Mold manufacturing method

A mold molding method that molds a mold by filling a frame, in which a model is placed, with self-hardening sand obtained by kneading sand, a binder, and a hardening accelerator, and removing the model after the self-hardening sand is hardened, so that a shape of the model is transferred to the hardened self-hardening sand,

• the mold molding method comprising:
• a binder reaction amount calculation step of calculating a reaction amount ΔC(θ, ti) [wt %] (i=1, 2) of the binder based on the following equations (1) and (2) using, as molding condition parameters when a specimen is molded using the self-hardening sand, temperature θ [° C.] of the sand before kneading, time t1 [min] from an end of the kneading to a time point when the model has been removed from the hardened self-hardening sand, and time t2 [min] from the time point just after the model has been removed from the hardened self-hardening sand to a time point just before the specimen is subjected to a compression test;
• a specimen room temperature compressive strength calculation step of calculating room temperature compressive strength σc(θ, t) [MPa] of the specimen by substituting the reaction amounts ΔC(θ, t1) and ΔC(θ, t2) calculated in the binder reaction amount calculation step into the following equation (3);
• a mold room temperature compressive strength prediction step of predicting room temperature compressive strength σca(θ, t) of the mold in advance by applying the room temperature compressive strength σc(θ, t) of the specimen calculated in the specimen room temperature compressive strength calculation step to room temperature compressive strength σca(θ, t) of the mold when the mold is molded using the self-hardening sand under the molding condition parameters;
• and
• a mold room temperature compressive strength extraction step of extracting room temperature compressive strength σce(θ, t) of the mold, under which the mold can be molded without damages and the model can be removed, from the predicted room temperature compressive strength σca(θ, t) of the mold by a test in advance,
• wherein when the mold is actually molded, the model is removed just after elapse of the time t1, as one of the molding condition parameters which satisfies the room temperature compressive strength σce(θ, t) extracted in the mold room temperature compressive strength extraction step:
• ΔC(θ,ti)=ΔCsat·{1−exp(−kditi)} (1)
• wherein
• ΔCsat:
• a saturated reaction amount [wt %] of the binder, and
• kdi(i=1, 2):
• reaction rate constant [l/min] of the binder;
• kdi=Ai exp(αiθ) (2)
• wherein
• Ai(i=1, 2) and αi (i=1, 2):
• parameters dependent on kind of the binder used;
• and
• σc(θ,t)={tan h(β·ΔC(θ,t1))+γ}+{tan h(ε(θ)·ΔC(θ,t2)−η)} (3)
• wherein
• β, γ and η:
• material parameters, and
• ε:
• constant determined by the temperature θ.