In order to successfully conduct the welding process, a welding arc is required. This is an electric discharge, which is characterized by a very high power and is quite long. It occurs between elements such as electrodes that are in a specific gas environment. For arcing, it is necessary to apply voltage to the electrodes.
General description of the arc
The main distinguishing features of the welding arc are its very high temperature and current density. Due to these two qualities, in the aggregate, the arc is capable of melting metals without any problems, the melting temperature of which is 3000 degrees Celsius. We can say that this arc is a conductor, which consists of volatile substances, and the main purpose is the conversion of electrical energy into heat. The electric charge itself is the moment the electric current passes through the gas medium.
Varieties of discharge
A welding arc is a discharge, and since there are several types of it, several types of the arc itself are distinguished:
- The first variety is called a glow discharge. This kind of appearance appears only in a low-pressure environment, and is used only in such things as plasma screens or fluorescent lamps.
- The second type is spark discharge. The appearance of this type occurs at a time when the pressure will be approximately equal to atmospheric. 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. It is this type that is most often used during welding. It occurs in the presence of atmospheric pressure, and its shape is continuous.
- The latter type is called corona. Most often occurs if the surface of the electrode is characterized by roughness and heterogeneity.
Arc nature
It is worth saying that an electric welding arc is not so complicated as it seems at first glance, to understand its nature is quite simple. An electric current is applied here, which flows through an element such as a cathode. After that, it enters the medium with ionized gas. At this moment, a discharge occurs, which is characterized by bright light and very high temperature. In general, a 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. It is dangerous for the human eye, and can also leave a light burn. For the above reasons, all welders should have good personal protective equipment.
Arc structure
The structure (structure) of the welding arc includes three main components, or sections - the anode and cathode section, as well as the arc column. It is worth noting that during the burning of the welding arc, active spots or regions that are characterized by the maximum temperature value will form in the sections of the anode and cathode . Through these two areas all the electric current that the power source generates will pass. At the same time, the largest voltage drop of the welding arc will also be recorded in these two sections. The arc column is located between these two zones, and such a parameter as the voltage drop, in this case will be minimal.
From the foregoing, we can conclude that, firstly, the power source of the welding arc can produce a fairly high voltage and current of high strength. Secondly, the length of the arc will consist of the totality of those areas that have been listed above. Most often, the length of such an arc is several millimeters, provided that the anode and cathode regions are respectively 10-4 and 10-5 cm. The most favorable arc length is 4-6 mm. It is with these indicators that it will be possible to achieve stable combustion and high temperature.
Arc Types
The difference between the welding arc is the supply circuit, as well as in the environment in which it can occur. There are currently two of the most common types of arcs:
- Arc of direct action. In this case, the welding machine should be parallel to the object that is being welded. An electric arc will occur when the angle between the metal workpiece and the electrode is 90 degrees.
- The second main variety is the welding arc of an indirect type of action. It arises only if two electrodes are used, and they are located at an angle of 40-60 degrees with respect to the surface of the metal part. An arc will arise between these two elements and weld the metal between them.
Classification
It is worth noting that there is a classification of the arc depending on the atmosphere in which it will occur. To date, three types are known:
- The first type is an open arc. When welding this type of arc, the arc will burn in the open air, and a small gas layer will form around it, which will include pairs of metal, electrodes and their coatings.
- Closed type. The combustion of such a welding arc is characterized by what is carried out under a layer of flux.
- The last variety is an arc with a gas supply. In such a case, a substance such as helium, argon or carbon dioxide is supplied to it. You can use some other types of gases.
The main difference between the latter type is that the supplied gases will prevent such a phenomenon as oxidation of the metal during welding.
A slight difference is observed in terms of the time of action 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 pulsed type of arc is a single exposure to a metal, a fine touch.
Work items, i.e. electrodes, can be carbon or tungsten. These electrodes are also called non-consumable. You can use metal elements, but they will melt in the same way as the workpiece. The most common type of electrode is steel, in terms of melting types. However, the use of non-consumable species is becoming increasingly popular today.
The moment of occurrence of the arc
A welding arc occurs at the moment when a quick circuit occurs. This happens when the electrode comes into contact with a metal workpiece. Due to the fact that the temperature is simply huge, 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, gas ionization occurs, which is why a welding arc appears.
Arc burning conditions
Under standard conditions, that is, at an average temperature of 25 degrees and a pressure of 1 atmosphere, the gas is not able to conduct electric current. The main requirement for the appearance 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 the constant maintenance of 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. An important role will be played by the ambient temperature. 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 any material can be processed with the obtained arc. To ensure a constant and high temperature, it is necessary that the power supply function as stable as possible. For this reason, the power source is the most important part when choosing a welding machine.
Arc Features
There are several points that distinguish the welding arc from other electrical discharges.
The first is a huge current density, which can reach several thousand amperes per square centimeter. This gives a huge temperature during operation. The distribution of the electric field between the electrodes in their space is quite uneven. A strong voltage drop is observed near these elements, but towards the center, on the contrary, it decreases significantly. We can not say about the dependence of temperature on the length of the column. The longer the length, the worse the heat, and vice versa. Using welding arcs, you can get a very different volt-ampere characteristic (CVC).
Welding inverter. Arc and its features
It’s worth starting right away with the main difference between an inverter power supply and a conventional transformer. Electric energy consumption is almost halved. The characteristic of the current that occurs when using the inverter, allows for faster ignition of the arc, and also provides stable combustion throughout the entire operation process.
The welding inverter itself is a rather complicated apparatus that performs operations to change the current to ensure the most stable arc operation. For example, the device is connected to the network and receives alternating current at the input, which it is able to convert into direct current. Further, direct current enters the inverter unit block, where it is again converted to alternating current, but with a much higher frequency than it was on the network. This current is transmitted to the transformer, where its voltage is significantly reduced, due to which its strength increases. After that, the rectified and tuned alternating current is transmitted to the rectifier, where it is converted into direct current and supplied for operation.