JP4539251B2 - Steel continuous casting method - Google Patents
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本発明は、鋳型内の溶鋼に移動磁場を印加して鋳型内の溶鋼流動を制御しながら鋳造する鋼の連続鋳造方法に関するものである。 The present invention relates to a continuous casting method of steel in which a moving magnetic field is applied to molten steel in a mold to control the flow of molten steel in the mold.
鋼の連続鋳造においては、鋳型内の溶鋼流動状態、特に溶鋼湯面近傍の流動は、モールドパウダーの巻き込みやノロカミの発生と関係しており、鋳片品質に多大な影響を及ぼすことが知られている。欠陥のない鋳片を製造するためには鋳型内の溶鋼流動を制御する技術が重要であり、そのため、鋳型内の溶鋼に磁場を印加して溶鋼湯面近傍における溶鋼流動を適正化する方法が従来から行われている。 In continuous casting of steel, the molten steel flow state in the mold, especially the flow in the vicinity of the molten steel surface, is related to the entrainment of mold powder and generation of swarf, and is known to have a great influence on the slab quality. ing. In order to produce a defect-free slab, it is important to control the flow of molten steel in the mold. Therefore, there is a method to optimize the flow of molten steel near the molten steel surface by applying a magnetic field to the molten steel in the mold. Traditionally done.
この磁場の印加方法の１つとして静磁場を印加する方法がある。例えば特許文献１には、鋳型長辺背面の溶鋼湯面近傍に相当する高さ位置に、鋳型幅全体に亘る静磁場を印加するための磁極を配置し、鋳造速度、浸漬ノズルの吐出角度、吐出孔面積、浸漬ノズルの浸漬深さ、鋳型幅に応じて印加する磁場強度を変更し、溶鋼湯面の流速を制御する方法が提案されている。一方、静磁場に代わって移動磁場を印加する方法も提案されている。例えば特許文献２には、鋳型長辺背面の鋳型幅方向に２分割以上に区分された移動磁場発生装置を配置し、溶鋼湯面に水平方向の旋回攪拌流を形成するように前記移動磁場発生装置から移動磁場を印加させ、溶鋼湯面の流速を０．１〜０．６ｍ／秒に制御する方法が提案されている。 One method of applying this magnetic field is to apply a static magnetic field. For example, in Patent Document 1, a magnetic pole for applying a static magnetic field over the entire mold width is arranged at a height position corresponding to the vicinity of the molten steel surface on the back side of the mold long side, the casting speed, the discharge angle of the immersion nozzle, A method has been proposed in which the magnetic field strength applied is changed according to the discharge hole area, the immersion depth of the immersion nozzle, and the mold width to control the flow rate of the molten steel surface. On the other hand, a method of applying a moving magnetic field instead of a static magnetic field has been proposed. For example, in Patent Document 2, a moving magnetic field generator divided into two or more sections in the mold width direction on the back side of the long side of the mold is arranged, and the moving magnetic field generation is performed so as to form a horizontal swirling stirring flow on the molten steel surface. A method has been proposed in which a moving magnetic field is applied from an apparatus to control the flow rate of the molten steel surface at 0.1 to 0.6 m / sec.
特許文献２は、移動磁場によって鋳型内の溶鋼湯面の流速を直接制御する方法であるが、移動磁場を溶鋼の吐出流の方向とは反対側の方向に移動させることで、浸漬ノズルから吐出される溶鋼の吐出流に制動力を作用させ、溶鋼の吐出流速を減速させることによって溶鋼湯面の流速を制御する方法も提案されている。例えば特許文献３には、鋳型長辺背面に配置した移動磁場発生装置により、鋳型短辺から鋳型中央の浸漬ノズルに向かって移動する移動磁場を印加し、溶鋼の吐出流速を減速させる方法が提案されている。この場合、移動磁場の周波数の下限は、吐出孔からの溶鋼の吐出流が磁場作用域を通過する間に、少なくとも移動磁場の作用を１周期以上受けるように設定し、一方、周波数の上限は、磁場の減衰（表皮効果）を考慮し、鋳型内部の溶鋼にも充分磁場の影響が届くように設定するとしている。また、特許文献４は、特許文献３を発展させ、移動磁場の強度の２乗と周波数との積が一定の条件下で、磁場の強度と周波数とを鋳造中に変更させることで溶鋼の流動を適正化する方法が提案されている。更に、特許文献５には、特許文献３及び特許文献４による鋳型内溶鋼の流動制御方法における溶鋼湯面の最適な流速パターンを具体的な数値として提案している。即ち、鋳型内湯面の溶鋼流速を鋳型短辺から浸漬ノズルに向いた流れを正で表し、逆方向の流れを負で表したときに、浸漬ノズルから鋳型短辺側に鋳型幅の１／４だけ離れた位置の溶鋼表面流速を−０．０７ｍ／秒から０．０５ｍ／秒の範囲内に維持することを提案している。
しかしながら、上記従来技術にはそれぞれ以下のような問題点がある。即ち、特許文献１のような静磁場を印加する方法では、磁場は常に溶鋼流に対して制動力として働くので、溶鋼流の停滞領域に対しては溶鋼流を活性化することができないという問題がある。一方、移動磁場を用いた特許文献２の方法では、磁場の移動方向に電磁力が働くので、制御の柔軟性を期待できるが、鋳造速度を増した場合には、浸漬ノズルから吐出される溶鋼流速自体が増加し、鋳型内の溶鋼湯面位置における溶鋼流速も速くなるため、この状態で旋回攪拌流を形成するように移動磁場を印加すると、鋳型内溶鋼湯面における溶鋼流速が更に増大し、モールドパウダーの巻込みを発生させるという問題がある。また、設定パラメータが多く、制御が複雑になるといった難しさもある。 However, each of the above conventional techniques has the following problems. That is, in the method of applying a static magnetic field as in Patent Document 1, since the magnetic field always acts as a braking force on the molten steel flow, the problem that the molten steel flow cannot be activated for the stagnant region of the molten steel flow. There is. On the other hand, in the method of Patent Document 2 using a moving magnetic field, since electromagnetic force acts in the moving direction of the magnetic field, control flexibility can be expected, but when the casting speed is increased, molten steel discharged from the immersion nozzle Since the flow velocity itself increases and the molten steel flow velocity at the molten steel surface position in the mold increases, applying a moving magnetic field to form a swirl stirring flow in this state further increases the molten steel flow velocity at the molten steel surface in the mold. There is a problem that the mold powder is involved. In addition, there are many setting parameters, which makes it difficult to control.
移動磁場による制動力を利用した特許文献３〜５の方法は、広範な鋳造速度に対応することが可能であり、有効な方法といえるものの、最適な溶鋼流速を得るための移動磁場の周波数に関して、特許文献３は下限値及び上限値を規定しているとはいうもののその範囲は広くて最適範囲が明確でなく、また、特許文献４及び特許文献５では周波数に関しては最適な範囲が提案されておらず、従って、最適な溶鋼流動を得る上で、移動磁場の周波数に関しては未だ改善する余地がある。 Although the method of patent documents 3-5 using the braking force by a moving magnetic field can respond to a wide casting speed, and can be said to be an effective method, regarding the frequency of the moving magnetic field to obtain the optimum molten steel flow velocity. Although Patent Document 3 defines the lower limit value and the upper limit value, the range is wide and the optimum range is not clear, and Patent Document 4 and Patent Document 5 propose an optimum range for the frequency. Therefore, there is still room for improvement in terms of the frequency of the moving magnetic field in obtaining the optimum molten steel flow.
本発明は上記事情に鑑みてなされたもので、その目的とするところは、浸漬ノズルから吐出される溶鋼の吐出流に移動磁場による電磁力を作用させて鋳型内の溶鋼流動を制御しながら連続鋳造するに際し、磁場強度を適正化することのみならず、移動磁場の周波数を鋳造条件に応じて適性化させることで溶鋼流動の制御を適性に行なうことのできる、鋼の連続鋳造方法を提供することである。 The present invention has been made in view of the above circumstances, and its object is to continuously apply the electromagnetic force generated by the moving magnetic field to the discharge flow of the molten steel discharged from the immersion nozzle to control the flow of the molten steel in the mold. Provided is a continuous casting method of steel that can appropriately control the flow of molten steel not only by optimizing the magnetic field strength but also by optimizing the frequency of the moving magnetic field according to the casting conditions. That is.
上記課題を解決するための本発明に係る鋼の連続鋳造方法は、磁場の移動方向が鋳型幅方向である移動磁場発生装置を用い、長辺及び短辺を有する矩形状鋳型の中央部に設置された浸漬ノズルから吐出される溶鋼に、鋳型短辺側から浸漬ノズル側に向かう移動磁場を印加して、鋳型短辺から鋳型幅の１／４だけ離れた位置における溶鋼湯面の表面流速が絶対値で０．０５ｍ／秒以下になるように鋳型内の溶鋼流動を制御しながら鋳造する鋼の連続鋳造方法であって、前記移動磁場は、移動磁場の周波数の下限値が、浸漬ノズルの吐出孔からの吐出流が磁場作用域を通過する間に少なくとも移動磁場の作用を１周期以上受ける周波数であり、且つ、移動磁場の周波数の上限値が、浸漬ノズルの吐出孔からの吐出流が吐出孔から鋳型長辺幅×１／２の１／３の距離の位置まで鋳型短辺方向に広がるまでに移動磁場の作用を１周期以上受けない範囲内であって、下記の（１）式を満たす範囲内の周波数であることを特徴とするものである。 The continuous casting method of steel according to the present invention for solving the above-mentioned problems uses a moving magnetic field generator in which the moving direction of the magnetic field is the mold width direction, and is installed at the center of a rectangular mold having a long side and a short side. By applying a moving magnetic field from the mold short side to the immersion nozzle to the molten steel discharged from the immersed nozzle, the surface flow velocity of the molten steel surface at a position away from the mold short side by a quarter of the mold width is A continuous casting method of steel for casting while controlling the flow of molten steel in a mold so that the absolute value is 0.05 m / sec or less, wherein the moving magnetic field has a lower limit frequency of the moving magnetic field, The frequency at which the discharge flow from the discharge hole receives at least one cycle of the action of the moving magnetic field while passing through the magnetic field application region, and the upper limit value of the frequency of the moving magnetic field is the discharge flow from the discharge hole of the immersion nozzle. Mold long side width from discharge hole × 1 / The position effect of the moving magnetic field to spread the mold short-side direction to a distance of 1/3 in a range of not subjected one cycle or more, characterized by a frequency in the range satisfying the following formula (1) It is what.
但し、（１）式において、ｆは移動磁場の周波数（Ｈｚ）、ｕは浸漬ノズルからの溶鋼吐出流の代表流速（ｍ／秒）、Ｌは鋳型中心から鋳型短辺までの距離（ｍ）である。 However, in the formula (1), f is the frequency (Hz) of the moving magnetic field, u is the representative flow velocity (m / sec) of the molten steel discharge flow from the immersion nozzle, and L is the distance (m) from the mold center to the mold short side. It is.
本発明によれば、浸漬ノズルからの吐出流に移動磁場の電磁力を作用させて鋳型内の溶鋼流動を制御する際に、印加する移動磁場の周波数を溶鋼の吐出流速及び鋳片幅に応じて設定するので、吐出流に過度の電磁力が作用せず、鋳型内の溶鋼流動を適切に制御することが可能となり、鋳型内湯面変動を適正化すると同時に溶鋼湯面の流速を所定の範囲に制御することができ、モールドパウダーの巻き込みのない、清浄で高品質の鋳片を安定して製造することが可能となる。 According to the present invention, when controlling the molten steel flow in the mold by applying the electromagnetic force of the moving magnetic field to the discharge flow from the immersion nozzle, the frequency of the moving magnetic field to be applied depends on the discharge flow rate and the slab width of the molten steel. Therefore, excessive electromagnetic force does not act on the discharge flow, it is possible to appropriately control the flow of molten steel in the mold, optimize the molten metal surface fluctuation in the mold, and at the same time set the flow rate of the molten steel surface within a predetermined range. Therefore, it is possible to stably produce a clean and high-quality slab free from mold powder.
以下、添付図面を参照して本発明を具体的に説明する。図１及び図２は、本発明を実施する際に用いたスラブ連続鋳造機の鋳型部位の概略図であり、図１は概略斜視図、図２は概略正面図である。 Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. 1 and 2 are schematic views of a mold part of a slab continuous casting machine used in carrying out the present invention, FIG. 1 is a schematic perspective view, and FIG. 2 is a schematic front view.
図１〜図２において、相対する鋳型長辺４と、この鋳型長辺４の内側に内装された相対する鋳型短辺５とから、水平断面が矩形状の鋳型１が構成されており、鋳型長辺４と鋳型短辺５とに囲まれて形成される鋳型１の内面空間の所定位置には、鋳型１の上方所定位置に配置されるタンディッシュ（図示せず）の底部に取り付けられた浸漬ノズル２が挿入されている。浸漬ノズル２の下部には、溶鋼７を鋳型短辺５の方向に向かって吐出するための一対の吐出孔６が備えられている。 In FIG. 1 to FIG. 2, a mold 1 having a rectangular horizontal cross section is constituted by an opposing mold long side 4 and an opposing mold short side 5 housed inside the mold long side 4. At a predetermined position in the inner surface space of the mold 1 formed by being surrounded by the long side 4 and the mold short side 5, it is attached to the bottom of a tundish (not shown) disposed at a predetermined position above the mold 1. An immersion nozzle 2 is inserted. A pair of discharge holes 6 for discharging the molten steel 7 in the direction of the mold short side 5 is provided below the immersion nozzle 2.
鋳型長辺４の背面には、浸漬ノズル２を境として鋳型長辺４の幅方向左右で２つに分割された合計４基の移動磁場発生装置３が、その鋳造方向の中心位置を吐出孔６の直下位置として、鋳型長辺４を挟んで対向して配置されている。それぞれの移動磁場発生装置３は電源（図示せず）と結線され、又、電源は、磁場の移動方向、周波数及び磁場強度を制御する制御装置（図示せず）と接続されており、制御装置から入力される磁場移動方向、周波数及び磁場強度に基づいて電源から供給される電力により、移動磁場発生装置３から印加される磁場強度、周波数及び磁場移動方向がそれぞれ個別に制御されるようになっている。 On the back side of the mold long side 4, a total of four moving magnetic field generators 3 divided into two on the left and right sides in the width direction of the mold long side 4 with the immersion nozzle 2 as a boundary are arranged at the center of the casting direction as discharge holes. As a position directly below 6, they are arranged to face each other with the mold long side 4 in between. Each moving magnetic field generator 3 is connected to a power source (not shown), and the power source is connected to a control device (not shown) for controlling the moving direction, frequency and magnetic field strength of the magnetic field. The magnetic field strength, frequency, and magnetic field moving direction applied from the moving magnetic field generator 3 are individually controlled by the power supplied from the power source based on the magnetic field moving direction, frequency, and magnetic field strength input from the mobile phone. ing.
この移動磁場発生装置３により印加される磁場は移動磁場であり、浸漬ノズル２からの溶鋼７の吐出流８に制動力を与える場合には、移動磁場の移動方向を鋳型短辺５の側から浸漬ノズル２の側とし、一方、浸漬ノズル２からの吐出流８に加速力を与える場合には、移動磁場の移動方向を浸漬ノズル２の側から鋳型短辺５の側とする。図１では、磁場が鋳型短辺５から鋳型１の中央部の浸漬ノズル２に向かって移動する状態を示しており、図１において、ＦX は溶鋼７の吐出流８に作用する電磁力を表し、ＶX は移動磁場の移動速度を表し、ＢY は移動磁場の磁束密度を表している。 The magnetic field applied by the moving magnetic field generator 3 is a moving magnetic field. When a braking force is applied to the discharge flow 8 of the molten steel 7 from the immersion nozzle 2, the moving direction of the moving magnetic field is changed from the mold short side 5 side. On the other hand, when the acceleration force is applied to the discharge flow 8 from the immersion nozzle 2, the moving magnetic field is moved from the immersion nozzle 2 side to the mold short side 5 side. FIG. 1 shows a state in which the magnetic field moves from the mold short side 5 toward the immersion nozzle 2 at the center of the mold 1. In FIG. 1, F X represents the electromagnetic force acting on the discharge flow 8 of the molten steel 7. represents, V X represents the moving speed of the moving magnetic field, B Y represents a magnetic flux density of the moving magnetic field.
移動磁場発生装置３には、図１に示すように複数の電磁コイル（但し図２では図示せず）が幅方向に並んで設置されており、隣り合う電磁コイルに流す電流の位相をずらすことにより、所謂リニアタイプの移動磁場を発生させている。その磁場の移動速度ＶX は、電磁コイルのポールピッチτと周波数ｆとから、下記の（２）式によって表される。電磁コイルのポールピッチとは、Ｓ極からＮ極までの距離である。 In the moving magnetic field generator 3, a plurality of electromagnetic coils (not shown in FIG. 2) are arranged side by side in the width direction as shown in FIG. 1, and the phase of the current flowing through the adjacent electromagnetic coils is shifted. Thus, a so-called linear type moving magnetic field is generated. The moving speed V X of the magnetic field is expressed by the following equation (2) from the pole pitch τ and the frequency f of the electromagnetic coil. The pole pitch of the electromagnetic coil is the distance from the S pole to the N pole.
ローレンツの法則より、発生する誘導電流ＪZ は下記の（３）で表される。但し、（３）式において、σは溶鋼の電気伝導度、ＶX は移動磁場の移動速度、ＢY は移動磁場の磁束密度である。 According to Lorentz's law, the generated induced current J Z is expressed by the following (3). In equation (3), σ is the electric conductivity of the molten steel, V X is the moving speed of the moving magnetic field, and BY is the magnetic flux density of the moving magnetic field.
電磁力ＦX は下記の（４）式で表され、主に磁場の移動方向と同じ向きに電磁力ＦX が作用する。 The electromagnetic force F X is expressed by the following equation (4), and the electromagnetic force F X acts mainly in the same direction as the moving direction of the magnetic field.
鋳造速度が速く、鋳型１における溶鋼流動を抑制したい場合には、磁場を両方の鋳型短辺５から浸漬ノズル２の方向に移動させ、電磁力ＦX によって浸漬ノズル２から吐出される溶鋼７の吐出流８を減速させる。逆に、鋳造速度が遅く、鋳型１における溶鋼流動を促進させたい場合には、磁場を浸漬ノズル２から鋳型短辺５の方向に移動させ、電磁力ＦX によって浸漬ノズル２から吐出される溶鋼７の吐出流８を加速させる。 When the casting speed is high and it is desired to suppress the molten steel flow in the mold 1, the magnetic field is moved from both mold short sides 5 toward the immersion nozzle 2 and the molten steel 7 discharged from the immersion nozzle 2 by the electromagnetic force F X is used. The discharge flow 8 is decelerated. On the contrary, when the casting speed is slow and it is desired to promote the molten steel flow in the mold 1, the magnetic field is moved from the immersion nozzle 2 toward the mold short side 5, and the molten steel discharged from the immersion nozzle 2 by the electromagnetic force F X. 7 discharge flow 8 is accelerated.
本発明者等は、磁場を鋳型短辺５から浸漬ノズル２の方向に移動させて鋳型内の溶鋼流動を制御する場合に、鋳型内における溶鋼湯面９の近傍の鋳型幅方向水平流速（以下、「表面流速」と呼ぶ）を適性に且つ効率良く制御することを目的として、印加する磁場の周波数の適正値を選択する方法について検討した。以下、検討結果について説明する。 When the inventors move the magnetic field from the mold short side 5 toward the immersion nozzle 2 to control the flow of molten steel in the mold, the horizontal flow velocity in the mold width direction in the vicinity of the molten steel surface 9 in the mold (hereinafter referred to as the following) The method of selecting an appropriate value of the frequency of the magnetic field to be applied was studied for the purpose of appropriately and efficiently controlling the “surface flow velocity”. Hereinafter, the examination results will be described.
連続鋳造中、溶鋼湯面９の上に添加したモールドパウダー１１の巻き込みを防止すると同時に、鋳型内の湯面変動を防止するためには、溶鋼湯面９の近傍の表面流速を低位に安定させることが必要である。例えば、前述した特許文献５では、鋳型幅１／４の鋳型短辺寄りの位置における表面流速を−０．０７ｍ／秒から０．０５ｍ／秒のゼロに近い範囲内に維持するのがよいと規定している。ここでは鋳型短辺５から浸漬ノズル２に向いた流れの方向を正としている。 During continuous casting, in order to prevent entrainment of the mold powder 11 added on the molten steel surface 9 and at the same time prevent fluctuations in the molten metal surface in the mold, the surface flow velocity in the vicinity of the molten steel surface 9 is stabilized at a low level. It is necessary. For example, in Patent Document 5 described above, it is preferable to maintain the surface flow velocity at a position near the mold short side of the mold width 1/4 within a range close to zero from −0.07 m / sec to 0.05 m / sec. It prescribes. Here, the flow direction from the mold short side 5 toward the immersion nozzle 2 is positive.
電磁力ＦX は、鋳型内の流動を平均的に分散させるために用いられるが、吐出流８の大きな運動量と電磁力ＦX とが直接対抗すると反って溶鋼７の流動を乱す場合があり、鋳型内の表面流速を制御することが難しくなる場合もあることが分かった。鋳型内の表面流速を十分に制御できない場合の鋳型内溶鋼の流動パターンの代表例の２つを、図３及び図４に示す。尚、図３及び図４は、鋳型１の向かって右側半分における鋳型内溶鋼の流速を電磁流体シミュレーションによって求めた結果を示す図であり、矢印が溶鋼７の流れの方向を表している。また、図中左側の上部部分が浸漬ノズル２で、図中右側端部が鋳型短辺５の内壁面位置に相当する。 The electromagnetic force F X is used to averagely disperse the flow in the mold. However, when the large momentum of the discharge flow 8 and the electromagnetic force F X directly oppose each other, the flow of the molten steel 7 may be disturbed. It has been found that it may be difficult to control the surface flow velocity in the mold. Two typical examples of the flow pattern of molten steel in the mold when the surface flow velocity in the mold cannot be sufficiently controlled are shown in FIGS. 3 and 4. 3 and 4 are diagrams showing the results of obtaining the flow velocity of the molten steel in the mold in the right half toward the mold 1 by electromagnetic fluid simulation, and the arrows indicate the flow direction of the molten steel 7. Further, the upper part on the left side in the figure corresponds to the immersion nozzle 2, and the right side end part in the figure corresponds to the position of the inner wall surface of the mold short side 5.
図３は、過剰に大きい電磁力ＦX が吐出流８に作用し、吐出流８が鋳型短辺５の方向に広がる前に下方に押し曲げられてしまった例であり、また図４は、電磁力ＦX が吐出流８に激しく衝突し、吐出流８が鋳型短辺５の方向に広がる前に上方に押し上げられてしまった例である。何れの場合も、吐出流８が鋳型短辺５の方向に広がる前に電磁力ＦX が過度に作用したことが原因である。 3 shows an example in which an excessively large electromagnetic force F X acts on the discharge flow 8 and the discharge flow 8 is bent downward before spreading in the direction of the mold short side 5, and FIG. This is an example in which the electromagnetic force F X violently collides with the discharge flow 8 and the discharge flow 8 is pushed upward before spreading in the direction of the mold short side 5. In any case, the reason is that the electromagnetic force F X acts excessively before the discharge flow 8 spreads in the direction of the mold short side 5.
これらの結果から、電磁力ＦX を作用させる際の周波数の適正範囲は、吐出流８が吐出孔６から１／２×鋳型幅（＝鋳型中心から鋳型短辺までの距離）の１／３の距離の位置まで鋳型短辺方向に広がるまでに大きな電磁力（即ち、移動磁場の作用を１周期以上）を受けない範囲が好適であることが分かった。この条件は下記の（５）式で表される。但し、この場合、電磁力の作用は磁場の極の向きには依らないので一周期は２τではなくτを用いた。また、（５）式において、ｆは移動磁場の周波数（Ｈｚ）、ｕは浸漬ノズル２からの吐出流８の代表流速（ｍ／秒）、Ｌは鋳型中心から鋳型短辺までの距離（ｍ）である。 From these results, the appropriate range of the frequency when the electromagnetic force F X is applied is that the discharge flow 8 is 1/2 of the discharge hole 6 × 1 × mold width (= distance from the mold center to the mold short side). It was found that a range in which a large electromagnetic force (that is, the action of the moving magnetic field for one cycle or more) is not received until the mold spreads in the direction of the short side of the mold up to the position of the distance of 5 mm is suitable. This condition is expressed by the following equation (5). However, in this case, since the action of the electromagnetic force does not depend on the direction of the pole of the magnetic field, τ is used instead of 2τ for one period. In equation (5), f is the frequency (Hz) of the moving magnetic field, u is the representative flow velocity (m / sec) of the discharge flow 8 from the immersion nozzle 2, and L is the distance from the mold center to the mold short side (m ).
この（５）式を整理することで、前述した（１）式を得ることができる。即ち、鋳型内の溶鋼流動を適正に制御するためには、印加する磁場の周波数は（１）式を満たすことが必要であることが分かった。 By arranging this equation (5), the aforementioned equation (1) can be obtained. That is, in order to appropriately control the molten steel flow in the mold, it was found that the frequency of the magnetic field to be applied must satisfy the equation (1).
ここで、吐出流８の代表流速ｕを定めるに当たり、吐出流８の流速を実測することは困難であるので、浸漬ノズル２の内孔の径（Ｄ）と溶鋼７の鋳造量とから算出される、浸漬ノズル２の内孔での溶鋼流速値を代表流速ｕとして用いてもよい。通常、浸漬ノズル２においては、浸漬ノズル２の内孔の断面積よりも２つの吐出孔６の断面積を合計した値の方が大きく、溶鋼７は、浸漬ノズル２の内孔における速度を保ったまま吐出孔６から吐出していると考えても問題ないからである。また、代表流速ｕの精度を高めるためには、予め水モデル実験などによって吐出流速を実測し、溶鋼流速に換算することもできる。 Here, since it is difficult to actually measure the flow velocity of the discharge flow 8 in determining the representative flow velocity u of the discharge flow 8, it is calculated from the diameter (D) of the inner hole of the immersion nozzle 2 and the casting amount of the molten steel 7. Alternatively, the molten steel flow velocity value in the inner hole of the immersion nozzle 2 may be used as the representative flow velocity u. Usually, in the immersion nozzle 2, the sum of the sectional areas of the two discharge holes 6 is larger than the sectional area of the inner hole of the immersion nozzle 2, and the molten steel 7 maintains the speed in the inner hole of the immersion nozzle 2. This is because there is no problem even if it is considered that the ink is discharged from the discharge hole 6 as it is. In order to increase the accuracy of the representative flow velocity u, the discharge flow velocity can be measured in advance by a water model experiment or the like and converted into the molten steel flow velocity.
また、鋳造に当たり、磁場の移動方向を鋳型短辺５から浸漬ノズル２に向いた方向とするか、或いはこの逆向きの方向にするかの目安としては、鋳型短辺５の近傍の表面流速が０．２ｍ／秒以下の場合には、吐出流８を加速させるべく浸漬ノズル２から鋳型短辺５に向いた方向とし、鋳型短辺５の近傍の表面流速が０．３ｍ／秒以上の場合には、吐出流８を減速させるべく鋳型短辺５から浸漬ノズル２に向いた方向とする。鋳型短辺５の近傍の表面流速は、鋳造条件毎に実測する或いは電磁流体シミュレーションを用いて算出するなどして予め求めておくことができる。但し、現在の高生産性を目的とした連続鋳造操業では、鋳型短辺５の近傍の表面流速はほとんどの場合に０．３ｍ／秒以上となるので、通常は磁場の移動方向を鋳型短辺５から浸漬ノズル２に向いた方向とすればよい。 Further, in casting, as a guideline whether the moving direction of the magnetic field is the direction from the mold short side 5 toward the immersion nozzle 2 or the opposite direction, the surface flow velocity in the vicinity of the mold short side 5 is In the case of 0.2 m / sec or less, in the direction from the immersion nozzle 2 toward the mold short side 5 in order to accelerate the discharge flow 8, the surface flow velocity in the vicinity of the mold short side 5 is 0.3 m / sec or more. In order to decelerate the discharge flow 8, the direction from the mold short side 5 toward the immersion nozzle 2 is set. The surface flow velocity in the vicinity of the mold short side 5 can be obtained in advance by actually measuring for each casting condition or calculating using a magnetohydrodynamic simulation. However, in the current continuous casting operation aiming at high productivity, the surface flow velocity in the vicinity of the mold short side 5 is 0.3 m / sec or more in most cases. The direction from 5 to the immersion nozzle 2 may be used.
この場合、鋳型内における表面流速の適正値は前述した特許文献５に記載されている通りであり、従って、鋳型短辺５から鋳型幅の１／４だけ離れた位置における表面流速が絶対値で０．０５ｍ／秒以下になるように、磁場強度を調整することが好ましい。また、移動磁場の周波数の下限値は、前述した特許文献３に記載されている通りであり、吐出孔６からの吐出流８が磁場作用域を通過する間に、少なくとも移動磁場の作用を１周期以上受けるように設定することが好ましい。 In this case, the appropriate value of the surface flow velocity in the mold is as described in Patent Document 5 described above. Therefore, the surface flow velocity at a position away from the mold short side 5 by 1/4 of the mold width is an absolute value. It is preferable to adjust the magnetic field strength so as to be 0.05 m / second or less. Further, the lower limit value of the frequency of the moving magnetic field is as described in Patent Document 3 described above, and at least the action of the moving magnetic field is 1 while the discharge flow 8 from the discharge hole 6 passes through the magnetic field action region. It is preferable to set so as to receive at least a cycle.
このように、印加する移動磁場の周波数を、鋳造条件に応じて（１）式を満足する範囲内とすることで、鋳型内の溶鋼流動を適切に制御することが可能となり、鋳型内湯面変動を抑えると同時に溶鋼湯面９の流速を所定の範囲に制御することができ、凝固シェル１０へのモールドパウダー１１の巻き込みのない、清浄で高品質の鋳片を安定して製造することが可能となる。 In this way, by setting the frequency of the moving magnetic field to be applied within the range that satisfies the formula (1) according to the casting conditions, it becomes possible to appropriately control the molten steel flow in the mold, and the fluctuation of the molten metal surface in the mold. At the same time, the flow rate of the molten steel surface 9 can be controlled within a predetermined range, and it is possible to stably produce a clean and high-quality slab without the mold powder 11 being caught in the solidified shell 10. It becomes.
本発明の効果を確認するために、図１に示すスラブ連続鋳造機を用い、印加する移動磁場の周波数を変化させたアルミキルド鋼の鋳造試験を実施した。試験では、鋳片のサイズを、厚みが２２０ｍｍ、幅が１６００ｍｍの一定とし、定常鋳造時の溶鋼の鋳造量を約５．７トン／分として鋳造した。用いた浸漬ノズルは、内孔の底部が凹状形状である所謂「プール付き」の２孔ノズルで、吐出角度が下向き２５度、内孔の直径（Ｄ）が９０ｍｍの浸漬ノズルである。この浸漬ノズルの内孔にアルミナ付着防止のために９Ｎｌ／分のアルゴンガスを吹き込んで鋳造した。移動磁場発生装置は、３相交流のリニア移動磁場型であり、電磁コイルのポールピッチτは０．７２ｍであり、電磁コイルの中心位置が溶鋼湯面から３８０ｍｍ離れた位置になるように設置した。 In order to confirm the effect of the present invention, an aluminum killed steel casting test was performed using the slab continuous casting machine shown in FIG. 1 and changing the frequency of the applied moving magnetic field. In the test, the slab was cast with a fixed thickness of 220 mm and a width of 1600 mm, and a casting amount of molten steel during steady casting of about 5.7 tons / min. The immersion nozzle used is a so-called “with pool” two-hole nozzle in which the bottom of the inner hole has a concave shape, and is an immersion nozzle having a discharge angle of 25 degrees downward and an inner hole diameter (D) of 90 mm. 9 Nl / min argon gas was blown into the inner hole of this immersion nozzle for casting to prevent alumina adhesion. The moving magnetic field generator is a three-phase AC linear moving magnetic field type, the pole pitch τ of the electromagnetic coil is 0.72 m, and the center position of the electromagnetic coil is set to be 380 mm away from the molten steel surface. .
試験は、印加する移動磁場の周波数を１Ｈｚ、２Ｈｚ，３Ｈｚ、４Ｈｚの４水準で実施し、鋳型内溶鋼が適正な流動（溶鋼湯面近傍の流速が平均的に抑制されている状態）で且つ鋳型の１／４幅位置における表面流速がゼロ近傍（絶対値で０．０５ｍ／秒以下）になるように磁場強度を調整した。 The test is performed at four levels of 1 Hz, 2 Hz, 3 Hz, and 4 Hz of the frequency of the moving magnetic field to be applied, and the molten steel in the mold is in an appropriate flow (a state in which the flow velocity near the molten steel surface is suppressed on average) and The magnetic field strength was adjusted so that the surface flow velocity at the 1/4 width position of the mold was close to zero (0.05 m / second or less in absolute value).
この場合、鋳型の１／４幅位置における表面流速を測定する方法として、図５に示す方法を用いた。即ち、図５に示すように、鋳型短辺５から鋳型幅の１／４だけ離れた位置に、長さ４１０ｍｍ、直径２０ｍｍのモリブデン-ジルコニア系サーメット製の浸漬棒１２を、その下端部が鋳型内の溶鋼中に浸漬され、その上端部付近が支点となって鋳型の幅方向に回転可能となるように取り付けた。浸漬棒１２の溶鋼中における浸漬深さは約１００ｍｍとした。このようにして鋳型内の溶鋼７に浸漬棒１２を浸漬すると、浸漬棒１２の浸漬部分は、溶鋼湯面９の直下の溶鋼流によって、その上端部付近の支点を中心として回転し、浸漬棒１２に働く重力と溶鋼湯面直下の溶鋼流による力が釣合った位置で停止する。停止した位置における鉛直線となす角度θから表面流速を求めることができる。本実施例では表面流速がゼロ近傍になるように調整するので、浸漬棒１２がほぼ鉛直になるように磁場強度を調整した。尚、図５に示す連続鋳造機では浸漬棒１２以外の構成は図２に示す連続鋳造機と同一構造となっており、同一の部分は同一符号により示し、その説明は省略する。 In this case, the method shown in FIG. 5 was used as a method of measuring the surface flow velocity at the 1/4 width position of the mold. That is, as shown in FIG. 5, a dip rod 12 made of molybdenum-zirconia cermet having a length of 410 mm and a diameter of 20 mm is placed at a position apart from the mold short side 5 by ¼ of the mold width, and its lower end is a mold. It was immersed in the molten steel inside, and it attached so that the vicinity of the upper end part could be rotated in the width direction of a casting_mold | template with a fulcrum. The immersion depth of the immersion rod 12 in the molten steel was about 100 mm. When the immersion rod 12 is immersed in the molten steel 7 in the mold in this manner, the immersion portion of the immersion rod 12 is rotated around the fulcrum near the upper end by the molten steel flow immediately below the molten steel surface 9, and the immersion rod 12 is stopped at a position where the gravity acting on 12 and the force of the molten steel flow just below the molten steel surface balance. The surface flow velocity can be obtained from the angle θ formed with the vertical line at the stopped position. In this embodiment, since the surface flow velocity is adjusted to be close to zero, the magnetic field strength is adjusted so that the dip rod 12 is substantially vertical. 5 has the same structure as that of the continuous casting machine shown in FIG. 2 except for the immersion rod 12, and the same parts are denoted by the same reference numerals and the description thereof is omitted.
磁場強度の調整の結果、磁束密度は、移動磁場の周波数が１Ｈｚのときには０．１２３５テスラ、２Ｈｚのときには０．１０１０テスラとなり、溶鋼の流動は非常に安定な状態で、且つ鋳型の１／４幅位置における表面流速をゼロ近傍に調整することができた。移動磁場の周波数が３Ｈｚのときには、磁束密度は０．０８８２テスラとなり、溶鋼流の揺らぎがやや大きかったものの、概ね鋳型の１／４幅位置における表面流速をゼロ近傍に調整することができた。しかしながら、移動磁場の周波数が４Ｈｚの場合には、溶鋼流動が安定せず、目的とする表面流速に安定して調整することができなかった。 As a result of adjusting the magnetic field strength, the magnetic flux density is 0.1235 Tesla when the frequency of the moving magnetic field is 1 Hz, and 0.1010 Tesla when the frequency of the moving magnetic field is 2 Hz, and the flow of the molten steel is in a very stable state and is 1/4 of that of the mold. The surface flow velocity at the width position could be adjusted to near zero. When the frequency of the moving magnetic field was 3 Hz, the magnetic flux density was 0.0882 Tesla, and although the fluctuation of the molten steel flow was slightly large, the surface flow velocity at the 1/4 width position of the mold could be adjusted to near zero. However, when the frequency of the moving magnetic field is 4 Hz, the molten steel flow is not stable and cannot be stably adjusted to the target surface flow velocity.
これらの結果を前述した（１）式により検証した。但し、（１）式を検証する際に、溶鋼吐出流の代表流速（ｕ）は、浸漬ノズルの内孔での溶鋼流速として２．１ｍ／秒（5700/(7000×60×π×0.0452 )=2.1）を採用した。この場合、溶鋼の密度を７０００ｋｇ／ｍ3 として計算している。鋳型中心から鋳型短辺までの距離（Ｌ）は０．８ｍである。 These results were verified by the aforementioned equation (1). However, when the equation (1) is verified, the representative flow velocity (u) of the molten steel discharge flow is 2.1 m / second (5700 / (7000 × 60 × π × 0.045 2 ) as the molten steel flow velocity in the inner hole of the immersion nozzle. ) = 2.1). In this case, the density of the molten steel is calculated as 7000 kg / m 3 . The distance (L) from the mold center to the mold short side is 0.8 m.
ｕ＝２．１ｍ／秒及びＬ＝０．８ｍを（１）式に代入すると、ｆ＜３．９が導かれる。移動磁場の周波数が４Ｈｚの場合には、鋳型内の溶鋼流動を十分に制御することができなかったことから、上記試験結果は（１）式と良く一致することが分かった。即ち、浸漬ノズルからの吐出流に移動磁場の電磁力を作用させて鋳型内の溶鋼流動を制御するには、印加する移動磁場の周波数は（１）式を満足する必要のあることが分かった。 Substituting u = 2.1 m / sec and L = 0.8 m into equation (1) leads to f <3.9. When the frequency of the moving magnetic field was 4 Hz, it was found that the molten steel flow in the mold could not be sufficiently controlled, and thus the above test result agreed well with the equation (1). That is, in order to control the molten steel flow in the mold by applying the electromagnetic force of the moving magnetic field to the discharge flow from the immersion nozzle, it was found that the frequency of the moving magnetic field to be applied must satisfy the equation (1). .
１ 鋳型
２ 浸漬ノズル
３ 移動磁場発生装置
４ 鋳型長辺
５ 鋳型短辺
６ 吐出孔
７ 溶鋼
８ 吐出流
９ 溶鋼湯面
１０ 凝固シェル
１１ モールドパウダー
１２ 浸漬棒
ＦX 電磁力
ＶX 移動磁場の移動速度
ＢY 移動磁場の磁束密度
DESCRIPTION OF SYMBOLS 1 Mold 2 Immersion nozzle 3 Moving magnetic field generator 4 Mold long side 5 Mold short side 6 Discharge hole 7 Molten steel 8 Discharge flow 9 Molten steel surface 10 Solidified shell 11 Mold powder 12 Immersion bar F X Electromagnetic force V X Movement speed of moving magnetic field Magnetic flux density of BY moving magnetic field
Claims (1)
ｆ＜(３ｕ)／(２Ｌ) …（１）
但し、（１）式において、ｆは移動磁場の周波数（Ｈｚ）、ｕは浸漬ノズルからの溶鋼吐出流の代表流速（ｍ／秒）、Ｌは鋳型中心から鋳型短辺までの距離（ｍ）である。 Using a moving magnetic field generator in which the direction of magnetic field movement is the mold width direction, the immersion nozzle from the mold short side to the molten steel discharged from the immersion nozzle installed at the center of the rectangular mold having long and short sides The moving steel flow in the mold is applied so that the surface flow velocity of the molten steel surface is 0.05 m / sec or less in absolute value at a position away from the mold short side by 1/4 of the mold width by applying a moving magnetic field toward the side. A continuous casting method of steel for casting while controlling the moving magnetic field, wherein the moving magnetic field has a lower limit value of the frequency of the moving magnetic field at least while the discharge flow from the discharge hole of the immersion nozzle passes through the magnetic field application region. And the upper limit of the frequency of the moving magnetic field is such that the discharge flow from the discharge hole of the immersion nozzle is a distance of 1/3 of the mold long side width × 1/2 from the discharge hole. Move until it spreads in the mold short side direction The action field in a range that does not undergo more than one period, characterized in that it is a frequency in the range satisfying the following equation (1), the continuous casting method of steel.
f <(3u) / (2L) (1)
However, in the formula (1), f is the frequency (Hz) of the moving magnetic field, u is the representative flow velocity (m / sec) of the molten steel discharge flow from the immersion nozzle, and L is the distance (m) from the mold center to the mold short side. It is.
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