As a precision-cast product, for example, a turbine blade used in a gas turbine is known. In the gas turbine, a working fluid is heated by a burner so as to be a high-temperature/high-pressure working fluid, and the turbine is rotated by the working fluid. That is, the working fluid compressed by a compressor is heated by the burner so as to increase the energy of the working fluid, the energy is recovered by the turbine so as to generate a rotation force, and hence electric power is generated by the rotation force. The turbine is provided with a turbine rotor, and the outer periphery of the turbine rotor is provided with at least one gas turbine blade.
Here, the gas turbine blade is exposed to a high temperature. As a countermeasure, a cooling medium flows in the gas turbine blade so as to cool the gas turbine blade. For this purpose, the gas turbine blade is provided with an internal cooling structure. Then, in order to form the internal cooling structure, a core having the same shape as a cooling medium flow passage is disposed and the core is removed after casting. The core is removed while being dissolved in an alkali (for example, NaOH or KOH) solution. As a result, for example, the internal cooling structure for the turbine blade is formed.
As the core, a ceramic core using ceramic particles has been used from the past (Patent Literature 1).
Here, a precision-casting core can be obtained by molding a silica material such as melted silica (SiO2) through injection molding or slip casting and performing a heat treatment thereon.
The injection molding method is a method of obtaining a compact by kneading ceramic powder and wax, injecting a material obtained by heating and melting the wax into a metal mold, and cooling and hardening the material.
Further, the slip casting method is a method of preparing slurry by mixing ceramic powder with water or the like, pouring the slurry into a mold formed of a material such as gypsum absorbing a solution, and drying the slurry so as to obtain a desired molded shape.