JPS61115685A - Manufacture of seam welded steel tube - Google Patents

Abstract

PURPOSE:To improve material yield, shape and quality by detecting the quantity of camber of a band plate, and at the same time, calculating the quantity of edge working, rolling reduction etc., and making an optimum control basing on the results of the calculation. CONSTITUTION:A camber detector 15 is provided on the exit side of the edge trimming device 14 of the band plate, and at the same time, an edge chamber working machine 17 is installed on the entrance side of skin pass rolls 22-26. When the quantity of chamber detected by the chamber detector 15 exceeds a set camber level Cs, the quantity of the camber Ci is sampled at every minute time DELTAT. Then, the quantity of the edge chamfer of the working device 17, the rolling reduction of rolls 29, 30a and the amount of the rotation control of bead cutting devices 32a, 32b are calculated by a central processing unit 13 basing on the sampling. Further, the band plate 10 is optimum-controlled basing on the calculated values. Accordingly, material yield, shape and quality are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] 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]

The outline of the manufacturing process of electric resistance welded steel pipes will be explained with reference to FIG.

In general, for ERW steel pipes, a coiled strip 10 is unwound by an uncoiler, flattened by a leveler 12, and then both sides of the strip are trimmed to a predetermined width by a trimming device 14, and the strip joints are A so-called pre-processing process is performed to finish the edge end face, and the strip is sequentially formed into a cylindrical shape using breakdown rolls 16 or cage rolls 20, and circumferential reduction is performed using fin pass rolls 22, 24, and 26. The joint edge portion 34a is then finished molded into a blank tube 34 of a predetermined shape and size while stably forming the joint edge portion by rolling the joint edge portion 34a.The joint edge portion 34a is then subjected to high frequency heating using the contact tip 27 and squeeze roll 30
It is manufactured by a series of steps in which the steel is upset welded by a bead cutting device 32 installed on the downstream side of the squeeze roll to remove the molten steel bead produced by the upset welding.

In manufacturing the above-mentioned electric resistance welded steel pipes, the shape of the strip,
In particular, the influence of the camber of the strip plate 10 on the formability and weldability of the raw tube is extremely large.

Here, the camber of the strip lO means that the center line of the strip lO is not a straight line but is arcuate or meandering along the longitudinal direction of the strip lO, as shown in FIG. 3, which shows a partial plane of the strip lO. Refers to the condition.

The strip plate having a camber can be formed as shown in FIG. 3(a) by adjusting the trimming allowance ΔW of the left and right edges in the side trimming process using a rotary shear one-way method or a milling method, which is a pre-processing step in manufacturing the electric resistance welded steel pipe. However, it can be processed to reduce the amount of camber to some extent.

For a large camber, it is not possible to perform sufficient adjustment processing due to the yield reduction caused by the set band width Ws and the trim loss ΔW indicated by diagonal lines in the figure, and as shown in Fig. 3 (b).
), the strip still has camber after trimming. If the camber correction were to be completely corrected by trimming, as shown in Figure 3 (C), the band width would be insufficient as W s '', and it would be difficult to manufacture a steel pipe with the specified outer diameter. There are cases where this is not possible.

If a strip with camber is rolled into a semi-cylindrical shape using a rough forming roll such as a breakdown roll □ or a cage roll in the forming process, and then finished forming into a blank pipe using a fin pass roll, which is a finishing forming roll, the above-mentioned result will be obtained. In the strip section with such camber, several forming defects as described below occur, leading to defective welding or defective bead cutting, resulting in a one-point decrease in yield.

For example, in the case of forming a band plate part having a camber that is convex to the left when viewed from the paper as shown in FIG. .

The forming behavior of a strip plate portion having camber in each forming process and the causal relationship of forming defects were clarified through a series of 117) camber investigation experiments conducted by the inventor.

As shown in FIG. 4(a), the band plate portion having camber is
In breakdown roll or cage roll forming in the rough forming area, the strip center is rotated clockwise with respect to the pass center as shown in Fig. 4(b), resulting in misalignment, a state that causes the so-called strip rolling phenomenon. Become.

The semi-cylindrical blank tube in a state where such rolling occurs is subjected to finish forming with the fin pass rolls in the subsequent stage, as shown in Fig. 4 (
As shown in C), the amount of molding of the left and right edge portions is significantly different. In other words, when the rolling state as shown in FIG. 4(b) is exhibited, the amount of forming processing on the left edge portion in fin pass roll forming is extremely large compared to the amount of processing on the right edge portion, as shown in FIG. 4(C). As shown in Fig. 4(f) and (g), the thickness increase at the left edge becomes large, and the plate thickness at the edge end surface joint becomes different when welding with a squeeze roll.
), which results in a step or wrap at the seam edge, causing welding defects and bead cutting defects.

In addition, when the amount of camber is large, the compression bending degree of the left and right edge portions in the fin pass roll is different, and the fourth
As shown in the example in Figure (c), the degree of compression bending of the right side edge portion becomes small, resulting in an insufficient amount of compression that is less than the appropriate amount of compression in fin pass roll forming. For this reason, Figure 4 (d
), edge waves are generated at the right edge, resulting in an open pipe that cannot be welded.

Furthermore, when there is a camber as described above, not only is there a difference in the amount of thickening at both edges, but there is also a difference in the amount of springback at both edges of the raw tube after fin pass forming, resulting in a raw tube with asymmetric left and right molding conditions. becomes. Is this by Finpass molding? 'This is because the circumferential compressive strain and bending strain applied to both edges of the tube differ depending on the rolling of the band due to the camber of the band.

For example, using the example shown in Fig. 4, after fin pass roll forming of the strip plate in the part with camber, the springback on the right edge is larger than that on the left edge, as shown in Fig. 4(e).・Relative height positions of edges are different. When the edges of a raw pipe exhibiting such a state are subjected to high-frequency heating and upset welding using a squeeze roll, uneven heating of the left and right edges as shown in Fig. 4 (h) occurs, and as shown in Fig. 4 (i). As shown, the seam becomes distorted, causing welding defects that make it difficult to remove oxides from the seam. In addition, since the forces acting on the left and right edges of the squeeze roll are different, the presser positions of the rolls are slightly different, resulting in discrepancies in the joining height of the left and right edges, and as mentioned above, this results in a step or wrap at the joint.
This results in welding defects and poor cutting of the inner and outer beads.

As shown in Figure 4 (j), after squeeze welding, that is, as the raw pipe having the camber described above progresses from fin pass forming to the downstream process, the weld seam rotates in the circumferential direction, which is called seam twist. This causes a bead cutting failure due to a deviation of the bead cutting position 1δ in the inner and outer bead cutting equipment installed after squeeze roll welding. For this reason, currently, the operator visually changes the bead cutting position, but the tracking is insufficient and bead cutting defects occur.

[Problem that the invention seeks to solve]

In order to solve the above-mentioned problems such as poor forming, poor welding, and poor bead cutting of a strip having a camber, the present invention processes the strip having a camber and controls the forming of the strip. The present inventors provide a method for manufacturing an electric resistance welded steel pipe with the aim of stabilizing plate forming, welding, and bead cutting. [Means for solving the problem] In order to elucidate the forming behavior in each forming process of the strip part and the causal relationship of forming defects, a series of camber investigation forming experiments were carried out, and the forming behavior was clearly understood by analyzing the data.

The present invention was completed based on this knowledge, and the forming defects that occur in each forming process of the strip plate part with camber are: - Difference in the amount of thickness increase on both edges in fin bath forming, Edge wave in cross-in pass forming. Occurrence: (1) Difference in the height of the raw tube edge after fin pass forming; (2) Occurrence of seam twist during bead cutting on the exit side of the squeeze roll.

The present invention prevents the occurrence of molding defects caused by these cambers by performing various controls based on the amount of camber obtained from a camber detector installed on the entrance side of the molding machine.

A control method for preventing the occurrence of each molding defect will be explained using the camber shown in FIG. 4 as an example.

The first is to resolve the difference in the amount of thickness increase on both edges during fin pass molding. In other words, in order to prevent excessive thickening of the edge on the convex side of the camber after fin pass roll forming, as explained in Fig. 4(C), After the edge on the convex side of the camber receives excessive reduction at the fin pass, it is sufficient to reduce the thickness of the edge on the convex side of the camber in advance so that the thickness of both edges becomes the same. Since the thickening occurs on the inner surface side of the raw tube where there is no roll restraint, in the present invention, the upper surface of the edge of the strip plate on the convex side of the camber is chamfered in advance as shown in FIG.

As the chamfer processing method in the present invention, the cutting device 1
4a and L4b, or a method of rolling the edge portion using a roll 14c or the like, any method that achieves the object of the present invention may be used.

The chamfer processing amount (Figure 5 a value, b value) is calculated from the actually measured camber detection amount using the relationship between the camber amount known in advance and the difference in the thickness increase of both edges in fin-nox molding. to be determined.

For example, the edge chamfer processing amount is the camber amount Ci, the fin angle θf, the strip strength σy, and the plate thickness t.

It is calculated from the outer diameter D and the fin path reduction amount r.

Chamfer processing amount a = f (Ci, θf, fy, t, D, r) b = g (ci
, θ5. cry, D, r) According to the above-mentioned invention, the edge plate thickness of the edge portion of the band plate for smoothing camber after fin pass forming becomes uniform.

Second, if the detected camber amount Ci of the strip plate exceeds the camber amount Cf set in the fin pass forming allowable standard, the edge on the concave side of the camber will be insufficiently processed by fin pass forming, as shown in Fig. 4(d). This results in the occurrence of so-called edge waves in which the edges are undulating.

Therefore, if the detected camber amount Ci exceeds the camber amount Cf set as the fin pass forming allowable standard, in addition to the edge chamfering of the present invention, when the camber portion of the strip is formed by fin pass roll forming, The reduction amount (reduction amount) is changed and controlled based on the fin pass roll reduction amount determined from the detected camber acid C1.

For the reduction control, control is performed in the direction of increasing the fin pass reduction to eliminate the insufficient compression bending of the concave edge of the camber and to provide a degree of processing within the appropriate reduction range.For example, the reduction control method is to use the first fin pass roll. There is a method of controlling the amount of glue reduction according to the detected amount of camber, or a method of controlling the total reduction of the fin paths by keeping the reduction distribution of the fin paths the same. The fin path reduction control amount is also the same as the edge chamfer processing amount (calculated and determined as a function of Ci, σy, t, D, r. When performing edge chamfer processing as described above, the amount of edge thickness increase due to the increase in radius 1 change in fin pass forming in the subsequent process is calculated in advance, and chamfer processing is performed with the amount of chamfer processing determined from the calculation. It is something that

The above control eliminates edge wave generation 1± in fin pass forming of the edge portion of the strip having camber.

By the chamfering control and/or fin path reduction control of the strip edges according to the present invention, the strip portion having a camber can be made even in thickness at both edges and prevented from generating edge waves after fin pass forming, and the strip plate portion having a camber can be made uniform in thickness and prevented from generating edge waves. Stabilization of tube forming is achieved.

The third technical means is as follows.

The raw tube having the camber controlled according to the present invention has different amounts of springback on both edges after fin pass forming, resulting in a raw tube with an asymmetric left and right molding state, and the relative height positions of both edges are different. exhibit a condition.

As shown in FIGS. 7(a) and 8(a) for the edge portion of the raw pipe 34 on the exit side of the fin pass roll 26, in the band plate portion having camber, the relative displacement in the height direction of the left and right edges yielding the value ΔH.

FIG. 7 shows the conventional case, and regardless of the presence or absence of this displacement amount ΔH, the left and right rolls are at the same height position as shown in FIG. 7(b).

Edge guide roll 29 or squeeze top roll 3
In the state of the raw tube 34 at 0a, as shown in FIG. 7(C), a difference in height remains between the two edge portions 37 and 37a due to the difference in springback 38° 38a.

A raw tube in such a state causes non-uniform heating of the left and right edges during high-frequency heating of the edges, resulting in defects such as distortion of the seam, step at the joint, and wrapping, as described above.

Therefore, in order to solve this problem, as shown in FIG. 8, the amount of pressure 'F' for rolling down both the left and right edge portions of the edge guide roll 29 and/or the squeeze ton roll 30a before the S/F C roll is controlled. . First, the relative displacement amount ΔH in the height direction of both edges of the raw pipe on the exit side of the final fin bass roll is predicted and calculated based on the detected amount of camber. Instead of this calculation, the above calculated value or The amount of reduction ΔHa is determined from the measured value, and the reduction of the edge guide roll 29 and/or squeeze top roll 30a in front of the squeeze roll is controlled based on the amount of reduction. Figure 6 is a plan view of the line configuration before the squeeze roll, Figure 7
The figure is an explanatory diagram showing an example in which there is no roll-down control, and FIG. 8 is an example in which roll-down control is performed.

The relative displacement amount ΔH in the height direction of both edges of the raw pipe at the final fin pass roll exit side is the camber amount Ci, the strip strength σy,
It is determined by the work hardening index n, plate thickness E, outer diameter D, and fin path reduction r, and when σy, n, t, D, and r are constant, the relationship between ΔH and Ci is as follows: ΔH=Chi(Ci) It has been revealed through numerous research studies conducted by the present inventors that there is a certain relationship. And the calculated Δ
From H, the roll reduction change amount ΔHa is.

ΔHa=αXΔH (α is a constant) is calculated and the roll lowering position control is performed.

High-frequency 7-pset welding is stabilized by the reduction control of the edge guide roll and/or squeeze top roll before the squeeze roll according to the present invention.・Fourthly, the welded pipe, which has been subjected to various controls according to the present invention and whose forming and welding have been stabilized, is processed by the inner and outer bead cutting device (3) shown in FIG. 9 installed after the squeeze roll.
2a, 32b), the weld bead is cut.

In this internal and external bead cutting, the occurrence of defects in the internal and external bead cutting is prevented by controlling the rotation of the internal and external bead cutting positions based on the seam twist amount θS calculated from the detected amount of camber.

The inventors' previous research studies have revealed that there is a certain relationship between the strip camber amount Ci and the seam twist amount θS. FIG. 9 shows an example of cutting position control of the inner and outer bead cutting device when seam twisting occurs due to the strip camber.

As described above, the present invention detects the amount of camber of the strip when manufacturing a strip having camber into a blank pipe, and first controls the edge chamfering of the camber portion based on the detected amount of camber. In order to equalize the thickness of both edges during fin pass forming, if the detected camber amount exceeds the standard value, in addition to controlling the edge chamfering,
By controlling the reduction of the fin pass, the generation of edge waves during fin pass molding is prevented. After the above control, by controlling the edge guide roll in front of the squeeze roll and/or the squeeze roll to the right and left, the relative positions of both edges of the raw pipe in the height direction are made the same, resulting in uneven edge heating. In addition, by preventing the occurrence of edge steps and wraps during upset welding with a squeeze roll, and controlling the bead cutting position of the bead cutting device after welding, it is possible to eliminate seam failure caused by camber. 8. Preventing the Occurrence of Defects FIG. 1 shows the overall structure of a method for controlling a strip plate having a camber according to the present invention.

Below, the implementation procedure of the method for manufacturing an electric resistance welded steel pipe having a camber according to the present invention will be explained based on examples of control outputs shown in FIGS. 1 and 10.

A strip camber detector 15 installed on the exit side of the edge trimming device 14 of the strip 10 detects the camber of the strip. The central processing unit 13 uses the strip camber amount to determine the magnitude of the detected camber early, and at the same time determines the necessity of each control according to the present invention. As a method of camber detection, for example, as shown in FIG. 10, the camber M Ci is detected and stored at every minute time ΔT from the time when the camber detection amount Ci exceeds the set camber detection level Cs. Then, in the central processing unit 13, from the detected camber amount Ci,
At the same time as calculating and determining the control amount for each control, the side of the strip on which each control is to be executed is determined. Furthermore, the delay time for each control execution is calculated from the mill speed and the distance from the camber detector to each control position, so that appropriate control can be performed when the strip having a camber of 5j Ct passes through each control position. Make it.

For example, the example shown in FIG. 10 shows an example of each control according to the present invention when there is a camber of a strip having a maximum camber amount Cmax in the length of the strip in the longitudinal force direction.

When the camber amount detected by the camber detector exceeds the set camber detection level Cs, the camber amount Ci is sampled at every minute time ΔT, and based on this, the edge chamfer processing amount ai, bi in the edge chamfer processing device 17 and the fin pass reduction control are changed. 1st fin pass reduction r IFQ edge guide roll 29
and the reduction amount ΔHia for changing the reduction position of the squeeze top roll 30a and the inner and outer bead cutting device 32a.
, 32b is calculated and output to each control device according to the control output delay time.

By the way, regarding the reduction control of the fin path, as shown in FIG.
It is sufficient to set f and control this value when the detection camber 1lcf exceeds it.

This is because there is a certain tolerance range for proper reduction of the fin path in which edge waves do not occur.If the amount of edge reduction due to camber is within this allowable reduction range, edge waves will not occur and therefore the amount of fin path reduction. There is no need to change it.

Further, in other controls according to the present invention, if the necessary camber limits of each control are investigated and understood in detail, it is possible to set the camber base value at the start of each control, similar to the fin pass reduction control.

[Effect]

As described above, when manufacturing an electric resistance welded steel pipe from a strip plate having camber, the present invention detects the amount of camber, controls the rechamfering process based on a calculated value obtained from the detected camber amount, and controls the rechamfering process based on the calculated value obtained from the detected camber amount. Based on the measured value of the relative height displacement of the edge between the tubes, by controlling the edge guide roll and/or the squeeze top roll in front of the squeeze roll to the left and right, the relative positions of both edges of the raw tube in the height direction are kept at the same height. In this way, it is possible to prevent uneven edge heating and occurrence of edge steps and wraps during upset welding with a squeeze roll.Also, the rotation of the bead cutting device can be controlled based on the camber amount detection. Beads can be cut accurately.

〔Example〕

An embodiment of the method for manufacturing an electric resistance welded steel pipe having a camber according to the present invention will be described in comparison with a conventional method. ERW steel pipes with the following specifications were manufactured.

Implemented pipe size: 24 inches x 6.35, API 5L
X, X60 Maximum camber amount of 45 mm and 5 mm at Nispan of approximately 25 m of band plate The case where forming control according to the manufacturing method of the present invention is used (Example) and the case where it is not used (Comparative Example) are shown.

When the forming control according to the present invention was carried out, there were no forming defects in the camber part or bead cutting defects at all, and the results of ultrasonic flaw detection (US T) of the welded part were shown in Figure 11 (a).
As shown in Figure 2, the results were good, and there were almost no micro defects below the defect detection level.

On the other hand, in the conventional method that does not perform camber control, when the camber amount is 45 mm, edge waves occur at the camber part during fin pass forming, resulting in an open pipe that cannot be welded, resulting in a yield drop of about 10% per coil. invited. When the camber amount was 35 mm, welding was possible, but the welding condition was not stable, and as shown in Fig. 11 (
As shown in the results of ultrasonic flaw detection in b), there are defects (
Penetrators) occurred, as well as defective bead cutting due to the occurrence of steps at the seam and seam twisting, resulting in a large number of minute defects, and in the end, the camber part became a defective product.

FIG. 12 shows comparative schematic diagrams of the welding and bead cutting states of a cross section in the direction C of the joint section when the camber amount is 35 mm. In the case of conventional molding, a penetrator 42 is generated due to the distortion of the seam line 33, and cutting defects 40 are observed on the inner and outer surfaces of the bead due to the stepped edge and seam twist.

〔Effect of the invention〕

According to the present invention, when manufacturing an electric resistance welded steel pipe from a strip plate having a camber, according to the forming control of the strip plate having a camber according to the present invention, the camber has conventionally caused forming defects, welding defects, bead cutting defects, etc. It has become possible to properly form and weld the strips, improve material yield, and manufacture ERW steel pipes with excellent welded shape quality.

[Brief Description of the Drawings] Fig. 1 is a process diagram showing the manufacturing process of ERW steel pipes to which the present invention is applied; Fig. 2 is an overall system diagram of the manufacturing process of ERW steel pipes;
The figure is a plan view showing the state of edge trimming of a band plate with camber, Figure 4 is an explanatory diagram showing the forming process of the band plate with camber, the welding and bead cutting processes, and the occurrence of defects. is an explanatory diagram showing the chamfer processing method, Figure 6 is a plan view of the raw tube manufacturing process between the final fin pass roll and squeeze roll, Figures 7 and 8
The figures are explanatory diagrams comparing the edge guide roll and squeeze top roll rolling states and edge forming states in the conventional method and the present invention method in the state of blank tube forming, respectively. Fig. 9 is an explanatory diagram showing the bead cutting position control method according to the present invention. Figure, 10th
The figure is an explanatory diagram showing the output side of molding control of the method of the present invention.
Figure 1 is a chart showing the results of ultrasonic flaw detection of a welded part of a strip plate with camber, where (a) is an example, and (b) is a comparative example (
FIG. 12 is a cross-sectional view in the C direction of a welded portion of a strip plate having a cross-section according to (&) the present invention and (b) a conventional method. It is. 10...Strip plate 12...Leveler 13...Central processing unit 14...Edge trimming device? 14a, 14b, L4c・-x-) Ji processing device 15...
- Camber detector 16...Breakdown roll 17...Edge chamfer processing device 20...Cage roll 22.24.26...Fin pass roll 25...Both edges of base tube height direction displacement detector 27... Contact tip 28... Seam guide roll 29... Edge guide roll 30... Squeeze roll

Claims (1)

[Scope of Claims] 1. In the production of electric resistance welded steel pipes in which continuously fed strips are sequentially formed into cylindrical blank pipes by continuous forming rolls and the joint edges are welded, (I) a step of detecting the amount of camber of the strip; (II) from the detected amount of camber, determining the amount of machining of the edge portion of the strip having the camber, the amount of reduction of the fin pass roll, and the amount of reduction of the squeeze roll or/and edge guide roll; a step of calculating the amount of reduction of the left and right edge portions and the amount of seam twist caused by the camber of the strip; (III) processing the edge portion of the strip and the amount of reduction of the fin pass roll according to the calculation results; 1. A method for manufacturing an ERW steel pipe, comprising: a process of optimally controlling a squeeze top roll or a left and right reduction of a squeeze roll in combination with cutting position control of a bead cutting device.