铝锭DC浇铸缺陷改良技术研究InvestigationofDefectimprovements.PDFVIP

鋁錠 DC 澆鑄缺陷改良技術研究 Investigation of Defect improvements in a Direct -Chill Cast Process of Aluminum Ingots 賴昆男(K.N. Lie) 陳彥勳(Y. H. Chen) 蔡孟村(M. T. Tsai) 遠東科技大學 台南市新市區中華路 49 號 Email: q6260@cc.feu.edu.tw 摘要 本文探討鋁錠澆鑄經由結晶器與噴水直接冷卻(DC)凝固過程中，其溫度場的變化。評估鋁湯澆鑄 過程中所產生的翹曲、裂紋和偏析等缺陷的因素。鋁錠凝固成形之諸缺陷來自澆鑄之急冷收縮效應以 及所產生的氣隙影響。急冷收縮造成翹曲和裂紋，氣隙阻熱效應則造成偏析和表面氣泡現象。本研究 分析鋁湯澆鑄速度與高度、冷卻水溫度與流量對溫度場的變化的影響 ，來評估模具與澆鑄過程的改善 之道。 於此本研究欲建立數值分析模式，分析鋁錠凝固過程中所釋出之潛熱與溫度場的變化、結晶器在 產生的氣隙時之冷卻效果以及噴水直接冷卻的影響。其中對於結晶器內熱傳遞係數的模擬、潛熱釋出 的熱傳遞模擬方式以及噴水直接冷卻之熱傳遞係數的模擬皆為數值分析結果正確與否的關鍵因素。鋁 錠澆鑄過程中由液態凝固成固態，溫度場的變化也由鋁湯之溫度 700~660℃冷卻至常溫，鋁錠的熱傳 遞物理特性也隨著溫度而改變。而且結晶器內的熱傳遞係數也隨著鋁錠 由液態凝固成固態以及氣隙的 產生而改變，再者噴水直接冷卻之熱傳遞係數也隨著鋁錠表面溫度而改變。如何正確使用諸熱傳遞特 性更是本研究的重要關鍵。藉由數值分析獲取鋁錠澆鑄過程中溫度場的變化之資訊，來探討鋁錠缺陷 的成因與改善之道。 關鍵詞 ：鋁錠鑄造，噴水直接冷卻，澆鑄速度，澆鑄高度 ABSTRACT The study investigates the cooling of aluminum ingot through direct chill (DC) processes in which liquid aluminum is cooling continuously in mold and then with water spray at the exit of mold. The defects of cast ingot appear as curl, tears, sweat and liquation. It has been approved that the curl and tears are caused by the higher rates of initial cooling and solidifying in mold and the sweat and liquation are caused by the isolation of heat transfer by air gap between cast solid surface and the mold wall. The research analyzes the variations of temperature profiles in the cast processes by the changes of cast speed, liquid head in mold, the temperature and density of water spray and assesses the improvements of mold and cast process for the better cast quality. The numerical analysis model is studied to investigate the temperature profiles in cooling processes with release of latent heat of solidification, the influence of air gap on cooling in mold and water spray. The numerical simulati