JPH02235512A - Method for controlling tension of retainer type mandrel mill - Google Patents

Abstract

PURPOSE:To uniformize the wall thickness of a tube stock over the full length by estimating the load torque of a motor at each stand by the current and the number of rotation of a roll driving motor through a specified formula to calculate the correction value for the number of rotation of the roll driving motor. CONSTITUTION:The load torque of the motor at each stand is estimated by the formula I from the current and the number of rotation of the roll driving motor 5 to obtain the average of the motor load torque before the tube stock is bitten by next stand from this estimated value. After the tube stock is bitten by next stand, the difference between the average and the estimated value is obtained, the correction value for the number of rotation of the roll driving motor is calculated by multiplying a coefficient by a deviation motor load torque value to correct the number of rotation of the roll driving motor by this calculated value. In the formula I, Kphi: field strength coefficient of roll driving motor, J: moment of inertia of roll driving system, T0: time constant of smoothing filter, Ia(s): variation of current of motor (expression in area S), n(s): variation of number of rotation of motor (expression in area S), TL(s): variation of load torque of motor (expression in area S), s: Laplace operator.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a tension control method for a caged mandrel mill, and in particular, in a hot rolling line for seamless steel pipes, the tension (or compression) applied to a material to be rolled (tube material) is controlled. The present invention relates to a tension control method for correcting the rotational speed of a roll drive motor so that the rotational speed of a roll drive motor (force) becomes a target value.

A conventional cage-type mandrel mill has a mechanism in which rolling is performed with a mandrel bar inserted into the inner surface of a tube material, and the rear end of the mandrel bar is held by a retainer that moves at a constant speed.

When rolling pipe materials using this caged mandrel mill, in order to make the wall thickness of the pipe materials uniform after rolling, the magnitude of the tension (compressive force) acting in the pipe axis direction between each stand is calculated, and this It is necessary to correct the rotation speed of the roll drive motor so that the calculated value becomes the target value.

On the other hand, in tandem mills for rolling steel bars,
The tension between each stand is measured by a spherical seat load cell, and tension control is performed by correcting the number of rotations of each roll so that the tension (or compressive force) reaches a target value based on this measured value.

However, the spherical seat load cell frequently breaks down and cannot continuously measure tension, so in caged mandrel mill lines, the rotation speed of the roll drive motor is corrected by ribs based on the operator's experience. For this reason, it is difficult to make the wall thickness of the pipe material uniform after rolling.
There is a need for a method of detecting tension and controlling tension during rolling.

Conventionally, as a method to meet such demands, for example, Japanese Patent Application Laid-Open No. 60-221107 discloses a tension detection method in rolling pipe material.

This method detects the rolling load of each stand, calculates the motor load torque by calculating the difference from the motor current, voltage, and rotation speed, and calculates the torque arm during pipe passage from the rolling load, motor load torque, etc. The friction coefficient during rolling is calculated by calculating and correcting the initial friction coefficient between the pipe material between the stands and the mandrel bar, and the pipe material tension (or compressive force) between each stand is calculated based on the detected rolling load and the calculated motor load torque. ) is a method of tension control by correcting the rotation speed so that it approaches the target value.

However, since this method calculates the mill drive motor load torque by differential calculation as described above, it is easily affected by signal noise and has the disadvantage that accurate calculation cannot be performed.

In addition, when calculating the coefficient of friction during rolling, there is a large error because the calculation is performed by calculating only the torque arm during pipe passage, and the torque arm is calculated by sequentially using the torque arms of the upstream stand, so there is an error. is accumulated. For this reason, it is difficult to accurately control the tension, such as errors occurring in the tube material tension (or compression force) during tube passage calculated using the torque arm.

Problems to be Solved by the Invention In view of the above-mentioned actual situation, the present invention has been developed to easily reduce the tension (or compression force) that acts on the pipe material between each stand when rolling the pipe material by a caged mandrel mill. This paper attempts to propose a tension control method for a retainer-type mandrel mill that can accurately detect tension and maintain the detected tension at a target value.

Means for Solving the Problems This invention calculates the motor load torque of each stand by performing calculations after performing measurement noise removal processing without directly performing differential calculation, thereby estimating the motor load torque. Taking into account the increased accuracy, the fact that the tube material to be rolled is heated in a rotary furnace, and the mandrel bar moves at a constant speed, the amount of variation in the motor load torque estimate is equal to the amount of variation in the tube material tension. Noting that they almost corresponded to each other, the tension control accuracy was improved by using the motor load torque estimated value as it was to find the difference from the target value and correcting the motor rotation speed.

That is, in the tension control method for a retainer type mandrel mill according to the present invention, the motor load torque of each stand is estimated from the roll drive motor current Ha and the rotation speed n using the following equation (1), and from the estimated value, the pipe material is Find the average value of the motor load torque until it bites into the stand, and after the next stand pipe bite, find the difference between the average value and the estimated value,
The gist of the present invention is to calculate a roll drive motor rotational speed correction value by multiplying the deviation motor load torque value by a coefficient, and to correct the rotational speed of the roll drive motor using the calculated value to control tension.

Kφ: Roll drive motor field strength coefficient J Moment of inertia of two-roll drive system To = Smoothing filter time constant Ia (S): Motor current variation (expressed in terms of S extinction)
n (s) ; Variation in motor rotation speed (expressed in S domain) TL (S) : Variation in motor load torque (expressed in S domain) S : Laplace operator action According to the above formula (1) By calculating and estimating the motor load torque value of each stand, even if the rotational speed signal contains noise, the differential calculation is performed after noise removal processing, so the differential calculation is always performed with high accuracy. In addition, the accuracy of estimating the motor load torque value is increased.

The tube to be rolled is heated in a rotary furnace, so there are almost no skid marks, and the rear end of the mandrel bar is held by a retainer and moved at a constant speed by a drive motor, so fluctuations in the relative speed between the mandrel bar and the tube can be ignored. Since the amount of variation in the estimated motor load torque value corresponds to the variation m in the hochal canal tension (or compression force), the estimated motor load torque value can be used as is.

When calculating the average motor load torque value until the pipe material bites into the next stand from this estimated motor load torque value, set t to an appropriate time while constantly monitoring the next stand rolling load P(t) (time t). (sec) Previous rolling load P
When the relationship with (t-△t) satisfies the following formula (2),
The average value of the motor load torque for an appropriate period of time Δ1 second before that time is determined.

P (t) - P (t + △1) > σ (σ: arbitrary value)・
...(2) Once the motor load torque average value is determined, the difference from the estimated motor load torque value is calculated, and the roll drive motor of each stand is calculated based on the value obtained by multiplying the deviation amount by an appropriate gain. The rotation speed is corrected and tension control is performed.

Embodiment FIG. 1 is a block diagram showing an embodiment of the present invention.
) is the multi-drying stand A1 of the cage type mandrel mill.
~ Rotation speed regulator installed in each of the 80,
(2) is a load cell that is also placed on multiple stands, (3) is a tube, and (4) is a mandrel bar whose rear end moves at a constant speed in the same direction as the tube (3). It is fixed to a trolley (not shown).

(5) is a mill drive motor, and (6) is an arithmetic control device.

That is, the voltage, current, and motor rotation speed of the mill drive motor (5) of each of the plurality of stands A1 to An are as follows.
Each is measured by a measuring device (not shown) and sent to the arithmetic and control unit (6) at the same timing.

The arithmetic and control unit (6) issues a command to adjust the interval and rotation speed of each mill before rolling the tube so that the wall thickness of the tube after rolling becomes a predetermined thickness, and adjusts the axis of the tube after rolling. Correct the motor rotation speed so that the wall thickness in both directions is uniform.

Next, a method of determining the amount of variation in the tension (or compressive force) of the tube material in each stand during rolling will be explained below.

The rolling torque G of each stand is calculated using the following equation (3).

G1=λ・6a−P1−−Rl(qf1 qb;)+μ
jRi Pi ・
・・・・・・(3) λ: Torque arm coefficient ed: Projected contact length of the reduced outer diameter part R: Effective roll radius μ: Friction coefficient of mandrel bar qb Backward tension (or pressure force) applied to the two pipes qf: Pipe material Forward tension (or compressive force) P applied to: Rolling load: Stand number The left side of the above equation (3) is the load torque of the mill drive motor (5), which is calculated by the following equation (4).

dn G=Kφ− I a 1−y −・−(
4) Kφ 1 Motor field strength coefficient ■a: Motor current n 1 rotation speed J: Moment of inertia The above equation (4) can be used to remove measurement noise as shown in the block diagram shown in Figure 2 without directly performing differential calculation. The calculation is performed after performing the processing for .

FIG. 3 shows the results of calculations based on actual machine data. From this figure, it can be seen that the motor load torque value increases immediately after the bite into the next stand.

Furthermore, the first term on the right side of equation (3) represents the first moment of the rolling load, the second term on the right side represents the tension (or compressive force) acting on the pipe material, and the third term on the right side represents the mandrel bar. (4) represents the frictional force between the pipe material (3).

The first term on the right side is affected by skid marks and the like due to a decrease in the temperature of the tube material (3), but since the tube material is actually heated in a rotary furnace, it is heated evenly and hardly fluctuates.

The third term on the right side is affected by changes in the relative speed between the pipe material (3) and the mandrel bar (4), but since the mandrel bar (4) is held at its rear end by a retainer and is moving at a constant speed, the relative The speed change is very small and hardly fluctuates.

Therefore, the motor load torque fluctuation on the left side corresponds to the pipe material tension (or compression force) fluctuation in the second term on the right side, and the amount of variation in the motor load torque value immediately after the next stand is caught in Fig. 3 is due to the pipe material tension. (or compressive force) fluctuations.

Next, the timing at which the pipe material gets caught in the next stand is detected, and the average value of the motor load torque calculated Δ'L (seconds) before that time T is determined.

Note that the value of ΔT1 is not particularly limited, but is 1
00 (msec)≦ΔT1≦200 (msec
) is appropriate.

The average motor load torque value is stored in the memory, and the difference between it and the estimated motor load torque value is determined.

Then, the calculated load torque deviation amount is used as a deviation signal, and the value is multiplied by an appropriate gain to obtain a rotation speed correction signal, and the rotation speed of the roll drive motor of each stand is corrected to perform tension control.

Effects of the Invention As explained above, according to the method of the invention, the amount of variation in tension (or compression force) acting on the raw pipe between each stand during rolling can be easily and accurately detected and maintained at the target value. This makes it possible to make the wall thickness of the rolled pipe material uniform over the entire length, which is highly effective in manufacturing seamless steel pipes.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a block diagram showing an example of calculation of motor load torque of the invention, and Fig. 3 (A) to (H>) are actual mandrel mill lines. This is a diagram showing an example of calculating the motor load torque from the measurement data of (A> is the rolling load of positive 2 stands, (B
) is the rolling load of the positive 3 stand, (C) is the rolling load of the positive 4 stand, (D) is the rolling load of the positive 5 stand, (E)
is motor load torque of positive 1 stand, (F) is rkL2
The motor load torque of the stand, (G) is the motor load torque of the positive 3 stand, and (H) is the motor load torque of the 111klL4 stand. 1... Rotation speed regulator 2... Load cell 3'
...Pipe material 4...Mandrel bar 5.
...Mill drive motor 6...Arithmetic control device Fig. 1

Claims (1)

[Claims] Rolling with a mandrel bar inserted into the inner surface of the pipe material,
In a cage-type mandrel mill in which the rear end of the mandrel bar is held so as to move at a constant speed, the motor load torque of each stand is estimated using the following formula from the roll drive motor current Ia and rotation speed n, and the estimated value is Find the average value of the motor load torque from the time until the pipe material is caught in the next stand, and after the pipe material is caught in the next stand, find the difference between the average value and the estimated value, and multiply the deviation motor load torque value by a coefficient. 1. A tension control method for a retainer type mandrel mill, comprising calculating a roll drive motor rotation speed correction value, and correcting the rotation speed of the roll drive motor based on the calculated value. T_L(s)(K_φ)/(1+T_O・s)・Ia(
s) - (s/J)/(1+T_O・s)・n(s) K_φ: Roll drive motor field strength coefficient J: Moment of inertia of roll drive system T_O: Time constant of smoothing filter Ia (s): Motor Current variation (expressed in S domain) n(s): Motor rotation speed variation (expressed in S domain) T_L(s): Motor load torque variation (expressed in S domain) s: Laplace operator