Origination of defects

such as shrinkage porosity

pin hole

gas hole and inclusion

in valve housing was analyzed. Aiming at these defects

through some measures

including adjusting pouring position

optimizing gating system and adding foam ceramic filter and arbitrary chill and arbitrary riser as well as strictly controlling melt quality

defects in the valve housing were eliminated basically

and passing rate of the valve housings for compression resistance testing exceeded 80%.