What is the temperature of the welding arc - Metals and their processing

What is a welding arc: structure, temperature, length and types

Without welding work, it is impossible to imagine the construction of bridge structures or the solution of production problems in many industries. To answer the question of what a welding arc is, it is necessary to delve into the description of the physical processes occurring in a gaseous environment between oppositely charged poles.

An electric arc converts the energy of the generated current into heat, instantly creating a temperature regime at which all metals known to science melt.

Brief description and history of invention

What arc is called a welding arc? This is a substance that carries the power of an electrical discharge flowing among the vapors of melting metal and additives. It has individual characteristics:

formation is characterized by large heat releases - the temperature reaches 6 thousand degrees;
this produces a powerful luminous flux, so the welder needs special equipment to protect the face and organs of vision, thick clothing and gloves;
it is an excellent conductor of high current current, and therefore poses a danger to humans;
the best way to reliably connect metal structures of varying complexity.

The primacy in who invented it and in the primary description of the physical phenomenon is still debated among pundits - the British chemist, physicist and geologist Sir Humphry Davy , who described the electric discharge arc in 1808, is officially considered the discoverer. The Russian scientist-inventor, professor of physics from the Medical-Surgical Academy of St. Petersburg V.V. Petrov discovered a similar phenomenon and described it in detail 6 years earlier than the Englishman.

Types of discharges

There are several types of similar discharges:

Smoldering. Formed at low pressure, used in fluorescent light sources.
Spark type. Characterized by an intermittent form, occurs at normal pressure: for example, lightning strikes or spark plug sparks in engines.
A non-intermittent electric arc that occurs at atmospheric pressure. Used for lighting or electric arc welding of metals.
Corona - the most interesting of all types, appears in a non-uniform field when one of the electrodes is many times larger than the other. It is used in industry to purify used gases from foreign inclusions of dust.

All discharges are extremely dangerous for living organisms - when working with them, you must strictly follow safety rules.

Nature of the phenomenon

A welding arc is an electric discharge that has high power and exposure time; it occurs between opposite poles located in a mixture of gases when voltage is applied to them. It is characterized by a bright luminous flux, high temperature, capable of melting metals for their reliable connection.

To prevent the light flux from burning the skin and retina of the eyes, special equipment is used to protect the performer.

Structure

What zones are called cathode and anode spots? The cathode spot is a source of electrons that heats up to a high temperature, which ensures the melting of metals. Up to 38% of the total thermal energy is concentrated here, and 12-18 V of voltage is also lost.

Anode spot - characterized by temperatures up to 26000C and the release of up to 42% of thermal energy. Voltage losses up to 11 V; due to the constant attack of electrons, it has the shape of a crater.

The arc column is a neutral section, it contains about 20% of the total heat and maximum temperature, voltage loss no more than 12 V.

Favorable pole length is up to 6 mm, at this size the arc temperature is stable, which has a beneficial effect on the strength of the seam.

When manually welding or in a mechanized environment with consumable electrodes in a shielding gas and using a direct current source, they use the reverse and direct polarity method, for example, when connecting thick-walled parts, the anode is connected to them to ensure maximum heat, as well as sufficient welding depth.

Kinds

direct impact, burns steadily between the parts being connected and the electrode;
indirect action - it is created by two electrodes, and the structure intended to be connected together is not involved in the general circuit;
three-phase option - one phase is connected to each participant in the process;
plasma - the column is compressed by protective gases.

To create an arc when using a transformer, you need to touch the workpieces being connected with an electrode, but modern equipment for welding allows you to activate the arc using a non-contact method; an oscillator is used for this.

Classification

The electric arc has different types, which directly depends on the type of welding performed and the environment where it is performed.

Open type. Welding is performed in an open space without the use of gas; only fumes of melting metal, electrode coating, and air molecules are involved.
Closed view. For this, flux is used, which protects the welding site from environmental influences.
Arc welding with a consumable electrode in shielding gas. Welding work is carried out using inert gas supplied under high pressure.

In addition, classification according to parameters is used:

current;
burning duration;
what electrodes are used;
principle of operation.

Moment of occurrence

The formation of an electric arc during welding is the result of a short circuit between opposite poles : at high temperatures, the metal begins to melt, and a strip of metal appears between the parts being connected .

Then a neck about 5 mm long is extended, the heating rises to maximum, the molecules of the air column are ionized, which is necessary to stabilize the arc, and the welded arc firmly connects the structures. Experienced welders keep the electrode at the same distance from the surface of the workpiece at all times. therefore, the resulting seam is smooth, without sag.

Combustion conditions

Gaseous substances are distinguished by one feature - under normal conditions they cannot conduct current, because their molecules are neutral at this moment. Ionization is required so that an electrical impulse appears in the connection zone . The second condition is that the temperature of the cathode must be constantly maintained at the same level; a similar state of the surrounding air also plays an important role.

The resulting arc must burn steadily, this is influenced by the current strength - the more powerful it is, the higher the temperature created in the welding zone, up to the maximum. When the performer complies with the agreed conditions, then any metal can be melted using welding. The power source is of no small importance, because the quality of the welded joint depends on the stable operation of the device.

Peculiarities

This physical phenomenon has individual differences:

In the column the density reaches 10-20 A/mm2.
The electric field is distributed unevenly - small values in the middle of the column and huge ones closer to the periphery.
Due to its properties in the form of a high density of gases, high temperature is concentrated in the arc; the shorter the length of the column, the faster it reaches its maximum.
By adjusting the arc length, differences in current-voltage characteristics are also obtained.

Welding is deservedly recognized as a reliable method of connecting various structures, which has no alternative . It is used in all areas of industry, but to obtain high-quality joints, it is necessary to take into account all parameters that affect the strength and ductility of the seam.

How is power determined?

This parameter depends on many reasons: the basis is the length of the column, then comes the power and high current supplied to the electrode. When extended, the arc does not fade; the power is affected only by the thickness of the column, as well as its density.

Duration

In practice, the continuous mode is most often used, and the pulse mode is used during resistance welding, when the connection does not occur with a continuous seam, but only at specially calculated points. Tightness in this mode is not ensured, but the connection of thin-walled housings is made firmly .

To obtain a hermetic connection, a roller moving along the edge of the workpiece becomes the electrode. The pulse is supplied with a small interval, so the metal melting zones partially overlap, resulting in a continuous seam. This technique is performed with automatic connection of pipelines.

Temperature zones

The central part of the arc column in any welding option has high temperature values, and next to the cathode or anode it accounts for only 60-70% of the total thermal energy. When connecting alternating current, there is no polarity because the arrangement of the poles changes at intervals of 50-60 oscillations per second.

The welding arc in this mode is much less stable, and its temperature is constantly changing. The advantages of this process of joining metals include simple and inexpensive equipment, as well as the complete absence of a negative phenomenon called magnetic blast.

Volt-ampere characteristics

There are three known analogues of external power supplies:

falling, when the voltage decreases and the strength and current density increases;
hard - the voltage value does not depend on the current strength;
increasing, the voltage increases along with the current strength.

The graph clearly shows a red diagram showing the voltage drop during arc formation, and then during stable combustion. The curves start from the point that indicates the idle speed of the transformer (about 50 V). At the moment of formation of the welding arc, the voltage drops quite sharply, but then stabilizes and becomes a constant value.

Inverter for welding work

Let us briefly note that the difference between an inverter and other welding machines is as follows:

Consumes half as much electricity.
The current parameters allow rapid arc formation.
Combustion stability during welding.
This is a complex design that can vary the current intensity for maximum arc stability.
It converts alternating current into direct current, but at a higher frequency and vice versa.
The product has a built-in step-down transformer.

The last phase consists of directing high frequency direct current to the rectifier and then to the electrode.

conclusions

We found out the nature of the occurrence of an electric arc, its technical characteristics, classification, as well as basic parameters. For a novice welder, everything described above is an axiom; the more theoretical knowledge, the faster the young performer will learn to correctly connect various metals and gain the necessary experience.

Source: https://svarka.guru/vidy/thermo/dugovaya/info.html

How is the power of a welding arc determined?

The power of the welding machine is one of the main characteristics that you need to pay attention to when choosing it.

In order to better understand all the intricacies associated with welding devices and understand the main points for calculating this parameter, it is necessary to clarify several important aspects. The information will be useful to know for all those involved in welding.

Main types of welding machines

Inverter device for welding.

Inverter welding machines are divided into three categories:

household;
semi-professional;
professional.

The noted division is made primarily based on the area and frequency of use of the device. To understand what kind of welding machine you need, you need to determine the conditions of its use.

Household ones are designed for short operating times. It is not possible to use such devices for constant and long-term welding. After only 5-10 minutes of use, the device must be allowed to “rest” for the same, and sometimes longer, period of time.

At the same time, the ability to connect such an inverter to a single-phase household network makes it very convenient for use at home. For quick welding of metal structures in the country or for home work, it is not so critical how many breaks the welding inverter takes.

Semi-professional class inverters are able to operate longer, which is achieved due to the features of their design. Such devices are used in the repair of pipes, the manufacture of frames and metal structures. They are usually powered from a three-phase network.

Professional-grade devices are capable of working without interruption throughout the day. Their welding current can reach 500 amperes. This means that the power consumption of a welding inverter of this type will be the greatest.

All household, some semi-professional and professional devices can be powered from a 220 volt network. At the same time, do not forget that the mains current cannot exceed 160 amperes.

When purchasing an inverter, you must calculate in advance how much power it needs and how much current it will consume.

Connecting a device with higher ratings may lead to the machine turning off or to burnout of the socket contacts, since the equipment is designed for a larger number of kilowatts.

So, what should you pay attention to when choosing a household inverter? First of all, on the welding current, the characteristics of which are indicated by the manufacturer in the passport or manual for the device.

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This criterion shows at what current the normal operation of the inverter will be ensured without overload, taking into account the continuous load. Of course, it is better to give preference to devices with a power reserve of 30-50% to the operating current.

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

Dependence of welding current on metal thickness and electrode diameter.

In a regular city power grid, there are often power surges. As a rule, such changes occur in both directions by 15-20% of the nominal value of 220 volts.

Typically, household and professional inverters are not so sensitive to such surges. Even with them, they are able to work effectively.

However, when connected to a generator, fluctuations can be significantly greater. In this regard, it is better to choose a welding machine with protection against voltage surges.

It is quite difficult to check all the parameters of devices directly upon purchase, even if the devices have digital displays. Even they can display incorrect information and mislead the buyer.

Calculation of device power

Before you begin calculating the power of the device, you need to know the following parameters:

range of input voltage and welding current;
welding arc voltage;
Efficiency of a specific device;
duration of switching on;
Power factor.

The welding current interval shows at what network parameters you can work. This is due to the fact that in reality the declared 220 volts are not observed in household electrical networks. Sometimes the voltage can be less than 200 V, and sometimes it can significantly exceed 220 V.

When connecting the welding machine to the mains, a voltage drop of 5-10 percent from the nominal value may be observed.

Schematic diagram of the current regulator.

In this regard, it is advisable to pay attention to models for which the operating range is stated to be from 150-170 to 220-250 volts. It is these devices that are able to provide the best power performance.

The welding current range determines its highest and lowest values. The power of the inverter directly depends on this characteristic. For household models, the minimum values can vary from 10 to 50 A, and the maximum - from 100 to 160 A.

One of the important characteristics of the inverter is the on-time. This parameter actually indicates how high quality a particular device is. The meaning of the criterion comes down to the ratio of work time to “rest”.

A high percentage, on the contrary, indicates that the device can be used for an extended period of time without interruption.

The power factor of a welding inverter directly depends on the duration of switching on. The calculation to determine this characteristic is determined from the ratio of continuous operation time to total time.

Let's look at everything using a simple example. Let's calculate the power of an inverter welding machine that worked for 4 minutes before the protection tripped. It then needed to cool for two minutes before it was ready to go.

So, to find out what coefficient this device has, you need to divide three by five - the total operating time, and multiply by one hundred. We get the desired value. For household mini versions and semi-professional equipment, the coefficient does not exceed 0.6-0.7.

Welding machine characteristics table.

Let's say there is a device that requires a power supply of 160-220 V, and its maximum current is 160 amperes with an arc voltage of 23 volts. Let the efficiency of such a device be 0.89, and the duty cycle 60%.

The parameters listed above are quite sufficient to calculate power consumption. It is necessary to multiply the current by the arc voltage and divide it all by the efficiency. The result is 4135 watts.

This value shows the power consumed directly during operation. However, as mentioned earlier, it is also necessary to take into account the duration of activation. To do this, you need to multiply 4135 by 0.6. The result is 2481.

This value is the average power. It is considered the most relevant and correct when determining energy consumption.

This approach is closest to reality. After all, it is very rare to encounter a situation where the inverter would work for days on end without interruptions. Pauses and delays always happen; you simply cannot do without them.

It is worth at least taking into account the time required to change electrodes or to prepare parts for welding.

Power table

When choosing a welding inverter, it is necessary to take into account other factors besides the kW consumed. This is especially true for professional models. They are subject to higher demands than household versions.

Required inverter power for welding different metals.

It is necessary to take into account the thickness of the materials being welded. The power of the inverter welding machine and the thickness of the electrodes will also depend on this criterion. The required parameters are shown in the table below.

It greatly simplifies the calculation of power consumption depending on operating conditions. In addition, this table will be useful for beginners who often wonder about choosing an electrode of the correct diameter.

Metal thickness, mm	Welding current, A	Electrode diameter, mm
1,5	30-50	2
2	45-80	2,5
3	90-130	3
4	120-160	3
5	130-180	4
8	140-200	4
10	150-220	4-5
15 or more	160-320	4-6

The intensity and volume of work is the criterion by which a device with a certain duration of operation is selected. As already described above, this parameter shows how long the device can work with wire of a certain thickness under given conditions.

The operating conditions of the inverter determine its protection class. If the device is to be used indoors, then IP21 certification will be sufficient, but if used outdoors, when the temperature is low or there is high humidity, IP21 protection will be required.

Schematic diagram of a welding inverter.

As for the power supply, household appliances can also be plugged into a regular outlet. Professional inverters usually operate from a three-phase network with a voltage of 380 volts.

In addition to the above criteria, you must also pay attention to additional parameters. The functionality of an inverter can greatly simplify certain operations.

For example, arc forcing by optimizing the current strength will prevent sticking. Hot start allows you to quickly ignite the arc. Anti-stick switches off the inverter if the electrode gets stuck.

The presence of a display on the device will never be superfluous. It can display operating modes, which greatly simplifies the operation of the device.

Bottom line

This article describes what parameters of the inverter operating mode determine the power; it is shown that it is influenced by the welding arc voltage, current strength, duration of activation, etc.

Heating concrete with a welding machine

In addition, various classes of welding machines are considered, as well as their features and differences. This material will definitely be useful to novice welders who are still thinking about purchasing a welding machine.

Source: https://respect-kovka.com/chem-opredelyaetsya-moschnost-svarochnoy-dugi/

Temperature and other important characteristics of the welding arc

The principle of electric arc welding is based on the use of the temperature of the electrical discharge that occurs between the welding electrode and the metal workpiece.

An arc discharge is formed due to electrical breakdown of the air gap. When this phenomenon occurs, gas molecules are ionized, its temperature and electrical conductivity increase, and it transitions to the plasma state.

The burning of a welding arc is accompanied by the release of a large amount of light and especially thermal energy, as a result of which the temperature rises sharply and local melting of the workpiece metal occurs. This is welding.

Basic properties of arc discharge

During operation, in order to initiate an arc discharge, the workpiece is briefly touched by the electrode, that is, a short circuit is created, followed by breaking of the metal contact and establishing the required air gap. In this way, the optimal length of the welding arc is selected.

With a very short discharge, the electrode may stick to the workpiece, melting occurs too intensely, which can lead to the formation of sagging. A long arc is characterized by instability of combustion and insufficiently high temperature in the welding zone.

Instability and visible bending of the welding arc shape can often be observed during the operation of industrial welding units with fairly massive parts. This phenomenon is called magnetic blowing.

Its essence lies in the fact that the welding arc current creates a certain magnetic field, which interacts with the magnetic field created by the current flowing through the massive workpiece.

That is, the deflection of the arc is caused by magnetic forces. The process is called blowing because the arc is deflected, as if under the influence of wind.

There are no radical ways to combat this phenomenon. To reduce the influence of magnetic blast, welding with a shortened arc is used, and the electrode is also placed at a certain angle.

Combustion medium

There are several different welding technologies that use electric arc discharges, differing in properties and parameters. The electric welding arc has the following types:

open. The discharge occurs directly in the atmosphere;
closed. The high temperature generated during combustion causes abundant release of gases from the burning flux. Flux is contained in the coating of welding electrodes;
in a protective gas environment. In this option, gas is supplied to the welding zone, most often helium, argon or carbon dioxide.

Protection of the welding zone is necessary to prevent active oxidation of the melting metal under the influence of atmospheric oxygen.

The oxide layer prevents the formation of a continuous weld; the metal at the joint becomes porous, resulting in a decrease in the strength and tightness of the joint.

To some extent, the arc itself is capable of creating a microclimate in the combustion zone due to the formation of an area of high pressure that prevents the flow of atmospheric air.

The use of flux allows for more active squeezing of air from the welding zone. The use of protective gases supplied under pressure solves this problem almost completely.

Discharge duration

In addition to the protection criteria, the arc discharge is classified by duration. There are processes in which arc combustion occurs in a pulsed mode.

In such devices, welding is carried out in short bursts. During the flash, the temperature manages to increase to a value sufficient for local melting of a small zone in which a point connection is formed.

Most of the welding technologies used use a relatively long arc burning time. During the welding process, the electrode constantly moves along the edges being joined.

The area of elevated temperature that creates the weld pool moves after the electrode. After moving the welding electrode, and therefore the arc discharge, the temperature of the traversed area decreases, crystallization of the weld pool occurs and the formation of a strong weld.

Arc discharge structure

The arc discharge area is conventionally divided into three sections. The areas immediately adjacent to the poles (anode and cathode) are called anode and cathode, respectively.

The central part of the arc discharge, located between the anode and cathode regions, is called the arc column. The temperature in the welding arc zone can reach several thousand degrees (up to 7000 °C).

Although the heat is not completely transferred to the metal, it is quite enough to melt. Thus, the melting point of steel, for comparison, is 1300-1500 °C.

To ensure stable combustion of an arc discharge, the following conditions are necessary: the presence of a current of about 10 Amperes (this is the minimum value, the maximum can reach 1000 Amperes), while maintaining the arc voltage from 15 to 40 Volts.

This voltage drop occurs in an arc discharge. The voltage distribution across the arc zones is uneven. Most of the applied voltage drop occurs in the anodic and cathodic zones.

It has been experimentally established that when welding with a consumable electrode, the greatest voltage drop is observed in the cathode zone. The highest temperature gradient is observed in this part of the arc.

Therefore, when choosing the polarity of the welding process, the cathode is connected to the electrode when they want to achieve its greatest melting, increasing its temperature. On the contrary, for deeper penetration of the workpiece, the cathode is attached to it. The smallest part of the voltage drops in the arc column.

When welding with a non-consumable electrode, the cathode voltage drop is less than the anodic one, that is, the high temperature zone is shifted towards the anode.

Therefore, with this technology, the workpiece is connected to the anode, which ensures good heating and protection of the non-consumable electrode from excessive temperature.

Manual arc welding modes: parameters, electrodes

Despite the emergence of new convenient equipment, manual welding does not lose its position. I am attracted by the ease of use and the absence of the need for large expenditures. In order for the weld to be of the highest quality, it is necessary to carry out preparatory work, which includes establishing the modes necessary for a particular type of material to meet the requirements of the technological process.

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The manual arc welding mode is the setting of parameters that maximally guarantee the formation of a weld that has the required dimensions and configuration, as well as the characteristics necessary for a particular connection.

The parameters of the manual arc welding mode are divided into fundamental and complementary. The selection and installation of parameters is made by the welder himself according to existing requirements.

The choice is influenced by the type of welded joint, the article number of the metal of the parts being welded and the current conductor, and the spatial arrangement.

Main settings

The most significant parameters of manual arc welding:

current;
voltage;
polarity;
electrode diameter;
speed;
amplitude of vibrations across the seam.

The type and size of these parameters are selected by the welder before starting work based on recommendations and personal experience.

Current value

This value significantly affects the quality of the resulting seam and the speed of the welding process. There is a direct relationship between the parameters: the amount of current during welding is set according to the diameter of the selected electrode, and the diameter, in turn, depends on the thickness of the elements being welded.

To more accurately calculate the current value, use a formula in which it is directly proportional to the diameter of the electrode. In this case, a correction factor is applied. It is different for different diameters. At what current value is manual arc welding carried out? With a weak current, the stability of the arc is disrupted, the seam will not be completely welded, which causes cracks to appear. An increased current value causes a rapid welding process and leads to increased spatter distribution.

Electrode diameter

The choice of welding mode for manual electric arc welding includes the need to correctly determine the required electrode diameters. Electrodes with a diameter greater than 6 mm are heavy, making it difficult to hold them in the desired direction for a long time. In addition, when using such electrodes, the root of the seam is poorly welded.

If a multi-pass option is used, then the first layer is carried out with a 2-3 mm electrode, and for subsequent layers a larger diameter can be used. This is of great importance when welding critical structures, since a smaller diameter provides better penetration of the root. With one pass, you can immediately use a large-diameter electrode.

When solving the problem of choosing the correct electrode diameter, the type of surfaces to be welded is considered. For example, electrodes of small diameter have proven themselves to be good for welding cast iron products. At the same time, the heat level decreases and a small cross-section bead is formed. If preliminary cutting of the edges has been carried out, then it is possible to use electrodes with a diameter of 3 mm, without focusing too much on the thickness of the parts.

Arc voltage

This parameter depends on the arc length, that is, the distance from the end of the electrode to the metal surface. The arc has different sizes. More arc means more voltage. Melting requires a significant amount of heat. The weld seam becomes wider and the penetration depth is smaller.

The voltage depends on the diameter of the electrode and the current value. It is in the range of 18-45 V. The optimal choice of manual arc welding mode regarding voltage involves welding with a short arc. In this case, the voltage will not exceed a value of 20 V. An important circumstance for obtaining a good seam is the constancy of the selected arc.

Speed

Covered electrode manual arc welding modes include speed setting. To avoid overfilling the bath and, as a result, the occurrence of smudges on the metal, you should select the optimal speed value and maintain it constant throughout the entire process. High speed will lead to insufficient weld penetration, which will cause cracks.

If the movement is too slow, the liquid metal will begin to collect in front of the arc. The seam will be uneven and lack of penetration will appear. To obtain a successful seam, the speed should be 35-40 m/hour. Then the weld pool will be on top of the surface of the edges, without forming a flow down. Its transition to the connection will be smooth, no sagging or undercuts will form.

The seam width decreases as the speed increases.

Polarity

As a rule, constant current is used for welding work. Direct polarity with constant current makes it possible to weld thick parts. To avoid burns when connecting thin metals, reverse polarity is included. AC welding is practically not used because it reduces productivity.

The choice of welding mode for manual arc welding lies, in particular, in the ability to carry out the process with different polarities. In the direct version, the current conductor is connected to the minus terminal, and the metal connection to the plus. The elements of the welded joint begin to melt more intensely than the electrode. This is an advantage when welding thick metal parts.

Reverse polarity is obtained by connecting the electrode to positive and the metal parts to negative. This provides an intense electrode melt that exceeds the melting of parts.

The explanation is quite simple and corresponds to physical laws. Where there is plus, there is more heating. Accordingly, with straight polarity, the parts being welded heat up higher. It becomes possible to connect large products. Using this type of polarity on thin parts will cause burns and the seam will be of poor quality. Therefore, to connect thin parts, reverse polarity is provided.

Features for vertical placement

Welding in a vertical position is more difficult compared to the horizontal version. Therefore, the choice of arc welding modes in this case is especially important.

How is the welding current adjusted in a vertical position? The first requirement relates to the arc - it must be short. The volume of the weld pool should not be large. To reduce it, electrodes with a small diameter should be used, and the current should be set 10-15% less than when welding is carried out in a horizontal position at the bottom.

Extra options

Electric arc welding modes include not only basic, but also parameters that complement them. Such arc welding modes also influence the final weld.

Electrode stick out

Electrode extension is the distance from the end of the electrode to the surface of the metal part. It influences the welding process and the size of the resulting seam.

Increasing this parameter reduces the stability of the arc. The metal begins to spatter more strongly. The small overhang makes it difficult to observe the welding process. Spraying occurs on the nozzle.

Electrode coating thickness

Manual arc welding modes include the characteristics of the electrodes, in particular, its coating, namely its thickness. This parameter is regulated by GOST 9466. Optimal coating requires its end size to be in the range of 0.5-2.5 mm. The use of current conductors with such a coating thickness ensures a durable seam that can withstand heavy loads.

Number of passes

The single-pass welding method involves welding in one layer. No oscillatory movements are made. It is used when welding parts of small thickness, when the seam width does not exceed 14-15 mm. At the same time, the magnitude of residual deformations decreases. For butt joints, especially when welding thick elements, several layers are used, and this method is called multi-pass.

A seam made in one pass has a larger pool. The advantages are the high productivity of the process and the cost-effectiveness of the method. Disadvantages include reduced weld ductility and too large heating zone. All seams in multi-pass welding are made with electrodes of the same size.

Interesting video

Source: https://osvarka.com/obuchenie-svarke/rezhimy-ruchnoy-dugovoy-svarki

Welding arc temperature: brief description, arc length and conditions for its occurrence

The welding arc itself is an electrical discharge that lasts for quite a long time. It is located between energized electrodes located in a mixture of gases and vapors. The main characteristics of the welding arc are quite high temperature, as well as high current density.

general description

An arc occurs between the electrode and the metal workpiece being worked with. The formation of this discharge occurs due to the fact that electrical breakdown of the air gap occurs. When such an effect occurs, gas molecules are ionized, not only its temperature increases, but also its electrical conductivity, and the gas itself turns into a plasma state.

The welding process, or rather the burning of an arc, is accompanied by such effects as the release of large amounts of heat and light energy. It is precisely because of the sharp change in these two parameters towards their large increase that the process of metal melting occurs, since in a local place the temperature increases several times.

The combination of all these actions is called welding.

Arc Properties

In order for an arc to appear, it is necessary to briefly touch the workpiece with which you want to work with the electrode. Thus, a short circuit occurs, as a result of which a welding arc appears, its temperature rising quite quickly. After touching, it is necessary to break the contact and establish an air gap. This way you can select the required arc length for further work.

If the discharge is too short, it is possible that the electrode will stick to the material being processed. In this case, the melting of the metal will take place too quickly, and this will cause the formation of sagging, which is extremely undesirable. As for the characteristics of an arc that is too long, it is unstable in terms of combustion.

In this case, the temperature of the welding arc in the welding zone will also not reach the required value. Quite often you can see a curved arc, as well as severe instability, when work is carried out with an industrial welding unit, especially if work is carried out on parts with large dimensions.

This is often called magnetic blowing.

Magnetic blowing

The essence of this method is that the welding arc current is capable of creating a small magnetic field, which may well interact with the magnetic field that is created by the current flowing through the element being processed.

In other words, the deflection of the arc occurs due to the fact that some magnetic forces appear. This process is called blowing because the deflection of the arc from the outside looks like it is due to strong wind. There are no real ways to get rid of this phenomenon.

In order to minimize the influence of this effect, you can use a shortened arc, and the electrode itself must be located at a certain angle.

Arc structure

Currently, welding is a process that is discussed in sufficient detail. Thanks to this, it is known that there are three arc burning regions. Those areas that are adjacent to the anode and cathode are the anode and cathode sections, respectively. Naturally, the temperature of the welding arc during manual arc welding will also differ in these zones.

There is a third section, which is located between the anode and cathode. This place is usually called the arc column. The temperature required to melt steel is approximately 1300-1500 degrees Celsius. The temperature of the welding arc column can reach 7000 degrees Celsius.

Although it is fair to note here that it is not completely transferred to the metal, however, this value is enough to successfully melt the material.

There are several conditions that must be created to ensure a stable arc. A stable current with a strength of about 10 A is required. With this value, you can maintain a stable arc with a voltage from 15 to 40 V. It is worth noting that the current value of 10 A is the minimum, the maximum can reach 1000 A.

The distribution of voltage across sections is uneven and is greatest in the anode and cathode. Voltage drop also occurs in an arc discharge. After carrying out certain experiments, it was found that if welding is carried out with a consumable electrode, the greatest drop will be in the cathode zone.

In this case, the temperature distribution in the welding arc also changes, and the greatest gradient occurs in the same area.

Knowing these features, it becomes clear why it is important to choose the correct polarity when welding. If you connect the electrode to the cathode, you can achieve the highest temperature of the welding arc.

Temperature zone

Regardless of the type of electrode used for welding, melting or non-consumable, the maximum temperature will be at the column of the welding arc, from 5000 to 7000 degrees Celsius.

The area with the lowest temperature of the welding arc shifts to one of its zones, the anodic or cathodic. These areas experience 60 to 70% of the maximum temperature.

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AC Welding

Everything described above concerned the procedure for welding with direct current. However, alternating current can also be used for these purposes. As for the negative aspects, there is a noticeable deterioration in stability, as well as frequent jumps in the combustion temperature of the welding arc.

One of the advantages is that you can use simpler, and therefore cheaper equipment. In addition, in the presence of a variable component, such an effect as magnetic blast practically disappears.

The last difference is that there is no need to select polarity, since with alternating current the change occurs automatically with a frequency of about 50 times per second.

It can be added that when using manual equipment, in addition to the high temperature of the welding arc with the manual arc method, infrared and ultraviolet waves will be emitted. In this case, they are emitted by a discharge. This requires maximum protection for the worker.

Arc burning environment

Today, there are several different technologies that can be used during welding. They all differ in their properties, parameters and welding arc temperature. What methods are there?

Open method. In this case, the discharge is burned in the atmosphere.
Closed method. During combustion, a fairly high temperature is formed, causing a strong release of gases due to the combustion of flux. This flux is contained in the coating, which is used to process welding parts.
Method using protective volatile substances. In this case, gas is supplied to the welding zone, which is usually presented in the form of argon, helium or carbon dioxide.

The presence of such a method is justified by the fact that it helps to avoid active oxidation of the material, which can occur during welding when the metal is exposed to oxygen.

It is worth adding that, to some extent, the temperature distribution in the welding arc occurs in such a way that a maximum value is created in the central part, creating a small microclimate of its own.

In this case, a small area with increased pressure is formed. Such an area can in some way impede the flow of air.

Using flux allows you to get rid of oxygen in the welding area even more effectively. If you use gases for protection, this defect can be eliminated almost completely.

Classification by duration

There is a classification of welding arc discharges according to their duration. Some processes are carried out when the arc is in a mode such as pulsed. Such devices weld in short bursts.

For a short period of time, while flashing occurs, the temperature of the welding arc manages to increase to such a value that is enough to produce local melting of the metal.

Welding occurs very precisely and only in the place where the device touches the workpiece.

However, the vast majority of welding equipment uses a long-lasting welding arc. During this process, the electrode continuously moves along those edges that need to be connected.

There are areas called weld pools. In such areas, the arc temperature is significantly increased, and it follows the electrode. After the electrode passes the area, the weld pool leaves after it, which is why the area begins to cool quite quickly. When cooled, a process called crystallization occurs. As a result, a weld seam occurs.

Column temperature

It’s worth examining the arc column and its temperature in a little more detail. The fact is that this parameter significantly depends on several parameters. Firstly, the material from which the electrode is made greatly influences. The composition of the gas in the arc also plays an important role. Secondly, the magnitude of the current also has a significant influence, since as it increases, for example, the arc temperature will also increase, and vice versa. Thirdly, the type of electrode coating, as well as the polarity, are quite important.

Arc elasticity

During welding, it is necessary to monitor the length of the arc very closely also because such a parameter as elasticity depends on it. In order to obtain a high-quality and durable weld as a result, it is necessary that the arc burns stably and uninterruptedly.

The elasticity of the welded arc is a characteristic that describes the uninterrupted combustion. Sufficient elasticity is visible if it is possible to maintain stability of the welding process while increasing the length of the arc itself.

The elasticity of the welding arc is directly proportional to such characteristics as the current used for welding.

Source: https://autogear.ru/article/386/525/temperatura-svarochnoy-dugi-opisanie-dlina-dugi-i-usloviya-ee-poyavleniya/

Welding arc temperature: description, arc length and conditions for its occurrence

Winter is not a hindrance to welding

Welding work has long been no longer considered the privilege of exclusively professionals. Currently, this method of joining metals is actively used in everyday life. At the same time, welding inverters are becoming increasingly popular. This is understandable: they are light, compact, easy to use and provide excellent seam quality. Most often, welding work is carried out in the warm season. Is it possible to do this at subzero temperatures? Let's try to figure it out.

Welding work in winter

The influence of temperature on the metal welding process

Low temperatures do have an impact on the welding process. The molten metal cools and crystallizes at a faster rate. This means that all dissolved gases do not have time to escape from the weld pool or non-metallic inclusions enter the slag.

This situation can lead to the formation of cracks or pores in the seams. The following statistics are known: when the temperature decreases from +20 °C to -50 °C, the residence time of the weld pool in the liquid state decreases by 10%.

This, in turn, leads to the fact that half of all detected defects relate specifically to non-metallic inclusions.

At low temperatures, heat removal from the welding zone increases. This impairs the penetration of the edges of the joined elements and can lead to the formation of another serious defect - lack of fusion. An additional danger comes from moisture condensation on the electrodes or metal. Water is a source of hydrogen, which promotes the formation of pores in joints. In addition, at low temperatures the ductility of steels and the mechanical properties of welds deteriorate.

All the above facts are true, but they are fully manifested at extremely low temperatures (from -40 ° C and below). Household welding rarely requires work in such difficult conditions. As a rule, we are talking about a temperature not lower than -10 °C.

Additionally, it should be taken into account that carbon steels are most often used for domestic purposes. If the thickness of the elements being connected is no more than 16 mm, you can work with them in the usual manner down to a temperature of -30 °C.

For low-alloy steels, this figure for the same thickness is slightly lower and amounts to -15 °C.

The lowest temperature is maintained in outer space. It is -273 °C, but even in such conditions it is possible to carry out welding work. They were first carried out in 1984 by Soviet cosmonauts S. Savitskaya and V. Dzhanibekov. For this purpose, a specially created electron beam welding apparatus was used.

The influence of temperature on the welding inverter

Low temperatures can affect not only metals, but also welding inverters. One of the main enemies of such technology is moisture. Its appearance inside the device can lead to short-circuiting of electronic components and their failure. Low temperatures under certain conditions can contribute to the formation of condensation in welding inverters.

Dew point

In this regard, it is important to remember the concept of dew point. In fact, this is the maximum surface temperature at which moisture appears on it in the form of condensation. In another way, this statement can be rephrased as follows: if the surface is colder than the dew point, then condensation will fall on it.

This value is not constant and directly depends on humidity. The higher it is, the closer the dew point is to the actual temperature. For example, in a shower with 100% humidity, the mirror fogs up at room temperature. The opposite situation occurs in a sealed double-glazed window.

There the humidity is close to zero, so condensation is never observed.

Moisture can condense in a welding inverter only in one case: if it has been left in the cold for some time and then moved into a warmer room. In such a situation, it is strictly forbidden to use it immediately.

The inverter must stand for one and a half to two hours so that its temperature becomes equal to the ambient temperature and the condensation that appears evaporates.

If the device is taken out of a warm room into the cold, condensation cannot form in it and this will not affect the performance of the device in any way.

How to perform welding work in cold weather?

In general, welding work at temperatures not lower than -10 °C can be performed using conventional household inverters without any negative consequences for the quality of the seams, the strength of the joints or the performance of the equipment itself. In more severe frosts, you should use semi-professional or professional models specifically designed for use at low temperatures. They are equipped with electronic elements that are resistant to cold.

Additionally, several activities should be highlighted that are recommended to be performed when carrying out welding work in winter:

If possible, avoid intersections of welds and sharp transitions in metal thickness.
Welding work should begin with seams that give maximum shrinkage (butt seams).
Minimize the volume of deposited metal.
During operation, increase the welding current by 10-15% and at the same time reduce the speed of movement of the electrode by approximately the same amount.
If possible, start and end welding on the lead strips.
Carefully clean the edges of the elements to be welded.
Instead of tacks, use, for example, clamps or other similar devices.
Use types of electrodes that are not prone to pore formation and ensure high ductility of seams: E50A, E46A or E42A with a basic coating. They must be thoroughly calcined before use.

Inverters for welding in winter

The effect of negative temperatures on the welder

Negative temperatures can affect not only metals or equipment, but also directly on welders. Working capacity in such conditions decreases, which means the risk of defects increases. The best way to avoid this situation is to use special winter protective clothing. Welding helmets deserve no less attention.

“Chameleons” are currently the most popular. Their main element is a light filter. It consists of several layers of liquid crystals and polarizing films. The light filter reacts to the intensity of light radiation and works automatically. It takes no more than 0.001 seconds to darken. This is quite enough to reliably protect the eyes from the harmful effects of ultraviolet radiation that occurs during welding.

The response time of the chameleon filter increases as the ambient temperature decreases. At -5 °C it is no longer 0.001 s, but 0.005-0.009 s. As a rule, such masks are intended for use at temperatures not lower than -10 ° C. In this case, they guarantee reliable eye protection. At lower temperatures, the light filter may simply not have time to work.

Conclusion

Thus, winter is not at all an obstacle to welding work. At temperatures down to -10 °C, ordinary household inverters are quite suitable for this purpose. To organize welding work in severe frosts, it is necessary to purchase specialized equipment.

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Source: https://vistek-weld.ru/reviews-articles/zima-ne-pomekha-dlya-svarki/

Arc temperature of manual electric arc welding – Machine tools, welding, metalworking