How to deal with slag during welding - Metals and their processing

Why the weld seam slags - Metalworker's Handbook

What causes defects to appear? What should a welder be able to do to avoid them? What should be done if defects occur? The main causes of defects in welding seams can be divided into three groups:

1. Quality and storage of basic and auxiliary materials;

2. Preparation for welding of main and auxiliary materials;

3. Welder qualification.

Poor arc ignition

Poor ignition - sticking of the electrode, excessive increase in arc length - leads to lack of penetration at the beginning of welding, slagging, and pore formation. Poor quality production of electrodes, namely excessive exposure of the end of the electrodes at the ignition site, results in a bunch of pores, the so-called “starting pores”.

It is necessary to stop, perform mechanical cleaning, removal, or cut out the defective beginning with a chisel, and only then resume the ignition.

Excessively “convex” rollers

Excessively “convex” beads when welding corner and butt joints lead to welding of subsequent beads to the slag, lack of penetration between the groove edge and the convex seam, or between deep recesses between the beads (Fig. 80).

Such rollers are usually obtained in the following cases:

low welding speed without manipulation - increase the forward movement of the electrode;
manipulating the “arc backward” when welding vertical and ceiling seams - switch to the “ladder” or “arc forward” method;
angle of inclination of the electrode (welding “backward angle”) for ceiling seams - switch to welding “forward angle” or at a right angle to the welding direction;
low welding current for the lower position - increase the current;
Excessive welding current for vertical and ceiling seams - reduce to a minimum.

During welding, it is necessary to monitor the completeness and geometry of the seam, the liquid pool and control it by manipulating the speed and inclination of the electrode. Edge delay is very important. The more we heat the edge, the better the liquid weld metal forms on it when the electrode moves to the other edge, and does not collect in the middle of the seam.

Undercuts

Undercuts lead to slagging and lack of penetration. In Fig. 81a shows undercuts: 1 - in the body of the weld section, very dangerous, especially when welding stainless steels.

An undercut is formed; 1) when the electrode leaves the edge early (the crater is not filled with electrode metal); 2) with a very short arc (“support welding”), when the “visor” of the coating trims the crystallizing weld metal; 3) when abruptly moving away from the edge. Liquid slag fills the undercut.

While we are melting the other edge, the slag solidifies in the undercut and when returning it it is not always possible to melt it. This leads to a defect.

To avoid this, a delay at the edge is necessary until the crater is completely filled with electrode metal. The transition to the other edge should be carried out smoothly, without sudden fluctuations.

Surges

Rice. 81b. If there is an excessive delay at the edge, a leak of liquid metal occurs, as well as with a high welding current, when the welder cannot cope with the liquid metal of the seam. Cut down the flood and clean it up.

Lack of penetration

In drawings, technical processes or welding reference books, the gap during assembly can be set from 0 to 2-3 mm.

Assembly without a gap or with a gap less than recommended when welding a V-shaped groove (without welding the weld root on the reverse side) will lead to defects - lack of penetration and slagging of the weld root (Fig. 82); and for 2-sided welding, X-shaped and V-shaped (with back welding on the reverse side), it will require additional costs and time for deeper sampling of the reverse side of the root of the weld, partial bevel of the edges and unnecessary consumption of electrodes to fill the deep sampling.

Fistulas

Fistulas in the weld crater at the end of welding occur when the welding current is excessive, and also when the arc is separated by lengthening the arc.

Shrinkage shell

Shrinkage cavity most often appears when welding a root bead, large metal thicknesses, large gaps and especially when welding austenitic steels, as well as excessively high current and an excessive size of the weld pool.

When shrinkage occurs, a crack sometimes appears in the crater of the roller. This sharply reduces labor productivity due to the need for mechanical cleaning after finishing each electrode. When welding pearlitic steels with rigid fastening of parts, a shell with a crack is most often formed, and when welding austenitic steels, the reason for the appearance of shells with cracks is low heat transfer and high linear expansion. It is necessary to bring the crater back to the seam or to the cutting edge.

It is recommended to carry out welding:

in a reverse stepwise manner;
continuously (by two welders) with arc interception;
using the "arc-to-arc" method.

Pores

Pores in a weld are formed for many reasons:

poor-quality edge preparation (dirt, scale, rust) - clean;
high moisture content leads to the formation of pores, it is necessary to preheat the welded edges and calcinate the electrodes;
drafts in the welding zone;
poor-quality electrodes: rusty metal rod, eccentric coating leads to a “peak” and an increase in arc length;
strong magnetic blast, which causes a large deflection of the arc, which increases its length;
mismatch between the base metal and filler material in terms of chemical composition. And other reasons that require preparation in a specific case.

Reasons that cause pores, depending on the qualifications of the welder:

unclear ignition of the arc (sticking, rise of the electrode after ignition to a very high arc length) and an attempt to remelt such ignition leads to defects;
long arc welding.

A detailed study of practical tips, practicing during training, and applying them in practice will help welders improve the quality of welding operations performed during the manufacture and installation of critical products for nuclear power plants, thermal power plants, chemical and other equipment at enterprises where high demands are placed on treacherous joints.

Tudvasev V.A. “Recommendations for welders”, 1996

Source: https://ssk2121.com/pochemu-shlakuetsya-svarochnyy-shov/

Why is there a lot of slag when welding - Machine tools, welding, metalworking

Metal arc welding is a common and universal method of joining metal. Arc welding technology: The electric current of the welding source forms an arc between the base metal and the consumable electrode. The coating burns on the electrode, which releases a gas that protects the area from oxygen. The superheated surrounding gas melts the metal, and the metal from the electrode is transferred to the weld pool.

The task for a beginner is to learn how to weld. Before we start burning electrodes, let's learn about the equipment used.

The job of a welding machine, no matter its size or shape, is to provide sufficient, regulated current to the electrode. The welding machine supplies direct or alternating current to the electrode.

Previously, transformers were used for welding. They are being replaced by compact and resistant to network sag welding inverters.

Welding of direct and reverse polarity

For alternating current, appropriate electrodes are used. Professional welders prefer direct current. In DC welding, the flow of electrons moves in one direction. The welding inverter allows you to select the polarity. Polarity is the direction in which electrons flow, depending on which terminal you connect the wires to.

https://www.youtube.com/watch?v=uQYXAoTen-Q

Reverse polarity when welding: plus on the electrode, minus on the ground terminal. Current flows from the negative to the positive terminal, so electrons move from the metal to the electrode. This causes the end of the electrode to become very hot. For conventional welding, use a plus on the electrode and a minus on the terminal.

Straight polarity when welding: minus on the electrode, plus on the ground terminal. The current flows from the electrode to the metal, the electrode is cold and the metal is hot. This is used in special electrodes for high-speed welding of sheet metal.

Welding equipment

Remember, different machines weld differently! Therefore, when training, use one device as much as possible. Insulated copper wires are also important. They come in different sizes (sections).

A quick-release clamp is placed at the end of the main wire; a 3 or 4 meter wire of a certain cross-section with an electrode holder of 200, 300 or even 500 A is attached to it (used for thick electrodes and high currents). For home use, 200 A is more convenient.

There are holders similar to pliers, and there is a welding holder into which you insert an electrode and turn the handle (if you need the electrode at different angles, bend it at the base). You also need a grounding terminal with a quick-release clamp.

Light filters

The brightness of the arc is approximately 10 thousand times higher than the brightness of light acceptable for the human eye. A protective filter will protect your eyes from getting burned when you look into a molten bath. They come in different numbers. A lower number means a lighter filter on the welder’s mask. People are sensitive to light differently.

The welder's filter should protect your eyes, but you should be able to see the weld pool clearly. If you use thick electrodes and high currents, you must use filters with a higher number. The filters for masks are fragile. To protect them from sparks or scratches, use protective plastic glass on the front and back.

When assembling the mask, use a seal and a clip. After installing the filter, look at the light and check that there are no gaps. If you see light during cooking, stop welding to avoid getting a retinal burn (bunny). Replace welding protective glasses when they are dirty or scratched.

Clean glass is important for a clear view of the weld pool.

Let's start welding!

Welding electrodes are coated with flux, which makes the welding process possible. When burned, the flux creates a protective gas and cleans the bath, displacing oxygen from the air, keeping it from combining with the molten metal, preventing the formation of pores, and also stabilizes the arc and maintains the purity of the molten metal. When the metal cools, weld slag is formed, which provides additional protection for the metal from air.

Welding is a gradual practice and is not difficult. First make sure everything is ready for welding. You should be comfortable at any time during welding! The electrode does not burn out immediately, so relax, grab the holder with both hands and lean on the table as steadily as possible. When everything is ready, begin the arc welding process, lower the welder's shield or adjust the clamp of the mask so that it lowers when you nod your head.

Light the arc like you light a match: strike the electrode against the metal and bring the end to the beginning of the seam. When struck, the electrode flux will begin to melt, which cleans the bath. To avoid marks, scratch in the direction of cooking.

After striking the electrode, the arc is ignited, the end of the electrode should be 3 mm from the surface, this creates a gap for the arc, and bright light comes from there.

When welding, look beyond the light and beyond the smoking sparks, focus on the molten pool behind the electrode.

It is more convenient to take the holder so that its lever is located under the thumb. To remove the electrode, grasp it with your left hand, press the lever and remove the electrode. If the electrode sticks, the flux on the tip is most likely damaged. Strike to burn the end of the electrode before filling the weld pool.

When the arc is ignited, form a bath. Here it takes some time to warm up the base metal. In time, this takes 2-3 small turns of the electrode around the weld pool. Further, during welding, the base metal warms up and the pool diverges. At first the bathtub is small, make sure that the bathtub is wide enough and does not change shape.

Arc gap control

When welding, keep the electrode above the metal. This is called the arc gap. Controlling this gap is the first and most important thing you need to learn. When moving along the seam, the electrode is consumed, so it must be lowered. Maintain a constant gap between the electrode end and the base metal.

If the gap is small, then there is no time to warm up the base metal, the seam will be convex with lack of fusion at the edges.

If the gap is too large, the arc will begin to jump, there will be poor penetration and it will be difficult to control the laying of the deposited metal.

A constant gap of normal size is the first step to controlling the weld pool and forming a high-quality seam with good penetration.

The better you control your arc length, the better your brew! When the arc passes through the gap, it melts the base metal and forms a weld pool. It also transfers metal from the electrode to the bath.

Seam formation. Weld defects

When welding, look at the sides of the seam; it should be level with the metal. The formation of the seam usually occurs in a circular or zigzag motion.

When making circular movements, move to the side and look to the right of the weld pool, then up to the boundary of the pool and slag, and then to the other side and simply distribute the pool in a circle. This is the arc welding technique.

Zigzag movements from side to side make a similar seam: look from one side, to the top of the tub and to the other edge. Whenever you change direction, remember that the molten bath follows the heat.

This seam is welded with an electrode that is moved quickly. The bath line is below the surface of the base metal. The intense arc of this electrode penetrated deep into the base metal, pushed the pool back and formed a seam.

When you move the bath across, the filling metal from the electrode moves behind, and if there is not enough metal around, you leave undercuts. An undercut is an empty space, a groove at the edge of a seam, below the level of the metal.

To avoid this, control the outer boundaries by observing the tub and thinning the surface. The arc force at the end of the electrode can be used to manipulate the bath. By tilting the electrode, we seem to be pushing the bath, rather than pulling. The more vertically we hold the electrode, the less convex the seam. And vice versa.

The electrode stands vertically, all the heat is concentrated under the electrode, the force of the arc presses down on the bath, this leads to deep penetration and spreads the bath around.

If the slope is too great, the arc will press in the direction of the seam, making the bath difficult to control.

There are situations when you need to weld a flat seam, and there are times when you need to push the bath back. Therefore, different electrode angles are used. We start with an angle between 45 and 90 degrees. It is more convenient, the weld pool is clearly visible, and it cooks normally.

Electrodes

The diameter of the electrode is determined by the diameter of the rod. Basic welding tables provide electrode diameter, metal thickness and current value for maximum productivity.

This often does not take into account the capabilities of the welder or the specifics of the situation. You can use a smaller diameter electrode for better control, but welding will take longer.

The exact current settings may vary and depend on the thickness of the metal, the position of the welder and his qualifications.

Welding process control

The purpose of the welding process is to heat the base metal until it melts, forming a weld pool. A low current will not warm up the base metal, and the weld pool will “run” behind the electrode. If there is a lot of current, then the base metal will be overheated, the arc will penetrate deep and push the metal back. At optimal current, the pool spreads, the outer edges are thin, and we control the welding process.

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Depending on the welding situation, the current settings vary. Thick metal dissipates heat, so more current is needed. Thin metal will melt quickly, so less current is needed. The exact current settings depend on the behavior of the bath. Start with the manufacturer's recommended settings and don't be afraid to increase or decrease the current.

Covered electrode welding depends on the temperature of the base metal, so we cannot talk about current without taking into account the welding speed. We move the electrode faster, less heat enters the base metal, so it is cooler. If we move slower, more heat comes in and the base metal will be hotter.

If you move the electrode too quickly, the metal will not be heated, the seam will be at the top, without penetration. If you move slowly, the metal heats up too much, causing the bath to spread out and become difficult to control. When the speed of movement matches the current, the bath spreads, but remains controllable.

The edges are thin and the seam is the same thickness.

With experience, you will be able to set a slightly higher current and increase the welding speed. Higher current melts better and you will get a smoother seam, but in this case it is more difficult to control the pool.

When finishing a weld, deposit a little more metal before removing the electrode to avoid a crater from splashing the lower layers of metal. Make 1-2 circles and scratch back along the seam.

Briefly about the basics

Strike the electrode to create an arc.
Extend the tub to the required width so that the seam is even.
Maintain a constant arc gap.
The welding current must be sufficient for the pool to spread.
Expand the weld pool using arc pressure.
Watch the edges and the seam that is forming.
Add weld metal before stopping.

Welding aluminum with direct current in argon

for domestic use - LEVSH-200 for professional use at 220V - PROFI ARC 200 for professional use at 380V - PROFI MMA 315

Source: https://stanki-info.com/pochemu-pri-svarke-mnogo-shlaka/

Welding slag as a prerequisite for the occurrence of slag inclusions

The main side effect of arc welding is welding slag. It is a by-product of non-metallic origin, which consists of either the molten electronic coating of the consumable electrode (in manual arc welding, including inverter welding) or molten welding flux (automatic submerged arc welding).

This material is a by-product because it must be removed after direct connection.

In the case when, for some reason, it begins to come into contact with the hardening part and becomes part of the resulting seam, this is a serious defect. This result is called slag inclusions.

They are visually visible on the surface of the product. You can remove slag inclusions when they are already completely in the hardened part only by drilling, and then weld it again.

The reason for the occurrence of slag inclusions is a situation when a small volume of metal hardens too quickly, as a result of which all the slag does not have time to “exit” beyond the weld pool area. If this defect is present, the connection will not be able to be used for its intended purpose.

Slag inclusions can be macroscopic or microscopic. The first ones appear in case of poor edge cleaning or its absence at all. They are a spherical material with elongated tails. Their occurrence can be avoided by thoroughly cleaning the edges of the parts being connected. Microscopic inclusions can arise during chemical reactions during the welding process, when the metal crystallizes.

Complete elimination of such manufacturing defects is impossible; with minor slag inclusions, the connection can be considered high quality.

There are certain conditions and signs under which the acceptable value of the presence of this type of defect on a product is established.

Such tolerances are established depending on the number, location and size of the defective seam; from the percentage ratio of the area of the entire defect to the area of deposited metal on the product; on the specific gravity of the deposited metal.

Reasons why a defect must be removed after work

When removing slag, the product visually looks better.
When many layers are produced.
Often the product needs to be coated on top, for example with paint.
To check how well the seam is made.

The main reasons for the appearance of slag inclusions

Rapid solidification of small volumes of metal, as a result of which the slag does not have time to go beyond the boundaries of the weld pool.
The use of electrodes and flux of high specific gravity and/or from refractory materials.
Low rates of metal deoxidation. Deoxidation involves the process of removing oxygen molecules from an already soft metal.
Oxygen is a harmful component for it, which deteriorates the quality.
High surface tension force of slag. At the same time, it does not float to the surface.
The edges of the parts or seam beads are poorly cleaned.
Poor quality of the electrode, or rather its coating, which melts unevenly; its particles end up in the weld pool.
Failure to comply with the rules and techniques and modes of connecting parts (choosing the wrong speed, angle of inclination of the electrode), changing the arc length for no reason.
Unprofessional welder. If you need a quality product, it is better to involve a specialist in this field in this difficult task.
If you want to do everything yourself, then before you take on important, complex work, you need to gain practice with simple connections.

This is what welding slag looks like after being removed from a seam.

Professional welders are able to immediately distinguish slag from metal during welding and “drive” it out during the work process, however, everyone has their own advice on how to do this.

Some argue that it is better to use new electrodes in which the coating is darker and the metal is red (this does not apply to rutile electrodes), others say that the metal is more liquid and the slag is viscous. Its viscosity is affected by temperature.

To prevent the slag from covering the weld pool, it is necessary to adjust the position of the electrode. The position must be such that the direction of the gas from the evaporation of the electrode coating blows this defect onto the surface of the seam. Under no circumstances should the welder leave it in the weld pool. Welding slag should quickly succumb to the crystallization process and be removed without much effort.

It is inevitable that slag gets into the finished joint; such a defect, if not impossible to eliminate, is often very difficult. That is why there are acceptable standards for the presence of “extra” inclusions in an already welded product.

For example, in the interstate standard regarding building steel structures (put into effect in 2001). The annex to this document provides requirements for the quality of welded joints and permissible defects.

The requirements for slag inclusions are shown in the table below.

Long defects	Not allowed
Short defects:
butt weld	h ≤ 0.2 S	h ≤ 0.25 S	h ≤ 0.3 S
fillet weld	h ≤ 0.2 K	h ≤ 0.25 K	h ≤ 0.3 K
Maximum inclusion size	2 mm	3 mm	4 mm

Thus, to ensure that slag appears correctly on the surface of the weld, you need to know how to distinguish it from the metal. If it is noticeable that the slag remains in the weld pool and does not come up, you need to change the angle of the electrode.

Before the joining process, it is necessary to take care of the proper condition of the edges, as well as the correct choice of modes and parameters. Electrodes must be chosen of high quality, then the weld will be of high quality. If all conditions are met, then the slag will be non-viscous, of low specific gravity, with low surface tension.

Only in this case, slag compounds will interact with the part, increasing its deoxidation rates, removing oxygen. And only then will the welding slag easily come out to the surface of the seam. Here you cannot do without the professionalism of the welder performing the work.

He must be able to distinguish slag from metal during welding and know why it appears in the first place. Only an experienced specialist will be able to make a high-quality and durable connection.

Source: https://svarkaed.ru/svarka/obuchenie-svarke/svarochnyj-shlak.html

How to cook without slag with an electrode?

Metal welds are a permanent connection that is made by welding under high temperatures.

Welded joints have several connection zones that are formed during the welding process itself:

Weld seam - this section of the welded joint is formed as a result of crystallization or as a result of any deformation that occurred during welding. Most often, both crystallization and deformation occur at the welding site.
Weld metal – formed as a result of melting of the base metal. As a rule, the melted or melted part of the structure is connected to the desired element by means of “sticking”. After the weld metal has cooled, the bonding is completely completed.
The base metal is the main part that is melted or welded.
Fusion Zone - This zone is usually located at the boundary or between the base or weld metal.
The heat-affected zone is a section of the base metal that is not subject to melting, but whose structure and properties change as a result of heating during welding or surfacing.

Thus, welds can be divided into several types:

Butt joints - this type of connection consists of two elements that are adjacent to each other at their end surfaces. This type of weld is very easy to technically construct and is used quite often.

Overlapped is the type in which all welded elements are located parallel to each other. Most often, they must additionally partially overlap each other.

Corner - in this type of welded joint, all elements are welded together at a certain angle.

T-joint - this type of connection is similar to a corner connection, but here it is required to weld exclusively to the side surface.

End - here you will need to weld the side surfaces of the material to each other.

Basics of electric welding

Having understood the types and types of weld joints, you can move on to the basics of electric welding. If you plan to study on your own, then you will need to stock up on all the necessary materials. Since you will most likely experience a slight failure the first time you practice, it is better to stock up on a large amount of material.

It is also important to know some terms and symbols before starting work:

A welding arc is a gas heated to incredibly high temperatures (about 5-7 thousand), so you need to handle welding with extreme care, otherwise you risk causing serious burns to yourself or others.
Arc Welding – This type of welding is done using an electric arc that heats gas to incredibly high temperatures. Upon contact with the surface of a metal product, the metal begins to melt, resulting in the formation of a so-called “weld pool”. After the metal cools, a weld appears.
Argon arc welding is practically the same as an arc type of welding, only argon must be used as the heated gas. This type of welding is very suitable for various reinforcement rods with a thickness of no more than 5 millimeters.

Preparatory work

For the reasons described above, it is best to carry out all welding work in a room where there is nothing to burn, otherwise you risk starting a fire. Having found a fire-safe room, you need to prepare all the materials necessary for the work. First of all, think about your protection, purchase a special welding mask, gloves for welding, and it is also advisable to additionally purchase a special suit that is made of fire-resistant material.

When you are sure that you have protected yourself from an accidental spark or burn, you need to purchase all the necessary tools for the job. These include:

You will definitely need the welding machine itself.
You will also need a small set of electrodes that will conduct enough electricity to heat the gas to the desired temperature.
A special small hammer that will be needed to beat off unnecessary slag.
And also a brush with hard bristles for removing various types of debris.
Transformer. Thanks to it, the normal alternating electrical current that passes through our sockets will be converted into direct current. Most of the welding machines in the world market operate using DC current only.

How to cook using electric welding

When everything is ready to begin the welding process, be sure to carefully check the surface of the elements that you are going to weld together for the presence of rust or any other defects. If any are found, it is recommended to try to eliminate them or replace the defective elements with better ones.

Now that everything is ready to go, you can start:

First you need to attach a special work clamp to your workpiece and insert the electrode into the welding holder. Then you need to try to light the arc. The electrode must be installed at an angle of about 70 degrees relative to the workpiece. To ignite the arc, it is necessary to move the electrode across the workpiece at a speed of approximately 7-10 cm per second. From the outside it will look like you are lighting a match. When a characteristic crackling sound and sparks appear, the gas arc itself will light up. If all this happened, then everything worked out for you.
Then, install the electrode at approximately the same angle. After installation, you will need to come into contact with the workpiece, and immediately raise the electrode slightly so that you end up with a small gap of 3-5 millimeters between the metal surface and the electrode. After contact with the metal, the arc begins to burn. However, not only the metal of the workpiece will melt, but also the arc itself. Try to maintain the gap dimensions and at the same time move the electrode horizontally or vertically (depending on which direction you need).
Also during the welding process, if you get too close (also due to low voltage) to the surface of the metal, your electrode may stick. To make it unstick, move it from side to side. Then light the arc again.
Try to tune the transformer as best as possible. After all, if there is too much current, the metal will melt like butter, and if there is too little current, the arc will simply go out.

How to weld a seam correctly

Having understood a little about the work of the arc and the welding itself, we begin to make seams. Seams in our case are divided only into horizontal and vertical.

Below is a short instruction for each of these types:

1. Horizontal seam

Making such a seam is as easy as shelling pears. It is enough just to gradually draw the arc horizontally, maintaining a gap of 3-5 millimeters. It is also advisable to secure the material on which you need to make a seam as best as possible.

When welding, you need to conduct the arc not very quickly, but not too slowly - this is necessary so that the gap between the metal materials is gradually filled with melted metal and at the same time has time to cool.

It is very advisable to try not to interrupt the seam, otherwise the alloy may turn out uneven.

2. Vertical seam

The process of welding vertical seams is quite similar to the process of welding horizontal seams, only in this case you need to weld at a different angle.

The most important principle in welding vertical seams is to follow a certain rule - never move the arc too fast or too slow.

Because in this case, if the metal is subjected to a lot of heat (the arc moves too slowly), it will gradually flow down, and if the arc moves too quickly, you may end up with a poor-quality seam.

Your task should be to merge both edges by melting them with a welding arc, while simultaneously directing drops of metal from the hot liquid end of the electrode into the same area.

How to cook pipes correctly

The process of welding pipes using electric welding is quite labor-intensive and requires a certain level of skill and accuracy. If you want to learn how to weld pipes on your own, then the best time to start is to try pipes on thick metal.

Small instructions:

We lay out all the pipes on a special table or stand where it will be convenient for you to work with them.
In this method, you will need to weld the pipe in two steps. The first step is to weld the first half ring in one direction, then the second in the other. Here you should use a top-down technique using a 4 mm organic-coated electrode.
If you are welding pipes with a small diameter, try to weld them with a continuous arc, but if the diameter of the pipe is large, then weld it using the method given in paragraph 2.

Case for heated electrodes

How to remove slag

During the work, you may develop various types of defects in the alloy areas - slag. Before you begin removing the slag, you must allow the seam to cool. When you are sure that the seam has cooled, tap it with a small hammer (it is best to purchase a special one for removing slag).

After tapping the slag, the main layer of slag will fly off on its own; the remaining layers can be removed using sandpaper.

Source: https://rem-serv.com/kak-varit-bez-shlaka-elektrodom/

Welding slag and metal: what are some ways to tell them apart during the welding process?

There are several ways to help distinguish metal from slag:

Color . During the welding process, under the influence of high temperatures, the metal begins to melt and acquire a reddish tint. After completing the welding work, the red color changes to a darker color. With slag the opposite is true. During welding work, it has a dark color, and at the moment when it begins to cool, it becomes lighter than the metal product.
Cooling rate . Welding slag hardens much more slowly than metal.
After cooling, the metal alloy has a more dense structure , while the slag is a loose “crust”.
When welding, steel has a more liquid consistency , slag has a viscous consistency.

Differences between a metal product and slag can be seen during the formation of the weld pool. Observing how the base material melts, you can see the following picture: a bright light is formed under the tip of the electrode, and clear boundaries of the weld pool and the contours of the seam appear beyond it. The lighter shade belongs to the metal, and the darker color outside of it belongs to the slag.

What are slag inclusions?

Slag inclusions are a serious defect that can harm not only the metal, but also the structure itself.

There are two types: macroscopic and microscopic slag inclusions, which can be found on the surface of a metal product. Defective inclusions can arise as a result of metal oxidation (oxide), flux, mechanical clogging of electrode coating particles, and contamination of edges.

The first variant of slag inclusions appears in the absence or poor cleaning of edges. Microinclusions arise, as a rule, as a result of chemical reactions that are formed during the welding process and crystallization of the metal. Both types of inclusions negatively affect the mechanical properties of the metal product.

Reasons for the formation of slag inclusions

The appearance of slag inclusions is influenced by the following factors:

Unprofessionalism of the welder . Often, beginners make mistakes when working with a welding machine, namely choosing the wrong speed, changing the arc length and the angle of inclination of the electrode and flux for no reason. Uneven movement of the tool also causes the formation of slag inclusions.
Poor edge cleaning.
Using a low quality electrode . In this case, the melting process occurs unevenly, and particles of the electrode coating fall into the weld pool.
The surface tension forces of the slag are high, which creates an obstacle to its release to the outside . This occurs due to the fact that in the surface layer of the slag there is an increased content of calcium, magnesium and aluminum oxide, leading to an increase in surface tension, at which the adhesion forces between the surface particles of the slag increase.
One of the reasons for the inability of slag to escape beyond the weld pool is the rapid solidification of the metal.
Operation of electrodes and flux made of refractory metals and high specific gravity.
Low rates of metal deoxidation . Deoxidation is the process of removing dissolved oxygen from metal alloys containing iron. As a rule, oxygen is a destroyer of the mechanical properties of metal.
The presence of industrial waste residues, rust, or oils on the product can slow down or worsen the heating and melting process in the weld pool.

Why does slag need to be removed during welding?

Slag remaining on the surface of a metal product can interfere with checking the quality of the resulting weld. The welding process of larger parts involves the application of several layers, so the presence of slag inclusions can lead to poor-quality joints and labor-intensive correction of such weld defects. Also, slag inclusions can extinguish the arc.

Consisting of oxides, slag inclusions are porous. They can reduce the strength of the metal and the entire structure due to the presence of fragility and the lack of strong bonds.

The presence of slag on the surface of the base material may prevent further processing of the product. This can be either grinding or applying a protective anti-corrosion coating.

Slag oxides can interact with the constituent components of a metal product during use, in particular with iron. This process involves the complete destruction of the structure.

Source: https://elsvarkin.ru/texnologiya/kontrol/shlak-i-metall/

Welding slag: reasons, how to distinguish it from metal, removal and purification

The joining of metal parts into integral structures is often carried out using arc welding. This is a fairly effective and simple welding technology, but its main side effect is welding slag.

What are slag inclusions

Welding slag is a glassy by-product material formed from the molten electrode coating or welding flux. The presence of slag inclusions is considered a very serious defect that can reduce the quality of the welded joint and the entire structure.

All slag inclusions arising on a metal surface during welding are divided into two types:

macroscopic . Formed when the edges being welded are insufficiently cleaned or absent;
microscopic . As a rule, they arise as a result of chemical reactions occurring during welding and crystallization of the metal.

Both types of inclusions have a negative impact on the mechanical characteristics of a metal product.

Reasons why slag inclusions form

Quite often, only specialists mastering welding technologies wonder why a lot of slag is formed at the connecting joints during welding. The appearance of such inclusions is due to various factors:

the metal cools faster than usual and the slag simply does not have time to leave the weld pool;
low quality electrodes used in welding. In this case, melting occurs unevenly and electrode particles enter the weld pool;
at low values of metal deoxidation, a lot of slag is formed during welding. This is a process in which oxygen molecules are eliminated from an already soft metal. They worsen the mechanical properties of the metal and destroy its structure;
poor-quality preparation and cleaning of welded edges from dirt, rust and oils;
high values of surface tension of the slag prevent it from floating to the surface;
the use of flux or electrodes made of refractory metals and with a high specific gravity;
non-compliance with welding modes and technology, for example, incorrectly selected angle of inclination or inappropriate speed of electrode movement.

In order to weld without slag or with a minimum amount of it, it is advisable to seek help from experienced welders. If you want to weld yourself, then you should learn how to weld the simplest elements and only then proceed to more complex ones.

How to distinguish slag from metal

Welders, especially beginners, face various problems and questions when creating metal products by welding. For example, many find it difficult to distinguish slag from metal when welding.

In reality, it is not difficult to distinguish between metal and slag inclusions. To do this, you should pay attention to the following factors:

color . Under the influence of high temperature, the metal melts during welding, acquiring a reddish tint. As the metal cools, the color of the reddened metal darkens. Slag behaves completely differently. It has a dark color directly during the welding process, and when it cools it becomes lighter;
cooling rate . Metal, unlike slag, hardens much faster;
the structure of the cooled metal alloy is more dense, and the slag inclusions form a loose crust;
fluidity _ When melted, the metal is more liquid, which contributes to its greater mobility. During the welding process, it is easy to see how it boils. The slag is more viscous and does not heat up as well.

You can distinguish slag from metal during welding directly at the moment when it appears in the weld pool. If you watch how the metal melts, you can see the appearance of a bright light under the tip of the electrode, and behind its outlines you can see the clear contours of the butt joint and the weld pool itself. Metal is identified by its light shade, slag by its dark shade.

Why does slag need to be removed?

Slag inclusions mainly consist of oxides due to their porous structure and significantly reduce the strength properties of the metal. During operation of a welded structure, oxides from the slag are capable of entering into a chemical reaction with iron, which leads to its destruction. Therefore, immediately after cooling, when the slag turns black, it must be removed.

At the initial stage of welding, the slag with oxides formed above the pool protects the metal from rapid cooling. Since the temperature of the metal decreases much more slowly, when removing slag after welding, the seams are more even and uniform.

There are other reasons why it is recommended to remove the slag formed at the joints after welding parts:

it is much easier to check the quality of the welded joint when there are no slag inclusions on it;
paint and varnish coatings are often applied to finished products, and the presence of slag inclusions significantly worsens the appearance of structures;
If it is necessary to perform a shock in several layers, you must first remove the slag and only then create the next layer.

Note! If the welding slag is not removed, it may be impossible to use the finished product due to defects present in the form of tops and non-metallic inclusions. This is especially important for structures that will be subject to high external loads during operation.

How to minimize slag inclusions when welding metals

Many novice craftsmen are concerned about the question “why is there a lot of slag when welding with an inverter?” Typically, such problems are observed during welding when the elements are in the lower position. In cases where the part is located on a slope, the slag drains much faster than the liquid metal mixture from the weld pool. Due to the fact that the slag did not have time to come out, it remains in the weld seam.

Also, slag formations appear when gaps are excessively large or when the current is insufficient in relation to the thickness of the metal. Much less often, problems with slag arise when creating vertical seams, while the seam remains on top and the slag flows down.

Some professional welders advise placing the workpiece on an incline and welding from top to bottom, while others suggest using slag-free electrodes with a dark coating for welding.

To prevent slag particles from getting inside the weld pool, the direction of the electrode should be coordinated. It must be positioned in such a way that when the electrode coating evaporates, the gas flow “blows” such a defect onto the outer surface of the connecting joint. You cannot leave slag in the weld pool. It should crystallize quickly, allowing you to remove it without much effort.

How to get rid of slag

To get rid of slag when welding, you can try to increase the arc. This will prevent slag formations from flowing under the weld pool.

By changing the polarity of the current when welding with an inverter and moving the electrode from minus to plus, you can prevent the accumulation of slag in the weld. You can’t stay in one place for too long; you need to move the arc quickly and evenly.

If the dimensions of the product allow, you can try to “drive” the slag back by changing the angle of inclination of the part. Inverter welding with reverse currents produces less slag. Such a device is best used by novice welders, as they prevent sticking of the electrode and greatly simplify the welding process.

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Source: https://osvarka.com/obuchenie-svarke/svarochnyy-shlak

Reasons for the appearance of large amounts of welding slag

When welding, a black loose crust is formed over the place where the metal is joined (seam) - welding slag. It consists of molten flux or electrode coating, oxidized metal. In the process of melting and joining the materials to be welded and the electrode, it closes the melting bath. Thanks to the slag, the seam cools slowly, without oxygen, and does not oxidize.

Once molten waste gets directly into the seam, it causes rapid destruction of the metal. You can prevent oxides from getting into the seam by changing the welding modes and position of the part.

How to distinguish slag from metal

To prevent leakage and clogging of the seam, you need to know how slag differs from metal when welding. As a rule, these are materials of different density and viscosity that heat up at different rates. At the beginning of welding, the metal begins to melt and turns red.

After welding is completed, it cools down faster and darkens. The slag is blown out of the bath onto the surface. At the beginning of work it is dark and poorly heated. It cools down more slowly and becomes lighter than the metal.

How to distinguish metal from slag - Welding area
By cleaning the seam and tapping it with a hammer, it is easy to recognize the metallic sheen of clean steel and black matte inclusions.

There is no pure iron in slag; it consists of oxides that are formed during the melting of metal and flux. The composition varies slightly depending on the coating of the rod, but basically consists of the same substances. The table shows data on the 3 types of electrodes used most frequently:

Substance, oxide	, % SSSI	, % OMM-5	, % C-3
gland	7,9	13,2	18,5
titanium	2,2	15,2	12,2
manganese	4,6	28,9	13,7
calcium	42	3,6	8,1
silica	43,3	39,1	47,5

The composition depends on the material of the rod itself and the coating.
Iron oxide is partially obtained as a result of contact of the material with air at high temperatures. How to see a weld pool and distinguish metal from slag

Welding slag as a prerequisite for the occurrence of welding inclusions

At the initial stage, the oxides protect the hot metal from rapid cooling and close the seam from above, blocking the access of air. Then they must be removed to check the quality of the connection, the presence of defects in the form of non-metallic inclusions, tops.

When welding parts of large thickness, several seams are applied in succession. Uncleaned slag will prevent normal contact and extinguish the arc. It will remain in the form of non-metallic inclusions - defects.

Reasons why a defect must be removed after work

Slag inclusions have a porous structure and consist of oxides. They reduce the strength of the metal. Immediately after cooling, when it turns black, the welding slag should be removed. It is porous, fragile without strong bonds.

Flux and slag vapors above the bath prevent oxidation of the metal during welding and help create a homogeneous structure. After it moves away from the part during the cooling process, it becomes unnecessary and interferes with further processing of the part. During operation of the product, oxides from the slag can enter into a chemical reaction with iron. The pieces falling off will break the mechanism.

The main reasons for the appearance of slag inclusions

When the weld seam is rapidly cooled, the slag does not have time to come out and solidifies in the metal. The reasons are:

low voltage;
slag flowing from the bath in front of the electrode;
incorrectly selected diameter;
rusty and dirty metal;
uneven movement of the tool.

The operating voltage is indicated on the package with electrodes. It can be exceeded a little, then the boiling metal in the bathroom will throw out slag. It is necessary to select the correct position of the metal to be welded, lift it from the end of the seam. Do not hold the electrode strictly perpendicular, but tilt it 10–15⁰ towards you.

The metal at the welding site should be shiny. It must be cleaned of household and industrial waste, scale, and oil. They interfere with the contact of the electric arc with the steel, impairing the heating and melting of the material in the bath.

To slow down the cooling of the weld and allow the slag to escape freely, large parts and alloyed metals are preheated to 200–400⁰. This relieves stress and allows steel with high carbon and alloy content to be welded.

HOW TO DEAL WITH SLAG DURING WELDING

Why does a lot of slag form when you cook with electrodes?

During the welding process, the electrode coating or flux dissolves. Some of the iron, sulfur and phosphorus from the material being welded burns out. The electrical conductivity of slag is less than that of metal, so it heats up worse and extinguishes the arc. Increased voltage and incorrectly selected operating parameters, electrodes contribute to metal burnout, oxidation of iron and other steel elements.

The reason why there is a lot of slag lies in its structure. All substances formed as a result of metal melting from an electric arc are lighter than steel, do not have strong bonds with each other and float to the surface.

Welding with an inverter for beginners, how to weld without slag inclusions

The inverter turns alternating current into direct current and allows you to change the polarity. Reverse current welding usually produces less slag.

The advantages of an inverter over a conventional welding machine are its small size and operation on current with a household voltage of 220 W and a frequency of 50 Hz. For beginners, it is important to be able to smoothly change the current strength.

Inverter devices have additional arc functions:

easier ignition;
emergency shutdown when stuck;
afterburner ignition.

All of them simplify the work of an inexperienced welder and prevent sticking of the electrode.
WELDING INVERTER. WELDING TECHNOLOGY

How to get rid

You can get rid of slag when welding with an inverter by changing the polarity of the current and moving the electrode from minus to plus. When working with thin metal, it is necessary to take into account its rapid cooling and do not apply high voltage; the sheet may burn out.

You can’t stay in one place for a long time; you need to move the arc evenly and quickly. A terminal from “–” is attached to a thin sheet, and “+” is applied to the electrode. The thick sheet heats up and cools down longer so that the slag has time to come out, minus is applied to the metal being welded, and plus is applied to the electrode.

How can a novice welder weld without slag inclusions?

Source: https://metalloy.ru/obrabotka/svarka/shlak

Reasons for the appearance of large amounts of welding slag: how to avoid it?

For many years, welding has been a viable process for erecting steel structures, repairing heavy equipment, constructing bridges and other similar structures.

This is not surprising as it offers the high deposition rates, excellent chemical and mechanical properties and weldability required for these applications. However, this does not mean that the process does not have its problems.

Fortunately, you can prevent some common slag problems and achieve the weld quality you desire.

How to distinguish slag from metal

Slag inclusions may be visible on the surface after cleaning or may be completely contained in the metal, but in the latter case they can only be detected on X-ray photographs of the weld, which require grinding or drilling to remove (followed by re-welding the area).

How to cook without slag inclusions

This is very easy to achieve if you know a few basic rules:

Avoid improper placement of welds, especially when making multiple passes on thick sections of metal, such as those required for root passes of welds or wide V-groove holes. Make sure there is enough space in the weld joint for additional passes, especially in joints that require multiple passes.
Maintain the correct angle and speed. In flat, horizontal and up positions, the drag angle should be between 15 and 45 degrees. In the vertical top position, your resistance angle should be between 5 and 15 degrees. If you experience slag inclusions at these angles, you should increase the drag angle slightly. Maintain a constant moving speed: If you move too slowly, the weld puddle will overtake the arc and create slag.
Then, proper welding heat input should be maintained, as too low heat input can also result in weld slag. Always use the manufacturer's recommended settings for a given wire diameter. If this does not help, increase the voltage until the switching on stops.

How to get rid

Removal is usually done using hand or power tools. Hand tools may include a welding or jackhammer with a sharp tip for effectively breaking up large pieces of slag, or wire brushes. Power tools include angle grinders with sanding discs or wire brush wheels.

Source: https://TehnoPanorama.ru/instrumenty/prichiny-poyavleniya-bolshogo-kolichestva-svarochnogo-shlaka-kak-izbezhat.html

Electric welding - how to properly weld pipes, types of pile seams and how to remove slag

Metal welds are a permanent connection that is made by welding under high temperatures.

Welded joints have several connection zones that are formed during the welding process itself:

Weld seam - this section of the welded joint is formed as a result of crystallization or as a result of any deformation that occurred during welding. Most often, both crystallization and deformation occur at the welding site.
Weld metal – formed as a result of melting of the base metal. As a rule, the melted or melted part of the structure is connected to the desired element by means of “sticking”. After the weld metal has cooled, the bonding is completely completed.
The base metal is the main part that is melted or welded.
Fusion Zone - This zone is usually located at the boundary or between the base or weld metal.
The heat-affected zone is a section of the base metal that is not subject to melting, but whose structure and properties change as a result of heating during welding or surfacing.

Thus, welds can be divided into several types:

Overlapped is the type in which all welded elements are located parallel to each other. Most often, they must additionally partially overlap each other.

Corner - in this type of welded joint, all elements are welded together at a certain angle.

T-joint - this type of connection is similar to a corner connection, but here it is required to weld exclusively to the side surface.

End - here you will need to weld the side surfaces of the material to each other.

How to distinguish slag from metal when welding

» Articles » How to distinguish slag from metal when welding

New welders face many problems and questions that arise during the process. So, at the first stages, many find it difficult to distinguish slag from metal, and how to expel this slag during welding. In this article we will talk about how to do this and what is needed to ensure a high-quality weld.

The main difference between melting metal and slag during welding is its fluidity. The metal is more liquid and mobile, and during the welding process itself you can clearly see how it boils in the weld pool. In turn, slag is more viscous and has a darker shade.

Situations often arise when slag floats onto the weld pool. In such a situation, the welder can hardly see anything, and to avoid this, he has to tilt the electrode in such a way that the gas stream (which evaporates from the coating) blows the slag back onto the weld. After this, the weld pool opens again and the welding site becomes clearly visible.

To draw an analogy, we can give the example of a basin of soapy water. To see the water through the foam, you need to blow it off and only then will you have a view of the water and all the contents in it.

Thus, a novice welder always needs to keep one rule in mind - under no circumstances should slag run into the weld pool, and then the quality of welds will be much better.

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Welding slag as a prerequisite for the occurrence of slag inclusions

This material is a by-product because it must be removed after direct connection.

In the case when, for some reason, it begins to come into contact with the hardening part and becomes part of the resulting seam, this is a serious defect. This result is called slag inclusions.

They are visually visible on the surface of the product. You can remove slag inclusions when they are already completely in the hardened part only by drilling, and then weld it again.

Complete elimination of such manufacturing defects is impossible; with minor slag inclusions, the connection can be considered high quality.

There are certain conditions and signs under which the acceptable value of the presence of this type of defect on a product is established.

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