Use of a sizing composition comprising organic ester compounds and particulate amorphous silicon dioxide in the foundry industry

Description

[0001] The present invention relates to the use of a sizing composition for the foundry industry for producing a coating on a foundry molding, in particular comprising certain organic ester compounds and particulate, amorphous silicon dioxide (SiO 2 ); as well as sized foundry moldings, in particular foundry molds and / or foundry cores, each comprising an aforementioned sizing composition. The invention further relates to a method for producing a foundry molding sized with a water-containing sizing composition. The invention also relates to a kit, including, inter alia, an aforementioned sizing composition. The invention is defined in the appended claims.

[0002] Lost-mold casting is a common process for producing near-net-shape components, particularly in metal casting. After casting, the mold is destroyed, and the casting is removed. Molds are negatives; they contain the cavity to be filled, which will result in the final casting. The inner contours of the future casting can be formed using cores. During mold production, the cavity can be formed into the mold material using a model of the final casting. Cores are usually formed in a separate core box.

[0003] For foundry molds (also referred to as "molds" for the purposes of the present invention) and foundry cores (also referred to as "cores" for the purposes of the present invention), the mold base materials used for foundry molds (also referred to as "molds" for the purposes of the present invention) and foundry cores (also referred to as "cores" for the purposes of the present invention) are predominantly refractory granular materials such as washed, classified quartz sand. Other suitable and known mold base materials include zircon sands, chromite sands, chamotte, olivine sands, feldspar-containing sands, and andalusite sands. A mold base material can also be a mixture of various of the aforementioned or other preferred mold base materials. The refractory mold base material is preferably in a free-flowing form so that it can be filled into a suitable hollow mold and compacted therein. The mold base material orThe corresponding molding material mixture (molding material) is compacted to increase the strength of the foundry mold. To produce the foundry molds, the molding materials are bound with inorganic or organic molding material binders. The molding material binder creates a strong bond between the particles of the molding material, so that the foundry mold acquires the required mechanical stability. In industrial practice, the production of molds and cores is regularly and advantageously carried out in shooting machines or molding machines, in which the particulate components are compacted and the binder hardens; this also applies to the molds and cores used in the present invention. Molds or cores for use in the foundry thus comprise (also for the purposes of the present invention) a molding material that is preferably compacted.

[0004] Both organic and inorganic molding binders can be used to produce foundry molds, and they can be cured using either a cold or hot process. Experts define cold processes as processes that are essentially carried out at room temperature without heating the foundry mold. Curing usually occurs through a chemical reaction, which is triggered, for example, by passing a gas as a catalyst through the molding mixture to be cured, which contains the mold base material and the molding binder, after molding. In hot processes, the molding mixture is heated to a sufficiently high temperature after molding, for example to drive off the solvent contained in the molding binder and / or to initiate a chemical reaction through which the molding binder is cured, for example by crosslinking.

[0005] Regardless of the curing mechanism, all organic molding binders have in common that they undergo thermal decomposition when liquid metal is poured into the foundry mold, potentially releasing pollutants such as benzene, toluene, xylenes, phenol, formaldehyde, and other, sometimes unidentified, thermolysis or cracking products. Although various measures have been taken to minimize these emissions, they cannot currently be completely eliminated from organic molding binders.

[0006] To minimize or prevent the emission of decomposition products during the casting process, mold binders based on inorganic materials and containing at most a very small proportion of organic compounds can be used. Such mold binder systems have been known for some time, for example, from documents GB 782205 A, US 6972059 B1, US 5582232 A, US 5474606 A, and US 7022178.

[0007] In the following, the term "inorganic molding binder" refers to a molding binder which consists predominantly, preferably more than 95% by weight, preferably more than 99% by weight, most preferably entirely of water and inorganic materials, so that the proportion of organic compounds in such an inorganic molding binder is preferably less than 5% by weight, preferably less than 1% by weight, and most preferably 0% by weight.

[0008] The term "inorganically bound" in the context of this text means that a mold or core has been bound with an inorganic molding material binder (as defined above). In an inorganically bound (preferably water glass-bound) mold or core, particles of a granular molding material and, if appropriate, other solid components are bound by an inorganic molding material binder (as defined above).

[0009] Of particular importance as a component of inorganic molding binders is alkali water glass. Alkali water glass refers to glassy, i.e., amorphous, water-soluble sodium, potassium, and lithium silicates, their mixtures, and the corresponding aqueous solutions, solidified from a melt. In the following, the term "water glass" refers to such amorphous, water-soluble sodium, potassium, and / or lithium silicates and / or their aqueous solutions and / or mixtures of the aforementioned silicates and / or their solutions, each of which has a molar modulus (molar ratio) of SiO 2 to M 2 O in the range from 1.6 to 4.0, preferably in the range from 1.8 to 2.5, where M 2 O denotes the total amount of lithium, sodium, and potassium oxide. The term "water glass-bound" means that a foundry molding, in particular a mold or core, was or is produced using a molding binder.which comprises or consists of water glass. For example, US 7770629 B2 proposes a molding material mixture which, in addition to a refractory mold base material, comprises a water glass-based molding material binder and a particulate metal oxide, wherein precipitated silica or pyrogenic silica is preferably used as the particulate metal oxide.

[0010] However, inorganic mold binders also have disadvantages compared to organic mold binders. For example, foundry molds or cores produced with known inorganic mold binders have comparatively low or lower stability to atmospheric humidity, water, or aqueous moisture. This makes it impossible to reliably store such foundry molds or cores for extended periods, as is common with organic mold binders.

[0011] Typically, especially in steel and iron casting, the surfaces of foundry molds, especially molds and cores, are coated with a coating called a "coating," especially those surfaces that come into contact with cast metal. Coatings form a boundary or barrier layer between the mold / core and the metal, among other things to specifically suppress failure mechanisms at these locations or to utilize metallurgical effects. In general, coatings in foundry technology are primarily intended to fulfill the following functions, known to those skilled in the art: Improving the smoothness of the casting surface; Separating the liquid metal from the mold or core as completely as possible; Avoiding chemical reactions between components of the mold / core and the melt, thereby facilitating the separation between the mold / core and the casting and / or avoiding surface defects on the casting such as gas bubbles, penetrations, ribs and / or flakes.

[0012] The above-mentioned and possibly other functions are generally adjusted and optimized or adapted to the respective intended purpose by the precise composition of the sizing or the sizing composition to be applied to the mold or core.

[0013] Sizing compositions for use in foundries usually contain or are composed of the following components: (i) one or more fine-grained refractories, i.e., fine-grained, refractory to highly refractory inorganic materials; (ii) a carrier fluid comprising one or more compounds (water, alcohols, etc.); and (iii) as further components, e.g., one or more sizing binders (hereinafter also referred to as "binders") and / or biocides and / or wetting agents and / or rheological additives. Ready-to-use sizing compositions for coating molds and cores are therefore usually suspensions of fine-grained, refractory to highly refractory inorganic materials (refractories) in a carrier fluid, e.g., an aqueous (i.e., water-containing) carrier fluid or a non-aqueous (i.e., no water-containing) carrier fluid; for details regarding the carrier fluid, see below.

[0014] The coating or coating composition is applied to the inner contour of the casting mold or to the core using a suitable application method, such as spraying, dipping, flooding, or brushing, and then dried there, forming a coating or coating film. The coating can be dried by applying heat or radiant energy, e.g., microwave radiation, or by drying in ambient air. In the case of coating compositions containing flammable compounds in the carrier liquid, drying can also be achieved by burning off these compounds.

[0015] In this text, in accordance with common professional understanding, "refractory" refers to masses, materials, and minerals that can withstand, at least for a short time, the thermal stress during casting or solidification of molten iron, usually cast iron. "Highly refractory" refers to masses, materials, and minerals that can withstand the pouring heat of molten steel for a short time. The temperatures that can occur during the casting of molten steel are usually higher than those that can occur during the casting of molten iron or cast iron. Refractory masses, materials, and minerals (refractories) and highly refractory masses, materials, and minerals are known to those skilled in the art, for example, from DIN 51060:2000-06.

[0016] Mineral oxides, silicates, or clay minerals are typically used as refractories in sizing compositions. Examples of refractories that are also suitable for the present invention are quartz (silicon dioxide), aluminum oxide, zirconium dioxide, aluminum silicates, phyllosilicates, zirconium silicates, olivine, talc, mica, graphite, coke, feldspar, diatomite, kaolins, calcined kaolins, metakaolinite, iron oxide, chromite, and bauxite, which can be used individually or in any combination. The refractory serves, among other things, to seal the pores in a foundry mold or core to prevent the penetration of liquid metal. Furthermore, the refractory provides thermal insulation between the foundry mold or core and the liquid metal. The refractory is usually provided in powder form.Unless otherwise stated, powdered refractories have an average grain size (preferably measured by light scattering according to ISO 13320:2009-10) in the range of 0.1 to 500 µm, preferably in the range of 1 to 200 µm. Materials that have melting points at least 200 °C above the temperature of the molten metal used and / or that do not react with the molten metal are particularly suitable as refractories.

[0017] The refractory materials are usually dispersed in a carrier liquid. The carrier liquid is one or the component of a sizing composition that is preferably liquid under standard conditions (20°C and 1013.25 hPa) and / or evaporable at 160°C and standard pressure (1013.25 hPa). Preferred carrier liquids, which are also suitable within the scope of the present invention, are selected from the group consisting of water and organic carrier liquids, as well as mixtures thereof with one another and / or with other components. Suitable organic carrier liquids are preferably alcohols, including polyalcohols and polyether alcohols. Preferred alcohols are ethanol, n-propanol, isopropanol (2-propanol), n-butanol, and glycol. Water and aqueous mixtures (including aqueous solutions) are often preferred as carrier liquids.

[0018] Size binders (binders) primarily serve to fix the refractory materials contained in a size composition to the molding material. Examples of binders that are also suitable within the scope of the present invention are synthetic resins (organic polymers) or synthetic resin dispersions such as polyvinyl alcohols, polyacrylates, polyvinyl acetates, and / or corresponding copolymers of the aforementioned polymers. Polyvinyl alcohols are preferred. Natural resins, dextrins, starches, and peptides are also suitable as binders.

[0019] Biocides prevent bacterial infestation. Examples of biocides also suitable for use in the present invention are formaldehyde, 2-methyl-4-isothiazolin-3-one (MIT), 5-chloro-2-methyl-4-isothiazolin-3-one (CIT), and 1,2-benzisothiazolin-3-one (BIT). The biocides, preferably the individual biocides mentioned, are typically used in a total amount of 10 to 1000 ppm, preferably in an amount of 50 to 500 ppm, each based on the total mass of the ready-to-use sizing composition (which is intended to be applied directly to a casting mold or core).

[0020] Rheological additives (extenders) are used to adjust the flowability of the sizing agent desired for processing. Other inorganic extenders suitable within the scope of the present invention include, for example, swellable clays, such as sodium bentonite or attapulgite (palygorskite). Other organic extenders suitable within the scope of the present invention include, for example, swellable polymers, such as cellulose derivatives, in particular carboxymethyl, methyl, ethyl, hydroxyethyl, and hydroxypropyl cellulose, plant mucilages, polyvinylpyrrolidone, pectin, gelatin, agar agar, polypeptides, and / or alginates. The aforementioned rheological additives or extenders are preferred ingredients of the sizing composition according to the invention.

[0021] Particularly in the case of aqueous sizing compositions (i.e., containing water as a carrier liquid or as a component of the carrier liquid), wetting agents can also be used to achieve better wetting of the molding material. Ionic and non-ionic wetting agents are known to those skilled in the art. For example, dioctyl sulfosuccinates are used as ionic wetting agents, and alkynediols or ethoxylated alkynediols are used as non-ionic wetting agents. The aforementioned wetting agents are also preferred ingredients of the aqueous sizing composition according to the invention.

[0022] A sizing composition may further contain defoamers, pigments, and / or dyes. Silicone or mineral oil, for example, can be used as defoamers. Examples of pigments are red and yellow iron oxide and graphite. Examples of dyes are commercially available dyes known to those skilled in the art. The aforementioned defoamers, pigments, and / or dyes are also preferred ingredients of the sizing composition according to the invention.

[0023] In order to meet the increasing demands in the areas of environmental protection and emissions protection, inorganic mold binders, in particular mold binders containing water glass, should become more important in the future in the production of molds and cores in the steel and iron casting sector. In order to achieve the desired or required casting quality, it is, as mentioned above, usually necessary or advantageous to coat inorganically bonded molds and cores with a coating. In the interests of environmental and emissions protection, it is therefore logically desirable to avoid the use of organic carrier liquids as far as possible when selecting the coating and to preferentially use water-based coatings, i.e. coatings with water as the sole carrier liquid or at least as the predominant component of the carrier liquid.

[0024] As stated above, foundry moldings, in particular molds and cores, which were produced with inorganic molding binders, in particular with molding binders containing water glass, have low stability against the effects of water or aqueous moisture. The water contained in water-based coating compositions can therefore damage the inorganically bonded molds and cores treated (coated) with them. This can, in particular, adversely reduce the strength of the molds and cores coated in this way. This particular problem, which is known in foundry technology (cf., for example, WO 00 / 05010A1), can only be inadequately addressed with the means used to date, including, for example, particularly intensive hardening of the molds and cores, complex processes for drying the applied coating or the adaptation of the molding material mixture.

[0025] Document WO 00 / 05010 states that a water-based coating can be applied in particular to cores and molds gassed with carbon dioxide and bound with sodium silicate, if the coating composition used contains a specific additive which is soluble or miscible with water, such as esters of polyhydric alcohols, carbonates, esters or lactones.

[0026] Document WO 2013 / 044904 A1 states that by combining certain clays as ingredients of a water-based sizing, sizings with an unusually high solids content can be produced, the viscosity of which is nevertheless comparable to commercially available, ready-to-use sizings, whereby the quality of the cores and molds coated with these sizings and bound with inorganic molding binders can be improved.

[0027] Documents DE 10 2011 115 025A1 and WO 2013 / 050022 A2 state that the addition of certain salts in a specific concentration range to an aqueous sizing composition can improve the quality of the sized inorganic cores and molds, in particular, increasing their storage stability. The salts are magnesium and / or manganese salts, particularly their sulfates and chlorides.

[0028] Documents DE 10 2011 115 024 A1 and WO 2013 / 050023 A2 state that the addition of certain additives to an aqueous sizing composition can improve the quality of the sized inorganic cores and molds, in particular increasing their storage stability. Esters of formic acid (methanoic acid) are used as an additive component of the sizing composition, with the chain length of the alcohol or alcohol mixture used in the esterification being, in particular, on average less than six and particularly preferably less than three carbon atoms.

[0029] The document DE 10 2006 040 385 A1 discloses temperature-stable BN mold release coatings based on ceramic and glassy binders; however, the document does not disclose the use for inorganically bonded molds or cores (based on corresponding granular molding materials) for use in foundries.

[0030] According to its abstract, document CN 105170890 A relates to the field of casting, in particular to a casting coating capable of improving the casting finish. The casting coating is characterized by comprising 15 to 20 parts by weight of diatomaceous earth, 2 to 5 parts of titanium dioxide, 2 to 3 parts of aluminum sulfate, 5 to 7 parts of silica sol (Ludox), 1 to 2 parts of a water-based crosslinking agent, 0.5 to 1 part of a water-based thickener, 1-2 parts of organic adhesives, 70-80 parts of ethyl alcohol, 1-2 parts of a bentonite suspending agent, 10-15 parts of n-octanol, 1-3 parts of maleic anhydride, and 20-25 parts of modified straw ash.

[0031] The German Patent and Trademark Office has searched the following prior art for the priority application for the present application: DE 10 2006 040 385 A1, WO 00 / 05 010 A1 and DE 10 2011 115 024 A1.

[0032] However, as our own investigations have shown, the problems mentioned above still exist to a relevant extent even when using the above-mentioned state of the art approach.

[0033] Based on the state of the art, there is therefore a need for further improved coating compositions for use in foundries, which should have or enable one or more, preferably all, of the following advantageous properties: the strength of the coated molds and / or cores produced thereby should be increased compared to molds and cores coated with known water-containing coatings or coating compositions, in particular if the molds and cores were produced with inorganic molding binders, in particular with water-glass-containing molding binders; the storage stability and the resistance to atmospheric humidity of the coated molds and / or cores produced thereby should be increased compared to molds and / or cores coated with known water-containing coatings or coating compositions; the storage stability of the coating composition itself should not be significantly impaired or should even be increased compared to known water-containing coating compositions; the application of the coating composition to hot molds and / or cores (iein particular to those molds and / or cores which have temperatures of more than 50 °C, preferably temperatures in the range from 50 to 100 °C) should be made possible or at least improved; the coated molds and cores which can be produced in this way should enable a high, preferably low-defect casting quality, particularly preferably a defect-free casting quality and / or smoothness of the casting surface; the use of inorganically bonded, in particular water glass-bonded foundry molds, in particular molds and / or cores, should also be made possible for iron and / or steel casting and the possibility of using them for these purposes should be expanded.

[0034] It was a general object of the present invention to provide a sizing composition for use in the foundry which has or enables one or more or all of the above-mentioned properties.

[0035] It was a primary object of the present invention to develop a sizing composition for use in foundries which can be used on foundry moldings, in particular inorganically bonded, in particular water glass bonded, foundry moldings, preferably molds and / or cores, without adversely affecting their properties, in particular their strengths.

[0036] A further object of the present invention was to provide coated inorganically bonded foundry moldings, in particular foundry molds and / or foundry cores, each comprising a coating composition to be specified according to the invention.

[0037] A further object of the present invention was to provide a corresponding process for producing an inorganically bonded foundry molding coated with a water-containing coating.

[0038] In addition, it was an object of the present invention to provide a kit containing, inter alia, a sizing composition to be specified according to the invention.

[0039] The invention is defined and described in more detail in the appended claims, including particularly preferred combinations of preferred parameters, properties and components of the invention. Special and / or preferred embodiments of the invention are described in more detail below. Unless otherwise stated, preferred aspects or embodiments of the invention can be combined with other aspects or embodiments of the invention, in particular with other preferred aspects or embodiments. The combination of respectively preferred aspects or embodiments with one another in turn results in preferred aspects or embodiments of the invention. Embodiments, aspects or properties which are described in connection with the present invention for the sizing composition according to the invention or are described as preferred apply accordingly.analogously also for their uses according to the invention, for methods according to the invention, for coated molds or cores according to the invention and for kits according to the invention.

[0040] If uses according to the invention, methods according to the invention, coated shapes or cores according to the invention and kits according to the invention are described below which "comprising" or "containing" more precisely defined embodiments, components or features, the corresponding variant of the said uses, methods, coated shapes or cores or kits, which is to be understood in a narrower scope and which "consists" of these more precisely defined embodiments, components or features, is also intended to be disclosed in each case.

[0041] According to the invention, the primary object and further aspects of the general object specified above are achieved by the use of a sizing composition comprising (a) water, (c) particulate, amorphous silicon dioxide and (d) one or more further refractory materials, for producing a coating on a mold or a core, wherein the mold is water glass bonded and / or wherein the core is water glass bonded, for use in the foundry, characterized in that the sizing composition further comprises (b) one or more organic compounds selected from the group consisting of propylene carbonate, γ-butyrolactone, diacetin, triacetin, dibasic ester, acetic anhydride, methyl carbonate and ε-caprolactone, where dibasic ester is a mixture of several dimethyl esters of glutaric acid, succinic acid and adipic acid.

[0042] Propylene carbonate (CAS RN 108-32-7) is particularly preferred as the organic compound in component (b); with regard to the above-mentioned compound of formula (I), in propylene carbonate, R1 is linked via an O atom (to the carboxyl group) and is linked to R2 to form a ring structure comprising a total of 5 ring atoms; the linked groups R1 and R2 contain a total of 3 C atoms.

[0043] The term "dibasic ester" refers to a mixture of several dimethyl esters of dicarboxylic acids, particularly glutaric acid, succinic acid, and adipic acid. The mixture contains a proportion in the range of 55 to 67 wt.% of dimethyl glutarate, 15 to 25 wt.% of dimethyl succinate, and 10 to 25 wt.% of dimethyl adipate.

[0044] For the purposes of the present invention, the term "particulate, amorphous silicon dioxide" refers to particulate synthetic silicon dioxide, preferably precipitated silica and / or fumed silica. Fumed silica is preferred.

[0045] In any case, for the purposes of the present invention, the particulate, amorphous silicon dioxide (component (c)) is not considered to be one of the other refractory materials of component (d).

[0046] Precipitated silica is known per se and can be obtained, for example, in a manner known per se by reacting an aqueous alkali silicate solution with mineral acids: the resulting precipitate is then separated off, dried and, if appropriate, ground. Pyrogenic silicas are also known per se and can preferably be obtained in a manner known per se by coagulation from the gas phase at high temperatures. The production of fumed silica can be carried out, for example, by flame hydrolysis of silicon tetrachloride, or, for the purposes of the present invention, preferably in an arc furnace by reducing quartz sand with coke or anthracite to silicon monoxide gas with subsequent oxidation to silicon dioxide. Another form of amorphous, particulate silicon dioxide preferred according to the invention is obtained during zirconium dioxide production.Another known possibility for producing particulate amorphous silicon dioxide is the spraying of a silicon dioxide melt: the primary, amorphous silicon dioxide particles are not produced by a grinding process (as in other preferred production processes).

[0047] The primary amorphous silicon dioxide particles ("primary particles") are often agglomerated after the above-mentioned production processes, i.e., present as agglomerates of primary particles. For the purposes of the present invention, the primary particles of the particulate, amorphous silicon dioxide are preferably (i) spherical and (ii) have a D90 value < 10 µm, preferably < 1 µm, determined by laser diffraction. The particle shape of the primary particles of the particulate, amorphous silicon dioxide is preferably spherical. The spherical shape of the primary particles can be determined, for example, by scanning electron microscopy. Preferably, the primary particles of the particulate, amorphous silicon dioxide are spherical and have a sphericity of 0.9 or more, determined by evaluating two-dimensional microscopic (preferably scanning electron microscopy) images.

[0048] As refractory materials (cf. component (d)), one or more substances are preferably 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.

[0049] The sizing composition used according to the invention is particularly suitable for producing a coating on an inorganically bonded, inventively water-glass-bonded foundry molding. The sizing composition can particularly preferably be used for producing a coating on a water-glass-bonded foundry molding, namely a mold and / or a core, which contains at least a portion of particulate amorphous silicon dioxide.

[0050] Waterglass-bonded molds and cores, including those containing particulate amorphous silicon dioxide (in addition to conventional granular molding materials), and their production are known per se, for example from documents WO 2006 / 024540 and WO 2009 / 056320. The aforementioned, known per se molds and cores are suitable for the purposes of the present invention.

[0051] Preferred is a sizing composition used for the inventive use, wherein the primary particles of the particulate, amorphous silicon dioxide (i) are spherical and / or (ii) have a D90 value of <10 µm, preferably <1 µm, determined by laser diffraction. Preferably, the primary particles of the particulate, amorphous silicon dioxide (i) are spherical and have a sphericity of 0.9 or more, determined by evaluating two-dimensional microscopic images. Modern commercially available electron microscopic or light microscopic systems enable digital image analysis and thus convenient determination of particle shape. Digital image analysis is preferred for sphericity studies.

[0052] The sizing composition used according to the invention is also suitable, not according to the invention, for producing a coating on a foundry molding bonded with water-soluble alkaline binders. Water-soluble alkaline binders are selected from known ester-curing phenolic resins, e.g., the no-bake binder systems known under the name "Alphaset®", as disclosed, for example, in document EP 85512, or the alkyl formate-curing phenol-formaldehyde resins known under the name "Betaset®", as disclosed, for example, in document EP 86615, as well as from the carbon dioxide-curing phenolic resins known under the name Carbophen®, as disclosed, for example, in document EP 2052798.

[0053] The foundry moldings which can be coated (coated) with the coating composition used for the use according to the invention can be produced in any known manner, for example by shooting, pouring or by 3D printing techniques.

[0054] Without guarantee of correctness, it is assumed that when the aqueous sizing composition used for the use according to the invention is used accordingly, bonding structures in the alkali silicate framework of a water glass-bonded, sized foundry molding (mold or core) are attacked due to the water content of the sizing composition, but that any temporary weakening of the bonding structure that may result therefrom is eliminated again by a further chemical reaction, such as an acid-base reaction, in the presence of the particulate, amorphous silicon dioxide, which ultimately results in increased strength of such sized, water glass-bonded foundry moldings compared to the prior art.The role of compounds of formula (I) in this process could be that they are hydrolyzed with release of the acid component and thereby provide acid in a suitable form and amount to contribute to the increased strength of inorganically bound foundry moldings.

[0055] In the sizing compositions used according to the invention, pH values < 5 may occur; pH values < 4 are also possible, in each case determined from the suspension, preferably according to the standard method DIN 19260:2012-10. The presence of acid in the aqueous phase cannot be excluded.

[0056] Preferred is the use according to the invention of an above-mentioned sizing composition, wherein component (d) comprises one or more substances selected from the group consisting of quartz, aluminum oxide, zirconium dioxide, aluminum silicates, layered silicates, zirconium silicates, olivine, talc, mica, graphite, coke, feldspar, diatomite, kaolins, calcined kaolins, metakaolinite, iron oxide and bauxite, and / or wherein the sizing composition comprises in or as component (c) a particulate, amorphous silicon dioxide which comprises as a minor component (i) zirconium dioxide and / or (ii) a Lewis acid, preferably zirconium dioxide.

[0057] The "D90 value" of the primary particles of the particulate, amorphous silicon dioxide refers to their particle size distribution. The particle size distribution is determined in a conventional manner by laser diffraction, preferably according to the standard method according to DIN ISO 13320:2009-10. The D90 values determined in this way for the cumulative frequency distribution of the volume-averaged size distribution function indicate that 90 vol.% of the primary particles have a particle size equal to or smaller than the specified value (e.g., 10 µm). Suitable devices for determining the particle size distribution are conventional laser diffraction devices, e.g., the "Mastersizer 3000" type from Malvern, Great Britain, or preferably the "Coulter LS 230" type from Beckman Coulter, USA. The measurement is preferably carried out using "Polarization Intensity Differential Scattering" ("PIDS") technology.The evaluation of the scattered light signals in the aforementioned laser diffraction methods is preferably carried out according to the Mie theory, which also takes into account the refraction and absorption behavior of the primary particles.

[0058] If the primary particles of the particulate, amorphous silicon dioxide are present as agglomerates and / or aggregates and / or in any other way as combinations of several primary particles, these are preferably gently separated mechanically or in a similar manner in a known manner before the particle size distribution of the primary particles is determined in order to exclude any falsification of the result as far as possible.

[0059] In the context of the present invention, the term "minor constituent" means that the particulate, amorphous silicon dioxide of component (c) contains only small amounts of such minor constituents, which may still originate, for example, as impurities or adhesions from previous manufacturing and / or processing methods of the particulate, amorphous silicon dioxide. These minor constituents are preferably present in an amount of no more than 18 wt.% (or mass fraction), particularly preferably in an amount of no more than 12 wt.%, most preferably in an amount of no more than 8 wt.%, in each case based on the total mass of the particulate, amorphous silicon dioxide of component (c).

[0060] One of the aforementioned minor components in component (c) can be a Lewis acid. However, several Lewis acids and / or mixtures thereof can also be included. For the purposes of the present invention, "Lewis acid" is understood to mean an acid according to the concept proposed by G.N. Lewis, according to which an acid is an electron pair acceptor, i.e., a molecule or ion with an incomplete noble gas configuration that can accept an electron pair provided by a Lewis base and form a so-called Lewis adduct with it. A Lewis acid is electrophilic, whereas a Lewis base is nucleophilic. Thus, molecules and ions that are not acids according to classical concepts can also be considered acids.

[0061] Furthermore, preference is given to the use according to the invention or to the preferred use according to the invention of a sizing composition comprising one or more or all of the following components: one or more biocides, one or more wetting agents, one or more rheological additives, and one or more binders, preferably polyvinyl alcohol.

[0062] Suitable biocides include conventional biocides such as microbicides, especially bactericides, algicides, and / or fungicides. Preferably, the biocides listed above can be used. The wetting agents listed above are preferably suitable as wetting agents. The rheological additives listed above are preferably suitable as rheological additives. The binders listed above are preferably suitable as binders. Polyvinyl alcohol is a particularly preferred binder.

[0063] Also preferred is an inventive or preferred inventive use of a sizing composition, wherein the ratio of the total mass of all organic compounds of formula (I) in relation to the total mass of the sizing 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 wherein an aqueous phase is present for which the ratio of the mass of component (a) to the total mass of the aqueous phase is greater than 50%, preferably greater than 70%, particularly preferably greater than 90%, and / or wherein the sizing composition has a solids content of less than 80% by weight, preferably less than 45% by weight, based on the total mass of the sizing composition, and / or wherein the sizing composition has a proportion of particulate, amorphous silicon dioxide of component (c) in the range from 1 to 30% by weight, preferably 5 to 20% by weight, particularly preferably 8 to 17% by weight, based on the total mass of the sizing composition, and / or wherein the sizing composition has a total proportion of particulate, amorphous silicon dioxide of component (c) and of further refractory materials of component (d) in the range from 25% by weight to 80% by weight, preferably 30 to 60% by weight, particularly preferably 45 to 55% by weight.-%, based on the total mass of the sizing composition.

[0064] The determination of the solids content in the sizing compositions used according to the invention is preferably carried out in accordance with the leaflet P79 of the Association of German Foundry Experts in the version dated March 1976, point 6.

[0065] The sizing composition to be used according to the invention is preferably ready-to-use, i.e., it is intended to be applied directly to a casting mold or core. However, the sizing composition to be used according to the invention can also be present as a concentrate, i.e., it is then intended to be diluted before application to a casting mold or core, in particular by adding water or an aqueous mixture. This applies to all embodiments of the present invention, unless otherwise stated or specified. The person skilled in the art will decide in each individual case whether a sizing composition is ready-to-use or should be further diluted.

[0066] A further preferred embodiment of the present invention is an inventive or preferred inventive use of a sizing composition 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 of 0.05 to 0.80 wt.%, based on the total mass of the sizing composition.

[0067] A preferred embodiment of this use according to the invention is one in which the coating on the mold or core is produced by an application method selected from the group consisting of spraying, dipping, flooding and brushing, preferably dipping.

[0068] Particularly preferred is a use according to the invention or preferred use according to the invention, wherein the water glass-bound form or the water glass-bound core contains particulate, amorphous silicon dioxide (preferably in addition to, for example, one or more conventional granular molding materials) and / or wherein the application of the sizing composition takes place on a water glass-bonded mold or a water glass-bonded core for use in iron or steel casting and / or wherein the application of the sizing composition takes place on a water glass-bonded mold or a water glass-bonded core for use in casting a molten metal with a temperature of > 900 °C, preferably > 1250 °C, preferably for use in casting a molten metal comprising iron and / or steel, and / or wherein the application of the sizing composition takes place on a water glass-bonded mold or a water glass-bonded core at a temperature of the water glass-bonded core or the water glass-bonded mold of > 50 °C, preferably > 70 °C, particularly preferably at a temperature < 100 °C. Surprisingly, under these conditions, a mold or core which is usable for subsequent treatment or processing steps is created or remains under these conditions.a usable core is obtained.

[0069] A use as described above is preferred as an agent for reducing the impairment of the flexural strength of a water glass-bonded core or a water glass-bonded mold caused by sizing with the water-containing sizing agent, wherein the water glass-bonded core or the water glass-bonded mold contains particulate, amorphous silicon dioxide.

[0070] Furthermore, the invention also relates to a method for producing a mold coated with a water-containing coating, preferably such a mold with a high flexural strength, or a core coated with a water-containing coating, preferably such a core with a high flexural strength, for use in the foundry, comprising the following steps: (1) Providing or preparing a sizing composition as disclosed for use according to the invention and / or as employed for the preferred use according to the invention, (2) Providing or preparing an unsized mold or an unsized core, wherein the provided or prepared unsized mold is water glass bonded or the provided or prepared unsized core is water glass bonded, and (3) Applying the provided or prepared sizing composition from step (1) to the provided or prepared mold or the provided or prepared core provided or prepared in step (2).

[0071] All aspects specified for the use of the sizing composition according to the invention, in particular their preferred features and combinations of features, are mutatis mutandisalso applicable to the process according to the invention for producing a mold coated with a water-containing coating.

[0072] In the context of the present invention, "high flexural strength" means a flexural strength of a foundry molding, preferably a core or a mold, which allows practical handling of the foundry molding without it breaking.

[0073] The sizing composition provided or produced in step (1) of the process according to the invention can be produced by methods known per se. For example, a suitable amount of water can be introduced into the initial charge, and the other components for producing the sizing composition can then be added to this initial charge in the desired amount while stirring with a suitable stirrer, such as a high-shear stirrer, e.g. a gear stirrer or a dissolver stirrer. If necessary, components can be broken down in a manner known per se before or during addition. For example, one or more rheological additives can optionally be broken down using a high-shear stirrer, before or after addition to the water initial charge, and individually or together with one or more refractory materials.If the one or more refractory materials are not digested together with any rheological additives added, they can also be digested individually and added to the water mixture. Subsequently, the other components of the sizing composition, for example, can be added to the water mixture—which may contain rheological additives and / or refractory materials—in any order and preferably with stirring, preferably with a high-shear stirrer. These components include one or more sizing binders, optionally one or more biocides, optionally one or more wetting agents, optionally one or more defoamers, optionally one or more pigments, and / or optionally one or more dyes.

[0074] The sizing composition provided or produced in step (1) of the process according to the invention can be ready-to-use for application to foundry moldings, i.e., for example, it can be present in a concentration suitable for use as an immersion bath for molds or cores. Likewise, the aforementioned sizing composition can also be prepared in a manner known per se first as a concentrate, which is only later diluted, e.g., shortly before use of the sizing composition, e.g., by further addition of water, to a ready-to-use concentration (or consistency), which is then suitable for application to molds and / or cores. If, within the scope of the present invention, quantities or ratios are specified with regard to the sizing composition used according to the invention, a ready-to-use sizing composition (which is intended to be applied directly to a casting mold orto be applied to a core), unless expressly stated otherwise. It is generally not necessary to mix the individual components of the sizing composition to be used according to the invention with one another immediately before a designated coating process on molds or cores; rather, mixing can take place much earlier because the storage stability of the sizing composition to be used according to the invention is high.

[0075] The unsized, waterglass-bonded mold provided or produced in step (2) of the process according to the invention or the unsized, waterglass-bonded core provided or produced can be produced in a manner known per se, for example as described in the documents WO 2006 / 024540 or WO 2009 / 056320.

[0076] The application in step (3) of the provided or produced sizing composition from step (1) to the provided or produced mold or the provided or produced core after step (2) of the process according to the invention can be carried out in a manner known per se, preferably according to the application methods indicated above as being suitable, particularly preferably by dipping the mold or the core in a sizing composition used according to the invention provided as an immersion bath.

[0077] A preferred method according to the invention or a preferred method according to the invention is one in which the provided or produced unsized mold or the provided or produced unsized core contains particulate, amorphous silicon dioxide, and / or in which the production of the unsized mold or the unsized core in step (2) is carried out by curing a provided or produced molding material mixture by gassing with carbon dioxide, by adding esters or phosphates or by gassing with hot air in a heated tool takes place.

[0078] The above-mentioned processes for curing a prepared or manufactured molding material mixture are known per se. Phosphates suitable for curing include, for example, aluminum phosphates.

[0079] In a further embodiment, a method according to the invention or a preferred method according to the invention is preferred, wherein the application to the provided or produced unsized form or the provided or produced unsized core takes place at a temperature of the provided or produced form or the provided or produced core of > 50 °C, preferably > 70 °C, particularly preferably at a temperature < 100 °C, and / or wherein the application to the provided or produced unsized form or the provided or produced unsized core takes place by an application method selected from the group consisting of spraying, dipping, flooding and brushing, preferably dipping.

[0080] The invention further relates to a coated mold or a coated core for use in foundries, each comprising a coating composition as disclosed for use according to the invention or as preferred according to the invention. In one variant of the present invention, the coated mold or the coated core can be produced by a process as disclosed above as being according to the invention or as preferred according to the invention for producing a mold coated with a water-containing coating or a core coated with a water-containing coating.

[0081] According to the invention, the above-specified inventive sized form and / or the above-specified inventive sized core is / are water glass bonded.

[0082] The above-mentioned sized mold according to the invention and / or the above-mentioned sized core according to the invention preferably each contain particulate, amorphous silicon dioxide. The present invention also provides an aforementioned sized mold according to the invention and / or preferred sized mold according to the invention or an aforementioned sized core according to the invention and / or preferred sized core according to the invention for use in casting a molten metal having a temperature of > 900 °C, preferably > 1250 °C, preferably for use in casting a molten metal comprising iron and / or steel.

[0083] Furthermore, the invention also relates to a kit containing in separate components (U) a sizing composition described in the process according to the invention or preferably according to the invention for producing a coating on a water glass-bonded mold or a water glass-bonded core, for use in foundry, (V) a binder comprising water glass, and (W) particulate, amorphous silicon dioxide.

[0084] It has been found that the sizing composition used according to the invention has and / or provides the following advantages over comparable sizing compositions known from the prior art: in particular an improved storage stability of the sized inorganically bound, preferably water glass-bonded, molds and / or cores that can be produced therewith; in particular an improved resistance to atmospheric moisture of the sized inorganically bound, preferably water glass-bonded, molds and / or cores that can be produced therewith; a comparable or even improved storage stability of the sizing composition (compared to sizing compositions known from the prior art); an improved possibility of application to hot molds and / or cores (iepreferably to those molds and / or cores which have temperatures of more than 50°C, preferably temperatures in the range from 50 to 100°C) - this property can, for example, enable a faster processing sequence in mass production and, ideally, a higher piece throughput per unit of time; an improved possible use of inorganically, in particular water glass, bonded foundry moldings, in particular molds and / or cores, for iron and / or steel casting, through appropriate use of the coatings or coating compositions according to the invention and / or an improved strength of the coated inorganically bonded, preferably water glass-bonded, molds and / or cores which can be produced therewith.

[0085] These benefits apply mutatis mutandis for the further objects or aspects of the present invention. Examples:

[0086] The examples given below are intended to describe and explain the invention in more detail without limiting its scope. Example 1: Preparation of sizing compositions.

[0087] The sizing compositions according to the invention ("SZ1", "SZ2") and the non-inventive comparative sizing compositions ("SZ3" and "SZ4") listed in Table 1 were prepared in a manner known per se by mixing the ingredients indicated in each case.

[0088] For this purpose, the required amount of water was placed in a beaker (batch size of approximately 2 kg of sizing composition as "concentrates" in each case, see Table 1), the rheological additives and the refractory materials (sheet silicates, zirconium powder, graphite) were added, and the mixture was then stirred for 3 minutes using a high-shear dissolver stirrer in a conventional manner. The other components of the sizing compositions (see Table 1) were then added in the specified proportions, and stirring was continued for a further 2 minutes using a high-shear dissolver stirrer. The dilutable concentrates of sizing compositions listed in Table 1 were obtained.

[0089] The information on "DIN grindings" in Table 1 means that the respective specified component of the sizing composition is in the ground state, whereby after sieving a sample of this component with a test sieve with a nominal mesh size in µm corresponding to the specified numerical value (e.g.: "80" means "test sieve with mesh size 80 µm") (according to DIN ISO 3310-1:2001-09), a residue in the range of 1 to 10 wt.% remains, based on the sample quantity used. Table 1: Sizing compositions according to the invention and not according to the invention (each obtained as dilutable "concentrates") Sizing 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 DIN 140 grinding) . / . . / . 26,0 11,0 Phyllosilicate (mica DIN 160 grinding) 12,0 12,0 . / . 18,0 Zirconium flour (zirconium silicate, DIN 60 grinding) 13,5 13,5 9,0 10,0 Graphite (DIN 80 grinding) 11,0 11,0 8,0 11,0 Polyvinyl acetate . / . . / . 0,9 . / . Biocide (benzisothiazolinone solution, 10% w / w aqueous solution) 0,3 0,3 0,3 0,3 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 Defoamers 0,1 1,0 . / . 0,1 Propylene carbonate 3,0 3,0 3,0 . / . Particulate, amorphous silicon dioxide 14,3 14,3 . / . . / . SUM: 100,0 100,0 100,0 100,0

[0090] The dilutable concentrates of sizing compositions listed above in Table 1 were then diluted with water to produce ready-to-use sizing compositions for the intended purpose (for application to molds or cores by means of a dipping process, preferably in the form of an immersion bath). The dilution used in each case, as well as other properties of the ready-to-use sizing compositions resulting from the dilution applied, are listed below in Table 1a:

[0091] As can be seen from Table 1a, the sizing compositions for the intended purpose, application to test cores by means of a dip application or a dip bath, were prepared in such a way that a good comparability of (i) their respective properties when applied to the test cores and (ii) the resulting properties of the coated test cores was ensured (densities and flow times were set as similar as possible).

[0092] The densities of the ready-to-use sizing compositions given in Table 1a were measured according to the standard test method DIN EN ISO 2811-2:2011 (Method A).

[0093] The flow times of the ready-to-use sizing compositions given in Table 1a were measured according to the standard test method DIN 53211 (1974) by determination with the DIN cup 4.

[0094] The pH values of the ready-to-use sizing compositions given in Table 1a were measured from the suspension according to the standard test method DIN 19260:2012-10.

[0095] Sizing compositions SZ1, SZ2, and SZ4 each contained attapulgite as a rheological additive. Sizing composition SZ3 is of the type described in document WO00 / 05010. Example 2: Investigation of the softening of foundry cores

[0096] To determine the softening of foundry cores (i.e., the maximum decrease in flexural strength), test cores (test specimens; according to "Core System 1" specified in Table 4) were produced in a conventional manner using a Multiserw core shooter (type LUT, gassing pressure: 2 bar, shot time: 3.0 s; shot pressure: 4.0 bar). One hour after core production, the test cores were coated (coated) with the above-mentioned ready-to-use coating compositions "SZ1", "SZ3", or "SZ4" (see Table 1a) at room temperature (25 °C) by immersion (conditions: 1 s immersion; 3 s holding time in the coating composition, 1 s removal). The wet layer thickness of the coatings was set to approximately 250 µm in each case. The coated test cores were then dried in a circulating air oven under the conditions specified below (1 hour at 120 °C) and the change in their flexural strength under the drying conditions was investigated.

[0097] The coated test cores were each dried for a period of one hour, with their flexural strengths (in N / cm 2< , according to the definition given in leaflet R 202 of the Association of German Foundry Experts, October 1978 edition) being measured at various times during the drying process and then again one hour after the end of the drying process using a standard testing device of the type "Multiserw-Morek LRu-2e", in each case using a standard measuring program "Rg1v_B 870.0 N / cm 2< " (3-point flexural strength).

[0098] Table 2 shows the values for the maximum decrease in flexural strength within the specified period under drying conditions in % for the tested coated test cores, each based on the flexural strength of the respective freshly coated (still wet) test core before the start of drying (initial value). Table 2: Strength loss of coated test cores under drying conditions Size type on test core Maximum decrease in flexural strength during drying, to % of the initial value Observation of core failure during drying SZ 1 72 No SZ 3 25 No SZ 4 0 Yes

[0099] The term "core failure" here and in the following means that a coated core became unusable during the drying process, i.e. the coated core was unusable for the measurement of flexural strength and for a subsequent casting.

[0100] The values given in Table 2 show, among other things, that the maximum decrease in flexural strength of a test core sized with a sizing composition according to the invention (SZ1) is significantly lower than with non-inventive comparative sizing compositions (SZ3 and SZ4). Furthermore, the values in Table 2 show that no usable sized cores could be produced with the non-inventive comparative sizing composition SZ4 under the selected conditions. Example 3: Investigation of the storage stability of coated and uncoated foundry cores

[0101] To determine the storage stability, water glass-bonded test cores (test specimens) were produced in a known manner and their flexural strengths were determined in an unsized state shortly after their production (one hour storage time, relative humidity in the range of 30 to 60%, storage temperature in the range of 20 to 25 °C) as stated above, see Table 3 (entry "Unsized after 1 h").

[0102] In addition, corresponding test cores as specified in Table 3 below were coated one hour after core production (i.e. at the same time interval after their production) at room temperature (25 °C) with the sizing compositions SZ1 and SZ4, respectively, by immersion (conditions: 1 s immersion; 3 s holding time in the sizing composition, 1 s removal from the sizing composition) and then dried for one hour at 120 °C in a circulating air oven. The coated, dried test cores were then subjected to a storage test for a period of seven days (provided that the production of the coated core was possible or unless core failure had been determined beforehand). The temperature during storage was 35 °C in each case, and the relative humidity was 75% in each case. After completion of the storage test, the flexural strengths of the test cores were determined as specified above.The results of this storage test are given below in Table 3. For all tests in Example 3, test cores ("Core System 1") were used, the manufacturing conditions of which are given below in Table 4. Table 3: Determination of the storage stability of coated and uncoated foundry cores Core system Uncoated after 1 h Finished with type SZ1 after storage Finished with type SZ4 after storage Uncoated during storage Flexural strength [N / cm 2 ] 1 300 131 not determinable Core failure after 131 min.

[0103] The values given in Table 3 show, among other things, that a test core sized with a sizing composition according to the invention (SZ1) still had > 40% of its initial strength after seven days of storage, whereas a test core sized with a non-inventive comparison sizing composition (SZ4) was unusable under comparable conditions; its flexural strength could no longer be determined under the conditions defined above because it broke during aging. An unsized comparison core failed under the test conditions after just 131 minutes, i.e. the application of a sizing composition according to the invention to a test core already led to stabilization of the test core under drying conditions. Table 4: Manufacturing conditions for core system 1 parameter Core System 1 Molding material (100 parts by weight) quartz sand Binder (2.2 parts by weight) Alkali water glass solution, 25-35 wt% water glass content in water (w / w) Additive (1.0 part by weight) Particulate, amorphous silicon dioxide Core box temperature 120 °C Fumigation temperature 150 °C Curing time 30 s

[0104] Core system 1 consisted only of the components molding material, binder and additive, as shown in Table 4: The binder shown for core system 1 in Table 4 was a commercially available alkali water glass binder "Cordis ®< 8511" (HA International).

[0105] The additive specified for core system 1 in Table 4 was a commercially available binder additive with the main component (≥ 95 wt%) particulate, amorphous silicon dioxide, "Anorgit ®< 8396" (Hüttenes-Albertus Chemische Werke GmbH). Example 4: Investigation of the flexural strength of coated foundry cores

[0106] Water glass bonded test cores (test specimens) were produced in a known manner (analogous to that described in Example 2, but after interim maintenance of the core shooter used) and their flexural strengths were determined for comparison purposes in an unsized state shortly after their production (one hour storage time at a temperature in the range of 20 to 25 °C, relative humidity 30 to 60%) as stated above (for the production conditions of the test cores see Table 6).

[0107] In addition, test cores were coated at different core temperatures by immersion (conditions: 1 s immersion; 3 s holding time; in the coating composition, 1 s removal from the coating composition) as indicated below in Table 5 (designation of the coating compositions as in Example 1) and dried for one hour at 120 °C in a convection oven. After cooling to room temperature and a storage time of 24 hours (relative humidity in the range of 30 to 60%, temperature in the range of 20 to 25 °C), the flexural strengths of the coated, dried test cores were determined as indicated above.

[0108] The results of the flexural strength determinations are given below in Table 5. Two different test cores ("Core System A" and "Core System B") were used, the manufacturing conditions of which are given below in Table 6. Table 5: Determination of the flexural strengths of coated and uncoated foundry cores Uncoated after 1 h Finished with type SZ1 Finished with type SZ2 Finished with type SZ2 Finished with type SZ4 core temperature . / . 25 °C 50 °C 90 °C 25 °C Core system Flexural strength [N / cm 2 ] A 350 260 320 330 Production of a coated core not possible B 350* 250 not determined not determined Production of a coated core not possible * Deviation of the measured value from the corresponding value in Table 3 for core system 1 is mainly considered as an effect of the maintenance of the core shooter.

[0109] The values given in Table 5 demonstrate that foundry cores coated with coating compositions according to the invention achieve high flexural strengths at different core temperatures. In particular, the values given in Table 5 demonstrate that foundry cores can be successfully coated with coating compositions according to the invention (SZ1, SZ2) even at higher core temperatures, for example, at core temperatures in the range of 50 to 100 °C, with good success (high flexural strengths). In contrast, with non-inventive comparative coating compositions (SZ4), no usable cores could be produced under comparable conditions; instead, they failed during drying. Table 6 : Manufacturing conditions for core systems A and B parameter Core System A Core System B molding material Quartz sand (100.0 parts by weight) Quartz sand (100.0 parts by weight) binder Alkali water glass solution, 25-35 wt% water glass content in water (w / w) (2.2 parts by weight) Alkali water glass solution, 25-35 wt% water glass content in water (w / w) (2.2 parts by weight) Additive Particulate, amorphous silicon dioxide (1.0 part by weight) Particulate, amorphous silicon dioxide (1.0 part by weight) Core box temperature 120 °C 120 °C Fumigation temperature 150 °C 150 °C Curing time 50 s 30 s

[0110] The binders and additives listed for core systems A and B in Table 6 corresponded to the binders ("Cordis ®< 8511") and additives ("Anorgit ®< 8396") listed in Table 4.

[0111] The above-mentioned core systems A, B and C each consisted only of the components molding material, binder and, if applicable, additive, as shown in Table 6.

Claims

1. Use of a refractory coating composition comprising (a) water, (c) particulate, amorphous silicon dioxide, and (d) one or more further refractories, for producing a coating on a mould or a core, wherein the mould is waterglass-bound and / or wherein the core is waterglass-bound, for use in the foundry, characterized in that the refractory coating composition further comprises (b) one or more organic compounds selected from the group consisting of propylene carbonate, γ-butyrolactone, diacetin, triacetin, dibasic ester, acetic anhydride, methyl carbonate and ε-caprolactone, wherein dibasic ester is a mixture of two or more dimethyl esters of glutaric acid, succinic acid and adipic acid.

2. Use according to Claim 1, wherein the primary particles of the particulate, amorphous silicon dioxide (i) are spherical and (ii) possess a D90 < 10 µm, determined by laser diffraction and wherein the primary particles of the particulate, amorphous silicon dioxide of constituent (c) possess a sphericity of 0.9 or more, determined by evaluation of two-dimensional microscope images and / or wherein dibasic ester is a mixture of two or more dimethyl esters of glutaric acid, succinic acid and adipic acid, and wherein the mixture of two or more dimethyl esters comprises a fraction in a range from 55 to 67 wt% of dimethyl glutarate, 15 to 25 wt% of dimethyl succinate and 10 to 25 wt% of dimethyl adipate.

3. Use according to either of the preceding claims, wherein constituent (d) comprises one or more substances selected from the group consisting of quartz, aluminium oxide, zirconium dioxide, aluminium silicates, phyllosilicates, zirconium silicates, olivine, talc, mica, graphite, coke, feldspar, diatomite, kaolins, calcined kaolins, metakaolinite, iron oxide and bauxite, and / or the organic compound in constituent (b) is propylene carbonate, and / or the refractory coating composition comprises in or as constituent (c) a particulate, amorphous silicon dioxide which as a secondary constituent comprises, in an amount of not more than 18 wt%, based on the total mass of said particulate, amorphous silicon dioxide, (i) zirconium dioxide and / or (ii) a Lewis acid, and / or the refractory 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.

4. Use according to any of the preceding claims, wherein in the refractory coating composition the ratio of the total mass of all organic compounds of constituent (b) in relation to the total mass of the refractory 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 wherein an aqueous phase is present for which the ratio of the mass of 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 wherein the refractory coating composition possesses a solids content of less than 80 wt%, preferably less than 45 wt%, based on the total mass of the refractory coating composition and / or wherein the refractory 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 refractory coating composition and / or wherein the refractory 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 refractory coating composition.

5. Use according to any of the preceding claims, wherein the refractory 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 refractory coating composition, and / or the coating is produced on the mould or the core by an application process selected from the group consisting of spraying, dipping, flow coating, and spreading, preferably dipping, and / or the waterglass-bound mould or the waterglass-bound core comprises particulate, amorphous silicon dioxide, and / or the refractory coating composition is applied to a waterglass-bound mould or a waterglass-bound core for use in the casting of iron or steel, and / or the refractory coating composition is applied to a waterglass-bound mould 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 the refractory coating composition is applied to a waterglass-bound mould or a waterglass-bound core at a temperature of the waterglass-bound core or the waterglass-bound mould of > 50°C, preferably > 70°C, more preferably at a temperature of > 50°C and < 100°C.

6. Process for producing a mould 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 refractory coating composition comprising (a) water, (b) one or more organic compounds selected from the group consisting of propylene carbonate, γ-butyrolactone, diacetin, triacetin, dibasic ester, acetic anhydride, methyl carbonate and ε-caprolactone, wherein dibasic ester is a mixture of two or more dimethyl esters of glutaric acid, succinic acid and adipic acid, (c) particulate, amorphous silicon dioxide, and (d) one or more further refractories, (2) providing or producing an uncoated mould or an uncoated core, wherein the provided or produced uncoated mould is waterglass-bound or the provided or produced uncoated core is waterglass-bound, and (3) applying the provided or produced refractory coating composition from step (1) to the provided or produced mould or the provided or produced core.

7. Process according to Claim 6, wherein the provided or produced uncoated mould or the provided or produced uncoated core comprises particulate, amorphous silicon dioxide, and / or wherein the uncoated mould or the uncoated core is produced in step (2) by curing a provided or produced moulding material mixture - by gassing with carbon dioxide, - by admixing esters or phosphates or - by gassing with hot air in a heated tool, and / or wherein the applying to the provided or produced uncoated mould or the provided or produced uncoated core takes place at a temperature of the provided or produced mould or provided or produced core of > 50°C, preferably > 70°C, more preferably at a temperature of > 50°C and < 100°C, and / or wherein the applying to the provided or produced uncoated mould 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.

8. Process according to either of Claims 6 and 7, wherein in the refractory coating composition, the primary particles of the particulate, amorphous silicon dioxide (i) are spherical and (ii) possess a D90 < 10 µm, determined by laser diffraction, and wherein the primary particles of the particulate, amorphous silicon dioxide of constituent (c) (i) possess a sphericity of 0.9 or more, determined by evaluation of two-dimensional microscope images, and / or in the refractory coating composition, constituent (d) comprises one or more substances selected from the group consisting of quartz, aluminium oxide, zirconium dioxide, aluminium silicates, phyllosilicates, zirconium silicates, olivine, talc, mica, graphite, coke, feldspar, diatomite, kaolins, calcined kaolins, metakaolinite, iron oxide and bauxite, and / or in the refractory coating composition, dibasic ester is a mixture of two or more dimethyl esters of glutaric acid, succinic acid and adipic acid and wherein the mixture of two or more dimethyl esters comprises a fraction in a range from 55 to 67 wt% of dimethyl glutarate, 15 to 25 wt% of dimethyl succinate and 10 to 25 wt% of dimethyl adipate; and / or in the refractory coating composition, the organic compound in constituent (b) is propylene carbonate, and / or the refractory coating composition comprises in or as constituent (c) a particulate, amorphous silicon dioxide which as a secondary constituent comprises, in an amount of not more than 18 wt%, based on the total mass of said particulate, amorphous silicon dioxide, (i) zirconium dioxide and / or (ii) a Lewis acid, and / or the refractory 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.

9. Process according to any of Claims 6 to 8, wherein in the refractory coating composition the ratio of the total mass of all organic compounds of constituent (b) in relation to the total mass of the refractory 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 in the refractory coating composition, an aqueous phase is present for which the ratio of the mass of 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 the refractory coating composition possesses a solids content of less than 80 wt%, preferably less than 45 wt%, based on the total mass of the refractory coating composition, and / or the refractory 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 refractory coating composition, and / or the refractory 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 refractory coating composition, and / or the refractory 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 refractory coating composition.

10. Coated mould or coated core for use in the foundry, in each case comprising a refractory coating composition as defined in any of Claims 6 or 8 to 9, preferably producible by a process according to any of Claims 6 to 9, wherein the coated mould is waterglass-bound and / or wherein the coated core is waterglass-bound.

11. Coated mould or coated core according to Claim 10, wherein the waterglass-bound mould and / or the waterglass-bound core comprises particulate, amorphous silicon dioxide, and / or 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.

12. Kit including in separate components (U) a refractory coating composition as defined in any of Claims 6 or 8 to 9 for producing a coating on a waterglass-bound mould or a waterglass-bound core, for use in the foundry, (V) a binder comprising waterglass, and (W) particulate, amorphous silicon dioxide.