What are the types of welds? Types of welded joints and seams. Types of welded joints. Welds

1. Steel welding technology

Preparation of structures for welding

Preparation of structures for welding is divided into three stages:

1. processing of edges to be welded;

2. assembly of structural elements for welding;

3. additional cleaning, if required, of joints assembled for welding.

The processing of the edges of the structures to be welded is carried out in accordance with the drawings of the structures and in accordance with the requirements of GOST 5264–80 and other GOSTs for the main types and structural elements of the seams welded joints. The edges of the joints for welding are processed on edge-cutting or milling machines, as well as by oxygen and plasma cutting on special machines. The dimensions of the edge elements must comply with the requirements of GOST.

An important step in preparing the structure for welding is assembly for welding. For manual arc welding, structures are assembled using assembly fixtures or tacks. The composition of the assembly fixtures: clamps 1 perform a variety of operations for the assembly of corner metal, beams, strips, etc.; wedges 2 are used to assemble sheet structures; levers 3 - for assembling corner metal and other structures; tightening angles 4 and corner clamps 8 - for assembling sheet structures; jacks 5 - for tightening shells, beams and other structures; gaskets with wedges 7 - for assembling sheet structures in compliance with the gap size; tie bars 10 and squares. And - for the assembly of sheet structures for welding without tacks. Other types of devices are also used.

Before assembly, the machined structural elements must be measured, their edges inspected, as well as the metal adjacent to them, thoroughly cleaned of rust, oil, paint, dirt, ice, snow, moisture and scale. In workshop conditions, structural elements are assembled on racks - plates with grooves for installing devices (bolts, ties, pins, etc.) in them that fasten the assembled elements according to the dimensions provided in the drawings. The simplest racks of horizontal beams mounted on racks 200–400 mm high are also used. 13.3 shows an example of assembling sheet structures using the simplest fixtures and assembling structures from profile metal - angular, I-beam, etc. The edges of the assembled structures to be welded must comply with the drawings and standards in their shape and dimensions.

The joints of the structures during assembly are fixed with tacks - short welds to fix the relative position of the parts to be welded. Tacks are placed at the locations of welds, with the exception of their intersections. The length of tacks for steels with a yield strength of up to 390 MPa must be at least 50 mm and the distance between them is not more than 500 m; for steels with a yield strength of more than 390 MPa, tacks must be 100 mm long and the distance between them is no more than 400 mm With a small thickness of the assembled parts (4–6 mm), the tacks can be shorter (20–30 mm) and the distance between them is 200–300 mm. When assembling bulky heavy structures on tacks that are turned over during welding, the location of the tacks and their size are indicated in the production design welding work. Tacks that are removed during welding must be carried out by welders who will subsequently weld the tacked joints.

Tacks give rigidity to the structure and prevent the movement of parts from shrinkage during welding, which can lead to the formation of cracks, especially in elements of great thickness. Therefore, assembly on tacks is used for metal thicknesses of 6–10 mm, and for larger thicknesses, assembly fixtures are used that fix the shape and dimensions of structures, but allow it to slightly move from welding shrinkage. Such devices are wedge ties (see 13.1).

Immediately before welding, the assembled joints are subject to mandatory inspection and, if necessary, additional correction of assembly defects and cleaning.

When welding in a vertical position, the current strength decreases by 10-20%, when welding horizontal seams - by 15-20% and when welding ceiling seams - by 20-25%.

The type of current and polarity are determined depending on the electrodes adopted for welding, for example, for MP-3 electrodes, alternating or direct current can be used, for UONII-13/45 electrodes, only direct current of reverse polarity, etc.

The speed of welding (moving the arc) largely depends on the qualifications of the welder and his ability to conduct the welding process with interruptions only to change the electrode. In addition, the welding speed is affected by the deposition rate of the electrodes used and the strength of the welding current. The greater the deposition rate and the current strength, the faster the arc moves and, consequently, the welding speed increases. It should be borne in mind that an arbitrary increase in the current strength can cause the electrode to overheat.

Coefficient /C, determined by the table. 13.1 depends on the type of electrode coating. For example, for electrodes with an acidic or rutile coating, the maximum value of the coefficient at a diameter of 3–4 mm is K=45; for electrodes with a basic coating with a diameter of 3–4 mm D»=40; with cellulose coating of the same diameter /(=30.

Based on the formula for the heat input of welding qn (Ch. 3), an approximate dependence of the heat input on the cross-sectional area of ​​the weld bead, J/mm, was derived

where Qo is a coefficient depending on the type of electrodes or wire used in mechanized welding methods; Fm–> bead cross-sectional area, mm2.

For electrodes of grades UONII-13/45 and SM-11, the value Qo=65 J/mm3. Thus, knowing the heat input, one can easily determine the cross section of the weld bead and vice versa.

2. Types of welded joints. Welds

The terms and definitions of the basic concepts for metal welding are established by GOST 2601–84. Welded joints are divided into several types, determined by the relative position of the parts to be welded. The main ones are butt, corner, tee, lap and end joints. To form these joints and ensure the required quality, the edges of structural elements connected by welding must be prepared in advance. Edge preparation forms for manual arc welding of steel and iron-nickel and nickel-based alloys are established by GOST 5264–80.

butt joint called the connection of two elements adjacent to each other end surfaces.

GOST 5264–80 provides for 32 types of butt joints, conventionally designated Cl, C2, C28, etc., with different edge preparation depending on the thickness, location of the welded elements, welding technology and the availability of edge processing equipment. For thick metal manual welding it is impossible to ensure the penetration of the edges to the full thickness, therefore, they make the cutting of the edges, i.e. bevel them on two or one side. The edges are beveled on a planer or thermal cutting (plasma, oxy-fuel). The total bevel angle is (50 ± 4) °, such preparation is called one-sided with a bevel of two edges. In this case, the amount of blunting (of the non-beveled part) and the gap must be maintained, the values ​​​​of which are set by the standard depending on the thickness of the metal. The seam of the butt joint is called the butt weld, and the welding seam is the smaller part of the double-sided seam, which is preliminarily performed to prevent burns during subsequent welding of the main seam or applied last, after it has been completed.

When preparing the edges of steel with a thickness of 8–120 mm. Both edges of the elements to be welded are beveled on both sides at an angle of (25 ± 2) ° each, while the total bevel angle is (50 ± ± 4) °, blunting and clearance are set by the standard depending on the thickness of the steel. Such preparation is called double-sided with a bevel of two edges. With this preparation, the processing of edges becomes more complicated, but the volume of deposited metal sharply decreases in comparison with one-sided preparation. The standard provides for several options for double-sided edge preparation: preparation of only one upper edge, used with a vertical arrangement of parts, preparation with uneven bevel thickness, etc.

Corner connection called the connection of two elements located at an angle and welded at the junction of their edges. There are 10 such compounds: from U1 to U10.

For a metal thickness of 3 - 60 mm, the edge of the adjacent element is beveled at an angle of (45 ± 2) 1 °, the weld is the main and under-weld. With the same thickness and through penetration, a back-weld can be dispensed with. Often, a corner joint with a steel lining is used, which provides reliable penetration of the elements over the entire section. With a metal thickness of 8–100 mm, two-sided cutting of the adjacent element is used at an angle of (45 ± 2) °.

tee connection called a welded joint in which the end of one element adjoins at an angle and is welded with fillet welds to the side surface of another element. The standard provides for several types of such connections: from T1 to T9. A common connection is for metal with a thickness of 2–40 mm. For such a connection, no beveling of the edges is done, but a smooth trimming of the adjacent element and a flat surface of the other element are ensured.

With a metal thickness of 3–60 mm and the need for a continuous seam between the elements, which is provided for by the design project, in the adjacent element, the edges are cut at an angle of (45 ± 2) °. In practice, a tee joint with a lining is often used with a steel thickness of 8–30 mm, as well as a joint with a double-sided bevel of the edges of the adjacent element with a steel thickness of 8–40 mm. All of these joints with beveled edges of the adjoining element provide a continuous seam and the best working conditions for structures.

Lap joint called a welded joint in which the elements welded by fillet welds are parallel and partially overlap each other. The standard provides for two such compounds: HI and H2. Sometimes varieties of lap joints are used: with an overlay and with spot seams connecting parts of structural elements.

Of the listed welded joints, the most reliable and economical are butt joints, in which the acting loads and forces are perceived in the same way as in whole elements that have not been subjected to welding, i.e. they are practically equivalent to the base metal, of course, with the appropriate quality of welding work. However, it must be borne in mind that the processing of the edges of butt joints and their adjustment for welding are quite complex, in addition, their use is limited by the peculiarities of the shape of the structures. Corner and tee joints are also common in structures. Lap joints are the easiest to work with, as they do not require preliminary cutting of edges, and their preparation for welding is easier than butt and fillet joints. As a result, and also because of the structural form of some structures, they have become widespread for connecting elements of small thickness, but are allowed for elements up to 60 mm thick. The disadvantage of lap joints is their inefficiency, caused by excessive consumption of the base and deposited metal. In addition, due to the displacement of the line of action of forces during the transition from one part to another and the occurrence of stress concentration, the bearing capacity of such joints is reduced.

In addition to the listed welded joints and seams, in manual arc welding, joints are used at sharp and obtuse angles according to GOST 11534–75, but they are much less common. For welding in shielding gas, welding of aluminum, copper, other non-ferrous metals and their alloys, welded joints and seams are used, provided for by separate standards. For example, the form of preparation of edges and seams of pipeline structures is provided for by GOST 16037–80, which defines the main dimensions of seams for various types of welding.

3. Welding of fittings of various classes

Currently, in construction, a large amount of welding work falls on the welding of reinforced concrete reinforcement. Welding is used in the manufacture of welded reinforcing products, embedded parts and the installation of prefabricated reinforced concrete structures (Table 2).

table 2

Welding method and its characteristics	Purpose	The position of the rods when welding	Type of welding
submerged arc without filler metal, automatic and semi-automatic	Manufacturing of embedded parts: lap joint of rods with flat elements	Static and dynamic
	Tee connection of rods with flat elements	vertical
Submerged arc bath in inventory forms, semi-automatic	Butt joints of releases of single reinforcement bars in the places of conjugation of reinforcement of products and precast concrete structures	Horizontal Vertical	Static, dynamic and repetitive
Single-electrode bath in inventory forms with a smooth inner surface, manual		Horizontal
Single electrode bath with steel grooved lining, manual		Horizontal
Single-electrode bath-suture with a steel grooved overlay, manual open arc with bare alloy wire, multi-layer sutures with a steel grooved overlay, semi-automatic		Horizontal Vertical
Single electrode with multi-layer seams with or without a steel grooved lining, manual	vertical	Static and dynamic
Long seams	Horizontal
Multi-electrode bath in inventory forms with a recess to form a reinforcement of the seam	Horizontal	Static, dynamic and repetitive Static and dynamic

The main types of welding during the installation of reinforcing products and precast concrete structures are manual arc and semi-automatic welding with coated electrodes or welding wire, respectively. To reinforce reinforced concrete structures, hot-rolled steel according to GOST 5781-75 * is used, round, smooth and periodic profile, which, depending on the mechanical properties, is divided into 5 classes: A-I, A-II, A-III, A-IV, A- V (Table 3).

Table 3

Reinforcement class	Welding methods
	broaching seams	multilayer seams, multi-electrode bath, single-electrode bath
A-I	E42A-F - UONI 13/45, SM-11, UP2/45, E42-T - ANO-5, ANO-6, ANO-1, E46-T - ANO-3, ANO-4, MR-1.MR -3, OZS-3, OZS-4, OZS-6, ZRS-2	E42A-F - UONI 13/45, SI-11, UP-2/45
A-II	E42A-F - UONI 13/45, SM-11.UP 2/45, OZS-2, E42T - ANO-5, ANO-6, ANO-1, E46T-ANO-3, ANO-4, MR-1, MR-3, OZS-3, OZS-4, OZS-6, ZRS-2	E42A-F - UONI 13/45, SM-11, UP2/45, OZS-2, E50A-F - UONI 13/55, DSK-50, UP 2/55, K-5A, E55-F - UONI 13 / 55U
A-III	E42A-F - UONI 13/45, SM-11, UP2/45, OZS-2 E50A-F - UONI 13/55, DSK-50, UP 2/55, K-5A E55-F - UONI 13/55U	E50A-F - UONI 13/55, DSK-50, UP 2/55, K-5A, E55-F - UONI 13/55U

Notes:

1. Brands of welding wire are listed in order of preference for use.

2. Diameter of solid welding wire 2–2.5 mm, flux-cored wire 2–3 mm.

3. An asterisk marks the brand of welding wire used only for welding class A-II fittings of grade 10GT.

Reinforcing steel bars of class A-1 should be produced round smooth; rods classes A-I I, A-III, A-IV and A-V periodic profile. Each class of reinforcing steel must comply with GOST 5781–75*.

4. Technological features that must be taken into account when welding reinforcement and embedded parts

Welding of reinforced concrete reinforcing bars in installation conditions

In reinforced concrete structures, the connection of reinforcement bars is carried out, as a rule, by one of the electric arc welding methods or semi-automatic, namely:

- without steel brackets;

- on steel brackets;

- with round overlays or with an overlap;

– in inventory forms (copper or graphite);

- overlap or tee with flat elements.

Before assembling the rebar conjugation assemblies, you should make sure that the steel classes, dimensions and relative position of the elements to be joined are consistent with the design and compliance with GOST 10922–92 of the assembled joints for welding.

The outlets of the rods, embedded products and connecting parts must be cleaned to bare metal on both sides of the edges or cutting by 20 mm from dirt, rust and other contaminants. Water, including condensation water, snow or ice must be removed from the surface of reinforcement bars, embedded parts and connecting parts by heating them with a flame of gas burners or blowtorches to a temperature not exceeding 100 ° C.

With increased, in comparison with the required, gaps between the joined rods, it is allowed to use one insert, which must be made of reinforcement of the same class and diameter as the joined rods. When butt welding rods with overlays, the increase in the gap must be compensated by a corresponding increase in the length of the overlays.

The length of each release of reinforcement from the concrete body must be at least 150 mm with normal gaps between the ends of the rods and 100 mm when using an insert. You should strive to manufacture products so that the length of the outlets allows for installation and welding without inserts, i.e. adjust the gap between outlets at the installation site using gas cutting.

Prefabricated reinforced concrete structures, mounted only on outlets, must be assembled in conductors that ensure the design position. Welding of reinforced concrete structure rods held by a crane is not allowed.

Prefabricated reinforced concrete structures with embedded parts should be assembled on tacks. Tacks should be placed in the places of subsequent welding seams. The length of the tacks should be 15–20 mm, and the height (leg) should be 4–6 mm. The number of tacks must be at least two. Tacks should be made using the same materials and of the same quality as those used for the main seams. Before welding the main seams, the surface of the tack and adjacent areas must be cleaned of slag and metal spatter. Tacks must be performed by trained welders with certificates for the right to perform these works.

The presence of burns and melting from arc welding on the surface of the working rods is not allowed. Burns should be cleaned with an abrasive wheel to a depth of at least 0.5 mm. In this case, the reduction in the cross-sectional area of ​​the rod (depressions in the base metal) should not exceed 3%. The place of mechanical cleaning should have smooth transitions to the body of the rod, and the risks from abrasive processing should be directed along the rod. Cutting the ends of the rods with an electric arc when assembling structures or cutting the edges of the rods is not allowed. These operations should be performed with special electrodes for cutting reinforcement of the brand OZR-2.

Manual arc welding reinforcement with extended seams

Manual arc welding of reinforcement is used for joining vertical and horizontal rods. The welded joint can be overlapped and with overlays. Lap joint is performed, as a rule, with extended seams, but arc points can also be used. In addition, it is possible to connect reinforcing bars with a long and short overlap, as well as with a one-sided or two-sided seam (Fig. 1).

Rice. 1. Lap welded reinforcement with extended seams - with a long overlap in a one-sided seam; b - with a short overlap and double-sided seams

Welded joints of reinforcement rods with overlays, round or angle can be long and short. In this case, the lining can be displaced along the length. Arc welding of reinforcement is performed with flank seams: two one-sided, two two-sided, four two-sided, one-sided with a "whisker" (Fig. 2). When welding reinforcement with double-sided seams when applying a second seam with reverse side joints in it, longitudinal hot cracks can occur. To prevent the occurrence of this type of cracks, a careful choice of the type of electrodes and strict adherence to the technological regime of arc welding are necessary. Depending on the diameter of the joined rods, extended welds can be single-pass and multi-pass. The current for arc welding is selected depending on the type of electrodes. In this case, when arc welding reinforcement in a vertical position, the current should be 10–20% less than for horizontal rods.

Manual arc welding of reinforcement with multilayer seams without additional technological elements

With small amounts of work and the presence of welders highly qualified arc welding of reinforcement with multilayer seams without forming elements is possible. In this way, it is recommended to arc weld butt joints of reinforcement in a vertical position of the following classes of reinforcing steel: A-1 (Ø 20–40 mm), A-2 (Ø 20–80 mm), A-3 (Ø 20–40 mm). The structural forms of the ends of the reinforcing bars when they are joined are shown in fig. 3. Forms of cutting, bevel angles and their direction, blunting and their dimensions, gaps between the ends of the rods are standardized.

Rice. 3. Butt welded joints of reinforcement made without additional elements

a - vertical single-row coaxial rods with free access on both sides to the place of welding; b-the same, with the availability of a connection on one side; in-horizontal coaxial rods with end cutting

Arc welding of fittings is performed with a single electrode. The weld is applied first on one side of the groove, then on the other for its entire width. In the process of melting the groove, the deposited metal is periodically cleaned of slag. The electric arc welding mode is set in accordance with the passport data of the electrodes. Usually, for this type of electric welding, electrodes with a calcium fluoride coating of the E55 or E50A type are used.

Manual arc welding of reinforcement with forced seam formation

In some cases, the project requires welded joints of reinforcement cross joints with forced formation of the weld. For such reinforcing products, it is recommended to use rods with a diameter of 14–40 mm made of steel of classes A-1, A-2, A-3. Previously, the rods are assembled in conductors, which ensure their tight adjoining to each other, or the fixation of the rods is achieved with the help of welding tacks. At the same time, the conductors and tacks should not interfere with the installation of the forming elements.

Manual arc spot welding with tack welding of two rods

In conditions construction site in the construction of monolithic reinforced concrete structures of buildings and engineering structures, grids and frames manufactured locally are widely used as reinforcing products. In such products there are many different cross joints, the welding of which is carried out using manual arc spot welding.

The limited use of most steel grades of classes A-2 and A-3 is due to the fact that during spot welding in the contact of the cross joint of the rods, heat is quickly removed from the deposited metal, which leads to local hardening of the steel, and consequently, to an increase in its brittleness. Particularly sensitive to these thermal effects are medium-carbon and low-carbon reinforcing steels.

Bathroom Semi-Automatic Submerged Arc Welding

Welding of reinforcement using the technique of semi-automatic welding of horizontal reinforcing bars is carried out using additional technological elements: detachable molds or removable linings (steel, copper, graphite). The most favorable conditions for the crystallization of the weld metal are created in copper and graphite forming devices, which makes it possible to obtain a weld metal with high mechanical properties.

Forming devices are installed symmetrically to the gap between the ends of the joined reinforcement bars (Fig. 4). At a distance of 40–50 mm from the vertical axis of the joint, 2–3 turns of corded asbestos are applied to the rods to tightly adjoin the reinforcement to the mold. Then 20–30 g of flux are poured into the melting space. If copper molds are used, then before they are installed, the flux is poured onto the bottom of the mold with a layer of 5–7 mm. This measure allows you to strengthen the weld at the bottom of the joint.

Rice. 4. Installation of detachable molds and a copper lining on the rods to be welded during bath welding of fittings

1 - hole asbestos; 2 - flux; 3 - centering frame - an indicator of the boundaries of the melting space

excite welding arc, touching the end of the wire to the lower edge of the end of the reinforcing bar. The penetration of the lower part of the end of the rod occurs with oscillatory movements of the wire across the axis of the rods for 5–15 s. Then a similar melting operation is performed with the second rod. Schemes of movement of the end of the electrode wire during welding of fittings when the bath is filled with liquid metal are shown in fig. 5. When welding reinforcement with a diameter of 45 mm or more, you can use an additive in the form of metal grains, sawdust, chopped wire in an amount of 25–35% of the weld metal volume. To maintain the optimal depth of the slag bath (15–20 mm), flux is periodically added in portions.

Rice. Fig. 5. Schemes of moving the end of the electrode wire (shown by arrows) during semi-automatic bath welding of horizontal reinforcement bars (the shape is not conventionally indicated)

a - in the initial period of penetration of the lower edges of the ends of the rods (k - the point of contact of the electrode wire with the ends of the rods to excite the arc); b - in the process of filling the groove of the rods; c-at the final stage 1 - flux; 2 - electrode wire; 3 - slag bath; 4 - weld metal.

Arc welding of butt joints of vertical submerged rods, as a rule, is performed in removable copper or graphite forms. After excitation of the arc, the end of the electrode wire is moved with oscillatory movements according to the scheme shown in Fig. 6. After complete penetration of the end of the lower rod, in order to avoid undercutting of the upper rod during electric welding, regulate the voltage, removing it in steps by 15–25% (2–4 times). The mode of bathtub arc welding of butt joints of vertical bars is similar to welding of horizontal reinforcing bars.

Rice. Fig. 6. Schemes of moving the end of the electrode wire during semi-automatic bath welding of rods with a bevel of the end of the lower rod to the welder (the shape is not conventionally indicated)

a - in the initial period of penetration of the lower part of the end of the lower rod; b - in the process of penetration of the middle part of the end of the lower rod; in the same way, the cut end of the upper rod and the melting of the cutting of the rods; d - at the final stage

1 - reinforcing bar; 2 - electrode wire; 3 - flux; 4 - slag bath; 5 - weld metal.

Semi-automatic welding of reinforcement with an open arc bare wire (SODGP) on a steel bracket-plate

Semi-automatic welding of bare wire open arc reinforcement (SODHP) is used for welding joints of vertical and horizontal rods when installing reinforcement of monolithic reinforced concrete structures and in installation conditions. This reinforcement welding is multi-layered and is carried out using alloyed welding wire with a diameter of 1.6 and 2 mm, grades Sv-20GSTYuA and Sv-15GSTYUTSA. The assembly of butt joints of reinforcing bars is carried out on the remaining steel grooved plates. These pads are attached to the reinforcing bars with two tacks.

Rice. 7. Technique of surfacing of multi-layer welds in arc welding of reinforcement with an open arc with bare wire horizontal joints of rods (numbers indicate the order of surfacing of layers)

When welding horizontal reinforcement bars, an alloying wire with a diameter of 2 mm is used. The sequence and scheme of wire movement when filling the groove is shown in fig. 7.

In the process of melting cutting, overheating of reinforcing bars is possible. To avoid this, it is recommended to sequentially arc weld the reinforcement of two or three joints. In this case, the cutting of the first joint is melted to 60–70% of its volume, after which they move to the second joint, and then to the third. Having filled the third joint with deposited metal by 60–70% of the volume, they again go to the first joint, fill its entire melting space with deposited metal and weld the remaining joints in the same sequence. The electric welding of the joint is completed by surfacing two flank seams with a leg of 8–12 mm. The joints of the vertical reinforcement bars are welded in the same way as the horizontal ones. After welding the butt space, the flank seams are applied from top to bottom. The sequence of the overlay of welded seams is shown in fig. 8.

Rice. 8. Technique of surfacing of multilayer seams when welding reinforcement with an open arc with bare wire of vertical joints of rods (numbers indicate the order of surfacing of layers)

With the indicated methods of welding reinforcement with an open arc with bare wire (SODGP), the following classes of reinforcing steels are recommended for horizontal and vertical rods (the diameter of the rods in mm is indicated in brackets): A-1 (20–40), A-2 (20–80), A-3 (20–40), At-3C (20–22), At-4C (20–28). The ratio of the diameters of the reinforcing bars (smaller to larger) should be in the range of 0.5–1.0. Steels of the At-3C and At-4C classes should be welded on an overlay bracket extended to 4d.

Wire for mechanized arc welding of fittings

In mechanized submerged arc welding, in shielding gases and without additional protection, with self-shielding wire and for welding with forced formation of a seam, a solid-section electrode wire and a tubular (powder), which is a round steel shell filled with powder, are used. For welding carbon and low-alloy structural steels in shielding gases, the following brands of electrode wire are used: Sv-08GS, Sv-12GS, Sv-08G2S, Sv-08GSMT. For welding with multilayer seams without additional protection of low-carbon, medium-carbon and low-alloy steels, alloyed electrode wire of the Sv-15GSTYUTS and Sv-20GSTYuA grades is used.

Cored wire is used for both welding and surfacing. For the manufacture of flux-cored wire, a cold-rolled strip of low-carbon steel grade 08KP is used. Currently, the industry produces five types of flux-cored wire (Fig. 9) with a diameter of 1.2–3.6 mm.

Flux-cored wire of a simple cross-section with one longitudinal slot Fluor-cored wire of a simple cross-section with two longitudinal slots Flux-cored wire of a complex cross-section with one molded end of the steel strip Fluor-cored wire of a complex cross-section with two molded ends of the steel tape Flux-cored wire of a tubular cross-section without a longitudinal slot

Figure 9. Cross-section of flux-cored wire of different types.

For arc welding of low-carbon, low-alloy and medium-alloy steels, depending on the welding method, various types and grades of flux-cored wire are used: general-purpose self-shielded wires of grades PP-AN1, PP-AN7, PP-2DSK; general purpose wires for welding in carbon dioxide grades PP-AN8, PP-AN21; self-shielded wires for welding with forced seam formation, for example, grades PP-AN15, PP-AN19N, PP-2VDSK; wire for welding in carbon dioxide with forced formation of a seam grades PP-AN5 and PP-ANZS.

Contact spot welding of fittings

The main type of reinforcement for reinforced concrete structures are intersecting bars in the form of meshes and flat frames. For welding such reinforcing structures, as well as for overlap welding of round reinforcing bars to flat-rolled elements (strip, angle and other section steel), resistance spot welding is used.

Resistance spot welding provides a number of advantages compared to other types of welding: the possibility of increasing labor productivity due to lower labor intensity in the manufacture of reinforcing cages and meshes compared to electric arc welding; low power consumption due to the use of hard welding modes using high current density for a very short period of time; the possibility of mechanization and automation of the process; no metal consumption (in electrodes).

Figure 10. Resistance spot welding of reinforcement

Scheme of current flow during resistance spot welding: 1 - secondary coil of the transformer; 2 - copper busbars; 3 - trunk; 4 – electrode holder; 5 - electrode; 6 - reinforcing bar

The essence of the process of resistance spot welding of reinforcement is as follows. From the secondary turn of the welding transformer through copper tires, trunks, electrode holders and electrodes, the current is brought to the intersection of the reinforcing bars clamped between the electrodes (Fig. 10). The electrodes are water cooled. The resistance at the point of contact of the reinforcing bars is many times greater than the resistance of the remaining sections of the circuit, therefore, it is in this place that heat is intensively released, which heats the metal of the reinforcing bars to a plastic state. Under the action of the compression force of the electrodes, they are welded.

To obtain welded joints of the required strength, it is necessary to perform welding in certain modes. The welding mode is selected depending on the diameter of the welded reinforcement and the grade of steel from which it is made. The correctness of the choice of the welding mode is checked by a control test of the shear strength of welded reinforcement specimens.

If the strength of the welded joints of the reinforcement due to lack of penetration turns out to be less than required, then the current density or the time of its flow is increased. If the strength is insufficient due to burnout, these same indicators are reduced accordingly.

With insufficient current density, welding of reinforcement may not be possible even if the current flow time is very long; if the density is too high, the reinforcing bars may burn out.

The current density in resistance spot welding machines is regulated by switching the stages of the welding transformer, and the duration of the current flow is controlled by moving the pointer on the electronic time controllers.

Used for contact spot welding. special machines, which are divided into single-point, two-point and multi-point ones according to the number of simultaneously welded grid nodes and flat frames.

Machines for spot welding are stationary and suspended; with one-sided and two-sided current supply; with pneumatic and pneumohydraulic electrode compression mechanism. The duration of current flow is controlled automatically.

In connection with the development of construction from reinforced concrete in the direction of creating large reinforced concrete panels and other elements, it became necessary to pre-assemble the assembly of reinforcing cages and meshes. For this purpose, mobile (suspended) welding machines have been created, since it is impossible to perform spot welding of such fittings on conventional welding machines due to its bulkiness and large mass.

Suspended welding machines are divided by design into two groups: with a built-in welding transformer and with a remote one. All machines are made according to the same scheme and consist of the following main units: a body with a handle, a welding transformer, a power pneumatic drive, an electrode part (pliers) and a suspension device that allows the machine and the pliers to rotate around its axis by 360 °.

Hanging machines with an external transformer, in addition, are supplied with current-carrying cables.

Rebar weldability

The weldability of carbon steel (GOST 380–71*) is ensured by the manufacturing technology and compliance with all chemical composition requirements for steel B and C. The supply of group B steel with a guarantee of weldability is specified in the order and in the certificate. Steel containing more than 0.22% carbon in finished rolled products is used for welded structures under conditions that ensure the reliability of the welded joint. Steel grades VST1, VST2, VSTZ of all categories and all degrees of deoxidation, including with high content manganese, and at the request of the customer, steel grades Bst1, Bst2, BstZ of the second category of all degrees of deoxidation, including those with a high manganese content, is supplied with a guarantee of weldability. The weldability of low-alloyed reinforcing steel of all grades, except for 80C, is also ensured by the chemical composition and manufacturing technology. Welding of thermally hardened reinforcing steel is not allowed due to its softening in the weld zone.

Reinforcing steel, heat-strengthened, weldable, has the index "C" in the brand designation. For example, the symbol for welded reinforcing steel with a diameter of 14 mm of class At-4: 14At-4C GOST 10884 - 81, and welded steel with increased resistance to stress corrosion cracking is indicated by the index "SK", At-5SK. According to GOST 10922–75, the temporary resistance of welded joints of reinforcing steel of class At, made by contact-butt, contact-spot and seam-butt welding, should not be less than the lowest value of the rejection minimum,

Low-carbon steels (carbon content up to 0.22%) belong to the category of well welded by all types of welding in low modes without additional technological operations. Medium carbon steels (0.23–0.45% carbon content) require these additional steps during the welding process. So, to increase the resistance of the weld metal to the formation of crystallization cracks, the amount of carbon in it is reduced by using welding electrodes with a reduced carbon content, as well as reducing the proportion of the base metal in the weld. Reducing the likelihood of formation of hardening structures in the weld metal can be achieved with the help of preliminary and concomitant heating of products.

Table 4. Preheating of steels (before welding)

Table 5. Heat treatment of steels after welding

Low alloy steels containing less than 2.5% alloying components and up to 0.22% carbon, as a rule, have good weldability. The low-carbon steel grades 18G2S, 25G2S, 25GS, 20KhG2Ts used for the manufacture of reinforcement of reinforced concrete structures are classified as satisfactorily weldable. These steels contain no more than 0.25% carbon. If carbon is greater than 0.25%, quench structures and cracks may occur in the weld zone, as well as pore formation due to carbon burnout. In table. 4 shows the recommended modes of heating heat-treated steels before, and in table. 5 after welding. It should be borne in mind that the recommended limit values ​​for the criteria for the weldability of steels are not constant and may change depending on the development welding technology and technology.

Flash butt welding of rebar

Flash butt welding is effective way connecting rods, since it does not require metal consumable electrodes for its implementation; provides high labor productivity, and also allows you to mechanize and automate the workflow.

The disadvantage of flash butt welding is the possibility of its use only in stationary conditions due to the significant mass of welding equipment and high consumption of electrical energy.

The essence of the flash butt welding process is as follows. An electric current is connected to the rods to be welded and, bringing the latter into contact, form a closed electrical circuit (Fig. 11).

Figure 11. Electric circuit for butt welding

1 - welded rods; 2 - clamping jaws; 3 - secondary coil of the welding transformer; 4 - primary winding of the welding transformer; Rm is the resistance of the welded rods; Rk - contact resistance

In this circuit, the joint of the rods has the greatest resistance to the flow of current, therefore, in this place the heat will be most intensively released, which will heat the ends of the rods to a plastic, and partially to a liquid state.

There are two methods of resistance welding:

flash butt welding

flash butt welding with intermittent flashing with preheating.

Flash butt welding of hot-rolled reinforcement rods made of steel grades A-2…A-4 (in any combination) should be performed by intermittent flashing with heating. Grade A-1 steel fittings must be welded by continuous flash welding; if the power of the machine is insufficient, they can also be welded by the method of flashing with heating.

To form an initial electric current at the ends of the reinforcement, it is necessary to remove paint or rust from them. If the reinforcing bars were cut off by a gas flame, then their ends are first cleaned of the slag crust with a chisel or hammer. The quality of welded butt joints is influenced by the cleanliness of the contact surface of the rods with the clamping jaws of the machine.

The mode of flash butt welding should ensure the production of equally strong rods of welded joints with a minimum consumption of electricity and time.

The main parameters of the welding mode are: current strength or its density, current flow duration, upsetting pressure, as well as installation length, i.e. dimensions of the ends of the rods protruding from the electrodes.

Depending on the current density (current per mm2 of surface), two modes of butt resistance welding are distinguished:

hard mode, characterized by a high current density for a short period of time (for rods of small diameters),

soft mode with low current density for a long period (for rods of large diameters).

Current density during continuous flash welding –10…50 A/mm2. The duration of the current flow varies from 1 to 20 s, depending on the diameters of the reinforcing bars; as the diameter increases, the duration of the current flow increases.

For the quality of the welded butt joint, the specific upset pressure on the end of the rod (kg / mm2) is also important; it is selected depending on the steel grade. The specific upsetting pressure for class A-1 steel is 30 ... 50 MPa, for classes A-2 and A-3 - 60 ... 80 MPa. The compression force of the reinforcing bars during heating should be 10 ... 12% of the upset pressure. The duration of closing and opening of the arc during the preparation of the rod for welding is chosen within 0.3–0.8 s.

Figure 12. Appearance of butt joints of reinforcement made by resistance electric welding with correct (a) and incorrect (b) welding modes

The correctness of the choice of welding mode is approximately judged by appearance welded joints (Fig. 12). With the correct mode of butt resistance welding, the ends of the reinforcing bars warm up sufficiently and, with mutual compression, acquire the shape shown in the figure. Confirmation of the correctness of the selected mode can be obtained only after laboratory tests of welded joints for strength.

In the process of work, the welder must monitor the condition of the contact sponges and periodically clean them from the emerging deposits. It is necessary to have a set of jaws of various shapes and sizes in order to avoid possible interruptions in work when changing the diameters of the welded reinforcement.

Figure 13. Template for checking the mixing of the axes of the rods in the joints made by contact welding

Welded rods must be straight. The displacement of the axes of the rods in the joints is allowed no more than 0.1 of their diameter. The length of the rod is measured with an accuracy of 1 mm. The offset axes at the junction is determined by a special template (Fig. 13). In addition to external inspection, the junction of the reinforcement is tapped with a hammer weighing 1 kg; there should not be a rattling sound.

Manufacturing of embedded parts

Embedded parts are made from reinforcing bars and rolled products (sheet and profile). Soft, well-welded steels are used, usually StZ of groups B and C. One of the most common is an embedded part, consisting of a steel plate and a reinforcing bar welded to it with a tee joint (Fig. 14).

Rice. 14. T-joint of an anchor rod with a flat element of an embedded part with countersunk holes

The rod with the plate is welded with welding machines type ADF-2001UHL4. For the tee connection of the rod with the plate, manual arc welding is used through a previously countersunk hole. After welding, the seam is cleaned flush with the plane of the plate. The plate can also be connected to the rod in the horizontal plane (Fig. 15).

Rice. 15. Connections of rods with flat elements in a horizontal plane

H - directions of weld welding; M - places of tacks

Often, the tee connection of a reinforcing bar with a steel plate is carried out using relief welding. In this case, resistance relief welding can be performed end-to-end, i.e. the rod is welded perpendicular to the plane of the plate (Fig. 16) and overlapped. Reliefs on the plates are obtained using mechanical presses or press shears. The reliefs are round or cylindrical in shape, and single or double in number. The welding mode is selected depending on the thickness of the elements of the embedded part to be connected and the number of welding points.

Rice. 16. T-joint by contact relief welding

1 - reinforcing bar; 2 - electrode; 3 - a flat element of the embedded part; dв is the diameter of the recess; dр is the diameter of the base of the relief; dn is the diameter of the rod; hr is the height of the relief; lp - rod protrusion from the electrode

If it is not possible to use contact welding for lap joint, manual arc welding can be used. With the help of welding, embedded parts are connected with elements of reinforcing structures. Depending on the class and grade of steel, the position of the axes of the elements to be joined and the type of weld (horizontal, vertical, lower), a welding method is chosen: contact (spot, embossed), bath, arc (multi-electrode, multilayer, spot, submerged seam).

New design and technological solutions related to the manufacture of embedded parts have been developed. Stamped and stamped-welded embedded parts appeared, which made it possible to reduce steel consumption by 1.5–2 times and increase labor productivity several times. A stamped embedded part is a product in which the plate (table) and the anchor (rod) are one. They are cut out from the same strip with a special stamp. The bending of stamped strips (anchors) and plates is carried out by bending dies. Production of stamped embedded parts. can be fully automated. The technological process for the production of stamped parts includes: punching; hole punching; relief landing (puklevka); notching anchors; bending; metallization. Some operations can be combined, such as punching, hole punching and embossing. The combination of stamping and welding of embedded parts also gives a great effect. In this case, the anchor is connected by welding to a specially prepared stamping relief plate.

5. Conditional images and designations of welded joints in design documentation

invisible - dashed line ( heck. 1g).

A visible single weld point, regardless of the welding method, is conventionally depicted with a “+” sign ( heck. 1b), which is performed by solid lines ( heck. 2).

Invisible single points are not depicted.

From the image of a seam or a single point, a leader line is drawn, ending with a one-way arrow (see Fig. heck. one). The leader line is preferably drawn from the image of the visible seam.

Symbols of seams of welded joints

Auxiliary signs for marking welds

Notes:

1. For front side one-sided seam of the welded joint takes the side from which welding is performed.

2. For the front side of the double-sided seam of the welded joint with asymmetrically prepared edges, take the side from which the main seam is welded.

3. Any side can be taken as the front side of a double-sided weld with symmetrically prepared edges.

In the symbol of the seam, auxiliary signs are made in solid thin lines.

Auxiliary signs must be the same height as the numbers included in the designation of the seam.

The sign |_\ is done with solid thin lines. The height of the sign must be the same as the height of the numbers included in the designation of the seam.

The technical requirements of the drawing or table of seams indicate the welding method by which a non-standard seam should be made.

Note. The content and dimensions of the columns of the table of seams are not regulated by this standard.

In the technical requirements or the table of seams in the drawing, a link is given to the corresponding regulatory and technical document.

It is allowed not to specify welding materials.

The number of identical seams is allowed to be indicated on the leader line, which has a shelf with an applied designation (see. heck. 10 a).

Note. Seams are considered the same if:

the same type and size structural elements in cross section;

they have the same technical requirements.

List of used literature

1. Manual arc welding, The book was written by a team of authors: chapter 25 I.G. Getia, the rest of the chapters - V.I., Melnik with the participation of B.D. Malysheva

2. Alekseev E.K., Melnik V.I. Welding in industrial construction - M Stroyizdat, 1977 -377 s

3. Aleshin N.P. Shcherbinsky V.G. Quality control of welding works - M Higher school, 1986 - 167 p.

4.http://www.stroy-armatura.ru

5. Interstate standard GOST 2.312–72* “Unified system of design documentation. Conditional images and designations of welded joints "(approved by the Decree of the State Committee for Standards of the Council of Ministers of the USSR dated May 10, 1972 No. 935)

Welded joints are a continuous hermetic splicing of two metal elements. The type and design of the weld is determined by the relative position of the parts relative to each other. The properties of the base metal and the requirements for structural strength determine the welding method (arc, contact). Let us consider in detail which seam designs are used when welding various surfaces.

Types of welded joints: a - butt; b - butt with flanging; in - lap; g - angular; d - tee; e - slotted; g - end; h - point; S is the thickness of the products to be welded.

Types of welded structures and their designation in the drawings

Depending on the spatial arrangement of the planes relative to each other, the following types of welding are used:

1. Butt: the planes to be welded are joined end-to-end, while they are on the same surface.
2. Overlap: the surfaces are located in close planes, parallel to each other, when welding, they partially overlap each other, forming an overlap.
3. Angle: Planes connect at an angle.
4. T-shaped: the end of one element is attached to the side surface of the second welding part, thus forming a T-shaped connection, which is called a brand.
5. End: two elements are placed side by side (side by side) and their ends are welded with one seam located along a common end.

Designation of welds in the drawing: a, c - visible seam - main line; b - visible single weld point - sign "+"; d - invisible seam - dashed line

Welds in the drawings are indicated by a line (if the seam is solid) and crosses (if it is a point). The presence of welding in the structure is indicated by a one-sided arrow with a callout, on which the letter designation of the seam is indicated. Butt and end joints are conventionally designated with the letter "C", lap joints - "H", corner - "U" and tee - "T".

If the seam is located on the visible side of the part (this side is shown in the drawing), then it is called "visible", denoted by a solid continuous line and information about it is placed above the extension line. If it is located on the reverse side, it is called invisible, denoted by a dash-dotted line and put a letter display under the extension line of the one-way arrow.

Spot welding is indicated by a cross.

Technological features of the execution of welds

Metal welding often requires technological preparation of elements. It consists in cleaning the surface and performing the so-called cutting (beveling edges).

Bevels can be made on both edges or on one, one or two sides of the ends to be welded. The process of making bevels is called cutting.

In cases where the cutting operation is absent in the manufacturing technology of the item, it is necessary to increase the welding current to weld the joint.

Preliminary cutting is most relevant for the butt arrangement of elements in electric arc welding.

Butt welding

Butt welding is the most durable type of connection. The edges are connected over the entire area of ​​​​their contact, which ensures the highest possible strength.

Butt welding can be carried out both by the arc method (electrode deposited with an electric arc), and by contact fusion without an electrode. For arc welding of structural parts, their preparation is necessary. It consists in making bevels of right angles. At the place of the bevel, a weld zone is formed, consisting of the filler material of the electrode (mainly outside) and the base metal (mainly inside).

If ends of different thicknesses are welded, then the bevel is performed on a thicker end in order to equalize the thickness of the surfaces to be joined in the welding zone and to prevent burn-through of a thinner element.

Edge cutting is not always technologically possible. Then the operation is performed without preliminary bevels by contact method. According to the contact welding technology, the parts are heated until they are melted by electric current (passing through them), after which they are squeezed for tight contact of the surfaces. In this case, strong interatomic bonds are formed between two metallic elements. Excess liquid metal, squeezed out of the fusion zone during squeezing of the contacting surfaces, is removed before solidification. This method is called flash welding.

There is and is used another way to make a joint, called resistance welding. It is used only for parts of a small section and requires preliminary cleaning of the places of future contact. The technology for its implementation is as follows:

• details are brought together and squeezed;
• they pass the welding current and heat up the metal elements, while the small size of the contact section ensures uniform heating of the metal;
• splicing of parts is carried out without reflow, in the solid phase.

Resistance butt welding is characterized by increased strength due to the absence of flashing. It does not form structures of accelerated cooling in the weld zone, does not create a wide heat-affected zone (with reduced strength), and forms a smaller amount of residual stresses.

Overlap design

Overlapping is often used to connect elements in assembly and mounting. It does not require preliminary preparation, beveling. When overlapping, welding can be performed with one or two seams: along the edge of one or the second surface to be welded, or along both edges. The advantages of the lap welded structure are the low probability of through burns and simple technological implementation. The resulting seam has a double thickness (compared to a butt joint), separated by a through gap. When combining parts, inaccuracies and small shifts are allowed, overlapped by the existing overlap.

Welding parts overlap has three disadvantages:

• slight waste of material: excessive thickness of the material in the overlap zone;
• the presence of an empty space between two welds requires high-quality penetration from both seams (to prevent moisture from penetrating into the gap);
• the lap construction is inferior to the butt joint in strength.

When the parts overlap, they are welded at the corners between the end of one part and the side of the other, so the technology for performing the overlap is determined by the methods of welding the corners.

Fillet welds: varieties of welded corner construction

There are about a dozen varieties of welded corners, their design is determined by the relative position of the parts, the length of the seam, the shape of the edge and its preparation.

Corner splicing is intended for structural connection parts, it does not carry significant loads. The joint angle of the surfaces to be welded determines the location of the weld (inside the corner, outside or on both sides).

The angle technique is the most complex, requiring skill and experience. The surfaces to be welded can be arranged in vertical-horizontal directions, or in diagonal-diagonal directions. With a diagonal arrangement, the welding technique is facilitated and accessible to a novice welder. When welding vertical and horizontal, welding becomes more complicated and requires a qualified approach to its implementation.

Fillet welds can be made in one layer or in several layers. With a single-layer connection, one layer is formed from the electrode filler material and the molten base metal. A multi-layer construction is necessary to ensure that there is no lack of penetration when the fillet joint is complicated by the inaccessibility of the surfaces to be welded. The possibility of lack of penetration increases with the vertical arrangement of one of the elements, which contributes to the flow of molten metal down and the displacement of the weld pool from the welding zone, followed by the formation of a void (lack of penetration). Therefore, when connecting parts in the planes vertical - horizontal, multilayer is provided. Moreover, if the place of welding after cooling has a convex surface, increased thickness, then this adds additional strength to the joint.

Preparation of surfaces for fillet welding involves making a bevel (or bevels) on one or both elements.

T-welding

The T-shaped design is a kind of angular. In this case, in both corners to be welded, welding is performed along the inner corner.

For a tee connection, one of the parts is placed horizontally, the second - vertically. It lies horizontally welded element, to whose side surface the end of another element is welded. The connection angle is always 90º. For a high-quality tee seam, a bevel (one or two) is performed at the end of the element to be welded. If the end is thin (up to 12 mm), there is no need for a bevel. If the thickness of the end is 12 - 40 mm, the bevel is made on one side. If the thickness of the element exceeds 40 mm, then a two-sided butt cut and two welds are required.

The technological implementation of welded tee welding is similar to welding an angle from the inside. Thin-walled parts are connected in the horizontal and vertical arrangement of the connected planes. Thick-walled parts, for which electrodes of increased thickness are used, forming a significant weld pool, are placed diagonally. To do this, first spot welding is performed between the vertical and horizontal parts, then they are rotated, placing the surfaces to be welded in a diagonal direction. In this case, the weld pool is in the "boat", does not spread and forms a high-quality welded joint. In some cases, with a small thickness of the vertical element, its complete penetration occurs.

Weld shape and bevel

According to the external shape, the seams can be convex, even and concave. Smooth and concave connections are considered economical and more durable (there is no sharp transition between the base and the thermal zone, there is no stress concentrator that contributes to destruction). Often, for critical parts, the formed bulge is removed mechanically (grinded).

The shape of the weld depends on the selected geometric dimensions of the joint. Namely:

• the size of the gap between the welded parts;
• the presence and number of beveled edges;
• bevel angle of the edges of the surfaces to be welded.

Bevels are performed for parts whose thickness is more than 3 mm, in order to achieve uniform penetration over the entire section. The presence of bevels along the edge of the welded surfaces provides better welding, the presence of a smooth transition from the seam through the welding zone to the base metal. The larger the bevel angle, the wider its plane, the smoother the transition between the welded structure of the seam and the unstressed structure of the metal of the part will be.

The difference in welded structures allows you to choose the optimal welding parameters, location and method of execution. The welding method used should provide the required quality of the joint at the lowest possible cost.

The quality of welding determines the performance characteristics of the finished product.