JP2611594B2 - Method of manufacturing slab for steel slab - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous casting method for applying an electromagnetic force to molten steel in a mold to suppress a wave on a molten metal surface.

[0002]

2. Description of the Related Art Generally, in continuous casting, molten steel is injected into a mold while being shielded from the atmosphere using an immersion nozzle in order to prevent oxidation of the molten steel. The immersion nozzle for continuous slab casting has a pair of discharge ports that open left and right at the lower end. Molten steel is discharged from these discharge ports substantially equally to the left and right from the center of the mold to the periphery.

In order to improve the productivity of a continuous casting machine, increasing the casting speed, that is, the speed of injecting molten steel into a mold, has been an issue in continuous casting in recent years. However, when the injection speed is increased beyond 1.5 m / min, the molten steel in the mold is violently disturbed, and the wavelength on the molten metal surface is several meters long so that the immersion nozzle becomes a fulcrum of the seesaw. , Various waves ranging from short wavelengths of several centimeters are generated, and the waves on the molten metal surface become large. Such a wave of the molten metal causes entrainment of the mold powder into the molten steel. In addition, the violent disturbance of the molten steel in the mold prevents the entrained mold powder and nonmetallic inclusions in the molten steel generated in the refining process from floating toward the molten metal surface in the mold, and as a result, the mold This makes it difficult to remove these inclusions from the molten steel inside. The inclusions incorporated in the slab in this way become apparent as defects on the surface or inside of the product that has undergone the final process, and significantly lower the quality of the product.

In order to prevent the inclusion of inclusions as described above, a magnetic field generator is provided in the mold, and the flow of the molten metal discharged from the immersion nozzle is pushed back from the short side of the mold to the immersion nozzle in the width direction of the mold. The force of the molten steel discharge flow is reduced by applying an electromagnetic induction force in the direction. As a result, techniques have been developed for reducing the wave of the molten metal surface and suppressing the disturbance of the molten steel in the mold (for example, Japanese Patent Publication No. 64-10305). It has been a target of normal operation to reduce the level change of the molten metal to about 5 mm or less.

[0005]

Since the magnetic field generator according to the present technology is of the linear moving magnetic field type as described above,
In the operation, an appropriate current value and frequency must be determined. Of these, the frequency was conventionally determined as follows. That is, to increase the damping rate of the molten steel discharge flow, the Lorentz force acting on the molten steel discharge flow must be increased. For that purpose, the relative speed between the molten steel discharge flow and the magnetic flux moving from the short side of the mold toward the immersion nozzle must be increased. Therefore, the moving speed of the magnetic flux,
That is, the frequency must be increased. However, when the frequency is increased, the magnetic permeability of the stainless steel mold copper plate and the molten steel constituting the mold frame decreases, and the magnetic flux density that effectively acts on the molten steel discharge flow from the immersion nozzle decreases. Therefore, the optimum frequency that satisfies these two conditions is set to 0.5 Hz.

FIG. 1 is a diagram showing a state in which the current frequency of a magnetic field generator is 0.5 Hz and the direction of movement of the magnetic field is from the short side to the immersion nozzle, and the current value is changed. It shows the magnitude of the wave. Here, the magnitude of the wave was represented by the average value of the level wave amplitude for 10 minutes at positions 40 mm away from the short side of the mold and 40 mm from the long side inside the mold, respectively. As shown in FIG. 2, the long-period wave height of the mold fluctuation near the short side of the mold generally consisting of a short-period wave of about 1 to 2 seconds and a long-period wave of about 10 seconds to 15 A peak height difference 32 between the maximum and the minimum of the short-period wave height at the time closest to the time indicating the minimum). Under conditions where the casting speed is relatively slow and the mold width is narrow (open inverted triangle and open square in the figure), the current value of the magnetic field generator is increased, and the effect of suppressing the surface wave is increased. However, under the conditions of relatively high casting speed and wide mold width (black triangle and black square in the figure), if the current value of the magnetic field generator is excessively increased, the effect of suppressing the surface wave wave becomes small, and on the contrary, the wave surface wave wave The result is to encourage.

The present invention solves the problems represented by the above,
In other words, in continuous slab casting, the molten steel flow flowing into the mold from the forked molten steel discharge hole at the bottom of the immersion nozzle applied the molten steel surface wave to the molten steel surface in the mold using a linear magnetic field generator installed in the mold to control the electromagnetic wave. The present invention provides an operation method showing the relationship between the setting of the current frequency of the magnetic field generator and the casting conditions for suppressing the surface wave motion under a wide casting condition.

[0008]

The magnetic field generator according to the present invention is of a linear moving magnetic field type, and the magnetic flux moves from the mold short piece side to the immersion nozzle side in a direction perpendicular to the slab drawing direction. Alternatively, the magnetic flux is at an angle toward the molten steel flow flowing from the forked molten steel discharge hole at the lower part of the immersion nozzle, that is, a direction inclined from a plane orthogonal to the slab drawing direction from the mold short side to the immersion nozzle side. Moving. Therefore, the magnetic flux density at one point in the mold changes periodically. In other words, the flow of the molten metal discharged from the immersion nozzle does not always intersect with the magnetic flux having a constant magnetic flux density in time. By the end of passing through the application area, a difference occurs in the total amount of the electromagnetic force received by the fragments of the melt flow.

The inventors have determined that the time required for a fragment of the molten metal stream discharged from the immersion nozzle to pass through the area to which the linear moving magnetic field is applied, and that the fragment of the molten metal stream discharged from the immersing nozzle determines the linear moving magnetic field While passing through the region, the number of times that the magnetic flux intersects this molten metal flow is determined by the width of the mold, the amount of molten steel discharged per time determined by the mold width and the casting speed, the molten steel discharge angle from the immersion nozzle, and the immersion depth of the discharge port of the immersion nozzle. And the current frequency of the magnetic field generator. Then, while the fragment of the molten metal stream discharged from the immersion nozzle passes through the application region of the linear moving magnetic field, the number of times that the magnetic flux intersects the molten metal stream depends on the number of times that the fragment having the molten metal stream from the immersion nozzle The difference in the time of ejection causes a difference in the total amount of the electromagnetic force received by the fragment of the melt flow before passing through the application area of the linear moving magnetic field ''. The magnitude of the phenomenon is determined I found it.

In order to reduce such a phenomenon, any fragment of the molten metal stream discharged from the immersion nozzle must cross the magnetic flux moving at the same number of times while passing through the region where the linear moving magnetic field is applied. It is to be. Two methods are conceivable for that purpose. The first is a method in which any fragment of the molten metal stream discharged from the immersion nozzle flows in the region where the linear moving magnetic field is applied for as long as possible. For this purpose, the casting speed is reduced to reduce the flow velocity of the molten metal flow discharged from the immersion nozzle, or the discharge angle of the immersion nozzle is made shallow, so that the molten metal flow discharged from the immersion nozzle flows through the area where the linear moving magnetic field is applied. It is necessary to allow the magnetic flux to flow parallel to the moving direction. However, if the casting speed is reduced, the production efficiency of the continuous caster is reduced, and if the discharge angle of the immersion nozzle is made shallow, the mold powder is entangled by the molten metal flow and the like, and inclusions are taken into the slab. Therefore, this method is not advisable.

Second, the current frequency of the magnetic field generator is increased to increase the moving speed of the magnetic flux, so that any fragments of the molten metal stream discharged from the immersion nozzle are as similar as possible while passing through the region where the linear moving magnetic field is applied. Is to cross the magnetic flux the number of times. According to the second method, there is no direct restriction on the casting speed and the discharge angle of the immersion nozzle. However, when the current frequency of the magnetic field generator is increased, the magnetic permeability decreases, and the magnetic flux density effectively acting on the molten steel discharge flow from the immersion nozzle decreases. Therefore, this current frequency is
It is desirable that the lowest frequency necessary for any piece of the molten metal stream discharged from the immersion nozzle to cross the magnetic flux as many times as possible while passing through the application region of the linear moving magnetic field.

The second method is a method discovered by the inventors through experiments on a continuous casting machine. The immersion nozzle is selected by selecting the current frequency of the magnetic field generator and adjusting the moving speed of the linear magnetic field. This is a method in which any fragment of the molten steel flow discharged from the apparatus is set to a frequency equal to or higher than the minimum frequency required to cross the moving magnetic flux (moving magnetic field) at least once while passing through the application region of the linear magnetic field. That is, since any fragment of the molten steel flow discharged from the immersion nozzle is subjected to the braking action of the magnetic flux density of at least one cycle of the linear magnetic field while passing through the application region of the linear magnetic field, the portion that is braked by the molten steel flow is not braked. The part cannot be biased. If the selected frequency is the lowest frequency or an integer multiple thereof, all the pieces of the molten steel flow are equally braked, so that the wave amount of the molten steel in the mold is further reduced.

According to the second method, the wave amount of the molten metal can be reduced without being directly restricted by the casting speed or the discharge angle of the immersion nozzle. However, when the current frequency of the magnetic field generator is increased, the magnetic permeability decreases and the magnetic flux density in the mold decreases. Therefore, the current frequency is set to the required minimum frequency obtained by the method described below or twice or three times the minimum required frequency. It is desirable that the frequency be an integral multiple such as double. This integral multiple value is the maximum value because the braking force applied by the moving magnetic flux to the fragment of the molten steel flow discharged from the immersion nozzle increases in proportion to the product of the square of the magnetic flux density and the frequency. It is effective to select a multiple value. The inventors have determined the minimum current frequency required in the second method as follows.

First, in the magnetic field generator according to the present invention, a time interval P [sec] at which a magnetic flux moving at a current frequency F [Hz] periodically passes through an application region of a linear moving magnetic field.
Can be expressed by the following equation (2). P = 1 / (N · F) (2) where the symbol N in equation (2) means the number of poles of the magnetic field generator.

On the other hand, FIG. 3 illustrates a case where the moving direction of the magnetic flux is a direction orthogonal to the direction of drawing the slab. As shown in FIG. 3, when the downward angle α of the discharge hole 29 of the immersion nozzle is large, 3 until the minute fragments of the molten steel flow discharged from the discharge holes 29 enter and deviate from the application region of the linear moving magnetic field, that is, the lower end 34 of the application region of the linear moving magnetic field in FIG.
, Ie, the effective braking time T [sec] can be expressed by the following equation (3). T = (W−D) / (V · sin θ) (3)

On the other hand, when the downward angle α of the discharge hole 29 of the immersion nozzle is small, or when the relative angle between the direction of the molten steel flow discharged from the discharge hole 29 of the immersion nozzle and the moving direction of the magnetic flux is small, the discharge hole 29 The molten metal discharged from the mold reaches the solidified shell on the short side of the mold before exiting above and below the linear moving magnetic field. In such a case, the time required for the fragment of the molten steel flow to exit the discharge hole 29 of the immersion nozzle and reach the solidified shell on the short side of the mold is the effective braking time T [sec], and the following equation (3) Alternatively, the time T can be obtained by the equation (4). T = A / (2V · cos θ) (4)

In the above formulas (3) and (4), V is a region in which the flow of the molten metal discharged from the immersion nozzle is applied with a linear moving magnetic field (where the applied region is a magnetic flux measured at the center in the thickness direction of the mold). The average flow velocity [m / sec] when passing through a region having a magnetic flux density of 1/2 of the maximum value as a time average value around the position where the time average of the density shows the maximum value is the center. The angle [rad] that the molten metal stream discharged from the immersion nozzle makes with the horizontal line when passing through the application region of the linear moving magnetic field, W is the width [m] of the application region of the linear moving magnetic field in the mold height direction, and D is the immersion nozzle. When the upper end of the discharge port is in the application region of the linear moving magnetic field, the distance [m] from the upper end of the discharge port of the immersion nozzle to the upper end of the application region of the linear moving magnetic field,
In other cases, D = 0 [m], and A means the casting width [m].

It is very difficult to directly measure the values of V and θ with an actual continuous casting machine. Then, the inventors reproduced actual casting with a 1/3 scale mold water model, and measured V and θ. However, V and θ do not take into account the effect of the discharge flow braking by the magnetic field generator.

From the above equations (2), (3) and (4), it can be seen that the total amount of magnetic flux intersecting while passing through the magnetic field application region is the same for any of the fragments of the molten steel flow discharged from the immersion nozzle. The minimum current frequency F required to be satisfied can be expressed as the following equation (5) or (6) from the relationship of P = T. When the molten steel flow discharged from the immersion nozzle escapes below the linear moving magnetic field, the following equation (5) is used. F = (V · sin θ) / {N · (W−D)} (5) If the molten steel flow discharged from the immersion nozzle does not escape above and below the linear moving magnetic field, the following equation (6) is used. Used. F = (2V · cos θ) / (N · A) (6) FIG. 3 is a schematic diagram for explaining symbols in the above formula (5), and the moving direction of the magnetic flux is orthogonal to the slab drawing direction. An example is shown in which the direction is the same.

FIG. 4 shows the relationship between the current frequency of the magnetic field generator and the maximum value of the time average of the magnetic flux density in the mold obtained by measuring the current frequency with a continuous casting machine and calculating from the measured values. . When the current frequency increases, the magnetic permeability of the stainless steel mold copper plate and the molten steel constituting the mold frame decreases, and the magnetic flux density decreases. The magnetic flux density value in the mold of each continuous casting machine is not necessarily the same as the actual equipment structure and performance.
Is not the same as According to our experiments, it is necessary to use a flux density value in the mold of at least 1200 gauss to effectively dampen the flow velocity of the molten steel flow discharged from the immersion nozzle, so the example of FIG. Then, 2.
A current frequency of 8 Hz or less is selected to adjust the moving speed of the linear magnetic field.

The value determined by the formula (5) or (6) is defined as the minimum value, and the maximum value is defined as the maximum value. The decrease in the magnetic permeability causes a significant decrease in the magnetic flux density which effectively acts on the molten steel discharge flow from the immersion nozzle. Operating the magnetic field generator in a current frequency range that does not have such a value, even under conditions where the casting speed is relatively high and the mold width is wide, the magnetic field for suppressing the surface wave in the mold well. The discoverers have found that this is a method of setting the current frequency of the generator.

Further, the present inventors have proposed a method for solving the inconvenience that the required minimum frequency or a frequency that is an integral multiple thereof cannot be immediately obtained because the values of V and θ cannot be directly measured in an actual continuous casting operation. Was found.

The casting width of the continuous casting is A [m], the casting thickness is B [m], the casting speed is C [m / sec], and the diameter area of the discharge hole of the immersion nozzle is S [m ^2]. ], Using the effective braking parameter E calculated by the following equation (6) or (7) based on these values, a wide range of casting conditions,
Casting width 0.7-2.6 m, casting thickness 0.1-0.3 m, casting speed 0.6-5.0 m / min, molten steel discharge angle α of immersion nozzle
From a downward angle of 60 ° to an upward angle of 15 °, and a casting capacity of up to 15 tons / min. For an operation up to a strand, an experiment using the above-described water model and an experiment using a continuous casting machine were conducted.

As a result, FIG. 13 shows the relationship between the effective braking parameter E, the molten steel discharge angle α of the immersion nozzle, and the required minimum frequency or a frequency F that is an integral multiple thereof.
And that they are arranged as shown in FIG. The effective braking parameter E is obtained by the following equation (6) or (7) according to the molten steel discharge angle α of the immersion nozzle. When −25 ° ≧ α ≧ −60 °, E = A · B · C / {N · (WD) · S} (6) When + 15 ° ≧ α> −25 °, E = 4 ・ B ・ C ・ (cos α) ² / (N ・ A ・ S)… (7)

Here, A is the casting width (m) of continuous casting, and B is
Is the casting thickness (m), C is the casting speed (m / sec), and S is the hole diameter area (m ² ) Respectively.
Note that the hole diameter area S corresponds to the area of a cross section orthogonal to the discharge direction axis of the discharge hole, and the cross sectional shape is a circle, an ellipse, a square, a rectangle, an oval, or the like. In FIG. 13, each straight line shown in the figure is represented by the following equation (8) according to the angle α of the molten steel discharge hole of the immersion nozzle. F = jE + k (8)

However, in the above equation (8), -35 °
When ≧ α ≧ −60 °, j = 0.30, k = 0, −25
When ° ≧ α> −35 °, j = 0.28, k = 0, +1
When 5 ° ≧ α> −25 °, j = 0.26 and k = 0.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is intended to suppress the level wave in the mold in a wide range of slab continuous casting conditions.
The method using electromagnetic braking force using a linear magnetic field generator installed in a mold and the optimum frequency according to casting conditions are clarified. Further, by calculating the effective braking parameter E from the casting conditions, there is provided a method for selecting an optimum frequency according to the molten steel discharge angle α of the immersion nozzle.

The moving magnetic flux of the linear magnetic field generator operating at the current frequency selected in the manner disclosed by the present invention causes turbulence in any piece of molten steel flow flowing into the mold from the forked molten steel discharge hole at the bottom of the immersion nozzle. Because it gives no electromagnetic braking force
The molten steel flow effectively suppresses the surface wave of the molten steel in the mold.

In the continuous casting operation in which the casting is continued by changing the mold width during casting, the present invention can be used to maintain a stable casting speed while maintaining a desired casting speed from a wide casting width to a narrow casting width. And stable slab quality can be easily obtained.

[0030]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 5 is a longitudinal sectional view showing a molten metal level control device used in the continuous casting method according to the present invention. The tundish 2 is provided on the upper part of the continuous casting mold 10, and is supplied with molten steel from a ladle (not shown). The tundish 2 is lined with a refractory 3 and the outside is covered with a steel shell 4. A sliding nozzle 5 is provided at the bottom of the tundish 2. The sliding nozzle 5 has a fixed plate 6 fixed to the steel shell 4 and a sliding plate 7 that slides on the fixed plate 6. The nozzle 5 opens and closes by sliding the sliding plate 7. .

An immersion nozzle 8 is mounted on the lower surface of the sliding plate 7. The lower end of the immersion nozzle 8 is immersed in the molten steel 1 in the mold 10, and the molten steel 1 is discharged from a pair of discharge ports 9 on the left and right sides.

A melt level sensor 14 is arranged facing the melt level in the mold so that the position of the melt level and its change can be detected. The level sensor 14 is connected to the monitoring input side of the sliding nozzle opening controller 16. In addition to the molten metal level sensor 14, two molten metal level sensors 17 are mounted near the short side of the mold, one on each of the two short sides. This level sensor 17 is not connected to the sliding nozzle opening degree control device 16 and is for observing the level wave suppression effect of the magnetic field generator according to the present invention. Further, a magnetic field generator 18 is mounted behind the long side copper plate on both sides of the mold. Table 1 shows the components of the molten steel provided for casting in which the present invention was attempted. Table 2 shows the operating conditions of the casting in which the present invention was attempted.

Table 3 shows the specifications of the magnetic field generator according to the present invention used in the casting for which the present invention was attempted. However, symbol B indicates the magnetic flux density at the time average value at the point where the time average of the magnetic flux density measured at the center in the thickness direction of the mold shows the maximum value. Symbol W is the width in the mold height direction of a region having a magnetic flux density of 1/2 of the maximum value as a time average value at a position where the time average of the magnetic flux density measured at the center in the thickness direction of the mold shows the maximum value. Is shown. FIG. 6 is a layout diagram of coils of the magnetic field generator according to the present invention. (First Embodiment) Next, a method for controlling the level of the molten metal in the mold using the above-described magnetic field generator will be described with reference to the operating conditions of casting listed in Table 2.

First, V and θ under the operating conditions of casting listed in Table 2 were measured with a 1/3 scale mold water model, and the measured values were converted to the actual scale.
The value of 5 m / sec, θ = 0.70 rad was obtained. Therefore,
The effective braking time T [sec] required for a minute fragment of the molten metal stream discharged from the immersion nozzle to enter and deviate from the application region of the linear moving magnetic field is calculated by the following equation (3). 56 (sec) ... (9)

Is calculated. Therefore, even under the condition that the casting speed is relatively high and the mold width is wide, in order to sufficiently suppress the level wave in the mold, in the magnetic field generator according to the present invention, the magnetic flux is applied to the area where the linear moving magnetic field is applied. It is necessary that the time interval P [sec] of the periodic passage be equal to or less than T obtained by the equation (9). The current frequency F of the magnetic field generator at that time
From equation (5), F = 0.89 (Hz)... (10)

Using the above results, in the magnetic field generating apparatus according to the present invention, the result of performing the continuous casting operation for suppressing the surface wave motion in the mold under the condition that the casting speed is relatively high and the mold width is wide is as follows. FIG.

The horizontal axis in FIG. 7 represents time. Time flows from right to left on the page. The vertical axis represents the level of the molten metal near the short side of the mold measured by the molten metal level sensor 17 in FIG. The operating conditions in FIG. 7 are as shown in Table 2.
FIG. 7 shows an example in which the magnetic field generator according to the present invention is not operated, and it can be seen that the molten metal surface near the short side of the mold is largely waved. The magnetic field generator was operated as follows in order to suppress the fluctuation of the molten metal level.

FIG. 8 shows a case where the magnetic field generator is operated at a current frequency of 0.5 Hz and a current value of 1080 A. This frequency is lower than the "lower limit F of the frequency for well suppressing the surface wave motion in the mold even under the condition that the casting speed is relatively high and the mold width is wide" obtained by the equation (10). Actually, as shown in FIG. 8, there is almost no effect of suppressing the mold surface wave near the short side of the mold, and rather promotes the wave wave near the mold short side.

FIG. 9 shows a case where the magnetic field generator is operated at a current frequency of 1.0 Hz and a current value of 1080 A. This frequency is higher than "the lower limit F of the frequency for well suppressing the surface wave motion in the mold even under the condition that the casting speed is relatively high and the mold width is wide" obtained by the equation (10). In fact, as shown in FIG. 9, it can be seen that the effect of suppressing the surface wave near the short side of the mold is great.

FIG. 10 shows a current frequency of 2.0 Hz,
This is a case where the magnetic field generator was operated at a current value of 1080 A. This frequency is higher than "the lower limit F of the frequency for well suppressing the surface wave motion in the mold even under the condition that the casting speed is relatively high and the mold width is wide" obtained by the equation (10). In fact, as shown in FIG. 10, it can be seen that the effect of suppressing the surface wave near the short side of the mold is great.

FIG. 11 is a graph summarizing the results shown in FIGS. 7 to 10, with the horizontal axis representing the current frequency and the vertical axis representing the level of the surface wave near the short side of the mold. The level wave is suppressed at a frequency higher than the lower frequency limit (0.89 Hz) for suppressing the level change in the mold obtained by the above equation (10). (Second embodiment)

FIG. 12 shows the change in the effect of suppressing the surface wave near the short side of the mold when the current value of the magnetic field generator is changed. The casting conditions for obtaining the results shown in FIG. 12 are as shown in Table 2. In the figure, black circles and black squares are examples under conditions where the casting speed is relatively slow and the mold width is narrow, and the current value is matched when the frequency of the magnetic field generator is both 0.5 Hz and 1.0 Hz. The effect of suppressing the surface wave near the short side of the mold is obtained. Under these casting conditions, V = 0.
67m / sec, θ = 0.43rad, W = 0.48m,
The lower limit current frequency F obtained by equation (4) is 0.43H
z, the effective braking parameter E is 1.2. On the other hand, the open circles and open squares in the figures indicate the same data as in FIGS. 8 and 9, respectively. The casting speed is relatively high, the casting width is wide, and the effective braking parameter E is 2.6. . Of these, the open circles indicate the case where the current frequency is lower than 0.59 Hz, which is lower than the lower limit of the current frequency F = 0.89 Hz. It can be seen that an increase in the current value results in promoting the surface wave near the short side of the mold. . On the other hand, the white square indicates the lower limit of the current frequency F =
It is a case where the current frequency higher than 0.89 Hz is 1.0 Hz, and it can be seen that an effect of suppressing the surface wave near the short side of the mold corresponding to the current value can be obtained.

FIG. 13 shows the casting width, casting thickness, casting speed,
The lower limit value of the current frequency for suppressing the surface wave motion in the mold by widely changing the casting conditions such as the type of the immersion nozzle is shown by casting a continuous casting machine and observing the results. The current frequency is on the vertical axis and the casting conditions are the effective braking parameters on the horizontal axis.
And the discharge direction axis of the discharge hole of the immersion nozzle in FIG.

When the molten steel flow discharged from the immersion nozzle escapes below the linear moving magnetic field, that is, −25 ° ≧ α
For ≧ −60 °, the effective braking parameter E = A ・ B ・ C /
It is represented by {N · (WD) · S}. On the other hand, when the molten steel flow discharged from the immersion nozzle does not escape above and below the linear moving magnetic field, that is, when + 15 ° ≧ α> −25 °, the effective braking parameter E = 4 · BC · (cos α) ²
A small value of 1 to 2 of the effective braking parameter E in /(N.A.S) represents a casting condition in which the casting width is relatively narrow or the casting speed is slow, and is used to suppress the surface wave of the molten metal. The line indicating the lower limit of the current frequency is below 0.8 Hz, but as the casting width becomes wider or the casting speed becomes faster, the value of parameter E increases to 3 or 4 and suppresses the surface wave. It has been found that the lower limit of the current frequency for performing the operation is increased by a straight line rising to the right, and the lower limit of the current frequency F is increased. However, the upper limit of the allowable current frequency of the decrease in the magnetic permeability is constant regardless of the casting width and the casting speed.

FIG. 13 also shows the casting example shown in FIG. Black circles, black squares, white circles, and white squares in FIG.
Black circles, black squares, white circles, and white squares in FIG. 12 have the same meanings. In the case of a casting width of 1550 mm represented by a white circle and a casting speed of 2.0 m / min, the angle α of the discharge hole of the immersion nozzle is 4
Because it is located below the lower limit of the current frequency straight line indicated by 5 degrees, the part of the molten steel flow discharged from the immersion nozzle receives the electromagnetic braking force and the part that does not receive the electromagnetic braking force is biased. The result was that the wave amount of the molten metal in the mold became large. In the example of a casting width of 950 mm represented by a black square and a casting speed of 1.6 m / min, the lower limit of the current frequency value is 0.43 Hz, but the current frequency of 1.0 Hz which is twice is used.

If the molten steel flow discharged from the immersion nozzle does not escape above and below the linear moving magnetic field, -25 ° ≧ α
An example of casting of ≧ −60 ° is also shown in FIG. The double circle in the figure is an example in which a casting width of 2100 mm, a casting thickness of 250 mm, and a casting speed of 2 m / min were cast at a molten steel discharge angle α of 15 ° downward, and the effective braking parameter E was 1.1. The lower limit of the current frequency is 0.40 Hz. Even at this reference current frequency, there was an effect of suppressing the surface wave motion, but even if the frequency was further increased, the value of the product of the square of the magnetic flux density and the frequency could be expected to increase. When casting with Hz, the surface wave was suppressed even better. Similarly, the white triangle in the figure indicates a casting width of 700 mm, a casting thickness of 250 mm,
In this example, the casting speed was 3 m / min and 1.5 m / min, and the molten steel discharge angle α of the immersion nozzle was cast downward at 5 °. The effective braking parameter E was 5.0 and 2.5, and the lower limit of the current frequency was 1.30.
Hz and 0.65 Hz. Double frequency at 3m / min casting speed
At 2.60 Hz and a casting speed of 1.5 m / min, the surface wave was successfully suppressed at 0.65 Hz.

FIG. 14 shows this relationship together with a straight line representing the lower limit current frequency and a straight line representing an integral multiple of the current frequency. In the example of the black square, the current frequency of 1.0 Hz is used, so that the fragments of the molten steel stream discharged from the immersion nozzle receive the electromagnetic braking force twice equally while passing through the region where the linear moving magnetic field is applied. Therefore, the amount of surface wave motion in the mold was suppressed to a satisfactory level. As described above, the selection of the frequency is not limited to the lower limit current frequency. Even at a frequency higher than the lower limit current frequency, and at a frequency twice or three times the lower limit current frequency, it is equal to or lower than the upper limit of the current frequency at which the magnetic permeability can be reduced. Then, the effect of suppressing the surface wave in the mold can be obtained.

[0049]

[Table 1]

[0050]

[Table 2]

[0051]

[Table 3]

[0052]

As described above, by operating the magnetic field generator within the range of the current frequency in the present invention,
Even under conditions where the casting speed is relatively high and the mold width is wide, it is possible to sufficiently suppress the surface wave motion in the mold. And
This prevents the mold powder from being caught in the molten steel caused by the wave of the molten metal in the mold. Also, since the molten steel in the mold is prevented from being violently disturbed due to the wave of the molten metal in the mold, entrained mold powder and nonmetallic inclusions in the molten steel generated in the scouring process are directed toward the molten metal in the mold. It does not prevent it from ascending, thereby facilitating removal of these inclusions from the molten steel in the mold.

[Brief description of the drawings]

FIG. 1 is a graph showing the magnitude of wave motion of a molten metal near a short side in a mold when the current value of a magnetic field generator is 0.5 Hz and the current value is changed.

FIG. 2 is a graph for explaining the definition of the level wave amplitude.

FIG. 3 is a schematic view of a part of a mold as viewed from a long side surface for explaining symbols in the formula (4).

FIG. 4 is a graph showing the relationship between the current frequency of the magnetic field generator and the maximum value of the time average of the magnetic flux density in the mold obtained by calculation.

FIG. 5 is a longitudinal sectional view showing a molten metal level control device used in the continuous casting method according to the present invention.

FIG. 6 is a wiring diagram showing a coil of the magnetic field generator according to the embodiment of the present invention as viewed from the upper surface of the mold.

FIG. 7 shows a result of performing a continuous casting operation in which a casting speed is relatively high and a mold width is wide and a mold surface wave near a short side in a mold is suppressed under a condition of a wide mold width in the magnetic field generator according to the embodiment of the present invention. It is a graph which shows each.

FIG. 8 shows a result of performing a continuous casting operation in which a casting speed is relatively high and a mold width is wide near a short side in a mold, under a condition of a relatively high casting speed and a wide mold width in the magnetic field generator according to the embodiment of the present invention. It is a graph which shows each.

FIG. 9 shows a result of performing a continuous casting operation for suppressing the surface wave motion near the short side in the mold under the condition that the casting speed is relatively high and the mold width is wide in the magnetic field generator according to the embodiment of the present invention. It is a graph which shows each.

FIG. 10 shows a magnetic field generator according to an embodiment of the present invention.
It is a graph figure which shows the result of having performed the continuous casting operation which suppresses the surface wave motion near the short side in a mold under the conditions where the casting speed is relatively high and the mold width is wide.

11 is a graph showing the results of FIG. 6 with the current frequency plotted on the horizontal axis and the level of the surface wave near the short side of the mold on the vertical axis.

FIG. 12 is a graph showing the change in the effect of suppressing the surface wave near the short side of the mold when the current value of the magnetic field generator is changed.

FIG. 13 is a graph showing an experimental result showing a relationship between a lower limit value of a current frequency for suppressing a surface wave motion in a mold, an effective braking parameter E calculated from casting conditions, and an angle α of a discharge hole of a submerged nozzle. FIG.

FIG. 14 is a graph showing a straight line indicating a lower limit of the current frequency for suppressing the surface wave motion in the mold, a straight line indicating a current frequency that is an integral multiple of the straight line, and a graph showing an experimental example.

[Explanation of symbols]

2 Tundish 3 Refractory 4 Steel 5 Sliding nozzle, 6 Fixing plate 7 Sliding plate 8 Immersion nozzle 9 Discharge port 10 Mold 14 Mold surface sensor 16 Controller 17 Mold surface sensor 18 Magnetic field generator 20 Mold upper end 21 Mold surface 22 Mold Lower end 23 W: width in the height direction of the mold of the application region of the linear moving magnetic field 24 width in the height direction of the coil of the magnetic field generator 25 D: immersion when the upper end of the immersion nozzle discharge port is in the application region of the linear moving magnetic field The distance from the upper end of the nozzle discharge port to the upper end of the application region of the linear moving magnetic field. 26 The angle α [degree] between the discharge direction axis of the discharge hole of the immersion nozzle and the horizontal plane. 27 V: The flow of the molten metal discharged from the immersion nozzle is the linear moving magnetic field. Application area (here, the application area is the position where the time average of the magnetic flux density measured at the center in the thickness direction of the mold shows the maximum value. The average flow velocity when passing through a region having a magnetic flux density of 1/2 of its maximum value as the time average value with the center as the center) 28 The coil of the magnetic field generator 29 The discharge port of the immersion nozzle 30 The mold near the short side of the mold Short-period wave of the wave 31 Long-period wave of the mold wave near the short side of the mold 32 Amplitude of the mold wave near the short side of the mold 33 Upper end of the application area of the linear moving magnetic field 34 Lower end of the application area of the linear moving magnetic field 35 Discharge of the immersion nozzle The hole diameter area S of the hole: the shape of the cross section perpendicular to the discharge direction axis of the discharge hole, that is, a circle, an ellipse,
The area is a square, rectangle, oval, etc.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Kazuo Okimoto 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Takashi Mori 1-1-2, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan (56) References JP-A-3-57542 (JP, A) JP-A-2-89544 (JP, A) JP-A-57-199549 (JP, A) JP-A-59-104258 (JP, A A)

Claims (4)

(57) [Claims] 1. A linear transfer for decelerating and adjusting the flow of molten steel in a mold.
Dynamic magnetic field typeMagnetic field generationMagnetic flux distribution is symmetrical with the immersion nozzle discharge hole in the center of the mold
And the moving direction of the magnetic field is two shortSideFrom mold center
In the direction toward the immersion nozzle ofA magnet that moves at the current frequency F in the application region of the linear moving magnetic field
The upper limit of the time interval P during which the field periodically passes ToThe moving magnetic field generated by the linear moving magnetic field type magnetic field generator is Every piece of molten steel stream discharged from the immersion nozzle
Moving magnetic field at least once during passage through the field application area
The lowest current frequency required to cross, When the magnetic field periodically passes through the application area of the linear moving magnetic field
Less than the interval, A magnet that moves at the current frequency F in the application region of the linear moving magnetic field
The lower limit of the time interval P during which the field passes periodically, The moving magnetic field generated by the linear moving magnetic field type magnetic field generator is  Molded water cooling box members and molded copper plates that make up the device
In the working area after damping due toAn electric field to which a magnetic field having a magnetic flux density of 1200 Gauss is applied.
Current frequency, When the magnetic field periodically passes through the application area of the linear moving magnetic field
More than the interval A method for producing a steel slab cast slab. 2. An application region of a linear moving magnetic field is set to a current frequency.
In the method of determining the upper limit of the time interval P during which the magnetic field moving at F periodically passes, the current frequency F of the linear moving magnetic field is set to be equal to or more than the value obtained by the following equation (a) or (b); 2. The steel slab casting according to claim 1, wherein the electromagnetic braking force is generated in the discharge flow of the molten steel from the immersion nozzle in the mold by adjusting a current value within a predetermined range. Method. When the molten steel flow discharged from the immersion nozzle escapes below the linear moving magnetic field, the current frequency F is obtained by the following equation (a). F = (V · sin θ) / {N · (W−D)} … (A) If the molten steel flow discharged from the immersion nozzle does not escape above or below the linear moving magnetic field, use the following equation (b).
The current frequency F is calculated as follows: F = (2V · cos θ) / (NA ·) (B) Here, in the above equations (A) and (B), F is the current frequency for generating a linear moving magnetic field. [Hz], V is the average flow rate [m / sec] when the melt flow discharged from the immersion nozzle passes through the application area of the linear moving magnetic field, θ is the application of the linear moving magnetic field when the melt flow discharged from the immersion nozzle is applied When passing through the area, the angle [rad
], W is the width [m] of the application area of the linear moving magnetic field in the height direction of the mold, D is linear movement from the upper end of the immersion nozzle discharge port when the upper end of the immersion nozzle discharge port is in the linear moving magnetic field application area. D = 0 [m], N represents the number of poles of the magnetic field generator, and A represents the casting width. 3. The application region of the linear moving magnetic field is set to a current frequency.
The lower limit of the current frequency at the time interval P at which the magnetic field moving at F periodically passes is determined by the effective braking parameter E obtained by the following equation (c) or (d) and the discharge hole of the immersion nozzle. the angle α of the discharge axis makes with the horizontal plane, electric linear moving magnetic field
The current frequency F and the current frequency F are in a relationship represented by the following equation (e). The current frequency F is set to a value equal to or higher than the value of the current frequency F obtained from the equation (e), and the current value is adjusted within a predetermined range. The method for producing a steel slab slab according to claim 1, wherein the electromagnetic braking force is generated in a discharge flow of the molten steel from the immersion nozzle in the mold. -25 ° ≧ α ≧ −60 °
In the case of, the effective braking parameter E is obtained by the following equation (c). E = A.B.C / {N. (WD) .S} (c) + 15 ° ≧ α> −25 ° The effective braking parameter E is obtained by the following equation (D). E = 4 · A · B · C · (cos α) ² / (N · A · S) (D) where the above equation (C) In formulas (A) and (D), A is the casting width (m) of continuous casting, B is the casting thickness (m), C
Represents the casting speed (m / sec), and S represents the hole diameter area (m ² ) of the discharge hole of the immersion nozzle. The hole diameter area S corresponds to the area of the cross section orthogonal to the discharge direction axis of the discharge hole. The cross-sectional shape is a circle, an ellipse, a square, a rectangle, an oval, and the like. The current frequency F is obtained by the following equation (E). F = jE + k (E) Here, in the above equation (E), −35 ° When ≧ α ≧ −60 °, j = 0.30, k = 0 −25 ° ≧ α> −35 °, j = 0.28, k = 0 + 15 ° ≧ α> −25 ° At this time, j = 0.26, k = 0. 4. An application region of a linear moving magnetic field is defined by a current frequency.
The lower limit of the current frequency at the time interval P during which the magnetic field moving at F periodically passes is determined by the effective braking parameter E obtained by the following equation (c) or (d) and the discharge hole of the discharge hole of the immersion nozzle. the angle α of the discharge axis makes with the horizontal plane, electric linear moving magnetic field
And the flow frequency F is in the relationship of the following formula (e), the value of the lowest current frequency F obtained from the relationship of the formula (e) or a value of an integral multiple thereof is set, and the current value is within a predetermined range. The method for producing a steel slab slab according to claim 1, wherein the electromagnetic braking force is generated in the discharge flow of the molten steel from the immersion nozzle in the mold by adjusting each of them. -2
When 5 ° ≧ α ≧ −60 °, the effective braking parameter E is obtained by the following equation (C). E = A · B · C / {N · (W−D) · S} (C) + 15 ° When ≧ α> −25 °, the effective braking parameter E is obtained by the following equation (D). E = 4 · A · B · C · (cos α) ² / (N · A · S) (D) Here, in the above formulas (c) and (d), A is the casting width (m) of continuous casting, B is the casting thickness (m), C is the casting speed (m / sec), and S is the discharge of the immersion nozzle. represents pore diameter hole area of (m ²⁾ respectively, should be noted that pore size area S corresponds to the area of the cross section perpendicular to the discharge axis of the discharge hole, the cross sectional shape circular, elliptical, square, rectangular, oval, etc. The current frequency F is obtained by the following equation (E). F = jE + k (E) Here, in the above equation (E), -35 ° ≧ α ≧ −60 ° When j = 0.30, k = 0−25 ° ≧ α> −35 °, j = 0.28, and k = 0 + 15 ° ≧ α> −25 °, j = 0. 26, k = 0.