JPH01181920A - Method for controlling rolling reduction of end part of band plate for electric resistance welded tube - Google Patents

Abstract

PURPOSE:To stably form the front and rear end part of a band plate and to prevent welded defect by controlling the rolling drafts at each forming stand when the front end part of the band plate is bitten at a 1st fin pass roll and when the rear part of the band plate runs out through the 1st fin pass roll. CONSTITUTION:When the front end part of the band plate is bitten by the fin pass rolls 20, 22, 24 and a squeeze roll 28, the rolling drafts at each forming stand are loosened to the rolling draft of the stationary part of the band plate. Then, the front end part of the band plate is bitten at the fin pass stand 22 and the rolling draft of a 1st fin pass stand 20 is controlled to the stationary part of the band plate. The succeeding forming stands receive the same rolling draft. When the rear end part of the band plate is formed by the fin pass rolls 20, 22, 24 and the squeeze roll 28, the rear end part of the band plate runs out through a breakdown roll 12, the rolling draft of the fin pass roll stand 20 is made stronger than the rolling draft to the previous stationary part of the band plate, as soon as the 1st fin pass stand 20 is passed through, the rolling reduction of a 2nd fin pass stand 22 is strengthened in the same way as mentioned before and the rolling draft is controlled in the succeeding stands in the same way.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to manufacturing an electric resistance welded steel pipe in which a seam line extends parallel to the tube axis from a finite length strip. The present invention relates to a method for controlling the reduction in the end portion of a strip of an electric resistance welded steel pipe, which is stably formed using fin pass rolls and squeeze rolls during the finish forming process.

[Prior Art] Generally, an electric resistance welded steel pipe whose seam line extends parallel to the tube axis is manufactured using a strip plate 10 cut in advance to the developed dimensions of the electric resistance welded steel pipe to be manufactured, as shown in FIGS. 10 and 11. is sequentially bent into a substantially circular arc shape by various forming rolls (breakdown roll 12, edge forming roll 14, outside cage roll 16, and inside cage roll 18) in the rough and intermediate forming stages, and then bent into a substantially circular arc shape in the final forming process. Seam edge 2 by fin pass roll 20.22.24
6a is stably formed to obtain an arc-shaped blank tube 26, the edge 26a of the blank tube 26 is subjected to high-frequency heating and upset welding is performed using a squeeze roll 28 to manufacture the tube. 30 is an electric resistance welded steel pipe.

In the production of such electric resistance welded steel pipes, fin pass rolls and squeeze rolls are used to round the strip, process the edges of the edge slit surface, prevent edge waves in the longitudinal direction of the edges, prevent edge fluctuations, upset join the edges, etc. This is an extremely important forming roll. Particularly in forming thin-walled pipes, the raw pipe edge 26a is
Since an edge wave 31 as shown in FIG. 3 is generated, conventionally, in order to prevent this, the tube is squeezed with a fin pass roll, that is, rolled down. For example, as described in JP-A-57-149018, a first fin pass strong reduction forming method has been proposed in which the reduction by the first fin pass roll is stronger than that in other stands. In addition, as a method of preventing edge waves, a downhill forming method is adopted, a method of strengthening the edge restraint of the raw pipe by installing edge guide rolls between stands, etc. are adopted.

However, the above conventional method is mainly aimed at preventing edge waves when forming the steady portion of the strip, and is not sufficiently effective when forming the leading and trailing ends of the strip when using a finite length strip. At the leading and trailing ends of the strip, edge waves occur and edge fluctuations occur due to a decrease in binding force, resulting in welding defects such as open pipes that cannot be welded and edge wrap during welding as shown in Figure 4. 32 is a weld bead.

Therefore, in order to stabilize the forming of the tip and rear end of the strip, the inventors developed an inter-stand guide roll that simultaneously restrains the edge and side portion of the blank pipe, as described in Japanese Patent Application Laid-open No. 80-111783. proposed, or published in Japanese Unexamined Patent Publication No. 1983-14
As described in Japanese Patent Application No. 452, a method has been proposed for stabilizing the forming of the strip, and in particular for preventing the generation of edge waves, by changing the rolling reduction distribution of the fin pass rolls between the leading and trailing ends of the strip and the stationary portion of the strip. There is.

[Problems to be solved by the invention] However, the above-mentioned Japanese Patent Application Laid-open No. 80-111783,
Although the methods described in JP-A No. 5111-144521 are more effective than the above-mentioned method for forming the steady portion of the strip, when thin materials are used, edge waves occur at the leading and trailing ends of the strip and welding occurs. However, as the wall thickness becomes thinner, edge wrap still occurs, and this tendency becomes more pronounced as the wall thickness becomes thinner, leading to a decrease in the pipe production yield. Also, JP-A-80-11
The method described in Japanese Patent No. 1783 has practical disadvantages in terms of hardware and productivity, such as restrictions on the installation of the device in an existing stand and time required for setting the device.

An object of the present invention is to stabilize the forming of the leading and trailing ends of a strip plate in the production of electric resistance welded steel pipes, and to prevent the occurrence of edge waves, edge wraps during welding, and welding defects caused by these.

[Means for Solving the Problems] The present invention involves sequentially bending and forming a strip into a substantially arc shape in rough and intermediate forming processes, and then finishing forming it into an arc shape using multiple sets of Huminpass rolls to produce a raw tube. After obtaining the raw pipe, the edges of the raw pipe are subjected to high frequency heating and upset welding using a squeeze roll to produce an ERW steel pipe. When inserting the tip of the strip into each forming stand, the amount of roll reduction of each forming stand is made looser than the amount of roll reduction of the steady section of the strip, and as the tip of the strip bites into the succeeding stand, it is inserted into the succeeding stand. The amount of roll reduction of the adjacent preceding stand is controlled to the amount of roll reduction relative to the steady section of the strip, and ■ Regarding the fin pass roll and squeeze roll forming of the rear end of the strip, the rear end of the strip is controlled by the upstream breakdown roll. After passing through each of the preceding stands, the amount of roll reduction of the subsequent stand adjacent to the preceding stand is made stronger than the amount of reduction with respect to the stationary portion of the strip up to that point.

[Function] The present invention was derived from the results of many years of experimental research by the inventors regarding the stabilization of the forming of the leading and trailing ends of the strip.

As shown in Fig. 5, the leading and trailing ends of the strip inserted into the fin pass roll set in the rolled-down state open in a trumpet shape after passing through the stand, making it extremely difficult to enter the next stand, resulting in forced forming. In this state, compressive stress acts on the edges, causing edge waves. As illustrated in Figs. 6 and 7, this phenomenon is related to the reduction of the fin pass rolls, that is, the fin pass reduction (ri). In particular, it has become clear that the increase in the horizontal frame of the raw pipe greatly affects the generation of edge waves.

FIG. 8 is a diagram showing the relationship between the first fin pass reduction, the forming of the tip of the strip, and the length of welding defects. This eighth
It is also clear from the results shown in the figure that loosening the first fin pass reduction is an effective means for reducing the length of forming defects at the tip of the strip. Here, each fin pass stand glue reduction ri is expressed as rj=100 or n (text, /!;L,) using the outer circumference length of the raw pipe on the outlet side of the i-th stand or i. Therefore, when inserting the tip of the strip into the fin pass roll and squeeze roll, the trumpet condition of the tip of the strip can be improved by making the amount of reduction of each forming stand less than the amount of reduction of the steady portion of the strip. , the horizontal elongation of the raw pipe is also suppressed, and it is possible to smoothly enter the strip from the stand to the next stand, and at the stage when the strip enters the next stand, the amount of reduction in the stand concerned can be suppressed to a steady amount of reduction. This was recognized. That is, when inserting the tip of the strip into each forming stand, the amount of roll reduction of each forming stand is made looser than the amount of roll reduction of the steady portion of the strip, and as the tip of the strip is bitten into the second fin pass stand, The amount of roll reduction of the first fin pass stand is controlled to the amount of roll reduction with respect to the steady portion of the strip, and as the tip of the strip bites into the third fin pass stand, the amount of roll reduction of the second fin pass stand is controlled to the amount of roll reduction relative to the steady portion of the strip. The subsequent forming stands also carry out similar reduction control.

Regarding the forming of the trailing edge of the strip, as the trailing edge of the strip passes through the forming rolls sequentially, the strip restraint force and the resulting longitudinal tension on the strip decrease, and the edges to be welded vary. This can lead to welding defects and edge wrap due to uneven heating of the left and right edges. In particular, in order to stabilize the forming of the steady portion of the strip in fin-pass roll forming, a first fin-pass strong reduction distribution forming method is adopted in which the first fin-pass roll is strongly reduced, as described in JP-A-57-149018. In this case, when the rear end of the strip passes through the first fin pass roll, the strip restraining force suddenly weakens, and when the edge is joined with the squeeze roll, the edge fluctuations tend to increase, resulting in poor welding. The occurrence becomes noticeable. Figure 9 is a diagram showing the relationship between the second fin pass reduction, the forming of the rear end of the strip, and the length of welding defects obtained from the inventors' experimental results. From the results shown in FIG. 9, it is clear that increasing the second fin pass reduction is an effective means of reducing the length of forming defects at the rear end of the strip when forming the rear end of the strip. became. Therefore, when forming fin pass rolls and squeeze rolls at the rear end of the strip, if the preceding roll stand bottoms out and the rolling amount at the next roll stand is controlled to be stronger than the rolling amount at the steady portion of the strip, it is possible to It is recognized that the restraint by the roll at the rear end is strengthened and stable edge welding becomes possible. That is, as the rear end of the strip passes through the upstream breakdown roll, the amount of roll reduction of the first fin pass stand is made stronger than the amount of reduction for the steady portion of the strip up to that point, and the rear end of the strip passes through the first fin pass stand. At the same time as the strip exits the pass stand, the subsequent forming suit stand performs similar rolling reduction control such that the roll reduction amount of the second fin pass stand is made stronger than the roll reduction amount for the stationary portion of the strip up to that point.

In carrying out the present invention, the method for controlling the rolling down of the leading and trailing ends of the strip according to the present invention and the prior art, for example, JP-A-80-
It is also possible to use it in combination with a guide roll device as described in Japanese Patent No. 111783, and when constructing a new mill, the effect will be even greater.

[Example] The present invention will be explained in detail below.

FIG. 1 is a schematic diagram illustrating the concept of the strip edge reduction control method of the present invention using a fin pass and squeeze roll reduction chart.

(A) First, the reduction control of the tip of the strip will be explained.

When the strip enters the fin pass roll, the rolling reduction r of all the fin pass stands is made smaller than the rolling reduction of the steady portion of the strip. The ratio (reduction rate) differs somewhat depending on the stand, and it is important to have a large reduction rate in the first fin pass roll stand (IF), which has a strong rolling reduction rate in the band steady section, and is highly effective. As shown in Figures 6 and 7, which are the results of the aforementioned research, this means that the effect of reduction on the degree of tip trumpet formation is extremely large in the first fin pass roll stand (IF), and in the first fin pass roll stand (IF). 2-fin pass roll stand (2F),
As you get to the 3rd Finpass Roll Stand (3F),
This is because it is recognized that the degree of influence will be smaller.

For example, it is preferable that the rolling reduction (r IF) at the time of inserting the tip of the strip in the first fin pass roll stand be small from the viewpoint of stabilizing the forming of the tip of the strip. In this case, it takes time to move the roll reduction position using the electric system, and the control time becomes long, making it impossible to provide a quick response when the strip tip passes, and as a result, the reduction control cannot be done in time to pass the strip tip. It is also possible that the occurrence of Therefore, the rolling reduction rate (r IF) when inserting the tip of the strip in the first fin pass roll stand must be determined by considering both of the above factors. By selecting a rolling reduction ratio of 50%, stabilization of the forming of the tip of the strip could be achieved. For subsequent roll stands, the rolling reduction ratio (r) at the time of inserting the tip of the strip is reduced based on the same concept.

That is, the tip of the strip passes through the first fin pass roll stand and is bitten by the second fin pass roll stand, and the rolling reduction rate of the first fin pass roll stand is changed to the rolling reduction ratio of the steady portion of the strip, and then the strip is rolled. The rolling reduction ratio of the subsequent stands is similarly controlled, such as when the tip of the plate bites into the third fine-pass roll stand and the rolling reduction ratio of the second fine-pass roll stand is changed to the rolling reduction ratio of the steady portion of the strip. As for the steady portion of the strip, the first fin pass strong pressure distribution molding method similar to the conventional method is performed.

(B) Next, the rolling control of the rear end of the strip will be explained. At the same time when the rear end of the strip passes through the breakdown roll (here, the first breakdown roll (IBD) is shown as a representative example), the rolling reduction of the first fin pass roll stand is calculated as the rolling reduction of the steady section of the strip. Increase it slightly more than that to strengthen the strip restraint by the roll. As a result of experiments, the rate of increase in the rolling reduction rate was found to be at least 5% increase in the steady-state rolling reduction rate at the first finpass roll stand, at least 20% increase at the second finpass roll stand, and by 30% at the third finpass roll stand. Above is 1 for squeeze roll stand (SQ)
The inventors have confirmed through numerous experiments that the molding improvement effect can be obtained by setting the increase to 0% or more. After that, the rear end of the strip passes through the first fin pass roll stand, and the rolling reduction rate of the second fin pass roll stand is increased to be higher than the steady part rolling ratio, thereby strengthening the restraint of the rear end of the strip. The rolling reduction ratio of the subsequent stand is also controlled in the same way.

Regarding the reduction of the squeeze roll, as shown by ■ in Fig. 1, the first fin pass roll stand at the rear end of the strip,
It is also useful for controlling the rear end of the strip to apply a control method that increases the rolling reduction ratio of the squeeze roll stand each time the second fin pass roll stand bottom is removed.

The control signal for changing the reduction in (A) and (B) above may be the load signal of the load cell installed in each stand, or the current signal of the drive motor of each stand. Alternatively, it is also possible to use a method of installing photoelectric switches inside and outside of each roll stand to detect the presence or absence of material. Either method can be used to control the rolling down of the fin pass and squeeze roll.

FIG. 2 is a block diagram of a control system used to implement the present invention. In FIG. 2, 10 is a strip plate, 12 is a breakdown roll, 20 is a first fin pass roll, 22 is a second fin pass roll, 24 is a third fin pass roll,
26 is a raw pipe, 28 is a squeeze roll, 30 is an electric resistance welded steel pipe,
Reference numeral 34 denotes a lowering motor and automatic positioning device, 36 a load cell, 38 a lowering screw, and 40 a lowering control setting circuit.

This reduction control setting circuit sets the fin pass roll roll reduction (amount of reduction) to approximately 50% of the steady-state reduction when the tip of the strip approaches the fin pass roll, and the tip of the strip is bitten by the second fin pass roll. At the same time, the automatic positioning device 34 for lowering the first fin pass roll by the electric motor is operated to lower the upper roll of the first fin pass roll to a predetermined position, that is, a position where steady-state reduction is applied. As a signal for the operation, a load detection signal from a load cell 36 installed on the upper roll of the second fin pass roll is used. and the third one at the tip of the strip.
The same reduction control as described above is also carried out when biting into the fin pass roll and squeeze roll.

In addition, the rolling down control setting circuit 40 also uses the reverse method of the above-mentioned method for the roll end of the trailing edge of the strip to detect that the trailing edge of the strip is passing through the breakdown roll by detecting the load using the load cell of the breakdown roll. The automatic positioning device 34 of the first fin pass roll is actuated based on the signal, and the reduction of the first fin pass roll is increased more than the steady-state reduction, and the upper roll position is controlled to a predetermined reduction position. Hereinafter, similar control is performed for the subsequent roll stand when the rear end of the strip comes off.

Hereinafter, specific examples of the present invention will be described.

The material used was a large-diameter thin-walled steel tube (outer diameter 2mm, wall thickness 8.35m), which tends to be unstable when forming the front and rear ends of the strip using conventional methods.
m, grade API 5LX70) There is. The appropriate fin pass reduction conditions for the steady section of the strip during the production of the above steel pipe are the first fin pass reduction (r IF) =
0.7%, second fin path reducigon (r 2F)
= 0.3%, third fin pass reduction formula (r 3
F) = 0.1% and the squeeze roll reduction (r SQ) is 0.1%.

Therefore, when each roll enters the tip of the strip, the rolling reduction rate of the roll stand is set to 50% of that of the steady part rolling rate.
Then, the tip of the band plate is bitten into the next stand, and the rolling reduction rate of the stand is set to the steady-state rolling rate.

In addition, when each roll at the rear end of the strip comes off, the first breakdown roll is set so that the strip comes off, and the first fin pass roll glue reduction (r IF) is increased by 5% of the rolling reduction rate of the steady section. The first fin pass roll is moved so that the rear end of the strip falls through, and the reduction y (r2F) of the second fin pass roll is increased by 25% of the rolling reduction rate in the steady section. As the bottom falls out, the third
The fin pass roll paste reduction (r 3F) is increased by 40% of the rolling reduction rate in the steady area, and the third fin pass roll is adjusted so that the rear end of the strip comes through and the reduction of the squeeze roll (r SQ) is increased by 40% of the rolling reduction rate in the steady area. Each is controlled so that it increases by 10%.

In this example, the above-mentioned rolling down control of the front and rear ends of the strip was performed based on the load detection signal of the load cell built into each roll stand.

As a result, in the conventional method, the unstable forming and welding length at the tip and rear end of the strip was 4.5 m, and that at the rear end was 4.3 m, but with the method of the present invention, the length at the tip of the strip was 2.5 m, and that at the rear end to 2.0 m, which was approximately halved, resulting in a significant improvement in material yield.

[Effects of the Invention] As described above, according to the present invention, when manufacturing an ERW steel pipe, the forming of the leading and trailing ends of the strip plate is stabilized, and edge waves and edge laps during welding, as well as welding defects caused by them, are prevented. Occurrence can be prevented.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing the concept of the rolling reduction control method of the present invention, Fig. 2 is a block diagram showing the control system used to implement the invention, Fig. 3 is a schematic diagram showing the generation situation of edge waves, Figure 4 is a schematic diagram showing the occurrence of edge rap.
The figure is a schematic diagram showing the forming situation of the tip of the strip in fin pass roll forming, FIG. 6 is a diagram showing the relationship between the first fin pass reduction and the opening situation of the tip and rear end of the strip, and FIG. A diagram showing the relationship between the first fin pass reduction and the shape of the aperity at the tip and rear end of the strip. Figure 8 shows the relationship between the first fin pass reduction, the forming of the tip of the strip, and the length of weld defects. 9 is a diagram showing the relationship between the second fin pass reduction, the forming of the rear end of the strip plate, and the length of defective welding. FIG. 10 is a plan view showing the electric resistance welded steel pipe manufacturing line.
The figure is a front view of FIG. 10. 10... Band plate, 12... Breakdown roll, 20.22.24... Fin pass roll, 26...
Raw pipe, 26a... Raw pipe edge, 28... Squeeze roll, 30... Electric resistance welded steel pipe, 34... Lowering motor and automatic positioning device, 36.
... Load cell, 38... Drop-down screw, 40... Drop-down control setting circuit. Agent Patent Attorney Osamu Shiokawa 1 Figure 3 Figure 4 Figure 5 Figure 6 Zhou Figure 7 Figure 8 Existing Figure 9 Figure 2 Finno<? Sridakushoso

Claims (1)

[Claims] (1) The strip is sequentially bent into a substantially arc shape in the rough and intermediate forming processes, and then finished formed into an arc shape using multiple sets of fin pass rolls to obtain a blank tube. When manufacturing ERW steel pipes by high-frequency heating and upset welding with squeeze rolls, (a) Insertion and forming of the tip of the strip into the fin pass roll and squeeze roll, and the tip of the strip into each forming stand. When inserting the forming stand, the amount of roll reduction of each forming stand is set to be less than the amount of roll reduction of the stationary part of the strip, and as the tip of the strip bites into the following stand, the amount of roll reduction of the preceding stand adjacent to the following stand is reduced. (b) Regarding the fin pass roll and squeeze roll forming of the trailing end of the strip, the trailing end of the strip is controlled to be the roll reduction amount relative to the steady portion of the strip, and each of the preceding stands including the upstream breakdown roll is 1. A method for controlling the roll-down of an end of an electric resistance welded steel pipe strip, the method comprising: increasing the roll roll-down amount of a subsequent stand adjacent to the preceding stand after the stand has come off, greater than the roll roll-down amount of a stationary portion of the strip up to that point.