GOALI: Online Dynamic Control of Cooling in Continuous Casting of Thin Steel Slabs

B.G. Thomas, J. Bentsman, S. Vapalahti, K. Zheng, B. Petrus, H. Li, H. Castillejos, F. Acosta

Continuous Casting Consortium, National Science Foundation GOALI DMI 05-00453

Project Overview

Temperature variations during cooling cause quality problems such as cracks, especially under transient conditions such as caused by changes in casting speed.  Setting the spray water flow rates to maintain optimal temperature profiles during process changes becomes increasingly difficult when the casting speeds are high and response times must be fast.  This project aims to develop a fundamentally-based online system to dynamically control the water flow rates in order to continuously optimize and stabilize cooling conditions in the thin slab casting process.  The system will use model-based predictive control, incorporating both online measurements of mold heat removal and on a high-speed finite-difference model of heat conduction and solidification during the process. 

National Science Foundation Support:

DMI 05-00453
5/1/2005 to 4/30/2008
NSF Program Director: Mary Reallf, (703) 292-7088
NSF Grants Official: Denise M. Giles, (703) 292-8212

Industry Support and Partnerships:

Nucor Steel, Decatur, Alabama
Nucor Steel is the GOALI partner of this project. We are implementing and testing our new models in their plant first, with their help and
support.

Cinvestav
Cinvestav is providing the laboratory experimental data for measuring the heat transfer coefficients during spray cooling.

Continuous Casting Consortium
The Continuous Casting Consortium is a University of Illinois center providing partial matching funds to the project. Students work on
projects related to both this project and to the center.

Delavan Spraying Technologies, Monroe, NC, and Spraying Systems, Wheaton, Illinois
Both of these companies have supplied technical information on the
spray nozzles used in continuous casting machine secondary cooling systems, needed to help our fundamental model investigations, in addition to funds for related student projects in the area.

Significant Results

A new online computer model-based control system is being created to control solidification and temperature development during the continuous casting of steel. It features an accurate and fundamentally-based dynamic software sensor of the spray-cooling region which is integrated with online measurements of mold heat extraction and other process parameters. By maintaining the steel temperature through operational transients, this system aims to enable faster and more efficient casting with improved quality of the steel product. This multi-faceted research project includes the development, validation, and calibration of the online control models, laboratory measurements to better characterize heat transfer during spray cooling, improved control algorithms, and increased understanding of defect formation in the continuous casting process. Work this past year has obtained several new findings, which are significant to the project goals. Most significant are:

- A novel modeling algorithm is able to update in real time, the complete solidification and temperature profile in two dimensions at every second during continuous online operation.
- The new control system maintains temperature more closely than the conventional control system currently in use at most plants.
- This new modeling tool is now available to study thin-slab casting behavior, to enable future process and control improvements
- New optimal control algorithms have been developed, with application to the equations governing heat transfer in continuous casting.

Future improvements to this novel model-based control system should revolutionize the control of continuous casting spray systems, with improved steel quality, and will have beneficial impact on related scientific fields and commercial processes.

Impact

This project has contributed to the 6 separate sub-disciplines of modeling and measurement of solidification heat transfer in continuous casting (better models), control of continuous casting (new tool: software system), better understanding of heat transfer in spray cooling; better understanding of defect formation in continuous casting, and better understanding of control theory and practice for these manufacturing processes.  Specifically:

A finite difference model, CON1D, has been optimized to run in an online environment under fully transient conditions.  It has been integrated into a control system and found to outperform the existing control system used at the steel plant.  It is currently being tested.  Spray cooling experiments have begun, new control algorithms have been developed, and new insights into defect formation have been found.  Future improvements to this novel model-based control system should revolutionize the control of continuous casting spray systems, with improved steel quality, and will have beneficial impact on related scientific fields and commercial processes.

NSF Publications

Kim, J. and J. Bentsman, "Robust Adaptive Control of Parabolic and Hyperbolic Varying Systems and its Multiresolution Finite-Dimensionalization," IEEE Transactions on Automatic Control (submitted),2006.

Kim, J. and J. Bentsman, "Multiresolution Finite-Dimensionalization of Parameter Update Laws in Adaptive Control of Distributed Parameter Systems," 45th IEEE Conference on Decision and Control, (San Diego, CA, Dec. 13-15, 2006), 2006, 2801-2806.

Kim, J. and J. Bentsman, "Disturbance Rejection in Robust Model Reference Adaptive Control of Parabolic and Hyperbolic Systems," 45th IEEE Conference on Decision and Control, (San Diego, CA, Dec. 13-15, 2006), 2006, 3083-3088.

B.G. Thomas, J. Bentsman, K. Zheng, S. Vapalahti, B. Petrus, A. Behera, A.H. Castillejos and F.A. Acosta, "Online Dynamic Control of Cooling in Continuous Casting of Thin Steel Slabs," in Proceedings of 2006 NSF Design, Service, and Manufacturing Grantees and Research Conference, W. DeVries and M. Leu, eds., (St. Louis, Missouri, July 24-27, 2006), 2006, 11p. Click here for a PDF version. (623 KB)

Zheng, K., B. Petrus, B.G. Thomas and J. Bentsman, "Design and Implementation of a Real-time Spray Cooling Control System for Continuous Casting of Thin Steel Slabs,," in AISTech 2007, Steelmaking Conference Proceedings, Indianapolis, May 7-10, 2007, Association for Iron and Steel Technology, Warrendale, PA, USA, 2007.