JP4309500B2 - Rolling method for cold tandem rolling mill - Google Patents

Description

したがって、ロールバイト出口の温度Ｔ_O は、式（１）を整理することによって式（２）で表わされる。
【数２】

ここで、Ｔ_w ：板冷却装置の冷却水温度
Ｔ_S ：板温度検出位置での板温度
Ｖ_O ：圧延機出側の板速度
ｈ ：圧延機出側の板厚
ρ_S ：板の密度
Ｃ_S ：板の比熱
ｈ_S ：板の熱伝達率
ｔ₁ ：板冷却装置から水切り装置までの距離を板が通過する時間
（ｔ₁ ＝Ｌ₁ ／Ｖ_O ）
Ｌ₁ ：板冷却装置から水切り装置までの距離
である。板の熱伝達率ｈ_S は実験を行って、冷却水量（単位時間単位面積当たりの冷却水供給量）との関係をあらかじめモデル化する必要がある。式（３）は、所要のパラメーターを含む熱伝達率モデル式の一般形を示している。
【数３】

Ｑ_w ：冷却水の供給量、
Ｗ ：板幅
【００２１】
なお、空冷の場合、空冷時間が約０．５秒以内（圧延速度約５００m/min 以上）では、空冷による温度変化は無視できる。したがって、前段スタンドの出側板温度は、そのまま板温度検出位置の板温度とみなすことができる。
【００２２】
上記温度データに基づいて定常状態でのロールバイト出口板温度を推定する。例えば、圧下の制御周期（ヒートスクラッチ防止をするための圧下の制御周期）を１分と設定し、過去１分間の板温度のデータ（この場合１２個、ただし、圧下条件は一定であるもののデータ）を用いて、最終的には一定値に漸近する漸近曲線を表す関数に代入し、重回帰を行うことによってその関数の定数を決定し、その漸近値を定常状態におけるロールバイト出口の板温度の推定値Ｔ_f とする。このような最終的には一定値に近づく漸近曲線を表す関数としては例えば、ａ・tan ｈ（ｃＸ）やａ＋ｂ（１−ｅ^-cx ）等がある。この関数で、ａ，ｂ，ｃは定数であり、最終的にはそれぞれａおよびａ＋ｂに漸近する。したがって、このような関数に測定した温度データを代入し、それぞれの漸近値ａあるいはａ＋ｂを求め、これを定常状態の板温度の推定値Ｔ_f とする。
【００２３】
また、このような方法の他に、例えば圧下の制御周期（ヒートスクラッチを防止するための圧下の制御周期）を例えば３０秒と設定し、この制御周期である３０秒間に得られた６個の温度データを直線回帰し、次の圧下の制御タイミング（次の圧下制御時期）となる３０秒後の板温度を推定して板温度の推定値Ｔ_f としてもよい。
【００２４】
つぎに、ヒートスクラッチ制御温度の設定について説明する。あらかじめワークロール速度や圧下率や圧延潤滑条件等を変えた実験によって、ヒートスクラッチが発生する最低のロールバイト出口板温度を求め、これを限界温度Ｔ_Lim とする。この限界温度を、ヒートスクラッチ制御目標温度Ｔ_L としてもよいが、このヒートスクラッチ制御目標温度Ｔ_L は前述した限界温度Ｔ_Lim よりも若干低い温度、例えば３〜６℃程度低い温度に設定することが好ましい。
【００２５】
このようにヒートスクラッチが発生しやすいスタンド、実施例では第４スタンドにおいて、ロールバイト出口の板温度の推定値Ｔ_f と前述したヒートスクラッチ制御目標温度Ｔ_L とを比較する。ΔＴ＝Ｔ_L −Ｔ_f が正の場合には、ヒートスクラッチは生じる可能性はないので圧延をそのまま続行する。ΔＴ＝Ｔ_L −Ｔ_f が負の値の場合には、ヒートスクラッチが生じる可能性があるので、ΔＴが正となるように圧下率を変更して圧延を行う。
【００２６】
以下に変更する圧下率の計算方法について説明する。
まず、圧延中の摩擦係数μと変形抵抗Ｋ_m を求める。圧延材の変形抵抗はあらかじめ引張試験によって式（４）に示す定数ａ、ε₀ ，ｎの値を求めておく。
【数４】

ここで、σ_y は圧延材の単純引張時の降伏応力であり、εはひずみである。
【００２７】
ところで、変形抵抗はひずみ速度の影響や板温度の影響を受けるので、式（４）から求められた変形抵抗Ｋ_ｍは必ずしも圧延時の正確な値ではない。そこで、この発明では、圧延荷重式および先進率式を連立させ、圧延時の変形抵抗と摩擦係数を求める。例えば、Ｈｉｌｌの荷重式を式（５）に示すように変形抵抗について展解して、変形抵抗を求める。また、Ｂｌａｎｄ ＆ Ｆｏｒｄの先進率式を式（６）に示すように摩擦係数について展解し、式（５）で求めた変形抵抗を式（６）に代入して摩擦係数を求める。式（５）および（６）中で添字Ｅは当該スタンドの圧延時における検出値および検出値に基づく計算値である。計算値は、先に述べたようにロードセルで検出した前張力を板断面積で割る、ロードセルで検出した圧延荷重からベンディング力を除外するなどして求めた値である。
【数５】

【数６】

【００２８】
上式で未知数は摩擦係数μ_E と変形抵抗式Ｋ_mEの中の定数（式（４）中のａ）の２個であり、他は既知数で方程式数は２個である。したがって、この方程式は解くことができる。なお、演算に当たっては、摩擦係数μ_E の初期値として０．０５程度が、変形抵抗式中の定数ａの初期値として引張試験によって求められた値が使われることが好ましい。
【００２９】
一方、この時のロールバイト出口のロールと圧延材との界面の上昇温度Ｔ′は、例えば小野らの式を用いれば式（７）で表される。
【数７】

【００３０】
Ｔ_ｄｍａｘは変形熱により増加するロールと圧延材との界面のロールバイト出口の温度上昇であり、式（９）で表される。Ｔ_ｆｍａｘは摩擦熱により増加する界面のロールバイト出口の温度上昇であり、式（８）で表される。
【数８】

【数９】

【００３１】
式（７）、（８）にそれぞれの当該スタンドの物性値および実測値、ならびに前述した式（５）、式（６）を用いる方法で求められた摩擦係数μ_Ｅおよび変形抵抗Ｋ_ｍＥを代入すれば、当該スタンドのロールバイト出口のロールと圧延材の界面の温度上昇Ｔ′の計算値Ｔ _Ｅ ′が求まる。
【００３２】
つぎに、圧下率を変えた場合の温度変化を推定するために、まず求められた摩擦係数μ_E および変形抵抗Ｋ_mE、ならびに圧下率以外は当該スタンドの実測値を用い、圧下率だけを変えた場合の圧延荷重Ｐと先進率ｆs を計算する。なお、厳密にいうと、圧下率を変化させると摩擦係数も変化する。しかし、圧延速度１０００m/min 以上ではほとんど流体潤滑が支配的になっているので、ヒートスクラッチが発生するような条件では摩擦係数に及ぼす圧下率の影響は無視してよい。
【００３３】
圧延荷重Ｐは、例えば式（１０）に示す Hill の荷重式を用いて計算する。先進率ｆs は、式（１１）に示す Bland & Ford の式を用いて計算する。ロール偏平ＲE ′は、式（１２）に示すHitchcook の式を用いて計算する。
【数１０】

【数１１】

【数１２】

【００３４】
式（１０）とロール偏平の式（１２）を用いて収束計算を行うことにより圧延荷重が求められ、式（１１）より先進率が求まる。これらの値を式（７）〜式（９）に代入することによって、圧下率条件を変更した際のロールバイト出口の界面の温度上昇Ｔ_ｍ′が求まる。すなわち、上記の当該スタンドでのロールバイト出口の界面の温度上昇の計算値Ｔ _Ｅ ′と、圧下率を変更したときのロールバイト出口の温度上昇の推定値Ｔ_ｍ′が得られる。ロールバイト出口におけるロールと圧延材の界面の温度とスタンド出側における板温度とは厳密には同じではないが、圧下率条件を変化させた場合の温度変化は同じであるとみなしてよい。したがって、このＴ_ｍ′とＴ_Ｅ′との差（ΔＴ′＝Ｔ_ｍ′−Ｔ_Ｅ′）と、先に述べたＴ_ＬとＴ_ｆとの差（ΔＴ＝Ｔ_Ｌ−Ｔ_ｆ）とを比べて、ΔＴ′がΔＴ以下（ΔＴ′≦ΔＴ）となるような圧下率条件を、例えばニュートン法などを用いて繰り返し計算によって求めることができる。当該圧延機の圧下率設定値を、上記のようにして得られた圧下率値に変更する。上述の関係を満たすヒートスクラッチの発生しない圧下率値をいくつか求めることができる。これら圧下率値の中から適切な圧下率値を圧延状況にあわせて選択すればよいが、最低の圧下率値ｒａｉｍを選定し、これに従って当該スタンドの圧下率設定値を変更することが望ましい。
【００３５】
なお、これらの制御の際、圧延荷重の変化量があらかじめ予測できるので、板厚精度や板形状の不良が発生しないように板厚および形状制御を行うこともできる。
【００３６】
以上はヒートスクラッチを圧延機ロールバイト出側の板温度で制御する方法について示したが、潤滑油によってはロールバイト出口の温度ではなく、ロールバイト内での上昇温度で制御する方がよい場合もある。その場合の方法について説明する。この場合には、圧延機入側でも板の温度Ｔｉを温度検出器によって検出する。温度検出器から圧延機入側までに水冷していない場合で、圧延速度５００m/min 以上ではたとえ潤滑油が板表面にかかったとしてもロールバイト入口の板温度に及ぼすそれらの影響は無視できる。したがって、前述のＴ_O の代わりにＴ_O ′＝Ｔ_O −Ｔｉを用いて同様にやればよい。
【００３７】
【実施例】
使用した冷間タンデム圧延機は図１に示したものと同じ５スタンドからなるタンデム圧延機であり、ヒートスクラッチが発生するスタンドとしての第４スタンドの圧延条件を表１に示す。
【表１】

【００３８】
操業条件において、同一サイズのコイルを同一の圧延条件で大量に圧延して行くと、ワークロールの平均温度が上昇し、第４スタンド出側の板温度が上昇して行く。これまでの操業データから、第４スタンド出側の板温度が約１６０℃以上であると、ヒートスクラッチが多発することが経験的に知られている。そこで、この発明を適用し、その効果を実験調査した。
【００３９】
あらかじめ実験によって求められたヒートスクラッチが発生する最低のロールバイト出口板温度である限界温度Ｔ_Lim は１６２℃であり、ヒートスクラッチ制御目標温度はＴ_L ＝１６２−４＝１５８℃とした。また、ヒートスクラッチ制御のための圧下率の制御周期を３０秒、サンプリング時間を５秒とし、その間の３０秒（６個）のデータからロールバイト出口の板温度を計算・直線回帰し、３０秒後のロールバイト出口板温度を求めてこれを板温度の推定値Ｔ_f とした。
【００４０】
図３は、第１の発明による効果を示す図であり、圧延コイル本数と第４スタンドロールバイト出側の板温度との関係を示す。図３中の○は従来の圧延方法の場合を、●は本発明を適用した際の場合をそれぞれ示す。従来の圧延方法ではコイル本数１１本目でロールバイト出口板温度の推定値は１６０℃以上となり、ヒートスクラッチが発生する危険があるので、ワークロール速度を９００m・min ^-1にまで減速して操業していた。しかし、この発明を適用することによって、圧下率を２８．６％から２３〜２５％に変更することにより、コイル本数３０本でも板温度は１５８℃以上になることはなくまたワークロール速度の低減をすることもなく圧延され、当然のことながらヒートスクラッチも発生しなかった。当然のことながら、第４スタンドの圧下率を変更すると板厚（製品板厚）が変化するので、不足した圧下率分は他のスタンドで調整する必要があることはいうまでもない。好ましくはヒートスクラッチの発生が最も少ない第１スタンドで調整する。
【００４１】
第３スタンドの板冷却条件を大幅に変えた場合、精度が悪化したので、第２の発明を適用した。すなわち、あらかじめ実験によって求められたヒートスクラッチが発生するロールバイト上昇温度である限界温度ΔＴ_Lim は１０８℃であり、ヒートスクラッチ制御目標温度はΔＴ_L ＝１０８−４＝１０４℃とした。また、圧下率の制御周期を３０秒、サンプリング時間を５秒とし、その間の３０秒（６個）のデータからロールバイト上昇温度を計算・直線回帰し、３０秒後のロールバイト上昇温度を求めてこれを板温度の推定値ΔＴ_f とした。この結果、第３スタンドの板冷却条件を大幅に変えても、ヒートスクラッチは発生しなかった。
【００４２】
【発明の効果】
ロールバイト内温度をヒートスクラッチが発生しない温度以下に高い精度で抑えることができ、生産性を阻害せずにヒートスクラッチの発生を防止することができる。
【図面の簡単な説明】
【図１】この発明を実施する冷間タンデム圧延機の一例を示す構成図である。
【図２】冷間タンデム圧延機中の２スタンドの拡大図である。
【図３】圧延材のロールバイト出口温度と圧延コイル本数との関係を示すグラフである。
【符号の説明】
１１ ワークロール
１３ 中間ロール
１５ バックアップロール
１７ 板厚検出器
２０ 板冷却装置
２２ 水切り兼張力検出装置
２４ 温度検出器
２６ 潤滑油供給装置
Ｓ 圧延材（板）[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a rolling method for preventing the occurrence of heat scratch without impairing productivity in a cold tandem rolling mill having a plurality of cold rolling mills.
[0002]
[Prior art]
In a cold tandem rolling mill, heat scratches may occur due to an increase in work roll speed or rolling reduction. A heat scratch is a seizure flaw generated by metal contact between a work roll and a rolled material as a result of an increase in the interface temperature between the roll and the rolled material in the roll bite and an oil film breaking in the roll bite. .
[0003]
When the heat scratch occurs, the surface defect of the product occurs, so that not only the product yield is lowered, but also the work roll of the stand where the heat scratch is generated needs to be changed, so that the productivity is remarkably lowered.
[0004]
The presence or absence of the occurrence of heat scratch can be predicted by the interface rising temperature in the roll bite during rolling. In actual operation, although the rolling schedule differs depending on the steel type, the same steel type is rolled under substantially the same rolling conditions (hereinafter also including cooling conditions), so the interface rising temperature can be substituted by the plate temperature on the stand exit side. Therefore, control is performed so that the plate temperature on the delivery side of the rolling mill is detected and the plate temperature is equal to or lower than the appropriate value based on the detected value.
[0005]
The above-described method of controlling the plate temperature on the stand exit side as the roll bite temperature is effective under almost the same rolling conditions (constant speed, coolant, etc.). For example, when cooling is not performed between the sheet temperature detector from the rolling mill roll bite exit side (air cooling), there is no significant problem. In the case of the i stand of FIG. 2, the upper and lower work rolls are cooled by the roll cooling device 30, but the cooling water is prevented from hitting the plate S by the draining device 32. Therefore, since the measurement value of the temperature detector 34 is not affected by roll cooling, it is possible to prevent i-stand heat scratching by the conventional technique.
[0006]
However, when cooling is performed between the sheet temperature detector from the rolling mill roll bite exit side (water cooling), it becomes a big problem. For example, in the case of (i-1) stand of FIG. 2, the plate S is cooled by the plate cooling device 20 on the exit side of the rolling mill, and the cooling water remains on the surface. The remaining cooling water is drained by the draining and tension detecting device 22, and then the temperature is measured by the temperature detector 24. Therefore, the influence of the plate cooling device 20 on the temperature detector 24 is large. Even if the amount of cooling water is the same, the temperature of the cooling water is affected. The water temperature is about 20 ° C. in the summer and about 5 ° C. in the winter. In summer and winter, the heat scratch control target temperature _TL of the control according to the prior art needs to be provided on the table according to the water temperature. Moreover, since it is necessary to confirm this heat scratch control target temperature _TL by experiment, the setting was a problem. Further, when the amount of water in the plate cooling device 20 is significantly changed, there is a problem that the influence of the amount of water cannot be ignored. Depending on the lubricant used, the accuracy may be improved by controlling the interface rise temperature (the temperature difference between the plates on the entrance and exit of the rolling mill) rather than controlling the plate surface temperature (maximum temperature).
[0007]
Regarding heat scratch prevention, for example, as disclosed in Japanese Patent Laid-Open No. 5-98283, a method using a rolling lubricant excellent in seizure resistance, or as disclosed in Japanese Patent Laid-Open No. 56-111505. In addition, there are a method for reducing the temperature of the plate and the work roll by controlling the amount of coolant, and a method for reducing the work roll speed as disclosed in Japanese Patent Laid-Open No. 6-63624. Both methods relate to a method of preventing an increase in the interface temperature between the work roll and the rolled material in the roll bite or preventing the oil film from breaking even if the interface temperature in the roll bite increases. However, the use of rolling lubricants with excellent seizure resistance may increase costs, and although the plate and roll temperature control by controlling the coolant amount is effective, there are some problems with its responsiveness. The decrease in the roll speed has a problem that the productivity decreases.
[0008]
As a method for preventing heat scratching without causing a decrease in productivity and an increase in manufacturing cost, Japanese Patent Laid-Open No. 60-49802 discloses changing the rolling schedule and tension, It is not clear how to predict the occurrence in advance and how to determine the amount of control.
[0009]
[Problems to be solved by the invention]
As a method of preventing heat scratch without causing a decrease in productivity and an increase in manufacturing cost as described above, when changing the tension, naturally, if the value is high, the rolling load is reduced, and the effect of preventing heat scratch However, if the tension is increased, the plate may break.If the tension is increased gradually while observing the rolling condition, the responsiveness deteriorates, heat scratches occur, and the plate thickness accuracy deteriorates. There is. Further, when the plate temperature on the stand exit side is detected and the tension is controlled based on the temperature, the control is performed when the temperature becomes higher than the temperature at which the heat scratch occurs, so that the heat scratch is temporarily generated. There is a risk.
[0010]
This invention makes it a subject to provide the rolling method in a cold tandem rolling mill which prevents generation | occurrence | production of a heat scratch, without inhibiting productivity.
[0011]
[Means for Solving the Problems]
The gist of the present invention is as follows.
1) Plate temperature, plate thickness, and plate speed on the stand exit side, and detection values of the cooling water temperature and flow rate of the plate cooling device installed between the stand exit side and the temperature detector that detects the plate surface temperature. The roll bite outlet plate temperature is estimated based on this value, and the reduction rate is controlled based on this value. 2) Stand entry / exit plate temperature, stand exit side plate thickness and plate speed detection values, or these detection values and stand Based on the detected values of the cooling water temperature and flow rate of the plate cooling device installed between the outlet side and the temperature detector that detects the plate surface temperature, the temperature rise in the roll bite in the rolled state is estimated, and this value is estimated. Control the rolling reduction based on
The present invention is based on the above gist, and the rolling method in the cold tandem rolling mill according to the first aspect of the present invention designates a stand where heat scratches are likely to occur in advance, from the rolling mill roll bite exit side in the designated stand. While performing plate cooling (water cooling) between the plate temperature detectors, rolling is performed by the following steps.
(A) Stand exit side plate temperature, rolling load, work roll speed, stand exit side plate speed, stand entry / exit plate thickness, stand entry / exit side tension, plate cooling water temperature, and plate cooling water supply amount 1 step (b) From the detected values of the stand exit side plate temperature, stand exit side plate thickness, stand exit side plate speed, plate cooling water temperature, and plate cooling water supply amount, the plate temperature is estimated multiple times, and the estimated Second step of estimating roll bite outlet plate temperature _Tf in the rolled state based on plate temperature data (c) When the roll bite outlet estimated plate temperature _Tf exceeds a preset heat scratch control target temperature _TL , Rolling material from the detected values of rolling load, work roll speed, stand exit side plate speed, stand entry / exit side plate thickness, and stand entry / exit side tension in the first step The third step (D) the detected value of the first step of obtaining a friction coefficient and deformation resistance, as well as a plate temperature increase T _{E 'in} the roll bite in the rolling state by the friction coefficient and deformation resistance obtained in the third step, reduction Roller bite inner plate temperature rise T _m ′ when the rate is changed, and the rolling rate obtained in the fourth step (e), the fourth step, where T _L −T _f ≧ T _m ′ −T _E ′ is determined. Fifth step of controlling the reduction rate using the rate as a target value.
The rolling method in the cold tandem rolling mill according to the second aspect of the invention designates in advance a stand where heat scratches are likely to occur, and plate cooling (water cooling) between the plate temperature detector from the rolling mill roll bite exit side in the designated stand. While performing, rolling is performed by the following steps.
(B) Stand entry side plate temperature, stand exit side plate temperature, rolling load, work roll speed, stand exit side plate speed, stand entry / exit side plate thickness, stand entry / exit side tension, plate cooling water temperature, and plate cooling water supply amount (B) Estimate the plate temperature multiple times from the detected values of the stand exit side plate temperature, stand exit side plate speed, stand exit side plate thickness, plate cooling water temperature, and plate cooling water supply amount. based on the estimated the plate temperature data, determine the roll bite outlet plate temperature T _f in the rolling state, the second for obtaining the elevated temperature [Delta] T _f in the roll bite in the rolling state from the T _f by subtracting the stand entry side temperature step (c) if the estimated temperature rise [Delta] T _f in the roll bite exceeds heat scratch control target temperature [Delta] T _L which is set in advance, the first Rolling load step, a third step of obtaining the work roll speed, stand delivery side speed, plate out stand incident and thickness, and the coefficient of friction and deformation resistance of the rolled material from the detected value of the stand entry-exit side tension (d) first Based on the detected value of the step and the friction coefficient and deformation resistance obtained in the third step, the plate temperature rise T _E ′ in the roll bite in the rolled state and the plate temperature rise T _m ′ when the rolling reduction is changed are obtained, Fourth step for obtaining a reduction ratio satisfying ΔT _L −ΔT _f ≧ T _m ′ −T _E ′ (e) Fifth step for controlling the reduction ratio using the reduction ratio obtained in the fourth step as a target value.
In these inventions, the cooling water of the plate cooling device installed between the stand outlet side plate thickness, the rolling load, other detected values, or these detected values and the temperature detector for detecting the plate surface temperature from the rolling mill outlet side. The friction coefficient and deformation resistance are obtained based on the detected temperature and flow rate values. Then, the roll bite outlet temperature or the rising temperature in the roll bite is obtained from these values, and the rolling reduction is controlled so that these do not exceed the heat scratch control target temperature. Therefore, the temperature inside the roll bite can be maintained below the temperature at which heat scratches do not occur.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows an example of a cold tandem rolling mill in which the rolling method of the present invention is implemented. Although the number of stands of the cold tandem rolling mill is usually 2 to 8, and 5 stands are shown in FIG. 1, the number of stands is not limited to this. The stands 1 to 5 are each composed of a work roll 11, an intermediate roll 13, and a backup roll 15. The stands where heat scratches are likely to occur vary depending on the reduction ratio, plate thickness, rolling load, tension, rolling material, lubrication conditions, etc. of each stand. Usually, heat scratches tend to occur at a later stage stand where the rolling load and work roll speed increase. In the cold tandem rolling mill of FIG. 1, the fourth stand 4 is in a state where heat scratches frequently occur because the final stand 5 is under light rolling dull rolling. In the case where there is a possibility that heat scratches may occur in a stand other than the subsequent stand, the present invention can be applied to those stands. A lubricating oil supply device 26 is disposed on the entry side of each stand. The final stand 5 includes a work roll cooling device 30 and a roll cooling drainer 32.
[0017]
In FIG. 1, a temperature detector 24 is provided after the draining and tension detecting device 22 on the entrance side and the exit side of the rolling stand of the fourth stand 4, and the plate temperature T of the plate S being rolled is detected at a constant cycle. Has been. The temperature detector 24 is preferably a non-contact type, for example, a radiation thermometer. The rolling load P of the fourth stand 4 is detected by a load cell (not shown). The tension (force per unit area) σ _b , σ _f on the entry side and exit side of the rolling mill can be obtained by dividing the total tension by the plate cross-sectional area (plate thickness / plate width). The total tension is detected by a load cell (not shown) of the draining / tension detecting device 22 provided on the inlet side and the outlet side of the rolling mill. A plate thickness measuring device 17 such as an X-ray plate thickness meter is provided on the entry side and the exit side of the fourth stand 4, and a plate speedometer (not shown) is provided on the exit side of the fourth stand 4 and the third stand 3. ), For example, a laser plate speedometer is provided. By these measuring instruments, the inlet side and outlet side plate thicknesses H and h of the fourth stand 4 and the inlet side and outlet side plate speeds V _I and V _O are detected, respectively. Work roll velocity V _R of the fourth stand 4 is detected by the rotation speed detector (not shown) the rotational speed of the motor that drives the work rolls 11, the detected rotational speed of the motor and the work roll diameter D and the gear It is obtained by calculating using the ratio. Further, the plate S is cooled by the plate cooling device 20 on the entrance side and the exit side of the fourth stand.
[0018]
In the tandem cold rolling mill, the work roll diameter D, the roll driving system gear ratio, the plate width W, the material thickness (H _S: thickness at entrance side of the first stand 1), and a simple tensile yield stress when the material σ _y is known and can be input in advance to a calculator (not shown). The rolling load of the present invention is a load required for plastic deformation of the material, and when the stand has a shape control device such as a bender, those forces were detected and obtained by the load cell described above. This means the load excluding the force of the bender etc. from the load.
[0019]
Next, a plate temperature estimation method will be described. The plate temperature detector 24 provided on the exit side of the rolling mill detects the plate temperature on the exit side of the rolling mill at a constant period τ (for example, 5 s), and estimates the plate temperature T _O at the exit of the rolling mill roll bite.
[0020]
In general, the plate temperature T _S when water cooling is performed is given by Equation (1).
[Expression 1]

Therefore, the temperature T _{O at} the roll bite outlet is expressed by equation (2) by rearranging equation (1).
[Expression 2]

Here, T _w : Cooling water temperature T _S of the plate cooling device: Plate temperature V _O at the plate temperature detection position: Plate speed h on the rolling mill exit side h: Plate thickness ρ _S on the rolling mill exit side: Plate density C _S : specific heat h of the plate h _S : heat transfer coefficient t ₁ : time for the plate to pass through the distance from the plate cooling device to the draining device (t ₁ = L ₁ / V _O )
L ₁ is the distance from the plate cooling device to the draining device. It is necessary to model the relationship between the heat transfer coefficient h _S of the plate and the amount of cooling water (cooling water supply amount per unit time unit area) through experiments. Expression (3) shows a general form of a heat transfer coefficient model expression including necessary parameters.
[Equation 3]

Q _w : Supply amount of cooling water,
W: Plate width [0021]
In the case of air cooling, a temperature change due to air cooling can be ignored if the air cooling time is within about 0.5 seconds (rolling speed of about 500 m / min or more). Therefore, the exit side plate temperature of the front stand can be regarded as the plate temperature at the plate temperature detection position as it is.
[0022]
A roll bite outlet plate temperature in a steady state is estimated based on the temperature data. For example, if the control cycle of reduction (control cycle of reduction to prevent heat scratching) is set to 1 minute, the plate temperature data for the past 1 minute (12 pieces in this case, but the reduction conditions are constant data) ) Is substituted into a function that represents an asymptotic curve that asymptotically approaches a constant value, and a constant of the function is determined by performing multiple regression, and the asymptotic value is determined as a plate temperature at the roll bite outlet in a steady state. _Is assumed to be an estimated value _Tf . Examples of such a function that represents an asymptotic curve that finally approaches a constant value include a · tan h (cX) and a + b (1−e ^−cx ). In this function, a, b, and c are constants, and finally asymptotically approach a and a + b, respectively. Accordingly, the measured temperature data is substituted into such a function to obtain the respective asymptotic values a or a + b, which are used as the steady state plate temperature estimated value T _f .
[0023]
In addition to such a method, for example, the control period of reduction (control period of reduction to prevent heat scratch) is set to 30 seconds, for example, and the six obtained in 30 seconds, which is the control period, are set. The temperature data may be linearly regressed to estimate the plate temperature 30 seconds after the next reduction control timing (next reduction control timing) to obtain an estimated value T _f of the plate temperature.
[0024]
Next, the setting of the heat scratch control temperature will be described. The minimum roll bite outlet plate temperature at which heat scratching occurs is determined in advance through experiments in which the work roll speed, rolling reduction, rolling lubrication conditions, and the like are changed, and this is _defined as the limit temperature T _Lim . The limit temperature may be set as the heat scratch control target temperature _TL , but the heat scratch control target temperature _TL is set to a temperature slightly lower than the limit temperature T _Lim described above, for example, about 3 to 6 ° C. Is preferred.
[0025]
The estimated value T _f of the plate temperature at the roll bite outlet and the above-described heat scratch control target temperature _TL are compared in the stand where heat scratches are likely to occur, in the fourth stand in the embodiment. If ΔT = T _L −T _f is positive, there is no possibility of heat scratching, so rolling is continued as it is. When ΔT = T _L −T _f is a negative value, there is a possibility of heat scratching, so rolling is performed with the rolling reduction changed so that ΔT becomes positive.
[0026]
A method for calculating the rolling reduction to be changed will be described below.
First, the friction coefficient μ and deformation resistance K _m during rolling are obtained. For the deformation resistance of the rolled material, the values of constants a, ε ₀ , and n shown in Equation (4) are obtained in advance by a tensile test.
[Expression 4]

Here, σ _y is the yield stress at the time of simple tension of the rolled material, and ε is the strain.
[0027]
Incidentally, the deformation resistance is affected by the strain rate of the impacts and the plate temperature, deformation resistance K _m obtained from the equation (4) is not necessarily exact value during rolling. Therefore, in the present invention, the rolling load formula and the advanced rate formula are combined to determine the deformation resistance and the friction coefficient during rolling. For example, Hill's load equation is developed for deformation resistance as shown in Equation (5) to determine the deformation resistance. Further, the advanced coefficient formula of Brand & Ford is developed for the friction coefficient as shown in Expression (6), and the deformation resistance obtained by Expression (5) is substituted into Expression (6) to obtain the friction coefficient. Equation (5) and (6) the subscript E is Ru calculation Nedea based on the detected value and the detection value at the time of rolling of the stand in. The calculated value is a value obtained by dividing the pre-tension detected by the load cell by the plate cross-sectional area as described above, or excluding the bending force from the rolling load detected by the load cell.
[Equation 5]

[Formula 6]

[0028]
In the above equation, there are two unknowns: a coefficient of friction μ _E and a constant (a in equation (4)) in the deformation resistance equation K _mE , the others are known and the number of equations is two. Therefore, this equation can be solved. In the calculation, it is preferable to use about 0.05 as an initial value of the friction coefficient μ _E and a value obtained by a tensile test as an initial value of the constant a in the deformation resistance equation.
[0029]
On the other hand, the rising temperature T ′ at the interface between the roll at the exit of the roll bite and the rolled material at this time is expressed by, for example, Expression (7) using the expression of Ono et al.
[Expression 7]

[0030]
T _dmax is the temperature rise at the exit of the roll bite at the interface between the roll and the rolled material, which is increased by the heat of deformation, and is expressed by equation (9) . T _fmax is the temperature rise at the exit of the roll bite at the interface that increases due to frictional heat, and is expressed by equation (8) .
[Equation 8]

[Equation 9]

[0031]
Substituting the physical property values and actual measured values of the respective stands into the equations (7) and (8), and the friction coefficient μ _E and the deformation resistance K _mE obtained by the method using the equations (5) and (6) described above. Then, the calculated value T _E ′ of the temperature rise T ′ at the interface between the roll at the exit of the roll bit of the stand and the rolled material is obtained.
[0032]
Next, in order to estimate the temperature change when the rolling reduction is changed, first, the friction coefficient μ _E and deformation resistance K _{mE obtained} and the measured values of the stand other than the _rolling reduction are used, and only the rolling reduction is changed. In this case, the rolling load P and the advance rate fs are calculated. Strictly speaking, changing the rolling reduction also changes the friction coefficient. However, since the fluid lubrication is almost dominant at a rolling speed of 1000 m / min or more, the influence of the rolling reduction on the friction coefficient may be ignored under the condition that heat scratch occurs.
[0033]
The rolling load P is calculated using, for example, Hill's load equation shown in Equation (10). The advanced rate fs is calculated using the Bland & Ford equation shown in equation (11). The roll flatness RE 'is calculated using the Hitchcook equation shown in equation (12).
[Expression 10]

[Expression 11]

[Expression 12]

[0034]
The rolling load is obtained by performing convergence calculation using equation (10) and roll flat equation (12), and the advanced rate is obtained from equation (11). By substituting these values into the equations (7) to (9), the temperature rise T _m ′ at the interface of the roll bite outlet when the rolling reduction condition is changed can be obtained. That is, the calculated value T _E ′ of the temperature rise at the interface of the roll bite outlet in the stand and the estimated value T _m ′ of the temperature rise at the roll bite outlet when the rolling reduction is changed are obtained. Although the temperature at the interface between the roll and the rolled material at the roll bite exit and the plate temperature at the stand exit side are not strictly the same, the temperature change when the rolling reduction condition is changed may be regarded as the same. Therefore, the difference between T _m ′ and T _E ′ (ΔT ′ = T _m ′ −T _E ′) and the difference between _TL and T _f described above (ΔT = _TL− T _f ) are obtained. In comparison, a rolling reduction condition such that ΔT ′ is equal to or smaller than ΔT (ΔT ′ ≦ ΔT) can be obtained by repeated calculation using, for example, the Newton method. The rolling reduction set value of the rolling mill is changed to the rolling reduction value obtained as described above. Several rolling reduction values that do not generate heat scratches that satisfy the above relationship can be obtained. An appropriate rolling reduction value may be selected from these rolling reduction values according to the rolling condition, but it is desirable to select the lowest rolling reduction value raim and change the rolling reduction setting value of the stand accordingly.
[0035]
In addition, since the amount of change in the rolling load can be predicted in advance during these controls, the thickness and shape can be controlled so that the plate thickness accuracy and plate shape defects do not occur.
[0036]
The above shows the method of controlling the heat scratch by the plate temperature on the exit side of the rolling mill roll bite, but depending on the lubricating oil, it may be better to control by the temperature rising in the roll bite, not the temperature at the exit of the roll bite. is there. A method in that case will be described. In this case, the temperature Ti of the plate is detected by the temperature detector even on the inlet side of the rolling mill. In the case where water cooling is not performed from the temperature detector to the rolling mill inlet side, even if the lubricating oil is applied to the surface of the plate at a rolling speed of 500 m / min or more, their influence on the plate temperature at the roll bite inlet can be ignored. Accordingly, we do it in the same manner by using a T _O '= T _O -Ti instead of the aforementioned T _O.
[0037]
【Example】
The cold tandem rolling mill used is a tandem rolling mill consisting of the same five stands as shown in FIG. 1. Table 1 shows the rolling conditions of the fourth stand as a stand where heat scratches occur.
[Table 1]

[0038]
Under the operating conditions, when a large number of coils of the same size are rolled under the same rolling conditions, the average temperature of the work roll rises and the plate temperature on the fourth stand outlet side rises. From operation data so far, it is empirically known that heat scratches frequently occur when the plate temperature on the outlet side of the fourth stand is about 160 ° C. or higher. Then, this invention was applied and the effect was experimentally investigated.
[0039]
The limit temperature T _Lim, which is the lowest roll bite outlet plate temperature at which heat scratches, which are obtained in advance by experiments, is 162 ° C., and the heat scratch control target temperature is T _L = 162−4 = 158 ° C. Also, the control cycle of the reduction ratio for heat scratch control is 30 seconds, the sampling time is 5 seconds, the plate temperature at the roll bite outlet is calculated from the data of 30 seconds (six) during that period, and linear regression is performed, 30 seconds The subsequent roll bite outlet plate temperature was determined and used as an estimated value T _f of the plate temperature.
[0040]
FIG. 3 is a diagram showing the effect of the first invention, and shows the relationship between the number of rolled coils and the plate temperature on the fourth stand roll tool outlet side. ◯ in FIG. 3 indicates the case of the conventional rolling method, and ● indicates the case when the present invention is applied. With the conventional rolling method, the estimated value of the roll bite outlet plate temperature is 160 ° C. or more with 11 coils, and there is a risk of heat scratching. Therefore, the work roll speed is reduced to 900 m · min ⁻¹ for operation. It was. However, by applying this invention, the reduction rate is changed from 28.6% to 23-25%, so that the plate temperature does not exceed 158 ° C. even with 30 coils and the work roll speed is reduced. It was rolled without any heat treatment and, of course, no heat scratch was generated. Of course, when the rolling reduction rate of the fourth stand is changed, the plate thickness (product plate thickness) changes, so it goes without saying that the insufficient rolling reduction amount needs to be adjusted by another stand. Preferably, the adjustment is performed with the first stand that generates the least heat scratches.
[0041]
Since the accuracy deteriorated when the plate cooling conditions of the third stand were changed significantly, the second invention was applied. That is, the limit temperature ΔT _Lim, which is a roll bite rising temperature at which heat scratches are obtained in advance by experiments, is 108 ° C., and the heat scratch control target temperature is ΔT _L = 108−4 = 104 ° C. Also, the rolling cycle control cycle is 30 seconds, the sampling time is 5 seconds, the roll bite rise temperature is calculated from the data of 30 seconds (six) during that period, and linear regression is performed to obtain the roll bite rise temperature after 30 seconds. This was taken as the estimated value ΔT _f of the plate temperature. As a result, no heat scratch was generated even when the plate cooling conditions of the third stand were significantly changed.
[0042]
【The invention's effect】
The temperature inside the roll bite can be suppressed with high accuracy below a temperature at which heat scratches do not occur, and generation of heat scratches can be prevented without impairing productivity.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing an example of a cold tandem rolling mill for carrying out the present invention.
FIG. 2 is an enlarged view of two stands in a cold tandem rolling mill.
FIG. 3 is a graph showing the relationship between the roll bite outlet temperature of the rolled material and the number of rolled coils.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 Work roll 13 Intermediate | middle roll 15 Backup roll 17 Plate thickness detector 20 Plate cooling device 22 Draining and tension detection device 24 Temperature detector 26 Lubricating oil supply device S Rolled material (plate)

Claims (2)

Cold tandem rolling, in which a stand that is prone to heat scratching is specified in advance, and rolling is performed in the next step while performing plate cooling (water cooling) between the plate temperature detector from the rolling mill roll bite exit side in the specified stand. Rolling method in the machine.
(A) Stand exit side plate temperature, rolling load, work roll speed, stand exit side plate speed, stand entry / exit plate thickness, stand entry / exit side tension, plate cooling water temperature, and plate cooling water supply amount 1 step (b) From the detected values of the stand exit side plate temperature, stand exit side plate thickness, stand exit side plate speed, plate cooling water temperature, and plate cooling water supply amount, the plate temperature is estimated multiple times, and the estimated Second step of estimating roll bite outlet plate temperature _Tf in the rolled state based on plate temperature data (c) When the roll bite outlet estimated plate temperature _Tf exceeds a preset heat scratch control target temperature _TL , Rolling material from the detected values of rolling load, work roll speed, stand exit side plate speed, stand entry / exit side plate thickness, and stand entry / exit side tension in the first step The third step (D) the detected value of the first step of obtaining a friction coefficient and deformation resistance, as well as a plate temperature increase T _{E 'in} the roll bite in the rolling state by the friction coefficient and deformation resistance obtained in the third step, reduction Roller bite inner plate temperature rise T _m ′ when the rate is changed, and the rolling rate obtained in the fourth step (e), the fourth step, where T _L −T _f ≧ T _m ′ −T _E ′ is determined. 5th step of controlling the reduction rate with the rate as the target value Cold tandem rolling, in which a stand that is prone to heat scratching is specified in advance, and rolling is performed in the next step while performing plate cooling (water cooling) between the plate temperature detector from the rolling mill roll bite exit side in the specified stand. Rolling method in the machine.
(B) Stand entry side plate temperature, stand exit side plate temperature, rolling load, work roll speed, stand exit side plate speed, stand entry / exit side plate thickness, stand entry / exit side tension, plate cooling water temperature, and plate cooling water supply amount (B) Estimating the plate temperature multiple times from the detected values of the exit side plate temperature, stand exit side plate speed, stand exit side plate thickness, plate cooling water temperature, and plate cooling water supply amount, based on the estimated the plate temperature data, a second step of obtaining a temperature rise [Delta] T _f at the roll bite outlet plate obtains a temperature T _f, the roll bite of the rolling state by subtracting the stand entry side temperature from T _f in the rolling state (c) when said estimated temperature rise [Delta] T _f in the roll bite exceeds heat scratch control target temperature [Delta] T _L which is set in advance, the first step Rolling load, the work roll speed, stand delivery side speed, thickness at delivery side of the stand incident and, and the stand from the detection value of the input and output side tension of the third step (d) a first step of obtaining a friction coefficient and deformation resistance of the rolled material Based on the detected value and the friction coefficient and deformation resistance obtained in the third step, the plate temperature rise T _E ′ in the roll bite in the rolled state and the plate temperature rise T _m ′ when the rolling reduction is changed are obtained, and ΔT _L Fourth step for obtaining a reduction rate satisfying −ΔT _f ≧ T _m ′ −T _E ′ (e) Fifth step for controlling the reduction rate with the reduction rate obtained in the fourth step as a target value.

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