Investigation of Defect improvements in a Direct-Chill Cast Process of aluminum ingots

• Main Authors: Tsai, Meng-Tsun, 蔡孟村
• Other Authors: Lie, Kun-Nan
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/57028693338620145313

碩士 === 遠東科技大學 === 機械工程研究所 === 99 === 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 simulations for the heat transfer coefficients in mold and under water spray and heat transfer with release of latent heat in phase change decide the correctness of numerical solutions. As the temperature of aluminum is cooled from liquid phase about 700~660oC to solid phase with the ambient temperature in the cast process, the properties of heat transfer are considered to be functions of temperature. The heat transfer coefficient in mold decreases sharply when the air gap forms with solidification and the heat transfer coefficient under water spray is also a function of surface temperature of cast aluminum. The correct solutions come out only with the correct simulations. The project employs numerical solution to predict the temperature in cast aluminum and studies the improving methods on the quality of cast ingot in DC process.