Gypsum-based investment material composition for casting, and method for manufacturing gypsum-based investment material composition for casting

A method for producing a gypsum-based embedding material composition for casting, the method comprising:

• mixing at least one co-pulverized material and a moisture-retaining component,
• wherein the at least one co-pulverized material is selected from the group consisting of a co-pulverized material of calcined gypsum and quartz, a co-pulverized material of calcined gypsum and cristobalite, and a co-pulverized material of calcined gypsum, quartz, and cristobalite,
• the composition comprises, as main components:
• calcined gypsum in an amount from 25 to 50 parts by mass, quartz in an amount from 40 to 65 parts by mass, and cristobalite in an amount from 10 to 35 parts by mass, relative to a total amount of the main components as 100 parts by mass,
• the composition further comprises the moisture-retaining component in an amount from 0.2 to 1.0 part by mass relative to the total amount of the main components as 100 parts by mass,
• the moisture-retaining component is a powdery moisture-retaining component or a liquid moisture-retaining component, and has a water content in a range of 1.5% or less,
• if quartz or cristobalite is absent from the at least one co-pulverized material, the absent quartz or the absent cristobalite is pulverized separately and added to the at least one co-pulverized material, so that the gypsum-based embedding material composition in a powder form having an average particle diameter in a range of 30 μm or less is prepared, and
• the composition is configured to form a gypsum-based embedding material with a leaving time in a range from 8 to 15 minutes when the gypsum-based embedding material is formed by adding a malaxation liquid to the composition so as to form a mixture of the composition and the malaxation liquid, setting the mixture, and heating the resulting set product of the mixture, wherein the leaving time is a time from the adding of the malaxation liquid to starting of the heating of the set product of the mixture.