EP3565679B1 - Use of a size composition containing an acid in the foundry industry - Google Patents

Description

The present invention relates to the use of a sizing composition, in particular comprising an aqueous phase with a pH of at most 5 and one or more refractory materials, in the foundry, as well as sized, water-glass-bound foundry mold bodies, in particular foundry molds and / or foundry cores, each of which is used according to the invention Include sizing composition. The invention further relates to a method for producing a sized, water-glass-bonded foundry molded body (mold or core). The invention also relates to a kit containing, inter alia, a size composition used according to the invention. The invention is defined in the appended claims.

Casting in a lost mold is a common method for producing near-net-shape components, especially in metal casting. After the casting, the mold is destroyed and the casting is removed. Molds are negatives, they contain the cavity to be poured, which results in the casting to be manufactured. The inner contours of the future casting can be formed by cores. During the production of the mold, the cavity can be formed in the molding material by means of a model of the casting to be produced. Cores are usually formed in a separate core box.

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 basic mold materials used are predominantly refractory granular materials such as washed, classified quartz sand. Further suitable and known basic molding materials are e.g. zircon sands, chromite sands, chamottes, olivine sands, sands containing feldspar and andalusite sands. A basic molding material can also be a mixture of various of the named or other preferred basic molding materials. The refractory basic molding material is preferably in free-flowing form so that it can be filled into a suitable hollow mold and compacted therein. The basic molding material or the corresponding molding material mixture (molding material) is compressed in order to increase the strength of the foundry mold. To produce the foundry molds, the basic mold materials are bound with inorganic or organic molding material binders (binders). The molding material binder creates a firm bond between the particles of the molding material, so that the foundry mold has the required mechanical stability. In industrial practice, molds and cores are regularly and advantageously produced in shooting machines or molding machines in which the particulate constituents are compacted and the binder hardened; this also applies to the molds and cores used in the context of the present invention.

For the production of foundry molds, both organic and inorganic molding material binders can be used, the hardening of which can take place in each case by cold or hot processes. The person skilled in the art describes processes which are carried out essentially at room temperature without heating the foundry mold as cold processes. The hardening usually takes place through a chemical reaction, which is triggered, for example, by the fact that a gas as a catalyst is passed through the molding material mixture to be hardened after molding, which contains the molding base material and the molding material binder. In hot processes, the molding material mixture is heated to a sufficiently high temperature after molding, for example to drive off the solvent contained in the molding material binder and / or to initiate a chemical reaction by which the molding material binder is hardened, for example by crosslinking.

Regardless of the hardening mechanism, all organic molding material binders have in common that they thermally decompose when liquid metal is poured into the foundry mold. B. benzene, toluene, xylenes, phenol, formaldehyde and other, partly unidentified, thermolysis or cracking products can release. Although it has been possible to minimize these emissions through various measures, they cannot currently be completely avoided with organic molding material binders.

In order to minimize or avoid the emission of decomposition products during the casting process, molding material binders can be used which are based on inorganic materials and, if need be, a very small proportion of organic compounds contain. Such molding material binder systems have been known for a long time, for example from the documents GB 782205 A , US 6972059 B1 , US 5582232 A , US 5474606 A and US 7022178 .

In the following, the term “inorganic molding material binder” denotes a molding material binder which consists predominantly, preferably more than 95% by weight, preferably more than 99% by weight, very particularly preferably completely, of water and inorganic materials, so that the proportion of organic compounds in such an inorganic molding material binder is preferably less than 5% by weight, preferably less than 1% by weight and very particularly preferably 0% by weight.

In the context of the present text, the expression “inorganically bound” means that a mold or a core has been bound with an inorganic molding material binder (as defined above).

Alkali waterglass is of particular importance as a component of inorganic molding material binders. Alkali waterglass is the term used to denote solidified, vitreous, i.e. amorphous, water-soluble sodium, potassium and lithium silicates, their mixtures and the corresponding aqueous solutions. In the following, the term "water glass" denotes 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 having a molar module (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 expression “water glass-bound” means that a foundry molded body, in particular a mold or a core, was produced or can be produced using a molding material binder which comprises water glass or consists of water glass. For example, in Scripture US 7770629 B2 proposed a molding material mixture which, in addition to a refractory molding base material, comprises a waterglass-based molding material binder and a particulate metal oxide, the particulate metal oxide preferably being precipitated silica or fumed silica.

Inorganic molding binders, however, also have disadvantages compared to organic molding binders. For example, foundry molds or cores produced with known inorganic molding material binders have a comparatively low or low stability towards atmospheric humidity or towards water or aqueous moisture. This means, for example, that such foundry molds or cores cannot be reliably stored for a longer period of time, as is customary with organic molding material binders.

• Verbesserung der Glätte der Gussstückoberfläche;
• Möglichst vollständige Trennung von flüssigem Metall und Form bzw. Kern;
• Vermeidung von chemischen Reaktionen zwischen Bestandteilen von Form/Kern und Schmelze, dadurch Erleichterung der Trennung zwischen Form/Kern und Gussstück und/oder
• Vermeidung von Oberflächenfehlern am Gussstück wie z.B. Gasblasen, Penetrationen, Blattrippen und/oder Schülpen.

Usually, especially in steel and iron casting, the surfaces of foundry moldings, in particular of molds and cores, are coated with a coating called a "coating", in particular those surfaces which come into contact with cast metal. Finishes form a boundary or barrier layer between the form / core and metal, among other things for the targeted suppression of error mechanisms at these points or for the use of metallurgical effects. In general, coatings in foundry technology should primarily fulfill the following functions:

• Improving the smoothness of the casting surface;
• As complete a separation as possible of liquid metal and form or core;
• Avoidance of chemical reactions between components of the mold / core and melt, thereby facilitating the separation between mold / core and casting and / or
• Avoidance of surface defects on the casting such as gas bubbles, penetrations, veins and / or scabs.

The functions mentioned above and possibly other functions are generally adjusted and optimized or adapted to the intended purpose in each case by the precise composition of the size or the composition of the size to be applied to the mold or the core.

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

The size or the size composition is applied to the inner contour of the casting mold or on the core by a suitable application process, for example spraying, dipping, flooding or brushing, and is dried there, so that a size coating or size film is produced. The size coating can be dried by adding Heat or radiant energy, for example by microwave radiation, or by drying in the room air. In the case of sizing compositions which contain combustible compounds in the carrier liquid, drying can also take place by burning off these compounds.

In the present text, "refractory" refers to masses, materials and minerals that can withstand the temperature load during casting or solidification of molten iron, usually cast iron, at least for a short time. "Highly refractory" refers to masses, materials and minerals that can withstand the casting heat of a steel melt for a short time. The temperatures that can occur when casting steel melts are usually higher than the temperatures that can occur when casting iron or cast iron melts. Refractory masses, materials and minerals (refractory materials) and highly refractory masses, materials and minerals are known to the person skilled in the art, for example from DIN 51060: 2000-06.

Mineral oxides, silicates or clay minerals are usually used as refractory materials in sizing compositions. Examples of refractory materials that are also suitable in the context of the present invention are quartz, aluminum oxide, zirconium dioxide, aluminum silicates, sheet silicates, 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 with one another. The refractory material serves, among other things, to close the pores in a foundry mold or a core against the penetration of the liquid metal. The refractory material also provides thermal insulation between the foundry mold or core and the liquid metal. The refractory material is usually provided in powder form. Unless otherwise stated, pulverulent refractory materials then have an average grain size (preferably measured by means of light scattering according to ISO 13320: 2009-10) in the range from 0.1 to 500 μm, preferably in the range from 1 to 200 μm. Particularly suitable refractory materials are those materials which have melting points which are at least 200 ° C. above the temperature of the molten metal used in each case and / or which do not react with the molten metal.

The refractories are mostly dispersed in a carrier liquid. The carrier liquid is one or the component of a sizing composition which is preferably liquid under normal conditions (20 ° C. and 1013.25 hPa) and / or can be vaporized at 160 ° C. and normal pressure (1013.25 hPa). Preferred carrier liquids, which are also suitable in the context of the present invention, are selected from the group consisting of water and organic carrier liquids and mixtures thereof with one another and / or with further constituents. 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 the carrier liquid.

Size binders (binders) are used primarily to fix the refractory materials contained in a size composition on the molding material. Examples of binders which are also suitable in the context 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.

Biocides prevent bacterial infestation. Examples of biocides which are also suitable in the context of the present invention are formaldehyde, 2-methyl-4-isothiazolin-3-one (MIT), 5-chloro-2-methyl-4-iosthiazolin-3-one (CIT) and 1,2 -Benzisothiazolin-3-one (BIT). The biocides, preferably the individual biocides mentioned, are usually 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 . a core to be applied).

Rheological additives (thickening agents) are used to adjust the flowability of the size required for processing. Inorganic thickening agents suitable for the purposes of the present invention are, for example, swellable clays such as sodium bentonite or attapulgite (palygorskite). Organic adjusting agents which are also suitable in the context of the present invention include, for example, swellable polymers such as cellulose derivatives, in particular carboxymethyl, methyl, ethyl, hydroxyethyl and hydroxypropyl cellulose; Plant mucilage, polyvinylpyrrolidone, pectin, gelatin, agar agar, polypeptides and / or alginates. The aforementioned rheological additives or adjusting agents are preferred ingredients of the size composition used according to the invention.

In the case of aqueous sizing compositions (i.e. containing water as the carrier liquid or part of the carrier liquid), wetting agents can also be used in order to achieve better wetting of the molding material. Ionic and nonionic wetting agents are known to the person skilled in the art. For example, dioctyl sulfosuccinates are used as ionic wetting agents and alkynediols or ethoxylated alkynediols are used as nonionic wetting agents. The aforementioned wetting agents are also preferred ingredients of the aqueous size composition used according to the invention.

A size composition can also 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 the person skilled in the art. The The aforementioned defoamers, pigments and / or dyes are also preferred ingredients of the size composition used according to the invention

In order to be able to meet the increasing requirements in the area of environmental and emission protection, inorganic molding material binders, in particular water glass-containing molding material binders, should also gain in importance in the production of molds and cores in the future in the field of steel and iron casting. In order to achieve the desired or necessary casting quality, as stated above, it is usually necessary or advantageous to coat inorganically bound molds and cores with a coating. In terms of environmental and emission protection, it is consequently worthwhile when selecting the size to avoid the use of organic carrier liquids as far as possible and preferably water-based sizes, i.e. sizes with water as the sole carrier liquid or at least as a predominant part of the Use carrier liquid.

As stated above, however, foundry moldings, in particular molds and cores which were produced with inorganic molding material binders, in particular with water glass-containing molding material binders, have a low stability to the action of water or aqueous moisture. The water contained in water-based sizing compositions can consequently damage the inorganically bound molds and cores treated (sized) with it. In particular, this can disadvantageously reduce the strength of the shapes and cores that are finished in this way. This particular problem known in foundry technology (cf. WO 00 / 05010A1 ) has hitherto only been inadequately countered with the means previously used, including, for example, particularly intensive hardening of the molds and cores, complex processes for drying the applied size or the adaptation of the molding material mixture.

In document WO 00/05010 It is stated that a coating based on water can in particular be applied to cores and molds gassed with carbon dioxide and bound with sodium silicate, if the composition of the coating used has a specific additive that is soluble in water or a water-miscible one such as esters of polyvalent Contains alcohols, carbonates, esters or lactones. The individual components of the coating system are preferably not mixed with one another until immediately before the coating process.

In document WO 2013/044904 A1 It is stated that by combining certain clays as ingredients of a water-containing size, sizes with an unusually high solids content can be produced, the viscosity of which is nevertheless comparable to commercially available, ready-to-use sizes, whereby the quality of the cores coated with these sizes and bound with inorganic molding material binders and shapes could be improved.

In the documents DE 10 2011 115 025 A1 and WO 2013/050022 A2 it is stated that when certain salts are added in a certain concentration range to an aqueous sizing composition, the quality of the sized inorganic cores and shapes can be improved, in particular their storage stability can be increased. The salts are salts of magnesium and / or manganese, in particular their sulfates and chlorides.

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

The document DE 27 30 753A1 describes a composition for coating molds which are used in the machining of molten metals, and molds which are coated with this composition. The aforementioned composition can contain, for example, formic acid or its salts.

The document DE 10 2006 040 385 A1 discloses temperature-stable BN mold release liners based on ceramic and vitreous binders; However, the document does not disclose the use for inorganically bound molds or cores (based on corresponding mold raw materials) for use in foundries.

JP S55 19415 discloses a size with a pH of 4.0-5.0 for resin-bonded molded bodies.

The German Patent and Trademark Office has researched the following prior art for the priority application for the present application: DE 10 2006 040 385 A1 , DE 10 2006 002 246 A1 and DE 10 2005 041 863 A1 .

However, as our own investigations have shown, the above-mentioned problems still exist to a relevant extent even with a procedure according to the stated prior art.

• die Festigkeit der damit herstellbaren geschlichteten Formen und/oder Kerne soll gegenüber mit bekannten wasserhaltigen Schlichten bzw. Schlichtezusammensetzungen geschlichteten Formen und Kernen erhöht werden, insbesondere soweit die Formen und Kerne mit anorganischen Formstoffbindemitteln, insbesondere mit wasserglashaltigen Formstoffbindemitteln, hergestellt wurden;

• die Lagerstabilität sowie die Beständigkeit gegenüber Luftfeuchtigkeit der damit herstellbaren geschlichteten Formen und/oder Kerne soll gegenüber mit bekannten wasserhaltigen Schlichten bzw. Schlichtezusammensetzungen geschlichteten Formen und/oder Kernen erhöht werden;
• die Lagerstabilität der Schlichtezusammensetzung selbst soll gegenüber bekannten wasserhaltigen Schlichtezusammensetzungen nicht signifikant verschlechtert sein oder sogar gesteigert werden;
• die Applikation der Schlichtezusammensetzung auf heiße Formen und/oder Kerne (d.h. insbesondere auf solche Formen und/oder Kerne, welche Temperaturen von mehr als 50 °C, vorzugsweise Temperaturen im Bereich von 50 bis 100 °C, aufweisen) soll ermöglicht oder zumindest verbessert werden;
• die damit herstellbaren geschlichteten Formen und Kerne sollen eine hohe Abgussgüte und Glätte der Gussstückoberfläche, vorzugsweise eine fehlerarme Abgussgüte, besonders bevorzugt eine fehlerfreie Abgussgüte, ermöglichen;
• der Einsatz von anorganisch gebundenen, insbesondere wasserglasgebundenen Gießereiformkörpern, insbesondere Formen und/oder Kernen, soll auch für den Eisen- und/oder Stahlguss ermöglicht bzw. die Möglichkeit des Einsatzes für diese Zwecke soll erweitert werden.

Based on the prior art, there is therefore a need for further improved sizing compositions for use in foundries which have or are intended to have one or more, preferably all, of the following advantageous properties:

• the strength of the sized shapes and / or cores that can be produced therewith is intended to be increased, in particular, compared with shapes and cores sized with known water-containing sizes or size compositions insofar as the molds and cores were produced with inorganic molding material binders, in particular with molding material binders containing water glass;

• the storage stability and the resistance to atmospheric humidity of the sized shapes and / or cores that can be produced therewith should be increased compared to shapes and / or cores sized with known water-containing sizes or size compositions;
• the storage stability of the size composition itself should not be significantly impaired or even increased compared to known water-containing size compositions;
• the application of the sizing composition to hot molds and / or cores (ie in 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 finished shapes and cores that can be produced therewith should enable a high casting quality and smoothness of the casting surface, preferably a low-defect casting quality, particularly preferably a fault-free casting quality;
• the use of inorganically bound, in particular water glass bound, foundry moldings, in particular molds and / or cores, should also be made possible for iron and / or steel casting or the possibility of use for these purposes should be expanded.

It was generally an object of the present invention to provide a sizing composition for use in foundries which possesses or enables one or more or all of the properties mentioned above.

It was a primary object of the present invention to enable the use of a sizing composition in the foundry, which can be used on inorganically bound, in particular water-glass-bound, foundry molded bodies, preferably molds and / or cores, without adversely affecting their properties, in particular their strengths influence.

A further object of the present problem was to provide sized, inorganically bound foundry moldings, in particular foundry molds and / or foundry cores, each of which comprises a size composition to be specified according to the invention.

Another object of the present invention was to provide a corresponding method for producing an inorganically bound foundry molded body sized with a water-containing size.

In addition, an object of the present invention was to provide a kit containing, inter alia, a size composition to be specified according to the invention.

The invention is defined or described in more detail in the appended claims. Specific and / or preferred embodiments of the invention are described in more detail below. Within the scope of the subject matter defined by the claims, 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 results in each case again in preferred aspects or embodiments of the invention. Embodiments, aspects or properties which are described or described as preferred in connection with the present invention for the sizing composition used according to the invention apply correspondingly or analogously also to methods according to the invention, for sized shapes or cores according to the invention and for kits according to the invention within the framework of the subject matter defined by the claims.

Insofar as size compositions used according to the invention, methods according to the invention, sized shapes or cores according to the invention and kits according to the invention are described below which "comprise" or "contain" certain embodiments, components or features, should, within the scope of the subject matter defined by the claims, in each case the corresponding variant, to be understood in a narrower scope, of the said uses, processes, structured forms or cores or kits, which "consists" of these specific embodiments, components or features.

1. (a) einen oder mehrere Feuerfeststoffe, und
2. (b) eine wässrige Phase mit einem pH-Wert von höchstens 5, vorzugsweise höchstens 4,

zur Herstellung eines Überzugs auf einer wasserglasgebundenen Form bzw. einem wasserglasgebundenen Kern, zur Verwendung in der Gießerei, wobei die wasserglasgebundene Form bzw. der wasserglasgebundene Kern partikuläres, amorphes Siliziumdioxid enthält.According to the invention, the primary object and further aspects of the general object specified above are achieved through the use of a sizing composition

1. (a) one or more refractories, and
2. (b) an aqueous phase with a pH of at most 5, preferably at most 4,

for the production of a coating on a water-glass-bound mold or a water-glass-bound core, for use in foundries, the water-glass-bound form or the water-glass-bound core containing particulate, amorphous silicon dioxide.

In addition to the particulate, amorphous silicon dioxide, larger amounts of conventional mold raw materials are usually present in the water-glass-bound mold or the water-glass-bound core. For the selection of preferred molding raw materials, see above.

The refractory materials in the sizing composition (cf. component (a)) are preferably one or more substances selected from the group consisting of quartz, aluminum oxide, zirconium dioxide, aluminum silicates, sheet silicates, zirconium silicates, olivine, talc, mica, graphite, coke, feldspar, diatomite , Kaolins, calcined kaolins, metakaolinite, iron oxide and bauxite.

For the purposes of the present invention, the pH value in a size composition is determined in each case from the or a suspension, preferably in accordance with the standard method DIN 19260: 2012-10.

The foundry mold bodies which can be coated (coated) with the sizing composition according to the invention can be produced in any manner known per se, for example by shooting, pouring or by 3D printing techniques.

Without guarantee of correctness, it is assumed that when the aqueous sizing composition according to the invention is used accordingly, bond structures in the alkali silicate framework of the waterglass-bound, sized foundry body (mold or core) are attacked due to the water content of the sizing composition, but temporarily possibly resulting weakening of the bond structure by a further chemical reaction , for example an acid-base reaction, can be eliminated again, as a result of which an increased strength of such sized, water-glass-bonded foundry moldings is achieved in comparison with the prior art.

A use according to the invention is preferred, the coated waterglass-bonded mold or the coated waterglass-bonded core, in comparison with a coated waterglass-bonded comparison mold or a coated waterglass-bonded comparison core, a comparison sizing composition for its or its production under otherwise identical conditions was used, which was obtained from the sizing composition by adding sodium hydroxide until a pH value of 7 was reached, has a less decreasing flexural strength on drying. Technically particularly relevant in industrial practice are those "acidic" sizing compositions (ie those comprising an aqueous phase with a pH of at most 5, preferably at most 4), their "alkaline" equivalents (pH 7 or higher) to coated water-glass-bound forms or lead cores that show a greater decrease in flexural strength on drying.

In addition, a use according to the invention is preferred, the coated water-glass-bound mold or the coated water-glass-bound core, in comparison with a coated water-glass-bound comparative form or a coated water-glass-bound comparative core, for its or its production under otherwise identical conditions a comparative Sizing composition was used, which was obtained from the sizing composition by adding sodium hydroxide until a pH of 7 was reached, have an increased storage stability.

In the context of the use according to the invention of a size composition, the water-glass-bound form or the water-glass-bound core contains particulate, amorphous silicon dioxide.

In the context of the present invention, the term “particulate, amorphous silicon dioxide” is understood to mean particulate synthetic silicon dioxide, preferably precipitated silica and / or pyrogenic silicas. Fumed silicas are preferred.

Precipitated silica is known per se and can, for example, be obtained in a manner known per se by reacting an aqueous alkali metal silicate solution with mineral acids: the resulting precipitate is then separated off, dried and, if necessary, ground. Pyrogenic silicas are also known per se and can preferably be obtained in a manner known per se at high temperatures by coagulation from the gas phase. Fumed silica can be produced, for example, by flame hydrolysis of silicon tetrachloride or, for the purposes of the present invention, preferably in an electric 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 in the production of zirconium dioxide. Another possibility, known per se, for the production of particulate amorphous silicon dioxide is the spraying of a silicon dioxide melt: the primary, amorphous silicon dioxide particles are not created here (as in other preferred manufacturing processes) by a grinding process.

The primary amorphous silicon dioxide particles (“primary particles”) are often agglomerated, ie as agglomerates of primary particles, according to the manufacturing processes mentioned above. 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 means of scanning electron microscopy. The primary particles of the particulate, amorphous silicon dioxide are preferably spherical and have a sphericity of 0.9 or more, determined by evaluating two-dimensional microscopic (preferably scanning electron microscopic) images.

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

• (b1) Wasser, und
• (b2) eine oder mehrere Säuren, vorzugsweise mit einem pKa < 5, bevorzugt mit einem pKa < 4,

umfasst,
wobei vorzugsweise das Verhältnis der Masse des Bestandteils (b1) zur Masse des Bestandteils (b2) im Bereich von 10:1 bis 200: 1, besonders bevorzugt im Bereich von 10:1 bis 100:1 liegt.According to one embodiment, a use according to the invention or preferred according to the invention of a size composition is likewise preferred, the aqueous phase (b)

• (b1) water, and
• (b2) one or more acids, preferably with a pKa <5, preferably with a pKa <4,

includes,
wherein the ratio of the mass of component (b1) to the mass of component (b2) is preferably in the range from 10: 1 to 200: 1, particularly preferably in the range from 10: 1 to 100: 1.

The one or more acids can be mixed in the usual form, ie solid or liquid and optionally diluted, preferably diluted with water, with further constituents of the sizing composition (i.e. in particular with refractory materials according to constituent (a) and water) when preparing the sizing composition to be used according to the invention according to component (b1)) so that the desired pH value is set or achieved.

The specified preferred ratio of the masses (b1) to (2) preferably applies, provided that the one or more acids of component (b2) are selected from the group of organic acids, as described in more detail below; the mass of the component (b2) relates to the total mass of the pure (i.e. without adhesions or water of crystallization, etc.) organic acid or organic acids. If an acid has several pKa values (e.g. citric acid), the lowest (first) pKa value is meant for the purposes of the present invention.

In a further embodiment of the inventive or preferred inventive use of a size composition, the ratio of the mass of component (b1) to the total mass of the aqueous phase (b) is preferably greater than 50%, preferably greater than 70%, particularly preferably greater than 90%.

In a further preferred embodiment of the inventive or preferred inventive use of a size composition, the aqueous phase preferably has a pH of at most 4.

A use according to the invention in which two or more of the preferred embodiments are implemented at the same time is generally preferred.

Particularly preferred combinations of preferred parameters, properties and components of the invention emerge in general from the appended claims.

A particularly preferred variant is a use according to the invention or a preferred use according to the invention of a size composition, component (b2) comprising one or more acids selected from the group consisting of inorganic and organic acids. The aforementioned organic acids are preferably selected from the group consisting of mono-, di- and tricarboxylic acids, preferably mono-, di- and tricarboxylic acids solid at 25 ° C. and 1013 mbar (or 1013 hPa). The organic acids selected from the group consisting of citric acid and oxalic acid are particularly preferred. The aforementioned inorganic acids are preferably selected from the group consisting of hydrochloric acid, nitric acid, phosphoric acid and acidic phosphates, e.g. aluminum phosphate, particularly preferably from the group consisting of hydrochloric acid, nitric acid and phosphoric acid.

The use of organic acids in combination with one or more inorganic acids in or as constituent (b2) is preferred. The use of organic acids in or as constituent (b2) is particularly preferred.

In the aforementioned preferred variant of the inventive use of a size composition, the ratio of the total mass of inorganic and organic acids of component (b2) to the total mass of the size composition is preferably in the range from 0.1 to 10% (i.e. in the range from 0.1 to 10% by weight) %), more preferably in the range from 0.5 to 5% (ie in the range from 0.5 to 5% by weight), even more preferably in the range from 1 to 5% (ie in the range from 1 to 5) % By weight), particularly preferably in the range from 1 to 3.5% (ie in the range from 1 to 3.5% by weight) and very particularly preferably in the range from 2.5 to 3.5% (ie im Range from 2.5 to 3.5% by weight).

Furthermore, a use according to the invention of a size composition is particularly preferred, preferably a use according to the invention designated as preferred, where component (a) comprises particulate, amorphous silicon dioxide, preferably particulate, amorphous silicon dioxide, the primary particles (i) of which are spherical and / or a D90 value <10 μm, preferably a D90 value of <1 μm, determined by means of laser diffraction, particularly preferably particulate, amorphous silicon dioxide, which as a secondary component (i) zirconium dioxide and / or (ii) a Lewis acid, very particularly preferably zirconium dioxide. The use according to the invention of a size composition is preferred, the primary particles of the particulate, amorphous silicon dioxide of component (a) (i) being spherical and / or (ii) having a D90 value <10 μm, preferably <1 μm, determined by means of laser diffraction . The primary particles of the particulate, amorphous silicon dioxide of the component (a) (i) are preferably spherical and have a sphericity of 0.9 or more as determined by evaluating two-dimensional microscopic images. Modern commercially available electron microscopic or light microscopic systems enable digital image analysis and thus a convenient determination of the particle shape. Digital image analysis is preferred for studies of sphericity.

In addition, a use according to the invention of a sizing composition is particularly preferred, preferably a use according to the invention designated as preferred, component (a) comprising one or more substances selected from the group consisting of quartz, aluminum oxide, zirconium dioxide, aluminum silicates, sheet silicates, zirconium silicates , Olivine, talc, mica, graphite, coke, feldspar, diatomite, kaolins, calcined kaolins, metakaolinite, iron oxide and bauxite.

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

If the primary particles of the particulate, amorphous silicon dioxide are present as agglomerates and / or aggregates and / or in some other way as combinations of several primary particles, they are preferably gently separated mechanically or in a similar manner in a manner known per se, before the determination of the particle size distribution of the primary particles is carried out, in order to rule out a falsification of the result as far as possible.

In the context of the present invention, the term "secondary constituent" means that the particulate, amorphous silicon dioxide of component (a) only contains such secondary constituents as impurities or adhesions from previous manufacturing and / or processing methods of the particulate, amorphous Can come from silicon dioxide. The mentioned secondary constituents are in an amount of not more than 18% by weight (or mass fraction), particularly preferably in an amount of not more than 12% by weight, most preferably in an amount of not more than 8% by weight % present, in each case based on the total mass of the particulate amorphous silicon dioxide of the component (a).

One of the aforementioned minor components in component (a) can be a Lewis acid. However, several Lewis acids and / or mixtures thereof can also be included. In the context 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. an electron pair acceptor. H. is 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 while a Lewis base is nucleophilic. Molecules and ions can therefore also be understood as acids that are not acids according to classical ideas.

In addition to the above-mentioned ingredients, the size compositions used according to the invention can also contain further ingredients, for example esters, lactones and / or acid anhydrides, for example methyl formate, ethyl formate, propylene carbonate, γ-butyrolactone, diacetin, triacetin, known "dibasic esters" (a mixture of several dimethyl esters of dicarboxylic acids, especially of glutaric acid, succinic acid and adipic acid), acetic anhydride, methyl carbonate and ε-caprolactone.

• ein oder mehrere Biozide,
• ein oder mehrere Netzmittel,
• ein oder mehrere rheologische Additive, und
• ein oder mehrere Bindemittel, vorzugsweise Polyvinylalkohol.

In one embodiment, a use of a size composition according to the invention or preferred according to the invention is preferred, the size composition 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.

Customary biocides such as microbicides, in particular bactericides, algicides and / or fungicides, are suitable as biocides. The biocides given above can preferably be used become. 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.

In a further embodiment, the use according to the invention of a size composition is preferred, the size composition having a solids content of less than 80% by weight, preferably less than 45% by weight, based in each case on the total mass of the size composition.

The size composition to be used according to the invention is preferably ready-to-use, that is to say it is intended to be applied directly to a casting mold or a core. The size composition to be used according to the invention can, however, also be in the form of a concentrate, which is then intended to be diluted before application to a casting mold or a core, in particular by adding water or an aqueous mixture. This applies to all configurations of the present invention, unless otherwise indicated or specified. The expert decides in each individual case whether a size composition is ready for use or should be diluted.

According to a further embodiment, a use according to the invention or according to the invention is particularly preferred, the size composition having one or more binders, preferably comprising polyvinyl alcohol, in a total amount of not more than 2% by weight, preferably in an amount in the range from 0.05 to 0.80% by weight, based in each case on the total mass of the size composition.

The determination of the solids content of a size composition to be used according to the invention takes place within the scope of the present invention in accordance with leaflet P79 of the Association of German Foundry Experts in the version of 1976, point 6.

According to another embodiment, the use of a sizing composition according to the invention or preferred according to the invention is particularly preferred, the application of the sizing composition to a water-glass-bound mold or a water-glass-bound core for use when pouring a metal melt at a temperature> 900 ° C, preferably> 1250 ° C, takes place, preferably for use when casting a molten metal comprising iron and / or steel.

In addition, the use of a size composition according to the invention or preferred according to the invention is particularly preferred, the size composition being applied to a water-glass-bound mold or a water-glass-bound core for use in iron or steel casting.

According to a further embodiment, the use of a sizing composition according to the invention or preferred according to the invention is particularly preferred, the application of the sizing composition to a water-glass-bound mold or a water-glass-bound core at a temperature of the water-glass-bound core or the water-glass-bound form of> 50 ° C, preferably> 70 ° C takes place, particularly preferably at a temperature of> 50 ° and <100 ° C. Surprisingly, under these conditions, a form or core that can be used for subsequent treatment or processing steps is obtained or retained under these conditions.

The invention also relates to the use of acid to set a pH value of at most 5, preferably a pH value of at most 4, in the aqueous phase of a size composition for application to a water-glass-bound mold or a water-glass-bound core. The aforementioned acid is preferably selected from the group consisting of inorganic and organic acids. The organic acids are preferably selected from the group consisting of mono-, di- and tricarboxylic acids, preferably mono-, di- and tricarboxylic acids solid at 25 ° C. and 1013 mbar, particularly preferably citric acid and oxalic acid. The inorganic acids are preferably selected from the group consisting of hydrochloric acid, nitric acid, phosphoric acid and acidic phosphates, e.g. aluminum phosphate, particularly preferably from the group consisting of hydrochloric acid, nitric acid and phosphoric acid. The water-glass-bound form or the water-glass-bound core comprises particulate, amorphous silicon dioxide, the acid preferably being used to adjust a pH value of at most 4.

1. (1) Bereitstellen oder Herstellen einer Schlichtezusammensetzung wie vorstehend im Rahmen der erfindungsgemäßen Verwendung einer Schlichtezusammensetzung definiert,
2. (2) Bereitstellen oder Herstellen einer ungeschlichteten, wasserglasgebundenen Form oder eines ungeschlichteten, wasserglasgebundenen Kerns, und
3. (3) Auftragen der bereitgestellten oder hergestellten Schlichtezusammensetzung aus Schritt (1) auf die in Schritt (2) bereitgestellte oder hergestellte Form bzw. den bereitgestellten oder hergestellten Kern.

The invention also relates to a method for producing a sized, water-glass-bound mold, preferably with high storage stability, or a sized, water-glass-bound core, preferably with high storage stability, for use in foundries, with the following steps:

1. (1) Providing or producing a size composition as defined above within the scope of the use according to the invention of a size composition,
2. (2) Providing or producing an unsized, water-glass-bonded mold or an unsized, water-glass-bonded core, and
3. (3) Applying the provided or manufactured size composition from step (1) to the mold provided or manufactured in step (2) or the provided or manufactured core.

The size composition provided or produced in step (1) of the process according to the invention can be produced by processes known per se. For example, water can be provided in a suitable amount and the other ingredients for the production of the size composition can then be added in the desired amount to this template while stirring with a suitable stirrer such as a high-shear stirrer, e.g. a gear stirrer or a dissolver stirrer. If necessary, constituents can be digested before or during the addition in a manner known per se. For example, if necessary, one or more rheological additives can be digested using a high-shear stirrer, before or after addition to the water receiver and individually or together with one or more refractory materials. If the one or more refractory materials are not digested together with the optionally added rheological additives, they can also be digested individually and added to the water receiver. Then, for example, the other constituents of the sizing composition can then be added to the water initial charge, which may contain rheological additives and / or refractory materials, in any order and preferably with stirring, preferably with a high-shear stirrer, such as one or more acids, optionally one or several size 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.

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

The unsized, water-glass-bonded form provided or produced in step (2) of the method according to the invention or the unsized, water-glass-bonded core provided or produced can be produced in a manner known per se, for example as in the documents WO 2006/024540 or WO 2009/056320 described.

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

The provided or manufactured mold or the provided or manufactured core contains particulate amorphous silicon dioxide. In a further preferred embodiment of the aforementioned method according to the invention or preferred according to the invention, the application to the mold takes place at a temperature of the core or the mold of> 50 ° C, preferably> 70 ° C, particularly preferably at a temperature of> 50 ° C and <100 ° C.

• (X) eine wasserglasgebundene Form bzw. einen wasserglasgebundenen Kern, und
• (Y) einen Überzug umfassend eine Schlichtezusammensetzung wie vorstehend im Rahmen der erfindungsgemäßen Verwendung einer Schlichtezusammensetzung definiert.

Another object of the present invention is also a sized mold or a sized core for use in foundries, each comprising

• (X) a water-glass-bonded form or a water-glass-bonded core, and
• (Y) a coating comprising a size composition as defined above in the context of the use according to the invention of a size composition.

In a preferred embodiment of this last-mentioned article according to the invention, the sized shape or the sized core can be produced according to an aforementioned method according to the invention or according to the preferred method.

The water-glass-bound form and / or the water-glass-bound core each contain particulate, amorphous silicon dioxide.

The above-disclosed form according to the invention and / or the above-disclosed core according to the invention is preferably used when casting a metal melt at a temperature> 900 ° C, preferably when casting a metal melt comprising iron and / or steel, particularly preferably when casting a metal melt comprising iron and / or or steel with a temperature> 1250 ° C.

• (U) eine Schlichtezusammensetzung umfassend
  1. (a) einen oder mehrere Feuerfeststoffe, und
  2. (b) eine wässrige Phase mit einem pH-Wert von höchstens 5
     zur Herstellung eines Überzugs auf einer wasserglasgebundenen Form bzw. einem wasserglasgebundenen Kern, zur Verwendung in der Gießerei,
• (V) ein Bindemittel umfassend Wasserglas, und
• (W) partikuläres, amorphes Siliziumdioxid.

The invention also relates to a kit comprising separate components

• (U) comprising a sizing composition
  1. (a) one or more refractories, and
  2. (b) an aqueous phase with a pH of 5 or less
     for the production of a coating on a water-glass-bound mold or a water-glass-bound core, for use in foundries,
• (V) a binder comprising water glass, and
• (W) Particulate, amorphous silicon dioxide.

In a preferred alternative, the kit according to the invention comprises a size composition as component (U), the size composition being defined as above in the context of the use according to the invention of a size composition.

• eine verbesserte Festigkeit der damit herstellbaren geschlichteten wasserglasgebundenen Formen und/oder Kerne, vorzugsweise wasserglasgebundener Formen und/oder Kerne, welche partikuläres, amorphes Siliziumdioxid enthalten;
• eine verbesserte Lagerstabilität der damit herstellbaren geschlichteten wasserglasgebundenen Formen und/oder Kerne, vorzugsweise wasserglasgebundener Formen und/oder Kerne, welche partikuläres, amorphes Siliziumdioxid enthalten;
• eine verbesserte Beständigkeit gegenüber Luftfeuchtigkeit der damit herstellbaren geschlichteten wasserglasgebundenen Formen und/oder Kerne, vorzugsweise wasserglasgebundener Formen und/oder Kerne, welche partikuläres, amorphes Siliziumdioxid enthalten;

• eine verbesserte Möglichkeit der Applikation auf heiße Formen und/oder Kerne (d.h. vorzugsweise auf solche Formen und/oder Kerne, welche Temperaturen von mehr als 50 °C, vorzugsweise Temperaturen im Bereich von 50 bis 100 °C, aufweisen), vorzugsweise auf wasserglasgebundene Formen und/oder Kerne, insbesondere auf wasserglasgebundene Formen und/oder Kerne, welche partikuläres, amorphes Siliziumdioxid enthalten; und/oder
• eine verbesserte Einsatzmöglichkeit von wasserglasgebundenen Gießereiformkörpern, insbesondere von Formen und/oder Kernen, vorzugsweise von wasserglasgebundenen Formen und/oder Kernen, welche partikuläres, amorphes Siliziumdioxid enthalten, für den Eisen- und/oder Stahlguss, durch erfindungsgemäße Verwendung der beschriebenen Schlichtenzusammensetzung.

It has been found that the use according to the invention of the size composition described above in particular has the following advantages over comparable or comparable size compositions known from the prior art and / or - depending on the aspect under consideration - justifies:

• an improved strength of the sized water-glass-bonded shapes and / or cores, preferably water-glass-bonded shapes and / or cores which contain particulate, amorphous silicon dioxide, which can be produced therewith;
• improved storage stability of the sized, water-glass-bound molds and / or cores, preferably water-glass-bound molds and / or cores which contain particulate, amorphous silicon dioxide, which can be produced therewith;
• an improved resistance to air humidity of the sized, water-glass-bound forms and / or cores, preferably water-glass-bound, which can be produced therewith Molds and / or cores which contain particulate, amorphous silicon dioxide;

• an improved possibility of application to hot molds and / or cores (ie preferably to those molds and / or cores which have temperatures of more than 50 ° C., preferably temperatures in the range from 50 to 100 ° C.), preferably to waterglass-bound molds and / or cores, in particular on waterglass-bound forms and / or cores which contain particulate, amorphous silicon dioxide; and or
• an improved possibility of using water-glass-bound foundry moldings, in particular molds and / or cores, preferably water-glass-bound molds and / or cores, which contain particulate, amorphous silicon dioxide, for iron and / or steel casting, through the use according to the invention of the coating composition described.

These advantages apply mutatis mutandis to the other aspects of the present invention.

Examples:

• The examples given below are intended to describe the invention in more detail and
• explain without limiting their scope.

Example 1: Preparation of Sizing Compositions.

The size composition according to the invention ("SZ1") specified in Table 1 and the comparison size compositions not according to the invention ("SZ2" or "SZ3") were produced in a manner known per se by mixing the ingredients specified in each case with one another:
For this purpose, the required amount of water was placed in a beaker (batch size approx. 2 kg each size composition as "concentrate", see Table 1), the rheological additives and the refractory materials (phyllosilicates, zirconium powder, graphite) were added and then with a high shear Dissolver stirrer opened for 3 minutes in a manner known per se. The other constituents of the size composition (cf. Table 1) were then added in the stated proportions and the mixture was stirred for a further 2 minutes using a high-shear dissolver stirrer. The dilutable concentrates of size compositions indicated in Table 1 were obtained in each case.

The information on "DIN grinding" in Table 1 means that the specified component of the size 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 that corresponds to the specified numerical value (e.g.: "80" means "test sieve with a mesh size of 80 µm") (according to DIN ISO 3310-1: 2001-09), in each case a residue in the range of 1 to 10% by weight remains, based on the amount of sample used. <u> Table </u> 1: Sizing compositions according to the invention and not according to the invention, each obtained as dilutable "concentrates" Sizing compositions ("concentrates"): SZ1 SZ2 SZ3 Ingredients : [% By weight] [% By weight] [% By weight] water 44.1 46.0 47.1 Rheological additive 1.5 5.0 1.5 Layered silicate (pyrophyllite, DIN 140 grinding) ./. 26.0 11.0 Layered silicate (mica, DIN 160 grinding) 25.0 ./. 18.0 Zircon flour (zircon silicate, DIN 60 grinding) 14.0 9.0 10.0 Graphite (DIN 80 grinding) 11.0 8.0 11.0 Polyvinyl acetate ./. 0.9 ./. Biocide (benzisothiazolinone, 10% solution w / w in water) 0.3 0.3 0.3 Modified starch ./. 0.3 ./. Polyvinyl alcohol 0.4 ./. 0.4 Iron oxide (yellow) ./. 1.2 ./. Wetting agents 0.6 0.3 0.6 Defoamer 0.1 ./. 0.1 Propylene carbonate ./. 3.0 ./. Citric acid 3.0 ./. ./. TOTAL: 100.0 100.0 100.0

The dilutable concentrates of sizing compositions given in Table 1 were then diluted with water to produce ready-to-use sizing compositions for the purpose provided here (for application to molds or cores by means of an immersion process, preferably in the form of an immersion bath). The dilution used in each case and other properties of the ready-to-use size compositions resulting from the dilution used are given in Table 1a below: <u> Table </u> 1a: Production and properties of ready-to-use (for immersion baths or immersion pools) size compositions Sizing compositions (ready-to-use for plunge pools or immersion baths): SZ1 SZ2 SZ3 Concentrate (according to Table 1), parts by weight: 100.0 100.0 100.0 Water, parts by weight 40.0 30.0 40.0 Properties of the ready-to-use sizing compositions resulting from the above-mentioned thinning: Density [g / ml] 1.32 1.36 1.35 Run-down time [s] 13.5 13.7 13.3 PH value 2.1 7.2 6.7

As can be seen from Table 1a, the size compositions for the purpose envisaged here, application to test cores by means of an immersion application or an immersion bath, were produced in such a way that (i) their respective properties when applied to the test cores and (ii) the resulting properties of the coated test cores were guaranteed (densities and flow times that were as similar as possible were set; however, a different pH value for size composition SZ1 according to the invention compared to size compositions SZ2 and SZ3 not according to the invention).

The densities of the ready-to-use size compositions given in Table 1a were measured in accordance with the standard test method DIN EN ISO 2811-2 (method A).

The flow times given in Table 1a for the ready-to-use size compositions were measured in accordance with the standard test method DIN 53211 (1974) by determination with the DIN cup 4.

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

The sizing compositions SZ1 and SZ3 each contained attapulgite as a rheological additive. Sizing composition SZ2 is different from that in document WO00 / 05010 described type.

Example 2: Investigation of the softening of foundry cores

To determine the softening of foundry cores (ie the maximum decrease in flexural strength), test cores (test specimens) were produced in a manner known per se (according to "core system 1" given in Table 4) in a core shooting machine from Multiserw (type LUT, gas injection pressure: 2 bar, shot time: 3.0 s; shooting pressure 4.0 bar). One hour after the core production, the test cores with the above-mentioned ready-to-use sizing compositions "SZ1", "SZ2" and "SZ3" (see Table 1a) were immersed at room temperature (25 ° C.) (conditions: 1 s immersion; 3 s holding time in the Sizing composition, 1s immersion) coated (sized). The wet layer thickness of the sizes was set to about 250 μm in each case. The sized test cores were then dried under the conditions given below (1 hour at 120 ° C.) in a forced-air oven, and the change in their flexural strength under the drying conditions was examined in each case.

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

In Table 2, the values for the maximum decrease in flexural strength under drying conditions are given in% for each of the examined sized test cores, in each case based on the flexural strength of the freshly sized (still wet) test core before the start of drying (initial value). <u> Table </u> 2: Decrease in strength of sized test cores under drying conditions Sizing type on test core Maximum drop in flexural strength on drying, to% of the initial value Observation of core failure during drying SZ1 80 No SZ 2 25th No SZ 3 0 Yes

The term "core failure" means here and in the following that a sized core became unusable during the drying process, i.e. the sized core was unusable for the measurement of the flexural strength as well as for a subsequent cast.

From the values given in Table 2 it can be seen, among other things, that the maximum drop in the flexural strength of a test core which was sized with a size composition according to the invention (SZ1) was significantly lower than with comparison size compositions not according to the invention (SZ2 or SZ3). . It can also be seen from the values in Table 2 that no usable sized cores could be produced with the comparative sizing composition SZ3 not according to the invention under the selected conditions.

Example 3 Investigation of the storage stability of sized and unsized foundry cores

To determine the storage stability, waterglass-bonded test cores (test specimens) were produced in a manner known per se (analogous to that described in Example 2) and their flexural strengths were each unsized 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 stated above, see Table 3 (entry "Unsized after 1 h").

In addition, corresponding test cores as indicated below in Table 3 were carried out one hour after core production (ie at the same time interval from their production) at room temperature (25 ° C.) with the size compositions SZ1 or SZ3 Dipping (conditions: 1 s immersion; 3 s holding time in the size composition, 1 s immersion) sized (designation of the size compositions as in Example 1) and each dried for one hour at 120 ° C. in a convection oven. The sized, dried test cores were then subjected to a storage test for a period of four days (as far as the production of the sized core was possible or as far as the failure of the core was not 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 indicated above. The results of this storage test are given in Table 3 below. Test cores (“core system 1”), the production conditions of which are given in Table 4 below, were used for all tests in Example 3. <u> Table </u> 3: Determination of the storage stability of sized and unsized foundry cores Core system Not settled after 1 h Finished with type SZ1 after storage (4d) Finished with type SZ3 after storage (4d) Not settled at / during storage Flexural strength [N / cm ² ] 1 300 149 not definable Core failure after 131 min.

The values given in Table 3 show, among other things, that a waterglass-bonded test core sized with a sizing composition according to the invention (SZ1) still had> 40% of the initial strength after storage for four days, while a test core sized with a comparative sizing composition not according to the invention (SZ3) Test core was unusable under comparable conditions; its flexural strength could no longer be determined under the conditions defined above, since it broke during aging. An unsized comparison core failed under the test conditions after just 131 minutes, ie the application of a size composition according to the invention to a test core already led to a stabilization of the test core under drying conditions. <u> Table </u> 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% by weight water glass content in water (w / w) Additive (1.0 part by weight) Particulate, amorphous silicon dioxide Core box temperature 120 ° C Aeration temperature 150 ° C Curing time 30 s

• Das für das Kernsystem 1 in Tabelle 4 angegebene Bindemittel war hierbei ein handelsübliches Alkali-Wasserglas-Bindemittel "Cordis® 8511" (Hüttenes-Albertus Chemische Werke GmbH).
• Das für das Kernsystem 1 in Tabelle 4 angegebene Additiv war hierbei ein handelsübliches Binder-Additiv mit dem Hauptbestandteil (≥ 95 Gew.-%) partikuläres, amorphes Siliziumdioxid, "Anorgit® 8396" (Hüttenes-Albertus Chemische Werke GmbH).

The core system 1 consisted only of the components molding material, binder and additive, as indicated in Table 4:

• The binder specified for core system 1 in Table 4 was a commercially available alkali water glass binder "Cordis® 8511" (Hüttenes-Albertus Chemische Werke GmbH).
• The additive specified for core system 1 in Table 4 was a commercially available binder additive with the main component (≥ 95% by weight) of particulate, amorphous silicon dioxide, "Anorgit® 8396" (Hüttenes-Albertus Chemische Werke GmbH).

Example 4: Investigation of the flexural strength of sized foundry cores

In a manner known per se (analogous to that described in Example 2, but after interim maintenance of the core shooting machine used), waterglass-bonded test cores (test specimens) each with and without a content of particulate, amorphous silicon dioxide were produced and their flexural strengths were each unsized shortly after for comparison purposes their production (one hour storage time at a temperature in the range from 20 to 25 ° C., relative humidity 30 to 60%) determined as stated above (for the production conditions of the test cores see Table 6).

In addition, test cores were sized by dipping as indicated in Table 5 below (conditions: 1s immersion; 3s holding time in the size composition, 1s immersion) (designation of the size compositions as in Example 1) and each 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 from 30 to 60%, temperature in the range from 20 to 25 ° C.), the flexural strengths of the sized, dried test cores were then determined as indicated above.

The results of the flexural strength determinations are shown in Table 5 below. In each case, three different test cores (core systems A, B and C) were used, the production conditions of which are given in Table 6 below. <u> Table </u> 5: Determination of the flexural strengths of sized and unsized foundry cores Not settled after 1 h Finished with type SZ1 Finished with type SZ3 Core system Flexural strength [N / cm ² ] A. 401 335 It is not possible to produce a sized core B. 413 * 317 It is not possible to produce a sized core C (without particulate, amorphous SiO2) 347 269 It is not possible to produce a sized core * Deviation of the measured value from the corresponding value in Table 3 for core system 1 is essentially interpreted as an effect of the maintenance of the core shooter.

It can be seen from the values given in Table 5 that foundry cores sized with a size composition according to the invention achieve high flexural strengths. Furthermore, the values given in Table 5 show that a size composition according to the invention (SZ1) was used successfully under various conditions Foundry cores can be finished with good results (high flexural strengths). With a comparison size composition not according to the invention (SZ3), however, no usable sized cores could be produced under comparable conditions. <u> Table </u> 6: Manufacturing conditions for core systems A, B and C parameter Core system A Core system B Core system C Molding material Quartz sand (100.0 parts by weight) Quartz sand (100.0 parts by weight) Quartz sand (100.0 parts by weight) binder Alkali water glass solution, 25-35% by weight water glass content in water (w / w) (2.2 parts by weight) Alkali water glass solution, 25-35% by weight water glass content in water (w / w) (2.2 parts by weight) Alkali water glass solution, 25-35% by weight water glass content in water (w / w) (3.2 parts by weight) Additive Particulate, amorphous silicon dioxide (1.0 part by weight) Particulate, amorphous silicon dioxide (1.0 part by weight) None Core box temperature 120 ° C 120 ° C 120 ° C Aeration temperature 150 ° C 150 ° C 150 ° C Curing time 50 s 30 s 50 s

The binders and additives given in Table 6 for core systems A, B and C corresponded in each case to the binders given in Table 4 (“Cordis® 8511”) and additives (“Anorgit® 8396”).

The above-mentioned core systems A, B and C each consisted only of the components molding material, binder and, if appropriate, additive, as indicated in Table 6.

Claims (13)

1. Use of a coating composition comprising

   (a) one or more refractories, and

   (b) an aqueous phase having a pH of at most 5, for producing a coating on a waterglass-bound mould or on a waterglass-bound core, for use in the foundry, where the waterglass-bound mould or the waterglass-bound core comprises particulate, amorphous silicon dioxide.
2. Use according to Claim 1, where the aqueous phase (b) comprises
   (b1) water, and
   (b2) one or more acids, preferably having a pKa
   < 5, preferably having a pKa < 4,
   where preferably the ratio of the mass of constituent (b1) to the mass of constituent (b2) is in the range from 10:1 to 200:1, very preferably in the range from 10:1 to 100:1,
   and/or
   where preferably the ratio of the mass of the constituent (b1) to the total mass of the aqueous phase (b) is greater than 50%, preferably greater than 70%, very preferably greater than 90%,
   and/or
   where preferably the aqueous phase possesses a pH of at most 4.
3. Use according to Claim 2,
   where
   the constituent (b2) comprises one or more acids which are selected from the group consisting of inorganic and organic acids,

   - where the organic acids are preferably selected from the group consisting of mono-, di- and tricarboxylic acids, preferably mono-, di- and tricarboxylic acids which are solid at 25°C and 1013 mbar, very preferably citric acid and oxalic acid,
   and/or

   - where the inorganic acids are preferably selected from the group consisting of hydrochloric acid, nitric acid, phosphoric acid, and acidic phosphates, very preferably from the group consisting of hydrochloric acid, nitric acid and phosphoric acid,
   and/or

   - where the ratio of the total mass of inorganic and organic acids of the constituent (b2) to the total mass of the coating composition is in the range from 0.1 to 10%, preferably in the range from 0.5 to 5%, more preferably in the range from 1 to 5%, very preferably in the range from in the range from 1 to 3.5%, and especially preferably in the range from 2.5 to 3.5%.
4. Use according to any of the preceding claims, where the constituent (a) comprises

   - particulate, amorphous silicon dioxide, preferably particulate, amorphous silicon dioxide whose primary particles (i) are spherical and possess a sphericity of 0.9 or more, determined by evaluation of two-dimensional microscope images, and/or (ii) possess a D90 < 10 µm, preferably a D90 of < 1 µm, determined by laser diffraction,
   very preferably particulate amorphous silicon dioxide which comprises as a secondary constituent in an amount of not more than 18 wt%, based on the total mass of the particulate amorphous silicon dioxide, (i) zirconium dioxide and/or (ii) a Lewis acid,

   and/or

   - 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.
5. Use according to any of the preceding claims, 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,

   and/or
   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
   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.
6. Use according to any of the preceding claims, where the 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
   where the 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
   where the 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, very preferably at a temperature of > 50°C and < 100°C.
7. Use of acid for setting a pH of at most 5 in the aqueous phase of a coating composition for application to a waterglass-bound mound or a waterglass-bound core, where the waterglass-bound mould or the waterglass-bound core comprises particulate, amorphous silicon dioxide,
   where preferably

   - the acid is selected from the group consisting of inorganic and organic acids, where the organic acids are preferably selected from the group consisting of mono-, di- and tricarboxylic acids, preferably mono-, di- and tricarboxylic acids which are solid at 25°C and 1013 mbar, very preferably citric acid and oxalic acid,
   and/or
   where the inorganic acids are preferably selected from the group consisting of hydrochloric acid, nitric acid, phosphoric acid, and acidic phosphates, very preferably from the group consisting of hydrochloric acid, nitric acid, and phosphoric acid,

   and/or

   - the acid is used for setting a pH of at most 4.
8. Process for producing a coated, waterglass-bound mould with high storage stability, or a coated, waterglass-bound core with high storage stability, for use in the foundry, comprising the following steps:

   (1) providing or producing a coating composition as defined in any of Claims 1 to 5,

   (2) providing or producing an uncoated, waterglass-bound mould or an uncoated, waterglass-bound core, where the mould provided or produced or the core provided or produced comprises particulate amorphous silicon dioxide, and

   (3) applying the provided or produced coating composition from step (1) to the provided or produced mould or the provided or produced core.
9. Process according to Claim 8, where application to the mould takes place at a temperature of the core or of the mould of > 50°C, preferably > 70°C, very preferably at a temperature of > 50°C and < 100°C.
10. Coated mould or coated core for use in the foundry, in each case comprising

    (X) a waterglass-bound mould or a waterglass-bound core, where the waterglass-bound mould and/or the waterglass-bound core comprises particulate, amorphous silicon dioxide, and

    (Y) a coating comprising a coating composition as defined in any of Claims 1 to 5.
11. Coated mould or coated core according to Claim 10, producible by a process according to either of Claims 8 and 9.
12. Coated mould or coated core according to either of Claims 10 and 11 for use in the casting of a metal melt at a temperature > 900°C, preferably for use in the casting of a metal melt comprising iron and/or steel.
13. Kit including in separate components

    (U) a coating composition comprising

    (a) one or more refractories, and

    (b) an aqueous phase having a pH of at most 5,
    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, and preferably comprising as component (U) a coating composition, where the coating composition is as defined in any of Claims 1 to 5.