.
Due to the relatively slow heating of the metal by the flame and the relatively low heat concentration during heating, the productivity of the gas welding process decreases significantly with an increase in the thickness of the metal being welded. For example, with a steel thickness of 1mm, the gas welding speed is about 10m/h, and with a thickness of 10mm, only 2m/h. Therefore, gas welding of steel with a thickness of more than 6 mm is less productive than arc welding and is used much less frequently.
The cost of combustible gas (acetylene) and oxygen in gas welding is higher than the cost of electricity in arc and resistance welding. As a result, gas welding is more expensive than electric welding.
The gas welding process is more difficult to mechanize and automate than the electric welding process. Therefore, automatic gas welding with multi-flame linear burners is used only when welding shells and pipes made of thin metal with longitudinal seams; gas welding is used for:

Manufacture and repair of products from thin-sheet steel (welding of vessels and tanks of small capacity, welding of cracks, welding of patches, etc.);
welding of pipelines of small and medium diameters (up to 100 mm) and fittings for them;
repair welding of cast iron, bronze and silumin products;
welding of products made of aluminum and its alloys, copper, brass, lead;
surfacing of brass on parts made of steel and cast iron;
welding of forged and ductile iron using brass and bronze filler rods, low-temperature welding of cast iron.

With the help of gas welding, almost all metals used in engineering can be welded. Metals such as cast iron, copper, brass, lead are easier to gas welding than arc welding. If we also take into account the simplicity of the equipment, then it becomes clear that gas welding is widely used in some areas of the national economy (at some engineering plants, agriculture, repair, construction and installation work, etc.).

For gas welding it is necessary:

1) gases - oxygen and combustible gas (acetylene or its substitute);
2) filler wire (for welding and surfacing);
3) related equipment and apparatus, including:
A. oxygen cylinders for storing oxygen;
b. oxygen reducers for reducing the pressure of oxygen supplied from cylinders to the burner or cutter;
V. acetylene generators for producing acetylene from calcium carbide or acetylene cylinders in which acetylene is under pressure and dissolved in acetylene;
G. welding, surfacing, hardening and other torches with a set of tips for heating a broom of various thicknesses;
d. rubber sleeves (hoses) for supplying oxygen and acetylene to the burner;
4) accessories for welding: glasses with dark glasses (light filters) to protect the eyes from the bright light of the welding flame, a hammer, a set of keys for the torch, steel brushes for cleaning metal and the weld;
5) Welding table or fixture for assembling and fixing parts during tacking, welding;
6) fluxes or welding powders, if required for welding this metal.

Materials used in gas welding.

Oxygen Oxygen at atmospheric pressure and ordinary temperature is a colorless and odorless gas, somewhat heavier than air. At atmospheric pressure and a temperature of 20 gr. the mass of 1m3 oxygen is 1.33 kg. The combustion of combustible gases and vapors of combustible liquids in pure oxygen occurs very vigorously at a high rate, and a high temperature occurs in the combustion zone.
To obtain a welding flame with a high temperature, it is necessary to quickly melt the metal at the welding site, a combustible gas or vapor of a combustible liquid is burned in a mixture with pure oxygen.
If compressed gaseous oxygen occurs with oil or fats, the latter may ignite spontaneously, which may cause a fire. Therefore, when handling oxygen cylinders and equipment, care must be taken to ensure that even slight traces of oil and grease do not fall on them. A mixture of oxygen from combustible liquids at certain ratios of oxygen and combustible substance explodes.
Technical oxygen is extracted from atmospheric air, which is subjected to processing in air separation plants, where it is purified from carbon dioxide and dried from moisture.
Liquid oxygen is stored and transported in special vessels with good thermal insulation. For welding, technical oxygen is produced in three grades: the highest, with a purity of at least 99.5%
1st grade purity 99.2%
2nd grade with a purity of 98.5% by volume.
The rest 0.5-0.1% is nitrogen and argon
Acetylene As a combustible gas for gas welding, acetylene is a compound of oxygen with hydrogen. At normal to and pressure, acetylene is in a gaseous state. Acetylene is a colorless gas. It contains impurities of hydrogen sulfide and ammonia.
Acetylene is an explosive gas. Pure acetylene is capable of exploding at an excess pressure of over 1.5 kgf/cm 2 , upon rapid heating to 450-500C. A mixture of acetylene with air explodes at atmospheric pressure if the mixture contains from 2.2 to 93% acetylene by volume. Acetylene for industrial purposes is obtained by the decomposition of liquid combustibles by the action of an electric arc discharge, as well as by the decomposition of calcium carbide with water.
Gas substitutes for acetylene. When welding metals, other gases and vapors of liquids can be used. For effective heating and melting of the metal during welding, it is necessary that the to of the flame be approximately twice as high as the melting to of the metal being welded.
Combustion of various combustible gases requires a different amount of oxygen supplied to the burner. Table 8 shows the main characteristics of combustible gases for welding.
Gas substitutes for acetylene are used in many industries. Therefore, their production and extraction on a large scale and they are very cheap, this is their main advantage over acetylene.
Due to the lower flame t of these gases, their use is limited to certain processes of heating and melting metals.
When welding steel with propane or methane, it is necessary to use a welding wire containing an increased amount of silicon and manganese used as deoxidizers, and when welding cast iron and non-ferrous metals, fluxes are used.
Gases - substitutes with low thermal conductivity are uneconomical to transport in cylinders. This limits their use for flame treatment.

Table 8 Main gases used in gas welding

Welding wires and fluxes

In most cases, in gas welding, a filler wire is used that is close in its chemistry. composition of the metal to be welded.
Do not use random wire of an unknown brand for welding.
The surface of the wire must be smooth and clean, free of scale, rust, oil, paint and other contaminants. The melting point of the wire must be equal to or somewhat lower than the melting point of the metal.
The wire should melt calmly and evenly, without strong spattering and boiling up, forming a dense homogeneous metal during solidification without foreign inclusions and other defects.
For gas welding of non-ferrous metals (copper, brass, lead), as well as stainless steel, in cases where there is no suitable wire, as an exception, strips cut from sheets of the same grade as the metal are used.
Fluxes Copper, aluminum, magnesium and their alloys, when heated during welding, react vigorously with oxygen in the air or welding flame (when welding with an oxidizing flame), forming oxides that have a higher melting point than metal. Oxides cover droplets of molten metal with a thin film and this greatly complicates the melting of metal particles during welding.
To protect the molten metal from oxidation and remove the resulting oxides, welding powders or pastes called fluxes are used. Fluxes previously applied to the filler wire or rod and the edges of the metal being welded melt when heated and form fusible slags that float to the surface of the liquid metal. A slag film covers the surface of the molten metal, protecting it from oxidation.
The composition of the fluxes is chosen depending on the type and properties of the metal to be welded.
Calcined borax, boric acid are used as fluxes. The use of fluxes is necessary when welding cast iron and some special alloy steels, copper and its alloys. When welding carbon steels are not used.

Apparatus and equipment for gas welding.

Water safety locks Water seals protect the acetylene generator and piping from backfire from the welding torch and torch. Backstroke is the ignition of an acetylene-oxygen mixture in the channels of a burner or cutter. The water lock ensures the safety of work during gas welding and cutting and is the main part of the gas welding station. The water lock must always be kept in good condition and filled with water up to the level of the control tap. A water seal is always included between the torch or torch and the acetylene generator or gas pipeline.

Figure 17 Scheme of the device and operation of the medium pressure water seal:
a - normal operation of the shutter, b - backfire

Cylinders for compressed gases

Cylinders for oxygen and other compressed gases are cylindrical steel vessels. A hole with a conical thread is made in the neck of the cylinder, into which a shut-off valve is screwed. Seamless cylinders for high pressure gases are made of carbon and alloy steel pipes. Cylinders are painted from the outside in word colors, depending on the type of gas. For example, oxygen cylinders in blue, acetylene in white, hydrogen in yellow-green for other combustible gases in red.
The upper spherical part of the cylinder is not painted and the passport data of the cylinder is embossed on it.
The cylinder at the welding post is installed vertically and secured with a clamp.

Cylinder valves

Valves for oxygen cylinders are made of brass. Steel for valve parts cannot be used because it corrodes strongly in compressed moist oxygen.
Acetylene valves are made of steel. It is forbidden to use copper and alloys containing more than 70% copper, since acetylene can form an explosive compound with copper - acetylene copper.

Reducers for compressed gases

Reducers are used to reduce the pressure of the gas taken from the cylinders (or gas pipeline), and to maintain this pressure constant, regardless of the decrease in gas pressure in the cylinder. The principle of operation and the main parts of all gearboxes are approximately the same.
By design, there are single-chamber and two-chamber gearboxes. Double chamber gearboxes have two reduction chambers working in series, give a more constant operating pressure and are less prone to freezing at high gas flow rates.
Oxygen and acetylene reducers are shown in fig. 18.

Figure 18 Reducers: a - oxygen, b - acetylene

Sleeves (hoses) are used to supply gas to the burner. They must have sufficient strength, withstand gas pressure, be flexible and not restrict the movements of the welder. The hoses are made of vulcanized rubber with fabric gaskets. Sleeves for acetylene and oxygen are issued. For gasoline and kerosene, gasoline-resistant rubber hoses are used.

Welding torches

The welding torch serves as the main tool for manual gas welding. In the burner, oxygen and acetylene are mixed in the required quantities. The resulting combustible mixture flows out of the burner mouthpiece channel at a given speed and, burning, gives a stable welding flame, which melts the base and filler metal at the welding site. The burner also serves to regulate the thermal power of the flame by changing the flow of combustible gas and oxygen.
Burners are injector and non-injector. Serve for welding, soldering, surfacing, heating of steel, cast iron and non-ferrous metals. The most widely used burners are injection type. The burner consists of a mouthpiece, connecting nipple, tip tube, mixing chamber, union nut, injector, body, handle, oxygen and acetylene nipple.
Burners are divided by flame power:

1. Micro-low power (laboratory) G-1;
2. Low power G-2. Consumption of acetylene from 25 to 700 l. per hour, oxygen from 35 to 900 l. at one o'clock. Are completed with tips No. 0 to 3;
3. Medium power G-3. Consumption of acetylene from 50 to 2500 l. per hour, oxygen from 65 to 3000 l. at one o'clock. Tips #1-7;
4. High power G-4.

There are also burners for acetylene substitute gases G-3-2, G-3-3. Are completed with tips from No. 1 on No. 7.

Gas welding technology.

Welding flame. External, type, temperature and influence of the welding flame on the molten metal depend on the composition of the combustible mixture, i.e. the ratio of oxygen to acetylene. By changing the composition of the combustible mixture, the welder changes the properties of the welding flame. By changing the ratio of oxygen and acetylene in the mixture, it is possible to obtain three main types of welding flame, fig. 19.

Figure 19 Types of acetylene-oxygen flame a - carburizing, b-normal, c - oxidizing; 1 - core, 2 - recovery zone, 3 - torch

For welding most metals, a normal (recovery) flame is used (Fig. 19, b). An oxidizing flame (Fig. 19, c) is used in welding in order to increase the productivity of the process, but it is imperative to use a wire containing an increased amount of manganese and silicon as deoxidizers, it is also necessary when welding brass and brazing. A flame with an excess of acetylene is used for hardfacing. A flame with a slight excess of acetylene is used for welding aluminum and magnesium alloys.
The quality of the deposited metal and the strength of the weld are highly dependent on the composition of the welding flame.
Metallurgical processes in gas welding. Metallurgical processes in gas welding are characterized by the following features: a small volume of the molten metal bath; high temperature and heat concentration at the welding site; High speed of melting and cooling broom; intensive mixing of the metal of a smooth bath with a gas flow of a flame and a filler wire; chemical interaction of molten metal with flame gases.
The main reactions in the weld pool are oxidation and reduction reactions. Magnesium and aluminum, which have a high affinity for oxygen, are most easily oxidized.
The acids of these metals are not reduced by hydrogen and carbon monoxide, so special fluxes are needed when welding metals. Iron and nickel oxides, on the contrary, are well reduced by carbon monoxide and flame hydrogen, therefore, fluxes are not needed for gas welding of these metals.
Hydrogen is able to dissolve well in liquid iron. With the rapid cooling of the weld pool, it can remain in the seam in the form of small gas bubbles. However, gas welding provides slower cooling of the metal compared to, for example, arc welding. Therefore, when gas welding carbon steel, all the hydrogen has time to leave the weld metal and the latter will turn out to be dense.
Structural changes in metal during gas welding. Due to slower heating, the zone of influence in gas welding is larger than in arc welding. The base metal layers directly adjacent to the weld pool are continuous and acquire a coarse-grained structure. In the immediate vicinity of the seam boundary there is a zone of incomplete melting. A base metal with a coarse structure characteristic of an unheated metal. In this zone, the strength of the metal is lower than the strength of the weld metal, therefore, the destruction of the welded joint usually occurs here.
Next is a section, non-recrystallization is also characterized by a coarse-grained structure, for which t of metal melting is not higher than 1100-1200C. Subsequent sections are heated to lower temperatures and have a fine-grained, normalized steel structure.
To improve the structure and properties of the weld metal and the heat-affected zone, hot forging of the weld and local heat treatment by heating with a welding flame or general heat treatment with heating in a furnace are sometimes used.
An illustration of gas welding methods is shown in fig. 20.

Figure 20

Features and modes of welding of various metals.

Welding of carbon steels

Low carbon steels can be welded by any gas welding method. The flame of the burner should be normal, with a power of 100-130dm 3 / h when welding on the right. When welding carbon steels, a wire made of mild steel Sv-8 Sv-10GA is used. When welding with this wire, part of the carbon, manganese and silicon burns out, and the weld metal receives a coarse-grained structure and its tensile strength is that of the base metal. To obtain a deposited metal of equal strength to the main one, Sv-12GS wire is used, containing up to 0.17% carbon; 0.8-1.1 manganese and 0.6-0.9% silicon.

Alloy steel welding

Alloy steels are less efficient conductors of heat than mild steels and therefore warp more when welded.
Low-alloy steels (for example, XCHD) are well welded by gas welding. When welding, use a normal flame and wire SV-0.8, SV-08A or SV-10G2
Chrome-nickel stainless steels are welded with a normal flame with a power of 75 dm 3 of acetylene per 1 mm of metal thickness. Apply wire SV-02X10H9, SV-06-X19H9T. When welding heat-resistant stainless steel, a wire containing 21% nickel 25% chromium is used. For welding stainless steel containing 3% molybdenum, 11% nickel, 17% chromium.

Cast iron welding

Cast iron is welded when correcting casting defects, as well as restoring and repairing parts: welding cracks, shells, when welding breakaway parts, etc.
The welding flame must be normal or carburizing, since the oxidizing flame causes local burnout of silicon, and grains of white cast iron are formed in the weld metal.

Copper welding

Copper has a high thermal conductivity, so when it is welded to the place of metal melting, a large amount of heat has to be carried out than when welding steel.
One of the properties of copper that makes welding difficult is its increased fluidity in the molten state. Therefore, when welding copper, no gap is left between the edges. Pure copper wire is used as filler metal. Fluxes are used to deoxidize copper and remove slag.

Welding brass and bronze

Brass welding. Gas welding is widely used for welding brass, which is more difficult to weld with an electric arc. The main difficulty in welding is the significant evaporation of zinc from brass, which begins at 900C. If the brass is overheated, then due to the evaporation of zinc, the seam will turn out to be porous. During gas welding, up to 25% of the zinc contained in brass can evaporate.
To reduce the evaporation of zinc, welding of brass is carried out with a flame with an excess of oxygen up to 30-40%. Brass wire is used as filler metal. As fluxes, calcined borax or gaseous flux BM-1 is used.

bronze welding

Gas welding of bronze is used in the repair of cast bronze products, surfacing of parts working on friction with a layer of antifriction bronze alloys, etc.
The welding flame must have a restorative character, since the burnout of tin, silicon, and aluminum from bronze increases with an oxidizing flame. As a filler material, rods or wire are used that are close in composition to the metal being welded. For deoxidation, up to 0.4% silicon is introduced into the filler wire.
To protect the metal from oxidation and remove oxides into slags, fluxes of the same compositions are used as in the welding of copper and brass.

Gas bonding or metal cutting was not possible until the Frenchman Devy realized in 1836 that acetylene (ethyne) based on calcium carbide could burn. Then they began to use it in street lamps and headlights of cars and steam locomotives. Much later, his compatriots Fouche and Picard described the "weld pool" in gas-melting welding based on the same acetylene.

But it was in the Soviet Union that the industrial production of acetylene and its “packaging” in strong white steel cylinders were first started. This made it possible to increase the productivity of welders by 20 percent, and not to lose acetylene by the same amount. So gas welding of metals - steel, cast iron and non-ferrous - became available in any, even remote, area.

Gas welding - a universal solution

It is difficult to find an industry wherever gas welding is used - a method of firmly connecting metals to each other in the melt stage with a flame of special temperatures. After all, acetylene burns at 3200-3400 degrees.

The technology of gas welding is simple. This method can replace electric arc, but not gas. But still the first priority on thin metals. The arc will simply melt them, as in open-hearth, and will not hold them together.

What is "gas"?

Acetylene is still widely used today, where small amounts of welding are needed, especially in emergency cases. Other combustible gases are also widely used: hydrogen and natural, propane (separately and in a mixture with butane) and petroleum, as well as gasoline and kerosene vapors.

But among them, etin is the king in terms of calorific value and thermality of the torch (this can be seen in the photo of gas welding) in its mixture with O2. And it is more than other gases used for these purposes.

Pros and cons of technology:

• no electrical supply required;
• inexpensive equipment and accessories;
• carried out only manually;
• not high quality products in terms of mechanics and durability.

What is needed for gas welding / cutting

Gas welding equipment is simple and easy to carry and transport. For any type of fuel, gas welding devices have an oxygen prefix. Because without it, the process is almost impossible.

The main equipment for gas welding: a cylinder or a generator (gas holder), a cutter. In the generator, calcium carbide produces acetylene (its formula is C2H2) mixed with water. In their work, they are more used by professional gas welders, since this method is explosive. Therefore, in everyday life, at car service stations, in various workshops, on ships, they use only bottled acetylene.

Cylinders with gas and oxygen. Oxygen does not burn, but increases combustion. When combined with various mineral or synthetic oils, including food grade oils, an explosion may occur.

Therefore, to service blue cylinders, almost medical sterility is required: clean gloves, well-washed or degreased keys, gearboxes.

Each type of gas has its own valve and reducer so that there is no additional reaction with the metal. Steel valves for acetylene, brass valves for oxygen and propane/butane. Reducers designed for a certain pressure are connected to them: acetylene - 2.5 MPa (5320 liters of gas in a cylinder), oxygen - 15 MPa (6000).

Porous material (charcoal) is poured into white cylinders and acetone is poured, and only after that acetylene is pumped. Inside, another chemical reaction takes place and additional acetylene is produced.

How to cook with gas welding? The mixing of oxygen with gases is of the same type. In the cutter, the flame enhancer is combined with ethine and the vapor exits the burner nozzle after being ignited by blue fire.

Welding differences

Hot setting of metals is carried out by the following methods:

Torch pitch to the left. Suitable for thin and high melting steel. The burner with the right hand of the worker moves to the left, and the welding wire is slightly further than the flame along the line of the future connection;

Movement to the right. The lever with the flame moves along the specified route, and the additive follows the burner. The energy of the flame is less dissipated, and the opening of the seam from this is not a right angle, but only 60-70 degrees.

It is used for iron from 3 mm and above, as well as with high thermal conductivity. In both cases, the diameter of the additive is consistent with the thickness of the bonded iron - half as much.

One practical subtlety of the Fouché and Picard method is the melt baths. If you cook metal correctly, then the bath constantly follows the burner. She is an indicator of quality welding.

At the place where the melting temperature arose, the metal, as it were, becomes liquid. It is at this moment that the filler wire enters the steel, it also melts, and this “river” flows along the seam. In it, the additive melt plays an important role as a seam-reinforcing material. The bath firmly holds thin strips and pipes made of steel with a low carbon content and alloying below five percent.

Differences in the connection of various seams:

• horizontally and ceilings, the right method is selected when the metal does not pour from the "bath";
• vertically and inclinations - by the left method;

This distinguishes the use of gas welding in various industries.

Photo of gas welding of metals