JPS58215251A - Electromagnetic stirring method of unsolidified molten steel in crater end in continuous casting of bloom - Google Patents

Abstract

PURPOSE:To prevent effectively the central segregation and center cavity of an ingot and to improve quality by forcing spiral flow in molten steel by means of a composite stirrer combined with electromagnetic coils of a linear motor type and a rotary motor type. CONSTITUTION:Spiral flow 12 directing toward a crater end 4 of a bloom 4 formed by drawing the molten steel 1 in a casting mold 2 continuously with roll aprons 3 is induced in the narrow unsolidified molten steel 1b enclosed by a thick solidified shell 1a near said creater end by using a composite stirrer 11 combined with a rotary motor type electromagnetic coil 10 which turns and flows the molten steel around the axial center at the center of said steel in the drawing direction for casting and a linear motor type electromagnetic coil 9 which propels the molten steel axially along the axial center. Additional one set of said stirrer 11 may be installed along the drawing direction for casting or the coil 9 may be combined on the down stream side of the coil 10.

Description

[Detailed Description of the Invention] This invention relates to a method for electromagnetic stirring of crater-end unsolidified molten sacrificial material in continuous bloom casting, and in particular proposes development results aimed at effectively improving the internal quality of continuous bloom cast slabs. That is.

In this case, a plume generally refers to a square piece of steel with a side length of 18 crn or more, or a rectangular cross section with a cross-sectional area equivalent to that of square, and is distinguished from a billet that is smaller than this. is taken as an example, but in this invention, such a billet is also referred to as a plume.

In recent years, electromagnetic stirring of slabs for blooming has come to be used in various fields as an effective means of improving the quality of slabs.

The electromagnetic stirring device is applied at various locations such as inside the mold, the secondary cooling zone directly below the mold, and the crater end, and its effects vary depending on the location.

In other words, at the upper part of the mold, surface bubble defects are prevented by promoting the floating of air bubbles and inclusions, and at the downstream side of the mold, internal quality is improved mainly by increasing equiaxed crystallinity, especially at the crater end. Stirring that is suitable for this purpose is to improve center segregation and center cavity.

Among these, stirring in the secondary cooling zone excluding the crater end of the mold is generally recognized to be quite effective, but stirring at the crater end still has many gaps.

This is because near the crater end, the solidified shell is thick and the lightning magnetic force is attenuated, making it difficult to reach the area.Also, there is little remaining molten steel, and the unsolidified space is narrow, so the resistance is large (therefore, the flow of molten steel is I don't think this is due to the fact that it is difficult to wake up J.

The conventional stirring method near the crater end is as follows:
It is roughly divided into two methods shown in Figures 1 and 2.
is molten steel, 2 is a mold, 8 is a roller apron, and 4 is a crater end. Fig. 1 shows a system in which a rotating magnetic field type rotary motor type coil 5 is used to stir unsolidified molten steel 1b surrounded by a solidified shell 1a in the vicinity of a crater end 4 through a rotating motion as shown by an arrow 6. It is. In addition, although the method uses the linear motor type coil 7 shown in Figure 2 and stirs with the axial flow motion indicated by the arrow 8 along the casting drawing direction, neither of these methods achieves sufficient effectiveness for the reasons mentioned above. In addition, in the actual casting process, due to uneven growth of the solidification front caused by fluctuations in casting speed, local cooling, and other high-temperature casting, A bridging phenomenon as shown in may occur, and as a result, the center cavity shown in (■) was almost powerless against remaining casting defects.

Therefore, there is a need for a stirring method that powerfully sends the unsolidified molten steel to the crater end.In view of such circumstances, this invention attempts to provide a more effective and powerful stirring method at the crater end. It is something.

This invention provides a rotary motor-type electromagnetic device that swirls and flows the molten steel around a central axis along the casting drawing direction when applying electromagnetic stirring to unsolidified molten steel at the end of the crate surrounded by the solidified shell of a bloom continuously cast slab. A composite start consisting of a coil and a near-motor type electromagnetic coil that also propels the coil in the axial direction along the central axis is subjected to the above-mentioned task to force a spiral flow toward the crater end into the unsolidified molten steel. This is a solution to this problem.

That is, by generating a spiral flow 1 in the molten steel, it is immediately effective to effectively replenish and fill the narrow rotor end, including the center cavity caused by the bridging phenomenon described above, with molten steel. I was scolded.

In the case of FIG. 4 showing an embodiment of the present invention, a composite starter 11 combining a linear motor type electromagnetic coil 9 and a rotary motor type lightning coil %%lO is used near the crater end as shown by arrow 1B. Stirring is performed using a spiral flow. When comparing swirling and axial flow for stirring at the crater end, swirling is more effective in terms of stirring force, so the basic arrangement is to use a rotary motor type electromagnetic coil 1o as shown in Figure 4. It is desirable to place it on the downstream side. However, it is also possible to arrange both of them in a Zen manner and create a configuration as shown in Figure 5.

Further, as an application example and modification example of the method of this invention, as shown in FIG. 6, a rotary motor type city magnetic coil #10.10'
i. A combination of eight pieces arranged upstream and downstream of the linear motor type electromagnetic coil 9, and as shown in FIG.
, 10' are sequentially arranged in the casting drawing direction.
Both the individual combinations can produce much more powerful agitation.

The effects of this invention can be summarized as follows.

l) Compared to the conventional method, the spiral flow of residual molten steel toward the crater end occurs at the crater end, which enables stronger and more effective stirring light, which eliminates the problems of center segregation and center cap. Effectively prevents Tei's jealousy 1
) 1. The quality of central dissection of slabs can be improved.

2) For the rotary motor type electromagnetic coil and the linear motor type electromagnetic coil 6, the necessary combination of excitation control is
Since the stirring motion can be adjusted, it is possible to select a device that matches the applied electrical properties, and there is also a large degree of freedom in the equipment.

8) Since a conventional stirring coil can be used, there is no need to worry about applying it to actual equipment.

4) Since a spiral flow toward the crater end can occur in the remaining molten steel, the bridging phenomenon itself is prevented from occurring.

Although this invention is intended for stirring at the crater end in continuous casting of square or round plumes, it can of course also be used for stirring strands upstream from that point or for stirring irregular cross-section strands other than square or round.

[Brief explanation of the drawing]

Figures 1 and 2 are cross-sectional views showing conventional crater end agitation invasion area B, Figure 8 is an explanatory diagram showing how cavities are formed due to the bridging phenomenon at the crater end, and Figure 4 is a diagram showing the structure of the present invention. A sectional view showing the basic configuration of the embodiment, FIG. 5 is a sectional view of another embodiment, FIG. 6 is a sectional view of another embodiment, and FIG. 7 is a sectional view of a modified embodiment. - Molten steel, la...solidified shell, ■b...unsolidified molten steel, 2...casting 1q, 8...roller apron, 4...
- Crater end, 9... Linear motor accompaniment electromagnetic coil, 10... Rotary motor type electromagnetic coil, 11...
Stara Suai. Patent applicant Kawasaki Steel Corporation Figure 1 Figure 2; J I-! Figure 1

Claims (1)

[Claims] When applying electromagnetic stirring to the unsolidified molten steel near the crater end surrounded by the solidified shell of the continuously cast L bloom slab, the molten steel is rotated around the central axis along the casting drawing direction. The composite star 2, which is a combination of a rotary motor type electromagnetic coil that propels the flow #J and a near motor type electromagnetic coil that also propels the same axially along the central axis, causes a spiral flow toward the crater end. A method for stirring crater-end unsolidified molten steel in bloom continuous casting, which is characterized by forcing molten steel into a crater end. 2. The method according to claim 1, wherein the mustard is a combination in which a rotary motor type electromagnetic coil is disposed at least one side downstream or upstream of a linear motor type electromagnetic coil. 2. The method according to claim 1, wherein the & Stark is a combination of rotary motor-type near-motor type can electromagnetic coils, which are sequentially arranged along the casting drawing direction.