Welding seams. Welding technique
Under the execution technique welds understand the choice of welding modes and techniques for manipulating the electrode or torch.
The excitation of an electric arc is carried out in two ways - by direct separation of the electrode and its separation along a curve. In the first method (back-to-back ignition), the electrode is brought perpendicular to the place where welding began and, after a relatively light touch on the workpiece, is taken up to
2.. .5 mm. The second method resembles the ignition of a match (striking). When the arc breaks, its re-excitation is carried out in front of the crater and on the base metal with a return to the deposited metal to bring the contaminants accumulated in the crater to the surface.
Arc length. The quality of the weld depends on the correct arc length. The ability to maintain an arc of constant length characterizes the qualifications of the welder.
With an increase in the length of the arc, the voltage of the latter increases, the proportion of heat spent on melting the electrode and the base metal and the width of the weld increase, and the depth of penetration and its convexity decrease. A long arc is characterized by a sharp sound, accompanied by pops, and a significant spatter of molten metal. In addition, intense oxidation and nitriding of the weld metal occur, waste losses increase, and the weld has an uneven surface. Normal consider the length of the arc, equal to (0.5 ... 1.1) da. .
the tal surface can be from left to right (c) and from right to left (b), and on the vertical - away from you (c) and towards you (d).
Regardless of the direction of welding, when applying lower and horizontal seams, the optimal angle of inclination of the electrode is 15 ... 30 ° from the vertical in the direction of the seam. With this position of the electrode, the metal of the welded workpieces is melted to the maximum depth, the conditions for the formation of the seam improve, the cooling rate of the weld pool decreases, the seam is dense and even. In practice, depending on the welding conditions, the angle of inclination of the electrode can differ significantly from the specified one.
When welding, the end of the electrode is told to move simultaneously in three directions.
The first movement is translational along the electrode axis towards the weld pool at a speed equal to the electrode melting rate,
The second movement is moving along the direction wB3 with a certain speed. At a high speed of movement of the electrode, the base metal does not have time to melt, resulting in lack of penetration. If the electrode speed is less than the optimum, overheating or through penetration of the metal (burn-through) occurs.
The weld formed as a result of the first two movements of the end of the electrode is called "thread". Its width at the optimal speed of the second movement is (0.8…1.5)d3. The root of the main weld is filled with a thread seam, thin workpieces are welded, surfacing works and welding of undercuts are performed.
The third movement is transverse oscillations along a certain trajectory (Fig. 7.3, a ... j), most often performed with constant frequency and amplitude, combined with the movement of the electrode along the seam and allowing to obtain a weld of the required width. The weld width should not exceed two or three electrode diameters, since a larger width may cause defects in the weld.
In cases where a large heating of the metal is required along the edges of the seam, for example, when welding high-alloy steels, during oscillatory motion, the middle of the path passes quickly, delaying the electrode along the edges.
End of welding. At the end of the weld, it is impossible to abruptly break the arc and leave a crater on the metal surface, which is a stress concentrator and a zone with high content harmful impurities. To avoid the formation of a crater, it is necessary to stop the oscillatory movements of the electrode and slowly lengthen the arc until it breaks. When welding blanks from low-carbon steel, the crater is sometimes brought to the side, onto the base metal. It is not recommended to weld the crater by interrupting and starting the arc several times, due to the formation of oxide and slag contamination of the metal.
Ways of suturing of various lengths. The method of applying a seam depends on the length of the latter and the thickness of the workpieces to be welded. Depending on the length, the seams are conditionally divided into short (up to 300 mm), medium (300 ... 1000 mm) and Long (over 1000 mm). Short seams are performed from beginning to end in one direction, medium and long - in sections 100 ..350 mm long. The lengths of the sections depend on the thickness of the workpieces to be welded and are selected so that each section can be welded with an integer number of electrodes (two, three, etc.). Seams of medium length are performed in sections from the middle to the ends or in a reverse stepwise manner. Long overlay seams
either in the reverse stepwise way, or in sections at once * throw. Schemes of suturing of various lengths are shown in fig. 7.4, a ... e.
Welding workpieces of large thickness is performed in several passes. According to the method of filling in the section, they are distinguished. e - multi-pass single-layer (Fig. 7.5, c), multi-layer (Fig. 7.5 o) and multi-pass multi-layer (Fig. 7.5, c) seams.
Multilayer seams are used to weld workpieces with a thickness of sz_; * greater than 8 mm. Welding with such seams (multilayer welding) and - * the following advantages over a single-layer one: the seam has a more - fine-grained structure due to the smaller volume of the weld pool; increased ductility and toughness of the weld metal;
residual welding stresses have lower values, since the heat released during the application of subsequent layers contributes to stress relaxation.
When applying a multilayer seam, first boil its root with electrodes of 02 ... 3 mm, then continue welding with electrodes of a larger diameter. Before applying the next layer, each previous one must be cleaned of slag. on one and the other side, which reduces the warpage of the product. For more uniform heating of the metal, the imposition of multi-joints is carried out in various ways (Fig. 7.6): “hor.
coy" (c), "cascade" (b) or "blocks" (c). Welding with these his * sobs is carried out in steps, selecting the length of the step so that the temperature of the metal at the root of the weld is at least 200 G | in the process of making a seam over the entire thickness (in this case, shrinkage cracks are not formed). As a rule, the length of the step * is in the range of 200 ... 400 mm.
The final (decorative) layer is performed with an electrode,
deviated from the vertical by 5 ... 20 ° to the side, opposite to the right direction of welding. The number of layers of a multilayer weld during welding is selected according to Table. 7.2.
7 2. The number of layers of a multilayer weld when making butt and fillet joints
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Connections
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Making butt joints in the lower position
welding with workpiece thickness up to 4 mm. Workpieces with a thickness of 4 ... -10 mm can also be welded without beveled edges, but with a double-sided seam. If the thickness of the blanks exceeds 10 mm, cutting of their edges is necessary.
When applying butt joints, it is necessary to pay special attention. combat attention to the uniformity of melting of both edges of the pile. welded workpieces and the correct choice of welding force to. ka. If the current strength is insufficient, the butt weld does not penetrate to the full depth, resulting in lack of penetration. Excessive current strength causes through penetration of the metal * la - burn through.
To obtain a defect-free seam, its root is first welded with a thread seam with reverse side silt apply lining. The advantages of welding with backing pads include improved weld quality and increased productivity, since the welder performs a one-sided weld in the maximum allowable modes.
Execution of corner, tee and lap joints in the lower position. When making such connections, welding is carried out with a vertical electrode "in the boat", inclined
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electrode "into the corner" or a vertical electrode with melted Welding with a vertical electrode "in the boat" Welding with an inclined electrode "in the corner" is performed for responsible products Welding technique, provide in a plane perpendicular to the seam (Fig. 7 8, a), and moving On-"burning. vertical seams. When applied vertically |
10.. . 15% less than when suturing in the lower position.
Vertical seams are applied in two ways (Fig. 7.9); from bottom to top (a) and from top to bottom (b). The first method welds workpieces with a thickness of more than 3 mm, and the second - up to 3 mm.
When welding from the bottom up, the arc is excited at the bottom of the weld. After the formation of a pool of molten metal, the end of the electrode is taken slightly up and to the side, allowing the deposited metal to harden. The hardened metal forms a "shelf", on which subsequent layers of metal are deposited. The recommended movement of the electrode is forward or backward with an inclination to the horizon at an angle of 45 ... 50 °, the trajectory of the transverse movement of its end is rectangular or curvilinear.
a - from bottom to top, b - from top to bottom; 1 - position of the electrode at the beginning of welding, 2 - position of the electrode "yes" during welding, 3 - seam, 4 - base metal
When welding from top to bottom, the arc is excited at the top of the weld with an electrode located perpendicular to the welding plane. After the formation of a bath of molten metal, the electrode is tilted down at an angle of 15 ... 20 ° to the horizon line. Welding is performed with a short arc at such a speed that the liquid metal does not flow under the arc. With this method of welding, transverse movements are not reported to the end of the electrode.
The imposition of horizontal seams. Horizontal seams are more difficult to lay than vertical ones. When performing joining< горизонтальных соединений скашивают кромку только у верхнег листа. Дугу возбуждают на горизонтальной кромке нижнего листа, перемещая затем на скошенную кромку верхнего листа.
Rice. 7 11 Positions of the electrode and the trajectory of movement of its end face during overhead welding
Changes in the angle of inclination of the electrode in the vertical plane in the trajectory of the transverse vibrations of the end of the electrode must correspond to those shown in Fig. 7.10.
Ceiling seams. Ceiling joints are
the most difficult to perform. Welding is carried out with a short arc with an electrode of 03 ... 4 mm at a current strength 15 ... 20% less than when welding in the lower position. The electrode should have a slight inclination to the direction of welding (Fig. 7-11), and the amplitude of transverse vibrations of its end should be minimal in order to reduce the volume of the weld pool. In addition to the transverse and translational, the welder informs the electrode and axial reciprocal forward movement, removing or bringing the electrode closer to the weld pool. Workpieces with a thickness of more than 8 mm are connected by multi-pass welding.
Arc ignition. There are two ways to strike an arc with coated electrodes - direct electrode tear-off and curved tear-off. The first method is called close ignition, the second one resembles the movement when lighting a match and is called striking.
Arc length. Immediately after ignition of the arc, the melting of the metal begins. The length of the arc must be constant. The welding performance and the quality of the welded seam largely depend on the correctly selected arc length.
The arc length equal to 0.5 ... 1.1 of the rod electrode diameter is considered normal. An increase in the length of the arc reduces the stability of its combustion, the depth of penetration of the base metal, increases the cost of waste and spattering of the metal, causes the formation of a weld with an uneven surface and increases the influence of the surrounding atmosphere on the molten metal.
The electrode feed rate into the arc must be equal to the electrode melting rate.
Electrode position. The inclination of the electrode during welding depends on the position of welding in space, the thickness and composition of the metal being welded, the diameter of the electrode, the type and thickness of the coating. The direction of welding can be from left to right, right to left, away from you and towards you (Fig. 26, a). Regardless of the direction of welding, the position of the electrode must be certain: it must be inclined to the axis of the weld so that the metal of the product is melted to the very depth. To obtain a tight and even seam when welding in the lower position on a horizontal plane, the angle of inclination of the electrode should be 15 ° from the vertical in the direction of the seam. Oscillatory movements of the electrode. To obtain a roller of the desired width, transverse oscillatory movements of the electrode are carried out. If the electrode is moved only along the weld axis without its transverse vibration, then the bead width is determined only by the strength of the welding current and welding speed and is 0.8 ... 1.5 of the electrode diameter. Such narrow (thread) rollers are used when welding thin sheets, when applying the first root layer of a multilayer weld, and in some other cases.
Most often, seams with a width of 1.5 to 4 electrode diameters are used, obtained using transverse oscillatory movements.
The most common types of transverse oscillatory movements of the electrode during manual welding(Fig. 27): straight lines along a broken line; crescent, turned ends to the deposited seam; crescent, turned ends to the direction of welding; triangles; loop-like with a delay in certain places. Transverse oscillations along a broken line are often used to obtain surfacing beads, in butt welding of sheets without beveled edges in the lower position, and in cases where there is no danger of burning through the part to be welded.
Crescent movements are used for butt welds with beveled edges and for fillet welds with a leg less than 6 mm, which are performed in any position with an electrode up to 4 mm in diameter.
Triangle movements are used when making fillet welds with a leg of a seam of more than 6 mm and butt edges with a bevel in any spatial position.
Loop-like movements are used in cases requiring greater heating of the metal along the edges of the seam, mainly when welding sheets of high-alloy steels. These steels have high fluidity and for satisfactory weld formation it is necessary to hold the electrode at the edges in order to prevent burn-through in the center of the weld and the outflow of metal from the weld pool during vertical welding.
Welding technique
Under the technique of making welds, they understand the choice of welding modes and methods of manipulating the electrode.
ELECTRIC ARC START
Arc ignition is one of the main operations of the welding process. Ignition is performed each time before the start of the welding process, re-ignition of the arc - during the welding process when it breaks.
Excitation of the welding arc is carried out by touching the surface of the workpiece to be welded with the end of the electrode, followed by rapid removal of the end of the electrode from the surface of the workpiece. In this case, if the gap is not too large, there is an instantaneous appearance of current and the establishment of an arc column. The contact of the electrode with the product should be short-term, otherwise it will be welded to the product ("stick").
To tear off the "adhered" electrode should be sharply turning it to the right and left. The arc can be excited either by a series of reciprocating movements with a light touch on the surface of the metal being welded and then retracted from the surface of the product by 2-4 mm, or by scratching movements with the end of the electrode along the surface of the product, which resemble the striking of a match. Use the most convenient way for you.
After starting the arc, the electrode must be held for some time at the deposition start point until a weld is formed and the base metal is melted. Simultaneously with the melting of the electrode, it is necessary to evenly feed it into the weld pool, thereby maintaining the optimal arc length. Indicators of the optimal arc length are a sharp crackling sound, even transfer of metal drops through the arc gap, and low spatter.
The length of the arc significantly affects the quality of the weld. The short arc burns steadily and calmly. She. provides a high-quality weld, since the molten metal of the electrode quickly passes through the arc gap and is less subject to oxidation and nitriding. But too short an arc can cause "sticking" of the electrode, the arc is interrupted, the welding process is disturbed. A long arc burns unsteadily with a characteristic hiss. The penetration depth is insufficient, the molten metal of the electrode is splashed and more oxidized and nitrided. The weld is shapeless, and the weld metal contains a large amount of oxides.
If during welding, for any reason, the welding arc goes out, a special arc re-ignition technique is used to ensure that the welding starts with good fusion and appearance. When re-igniting, the arc should be excited at the leading edge of the crater, then through the entire crater it should be transferred to the opposite edge, to the newly deposited metal, and then forward again, in the direction of the welding being carried out. If the electrode is not pulled back far enough when the arc is re-ignited, a depression will remain between the start and end of the weld. If, however, the electrode is pulled back too far during re-ignition, then a high bulge forms on the surface of the weld bead.
The position and movement of the electrode during welding. During welding, the following movements are reported to the electrode:
translational along the electrode axis towards the weld pool, while in order to maintain a constant arc length, the speed of movement must correspond to the melting rate of the electrode;
movement along the line of the welded seam, which is called the welding speed; the speed of this movement is set depending on the current, the diameter of the electrode, the rate of its melting, the type of seam and other factors;
moving the electrode across the seam to obtain a seam wider than the thread roller, the so-called broadened roller.
If the welding speed is too high, the deposited beads turn out to be narrow, with a small bulge, with large flakes. If the electrode movement speed is too slow, the weld bead has too much bulge, the seam is uneven in shape, with sagging along the edges.
The position of the electrode during welding should correspond to fig. 2. Welding is carried out in the direction both from left to right and from right to left, from oneself and towards oneself.
Rice. 2. Angle of inclination of the electrode: a - in the horizontal plane; b - in the vertical plane.
At the end of the weld, it is impossible to abruptly break the welding arc and leave a crater on the metal surface, which is a stress concentrator and a zone with a high content of harmful impurities. To avoid the formation of a crater, it is necessary to stop moving the electrode, i.e., make a delay of 1-2s, then move back 5 mm and break the arc with a quick upward and backward movement.
If the welding is not completed correctly, a deep crater is always formed at the end of the seam, where the arc went out. The crater can serve as an indicator of the depth of penetration, however, at the end of welding and surfacing, these craters must be filled and welded. This is done by initiating an arc in the crater, establishing a short arc and holding the electrode in this position until the crater is filled with molten metal. It is not recommended to weld the crater by interrupting and starting the arc several times, due to the formation of oxide and slag contamination of the metal.
A weld formed as a result of two movements of the end of the electrode (translational and along the seam line) is called "thread". Its width at the optimum welding speed is (0.8-1.5) de. The root of the seam is filled with a thread seam, thin workpieces are welded, surfacing work is performed and undercuts are welded.
For bead surfacing without transverse vibrations of the electrode, it is necessary to initiate an arc, stretch it and hold it in one place for some time to warm up the base metal. Then gradually reduce the length of the arc gap until a weld pool of the appropriate size is formed. It should fuse well with the base metal until the moment when the forward movement of the electrode begins in the direction of welding. In this case, it is recommended to perform small movements of the electrode along the axis of the seam. However, most welders prefer to move the electrode along the axis of the weld without any longitudinal oscillations, determining the welding speed from the formation of the bead.
When welding beads in reverse polarity, some electrodes tend to undercut. To prevent this tendency, do not move the arc behind the crater until enough metal has been deposited so that the weld is the correct size and the undercut is filled with weld metal.
Transverse oscillations of the electrode along a certain trajectory, performed at a constant frequency and amplitude and combined with movement along the seam, make it possible to obtain a weld of the required width. The transverse oscillatory movements of the end of the electrode are determined by the shape of the groove, the size and position of the seam, the properties of the material being welded, and the skill of the welder. Wide seams (1.5-5)d3 are obtained using transverse vibrations shown in fig. 3.
Rice. 3. The main methods of transverse movements of the electrode end
To make a broadened bead, it is necessary to set the electrode to the position shown in fig. 4. In this case, it should be borne in mind that transverse vibrations are performed by the electrode holder, the position of the electrode at any point in the seam is strictly parallel to its original position. The angle of inclination of the electrode in the vertical and horizontal planes should not change during oscillatory movements along the surface of the weld.
Rice. 4. The position of the electrode when surfacing beads with transverse vibrations
The oscillations of the electrode must be made with an amplitude not exceeding three diameters of the electrode used. During the bead formation process, the molten layer must be maintained in a molten state. If you move the electrode too far and delay its return, then cooling and crystallization of the metal of the weld pool is possible. This leads to the appearance of slag inclusions in the weld metal and worsens it. appearance.
When welding, it is necessary to carefully observe the weld pool, monitor its width and depth of penetration, while not moving the electrode too quickly. Stop the electrode momentarily at the end of each movement. The amplitude of transverse vibrations should be slightly less than the required width of the deposited bead.
When welding in straight polarity, as a rule, there are no problems with undercuts. When welding with reverse polarity, there may be problems with undercuts. The problem of undercutting can be overcome by holding the arc for a longer time at the extreme points of transverse movements, as well as by performing these movements with an amplitude not exceeding that required to obtain the desired width of the deposited bead.
The convexity of the weld will be less than when welding with straight polarity, the penetration will be deeper. There will be less slag, it will be less fluid and it will crystallize a little faster than when welding with straight polarity.
On a vertical surface, narrow horizontal beads are deposited, as a rule, on the reverse polarity, while the welding current should not be too high.
Welding should be done on a short arc. When welding, care must be taken to ensure that the metal of the weld pool does not flow down or form a bulge on the lower edge. To do this, it is necessary to make reciprocating movements of the electrode in the direction of the axis of the weld. Each new bead should overlap the previously welded bead adjacent to it by at least 45-55%. To prevent the formation of undercuts, it is necessary to oscillate the electrode within the convexity of the weld bead. In most cases, welding in a vertical position is performed from the bottom up, especially for critical joints. This welding technique is widely used in the construction of pipelines. high pressure, in shipbuilding, in the construction of pressure vessels and in civil works.
The surfacing of narrow beads on a surface in a vertical position, when welding from the bottom up, is carried out at the reverse polarity of the welding current, while the welding current should not be too high. The position of the electrode must correspond to that shown in fig. 5. It is necessary to use the reciprocating movement of the electrode. The surfacing of the beads should be carried out with a short arc, in the upper part of the trajectory of the electrode oscillations, the arc should be stretched, but it should not be allowed to break in this area.
Rice. Fig. 5. Position of the electrode during surfacing of narrow beads without transverse oscillations of the electrode in a vertical position from the bottom up
This type of electrode movement allows the deposited metal to crystallize, forming a step on which the next portion of the electrode metal is deposited. Some welders prefer to maintain a constant weld pool, which they slowly build up from the bottom up while using small oscillatory movements of the electrode. This way of conducting the welding process leads to the surfacing of the bead with a large convexity, as well as to the appearance of the probability of cracks in the weld metal.
The method of performing welding with longitudinal vibrations of the electrode allows you to get a flatter weld with a low convexity, and also reduces the risk of slag inclusions.
Welding in a vertical position from top to bottom is quite rare in industry, especially when ordinary work. The scope of this method of conducting the welding process is usually limited to welding work during the construction of main pipelines and when welding sheet metal. When surfacing on a flat surface, this method of welding leads to a not very deep penetration, there is also a risk of slag inclusions.
The surfacing of narrow beads in a vertical position from top to bottom is carried out on the reverse polarity, while it is necessary to reverse Special attention for welding current. The position of the electrode must correspond to that shown in fig. 6.
Rice. Fig. 6. The position of the electrode during surfacing of narrow beads without transverse vibrations of the electrode in a vertical position from top to bottom.
During the welding process, it is necessary to maintain a very short arc so that the slag does not flow into the head of the weld pool. Transverse vibrations of the electrode, as a rule, are not used, so the movement speed is quite high. This explains the small width of the beads deposited in this way, as well as their small convexity. Undercuts are almost non-existent.
Welding with transverse vibrations of the electrode in a vertical position is very often used in the construction of high-pressure pipelines, high-pressure vessels, in the welding of ship structures, as well as in the manufacture of metal structures. This welding technique is very often used for welding multi-run groove welds, as well as fillet welds in a vertical position.
The surfacing of beads with transverse oscillations of the electrode in a vertical position, as a rule, is performed from the bottom up at the reverse polarity of the welding current. Welding in straight polarity in this position is rarely used. Even rarer is welding in the top-down position.
When welding beads with transverse vibrations of the electrode in a vertical position, the welding current should not be too high, but it should be sufficient for good penetration. The position of the electrode should at least approximately correspond to that shown in fig. 7.
A shelf no more than 12 mm wide is welded in the lower part of the joint, while the electrode displacement from the axis of the weld should not exceed 3 mm. The electrode must be moved along a trajectory (Fig. 7b). To prevent the appearance of undercuts, it is necessary to make short stops of the electrode when it reaches the side edges of the weld.
Rice. Fig. 7. The position of the electrode during the surfacing of beads in a vertical position from the bottom up with transverse vibrations of the electrode (a) and the trajectory of the electrode (b).
Welding can also be done by keeping the weld pool in constant motion, being very careful not to let the molten metal of the weld pool flow out. If this condition is met, the electrode can be moved upwards along any side of the welded joint, while it is necessary to<растяжение>welding arc, but do not allow it to break. Do not keep the arc too long outside the crater - this can cool the crater and cause excessive spatter of metal before the seam.
When welding beads with straight polarity, the welding current should be slightly higher than when welding with reverse polarity. Since the deposition rate is higher when welding with straight polarity, as well as the amount of slag is greater, the speed of movement of the electrode must be higher. Undercuts do not constitute any significant problem, so there is no need to hold the electrode on the side surfaces of the edges to be welded.
The surfacing of beads in a vertical position with transverse vibrations of the electrode in a vertical position from top to bottom is carried out at reverse polarity, while paying special attention to the setting of the welding current. The position of the electrode must correspond to that shown in fig. 8. During the welding process, it is necessary to maintain a very short arc so that the slag does not flow into the head of the weld pool. To prevent the appearance of undercuts, it is necessary to make short stops of the electrode when it reaches the side edges of the weld.
Rice. Fig. 8. The position of the electrode during the surfacing of beads in a vertical position from top to bottom with transverse vibrations of the electrode (a) and the trajectory of the electrode (b)
Despite the fact that the industry is currently heading for the complete elimination of welding in the overhead position due to appropriate positioning, today every welder must be able to weld in this spatial position. Welding in the overhead position is common in the construction of pipelines, in shipbuilding and in construction and installation work.
Rice. 9. The position of the electrode when surfacing narrow beads in the overhead position
The surfacing of narrow beads in the overhead position can be carried out both in reverse and in direct polarity. The amount of welding current with reverse polarity is the same as when welding in a vertical position. When welding with straight polarity, this value is slightly higher. The position of the electrode must correspond to that shown in fig. 9. The welder must be in such a position as to be able to observe the weld metal and the welding arc. This is especially important when welding pipes, but it often happens that the direction of welding should be directed towards the welder.
During the welding process in reverse polarity, a short arc must be maintained, the weld pool must not be too hot. When welding with straight polarity, the arc length should be slightly longer. Slight oscillations of the electrode back and forth relative to the direction of welding serve to preheat the weld, in addition, they help prevent leakage of molten slag into the head of the weld pool. Some straight polarity welders prefer to move the electrode during welding in very small areas, with attention to the danger of a weld with a large bulge, as well as the formation of a thick slag crust. When welding with straight polarity, the risk of undercuts is virtually eliminated.
In many cases, when making welded joints in the overhead position, it becomes necessary to weld beads with transverse oscillations of the electrode. This is much more difficult than surfacing narrow beads.
Surfacing of beads with transverse oscillations of the electrode in the overhead position is carried out at reverse polarity. The welding current must not be too high. The position of the electrode must correspond to that shown in fig. 10a. Of great importance is the maintenance of a short arc, as well as the stability of the arc gap across the entire width of the deposited bead.
Hardfacing can be done by moving the entire weld pool, but care must be taken to prevent the weld pool molten metal from becoming too fluid, which will eventually cause the weld pool to flow out. If this obstacle is removed, then the electrode can be moved forward along any of the edges to be welded (Fig. 106). In this case, the lengthening of the arc is allowed, without its breakage.
The welding arc must not be allowed to remain in the crater for more time than is necessary for its complete welding. The electrode must move quickly across the face of the weld so as not to overheat the metal deposited in the middle of the weld.
When welding in an overhead position, undercutting problems can occur. They are solved by electrode delays on the side edges of the connection. It is recommended not to exceed the width of the weld over 20 mm.
Rice. Fig. 10. The position of the electrode during the surfacing of beads with transverse vibrations of the electrode in the overhead position (a) and the trajectory of the electrode (b)
END JOINT WELDING IN LOWER POSITION
End connections are widely used in vessel designs that are not subjected to high pressure. End connections are very economical connections, but they do not withstand significant tensile or bending loads. Few electrodes are required to make this joint because the proportion of deposited metal in the weld metal is small. End joint welding does not present any difficulties and can be performed in a wide range of welding modes, both in direct polarity and in reverse.
During welding, in order to completely cover the entire surface of the joint, it is recommended to make small transverse oscillations of the electrode. However, one should be aware of the danger of being carried away by such fluctuations. With excessively wide fluctuations of the electrode, the metal will begin to hang from the edges of the connection. Care must be taken to melt both edges and ensure good penetration.
BUTT JOINT WELDING WITHOUT BELIVER IN LOWER POSITION
This type of welded joint is widely used in industry for conventional structures. With double-sided welding of metal, the thickness of which does not exceed 6 mm, this connection will be very strong. However, as a rule, such joints are welded on one side only. In this case, the strength will be determined by the penetration depth, which, in turn, depends on the diameter of the electrodes used, the value of the welding current, the size of the gap between the parts, and also on the thickness of the parts to be welded. With one-sided welding, obtaining full penetration without a gap between the edges to be welded for metal with a thickness of more than 5 mm is very problematic.
Welding of the butt joint without bevel edges to ensure increased heat input is carried out at reverse polarity. When welding, it is necessary to ensure reciprocating movement of the electrode along the axis of the weld. This will lead to preheating of the metal before the weld, minimize the risk of burn-through, and ensure that the molten slag is forced out to the surface of the weld pool, which eliminates the possibility of the formation of non-metallic slag inclusions in the weld metal.
In the welding process, it is especially important to maintain a constant speed and uniformity of movement of the electrode along the axis of the weld, as well as the size of the gap between the electrode and the workpiece (arc length). If the electrode movement speed is too high, the seam turns out to be narrow, undercuts are formed. If the welding speed is too low, the weld pool heats up to a temperature at which burn-through is possible.
An arc that is too long results in poor weld appearance, poor penetration, excessive spatter, and poor mechanical properties of the weld metal.
WELDING IN THE LOWER POSITION OF THE T-JOINT (WELDING IN THE "BOAT") WITH A SINGLE-PASS FILLENTION WELD
When forming a fillet weld, in order to avoid lack of penetration, the surfaces to be welded are tilted to the horizontal plane at an angle of 45 ° - welding "into the boat" (Fig. 11a), and when tilted at an angle of 30 or 60 ° - into an asymmetric "single" (Fig. 116). Welding is performed at increased values of welding current, both on direct and reverse current polarity. Welding on reverse polarity is performed with a short arc, and undercuts may occur. The position of the electrode during welding should correspond to that shown in fig. 11c
Rice. 11. The position of the electrode when welding "in the boat": a - welding into a symmetrical "boat"; b - welding in asymmetric<лодочку>; c - spatial position of the electrode
At the beginning of the welding process, the electrode must be brought to the edge of the plate to be welded. After heating the edge of the plate with a stretched arc, the application of a weld of the required width and depth of penetration begins. In this case, small reciprocating movements are made by the electrode in the direction of the axis of the weld. This provides preheating of the root of the weld and prevents leakage of molten slag in front of the head of the weld pool.
The electrode must be directed directly to the root of the weld, the welding arc must not be allowed to reach the surface of the plate outside the weld formation area. Welding is not allowed too a large number metal in one pass.
WELDING IN THE LOWER POSITION OF THE T-JOINT (WELDING INTO THE "BOAT") WITH A MULTIPLE FILLET WELD.
Very often, when welding a tee joint in the lower position, it is necessary to perform multi-pass welding. Single-pass fillet welds must have legs that exceed the diameter of the electrode used by no more than 1.5-3.0 mm. In multi-pass welding of fillet welds, the number of layers is determined based on the diameter of the electrode, while the thickness of each layer should not exceed (0.8-1.2) de.
Since the tee joint in the lower position forms edges, similar to a beveled butt joint, welding can be performed using the transverse oscillation welding technique, while the seam width should not exceed (1.5-5) dee. If the weld layer exceeds the allowable weld width, then the surfacing of each layer is carried out with the required number of beads.
When welding this joint, the first pass is made with an electrode 4-6 mm thick without transverse vibrations. Subsequent passes are made with smaller diameter electrodes. When welding these passes, it is necessary to use transverse oscillations of the electrode, while the amplitude of the oscillations of the electrode should not exceed the allowable width of the seam.
When welding with reverse polarity, a slightly shorter arc length is maintained than with straight polarity. In this case, it is necessary to carefully control the welding process in order to avoid the appearance of possible undercuts. For this, electrode delays can be applied at the extreme points of the amplitude of the transverse oscillations of the electrode, while carefully controlling the width of the weld and the amplitude of the transverse oscillations of the electrode.
Before surfacing each layer or bead, it is necessary to carefully clean the surface of the weld from slag, otherwise the appearance of slag inclusions is inevitable. At the beginning and when welding is resumed, the craters of the weld beads must be carefully sealed.
WELDING THE ELBOW WITH THE OUTER CORNER IN THE LOWER POSITION
Fillet joints with external fillet welds are much less common than butt, lap and tee joints. This joint is highly adaptable as it is very easy to prepare for welding and the welding mode parameters are similar to those used in bevel butt welding.
To ensure maximum strength in a welded joint, it is necessary to obtain penetration from the back side. Adding an inside fillet weld to an outside fillet weld greatly increases the strength of the entire fillet joint. As already noted, the cost of preparing such a joint is very small, however, when welding such joints from thick metal, a significant amount of costs will be the cost of the electrodes.
Welding of a fillet joint with an outer corner in the lower position is performed with reverse polarity. When welding this joint, the position of the electrode must correspond to that shown in fig. 12. In the first pass, a welding technique is used that is applied when applying a narrow seam, without transverse vibrations. The value of the welding current must not be too high. The weld in the first pass must ensure complete penetration of the reverse side of the joint and good fusion with both plates. Of great importance to achieve this goal is to maintain a short arc.
Rice. 12. Position of the electrode when welding a fillet joint with an outer corner in the lower position
When performing the second, third and subsequent passes, the welding current should be set to a higher mode. When performing these passes, the technique of transverse oscillations of the electrode is used. The third pass must be made with a wider oscillation amplitude than the second. The technique for making the second and subsequent passes is similar to making these passes when welding into a "boat" with a multi-pass fillet weld.
During welding, it is necessary to monitor the limitation of the width of the transverse vibrations of the electrode. To eliminate undercuts, it is recommended to make a short stop of the electrode at the extreme points of the trajectory of transverse oscillations. Make sure that good fusion is achieved with the previously applied layers and with both surfaces of the plate. The last pass shouldn't have too great height. After each pass, it is necessary to carefully clean the deposited metal from the slag crust.
BUTT WELDING WITH A BELIVER ON A LINER IN THE LOWER POSITION
This type of welded joint is often used in welding pipelines, pressure vessels and ship structures.
Welding of this connection is carried out on reverse polarity. For the first pass, a low value of the welding current is set. The position of the electrode must correspond to that shown in fig. 13. Welding is carried out with a narrow bead without transverse vibrations of the electrode. Care must be taken during welding to ensure good fusion with the backing and groove surfaces at the root of the joint. The seam surface should be as flat as possible.
Rice. 13. The position of the electrode when welding the butt joint with beveled edges on the lining in the lower position
The second, third and subsequent passes can be made at higher welding currents. Movement along the axis of the seam should not be too fast, otherwise the surface of the seam will be uneven, with large scales, pores may appear. The transverse movements of the electrode must be limited by the required width of the seam. This will ensure that undercuts do not occur. During welding, it is important to monitor the length of the arc, carefully remove slag from the superimposed layers, and ensure that the superimposed weld has fusion with the previous layers and with the edges to be welded. When applying the last layer, use the groove edges as an indication in determining the required joint width.
BUTT JOINT WELDING WITH A BELIVER IN THE LOWER POSITION
This type of connection is often found in the welding of pipelines, as well as in the welding of critical joints.
Welding of this connection is carried out on reverse polarity. The position of the electrode must correspond to that shown in fig. fourteen.
Rice. 14. The position of the electrode when welding the butt joint with beveled edges in the lower position
On fig. 15a shows the order of layers/beads in a beveled butt weld in the down position. The first pass is intended for welding the root of the seam and is usually performed with electrodes with a diameter of 3 mm, while the welding current should not be too high. Welding is carried out on a short arc with reciprocating movements relative to the line of the weld, while it is necessary to ensure that the electrode itself remains in the gap of the root region of the welded joint all the time. During welding, interruption of the arc should not be allowed when the electrode is moved forward and care must be taken that metal drops do not fall in front of the seam, this can interfere with the welding process and its progress. A small bead should form on the back of the joint. The front surface of the first pass should have a minimum convexity.
Rice. 15. Butt joint welding with beveled edges in the lower position: a - layer stacking order; b - the trajectory of the electrode during the last pass; in - welded joint
The second and subsequent passes are made at higher values of the welding current and electrodes of a larger diameter. Surfacing is carried out with transverse oscillations of the electrode, while it is important to ensure the constancy and uniformity of oscillations and movement of the electrode along the weld axis, otherwise the resulting weld will not be uniform in quality and appearance. During welding, care must be taken to avoid undercuts (Fig. 156). It is necessary to obtain fusion with the previously deposited layers, as well as with the side edges of the groove of the welded product. Front side the second and subsequent layers should have a flat surface. It is necessary to carefully clean each layer of slag along its entire length.
The final pass is performed with the same type of electrode as the previous ones. The execution technique is the same when performing the second and subsequent passes, except that during the final pass, the amplitude of the transverse oscillations of the electrode will be greater. To control the width of the facing seam, it is necessary to use beveled edges of the butt joint. The surface of the facing seam should be slightly convex.
LOW PLATE WELDING
This type of connection is widely used in industry, in particular in tanks, building and ship structures. The lap joint is very economical, it does not require any significant preparation and assembly costs. The maximum strength of the lap joint is achieved when it is welded on both sides with a fillet weld.
Welding of this connection is carried out both in direct and reverse polarity, while the welding current should not be too large. The position of the electrode must correspond to that shown in fig. 16.
Rice. 16. Welding the lap joint in the lower position: a - preparation of the joint for welding; b - the position of the electrode when welding with a single-pass seam of equal thickness; c - the position of the electrode during the second and third passes when performing a multi-pass weld; d - the position of the electrode when welding different thicknesses
Lap welding in the down position requires a very short arc in straight polarity and an even shorter arc in reverse polarity. The arc must be oriented in the direction of the connection root and the horizontal surface of the plate. During welding, it is necessary to perform, relative to the axis of the welded seam, small reciprocating oscillations of the electrode. This contributes to the preheating of the joint in front of the moving welding arc, ensures the creation of a full-sized bulge and covers the tail of the weld pool with a slag crust.
It is absolutely essential for a good joint to have complete penetration at the root of the weld and good fusion to both surfaces of the two plates. When welding with straight polarity, the upper edge of the top plate tends to burn through, so when welding, you must constantly be wary of both underfilling the weld bead and that the welding arc is not short enough. Undercuts appear very rarely.
When welding in reverse polarity, attention should be paid to maintaining a shorter arc, as well as eliminating possible undercut, both on the flat surface of the plate and along the top edge of the top plate. To reduce the likelihood of undercuts, arc movement should be limited to the dimensions of the weld.
LAP WELDING IN A HORIZONTAL POSITION
Lap joint welding in a horizontal position with a single pass fillet weld in straight polarity is often used in tank and building structures.
When welding this joint, the welding current should not be too high. The electrode must be directed to the root of the seam. The position of the electrode during welding should correspond to that shown in fig. 17. Welding is best done with small reciprocating movements of the electrode in the direction of the axis of the weld, slight transverse oscillations of the electrode can also be used. The weld pool must not be too hot, as this will cause cracks in the weld metal.
Rice. 17. Position of the electrode when welding a lap joint in a horizontal position
When welding, special attention should be paid to the movement of the electrode in order to prevent the appearance of burns through the edge of the plate, and also to ensure that the welding arc does not come into contact with the surface of the vertical plate outside the weld, otherwise undercuts are inevitable.
LOWER WELDING
A large proportion of the welds performed in practice by the welder are fillet welds performed in the lower position. Welding technology can include both single-pass and multi-pass welding with all types of electrodes. Although electrodes designed for reverse polarity welding are not best type electrodes for making single-pass fillet welds, the use of these electrodes for such purposes is a fairly common practice.
When welding a T-joint in the down position with straight polarity, the welding current must be sufficient to produce a large weld pool. When welding in reverse polarity, the welding current should be somewhat less. The position of the electrode when welding in direct polarity must correspond to that shown in fig. 18a, on reverse polarity - fig. 18b.
Rice. 18. The position of the electrode when welding a tee joint in the lower position: a - on direct polarity; b - on reverse polarity
The electrode must be directed to the root of the welded joint. When welding with reverse polarity, the arc length should be shorter. The movement of the electrode must be carried out evenly throughout the joint, without losing the weld pool.
However, some welders prefer to use small reciprocating movements of the electrode in the direction of the weld axis. This can have a positive effect in the form of preheating of the edges to be welded and the root of the joint located in front of the moving electrode, improve the formation of deposited metal on the vertical plane of the plate, and also help prevent leakage of molten slag into the head of the weld pool. When welding with straight polarity, undercuts are never a problem. Reverse polarity welding requires increased measures to prevent undercuts.
WELDING A T-JOINT IN THE LOWER POSITION WITH A MULTI-PASS WELD
Large fillet welds are very often made by repeatedly applying narrow beads without transverse vibrations of the electrode. In most cases, the facing layer or the last bead is made without lateral oscillation of the electrode, in some cases it is required that the last pass be performed with lateral oscillation. In particular, these are the requirements for welding pipelines and pressure vessels. Welding can be performed on both direct and reverse polarity of the welding current.
When making this connection, the welding current is set to the same as when welding with a narrow single-pass seam. The position of the electrode will change depending on the sequence of layers (Fig. 19a). The movement of the electrode is similar to the movement when welding with a single-pass seam. The location or layout of the beads on the sides must be carried out in such a way that the facing layer exactly matches the specified size of the leg of the fillet weld. The order of superposition of layers is shown in fig. 19b.
Rice. Fig. 19. The position of the electrode when welding a tee joint with a multi-pass weld in the lower position (a) and the order of applying layers (b)
The technique for performing the facing layer is rather complicated. Welding current should not be too small. The position of the electrode must correspond to that shown in fig. 20a. The scales are stacked in a diagonal plane. Metal droplets are applied only when the electrode moves down. Moving the electrode up should be done quickly, on the most stretched arc, but without breaking the arc.
Rice. Fig. 20. The position of the electrode during the execution of the facing layer (a) and the trajectory of the oscillatory movements of the electrode (b)
Two parallel edges of previously made weld beads can serve as indicators of the width of the electrode movement during welding of the facing layer. To prevent the appearance of undercuts, it is necessary to hold the electrode at the upper and lower edges of the weld. It must be remembered that in multi-pass welding, thorough cleaning of the slag crust of each superimposed layer is required.
When welding in reverse polarity, significant difficulties can arise due to the appearance of undercuts. You can get rid of these problems by all the previously described methods.
WELDING OF A T-JOINT IN THE LOWER POSITION WITH A MULTIPLE WELD USING TRANSVERSAL OSCILLATIONS OF THE ELECTRODE
In practice, quite often there are cases when it is necessary to weld fillet welds of large cross-section in the lower position. Usually, multi-pass welding is used for this, using the technique of transverse oscillations of the electrode. Most often, such seams are found in shipbuilding and installation work.
Welding of this type of connection is carried out on reverse polarity. The welding current is set to high. The position of the electrode must correspond to that shown in fig. 21. The first pass is carried out in the same way as in the case of conventional single-pass fillet welding. The surface of the first roller should be as flat as possible.
Rice. Fig. 21. The position of the electrode when welding a tee joint with a multi-pass weld in the lower position using transverse oscillations of the electrode
The second seam is superimposed with transverse oscillations of the electrode over the first. The electrode must be directed to a vertical plate in order to ensure the transfer of metal from the electrode to this surface. Transverse fluctuations of the electrode should not go beyond the required width of the seam being performed. Otherwise, undercuts may occur. It is necessary to ensure good fusion of the applied welds with the surface of the previously deposited layers and with the surface of the plate to be welded.
BUTT WELDING WITH A BELIVER ON A LINER IN A HORIZONTAL POSITION
This connection, as well as the spatial position in which it is located, is very often found in the welding of pipes, tanks, as well as in shipbuilding work.
Welding is carried out on reverse polarity with both narrow beads without transverse oscillations, and with transverse oscillations of the electrode. The first pass is carried out at higher welding current values without transverse oscillations of the electrode. The position of the electrode must correspond to that shown in fig. 22. When welding, it is necessary to ensure guaranteed fusion with the lining, as well as with the edges of the root part of the joint.
Rice. Fig. 22. The position of the electrode when welding a butt joint with beveled edges on the lining in a horizontal position
The second and all subsequent passes can be made with even higher welding currents. The position of the electrode when welding with narrow beads without transverse vibrations of the electrode should correspond to that shown in fig. 22. It is very important that all seams have good fusion with the surface of previously applied layers, as well as with the surface of the groove edges. Care must be taken to prevent undercuts.
BUTT JOINT WELDING WITH A BELIVER IN A HORIZONTAL POSITION
This connection, as well as the spatial position in which it is located, is very common when welding pipes, as well as critical butt joints. When performing some work, there are sometimes requirements that these seams be made with transverse oscillations of the electrode, however, in most cases, welding with narrow beads without transverse oscillations of the electrode is used.
Welding is done with reverse polarity. Welding current during the first pass should not be too high. The position of the electrode when welding with narrow beads without transverse vibrations should correspond to fig. 23, and when welding with transverse vibrations - fig. 24a.
Rice. 23. The position of the electrode when welding a butt joint with beveled edges in a horizontal position: narrow rollers without transverse vibrations of the electrode.
When welding, it is necessary to maintain a short arc gap, forcing the electrode metal to be welded directly into the root gap of the joint. When welding, you can use the reciprocating movement of the electrode. When moving forward, the welding arc must not be allowed to break.
It is necessary during such movements to provide preheating of the metal before the weld being welded. At the same time, care must be taken to ensure that the molten metal of the weld pool solidifies quickly enough and does not flow onto the bottom plate. There must be full penetration on the reverse side of the joint.
For the second and subsequent passes, the welding current can be increased significantly. It is possible to use welding with narrow beads, without transverse vibrations. you can also use welding with transverse oscillations of the electrode (Fig. 24b). It is important to ensure guaranteed fusion of all passes with the surface of all previous passes, as well as with the surfaces of the plates to be welded. During welding, it is necessary to monitor the appearance of undercuts.
Rice. 24. The position of the electrode when welding a butt joint with beveled edges in a horizontal position: a - welding with transverse oscillations of the electrode; b - an example of transverse movements of the electrode end
BUTT JOINT WELDING WITH A BELT OF ONE EDGE IN A HORIZONTAL POSITION
Most often, when making butt joints in a horizontal position, the edge is beveled only at the top sheet. The arc is excited on the horizontal edge of the bottom sheet, then moved to the beveled edge of the top sheet. The welding technique is no different from that described above, except for the order in which the layers are applied.
Lap joint welding in a vertical position from the bottom up. When performing responsible welding work with the use of lap joints in a vertical position, as a rule, welding is carried out from the bottom up. Such welding takes place when performing welding work in shipbuilding, in the manufacture of high-pressure vessels, as well as in the manufacture of metal structures.
When welding small thicknesses, as well as for making the first passes in multi-pass welds performed when welding lap joints, single-pass fillet welds are used. When performing these seams, it is necessary to install not very great importance welding current. The position of the electrode must correspond to that shown in fig. 25.
Rice. 25. Position of the electrode when welding a lap joint in a vertical position from the bottom up
On the lower part of the joint, a deposited metal flange is formed, having dimensions corresponding to the dimensions of the weld. Reciprocating movements of the electrode should be used. When transferring the electrode metal, a short arc should be maintained; when moving up, the arc should be stretched, while not allowing it to break. When the electrode is above the weld pool, small transverse movements of the electrode can be made. This contributes to a better formation of the weld. During welding, care must be taken to ensure that the movements of the electrode are always kept within the width of the seam so that the edge of the upper plate is not burned, and no undercuts appear on the flat surface of the plate.
To perform welds of thick lap joints, multi-pass or single-pass welding with transverse electrode movements is used. In multi-pass welding, the first pass is performed by a narrow bead without transverse movement of the electrode. When performing the second pass, the welding current must be sufficient to ensure guaranteed penetration in the root of the joint and fusion with the edges. The position of the electrode and the trajectory of the movement of the electrode must correspond to those shown in fig. 26a. At the same time, keeping the electrode above the surface of the weld pool, you need to move it up, while moving the weld pool to the sides, alternately to the left, then to the right.
Rice. Fig. 26. The position of the electrode when welding a lap joint in a vertical position from the bottom up with a multi-pass fillet weld (a) and a single-pass fillet weld with transverse movement of the electrode (b)
Uniform movements of the weld pool, performed during the welding process, make it possible to obtain a smooth surface of the weld with a small convexity. Momentary stops at the extremes of the lateral vibration will prevent undercutting, but care must be taken not to burn through the edge of the top plate.
Lap joint welding can also be performed with a single-pass fillet weld with transverse oscillations of the electrode. The position of the electrode and the trajectory of the movement of the electrode must correspond to those shown in fig. 26b. The welding technique is similar to the second pass in multi-pass welding. The difference lies in the fact that the electrode must be placed at a large angle to the bottom plate and the movement delays must be performed only on the bottom plate.
WELDING OF A T-JOINT IN A VERTICAL POSITION WITH A SINGLE PASS FILLENTION WELD
Welding of this joint is often found in industrial practice. Welding vertical joints is most often done from the bottom up, although there are cases when it is necessary to weld from the top down. The choice of the number of passes is determined by the purpose of this connection, as well as the thickness of the plates to be welded.
When welding a tee joint in a vertical position with a single-pass fillet weld without transverse movement of the electrode, the welding current must be large enough to ensure good penetration in the root of the joint, as well as with the surfaces of the plates. The position of the electrode should approximately correspond to that shown in fig. 27.
Rice. 27. Position of the electrode when welding a tee joint in a vertical position with a single-pass fillet weld
Welding is performed on reverse polarity with the electrode fluctuating up and down. At the moment of transferring the electrode metal, it is necessary to maintain a short arc; when moving the electrode upwards, the arc should be stretched, but at the same time, the arc should not be broken. It is necessary to periodically remove the electrode from the weld pool in order to avoid overheating of the metal being welded and its subsequent cracking or leakage of the weld pool. At the same time, it is necessary to keep the weld pool in one place, until the required penetration, fusion with the edges to be welded and the formation of a weld of the required contour without undercuts is obtained.
Welding of a tee joint in a vertical position can also be performed with a single-pass fillet weld with transverse oscillations of the electrode. The position of the electrode and the trajectory of the movement of the electrode must correspond to those shown in fig. 28. The welding technique is similar to the second pass in multi-pass welding.
Rice. Fig. 28. The position of the electrode when welding a tee joint in a vertical position with a single-pass fillet weld with transverse movements of the electrode (a) and the trajectory of the electrode (b)
WELDING OF A T-JOINT IN A VERTICAL POSITION WITH A MULTI-PASS FILLENTION
Welding of this connection is carried out from the bottom up, usually on reverse polarity, but sometimes direct polarity is also used for this purpose. The weld can be made with narrow beads, without transverse oscillations (Fig. 29a), but much more often it is performed with transverse movements of the electrode (Fig. 29b).
Rice. 29. Multi-pass weld made with narrow beads without transverse vibrations of the electrode (a) and with transverse vibrations (b)
When welding a multi-pass weld with transverse vibrations, the first pass is similar to making a single-pass weld; it is performed without transverse movements of the electrode or, in some cases, with small transverse vibrations (Fig. 29b). The position of the electrode during the second pass should correspond to that shown in Fig. 30. Welding current must be sufficient to ensure guaranteed penetration in the root of the joint and fusion with the edges.
Rice. 30. The position of the electrode when welding a tee joint in a vertical position with a multi-pass
During welding, it is necessary to keep the electrode above the surface of the weld pool, move the weld pool up, at the same time shifting it to the sides, alternately to the left, then to the right. Uniform movements of the weld pool, performed during the welding process, make it possible to obtain a smooth surface of the weld with a small convexity, and short-term stops of the electrode at the extreme points of transverse movements will prevent the appearance of undercuts. During welding, it is necessary to maintain a short arc, but avoid touching the electrode with the molten metal of the weld pool.
When using a large diameter electrode, it is necessary to increase the welding current. The position of the electrode during welding of the third pass is similar to the second pass. When using an electrode of large diameter and with an increase in the welding current, it is desirable to accelerate the movement of the electrode upwards when the weld pool reaches the extreme point of the trajectory of transverse oscillations. In this case, it is necessary to pay attention to the continuation of the burning of the arc during all these movements. When moving the arc up, it must be stretched. After sufficient cooling of the weld pool, the electrode returns to the crater, and additional metal is deposited.
During welding, it is necessary to maintain a constant width of the trajectory of transverse oscillations, to ensure that it does not exceed the width of the finished weld.
BELIVERED BUTT WELDING ON A LINER IN A VERTICAL POSITION
This type of connection is quite common in the construction of pipelines, pressure vessels, as well as in ship structures. Welding is done in reverse polarity from bottom to top.
First pass. The welding current must be large. The position of the electrode must correspond to that shown in fig. 31. When welding, the technique of surfacing narrow beads is used, without transverse vibrations, in a vertical position. The seam must have good fusion with the backing and with the surfaces of both edges at its root.
When welding, it is necessary to ensure that the front surface of the seam is as flat as possible. If the root gap in the weld is very wide, then two or three passes must be made to complete the back-weld. During the welding process, care must be taken to ensure that all superimposed layers have good fusion with each other.
Rice. Fig. 31. The position of the electrode when welding a butt joint with beveled edges on a lining in a vertical position
Second pass. The welding current must not be too high. When making a seam, the technique of welding with transverse oscillations of the electrode is used. As guides, by which the width of these transverse vibrations can be determined, the edges of previously deposited beads are used. When welding, it is necessary to ensure that the surface of the weld is flat, to avoid undercuts. The weld seam must not form sharp edges, as slagging can form in such edges.
Third pass. The magnitude of the welding current should be such that both good penetration and fusion, and a small bulge of the weld are ensured. Transverse fluctuations of the electrode should not go beyond the beveled edges of the groove. In order to avoid the appearance of undercuts, it is necessary to delay the electrode at the extreme points of the trajectory of transverse oscillations. To prevent the appearance of excessive bulge of the weld, the welding speed must be sufficiently high.
BUTT JOINT WELDING WITHOUT BELIVER IN VERTICAL POSITION
Welding of this connection is carried out from the bottom up on the reverse polarity with a multi-pass seam. The technique of welding a root pass with a large gap in a butt joint without beveling edges is quite complicated.
First pass. The welding current should not be too large, but at the same time it should be sufficient to guarantee the penetration of the root part of the joint and the formation of a sufficient bulge on the reverse side of the joint. The position of the electrode must correspond to that shown in fig. 32. When welding the first pass, the technique of welding with narrow beads is used without transverse vibrations of the electrode; It is necessary to achieve a slight bulge on the reverse side of the root of the seam.
Rice. Fig. 32. The position of the electrode when welding a butt joint without bevel edges in a vertical position
Second pass. The value of the welding current and the position of the electrode practically do not differ from those in the first pass. It is impossible to produce transverse vibrations with too large an amplitude. The speed of movement of the electrode must be such that there is no excessive bulge of the seam and no undercuts are formed.
WELDING A JOINT WITH OUTSIDE FILLET WELD
These welded joints are often encountered in practice. Welding is carried out in reverse polarity from bottom to top using the technique of transverse oscillations of the electrode, in addition, due to the fact that the edges to be welded are not beveled, in this case a shallow penetration is sufficient.
First pass. The welding current must not be too high. The position of the electrode must correspond to that shown in fig. 33. The technique of performing a root pass with reciprocating movements of the electrode is used.
Rice. 33. The position of the electrode when welding a joint with an external fillet weld in a vertical position
Second and third passes. Welding current must be increased compared to the first pass. During welding, it is necessary to ensure good fusion with the previously deposited layers, as well as with the welded edges of the base metal, pay attention to the possibility of undercuts. The front surface of the seams should be flat.
Fourth pass. The value of the welding current and the position of the electrode are similar to those used in the welding of the previous passes. When welding, use the technique of transverse oscillations of the electrode. The front surface of the seam should have a slight bulge. Use the edges of the plates as the seam boundary.
Rice. 34. Welding of a butt joint with beveled edges in a vertical position (a) and the trajectory of the electrode (b)
BUTT JOINT WELDING
These welded joints are very common when welding pipes and critical butt joints. Welding is performed on reverse polarity from the bottom up with a multi-pass weld with transverse oscillations of the electrode.
First pass. Welding current must be large enough. The position of the electrode must correspond to that shown in fig. 34a. A root pass welding technique is used, in which up and down oscillations of the electrode are applied. It is allowed to perform welding with small transverse movements of the electrode (Fig. 34b).
Moving the electrode up should be carried out at a distance not exceeding 50 mm. It is necessary to ensure that these movements do not break the arc. Full penetration must be ensured along the entire reverse side of the joint. The front surface of the seam should be as flat as possible.
Second and third passes. Welding current can be increased. The position of the electrode is similar to that used in the welding of the first pass. The welding technique with transverse oscillations of the electrode is used. On fig. 34b shows the trajectory of the electrode. To obtain a weld of uniform quality and appearance, it is necessary to maintain the constancy of the longitudinal and transverse movements of the electrode.
Lateral movements of the electrode must be carried out quickly in order to prevent the appearance of excessive bulge in the central part of the weld. Throughout the entire welding time, it is necessary to maintain a short arc, make sure that the movements of the electrode remain within the width of the weld. To prevent the appearance of undercuts, stop the electrode at the extreme points of the trajectory of their movement.
In some cases, welding of a butt joint with a beveled edge can be done from top to bottom (Fig. 35a) or with a single-pass weld with transverse vibrations (Fig. 356). The technique for performing a single-pass weld is similar to performing the second and third passes in multi-pass welding.
Rice. Fig. 35. Welding of a butt joint with beveled edges from top to bottom (a) and the trajectory of the movement of the electrode in single-pass welding with transverse vibrations (b)
WELDING OF A T-JOINT IN THE CEILING POSITION WITH A SINGLE PASS FILLENTION WELD
This welded joint and position during welding is very common in shipbuilding and in the manufacture of metal structures.
Welding of a tee joint in the overhead position with a single-pass fillet weld is carried out in reverse polarity, while the welding current should not be too large. The position of the electrode must correspond to that shown in fig. 36a. During welding, reciprocating movements of the electrode are used. When welding metal, it is necessary to maintain a short arc. When moving forward, the arc should not break.
Rice. 36. Position of the electrode when welding a tee joint in the overhead position with a single-pass fillet weld
During welding, special attention must be paid to ensure good fusion and penetration at the root of the joint, as well as with the side edges. Leakage of slag into the head of the weld pool must not be allowed; to prevent the appearance of excessive height and convexity of the weld, do not allow overheating of the weld pool.
WELDING OF A T-JOINT IN THE CEILING POSITION WITH A MULTI-PASS FILLET WELD.
If it is necessary to perform fillet welding in the overhead position in more than one pass, the welding technique without transverse oscillations of the electrode is used. Welding is performed on reverse polarity, while the welding current should not be too large. The position of the electrode must correspond to that shown in fig. 37a.
Rice. Fig. 37. The position of the electrode when welding a tee joint in the overhead position with a multi-pass fillet weld (a) and the order of applying layers (b)
The sequence of overlay layers is shown in fig. 37b. For welders with little experience, there may be some difficulty in maintaining the correct proportions of the seams. However, with experience, these difficulties will be overcome. Each pass must have good fusion with adjacent beads and with the surface of the edges to be welded. The face of each pass should be as flat as possible.
FLAP JOINT WELDING WITH A SINGLE PASS FILLET WELD IN THE CEILING POSITION
This welded joint and welding position is very common in tank construction and shipbuilding. Due to the dimensions and characteristic features of these objects, their tilting for welding is not advisable. Most of these jobs are done in reverse polarity, but there are also cases where it is necessary to weld the lap joint in the overhead position and in straight polarity.
The value of the welding current when welding in reverse polarity should not be too large. When welding with straight polarity, the value of the welding current should be slightly higher than when welding a similar joint with reverse polarity. The position of the electrode must correspond to that shown in fig. 38.
Rice. 38. The position of the electrode when welding a lap joint with a single-pass fillet
When welding, oscillatory movements of the electrode in the direction of welding can be used. When moving the electrode forward, care must be taken not to break the welding arc. Such movements of the electrode serve to preheat the edges before surfacing the electrode metal on them and help prevent overheating of the weld pool, thereby preventing the formation of sagging and excessive bulge. In addition, such movements of the electrode and the welding arc cause the slag to be pushed into the tail of the weld pool. When welding, the welding arc must not be allowed to reach the surface of the upper plate, and it should be ensured that the welding arc does not go beyond the boundaries of the outer surface of the weld during its movements.
When welding in direct polarity, slag control is somewhat difficult. The weld tends to be excessively bulged and the weld pool flows out onto the vertical surface of the plate edge. Undercuts do not meet.
WELDING OF A T-JOINT WITH A MULTIPLE FILLET WELD WITH TRANSVERSAL VIBRATIONS IN THE CEILING POSITION
A welder in his practice more than once has to deal with the need to perform fillet welds of a large cross section in the overhead position with electrodes of large diameter.
First pass. Welding current must be large enough. The position of the electrode must correspond to that shown in fig. 39a. The length of the welding arc should be small; when welding, it is necessary to use transverse vibrations of the electrode (Fig. 39b). Movements of the electrode must be carried out with fast sliding movements, at the same time it is necessary to ensure that this does not cause a significant increase in the length of the arc.
During welding, you need to pay attention to maintaining a stable burning of the welding arc, to prevent its breakage. After the crystallization of the crater, return to it and digest the crater. This helps to prevent overheating of the weld pool and the appearance of cracks in the weld metal. The root part of the weld is preheated before the electrode metal is deposited on it. In addition, this welding technique tends to push the slag into the upper part deposited metal. The ability to control the deposited metal and the welding arc is improved, the appearance of undercuts, sagging and excessive bulge of the weld is prevented, the appearance of the weld surface is improved, it becomes more uniform.
Rice. Fig. 39. The position of the electrode when welding a tee joint with a multi-pass fillet weld with transverse vibrations in the overhead position (a) and the trajectory of the electrode (b)
Second pass. The second pass is performed in the same way as the first one, with the only difference being that large quantity electrode metal. The second pass is usually more difficult for welders than the first pass.
BUTT JOINT WELDING WITH A BELIVER ON A LINED MULTIPLE WELD IN THE CEILING POSITION.
This type of weld and welding conditions are often encountered in pipe and tank welding when welding is performed on ring backings.
First pass. Welding is done with reverse polarity. Welding current must be large enough. The position of the electrode must correspond to that shown in fig. 40. To ensure good metal transfer, it is necessary to maintain a short arc. The movement of the electrode must be sliding. Care must be taken to ensure guaranteed fusion in the backing area and between the edges at the root of the joint. The face of the weld should have as little convexity as possible.
Second and subsequent passes. Welding current is still high. Welding is performed using the technique of sliding movements of the electrode, without its transverse movements. If the metal begins to overheat, it is necessary to lengthen the arc and move the electrode forward until the crater with the overheated weld pool cools down.
Rice. Fig. 40. The position of the electrode when welding a butt joint with beveled edges on a lining with a multi-pass weld in the overhead position and the order of applying layers
It is necessary to ensure guaranteed fusion both with the surfaces of previously deposited beads and with the groove walls. Attention should be paid to the unconditional need to clean the weld surface from slag after each pass.
BUTT JOINT WELDING WITHOUT BEDDING MULTIPLE WELD IN THE CEILING POSITION
Such a connection in such a spatial position is extremely rare. It is very difficult to perform such a weld seam with high quality, this requires some training. Welding is done with reverse polarity.
First pass. The welding current must not be too high. The position of the electrode must correspond to that shown in fig. 41. welding arc should be short. To ensure complete penetration on the reverse side, the electrode must always be in the gap between the edges to be welded. In addition, this position of the electrode ensures fusion with the root edges of the welded plates. When welding, reciprocating movements of the electrode are used.
Rice. Fig. 41. The position of the electrode when welding a butt joint without cutting edges with a multi-pass weld in the overhead position
Second pass. The welding current must not be too high. When welding, it is necessary to maintain a short arc and make small oscillatory movements of the electrode, performed by light sliding, make sure that the transverse oscillations of the electrode are not too wide.
BUTT JOINT WELDING WITH A BELT WITH A MULTI-PASS WELD IN THE CEILING POSITION
This type of welded joint and the conditions under which it is performed is often encountered when welding pipes and metal structures from sheet metal.
Welding of a butt joint with a beveled edge with a multi-pass weld is carried out at reverse polarity with transverse oscillations of the electrode. The welding current during the first pass should not be too high, but at the same time it should ensure guaranteed penetration from the back side. The position of the electrode must correspond to that shown in fig. 42. The execution of the first, root, pass is similar to welding the first pass in the previously considered joints. The face of the weld must be flat. On the reverse side, a small roller should form.
Rice. Fig. 42. The position of the electrode when welding a butt joint with a beveled edge with a multi-pass weld in the overhead position
Second and subsequent passes. The welding current should be slightly higher than during the first pass. The welding technique with transverse oscillations of the electrode is used. Movements of the electrode in the transverse direction must be carried out with quick movements so that too much convexity is not obtained in the central part of the weld. In addition, the trajectory of the transverse movements of the electrode should not go beyond the width of the weld.
To prevent the appearance of undercuts, the electrode delay is used at the extreme points of the trajectory of transverse vibrations. It must be remembered that undercuts appear as a result of the arc "licking" the metal on the surface of the plate with subsequent non-deposition of the electrode metal in this place.
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The order of suturing. When choosing the order of suturing, it is necessary to strive to ensure that the residual stresses are the smallest. For this purpose, complex welded products should be divided into separate units. At the same time, the units are first welded, from which a complex product is subsequently assembled and welded. Particular care should be taken in choosing the order of welding of double-sided seams.
To reduce internal stresses and prevent cracking, both sides must be welded simultaneously. Therefore, it is very useful to weld alloy steel structures in a rotary fixture.
In multi-layer welding, beads should be applied with the same cross section and length as possible. This is necessary to reduce the hardening zone of the welded steel. In FIG. 95, and the temper zone is shown with radial shading. The hardening zone is located between the hatching and the bead boundary. When applying subsequent rollers, the hardening zone of the previously applied rollers heats up, as a result of which it is tempered (Fig. 95, b). As a result of this welding method, the entire heat-affected zone can be uniformly tempered.
If the rollers are superimposed with different sections and in different position(Fig. 95, c), the tempering zones will not completely overlap the hardening zones of the previous rollers, and large layers of hardened steel will remain in the seam.
Annealing roller. The last beads of the weld give a hardening zone, which can be released by applying an annealing bead applied only to the weld metal.
Along the boundaries of the annealing roller, there is also a layer that is heated to the quenching temperature. Therefore, it is necessary to weld in such a way that this layer necessarily passes through the non-hardening deposited metal.
The annealing bead must be applied at a certain distance from the base metal, since at a small distance a hardening zone may appear in the steel. The distance between the edges of the annealing roller and the base metal must be selected in accordance with Table. 69, which shows the approximate values of the hardening zone and the dependence on the diameter of the electrode, at medium current strength and welding speed.
Examples of applying annealing beads when welding butt and tee joints are shown in Fig. 96.
Table 69
If the welded joint consists of two steels: low-carbon 1 and alloy 2, then the annealing bead 3 is applied closer to the low-carbon steel (Fig. 97). If welding is carried out with a wide seam, over 30 mm, then two annealing rollers are superimposed nearby.
The annealing bead should be deposited at the specified welding time. If you put a roller on a very hot seam, the hardened zone will not be released. It is impossible to make surfacing after the seam is completely cooled, since this may end the hardening process from previously applied beads and cracks may appear in these places. That's why the annealing bead must be deposited after the seam has completely darkened when the temperature is 200-300°.