JPH10211520A - Manufacture of uoe steel tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain the generation of peaking with the existing equipment as it is by executing C forming of the steel plate with a C press so that the length of the bending zone in the case of C forming becomes the specified times or more the plate thickness of the steel plate and moreover the length of the straight line part remaining after bending becomes the specified times or less the plate thickness of the steel plate. SOLUTION: C forming ending both end parts in the width direction of the steel plate with the C press is applied, the obtained C formed body is formed with a U press, next the obtained U formed body is O formed with an O press, thereafter the tube is manufacture by welding the butting part of the O formed body. In this case, C forming of the steel plate with the C press is executed under the condition that the length of the bending zone Lc at the time of C forming becomes 3.5 times or more the plate thickness of the steel plate and moreover the length of the zone Lf not yet deformed becomes 1.5 times or less the plate thickness of the steel plate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a UOE steel pipe, and more particularly to a method for efficiently manufacturing a thick-walled, high-strength UOE steel pipe.

[0002]

2. Description of the Related Art The production of a welded steel pipe by the UOE system is performed by the steps shown in FIG. First, the both ends 1a and 1b in the width direction of the steel plate 1 which is the material of the UOE steel pipe are
After being formed into a C-formed body 3 by bending by a press 2, the obtained C-formed body 3 is formed by a U-press 4 so that the cross-section in the width direction after forming is substantially U-shaped over the entire length direction. U molding is performed to prepare a U molded body 5. Next, the obtained U-formed body 5 was subjected to O-shaping by an O-press 6 so that the cross-section in the width direction after forming was substantially O-shaped over the entire length direction to obtain an O-formed body 7, which was obtained. O molded body 7
Is welded, and after a pipe expansion process, the U
OE steel pipe is manufactured.

[0003] In recent years, UOE steel pipes manufactured as described above have been required to have high wall thickness and high tension. In particular, demand for thick wall pipes having a wall thickness of 40 mm or more has been increasing. When manufacturing such a thick-walled tube, as shown in FIG. 5, the cross-sectional shape of both sides of the butted portion 7a of the O-formed body 7 does not have the same curvature as the other parts of the O-formed body 7. Therefore, O
The cross-sectional shape of the molded body 7 does not become the ideal perfect circular shape shown by the dotted line in FIG. 5, and there is a problem that a steep portion having the abutting portion 7 a as a vertex is partially formed. The formation of such a steep portion is called peaking, and the amount H of the steep portion protruding from the ideal perfect circular shape shown in FIG. 5 is called the peaking amount.

The cause of the above-mentioned peaking is as follows. In other words, when preparing a circular steel pipe by bending a steel plate, both ends of the steel plate serving as the butted portion of the tube have no binding force even when the bending is performed, and have a property of returning to an original state. For this reason, portions within a certain range from both ends of the steel plate after the bending process are not arcuate but linear.

In order to prevent the occurrence of such peaking, generally, as shown in FIG. 4, both ends 1a and 1b in the width direction of the steel sheet 1 are formed with a smaller curvature than other parts by the C press 2. Bending is performed so that peaking does not occur even if both end portions bent in the final bending process return to the original state.

However, as described above, even if the both ends in the width direction of the steel sheet are previously bent with a smaller curvature than the other parts by the C press, a part of a certain range from both ends becomes larger or smaller arc-shaped. Inevitably, the occurrence of a linear portion is inevitable.
It tends to increase as the wall thickness increases.

That is, even if both ends in the width direction of the steel sheet are previously bent with a smaller curvature than the other parts by the C press, peaking is likely to occur when the steel sheet is thick. The occurrence of peaking is difficult to correct even in the subsequent steps, and causes shape defects.

[0008] The peaking can be reduced by increasing the equipment capacity of the O-press machine and imparting sufficient compressive strain to the steel sheet, but it requires enormous equipment investment. For this reason, there is a demand for the development of a technology capable of manufacturing a thick-walled high-strength steel plate with an existing O-press machine, and the following technology has already been proposed.

(1) Japanese Patent Application Laid-Open No. 53-112260 [0009] An O-press is used to form a substantially circular base tube by forming a groove with the top as a top, and the obtained substantially circular base tube is connected to a tube. By turning the shaft 90 degrees about the axis and forming the groove again so that the groove portion is located at the lowest point, the forming load per O forming is reduced (hereinafter referred to as Prior Art 1).

(2) Japanese Patent Publication No. 60-40934 The limit value of the undeformed band width (the range of the end portion of the steel sheet which remains as a straight line without forming an arc shape) Lf in the C forming is determined.
O necessary for correcting peaking by reducing
This is a method of reducing the forming load, and in order to further reduce Lf, forming is performed so that only the plate end comes into contact in C forming (hereinafter referred to as prior art 2).

[0011]

However, the prior art 1 requires a device for rotating the tube after O-forming by 90 degrees around the tube axis and stabilizing the tube in the lower mold. However, there is a problem that the equipment needs to be enhanced and the molding process becomes complicated.

In the prior art 2, for example, the outer diameter 60
In the case of a 9.6 mm steel pipe, Lf ≦ 39 mm must be satisfied. However, the forming force in such an end bending process increases as Lf decreases, and in particular, when Lf is less than the plate thickness, Very large forming force is required. For example, when the plate thickness is 50 mm, the predetermined Lf becomes smaller than the plate thickness, the required C forming load increases, and it is necessary to increase the equipment such as increasing the size of the C press.

[0013] Accordingly, an object of the present invention is to solve the above-mentioned problems, to suppress the occurrence of peaking in existing equipment, and to provide a thick-walled, high-strength UOE steel pipe without requiring capital investment and in a process. It is an object of the present invention to provide a method which can be manufactured without increasing complexity.

[0014]

According to the present invention, a steel sheet is formed by using C
The C-shaped body is bent by pressing both ends in the width direction, the obtained C-shaped body is U-shaped by a U-press, and the obtained U-shaped body is O-shaped by an O-press. U by welding
In the method for manufacturing an OE steel pipe, in the C forming of the steel sheet by the C press, the length of the bending region at the time of the C forming is 3.5 times or more the thickness of the steel sheet, and the straight portion remaining after the bending is formed. It is characterized in that it is performed under conditions such that the length is 1.5 times or less the thickness of the steel plate.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, UOE steel pipe is
Since it is manufactured through three molding steps of C molding, U molding and O molding, it has been conventionally unclear in which step the amount of peaking generated during O molding is affected by what factors. The inventors of the present invention have investigated the effect of the shape of the molded article during the C molding on the amount of peaking, and have found the following.

FIG. 3 is a cross-sectional view of the C-formed body 3 when both ends 1a and 1b of the steel plate 1 as a material of the UOE steel pipe are C-formed (end bent) by a C press. As shown in FIG. 3, both end surfaces 1 a ′, 1
Bending is performed by a C press so that a range of a certain distance Lc indicated by a dotted line from b ′ (hereinafter referred to as a bending region) has a radius of curvature r smaller than the radius R of the final product.

By this bending, both ends 1 of the steel sheet 1 are formed.
a and 1b are bent at a curvature of Rc with a point 1d at a distance of Lc from both end faces 1a 'and 1b' as a bending start point. However, not all the regions of both ends 1a and 1b of the steel plate 1 are bent by the curvature Rc, and a range of a fixed distance Lf from the both end surfaces 1a 'and 1b' to the point 1c (hereinafter, referred to as an undeformed region). Bending is not performed and the straight shape is maintained.

It is considered that the peaking amount becomes smaller as the value of the above-described linear undeformed area (Lf) becomes smaller. In order to reduce the undeformed area (Lf), the bending area Lc is reduced, and the bending start point 1d is
It is only necessary to approach both end faces 1a 'and 1b' of
The closer the bending start point 1d is to both end faces 1a 'and 1b' of the steel sheet 1, the more difficult it becomes to bend.
As a result, C molding cannot be performed, and the peaking amount increases instead. Therefore, in order to reduce the peaking amount, the bending area (Lc) and the undeformed area (Lf)
Must be limited to a certain range.

FIG. 1 shows the relationship between the bending area Lc / t (t: the thickness of the steel sheet as the material) and the peaking amount in the relationship between the bending radius (Rc) and the radius or diameter (OD) of the product. FIG. As is apparent from FIG.
If c / t is set to 3.5 or more and the bending radius (Rc) is made as small as possible, the peaking amount becomes 0 or close to 0, and there is no practical problem.

FIG. 2 shows the relationship between the undeformed area Lf / t (t: the thickness of the steel sheet as the material) and the peaking amount in the relationship between the bending radius (Rc) and the radius or diameter (OD) of the product. It is a graph shown. As is apparent from FIG.
If f / t is set to 1.5 or less and the bending radius (Rc) is made as small as possible, the peaking amount becomes 0 or close to 0, and there is no practical problem.

From the above, according to the present invention,
The length of the bending area (Lc) when the steel sheet is C-formed by the C press is limited to 3.5 times or more the thickness of the steel sheet, and the straight portion remaining after the bending, that is, the undeformed area (Lf). Was limited to 1.5 times or less the thickness of the steel sheet.

As described above, the length of the bending region (Lc) is at least 3.5 times the thickness of the steel plate and the undeformed region (Lc)
f) If the steel sheet is C-formed under the condition that the length is 1.5 times or less the thickness of the steel sheet, the occurrence of peaking is suppressed, and a thick-wall high-strength UOE steel pipe requires special capital investment. It can be manufactured without any complicated steps.

[0023]

Next, the present invention will be described with reference to embodiments. A steel sheet having a thickness of 40.7 mm, a width of 2538 mm, a length of 12 m, a yield strength of 411 kgf / mm ² and a tensile strength of 551 kgf / mm ² was C-formed under the following conditions within the scope of the present invention.

The length of the bending area (Lc): 173 mm The length of the undeformed area (Lf): 56 mm Bending radius (Rc): R160 Pressure: 1500 t The U-shaped body is formed by U-forming with a pressing force of 1300 t to form a U-formed body.
It was O-shaped with 4100t. The peaking amount of the obtained O compact was mm. After the butted portion of the O-formed body thus obtained was welded by a submerged arc welding machine, a true round UOE steel pipe having a diameter of 800 mm could be manufactured through a pipe expansion process.

COMPARATIVE EXAMPLE A steel sheet having the same dimensions and strength as the above example was C-formed under the following conditions outside the scope of the present invention.
Forming and O-forming were performed to produce a 800 mm diameter UOE steel pipe.

The length of the bending region (Lc): 85.4 mm The length of the undeformed region (Lf): 65 mm The bending radius (Rc): R210 mm As a result, the peaking amount of the obtained O-formed body is 5 mm, In the subsequent steps, peaking could not be corrected, and the product had a poor shape.

[0027]

As described above, according to the present invention,
It is possible to suppress the occurrence of peaking with the existing equipment, and to produce a UOE steel pipe having a large thickness and a high strength without requiring capital investment and without complicating the process. It is.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between Lc / t and a peaking amount.

FIG. 2 is a graph showing a relationship between Lf / t and a peaking amount.

FIG. 3 is a cross-sectional view of a C compact.

FIG. 4 is a manufacturing process diagram of a welded steel pipe by a UOE method.

FIG. 5 is an explanatory diagram showing a peaking amount.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steel plate 1a, 1b Both ends of steel plate 1a ', 1b' Both end surfaces of steel plate 2 C press 3 C compact 4 U press 5 U compact 6 O press 7 O compact

Claims (1)

[Claims] 1. A steel sheet is C-formed by bending both ends in the width direction by a C press, the obtained C-formed body is U-formed by a U-press, and then the obtained U-formed body is O-formed by an O-press. And then forming a pipe by welding the butted portion of the O-formed body. The method of manufacturing a UOE steel pipe, wherein the C-forming of the steel sheet by the C-press is performed in such a manner that the bending area at the time of the C-forming has a thickness of the steel sheet. A method for producing a UOE steel pipe, wherein the method is carried out under conditions such that the length of the straight portion remaining after bending is 3.5 times or more and 1.5 times or less the thickness of the steel sheet. .