What the article is about:
If metal is burned during welding
You can weld thin metal only with a good hand and a little experience in welding. It is much easier to weld workpieces with a thickness of 4-6 mm, but here, too, problems arise in the form of lack of penetration, etc.
From this article you will learn how to weld thin-walled metal without burning it. The article is of a recommendatory nature. For a detailed study of this material, it is recommended to read about the settings of the welding inverter and the selection of current.
Causes of burn-through
Welding work is accompanied by various activities, where ultimately both objective and subjective reasons may arise that cause burn-through of the weld. Objective reasons include the natural properties of metals, which can affect the quality of work to varying degrees. All characteristics associated with the technological process of welding - equipment, accompanying materials, etc. are of a subjective nature. to some extent, it is possible to justify the occurrence of the cause of weld burn-through on the part of the welder only by objective signs, and even then, laboratories give an opinion about the properties of the metal, which the welder must know about before starting production work.
Taking into account the normative and regulatory provisions, the only correct definition of the occurrence of a defect is given, where weld burn-through is a complex of mutually exclusive factors that worsen the technical properties of the metal products being welded.
- Incorrect preparation mode for surfaces to be welded.
- Inconsistency or malfunction of process equipment.
- Incorrect selection of the class of fluxes or shielding gases, which became the basis for the causes of burn-through.
- Low qualification of a welder.
- Violation of the welding process, in particular deviation from technical documentation, incorrect selection of welding equipment, as well as related materials.
The last category has several justifications, allowing you to see the weld burn-through only in the photo, where a specialist and supervisory structures make the appropriate technical conclusion and recommendations. Violation of the technical process is caused by non-compliance with the current parameter of the welding equipment, incorrect choice of arc length, etc.
What problems arise when welding thin-walled products?
Most often, when welding thin-walled products, problems of this kind arise:
- A hole forms in the product, which subsequently becomes problematic to weld;
- A thin-walled product is deformed under the influence of high temperature. If it is a piece of thin steel, then it bends and warps.
- The electrode sticks to the metal.
Burning through metal during welding is a series of mistakes made by the welder. Excess welding current or incorrectly selected electrode diameter will lead to a hole appearing in a thin-walled product.
The electrode sticks to the metal in several cases, when it is damp, there is little welding current, or the product being welded has a large amount of rust. You should thoroughly clean the metal before welding, and also make sure that the electrodes are completely dry, without damaged coating.
Or the opposite happens, when a novice welder is afraid to burn through thin metal and holds the electrode too far from the surface. In this case, lack of penetration of the weld seam appears, and the molten metal from the electrode simply spreads over the surface of the metal.
Types of defects
According to the general principles and provisions of technology associated with welding equipment, there are two types of defects:
- External. These are visible defects that can be seen with the naked eye. Such defects include lack of penetration, as well as burn-through of the weld.
- Internal. These types include cracks, chips, tension, pores, which can be identified in the laboratory.
Type of seam burn
Each defect detection system has its own rules and regimes, which have regulations developed by state standards.
How to solve the problem of burning metal when welding
For welding thin-walled products, it is best to use an inverter for welding. There is a smooth current adjustment and a reverse polarity mode, which will prevent burning through thin metal. Read what direct and reverse polarity of an inverter gives you by clicking on the highlighted link.
Secondly, do not use thick electrodes for welding, the diameter of which is more than 3 mm. Thick electrodes require a decent welding current, and if it is made less so as not to burn through the metal, then the electrode will stick to the surface all the time and it will not be possible to weld the part normally.
Thirdly, properly prepare the workpieces to be welded. If there is dirt, rust, or traces of paint on their surface or at the joints, be sure to get rid of them. Any contamination prevents the welding arc from igniting, which ultimately leads to numerous welding defects.
Also, give the product time to cool, otherwise it will be severely deformed under the influence of high temperature. Don't try to cook everything at once in one pass. In order not to burn through the metal, you will have to adapt and try to move the electrode as quickly as possible, but at the same time, as close to the metal as possible. A large separation of the electrode from the surface will lead to an increase in the arc, which will instantly burn through thin metal.
What causes metal to burn through most often?
A thin metal for a welder can be considered a metal whose thickness barely reaches two millimeters. Most often it is one or one and a half millimeters. So, welding such metal with electrodes is quite problematic, due to the constant formation of burns.
Most often, these burns are associated with the following:
- The welding current is set incorrectly;
- Electrodes that are too thick are used;
- The welder welds with a long arc instead of using a short arc;
- Welding is carried out with a continuous seam, which, in addition to burns, leads to other problems, such as metal deformation as a result of high temperatures;
- Dirty and uncleaned metal;
- Inconvenient welding mask;
- Lack of any experience of the welder.
So, in order to decide on each of the above problems, you need to carefully consider each one.
Weld defects (diagram)
All types of seam defects are divided into three groups:
- external, the main ones of which include: cracks, undercuts, sagging, craters;
- internal, among which the most common are: porosity, lack of penetration and foreign inclusions;
- through - cracks, burns.
Main welding defects, their characteristics, causes and methods of correction
Cracks
. These are the most dangerous welding defects that can lead to almost instantaneous destruction of welded structures with the most tragic consequences. Cracks vary in size (micro- and macrocracks) and time of occurrence (during the welding process or after it).
Most often, the reason for the formation of cracks is non-compliance with welding technology (for example, incorrect placement of seams, leading to stress concentration), incorrect choice of welding materials, sudden cooling of the structure. Their occurrence is also facilitated by the increased content of carbon and various impurities in the weld - silicon, nickel, sulfur, hydrogen, phosphorus.
Correcting a crack consists of drilling out its beginning and end in order to prevent further spread, removing the seam (cutting out or cutting out) and welding.
Undercuts
.
Undercuts are indentations (grooves) at the transition point between the base metal and the weld. Undercuts are quite common. Their negative effect is expressed in a reduction in the cross-section of the seam and the appearance of a source of stress concentration. Both weaken the seam. Undercuts occur due to increased welding current. Most often, this defect occurs in horizontal seams. It is eliminated by surfacing a thin weld along the undercut line. Weld undercuts
Beads
. Sagging occurs when molten metal flows onto the base metal, but does not form a homogeneous connection with it. A weld defect occurs for various reasons - due to insufficient heating of the base metal due to low current, due to the presence of scale on the edges being welded, which prevents fusion, and an excessive amount of filler material. Sagging is eliminated by cutting and checking for lack of penetration in this place.
Weld bead
Burns
. Burn-throughs are welding defects that manifest themselves in through penetration and leakage of liquid metal through a through hole in the seam. In this case, a sag usually forms on the other side. Burn-throughs occur due to excessively high welding current, insufficient speed of movement of the electrode, a large gap between the edges of the metal, too small a thickness of the backing or its loose fit to the base metal. The defect is corrected by stripping and subsequent welding.
Burn through of welded joint
Lack of penetration
. Lack of penetration is a local lack of fusion of the deposited metal with the base metal, or between the weld layers. This defect also includes non-filling of the seam section. Lack of penetration significantly reduces the strength of the seam and can cause structural failure.
Failure to fill and lack of penetration of the seam
The defect occurs due to low welding current, improper edge preparation, excessively high welding speed, the presence of foreign substances (scale, rust, slag) and contamination on the edges of the parts being welded. When correcting, you need to cut out the area of lack of penetration and weld it.
Craters
. These are defects in the form of a depression resulting from a break in the welding arc. Craters reduce the strength of the weld due to a decrease in its cross-section. They may contain shrinkage looseness that contributes to the formation of cracks. Craters must be cut down to the base metal and welded.
Weld crater
Fistulas
. Fistulas are suture defects in the form of a cavity. Like craters, they reduce the strength of the weld and promote the development of cracks. The usual method of correction is cutting out the defective area and welding it.
Fistula welds
Foreign inclusions
. Inclusions can consist of various substances - slag, tungsten, metal oxides, etc. Slag inclusions are formed when the slag does not have time to float to the surface of the metal and remains inside it. This happens when the welding mode is incorrect (excessive speed, for example), poor stripping of the metal being welded or the previous layer during multilayer welding.
Foreign inclusions in the welded joint
Tungsten inclusions occur during welding with a tungsten electrode, while oxide inclusions occur due to poor solubility of oxides and excessively rapid cooling.
All types of inclusions reduce the cross-section of the seam and form a focus of stress concentration, thereby reducing the strength of the joint. The defect is eliminated by cutting and brewing.
Porosity
. Porosity is cavities filled with gases. They arise due to intense gas formation inside the metal, in which gas bubbles remain in the metal after it has solidified. Pore sizes can be microscopic or reach several millimeters. Often a whole cluster of pores appears in combination with fistulas and conchas.
Porosity in the weld
The occurrence of pores is facilitated by the presence of contaminants and foreign substances on the surface of the metal being welded, high carbon content in the filler material and base metal, too high welding speed, due to which the gases do not have time to escape, and increased humidity of the electrodes. Like other defects, porosity will reduce the strength of the weld. The area with it must be cut down to the base metal and welded.
Overheating and burning of metal
. Burnout and overheating occur due to excessively high welding current or low welding speed. When overheated, the size of the metal grains in the weld and heat-affected zone increases, as a result of which the strength characteristics of the welded joint, mainly impact strength, decrease. Overheating is eliminated by heat treatment of the product.
Overburning is a more dangerous defect than overheating. Burnt metal becomes brittle due to the presence of oxidized grains that have little mutual adhesion. The reasons for burnout are the same as overheating, and in addition there is also insufficient protection of the molten metal from nitrogen and oxygen in the air. The burnt metal must be completely cut out and the area welded again.
Burnt weld metal
MetalloPraktik.ru
There are three types of “burn-through” defect on tinplate:
— burn-through from current rollers;
— burn-through from electrodes;
- microburn.
Characteristics of defects (photo below):
Burn-through from current rollers is a coating defect in the form of matte melted arc-shaped spots located in a path along the length of the strip. Burns from contamination of the current rollers are formed in the form of dots and small stripes with pressure of a matte color until the coating melts, and black on the melted sheet.
To correctly identify the location of the defect, remember that:
– the burn from the first current roller of tinning is blue oxide spots on the black sheet at the bottom of the strip, which after tinning become white matte;
– burn-through from the remaining current tinning rollers represents a failure of a point with matte-colored pressure on the melted surface at the bottom of the strip;
– burn-through from the current rollers of the reflow furnace or from passivation represents black double-sided dots on the melted surface of the strip; When observed under a microscope, the defect appears as a “crater” on the front side and a bulge (selling) on the back side of the sheet.
Burns from electrodes on the surface of tinplate are formed in the form of black spots, sagging, and smears of various shapes on the melted surface of the strip due to contact with the electrodes. Burns in the form of gray-white anode strips 30-110 mm wide are formed on the surface of the tin due to the curvature of the tin anode and its approach to the strip.
The “microburn” defect on the surface of tinplate is formed in the form of small black dots or a drop-shaped shape. The points are located on both sides of the strip strictly opposite each other.
Cause of the defect:
1 The presence of a film of water between the strip and the surface of the roller, leading to the formation of an arc;
2 The surface of the current roller or strip is dirty;
3 Loose contact of the strip with the current tinning rollers due to the small gap between the strip and the electrodes;
4 Unsatisfactory metal flatness;
5 Too much degreasing or etching current;
6 Curvature of the tin anode and its approach to the strip;
7 Arc formation from stuck tin or foreign body.
8 Touching the degreasing, pickling, passivation electrodes with a strip.
Elimination of defects:
1 Before applying the coating, soak the strip in tinning electrolyte.
2 Promptly clean the surface of the current rollers with a scraper.
3 Adjusting the pressure of the tinning pressure rollers, increasing the strip tension.
4 Restoring the gap between the electrodes and the strip.
5 Improve the quality of rental cleaning.
6 Ensuring a consistent surface of the pressure rollers.
7 Timely cleaning of the reflow furnace from adhering tin dust particles.
8 Task for metal tinning units without form defects.
The metal becomes substandard.
Photo defects:
We recommend that you read the articles:
- Coating defect during tinning of tin plate “tin drops”
- Coating defect “Half-break” on tinplate
- Defect (photo) of the “neoplastic” coating on the surface of tinplate
- Defect “Coating abrasion” on sheet metal
- Coating defect on tinplate “tin smears”
