RU2663674C1 - Method of production of steel pipe and pressing die used in this method - Google Patents

Abstract

FIELD: technological processes.SUBSTANCE: invention relates to a method for producing a steel pipe by bending a sheet material and a pressing die for carrying out the method. Curled sheet material is subjected to at least one bending operation in the widthwise direction of the sheet to form a preform having a U-shaped cross-sectional shape. Open pipe with a longitudinal gap between the side edges is formed by applying a bending force to the workpiece for the purpose of pressing, as a result of which the end surfaces of the side edges of the open pipe are connected to each other to form a steel pipe. Slightly curved portion having a slight bend compared to other areas or a non-bent portion that is not bent on at least a portion of the sheet material during bending and applying a bending force to a portion located from the center of the slightly curved portion or the non-curved portion in the direction of the edge portion of the sheet material at a distance of at least W/4, where W is the width of the sheet material, without restricting the slightly curved portion or the non-curved portion, in the process of pressing the blank to form an open tube. Press stamp includes two bending tools having a forming surface.EFFECT: possibility to increase the efficiency of forming a steel pipe having a high roundness, with a relatively small bending force is a result of the invention.10 cl, 15 dwg, 7 tbl, 9 ex

Description

Technical field

The object of the present invention is a method for the production of large diameter steel pipes with a large wall thickness used in the construction of trunk pipelines and similar structures, in which a thick sheet material is molded to give it a predetermined U-shape by bending, after which the resulting billet is subjected to further pressing, giving it the shape of an open pipe with a gap extending along the length between the unconnected sheet edges in width, and then connecting the end surfaces with each other, resulting in a steel pipe, wherein the pressing die is used in the practice of the method.

State of the art

In the production of steel pipes of large diameter with a large wall thickness, used to create trunk pipelines and similar structures, the so-called UOE technology is widely used, which consists in pressing a steel sheet of a certain length, width and thickness in order to give it a U-shape, further pressing the resulting workpiece in order to give it an O-shape and obtain an open pipe, and subsequent butt welding of the unconnected pipe edges, after which the diameter of the resulting pipes (so-called pipe expansion) in order to improve the roundness of the pipe.

However, in the aforementioned UOE molding technology, since a large pressing force is required in the process of pressing a steel sheet to obtain a U-shaped and O-shaped, it is impossible to do without large-sized presses.

As a consequence of this, various methods have recently been considered to reduce the pressing force in the production of steel pipes of this type.

In the prior art on this subject, JP-A-S55-139117 discloses a method for pre-pressing a material into a C-shape, followed by pressing into a U-shape, and then pressing into an O-shape, so that the type of deformation of the pressed material becomes the corresponding matrix elements in both the upper and lower parts, in the process of pressing with giving an O-shaped. Further, JP-A-H11-285729 discloses a method for changing the position of the abutting edges of a U-shaped steel sheet relative to the matrix elements by performing many pressing operations of a U-shaped steel sheet with its rotation to give an O-shaped, and in JP-A- 2002-178025 discloses a method of performing pressing with giving an O-shaped blank to a U-shaped obtained by pressing with giving a U-shaped with a liner used to obtain a pipe with a larger outer diameter from a pipe of medium outer diameter.

As other documents of the prior art, JP-A-2005-21907 is disclosed, which discloses a molding method that uses a voltage detector capable of measuring the inclination or warping of a bending element mounted on an inclined plane, and the bending element can be tilted or moved in parallel , depending on the detection of tilt or distortion by the voltage detector, and this bending element tilts or moves in parallel with the purpose of pressing, so that the distortion is less than the slope or the distortion of the bending element when pressing the material to give it a pipe shape. JP-A-2012-250285 discloses a method for forming a split pipe from a non-circular preform by slightly molding compared to other bending operations, using at least one bending operation with the left and right sides of the sheet material exposed to the center, determined by the place of passage of the longitudinal axis of the upper tool, acting on the gradually bent sheet material, with subsequent molding of the finished split pipe by means of the attached I'm pressing force exerted on the region formed a little earlier on both sides from the center of the workpiece outside the non-circular shape. In addition, US Pat. No. 4,149,399 discloses a method for forming a pipe with a split section by plastic deformation of only a flat part in at least one place of a workpiece having a flat part between at least two curved sections of a given curvature.

Disclosure of the invention

The problem solved by the present invention

At the same time, conventional pressing technologies have their drawbacks described below, and therefore there is still room for improvement.

For example, as indicated in JP-A-S55-139117, JP-A-H11-285729 and JP-A-2002-178025, the circumferential length of the forming surface of the matrix is set to be almost equal to the width of the sheet material (source sheet), and the sheet material is shaped into a pipe by introducing the elongated portion of the material into contact with the forming surface of the matrix during deformation during pressing to give an O-shape in order to give it the shape of the forming surface of the matrix. However, with an increase in the contact area of the material with the matrix, the pressing force gradually increases, and the need for a more powerful press arises.

In a technology aimed, in particular, at molding parts from high-strength materials of large thickness, a high pressing force is required, and thus, the process of pressing the material to give it an O-shape is not completely carried out, as a result of which it is impossible to avoid a decrease in the quality of the mold.

At the same time, when molding by the methods described in JP-A-2005-21907, JP-A-2012-250285 and US 4149399, although with these methods there is no increase in pressing force, as in JP-A-S55-139117 , JP-A-H11-285729 and JP-A-2002-178025, since the left and right sides of the material being molded or the non-circular blank are molded separately, in the case of differences in deformations on the left and right sides, there is a risk of a stepwise height difference (displacement) of the lateral edges of the pipe, which subsequently need to be welded. In addition, in these methods, when trying to simultaneously give the material the desired shape, the deformation is locally concentrated, resulting in a risk of worsening roundness. Thus, several times there is the inevitability of deformation of the molded material, and, in addition, there is a limit on the efficiency of the production process.

The objective of the present invention is to create an effective method for the production of steel pipes of high roundness, which does not require the use of increased bending force (bending load), as well as a pressing die for this method.

Solution

The present invention proposes a method for manufacturing a steel pipe by performing at least one bending operation of sheet material with curved edge portions in the width direction in order to obtain a workpiece with a U-shaped cross section, pressing the resulting workpiece by applying a bending force to form an open pipe with a gap in the longitudinal direction, and butt joints of the end surfaces of the gap of the open pipe, characterized in that at least on the part of the sheet material In the bending process, a slightly curved section is created with a slight bend compared to other sections, or a non-curved section, in which there is no bending, and a bending force is applied to the part located at a distance W / 4 (where W is the width of the sheet material) from the center slightly a curved section or a non-curved section towards the lateral edge of the sheet material, without restricting a slightly curved section or a non-curved section in the process of pressing a workpiece to shape the open pipe. In the present description, the term open pipe is used to denote a pipe billet, i.e. sheet material, which was given a cylindrical shape, with a gap between its lateral edges facing each other.

The proposed method for the production of steel pipes of the above configuration has the following distinctive features, which are preferred to solve the problems of the present invention:

1) The center of a slightly curved section or a non-curved section is located on a section located at a distance W / 4 from the edge section of the sheet material;

2) The length of a slightly curved section or a non-curved section in the direction along the width of the sheet material is not more than 10% of the width of the sheet;

3) When applying a bending force to compress the workpiece, the workpiece rests on a part located not on the same line with the action line of the bending force, and if the opening angle of the workpiece, determined by the construction of the part serving as a support for the workpiece, is determined as θs, and the angle of the action line the bending force applied to the workpiece is defined as θf, then the pressing of the workpiece begins under the condition θf> θs;

4) The pressing die used for pressing the workpiece contains a forming surface that, during the pressing of the workpiece, does not come into contact with a slightly curved section or a non-curved section;

5) In the process of pressing the workpiece, a bending force is simultaneously applied to the sections, each of which is located at a distance W / 4 from the center of the slightly curved section or the non-curved section towards the side edges of the sheet material; Besides,

6) In the process of pressing the workpiece, forming the center of the pressing stamp used for pressing the workpiece coincides with the center of the workpiece in width; and

7) During the pressing process, the workpiece is held in a U-shaped position, in which its gap between the lateral edges is directed upward and rests on the center of the workpiece in width, located at the lowest point.

In addition, the present invention provides a pressing die, preferably used in the above method of manufacturing a steel pipe, characterized in that the pressing die comprises two bending elements between which a workpiece is placed, each of which contains a forming surface that is not included in the pressing process of the workpiece contact with a slightly curved portion or a non-curved portion.

A compression stamp of the above configuration contains the following features that are preferred to solve the problem of the present invention:

1) At least one of the bending elements contains an arcuate surface, the center of the width of which coincides with the forming center of the pressing stamp, and a forming surface containing an inclined surface connected to both edges of the curved surface and directed towards the forming center of the pressing stamp.

In addition, the arcuate surface has a central angle of at least 28 °, the angle formed by the inclined surface and a straight line intersecting with a straight line passing through the center along the width of the arcuate forming surface is preferably at least 14 °, and the arcuate surface may have a radius whose value is not more than 1.2 of the diameter of the steel pipe produced.

The beneficial effect of the invention.

In the method of producing a steel pipe according to the present invention, in the case when at least one bending operation is performed on a sheet material with curved edge portions in the width direction in order to obtain a workpiece with a U-shaped cross-section, the obtained workpiece is pressed by applying a bending force with the aim of forming an open pipe with a gap in the longitudinal direction, and butt jointing the end surfaces of the gap of the open pipe, at least on a part of the sheet During bending, a slightly curved section is created with a slight bend compared to other sections, or a non-bent section without bending, and a bending force is applied to the part at least W / 4 (where W is the width of the sheet material ) from the center of the slightly curved section or non-curved section towards the lateral edge of the sheet material, without restricting the slightly curved section or non-curved section in the process of pressing the workpiece into a shape about open pipe. Thus, this method makes it possible to efficiently form a high-circularity steel pipe using a relatively small bending force.

According to the above method of manufacturing a steel pipe, since a slightly curved section or a non-curved section is created located at a distance W / 4 from the edge section of the sheet material, in the process of pressing a workpiece with a U-shaped cross-section to give it an open pipe shape, this section is not limited pressing stamp, and, thus, it is possible to reduce the reaction force during molding.

In the method of manufacturing a steel pipe according to the present invention, since the length of the slightly curved section or the non-curved section in the width direction of the sheet material is not more than 10% of the sheet width, this makes it possible to obtain an open pipe with a small gap between the side edges, while maintaining high dimensional accuracy.

In the method of manufacturing a steel pipe according to the present invention, in the process of pressing a workpiece by applying a bending force thereto, the workpiece is supported by an element located at least at some distance from the action line of the bending force, and if the opening angle of the workpiece determined by the construction of the part, serving as a support for the workpiece, is determined as θs, and the angle of the line of action of the bending force applied to the workpiece is determined as θf, then the process of pressing the workpiece begins under the condition θf> θs, so that when a slightly bent section or a non-bent section is deformed, this section deviates outward.

In the method for manufacturing a steel pipe according to the present invention, in the process of pressing a workpiece, since a pressing die is used that contains a forming surface that is not in contact with a slightly curved portion or a non-curved portion, this enables compression to be performed with a reduction in bending force.

In the method of manufacturing a steel pipe according to the present invention, since in the process of pressing the workpiece, a bending force is simultaneously applied to the sections (two sections), each of which is located at a distance W / 4 from the center of the slightly curved section or the non-curved section towards the side edges of the sheet material, no displacement of the lateral edges of the open pipe relative to each other is formed.

In the method of manufacturing a steel pipe according to the present invention, since the forming center of the pressing die used in the pressing process of the workpiece coincides with the center along the width of the workpiece, this makes it possible to uniformly bend the sections corresponding to the side edges of the open pipe from the left and right sides, and a large displacement of the side edges do not occur.

In the method of manufacturing a steel pipe according to the present invention, since the workpiece is held in a U-shape and supported by its lower part (the central part of the workpiece in width), this allows symmetrical deformation of the workpiece at the center boundary in the width direction, which makes it possible to obtain an open pipe high roundness.

The pressing die used in the method of manufacturing a steel pipe according to the present invention contains two bending elements between which the workpiece is placed, and a forming surface with a cross-sectional shape, which ensures that during the pressing of the workpiece using the bending element, this forming surface does not come into contact with a slightly curved portion or a non-curved portion. Thus, the reaction force during molding is reduced, which makes it possible to efficiently produce steel pipe.

In addition, since the pressing stamp according to the present invention contains bending elements, at least one of which has an arcuate surface, the center of the width of which coincides with the forming center of the pressing stamp, and a forming surface with a slope connected to each of both edges of the arcuate surface and directed in the direction of the forming center of the pressing stamp, this makes it possible to obtain a steel pipe of high roundness without the formation of a displacement of the side edges.

In the pressing die according to the present invention, when the central angle of the arcuate surface is at least 28 °, and the angle between the inclined surface and the straight line intersecting with the straight line passing through the center along the width of the arcuate molding surface is at least 14 °, during the pressing of the workpiece, it provides reliable possibility of deformation of a slightly curved section or a non-curved section with a deflection outward.

In addition, in the pressing die according to the present invention, the slightly curved portion or the non-curved portion is not limited to the forming surface of the pressing die, since the arcuate surface has a diameter not exceeding 1.2 of the diameter of the steel pipe produced during the pressing of the workpiece, thereby reducing the reaction force when molding.

A brief description of the drawings.

FIG. 1 is a diagram of preferred punch and die used to create a blank having a U-shaped cross section.

FIG. 2 is a diagram of a preferred pressing die used for forming an open pipe.

FIG. 3 is a flowchart of forming sheet material to obtain a blank with a U-shaped cross section.

FIG. 4 is an enlarged cross-sectional diagram of a blank with a U-shaped cross section.

FIG. 5 is a schematic diagram of a process for pressing a workpiece with a U-shaped cross-section to obtain an open pipe.

FIG. 6 is a graph showing the relationship between the value of the roundness index and the outer diameter and the length of a slightly curved portion or a non-curved portion to the width of the sheet.

FIG. 7 is a graph showing the relationship between the gap (mm) and the length of a slightly curved portion or a non-curved portion to the sheet width.

FIG. 8 is a dependency graph showing the relationship between the gap (mm) of a workpiece with a U-shaped cross section and the length of a slightly curved portion or non-curved portion to the sheet width.

FIG. 9 is an enlarged diagram of the main elements of the upper part of the stamp.

FIG. 10 is a graph showing the relationship between the angle θd of the forming surface of the upper part of the die and the direction θf of the application of force.

FIG. 11 - capture of metal by the upper part of the stamp.

FIG. 12 is a state diagram in which a gap is formed between the upper part of the stamp and the workpiece.

FIG. 13 is a graph of the relationship showing the relationship between the radius of the arc segment of the surface of the upper part of the stamp to the radius of the steel pipe and the index of insufficient deformation

FIG. 14 is a graph showing the relationship between the radius of the arc segment of the surface of the bottom of the stamp to the radius of the steel pipe and the molding force to the free bending force of a slightly curved or non-curved portion.

FIG. 15 is a diagram of the contact of the upper and lower parts of the stamp with each other.

The implementation of the invention

The following is a detailed description of an embodiment of the present invention with reference to the attached drawings.

In FIG. 1 and 2 schematically show the preferred punch, die, and, accordingly, the pressing stamp used in the implementation of the inventive method for manufacturing a steel pipe.

In FIG. 1 shows the punch and die used in forming sheet material in order to obtain a blank with a U-shaped cross section by bending the sheet material in the longitudinal direction, and FIG. 2 depicts a pressing die used in molding the resulting preform in order to obtain an open pipe with a gap in the longitudinal direction by applying a bending force to the preform with a U-shaped cross section.

Reference numeral 1 in FIG. 1 shows a matrix installed in the place where the sheet material S is supplied. The matrix 1 includes left and right rod-shaped elements 1a and 1b serving as a support for the sheet material S in two places in the feed direction; this matrix provides the ability to change the distance e between the specified rod-shaped elements 1a and 1b depending on the size of the steel pipe produced.

Reference numeral 2 denotes a punch that can move towards and away from die 1. The punch 2 comprises a head 2a having a downwardly convex forming surface that comes into contact with the sheet material S in order to bend it and give it a curved shape, and a stem 2b connected to the rear (upper) edge of the punch head 2a and having the same width to provide support for the punch head 2a.

Although the specific construction of the punch rod 2b is not shown here, its upper part is connected to a drive device, such as a hydraulic cylinder, and with this drive device, the punch rod 2b can exert a bending force on the punch head 2a. Further, reference numeral 3 denotes rolls that perform the function of a device for transporting sheet material S.

In addition, reference numeral 4 in FIG. 2 indicates the upper part of the die (bending tool), and reference numeral 5 denotes the lower part of the die (bending tool) mating with the upper part of the die 4. A workpiece (having a U-shaped cross-section) made using matrix 1 and punch 2, placed between the upper part of the stamp 4 and the lower part of the stamp 5, and a bending force is applied to the blank to form an open pipe.

The upper part of the die 4 may contain an arcuate surface 4a, the center of the width of which coincides with its forming center, and forming surfaces (inclined surfaces) 4b connected to each of both sides of the arcuate surface 4a and inclined towards the forming center of the pressing die. The lower part of the stamp 5 may contain a forming surface, which during the pressing of the workpiece does not come into contact with a slightly curved section or a non-curved section. In addition, the upper part of the die 4 may include a pressing die having a forming surface which during the pressing of the workpiece does not come into contact with a slightly curved portion or a non-curved portion. As the lower part of the stamp 5, it is also possible to use the lower part containing an arcuate surface, the center of which width coincides with its forming center, and inclined surfaces connected to each of both sides of the arcuate surface 4a and inclined towards the forming center of the pressing stamp.

In order to form the tube used as the initial sheet material S and give it a tubular shape, first, edge crimping (also called edge bending) is performed on the sections of the lateral edges of the sheet material S.

The operation of crimping the edge is performed on the edge sections of the sheet in width, which are harder to bend using the matrix 1 and the punch 2, which makes it possible to obtain a pipe with a high degree of roundness.

It should be noted that the roundness of the steel pipe is an indicator of how close the cross-sectional shape of the steel pipe is to the circumference. In particular, for an embodiment in which the steel pipe to be manufactured is divided into twelve equal sections or twenty-four sections in a circumferential direction at any point in the pipe along the length in order to measure the outer diameter at opposite points, the pipe has a maximum diameter D _max and a minimum diameter D _min , and, accordingly, the roundness of the pipe is determined as the difference of the indicated values, i.e. roundness = D _max - D _min . Thus, the closer the roundness is to 0, the more the cross-sectional shape of the steel pipe is closer to the ideal circumference.

Sheet material S with extruded edge portions is placed on the matrix 1, as shown in FIG. 1, and bend it (three-point bending) over the entire width of the sheet, as shown in FIG. 3, with periodic movement of the sheet material S by a certain amount of feed, resulting in a blank with a U-shaped cross section as a whole.

As a result of this bending operation, a blank S _{1 is} obtained containing slightly curved sections (sections with a slight degree of bending) or non-curved sections P (sections without bending) located at a distance W / 4 from the side edges, as shown on an enlarged scale in FIG. four.

A slightly bent portion P can be obtained by reducing the amount of bending created by the punch 2, and a non-bent portion P can be obtained by skipping the bending operation using the punch 2 while increasing the feed rate of the sheet material S.

In FIG. 3 shows in more detail a flow diagram for bending and feeding sheet material S, such as sheet material S preliminarily bent, sequentially from top to bottom in the left column, from top to bottom in the center column, and again from top to bottom in the right column; wherein in FIG. 3, the arrows show the direction of movement of the punch 2 and sheet material S during each operation.

As the punch 2 for bending the sheet material S, a punch having a practically inverted T-shape, in which the width of the head 2a is greater than the width (thickness) of the punch rod 2b, can be used. In this case, in one operation, a larger area of the sheet material can be bent compared to a configuration in which the width of the punch head 2a is substantially equal to the width (thickness) of the punch rod 2b, as shown in FIG. 1, thereby reducing the duration of bending operations.

After receiving the blank S ₁ with a U-shaped cross-section, in order to give it the shape of an open pipe, this blank S _{1 is} pressed using the upper part of the die 4 and the lower part of the die 5 shown in FIG. 2.

During the pressing operation, the workpiece S _{1 is} set in a U-shaped position, so that the open area is directed upward, and the workpiece itself is located on the lower part of the stamp 5, so that its lower edge, i.e. center in width, becomes a support. Thus, as shown in FIG. 5, the upper part of the die 4 exerts a bending force simultaneously on two edge portions of the sheet material S located at a distance W / 4 from the slightly curved or non-curved portions P towards the side edges.

In such pressing, since the preform S ₁ rests on the lower part of the punch 5 at a point located at least at a distance from the line of action of the bending force, and the slightly curved portion or non-curved portion P is not held by the pressing die, the preform S ₁ takes a tubular shape, without requiring excessive bending effort.

As for the lower part of the stamp 5, although in the present embodiment, the lower part is used with a forming surface that does not hold the slightly curved section or non-curved section P when the forming surface is arched and has a concave shape, it can be obtained using a diameter larger than the diameter of the steel pipes. In addition, the forming surface may be flat, and with it the workpiece S ₁ may come into linear contact.

During the pressing operation of the workpiece S ₁ to give it the shape of an open pipe, according to the present invention, a bending force is applied to at least a part located at a distance W / 4 from the center of the slightly curved portion or non-curved portion P. The reason for this is as follows.

(где F - изгибающее усилие, r - радиус окружности) в положении с отклонением на угол ϕ от направления действия изгибающего усилия, и становится максимальным в положении с отклонением на угол 90° от направления действия изгибающего усилия, и деформация также становится максимальной. Таким образом, при приложении изгибающего усилия по линии действия, отклоненной от центра слегка изогнутого участка или неизогнутого участка P на 90°, то есть, на 1/4 полной длины окружности, происходит эффективная деформация слегка изогнутого участка или неизогнутого участка P. В этот момент, изгибающий момент является максимальным в положении с отклонением от линии действия изгибающего усилия на 90°, и по мере удаления от этого положения, он начинает уменьшаться. С целью обеспечения достаточной пластической деформации слегка изогнутого участка или неизогнутого участка P, предпочтительно, прикладывают изгибающее усилие, создающее отклонение на величину W/4 ± 0,07 W.If the preform S ₁ is generally circular, the bending moment (M) is $$F\times r\times \cos \varphi$$

(where F is the bending force, r is the radius of the circle) in a position with a deviation of an angle ϕ from the direction of action of the bending force, and becomes maximum in a position with a deviation of 90 ° from the direction of action of the bending force, and the deformation also becomes maximum. Thus, when a bending force is applied along the line of action deviated from the center of the slightly curved section or the non-curved section P by 90 °, that is, by 1/4 of the full circumference, effective deformation of the slightly curved section or the non-curved section P. occurs. , the bending moment is maximum in the position deviating from the line of action of the bending force by 90 °, and as it moves away from this position, it begins to decrease. In order to ensure sufficient plastic deformation of the slightly curved portion or the non-curved portion P, a bending force is preferably applied to create a deflection of W / 4 ± 0.07 W.

In addition, in the present invention, the center of the slightly curved portion or the non-curved portion P is located in a portion located at a distance W / 4 from the lateral edge of the sheet material S, the reason for which will be explained below.

As already mentioned above, although the bending force is preferably applied in a direction deflected by a distance W / 4 from the center of the slightly curved portion or the non-curved portion P in the width direction of the sheet material, since its shape changes during the pressing operation of the workpiece S ₁ to give the shape of the open pipe, the position of the contact point of the workpiece with the upper part of the stamp 4 changes, and the direction of action of the bending force also changes. If the slightly curved section or non-curved section P is located at a distance W / 4 from the lateral edge of the sheet material S, the point of application of bending force is always located on the edge section of the sheet material S, which ensures maximum deformation of the slightly curved section or non-curved section P. Thus , this makes it possible to deform a slightly curved portion or a non-curved portion P with just one operation, without changing the bending position. In addition, to ensure sufficient deformation of the slightly curved portion or non-curved portion P, the slightly curved portion or non-curved portion P is preferably located at a distance W / 4 ± 0.07 W from the point of application of the bending force, i.e. edge section of sheet material.

According to the present invention, if a slightly curved portion is present in a portion of the sheet material S, in particular in a portion containing a portion located W / 4 from the edge portion of the sheet material S, or if the non-curved portion P in which there is no bending is provided bending the sheet material S, the length L (see FIG. 4) of the slightly curved section or the non-curved section P in the width direction of the sheet material S is preferably not more than 10% of the sheet width. The reason for this is as follows.

When a bending force is applied to a U-shaped workpiece S ₁ having a slightly curved section or a non-curved section P of length L located at a distance W / 4 from the slightly curved section or non-curved section P, the bending moment acts on the slightly curved section or unbent section P, and this section is deformed.

(где F - изгибающее усилие, r - радиус окружности) в положении с отклонением на угол ϕ от направления действия изгибающего усилия, и становится максимальным в положении с отклонением на угол 90° от направления действия изгибающего усилия, и деформация также становится максимальной. Однако величина деформации слегка изогнутого участка и неизогнутого участка Р является неодинаковой. Таким образом, форма поперечного сечения получаемой открытой трубы отличается от идеальной окружности.When the workpiece S ₁ as a whole takes a circular shape, the bending moment (M) is $$F\times r\times \cos \varphi$$

(where F is the bending force, r is the radius of the circle) in a position with a deviation of an angle ϕ from the direction of action of the bending force, and becomes maximum in a position with a deviation of 90 ° from the direction of action of the bending force, and the deformation also becomes maximum. However, the amount of deformation of the slightly curved portion and the non-curved portion P is not the same. Thus, the cross-sectional shape of the resulting open pipe is different from the ideal circle.

We studied the relationship between the ratio of the deviation from the ideal circumference to the outer diameter of the pipe on the ratio of the length L of a slightly curved section or non-curved section P of the workpiece S ₁ with a U-shaped cross section to the sheet width for a pipe with a wall thickness of 38.1 mm, made from standard Gr. X65 American Petroleum Institute (ANI). As can be seen from FIG. 6, the magnitude of the deviation increases as the length of the slightly curved portion or the non-curved portion P increases and the outer diameter decreases. For a pipe with an external diameter of 559 mm, when the length of the slightly curved section or non-curved section P exceeds 10% of the sheet width, the deviation is more than 1.5% of the external diameter.

And although according to the ANI standard, which is the general standard used in the production of pipes for main pipelines, the shape correction coefficient of the pipe expansion coefficient (i.e. the degree of increase in diameter during expansion) is about 1.5% in the process of pipe expansion after connection (welding ) the edges of the longitudinal gap, if the deviation is more than 1.5% of the outer diameter, the accuracy of the finished pipe in size may be insufficient. Thus, in the present invention, the length L of the slightly curved portion or the non-curved portion P in the width direction of the sheet material S is preferably selected to be no more than 10% of the width of the sheet. In addition, in order to ensure sufficient plastic deformation of the slightly curved portion or the non-curved portion P, the length L is preferably selected in the range W / 4 ± 0.07 W from the direction of action of the bending force.

Further, as the length L of the slightly bent portion or the non-bent portion P increases, the gap between the edges of the open pipe increases due to the spring effect when the bending force is removed, as shown in FIG. 7, and the connection of the end surfaces of the edges can become difficult, which in some cases can create limitations.

In FIG. Figure 8 is a graph showing the dependence of the gap between the lateral edges (opening the U-shape) of the workpiece S ₁ with the U-shaped section on the length L of a slightly curved section or non-curved section P. Despite the fact that when the length L is reduced, a slightly curved section or unbuckled portion P dimensional accuracy is improved because the gap between the side edges of the workpiece ₁ S also decreases when the gap between the side edges becomes less than the width of the punch 2 becomes impossible to raise the punch after course 2 bending operation (the last operation in FIG. 3), and it becomes impossible to remove the preform from the press S _1. Thus, the lower limit of the length L is set depending on the size of the equipment used or the size of the steel pipe produced. For example, in the manufacture of a steel pipe with an external diameter of 559 mm using a press with a punch 2 having a width of 150 mm, it is necessary that the L / W ratio be at least 0.05.

According to the present invention, if the opening angle determined by the construction of the supporting part on which the workpiece S ₁ is mounted is θs and the angle between the direction of action of the bending force and the vertical (angle of bending force) is θf, pressing of the workpiece S ₁ begins under the condition θf> θs . However, the portion on which the preform S ₁ , which meets this condition, rests, is practically absent on the line of action of the bending force, and a slightly curved portion or non-bent portion P can reliably move away from the center when a relatively small bending force is applied.

Further, if the center of the workpiece in width is located in the lower part (the area on which the workpiece stands in a U-shaped position, in which the gap between the edges of the workpiece is facing up, and a straight line q passing through the center of the workpiece and symmetrically dividing the workpiece into two parts, is considered the reference line, the opening angle θs of the workpiece S ₁ is defined as the angle between the reference line and the straight line r connecting the center of the workpiece in width (W / 2) with the side edge of the workpiece S ₁ (see Fig. 5). In addition, the angle (direction) of bending force is determined Design of the pressing die and friction, if the angle forming the surface of the pressing punch relative to the horizontal plane is defined as the angle θd, and a coefficient of surface friction of the pressing die - as the μ, θf is the angle ^{θf = θd - tan -1 (μ} ) ( see FIG.. 9).

If the forming surface of the upper part of the die 4 contains an arcuate surface 4a, the center of the width of which coincides with the forming center O of the pressing die, and a pair of forming surfaces 4b connected to each of the edges of the arched surface 4a, and directed towards the forming center O of the pressing die, forming surface 4b may be a straight inclined surface or a curved inclined surface.

The central angle θc of the arcuate surface 4a is selected to be at least 28 °, and the forming surface 4b is deformed so as to surely deflect the slightly curved portion or non-curved portion P to the outside during pressing of the workpiece S ₁ . Thus, the angle θd between the horizontal line and the straight line passing through the center along the width of the arcuate surface 4a can be chosen equal to at least 14 ° (see Fig. 2).

Below we will explain why the central angle θc of the arcuate surface 4a of the upper part of the die 4 should be selected at least 28 °. In FIG. 10 is a graph illustrating the dependence of the direction θf (angle of bending force) on the angle θd of the forming surface 4b of the upper part of the die 4 obtained for a typical lubrication state (in the case where the friction coefficient is 0.1).

As can be seen from FIG. 10, the larger the angle θd of the forming surface of the upper part of the die 4, the greater the direction of the angle θf of the bending force, and the slightly curved portion or the non-curved portion P is easily deflected outward. For example, when a pipe with an external diameter of 559 mm is produced using a press with a punch 2 of a width of 150 mm (an example of the minimum size in paragraph (0055)), the minimum value of the L / W ratio is 0.05 and the opening angle θs of the workpiece S ₁ is 9 °. At this moment, if the angle θd of the pressing die is not less than 14 °, the direction θf of the force is larger than the opening angle θs of the workpiece S ₁ . In addition, the opening angle θs of the workpiece S _{1 is} geometrically determined by the ratio of the length L to the sheet width W of the slightly curved section or the non-curved section P, and as the ratio L / W increases, the opening angle θs of the workpiece S ₁ also increases. Thus, in some cases, it may be necessary to further increase the central angle θc of the arcuate surface 4a of the upper part of the die 4.

At the same time, if the angle θd of the forming surface 4b of the upper part of the die 4 is large, the opening part of the pressing die becomes smaller than the maximum width of the workpiece S ₁ with a U-shaped cross-section, and, as shown in FIG. 11, since the upper part of the stamp 4 can cut into the workpiece S ₁ and “bite” it, its upper limit value is set depending on the maximum width of the workpiece S ₁ .

When pressing the preform S ₁ , when a bending force is simultaneously applied to each of the parts (two points) located at a distance W / 4 from the slightly curved portion or the non-curved portion P towards the edges (side edges of the preform S ₁ ) of the sheet S, it is useful combine the forming center O of the pressing die used for pressing the workpiece S ₁ with the center of the width W / 2 of the workpiece S ₁ , thereby avoiding the occurrence of a stepwise height difference (offset) between the side edges of the open pipe S ₂ .

The radius of the arcuate surface 4a of the upper part of the stamp 4 should be no more than 1.2 times the diameter of the steel pipe produced. The reason for this is as follows.

With a small radius of the arcuate surface 4a of the upper part of the die 4, as shown in FIG. 12, during molding, a space is formed between the upper part of the die 4 and the workpiece S ₁ , and there is a possibility of mutual displacement of the side edges; the minimum value of the above radius should be selected depending on the shape near the edge of the sheet, determined by the technology of crimping the edges, so as to ensure contact in the range near the sheet thickness from the edge of the sheet.

In FIG. 13 shows the relationship between (radius of the arcuate surface 4a of the upper part of the die 4 / radius of the steel pipe) and the index (index of insufficient deformation) at which the slightly curved section or non-curved section P remains in its original form (i.e., non-curved). As the radius of the arcuate surface 4a of the upper part of the die 4 increases, the restriction is insufficient, and thus the slightly curved portion or non-curved portion P remains in its original state. If the value of 1.0 is chosen as the reference value of the index of insufficient deformation, then, in order not to exceed this reference value, it is desirable that, when pressing, the radius of the arcuate surface 4a of the upper part of the die 4 decreases by no more than 1.2 times from the radius of the produced steel pipe.

Furthermore, if the lower part of the die 5a has an arcuate surface 5a, the forming surface of which has a concave shape, as shown in FIG. 5, it is necessary that its diameter be larger than the outer diameter of the steel pipe being produced, so that the shape of the workpiece S ₁ with a U-shaped cross section coincides with the shape of the pressing stamp.

FIG. 14 is a graph of the relationship between the molding force and the free bending force of a slightly bent or non-bent portion P versus the ratio of the radius of the arcuate surface 5a of the lower part of the die 5 to the radius of the steel pipe. With a small radius of the arcuate surface 5a of the lower part of the die 5, since when pressing the workpiece S _{1, the} slightly curved portion or non-curved portion P is limited by the pressing die, the molding force is increased. In particular, if the radius of the arcuate surface 5a of the lower part of the die 5 is less than 1.05 of the diameter of the steel pipe produced, the molding force increases sharply. Thus, it is desirable that the radius of the arcuate surface 5a of the lower part of the die 5 is not less than 1.05 of the diameter of the steel pipe produced. When choosing the radius of the arcuate surface 5a of the lower part of the stamp 5 is not less than 1.07 of the diameter of the steel pipe produced, pressing can only be performed with a force not exceeding 2 times the force exerted when the pressed workpiece S ₁ is in an unlimited state.

With a large radius of the arcuate surface 5a of the lower part of the die 5, as shown in FIG. 15, since contact with the upper part of the die 4 is unavoidable, the desired pressing intensity is not achieved, the deformation of the slightly curved portion or the non-curved portion P may not be sufficient, or the divergence of the side edges may increase, so that the shape of the lower part of the die 5 must be selected taking into account the shape of the upper part die 4. When using the lower part of the die 5 with an arcuate concave surface 5a, you can directly use the matrix used in the production of steel pipe by technology UO without any changes, and there is no need to manufacture a matrix. However, as long as the limitation of the slightly curved portion or the non-curved portion P can be avoided, the lower part of the die 5 can be used in the same configuration as the upper part of the die 4.

Further, although in the considered example, the forming surface (inclined surface) 4b is made in the form of an arcuate surface 4a, and the forming surface (inclined surface) 4b is used as the upper part of the die 4, until the condition θs> θf is satisfied at the beginning of the pressing process , it is possible to use a pressing die with a forming surface formed by an arcuate surface 5a, as on the lower part of the die 5, and possible designs are not limited to the considered configuration.

As the lower part of the stamp 5, a matrix such as matrix 1 in FIG. 1, which serves as a support for the workpiece S ₁ at two points, i.e. matrix of roller type. Even when using the die, since when pressing a slightly curved portion or a non-curved portion P is not limited to the forming surface of the pressing die, the workpiece S ₁ can be shaped into a tube using a relatively small bending force.

After crimping the open pipe S ₂ using the upper part of the stamp 4 and the lower part of the stamp 5, and closing the side edges, welding is performed using a welding unit (connecting means), and then the corresponding expansion of the resulting steel pipe is performed.

As a welding unit (connecting means), for example, a machine is used that includes three types of welding machines, namely, a tack welding machine, an internal surface welding machine and an external surface welding machine. In the welding unit, the apparatus for welding the inner surface by means of molding rolls continuously introduces end-to-end pipe surfaces into close contact with each other and welds these surfaces in close contact along the entire length.

Then, the crosslinked pipe is welded (using submerged arc welding) from the side of the inner surface using the apparatus for welding the inner surface, after which it is welded (using submerged arc welding) from the outer surface using the installation for welding the outer surface.

The relative position of the welding unit (connecting means) and the pressing die (upper part of the die 4 and the lower part of the die 5) for pressing the workpiece S _{1 is} not particularly limited and can be arbitrarily changed.

Example 1

In order to form a steel pipe with a diameter of 36 inches from plate steel for the production of pipes for main pipelines (ANI grade X60) with a thickness of 38.1 mm and a width of 2711 mm, this sheet material was placed on a matrix with a distance of 450 mm between the rod-shaped elements, and produced its three-point press bending, starting from a point at a distance of 1120 mm from the center along the width of the sheet material, when feeding sheet material at 224 mm, through 11 bending operations (five bending operations from the right edge of the sheet material five operations bending from the left edge of the sheet material) with a punch having a radius forming surface 308 mm. During these operations, the bending value was set so that the punch head reached a position of 15.8 mm from the line connecting the upper points of the rod-shaped elements, and during one operation the sheet was bent by 30 °. However, at points at a distance of 672 mm from the center along the width of the sheet material (after the third feed from the left edge and the third feed from the right edge), the bending operation was not performed, as a result of which an unbent section was formed in the region from the point 571 mm to the point 795 mm. Then, while holding a workpiece with a U-shaped cross-section obtained by bending in a U-shaped position so that the open hole of the tube stock is directed upward, the workpiece is pressed to give it the shape of an open tube, until the distance between extreme points (the upper point of the part R of the curved surface of the upper part of the pressing stamp and the lower point of the part R of the curved surface of the lower part of the pressing stamp) did not reach 880 mm. The pressing was carried out using the upper part of the stamp containing an arched surface of radius R = 457.2 mm with a central angle θc = 60 °, and a flat surface connected to the arched surface at an angle of θd = 30 °, and the lower part of the stamp with a concave arched surface with a radius R = 502.9 mm. In this case, the degree of decrease in the bending force of the pressing die, the change in the gap between the edges of the open pipe, the amount of displacement of the edges and the roundness of the steel pipe after the welding operation were investigated.

As a result, after pressing to be U-shaped under standard conditions by pressing to be O-shaped with a compression ratio of 0.2% using a pressing die of radius R = 452.6 mm according to the present invention, when compared with a conventional manufacturing method steel pipe with an external diameter of 36 inches and a thickness (wall thickness) of 38.1 mm, it was confirmed that the bending force when pressed into an O-shape is reduced by about 15% compared to the bending force when pressing by the conventional method.

In addition, it turned out that it is possible to produce a steel pipe with a gap of 21 mm between the lateral edges of an open pipe, a displacement of the edges after welding (steel pipe) of 0.1 mm, a roundness of 5.2 mm and a difference in outer diameter of 36 inches is only 0, 6%

Example 2

As in Example 1, in order to form a steel pipe with a diameter of 36 inches from plate steel for the production of pipes for main pipelines (grade X60 according to ANI classification) with a thickness of 38.1 mm and a width of 2711 mm, this sheet material was placed on a matrix with a distance of 450 mm between the rod-shaped elements, and its three-point press bending was performed with bending by 30 ° during one operation, starting from a point at a distance of 1120 mm from the center along the width of the sheet material, when feeding sheet material by 224 mm, through 11 bending operations (five bending operations from the right edge of the sheet material and five bending operations from the left edge of the sheet material), using a punch with a radius of the forming surface of 308 mm During these operations, the bending value was set so that the punch head reached a position of 15.8 mm from the line connecting the upper points of the rod-shaped elements, and during one operation the sheet was bent by 30 °. However, at points at a distance of 672 mm from the center along the width of the sheet material (after the third feed from the left edge and the third feed from the right edge), a slightly curved section was formed in the area from 571 mm to 795 mm by limiting the bend to 8.8 mm and performing bending by 10 °.

Then, while holding a workpiece with a U-shaped cross-section obtained by bending in a U-shaped position so that the open hole of the tube stock is directed upward, the workpiece is pressed to give it the shape of an open tube, until the distance between extreme points (the upper point of the part R of the curved surface of the upper part of the pressing stamp and the lower point of the part R of the curved surface of the lower part of the pressing stamp) did not reach 880 mm. The pressing was carried out using the upper part of the stamp containing an arched surface of radius R = 457.2 mm with a central angle θc = 60 °, and a flat surface connected to the arched surface at an angle of θd = 30 °, and the lower part of the stamp with a concave arched surface with a radius R = 502.9 mm. In this case, the degree of decrease in the bending force of the pressing die, the change in the gap between the edges of the open pipe, the amount of displacement of the edges and the roundness of the steel pipe after the welding operation were investigated.

As a result, after pressing to be U-shaped under standard conditions by pressing to be O-shaped with a compression ratio of 0.2% using a pressing die of radius R = 452.6 mm according to the present invention, when compared with a conventional manufacturing method steel pipe with an external diameter of 36 inches and a thickness (wall thickness) of 38.1 mm, it was confirmed that the bending force when pressed into an O-shape is reduced by about 15% compared to the bending force when pressing by the conventional method.

It turned out that it is possible to produce a steel pipe with a gap of 16 mm between the lateral edges of an open pipe, a displacement of the edges after welding (steel pipe) of 0.1 mm, a roundness of 8.2 mm and a difference in outer diameter of 36 inches is only 0.9%.

Example 3

In order to form a steel pipe with a diameter of 42 inches from plate steel for the production of pipes for main pipelines (ANI grade X80) 44.5 mm thick, 3180 mm wide and 12.2 mm long, this sheet material was placed on a matrix with a distance of 500 mm between the rod-shaped elements, and its three-point press bending was performed using a punch with a radius of the forming surface of 360 mm, as a result of which a blank with a U-shaped cross-section with a different arrangement and length of the unbent section was obtained and from the edge portion.

Then, the lower part of the stamp with a concave arcuate surface with a radius of R = 609.6 mm was mounted on a rod-shaped element and extruded from the billet obtained with bending with a U-shaped cross section into the shape of an open pipe, until the distance between the extreme points (the upper point of the part R of the curved surface of the upper part of the pressing stamp and the lower point of the part R of the curved surface of the lower part of the pressing stamp) did not reach 1027 mm.

When pressing a billet with giving it the shape of an open pipe, we studied the change in the bending force of the pressing stamp, the size of the gap between the edges of the open pipe, the amount of displacement of the edges and the roundness of the steel pipe after the welding operation. The results are shown in Table. 1 together with the location of the point of application of the bending force and the shape of the workpiece.

В операциях 2 - 6, при повышении изгибающего усилия к точке, удаленной от неизогнутого участка на расстояние от 0,19 до 0,31 ширины листа, округлость и смещение были хорошими. Однако в ходе операции 1, при расстоянии 0,16 от точки приложения изгибающего усилия до центра неизогнутого участка, т.е. ближе к неизогнутому участку, округлость равна 18,1 мм, что превышает 1,5 % диаметра трубы, и смещение также равно 1,5 мм, что выше, чем в других случаях.

In operations 2-6, with increasing bending force to a point remote from the non-bent portion by a distance of 0.19 to 0.31 sheet widths, roundness and offset were good. However, during operation 1, at a distance of 0.16 from the point of application of the bending force to the center of the non-bent portion, i.e. closer to the bent section, the roundness is 18.1 mm, which exceeds 1.5% of the pipe diameter, and the displacement is also 1.5 mm, which is higher than in other cases.

In addition, when the point of application of the bending force is removed from the non-bent portion, the bending force decreases.

In operations nos. 7–10, when a non-curved section was located from a sheet edge in width at a distance of 0.28 to 0.19, satisfactory roundness was obtained, but in operation 11, in which a non-curved section was located close to the edge of the sheet in width , the resulting roundness was 17.1 mm, which exceeds 1.5% of the diameter of the steel pipe produced.

In addition, in operations nos. 12–15, with a length of a non-curved section not exceeding 0.12 sheet widths, a satisfactory roundness was obtained, but during operation No. 16, in which a long curved section was large, a roundness of 19.2 mm was obtained that exceeds 1.5% of the diameter of the produced steel pipe.

Example 4

In order to form a steel pipe with a diameter of 42 inches from plate steel for the production of pipes for main pipelines (ANI grade X80) 44.5 mm thick, 3180 mm wide and 12.2 mm long, this sheet material was placed on a matrix with a distance of 500 mm between the rod-shaped elements, and its three-point press bending was performed using a punch with a radius of the forming surface of 360 mm, as a result of which a blank with a U-shaped cross-section with a different arrangement and length of the unbent section was obtained and from the edge portion.

Then, while holding a workpiece with a U-shaped cross-section obtained by bending in a U-shaped position so that the open hole of the tube stock is directed upward, the workpiece is pressed to give it the shape of an open tube, until the distance between extreme points (the upper point of the part R of the curved surface of the upper part of the pressing stamp and the lower point of the part R of the curved surface of the lower part of the pressing stamp) did not reach 1027 mm. The pressing was carried out using the upper part of the stamp containing an arched surface of radius R = 533.4 mm with a central angle θc = 60 °, and a flat surface connected to the arched surface at an angle of θd = 30 °, and the lower part of the stamp with a concave arched surface of radius R = 609.6 mm, in a position in which the upper part of the stamp was in contact with both edge sections of the sheet in width. In this case, the degree of decrease in the bending force of the pressing die, the change in the gap between the edges of the open pipe, the amount of displacement of the edges and the roundness of the steel pipe after the welding operation were investigated. The results are shown in Table. 2 together with the location of the point of application of the bending force and the shape of the workpiece. The same forms as in Example 3 are denoted by the same numbers.

In operations nos. 7 to 10, when the non-curved section was located at a distance of 0.28 to 0.19 from the edge of the sheet in width, a satisfactory roundness was obtained. However, in operation No. 11, in which the non-bent section was located close to the edge section of the sheet in width, the roundness was 16.5 mm, which exceeds 1.5% of the diameter of the steel pipe produced.

In addition, in operations Nos. 12-15, in which the length of the unbent section did not exceed 0.12 of the sheet width, a satisfactory roundness was obtained. However, in operation No. 16, in which the length of the unbent section was large, the roundness was 17.1 mm, which exceeds 1.5% of the diameter of the steel pipe produced. In addition, all displacement values do not exceed 0.2 mm, which is less than in Example 3, in which bending was performed from each edge separately.

Example 5

In order to form a steel pipe with a diameter of 22 inches from plate steel for the production of pipes for main pipelines (ANI grade X80) with a thickness of 31.8 mm, a width of 1640 mm and a length of 12.2 mm, this sheet material was placed on a matrix with a distance of 400 mm between the rod-shaped elements, and its three-point press bending was performed using a punch with a radius of the forming surface of 188 mm, as a result of which a blank with a U-shaped cross-section with a different arrangement and length of the unbent section was obtained and from the edge portion.

Then, the lower part of the stamp with a concave arcuate surface with a radius of R = 330.2 mm was mounted on a rod-shaped element and extruded from the billet obtained with bending with a U-shaped cross section into the shape of an open pipe, until the distance between the extreme points (the upper point of the part R of the curved surface of the upper part of the pressing stamp and the lower point of the part R of the curved surface of the lower part of the pressing stamp) did not reach 538 mm.

When pressing a billet with giving it the shape of an open pipe, we studied the change in the bending force of the pressing stamp, the size of the gap between the edges of the open pipe, the amount of displacement of the edges and the roundness of the steel pipe after the welding operation. The results are shown in Table. 3 together with the location of the point of application of the bending force and the shape of the workpiece.

In operations 2-6, with increasing bending force to a point remote from the non-bent portion by a distance of 0.19 to 0.31 sheet widths, both roundness and offset were good. However, during operation No. 1, at a distance of 0.16 from the point of application of the bending force to the center of the non-bent portion, i.e. closer to the bent section, the roundness was 10.1 mm, which exceeds 1.5% of the diameter of the steel pipe produced, and the displacement was 1.4 mm, which is higher than in other cases.

In addition, when the point of application of the bending force is removed from the non-bent portion, the bending force decreases. In operations nos. 7–10, when the non-curved section was located at a distance from 0.28 to 0.19 in width from the edge of the sheet, satisfactory roundness was obtained, but in operation No. 11, in which the non-curved section was located close to the edge of the sheet along width, the resulting roundness was 10.6 mm, which exceeds 1.5% of the diameter of the produced steel pipe. In addition, in operations nos. 12 to 14, when the length of the non-curved section was not more than 0.12 of the sheet width, a satisfactory roundness was obtained, but during operation No. 15, in which the length of the non-curved section was large, a roundness of 11.2 mm was obtained that exceeds 1.5% of the diameter of the produced steel pipe.

Example 6

In order to form a steel pipe with a diameter of 22 inches from plate steel for the production of pipes for main pipelines (ANI grade X80) with a thickness of 31.8 mm, a width of 1640 mm and a length of 12.2 mm, this sheet material was placed on a matrix with a distance of 400 mm between the rod-shaped elements, and its three-point press bending was performed using a punch with a radius of the forming surface of 188 mm, as a result of which a blank with a U-shaped cross-section with a different arrangement and length of the unbent section was obtained and from the edge portion.

Then, while holding a workpiece with a U-shaped cross-section obtained by bending in a U-shaped position so that the open hole of the tube stock is directed upward, the workpiece is pressed to give it the shape of an open tube, until the distance between extreme points (the upper point of the part R of the curved surface of the upper part of the pressing stamp and the lower point of the part R of the curved surface of the lower part of the pressing stamp) did not reach 538 mm. The pressing was carried out using the upper part of the stamp containing an arched surface of radius R = 279.4 mm with a central angle θc = 60 °, and a flat surface connected to the arched surface at an angle of θd = 30 °, and the lower part of the stamp with a concave arched surface with a radius R = 330.2 mm, in a position in which the upper part of the stamp was in contact with both edge sections of the sheet in width. In this case, the degree of decrease in the bending force of the pressing die, the change in the gap between the edges of the open pipe, the amount of displacement of the edges and the roundness of the steel pipe after the welding operation were investigated. The results are shown in Table. 4 together with the location of the point of application of the bending force and the shape of the workpiece. The same forms as in Example 5 are denoted by the same numbers.

В операциях №№ 7 - 10, при расположении неизогнутого участка на расстоянии от 0,28 до 0,19 от краевого участка листа по ширине, была получена удовлетворительная округлость. Однако в операции № 11, при которой неизогнутый участок был расположен близко к краевому участку листа по ширине, полученная округлость составила 9,8 мм, что превышает 1,5% диаметра производимой стальной трубы.

In operations nos. 7 to 10, when the non-curved section was located at a distance of 0.28 to 0.19 from the edge of the sheet in width, a satisfactory roundness was obtained. However, in operation No. 11, in which the non-bent section was located close to the edge section of the sheet in width, the resulting roundness was 9.8 mm, which exceeds 1.5% of the diameter of the steel pipe produced.

In addition, in operations Nos. 12-14, in which the length of the non-curved portion did not exceed 0.12 of the sheet width, a satisfactory roundness was obtained. However, in operation No. 15, in which the length of the unbent section was large, the roundness was 10.1 mm, which exceeds 1.5% of the diameter of the steel pipe produced. In addition, all displacement values do not exceed 0.3 mm, which is less than in Example 3, in which bending was performed from each edge separately.

Example 7

In order to form a steel pipe with a diameter of 36 inches from plate steel for the production of pipes for main pipelines (ANI grade X60) 38.1 mm thick, 2711 mm wide and 12.2 mm long, this sheet material was placed on a matrix with a distance of 450 mm between the rod-shaped elements, and its three-point press bending was performed using a punch with a radius of the forming surface of 308 mm, as a result of which a workpiece with a U-shaped cross-section with unbent sections 109 mm and 224 mm long was arranged, located GOVERNMENTAL at a distance of 683 mm from the edge portions.

Then, while holding a workpiece with a U-shaped cross-section obtained by bending in a U-shaped position so that the open hole of the tube stock is directed upward, the workpiece is pressed to give it the shape of an open tube, until the distance between extreme points (the upper point of the part R of the curved surface of the upper part of the pressing stamp and the lower point of the part R of the curved surface of the lower part of the pressing stamp) did not reach 880 mm. The pressing was carried out using the upper part of the stamp containing an arched surface with a radius R = 457.2 with different central angles, and a flat surface connected to an arched surface, and the lower part of the stamp with a concave arched surface with a radius R = 502.9 mm, in a state in which the upper part of the stamp was in contact with both edge sections of the sheet in width. In this case, the degree of decrease in the bending force of the pressing stamp, the gap between the edges of the open pipe and the roundness of the steel pipe after the welding operation were investigated. In Tab. Figure 5 shows the results obtained, as well as the values of the length of the unbent section, the opening angle θs of the workpiece with a U-shaped cross section, the central angle of the upper part of the punch and the opening angle θf of the bending force.

Table 5

No. The length of the bent section
[mm] Opening angle θs
[hail.] Central angle θc of the upper part of the stamp
[hail.] Bending Angle θf
[hail.] Edge distance
[mm] Roundness
[mm] one 109 7.2 5,0 2.1 240 - 2 109 7.2 10.0 7.1 120 15.7 3 109 7.2 15.0 12.1 40 7.1 four 224 14,4 15.0 12.1 240 - 5 224 14,4 20,0 17.1 31 6.2 6 224 14,4 30,0 27.1 21 5.2

In operations Nos. 3, 5 and 6, provided θf> θs, the distance between the edges is also small, and the roundness is also good. And vice versa, in operations nos. 1, 2 and 4, provided θf <θs, the distance between the edges was large, and in operations nos. 1 and 4, the distance between the edges was too large to perform welding. In addition, in operation No. 2, in addition to the fact that welding was impossible, the roundness was 15.7 mm, which exceeds 1.5% of the diameter of the steel pipe produced.

Example 8

In order to form a steel pipe with a diameter of 28 to 38 inches from plate steel for the production of pipes for trunk pipelines (ANI grade X60) with a thickness of 38.1 mm and a length of 12.2 mm, three-point press bending of this sheet material was carried out, as a result of which a blank with a U-shaped cross-section was obtained with an unbent portion of 0.08 of the sheet width located at a distance of about W / 4 from the edge of the sheet in width.

Then, while holding a workpiece with a U-shaped cross-section obtained by bending in a U-shaped position so that the open hole of the tube stock is directed upward, the workpiece is pressed to give it the shape of an open tube, until the distance between extreme points (the upper point of the part R of the curved surface of the upper part of the pressing stamp and the lower point of the part R of the curved surface of the lower part of the pressing stamp) did not reach 0.96 of the outer diameter. The pressing was carried out using the upper part of the stamp containing an arched surface with a radius R = 457.2 mm with a central angle θc = 60 °, and various radii connected to the arched surface at an angle θd = 30 °, and the lower part of the stamp with a concave arched surface with a radius 50.8 mm larger than the outer diameter in the position in which the upper part of the stamp was in contact with both edge sections of the sheet in width. In this case, the change in the bending force of the pressing stamp, the displacement of the edges and the roundness of the steel pipe after the welding operation were investigated. The results are presented in Table. 6 together with the values of the outer diameter of the steel pipe and the ratio of the radius of the upper part of the stamp to the outer radius of the steel pipe.

Table 6

No. Outer diameter of steel pipe
[mm] The ratio of the radius of the upper part of the stamp to the outer radius of the steel pipe Roundness
[mm] Bias
[mm] one 965.2 0.95 5.7 1,0 2 914.4 1.00 5.2 0.2 3 863.6 1.06 6.2 0.1 four 812.8 1.13 8.3 0.2 5 762.0 1.20 10,2 0.3 6 711.2 1.29 17,2 0.2

In operations Nos. 1-5, in which the ratio of the radius of the upper part of the stamp to the outer radius of the steel pipe did not exceed 1.2, the roundness was good, and the smaller the value of the above ratio, the better the circumference. In addition, in operation No. 1, in which the radius of the upper part of the stamp was less than the external radius of the steel pipe, the displacement was greater than in operations No. 2-5, in which the value of the above ratio was not less than 1.0. At the same time, in operation No. 6, in which the ratio of the radius of the upper part of the stamp to the external radius of the steel pipe was large, the resulting roundness was 17.2 mm, which exceeds 1.5% of the diameter of the steel pipe produced.

Example 9

In order to form a steel pipe with a diameter of 36 inches from plate steel for the production of pipes for main pipelines (ANI grade X60) 38.1 mm thick, 2711 mm wide and 12.2 mm long, this sheet material was placed on a matrix with a distance of 450 mm between the rod-shaped elements, and its three-point press bending was performed using a punch with a radius of the forming surface of 308 mm, as a result of which a workpiece with a U-shaped cross-section with an unbent section of 224 mm long located on p Normal distance of about 683 mm from the edge portion of the sheet.

Then, while holding a workpiece with a U-shaped cross-section obtained by bending in a U-shaped position so that the open hole of the tube stock is directed upward, the workpiece is pressed to give it the shape of an open tube, until the distance between extreme points (the upper point of the part R of the curved surface of the upper part of the pressing stamp and the lower point of the part R of the curved surface of the lower part of the pressing stamp) did not reach 880 mm. The pressing was carried out using the upper part of the stamp containing an arched surface of radius R = 457.2 mm with a central angle θc = 60 ° and various radii R connected to the arched surface at an angle of θd = 30 °, and the lower part of the stamp with a concave arched surface with different radii, in a state in which the upper part of the stamp was in contact with both edge sections of the sheet in width. In this case, a study was made of the bending force (load) of the pressing stamp. In Tab. 7 illustrates the relationship between the deformation of the bottom of the stamp, the ratio of the radius of the bottom of the stamp to the outer radius of the steel pipe, and the bending force.

Table 7

No. The radius of the bottom of the stamp
[mm] The ratio of the radius of the lower part of the stamp to the outer radius of the steel pipe An effort
[MH] one 482.6 1.06 75 2 508.0 1,11 fifty 3 533.4 1.17 35 four 558.8 1.22 35

With increasing radius of the lower part of the stamp, the bending force increases. In operations Nos. 3 and 4, in which the ratio of the radius of the lower part of the stamp to the outer radius of the steel pipe was greater than 1.15, there was no contact with the pressing stamp, and the bending force was no more than half the amount of bending force obtained in operation No. 1.

Industrial applicability

The present invention makes it possible to efficiently produce a steel pipe with high roundness without using excessively high pressure.

Notation Used:

1 matrix

1a rod element

1b rod element

2 punch

2a punch head

2b punch stock

3 feed roller

4 stamp top

4a arcuate surface

4b forming surface (inclined surface)

5 bottom of the stamp

5a arcuate surface

S sheet material

S ₁ blank

S ₂ open pipe

Claims (27)

1. A method of manufacturing a steel pipe, comprising at least one operation of bending sheet material with edges curved in width in the direction along the sheet width to form a workpiece with a U-shaped cross section, wherein an open pipe with a longitudinal gap between the side edges is formed by application bending force to the workpiece for pressing, and the end surfaces of the side edges of the open pipe are connected to each other end-to-end to form a steel pipe, characterized in that yayut obtaining a slightly curved portion having a slight bend compared to other regions, or obtaining a non-curved portion having no bend at least on a portion of the sheet material during bending, and applying bending force to the part located from the center of the slightly curved portion or the non-curved portion in the direction of the edge portion along the width of the sheet material at a distance of at least W / 4, where W is the size of the sheet material in width, without limiting the slightly curved portion or the non-curved portion in the process of pressing the workpiece into an open pipe. 2. The method according to p. 1, characterized in that the center of the slightly curved section or the non-curved section is located on a section located at a distance W / 4 from the edge section along the width of the sheet material. 3. The method according to p. 1 or 2, characterized in that the length of the slightly curved section or non-curved section in the direction along the width of the sheet material is not more than 10% of the width of the sheet. 4. The method according to p. 1 or 2, characterized in that when applying a bending force for pressing, the workpiece is supported on a part located not on the same line with the action line of the bending force, while if the opening angle of the workpiece is θ _s , but the bending angle force is θ _f , then the pressing of the workpiece begins under the condition θ _f > θ _s . 5. The method according to p. 3, characterized in that when applying a bending force for pressing, the workpiece is supported on a part located not in line with the action line of the bending force, while if the opening angle of the workpiece is θ _s and the angle of the bending force is θ _f , then pressing the workpiece begins under the condition θ _f > θ _s . 6. The method according to any one of paragraphs. 1, 2 or 5, characterized in that in the process of pressing the workpiece using a pressing stamp containing a forming surface that is not in contact with a slightly curved section or a non-curved section. 7. The method according to p. 3, characterized in that in the process of pressing the workpiece using a pressing stamp containing a forming surface that is not in contact with a slightly curved section or a non-curved section. 8. The method according to p. 4, characterized in that in the process of pressing the workpiece using a pressing stamp containing a forming surface that is not in contact with a slightly curved section or a non-curved section. 9. The method according to any one of paragraphs. 1, 2, 5, 7 or 8, characterized in that during the pressing of the workpiece, a bending force is simultaneously applied to the sections, each of which is located at a distance W / 4 from the center of the slightly curved section or the non-curved section towards the edges along the width of the sheet material . 10. The method according to p. 3, characterized in that during the pressing of the workpiece a bending force is simultaneously applied to the sections, each of which is located at a distance W / 4 from the center of the slightly curved section or non-curved section towards the edges along the width of the sheet material. 11. The method according to p. 4, characterized in that in the process of pressing the workpiece, a bending force is simultaneously applied to the sections, each of which is located at a distance W / 4 from the center of the slightly curved section or non-curved section towards the edges along the width of the sheet material. 12. The method according to p. 6, characterized in that during the pressing of the workpiece a bending force is simultaneously applied to the sections, each of which is located at a distance W / 4 from the center of the slightly curved section or non-curved section towards the edges along the width of the sheet material. 13. The method according to any one of paragraphs. 1, 2, 5, 7, 8, 10-12, characterized in that when pressing the workpiece, the forming center of the pressing die used for pressing the workpiece coincides with the center of the workpiece in width. 14. The method according to p. 3, characterized in that when pressing the workpiece, the forming center of the pressing stamp used for pressing the workpiece coincides with the center of the workpiece in width. 15. The method according to p. 4, characterized in that when pressing the workpiece, the forming center of the pressing stamp used for pressing the workpiece coincides with the center of the workpiece in width. 16. The method according to p. 6, characterized in that when pressing the workpiece, the forming center of the pressing stamp used for pressing the workpiece coincides with the center of the workpiece in width. 17. The method according to p. 9, characterized in that when pressing the workpiece, the forming center of the pressing stamp used for pressing the workpiece coincides with the center of the workpiece in width. 18. The method according to any one of paragraphs. 1, 2, 5, 7, 8, 10-12, 14-17, characterized in that the preform is held in a U-shape with an upwardly directed gap between the side edges, the preform being supported on its lower part. 19. The method according to p. 3, characterized in that the preform is held in a U-shape with an upwardly directed gap between the side edges, the preform being supported on its lower part. 20. The method according to p. 4, characterized in that the workpiece is held in a U-shaped position with an upward gap between the side edges, while the workpiece is supported on its lower part. 21. The method according to p. 6, characterized in that the workpiece is held in a U-shape with an upwardly directed gap between the side edges, while the workpiece is supported on its lower part. 22. The method according to p. 9, characterized in that the workpiece is held in a U-shape with an upwardly directed gap between the side edges, the workpiece resting on its lower part. 23. The method according to p. 13, characterized in that the preform is held in a U-shape with an upwardly directed gap between the side edges, the preform being supported on its lower part. 24. A pressing stamp for the production of steel pipe by the method according to any one of paragraphs. 1-23, containing two bending tools made with the possibility of placing between themselves the workpiece, and the bending tools have a forming surface, which during the pressing of the workpiece does not come into contact with a slightly curved section or a non-curved section. 25. The pressing stamp according to claim 24, characterized in that at least one of the bending tools comprises an arcuate surface, the center of the width of which coincides with the forming center of the pressing stamp, while the forming surface has an inclined surface connected to both edges of the arcuate surface and directed towards the forming center of the pressing stamp.

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