JPS61140355A - Electromagnetic stirrer for controlling molten steel flow in casting mold - Google Patents

Abstract

PURPOSE:To produce a steel slab which has no segregation of impurities and is clean in both the front layer and inside by continuous casting by providing static magnetic field coils on the long side faces of a rectangular-shaped casting mold of a continuous casting and moving magnetic field type coils to the position upper than the molten steel surface in the casting mold to brake the flow of the molten steel in the mold. CONSTITUTION:Two pairs of the static magnetic field generating coils 2 are attached to the long side faces of the continuous casting mold 3 for production of the steel slab having >=2.5 ratio of the length between the long side and short side and two pieces of the moving magnetic field type electromagnetic coils 1 are disposed to the position upper than the molten steel surface 4 in the mold 3 with an immersion nozzle 6 from a tundish inbetween. The molten steel flow supplied by the nozzle 6 is braked by the coils 2 and the molten steel on the surface 4 is horizontally moved toward the short side of the mold 3 from the central part by the coils 1, by which the segregation of the impurities in the molten steel in the mold is obviated. The continuous casting slab which is clean in both the front and rear surfaces and the inside is thus obtd.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an electromagnetic device for controlling the flow of molten steel in a mold in continuous casting of steel, and more specifically, for continuous casting of slabs having a high degree of cleanliness both on the surface and inside. Relating to a device for

[Conventional technology]

When continuously casting slabs with excellent cleanliness, the flow of molten steel discharged from the molten steel supply nozzle immersed in the mold, that is, the immersion nozzle, is braked to suppress the flow of molten steel that reaches deep inside the crater. It is a well-known fact that levitation of oxide-based inclusions within the substrate is promoted. For this reason,
Although many methods have been tried, the reality is that there are few that can be easily applied to actual continuous casting machines.

JP-A-57-17356 discloses the invention of an electromagnetic brake method for braking the above-mentioned discharged molten steel flow as a result of research and development in which the inventors also participated. This method is extremely easy to implement, and its effect on so-called inclusion accumulation, which is generally observed in curved continuous casting machines, is significant.

However, in cold-rolled steel sheets where the cleanliness of the surface layer of the slab is a problem, even the above-mentioned electromagnetic brake does not provide much improvement. This is inevitable considering the nature of the wood used in the electromagnetic brake.

On the other hand, it is also theoretically possible to stir the molten steel horizontally or vertically using an electromagnetic stirring device built into the mold, thereby achieving the effect of cleaning so-called inclusions. However, under normal operating conditions, a solidified shell of about 8 mm has already grown 100 mm below the upper surface of the molten steel in the mold, so it is essential to strongly stir the molten steel during this time. This is difficult for the following reasons. For example, if an electromagnetic stirring coil is installed in a continuous casting mold to perform vertical stirring or horizontal rotational stirring, In addition, it is practically difficult to design an electromagnetic stirring coil for generating a moving magnetic field on the short side.

2) In horizontal stirring, there are many difficulties in the design of the electromagnetic stirring coil, which cannot perform strong stirring within 100 mm from the upper surface of the self-melting steel of the continuous casting mold. That is, a considerably large coil is required to maintain the stirring force in this part, and it is difficult to incorporate it into the mold. On the other hand, the flow near the corners of the mold becomes non-uniform, and an abnormal increase in inclusions sometimes occurs.

3) In any case, the molten steel flow discharged from the nozzle and the electromagnetic stirring flow interfere with each other, and it is difficult to maintain the symmetry of the molten steel flow in the mold.

On the other hand, Japanese Patent Publication No. 55-54245 describes a method in which an electromagnetic stirring coil approaches the molten metal surface on the upper surface of the mold from above.
Disclosed in the issue. In this case, four small electromagnetic coils are installed in a mold with a circular or rectangular cross section, and the electromagnetic coils are energized to generate a circular flow in a horizontal plane.

This method is said to avoid deterioration in maintainability when incorporating an electromagnetic coil into a continuous casting mold. However, in this method, four electromagnetic coils are installed above a mold with a circular or rectangular cross section, and the rectangular cross section to which this method can be applied is a square cross section with no large difference in the long side dimensions of a short fist, such as a bloom. This is thought to mean a cross section with a similar shape.

This method cannot be applied to a so-called slab type cross section in which the length ratio of the long side to the short side is 4 or more.

It should be noted that the above electromagnetic stirring method is essentially not capable of improving the accumulation of inclusions in the slab.

[Problem that the invention seeks to solve]

The present invention aims to provide an electromagnetic device that can be applied to a mold for continuous casting of slabs having a length ratio of long side to short side of 2.5 or more, and can obtain slabs with excellent cleanliness. purpose.

- [Means for solving the problem] The present invention targets a mold with a slab-like cross section, and in order to achieve the above object, molten steel is stirred using an electromagnetic stirring coil suspended from above the mold under conditions where dielectric loss can be almost ignored. At the same time, the discharged molten steel flow is braked by a static magnetic field generator built into the mold.

That is, the present invention includes a static magnetic field generator disposed on the 0-long side of a continuous casting mold to brake the flow of molten steel supplied into the mold, and a static magnetic field generator disposed above the mold to suppress the flow of molten steel near the upper surface of the molten steel in the mold. This is an electromagnetic device for controlling the flow of molten steel in a mold, characterized by comprising a moving magnetic field generating device that causes the flow of molten steel from the center of the horizontal section to the short side.

FIG. 1 is (a) a schematic side view and (b) a plan view of a mold equipped with an electromagnetic device according to the present invention, showing the relationship between the mold internal dimension 3 and the electromagnetic device. Molten steel is supplied into the mold from above through a submerged nozzle 6, where a solidified shell 5 is formed and drawn out below the mold as a slab.

A generator consisting of two groups of static magnetic field coils is disposed on the long sides of the mold and brakes the flow of molten steel supplied into the mold. A moving magnetic field generator comprising a moving magnetic field type coil is disposed above the upper surface 4 of the molten steel. The moving magnetic field generator moves the molten steel near the upper surface of the molten steel in the mold from the center of the horizontal section to the shorter side of the mold. This coil is suspended from above, for example, and this hanging coil is an electromagnetic coil with a width of about 1/2 of the long side of the mold and a thickness slightly smaller than the short side of the mold from above the continuous casting mold. One piece is placed above each surface divided into two by a submerged nozzle located approximately in the center of the area. This coil has a large number of units arranged inside an electromagnetic coil with the intention of causing the molten steel to flow laminarly in the short side direction from the immersion nozzle on the upper surface of the molten steel in the mold.

[Effect]

The static magnetic field generating coil 2 brakes the flow of molten steel, and the moving magnetic field type coil 1 horizontally moves the molten steel on the upper surface of the molten steel. Due to these effects, the molten steel does not segregate with impurities, and it is possible to continuously cast slag with clean surfaces and internal valves.

〔Example〕

Low-carbon A-killed steel melted in a 275-ton converter using Ar flashing is cast into a 220mm thick slab caster using a continuous slab caster.
It was cast into a cross section with an X width of 1550 mm.

At this time, the effects of the electromagnetic stirring and electromagnetic brake according to the present invention were investigated under 5 normal casting conditions. The conditions for electromagnetic stirring and electromagnetic brake are as follows.

Electromagnetic stirring: 60Hz, 180 kVA, magnetic flux density on the surface of the molten steel: 800 Gauss Electromagnetic brake: DC, 800 kVA, magnetic flux density of the molten steel in the i-type: 2,000 Gauss The effects of the present invention are summarized in Table 1. It is clear that the combined use of stirring and electromagnetic brakes makes it possible to produce slabs with extremely high cleanliness.

What is particularly important to note in Table 1 is that even during high-speed casting, there is no increase in the amount of inclusions inside the slab, and there are no casting accidents such as breakouts. It is possible to choose.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a device according to an embodiment of the present invention, showing (a) a side view and (b) a plan view. ■... Moving magnetic field type electromagnetic coil, 2... Static magnetic field generating coil, 3... Mold internal dimensions, 4... Mold internal temperature steel upper surface, 5... Solidified shell, 6... Immersion nozzle.

Claims (1)

[Claims] 1. A static magnetic field generator disposed on the longer side of a continuous casting mold to brake the flow of molten steel supplied into the mold, and a static magnetic field generator disposed above the mold to suppress the flow of molten steel near the upper surface of the molten steel in the mold. 1. An electromagnetic device for controlling the flow of molten steel in a mold, comprising a moving magnetic field generating device that causes molten steel to flow from the center of the horizontal section to the short side.