考虑圆坯周向冷却均匀性的传热模型研究及应用

Research and Application of Solidification Heat-transfer Model Considering the Cooling Uniformity Around the Circumference of Round Billet

圆坯周向上冷却的均匀性对铸坯的质量有着重要影响,易引发纵裂纹、椭圆度等质量问题。基于此,特建立圆坯的径向和周向二维凝固传热模型,充分考虑其在圆周向上喷淋冷却的均匀性。利用喷嘴与圆坯间的几何映射关系,结合喷嘴冷态性能测试数据,推导并计算出沿圆坯周向上的水流密度分布。相比于板坯等平面喷淋,圆坯曲面喷淋沿周向上水流密度衰减更为急剧,喷淋的均匀性更不易控制。将模型应用于某大圆坯连铸机的凝固传热计算,考察了铸坯各二冷区末端周向上的冷却均匀性,其中一区最大温度偏差19℃,二区12℃,三区7℃,四区5℃。除此之外,计算了铸机保温罩设计对铸坯温度场的影响,相比于无保温罩,铸坯表面温度在保温罩出口区域提升了61℃,凝固终点向后推移了约1m。

The cooling uniformity around the circumference of round billet has important influence on the quality of billet. It is easy to cause quality problems of billet such as longitudinal crack and ovality. A two dimensional heat-transfer mathematical model including radial and circumferential direction was established to consider the cooling uniformity around the circumference. Combined with the test data of cold characteristics of nozzle,the flow density distribution around the circumference was calculated according to the geometric relation of nozzle and round billet. The flow density decreases more sharply around the circumference by comparison with the spray on flat such as slab,resulting in more difficult control of uniform spray. The model was used to calculate the solidification heat transfer of a large round billet continuous casting machine to investigate the cooling uniformity around the circumference at the end of each secondary cooling zone. The maximum temperature deviation is 19 ℃,12 ℃,7 ℃ and 5 ℃ from the first zone to fourth zone. In addition,the influence of heat cover on the billet temperature field was calculated. The billet surface temperature at the exit of heat cover elevated 61 ℃,and the final solidification point moved back about 1 m compared with no heat cover.