Research overview of formation and heat transfer of slag film in mold during continuous casting
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摘要: 介紹了模擬結晶器內渣膜形成的實驗方法, 綜述了國內外學者在保護渣傳熱方面所做的研究工作, 包括固態渣膜的界面熱阻、保護渣的導熱系數、輻射傳熱以及渣膜的光學性質, 并提出了今后在渣膜形成及傳熱研究中有待進一步完善的內容和方向.現有的研究結果表明利用熱絲法可以對渣膜的形成過程進行原位觀察, 采用水冷銅探頭法可以獲取用于研究渣膜微觀組織的固態渣膜樣品.渣膜的界面熱阻在0.0002~0.002 m2·K·W-1之間.在800℃以下, 保護渣的導熱系數在1.0~2.0 W·m-1·K-1范圍內, 且隨溫度的升高而逐漸增加.渣膜中的晶體一方面可以增加渣膜的界面熱阻, 另一方面可以提高固態渣膜的反射率, 起到降低輻射熱流的作用.此外, 過渡族金屬氧化物的加入以及固態渣膜中彌散分布的微小顆粒也能改變渣膜的光學性質, 從而影響通過渣膜的輻射傳熱.Abstract: Mold flux, which plays an important role in continuous casting, occurs when liquid slag on top of the molten steel infiltrates the gap between the shell and mold. During this process, a liquid slag film forms on the shell side, whereas a solid slag film forms on the mold side. The behavior of the slag film between the shell and mold has a significant effect on the sequence casting and quality of the slab surface. To investigate the in-mold behavior and heat transfer of slag film, researchers have simulated the formation of slag film in the laboratory. Measurements and theoretical calculations have been performed to study the heat transfer of slag film. In this paper, the experimental methods used to simulate the formation of slag film were described and the research related to heat transfer in slag film was summarized, including the interfacial thermal resistance, the thermal conductivity of the mold flux, radiative heat transfer, and optical properties of the slag film. The issues related to the formation and heat transfer of slag film were also identified, that require further investigation. The results of recent studies indicate that the hot thermocouple technique could be applied to observe the formation of slag film, and the copper-finger dig test could be used to obtain samples for investigations related to the microstructure of solid slag film. The interfacial heat resistance is reported to be between 0.0002 and 0.002 m2·K·W-1. The thermal conductivity of mold flux at 800℃ ranges from 1.0-2.0 m2·K·W-1, and increases with increased temperature. Crystals in the solid slag film not only increase the interfacial heat resistance, but also decrease the radiative heat flux by reducing the reflectivity of slag film. Furthermore, due to the resulting change in optical properties, the addition of transition metal oxides and fine particles dispersed in slag film may also influence the radiative heat transfer through slag film.
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Key words:
- continuous casting /
- mold flux /
- slag film /
- interfacial thermal resistance /
- radiation
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圖 2 熱絲法實驗裝置示意圖. (a) 工業攝像機；(b) 樣品室；(c) 單熱電偶；(d) 雙熱電偶；(e) 加熱裝置；(f) 計算機
Figure 2. Schematic diagram of experimental apparatus for hot thermocouple technique: (a) industrial camera; (b) sample chamber; (c) single hot thermocouple; (d) double hot thermocouple; (e) hot thermocouple driver; (f) computer
圖 3 雙絲法模擬的渣膜形成過程, 其中通道1和2分別為模擬結晶器側固渣溫度和坯殼側液渣溫度條件. (a) 10 s；(b) 50 s；(c) 300 s；(d) 301 s[10]
Figure 3. Formation process of slag film simulated by DHTT, where Channel 1 and 2 simulate the temperature condition of solidified slag film near the mold wall and liquid slag near the shell, respectively: (a) 10 s; (b) 50 s; (c) 300 s; (d) 301 s[10]
圖 4 浸入式水冷銅探頭法示意圖
Figure 4. Schematic of the experimental apparatus for copper-finger dig test
圖 6 保護渣固態渣膜與結晶器的界面示意圖
Figure 6. Interface diagram between the solid slag film and mold
圖 10 光線在坯殼與固態渣膜之間的多重反射. (a) 能量由坯殼表面發射；(b) 能量由固液界面發射
Figure 10. Multiple reflections between the shell and solid slag film: (a) emission from the shell; (b) emission from the interface
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