Editing of strip metal is carried out in the following order. On the convex side, the boundaries of the bends are marked with chalk. The strip is located on correct plate so that it lies flat on the slab with a bulge up, touching at two points. For dressing, a hammer with a round smooth polished head is used. Hammers with a square head should not be used, as they leave traces in the form of nicks (squares, corners). Impacts are applied to the convex parts, adjusting the impact force depending on the thickness of the strip and the magnitude of the curvature; the greater the curvature and the thicker the strip, the stronger the blows. As the strip is straightened, the impact force is weakened and more often the strip is turned over from one side to the other until it is completely straightened. With several bulges, the chals are straightened closest to the ends, and then located in the middle.

Rice. 87. Editing of metal: a - eye check; 6 - the moment of editing

The results of editing (straightness of the workpiece) are checked by eye (Fig. 87), and more precisely, on a marking plate along the clearance or by applying a ruler to the strip.

Editing of narrow crescent-shaped blanks is carried out on a plate under the ruler. To do this, the workpiece is placed on the plate, with one hand pressed against the plate and a hammer (wooden or steel with a convex striker)

starting from the shorter concave edge of the curved workpiece, i.e., the one where the metal fibers are compressed and need

Rice. 88. Editing a strip with crescent curvature (a) and editing scheme sheet metal: 6, c - bent blanks; d, e - distribution of shocks

can be stretched so that the workpiece is leveled. At the beginning of dressing, the impacts on the concave edge should be stronger, and as you approach the opposite edge, weaker and weaker. This achieves that the concave, shorter edge is gradually extended and the workpiece is straightened (Fig. 88, a), which is controlled by a ruler.

After checking by eye on the convex side, the boundaries of the bends are marked with chalk. Then a bar is placed on a slab or anvil (Fig. 89) so that the curved part is bulge up. Impacts are applied with a hammer on the convex part from the edges of the bend to the middle part, adjusting the impact force depending on the diameter of the rod and the size. .

The invention relates to metallurgy, in particular to the finishing of flat products, and can be used in straightening steel strips with periodic longitudinal corrugations. The method includes multiple elastic-plastic alternating longitudinal bending of the strip with its simultaneous transverse bending due to an increase in the deflection of the edge sections along the width of the strip in comparison with its middle part. The value of the deflection of the edge sections is made greater than the value of the deflection of the middle part at the first bend, and at each subsequent bend it is less than at the previous one, while the value of the longitudinal bends is successively reduced in the course of editing from the given value to zero. The wear of the rollers is reduced while ensuring high-quality straightening. 1 ill.

Drawings to the RF patent 2255825

The invention relates to the finishing of flat products and can be used in straightening steel strips with periodic longitudinal corrugations.

The technology of straightening strip (sheet) metal is described in sufficient detail in the book by A.Z. Slonin and A.L. Sonin “Straightening of sheet and section metal”. - M.: Metallurgy, 1981. For straightening, special roller machines are used, in which an alternating elastic-plastic buckling of a moving metal, such as strip steel, is carried out.

Sheet profiles with periodically repeating corrugations (profiles of high rigidity) are made by cold local deformation; Corrugated strips are straightened on straightening machines, containing rollers with calibers for the passage of corrugations, since straightening is carried out only on flat inter-corrugated sections of these strips before being cut to length.

A known method of straightening sheet metal, mostly boxy, in a multi-roller machine with an asymmetric arrangement of sectional support rollers along the length of the working roller barrel (see US Pat. There is also known a method of straightening a strip, in which, to improve the quality of straightening, the bending arrow of the strip with rollers and the value of its tension are selected depending on the yield strength and thickness of the metal (see AS USSR No. 1469660, class B 21 D 1/02, publ. 09.01.87).

A disadvantage of the known methods for straightening strip metal is their inapplicability for straightening corrugated strips with periodic corrugations.

The process of straightening sheet profiles with periodic (closed) corrugations has a number of features, due both to the geometry of these profiles and to the patterns of formation of closed corrugations. Their formation is carried out due to the local drawing of the metal in the deformation zone, and this zone, located in the middle of the strip width, receives metal both from the flat near-corrugation sections and (partially) from the near-edge sections of the workpiece.

As a result, an excess of metal is formed in the areas where the corrugations are located, which leads to the formation of waviness in the middle of the width of the corrugated strip, i.e. warping, and this worsens the performance of the profiles. Therefore, when straightening corrugated strips, only the near-edge sections of the strip are subjected to repeated bending with rollers in order to equalize their length with the middle part along the width of the workpiece due to stretching, or to make the stretching of these sections larger than that of the middle part.

The closest analogue to the claimed object is a method of editing the strip along.with. USSR No. 1532115, class. In 21 D 1/02, publ. in BI No. 48, 1989

This method includes multiple elastic-plastic alternating bending of the corrugated strip with its simultaneous transverse bending due to an increase in the deflection of the edge sections along the width of the strip in comparison with its middle part and is characterized by the fact that the deflection of the edge sections is greater by (3.18 ... 3. 22), where S is the strip thickness.

The disadvantage of the described straightening method is the increased wear of the straightening machine rollers.

Indeed, when dressing according to this method, the amount of overlap of all the rollers of the straightening machine (- see the drawing) is the same, i.e. the value f of the strip bending arrow remains constant in the course of its movement. But as the number of strip bends increases, so does its hardening (hardening), which inevitably increases the pressure of the metal on each subsequent roller of the machine. As a result, the wear of each such roller is greater than the previous one, and the maximum wear is on the last (in the direction of the strip) pair of rollers, which forces them to be replaced when the first rollers are operational.

The technical objective of the invention is to reduce the wear of the rollers of the straightening machine when straightening strips with periodically repeating longitudinal corrugations.

To solve this problem, with multiple elastic-plastic alternating buckling of a strip of thickness S with its simultaneous transverse bending due to an increase in the deflection of the edge sections along the width of the strip in comparison with its middle part, the deflection of the edge sections is made greater than that of the middle part of the strip, at the first bend by the value of a at each subsequent bend is less than at the previous one by a factor, where K = 3.48 ... 3.52 for strips with a tensile strength B> 465 MPa and K = 2.98 ... 3.02 - with B >465 MPa, and n - the number of bends of the strip during editing, while the value of the longitudinal bends is successively reduced in the course of editing from a given to zero.

The above mathematical relationships were obtained by processing experimental data and are empirical.

The essence of the proposed technical solution is to consistently reduce the values ​​of both transverse and longitudinal bends of the formed strip. In addition to reducing the load on the rollers of the straightening machine (see above), a decrease in the absolute value of the buckling (i.e., its arrow f) well corrects the waviness and warping of thin sheets (with S 4.9 mm; see V.F. Zotov and V .I.Elin “Cold rolling of metal” - M.: Metallurgiya, 1988, p.121), which should also include high rigidity profiles with a thickness of 2 ... 4.5 mm.

In addition, to ensure high-quality editing, the values ​​of the first transverse bends of the strip are taken somewhat larger (taking into account their subsequent decrease) than according to the known method of editing, taken as the closest analogue.

The proposed editing method can be implemented on the correct machine described in A.S. USSR No. 1532115, in which all the lower rollers are made of smooth cylindrical, and the upper ones - with circular grooves for passing the formed corrugations.

The editing scheme according to the claimed method is shown in the drawing (arrow - direction of movement of the strip, Roman numerals - serial numbers of bends); shows the editing of the middle part along the width of the strip.

The top 1 and bottom 2 rollers of the straightening machine are staggered, with each row of rollers - top and bottom - lying on the same axis: 1 1 and 2 2 .

The amount of overlap of the rollers decreases in the direction of the strip so that in the plane yy the value of the buckling of the strip f=0. The design of the upper rollers is chosen such that, simultaneously with the longitudinal bend shown in the drawing, there is also a transverse bend of the strip 3 with a maximum value at I bend and with a gradual decrease to its minimum value in the yy plane (V bend), where the straightened strip becomes almost flat .

The recommended values ​​and are chosen (experimentally - see below) so that the load on all rollers from the strip hardened at each bend is approximately the same, which ensures uniform wear of the rollers and prolongs their working campaign.

An experimental verification of the proposed method was carried out on a seven-roller straightening machine of a roll forming unit 1-5 × 300-1650 of the Magnitogorsk Iron and Steel Works, designed for the production of high rigidity sheet profiles with longitudinal closed corrugations, part of the assortment of which is given in the reference book, ed. I.S.Trishevsky “Bent rolled profiles”. - M.: "Metallurgy", 1980, p.230-231.

For this purpose, when straightening profiles made of steels 3, 10kp, 09G2 and 10KhNDP with a thickness of 2 ... 4.5 mm, the values ​​of the transverse bending of the strips were varied, i.e. the difference in the deflections of the edge sections and the middle part along the width of the strip. In the experiments, the quality of dressing was recorded (according to the non-flatness of the profiles) and the degree of wear of the rollers of the straightening machine.

The best results (wave height within 2... 8 mm and absence of cracks in the places of corrugation bending at the maximum duration of the working campaign of the rollers) were obtained by implementing the proposed method. Deviations from the recommended parameters worsened these indicators.

So, an increase to (3.53 ... 4.05) for steels with B> 465 MPa and up to (3.03 ... 3.60) for steels with B<465 МПа вызывали повышенный износ первых трех роликов машины, а на профилях из более прочной стали в отдельных случаях наблюдалось появление трещин у гофров. Уменьшение (ниже рекомендуемых величин) ухудшало геометрию полос (возрастала неплоскостность).

With a decrease in the difference in the values ​​of the transverse deflections of individual sections of the corrugated strips, mainly uneven wear of the rollers occurred with a reduction in their working campaign by 12 ... 45%.

Control editing using the technology according to the known method, taken as the closest analogue (see above), practically gave the same level of quality to the profiles, but the duration of the working campaign of the clips was reduced by almost 1.5 times.

Thus, experimental verification confirmed the acceptability of the proposed technical solution for the task and its advantages over the known object.

According to the Central Laboratory of Control of OAO MMK, the use of the found straightening method will extend the working campaign of the rollers of the straightening machine for straightening high rigidity profiles by at least 1.5 times with a corresponding reduction in production costs.

Example of a specific implementation

1. A corrugated strip with a thickness of S = 2 mm made of steel with B> 465 MPa is corrected with n = 5 (i.e. in a seven-roller straightening machine - see the drawing). The amount of overlap decreases successively from 1.9 mm to 0.

Edit options:

SUBSTANCE: group of inventions relates to the field of metal forming and can be used for straightening a metal strip with a thickness of ≤1 mm. Between sets of braking and pulling rollers, a tensile stress is created in the metal strip, amounting to at least 70% of the yield strength. In at least one group of a plurality of regular rollers, the longitudinal curvature is corrected by alternating bending. At the same time, the diameter of the straightening rollers allows the strip to follow the curvature of the straightening rollers at the selected tension. Moreover, their diameter increases within the group from roller to roller. The longitudinal curvature decreases and the flatness of the strip increases. 2 n. and 18 z.p. f-ly, 3 ill.

The invention relates to a method for straightening a metal strip, in particular a thin metal strip up to 1 mm thick, in which a tensile stress of at least 70% of the yield strength is created in the metal strip between sets of braking and pulling rollers, and the strip is straightened between sets of braking and pulling rollers. and pull rollers in a group of a plurality of correct rollers. For the purposes of the invention, a metal strip is understood in particular to mean a thin metal strip with a thickness of 0.02-1.0 mm, preferably 0.05-0.5 mm.

The aim of straightening a metal strip is to make the strip as flat as possible. At the same time, in practice, a distinction is made, in principle, different types strip irregularities. In addition to waviness and crescent, which are explained by the difference in length over the width of the strip, curvature often occurs, and a distinction is made between longitudinal curvature and transverse curvature. The straightening of the strips often takes place using tension, for example by stretching or bending-tensile straightening.

Thus, stretching installations are known in which a tensile stress is applied between sets of brake and pulling rollers, as a result of which the required stretching is achieved for the desired stretching. During the drawing process, the plastic elongation of the respective strip is obtained from the reduction in thickness and width of the strip. For example, a method is known for continuously drawing thin strips, in particular metal strips made of steel, aluminum, etc., with a thickness of 0.05-0.5 mm, in which the strip in a pair of drawing rollers located between sets of braking and pulling rollers is subjected to stretching required for its stretching in the plastic region. In this case, with the help of a pair of drawing rollers, 5-25% tension is created for plastic stretching, and with the help of sets of braking and pulling rollers, 75-95% stretching is created for elastic or partially plastic stretching of the strip. At the same time, the diameter of the draw rollers is 1500 times larger. maximum thickness stripes (DE 3912676 C2).

With the help of stretching, it is possible in practice to achieve a high flatness and eliminate, in particular, waviness and crescent. Since, however, during drawing, the strip usually finds itself in the plastic region on the last tension roller, a significant longitudinal curvature often remains in the strip during drawing, which corresponds to the diameter of the tension roller, minus the elastic pressing. However, it is possible to eliminate this longitudinal curvature, for example, in the range low voltage stretching, by means of an adjustable corrective roller. However, for thin strips, the required corrector roller diameter is very small to provide partially plastic counterbending. Therefore, it is often necessary to support such a flexural straightening roller in a support roller cassette against deflection. In high speed installations, these rollers are prone to vibrations and can cause unwanted ripples on the strip surface. Vibrations can be sufficiently damped by the sprayed liquid, but in this case it must be removed again in the strip cleaning process, which is associated with increased equipment and operating costs. In addition, the position of the correction roller has to be readjusted for each strip thickness/strip material combination.

Alternatively, the strips are often straightened in practice during the tensile bending straightening process. In this case, the strip bends around certain number straightening rollers of small diameter and, by superimposing bending and stretching, is plastically elongated by an elongation factor so that waviness is (approximately) eliminated.

While the first straightening rollers mainly create the elongation ratio, the last straightening rollers serve mainly to correct curvature. On the first correct rollers, the strip accepts or does not accept the diameter of the rollers, depending on the tension, the diameter of the rollers and the wrapping angle. However, on the last correct rollers, the strip does not take their diameter, since for different strips it is necessary to set the optimal radii of curvature according to the wrapping angle accordingly. For this reason, at least the last correct rollers are set differently for different strips. In practice, this often leads to high costs when commissioning. Otherwise, the relatively small diameters of the rollers are also disadvantageous. Due to the bending and small diameters of the rollers, the strip has relatively high residual stresses in its thickness, which may be undesirable during further processing. In the case of thin strips, a large number of straightening rollers are required in order to eliminate the longitudinal permanent curvature to the desired extent.

From EP 0790870 B1 a device for straightening metal strips is known, in which between sets of braking and pulling rollers there is a bending-tensile stand, a correcting roller device and a multi-roller straightening block. The latter contains a large number of working rollers supported on support rollers. All working rollers of the bending-tensile stand, the corrective roller device and the multi-roller straightening block rotate due to friction between them and the strip, i.e. they are not rotated. In a multi-roller straightening block, the diameters of the working rollers can increase from roller to roller. However, the diameters, as is common in multi-roller or tensile bend straightening, are relatively small. This known installation provides for setting the position of the correct rollers and, therefore, the immersion depth depending on the properties of the strip.

Known methods (for example, bending-tensile straightening, on the one hand, and stretching, on the other hand) are also combined with each other. Thus, a method is known for continuously straightening thin metal strips, which, on the one hand, involves stretching, and on the other hand, bending-tensile straightening (DE 19509067 A1).

From US 6240762 B1, a method is known for straightening a metal strip in a bending-tensile straightening or drawing process, after which the straightening process is carried out in a roller straightening block at low stretch of the strip.

Finally, EP 1311354 B1 describes a method and apparatus for stretch straightening a metal strip, wherein it passes through sets of brake and pull rollers and is stretched between both sets during its drawing, and in an additional set of rollers located between the sets of brake and pull rollers to increase the coefficient hoods - bending in tension. In this case, with the help of this additional set of rollers, the main part of the stretching is carried out. The traction rollers of the intermediate roller set may have a different diameter than the rollers of the braking and traction roller sets. In this case, the inner drive rollers of this central set of rollers can have a smaller diameter compared to the rollers of the brake and drive roller sets.

The invention is based on the problem of providing a method for straightening a metal strip, in particular a thin metal strip, with which strips of high flatness and, in addition, less longitudinal curvature with low residual stresses can be economically obtained. In addition, an installation must be created to implement this method.

This problem is solved by a method of straightening a metal strip, in particular a thin metal strip, with a thickness of ≤1 mm, in which a tensile stress below the yield strength of at least 70% of the yield strength is applied to the metal strip between sets of braking and pulling rollers, and the strip is straightened in the process of bending-tensile straightening and/or drawing, between sets of braking and pulling rollers, in at least one group of several straightening rollers, the longitudinal curvature is corrected or eliminated by bending and predominantly alternating bending, the diameter of the straightening rollers and the wrapping angle are so large, that the strip at the selected tension follows the curvature of the straightening rollers or takes the curvature of the straightening rollers, and the diameter increases from the straightening roller to the straightening roller in the direction of the strip movement.

The longitudinal curvature is corrected in the intermediate group of leveling rollers, mainly by alternating bending of the strip exclusively around the leveling rollers. large diameter and with sufficiently large wrapping so that the strip takes on the curvature of the rollers. Because the strip follows the curvature of the rollers, adjusting the plunging depth has no effect on the dressing result. Therefore, within the scope of the invention, particular attention has been paid to ensuring that the position of the straightening rollers and thus the immersion depth of one straightening roller between two adjacent straightening rollers of a group is firmly set and does not change during strip straightening and/or when straightening strips of different thicknesses.

Surprisingly, the proposed method makes it possible to cost-effectively obtain flat strips of minimal longitudinal curvature with low residual stresses. The risk of ripples is prevented without the need for spray liquids. Of particular importance is the fact that within the group of straightening rollers, between the sets of pulling and braking rollers, several straightening rollers of a relatively large diameter are provided, namely such that, with the selected stretching of the strip, it follows the curvature of the straightening rollers, namely without the need to change the installation of the rollers. depending on strip thicknesses and strength ranges. With a suitable number of straightening rollers and hence curvature-correcting rollers of suitable diameters, and in particular with a suitable diameter gradation, strips of very low longitudinal permanent curvature can be obtained. The choice of the number of correct rollers and their diameters, as well as the gradation of diameters, can be carried out depending on the specified tolerance for longitudinal curvature, for example, k=1/R=±0.001. The required number of straightening rollers and the optimum gradation of predominantly successively increasing roller diameters depend on the minimum strip thickness at maximum yield strength. The straightening roller group comprises, for example, three, preferably at least four straightening rollers, particularly preferably five or more straightening rollers, the diameters within such a group increasing from roller to roller. This leads to the fact that the curvature of the strip from roller to roller decreases, resulting in a successive decrease in the longitudinal curvature. All leveling rollers advantageously have a diameter of at least 500 times, for example at least 1000 times the thickness of the strip to be straightened, and advantageously also the maximum thickness of the strip to be straightened in such an installation. The tensile stress between the brake and drive roller sets is advantageously set to at least 75%, particularly preferably at least 85% of the yield strength. In this case, it may be appropriate to set the tensile stress to a value of 90% of the yield strength or more. Tensile stress can be below the yield strength, as well as in the range of the yield strength or above the yield strength. For the purposes of the invention, yield strength is understood to be the yield strength or plastic elongation R p0.2 , i.e. stress in a pure tensile test at which the plastic elongation is 0.2%. Therefore, within the scope of the invention, the straightening of the strip between sets of braking and pulling rollers takes place by means of plastic elongation, for example stretching and/or stretching with bending, the curvature being corrected, however, by alternating bending around the straightening rollers of the group.

The diameter of the correct rollers of the group increases from roller to roller, preferably by a factor of 1.05-1.5, particularly preferably by a factor of 1.15-1.3. At the same time, within the group of correct rollers, it is possible to work with a constant or variable coefficient.

Compared to conventional stretching, strips of substantially lower longitudinal curvature are always obtained. The resulting residual stresses across the strip width are noticeably lower than the residual stresses that can be achieved by bending-tensile straightening.

The number of straightening rollers or curvature correcting rollers and the gradation of their diameters are calculated particularly preferably on the basis of a mathematical model which takes into account as input parameters the thickness or thickness range of the strip, modulus of elasticity, Poisson's ratio, stress-strain curves, required elongation ratio to eliminate waviness, expected fluctuations in stretch or stretch ratio of the strip, expected fluctuations in strength (within the product), expected fluctuations in strip thickness (within the product) and/or the value of the maximum allowable longitudinal residual curvature. The mathematical model then calculates for the various strips, based on the configuration of the rollers, the required strip tensile stresses and the resulting longitudinal permanent curvature. The necessary number of rollers for correcting curvature and the optimal gradation of roller diameters depend on the minimum strip thickness at which a certain longitudinal residual curvature must still lie within the tolerance. Of particular importance is the fact that such a calculation on the basis of a mathematical model can be carried out for certain ranges and that then during commissioning and, in particular, also during operation, it is no longer necessary to change the parameters and, in particular, change the immersion depth of the correct rollers. On the contrary, the invention proposes that the position of the leveling rollers and, consequently, the depth of their immersion between two adjacent straightening rollers within their group in the installation is fixed and does not change, in particular during straightening, but also when changing the strip material and/or strip thickness. By appropriately adapting the relatively large diameters of the rollers, with the metal strip taking on the curvature of these rollers, strips with a certain thickness range and thus also strips of different thicknesses can be straightened with excellent results with a single fixed configuration. Even if the position of the straightening rollers and, consequently, the immersion depth is firmly set and, therefore, the dressing is carried out with a fixed configuration, this does not exclude within the scope of the invention that it is technologically possible to “open” a group of straightening rollers and, therefore, push them apart, to (temporarily) pass the strip through it without bending, for example, when a junction between the beginning and end of the strip is passed through the installation (for example, a weld). All straightening rollers are then brought back into a fixed or fixed configuration in which the strips are machined in the desired thickness range without further adjustment.

Within the scope of the invention, only one set of straightening rollers is provided between the sets of brake and traction rollers, in which the diameters increase from roller to roller, so that, consequently, all the rollers of the group have different diameters. However, the invention also includes embodiments where, within such a group of increasing roller diameters, (each) two adjacent rollers have the same diameter. In addition, within the scope of the invention, there are one or more additional straightening rollers before and/or behind the group of straightening rollers. Thus, for example, it may be expedient if, in front of the group of leveling rollers, there are one or more additional leveling rollers, and their diameter is preferably less than or equal to the diameter of the first leveling roller of the group. Preferably, however, the diameter of these additional leveling rollers is chosen to correspond to at least 500 times the (minimum) strip thickness. These additional leveling rollers can also be located between the braking and traction roller sets. However, the invention also includes variants in which the strip is processed in several zones, for example several stretching zones, whereby, therefore, several sets of tension rollers are arranged one behind the other to form several processing zones, for example, drawing zones. The proposed group of correct rollers to eliminate longitudinal curvature is in this case always located in the last processing zone, for example the last stretching zone. After the curvature has been corrected by means of the straightening rollers, therefore, no further deformation occurs, so that the final result of the straightened and, moreover, devoid of longitudinal curvature of the strip is retained.

Within the scope of the invention, all correct rollers of a group are not driven. However, the invention also includes variants in which one, several or all of the correct rollers of the group are driven into rotation. This possibility arises, for example, when (very) large regular rollers with large inertial moments are used. The drive of one or more straightening rollers then makes it possible, in particular, to avoid slippage when the plant is started up.

The subject of the invention is also a plant for straightening a metal strip, in particular a thin metal strip with a thickness of ≤1 mm, in the manner described above. Such an installation contains at least one set of braking rollers and one set of pulling rollers, as well as at least one group of several correct rollers located between the sets of braking and pulling rollers. The diameter of the straightening rollers within a group increases from roller to roller in the direction of the strip movement. The diameter of the straightening rollers is at least 500 times and preferably at least 1000 times the (minimum) strip thickness. The diameter of the correct rollers within the group increases from roller to roller by a factor of 1.05-1.5, preferably 1.15-1.3. In practice, for example, regular rollers with a diameter of 100-2000 mm, for example 200-1600 mm, preferably 300-1500 mm, can be used in the group.

The invention is illustrated in more detail by the drawings, which show the following:

figure 1 - installation for editing a metal strip by the proposed method;

figure 2 is a modified version of the object of figure 1;

3 is a fragment of another preferred embodiment of the invention.

The figures show an installation for straightening a metal strip, in particular a thin strip 1 with a thickness of ≤1 mm. Such an installation contains in its fundamental design a set of 2 braking and a set of 3 pulling rollers. In this example, set 2 contains only one pair of rollers, ie. two braking rollers 2.1, 2.2, and set 3 - also only one pair of rollers, i.e. two pull rollers 3.1, 3.2. It should be noted that the invention also includes variants with sets of a larger number of tension rollers, for example four or six rollers. With these sets 2, 3 tension rollers in the metal strip 1 creates a tension or tensile stress of at least 75%, preferably at least 90% of the yield strength. Between sets 2, 3 within the framework of the invention is a group 4 of the correct rollers 4.1-4.7. In this group 4, the longitudinal curvature of the strip is eliminated due to alternating bending. In this case, the diameter D1-D7 of the rollers of the group 4 is relatively large, namely so large that the strip 1 follows the curvature of all these regular rollers within the group under the selected tension. Figure 1 shows that the diameter D1-D7 of the straightening rollers 4.1-4.7 of the group 4 increases from roller to roller in the direction R of the strip and therefore becomes larger. In this example, group 4 contains seven regular rollers, the diameter D1-D7 increasing from roller to roller by a factor of about 1.25. In this case, the position of the correct rollers 4.1-4.7 inside the installation is firmly set. Regulation of the position or depth of immersion is not provided within the scope of the invention. On the contrary, due to a one-time calculation of the parameters, it is possible to perfectly straighten with a small residual longitudinal curvature for strips of different thicknesses without the need to adjust the immersion depth of the individual rollers.

While figure 1 shows the first option, in which between the set 2 of the braking and the set 3 of the pulling rollers there is only a group of 4 correct rollers, figure 2 shows a modified version in which in front of the group 4 of the correct rollers 4.1-4.6 there are additional rollers 5.1-5.3. Their diameter D" corresponds to the diameter D1 of the first straight roller of group 4.

Figure 3 shows a variant in which additional regular rollers 5.1-5.4 are located in front of the correct rollers 4.1-4.7 of group 4. They have a relatively small diameter D" and form, as it were, flexural-tensile rollers. For this reason, each of the rollers 5.1-5.4 is supported by supporting rollers 6. In this embodiment, in front of the group of straightening rollers, there is, therefore, a group of flexural-tensile rollers 5.1-5.4. Sets of braking and pulling rollers in figure 3 are not shown.

The wrapping angles can be adjusted in practice, if necessary, (substantially) larger than shown in the figures. Wrapping angles of up to 180° or even more are useful. In this respect, the first roller 3.1 of the set 3 can be (at the same time) an integral part of the group 4 and therefore also participate in the plastic deformation of the strip due to bending.

1. A method for straightening a thin metal strip with a thickness of ≤1 mm, which includes creating a tensile stress in the metal strip between sets of braking and pulling rollers, amounting to at least 70% of the yield strength, and straightening the strip by bending-tensile straightening and/or drawing using a set of correct rollers, and between sets of braking and pulling rollers, at least one group of a plurality of regular rollers, the longitudinal curvature of a thin metal strip is corrected by bending it, while regular rollers are used, the diameter of which allows the strip to follow their curvature at the selected tension, and the diameter of the regular rollers in within the group increases in the direction of the strip from roller to roller.

2. The method according to claim 1, characterized in that the position of the straightening rollers and, consequently, the immersion depth of one straightening roller between two adjacent straightening rollers of the group is fixed and does not change during straightening of the strip and/or strips of different thickness.

3. Method according to claim 1 or 2, characterized in that the group of leveling rollers comprises at least three leveling rollers, preferably at least four leveling rollers, particularly preferably at least five leveling rollers with increasing diameter from roller to roller.

4. Method according to claim 1 or 2, characterized in that the diameter of the straightening rollers is at least 500 times, preferably at least 1000 times the thickness of the strip to be straightened.

5. Method according to claim 1 or 2, characterized in that the tensile stress is at least 75%, preferably at least 85%, for example at least 90% of the yield strength.

6. The method according to claim 1 or 2, characterized in that the diameter of the group of straightening rollers increases from roller to roller by a factor from 1.05 to 1.5.

7. The method according to claim 6, characterized in that the diameter of the correct rollers of the group increases from roller to roller by a factor from 1.15 to 1.3.

8. The method according to claim 1 or 2, characterized in that the number of regular rollers of the group and the gradation of their diameters are calculated on the basis of a mathematical model that takes into account as input parameters the thickness or range of thicknesses of the strip, the modulus of elasticity, Poisson's ratio, stress-strain curves , the required stretch ratio to eliminate waviness, the expected variation in stretch or stretch ratio of the strip, the expected variation in strength, the expected variation in strip thickness, and/or the value of the maximum allowable longitudinal residual curvature.

9. Method according to claim 1 or 2, characterized in that the thickness of the straightened strip is 0.02-1.0 mm, for example 0.05-0.5 mm.

10. The method according to claim 1 or 2, characterized in that one or more additional straightening rollers are installed before and/or behind the group of straightening rollers.

11. Method according to claim 10, characterized in that the diameter of the additional straightening rollers is less than or equal to the diameter of the first straightening roller of the group.

12. Method according to claim 1 or 2, characterized in that one, a plurality or all of the regular rollers of the group are driven or not driven.

13. Installation for straightening a metal strip (1), in particular a thin metal strip with a thickness of ≤1 mm, in accordance with the method according to any one of claims 1 to 12, containing at least one set (2) of brake rollers and one set (3 ) pulling rollers and at least one group (4) located between sets (2, 3) of a plurality of correct rollers (4.1-4.7), moreover, the diameter (D1-D7) of correct rollers (4.1-4.7) allows the strip (1) to the selected tension follows the curvature of the straightening rollers (4.1-4.7), with their diameter (D1-D7) increasing from roller to roller in the direction (R) of the strip movement.

14. Installation according to claim 13, characterized in that the position of the correct rollers (4.1-4.7) and, consequently, the depth of immersion of one correct roller between two adjacent correct rollers of the group (4) are fixed.

15. Installation according to claim 13 or 14, characterized in that the group (4) contains at least three rollers, preferably at least four rollers, particularly preferably at least five rollers with a diameter increasing from roller to roller (D1-D7 ).

16. Installation according to claim 13 or 14, characterized in that the diameter (D1-D7) of the straightening rollers of group (4) is at least 500 times, preferably at least 1000 times the thickness of the strip to be straightened.

17. Installation according to claim 13 or 14, characterized in that the diameter (D1-D7) of the correct rollers (4.1-4.7) of group (4) increases from roller to roller by a factor from 1.05 to 1.5, preferably from 1 .15 to 1.3.

18. Installation according to claim 13 or 14, characterized in that one or more additional straightening rollers (5.1-5.3) are located in front of and/or behind the group (4) of straightening rollers.

19. Installation according to claim 13 or 14, characterized in that it is made with a plurality of processing zones, for example, one or more stretching zones and / or one or more bending-tensile zones, while the group (4) of straightening rollers is located in the last zone processing, for example in the last stretching zone, or forms the last processing zone.

20. Installation according to claim 13 or 14, characterized in that one, a plurality or all of the correct rollers of the group are made driven or not driven in rotation.

The invention relates to the field of metal forming, in particular to devices for turning over a straightening machine, containing a plurality of rolls spaced from each other and mounted for rotation on the chassis, and means for attaching it to the turning device. The turning device comprises two posts extending vertically from the plinth, means for holding and fastening the leveling machine, designed to interact with the means for fastening the straightening machine, while the holding and fastening means are located between the posts, the drive means for rotating the holding and fastening means around a horizontal axis between the first a position in which, when the straightening apparatus is connected to the turning device, the rolls of the straightening apparatus are directed downwards, and a second position, in which, when the straightening apparatus is connected to the turning device, the rolls of the straightening apparatus are directed upwards, driving means for vertical translation of the holding and fastening means. In this case, each drive means is connected to one of the racks. Simplified construction. 17 w.p. f-ly, 7 ill.

The invention relates to the processing of metals by pressure and can be used for straightening rolled strip. A plurality of vertical beams extend from the fixed lower support and are connected to the fixed upper support. Beams are located on both sides of the longitudinal axis of the strip. The lower straightening stand is stationary during operation and rests on a fixed support. The upper straightening stand is fixed on the upper support with the possibility of moving with the help of means of movement in relation to the fixed upper support between the rest position and the straightening position, in which the strip is provided with an undulating path of movement. In this case, each stand contains a plurality of rolls spaced from each other and mounted for rotation in support bearings with axes perpendicular to the longitudinal axis of movement of the rolled product. The deflection of the right stands is compensated. 2 n. and 17 z.p. f-ly, 5 ill.

The invention relates to the field of metal forming and can be used for straightening long parts reinforced with ribs. The straightening of the reinforced parts is carried out by successive compression of the ribs and web of the reinforced part by rollers when calculating the compression force of the rollers and their area of ​​​​impact, depending on the deflection of the part in two perpendicular planes and angles of twisting of the cross sections of the part. Straightening is carried out using a device made in the form of a set of rollers, the bodies of which are in the form of crimped elements in the form of brackets, crimping rollers are installed at the ends of the brackets, while one of the rollers is equipped with a drive shaft, and the second with a micrometric loading mechanism. At the same time, movable stops are installed on the body of each bracket to adjust the position of the rollers on the crimped element. The quality of long parts reinforced with ribs is improved. 3 n.p. f-ly, 4 ill.

The invention relates to the field of metal forming and can be used for flat tensile testing of sheet materials with the possibility of eliminating transverse deformations. Clamps for fixing the transverse edges of the sheet material are made in the form of transverse guide beams and clamping bars, fixedly fixed on sheet material and on the guide beams, which ensures the retention of the sheet and prevents its transverse deformation. 1 ill.

The invention relates to a method for straightening a metal strip, in particular a thin metal strip up to 1 mm thick, in which a tensile stress of at least 70 times the yield strength is created in the metal strip between sets of braking and pulling rollers, and the strip is straightened between sets of braking and pulling rollers. pulling rollers in a group of many correct rollers

RECOVERY OF PARTS BY EDIT

During operation, many machine parts (shafts, axles, levers, beams) and elements of metal structures receive residual deformations in the form of bending, twisting, warping, dents. To eliminate these defects, straightening by mechanical, thermomechanical and thermal methods is used.

mechanical straighteningproduced by applying a load to a deformed object or hardening. In the first case, it is performed in a cold state or with heating. In a cold state, shafts with a diameter of up to 200 mm are corrected, if the deflection does not exceed 1 mm per 1 m of the shaft length. For dressing, the shaft 4 is mounted on prisms or supports 5 of a screw or hydraulic press with the convex side up and it is acted upon by the press rod 3 through the gasket 2 made of non-ferrous alloy so that the shaft bends in the opposite direction by the value f 1 >f. The accuracy of editing is controlled by indicator 1.

Disadvantages of dressing without heating - this is the danger of returning the part to a deformed state, reducing its fatigue strength and bearing capacity. The first drawback is due to the fact that during cold dressing, significant unbalanced residual stresses arise in the part, which, as a result of their redistribution over time, return the part to a warped state.

The decrease in fatigue strength, which can reach 1540%, occurs due to the formation of zones with tensile stresses in the surface layer of the part.

To improve the quality of cold straightening, the following methods are used:

exposure of the part under pressure for a long time;

carrying out editing in two stages, when, eliminating the deflection of the part, at the first stage it is bent in the opposite direction, and at the second, editing is carried out in the opposite direction;

stabilization of the state of the part after straightening by subsequent heat treatment (heating to a temperature of 400450 °C with holding at it for 0.51 h). In each specific case, the heating temperature is assigned depending on the amount of deformation, the material of the part and the type of its heat treatment during manufacture, as well as in preparation for restoration.

The latter method gives the best results, but when heated, there may be a danger of damaging the heat treatment of the part, in addition, it is more expensive than the first two.

Straightening with heating (thermomechanical straightening method)) subject parts with significant deformations, for example, for shafts with a deflection of more than 8 mm per 1 m of its length. The method differs in that before applying an external force, the part is uniformly heated over the entire deformed section. Heating is carried out gas burners up to the annealing temperature (750800 °C). After straightening, the part is subjected to heat treatment to obtain the necessary structure and mechanical properties of the metal.

Straightening with local heating (thermal straightening method)) is based on the use of internal stresses arising from such heating of the part. If a part of a significant mass is subjected to rapid local heating to a temperature of 800900 ° C at the place of the greatest deflection on the convex side, then the metal in the heating zone, not being able to expand freely, receives a plastic compression deformation. With the subsequent cooling of the heated area, the volume of the metal decreases even more, as a result of which tensile stresses arise, causing the part to straighten. The effectiveness of this dressing method is increased by fixing the ends of the part.

Large shafts and thick sheet material are corrected in this way.

Editing by local hardening (chasing) is based on the action of the residual internal compressive stresses arising from it, which cause a stable deformation of the part.

For dressing in this way, the concave section of the surface of the part is riveted pneumatically or hand hammer with a spherical head. The choice of the site and the degree of hardening is made taking into account the place of the bend and its area.

Hardening does not have the disadvantages inherent in pressure straightening. Its main advantages are: high straightening accuracy (up to 0.02 mm) and stability over time; no noticeable decrease in fatigue strength; the possibility of editing due to riveting of unloaded parts of the part.

Straightening and straightening without heatingused if the wall thickness of the parts does not exceed 1 mm. Produce first preliminary alignment parts knocking out dents to the level of an undamaged surface, and then final leveling straightening. The accuracy of editing is controlled tactilely and visually, as well as by templates.

RESTORATION OF MACHINE PARTS BY WELDING AND SURFACE

General information

Three types are used in repair welding work welding, surfacing and welding. The main purpose of welding is to restore the integrity of a part, to create permanent connections between parts of one part or different parts. Welding is the process of applying a layer of metal to the surface of a part. In the repair industry, it is used to create an allowance for further processing on the outer and inner surfaces of worn parts in order to restore their original shape and size. It is also used in the manufacture of new parts, such as plain bearings. In repair production, surfacing is effective due to the fact that the restored part is often not only cheaper than a new part, but also does not concede, and sometimes even surpasses it in performance due to the properties of the surfacing layer. Wear resistance, chemical resistance and other necessary properties of the deposited surfaces are usually provided by alloying directly in the surfacing process. Welding eliminates cracks, holes and other defects to restore the integrity and tightness of parts.

Types of welding . From a physical point of view, welding is the process of the formation of interatomic bonds between the materials being welded as a result of their melting or plastic deformation in the contact zone and the formation of a weld. Welding allows you to connect homogeneous and dissimilar metals and alloys, metals with some non-metallic materials(ceramics, glass) and plastics. In the repair industry, welding is mainly used to restore the integrity of products (eliminate breaks, tears and other damage), fix additional repair parts, strengthen metal structures by installing additional brackets, linings, etc., as well as for technological purposes to temporarily fix the relative position structural elements, etc. The main types of welding used in repair production are given in Table. 4.1.

Table 4.1

Varieties and technical capabilities welding methods.

The conditions necessary for the formation of metallic bonds can be created by thermal, mechanical or thermomechanical effects on materials in the welding zone. In accordance with the type of energy impact, welding methods are distinguished: melting (thermal), pressure (mechanical) and thermomechanical.

Fusion weldingis carried out without applying an external mechanical load due to fusion either only of the edges of the parts to be joined, or with the addition of filler material (arc, gas, plasma, electroslag, electron beam, laser and other types of welding). The filler material is used in the form of electrodes, rods, wires, tapes, mixtures of powders, etc.

At pressure weldingmetallic bonds between the welded materials are provided due to their plastic deformation at a temperature below the melting point. Based on this principle different kinds welding: cold, ultrasonic, diffusion, explosion, etc. To reduce the deformation force, except for mechanical impact, the parts to be joined are heated (by passing an electric current or due to friction between them) until the materials being welded are brought into a plastic state. Thermomechanical types of welding are based on this, for example, electrocontact, resistance (flash), high-frequency, diffusion, friction welding.

In the repair industry, thermal types of welding are usually used. The most commonly used heat sources are: electric arc (electric arc or electrothermal welding), electric current (induction, electroslag), gas flame (thermal gas welding), plasma (plasma welding), less often laser radiation (laser welding), electron energy (electronic beam welding), etc.

According to the degree of automation, manual and mechanized types of welding (surfacing) are distinguished. Mechanized include automatic and semi-automatic methods of welding and surfacing. With automated methods, the supply of welding materials, the movement of the welding arc along the seam, as well as its excitation and maintenance of combustion are mechanized. With semi-automatic methods, the supply of electrode wire and auxiliary materials is mechanized.

Main advantages of mechanized methodscompared to manual are: more high quality welding work due to the stability of the technological process, increasing labor productivity and reducing the cost of restoring parts, lower requirements for the qualifications of workers.

Most widely mechanized methods welding and surfacing are used to restore parts such as bodies of revolution.

The choice of a welding method that is rational for specific repair conditions depends on the technical, economic and organizational conditions of production and operational requirements for the repaired part.

Defects in welding and surfacing and measures to combat them. High temperature in the welding zone causes harmful processes: metal oxidation, burnout and spattering of alloying elements, saturation of the deposited metal with nitrogen and hydrogen, etc. As a result, structural changes occur in the metal, its plasticity decreases, internal tensile stresses are formed, which can cause warping of parts and the formation of cracks in them.

Oxidation and burnout of alloying elements(carbon, manganese, silicon, etc.) occurs as a result of the interaction of molten metal with atmospheric oxygen. In addition, in the absence of reliable protection, nitrogen can enter the welding zone from the air, which worsens the ductility of the metal. Therefore, reliable protection of molten metal is essential condition quality welding.

To fulfill this condition, special coatings (coatings) of electrodes and fluxes are used, during the melting of which a gas shell and slag are formed, which protect the metal from interaction with the environment. The type of welding when flux is used for protection is called submerged arc welding. To protect the welding zone, a gaseous medium is often used (welding in carbon dioxide, argon, etc.).

The applied electrode coatings and fluxes should be as dehydrated as possible by thorough drying, since the moisture contained in them is a source of hydrogen saturation of the metal. If it is present, the porosity of the deposited metal and residual internal stresses increase.

Splashing of liquid metal during weldingoccurs due to the release of carbon dioxide and carbon monoxide. Metal loss is reduced by using low carbon electrodes, flux cored electrodes, thorough cleaning welded surfaces from oxides and the introduction of deoxidizing elements (manganese, silicon) into electrode coatings and fluxes. Spatter is also reduced when the end of the electrode is oscillating by applying a magnetic field to the welding zone.

Structural changes in the metal being weldedare mainly due to uneven heating of the part in the near-weld zone (heat-affected zone) and cause deterioration of the mechanical properties of the metal in this zone. The dimensions of the heat-affected zone depend on chemical composition welded metal, method and mode of welding and, for example, with electric arc welding are 35 mm, and with gas 2530 mm. An increase in the welding current (power of the gas flame) leads to an expansion of the heat-affected zone, and the welding speed leads to its decrease.

Due to uneven heating and structural transformations, internal stresses arise in the heat-affected zone. If they exceed the yield strength of the material, then the part is deformed. Structural changes and internal stresses can cause hot cracks at high temperatures (for carbon steels 12001350 °C), and cold cracks at temperatures below 400 °C.

hot cracks are a consequence of elastic-plastic deformation during solidification of the metal under the action of tensile stresses. Effective measures to combat this phenomenon are the preheating of the base metal, the rational welding mode and the sequence of applying individual sections of the seam. The heating temperature, depending on the chemical composition of the deposited metal and the design of the part, can be 150700 °C. Chemical elements that increase the strength of the weld and prevent the formation of hot cracks are manganese, nickel and chromium, and harmful impurities in the weld metal carbon silicon, phosphorus, sulfur, hydrogen.

cold cracksare hardened and brittle. Hardening cracks occur in medium- and high-carbon steels at the fusion line of the weld with the base metal and are caused by a stress drop. The probability of formation of hardening cracks decreases with a decrease in the strength of the welding current and an increase in the deposition rate. The danger of brittle cracks is that, having arisen in the deposited layer, they propagate into the base metal. To prevent their formation, preheating of the part and its slow cooling after welding are used.

Typical defect weld is porosity , due to the formation in the liquid metal or the entry into it from the outside of bubbles of various gases (nitrogen, carbon dioxide, hydrogen, etc.). Porosity reduction is achieved by: slowing down the process of cooling the welding site, which facilitates the release of gas bubbles; reliable protection electric arc from air; release of the weld pool from nitrogen and hydrogen by converting them into compounds that turn into slag; application rational regime welding.

At wrong mode welding, the following defects are also possible: molten metal flows that occur at a high melting rate of the electrode material or insufficient temperature of the part; undercooking poor-quality fusion of the electrode and base materials; burnout unacceptable oxidation of molten metal, etc.

The quality of welded joints during thermal welding significantly depends on the weldability of materials, which is characterized by their tendency to form welding defects (cracks, pores, etc.). On this basis, materials are divided into good, satisfactory, limited and poorly welded. Due to defects, the physical and mechanical properties of welded joints can differ significantly from the properties of the materials being welded.

Types and technology of surfacing.

Surfacing restores up to 75% of all worn parts of machines and mechanisms.

The availability of this method for any enterprise, the simplicity of the process and equipment, the ability to provide the required physical and mechanical properties deposited metal provided him with a wide application. At the same time, surfacing has the same drawbacks as welding: a change in the structure of the base metal, the occurrence of internal stresses in parts and their deformation, etc.

Depending on the material of the repaired part and the operational requirements for it, the following surfacing materials are used: steels (carbon, alloyed); iron-based alloys (high-chromium cast irons, alloys with alloying elements); alloys based on nickel and cobalt; carbide alloys (with tungsten or chromium carbide); copper alloys; powder materials, The main surfacing methods used in repair production are shown in the table.

Varieties and purpose of surfacing methods

According to the degree of mechanization of the process, manual and mechanized surfacing is distinguished.

Manual arc surfacingthe simplest and most common method in the repair industry. It is performed with a short arc at a minimum welding current.

From mechanized methodswhen repairing, semi-automatic and automatic surfacing under a flux layer, in a shielding gas environment, vibro-arc surfacing are more often used, which at the same time provide an increase in productivity and quality of surfacing works

Electroslag welding, which is carried out due to the passage of electric current through the molten slag, is used for a large amount of surfacing work and the thickness of the deposited layer is more than 5 mm.

It is characterized by high productivity and quality of the deposited layer, its low tendency to form cracks and pores.

Increasingly, in the restoration and manufacture of machine parts, for example, plain bearings, surfacing based oninduction heatingfiller material with high frequency currents. The filler material may be a mixture of powders in a loose or compressed state, a cast ring, etc.

Arc surfacing with a non-consumable electrodeused mainly for hard granular and powder alloys. Arc surfacing with a tungsten electrode in shielding gases (argon) is performed using cast filler rods (usually from nickel and cobalt alloys). In this way, a very small depth of penetration and thin deposited layers are obtained.

There are many types of hardfacing using gas flame, plasma arc using flux-cored wire and plate electrode.

Recently, the use oflaser claddingto give certain properties to the working surfaces of new and restored parts. Local thermal effects, minimal mixing of the weld and base metals, and minor deformations of the repaired parts are significant advantages of laser cladding.

The disadvantage of hardfacing methodsis the presence, as a rule, in the surface layer of the restored parts of tensile residual stresses, which can cause cracks, distortion of the shape of the deposited parts, and a decrease in their fatigue strength. To exclude this, heating of parts before surfacing is used, as well as subsequent processing of the deposited layer by surface plastic deformation.

From a technological point of view, the surfacing of parts made of low-alloy and low-carbon steels (up to 0.4% C) is most simply performed, in which the possibility of cracking is practically eliminated. Therefore, such surfacing is often used to restore heavily worn parts, as well as a sublayer for subsequent surfacing with other materials. With a carbon content of more than 0.4%, as well as when surfacing parts made of alloyed steels, heating is necessary to prevent the formation of cracks, especially massive products. For the same purpose, surfacing is carried out at minimum values ​​of current and voltage.

For surfacing of stainless steels, which are most sensitive to hot cracking, it is recommended to apply intermediate layers and use electrode wire grades SvKh18N10T and SvKh17N13N2T.

Preheating and undercoating are also recommended for high hardness and wear resistant hardfacings, particularly high chromium irons, as these hardfacings are prone to cold cracking, especially on large parts.

Corrosion-resistant and heat-resistant nickel alloys, including those alloyed with molybdenum and chromium, are deposited mainly in the form of powders.

Technological process of surfacingin all cases includes cleaning and inspection of the part in order to detect cracks, films, tears and other defects. Detected defects are removed by punching, turning and welding before surfacing.

Before surfacing, parts made of medium carbon steels must be preheated to prevent unwanted structural changes in the metal. For example, for steels containing more than 0.3% carbon, the heating temperature is in the range of 200400 °C. It is controlled by thermoelectric pyrometers, thermometers, thermal pencils and other means.

Surfacing schemes and equipment useddepend on the shape of the parts, serial production and technical equipment of the enterprise. For example, surfacing schemes for cylindrical and conical parts differ in the following main features:

the location of the deposited metal beads (along the helical line and along the rectilinear generatrices along the axis of the part);

by type of surfacing process (single-electrode single-arc process; multi-electrode single-arc; two-electrode, etc.);

according to the degree of process automation (manual and mechanized).

The necks of long shafts of small diameters are more advantageously deposited with longitudinal beads. The end surfaces of parts such as disks are welded with concentric or spiral beads. Spherical surfaces are welded in the same way.

The surfacing scheme should not cause significant residual deformations of the restored parts. For example, when surfacing cylindrical parts with longitudinal beads, deformations are minimal if they are applied in two or four zones around the circumference, turning the part after surfacing each bead by 180°.

More effective way surfacing of cylindrical surfaces is the imposition of rollers along a helical line, since the continuity of the process, higher productivity and the least warpage of parts are ensured.

For surfacing, converted lathes or special installations are usually used.

Arc welding

general characteristics. Electric arc welding compared to other types of thermal welding is used more widely in the repair industry, due to its following advantages:

simplicity of the technological process and the equipment used;

the ability to restore parts from various construction materials(steel, cast iron, aluminum, titanium, etc.);

high productivity and low cost;

ample opportunities for the thickness and composition of the deposited layer (anti-friction, acid-resistant, heat-resistant, etc.).

The melting of the materials to be welded is carried out by an electric arc, which is a stable electric discharge in an ionized mixture of gases and vapors formed when exposed to high temperature on the materials to be welded and the protective environment The ignition of the arc is carried out as a result of a short circuit between the electrode and the workpiece to be welded or an electric discharge created by a separate source of alternating current - an oscillator.

On fig. 4.18 shows a diagram of an arc discharge. The most active and heated area of ​​the cathode zone 2 of the arc discharge is the cathode spot 7. In the anode zone 5 there is an anode spot 4. The cathode and anode zones are interconnected by an arc column 3, the temperature in which reaches 60007000 °C. The shape and dimensions of the electric arc are determined by the strength of the current, the material and diameter of the electrode, the composition and pressure of the resulting gases.

Rice. 4.18. Arc discharge scheme: 1 cathode spot; 2 cathode zone; 3 pillar arc; 4 anode spot; 5 anode zone

Arc powercarried out by direct or alternating current. Direct current provides a more stable burning of the electric arc and allows you to adjust the temperature of the part by setting the direct or reverse polarity, since more heat is generated at the positive pole than at the negative one (the temperature is 4200 and 3500 ° C, respectively). Therefore, it is recommended to weld parts of small thickness (in order to avoid burn-through) with reverse polarity, and with an increased penetration depth, use direct polarity.

In the first case, the electrode is connected to the positive pole (anode), in the second - to the negative (cathode). When using direct current, welding conditions are improved in various spatial positions of the seam. When welding with alternating current, approximately the same amount of heat is generated on the electrode and the workpiece. They weld low-carbon and low-alloy steels, which are insensitive to overheating and weld well.

Depending on the method of melting the materials to be welded, the following are distinguished:main types arc welding:

welding with a non-consumable (graphite or tungsten) electrode 1 by melting with a direct arc 2 only the base metal 3 or additionally a filler rod 4

welding with simultaneous melting of the base metal 3 and consumable electrode 1 under the action of a direct arc 2;

fusion welding of the base metal 5 with an indirect arc 3 burning between two, usually non-consumable, electrodes 1;

welding with a three-phase arc 6 burning between two electrodes 1, as well as between them and the base metal 3.

The molten metal is always transferred from the electrode to the base metal, and not vice versa, which is explained by the action of electromagnetic forces, the surface tension of the molten metal, and the movement of gases.

Rice. 4.19. Arc welding schemes: a, c non-consumable electrode; b, d melting

electrode

The types of arc welding differ in the type of filler material, the method of protecting the arc and molten metal, and the degree of mechanization of the process.

Filler materials for electric arc weldingare used in the form of electrodes (coated with a special layer of metal rods or metal tubes filled with powdered materials), welding wire (solid and flux-cored) and metal rods.

Molten metal protectionfrom interaction with air can be ensured by melting the electrode coating with an electric arc, bulk materials (flux) supplied to the arc burning zone and special components contained in flux-cored electrodes and flux-cored wire, as well as the use of shielding gases.

According to the degree of mechanizationThe following types of welding are distinguished: manual, semi-automatic and automatic.

Manual arc welding

Application area. Manual arc welding is used to seal (weld) cracks, holes, eliminate gaps, spalls and other mechanical damage to machine parts and metal structures: machine beds or frames, gearbox housings, brackets, gear wheel hubs, pulleys, etc. Often, manual welding is used to connect pipelines, manufacture individual parts of metal structures and spare parts for machines. It is convenient when performing short curved seams in any spatial position, when suturing in hard-to-reach places, as well as during installation and assembly work.

Manual arc welding is also used for surfacing - applying a layer of metal on the surfaces of parts with significant wear to restore their strength. Most often, parts made of carbon and alloy steels are deposited (body parts, sprockets, shaft journals, worn teeth of large gears, cams, etc.). Surfacing is also used to repair parts made of cast iron and non-ferrous alloys.

In addition to welding and surfacing with a single electrode, the following types of these works are used:

welding (surfacing) with a small-diameter electrode beam (in this case, an increase in welding current is required);

welding with a lying plate electrode a layer of flux is poured onto the surface of the part to be restored and a plate electrode is laid, which is melted when the arc burns;

surfacing with a tubular electrode filled with a powdered filler to obtain a layer with special properties;

welding and surfacing with a non-consumable carbon electrode when the filler material is fed into the arc burning zone.

Electric welding technology. The technological process of restoring parts using welding (surfacing) generally includes the preparation of parts, the performance of welding work, and subsequent (if necessary) thermal, mechanical and metalwork processing.

Preparing for welding. Preparing the part for welding great importance to ensure their quality. It consists in cleaning the welded areas and cutting edges - the formation of bevels (chamfers) of certain sizes and shapes on the welded objects. With a thickness of the metal being welded more than 6 mm, a V-shaped is used, and with a thickness of more than 15 mm, an X-shaped cutting of the edges, each at an angle of 3035 °.

Rice. 4.20. Types of cutting edges for welding (a) and the shape of welds (b)

With a steel thickness of up to 6 mm, welding is possible without cutting edges, and with a thickness of up to 3 mm, instead of cutting edges, they are flanged.

Cutting edges for welding is necessary to ensure complete penetration through the thickness of the part. To prevent through burn-through and leakage of molten metal, a ribbon 13 mm wide is left between the chamfers.

Methods for preparing parts with typical defects before welding are given in the table.

Table 4.3

Ways to prepare parts for welding

Performing welding. Manual arc welding is used with a small length of welds and when surfacing small surfaces, when mechanized welding methods are not feasible or inefficient. Welding or surfacing is performed with a welding electrode 7 (Fig. 4.21), which is manually fed to the workpiece 1 and moved along it. An electric arc burns between the electrode and the workpiece, causing them to melt. As a result, a weld pool 9 of liquid metal is formed, which fills the gap between the parts to be welded, and a liquid slag pool 4 on the surface of the molten metal.

Rice. 4.21. Process Diagram manual welding: 1 welded part;

2 slag crust; 3 weld; 4 slag bath; 5 gas shell; 6 electrode coating; 7 electrode rod; 8 electric arc; 9 welding pool

As the arc moves, the weld pool solidifies and a weld 3 is formed. The liquid slag, after solidification, forms a solid slag crust 2, which is destroyed and removed. There should be no gaps in welding, funnels, cracks, unchecked places, seam good quality has a wavy scaly surface, the same along the entire length.

Together with the rod, the electrode coating 6 also melts, forming a protective gas shell 5 around the arc 8.

Manual welding allows you to make seams in various spatial positions: lower, vertical, horizontal and ceiling (Fig. 4.22). When welding on a vertical plane, the current is reduced by 1015%, in the overhead position by 1520% compared to the current for welding in the lower position.

When performing welding work, it is recommended to position the part, if possible, so that the seam is in the lower position, and the arc should be as short as possible. Holes are welded along the perimeter until the entire hole is filled. Then welding is done on the other side.

Rice. 4.22. Possible spatial positions of the seam in manual welding: a lower; b vertical: c horizontal; d ceiling

Metal with a thickness of over 10 mm is welded with a multi-layer seam. Uncut cracks are recommended to be welded with transverse seams, which, when cooled, tighten the crack so tightly that the crack becomes watertight.

Welding can be performed without preheating the part (cold welding) or with preheating up to 650850 °C (hot welding). Hot welding provides higher quality and is used in critical cases.

Electrodes for welding and surfacing of steel products. Electrodes for manual welding are wire rods 300400 mm long, 1.612 mm in diameter coated (thin chalk or thick special coating). A thin coating has a thickness of 0.15 ... 0.3 mm, and a thick one 0.25 ... 0.35 d, where d is the electrode diameter, mm. Thin-coated electrodes are used for welding non-critical parts, since it is intended only to ensure stable arc burning.

Thick coatingsare protective and alloying and make it possible to obtain deposited metal with the required mechanical properties, which is necessary for welding and surfacing of critical parts. Such coatings, in addition to stable arcing, also protect the molten metal from exposure to air and obtain a weld metal with a given composition and properties by alloying the molten metal with the elements contained in the coating. Therefore, the composition of the thick electrode coating includes stabilizing, gas-forming, slag-forming, deoxidizing, alloying and binding components.

Electrode coatings can be acidic (indicated by the letter A), basic (B), rutile (R), organic (O), cellulose (C), others (P).

Acid coated electrodes are used for welding low carbon and low alloy steels. They allow welding in all spatial positions on a variable and DC. It is possible to weld metal in the presence of rust and scale on the welded surfaces. However, electrodes with such coatings are toxic due to the release of manganese compounds.

Rutile-coated electrodes are used for welding critical structures made of low-carbon and low-alloy steels.

Basic coated electrodes are used for welding critical structures made of steels of all classes. It is possible to alloy the weld seam material by introducing alloying elements into the coating. The quality of welding with such electrodes is improved if it is performed on a direct current of reverse polarity, and the electrodes are annealed at a temperature of 400450 ° C before welding.

The cellulose coating contains organic matter with a small amount of slag-forming components that create good gas shielding and form a small amount of slag when welding on AC and DC low-carbon and low-alloy steels. Electrodes with such a coating are especially effective when welding must be carried out in various spatial positions.

When restoring machine parts by manual welding, electrodes with a diameter of 1.2 to 5.0 mm are usually used.According to the purpose, the electrodes are dividedinto five classes: for welding carbon and low alloy structural steels with σ in < 600 МПа, легированных конструкционных сталей с σ in > 600 MPa, alloyed heat-resistant steels, high-alloy steels with special properties and for hardfacing surface layers with special properties. The required mechanical properties of the welded joint are provided by the choice of the appropriate brand of electrode.

Electrodes for welding structural steels are divided into types: E38, E42, E42A, etc., where the letter E indicates that the electrode is intended for welding, the numbers indicate σ in deposited metal in 10-1 MPa, and index A that the weld deposited with this electrode has increased plastic properties.

The designation of the type of surfacing electrode includes: a combination of letters "EN" (surfacing electrode), the main chemical elements that make up the deposited layer, and their average percentage. If the designation of the electrode type contains the letter U, then the carbon content is given in tenths of a percent, and if it is absent, then in hundredths. The numbers after the hyphen at the end of the designation indicate the hardness of the deposited layer (HRC e).

For example, the EN-U30Kh23R2S2TG electrode brand is deciphered as follows: EN surfacing electrode; U30 carbon content in the deposited layer 3%; X23 chromium 23%; Р2 boron 2%; C2 silicon 2%; T titanium 1%; G manganese 1%. The designation EN-14G2Kh-30 is deciphered as follows: surfacing electrode, the deposited layer contains 0.14% carbon, 2% manganese, 1% chromium and has a hardness of 30HRC3.

Sometimes in the designation of the electrode brand, the hardness of the deposited layer is indicated in HB, for example, OZN-300, T-590.

Electrode rods for welding steel products are made of steel welding wire, which, in accordance with the standard, is produced with a diameter of 0.212 mm. It is also used as a consumable electrode in mechanized submerged arc welding and in shielding gases, as a filler material in non-consumable electrode arc welding and gas welding.

Welding wiredepending on the composition, it is divided into three groups: low-carbon (Sv-08A, Sv-08GS, etc.), alloyed (Sv-18KhMA; Sv-10Kh5M, etc.) and high-alloyed (Sv-06Kh19N10MZT; Sv-07Kh25N13, etc.) .

welding wiremanufactured with a diameter of 0.38 mm of the following grades: carbon (Np-25, Np-45, Np-65, etc.); alloyed (Np-40G, Np-65G, Np-ZOHGSA, Np-5KhNM), etc.); highly alloyed (Np-20X14, Np-40X13, Np-40X2V8T, Np-X20H80T, etc.).

In wire grades, “Sv” means welding, “Np” surfacing, and subsequent letters and numbers its composition.

The quality of welding and surfacing significantly depends on the correct choice of the electrode. The type and brand of the electrode is selected from the reference tables depending on the material and purpose of the welded part. For welding, the electrode rods are usually low-carbon wire Sv-08, Sv-08GA, etc. For welding structural low-carbon and low-alloy steels of the type 15X, 20X, electrodes E-38, E-42, E-42A, E-46 are used.

The most common electrodes are grades UONI-13/45; UONI-13/55, etc., which are produced with a diameter of 25 mm with a coating thickness of 0.61.2 mm.

The diameter of the electrode depends on the thickness of the part, the type of seam and its position in space. With vertical and ceiling joints, the diameter of the electrode should not exceed 4 mm.

For surfacing by manual arc welding of parts made of low-carbon steels that have not been subjected to thermal or chemical-thermal treatment, conventional welding electrodes are used. Surfacing of parts from medium carbon and alloy steels, hardened, as well as from mild steel, but with a hardened surface, is carried out only with special welding electrodes.

To obtain a wear-resistant coating on parts made of low-carbon, medium-carbon and low-alloy steels, electrodes of the OZN-300, 03H-350, 03H-400 grades are used. These electrodes have a core made of alloyed wire, respectively EN-15GZ-25; EN-18G4-35 and EN-20G4-40.

Good wear resistance of parts working with impact load, is provided by surfacing with the T-590 electrode, and for parts operating with a moderate impact load, with the T-620 electrode. These electrodes are made from Sv-08A welding wire coated with chromium, boron, silicon, manganese and other alloying elements. Therefore, the layer deposited with such electrodes is an alloy alloyed with these elements. The T-590 brand electrode is used to weld machine parts operating under conditions of intense wear.

Arc Power Sources. To power the welding arc in electric arc welding, AC sources (welding transformers) and DC sources are used.

Welding transformers convert the mains voltage (220 or 380 V), lowering it to the required level for welding. Transformers are produced for manual arc welding with coated electrodes and mechanized submerged arc welding. For manual welding, surfacing and cutting of metals, transformers TS-300, TD-300, TD-500, OSTA-350, etc. are used. In the designations of transformer models, the numbers 300, 500, 350 mean the nominal strength of the welding current (in A).

DC sources are divided into welding rectifiers (VS-300, VDG-302, VDG-601, etc.), welding converters (PSO-ZOO, PS-500, PS-1000, etc.), consisting of an AC motor and a generator direct current, and welding units (ASB-300-7, ADD-303, ASDP-500G-ZM, etc.), which are equipped with an internal combustion engine (GAZ-320, YaAZ-240G, etc.).

Modern power sources include inverter rectifiers, in which the mains voltage is converted to high-frequency (up to 60 kHz), which is reduced by a small-sized transformer to the level of welding voltage. The mass of inverter rectifiers is about 10 times less than other types of rectifiers.

A significant reduction in heat generation during welding is provided by pulsed welding current sources, which make it possible to obtain current in the form of pulses various shapes(rectangular, exponential) with different times and the pulse repetition period. This eliminates burn-through when welding products of small thickness.

At repair enterprises, welding is carried out mainly with alternating current from welding transformers STE, STN, TS and TSK, which are easier to operate, more durable and have more high efficiency than rectifiers and DC generators. However, in some cases (low current welding with coated electrodes and submerged arc welding), they do not provide stable arcing.

Welding modes.

The main parameters of manual arc welding are current strength and welding speed. The current strength depends on the diameter of the electrode:

I=kd,

where I current, A; d electrode diameter, mm; k coefficient equal to 4060 for electrodes with a core made of low carbon steel and 3540 for electrodes with a high-alloy steel rod when welding in the lower position, A/mm.

When welding holes of small diameter in massive parts, to ensure the required penetration, it is recommended to choose a current strength of 1015% more than indicated above.

The arc voltage varies within 1630 V.

The electrode diameter is chosen depending on the thickness of the metal to be welded:

Metal thickness, mm 0.51.0 1.02.0 2.05.0 5.010.0 over 10

Electrode diameter, mm 1.01.5 1.52.5 2.54.0 4.06.0 5.08.0

The welding speed is selected based on the need to penetrate the welded section and fill the groove with deposited metal (v = 57 m/h is assumed in calculations).

Features of electric arc welding and surfacing of parts depending on the content of carbon and alloying elements. Parts made of low-carbon and low-alloy steels with a carbon content of up to 0.3% are welded quite well and do not require heat treatment after welding.

Satisfactory weld quality is obtained when welding steels with an average carbon content of 0.30.4%. To improve the quality of welding of parts with a thickness of more than 15 mm, it is recommended to heat them up to a temperature of 200 °C before welding, and after welding, temper them at a temperature of 650 °C.

With an increase in the carbon content above 0.45%, the weldability of steel deteriorates, the porosity of the weld and the content of oxides in it increase. Therefore, steel 45 and steel 50, as well as low-alloy steels with the same carbon content, have limited weldability. After welding, normalization is recommended.

Alloy weldingsteels presents certain technological difficulties, since due to their lower thermal conductivity they are prone to overheating and embrittlement, and the impurities present in them combine with oxygen and remain in the deposited layer in the form of refractory oxides. In addition, alloy steels are prone to self-hardening, which causes an increase in hardness and internal stresses and can lead to cracking.

To reduce welding stresses and deformations, to prevent the formation of cracks, it is necessary to periodically interrupt the process to cool the welded parts. When welding cracks, adjacent sections of the part should be heated, which reduces internal stresses and its warpage after welding. For the same purpose, medium-carbon, high-carbon and alloy steels are recommended to be welded with direct current at reverse polarity, which reduces the risk of overheating and the formation of hardening cracks. At the same time, current strength is assigned depending on the thickness of the part being welded, given that with its increase, in addition to increasing productivity, the strength and ductility of the weld material improve.

With a significant thickness of the parts, the seam is formed in several rows. The arc should be as short as possible, since with an increase in its length, the quality of the seam deteriorates.

When surfacing a case-hardened or hardened partit is pre-annealed. To do this, it is heated to 900 ° C, and then slowly cooled. Tempering reduces the hardness of the material, tensile strength and elastic limit, but increases the toughness, which improves the quality of the deposit. After welding and machining the part can be carburized and hardened again to restore its original hardness.

An increase in labor productivity and an improvement in the quality of surfacing during the restoration of steel parts is ensured by the use of hydrogen-saturated wire. For this, the electrode wire is etched in a 510% sulfuric acid solution. The rate of surfacing with such wire increases by about 2 times. Welding with pickled wire is carried out with direct current with reverse polarity.

Disadvantages of manual arc welding and surfacingare relatively low productivity, the dependence of the quality of work on the qualifications of the welder, increased consumption of electrodes due to their incomplete use, splashing and burnout of molten metal. More productive are mechanized arc welding and surfacing in protective solid, gaseous and liquid media.

Study guide for preparation
workers in production

Locksmith workshop

Editing of metal of round section

Editing of round metal is carried out on a plate, prisms or using a hand press.

Training task 1 for straightening a round steel bar on a plate is performed in the following order.

1. The boundaries of the bends are determined by eye and marks are made with chalk.

2. On left hand put on a mitten; in right hand take a hammer with soft inserts, in the left - a round bar and take a working position.

3. The bar is placed on the plate so that the curved part is bulge up.

4. Hammer blows are applied on the convex part from the edges of the bend to its middle part (Fig. 57), adjusting the impact force depending on the diameter of the rod and the amount of curvature. As the curvature straightens, the impact force is weakened. Editing is completed with light blows, turning the bar around its axis. If there are several bends, the extreme bends are ruled first, and then those located in the middle.

Rice. 57. Editing a round bar on a plate

Training task 2 consists in straightening a round bar on prisms.

A round bar, located on prisms, occupies a stable position when straightening. This editing method is used to edit steel pipes. For dressing, use wooden hammers or use linings.

The editing sequence is as follows.

1. Determine the border of the bend, marking it with chalk.

2. Two prisms are installed on the plate.

3. The bar is placed in the prisms so that its curved part is turned upwards, and the bar lies tightly in the corner recesses of the prisms.

4. Hammer blows are applied to the convex part of the bar from the edges of the bend to its middle part (Fig. 58).

Rice. 58. Straightening a round bar on a plate using prisms

The quality of the dressing is checked by eye or by rolling the bar on the plate, while observing the density of contact between the surface of the bar and the surface of the plate along its entire length.