| 摘要 |
PROBLEM TO BE SOLVED: To reduce the tensile stress caused by high cycle fatigue by disposing a shrinkage restraining member which is abutted on an insered core and restrains the thermal shrinkage of the core, and pouring molten metal. SOLUTION: The shrinkage restraining member 42 for restraining the thermal- shrinkage of the salt core 26 is joined with a preform 41 for lip part, and after separately heating up the salt core 26 and the preform 41 for lip part, the salt core 26 is fitted to the shrinkage restraining member 42 to be held to pour molten metal. The salt core 26 having thermal-expansion coefficient larger than that of the preform 41 for lip part is inserted in the state of adding the residual stress. The preform 41 is inserted into the lip part in a combustion chamber formed at the tip part of a piston in an engine for car, and it is desirable to insert the other preform 41 into the groove part of a piston ring. The preheating temperature is 300-600 deg.C and the temperature when it is disposed into a mold, is desirable to be (the preheating temperature -50 deg.C) to (the preheating temperature -300 deg.C).
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