A Framework for Soft Sensing of Liquid Pool Length of Continuous Casting Round Blooms
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TRODUCTION
CONTINUOUS casting process is now the predominant solidification process of steel. In the process, the molten steel is pouring into a water-cooled copper mold to form the initial shell with the corresponding shape, such as slab, billet, or bloom. After passing through the mold, the shell enclosing the molten steel moves down into the secondary cooling zone (SCZ), where further cooling takes place by water sprays and the shell grows increasingly. On exit from the SCZ, the strand cools off by radiation in the air and finishes the solidification gradually. Then the strand is cut into segments of fixed length, and transported for further processing. As shown in Figure 1. In the continuous casting process, liquid pool length is a vital parameter for solidification control as it can directly reflect the solidification state. First, the liquid pool length is important to determine the casting speed. In most cases, to avoid the straightening cracks, the casting speed is limited as the end point of the liquid pool finishes solidification before the straightener. Second, liquid pool length is the key parameter to determine the proper position for soft reduction and final electromagnetic stirring, which are the two main technologies for greatly improving the center quality of continuous casting products at present. Third, liquid pool length can be used to determine the electric current
JIAN YANG, Ph.D. Student, ZHI XIE and JING NING, Professors, are with the College of Information Science and Engineering, Northeastern University at Shenyang, Liaoning, P.R. China 110819. Contact e-mail: [email protected] WENHONG LIU, Associate Professor, is with State Key Laboratory of Synthetical Automation for Process Industries, Northeastern University at Shenyang, Liaoning, P.R. China 110819. ZHENPING JI, Professor, is with the College of Information Science and Engineering, Shenyang Ligong University at Shenyang, P.R. China 110159. Manuscript submitted September 28, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS B
of final electromagnetic stirring to control the flow speed of liquid steel in the mushy zone. However, it is difficult to measure the liquid pool length by direct hardware measurement, such as nailshooting[1] and wedging method.[2] A probable reason is that it costs too much using these present techniques to finish the shell-thickness measurements along the casting direction until the final solidification point is found, and there are so many steel grades. Furthermore, during the whole measuring process, the final solidification point will change its position when the casting conditions are changing. Non-contact techniques including ultrasound scanning[3] and new developing vibration method[4] will encounter the problem of low precision due to that the mushy zone cannot be strictly distinguished with the solidified shell by these sensors. So in this paper, a framework based on heat transfer model for soft sensing of the liquid pool length of the continuous casting round bloom has been presented. The framework includes three parts: the
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