Method for manufacturing welded tube and welding device

Abstract

To provide a method for manufacturing a welded tube which enlarges a process window of upset welding, and can secure good welding quality.SOLUTION: A method for manufacturing a welded tube includes the steps of: molding a metal plate (10) into a tube shape so that both ends (11L and 11R) of the metal plate (10) face each other while conveying the metal plate (10); and adjusting an interval of the opposite both ends (11L and 11R) by a seam guide (31), heating and melting both ends (11L and 11R), and then pressurizing the metal plate (10) using a squeeze roll (33) so that both ends (11L and 11R) which approach each other toward the downstream in the conveyance direction of the metal plate (10), and are brought into contact with each other are pressed against each other, and welding both ends (11L and 11R). In the welding step, an angle (θ) formed by both ends (11L and 11R) which approach each other toward the downstream in the conveyance direction and are brought into contact with each other is 5.0° or more.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present disclosure relates to a method for manufacturing an electric resistance welded pipe. The present disclosure also relates to a welding apparatus, and more particularly to a welding apparatus that welds opposing ends of a metal plate that is being transported and formed into a tubular shape. [Background technology]

[0002] Electric resistance welded pipes, also known as electric resistance welded pipes, are manufactured through a forming process, a welding process, a shaping process, and the like. In the forming process, a metal plate unwound from a coil is formed into an open pipe shape. In the welding process, both ends of the open pipe-shaped metal plate are joined by upset welding to form an electric resistance welded pipe. In the shaping process, the shape of the electric resistance welded pipe is adjusted.

[0003] In the manufacturing process of electric resistance welded pipes, a heating device and a squeeze roll are usually used in the welding process. Patent Document 1 discloses that both ends of a metal plate are welded using a work coil as a heating device and a squeeze roll including a pair of side rolls and a pair of top rolls. When a high-frequency current flows through the work coil, an induced current is generated at both ends of the metal plate, and both ends are heated. The squeeze roll presses the open pipe-shaped metal plate from the outer periphery side to press both ends in a molten state. A seam guide roll is arranged upstream of the work coil in the conveying direction of the metal plate. The seam guide roll adjusts the distance between both ends of the open pipe-shaped metal plate. The both ends of the metal plate approach each other as they move downstream from the seam guide roll, and come into contact before the squeeze roll. In the embodiment of Patent Document 1, the angle formed by both ends of the metal plate is 3.3°. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2009-241079 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the manufacturing process of electric resistance welded pipes, for example, when there is a restriction on the welding speed, the process window of upset welding may be narrowed. When the process window is narrow, the welding conditions are likely to deviate from the process window when they vary due to, for example, the characteristics of the raw metal plate. As a result, welding defects are likely to occur, and it is difficult to stably ensure good welding quality.

[0006] An object of the present disclosure is to provide a method for manufacturing an electric-welded pipe that can expand the process window of upset welding and ensure good welding quality. [Means for solving the problem]

[0007] The method for manufacturing an electric-resistance welded pipe according to the present disclosure includes the steps of: forming a metal sheet into a tubular shape while conveying the metal sheet so that both ends face each other; adjusting the distance between the both ends with a seam guide, heating and melting the both ends, and then applying pressure to the metal sheet using a squeeze roll to press the both ends, which come closer to each other as they move downstream in the conveying direction of the metal sheet, against each other, thereby welding the both ends. In the welding step, the angle between the both ends, which come closer to each other as they move downstream in the conveying direction, is 5.0° or more. Effect of the Invention

[0008] According to the method for producing an electric resistance welded pipe according to the present disclosure, the process window of upset welding can be expanded, thereby ensuring good welding quality. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of a manufacturing facility for an electric resistance welded steel pipe according to an embodiment. [Diagram 2] FIG. 2 is a cross-sectional view showing an example of a seam guide included in the manufacturing equipment shown in FIG. [Diagram 3]FIG. 3 is a front view of a squeeze roll included in the production equipment shown in FIG. [Figure 4] FIG. 4 is a plan view of the production facility shown in FIG. 1, showing the squeeze roll and its vicinity. [Diagram 5] FIG. 5 is a schematic diagram showing changes in the welding state depending on the input power and the welding speed, and is a diagram for explaining the effects of the embodiment. [Figure 6] FIG. 6 is a diagram showing the relationship between the standardized squeeze roll diameter, the standardized seam guide width, and the convergence angle at both ends of the metal sheet. [Figure 7] FIG. 7 is a graph showing the relationship between the normalized squeeze roll diameter and the normalized seam guide width. [Figure 8] FIG. 8 is a schematic diagram showing changes in the welding state depending on the input power and the welding speed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] In general, the state of welding (electric resistance welding) during the manufacture of electric resistance welded pipes changes depending on the input power (heat input) and the welding speed. Figure 8 is a schematic diagram (CPD diagram) showing the change in the welding state depending on the input power and the welding speed. When high-frequency electric resistance welding is performed, both ends of the metal plate gradually approach each other as they move downstream in the conveying direction. When both ends of the metal plate approach each other, the both ends are strongly heated and melted due to the proximity effect, and when molten metal accumulates at these ends, the accumulated molten metal is discharged by electromagnetic repulsion. In addition, the melting of both ends progresses from the corners on the inner and outer surfaces of the open pipe-shaped metal plate toward the center of the plate thickness. Line A in Figure 8 is a line representing the condition in which the speed at which both ends of the metal plate approach each other coincides with the speed at which the molten metal generated by melting is discharged from between the ends. Line B in Figure 8 is a line representing the condition in which the entire thickness of both ends of the metal plate melts. The welding speed at the intersection of line A and line B is the critical welding speed Vm. The phenomenon of electric resistance welding changes significantly at the critical welding speed Vm.

[0011] In the CPD diagram of FIG. 8, the region below line B is the region of welding conditions called Type 1. When welding is performed under Type 1 welding conditions, the entire thickness of both ends of the metal plate does not melt, and there is a high possibility of cold welding defects occurring. The region above line A where the welding speed is equal to or higher than the critical welding speed Vm is the region of welding conditions called Type 2. Under Type 2 welding conditions, welding with low defects is possible. The region between line A and line B where the welding speed is equal to or higher than the critical welding speed Vm is the region of welding conditions called Type 1 where fusion welding is possible. When the welding speed is lower than the critical welding speed Vm, part of the region above line B is the region of Type 2 welding conditions, but most of the region is the so-called Type 3 welding conditions. Under Type 3 welding conditions, both ends of the metal plate are in a state of excessive heat input, and welding defects such as penetrators occur.

[0012] In order to ensure welding quality, it is generally considered preferable to perform welding at a welding speed above the critical welding speed Vm under type 2 welding conditions, or under type 1 welding conditions that allow fusion welding. However, in the case of type 2 welding conditions, an area called a slit is generated where the approach speed of both ends of the metal plate and the discharge speed of the molten metal are balanced. It is known that arcing occurs frequently in the slit, which causes spatter. If the spatter adhering to the inner and outer surfaces of the metal plate is pressed down by, for example, a squeeze roll, there is a possibility that surface defects such as scratches will remain on the electric resistance welded pipe after welding.

[0013] For example, in small-diameter electric resistance welded pipes used in vehicles, surface defects caused by spatters may not be tolerated. In this case, electric resistance welding must be performed under the first-class welding conditions that allow fusion welding in order to prevent the generation of spatters. However, electric resistance welding aiming for the first-class welding conditions that allow fusion welding tends to have a narrow process window.

[0014] For example, when electric resistance welding is performed on a thin metal plate, the critical welding speed Vm becomes high. However, in the manufacture of electric resistance welded pipes, intermediate welding of the metal plate is performed on the inlet side of the welding device, and the metal plate that has become an electric resistance welded pipe is cut off on the outlet side of the welding device, so that it is difficult to increase the welding speed to a welding speed sufficiently away from the critical welding speed Vm due to the constraints of the manufacturing equipment. Therefore, electric resistance welding must be performed at a welding speed close to the critical welding speed Vm. For example, when electric resistance welding is performed on a thick metal plate, an upper limit of the welding speed is set in order to melt the entire thickness of the metal plate. Also, for example, when manufacturing a large-diameter thin-walled electric resistance welded pipe, electric resistance welding may have to be performed at a welding speed near the critical welding speed Vm in order to prevent the end portions of the metal plates from lapping due to forming fluctuations. When the electric resistance welding speed approaches the critical welding speed Vm, the heat input range (input power range) that is the first type welding condition that allows fusion welding is more limited, and the process window becomes narrower. Therefore, when the welding conditions vary due to the thickness, width, strength, etc. of the metal plate as the raw material, the welding conditions can easily deviate from the process window, resulting in a problem of continuous defects during electric resistance welding.

[0015] As a result of intensive research, the inventors have found that in electric resistance welding, the angle (convergence angle) formed by both ends that converge in a V shape toward the downstream of the conveyance direction of the metal plate has a large effect on the critical welding speed Vm. The inventors have also found that the critical welding speed Vm can be lowered by increasing the convergence angle, and the process window in electric resistance welding can be expanded. After further research, the inventors have completed a manufacturing method for electric resistance welded pipe according to an embodiment.

[0016] A method for manufacturing an electric-resistance welded pipe according to an embodiment includes a process for forming a metal plate into a tubular shape while conveying the metal plate so that both ends face each other, and a process for adjusting the distance between the both ends with a seam guide, heating and melting the both ends, and then pressing the metal plate with a squeeze roll so as to press the both ends, which come closer to each other and come into contact as they move downstream in the conveying direction, against each other, thereby welding the both ends. In the welding process, the angle formed by the both ends, which come closer to each other and come into contact as they move downstream in the conveying direction, is 5.0° or more (first configuration).

[0017] In the manufacturing method of electric resistance welded pipe according to the first configuration, in the welding process, the angle (convergence angle) between both ends of the metal plates that approach and contact as they move downstream in the conveying direction is ensured to be 5.0° or more. This allows the critical welding speed Vm to be lowered, and the heat input range that provides the first type welding condition that allows fusion welding is wider than that of conventional upset welding when compared at the same welding speed. In other words, the process window of upset welding can be widened. Therefore, even if the welding conditions fluctuate due to, for example, the characteristics of the metal plates, the welding conditions are less likely to deviate from the process window, and the occurrence of welding defects can be suppressed. Therefore, good welding quality can be ensured.

[0018] The squeeze roll may include a pair of side rolls. The side rolls are disposed on both sides of the metal sheet as viewed along the conveying direction. Each side roll has a concavely curved side surface toward the central axis. The width of the seam guide is W SG , the diameter of the side roll at the bottom is D SR , the radius of curvature of the side is R SR And W SG / R SR Standardized seam guide width Y, D SR / R SR When the normalized squeeze roll diameter is X, it is preferable that the normalized seam guide width Y and the normalized squeeze roll diameter X satisfy the following formulas (second configuration). Y≦0.80 X≧3.60 Y≧0.003X 2 -0.025X+0.6

[0019] According to the study by the inventors, the convergence angle at both ends of the metal sheet is greatly affected by the seam guide width and the squeeze roll diameter, and the convergence angle at both ends of the metal sheet can be enlarged by adjusting both the seam guide width and the squeeze roll diameter. More specifically, as in the second configuration, the normalized seam guide width Y and the normalized squeeze roll diameter X, which are normalized by the radius of curvature of the side surface of the side roll, are Y≧0.003X 2By satisfying -0.025X+0.6, the convergence angle at both ends of the metal plate is easily expanded, which expands the process window of upset welding and ensures stable good welding quality.

[0020] In the second configuration, the normalized squeeze roll diameter X is 3.60 or more. This ensures the rigidity of the squeeze roll. This makes it possible to suppress a decrease in the life of the squeeze roll. In addition, it is possible to suppress the occurrence of defective shapes of electric-resistance welded pipes, and electric-resistance welded pipes can be stably manufactured.

[0021] In the second configuration, the normalized seam guide width Y is 0.80 or less. In this case, the distance between both ends of the metal plates before welding is not excessively large, so that the both ends are properly butted together during welding. This makes it possible to prevent the occurrence of defective shapes in the electric-resistance welded pipe, and to stably manufacture electric-resistance welded pipe.

[0022] The outer diameter of the electric resistance welded pipe may be 10 mm or more and 110 mm or less (third configuration).

[0023] A welding device according to an embodiment welds opposing ends of a metal plate that is being formed into a tubular shape while being transported. The welding device includes a seam guide and a squeeze roll. The seam guide adjusts the distance between the opposing ends of the metal plate. The squeeze roll is disposed downstream of the seam guide in the transport direction of the metal plate. The squeeze roll includes a pair of side rolls. Each of the side rolls has a side surface that is concavely curved toward the central axis. The width of the seam guide is W. SG , the diameter of the side roll at the bottom is D SR , the radius of curvature of the side is R SR And W SG / R SR Standardized seam guide width Y, D SR / R SR is the normalized squeeze roll diameter X, the normalized seam guide width Y and the normalized squeeze roll diameter X satisfy the following formulas (fourth configuration). Y≦0.80 X≧3.60 Y≧0.003X 2 -0.025X+0.6

[0024] Radius of curvature of the side roll R SR may be 5 mm or more and 55 mm or less (fifth configuration).

[0025] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. In each drawing, the same or corresponding components are denoted by the same reference numerals, and the same description will not be repeated.

[0026] [Electric resistance welded pipe manufacturing equipment] Fig. 1 is a schematic diagram showing the configuration of an electric-resistance welded pipe manufacturing equipment 100. Referring to Fig. 1, the manufacturing equipment 100 forms a strip-shaped metal sheet 10 into an electric-resistance welded pipe while transporting it along its longitudinal direction. The metal sheet 10 is typically a steel sheet (steel strip). However, the metal sheet 10 may be a metal sheet other than a steel sheet, such as an aluminum alloy sheet.

[0027] The manufacturing facility 100 includes a forming device 20, a welding device 30, and a shaping device 40. The forming device 20, the welding device 30, and the shaping device 40 are arranged in this order from upstream to downstream in the conveying direction of the metal sheet 10.

[0028] The metal sheet 10 unwound from a coil is continuously supplied to the forming device 20. Both ends 11L, 11R in the width direction of the metal sheet 10 may be smoothed, for example, by an edge mirror 50, before being fed into the forming device 20. The forming device 20 includes, for example, a breakdown roll group 21 and a fin pass roll group 22. The breakdown roll group 21 and the fin pass roll group 22 are arranged in this order from upstream to downstream in the transport direction of the metal sheet 10.

[0029] The forming device 20 forms the metal sheet 10 being transported into a tubular shape (open pipe shape). The breakdown roll group 21 and the fin pass roll group 22 each include a plurality of rolls. The breakdown roll group 21 performs bending processing on both end portions 11L, 11R of the metal sheet 10. The breakdown roll group 21 bends both end portions 11L, 11R of the metal sheet 10 upward on the paper surface of FIG. 1, and the entire metal sheet 10 is curved into an arc shape. The fin pass roll group 22 performs finish forming on the metal sheet 10 so that the metal sheet 10 has a substantially circular cross section.

[0030] The welding device 30 welds the opposing ends 11L, 11R of the metal plate 10 that is being formed into a tubular shape while being transported. The welding device 30 includes a seam guide 31, a heating device 32, and a squeeze roll 33.

[0031] The seam guide 31 is disposed downstream of the fin pass roll group 22 in the conveying direction of the metal sheet 10. FIG. 2 is a cross-sectional view showing an example of the seam guide 31. As shown in FIG. 2, the seam guide 31 is disposed between both ends 11L, 11R of the generally tubular metal sheet 10, and adjusts the distance between the opposing ends 11L, 11R. The seam guide 31 has a width W SG W SG is the length of the portion of the seam guide 31 disposed between the ends 11L and 11R of the metal plate 10. In other words, W SG is the maximum linear distance from the position where one end 11L of the metal plate 10 abuts on the seam guide 31 to the position where the other end 11R abuts on the seam guide 31.

[0032] Returning to FIG. 1, the heating device 32 is disposed downstream of the seam guide 31 in the conveying direction of the metal sheet 10. The heating device 32 is configured to heat and melt both ends 11L, 11R of the metal sheet 10. The heating device 32 is typically an electric resistance heating device. The heating device 32 may be a high-frequency heating device. In this case, the heating device 32 supplies a high-frequency current to the metal sheet 10 and melts both ends 11L, 11R of the metal sheet 10 by Joule heat. The heating device 32 can supply a high-frequency current to the tubular metal sheet 10 by induction or directly using electrodes such as a work coil or a contact tip.

[0033] The squeeze roll 33 is disposed downstream of the seam guide 31 and the heating device 32 in the conveying direction of the metal sheet 10. The squeeze roll 33 is configured to apply pressure to the metal sheet 10 to press both ends 11L, 11R against each other.

[0034] FIG. 3 is a view (front view) of the squeeze roll 33 as viewed from the downstream side along the conveying direction of the metal sheet 10. Referring to FIG. 3, the squeeze roll 33 includes a pair of side rolls 331L, 331R. The side rolls 331L, 331R are arranged on both sides of the tubular metal sheet 10 as viewed along the conveying direction of the metal sheet 10. The side rolls 331L, 331R may be capable of approaching and moving away from the metal sheet 10. One side roll 331L is arranged on the left side of the other side roll 331R on the paper surface of FIG. 3. Hereinafter, for convenience of explanation, the left and right on the paper surface of FIG. 3 will be simply referred to as the left and right, and the top and bottom on the paper surface of FIG. 3 will be simply referred to as the top and bottom.

[0035] The side rolls 331L and 331R are disposed at substantially the same position in the conveying direction of the metal sheet 10. Each of the side rolls 331L and 331R has a central axis A SR Each of the side rolls 331L and 331R has a central axis A SR The shape is symmetrical (axially symmetrical) with respect to the central axis A SR Each of the side rolls 331L and 331R includes a side surface 331a. The side surface 331a is disposed about a central axis A.SR In each of the side rolls 331L and 331R, the side surface 331a is an annular surface having a center axis A. SR The side surface 331a has a concave curved shape. SR is, for example, 5 mm or more and 55 mm or less. SR is approximately half the outer diameter of the electric resistance welded pipe to be manufactured. The side rolls 331L, 331R come into contact with the tubular metal sheet 10 at their respective side surfaces 331a.

[0036] The side rolls 331L and 331R have a concavely curved side surface 331a, and therefore the diameter of the side rolls 331L and 331R is reduced from the outside toward the center in the axial direction. SR has.

[0037] In each of the side rolls 331L and 331R, the radius of curvature R of the side surface 331a SR Diameter D SR Ratio:D SR / R SR is defined as the normalized squeeze roll diameter X. Also, the curvature radius R of the side surface 331a of the side rolls 331L and 331R is defined as SR Width W of seam guide 31 SG (FIG. 2) is defined as the normalized seam guide width Y. The normalized squeeze roll diameter X and the normalized seam guide width Y preferably satisfy the following formulas. Y≦0.80 X≧3.60 Y≧0.003X 2 -0.025X+0.6

[0038] The squeeze roll 33 may include other rolls in addition to the side rolls 331L, 331R. Although not shown, the squeeze roll 33 may include, for example, a pair of top rolls that contact the metal sheet 10 near both ends 11L, 11R. The squeeze roll 33 may include a receiving roll that contacts the metal sheet 10 from below.

[0039] Referring again to Fig. 1, the metal sheet 10 becomes an electric-resistance welded pipe by welding both ends 11L, 11R by the welding device 30. The shaping device 40 adjusts the shape of the portion of the metal sheet 10 that has become an electric-resistance welded pipe. A seam normer 60 may be disposed between the welding device 30 and the shaping device 40. The shaping device 40 includes, for example, a plurality of roll stands aligned in the conveying direction of the metal sheet 10. Each of the roll stands may include a plurality of rolls that define a caliber.

[0040] [Method of manufacturing electric resistance welded pipes] Next, a method for producing an electric-resistance welded pipe according to the present embodiment will be described. The method for producing an electric-resistance welded pipe according to the present embodiment includes a forming step and a welding step. The production method may further include a shaping step.

[0041] (molding process) 1, in the forming process, the metal sheet 10 is formed into a tubular shape with both ends 11L, 11R facing each other. More specifically, the metal sheet 10 is unwound from a coil, and then continuously fed to a forming device 20, where it is formed into a tubular shape. By passing through the forming device 20, the metal sheet 10 is formed into an open pipe shape with both ends 11L, 11R facing each other and spaced apart in the circumferential direction.

[0042] (Welding process) In the welding process, the distance between the opposing ends 11L, 11R of the metal sheet 10 is adjusted by the seam guide 31, and the ends 11L, 11R are heated and melted, and then the metal sheet 10 is pressed by a squeeze roll 33 so as to press the ends 11L, 11R against each other, thereby welding the ends 11L, 11R. More specifically, the metal sheet 10 formed into a tubular shape through the forming process is continuously fed to the welding device 30. The metal sheet 10 is fed to the heating device 32 through the seam guide 31. The ends 11L, 11R of the metal sheet 10 are heated by the heating device 32 and start to melt.

[0043] The metal sheet 10 with both ends 11L, 11R molten is supplied to the squeeze roll 33. The both ends 11L, 11R of the metal sheet 10 approach each other and come into contact with each other as they move downstream in the conveying direction. The squeeze roll 33 presses the metal sheet 10 with both ends 11L, 11R in contact from the outer surface side. As a result, the both ends 11L, 11R of the metal sheet 10 are pressed against each other.

[0044] FIG. 4 is a plan view of the manufacturing facility 100 when an electric resistance welded pipe is being manufactured from a metal plate 10, and shows the squeeze roll 33 and its vicinity.

[0045] 4, in the welding process, both ends 11L, 11R of the metal plate 10 heated by the heating device 32 to a molten state approach each other as they move downstream in the conveying direction, and finally come into contact with each other. That is, both ends 11L, 11R of the metal plate 10 converge into a V-shape in a plan view of the manufacturing equipment 100. When the angle formed by both ends 11L, 11R converging in a V-shape is defined as a convergence angle θ, the convergence angle θ is 5.0° or more. The convergence angle θ may be 8.0° or less. Both ends 11L, 11R of the metal plate 10 converge into a V-shape and come into contact with each other on the upstream side of the conveying direction relative to the squeeze roll 33.

[0046] Returning to Fig. 1, both ends 11L, 11R of the metal sheet 10 that have passed through the squeeze rolls 33 are solidified and joined by natural cooling as they are transported downstream. As a result, the metal sheet 10 becomes an electric resistance welded pipe having a welded part extending in the longitudinal direction. The outer diameter of the electric resistance welded pipe is, for example, 10 mm or more and 110 mm or less.

[0047] Immediately after the welding process, weld beads are formed on the inner and outer surfaces of the electric resistance welded pipe. The weld beads can be cut and removed, for example, by a bead cutting machine (not shown). After welding, the welded part may be heat treated by a seam normalizer 60.

[0048] (Standard process) In the shaping process, the shape of the electric resistance welded pipe formed through the welding process is adjusted. More specifically, the electric resistance welded pipe is continuously fed to the shaping device 40 and shaped into a final shape. For example, the electric resistance welded pipe may be subjected to a slight drawing process by passing through a plurality of roll stands included in the shaping device 40. This allows the electric resistance welded pipe to be finished so that its cross section is perfectly circular and its outer diameter falls within the dimensional tolerances.

[0049] [effect] In the welding process of the electric-resistance-welded pipe manufacturing method according to this embodiment, both end portions 11L, 11R of the metal sheet 10 converge in a V-shape toward the downstream of the conveying direction. The both end portions 11L, 11R that are in contact with each other are upset by a squeeze roll 33. In this embodiment, the convergence angle θ of both end portions 11L, 11R of the metal sheet 10 is expanded to 5.0° or more. This allows the critical welding speed Vm to be reduced.

[0050] As shown in Fig. 5, when the critical welding speed Vm is lowered, the range of the first type welding conditions that allow fusion welding is expanded even if the welding speed is the same. In other words, the process window when upset welding is performed on both ends 11L, 11R of the metal plate 10 under the first type welding conditions that allow fusion welding is expanded. Therefore, even if the welding conditions vary due to the characteristics of the metal plate 10, which is the raw material, the welding conditions are less likely to deviate from the process window, and the occurrence of welding defects can be suppressed. Therefore, good welding quality can be ensured.

[0051] The manufacturing method according to the present embodiment can expand the process window for the first type welding conditions that allow fusion welding, and is therefore particularly suitable for use in small-diameter electric resistance welded steel pipes that require electric resistance welding under the first type welding conditions that allow fusion welding. The manufacturing method according to the present embodiment is applied to the manufacture of small-diameter electric resistance welded steel pipes that are, for example, 10 mm or more and 110 mm or less.

[0052] FIG. 6 is a diagram showing the relationship between the normalized squeeze roll diameter X, the normalized seam guide width Y, and the convergence angle θ obtained by the present inventors. As shown in FIG. 6, both the normalized squeeze roll diameter X and the normalized seam guide width Y affect the increase in the convergence angle θ. Specifically, the smaller the normalized squeeze roll diameter X, the greater the contribution rate of the normalized seam guide width Y to the increase in the convergence angle θ, but when the normalized squeeze roll diameter X is large, the contribution rate of the normalized seam guide width Y to the increase in the convergence angle θ is small. In other words, when the normalized squeeze roll diameter X is large, the convergence angle θ is difficult to increase even if the normalized seam guide width Y is increased. In order to increase the convergence angle θ, it is preferable to adjust both the normalized squeeze roll diameter X and the normalized seam guide width Y in a well-balanced manner.

[0053] In this embodiment, the normalized squeeze roll diameter X and the normalized seam guide width Y are preferably Y≧0.003X 2 The range is set to satisfy -0.025X+0.6. This makes it easier to enlarge the convergence angle θ at both ends 11L, 11R of the metal plate 10, and makes it possible to more reliably make the convergence angle θ 5.0° or more. This makes it easier to enlarge the process window of upset welding, and makes it possible to more stably ensure good welding quality.

[0054] In this embodiment, the normalized squeeze roll diameter X is preferably 3.60 or more. This ensures the rigidity of the squeeze rolls 33, particularly the side rolls 331L, 331R. This makes it possible to suppress a decrease in the life of the squeeze rolls 33. In addition, it is possible to suppress the occurrence of defective shapes of electric-resistance welded pipes, enabling stable production of electric-resistance welded pipes.

[0055] In this embodiment, the normalized seam guide width Y is preferably 0.80 or less. In this case, the distance between both ends 11L, 11R of the metal plate 10 before welding is not excessively large, so that both ends 11L, 11R tend to be properly butted together during welding. This makes it possible to prevent the occurrence of defective shapes in the electric-resistance welded pipe, and allows for stable production of electric-resistance welded pipe.

[0056] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present disclosure. EXAMPLES

[0057] The present disclosure will be described in more detail below with reference to examples, although the present disclosure is not limited to the following examples.

[0058] In order to confirm the effect of the present disclosure, a manufacturing test was conducted on an electric resistance welded pipe (φ76.3×t2.0 mm) that is relatively large in diameter and thin among small-diameter electric resistance welded pipes and difficult to increase the pipe-making speed. In this test, the welding heat input was changed while pipe-making was performed at 52 m / min for multiple test examples with different standardized squeeze roll diameters X and / or standardized seam guide widths Y, and the heat input range (proper heat input range) of the first condition that allows fusion welding was evaluated using a known welding monitoring technique. Specifically, the maximum value of the heat input when no inter-slit arc was observed under the second type welding condition was set as the upper limit, and the welding heat input was reduced from the maximum value by 1% increments relative to the maximum value, and the minimum value of the heat input when no cracks were generated in a flattening test performed on the welded sample was set as the lower limit. The difference between the upper limit and the lower limit was determined as the heat input range (proper heat input range) of the first condition that allows fusion welding. The conditions and results of this test are shown in Table 1.

[0059] [Table 1]

[0060] In this test, the heat input range (proper heat input range) of the first condition for which fusion welding is possible was evaluated as poor when it was less than 3% (<3%), good when it was 3% or more (3%≦), and excellent when it was more than 10% (10%<). As shown in Table 1, in test examples 2 to 4, 6 to 8, and 12 in which the convergence angle θ was 5.0° or more, the heat input range of the first condition for which fusion welding is possible was 3% or more, and the evaluation of the effect of expanding the proper heat input range was good or excellent. In particular, in test examples 4, 7, and 8 in which the convergence angle θ was 6.0° or more, the heat input range of the first condition for which fusion welding is possible was 10% or more, and the evaluation of the effect of expanding the proper heat input range was excellent. Therefore, it was confirmed that the process window (proper heat input range) of upset welding is expanded by setting the convergence angle θ at both ends of the metal plate to 5.0° or more.

[0061] Fig. 7 is a graph showing the relationship between the normalized squeeze roll diameter X and the normalized seam guide width Y obtained from the results of this test. In Fig. 7, the normalized squeeze roll diameter X is taken on the horizontal axis and the normalized seam guide width Y is taken on the vertical axis, and the normalized squeeze roll diameter X and the normalized seam guide width Y of each test example are plotted. In the graph of Fig. 7, when an approximation curve is drawn to separate the plots of the test examples that were evaluated as excellent or good in this test from the plots of the test examples that were not evaluated, the equation of this approximation curve is Y=0.003X 2 The result was -0.025X+0.6.

[0062] From FIG. 7, if the normalized squeeze roll diameter X and the normalized seam guide width Y are in the region above the approximate curve, that is, Y≧0.003X 2 In the case of -0.025X+0.6, it can be said that the process window (appropriate heat input range) can be expanded.

[0063] As shown in Table 1, in Test Example 13 in which the normalized seam guide width Y was greater than 0.80, the electric resistance welded pipe manufactured from the metal plate did not have a circular shape, and defective forming was confirmed. Therefore, from the viewpoint of avoiding defective forming, the normalized seam guide width Y is preferably 0.80 or less.

[0064] In Test Example 14, in which the normalized squeeze roll diameter X was less than 3.60, a poor SQ reduction was confirmed. SQ reduction is a phenomenon in which the circumference of a tube becomes shorter when a metal plate formed into a tube shape is pressed by a squeeze roll to promote the discharge of molten metal from both ends of the butted metal plate. SR When the diameter X is small, the squeeze roll does not apply pressure well, resulting in poor welding. In Test Example 14, it is considered that poor SQ reduction occurred due to insufficient rigidity of the side roll. Therefore, from the viewpoint of avoiding poor SQ reduction, the normalized squeeze roll diameter X is preferably 3.60 or more. [Explanation of symbols]

[0065] 10:Metal plate 11L, 11R: End 30: Welding equipment 31:Seam guide 33: Squeeze roll 331L, 331R: Side roll 331a: Side

Claims

1. A method for manufacturing an electric resistance welded pipe, comprising the steps of: A step of forming a metal plate into a tubular shape while conveying the metal plate so that both ends of the metal plate face each other; a step of adjusting the distance between the opposing ends by a seam guide, heating and melting the ends, and then pressing the metal plate using a squeeze roll so that the ends, which approach and come into contact with each other as they move downstream in the conveying direction of the metal plate, are pressed against each other to weld the ends; Equipped with the welding step forms an angle between the two ends that approach each other and come into contact with each other downstream in the conveying direction of the sheet, the angle being 5.0° or more.

2. The method according to claim 1, The squeeze roll includes a pair of side rolls arranged on both sides of the metal plate as viewed along the conveying direction, each of the side rolls having a concave curved side surface toward a central axis, The width of the seam guide is W ＳＧ , the diameter of the side roll at the bottom of the side surface is D ＳＲ , the radius of curvature of the side surface is R ＳＲ And, W ＳＧ / R ＳＲ Standardized seam guide width Y, D ＳＲ / R ＳＲ A manufacturing method in which, when the normalized squeeze roll diameter X is defined as the normalized seam guide width Y and the normalized squeeze roll diameter X satisfy the following formulas. Y≦0.80 X≧3.60 Y≧0.003X ２ -0.025X+0.6

3. The method according to claim 1 or 2, The manufacturing method, wherein the outer diameter of the electric-resistance welded pipe is 10 mm or more and 110 mm or less.

4. A welding apparatus for welding opposite ends of a metal plate which is being formed into a tubular shape while being transported, comprising: A seam guide that adjusts the distance between the opposing ends; A squeeze roll is disposed downstream of the seam guide in the conveying direction of the metal sheet, the squeeze roll including a pair of side rolls each having a side surface concavely curved toward a central axis; Equipped with The width of the seam guide is W ＳＧ , the diameter of the side roll at the bottom of the side surface is D ＳＲ , the radius of curvature of the side surface is R ＳＲ And, W ＳＧ / R ＳＲ Standardized seam guide width Y, D ＳＲ / R ＳＲ A welding apparatus, wherein, when the normalized squeeze roll diameter X is defined as the normalized seam guide width Y and the normalized squeeze roll diameter X satisfy the following formulas. Y≦0.80 X≧3.60 Y≧0.003X ２ -0.025X+0.6

5. The welding device according to claim 4, The radius of curvature R ＳＲ The welding device has a diameter of 5 mm or more and 55 mm or less.

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