JPH10175079A - Manufacture of resistance welded tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent tucking flaws from generating, in producing a resistance welded tube using a two-roll type squeeze roll, by removing the fin flaws generating on both sides of a resistance welding part, together with beads on the outer face of the weld simultaneously by means of a cutting tool before advancing to the forming roll. SOLUTION: With a specific interval set in the tube feeding direction on the downstream side of a two-roll type squeeze roll 4, two cutting tools 11a, 11b are arranged in a zigzag in accordance with the space between the two flanges 4a of the squeeze roll 4. Using these cutting tools 11a, 11b, fin flaws 7 from both flanges 4a of the squeeze roll 4 are cut and removed on one side each time, together with the beads 5a on the outer face of the weld. In this case, the cutting depth is set to be within 0.8mm. Consequently, the tucking flaws (due to the reduction of the fin flaws by the forming roll) are prevented from generating, which ordinarily occurs on both sides of the outer resistance welded part of the tube after forming.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric resistance welding method in which a metal strip is continuously formed into a cylindrical shape by a group of forming rolls, and edges at both ends are joined by an electric induction welding method to form a pipe. The present invention relates to a method for manufacturing a pipe.

[0002]

2. Description of the Related Art As shown in FIG. 5, an ERW pipe is formed by continuously forming a strip of material into a cylindrical shape by a group of forming rolls 1 to form an open pipe 2. The edge portion 2 a is intensively heated by Joule heat by an electric current by an induction heating coil 3 connected to a high frequency power supply, and is pressed and joined laterally by a squeeze roll 4 to form a pipe 5. At this time, the two-roll squeeze roll 4 shown in FIG. 6 often has the same structure regardless of the size of the open pipe 2.

[0003] Such a two-roll squeeze roll is
In general, the pressurizing operation on an open pipe is simple, there are few working errors, and the number of rolls used is small, so that there is a feature that the number of steps for changing the outer diameter of the pipe can be reduced.

However, when manufacturing an electric resistance welded tube,
As shown in FIG. 5, the open pipe 2 passing through the group of forming rolls 1 is further narrowed down by the squeeze roll 4,
Since the edges 2a at both ends are bent and joined,
When a two-roll squeeze roll as shown in FIG. 6 is used, there is a disadvantage that a great frictional resistance is generated between the flange portion 4a of the squeeze roll 4 and the edge portion 2a of the open pipe 2. I have. In FIG. 5,
Reference numeral 6 denotes an external bead cutting bit (hereinafter simply referred to as a “bite”) for cutting a welded external bead 5 a of the pipe 5.

[0005] This open pipe 2 has a large friction resistance.
When the thickness becomes thicker, the outer surface of the edge portion is cut off, and the excess thickness is increased so that the excess thickness is bitten out of the squeeze roll. As a result, as shown in FIG. 7, a biting flaw 7 is formed at a portion of the outer surface side of the edge portion 2a which is in contact with the flange portion 4a.

[0006] The biting flaw 7 is formed by a group of regular rolls 8 (see FIG.
8), resulting in rash-like flaws 9 on both sides of the ERW weld as shown in FIG. Since such rashes 9 are minute, they usually do not cause a problem. However, they are extremely harmful to drawing, expanding and bend pipes, and as a result of strict surface inspection, most products Will be rejected.

[0007] As a technique for preventing such rashes 9, there is a method employing a multi-roll squeeze roll. For example, when a four-roll squeeze roll 10 as shown in FIG. 9 is used, the edge 2a of the open pipe 2 can be pressed down and formed from above by the upper roll 10a without difficulty. There is no frictional resistance that would occur when a roll-type squeeze roll is used, and no biting flaw 7 is formed.

[0008]

However, when a multi-roll squeeze roll is used, the number of man-hours required for changing the outer diameter of a pipe increases with an increase in the number of rolls, thereby deteriorating the operation rate. become. Therefore, in a practical operation, it is disadvantageous to use a multi-roll squeeze roll.

In addition, in the electric resistance welding method, it is indispensable that the butt shape of the edges at both ends of the open pipe is properly maintained. However, when a multi-roll squeeze roll is used, the butt shape is not sufficient. It is difficult to accurately reset each roll to a good condition. Therefore, since it is difficult to obtain an appropriate butting shape with good reproducibility, it is necessary to check the butting shape each time the squeeze roll setting is changed, which leads to a deterioration in the operation rate and the pipe production yield.

Although the squeeze roll is a multi-roll type squeeze roll having the above-mentioned problems, in the case of a large-diameter pipe making machine, the roll unit cost is reduced by dividing and reducing the size of the roll, and the cost of polishing and rework is reduced. Therefore, multi-roll squeeze rolls are widely used. In addition, even in a small-diameter thick-wall pipe-making machine, a multi-roll squeeze roll, which is unavoidably disadvantageous in operation, is used in order to prevent the above-mentioned flaw-like flaw.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and it has been found that even small-sized thick-walled pipe-making machines having an outer diameter of 152.4 mm or less and a wall thickness of 9.0 mm or more have a rash-like flaw. An object of the present invention is to provide a method for manufacturing an electric resistance welded pipe that can employ a two-roll squeeze roll that is advantageous in operation without generating the squeeze roll.

[0012]

In order to achieve the above-mentioned object, a method of manufacturing an electric resistance welded pipe according to the present invention is to adjust a distance between two flange portions of a squeeze roll with respect to a line conveying direction. They are arranged in a zigzag pattern. And, by setting the cutting depth of the staggered cutting tool to 0.8 mm or less, the biting flaws generated on both sides of the electric resistance welded portion can be efficiently removed before entering the fixed form roll. Can be removed.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have conducted various tests and studies to achieve the above-mentioned object. As a result, in order to efficiently remove the flaws formed on both sides of the ERW weld when using a two-roll squeeze roll before entering the fixed roll, it is necessary to use a welding tool to weld the outer surface bead. At the same time, they found that cutting was effective.

[0014] However, a cutting tool having a wide cutting surface capable of simultaneously cutting out the flaws generated on both sides of the electric resistance welded portion becomes a very large cutting tool in order to guarantee the strength of the shank and the tip. As a result, the unit cost of the tool increases and the manufacturing cost deteriorates. In general, it is necessary to select the rake angle and blade strength of the cutting tool according to the cutting resistance of the work to be cut, but at the same time cut the weld outer surface bead softened by induction heating and the room temperature pipe base material with a wide tool. Then, the cut surface of the pipe base material is roughened or peeled, resulting in poor surface properties. Therefore, conventionally, it has not been performed to remove the flaws by cutting with a cutting tool.

However, as a result of further study by the inventor, the present inventor has found that two cutting tools having a normal width are staggered in accordance with the distance between the two flange portions of the two-roll squeeze roll in the line conveyance direction. If the cutting depth of these cutting tools is set to 0.8 mm or less, the cutting surface of the pipe base material will not be roughened or peeled, and the flaws formed on both sides of the ERW weld will be standardized. The present inventors have found that it is possible to efficiently remove the material before entering the roll, and have made the present invention.

That is, the method for manufacturing an electric resistance welded tube according to the present invention comprises:
In a method for manufacturing an electric resistance welded pipe, both edges of an open pipe are intensively heated by Joule heat generated by a high-frequency current and pressurized and joined from a lateral direction by a two-roll squeeze roll.
The cutting tools are arranged in a zigzag manner in accordance with the distance between the two flange portions of the squeeze roll in the line transport direction, and the cutting is performed with the cutting depth of the cutting tools within 0.8 mm.

According to such a method for manufacturing an electric resistance welded pipe of the present invention, it is possible to prevent a fog-like flaw generated on both sides of the electric resistance welded portion on the outer surface of the pipe due to the engagement of the squeeze roll from both flange portions. Can be.

In the present invention, the width of the cutting surface of the two cutting tools arranged in a staggered manner in accordance with the distance between the two flange portions of the squeeze roll in the line transport direction is:
It is sufficient that each of them is at least half of the distance between the two flange portions of the squeeze roll, and the outer diameter depends on the outer diameter of the pipe.
For a small diameter tube up to 4 mm, usually a width of about 20 mm is sufficient. In addition, if the curvature of the cutting surface is selected to be slightly larger than the outer surface curvature of the pipe, there is no problem,
For example, when manufacturing a small-diameter pipe having an outer diameter of 100 to 152.4 mm, one kind of cutting tool having a curvature radius of 100 mm can sufficiently cope with it.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a method for manufacturing an electric resistance welded tube according to the present invention will be described with reference to an embodiment shown in FIGS. FIG. 1 is a front view schematically illustrating a method for manufacturing an electric resistance welded tube according to the present invention, and FIG. 2 is a side view of FIG. In FIGS. 1 and 2, FIG.
9 denote the same or corresponding parts,
Detailed description is omitted.

In FIG. 1 and FIG. 2, reference numerals 11a and 11b denote cutting tools which are arranged downstream of the two-roll squeeze roll 4 at a predetermined interval in the line conveying direction.
These cutting tools 11a and 11b are bitten out of both flange portions 4a of the squeeze roll 4 so that one side of each of the biting flaws 7 generated on both sides of the electric resistance welded portion on the outer surface of the pipe 5 and the welding outer surface bead 5a. Are arranged in a staggered manner in accordance with the distance between the flange portions 4a.

These cutting tools 11a and 11b are attached to a cutting tool holding stand 13 via, for example, actuators 12a and 12b, and
Is operated to move the cutting tools 11a and 11b in the vertical direction. For example, the cutting surface ends of the cutting tools 11a and 11b are moved upward by 200 mm and downward by 1 mm from the outer surface contact position of the pipe 5.
It can be adjusted within the range of 00 mm.

In the method of the present invention, two bytes 11a, 1
1b are arranged in a staggered manner in accordance with the distance between the two flange portions 4a of the squeeze roll 4 in the line transport direction, and the cutting depth of these cutting tools is 0.8 mm or less. Therefore, when the pipe 5 is manufactured by heating both edges 2a of the open pipe 2 by the induction heating coil 3 and pressing and joining the pipe 5 laterally with the two-roll squeeze roll 4, the flange 4a of the squeeze roll 4 is used. Even if biting flaws 7 are generated on both sides of the outer surface electric resistance welded portion of the pipe 5 due to biting from the pipe 5, these biting flaws 7 are cut and removed together with the welding outer surface bead 5a by the two cutting tools 11a and 11b. Is done. As a result, no fog-like flaws occur on both sides of the outer surface electric resistance welded portion of the pipe 5 after the fixed shape.

Next, a description will be given of the results of an experiment performed to confirm the effects of the method of the present invention. [Part 1] C: 0.23% by weight, Si: 0.13% by weight,
From a steel strip containing Mn: 0.81% by weight and Al: 0.04% by weight, the balance being Fe and unavoidable impurities, 10 m /
An ERW steel pipe having an outer diameter of 152.4 mm and a wall thickness of 14.3 mm was produced at a constant pipe-making speed of 1 minute. The distance between the flange portions of the two-roll squeeze roll used in this production was 20 mm.

During the manufacture of the above-mentioned ERW steel pipe, the flaws formed on both sides of the ERW weld on the outer surface of the pipe due to the protruding from the flange portion of the squeeze roll and the bead on the outer surface of the weld are removed by a 15 mm tool bit. It is manufactured by moving the tip of the cutting surface of two cutting tools whose center distance L (see FIG. 2) is 5 mm in a range of 1.2 mm below the pipe outer surface contact position, and corresponds to each cutting depth. After collecting the product to be inspected, it was subjected to an outer surface inspection, and a defect having a flaw having a depth of 0.1 mm or more was determined as a defective material, and a defect rate was determined.

The results are shown in FIG. 3. As shown in FIG. 3, as the cutting depth of the outer surface of the pipe increases, the defect rate of the outer surface inspection decreases. In this experiment, the height of the biting flaw was about 0.3 mm. Therefore, when the cutting depth was 0.3 mm or more, there was no defective material. However, when the cutting depth exceeded 0.8 mm, the defect rate of the outer surface inspection increased. This is because when the cutting depth exceeds 0.8 mm, the cut surface of the pipe base material is roughened or peeled, resulting in poor surface properties. In other words, by setting the cutting depth of the two cutting tools arranged in a staggered manner to 0.8 mm or less, while maintaining a good cutting surface property, the burrs generated on both sides of the electric resistance welded portion on the outer surface of the pipe. It turned out that a flaw can be prevented.

[Part 2] With all the pipe-making tools removed from the squeeze roll unit of the pipe-making machine,
A two-roll squeeze roll having an outer diameter of 152.4 mm was incorporated, and the time required for immediately forming a pipe was measured. Further, the same measurement was performed on a 4-roll squeeze roll having the same outer diameter. In addition, each roll assembling work was performed by two people. The results are shown in FIG. 4. As compared with the case of the four-roll squeeze roll, the time required for assembling the roll is shorter in the case of the two-roll squeeze roll, which is advantageous in terms of improving the pipe production efficiency. There was found.

[0027]

As described above, according to the method for manufacturing an electric resistance welded pipe of the present invention, the two roll type squeeze rolls are formed on both sides of the electric resistance welded portion on the outer surface of the pipe due to biting from both flange portions. Can be effectively prevented
Using a two-roll squeeze roll that is advantageous in actual operation,
An electric resistance welded tube having good surface properties can be stably manufactured.

[Brief description of the drawings]

FIG. 1 is a front view schematically illustrating a method for manufacturing an electric resistance welded tube according to the present invention.

FIG. 2 is a side view of FIG.

FIG. 3 is a graph showing a relationship between an outer surface cutting depth and an outer surface inspection failure rate.

FIG. 4 is a graph showing the time required for assembling rolls of a two-roll squeeze roll and a four-roll squeeze roll.

FIG. 5 is a front view schematically illustrating a conventional method for manufacturing an electric resistance welded tube.

6 is a schematic view of a two-roll squeeze roll as viewed from the side in FIG.

FIG. 7 is a schematic cross-sectional view of biting flaws generated on both sides of an outer surface electric resistance welded portion of a pipe due to biting from a flange portion of a two-roll squeeze roll.

FIG. 8 is a schematic cross-sectional view of a fog-like flaw generated on both sides of an electric resistance welded portion when the biting flaw illustrated in FIG. 7 is crushed by a fixed roll group.

FIG. 9 is a schematic view of a four-roll squeeze roll.

[Explanation of symbols]

 2 Open pipe 2a Edge 3 Induction heating coil 4 2-roll squeeze roll 4a Flange 11a byte 11b byte

Claims (1)

[Claims] 1. A method for manufacturing an electric resistance welded pipe in which both edges of an open pipe are intensively heated by Joule heat generated by a high-frequency current, and are pressed and joined laterally by a two-roll squeeze roll. The bead cutting tools are arranged in a zigzag pattern in the line conveyance direction in accordance with the distance between the two flange portions of the squeeze roll, and the cutting is performed with the cutting depth of these external bead cutting tools set to 0.8 mm or less. Manufacturing method of ERW pipe.