Semiautomatic welding what polarity. The polarity of the welding current is direct and reverse.
There are two main types of DC welding:
welding process with direct polarity; reverse polarity welding process.
In the first case , while to the product plus. DC welding of reverse polarity implies a situation where the product receives a minus, and the electrode receives a plus.
Influence of polarity in welding
What is the effect of DC polarity?
Welding with direct and reverse polarity forms a cathode and anode spot on the tip of the electrode. During welding, the cathode spot is formed on the minus, while the anode spot is formed on the plus.
In the area of the anode spot, the temperature is much higher (up to 3900 o C) than in the area of the cathode spot (up to 3200 o C). During direct polarity welding, most of the heat is concentrated on the product itself, which causes the deepening of the weld root.
That is why reverse polarity welding is mainly used on thin sheet steel products or when necessary. Reverse polarity welding is also practiced when working with stainless, alloy and high carbon steels, which are very sensitive to overheating.
IMPORTANT: during AC welding, the polarity can change very rapidly (up to 100 times per second), so there is no polarity rule in this process.
Features of DC welding (general provisions)
No matter what polarity welding electrodes used in work, welding with direct and reverse polarity has some features:
- it is recommended to use a clamping clamp (it will not allow damage to the welded part in the place where the cable with a negative or positive charge is connected due to the appearance of microcharges);
- in comparison with the process using alternating current, welding using direct current is recognized as more “neat”, that is, during operation, such an amount of metal spatter is not formed, and Weld more even;
- due to the fact that the cathode and anode are always heated differently, the connection method will determine how much metal will be transferred to the workpiece.
Straight polarity welding
Straight welding polarity is the welding of parts to which the welding cable is connected to the “+” terminal of the welding machine. At this time, the electrode receives a negative charge through the electrode holder.
Since the temperature is much higher at the anode, which is the positive pole, the straight polarity current is best used on heavy-walled steel parts. A characteristic feature of the polar type of connection is considered to be the fact that the most effective scope of its application is where the temperature is required as high as possible.
Reverse polarity welding
DC welding of reverse polarity involves connecting a negative charge to the workpiece with a “-” terminal. At this time, the electrode receives a positive charge through the electrode holder.
Reverse polarity welding provides emission more heat on the electrode, while the heating of the part, on the contrary, decreases. Thanks to this, a more “delicate” welding is produced, which significantly reduces the likelihood of burn-through in the part.
Welding process control
DC welding (polarity) is the task of heating the base metal as best as possible until it melts, so that a weld pool forms. If, for example, the current is too low, then the welding surface of the metal will not be heated properly. If the current is too high, then the metal will warm up so well that the arc will penetrate inward, pushing the metal back.
Direct welding polarity helps to organize an environment in which the weld pool will spread, the movement of the electrode can easily control the entire welding process.
The faster the electrode moves, the less heat will flow to the surface of the base metal, so it will not warm up as well. If you move the electrode more slowly, then more heat will flow, therefore, the metal will warm up much better.
IMPORTANT: professional welders immediately put a little more current at once, and the welding speed is simply regulated by the electrode (the speed of its movement along the surface of the workpiece to be welded). During the completion of the seam, it is recommended to deposit a little more metal so that a crater does not form.
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Electric arc welding can be carried out using equipment that generates direct or alternating current. If work on alternating current has no nuances in the matter of the correct connection of the mass and the electrode holder, then when welding on direct current, the polarity of the welding electrodes is of great importance.
General concepts
depending on which pole welding machine connected to the holder, the type and features of the welding mode are determined:
- Welding in direct polarity involves connecting the positive pole to the workpieces to be joined (mass), and the negative pole to the electrode holder.
- To perform work with reverse polarity, the poles are reversed (plus for the holder, minus for ground).
Regardless of which polarity of the electrodes is used, DC welding has common features compared to the use of alternating voltage:
Welding with straight polarity
With this method of connecting the electrodes, the workpiece is subjected to greater heating, and not the electrode.. This mode is characterized by the release of much more heat.
Therefore, straight polarity welding is recommended for the following operations:
- Cutting metal with any type of electrodes.
- Welding workpieces of considerable thickness.
- Working with metals having a higher melting point.
It is in these cases that it is necessary to heat the workpieces to more high temperatures, for the performance of these works requires a significant heat release.
Reverse polarity welding
In this case, the electrode is subjected to greater heating, so a smaller amount of thermal energy is transferred to the workpiece.
Due to this, reverse polarity electrodes allow you to work in a softer (delicate) mode.
This is true in many cases, for example, welding of stainless or thin sheet steel, alloys that are sensitive to heat.
Also, such a connection is used for work in a shielding gas environment or under a flux.
Determining the required polarity
There is a lot of controversy about how to determine the polarity of the electrodes during welding, with each side giving seemingly correct arguments. Opponents of the above version refer to textbooks on welding technology published in the middle of the last century, believing that the information indicated in them is the most correct.
But it is worth considering that since then there has been a significant improvement welding technology and consumables. Therefore, relying on recommendations regarding outdated technologies is still not worth it. The choice of polarity described above is considered the most correct.
There is another group of welders who believe that it is better (or rather more convenient) to perform any work exclusively on reverse polarity. This is primarily due to the fact that in this mode the electrodes stick less and there is no risk of burning through the metal. But the advent of inverter welding technology has solved this problem.
It is worth paying attention to the type of electrodes. There are brands that can only be used with direct or reverse polarity, violating the manufacturer's recommendations can not only complicate the welding process, but also make it impossible in principle.
To date, manufacturers already offer electrodes that can operate at any voltage and different polarity.
The correct choice of the polarity of the electrode connection helps to simplify the welding process and improve the quality of the weld.
Most modern welding machines have a block of rectifier diodes in their design, which, in turn, provides a constant welding current. For devices that use wire as a welding material (semi-automatic welding machines), this is a prerequisite. For devices that use electrodes for operation, this is already an option that allows you to use almost any brand of electrodes for welding.
Classification of the welding arc by DC polarity:
a - direct polarity; b - reverse polarity
When working semi-automatically, it is necessary to observe the polarity of the connection. So, welding with a conventional copper-plated wire in a shielding gas environment is carried out with a current of direct polarity. That is, a plus is applied to the product, and a minus to the holder (direct polarity during welding). With this connection, the current flows from the wire to the product, and therefore the heating of the product is higher than that of the welding wire. And this is natural. The parts to be welded have a much larger area, respectively, they require more heating to form a weld pool. The wire, which has a smaller area, melts quite easily and enters the welding site already in the form of a molten drop. The flowing current, and it flows precisely from plus to minus, captures the melted material, again contributing to the formation of a high-quality weld pool.
Judging by the comments of visitors to our site, there was a little confusion about the direction in which the current flows in the circuit. Let's try to clarify this issue!
It must be understood that the "direction of current" in electrical engineering is more of a convention adopted for drawing circuits. Traditionally, in diagrams, it is customary to draw from plus to minus, as if the current flow is from plus to minus, although the actual movement of charge carriers in most cases occurs in the opposite direction! If the conductor is a metal (wire, electrode, etc.), the real charge carriers - electrons - fly from minus to plus (because electrons are negatively charged particles). If the conductor is an ionized gas or liquid with ions, then the ions fly in both directions.
When working semi-automatically without a protective gas environment, a special flux-cored (flux) wire is used. In this case, the polarity of connecting the holder and the "mass" is necessarily changed. That is, on the ground "minus", and on the holder plus (reverse polarity during welding). This is due to the fact that the melting point of the flux is approximately the same as the melting point of the metal, however, in order to obtain a high-quality weld, it is necessary that the flux burns out and forms a small gaseous cloud in which the welding process will take place. As noted above, the current flows from minus to plus, and therefore the fall of the molten metal drop will be somewhat lower, which will ensure less heating of the metal being welded, since the latter is not cooled by the shielding gas medium and the formation of the weld pool will be approximately the same as with gas welding.
Welding of non-ferrous metals, in particular aluminum, is carried out, as a rule, with a special tungsten electrode. In this case, direct polarity is usually used when welding - minus on the electrode. This type of connection allows you to get a high temperature in the heating zone, which is especially critical for the same aluminum, since it is initially necessary to “break through” the oxide film, especially since the melting temperature of the latter is much higher than that of the metal itself.
Direct polarity, among other things, allows you to get a more concentrated and narrow electric arc, deeper penetration of the metal, and, accordingly, a better weld and, importantly, use a smaller diameter of an expensive tungsten electrode, as well as reduce the consumption of no less cheap gas.
When connecting a tungsten electrode in reverse polarity when welding - with a plus on the holder - the seam is less deep. This method is good for welding thin plates - in this case there is no danger of burning through the material being welded. However, another disadvantage is the effect of "magnetic blowing". In this case, the resulting arc turns out to be wandering and the seam turns out to be less beautiful and tight.
Depending on a number of factors, welding arc, supplied during DC welding, can have direct or reverse polarity. In the first case, a "plus" charge is supplied to the processed elements, and a "minus" charge is supplied to the electrode. Reverse polarity during welding is distinguished by the supply of "plus" and "minus" to the electrode to the part. Read more about the specifics of the methods below.
Process features
The dimensions and shape of the resulting seam also depend on the location of the poles. For example, deeper penetration is possible with a direct reversed current, which is due to increased heat generation at the anode and cathode.
It is important to remember that the faster the welding process is carried out, the smaller the width of the seam and the depth of penetration.
What equipment to use
The reverse direction is in demand in the work of special installations. The specificity is that the machine feeds the wire at a certain speed to the workpiece, so several types of welding can be selected.
For example, in a shielding gas environment (when argon or carbon dioxide is used), or using powder-treated wire. Reverse current direction is applicable when working with gases, direct current when the process is carried out with flux-cored wire (also known as flux-cored wire).
Semi-automatic welding involves a number of process changes. Firstly, the connection of the "derzhak" and "mass" changes - on the first "plus", on the second "minus" (reverse). This is done so that the flux burns out completely, and the welding process takes place inside the resulting gaseous cloud. The metal will warm up less, and the splashing of drops will be minimized.
The straight line is used for welding non-ferrous metals, when the tungsten electrode acts as a working consumable. Thus, an increase in temperature in the heating zone is achieved, which can be critical for, for example, aluminum.
When working with alternating current, the user's task is to change consumables in a timely manner. Professionals or advanced amateurs prefer direct current as a reliable guarantee of high-quality welding. Working with the inverter allows you to choose one of two well-known options. Direct and reverse polarity during welding act as methods, each of which has its own advantages and disadvantages. The choice of direction is dictated by a number of factors, the main of which are the material of consumables and the equipment used.
If you know other specific features of the choice of welding parameters, share the information in the comments to the article.
Polarity welding current is one of the important parameters affecting the quality weld. After all, the direction of current movement, that is, electrons in the metal, depends on it, which affects the process of making a seam, arc burning, the formation of a weld pool and, as a result, the quality of a welded joint.
Regarding the physical meaning, as well as the terms "direct" and "reverse", I wrote a separate article earlier. And now I will tell you the basic principles of using direct and reverse polarity of welding current. And the main thing you need to know: where the “+” is, it heats up more. Accordingly, when welding on current with reverse polarity, when the “+” is on the electrode, it heats up more than in the case of a straight line. And the part, on the contrary, heats up more when welding on a current of direct polarity.
Subtleties and features
With detail, the situation is somewhat more tricky. When the “+” is on the part, the penetration spot is wider, but the depth is no more, or even less, than when the part is “-“. With a “minus” on the part, the spot of the weld pool is smaller, but its depth can be no less, or even more, than when welding with direct polarity current. Due to this, when there is a “minus” on the part, it is better to control the movement of the weld pool.
How to use it in practice? There are many options. Usually, the direct polarity of the welding current is used by default - especially when it is necessary to warm up and weld the parts strongly. Reverse polarity is used when it is necessary to control the movement of the weld pool more precisely. For example, these are some views, especially from top to bottom. Also, welding at reverse polarity current can help when making ceiling seams and - in fact, in this case, the part warms up less, and this will minimize metal runoff when making vertical and ceiling seams and through metal penetration when welding a thin sheet.
The polarity of the welding current also depends on the electrodes
One more important point- this . Not all electrodes allow the use of welding current of any polarity. For example, with electrodes with the main type of coating, welding should be carried out only with a “minus” on the metal being welded. Such electrodes include, for example, UONI-13/55 electrodes. In any case, always check that the actual polarity of the welding current is correct for the specific electrodes used.
Summary
So, it is important to understand that the choice of the direction of the welding current depends on spatial position weld, selected electrodes, metal thickness and personal skills of the welder. If all these conditions are met, then the seams will be of high quality, reliable and aesthetic.
And most importantly, experiment! I say this very often, because in fact, only an experiment will give you the most accurate and correct answers to your questions!
Perhaps I opened this topic a little chaotically, so if you have any questions, write them in the comments. And also be sure to tell us about your experience with the use of direct and reverse polarity!