JPH03198901A - Control method of wall thickness of tube with stretch reducer - Google Patents

Abstract

PURPOSE:To manufacture a steel tube with a wall thickness of a high accuracy by shortening control pitch by giving the variance of revolving speed corresponding to the variation of thickness of base material at each stand of a stretch reducer mill. CONSTITUTION:A thickness gage 3 for base material and a PLG (pulse generator) 6 are arranged on the inlet side of the stretch reducer SR mill 5 and the revolving speed of roll is operated with a CPU (computer) 2 based on the thickness signal of base material. And, the rotating speed of roll of each stand is controlled by the instruction of a speed control system 1 corresponding to the tracking state of the thickness of base material. Thus, the control of each individual SR stand is made possible and the variation of wall thickness of finished steel tube can be remarkably controlled by minimizing control pitch.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to continuous rolling of steel pipes in a stretch reducer mill (hereinafter referred to as SR mill). The present invention relates to a method for manufacturing a steel pipe with high accuracy of ζ wall I'd by minimizing the variation in the longitudinal wall thickness of a finished steel pipe due to jg-1 (hereinafter referred to as material thickness) in the main pipe.

[Prior art] Normally, an SR mill has about 6 to 24 rolling stands each incorporating 2 to 40 rolls, and by applying a difference in the number of rotations of the rolls between the stands, a tensile force is applied to the material. It is widely used as equipment for manufacturing small to medium diameter pipes. In addition, SR mills are generally placed in the final process of manufacturing welded steel pipes and seamless steel pipes, and perform finish rolling to reduce the outer diameter of the raw pipe manufactured in the previous process and increase or decrease the wall thickness to produce the desired medium or small diameter pipe. Used as a machine. Therefore, the longitudinal wall thickness of the product steel pipe and its accuracy are determined by the SR mill.

Now, when continuously rolling steel pipes with an SR mill, the variation in the longitudinal wall thickness of the finished steel pipes depends on the material thickness, so
In order to keep the wall thickness of the finished steel pipe constant despite variations in material thickness, it is necessary to adjust the tensile force between each stand of the SR mill according to variations in material thickness.

FIG. 2 schematically shows a conventional general SR mill control method. The figure shows a case where the rotation speed of all stands is changed simultaneously based on the rotation speed change of each roll calculated from the material thickness variation. The solid line ■ is the rotation speed pattern when the average material thickness is to, and the broken line ■ is the rotation speed pattern when the average material thickness is to+ΔL
This shows the rotational speed pattern when the speed changes to . In this case, the control pitch becomes the SRR mill length, but the variation in material thickness between the pitches remains as is. This is shown in FIG. FIG. 3 schematically shows that the material thickness changes downward to the right from the thicker side to the thinner side between the control pitches L.

Now, if the material thickness gradient is δ, then from Figure 3-(a), δ=Δ
t/L, that is, the variation in wall thickness of the finished 1-0 steel pipe for 1 part of the control pitch is δL, and it is impossible to reduce it below this value.

Also, as wall thickness control technology in SR mill during continuous rolling.
C is a method of calculating the tension necessary to obtain a certain finished thickness from the material jy, as disclosed in Japanese Patent Publication No. 54-24394, and calculating the roll rotation speed of the SR mill, or Massflo as published in No. 64-40111
- Methods have been proposed to calculate the roll rotation speed from certain conditions, but in each case it is unclear how to apply the roll rotation speed, which is the calculation result, to the control of an SR mill consisting of multiple stands. Not shown. Furthermore, in either method, if the control pinch is larger than the material thickness variation pitch, control is impossible.

That is, in order to manufacture steel pipes with high wall thickness accuracy, it is necessary to make the material thickness uniform by shortening the control pitch as much as possible, but there is a drawback in that no means for this purpose are shown.

[Problem that the invention seeks to solve]

As mentioned in 111, when controlling the wall thickness while continuously rolling a steel pipe with an SR mill, the control pitch is important,
Although making this as short as possible leads to minimizing longitudinal variation in the wall thickness of finished steel pipes, this method has traditionally been difficult to improve wall thickness accuracy in SR mills. I couldn't do it. Therefore, in recent years, requirements for steel pipe dimensions, particularly wall thickness accuracy, have become significantly stricter due to the need to omit secondary processing of steel pipes, but this conventional technology has been difficult to meet.

The present invention focuses on this point and provides a method for manufacturing steel pipes with high wall thickness accuracy by shortening the roll rotation speed control pitch in an SR mill.

[Means for solving problems]

The present invention is capable of controlling the rotation speed of each stand of the SR mill according to the thickness of the material while continuously rolling steel pipes with the SR mill. By shortening the control pinch by applying a change in the rotation speed, and by performing high-precision tracking of the material thickness to each stand in the SR mill, which is required due to the shortening of the control pitch, the problems of the conventional technology were solved. This solves the problem and makes it possible to manufacture steel pipes with high wall thickness accuracy.

Examples of the present invention will be described below. In the present invention, S
The control pitch is shortened by changing the rotational speed of the R mill for each stand or for every several stands, and an example in which this method is implemented in two groups is schematically shown in FIG. 1. In FIG. 1-(A), the solid line (■) shows the rotational speed pattern when the average material thickness is to, and the broken line (■) shows the rotational speed pattern when the average material thickness jyb changes to LO+Δt.

When the base t,+thickness changes by ΔL as shown in FIG. At this time, the rear group takes the rotation speed pattern of the solid line ■, based on the rotation speed of the final stand of the front group (thick line ■).

Next, as shown in Fig. 1-(c), when the portion of material thickness LO + ΔL reaches the rear group, the former group returns to the number of revolutions pattern shown by the solid line, but the latter group returns to the final stand revolutions of the former group. The rotation pattern shown by the dashed line is based on (thick line ■).

As a result, as shown in Figure 3-(b), in the conventional all-stand simultaneous control method, the thickness variation of the finished steel pipe is δL, but in the case of the present invention, it can be controlled to δL/2. , the wall thickness of the finished steel pipe can be made more uniform.

As mentioned above, the control wholesale pitch depends on the number of stands grouped, but this is mainly determined by the rolling speed and the response of the mill drive system, and by controlling each stand, the minimum control pitch can be reduced to the minimum stand distance. (It is possible to do this, and variations in wall thickness of finished steel pipes can be significantly suppressed.

As described above, controlling each SR stand individually or in groups of several stands presupposes extremely accurate tracking of the material thickness. Conventionally, in the case of rolling one by one (discontinuous rolling), the leading and trailing ends are detected between the SR stands, but this cannot be applied in the case of continuous rolling. Therefore, in the present invention, by adopting the tracking method described below, high-precision tracking that can be applied to control of each single stand in continuous rolling has been realized.

Next, an example of continuous rolling is shown in FIG.

In the figure, a material thickness gauge 3 and a length measuring PLG (pulse generator) 6 are placed on the entry side of the SRR mill, and the material thickness signal is delayed until the No. 1 stand. Also, SRR mill personnel will install a speedometer 4 on the outlet pot. Regarding speedometer 4, it is SR Mill No.

One stand and final stand revolutions may also be used.

In the present invention, the material thickness signal delayed to the SRR mill stand 011 is calculated at each stand exit speed in the SR mill by calculating the exit speed of each stand using the following formula using the measured value of the exit speed. Track to stand.

Vi-VInXf 1Xf2X...fi ・
...0 type % type % ■i: Mini 1st stand speed fi: I-th stand advanced rate V 1n10ut: S 15 people, exit speed Next, the material relay part that is inevitable for continuous rolling is rolled at each stand of the SR mill. By detecting changes in the motor current of each stand when the stand is turned on, confirm and correct the tracking results from (2).

Conventionally, the SR mill was used as a means of confirmation and correction.
There are methods such as installing a sensor that can detect the relay part on the output side, but the above method of detecting the relay part using the motor current of each stand makes it possible to guarantee tracking accuracy for each stand. Become.

As described above, by correcting the calculation result from the speed using the transit time of each SR mill stand in the relay section, highly accurate tracking is always achieved.

On the other hand, in Fig. 4, there is a gap in the material thickness signal, and the CPU
(Computer) 2 calculates the roll rotation speed, and speed control system 1
The rotation speed of each stand roll is controlled by the instructions.

As a result, control for each single SR stand becomes more efficient, and by minimizing the control pitch, it becomes possible to significantly control variations in wall thickness of the finished steel pipe.

An example of the effects of the present invention is shown in FIG. Figure 5-(a) shows the pipe average wall thickness distribution when each stand is controlled according to the present invention, and Figure 5-(b) shows the pipe average wall thickness distribution when all stands are controlled simultaneously in the conventional method. shows.

It can be seen that the variation in the average pipe thickness rt is significantly improved by controlling the roll rotation speed for each stand based on the present invention.

[Effect of the invention] As explained below, according to the method of the present invention, conventionally,
It is now possible to control the wall thickness using the tension of each roll stand, which was impossible in continuous rolling with replacement using a stretch reducer, and at the same time, the variation in thickness of the material is reduced through the stretch reducer, and at the same time, the variation in wall thickness is suppressed. This has made it possible to make the wall thickness uniform, making it possible to supply steel pipes with highly accurate wall thickness.

[Brief explanation of drawings]

Figure 1 shows two groups or more of the SRR mirtando of the present invention.
Figure 2 shows the case where control is divided into two parts.
Diagram when controlling the mill rule rotation speed of all stands at the same time,
Figure 3 is a diagram schematically showing the longitudinal distribution of the wall thickness of a finished steel pipe when controlled according to Figures 1 and 2.
The figure is a block diagram of an SR mill control system including a high-precision tracking system for each stand in the SR mill for material thickness, which is a premise of the present invention, and FIG. 5 is a diagram showing the effects of the present invention. ■... Speed control system, 2... Roll rotation speed, tracking calculator, 3... Material thickness measuring device, 4...
Pipe velocity meter, 5...Stretch reducer mill 6...
・Pulse generator for length measurement. Applicant Nippon Steel Corporation

Claims (1)

[Claims] 1. During continuous rolling of steel pipes in a stretch reducer, when changing the roll rotation speed of the stretch reducer according to changes in material thickness, the material thickness is detected in the mill by detecting the relay part with the motor current of each stand of the SR mill. By tracking with high accuracy, the roll rotation speed is changed for each stand of a stretch reducer mill consisting of multiple stands, or for each group of several stands, thereby suppressing variations in the thickness of finished steel pipes. A method of controlling pipe wall thickness using a stretch reducer.