抄録
Vacuum suction pressure at the surface of the Vacuum Process mold is smaller than that inside the mold. Metal penetration is prevented by reducing the vacuum suction pressure of the pump and by using fine silica sand. This is due to the decreased pressure difference at the metal-mold interface. The use of fine silica sand also increases the critical penetrating pressure ΔPi*. For sand of different sizes, ΔPi* is expressed as −4σ cos θ/αDP. The mean sand diameter DP is obtained as 1/{Σ(W/DP)}, where W is the weight fraction of the sand whose diameter is DP. The notation σ is the surface tension of the metal, θ is the contact angle of the metal with silica sand and α is the ratio of the effective pore diameter to the mean sand diameter, which was about 0.75 for both mercury and aluminum.
