JPH09239447A - Manufacture of uoe steel tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce peaking without changing an existing manufacturing equipment and to inexpensively produce a thick and high-strength steel tube sufficient in shape and quality by regulating the length of bending range at the C-forming time to specific times or above of the thickness. SOLUTION: In the production of an UOE steel tube, the length of bending range at the C-shape forming time is regulated to >=3.5 times of the thickness. In such a way, peaking is restricted with an existing production equipment, the UOE steel tube responding to the demand of thick and high strength can be produced. The C-shape bending range 3 is a part from the start point of bending radius r with an upper die and a lower die to the edge 5 of one side of an object to be bent 1. It is reguired that the length Lc of this C-shape bending range 3 is >=3.5 times of the thickness t.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for manufacturing a UOE steel pipe, and more particularly to an efficient method for manufacturing a thick and high strength UOE steel pipe.

[0002]

2. Description of the Related Art The UOE method is a typical method for manufacturing a welded steel pipe. As shown in FIG. 3, a steel plate (material to be molded) 1 which is a pipe material is first C-formed (end-bent). ,
Then, after U-forming, it is formed into a circular shape by O-pressing, the butt portion 2 is further welded, and then a predetermined shape and dimension is obtained by a pipe expanding machine. With respect to such UOE steel pipes, it has recently been required to increase the wall thickness and tensile strength, and in particular, the demand for thick wall pipes having a wall thickness of 40 mm or more is increasing.

A problem in forming such a thick-walled pipe is that O
The peaking after molding is increased. That is, since the deformation in the vicinity of the abutting portion at the time of O molding by the O press is insufficient, peaking (sharpness of the abutting portion) occurs. In the thick-walled steel pipe, the shape in the vicinity of the abutted portion remains uncorrected in the subsequent steps, which causes a defective shape. Peaking is reduced by increasing the O press power and giving sufficient compressive strain, but the following technology is proposed to enable the production of thick high-strength steel pipes within the existing pressing force. Has been done.

1) Method of Japanese Unexamined Patent Publication No. 53-112260 In this method, molding is performed with an O-press with the groove portion at the top to make a substantially circular shape, and in the next step, a pipe which becomes a substantially circular shape is rotated, It is a method of reducing the required O molding load by installing the groove portion at a position of 90 degrees and molding again. 2) Method of Japanese Examined Patent Publication No. 4094034 This method is a method of setting a limit value of the undeformed band width Lf in C forming and reducing it to reduce the O forming load required for straightening peaking. Further, in order to reduce the undeformed band width Lf, the method is a method of forming so that only the plate ends contact in C forming.

[0005]

However, these conventional methods have the following problems. Conventional method 1)
Then, it is indispensable to install a device that rotates the pipe and stabilize and install it again in the lower mold, which requires an increase in conventional equipment and complicates the process. In the conventional method 2), for example, the outer diameter
For products of 609.6 mm, Lf ≤ 39 mm. In such end bending, the forming force required to reduce the undeformed band width Lf increases as the undeformed band width decreases, and particularly when the width is less than the plate thickness, a very large forming force. Will be required. For example, when the plate thickness becomes 50 mm, the predetermined Lf becomes less than the plate thickness, the required C forming load becomes large, and it is necessary to increase the equipment such as increasing the size of the C press.

The present invention has been made in order to solve the above-mentioned problems, and it is possible to suppress the peaking with the existing manufacturing equipment and to meet the demand for thick and high strength.
It is an object of the present invention to provide a method for manufacturing a steel pipe.

[0007]

A method of manufacturing a UOE steel pipe according to the present invention is characterized in that, in a manufacturing process of a UOE steel pipe, a length of a bending region at C forming is 3.5 times or more of a plate thickness. It is what

At the time of forming a UOE steel pipe, the steel pipe is formed through the three steps of C forming → U forming → O forming.
The influencing factors of each process that influence the amount of peaking after molding were unclear. As a result of investigating the influence of the C-shaped shape that affects the peaking amount, the inventors of the present invention have shown that, as shown in FIGS. 1 and 2, the radius r after C-forming is the length of a portion bent to the outer diameter or less of the steel pipe. It was found that the length (the length Lc of the C-bending region 3) has an influence. FIG. 1 is an experimental result showing the relationship between C molding conditions and peaking, in which the horizontal axis represents the C molding parameter Lc / t and the vertical axis represents the peaking value (mm). The peaking target value after O molding is 2 mm
In order to set the following, the length Lc of the C bending region 3 is set to the plate thickness t.
Must be 3.5 times or more.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 is an explanatory view showing a bending region at the time of C molding in the present invention. The bending region at the time of C molding in the present invention, that is, the C bending region 3 is a portion from the starting point 4 of the bending radius r by an upper mold and a lower mold (not shown) to one edge 5 of the material 1 to be molded. The bending radius r is equal to or less than the outer diameter D of the steel pipe after O forming. And this C bending region 3
It is necessary that the length Lc of the above is 3.5 times or more of the plate thickness t. Further, it is desirable that the length Lf of the straight line portion from the end point 6 of the bending radius r to the edge 5 be as short as possible.

As a concrete example, various pipe forming tests with an outer diameter of 24 to 48 inches and t / D = 2.4 to 8.2% were carried out to find the length Lc of the C bending region and the peaking after O molding. I investigated the relationship. The result is shown in FIG. From the figure, L
It can be seen that the peaking decreases with an increase in c, and when the value exceeds 3.5 times the plate thickness t, the peaking value after O molding becomes 2 mm or less.

[0011]

As described above, according to the present invention, it is possible to reduce the peaking, which is a problem when forming a UOE steel pipe of a thick wall material, without changing the existing manufacturing equipment, and at a low cost and in a shape, There is an effect that a high-quality thick-walled high-strength steel pipe can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between C molding conditions and peaking in the present invention.

FIG. 2 is an explanatory view showing a bending region at the time of C forming in the present invention.

FIG. 3 is a diagram showing a forming process of a UOE steel pipe.

[Explanation of symbols]

 1 Molded material 3 C bending area

Claims (1)

[Claims] 1. A method of manufacturing a UOE steel pipe, characterized in that, in a process of manufacturing a UOE steel pipe, a length of a bending region at C forming is 3.5 times or more of a plate thickness.