Porosity is one of common precision casting defects and porosity is refers to the individual location precision castings. Smooth hole defects. Stomatal usually are found after machining.

Reasons: 1. The majority of cases appear porosity is mainly due to inadequate precision cast molding shell roasting, when pouring molten steel shell of gas instantaneous generation cannot successful eduction, which formed in the liquid metal into the pores; 2. Because the shell making technology or shell mold material, shell permeability is poor, is difficult to exhaust gas in the cavity, formed in the liquid metal into the pores; 3. When pouring into liquid steel in the air blow hole to discharge thus caused.