Mould material mixture containing resols and amorphous silicon dioxide, moulds and cores produced therefrom and method for the production thereof

1. A mold material mixture for producing molds or cores comprising:

a refractory mold material, such that more than 80% by weight of the mold material mixture comprises the refractory mold material,

alkaline resols and water as a binder or as a binder component, such that the alkaline resols amount to 1 to 10% by weight of the weight of the refractory mold material; and

amorphous SiO 2 as additive, wherein the amorphous SiO 2 is a particulate having a mean particle diameter between 0.05 μm and 10 μm, as determined by dynamic light scattering and is present in the range of 0.1 to 2% by weight of the weight of the refractory mold material.

2. The mold material mixture according to claim 1 , wherein the mold material mixture is obtained by bringing together:

component (A), having amorphous SiO 2 in powder form, with no water and no resol,

component (B), a binder component comprising the alkaline resol, water and no amorphous SiO 2 and

component (F), a free-flowing refractory comprising the refractory mold material and no resol.

3. The mold material mixture according to claim 1 , wherein the refractory mold material comprises quartz sand, zirconia sand, chrome sand; olivine, vermiculite, bauxite, fireclay, glass beads, granular glass, aluminum silicate microspheres and mixtures thereof.

4. The mold material mixture according to claim 1 , wherein the refractory mold material has mean particle diameters of 100 μm to 600 μm, determined by sieve analysis.

5. The mold material mixture according to claim 1 , wherein the amorphous silicon dioxide has a surface area determined by BET of between 1 and 200 m 2 /g.

6. The mold material mixture according to claim 1 , wherein the amorphous silicon dioxide is selected from the group consisting of: precipitated silica, pyrogenic silicon dioxide produced by flame hydrolysis or in an electric arc, amorphous silicon dioxide produced by thermal decomposition of ZrSiO 4 , silicon dioxide produced by oxidation of metallic silicon with an oxygen-containing gas, quartz glass powder with spherical particles produced from crystalline quartz by melting and rapid recooling, and mixtures thereof.

7. The mold material mixture according to claim 1 , wherein the mold material mixture contains the amorphous silicon dioxide in quantities of 0.1 to 2 wt.-%, based on the refractory mold material.

8. The mold material mixture according to claim 1 , wherein the amorphous silicon dioxide has a water content of less than 5 wt.-%.

9. The mold material mixture according to claim 1 , wherein the resols are CO 2 -curable.

10. The mold material mixture according to claim 1 , wherein the mold material mixture contains oxyanions.

11. The mold material mixture according to claim 10 , wherein the oxyanions contain at least one of boron and aluminum, and, when both are present, the Al:B atomic ratio is 0.05:1 to 1:1.

12. The mold material mixture according to claim 1 , wherein the mold material mixture contains 10 to 40 wt.-% caustic materials.

13. The mold material mixture according to claim 1 , wherein the resols are added in the form of an aqueous alkaline solution.

14. The mold material mixture according to claim 2 , wherein a curing agent is added to the mold material mixture as a constituent of component (B) or as an additional component.

15. The mold material mixture according to claim 10 , wherein the oxyanions are part of the binder or the binder component.

16. A method for producing molds or cores comprising:

providing a mold material mixture according to claim 1 by bringing together and mixing the following components:

component (A), having amorphous SiO 2 in powder form, with no water and no resol,

component (B), a binder component comprising an alkaline resol, water and no amorphous SiO 2 and

component (F), a free-flowing refractory comprising a refractory mold material and no resol;

introducing the mold material mixture into a mold, and

curing the mold material mixture by introducing carbon dioxide into the mold.

17. The method according to claim 16 , wherein the mold material mixture, for curing, is exposed to a temperature of 5 to 60° C.

18. A multicomponent system for producing molds or cores comprising:

component (A), having amorphous SiO 2 in powder form, no water and no resol,

component (B), a binder component comprising the alkaline resol, water and no amorphous SiO 2 and

component (F), a free-flowing refractory component comprising the refractory mold material and no resol.

19. A method for producing molds or cores comprising the steps of:

providing a mold material mixture by bringing together and mixing the following components:

component (A), having amorphous SiO 2 in powder form, with no water and no resol,

component (B), a binder component comprising an alkaline resol, water and no amorphous SiO 2 and

component (F), a free-flowing refractory comprising a refractory mold material and no resol,

introducing the mold material mixture into a mold, and

curing the mold mixture in the mold by either:

adding at least one ester, liquid at room temperature, as a curing agent when mixing the components; or

introducing at least one gaseous ester into the mold.