JPH0542376A - Manufacture of electric resistance welded steel tube - Google Patents

Abstract

PURPOSE:To obtain the electric resistance welded steel tube excellent in both welding quality and surface quality by forming a band steel into a cylindrical shape in order by a forming roll group, melting an edge part by a high-frequency current and then, welding this with pressure by squeeze rolls. CONSTITUTION:The squeeze rolls 1 are made to a two-roll type having flanges up and down or a three-roll type in combination of a side roll 2 having only an upper flange and a bottom roll 3 having charge of 1/4-1/2 of the groove in squeezing. A rotation axis of the side roll 2 is inclined in the proceeding direction of the tube and the squeeze roll groove is formed into a vertical elliptical shape having the ratio of the major axis to the minor axis close to complete roundness as much as possible to the extent that the projection groove in the proceeding direction of the tube does not enter the inside of complete roundness with the minor axis of an ellipse as the diameter when the rotation axis is inclined. Consequently, the electric resistance welded tube excellent in both welding quality and surface quality is obtained stably without deteriorating the advantage of the two-roll type where the squeeze roll exchange and positional adjustment are easily carried out.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an electric resistance welded steel pipe in which a strip steel is sequentially formed into a cylindrical shape by a forming roll group, an edge portion is melted by a high frequency current, and then pressure-welded by a squeeze roll.

[0002]

2. Description of the Related Art ERW steel pipe is manufactured by continuously forming a strip of raw material into a cylindrical shape by a group of forming rolls, and then joining the joints by an electric resistance welding method. In this welding, both edges of the open pipe after molding are intensively heated and pressed by Joule heat due to electric current, and are classified into direct current method, low frequency method and high frequency method according to the frequency of the current used. .. Recently, the high frequency method has many advantages in terms of quality and efficiency.

In the production of the above-mentioned electric resistance welded steel pipe, a squeeze roll for pressurizing and press-contacting both edge portions of a steel strip formed into a cylindrical shape and heated is generally a side roll 12 having upper and lower flanges 11 as shown in FIG. , 2 roll type that restrains the open pipe 13 from the side by
As shown in FIG. 4, the upper flange 16 of the side rolls 15, 15 is made smaller, and the two edges of the open pipe 17 are constrained from above by the top pressure rolls 18, 18 (hereinafter referred to as four roll type). The two-roll type can be roughly divided into small diameter sizes.
The 4-roll type is mainly used for manufacturing medium diameter sizes.

Comparing the above two types, the 2-roll type has a shorter roll changing time than the 4-roll type.
Although the position adjustment is easy, the welding quality (hereinafter referred to as V angle), which will be described later, becomes small, which may deteriorate the welding quality. On the other hand, the 4-roll type has many positions for adjusting the roll position, requires skill to perform proper adjustment, and has poor reproducibility, but the V angle can be considerably increased as compared with the 2-roll type. The butt shape also has the advantage that it can be freely adjusted from the I-shape in which the opposite end surfaces of the open pipe are parallel to the V-shape in which the opposite end surfaces are slightly open outward.

The welding phenomenon in the production of electric resistance welded steel pipe is a speed (Va) at which both edges approach along a V-shape, as shown in Iron Making Research No. 297 (1979) P84-.
And the speed (Vr) at which the edge is scraped off because the molten steel generated by heating is discharged by the electromagnetic force. That is, in welding with low speed or high heat input, Va
<Vr causes molten steel slits to repeatedly grow and disappear, and flashes and penetrators frequently occur. Conversely, in high-speed or low heat input welding, when Va> Vr, no slit growth is observed and cold welding easily occurs. Therefore, in order to obtain stable welding quality, it is necessary for Va to be slightly larger than Vr, and it is necessary to increase the welding speed or increase the V angle, but the welding speed has an upper limit due to the mill line. Since it is prescribed, it is common to adjust the V angle.

As for the difference in V angle depending on the squeeze roll diameter, it is known that in the case of the two-roll type, the V angle increases as the diameter of the upper flange decreases. As a method of increasing the V angle other than the squeeze roll diameter, a method of widening the fin plate width of the final fin pass or the seam guide roll (Japanese Patent Laid-Open No. 63-64654) or a special adjustment before the squeeze roll is performed. A method of providing a device (Japanese Patent Laid-Open No. 62-156082) has been proposed.

There is a limit to reducing the roll diameter in order to increase the V angle because it is necessary to secure the rigidity of the squeeze roll shaft. If the flange diameter is reduced,
Since the restraint of the edge portion after the upset is released early, there is a possibility that the molten steel that has been discharged and oxidized once flows back due to the springback of the pipe and welding defects may occur. As a countermeasure, a method of providing backup rolls and arranging small-diameter squeeze rolls in multiple stages (Japanese Patent Laid-Open No. 50-47846) has been proposed, but there is a limit to reducing the distance between the squeeze rolls. Backflow of molten steel immediately after the first squeeze is inevitable.

A method for increasing the fin plate width of the final fin pass and the plate width of the seam guide roll disclosed in JP-A-53-64654, and JP-A-62-15.
In the method of adjusting before the squeeze roll disclosed in Japanese Patent No. 6082, in the case of the two-roll type, the distance between edges in the heating stage becomes large, the proximity effect hardly appears, and the welding efficiency deteriorates. The V angle of the part does not become so large.

[0009]

In order to confirm the above phenomenon, the difference in edge locus between the two-roll type and the four-roll type was investigated under the same conditions. As a result, the two-roll type has an almost two-dimensional edge locus near the squeeze roll, whereas the four-roll type has a three-dimensional locus. Also, comparing the projected shapes from above, the 4-roll type has a large V angle and the edge approaches linearly toward the welding point, whereas
It was understood that the roll type has a V angle to some extent away from the welding point, but the V angle becomes smaller as it gets closer to the welding point, and becomes asymptotic to the seam line. That is, in the 2-roll type, it is very difficult to increase the V angle, and it is difficult to obtain stable welding quality.

As a result of further research, by inclining the rotary shaft of the squeeze roll in the direction of advance of the pipe by a predetermined angle, the height of the flange at the time of engagement becomes higher than when the rotary shaft is vertical, and the restraint of the edge starts. It has the same effect as the point moves backward and the roll diameter becomes smaller. Also, because the flange is inclined, the edge draws a three-dimensional trajectory close to that of a 4-roll type, and the rotation axis is vertical. It has been clarified that a V angle much larger than that of the two-roll type can be obtained, and a patent application has already been made (Japanese Patent Application No. 3-47587). However, as the inclination angle of the rotary shaft of the squeeze roll increases, roll marks are more likely to occur due to the entrance-side lower flange and the exit-side upper flange. As a countermeasure against this, as shown in FIG. 5, a squeeze roll 1 is combined with a side roll 2 having only an upper flange 6 and a bottom roll 3 which is responsible for 1/4 to 1/2 of the hole type in the squeeze. By using a roll type and inclining the rotating shaft 4 of the side roll 2 in the traveling direction of the pipe 5 by 1 to 10 degrees,
It has been clarified that the roll mark can be prevented from being generated by the lower flange, and a patent application has already been filed (Japanese Patent Application No. 3-68051).

An object of the present invention is to provide a method for stably producing an electric resistance welded steel pipe excellent in welding quality and surface quality in the production of the electric resistance welded steel pipe by preventing generation of a roll mark due to the remaining upper flange. Especially.

[0012]

[Means for Solving the Problems] The inventors of the present invention have conducted earnest research to achieve the above object. As a result, in order to prevent the occurrence of the roll mark, the hole shape of the squeeze roll is an elliptical shape having a predetermined aspect ratio determined by the inclination angle of the rotation axis of the squeeze roll, and the direction of travel of the pipe. It has been clarified that it is effective to make the projected hole type of (3) close to a perfect circle, and the present invention has been reached.

That is, according to the present invention, in a method for producing an electric resistance welded steel pipe in which a strip steel is sequentially formed into a cylindrical shape by a forming roll group, an edge portion is melted by a high frequency current, and then pressure-welded with a squeeze roll, the squeeze roll is moved up and down. 2 roll type with flange, the rotation axis of the squeeze roll is inclined 1 to 5 degrees from the vertical direction to the traveling direction of the pipe, and the squeeze roll hole type is projected to the traveling direction of the pipe when the rotation axis is inclined. The hole type is a vertical elliptical shape having a major / minor diameter ratio as close as possible to a perfect circle, as long as it does not enter inside a perfect circle having the minor axis of the ellipse as its diameter.

Further, in a method for producing an electric resistance welded steel pipe in which a strip steel is sequentially formed into a cylindrical shape by a forming roll group, an edge portion is melted by a high frequency current, and then pressure-welded with a squeeze roll, the squeeze roll is provided only on the side of the upper flange. The roll is a 3 roll type that combines a bottom roll that takes up 1/4 to 1/2 of the squeeze hole type, and the rotation axis of the side roll is tilted 1 to 10 degrees from the vertical direction to the traveling direction of the pipe. , When the squeeze roll hole type is tilted with respect to the axis of rotation, the projection hole type in the direction of travel of the pipe does not enter inside the true circle with the minor axis of the ellipse as the diameter The ratio is a vertical ellipse.

[0015]

In the present invention, the squeeze roll is a two roll type having upper and lower flanges, or the squeeze roll is a side roll having only an upper flange and a bottom roll having about 1/4 to 1/2 of the squeeze hole type. Combined 3
As shown in FIG. 1, when the squeeze roll hole type is tilted so that the rotation axis of the side roll is inclined in the pipe advancing direction and the rotation axis is inclined, the projection hole type in the advancing direction of the pipe is elliptical. The vertical elliptical shape has a major / minor diameter ratio that is as close to a perfect circle as possible within the range where it does not enter the inside of a perfect circle whose diameter is the minor diameter of the side roll. In comparison, the height of the upper flange becomes higher, the restraint start point of the edge moves rearward, and the roll diameter becomes smaller, which is the same effect. Further, since the distance from the start of the restraint of the edge to the peak upset is shortened, the upset effectively acts on the edge portion, the upset is quickly performed, and the molten steel is discharged well. In addition, because the upper flange is inclined, the edge draws a three-dimensional trajectory similar to the 4-roll type, and a much larger V angle is obtained compared to the 2-roll type in which the rotation axis faces the vertical direction. You can

Furthermore, since the height of the upper flange is low on the exit side of the squeeze roll, the upper flange is edged for a while even after passing through the line (squeeze roll center) connecting the squeeze roll shafts on both sides. Therefore, the same effect as that of increasing the roll diameter can be obtained, and the above-mentioned problem of molten steel backflow can be solved. Furthermore, by tilting the rotation axis of the side roll in the direction of travel of the pipe, if the open pipe twists to the left or right when entering the squeeze roll, the contact length with the left and right side rolls will change, resulting in a frictional force. There is an imbalance, which has the effect of correcting twist. Moreover, when the rotation axis of the squeeze roll hole type is inclined, the projection hole type in the traveling direction of the pipe does not enter the inside of the perfect circle having the minor axis of the ellipse as its diameter. Due to the vertical elliptical shape having the diameter ratio, there is no portion for locally pressing the pipe in the projection hole type, which is caused by the flange of the squeeze roll, as in the case of using the perfect side roll shown in FIG. Generation of roll marks can be suppressed.

The larger the inclination angle of the rotary shaft of the side roll, the larger the V angle and the better the welding quality. However, the influence of the inclination angle on the V angle becomes larger as the pipe outer diameter becomes smaller. The inch size is sufficiently effective at about 1 degree, while the 7 inch size requires an inclination angle of 3 to 5 degrees. This is the reason why the inclination angle of the rotating shaft of the squeeze roll is set to 1 to 10 degrees.

[0018]

Example 1 A comparative example in which a squeeze roll having a two-roll type hole having a perfect circular shape is tilted in the pipe advancing direction together with the squeeze roll block as shown in Table 2, and a squeeze roll type has a rotating shaft tilted. When squeezing the squeeze roll with a vertical elliptical shape having a major / minor diameter ratio that is as close to a perfect circle as possible, the projection hole type in the tube advancing direction does not enter inside the perfect circle whose diameter is the minor axis of the ellipse. For each of the methods of the present invention in which the roll block and the pipe are inclined in the direction of travel of the pipe as shown in Table 2, a raw material having the composition shown in Table 1 is formed into an open pipe by a group of forming rolls, and then a welding speed 1 is obtained by a high frequency induction method.
Welding was performed at 5 m / min and an upset amount of 3.5 mm, and an electric resistance welded steel pipe having an outer diameter of 177.8 mm and a wall thickness of 13.7 mm was manufactured as a prototype. In the method of the present invention, the longitudinal / elliptical squeeze roll has a major / minor diameter ratio of 1.01 at an angle of rotation of 1 degree.
It was 1.03 at 3 degrees and 1.07 at 5 degrees.

[0019]

[Table 1]

[0020]

[Table 2]

As shown in Table 2, the larger the inclination angle of the rotary shaft of the squeeze roll, the larger the V angle and the better the welding quality, but the deeper the half-face roll mark becomes, and the inclination angle is 5 degrees in the comparative example. If it exceeds, it will deepen rapidly and not be put to practical use. However, in the method of the present invention, no roll mark was generated even when the inclination angle was 5 degrees.

Example 2 A side roll having a perfect circular hole shape only with an upper flange is inclined along the direction of travel of the pipe together with the block as shown in Table 3, and 1/4 to 1/2 of the hole type is received by the bottom roll. When the rotation axis of the squeeze roll hole type is tilted and the comparative example provided, the projection hole type in the tube advancing direction is as perfect as possible within the range of not entering the inside of the perfect circle having the minor axis of the ellipse as the diameter. For each of the methods of the present invention in which the longitudinal and elliptical shapes having similar major and minor diameter ratios were made, the raw materials having the compositions shown in Table 1 were formed into open pipes by forming rolls, and then the welding speed was set to 15 by the high frequency induction method.
Welding was performed at m / min and an upset amount of 3.5 mm, and an electric resistance welded steel pipe having an outer diameter of 177.8 mm and a wall thickness of 13.7 mm was manufactured as a prototype. The major-minor-diameter ratio of the vertical elliptical squeeze roll in the method of the present invention is 1.07 at a tilt angle of the rotating shaft of 5 degrees and 1: 1.
It was 1.20 at 0 degrees.

[0023]

[Table 3]

As a result of the trial production, the V angle in the vicinity of the welding point was about 1 to 4 degrees in the comparative example and expanded to about 4.5 degrees in the case of the method of the present invention. Also in the comparison of welding quality, in the case of the method of the present invention, the incidence of penetrator is about 80 of that of the comparative example.
%, And in the case of the comparative example, the rotation axis inclination angle is 5
A roll mark having a depth of ≦ 0.1 mm and a depth of 0.1 to 0.2 mm was observed at 10 °, but in the case of the method of the present invention, the roll mark did not occur at the rotation axis inclination angle of 5 °. Only roll marks with a depth of 0.1 mm or less were generated.

[0025]

As described above, according to the present invention,
The squeeze roll is a three-roll type that combines a side roll with only an upper flange and a bottom roll that handles 1/4 to 1/2 of the hole type in the squeeze, and the rotation axis of the side roll with respect to the traveling direction of the pipe. Inclining the squeeze roll die by 1 to 10 degrees and making the squeeze roll die a perfect circle within the range where the projection die in the pipe advancing direction does not enter inside the true circle with the minor axis of the ellipse as the diameter when the rotation axis is inclined. By adopting a vertical elliptical shape with a similar major / minor diameter ratio, an electric resistance welded steel pipe with excellent welding quality and surface quality can be obtained without compromising the advantages of the two-roll type, which makes squeeze roll replacement and position adjustment extremely easy. be able to.

[Brief description of drawings]

FIG. 1 is an image view of a vertical elliptical squeeze roll according to the present invention.

FIG. 2 is an image diagram of a perfect circular squeeze roll according to a conventional method.

FIG. 3 is a front view showing a conventional two-roll type structure.

FIG. 4 is a front view showing a structure of a conventional 4-roll type.

FIG. 5 is a side view showing a conventional three-roll type structure.

[Explanation of symbols]

 1 Squeeze roll 2, 12, 15 Side roll 3 Bottom roll 4 Rotating shaft 5 Pipe 11 Flange 13, 17 Open pipe 16 Top flange 18 Top pressure roll

Claims (2)

[Claims] 1. A method for producing an electric resistance welded steel pipe, in which strip steel is sequentially formed into a cylindrical shape by a forming roll group, an edge portion is melted by a high frequency current, and then pressure-welded with a squeeze roll, the squeeze roll having upper and lower flanges. 2 roll type, the squeeze roll rotation axis is inclined from the vertical direction to the pipe traveling direction by 1 to 5 degrees, and when the squeeze roll hole die is inclined, the projection hole type in the pipe traveling direction is A method for producing an electric resistance welded steel pipe, characterized in that the elliptical shape has a major / minor diameter ratio that is as close to a perfect circle as possible within a range that does not enter inside a perfect circle having the minor axis of the ellipse as a diameter. 2. A method for producing an electric resistance welded steel pipe in which strip steel is sequentially formed into a cylindrical shape by a forming roll group, an edge portion is melted by a high-frequency current, and then pressure-welded with a squeeze roll, in which the squeeze roll is a side having only an upper flange. The roll is a 3 roll type that combines a bottom roll that takes up 1/4 to 1/2 of the squeeze hole type, and the rotation axis of the side roll is tilted 1 to 10 degrees from the vertical direction to the traveling direction of the pipe. , When the squeeze roll hole type is tilted with respect to the axis of rotation, the projection hole type in the direction of travel of the pipe does not enter inside the true circle with the minor axis of the ellipse as the diameter A method for manufacturing an electric resistance welded steel pipe, which has a vertical elliptical shape with a specific ratio.