铸拉工艺极限速度的计算

CALCULATION ABOUT LIMIT SPEEDS IN CAST DRAWING

用结晶器壁内表面光洁度的假设，提出了处理结晶器、铸件有间隙接触问题的方法，避免了测定铸件表面温度或结晶器热流密度这一难题，建立了铸拉时的温度场，得到了铸件的温度分布、液穴形状及结晶器与铸件间间隙值与工艺参数的关系。同时，提出了一种新的摩擦计算模型，并求得了摩擦应力与间隙值、表面光洁度和铸件表面剪切强度之间的关系。然后根据限制铸拉速度的主要缺陷，即凝固壳断裂和冷隔，通过计算铸件截面承受的摩擦力、热应力和液穴形状，得到了铸拉工艺的极限速度，计算值与实测值吻合。

By the assumption of the roughness about the inner of crystallizer, a way was proposed to deal with the contacting boundary between crystallizer and ingot, which resulted in avoiding measuring the surface temperature of ingot or the heat flow intensity of crystallizer; the temperature field in the cast drawing process was established, which included the temperature distribution, the shape of liquid cave, and the gap size between crystallizer and ingot along vertical direction under different technological conditions. Also, a new model was proposed to calculate the friction between crystallizer and ingot, and the relation of frictional stress between the gap size, the roughness and the surface temperature of ingot was obtained. Then, the limit speeds of cast drawing were calculated according to the main technical defects, i.e. the cold shut and the solid break, the calculation value corresponded with the measured results.