• Journal of Mechanical Science and Technology
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• v.18 no.3
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• pp.379-387
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• 2004

A novel flatness sensing system which is called the Flatness Sensing Inter-stand Looper(FlatSIL) system is suggested and a self-tuning PI control system using the FlatSIL is designed for improving the flatness of hot strip in finishing mill processes. The FlatSIL system measures the tension along the direction of the strip width by using segmented rolls, and the tension profile is approximated through the tension of each segmented roll. The flatness control system is operated by using the tension profile. The proposed flatness control system as far as the tension profile-measuring device works for the full strip length during the strip rolling in finishing mills. The generalized minimum variance self-tuning (GMV S-T) PI control method is applied to control the flatness of hot strip which has a design parameter as weighting factor for updating the PI gains. Optimizing the design parameter in the GMV S-T PI controller, the Robbins-Monro algorithm is used. It is shown by the computer simulation and experiment that the proposed GMV S-T PI flatness control system has better performance than the fixed PI flatness control system.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2013.05a
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• pp.513-514
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• 2013

• 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 Mechanical Science and Technology
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• v.15 no.2
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• pp.225-231
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• 2001

A mathematical model for the analysis of roll gap phenomena in the strip temper rolling process is described. A new approach to solve the roll indentation and diverging problem in modeling of severe temper rolling cases is obtained by adopting the preliminary displacement principle of two contacted rough bodies to describe the friction behavior in the roll gap. The mechanical peculiarities of the temper rolling process, such as a high friction value with high roughness rolls and a non-circular contact arc, low reduction and non-negligible entry and exit elastic zones as well as central preliminary displacement zone etc., are all taken into account. The deformation of work rolls is calculated with the influence function method and an arbitrary contact are shape is permitted. The strip deformation is modeled by the slab method and the entry and exit elastic deformation zones are included. The preliminary displacement principle is used to determine the boundaries and to calculate the friction of the central preliminary displacement zone. The model is calibrated against the production mill data and installed in the setup computer of a temper rolling mill in POSCO. The validity and precision of the model have been proven through a comparison of the measured roll forces and the predicted ones.

• Transactions of Materials Processing
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• v.23 no.7
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• pp.425-430
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• 2014

The aim of the current study was to predict the plastic deformation behavior of a heated slab during hot rough rolling. FE-simulations were performed to investigate the metal flow and to locate the position of surface material from the slab through the rough rolling and onto the strip, using a material point tracking technique. In addition, experimental hot rolling trials were conducted where artificial defects were impressed onto a heated slab in order to validate the FE-simulation results. The simulated results show the same tendency of deformation behavior as the experimental measurements. The movement of slab defects from the side surface towards the strip center is directly linked to the extent of lateral spread during the rolling.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.432-435
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• 2005

Extensive width reduction of slabs is an important technology to achieve continuous production between the steelmaking and hot rolling processes. Conventionally, a vertical roll process has been used to achieve extensive width reduction. However, it is impossible to avoid the defects such as dog-bone, fish tail and camber. The deformation behavior in the width sizing process is more favorable than that in conventional vertical rolling edger, i.e. the material better flows toward the center of slab. This study is carried out to investigate the deformation of slab by two-step sizing press. The FE-simulation is utilized to predict plastic deformation mode in compression by a sizing press of slabs far hot rolling. In this paper, the various causes of the asymmetrical rolling phenomena are mentioned for the purpose of understanding of rolling conditions. Analytical results of slab-deformation by sizing press are presented below in this study.

• Proceedings of the KIEE Conference
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• 1988.11a
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• pp.56-59
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• 1988

The main purpose of Set-up control of hot strip mill plant is to obtain the most regular thickness. Then the learning or adaptive computer control in hot strip rolling mill has been developed. But it is very difficult to keep the inter-stands load distribution ratio uniform; so that the deviation of strip flatness is not avoidable. This leads to the degradation of quality of the products. In this report, an improved method base on the steepest descent method including the computation of optimum step size. This method is applied to the off-line simulation. In consequence, the better balances of inter-stands load distribution is achieved in addition to improvements of output thickness of hot strip mill in POSCO.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.5
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• pp.829-837
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• 1992

This paper presents a new approach for the analysis of hot strip rolling processes. The approach is based on the finite element method and capable of predicting velocity field in the strip, temperature field in the strip, temperature field in the roll, and roll pressure. Basic finite element formulations for heat transfer analysis are described with emphasis on the treatment of numerical instability resulting from a standard Galerkin formulation. Comparison with the theoretical solutions found in the literature is made for the evaluation of the accuracy of the temperature solutions. An iterative scheme is developed for dealing with strong correlations between the metal flow characteristics and the thermal behavior of the roll-strip system. A series of process simulations are carried out to investigate the effect of various process parameters including interface friction, interface heat transfer coefficient, roll speed, reduction in thickness, and spray zone. The results are shown and discussed.

• Journal of Institute of Control, Robotics and Systems
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• v.15 no.10
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• pp.1062-1070
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• 2009

The strip shape for the stainless steel process has made an issue of the strip quality, and hence the shape control method is developed at the Sendzimir rolling mill (ZRM). ZRM is a stainless cold rolling mill and has actuators for the shape control. They are first intermediate rolls and top crown rolls, which are controlled horizontally and vertically, respectively. The shape control of the stainless steel rolling process has difficulty in obtaining the symmetrical shape. The objective of the shape control is to minimize the shape deviation and to maintain stable state, which keeps symmetrical shape pattern in the lateral direction. The method of the shape recognition employs a least squares method and neural network. The shape deviation is the difference between the target shape and actual shape and is controlled by the fuzzy shape control. The fuzzy shape control using operator's informative knowledge is proposed in this paper. The experiments are carried out online for various stainless materials and sizes. The productivity of the rolling process has increased from 9.0 to 9.4 tons per hour.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.08a
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• pp.403-411
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• 1999

The steel plate for shadow mask is used in a Cathode-ray tube of TV monitor and is the strictest product in surface quality because hundreds thousand of holes are perforated in a plane of 25 ${\times}$25 inches. To mass-produce this product, a reversible cold rolling mill for silicon steel was used and the rolling technology and the activity for quality improvement are described in this work. Because the steel plate is a mild steel, which is very sensitive to strip-breakage even in a low tension, we reset the minimum tension values matching to the operating conditions. The roll mark due to the multi-segmented araangement of shape controlling roll was prevented by hardening the intermediate shape controlling roll and by changing the existing working-roll into a HSS (Hig Speed Steel) roll. The scratch caused by the speed difference between a idle roll and a strip was prevented by increasing the roll roughness. With these activities, the steel plate for shadow mask can be stable. The continuous improvement of quality is, however, required for the customer satisfaction both of domestic and overseas market.