JPH08309419A - Method for controlling tension in tandem mill for bar for tubing - Google Patents

Abstract

PURPOSE: To uniformize thickness and to improve the quality of a tube and yield by obtaining tension component torque of every stand of a tandem mill for tubing and solving an equation of force acted on the tubing at every stand by using the method of least square. CONSTITUTION: For an (i-1)th stand 3 (#i-1), i-th stand 3 (#1) and (i+1)th stand 3 (#i+1) in the state where the tubing 1 is bitten, rolling torques TLi are calculated based on the number ni of revolution of each roll driving motor M and motor current Iai. The tension component torques are calculated from each of these rolling torques TLi and rolling load P1 detected by a load detector 4, thereby the equations of force is prepared for every stand. By utilizing that the back tension of the most upstream stand by which the tubing 1 is bitten and the front tension of the most downstream stand are respectively zero and solving the equations by the method of least square, the tension between stands is obtained. The tension is compared with the target value and the correction amount of the revolving number of roll at each stand is obtained in accordance with the deviation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the tension of a tandem mill for pipes, which controls the tension or compression force to be applied to the pipes.

[0002]

2. Description of the Related Art In a hot rolling line for seamless pipes, there is a close relationship between the tension or compression force to be applied to the pipe material during rolling and the wall thickness and outer diameter of the pipe material, which is inappropriate. The application of tension or compression force not only causes breakage, perforation, and deformation of the pipe material, but also causes variations in wall thickness and outer diameter. Therefore, appropriate application of tension or compression force to the pipe material is an important issue. Has become. For this reason, various tension control methods such as mandrel mills have been conventionally proposed, but since the detection accuracy of the tension applied to the pipe material during rolling or the compression force itself is low, sufficient tension or compression force control is possible. The current situation is that accuracy has not been obtained.

As a countermeasure against this, the following method (special
(Kaisho 62-244511) has been proposed. That is,
Detection or calculation for each stand i of the tandem rolling mill for pipe materials
Rolling load P _i, Rolling torque TL_iBased on below
Tension component torque TF according to equation (1)_iAnd calculate (2)
As shown in the formula, the stand that bites the pipe material (#J
Tando ~ #K Stand, J ≦ K)
Rear tension F_J-1Taking advantage of the fact that is zero, (3)
According to the formula, the tension applied to the pipe material from the upstream stand in order
Calculate and match the calculated tension with the target tension
This is a method of controlling the roll rotation speed of each stand.

TF _i = (F _i-1 −F _i ) R _i = 2 (TL _i −β _i P _i ) (note that i = J, ..., K) (1) F _J-1 = 0 (( 2) F _i = F _i-1 −TF _i / R _i (note that i = J, ..., K) (3) where F _i : #i stand front tension, R _i : #i stand equivalent roll diameter, β _i : #i stand tension calculation parameter, TL _i : #i stand rolling torque, P _i : #i stand rolling load, TF _i : #i stand tension component torque

[0005]

By the way, in such a conventional control method, since the tension acting on the pipe material is sequentially calculated from the upstream stand to the downstream stand, the error generated in the calculation process is accumulated. In the downstream stand, the accuracy of the tension calculation becomes poor, and the fluctuation of the tube tension caused by the tube material passing through the former stand appears as it is as the fluctuation of the tube tension between the latter stands, so the tension control is performed based on these detected tensions. If this is done, there is a problem that the wall thickness of the pipe material becomes uneven in the longitudinal direction.

The present invention has been made in view of the above circumstances, and an object thereof is to obtain a force balance formula based on a tension component torque for each stand in a tandem mill in which a pipe material is bitten. By using the least squares method to solve these force balance equations, it is possible to accurately calculate the tension acting on the pipe material and to reduce the effect on the pipe material tension fluctuation between the latter stage stands due to the former stage stand-out. It is to provide a tension control method for a tandem mill for pipe materials.

[0007]

A tandem mill tension control method for a pipe material according to the present invention is a tandem mill for controlling a tension on a pipe material by controlling a rotation number of a motor for driving a roll of each of a plurality of stands. In the tension control method of 1), for each stand in a state in which the pipe material is bitten, the tension component torque is obtained based on the rolling load and the rolling torque detected or calculated for each stand, and for each stand based on this tension component torque. Create a balance formula of the force acting on the pipe material, solve this force balance formula by the least squares method, calculate the tension acting on the pipe material, compare it with the target value, and correspond to the deviation of each stand. It is characterized by including a process of obtaining the roll rotation number correction amount of.

[0008]

According to the present invention, a force balance equation is established for each stand in which the pipe material is engaged, and this is solved by the least-squares method to obtain the tension acting on the pipe material for each stand. Is calculated, and the roll rotation speed correction amount is obtained corresponding to the deviation between the tension and the target value, whereby accurate tension calculation and accompanying tension correction can be performed.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings showing the embodiments thereof. FIG. 1 is a block diagram showing a control system for carrying out a tension control method for a tandem mill according to the present invention. In the figure, # i-1, #i, # i + 1 are continuous i-1 stand, i-th stand. Stand, i + 1 stand (i
Is a stand number), 1 is a pipe material, and 2 is a mandrel bar. The pipe material 1 is stretched and rolled by being passed through each stand constituting the mandrel mill from the direction of the arrow with the mandrel bar 2 inserted therein.

Each of the stands # i-1, #i and # i + 1
Each pair of caliber rolls 3 and rolls driving them
A drive motor M is installed, and a load set is provided for each stand.
Load detector (LC) 4 composed of
(Only the # 1 stand is shown in FIG. 1).
Each roll drive motor M has a number of times for detecting its rotation speed.
Turn detector (TG) 5, motor power for roll drive motor M
Flow detector 6 and a roll drive motor M
A turn number regulator (ASR) 7 is attached. Other figures
8 is a rolling torque calculation device, and 9 is a calculation control device.
It First, the rolling torque calculation device 8 is
The number of motor revolutions taken in n _iAnd from the motor current detector 6
Captured motor current I_aiRolling torque TL based on_i
Is calculated and given to the arithmetic and control unit 9.

On the other hand, the arithmetic and control unit 9 has a stand (#J stand to #K stand, J≤, where the pipe material 1 is bitten.
If any one of K) is #i,
Based on the rolling torque TL _{i of} the stand and the rolling load P _i of the stand i detected by the load detector 4, the tension component torque TF _i acting on the #i stand is calculated according to the following equation (4). TF _i = (F _i-1 −F _i ) R _i = 2 (TL _i −β _i P _i ) (where i = J, ..., K) (4) F _J-1 = 0, F _K = 0 Here, F _i-1 : #i stand rear tension, F _i : #i stand front tension, TL _i : #i stand rolling torque, P _i : #i stand rolling load, β _i : #i stand tension calculation parameter , R _i : #i stand equivalent roll diameter

Here, the tension calculation parameter β _i may be calculated (or estimated) using a conventionally known method (method disclosed in Japanese Patent Laid-Open No. 2-217109). Further, since the formula (4) is established for the stand in which the pipe material is bitten, K−
There will be J + 1 balance equations, and F ₀ = ... =
F _J-1 = 0, F _K = ... = F _N = 0 (N: total number of stands)
_Therefore , the variables are _{K- J} of F _J , ..., F _K-1 .
Therefore, the number of balance equations is always increased by one with respect to the number of variables F _i in equation (4). Therefore, the equation (4) is solved according to the least squares method, the front tension F _i of the #i stand is calculated, and this is added and compared with the target tension at the alignment point 10.
PI calculation is performed by the I controller 11, and this is output to the rotation speed adjuster 7 as a control signal. The rotation speed adjuster 7 adjusts the rotation speed of the roll drive motor M in response to the control signal, and corrects the tension on the pipe material 1 so as to match the target value.

Next, the calculation processing steps of the rolling torque calculation device 8 and the calculation control device 9 will be described with reference to the flowchart shown in FIG. FIG. 2 is a flowchart showing a calculation process in the calculation control device 9 and the rolling torque calculation device 8. Now, with the stand in the state where the pipe material 1 is bitten,
#I, load detector 4, for each of these stands
The rolling torque P _i and the rolling torque TL _i are respectively detected or calculated by the rolling torque calculation device 8 (step S1).

Next, in the arithmetic and control unit 9, the stand # is calculated based on the rolling load P _i and the rolling torque TL _i according to the equation (4).
The tension component torque TF _i of _i is calculated (step S
2). The equation (4) representing the relationship between the calculated tension component torque TF _i of the stand #i and the tension acting on the stand #i is calculated according to the following equation. The front tension of all stands #J to #K in the state in which the pipe material 1 is bitten is solved by solving it by using the least squares method by utilizing the fact that the front tension of the most downstream stand that bites the F _{J to} F _k are calculated (step S3). Finally, the calculated tension applied to the pipe material 1 between the stands is compared with a target value, a roll rotation speed correction amount is calculated so as to match this with the target value, and the roll rotation speed is corrected (step S4).

An example of pipe material tension control between stands # 1 and # 2 and between stands # 2 and # 3 when tension control is performed by applying the method of the present invention and the conventional method to a six-stand mandrel mill is shown in FIG. , As shown in FIG. 3 and 4, the horizontal axis represents time and the vertical axis represents tension. In the method of the present invention, as shown in FIG. 3, the fluctuation of the pipe tension between the rear stands due to the removal of the front stand of the pipe material and the like is significantly reduced compared to the conventional method shown in FIG. 4, and the tension control is performed based on this detected tension. It was confirmed that the thickness of the pipe material in the longitudinal direction can be made uniform by performing the above.

On the other hand, in the prior art (Japanese Patent Laid-Open No. 62-2 / 1987).
No. 44511), the tube tension between the stands # 1 to # 2 and the stands # 2 to # 3 is as shown in FIG.
Fluctuations in the pipe material tension (part A in FIG. 4) appear as they are as fluctuations in the pipe tension tension between the rear stands # 2 to # 3 (part A in FIG. 4A). Therefore, as a result of controlling the tension based on the detected tension, it is unavoidable that the wall thickness of the pipe material in the longitudinal direction is not uniform.

[0017]

As described above, according to the method of the present invention, it is possible to accurately detect the tension acting on the pipe material, and reduce the influence of the fluctuation of the pipe material tension caused by the removal of the front stand on the pipe material tension between the rear stands. By controlling the tension based on this pipe material tension value, the tension can be controlled with high accuracy over the entire length of the pipe material, the wall thickness can be made uniform, the pipe quality can be improved, and the yield can be increased. ,
The present invention has excellent effects.

[Brief description of drawings]

FIG. 1 is a block diagram showing a control system for implementing a tension control method for a tandem mill according to the present invention.

FIG. 2 is a flowchart showing a calculation process of a rolling torque calculation device and a calculation control device.

FIG. 3 is a graph showing a control result of tension (compressive force) by the method of the present invention.

FIG. 4 is a graph showing a control result of tension (compressive force) by a conventional method.

[Explanation of symbols]

 1 Tubular Material 2 Mandrel Bar 4 Load Detector 5 Rotation Speed Detector 6 Motor Current Detector 7 Rotation Speed Adjuster 8 Rolling Torque Calculator 9 Calculation Controller

Claims (1)

[Claims] 1. A tension control method for a tandem mill, which controls the tension on a pipe material by controlling the rotational speed of a motor that drives a roll of each of the plurality of stands. The tension component torque is calculated based on the rolling load and rolling torque detected or calculated for each stand, and the balance formula of the force acting on the pipe material is established for each stand based on this tension component torque. The tandem for pipe material is characterized by including a process of solving by the square method to calculate the tension acting on the pipe material, comparing this with a target value, and obtaining the roll rotation speed correction amount of each stand corresponding to the deviation. Mill tension control method.