JPS61199557A - Device for controlling flow rate of molten steel in mold for continuous casting - Google Patents

Abstract

PURPOSE:To brake the molten steel flow over the entire region in a mold for continuous casting and to obtain an ingot having excellent quality by supplying DC current to a coil which is disposed on the outside of the mold in such a position where the axial center thereof is perpendicular. CONSTITUTION:A conductive pipe 31 is wound around the mold 21 by which the coil 30 having the perpendicular axial direction is formed on the outside of the mold 21. A DC power source 32 is connected to the coil 30 and electricity is conducted from the power source 32 to the coil 30. The discharge flow of the molten steel from a discharge port 25 of an immersion nozzle 24 flows diagonally downward in the device constituted in the above-mentioned manner. The speed components in the horizontal direction out of the speed components in the horizontal direction and vertical direction of the molten steel flow receives the influence of a magnetic field and the braking force is horizontally applied on the molten steel flow. The braking force can be controlled by changing the intensity of the magnetic field. The non-metallic inclusions in the ingot are decreased in the above-mentioned manner.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an in-mold molten steel flow rate control device for continuous casting, which is capable of controlling the flow rate of molten steel discharged from a submerged nozzle or the like in a continuous casting mold. .

[Conventional technology and its problems]

In continuous casting of steel, molten steel in a tundish S1 is injected into a mold 3 through a submerged nozzle 2 (as shown in FIG. 4). The mold 3 has a pair of short side walls 3 & and long side walls 3.
The molten steel is cooled by the mold 3 to form a solidified shell. The slab containing unsolidified molten steel inside is continuously pulled out from the mold 3 and further cooled in a secondary cooling zone.

In this case, the molten steel flows out from the discharge port 5 of the immersion nozzle 2 as shown by the arrow in the figure, collides with the short side wall 3a, and forms a downward flow 4a and a branch flow 4b branching from this downward flow into the mold 3. is formed. The downward flow 41 penetrates deeply into the mold, as shown.

As the casting speed of continuous casting increases, the amount of molten steel injected per unit time increases, and if the diameter of the discharge port 5 is constant, the discharge flow rate of molten steel increases. Then, the short side wall 3a
The high-temperature molten steel flow that collides with the steel flows at high speed and in large quantities, causing re-melting of the solidified shell, which ultimately retards the growth of the solidified shell in the area where the molten steel flow collides. When the solidified shell becomes partially thin in this way, non-uniform cooling occurs, and the solidified shell ruptures due to thermal stress caused by this cooling inconsistency or volumetric contraction during solidification, which is called a breakout. There is a risk of a serious accident occurring.

Further, the downward flow 4a of molten steel discharged from the immersion nozzle flows into the mold 3.
If the nonmetallic inclusions penetrate deeply into the molten steel, it becomes difficult to float and separate the nonmetallic inclusions contained in the molten steel.

As a result, non-metallic inclusions are trapped within the slab, deteriorating the quality of the slab.

Techniques that attempt to solve these problems include a moving magnetic field generator (Japanese Patent Laid-Open No. 160862/1986) or a static magnetic field generator (Iron & 5teel Eng).

May 1984. P41) is known.

In the former case, as shown by the broken line in FIG. 4, a moving magnetic field generating device 10 is installed outside the long side wall 3b to generate a moving magnetic field in the molten steel along the discharge flow of the molten steel. With this, it is possible to apply a braking force to the molten steel flow, but the area where the braking force due to such a magnetic field is applied is near the wall of the mold.
It is difficult to apply braking force to the internal molten steel flow. In order to apply sufficient braking force to the molten steel flow inside the mold, it is necessary to increase the power of the device.

In the latter case, as shown in a plan view near the mold in FIG. 5, a static magnetic field generator 13 is installed on the long side wall 12 of the mold 11. However, even in this technology, the area where the flow velocity of the discharge flow of molten steel can be controlled is the static magnetic field generator 13.
It is only close to the former and has the same drawbacks as the former.

[Failure to solve the problem]

This invention was made in view of such circumstances, and
Control of the flow rate of molten steel in the mold for continuous casting, which can brake the discharge flow of molten steel in the mold with high efficiency, reduce the flow velocity, and promote the formation of a healthy solidified shell and the floating of non-metallic inclusions. The purpose is to provide equipment.

The in-mold molten steel flow rate control device for continuous casting according to the present invention includes:
A coil is installed on the outside of a continuous casting mold so that the axis of the coil is substantially vertical, and a direct current is supplied to the coil to surround the mold so that the steel inside the mold becomes substantially vertical. It is characterized by having a supply device that forms a vertical magnetic field.

〔Example〕

Embodiments of the present invention will be specifically described below with reference to FIG. Molten steel in a tundish (not shown) is injected into the mold 21 through a submerged nozzle 24.

The mold 21 has a rectangular tube shape having a pair of short side walls 22 and a long side wall 23. The molten steel is cooled by the mold 21 to form a solidified shell, and the slab 26 containing unsolidified molten steel inside is pulled out of the mold 21 and further cooled in a secondary cooling zone, where it is completely solidified.

A current-carrying tube 31 is wound around the mold 21, thereby forming a coil 30 with the coil axis substantially vertical on the outside of the mold 21. The upper and lower ends of the coil 30 are located at a distance of about 15,011 cm in the vertical direction from the center corresponding to the discharge port 25 of the immersion nozzle 24, and therefore the height of the coil 30 is about 300 cm. be. The current-carrying pipe 31 is made of a conductive material and is cooled by allowing cooling water to flow inside.

A DC power supply 32 is connected to the coil 30, and a DC current is applied to the coil 30 by the DC power supply 32.

In the device configured in this way, the immersion nozzle 24
A discharge flow of molten steel flows obliquely downward toward the short side wall 22 of the mold 21 from the discharge port 25 of the mold 21 .

The molten steel discharge flow collides with the solidified shell on the short side wall 22 side and branches into a downward flow and a branch flow. On the other hand, from the DC power supply 32 to the coil 30
When a direct current is supplied to the mold 21, a substantially vertical direct current magnetic field H extending in the axial direction of the coil is formed in the molten steel in the mold 21. This magnetic field H is directed vertically downward when a direct current is applied to the coil 30 in a clockwise direction when viewed from above the mold, and is directed vertically upward when the current is applied in the opposite direction.

Since the molten steel flow discharged from the discharge port 25 advances diagonally downward from the discharge port 25 toward the short side wall 22, the molten steel flow velocity has a horizontal velocity component vH and a vertical velocity component vv. On the other hand, a vertically extending magnetic field H formed by the coil 30 acts on such a molten steel flow. Then, since the horizontal velocity component vH and the magnetic field H are perpendicular to each other, a voltage proportional to the velocity vH is induced in the molten steel flow, and a current flows in the molten steel in a direction perpendicular to the velocity vH and the magnetic field H. As a result, the molten steel flow receives an electromagnetic force in the direction opposite to the velocity vH, and therefore, a braking force acts on the molten steel flow in the horizontal direction. This braking force can be controlled by adjusting the current applied to the coil 30 and the strength of the magnetic field H, so it can be controlled by adjusting the casting speed of continuous casting and the diameter of the outlet of the submerged nozzle used. By controlling the braking force applied to the molten steel flow accordingly, it is possible to form a molten steel flow trajectory in the mold that is optimal in terms of operation and slab quality.

Next, the results of measuring the slab quality and solidified shell thickness by controlling the flow rate of molten steel in the mold according to the present invention will be explained.

A slab with a thickness of 250 fl and a width of 1500 mg was cast at a casting speed of 1.8 m and 7 minutes using a curved continuous slab casting machine with a curvature of 10.5 m. The cast steel was a low-order aluminum killed steel for thin plates, and after casting, the slab was subjected to a sulfur print test to determine the inclusion index in the surface layer. Furthermore, during casting, sulfur was added to the molten steel in the mold, and after casting, the slab was sulfur printed and the thickness of the solidified shell on the short side of the slab in the mold was measured. These tests were conducted in cases where the flow velocity of the molten steel flow was controlled according to the present invention, in which the flow velocity of the molten steel flow was not controlled at all (case A), and in which the flow velocity was controlled by a moving magnetic field shown by the broken line in Fig. 4. If (Case B)
The case where the flow velocity was controlled by a static magnetic field (Case C) shown in FIG. 5 was also conducted for comparison. In addition, regarding the present invention, case B, and case C, the electric capacity is 120 kW.

The measurement results are shown in FIG. 2 for the inclusion index and in FIG. 3 for the solidified shell thickness. As is clear from FIG. 2, it goes without saying that the amount of nonmetallic inclusions is extremely reduced when the flow rate is controlled compared to when the flow rate is not controlled (Case A), and in the case of the present invention. The flow rate is even lower than that when the flow rate is controlled using the conventional technology (cases B and C). On the other hand, as shown in FIG. 3, the thickness of the solidified shell on the short side of the mold is thicker in the case of the present invention than in the other cases A, B, and C. It can be seen that a is formed. In this way, in the present invention, the slab quality and operational stability can be improved compared to the conventional method, despite the same electric power K.

In addition, also in this invention, in order to provide a large braking force to the molten steel flow, it is necessary to increase the strength of the magnetic field H. However, in order to increase the magnetic field H, it is necessary to apply a large amount of power to the coil, which has the disadvantage of increasing the size of the device. Therefore, the inventors of the present application variously changed the current flowing through the coil to adjust the strength of the magnetic field H that acts on the molten steel flow.
The relationship between slab quality and solidified shell thickness was investigated. As a result, by creating a magnetic field of approximately 500 oersted on the central axis of the mold, slab quality and operational stability can be improved compared to conventional methods, and when the magnetic field strength is 1500 oersted, extremely excellent effects can be obtained. It turned out that it can be done.

This invention is not limited to the above embodiments, and various modifications are possible. In particular, the present invention is of course applicable not only to slab-type continuous casting machines but also to plume- or billet-type continuous casting machines in which the side walls of the molds have approximately the same width dimension. Furthermore, a normal conducting coil, a superconducting coil, or the like can be used as the coil, but it goes without saying that a superconducting coil can apply a stronger magnetic field to even smaller equipment.

〔Effect of the invention〕

According to this invention, not only the area near the side wall of the mold,
Braking force can be applied to the molten steel flow with high efficiency even in the internal region, and the molten steel flow speed can be controlled according to the casting speed and the like. This can prevent the molten steel flow from penetrating deeply into the mold, and can reduce non-metallic inclusions in the slab. In addition, the energy when the molten steel flow collides with the solidified shell is reduced, and remelting of the solidified shell is suppressed, so a healthy solidified shell is formed and the operation becomes stable. In this way, this invention has extremely high practicality.

[Brief explanation of drawings]

Fig. 1 is a schematic perspective view showing an embodiment of the present invention, Figs. 2 and 3 are graphs showing the effects of the invention, Fig. 4 is a vertical sectional view showing the prior art, and Fig. 5 is a conventional It is a plane that shows technology. 21: mold, 22: short side wall, 23: long side wall, 24: immersion nozzle, 25: discharge port, 30: coil, 31: energizing pipe,
32: DC power supply. Applicant's agent Patent attorney Takehiko Suzue Figure 2
Figure 3

Claims (1)

[Claims] A coil is installed on the outside of a continuous casting mold so that the axis of the coil is substantially vertical, and a direct current is supplied to this coil to surround the mold so that the coil axis is substantially vertical to the molten steel inside the mold. 1. An in-mold molten steel flow rate control device for continuous casting, comprising a power supply device that forms a magnetic field in a direction.