A set of testing apparatus was designed to measure the interface back pressure of coated sand mold（core） during pouring through the gas pressure acquisition system

and the measurement method was optimized. The effects of casting temperature

gas emission of coated sand

height of metal hydrostatic head and length of sand core on the measurement results were investigated. The results indicate that the duration of maximum interface back pressure and peak pressure is increased with the increase of pouring temperature and gas production of coated sand. When the height of the metal hydraulic static pressure head is insufficient

the gas enters the metal liquid in form of a bubble

thus reducing the interface back pressure. The maximum interfacial backpressure is obviously increased with the core length increase

where the influence of core length on the interface back pressure is greater than that of the gas-emissim of coated sand.

proving that the most critical factor for porosity defects is casting structure

and the optimal scheme to reduce porosity defects is to set up a reasonable exhaust system.