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水平连铸棒材的横截面中存在一个由液芯区转变而成的圆形区域。由于冷却中热量传输不对称和成分偏析的原因,这个区域中的石墨为A、B型且尺寸粗大,淬硬性元素含量低于先行冷凝壳层中的含量,导致硬度偏低。另一方面,由于地心引力的存在,结晶器石墨套与冷凝壳层间的上部有一个月牙形的气隙,严重阻碍了壳层中热量向上方的传输,最终造成了液芯区在横截面上的偏心分布。在随后的冷加工钻削中,若环套的壁较厚,这个液芯区往往不能全部切削掉,而是留下了一个月牙形的液芯区,致使环套在该位置首先磨损。用垂直连铸方法拉制空心型材,避免了地心引力的干扰从而消除了月牙形气隙,型材横断面中没有了液芯区,所获得的铸态组织细密,硬度均匀,内孔耐磨性一致。
In the cross section of the horizontal continuous casting bar, there is a circular area transformed from the liquid core area. Due to the heat transfer asymmetry and component segregation in cooling, the graphite in this region is of type A and B, and the size is coarse. The content of hardenable elements is lower than that in the pre-condensed shell, resulting in low hardness. On the other hand, due to the existence of gravity, there is a crescent-shaped air gap between the mold graphite jacket and the upper part of the condensed shell, which seriously hinders the transmission of the heat in the shell to the upper part, Eccentric distribution on cross section. In the subsequent cold working drilling, if the wall of the collar is thick, this core area can not always be cut off, but a crescent-shaped core area is left behind, causing the collar to wear first. Using vertical continuous casting method to draw hollow profile, to avoid the interference of the gravity to eliminate the crescent-shaped air gap, profile cross-section without the liquid core area, obtained as-cast microstructure, uniform hardness, bore wear Consistency.