Cores for die casting

A method of producing cores for use in diecasting, comprising the steps of

• (a) producing a molding material mixture by mixing components (A), (B) and (C)
• (b) shaping the molding material mixture
• (c) thermally curing the shaped molding material mixture to form a main body of [the] a core to be produced
• (d) applying
• a composition (D)
• or a coating composition formed by diluting a composition (D) with carrier liquid (D1)
• to the main body and then drying, such that a coating is produced on the main body, forming a core comprising the main body and a coating disposed atop the main body, which extends at least over an entire surface of the core that comes into contact with a metal melt in the casting operation,
• wherein components (A), (B), and (C), and composition (D) are defined as follows:
• A) a mold base material selected from the group consisting of quartz sand, chromium ore sand, olivine sand, aluminum silicate sands and mixtures thereof;
• (B) particulate amorphous silicon dioxide or an additive mixture comprising particulate amorphous silicon dioxide;
• (C) a solution or dispersion comprising waterglass or a kit comprising raw materials for production of a solution or dispersion comprising waterglass;
• (D) a composition for production of a coating, said composition comprising
• (D1) a carrier liquid selected from the group consisting of water and mixtures of water with one or more alcohols;
• (D2) a constituent from the group consisting of
• (D2a)dissolved in the carrier liquid, one or more acids, where the aqueous phase formed by the carrier liquid with the acids dissolved therein has a pH of 5 or less,
• (D2b) one or more organic compounds of the formula (I)
• where R1 and R2
• are each monovalent groups independently containing 1 to 26 carbon atoms, where the R1 group is attached via a carbon atom present in the R1 group or via an oxygen atom present in the R1 group, and where the R2 group is attached via a carbon atom present in the R2 group,
• or
• are joined to one another to form a ring structure, such that the ring structure comprises a total of 4 to 7 ring atoms and the R1 and R2 groups comprise a total of 2 to 26 carbon atoms, where the R1 group is attached via a carbon atom present in R1 group or via an oxygen atom present in the R1 group, and where R2 group is attached via a carbon atom present in the R2 group;
• (D3) one or more refractories in the form of particles
• (D4) one or more refractories in the form of grainy particles wherein the proportion of the one or more refractories (D3) is in the range from 15% to 80%, based on the total mass of one or more refractories (D3) and one or more refractories (D4) in component (D).