JPH0219726B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to start-up control of a tandem rolling mill, and particularly to start-up control when the mill stops with rolled material in the stand of the tandem rolling mill. Regarding.

[Conventional technology]

When restarting a tandem rolling mill after stopping, the static friction coefficient of the back-up roll bearing is different for each stand, the backlash of the reducer between the mill motor and the rolls is different for each stand, and the static error and response of the speed control system. A large abnormal tension is generated in the rolled material between each stand due to the following reasons: the coefficient of friction between the strip and the roll increases at low speeds, and the thickness of the morgoil oil film becomes thinner at low speeds. , which induces plate rupture.

Among the causes of this abnormal tension generation, ~ appears as variations in the start timing when starting the mill, and accounts for nearly 80% of the abnormal tension generation.

Methods for reducing this abnormal tension at startup include reducing the bearing friction of the back-up roll shown in Figures 1a and 1b, and reducing the droop rate D in the speed control system 7 shown in Figure 2. Methods for increasing the size have been known for a long time, and some of them have been implemented.

FIG. 1a shows a bearing section in which all the bearings 2 of the back-up roll 1 are roller bearings 3 to reduce the static friction of the bearings.

Figure 1b shows that a hydrostatic device 4 is installed on the bearing 2 of a back-up roll 1 using a plain bearing 5, and when restarting a roll that has been stopped for a long time and the friction of the bearing has increased, lubrication is provided from the bottom of the bearing. A bearing section is shown in which oil is ejected toward the sliding bearing 5 to lift the sliding bearing 5 and bring the bearing surface into a state of fluid lubrication to reduce bearing friction.

FIG. 2 shows a device configuration in which a droop rate circuit 8 is added to the speed control system 7 to prevent the occurrence of abnormal tension T'. A rolled material 6 being rolled with a constant tension T is located between the i stand and the i+1 stand driven by the speed control systems 7i and 7i ₊ 1. Without the droop rate circuit 8, if an abnormal tension T'(T'>T) is applied to the rolled material 6, the abnormal tension T' will not be corrected because the speeds of the rolls of stands i and i+1 are controlled.
Induces plate breakage within a short period of time. Therefore, a droop rate circuit 8 is added to the speed control system 7 of an actual rolling mill to take measures to prevent this.

The function of this droop rate circuit 8 will be explained with reference to FIG. When abnormal tension T' occurs in the rolled material 6 between the i stand and the i+1 stand, the current I of the roll drive motor of the i+1 stand increases. Accordingly, the abnormal tension generated in the rolled material 6 by lowering the roll speed by Δn than the speed at constant rolling tension T
Prevent the occurrence of T′.

[Problem to be solved by the invention]

Among these methods of reducing abnormal tension T', method 1a
The method shown in the figure cannot cope with high-pressure rolling or high-speed rolling, and cannot cope with improvement in operability. The method shown in Fig. 1b has the problem that it becomes extremely difficult to manage the roll bearings, resulting in poor maintainability and workability.Furthermore, the method of adding the droop rate circuit 8 shown in Fig. 2 has the problem that the droop rate D is If it is made too large, the target value of the product board thickness cannot be obtained, and the problem of increased off-gauge appears contrary to the purpose of preventing the occurrence of abnormal tension T'. Moreover, this droop rate circuit 8 is
This is effective in suppressing abnormal tension T' while the roll is rotating, but when restarting the roll while the friction of the sliding bearing 5 is large, a large current is applied to the roll drive motor, which causes the roll to start up even more. An abnormal tension T' is generated in the rolled material 6 between the stand and the stand that rotates quickly.

The present invention aims to align the starting timing of the work rolls of each stand and improve the uniform speed of the work rolls of each stand immediately after starting the work rolls, thereby improving the rethreading property of the rolled material in the stands. purpose.

[Means to solve the problem]

After examining various causes of the abnormal tension T' when restarting the mill, we found that from the stopped state until just after the work roll starts rotating, there is a difference in the backlash (play) of the power transmission mechanism from the mill motor to the work roll of each stand, One cause is that the timing from starting the mill motor of each stand to starting the work roll varies due to differences in the friction of the sliding bearing 5 of the back-up roll. The inventors have discovered that one of the causes of the acceleration up to the sheet threading speed is the uneven startup of the work roll rotational speeds of each stand.

Therefore, in the present invention, when starting the mill motor of the work roll of each stand of the tandem rolling mill with the rolled material placed between the stands, the mill motor is started and the power transmission mechanism is transmitted between the mill motor and the work roll. After the delay time, the work rolls are started by applying a pulsed current to the mill motor to give the rolls a pulsed starting torque that overcomes the large static friction of the back-up roll bearings of each mill. The droop rate is set to virtually zero, and after the work roll starts, a droop rate larger than normal is given to each mill motor until the specified threading speed is reached to balance the tension generated by changes in the speed ratio of each stand. .

[Effect]

As mentioned above, the mill motor current is increased to start the work roll after the power transmission mechanism delay time between the mill motor and the work roll after starting the mill motor, so each stand The power transmission mechanism from the mill motor to the work roll is configured to transmit power to the work roll without delay due to the rotation of the mill motor. This eliminates differences in work roll starting timing due to differences in backlash of the power transmission mechanisms of the respective mills.

When starting the work rolls, as mentioned above, a pulsed current is applied to the mill motor to provide the work rolls with a pulsed starting torque that overcomes the large static friction of the back-up roll bearings in each mill. Therefore, the work rolls of each mill are started quickly, and the difference in start timing of work rolls between mills is small. Since the droop rate of each mill motor is set to substantially zero when the work rolls are started, the rotational speed of the mill motors is not reduced due to an increase in the load current of the mill motors when the work rolls are started. Work rolls start up and speed up quickly.

After starting the work rolls in this way, as mentioned above, each mill motor gives a larger droop rate than usual until the predetermined sheet threading speed is reached, so the tension in the rolled material is reduced due to the difference in work roll start-up speed between each mill. When the tension increases, the speed of the mill motor whose rotational load (load current) increases due to this tension decreases, thereby suppressing the increase in tension. In other words, uniform speed among mills immediately after starting the work rolls is improved.

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.

〔Example〕

The inventors of the present invention investigated speed variations and occurrence of abnormal tension through various on-site experiments, and found that the start-up time of the work roll depends on the lubrication state of the back-up roll sliding bearing 5, that is, the magnitude of the static friction coefficient. It was found that the time varies by about 0.1 to 0.3 seconds. As an example, Fig. 4 shows the relationship between speed variation and tension when a plate breaks, and Fig. 5 shows the rolling force applied to the rolls of the stand to determine the relationship between the lubrication state of the sliding bearing 5 and the required starting torque. An example of the current value required to start the roll according to the difference in stopping time after stopping the roll by adding .

As shown in Figure 5, due to the difference in the lubrication state of the back-up roll plain bearing 5, the required torque to start the work roll changes from 2000A to 8000A in terms of the motor current for driving the work roll, and this difference causes a variation of 6000A. I found out.

The current rise in the conventional speed control system 7 is slow at tens of thousands of amperes/second, so if the lubricating state of the sliding bearing 5 varies by 6000 A in current, the start timing t of the work rolls of each stand will differ. .

This variation t in startup timing generates abnormal tension T' in the rolled material 6 between the stands, and furthermore, the disturbance in uniform speed between the stands after work roll startup promotes the increase in abnormal tension T' and induces plate breakage. It is something that makes you

In order to implement the present invention in one embodiment, a speed control system 7 of a tandem rolling mill to which a startup control circuit 14 is added
is constructed as shown in FIG.

That is, the speed control system 7 includes a rotary generator 23 that detects the rotation of the work roll drive motor 22;
An adder 18 compares the signal F of the rotary generator 23 and the speed command signal R and outputs the difference between them, and compares the output of this adder 18 with the output signal D of the droop rate circuit 8 and outputs the difference between them. A speed control amplifier 9 converts the output signal of this adder 19 into a current command, the output signal of this speed control amplifier 9 is used as a current command signal I _R , and this signal I _R is used as a starting current circuit 14 An adder 20 adds the signal _Ip from
Current control amplifier 10, voltage command signal to be changed to V _R
An adder 21 that compares V _R and voltage feedback signal V _F and outputs the difference between them;
Voltage control amplifier 1 that controls the voltage by the output signal of
1, a pulse generator 12 which generates a firing pulse for the thyristor according to its signal, and a thyristor 13.

The starting control circuit 14 also includes a starting current setting device 15 that determines the peak value of the pulsed current, and a backlash absorbing device that prevents sudden impact force from being applied to a machine with backlash such as a reducer due to the pulsed current. timer 1
6, and a differentiating circuit 17 that converts the step signal obtained by the operation of the backlash absorption timer 16 into a pulsed starting current command Ip.

Next, the drooping rate circuit 8 includes a timer 26 that takes out a signal from the starting drooping rate setter 24 that gives a large drooping rate immediately after starting the work roll, and a timer 27 that changes the drooping rate to a signal from the normal drooping rate setter 25. Instead of using these timers, the actual speed may be detected by the rotary generator 23 and controlled by the signal.

Next, the operation of the activation control circuit 14 will be explained.

A current command value necessary to generate enough torque to overcome the static friction of the sliding bearing 5 is given in advance to the starting current setting device 15.

After the start-up command is issued, the current I _F of the work roll drive motor 22 rises at tens of thousands of amperes/second according to the speed command R of the speed control system 7. Mechanical backlash such as backlash of the speed reducer is absorbed by the rotation of the roll drive motor 22 based on the speed command R.

When the backlash absorption timer 16, which is set to the time from when the startup command is issued until the backlash is absorbed, times out and operates, the gap between the setting device 15 and the differentiating circuit 17 is closed, and the differentiating circuit 17 receives a step signal. In addition, the rising edge of this signal is output by the differentiating circuit 17 as a pulse-like signal Ip. This signal Ip and the current command I _R generated by the speed control amplifier 9 of the speed control system 7 are added together by an adder 20 to obtain a torque that overcomes the static friction of the sliding bearing 5.

Next, the operation of the droop rate circuit 8 will be explained.

Due to the pulsed starting current command Ip output by the starting control circuit 14, a large pulsed current I _F corresponding to Ip (the peak corresponding to Ip shown in FIG. 7) flows through the motor 22, and the motor 22 Gives a large starting torque to the work roll. At this time, the motor 22
When the droop rate circuit 8 acts to lower the motor speed in response to this increase in current, the output of the speed control amplifier 9 decreases, eventually lowering the current value of the motor 22 and slowing down the start-up of the work roll. In order to avoid this, in the droop rate circuit 8, both the setter 24 that gives a high droop rate and the setter 25 that gives a normal droop rate during steady plate passing are separated from the adder 19. As a result, the droop rate circuit 8 makes the droop rate zero. This allows the work roll to be started reliably and at a high startup speed.

However, after the work roll starts like this, if the static friction coefficient of the sliding bearing 5 is small,
The extra torque after starting the work roll acts in the direction of accelerating the work roll. When the pulsed starting current command Ip reaches its peak value, the work rolls of all stands have started rotating (started), so the droop rate that was set to 0 to balance the tension between the stands has now been changed. Set to a larger value than normal. That is, the timer 26, which is set at the time when the starting current command Ip reaches its peak value, operates and connects the starting droop rate setter 24 to the adder 19.
The drooping rate circuit 8 is set to a large drooping rate, and this is maintained even after the pulsed starting current command Ip disappears until a constant sheet threading speed is reached. During this time, the speed command signal R continues to rise under this large drooping rate to accelerate the work roll, and when the speed reaches a constant speed after acceleration, the timer 27 set to the acceleration time operates, and the setting device 24 is separated from the adder 19, and the setter 25 is connected to the adder 19. As a result, the drooping rate circuit 8 sets the normal drooping rate, and thereafter starts normal rolling.

FIG. 7 is a time chart showing the operation timing of the starting control circuit 14 and the drooping rate circuit 8, and shows the speed v and current I _F of the work roll drive motor 22,
The timings of the drooping rate set value D of the drooping rate circuit 8, the speed command R of the speed control system 7, the starting current command Ip output from the starting control circuit 14, the operations of the timers 16, 26, 27, etc. are shown.

The starting current command Ip, the timer 16, the timer 26, and the timer 27 start counting time, and when the backlash G of the machine such as the reducer is absorbed, the timer 16 completes the time counting, and the starting control circuit 14 outputs a pulsed signal. The starting command Ip is added with the current command I _R converted by the speed control amplifier 9 to become a motor current I _F and generate a driving torque.

According to the starting current command Ip, the timer 26 completes time counting at the point where the motor current I _F reaches its peak, the drooping rate value D is switched from 0 to the starting drooping rate value (high value), and then the motor completes acceleration. By the time,
When the timer 27 finishes counting the time, the droop rate D changes to the normal droop rate value.

〔Effect of the invention〕

As explained in detail above, according to the control method of the present invention, the rolled material 6 between the stands when restarting rolling is
An excellent effect can be obtained in that abnormal tension applied to the plate can be suppressed to a minimum and plate breakage can be prevented.

[Brief explanation of drawings]

FIG. 1a and FIG. 1b are sectional views showing the structure of a bearing for a back-up roll of a tandem rolling mill, respectively. FIG. 2 is a block diagram showing a general configuration of a conventional speed control device having a drooping rate, and FIG. 3 is a graph showing its drooping rate control characteristics.
Figure 4 is an explanatory diagram showing the roll rotation speed and tension behavior of each stand when plate breakage occurs during roll startup, and Figure 5 is an explanatory diagram showing the roll stoppage time, that is, the lubrication state of the back-up roll bearing, and the roll It is a graph showing the torque required for driving in terms of the current of the roll drive motor. FIG. 6 is a block diagram showing an example of the configuration of an apparatus for implementing the present invention, and FIG. 7 is a time chart showing the timing of generation of signals in each part in the apparatus configuration. 1: Backup roll, 2: Bearing, 3: Roller bearing, 4: Hydrostatic device,
5: Sliding bearing, 6: Rolling machine, 7: Speed control system, 8: Droop rate circuit, 9: Speed control amplifier, 1
0: Current control amplifier, 11: Voltage control amplifier, 1
2: Pulse generator, 13: Thyristor, 14: Starting control system, 15: Starting current setter, 16: Timer, 17: Differentiator circuit, 18 to 21: Adder, 2
2: Roll drive motor, 23: Rotary generator, 2
4: Start droop rate setter, 25: Normal droop rate setter, 26, 27: Timer.

Claims (1)

[Claims] 1. In starting the mill motor of the work roll of each stand of the tandem rolling mill with the rolled material placed between the stands, the mill motor is started and the power transmission mechanism between the mill motor and the work roll is activated. After the transmission delay time, the mill motor is energized with a pulsed current that provides the roll with a pulsed starting torque that overcomes the large static friction of the back-up roll bearing of each mill to start the work rolls, and at this startup, each mill motor After the work roll starts, the drooping rate of the stand is set to virtually zero, and after the work roll starts, a drooping rate larger than usual is given to each mill motor until the predetermined threading speed is reached, thereby balancing the tension generated by the change in the speed ratio of each stand. A starting control method for a tandem rolling mill, characterized in that: