JPS62192210A - Method for controlling tube wall thickness for reducing mill - Google Patents

Abstract

PURPOSE:To make a tube wall thickness in the longitudinal direction uniform and to improve the yield by setting the target tension at each stand at realtime in accordance with variations in wall thickness and outer diameter of a tube stock and in tension at upstream stands. CONSTITUTION:The wall thickness and outer diameter of a tube stock 3 is obtained based on a spring back amount detected by load cells 10 and 11 at stands 5, 6, and 7 of a mandrel mill 2. When a tube stock 4 is bitten by rolls of a stand 1 of a stretch reducer 1, a wall thickness in the outlet side of the stand 1 is obtained based on an outer diameter and a wall thickness of the tube stock 4 in the inlet side of the stand 1. Next, the target unit tension between the stands 1 and 2 is set by obtaining the target stretch coefficient of the stands 1 and 2 based on the wall thickness in the outlet side of the stand 1 when the tube stock 4 is bitten by rolls of the stand 2. A unit tension of a measured tension between the stands 1 and 2 gotten by a simultaneous load detector 13 is obtained. Then, a difference between the target unit tension and the measured unit tension is adjusted to be zero by a roll circumferential speed of the stand 1.

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] A reduction rolling mill (stretch reducer) usually has a
Consisting of stands, typically 5 to 7 per stand
The outer diameter of the product is fixed by reducing the outer diameter by reducing the outer diameter by 50%, and at the same time, the number of rotations of the rolls of each stand is set to generate tension between the stands to process the wall thickness.

If the slope of the roll circumferential speed leading to the No. 1 to No. n stands (No. n: the final stand number used for rolling) is made steeper, the tension between the stands will become stronger, the product thickness will become thinner, and It is well known that if the slope is loosened and the tension between each stand is reduced, the product wall thickness will be thicker.

As a method for controlling the wall thickness of a tube in a stretch reducer, for example, as disclosed in Japanese Patent Application No. 58-227988 filed by Mizu Applicant, a target tension is set in advance for each roll stand, and the difference between this target tension and the measured tension is There is a method of controlling the roll rotation speed so that the deviation is zero.

Furthermore, the method disclosed in JP-A No. 52-83147 increases or decreases the wall thickness by increasing or decreasing the tension by accelerating or decelerating the roll circumferential speed of each stand based on the wall thickness distribution in the longitudinal direction of the raw tube. This is a method of controlling

[Problems to be Solved by the Invention] However, according to the method disclosed in Japanese Patent Application No. 59-227988, the target tension must be set in advance for each stand, but the target tension is originally based on the flesh of the raw pipe. It is difficult to make the wall thickness uniform in the longitudinal direction of the tube after rolling unless the thickness, outer diameter, tension at the upstream stand, etc., in other words, are appropriately changed according to variations in the entrance wall thickness of each stand. .

Furthermore, the method of JP-A-52-83147 cannot deal with variations in tension between each stand that occur when rolling a pipe with a stretch reducer, and it is also difficult to make the wall thickness uniform in the longitudinal direction of the pipe. Can not.

The present invention was developed as a result of studies to solve such problems, and it sets the target tension of each stand in real time according to the wall thickness and outer diameter of the raw pipe and the fluctuations in tension at the upstream stand. The purpose of this is to make the wall thickness of the pipe uniform in the longitudinal direction.

[Means for Solving the Problems] The present invention provides a method for controlling the wall thickness of a pipe in a reducing rolling mill comprising a plurality of roll stands, in which (a) the wall thickness and outer diameter of the raw pipe on the entry side of the reducing rolling mill are controlled; 1st step of continuously measuring (b) 2nd step of continuously measuring the tension between each stand (c) 3rd step of tracking the wall thickness on the outlet side of the upstream stand to the inlet side of the stand in synchronization with the pipe speed Step (d) Calculate the wall thickness on the exit side of each stand based on the results of the first, second, and third steps Fourth step (e) Calculate the wall thickness on the exit side obtained in the fourth step as follows. A fifth step (f) of feeding forward to the stands, determining a target stretch coefficient for each stand, and calculating a target tension between each stand based on the target stretch coefficient.The target tension determined from the fifth step and the second step. 6th step (g) of calculating the deviation of the measured tension of the 7th step (h) of calculating the amount of correction of the roll circumferential speed from the deviation obtained in the 6th step; based on the amount of correction of the roll circumferential speed obtained in the 7th step. The eighth step is to control the circumferential speed of the roll of the stand.

[Function] Hereinafter, the function of the present invention will be explained with reference to FIGS. 1 and 3.

In FIG. 1, 2 is a mandrel mill for forming the raw pipe 3 of the stretch reducer 1.

10 is a load cell installed in the thick finishing stand of the mandrel mill 2, in this example #5 and #6 stands, and measures the wall thickness of the raw pipe 3 by capturing the springback amount of the #5 and #6 stands. do.

11 is a load cell installed on the outer diameter finishing stand, in this example #7 stand, 12 is a bulge meter installed on the exit side of #7 stand, and from the load cell 11 and bulge meter 12, the output side of mandrel mill 2 is Measure the outer diameter of the raw pipe 3.

13 is a load detector installed in each stand of the stretch reducer 1, and detects the tension between each adjacent stand. 4 shows the tube rolled at each stand of the stretch reducer.

5 receives the signals of the wall thickness and outer diameter of the raw pipe 3 and the signals of the load detector 13 of each stand of the stretch reducer l, sets the target tension between each stand, and controls the roll circumferential speed. It is a computing device.

The control flowchart of the arithmetic unit 5 shown in FIG. 3 will now be described.

When the tube 4 is caught in the roll of the #l stand of the stretch reducer 1, the #1 stand is The exit wall thickness (tl) is determined.

When tube 4 is caught in the roll of #2 stand, #
Determine the target stretch coefficient (Zal, Z a2) of #1.2 stand from the exit side wall thickness (tl) of stand #1.
1. Set the target unit tension (τal) between stands #2. #l and #2 obtained from the load detector 13 at the same time
Find the unit tension (τ1) of the measured tension between the stands,
The difference between the target unit tension and the measured unit tension is adjusted to zero by the roll peripheral speed of the #1 stand. In this way, when the tube 4 is caught in the roll of the #i+1 stand, the thickness of the #1~i1~l stand (tl~
#1~i1~l stand stretch coefficient (2
1~Z ai+1) and between #1 and #2 stands~#
Target unit tension (τ
at~τai). At the same time, the unit tension (τ1~
The difference (Δ
τ1 to Δτi) are adjusted to zero by #1 to #i1 to #l stand peripheral speeds.

[Example] Hereinafter, the present invention will be explained in detail for each step.

(a) First step of measuring the wall thickness and outer diameter of the raw pipe.

As shown in FIG. 1, the thick finishing stand of mandrel mill 2, in this example #5. The springback amount of the #5 stand is calculated using the load cell 10 (load meter), the initial setting value between the rolls of each stand is added thereto, and the mandrel bar diameter is subtracted from that value to obtain wall thickness x 2. The outer diameter measurement is done on the outer diameter finishing stand, in this example #
Using the bulge gauge 12 located downstream of stand #7, we know the length of the raw tube, calculate the springback amount of stand #7 using load cell (load meter) 11, and add the initial roll-to-roll setting value of stand #7 to it. Then, the short axis of the raw pipe is known, and the average value of the outer diameter of the ellipse is determined from the long axis and the short axis of the raw pipe. The outputs of the wall thickness and outer diameter thus obtained are input to the calculator 5.

(b) Second step of actually measuring the tension between each stand.

As disclosed in Japanese Patent Application Laid-open No. 80-174207 by the present applicant, a load detector 1 is installed between the mill stand and the roll stand.
3 is installed, and the load detector 13 measures the stress in the rolling direction acting on the roll stand and the stress in the rolling direction acting on each adjacent roll stand. From the mutual relationship, the stress between the adjacent roll stands is measured. Find the tension. The output obtained thereby is input to the arithmetic unit 5.

(c) A third step of tracking the wall thickness on the outlet side of the upstream stand to the inlet side of the stand in synchronization with the pipe speed.

#il The output signal of the outlet side wall thickness ti of the stand pipe 4 (the thickness calculation formula is shown in the next section) is input to the calculator 5, and is tracked in synchronization with the rolling speed of the pipe 4, so that the wall thickness ti is #i
When it is caught in the roll of the +1 stand, the arithmetic unit 5 outputs a signal multiplied by the wall thickness ti. Generally, if the #il stand exit pipe speed Vi is Hi, the tracking time Hi
is 19=mu=/V, t...
It is expressed as (2).

In addition, Ha is calculated as follows.

and Mii =/! −Maru=〈Snake! 1oi-(rl-?Qi hit 800.仝) However, a'lθi, d'-
Pri is a value obtained from equation (11) shown in the next section.

Here, α: forward tension influence coefficient, β: rear tension influence coefficient, γ: elongation influence coefficient, subscript tree: value at lock-on.

Note that the symbols used in the above and below explanations are defined as follows. The main items are shown in Figure 2.

t: Exit side wall thickness, te: Inlet side wall thickness, D: Exit side outer diameter, De
: Inlet outside diameter, T: Tension, τ: Tension per unit surface area (
uni/) tension), Z: stretch coefficient, σ cross: stress in tube axis direction, kf: deformation resistance, input: wall thickness/outer diameter ratio 1. S'
9. : Pipe axial logarithmic strain, deθ: Tangential logarithmic strain, fr: Radial logarithmic strain, υT: Roll circumferential speed, J
= advance rate, ε: elongation subscript i: #i stand, o: reference value, d: deviation from reference value, a: target value, Δ:: correction amount from current value, (d) first step, A fourth step of calculating the wall thickness on the exit side of each stand based on the results of the second and third steps.

The outer diameter (Del) and wall thickness (te) of the raw pipe 3 in the first step
l) and the inter-stand tension T1 from the load detector 13 in the second step to calculate the exit side wall thickness ti of the #i stand, and the calculation formula is shown below. The wall thickness ti obtained from the calculation formula is set as the entry side wall thickness (tei÷1) of the #i+1 stand by tracking in the third step.

1i = tQ,, -ef'yi

,,,(lo)(6)~(lO) In the equations, Zi,
Since there are 5 equations with input i, '/θi, 'j' ri, and ti, it is not unsolvable as is, but since it is nonlinear, it becomes quite complicated. Therefore, the following criteria are used. Linearize around a value.

From formula (11), find dti, zul=zuonojulji
61. From (I2), the thickness of the exit side of the #i stand is determined. Note that the tension on the entry side of #1 stand is usually 0.
'', so TO=0, dTo=o Furthermore, in the stretch reducer, the variation in the outer diameter on the exit side of each stand is practically negligible, so dDei=0 (however, i
#1).

(e) A fifth step in which the exit wall thickness obtained in the fourth step is fed forward to the next stand, a target stretch coefficient for each stand is determined, and a target tension between each stand is calculated based on the target stretch coefficient. Process.

To set the exit wall thickness ti obtained in the fourth step to the target value (
12) Formula nioite, dti=O)-Lteti=to
Let it be i. When formulating (11) as d ti = O, formula (13) is obtained.

Then, Zai becomes a target stretch coefficient such that the exit wall thickness of each stand becomes the target value.Next, based on this target stretch coefficient, the target value of the tension between each stand is calculated. Here, if we consider the case where tube 4 is being rolled on stands #1 to #n, from equation (6), the number is n and the unit tension, which is the manipulated variable, is n-1, so all This indicates the error since the stretch coefficient cannot be set to the target value.

Here, vV: weighting coefficient matrix, and subscript T: transposed matrix.

(f) A sixth step of calculating the deviation between the target tension of the fifth step and the measured tension of the second step.

For each stand, the deviation between the target tension (unit tension) obtained by equation (17) and the measured tension (unit tension) obtained in the second step is calculated.

(g) A seventh step of calculating a correction amount of the roll circumferential speed from the deviation obtained in the sixth step.

The relationship between the tension deviation and the roll circumferential speed correction amount determined by the calculation formulas shown in equations (18) to (23) is calculated.

In general, E: Young's modulus, L: distance between stands, b = backward movement rate, where υ
If ri is changed by Δυri, in equation (5), as a practical equation and No.
z2) From equations (18), (20), and (22), however, use the S nila plus operator. Here, each term in equation (23) is replaced as follows. However, since we are considering the case where the frequency is -0, we set S=0.

≠W~-)AL, it-t-(2 cycles) Now, considering the case where the pipe is being rolled on stands #1 to #n, from equation (23), it is expressed as follows.From equation (28), mu ℃ Da = jl-'A ・Δd
-1-[3°) (h) Eighth step of controlling the roll circumferential speed of the stand based on the roll circumferential speed correction amount obtained in the seventh step.

In the first stage, the roll standard peripheral speed for each stand is
The roll circumferential speed on an execution basis is obtained by adding the roll circumferential speed correction amount for each stand determined in the process.

In the second stage, the execution base roll peripheral speed of the first stage is set as the roll reference peripheral speed, and the result obtained by adding the roll peripheral speed correction amount obtained in the seventh step is set as the next execution base roll peripheral speed.

In this way, the roll peripheral speed of the stand is controlled one after another in real time based on the roll correction peripheral speed instruction from the seventh step.

Hereinafter, embodiments of the present invention will be specifically described based on FIG.

In the rolling process in the mandrel mill 2, the raw tube 3 whose wall thickness tel and outer diameter Del have been measured (the measuring method is as described above) is rolled by the rolls of the stretch reducer 1. At the time when it is bitten by the roll of the #1 stand with a gap set, the target stretch coefficient Zal of the #1 stand is determined from the wall thickness tel and the outer diameter Del of the raw pipe 3 from equations (13) and (14). Furthermore, the wall thickness t1 on the exit side of the #1 stand is determined based on equation (11). Note that since the tension on the entrance side of #1 stand is zero, TI = 0. dT=0°Next, when the pipe 4 was caught in the #2 stand roll, the outlet wall thickness t1 of the #l stand was tracked to the #2 stand in synchronization with the pipe fastening door of the #l stand. 2 stand entrance wall thickness te
2, the target stretch coefficient Za2 of #2 stand is (1
3), the wall thickness te of the above-mentioned raw pipe 3 is obtained from formula (14).
The target stretch coefficient Zal of the #1 stand is obtained from equations (13) and (14) from l and outer diameter Del, and τa1 is obtained from equation (17) from this Zal and Za2. At the same time #1
The actually measured unit tension τ1 is calculated from the actually measured tension T1 between the #2 stand and the deviation Δτl between this τa1 and τl. From this △τ1, the roll correction circumferential speed Δυr1 is (3
0) to control the roll circumferential speed of the #1 stand.

In addition, the exit wall thickness t2 of the #2 stand is the above τ1 and te.
2 to equation (11).

In this way, τi and τai are sequentially calculated in the same manner from the #3 stand onwards, and the roll corrected circumferential speed Δυri is calculated from this deviation Δτi, thereby controlling the roll circumferential speed of the #i stand.

As described above, the wall thickness on the outlet side of the upstream stand is tracked up to the inlet side of the stand in synchronization with the pipe speed, the target stretch coefficient is calculated from the wall thickness on the outlet side of the upstream stand, and the target tension is set from there. The difference between this and the measured tension is determined to correct the roll circumferential speed of the stand. In this way, by setting the target tension of each stand in real time, the wall thickness in the longitudinal direction of the pipe can be made uniform.

FIG. 4 shows the wall thickness distribution in the longitudinal direction of pipes having an outer diameter of 80.3 mm and a fat wall thickness of 4.88 layers rolled by the conventional method and the stretch reducer according to the present invention. According to FIG. 4, it is recognized that the wall thickness is made uniform by the present invention.

[Effects of the Invention] The present invention sets the target tension of each stand in real time according to changes in the wall thickness and outer diameter of the raw pipe and the tension in the upstream stand, and makes it possible to reduce the deviation between the target tension and the measured tension to zero. By increasing or decreasing the circumferential speed of the rolls, the wall thickness in the longitudinal direction of the pipe can be made uniform. Therefore, by obtaining a stable wall thickness of the tube according to the present invention, it is possible to improve the number of good products.

[Brief explanation of drawings]

FIG. 1 is a layout diagram showing a rolling line used in carrying out the present invention, FIG. 2 is a schematic diagram showing the rolling state according to the present invention, FIG. FIG. 3 is a diagram comparing and showing wall thickness distributions according to the invention and a conventional method. 1... Stretch reducer, 3... Main pipe, 4...
- Pipe, 5... Computing unit, 1O111, 13... Load cell, 12... Bulge meter. Agent Patent Attorney Osamu Shiokawa 4th Length from tip [) Length from rear end b) Length 1)

Claims (1)

[Scope of Claims] A method for controlling the wall thickness of a pipe in a reducing rolling mill comprising a plurality of roll stands, including (a) a first step of continuously measuring the wall thickness and outer diameter of the raw pipe on the entry side of the reducing rolling mill; (b) a second step of continuously measuring the tension between each stand; (c) a third step of tracking the wall thickness on the outlet side of the upstream stand to the inlet side of the stand in synchronization with the pipe speed; (d) a first step; Based on the results of the second and third steps, the wall thickness on the outlet side of each stand is calculated. (e) The outlet side wall thickness obtained in the fourth step is fed forward to the next stand, and each A fifth step (f) of determining the target stretch coefficient of the stand and calculating the target tension between each stand based on the target stretch coefficient. Calculating the deviation between the target tension determined in the fifth step and the actual tension in the second step. 6th step (g) Calculate the roll circumferential speed correction amount from the deviation obtained in the 6th step. 7th step (h) Calculate the roll circumferential speed of the stand based on the roll circumferential speed correction amount obtained in the 7th step. A method for controlling the wall thickness of a pipe in a reducing rolling mill, characterized by comprising each step of the eighth controlling step.