JPH0673733B2 - Method of controlling molten steel temperature in tundish at the beginning of casting - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for controlling the temperature of molten steel in a tundish in continuous casting, particularly in the initial stage of casting.

[Prior Art] In order to control the molten steel temperature in the tundish in the middle casting period of continuous casting, an automatic control method by feedback control or feedforward control is generally adopted by combining an induction heating device and a continuous temperature measuring element. Has been.

However, the continuous temperature measuring element cannot accurately measure temperature until it reaches a thermal equilibrium state with the molten steel after being immersed in the molten steel in the tundish. For this reason, a typical pattern control was performed in which actual molten steel temperature measurement was not performed immediately after the start of casting, which is the most important temperature control.

For example, according to Japanese Patent Laid-Open No. 61-249655, in controlling the temperature of molten steel, program control is performed at the beginning of casting, and when temperature measurement is stable, feedback control is performed based on the measured value by a continuous thermometer. Was there.

[Problems to be Solved by the Invention] However, the pattern control in the conventional method has the following problems. That is, when the molten steel temperature ≧ the target temperature, the molten steel temperature> the target temperature due to induction heating, and the solidified shell thickness in the mold becomes insufficient, which may cause an operational trouble such as breakout.

When the molten steel temperature <target temperature, if the initial setting voltage in pattern control is insufficient, the molten steel temperature remains the target temperature even if induction heating is performed, and the viscosity of the molten steel becomes excessive, resulting in nozzle clogging. However, casting becomes impossible.

On the other hand, even with the technique described in the above publication, such a problem cannot be solved because only pattern control is performed at the initial stage of casting.

Therefore, the main object of the present invention is to obtain an instantaneous accurate measurement from the beginning of pouring, that is, from the start of pouring to the point of reaching the thermal equilibrium of the continuous temperature measuring element which enables the start of temperature control by the continuous temperature measuring element. A consumable thermometer capable of measuring temperature is used to measure the temperature of molten steel, and by correcting the pattern control in the initial stage of casting, a method is provided that enables accurate control of the molten steel temperature in the initial stage of casting. Especially.

[Means for Solving the Problems] The present invention for solving the above problems detects molten steel in a tundish for continuous casting by a continuous temperature measuring element which takes a long time to reach a thermal equilibrium state with the molten steel. When performing feedback temperature control using the induction heating device based on the temperature signal from the continuous temperature measuring element, the temperature history of the charge from the steelmaking stage to the inside of the ladle, the thermal history of the ladle, and the preheating of the tundish. The molten steel temperature in the tundish in the initial casting stage of continuous casting is predicted and calculated based on the initial conditions that determine the molten steel temperature in the initial casting stage, such as temperature, and the induction heating power pattern is set based on this predicted calculation result. When the molten steel is poured from the pan into the tundish, and when the molten steel depth in the tundish reaches the molten steel depth that does not produce the pinch effect, the induction heating power pattern is used. After the induction heating is started and after the pouring is started, at least one sampling measurement is performed by a consumable thermometer capable of measuring temperature in a short time within a period until the continuous temperature measuring element reaches a thermal equilibrium state with the molten steel in the tundish. The temperature of the induction heating power is corrected based on the temperature measurement result of the consumable thermometer, and after the continuous temperature measuring element has substantially reached the thermal equilibrium state, the temperature of the induction heating power pattern is changed. Instead of the control, the induction heating power is feedback-controlled based on the temperature measured by the continuous temperature measuring element.

[Operation] Generally, a continuous temperature measuring element that is normally used takes a long time to reach thermal equilibrium with the object to be measured, and accurate temperature measurement cannot be performed during that time.

In the present invention, after pouring molten steel from the ladle into the tundish,
In the process of setting the induction heating pattern, starting the induction heating, and controlling the induction heating pattern in the initial stage until the continuous temperature measuring element reaches thermal equilibrium and accurate temperature measurement becomes possible, at least once Since the sampled temperature is measured by a consumable thermometer that can measure temperature over time, and the induction heating pattern is corrected based on the temperature measurement result, the molten steel temperature can be accurately controlled even within the above period. . In the initial stage of pouring, even if the induction heating pattern can be set by a multiple regression equation from past results, at the time of abnormality, the setting of the induction heating pattern is not appropriate, whereas according to the present invention. As described above, the accuracy of molten steel temperature control in the early stage of casting is improved, and even if there is an abnormality, the target molten steel temperature can be controlled with certainty, which greatly contributes to quality improvement in the initial stage of casting.

[Specific Structure of the Invention] The present invention will be described in more detail below.

FIG. 1 is a schematic diagram for explaining a molten steel temperature control method in a tundish according to the present invention. In the figure, 1 is a ladle,
Molten steel 4 is poured into a tundish 3 through a nozzle 2 into a receiving chamber RA partitioned by a weir 3a. In the process of circulating between the receiving chamber RB and the pouring chamber RA in the tundish 3 through the communication hole 3b, the molten steel 4 is heated by the induction heating device 5 and the required temperature is maintained, The continuous casting mold 7, through the injection ports 6 formed at the bottom of the pouring chamber 3b,
It is poured into 7 and becomes cast pieces 8 and 8.

By the way, the temperature of the molten steel cast into the molds 7, 7 has a great influence on the quality of the product and the like, and therefore, an appropriate temperature control is required. In this respect, the temperature measurement of the molten steel 4 after the start of casting into the molds 7, 7 is generally performed by a continuous thermometer 9 immersed in the molten steel 4. The temperature signal from the continuous thermometer 9 is input to the induction heating device control computer 11 via the temperature calculator 10, and after the comparison calculation of the current molten steel temperature and the target temperature, the induction heating to be the target temperature is performed. The required voltage value is corrected and input to the induction heating control device 12 to control the induction heating device 5 so that the required voltage is obtained.

In order for such temperature control to be possible, it is premised that the continuous thermometer 9 is in a thermal equilibrium state with the molten steel 4, as described above. However, since the continuous thermometer 9 has not yet reached the thermal equilibrium in the initial period from the time of pouring the tundish to the start of casting, the temperature controllability is extremely poor based on the temperature signal. Therefore, there is no choice but to rely on the pattern control in the initial stage as described above. However, as described above, there are many problems in continuing the temperature control according to the preset control pattern.

In view of this point, in the present invention, in order to measure the molten steel temperature until the continuous thermometer 9 can be measured, the consumable thermometer 14 having a thermocouple is immersed in the molten steel 4 at least once. Temperature measurement of molten steel at the initial stage. The temperature signal from the consumable thermometer 14 is input to the induction heating device control computer 11 through the temperature calculator 15, and the casting initial stage based on the operating condition 13 given from the host computer based on the current temperature signal. After the induction heating voltage pattern is corrected, it is input to the induction heating device 5 via the induction heating control device 13 to control the temperature of the molten steel 4.

Next, the specific operation procedure of the method of the present invention will be described with reference to the flow sheet of FIG. First, in the present invention, the operating conditions (molten steel temperature after ladle treatment, time required from the end of ladle treatment to the start of continuous casting and casting, ladle information, tundish heating conditions, etc.) (I) and tundish Each value of the target temperature (II) is input to the calculator (III) (calculator 11 in FIG. 1), and induction heating voltage pattern determination (IV) at the start of pouring is performed. Next, when molten steel is poured from the ladle into the tundish, and when the molten steel depth in the tundish exceeds the minimum molten steel depth at which the pinch effect described below does not occur, that is, the molten steel depth in the tundish ≧ H ₀ When it becomes (V), the induction heating voltage pattern control is started (VI). Next, start casting (VII) and, as described above, measure molten steel temperature in the tundish with a consumable thermometer (VIII).
Is performed about 1 to 5 times, based on the difference between the measured temperature and the tundish target temperature, automatic correction (IX) of the induction heating voltage pattern control is performed, and induction heating is continued by this corrected voltage pattern. Automatic correction is repeated each time the temperature is measured by the consumable thermometer (X), and when the continuous thermometer reaches thermal equilibrium and becomes measurable (XI), feedback control by continuous temperature measurement (XII) is performed by a known method. ), And continuous casting is continued.

The pinch effect means that when electric power is applied to the induction heating device when the static pressure of molten steel in the tundish is less than or equal to a predetermined value, the molten steel in the groove-type induction furnace is compressed / expanded due to electromagnetic induction force. This is a phenomenon in which the impedance of the circuit becomes infinite at this moment. Therefore, it is necessary to control the induction heating voltage after the static pressure of molten steel, that is, when the molten steel depth in the tundish exceeds a predetermined value H ₀ .

Next, the effect of the present invention will be specifically described with reference to FIG. The figure shows an example of manufacturing a normal steel bloom of 409 mm x 530 mm.

First, when the casting speed (m / min) is set as shown in line (a), the weight of molten steel in the tundish (Ton) is set as shown in line (b). Next, the induction heating voltage pattern is often set as shown by the broken line (c) in the conventional method, but is corrected by the method of the present invention based on the actual measurement value of the consumable thermometer, and the solid line (d) To set. As a result, the molten steel temperature in the tundish approximates to the target temperature as indicated by the solid line (e).
On the other hand, in the conventional method based on the induction heating voltage setting pattern of the line (c) which is not corrected, the curve is as shown by the broken line (f). As described above, in the present invention, it is understood that by correcting the induction heating voltage pattern with the consumable thermocouple, it becomes possible to perform accurate temperature control at the initial stage of casting.

[Advantages of the Invention] As described above, according to the present invention, it is possible to significantly improve the control accuracy of the molten steel temperature in the tundish even in the initial stage of casting.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining the present invention, FIG. 2 is a flowchart of an operating procedure of the method of the present invention, and FIG. 3 is a diagram showing a temperature control method of the present invention in comparison with a conventional method. 1 ... Ladle, 3 ... Tundish, 4 ... Molten steel, 5 ...
… Induction heating device, 7 …… Mold, 9 …… Continuous thermometer,
14-Consumable thermometer (thermocouple)

Claims (1)

[Claims] 1. A molten steel in a tundish for continuous casting is detected by a continuous temperature measuring element which takes a long time to reach a thermal equilibrium state with the molten steel, and an induction heating device is activated based on a temperature signal from the continuous temperature measuring element. When performing feedback temperature control using the above, based on the initial conditions that determine the molten steel temperature in the initial stage of casting, such as the temperature history of the charge from the steelmaking stage to the inside of the ladle, the heat history of the ladle, and the preheating temperature of the tundish. Then, the molten steel temperature in the tundish at the initial stage of continuous casting is predicted and calculated, and the induction heating power pattern is set based on this predicted calculation result, and the molten steel in the tundish is poured from the ladle into the tundish. When the depth reaches the molten steel depth that does not generate the pinch effect, induction heating is started by the induction heating power pattern, and after the pouring starts, the continuous temperature measuring element Is sampled at least once by a consumable thermometer that can measure the temperature in a short time within the period until it reaches thermal equilibrium with the molten steel in the tundish. After the induction heating power pattern is corrected and after the continuous temperature measuring element has substantially reached the thermal equilibrium state, instead of the temperature control by the induction heating power pattern, induction is performed based on the temperature measurement value by the continuous temperature measuring element. A method for controlling a molten steel temperature in a tundish in an early stage of casting, which is characterized by performing feedback control of heating power.