What gas is not used in gas welding?

What gas is used in welding?

The possibility of semi-automatic welding of materials in a carbon dioxide environment was discussed in the mid-twentieth century. This technique was developed by N.M. Novozhilov. and Lyubavsky K.V. - Soviet researchers. This welding method, due to the low cost of carbon dioxide and its high degree of productivity, has become quite popular in the construction and manufacturing industries, and, of course, in everyday life.

The essence of gas welding technology

According to this technique, carbon dioxide, which provides protection in the area being connected, is divided into O2, carbon monoxide, under the influence of the high temperature of the arc. As a result, the flow of the resulting gas mixture protects the material welding zone from the negative effects of environmental air and interacts with carbon and iron.

To prevent the oxidation of CO2, manganese and silicon are introduced into the rod for gas welding, which are more chemically active than iron; they are oxidized first. Therefore, as long as Mn and Si are present at the junction of metal products, carbon and iron will not be oxidized.

To obtain high-quality welds when welding carbon steels, the manganese/silicon ratio is 1/2. The resulting oxides of manganese and silicon do not dissolve in the weld pool during work; they form a low-melting compound after reacting with each other. This compound is easily removed from metal in a liquid state.

Features of welding work in a carbon dioxide environment

Semi-automatic welding in a carbon dioxide environment is performed with direct current of reverse polarity, since direct polarity current negatively affects the stability of the arc (the weld will have defects).

Welding can also be done using alternating current, but then an oscillator must be used in the circuit.

Gases used for gas welding

There are several options for types of welding. They differ from each other in the technology of forming a weld pool, which has a high temperature, the purpose of which is joining, cutting metals and their alloys. This can be done with a gas flame, ultrasound or electric arc. The principle of joining metals is based on melting the edges of individual metal structures to further join them together, resulting in a weld.

Depending on the gas used for welding, the temperature will differ. For example, when interacting with calcium carbide H2O, acetylene is released. During the reaction of this element with oxygen, the flame temperature can reach more than 3000ºC.

Welding gases are all butanes, propanes, benzenes, MAF, kerosenes, etc. When using any gases for welding, the presence of oxygen is required - this is a combustion catalyst. O2 must be pure and high quality. The maximum temperature will depend on this.

Gas composition

The gas composition must contain pure oxygen, which makes it possible to obtain the maximum combustion temperature and important flame indicators. The completeness of combustion of combustible components will depend on the quality of this component, and the oxidation and reduction characteristics obtained by the flame will depend on its quantity.

There are special requirements for gas storage conditions. The use of special containers (cylinders) is mandatory because:  

• most welding gases are toxic;
• technical oxygen is a powerful catalyst.

If you use atmospheric oxygen, the welds will not be smooth. Moreover, after melting and subsequent joining, the metal will lose its original qualities. The use of standard oxygen, which is contained in the atmosphere, is not effective enough. It contains various impurities that significantly reduce the rate of combustion of the components, and this accordingly affects the temperature of the burner flame.

Gases for welding

Important! It is necessary to observe the proportions of gas mixtures when using any type of gas. The choice itself will depend on the material being welded. For example, to join steel samples, the gas composition must contain 18% carbon dioxide, and to join stainless steel materials, the mixture must consist of 98% argon.

Mechanized gas shielded welding involves the use of active, inert gases. They do not dissolve in metals and are not poisonous.

Types of gases:

• N2 is nitrogen, a colorless, odorless gas. Used for joining copper materials. There are four types of nitrogen with different contents of the substance.
• He – helium, a colorless, odorless gas, lighter than air. There are two types of helium: technical, high-frequency. Due to its high cost, this gas is less in demand on the market. Helium is intended for joining samples of aluminum, pure metals, and steel.
• Ar – argon, a colorless, odorless gas, weighs 1.5 times more than air, does not burn. There are two types of this gas: 1st grade (for samples made of aluminum, steel), premium grade (for semi-automatic welding in a shielded gas environment of samples from rare metal alloys).

Active gases protect the welding area from air. They react and dissolve in metals.

• Carbon dioxide (CO2) is characterized by increased oxidative characteristics and has a specific odor. Its mass is 1.5 times that of air, it dissolves in H2O. I distinguish three types of this gas, which are used for welding cast iron materials, low and medium carbon metal alloys, corrosive, low alloy steel samples. Important to remember! Gas shielded welding does not involve the use of carbon dioxide.
• Oxygen O2 is a fairly powerful catalyst, colorless, tasteless, odorless, does not burn, but supports combustion. Used in combination with inert components.

The most popular gas mixtures, which improve the quality of the seam, improve the joining process itself:

• carbon dioxide plus oxygen
• argon plus helium
• carbon dioxide plus argon
• carbon dioxide "plus" oxygen "plus" argon
• oxygen plus argon

Advantages and disadvantages of gas welding

Gas shielded welding is characterized by melting of the material. The process itself is based on the connection of individual elements of preheated metal until melting. To do this, a high-temperature burner flame is used, which is formed during the combustion of a gas composition with oxygen. The gap between the samples is filled with pre-melted metal wire.

• fairly simple welding technology;
• there is no need to purchase expensive, technically complex equipment;
• no need for a special power source;
• The welder has the ability to adjust the rate of heating and cooling of the material being joined by welding, changing the power and the position of the burner flame relative to the point being welded.

Source: https://electrod.biz/tehnologii/gaz-dlja-svarki.html

Gas welding: what gases, wire and fluxes are used for it?

Gas welding is the process of joining metals by heating the welded edges with a high-temperature flame formed by the combustion of a mixture of flammable gas and oxygen. Oxygen in this case acts as a catalyst.

Oxygen

At ordinary temperature and pressure, the gas is colorless and odorless. For welding work, technical oxygen is in demand, extracted from the air and processed in air separation units, of three grades:

• highest, purity by volume – 99.5%;
• 1st – 99.2%;
• 2nd – 98.5%.

The remainder is argon and nitrogen.

When flammable gases or vapors of flammable liquids are mixed with oxygen in certain proportions, intense combustion begins, releasing a large amount of heat.

To store technical oxygen, special blue-painted cylinders with a volume of 40 dm3 (40 l) are used. The inscription “Oxygen” is in black. The mass of such a cylinder without a cap and shoe is 60 kg.

Attention! Extreme caution must be used when using oxygen cylinders due to the high pressure inside them. There is another danger - high gas activity upon contact with organic substances (oils or fats). Pure oxygen is a very strong oxidizing agent, which, when interacting with hydrocarbons, causes a fire with a large release of heat, which provokes an explosion.

How much oxygen is contained in a 40 liter cylinder?
The nominal gas pressure in the cylinder at +20°C is 14.7 MPa (according to GOST 5583). Under such conditions, it holds 6.3 m3 of oxygen, and its mass is 8.3 kg.

Acetylene

This gas is the first and main representative of alkynes of the homologous series. According to the IUPAC international nomenclature of chemical compounds, its name is ethin. Formula – C2H2. Acetylene is colorless, flammable, and explosive when mixed with air. The gas, due to the triple bond in the molecule, easily participates in addition reactions. During its combustion, a significant amount of heat is released, which is used in an acetylene torch.

Acetylene cannot be used in its pure form, since in its free form it is very explosive. To fill the container, it is broken into small particles by dissolving in acetone. This method allows you to reduce the explosion hazard of acetylene and fill a sufficiently large amount of gas into the cylinder. They use cylinders painted white, the inscription is red. During operation, it is necessary to maintain the vertical position of the cylinder and leave residual pressure, which will reduce losses.

How much acetylene is contained in a 40 liter cylinder?
Technical acetylene corresponding to GOST 5457 is pumped into the cylinder, and the following is placed in it:

• by volume – 5.3 m3;
• by mass – 5 kg of gas.

Preparation of acetylene from calcium carbide

A common way to produce acetylene for welding is from water and calcium carbide in acetylene generators during the welding process.

Calcium carbide is a hard, lump-like material that has a distinct garlicky odor. A characteristic feature of this material is its intense absorption of water. Technical calcium carbide contains, in addition to CaC2, impurities: calcium oxide, coke and others.

Definition!
Number of liters of acetylene gas at a pressure of 760 mmHg. Art. and +20°C, produced from 1 kg of carbide as a result of mixing with water, is called a displacement.

Is it possible to determine the quality of calcium carbide by color?
The purer the calcium carbide, the more acetylene is obtained from the decomposition of 1 kg of product (the higher its displacement). When the content of pure CaC2 is 60-75%, the fracture of the material has a gray color, which turns into purple as the percentage of CaC2 increases. High percentage calcium carbide (80% CaC2) can range in color from light brown to bluish-black.

Types of generators for producing acetylene from calcium carbide

GOST 5190 defines several classification criteria for acetylene generators:

• according to the pressure of the resulting gas: low - up to 0.01 MPa, medium - 0.07-0.15 MPa, high - more than 0.15 MPa;
• by productivity: 0.3-160 m3;
• by method of application: stationary and mobile;
• according to the operating principle: “carbide to water”, “water to carbide” according to “dry” and “wet” processes.

Let's look at the main types of acetylene generators.

"Carbide into water"

This is the most popular equipment. Operating principle of the industrial version:

• carbide is periodically fed from the hopper in separate portions into the gas-forming chamber through a feeder; the gas-forming chamber contains water;
• Carbide is supplied periodically when the pressure in the water tank drops below a set level;
• in the gas-forming chamber, as a result of the reaction of carbide and water, acetylene is formed, which is supplied to the acetylene hose;
• the sediment - slaked lime - is removed through the outlet valve.

In home workshops, small industries and construction sites, a mobile acetylene generator of the ASP-10 type with a capacity of 1.25 m3/hour is in demand. Its one-time use is 3.5 kg of calcium carbide with an optimal fraction of 25-80 mm. Without recharging, it can work for 0.8 hours.

The unit consists of a housing with a lid and membrane, a basket for carbide, a safety valve and a liquid seal, drain fittings, a tray, and a pressure gauge. At the top of the housing there is a gas generator, in which the decomposition of CaC2 occurs with the generation of acetylene.

Acetylene accumulates in the gas collector.

The advantages of such generators are: the most complete decomposition of calcium carbide (up to 95%), good cooling, and ease of maintenance.

“Water on carbide” according to the “wet” process principle

The principle of operation of the equipment is to periodically supply water to the carbide loaded into the retort. The resulting gas exits into the gas collection chamber, from where it enters the welding hose through a selector.

Advantages of the devices: reliability and simplicity of design. Minuses:

• the possibility of acetylene overheating due to a small amount of water;
• incomplete decomposition of carbide;
• low productivity.

“Water on carbide” according to the “dry” process principle

Carbide is supplied to the generator drum and water is supplied, the amount of which is twice that required for complete decomposition of the carbide. Thanks to the high temperature, excess water evaporates. The slaked lime falls down through the lattice walls and is discharged outside the unit. Due to the evaporation of water, lime becomes dry, which is why the process got its name. The resulting acetylene is fed into the welding hose through a selector.

Advantages of the process: ease of equipment maintenance and lime removal. The operation of stationary generators of medium performance level is based on this principle.

Acetylene substitute gases

For welding metals, not only acetylene can be used, but also other gases, as well as vapors of flammable liquids.

Definition!
For welding metals and alloys, gases can be used that are capable of producing a flame temperature twice as high as the Tmelt of the materials being processed.

Substitute gases produced on an industrial scale are generally cheaper than acetylene and are easy to purchase, so they can significantly reduce the cost and simplify welding work. But, compared to acetylene, they all have a lower combustion temperature. Therefore, their use is usually limited to areas where very high flame temperatures are not required:

• welding of low-melting non-ferrous metals (aluminum and magnesium), their alloys, lead;
• high and low temperature soldering;
• surface hardening;
• welding of thin sheet rolled steel;
• surface and separation oxygen cutting.

Substitute gases are especially widely used during oxygen cutting, in which the flame temperature does not affect the quality of the process, but only determines the preheating time of the material.

Can propane and methane be used for gas welding?
These gases can be used for welding, but only with the additional use of silicon and manganese-containing wire. Silicon and manganese act as deoxidizers. When welding cast iron and non-ferrous metals with these gases, it is necessary to use fluxes.

What welding wire is used for gas welding?

For welding, wire, rods and granules with a chemical composition similar to the metal being welded are usually used as filler materials. Their melting point must be equal to or lower than that of the material being processed. The surface of the wire is clean, free of rust, oil, and scale. Wire for gas welding and surfacing is produced in accordance with the same standard as for arc welding - GOST 2246.

What to do if it is not possible to obtain welding wire of the required composition?
When working with stainless steel, copper, brass or lead, as an exception, use strips of materials of the same grade as the metal being welded.

How to choose a wire in accordance with the material being welded and the operational purpose of the product being manufactured?

• For critical welded metal structures and products, it is recommended to use manganese and silicon-manganese wire: Sv-08GA, Sv-10G2, Sv-08GS, Sv-08G2S.
• For low-alloy grades, low-alloy wire containing chromium is used.
• Rods produced in accordance with GOST 2671 are intended for cast iron. They are divided into grade A, which is in demand for hot welding with general preheating of the product, and grade B, for welding with local heating. The NC-1 and NC-2 grades are used for low-temperature gas welding of cast elements.
• For welding aluminum and alloys based on it, wire is designed that complies with GOST 7871: Sv-A1, Sv-AMts, Sv-AK-5, Sv-AMg.
• For copper and its alloys, filler wire is produced, regulated by GOST 16130 (M1, MSr1), or rods M1r and M3r.

Purpose of fluxes for gas welding

When heated during the welding process, copper, aluminum, magnesium and alloys based on them intensively interact with oxygen in the air or welding flame. As a result, oxides are formed on the metal surface, the melting point of which exceeds the melting point of the base metal. The oxide film greatly complicates welding.

Special pastes or powders, that is, fluxes, help prevent the appearance of surface oxide films. These compounds are pre-applied to the edges of the elements to be welded and the welding wire (rods). When heated, fluxes form low-melting slags, which prevent the formation of refractory oxides.

The functions of fluxes are performed by: calcined borax, boric acid, oxides and salts of lithium, barium, potassium, fluorine, sodium and others.
The type of composition is determined by the properties of the metal being welded. The flux base for oxygen cutting is iron powder. Fluxes can also be used for special alloy steels and cast iron.

They are not used for ordinary “black” steels.

Source: https://www.navigator-beton.ru/articles/gazovaya-svarka.html

Which shielding gas to use when welding and cutting: choice and features | Tiberis

Auto repair shop workers, installers and other welding specialists often use natural gas and various gas mixtures during welding. You will learn about what types of gases there are, their features and properties from our article. We will also provide recommendations on the selection and use of one or another shielding gas for different welding methods and depending on the material being welded.

Why are shielding gases needed when welding and cutting?

Shielding gas is an important component that ensures productivity and decent quality of the welding process.

The name of the shielding gas speaks for itself; it is needed to protect the hardening molten weld seam from oxidation, as well as from moisture and impurities in the air that can reduce the resistance of the seam to corrosion processes, lead to the appearance of pores and weaken the strength of the seam, affecting the geometry of the weld connections. In addition, the shielding gas cools the welding gun.

What types of gases are used for welding and cutting: their properties and application features

Inert and active gases, as well as their mixtures, are used as shielding gases used for welding.

1. Inert gases for welding . Inert gases are gases that are not capable of chemical reactions and are practically insoluble in metals. The atoms of such gases are endowed with outer electron shells filled with electrons, which explains their chemical inertness. These include argon, helium and their mixtures.

Argon ( Ar ) is an inert gas that does not enter into chemical reactions with molten metal and other gases in the arc combustion zone.

The advantages of this inert gas include the fact that it is 38% heavier than air; argon displaces it from the welding zone and reliably isolates the weld pool from contact with the atmosphere.

Most often, Ar is used as a shielding gas in the process of argon arc TIG welding and MIG/MAG welding. Examples of metals welded using argon and application features are given below in Table 1.

Argon is in demand as a shielding gas:

• in construction and mechanical engineering (when welding parts made of high-alloy steel; rapid cutting of metals, including thick sheets of refractory metals);
• in the mining industry and metallurgy (metal smelting; removal of gas inclusions from liquid steel).

Helium ( He ), like Ar, is chemically inert, but differs from it in that it is much lighter than air, which makes protecting the weld pool a more complex process that requires large amounts of shielding gas.

Helium is used as an inert shielding gas during welding of stainless steels, non-ferrous metals and alloys, active and chemically pure materials. It provides increased penetration, and therefore is sometimes used to melt thick metal sheets or obtain a specially shaped weld.

But due to the increased consumption and high cost of helium compared to argon, its scope of application is quite limited.

Helium (He) is used as a shielding gas:

• when welding stainless steels, non-ferrous metals and alloys, chemically pure and active materials.

1.1. Inert gas mixtures usually include argon and helium. Having a higher density than helium, such mixtures provide more reliable protection of the weld pool metal from air.

If it is necessary to weld chemically active metals, an inert mixture containing 60-65 vol. is often used. % He, 40-35 vol. %Ar. Inert gas mixtures are noticeably more expensive than pure argon, but provide a more intense release of heat from the electric arc at the welding site. This is significant for semi-automatic welding of metals characterized by high thermal conductivity.

2. Active gases for welding . These are gases that protect welding from air access and at the same time enter into chemical reactions with the metal being welded or physically dissolve in it.

Carbon dioxide ( CO2 ) (carbon dioxide) is a colorless, non-poisonous gas, soluble in water, and heavier than air.

Carbon dioxide gas for welding should not contain mineral oils, glycerin, hydrogen sulfide, hydrochloric, sulfuric and nitric acid, alcohol, ethers, ammonia, organic acids and water. Due to the rarity of grade 1 welding carbon dioxide, grade 2 welding carbon dioxide and food grade carbon dioxide are used for welding.

But, an increased content of water vapor in such carbon dioxide during welding leads to the appearance of pores in the seams and a decrease in the plastic properties of the welded joint.

In the welding process, solid carbon dioxide can also be used, corresponding to GOST 12162-66 of two grades - food grade and technical grade. When welding low-carbon and low-alloy structural steels, a gas mixture of carbon dioxide and oxygen (CO2 + + O2) is also used. Use a mixture that includes 30 vol. % oxygen. The mixture of CO2 + O2 has a more intense oxidizing effect on liquid metal, in contrast to pure carbon dioxide.

Carbon dioxide is used as a protective agent:

• in construction and mechanical engineering (electric welding; fine sharpening processes, cold fitting of machine parts)

Oxygen ( O ) is included in the gas mixtures CO2 + O2 and Ar + O2. It is a colorless, odorless gas that supports combustion. In case of cooling to a temperature of -183 degrees. Celsius, oxygen turns into a mobile blue liquid, and at a temperature of -219 degrees.

Celsius freezes. Oxygen guarantees a very wide weld profile, characterized by shallow penetration, and also provides a high heat input to the metal surface.

Oxygen-argon mixtures are distinguished by a special weld penetration profile, reminiscent of a “nail head”.

Oxygen as a protective gas is sometimes necessary:

• in construction and mechanical engineering (oxygen-acetylene gas cutting and gas welding of metals, surfacing and spraying of metals, plasma cutting of metals)

Hydrogen ( H ) is colorless, odorless, and flammable. Hydrogen is not suitable for martensitic or ferritic steels due to cracking, but can be used in concentrations of 30 to 40% for plasma cutting stainless steel to increase power and reduce slag.

• Hydrogen has found application in atomic hydrogen welding.

Nitrogen ( N ) is a colorless and odorless gas that does not burn and does not support combustion. In accordance with GOST 9293-59, nitrogen comes in four grades: electric vacuum, gaseous gaseous 1st grade, gaseous 2nd grade and liquid. The inclusion of nitrogen in these varieties must be, respectively, no less than vol.%: 99.5; 99.9; 99 and 96. The main impurity in each of them is oxygen.

Nitrogen is most often used as a shielding gas:

2.1. Mixtures of inert and active gases are increasingly used in the process of consumable electrode welding of steels of various classes due to their technological advantages. These include:

• high arc stability, favorable character of electrode metal transfer through the arc,
• the degree of chemical action on the metal surface of the weld pool is lower when compared with active gases.

The addition of a small amount of oxygen or other oxidizing gas to argon significantly increases the stability of arc combustion and improves the quality of formation of welded joints. Oxygen in the arc atmosphere provides fine-droplet transfer of the electrode metal.

Selecting a gas for a specific type of metal being welded

What gas is used when welding a particular metal is one of the most frequently asked questions for beginners in welding on thematic forums. Examples of the use of various shielding gases and gas mixtures for welding various metals are given in the table.

Metal to be welded	Shielding gas used in welding	Features of the welding process
Carbon steel	75% Ar+25% CO2	High speed of the welding process without burning through metal up to 3 mm thick, minimum deformation and spatter formation
CO2	Deep penetration, high welding speed
Stainless steel	90% He,5% Ar+2.5% CO2	No oxidation of the welded metal and no burn-through, small heat-affected zone,
Low alloy steel	60-70% He+25-35% Ar+4.5% CO2	High impact strength, minimal reactivity,
75% Ar+25% CO2	Sufficient strength, small spatter along the contour of the welded joint, high arc stability.
Aluminum and its alloys	Ar	Stable arc and excellent transfer of electrode material during the welding process of thick parts. up to 25 mm
35% Ar+65% He	Greater heat input compared to welding with pure argon, improved fusion characteristics, used when welding thick metal. 25- 76 mm
25% Ar5% He	Maximum heat input, low porosity, used when welding metal over 76 mm
Magnesium alloys	Ar	Impeccable seam quality (cleanliness)
Stainless steel	Ar-1%O	Improved arc stability, good weld bead fusion, more fluid controllable weld pool, minimal burn-through when welding heavy stainless steels
Ar+2% O	Stable arc, fusion and welding speed than 1% oxygen, used for welding thin stainless steels
Carbon steel	Ar+1-5% O	Improved arc stability, excellent weld bead contour fusion, more fluid controlled weld pool, minimal burn-through, faster welding speed compared to pure argon welding
Ar +3-10%	Beautiful weld seam, welding only with electrode positioning, minimal spatter formation
Low alloy steels	Ar+2% O	Low risk of burn-through, weld strength
Titanium	Ar	Good arc stability
Copper, nickel and their alloys	Ar	It is characterized by good fusion, reduced metal fluidity, and is used for welding thick metal. up to 3 mm
Ar+80-75% He	Characterized by increased heat input
Copper, duplex steel
N	Demanded for protecting the root of the seam. Reduces the formation of oxide films at the root of the weld

By correctly determining the type of shielding gas, you will ensure the efficiency and quality of welding, as well as guarantee an excellent welded joint and penetration depth, increase the reliability of the created seam and the quality of the part. The selection of a suitable shielding gas and its quality significantly influence the consumption of welding consumables, the labor of the welder and the correction of defects and the final processing of the weld joint.

If you have any questions on the topic, we recommend that you find the most up-to-date information on our website, or directly contact Tiberis consultants.

Source: https://www.tiberis.ru/stati/vybor-zashhitnogo-gaza-dlja-svarki

What you need to know about gas welding

Gas welding is the joining of metal parts by melting. Historically, this is one of the first types of welding to appear. The technology was developed at the end of the 19th century.

Subsequently, with the development of electric welding technologies (arc and resistance), the practical value of gas welding decreased somewhat, especially for joining high-strength steels. But it is still successfully used for joining cast iron, brass, bronze parts, for fusing techniques and in many other cases.

Essence of the process

The essence of the method is that a high-temperature welding gas flame heats the edges of the parts being welded and part of the filler material (electrode part).

The metal goes into a liquid state, forming a so-called weld pool - an area protected by a flame and a gaseous environment that displaces air. The molten metal slowly cools and solidifies. This is how the weld seam is formed.

A mixture of some flammable gas with pure oxygen, which plays the role of an oxidizing agent, is used. The highest temperature - from 3200 to 3400 degrees - is produced by acetylene gas, obtained directly during welding from the chemical reaction of calcium carbide with ordinary water. In second place is propane - its combustion temperature can reach 2800 °C.

Less commonly used:

• methane;
• hydrogen;
• kerosene vapor;
• bluegas.

All alternative gases and vapors have a flame temperature significantly lower than that of acetylene, so welding with alternative gases is practiced less frequently, and only for non-ferrous metals - copper, brass, bronze and others, with a low melting point.

Gas welding has features compared to electric welding, which form both its disadvantages and advantages.

Advantages and disadvantages

Like any thing or phenomenon, the advantages of gas welding are a direct reflection of its disadvantages, and vice versa.

The main characteristic of gas welding is a lower heating rate of the melted zone and wider boundaries of this zone. In some cases this is a plus, in others it is a minus.

This is a plus if you need to weld parts made of tool steel, non-ferrous metals or cast iron. They require smooth heating and smooth cooling. There are also a number of steels for specialized purposes for which this particular processing mode is optimal.

Other advantages include:

• low complexity of the gas welding technological process;
• availability, adequate cost of equipment;
• availability of a gas mixture or calcium carbide;
• no need for a powerful energy source;
• flame power control;
• flame type control;
• possibility of mode control.

There are four main disadvantages of gas welding. The first is precisely the low heating rate and high heat dissipation (relatively low efficiency). Because of this, it is almost impossible to weld metal thicker than 5 mm.

The second is too wide a thermally affected zone, that is, a heating zone. The third is cost. The price of acetylene consumed during gas welding is higher than the price of electricity spent on the same amount of work.

Its fourth drawback is its weak mechanization potential. Due to its operating principle, only manual gas welding can actually be implemented.

A semi-automatic method is not possible; an automatic method can only be done using a multi-flame torch, and only when welding thin-walled pipes or other tanks. This method is complex and cost-effective only in the production of hollow tanks made of aluminum, cast iron or some of their alloys.

Standards

GOST for gas welding is a special issue. Due to the fact that the quality of a weld in gas welding largely depends on the skill of the welder, it is determined subjectively.

The nature of the gas welding process is exclusively manual; there is no specific GOST for gas welding . But there is GOST 1460-2013 - for calcium carbide, from which gas for welding is produced.

In addition, various GOSTs define parameters such as types of filler wire, pressure in the gearbox and cylinder, and requirements for the acetylene generator. There are specific requirements for the types of hoses and burners used, related to operational safety.

Standard equipment set

Gas welding or cutting (a technologically simpler process) requires equipment. First of all, this is an acetylene generator or a source of other flammable gas (propane, hydrogen, methane). You will also need a cylinder with an oxidizer - oxygen, a burner, a compressed gas reducer (flow regulator) and connecting hoses.

Various auxiliary devices can be used, for example, a piezo ignition element, a safety water seal for protection against backfire (lately an almost mandatory element), and others.

A distinctive feature of this type of welding is that it does not require power supply, so work can be carried out practically in “field” conditions. Largely because of this advantage, gas welding is still actively used.

Types of flame

One of the advantages of gas welding is the ability to use fire with different chemical properties: oxidizing, reducing, with a high acetylene content.

A “normal” flame is considered to be a reducing flame, in which the metal is oxidized at the same rate as it is reduced. It is used in most cases. To join parts made of bronze and other alloys containing tin, only reducing fire is used.

An oxidizing flame is formed when the amount of oxygen in the gas mixture increases. In some cases it is preferable and even necessary, such as when joining brass and brazing.

A special property of the oxidizing flame is the ability to increase the speed of gas welding. But in this case it is necessary to use a special additive containing deoxidizing agents - manganese and silicon.

If you use the same material as a filler wire with an oxidizing flame as in the parts being welded (with the exception of brass), the weld will come out brittle, with a large number of pores and cavities.

A flame with an increased content of flammable gas is used for surfacing another part made of a harder alloy onto any part, as well as when welding parts made of cast iron and aluminum.

Technology and methods

The gas welding technique greatly depends on the specifics of the metals and alloys being welded, the shape of the parts, the direction of the seam and other factors.

The main purpose of gas welding is the processing of cast iron and non-ferrous metals, which lend themselves to it better than arc welding. It “takes” alloy steel worst of all - due to the low heat transfer coefficient, parts made from it warp greatly when cooked with gas.

There are “right” and “left” gas welding techniques. There are also technologies for welding with beads, baths and multi-layer welding.

The “right” method is when the welding nozzle is moved from left to right, and the additive is supplied following the movement of the fiery jet. The flame is directed at the end of the wire, so that the molten composition - the melting point of the additive is usually lower than that of the base material - lies evenly in the seam.

With the “left” method of gas welding - it is considered the main one - they do the opposite. The burner moves from right to left, the additive is fed towards it. This method is simpler, but is only suitable for thin sheets of metal. In addition, with it there is more consumption of filler wire and combustible gas than with the “right” one.

Roller welding is a more labor-intensive method, suitable only for sheet material. The seam is formed in the form of a roller, but the quality of the seam is very high, without the formation of slag, pores and air gaps.

Pool welding is a method that requires great skill from the welder. In this case, the filler wire is laid into the seam in a spiral manner, passing through different sections of the flame. Each new turn of the spiral slightly overlaps the previous one. The method is well suited for joining sheets of low-carbon steel.

Multilayer welding is the most technologically complex method. Its basics are like surfacing one layer on top of the next. In this case, ideal heating of all underlying layers is achieved. The main thing is to control that the joints of the seams of different layers are not located one under the other.

In each of these types of gas welding, different fluxes can be used, depending on the metal being processed. Their task is to protect the surface of the seam from the formation of oxides that impair its quality.

Source: https://svaring.com/welding/vidy/gazovaja-svarka

Choosing a welding shielding gas

Shielding gas plays a vital role in the process of creating a high-quality welded joint for the following types of welding:

• MIG - Metal Inert Gas. A method of arc welding in a protective atmosphere of inert gas using a consumable electrode in the form of steel or other wire, depending on the type of metal being joined.
• MAG - Metal Active Gas. The same method of semi-automatic welding, but in an active gas environment.
• TIG - Tungsten Inert Gas. Technology of arc welding in an inert gas environment with a non-consumable electrode.

Why is shielding gas needed in welding?

The weld pool is exposed to the negative influence of oxygen from the atmosphere, which can weaken the corrosion resistance of the weld, reduce its strength and lead to the formation of pores. The gas flow encloses the weld pool in a protective shell, protecting it from harmful external influences of atmospheric air, thereby protecting the solidifying molten weld from oxidation, as well as from impurities and moisture contained in the air.

Types of protective gases.

Inert. A type of gas that does not chemically interact with the heated metal and does not dissolve in it. Designed for welding aluminum, magnesium, titanium and their alloys, which when heated are prone to vigorous interaction with oxygen, nitrogen and hydrogen.

Example: Argon, Helium, Nitrogen (only when welding copper and copper alloys).

Active. They enter into a chemical interaction with the metal being welded and dissolve in it.

Example: Carbon dioxide, Hydrogen, Oxygen, Nitrogen.

Colorless, non-toxic, explosion-proof gas, tasteless and odorless. Typically used for TIG welding of all materials and MIG welding of non-ferrous metals such as aluminum. Argon is chemically inert, which makes it suitable for welding reactive and refractory metals. This gas has low thermal conductivity and ionization potential, resulting in low heat transfer to the outer region of the welding arc. As a result, a narrow arc column is formed, which in turn creates a welding seam profile traditional for welding in pure argon: deep and relatively narrow. Stored and transported in gray cylinders with green inscription.

Lighter than air, odorless, colorless, tasteless, non-toxic. It is a monatomic inert gas. Most often used for TIG welding of non-ferrous metals and for overhead position welding. Has high thermal conductivity and ionization potential. When welding with helium, the profile of the weld is wide, well wetted along the edge and with a fairly high heat input. Due to these features, it is most often used as an additive to argon and is used for welding chemically pure or active metals, aluminum or magnesium alloys, to ensure a large penetration depth. Stored and transported in brown cylinders with white lettering.

Carbon dioxide provides fairly deep penetration, so it is popular when welding thick metal. The disadvantages of welding in a carbon dioxide environment include a less stable welding arc, leading to large spatter formation. It can also only work on a short arc. Typically used for semi-automatic short arc MAG welding and MAG cored wire welding. Stored and transported in black cylinders with yellow inscription.

Welding gases used as components of the welding gas mixture:

Gas mixtures have higher technological performance than pure gases. When using them in the welding process, we get: fine-droplet transfer of liquid metal, the formation of a high-quality seam, and a reduction in losses due to spattering.

Oxygen is a diatomic, active protective gas. Typically used for MIG MAG welding as one of the components of the welding mixture, in a concentration of less than 10%. Oxygen provides a very wide weld profile with shallow penetration and high heat input to the metal surface. Oxygen-argon mixtures have a characteristic weld penetration profile in the form of a “nail head”. Oxygen is also used in ternary mixtures with CO2 and argon, where it provides good wettability and the benefits of jet transfer. Stored and transported in blue cylinders with black lettering.

Hydrogen is a diatomic, active gas. Used when welding austenitic stainless steel to remove oxide and increase heat input. The result is a wide weld seam with increased penetration. The concentration in the welding mixture is usually no more than 10%, and when plasma cutting stainless steel from 30 to 40%. Stored and transported in green cylinders with red inscription.

Nitrogen is used least often for protective purposes of the weld pool. It is mainly used to improve corrosion resistance in duplex steels. Stored and transported in black cylinders with yellow inscription.

Welding gas mixtures:

They differ from chemically pure gases by higher technological indicators. They allow for fine-droplet transfer of liquid metal, form a better-quality seam and reduce losses due to spattering. Using a combination of welding gases, it is possible to increase the productivity of the welding process, increase the penetration depth, stabilize the electric arc, and improve the quality of the welded joint.

	TIG welding	MIG/MAG welding
Welding gas or mixture	steel	stainless steel steel	aluminum	steel	stainless steel steel	aluminum
Argon (Ar)	+	+	+	+
Helium (He)	+
Carbon dioxide (CO2)	+
Ar/CO2 mixture	+	+
Ar/O2 mixture	+	+
Ar/He mixture	+	+	+	+
Ar/CO2/O2 mixture	+
Ar/H2 mixture	+
He/Ar/CO2 mixture	+
Ar/He/CO2 mixture	+	+

The cost of welding gas compared to the overall cost of welding:
Do not underestimate welding gas by focusing solely on the equipment. If you carefully approach the issue of correctly selecting the required shielding gas, this will affect not only the quality of the welded joint and its geometry, but will also help avoid the costs of correcting defects and processing the final seam. Also, the choice of a suitable gas affects the consumption of welding materials by reducing spatter.

Source: https://www.svarbi.ru/articles/vybiraem-svarochnyy-zashchitnyy-gaz/

Features of gas welding

There are different ways to connect metal parts. The most effective technology is heat treatment, which includes several methods. One of the most popular is gas welding.

Gas welding of metal pipe

The essence of the process

The essence of the gas welding method is that a hot gas stream is supplied through a special nozzle to the working surfaces. It heats the edges of parts to critical temperatures, melts the filler material, which is fixed to the nozzle or supplied to the heating site from the other side.

Gas displaces air from the heating site. Therefore, no oxide film is formed. Gradually the metal cools, the parts come together. Before carrying out work, you need to learn how to choose gases for welding:

1. The most popular mixture is oxygen with acetylene.
2. Propane with oxygen.
3. Hydrogen with oxygen.
4. Methane with oxygen.

To weld metal parts, you can use any flammable gas with the addition of oxygen. However, the best option is acetylene. This is due to the operating temperature that this gas can provide - up to 3400 degrees Celsius. For propane, this figure reaches 2800 degrees.

Application area

To understand where the technology of thermal joining of metals is used, you need to understand what materials can be welded using this method:

1. Thin sheets of steel, tin (up to 5 mm).
2. Cast iron.
3. Non-ferrous metals.
4. Tool steel.

Technology and methods of gas welding

Before starting welding work, it is necessary to prepare the working surfaces. They are cleaned of rust, dirt, and plaque. Next, the master needs to choose a gas welding technology. Each of the individual methods has certain execution features. Gas welding methods:

1. Left way. Used when working with non-ferrous metals and low-melting alloys. The nozzle should move from right to left.
2. Right way. Used for low-melting metals. The filler wire must be moved following the flame.
3. Through roller. Initially, it is necessary to secure the sheets of metal vertically to the gap. Use a torch to melt the edges. Once you have a hole, melt it on all sides to create a seam.
4. Multilayer welding. To make a high-quality seam, you will need to spend a large amount of gas.
5. Connection by baths. This method is used to secure corners or join joints of metal sheets. It is important that the thickness of the workpieces does not exceed 3 mm.

It is important to be responsible when choosing a working mixture. It can be a mixture of oxygen with:

1. Methane.
2. Propane.
3. Acetylene.
4. Hydrogen.

To weld metal sheets with a thickness of more than 5 mm, you must use a double roller. The burner is fired in the right way.

Equipment

Types of equipment for gas welding:

1. Gasoline-oxygen.
2. Acetylene-oxygen.
3. Kerosene-oxygen.
4. Propane-oxygen.

Other key elements of a gas welding machine include:

1. Safety lock. This part ensures safety during operation.
2. Gas cylinders. According to GOST, they must be painted a certain color, depending on what is inside.
3. Valve installed on the cylinder. Must be made of brass.
4. The gearbox is a key element of the equipment. Provides reliable connection of the burner to the cylinder.
5. Burner for supplying the working mixture. There are two types - acetylene, propane. It is a working part of the equipment on which valves are located to regulate the supply of gases. They are mixed using a system of tubes that are located on the burner.

At the outlet of the cutter there is a nozzle through which the finished mixture is supplied to the working surface.

Pipe welding stages

After selecting a gas for welding, the welder must prepare the equipment and check the functionality of individual elements. Next, the work begins. The gas welding technique consists of several stages that must proceed sequentially:

1. Preparation of working surfaces. They are marked and cleaned of plaque, dirt, and rust.
2. To begin connecting individual metal elements, you need to grab them with a welding machine.
3. Align the workpieces relative to each other. Additionally, check the accuracy. Start uniform heating of the working part of the equipment. After heating the metal until it begins to melt, the cutter must be slowly moved along the boundaries of the future weld and filler material must be fed into the working area.

Using a cutter, you can separate metal workpieces into parts.

Cleaning a metal surface

Safety precautions

Before you start working, it is important to study the safety rules and adhere to them:

1. Do not use the equipment near flammable substances or liquids.
2. Work only in a well-ventilated area. If the building is not ventilated, take breaks during work so that the welder can get some fresh air. It is advisable to use a respirator.
3. It is important to check that the equipment elements are not stained with oil.
4. To cool the nozzle, there should be a container with cold water nearby.
5. Prepare the work area before welding begins. Interference during operation can lead to injuries and defective workpieces.
6. Use safety glasses, a special welding suit, and gloves.

Before starting work, check how securely the connecting hoses are connected. There should be no gas leak.

Gas welding is a popular method of thermal joining of metal parts.
Before starting welding work, you need to familiarize yourself with the features of the technological process, prepare the equipment and parts to be welded. In order not to harm the body, it is important to follow safety rules. Gas welding first steps - Welding territory
Gas welding for beginners (lower position of the seam)

Features of gas welding Link to main publication

Source: https://metalloy.ru/obrabotka/svarka/gazovaya

Gases used in gas welding

Gas welding is the melting of the edges of the parts to be joined in a high-temperature torch flame to form a seam. The choice of gas for welding depends on many factors:

• metal to be joined;
• desired seam shape;
• type of gas equipment;
• working conditions;
• properties of chemical composition;
• required melting temperature.

Let's list what gases are used in gas welding: it can be acetylene, MAF, propane, butane, benzene, kerosene, oxygen, coke and carbon dioxide and others. The most actively used is acetylene, which in the presence of oxygen gives a temperature of 3 thousand degrees.

Acetylene substitutes

Substitute gases for C2H2 include propane and propane-butane mixture, hydrogen, coke oven gas, gasoline, and kerosene. They have fairly high calorific values. However, for high-quality work, more oxygen is required, and the flame t is still lower than that of acetylene. Therefore, propane, butane and other options are used more often in the manufacture of metal structures from non-ferrous, low-melting metals. It is difficult to join steel with them.

Carbon dioxide

Carbon dioxide (CO2) has a strong odor and pronounced oxidizing properties. It dissolves well in water and weighs one and a half times more than air. There are 3 types of substances that are used to join cast iron, carbon metals and alloys, corrosive steels and low-alloy structures.

Protective elements

Gas welding also uses inert gases, which serve to protect the weld pool from air. They do not interact with metal and do not dissolve in it; they are colorless and odorless.

• Argon. Non-flammable, 1.5 times heavier than air. The highest grade is used for argon arc welding of active, rare metals and alloys. The first is suitable for aluminum and steel products.
• Helium. Lighter than air. Recommended for gas welding of pure and active metals, as well as aluminum and steel.
• Nitrogen. Suitable for copper and copper alloys. There are 4 types of nitrogen with different proportions of the substance.

Welding mixtures improve the process and quality of the weld in the manufacture of metal structures: helium with argon, argon with oxygen and/or carbon dioxide as an assistant, and others.

Source: http://kra-ber.ru/gazy-ispolzuemye-pri-gazovoj-svarke/

What gas is needed for semi-automatic welding, choice of gas or mixture of mechanized welding

A semi-automatic welding machine improves both the quality of the seam and the speed of the welder. Mechanized welding does not involve replacing electrodes - instead of rods, such a machine uses wire fed from a reel. Therefore, the welder does not have to break the seam, wasting time and violating the tightness of the connection.

In addition, operation in a semi-automatic mode makes it possible to join workpieces with a thickness ranging from tenths of a millimeter to several centimeters, and the structural material of the joined elements can be almost any metal or alloy.

However, these advantages are not possible without the use of a special gas that protects the weld pool.

What gas is needed for mechanized welding?

Semi-automatic welding technology involves the use of active and/or shielding gas as a flux. The first changes the physical and chemical characteristics of the seam, the second protects the metal from oxidation, which is especially important when joining workpieces made of aluminum or rapidly oxidizing alloys.

Typical representatives of the inert group of gases are argon (Ar) and helium (He). The active group includes nitrogen (N), oxygen (O) and carbon dioxide (CO2). The most popular mixtures are:

• argon-helium composition (Ar + He) - a protective medium that increases the thermal power of the arc;
• argon-carbon dioxide composition (Ar + CO2) - an inertly active medium that reduces electrode splashing;
• argon-oxygen gas mixture (Ar + O2) - an inert active medium for low-alloy and alloy steels;
• carbon dioxide-oxygen mixture (CO2 + O2) is an active medium that increases the productivity of the semi-automatic device.

Criteria for choosing a gas or mixture for a semi-automatic machine

When choosing a mixture or a technically homogeneous medium, it is customary to pay attention to the following criteria: the type of structural material of the workpieces being welded, the thickness of the seam being formed, the diameter of the welding wire.

As a result, choosing a mixture for welding work comes down to studying a table that shows the compositions recommended for each metal or alloy, taking into account the depth of the weld pool and other characteristics.

In addition, an experienced welder takes into account the “bonus” effect that a particular environment provides. For example, carbon dioxide gases ensure minimal spattering of the filler metal (electrode), so it is convenient to weld ceiling seams with their help. In this case, CO2 will protect the welder from contact with drops of molten metal.

Semi-automatic welding technology

The operating principle of the semi-automatic welding machine is based on a well-studied electric arc process. The potential difference between the electrode and the workpiece allows the formation of an electric arc, the temperature of which is sufficient to melt the filler and welded metal. The frozen additive contacts the metal of the workpiece at the atomic level, forming a weld with a strength of up to 90% of that of the main structural material.

However, the operation of a semi-automatic device also has its own characteristics. Firstly, the electrode wire is fed into the weld pool area in a continuous flow, passing through a conductive nozzle.

Moreover, the consumption of filler metal can be adjusted manually by pressing the feed button. Secondly, instead of the classic “solid” flux, which forms a gas cloud when the arc burns, the semiautomatic device uses gas mixtures or technically clean media.

Moreover, the gas supply is carried out continuously, both before the arc appears and after it breaks.

Thanks to this, the amount of spatter is reduced, the arc parameters are stabilized, the welder’s labor productivity is increased and the overall labor intensity of any welding process is reduced.

Features of gas welding

The technique of working with a semi-automatic machine is practically no different from the principles of using classical welding machines. Using a semi-automatic machine, you can weld horizontal and vertical seams, tack workpieces, weld sealed joints, form butt and overlap joints.

The method of forming seams with a semi-automatic welding machine does not differ from classical methods implemented using MMA equipment. Temperature conditions and welding current are determined according to the generally accepted scheme - based on the thickness of the joints and the diameter of the electrode.

The only individual feature that the semi-automatic gas welding process has is the ease of joining thin workpieces. Therefore, the semi-automatic machine is used mainly in body repair and during the assembly of thin-sheet metal structures.

The main advantages of welding with gas protection

1. There is a narrow zone of high-temperature influence, so MIG-MAG processes do not change the properties of the metals being welded.
2. No smoke in the weld pool area, which facilitates visual inspection of the quality of the seam.
3. Versatility of application - MIG-MAG processes are compatible with any metal: from titanium or aluminum to high-alloy or structural steel.
4. There are no restrictions on the spatial position of the part - by adjusting the burner pressure, you can weld ceiling or inclined seams without experiencing any difficulties.
5. There are no restrictions on thickness - this technology allows welding sheet blanks with a thickness of 0.2-0.5 millimeters. The upper limit of weld thickness is determined only by the skill of the welder.
6. There is no need to clean the seams even with multi-layer surfacing - the flux evaporates after stopping the supply of the mixture from the burner.
7. The highest possible labor productivity even with an average welder qualification.

All these advantages will become available only if a high-quality mixture prepared in accordance with GOST and TU is supplied.

Poor quality compositions will lead to loss of strength characteristics.

ITC Promexservice LLC is ready to provide the customer with high-quality gas for semi-automatic welding, in any volume, with delivery throughout Moscow or the Moscow region. We work with large companies and individuals, offering high quality and low prices. ITC Promexservice has been the leader in the technical gases market since 1999.

Source: https://itc-pex.ru/info/articles/gaz-dlya-svarki-poluavtomatom/

Welding gas: what it is, where it is used, features of use, pros and cons

Beginning welders usually try to use simple welding methods. Most people use manual arc welding.

For most repair work or the manufacture of simple parts, this is enough. However, sooner or later you will want to try something new and improve your skills.

The next step after manual welding can be welding using semi-automatic equipment. With this method, shielding gas is used to protect the surfaces being welded from oxidation.

Below you will find out which one and how to use it for welding work.

Welding gas

Semi-automatic welding uses inert gases such as argon, helium, carbon dioxide. Less commonly used are hydrogen, nitrogen and oxygen. It is served in cylinders of various sizes.

The most common volume is 40 liters. During welding, the gas forms a protective zone that protects the arc from exposure to the atmosphere, and the welded surfaces from oxidation and pores. When using it, the seam turns out smooth and of high quality.

Experienced welders know the recipes for mixtures, the use of which allows you to take advantage of the advantages of each of the gases that make up the mixture.

Characteristics

Let us dwell in more detail on the various types of gaseous substances used for welding work.

Most often used for these purposes. There is even a separate welding method that uses its name - argon arc. Inert, colorless and odorless, not chemically active towards metals and other substances. Much heavier than air, due to this it creates a reliably protected zone in the welding area.

It comes second in popularity. It is also inert, however, unlike argon, helium is lighter than air. Due to this, much more is consumed.

Considering that its cost is noticeably higher than that of argon, this is a significant drawback. However, this does not prevent its frequent use.

It is especially widely used when working with metals coated with an oxide film. These are metals such as stainless steel, aluminum, etc. When using helium, metals melt evenly, which is especially important when welding parts of large thickness.

In addition to pure helium and argon, mixtures are often used. The most common proportion is 60% helium and 40% argon.

The mixture is quite expensive, but it can be used to qualitatively weld materials with high thermal conductivity. The risk of burning through the metal is greatly reduced.

Colorless, heavier than air. Due to this, the welding area is reliably protected. There are two categories. The first category is recommended for use, however, due to its cost and scarcity, attention is often paid to the second category. The big minus of carbon dioxide of the second category is the presence of water vapor in the composition. When used, may cause the formation of pores in the metal. The problem can be avoided by adding some argon to the carbon dioxide.

It is not used in its pure form, as it causes oxidation of the surface, which negatively affects the quality of the seam. It is usually added to mixtures when it is necessary to obtain a wide and shallow joint.

It is colorless and odorless. Typically used for plasma cutting of stainless steel, achieving very good results. When welding other metals, it can cause the formation of defects, such as cracks. Requires increased attention to compliance with safety regulations due to increased flammability.

Also colorless and odorless, non-flammable. Used in liquid and gaseous form. The scope is also narrow; it is used mainly only when welding copper. When welding other metals, it can negatively affect the strength of the seam.

Choosing gas for welding

To make it easier for you to choose the right gas for welding work, we present you with a correspondence table.

Finally

Develop, experiment, try mixtures with different proportions, and you will see how the quality of the weld improves.

If you don’t want to experiment, use reference materials and select the appropriate gas or mixture for your work. We wish you success in your work!

Source: https://prosvarku.info/rashodnye-materialy/svarochnyj-gaz