| 摘要 |
A ceramic shell mold for directional solidification of a single crystal metal article has an improved starter section which converts columnar grain growth to single crystal grain growth. The pitch or lead of the helix is chosen so that the separation between adjacent turns of the helix is less than twice the thickness of the layered ceramic shell material which comprises the mold. Thus, when the ceramic shell mold is formed by the repetitive application of layers of ceramic to a wax pattern, the gap between adjacent turns of the helix will be bridged when the mold has reached 50-80% of its final thickness. Then, continued accumulation of ceramic layers bridges the turns of the helix thereby giving it strength. A helical passage diameter in the 8-10 mm range significantly increases single crystal casting yields compared to smaller diameters commonly used heretofore. |
