Direct shell-making method was adopted in producing narrow flow-channel close impeller to avoid using water-soluble sand core and to reduce production cost.The practical production shows that the shell-mold was poured with sand slurry at inlet and outlet and was poured with dry sand at middle after stuccoing three layers face sand

which not only ensure the quality of the castings to decrease the scraps

but also easily remove the shell-mold sand in flow-channel.