JP3796130B2 - Method for continuous casting of molten metal - Google Patents

Description

【００１０】
本発明は上記鋳造方法において、通電する交流電流を大電流通電期間と小電流通電期間に周期的に変化させながら鋳造を行う。
【００１１】
本発明に係る上述の連続鋳造方法によって、溶融金属のメニスカス挙動を安定化させ、潤滑改善効果と鋳片表面性状改善効果を安定して得ることのできる。
【００１２】
【発明の実施の形態】
溶融金属の連続鋳造プロセスにおいて、図１の電磁力発生原理の概要図に示されるとおり、ソレノイダル状電磁コイル４に交流電流を通電し、鋳型内に注入され凝固を開始せんとする溶融金属２に電磁力７を印加しながら連続鋳造するもので、誘導電流９と誘導磁場８の方向から前記電磁力７の方向に作用する。すると、図３（ａ）に示すように電磁力７によって凝固シェル５先端との間隔が拡大され、鋳型壁と凝固シェル間に潤滑材としてのパウダー供給が促進され、鋳片の表面性状が改善される。
【００１３】
さらには、直流磁場を印加すると、前記電磁力７により溶融金属内に誘起される溶鋼流動が抑制される。
【００１４】
本発明者は、鋳型内の直流磁束密度の最大値と鋳型内の交流磁束密度の最大値の比が０．４未満の場合、直流磁界による溶融金属の流動の抑制効果が小さすぎ、溶融金属プールメニスカスの擾乱を引き起こして交流電磁力印加の効果の妨げとなり、鋳片の表面性状改善効果が低減してしまうことを見出した。
【００１５】
また、本発明者は、鋳型内の直流磁束密度の最大値と鋳型内の交流磁束密度の最大値の比が６．５より大きい場合、直流磁界による溶融金属の流動の抑制効果が大きすぎ、メニスカスへの温度供給が低減し、鋳片の表面性状が悪化してしまうことを見出した。
【００１６】
本発明者は、鋳型内の直流磁束密度の最大値と鋳型内の交流磁束密度の最大値の比を０．４以上、６．５以下とすることにより、溶融金属メニスカスの安定性と温度供給を保持し、潤滑改善効果と鋳片表面性状改善効果を安定して得ることができることが可能になった。
【００１７】
また、本発明は上記鋳造方法において、図２に示すように通電する交流電流を大電流通電期間と小電流通電期間に周期的に変化させることにより、図３（ａ）〜（ｃ）に示すような凝固殻と鋳型間の間隙のくびれが周期的に発生してパウダー供給がさらに促進され、潤滑改善効果と鋳片表面性状改善効果を安定して得ることができることが可能になった。
【００１８】
このような磁場の印加により、溶融金属の初期凝固不安定性が抑制され、潤滑改善効果と鋳片表面性状改善効果を安定して得ることができる。
【００１９】
【実施例】
本発明の実施例として、下記試験条件によって鋳造した。

上記試験条件で得られた結果を表１に示す。なお、この表１は鋳造時の鋳型内の直流磁束密度の最大値と鋳型内の交流磁束密度の最大値の比を示しているものである。
【００２０】
【表１】

【００２１】
図４から明らかなように、Ｂ_DC／Ｂ_ACが０．４以上になると、直流磁場の流動制動効果により溶鋼湯面変動が小さくなり、メニスカス形状を安定的に保持できるようになる。
【００２２】
次に、図５から明らかなように、Ｂ_DC／Ｂ_ACが６．５より大きくなると、直流磁場の流動制動効果が大きくなり、湯面へ温度供給が不十分になることがわかる。
【００２３】
図６から明らかなように、以上説明した機構により、鋳型内の直流磁束密度の最大値と鋳型内の交流磁束密度の最大値の比を０．４以上、６．５以下とすることにより、溶融金属メニスカスの安定性と温度供給を保持し、潤滑改善効果と鋳片表面性状改善効果を安定して得ることができることが確認できた。
【００２４】
【発明の効果】
以上説明したように本発明は、鋳型内の直流磁束密度の最大値と鋳型内の交流磁束密度の最大値の比を０．４以上、６．５以下とすることにより、溶融金属メニスカスの安定性と温度供給を保持し、潤滑改善効果と鋳片表面性状改善効果を安定して得ることができることができるので工業的効果は甚大である。
【図面の簡単な説明】
【図１】本発明の電磁力を示す図である。
【図２】従来のステップ状で非通電期がないモードを示す図である。
【図３】従来の電磁力による変形を示し、（ａ）変形したメニスカス、（ｂ）静止メニスカス、（ｃ）繰り返し時の凝固シェルを示す図である。
【図４】鋳造時の湯面変動を渦流式メニスカスレベル計にて測定した結果であり、（ａ）は交流磁場の連続的印加条件、（ｂ）は交流磁場の間欠印加条件である。
【図５】鋳造時の湯面における溶鋼温度を測定した結果であり、（ａ）は交流磁場の連続的印加条件、（ｂ）は交流磁場の間欠印加条件である。
【図６】得られた鋳片の表面素度を測定した結果であり、（ａ）は交流磁場の連続的印加条件、（ｂ）は交流磁場の間欠印加条件である。
【符号の説明】
１…鋳型
２…溶融金属
３…メニスカス
４…電磁コイル
５…凝固シェル
６…電磁場付加メニスカス
７…電磁力
８…誘導電流
９…誘導磁場[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for continuously casting a slab from a molten metal, and relates to a method for continuously casting a molten metal, characterized in that a lubrication improving effect and a slab surface property improving effect can be stably obtained.
[0002]
[Prior art]
In continuous casting, the powder melted by the heat from the molten metal flows into these gaps by the relative movement of the mold that vibrates up and down and the solidified shell that is drawn at a constant speed. The tip of the meniscus solidified shell is deformed by the dynamic pressure generated when the molten powder flows. Since this deformation is repeated in the mold oscillation cycle, periodic ridges called oscillation marks are formed on the surface of the slab.
[0003]
Here, it is known that the formation of regular oscillation marks having a normal depth contributes to the stabilization of casting operation and slab surface quality. As a method for controlling the initial solidification described above, when an electromagnetic force is applied to the molten metal in the mold by an electromagnetic coil as described in JP-A No. 64-83348, an alternating magnetic field is applied in a pulsed manner. In addition, a method has been proposed in which electromagnetic force is intermittently applied to further improve surface properties in powder casting.
[0004]
As shown in the above-mentioned Japanese Patent Application Laid-Open No. 64-83348, the electromagnetic force is intermittently applied to the molten metal in the mold by the electromagnetic coil, thereby further increasing the flow of the powder between the solidified shell and the mold wall. The surface quality of the slab was improved.
[0005]
However, when the mold cross section is large, there are cases where unstable waves are generated on the surface of the molten metal. This wave has a problem of causing disturbance of the molten metal pool meniscus and hindering the effect of applying electromagnetic force, and reducing the effect of improving the surface properties of the slab.
[0006]
In addition, when an electromagnetic force is applied to molten metal in a mold by an electromagnetic coil as described in JP-A-5-293613, a direct current is superimposed on an alternating current, and an electromagnetic force by an alternating magnetic field is applied in the vicinity of the meniscus. In addition, a method for suppressing the flow in the molten metal that is generated simultaneously by a DC magnetic field has been proposed.
[0007]
However, if the effect of suppressing the flow of the molten metal due to the DC magnetic field is too small, the molten metal pool meniscus is disturbed to hinder the effect of applying the AC electromagnetic force, and the effect of improving the surface property of the slab is reduced. In addition, when the effect of suppressing the flow of the molten metal by the DC magnetic field is too great, the temperature supply to the meniscus is reduced and the surface properties of the slab are deteriorated. That is, the method of independently controlling the alternating magnetic field and the direct magnetic field cannot stably obtain the effect of improving the surface property of the slab.
[0008]
[Problems to be solved by the invention]
The present invention relates to a method for continuously casting a slab from molten metal, and by limiting the range of the alternating magnetic field strength and the direct magnetic field strength applied to the meniscus portion, the molten metal meniscus behavior is stabilized, and the lubrication improving effect is obtained. It aims at providing the casting method which can acquire the slab surface property improvement effect stably.
[0009]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, the present invention provides a solenoid type electromagnetic coil disposed around a mold having a flat rectangular cross-sectional shape or embedded in a mold wall so that an alternating current is passed through the solenoid type electromagnetic coil. When casting is performed while applying electromagnetic force to the molten metal in the mold and changing the meniscus shape, a DC magnetic field expressed by the following formula (1) is superimposed.
[Expression 2]

[0010]
In the above casting method, the present invention performs casting while periodically changing an alternating current to be passed between a large current conduction period and a small current conduction period.
[0011]
By the above-described continuous casting method according to the present invention, the meniscus behavior of the molten metal can be stabilized, and the lubrication improving effect and the slab surface property improving effect can be stably obtained.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
In the continuous casting process of molten metal, as shown in the schematic diagram of the principle of electromagnetic force generation in FIG. 1, an alternating current is passed through the solenoid coil 4 and injected into the mold to start solidification. The casting is carried out while applying the electromagnetic force 7, and acts in the direction of the electromagnetic force 7 from the direction of the induced current 9 and the induced magnetic field 8. Then, as shown in FIG. 3 (a), the space between the tip of the solidified shell 5 is expanded by the electromagnetic force 7, the supply of powder as a lubricant between the mold wall and the solidified shell is promoted, and the surface property of the slab is improved. Is done.
[0013]
Furthermore, when a DC magnetic field is applied, the molten steel flow induced in the molten metal by the electromagnetic force 7 is suppressed.
[0014]
When the ratio between the maximum value of the DC magnetic flux density in the mold and the maximum value of the AC magnetic flux density in the mold is less than 0.4, the inventor has too little effect of suppressing the flow of the molten metal due to the DC magnetic field. It has been found that the disturbance of the pool meniscus causes disturbance of the effect of application of AC electromagnetic force and the effect of improving the surface properties of the slab is reduced.
[0015]
In addition, when the ratio between the maximum value of the DC magnetic flux density in the mold and the maximum value of the AC magnetic flux density in the mold is larger than 6.5, the inventor has an excessively large effect of suppressing the flow of the molten metal due to the DC magnetic field, It has been found that the temperature supply to the meniscus is reduced and the surface properties of the slab are deteriorated.
[0016]
The inventor makes the ratio of the maximum value of the DC magnetic flux density in the mold and the maximum value of the AC magnetic flux density in the mold to be 0.4 or more and 6.5 or less, so that the stability of the molten metal meniscus and the temperature supply are improved. Thus, it is possible to stably obtain the lubrication improving effect and the slab surface property improving effect.
[0017]
Further, in the above casting method, the present invention is shown in FIGS. 3 (a) to 3 (c) by periodically changing the alternating current to be supplied as shown in FIG. 2 between a large current supply period and a small current supply period. Such narrowing of the gap between the solidified shell and the mold is periodically generated to further promote the powder supply, and it is possible to stably obtain the lubrication improving effect and the slab surface property improving effect.
[0018]
By applying such a magnetic field, the initial solidification instability of the molten metal is suppressed, and the lubrication improving effect and the slab surface property improving effect can be stably obtained.
[0019]
【Example】
As an example of the present invention, casting was performed under the following test conditions.

Table 1 shows the results obtained under the above test conditions. Table 1 shows the ratio of the maximum value of the DC magnetic flux density in the mold during casting to the maximum value of the AC magnetic flux density in the mold.
[0020]
[Table 1]

[0021]
As is apparent from FIG. 4, when B _DC / B _AC is 0.4 or more, the molten steel surface fluctuation is reduced by the flow braking effect of the DC magnetic field, and the meniscus shape can be stably maintained.
[0022]
Next, as is apparent from FIG. 5, it is understood that when B _DC / B _AC is greater than 6.5, the flow braking effect of the DC magnetic field increases, and the temperature supply to the molten metal surface becomes insufficient.
[0023]
As apparent from FIG. 6, by the mechanism described above, the ratio of the maximum value of the DC magnetic flux density in the mold and the maximum value of the AC magnetic flux density in the mold is set to 0.4 or more and 6.5 or less, It was confirmed that the stability and temperature supply of the molten metal meniscus can be maintained, and the lubrication improving effect and the slab surface property improving effect can be stably obtained.
[0024]
【The invention's effect】
As described above, the present invention stabilizes the molten metal meniscus by setting the ratio of the maximum value of the DC magnetic flux density in the mold to the maximum value of the AC magnetic flux density in the mold to be 0.4 or more and 6.5 or less. The effect of improving lubrication and the effect of improving the slab surface property can be stably obtained while maintaining the properties and temperature supply, and the industrial effect is enormous.
[Brief description of the drawings]
FIG. 1 is a diagram showing electromagnetic force of the present invention.
FIG. 2 is a diagram showing a conventional step-like mode without a non-energization period.
FIG. 3 is a diagram showing deformation by a conventional electromagnetic force, and shows (a) a deformed meniscus, (b) a stationary meniscus, and (c) a solidified shell during repetition.
FIGS. 4A and 4B are results obtained by measuring fluctuations in the molten metal surface during casting with an eddy current meniscus level meter. FIG. 4A shows a condition for continuous application of an alternating magnetic field, and FIG.
FIG. 5 shows the results of measuring the molten steel temperature on the molten metal surface during casting, where (a) shows the continuous application condition of the alternating magnetic field, and (b) shows the intermittent application condition of the alternating magnetic field.
FIG. 6 shows the results of measuring the surface texture of the obtained slab, where (a) shows the continuous application condition of the alternating magnetic field, and (b) shows the intermittent application condition of the alternating magnetic field.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Mold 2 ... Molten metal 3 ... Meniscus 4 ... Electromagnetic coil 5 ... Solidification shell 6 ... Electromagnetic field addition meniscus 7 ... Electromagnetic force 8 ... Induction current 9 ... Induction magnetic field

Claims (2)

A solenoid type electromagnetic coil is disposed so as to surround a mold having a flat rectangular cross section or is embedded in a mold wall, and an electromagnetic current is applied to the molten metal in the mold by passing an alternating current through the solenoid type electromagnetic coil. Then, when performing casting while changing the meniscus shape, a continuous casting method of molten metal characterized by superimposing a DC magnetic field represented by the following formula (1).

An alternating current having a large current energizing period and a small current energizing period in which a solenoid type electromagnetic coil is disposed so as to surround a mold having a flat rectangular cross section or embedded in a mold wall, and the amplitude or waveform is periodically changed. The molten metal continuous casting method according to claim 1, wherein the solenoid-type electromagnetic coil is energized to apply electromagnetic force to the molten metal in the mold to perform casting while changing the meniscus shape.

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