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

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.

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.

Advantages of cold metal welding

The technology has undeniable advantages:

Zero electricity or gas consumption.
A neat and durable seam does not require further processing.
There is no need for lengthy training or special equipment.
Makes it possible to firmly connect different metals, for example, aluminum and copper, which are practically not connected by other methods.
Makes it possible to repair parts and pipelines without dismantling them, not only in a cold, but also in a hot state.
Repair of live electrical installations, containers and pipes under low pressure and even with flammable materials.
There are no deformations caused by residual stresses in the metal that arise after hot welding.
Highly environmentally friendly process, no hazardous waste.

Neat seam of cold welded linoleum

In addition to all of the above, low labor intensity and low price of consumables make the method economically profitable.

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.

Types of cold welding

The following types are used:

Spot. For connecting aluminum and copper conductors, gluing copper ends to aluminum wires.
Suture. For the production of thin-walled vessels, sealed containers and equipment casings.
Butt. For connecting wires or ring-shaped products.
Tavrovaya. For connecting elements of rolled profiles.
Shifting. For connecting pipes of heating or water supply circuits, as well as components of electrical distribution networks on railways.

Depending on the packaging method, there are:

Liquid Weld - Supplied as two separate components, a plasticizer and a hardener, which are mixed before use.
Plasticine-shaped, supplied in the form of a bar, which is kneaded and mixed before use.

Two-component cold welding is more difficult to use, but is more economical in use.

Plasticine cold welding

Liquid cold welding

According to their intended purpose, they are distinguished:

liquid welding for metal is used for gluing most metals and contains a filler in the form of metal powder;
liquid welding for car repairs, characterized by increased resistance to vibrations, also contains a filler;
universal, connecting metals, wood or plastic in any combination. The strength of such a connection will be low;
for work in special conditions, such as underwater, high-temperature, aggressive environments, etc.

Heat resistant cold welding

Heat-resistant cold welding is very popular among car enthusiasts who repair mufflers and other exhaust system elements.

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.

Welding principle

As mentioned above, the principle of fusion welding is based on the process of mixing molten metal in the welding zone, forming a strong, permanent joint. The thermal energy source, which has a fairly large power, concentrates thermal energy on a small area of the weld pool. It is in this bath that the alloy brought to the melting point is located, which is fed there either using an electrode or with a special wire (in the case of welding with a fireproof electrode). By moving the source of thermal energy along the edge of the parts being joined, the weld pool is also moved, gradually adding filler material to it. After cooling, the bath material crystallizes, which leads to the formation of a strong weld.

The process of igniting a high-temperature arc consists of three sequential steps. First, the electrode touches the workpiece, resulting in a short circuit that causes the tip to heat up. Next, the tip is moved a short distance from the part; this distance is selected experimentally. It should be such that the arc is most stable. Heating the electrode is necessary for stable exo-emission of electrons, which also guarantees a stable electric arc.

Fusion welding principle

When the electrode melts, the filler material is transferred into the weld pool, and the parts are joined. On some welding machines designed for welding with a fireproof electrode, arc ignition is non-contact. It is performed by a special device called an oscillator.

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 voltage distribution across areas is uneven and most of all it 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.

Security measures

The components that make up the mixture are highly chemically active and strongly irritate the skin and mucous membranes. If ingested, they cause life-threatening poisoning. Therefore, when working, it is necessary to strictly observe safety measures:

Be sure to wear rubber or plastic gloves

Be sure to wear rubber or plastic gloves.
When working with a plastic compound, be sure to test the effect of the components on the glove material. If they dissolve, gloves should be taken from a different material.
Wear safety glasses or a transparent protective shield. It is especially important to observe this point when working from below the object being repaired - a car, pipeline, etc., in order to prevent pieces of the substance from getting on the face and mucous membranes of the eyes and mouth.
In case of accidental contact with skin, rinse immediately with plenty of clean running water.
In case of ingestion, drink plenty of fluids, preferably milk, and consult a doctor immediately.
Keep away from children! Playing with a plasticine-like substance can end in a hospital or morgue.
Do not use for repairing dishes and containers that come into contact with food.

After hardening, the components of the mixture lose their chemical activity and are absolutely safe to touch with your hands.

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.

Features of electrode welding

In addition to learning how to weld properly, you need to know that it has a number of advantages and disadvantages. The quality of work directly depends on the equipment. The more expensive it is, the more powerful and better quality it is. Hand-held devices must perform the following functions:

connect parts even in hard-to-reach places:
have the ability to weld in all positions;
weld all types of metal.

In addition, this device also has some disadvantages:

low efficiency compared to other technologies;
the quality of metal joining directly depends on the skill of the welder;
During operation, harmful fumes and sparks arise that negatively affect vision.

Regarding the last point: electric arc welding requires a special uniform for the operator and the use of special glasses and a “chameleon” mask, which protects vision, but at the same time provides good visibility.

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.

Where is metal heated welding used and what equipment is needed?

The base material is most often subjected to preheating at a distance from the welded joint. Let's look at an example. A is a specific area of a fillet weld.

To calculate the distance from it to the place where preheating should be carried out, two problems will need to be solved:

When the metal thickness is equal to or less than 50 mm, the calculated value should not be more than 50 mm from the welded joint.
When the material thickness is more than 50 mm, the distance from the seam for preheating is taken to be less than 75 mm. This is indicated in the certification instructions for workers performing quality control of welded joints - CSWIP 23.4.

Today, manufacturers offer several types of different equipment for determining the control, indication and measurement of metal preheating temperature. It is used in a number of commercial industries.

Let's consider the main measuring instruments and temperature sensors used for this purpose:

Contact thermometer – used to measure temperatures not exceeding +350 °C. The device is based on a “thermistor” - a temperature meter. The resistance of the latter decreases when heated, therefore, it is inversely proportional to temperature. The difficulty with this device is the “periodic calibration” that must be carried out to obtain accurate measurement results.
Thermal pencil and thermal paste, which contain a material that changes color and melts under the influence of different heating temperatures. Their advantages are low cost and ease of use. The disadvantage is that the measurement result is not very accurate.
Thermocouple. The principle used in this device is the calculation of the thermoelectric potential difference between the material being welded and the heated weld metal in order to calculate the temperature. The device should be used during and after welding, as well as for heat treatment. It continuously monitors cooling and heating temperatures over a wide range. However, it requires regular calibration, which is considered a rather big drawback.

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.

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.

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.

How to use cold welding correctly

To obtain a good seam, careful execution of the following steps is of utmost importance:

Technological process of cold welding

Clean the bonded surfaces from oil, fat and mechanical contaminants. Cleaning can be mechanical (abrasives, steel brush), chemical (solvents and degreasers) and combined.
All actions are carried out only in protective gloves.
Squeeze the two-component composition out of the tubes and mix the components well.
Separate the required amount of plasticine-shaped composition from the block with a spatula and carefully close the remaining block.
Knead the composition. It should heat up slightly, maintaining plasticity; once the required consistency is achieved, apply the mixture to the surfaces to be glued.
Securely press the surfaces together by wrapping the parts with an elastic band.
If pipes are being repaired, the composition must be applied with several smoothing movements.
After the time specified in the technical specifications as the initial drying time (90% of the glue sets), the tourniquet can be removed.
The repaired product can only be used after the final hardening time has passed, usually 24 hours.

It is better to remove the remaining adhesive with a spatula after applying and applying the tourniquet. If they have already hardened, they can be removed by lightly tapping them with a hammer.

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.

Characteristics and composition of cold welding

The main characteristics of cold welding are:

Presence and composition of filler.
The initial drying time is the so-called time. “setting”, during this time the composition must be applied to the gluing area and leveled.
Final curing time - the product cannot be used before this period.
Application temperature - the recommended temperature at which the mixture can be applied to the surface.
Maximum operating temperature.

The plastic cold seal adhesive composition can consist of one or two components. Its required components are:

The adhesive base is in the form of epoxy resin, which determines the plastic properties.
The filler is metal powder, evenly distributed throughout the volume.
Quality improving additives, such as sulfur.

The quality of a weld obtained by cold welding depends on conditions such as:

Quality of adhesive material.
Preparing the surfaces of parts for gluing.
Compliance with technology.

The strength of the resulting seam in real conditions will be lower than that of a seam produced by the hot method.

Therefore, the technology is best applicable for local repairs of lightly loaded products.

Arc welding technology

Electric arc welding is performed using a specific technology to ensure a good, smooth and durable connection of products.

There are several ways to ignite an arc:

spot, in which the welder precisely hits the product with a conductor;
striking method.

The properties of conductors may also differ with different ignition methods. This is due to the coating on it. Some are easier to set on fire, some are more difficult, but each type of material has its own advantages and disadvantages.

Creating an arc with a new electrode is much easier. It is enough to touch the metal with it and immediately lift it to a distance of 2-3 millimeters. When a conductor is repeatedly ignited, a slag film appears at its end. In this case, you need to point the material several times until a spark is formed.

The arc length is a value that indicates the gap between the electrode and the parts between which the electrical discharge occurs. This indicator directly depends on the diameter of the electrode and is selected from 0.5 to 1.2 of its diameter. To obtain a high-quality seam, the electrode must be kept as close to the part as possible.

Preparatory stage

Before you weld metal with electrodes, you need to prepare everything. First, connect the device. Secondly, clean the parts and secure them securely so that they do not “walk” under the device. Third, the welder must wear a protective mask.

To begin with, it is recommended to practice how the material is ignited on metal in order to get an idea of which method will work best.

Arcing

When welding for beginners, it is recommended to maintain a short arc to create a perfect path, without flaws. You won't be able to do it the first time - you need to practice for a while.

The shorter the arc, the fewer metal drops it produces and the easier it is to create high-quality fusion. In this case, the conductor melts evenly and smoothly, providing sufficient penetration depth. A beginner can control the length of the arc by the sound of the equipment. When short it is uniform, when long it is loud and sharp.

Theoretically, everyone knows how to weld metal, but in practice it takes a long time to learn how to create a high-quality arc. If it breaks, it needs to be re-excited and the gaps in the seams “soldered”. The quality of the arc depends on the current strength, and the quality of the seam depends on it.

If you use the wrong approach, you can cause a burn on the product, where the material will subsequently begin to deteriorate.

Seam formation

To join metal by electric welding, it is important to create a reliable and high-quality alloy between the materials. There are several types of basic seams:

Thread is the easiest way that even a novice craftsman can create. It is characterized by longitudinal translational movements and a width of no more than 3 mm. It does not create a secure hold and can be used on thin and insignificant parts. It is recommended to start training with this path for young masters, in order to then move on to more complex technologies.
The longitudinal-transverse type is created in accordance with the name. That is, in this case, you need to have the knowledge and skills of how to correctly guide the electrode in several directions - vertically and horizontally. This track is much stronger than the previous one. It is durable and has a width of 1-1.5 centimeters. The most common technology for such a seam is a zigzag, in which the conductor is drawn from edge to edge 10-15 mm in each direction. At the same time, it is very important to maintain the arc length in order to obtain an ideal path with minimal slag impurities.
When the working element moves in three different directions, a strong, “dead” and reliable seam is created. Initially, it begins as a longitudinal-transverse one, but then you need to create return movements that allow you to re-work the welded line for greater reliability of fastening the materials. Here it is necessary to hold the device correctly, otherwise, if the slope is too large, the connecting track will turn out to be thick and uneven.

Upon completion of the work, it is imperative to knock off the slag from the joint in order to leave a perfectly even weld strip. If done incorrectly, the path will be uneven, with gaps and deformations. In addition to the aesthetic appearance, such quality of cooking may affect the further operation of these products.

How to adjust arc length

Not only electrical quantities, but also the quality of welding depend on this parameter. They strive to make the arc as short as possible, within 3-4 mm.

With a longer length, the following negative phenomena are observed:

Drops of molten metal from the electrode on the way to the weld pool manage to absorb a lot of oxygen and nitrogen from the air. As a result, the seam loses strength, ductility and toughness.
The discharge moves along the surface of the workpiece (wandering), as a result of which the heat is distributed over a relatively large area. The penetration depth decreases; drops of melt from the consumable, falling on unheated metal, do not merge with it, but bounce off.

A short arc produces a dry crackling sound, reminiscent of oil sizzling in a hot frying pan.

With a long welding arc, negative phenomena are observed.

The seam she made looks neat and has the following characteristics:

Correct form.
Smooth convex surface.

The seam, made with a long arc, has uneven outlines, and drops of molten metal stick along it.