It was believed after the reason analysis that the blowhole defect was caused by the gas evolution of sand cores after being heated and the improper pouring system design which leading to the gas immixture.

But it\'s easy to make linear porosity in welding.

Through judging correctly appearance features, surface colors of endogenous reaction porosity in the course of sand mould casting, this paper analyzes the formation reasons of the endogenous reaction porosity, and advances some preventive measures according to the formation reasons.