PURPOSE: To easily and efficiently execute takeout of a sand core by using furan resin as organic binder and removing molding sand with at least one of shot blasting and sand blasting under room temp. atmosphere at the time of removing the sand core.
CONSTITUTION: At the time of manufacturing the collapsible sand core 4, the furan resin is used as the organic binder mixed in the sand and as the collapsible sand core 4 is discharged with the shot blasting or the sand blasting, remaining of the sand is not developed in every corner. Further, as shock at the time of treating the blasting is sufficiently little, deformation and crack in a casting are not developed. Further, by adding the furan resin in the sand, the collapsibility of sand core is extremely good at the time of removing the collapsible sand core 4 after executing die casting and the sand core can be sufficiently removed under the room temp. atmosphere. Then, at the time of removing the sand core, as heating temp. of the casting is sufficient to be low and the heating is unnecessary, the deformation and damage in the casting caused by heating treatment can be prevented.