JPH04138859A - Method for controlling molten steel level in mold in continuous casting - Google Patents

Abstract

PURPOSE:To stably control a molten steel level in a mold by detecting the molten steel level in the mold and selectively using a system for automatically adjusting stopper opening degree and a system for automatically adjusting nozzle opening degree according to a casting condition. CONSTITUTION:The molten steel level detected with a level detector 18 is inputted to a controller 19 and compared with the molten steel level preset value inputted in the controller 19 and its deviation is obtd. and outputted to a stopper opening degree adjuster 21. According to the deviation, the adjuster 21 drives a cylinder 22 and by adjusting the stopper opening degree, the molten steel level is controlled. The control of the molten steel in the mold with SN 16 is executed similarly, as well and the molten steel level detected with the level detector 18 is outputted to a controller 23 and the deviation from the beforehand inputted molten steel level value is obtd. and outputted to an SN opening degree adjuster 25. According to the deviation, the adjuster 25 drives a cylinder 26, and by adjusting the SN opening degree, the molten steel level is controlled. The control of molten steel level in the mold is executed with both systems according to the casting condition, either between both systems is selected.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for controlling the level of molten steel in a mold in a continuous casting machine for accurately controlling the level of molten steel in a mold to a set level in continuous casting.

Conventional technology The stabilization of the molten steel level in the mold in continuous casting is
A powder film of a constant thickness is uniformly formed on the surface of the slab, forming a uniform solidified shell to prevent surface flaws and reducing the entrainment of powder into the molten steel, resulting in casting with good internal quality. is an essential requirement for manufacturing pieces.

Conventionally, methods for controlling the level of molten steel in a mold at a constant level include one method using a stone bar and the other using a sliding nozzle (hereinafter referred to as SN) method.

FIG. 9 schematically shows the control of the Rm level in the mold using the stopper method, in which the level meter 2 detects the molten steel level in the mold 1, and the regulator 3 determines the deviation from the target level value.

Then, the stopper cylinder 4 is driven so that this deviation becomes 0, and the stone bar 5 is raised and lowered to control the flow rate of the cableway.

Due to its structure, level control using this method allows level control at low flow rates such as at the start and end of casting, but on the other hand, as seen in the stopper flow characteristics in Figure 10, flow control at high flow rates during continuous casting is possible. There is an rjIB point where the reproducibility and stability of level control accuracy are poor due to deviation from the center of the nozzle due to stopper percentage error, bending during stopper preheating, etc.

On the other hand, in the SN method, as shown in FIG.
This system is designed to adjust the opening degree of the flow rate, but as can be seen from the SN flow rate characteristics in Figure 11, this method basically provides good flow control from low flow rates to high flow rates. In addition, it is difficult for SN set variations and deformation due to preheating to occur, and the stability of level control is excellent. As shown in Fig. 12, the area of the shelf becomes large, which causes solidification of molten steel, which may clog the nozzle and cause problems in stopping casting.

This phenomenon may occur when the molten steel temperature is low even during high flow rate control.

Problems to be Solved by the Invention The object of the present invention is to enable stable control of the level of molten steel in the mold from the start of casting to the end of casting in continuous casting, and over a wide range of molten steel temperature and flow rate control. .

Means for Solving the Problems In order to achieve the above object, the present invention detects the molten steel level in the mold, controls the stopper cylinder so that the deviation from the target level value becomes 0, and raises and lowers the stopper to adjust the stopper opening degree. Depending on the casting conditions, two methods are used: a method that automatically adjusts the level of molten steel in the mold, and a method that automatically adjusts the nozzle opening by controlling the cylinder so that the deviation between the detected value of the molten steel level in the mold and the target level value is 0. This is an attempt to control the level of molten steel within the mold.

Change the level control method from stopper method to SN during continuous casting
When changing to the method, without disturbing the molten steel level, the stopper opening degree should be gradually increased as a function of time, preferably based on a multidimensional equation No. 2 as a function of time, when controlling the level by the stopper method. At the same time, level control using the SN method is started, and when the stopper opening degree reaches full open, the level control is automatically shifted to level control using only the SN method. On the other hand, when automatically transitioning from level control using the SN method to level control using the stopper method, S
During level control using the N method, level control using the stopper method is started at the same time as the 38-degree degree is gradually increased as a function of time, and when the 38-degree degree is fully opened, it automatically shifts to level control using the stopper method alone. let

Operation Fig. 1 shows a continuous casting machine used to carry out the method of the present invention, in which molten copper 12 from a ladle 11 is injected into a tundish 14 through a nozzle 13, and then a caster 15 is driven by a command from a control device. Alternatively, the flow rate of molten IIl may be adjusted using 5NI6 so that it is injected into the mold 17.

The level of molten steel in the mold is controlled by the stopper 15 as follows.

The molten steel level value detected by the level detector 18 is input to the regulator 19, and compared with the molten steel level setting value inputted in advance to the regulator 19, the deviation is determined and output to the stopper opening degree regulator 21. do. The stopper opening degree controller 21 also receives the stopper opening degree detected by the opening degree detector 20 of the stopper/par 15, and the adjuster 21 drives the cylinder 22 according to the deviation. Then, adjust the stopper opening to control the molten steel level.

In the same way, the molten steel level in the mold is controlled by the SN, and the molten steel level value detected by the level detector 18 is adjusted by the regulator 2.
3, the deviation from the pre-input molten steel level set value is determined and output to the SN opening degree regulator 25. The SN opening detected by the opening detector 24 is also input to the SN opening regulator 25, and the regulator 25 drives the cylinder 26 according to the deviation to adjust the SN opening and adjust the molten steel level. Control.

As described above, the molten steel heat in the mold is controlled by both the stopper method and the SN method, and one of the methods is selected depending on the casting conditions.

Next, change the level control method from the stopper method to the SN method or from the SN method to the stopper method during continuous casting.
A method of changing the tiR level without causing disturbance will be explained.

FIG. 2 shows the opening adjustment situation when automatically transitioning from the one-stopper type level control to the SN type level control, and the SN opening degree is fully open when level control is performed by the stopper type in range A. When shifting to level control using the SN method, the stopper opening degree adjuster 21 adjusts the cylinder 16 according to the stopper opening degree increase rate set in the adjuster 19 in advance.
is driven to increase the stopper opening degree. This range B
In order to control the molten steel level to a constant level in response to the gradually increasing stopper opening, SN is used as a level detector 1.
The SN opening degree regulator 25 gradually reduces the SN opening degree from the fully open state based on the deviation from the target level value determined by the regulator 23 according to the molten steel level value detected by 8. Then, when the stopper opening degree reaches the full opening, the stopper is fixed, and the molten steel level control is performed solely by the range C03N method.

When shifting from the stopper method to the SN method, as described above, the stopper opening is increased according to the stopper opening increase rate set in advance in the regulator 19, but if the increase rate is constant, the 10th As shown in the figure, the amount of change in the flow rate of molten steel discharged from the nozzle when the stopper opening degree starts to increase is large, which induces fluctuations in the molten steel level. Therefore, the rate of increase in the stopper opening is set in the controller as a multidimensional function of time, and as shown in Figure 3, the rate of increase in the stopper opening is set at a small rate at the beginning of the increase in strike and par, and at a large rate at the later stage. and keep the amount of change in the flow rate of molten steel discharged from the nozzle constant,
Fluctuations in the molten steel level can be suppressed.

Figure 4 shows the opening adjustment status when transitioning from the SN method to level control using the stopper method, and corresponds to the gradual increase in the SN opening as in the case of transitioning from the one-stopper type to the SN method. The stopper opening degree is gradually reduced from the fully open state so that the deviation between the molten steel level value and the target level value becomes 0.

Example 1 After starting casting, the level of molten steel in the mold was controlled using a stopper method with the SN opening fully open.

Thereafter, the system was automatically switched to the SN method, and the stomper opening was increased at a rate of 3%/sec. As shown in FIG. 5, the fluctuation in the molten steel level during the automatic switching from the stomper method to the SN method was small, and although slight cracks occurred on the surface of the slab, they were not large enough to require surface maintenance.

Example 2 After the start of casting, the level of molten steel in the mold was controlled using a stopper method with the SN ratio fully open. Then S
The system was automatically switched to the N method and the stopper opening was increased based on a quadratic function of time. As shown in FIG. 6, there was no disturbance in the molten steel level during automatic switching from the stopper method to the SN method, and no surface cracks were observed in the slab.

According to each of the above-mentioned Examples, as described above, it was possible to stably control the level of molten sea bream in the mold over the entire range from the start to the end of casting.

Comparative Example 1 The molten steel level was controlled only by the stopper method with the SN opening degree fully open from the start to the end of casting. As a result, as shown in FIG. 7, the control accuracy of the molten steel level deteriorated under conditions where the casting speed in the middle stage of casting was high.

Comparative Example 2 After the start of casting, the molten steel level was controlled using a stopper method with the SN opening fully open, and then the molten steel level was manually controlled from the stopper method to the SN method.

As a result, SN
However, as shown in Figure 8, fluctuations in the molten steel level and surface cracks on the slab occurred while manually switching from the stopper method to the SN method. I let it happen.

Effects of the Invention The present invention is configured as described above, and has the following effects.

In the method for controlling the level of molten steel in a mold according to claim 1, it is possible to select a superior method between a stopper method and a sliding nozzle method depending on casting conditions,
Furthermore, if an abnormality occurs in the control system using one of the methods, it is possible to switch to another method for controlling the molten steel level, and it is possible to prevent large fluctuations in the molten steel level due to manual control.

In the method according to claim 2 or 4, it is possible to smoothly transition from the stopper method to the sliding nozzle method or from the sliding nozzle method to the stopper method, thereby achieving a stable molten steel level regardless of the casting conditions. control, and can improve the surface and internal quality of slabs.

In the method according to claim 3, the change amount of the flow rate of molten steel discharged from the nozzle is kept constant by changing the stopper at a small rate of increase in the early stage of the rise and at a large rate of increase in the latter stage, thereby suppressing fluctuations in the level of the molten steel. be able to.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of the molten steel level control device used in the method of the present invention, Figure 2 is the stopper type to SN type, and Figure 3 is the S
A diagram showing the opening adjustment situation when transitioning from the N method to the stopper method, Figure 4 is a diagram showing the situation when the stopper opening is increased based on a quadratic function equation of time, and Figure 5 is a diagram showing the situation when the stopper opening is adjusted based on the quadratic function equation of time. Figure 6 shows the opening adjustment status of Example 1, Figure 7 shows the opening adjustment status of Comparative Example 1, and Figure 8 shows the opening adjustment status of Comparative Example 2. , Fig. 9 is a schematic diagram of a molten steel level mm device used in the conventional method, Fig. 10 is a diagram showing the relationship between the stopper opening degree and the molten steel discharge flow rate, and Fig. 11
The figure shows the relationship between SN opening degree and molten steel level discharge flow rate,
FIG. 12 is a cross-sectional view of SN. 15...Stopper 16...5N17...Mold 1
8...Level detector 19...Adjuster 20...Opening degree regulator 21...Stopper opening degree regulator 22...Cylinder 23...Adjuster

Claims (4)

[Claims] (1) A method that detects the molten steel level in the mold, controls the stopper cylinder so that the deviation from the target level value is 0, and automatically adjusts the stopper opening by raising and lowering the stopper, and molten steel level in the mold. The level of molten steel in the mold is controlled by controlling the cylinder and automatically adjusting the opening of the sliding nozzle so that the deviation between the detected value and the target level value is 0, depending on the casting conditions. A method for controlling the level of molten steel in a mold in continuous casting, characterized by: (2) When changing the level control method from the stopper method to the sliding nozzle method during continuous casting, the stopper opening degree is gradually increased as a function of time during level control using the stopper method, and at the same time, level control using the sliding nozzle method is started. 2. The method for controlling the level of molten steel in a mold in continuous casting according to claim 1, wherein the level control is automatically performed using a sliding nozzle method alone when the stopper opening is fully opened. (3) The method for controlling the level of molten steel in a mold in continuous casting according to claim 2, wherein the increase in the stopper opening degree is performed based on a multidimensional equation as a function of time. (4) When changing the level control method from the sliding nozzle method to the stopper method during continuous casting, the opening degree of the sliding nozzle is gradually increased as a function of time when level control is performed using the sliding nozzle method, and at the same time the level control method using the stopper method is changed. 2. The method for controlling the level of molten steel in a mold in continuous casting according to claim 1, wherein the level control is automatically performed using a stopper method only when the sliding nozzle opening is fully opened.