JPH0445247B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for forming a strip in the manufacturing process of electric resistance welded steel pipes, and more particularly to a method for controlling the forming of a strip having camber.

[Conventional technology]

An outline of the manufacturing process of an electric resistance welded steel pipe will be explained with reference to FIG.

Generally, electric resistance welded steel pipes are made of coiled strips 1
0 by an uncoiler and flattened by a leveler 12, the side of the strip surface is trimmed by a trimming device 14.
Then, the strip is processed to a predetermined width, and the end surface of the edge of the strip joint is subjected to so-called pre-treatment, and the strip is sequentially formed into a cylindrical shape using breakdown rolls 16 or cage rolls 20, etc. Then, by applying circumferential reduction with the fine pass rolls 22, 24, and 26, stable forming of the seam edge portion is performed, and finish forming is performed into the blank pipe 34 of a predetermined shape and size. The seam edge portion 34a is high-frequency heated by the contact tip 27 while the edge is guided by the squeeze roll 30a, and the edge portion 34a is upset welded by the squeeze roll 30 while the edge portion is guided by the squeeze roll 30a. It is manufactured through a series of steps in which the bead is removed by a bead cutting device 32 installed on the downstream side of the squeeze stop roll. In addition, Edge Guide Roll 2
9 is located on the upstream side of the contact tip, and the squeeze stop roll 30a is located on the downstream side of the contact tip.

In manufacturing the above-mentioned electric resistance welded steel pipes, the shape of the strip, particularly the camber of the strip 10, has a very large influence on the formability and weldability of the raw pipe.

Here, the gear band of the strip plate 10 means that the center line of the strip plate 10 is not a straight line but is arcuate or meandering along the longitudinal direction, as shown in FIG. 2, which shows a partial plane of the strip plate 10. Refers to the condition.

The band plate having the camber is trimmed by adjusting the trimming allowance of the left and right edges in the side trimming process using the rotary shear method or the milling method, which is a pre-processing step in the manufacturing of the electric resistance welded steel pipe.
As shown in Figure a, it is possible to process to reduce the amount of camber to some extent, but for a large camber, the yield is determined by the set strip Ws and the trim loss ΔW indicated by diagonal lines in the figure. Due to the lowering, it was not possible to carry out sufficient adjustment processing, and as shown in FIG. 3B, the strip plate still has a camber even after the trimming processing. If the camber correction were to be performed completely by trimming, the band width would be insufficient as Ws*, as shown in Figure 3c, and it would be impossible to manufacture a steel pipe with the specified outer diameter. There are cases where

As a method for correcting the camber of a rolled product coil, for example, there is a method of correcting the coil camber using a camber correction device on the molding entry side as shown in Japanese Patent Application Laid-Open No. 53-100157, but this method has the following difficulties. It was hot.

(1) Rolling and stretching the coil requires a large-scale straightening device, resulting in high equipment costs.

(2) When one edge is rolled and stretched for camber correction, the thickness of the left and right edges will be different due to the decrease in the thickness of one edge, resulting in edge wrap and bead cutting defects in welding upsets. .

(3) The edge portion of the coil that has been elongated by straightening rolling tends to be wavy in the longitudinal direction.

On the other hand, if a strip having a camber is rolled into a semi-cylindrical shape using rough forming rolls such as breakdown rolls or cage rolls in the forming process, and then finished forming into a blank pipe using a finish forming roll, fin pass rolls, the above-mentioned results are obtained. In a band plate portion having such a camber, the amount of spring back at both edges of the raw pipe after finpass forming is different, resulting in a raw pipe whose forming conditions on the left and right sides of the welded part are asymmetrical. This is because the compressive strain and bending strain in the circumferential direction applied to both edges of the blank tube during finpass forming differ depending on the rolling of the strip due to the camber of the strip.

For example, in the case of forming a strip plate portion having a camber as shown in FIG. 4A, the forming condition of the strip plate portion having a camber and occurrence of molding defects in each forming process will be explained. As shown in FIG. 4a, the band plate portion having a camber convex to the left toward the paper surface has a spring back 28a on the right edge 37, as shown in FIG. 4b, after fin pass forming. The spring back 38 becomes larger, and the relative height positions of the left and right edges 37, 37a differ. When the edges of a raw pipe exhibiting such a state are subjected to high-frequency heating and upset welded using a squeeze roll, uneven heating of the left and right edges occurs as shown in Figure 4c with the high temperature area shaded 39. , the seam becomes distorted as shown in FIG. 4d, making it difficult to discharge oxides from the seam, resulting in welding defects. In addition, since the forces acting on the roll of the left and right edges of the squeeze roll are different, the presser position of the roll is slightly different,
A discrepancy in the height of the left and right edge joints occurs, resulting in a step or a wrap at the joint as described above, leading to welding defects and poor cutting of the inner and outer beads.

[Problem that the invention seeks to solve]

In the present invention, when forming a strip plate having a camber as described above into a cylindrical blank pipe and welding the joint edge portion, the camber portion is formed and controlled according to the amount of camber, so that both edge portions are welded. The present invention provides a method for forming an electric resistance welded steel pipe with the aim of eliminating height differences and welding defects.

[Means for solving problems]

The present inventors carried out a series of camber investigation molding experiments in order to elucidate the forming behavior in each forming process of a strip section having a camber and the causal relationship of forming defects, and by analyzing the data, the forming behavior was investigated. I investigated and figured it out.

The present invention was completed based on this knowledge, and when manufacturing an electric resistance welded steel pipe in which continuously fed strips are formed into a cylindrical raw pipe and the joint edges are welded, the raw pipe is The amount of reduction of the squeeze top roll or the amount of reduction of the squeeze top roll and edge guide roll, and the side of the strip to be controlled are determined from the relative height displacement amount of both edge portions, and the amount of reduction is controlled in accordance with the determination. This is a method for controlling the forming of a strip plate having a camber, characterized by the following.

In the present invention, the reference position for the rolling reduction amount is the set position of each roll with respect to the strip plate without camber. This standard value is determined for each pipe size.

The present invention prevents differences in the heights of both edges of the blank tube after fin pass forming due to camber by controlling forming based on the relative height displacement amount of both edges of the blank tube.

The relative height displacement of both edges of the raw tube can be calculated by calculation from the measurement value of a camber detector installed on the input side of the molding machine, or the relative height displacement of both edges of the raw tube can be calculated on the exit side of the fine pass roll. It is also possible to use an actual value measured by installing a detector to detect the . In addition to the camber of the strip, the relative height displacement between the edges of the raw pipe occurs due to variations in the arrangement accuracy of the equipment and the strength of the material of the strip, but it is mostly due to the camber of the strip. Others can be ignored. Regarding the method of calculating the relative height displacement amount of both edge parts from the measurement value of the camber detector, Fig. 5 shows the amount of strip camber Ci and the final fin which were elucidated by the inventors through numerous research studies. The relationship between the relative displacement amount ΔH in the height direction of both edges of the raw pipe on the exit side of the pass roll is illustrated. This relative displacement in the height direction ΔH is determined by the camber amount Ci, the strip strength σy, the work hardening index n, the strip thickness t, the outer diameter D, and the fin pass reduction r, and σy, n, t, D,
When r is constant, there is a certain relationship between ΔH and Ci as shown in FIG. 5, ΔH=f(Ci).

From FIG. 5, it can be seen that there is a unique relationship in which the relative displacement amount ΔH in the height direction of both edges of the raw tube at the exit side of the final fin pass roll increases as the camber amount Ci increases. This relationship is stored in the controller, and the relative displacement amount ΔH in the height direction is calculated from the pipe forming conditions and the camber amount. This relative displacement amount ΔH is determined by the fine path roll 26 as shown in FIG.
A height direction displacement detector 25 may be provided immediately after the height direction displacement detector 25 for direct measurement.

Calculate the downward displacement amount ΔHa of the squeeze top roll or squeeze top roll and edge guide roll from ΔH obtained by any of the above methods using the following formula, ΔHa=αΔH (α=constant), and control the roll bottom position. .

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 9 shows an example of control output.

FIG. 9 is an explanatory diagram of camber detection and the amount of reduction of the squeeze top roll or the amount of reduction of the squeeze top roll and the edge roll.
3 shows an example of control according to the invention when there is a camber of the strip with Cmax.

In FIG. 1, the camber of the strip is detected by a strip camber detector 15 installed on the exit side of the strip edge trimming device 14.

As a method of camber detection, for example, as shown in FIG. 9, a camber amount Ci is detected every minute time ΔT from the time when the camber detection amount exceeds a set camber detection level Cs, and this is stored in the central processing unit 13. . The set camber detection level Cs is a camber amount that serves as a reference for starting a calculation to be read into the central control unit when performing camber detection and controlling, and is set in advance as an initial value. For values below Cs, the amount of camber is small, so there is no need to control it.
Due to the accuracy of the camber detector, camber below Cs cannot be detected accurately. Incidentally, the value of Cs is a minute value of about 0.5 mm.

The central processing unit 13 calculates and determines the control amount of the squeeze top roll 30a or the control amount ΔHa of the squeeze top roll 30a and the edge guide roll 29 based on the detected camber amount Ci, and at the same time determines the control amount of the strip to be controlled. Determine the side of

Furthermore, the central processing unit 13 determines the delay time for implementing the rolling down control of the squeeze top roll 30a or the rolling down control of the squeeze top roll 30a and the edge guide roll 29 based on the mill speed and the distance from the camber detector to the roll position to be controlled. and outputs a command to perform appropriate control when the strip portion having the camber amount Ci passes the position of the squeeze stop roll 30a or the edge guide roll 29 to be controlled.

The above method is shown in a flowchart in FIG.

[Effect]

As described above, the present invention detects the amount of camber when manufacturing a strip plate having camber into a blank pipe,
Based on the calculated value obtained from the detected camber amount or the actual measured value of the relative height displacement of both edges of the raw pipe,
By determining the amount of reduction of the squeeze top roll or the amount of reduction of the squeeze top roll and edge guide roll, and the side of the strip to be controlled, and controlling the amount of reduction according to these determinations, the height of both edges of the blank pipe can be increased. Correct the relative position in the vertical direction to the same height position. This results in uneven edge heating and edge steps during upset welding with squeeze rolls.
It is possible to prevent the occurrence of lapping.

FIG. 6 is a partial plan view of the raw tube 34 in the vicinity of the fin pass roll 26 and squeeze rolls 30a, 30b, and 30c, and FIGS. 7 and 8 show a comparison of the conventional method and the present tube forming state, respectively. FIG.

The raw pipe 34 on the exit side of the fine pass roll 26
As shown in FIGS. 7a and 8a in the B-B arrow view of the edge portion, in the band plate portion having a camber, a relative displacement amount ΔH in the height direction of the left and right edges occurs.

Conventionally, the left and right rolls are at the same height regardless of the presence or absence of this displacement amount ΔH. This situation is shown in Figure 7b. FIG. 7b shows the edge guide roll 2 in the C-C arrow direction or D-D arrow direction in FIG.
9 or the state of the squeeze top roll 30a. As a result, the state of the raw tube 34 on the edge guide roll 29 or the squeeze top roll 30a changes due to the difference in the spring backs 38, 38a, as shown in FIG. 7c.
There is a difference in height at 7a.

Next, from the displacement amount ΔH obtained by the calculation or actual measurement, the side to be rolled down and the amount of reduction ΔHa of both the left and right edge portions by the edge guide roll 29 before the squeeze roll and the squeeze stop roll 30a are determined, and as shown in FIG. 8b. As shown, the amount of reduction of the squeeze top roll or the reduction of the squeeze top roll and edge guide roll is controlled based on the amount of reduction ΔHa.

The roll reduction displacement amount ΔHa is a value applied to both the squeeze top roll and the edge guide roll, and may be the same value. The interval between the edge guide roll position and the squeeze stop roll position is several hundred mm or less, and the spring back amount of the raw pipe hardly changes.

FIG. 8b is a view taken along the line CC or D-D in FIG. 6. FIG. 8c shows a cross section of the raw tube 34 in the squeeze stop roll subjected to rolling control as described above, and the difference in height between both edges is zero.

[Example] The effects of controlling the forming of a band plate when it has a camber according to the present invention will be explained in comparison with conventional forming. We manufactured ERW steel pipes with the following specifications.

Implemented pipe size: 24 inches x 6.35mm thickness API 5LX,
X60 Strip camber amount: Span of approximately 25 m, maximum camber amount of approximately 35 mm Figure 11 shows a case where the forming control of the present invention is used (example) and a case where it is not used (comparative example).

Figure 11 shows the results of an ultrasonic flaw detection test (UST) conducted to check the quality of welded parts.
In FIG. 11, the "defect level" means that an ultrasonic flaw detection test is performed in advance using an artificial defect (reference defect), and the magnitude of the detection signal is defined as the "defect level", and a case exceeding that level is determined to be a defect. A small signal below the "defect level" is basically not considered a defect and is not excluded as a defective pipe. However, the first
If severe micro-defects are continuous as shown in Figure 1b, defects such as poor bead cutting may have occurred, and maintenance is often required.

When the forming control according to the present invention was carried out, there were no forming defects or bead cutting defects in the camber part, and the results of ultrasonic flaw detection (UST) of the welded part were good as shown in Figure 11a. There were almost no occurrences of minute defects below the detection level.

On the other hand, although welding was possible using the conventional method without camber control, the welding condition was unstable and
As shown in the results of ultrasonic flaw detection in FIG. 11b, a defect (penetrator) occurred in the welded part, and the camber part eventually became a defective product.

〔Effect of the invention〕

In the case of manufacturing an electric resistance welded steel pipe from a strip plate having camber, the present invention is capable of determining the reduction amount of the squeeze top roll based on the calculated value from the camber amount or the measured displacement amount of the relative height displacement of both edges of the raw tube. Alternatively, since the reduction amount of the squeeze top roll and edge guide roll is controlled, it is possible to properly form and weld strips that conventionally caused forming defects, welding defects, bead cutting defects, etc. due to canvas, and improve material yield. This has made it possible to manufacture ERW steel pipes with excellent weld shape quality.

[Brief explanation of drawings]

Fig. 1 is a process diagram showing the manufacturing process of an electric resistance welded steel pipe to which the present invention is applied, Fig. 2 is a plan view showing the camber of the strip plate, and Fig. 3 is a plan view showing the state of edge trimming of the band plate having the camber. Figure 4 is an explanatory diagram showing the forming condition and defect occurrence situation in the forming process of a strip plate having camber, and Figure 5 is a graph showing the relationship between the amount of camber and the relative displacement amount in the height direction of both edges of the raw pipe. , Figure 6 is a plan view of the raw pipe manufacturing process between the final fine pass roll and squeeze roll, Figure 7
Fig. 8 is an explanatory diagram comparing the state of forming tubes by the conventional method and the method of the present invention, respectively, and Fig. 9 is the control in the edge guide roll and squeeze top roll reduction amount control method of the band plate having a camber according to the present invention. FIG. 10 is a flowchart showing the procedure of the method of the present invention, and FIG. 11 is a chart showing the ultrasonic flaw detection results of a welded part of a strip having a camber. This is a comparative example (conventional example). 10... Band plate, 12... Leveler, 13... Central processing unit, 14... Edge trimming device, 15
...Camber detector, 16...Breakdown roll, 18...Edge forming roll, 20...Cage roll, 22, 24, 26...Fin pass roll, 25...Both edges of base tube height direction displacement detector ,
28... Seam guide roll, 29... Edge guide roll, 30... Squeeze roll, 30a...
...Squeeze top roll, 30b...Squeeze side roll, 34...Main pipe.

Claims (1)

[Claims] 1. When manufacturing an ERW steel pipe by forming a continuously fed strip 10 into a cylindrical raw pipe and welding the joint edges, a squeeze stop is determined from the relative height displacement of both edges of the raw pipe. The rolling reduction amount of the roll 30a or the rolling reduction amount of the squeeze top roll 30a and the edge guide roll 29, and the strip plate 1 to be controlled.
1. A method for controlling the forming of a strip plate having a camber, characterized in that the side of 0 is determined and the reduction amount is controlled in accordance with the determination.