Method for manufacturing mold

A method for manufacturing a mold, comprising the steps of:

• (a) expanding a powder mixture containing sodium chloride powder, magnesium sulfate powder and polyvinyl pyrrolidone powder in a plane on a table to form a layer and then selectively spraying a spray liquid that is free of a binder component and contains ethanol and water through a nozzle on this powder mixture layer to make a bonding strength among particles of the powder mixture layer in a sprayed region higher than that among particles of the powder mixture layer in an unsprayed region;
• (b) further expanding the powder mixture on the powder mixture layer after spraying and then selectively spraying the spray liquid through the nozzle on this powder mixture layer;
• (c) repeatedly conducting the step (b) over several times to form a mold shaped by the sprayed regions;
• and
• (d) taking out the muld.

A method for manufacturing a mold, comprising the steps of:

• (a) expanding a powder mixture containing a water-soluble first inorganic salt powder, a second inorganic salt powder consisting of magnesium sulfate, and a water-soluble organic polymer powder in a plane on a table to form a layer and then selectively spraying a spray liquid that is free of a binder component and contains at least one selected from the group consisting of a water-miscible organic solvent and water through a nozzle on this powder mixture layer to make a bonding strength among particles of the powder mixture layer in a sprayed region higher than that among particles of the powder mixture layer in an unsprayed region;
• (b) further expanding the powder mixture on the powder mixture layer after spraying and then selectively spraying the spray liquid through the nozzle on this powder mixture layer;
• (c) repeatedly conducting the step (b) over several times to form a mold shaped by the sprayed regions;
• (d) taking out the mold;
• and
• (e) heating the mold at a temperature at which the first and second inorganic salts are not fused and above a temperature at which the water-soluble organic polymer is burned out.

A method for manufacturing a mold, comprising the steps of:

• (a) expanding a powder mixture containing a water-soluble first inorganic salt powder, a water-soluble second inorganic salt powder having a melting point lower than that of the first inorganic salt, and a water-soluble organic polymer powder in a plane on a table to form a layer and then selectively spraying a spray liquid that is free of a binder component and contains at least one selected from the group consisting of a water-miscible organic solvent and water through a nozzle on this powder mixture layer to make a bonding strength among particles of the powder mixture layer in a sprayed region higher than that among particles of the powder mixture layer in an unsprayed region;
• (b) further expanding the powder mixture on the powder mixture layer after spraying and then selectively spraying the spray liquid through the nozzle on this powder mixture layer;
• (c) repeatedly conducting the step (b) over several times to form a mold shaped by the sprayed regions;
• (d) taking out the mold;
• and
• (e) heating the mold at a temperature at which the first inorganic salt is not fused but the second inorganic salt is fused.