1, stomata The cause of the pores is that there is too much moisture in the molding material or contains a large amount of gas-generating substances; the sand and core sand have poor gas permeability; the casting speed is too fast. 2, trachoma The cause of the blisters is that the sand is not strong enough; the sand is not tight enough; the pouring speed is too fast. 3, shrinkage hole The reason f...