What gas is used for semi-automatic welding - Metals and their processing

Criteria for choosing shielding gas for semi-automatic welding. Types of gases used

Unlike manual arc welding, the use of semi-automatic welding in most cases involves working with an uncoated consumable electrode, which requires constant protection of the weld pool from the harmful effects of atmospheric air. In addition, some metals that are prone to rapid surface oxidation place special demands on the quantity and quality of the external environment around the joint of the workpieces being welded.

What gases are used for semi-automatic welding

Reliable protection of weld pools during semi-automatic welding is provided by active gases (MAG method) and inert gases (MIG method), as well as their mixtures. They form an environment impenetrable to atmospheric air and retain it from the moment the melting begins until the crystallization of the bath. The choice of a specific protective material is determined by the composition and characteristics of the workpieces, the welding mode, and the required quality of the seam. Let's look at the most popular gases.

Argon

The monatomic inert gas argon (Ar) has found wide application both in pure form and as part of gas mixtures. It is heavier than air, colorless, odorless and cannot be felt in the air, but is dangerous in high concentrations. Most often, argon is used to join workpieces made of non-ferrous metals and their alloys, including brittle and chemically active ones.

Among the advantages of gas:

preventing all extraneous chemical reactions;
deep penetration with small weld width;
fast ignition and stable arc burning;
relatively low consumption.

The main disadvantage of argon is its high cost. In addition, in some cases, gas can contribute to increased spattering of metal from the weld pool, and also does not always provide sufficient arc energy.

Thus, the joining of thick workpieces made of refractory materials is often carried out not with pure argon, but with argon-containing mixtures.

Helium

The “main inert gas” helium (He) is much lighter than air, colorless and odorless. Most often, pure helium is used for critical welding of workpieces made of aluminum and its alloys. When working with other non-ferrous metals, mixtures of Ar-He and Ar-He-CO2 with different proportions of components can be used.

The use of pure helium in MIG and TIG welding provides the following advantages:

high thermal conductivity and, as a result, the possibility of applying wide seams;
high arc energy , which varies slightly with changes in its length;
reliable isolation of the weld pool from any chemical influence.

However, it is important to remember that helium is expensive and runs out quickly.

It tends to increase the spattering of molten material, and an inexperienced welder may have great difficulty igniting an arc in a helium environment.

Carbon dioxide

Carbon dioxide is an active gas; it is 1.5 times heavier than air, colorless and has a barely noticeable odor. It is the only non-inert gas that can be used in its pure form. Most often, carbon dioxide is used to protect the weld pool when working with powder electrodes and/or short arcs.

This is due to its following advantages:

extremely high arc energy;
fast and deep penetration;
very low cost.

Carbon dioxide does not completely eliminate extraneous chemical reactions, so it is not recommended for use in its pure form with active metals.

In addition, it makes the arc unstable and provokes splashing of the molten substance, which makes welding difficult.

Pyrolysis gas

When wood and some other fibers are heated to a temperature of at least 450℃, several gases are released (hydrogen, methane, ethane, propylene, etc.), which, when mixed, form pyrolysis gas with a combustion temperature of up to 1100℃.

Compared to other media, pyrolysis has the following advantages:

ease of synthesis;
relative cheapness;
gentle development of the weld pool without the risk of burn-through of workpieces.

At the same time, the material does not exclude the possibility of oxidative reactions occurring when working with chemically active metals. Its combined use with other gases is not recommended, but depletion by removing excess fractions can improve the quality of pyrolysis gas.

Hydrogen

The monatomic gas hydrogen is the most abundant and lightest substance in the world. When it burns, up to 140 kJ of heat is released per gram, which is 2.5 times higher than the energy output of natural gas and 1.5-2 times higher than that of inert substances.

When used as a protective welding medium, hydrogen guarantees:

uniform penetration of the bath;
formation of a relatively narrow, neat seam;
easy ignition and stable arc burning;
protection against the vast majority of oxidative reactions.

The gas is cheap and easy to synthesize industrially. It is recommended to use it for welding thick workpieces, including those made of refractory metals.

The main risk here is associated with the explosion hazard of compressed hydrogen and the hydrogen-oxygen mixture (the so-called detonating gas). Therefore, special requirements are imposed on the conditions for filling, storing and using hydrogen cylinders.

Coke gas

The material is released when coal is heated to a temperature of 900-1100℃. Its main components are hydrogen, methane and carbon oxides; in addition, it may contain resins, hydrogen sulfide, and ammonia.

The presence of these impurities makes coke oven gas unsuitable for welding most non-ferrous metals.

When working with steel workpieces, the coke environment guarantees:

careful processing of the joint without overheating or burning;
stable arc burning;
low spatter.

To improve the properties of the seam, physical and chemical purification of coke oven gas is carried out, during which mechanical impurities are partially captured and bound, and unwanted gas fractions are removed.

Criteria and features of gas selection

The choice of the type of protective environment for semi-automatic welding is carried out on the basis of information about the type and grade of metal of the workpieces, which, in turn, indicates their physical and chemical characteristics. In the case of welding dissimilar materials, the less stable and/or more refractory is considered the main one. In addition, the following must be taken into account:

Geometric parameters of workpieces and the method of their preparation for welding.
Availability and type of heat treatment of workpieces.
Technological features of the welding process , requirements for seam quality.
Technical characteristics of the equipment and consumables used.
External conditions, including : temperature, humidity, presence and strength of wind, ease of access to the joint.
Economic indicators (cost and estimated gas consumption).

The table below shows popular types of metals, as well as gases and gas mixtures recommended as a protective environment for welding them.

Material	Low carbon steel	Alloy steel, medium or high carbon	Aluminum and aluminum-containing alloys
Ar	Yes	Yes	Yes
He	No	No	Yes
CO2	Yes	Yes, limited	No
Ar+CO2	Yes	Yes	No
Ar+O2	Yes	Yes, limited	No
Ar+He	No	Yes	Yes
Ar+CO2+O2	Yes	Yes, limited	No
Ar+H2	Yes, limited	Yes	No
Ar+He+CO2	Yes	Yes	No
He+Ar+CO2	No	Yes	No

All of these gases are suitable for MIG and MAG welding; for the TIG method, argon or helium in pure form, as well as a mixture of them, are recommended. Sometimes when working with a consumable electrode, a mixture of argon and hydrogen is used. It is important to consider that the correct choice of shielding gas depends on:

quality and neatness of the seam;
work safety;
financial and labor costs.

It is not allowed to change the protective environment during the welding process, even if it takes place layer by layer with complete crystallization. The gas supply should begin 15-30 seconds before ignition of the arc and end after the bath has solidified.

Cylinder marking

Source: https://elsvarkin.ru/materialy/vybor-zashhitnogo-gaza/

Gas for semi-automatic welding

Semi-automatic welding machines work primarily with wire, which does not have a protective environment, unlike an electrode. But the weld pool in this case remains susceptible to the negative influence of oxygen from the atmosphere. Because of this, the quality of the resulting seam drops sharply and the connection becomes extremely unreliable.

To isolate the bath from anything that could harm it, you should use gas for semi-automatic welding. It turns out to be much more effective than electrode coating, although it is more expensive.

The cost of the welding process turns out to be higher, but gas allows you to work with almost all metals and workpieces of any thickness.

Carbon dioxide for semi-automatic welding

Application area

Shielding gas for semi-automatic welding is used in many areas. Without it, not a single semi-automatic welding process can be carried out, except for those when self-shielding wire is used. Most often it is used by professionals, since the use of a semi-automatic device relates more to highly skilled work.

Gas is used in equipment and car repair shops. This is often used when assembling metal structures from non-ferrous metals. Almost all production enterprises where there is a need to work with metal have semi-automatic machines that operate using a gas protective atmosphere.

There is no specific connection to the model of the device itself.

Types of welding gases

When choosing what gas is needed for semi-automatic welding, you need to know its properties. The same applies to the welding mixture for semi-automatic machines.

Acetylene is one of the most common types. It has earned high popularity due to the highest combustion temperature among other welding substances. Acetylene can be obtained through the interaction of calcium carbide and water. Calcium carbide even absorbs the moisture that is in the atmosphere, therefore, special safety measures are required for storage. To produce this gas, acetylene generators are often used. The substance is lighter than air, has no color, but has a sharp, specific odor. Due to its high combustion temperature, it is often used for cutting metal.
Hydrogen is also colorless, but also smells nothing. It is a highly explosive gas because when mixed with air or pure oxygen it produces an explosive gas. The pressure for hydrogen cylinders should not exceed 15 MPa for safety reasons. Special generators are used to produce hydrogen. This can also be achieved through water synthesis, when hydrogen and oxygen are separated.
Coke oven gas is colorless. It gives off a sharp, specific smell of hydrogen sulfide. It is a kind of by-product that is obtained during the extraction of coke, which is obtained from coal. It can even be transported through a pipeline, since it is a relatively safe substance.
Natural gas, which includes propane, butane and methane, is also used for welding. These are relatively inexpensive and common options designed to handle most welding procedures. There are no problems with storage and transportation here. The place of production is gas fields
Pyrolysis gas appears during the breakdown of oil and various products that contain it. The substance causes corrosion on the mouthpieces in the burners, which leads to their unusable condition. Before direct use, the gas is pre-cleaned. It is used not only for welding, but also for cutting metal products.

Source: https://svarkaipayka.ru/material/zashhitnyie-gazyi/gaz-dlya-svarki-poluavtomatom.html

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.

THIS IS INTERESTING: How to solder

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

There is a narrow zone of high-temperature influence, so MIG-MAG processes do not change the properties of the metals being welded.
No smoke in the weld pool area, which facilitates visual inspection of the quality of the seam.
Versatility of application - MIG-MAG processes are compatible with any metal: from titanium or aluminum to high-alloy or structural steel.
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.
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.
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.
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/

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

Gas consumption when welding semi-automatically

Semi-automatic welding is usually carried out in a gas environment using wire. The process is electric arc welding, using thermal energy emanating from an electric arc that connects the metal surface of the workpiece and the end of the electrode. What gas is needed for semi-automatic welding?

Gases used for welding

It is necessary to select gas for semi-automatic welding based on its properties.

Acetylene

Characteristics:

colorless;
lighter than air;
has a specific smell.

This is one of the most common gases used in this field of activity. It has the highest combustion temperature among other types of gas and has high polarity. Often used due to the high combustion temperature when cutting metal structures.

Specialized generators are used to produce acetylene. Acetylene can be obtained by combining water with calcium carbide, which can even absorb moisture from the atmosphere. Therefore, according to the safety requirements for this chemical compound, special storage conditions are provided.