JPH06277802A - Equipment for continuously casting metal - Google Patents

Abstract

PURPOSE:To secure the flow rate of lubricant according to a casting condition by forming the width of parallel slits in the casting direction at the outer wall side of a mold in wider than the slits at the inner wall side of the mold. CONSTITUTION:Molten metal 5 is supplied into the mold 2 of the water cooling structure in the inner part having plural slits 1 from an immersion nozzle 4. The lubricant 6 is charged on the molten metal 5. The lubricant 6 is melted by the heat of the molten metal 5 to form the molten powder bath 9, and the lubricant is allowed to flowed into gap between the mold 2 and a solidified shell 7. Electric current is applied to an electric conductive coil 3 at the outer periphery of the mold 2 to impress electromagnetic force and meniscus is curved to improve flow-in of the lubricant 6. As the width of the slits 1 at the inner wall side of the mold 2 is made as conventional and the width thereof at the outer wall side is made larger, damping of the magnetic field by casting 2 is relaxed and invasion of the magnetic flux into the casting 2 is improved and the electromagnetic field is effectively acted to the molten metal 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous casting apparatus for simplifying the operation, speeding up the casting, and improving the surface quality of a slab in the continuous casting of metal.

[0002]

2. Description of the Related Art In continuous casting, powdery or granular lubricant called powder is put into molten metal containing meniscus in a mold for operation. Part of the powder melts and flows between the mold and the slab, and plays a role of preventing seizure, a lubricating action between the two, and thermal relaxation. However, in order to obtain the inflow amount that matches the casting conditions, it is necessary to use a lubricant with physical properties suitable for each casting condition, such as changing the lubricant between the initial casting phase and the stationary phase, and using high-speed casting. Attempts are sometimes made to use special lubricants. In addition, vertical vibration called oscillation is applied to the mold to promote the inflow of lubricant. However, due to this minute vibration, a periodic crease called an oscillation mark, which is orthogonal to the casting direction, is generated on the surface of the cast slab, resulting in a surface defect.

Therefore, several devices utilizing electromagnetic force have been proposed for the method of controlling the inflow amount. In order to supply the lubricant between the surface of the slab and the inner surface of the mold, an electromagnetic force for bending the meniscus portion is applied to the mold. In addition, in the continuous casting device that applies electromagnetic force near the initial solidification part, not only the inflow control mechanism of the lubricant by controlling the shape of the meniscus but also the effect of gentle cooling near the initial solidification by high frequency induction heating, and the oscillation The effect of reducing the ration mark is obtained.

In Japanese Unexamined Patent Publication No. 52-32824, a current-carrying coil is embedded inside a mold so as to surround the inner wall of the mold and insulated by a refractory material. By supplying an alternating current to the current-carrying coil, the meniscus portion is formed. Is curved to promote the inflow of lubricant. However, in this method, since a low-frequency alternating current passes through the mold, there is a problem that the lubricant is caught in the molten metal and the electromagnetic effect cannot be expected because the magnetic field strength is attenuated on the long side of the thin slab. Problems also arise.

The casting device shown in Japanese Patent Laid-Open No. 64-83348 is a mold similar to the one described in Japanese Patent Laid-Open No. 52-32824, in which a meniscus is vibrated by supplying a pulsed current to a current-carrying coil, and a mold is cast. As the gap between the inner surface and the inner surface changes periodically, the lubricant is shelled without using oscillation.
It is intended to be poured between molds. However, as is the case with the above-mentioned Japanese Patent Laid-Open No. 52-32824, it is difficult to obtain a sufficient electromagnetic force with this device because the magnetic field is greatly attenuated by the mold.

Japanese Unexamined Patent Publication (Kokai) No. 2-274351 discloses a device similar to the one described above in which a low frequency current is caused to flow instead of a pulse current, but this also has the above problem. Therefore, the present inventors have proposed a device in which a slit is provided in the upper part of the mold and a secondary induced current is generated in the molten metal to effectively apply an electromagnetic force (see Japanese Patent Laid-Open No. 4-138843).

[0007]

However, the above-mentioned Japanese Unexamined Patent Application Publication No.
When the slit is provided in the mold as in the device described in Japanese Laid-Open Patent Publication No. 138843, the shell of the initial solidification part is very thin, and the molten metal is inserted into the slit part due to some fluctuation of the molten metal surface during casting. The molten metal (hereinafter referred to as the "jug") solidifies in the slit and the shell is restrained by the mold,
The problem occurs that causes a breakout. In order to prevent this hot water, it is desirable to make the slit width on the inner surface of the mold as small as possible. However, on the other hand, if the width of the slit is small, the penetration of the magnetic flux into the molten steel in the mold becomes small, so that a sufficient effect of the electromagnetic force may not be obtained.

Further, even if the slit width is made small, there is a case where the hot water is a problem. In this case, a method of filling the slit with an insulating material having a low electric conductivity such as a refractory material is used.However, since the refractory material generally has low elasto-plasticity, a refractory material with a high hardness that can withstand friction with the solidified shell should be used. It is difficult to fill a narrow slit.

In order to apply a large magnetic field to the molten metal in the mold, it is necessary to lengthen the slits to some extent. However, in reality, if an electromagnetic field can be applied near the initial solidification, the above-mentioned effects of promoting lubricant inflow and improving the surface properties can be obtained.If heating by Joule heat occurs more downward than necessary, shell growth is delayed and breakout occurs. Will increase the risk of.

An object of the present invention is to apply an electromagnetic force to a molten metal melt in a mold through a mold having a slit to easily obtain a lubricant injection amount according to casting conditions, and to cool slowly by induction heating. In a continuous casting apparatus that facilitates the production of a slab having good surface properties and internal quality, it is to properly impart a large magnetic field to the molten steel in the mold while preventing pouring into the slit. .

[0011]

Means for Solving the Problems The present inventor has obtained the following findings as a result of various studies on means for solving the above problems. (a) Slit width on the mold inner wall side is the same as before, and if the slit width on the mold outer wall side is larger than that on the mold inner wall side, the attenuation of the magnetic field by the mold is relaxed and the penetration of magnetic flux into the mold is increased. The electromagnetic field can be applied to the molten metal more effectively. (b) A slit having a width on the outer wall side of the mold larger than that on the inner wall side of the mold is more likely to insert a refractory material than a conventional slit having a parallel width. (c) The slit whose width on the mold outer wall side is larger than the width on the mold inner wall side may have a part parallel to the mold thickness direction, and the width of the slit on the mold outer wall side is changed in the casting direction. May be.

The present invention has been made based on the above findings, and the gist thereof is as follows (1), (2), (3) and (4)
In the continuous casting equipment. (1) A continuous casting device for a metal, comprising a metal mold having an internal water-cooling structure having a plurality of slits parallel to the casting direction and a current-carrying coil for guiding a high-frequency current circulating around the mold, wherein the slits Is a continuous casting device for metal, wherein the width of the outer wall of the mold is wider than that of the inner wall of the mold. (2) The continuous casting apparatus for metal according to (1), wherein the slit has a part parallel to the thickness direction of the mold. (3) The continuous casting apparatus for metal according to (1), wherein the slit has a width on the outer wall side of the mold that changes in the casting direction.

[0013]

The operation of the continuous metal casting apparatus of the present invention will be described in more detail with reference to FIGS. As shown in FIGS. 1 to 3, a high frequency energizing coil 3 is wound around a mold 2 having an internal water cooling structure having a plurality of slits 1 in the casting direction at a portion corresponding to the vicinity of a meniscus of molten metal for several turns. The molten metal 5 is supplied into the mold 2 from the immersion nozzle 4. Powdered or granular lubricant on the molten metal 5
(Powder) 6 is charged and a part of this is melted by the heat of the molten metal 4 to form a molten powder bath 9. A part of the melted lubricant flows between the mold 2 and the solidified shell 7.
In the conventional operation, the inflow of the lubricant is promoted by applying a minute vibration called oscillation to the mold.

Further, a current is supplied to the energizing coil on the outer periphery of the mold to apply an electromagnetic force in the vicinity of the initially solidified portion of the molten metal in the mold, thereby bending the meniscus as described above. At that time, since the gap between the surface of the molten metal and the mold becomes large and deep, the inflow of the lubricant can be promoted. Further, the Joule heat generated by the induced current generated in the molten metal causes the slow cooling casting, and the effects of improving the surface properties such as crack prevention and reduction of oscillation marks can be obtained.

In the apparatus provided by the present invention, as shown in FIG. 1 (b), the slit width on the mold inner wall side is the same as the conventional one, and the slit width on the mold outer wall side is made larger than that on the mold inner wall side. It is possible to relax the attenuation of the magnetic field, enhance the penetration of the magnetic flux into the mold, and effectively apply the electromagnetic field to the molten metal.

Here, a very high precision processing is required to reduce the slit width on the inner wall side of the mold to a width of about 0.2 to 0.3 mm in order to prevent hot water from pouring. As shown in Fig. 2 (b), in the device that widens the slit width on the mold outer wall side and also has the parallel part L, although the magnetic field is slightly attenuated, the slit part is easy to process, so the manufacturing cost is high. In addition, the strength of the slit part on the inner wall side of the mold is increased and durability performance is increased. of course,
It goes without saying that a magnetic field strength higher than that of the conventional mold can be obtained.

Further, by using the apparatus shown in FIG. 1, it is possible to easily fill a narrow slit with a refractory material, which has been difficult in the past, by inserting a wedge-shaped high refractory material from the inner wall of the mold. become. The filled refractory material may be fixed by wrapping an insulating tape around the outer wall of the mold, and the smoothness of the inner surface of the mold does not matter if cutting is performed after the refractory material is inserted. It is desirable that the refractory used at this time has a high hardness such as silicon nitride.

Further, in order to obtain a proper magnetic field distribution, FIG.
As shown in (b), the slit width on the outer wall side of the mold can be changed in the casting direction. For example, by making the upper width larger than the lower width, it is possible to selectively increase only the magnetic flux density near the initial solidification, that is, in the meniscus portion. As a result, the initial solidification portion can accelerate warming and cooling by Joule heat due to the application of the electromagnetic field, prevent excessive heating in the lower portion of the slit, prevent breakout, and perform stable operation.

Needless to say, the above-mentioned effects can be obtained regardless of the steel type. In addition, although the mold cross section shown in FIGS. 1 to 3 is circular, there is no problem if it is rectangular or square.

[0020]

【Example】

(Example 1) A round-section cast slab was manufactured using the apparatus of the present invention shown in FIG. The dimensions and manufacturing conditions of this device are as follows. Mold: Inner diameter 150 mm, wall thickness 30 mm, length 700 mm Slit: Length 150 mm x 32 pieces, inner wall side width 0.2 mm, outer wall side width 2.0 mm, filled refractory silicon nitride energizing coil: outer shape 30 mm, wall thickness 2 mm, Number of windings 2, current effective value 900 AT (ampere turn), frequency 35KHz Steel type: S45C (composition is as shown in table 1) Casting speed: 3.5m / min Powder: composition is as shown in table 2

[0021]

[Table 1]

For casting, while feeding molten steel into the mold with a dipping nozzle, continuous casting powder was put in the upper part to obtain 3.5 m / min.
Drawing was performed for 10 minutes at a speed of min, and casting was performed while applying mold vibration of about 4.0 Hz at this time. Although there were several small jugs on the surface of the slab, there was no casting problem. Further, no surface defects such as cracks and flaws and center segregation were observed, and extremely good cast pieces were obtained.

In order to confirm the slow cooling effect, sulfur printing was performed from FeS added in the molten steel during casting, and the solidification coefficient k was calculated from the growth degree of the solidified shell, and it was about 19 (mm / min ^0.5 ). . Further, the thickness of the lubricant collected from the surface of the slab after casting was measured and found to be 1.37 mm on average. The oscillation marks were greatly reduced and the mark depth was measured and averaged 0.07 mm.

Example 2 Casting was performed using the apparatus of the present invention shown in FIG. The structure of the template is as follows. Mold: Inner diameter 150 mm, wall thickness 30 mm, length 900 mm Slit: Length 150 mm x 32 pieces, inner wall side width 0.2 mm, outer wall side width 2.0 mm, parallel part get length 1.0 mm Other conditions are as in Example 1 Same as above. The thickness of the lubricant adhering to the surface of the slab recovered after casting was 1.42 mm on average,
The solidification coefficient was about 18 (mm / min ^0.5 ), and the oscillation mark depth was 0.05 mm on average.

Example 3 Casting was performed using the apparatus of the present invention shown in FIG. The structure of the template is as follows. Mold: Inner diameter 150 mm, wall thickness 30 mm, length 900 mm Slit: Length 150 mm x 32 pieces, inner wall side width 0.2 mm, outer wall side upper length 100 mm, outer wall side width 2.0 mm, outer wall side lower
The length was 50 mm, the outer wall side width was 1.0 mm, and other conditions were the same as in Example 1. The thickness of the lubricant adhered to the surface of the slab collected after casting was 1.33 mm on average.
The solidification coefficient was about 19 (mm / min ^0.5 ) and the depth of oscillation marks was 0.05 mm on average, which was hardly observed in some areas. From the appearance of the slab, no trace of shell breakage was found in the mold, and a very good slab was obtained.

(Comparative Example) For comparison, without applying electromagnetic force,
Casting was performed using a conventional mold without slits. Other conditions were the same as in Example 1. As a result, traces of breakage of the solidified shell, which seems to be restrained, were observed in several places in the cast slab. The solidification coefficient k was about 23 (mm / min ^0.5 ), and the thickness of the recovered lubricant was 0.81 mm on average. On the surface of the slab, clear oscillation marks were observed over the entire length, and the average mark depth was 0.36 mm. Further, surface defects such as vertical cracks were slightly generated. The measurement results obtained in Examples 1 to 3 and Comparative Example are summarized in Table 3 above.

[0027]

[Table 3]

From the results shown in Table 3, it can be seen that the effects of Examples 1 to 3 in which the mold of the present invention is used for casting are superior to those of the comparative example using the conventional mold.

[0029]

INDUSTRIAL APPLICABILITY In the apparatus of the present invention, a magnetic field is effectively applied to the molten metal by causing an alternating current to flow through the current-carrying coil, and the flow path between the mold and the solidification shell is controlled to control the lubricant according to the casting conditions. It is possible to secure a large inflow amount of and to realize slow cooling casting by heating. This prevents seizure between slab molds during high speed casting,
By improving the surface properties, it becomes possible to stably produce a good cast piece.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of a casting apparatus of the present invention.
FIG. 1A is a diagram showing a part of a vertical section, and FIG. 1B is a diagram showing a part of a horizontal section in the AA ′ direction shown in FIG.

FIG. 2 is a sectional view showing an example of a casting apparatus of the present invention.
2A is a diagram showing a part of the vertical cross section, and FIG. 2B is a diagram showing a part of the horizontal cross section in the AA ′ direction shown in FIG.

FIG. 3 is a sectional view showing an example of the casting apparatus of the present invention.
FIG. 3A is a partially sectional perspective view, and FIG. 3B is a partially enlarged perspective view of the slit.

[Explanation of symbols]

1: Slit 2: Mold 3: Energizing coil 4: Immersion nozzle 5: Molten metal 6: Lubricant 7: Solidified shell 8: Molten metal interface 9: Molten powder bath 11: Refractory L: Parallel part of slit

Claims (3)

[Claims] 1. A continuous casting device for metal, comprising: a metal mold having an internal water-cooling structure having a plurality of slits parallel to a casting direction; and a current-carrying coil for guiding a high-frequency current circulating around the mold. In the continuous casting device for metals, the slit has a width on the outer wall side of the mold wider than that on the inner wall side of the mold. 2. The continuous casting apparatus for metal according to claim 1, wherein the slit has a part parallel to the thickness direction of the mold. 3. The slit has a width on the outer wall side of the mold that changes in the casting direction.
A continuous casting device for the metal described.