KR20050002222A - Method for controlling the magnetic field of width of continuous casting mold - Google Patents

Abstract

PURPOSE: To provide a method for controlling a magnetic field in width direction of continuous casting mold, the method for improving quality of slab by differently controlling magnitude of magnetic field in a width direction of casting of continuous casting mold, thereby supplying flow of molten steel to a short side portion of the mold. CONSTITUTION: In a method for controlling a magnetic field in a width direction of the mold to optimize flow of molten steel discharged from a submerged entry nozzle in a mold of the continuous casting process, the method comprises a step of installing the core plates on the magnetic field core in such a way that the number(thickness) of core plates(12) to be attached to a magnetic field core(13) installed at a long side portion(14) is getting decreased as it goes from the center of the long side port to both sides thereof in order to change magnitudes of the magnetic field impressed to a short side portion(9) and a central portion of the continuous casting mold; and a step of reducing depth of a hook that is a boundary layer of solidified shell by changing a ratio of the magnitudes of the magnetic field impressed to the short side portion and the central portion of the continuous casting mold, thereby supplying molten steel flow to the short side portion to perform soft cooling of slab.

Description

METHOD FOR CONTROLLING THE MAGNETIC FIELD OF WIDTH OF CONTINUOUS CASTING MOLD}

In the present invention, in controlling the molten steel flow in a mold by using a direct current in a mold of a continuous casting process in a steel mill, a method of controlling the width in the continuous casting mold in which the continuous casting mold optimizes the flow in the mold by controlling the magnetic field strength in each casting width direction. In more detail, the molten steel flow supply to the continuous casting mold short side portion is secured to prevent the temperature decrease of the short side portion to promote the cooling of the slab, and to control the influence on the flow by Ar The present invention relates to a widthwise magnetic field control method of a continuous casting mold for improving the quality of slab.

In general, as shown in Figure 1, the continuous casting process for producing a molten steel in a solid state slab (slab) of the molten steel contained in the steel ladle (1) temporarily suspended in the tundish (2) of the continuous casting machine After storage, the molten steel is supplied to the continuous casting mold 3 and cooled to produce slabs.

In particular, in the mold 3 of the continuous casting process, a technique of applying a current value to the discharged molten steel to form a magnetic field to control the discharge flow rate has been used. In recent years, the control method has been diversified. Interest is also increasing.

The flow control method in the mold 3 through the magnetic field includes a molten steel flow control method using a fixed magnetic field formed by using a direct current, a molten steel flow control technology using a flow magnetic field formed by using an alternating current, and such a fixed magnetic field and flow. There is a technology that uses the magnetic field at the same time, the application of these technologies requires a lot of equipment cost, such as magnetic field core, control device, various software.

However, in the combustion casting mold 3 as described above, a technique of applying a current value to the discharged molten steel to form a magnetic field to control the discharge flow rate, among which a method of controlling the flow in the mold using a fixed magnetic field As shown in FIG. 4, as shown in the existing magnetic field control apparatus in the performance mold, the strengths of the magnetic fields formed in all regions in the mold are equal.

Therefore, the molten steel discharged from the immersion nozzle 4 is applied with the same current value in the casting width direction irrespective of the operating conditions such as the casting width and the Ar flow rate.

In general, when the casting speed increases, the magnetic field current value applied according to the casting speed is generally applied to increase the current value in order to stabilize the surface and compensate the temperature of the surface.

When the magnetic field strength is uniformly applied in the casting width direction in this way, as shown in FIG. 2, the molten steel discharged from the immersion nozzle 4 is fitted to the mold short side portion 9 and the upstream flow 7 and the downstream flow ( It is divided into two flows of 8), of which the upstream 7 is not flowed to the upper short side portion 9 by the magnetic field break applied to the upper portion, and is further directed to the mold central portion 10.

Therefore, the supply of molten steel to the short side portion 9 in the mold 3 is reduced, so that the cooling of the slab is performed, and as is generally known, the shortening portion 9 is caused by the cooling of the slab. The depth of the hook (solidification boundary layer generated during mold vibration) is increased in the solidification cell of the hook, and the hook is caught by air bubbles or inclusions, which occurs as a defect during cold rolling, which greatly affects the quality.

In order to solve the above problems, the present invention provides a magnetic field in the casting width direction of the continuous casting mold to prevent slab cleanliness generated at the end of continuous casting and deterioration of steelmaking defects during rolling, and to achieve a proper flow in the mold. By controlling the strength differently, the width of the continuous casting mold capable of suppressing the generation of bubbles and inclusions by reducing the hook depth, which is the boundary layer of the solidification cell, through the cooling of slab through the supply of molten steel to the mold short sides. Its purpose is to provide a directional magnetic field control method.

1 is a conceptual diagram of a continuous casting process to which the present invention is applied;

2 is a conceptual diagram illustrating the necessity of molten metal flow control in a continuous casting mold;

Figure 3 is a side view showing a magnetic field control device inside the continuous casting mold;

4 is a plan view showing a magnetic field control device in the continuous casting mold;

5 is a plan view showing a magnetic field control device applied to the widthwise magnetic field control method of the continuous casting mold according to the present invention;

6 is a conceptual diagram schematically showing an apparatus for measuring magnetic field strength inside a continuous casting mold;

7 is a graph showing the results of measuring the magnetic field strength of the continuous casting mold to which the widthwise magnetic field control method of the continuous casting mold according to the present invention is applied;

8 is a graph showing the measured values of the strength of the magnetic field applied to the continuous casting mold 600A and 300A applied to the widthwise magnetic field control method of the continuous casting mold according to the present invention;

9 is a graph showing the trend line and the reliability of the difference value of the magnetic field to which 600A and 300A is applied to the continuous casting mold to which the widthwise magnetic field control method of the continuous casting mold according to the present invention is applied;

10 is a graph showing the trend line and the reliability of the difference with the measured value for the correction of the calculated value according to the widthwise magnetic field control method of the continuous casting mold according to the present invention;

11 is a graph showing the ratio of the [short side / center] magnetic field strength of the continuous casting mold to which the widthwise magnetic field control method of the continuous casting mold according to the present invention is applied.

♣ Explanation of symbols for main part of drawing ♣

3: Continuous casting mold 4: Immersion nozzle 9: Short edge 10: Center portion

14: Long side 13: Magnetic field core 12: Core plate

In order to achieve the above object, the present invention is a method for controlling the magnetic field in the width direction of the mold for the optimization of the molten steel discharged from the immersion nozzle in the mold of the continuous casting process, the short side and the central portion of the continuous casting mold Reducing and installing the number (thickness) of the core plate attached to the magnetic field core installed in the long side part so as to change the magnetic field intensity applied to the two sides toward the both sides starting from the center of the long side part; It is characterized in that it comprises a step of reducing the depth of the hook which is the boundary layer of the solidification cell by supplying molten steel to the short side by varying the ratio of the magnetic field strength applied to the short side and the center of the continuous casting mold A method of controlling the widthwise magnetic field of a continuous casting mold is provided.

In addition, the present invention is to change the ratio of the magnetic field strength applied to the short side and the center of the continuous casting mold to reduce the depth of the hook, which is the boundary layer of the coagulation cell magnetic field applied to the short side and the center according to the following equation Provided is a widthwise magnetic field control method of a continuous casting mold, wherein the ratio of the intensity is varied.

Here, y is the maximum current value applied, and x is the ratio of the magnetic field strength applied to the short side portion 9 and the central portion 10.

Hereinafter, with reference to the accompanying drawings will be described in detail the configuration of the present invention.

3 is a side view showing a magnetic field control device inside the continuous casting mold, Figure 4 is a plan view showing a magnetic field control device inside the continuous casting mold.

As shown in FIG. 3, the basic system for forming the fixed magnetic field in the upper and lower parts in the direction viewed from the side with respect to the center of the continuous casting mold 3 in the width direction is shown in FIG. 4. As shown, when a predetermined current value is applied inside the playing mold 3, it can be seen that regions of the same value of the magnetic field strength are formed in the upper and lower portions.

5 is a plan view showing a magnetic field control device applied to the widthwise magnetic field control method of the continuous casting mold according to the present invention.

The present invention is a method for differently setting the magnetic field strength of the upper portion in the width direction, the most appropriate setting method, as shown in Figure 5, the mounting of the upper core plate (Core Plate) 12 having a thickness of 20mm By varying the number, four plates are mounted at the center of the mold long side portion 14, and one core plate 12 is also placed at the side closest to the mold short side portion 9 to improve the supply ability of the molten steel. It did not install, reducing the break performance.

That is, the number of core plates 12 mounted on the magnetic field core 13 was decreased one by one from four mold center portions to the mold short side portion 9.

FIG. 6 is a conceptual view schematically illustrating an apparatus for measuring magnetic field strength inside a continuous casting mold. The measuring sensor 20 is inserted into the center of a mold 3 and then connected to an electrical signal thereto (Gauss / Tesla Meter). 21).

7 is a graph showing the measurement results of the magnetic field strength of the continuous casting mold applying the widthwise magnetic field control method of the continuous casting mold according to the present invention, Figure 8 is a widthwise magnetic field control method of the continuous casting mold according to the present invention This is a graph showing the measured values of the magnetic field applied 600A and 300A to the continuous casting mold applied.

The measurement is shown in Figure 7 based on the maximum value for the measured value after measuring the magnetic field strength while lowering the measuring sensor 20 from the top to the bottom in the width direction for each applied current value.

As a result of the measurement, the magnetic field strength was changed depending on the number of core plates 12 mounted. As the number of core plates 12 mounted was increased, the magnetic field strength value increased, and the smaller the magnetic field strength value decreased.

FIG. 9 is a drawing again to correct the difference for 600A and 300A for the result of deriving the trend curve and the trend curve equation according to the applied current value for the measured magnetic field strength.

When the current values 600A and 300A are applied, the trend curves for the maximum magnetic field strengths according to the width positions formed in the mold 3 are represented by Equations 1 and 2, respectively.

Here, y is the maximum magnetic field intensity Tesla according to the distance from the mold center 0 according to each applied current value, and x is the distance (mm) from the mold center 0.

FIG. 9 is a graph illustrating trend lines and reliability of a difference value of magnetic fields to which 600 A and 300 A are applied to a continuous casting mold to which a widthwise magnetic field control method of the continuous casting mold according to the present invention is applied.

In addition, as shown in FIG. 9, when 600 A and 300 A are applied to the magnetic field core 13 of the mold 3, the core plate 12 decreases in the casting width direction with respect to a difference thereof, that is, an absolute value for 300 A. It is a schematic diagram of the changing magnetic field strength, which can be expressed by Equation 3 below, and confidence in the value (R2 = 1).

Here, y is the difference value Tesla at 600A and 300A application according to the distance from the mold center (0), and x is the distance (mm) from the mold center (0).

FIG. 10 is a graph illustrating a trend line and a reliability of a difference from a measured value for correcting a calculated value according to a widthwise magnetic field control method of a continuous casting mold according to the present invention.

Table 1 and Figure 10 shows the intermediate process to derive the following Table 2.

That is, Table 1 is not considering the difference between the actual measured value, the value obtained by calculating each current value for the absolute value 300A of FIG. 9, the correction process for the difference between the calculated value and the measured value Table 2 considers the values (Fig. 10).

10 is the same as Equation 4 below.

Here, y is the difference between the measured value and the calculated value for the maximum magnetic field intensity Tesla, and x is the distance in mm from the mold center (0).

Table 2 described above is the maximum magnetic field strength value applied in the width direction that can be obtained for each current value when the core plate 12 having the shape shown in FIG. 5 is set.

11 is a graph showing the ratio of the [short side / center] magnetic field strength of the continuous casting mold to which the widthwise magnetic field control method of the continuous casting mold according to the present invention is applied.

FIG. 11 is a ratio of the magnetic field strength of the appropriate [short side / center] derived from the present invention, and the equation for the derived magnetic field strength is expressed by Equation 5 below.

Here, y is the maximum current value applied, and x is the ratio of the magnetic field strength of the [short side / center].

Hereinafter, application examples of the technical contents of the present invention in more detail in the application to the present invention.

EXAMPLE

As described above, the number of core plates 12 mounted on the magnetic field core 13 of the continuous casting mold 3 gradually decreases from the center of the long side portion 12 toward the short side portion 9 so as to mount the magnetic field core. The results of casting by applying current values of 300A and 600A to (13) were investigated by measuring the steelmaking defect rate index and the short side hook depth index, and the results are shown in Table 3.

In Table 3, when the magnetic field strength ratio is 1, the magnetic field strengths of the short side portion 9 and the central portion 10 of the mold 3 are the same. In contrast to the present invention, the short side 9 indicates that the magnetic field is stronger than the central portion 10.

For each applied current value (300A, 600A), the steelmaking defect rate index is a value obtained by converting the value of the largest defect occurrence rate as 1, and the short side solidification shell boundary layer hook depth is also the deepest value. Is the value converted into one.

As a result of the comparative analysis for each case, the magnetic field strength is controlled in the width direction as described above, and the intensity is set to decrease the strength of the magnetic field while moving from the central portion 10 to the short side portion 9, that is, the short side portion / It was found that setting the ratio of the central magnetic field strength to 0.532 or 0.405 has the smallest steelmaking defect rate index and the short side hook depth index, thereby improving cast quality.

The present invention reduces the collection of bubbles / inclusions by reducing the hook depth, which is the boundary layer of the solidification cell through the slow cooling of the cast steel through the supply of molten steel to the mold short side portion 9 by controlling the magnetic field strength in the casting width direction differently. Of course, in the center of the mold width direction to maintain a certain breaking effect to reduce the large fluctuations in the flow pattern in the mold due to Ar flowing through the immersion nozzle.

Therefore, according to the present invention, the depth of the solidification boundary layer and the bubbles / There is an effect that can improve the quality by preventing the collection of inclusions.

Claims (2)

In the method of controlling the width direction magnetic field of the mold (3) for the optimization of the molten steel flow discharged from the immersion nozzle (4) inside the mold (3) of the continuous casting process, The number of core plates 12 mounted on the magnetic field core 13 installed on the long side portion 14 so as to change the magnetic field strength applied to the short side portion 9 and the central portion 10 of the continuous casting mold 3. (Thickness) is installed by decreasing coupling toward both sides from the center of the long side portion 14; By changing the ratio of the magnetic field strength applied to the short side portion 9 and the central portion 10 of the continuous casting mold (3) by supplying molten steel to the short side portion (9) to achieve a complete cooling of the cast slab boundary layer of the solidification cell Width direction magnetic field control method of the continuous casting mold, characterized in that the step of reducing the depth of the in-hook. The method according to claim 1, The step of reducing the depth of the hook, which is the boundary layer of the coagulation cell, by changing the ratio of the magnetic field strengths applied to the short sides 9 and the central portion 10 of the continuous casting mold 3 according to the following equation 9 And a ratio of the magnetic field strength applied to the central portion 10 in the widthwise magnetic field control method of the continuous casting mold. Here, y is the maximum current value applied, and x is the ratio of the magnetic field strength applied to the short side portion 9 and the central portion 10.