JPH05212500A - Device for continuous casting - Google Patents

Abstract

PURPOSE:To enable casting of a cast slab having easy treatment without surface defect by extending a stepping part to the upper part of a mold, fitting a ceramic mold to the stepping part and forming the outer surface of the ceramic mold to a projecting curved surface. CONSTITUTION:The stepping part 11 reaching the upper end is extended up to the upper end of the mold 3 and in this part, the ceramic mold 4 is fitted. Since the solidified part at the initial stage of the cast slab is slowly cooled by using the ceramic mold 4 and a shell at the connecting part between a connected refractory part and the ceramic mold 4 is not formed and the shell in the mold is formed, the cast slab having no surface defect is obtd. Further, since the outer surface of the ceramic mold is formed to the recessed curving surface, the thickness of the ceramic mold becomes large at the lateral center part having large heat loading and the ceramic mold 4 has high rigidity, the projection of the ceramic mold 4 to the molten steel side is reduced. By this method, the rectangular cast slab having no surface defect and uneven thickness can continuously be cast.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for continuous casting of molten metal suitable for producing a rectangular slab having few surface defects.

[0002]

2. Description of the Related Art The continuous casting method shown in FIG. 3 is mainly used for casting molten metal, especially molten steel. In this method, the molten steel 6 of the tundish 1 is continuously injected into the mold 3 from the injection hole 2a through the dipping nozzle 2, and then from the mold 3 through the guide roller 5 and the solidification shell 7 by the pinch roll 8. Be withdrawn. Structurally tundish 1 and mold 3
And are separated. On the upper surface of the molten steel in the mold 3, a flux 10 mainly composed of an oxide is added as a so-called powder to prevent oxidation and cooling of the upper surface of the molten steel.

However, in this method, the immersion nozzle 2
There is a problem that the molten steel surface fluctuates due to the injection flow from the inside of the mold, or there is a problem of partial remelting of the solidified shell 7 in the mold, which may cause defects on the surface of the slab. Recently, there is a growing need for a near-net continuous casting method that casts a slab that is as close to the shape of the final product as possible from the viewpoint of process saving, but when performing such near-net continuous casting in the conventional continuous casting method, When casting a slab with a small cross section, it is almost impossible to add the flux to the upper surface of the molten steel and sufficient heat retention is not possible, so many immersion nozzle blockages and solidification of molten steel around the immersion nozzle are observed. Therefore, it was impossible to use the immersion nozzle.

On the other hand, in recent years, a continuous casting method using a tundish-mold direct connection type apparatus has been proposed. As shown in the conceptual views of FIGS. 4 and 5, in this tundish-mold direct connection type continuous casting apparatus, the immersion nozzle is removed and the tundish and the mold are integrated. According to this method, since there is no concern about blockage of the dipping nozzle or entrainment of powder, it is considered to be particularly effective for casting of small cross-section slabs, and a process saving (particularly hot rolling process) is possible.

Furthermore, since molten steel is not exposed to the ambient atmosphere from the tundish to the mold, it can be expected to produce clean slabs. However, water-cooled copper mold 3
A solidified shell is generated at the contact point between the refractory 9 and the connection refractory 9, resulting in slab defects such as a drawing mark and a hot tear as shown by symbols M and T in FIG. Here, the drawing mark M is the seam of the old and new shells (shell from the water-cooled copper mold and the shell from the connecting refractory) that appears at each drawing pitch, and the hot tier T is the surface lateral crack that appears at each drawing pitch. .. Since these defects directly become product defects, it is necessary to remove them by cutting prior to rolling.

[0006] As one of the measures for preventing the extraction marks from occurring in the tundish-mold direct connection type continuous casting, a method of inserting a ceramics mold into a copper mold is adopted. For example, Japanese Unexamined Patent Publication (Kokai) No. 52-50929 discloses a mold in which a refractory material and a graphite tube are inserted, and Japanese Unexamined Patent Publication (Kokai) No. 58-151939 discloses a heat-, lubrication- and corrosion-resistant cermet conduit-casting of steel. Has been shown to be.

Further, Japanese Laid-Open Patent Publication No. 64-27743 discloses a method of applying compressive stress to an interpolated ceramic material by a method such as shrink fitting in order to improve the thermal shock resistance of the ceramic.
Japanese Unexamined Patent Publication No. 1-286967 describes a method of manufacturing a ceramics mold which is inserted into a water-cooled copper mold having excellent thermal shock resistance and thermal stress resistance. The reason for using the ceramic mold is to alleviate the cooling, and the effect thereof is to reduce the drawing mark as described in Mitsubishi Steel Making Technique Vol. 19, No. 12 (19885).

However, all of the above methods are practically limited to round slabs, and square slabs having a rectangular cross section (slab,
It was difficult to manufacture the blooms and billets) because the mold was deformed, as can be seen from FIG. 7 showing the deformation of the mold. Here, FIG. 7 shows a state of bending of the mold during casting in the case of a mold having a flat casting wall in which the ceramics mold 4 is inserted on the upper part of the water-cooled copper mold 3, and considerable deformation is observed. I understand.

A tundish of a square slab using a ceramics mold-a CC method directly connected to a mold is disclosed in JP-A-62-
Japanese Patent No. 45449 describes a method for preventing deformation of the graphite mold by providing a water cooling jacket for extrapolating the graphite mold in a divided manner in the width direction. However, the efficiency of assembling the mold was poor and it was not practical.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a continuous casting mold which is easy to handle and is capable of casting a slab having a rectangular cross section without surface defects.

[0011]

As one of the reasons why the tundish-mold direct connection type continuous casting method using a ceramics mold cannot be applied to the casting of a square slab, as described above with reference to FIG. The ceramic mold may be deformed by heat load. When the ceramic mold is deformed, there arises the following problems: 1) variation in wall thickness of the slab, 2) insufficient heat removal due to poor contact between the ceramic and water-cooled copper, and 3) damage to the ceramic.

Here, the present invention is a continuous casting apparatus for producing a slab having a rectangular cross section, which comprises a mold part directly connected to a tundish at the upper end, the mold part extending up to the upper end of the mold part. The mold body of a water-cooled copper mold provided with a stepped portion on the top and a ceramics mold inserted in the stepped portion, the outer surface of the ceramics mold and the surface in contact with the water-cooled copper mold, at least the mold The continuous casting apparatus is characterized in that the long side is formed of a curved surface that is convex toward the outside of the mold.

As described above, the continuous casting apparatus according to the present invention comprises the mold portion, and as a mode of direct connection with the tundish, the above-mentioned ceramic mold is usually fixed to the bottom portion of the tundish through the connecting refractory. That is. Further, the upper end of the ceramic mold may be directly fixed to the tundish bottom by a pressing plate or the like. The molten steel from the tundish is not limited to a specific type as long as it does not leak from the connection between the tundish and the mold or come into contact with the atmosphere during or during casting. The casting direction may be vertical or horizontal.

The proportion of the copper mold body in the longitudinal direction of the ceramic mold occupies at least half of the length of the ceramic mold body. On the other hand, the ceramic mold body has the purpose of cooling immediately after casting. Since it is mitigation, there is no particular limitation as long as it is realized.

[0015]

Next, the operation of the present invention will be described in detail with reference to the accompanying drawings. The same members are designated by the same reference numerals in the accompanying drawings. FIG. 1 is a schematic explanatory view of an apparatus for continuous casting according to the present invention.
The molten steel 6 therein is poured into the mold 3, and the solidified shell 7 is pulled out by the pinch roll 8 via the guide roller 5.
The upper end of the mold 3 is directly connected to the main body of the tundish 1 via the connecting refractory material 9.

Here, according to the present invention, the step portion 11 is extended to the upper end of the mold 3 and the ceramic mold 4 is fitted in the portion. According to the present invention, since the initial solidification portion of the slab is cooled slowly by using the ceramic mold 4, a shell is generated at the connecting portion of the connecting refractory 9 and the ceramic mold 4 (point a in FIG. 1). Instead, a shell is formed in the mold, so that a slab with no surface defects is obtained. Further, since the outer surface of the ceramics mold 4 is a convex curved surface, the thickness increases at the center of the width where the heat load is large, and the ceramics mold 4 has rigidity, so that the protrusion of the ceramics mold 4 to the molten steel side is reduced. It

FIG. 2 shows the ceramics mold 4 in a plan view. In the figure, the surrounding water-cooled copper mold 3 is a ceramic mold 4.
The surface in contact with the outer surface of is a convex curved surface, and similarly, the outer surface of the ceramics mold is a convex curved surface like the copper mold. This is because the bending of the ceramics mold toward the molten steel side is reduced by increasing the second moment of area at the center of the side. The mold is formed into a rectangular shape by laminating four plates. Generally, it is sufficient to provide such a thick portion only on the long side, but it may be provided on the short side if necessary.

That is, FIG. 2 (a) shows that the slab thickness (t) is 30
The relationship between the ceramic mold in the case of exceeding mm and the copper mold around it is shown. As shown therein, the copper mold 3 has a structure in which the ceramic mold 4 can be inserted, and
The outer surface of the ceramic mold 4 and the surface of the copper mold 3 in contact with the ceramic mold are curved surfaces that are convex toward the outside of the mold on both the long and short sides of the mold. Like the bending of the beam, the moment is maximum at the center,
At the center, the second moment of area is large and the bending is small.

FIG. 2 (b) shows the relationship between the ceramic mold and the copper mold in the case of a thin cast piece having a wall thickness of more than 10 mm and not more than 30 mm. In this case, as shown in FIG. It is not necessary to add curvature to the short side. Figure 2 (c) shows that the thickness of the slab is 10 mm.
As shown below, showing the case of a thin cast piece,
With such a thin slab, it is not necessary to insert a ceramics mold on the shorter side of the mold as shown in FIG. 2 (c).

This apparatus is particularly effective for manufacturing thin cast pieces having a wall thickness of 30 mm or less among square cast pieces, but can sufficiently cope with slabs, billets and blooms having a wall thickness of 30 mm or more.

The apparatus for continuous casting according to the present invention is 70
It can also be applied to wide slabs with a width of 0 mm or more. In addition, the ceramic mold having a convex surface facing the outside has a width of 400
In the case of a slab with a rectangular cross section of ~ 1200 mm, the convex surface may be arcuate or parabolic, and the maximum amount of convex parts is
20 mm is enough. Finally, the radius of the arc on the outer surface of the ceramic mold is determined by the shape of the slab (slab, billet, bloom), width, and ceramic material.

[0022]

EXAMPLES The present invention will be described below based on examples carried out by using the apparatus shown in FIG. Casting is 400, 800 mm wide,
The test was performed on thin cast pieces having a wall thickness of 10 and 30 mm. The ceramic mold and the copper mold were provided with an arc only on the long side, and the radius of curvature was 6000 mm for the slab 800 mm wide and 4000 mm for the slab 400 mm wide.

Cast metal is SUS304 stainless steel and carbon steel
(C steel: C content 0.2%), and the temperature of the molten metal in the tundish was 40 to 50 ° C. higher than the liquidus temperature. The drawing cycle was 100 cpm and intermittent drawing was performed, and the casting speed was variously changed according to the shape of the slab and the mold material.

Table 1 shows the casting conditions and results of the implementation. The conditions and results of the comparative examples are shown in Tables 2 and 3.
The results in Table 2 are those obtained when casting was performed using a conventional mold in which the ceramic mold outer surface and the copper mold inner surface were straight and no arc was provided. In particular, Table 3 shows that the ceramic mold was not used and only the copper mold was used. This is the case when cast.

As is clear from the results of Table 2, in Experiment Nos. 19 to 36 of Comparative Examples, when casting a 400 mm wide slab, the ceramic mold was displaced to the molten steel side and the wall thickness of the slab fluctuated.
During the casting of 0 mm width slab, the ceramic mold was largely displaced and damaged. Further, as is clear from the results of Table 3, in Experiment Nos. 37 to 42 of Comparative Examples, a drawing mark on the surface of the slab,
There was a flaw called Hot Tier. On the other hand, Table 1
In each of the examples of the present invention (Experiment Nos. 1 to 18), good slabs without surface defects of the drawn marks and hot tears and wall thickness variation could be obtained.

[0026]

[Table 1]

[0027]

[Table 2]

[0028]

[Table 3]

[0029]

As described above, according to the present invention, it is possible to continuously cast a rectangular slab without surface defects and wall thickness fluctuation, and it is possible to significantly reduce the number of manufacturing steps by saving steps and energy. ..

[Brief description of drawings]

FIG. 1 is a sectional view of an essential part of an embodiment of a continuous casting apparatus of the present invention.

2 (a), 2 (b) and 2 (c) are transverse cross-sectional views of a casting mold portion of a continuous casting apparatus according to the present invention, according to the thickness of a cast piece.

FIG. 3 is a conceptual diagram of a conventional continuous casting method.

FIG. 4 is a conceptual diagram of a tundish-mold direct connection type continuous casting method.

FIG. 5 is a conceptual diagram of another tundish-mold direct connection type continuous casting method.

FIG. 6 is a partial cross-sectional view of a slab for explaining a drawing mark and a hot tear.

FIG. 7 is an explanatory diagram of mold deformation during casting of a square slab.

[Explanation of symbols]

 1: Tundish 2: Immersion nozzle 2a: Injection hole 3: Water-cooled copper mold 4: Ceramics mold 5: Guide roll 6: Molten steel 7: Solidified shell 8: Pinch roll 9: Connection refractory

Claims (2)

[Claims] 1. A continuous casting apparatus for producing a slab having a rectangular cross section, which comprises a mold part directly connected to a tundish at the upper end, wherein the mold part is a step part extending to the upper end of the mold part. A mold body of a water-cooled copper mold having an upper part thereof, and a ceramics mold inserted in the step portion, and a surface contacting the outer surface of the ceramics mold and the water-cooled copper mold is at least the long side of the mold. An apparatus for continuous casting, characterized in that the curved surface is convex toward the outside of the mold. 2. The continuous casting apparatus according to claim 1, wherein a ceramics mold is inserted only on the long side of the mold.