Continuous casting of hollow billets

Continuous casting technology of hollow billets has been developed for near-net-shape casting of pipe. A cylindrical water cooled copper mould was used as a core to make a hole at the center of the round billet, while the hot-top casting technique was applied in order to provide space for the submerged entry nozzle and to cast tube blanks of thin wall thickness. A pilot scale casting of a 160mm-diameter billet, which has a 100mm-diameter hole, was conducted and the metallurgical investigation of the billet quality and the numerical analysis were performed to determine the optimum casting conditions. The hot-top casting technique, in which the induction heating (IH) of the oscillating ceramic mould stabilizes the solidification start level, enables both the smooth surface and the thin wall thickness of the hollow billet. The combination of the IH type hot-top casting technique and a water cooled copper mould, create a favourable condition at the shell exterior for generating equiaxed crystal as both fluid flow and thermal conditions, promote high equiaxed structure ratio and elimination of macrosegregation in hollow billets.