The welding arc itself is an electric discharge that has existed for a long time. It is located between live electrodes located in a mixture of gases and vapors. The main characteristics of the welding arc are temperature and rather high, as well as high current density.
general description
An arc arises between the electrode and the metal workpiece with which work is being conducted. The formation of this discharge occurs due to the electrical breakdown of the air gap. When such an effect occurs, ionization of the gas molecules occurs, not only its temperature, but also the electrical conductivity increases, the gas itself goes into a plasma state. The welding process, or rather arc burning, is accompanied by effects such as the release of a large amount of heat and light energy. It is precisely because of a sharp change in these two parameters towards their large increase that the process of metal melting occurs, since in the local place the temperature increases several times. The combination of all these actions is called welding.
Arc Properties
In order for the arc to appear, it is necessary to briefly touch the workpiece with the electrode with which you need to work. Thus, a short circuit occurs, as a result of which a welding arc appears, its temperature rises quite quickly. After touching, it is necessary to break the contact and establish an air gap. So you can choose the required arc length for further work.
If the discharge turns out to be 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 too long, it is unstable in terms of burning. The temperature of the welding arc in the welding zone in this case will also not reach the desired value. Quite often, you can see a curved arc, as well as strong instability, when work is carried out by a welding unit for industrial use, especially if work is being carried out with parts that have large dimensions. This is often called magnetic blasting.
Magnetic blast
The essence of this method is that the welding current of the arc is able to create a small magnetic field, which may well come into interaction with the magnetic field, which is created by the current flowing through the processed element. In other words, the deflection of the arc is due to the fact that some magnetic forces appear. This process is called blasting because the deflection of the arc from the side looks as if it is due to strong winds. There are no real ways to get rid of this phenomenon. In order to minimize the effect of this effect, you can use a shortened arc, and the electrode itself should be located at a certain angle.
Arc structure
At present, welding is a process that has been disassembled in sufficient detail. Thanks to this, it is known that there are three areas of arc burning. Those areas that are adjacent to the anode and cathode, respectively, the anode and cathode section. Naturally, the temperature of the welding arc in manual arc welding will also differ in these areas. There is a third section, which is located between the anode and cathode. This place is called the arc column. The temperature required to melt the steel is approximately 1300-1500 degrees Celsius. The temperature of the arc column can reach 7000 degrees Celsius. Although it is fair to say here that it is not completely transferred to metal, however, that value is enough to successfully melt the material.
There are several conditions that must be created in order to provide a stable arc. A stable current with a force of about 10 A is required. With this value, a stable arc with a voltage of 15 to 40 V can be maintained. It should be noted that the current value of 10 A is minimum, the maximum can reach 1000 A. The voltage distribution in the sections is uneven and most of all it in the anode and cathode. Voltage drop also occurs in an arc discharge. After conducting certain experiments, it was found that if welding with a consumable electrode is carried out, the greatest drop will be in the cathode zone. In this case, the temperature distribution in the welding arc also changes, and the largest gradient falls on the same section.
Knowing these features, it becomes clear why it is important to choose the right polarity during welding. If you connect the electrode to the cathode, then you can achieve the highest temperature of the welding arc.
Temperature zone
Despite what kind of electrode is being welded, melting or non-consumable, the maximum temperature will be exactly at the column of the welding arc, from 5000 to 7000 degrees Celsius.
The area with the lowest temperature of the welding arc is shifted to one of its zones, anode or cathode. In these areas, from 60 to 70% of the maximum temperature value is observed.
AC welding
Everything described above related to the procedure for conducting DC welding. However, for these purposes, you can use alternating current. As for the negative aspects, here is a marked deterioration in stability, as well as frequent jumps in the combustion temperature of the welding arc. Of the advantages, it is possible to 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 the lack of the need to choose the polarity, since with alternating current the change occurs automatically at 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, a discharge emits them. This requires maximum protection for the employee.
Arc Burning Medium
Today, there are several different technologies that can be used during welding. All of them differ in their properties, parameters and temperature of the welding arc. What methods are there?
- Open way. In this case, the discharge is burning in the atmosphere.
- Closed way. During combustion, a sufficiently high temperature is formed, causing a strong emission of gases, due to the combustion of the flux. This flux is contained in the coating, which is used to process welding parts.
- A method using protective volatile substances. In this case, a 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 in that it helps to avoid active oxidation of the material, which can occur during welding, when oxygen affects the metal. It is worth adding that to some extent the temperature distribution in the welding arc is such that a maximum value is created in the central part, creating a small own microclimate. In this case, a small area with an increased pressure value is formed. Such an area is able in some way to prevent the flow of air.
The use of flux allows you to get rid of oxygen in the field of action of welding even more efficiently. If you use gases for protection, this defect can be eliminated almost completely.
Classification by Duration
There is a classification of welding arc discharges by their duration. Some processes are carried out when the arc is in such a mode as pulsed. Such devices conduct welding in short flashes. For a short period of time until the flashing occurs, the temperature of the welding arc has time to rise to such a value that is enough to produce local melting of the metal. Welding takes place very precisely and only in the place where the workpiece is touched.
However, the vast majority of welding equipment uses a continuous arc. During this process, the electrode moves continuously along the edges that need to be connected.
There are areas called weld pools. In such areas, the temperature of the arc is significantly increased, and it follows the electrode. After the electrode passes the section, the weld pool leaves after it, because of which the section begins to cool quite quickly. During cooling, a process called crystallization occurs. As a result of this, a weld seam appears.
Post temperature
A little more detail is to disassemble the arc column and its temperature. The fact is that this parameter is significantly dependent on several parameters. Firstly, the material from which the electrode is made is strongly affected. The gas composition in the arc also plays an important role. Secondly, the current value also has a significant effect, since when it increases, for example, the arc temperature will 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 closely monitor the length of the arc 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 without interruption. The elasticity of the welded arc is a characteristic that describes the continuity of combustion. Sufficient elasticity is visible if it is possible to maintain the stability of the welding process with an increase in the length of the arc itself. The elasticity of the welding arc is directly proportional to a characteristic such as the current strength used for welding.