JPH01293942A - Method for continuously casting wide width thin slab and casting machine thereof - Google Patents

Abstract

PURPOSE:To uniformize supply of molten metal into a mold and to obtain a wide width thin slab without double skin by arranging plural flat nozzles at the prescribed interval along long side direction of flat mold and supplying molten metal into the mold from each flat nozzle. CONSTITUTION:The plural flat nozzles 5 are arranged at the prescribed interval along long side direction of the flat mold 1. Successively, the molten metal M is supplied into the mold 1 from each flat nozzle 5. Then, by making plural number of the flat nozzles 5, width per one piece of the flat nozzle 5 becomes narrow. Therefore, by arranging the prescribed interval between the nozzles, distance, which the molten metal M runs from the flat nozzle side to the center part of the nozzle, becomes short, and dent of molten metal at the center part of the nozzle becomes shallow and the wide width thin slab having excellent surface characteristic without double skin can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a continuous casting method for wide thin slabs and a casting machine therefor.

[Prior Art] Recently, continuous casting methods and casting machines for wide thin slabs have been actively developed. Direct production of wide thin slabs with a thickness of several millimeters to several tens of millimeters close to the final shape from molten metal such as molten steel requires multiple stages of rough rolling and intermediate rolling in the production of metal thin strips. It is possible to omit the rolling process, which simplifies the process and equipment. Furthermore, since there is no need to heat the material between each process, energy savings can also be expected.

For continuous casting of wide thin slabs, flat molds with square, round, oval, etc. sides are used, and molten metal is supplied from the tundish to the mold through a flat nozzle that extends along the long sides of the mold. be done. In this case, there is one flat nozzle. As such a continuous casting method, for example, there is a belt type continuous casting method, which is disclosed in Japanese Patent Application Laid-Open No. 58-10
This method is disclosed in Japanese Patent Application Laid-open No. 7255, Japanese Patent Application Laid-Open No. 166145/1984, and others.

A method of supplying molten metal through a plurality of nozzles in continuous casting is known from JP-A-55-16752 [Direct thin plate rolling method from molten steel]. but,
In this known method, - between a pair of rolls (corresponding to a mold) via a slider from a multi-nozzle lined up;
supply molten steel to That is, this known method does not directly supply molten metal to the mold via a nozzle. Also, the nozzle is not an immersion type. Therefore, with regard to the supply of molten metal to the mold, the present invention is completely different from the above-mentioned known methods.

[Problems to be Solved by the Invention] In the conventional continuous casting method for wide thin slabs in which molten metal is directly supplied to a mold from a flat nozzle, there is only one flat nozzle, as described above. On the other hand, when casting wide thin slabs, the mold is flat, so the distance between the inner wall surface of the mold and the outer surface of the flat nozzle becomes narrow. For example, the distance between the two surfaces is on the order of 3-20'mm. For this,
As shown in FIG. 5, the molten metal M supplied from the flat nozzle 7 to the mold 1 cannot fully reach the width center part 3 of the flat nozzle 7 (or the center part in the long side direction of the mold 1). The molten metal surface m was lowered at the center 3 of the flat nozzle, and a depression d was formed in the molten metal surface m at the center. As a result, the supply of the molten metal M became non-uniform and unstable, and double roughening occurred on the surface of the slab (slab) S. This phenomenon became more pronounced as the aspect ratio of the flat nozzle 7 or the casting speed increased.

The above-mentioned double roughness causes scratches to occur during rolling.

Therefore, the present invention aims to provide a method and a casting machine that can continuously cast wide thin slabs without double skin using a flat nozzle.

[Means for Solving the Problems] The continuous casting method for wide thin slabs of the present invention is a method for continuously casting wide thin slabs by injecting molten metal from a tundish into a flat mold through a submerged flat nozzle. As shown in FIG. 1, a plurality of flat nozzles 5 are arranged at predetermined intervals along the long side direction of the flat mold 1, and molten metal M is supplied to the mold 1 from each flat nozzle 5.

Further, the continuous casting machine for wide thin slabs of the present invention includes a tundish, an immersed flat nozzle provided at the bottom of the tundish, and a flat mold placed below the tundish, and melts through the flat nozzle. In a casting machine that continuously casts wide thin slabs by injecting metal into a flat mold, a plurality of flat nozzles 5 are arranged along the long side direction of the flat mold 1 at predetermined intervals.

In the casting method and casting machine described above, the mold may be a fixed mold or a movable mold such as a belt type.

The inventors of the present application have obtained the following findings as a result of various experiments and analyzes of continuous casting processes using flat nozzles.

FIG. 2 shows the relationship between the depth of the depression d and the number of double skins per unit area. Moreover, FIG. 3 shows the relationship between the nozzle width (dimension along the long side direction of the mold) and the depth of the recess d. Here, the depth of the depression d is the deviation between the highest value and the lowest value in the width direction of the molten metal surface in the mold. As is clear from these figures, when the nozzle width is 600 mm or less, the depth of the recess is 6 mm or less, and double skin does not occur. Therefore, it is desirable that the nozzle width is 800 mm or less.

On the other hand, if the nozzle width is too narrow, the number of nozzles will increase and the structure of the casting equipment will become complicated, so the nozzle width should be 100 +
It is desirable that the thickness be at least nm. When the aspect ratio of a flat nozzle becomes high, it becomes difficult to manufacture the nozzle, so the nozzle aspect ratio must also be taken into consideration when determining the nozzle width. When the above-mentioned nozzle width is adopted, the aspect ratio of the flat nozzle used in the present invention is generally 2 or more or more than 1 in terms of the nozzle thickness. Furthermore, in order to uniformly supply the molten metal into the mold, it is appropriate that the distance between adjacent flat nozzles be approximately 50 mm or more, based on the knowledge shown in FIG. Figure 4 summarizes the relationship between the nozzle gap (mm) and the depth of the depression in the molten metal surface in continuous casting using two flat nozzles. As shown in Figure 2, the nozzle gap at which the critical concavity depth of 6m+n is achieved is 50mm, which gradually decreases as the nozzle gap increases, and becomes a nearly stable value at 100mm, so it is desirable to set it to 100mm or more. Furthermore, for the same reason, it is appropriate that the distance between the short side of the mold and the flat nozzle is 50 mm or more. From these appropriate nozzle widths and nozzle spacing, the number of nozzles is 2.
It will be about 5 pieces.

In order to uniformly supply the molten metal into the mold, it is preferable to arrange the flat nozzles so as to be symmetrical with respect to the center line of the long side and the center line of the short side of the mold.

[Function] By providing a plurality of flat nozzles, the width of a single flat nozzle becomes narrower. However, if a predetermined interval is provided between the nozzles, the distance that the molten metal wraps around from the side edge of the flat nozzle to the center of the nozzle becomes shorter, and the depression in the molten metal surface at the center of the nozzle becomes shallower.

[Example] Wide thin steel slabs were continuously cast under the following conditions.

Casting machine: Double-held continuous casting machine Mold (slab) cross-sectional dimensions: Long side 1200m x Short side 50m
m Nozzle outer diameter dimensions: width 400 x thickness 50 mm Number of nozzles: 2 Nozzle spacing: 200 mm Nostle immersion depth: 50 mm Casting speed: 10 m/m1n - As a result of casting under the above conditions, the molten steel surface at the center of the nozzle was The depth of the dent was 2 mm. In addition, 2
No heavy skin occurred at all. The obtained wide thin slab was hot rolled to a thickness of 2 mm, and no scratches or other flaws were produced on the rolled plate.

For comparison with this invention, a wide thin slab was continuously cast under the same conditions as above using a flat nozzle with outer diameter dimensions of 800 mm width x 50 mm thickness. As a result, the depth of the dent on the molten steel surface at the center of the nozzle was 10 mm.
Double skin appeared on the slab surface. In addition, bald spots occurred during hot rolling.

[Effects of the Invention] In the present invention, molten metal is supplied into the mold from a plurality of flat nozzles. Therefore, the supply of molten metal into the mold becomes uniform, and the depression in the molten metal surface at the center of the nozzle becomes shallow. As a result, it is possible to obtain a wide thin slab with an excellent surface P shape without double skin.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing an example of the arrangement of the flat nozzle of the present invention, Fig. 2 is a line section showing the relationship between the depression depth of the molten metal surface and the number of double skins, and Fig. 3 is the nozzle width and melting. FIG. 4 is a diagram showing the relationship between the nozzle spacing and the depth of the recess on the metal surface; FIG. 5 is a perspective view showing the arrangement of conventional flat nozzles. ■... Mold, 3... Center part of flat nozzle, 5゜7... Flat nozzle, M... Molten metal, S...
Slab, d...concavity on molten metal surface, m...molten metal surface.

Claims (1)

[Claims] 1. In a method of continuously casting wide thin slabs by injecting molten metal into a flat mold from a tundish through a submerged flat nozzle, the method is performed by casting a thin slab at a predetermined interval along the long side of the flat mold. 1. A continuous casting method for a wide thin slab, characterized in that a plurality of the flat nozzles are arranged in a mold, and molten metal is supplied from each flat nozzle to a mold. 2. It is equipped with a tundish, an immersed flat nozzle provided at the bottom of the tundish, and a flat mold placed below the tundish. A continuous casting machine for continuous casting of wide thin slabs, characterized in that a plurality of the flat nozzles are arranged at predetermined intervals along the long side direction of the flat mold. 3. The continuous casting machine for wide thin slabs according to claim 2, wherein the width of the flat nozzle is 100 to 600 mm.