What is reverse polarity when welding - Metals and their processing

What is reverse polarity when welding?

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In short, the part melts as a result of the formation of an electric arc formed from the anode - the electrode with a positive charge of the electric current source, and the negative cathode. The source of electric current is a welding machine, the anode and cathode are a holder and a wire with a terminal attached to a metal workpiece.

When the electrode approaches the workpiece, an electric arc is formed between them, which heats the workpiece to a high temperature, melting and mixing of the heated surfaces occurs. If the anode is a part, electric welding occurs in direct polarity mode.

Reverse polarity in arc welding occurs when a positive charge is applied to the welding machine holder.

Application of different connection

The difference in connection values of the power source significantly affects the result of the work. Basically, polarity is the movement of electrons from a negative charge to a positive charge.

It should be taken into account that the “positive” source of electric current always has the highest heating temperature (this phenomenon is widely used in electric welding).

With direct welding polarity, the metal heats up much hotter than the electrode - by more than four thousand degrees Celsius, while reverse polarity allows you to achieve the maximum temperature of the electrode.

To connect refractory materials or metal of significant thickness, it is more advisable to connect the part as an anode. This will ensure maximum heating of the metal and a smaller melting area. The same rule applies when cutting or making holes in workpieces.

When working with thin sheets or low-melting material, the ideal choice would be reverse polarity electric welding - the largest melting area, as well as the high temperature of the electrode, will avoid burning through the workpiece and create an aesthetic weld.

When preparing for welding work, it is necessary to pay attention to the type of electric current, its strength, the material of the electrodes, and the speed of movement of the holder when processing the workpiece.

Electric current happens:

An inverter welding machine, when connected to the network, converts alternating electric current into direct current, which is considered the most suitable. When using direct electric current, the welding seam is more accurate, without splashing molten metal.

There is practically no difference in connecting “plus” and “minus” using alternating current. Alternating current in electric welding has one of the advantages - low cost. By increasing the current, the temperature of the weld spot and its depth increase.

Such parameters can be adjusted by the speed of movement of the holder: the higher the speed, the lower the temperature and the depth of electric welding. It is necessary to pay attention to the recommendations of the electrode manufacturer: application may vary depending on the selected anode and cathode connection.

An incorrectly selected consumable material can significantly deteriorate the quality of the seam as a result of non-compliance with the instructions for its use. It takes longer to start the electric arc when welding with reverse polarity.

General recommendations

The quality, as well as the speed of welding work, depend on the training of the worker, the welding machine and consumables.

It is necessary to carefully read and strictly follow the requirements of the manufacturers' instructions for the device and electrodes regarding welding mode: force, current voltage, arc distance, speed of movement of the holder.

The correct choice of direct or reverse welding polarity will allow you to perform the work efficiently and without unnecessary material costs.

Sergey Odintsov

electrod.biz

Reverse polarity when welding

Unlike traditional gas welding, the electric arc method has a number of features. One of the most significant of them is considered to be the arc temperature, which can reach 5000 ºС, which is much higher than the melting point of any existing metal. This partly explains the wide variety of methods and technologies of this welding method, which make it possible to solve a wide variety of problems and applications with its help.

In electric arc welding, it is possible to use several types of arc, electrodes with different properties and different degrees of mechanization.

In this case, the process can be carried out by an electric arc fed by currents of various types (direct or alternating), with direct and reverse polarity in welding seams of different spatial positions.

In addition to these factors, the speed of welding, diameter, type and brand of electrode and arc voltage with the strength of the welding electric current are of great importance for the welding mode. Each of these parameters can significantly influence the progress of the process and requires careful consideration in the welding mode.

In selecting the diameter of the electrode, in addition to the thickness of the metals being processed, the location of the seam in space, as well as the number of welding layers, is important. Of the various options for spatial positions, the lower one is preferable as the most convenient. Based on the selected diameter of the electrode, taking into account the location of the seam, the strength of the welding electric current is determined. In determining its type with polarity, in addition to the thickness of the metal being processed, its type and physicochemical properties influence.

When welding with direct current of reverse polarity, a large amount of heat is generated at the electrode. Therefore, it is used for thin metals, helping to avoid burn-through. Reverse polarity is also necessary when welding with an inverter when processing high-alloy steels, so as not to overheat them. In all other cases, alternating current is usually used as it is cheaper than direct current.

Welding with direct and reverse polarity current

Welding with straight polarity means that in its process, current is supplied from the welding rectifier to the workpiece with a positive charge. In this case, the “plus” terminal of the device is connected to the product using a cable. Accordingly, a negative charge is supplied to the electrode connected to the minus terminal through the electrode holder.

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The anode, which is the positive pole, has a higher temperature than the cathode, which serves as the negative pole. Therefore, the use of electric currents of direct polarity is advisable in welding workpieces with thick walls.

It is also justified for cutting metal products and in other situations that require the release of a significant amount of heat, which is what characterizes this type of connection.

When welding with reverse polarity current, the opposite connection order is required. The negative charge from the negative terminal is applied to the structure being welded, and the positive charge from the positive terminal is directed to the electrode. With a given polarity of the welding electric current, in comparison with a direct connection, a larger volume of heat is generated at the electrode end with relatively less heating of the workpiece, which facilitates “delicate” welding.

It is used when there is a possibility of burning through the workpieces. Therefore, welding with reverse polarity electrodes is suitable for working with stainless and alloy steels, other alloys that react to overheating, as well as for joining thin-sheet metal structures. No less effective is connecting reverse polarity in the welding process using an electric arc, gas protection and flux-cored welding.

Regardless of the power supply polarity used, there are a number of general factors that should be taken into account. If direct current is used, the resulting seam will be neater, without a lot of metal spatter. This is explained by the absence of frequent changes in polarity when working with direct electric current, which distinguishes it favorably from alternating current.

If consumable electrodes are used for welding, then due to the different heating of the anode and cathode, the method of connecting the electric current can affect the volume of molten electrode metal transferred to the product. To prevent possible burns of the workpieces being welded in the area where the power cable is connected, no matter what charge (positive or negative), it is necessary to use a clamping clamp.

What determines the choice of polarity?

The choice of electric current polarity is limited by the electrode coating material used for welding. An example of this is the welding process using carbon electrodes, which heat up more strongly when welding with reverse polarity and are destroyed more quickly. And uncoated wire, for example, burns better with direct polarity than with reverse polarity, and does not burn at all when powered by alternating current.

The depth of penetration and the width of the resulting seam largely depend on the parameters of the welding mode. Thus, with an increase in the strength of the welding electric current, even at a constant welding speed, the penetration increases, that is, the depth of metal penetration increases.

This is explained by an increase in the heat input of the arc, which depends on the amount of heat passing through a unit length of the welded seam. As welding currents increase, the pressure exerted by the arc on the surface of the molten pool also increases.

Under its influence, molten metal can be forced out from under the arc, this is fraught with through penetration of the part.

The shape and size of the seam formed can also be influenced by the type of electric current and its polarity. Thus, a direct current of reverse polarity can provide a much greater depth of penetration than a direct current with direct polarity, this is due to the unequal volumes of heat generated at the anode and cathode. As the speed of the welding process increases, the width of the seam and the depth of penetration decrease.

Source: https://samsvar.ru/stati/chto-takoe-obratnaya-polyarnost-pri-svarke.html

What is reverse polarity when welding with an inverter?

The advent of inverter welding machines has helped to open up new areas of application. Thanks to this, every home master can use it for their own purposes. But not all owners know the features of such tools. Particularly relevant is the question of what reverse and direct polarity are when welding with an inverter. It is this topic that will be discussed in the article.

A little about the basics

Why do you need this type of welding machine? Most often, a welding inverter is used for electric arc welding. It is this that allows you to connect or separate workpieces made of steel of various types. Before using such a device, it is necessary to select two main parameters - welding current and type of electrodes. After this, you can safely begin working with this unit.

How to use the inverter

Having learned about the basics of using this device, you need to consider how to operate it. This includes the following stages:

The surface of the material is separated from dirt and rust. This will be needed in order to form a reliable seam;
Select the welding current mode and electrode type. Here it is important to consider both the material and the parameters of the weld;
Connect the positive terminal to a metal surface to carry out the necessary operations;
We connect the minus to the electrode holder;
We form an arc, then use a hammer to remove scale from the resulting seam.

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This is the standard sequence of actions. However, it does not take into account the shape of the connection and the orientation of the electrode. Such subtleties are necessary to form special types of seams for welding. The latter are used for cylindrical containers (separators in the oil and gas industry, construction tanks).

Choosing the right model

For all units, both direct and reverse polarity are available when welding with an inverter. But such inverters must have additional characteristics, which determine the scope of application, speed and comfort of the work performed. And therefore it is necessary to take a professional approach to choosing a welding inverter. The recommended functionality of such a unit is as follows:

Hot start for rapid arc formation;
Anti-stick allows you to form a seam of the correct shape (as smooth as possible);
Automatically activated when there is molten metal at the end of the electrode. A short increase in current will avoid sticking;
Alternating current for working with aluminum workpieces;
To work in rooms with high humidity or a small area, a reduced idle value is required;
The type of indication is also important, ideally digital symbols of the parameter.

In addition, you need to clearly select the welding current, since it directly depends on the diameter of the electrode used and the thickness of the material. The most commonly used electrodes are the ANO and MR brands, which are suitable for creating a seam on metal surfaces. If you need to weld aluminum structures or several alloys, you will need special materials, including additives.

Application of direct and reverse polarity

The change in polarity occurs due to ongoing processes. In addition to selecting the basic parameters, you can swap the connected terminals. As a result, current will flow from the negative element to the positive one and the first one will heat up to the required values.

Direct polarity is needed in cases where deep seams are processed on thick workpieces. Here the minus is connected to the electrode, the metal has a plus. It is also good to use this polarity when welding cast iron and deep penetration of the main metal (aluminum, iron, and so on).

Reverse polarity (plus to the electrode, minus to the metal) . The metal is cold, the electrode heats up. It is used only for thin-walled workpieces, since the electrode fails very quickly. Depending on the goals of the process, the wizard applies one of the operating modes.

It should also be taken into account that with alternating current low-carbon steels are welded with rutile-coated electrodes, in the presence of magnetic blast of thick-sheet structures made of low-carbon steels.

There is no dependence on the type of polarity; you can use any one that is convenient for a novice specialist.

Summarize. We looked at what a welding inverter is and why you need to know about direct and reverse polarity.

Often, novice craftsmen do not know the specifics of the work, which is why difficulties arise when melting metal or welding structures made of various alloys. However, changing polarities is quite simple.

By changing the terminals with each other, you can achieve the necessary parameters for working with different products. Study welding inverters carefully, and your work will become noticeably more comfortable!

Source: https://crast.ru/instrumenty/chto-takoe-obratnaja-poljarnost-pri-svarke

Reverse polarity welding with an inverter - Direct and reverse polarity when welding with an inverter

alexxlab | 07.07.2019 | 0 | Questions and answers

Direct and reverse polarity when welding with an inverter

Welding metals with direct current can be carried out in two modes: with direct polarity and reverse polarity. Direct polarity when welding is when a minus is connected to the electrode, and a plus to the metal workpiece. When welding with reverse polarity current, the opposite is true, that is, the plus is connected to the rod, and the minus to the product.

Why is all this needed?

When welding with direct current, a thermal spot is formed at the tip of the electrode, which has a high temperature. Depending on which pole is connected to the electrode, the temperature at its tip will depend, and accordingly the mode of the welding process will depend. For example, if a plus is connected to a consumable, then an anode spot forms at its end, the temperature of which is 3900C. If it is minus, then you get a cathode spot with a temperature of 3200C. The difference is significant.

What does it give?

When welding with direct polarity current, the main temperature load falls on the metal workpiece. That is, it heats up more, which allows the root of the weld to be deepened.
When welding with reverse polarity current, the temperature concentration occurs at the tip of the electrode. That is, the base metal heats up less. Therefore, this mode is mainly used when joining workpieces with small thickness.

It should be added that the reverse polarity mode is also used when joining high-carbon and alloy steels and stainless steel. That is, those types of metals that are sensitive to overheating.

Attention! Since the temperatures at the anode and cathode spots are different, the consumption of the electrode itself will depend on the correct connection of the welding machine. That is, reverse polarity when welding with an inverter means excessive consumption of electrodes.

In the process of welding with direct current, it is necessary to ensure that the metal of the workpieces warms up well, almost to a molten state. That is, a weld pool should form. It is the direct and reverse polarity of the welding mode that affects the quality of the bath.

If the current strength is high, and therefore the heating temperature is also high, then the metal will heat up to such a state that the electric arc will simply repel it. There is no need to talk about any connection here.
If the current, on the contrary, is too small, then the metal will not heat up to the required state. And this is also a minus.

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With straight polarity, an environment will be created inside the bath that is easy to control with the electrode. It spreads, so one movement of the rod creates the direction of the weld. At the same time, the welding depth can be easily controlled.

By the way, the speed of the electrode directly affects the quality of the final result. The higher the speed, the less heat enters the welding zone, the less the base metal of the workpiece warms up. By decreasing the speed, the temperature inside the weld pool increases. That is, the metal warms up well. Therefore, experienced welders set the current on the inverter to more than necessary. But the quality of the weld is controlled precisely by the speed of movement of the electrode.

As for the electrodes themselves, the choice of polarity is determined by the material from which it is made or the type of coating.

For example, using reverse polarity in DC welding, which uses a carbon electrode, leads to rapid consumption of weld rods. Because at high temperatures the carbon electrode begins to deteriorate.

Therefore, this type is used only in straight polarity mode. A clean, uncoated metal rod, on the other hand, fills the weld seam well when the polarity is reversed.

The depth and width of the weld also depends on the mode used. The higher the current, the greater the penetration. That is, the depth of the weld increases. It's all about the heat input on the arc. Essentially, it is the amount of thermal energy passing through a unit length of the weld.

But it is impossible to increase the current indefinitely, even regardless of the thickness of the metal workpieces being welded. Because thermal energy creates pressure on the molten metal, which causes it to be displaced. The end result of such electric welding at high current is burning through the weld pool.

If we talk about the influence of direct and reverse polarity when welding with an inverter, then a greater penetration depth can be provided by the reverse polarity mode.

Some features of welding with direct polarity

What is straight polarity is defined. Some qualities of welds are indicated when carrying out the joining process in direct polarity mode. But some subtle points remain.

Metal from electrodes or filler materials is transferred into the weld pool in large drops. Firstly, this is a large splash of metal. Secondly, an increase in the penetration coefficient.
In this mode, the electric arc is unstable.
On the one hand, there is a decrease in the depth of penetration, on the opposite, there is a decrease in the penetration of carbon into the mass of the metal of the workpiece.
Proper heating of the metal.
Less heating of the electrode rod or filler wire, allowing the welder to use higher currents.
With some welding consumables, an increase in deposition rate is observed. For example, when using consumable electrodes in inert and some active gases. Or when using filler materials that are applied under certain types of fluxes, for example, OSC-45 grade.
By the way, direct polarity also affects the composition of the material found in the seam between two metal workpieces. Usually there is practically no carbon in the metal, but silicon and manganese are present in large quantities.

Features of welding with reverse polarity current

Welding thin workpieces is a process with increased difficulty, because there is always the danger of burns. Therefore, they are connected in reverse polarity mode. But there are other methods to reduce the danger.

Reduce the current potential to reduce the temperature on the workpiece.
Welding is best done with an intermittent seam. For example, make a small section at the beginning, then move to the center, then start joining from the opposite side, then start cooking the intermediate sections. In general, the scheme can be changed. In this way, you can avoid warping of the metal, especially if the length of the joint is more than 20 cm. The more welded sections, the shorter each section, the lower the percentage of metal warping.
Very thin metal pieces are welded by periodically interrupting the electric arc. That is, the electrode is pulled out of the welding zone, then quickly ignited again, and the process continues.
If overlap welding is carried out, the two workpieces must be pressed tightly against each other. A small air gap leads to burnout of the upper part. To create a tight fit, you need to use clamps or any weight.
When connecting workpieces, it is better to minimize the gap between the parts, and ideally there would be no gap at all.
To weld very thin workpieces with uneven edges, it is necessary to place a material under the joint that would absorb the heat of the process well. Typically a copper plate is used for this. It can also be made of steel. In this case, the greater the thickness of the auxiliary layer, the better.
It is possible to flange the edges of the welded products. The flanging angle is 180°.

Experts recommend that before you start welding thin workpieces with reverse polarity, it is better to practice a little on a defective sheet of metal. It's better to spend time training than patching burn holes.

Source: https://stankotec.ru/raznoe/svarka-obratnoj-polyarnostyu-invertorom-pryamaya-i-obratnaya-polyarnost-pri-svarke-invertorom.html