JPWO2020054051A1 - Manufacturing method of steel pipe and press die - Google Patents

Abstract

A plate material whose ends have been bent at both ends in the width direction is bent three times or more along the width direction to form a molded body having a U-shaped cross section, and the molded body is pressed. This is a method for manufacturing a steel pipe in which an open pipe having a seam gap portion in the longitudinal direction is formed and then the seam gap portion is joined to form a steel pipe, and the width of the plate material before end bending is defined as the plate width W. The body has a lightly machined part that is given a smaller curvature than other areas, or an unprocessed part that omits bending, centering on a part that is W / 4 away from the end of the plate width, and is open. The outer diameter of the steel pipe has a range of 20 [%] or more of the plate width W centered on the bottom of the U-shaped cross section and a range of 10 [%] or more of the plate width W from the end of the plate width. Pressing is performed so that the shape is inscribed in an arc having the same or substantially the same diameter as.

Description

The present invention relates to a method for manufacturing a steel pipe and a press die used in the method for manufacturing the steel pipe.

Conventionally, UOE forming technology has been widely used as a technology for forming steel pipes. This UOE forming technology is an open pipe which is a pipe body in which a steel plate is first pressed into a U shape and then pressed into an O shape, and has a seam gap between the width ends facing each other in the circumferential direction. Then, the seam gap portion of this open pipe is butt-joined by welding to form a steel pipe, and then the pipe is expanded to further expand the diameter of the steel pipe. However, the UOE forming technology requires a high pressing force in the process of pressing a steel plate into a U-shape or an O-shape to form an open tube, so that a large-scale press machine must be used. There is no situation.

Therefore, in manufacturing a steel pipe, as a technique for forming an open pipe by reducing the pressing force, for example, the widthwise end portion of the steel sheet is bent to give the end bent portion, and then the steel pipe is supported by the punch support. A press bend method has been put into practical use in which a steel plate is formed into a substantially circular shape by performing a plurality of three-point bending presses with a punch and a die to form an open pipe. On the other hand, the opening amount of the seam gap portion of the open pipe formed by this press bend method is larger than the width of the punch support, but if this opening amount is too large, the seam gap portions are welded to each other. The force required to close the seam gap by abutting the width edges facing each other increases, and the equipment for closing the seam gap increases in size. In addition, a force that tries to open the seam gap due to springback acts on the welded part after welding the seam gap that has an excessively large opening amount, so that welding defects are likely to occur. If the force is too large, welding is performed. The part breaks.

Therefore, Patent Documents 1 to 4 disclose techniques for reducing the opening amount of the seam gap portion of the open pipe after press bending. Patent Document 1 discloses a technique in which the width of the punch support is reduced and the opening amount of the seam gap portion of the open pipe is reduced by allowing the joint portion between the punch tip portion and the punch support to rotate freely. ing. In Patent Document 2, an interval holding means for restricting the movement of the plate material in a direction orthogonal to the movement direction of the punch is provided, and a large pressure is applied in the final bending process without the plate width end contacting the punch support. A technique for reducing the opening amount of the seam gap portion of an open pipe is disclosed. Patent Document 3 discloses a technique of measuring the gap between the plate width end portion and the punch support after the final reduction step and reducing the gap as much as possible to reduce the opening amount of the seam gap portion of the open pipe. There is. Further, in Patent Document 4, the press bend forming step up to that point is determined by determining the reduction amount by the punch in the final process based on the time when the interval between the plate width ends becomes a predetermined value at the time of reduction in the final bending process. Disclosed is a technique for reducing the opening amount of the seam gap portion of the open pipe regardless of the difference in shape caused in.

However, in the techniques disclosed in Patent Documents 1 to 4, the opening amount of the seam gap portion of the open pipe cannot be made smaller than the width of the punch support. Therefore, Patent Documents 5 to 9 disclose a technique for further processing the open pipe after press bend molding to reduce the opening amount of the seam gap portion. Patent Document 5 discloses a technique for forming a steel pipe after press bending with a small load by performing hot roll forming. In Patent Document 6, a strain detector capable of detecting the inclination or strain of the pressing material mounted on the slide is provided, and the pressing material can be tilted in response to the detection of the inclination or strain of the strain detector. When the molding material is press-formed into a pipe shape by arranging it so as to be able to move in parallel, the pressing material is tilted or moved in parallel so that the amount of strain is smaller than the amount of inclination or strain of the pressing material. The molding technique is disclosed. In Patent Document 7, at least one bending step acting on the inner surface of the plate material on the left and right sides with respect to the center defined by the longitudinal axis of the upper tool entering the plate material to be gradually formed, as compared with other bending steps. By performing a slight molding, a slit tube with a non-circular preform is formed, which then acts on the non-circular preform from the outside, each time appropriately, in the pre-slightly molded regions on both sides of the center. A technique for forming a completed slit tube by applying a pressing force is disclosed. Further, in Patent Document 8, a molded product having a flat portion between portions bent to at least two pipe curvatures is subjected to plastic deformation at least one flat portion to obtain a predetermined curvature. , A technique for forming a pipe with a closed slit portion is disclosed. Further, in Patent Document 9, a molded body is provided with a lightly machined portion having a very slight curvature as compared with other regions, or an unprocessed portion without bending is provided, and a molded body is reduced to form an open pipe. Disclosed is a method of forming a pipe in which a slit portion is closed by applying a pressing force without restraining a lightly processed portion or an unprocessed portion. Further, at the time of pressing, it is recommended that the molded body is held by the mold in a U-shaped posture with the open portion facing upward, and is supported by the lowermost end of the molded body.

Patent Documents 10 and 11 disclose a technique for manufacturing a UOE pipe having a product diameter different from the inner diameter of the O-press die and the outer diameter of the product pipe. The mold disclosed in Patent Document 10 has a shape in which the inner surface of the upper and lower dies is cut out only in a part of a horizontally oblong circle, and the operation of the mold is described in FIG. 3 (a) of Patent Document 10. In FIG. 4A, the O-tube is in contact with the entire inner surface of the O-press die. Further, in Patent Document 11, an arc having a radius larger than the outer diameter of the product is formed on the inner surface, and a mold is used in which the end face is ground in advance and the gap is sufficiently large, and the mold is filled with a material to determine the predetermined value. A method of forming a circular shape by rotating the formed pipe by about 90 [°] and performing O-press again is disclosed. Even in the first O-pressing process at this time, the steel pipe is in close contact with the entire surface of the mold.

Japanese Unexamined Patent Publication No. 2004-82219 Japanese Unexamined Patent Publication No. 2011-56524 International Publication No. 2014/188468 International Publication No. 2014/192043 Japanese Unexamined Patent Publication No. 2005-324255 Japanese Unexamined Patent Publication No. 2005-21907 Japanese Unexamined Patent Publication No. 2012-250285 U.S. Pat. No. 4,149,399 International Publication No. 2016/08467 Japanese Unexamined Patent Publication No. 2003-39115 JP-A-2002-178026

However, the technique disclosed in Patent Document 5 has a problem that the manufacturing cost is significantly increased when the consumption of heat energy required for heating is included. In addition, this technique may impair the characteristics of a plate material manufactured through a processing heat treatment process in order to have strength, toughness, and weldability. In the techniques disclosed in Patent Documents 6 to 8, since the molding material or the non-circular preform is molded separately on the left and right, if the deformation amount is different on the left and right, the seam gap portion or the slit portion which becomes the welded portion is formed. In addition, there is a concern that a step (mismatch) will be formed. Further, in these techniques, if it is attempted to deform to a desired shape at one time, the deformation may be concentrated locally and the roundness of the steel pipe may be deteriorated. Therefore, it is indispensable to perform the deformation multiple times. There is a limit to efficient molding. Further, in the technique disclosed in Patent Document 9, since the radius of the lower mold is larger than the outer diameter of the pipe, bending back is performed at the lowermost end of the U-shaped molded body, and the deformation is such that the gap portion is opened. Therefore, it may not be possible to reduce the distance between the slit portions. Further, in the techniques disclosed in Patent Documents 10 and 11, since the pressing process is performed in a state where the O-tube is in close contact with the entire surface of the mold, a high pressing force is required as described above, so that a large-scale pressing machine is required. There is no change in the situation where we have no choice but to use.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for manufacturing a steel pipe and a press die capable of efficiently forming a steel pipe having a high roundness.

In order to solve the above-mentioned problems and achieve the object, the method for manufacturing a steel pipe according to the present invention is to bend a plate material having end bending processing at both ends in the width direction three times or more along the width direction. A molded body having a U-shaped cross section is formed by processing, and then the molded body is pressed to obtain an open pipe having a seam gap in the longitudinal direction thereof, and then the seam is formed. In a method for manufacturing a steel pipe in which gaps are joined to form a steel pipe, when the width of the plate material before the end bending process is the plate width W, the molded body is separated from the plate width end by W / 4. It has a lightly machined part that is given a small curvature compared to other areas, or an unprocessed part that omits bending, and the shape of the open pipe is the maximum of the U-shaped cross section. The range of 20 [%] or more of the plate width W and the range of 10 [%] or more of the plate width W from the plate width end are the same diameter or substantially the same diameter as the outer diameter of the steel pipe centering on the lower part. It is characterized in that it is pressed so as to have a shape inscribed in the arc of.

Further, in the above-described invention, the method for manufacturing a steel pipe according to the present invention has a plate width W centered on the lowermost portion of the U-shaped cross section inscribed in an arc having the same or substantially the same diameter as the outer diameter of the steel pipe. The range of 20 [%] or more was defined as A, and the total of the range of 10 [%] or more of the plate width W from both ends of the plate width inscribed in an arc having the same or substantially the same diameter as the outer diameter of the steel pipe was defined as B. When, it is characterized in that the equation (1) is satisfied.
2 | AB | / (A + B) <0.4 ... (1)
Here, | AB | indicates the absolute value of AB.

Further, in the method for manufacturing a steel pipe according to the present invention, in the above invention, one of the pair of dies is molded into the other die so that the U-shaped open side of the molded body faces each other. When the body is placed and the molded body is sandwiched between the pair of dies and the molded body is pressed, the other mold is in a state where the molded body is placed on the other mold. Then, the press processing is completed without contacting the molded body except for a range in which the shape is inscribed in an arc having the same or substantially the same diameter as the outer diameter of the steel pipe, centering on the lowermost portion of the U-shaped cross section. In this state, a part of the other mold is provided with a processed surface that does not come into contact with the open tube, and the one mold has the molded body placed on the other mold. It is characterized in that a part of the one die is provided with a processed surface that does not come into contact with the open tube in a state where the molded body does not come into contact and the press processing is completed.

Further, in the method for manufacturing a steel pipe according to the present invention, in the above invention, a mold having a radius of an arc portion within a range of ± 3.5 [%] with respect to a radius corresponding to the outer radius of the steel pipe is used. It is characterized in that it is pressed.

Further, in the method for manufacturing a steel pipe according to the present invention, in the above invention, when the molded body is pressed, the center of the press die used for the press working of the molded body and the center in the width direction of the molded body are formed. It is characterized by being in agreement.

Further, the method for manufacturing a steel pipe according to the present invention is characterized in that, in the above invention, the molded body is held in a U-shaped posture with the U-shaped open side facing upward.

Further, the press die according to the present invention is a press die used in the method for manufacturing a steel pipe of the above invention, and the press die is composed of a pair of pressing bodies that sandwich the molded body, and each die. ± 3.5 [%] with respect to the radius corresponding to the outer radius of the steel pipe so that the arc center is located at a position corresponding to the processing center of each mold on the surface of the mold that can come into contact with the molded body. ] Is formed, the central angle of the arc portion in each mold is 70 degrees or more, and the total angle of the central angles of both molds is less than 360 degrees. It is characterized by.

Further, the press die according to the present invention is characterized in that, in the above invention, the angles of the central angles of both dies are the same.

Further, in the above invention, the press die according to the present invention is a straight line portion connected to both ends of the arc portion in the arc direction, or a small curvature arc portion having a curvature smaller than that of the arc portion. It is characterized by having.

Further, the method for manufacturing a steel pipe according to the present invention is characterized in that the press die of the above invention is used in the method for manufacturing a steel pipe of the above invention.

In the steel pipe manufacturing method and the press die according to the present invention, there is an effect that a steel pipe having a high roundness can be efficiently formed.

FIG. 1 is an external perspective view of a die, a punch, and the like used to form a molded body having a U-shaped cross section by the press bend method according to the embodiment. FIG. 2 is a diagram showing a procedure for molding a molded body having a U-shaped cross section by a press bend method. FIG. 3 is a cross-sectional view of a molded body having a U-shaped cross section. FIG. 4 is a diagram schematically showing a process of forming an open tube by applying O-press to a molded body. FIG. 5 is an explanatory view of an arc portion, a straight portion, and a central angle of the upper mold and the lower mold. FIG. 6 is a graph showing the relationship between the opening amount of the seam gap portion of the open pipe and the restraint range together with the press load. FIG. 7 is a diagram schematically showing a deformation state when an open tube is formed by using an upper mold and a lower mold having a restraint range of 0 degrees. FIG. 8 is a graph showing the relationship between the restraint range and the roundness of the steel pipe before the pipe expansion when the seam gap portion of the open pipe is closed by welding. FIG. 9 is a graph showing the relationship between the restraint range and the press load. FIG. 10 is a graph showing the result of the opening amount of the seam gap portion of the open pipe when the individual restraint ranges of the upper mold and the lower mold are changed. FIG. 11 is a graph showing the result of the roundness of the steel pipe before expansion, which is formed by closing the seam gap portion of the open pipe by welding when the individual restraint ranges of the upper mold and the lower mold are changed. Is. FIG. 12 is a graph showing the result of the press load when the individual restraint ranges of the upper die and the lower die are changed. FIG. 13 shows the opening of the seam gap portion when the length of the lightly processed portion or the unprocessed portion of the molded body after press bending is changed while the restraint range of the upper mold and the restraint range of the lower mold are the same. It is a graph which shows the result of the quantity. FIG. 14 shows the steel pipe before expansion when the length of the lightly processed portion or the unprocessed portion of the molded body after press bending is changed while the restraint range of the upper mold and the restraint range of the lower mold are the same. It is a graph which shows the result of roundness. FIG. 15 shows the result of the press load when the restraint range of the upper mold and the restraint range of the lower mold are the same and the lengths of the lightly processed portion or the unprocessed portion of the molded body after press bending are changed. It is a graph. FIG. 16 is a graph showing the result of the opening amount of the seam gap portion of the open pipe when the radii of the arc portions of the upper mold and the lower mold are changed. FIG. 17 is a graph showing the result of the press load when the radius of the arc portion of the upper die and the lower die is changed.

Hereinafter, a method for manufacturing a steel pipe according to the present invention and an embodiment of a press die used in the method for manufacturing the steel pipe will be described. FIG. 1 is an external perspective view of a die 1 and a punch 2 used for molding a molded body having a U-shaped cross section by the press bend method according to the present embodiment. The die 1 is arranged in a transport path of the plate material S formed by a plurality of transport rollers 3, and is composed of a pair of left and right rod-shaped members 1a and 1b that support the plate material S at two locations along the plate material transport direction. Has been done. Further, the interval e of the rod-shaped members 1a and 1b in the plate material transport direction can be changed according to the size of the steel pipe to be finally formed.

The punch 2 is movable in the direction of approaching and separating from the die 1, and is the same as the downwardly convex punch tip 2a that presses the plate material S and the back surface (upper end surface) of the punch tip 2a. It is composed of a punch support 2b that is connected by the width of the punch and supports the punch tip 2a. The upper end of the punch support 2b is connected to a driving means (not shown), and the driving means can apply a pressing force to the punch tip 2a.

Figure 2 shows a procedure for molding the molded body S ₁ forming a U-shaped cross section by pressing bend method. In this procedure, for the plate material S that has been subjected to the edge bending process in advance, the order is from top to bottom in the left column of FIG. 2, then from top to bottom in the center row of FIG. 2, and finally in the right column of FIG. In the above, an example in the case of performing bending processing and feeding of the plate material S is specifically shown. Further, the arrows attached to the punch 2 and the plate material S in FIG. 2 indicate the moving directions of the punch 2 and the plate material S at each stage.

In order to form the plate material S into a tubular shape using the plate material S as a starting material, first, the plate material S is subjected to edge bending. This end bending process is performed on the plate width end portion, which is relatively difficult to bend as compared with the case where the plate material S is bent using the die 1 and the punch 2, and the end bending process of the plate material S By providing the end bending portion at the plate width end portion, it becomes easier to obtain a steel pipe with a high roundness as compared with the case where the end bending portion is not provided. The roundness of the steel pipe is an index showing how close the cross-sectional shape of the steel pipe is to a circle, and the difference between the maximum and minimum amount of fluctuation from the approximate arc on the entire circumference of the steel pipe is calculated by the steel pipe diameter. It is a value indicated by the divided rate. For example, at an arbitrary pipe length position of a steel pipe having an outer diameter D, the pipe is divided into 8 equal parts, 12 equal parts, 16 equal parts, or 24 equal parts in the circumferential direction, and the outer diameters at opposite positions are measured. When the maximum diameter and the minimum diameter are D _max and D _min , respectively, the roundness [%] is defined by {(D _max −D _min ) / D} × 100. The closer the roundness is to 0, the closer the cross-sectional shape of the steel pipe is to a perfect circle.

The plate material S provided with the edge bending portion is placed on the die 1 shown in FIG. 1, and while the plate material S is intermittently fed at a predetermined feed amount, the plate material S is performed by the procedure shown in FIG. along the width direction it is 3 times or more the bending undergone a is formed into the molded body S ₁ forming a U-shaped cross section as a whole.

Figure 3 is a cross-sectional view of a shaped body S ₁ forming a U-shaped cross section. When the width of the plate material S before the edge bending process is the plate width W, as shown in FIG. 3, a part of the molded body S ₁ , particularly the W / 4 portion which is a portion separated by W / 4 from the plate width end, respectively. An unprocessed portion P in which bending is omitted is provided around the center. The unprocessed portion P can be provided by increasing the feed of the plate material S and omitting the pressing by the punch 2. Incidentally, a portion of the molded body S _1, in particular about respective from strip width end W / 4 parts of the unprocessed portion P without curvature than the other portion in comparison with a small (other portions, very small A lightly machined portion (with a curvature) may be provided. In that case, "unprocessed portion P" may be appropriately read as "lightly processed portion" in the following description. The lightly machined portion can be provided by reducing the amount of pressing applied by the punch 2 to be smaller than that of other portions.

Further, the shape of the punch 2 shown in FIGS. 1 and 2 is an I-shape in which the width of the punch tip portion 2a in the plate material transport direction and the width of the punch support 2b in the plate material transport direction are the same. However, the shape of the punch 2 is not limited to this. For example, as the punch 2, a punch 2 having a substantially inverted T shape in which the width of the punch tip portion 2a in the plate material transport direction is larger than the width of the punch support 2b in the plate material transport direction can also be used. When the widths of the punch supports 2b in the plate material transport direction are the same, it is better to use the substantially inverted T-shaped punch 2 than to use the I-shaped punch 2 with respect to the plate material S with one pressing. Therefore, a larger area can be pressed, and the number of times of pressing can be reduced.

Subjected to bending by the press bending method with respect to the plate material S, After shaping the shaped bodies S ₁ forming a U-shaped cross-section, the upper mold 4 and the lower mold 5 are a pair of molds as shown in FIG. 4 comprising a molded body S ₁ using a press mold to O-shape by performing O press pressing, between the plate width end portions which face each other in the circumferential direction is a tubular body having a seam gap G open pipe to form the S _2.

Next, a procedure for forming the open tube S ₂ by applying an O-press to the molded body S ₁ will be described with reference to FIG. First, as shown in FIGS. 4 (a), (as U-shaped open side of the molded body S ₁ is directed upward) upper mold 4 and the molded body S ₁ of the U-shape so that the open side faces, bottom The molded body S ₁ is installed in the mold 5, and the molded body S ₁ is sandwiched between the upper mold 4 and the lower mold 5. Further, when pressing of the molded body S ₁ is designed so as to coincide with the processing center of the press die, and a center in the width direction of the molded body S _1. As a result, the plate width end portion can be pressed evenly on the left and right sides of the U-shaped open side of the molded body S1.

As shown in FIG. 5, the surface that may contact the shaped body S ₁ of the upper mold 4 and the lower mold 5, the center angle θ a outer diameter and the same diameter or substantially the same diameter of the steel pipe to be molded Arc portions 4a and 5a are formed, and this range is pressed into a shape inscribed in an arc having the same or substantially the same diameter as the outer diameter of the steel pipe. For example, the case where the central angle θ is 360 degrees corresponds to the case where 100 [%] of the plate width is pressed into the inscribed shape. Hereinafter, the central angles θ of the arc portions 4a and 5a will be referred to as a restraint range, and the value obtained by dividing the angle by 360 degrees will be inscribed in an arc having the same or substantially the same diameter as the outer diameter of the steel pipe. It will be in the range to be pressed. Arc portion 4a is arc center to a position which coincides with the processing center O _p4 of the upper mold 4 is positioned, the arc portion 5a, arc center is located at a position which coincides with the processing center O _p5 of the lower die 5 doing. Further, the upper mold 4 has straight portions 4b ₁ and 4b ₂ connected to both ends of the arc portion 4a in the arc direction, and the lower mold 5 has straight portions connected to both ends of the arc portion 5a in the arc direction, respectively. It has parts 5b ₁ and 5b ₂ . The upper mold 4 and the lower mold 5 have a small curvature arc portion having a smaller curvature than the arc portions 4a and 5a instead of the straight portions 4b ₁ , 4b ₂ , 5b ₁ , 5b _2. May be good. In the present invention, from the viewpoint of enhancing the symmetry of the finally obtained steel pipe, the straight portions 4b ₁ , 4b ₂ , 5b ₁ , 5b ₂ or the small curvature arc portion connected to the arc portions 4a, 5a is the processing center. It is preferable that it is symmetrical with respect to _Op4 and _Op5 , that is, with respect to the centers of the arc portions 4a and 5a. Further, it is preferable to perform press working using a die having an arc portion radius within a range of ± 3.5 [%] with respect to a radius corresponding to the outer radius of the steel pipe. The reason will be described later.

Next, the molded body S ₁ sandwiched by the upper mold 4 and the lower die 5, subjected to O pressing and rolling in the upper mold 4, as shown in Figure 4 (b). At this time, the circular arc portion 4a, 5a and opposite portions of the upper mold 4 and the lower mold 5 in the molding member S ₁ is constrained by upper mold 4 and the lower mold 5, non-molded body S ₁ The processed portion P is not constrained by the upper mold 4 and the lower mold 5. Therefore, with a small pressing force than the pressing force required when the entire circumference of the shaped body S ₁ is constrained by the upper mold 4 and the lower mold 5, open pipe S as shown in FIG. 4 (c) ₂ can be molded.

Then, in the manufacturing method of a steel pipe according to the present embodiment, a press die composed of upper mold 4 and the lower die 5 which, the shape of the open pipe S _2, the plate around the bottom of the U-shaped cross section A range of 20 [%] or more of the width W (corresponding to a central angle θ of 70 degrees or more) and a range of 10 [%] or more of the plate width W (corresponding to a central angle θ of 35 degrees or more) from the plate width end. but as a shape inscribed in a circular arc of the outer diameter and the same diameter or substantially the same diameter of the steel tube, the molded body S ₁ pressing.

Then, in the present embodiment, from the viewpoint of improving the shape of the steel pipe finally obtained, the range in which the open pipe S ₂ is inscribed in the mold is substantially the same on the upper mold 4 side and the lower mold 5 side. The size is preferable. That is, A is a range of 20 [%] or more of the plate width W centered on the lowermost part of the U-shaped cross section inscribed in an arc having the same or substantially the same diameter as the outer diameter of the steel pipe, and has the same diameter as the outer diameter of the steel pipe. Alternatively, it is preferable that the equation (1) is satisfied, where B is the sum of the range of 10 [%] or more of the plate width W from both ends of the plate width inscribed in an arc having substantially the same diameter.
2 | AB | / (A + B) <0.4 ... (1)
Here, | AB | indicates the absolute value of AB.
The meaning of the equation (1) will be described in detail later.

In the method for producing a steel pipe according to the present embodiment, the open pipe S _2, certainly is inscribed in a mold in a predetermined range, in order to obtain a good shape, as shown in FIG. 5, the press working moldings _{S 1} before being subjected, in a U-shaped cross section, the tangent TL ₁ in W / 2 parts is a plate width central portion, the angle between the tangent line _TL 21, _{TL 22} in W / 4 parts θ It is preferable that ₁₁ , θ ₁₂ is 35 degrees or more and less than 90 degrees. Further, in the molded body S ₁ before being pressed, the angles θ ₂₁ and θ ₂₂ formed by the tangents TL ₃₁ and TL ₃₂ at the plate width end and the tangents TL ₂₁ and TL ₂₂ at the W / 4 portion are formed. It is preferably 35 degrees or more and less than 90 degrees. Further, in order to make the inscribed range on the upper mold 4 side and the lower mold 5 side the same, the sum of the angles θ ₁₁ and θ ₁₂ formed by the tangent line TL ₁ and the tangent lines TL ₂₁ and TL ₂₂ and the tangent line. It is preferable that the sum of the angles θ ₂₁ and θ ₂₂ formed by the TL ₃₁ and TL ₃₂ and the tangents TL ₂₁ and TL ₂₂ is substantially the same.

It should be noted that these angles, following the reasons, mold shape during processing equipment and for bending the molded body S ₁ of the U-shaped, the shaped body S ₁ of U-shape open pipe S ₂ It is necessary to determine in consideration of. If these angles are too large, the distance between the plate width ends will be small. The distance is, the smaller than the width of the punch support 2b when bending the molded body S ₁ of the U-shape, making it impossible to obtain a molded product S ₁ of the U-shape. On the other hand, if these angles are too small, the distance between the plate width ends of the U-shaped body S ₁ is increased, when the molded body S ₁ of the U-shaped is placed in a mold, the plate width The end becomes larger than the opening of the upper mold 4, and the processing force cannot be applied. Further, the distance between the left and right unprocessed portions P becomes too large, and the lower mold 5 cannot be placed correctly.

Further, the molded body S ₁ to the lower mold 5, which is the other die so that one of the upper mold 4 is a mold with U-shaped open side of the molded body S ₁ is opposite of the pair of molds the is placed, in the molded body S ₁ by sandwiching the molded product S ₁ by the upper mold 4 and the lower die 5 Upon performing press working, the upper mold 4 and the lower die 5, as follows It has a machined surface. That is, the lower mold 5, in a state of placing the molded bodies S ₁ to the lower mold 5, around the bottom of the U-shaped cross-section, 20% or more in the plate width W (center angle θ is 70 A part of the lower die 5 is provided with a processed surface that does not come into contact with the open tube S ₂ in a state where the molded body S ₁ does not come into contact with the molded body S ₁ except for the range of (corresponding to a degree or more). Further, the upper die 4 is opened in a part of the upper die 4 in a state where the molded body S ₁ is placed on the lower die 5 and the molded body S ₁ does not come into contact with the lower die 5 and the press working is completed. and a working surface that does not contact the tube S _2.

Then, in the present embodiment, when pressing of the molded body S _1, that the center of the press die used for press working of the compact S _1, and the center in the width direction of the molded body S ₁ is match preferable. This is because the addition of symmetric force relative to the center in the width direction of the molded body S _1, it contributes to the shape accuracy of the finally obtained steel pipes.

Then, in the present embodiment, the molded body S ₁ is preferably held in a U-posture with its U-shaped open side upwards. This is partly because it is easier to work by pressing in this position. As another reason, if the case with its U-shaped open side downward, since the own weight of the molded body S ₁ is applied to the plate width end portions of the molded article S _1, or the plate width ends, This is to avoid scratches on the mold as it may be scratched.

In the present embodiment, when forming the open pipe S ₂ is subjected to O press the molded body S ₁ with upper mold 4 and the lower mold 5, the raw portion P in the molding material S ₁ The pressing force is applied to a portion separated by W / 4 from the center toward the end of the plate width, and the reason is as follows. That is, the bending moment when the whole of the molded body S ₁ is becomes circular, the position where the central angle away by an angle φ from the pressing unit, M = F · r · cosφ (F: pressing force, r: circle Radius), the maximum at a position 90 degrees away from the pressing portion, and the maximum deformation. Therefore, by applying a pressing force at a position 90 degrees from the center of the unprocessed portion P, that is, a position separated by 1/4 of the entire circumference, the unprocessed portion P is effectively deformed. At this time, the bending moment is maximum at a position 90 degrees away from the position where the pressing force is applied, and becomes smaller as the distance from this position is increased. Therefore, in order for the unprocessed portion P to undergo sufficient plastic deformation, it is necessary to apply a pressing force to a portion separated by W / 4 ± 0.07 W from the center of the unprocessed portion P toward the end of the plate width. preferable.

Further, in the present embodiment, the center of the unprocessed portion P is provided at a portion including a position separated by W / 4 from the plate width end, and the reason is as follows. That is, as described above, it is desirable that the pressing force is applied to a portion separated by W / 4 from the center of the unprocessed portion P toward the plate width end portion, but the molded body S ₁ is an open tube S ₂ . in step, the shape of the molded body S ₁ changes, also changes the position for adding the contact position changes the pressing force of the upper mold 4 and the molded body S _1. When the unprocessed portion P is provided at a portion of the molded body S ₁ including a position separated by W / 4 from the plate width end, the portion to which the pressing force is applied is always the plate width end of the molded body S ₁ . The unprocessed portion P is most deformed. By doing so, the raw portion P can be deformed by one pressing without changing the pressing position. Further, the raw portion P, preferably provided from the position i.e. the plate width ends of the molded body S ₁ adds a pressing force in the range of W / 4 ± 0.07W.

Further, the pressing early stages such as shown in FIG. 4 (a) and 4 (b), since the plate width end portions are in contact with the upper mold 4, the unprocessed portion P from the plate width ends of the molded body S ₁ It is preferable to provide it in a portion including a portion separated by W / 4.

6, the relationship between the restraint range and amount of opening of the seam gap G of the open pipe S _2, is a graph showing together with the press load. The relationship between the opening amount and the restraining range shown in FIG. 6, and the press load, the both end portions of the open pipe S ₂ performs expanded tube straightening by the expansion ratio 1 [%] after welding, the tensile strength 630 [ MPa], outer diameter 660.4 [mm], pipe thickness 40.0 [mm] when forming a steel pipe.

Moldings S ₁ after pressing the bend, the raw portion P of length W / 12 provided from both sides of the plate width end in a portion of the respective W / 4, and the tangent at plate width central portion, W from the plate width end The angles θ ₁₁ and θ ₁₂ formed by the tangent at the W / 4 part, which is a part separated by 4/4, are 75 degrees, and the angles θ ₂₁ and θ ₂₂ formed by the tangent at the plate width end and the tangent at the W / 4 part. Has a shape of 75 degrees. This is a case where the molded body S ₁ is sandwiched between the upper mold 4 and the lower mold 5 having the same restraint range. Further, the pressing amount is set so that the distance connecting the W / 2 portions of the open pipe S ₂ is equal to the diameter before the pipe expansion (the vertical diameter of the reduction amount in the O press is the diameter before the pipe expansion. I try to match). 6, the larger the constraint range, it can be seen that the amount of opening of the seam gap G of the open pipe S ₂ becomes small.

Figure 7 is a diagram schematically showing a modified situation when the constraint range was molded open pipe S ₂ with the upper mold 4 and the lower mold 5 of 0 degrees. When the restraint range of the upper mold 4 and the lower mold 5 is 0 degrees, the upper mold 4 contacts only both ends of the molded body S ₁ , and the lower mold 5 only contacts the central portion of the plate width of the molded body S _1. This is a case where the arcuate portions 4a and 5a are formed into arcs having a diameter 1.16 times the outer diameter of the steel pipe so as to make contact with each other. As shown in FIG. 7 (a), the cross section of the shaped body S ₁ so that only the 6 o'clock portion when regarded in a clockwise is in contact with the lower mold 5, the diameter of the circular arc portion 5a of the lower die 5 steel The diameter is larger than the diameter. Therefore, as shown in FIG. 7 (b), 6 o'clock portion and the vicinity thereof of the molding S ₁ is in O press, occurs bent back as fit in the circular arc portion 5a of the lower die 5, the radius of curvature It is larger than the steel pipe diameter. Large Therefore, after the O press, the opening amount of the seam gap G of the open pipe S ₂ as shown in FIG. 7 (c), in conjunction with spring back at the 3 o'clock parts and 9:00 parts of the molded body S ₁ It becomes a thing.

Figure 8 is a graph showing the constrained range, the relationship between the roundness of the steel pipe before pipe expansion when closing the weld seam gap portion G of the open pipe S _2. From FIG. 8, when the restraint range is 60 degrees, the roundness is worse than when the restraint range is 0 degrees, but when the restraint range is increased, the roundness is improved and the restraint range is 70 degrees. It can be seen that in the above cases, the roundness is better than when the restraint range is 0 degrees. Further, it can be seen that the roundness is the best when the restraint range is 100 to 110 degrees.

FIG. 9 is a graph showing the relationship between the restraint range and the press load. From FIG. 9, it can be seen that the press load increases as the restraint range increases. For that reason, increasing the constraint range, restraint in an amount ranging opening of the seam gap G of the open pipe S ₂ becomes small, minute the pressing load increases, the pressing equipment is increased in size, the desired opening amount is obtained It is desirable to reduce the range. For example, the press load, 90 [%] when the individual restraint range of the upper die 4 and the lower mold 5 for restraining the entire periphery of the shaped body S ₁ in the upper mold 4 and the lower mold 5 is 180 degrees In order to make the following, the restraint range may be 150 degrees or less.

Figure 10 is a graph showing the results of the amount of opening of the seam gap G of the open pipe S ₂ with changes in individual restraining range of the upper die 4 and the lower mold 5. 11, the upper mold 4 and with changes in individual restraining range of the lower die 5, roundness of the steel pipe before pipe expansion molded by closing the seam gap portion G of the open pipe S ₂ by welding It is a graph which shows the result of. FIG. 12 is a graph showing the result of the press load when the individual restraint ranges of the upper die 4 and the lower die 5 are changed. In FIGS. 10 to 12, steel pipes having a tensile strength of 630 [MPa], an outer diameter of 660.4 [mm], and a pipe thickness of 40.0 [mm] similar to those in FIGS. 6, 8 and 9 are targeted. The horizontal axis is the average value of the restraint ranges of the upper mold 4 and the lower mold 5, and the symbols in the graph are changed for each restraint range of the lower mold 5. In the figure, for example, "lower 60 degrees" means that the restraint range in the lower mold 5 is 60 degrees.

From Figure 10, regardless of the individual restraint range of the upper die 4 and the lower mold 5, the average value of the constraint range of the upper die 4 and the lower mold 5 is large, the open pipe S ₂ seam gap G It can be seen that the opening amount of is small. Further, from FIG. 11, it can be seen that when the restraint range of either the upper mold 4 or the lower mold 5 is less than 60 degrees, the roundness of the steel pipe is deteriorated. Therefore, the individual restraint ranges of the upper mold 4 and the lower mold 5 do not necessarily have to be the same for the upper mold 4 and the lower mold 5, but in order to obtain a shape in which the roundness of the steel pipe is good. It is desirable that the restraint range of the upper mold 4 and the lower mold 5 is set to a restraint range exceeding 60 degrees for both. Further, from FIG. 12, it can be seen that the larger the average value of the restraint ranges of the upper die 4 and the lower die 5, the larger the press load. Therefore, when the upper limit value of the allowable press load is set, the range of the average value of the applicable restraint ranges of the upper die 4 and the lower die 5 is determined according to the upper limit value of the press load.

Further, in FIG. 11, the difference between the upper and lower restraint ranges is 30 degrees, and the difference is 29 [%] of the average value of the upper and lower restraint ranges, 90 degrees above / 90 degrees below, and 90 degrees above / 120 below. At 120 degrees above / 90 degrees below, the roundness after welding and before pipe expansion is very excellent at 1.5 [%] or less. On the other hand, the difference in the vertical restraint range is 30 degrees, but the difference is as large as 40 [%] of the average value of the vertical restraint range, and the one with 90 degrees above / 60 degrees below is a perfect circle after welding and before pipe expansion. The degree is slightly worse at 2.0 [%]. By reducing the difference between the upper and lower restraint ranges in this way, a good shape can be obtained. That is, in the present invention, the difference between the upper and lower restraint ranges is preferably less than 40 [%] of the average value of the upper and lower restraint ranges, and more preferably 30 [%] or less. Further, it is preferable that the difference between the upper and lower restraint ranges is less than 30 degrees. In other words, the relationship between the difference between the upper and lower restraint ranges and the average value of the upper and lower restraint ranges is that the plate width W is centered on the bottom of the U-shaped cross section inscribed in an arc having the same or substantially the same diameter as the outer diameter of the steel pipe. When the range of 20 [%] or more is defined as A, and the total of the range of 10 [%] or more of the plate width W from both ends of the plate width inscribed in an arc having the same or substantially the same diameter as the outer diameter of the steel pipe is defined as B. , It is preferable to satisfy the formula (1).
2 | AB | / (A + B) <0.4 ... (1)
Here, | AB | indicates the absolute value of AB.

13, as the same a restricting range of constraint range and a lower mold 5 of the upper mold 4, the seam gaps in the case of changing the length L of the unprocessed portion P of the molded article S ₁ after the pressing bend It is a graph which shows the result of the opening amount of G. 14, as the same a restricting range of constraint range and a lower mold 5 of the upper mold 4, before pipe expansion in the case of changing the length L of the unprocessed portion P of the molded article S ₁ after the pressing Bend It is a graph which shows the result of the roundness of a steel pipe. 15, as the same a restricting range of constraint range and a lower mold 5 of the upper mold 4, the result of the press load in case of changing the length L of the unprocessed portion P of the molded article S ₁ after the pressing Bend It is a graph which shows. In FIGS. 13 to 15, the angles formed by the tangent line at the center of the plate width and the tangent line at the W / 4 portion, which is a portion separated by W / 4 from the plate width end, are θ ₁₁ , θ ₁₂ , and the plate width end. When the angles formed by the tangent line in the portion and the tangent line in the W / 4 portion are set to θ ₂₁ and θ ₂₂ , these angles are all set to the same value and are changed according to the width of the unprocessed portion P, respectively. The horizontal axis is the average value of the restraint range of the upper mold 4 and the restraint range of the lower mold 5.

From Figure 13, the unprocessed portion P of the length L and the tangent of the angle theta ₁₁ of the molded body _{S 1, θ 12, θ 21} , regardless of the angle of theta _22, lower die and constraining the range of the upper die 4 The larger the average value with the restraint range of 5, the smaller the opening amount of the seam gap portion G, and when the average value between the restraint range of the upper mold 4 and the restraint range of the lower mold 5 is the same. It can be seen that the longer the length L and the smaller the angles of the angles θ ₁₁ , θ ₁₂ , θ ₂₁ and θ ₂₂ formed by the tangents, the smaller the opening amount. Further, it is seen from FIGS. 14 and 15, when the average value of the constraint range of the constraint range and a lower mold 5 of the upper mold 4 are the same, the roundness and the press load of the steel pipe, the molded body S ₁ It can be seen that there is almost no difference depending on the length L of the machined portion P and the angles of the tangents θ ₁₁ , θ ₁₂ , θ ₂₁ and θ ₂₂ . Thus, when the average value of the constraint range of the constraint range and a lower mold 5 of the upper mold 4 are the same, the length L of the unprocessed portion P of the molded body S ₁ long, tangential angle of θ _{11, θ 12, θ 21,} by reducing the angle of theta _22, without causing the difference in roundness and the press load of the steel pipe by the length L, a open open pipe S ₂ of the seam gap G It is possible to reduce the amount.

Figure 16 is a graph showing the results of the amount of opening of the seam gap G of the open pipe S ₂ in the case of changing the arcuate portion radius of the upper die 4 and the lower mold 5. FIG. 17 is a graph showing the result of the press load when the arc portion radii of the upper die 4 and the lower die 5 are changed. In FIGS. 16 and 17, the central angles of the arc portions 4a and 5a of the upper mold 4 and the lower mold 5 are set to 45 degrees, and the arc portion radius which is the radius of the arc portions 4a and 5a is changed to pull. It shows a case where a steel pipe having a strength of 630 MPa, an outer diameter of 660.4 [mm], and a pipe thickness of 40.0 [mm] is pressed down by an O-press so that the vertical diameter matches the diameter before the pipe expansion. Further, the horizontal axis of FIGS. 16 and 17 is the ratio of the radius of the arc portion to the radius of the outer diameter of the steel pipe (radius corresponding to the outer diameter of the steel pipe), and is greater than 1.0 when the radius of the arc portion is larger than the outer radius of the steel pipe. When the radius of the arc portion is smaller than the outer radius of the steel pipe, it becomes smaller than 1.0.

As shown in FIG. 16, when the arc portion radius of the upper mold 4 and the lower mold 5 is equal to the outer radius of the steel pipe (the horizontal axis of FIG. 16 is 1.0), the opening amount of the seam gap portion G becomes the smallest. ing. Meanwhile, since the upper die 4 and the arcuate portion radius of the lower die 5 is greater than the steel pipe outer radius, deformation bent back at six portions and the vicinity thereof of the molding S ₁ as shown in FIG. 7 occurs, As the radius of the arc portion of the upper mold 4 and the lower mold 5 increases, the opening amount of the seam gap portion G increases. Further, when the arc portion radius of the upper mold 4 and the lower mold 5 is smaller than the outer radius of the steel pipe, bending back deformation occurs at the portion where the arc portions 4a and 5a of the upper mold 4 and the lower mold 5 are completed. As the radius of the arc portion becomes smaller, the opening amount of the seam gap portion G becomes larger. As described above, it is most desirable that the arc portion radius of the upper mold 4 and the lower mold 5 is the same as the steel pipe outer radius, but the arc portion radius of the upper mold 4 and the lower mold 5 corresponds to the steel pipe outer radius. When ± 3.5 [%], the opening amount of the seam gap portion G is suppressed to 40 [mm] or less.

However, as can be seen from FIG. 17, the press load increases as the radius of the arc portion decreases, and especially when the radius of the arc portion is small, it is necessary to determine the radius in consideration of the load of the press machine. is there.

[Example 1]
Edge bending is performed on a steel plate having a length of 1000 [mm], a plate thickness of 40 [mm], and a tensile strength of 635 [MPa], which is processed to a plate width W of 1928 [mm] by providing a groove using an edge mirror. after was prepared molded body S ₁ subjected to press bending process. Next, with respect to the molded body S _1, with the upper mold 4 and the lower mold 5 of the various constraint range, by performing the O pressing by a press machine 30 [MN], moldings A, B Molded. Tables 1 and 2 show the shapes of the molded bodies A and B. The first letters A and B in "No." in Tables 1 and 2 indicate the shape of the molded body (molded bodies A and B), and the numbers after the letters A and B are the upper metal. The combination of the restraint ranges of the mold 4 and the lower mold 5 is shown.

In Table 1, as a condition A, an unprocessed portion having a width of 160 [mm] (W / 12) centered on the W / 4 portion from the plate width end is provided, and a tangent line at the plate width end and a W / 4 portion are provided. The molded body A is shown in which the angles θ ₂₁ and θ ₂₂ formed by the tangents are 65 degrees, and the angles θ ₁₁ and θ ₁₂ formed by the tangents at the center of the plate width and the tangent at the W / 4 portion are 73 degrees. In Table 2, as condition B, an unprocessed portion is provided with a width of 321 [mm] (W / 6) (twice the width of condition A) centering on the W / 4 portion from the plate width end, and the plate width end portion is provided. The angles θ ₂₁ and θ ₂₂ formed by the tangent line in the W / 4 part and the tangent line in the W / 4 part are 59 degrees, and the angles θ ₁₁ and θ ₁₂ formed by the tangent line in the center of the plate width and the tangent line in the W / 4 part are 61 degrees. The molded body B is shown. The molded bodies A and B are symmetrical with respect to the straight line connecting the center of the plate width end portion and the plate width 1/2, and the values of the plate width 1/2 portion are shown in Tables 1 and 2. Shown. The reduction amount at the time of O-press was set so that the distance between the outer surface side of the W / 2 portion and the outer surface side of the plate width end portion was 654 [mm].

Then, after measuring the opening amount of the open pipe S ₂ after O-pressing the molded bodies A and B, the seam gap portion G of the open pipe S ₂ is welded to form a steel pipe having an outer diameter of 654 [mm]. The diameter was measured at eight points at a pitch of 22.5 degrees in the circumferential direction, and the difference between the maximum and minimum diameters was determined. Tables 1 and 2 also show the mold shape (constraint range), press load, opening amount, and roundness. The roundness at this time is a number obtained by dividing the difference between the maximum and the minimum by the outer diameter of the steel pipe (the average value of all the measured values of the diameter).

In the welding machine used in this embodiment, if the opening amount after O-pressing exceeds 40 [mm], the opening cannot be closed, and the opening is closed by another press. After provisionally welding both ends and the center in the pipe axis direction, the entire length of the seam gap portion G was main welded. Regarding the roundness, 2.5 [%] was used as a guideline for passing before the pipe expansion. This is because if the roundness before tube expansion is 2.5 [%] or less, the roundness after tube expansion can be a good value of 1.0 [%] or less.

No. 1 in Table 1, which is the scope of the examples of the present invention. A1 to A7, A9, A10, No. in Table 2. In B1 to B7, B9, and B10, the opening amount is small and the roundness is also good. In particular, when the restraint range is 90 degrees to 110 degrees, the roundness is 1.0 [%] or less even if the pipe is not expanded. Further, the smaller the average value of the restraint range, the smaller the press load.

On the other hand, the restraint range of the upper mold 4 and the lower mold 5 is a combination of 60 degrees and 90 degrees. A8, A11, No. in Table 2. In B8 and B11, the opening amount is small, but the roundness is poor. In addition, No. 1 in Table 1 in which the average value of the restraint range is 60 degrees or less. A12 to A16, No. in Table 2. In B12 to B16, the opening amount is large, and in particular, No. 1 in Table 1. A15, A16, No. in Table 2. In B16, the roundness could not be measured because the welded portion after welding the seam gap portion G was broken.

Further, in the case where the molded body B having a width of the unprocessed portion larger than that of the molded body A was used, the press load and the roundness were substantially the same as those using the molded body A, but the opening amount. Is getting smaller.

Although the embodiment to which the present invention is applied has been described above, the present invention is not limited by the description and the drawings which form a part of the disclosure of the present invention according to the present embodiment. That is, all other embodiments, examples, operational techniques, and the like made by those skilled in the art based on the present embodiment are included in the scope of the present invention.

[Example 2]
Edge bending is performed on a steel sheet having a length of 1000 [mm], a plate thickness of 31.8 [mm], and a tensile strength of 779 [MPa], which is processed to a plate width of 1639 [mm] by providing a groove using an edge mirror. after was prepared molded body S ₁ subjected to press bending process. Next, with respect to the molded body S _1, with the upper mold 4 and the lower mold 5 of the various constraint range, by performing the O pressing by a press machine 30 [MN], moldings A, B Molded. Tables 3 and 4 show the shapes of the molded bodies A and B. The first letters A and B in "No." in Tables 3 and 4 indicate the shape of the molded body (molded bodies A and B), and the numbers after the alphabets A and B are the upper metal. The combination of the restraint ranges of the mold 4 and the lower mold 5 is shown.

In Table 3, as a condition A, an unprocessed portion having a width of 137 [mm] (W / 12) centered on the W / 4 portion from the plate width end is provided, and a tangent line at the plate width end and a W / 4 portion are provided. The molded body A is shown in which the angles θ ₂₁ and θ ₂₂ formed by the tangents are 65 degrees, and the angles θ ₁₁ and θ ₁₂ formed by the tangents at the center of the plate width and the tangent at the W / 4 portion are 72 degrees. In Table 4, as condition B, an unprocessed portion is provided with a width of 273 [mm] (W / 6) (twice the width of condition A) centered on W / 4 from the plate width end, and the plate width end is provided. Molding where the angles θ ₂₁ and θ ₂₂ between the tangent and the tangent at the W / 4 part are 59 degrees, and the angles θ ₁₁ and θ ₁₂ between the tangent at the center of the plate width and the tangent at the W / 4 part are 61 degrees. Shows body B. The molded bodies A and B are symmetrical with respect to the straight line connecting the center of the plate width end portion and the plate width 1/2, and Tables 3 and 4 show the values of the plate width 1/2 portion. Shown. Further, the reduction amount at the time of O-press was set so that the distance between the outer surface side of the W / 2 portion and the outer surface side of the plate width end portion was 553 [mm].

Then, after measuring the opening amount of the open pipe S ₂ after O-pressing the molded bodies A and B, the seam gap portion G of the open pipe S ₂ is welded to form a steel pipe having an outer diameter of 553 [mm]. The diameter was measured at eight points at a pitch of 22.5 degrees in the circumferential direction, and the difference between the maximum and minimum diameters was determined. Tables 3 and 4 also show the mold shape (constraint range), press load, opening amount, and roundness. The roundness at this time is a number obtained by dividing the difference between the maximum and the minimum by the outer diameter of the steel pipe.

In the welding machine used in this embodiment, if the opening amount after O-pressing exceeds 40 [mm], the opening cannot be closed, and the opening is closed by another press. After provisionally welding both ends and the center in the pipe axis direction, the entire length of the seam gap portion G was main-welded. As for the roundness, 2.5 [%] was used as a guideline for passing before the pipe was expanded to 1.0 [%] or less by expanding the pipe.

No. 3 in Table 3, which is the scope of the examples of the present invention. A1 to A7, A9, A10, No. in Table 4. In B1 to B7, B9, and B10, the opening amount is small and the roundness is also good. In particular, when the restraint range is 90 degrees to 110 degrees, the roundness is 1.0 [%] or less even if the pipe is not expanded. Further, the smaller the average value of the restraint range, the smaller the press load.

On the other hand, the restraint range of the upper mold 4 and the lower mold 5 is a combination of 60 degrees and 90 degrees. A8, A11, No. in Table 4. In B8 and B11, the opening amount is small, but the roundness is poor. In addition, No. 1 in Table 3 in which the average value of the restraint range is 60 degrees or less. A12 to A16, No. in Table 4. In B12 to B16, the opening amount is large, and in particular, No. A15, A16, No. in Table 4. In B16, the roundness could not be measured because the welded portion after welding the seam gap portion G was broken.

Further, in the case where the molded body B having a width of the unprocessed portion larger than that of the molded body A was used, the press load and the roundness were substantially the same as those using the molded body A, but the opening amount. Is getting smaller.

[Example 3]
Edge bending is performed on a steel sheet having a length of 1000 [mm], a plate thickness of 50.8 [mm], and a tensile strength of 779 [MPa], which is processed to a plate width of 2687 [mm] by providing a groove using an edge mirror. after was prepared molded body S ₁ subjected to press bending process. Next, with respect to the molded body S _1, with the upper mold 4 and the lower mold 5 of the various constraint range, by performing the O pressing by a press machine 30 [MN], moldings A, B Molded. Tables 5 and 6 show the shapes of the molded bodies A and B. The first letters A and B in "No." in Tables 5 and 6 indicate the shape of the molded body (molded bodies A and B), and the numbers after the alphabets A and B are the upper metal. The combination of the restraint ranges of the mold 4 and the lower mold 5 is shown.

In Table 5, as a condition A, an unprocessed portion having a width of 224 [mm] (W / 12) centered on the W / 4 portion from the plate width end is provided, and a tangent line at the plate width end and a W / 4 portion are provided. The molded body A is shown in which the angles θ ₂₁ and θ ₂₂ formed by the tangents are 73 degrees, and the angles θ ₁₁ and θ ₁₂ formed by the tangents at the center of the plate width and the tangent at the W / 4 portion are 72 degrees. In Table 6, as condition B, an unprocessed portion is provided with a width of 448 [mm] (W / 6) (twice the width of condition A) centered on W / 4 from the plate width end, and the plate width end is provided. The angles θ ₂₁ and θ ₂₂ between the tangent and the tangent at the W / 4 part are 58 degrees, and the angles θ ₁₁ and θ ₁₂ between the tangent at the center of the plate width and the tangent at the W / 4 part are 59 degrees. The molded body B is shown. The molded bodies A and B are symmetrical with respect to the straight line connecting the center of the plate width end portion and the plate width 1/2, and Tables 5 and 6 show the values of the plate width 1/2 portion. Shown. Further, the reduction amount at the time of O-press was set so that the distance between the outer surface side of the W / 2 portion and the outer surface side of the plate width end portion was 905 [mm].

Then, after measuring the opening amount of the open pipe S ₂ after O-pressing the molded bodies A and B, the seam gap portion G of the open pipe S ₂ is welded to form a steel pipe having an outer diameter of 905 [mm]. The diameter was measured at eight points at a pitch of 22.5 degrees in the circumferential direction, and the difference between the maximum and minimum diameters was determined. Tables 5 and 6 also show the mold shape (constraint range), press load, opening amount, and roundness. The roundness at this time is a number obtained by dividing the difference between the maximum and the minimum by the outer diameter of the steel pipe.

In the welding machine used in this embodiment, if the opening amount after O-pressing exceeds 40 [mm], the opening cannot be closed, and the opening is closed by another press. After provisionally welding both ends and the center in the pipe axis direction, the entire length of the seam gap portion G was main welded. As for the roundness, 2.5 [%] was used as a guideline for passing before the pipe was expanded to 1.0 [%] or less by expanding the pipe.

No. 1 in Table 5, which is the scope of the examples of the present invention. A1 to A7, A9, A10, No. in Table 6. In B1 to B7, B9, and B10, the opening amount is small and the roundness is also good. In particular, when the restraint range is 90 degrees to 110 degrees, the roundness is 1.0 [%] or less even if the pipe is not expanded. Further, the smaller the average value of the restraint range, the smaller the press load.

On the other hand, the restraint range of the upper mold 4 and the lower mold 5 is a combination of 60 degrees and 90 degrees. A8, A11, No. in Table 6. In B8 and B11, the opening amount is small, but the roundness is poor. In addition, No. 1 in Table 5 in which the average value of the restraint range is 60 degrees or less. A12 to A16, No. in Table 6. In B12 to B16, the opening amount is large, and in particular, No. A15, A16, No. in Table 6. In B16, the roundness could not be measured because the welded portion after welding the seam gap portion G was broken.

Further, in the case where the molded body B having a width of the unprocessed portion larger than that of the molded body A was used, the press load and the roundness were substantially the same as those using the molded body A, but the opening amount. Is getting smaller.

[Example 4]
In order to manufacture a steel pipe with a target outer diameter of 621 [mm] to 687 [mm], a plate with a length of 1000 [mm] and a plate width of 1826 to 2032 [mm] was processed by providing a groove using an edge mirror. thickness 40 [mm], the steel sheet of the tensile strength 635 [MPa], after bending an end were prepared molded body _{S 1} subjected to press bending process. Next, with respect to the molded body _{S 1,} arcuate portion radius 327 mm, using a variety of upper mold 4 and the lower mold 5 of the restraint range 45 degrees, perform O pressing by a press machine 30 [MN], molding The bodies D1 to D11 were molded. Table 7 shows the molding conditions of the molded bodies D1 to D11. The molded bodies D1 to D11 are provided with an unprocessed portion having a width of W / 12 centered on the W / 4 portion from the plate width end according to the initial plate width W, and the tangent line at the plate width end portion and W / The angles θ ₂₁ and θ ₂₂ formed by the tangents in the four parts were set to 75 degrees, and the angles θ ₁₁ and θ ₁₂ formed by the tangents in the central part of the plate width and the tangents in the W / 4 part were set to 75 degrees. Further, in the O press, the distance between the outer surface side of the W / 2 portion and the outer surface side of the plate width end portion was reduced so as to be a value corresponding to the initial plate width W as shown in Table 7. Table 7 shows the outer diameter of the steel pipe after O-press reduction.

Then, to measure the amount of opening of the open pipe _{S 2} after O press these moldings D1 to D11. Table 7 also shows the press load and opening amount as a result.

The ratio of the arc portion radius to the outer radius of the steel pipe is 1.00. When the opening amount of D6 is the smallest and the outer radius of the steel pipe is small or large, the opening amount is large. Further, the opening amount of 40 [mm] or less that can be closed by the welding machine used in Example 1 is No. 1 in Table 7. It is D2 to D10, and the ratio of the radius of the arc portion to the outer radius of the steel pipe is 0.96 to 1.04. Further, the opening amount of 50 [mm] in which the welded portion was not broken in Example 1 was also found in No. 7 of Table 7. It is D2 to D10, and the ratio of the radius of the arc portion to the outer radius of the steel pipe is 0.96 to 1.04.

The opening amount that can be closed by welding the seam gap portion G and the opening amount that does not cause the welded portion to break differ depending on the welding equipment and the welding method, but the radius of the arc portion of the upper mold 4 and the lower mold 5 The guideline for is 0.96 to 1.04 of the outer radius of the steel pipe.

According to the present invention, it is possible to provide a method for manufacturing a steel pipe and a press die capable of efficiently forming a steel pipe having a high roundness.

1 Die 1a Rod-shaped member 1b Rod-shaped member 2 Punch 2a Punch tip 2b Punch support 3 Conveying roller 4 Upper mold 4a Arc part 4b ₁ Straight part or small curvature arc part 4b ₂ Straight part or small curvature arc part 5 Lower mold 5a Arc part 5b ₁ Straight line part or small curvature arc part 5b ₂ Straight part or small curvature arc part

In order to solve the above-mentioned problems and achieve the object, the method for manufacturing a steel pipe according to the present invention is to bend a plate material having end bending processed at both ends in the width direction three times or more along the width direction. A molded body having a U-shaped cross section is formed by processing, and then the molded body is pressed to obtain an open pipe having a seam gap in the longitudinal direction thereof, and then the seam is formed. a method of manufacturing a steel pipe and steel pipe by joining gap, when the width of the plate before bending said end a plate width W, the shaped body is spaced et W / 4 or the plate width end It has a lightly machined part that is given a small curvature compared to other areas, or an unprocessed part that omits bending, and the shape of the open pipe is the maximum of the U-shaped cross section. The range of 20 [%] or more of the plate width W centering on the lower portion and the range of 10 [%] or more of the plate width W from the plate width end are the same diameter or substantially the same diameter as the outer diameter of the steel pipe. Pressing is performed using a mold having an arc portion radius within a range of ± 3.5 [%] with respect to a radius corresponding to the outer radius of the steel pipe so as to have a shape inscribed in the arc. It is characterized by that.

Further, the press die according to the present invention is a press die used in the method for manufacturing a steel pipe of the above invention, and the press die is composed of a pair of dies that sandwich the molded body, and each die. ± 3.5 [%] of the radius corresponding to the outer radius of the steel pipe so that the arc center is located at a position corresponding to the processing center of each mold on the surface of the mold that can come into contact with the molded body. ] Is formed, the central angle of the arc portion in each mold is 70 degrees or more, and the total angle of the central angles of both molds is less than 360 degrees. It is characterized by.

Claims (10)

A plate material whose ends have been bent at both ends in the width direction is bent three times or more along the width direction to form a molded body having a U-shaped cross section, and then the molded body is pressed. This is a method for manufacturing a steel pipe, which is a pipe body having a seam gap portion in the longitudinal direction thereof to form an open pipe, and then the seam gap portion is joined to form a steel pipe.
When the width of the plate material before the edge bending process is the plate width W,
The molded body has a lightly machined portion having a small curvature as compared with other regions or an unprocessed portion in which bending is omitted, centering on a portion separated by W / 4 from the plate width end. ,
The shape of the open pipe includes a range of 20 [%] or more of the plate width W centering on the lowermost portion of the U-shaped cross section and a range of 10 [%] or more of the plate width W from the plate width end. Is inscribed in an arc having the same or substantially the same diameter as the outer diameter of the steel pipe.
A method for manufacturing a steel pipe, which is characterized by being pressed. A is a range of 20 [%] or more of the plate width W centered on the lowermost part of the U-shaped cross section inscribed in an arc having the same or substantially the same diameter as the outer diameter of the steel pipe. The first aspect of claim 1 is that the equation (1) is satisfied, where B is the sum of the range of 10 [%] or more of the plate width W from both ends of the plate width inscribed in an arc having the same diameter or substantially the same diameter. The method for manufacturing a steel pipe according to the description.
2 | AB | / (A + B) <0.4 ... (1)
Here, | AB | indicates the absolute value of AB. The molded product is placed on the other mold so that one of the pair of molds and the U-shaped open side of the molded product face each other, and the molded product is mounted on the pair of molds. When sandwiching and pressing the molded product,
The other mold is
With the molded body placed on the other mold, the range of the shape that is inscribed in an arc with the same or substantially the same diameter as the outer diameter of the steel pipe is centered on the lowermost part of the U-shaped cross section. Except that the molded body does not come into contact,
When the press working is completed, a part of the other die is provided with a machined surface that does not come into contact with the open pipe.
One of the molds is
In the state where the molded body was placed on the other mold, the molded body did not come into contact with each other.
The method for manufacturing a steel pipe according to claim 1 or 2, wherein when the press working is completed, a part of the one die is provided with a machined surface that does not come into contact with the open pipe. Claims 1 to 3, wherein the press working is performed using a die having a radius of an arc portion in a range of ± 3.5 [%] with respect to a radius corresponding to the outer radius of the steel pipe. The method for manufacturing a steel pipe according to any one item. Any of claims 1 to 4, wherein when the molded product is pressed, the center of the press die used for the press working of the molded product coincides with the center in the width direction of the molded product. The method for manufacturing a steel pipe according to item 1. The method for manufacturing a steel pipe according to any one of claims 1 to 5, wherein the molded body is held in a U-shaped posture with the U-shaped open side facing upward. A press die used in the method for manufacturing a steel pipe according to any one of claims 1 to 6.
The press die is composed of a pair of pressing bodies that sandwich the molded body, and an arc center is located at a position corresponding to the processing center of each die on a surface of each die that can come into contact with the molded body. As described above, an arc portion having a radius within a range of ± 3.5 [%] is formed with respect to the radius corresponding to the outer radius of the steel pipe.
A press die characterized in that the central angle of the arc portion in each die is 70 degrees or more, and the total angle of the central angles of both dies is less than 360 degrees. The press die according to claim 7, wherein the central angles of both dies are the same. The press according to claim 7 or 8, wherein each die has a straight portion or a small curvature arc portion having a curvature smaller than that of the arc portion, which is connected to both ends of the arc portion in the arc direction. Mold. The method for manufacturing a steel pipe according to any one of claims 1 to 6, wherein the press die according to any one of claims 7 to 9 is used.

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