JPS61108414A - Method for controlling wall thickness of pipe in drawing mill - Google Patents

Abstract

PURPOSE:To improve the accuracy of a wall thickness of pipe, by measuring a tension between adjoining stands as well as computing the deviation between the measured tension and a target one and controlling the number of revolutions of a rolling stand of the pipe end so as to make the deviation to be zero. CONSTITUTION:Each stand of a stretch reducer 7 is driven by a motor 6, and is provided with a tension detecting device 2. The device 2 has shearing type load detectors (load cell) 12, which are incorporated in upper and lower rails 10 and 11 respectively. As the forces acting between a roll stand 13 and the upper and lower rails 10, 11 are respectively transmitted through the detectors 12, the stress acting on the stand 13 in the rolling direction is obtained. An interstand tension is computed based on said stress and each boundary conditions, and the deviation between the computed tension and a target tension is inputted to a computer 4, to control the number of revolutions of a stand of the pipe end. In this way, the accuracy of a wall thickness of pipe is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for controlling the wall thickness of a pipe in a reducing mill of a seamless steel pipe production line.

[Prior Art] Generally, when a tube is rolled using a reduction rolling a (stretch reducer), a finished tube having a wall thickness distribution in the longitudinal direction as shown in FIG. 2 is obtained. The thick wall portion at the tip and rear end of the finished tube is caused by the inability to apply appropriate tension during rolling in the reducing mill. In the prior art, there are mainly two methods to solve the above problems.

Namely, (1) Stretch reducer tip/rear end control according to Japanese Patent Publication No. 411-37340, (2) Japanese Patent Publication No. 52-3
Stretch reducer-tension control based on longitudinal thickness distribution of mandrel mill rolling machine according to No. 7853 and JP-A-52-83147.

[Problems to be Solved by the Invention] However, the above prior art has the following problems. In other words, in the method (1) above, the rotation speed control at the tip and rear end of the tube is determined by experience and the control is in an open loop, so the accuracy is extremely poor from the perspective of optimal tension control. The method is.

Online wall thickness measurement technology after mandrel mill rolling has not been published and is considered technically unfeasible at this stage. Even if there is a wall thickness measurement technique using a mandrel mill, the conventional technique is insufficient.

That is, during straight and chill reducer rolling, dynamic tension fluctuations occur at the luminescent rear end, and the tension fluctuations of the stretch reducer cannot be absorbed by control.

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the prior art and to provide an extremely accurate stretch reducer technique for controlling the thickness of the luminescent rear end during rolling.

Means to solve problem E] Book! In a method for controlling the wall thickness of a pipe in a reducing rolling mill consisting of multiple roll stands, Akira actually measures the tension between adjacent stands, calculates the deviation between the measured tension and the target tension at each part in the longitudinal direction of the pipe, and calculates the above-mentioned The rotation speed of the stand that rolls the end portion of the pipe with the deviation is controlled so that the deviation becomes zero, and the rotation speed of the stand that rolls the portion without the deviation is kept at the standard rotation speed. This is what I did.

[Function] According to the present invention, when rolling the tip and rear ends of a tube, the rotation speed of the corresponding stand is controlled so that the tension between the corresponding stands becomes the target tension, and the rotation speed of the corresponding stand is controlled so that the tension between the corresponding stands becomes the target tension. This makes it possible to obtain finished pipes with uniform wall thickness.

[Example] In Stretch Reso users, the outer diameter of the tube is reduced using a number of stands arranged in tandem without the use of internal tools. In addition to this outer diameter reduction, a change in wall thickness also generally occurs. However, its magnitude is determined by the state of stress generated in the rolled tube.The stress state of the rolled tube is determined by the longitudinal elongation as XL.

(KL = force in the longitudinal direction of the pipe, S = pipe cross-sectional area, Rf = deformation resistance of the rolled pipe), which changes by giving a step difference to the rotation speed of each stand. Longitudinal elongation
The larger L becomes, the thinner the tube becomes. In order to obtain a tube with a desired wall thickness, the rotational speed sequence of the rolling mill may be set so that the necessary longitudinal elongation occurs in each stand.The present invention is a stretch reducer.
The purpose of the present invention is to propose a control method that essentially reduces the length of the thick-walled leading and trailing ends when rolling a tube in comparison with known methods.

The method of the present invention will be explained with reference to FIG. In this figure, 1 is a rolled pipe, 2 is a tension detector, 3 is a tension calculator, 4 is a control computer, 5 is a motor controller, 6 is a motor, and 7 is a stretch reducer. Eight of the stretch reducer stands and tension detection device 2 are shown. The tension between the stretch reducer and each stand during rolling is measured by the method proposed by the present applicant and will be described later (Japanese Patent Application No. 59-02711911), and input into the control computer 4. FIG. 4 shows an example of measuring the tension between the stands in the case of the control amount according to the present invention, and there is a clear excess or deficiency in tension at the luminous rear end compared to the center of the tube. Here, the inter-stand tension is compatible with KL shown in equation (1). Further, if the control amount of the longitudinal elongation XL is ΔXL, and the wall thickness control amount is Δt, the following formula (2) holds true.

Δt = f+ (4X L) −(2
) Next, if the deviation between the target tension and the measured tension to obtain the target wall thickness is ΔKL, then ΔX L = f2 (ΔK L )
-(3) The following equation (4) is derived from the above equations (2) and (3).

8t-f, (fz(ΔK L)) = f3(ΔKI
, )...(4) That is, according to the above equation (4), by detecting the deviation ΔKL of the actual measured tension from the target value, the deviation ΔL of the actual wall thickness in the longitudinal direction of the pipe from the target value can be found. .

Next, in the stretch reducer, the wall thickness on the exit side decreases as the upstream stand becomes slower or the downstream stand becomes faster relative to the roll circumferential speed and distribution of each stand.

When the wall thickness of the rolled pipe is the standard (?), the gradient β of the roll circumferential speed of each stand and the deviation Δt from the target value of the finished pipe
' A quantitative relationship as shown in equation (5) below holds true.

β=Cicada (Δt') ... (5) If there is a deviation from the target value of ΔL in the rolled tube, that part should be rolled at the roll circumferential speed gradient of β' shown in equation (8) below. 6 or above, which makes it possible to obtain the target wall thickness, the roll circumferential velocity gradient of each stand of the stretch reducer is determined in accordance with the measured tension, as shown in FIG.

β'=f4(Δt) (8) Note that the target tension shown in FIG. 1 is just one example.

Here, the stretch reducer - the timing of the rolling material biting and bottom removal of each stand can be calculated accurately from the tension measurement signal, and the roll circumferential speed of each stand is determined from the time when the rolled material is biting, and the material bottom is removed according to a time-varying model. Just change the amount until it comes off, <,,=t'''05"c
*hd4f@5[1iaKy"11. In Fig. 5, for example, the roll circumferential speed iJl of the first stand of the stretch reducer can be changed over time like β'. Similarly, for the other stands, The roll circumferential speed may be set according to the roll circumferential speed pattern shown in FIG. 5 between the biting of the rolled material and the end of the roll.

The control computer 4 calculates the above (4) from the longitudinal distribution of tension.
) and formula (6), and during rolling with the stretch reducer 7, the motor 6 of each stand is driven and controlled via the motor control device 5 according to the roll circumferential speed control pattern calculated above. .

The tension detection device I2 that measures the tension T (i) between each stand during stretch reducer rolling will be described in detail below.

That is, in carrying out the present invention, the above-mentioned special consultant
As shown in No.-27999, Figure 6 (A), CB
), a load sensor (load cell) 12 of a rolling type is installed in the upper rail 10 and lower rail 11 of the mill stand, and the roll stand 13 and upper rail l
The force acting between O1 and the lower rail 11 is f4ff! It passes through a detector 12, thereby making it possible to measure the stress in the rolling direction acting on the roll stand 13. A detailed installation diagram of the lower part of the roll stand 13 is shown in FIG. P(+) indicates forward stress, P(-) indicates backward stress, Fig. 6(A), CB
) shows an example in which four load detectors 12 are installed on each roll stand 13. By using four load detectors 12 in this way, vertical and horizontal unbalanced loads can be prevented during rolling. Even under conditions that act on the roll stand 13, it is possible to detect stress in the rolling direction with high accuracy.

That is, the measured values of each load detector 12 of the i-th stand are P (il), P (i2), P (i3) P
(th), the rolling direction stress P(i) acting on the i-th stand is calculated by the following equation (7).

P (i) = P (it) + P'(i2) + P
(i3)+P (i4)...(7) From the above,
Measure the rolling direction stress P(i) of the i-th stand t'T f
Next, a method for calculating the tension of the stand 1111 will be explained with reference to FIG. In this Figure 8,
P (i) is the stress in the rolling direction of the first stand (detector measurement (1), T f (i) is the front tension of the i-th stand, T b (i) is the rear tension of the i-th stand. (A) in the figure shows a case where the material is caught only in the first stand, and the tension acting on the material is zero.In other words, in (A) of Fig. 8, the tip of the material is in the first stand. Second
It is a state between the stands, and its boundary condition is Tf(
1)=Tb(1)=0. CB) in Figure 8 is a state where the tip of the material is between the second stand and the third stand, and the boundary condition is Tf (2) = Tb (+) = 0
．． Tb(2)=Tf(1), and (C
) is the state where the tip of the material is between the third and fourth stands, and the boundary condition is Tf (3) = T b
(1) = 01Tb(2)=Tf(1)Tb(3)
= T f (2), similarly below, under the condition that the tip of the material is between the i-th stand and the i+1-th stand, the boundary conditions shown in the following equations (8) 2 to (10) and equation (11) are satisfied. A balanced formula is established.

Tb(+)=0...(8)Tf(
i)=O...(8) T b (i) = T f (i-1) ・
...(10) P (i) = T f (i) - T b
(i) ... (+1) However, P(i) assumes that the forward stress in the rolling direction is a positive value and the backward stress is a negative value. (8
)2~(10) boundary conditions and rolling direction stress P(1
), the inter-stand tension T (i) between the i-th stand and the i + 1-th stand can be calculated as T (i) = T f (i).

Hereinafter, specific implementation results of the present invention will be explained. Total 2
First half of the stretch reducer consisting of 4 stands 10
As the stand passes through the phosphorescent rear end, the main tube with dimensions of 80.0-■φ It was rolled into a product of t. (Here, φ indicates the outer diameter and t indicates the wall thickness.)
At that time, the transition in the thickness of the crop at the rear end of the luminous area is shown in Figure 9. In Figure 9, the white circles indicate the change in thickness when the control of the present invention is performed, and the black circles indicate the transition in thickness when using the conventional method. It is. The amount of cropping was as shown in Table 1.

Table 1 [Effects of the Invention] As described above, the present invention provides a method for controlling the wall thickness of a tube in a reducing rolling mill consisting of a plurality of roll stands, in which the tension between adjacent stands is actually measured.

The deviation between the measured tension and the target tension at each part in the longitudinal direction of the pipe is calculated, and the rotation speed of the stand that rolls the end of the pipe with the deviation is controlled so that the deviation becomes zero, and the part without the deviation is The rotational speed of the stand used for rolling the material remains at the standard rotational speed. Therefore, according to the present invention, it is possible to substantially reduce the crop length of the luminescent rear end portion. Furthermore, according to the present invention, it is possible to automatically control the tension to always maintain an appropriate tension, and it is also possible to reduce variations in crop length.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the control concept of the present invention, Fig. 2 is a diagram showing the wall thickness distribution of a stretch reducer-finished pipe, and Fig. 3 is a control system diagram showing an example of the control device of the present invention. 4
The figure is a diagram showing the measurement results of tension between stands, Figure 5 is a diagram showing the roll peripheral speed control pattern of each stand, and Figure 6 is a diagram showing the measurement results of tension between stands.
Figure (A) is a front view showing the installation state of the load detector.
Figure (B) is a side sectional view taken along line B-B in Figure 6 (A), Figure 7 is a partially cutaway front view of the load detector in Figure 6 (A), and Figure 8 is FIG. 9 is a schematic diagram showing the relationship between the stress in the rolling direction and the tension between the stands, and FIG. 9 is a diagram showing the thickness state of the luminescent rear end portion according to the present invention. l...Rolled pipe, 2...Tension detection device, 3...Tension calculator, 4...Control computer, 5...Motor control'a
Device. 6...Motor. Agent Patent Attorney Osamu Shiokawa s3 diagram

Claims (2)

[Claims] (1) In a method for controlling the wall thickness of a pipe in a reducing rolling mill consisting of a plurality of roll stands, the tension between adjacent stands is actually measured, the deviation between the measured tension and the target tension at each part in the longitudinal direction of the pipe is calculated, and the The rotation speed of the stand that rolls the tube end portion with the deviation is controlled so that the deviation becomes zero, and the rotation speed of the stand that rolls the portion without the deviation is controlled,
A method for controlling the wall thickness of a pipe in a reducing rolling mill, which is characterized by rolling at a standard rotation speed. (2) A method for controlling the wall thickness of a tube in a reducing rolling mill according to claim 1, wherein the timing of biting and tailing of the tube end with respect to each of the stands is determined by a tension measurement signal.