JPH0270361A - Apparatus and method for continuously casting molten metal - Google Patents

Abstract

PURPOSE:To make suitably of cast slab shape in continuous casting and to restrain defect below the surface by arranging conductive annulus ring near outer circumference of molten metal meniscus in a mold. CONSTITUTION:An electromagnetic coil 5 is set at outer circumference of the mold 1 in continuous casting apparatus. Further, the conductive annulus ring (magnetic screen) 6 is set near the outer circumference of the molten metal meniscus 3 in the mold 1. The electromagnetic force is given to the molten metal 2 in the mold 1 with the electromagnetic coil 5 to execute the continuous casting. Then, the conductive circle 6 is set near outer circumference of the meniscus 3 to control shape of the meniscus 3 and flow of the molten metal. By this method, the cast slab shape is made to suitable with the continuous casting and the defect below the surface can be restrained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention stabilizes the meniscus shape of the molten metal and the flow of the molten metal in the mold when continuously casting molten metal to produce a slab. The present invention relates to a continuous casting apparatus and method that can significantly improve the shape and internal quality of slabs.

Conventional technology In a method of continuously manufacturing slabs by applying electromagnetic force to molten metal poured into the mold using an electromagnetic coil installed around the outer periphery of the continuous casting mold (hereinafter abbreviated as ELM casting). performs casting while applying alternating current to the electromagnetic coil. This electromagnetic force has the effect of reducing the static pressure of molten steel and stirring the molten metal in the mold when solidifying the molten metal in the mold.
It is disclosed in Japanese Patent No. 32824.

FIG. 5 is a sectional view of the device used therein. That is, when an electromagnetic force is applied to the molten metal 2 poured into the inner space of the mold 1, the meniscus 3 curves in the shape shown in the figure.

FIG. 6 is a diagram illustrating that the meniscus 3 curves when an alternating current (2) is passed through the electromagnetic coil 5. The alternating current I generates a time-varying magnetic field H around the mold l. Furthermore, eddy currents i are induced in the molten metal within the mold 1 due to temporal changes in the magnetic field H. This magnetic field H and eddy current i interact with each other, and a restraining force F acts toward the center of the mold 1. This restraining force F acts on the molten metal 2.
is squeezed toward the center of the mold l, and the meniscus 3 curves upward in a convex shape. The shape of the meniscus 3 is mainly determined by the balance between the restraining force F and the static pressure P of the molten metal 2.

By curving the meniscus 3 in this way, the powder 4 floating on the molten metal is collected around the mold 1 where the meniscus 3 is low, and the molten metal 2 or the solidified shell and the inner surface of the mold 1 are brought together by the oscillation of the mold. A sufficient amount will be sent in between.

The slabs produced as a result of these methods have greatly improved surface properties, internal quality, etc. compared to those without electromagnetic force, and productivity can also be improved by setting a high casting speed. .

Problems to be Solved by the Invention However, simply applying an electromagnetic force causes the following phenomenon, and is not necessarily satisfactory, especially during high-speed, high-flux-density casting.

For example, when the magnetic density in the mold exceeds 500 gauss, the flow of molten steel with a protruding part at the center of the meniscus becomes large, and the meniscus shape does not become a stable convex shape.
It becomes unstable with ripples and fluctuations. As a result of this, the cross-sectional shape of the slab deteriorated, and in particular, the roundness of the round bloom slab deteriorated significantly. Furthermore, a new problem occurred on the surface of round bloom slabs cast at 700 gauss or higher, such as dented grooves parallel to the casting direction.

For these reasons, the magnetic flux density in ELM casting is at most 1.
The magnetic flux density remained at around 0.000 g and 100 O, and slabs cast by ELM with a magnetic flux density higher than this required surface preparation, resulting in a decrease in yield. In addition, in ELM casting with high magnetic flux density, the flow of the molten metal becomes large, and many surface defects such as powder entrainment occur, especially on the meniscus surface due to the influence of the flow from the center of the meniscus to the outer periphery.

Therefore, the present invention does not cause such problems.

The object of the present invention is to provide an apparatus and method for producing slabs with stable meniscus shape and molten metal flow and excellent surface properties at high speed and high magnetic flux density.

Means for Solving the Problems In order to achieve the object, the present invention provides a continuous casting device in which an electromagnetic coil is installed around the outer periphery of a continuous casting mold. This continuous casting device for molten metal is characterized by being installed near the outer periphery of a metal meniscus.

In addition, when performing continuous casting while applying electromagnetic force to the molten metal poured into the mold by an electromagnetic coil installed around the outer periphery of the continuous casting mold, a conductive ring (magnetic screen) is inserted into the molten metal. This continuous casting method for molten metal is characterized in that the mold is installed near the outer periphery of the meniscus to control the shape of the meniscus and the flow of molten metal within the mold.

Magnetic screen (conductive ring) near the outer periphery of the working meniscus
By installing the mold, the magnetic field distribution inside the mold changes.

FIG. 1 is a sectional view of an embodiment in which a magnetic screen 6 is installed during ELM casting. In this case, the magnetic screen 6 is made of copper;
is the outer periphery of the mold directly above the molten metal meniscus 3, and is installed directly above the electromagnetic coil 5.

FIG. 2(a) shows an outline of the magnetic field distribution H in the mold when the magnetic screen 6 of the present invention is installed, in comparison with the case without the magnetic screen shown in FIG. 2(b).Mold 1
The molten metal 2 inside the mold is heated by the electromagnetic coil 5 installed on the outer periphery.
In addition, eddy current i° is induced within the magnetic screen 6 as well. Because of this i', the magnetic field distribution H within the mold acts more concentratedly on the outer periphery of the meniscus than in the case without the magnetic screen 6. Therefore, the restraining force F acts intensively on the outer periphery of the meniscus, and for example, as shown in Fig. 1,
When the magnetic screen 6 is placed above or below the position shown in FIG. 1, the shape of the meniscus becomes
The steep shape gradually changes to a gentle convex shape, and the flow of the molten metal gradually decreases. As long as the position of the lower end of the magnetic screen is within 2501 points below E from the same height as the meniscus, there is no practical problem in the operation and effect of the magnetic screen.

Furthermore, by changing the position of the magnetic screen 6.

When the magnetic screen shown in Figure 1 is installed 300 mm above or below the same height as the meniscus, the flow of molten metal on the meniscus surface 3 is almost suppressed, and the molten metal flow rate becomes 0.
becomes. If installed further above or below, Fig. 2(b)
The pattern is similar to that of the molten metal flow 7 without the magnetic screen shown in FIG.

Therefore, in one aspect of the present invention, the magnetic screen 6 is
It is preferable to install the magnetic screen 6 near the outer periphery of the meniscus of the molten metal in the mold so that the lower end of the magnetic screen 6 is located within 250 layers of the outer periphery above and below the meniscus 3.If the magnetic screen is within this range, The shape of the meniscus and the flow of the molten metal become stable.

The material of the magnetic screen in the present invention may be any conductive material such as copper, aluminum, or stainless steel, and the shape of the magnetic screen must be limited to the rectangular cross section shown in FIG. 1 and FIG. 2(a). Not.

It is also possible to take any cross-sectional shape, such as circular or square, depending on the space within the mold. By freely controlling the meniscus shape and molten metal flow in this manner, stable meniscus shape and molten metal flow can be created.

Note that the mechanism and method for moving or adjusting the position of the magnetic screen in the vertical direction are not particularly limited, and a commonly used mechanical elevating mechanism driven by a motor can be used.

EXAMPLES Hereinafter, features of the present invention will be specifically explained by examples with reference to one drawing.

Molten steel having the compositions shown in Tables 1 and 2 was cast by ELM.

Table 1 Table 2 (Unit: Weight 50 (Unit: Double weight) As a mold for sea urchin, as shown in Figure 1, an electromagnetic coil 5 is installed around the mold around the meniscus, and a round bloom is continuously formed. A mold with a columnar internal space with an inner diameter of 200 mm was used for casting.The main casting conditions during casting were as follows.
Shown in the table.

(Left below) As shown in Table 3, the casting speed and the magnitude of the applied magnetic flux density were varied, and cases with and without a magnetic screen were compared. The lower edge of the magnetic screen was at the same height as the meniscus.

Figure 3 shows the results of measuring the diameter of the manufactured round bloom. The diameter of the slab shown in the figure is the width of deviation from the standard diameter of the slab. As is clear from this figure, when a magnetic screen is installed, there is not much difference in the casting area where the magnetic flux density is relatively low compared to when there is no magnetic screen, but in contrast, in the casting area where the magnetic flux density is relatively high. The roundness of the slab obtained with V was improved.

FIG. 4 is a graph comparing the existence rate of inclusions under the cast slab in each ELM casting region with and without a magnetic screen. On the vertical axis of the graph, 100X corresponds to the number of inclusions without the magnetic screen, and white circles correspond to the number of inclusions with the magnetic screen. In the case of cast slabs using a magnetic screen, a significant improvement in this under-desk inclusion was observed in the relatively high magnetic flux density regions of casting regions (1) to (V).

As described in detail, in the present invention, the shape of the meniscus and the flow of the molten metal are controlled by causing the magnetic field distribution within the mold to act intensively on the outer periphery of the meniscus using a magnetic screen. Therefore, underboard inclusions caused by uneven powder inflow or molten metal flow on the meniscus are suppressed, and in ELM casting, the shape of the slab can be optimized and underboard defects can be suppressed. Furthermore, since it is extremely easy to change various magnetic screen shapes and the relative positions of the meniscus and the magnetic screen, it is possible to precisely control the meniscus shape and the molten metal flow. In this way, according to the present invention, it is possible to improve the quality of ELM cast slabs.

[Brief explanation of the drawing]

FIG. 1 is an elevational view illustrating a state in which the magnetic screen of the present invention is attached to an ELM, and FIG. 2 is an explanatory diagram showing the operation of the present invention. FIGS. 3 and 4 are graphs illustrating the invention in detail. Figure 5 shows the conventional ELMjl
FIG. 6, an elevational view showing the casting mold, is a diagram for explaining that the meniscus is curved by electromagnetic force. l... Mold, 2. Fist, molten metal, 3. Fist, molten metal meniscus, 4. Series of cast powder, 5. Electromagnetic coil, 6. Conductive ring (magnetic screen), 7. ... Molten metal flow.

Claims (1)

[Scope of Claims] 1. A continuous casting apparatus in which an electromagnetic coil is installed around the outer periphery of a continuous casting mold, characterized in that a conductive ring is installed near the outer periphery of a molten metal meniscus in the mold. continuous casting equipment. 2. When performing continuous casting while applying electromagnetic force to the molten metal poured into the mold by an electromagnetic coil installed around the periphery of the continuous casting mold, a conductive ring is placed near the periphery of the molten metal meniscus. A method for continuous casting of molten metal, characterized by controlling the meniscus shape and the flow of molten metal in the mold.