• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1091-1096
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• 2003

It is very important to find out causes of strip pinching for the high quality of products and for the stable operation of hot roiling system. We have examined the strip pinching from three points of view to find out the causes of strip pinching in hot rolling system: strip shape, rolling operation conditions, and behavior of strip. Wedge, off center, and difference of rolling force through CMD are found to possibly provide major initial causes of strip pinching. Generally strip pinching occurred in the tail of strip. Thus, computer simulations by using a FEM code were also carried out to find out the initial mechanism of strip pinching depending upon the force and geometric boundary conditions at the time of strip tail rolling. The strong compression force effect due to the sudden release of strip tail from the work roll and non-uniform strip tail shape (ex. Tongue tail) across the CMD were found to provide possible major causes of strip pinching.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.08a
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• pp.336-345
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• 2004

Investigated via a series of finite-element(FE) process simulation is the effect of diverse process variables on some selected non-dimensional parameters characterizing the thermo-mechanical behavior of the roll and strip in hot strip rolling. Then, on the basis of these parameters, on-line models are derived for the precise prediction of the temperature changes occurring in the bite zones as well as in the inter-stand zones in a finishing mill. The prediction accuracy of the proposed models is examined through comparison with predictions from a FE process model.

• Journal of Power System Engineering
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• v.12 no.1
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• pp.72-79
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• 2008

This paper designs a looper-tension controller for mass-flow stabilization in hot strip finishing mills. By Newton's 2nd law and Hooke's law, nonlinear dynamic equations on the looper-tension system are firstly derived, and linearized by a linearization algorithm using a Taylor's series expansion. Moreover, a tension calculation model is obtained from the nonlinear dynamic equations which is called as a soft sensor of strip tension between two neighboring stands. Next, a looper-tension servo controller is designed by an ILQ(Inverse Linear Quadratic optimal control) algorithm, and it is combined with a minimal disturbance observer which to attenuate speed disturbances by AGC and operator interventions, etc.. Finally, it is shown from by a computer simulation that the proposed ILQ controller with a disturbance observer is very effective in stabilizing the strip mass-flow under some disturbances, moreover it has a good command following performance.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.08a
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• pp.175-183
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• 2004

In hot strip rolling, a capability for precisely predicting roll force is crucial for sound process control. In the past, on-line prediction models have been developed mostly on the basis of Orowan's theory and its variation. However, the range of process conditions in which desired prediction accuracy could be achieved was rather limited, mainly due to many simplifying assumptions inherent to Orowan's theory. As far as the prediction accuracy is concerned, a rigorously formulated finite element(FE) process model is perhaps the best choice. However, a FE process model in general requires a large CPU time, rendering itself inadequate for on-line purpose. In this report, we present a FE-based on-line prediction model applicable to precision process control in a finishing mill(FM). Described was an integrated FE process model capable of revealing the detailed aspects of the thermo-mechanical behavior of the roll-strip system. Using the FE process model, a series of process simulation was conducted to investigate the effect of diverse process variables on some selected non-dimensional parameters characterizing the thermo-mechanical behavior of the strip. Then, it was shown that an on-line model for the prediction of roll force could be derived on the basis of these parameters. The prediction accuracy of the proposed model was examined through comparison with measurements from the hot strip mill.

• Journal of Institute of Control, Robotics and Systems
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• v.11 no.6
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• pp.518-523
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• 2005

Strip off-center is one of the major problems in hot strip mill line. The key to good centering is having good equipment, modern control systems, excellent maintenance and an understanding of milling process. Therefore, this study aims to develop a system that is useful for quantitative analysis of strip off-center. In this study, the measuring method of strip off-center was thoroughly studied and the exclusive control board to line scan camera were designed. Also, the manipulated type housing for line scan camera was developed to adjust initial parameters for strip width and center line. In order to check the accuracy and usefulness of the developed system, FM stand in $\#2$ Hot Strip Factory in Pohang Steel Works was targeted.

• Proceedings of the KIEE Conference
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• 1986.07a
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• pp.128-131
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• 1986

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.211-214
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• 2008

The Mechanical properties of steel in hot strip mill were associated with the various rolling conditions such as alloy composition, plastic deformation, cooling history and so on. After coiling process of strip which is the end of hot rolling process, the coil can be the final product or can be applied by another process, that is, cold rolling or skin pass rolling with the additional changes of mechanical properties. Skin pass rolling process with the small reduction affects the mechanical properties of the strip. Because many kinds of hot strips are delivered to the customers after the skin pass process, it is important for us to know the skin pass effects for the mechanical properties of the hot rolling strip. In this study, the variations of mechanical properties of the strip after the skin pass rolling will be discussed. Then, the mathematical model will be proposed for the prediction of mechanical properties of the final products with the comparison between measured and calculated values.

• Journal of Institute of Control, Robotics and Systems
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• v.13 no.4
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• pp.377-384
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• 2007

This paper studies on the relation between linearization methods and controller gains in the looper ILQ(lnverse Linear Quadratic optimal control) system for hot strip finishing mills. Firstly, two linear models arc respectively derived by a linearization method using Taylor's series expansion and a static state feedback linearization method, respectively, and the linear models are compared with the nonlinear model. Secondly, the looper servo controllers are respectively designed on the basis of two linearization models. Finally, the relation between the performances of two ILQ servo controllers and the linearization methods, and the structures and control gains of two controllers are evaluated by a computer simulation.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.955-958
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• 2003

Strip top mark is one of the major problem areas in hot strip coiling operation. The key for good coiling is having a precise detection instrument of strip head end and an understanding of QOC(quick open control) control algorithm and mechanism. Therefore, this study aims at developing QOC monitoring system that is useful for avoiding strip top mark at coiling process. In this study, strip movement between mandrel and unit roll(wrapper roll) was thoroughly studied using high speed camera. The monitoring system was developed to calculate QOC open time and to estimate optimal open time values for good coiling operation. Its performance has been proven by extensive field tests on downcoiler of #2 Hot Strip Mill Line in Pohang Works.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.403-407
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• 2005

This paper proposes a looperless tension control algorithm which is robust to disturbance and tensional variation in rolling process using SVR(Support Vector Regression). Hot rolling process which is global technology to coil steel after continuous finishing process for welded bars followed by roughing mill process, becomes hot issue. Finishing mill process not only makes it possible to produce ultra thin steel strip(0.8 mm) but enhance the quality of terminals of coil, which increases the productivity due to faster process. Constant tension control between stands in hot rolling process is essential to enhance the quality of steel. Sensorless tension control is under research by some advanced companies to replace the conventional tension control method because in continuous finishing mill process, it is impossible to install the looper used in conventional control system. Simulation results show the effectiveness of the proposed algorithm.