Evaporative pattern casting method

A casting method using a lost foam, comprising embedding, in foundry sand, a casting pattern formed by applying a mold wash to a surface of a foam pattern;

• and pouring a molten metal into the casting pattern and losing the foam pattern to replace the foam pattern with the molten metal, thereby making a casting with a thickness T [mm], the casting including a hole with a diameter of 12 mm or less and a length l [mm],
• the casting method comprising the steps of:
• determining a thermal decomposition amount ΔC(θ,t) [wt %] of a resin binder when the mold wash is exposed at a temperature θ [° C.] for a time t [sec], from the following formulae (1) to (3), wherein ΔCsat(θ) [wt %] is a critical thermal decomposition amount of the resin binder contained in the mold wash at a temperature θ [° C.], kd [1/sec] is a thermal decomposition rate constant of the resin binder, θs [° C.] is a temperature at which thermal decomposition of the resin binder starts, and A, α, and τ3 are material parameters relying on a material of the mold wash, respectively;
• determining a room temperature transverse rupture strength σb(θ,t) [MPa] of the mold wash after receiving thermal loads from the following formula (4), wherein σc0 [MPa] is a room temperature transverse rupture strength of the mold wash before receiving thermal loads, σc1 [MPa] is a room temperature transverse rupture strength of the mold wash after the resin binder is completely thermally decomposed, σs(θ,t) [MPa] is a strength increase caused by reaction and sintering among aggregates contained in the mold wash, and γ is a material parameter relying on the material of the mold wash;
• and
• performing casting with the mold wash having the room temperature transverse rupture strength σb(θ,t) after receiving thermal loads being equal to or larger than a threshold value σcr [MPa]:
• ΔC(θ,t)=ΔCsat(θ)·{1−exp(−kdt)} (1)
• ΔCsat(θ)=tanh{β(θ−θs)}×100 (2)
• kd=A exp(αθ) (3)
• σb(θ,t)=σc0−(σc0−σc1)tanh(γΔC(θ,t))+σs(θ,t) (4).