JP3826727B2 - Method and apparatus for determining solidification state of slab and method for producing continuous cast slab - Google Patents

Description

【００３４】
鋳片の温度分布は、大まかには伝熱計算で容易に求まるため、予め鋳片の厚み、操業条件に応じて平均温度を求めておけば伝播時間が求められる。従って、この伝播時間を超えない範囲で最大のパルス幅を設定することで、最大のＳ／Ｎ改善が得られる。
【００３５】
第３のＳ／Ｎ改善方法は、平均回数を16回以上かつ平均後の透過信号が小さくならない範囲に設定した平均回数で、相関後の信号または受信信号を送信信号に同期して加算平均するものである（以下、「加算平均によるＳ／Ｎ改善」という場合がある）。ここでは特開昭53-57088号公報と同様に、同期加算平均を行うようにしているが、鋳片温度は操業状態によって様々に変化するため、図６に示すように透過信号の現れる位置は刻一刻変化することになる。この結果、伝播時間の変化率が大きい時、平均処理後に透過信号が小さくなってしまい、凝固状態の判定精度が低くなる。図６は平均回数が２回の場合を示しているが、平均回数がさらに多いと、より伝播時間の変化割合は増えてしまうため、より透過信号が小さくなる。これを避けるため、平均後の透過信号が小さくならない範囲に設定するようにしている。ここで、Ｓ／Ｎ比を最大にする平均回数は次のように定められる。
【００３６】
透過信号を周波数ｆの正弦波とし、透過信号の単位時間あたりの伝播時間変化率をτ（=(t2-t1)/T）、パルス繰り返し周波数をPRF（=1/Tprf）、平均回数をＮとすると、加算平均後の透過信号の振幅Xsは以下の式で表される。
【００３７】
【数２】

【００３８】
また、ノイズの振幅Xnは
【００３９】
【数３】

【００４０】
である。
【００４１】
よって、平均後のＳ／Ｎ比改善量αとして、
【００４２】
【数４】

【００４３】
が得られる。そこで、これらの式に基づいて最大の平均回数を求めれば良い。
従って、これを超えない範囲で平均回数を設定することで、最大のＳ／Ｎ改善を得るようにする。
【００４４】
以上、個々のＳ／Ｎ改善方法について説明したが、１番目の「表層冷却によるＳ／Ｎ改善」は電磁超音波の発生原理を利用したもの、２番目の「バースト波によるＳ／Ｎ改善」は送信信号とノイズとの相関を利用したもの、３番目の「加算平均によるＳ／Ｎ改善」はノイズの時間ランダム性を利用したものであり、これらのＳ／Ｎ改善効果は全て異なる原理で得ている。従って、Ｓ／Ｎ改善量は加算されていくこととなり、大きなＳ／Ｎ改善量が得られることになる。
【００４５】
これらのＳ／Ｎ改善方法や送信信号の高出力化方法を適宜組み合わせていくと、ある段階で電磁超音波センサにタッチロールを付けて鋳片に接触させるようなことをしなくても構わないほど、リフトオフを広く取ることができるようになる。従来技術では、リフトオフはせいぜい2mmであり、発明者が知る限り、現実に、完全非接触でかつ連続的に連続鋳造鋳片の凝固状態を判定できるシステムは存在しない。しかし、本発明では上記したＳ／Ｎ改善方法同士、あるいはＳ／Ｎ改善方法と送信信号の高出力化方法を組み合わせることで、従来は不可能であった完全非接触かつ連続的な連続鋳造鋳片の凝固状態判定を現実に可能なものとした。
【００４６】
上記課題を解決するために、具体的には以下のような手段が提供される。
（１）連続鋳造鋳片に対し、電磁超音波の横波を透過させることによりその凝固状態を判定する方法であって、前記鋳片の表層部の所定領域がγ相からα相へ相変態するまで当該鋳片を冷却する冷却ステップと、前記冷却ステップにて冷却された鋳片の所定領域に対し、横波用の送信用電磁超音波センサによって、送信信号としての横波超音波を送信する送信ステップと、前記送信信号が鋳片を透過した透過信号を、横波用の受信用電磁超音波センサによって、受信する受信ステップと、前記受信ステップにおいて受信した受信信号に基づき、前記鋳片の凝固状態を判定する判定ステップとを有することを特徴とする鋳片の凝固判定方法。
（２）前記送信用電磁超音波センサ及び前記受信用電磁超音波センサは、鋳片と非接触状態にあることを特徴とする上記（１）に記載の鋳片の凝固判定方法。
（３）連続鋳造鋳片に対し、電磁超音波の横波を透過させることによりその凝固状態を判定する方法であって、前記鋳片の表層部の所定領域がγ相からα相へ相変態するまで当該鋳片を冷却する冷却ステップと、前記電磁超音波が鋳片を透過する伝播時間を超えない時間の最大数に対し、その５０％から１５０％の範囲に設定されたパルス幅内で、周波数、振幅もしくは位相のいずれか、またはこれらの任意の組み合せにより変調したバースト状の送信信号を、前記冷却ステップにて冷却された鋳片の所定領域に対し、鋳片と非接触状態にある横波用の送信用電磁超音波センサによって送信する送信ステップと、前記送信信号が鋳片を透過した透過信号を、鋳片と非接触状態にある横波用の受信用電磁超音波センサによって、受信する受信ステップと、前記受信ステップにおいて受信した受信信号に対し、前記送信信号と同一または類似の波形の参照信号を用いて相関演算を行い、前記鋳片の凝固状態を判定する判定ステップとを有することを特徴とする鋳片の凝固判定方法。
（４）連続鋳造鋳片に対し、電磁超音波の横波を透過させることによりその凝固状態を判定する方法であって、前記鋳片の表層部の所定領域がγ相からα相へ相変態するまで当該鋳片を冷却する冷却ステップと、前記冷却ステップにて冷却された鋳片の所定領域に対し、鋳片と非接触状態にある横波用の送信用電磁超音波センサによって、送信信号としての横波超音波をパルス単位で繰り返し送信する送信ステップと、前記送信信号が鋳片を透過した透過信号を、鋳片と非接触状態にある横波用の受信用電磁超音波センサによって、受信する受信ステップと、前記受信ステップで受信された受信信号における各パルスを加算平均するとともに、その加算平均回数を、１６回以上、かつ、信号伝播時間の変化がパルス加算による信号強度の相殺低下を生じさせない程度の時間幅に相当するパルス回数以下として信号処理し、この信号処理結果に基づいて前記鋳片の凝固状態を判定する判定ステップとを有することを特徴とする鋳片の凝固判定方法。
（５）連続鋳造鋳片に対し、電磁超音波の横波を透過させることによりその凝固状態を判定する方法であって、前記鋳片の表層部の所定領域がγ相からα相へ相変態するまで当該鋳片を冷却する冷却ステップと、前記電磁超音波が鋳片を透過する伝播時間を超えない時間の最大数に対し、その５０％から１５０％の範囲に設定されたパルス幅内で、周波数、振幅もしくは位相のいずれか、またはこれらの任意の組み合せにより変調したバースト状の送信信号を、前記冷却ステップにて冷却された鋳片の所定領域に対し、鋳片と非接触状態にある横波用の送信用電磁超音波センサによってパルス単位で繰り返し送信する送信ステップと、前記送信信号が鋳片を透過した透過信号を、鋳片と非接触状態にある横波用の受信用電磁超音波センサによって、受信する受信ステップと、前記受信ステップで受信された受信信号における各パルスを加算平均する第１の信号処理と、受信信号に対し前記送信信号と同一または類似の波形の参照信号を用いて相関演算を行う第２の信号処理とを、第１，第２の信号処理の順あるいは第２，第１の信号処理の順に実行し、その信号処理結果に基づいて前記鋳片の凝固状態を判定するとともに、前記第１の信号処理における加算平均回数を、１６回以上、かつ、信号伝播時間の変化がパルス加算による信号強度の相殺低下を生じさせない程度の時間幅に相当するパルス回数以下とする判定ステップとを有することを特徴とする鋳片の凝固判定方法。
（６）前記信号伝播時間の変化がパルス加算による信号強度の相殺低下を生じさせない程度の時間幅に相当するパルス回数は、２５６回とすることを特徴とする上記（４）又は（５）に記載の鋳片の凝固判定方法。
（７）前記送信用電磁超音波センサ及び前記受信用電磁超音波センサは、前記鋳片との距離を４ｍｍ以上離して設置されることを特徴とする上記（２）乃至（６）のうち何れか一項に記載の鋳片の凝固判定方法。
（８）前記送信用電磁超音波センサ及び又は前記受信用電磁超音波センサは、電磁超音波の送受信に電磁石を用いるとともに、当該電磁石の励磁電流を、凝固判定に必要な計測時間よりは長時間継続するパルス電流としたことを特徴とする上記（１）乃至（７）のうち何れか一項に記載の鋳片の凝固判定方法。
（９）溶鋼を凝固させつつ、連続鋳造鋳片をモールドから引き抜く引抜ステップと、前記引抜ステップにて引き抜かれた鋳片内部の凝固状態を、上記（１）乃至（８）何れかに記載の鋳片の凝固判定方法により判定する凝固判定ステップと、前記凝固判定ステップにおける判定結果に基づき、鋳片の鋳造速度又は冷却を制御する制御ステップとを有することを特徴とする連続鋳造鋳片の製造方法。
（１０）連続鋳造鋳片に対し、電磁超音波の横波を透過させることによりその凝固状態を判定する装置であって、前記鋳片の表層部の所定領域がγ相からα相へ相変態するまで当該鋳片を冷却する冷却手段と、前記冷却手段にて冷却された鋳片の所定領域に対し、鋳片と非接触状態にある横波用の送信用電磁超音波センサによって、送信信号としての横波超音波を送信する送信手段と、前記送信信号が鋳片を透過した透過信号を、鋳片と非接触状態にある横波用の受信用電磁超音波センサによって、受信する受信手段と、前記受信手段において受信した受信信号に基づき、前記鋳片の凝固状態を判定する判定手段とを有することを特徴とする鋳片の凝固判定装置。
（１１）前記送信用電磁超音波センサ及び又は前記受信用電磁超音波センサは、電磁超音波の送受信に電磁石を用いるとともに、当該電磁石の励磁電流を、凝固判定に必要な計測時間よりは長時間継続するパルス電流としたことを特徴とする上記（１０）に記載の鋳片の凝固判定装置。
【００４７】
【発明の実施の形態】
以下、本発明の実施の形態について説明する。
【００４８】
（第１の実施形態）
図１は本発明の第1の実施形態に係る鋳片の凝固状態判定装置の一例を示す構成図である。
【００４９】
同図においては、炭素鋼の連続鋳造鋳片１を連続鋳造ロール２が鋳片１を挟みこむとともに、図中右側へ引き抜いている。鋳片１の内部には未凝固部７が存在し、その先端がクレータエンド７ａである。また、ロール２間に設けられた水冷用ノズル５は、連続鋳造鋳片１の表層部に対して水を放出して冷却し、その所定領域６をγ相からα相へ変態させている。
【００５０】
鋳片の凝固状態判定装置は、鋳片１をα相変態した位置で挟んで対向配置させた送信用横波電磁超音波センサ３及び受信用横波電磁超音波センサ４からなるセンサ部と、送信用横波電磁超音波センサ３に送信信号を出力する送信出力系８，９（１４，１５），１６と、受信用横波電磁超音波センサ４にて受信した受信信号を処理する受信処理系１０，１１，１２，１３，１７とからなっている。
【００５１】
送信用横波電磁超音波センサ３は、送信信号を横波の電磁超音波として発信し、電磁超音波が鋳片１を透過した透過信号を受信用横波電磁超音波センサ４が受信する。この受信信号を処理することによりクレータエンド７ａの位置検出が行われる。なお、図１においては、センサ３，４の位置では鋳片内部が完全に凝固しており、クレータエンド７ａはセンサ部上流にある。
【００５２】
また、送信出力系は、送信信号のトリガー信号発生部８と、送信信号発生部９と、バースト波のパルス幅を設定するパルス幅設定部１６とから構成される。送信信号発生部９は、さらにトリガー信号に基づいて設定されたパルス幅のバースト波を発生するバースト波発生部１４と、発生したバースト波を増幅して送信信号としてセンサ３に出力する電力増幅部１５とからなっている。
【００５３】
一方、受信処理系は、受信信号の増幅部１０、同期加算平均部１２、平均回数設定部１３、相関処理部１７、及び、受信信号から透過信号を抽出して凝固状態を判定する評価部１１とから構成されている。
【００５４】
次に、以上のように構成された本実施形態における鋳片の凝固状態判定装置の動作について説明する。
【００５５】
まず、トリガー信号発生部８から、送信のタイミング信号が出ると、バースト波発生部１４は、周波数、振幅もしくは位相のいずれか、またはこれらの任意の組み合せにより変調したバースト状の送信信号を発生する。ここで、パルス幅は、パルス幅設定部１６にて指定された値とする。送信信号は電力増幅部１５で増幅され、送信用横波電磁超音波センサ３に印加される。
【００５６】
図２は本実施形態の電磁超音波センサの構造例を示す図である。
【００５７】
同図に示すように、送信用横波電磁超音波センサ３はコイル１９を備えており、連続鋳造鋳片１の表層部でα層に変態している所定領域６に、送信信号による高周波の振動磁場Bvを鋳片の表面に平行な方向に加える。この結果、鋳片の表面に平行な応力が磁歪によってかかるため、せん断波すなわち横波が発生することになる。なお、ここで送信用横波電磁超音波センサ３は垂直方向に磁極を持つ磁石２０も備えているが、これは静磁場Bsにより磁歪の効果を増すために用いられる。この磁石は永久磁石でも電磁石でも良い。
【００５８】
このようにして、発生した横波超音波は鋳片を透過し、送信とは反対側の表面に到達する。こちら側には、図２と同様の受信用横波電磁超音波センサ４が対向しており、連続鋳造鋳片１の表層部でα層に変態している部分６に、磁石２２により静磁場Bsがかけられている。ここに、横波が到達すると、磁歪の逆効果として、この部分の透磁率が変化する。この結果、受信用横波電磁超音波センサ４のコイルを横切る磁束Bsが高周波で振動的に変化するため、電磁誘導によってセンサコイル２１に電圧が発生し、受信信号が得られる。
【００５９】
この受信信号は増幅部１０で増幅された後、同期加算平均部１２に入力され、平均回数設定部１３により設定された回数だけ平均化される。同期加算平均部１２は種々の方法で実施可能だが、ここではA/D変換を行って数値化し、トリガー発生部８の信号に同期して計算機によって平均化するようにした。演算式は以下の方法などを適用することができる。
【００６０】
【数５】

【００６１】
平均された受信信号は、相関処理部１７に入力される。ここでは、既に数値化されているので、具体的にはさらに計算を行っていることが相関処理部１７に相当する。相関処理は以下の式で実施できるが、直接この式を計算しないで、入力信号をＦＦＴしたものと参照信号をＦＦＴしたものの共役とを乗算し、その結果を逆ＦＦＴして出力を得るのが最も高速に処理できるため有用である。
【００６２】
【数６】

【００６３】
なお、バースト波発生部１４は、周波数、振幅もしくは位相のいずれか、またはこれらの任意の組み合せにより変調したバースト状の送信信号を発生するが、変調方式はどの方式でも良い。変調方式の一例として、周波数変調であるチャープ波の例を次の式で示す。
【００６４】
【数７】

【００６５】
チャープ波は自己相関関数が鋭い性質を持つ波形である。鋳片を透過してきた受信信号の波形は、送信信号と相似であるから、相関処理部１７を通過した受信信号は、送信信号のパルス幅より短くなるパルス圧縮効果が得られ、パルス幅の短い鋭い波形となる。これは、評価部１１で凝固状態の判定を行う際に以下の点で有用である。一つ目は、透過信号の強度を求める際、透過信号の時間帯だけにゲートをかけて、その中の最大値を求めれば良いが、パルス幅の短い鋭い波形だとゲートの幅を狭くできるので、余分なノイズを拾わなくなる。二つ目は、透過信号の伝播時間を求める際、短いパルスだと時間の精度が高くなり、より精度良い鋳片の凝固状態判定ができるようになる。
【００６６】
以上のようにして、相関処理の出力を得て、評価部１１で凝固状態の判定を行う。これも計算で実施できるので、同期加算平均部１２、相関処理部１７、評価部１１は一つあるいは複数の計算機で実施できる。
【００６７】
次に各部の設定値について、実施例を示す。
【００６８】
［表層冷却によるＳ／Ｎ改善］
まず、連続鋳造鋳片の表層部を相変態させる条件は次のようにした。
【００６９】
ここでは、センサ手前の鋳片の表面温度は900℃で、水冷用ノズル５の水量は-20℃/sの冷速が得られる量とし、鋳片の移動速度は2.4mpm(40mm/s)とする。被測定材の連続冷却変態線図（ＣＣＴ）は図３のようであったため、冷却速度-20℃/sの時の変態開始温度（曲線a）は約620℃である。図４で説明した磁歪の効果を得るためには、変態開始よりも温度を下げて変態終了温度（曲線b）に近づければ良いので、表層部が620℃以下となるようにする。下げれば下げるほど効果は大きくなるため、表面割れなどがないように、品質上の制約から温度を決めれば良い。ここでは、表層の温度を600℃まで冷やすとすると、280℃低下させれば良い。従って、冷却ゾーン長（冷却水をかける長さ）は280℃/20(℃/s)*40(mm/s)＝560mmとした。
【００７０】
以上の条件で、実際に透過信号のＳ／Ｎを測定すると、冷却しないでローレンツ力で電磁超音波を発生させた場合に比較して、冷却して相変態させ磁歪で電磁超音波を発生させた場合は10dBのＳ／Ｎ改善効果があった。
【００７１】
なお、電磁超音波の周波数を考慮し、振動磁場の浸透深さ程度までが相変態開始するように冷却するとより感度を高くすることができる。
【００７２】
［バースト波によるＳ／Ｎ改善］
次に送信信号は次のようにした。
【００７３】
透過信号は、送信後、図５に示すように伝播時間分だけ遅れた位置に現れる。従って、送信信号の漏れ込みが透過信号に重ならないように、この伝播時間より送信信号のパルス幅を短くすれば良い。ここで伝播時間は、鋳片厚み、鋳片温度、音速とから決定される。音速は鋳片温度と鋼種に依存し、横波で炭素鋼の場合、概略3000-0.65T(m/s)である。すなわち温度が低いほど音速は遅くなり、伝播時間は短くなる。
【００７４】
従って、適用しようとする測定位置において、鋳片の温度が最も低くなる場合が最も伝播時間が短くなる場合であるから、この時の伝播時間が最大数である。そこで、送信信号のパルス幅はこの値の近傍に設定すれば良い。本発明は鋳片の凝固状態を判定するために使うので、鋳片の温度が最も低くなる場合とは、軸心の温度で1100℃程度、平均温度で1000℃程度と考えれば良い。
【００７５】
パルス幅の許容範囲は以下のように決められる。Ｓ／Ｎはパルス幅の√にほぼ比例するため、パルス幅を1/2位に短くすると6dB近く低下して効果が少なくなってしまう。一方、長すぎると透過信号に重なってしまうようになるが、波形の両端は、センサや増幅器の特性により多少振幅が小さくなるため、パルス幅は上記最大値の1.5倍位まで許容できる。このため、Ｓ／Ｎ向上効果の出るパルス幅の範囲としては最大数の50%以上、150%以下が望ましく、最適な範囲としては80%以上、120%以下が望ましい。
【００７６】
下表に、厚み200mm,250mm,300mmの鋳片について定めた送信信号の最適なパルス幅を示す。ここでは最低の温度を平均温度で1000℃とし、その時の音速は2350m/sとした。
【００７７】
【表１】

【００７８】
なお、送信信号の漏洩信号が大きい場合、漏洩信号により受信アンプが飽和し、いわゆる追い込み現象によりしばらくの時間不感帯になる場合がある。従って、追い込みがある場合は、上表の値からこの追い込み時間を引いた値にパルス幅を設定すれば良い。
【００７９】
表１の内、鋳片厚み250mm、パルス幅100μs、周波数100kHzの場合について、実際に透過信号のＳ／Ｎを測定すると、100kHzの１波のsin波に比較して、12dBのＳ／Ｎ改善効果があった。従って、上記のパルス幅の範囲に設定することで最低6dBのＳ／Ｎ改善効果が得られる。
【００８０】
［加算平均によるＳ／Ｎ改善］
次に同期加算平均の平均回数は次のようにした。
【００８１】
鋳造中の温度変化による伝播時間の変化率が大きい場合ほど、図６に示すように、平均化によって透過信号が小さくなってしまう可能性がある。そこで、伝播時間の変化率について様々な実験を繰り返した結果、同変化率がかなり大きくなる場合において、0.03μs/s〜0.3μs/s程度であった。そこで、この値をパラメータとし、超音波の周波数100kHz、パルス繰り返し周波数100Hzの場合の場合について、（２）式に基づいて、平均回数と透過信号の振幅の関係を求めると図７のようになった。
【００８２】
同図によれば、単位時間あたりの伝播時間の変化率τが最も早い0.3μs/sの時に平均回数256回程度までなら、振幅の低下はほとんどないことから、この場合は、平均回数の最大数は256と定められる。この時のＳ／Ｎ改善効果は（４）式のように√平均回数であるから24dBが得られた。なお、上記最大数の算出に当たっては、透過信号強度の低下が１dB前後であれば振幅の低下がほとんどないことを基準にしている。すなわち「伝播時間の変化率τ0.3μs/sの時に平均回数の最大数256回」という値は、透過信号強度の低下１dBの場合である。伝播時間の変化率τが他の値となる場合にも、同様な基準により平均回数の最大数が算出される。
【００８３】
また、平均回数が少ないとＳ／Ｎ向上効果は少なくなるので、効果の出る範囲としては16回以上が望ましい。この場合、+12dBの効果がある。反対に平均回数が多すぎると図６のように振幅が小さくなるため、上記最大数の２倍程度以内が望ましい。最適な範囲としては上記最大数の50%以上、200%以下が適当である。
【００８４】
なお、式(2)から明らかなように、超音波の周波数やパルス繰り返し周波数を変更する場合は、τを比例させて変化させた点で図７を読むことで、図７から平均回数と透過信号の振幅の関係を求めることができる。
【００８５】
さて、以上の効果は上述のように全て独立のため、これらを全て組み合わせることにより、10+6+12＝28dBのＳ／Ｎ改善効果が得られる。
【００８６】
電磁超音波センサのリフトオフ感度特性は-4dB/mm程度であるため、28/4＝+7mmリフトオフを広くすることができるようになる。
【００８７】
このように、本発明の実施の形態に係る鋳片の凝固状態判定方法及び装置によれば、Ｓ／Ｎ改善によりリフトオフを十分に大きくすることができるので、電磁超音波センサをタッチロールも何も使わずに、連続鋳造鋳片に対し完全に非接触の状態で連続鋳造機内へ設置し、安定かつ連続的に鋳片内の凝固状態を精度よく計測し判定することができる。これにより、連続的にクレータエンド位置を検出することができる。
【００８８】
なお、本実施形態においては、「表層冷却によるＳ／Ｎ改善」、「バースト波によるＳ／Ｎ改善」及び「加算平均によるＳ／Ｎ改善」のすべてを組み合わせた場合を説明したが、これらすべてを組合さなくてもセンサ非接触を実現できる場合がある。具体的には、完全に非接触で計測可能なリフトオフ改善量としては従来技術(1〜2mm)より望ましくは+7mm以上あれば良いが、+4mm以上でも良い。そこで、センサのリフトオフ特性がおよそ-4dB/mmであることを考慮すると、従来より16dB以上のＳ／Ｎ改善があればセンサ〜鋳片間を非接触とすることが可能である。
【００８９】
したがって、「表層冷却によるＳ／Ｎ改善」、「バースト波によるＳ／Ｎ改善」及び「加算平均によるＳ／Ｎ改善」は、センサ非接触を実現できる範囲で種々組み合わせることが可能である。例えば「表層冷却によるＳ／Ｎ改善」及び「バースト波によるＳ／Ｎ改善」の組み合せでは10+6＝16dBのＳ／Ｎ改善効果が得られ、リフトオフ感度特性は-4dB/mm程度として、16/4＝+4mmリフトオフ改善が得られる。同様に、「表層冷却によるＳ／Ｎ改善」及び「加算平均によるＳ／Ｎ改善」、「バースト波によるＳ／Ｎ改善」及び「加算平均によるＳ／Ｎ改善」、あるいは、平均回数を64回以上にした「加算平均によるＳ／Ｎ改善」のみにより、それぞれ約+5.5mm、+4.5mm、+4.5mmのリフトオフ改善が得られる。
【００９０】
（第２の実施形態）
本実施形態は、第１の実施形態で説明したＳ／Ｎ改善方法に、電磁超音波センサの高性能化方法を組み合わせるものである。これにより、完全非接触計測が可能なまでにリフトオフを大きくする。すなわち、本実施形態では図２の電磁超音波センサの磁石２２を電磁石とし、その磁化力を増すために尖頭値の高いパルス状の電流を磁化電流に用いている。Ｓ／Ｎを改善するためには磁化電流を増やせば良い。しかし、直流で電流を大きくすることは、電磁石が発熱してしまうために困難である。これに対し、パルス磁化電流を用いることで、電磁石の発熱を抑えるとともに、強力な磁場を形成することができる。
【００９１】
図８は本発明の第２の実施形態に係る鋳片の凝固状態判定装置の一例を示す構成図であり、図１と同一部分には同一符号を付して説明を省略し、ここでは異なる部分についてのみ述べる。
【００９２】
この鋳片の凝固状態判定装置は、パルス磁化電流を用いるためのパルス磁化電流発生部18を備える他、第１の実施形態と同様に構成されている。
【００９３】
パルス磁化電流発生部１８は、トリガー信号発生部８の信号に同期してパルス磁化電流を発するようになっている。パルス磁化電流の継続時間は超音波計測に関わる時間とすればよく、伝播時間の約２倍以上の200μs以上が適当である。この程度であれば、送信パルスの繰返し周期に対する時間は1/50程度であるから、磁化電流による発熱量は非常に少なく、大電流を流すことができる。
【００９４】
直流電流を用いた場合には磁化電流3A程度が限界であったが、パルス磁化電流を用いると尖頭値で10Aが可能となり、約10dBのＳ／Ｎ改善が得られる。
【００９５】
このように、本発明の実施の形態に係る鋳片の凝固状態判定方法及び装置によれば、第１の実施形態と同様な構成を備えるとともに、パルス磁化電流により電磁超音波を発信および受信するようにしたので、第１の実施形態と同様な作用効果が得られる他、電磁超音波センサの感度を高めることができる。これにより、一層容易に、連続鋳造鋳片に対する完全非接触のセンサ設置、連続的な凝固状態計測及びクレータエンド位置検出を行うことができる。
【００９６】
したがって、本実施形態の場合には、電磁超音波センサの高性能化方法を組み合わせることで、Ｓ／Ｎ改善方法としては、上記した「表層冷却によるＳ／Ｎ改善」、「バースト波によるＳ／Ｎ改善」又は「加算平均によるＳ／Ｎ改善」を単独で用いることも可能となる。具体的には、「表層冷却によるＳ／Ｎ改善」のみで+5mm、「バースト波によるＳ／Ｎ改善」のみで+4mm、「加算平均によるＳ／Ｎ改善」のみで+5mmのリフトオフ改善を得ることができる。
【００９７】
なお、直流電流を用いる場合であっても、以下▲１▼及び／又は▲２▼の方法を用いることにより磁化電流を10A程度に上げることが可能となり、前記パルス磁化電流を用いた場合と同様の電磁超音波センサの高性能化を達成することができる。これにより、前記パルス磁化電流を用いた場合と同様に各Ｓ／Ｎ改善方法を単独で用いた場合においても充分なリフトオフ改善効果を有し、連続鋳造鋳片に対する完全非接触のセンサ設置、連続的な凝固状態計測及びクレータエンド位置検出を行うことが可能となる。
▲１▼電磁石に用いる銅線を太くすることによって銅線の抵抗を下げ、磁化電流を大きくした場合の発熱を少なくする。
▲２▼電磁石の冷却に用いる冷却水あるいは冷却オイルの循環を速くして冷却能力を大きくする。
【００９８】
ただし、現実の連続鋳造機では、多くの場合、前記▲１▼、▲２▼を行うスペースを確保できない。従って、上述した何れかのＳ／Ｎ改善方法の１つと前記▲１▼、▲２▼を組み合わせることは困難性が高いことがある。
【００９９】
（第３の実施形態）
本実施形態においては、第１、第２の実施形態で説明した鋳片の凝固判定方法を利用した連続鋳造鋳片の製造方法を説明する。
【０１００】
図９は本発明の第３の実施形態に係る連続鋳造鋳片の製造方法を説明するための設備構成例を示す図であり、図１〜図８と同一部分には同一符号を付して説明を省略し、ここでは異なる部分についてのみ述べる。
【０１０１】
同図に示す連続鋳造機及び鋳片の凝固判定装置は、第１又は第２の実施形態と同様に構成されている。ここで、電磁超音波センサ３，４は連続鋳造機の末端部に取り付けられている。
【０１０２】
センサ３，４よりも下流には、鋳片を切断するためのカッター２１が設けられている。また、その遥か上流の連続鋳造鋳片１の引抜開始位置には、溶鋼を保持する鋳型２２が設けられ、鋳型２２からの引き抜き直後下流には、鋳片１を冷却するための２次冷却帯２３が設けられている。
【０１０３】
次に、本実施形態の連続鋳造鋳片の製造方法について説明する。
【０１０４】
まず、横波電磁超音波が透過している場合、クレータエンド７ａは鋳造機末端までは届いていないと判断される。ここで、鋳造速度が上がり、クレータエンド７ａが下流に延びてきてセンサ３，４を通過すると、透過信号がなくなるので、センサ３，４による計測で同位置にクレータエンド７ａが到達したと判断される。
【０１０５】
この時には、カッター２１までわずかの距離しかないので、鋳造速度をゼロに近い値まで下げるようにする。こうすると、鋳片の凝固は早まるので、クレータエンド７ａは上流に向かうようになる。その後、センサ３，４により透過信号が現れたのを確認したら、また鋳造速度を速くし、定常の操業に戻すようにする。以上のようにすれば、鋳造速度を高速に保ち、高い生産性を得ることができる。
【０１０６】
なお、ここでクレータエンドがセンサを通過する直前の伝播時間（以後、Δtcとする）を記憶するようにすると、次のような製造方法も可能となる。すなわち、センサにクレータエンドが近づいてくると、鋳片温度が高くなってくるので、伝播時間が長くなってくる。そこで、伝播時間を連続的に計測し、この伝播時間がΔtcに近づいてきたら、鋳造速度を少しだけ抑える、または、二次冷却２３の流量を増やしてより鋳片を冷却するようにする。一方、伝播時間がΔtcから短い側に遠ざかっていったら、鋳造速度を少しだけ上げる、または、二次冷却２３の流量を減らして鋳片の冷却を弱めるようにする。このようにすると、常に鋳造速度が最高速に近い状態に保つことができ、大幅に生産性を高めることができる。
【０１０７】
なお、以上の実施形態では、センサ３，４を鋳造機の末端に取り付けた場合を示したが、センサ３，４を軽圧下帯の近傍に取り付け、クレータエンド７ａを常に軽圧下帯に位置させるような製造の場合も同様に実施できる。
【０１０８】
このように、本発明の実施の形態に係る連続鋳造鋳片の製造方法によれば、第１又は第２の実施形態の鋳片の凝固判定装置からの計測結果を利用して、鋳造速度や鋳片冷却を制御するようにしたので、鋳造速度を高速化したり、軽圧下製造を安定して行い、品質を向上させたりすることができる。
【０１０９】
なお、本発明は、上記各実施の形態に限定されるものでなく、その要旨を逸脱しない範囲で種々に変形することが可能である。また、各実施形態は可能な限り適宜組み合わせて実施してもよく、その場合組み合わされた効果が得られる。
【０１１０】
例えば各実施形態においては、各センサ３，４は鋳片１を挟んで対抗配置され、センサ３からの入射信号は鋳片の表裏に向けて透過することになる。しかし、本明細書で「信号が透過する」という場合には、信号が鋳片の内部所定位置まで透過し当該所定位置で反射されて入射面に戻ってくる場合も含む。この場合には、受信用横波電磁超音波センサ４は、鋳片に対し、送信用横波電磁超音波センサ３と同一面側に配置されることになる。本発明は、各センサ３，４をこのように配置させても実現できるものである。
【０１１１】
また、実施形態に記載した手法は、計算機（コンピュータ）に実行させることができるプログラム（ソフトウエア手段）として、例えば磁気ディスク（フロッピーディスク、ハードディスク等）、光ディスク（ＣＤ−ＲＯＭ、ＤＶＤ、ＭＯ等）、半導体メモリ（ＲＯＭ、ＲＡＭ、フラッシュメモリ等）等の記録媒体に格納し、また通信媒体により伝送して頒布することもできる。なお、媒体側に格納されるプログラムには、計算機に実行させるソフトウエア手段（実行プログラムのみならずテーブルやデータ構造も含む）を計算機内に構成させる設定プログラムをも含む。本装置を実現する計算機は、記録媒体に記録されたプログラムを読み込み、また場合により設定プログラムによりソフトウエア手段を構築し、このソフトウエア手段によって動作が制御されることにより上述した処理を実行する。なお、本明細書でいう記録媒体は、頒布用に限らず、計算機内部あるいはネットワークを介して接続される機器に設けられた磁気ディスクや半導体メモリ等の記憶媒体を含むものである。
【０１１２】
【発明の効果】
以上詳記したように本発明によれば、Ｓ／Ｎ比を改善することで、より正確に連続鋳造鋳片のクレータエンド位置の検出ができる鋳片の凝固状態判定方法を提供することができる。
【０１１３】
また、完全非接触で連続鋳造鋳片のクレータエンド位置を検出することができる鋳片の凝固状態判定方法及び装置を提供することができる。
【０１１４】
また、本発明によれば、完全非接触の計測で得られる連続鋳造鋳片の凝固状態情報を利用して生産性又は品質を高めることができる連続鋳造鋳片の製造方法を提供することができる。
【図面の簡単な説明】
【図１】本発明の第1の実施形態に係る鋳片の凝固状態判定装置の一例を示す構成図である。
【図２】本発明の第1の実施形態に係る電磁超音波センサの構造例を示す図である。
【図３】本発明の説明に係る被測定材料の連続冷却変態線図である。
【図４】本発明の説明に係る横波電磁超音波の発生メカニズムを示す図である。
【図５】本発明の説明に係る送信信号と伝播時間の関係を示す図である。
【図６】本発明の説明に係る伝播時間の変化と平均処理の関係を示す図である。
【図７】本発明の第1の実施形態に係る鋳片の凝固状態判定装置の一例を示す構成図である。
【図８】本発明の第２の実施形態に係る鋳片の凝固状態判定装置の一例を示す構成図である。
【図９】本発明の第３の実施形態に係る連続鋳造鋳片の製造方法を説明するための設備構成例を示す図である。
【図１０】従来技術の説明に係る電磁超音波の熱間での特性例を示す図である。
【図１１】従来技術を示す構成図である。
【図１２】従来技術の説明に係る磁束密度の温度特性を示す図である。
【符号の説明】
１ 連続鋳造鋳片
２ 連続鋳造ロール
３ 送信用横波電磁超音波センサ
４ 受信用横波電磁超音波センサ
５ 水冷用ノズル
６ 所定領域
７ 未凝固部
７ａ クレータエンド
８ トリガー信号発生部
９ 送信信号発生部
１０ 受信信号の増幅部
１１ 評価部
１２ 同期加算平均部
１３ 平均回数設定部
１４ バースト波発生部
１５ 電力増幅部
１６ パルス幅設定部
１７ 相関処理部
１８ パルス磁化電流発生部
１９ コイル
２０ 磁石
２１ カッター
２２ 鋳型
２３ ２次冷却帯[0001]
BACKGROUND OF THE INVENTION
TECHNICAL FIELD The present invention relates to a slab solidification state determination method and apparatus for determining a solidification state of a slab by transverse electromagnetic ultrasonic waves in continuous casting of a steel material, and a method for manufacturing a continuous cast slab.
[0002]
[Prior art]
In the casting process in steel production, the slab whose surface layer part solidified is continuously drawn out from the mold holding the molten steel, and as the drawing progresses, the solidified part of the slab is brought to the center part and completely solidified. Casting methods are widely used.
[0003]
Here, it is very important to determine where the fully solidified end (crater end) of the continuous cast slab is located in the slab in the continuous drawing process. This is because detecting the position of the crater end greatly contributes to the improvement of the productivity and quality of the slab.
[0004]
For example, when the casting speed is increased in order to improve productivity, the crater end moves to the downstream side of the slab. Here, if the position exceeds the cutting position by the slab cutter, there is a possibility that a major accident such as molten steel leakage will occur. Therefore, when the crater position is not clearly known, it is impossible to increase the casting speed.
[0005]
Further, in the light reduction operation for reducing the center segregation of solidification and improving the quality, it is necessary to control the casting speed and the secondary cooling amount so that the crater end is positioned in the vicinity of the light reduction zone. In order to meet these requirements, it is necessary to continuously measure the solidification state of the slab.
[0006]
Therefore, various methods have been proposed so far in order to determine the solidified state inside the slab.
[0007]
For example, in order to determine complete solidification / non-solidification inside a slab, a method for determining the transmission intensity of ultrasonic transverse waves is known. The shear wave has a property of transmitting only the solid phase and not transmitting if there is a liquid phase. Therefore, it is determined that the solid wave is completely solidified by transmitting a transverse wave in the thickness direction of the slab, and if a signal transmitted through the slab is detected, it is determined that an unsolidified portion remains if no signal is obtained. it can. As a method of using this property and determining a specific position of the crater end, a method of using the propagation time of the transmitted wave is also known.
[0008]
Here, an electromagnetic ultrasonic method, which is an electromagnetic ultrasonic wave transmission / reception method, is known as a method for generating and detecting transverse ultrasonic waves in a hot slab.
[0009]
In Japanese Patent Application Laid-Open No. 52-130422, as shown in FIG. 10, a slab is sandwiched between two electromagnetic ultrasonic sensors for transverse waves, and the transmission intensity of the transverse ultrasonic waves is measured.
[0010]
In Japanese Patent Application Laid-Open No. 62-148850, an electromagnetic ultrasonic sensor capable of simultaneously generating a longitudinal wave and a transverse wave is used, and the coagulation state is determined by the transmission intensity of the transverse wave. At the same time, even if there is an unsolidified part, it is possible to check for lift-off fluctuations and sensor abnormalities by using a transmitted longitudinal wave signal.
[0011]
In Japanese Patent Laid-Open No. 10-197502, the resonance frequency of the transverse wave in the slab is measured, and the center solid phase ratio (the ratio of the solid phase in the solid-liquid coexisting phase of the slab axis) is determined from the resonance frequency between 0.25 and 1.0. The solid phase ratio is estimated from the obtained transverse wave transmission time.
[0012]
However, these transverse wave ultrasonic methods have a problem of low sensitivity. For example, in the continuous casting of carbon steel, the temperature of the material is as high as 1000 ° C. or higher. However, as shown in Fig. 11 (Non-destructive inspection Vol.34, No.11, pp.796-803 Fundamentals and Applications of Electromagnetic Ultrasound, Kawashima) It is known that the sensitivity of sound waves is extremely low. In order to accurately determine the moment when the solidification state of the shaft center changes from the liquid phase to the solid phase or from the solid phase to the liquid phase, it is necessary to detect a weak signal whether the intensity of the transmitted signal is output or not. However, since the sensitivity of the transverse electromagnetic ultrasonic waves is extremely low as described above, accurate measurement is difficult.
[0013]
In addition, the sensitivity of the electromagnetic ultrasonic sensor becomes weaker as the lift-off (gap between the material and the sensor) is released. Therefore, the lift-off must be narrowed to detect weak signals. Generally, the lift-off is about 2 mm. Is the limit. In order to keep this in the continuous casting machine, it is necessary to devise such as attaching a touch roll to the sensor and pressing it against the slab with this touch roll as disclosed in, for example, Japanese Patent Application Laid-Open No. 11-183449. Even in this case, if it is continuously used in an environment where the temperature exceeds several hundred degrees Celsius and there are many scales, the scale may be clogged between the sensor and the slab and the sensor may be destroyed, or the touch roll may stick. As described in Japanese Patent Laid-Open No. 60-11110, there remains a problem that the sensor is caught in a casting roll. For this reason, it is difficult to realize stable and continuous determination of the solidified state of the slab.
[0014]
Therefore, it is necessary to increase the sensitivity of the electromagnetic ultrasonic sensor, widen the lift-off, and make it possible to measure completely without contact with the slab without using a touch roll, etc., and a method for improving the sensitivity of the electromagnetic ultrasonic sensor The following techniques have been proposed.
[0015]
In JP-A-53-106085, electromagnetic ultrasonic waves by Lorentz force are used, and a cooling fluid is sprayed on hot steel to bring the material temperature below the Curie point, thereby obtaining a strong magnetic field and increasing electrical conductivity. ing. Since the driving force of electromagnetic ultrasonic waves by the Lorentz force is F = B × J, the sensitivity increases as B and J increase.
[0016]
In Japanese Patent Laid-Open No. 2000-266730, a burst-like transmission signal modulated by any one of frequency, amplitude, or phase within a predetermined pulse width, or any combination thereof is used, and the received signal is the same as the transmission signal. Alternatively, the correlation calculation is performed using a reference signal having a similar waveform. Although the correlation between the reception signal and the transmission signal is high, the correlation between the noise and the transmission signal is low, so that the S / N (signal to noise ratio) is improved by the correlation calculation.
[0017]
In Japanese Patent Laid-Open No. 53-57088, received signals are averaged in synchronization with an electromagnetic ultrasonic generator. Since the noise is a random waveform at each pulse repetition, the S / N is improved by averaging.
[0018]
[Problems to be solved by the invention]
However, in the method of spraying the cooling fluid disclosed in Japanese Patent Laid-Open No. 53-106085, the absolute value of the magnetic flux density is still small in the vicinity of the Curie point as shown in FIG. The effect to obtain cannot be obtained. However, due to the material of the slab, too much cooling is a problem, so it cannot be cooled too much. In addition, the conversion efficiency of electromagnetic ultrasonic waves by Lorentz force may be very low from the beginning, and the S / N improvement effect is small.
[0019]
In the method using a burst wave disclosed in Japanese Patent Laid-Open No. 2000-266730, if this is applied to electromagnetic ultrasonic waves, the received signal is very weak compared to the transmitted signal, and therefore the transmitted signal leaks into the received signal. For this reason, if the pulse width of the burst wave is too long, the transmission signal hides the slab transmission signal, so that the pulse width cannot be made too long. Especially when applying to continuous casting, the internal temperature of the slab changes variously during operation, so the position where the transmission signal appears varies, but considering this, the pulse width cannot be made very long and the S / N is improved. Less effective.
[0020]
In the method using synchronous addition averaging disclosed in JP-A-53-57088, in the case of continuous casting, the position where the transmission signal appears varies as described above. There is a problem that becomes. For this reason, the average number of times cannot be increased so much and the S / N improvement effect is small.
[0021]
As described above, the conventional technology does not have a sufficient S / N improvement effect, and the lift-off of the electromagnetic ultrasonic sensor cannot be increased to the extent that non-contact measurement is performed. For this reason, it has not been realized to measure and detect the crater end completely in a non-contact manner without using any touch roll for the continuous cast slab.
[0022]
The present invention has been made in consideration of such circumstances, and a first object of the present invention is to improve the S / N ratio, thereby enabling more accurate detection of the crater end position of a continuous cast slab. Another object of the present invention is to provide a method for determining the solidification state of a cast slab.
[0023]
A second object of the present invention is to provide a slab solidification state determination method and apparatus capable of detecting the crater end position of a continuous cast slab in a completely non-contact manner.
[0024]
The third object is to provide a method for producing a continuous cast slab that makes it possible to improve productivity or quality by using solidification state information of the continuous cast slab obtained by complete non-contact measurement. It is in.
[0025]
[Means for Solving the Problems]
The inventor has conducted various experiments and discussions on the sensitivity when applying transverse wave electromagnetic ultrasonic waves to continuous casting, and as a result, the following S / N improvement methods are appropriately combined (in some cases alone) to complete the sensitivity. We found that sensor lift-off that can be measured without contact can be realized.
[0026]
In the first S / N improvement method, the surface layer portion of the material to be measured is phase-transformed by cooling, and a transverse electromagnetic transmitting ultrasonic sensor and a receiving electromagnetic ultrasonic sensor are disposed in the vicinity of the cooled portion. (Hereinafter sometimes referred to as “S / N improvement by surface cooling”).
[0027]
This method is different from Japanese Patent Application Laid-Open No. Sho 53-106085 in that phase transformation is performed by cooling and that an electromagnetic ultrasonic sensor for transverse waves is used. In the cooling process, when the cooling rate is high and the cooling time is short, even if the measured material is lowered below the Curie point, the crystal remains in the γ phase for a while due to overcooling, and the magnetism is immediately recovered. do not do. Therefore, in the present invention, cooling is performed until phase transformation is performed so that the magnetism is reliably recovered. In this way, although the transverse electromagnetic ultrasonic wave is applied to the magnetic body, a new effect that the magnetostrictive effect is dominant rather than the Lorentz force as the generation mechanism of the ultrasonic wave can be obtained.
[0028]
This is illustrated in FIG. At temperatures higher than the Curie point, the transverse electromagnetic ultrasonic waves are generated only by the Lorentz force. When cooled here, magnetism recovers at a temperature slightly lower than the Curie point due to supercooling. With this, the effect of Lorentz force increases, but here the effect of magnetostriction also comes out. The effect of magnetostriction is even greater than that of Lorentz force. Higher sensitivity than ultrasound can be obtained. Therefore, if the surface layer portion of the material to be measured is phase-transformed by cooling, and a transverse electromagnetic transmitting ultrasonic sensor and a receiving electromagnetic ultrasonic sensor are disposed in the vicinity of the cooled portion, a significant improvement in sensitivity can be obtained. be able to.
[0029]
Here, as the surface layer portion of the material to be measured that needs to undergo phase transformation by cooling, the width is not less than the coil width of the electromagnetic ultrasonic sensor, the length is not less than the coil length of the electromagnetic ultrasonic sensor, and the depth is used. The penetration depth at the frequency of the sound wave, for example, about 0.1 to 0.2 mm or more is desirable if the frequency is 1 MHz. In addition, it is desirable that all surface layer portions that need to undergo phase transformation are α phases, but the method of phase transformation from the γ phase to the α phase in the surface layer portion changes in a complex manner depending on the cooling conditions, the composition state of the surface layer portion, etc. Therefore, even if the γ phase remains partially, the effect of the present invention can be obtained if the γ phase is transformed to the α phase for a certain degree.
[0030]
The second S / N improvement method is to make the maximum pulse width within a range where the burst wave pulse width of the transmission signal does not exceed the propagation time (hereinafter referred to as “S / N improvement by burst wave”). Sometimes). Specifically, a burst shape modulated by either frequency, amplitude, or phase, or any combination thereof within a predetermined pulse width set in the vicinity of the maximum number determined from the slab thickness, slab temperature, and sound velocity. Is applied to a transmission electromagnetic ultrasonic sensor to transmit a transverse wave ultrasonic wave into the slab. This is received by a reception electromagnetic ultrasonic sensor, and correlation calculation is performed on the received signal using a reference signal having the same or similar waveform as the transmission signal.
[0031]
Here, similarly to Japanese Patent Laid-Open No. 2000-266730, a modulated transmission signal is used to perform correlation calculation of a received signal. The difference is that the pulse width of the transmission signal is set in the vicinity of the maximum number determined from the slab thickness, slab temperature, and sound speed in order to obtain the maximum effect.
[0032]
As shown in FIG. 5, the signal transmitted through the slab appears at a position delayed from the transmission signal by the propagation time. The propagation time dT can be estimated from the slab thickness d, the slab temperature T (x), and the speed of sound C (T) as follows. Here, Ta is the average temperature of the slab.
[0033]
[Expression 1]

[0034]
Since the temperature distribution of the slab is roughly determined by heat transfer calculation, the propagation time can be determined if the average temperature is determined in advance according to the thickness of the slab and the operating conditions. Therefore, the maximum S / N improvement can be obtained by setting the maximum pulse width within the range not exceeding the propagation time.
[0035]
In the third S / N improvement method, the average number of times is set to a range in which the average number of times is 16 or more and the transmitted signal after averaging is not reduced, and the correlated signal or the received signal is added and averaged in synchronization with the transmission signal. (Hereinafter, it may be referred to as “S / N improvement by addition averaging”). Here, as in JP-A-53-57088, synchronous addition averaging is performed. However, since the slab temperature varies depending on the operating state, the position where the transmission signal appears is as shown in FIG. It will change every moment. As a result, when the change rate of the propagation time is large, the transmission signal becomes small after the averaging process, and the determination accuracy of the coagulation state is lowered. Although FIG. 6 shows a case where the average number is two, if the average number is further increased, the change rate of the propagation time is further increased, so that the transmission signal becomes smaller. In order to avoid this, the average transmission signal is set in a range that does not become small. Here, the average number of times to maximize the S / N ratio is determined as follows.
[0036]
The transmitted signal is a sine wave of frequency f, the propagation time change rate per unit time of the transmitted signal is τ (= (t2-t1) / T), the pulse repetition frequency is PRF (= 1 / Tprf), and the average number is N Then, the amplitude Xs of the transmission signal after the averaging is expressed by the following equation.
[0037]
[Expression 2]

[0038]
The noise amplitude Xn is
[0039]
[Equation 3]

[0040]
It is.
[0041]
Therefore, as the S / N ratio improvement amount α after averaging,
[0042]
[Expression 4]

[0043]
Is obtained. Therefore, the maximum average number of times may be obtained based on these equations.
Therefore, the maximum S / N improvement is obtained by setting the average number of times within a range not exceeding this.
[0044]
Although the individual S / N improvement methods have been described above, the first “S / N improvement by surface cooling” uses the principle of generation of electromagnetic ultrasonic waves, and the second “S / N improvement by burst waves”. Uses the correlation between the transmitted signal and noise, and the third “S / N improvement by averaging” uses the time randomness of noise, and these S / N improvement effects are all based on different principles. It has gained. Therefore, the S / N improvement amount is added, and a large S / N improvement amount is obtained.
[0045]
If these S / N improvement methods and transmission signal high output methods are appropriately combined, there is no need to attach a touch roll to the electromagnetic ultrasonic sensor at a certain stage and bring it into contact with the slab. The more lift-off can be taken. In the prior art, the lift-off is at most 2 mm, and as far as the inventor knows, there is actually no system that can determine the solidification state of a continuous cast slab continuously and completely without contact. However, in the present invention, the above-described S / N improvement methods or a combination of the S / N improvement method and the method for increasing the output of the transmission signal allows complete non-contact and continuous continuous casting that was impossible in the past. The determination of the solidification state of the piece was made possible in practice.
[0046]
In order to solve the above problems, specifically, the following means are provided.
(1) A method for determining a solidified state of a continuous cast slab by transmitting a transverse wave of electromagnetic ultrasonic waves, the surface layer portion of the slab Predetermined region of γ phase to α phase A cooling step of cooling the slab until phase transformation, and a slab cooled in the cooling step Predetermined area In contrast, a transmission step of transmitting a transverse wave ultrasonic wave as a transmission signal by means of a transverse wave transmission electromagnetic ultrasonic sensor, and a transmission signal obtained by transmitting the transmission signal through a slab, a transverse wave reception electromagnetic ultrasonic sensor. And a determination step of determining a solidification state of the slab based on the reception signal received in the reception step.
(2) The transmitting electromagnetic ultrasonic sensor and the receiving electromagnetic ultrasonic sensor are in a non-contact state with the slab. Above (1) The solidification judgment method of slab described in 2.
(3) A method for determining a solidified state of a continuous cast slab by transmitting a transverse wave of electromagnetic ultrasonic waves, the surface layer portion of the slab Predetermined region of γ phase to α phase A cooling step for cooling the slab until phase transformation, and a pulse width set in a range of 50% to 150% of the maximum number of times that the electromagnetic ultrasonic wave does not exceed the propagation time through the slab A slab in which a burst-like transmission signal modulated by any one of frequency, amplitude or phase, or any combination thereof is cooled in the cooling step. Predetermined area On the other hand, a transmission step of transmitting by a transverse electromagnetic transmitting ultrasonic sensor in a non-contact state with the slab, and a transmission signal transmitted through the slab by the transmission signal for the transverse wave in a non-contact state with the slab The reception electromagnetic wave sensor for reception and the reception signal received in the reception step are subjected to correlation calculation using a reference signal having the same or similar waveform as the transmission signal, And a determination step of determining a solidification state.
(4) A method for determining a solidified state of a continuous cast slab by transmitting a transverse wave of electromagnetic ultrasonic waves, the surface layer portion of the slab Predetermined region of γ phase to α phase A cooling step of cooling the slab until phase transformation, and a slab cooled in the cooling step Predetermined area In contrast, a transmission step of repeatedly transmitting a transverse wave ultrasonic wave as a transmission signal in units of pulses by a transverse wave electromagnetic ultrasonic sensor in a non-contact state with the slab, and the transmission signal transmitted through the slab The reception step of receiving a signal by a receiving electromagnetic ultrasonic sensor for transverse waves in a non-contact state with the slab, and averaging the respective pulses in the reception signal received in the reception step, and the average number of additions Is processed 16 times or less and the number of pulses is equal to or less than the number of pulses corresponding to a time width such that the change in signal propagation time does not cause a decrease in canceling of the signal intensity due to pulse addition. And a determination step for determining the solidification state of the slab.
(5) A method for determining a solidified state of a continuous cast slab by transmitting a transverse wave of electromagnetic ultrasonic waves, the surface layer portion of the slab Predetermined region of γ phase to α phase A cooling step for cooling the slab until phase transformation, and a pulse width set in a range of 50% to 150% of the maximum number of times that the electromagnetic ultrasonic wave does not exceed the propagation time through the slab Within a burst-like transmission signal modulated by either frequency, amplitude or phase, or any combination thereof, For a predetermined area of the slab cooled in the cooling step, A transmission step of repeatedly transmitting in units of pulses by a transmission electromagnetic ultrasonic sensor for transverse waves in a non-contact state with the slab, and a transmission signal through which the transmission signal has passed through the slab, a transverse wave in a non-contact state with the slab A reception step of receiving by the receiving electromagnetic ultrasonic sensor, a first signal processing for averaging each pulse in the reception signal received in the reception step, and the same or similar to the transmission signal for the reception signal The second signal processing for performing the correlation operation using the reference signal of the waveform is executed in the order of the first and second signal processing or the order of the second and first signal processing, and based on the signal processing result The solidification state of the slab is determined, the average number of additions in the first signal processing is 16 times or more, and the change in the signal propagation time causes a decrease in signal strength cancellation due to pulse addition. Coagulation determining process of the slab, characterized in that it comprises a determination step of the pulse number below corresponds to no much time width.
(6) The number of pulses corresponding to a time width such that the change in the signal propagation time does not cause a decrease in cancellation of the signal intensity due to pulse addition is 256 times. (4) or (5) above The solidification judgment method of slab described in 2.
(7) The transmission electromagnetic ultrasonic sensor and the reception electromagnetic ultrasonic sensor are installed with a distance of 4 mm or more from the cast piece. (2) to (6) above The solidification determination method of the slab as described in any one of these.
(8) The transmission electromagnetic ultrasonic sensor and / or the reception electromagnetic ultrasonic sensor use an electromagnet for transmission / reception of electromagnetic ultrasonic waves, and the excitation current of the electromagnet is longer than the measurement time required for solidification determination. Characterized by a continuous pulse current (1) to (7) above The solidification determination method of the slab as described in any one of these.
(9) While solidifying the molten steel, a drawing step of drawing the continuous cast slab from the mold, and a solidification state inside the slab drawn in the drawing step, (1) to (8) above Continuously characterized by comprising a solidification determination step determined by a solidification determination method for a slab according to any one of the above, and a control step for controlling a casting speed or cooling of the slab based on a determination result in the solidification determination step. A method for producing cast slabs.
(10) A device for determining a solidified state of a continuous cast slab by transmitting a transverse wave of electromagnetic ultrasonic waves, the surface layer portion of the slab Predetermined region of γ phase to α phase Cooling means for cooling the slab until phase transformation, and slab cooled by the cooling means Predetermined area On the other hand, a transmission means for transmitting a transverse wave ultrasonic wave as a transmission signal by a transverse wave transmission electromagnetic ultrasonic sensor in a non-contact state with the slab, and a transmission signal obtained by transmitting the transmission signal through the slab, A receiving means for receiving by a receiving electromagnetic ultrasonic sensor for transverse waves in a non-contact state with the piece; and a judging means for judging a solidified state of the slab based on a received signal received by the receiving means. A slab solidification determination device characterized by the above.
(11) The transmission electromagnetic ultrasonic sensor and / or the reception electromagnetic ultrasonic sensor use an electromagnet for transmission and reception of electromagnetic ultrasonic waves, and the excitation current of the electromagnet is longer than the measurement time required for solidification determination. Characterized by a continuous pulse current Above (10) The slab solidification determination device according to 1.
[0047]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
[0048]
(First embodiment)
FIG. 1 is a configuration diagram showing an example of a slab solidification state determining apparatus according to a first embodiment of the present invention.
[0049]
In the figure, a continuous cast slab 1 of carbon steel is pulled out to the right in the figure while a continuous cast roll 2 sandwiches the slab 1. An unsolidified portion 7 is present inside the slab 1 and its tip is a crater end 7a. The water cooling nozzle 5 provided between the rolls 2 cools the surface layer portion of the continuous cast slab 1 by discharging water to transform the predetermined region 6 from the γ phase to the α phase.
[0050]
The slab solidification state determination apparatus includes a sensor unit including a transmission transverse wave electromagnetic ultrasonic sensor 3 and a reception transverse wave electromagnetic ultrasonic sensor 4 which are disposed opposite to each other with the slab 1 sandwiched at a position where the α phase has been transformed, and a transmission piece. Transmission output systems 8, 9 (14, 15), 16 that output transmission signals to the transverse electromagnetic ultrasonic sensor 3, and reception processing systems 10, 11 that process reception signals received by the reception transverse wave electromagnetic ultrasonic sensor 4. , 12, 13 and 17.
[0051]
The transmitting transverse wave electromagnetic ultrasonic sensor 3 transmits a transmission signal as a transverse electromagnetic ultrasonic wave, and the receiving transverse wave electromagnetic ultrasonic sensor 4 receives a transmission signal in which the electromagnetic ultrasonic wave has passed through the slab 1. The position of the crater end 7a is detected by processing this received signal. In FIG. 1, the inside of the slab is completely solidified at the positions of the sensors 3 and 4, and the crater end 7a is upstream of the sensor portion.
[0052]
The transmission output system includes a transmission signal trigger signal generation unit 8, a transmission signal generation unit 9, and a pulse width setting unit 16 for setting the pulse width of the burst wave. The transmission signal generation unit 9 further includes a burst wave generation unit 14 that generates a burst wave having a pulse width set based on the trigger signal, and a power amplification unit that amplifies the generated burst wave and outputs it to the sensor 3 as a transmission signal It consists of 15.
[0053]
On the other hand, the reception processing system includes a reception signal amplification unit 10, a synchronous addition averaging unit 12, an average number setting unit 13, a correlation processing unit 17, and an evaluation unit 11 that extracts a transmission signal from the reception signal and determines a coagulation state. It consists of and.
[0054]
Next, the operation of the slab solidification state determination device in the present embodiment configured as described above will be described.
[0055]
First, when a transmission timing signal is output from the trigger signal generator 8, the burst wave generator 14 generates a burst-like transmission signal modulated by any one of frequency, amplitude, and phase, or any combination thereof. . Here, the pulse width is a value designated by the pulse width setting unit 16. The transmission signal is amplified by the power amplifier 15 and applied to the transmission transverse wave electromagnetic ultrasonic sensor 3.
[0056]
FIG. 2 is a view showing a structural example of the electromagnetic ultrasonic sensor of the present embodiment.
[0057]
As shown in the figure, the transmission transverse wave electromagnetic ultrasonic sensor 3 includes a coil 19, and a high-frequency vibration due to a transmission signal is generated in a predetermined region 6 that is transformed into an α layer in the surface layer portion of the continuous cast slab 1. A magnetic field Bv is applied in a direction parallel to the surface of the slab. As a result, since a stress parallel to the surface of the slab is applied by magnetostriction, a shear wave, that is, a transverse wave is generated. Here, the transmission transverse wave electromagnetic ultrasonic sensor 3 also includes a magnet 20 having a magnetic pole in the vertical direction, which is used to increase the effect of magnetostriction by the static magnetic field Bs. This magnet may be a permanent magnet or an electromagnet.
[0058]
In this way, the generated transverse wave ultrasonic wave passes through the slab and reaches the surface opposite to the transmission side. On this side, a receiving transverse wave electromagnetic ultrasonic sensor 4 similar to that shown in FIG. 2 is opposed, and a static magnetic field Bs is applied by a magnet 22 to a portion 6 that is transformed into an α layer in the surface layer portion of the continuous cast slab 1. Has been applied. When the transverse wave reaches here, the permeability of this portion changes as an adverse effect of magnetostriction. As a result, the magnetic flux Bs traversing the coil of the receiving transverse wave electromagnetic ultrasonic sensor 4 changes in a vibrational manner at a high frequency, so that a voltage is generated in the sensor coil 21 by electromagnetic induction, and a received signal is obtained.
[0059]
The received signal is amplified by the amplifying unit 10, then input to the synchronous addition averaging unit 12, and averaged by the number of times set by the average number setting unit 13. The synchronous addition averaging unit 12 can be implemented by various methods, but here, A / D conversion is performed to digitize, and averaging is performed by a computer in synchronization with the signal of the trigger generation unit 8. The following methods can be applied to the arithmetic expression.
[0060]
[Equation 5]

[0061]
The averaged received signal is input to the correlation processing unit 17. Here, since it has already been quantified, the fact that further calculation is performed corresponds to the correlation processing unit 17. The correlation processing can be performed by the following formula, but without directly calculating this formula, the input signal is multiplied by the FFT of the reference signal and the conjugate of the FFT of the reference signal, and the result is inverse FFT to obtain an output. This is useful because it can be processed at the highest speed.
[0062]
[Formula 6]

[0063]
The burst wave generation unit 14 generates a burst-like transmission signal modulated by any one of frequency, amplitude, or phase, or any combination thereof, but any modulation method may be used. As an example of the modulation method, an example of a chirp wave that is frequency modulation is shown by the following equation.
[0064]
[Expression 7]

[0065]
A chirp wave is a waveform having a sharp autocorrelation function. Since the waveform of the reception signal that has passed through the slab is similar to the transmission signal, the reception signal that has passed through the correlation processing unit 17 has a pulse compression effect that is shorter than the pulse width of the transmission signal, and has a short pulse width. Sharp waveform. This is useful in the following points when the evaluation unit 11 determines the solidified state. First, when determining the intensity of the transmitted signal, it is sufficient to apply the gate only to the time zone of the transmitted signal and determine the maximum value, but a sharp waveform with a short pulse width can narrow the gate width. So you won't pick up extra noise. Secondly, when the propagation time of the transmission signal is obtained, if the pulse is short, the time accuracy becomes high and the solidification state of the slab can be determined with higher accuracy.
[0066]
As described above, the correlation processing output is obtained, and the evaluation unit 11 determines the coagulation state. Since this can also be performed by calculation, the synchronous addition averaging unit 12, the correlation processing unit 17, and the evaluation unit 11 can be implemented by one or a plurality of computers.
[0067]
Next, an example is shown about the setting value of each part.
[0068]
[S / N improvement by surface cooling]
First, the conditions for phase transformation of the surface layer portion of the continuous cast slab were as follows.
[0069]
Here, the surface temperature of the slab in front of the sensor is 900 ° C, the amount of water in the water cooling nozzle 5 is such that a cooling rate of -20 ° C / s can be obtained, and the moving speed of the slab is 2.4 mpm (40 mm / s) And Since the continuous cooling transformation diagram (CCT) of the material to be measured was as shown in FIG. 3, the transformation start temperature (curve a) at a cooling rate of −20 ° C./s is about 620 ° C. In order to obtain the magnetostriction effect described with reference to FIG. 4, the temperature may be lowered from the transformation start to be close to the transformation end temperature (curve b), so that the surface layer portion is set to 620 ° C. or lower. The lower the value, the greater the effect. Therefore, the temperature should be determined based on quality constraints so that there are no surface cracks. Here, if the temperature of the surface layer is cooled to 600 ° C., it may be reduced by 280 ° C. Therefore, the cooling zone length (the length for applying cooling water) was 280 ° C./20 (° C./s)*40 (mm / s) = 560 mm.
[0070]
Under the above conditions, when the S / N of the transmission signal is actually measured, compared to the case where electromagnetic waves are generated by Lorentz force without cooling, the electromagnetic waves are generated by magnetostriction by cooling and phase transformation. In this case, there was an S / N improvement effect of 10 dB.
[0071]
In addition, in consideration of the frequency of electromagnetic ultrasonic waves, the sensitivity can be further increased by cooling so that the phase transformation starts up to the penetration depth of the oscillating magnetic field.
[0072]
[S / N improvement by burst wave]
Next, the transmission signal was as follows.
[0073]
After transmission, the transmitted signal appears at a position delayed by the propagation time as shown in FIG. Therefore, the pulse width of the transmission signal may be made shorter than the propagation time so that the leakage of the transmission signal does not overlap the transmission signal. Here, the propagation time is determined from the slab thickness, slab temperature, and sound velocity. The speed of sound depends on the slab temperature and steel type, and is approximately 3000-0.65 T (m / s) in the case of carbon steel with transverse waves. That is, the lower the temperature, the slower the sound speed and the shorter the propagation time.
[0074]
Therefore, since the case where the temperature of the slab becomes the lowest at the measurement position to be applied is the case where the propagation time becomes the shortest, the propagation time at this time is the maximum number. Therefore, the pulse width of the transmission signal may be set in the vicinity of this value. Since the present invention is used to determine the solidification state of the slab, the lowest temperature of the slab can be considered to be about 1100 ° C. at the center temperature and about 1000 ° C. at the average temperature.
[0075]
The allowable range of the pulse width is determined as follows. Since S / N is almost proportional to the pulse width √, if the pulse width is shortened to about 1/2, the effect is reduced by nearly 6 dB. On the other hand, if it is too long, it will overlap with the transmitted signal, but the amplitude at both ends of the waveform will be somewhat smaller due to the characteristics of the sensor and amplifier, so that the pulse width can be allowed up to about 1.5 times the maximum value. For this reason, the range of the pulse width that produces the S / N improvement effect is preferably 50% or more and 150% or less of the maximum number, and the optimum range is preferably 80% or more and 120% or less.
[0076]
The table below shows the optimum pulse width of the transmission signal determined for slabs with thicknesses of 200mm, 250mm and 300mm. Here, the lowest temperature was set to 1000 ° C. as an average temperature, and the sound speed at that time was set to 2350 m / s.
[0077]
[Table 1]

[0078]
When the leak signal of the transmission signal is large, the reception amplifier may be saturated due to the leak signal, and there may be a dead zone for a while due to a so-called driving phenomenon. Therefore, if there is a drive-in, the pulse width may be set to a value obtained by subtracting the drive-in time from the value in the above table.
[0079]
In Table 1, when the slab thickness is 250mm, the pulse width is 100μs, and the frequency is 100kHz, the S / N of the transmitted signal is actually measured, and the S / N improvement of 12dB compared to the sin wave of 100kHz. There was an effect. Therefore, an S / N improvement effect of at least 6 dB can be obtained by setting the above pulse width range.
[0080]
[S / N improvement by averaging]
Next, the average number of synchronous addition averages was as follows.
[0081]
As the rate of change of propagation time due to temperature change during casting is larger, as shown in FIG. 6, there is a possibility that the transmission signal becomes smaller due to averaging. Therefore, as a result of repeating various experiments on the change rate of the propagation time, it was about 0.03 μs / s to 0.3 μs / s when the change rate became considerably large. Therefore, when this value is used as a parameter, the relationship between the average number of times and the amplitude of the transmitted signal is obtained based on the equation (2) in the case of an ultrasonic frequency of 100 kHz and a pulse repetition frequency of 100 Hz as shown in FIG. It was.
[0082]
According to the figure, when the rate of change of propagation time per unit time τ is the earliest 0.3 μs / s, if the average number of times is up to about 256, there is almost no decrease in the amplitude. The number is set to 256. Since the S / N improvement effect at this time is the average number of times as shown in the equation (4), 24 dB was obtained. The calculation of the maximum number is based on the fact that there is almost no decrease in amplitude if the decrease in transmitted signal intensity is around 1 dB. That is, the value of “the maximum number of average times 256 times when the propagation time change rate τ 0.3 μs / s” is a case where the transmission signal intensity decreases 1 dB. Even when the change rate τ of the propagation time takes another value, the maximum number of average times is calculated based on the same criteria.
[0083]
Further, since the S / N improvement effect is reduced when the average number is small, the effective range is preferably 16 times or more. In this case, there is an effect of +12 dB. On the other hand, if the average number is too large, the amplitude becomes small as shown in FIG. As the optimum range, 50% or more and 200% or less of the maximum number is appropriate.
[0084]
As is clear from equation (2), when changing the frequency of ultrasonic waves and the pulse repetition frequency, reading the FIG. 7 in terms of changing τ in proportion, the average number of times and transmission from FIG. The relationship of the signal amplitude can be obtained.
[0085]
Since the above effects are all independent as described above, an S / N improvement effect of 10 + 6 + 12 = 28 dB can be obtained by combining them all.
[0086]
Since the lift-off sensitivity characteristic of the electromagnetic ultrasonic sensor is about −4 dB / mm, 28/4 = + 7 mm can be widened.
[0087]
As described above, according to the method and apparatus for determining the solidification state of the slab according to the embodiment of the present invention, the lift-off can be sufficiently increased by improving the S / N. Can be installed in the continuous casting machine in a completely non-contact state with respect to the continuous cast slab, and the solidification state in the slab can be measured and judged accurately with high accuracy. Thereby, the crater end position can be detected continuously.
[0088]
In the present embodiment, the case where “S / N improvement by surface layer cooling”, “S / N improvement by burst wave” and “S / N improvement by addition averaging” are all combined has been described. In some cases, sensor non-contact can be realized without combining the two. Specifically, the lift-off improvement amount that can be measured completely in a non-contact manner is desirably +7 mm or more, more preferably +4 mm or more than the conventional technique (1 to 2 mm). Therefore, considering that the lift-off characteristic of the sensor is about −4 dB / mm, it is possible to make the sensor and the slab non-contact if there is an S / N improvement of 16 dB or more compared to the conventional technique.
[0089]
Therefore, “S / N improvement by surface cooling”, “S / N improvement by burst wave”, and “S / N improvement by addition averaging” can be variously combined within a range in which sensor non-contact can be realized. For example, in the combination of “S / N improvement by surface cooling” and “S / N improvement by burst wave”, an S / N improvement effect of 10 + 6 = 16 dB is obtained, and the lift-off sensitivity characteristic is about −4 dB / mm. / 4 = + 4mm Liftoff improvement is obtained. Similarly, “S / N improvement by surface cooling” and “S / N improvement by addition average”, “S / N improvement by burst wave” and “S / N improvement by addition average”, or averaging times 64 times Only by the above-described “S / N improvement by addition averaging”, lift-off improvements of about +5.5 mm, +4.5 mm, and +4.5 mm can be obtained, respectively.
[0090]
(Second Embodiment)
In this embodiment, the S / N improvement method described in the first embodiment is combined with a method for improving the performance of an electromagnetic ultrasonic sensor. This increases the lift-off until complete non-contact measurement is possible. That is, in this embodiment, the magnet 22 of the electromagnetic ultrasonic sensor in FIG. 2 is an electromagnet, and a pulsed current having a high peak value is used as the magnetizing current in order to increase the magnetizing force. In order to improve the S / N, the magnetizing current may be increased. However, it is difficult to increase the current with direct current because the electromagnet generates heat. On the other hand, by using the pulse magnetization current, it is possible to suppress the heat generation of the electromagnet and to form a strong magnetic field.
[0091]
FIG. 8 is a block diagram showing an example of a slab solidification state determination apparatus according to the second embodiment of the present invention. The same parts as those in FIG. Only the part is described.
[0092]
This slab solidification state determination device includes a pulse magnetization current generator 18 for using a pulse magnetization current, and is configured in the same manner as in the first embodiment.
[0093]
The pulse magnetization current generator 18 generates a pulse magnetization current in synchronization with the signal of the trigger signal generator 8. The duration of the pulse magnetizing current may be a time related to ultrasonic measurement, and is appropriately 200 μs or more, which is about twice or more the propagation time. At this level, since the time for the repetition period of the transmission pulse is about 1/50, the amount of heat generated by the magnetizing current is very small and a large current can flow.
[0094]
When a direct current is used, the magnetizing current is about 3 A, but when a pulsed magnetizing current is used, a peak value of 10 A is possible, and an S / N improvement of about 10 dB is obtained.
[0095]
As described above, according to the method and apparatus for determining the solidification state of the slab according to the embodiment of the present invention, the apparatus has the same configuration as that of the first embodiment, and transmits and receives electromagnetic ultrasonic waves by the pulse magnetization current. Since it did in this way, the effect similar to 1st Embodiment is acquired, and the sensitivity of an electromagnetic ultrasonic sensor can be raised. As a result, it is possible to more easily perform complete non-contact sensor installation, continuous solidification state measurement, and crater end position detection for a continuous cast slab.
[0096]
Therefore, in the case of the present embodiment, by combining the high performance method of the electromagnetic ultrasonic sensor, the S / N improvement methods include the above-described “S / N improvement by surface cooling”, “S / N by burst wave”. N improvement "or" S / N improvement by addition averaging "can be used alone. Specifically, "S / N improvement by surface cooling" only + 5mm, "S / N improvement by burst wave" only + 4mm, "S / N improvement by addition averaging" only + 5mm lift-off improvement Obtainable.
[0097]
Even when a direct current is used, the magnetizing current can be increased to about 10 A by using the method (1) and / or (2) below, which is the same as when the pulsed magnetizing current is used. High performance of the electromagnetic ultrasonic sensor can be achieved. As a result, as in the case of using the pulse magnetizing current, even when each S / N improvement method is used alone, it has a sufficient lift-off improvement effect. It is possible to perform solidification state measurement and crater end position detection.
(1) By increasing the thickness of the copper wire used for the electromagnet, the resistance of the copper wire is lowered and the heat generation when the magnetizing current is increased is reduced.
(2) Increase the cooling capacity by speeding up the circulation of cooling water or cooling oil used for cooling the electromagnet.
[0098]
However, in an actual continuous casting machine, in many cases, it is not possible to secure a space for performing the above (1) and (2). Therefore, it may be difficult to combine one of the above S / N improvement methods with the above-mentioned (1) and (2).
[0099]
(Third embodiment)
In the present embodiment, a method for manufacturing a continuous cast slab using the slab solidification determining method described in the first and second embodiments will be described.
[0100]
FIG. 9 is a view showing an example of the equipment configuration for explaining the method for producing a continuous cast slab according to the third embodiment of the present invention, and the same parts as those in FIGS. Description is omitted, and only different parts are described here.
[0101]
The continuous casting machine and the slab solidification determination device shown in the figure are configured in the same manner as in the first or second embodiment. Here, the electromagnetic ultrasonic sensors 3 and 4 are attached to the end of the continuous casting machine.
[0102]
A cutter 21 for cutting the slab is provided downstream of the sensors 3 and 4. Further, a casting mold 22 for holding molten steel is provided at the drawing start position of the continuous cast slab 1 far upstream, and a secondary cooling zone for cooling the slab 1 is provided immediately downstream from the casting mold 22. 23 is provided.
[0103]
Next, the manufacturing method of the continuous cast slab of this embodiment is demonstrated.
[0104]
First, when the transverse electromagnetic ultrasonic wave is transmitted, it is determined that the crater end 7a has not reached the end of the casting machine. Here, when the casting speed increases and the crater end 7a extends downstream and passes through the sensors 3 and 4, the transmission signal disappears, so that it is determined by the measurement by the sensors 3 and 4 that the crater end 7a has reached the same position. The
[0105]
At this time, since there is only a short distance to the cutter 21, the casting speed is lowered to a value close to zero. In this way, the slab solidifies faster, so the crater end 7a is directed upstream. Thereafter, when it is confirmed by the sensors 3 and 4 that a transmission signal has appeared, the casting speed is increased again to return to a normal operation. As described above, the casting speed can be kept high and high productivity can be obtained.
[0106]
If the propagation time immediately before the crater end passes through the sensor (hereinafter referred to as Δtc) is stored, the following manufacturing method is also possible. That is, as the crater end approaches the sensor, the slab temperature increases, so the propagation time increases. Therefore, the propagation time is continuously measured, and when the propagation time approaches Δtc, the casting speed is slightly reduced or the flow rate of the secondary cooling 23 is increased to cool the slab more. On the other hand, if the propagation time is away from Δtc, the casting speed is increased slightly, or the flow rate of the secondary cooling 23 is decreased to weaken the cooling of the slab. In this way, the casting speed can always be kept close to the maximum speed, and the productivity can be greatly increased.
[0107]
In addition, although the case where the sensors 3 and 4 were attached to the terminal of a casting machine was shown in the above embodiment, the sensors 3 and 4 are attached to the vicinity of a light pressure lower belt, and the crater end 7a is always located in a light pressure lower belt. In the case of such manufacture, it can be similarly carried out.
[0108]
Thus, according to the method for manufacturing a continuous cast slab according to the embodiment of the present invention, the measurement result from the slab solidification determining device of the first or second embodiment is used to determine the casting speed or Since the slab cooling is controlled, it is possible to increase the casting speed, to stably perform the light pressure production, and to improve the quality.
[0109]
In addition, this invention is not limited to said each embodiment, It can change variously in the range which does not deviate from the summary. In addition, the embodiments may be appropriately combined as much as possible, and in that case, the combined effect is obtained.
[0110]
For example, in each embodiment, the sensors 3 and 4 are arranged to face each other with the slab 1 interposed therebetween, and an incident signal from the sensor 3 is transmitted toward the front and back of the slab. However, in the present specification, the phrase “the signal is transmitted” includes the case where the signal is transmitted to a predetermined position inside the slab, reflected at the predetermined position, and returned to the incident surface. In this case, the reception transverse wave electromagnetic ultrasonic sensor 4 is arranged on the same surface side as the transmission transverse wave electromagnetic ultrasonic sensor 3 with respect to the cast piece. The present invention can also be realized by arranging the sensors 3 and 4 in this way.
[0111]
The method described in the embodiment is a program (software means) that can be executed by a computer (computer), for example, a magnetic disk (floppy disk, hard disk, etc.), an optical disk (CD-ROM, DVD, MO, etc.). It can also be stored in a recording medium such as a semiconductor memory (ROM, RAM, flash memory, etc.), or transmitted and distributed by a communication medium. The program stored on the medium side includes a setting program that configures software means (including not only the execution program but also a table and data structure) in the computer. A computer that implements this apparatus reads a program recorded on a recording medium, constructs software means by a setting program as the case may be, and executes the above-described processing by controlling the operation by this software means. The recording medium referred to in this specification is not limited to distribution, but includes a storage medium such as a magnetic disk or a semiconductor memory provided in a computer or a device connected via a network.
[0112]
【The invention's effect】
As described in detail above, according to the present invention, it is possible to provide a slab solidification state determination method capable of more accurately detecting the crater end position of a continuous cast slab by improving the S / N ratio. .
[0113]
Moreover, the solidification state determination method and apparatus of the slab which can detect the crater end position of a continuous cast slab without complete contact can be provided.
[0114]
Moreover, according to this invention, the manufacturing method of the continuous cast slab which can improve productivity or quality using the solidification state information of the continuous cast slab obtained by complete non-contact measurement can be provided. .
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing an example of a slab solidification state determining apparatus according to a first embodiment of the present invention.
FIG. 2 is a diagram showing a structural example of an electromagnetic ultrasonic sensor according to the first embodiment of the present invention.
FIG. 3 is a continuous cooling transformation diagram of a material to be measured according to the description of the present invention.
FIG. 4 is a diagram illustrating a generation mechanism of transverse electromagnetic ultrasonic waves according to the description of the present invention.
FIG. 5 is a diagram showing a relationship between a transmission signal and a propagation time according to the description of the present invention.
FIG. 6 is a diagram showing a relationship between a change in propagation time and an average process according to the description of the present invention.
FIG. 7 is a configuration diagram showing an example of a slab solidification state determination device according to the first embodiment of the present invention.
FIG. 8 is a configuration diagram showing an example of a slab solidification state determining apparatus according to a second embodiment of the present invention.
FIG. 9 is a diagram showing an example of equipment configuration for explaining a method for producing a continuous cast slab according to a third embodiment of the present invention.
FIG. 10 is a diagram showing an example of hot characteristics of electromagnetic ultrasonic waves according to the description of the prior art.
FIG. 11 is a block diagram showing a conventional technique.
FIG. 12 is a diagram showing temperature characteristics of magnetic flux density according to the description of the prior art.
[Explanation of symbols]
1 Continuous cast slab
2 Continuous casting roll
3 Transverse wave ultrasonic sensor for transmission
4 Receiving transverse wave ultrasonic sensor
5 Water cooling nozzle
6 Predetermined area
7 Unsolidified part
7a Crater end
8 Trigger signal generator
9 Transmission signal generator
10 Received signal amplifier
11 Evaluation Department
12 Synchronous averaging unit
13 Average number of times setting part
14 Burst wave generator
15 Power amplifier
16 Pulse width setting part
17 Correlation processing section
18 Pulse magnetizing current generator
19 coil
20 magnets
21 cutter
22 Mold
23 Secondary cooling zone

Claims (11)

A method for determining the solidification state of a continuous cast slab by transmitting a transverse wave of electromagnetic ultrasonic waves,
A cooling step of cooling the slab until a predetermined region of the surface layer portion of the slab is transformed from a γ phase to an α phase ;
A transmission step of transmitting a transverse wave ultrasonic wave as a transmission signal by a transverse wave electromagnetic ultrasonic sensor for a predetermined region of the slab cooled in the cooling step;
A reception step of receiving the transmission signal through which the transmission signal has passed through the slab by a receiving electromagnetic ultrasonic sensor for transverse waves;
And a determination step of determining a solidification state of the slab based on the received signal received in the reception step. The method for determining solidification of a slab according to claim 1 , wherein the electromagnetic ultrasonic sensor for transmission and the electromagnetic ultrasonic sensor for reception are in a non-contact state with the slab. A method for determining the solidification state of a continuous cast slab by transmitting a transverse wave of electromagnetic ultrasonic waves,
A cooling step of cooling the slab until a predetermined region of the surface layer portion of the slab is transformed from a γ phase to an α phase ;
Within the pulse width set in the range of 50% to 150% of the maximum number of times that the electromagnetic ultrasonic wave does not exceed the propagation time of passing through the slab, either frequency, amplitude or phase, or these A burst-like transmission signal modulated by any combination of the above is transmitted to a predetermined area of the slab cooled in the cooling step by a transmission electromagnetic ultrasonic sensor for transverse waves in a non-contact state with the slab. Sending step;
A reception step of receiving the transmission signal through which the transmission signal has passed through the slab by a receiving electromagnetic ultrasonic sensor for transverse waves in a non-contact state with the slab;
A determination step of performing a correlation operation on the reception signal received in the reception step using a reference signal having the same or similar waveform as the transmission signal and determining a solidification state of the slab. A method for determining the solidification of a slab. A method for determining the solidification state of a continuous cast slab by transmitting a transverse wave of electromagnetic ultrasonic waves,
A cooling step of cooling the slab until a predetermined region of the surface layer portion of the slab is transformed from a γ phase to an α phase ;
Transmission in which a transverse wave ultrasonic wave as a transmission signal is repeatedly transmitted in units of pulses to a predetermined region of the slab cooled in the cooling step by a transverse wave transmission electromagnetic ultrasonic sensor in a non-contact state with the slab. Steps,
A reception step of receiving the transmission signal through which the transmission signal has passed through the slab by a receiving electromagnetic ultrasonic sensor for transverse waves in a non-contact state with the slab;
While averaging the respective pulses in the received signal received in the reception step, the average number of additions is 16 times or more, and a time that the change in the signal propagation time does not cause a decrease in signal strength cancellation due to pulse addition. A slab solidification determination method, comprising: a signal processing for processing the number of pulses equal to or less than a width and determining a solidification state of the slab based on the signal processing result. A method for determining the solidification state of a continuous cast slab by transmitting a transverse wave of electromagnetic ultrasonic waves,
A cooling step of cooling the slab until a predetermined region of the surface layer portion of the slab is transformed from a γ phase to an α phase ;
Within the pulse width set in the range of 50% to 150% of the maximum number of times that the electromagnetic ultrasonic wave does not exceed the propagation time of passing through the slab, either frequency, amplitude or phase, or these A burst-like transmission signal modulated by an arbitrary combination of the above is transmitted in units of pulses by a transverse wave transmission electromagnetic ultrasonic sensor in a non-contact state with the slab with respect to a predetermined area of the slab cooled in the cooling step. Sending step to send repeatedly at
A reception step of receiving the transmission signal through which the transmission signal has passed through the slab by a receiving electromagnetic ultrasonic sensor for transverse waves in a non-contact state with the slab;
First signal processing for adding and averaging the pulses in the reception signal received in the reception step, and a second signal for performing correlation calculation on the reception signal using a reference signal having the same or similar waveform as the transmission signal The processing is executed in the order of the first and second signal processing or the order of the second and first signal processing, and the solidification state of the slab is determined based on the signal processing result, and the first A determination step in which the average number of additions in the signal processing is 16 times or more, and the number of pulses is equal to or less than the number of pulses corresponding to a time width such that a change in signal propagation time does not cause a decrease in signal intensity cancellation due to pulse addition. A method for determining solidification of a cast slab. 6. The solidification of a slab according to claim 4 or 5 , wherein the number of pulses corresponding to a time width that does not cause a decrease in signal intensity cancellation due to pulse addition is caused to be 256 times. Judgment method. 7. The transmission electromagnetic ultrasonic sensor and the reception electromagnetic ultrasonic sensor are installed at a distance of 4 mm or more from the slab, according to claim 2 . A method for determining the solidification of a slab. The transmission electromagnetic ultrasonic sensor and / or the reception electromagnetic ultrasonic sensor use an electromagnet for transmission and reception of electromagnetic ultrasonic waves, and a pulse that continues the excitation current of the electromagnet for a longer time than the measurement time required for solidification determination. The method for determining solidification of a slab according to any one of claims 1 to 7 , wherein the current is an electric current. A drawing step of drawing the continuous cast slab from the mold while solidifying the molten steel;
A solidification determination step for determining a solidification state inside the slab drawn in the drawing step by the solidification determination method for a slab according to any one of claims 1 to 8 ,
And a control step of controlling the casting speed or cooling of the slab based on the determination result in the solidification determining step. A device for determining the solidification state of a continuous cast slab by transmitting a transverse wave of electromagnetic ultrasonic waves,
A cooling means for cooling the slab until a predetermined region of a surface layer portion of the slab is transformed from a γ phase to an α phase ;
Transmission means for transmitting a transverse wave ultrasonic wave as a transmission signal by means of a transverse wave transmission electromagnetic ultrasonic sensor in a non-contact state with the slab for a predetermined region of the slab cooled by the cooling means;
Receiving means for receiving the transmission signal through which the transmission signal has passed through the slab by a receiving electromagnetic ultrasonic sensor for transverse waves in a non-contact state with the slab;
An apparatus for determining solidification of a slab, comprising: determination means for determining a solidification state of the slab based on a reception signal received by the receiving means. The transmission electromagnetic ultrasonic sensor and / or the reception electromagnetic ultrasonic sensor use an electromagnet for transmission and reception of electromagnetic ultrasonic waves, and a pulse that continues the excitation current of the electromagnet for a longer time than the measurement time required for solidification determination. The slab solidification determining device according to claim 10 , wherein the current is an electric current.

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