The Estimation and Control of the Electroslag Remelting Melt Rate by Mechanism-Based Modeling
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I.
INTRODUCTION
THIS article is organized as follows. Section I introduces related research and the proposed approach. Section II discusses the modeling procedures and the coefficient modification method. The model validity is evaluated using practical application data in Section III. Section IV serves as a conclusion. The deduction of the melt rate equation is presented in Appendix A. The symbols and explanations are listed in the Nomenclature table. A. Electroslag Remelting Electroslag remelting (ESR) technology has been employed effectively in the metallurgy of special steel and alloy steel. The fine-grained, high-purity ingot products are used widely in the production of turbine disks for aircraft engines, aeronautical bearings, submarine shells, gun steels, titanium alloys for astronautics, crank axles for ships, cold rollers, and high-speed tool steels. In the ESR process, a high current passes through the consumable electrode and the molten slag. Then, the electrode melts in the superheated slag pool and resolidifies in the molten, water-cooled mold. Highquality solidification processes require that the melt rate of the electrode be stable. Thus, the melted metal per minute is rather small compared with the ingot mass. As a result, the nonmetal impurities in the molten pool are more likely to conglomerate and float, and the molten metal droplet detached from the electrode tip will be filtered fully in the slag pool. The ESR mechanism is illustrated in Figure 1(a), and its equivalent circuit is shown in Figure 1(b). The slag resistance is a timevarying parameter in the ESR process.
WANZHOU LI, Professor, and WEIYU WANG, YUECHEN HU, and YIXING CHEN, Students, are with the Department of Automation, Tsinghua University, Beijing 100084, P.R. China. Contact e-mail: [email protected] Manuscript submitted August 6, 2011. Article published online December 6, 2011. 276—VOLUME 43B, APRIL 2012
Major technological parameters affecting the ESR process include the following: (a) Electric current density, i.e., the current per unit cross-sectional area of the electrode (A/cm2). The ratio of the current density to the electrode diameter is restricted to a range so that the ESR process is stable. A ratio exceeding either the upper or the lower limit will result in an unstable remelting or an arc process. As the electrode diameter increases, the current density for stable remelting decreases. Specific data depend on the fill ratio. (b) Fill ratio, i.e., the ratio of the electrode diameter to the inner diameter of the crucible. This parameter affects heavily the stability, quality, and power consumption of remelting. When the fill ratio is large, an increase in power and the skin effect will lead to a flat end-profile of the electrode, a shallow electrode immersion, sparsely distributed molten droplets, a homogenized slag–metal interface temperature, and an inverse-trapezoidal shape of the molten pool bottom. Under this condition, if a larger power is used, then solidification tends to be upright while the pool bottom is still relative
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