The gas welding process is the welding of metals. Economic component of gas welding

And cutting metals allows you to connect parts together metal structures in industry and everyday life. It's such technological process, in which a flammable gas substance with pure oxygen, under the influence of high temperatures, adheres to the edges of surfaces. The distance between them is filled with molten material, the source of which is the filler wire.

Advantages and disadvantages of gas welding

Gas welding - quite simple technology which has many positive aspects:

• Possibility to carry out welding work offline. This does not require a powerful source of energy.
• Availability of simple oversized equipment that is easy to transport.
• The welding process is adjustable. The gas burner allows you to vary the operating high temperature, heating speed and fire angle.

And also great possibilities of use: processing is used to connect elements of products made of carbon steel, lead, copper, cast iron, brass, bronze, silumin, aluminum and its alloys.

There are also disadvantages when carrying out welding work:

• Large heating area, creating conditions for deformation of neighboring elements.
• The gas welding process is a high-risk job. Compressed oxygen and flammable mixtures require precautions.
• Gas welding is intended for metals up to 5 mm thick.
• Lack of automation gas burner.
• High demands on the welding profession.

Types of gases used

Gas welding and metal cutting are aimed at local melting of a section of a part. Used as a combustible material different types. Their choice is determined by many factors. The main ones are the temperature of the fire and the amount of heat during combustion. There are several chemicals used in welding.

The most important element for soldering and cutting. It is used as a catalyst necessary to activate metal processing processes. It is characterized by the absence of color and odor, poor solubility in water and alcohol. Oxygen is an active chemical compound. It is kept in special containers under constant pressure. For oxygen welding, three types of technical gas are used. Each species depends on the purity of oxygen. This property affects the quality of parts processing.

Acetylene

The most common type, as it provides a high temperature compared to other flammable substances. It is formed on the basis of calcium carbonate with water. The chemical absorbs moisture from the atmosphere and breaks down under its influence, so the compound is stored in closed drums. Acetylene is explosive. However, this quality disappears if the mixture is dissolved in liquid.

Hydrogen

It is odorless and colorless. Becomes explosive on contact with air. The chemical element is stored in steel cylinders under pressure.

Coke gas

It is formed through the processing of coal. This is a colorless mixture of flammable substances with a pronounced hydrogen sulfide odor, which is transported through pipelines.

They are based on methane, extracted from the bowels of the Earth.

Gasoline and kerosene

Oil refining industry products. They appear as colorless liquids with an odor that evaporate easily. The gas burner feeds them through evaporators to produce steam.

It is subject to purification, as it consists of hydrocarbons and carbon monoxide. It is a by-product of oil refining plants.

Materials suitable for gas welding

Gas welding is indispensable in industry, construction, agriculture. It allows you to fasten a large number of metals.

Welding cast iron is necessary to eliminate defects, cracks, and broken parts of the product. The gas burner should have a low flame to avoid graininess weld seam.

Soldering bronze involves the use of a reduction flame. The work uses wire identical to the material being welded.

Copper processing does not require a gap between the edges. This is due to the fluidity of the material, which can complicate the gas welding process.

Carbon steels can be joined using different welding methods. The seams become coarse-grained due to the use steel wire low carbon.

Necessary equipment for gas welding

Gas welding equipment is used to join or cut metal elements under high temperature. It involves the use of different types of devices and accessories, depending on the type of work performed. Several components are used to process metal.

Water or liquid seal

Protects parts of devices from the backlash of the welding flame. This can happen when the gas flow rate is less than the combustion speed, or when the burner mouthpiece passages are clogged. All generators are equipped with this safety device.

Gas cylinders

Special cylindrical tanks with valves for storing and transporting chemicals. You can tell what type they contain by color.

Gearbox

Reduces gas pressure or keeps it at a certain level. The device is available in direct and reverse action. This is an important element of gas equipment that determines the performance of the entire system. There are different types of devices, including an oxygen reducer. It is adapted to aggressive environments and has blue markings.

Gas hose

Provides supply of flammable liquids. It is made using special technology. This is a multi-layer product that can withstand aggressive environments, with an internal diameter of no more than 16 mm. Depending on the category, hoses are marked red, yellow and blue.

It is the main part of welding equipment. It produces a flame, which is necessary for heating and melting metal. By design, the product comes in two types: injection and non-injection. The gas burner operates at different powers. The choice depends on the amount of gas supplied per unit time.

Special table

Increases the welder’s work convenience, as it performs several functions:

• fixes workpieces;
• stores auxiliary tools;
• is a ground loop.

The design may have a rotating or static tabletop.

Gas cutters

Dismantling metal structures and cutting rolled products is impossible without a gas cutter. Models of such a device have the same operating principle, but differ in size, design, and the presence of additional parts. Using a gas cutter, you can work with workpieces of large thickness. Cutting occurs due to the fact that the combustion temperature is less than the melting temperature.

The process is conventionally divided into periods:

1. The treated area is heated to the desired temperature. To produce a flame, oxygen is mixed with a flammable substance in a certain dosage.
2. Oxygen promotes deoxidation of the metal, combustion products are removed from the working area.

There are two types of gas cutter design:

• Injection - two-pipe, when technical oxygen is divided into two streams.
• Injectorless, or three-pipe, in which the oxygen and gas flow moves through different tubes, mixing inside the head.

Technological process of gas cutting

In the manufacture of metal structures, not only gas welding is used, but also metal cutting. It allows you to work with the following workpieces:

• discs, rings;
• contour elements combining straight and curved lines made of steel up to 200 mm thick:
• parts of complex configuration;
• sheets more than 4 mm thick;
• from No. 16;
• from No. 20.

To obtain a high-quality cut, the metal surface is first cleaned of dirt, paint, oil or rust. Metal cutting is a thermal processing method divided into stages:

• The heater brings the temperature to 1100 0 C.
• A gas burner supplies oxygen to the work area.
• The jet, in contact with the metal, ignites. The flame core should be located at a distance of 1 to 1.5 mm from the surface to be treated.
• Under stable gas supply conditions, the flow easily cuts the workpiece. The speed of the jet depends on the chemical composition of the material being cut.

Safety precautions

Gas welding and cutting cannot be done without following safety regulations. While working, a welder is exposed to all sorts of potential hazards. Comprehensive precautions:

The following protection is needed from electric shock:

• Grounding the device.
• Insulation of conductive parts of equipment.
• Dry, undamaged clothing.
• Exclusion of work in wet weather.

Eye protection requires the use of a special mask with light filters.

Gas welding poses a risk of burns, explosions and fires. The following will help you avoid an emergency:

• Equipment for workwear.
• Absence of open combustible and flammable substances in the work areas.
• Availability of fire extinguishing equipment.
• Compliance with the technological regime.

The following are used against poisoning by toxic fumes:

• Respirators.
• Effective ventilation in the room.
• Masks similar to gas masks.

>> >> >>Gases for gas welding

Gases for gas welding and metal cutting. Gas mixtures for welding

As flammable gases for gas welding Acetylene, hydrogen, natural gas and others are used. Gas mixtures are also used for welding, such as petroleum gas, propane-butane gas mixture, and pyrolysis gas. In addition, vapors of flammable liquids - gasoline and kerosene - are used.

The table shows the most common gases and gas mixtures for gas welding and gas cutting, indicating their main properties and scope of application:

Gas	Density under normal conditions, kg/m2	Heat of combustion under normal conditions, kJ/m 3	Flame temperature in a mixture with oxygen, °C	Acetylene replacement rate	Explosion limit (%) when mixed with:		Application area
					air	oxygen
Acetylene	1,09	529200	3200		2,2-81,0	2,3-93,0	All types of gas welding
Hydrogen	0,084	10080	2400		3,3-81,5	2,6-95,0	For welding thin metal (up to 2mm), welding cast iron, aluminum, brass
Coke	0,4-0,55	14700-18480	2000-2300		4,5-40,0	40,0-75,0	For soldering, welding of low-melting metals, oxygen cutting
Oil	0,87-1,37	36540-62160	2000-2400		3,8-24,6	10,0-73,6	Same
Methane	0,67	33600	2400-2700		4,8-16,7	5,0-59,2	Same
Propane	1,88	87360	2600-2800		2,0-9,5	2,0-48,0	Soldering and welding of non-ferrous metals, gas cutting, welding of steels up to 6 mm thick, straightening, fire cleaning
Butane	2,54	116760	2400-2500	0,45	1,5-8,5	2,0-45,0	Same
Petrol	0,7-0,76	42840	2400		0,7-6,0	2,1-28,4	Gas cutting of steels, soldering and welding of low-melting metals
Kerosene	0,82-0,84	42000	2300		1,4-5,5	2,0-28,0	Same

The choice of one gas or another for welding depends not only on the temperature of the flame, but also on the amount of heat (calorific value) that is obtained during its combustion. The acetylene replacement coefficient indicated in the table is the ratio of the replacement gas consumption to the acetylene consumption at the same effective thermal power. This coefficient is necessary if it is necessary to replace acetylene with another flammable gas.

Acetylene for gas welding

Acetylene is one of the most common gases used for gas welding. Acetylene has become most widespread due to the fact that the acetylene-oxygen gas flame has the highest temperature compared to other flammable gases and gas mixtures (see table above).

Acetylene is formed by the interaction of calcium carbide CaC 2 with water. Calcium carbide is able to absorb moisture from the atmosphere and decompose under its influence. Therefore, it is stored in sealed steel roofing drums. The capacity of such drums is 100-130 kg. Calcium carbide is obtained by fusing coke and burnt lime in electric furnaces:

CaO + 3C = CaС 2 + CO

Acetylene C 2 H 2 is a chemical compound of carbon and hydrogen. To produce acetylene, they use carbide and water. The chemical interaction of calcium carbide and water proceeds intensely, with a large release of heat Q:

CaC 2 + 2H 2 O = C 2 H 2 + Ca(OH) 2 + Q

From 1 kg of calcium carbide you can get up to 300 liters of acetylene. Under normal conditions, acetylene is colorless and has a strong, specific odor. Acetylene is lighter than air, its density is 1.09 kg/m3.

Acetylene is explosive if it is mixed with air and its concentration is 2.2-81% by volume. When mixed with oxygen, acetylene is explosive at a concentration of 2.8-93% by volume. The most explosive are acetylene-oxygen mixtures containing 7-13% acetylene.

When dissolved in liquid, the explosiveness of acetylene is significantly reduced. In practice, acetylene is dissolved in acetone, 1 liter of which can dissolve up to 20 liters of acetylene. We talked about this in the article: "".

In addition to calcium carbide, sources of acetylene include natural gas, oil and coal. Acetylene obtained from natural gas is called pyrolysis acetylene.

Hydrogen for gas welding

Hydrogen is a colorless, odorless gas. When mixed with oxygen or air, it forms an "explosive gas" which is explosive. Therefore, in the case of using hydrogen for welding metals, it is necessary to strictly adhere to safety rules during its storage, transportation and use.

Hydrogen is stored and transported in steel gas-welding cylinders at a pressure not exceeding 15 MPa. It can be obtained by decomposing water into hydrogen and oxygen using electrolysis. Hydrogen is also synthesized in special hydrogen generators by chemical reaction sulfuric acid H2SO4 and zinc, or iron filings. In this case, zinc or iron sulfates are formed, and the released hydrogen accumulates inside the generator.

Coke gas for welding

Coke oven gas is a colorless mixture of flammable gases with a pungent odor of hydrogen sulfide. Coke oven gas is produced in the process of producing coke from coal. The composition of coke oven gas includes hydrogen, methane and other hydrocarbons. This gas is transported through pipelines.

City gas and natural gas for welding

City gas consists of several gases: methane 70-95%, hydrogen, the volume fraction of which can reach 25%, heavy hydrocarbons with their volume fraction up to 1%, nitrogen 3% and carbon dioxide up to 1%. City gas is transported through pipelines under a pressure of 0.3 MPa.

Natural gas is extracted from gas fields. Its basis is methane CH 4, the content of which in natural gas is 93-99%.

Petroleum gas, natural gas and propane-butane mixture for gas welding

Pyrolysis gas is a mixture of flammable gases formed during the breakdown of oil, fuel oil and other petroleum products when exposed to high temperatures. Pyrolysis gas contains sulfur compounds, which cause corrosion of mouthpieces. Therefore, this gas undergoes thorough purification before use.

Petroleum gas is a by-product of oil refineries. It is mainly used for cutting and and.

Propane-butane mixtures are colorless and odorless mixtures. They consist of propane C 3 H 8 and butane C 4 H 10. This mixture has the highest calorific value, i.e., when it burns, the most is released. large quantity warmth.

Gasoline and kerosene for gas welding

Gasoline and kerosene are products of petroleum refining. They are colorless liquids with a specific odor and evaporate easily. They are used in gas-flame processing, supplying them in the form of vapor. To do this, special evaporators are provided in welding cutters or torches that convert gasoline and kerosene from a liquid state to a vapor state. Vaporizers are heated by an auxiliary flame or by electricity.

Oxygen for gas welding

Oxygen for gas welding is necessary to ensure the combustion of flammable gases or flammable liquid vapors. Oxygen is slightly heavier than air and its density is 1.33 kg/m3. Oxygen is very chemically active and it supports the combustion of gases during gas welding, generating a large amount of heat.

Oxygen is stored and transported in oxygen gas cylinders under a pressure of 15 MPa. A 40L cylinder is capable of storing up to 6m3 of oxygen under a pressure of 15MPa. In addition to gas cylinders, oxygen can be supplied to the welding site in a liquid state in special containers.

To convert liquid oxygen into gaseous oxygen, gasifiers and pumps with evaporators for liquid oxygen are used. Oxygen is supplied through a gas pipeline. Transporting oxygen in a gaseous state makes it possible to reduce the volume of shipping containers by approximately 10 times, because From 1 liter of liquid oxygen, under normal conditions, 860 liters of gaseous oxygen are obtained.

According to GOST 5583, technical oxygen is used for oxy-fuel and metal cutting, which comes in three grades. The first grade has a purity of 99.7% oxygen. Second grade with a purity of 99.5 oxygen. The third grade contains at least 99.2% oxygen by volume.

The purity of oxygen is of great importance for gas welding and metal cutting. When oxygen purity decreases by 1%, oxygen consumption decreases and increases by approximately 1.5%.

Gas welding with full responsibility can be called the queen of welding fields.

Everything about it is good: it is easy to use, equipment for gas welding is quite inexpensive, and economical in consumption electrical energy, the list of advantages goes on.

If we started with the pros, it would be fair to dwell on the cons. The disadvantage of the heating rate of the metal is that it is low.

In addition, the working area with this method is “spread out” - a very large heating zone for the metal, due to which a lot of thermal energy is lost. There is also such an unpleasant phenomenon as warping.

Thus, the productivity of the working process is not very high, and with increasing thickness of the edges of the workpieces being welded, it decreases even more.

Therefore, if your metal sheet is more than six millimeters thick, start thinking about using gas welding somewhere else. It is better to cook a thick edge, for example, using the arc method.

Injector and non-injector burner.

Gas welding is not the most expensive welding method, this is well known. But the gas for welding is acetylene and oxygen, which they like to use as a welding gas mixture, still cost more than electricity.

And if you add the rather high risks of explosions and serious fire danger that instantly arise if flammable liquids, gases, oxygen cylinders and elemental calcium carbide are handled incorrectly, the enthusiasm decreases a little.

Gas welding technology is excellent for a wide range of welding jobs: from joining aluminum and steel parts to working on bronze and cast iron.

Let us immediately note that gas welding is capable of almost all metals, including such capricious metals as copper, lead or cast iron: they are welded more easily by gas technology than by any other.

Technical aspects of the gas welding process

The peculiarity of gas welding is the democratic nature of its seams, which can be made in all positions in space - from the bottom to the ceiling.

The most difficult situation is with ceiling seams, since in this case the molten metal must be maintained and quickly distributed along the entire length of the seam using the increased pressure of the gas mixture from the flame.

The most popular seams with this method are butt seams. Gas welding is not friendly with overlapping and T-joints. The fact is that both types of seams require extremely high heating of the metal. In addition, this method has a high risk of severe warping.

If the edges of the workpieces are thin and beaded, they are cooked without using filler wire with the formation of continuous or intermittent seams, which can also be single- or multi-layer.

It is clear that before welding it is necessary to clean the edges and surfaces of metal workpieces in the most thorough manner.

One of the most important technical components of the gas burner is manipulation of the gas burner. The gas welding technique involves keeping the flame about 5 mm from the end of the core, without touching the metal surface.

The weld pool is formed under the pressure of gases on the liquid metal, they seem to inflate it around the edges.

The filler wire is immersed in the weld pool. The heating intensity of the working area can be changed. This is done by changing the angle of inclination of the copper mouthpiece of the burner to the surface of the workpiece. The dependence here is direct and understandable: the greater the angle of inclination, the higher the heating of the metal from the flame.

The torch mouthpiece should be moved along the seam. At the same time, it is necessary to monitor the condition of the weld pool: the metal in it must be protected by gas pressure from the unwanted effects of ambient air. This must be done to protect the metal from the oxide film.

The most popular methods

Welding in the lower position.

Gas welding methods can be described and listed in several thick volumes.

Let's take the most common of them:

Left welding

The left-hand method of gas welding is the most common among craftsmen of any qualification. Used to join metals with thin edges and low melting points. Left and right welding are two sides of the same coin, it’s easy to remember.

Right welding

The right welding method is suitable for working with metals with a thickness of more than 3 mm and high thermal conductivity. It should be noted that the weld seam during right-hand welding is of higher quality due to better protection of the metal by the flame.

The use of flame heat with the right method is more economical, and the process speed is almost 20% higher. To the same piggy bank of advantages you can add savings in gas costs of about 10%.

The filler wire must be taken with a diameter that is exactly half the thickness of the metal workpiece. The wire cannot be thicker than 8 mm.

Welding using through bead

This gas welding technology involves the gradual, step by step, movement of the flame to melt the upper edge of the hole in the workpiece and apply a layer of molten metal to the lower edge of the same hole.

First, the metal sheets are fixed vertically, leaving a gap between them half the thickness of the workpiece itself. The seam is formed in the form of a roller, which connects the parts. It is dense, without any pores or slag residues.

Welding using baths

Here the name speaks for itself. The principle of the method is the formation of more and more new pools along the seam. As soon as one of them is formed, the end of the filler wire is inserted into it, melts there, and then moves to the reduction section of the burner fire.

Meanwhile, the nozzle mouthpiece moves further along the seam - to the next section. Each new bath overlaps the previous one by approximately one third of the wire diameter.

This method is used to connect thin sheets when it is necessary to make butt or corner types of seams. This is a favorite type of welding for pipes made of low-alloy steel or low-carbon alloys.

Multilayer gas welding

It is used for very critical types of work, as it is characterized by rather low productivity, and welding gases are required here for large volume- the method is not cheap. In it, the lower layers are annealed during surfacing of the upper and subsequent layers.

The result is excellent forging of each layer before the formation of the next seam. This method significantly improves the quality of the weld metal.

The process occurs in short sections. Pay special attention to cleaning the surface of the underlying layer before applying the next one.

Oxidizing flame and deoxidation welding

Cylinders for gas welding.

This technology was created for joining parts made of low-carbon steel alloys. The flame here has a sharply oxidizing character, as a result of which iron oxides are formed in the weld pool. If there is oxidation, so-called deoxidation is also necessary.

This is achieved using a special filler wire with high proportions of manganese and silicon. An excellent method with productivity 10% higher than other methods.

Nuances with different seams and different metals

Horizontal seams are formed using the right-hand gas welding method. There are situations when the process is carried out from right to left with the mouthpiece at the bottom of the bath and the wire at the top. This way the seam is formed faster and easier, and the molten metal in the bath does not flow down.

Vertical seams, on the contrary, are made in the left way with a bottom-up direction. If the metal is thick, use a double bead seam.

Ceiling seams are one of the most difficult to perform. Here you first need to heat the edges of the workpiece, then until they melt, a wire is placed in the bath, which quickly melts.

The liquid metal in the bath is kept from flowing down by the pressure of the gases from the burner. Welding is done in the right way. It is best to use multi-layer seam technology with multiple passes.

Low carbon steel can be welded with almost any gas. It is important to select the correct filler wire: it must also be made from low carbon steel.

Alloy steels come in very different compositions. Therefore, there is not and cannot be a single method of gas welding for them. If the alloy is heat-resistant and stainless, parts made from it are welded using wire containing nickel and chromium.

There are certain brands that can only be welded using molybdenum as a filler wire.

Copper and its alloys always require a high flame. During melting, it is extremely fluid, so the gap must be kept minimal. In addition to copper wire, flux mixtures are used to deoxidize the weld metal.

Brass is a very difficult metal to work with due to its composition. There is a high risk of pore formation in the weld due to the volatility of zinc. This risk can be significantly reduced by supplying more oxygen to the burner mixer and using brass wire as an additive.

Bronze is another capricious alloy. During welding, it is important not to burn out its important elements from the composition: tin, silicon and aluminum. Therefore, the flame should be reducing, and the additive should be bronze with the addition of silicon, which will help further deoxidize the seam.

Advantages and disadvantages of welding with a gas torch

Gas welding of metals has a solid list of advantages:

• The method does not involve the purchase and use of complex and expensive equipment. It does not require, for example, an inverter or semi-automatic device.
• Consumables used in gas welding are widely available on the market; you can find any composition or model without difficulty.
• No special protective equipment is required, even when gas pipe welding.
• The main welding parameters are well regulated: the flame of any required power, the level of metal heating temperature.

Gas torch welding method.

There are some disadvantages too:

• Heating of the metal is too slow, especially in comparison with an electric arc.
• The heating zone around the gas burner is too large, resulting in a lot of energy being lost to no avail.
• The heat from the burner is diffuse and difficult to concentrate.
• The method is still more expensive than the electric arc method: the price of gases is higher than the cost of electricity.
• As the thickness of the workpiece edges increases, the speed of the work process decreases due to high heat dissipation.
• It is almost impossible to automate the process.

A few words about consumables

What gas is used for welding is not an unimportant question that you need to understand in order to make the right choice. The types of gases used vary and the choice depends on several factors.

Oxygen

Oxygen, for example, is completely colorless and odorless. It has a special role; it acts as a catalyst for metal melting processes during welding. Oxygen is stored and transported in cylinders with constant pressure. This is not an easy task, but it is quite doable.

The main thing is to know and follow the safety rules when handling oxygen cylinders and the gas itself. For example, the presence of technical oil can lead to fire: therefore, it is necessary to strictly exclude the slightest contact with such oil.

Gas burner flame.

In no case should there be a source of heat or direct sunlight in the rooms where cylinders are stored.

How to obtain welding oxygen: it is done quite simply - from atmospheric air using specialized equipment.

Oxygen is divided into three types based on purity:

• premium grade with a gas concentration of 99.5%;
• first grade with 99.2%;
• the second – with 98.5%.

Acetylene

This is the second most popular gas used in gas welding for both welding and cutting. It is also colorless and odorless. Acetylene may explode if pressurized or heated. It is made from calcium carbide and water.

Acetylene is not the best cheap gas, but its advantage makes it very popular among welders. It's all about the combustion temperature - it is remarkably high for acetylene, especially in comparison with cheaper gases such as methane, propane or kerosene vapor.

Flux and filler wire

These are the main participants in the process of weld formation. The filler wire must be absolutely free from the slightest signs of dirt or corrosion. Sometimes, instead of wire, you can use a strip of the same metal as the workpiece for welding.

Fluxes are necessary to protect the weld pool from the harmful effects of external factors. Most often as constituent elements flux mixtures take borax and boric acid, which can be applied directly to the workpiece to be welded or to the filler wire.

The only metal that can do without a flux mixture is carbon steel. Well, a special need for the presence of flux arises when welding copper, aluminum and their alloys.

Necessary equipment for gas welding

Water seal

This is a simple and effective protection of the pipe, acetylene generator and other elements from fire in the form of reverse draft from a gas burner. The water in this seal must be at a level that needs to be monitored. It is usually located between the burner and the acetylene pipe.

Gas cylinders

These cylinders are of different colors depending on the type of gas. A strict rule applies to all cylinders: never paint top part so that there is no contact between paint and gas. Another technical nuance: copper valves cannot be installed on acetylene cylinders due to the high risk of explosion from the interaction of acetylene and copper.

Hoses for various purposes

Hoses are needed for many things: supplying gases and hot liquids. In addition, they must work under pressure, so these are not garden hoses for watering a vegetable garden, but serious devices with special technical characteristics.

• with a red stripe for pressure up to 6 atmospheres;
• with a yellow stripe for flammable substances;
• with a blue stripe for pressure up to 20 atmospheres.

Gas-burners

Gases and vapors from flammable liquids are mixed in the burner mixer. They are produced in a huge variety, divided into injection and burners without it, of different powers and so on.

Gearbox

A necessary item where there is high gas pressure.

Reducers reduce the pressure of the gas leaving the cylinder. They come in two types: direct and reverse acting. Advanced models with silver plating are available for working with liquefied gas: they do not allow such gas to freeze at the outlet of the cylinder.

Gas station

This is a special work table for welding. The best option post - a table top with the ability to rotate and fix it. A good post is equipped with exhaust ventilation and a good storage system for welding tools.

Gas welding: hybrid version with semi-automatic

This technique adds the use of an electric arc and a shielding gas - most often argon. In this situation, the technology can well be called hybrid.

Gas welding seams.

Here are the steps involved:

• connecting the device to the network;
• fixing the filler wire through the hole in the torch;
• adjusting gas pressure using a reducer;
• determination and setting of filler wire feed speed;
• regulation of other parameters - welding current and voltage;
• fixing the burner at an angle to the surface of the workpiece before igniting the burner;
• start of welding.

It should be noted that the technical characteristics of all Supplies, as well as equipment elements, are clearly and clearly stated in GOSTs. In other words, the gas welding process is well regulated.

For example, the following parameters fall under GOST standards:

• characteristics of the acetylene generator;
• hose types;
• gas pressure regulated by a reducer;
• type of gas burners;
• types of filler wire;
• standards for gas cylinders, etc.

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

Gas welding is used in the manufacture and repair of products made of thin-sheet steel 1-3 mm thick, installation of pipes of small and medium diameters, connections and assemblies made from thin-walled pipes, welding of products made of aluminum and its alloys, copper, brass and lead, welding of cast iron with using cast iron, brass and bronze rods as an additive, surfacing 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. It is most widely used in construction and installation work, in agriculture and in repair work.

To perform welding work, it is necessary that the welding flame has sufficient thermal power. The power of the burner flame is determined by the amount of acetylene passing through the burner in one hour and is adjusted by the burner tips. The flame power is selected depending on the thickness of the metal being welded and its properties. The amount of acetylene per hour required per 1 mm of the thickness of the metal being welded is established by practice.

Example. When welding low-carbon steel, 100-130 dm3 of acetylene per hour is required per 1 mm of the thickness of the metal being welded.

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

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

The heating rate is regulated 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 burner mouthpiece (b)

The size of the angle 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 torch mouthpiece to the surface of the metal being welded. At the beginning of welding, for better heating of the metal, the inclination angle is set larger, then, as the metal being welded warms up, it is reduced to a value corresponding to the given thickness of the metal, and at the end of welding, it is gradually reduced in order to better fill and prevent burnout of the metal.

The burner handle can be located along the axis of the seam or perpendicular to it. This or that position is selected depending on the working conditions (conveniences) of the gas welder, so that the welder’s hand is not heated by the heat emitted by the heated metal.

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

Method 1, in which the flame is periodically diverted to the side, is not recommended for use in gas welding, since this may cause oxidation of the molten metal with atmospheric oxygen. 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 additive can perform the same oscillatory movements, but in the direction opposite to the movements of the end of the burner mouthpiece.

It is not recommended to remove the end of the filler wire from the weld pool and especially from the recovery zone of the flame. The movements made by the end of the torch tip 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 down position, the crescent motion is most common.

Gas welding technique

Gas welding is a universal method, but when performing it, you must remember that a fairly large area around the welded joint is exposed to heat. Therefore, it is impossible to exclude the occurrence of warping and the development of internal stresses in structures, and they are more significant than with other welding methods. In this regard, gas welding is more suitable for such joints for which a small amount of deposited metal and low heating of the base metal are sufficient. First of all, we are talking about butt, corner and end connections (regardless of their spatial position - bottom, horizontal, vertical or ceiling), while T-joints and overlaps should be avoided (although they can also be carried out).

In order for the weld to have high mechanical properties, the following steps must be performed:

– prepare the edges of the metal;

– select the appropriate burner power;

– adjust the burner flame;

– take the necessary filler material;

– correctly orient the torch and determine the trajectory of its movement along the seam being performed.

As with arc welding, with gas, the edge of the metal being welded must be prepared. They are cleaned (20–30 mm on each side) of rust, moisture, oil, etc. To do this, just warm the edges. In the case of welding non-ferrous metals, mechanical and chemical methods cleaning.

When making butt joints (Table 42), you should remember some rules for cutting edges:

– when welding thin sheet metal (up to 2 mm), additives are not used – it is enough to flange the edges, which then melt and form a bead weld. This option is also possible: butt weld the edges without cutting or gap, but using filler material;

– when welding metal with a thickness of less than 5 mm, you can do without bevel of edges and carry out one-sided gas welding;

– when joining metal with a thickness of more than 5 mm, the edges are beveled at an angle of 35–40° so that the total opening angle of the seam is 70–90°. This will allow the metal to be welded to its full thickness.

Table 42. PRELIMINARY PREPARATION OF THE EDGES OF THE METAL TO BE WELD WHEN MAKING BUTT JOINTS

Note: a – gap size; a1 – magnitude of dullness; S and S1 – metal thickness.

When making corner joints, filler material is not used, and the seam is formed by melting the edges of the metal.

Lap and T-joints are allowed only when welding metal up to 3 mm thick, since with greater thickness the local heating of the metal is uneven, which leads to the development of significant internal stresses and deformations, as well as the appearance of cracks in both the weld metal and the base metal.

To ensure that the parts do not move during the welding process and the gap between them does not change, they are fixed either with special devices or with tacks. The length, quantity and spacing between the latter depend on the thickness of the metal, the length and configuration of the seam:

– if the metal is thin and the seams are short, the length of the tacks is 5–7 mm with an interval between them of 70–100 mm;

– if the metal is thick and the seams are long, then the length of the tacks is increased to 20–30 mm, and the distance between them is increased to 300–500 mm.

During the welding process, the torch flame is directed at the metal so that it falls into the reduction zone and is 2–6 mm from the core. When welding low-melting metals, the torch flame is mainly oriented towards the filler material, and the core zone is moved to an even greater distance from the weld pool.

When welding, it is necessary to regulate the rate of heating and melting of the metal. To do this, resort to the following actions (Fig. 91):

– change the angle of the mouthpiece;

– manipulate the mouthpiece itself.

Rice. 91. Methods for adjusting the rate of heating and melting of metal by changing: a – the angle of inclination of the mouthpiece; b – trajectories of movement of the mouthpiece and wire; 1 – when welding thin sheet metal; 2, 3 – when welding thick sheet metal

When welding, you must ensure that:

– the flame core was not in contact with the molten metal, since the latter could become carbonized as a result;

– the weld pool was protected by a torch zone and a reduction zone, otherwise the metal would be oxidized by atmospheric oxygen.

When using a gas burner, you must follow the rules for handling it:

1. If the burner is in good condition, then the flame it produces is stable. If any deviations are observed (the combustion is unstable, the flame comes off or goes out, backfires occur), it is necessary to reverse Special attention on the burner components and adjust it.

2. To check the injection burner, connect the oxygen hose and attach the tip to the body. After tightening the union nut, carefully unscrew the acetylene valve, set the appropriate oxygen pressure using the oxygen reducer, and then open the oxygen valve.

3. If a finger attached to the acetylene nipple is stuck, this means that oxygen is creating a vacuum. If this does not happen, the injector, mixing chamber or mouthpiece may be clogged. They should be cleaned.

4. Repeat the vacuum (suction) check. Its value is determined by the gap between the end of the injector and the entrance to the mixing chamber. By unscrewing the injector, the gap is adjusted.

There are two methods of gas welding (Fig. 92):

Rice. 92. Methods of gas welding (the arrow indicates the direction of welding): a – left; b – right; 1 – filler wire; 2 – welding torch

– left-hand welding, in which the torch is moved from right to left and held behind the filler wire. In this case, the welding flame is oriented towards the seam that has not yet been welded. This method does not sufficiently protect the metal from oxidation and is accompanied by partial loss heat and gives low welding performance;

– right-hand welding, in which the torch is moved from left to right and held in front of the filler wire. In this case, the flame is oriented towards the completed weld and the end of the filler wire. This method makes it possible to direct a larger amount of heat to melt the metal of the weld pool, and the oscillatory transverse movements of the nozzle and wire are carried out less frequently than with the left method. In addition, the end of the filler wire is constantly immersed in the weld pool, so it can be used to stir it, which promotes the transition of oxides into slag.

The right method is usually used if the thickness of the metal being welded exceeds 5 mm, especially since in this case the welding flame is limited on the sides by the edges of the product, and at the rear by a bead of deposited metal. Thanks to this, heat loss is reduced and it is used more efficiently.

The left method has its advantages, since, firstly, the weld is always in the welder’s field of vision and he can adjust its height and width, which is of particular importance when welding thin sheet metal; secondly, when welding, the flame can spread over the surface of the metal, reducing the risk of burnout.

When choosing one or another welding method, you must also be guided by the spatial position of the weld:

– when making the bottom seam, the thickness of the metal should be taken into account. It can be applied both right and left. This weld is the easiest because the welder can observe the process. In addition, the liquid filler material flows into the crater and does not pour out of the weld pool;

– for a horizontal seam, the right method is preferable. To prevent liquid metal from leaking out, the walls of the weld pool are made with some distortion;

– for a vertical seam on the rise - both left and right, and for a vertical seam on the descent - only the right method;

– it is easier to apply a ceiling weld in the right way, since the flame flow is directed towards the seam and prevents liquid metal from flowing out of the weld pool.

A method that guarantees high quality welds is pool welding (Fig. 93).

Rice. 93. Welding with pools: 1 – welding direction; 2 – trajectory of movement of the filler wire; 3 – trajectory of the mouthpiece

This method is used for welding thin sheet metal and pipes made of low-carbon and low-alloy steels with lightweight seams. It can also be used when welding butt and corner joints with a metal thickness of up to 3 mm.

The pool welding process proceeds as follows:

1. Having melted metal with a diameter of 4–5 mm, the welder places the end of the filler wire into it. When its end is melted, he introduces it into the reducing zone of the flame.

2. At the same time, the welder, slightly moving the mouthpiece, makes circular movements with it to form the next bath, which should slightly (by about a third of the diameter) overlap the previous one. In this case, the wire must continue to be kept in the reducing zone to prevent its oxidation. The flame core must not be immersed in the weld pool, otherwise carburization of the weld metal will occur.

When gas welding, seams can be single or multi-layer. If the metal thickness is 8-10 mm, the seams are welded in two layers, with a thickness of more than 10 mm - three layers or more, and each previous seam is first cleaned of slag and scale.

Multi-pass welds are not used in gas welding, since it is very difficult to apply narrow beads.

During gas welding, internal stresses and deformations arise, since the heating area is more extensive than, for example, during arc welding. To reduce deformations, appropriate measures must be taken. For this we recommend:

– heat the product evenly;

– select an adequate welding mode;

– evenly distribute the deposited metal over the surface;

– adhere to a certain order of sutures;

– do not get carried away with doing tacks.

Various methods are used to combat deformation:

1. When making butt joints, the weld is applied using a reverse-step or combined method, dividing it into sections 100–250 mm long (Fig. 94). Since the heat is evenly distributed over the surface of the weld, the base metal is practically not subject to warping.

Rice. 94. The sequence of applying a seam when welding butt joints: a – from the edge; b – from the middle of the seam

2. Reduction of deformations is facilitated by their balancing when the subsequent seam causes deformations opposite to those caused by the previous seam.

3. The method of reverse deformation is also used, when before welding the parts are laid so that after welding, as a result of the action of deformation, they take the desired position.

4. Preheating the products being joined also helps combat deformation, resulting in a smaller temperature difference between the weld pool and the product. This method works well when repairing cast iron, bronze and aluminum products, as well as if they are made of high-carbon and alloy steels.

5. In some cases, they resort to forging the weld (in a cold or hot state), which improves the mechanical characteristics of the seam and reduces shrinkage.

6. Heat treatment is another way to eliminate developed stresses. It can be preliminary, carried out simultaneously with welding, or the finished product is subjected to it. The heat treatment mode is determined by the shape of the parts, the properties of the metals being welded, conditions, etc.

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