JPH071085A - Steel continuous casting equipment - Google Patents

Abstract

PURPOSE:To prevent a backup frame from being heated and molten by making using Ni-Cr-Fe non-magnetic stainless steel for a coil providing part of the backup frames and specifying the thickness thereof as the value shown the inequality. CONSTITUTION:A heating coil 1 is assembled at a meniscus level in the backup frames 3 supporting the mold cooling plates 2. In order to improve the permeating ratio of electromagnetic waves, the material of the mold uses the Ni-Cr-Fe non-magnetic stainless steel having low electric conductivity and high not strength and capable of reducing thickness. Further, the thickness D is specified as the value shown by the inequality. In the inequality,mu is the magnetic permeability of the non-magnetic stainless steel, sigma is electric conductivity of the non- magnetic stainless steel, f is frequency in the high-frequency wave. Therefore, the problems such as the damage of the coil heating just above the surface of molten steel 4, the danger of steam explosion, coil removing work at the time of changing an immersion nozzle 5 or a tundish, and contamination caused by mold powder can be dissolved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel continuous casting apparatus capable of producing a slab having excellent surface properties by induction heating the molten steel surface in a mold in a steel continuous casting process.

[0002]

2. Description of the Related Art Generally, the surface texture of a slab obtained by a continuous casting process of steel is strongly influenced by a so-called initial solidification state in which molten steel starts solidification in a mold. Factors involved in this are (1) vibration conditions of the mold, (2) friction (lubrication) conditions between the mold and the slab, (3) thermal conditions near the meniscus, (4) molten steel flow in the mold. The state etc. are mentioned. Actually, these are complicatedly related, and the initial solidification state is determined, but it is considered that the influence of the thermal conditions of the meniscus portion on the surface properties of the slab is most dominant.

Methods for changing the thermal conditions include a method of changing the amount of heat removal by changing the material of the mold and a method of heating the meniscus portion from the outside.
As a method of changing the material of the mold, JP-A-3-26414 is known.
As disclosed in Japanese Patent No. 3, there is a method of using a Ni—Cr—Fe alloy having a low thermal conductivity and a high hot strength as a casting material.

On the other hand, as a method for heating the surface of the molten steel in the mold, there is a proposal such as arc heating.
As disclosed in Japanese Patent No. 8565, there is a method in which a high frequency current is passed through a coil and the surface of molten steel is induction-heated by a high frequency electromagnetic field generated. According to this technique, the heat supply to the meniscus portion can be controlled independently of the casting conditions, and this is an advantageous method in that the molten steel surface can be heated uniformly. Specifically, a method has been proposed in which a flat coil is installed directly above the surface of the molten steel in the mold, and heating is performed from above the surface of the molten steel. At this time, in order to prevent melting loss due to Joule heat generation caused by passing an electric current, the coil is usually structured such that a hollow copper pipe is used and cooling water is passed through the hollow copper pipe.

[0005]

The problem of the above-mentioned method of changing the mold material is that the thermal condition of the meniscus portion cannot be controlled independently of the casting condition. Therefore, it is impossible to perform casting under constant thermal conditions regardless of changes in casting conditions. On the other hand, the problems of the induction heating method using the flat coil are as follows.

(A) In order to increase the heating efficiency, it is necessary to bring the heating coil close to the molten steel surface. However, the rising of the molten steel surface causes the coil to be immersed in the molten steel and damage the coil. Therefore, the cooling water of the coil leaks from the damaged portion and comes into contact with molten steel to cause a steam explosion, which poses a safety problem and is difficult to approach.

(B) A vortex flow level meter is provided right above the surface of the molten steel to measure the level of the level of molten metal, but there is a risk that the level coil will be heated by the heating coil and damaged. . (C) When the immersion nozzle is replaced or the tundish is replaced, it is necessary to remove it in order to prevent damage to the coil.

(D) On the surface of the molten steel, a mold powder is placed for the purpose of heat retention, absorption of non-metallic inclusions, lubrication of mold-cast slab, etc. In order to secure a certain amount or more of mold powder during operation, Although it is constantly replenished, the heating coil is exposed to such bad conditions, and therefore it is necessary to maintain strict maintenance.

[0009]

The present invention uses the following means in order to solve the above problems. (1) A heating coil is arranged in the backup frame on the back side of the opposite side wall of the mold. (2) As a material of the mold, a metal having low electric conductivity and high hot strength is used. As an example, a Ni-Cr-Fe based alloy is used. (3) In order to prevent the backup frame itself from being melted by heating due to the induction heating coil arranged in the backup frame, the coil disposing portion is partially made of non-magnetic stainless steel. In this case, it is preferable that the thickness D be D ≧ 1 / {√ (πμσf)}.

Where μ: permeability of non-magnetic stainless steel (≈4π × 10 ⁻⁷ H /
m) σ: electric conductivity of non-magnetic stainless steel f: high frequency

[0011]

1 and 2 are a horizontal sectional view and a vertical sectional view of an embodiment of the present invention. According to the present invention, the heating coil 1 is incorporated at the level of the meniscus 4a in the backup frame 3 supporting the mold cooling plate 2 as shown in FIGS. Therefore, it is possible to solve the problems of damage to the coil, danger of steam explosion, coil removal work when replacing the immersion nozzle 5 or the tundish, contamination by mold powder, etc. in the prior art of heating from just above the surface of the molten steel 4.

On the other hand, when high-frequency heating is performed from the back of the mold, electromagnetic waves are absorbed in the mold, and electric power must be increased more than necessary in order to supply the necessary heat to the surface of the molten steel. Assuming that the electric conductivity of the mold is σ _m , the magnetic permeability is μ _m , the thickness is d, and the frequency of the electromagnetic wave is f, the electromagnetic wave transmittance η _t
Is expressed as _{η t = exp {-√ (πμ} m σ m f) d} ...... (1). Therefore, as the material of the mold, a material having a small electric conductivity σ _{m and} a high hot strength in order to reduce the thickness d is preferable. As an example, Ni-
Although a Cr—Fe based alloy can be used, other materials can be used as long as they do not violate the above-mentioned gist.

On the other hand, induction heating similarly occurs for a backup frame incorporating a coil. Normal,
Carbon steel is selected as the material for the backup frame. The electric conductivity of carbon steel is about 10 ⁷ Ω ^-1 m ^-1 , but the relative magnetic permeability (ratio of the magnetic permeability to the magnetic permeability of vacuum) is about 7,000, which is extremely large. Therefore, there is a risk that the very surface of the backup frame, which is in contact with the heating coil, is heated and melted. Therefore, the surface in contact with the heating coil is surrounded by a non-magnetic material having a relative magnetic permeability of about 1, and electromagnetic waves are gradually attenuated in the non-magnetic material to prevent heating and melting damage of the backup frame. As an example, non-magnetic stainless steel (SUS304 etc.) 6 is used. At this time, the thickness D of the non-magnetic stainless steel 6 is preferably D ≧ 1 / {√ (πμσf)}. Here, μ and σ are the magnetic permeability and electric conductivity of non-magnetic stainless steel.

[0014]

EXAMPLE FIG. 3 is a diagram schematically showing a method for measuring the heating condition on the backup frame side. Thermocouples were embedded at a position 1 mm from the surface of the stainless steel material and a position 1 mm from the surface of the backup frame, and the temperature change was measured. The experimental conditions are as follows.

Heating frequency: 1 kHz Heating power: 200 kW Stainless steel Thickness: 0 mm, 10 mm, 20 mm The mold cooling water and the coil cooling water were flown. The results of temperature measurement are shown in FIG. (A) has a thickness of 0 mm, (b) has a thickness of 10 mm, and (c) has a thickness of 20 mm. The horizontal axis shows the time from the start of heating, and the vertical axis shows the temperature rise. The ◯ mark is the temperature of the backup frame, and the X mark is the temperature of the stainless steel. In (a), the temperature rise was so severe that the power was turned off midway. In (b) and (c), the temperature rise on the backup frame side was suppressed.

[0016]

According to the present invention, a metal having a low electric conductivity and a high hot strength is used as a mold, and when a high frequency heating is performed from the back surface of the mold, a part of the backup frame contacting the coil is made of non-magnetic stainless steel. By covering with steel, it was possible to prevent the backup frame from melting by heating.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of the device of the present invention seen from above.

FIG. 2 is a side sectional view of the device of the present invention.

FIG. 3 is a schematic view showing an effect measuring method of the device of the present invention.

FIG. 4 is a graph showing the results of measuring the effect of the device of the present invention.

[Explanation of symbols]

1 high frequency heating coil 2 mold cooling plate 3 backup frame 4 molten steel 4a meniscus 5 immersion nozzle 6 non-magnetic stainless steel 7 thermocouple (thermometer)

Claims (3)

[Claims] 1. A metal having a low electric conductivity and a high hot strength is used for a continuous casting mold, and a high frequency induction heating coil is provided in a back-up frame on the back side of the opposite side wall of the mold so that the inside of the mold is filled with the coil. In the continuous casting apparatus for induction heating the surface of molten steel, the coil disposing portion of the backup frame is made of non-magnetic stainless steel, the continuous casting apparatus for steel. 2. The steel continuous casting apparatus according to claim 1, wherein the mold is a Ni—Cr—Fe based alloy. 3. The continuous casting apparatus for steel according to claim 1, wherein the thickness D of the non-magnetic stainless steel is D ≧ 1 / {√ (πμσf)}. Where μ: Permeability of non-magnetic stainless steel (≈4π × 10 ^-7 H /
m) σ: electric conductivity of non-magnetic stainless steel f: high frequency