| 摘要 |
PURPOSE:To improve the collapsibility of a core after casting by arranging coated layer for preventing molten metal penetration on the outer surface of core body formed as hardening refractory grain by resin and heat-treating this core to make a part of the resin to decompose. CONSTITUTION:The core body 4 is formed as hardening, for example by blending phenol resin as binder to the core sand having 100-200 mesh grain size and the coated layer for preventing the molten metal penetration, for example a second layer 6 on a first layer 5, on the outer surface of this core body is formed. The cores 2, 3 formed the coated layers 5, 6 is introduced into a heating furnace and a part of the resin in the core body 4 is uniformly thermal- decomposed by reaction with oxygen in the air enclosed in the inner part, to improve the collapsibility as keeping the strength. This heating treatment is executed to 160-240 deg.C treating temp. for 1-15hr holding time. In this way, the core improving the collapsibility after casting, can be obtd.
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