Classification of welding joints. Welding seams. Results of violation of welding technology

Welds and connections

A permanent connection that has been made by welding is called a welded joint. It consists of several zones (Fig. 77):

Weld seam;

Fusion;

Rice. 77. Zones of a welded joint: 1 - welded seam; 2 - fusion; 3 - thermal influence; 4 - base metal

Thermal influence;

base metal.

By length, welded joints are:

Short (250–300 mm);

Medium (300–1000 mm);

Long (more than 1000 mm). Depending on the length of the weld, the method of its execution is also chosen. With short joints, the seam is carried out in one direction from the beginning to the end; the middle sections are characterized by suture in separate sections, and its length should be such that a whole number of electrodes (two, three) is enough to complete it; long joints are welded in the reverse step method, which was mentioned above.

By type, welded joints (Fig. 78) are divided into:

1. Butt. These are the most common compounds in various ways welding. They are preferred because they are characterized by the lowest intrinsic stresses and strains. As a rule, sheet metal structures are welded with butt joints.

Rice. 78. Views welded joints: a - butt; b - tee; in - angular; g - lap

Rice. 78 (end). d - slotted; e - end; g - with overlays; 1–3 – base metal; 2 - overlay: 3 - electric rivets; h - with electric rivets

The main advantages of this joint, which can be counted on under the condition of careful preparation and adjustment of the edges (due to the blunting of the latter, burn-through and metal leakage during welding are prevented, and their parallelism ensures a high-quality uniform seam) are the following:

Minimum consumption of base and deposited metal;

The smallest time interval required for welding;

The connection made can be as strong as the base metal.

Depending on the thickness of the metal, the edges during arc welding can be cut at different angles to the surface:

At a right angle, if steel sheets with a thickness of 4–8 mm are connected. At the same time, a gap of 1–2 mm is left between them, which facilitates the welding of the lower parts of the edges;

At a right angle, if metal up to 3 and up to 8 mm thick is connected with one- or two-sided welding, respectively;

With one-sided beveled edges (V-shaped), if the thickness of the metal is from 4 to 26 mm;

With a double-sided bevel (X-shaped), if the sheets have a thickness of 12–40 mm, and this method is more economical than the previous one, since the amount of deposited metal is reduced by almost 2 times. This means saving electrodes and electricity. In addition, for a double-sided bevel, deformations and stresses during welding are less characteristic;

The bevel angle can be reduced from 60° to 45° when welding sheets with a thickness of more than 20 mm, which will reduce the amount of deposited metal and save electrodes. The presence of a gap of 4 mm between the edges will provide the necessary penetration of the metal.

When welding metal of different thicknesses, the edge of the thicker material is beveled more strongly. With a significant thickness of parts or sheets connected by arc welding, cup-shaped edge preparation is used, and with a thickness of 20–50 mm one-sided preparation is carried out, and with a thickness of more than 50 mm - two-sided preparation.

The above is clearly shown in Table. 44.

2. Lap, most often used in arc welding of structures, the metal thickness of which is 10–12 mm. This option differs from the previous connection by the absence of the need to prepare the edges in a special way - just cut them off. Although the assembly and preparation of metal for a lap joint is not so burdensome, it should be taken into account that the consumption of the base and weld metal increases compared to butt joints. For reliability and to avoid corrosion due to moisture ingress between the sheets, such joints are welded on both sides. There are types of welding where this option is used exclusively, in particular with spot contact and roller welding.

3. T-shaped, widely used in arc welding. For them, the edges are beveled on one or both sides, or they do without a bevel at all. Special requirements apply only to the preparation of a vertical sheet, which must have an equally cut edge. With one- and two-sided bevels, the edges of the vertical sheet provide a gap of 2-3 mm between the vertical and horizontal planes in order to weld the vertical sheet to its full thickness. A one-sided bevel is performed when the design of the product is such that it is impossible to weld it on both sides.

Table 44

The choice of butt joint depending on the thickness of the metal

5. Welt, which is resorted to in cases where an overlapping seam of normal length does not provide the necessary strength. Such connections are of two types - open and closed. The cut is made using oxygen cutting.

6. End (side), in which the sheets are laid one on top of the other and welded at the ends.

7. With overlays. To perform such a connection, the sheets are docked and the joint is covered with an overlay, which, of course, entails additional metal consumption. Therefore, this method is used when it is not possible to perform a butt or overlap seam.

8. With electric rivets. This connection is strong, but not tight enough. For him, the top sheet is drilled and the resulting hole is welded in such a way as to capture the bottom sheet.

If the metal is not too thick, then drilling is not required. For example, in automatic submerged arc welding, the top sheet is simply fused by the welding arc.

The structural element of a welded joint, which, during its execution, is formed due to the crystallization of molten metal along the line of movement of the heating source, is called a weld. The elements of its geometric shape (Fig. 79) are:

Width (b);

Height (h);

Leg value (K) for corner, lap and tee joints.

The classification of welds is based on various features, which are presented below.

Rice. 79. Elements of the geometric shape of the weld (width, height, leg size)

1. By connection type:

Butt;

Corner (Fig. 80).

Rice. 80. Fillet weld

Fillet welds are practiced with some types of welded joints, in particular with lap, butt, fillet and overlays.

The sides of such a seam are called legs (k), zone ABCD in fig. 80 shows the degree of weld convexity and is not taken into account when calculating the strength of the welded joint. When performing it, it is necessary that the legs are equal, and the angle between the sides OD and BD is 45 °.

2. By type of welding:

arc welding seams;

Seams of automatic and semi-automatic submerged arc welding;

Seams of arc welding in the environment of protective gases;

Seams of electroslag welding;

seams contact welding;

Seams of gas welding.

3. According to the spatial position (Fig. 81), in which welding is performed:

Rice. 81. Welds depending on their spatial position: a - lower; b - horizontal; c - vertical; g - ceiling

Horizontal;

vertical;

Ceiling.

The bottom seam is the easiest to make, the ceiling seam is the hardest.

In the latter case, welders undergo special training, and the ceiling seam is easier to make with gas welding than with arc welding.

4. By length:

Continuous;

Intermittent (Fig. 82).

Rice. 82. Intermittent weld

Intermittent seams are widely practiced, especially in cases where there is no need (strength calculation does not imply a continuous seam) to tightly connect products.

The length (l) of the sections to be joined is 50–150 mm, the gap between them is approximately 1.5–2.5 times greater than the welding zone, and together they form a weld pitch (t).

5. According to the degree of convexity, i.e., the shape of the outer surface (Fig. 83):

Normal;

convex;

Concave.

The type of electrode used determines the convexity of the weld (a‘). The greatest convexity is typical for thin-coated electrodes, and thick-coated electrodes give normal seams, since they are characterized by greater fluidity of the molten metal.

Rice. 83. Welds that differ in the shape of the outer surface: a - normal; b - convex c - concave

Empirically, it was found that the strength of the seam does not increase with an increase in its convexity, especially if the joint "works" under variable loads and vibration. This situation is explained as follows: when making a seam with a large convexity, it is impossible to achieve a smooth transition from the bead of the seam to the base metal, therefore, at this point, the edge of the seam is cut, as it were, and stresses are mainly concentrated here.

Under conditions of variable and vibrational loads in this place, the welded joint may be subject to destruction. In addition, convex welds require an increased consumption of electrode metal, energy and time, i.e., it is an uneconomical option.

6. By configuration (Fig. 84):

Rectilinear;

Ring;

Rice. 84. Welds of various configurations: a - straight; b - ring

vertical;

Horizontal.

7. In relation to the acting forces (Fig. 85):

flank;

End;

Combined;

Oblique. The vector of action of external forces can be parallel to the axis of the weld (typical for flank), perpendicular to the axis of the weld (for end joints), pass at an angle to the axis (for oblique ones), or combine the direction of flank and end forces (for combined ones).

8. According to the method of holding the molten weld metal:

Without linings and pillows;

On removable and remaining steel linings;

Rice. 85. Welds in relation to the acting forces: a - flank; b - end; c - combined; g - oblique

On copper, flux-copper, ceramic and asbestos linings, flux and gas cushions.

When applying the first layer of the seam, the main thing is to be able to keep the liquid metal in the weld pool.

To prevent it from leaking, use:

Steel, copper, asbestos and ceramic linings that are brought under the root seam. Thanks to them, it is possible to increase the welding current, which ensures through penetration of the edges and guarantees one hundred percent penetration of parts. In addition, the linings keep the molten metal in the weld pool, preventing the formation of burns;

Inserts between welded edges that perform the same functions as gaskets;

Hemming and welding of the root of the seam from the opposite side, while not striving for through penetration;

Flux, flux-copper (when submerged arc welding) and gas (when manual arc, automatic and argon-arc welding) pads that are brought or fed under the first layer of the seam. Their purpose is to prevent metal from flowing out of the weld pool;

Joints in the lock when making butt welds, which prevent burns in the root layer of the seam;

Special electrodes, the coating of which contains special components that increase the surface tension of the metal and prevent it from flowing out of the weld pool when making vertical seams from top to bottom;

A pulsed arc, due to which a short-term melting of the metal occurs, which contributes to faster cooling and crystallization of the weld metal.

9. On the side on which the seam is applied (Fig. 86):

Unilateral;

Bilateral.

10. According to the materials to be welded:

On carbon and alloy steels;

Rice. 86. Welds, differing in their location: a - one-sided; b - bilateral

On non-ferrous metals;

On bimetal;

On foam and polyethylene.

11. According to the location of the parts to be connected:

At an acute or obtuse angle;

Right angle;

In one plane.

12. By the volume of deposited metal (Fig. 87):

Normal;

Weakened;

Reinforced.

13. By location on the product:

Longitudinal;

Transverse.

14. According to the shape of the welded structures:

On flat surfaces;

on spherical surfaces.

15. By the number of deposited beads (Fig. 88):

Single layer;

Multilayer;

Multipass.

Before carrying out welding work, the edges of the products, structures or parts to be joined must be suitably prepared, since the strength of the seam depends on their geometric shape.

Rice. 87. Welds, differing in the volume of deposited metal: a - weakened; b - normal; c - reinforced

Rice. 88. Welds, differing in the number of deposited beads: a - single-layer; b - multilayer; c - multilayer multipass

The elements of form preparation are (Fig. 89):

Bevel angle (?), which must be performed if the metal thickness is more than 3 mm. If you skip this operation, then such Negative consequences, as lack of penetration over the cross section of the welded joint, overheating and burnout of the metal. Edge preparation makes it possible to weld several layers of a small section, due to which the structure of the welded joint is improved, and internal stresses and deformations are reduced;

Rice. 89. Elements of preparing chrome

Gap between joined edges (a). The correctness of the set gap and the selected welding mode determine how complete the penetration will be over the joint cross section during the formation of the first (root) layer of the weld;

Edge blunting (S) necessary to give the root pass process a certain amount of stability. Ignoring this requirement leads to metal burnout during welding;

The length of the bevel of the sheet if there is a difference in thickness (L). This element allows for a smooth and gradual transition from a thicker part to a thin one, which reduces or eliminates the risk of stress concentration in welded structures;

Offset of edges relative to each other (?). Since this reduces the strength characteristics of the joint, and also contributes to lack of penetration of the metal and the formation of stress centers, GOST 5264–80 establishes acceptable standards, in particular, the displacement should be no more than 10% of the metal thickness (maximum 3 mm).

Thus, when preparing for welding, the following requirements must be met:

Clean edges from dirt and corrosion;

Remove chamfers of the appropriate size (according to GOST);

Set the gap in accordance with GOST, developed for a particular type of connection.

Some types of edges have already been mentioned earlier (although they were considered in a different aspect) when describing butt joints, but nevertheless it is necessary to focus on this again (Fig. 90).

The choice of one or another type of edges is determined by a number of factors:

Welding method;

The thickness of the metal;

The method of connecting products, parts, etc.

A separate standard has been developed for each welding method, which specifies the shape of the edge preparation, the size of the seam and the allowable deviations. For example, manual arc welding is carried out in accordance with GOST 5264-80, contact - in accordance with GOST 15878-79, electroslag - in accordance with GOST 15164-68, etc.

Rice. 90. Types of edges prepared for welding: a - with a bevel of both edges; b - with a bevel of one edge; c - with two symmetrical bevels of one edge; g - with two symmetrical bevels of two edges; e - with a curvilinear bevel of two edges; e - with two symmetrical curvilinear bevels of two edges; g - with a bevel of one edge; h - with two symmetrical bevels of one edge

In addition, there is a standard for the graphic designation of the weld, in particular GOST 2.312–72. For this, an inclined line with a one-sided arrow is used (Fig. 91), which indicates the section of the seam.

The weld characteristics, recommended welding method and other information are presented above or below a horizontal flange connected to a slanted arrow line. If the seam is visible, i.e., located on the front side, then the seam characteristic is given above the shelf, if invisible - below it.

Rice. 91. Graphic designation of welds

The symbols of the weld also include additional signs (Fig. 92).

Letter designations are accepted for various types of welding:

Arc welding - E, but since this type is the most common, the letter may not be indicated in the drawings;

Gas welding - G;

Electroslag welding - Sh;

Welding in an inert gas environment - I;

Explosion welding - Vz;

Plasma welding - Pl;

Contact welding - Kt;

Welding in carbon dioxide - U;

Friction welding - Tr;

Cold welding - X.

If necessary (if several welding methods are implemented), the letter designation of the welding method used is placed before the designation of one or another variety:

Rice. 92. Additional designations of the weld: a - intermittent weld with a chain sequence of sections; b - intermittent seam with a checkerboard sequence of sections; in - a seam along a closed contour; d - seam along an open contour; d - mounting seam; e - seam with removed reinforcement; g - a seam with a smooth transition to the base metal

Manual - R;

Semi-automatic - P;

automatic - a.

Arc submerged arc - F;

Welding in active gas with a consumable electrode - UP;

Welding in an inert gas with a consumable electrode - IP;

Welding in an inert gas with a non-consumable electrode - IN.

For welded joints, there are also special letter designations:

Butt - C;

T-shaped - T;

Lap - H;

Angular - U. According to the numbers affixed after the letters, the number of the welded joint is determined according to GOST for welding.

Summarizing the above, we can state that the symbols for welds add up to a certain structure (Fig. 93).

For the permanent connection between metal parts by welding, various types of welded joints are used.

An integral connection of parts made of metal blanks and obtained by melting their edges with an electric arc or gas. At the same time, additional metal is deposited, it can be a molten electrode or a rod specially fed into the heating zone. As a result of these manipulations, a welding seam is formed at the junction of the workpieces.

Used to connect metal parts different kinds welding. The list of welding technologies is quite large, but the main types include:

• electric arc;
• flame;
• plasma;
• laser and many others.

Main types of welding joints

All issues related to welding are, one way or another, standardized. One of the fundamental documents is GOST 2601-92. This document normalizes the terms and basic concepts in the field of welding. The same document defines the main types of connections by welding. These include:

Butt

The ends are tightly adjacent to each other. This is a widely used type of joint that can be obtained using various welding technologies. Butt welds have a number of advantages, in comparison with others - high speed performance of work, respectively, high productivity of the work performed. Minimum material consumption. High strength of the welded joint, of course, it is achieved in full compliance with all technological norms and rules. But the use of a butt joint requires preliminary preparation of the edges, that is, to prepare a chamfer, in addition, it is necessary to ensure the accuracy of the installation of the workpieces.

This type is used to connect sheet, pipe and rolled products.

Lap

With this assembly method, the workpieces are arranged so that their planes are parallel to each other and at the same time partially overlap each other. Connections of this type are most often used when performing spot and resistance welding. In other cases, when performing such a seam, the consumption of the metal itself and electrodes unreasonably increases. When making an overlap connection, there is no need for preliminary cutting of the edges. But in any case, the sheets must be cut using special equipment, such as mechanical scissors. To avoid corrosion that can occur between sheets of metal, it is advisable to weld such a joint along its entire length.

It is advisable to use such fastening of workpieces if their thickness does not exceed 10 mm.

Angular

The blanks are placed relative to each other at a certain angle, and the seam lies at the point of their contact.

Corner joints can be single or double sided. They are used when merging parts from sheet metal, fittings and pipes. The angle can be different, it all depends on the purpose of the structure. A slight complication is that it is necessary to cut the edges of the adjacent workpiece.

Tavrovoe

The end face of one workpiece is adjacent to the plane of the other, most often at a right angle.

A part installed vertically must necessarily have a cut edge. Thus, the adjunction of one part to another is ensured. By the way, when preparing it for welding, depending on the thickness, preliminary cutting of the edge may be required. If the metal is quite thick, for example, over 20 mm, then the chamfer must be removed from both sides of the workpiece. This approach will ensure the penetration of the connection.

End

This form of surface fusion, in which the edges of the workpieces to be welded are adjacent to each other and the resulting part resembles a sandwich in section.

Connections made by welding have become widespread in industry and construction. Welding is widely used to replace forged products and parts that are made using casting.

Technological features of welding

Any work has its secrets, which are mostly owned by professionals and welding is no exception. For example, when making a tee joint consisting of sheets of different thicknesses, the electrode holder should be set so that the angle between it and the thick sheet is 60 degrees.

Another feature of the T-type implementation is the installation of sheets in the "boat", that is, the angle between the workpiece and the horizontal plane should be 45 degrees. With this form of installation of workpieces, the electrode can be installed strictly vertically. As a result, the welding speed increases and the likelihood of such defects as undercut decreases, by the way, this is the most common defect in the T-weld. Depending on the thickness of the metal, it may be necessary to make several passes with the electrode. Welding in the "boat" is used when using automatic welding.

Classification by connection location

In addition to the above qualification, welds can be classified according to other characteristics. One of these is the degree of convexity.

Welds can be divided into:

• normal;
• convex;
• concave.

In many ways, this parameter depends on the parameters of the welding materials and on the modes of the welding machine. If a long arc is used when welding, the seam will come out even and wide. When using a short arc, the width of the seam will decrease, and it will become convex. We must not forget that the quality and geometry of the seam is of great importance to the speed of the electrode and, of course, the shape and dimensions of the groove.

Welds can be classified according to their position in space. That is, they can be located - below, vertically and on the ceiling.

The optimal location of the weld is considered to be the bottom. This type of seam is recommended to be used when developing working documentation for products. The welder, when processing the bottom seam, is on top of it and perfectly sees both the movement of the electrode and the process of seam formation.

Vertical or overhead welds should only be performed by qualified welders. The ceiling location of the seam is the most time-consuming and unsafe work.

Qualification of welded joints by length

Permanent joints obtained by welding can be divided into continuous and intermittent. The first ones are performed where it is necessary to ensure the tightness of the connection or where, according to strength requirements, it is impossible to apply the second option (intermittent)

Normative base

Welding joints can be classified according to different parameters - this is the geometry of the seam, and the type of connection, and much more. When designing a product in which welds will be used, the designer must first of all be guided by the results of strength calculations. And only after that choose the method of connecting the blanks.

In their work, designers and manufacturers should be guided by the following documents:

• GOST 2601-84;
• GOST5264;
• GOST15878;
• GOST 15164.

Based on data from these normative documents, it is necessary to determine the weld geometry and the type of welding. The criteria for edge separation, if any, must then be established. At the last stage, the permissible and maximum deviations of the dimensions of the seam are determined.

Weld defects

Welding work is considered especially responsible. And this is understandable. Welding is also used in the manufacture of pressure vessels, pipelines and boilers. And the quality of the connection made depends on the performance and, most importantly, the safety of the equipment. Almost all industries and construction sites. Where is welding used? various methods quality control. In accordance with the requirements of GOST 3242-79, several control methods are provided for the control of welding joints. Among them are such as:

• Visual, it is used in the control of irresponsible compounds.
• Ultrasonic - it is used to control different types of compounds.

For particularly critical ones, for example, on bridge structures or high-pressure pipelines, the welder must leave an imprint of a personal brand.

Welding is still one of the most popular methods for producing one-piece structures from metals and polymers. Such popularity also determines the variety of welded joints, which are somewhat similar to each other, but in some ways fundamentally different. In this article, we will consider all the main types of thermal welding joints.

So what are welded joints? The types of welding joints are as follows:

Butt

The most widely used variety, which can be one- and two-sided, with a removable and non-removable lining and without it at all. Butt welding can be used to connect parts with flanging, with a locking edge, as well as with a variety of bevels: two-sided and one-sided, symmetrical and asymmetric, broken and curved.

Angular

As it becomes clear from the name itself, this connection welds corner structures. Besides, with the help of corner joints, welds structural elements in hard-to-reach places. This type connections are used in the following cases:

• Bevels (one-sided or two-sided) are available at the edges of the two parts to be joined;
• The edges of the parts to be joined have no bevels;
• One edge has a fold.

In other cases, the corner connection cannot be used, because due to the complexity of the edges, the quality of the connection deteriorates sharply.

Tavrovoe

It is used for welding T-shaped structures, as well as for parts that are connected at a slight angle to each other. This connection is compatible with the following types of edges:

• There is no bevel;
• The edge can have symmetrical or asymmetrical one- and two-sided bevels;
• On the edge there is a curvilinear one- or two-sided bevel located in one plane.

A small number of edges to which the tee connection is applicable is explained by the complex geometry of the parts to be joined.

overlap

This type of welding connects the ends of parts or structural elements. Welding overlaps are carried out only with edges without bevels.

end

A rather rare type of connection, since it involves welding one part to the end of another. Therefore, often the main types of welding joints do not include the end joint in a separate item, but combine it with an overlap joint.

Seam classifications

Also, the types of welded joints differ in the seam obtained as a result of welding. The current standards imply several classifications:

By spatial arrangement

According to their location, welds can be:

• Lower, if their angle relative to the horizontal does not exceed 60 degrees;
• Vertical, if their angle relative to the horizontal is in the range of 60-120 degrees;
• Ceiling, if their angle relative to the horizontal is in the range of 120-180 degrees.

By their continuity

Welds can be continuous (no breaks) or discontinuous (there are breaks). The latter are most characteristic of angular and tee joints.

By the nature of the breaks, intermittent seams are divided into:

• Chain - breaks are uniform, as if cells in a chain;
• Chess - gaps move small seams relative to each other, like white cells on a chessboard;
• Dotted - similar to checkerboard seams, only the seams do not look like dashes, but as single dots.

Note that continuous seams are more reliable and more resistant to corrosion damage, but often they cannot be used for technological reasons.

By type of welded joint

Welded joints differ from each other also in the resulting seam:

• Butt is obtained with the same connection of parts;
• Corner is formed not only when welding parts with corners, but also when tee and butt welding;
• Welding is obtained by tee welding and by overlapping parts whose thickness does not exceed 1 cm;
• Electric riveting is obtained by welding tee joints and overlapping. The technology for performing these seams is as follows. Metal parts whose thickness does not exceed 3 mm are welded without pre-treatment, because the electric arc pierces through them. If the thickness of the parts to be welded exceeds 3 mm, then one part is drilled and the second part is already welded through it;
• End are obtained by welding parts with their ends.

By the nature of the profile section

This classification indicates the shape of the section of the weld in the section:

• Convex protrude in a semicircle above the surface of the connected parts;
• Concave form a slight depression relative to the surface of the connected parts;
• Normals form one line with the surface;
• Special. Formed at the junction of parts with an angle or tee. In cross section, they look like an isosceles triangle.

The internal section determines the operational characteristics of welded joints. So, for example, a convex section gives good resistance to static loads, such seams are considered reinforced. While concave, on the contrary, are considered weakened, but they better withstand dynamic and multidirectional loads. The performance characteristics of normal welds are similar to those of concave welds. Special seams perfectly cope with variable loads. They also reduce the stress that occurs in welded parts during their daily operation.

According to the technology of welding work

Here, welds are classified along the course of the electrode during welding:

• Longitudinal is formed when the electrode moves along the junction of the parts to be joined;
• Transverse is obtained when the electrode moves across the junction of the parts to be joined;
• Oblique is formed when the electrode moves at a certain angle relative to the extreme points of its trajectory;
• Combined is formed by the alternate use of the three above seams.

By number of layers

The intended welding work is carried out in one or several layers (passages). With one pass, a bead of molten metal is formed. Rollers can be performed on one or on different levels. In the first case, one layer will consist of several rollers. The furthest bead from the facing level is called the root of the seam.

Multi-layer and multi-pass welded joints are used when welding thick-walled elements or to avoid thermal deformations in the steel alloy structure.

To avoid thermal deformations and burns, a backing seam is often used. Facing is used to improve appearance welded joint of structural elements welded to each other.

Results of violation of welding technology

In case of violation of the welding technology at the junction, the following may occur:

• Burns (undercuts) - zones of critical heating of the metal, in which, under the influence of high temperatures, various chemical reactions began (crystal corrosion, etc.);
• Lack of penetration - zones in which the temperature was insufficient for the mutual penetration of the edges into each other and the formation of a single monolithic structure;
• Non-fusion - the edges to be joined did not heat up to the melting temperature and did not fuse with each other;
• Slag clogging - concentration points of slag substances that have penetrated in a liquid state from low-quality electrodes into the weld pool and, upon solidification, formed foreign crystalline inclusions;
• Pores appear due to spattering metal due to sudden peak temperatures in the weld pool;
• Cracks appear due to poor-quality connection of two grades of steel with different melting points;
• Microcavities arise due to uneven heating and cooling of the metal.

Quality control technologies

All types of welded joints must be checked. Depending on the requirements for the quality of work, the following quality control technologies are performed:

• Visual inspection allows you to determine only visible quality violations (slag inclusions, cracks, burns, etc.);
• Length and width measurements indicate the conformity of the result obtained terms of reference and GOST;
• Leak test by pressure test. It is used in the manufacture of various containers;
• Special instrumentation set characteristics internal structure the resulting welded joint;
• Laboratory studies allow you to determine the behavior of a welded structure under the influence of various loads and chemicals.

The basis of the welding process is the connection metal elements and parts made of other materials by melting their edges. The place where the elements join is a seam, the art of which is the main thing for any welder. In the welding process, various types of element connections and welds are used, the choice of which is regulated by the conditions and requirements for welding.

If you intend to master welding, then first of all you need to figure out what seams and joints are.

Weld joints refer to the way in which the parts to be welded are connected. There are several basic types, the use of which allows you to dock any elements:

• Butt;
• Angular;
• Tavrovoe;
• end;
• With rivets.

Welds are methods of welding metal elements, representing the way in which the parts will be connected to each other. Types of welds are distinguished by various characteristics, exciting the method of joining parts, the requirements for the created element, the thickness of the original metal, etc.

Classification of welds

Welding work involves big variety welds and joints. Types of welds can be distinguished according to various criteria. Let's introduce some of them:

• According to outward appearances: concave, convex, flat. Concave ones give the connection some weakness, convex ones, on the contrary, are considered reinforced and are used when it is necessary to create a strong weld that is resistant to heavy loads;
• By execution method: single-sided or double-sided. Welding can be done both from two sides (which is much more common, as it gives the part greater strength), and from one side;
• By number of passes: single-pass and multi-pass. The second are large and durable;
• According to the number of welded layers: single and multilayer. The latter are used in welding work with thick metals;
• By length: point, chain, checkerboard, intermittent, solid. This characteristic reflects how the weld was made along the entire seam. Spot are typical for contact welding. The remaining names speak of the length of smaller seams that form a longer main one;
• In the direction of impact: transverse (the impact is perpendicular), longitudinal (the impact is parallel to the seam), combined (combines the transverse and longitudinal), angular (the force is applied at an angle);
• By functionality: strong, dense, airtight. This characteristic is associated with the further operation of the part, which dictates the need to follow special requirements;
• By width: threaded (the seam is equal to the diameter of the electrode) and expanded (created during oscillatory movements).

This classification represents an almost complete encyclopedia of types of welding methods.

It is necessary for a professional to know and be able to apply them, for an amateur it is quite enough to master the main types of welding seams, which are quite enough for welding almost all types of joints.

Varieties of welded joints

Let's move on to the types of welded joints, that is, how the parts to be welded are connected. There are several main varieties:

1. Butt method is the most popular and commonly used type. It is characterized by minimal internal stress and is less likely to deform during welding. Differs in the high durability sufficient for operation of a product at dynamic and static loadings.
   The butt method represents the conjugation of the ends of two elements. If the metal sheets are quite thin, then they do not require preliminary preparation before welding. Thicker metal must be prepared by beveling its edges for deeper cooking. This rule works with a workpiece thickness of more than 8 mm. If the metal is more than 12 mm in thickness, then it is necessary to bevel the edges on both sides and make a double-sided connection. Welding is carried out in a horizontal plane.
2. Lap joint has a scope of application in the construction industry, where it is used in arc welding with a thickness of metal elements up to 12 mm. The metal does not require preliminary preparation, but it is important to ensure that water does not get between the elements. It is recommended to weld on both sides;
3. Corner connection allows you to weld elements at any angle to each other. For greater reliability of the seam, the edges of the parts to be joined are usually beveled, which allows for deeper welding. Also, the strength of the product is given by welding on both sides;
4. T-way used when creating building elements(trusses, beams, etc.) representing the letter "T". Depending on which method was used, it can be single-sided or double-sided, elements of various thicknesses are often welded. Welding around the entire perimeter usually occurs in one step. Modern market offers devices for carrying out T-mounting in automatic mode;
5. rivet connection implies obtaining a sufficiently strong constituent element. Holes are made in the upper element with a drill or otherwise, and through them the upper element is welded to the lower one. There are various types of rivet seams, among them the most common are those in which rivets are used - special elements for fastening two parts;
6. end method involves welding two elements that are aligned at the ends. In this case, one element is at an angle to the other and is welded to one of its side planes.

The listed types of welded joints and seams have detailed description and execution schemes, which are given in GOSTs for welding.

Summing up

Knowledge of the types of joints and seams in welding work is basic and provides the basis for the application of welding skills in practice. This theoretical experience allows you to correctly choose the required type of joining of elements and the method of their welding, which will guarantee the resulting part with the strength characteristics that are planned during its creation.

Welding provides permanent connections of metals due to the establishment of strong interatomic bonds between the elements (during their deformation). What are welders experts know. The seams obtained with their help are able to connect the same and dissimilar metals, their alloys, parts with additions (graphite, ceramics, glass), plastic.

Basis of classification

Experts have developed a classification of welds according to the following principle:

• the way they are carried out;
• external characteristics;
• number of layers;
• location in space;
• length;
• appointment;
• width
• operating conditions of welded products.

According to the method of execution, welding seams are one-sided or two-sided. External parameters make it possible to classify them into reinforced, flat and weakened, which experts call convex, normal and concave. The first types are able to withstand static loads for a long time, but they are not economical enough. Concave and normal joints withstand dynamic or alternating loads well, since the transition from metal to seams is smooth, and the risk of stress concentration that can destroy them is below indicator 1.

Welding, taking into account the number of layers, can be single-layer or multi-layer, and in terms of the number of passes, it can be single-pass and multi-pass. Multilayer junctions are used to work with thick metals and their alloys and, if necessary, to reduce the heat-affected zone. A passage is a movement (1 time) of a heat source in the process of surfacing or welding parts in one direction.

The bead is the part of the suture metal that can be deposited in a single pass. Welding layer - metal junction with several beads located at the same level of the cross section. Focusing on their position in space, the seams are subdivided into lower, horizontal, vertical, in a “boat”, semi-horizontal, semi-vertical, ceiling, semi-ceiling. The characteristic of discontinuity or continuity speaks of length. The first types are used for butt welds.

Principles of classification

Solid connections can be short, medium and long. Allocate tight, strong and durable seams (according to their purpose). The width helps to subdivide them into the following types:

• broadened, which are made with transverse, oscillatory movements of the electrode;
• thread, the width of which may slightly exceed or coincide with the diameter of the electrode.

The conditions under which welded products will be used in the future suggest that junctions can be working and non-working. The former carry loads well, while the others are used to connect parts of a welded product. Welded joints are classified into transverse (in which the direction is perpendicular to the weld axis), longitudinal (in the direction parallel to the axis), oblique (with a direction placed at an angle to the axis) and combined (the use of transverse and longitudinal welds).

The method of holding hot metal allows subdividing into created:

• on the remaining and on removable steel linings;
• without additional linings, pillows;
• on linings of flux-copper, copper, asbestos or ceramics;
• on gas and flux pads.

The material that is used in the process of welding elements is classified into compounds of non-ferrous metals, steel (alloyed or carbon), vinyl plastic and bimetals.

Depending on the location relative to each other of the parts of the products that are to be welded, there are junctions at a right angle, at an obtuse or acute angle and located in the same plane.

Permanent connections that occur when using welding are:

• corner;
• butt;
• tee;
• lap or end.

Corner views are used during construction work. They involve a reliable connection of elements that are located relative to each other at a certain angle and welded at the junction of the edges.

Butt types have found application in the welding of tanks or pipelines. With their help, parts are welded with ends that are located on the same surface or in the same plane. The thickness of the surfaces does not have to match.

Lap types are used in the manufacture of metal containers, in construction work and when welding tanks. This type assumes that one element is superimposed on another located in a similar plane, partially overlapping each other.