JPH0866746A - Horizontal continuous casting apparatus - Google Patents

Abstract

PURPOSE: To efficiently impress electromagnetic field to molten metal and to prevent the surface defect caused by the static pressure of the molten metal by arranging slits to be radially arranged in larger number at the part high in static pressure in a mold than at the part low in static pressure. CONSTITUTION: A part including the tip part of a tundish nozzle 5 in the intermediate part of a mold 1 and a brake ring 6, i.e., the neighborhood of a triple point P where the brake ring 6, the mold 1 and the molten metal 3 are in contact, is divided in segments by the radially arranged slits 1a. The number of these slits 1a at the part high in static pressure in the mold, i.e., at the lower part in the mold 1 is made larger than at the part low in static pressure in the mold, i.e., at the upper part in the mold 1 so as to impress the higher frequency electromagnetic field at the part high in static pressure in the mold.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention eliminates surface defects of a cast slab caused by a contact point between a connecting refractory for connecting a tundish nozzle and a water-cooled mold (hereinafter simply referred to as "mold") and molten metal. However, the present invention relates to a horizontal continuous casting apparatus capable of producing a slab having excellent surface properties.

[0002]

2. Description of the Related Art As a continuous casting method which is expected to reduce facility costs and float inclusions by making the pouring velocity uniform, there is a horizontal continuous casting method in which a slab is horizontally drawn. In this horizontal continuous casting, the tundish and the mold are connected via a refractory tundish nozzle. The connection between the mold and the tundish nozzle is called triple point as the contact point between the molten metal, the mold and the refractory.

In such horizontal continuous casting, there is no problem if the molten metal begins to solidify at the point of contact with the mold and the solidified shell gradually grows from this point of contact, but there is no problem with the tundish connected to the mold. Since the nozzle is also cooled, solidification also starts from the point of contact with the tundish nozzle.
Since the solidification shell generation point on the tundish nozzle side and the middle point between the solidification shell generation point on the mold side are thin and the solidification shell strength at that part is weak,
If the slab is pulled out in this state, the solidified shell may break and cause breakout.

For this reason, conventionally, not only continuous drawing but also intermittent drawing is adopted to increase the strength of the solidified shell, and a refractory ring (break ring) having good lubricity is provided at the connecting portion between the tundish nozzle and the mold. Measures have been taken such as inserting a plug to alleviate the sticking of the solidified shell.

Although the frequency of breakouts could be reduced by such measures, the formation of a solidified shell on the tundish nozzle side causes periodic flaw-like surface defects due to intermittent drawing on the surface of the slab. In addition, the life and cost of connected refractories are problems.

In order to solve the above-mentioned problems in the prior art, a method utilizing electromagnetic force has been proposed. First, in JP-B-64-5985, an electromagnetic field generating means by an alternating current is arranged near the boundary between the tundish nozzle and the mold to squeeze the molten metal near the boundary to eliminate the contact of the molten metal with the tundish nozzle. A horizontal continuous casting apparatus has been proposed which prevents the solidified shell from sticking. Further, in order to prevent the solidification starting point in the circumferential direction from being different due to the difference in the static pressure of the molten metal in the vertical direction in the slab, a current-carrying coil near the triple point (hereinafter simply referred to as “coil”) is provided. A method of moving upward and strengthening the magnetic field below has also been proposed.

However, in order to apply a large electromagnetic force at the triple point, it is necessary to bring the coil close to the end of the mold, but if it is too close, a short circuit will occur with the mold, and Joule heat will concentrate at the corners of the mold. However, in reality, it is impossible to effectively apply the voltage to the triple point. Similarly, in a continuous casting device in which the tundish and the mold are directly connected,
JP-A-1-284469 and JP-A-2-133145 also propose a method of applying an electromagnetic force near the inlet of the mold, but it has the same problem as in JP-B-64-5985.

Therefore, in Japanese Unexamined Patent Publication No. 3-133542,
Rather than direct electromagnetic force from the coil, a slit extending in the casting direction is formed at the top or middle of the mold, and a high-frequency current-carrying coil is placed on the outer periphery of the slit to positively flow an induction current to the mold. A method for secondarily applying an electromagnetic force to molten metal has been proposed to solve the above-mentioned problems.

[0009]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
When the method proposed in No. 542 is applied to a horizontal continuous casting apparatus, an electromagnetic field can be efficiently applied to molten metal,
As mentioned above, based on the difference in the static pressure of the molten metal in the slab, the regions held in non-contact by the electromagnetic force are different in the upper and lower, so that a slab with uneven surface texture in the circumferential direction can be obtained. Will be done. A method of moving the coil upward to strengthen the magnetic field below can be considered, but in general, in order to apply an electromagnetic field efficiently, it is better to minimize the distance between the outer circumference of the mold and the inner circumference of the coil. The reality is that there is almost no range. In addition, JP-A-5-285
No. 598 also proposes a continuous casting device that efficiently applies an electromagnetic force into a mold according to the same principle.
Since the one proposed in -285598 is a mold having a structure in which segments insulated from each other by a slit are opened in the front and rear, thermal deformation is likely to occur, the slit may open, and the occurrence of a jug may occur frequently. is there.

The present invention has been made in view of the above-mentioned conventional problems, and it is possible to efficiently apply an electromagnetic field to the molten metal and prevent surface defects caused by the static pressure of the molten metal in the slab. The object is to provide a horizontal continuous casting device.

[0011]

In order to achieve the above object, in the horizontal continuous casting apparatus of the present invention, the tip of the tundish nozzle is inserted up to the middle of the mold, and the tip or tundish of the tundish nozzle is inserted. On the outer periphery of the mold near the tip of the break ring interposed between the dish nozzle and the mold, a coil capable of applying a high frequency current is arranged coaxially with the mold, and a portion including the tip of the tundish nozzle in the middle part of the mold. The horizontal continuous casting apparatus divided into segments by radially provided slits, the number of the slits, the static pressure in the mold is higher than the low portion, or the axial center of the inner periphery of the mold. It is eccentric to the one where the static pressure in the mold is higher than the axial center of the outer circumference, and it is further inserted in the inner peripheral surface of the mold in the horizontal continuous casting device and in the middle of it. With each other to or a space is provided between the been tundish nozzle outer peripheral surface.

[0012]

According to the horizontal continuous casting apparatus of the present invention, the number of the slits in the intermediate portion including the tip of the tundish nozzle, which is inserted into the mold halfway and is divided into segments by the radially provided slits, is defined as By making more parts with high internal static pressure than low parts, or by eccentric to the one with higher internal static pressure than the axial center of the mold outer circumference coaxial with the coil axial center of the inner circumference of the mold. Therefore, the electromagnetic field at the higher static pressure of the molten metal can be strongly applied. Further, since the space is provided between the inner peripheral surface of the mold and the outer peripheral surface of the tundish nozzle inserted halfway, heat removal from the mold to the tundish nozzle is reduced, and cooling of the tundish nozzle can be suppressed.

The basic idea of the horizontal continuous casting apparatus of the present invention is to cancel the difference in the static pressure of the molten metal on the inner surface of the mold by the difference in the magnitude of the magnetic field (magnetic pressure) applied to that position. . That is, in the apparatus configuration shown in FIG.
In order for the total pressure toward the center of the above formula to be equal above and below the mold 1, it is necessary to satisfy the following formula 1.

[0014]

## EQU1 ## B ₀ ² / 2μ-ρgH ₀ = B ² / 2μ-ρgH where B: magnetic flux density H: holding height of the molten metal 3 in the tundish 2 B ² / 2μ: magnetic pressure ρgH: molten metal 3 Static pressure of the subscript 0: above the inner surface of the mold No subscript: below the inner surface of the mold

Therefore, the relationship between the magnetic flux densities B ₀ and B generated above and below the inner surface of the mold 1 by the coil 4 arranged on the outer periphery of the mold 1 is represented by the following formula 2.

[0016]

## EQU2 ## B = {2 μρg (H−H ₀ ) + B ₀ ² } ^1/2 = { ² μρg R + B ₀ ² } ^1/2 where R is the inner diameter of the mold 1 or B / B ₀ = {2 μρg (H- H ₀ ) / B ₀ ² +1} ^1/2 = {2μρg R / B ₀ ² +1} ^1/2

That is, in order for the total pressure in the center of the mold 1 to be the same above and below the mold 1, the magnetic flux density B obtained by the above-mentioned formula 2 is required below the inner surface of the mold 1, and the inner surface of the mold 1 is required. It depends on the difference in the holding height of the molten metal 3 above and below (the size of the inner diameter of the mold 1). Therefore, if the number of slits is made different above and below the mold 1 or the eccentricity of the inner circumference of the mold 1 is determined so as to satisfy this condition, the melting will occur above and below the inner surface of the mold 1 regardless of the presence of voids at the triple points. The contact state between the metal 3 and the mold 1 is the same in terms of shape (including internal flow) and thermal, and it is possible to manufacture a slab having a good surface layer and uniform in the circumferential direction.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A horizontal continuous casting apparatus of the present invention will be described below with reference to the embodiments shown in FIGS. FIG. 1 is an explanatory view of a horizontal continuous casting apparatus of the present invention corresponding to claim 1, (a)
Is a sectional front view, (b) is an AA sectional view of (a), FIG. 2 is an explanatory view of a horizontal continuous casting apparatus of the present invention corresponding to claim 2, and (a) is a sectional view. The front view shown, (b) is CC sectional drawing of (a), FIG. 3 is explanatory drawing of the horizontal continuous casting apparatus of this invention corresponding to Claim 3, (a) is a front view shown by a cross section, FIG. 4B is a sectional view taken along line DD of FIG. 4A, and FIG.
FIGS. 13A and 13B are explanatory views in the vicinity of a solidification shell starting point when a horizontal continuous casting apparatus shown in Japanese Patent Laid-Open No. 133542 is used, and FIG.

1 to 3, the mold 1 has a connecting side (hereinafter, referred to as "inlet side 1b") with the tundish 2,
The diameter of the solidification shell 3a is larger than that of the extraction side (hereinafter, referred to as “outlet side 1c”), and the tip of the tundish nozzle 5 is inserted halfway through the mold 1. A break ring 6 which is a refractory having good lubricity is provided between the tip of the tundish nozzle 5 and the mold 1. In addition, on the outer periphery of the mold 1 near the tip of the break ring 6, a coil 4 is arranged coaxially with the mold 1, and a slab is horizontally or continuously drawn by a drawing device (not shown) while applying a high frequency current. Pull out intermittently. In addition,
The inner diameter of the mold on the inlet side 1b of the mold 1 needs to be such that heat removal from the molten metal 3 passing through the water-cooled mold 1 up to the end of the inlet side 1b can be suppressed.

In the horizontal continuous casting apparatus described above, FIG.
In the embodiment shown in FIG. 3, the tip of the tundish nozzle 5 and the portion including the break ring 6 in the middle portion of the mold 1, that is, the break ring 6, the mold 1 and the molten metal 3 are included.
Slits 1 provided radially near the triple point P where
It is divided into segments by a. The number of these slits 1a is such that a portion having a high static pressure in the mold, that is, a lower portion in the mold 1, is a portion having a low static pressure in the mold, that is, the mold 1
More high frequency electromagnetic field can be applied to the portion where the static pressure inside the mold is higher than the upper part inside.

In addition, slits 1a are formed on the outlet side 1c and the inlet side 1b of the mold 1 in order to prevent the segment divided by the slits 1a from being opened by the heat of the molten metal 3 to generate a water heater. In addition, the inlet side 1b and the outlet side 1c are connected and not electrically insulated.
Further, the slit 1a is formed so that the tip of the tundish nozzle 5 and the break ring 6 are located at the substantially central portion.

By the way, the slit 1a formed in the mold 1
In order to apply a uniform magnetic field to the inside, the number of 4 is necessarily 4 or more, and it depends on the inner diameter of the mold, but it is better that each segment has a cooling structure.
Further, it is preferable that the width of the slit 1a is as narrow as possible so as not to cause hot water. Further, it is sufficient that the slit 1a has a range of about three times as large as the coil 4 having a width capable of intensively covering the triple point P portion.

In the embodiment shown in FIG. 2, the axial center of the inner periphery of the mold 1 is higher than the axial center of the outer periphery of the mold 1, which has the same axial center as the coil 4, that is, the mold 1 has a static pressure. It is eccentric to the lower part of the inside. That is, the mold wall has a thick wall above the mold 1 and the mold wall has a thin wall below the mold 1. With such a structure, more high-frequency electromagnetic fields can be applied to a portion where the static pressure inside the mold is high. There is.

Further, in the embodiment shown in FIG. 3, a space 7 is provided between the inner peripheral surface of the mold 1 and the outer peripheral surface of the tundish nozzle 5.
Is provided to reduce the heat removal from the mold 1 to the tundish nozzle 5 to suppress the cooling of the tundish nozzle 5.

The horizontal continuous casting apparatus of the present invention is constructed as described above, and the frequency of the high frequency current applied to the coil 4 is preferably about 1 KHz to several tens KHz. The stable free surface can be retained. Further, since it also has the effect of heating the vicinity of the epidermis in a concentrated manner, it is desirable that it is as high as possible.

In the horizontal continuous casting apparatus of the present invention, the electromagnetic force applied to the slab makes the vicinity of the triple point P non-contact to prevent the solidified shell 3a from sticking to the break ring 6 and when it sticks to the scale. Melts the solidified shell 3a fixed by high frequency heating.

At this time, when the conventional mold 1 having an axially symmetric structure is used, the triple point P is caused by the difference in static pressure in the slab.
Since the regions which are held in non-contact with each other are different as shown in FIG. 4 (a), the solidification start points are displaced vertically, and a slab having a uniform surface texture cannot be manufactured. Further, even when the static pressure is excessively high and the vicinity of the triple point P is not held in a non-contact manner,
Since the contact pressure with the mold 1 is different and the cooling state is also different, the heating effect is different at the top and bottom of the slab, and the surface properties are not uniform as well. Then, in the worst case, the solidified shell 3a breaks, causing a breakout.

On the other hand, when the horizontal continuous casting apparatus of the present invention as described above is used, the electromagnetic field can be strongly applied downward, so that as shown in FIG.
Therefore, the regions that are held in non-contact are the same in the upper and lower parts, and the heating and cooling balance can be kept uniform in the upper and lower parts. Therefore, as a result, it is possible to manufacture a uniform slab having excellent surface properties and avoid breakout.

Next, the results of experiments conducted to confirm the effects of the present invention will be described. [Experiment 1] Using the horizontal continuous casting apparatus shown in FIG. 1 having the following dimensions and structure, the molten metal (S
45C) was cast and continuous casting was performed at a speed of 2.0 m / min. During the casting, FeS (iron sulfide) was added in the tundish. Mold: made of copper, inner diameter 250 mm, wall thickness 30 mm, length 700 mm Slit length 120 mm × width 0.2 mm × 36 slits 12 slits were formed in the upper half of the mold and 24 slits were formed in the lower half of the mold. Coil: Cross-sectional shape 10 × 15 angles, number of windings 4, effective current value 14kAT frequency 20kHz Triple point position: slit intermediate position

[0030]

[Table 1]

Casting was completed in a stable state without breakout. The obtained slab was a clean slab with no surface defects. Also, cutting out the cast slab after casting, when examining the state of growth of the solidified shell by sulfur printing, the solidified shell is starting to grow from the same position above and below the mold, the non-contact holding state or temperature above and below the mold. It is estimated that the state was created.

[Experiment 2] Continuous casting was performed using the horizontal continuous casting apparatus shown in FIG. The basic conditions were the same as in Experiment 1, but only the template having the following structure was used. Mold: made of copper, inner diameter 250 mm, length 700 mm, mold upper wall thickness 40 mm, mold lower wall thickness 20 mm, slit length 120 mm × width 0.2 mm × 30, and the number of slits was formed evenly at the top and bottom of the mold.

Casting was completed in a stable state without breakout. The obtained slab was a clean slab with no surface defects.

[Experiment 3] Continuous casting was performed using the horizontal continuous casting apparatus shown in FIG. The basic conditions were the same as in Experiment 1, but a space was provided between the mold and the tundish nozzle to suppress cooling from the mold. Space between mold and tundish nozzle: 10mm

The surface properties of the cast slab were even better than those obtained in Experiment 1. This is presumed to be because, compared with Experiment 1, the temperature drop of the molten metal passing through the tundish nozzle could be suppressed, and thus the generation of the solidified shell at the triple point could be suppressed more effectively.

[Comparative Example 1] As a comparison, casting was performed in a state where a high frequency was applied, using a casting mold in which the slit structure of the casting mold was axisymmetric. The obtained slab has surface defects due to the solidified shell in which the surface properties of the lower part of the mold are slightly fixed compared to the properties of the upper part of the mold, and the same non-contact holding state or temperature state is provided above and below the mold. It is thought that it was not done. From the result of the sulfur print, it was confirmed that the starting position of the solidified shell formation was different between the upper and lower parts.

Comparative Example 2 For comparison, casting was performed without applying a high frequency electromagnetic field. The equipment specifications and operating conditions were the same as in Experiments 1 to 3 except that the coil was not energized. In each of the comparative examples, a breakout occurred after the dummy bar head came out of the mold outlet for a while after the start of casting, and the casting had to be stopped. In the comparative example, the solidified shell was probably fixed to the break ring at the triple point and grew as it was, so that the solidified shell ruptured when the slab came out at the mold outlet. Observation of the surface properties of the remaining cast slab revealed that considerable surface defects had occurred.

[0038]

As described above, in the horizontal continuous casting apparatus of the present invention, the tip portion is inserted halfway through the mold, and the intermediate portion including the tip of the tundish nozzle divided into segments by the slits provided radially. In the number of the slits, the high static pressure in the mold is made larger than the low part, and the axial center of the inner circumference of the mold is the static pressure in the mold from the axial center of the outer circumference of the coil axis and the coaxial center of the mold. Since it is eccentric to the higher side, it is possible to strongly apply the electromagnetic field at the side where the static pressure of the molten metal is high, and there is no difference in the influence of the electromagnetic force due to the difference in the static pressure of the molten metal between the upper and lower sides of the slab. It is possible to manufacture a slab that is uniform in the circumferential direction and has excellent surface properties. Further, since the space is provided between the inner peripheral surface of the mold and the outer peripheral surface of the tundish nozzle inserted halfway, heat removal from the mold to the tundish nozzle is reduced, and cooling of the tundish nozzle can be suppressed.

[Brief description of drawings]

FIG. 1 is an explanatory view of a horizontal continuous casting apparatus of the present invention corresponding to claim 1, (a) is a cross-sectional front view, and (b) is an AA cross-sectional view of (a).

FIG. 2 is an explanatory view of a horizontal continuous casting apparatus of the present invention corresponding to claim 2, (a) is a front view showing a cross section, and (b) is a CC sectional view of (a).

FIG. 3 is an explanatory view of a horizontal continuous casting apparatus of the present invention corresponding to claim 3, (a) is a sectional front view, and (b) is a DD sectional view of (a).

FIG. 4 is an explanatory diagram in the vicinity of the solidification shell starting point when the horizontal continuous casting apparatus of the present invention is used and when the horizontal continuous casting apparatus disclosed in Japanese Patent Laid-Open No. 3-133542 is used. Conventionally, (b) shows the present invention.

FIG. 5 is a diagram illustrating the concept of the present invention.

[Explanation of symbols]

 1 Mold 1a Slit 4 Coil 5 Tundish Nozzle 6 Break Ring 7 Space

Claims (3)

[Claims] 1. The tip of a tundish nozzle is inserted halfway through the mold, and the tip of the tundish nozzle or the outer periphery of the mold near the tip of a break ring interposed between the tundish nozzle and the mold.
A coil that can apply high frequency current is placed coaxially with the mold,
A portion including the tip of the tundish nozzle in the middle portion of the mold, in a horizontal continuous casting apparatus divided into segments by radially provided slits, the number of slits, the high static pressure in the mold portion is lower than the lower portion. Horizontal continuous casting equipment characterized by many things. 2. The tip of a tundish nozzle is inserted halfway through the mold, and the tip of the tundish nozzle or the outer periphery of the mold near the tip of a break ring interposed between the tundish nozzle and the mold,
A coil capable of applying high-frequency current is arranged coaxially with the outer periphery of the mold, a portion including the tip of the tundish nozzle in the middle part of the mold, in a horizontal continuous casting device divided into segments by radially provided slits, A horizontal continuous casting apparatus, characterized in that the center axis of the inner periphery of the mold is eccentric so that the static pressure inside the mold is higher than the center axis of the outer periphery. 3. The horizontal continuous casting apparatus according to claim 1 or 2, wherein a space is provided between the inner peripheral surface of the mold and the outer peripheral surface of the tundish nozzle inserted halfway in the mold. apparatus.