To fix a core to the inner peripheral surface of an annular ring at the time of preheating by using a material having larger thermal expansion coefficient than that of the material of the annular ring to the soluble core.
A piston ring is provided with an annular hollow part for cooling in the inside of the annular ring 10 holding a top ring groove. In order to form the hollow part for cooling, the soluble core 20 using the material, e.g. salt core, having larger thermal expansion coefficient than that of the material of the annular ring 10, e.g. iron-base material, is prepared and set to the inside of the annular ring 10. Then, at the time of heating, the expanding quantity of the soluble core 20 becomes so larger than the expanding quantity of the annular ring 10 as to hold the outer periphery of the soluble core 20 with the inner periphery of the annular ring 10, and the ring and the core can be integrated. Thereafter, these are set in the mold 40 and pertinent piston is formed by pouring molten metal into the mold 40.
KAMIYA TAKANORI
HARA SOUICHI
KAGAMI YOSHIAKI
