What is an electric welding arc - Metals and their processing

Welding electric arc is - Machine tools, welding, metalworking

For more than half a century, welding has been one of the most important crafts for humans. Thanks to the welding machine, spaceships are built, factories operate, and for many craftsmen, welding has turned into a hobby. But even the most technologically advanced welding machine will not bring the desired result without a stable welding electric arc and its quality characteristics.

The electric welding arc allows you to reliably weld even the most complex metal structures. To obtain high-quality welds, you need to take into account all its characteristics, know the features and structure of the arc. Additionally, it is important to consider the temperature and arc voltage when manual arc welding. From this article you will learn what a welding arc is and the essence of the processes occurring in it, and learn to apply the acquired knowledge in practice.

Welding arc: definition

So, what is a welding arc and what are its characteristics? Electrodes energized in a mixture of gases and vapors form a powerful discharge. What is an electrical discharge? A discharge is the result of an electric current passing through a gas. Well, the result of the whole process is generally called a welding arc.

The welding arc and its properties are characterized by high temperature and current density, so the arc is capable of melting almost any metal. In simpler terms, the welding arc is an excellent conductor that converts the received electrical energy into thermal energy. Due to this thermal energy, the metal melts.

The essence and structure of the arc

The essence of the welding arc is extremely simple. Let's divide the process into several points:

First, an electric current passes through the cathode and anode region and penetrates into the gaseous environment. An electrical discharge with a strong glow is formed.
An arc is formed. The temperature of the welding arc can reach up to 10 thousand degrees Celsius, and this is enough to melt almost any material.
Then the current from the arc passes to the metal being welded. That's all its characteristics.

The glow and temperature of the discharge are so strong that they can cause burns and deprive the welder of his vision. Therefore, craftsmen use welding masks, protective gloves and a suit. Never weld without proper protection.

https://www.youtube.com/watch?v=LFZO_g1QZyU

The structure of the welding arc is shown in the picture below.

During arc burning, spots are formed in the area of the cathode and anode where the temperature reaches its limit. It is through the anode and cathode areas that electric current passes, and in these areas the voltage drops significantly, but on the column the voltage of the welding arc is maintained, since the column is located between the anode and the cathode.

Many beginners ask how to measure arc length. Just look at the cathode and anode areas, as well as the welding column. Their combination is called a long welding arc. The average length is 5 millimeters. In this case, the temperature of the resulting thermal energy is optimal and allows most welding work to be performed.

Now that we have learned what a welding arc is, let's turn to the varieties.

Types of welding arc

The welding arc and its characteristics may differ in the direct and indirect action of the welding current, as well as in the atmosphere in which they are formed. Let's look at this topic in more detail.

The direct action of the welding arc is characterized by a special direction of the current.

The electrode is positioned almost parallel to the surface to be welded and the arc is formed at an angle of 90 degrees. The electric welding arc and its characteristics can also be of indirect action. It can only be formed using two electrodes located at an angle above the surface of the part being welded. Here a welding arc also occurs and the metal melts.

As we wrote above, welding arcs are also divided according to the atmosphere in which they are formed. Here is their brief classification:

Open environment. In an open environment (atmosphere), an arc is formed by oxygen from the air. A gas is formed around it, containing vapors of the metal being welded, the selected electrode and its coating. This is the most common medium used in arc welding.
Closed environment. In a closed environment, the arc burns under a thick layer of protective flux and a gas is also formed, but containing not only metal and electrode vapors, but also flux vapors.
Gas environment. The arc is ignited and one of the types of compressed gas is supplied (it can be helium or hydrogen). An additional supply of compressed gas also protects the parts being welded from oxidation; the gases form a neutral environment. Here, as in other cases, a gas is formed, which contains vapors of the metal, electrode and compressed gas, which the welder additionally supplies during the burning of the arc.

Welding arcs can also be stationary or pulsed. Stationary ones are used for long, painstaking work without the need to frequently move the arc. And pulse is used for fast one-time work.

Also, the welding arc and its characteristics can be indirectly classified according to the type of electrode used in the work (for example, carbon or tungsten, consumable and non-consumable). Experienced welders most often use a non-consumable electrode to better control the quality of the resulting welded joint. As you can see, the welding process with a simple welding arc can have many features, and they need to be taken into account in your work.

Under what conditions does an arc burn?

In an ordinary workshop or in your garage, the average temperature is 20 degrees Celsius, and the pressure does not exceed one atmosphere. Under such conditions, the gas is practically unable to conduct electric current and thereby form an arc. To solve this problem, you need to add ions to the resulting gases. This is what professional craftsmen call ionization.

Also in the cathode region it is necessary to constantly maintain a constant temperature. This is necessary for the arc to occur and maintain combustion. But since it is in the area of the cathode and anode that the temperature can drop faster, many beginners have a lot of problems.

In addition, the temperature of the cathode region can vary greatly depending on the temperature in the room where the welding process takes place. Problems can be avoided if you monitor the health of the power source and the stability of the electricity supply (a particularly important point for home welders with unstable voltage in the household electrical network).

All this has a great influence on the properties of the welding arc and the essence of the processes occurring in it.

Arc Features

The welding arc and its characteristics have a number of features that need to be taken into account in your work:

As we have said many times, the arc has a very high temperature. It is achieved due to the high density of electric current (density can reach thousands of amperes per square centimeter). For this reason, it is important to set up the machine correctly and be careful when welding thin metals.
The electric field is unevenly distributed between the electrodes if two of them are used. At the same time, the voltage in the welding column practically does not change, but in the cathode region this voltage decreases noticeably, which can lead to deterioration in the quality of the weld.
In the welding column, in turn, the highest temperature is observed, which cannot be said about other parts of the arc. Keep in mind that if you need to increase the arc length, you will likely lose some of that temperature. This indicator is especially important when welding metals with a high melting point.

You can also adjust the voltage drop of the welding arc by selecting the current density. The higher the current density, the more likely it is that the welding arc voltage will drop.

But there are cases when the voltage of the welding arc increases due to increasing current. To control this process you will need some experience. Don't be afraid to experiment if your job allows you.

These were the main properties of the welding arc that you should pay attention to.

Instead of a conclusion

Source: https://stanki-info.com/svarochnaya-elektricheskaya-duga-predstavlyaet-soboy/

Welding machine. Types and features. Welding and arc. Application

People have long been dealing with metal products: household items, jewelry, weapons, equipment, etc. People learned to make forged products, melt and stamp cast iron. And when steel appeared, pipelines, ships, houses, cars and other structures began to be built from metal products. Currently, steel makes up 90% of the total volume of metal consumed. Ferrous metallurgy has learned to smelt high-quality structural materials.

Already at that time it was necessary to create a reliable way to connect large metal elements; bolts and rivets could no longer cope with heavy loads. In 1882, the Russian engineer Benardos created arc welding of metal parts using a carbon electrode. And four years later he filed a patent for metal welding technology. This is how the first welding machine appeared.

Engineer Slavyanov in 1888 publicly demonstrated submerged arc welding with a consumable electrode, which was called electric metal casting. Slavyanov proved that arc welding makes it possible to weld ferrous and non-ferrous metals. In subsequent years, metals began to be welded with three-phase alternating current, and this technology was used on an industrial scale.

Features of the welding process

Arc welding technology is very widespread, since with the help of this technology a strong permanent connection of metal parts is formed. The high strength of the connection is explained by the continuity of the resulting molecular structures and metal bonds.

The main factor in the welding process is high temperature. In theory, such connections between metal atoms are achieved by increased mechanical pressure. However, this method is not suitable for steel, and is only suitable for metals with low hardness, such as lead.

How does an electric arc occur?

The welding machine is capable of creating high temperatures to melt metal using an electric arc. It is formed by a short circuit between two electrodes that are located at close range. The voltage at the electrodes is gradually increased until an air breakdown occurs. In this case, electrons are emitted from the cathode, which increase the temperature from the action of electric current and move to the ionized atoms of the anode.

Further events develop at high speed: an electric arc occurs and the circuit closes. As a result, the air gap is ionized and plasma is formed, which is a special property of gas. The air gap reduces its resistance, as a result of which the current increases, and the temperature of the arc increases, the arc begins to conduct current and completes the circuit. This phenomenon is called ignition. By adjusting the required gap between the electrodes, the arc is stabilized.

Welding process

If an electric discharge is created between electrodes that are independent of the parts being welded, then it acts indirectly during welding. Usually the arc is ignited directly between the electrode and the part that is part of the circuit.

Electric current is connected from the welding machine to the workpiece, the temperature of the electric arc rises and melts the parts. This creates a “welding pool” in which the metal remains in liquid form for some time.

The molten metal of the electrode falls into the same bath.

During the welding process, the burning electrode coating creates a gas shell and a liquid slag bath around the arc. When the electric arc is gradually removed from the working area, a welding seam is created, on the surface of which a crust of slag forms in the form of a kind of shell.

There are welding methods with a non-consumable electrode made of tungsten or graphite. For example, during argon welding, the seam is filled with molten welding wire.

The choice of high-quality electrodes for welding is an important factor determining the reliability and strength of the future weld. What is meant here is not the diameter of the electrode, but the composition of its material. Wire and electrodes of different brands can be better combined with different melting depths and arc lengths.

Coating of electrodes can significantly influence the progress of welding, as well as change the chemical composition and parameters of the seam.

During the welding process, the welding site must be protected from air to prevent metal oxidation. Therefore, it is necessary to create a protective environment around the work area.

There are two options to solve this problem:

MIG – MAG technology , in which inert gas is supplied to the welding zone.
Combustion of the electrode shell. In this case, a gas dome is created around the welding zone, protecting it from air. During combustion, the electrode shell removes oxygen from the weld area.
The electrode coating contains substances that ionize the electric arc, clean and alloy the weld metal, thereby improving its physical parameters.

Metal welding is a unique process, since the required temperature regime depends directly on the electrical parameters. To obtain a high-quality seam, it is necessary to create conditions for a stable electric arc.

A constant, uniform arc can avoid seam defects. The larger the size of the parts being welded, the thicker the welding electrodes are required, and the greater the current required.

A feature of welding is that with constant current the electric arc is more stable, since there is no change in the polarity of the current. In this case, the seam is formed with a higher quality. Although aluminum and its alloys are welded better by an AC welding machine.

The skill of the welder when welding plays a big role, since the welder must choose the length of the arc, maintain its combustion and correctly move the electrode along the seam, carefully melting the metal of the parts.

The strength, quality and appearance of the seam depend on the professional qualities of the welder.

Types and features of the device

Any electric arc welding machine must accept electric current from the network and reduce its voltage, increasing the current to the required value (from 100 to 200 amperes). In this case, the frequency of the current can change, or a direct current can be formed from an alternating current. The only exceptions are devices in which the electric arc is created from the energy of batteries or generators with an internal combustion engine.

In other words, each welder is a kind of energy converter. There are several different devices for welding metals with an electric arc. Each of them has its own device features, advantages and disadvantages, which should be taken into account when choosing a device in a retail chain.

Transformer welding machine

This is the most common type of welding machine. Such devices are inexpensive, reliable in operation and have a simple design. Electrical energy in this device is converted using a transformer operating at a household current frequency of 50 hertz. The current value is adjusted by a mechanical device for changing the magnetic flux in the magnetic circuit.

Receiving energy from the electrical network, the primary winding magnetizes the core. At this time, a low voltage alternating current of about 70 volts is generated on the secondary winding, with a high current strength that can reach 200 amperes. This current creates an electric arc to weld the parts. The magnitude of voltage and current on the secondary winding depends on the number of its turns. The fewer turns, the greater the current and the less voltage.

Advantages

Unpretentiousness and reliability in work.
Lack of electronic elements.
Convenient repair and maintenance due to the simple device.
Low cost than an inverter welding machine.

Flaws

Large overall dimensions and weight.
Low efficiency, consumes a lot of electricity, which does not allow connecting it to a household network.
Without experience in welding, it is difficult to hold the electric arc.
The quality of the seam is low, since the welding machine runs on alternating current.

Due to its low cost, such a welding machine is used in industry and in domestic conditions, where the network power is sufficient.

Welding straighteners

Such devices are similar in design to welding transformers. In them, the electric current does not change frequency and is formed on the windings of a low voltage transformer.

After the voltage is reduced, the electric current passes through a block of selenium or silicon rectifiers, which are semiconductor diodes that pass electric current in one direction. As a result, direct current is supplied to the welding electrode.

Therefore, when welding parts, the electric arc is stable, does not interrupt and provides a high-quality seam.

The design of rectifiers is more complicated, in contrast to a transformer welder, since most often it is necessary to create fan cooling of semiconductor elements. Typically, such devices are equipped with auxiliary chokes, which makes it possible to create the necessary output current parameters - it is filtered and smoothed.

The set of welding rectifiers may include measuring protective and ballast devices. When operating a welding rectifier, current and temperature stability are important. To do this, fuses, relays , thermostats, etc. Three-phase rectifiers have become the most popular, as the most functional devices.

Electric arc: discharge force in action

Our website svarak.ru publishes articles on this topic. For the first time, the phenomenon of a voltaic arc was observed by the Russian academician Petrov, who received a spark discharge.

The Voltaic arc is characterized by two properties:

releasing a large amount of heat
strong radiation.

Both properties of the electric arc are used in technology.

For welding technology, the first property is a positive factor, the second - a negative one.

Any electrically conductive materials can serve as electrical conductors for an electrical discharge. Most often, carbon and graphite rods of round cross-section (arc lamps) are used as conductors.

A typical option between two coals is shown in the figure.

The top electrode is connected to the positive pole of the machine (anode). The second carbon is connected to the negative pole (cathode).

Electric welding arc

Temperature of the electric arc, its effect.

The heat release is not the same at different points of the arc. At the positive electrode 43% of the total amount is released, at the negative 36% and in the arc itself (between the electrodes) the remaining 21%.

Diagram of zones and their temperatures in the welding arc

In this regard, the temperature at the electrodes is not the same. The anode has about 4000°C , and the cathode 3400°. On average, the temperature of the electric arc is considered to be 3500° C.

Due to the different temperatures at the poles of the voltaic arc, carbon conductors

come in various thicknesses. Positive coal is taken thicker, negative -

thinner. The arc rod (middle part) consists of a stream of electrons emitted by the cathode, which rush towards the anode at great speed. Possessing high kinetic energy, they hit the anode surface, converting kinetic energy into thermal energy.

The greenish halo surrounding it is the site of chemical reactions occurring between the vapors of the substance of the electrodes and the atmosphere in which the voltaic arc burns.

The process of creating a welding arc

The occurrence of an electric arc

The process of formation of a voltaic arc is presented in the following form. At the moment the electrodes come into contact, the passing current releases a large amount of heat at the junction, since there is a large electrical resistance here (Joule’s law).

Thanks to this, the ends of the conductors heat up to a light glow, and after disconnecting the electrodes, the cathode begins to emit electrons, which, flying through the air gap between the electrodes, split the air molecules into positively and negatively charged particles (cations and anions).

As a result, the air becomes electrically conductive.

In welding technology, the greatest application is the discharge between metal electrodes, one electrode being a metal rod, which at the same time serves as a filler material, and the second electrode being the part being welded itself.

The process remains the same as in the case of carbon electrodes, but here a new factor appears. If in a carbon arc the conductors gradually evaporated (burned out), then in a metal arc the electrodes melt very intensively and partially evaporate. Due to the presence of metal vapors between the electrodes, the resistance (electric) of a metal arc is lower than that of a carbon arc.

A carbon discharge burns at an average voltage of 40-60 V, while the voltage of a metal arc averages 18-22 V (with a length of 3 mm).

Arc length, crater, penetration.

The electric arc welding process itself proceeds as follows.

As soon as we touch the energized electrode to the product and immediately withdraw it to a certain distance, a voltaic arc is formed and the melting of the base metal and the metal of the conductor immediately begins. Consequently, the end of the electrode is always in a molten state, and the liquid metal from it in the form of drops transfers to the seam being welded, where the metal of the electrode is mixed with the molten metal of the product being welded.

Studies have shown that about 20-30 such drops transfer from the electrode per second, i.e. this process occurs very quickly.

Although the voltaic arc develops a very high temperature, it releases heat in a very small space just under the arc.

Arc length diagram

If we look through dark glasses at an arc excited by a metal electrode, we will be convinced that at the point where the arc is formed between the electrode and the base metal, a white-hot surface stands out on the base metal, which directly under the blown hole looks like a depression filled with liquid metal.

It seems as if this depression was formed by blowing out liquid metal with an arc. This depression is called the weld pool.

It is surrounded by metal heated to white heat, and the heating temperature of the adjacent area quickly drops to a red color and already at a short distance, the value of which varies depending on the diameter of the electrode and the current strength, the temperature is compared with the temperature of the object being welded.

Good and bad welding arc, how to distinguish? Useful tips

The distance between the end of the electrode and the bottom of the bath, i.e., the surface of the molten metal, is called the arc length. This value is very important in welding technology. To obtain good welding, it is necessary to take the arc length as short as possible, that is, keep the arc shorter, and its length should not exceed 3-4 mm.

Of course, the arc length is not a constant value, since the end of the electrode melts all the time and, therefore, the distance between it and the crater would increase; if the electrode were held motionless until the connection was broken.

Therefore, when welding, it is necessary to constantly bring the electrode closer to the base metal as it melts in order to maintain the arc length approximately constant within 2-4 mm.

The need to maintain a short arc (i.e., no longer than 3-4 mm) is caused by the fact that the molten metal of the electrode absorbs oxygen and nitrogen from the air surrounding the arc during its transition from the electrode to the crater, which worsens its mechanical qualities (relative elongation and impact resistance ). It is clear that the less time the liquid metal passes through the air, the less harmful the effect of air will be.

Short:

With a short arc, this time will be less than with a long arc and, therefore, the electrode metal will not have time to absorb as much oxygen and nitrogen as it could, covering a long distance due to the long arc.

Since the desire of every welder should always be to obtain the best quality weld, a short arc is therefore a prerequisite for good welding.

A short arc can be distinguished not only by sight, but also by hearing, since a short arc produces a characteristic dry crackling sound, reminiscent of the sound of oil being poured onto a hot frying pan. Every welder should be familiar with this sound of a short arc.

Long:

With a long arc (i.e., with a length greater than 4 mm), we will never get a good seam. Not to mention the fact that with a long arc there will be strong oxidation of the weld metal, the seam itself also has a very uneven appearance.

This happens because a long discharge is less stable than a short one; the spark tends to wander and deviate to the sides from the welding site, as a result of which the heat generated by it is not the same as with a short arc, but spreads over a larger area.

Due to this, the heat emitted by the arc does not all go towards melting the metal at the welding site, but is partially dissipated in vain over a large surface.

With a long arc, therefore, poor penetration is obtained, and, in addition, drops from the electrode, falling onto a poorly heated place, do not fuse with the base metal, but are splashed to the sides.

By appearance, you can always immediately distinguish a seam welded with a short or long arc. A seam welded correctly with a short arc has the correct outline, a smooth convex surface and a clean, shiny appearance. A seam welded with a long arc has an uneven, shapeless appearance and is surrounded by numerous drops and splashes of frozen metal from the electrode. Such a seam, of course, is completely unsuitable.

Arc protection

Examples of protective suits against electric arc

If welding machines use an arc, then many other machines and in addition a person should avoid it. The risk of arcing on equipment depends on several factors:

frequency of use of the equipment by the employee;
experience and knowledge of workers dealing with hardware
equipment wear level;

If a person is not wearing the necessary personal protective suit and falls into the area of effect of the electric arc, the chances of survival decrease quite sharply. The risk of severe burns is extremely high.

Table

Table: degree of exposure to electric arc

What are the possibilities for protection from email? Dougie?

comply with all necessary safety rules and regulations;
in case of prolonged use of protective material, frequent washing, the suit should not deteriorate; (it all depends on the model);
the fabric must have a maximum of 2 seconds of residual combustion;
you must wear special shoes that have an antistatic effect and also have a suit for protection against electric arcs .

Source: http://svarak.ru/osnovyi-svarki/elektricheskaya-duga-sila-razryada-deystvii/

Welding arc

A welding arc is an electric arc discharge in an ionized mixture of gases, metal vapors and components that make up electrode coatings, fluxes and other means.

Physical and electrical properties of the welding arc

For an electrical discharge to occur, the gas gap between the electrodes must be ionized. The ionization process proceeds in the following order. When the end of the electrode and the workpiece come into contact, the protrusions of the rough surfaces are instantly heated by current to the melting and evaporation temperature due to the high ohmic resistance of the contact.

After the electrode is separated from the product, the heated end of the electrode (negative pole) begins to emit electrons, rushing to the anode under the influence of the potential difference between the electrodes. When colliding with electrode metal particles, which are present in the form of vapors in the interelectrode gap, electrons ionize them. Ionization instantly covers the entire interelectrode gap, and it becomes electrically conductive.

During the arcing process, ionization is maintained due to high temperature.

The arc voltage is equal to the sum of the voltage drops in its three main (Fig. 1) areas:

Uд=Uк+ Uc+ Ua =f(Iд),

where Ud is the arc voltage, V; UK is the voltage drop at the cathode, V; Uc is the voltage drop in the arc column, V; Ua is the voltage drop across the anode, V; Id is the current strength in the arc.

Fig.1. Arc voltage drop distribution

The dependence of the arc voltage on the strength of the welding current is called the static (volt-ampere) characteristic of the arc.

In general, the static characteristics of the arc are shown in Fig. 2. At low current values in the electrode (region 1), the static characteristic of the arc decreases. At average current values (for manual and automatic submerged arc welding), the arc voltage does not depend on the current strength (region 2, hard characteristic). In this case, with sufficient accuracy, the static characteristic can be expressed by the equation

Ud= a+ bld,

where ld is the length of the arc, mm; a, b are constant coefficients depending on the material of the electrodes, pressure and properties of the gaseous medium.

Fig.2. General view of the static characteristics of the arc

From this equation it follows that the voltage on the arc, all other things being equal, will depend on the length of the arc column.

An increasing static characteristic of the arc (region 3, see Fig. 2) is obtained at high current strength (with automatic submerged arc welding or when welding in a shielding gas environment).

AC welding arc

Due to the fact that the instantaneous values of the alternating current pass through zero 100 times per second, and the cathode spot, which is the source of electron emission, also changes its location, the ionization of the arc gap turns out to be less stable and the welding arc is less stable, other things being equal, compared to the arc direct current.

If the arc is connected to an alternating current circuit in series with an active resistance, then the instantaneous values of the source voltage and welding current are in phase. During each half-cycle, the arc dies out and is re-ignited (restored) after a certain period of time until the voltage of the current source rises to a certain value, called the re-ignition voltage.

Ignition of the arc is characterized by the beginning of the passage of current in the welding circuit. In each half-cycle there is a break in the passage of current when the arc fades. These breaks are called arc extinction times.

The moment of extinction occurs at a slightly lower instantaneous value of the source voltage than at the moment of ignition, for which higher values are required to obtain ionization of the cooled gap.

The arc extinction time depends on the maximum arc ignition voltage and the frequency of the alternating current.

The arc recovery time decreases with increasing open circuit voltage and when using higher frequencies. This time also decreases when the ignition voltage is reduced. Of these measures to increase the stability of the arc, the most common is to reduce the ignition voltage, which is achieved by using electrodes with ionizing coatings.

The magnitude of the ignition voltage depends on a number of factors, primarily on the magnitude of the arc current. As the welding current increases, the arc ignition voltage decreases.

For open arc welding, the ignition voltage Uz and arc voltage Ud have the following relationship:

Uз = (1.3 – 2.5) Uд

When welding at high currents under submerged arc, the ignition voltage is almost equal to the arc voltage.

Increasing the open circuit voltage of the power supply is limited by safety regulations, and the use of high frequencies requires the use of special equipment.

A generally accepted measure to increase the stability of an alternating current welding arc is to include coils with a steel core (chokes) in the welding circuit, which allow welding to be carried out with metal electrodes at a welding transformer voltage of the order of 60 - 65V and a standard frequency. In this case, the coating of the electrodes must contain a sufficient amount of ionizing components.

Source: http://oitsp.ru/welding_article/svarochnaya-duga

What is a welding arc

The welding arc has been used by mankind for the permanent, hermetically sealed connection of metals for more than a century. The physicist Volt studied it. Then welding devices appeared. An electrical discharge occurs when there is a short circuit between the electrode and the part being welded. Electrical energy is converted into thermal energy and a melt pool is formed. A diffuse homogeneous layer of metal is created at the site of the welded joint.

Having studied the current-voltage characteristics of the process, scientists improved the welding process and created welding machines that support stable arc burning.

What is a welding arc, definition

What can be called a welding arc is, in fact, a long-lasting conductor consisting of ionized particles, existing in time thanks to a supporting electric field. An arc discharge is characterized by a continuous form, high temperature, and occurs in a gas environment capable of ionization.

In welder's textbooks, the definition of a welding electric arc is as follows: this is a long-term electrical discharge in a plasma consisting of a mixture of ionized air or shielding gases, as well as evaporated components of the filler and base metal.

Nature and structure

In a short time, the metal can be heated to its melting temperature using a powerful welding arc. Its properties are characterized by current density and current-voltage indicators.

From the point of view of electrical engineering, an arc column is an ionized gas conductor between the cathode and anode with high resistance and the ability to glow.

A detailed examination of the structure of the welding arc will help to understand the essence of temperature effects. The average length of the electric arc is 5 mm, it is divided into main zones:

anodic, it is no more than 10 microns;
cathode, it is 10 times smaller than the anode;
pillar - a visible luminous strip.

The temperature of the welding arc is determined by the flow of free electrons. They are formed at the cathode spot. It heats up to 38% of the plasma temperature. In an arc column, electrons move towards the anode and positive particles move towards the cathode. The column has no charge of its own; it remains neutral. Inside, the particles are heated to 10,000°C, while the metal is heated on average to 2350°C, the standard temperature of the melt bath is 1700°C.

The place where electrons enter and are neutralized is called the anode spot. Its temperature is 4–6% higher than that of the cathode.

The voltage in the anode and cathode zones is significantly reduced, and no glow occurs. Only plasma that emits ultraviolet, infrared and light waves is visible. They are harmful to the organs of vision and skin. Therefore, welders use personal protective equipment.

Welding arc: what it is, temperature and structure, features and characteristics

The modern industrial sector involves welding processes that are used in different directions.

In order to carry out this work efficiently, reliably, quickly and without spending much effort, it is necessary to understand the concept of a welding arc - what it is, what its features are and other points that are useful in the work.

What is a welding arc?

A welding arc is an electrical discharge with high power and long duration, passing between energized electrodes in gas mixtures.

The welding element in question is characterized by high temperature and current density, due to which the mechanism can melt any metal with a melting point greater than 3000 degrees.

In addition, this part in the welding tool acts as a gas conductor, with the help of which thermal energy is converted from electrical energy. An electric charge, in turn, is the passage of an energized current through gases.

Methods for igniting a welding arc.

There are several main types of electric charge with which the combustion process occurs:

Smoldering.
May occur due to low blood pressure. Used for lighting process in fluorescent lamp and plasma screen.
Spark.
Appears after the pressure reaches atmospheric pressure. Has an intermittent shape. The mechanism of action can be compared to lightning. Used to ignite an internal combustion engine.
Arc.
Used during welding work or for simple lighting. It has a continuous shape, appears due to atmospheric pressure.
Crown.
Appears if the electrode is structurally rough, non-uniform, there is no additional electrode, in other words, a trickle appears. Used to clean the gas mixture from dirt and other foreign objects.

Varieties

There are several classifications of the element in question, which have different current supply schemes and the environment where it appears.

Arc welding is divided into the following types:

With direct action.
In this case, the equipment is installed parallel to the metal product that needs to be welded. The arc, in turn, becomes at right angles towards the electrodes and the metal surface.
With indirect action.
Appears when using two electrodes that are located at an angle of 50 degrees from the work being welded. An arc appears between the electrode and the material being welded.

The appearance of a welding arc.

In addition, it can be divided according to the principle of the atmosphere where the welding arc appears:

Open sphere.
The arc can burn in an open space with the formation of a gas phase, which contains vapor of the metal, electrode and surfaces after processing with a welding tool.
Closed sphere.
The arc burns under flux. In the gas phase near the arc, vapor from the material, electrodes and the flux layer itself enters.
With supply of gas mixture.
The arc may contain compressed gas such as helium, carbon dioxide, hydrogen, argon and other gaseous impurities. They are necessary so that the welded surface of the product is not subject to oxidation. Thanks to their supply, the environment is restored or becomes neutral to external factors. The gas supplied for operation, steam from the product being welded and the electrodes enter the arc.

In addition to the listed classifications, we can also distinguish types by duration of action:

classic is used for constant use;
pulse – for one-time use.

One of the most popular parts is steel, i.e. consumable electrode. However, today most professionals prefer non-melting, from which we can conclude that the types of elements under consideration are quite different from each other.

Combustion conditions

Under standard conditions, the temperature in the welding arc column reaches 7000 degrees, at its maximum value. Using the cathode, it is necessary to achieve a constant temperature at which the arc will occur and burn. In this case, factors such as diameter, size and ambient temperature are also taken into account.

Classification of the welding arc.

It is important to ensure that the value does not fluctuate, so you can weld absolutely any material. A working power source is the key to a constant temperature indicator of the element; this is what influences the operating properties of the element.

The main areas of the welding arc are the work of ionized gas, as well as the use of an alkaline or alkaline earth group in the form of potassium or calcium to promote a reliable and good burning of the welding arc. The question in what environment a welding arc can burn is quite relevant.

It is necessary to take into account many physical and chemical factors, be able to calculate how much energy is expended to remove an electron from an atom, depending on the nature of the new gas formation, etc.

Bottom line

Based on all that has been said, we can conclude that when arc welding, metal structures are held together most reliably. Welding work greatly influences the industrial sphere of today, due to the ability to solder different materials to each other under the high temperature of the welding arc.

To obtain a high-quality and reliable seam, you need to use the forces acting in the welding arc, study its entire characteristics, understand each value of current density, temperature, voltage, which will make it possible to carry out the procedure quickly and without difficulties.

Source: https://tutsvarka.ru/vidy/svarochnaya-duga

What is a welding arc, its definition

A welding arc is considered to be a very large electrical discharge in terms of power and duration that exists between the electrodes to which voltage is applied in a mixture of gases.

Its properties are characterized by high temperature and current density, thanks to which it is capable of melting metals with a melting point above 3000 degrees.

In general, we can say that an electric arc is a conductor made of gas that converts electrical energy into thermal energy. Electric charge is the passage of electric current through a gaseous medium.

There are several types of electrical discharge:

Glow discharge. Occurs at low pressure, used in fluorescent lamps and plasma screens;
Spark discharge. Occurs when the pressure is equal to atmospheric pressure and has an intermittent shape. Lightning corresponds to a spark discharge; it is also used to ignite internal combustion engines;
Arc discharge. Used for welding and lighting. It is characterized by a continuous form and occurs at atmospheric pressure;
Crown. It occurs when the body of the electrode is rough and inhomogeneous, the second electrode may be missing, that is, a jet appears. Used to purify gases from dust;

Emergence

It occurs during a rapid short circuit, that is, when the electrode comes into contact with the surface of the material being welded, due to the colossal temperature, the surface of the material melts, and a small strip of molten material forms between the electrode and the surface.

By the time the electrode and the material being welded diverge, a neck of material is formed, which instantly breaks and evaporates due to the high current density. The gas becomes ionized and an electric arc occurs. You can excite her by touching or scratching.

Peculiarities

It has the following features compared to other electric charges:

High current density, which reaches several thousand amperes per square centimeter, due to which very high temperatures are achieved;
Uneven distribution of the electric field in the space between the electrodes. Near the electrodes the voltage drop is very high, when in the column it is the opposite;
Huge temperature, which reaches the highest values in the column due to the high current density. As the length of the column increases, the temperature decreases, and when it narrows, on the contrary, it increases;
Using welding arcs, you can obtain a wide variety of current-voltage characteristics - the dependence of the voltage drop on the current density at a constant length, that is, steady combustion. At the moment, there are three current-voltage characteristics.

The first is falling, when with an increase in strength and, accordingly, current density, the voltage drops. The second is hard, when a change in current does not affect the voltage value in any way, and the third is increasing, when as the current increases, the voltage also increases.

Thus, the welding arc can be called the best and most reliable way of fastening metal structures. The welding process has a major impact on today's industry because only the high temperature of the welding arc is capable of holding most metals together.

To obtain high-quality and reliable seams, it is necessary to correctly and correctly take into account all the characteristics of the arc, monitor all values, thanks to this the procedure will be quick and most effective. It is also necessary to take into account the properties of the arc: current density, temperature and voltage.

Source: https://svarkalegko.com/tehonology/vse-o-svarochnoj-duge.html

Electric arc: what is it, causes, properties

Everyone had to observe spark discharges, including people who were far from knowledge of electrical engineering. Thunderstorms are accompanied by giant spark discharges. The release of enormous energy concentrated in the electrical discharge of lightning (see Fig. 1) is accompanied by a blinding flash of a hot barrel. One of the types of spark discharges created by humanity is an arc discharge, or simply, an electric arc.

Rice. 1. Lightning discharge

To date, the reasons for the occurrence and properties of an electric arc have been studied in detail by science. Physicists have found that in the area of its combustion there is a huge concentration of charges that form the plasma of the barrel. The temperature of the column reaches several thousand degrees.

What is an electric arc?

This mysterious phenomenon was first described by the Russian scientist V. Petrov. He created an electric arc using a battery consisting of thousands of copper and zinc plates. Studying the process of igniting an arc with direct current, the scientist came to the conclusion that the air gap between the electrodes under certain conditions becomes electrically conductive.

One of the conditions for the occurrence of electrical breakdown is a sufficiently high potential difference at the ends of the electrodes. The higher the voltage, the larger the gas gap the discharge can bridge. In this case, an electrically conductive gas column is formed, which becomes very hot during the burning of the arc.

Rice. 2. Electric arc

A reasonable question arises : “Why does air, which is an excellent insulator in its normal state, suddenly become a conductor?”

There can be only one explanation - charge carriers are formed in the arc barrel, capable of moving under the influence of an electric field. Since there are no free electrons in air, unlike metals, only one conclusion suggests itself - ionization of gases (see Fig. 3). That is, starting the process of gas saturation with ions that are carriers of electric charge.

Rice. 3. Physics of the electric arc

Air ionization occurs under the influence of various types of radiation, including X-ray and cosmic irradiation. Therefore, there are always small amounts of ions in the air. But since the ions almost immediately recombine (turn into neutral atoms and molecules), the concentration of charged particles is always tiny. It is impossible to produce an arc flash at such a concentration.

For an arc discharge to occur, an avalanche-like ionization process is required. It can be caused by the strong heating of the gas that occurs during ignition.

When the contacts open, electrons are emitted and accumulate in a very small space. Under the influence of electric field strength, negative charges rush towards the electrode with a positive sign.

When the breakdown voltage is reached, a spark discharge occurs between the electrodes, heating the area between the electrodes. If the current is large enough, then the amount of heat will be sufficient to trigger an avalanche-like process of air ionization.

In an area called the arc gap, a barrel is formed, called an arc column, consisting of hot conductive plasma. A current flows through this barrel, maintaining the heating of the plasma. This is how the arc discharge ignites.

Saturation of the plasma barrel with ions of different signs leads to a significant increase in the current density, as well as to the recombination of some of the ions. Warming up the plasma also leads to an increase in pressure in the barrel. Therefore, some of the ions escape into the surrounding space.

If the formation of new charges is not maintained, the arc will be extinguished. As we have already found out, stable combustion is accompanied by 2 factors: the presence of voltage between the electrodes and maintaining a high plasma temperature. Excluding one of them will lead to arc extinguishing.

Thus, we can formulate the definition of an electric arc . Namely, an electric arc is a type of spark discharge, accompanied by a high current density, burning duration, and a small voltage drop across the barrel, characterized by increased gas pressure in which a high temperature is maintained.

An electric arc differs from a conventional discharge in that it burns longer.

Structure

The electric arc consists of three main zones:

cathode;
anodic;
plasma column.

In welding arcs, the dimensions of the cathode and anode zones are small compared to the length of the column. The thickness of these zones is thousandths of a millimeter. In the area of the cathode voltage drop (at the end of the negative electrode), the presence of cathode spots is observed, which are formed as a result of strong heating.

Figure 4 shows a diagram of the structure of the arc created by the welding machine.

Rice. 4. Welding arc structure

Please note: for the purpose of clarity, the electrode zones are greatly exaggerated in the picture. In reality, their thickness is measured in microns.

Properties

The high current density in the shaft of the electric arc determines its main properties:

Extremely high temperature of the plasma barrel and near-electrode zones.
Long-term combustion, while maintaining the conditions for the formation of ions.

These properties must be taken into account when combating the occurrence of an electric arc, and when using it in some areas.

Useful Application

Oddly enough, physicists found application for this electrical phenomenon even at the stage of development of the science of electricity. An example of this is the Yablochkov light bulb . It consisted of two carbon electrodes, between which an electric arc was ignited.

This lamp had two drawbacks. The electrodes quickly wore out (burned out), and the light spectrum shifted to the ultraviolet zone, which negatively affected vision. For these reasons, arc lamps did not find widespread use and were quickly replaced by incandescent lamps, which exist to this day.

The exception is arc-discharge lamps, as well as high-power spotlights used primarily for military purposes.
The arc discharge has been widely used in practice since the invention of the welding machine. Arc welding is used for welding metals. (see Fig. 5)

Rice. 5. Arc welding

Using plasma conductivity, including special welding electrodes in the welding circuit, a high temperature is achieved in a concentrated spot. By adjusting the welding current, the welder has the opportunity to adjust the machine to the desired temperature of the arc discharge. To protect the barrel from heat loss, the metal electrodes are coated with a special mixture that ensures combustion stability.

An electric arc is used in blast furnaces for melting metals. Arc melting is convenient in that you can regulate its temperature by changing the current parameters.

Along with useful applications, in electrical engineering we often have to deal with arc discharges. An uncontrolled arc discharge can cause significant damage on power lines, industrial and domestic networks.

Rice. 6. Arc discharge on power lines

Causes

Based on the definition, we can name the conditions for the occurrence of an electric arc:

the presence of multipolar electrodes with high currents;
creation of a spark discharge;
maintaining voltage on the electrodes;
providing conditions for maintaining the temperature of the barrel.

A spark discharge occurs in two cases: during short-term contact of the electrodes or when approaching breakdown parameters. A powerful electrical breakdown always ignites the barrel.

While maintaining the optimal arc length, the plasma temperature is maintained independently. However, as the gap between the electrodes increases, intense heat exchange occurs between the barrel and the surrounding air. Eventually, in the barrel, due to a drop in temperature, the formation of ions will stop like an avalanche, resulting in the extinguishing of the flame.

Breakdowns often occur on high-voltage power lines. They can lead to the destruction of insulators and other negative consequences. A long electric arc goes out quite quickly, but even in a short burning time its destructive power is enormous.

An arc tends to form when contacts open. In this case, the switch contacts quickly burn out, the electrical circuit remains closed until the barrel disappears. This is dangerous not only for networks, but also for humans.

Extinguishing methods

It should be noted that arc extinction occurs for various reasons. For example, as a result of cooling of the column, a voltage drop, or when the air between the electrodes is displaced by external vapors that prevent ionization.

In order to prevent the formation of arcs on high-voltage power line wires, they are spaced over a long distance, which eliminates the possibility of breakdown. If a breakdown between the wires does occur, the long barrel will quickly cool and extinguishment will occur.

To cool the barrel, it is sometimes divided into several components. This principle is often used in the designs of air circuit breakers designed for voltages up to 1 kV.

Some circuit breaker models contain multiple arc chutes to promote rapid cooling.

Rapid ionization can be achieved by evaporating certain materials surrounding the space of the moving knives. High-pressure evaporation blows away the plasma of the barrel, resulting in extinguishing.

There are other methods: placing contacts in oil, auto-blowing, using electromagnetic damping, etc.

Exposure to humans and electrical equipment

An electric arc poses a danger to humans due to its thermal effects, as well as the ultraviolet effect of the emitting light. High AC voltage poses a huge danger. If an unprotected person is at a critically close distance from live parts of devices, an electrical breakdown may occur with the formation of an arc. Then, in addition to the effect of current, the body will be affected by a thermal component.

The spread of an arc discharge through structural parts of equipment threatens to burn out electronic elements, boards and connections.

Source: https://www.asutpp.ru/elektricheskaya-duga.html

Welding arc - Description and characteristics

In order to successfully carry out the welding process, a welding arc is required. This is an electrical discharge, which is characterized by very high power and is quite long-lasting. It occurs between elements such as electrodes, which are located in a certain gaseous environment. For an arc to occur, voltage must be applied to the electrodes.

General description of the arc

The main distinguishing properties of the welding arc are its very high temperature and current density. Thanks to these two qualities together, the arc can easily melt metals whose melting point is 3000 degrees Celsius.

We can say that this arc is a conductor that consists of volatile substances, and its main purpose is the conversion of electrical energy into thermal energy. The electric charge itself is the moment of passage of electric current through a gaseous medium.

Types of discharge

A welding arc is a discharge, and since there are several types of it, there are several types of the arc itself:

The first type is called a glow discharge. This type occurs only in a low-pressure environment, and is used only in things like plasma screens or fluorescent lamps.
The second type is a spark discharge. The appearance of this type occurs at a time when the pressure is approximately equal to atmospheric pressure. It differs in that it has a rather discontinuous shape. A striking example of such a discharge is lightning.
A welding arc is an arc discharge. This is the type most often used during welding. It occurs in the presence of atmospheric pressure, and its shape is continuous.
The last type is called crown. Most often it occurs when the electrode surface is rough and heterogeneous.

Nature of the arc

It is worth saying that the electric welding arc is not as complicated as it seems at first glance; it is quite simple to understand its nature. This uses an electric current that flows through an element such as a cathode. After this, it enters an environment with ionized gas.

At this moment, a discharge occurs, which is characterized by bright light and very high temperature. In general, the welding arc can have a temperature ranging from 7,000 to 10,000 degrees Celsius. After passing this stage, the current will pass to the material that is being welded.

We can say that the source of the welding arc is an electric current that has undergone changes.

Due to such high temperatures, the arc will emit infrared and ultraviolet rays, which are harmful to human health. This is dangerous to a person's eyes and can also cause light burn. For the above reasons, all welders should have good personal protective equipment.

Arc structure

The structure (structure) of a welding arc includes three main components, or sections - the anode and cathode sections, as well as the arc column. It is worth noting that during the burning of the welding arc, active spots or areas will form in the anode and cathode areas, which are characterized by a maximum temperature value.

All the electrical current produced by the power source will pass through these two areas. At the same time, the greatest drop in the welding arc voltage will also be recorded in these two areas. The arc column is located between these two zones, and such a parameter as the voltage drop will be minimal in this case.

From all of the above, we can conclude that, firstly, the power source of the welding arc can produce a fairly high voltage and high current. Secondly, the length of the arc will consist of the totality of those areas that were listed above.

Most often, the length of such an arc is several millimeters, provided that the anode and cathode regions are 10-4 and 10-5 cm, respectively. An arc of 4-6 mm is considered the most favorable length.

It is with these indicators that it will be possible to achieve stable combustion and high temperatures.

The difference between a welding arc lies in the supply pattern, as well as in the environment in which it can occur. Currently, there are two most common types of arc:

Direct arc. In this case, the welding machine must be positioned parallel to the object being welded. An electric arc will occur when the angle between the metal workpiece and the electrode is 90 degrees.
The second main type is an indirect type of welding arc. It occurs only if two electrodes are used, and they are located at an angle of 40-60 degrees relative to the surface of the metal part. An arc will occur between these two elements and weld the metal together.

Classification

It is worth noting that there is a classification of the arc depending on the atmosphere in which it will occur. Today there are three types known:

The first type is an open arch. When welding of this type, the arc will burn in the open air, and a small gas layer will form around it, which will include vapors of the metal, electrodes and their coating.
Closed type. The combustion of such a welding arc is characterized by the fact that it occurs under a layer of flux.
The last type is an arc with gas supply. In this case, a substance such as helium, argon or carbon dioxide is supplied to it. Several other types of gases can be used.

The main difference between the latter type is that the supplied gases will prevent such phenomena as metal oxidation during welding.

A slight difference is also observed in terms of the duration of such an arc. According to its characteristics, the welding arc can be stationary or pulsed. Stationary is used for continuous welding of metals, that is, it is continuous. The pulse type of arc is a single impact on the metal, a precise touch.

Working elements, that is, electrodes, can be carbon or tungsten. These electrodes are also called non-consumable electrodes. You can also use metal elements, but they will melt in the same way as the workpiece. The most common type of electrode is steel when it comes to consumable types. However, the use of non-melting types is becoming increasingly popular today.

The moment of arc occurrence

A welding arc occurs when a rapid short circuit occurs. This happens when the electrode comes into contact with a metal workpiece.

Due to the fact that the temperature is simply enormous, the metal begins to melt, and a thin strip of molten metal appears between the electrode and the workpiece.

When the electrode and metal diverge, the latter evaporates almost instantly, since the current density is very high. Next, the gas ionizes, which is why a welding arc appears.

Arc conditions

Under standard conditions, that is, at an average temperature of 25 degrees and a pressure of 1 atmosphere, the gas is not capable of conducting electric current. The main requirement for the occurrence of an arc is the ionization of the gaseous medium between the electrodes. In other words, the gas must contain some charged particles, electrons or ions.

The second important condition that must be observed is to constantly maintain the temperature at the cathode. The required temperature will depend on characteristics such as the nature of the cathode, as well as its diameter and size. Ambient temperature will also play an important role.

The welding arc must be stable and at the same time have a huge current strength, which will give a high temperature indicator (7 thousand degrees Celsius or more). If all conditions are met, then the resulting arc can process any material. To ensure a constant and high temperature, it is necessary for the power source to function as stably as possible.

It is for this reason that the power source is the most important part when choosing a welding machine.

Welding inverter. Arc and its features

It’s worth starting right away with the main difference between an inverter power source and a conventional transformer one. Electrical energy consumption has been reduced by almost half. The characteristic of the current that occurs when using an inverter allows for faster ignition of the arc, and also ensures stable combustion throughout the entire operation process.

The welding inverter itself is a rather complex device that performs operations to change the current to ensure the most stable operation of the arc. For example, a device is connected to the network and receives alternating current as an input, which it is able to convert into direct current.

Next, the direct current enters the inverter block, where it is again converted into alternating current, but at a much higher frequency than it was in the network. This current is transferred to the transformer, where its voltage is significantly reduced, causing its strength to increase.

After this, the rectified and tuned alternating current is transferred to the rectifier, where it is converted into direct current and supplied for operation.

Source: https://FB.ru/article/387046/svarochnaya-duga---eto-opisanie-i-harakteristiki

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