Patent ID: 7096919

Claim:
An evaporative pattern casting process for casting a product, which comprises pouring a molten metal in a mold in which a pattern made of an expanded synthetic resin is embedded in molding sand, and evaporating the pattern with the molten metal, while gas generated by evaporation of the pattern is discharged outside the mold through a discharging passage comprising a discharged gas suppressing means, wherein the ventilation of the discharging passage is controlled on the basis of the material and the shape of the pattern and the kind of the molten metal and the temperature of the molten metal, wherein the ventilation of the discharging passage is controlled on the basis of the following formula (1): 0.3 K*≦K≦ 10 K* (1) wherein K* is defined as follows: K *=√{square root over (2)} cαS c /√{square root over (ρ)}(2) ρ: density (kg/m 3 ) of the molten metal, c: flow coefficient 0.3, α: magnifying power of the volume when the pattern is evaporated, and S c : sectional area (m 2 ) of the passage for the molten metal, and K is a constant decided by applying the result of a ventilation test to the following formula (3) on the basis of the method of least squares: Q=K√{square root over (k)} (3) Q: flow rate (m 3 /s) of the gas discharged from the discharging passage comprising the discharged gas suppressing means, and p: pressure loss (Pa) in the discharging passage comprising the discharged gas suppressing means.