JPH06234020A - Manufacture of electric resistance welded tube - Google Patents

Abstract

PURPOSE:To improve space accuracy of an open pipe and to attain the satisfactory welding quality by forming coarsely a steel strip into the ellipse open pipe and then, forming this at a final stand of a fin-pass roll finishing stage by using specified rolls. CONSTITUTION:Both side edges of the steel strip are bent to the center and formed coarsely into the longitudinal ellipse open pipe. This pipe is finish-formed close to complete roundness by fin-pass rolls by adjusting a roll gap according to the tube forming diameter. This open pipe is then welded under restrictions of squeeze rolls and further, finishing of the outside diameter is made by sizing rolls. In the manufacturing method of this electric resistance welded tube, the roll gap 5 of upper and lower rolls 1 and 2 as the rolls of the fin-pass roll final stand is regulated in the range of a central angle 5-45 deg. below from a horizontal center line 4 of an open pipe cross section 3. Consequently, the shape accuracy of the open pipe before welding can be improved.

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 an electric resistance welded steel pipe, and more particularly to a method for manufacturing an electric resistance welded steel pipe which also serves as a forming roll for the electric resistance welded steel pipe having different outer diameters. At the end of the roll forming process, when forming the cross section of the open pipe into a shape close to a perfect circle, by using the roll whose roll gap is below the horizontal center line of the cross section of the open pipe, the open pipe before welding can be used. The present invention provides a method for producing an electric resistance welded steel pipe having excellent shape accuracy and good welding quality.

[0002]

2. Description of the Related Art Generally, an electric resistance welded steel pipe is formed by passing a steel strip through a pair of breakdown rolls, which are drum-shaped and drum-shaped, and a fin pass roll, which is a hole-shaped roll, and gradually transforms the steel strip into a cylindrical open pipe. Bend and squeeze roll to weld both ends of open pipe with high frequency current,
Then, a manufacturing procedure of finishing to a predetermined outer diameter with a sizing roll is performed.

The roll used in such a series of steps needs to be replaced each time the outer diameter of the electric resistance welded steel pipe to be manufactured is different, and not only the productivity is seriously impaired by the work stoppage due to the roll replacement. However, the number of rolls that must be prepared becomes large, and there is a problem in that the management labor and roll cost are increased.

[0004]

With respect to this point, the inventors of the present invention are able to provide a method for producing an electric resistance welded steel pipe which can be used as a forming roll over a wide range of outer diameters and which has an excellent roundness. It was disclosed in Japanese Patent Publication No. 4-42097. The method is to perform a rough forming process that mainly bends both side edges and the center part in the width direction of the steel strip, and then use fin pass rolls with adjustable gaps between the upper and lower rolls to reach the end stage of the forming process. In addition, by adjusting the roll gap according to the diameter of the pipe, an open pipe close to a perfect circle is finish-formed, and then welding is performed under restraint by a squeeze roll, and then outer diameter finish is performed by a sizing roll. The upper and lower rolls can form an open hole type that can be used for a plurality of types of steel pipes having different outer diameters up to the maximum pipe making diameter to be made, based on the smallest pipe making diameter to be made,
A two-roll type fin pass roll, in which a longitudinally elongated oval open pipe is bent by a multi-step forming process of the fin pass roll without restraint in a direction parallel to the roll axis, It can be finish-molded into an open pipe that is close to a perfect circle.

At this time, the roll which is formed into an open pipe close to a perfect circle at the final stage of the fin pass is normally divided into upper and lower parts at the horizontal center position of the cross section of the open pipe having the smallest diameter, and thus the roll of the open pipe having the largest diameter is formed. Also in this case, the roll gap is located near the upper and lower centers of the cross section of the open pipe. When using this roll to apply a vertical reduction to a vertically elongated oval open pipe to make it a shape close to a perfect circle, seeing from the distribution of bending moments applied to each part of the open pipe in the circumferential direction, Since there is no restraint on the side part of the open pipe, it does not become a shape close to a perfect circle, and there are overbent and underbent areas,
The shape may be unfavorable.

As described above, when the open pipe before welding is not in a predetermined shape, when the squeeze roll is upset, extra processing other than drawing is added and the entire roll hole die is not filled with the material. However, there is a problem that the welding quality is adversely affected and the welding quality is likely to be unstable. The present invention has been made in view of the above circumstances,
When forming an open pipe close to a perfect circle at the end of the finpass roll forming process, by using a roll with a roll gap below the horizontal center line of the cross section of the open pipe, The purpose is to improve the shape accuracy and obtain good welding quality.

[0007]

SUMMARY OF THE INVENTION The present invention is a rough forming process in which both side edges and a central part of a steel strip are mainly bent to form a vertically elongated oval open pipe, and a vertical roll gap is set according to a pipe forming diameter. In the process of manufacturing the electric resistance welded steel pipe, the fin pass roll finishing forming process to adjust to an open pipe close to a perfect circle, the welding process to weld under constraining by the squeeze roll, and the outer diameter finishing process using the sizing roll An electric resistance welded steel pipe characterized in that the upper and lower roll gaps of the stand are formed by using rolls whose center angle is in the range of 5 ° to 45 ° downward from the horizontal center line of the open pipe cross section in the fin pass roll. Is a manufacturing method.

[0008]

As disclosed in Japanese Examined Patent Publication No. 4-42097, a normal fin pass roll is divided into an upper part and a lower part of a horizontal line passing through the center of the cross section of the open pipe having the smallest diameter that can be formed by the fin pass roll. The roll gap is near the center of the open pipe cross section. When vertical rolling is applied to the vertically elongated oval open pipe 6 with this roll to process it into a shape close to a perfect circle, the distribution 7 of bending moment applied to the open pipe is as shown in FIG. The portion a on the pipe side has a large bending moment because the moment arm is long, and the portion c on the pipe bottom receives a bending-back moment opposite to the portion a. The intermediate portion b between the portion a and the portion c is a portion where the moments in both directions overlap and the moment becomes zero. When the open pipe is machined under this moment distribution 7, the portion a has no lateral restraint, and therefore bulges outward from a predetermined shape and bends. Finally, the portion a is excessively bent and the portion b is insufficiently bent, and the cross section of the pipe 6 before welding has an irregular shape with respect to a perfect circle, as shown in FIG. 3B.

On the other hand, the fin-pass roll used for vertical compression of the open pipe according to the present invention has a central angle range of 5 ° to 45 ° below the upper and lower center lines 4 in the cross section 3 of the open pipe as shown in FIG. It is divided so that the roll gap 5 is inside. The allowable range of the roll gap 5 is 5 ° below the horizontal center line 4 of the open pipe cross section of the maximum diameter that can be formed by the fin pass roll.
The reason why the angle is within the range of up to 45 ° is that if the angle is less than 5 °, the outward bending of the pipe side a cannot be sufficiently prevented, and if the angle exceeds 45 °, that portion is excessively bent and the cross-sectional shape is Is worse.

FIG. 2 illustrates this.
When the vertically elongated oval open pipe 6 is processed into a shape close to a perfect circle by the upper and lower rolls, the bending moment distribution 7 is initially the same as in the conventional case, as shown in FIG. After that, when the deformation progresses and the side part of the open pipe bends to the flange part of the upper roll, this part is not further deformed outside, and this becomes a new fulcrum, as shown in FIG. 2 (b). A new bending moment 8 is applied to the material of the roll gap portion. Therefore, the portion b which is insufficiently bent in the initial stage is bent by the bending moment 8, and the final shape of the open pipe 6 is close to a predetermined perfect circle as shown in FIG. 2 (c).

In the rough forming step of the present invention, the degree of bending of both side edges of the steel strip and the widthwise central portion is 0.8R _{1 to} 1.2R _{1 with} respect to the minimum radius R _{1 of} the product to be produced.
It is preferable that the area excluding the both edges and the central portion in the width direction is 1.5R _{2 to} 10R ₂ with respect to the maximum product radius R ₂ , and the aspect ratio of the open pipe after fin-pass molding is the product. Roundness of 1.05, 1.05 from the viewpoint of preventing material deterioration
The following is preferable.

[0012]

[Example] Product minimum diameter 48.6 mmφ to product maximum diameter 6
4 (a) and 4 (b) show comparisons between the method of the present invention and the conventional method of the final stage roll hole die of the fin-pass roll capable of producing a pipe of up to 0.5 mmφ. In the method of the present invention, the roll gap is below the horizontal center line of the maximum diameter open pipe cross section.
It is in the range of ° to 33 °, which satisfies the condition of being in the range of 5 to 45 °.

Further, using this fin roll, 60.
Fin pass exit side when 5 mmφ x 6.0 mmt pipe is made
The distribution of the pipe curvature in the circumferential direction of the present invention is compared with the conventional method.
A comparison is shown in FIG. Here, the target shape has a radius of 32.
It is a true circle of 07 mm. In FIG. 5, 10 is the design curvature, 11
Is the curvature distribution of the example, and 12 is the curvature distribution of the comparative example.
In the comparative example, variations in curvature due to overbending and underbending
Width is 0.024mm ^-1While there is a degree, in the example
The width of the curvature variation is 0.006 mm^-1And about 1 of the comparative example
/ 4, the fin pass roll exit side, that is, before welding.
The shape accuracy of the open pipe has been greatly improved.

FIG. 6 shows the occurrence rates of welding defects in the method of the present invention and the conventional method in comparison. According to the method of the present invention, welding defects are greatly reduced and welding quality is stabilized as compared with the conventional method.

[0015]

According to the present invention, the shape accuracy of the open pipe before welding can be improved and the welding quality can be stabilized.

[Brief description of drawings]

FIG. 1 is a schematic view showing the shape of a fin roll according to the method of the present invention.

FIG. 2 is a schematic diagram showing bending moment applied to a pipe and deformation of the pipe according to the method of the present invention.

FIG. 3 is a schematic diagram showing a bending moment applied to a pipe and deformation of the pipe by a conventional method.

FIG. 4 is a comparison view of a fin hole final stage roll hole type in the method of the present invention and the conventional method.

FIG. 5 is a comparative diagram of pipe curvature on the exit side of the fin path.

FIG. 6 is a comparison diagram of occurrence rates of welding defects.

[Explanation of symbols]

1 Upper roll 2 Lower roll 3 Open pipe cross section 4 Center line 5 Roll gap 6 Open pipe 7 and 8 Bending moment distribution

Claims (1)

[Claims] 1. A rough forming process in which both side edges and a central portion of a steel strip are mainly bent to form a vertically elongated oval open pipe, and an upper and lower roll gaps are adjusted according to a pipe making diameter to open a nearly perfect circle. In the process for producing electric resistance welded steel pipes, which comprises a fin pass roll finishing forming process for forming a pipe, a welding process for welding under restraint using a squeeze roll, and an outer diameter finishing process using a sizing roll, the upper and lower roll gaps of the fin stand roll final stand are open pipes. A method for producing an electric resistance welded steel pipe, which comprises forming using a roll having a central angle within a range of 5 ° to 45 ° downward from a horizontal center line of a cross section.