Method to prevent gap in cylindral seeds around an internal ceramic core

A process for casting a single crystal axis-symmetric thick walled tube comprising forming a axisymmetric single crystal ring seed around a circular internal core, wherein the ring seed has an inner diameter and a taper on the inner diameter, and wherein the internal core has an outer diameter and a matching taper on the outer diameter, the matching taper matching the taper of the inner diameter of the ring seed, and the internal core being free to translate in a vertical direction relative to the ring seed; and heating the ring seed so as to expand the ring seed relative to the internal core, and allowing the circular internal core to translate relative to the ring seed in a direction of the force of gravity, thereby maintaining contact between the circular internal core and the ring seed.