COATING COMPOSITION, COMPRISING ORGANIC ESTER COMPOUNDS AND PARTICULATE, AMORPHOUS SILICON DIOXIDE, FOR USE IN THE FOUNDRY INDUSTRY

Abstract

The present invention describes a coating composition for the foundry industry, for use in the foundry, in particular comprising certain organic ester compounds of a formula (I) and particulate, amorphous silicon dioxide (SiO.sub.2); and also coated foundry molding elements, especially foundry molds and/or foundry cores, which each comprise a coating composition of the invention. The invention further describes the use of a coating composition of the invention for producing a coating on a foundry molding element and a method for producing a foundry molding element coated with a water-containing refractory coating. The invention likewise describes a kit whose contents include a coating composition of the invention.

Claims

1. The method of a coating composition comprising (a) water, (b) one or more organic compounds of the formula (I) ##STR00004## where R1 and R2 are each monovalent groups which independently of one another each contain 1 to 26 C atoms, where R1 is attached via one of the C atoms contained in the group or via an O atom contained in the group, and where R2 is attached via a C atom contained in the group, or are linked to one another to form a ring structure such that the ring structure comprises a total of 4 to 7 ring atoms and the groups R1 and R2 comprise a total of 2 to 26 C atoms, where R1 is attached via one of the C atoms contained in the group or via an O atom contained in the group, and where R2 is attached via a C atom contained in the group, and (c) particulate, amorphous silicon dioxide, and (d) one or more further refractories, for producing a coating on a mold or a core, for use in the foundry.

2. The method as claimed in claim 1, where the primary particles of the particulate, amorphous silicon dioxide (i) are spherical and/or (ii) possess a D90<10 μm, determined by laser diffraction, where preferably the primary particles of the particulate, amorphous silicon dioxide of constituent (i) are spherical and possess a sphericity of 0.9 or more, determined by evaluation of two-dimensional microscope images.

3. The method as claimed in claim 1, where the constituent (d) comprises one or more substances selected from the group consisting of quartz, aluminum oxide, zirconium dioxide, aluminum silicates, phyllosilicates, zirconium silicates, olivine, talc, mica, graphite, coke, feldspar, diatomite, kaolins, calcined kaolins, metakaolinite, iron oxide, and bauxite, and/or where the one or more organic compounds of the formula (I) in constituent (b) are selected from the group consisting of esters, lactones, and acid anhydrides and are preferably water-soluble, more preferably are selected from the group consisting of methyl formate, ethyl formate, propylene carbonate, γ-butyrolactone, diacetin, triacetin, dibasic ester, acetic anhydride, methyl carbonate, and ε-caprolactone, and very preferably is propylene carbonate, where the coating composition comprises in or as constituent (c) a particulate, amorphous silicon dioxide which as a secondary constituent comprises (i) zirconium dioxide and/or (ii) a Lewis acid.

4. The method as claimed in claim 1, where the coating composition comprises one or more or all of the following constituents: one or more biocides, one or more wetting agents, one or more rheological additives, and one or more binders, preferably polyvinyl alcohol.

5. The method as claimed in claim 1, where in the coating composition the ratio of the total mass of all organic compounds of the formula (I) in relation to the total mass of the coating composition is in the range from 0.1 to 10%, preferably in the range from 1 to 5%, preferably in the range from 2.5 to 3.5%, and/or where an aqueous phase is present for which the ratio of the mass of the constituent (a) to the total mass of the aqueous phase is greater than 50%, preferably greater than 70%, more preferably greater than 90%, and/or where the coating composition possesses a solids content of less than 80 wt %, preferably less than 45 wt %, based on the total mass of the coating composition, where the coating composition possesses a fraction of particulate, amorphous silicon dioxide of constituent (c) in the range from 1 to 30 wt %, preferably 5 to 20 wt %, more preferably 8 to 17 wt %, based on the total mass of the coating composition and/or where the coating composition possesses a total fraction of particulate, amorphous silicon dioxide of constituent (c) and of further refractories of constituent (d) in the range from 25 wt % to 80 wt %, preferably 30 to 60 wt %, more preferably 45 to 55 wt %, based on the total mass of the coating composition.

6. The method as claimed in claim 1, where the coating composition comprises one or more binders, preferably comprising polyvinyl alcohol, in a total amount of not more than 2 wt %, preferably in an amount in the range from 0.05 to 0.80 wt %, based on the total mass of the coating composition.

7. The method as claimed in claim 1, where the coating is produced on the mold or the core by an application method selected from the group consisting of spraying, dipping, flow coating, and spreading, preferably dipping.

8. The method as claimed in claim 1, where the mold is waterglass-bound and/or where the core is waterglass-bound.

9. The method as claimed in claim 1, where the waterglass-bound mold or the waterglass-bound core comprises particulate, amorphous silicon dioxide and/or where the coating composition is applied to a waterglass-bound mold or a waterglass-bound core for use in the casting of iron or steel and/or where the coating composition is applied to a waterglass-bound mold or a waterglass-bound core for use in the casting of a metal melt with a temperature >900° C., preferably >1250° C., preferably for use in the casting of a metal melt comprising iron and/or steel, and/or where the coating composition is applied to a waterglass-bound mold or a waterglass-bound core at a temperature of the waterglass-bound core or the waterglass-bound mold of >50° C., preferably >70° C., more preferably at a temperature <100° C.

10. A coating composition comprising (a) water, (b) one or more organic compounds of the formula (I) ##STR00005## where R1 and R2 are each monovalent groups which independently of one another each contain 1 to 26 C atoms, where R1 is attached via one of the C atoms contained in the group or via an O atom contained in the group, and where R2 is attached via a C atom contained in the group, or are linked to one another to form a ring structure such that the ring structure comprises a total of 4 to 7 ring atoms and the groups R1 and R2 comprise a total of 2 to 26 C atoms, where R1 is attached via one of the C atoms contained in the group or via an O atom contained in the group, and where R2 is attached via a C atom contained in the group, and (c) particulate, amorphous silicon dioxide, and (d) one or more further refractories, for producing a coating on a mold or a core, for use in the foundry.

11. The coating composition as claimed in claim 10, where the primary particles of the particulate, amorphous silicon dioxide (i) are spherical and/or (ii) possess a D90<10 μm, determined by laser diffraction, where preferably the primary particles of the particulate, amorphous silicon dioxide of constituent (b) (i) are spherical and possess a sphericity of 0.9 or more, determined by evaluation of two-dimensional microscope images.

12. The coating composition as claimed in claim 10, where the constituent (d) comprises one or more substances selected from the group consisting of quartz, aluminum oxide, zirconium dioxide, aluminum silicates, phyllosilicates, zirconium silicates, olivine, talc, mica, graphite, coke, feldspar, diatomite, kaolins, calcined kaolins, metakaolinite, iron oxide, and bauxite, and/or where the one or more organic compounds of the formula (I) in constituent (b) are selected from the group consisting of esters, lactones, and acid anhydrides and are preferably water-soluble, more preferably are selected from the group consisting of methyl formate, ethyl formate, propylene carbonate, γ-butyrolactone, diacetin, triacetin, dibasic ester, acetic anhydride, methyl carbonate, and ε-caprolactone, and very preferably is propylene carbonate, and/or where the coating composition comprises in or as constituent (c) a particulate, amorphous silicon dioxide which as a secondary constituent comprises (i) zirconium dioxide and/or (ii) a Lewis acid.

13. The coating composition as claimed in claim 10, comprising one or more or all of the following constituents: one or more biocides, one or more wetting agents, one or more rheological additives, and one or more binders, preferably polyvinyl alcohol.

14. The coating composition as claimed claim 10, where the ratio of the total mass of all organic compounds of the formula (I) in relation to the total mass of the coating composition is in the range from 0.1 to 10%, preferably in the range from 1 to 5%, preferably in the range from 2.5 to 3.5%, and/or where an aqueous phase is present for which the ratio of the mass of the constituent (a) to the total mass of the aqueous phase is greater than 50%, preferably greater than 70%, more preferably greater than 90%, and/or where the coating composition possesses a solids content of less than 80 wt %, preferably less than 45 wt %, based on the total mass of the coating composition, and/or where the coating composition possesses a fraction of particulate, amorphous silicon dioxide of constituent (c) in the range from 1 to 30 wt %, preferably 5 to 20 wt %, more preferably 8 to 17 wt %, based on the total mass of the coating composition and/or where the coating composition possesses a total fraction of particulate, amorphous silicon dioxide of constituent (c) and of further refractories of constituent (d) in the range from 25 wt % to 80 wt %, preferably 30 to 60 wt %, more preferably 45 to 55 wt %, based on the total mass of the coating composition.

15. The coating composition as claimed in claim 10, comprising one or more binders, preferably comprising polyvinyl alcohol, in a total amount of not more than 2 wt %, preferably in an amount in the range from 0.05 to 0.80 wt %, based on the total mass of the coating composition.

16. The method of particulate, amorphous silicon dioxide in a coating composition comprising (a) water, (b) one or more organic compounds of the formula (I) ##STR00006## where R1 and R2 are each monovalent groups which independently of one another each contain 1 to 26 C atoms, where R1 is attached via one of the C atoms contained in the group or via an O atom contained in the group, and where R2 is attached via a C atom contained in the group, or are linked to one another to form a ring structure such that the ring structure comprises a total of 4 to 7 ring atoms and the groups R1 and R2 comprise a total of 2 to 26 C atoms, where R1 is attached via one of the C atoms contained in the group or via an O atom contained in the group, and where R2 is attached via a C atom contained in the group, and (d) one or more further refractories, for increasing the storage stability of the coating composition and/or as a means for reducing the detrimental effect, due to the coating with the water-containing refractory coating, on the flexural strength of a waterglass-bound core or waterglass-bound mold.

17. The method as claimed in claim 16, where the waterglass-bound core or waterglass-bound mold comprises particulate, amorphous silicon dioxide.

18. The method as claimed in claim 16, where the primary particles of the particulate, amorphous silicon dioxide in the coating composition (i) are spherical and/or (ii) possess a D90<10 μm, determined by laser diffraction, where preferably the primary particles of the particulate, amorphous silicon dioxide of constituent (i) are spherical and possess a sphericity of 0.9 or more, determined by evaluation of two-dimensional microscope images.

19. A process for producing a mold coated with a water-containing refractory coating or a core coated with a water-containing refractory coating, for use in the foundry, comprising the following steps: (1) providing or producing a coating composition as claimed in claim 10, (2) providing or producing an uncoated mold or an uncoated core, and (3) applying the provided or produced coating composition from step (1) to the provided or produced mold or the provided or produced core.

20. The process as claimed in claim 19, where the provided or produced uncoated mold is waterglass-bound or the provided or produced uncoated core is waterglass-bound.

21. The process as claimed in claim 19, where the provided or produced uncoated mold or the provided or produced uncoated core comprises particulate, amorphous silicon dioxide, and/or where the uncoated mold or the uncoated core is produced in step (2) by curing a provided or produced molding material mixture by gassing with carbon dioxide, by admixing esters or phosphates or by gassing with hot air in a heated tool.

22. The process as claimed in claim 19, where the applying to the provided or produced uncoated mold or the provided or produced uncoated core takes place at a temperature of the provided or produced mold or provided or produced core of >50° C., preferably >70° C., more preferably at a temperature <100° C., and/or where the applying to the provided or produced uncoated mold or the provided or produced uncoated core takes place by an application process selected from the group consisting of spraying, dipping, flow coating, and spreading, preferably dipping.

23. A coated mold or coated core for use in the foundry, in each case comprising a coating composition as claimed in claim 10.

24. A coated mold or coated core, producible by the process as claimed in claim 19.

25. The coated mold or coated core as claimed in claim 23, where the coated mold is waterglass-bound and/or the coated core is waterglass-bound.

26. The coated mold or coated core as claimed in claim 25, where the waterglass-bound mold and/or the waterglass-bound core comprises particulate, amorphous silicon dioxide.

27. The coated mold or coated core as claimed in claim 23 for use in the casting of a metal melt having a temperature >900° C., preferably >1250° C., preferably for use in the casting of a metal melt comprising iron and/or steel.

28. A kit including in separate components (U) a coating composition as claimed in claim 10 for producing a coating on a waterglass-bound mold or a waterglass-bound core, for use in the foundry, (V) a binder comprising waterglass, and (W) particulate, amorphous silicon dioxide.

Description

EXAMPLES

[0177] The examples given below are intended to describe and explain the invention in more detail without limiting its scope.

Example 1: Production of Coating Compositions

[0178] The inventive coating compositions indicated in Table 1 (“SZ1”, “SZ2”) and also the noninventive, comparative coating compositions (“SZ3” and “SZ4”) were produced in a conventional way by mixing the respectively indicated ingredients with one another.

[0179] For this purpose in each case the required amount of water was introduced initially in a glass beaker (batch size in each case around 2 kg of coating composition as “concentrates”, cf. Table 1), the rheological additives and the refractories (phyllosilicates, zircon flour, graphite) were added, and these ingredients were then incorporated in a conventional way using a high-shear dissolver stirrer for 3 minutes. The other constituents of the coating compositions (cf. Table 1) were then added in the proportions indicated, followed by stirring for a further 2 minutes with a high-shear dissolver stirrer. This gave the dilutable refractory coating-composition concentrates indicated in Table 1 in each case.

[0180] The references to “DIN grinds” in Table 1 denote that the respectively indicated constituent of the coating composition is present in the ground state and, after the sieving of a sample of this constituent with an analytical sieve having a nominal mesh size in μm corresponding to the stated numerical value (e.g.: “80” denotes “analytical sieve with mesh size 80 μm”) (according to DIN ISO 3310-1:2001-09), a residue remains in each case that is in the range from 1 to 10 wt %, based on the amount of sample used.

TABLE-US-00001 TABLE 1 Inventive and noninventive coating compositions (each obtained as dilutable “concentrates”) Coating compositions: (“concentrates”) SZ1 SZ2 SZ3 SZ4 Ingredients: [wt %] [wt %] [wt %] [wt %] Water 43.3  42.9  46.0  47.1 Rheological additive 1.5 1.5 5.0  1.5 Phyllosilicate (pyrophyllite ./. ./. 26.0  11.0 DIN 140 grind) Phyllosilicate (mica DIN 160 12.0  12.0  ./. 18.0 grind) Zircon flour (zirconium 13.5  13.5  9.0 10.0 silicate, DIN 60 grind) Graphite (DIN 80 grind) 11.0  11.0  8.0 11.0 Polyvinyl acetate ./. ./. 0.9 ./. Biocide (benzisothiazolinone 0.3 0.3 0.3  0.3 solution, 10% (wt/wt) aqueous solution) Modified starch ./. ./. 0.3 ./. Polyvinyl alcohol 0.4 0.4 ./.  0.4 Iron oxide (yellow) ./. ./. 1.2 ./. Wetting agent 0.6 0.1 0.3  0.6 Defoamer 0.1 1.0 ./.  0.1 Propylene carbonate 3.0 3.0 3.0 ./. Particulate, amorphous silicon 14.3  14.3  ./. ./. dioxide TOTAL: 100.0  100.0  100.0  100.0 

[0181] The dilutable refractory coating-composition concentrates indicated in Table 1 above were subsequently diluted with water to produce coating compositions ready for use for the purpose intended here (for application to molds and/or cores by means of a dipping operation, preferably in the form of a dipping bath). The respective dilution employed and also other properties of the ready-to-use coating compositions resulting in each case from the dilution employed are indicated below in Table 1a:

TABLE-US-00002 TABLE 1a Production and properties of ready-to-use (for dipping bath or dipping tank) coating compositions Coating compositions (ready to use for dipping tank or dipping bath): SZ1 SZ2 SZ3 SZ4 Concentrate (as per 100.0 100.0 100.0 100.0 Table 1), parts by weight: Water, parts by weight 35.0 40.0 30.0 40.0 Properties of the ready-to-use coating compositions resulting from the above dilution: Density [g/ml] 1.32 1.26 1.36 1.35 Flow time [s] 13.0 13.0 13.7 13.3 pH 6.7 6.7 7.2 6.7

[0182] As is apparent from Table 1a, the coating compositions for the purpose intended here, application to test cores by means of a dipping application or a dipping bath, were produced in such a way as to ensure easy comparability (i) of their respective properties on application to the test cores and also (ii) of the respectively resulting properties of the coated test cores (densities and flow times were set to be as similar as possible).

[0183] The densities of the ready-to-use coating compositions, indicated in Table 1a, were measured according to the standard test method DIN EN ISO 2811-2:2011 (method A).

[0184] The flow times of the ready-to-use coating compositions, indicated in Table 1a, were measured according to the standard test method DIN 53211 (1974) by determination with the DIN 4 cup.

[0185] The pH values of the ready-to-use coating compositions, indicated in Table 1a, were measured in accordance with the standard test method DIN 19260:2012-10 in each case from the suspension.

[0186] The coating compositions SZ1, SZ2, and SZ4 each contained attapulgite as rheological additive. Coating composition SZ3 is of the type described in document WO00/05010.

Example 2: Investigation of the Softening of Foundry Cores

[0187] To determine the softening of foundry cores (i.e., the maximum drop in flexural strength), test cores (test specimens; in accordance with the “core system 1” indicated in Table 4) were produced conventionally in a core shooting machine from Multiserw (model LUT, gassing pressure: 2 bar, shot time: 3.0 s; shooting pressure 4.0 bar). An hour after core production, the test cores were coated (coated) with the above-stated ready-to-use coating compositions “SZ1”, “SZ3” and “SZ4” (cf. Table 1a) at room temperature (25° C.) by dipping (conditions: 1 s immersion; 3 s hold time in the coating composition, 1 s removal). The wet film thickness of the refractory coatings was adjusted in each case to about 250 μm. Thereafter the coated test cores were dried in a forced-air oven under the conditions indicated below (1 hour at 120° C.), and in each case the change in their flexural strength under the drying conditions was investigated.

[0188] The coated test cores were each dried over a period of an hour, during which their flexural strengths (in N/cm.sup.2, corresponding to the definition as indicated in data sheet R 202 of the Verein Deutscher Gießereifachleute, October 1978 edition) were measured at different times during the drying and then once more one hour after the end of the drying operation using a standard testing instrument of the type “Multiserw-Morek LRu-2e”, in each case with a standard measurement program “Rg1v_B 870.0 N/cm.sup.2” (3-point bending strength).

[0189] Table 2, for the coated test cores investigated, reports in each case the values for the maximum dropping of flexural strength within the stated time under drying conditions, in %, based in each case on the flexural strength of the respective freshly coated (still wet) test core before the start of drying (initial value).

TABLE-US-00003 TABLE 2 Drop in strength of coated test cores under drying conditions Maximum drop in flexural Observation of Type of refractory strength on drying, as % core failure coating on test core of the initial value during drying SZ 1 72 No SZ 3 25 No SZ 4 0 Yes

[0190] The expression “core failure” denotes here and below in each case the invalidation of a coated core during the drying procedure, meaning that the coated core was in each case unusable for the measurement of flexural strength and also for a subsequently envisaged casting procedure.

[0191] From the values reported in Table 2 it can be seen, among other things, that the maximum drop in the flexural strength of a test core coated with an inventive coating composition (SZ1) is significantly smaller than with noninventive, comparative coating compositions (SZ3 and SZ4). It is further apparent from the values in Table 2 that with the noninventive, comparative coating composition SZ4 it was not possible under the selected conditions to produce any usable coated cores.

Example 3: Investigation of the Storage Stability of Coated and Uncoated Foundry Cores

[0192] To determine the storage stability, waterglass-bound test cores (test specimens) were produced in a conventional way and their flexural strengths were determined in each case uncoated shortly after their production (one hour storage time, relative humidity in the range from 30 to 60%, storage temperature in the range from 20 to 25° C.) as indicated above; cf. Table 3 (entry “Uncoated after 1 h”).

[0193] Furthermore, corresponding test cores were coated as indicated below in Table 3 one hour after core production (i.e. after the same respective time interval from their production) at room temperature (25° C.) with the coating compositions SZ1 and SZ4, in each case by dipping (conditions: 1 s immersion; 3 s hold time in the coating composition, 1 s removal) (the coating compositions are designated as in Example 1) and then dried in each case for an hour at 120° C. in a forced-air oven. The coated, dried test cores were then subjected to a storage test for a duration of seven days (insofar as it was possible to produce the coated core or insofar as core failure was not observed before). The temperature during the storage was in each case 35° C.; the relative humidity was in each case 75%. After the end of the storage test, the flexural strengths of the test cores were determined as indicated above. The results of these storage tests are reported below in Table 3. The test cores (“core system 1”) used for all of the tests in Example 3 are cores whose production conditions are specified below in Table 4.

TABLE-US-00004 TABLE 3 Determination of the storage stability of coated and uncoated foundry cores Coated with Coated with Uncoated type SZ1 type SZ4 Uncoated Core after 1 h after storage after storage on storage system Flexural strength [N/cm.sup.2] 1 300 131 not core failure determinable after 131 min.

[0194] From the values reported in Table 3 it can be seen, among other things, that a test core coated with an inventive coating composition (SZ1) after seven-day storage still had >40% of the initial strength, whereas a test core coated with a noninventive, comparative coating composition (SZ4) was unusable under comparable conditions; its flexural strength was no longer determinable under the conditions defined above, since it fell apart during storage. Under the test conditions, an uncoated comparative core failed after just 131 min., i.e., just the application of an inventive coating composition to a test core resulted in the test core being stabilized under drying conditions.

TABLE-US-00005 TABLE 4 Production conditions for core system 1 Parameter Core system 1 Molding material (100 parts by Silica sand weight) Binder (2.2 parts by weight) Alkali metal waterglass solution, 25-35 wt % waterglass content in water (wt/wt) Additive (1.0 part by weight) Particulate, amorphous silicon dioxide Core box temperature 120° C. Gassing temperature 150° C. Cure time 30 s

[0195] Core system 1 consisted only of the molding material, binder, and additive constituents, as indicated in Table 4:

[0196] The binder indicated in Table 4 for core system 1 was a commercial alkali metal waterglass binder “Cordis® 8511” (HA International).

[0197] The additive indicated in Table 4 for core system 1 was a commercial binder additive whose main constituent 95 wt %) was particulate, amorphous silicon dioxide, “Anorgit® 8396” (Huttenes-Albertus Chemische Werke GmbH).

Example 4: Investigation of the Flexural Strength of Coated Foundry Cores

[0198] Waterglass-bound test cores (test specimens) were produced in a conventional way (analogous to that described in Example 2, but after interim maintenance of the core shooting machine used) and their flexural strengths were determined for comparative purposes in each case uncoated shortly after their production (one hour storage time at a temperature in the range from 20 to 25° C., relative humidity 30 to 60%) as indicated above (for the production conditions of the test cores, see Table 6).

[0199] Furthermore, test cores as indicated below in Table 5 were coated at different core temperatures by dipping (conditions: 1 s immersion; 3 s hold time; in the coating composition, 1 s removal) (designation of the coating compositions as in Example 1) and dried in each case in a forced-air oven at 120° C. for an hour. After cooling to room temperature and a storage time of 24 hours (relative humidity in the range from 30 to 60%, temperature in the range from 20 to 25° C.), the flexural strengths were then determined as indicated above on the coated, dried test cores.

[0200] The results of the determinations of the flexural strengths are reported below in Table 5. In this case, two different test cores (“core system A” and “core system B”) were used, the production conditions for each of which are reported below in Table 6.

TABLE-US-00006 TABLE 5 Determination of the flexural strengths of coated and uncoated foundry cores Uncoated Coated Coated Coated Coated after with type with type with type with type 1 h SZ1 SZ2 SZ2 SZ4 Core temperature Core ./. 25° C. 50° C. 90° C. 25° C. system Flexural strength [N/cm.sup.2] A 350  260 320 330 production of a coated core not possible B 350* 250 not not production of deter- deter- a coated core mined mined not possible *Deviation in the measured value from the corresponding value in Table 3 for core system 1 is interpreted essentially as a consequence of the maintenance on the core shooting machine.

[0201] From the values reported in Table 5 it can be seen that foundry cores coated with inventive coating compositions at different core temperatures achieve high flexural strengths. In particular the values reported in Table 5 show that with inventive coating compositions (SZ1, SZ2) foundry cores can be coated successfully even at relatively high core temperatures, for instance at core temperatures in the range from 50 to 100° C., with good success (high flexural strengths). With noninventive, comparative coating compositions (SZ4), on the other hand, under comparable conditions, it was not possible to produce usable cores, these cores instead failing in the course of drying.

TABLE-US-00007 TABLE 6 Production conditions for core systems A and B Parameter Core system A Core system B Molding Silica sand (100.0 Silica sand (100.0 material parts by weight) parts by weight) Binder Alkali metal waterglass Alkali metal waterglass solution, 25-35 wt % solution, 25-35 wt % waterglass content in waterglass content in water (wt/wt) water (wt/wt) (2.2 parts by weight) (2.2 parts by weight) Additive Particulate, amorphous Particulate, amorphous silicon dioxide silicon dioxide (1.0 part by weight) (1.0 part by weight) Core box 120° C. 120° C. temperature Gassing 150° C. 150° C. temperature Cure time 50 s 30 s

[0202] The binders and additives indicated for the core systems A and B in Table 6 corresponded in each case to the binders (“Cordis® 8511”) and additives (“Anorgit® 8396”) indicated in relation to Table 4.

[0203] The above-stated core systems A, B and C consisted in each case only of the molding material, binder and optionally additive constituents, as indicated in Table 6.