Six cylinder block is an important part of marine engine. The casting structure is shown in the figure, and its technical quality requirements are high. ZHY casting is produced by sand coated iron mold casting process. Its original mold structure is completely designed according to the resin sand casting mold. After trial production, it is found that there are different degrees of casting pores on the upper surface ribs and bosses of the casting. Some casting pores can be found only after shot blasting, and some subcutaneous casting pores can be found only after processing, Most of these casting pores are distributed on the cylinder top of the casting and the upper surface of the water jacket of the upper half of the casting.

The analysis shows that the causes of casting porosity are:

(1) There is no exhaust needle at the core head of water jacket, which is easy to produce casting pores;

(2) The number of exhaust needles is small, which is easy to produce casting pores;

(3) Two exhaust needles are not in the middle of the core head position, the exhaust is not smooth, and it is easy to produce casting pores;

(4) The peripheral core head is not provided with exhaust, so the peripheral core head cannot exhaust the gas out of the mold, which is easy to produce casting pores.