JPS5945012A - Method for controlling speed-drooping rate in tandem rolling mill - Google Patents

Abstract

PURPOSE:To prevent surely sheet-break at the time of a low sheet-passing speed without impairing a function for preventing sheet-break at the time of stationary rolling, by correcting continuously a speed-drooping rate in accordance with a rolling speed, and making respectively the speed drooping rates large and small at the times of a low and a high rolling speeds. CONSTITUTION:When a speed drooping rate Zi set by a setting device 12 is 5%, a corrected speed-drooping the Z'i, (=Zi) is 5% till a rolling speed reaches 5% speed (sheet passing speed), from the figure. On the other hand, when the rolling speed exceeds 5%, an output of a correcting-function generating device 14 decreases rapidly to 0.25 at about 60% rolling speed, then the Z'i at this time becomes 1.25%. Because of having said correcting function of the speed-drooping rate depending on the rolling speed, a large drooping characteristic is obtained at the sheet passing speed, and after finishing the passing of sheet, the drooping characteristic is rapidly and continuously decreased with the increase of the rolling speed, thereby the speed of each stand at the time of acceleration is maintained in order. In a state of high speed running, a function of sheet thickness control is secured by the least drooping characteristics capable of absorbing a sudden tension caused by disturbance.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a speed droop rate control method for a tandem rolling mill, and in particular, the droop characteristics are controlled so that the speed of each rolling stand is lower than the set speed by a predetermined speed droop rate. This invention relates to an improvement in a method for controlling the speed droop rate of a tandem rolling mill.

Generally, in a tandem rolling mill, since the rolled material is simultaneously bitten by each rolling stand, it is necessary to keep the speed ratio of each rolling stand constant.

It is desirable that this speed ratio is maintained not only during steady rolling and acceleration/deceleration periods, but also during sheet threading and tailing. However, if speed control is performed at a constant speed ratio for each rolling stand, breakage is likely to occur particularly when the rolled material is a thin plate. Therefore, conventionally, the speed of the rolling mill motor of each rolling stand is lowered by a predetermined speed drooping rate than the set speed, and a regulator is provided to provide drooping characteristics. This prevents plate breakage due to excessive tension caused by preset errors in speed and rolling position during low speed rolling, and also prevents plate breakage due to excessive tension caused by various disturbances during steady rolling. This is to prevent breakage.

The drooping characteristic of the regulator is represented by a speed drooping rate Zi,
Generally, it is defined by the following formula.

Zi=Irate/I×Δv/vTOP×100 [%]
・・・・・・(1) Here, Irate is the rated current (
A), I is the load current (A), Δv is the speed drop due to the speed droop rate (rpm), vTOP is the rated maximum speed (r
pm).

Normally, the speed drooping rate Zi is set arbitrarily to avoid rolling troubles, but providing such a drooping characteristic requires the automatic speed control system (A) of each rolling stand.
This causes a shift in the response speed of the SR system (referred to as the SR system), and
This is undesirable because it slows down the response speed of the ASR system itself, causes tension disturbances due to deviations in speed uniformity immediately after adjustment, and causes sheet pressure fluctuations due to deterioration of sheet pressure controllability during steady rolling.

In other words, when the cross-sectional area of the rolled material is A and the speed is V, there is a relationship between the speed variation ΔV and the tension variation ΔT as shown in the following equation, and tension disturbances due to deviations in speed uniformity are arise.

ΔT/A∝ΔT/V (2) Also, let the set speed of the i-th rolling stand (hereinafter referred to as the i-th stand) be vi, and the advance rate be fi. Then, there is a constant mass flow relationship between the outlet side plate pressure hi of the i-th stand and the speed drop Δvi due to the speed droop rate Zi, as shown in the following equation, and when the speed drop Δvi changes, the outlet side plate pressure hi also changes.

hi(vi-Δvi)・(1+fi)=constant...
・(3) On the other hand, in order to eliminate the above-mentioned drawbacks, as shown in Japanese Patent Publication No. 57-9886, rolling is carried out by setting the speed droop rate of the tandem rolling mill to zero at the front stage stand and almost zero at the rear stage stand. A method of controlling the speed of a tandem rolling mill for rolling thin plates has been proposed, which is characterized in that the speed drooping rate is automatically increased above the speed drooping rate when the rolling mill is started.

However, this method changes the speed droop rate in a sequence control manner only at startup, and is particularly aimed at preventing plate breakage due to excessive tension caused by errors in speed setting and rolling position setting during steady rolling. , speed droop rate cannot perform its original function.

In addition, with this method, which reduces the speed droop rate in a sequential manner, the responsiveness of the speed control system changes suddenly at the point where the speed droop rate changes, which causes disturbances to tension control and plate thickness control, which is undesirable. It had the following problems.

The present invention has been made in order to eliminate the above-mentioned conventional drawbacks, and is capable of preventing plate breakage at low speeds, including when starting and stopping a rolling mill, without impairing the plate breakage prevention function due to the rate of speed droop during steady rolling. An object of the present invention is to provide a speed drooping rate control method for a tandem rolling mill, which can reliably prevent the above-mentioned speed droop rate and which does not cause disturbance to tension control or plate thickness control due to a change in the speed droop rate.

The present invention provides a speed droop rate control method for a tandem rolling mill in which the speed of each rolling stand is controlled with a drooping characteristic so that the speed is lower than the set speed by a predetermined speed droop rate. The drooping rate is continuously corrected according to the rolling speed so that the speed drooping rate is large at low speeds including starting and stopping the rolling mill, and small at high speeds. The purpose has been achieved.

Further, the speed drooping rate is exponentially corrected according to the rolling speed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a speed control device for a tandem rolling mill, in which the method for controlling the speed drooping rate of a tandem rolling mill according to the present invention is adopted, will be described in detail below with reference to the drawings.

As shown in FIG. 1, this embodiment includes a speed setting device 10 for setting a set speed vi of the rolling stand, and a speed drooping device 10 for manually setting the speed drooping rate Zi of the rolling stand. A rate setting device 12 and a correction for generating a speed drooping rate correction coefficient for continuously correcting the speed drooping rate Zi of the speed drooping rate setting device 12 output according to the set speed vi of the speed setting device 10 output. Function generator 14
and a speed drooping rate that is continuously corrected according to the rolling speed by multiplying the speed drooping rate correction coefficient output from the correction function generator 14 by the speed drooping rate Zi output from the speed drooping rate setting device 12. a multiplier 16 for obtaining Z'i; a speed detector 2 for detecting the pattern of the set speed vi of the output of the speed setter 10 and the rotational speed of the rolling mill drive motor 18;
The variable voltage power source of the rolling mill driving motor 18 is adjusted so that the speed feedback signal of 0 output and the speed drooping rate Zi' corrected according to the rolling speed of the multiplier 16 output are compared, and the deviation becomes zero. Thyristor device 2 that constitutes
2, and an ASR system 24 that controls the 2.

The correction function generator 14 is configured to generate a speed drooping rate correction coefficient that decreases exponentially in accordance with the rolling speed, as shown in FIG. 2, for example.

Further, the ASR system 24, as shown in FIG.
A speed drop obtained from the set speed vi of the output of the speed setter 10 by multiplying the current command I of the output speed control device 28 by the speed droop rate Zi' of the output of the multiplier 16 using the multiplier 30. Minus Δv (vi - Δv
i) and the speed feedback signal output from the speed detector 20;
A speed control device 28 that produces a current command I according to an output deviation signal, a current control device 32 and a current rate control device that control the thyristor device 22 according to the current command I output from the speed control device 28. It is composed of 34. This ASR system 24 can be configured using, for example, a direct digital control method (referred to as a DDC method).

The action will be explained below.

Now, the speed drooping rate Zi set by the speed drooping rate setting device 12
If the rolling speed is 5%, from Figure 2, the rolling speed is 5%.
Until the speed (sheet threading speed) is reached, the corrected speed drooping rate Zi' (=Zi) is 5%. On the other hand, the rolling speed is 5
% speed or higher, the output of the correction function generator 14 suddenly decreases to 0.25 at about 60% speed, so the corrected speed droop rate Zi' at this time is 1.25%.

By having such a correction function of the speed droop rate depending on the rolling speed, a large drooping characteristic can be provided at the time of sheet threading, and after the sheet threading is completed (for example, after winding on a tension reel),
As the rolling speed increases, the drooping characteristics are rapidly and continuously reduced, maintaining the uniform speed of each rolling stand during acceleration, and under high-speed operating conditions, the drooping characteristics are reduced rapidly and continuously. The drooping characteristics ensure plate thickness control performance.

In this embodiment, since the ASR system 24 is constructed using the DDC method, precise control can be easily realized. Note that the configuration of the ASR system 24 is not limited to this, and may be configured as a normal speed control system.

In the embodiment described above, the set value of the speed droop rate was manually set using the speed droop rate setting device 12, but the method of setting the speed droop rate is not limited to this. It is also possible to configure the settings so that they are automatically set externally using a preset computer.

As explained above, according to the present invention, it is possible to reliably prevent plate breakage during low speed rolling without impairing the plate breakage prevention function due to the speed droop rate during steady rolling.
Moreover, it has an excellent effect in that the tension control and plate thickness control are not disturbed by changes in the speed drooping rate.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of a speed control device for a rolling mill in which the speed droop rate control method for a tandem rolling mill according to the present invention is adopted, and FIG. FIG. 3 is a diagram illustrating an example of the relationship between rolling speed and speed drooping rate correction coefficient in the correction function generator according to the present invention. 10... Speed setting device, 12... Speed droop rate setting device,
14... Correction function generator, 16... Multiplier, 18.
...Rolling mill drive motor, 20...Speed detector, 22
...Thyristor device, 24...ASR system, 26...
- Adder, 28... Speed control device, 30... Multiplier, 32... Current control device, 34... Current rate control device. Agent Satoshi Takaya (and 1 other person)

Claims (2)

[Claims] 1. In a method for controlling a speed drooping rate of a tandem rolling mill, the speed of each rolling stand is controlled with a drooping characteristic so that the speed is lower than a set temperature by a predetermined speed drooping rate. A tandem characterized in that the speed drooping rate is continuously corrected according to the rolling speed so that the rate of speed droop is large at low speeds including starting and stopping the rolling mill, and small at high speeds. A method for controlling the speed droop rate of a rolling mill. 2. The speed droop rate control method for a tandem rolling mill according to claim 1, wherein the speed droop rate is corrected exponentially depending on the rolling speed.