Since the external characteristics of casting defects are characterized by porosity, the following measures have been taken:

(1) Reduce the gas generation of sand core. Extend the core baking time of the main core for 1 hour, the gas generation of the main core will decrease from 14.5 mL/g to 12~13 mL/g, add two exhaust needles with a diameter of 10 mm at the highest point, add the blank holder riser, and increase the pouring temperature from 1400~1420 ℃ to 1440 ℃.

(2) Increase the refining process and keep it at 1500~1530 ℃ for 15 minutes.

(3) Add overflow tank.

(4) Increase the pouring head.

(5) The numerical simulation software is used for simulation analysis to change the size of the gating system and reduce the pouring entrainment.

The verification results show that the improvement effect is not obvious, and the effect of some schemes is getting worse. The most extreme measure is to open the highest point and add 2 gating cups for exhaust (as shown in the figure). The exhaust hole is as large as the sprue. The exhaust effect is very ideal during pouring. The combustion flame is close to 1.7 m, but the casting porosity is larger.