A.C.(eng. alternating current) - alternating current.
DC(eng. direct current) - D.C..
MMA(eng. Manual Metal Arc) - manual arc welding with stick electrodes. Known here as RDS.
TIG(eng. Tungsten Inert Gas) - manual welding tungsten non-consumable electrodes in a protective gas (argon).
MIG/MAG(English: Metal Inert/Active Gas) - semi-automatic arc welding with consumable electrode wire in an inert (MIG) or active (MAG) gas environment with automatic wire feed.
PV(PR, PN, PVR) - on duration - the time that the device is capable of operating at a certain current (the current is indicated along with the PV) before automatically shutting down due to overheating. The duty cycle value is indicated as a percentage relative to the standard cycle, taken to be 10 or 5 minutes. If the duty cycle is 50%, this means that with a cycle of 10 minutes, after 5 minutes of continuous operation, 5 minutes of downtime are required to cool the device. This parameter can be equal to 10%, so you must pay attention to it. The concepts: switching duration (DS), operating duration (OL), load duration (LOD) have different meanings, but the essence is the same - welding continuity.
An easy-to-understand diagram of a welding transformer looks like this:
A simple diagram of a welding transformer: 1 - transformer; 2 - reactor with variable inductance; 3 - electrode; 4 - part to be welded.
To limit the short circuit current and stable arcing, the transformer must have a steeply falling external current-voltage characteristic ( . To do this, they either use transformers with increased dissipation, as a result of which the short-circuit resistance is several times greater than that of conventional power transformers. Or, in a circuit with a transformer with normal dissipation, a reactive coil with a high inductive reactance is included - a choke (the choke can be connected not to the secondary winding circuit, but to the primary circuit, where the current is lower). If the inductance of the inductor can be changed, by adjusting it, the shape of the external current-voltage characteristic of the transformer and the arc current I 21 or I 22, corresponding to the arc voltage Ud, are changed.
Welding current regulation. The current strength in welding transformers can be regulated by changing the inductive reactance of the circuit (amplitude regulation with normal or increased magnetic scattering) or using thyristors (phase regulation).
In amplitude control transformers, the necessary parameters of the welding current are provided by moving moving coils, magnetic shunts or using a separate reactive coil as in the figure above. In this case, the sinusoidal shape of the alternating current does not change.
Diagram of a welding transformer with moving windings: 1 - primary winding, 2 - secondary, 3 - rod magnetic circuit, 4 - screw drive.
Diagram of a welding transformer with a movable magnetic shunt: 1 - primary winding, 2 - secondary, 3 - rod magnetic circuit, 4 - movable magnetic shunt, 5 - screw drive.
It can be a simple matter of switching the number of transformer winding turns used to reduce the no-load voltage and therefore the welding current.
Transformers with thyristor (phase) regulation consist of a power transformer and a thyristor phase regulator with two back-to-back thyristors and a control system. The principle of phase control is to convert the sinusoidal shape of the current into alternating pulses, the amplitude and duration of which are determined by the angle (phase) of the thyristors.
Scheme of a welding transformer with thyristor control. BZ - task block, BFU - phase control block.
The use of a thyristor phase regulator allows you to obtain welding machine, the characteristics of which compare favorably with the characteristics of a transformer with amplitude regulation. In more complex schemes control than in the figure above, a rectangular alternating current is generated. And at the same time, for example, an increased speed of transition of the pulse through the zero value is achieved, as a result of which the time of no-current pauses is reduced and the stability of the arc burning and the quality of the weld are increased. What cannot be said about the oscillogram shown above, the current-free intervals on it are larger than those of transformers with amplitude regulation and the quality of welding is worse.
Another advantage of thyristor devices is the simplicity and reliability of the power transformer. The absence of steel shunts, moving parts and associated increased vibrations makes the transformer easy to manufacture and durable in operation.
Depending on the type of supply network, welding transformers are single-phase and three-phase. The latter, as a rule, can also be connected to single-phase network. The figure below shows single-phase and three-phase transformers with current regulation by a magnetic shunt.
Advantages and disadvantages of welding transformers. The advantages of welding transformers include relatively high efficiency (70-90%), ease of operation and repair, reliability and low cost.
The list of shortcomings is more extensive. First of all, this is the low stability of the arc, due to the properties of the alternating current itself (the presence of no-current pauses when the electrical signal passes through zero). For high-quality welding, it is necessary to use special electrodes designed to operate with alternating current. Fluctuations in input voltage also have a negative impact on the stability of the arc.
A welding transformer cannot be used to weld stainless steel, which requires direct current, and non-ferrous metals.
If the power of the AC welding machine is large enough, its weight can cause some difficulties when moving the transformer from place to place.
And, nevertheless, an inexpensive, reliable and unpretentious welding transformer is not such a bad choice for the home. Especially if you rarely cook, and you don’t have enough money to buy a more functional model.
Welding rectifiers
Welding rectifiers are devices that convert alternating mains voltage into constant pressure electric welding There are many schemes for constructing welding rectifiers with various mechanisms for generating output parameters of current and voltage. Are used various ways current regulation and formation of the external current-voltage characteristic of rectifiers ( read about the current-voltage characteristic at the end of the article): changing the parameters of the transformer itself (moving coils and sectioned windings, magnetic shunts), using a choke, phase regulation using thyristors and transistors. In the simplest devices, current regulation is carried out by a transformer, and diodes are used to rectify it. The power part of such devices consists of a transformer, a rectifier unit with uncontrolled valves and a smoothing choke.Block diagram of a welding rectifier: T - transformer, VD - rectifier block on uncontrolled valves, L - smoothing choke.
The transformer in such a circuit is used to lower the voltage, form the necessary external characteristic and regulate the mode. More modern and advanced devices include thyristor rectifiers, in which mode control is provided by a thyristor rectifier unit that performs phase control of the moment the thyristors are turned on. The formation of the necessary external characteristics is carried out by introducing feedback on the welding current and output voltage.
Block diagram of a welding rectifier: T - transformer, VS - thyristor rectifier unit, L - smoothing choke.
Sometimes a thyristor regulator is installed in the primary winding circuit of a transformer, then the rectifier unit can be assembled from uncontrolled valves - diodes.
Block diagram of a welding rectifier: VS - thyristor rectifier block, T - transformer, VD - rectifier block on uncontrolled valves, L - smoothing choke.
Semiconductor elements of rectifiers require forced cooling. To do this, radiators are placed on them, blown by a fan.
The figure below shows a diagram of a welding rectifier, in which changing the resistance of the transformer and regulating the current is ensured using a magnetic shunt - by closing or opening it using the handle on the front panel of the device.
Schematic electrical diagram of a welding rectifier with a magnetic shunt: A - circuit breaker, T - transformer, Др - magnetic shunt, L - light-signal fittings, M - electric fan, VD - diode rectifier unit, RS - shunt, PA - ammeter.
Single-phase AC voltage rectification circuits are used in circuits with low power consumption. Compared to single-phase, three-phase circuits provide significantly less rectified voltage ripple. The operation of a three-phase Larionov bridge rectifier circuit using diodes, used in many welding rectifiers, is shown in the figure below.
Advantages and disadvantages of welding rectifiers. The main advantage of rectifiers, compared to transformers, is their use of direct current for welding, which ensures reliable ignition and stability of the welding arc and, as a result, a better quality weld. It is possible to weld not only carbon and low-alloy steel, but also stainless steel and non-ferrous metals. It is also important that welding with a rectifier produces less spatter. In essence, these advantages are quite enough to provide a clear answer to the question of which welding machine to choose - a transformer or a rectifier. Unless, of course, you take into account prices.
The disadvantages include the relatively large weight of the devices, loss of part of the power, and a strong “dip” of voltage in the network during welding. The latter also applies to welding transformers.
Welding inverters
The word "inverter" in its original meaning means a device for converting direct current into alternating current. The figure below shows a simplified diagram of an inverter-type welding machine.
Block diagram of a welding inverter: 1 - mains rectifier, 2 - mains filter, 3 - frequency converter (inverter), 4 - transformer, 5 - high-frequency rectifier, 6 - control unit.
The operation of the welding inverter occurs as follows. An alternating current with a frequency of 50 Hz is supplied to the network rectifier 1. The rectified current is smoothed by filter 2 and converted (inverted) by module 3 into alternating current with a frequency of several tens of kHz. Frequencies of 100 kHz are currently being achieved. This stage is the most important in the operation of a welding inverter, allowing it to achieve enormous advantages compared to other types of welding machines. Next, using transformer 4, the high-frequency alternating voltage is reduced to no-load values (50-60V), and the currents are increased to the values necessary for welding (100-200A). High-frequency rectifier 5 rectifies alternating current, which performs its useful work in the welding arc. By influencing the parameters of the frequency converter, they regulate the mode and form the external characteristics of the source.
The processes of current transition from one state to another are controlled by control unit 6. In modern devices, this work is performed by IGBT transistor modules, which are the most expensive elements of a welding inverter.
The feedback control system generates ideal output characteristics for any electric welding method ( read about the current-voltage characteristic at the end of the article). Due to the high frequency, the weight and dimensions of the transformer are reduced significantly.
The following types of inverters are produced according to their functionality:
- for manual arc welding(MMA);
- for argon-arc welding with non-consumable electrode (TIG);
- for semi-automatic welding in shielding gases (MIG/MAG);
- universal devices for working in MMA and TIG modes;
- semi-automatic machines for operation in MMA and MIG/MAG modes;
- devices for air plasma cutting.
As you can see, a significant part of the volume is occupied by radiators of the cooling system.
Advantages of inverters. The advantages of welding inverters are great and numerous. First of all, their low weight (4-10 kg) and small sizes, allowing you to easily move the device from one welding location to another. This advantage is due to the smaller size of the transformer due to the high frequency of the voltage it converts.
The exclusion of the power transformer from the circuit also made it possible to get rid of losses due to heating of the windings and magnetization reversal of the iron core and achieve high efficiency (85-95%) and an ideal power factor (0.99). When welding with an electrode with a diameter of 3 mm, the power consumed from the network for an inverter-type welding machine does not exceed 4 kW, and for a welding transformer or rectifier this figure is 6-7 kW.
The inverter is capable of reproducing almost all types of external current-voltage characteristics. This means that it can be used to perform all main types of welding - MMA, TIG, MIG/MAG. The device provides welding of alloy and stainless steels and non-ferrous metals (in MIG/MAG mode).
The device does not require frequent and long-term cooling during intensive work, as required by other household types of welding machines. Its PV reaches 80%.
The inverter has smooth adjustment of welding modes in a wide range of currents and voltages. It has a much wider welding current adjustment range than conventional machines - from several amperes to hundreds and even thousands. For domestic use, low currents are especially important, allowing welding with thin (1.6-2 mm) electrodes. Inverters ensure high-quality seam formation in any spatial position and minimal spatter during welding.
Microprocessor control of the device provides stable feedback on current and voltage. This allows you to provide the most useful and convenient functions of Arc Force, Anti Stick and Hot Start. The essence of all of them is a qualitatively new control of the welding current, which makes welding as comfortable as possible for the welder.
- The Hot Start function automatically increases the current at the beginning of welding, making it easier to ignite the arc.
- The Anti Stick function is a kind of antipode to the Hot Start function. When the electrode comes into contact with the metal and there is a threat of sticking, the welding current is automatically reduced to values that do not cause the electrode to melt and weld to the metal.
- The Arc Force function is implemented when a large drop of metal separates from the electrode, shortening the length of the arc and threatening sticking. An automatic increase in welding current prevents this for a very short time.
These convenient features allow unskilled welders to successfully weld the most complex metal structures. For those who have at least once worked with a welding inverter, the question of which welding machine is better does not exist. After a transformer or rectifier, working with an inverter becomes a pleasure. You no longer need to “poke” the electrode in order to ignite an arc that does not want to ignite, or frantically tear it off if it is tightly welded. You can simply place the electrode on the metal and, tearing it off, calmly light an arc - without worrying that the electrode may weld.
Inverter welding machines can be used when there are large drops in network voltage. Most of them provide welding in the mains voltage range of 160-250V.
Disadvantages of welding inverters. It is difficult to talk about the shortcomings of such a perfect device as this welding inverter and yet they exist. First of all, this is the relatively high price of the device and the high cost of its repair. If the IGBT module fails, you will have to pay an amount equal to 1/3 - 1/2 of the cost of a new device.
The inverter places increased demands, compared to other welding machines, on storage and operating conditions due to its electronic filling. The device reacts poorly to dust, since it worsens the cooling conditions of the transistors, which get very hot during operation. They are cooled using aluminum radiators, the deposition of dust on which impairs heat transfer.
Doesn't like electronics and low temperatures. Any sub-zero temperature is undesirable due to the appearance of condensation on the boards, and minus 15°C can become critical. Storage and operation of the inverter in unheated garages and workshops in winter are undesirable.
Semi-automatic welding machines
Speaking about welding equipment, we cannot ignore semi-automatic devices - devices for welding in a protective gas environment with a mechanized feed of welding wire.
Semi-automatic welding comprises:
- current source;
- control unit;
- welding wire feed mechanism;
- a gun (torch) with an electrical hose through which protective gas, wire and an electrical signal are supplied;
- gas supply system consisting of a gas cylinder, an electromagnetic gas valve, gas reducer and a hose.
Welding rectifiers or inverters are used as a current source. The use of the latter improves the quality of welding and increases the quantity of welded materials.
According to their design, semi-automatic welding machines come in double-body and single-body types. With the latter, the power source, control unit and wire feed mechanism are located in one housing. For double-body models, the wire feed mechanism is placed in a separate unit. Usually these are professional models that support long-term operation at high current. Sometimes they are equipped with a water cooling system for the gun.
Semi-automatic welding in MMA mode is no different from working with a conventional welding machine. When using the MIG/MAG mode, an electric arc burns between a continuously supplied melting welding wire and material. Carbon dioxide (or its mixture with argon), supplied through the gun, protects the welding area from the harmful effects of oxygen and nitrogen contained in the air. High-alloy and stainless steels, aluminum, copper, brass, and titanium are welded using semi-automatic welding machines.
Semi-automatic welding is one of the most modern technologies arc welding, ideal not only for production, but also for home use. Semi-automatic devices have become widespread in industry and everyday life. There is information that currently in Russia up to 70% of all welding work are produced by semi-automatic welding machines. This is facilitated by the wide functionality of the equipment, high quality welding and ease of operation. The semi-automatic welding machine is very convenient for welding thin metal, in particular, automobile bodies. Not a single car service enterprise can do without this most convenient equipment.
Selecting a welding machine
The choice of welding machine should be made for specific needs. Before you go to the store, you need to know the answers to the following questions.- What metal - by grade and thickness - will be welded?
- Under what conditions will the work be carried out?
- To what extent?
- What are the requirements for the quality of work and qualifications of a welder?
- And finally, how much money can be spent on purchasing a welding machine?
Depending on the answers to these questions, the requirements for the purchased equipment should be formed.
If you have to weld not only carbon and low-alloy steel, but also high-alloy and stainless steel, then the choice must be made between a welding rectifier and an inverter. If you have to weld metals that require protection from oxygen or nitrogen in the air, for example aluminum, then you will need welding in a protective gas environment, which can be provided by a semi-automatic machine with the MIG/MAG mode.
In general, if we talk about the versatility of the equipment, then best choice, perhaps, there will be a semi-automatic with MMA and MIG/MAG modes. Its presence will allow you to perform almost any metal welding work that you encounter in everyday life.
If you have to deal with thin (thinner than 1.5 mm) metal, preference should again be given to a semi-automatic machine.
Work at sub-zero temperature, especially at values below 10-15 °C, is undesirable for inverters. Heavy dust also has a bad effect on them. The conclusion is this. If you have to work at very low temperatures in very dusty conditions, you may have no other option but to choose a welding machine without state-of-the-art electronics - a welding transformer, a diode rectifier, or a semi-automatic device based on the latter.
High requirements for welding quality and low qualifications of the welder clearly favor the choice of a welding inverter with its ease of use and the Arc Force, Anti Stick, and Hot Start functions.
A large volume of work requires a high PV (on-time) from the welding machine, otherwise too much time will be spent on downtime during its cooling. PV is one of the characteristics that distinguishes household welding machines from professional ones. For the latter, it is quite large or even reaches 100%, which means that the device can work without interruption for as long as desired. If we talk about household models, the PV of inverters is significantly superior to the PV of welding transformers and rectifiers. It is better to take 30% as the minimum PV value.
When choosing a welding machine, you need to think about your neighbors. If you have to cook a lot, and the voltage in the network is low and unstable, you should choose a welding machine for your home taking into account the power it consumes. The constant blinking of lights that occurs during the operation of powerful welding transformers and rectifiers arouses universal hatred towards welding neighbors. The inverter, with its economical energy consumption and anti-stick electrode function, will not harm good neighborly relations. When the electrode comes into contact with the metal being welded, the welding transformer drains the supply network, while the inverter simply reduces the welding current (terminal voltage), plus the inverter is more efficient at low network voltage.
Basic requirements for current sources for welding
To meet their intended purpose, current sources must meet certain requirements, the main ones of which include the following:- The open circuit voltage must ensure ignition of the arc, but not be higher than values that are safe for the welder;
- power sources must have devices that regulate the welding current within the required limits;
- welding machines must have a given external current-voltage characteristic consistent with the static current-voltage characteristic of the welding arc.
An arc can occur either in the event of a breakdown of gas (air), or as a result of contact of electrodes with their subsequent removal to a distance of several millimeters. The first method (air breakdown) is only possible at high voltages, for example, at a voltage of 1000V and a gap between the electrodes of 1 mm. This method of arc initiation is usually not used due to the danger of high voltage. When feeding the arc with high voltage current (more than 3000V) and high frequency (150-250 kHz), you can get an air breakdown with a gap between the electrode and the workpiece of up to 10 mm. This method of igniting the arc is less dangerous for the welder and is often used.
The second method of igniting the arc requires a potential difference between the electrode and the product of 40-60V, therefore it is used most often. When the electrode comes into contact with the workpiece, a closed welding circuit is created. At the moment when the electrode is removed from the product, the electrons, which are located on the cathode spot heated by the short circuit, are separated from the atoms and move to the anode by electrostatic attraction, forming an electric arc. The arc stabilizes quickly (within a microsecond). The electrons that leave the cathode spot ionize the gas gap and a current appears in it.
The arc ignition speed depends on the characteristics of the power source, the current strength at the moment of contact of the electrode with the product, the time of their contact, and the composition of the gas gap. The speed of arc initiation is influenced, first of all, by the magnitude of the welding current. The greater the current value (at the same electrode diameter), the larger the cross-sectional area of the cathode spot becomes and the greater the current will be at the beginning of arc ignition. A large electron current will cause rapid ionization and transition to a stable arc discharge.
As the electrode diameter decreases (i.e., as the current density increases), the transition time to a stable arc discharge is further reduced.
The arc ignition speed is also affected by the polarity and type of current. With direct current and reverse polarity (i.e., the plus of the current source is connected to the electrode), the arc initiation speed is higher than with alternating current. For alternating current, the ignition voltage must be at least 50-55V, for direct current - at least 30-35V. For transformers that are designed for a welding current of 2000A, the no-load voltage should not exceed 80V.
Re-ignition of the welding arc after its extinction due to short circuits by drops of electrode metal will occur spontaneously if the temperature of the electrode end is high enough.
The external current-voltage characteristic of the source is the dependence of the terminal voltage and current.
In the diagram, the source has a constant electromotive force (Eu) and internal resistance (Zi), consisting of active (Ri) and inductive (Xi) components. At the external terminals of the source we have voltage (Ui). In the “source-arc” circuit there is a welding current (Id), the same for the arc and the source. The load of the source is an arc with active resistance (Rd), the voltage drop across it Ud = I Rd.
The equation for the voltage at the external terminals of the source is as follows: Ui = Ei - Id Zi.
The source can operate in one of three modes: idle, load, short circuit. When idling, the arc does not burn, there is no current (Id = 0). In this case, the source voltage, called the open circuit voltage, has a maximum value: Ui = Ei.
When there is a load, current (Id) flows through the arc and the source, and the voltage (Ui) is lower than during no-load by the amount of the voltage drop inside the source (Id Zi).
In case of a short circuit Ud=0, therefore the voltage at the source terminals Ui=0. Short circuit current Ik=Ei/Zi.
Experimentally external characteristic source is measured by measuring voltage (Ui) and current (Id) with a smooth change in load resistance (Rd), while the arc is simulated by a linear active resistance - a ballast rheostat.
The graphical representation of the obtained dependence is the external static current-voltage characteristic of the source. As the load resistance decreases, the current increases and the source voltage decreases. Thus, in the general case, the external static characteristic of the source is falling.
There are welding machines with steeply falling, flat falling, rigid and even increasing current-voltage characteristics. There are also universal welding machines, the characteristics of which can be steep and rigid.
External current-voltage characteristics of welding machines: 1 - steeply falling, 2 - flat falling, 3 - hard, 4 - increasing.
For example, a conventional transformer (with normal dissipation) has a rigid characteristic, and an increasing characteristic is achieved through feedback, when the electronics increases the source voltage as the current increases.
When manual arc welding, welding machines with a steeply falling characteristic are used.
The welding arc also has a current-voltage characteristic.
First, with an increase in current, the voltage drops sharply, as the cross-sectional area of the arc column and its electrical conductivity increase. Then, with increasing current, the voltage remains almost unchanged, since the cross-sectional area of the arc column increases in proportion to the current. Then, with increasing current, the voltage increases, since the area of the cathode spot does not increase due to the limited cross-section of the electrode.
As the arc length increases, the current-voltage characteristic shifts upward. A change in the diameter of the electrode is reflected in the position of the boundary between the rigid and increasing sections of the characteristic. How larger diameter, the higher the current, the end of the electrode will be filled with a cathode spot, while the increasing section will shift to the right (shown in the figure below by a dotted line).
Stable arc burning is possible provided that the arc voltage is equal to the voltage at the external terminals of the power source. Graphically, this is expressed in the fact that the characteristics of the welding arc intersect with the characteristics of the power source. The figure below shows three arc characteristics of different lengths - L 1, L 2, L 3 (L 2 >L 1 >L 3) and the steep characteristic of the power source.
The intersection of the current-voltage characteristics of the source and arc (L 2 >L 1 >L 3).
Points (A), (B), (C) express zones of stable arc burning at different arc lengths. It can be seen that the greater the slope of the source characteristic, the less will be the change in welding current when the arc length fluctuates. But the arc length is maintained manually during the combustion process, and therefore cannot be stable. That is why, only with a steeply falling characteristic of the transformer, vibrations of the tip of the electrode in the welder’s hands will not greatly affect the stability of the arc and the quality of welding.
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Welding as a method of permanently joining metals entered our lives a little over a hundred years ago, but its importance today cannot be overestimated. Welding is used to perform a significant amount of diverse work in various fields, from microelectronics to the manufacture of multi-ton structures. Because metals and alloys can come in different shapes, sizes, and chemical compositions, a variety of related technologies, tools, and devices have been developed. But the main method has long and deservedly been considered electric welding (and sometimes cutting) of metals, primarily low-alloy steels. Among the advantages of electric welding is the fast and reliable connection of materials at minimal cost. However, if necessary, you can use a welding machine to cut metal, even in hard to reach places, where another tool simply won’t fit. In recent decades, welding machines have been manufactured using electronic components, which has significantly reduced their weight and dimensions and made it possible to further expand their use in everyday life.
Let's figure out what types of welding machines there are and how they are distinguished.
WELDING CURRENT SOURCES
This is the main part of any welding machine, converting the mains voltage into direct or alternating current with specified parameters. Types of welding machines according to the type of current source are classified into:
Welding transformers. Traditional and at the same time structurally the simplest source of welding current. Its main component is the transformer itself, which reduces the mains voltage to welding voltage. Adjust the current various methods, the most common of which is changing the distance between the primary and secondary windings. All transformers have one common feature - they produce alternating current at the output. In order to weld non-ferrous metals using a “trans” or improve the stability of the arc, it is necessary to introduce additional heavy and bulky elements into the design, and the transformer itself weighs quite a bit. At the same time, to perform critical work, special electrodes for alternating current are required.
The efficiency of the transformer is quite high (up to 90%), but part of the energy is spent on heating. For cooling in modern models Fans of considerable power are also used: after all, a device weighing several tens or even hundreds of kilograms must be cooled. Currently, this type of welding power source is used infrequently, but transformers, in addition to efficiency, have two more important advantages: low price and durability, which is why they are still in demand.
Welding rectifiers. Rectifiers are devices that convert alternating current into direct current. They consist of a step-down transformer, a rectifier (diode) unit, as well as regulation, starting and protection devices. This design, although more complex than a transformer, provides much more stable output characteristics of the welding current and electric arc. The quality of the seam is also much higher in the end. The price of rectifiers is not much different from the price of transformers, reliability is also high: there is practically nothing to break in them.
The main disadvantages are the same as those of a transformer - high weight, complexity of operation, and strong voltage drop in the network during the welding process.
Inverters. This is the most modern type of welding machine. Unlike conventional welding machines, in which the power transformer operates at a mains voltage frequency of 50 Hz, the welding inverter uses high-frequency current (several tens of kilohertz). At the same time, to transmit the necessary energy, a transformer of much smaller size and weight is required, and welding takes place at a constant current of good quality, which also affects the quality of the seam. A conventional 160 A welding transformer weighs at least 18 kg, and a 160 A welding inverter power transformer weighs no more than 300 grams and is comparable in size to a pack of cigarettes, while the weight of the entire inverter, with the housing and all electronics, is 3–7 kg . The inverter consists of a rectifier, surge protector, a converter to high frequency alternating voltage, a welding transformer, another rectifier and a control circuit. The welding inverter has a much wider range of welding current adjustment than a conventional machine, which is especially important when welding with thin electrodes. Another “plus” is that with inverters, as a rule, this adjustment is much more accurate and the output parameters are much more stable, which greatly simplifies the selection of the optimal operating mode.
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Today, inverters are increasingly used for welding work. Their production and sales are growing, and their use is becoming commonplace. Inverter welders today can be found in a small workshop, in a large industrial enterprise, construction site or simply in the management of a private house. What are their differences from ordinary (transformer) welding machines? Let's look at six parameters that are important for any device, and how the inverter differs from traditional devices in these parameters. We especially note that Resanta welding machines are sold at the link http://www.avtogen.ru/svarochnye_invertory/brand-is-resanta/, look at the prices.
The quality of the resulting seam
It should be mentioned right away that the quality of the weld is most influenced by the professionalism of the welder, and not by the type of device used. However, with equal worker skills, such a feature of the inverter comes into play as the stability of the direct welding current, which does not depend on changes in the supply voltage. Accordingly, this current gives a more stable arc and a minimum of metal spatter. The seam will naturally be better.
Smooth regulation of the welding current, carried out over a fairly wide range, is of considerable importance. This allows you to select the current so that it is optimal for the specific parts being welded and the electrode used. It is clear that a correctly set current will also affect the quality of the seam, all other things being equal.
Mobility, dimensions and weight
The inverter converts the alternating current of the network into direct current, which, using transistor circuits, is changed into high-frequency alternating current (about 50,000 Hz). This current is converted by a high-frequency transformer into welding current, which forms an electric arc. The principle used in inverters makes it possible not only to obtain excellent current-voltage characteristics that allow achieving high quality welding, but also to eliminate a bulky power transformer from the design of the device.
Thanks to the use of high frequencies, the dimensions and weight of the transformer are reduced several times, and this leads to the fact that the weight and dimensions of the entire device are reduced. For comparison, conventional welding machines (transformer type) weigh from 20-25 kg or more, and inverters weigh between 4-10 kg. It is clear that the mobility of units with such a difference in weight does not make sense to compare; the inverter definitely wins in this parameter.
Power consumption
Compared to other types of welding machines, an inverter consumes relatively little energy and takes less time to operate. When working with electrodes with a diameter of 3 mm, the consumption of a conventional welding machine is about 7 kW, and even the cheapest and simplest inverter is unlikely to exceed 4 kW. On Idling consumption drops by an order of magnitude.
The main advantage is that energy is consumed only in the amount necessary for welding. Work with a 4 mm electrode can be carried out at a current value of 160A, however, at a supply voltage of about 180 volts, the quality with such an electrode will not be the best. In this case, a higher power device or the use of thinner electrodes is needed.
Efficiency
The efficiency of an inverter-type welding machine is above 90%; accordingly, almost all the energy consumed goes into use, that is, it is used in the arc. The absence of a power transformer not only reduces the weight of the device, but also eliminates losses due to magnetization of the iron cores and heating of the windings due to the mutual influence of magnetic fields. There is no energy loss on the control shunt.
From this we can conclude that the efficiency of the inverter is clearly higher than the efficiency of conventional welders, losses tend to minimum values.
Price
Comparing the prices of welding machines, you can see that the cost of inverters has seriously approached the price of traditional devices. If earlier inverters were 2 times or more expensive, today the difference rarely exceeds 20%. Manufacturers from China played an important role here - prices for their products have always been highly competitive.
Reliability and unpretentiousness
The electronic control of inverters provides reliable feedback between the parameters of the arc current and the output properties of the device - when ignited, the device creates an additional impulse that facilitates the formation of the arc. A short circuit almost instantly causes the welding current to turn off - this eliminates the effect of “sticking” of the electrode. The ease of operation and reliability of the device benefit from this.
Their sensitivity to dust and humidity negatively affects the operation of inverters. It is necessary, if possible, to protect the inside of the device from dust entering through ventilation holes, it’s a good idea to clean the device periodically. The inverter should be stored in a warm, dry room to prevent moisture from forming on the board elements.
The inverter device does not withstand falls and shocks very well, which is due to the presence of electronic filling. In terms of unpretentiousness, this type of welder is inferior to conventional welding transformers.
If necessary independent conduct welding work, the question arises: what type of welding machine to purchase. Welding is the creation of permanent connections between welded parts at the atomic level. The welded connection is one of the strongest and therefore is used quite often.
During electric welding, heating and melting of the metal occurs due to the formation of an electric arc between the end part of the electrode and the surface to be welded. Sources of arc formation and maintenance are divided into several types:
- Transformer.
- Inverter.
- Rectifiers.
- Welding units based on internal combustion engines.
Let's consider two types that are most widely used: a welding machine based on a transformer and an inverter source of electric arc.
This is the simplest of welding machines that uses alternating current. It works using a transformer that regulates the mains voltage to the welding voltage. Transformer or induction welding machines are divided according to the following criteria:
- Power (the greater the welding current, the thicker the metal it can be processed).
- The number of posts, that is, jobs (how many people can work at the same time).
- Voltage (single-phase or three-phase network).
Its advantage is that it is simpler and reliable design, low cost, high maintainability.
The disadvantages include the dependence of the arc on power surges, large weight and overall dimensions, and strong heating during work.
What is an inverter?
An inverter welding machine or simply an inverter is one of the energy sources for electric arc welding, which is based on use of high frequency current. Its operation is carried out by power electronics and a small transformer.
Its advantages are considered to be low energy consumption, compactness, low weight and size, and fairly high quality seams.
The negative aspects of the inverter include the relatively high cost, fear of moisture, dust and low temperatures (typical of budget models), sensitivity to voltage surges, and expensive repairs.
What do an inverter and a transformer welding machine have in common?
The similarity of these devices is their purpose - the formation and maintenance of an electric arc. But there are still some points that unite them:
- The devices under consideration are united by the presence of a transformer, but different sizes. Due to the preliminary receipt of high frequency current, inverters do not need to use large transformers. To obtain a current of 160 A, a transformer weighing 0.25 kg is needed. To obtain the same current in inductive devices, a transformer weighing 18-20 kg is required.
- Possibility of smooth current adjustment. Transformer devices have this opportunity due to changing the size of the air gap in the magnetic circuit.
- The devices are powered from a household (220V) or industrial (380V) network.
- Most welding machines have short circuit protection.
What is the difference between an inverter and a transformer source of electric arc?
- The dimensions and weight of a transformer-type welding machine are larger than that of an inverter. Industrial designs can weigh more than one hundred kilograms.
- Operating principle. In the inverter, the alternating current of the network is converted by the primary rectifier into direct current, then again into high-frequency alternating current and then again changes to direct current at the secondary rectifier. In transformer-type welding machines, the current strength changes due to changes in the position of the magnetic core, that is, the core of the step-down transformer or the inclusion of a different number of turns of windings in the circuit.
- The inverter has a more stable arc due to the stability of the welding current, which affects the quality of the seam.
- The difference is in the design. The inverter is more complex and can be equipped with the following additional functions: HOT START– increasing the initial current to improve ignition of the welding arc. ARC FORCE- increasing the welding current to speed up the melting process and prevent sticking, that is, the arc is forced. ANTI-STICK– reduction of current when the electrode sticks to increase the time for its separation and protection from overload.
- The process of learning to work on a transformer is more complex and time-consuming. However, having mastered these skills, you can easily work on an inverter.
- The inverter produces direct current, the transformer operates on alternating current with a household power supply frequency of 50 Hz.
- The power factor of the inverter is the highest of all welding equipment, and the efficiency exceeds transformer analogues by 20-30%.
- Wide range of welding current changes.
- The inverter has such an indicator as the intermittency coefficient (IC). It determines the time of continuous operation at maximum welding current. That is, if the CP is 50%, then after 10 minutes of operation it needs 5 minutes to cool down. Such requirements are not imposed on a transformer welding machine.
- Possibility of using electrodes designed for both direct and alternating current.
Today there is a fairly wide selection of welding equipment on the market from various manufacturers. The choice of welding machine should be made based on the tasks that will be performed with its help.
