WO2014192043A1 - Method for press-molding steel pipe and method for producing steel pipe - Google Patents

Abstract

Provided are: a method for press-molding a steel pipe having a low variability of the seam gap at an abutted section; and a method for producing a steel pipe. The method molds a steel pipe by subjecting a steel plate to a plurality of repetitions of press bending processing to mold the steel plate and is characterized in that, from the state in which an open pipe that is the molded member has a specific seam gap during the final repetition of press bending processing, in accordance with a predetermined relationship between the specific seam gap and a further needed additional rolling reduction, subjects the open pipe to additional rolling reduction processing that is on the basis of the relationship from the state in which the open pipe that is the molded member has the specific seam gap during the final repetition of press bending processing.

Description

Steel pipe press forming method and steel pipe manufacturing method

The present invention relates to a method for forming a thick-walled steel pipe by press bending and a method for manufacturing the steel pipe.

As a method for forming a thick-walled steel pipe, there is a press forming method using an upper and lower mold shown in FIG. 3 (hereinafter also referred to as a bending press).

In the forming method, when a steel plate having a predetermined width and length is formed into a steel pipe whose length direction is the pipe axis direction, bending processing (hereinafter referred to as edge bending) is performed on the width end portion of the steel plate. And then bending it a plurality of times in the width direction of the steel sheet to form a cylinder.

In the main forming step subsequent to the end bending, as shown in FIG. 3, the two dies 1a and 1b of the lower mold are adjusted to a predetermined interval, the steel sheet S is set thereon, and the tip of the punch 2 of the upper mold The punch tip 22 is pushed into a position corresponding to the distance between the two dies 1a and 1b, bending deformation is performed, and then the steel sheet S is moved by a predetermined length in the width direction and the upper die is pushed again. Repeat once.

Usually, the steel sheet is sequentially formed from the end (A in the figure) on the one side in the width direction of the steel sheet toward the center part (C in the figure) in the width direction of the steel sheet (first half), and formed to the front of the center part in the width direction of the steel sheet. After that, the steel sheet is formed in order from the end (B in the drawing) on the opposite side in the steel plate width direction toward the central portion (C in the drawing) in the steel plate width direction (second half), and finally the central portion in the steel plate width direction (in the drawing). Apply a reduction to C) (final). In this way, an open pipe is manufactured, which is a tubular body that is formed into a cylindrical shape and whose plate ends facing each other are not welded. In FIG. 3, the dotted line is the position of the steel sheet S in a state where the punch 2 is not in contact with the steel sheet S. In FIG. 3, table rollers (not shown) are provided on the left and right sides of the dies 1a and 1b. For example, the table roller can support the points B and C in a dotted line shape in the upper left diagram of FIG. 3 and can convey the steel plate S in the left-right direction in the drawing.

Fig. 4 is a schematic diagram of an open tube. As shown in FIG. 4, the open tube 3 is a tube in which a plate material as a material is formed into a cylindrical shape, and plate end portions (open seam edges) 31 a and 31 b facing each other are not welded. . A gap g between facing open seam edges is a seam gap. The tube axis direction L of the open tube 3 coincides with the longitudinal direction of the punch.

The open pipe is then transported in the longitudinal direction of the steel pipe (the direction perpendicular to the paper surface) and sent to the next process. For this reason, after the final pass forming, which is the final bending process, the seam gap g of the open tube 3 must be wider than the thickness of the punch beam 21 that supports the punch tip 22 of the upper mold.

Then, the above-mentioned seam gap g of the open pipe 3 is constrained by a reduction device, and in this state, the abutted open seam edges are welded by a welding machine to obtain a straight seam welded steel pipe. If necessary, the cylindrical shape is corrected by expanding or reducing the diameter of the welded steel pipe.

For the adjustment and setting of the pressing conditions at this time, a press die provided with a mechanism for adjusting the interval between the dies of the lower die disclosed in Patent Document 1 can be used.

Japanese Unexamined Patent Publication No. 11-129031

¡When the open seam edge is constrained by a reduction device so as to close the seam gap of the open pipe and the open seam edge that is butted in that state is welded by a welding machine, there is an upper limit on the restraining force of the reduction device. For this reason, it is impossible to restrain the open seam edge by restraining the open pipe having a seam gap of a certain amount or more determined by the steel pipe size. As a result, the abutted open seam edges cannot be welded.

Therefore, the seam gap is required to be as small as possible in the final press at the bending press.

The final press adjusts the open pipe seam gap by gradually increasing the amount of punch reduction. When the punch press amount of the final press is increased, the seam gap amount is decreased. Conversely, when the punch press amount is small, the seam gap amount is increased.

When the punch pressure is released, spring back occurs, so the open pipe seam gap after the reduction is larger than the open pipe seam gap under reduction. For this reason, in order to reduce the spring back after the release of the reduction, in the final press, the punch reduction amount is increased, and even after the open seam edge contacts the punch support portion, the punch reduction amount is further increased. There is a technology to bend the open pipe.

However, if the amount of punch reduction is excessive, the open seam edge of the open pipe strongly sandwiches the punch support portion, and there is a possibility that the pipe must be cut over the entire length in order to remove the pipe. .

In order to avoid such troubles, it is usually noted that the amount of punch reduction does not become excessive, but as a result, the seam gap tends to be large.

In addition to this, the yield strength of the steel sheet also affects the seam gap. This is because when the steel sheet is subjected to bending deformation, the amount of springback after the bending deformation varies depending on the yield strength of the steel sheet. For example, when the final pass press molding is performed under the same pressing conditions and the press load is completely removed, the seam gap is small when the yield strength of the steel sheet S is low, and the seam gap is high when the yield strength of the steel sheet S is high. Becomes larger.

As mentioned above, the seam gap tends to be large because it is usually noted that the amount of punch reduction is not excessive. Here, when the influence of the yield strength of the steel plate is further overlapped, the variation in the seam gap is also increased. If the seam gap is too large, the restraining force required to close and restrain the seam gap during welding becomes large, so that the reduction device becomes large. Further, in order to cope with variations in the seam gap, it takes a lot of time to manually adjust the reduction amount of the reduction device in the welding machine.

Therefore, in order to suppress the variation in the seam gap after pressing, there is a technique for adjusting the pressing conditions for each steel sheet, or by previously creating a table of the relationship between the yield strength of the steel sheet and the pressing conditions, and determining the pressing conditions based on the table. is there.

In the technique described in Patent Document 1, the bending shape can be adjusted by adjusting the die interval of the lower mold. For variations in the amount of springback, after measuring the shape after forming the steel plate into the steel pipe in the first step, the second step adjusts the die interval of the lower mold and performs correction processing. . In other words, according to the technique described in Patent Document 1, after the molding process of the first step, the unloaded state, that is, the bending shape in the state where the spring back is generated is measured, and according to the measurement result By adjusting the pressing conditions such as the amount of rolling, the load and the die interval of the lower die, the correction process as the second step is performed. Therefore, in order to reset the die interval of the lower mold, it takes time for the resetting. In particular, when a plurality of correction processes are performed for forming a single steel pipe, there is a problem that the production efficiency is greatly reduced because the number of shape measurements is also multiple. And since it is necessary to set the conditions for such correction processing for each steel plate, when manufacturing steel pipes from a large number of steel plates having variations in the amount of springback, a significant reduction in production efficiency is avoided. I can't.

Therefore, an object of the present invention is to provide a method for press forming a steel pipe with little variation in seam gap.

The gist of the present invention is as follows.

[1] A method of forming a steel pipe by applying a plurality of press bending processes to a steel sheet to form a steel pipe, and the open pipe as a molding material has a specific seam gap during the final press bending process. In accordance with a predetermined relationship between the additional reduction amount further required from the state of the steel and the specific seam gap, the open pipe as the molding material is subjected to the specific seam gap during the final press bending process. The method of press forming a steel pipe, characterized in that the open pipe is subjected to processing of the additional reduction amount based on the above relationship from the state.

[2] The steel pipe press forming method according to [1], wherein the specific seam gap is a seam gap at the time when the open seam edge of the steel plate contacts the punch beam of the upper mold.

[3] A method for manufacturing a steel pipe, characterized in that an open seam edge of an open pipe formed by the press forming method according to [1] or [2] is butted and welded.

According to the present invention, by pressing under a predetermined condition, a press material with little variation in seam gap can be obtained, so that there is no need for correction processing and setting adjustment of the die interval of the lower die, and the production efficiency is greatly improved. .

FIG. 1 is a diagram showing the relationship between the yield strength difference and the seam gap according to the present invention. FIG. 2 is a diagram showing the relationship between the yield strength difference and the seam gap according to the prior art. FIG. 3 is a schematic diagram for explaining a forming process in the steel pipe manufacturing process. FIG. 4 is a schematic diagram of an open tube. FIG. 5 is a schematic diagram for explaining the end bending molding process, FIG. 5A shows a set state during end bending, FIG. 5B shows a state after end bending load, and FIG. 5C shows a state after end bending unloading. FIG. 6 is a schematic diagram for explaining the press forming process, FIG. 6A shows a loaded state, FIG. 6B shows a state after unloading, and FIG. 6C shows a tube cross-sectional shape after press forming.

In the API standard, which is a general standard for line pipes, which are the main applications of straight seam welded steel pipes, the range from the upper limit to the lower limit of the yield strength of welded steel pipes of X80 grade is 138 MPa. The yield strength range is about the same in the steel plate. In particular, when manufacturing a steel pipe having a high yield strength, the steel sheet as a raw material is manufactured by the TMCP method, and therefore the yield strength is likely to vary due to variations in the component conditions, rolling conditions, and cooling conditions.

Hereinafter, a case where an API X80 grade steel pipe having an outer diameter of 1219 mm and a pipe thickness of 31.8 mm is formed will be described, but the present invention is not limited to the embodiment described below.

First, end bending was performed as shown in FIG. In FIG. 5, 41 is an end bending lower mold, and 42 is an end bending upper mold. End bending was performed so that the end bending angle j (FIG. 5B) was 28 degrees during press loading in a range h (FIG. 5A) having a width of 240 mm at the end in the width direction of the steel plate. The bending angle k (FIG. 5C) at the end in the width direction of the steel plate after the unloading of the press load was 23 degrees.

Next, the punch 2 (upper die) having a radius R of the punch tip 22 shown in FIG. 6A was bent 11 times sequentially from the steel plate width direction end to the steel plate width direction. The molding method at this time is shown in FIG. In FIG. 6A, the punch 2 (upper die) is composed of a punch beam 21 and a punch tip 22 and the lower die is composed of dies 1a and 1b. The total value of the eleven bending angles and the bending angle of the end bending are combined to obtain the entire bending angle (f in FIG. 6C) excluding the seam gap. Specifically, with a steel plate having a yield strength of 640 MPa, the bending angle (d in FIG. 6A) at the time of bending per bending process is set so that the bending angle after unloading (e in FIG. 6B) is 29 degrees. Bending was performed at 35 degrees. As for the bending range of the steel sheet S, the range a in FIG. 6A indicates the bending range up to the previous time, the range b in FIG. 6A indicates the current bending range, and the range c in FIG. In such bending, the amount of bending is generally adjusted by directly controlling the amount of movement of the punch 2 with a press device. Here, the amount by which the punch 2 is lowered from the state in which the punch tip 22 is in contact with the upper surface position of the steel plate (hereinafter, the amount by which the punch 2 is lowered from a certain reference point is referred to as the amount of reduction, and unless otherwise specified, the upper surface of the steel plate. Processing was performed with a fixed position).

FIG. 2 shows the relationship between the yield strength difference, which is the difference in the yield strength of the steel plate with respect to 640 MPa, which is the standard value of the yield strength of the steel plate, and the seam gap when unloaded after pressing.

Even if the bending shape is the same when bent, that is, during the rolling, the amount of springback is large for materials with high yield strength. Therefore, the bending angle after forming becomes small, and the seam gap in the unloaded state becomes large. As shown in FIG. 2, when the yield strengths of the raw steel plates differ by 160 MPa, the difference in seam gap in the unloaded state after pressing becomes 170 mm. This corresponds to 14% of the outer diameter, which is a very large value.

Therefore, the bending process in the intermediate process is performed by the conventional forming method, and the relationship between the yield strength difference when the amount of reduction in the final forming pass (11th) is changed and the seam gap in the unloaded state after pressing. Is shown in FIG. In FIG. 1, the result (graph b) of the prior art shown in FIG. 2 is entered for reference.

Graph c is an example of the present invention, in which the open seam edge is further reduced by 9 mm after contacting the punch beam 21 of the upper mold so that the deformation amount in the final forming pass (the 11th time) is the same. The difference in seam gap in the unloaded state after pressing is as small as 20 mm, and it can be seen that a substantially uniform seam gap can be obtained regardless of the yield strength of the steel sheet.

Graph a is an example where the open seam edge is rolled down until it touches the punch beam part of the upper mold. Compared to the prior art (graph b, constant reduction), the deviation of the seam gap in the unloaded state after pressing is smaller, but the seam gap in the unloaded state is larger than in the above-described example of the present invention. .

The reason why the open seam edge is further reduced by 9 mm after contacting the punch beam 21 of the upper die is based on the following technical idea.

When manufacturing a plurality of steel pipes of the same size, first, a plurality of open pipes of the same size are formed. Here, since the pressing conditions are basically constant, the deformation mode from the steel plate as the material to the open pipe is basically the same. Therefore, if the amount of reduction to be further added is made constant from a certain shape in the middle of the final press, the seam gap in the state of unloading after the final press becomes constant.

As described above, when an open tube is formed from a steel plate using two dies 1a and 1b and one punch 2, a certain specific partway through the final press in which the reduction amount to be further added is constant. Adopting a seam gap as a shape index is simple and effective.

In the above-described example, both of the open seam edges are in contact with the two punch beams 21 as seam gaps as an index of a specific shape in the middle of the final press in which the amount of reduction to be further added is constant. The time point was adopted. Here, from the point when both open seam edges come into contact with the punch beam 21 of the upper die 2, the amount of reduction to be further added is preliminarily preformed or refer to past production results. To grasp and decide.

It should be noted that when the reference of the seam gap, which is an index of a shape with a constant reduction amount to be added, is set at a point in time when both open seam edges are in contact with 2 21, that is, the seam gap is the punch beam 21. However, the present invention is not limited to this. For example, the determination that the seam gap has reached a specific value can be made by using, for example, a detector that can measure the end position of the plate at any time or a simple detector that determines that a certain position has been reached. Is possible.

Specifically, for example, a light emitter and a light receiver are provided in the punch beam 21, and the amount of light received by the light receiver changes due to the open seam edge of the open tube blocking the route from the light projector to the light receiver. The position of the edge can be detected. Further, if the time point when the open seam edge comes into contact with the punch beam 21 of the upper mold 2 is detected, the position of the plate end portion is not always measured. For example, it can be realized by changing the electrical continuity state due to the contact between the open seam edge and the punch beam 21 or by providing a piezoelectric element in the planned contact portion in advance to confirm the presence or absence of the contact. .

From the state in which the open pipe has a specific seam gap during the reduction of the final press, as a control method for processing the additional reduction amount required, for example, when the specific seam gap amount is reached, A signal may be sent to the reduction control device of the press forming apparatus, and the additional reduction amount determined in advance may be separately processed using this signal as a trigger. The additional reduction amount can be measured by measuring the movement amount of the punch 2. When the specific seam gap is the same as the thickness of the punch beam 21, that is, when the time point when the open seam edge contacts the punch beam 21 is used as a reference, the open seam edge that contacts the punch beam 21 is the punch beam 21. It is also possible to detect the amount of sliding up 21 and control the amount of additional reduction based on the amount of sliding up.

In order to manufacture a steel pipe using the open pipe manufactured by the above press forming method, the open seam gap of the open pipe is continuously tack-welded using the continuous tack welding apparatus, and then the inner surface is welded and then the outer surface is welded. The main welding may be performed in the order of welding. It is preferable that the roundness of the steel pipe can be improved by expanding the pipe with the pipe expanding apparatus using the pipe expanding apparatus. In the pipe expansion process, the pipe expansion ratio (ratio of the outer diameter change amount before and after the pipe expansion to the outer diameter of the pipe before the pipe expansion) is usually performed in the range of 0.3% to 1.5%. From the viewpoint of a balance between the roundness improvement effect and the capacity required for the tube expansion device, the tube expansion rate is preferably in the range of 0.5% to 1.2%.

In order to manufacture a steel pipe having an outer diameter of 1219 mm, a pipe thickness of 31.8 mm, and a length of 12 m, ten steel plates having an API X80 grade and a length of 24 m are prepared, and each steel plate is divided into three in the longitudinal direction to obtain 10 test materials. Three sheets / group x 3 groups were prepared. The plate width of these steel plates was machined to 3,693 mm, and each of both end portions in the width direction of the steel plate was subjected to press forming after end-bending a range of 180 mm width with a R380 mm mold.

In press molding, the upper die punch 2 uses a punch tip 22 having a radius of R415 mm, and the lower die 1 has an R100 mm die interval of 540 mm (the interval is two dice 1a of the lower die, 1b), and was divided into 11 times. The thickness of the punch beam 21 is 100 mm.

Table 1 shows the width direction set position from the first pass to the tenth pass (distance from the center of the plate width at the center of the two dies of the lower mold) and the amount of reduction. The amount of reduction was determined such that when the yield strength of the steel sheet was 615 MPa, the bending at the entire circumference excluding the seam gap portion was the sum of the end bending and the 11 press formings. *

As the forming sequence of the main forming process, as shown in the press process diagram of FIG. 3, passes 1 to 5 mean the first half process, and passes 6 to 10 mean the second half process. Passes 1 to 5 corresponding to the first half of the process are sequentially formed from one end in the width direction of the steel sheet toward the center in the width direction of the steel sheet, and are formed to the front by the width of one press at the center in the width direction of the steel sheet. . Next, the passes 6 to 10 corresponding to the latter half process are sequentially formed from the opposite end of the steel plate in the width direction toward the center portion in the steel plate width direction. Lastly (11th pass), rolling is applied to the central part in the width direction of the steel sheet.

Using 10 steel plates with different yield strengths (steel Nos. A to J), the steel plate width direction position shown in Table 1 (the steel plate width direction position in the table is the distance in the A direction from the center C of the steel plate +, the B direction) In each case, the steel plate was pressed for 10 passes, and then the 11th pass was pressed to measure the seam gap in the unloaded state after pressing. The results (relationship between steel plate yield strength and seam gap after pressing) are shown in Table 2.

In the final pass (11th pass), the center of the plate width is set to be the center of the lower die, and in the present invention example, the width of the steel plate is set so that the seam gap after pressing is 125 mm with a steel plate having a yield strength of 615 MPa. After the end, that is, the oven seam edge of the open tube, contacted the punch beam 21, it was further reduced by 9 mm. In Comparative Example 1, the reduction amount, which is the amount by which the punch 2 is lowered from the upper surface position of the steel plate so as to have a seam gap of 100 mm in the unloaded state after pressing with a 560 MPa steel plate having the lowest yield strength, is 48. It was 6 mm. In Comparative Example 2, first, the oven seam edge of the open tube is rolled down until it comes into contact with the punch beam 21, and the seam gap in the unloaded state after the press is confirmed. After adjusting the interval, the reduction was repeated again.

The present invention example has a small variation in seam gap (= maximum value−minimum value) after pressing of 10 steel pipes, a short time required for press forming, and a good steel pipe shape and high working efficiency are compatible.
On the other hand, in Comparative Example 1, although the time required for press forming is slightly shorter, in the steel plate J having the lowest yield strength, the open seam edge is in a state of sandwiching the punch beam 21, so that the forming material (open tube) is taken out. Since it was necessary to stop the line, it was difficult to adopt as industrial production. In Comparative Example 2, although the shape is stable, the required time is 1.4 times that of the present invention example, and the production efficiency is inferior.

The steel pipe press forming method and the steel pipe manufacturing method of the present invention are not limited to the manufacturing of large-diameter and thick-walled steel pipes, and can be applied to all methods of manufacturing steel pipes by performing a three-point bending press. it can.

DESCRIPTION OF SYMBOLS 1a, 1b Dies 2 Punch 21 Punch beam 22 Punch tip part 3 Open pipe 31a, 31b Plate edge part 41 End bending lower mold 42 End bending upper mold

Claims (3)

1. A method of forming a steel pipe by applying multiple times of press bending to a steel sheet to form a steel pipe, from the state where the open pipe, which is the material to be formed, has a specific seam gap during the final press bending process Furthermore, according to a predetermined relationship between the required additional reduction amount and the specific seam gap, the open pipe as the molding material became the specific seam gap during the final press bending process. A press forming method of a steel pipe, wherein the open pipe is subjected to processing of the additional reduction amount based on the relation from the state.
2. 2. The steel pipe press forming method according to claim 1, wherein the predetermined seam gap is a seam gap at the time when an open seam edge of a steel plate comes into contact with a punch beam of an upper mold.
3. A method for manufacturing a steel pipe, characterized in that an open seam edge of an open pipe formed by the press forming method according to claim 1 or 2 is abutted and welded.

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