JP3591366B2

JP3591366B2 - Continuous pickling method and continuous pickling apparatus

Info

Publication number: JP3591366B2
Application number: JP10436699A
Authority: JP
Inventors: 孝一武内; 俊彦野中; 武雄片岡
Original assignee: Sumitomo Metal Industries Ltd
Current assignee: Nippon Steel Corp
Priority date: 1999-04-12
Filing date: 1999-04-12
Publication date: 2004-11-17
Anticipated expiration: 2019-04-12
Also published as: JP2000297390A

Description

【０００１】
【発明の属する技術分野】
本発明は、連続酸洗方法および連続酸洗装置に関し、より具体的には、例えば、熱間圧延を終了した鋼帯の表面に生成したスケールを除去するための連続酸洗方法および連続酸洗装置に関する。
【０００２】
【従来の技術】
周知のように、熱間圧延を行われた鋼帯の表面には、酸化物からなるスケールが生成される。このスケールは、一般的に、鋼帯を例えば塩酸等からなる酸洗液に連続的に浸漬させる酸洗を行われることによって、除去される。この酸洗は、通常、３槽〜５槽程度の酸洗槽を備える連続酸洗装置を用いて行われる。
【０００３】
図４は、４槽の酸洗槽２ａ〜２ｄを備える連続酸洗装置１を模式的に示す説明図である。同図に示すように、連続酸洗装置１の第１槽２ａ、第２槽２ｂ、第３槽２ｃおよび第４槽（最終槽）２ｄに、鋼帯３を順次連続的に通板させることにより、酸洗が行われる。各酸洗槽２ａ〜２ｄに収容される酸洗液は、鋼帯３との反応や鋼帯３による持ち出しにより、徐々に減少する。そのため、この連続酸洗装置１では、最終槽２ｄに酸液供給装置４から酸液を供給し、隣接する各酸洗槽２ａ〜２ｄの間に設けられた酸液輸送配管５ａ〜５ｃにより、酸洗液を下流側の酸洗槽から上流側に隣接する酸洗槽へ順次輸送する。そして、第１槽２ａからオーバーフローする酸洗液を、回収装置６に送って回収し、再利用する。
【０００４】
連続酸洗装置１では、酸洗液をこのように各酸洗槽２ａ〜２ｄ間で循環させるため、各酸洗槽２ａ〜２ｄに収容される酸洗液の酸濃度は異なる。例えば、最終槽２ｄでは１２％程度であり、第１槽２ａでは３％程度である。また、第２槽２ｂ、第３槽２ｃでは、最終槽２ｄと第１槽２ａとの中間の濃度となる。
【０００５】
この連続酸洗装置１では、最終槽２ｄへの酸液の供給量を決定するには、少なくとも最終槽２ｄに収容された酸洗液の酸濃度を測定する必要がある。しかし、これまでの酸濃度測定技術では、酸洗液の酸濃度を短時間で測定することはできなかった。例えば、公知の滴定式分析計を用いて最終槽２ｄに収容された酸洗液の酸濃度を測定すると、試薬導入からデータ出力までの１回のサンプリングに約１５分間を要してしまう。このため、最終槽２ｄへの酸液の供給が大幅に遅れてしまい、この間に過渡的に鋼帯に酸洗不良が発生してしまう。
【０００６】
そこで、酸洗液の酸濃度を短時間で測定できないことを補償するために、例えば、特開昭５７−１７４４７３号公報には、酸洗液の酸濃度を測定せずに鋼帯の寸法や材質等に基づいて酸液の供給量を演算により求める発明が、また特開平７−５４１７５号公報には、酸洗液の酸濃度を測定せずに酸洗の前後における鋼帯の板厚の測定値に基づいて酸液の供給量を演算により求める発明が、それぞれ提案されている。これらの従来の技術によれば、酸液を供給される酸洗槽（図４の連続酸洗装置１では最終槽２ｄ）に収容された酸洗液の酸濃度を、目標値に制御することができる。
【０００７】
【発明が解決しようとする課題】
しかし、これらの従来の技術では、酸液を供給される酸洗槽以外の酸洗槽に収容される酸洗液の酸濃度を高くすることができないため、連続酸洗装置１を備える酸洗工程の生産性を向上させること、つまり酸洗速度を向上させることができない。
【０００８】
すなわち、連続酸洗装置１の酸洗速度を向上するには、酸液を供給される最終槽２ｄへの酸液の供給量を増加して、各酸洗槽２ａ〜２ｄに収容される酸洗液の酸濃度を高める必要がある。しかし、最終槽２ｄの酸洗液の酸濃度が約１２％を越えると、酸洗液である塩酸の蒸気圧が高くなり、最終槽２ｄにおいて蒸発による塩酸の消費量が増加し、酸洗液に要するコストが著しく増加してしまう。このため、最終槽２ｄ以外の各酸洗槽２ａ〜２ｃに収容される酸洗液の酸濃度を高めることができず、酸洗速度を向上することができない。
【０００９】
本発明の目的は、酸液を供給される酸洗槽からの酸洗液の蒸発量をできるだけ抑制しながら、各酸洗槽に収容された酸洗液の酸濃度を高めて所望の値に近づけ、これにより、酸洗の生産性を向上することができる連続酸洗方法および連続酸洗装置を提供することである。また、本発明の目的は、このような連続酸洗方法および連続酸洗装置を、既存の連続酸洗設備をできるだけ改造することなく提供することである。
【００１０】
【課題を解決するための手段】
本発明は、連続酸洗装置を構成する複数の酸洗槽のうちの２以上の酸洗槽にそれぞれ収容された酸洗液の酸洗時における酸消費量の予測値を、酸洗時の酸洗条件に基づいて算出し、算出した予測値に基づいて２以上の酸洗槽それぞれへの酸液供給量を決定して酸液を供給し、酸液を供給された２以上の酸洗槽にそれぞれ収容される酸洗液の酸濃度を連続的に測定し、測定された酸濃度の連続的な測定値に基づいて、２以上の酸洗槽にそれぞれ収容された酸洗液の酸濃度が目標値に一致するように、２以上の酸洗槽への酸液供給量を制御することを特徴とする連続酸洗方法である。
【００１１】
この本発明にかかる連続酸洗方法では、（ｉ）２以上の酸洗槽が少なくとも最終酸洗槽を含むこと、（ｉｉ）連続酸洗装置が、下流側の酸洗槽に収容された酸洗液を上流側に隣接する酸洗槽へ順次オーバーフローさせる型の連続酸洗装置、または下流側の酸洗槽に収容された酸洗液を上流側に隣接する酸洗槽へ順次輸送する型の連続酸洗装置であること、（ｉｉｉ）酸濃度の連続的な測定値が、少なくとも、２以上の酸洗槽にそれぞれ設けられた酸洗液循環流路に配置された密度計からの連続的な出力値を用いて、測定されることが例示される。特に、この（ｉｉｉ）項の場合には、酸濃度の連続的な測定値が、酸洗槽または酸洗液循環流路に配置された温度計および導電率計それぞれからの連続的な出力値を用いて測定されることが、さらに例示される。
【００１２】
また、別の観点からは、本発明は、連続酸洗装置を構成する複数の酸洗槽のうちの２以上の酸洗槽と、２以上の酸洗槽へそれぞれ酸液を供給する酸液供給系と、２以上の酸洗槽にそれぞれ収容された酸洗液の酸濃度をそれぞれ連続的に測定する酸濃度連続測定装置と、２以上の酸洗槽にそれぞれ収容された酸洗液の酸洗時における酸消費量の予測値を、酸洗時の酸洗条件からそれぞれ算出し、算出した予測値に基づいて酸液供給量を決定して酸液供給系へ酸液供給信号を出力するとともに、酸液供給系から２以上の酸洗槽へ酸液が供給された後に酸濃度連続測定装置から出力される酸濃度の連続的な測定値に基づいて、２以上の酸洗槽にそれぞれ収容された酸洗液の酸濃度が目標値になるように、酸液供給系へ酸液供給信号を出力する制御装置とを組み合わせて備えることを特徴とする連続酸洗装置である。
【００１３】
この本発明にかかる連続酸洗装置では、（ｉｖ）２以上の酸洗槽が少なくとも最終酸洗槽を含むこと、（ｖ）連続酸洗装置が、下流側の酸洗槽に収容された酸洗液を上流側に隣接する酸洗槽へ順次オーバーフローさせる型の連続酸洗装置、または下流側の酸洗槽に収容された酸洗液を上流側に隣接する酸洗槽へ順次輸送する型の連続酸洗装置であること、（ｖｉ）酸濃度連続測定装置が、酸洗槽に接続され、酸洗槽から取り出された酸洗液の流路の一部に設けられた本体と、この本体の内部を流れる酸洗液の密度を測定する密度計と、流路または酸洗槽における酸洗液の温度を測定する温度計と、流路または酸洗槽における酸洗液の導電率を測定する導電率計と、密度、温度計および導電率計それぞれの測定結果に基づいて流路の一部を流れる酸洗液の酸濃度を演算する演算装置とを組み合わせて備えることが、いずれも例示される。
【００１４】
【発明の実施の形態】
以下、本発明にかかる連続酸洗方法および連続酸洗装置の実施の形態を、添付図面を参照しながら詳細に説明する。なお、以降の実施の形態の説明では、酸洗液が塩酸であるとともに、後述する図２に示す酸濃度連続測定装置１３を用いた場合を例にとる。
【００１５】
図１は、本実施形態の連続酸洗装置１０の構成を模式的に示す説明図である。同図に示すように、この連続酸洗装置１０は、酸洗槽１１ａ〜１１ｄと、酸液供給系１２と、酸濃度連続測定装置１３ｃ、１３ｄと、制御装置１４とを備える。以下、これらの構成要素について、順次説明する。
【００１６】
〔酸洗槽１１ａ〜１１ｄ〕
この連続酸洗装置１０は、４つの酸洗槽１１ａ〜１１ｄを有する。酸洗槽１１ａが第１槽であり、酸洗槽１１ｂが第２槽であり、酸洗槽１１ｃが第３槽であり、さらに酸洗槽１１ｄが最終槽である。
【００１７】
酸洗される鋼帯１５は、第１槽１１ａ、第２槽１１ｂ、第３槽１１ｃおよび最終槽１１ｄの順に、各酸洗槽１１ａ〜１１ｄに収容された酸洗液に浸漬される。そして、最終槽１１ｄを出た鋼帯１５は、次工程に送られる。
【００１８】
また、この連続酸洗装置１０では、下流側の酸洗槽に収容された酸洗液が上流側に隣接する酸洗槽へ順次オーバーフローする。すなわち、最終槽１１ｄに収容された酸洗液が第３槽１１ｃへオーバーフローし、第３槽１１ｃに収容された酸洗液が第２槽１１ｂへオーバーフローし、第２槽１１ｂに収容された酸洗液が第１槽１１ａへオーバーフローする。そして、第１槽１１ａからオーバーフローする酸洗液は、図示しない回収装置に送られて回収され、再利用される。
本実施形態の酸洗槽１１ａ〜１１ｄは、以上のように構成される。
【００１９】
〔酸液供給系１２〕
本実施形態の連続酸洗装置１０は、酸液供給系１２を有する。本実施形態の酸液供給系１２は、第３槽１１ｃに酸液を供給する第３槽酸液供給装置１２ｃと、最終槽１１ｄに酸液を供給する最終槽酸液供給装置１２ｄとにより構成される。第３槽酸液供給装置１２ｃおよび最終槽酸液供給装置１２ｄは、いずれも、電磁式のダイヤフラム弁１６を介して、図示しない酸液供給源に接続されている。第３槽酸液供給装置１２ｃおよび最終槽酸液供給装置１２ｄにそれぞれ設けられたダイヤフラム弁１６は、いずれも、後述する制御装置１４に接続されており、制御装置１４から出力される酸液供給信号によって弁の開度が制御される。これにより、第３槽酸液供給装置１２ｃから第３槽１１ｃへの酸液の供給量と、最終槽酸液供給装置１２ｄから最終槽１１ｄへの酸液の供給量とが、個別に制御される。
【００２０】
なお、本実施形態では第３槽１１ｃおよび最終槽１１ｄに酸液を供給するようにしているが、第２槽１１ｂやさらには第１槽１１ａにも、第３槽酸液供給装置１２ｃおよび最終槽酸液供給装置１２ｄと同様の酸液供給装置をそれぞれ設けて、酸液を個別に供給するようにしてもよい。
本実施形態の酸液供給系１２は、以上のように構成される。
【００２１】
〔酸濃度連続測定装置１３ｃ、１３ｄ〕
本実施形態では、第３槽１１ｃには酸濃度連続測定装置１３ｃが設けられるとともに、最終槽１１ｄには酸濃度連続測定装置１３ｄが設けられる。酸濃度連続測定装置１３ｃおよび酸濃度連続測定装置１３ｄは、同一のものであるため、以降の説明では酸濃度連続測定装置１３ｄを例にとって説明する。
【００２２】
図２は、本実施形態の酸濃度連続測定装置１３ｄの内部構造を示す説明図である。図２中の破線矢印は酸洗液の流れを示す。
図２に示すように、この酸濃度連続測定装置１３ｄは、ポンプ１７ｄにより最終槽１１ｄから圧送された酸洗液を連続的に一方向へ流すための循環流路１８ｄの一部を内蔵する筒状の酸濃度連続測定装置本体１９ｄと、循環流路１８ｄの一部を流れる酸洗液を連続的に測定する密度計２０ｄ、温度計２１ｄおよび導電率計２２ｄとを備える。
【００２３】
本実施形態における酸濃度連続測定装置本体１９ｄは、筒型状のものであってサンプルである酸洗液を最終槽１１ｄから連続的に流して最終槽１１ｄへ戻すことができる構造であればよく、特定の構造には限定されない。
【００２４】
酸濃度連続測定装置本体１９ｄの材質は、酸洗液に浸食されない程度の耐酸性を有するものであればよく、本実施形態ではポリプロピレン製とした。また、酸濃度連続測定装置本体１９ｄの内部に形成される循環流路１８ｄの一部は、できるだけエルボ等の流速低下部が少ないストレート状に形成してある。これにより、酸濃度連続測定装置本体１９ｄの内部において、酸洗液の流れが低下することによる詰まりの発生が可及的抑制される。
【００２５】
さらに、循環流路１８ｄの一部を流れる酸洗液の流速は、密度計２０ｄ、温度計２１ｄおよび導電率計２２ｄそれぞれの測定精度を維持するために、２ｍ／ｓｅｃ以下であることが望ましい。本実施形態の酸濃度連続測定装置１３ｄの酸濃度連続測定装置本体１９ｄの内部では、下方に位置する循環流路１８ｄが、排出用配管２３ｄと略同じ高さ位置に形成されている。これにより、ポンプ１７ｄにより圧送されてきた酸洗液は、図中の破線矢印で示すように、酸濃度連続測定装置本体１９ｄの内部における最底部付近において一旦滞留してから、排出用配管２３ｄへと導かれる。このため、本実施形態の酸濃度連続測定装置１９ｄでは、循環流路１８ｄを流れる酸洗液の流速を、密度計２０ｄ、温度計２１ｄおよび導電率計２２ｄの測定精度の観点から望ましい流速である２ｍ／ｓｅｃ以下に容易に設定・管理し、測定精度の向上を図ることができる。本実施形態では、酸洗液の流速が１ｍ／ｓｅｃになるように、酸濃度連続測定装置本体１９ｄの各部寸法を設定した。
【００２６】
また、本実施形態では、密度計２０ｄには、二つの検出部２０ｄ−１、２０ｄ−２を有する公知の差圧センサー方式の密度計を用いた。二つの検出部２０ｄ−１、２０ｄ−２は、所望の密度測定精度を確保するために、循環流路１８ｄの一部の形成方向に関する距離ｄ_１が少なくとも５００ｍｍとなるように離して、酸濃度連続測定装置本体１９ｄの長手方向略中央の胴部に設置される。
【００２７】
また、検出部２０ｄ−１、２０ｄ−２の設置部では、酸洗液の流通方向と直交する方向（図２における左右方向）に関する分流部の突出量ｄ_２を、できるだけ小さく設定してある。これにより、分流部における酸洗液の滞留が抑制され、酸洗液の詰まりが確実に防止される。
【００２８】
本実施形態では、温度計２１ｄには公知の白金抵抗体式の温度計を用いた。また、導電率計２２ｄにも公知の電磁誘導型の導電率計を用いた。温度計２１ｄおよび導電率計２２ｄは、ともに、循環流路１８ｄの一部の出側で測定を行うことができるように、酸濃度連続測定装置本体１９ｄの底部に設置される。
【００２９】
なお、本実施形態では、温度計２１ｄおよび導電率計２２ｄは、いずれも、酸濃度連続測定装置本体１９ｄに設けた。これは、温度計２１ｄおよび導電率計２２ｄをともに密度計２０ｄの近傍に配置することにより、測定誤差を可及的低減するためである。しかし、温度計２１ｄ、導電率計２２ｄは、必ずしも酸濃度連続測定装置本体１９ｄに配置する必要はない。温度計２１ｄ、導電率計２２ｄを、最終槽１１ｄの内部または、最終槽１１ｄと酸濃度連続測定装置本体１９ｄとの間の循環流路１８ｄを構成する配管等に設置して、循環する酸洗液の温度、導電率を測定することとしてもよい。この場合、密度計２０ｄの設置部近傍における温度、導電率の値と、温度計２１ｄ、導電率計２２ｄの設置部における測定データとの偏差を予め求めておき、これらの偏差を用いて温度計２１ｄ、導電率計２２ｄの設置部における測定データを補正すればよい。これにより、温度計２１ｄおよび導電率計２２ｄを密度計２０ｄの近傍に配置しなくとも、測定誤差が可及的低減される。
【００３０】
この酸濃度連続測定装置１３ｄは、本実施形態では、最終槽１１ｄの外壁面近傍に設置される。そして、酸濃度連続測定装置１３ｄは、最終槽１１ｄの近傍に設置したポンプ１７ｄにより最終槽１１ｄに収容された酸洗液を一方向へ流す。これにより、酸濃度連続測定装置１３ｄは、連続的に酸洗液の密度、温度および導電率をいずれも測定することが可能である。
【００３１】
このように、本実施形態の酸濃度連続測定装置１３ｄで用いる密度計２０ｄ、温度計２１ｄおよび導電率計２２ｄには、いずれも、高い使用実績を有する公知の工業計器を使用する。このため、本実施形態の酸濃度連続測定装置１３ｄは、極めて高い精度で正確に、酸洗液の密度、温度および導電率を求めることができる。
【００３２】
また、本実施形態の酸濃度連続測定装置１３ｄの近傍には、密度計２０ｄにより連続的に測定された密度と、温度計２１ｄにより連続的に測定された温度と、導電率計２２ｄにより連続的に測定された導電率とに基づいて、酸洗液の酸濃度を演算する演算装置（図示しない）が設置される。この演算装置により酸洗液の酸濃度が連続的に演算される。この演算装置による演算結果は、後述する制御装置１４へ入力される。
【００３３】
なお、本実施形態の酸濃度連続測定装置１３ｄによる「連続的な測定」とは、例えば公知の滴定式分析計を用いた場合の測定ピッチ（約１５分間）に比べて極めて短い測定ピッチでの測定を意味しており、例えば、測定ピッチが１分間以下、望ましくは１０秒間以下である酸濃度測定を意味する。
【００３４】
また、本実施形態の酸濃度連続測定装置１３ｄでは、酸濃度連続測定装置本体１９ｄを筒型状単管式とする。このため、以下に列記する効果（ｉ）〜（ｖｉｉ）が奏せられる。
【００３５】
（ｉ）循環流路１８ｄの形状をできるだけ直線状とするとともに、距離ｄ_２をできるだけ小さく設定する。このため、循環流路１８ｄ内、特に密度計２０ｄ、温度計２１ｄおよび導電率計２２ｄそれぞれの近傍における酸洗液の滞留が防止され、酸洗液を連続的に流すことができる。
【００３６】
（ｉｉ）酸洗液は、循環流路１８ｄ内を連続的に流れる。このため、循環流路１８ｄ内における酸洗液の偏析が防止され、別々に採取した複数種の酸洗液をも同一条件で正確に測定することができる。
【００３７】
（ｉｉｉ）ポンプ１７ｄにより酸洗液を常時流すため、酸濃度連続測定装置本体１９ｄのメンテナンス性および内部洗浄性がいずれも著しく向上し、酸洗液の詰まりを解消しながら連続測定を行うことができる。
【００３８】
（ｉｖ）酸洗液の密度、温度および導電率を連続的に測定するため、酸洗液の酸濃度を連続的に測定することができる。これにより、この酸濃度連続測定装置１３ｄを、例えば連続酸洗設備の最終酸洗槽の酸濃度に関するフィードバック制御、または、フィードバック制御およびフィードフォワード制御と組合せることにより、最終酸洗槽の酸濃度を連続的かつ高精度で自動制御することも可能となる。
【００３９】
（ｖ）酸濃度連続測定装置１３ｄは、図１および図２に示すように、極めて簡単な外部形状を有する。このため、例えば連続酸洗設備等への設置の自由度が高い。
【００４０】
（ｖｉ）酸濃度連続測定装置１３ｄの内部は、図２に示すように、簡単な内部構造を有する。このため、循環流路１８ｄを流れる酸洗液の流速を、密度計２０ｄ、温度計２１ｄおよび導電率計２２ｄの測定精度の観点から望ましい流速である２ｍ／ｓｅｃ以下に、容易に設定・管理することができる。したがって、酸濃度連続測定装置１３ｄは、測定精度の維持が容易である。
【００４１】
（ｖｉｉ）酸濃度連続測定装置１３ｄは簡単な構造であるため、酸洗槽の近傍に容易に設置することができる。このため、酸洗槽から酸洗液を分流させる循環流路１８ｄを構成する配管の長さを可及的短くすることができる。これにより、酸洗液が酸洗槽を出てから酸濃度連続測定装置１３ｄに到達して測定されるまでの間のタイムロスを可及的短縮することができる。このため、酸濃度連続測定装置１３ｄは、制御精度の低下を抑制できる。
【００４２】
なお、本実施形態では、第３槽１１ｃおよび最終槽１１ｄにそれぞれ酸濃度連続測定装置１３ｃ、１３ｄを設けたが、図１に図示するように、第２槽１１ｂにも酸濃度連続測定装置１３ｂを設け、さらに必要に応じて第１槽１１ａにも酸濃度連続測定装置１３ａを設け、これらの出力値も制御装置１４に入力するように構成してもよい。
本実施形態の酸濃度連続測定装置１３ｃ、１３ｄは、以上のように構成される。
【００４３】
〔制御装置１４〕
本実施形態の連続酸洗装置１０は、制御装置１４を有する。
この制御装置１４は、第３槽１１ｃに収容された酸洗液の酸洗時における酸消費量と、最終槽１１ｄに収容された酸洗液の酸洗時における酸消費量とを、いずれも、近似式を用いて算出する。第３槽１１ｃおよび最終槽１１ｄそれぞれにおける酸消費量の予測計算は、酸洗ライン制御装置２４から入力される、鋼帯１５の材質や寸法、通板速度、酸液組成、酸液温度さらには各槽の寸法等といった酸洗時の酸洗条件に基づいて行われるが、特定の手段には限定されない。公知の手段により予測計算を行えばよい。
【００４４】
例えば、単位面積当たりの減少量（本明細書では「酸洗減量値」という。）を時間に対して１次式を用いて近似する場合、酸洗時間と酸洗減量値との関係は比例関係になる。図３は、この関係の一例を示すグラフである。
【００４５】
図３にグラフで示すように、酸洗時間と酸洗減量値との関係は、原点Ｏを起点とする直線関係となる。すなわち、第１槽１１ａを通過する時刻ｔ_１における酸洗減量値ｍ_１、第２槽１１ｂを通過する時刻ｔ_２における酸洗減量値ｍ_２、第３槽１１ｃを通過する時刻ｔ_３における酸洗減量値ｍ_３、および最終槽１１ｄを通過する時刻ｔ_４における酸洗減量値ｍ_４は、いずれも、同一の直線上に位置し、酸洗が完了した時刻ｔ_４以降は酸洗減量値が一定となる。この直線の傾きが酸洗速度を示し、酸洗される鋼帯１５の材質や、酸洗条件（酸洗液の温度や組成等）により規定される。
【００４６】
したがって、各酸洗槽１１ａ〜１１ｄにおける酸消費量は、各酸洗槽１１ａ〜１１ｄそれぞれを通過するのに要した時間と、図３のグラフの直線の傾きと、鋼帯１５の寸法（幅）とを掛け合わせた値として、求められる。このようにして、各酸洗槽１１ａ〜１１ｄそれぞれにおける酸洗液の消費量を算出することができる。なお、本実施形態のように、酸洗時間と酸洗減量値との関係を直線で近似するのではなく、図３に一点鎖線で示すように、実際の酸洗曲線に近いＳ字状曲線により近似すれば、より高精度に各酸洗槽１１ａ〜１１ｄにおける酸消費量を算出することができる。
【００４７】
また、制御装置１４は、このようにして算出した第３槽１１ｃおよび最終槽１１ｄそれぞれにおける酸消費量の予測値に基づいて、第３槽１１ｃおよび最終槽１１ｄそれぞれへの酸液供給量を決定する。そして、制御装置１４は、酸液供給系１２のダイヤフラム弁１６へ酸液供給信号を出力して、必要供給量の酸液を、第３槽１１ｃおよび最終槽１１ｄそれぞれへ供給する。
【００４８】
さらに、制御装置１４は、第３槽酸液供給装置１２ｃから第３槽１１ｃへ酸液を供給するとともに最終槽酸液供給装置１２ｄから最終槽１１ｄへ酸液を供給した後に、酸濃度連続測定装置１３ｃ、１３ｄから出力される酸濃度の連続的な測定値に基づいて、酸液供給系１２へ酸液供給信号を再度出力して、第３槽１１ｃおよび最終槽１１ｄにそれぞれ収容された酸洗液の酸濃度が目標値に一致するように、微調整する。
【００４９】
本実施形態の制御装置１４は、以上のように構成される。
次に、４つの酸洗槽１１ａ〜１１ｄと、酸液供給系１２と、酸濃度連続測定装置１３ｃ、１３ｄと、制御装置１４とを備える本実施形態の連続酸洗装置１０により、鋼帯１５に酸洗を行う状況を経時的に説明する。
【００５０】
〔酸消費量の予測計算〕
図１に示す連続酸洗装置１０により、鋼帯１５に酸洗が行われている。
ここで、制御装置１４により、第３槽１１ｃおよび最終槽１１ｄにそれぞれ収容された酸洗液の酸消費量の予測値が、酸洗ライン制御装置２４から入力される前述した酸洗条件に基づいて、算出される。
【００５１】
ここで、予測計算の種類にかかわらず、この算出値には、必ず実際の酸消費量に対する誤差が存在する。そこで、本実施形態では、後述するように、酸濃度の連続的な測定値を用いて酸液の供給量を制御することにより、この誤差を可及的に低減する。
【００５２】
〔算出値に基づく酸液の供給〕
次に、制御装置１４により、このようにして予測した第３槽１１ｃおよび最終槽１１ｄにそれぞれ収容された酸洗液の酸消費量に基づいて、第３槽１１ｃおよび最終槽１１ｄそれぞれへの酸液供給量が決定される。
【００５３】
そして、制御装置１４から、第３槽酸液供給系１２ｃおよび最終槽酸液供給系１２ｄそれぞれのダイヤフラム弁１６、１６へ酸液供給信号が出力され、第３槽１１ｃおよび最終槽１１ｄそれぞれへ、決定された供給量の酸液が供給される。
【００５４】
〔酸濃度の連続測定〕
このようにして、第３槽１１ｃおよび最終槽１１ｄそれぞれへ、決定された供給量の酸液が供給された後に、酸濃度連続測定装置１３ｃにより第３槽１１ｃに収容された酸洗液の酸濃度が連続的に測定されるとともに、酸濃度連続測定装置１３ｄにより最終槽１１ｄに収容された酸洗液の酸濃度が連続的に測定される。これらの連続的な測定値は、制御装置１４に送られる。
【００５５】
〔連続測定結果に基づく酸液の供給〕
制御装置１４では、これらの連続的な測定値と、第３槽１１ｃおよび最終槽１１ｄにそれぞれ収容された酸洗液の酸濃度の目標値との偏差が求められる。そして、この偏差が零になるように、制御装置１４から第３槽酸液供給系１２ｃおよび最終槽酸液供給系１２ｄそれぞれのダイヤフラム弁１６、１６へ酸液供給信号が出力され、第３槽１１ｃおよび最終槽１１ｄそれぞれに対する酸液の供給量が制御される。
【００５６】
これにより、第３槽１１ｃおよび最終槽１１ｄそれぞれへの酸液供給量の予測計算結果が有する誤差が補正され、第３槽１１ｃおよび最終槽１１ｄのみならず、第２槽１１ｂに収容された酸洗液の酸濃度を、目標値に迅速かつ正確に近づけることができる。
【００５７】
本実施形態において、最終槽１１ｄだけでなく第３槽１１ｃにも酸液を供給するのは、このように、第３槽１１ｃや第２槽１１ｂにそれぞれ収容された酸洗液の酸濃度を高め、目標値に近づけるためである。したがって、第４槽が最終槽１１ｄとなる本実施形態では、最終槽１１ｄおよび第３槽１１ｃに酸液を供給したが、例えば第５槽が最終槽となる連続酸洗装置の場合には、最終槽および第３槽それぞれに酸液を供給することが望ましい。
【００５８】
本実施形態では、連続測定結果に基づく酸液の供給を、最終槽１１ｄだけでなく第３槽１１ｃに対しても行うため、最終槽１１ｄに収容された酸洗液の酸濃度を１２％超に上昇させることなく、第３槽１１ｃに収容された酸洗液の酸濃度を高めて目標値に近づけることができる。このため、最終槽１１ｄからの酸洗液の蒸発を防止しながら、第３槽１１ｃに収容された酸洗液の酸濃度を高めて目標値に近づけることができる。このため、各酸洗槽１１ａ〜１１ｄそれぞれの酸洗能力をいずれも充分に発揮させて、鋼帯１５の酸洗を行うことができる。したがって、本実施形態によれば、連続酸洗装置１０の全体の生産性を向上することができる。
【００５９】
また、本実施形態は、既存の連続酸洗装置の第３槽１１ｃおよび最終槽１１ｄの近傍に酸濃度連続測定装置１３ｃ、１３ｄを設け、これらの酸濃度連続測定装置１３ｃ、１３ｄからの出力信号を制御装置１４へ送るとともに、制御装置１４のソフトを一部変更するだけで、実施することができる。このため、既存の連続酸洗設備をできるだけ改造せずに実施できる。
このように、本実施形態によれば、従来の生産設備を大幅に改良することなく、不良率の低減と生産性の向上とをともに図ることができる。
【００６０】
【実施例】
さらに、本発明を実施例を参照しながら、より具体的に説明する。
図１に示す連続酸洗装置１（各酸洗槽１３ａ〜１３ｄの容量：５０ｍ^３、酸洗液の温度：９０℃）を用い、本発明にかかる連続酸洗方法と、比較例の連続酸洗方法とを用いて、鋼帯１５の酸洗を１ヵ月間行った。なお、この型の連続酸洗装置を用いた酸洗では、通常、本実施例における操業期間の１ヵ月間に、操業条件の様々な変動が殆ど全て発生するため、本発明の有用性を評価するには充分な期間である。
【００６１】
本発明例は、制御装置１４により、鋼帯１５の材質および酸洗条件（酸洗液の温度および酸濃度）を用い、鋼種毎に予め求めた１次近似式に基づいて、第３槽１１ｃおよび最終槽１１ｄそれぞれに収容された酸洗液の消費量を予測計算し、この結果により第３槽１１ｃおよび最終槽１１ｄそれぞれに給酸を行うとともに、この給酸後に、酸濃度連続測定装置１３ｃ、１３ｄからの連続測定値に基づいて、第３槽１１ｃおよび最終槽１１ｄそれぞれに収容された酸洗液の酸濃度がいずれも１２±０．５％になるように、第３槽酸液供給系１２ｃおよび最終槽酸液供給系１２ｄそれぞれのダイヤフラム弁１６、１６を、いずれもオン／オフ制御した。
【００６２】
一方、比較例は、最終槽１１ｄのみに給酸を行い、給酸によりオーバーフローした酸液を第３槽１１ｃ、第２槽１１ｂへ順次輸送し、第１槽１１ｃから廃酸を行うとともに、最終槽１１ｄに収容された酸洗液の酸濃度が１２±０．５％になるように、最終槽酸液供給系１２ｄのダイヤフラム弁１６を、オン／オフ制御した。
【００６３】
なお、本発明例および比較例ともに、オペレータの判断により脱スケール不良が発生しない程度に通板速度を高めて、酸洗を行った。
そして、第２槽１１ｂ〜最終槽１１ｄにそれぞれ収容された酸洗液の酸濃度の変化幅と、脱スケール不良発生率および生産性を測定した。結果を表１にまとめて示す。
【００６４】
【表１】

【００６５】
表１から明らかなように、本発明例により、各酸洗槽１１ａ〜１１ｄにそれぞれ収容された酸洗液の酸濃度が、目標値を超えない範囲で高まるとともに安定化した。これにより、脱スケール不良発生率が大幅に低減され、かつ生産性も顕著に向上した。
【００６６】
（変形形態）
実施形態および実施例の説明では、４槽の酸洗槽を備える連続酸洗装置を用いた。しかし、本発明は、この形態には限定されず、複数の酸洗槽を備える連続酸洗装置に対して同様に適用される。
【００６７】
また、実施形態および実施例の説明では、第３槽および最終槽に収容された酸洗液の酸消費量を予測し、これらの酸洗槽に酸液を供給する場合を例にとった。しかし、本発明は、この形態には限定されず、第３槽および最終槽以外の他の酸洗槽に収容された酸洗液の酸消費量も予測し、これらの酸洗槽にも酸液を供給するようにしてもよい。これにより、各酸洗槽に収容された酸洗液の酸濃度を、さらに高精度で制御することができる。
【００６８】
また、実施形態および実施例の説明では、図２に示す酸濃度連続測定装置を用いた場合を例にとった。しかし、これはあくまでも酸濃度連続測定装置の例示であり、本発明は図２に示す酸濃度連続測定装置には限定されない。本発明は、図２に示す酸濃度連続測定装置以外でも、酸洗槽にそれぞれ収容された酸洗液の酸濃度を連続的に測定することができる酸濃度連続測定装置であれば、同様に適用することができる。
【００６９】
また、実施形態および実施例の説明では、少なくとも最終槽に酸液を供給される連続酸洗装置を用いた。しかし、本発明は、この形態には限定されず、最終槽には酸液を供給されない連続酸洗装置にも対しても、同様に適用される。
【００７０】
また、実施形態および実施例の説明では、下流側の酸洗槽に収容された酸洗液を上流側に隣接する酸洗槽へ順次オーバーフローさせる型の連続酸洗装置を用いた。しかし、本発明は、この形態には限定されず、複数の酸洗槽を有する連続酸洗装置であれば同様に適用される。例えば、図４に示すように、下流側の酸洗槽に収容された酸洗液を上流側に隣接する酸洗槽へ順次輸送する型の連続酸洗装置に対しても、同様に適用される。
【００７１】
さらに、実施形態および実施例の説明では、酸液が塩酸である場合を例にとった。しかし、本発明は、この形態には限定されず、例えば硫酸等の、鋼板に酸洗処理を行うことはできる酸液であれば、等しく適用される。
【００７２】
【発明の効果】
以上詳細に説明したように、本発明により、各酸洗槽からの酸洗液の蒸発量をできるだけ抑制しながら、各酸洗槽に収容された酸洗液の酸濃度を、いずれも高めて目標値に近づけることができ、これにより、酸洗の生産性を向上することができる連続酸洗方法および連続酸洗装置を、既存の連続酸洗設備をできるだけ改造せずに、提供できることになった。
かかる効果を有する本発明の意義は、極めて著しい。
【図面の簡単な説明】
【図１】実施形態の連続酸洗装置の構成を模式的に示す説明図である。
【図２】実施形態の酸濃度連続測定装置の内部構造を示す説明図である。
【図３】酸洗時間と酸洗減量値との関係の一例を示すグラフである。
【図４】４槽の酸洗槽を備える従来の連続酸洗装置を模式的に示す説明図である。
【符号の説明】
１０連続酸洗装置
１１ｃ第３槽
１１ｄ最終槽
１２酸液供給系
１３ｃ、１３ｄ酸濃度連続測定装置
１４制御装置[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a continuous pickling method and a continuous pickling apparatus, and more specifically, for example, a continuous pickling method and a continuous pickling method for removing scale generated on the surface of a steel strip after hot rolling. Equipment related.
[0002]
[Prior art]
As is well known, oxide scale is generated on the surface of the hot-rolled steel strip. This scale is generally removed by performing pickling in which the steel strip is continuously immersed in a pickling solution such as hydrochloric acid. This pickling is usually performed using a continuous pickling apparatus provided with about 3 to 5 pickling tanks.
[0003]
FIG. 4 is an explanatory view schematically showing a continuous pickling apparatus 1 including four pickling tanks 2a to 2d. As shown in the figure, the steel strip 3 is sequentially and continuously passed through the first tank 2a, the second tank 2b, the third tank 2c, and the fourth tank (final tank) 2d of the continuous pickling apparatus 1. With this, pickling is performed. The pickling liquid contained in each of the pickling tanks 2a to 2d gradually decreases due to the reaction with the steel strip 3 and the removal by the steel strip 3. Therefore, in the continuous pickling apparatus 1, an acid solution is supplied from the acid solution supply device 4 to the final tank 2d, and the acid solution transport pipes 5a to 5c provided between the adjacent pickling tanks 2a to 2d are used. The pickling liquid is sequentially transported from the pickling tank on the downstream side to the pickling tank adjacent on the upstream side. Then, the pickling liquid overflowing from the first tank 2a is sent to the collecting device 6 to be collected and reused.
[0004]
In the continuous pickling apparatus 1, since the pickling liquid is circulated between the pickling tanks 2a to 2d in this manner, the acid concentrations of the pickling liquids contained in the pickling tanks 2a to 2d are different. For example, it is about 12% in the last tank 2d and about 3% in the first tank 2a. In the second tank 2b and the third tank 2c, the concentration is intermediate between the final tank 2d and the first tank 2a.
[0005]
In the continuous pickling apparatus 1, in order to determine the supply amount of the acid solution to the final tank 2d, it is necessary to measure at least the acid concentration of the pickling liquid contained in the final tank 2d. However, the conventional acid concentration measurement technique cannot measure the acid concentration of the pickling solution in a short time. For example, when the acid concentration of the pickling solution contained in the final tank 2d is measured using a known titration analyzer, one sampling from the introduction of the reagent to the output of the data requires about 15 minutes. For this reason, the supply of the acid solution to the final tank 2d is greatly delayed, and during this time, the pickling failure occurs transiently in the steel strip.
[0006]
Therefore, in order to compensate for the inability to measure the acid concentration of the pickling solution in a short time, for example, Japanese Patent Application Laid-Open No. 57-174473 discloses a method for measuring the dimensions of a steel strip without measuring the acid concentration of the pickling solution. Japanese Patent Application Laid-Open No. 7-54175 discloses an invention for calculating the supply amount of an acid solution based on a material or the like, and discloses a method of measuring the thickness of a steel strip before and after pickling without measuring the acid concentration of the pickling solution. Inventions for calculating the supply amount of the acid solution based on the measured value by calculation have been proposed. According to these conventional techniques, the acid concentration of the pickling liquid contained in the pickling tank (the last tank 2d in the continuous pickling apparatus 1 in FIG. 4) to which the acid liquid is supplied is controlled to a target value. Can be.
[0007]
[Problems to be solved by the invention]
However, according to these conventional techniques, it is impossible to increase the acid concentration of the pickling solution contained in the pickling tank other than the pickling tank to which the acid solution is supplied. It is not possible to improve the productivity of the process, that is, to improve the pickling speed.
[0008]
That is, in order to improve the pickling speed of the continuous pickling apparatus 1, the supply amount of the acid solution to the final tank 2d to which the acid solution is supplied is increased, and the acid stored in each of the pickling tanks 2a to 2d is increased. It is necessary to increase the acid concentration of the washing solution. However, when the acid concentration of the pickling liquid in the final tank 2d exceeds about 12%, the vapor pressure of the hydrochloric acid as the pickling liquid increases, and the consumption of hydrochloric acid by evaporation in the final tank 2d increases. Cost increases significantly. For this reason, the acid concentration of the pickling liquid contained in each of the pickling tanks 2a to 2c other than the final tank 2d cannot be increased, and the pickling speed cannot be improved.
[0009]
An object of the present invention is to increase the acid concentration of the pickling liquid contained in each pickling tank to a desired value while minimizing the amount of evaporation of the pickling liquid from the pickling tank supplied with the acid liquid. It is an object of the present invention to provide a continuous pickling method and a continuous pickling apparatus that can improve the productivity of pickling. It is another object of the present invention to provide such a continuous pickling method and a continuous pickling apparatus without modifying existing continuous pickling equipment as much as possible.
[0010]
[Means for Solving the Problems]
The present invention is a method for pickling a pickling solution contained in at least two pickling tanks among a plurality of pickling tanks constituting a continuous pickling apparatus, the estimated value of acid consumption during pickling. An acid solution is supplied to each of the two or more pickling tanks based on the calculated predicted values, and the acid solution is supplied. The acid concentration of the pickling liquid stored in each of the pickling tanks is continuously measured, and the acid of the pickling liquid stored in each of the two or more pickling tanks is continuously measured based on the continuously measured acid concentration. A continuous pickling method characterized by controlling the supply amount of an acid solution to two or more pickling tanks so that the concentration matches a target value.
[0011]
In the continuous pickling method according to the present invention, (i) the two or more pickling tanks include at least a final pickling tank, and (ii) the continuous pickling apparatus includes the pickling tank accommodated in the downstream pickling tank. A continuous pickling apparatus of the type in which the washing liquid overflows sequentially to the pickling tank adjacent to the upstream side, or a type in which the pickling liquid contained in the downstream pickling tank is sequentially transported to the pickling tank adjacent to the upstream side. (Iii) a continuous measurement value of the acid concentration is at least continuously measured from a densitometer arranged in a pickling liquid circulation channel provided in each of two or more pickling tanks. It is exemplified that measurement is performed using a typical output value. In particular, in the case of this item (iii), the continuous measurement value of the acid concentration is obtained by the continuous output value from each of the thermometer and the conductivity meter arranged in the pickling tank or the pickling liquid circulation channel. It is further exemplified that is measured using
[0012]
Further, from another viewpoint, the present invention relates to an acid solution for supplying an acid solution to two or more pickling tanks among a plurality of pickling tanks constituting a continuous pickling apparatus, and supplying an acid solution to each of the two or more pickling tanks. A supply system, an acid concentration continuous measuring device for continuously measuring the acid concentration of each of the pickling liquids contained in the two or more pickling tanks, and the pickling liquids contained in the two or more pickling tanks. Predicted values of acid consumption during pickling are calculated from the pickling conditions during pickling, and the acid solution supply amount is determined based on the calculated predicted values and an acid solution supply signal is output to the acid solution supply system. The acid solution is supplied from the acid solution supply system to the two or more pickling tanks, and then the acid solution is continuously supplied to the two or more pickling tanks. A control device that outputs an acid solution supply signal to the acid solution supply system so that the acid concentration of the pickled solution contained therein becomes a target value. A continuous pickling apparatus, characterized in that it comprises a combination of and.
[0013]
In the continuous pickling apparatus according to the present invention, (iv) the two or more pickling tanks include at least a final pickling tank, and (v) the continuous pickling apparatus includes the pickling tank accommodated in the downstream pickling tank. A continuous pickling apparatus of the type in which the washing liquid overflows sequentially to the pickling tank adjacent to the upstream side, or a type in which the pickling liquid contained in the downstream pickling tank is sequentially transported to the pickling tank adjacent to the upstream side. (Vi) a device for continuously measuring an acid concentration, which is connected to a pickling tank and provided in a part of a flow path of a pickling solution taken out of the pickling tank; A density meter for measuring the density of the pickling liquid flowing inside the main body, a thermometer for measuring the temperature of the pickling liquid in the flow path or the pickling tank, and a conductivity meter for the pickling liquid in the flow path or the pickling tank. Flow through a part of the flow channel based on the measurement result of the conductivity meter to be measured and the density, thermometer and conductivity meter. Both examples are provided in combination with a calculation device for calculating the acid concentration of the pickling solution.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of a continuous pickling method and a continuous pickling apparatus according to the present invention will be described in detail with reference to the accompanying drawings. In the following description of the embodiment, an example is given in which the pickling solution is hydrochloric acid and an acid concentration continuous measurement device 13 shown in FIG. 2 described later is used.
[0015]
FIG. 1 is an explanatory diagram schematically showing a configuration of a continuous pickling apparatus 10 of the present embodiment. As shown in FIG. 1, the continuous pickling apparatus 10 includes pickling tanks 11a to 11d, an acid solution supply system 12, continuous acid concentration measuring devices 13c and 13d, and a control device 14. Hereinafter, these components will be sequentially described.
[0016]
[Pickling tanks 11a to 11d]
This continuous pickling apparatus 10 has four pickling tanks 11a to 11d. The pickling tank 11a is a first tank, the pickling tank 11b is a second tank, the pickling tank 11c is a third tank, and the pickling tank 11d is a final tank.
[0017]
The steel strip 15 to be pickled is immersed in a pickling solution contained in each of the pickling tanks 11a to 11d in the order of the first tank 11a, the second tank 11b, the third tank 11c, and the final tank 11d. Then, the steel strip 15 that has left the final tank 11d is sent to the next step.
[0018]
In the continuous pickling apparatus 10, the pickling liquid contained in the pickling tank on the downstream side sequentially overflows to the pickling tank adjacent on the upstream side. That is, the pickling liquid stored in the final tank 11d overflows to the third tank 11c, the pickling liquid stored in the third tank 11c overflows to the second tank 11b, and the acid stored in the second tank 11b. The washing liquid overflows to the first tank 11a. Then, the pickling liquid overflowing from the first tank 11a is sent to a collecting device (not shown) to be collected and reused.
The pickling tanks 11a to 11d of the present embodiment are configured as described above.
[0019]
[Acid supply system 12]
The continuous pickling apparatus 10 of the present embodiment has an acid solution supply system 12. The acid solution supply system 12 of the present embodiment includes a third tank acid solution supply device 12c that supplies an acid solution to the third tank 11c, and a final tank acid solution supply device 12d that supplies an acid solution to the final tank 11d. Is done. The third tank acid solution supply device 12c and the final tank acid solution supply device 12d are both connected to an acid solution supply source (not shown) via an electromagnetic diaphragm valve 16. Each of the diaphragm valves 16 provided in the third tank acid solution supply device 12c and the final tank acid solution supply device 12d is connected to a control device 14, which will be described later, and supplies the acid solution output from the control device 14. The opening of the valve is controlled by the signal. Thereby, the supply amount of the acid solution from the third tank acid solution supply device 12c to the third tank 11c and the supply amount of the acid solution from the final tank acid solution supply device 12d to the final tank 11d are individually controlled. You.
[0020]
In the present embodiment, the acid solution is supplied to the third tank 11c and the final tank 11d. However, the third tank acid solution supply device 12c and the final tank 11c are also supplied to the second tank 11b and the first tank 11a. An acid solution supply device similar to the tank acid solution supply device 12d may be provided, and the acid solution may be individually supplied.
The acid solution supply system 12 of the present embodiment is configured as described above.
[0021]
[Acid Concentration Measuring Apparatus 13c, 13d]
In the present embodiment, the third tank 11c is provided with a continuous acid concentration measuring device 13c, and the final tank 11d is provided with a continuous acid concentration measuring device 13d. Since the continuous acid concentration measuring device 13c and the continuous acid concentration measuring device 13d are the same, the following description will be made by taking the continuous acid concentration measuring device 13d as an example.
[0022]
FIG. 2 is an explanatory diagram showing an internal structure of the continuous acid concentration measuring device 13d of the present embodiment. The broken arrows in FIG. 2 indicate the flow of the pickling solution.
As shown in FIG. 2, the acid concentration continuous measuring device 13d is a cylinder having a part of a circulation flow path 18d for continuously flowing the pickling liquid pumped from the final tank 11d by a pump 17d in one direction. An acid concentration continuous measuring device main body 19d, a density meter 20d, a thermometer 21d, and a conductivity meter 22d for continuously measuring the pickling liquid flowing through a part of the circulation channel 18d.
[0023]
The acid concentration continuous measuring device main body 19d in the present embodiment may have a cylindrical shape, and may have a structure in which the pickling liquid as a sample can be continuously flowed from the final tank 11d and returned to the final tank 11d. However, it is not limited to a specific structure.
[0024]
The material of the acid concentration continuous measuring device main body 19d may be any material having acid resistance that does not corrode by the pickling liquid. In the present embodiment, the material is made of polypropylene. Further, a part of the circulation flow path 18d formed inside the acid concentration continuous measurement device main body 19d is formed in a straight shape with as few as possible a reduced flow velocity portion such as an elbow. As a result, the occurrence of clogging due to a decrease in the flow of the pickling liquid inside the acid concentration continuous measuring device main body 19d is suppressed as much as possible.
[0025]
Further, the flow rate of the pickling liquid flowing through a part of the circulation channel 18d is desirably 2 m / sec or less in order to maintain the measurement accuracy of each of the density meter 20d, the thermometer 21d and the conductivity meter 22d. Inside the main body 19d of the continuous acid concentration measuring device 13d of the continuous acid concentration measuring device 13d of the present embodiment, the lower circulation channel 18d is formed at a position substantially equal to the height of the discharge pipe 23d. As a result, the pickling solution pumped by the pump 17d temporarily stays near the bottom of the inside of the acid concentration continuous measuring device main body 19d as shown by the broken line arrow in the drawing, and then flows to the discharge pipe 23d. It is led. Therefore, in the acid concentration continuous measuring device 19d of the present embodiment, the flow rate of the pickling liquid flowing through the circulation flow path 18d is a desirable flow rate from the viewpoint of the measurement accuracy of the density meter 20d, the thermometer 21d, and the conductivity meter 22d. It can be easily set and managed at 2 m / sec or less to improve the measurement accuracy. In the present embodiment, the dimensions of each part of the acid concentration continuous measuring device main body 19d are set such that the flow rate of the pickling solution is 1 m / sec.
[0026]
In the present embodiment, a known differential pressure sensor type density meter having two detection units 20d-1 and 20d-2 is used as the density meter 20d. The two detectors 20d-1 and 20d-2 are provided with a distance d in a direction in which a part of the circulation channel 18d is formed in order to secure a desired density measurement accuracy. ₁ Is set to be at least 500 mm 2, and is installed on a body portion substantially at the center in the longitudinal direction of the acid concentration continuous measuring device main body 19d.
[0027]
In addition, in the installation part of the detection units 20d-1 and 20d-2, the protrusion amount d of the branch part in the direction (left-right direction in FIG. 2) orthogonal to the flow direction of the pickling liquid ₂ Is set as small as possible. Thereby, the stagnation of the pickling liquid in the branch portion is suppressed, and the clogging of the pickling liquid is reliably prevented.
[0028]
In the present embodiment, a known platinum resistor-type thermometer is used as the thermometer 21d. A well-known electromagnetic induction type conductivity meter was used as the conductivity meter 22d. Both the thermometer 21d and the conductivity meter 22d are installed at the bottom of the acid concentration continuous measuring device main body 19d so that measurement can be performed at a part of the outlet of the circulation flow path 18d.
[0029]
In this embodiment, both the thermometer 21d and the conductivity meter 22d are provided in the acid concentration continuous measuring device main body 19d. This is because the measurement error is reduced as much as possible by arranging both the thermometer 21d and the conductivity meter 22d near the density meter 20d. However, the thermometer 21d and the conductivity meter 22d need not always be arranged in the acid concentration continuous measuring device main body 19d. A thermometer 21d and a conductivity meter 22d are installed inside the final tank 11d or in a pipe or the like constituting a circulation flow path 18d between the final tank 11d and the acid concentration continuous measuring device main body 19d, and circulating pickling. The temperature and conductivity of the liquid may be measured. In this case, deviations between the values of the temperature and conductivity near the installation part of the density meter 20d and the measurement data at the installation parts of the thermometers 21d and 22d are determined in advance, and these deviations are used to calculate the thermometer. 21d and the measurement data in the installation part of the conductivity meter 22d may be corrected. Thereby, the measurement error can be reduced as much as possible without disposing the thermometer 21d and the conductivity meter 22d in the vicinity of the density meter 20d.
[0030]
In this embodiment, the acid concentration continuous measurement device 13d is installed near the outer wall surface of the final tank 11d. Then, the acid concentration continuous measuring device 13d allows the pickling liquid contained in the final tank 11d to flow in one direction by the pump 17d installed near the final tank 11d. Thereby, the acid concentration continuous measuring device 13d can continuously measure all of the density, temperature, and conductivity of the pickling liquid.
[0031]
As described above, as the densitometer 20d, the thermometer 21d, and the conductivity meter 22d used in the acid concentration continuous measurement device 13d of the present embodiment, well-known industrial instruments having high use results are used. For this reason, the acid concentration continuous measuring device 13d of the present embodiment can accurately and accurately obtain the density, temperature, and conductivity of the pickling solution with extremely high accuracy.
[0032]
In the vicinity of the acid concentration continuous measurement device 13d of the present embodiment, the density continuously measured by the density meter 20d, the temperature continuously measured by the thermometer 21d, and the continuous measurement by the conductivity meter 22d. An arithmetic unit (not shown) for calculating the acid concentration of the pickling solution based on the measured conductivity is installed. The arithmetic unit continuously calculates the acid concentration of the pickling solution. The calculation result of this calculation device is input to the control device 14 described later.
[0033]
The “continuous measurement” by the acid concentration continuous measurement device 13d according to the present embodiment refers to, for example, a measurement pitch that is extremely short as compared with a measurement pitch (about 15 minutes) using a known titration analyzer. This means measurement, for example, acid concentration measurement with a measurement pitch of 1 minute or less, preferably 10 seconds or less.
[0034]
In the acid concentration continuous measuring device 13d of the present embodiment, the acid concentration continuous measuring device main body 19d is a cylindrical single tube type. Therefore, the following effects (i) to (vii) can be obtained.
[0035]
(I) The shape of the circulation channel 18d is made as straight as possible and the distance d ₂ Is set as small as possible. This prevents the pickling liquid from staying in the circulation flow path 18d, particularly in the vicinity of each of the density meter 20d, the thermometer 21d, and the conductivity meter 22d, and allows the pickling liquid to flow continuously.
[0036]
(Ii) The pickling liquid flows continuously in the circulation channel 18d. For this reason, segregation of the pickling liquid in the circulation channel 18d is prevented, and a plurality of types of pickling liquid separately collected can be accurately measured under the same conditions.
[0037]
(Iii) Since the pickling solution is constantly flowed by the pump 17d, both the maintainability and internal cleanability of the acid concentration continuous measuring device body 19d are significantly improved, and continuous measurement can be performed while eliminating the clogging of the pickling solution. it can.
[0038]
(Iv) Since the density, temperature, and conductivity of the pickling solution are continuously measured, the acid concentration of the pickling solution can be continuously measured. Thus, by combining the acid concentration continuous measuring device 13d with, for example, feedback control relating to the acid concentration of the final pickling tank of the continuous pickling equipment, or feedback control and feedforward control, the acid concentration of the final pickling tank is Can be automatically controlled continuously and with high precision.
[0039]
(V) The acid concentration continuous measurement device 13d has an extremely simple external shape as shown in FIGS. For this reason, there is a high degree of freedom in installation in a continuous pickling facility or the like.
[0040]
(Vi) The inside of the acid concentration continuous measurement device 13d has a simple internal structure as shown in FIG. For this reason, the flow velocity of the pickling liquid flowing through the circulation flow path 18d is easily set and managed to be 2 m / sec or less, which is a desirable flow velocity from the viewpoint of the measurement accuracy of the density meter 20d, the thermometer 21d, and the conductivity meter 22d. be able to. Accordingly, the acid concentration continuous measuring device 13d can easily maintain the measurement accuracy.
[0041]
(Vii) Since the acid concentration continuous measurement device 13d has a simple structure, it can be easily installed near the pickling tank. For this reason, the length of the pipe constituting the circulation channel 18d for diverting the pickling solution from the pickling tank can be made as short as possible. As a result, the time loss between the time when the pickling solution leaves the pickling tank and the time when it reaches the acid concentration continuous measuring device 13d and is measured can be reduced as much as possible. For this reason, the acid concentration continuous measurement device 13d can suppress a decrease in control accuracy.
[0042]
In this embodiment, the third tank 11c and the final tank 11d are provided with the acid concentration continuous measuring devices 13c and 13d, respectively. However, as shown in FIG. 1, the second tank 11b is also provided with the acid concentration continuous measuring device 13b. It is also possible to provide a continuous acid concentration measuring device 13a in the first tank 11a if necessary, and to input these output values to the control device 14.
The acid concentration continuous measuring devices 13c and 13d of the present embodiment are configured as described above.
[0043]
[Control device 14]
The continuous pickling apparatus 10 of the present embodiment has a control device 14.
The controller 14 reduces the acid consumption of the pickling liquid contained in the third tank 11c when pickling and the acid consumption of the pickling liquid contained in the final tank 11d when pickling. , Using an approximate expression. The prediction calculation of the amount of acid consumption in each of the third tank 11c and the final tank 11d is based on the material and dimensions of the steel strip 15, the passing speed, the acid solution composition, and the acid solution temperature, which are input from the pickling line control device 24. The pickling is performed based on pickling conditions at the time of pickling, such as the size of each tank, but is not limited to a specific means. The prediction calculation may be performed by a known means.
[0044]
For example, when the amount of reduction per unit area (hereinafter referred to as “pickling weight loss value”) is approximated with respect to time using a linear expression, the relationship between the pickling time and the pickling weight loss value is proportional. Become a relationship. FIG. 3 is a graph showing an example of this relationship.
[0045]
As shown in the graph of FIG. 3, the relationship between the pickling time and the pickling weight loss value is a linear relationship starting from the origin O. That is, the time t passing through the first tank 11a ₁ Pickling loss value m ₁ , Time t when passing through the second tank 11b ₂ Pickling loss value m ₂ At time t when passing through the third tank 11c ₃ Pickling loss value m ₃ , And the time t passing through the last tank 11d ₄ Pickling loss value m ₄ Are located on the same straight line and the time t at which the pickling is completed ₄ Thereafter, the pickling weight loss value becomes constant. The slope of this straight line indicates the pickling speed, and is defined by the material of the steel strip 15 to be pickled and the pickling conditions (temperature and composition of the pickling liquid).
[0046]
Therefore, the amount of acid consumed in each of the pickling tanks 11a to 11d is determined by the time required to pass through each of the pickling tanks 11a to 11d, the inclination of the straight line in the graph of FIG. ) Is obtained by multiplying In this manner, the consumption of the pickling solution in each of the pickling tanks 11a to 11d can be calculated. Note that, as in the present embodiment, the relationship between the pickling time and the pickling weight loss value is not approximated by a straight line, but as shown by a dashed line in FIG. 3, an S-shaped curve close to the actual pickling curve. By approximating, the acid consumption in each of the pickling tanks 11a to 11d can be calculated with higher accuracy.
[0047]
Further, the control device 14 determines the supply amount of the acid solution to each of the third tank 11c and the final tank 11d based on the predicted value of the acid consumption in each of the third tank 11c and the final tank 11d calculated as described above. I do. Then, the control device 14 outputs an acid solution supply signal to the diaphragm valve 16 of the acid solution supply system 12, and supplies the required amount of the acid solution to each of the third tank 11c and the final tank 11d.
[0048]
Further, the control device 14 supplies the acid solution from the third tank acid solution supply device 12c to the third tank 11c and supplies the acid solution from the final tank acid solution supply device 12d to the final tank 11d, and then continuously measures the acid concentration. An acid solution supply signal is again output to the acid solution supply system 12 based on the continuous measurement of the acid concentration output from the devices 13c and 13d, and the acid contained in the third tank 11c and the final tank 11d are respectively returned. Make fine adjustments so that the acid concentration of the washing solution matches the target value.
[0049]
The control device 14 of the present embodiment is configured as described above.
Next, the steel strip 15 is provided by the continuous pickling apparatus 10 of the present embodiment including the four pickling tanks 11a to 11d, the acid solution supply system 12, the acid concentration continuous measuring devices 13c and 13d, and the control device 14. The situation in which acid pickling is performed will be described with time.
[0050]
(Estimation calculation of acid consumption)
The pickling is performed on the steel strip 15 by the continuous pickling apparatus 10 shown in FIG.
Here, the predicted value of the acid consumption of the pickling liquid stored in the third tank 11c and the final tank 11d, respectively, is determined by the control device 14 based on the aforementioned pickling conditions input from the pickling line control device 24. Is calculated.
[0051]
Here, regardless of the type of prediction calculation, the calculated value always has an error with respect to the actual acid consumption. Therefore, in the present embodiment, as will be described later, this error is reduced as much as possible by controlling the supply amount of the acid solution using a continuous measurement value of the acid concentration.
[0052]
[Supply of acid solution based on calculated value]
Next, based on the acid consumption of the pickling liquid stored in the third tank 11c and the final tank 11d predicted in this manner, the controller 14 controls the acid supply to the third tank 11c and the final tank 11d, respectively. The liquid supply amount is determined.
[0053]
Then, the control device 14 outputs an acid solution supply signal to the

diaphragm valves

16 and 16 of the third tank acid solution supply system 12c and the final tank acid solution supply system 12d, respectively, to the third tank 11c and the final tank 11d, respectively. The determined supply amount of the acid solution is supplied.
[0054]
(Continuous measurement of acid concentration)
In this way, after the determined supply amount of the acid solution is supplied to each of the third tank 11c and the final tank 11d, the acid concentration of the pickling liquid stored in the third tank 11c by the acid concentration continuous measurement device 13c. While the concentration is continuously measured, the acid concentration of the pickling liquid contained in the final tank 11d is continuously measured by the acid concentration continuous measuring device 13d. These continuous measurements are sent to the controller 14.
[0055]
(Supply of acid solution based on continuous measurement results)
The controller 14 calculates the deviation between the continuous measurement values and the target value of the acid concentration of the pickling liquid stored in the third tank 11c and the final tank 11d. Then, an acid solution supply signal is output from the control device 14 to the

diaphragm valves

16 and 16 of the third tank acid solution supply system 12c and the final tank acid solution supply system 12d, respectively, so that this deviation becomes zero. The supply amount of the acid solution to each of the tank 11c and the final tank 11d is controlled.
[0056]
This corrects the error in the prediction calculation result of the supply amount of the acid solution to each of the third tank 11c and the final tank 11d, and corrects the acid contained in the second tank 11b as well as the third tank 11c and the final tank 11d. The acid concentration of the washing liquid can be quickly and accurately brought close to the target value.
[0057]
In the present embodiment, the acid solution is supplied not only to the final tank 11d but also to the third tank 11c in such a manner that the acid concentration of the pickling liquid stored in each of the third tank 11c and the second tank 11b is adjusted. It is for raising and approaching a target value. Therefore, in this embodiment in which the fourth tank is the final tank 11d, the acid solution is supplied to the final tank 11d and the third tank 11c. For example, in the case of a continuous pickling apparatus in which the fifth tank is the final tank, It is desirable to supply an acid solution to each of the final tank and the third tank.
[0058]
In the present embodiment, since the supply of the acid solution based on the continuous measurement result is performed not only in the final tank 11d but also in the third tank 11c, the acid concentration of the pickling liquid contained in the final tank 11d is more than 12%. The acid concentration of the pickling liquid contained in the third tank 11c can be increased to approach the target value without increasing the acid concentration. For this reason, while preventing evaporation of the pickling liquid from the final tank 11d, the acid concentration of the pickling liquid contained in the third tank 11c can be increased to approach the target value. For this reason, the pickling tanks 11a to 11d can be fully pickled, and the steel strip 15 can be pickled. Therefore, according to the present embodiment, the overall productivity of the continuous pickling apparatus 10 can be improved.
[0059]
In the present embodiment, the acid concentration continuous measuring devices 13c, 13d are provided near the third tank 11c and the final tank 11d of the existing continuous acid pickling device, and the output signals from these acid concentration continuous measuring devices 13c, 13d are provided. Is transmitted to the control device 14 and the software of the control device 14 is only partially changed. For this reason, the existing continuous pickling equipment can be implemented as little as possible.
As described above, according to the present embodiment, it is possible to reduce both the defect rate and improve the productivity without significantly improving the conventional production equipment.
[0060]
【Example】
Further, the present invention will be described more specifically with reference to examples.
Continuous pickling apparatus 1 shown in FIG. 1 (capacity of each pickling tank 13a to 13d: 50 m) ³ And the temperature of the pickling solution: 90 ° C.), and the steel strip 15 was pickled for one month using the continuous pickling method of the present invention and the continuous pickling method of the comparative example. In addition, in pickling using this type of continuous pickling apparatus, almost all various changes in operating conditions occur during one month of the operating period in the present embodiment, so that the usefulness of the present invention is evaluated. That's enough time to do it.
[0061]
In the example of the present invention, the controller 14 uses the material of the steel strip 15 and the pickling conditions (the temperature and the acid concentration of the pickling solution) and the third tank 11c based on a first-order approximation formula obtained in advance for each steel type. And the consumption of the pickling liquid contained in each of the final tanks 11d is predicted and calculated, and based on the result, the third tank 11c and the final tank 11d are each supplied with an acid. , 13d so that the acid concentration of the pickling solution contained in each of the third tank 11c and the final tank 11d is 12 ± 0.5%. Each of the

diaphragm valves

16 and 16 of the system 12c and the final tank acid solution supply system 12d was on / off controlled.
[0062]
On the other hand, in the comparative example, acid was supplied only to the final tank 11d, the acid solution overflowed by the acid supply was sequentially transported to the third tank 11c and the second tank 11b, and waste acid was discharged from the first tank 11c. The on / off control of the diaphragm valve 16 of the final tank acid solution supply system 12d was performed so that the acid concentration of the pickling solution contained in the tank 11d was 12 ± 0.5%.
[0063]
In addition, in both the present invention example and the comparative example, pickling was performed by increasing the sheet passing speed to such an extent that the descaling failure did not occur by the judgment of the operator.
Then, the width of change in the acid concentration of the pickling solution contained in each of the second tank 11b to the last tank 11d, the rate of occurrence of descaling failure, and the productivity were measured. The results are summarized in Table 1.
[0064]
[Table 1]

[0065]
As is clear from Table 1, according to the example of the present invention, the acid concentration of the pickling liquid contained in each of the pickling tanks 11a to 11d was increased and stabilized within a range not exceeding the target value. As a result, the rate of occurrence of descaling failure was significantly reduced, and productivity was significantly improved.
[0066]
(Modified form)
In the description of the embodiment and the examples, a continuous pickling apparatus including four pickling tanks was used. However, the present invention is not limited to this mode, and is similarly applied to a continuous pickling apparatus having a plurality of pickling tanks.
[0067]
Further, in the description of the embodiment and the examples, the case where the acid consumption of the pickling liquid stored in the third tank and the final tank is predicted and the acid liquid is supplied to these pickling tanks is taken as an example. However, the present invention is not limited to this mode, and also estimates the acid consumption of the pickling liquid contained in the pickling tanks other than the third tank and the final tank, and the pickling tanks also pick up the acid. A liquid may be supplied. Thereby, the acid concentration of the pickling liquid contained in each pickling tank can be controlled with higher precision.
[0068]
Further, in the description of the embodiment and the examples, the case where the acid concentration continuous measuring device shown in FIG. However, this is merely an example of the continuous acid concentration measuring device, and the present invention is not limited to the continuous acid concentration measuring device shown in FIG. The present invention is not limited to the acid concentration continuous measuring device shown in FIG. 2, but may be any acid concentration continuous measuring device capable of continuously measuring the acid concentration of the pickling solution contained in the pickling tank. Can be applied.
[0069]
Further, in the description of the embodiment and the examples, a continuous pickling apparatus in which an acid solution is supplied to at least the final tank is used. However, the present invention is not limited to this mode, and is similarly applied to a continuous pickling apparatus in which an acid solution is not supplied to the final tank.
[0070]
In the description of the embodiment and the examples, a continuous pickling apparatus of a type in which the pickling liquid stored in the pickling tank on the downstream side is sequentially overflowed to the pickling tank adjacent on the upstream side is used. However, the present invention is not limited to this form, and is similarly applicable to a continuous pickling apparatus having a plurality of pickling tanks. For example, as shown in FIG. 4, the present invention is similarly applied to a continuous pickling apparatus of a type in which a pickling solution contained in a downstream pickling tank is sequentially transported to an adjacent pickling tank on the upstream side. You.
[0071]
Further, in the description of the embodiment and the examples, the case where the acid solution is hydrochloric acid is taken as an example. However, the present invention is not limited to this form, and is equally applicable to any acid solution, such as sulfuric acid, capable of performing a pickling treatment on a steel sheet.
[0072]
【The invention's effect】
As described in detail above, according to the present invention, while suppressing the amount of evaporation of the pickling solution from each pickling tank as much as possible, while increasing the acid concentration of the pickling solution contained in each pickling tank, It is possible to provide a continuous pickling method and a continuous pickling apparatus capable of improving the pickling productivity by approaching the target value, thereby improving the existing continuous pickling equipment as much as possible. Was.
The significance of the present invention having such an effect is extremely remarkable.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram schematically showing a configuration of a continuous pickling apparatus of an embodiment.
FIG. 2 is an explanatory diagram showing an internal structure of the acid concentration continuous measurement device of the embodiment.
FIG. 3 is a graph showing an example of the relationship between the pickling time and the pickling weight loss value.
FIG. 4 is an explanatory view schematically showing a conventional continuous pickling apparatus including four pickling tanks.
[Explanation of symbols]
10 Continuous pickling equipment
11c Third tank
11d Last tank
12 Acid solution supply system
13c, 13d Acid concentration continuous measuring device
14 Control device

Claims

A predicted value of acid consumption during pickling of pickling liquids contained in two or more pickling tanks among a plurality of pickling tanks constituting a continuous pickling apparatus is calculated by pickling conditions at the time of pickling. Is calculated based on
An acid solution is supplied by determining an acid solution supply amount to each of the two or more pickling tanks based on the calculated predicted value,
The acid concentration of the pickling solution contained in each of the two or more pickling tanks to which the acid solution has been supplied is continuously measured, and the acid concentration of the acid solution is measured based on a continuous measurement of the acid concentration. Controlling the supply amount of the acid solution to the two or more pickling tanks so that the acid concentrations of the pickling liquids stored in the pickling tanks respectively match the target values. Washing method.

The continuous pickling method according to claim 1, wherein the two or more pickling tanks include at least a final pickling tank.

The continuous pickling apparatus is a continuous pickling apparatus of a type in which the pickling liquid contained in a downstream pickling tank is sequentially overflowed to an adjacent pickling tank on the upstream side, or is contained in a downstream pickling tank. The continuous pickling method according to claim 1 or 2, wherein the pickling solution is a continuous pickling apparatus of a type that sequentially transports the pickled solution to an upstream pickling tank.

The continuous measurement value of the acid concentration is measured at least using a continuous output value from a densitometer disposed in a pickling liquid circulation channel provided in each of the two or more pickling tanks. The continuous pickling method according to any one of claims 1 to 3.

The continuous measurement value of the acid concentration, together with the continuous output value from the density meter, the continuous measurement values from the thermometer and the conductivity meter disposed in the pickling tank or the pickling liquid circulation channel, respectively. The continuous pickling method according to claim 4, wherein the measurement is performed using an appropriate output value.

Two or more pickling tanks out of a plurality of pickling tanks constituting a continuous pickling apparatus;
An acid solution supply system for supplying an acid solution to each of the two or more pickling tanks;
An acid concentration continuous measuring device for continuously measuring the acid concentration of the pickling solution contained in each of the two or more pickling tanks,
Predicted values of acid consumption at the time of pickling of the pickling liquid stored in the two or more pickling tanks are calculated from the pickling conditions at the time of pickling, and the acid value is calculated based on the calculated predicted values. Along with determining an amount of liquid supply and outputting an acid solution supply signal to the acid solution supply system, the acid solution is supplied from the acid solution supply system to the two or more pickling tanks. The acid solution supply system is controlled such that the acid concentrations of the pickling liquids stored in the two or more pickling tanks respectively match the target values based on the continuously measured acid concentration values output. A continuous pickling apparatus comprising a combination of a control device that outputs an acid solution supply signal.

The continuous pickling apparatus according to claim 6, wherein the two or more pickling tanks include at least a final pickling tank.

The continuous pickling apparatus is a continuous pickling apparatus of a type in which the pickling liquid contained in a downstream pickling tank is sequentially overflowed to an adjacent pickling tank on the upstream side, or is contained in a downstream pickling tank. The continuous pickling apparatus according to claim 6 or 7, wherein the continuous pickling apparatus is of a type that sequentially transports the pickled liquid to an upstream pickling tank.

The acid concentration continuous measurement device,
A main body connected to the pickling tank and provided in a part of a flow path of the pickling solution taken out of the pickling tank;
A density meter for measuring the density of the pickling liquid flowing inside the main body,
A thermometer for measuring the temperature of the pickling solution in the flow path or the pickling tank;
A conductivity meter for measuring the conductivity of the pickling liquid in the flow path or the pickling tank,
9. The computer according to claim 6, further comprising: an arithmetic unit configured to calculate an acid concentration of the pickling liquid flowing through a part of the flow path based on the measurement results of the density, the thermometer, and the conductivity meter. The continuous pickling apparatus according to any one of the above.