JPH11267813A - Control method of molten steel surface level mold of continuous casting machine and control equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the increase in the molten steel surface level fluctuation when the clogging in the nozzle for the molten metal injection happens. SOLUTION: Under the normal operating state, level deviation e(t) between molten steel surface level target value r(t) in a mold and molten steel surface level measured value y(t) in the mold is input into the first compensator 13 having the integral function and also into the second compensator 14 which does not have the integral function, and the sliding nozzle gate opening order MV(t) is obtained from the sum of this output and the opening order is given to an actuator 7. On the other hand, when the molten metal injection volume becomes the saturation state due to the generation of the clogging of a sliding nozzle gate 3 or a submerged nozzle 4, an output of the first compensator 13 is stopped, and an output of the second compensator 14 is made to be the sliding nozzle gate opening order MV(t).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and a device for controlling a molten metal level in a continuous casting machine, which adjusts a molten metal pouring amount so as to stably maintain a molten metal level in a mold at a target value.

[0002]

2. Description of the Related Art When the level of a molten metal in a mold fluctuates in a continuous casting process, powder on the molten metal surface is caught in the molten metal, and the powder caught in the molten metal becomes a skin defect of a slab as it is and after rolling. This will result in flaws in the product.
For this reason, controlling the fluctuation in the level of the molten metal has a very important meaning in improving the quality of the product. Various factors are known to cause the level change of the molten metal, but it is caused by unsteady bulging in which the solidified shell of the slab periodically expands and contracts due to the fluctuation of the static pressure of the unsolidified molten metal in the slab due to drawing of the slab Disturbances such as fluctuations in the amount of molten metal flowing out of the casting mold and non-uniformity in the flow rate of molten metal due to the progress of clogging in the immersion nozzle can be said to be the main causes.

As a countermeasure against this, conventionally, the level of the molten metal is measured at a predetermined time interval by a molten metal level sensor.
Compare the measured level value with the target level, adjust the opening of the sliding nozzle gate or stopper provided at the bottom of the tundish to eliminate the level deviation, and place it in the mold. Adjust the amount of molten metal
2. Description of the Related Art While supplying a molten metal amount corresponding to an amount of a molten metal to be drawn as a cast slab to a mold, compensation of fluctuation in the molten metal injection amount due to the disturbance is performed to make the molten metal volume in the mold constant.

[0004] By the way, a level control device for adjusting the opening of a sliding nozzle gate or a stopper necessary for maintaining the level of a molten metal at a predetermined target value usually includes a measured level of the molten metal and a level of the molten metal. An element for temporally integrating a level deviation from a target value, for example, a PID adjusting device, is provided. A sliding nozzle is provided so that an average value of the liquid level is made to substantially coincide with the target value of the liquid level by the operation of the integrating element. An opening command for the gate or stopper actuator is calculated.

[0005] However, during operation of the continuous casting machine, nozzle clogging occurs because inclusions in the molten metal adhere to the opening of the sliding nozzle gate or the inside of the immersion nozzle. For example, if the nozzle clogging occurs in the sliding nozzle, the following inconvenience is caused.

That is, when the nozzle clogging is slight, the gain of the amount of molten metal injected into the casting mold with respect to the change in the opening of the sliding nozzle gate is reduced. Performance is lost, and the fluctuation level of the molten metal level becomes larger than in the case where there is no nozzle clogging. When nozzle clogging proceeds, the amount of molten metal injected into the mold is saturated at a certain upper limit. For this reason, even if the molten metal level control device outputs an opening command value such as to open the sliding nozzle gate, the molten metal injection amount is insufficient with respect to the molten metal outflow amount fluctuation due to disturbance, and the nozzle clogging is slight. In comparison with this, the fluctuation range of the molten metal level becomes larger.

If the nozzle clogging is further advanced, the molten metal injection amount is insufficient with respect to the amount of molten metal flowing out of the mold as a slab, the level of the molten metal continues to drop, and the slab drawing speed is reduced. Therefore, the amount of molten metal flowing out of the mold must be reduced, and efficient casting becomes impossible. As a countermeasure for the above, JP-A-64-5374 has been proposed.
In Japanese Patent Application Laid-Open Publication No. 7-107, a control parameter of a PID adjusting device in a sliding nozzle gate is corrected based on an estimated value of a molten metal injection amount gain with respect to a sliding nozzle gate opening degree, and a loop gain of a molten metal level control device is kept optimal. A method is disclosed. Also, Japanese Unexamined Patent Publication No.
No. 27762 discloses a similar method at the time of flow rate adjustment by a stopper.

In these methods, as long as the clogging is slight and the upper limit of the flow rate of the sliding nozzle or the immersion nozzle always exceeds the molten metal injection amount necessary to compensate for the fluctuation of the molten metal outflow amount due to the above-described disturbance. The effect of suppressing fluctuations in the level of the molten metal can be expected.

[0009]

On the other hand, these conventional methods have no effect on the above-mentioned disadvantages.
This is because the fluctuation of the molten metal level when the molten metal injection amount is saturated is larger than that when the nozzle clogging is slight due to the following two factors. (A) When the molten metal injection amount is saturated, the molten metal injection amount for replenishing the increase in the molten metal outflow amount from the mold due to disturbance becomes insufficient. As a result, the fluctuation width in the direction in which the level of the molten metal decreases is increased.

(B) Even after the amount of molten metal flowing out of the mold due to disturbance is reduced and the level of the molten metal is turned upward, while the measured level of the molten metal is below the target level, the level of the molten metal is maintained. The integral element of the control device accumulates the level deviation, and continuously calculates the opening command value in the direction in which the sliding nozzle gate opens beyond the opening corresponding to the upper limit of the molten metal injection amount. However, since the molten metal injection amount is saturated with respect to the opening of the sliding nozzle gate, the molten metal injection amount into the mold during this period is constant, and in addition, the molten metal level measured value exceeds the molten metal level target value, and The amount of molten metal injected into the mold does not decrease until the element gradually reduces the accumulated amount of the level deviation and closes the opening command value of the sliding nozzle gate below the opening corresponding to the upper limit of the molten metal injection amount.

As a result, while the molten metal inflow is saturated, the level fluctuation width increases in the direction in which the molten metal level rises. In the case of the above factor (a), it is difficult to avoid a shortage of the molten metal injection amount when the molten metal injection amount is saturated. The present invention solves the problem of the factor (b) in the case where the molten metal injection amount is insufficient when the nozzle clogging progresses and the molten metal injection amount is saturated, and suppresses the fluctuation of the molten metal level. It is intended to provide a device.

[0012]

According to a first aspect of the present invention, there is provided a method for controlling a mold level in a mold of a continuous casting machine, the method comprising the steps of: In the mold level control method for controlling the opening level of the molten metal injection nozzle to maintain the mold level in the mold so as to maintain the mold level target value, a first value obtained by time-integrating the level deviation with the first value. ,
A second processing in which the level deviation does not include the integration processing;
And the sum of the above values as the nozzle opening command for the actuator, and when the molten metal injection amount from the nozzle to the mold is in a saturated state, and the measured molten metal level is below the molten metal level target value. , The first value being zero.

According to a second aspect of the present invention, there is provided a mold level control device in a mold of a continuous casting machine, wherein an opening degree of a molten metal injection nozzle with respect to a mold is determined based on a level deviation of a measured level value with respect to a target level value in the mold. A first means for operating an adjusting actuator to output a value obtained by performing a time integration process on the level deviation, in a mold level control device for controlling the mold level in the mold to maintain the mold level at a target level;
A second unit that outputs a value obtained by performing a process that does not include an integration process on the level deviation; a switching unit that switches operation and non-operation of the first unit; and an output of the first and second units. Means for outputting as a nozzle opening command to the actuator, and detecting whether or not the molten metal injection amount into the mold is saturated with respect to the change in the nozzle opening, and is in a saturated state, and When the level deviation is positive, a saturation detecting means for operating the switching means to deactivate the first means is provided.

According to the first and second aspects of the present invention, when it is detected that the amount of molten metal injected into the mold is saturated due to nozzle clogging, the integration process for the nozzle opening adjustment actuator is performed. By stopping the output of the value, fluctuations in the level of the molten metal level in the mold can be suppressed, and the occurrence of subcutaneous defects in the slab due to entrainment of the powder can be reduced.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings showing the embodiments. FIG. 1 is a block diagram showing a configuration of a mold level control device in a mold of a continuous casting machine according to the present invention. In the figure, reference numeral 1 denotes a mold, and 2 denotes a tundish for supplying molten metal to the mold 1. Tundesh 2
Has an immersion nozzle 4 suspended from the bottom wall thereof with a sliding nozzle gate 3 interposed therebetween.
Is positioned while being immersed in the molten metal 8 in the mold 1.

The sliding nozzle gate 3 is provided with an actuator 7 composed of a hydraulic cylinder or the like for opening and closing the sliding nozzle gate 3. The opening of the sliding nozzle gate 3 is adjusted by operating the actuator 7. It is. Reference numeral 10 denotes a control system for the actuator 7, which is a given molten metal level target value r.
The level deviation e between (t) and the measured level y (t) of the molten metal level sensor 5 that is exposed in the mold 1.
A subtracter 11 for obtaining and outputting (t), and a level deviation e
(T) is input via the switch 12 as a switching means,
A first compensator 13 for performing predetermined processing on the level deviation e (t) and outputting the same, a second compensator 14 for directly receiving the level deviation e (t), and first and second compensators 13,1
4 is provided with an adder 15 that adds the outputs of the outputs 4 and outputs the result to the actuator 7 and a molten metal injection amount saturation detecting unit 16.

The first compensator 13 integrates the level deviation e (t) with time as shown in the following equation (1), and multiplies the value by a control parameter K1 to obtain a sliding nozzle gate opening command MV1. Output to the adder 15 as (t). MV1 (t) = K1∫e (t) dt (1)

The second compensator 14 does not have an integrator and has a characteristic represented by a transfer function C (s). Sliding nozzle gate opening command MV2 (t) according to equation 2)
Is calculated and output to the adder 15. ^{MV2 (t) = L - [} C (s) L [e (t)]] ... (2) where L: Laplace transformation L ^-: inverse Laplace transform

If the transfer function C (s) of the second compensator 14 is replaced with a constant KP, the equation (2) can be rewritten as the following equation (3). MV2 (t) = KP × e (t) (3) The adder 15 outputs the sliding nozzle gate opening command M
A sliding nozzle gate opening command MV (t), which is the sum of V1 (t) and MV2 (t), is given to the actuator 7 of the sliding nozzle gate 3.

The molten metal injection amount saturation detecting means 16 measures a molten metal level y (t) in the mold 1, which is a measured value of the molten metal level sensor 5, and a drawing speed which is a measured value of the slab drawing speed meter 6. Based on Vc (t), the sliding nozzle gate opening command MV (t), and the sectional area of the mold, it is determined whether the amount of molten metal injected into the mold is not saturated or the amount of molten metal injected is saturated. , When it is not saturated, the switch 12 is kept closed, and when it is saturated, the measured level y (t) is the target level r (t).
In the following cases, in other words, when the level deviation e (t)> 0, the switch 12 is opened. Whether the nozzle is saturated or not depends on the opening of the sliding nozzle gate,
In other words, the determination is made based on whether or not the molten metal injection amount changes in accordance with the expansion and contraction of the cylinder rod of the actuator 7. The gate opening may be slightly changed to check whether the injection amount of the molten metal from the nozzle is saturated or not. May be determined based on whether or not has changed.

As a result, when in the unsaturated state,
The level deviation e (t) is input to the first and second compensators 13 and 14, and the respective outputs MV1 (t) and MV2 (t) are added by the adder 15, and as shown in the following equation (4). The added value is output to the actuator 7 as the sliding nozzle gate opening command MV (t). MV (t) = MV1 (t) + MV2 (t) (4)

On the other hand, when the switch is in a saturated state,
2 is released, and the level deviation e (t) is
And output MV2 as shown in the following equation (5).
(T) is the opening degree command MV of the sliding nozzle gate 3
(T) is output to the actuator 7. MV (t) = MV2 (t) (5)

[0023]

EXAMPLE The molten metal outflow from the mold 1 due to the drawing of the slab 9 is 50% of the designed upper limit of the molten metal injection amount, and the fluctuation of the molten metal outflow from the mold 1 due to disturbance is the designed upper limit of the molten metal injection amount. ± 6%, and the molten metal injection amount into the mold 1 was saturated at 52% of the upper limit in design, and the apparatus of the present invention and the conventional apparatus were applied. In the above state, the molten metal can be injected into the mold 1 so as to be balanced with the molten metal outflow from the mold 1 due to the drawing of the slab 9, but it is necessary to completely compensate for the variation in the molten metal outflow from the mold 1 due to disturbance. Means that the amount of molten metal injected into the mold is insufficient.

FIG. 2 shows the level of the molten metal in the case where the conventional technique of performing the level control by inputting the output of the integrator to the actuator 7 of the sliding nozzle gate and the case where the present invention is implemented. (FIG. 2 (a)),
Sliding nozzle gate opening command (FIG. 2B),
It is a graph which showed a time transition of each molten metal injection flow rate (FIG. 2 (c)).

As shown in FIG. 2 (c), even when the molten metal injection amount is saturated at a predetermined level,
At the timing when the liquid level exceeds the target level as shown in FIG. 2A, a sliding nozzle gate opening command is issued as shown in FIG. 2B to the nozzle closing side, in other words, the nozzle opening degree is reduced. The rise in the level of the molten metal is 13 mm in the prior art by switching to, but can be reduced to 8 mm in the apparatus of the present invention, and it can be seen that the fluctuation in the level of the molten metal can be reduced.

[0026]

As described above, in the apparatus of the present invention, even when the molten metal supply nozzle is clogged and the injection amount of the molten metal is saturated, fluctuations in the level of the molten metal in the mold can be effectively suppressed. , Prevents the occurrence of subepidermal defects in the slab,
The product quality after rolling can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a mold level control device in a mold of a continuous casting machine according to the present invention.

FIG. 2 is a graph showing a comparison test result between the device of the present invention and a conventional device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mold 2 Tundish 3 Sliding nozzle gate 4 Immersion nozzle 5 Metal surface level sensor 6 Casting speedometer 11 Subtractor 12 Switch 13 First compensator 14 Second compensator 15 Adder 16 Molten metal injection amount saturation detection means

Claims (2)

[Claims] An actuator for adjusting the opening of a molten metal injection nozzle with respect to a mold is operated based on a level deviation of a measured value of a molten metal level with respect to a target value of a molten metal level in the mold to set the molten metal level in the mold to the target. In the mold level control method for controlling the level in the mold to maintain the value, a sum of a first value obtained by performing a time integration process on the level deviation and a second value obtained by performing a process not including the integration process on the level deviation is obtained. In addition to the nozzle opening command for the actuator, the first value is set when the molten metal injection amount from the nozzle to the mold is in a saturated state and the measured level value is below the target level value. A method for controlling a level of a molten metal in a mold of a continuous casting machine, wherein the method is set to zero. 2. An actuator for adjusting an opening of a molten metal injection nozzle with respect to a mold is operated based on a level deviation of a measured value of a molten metal level with respect to a target value of a molten metal level in the mold to set a molten metal level in the mold. In a mold level control device in a mold for controlling to maintain the level deviation, a first means for outputting a value obtained by performing a time integration process on the level deviation, and outputting a value obtained by performing a process not including an integration process on the level deviation. A second means, a switching means for switching between operation and non-operation of the first means, and a means for adding the outputs of the first and second means and outputting the result as a nozzle opening command to the actuator. Detecting whether or not the amount of molten metal injected into the mold is saturated with respect to a change in the nozzle opening, and if the level is positive and the level deviation is positive, the first means is not operated; Continuous caster mold molten steel surface level controller, characterized in that it comprises a saturation detection means for operating the switching means so as to.