Process for the production of casting moulds for metal processing using a moulding material mixture with improved flowability

Abstract

Method for producing casting moulds for metal processing comprising at least the following steps: - Production of a moulding material mixture comprising at least: - a refractory molding material; - a water glass-based binder; - a proportion of a particulate metal oxide, wherein the particulate metal oxide is synthetically produced amorphous silicon dioxide; and - a proportion of at least one surfactant; wherein the binder is provided as a two-component system, wherein a first liquid component contains the water glass and a second solid component contains the particulate metal oxide, wherein the surfactant is an octyl sulfate or a 2-ethylhexyl sulfate as a surfactant and the surfactant is added to the liquid component and the surfactant is dissolved in the binder; - molding the molding material mixture, whereby the molding material mixture is shot into a mold by means of a core shooter with the aid of compressed air; and - Curing the molded molding mixture by heating the molded molding mixture to evaporate the water contained in the binder, thereby obtaining the casting mold.

Description

[0001] The invention relates to a method for producing casting molds for metal processing using a molding material mixture which comprises at least one refractory mold base material, a water glass-based binder, and a portion of a particulate metal oxide which is synthetically produced silicon dioxide.

[0002] Casting molds for the production of metal bodies are essentially manufactured in two types. The first group consists of so-called cores or molds. These are used to assemble the casting mold, which essentially represents the negative mold of the casting to be produced. A second group consists of hollow bodies, so-called risers, which act as compensation reservoirs. These hold liquid metal, with appropriate measures ensuring that the metal remains in the liquid phase longer than the metal in the casting mold forming the negative mold. If the metal solidifies in the negative mold, liquid metal can flow from the compensation reservoir to compensate for the volume contraction that occurs during the solidification of the metal.

[0003] Casting molds are made of a refractory material, such as quartz sand, whose grains are bonded together by a suitable binder after the mold has been formed to ensure sufficient mechanical strength. Therefore, a refractory mold base material treated with a suitable binder is used to manufacture casting molds. The refractory mold base material is preferably in a free-flowing form so that it can be poured into a suitable hollow mold and compacted there. The binder creates a strong bond between the particles of the mold base material, giving the mold the necessary mechanical stability.

[0004] Casting molds must meet various requirements. During the casting process itself, they must first demonstrate sufficient stability and temperature resistance to contain the liquid metal into the hollow mold formed from one or more casting (partial) molds. Once the solidification process begins, the mechanical stability of the casting mold is ensured by a solidified metal layer that forms along the walls of the hollow mold. The material of the casting mold must then decompose under the influence of the heat emitted by the metal in such a way that it loses its mechanical strength, i.e. the cohesion between individual particles of the refractory material is eliminated. This is achieved, for example, by the binder decomposing under the influence of heat.After cooling, the solidified casting is shaken, whereby ideally the material of the casting molds disintegrates into a fine sand that can be poured out of the cavities of the metal mold.

[0005] Both organic and inorganic binders can be used to produce the casting molds, and curing can be achieved using either a cold or hot process. Cold processes are those that are essentially carried out at room temperature without heating the casting mold. Curing usually occurs through a chemical reaction, triggered, for example, by passing a gas catalyst through the mold to be cured.

[0006] In hot processes, the molding material mixture is heated to a sufficiently high temperature after molding, for example to expel the solvent contained in the binder or to initiate a chemical reaction by which the binder is cured, for example by crosslinking.

[0007] Currently, organic binders are often used for the production of casting molds, where the curing reaction is accelerated by a gaseous catalyst or where the curing reaction is achieved by reaction with a gaseous hardener. These processes are referred to as "cold box" processes.

[0008] An example of the production of casting molds using organic binders is the so-called Ashland cold box process. This is a two-component system. The first component consists of a solution of a polyol, usually a phenolic resin. The second component is a solution of a polyisocyanate. According to US Pat. No. 3,409,579 A, ​​the two components of the polyurethane binder are reacted by passing a gaseous tertiary amine through the mixture of mold base and binder after molding.

[0009] The curing reaction of polyurethane binders is a polyaddition reaction, meaning it does not release byproducts such as water. Other advantages of this cold-box process include high productivity, dimensional accuracy of the molds, and good technical properties, such as mold strength, processing time of the mold base and binder mixture, etc.

[0010] Heat-curing organic processes include the hot-box process based on phenolic or furan resins, the warm-box process based on furan resins, and the croning process based on phenol novolak resins. In both the hot-box and warm-box processes, liquid resins are processed into a molding material mixture with a latent hardener that only becomes effective at elevated temperatures. In the croning process, molding materials such as quartz, chrome ore, zircon sand, etc., are coated with a phenol novolak resin that is liquid at a temperature of approximately 100 to 160 °C. Hexamethylenetetramine is added as a reactant for subsequent curing. In the above-mentioned heat-curing technologies, molding and curing take place in heatable tools that are heated to temperatures of up to 300 °C.

[0011] Regardless of the curing mechanism, all organic systems have one thing in common: they thermally decompose when the liquid metal is poured into the casting mold. This can release pollutants such as benzene, toluene, xylenes, phenol, formaldehyde and higher, sometimes unidentified cracking products. Although various measures have been taken to minimize these emissions, they cannot be completely avoided with organic binders. Such undesirable emissions also occur when the metals are poured in inorganic-organic hybrid systems which contain a proportion of organic compounds, such as the binders used in the resol-CO2 process. To avoid the emission of decomposition products during the casting process, binders must be used which are based on inorganic materials or which contain at most a very small proportion of organic compounds.Such binder systems have been known for some time. Binder systems have been developed that can be cured by introducing gases. One such system is described, for example, in GB 782 205, in which an alkali water glass is used as the binder, which can be cured by introducing CO2. DE 199 25 167 describes an exothermic feeder mass containing an alkali silicate as the binder. Furthermore, binder systems have been developed that are self-curing at room temperature. One such system, based on phosphoric acid and metal oxides, is described, for example, in US Pat. No. 5,582,232. Finally, inorganic binder systems are known that are cured at higher temperatures, for example in a hot tool.Such heat-curing binder systems are known, for example, from US 5,474,606, in which a binder system consisting of alkali water glass and aluminum silicate is described.

[0012] However, inorganic binders also have disadvantages compared to organic binders. For example, casting molds made with water glass as a binder have relatively low strength. This leads to problems, especially when removing the casting mold from the tool, as the mold can break. Good strength at this stage is particularly important for the production of complex, thin-walled molded parts and their safe handling. The reason for the low strength is primarily that the casting molds still contain residual water from the binder. Longer residence times in the hot, closed tool are only of limited help, as the water vapor cannot escape sufficiently.To achieve the most complete drying of the casting molds possible, WO98 / 06522 proposes leaving the molding material mixture in a temperature-controlled core box after demolding only long enough for a dimensionally stable and load-bearing edge shell to form. After opening the core box, the mold is removed and then completely dried using microwaves. However, this additional drying process is complex, increases the production time of the casting molds, and significantly increases the cost of the manufacturing process, not least due to the energy costs.

[0013] To ensure the flowability of a refractory molding material mixture based on a water glass binder, relatively large amounts of water glass are required. However, this leads to a reduction in the refractoriness of the mold and poor disintegration after the casting process. Therefore, only a small proportion of the used molding sand can be reused for mold production.

[0014] DE 29 09 107 A describes a process for producing casting molds from granular and / or fibrous material with sodium or potassium silicate as a binder, wherein a surface-active substance, preferably a surfactant, silicone oil or a silicone emulsion, is added to the mixture.

[0015] EP 1 095 719 A2 describes a waterglass-based binder system. The binder system contains waterglass and a hygroscopic base, as well as an emulsion solution containing 8 to 10% silicone oil, based on the binder quantity. The silicone oil has a boiling point of 250 °C. The silicone emulsion is added to control the hygroscopic properties and improve the flowability of the molding material mixture.

[0016] US Pat. No. 5,711,792 describes a binder composition for the production of casting molds, comprising an inorganic binder consisting of an aqueous solution containing polyphosphate chains and / or borate ions, as well as a water-soluble surfactant. The addition of the water-soluble surfactant increases the flowability of the molding material mixture.

[0017] Another weakness of the inorganic binders known to date is the low stability of the molds produced with them to high humidity. This makes it impossible to reliably store the molded bodies over extended periods, as is common with organic binders.

[0018] Casting molds made with water glass as a binder often exhibit poor decomposition after metal casting. Particularly if the water glass has been hardened by treatment with carbon dioxide, the binder can vitrify under the influence of the hot metal, causing the casting mold to become very hard and difficult to remove from the casting. Attempts have therefore been made to add organic components to the molding mixture that combust under the influence of the hot metal and facilitate decomposition of the casting after casting by forming pores.

[0019] DE 2 059 538 describes core and molding sand mixtures containing sodium silicate as a binder. To improve the disintegration of the casting mold after metal casting, glucose syrup is added to the mixture. The molding sand mixture, processed into a casting mold, is set by passing carbon dioxide gas through it. The molding sand mixture contains 1 to 3 wt.% glucose syrup, 2 to 7 wt.% of an alkali silicate, and a sufficient amount of core or molding sand. The examples showed that molds and cores containing glucose syrup exhibit far better disintegration properties than molds and cores containing sucrose or pure dextrose.

[0020] WO 2006 / 024540 A2 describes a molding material mixture for producing casting molds for metal processing, which comprises at least one refractory mold base material and a waterglass-based binder. A portion of a particulate metal oxide selected from the group consisting of silicon dioxide, aluminum oxide, titanium oxide, and zinc oxide is added to the binder. Precipitated silica or fumed silica is particularly preferably used as the particulate metal oxide. The particulate metal oxide, particularly silicon dioxide, allows for very easy disintegration of the casting mold after metal casting, so that minimal effort is required to remove the casting mold.

[0021] However, the addition of particulate metal oxide to the molding material mixture significantly impairs the flow properties of the molding material mixture, making it difficult to achieve a uniform fill level in the model and thus a uniform density of the mold during mold production. In the worst case, this can result in areas within the mold where the molding material mixture is not compacted at all. These defective areas are transferred to the casting, rendering it unusable. Another problem is uneven compaction of the molding material mixture, which increases the mold's brittleness. This makes automation of the casting process difficult, as the molds are difficult to transport without damage.It is therefore preferable to add a portion of a platelet-shaped lubricant, such as graphite, mica or talc, to the refractory molding material mixture, which is intended to reduce the friction between individual sand grains so that even more complex casting molds can be produced without major difficulties.

[0022] However, with the increasing complexity of core geometries, ever-increasing demands are being placed on the flowability of the molding material mixture. While these problems were previously solved by the use of organic binders, the successful introduction of inorganic binders into large-scale foundry production has led to a desire to provide suitable inorganic binders or refractory molding material mixtures for even very complex casting molds.

[0023] The invention was therefore based on the object of providing a method for producing casting molds for metal processing, which comprises at least one refractory mold base material and a binder system based on water glass and enables the production of casting molds with very complex geometries, which may, for example, also include thin-walled sections.

[0024] This object is achieved by a method having the features of patent claim 1. Advantageous developments of the method according to the invention are the subject of the dependent patent claims.

[0025] By adding at least the surfactant, the flowability of the molding material mixture can be significantly improved. A significantly higher density is achieved during mold production, i.e., the particles of the refractory molding material are packed much more densely. This increases the stability of the mold, and even in geometrically challenging sections of the mold, defects that cause a deterioration in the casting appearance can be significantly reduced. A further advantage of using the molding material mixture according to the invention to produce casting molds is that the mechanical stress on the molding tools is significantly reduced. The abrasive effect of the sand on the tools is minimized, thus reducing maintenance costs.

[0026] The increased flowability of the molding material mixture also enables a reduction in the shooting pressures on the core shooting machines without having to accept poorer core compaction.

[0027] The molding material mixture according to the invention for producing casting molds for metal processing comprises at least: a refractory molding material; a water glass-based binder; a portion of a particulate metal oxide selected from the group consisting of silicon dioxide, aluminum oxide, titanium oxide and zinc oxide; According to the invention, a proportion of at least one surface-active substance is added to the molding material mixture.

[0028] Common materials for the production of casting molds can be used as refractory base materials. Suitable materials include quartz or zirconium sand. Fibrous refractory base materials, such as fireclay fibers, are also suitable. Other suitable refractory base materials include olivine, chrome ore sand, and vermiculite.

[0029] Furthermore, artificial molding materials can also be used as refractory molding materials, such as hollow aluminum silicate spheres (so-called microspheres), glass beads, glass granules, or spherical ceramic molding materials known under the name "Cerabeads®" or "Carboaccucast®". These spherical ceramic molding materials contain minerals such as mullite, corundum, and β-cristobalite in varying proportions. They contain aluminum oxide or silicon dioxide as their main components. Typical compositions contain, for example, Al2O3 and SiO2 in approximately equal proportions. In addition, other components can be included in proportions of < 10%, such as TiO2, Fe2O3. The diameter of the spherical molding materials is preferably less than 1000 pm, in particular less than 600 µm. Synthetically produced refractory molding materials are also suitable, such as mullite (x Al2O S· ySiO2, with x = 2 to 3, y = 1 to 2; ideal formula: Al2SiO3). These artificial molding materials do not have a natural origin and may have been subjected to a special molding process, such as in the production of hollow aluminum silicate microspheres, glass beads, or spherical ceramic molding materials.

[0030] According to one embodiment, glass materials are used as refractory artificial molding materials. These are used, in particular, either as glass beads or as glass granules. Conventional glasses can be used as the glass, with glasses with a high melting point being preferred.

[0031] Suitable materials include glass beads and / or glass granules made from broken glass. Borate glasses are also suitable. The composition of such glasses is shown in the table below. Table: Composition of glasses ingredient broken glass Borate glass SiO2 50 - 80 % 50 - 80 % Al2O3 0-15 % 0-15 % Fe2O3 < 2 % < 2 % M II O 0-25% 0-25% <h2 style=";text-align:left;direction:ltr">M<h2 style=";text-align:left;direction:ltr"> I <h2 style=";text-align:left;direction:ltr"> 2O 5 - 25 % 1-10 % B2O3 < 15 % Otherwise. < 10 % < 10 % M II Alkaline earth metal, e.g. Mg, Ca, Ba M I Alkali metal, e.g. Na, K

[0032] In addition to the glasses listed in the table, other glasses whose content of the above-mentioned compounds lies outside the specified ranges can also be used. Special glasses can also be used that contain other elements or their oxides in addition to the oxides mentioned.

[0033] The diameter of the glass beads is preferably 1 to 1000 µm, more preferably 5 to 500 µm and particularly preferably 10 to 400 µm.

[0034] Casting tests with aluminum have shown that when using synthetic molding materials, especially glass beads, glass granules, or microspheres, less molding sand adheres to the metal surface after casting than when using pure quartz sand. The use of synthetic molding materials therefore enables the production of smoother casting surfaces, while costly post-treatment by blasting is either not required or at least required to a significantly lesser extent.

[0035] It is not necessary to form the entire mold base material from the synthetic mold base materials. The preferred proportion of the synthetic mold base materials is at least about 3 wt. %, more preferably at least 5 wt. %, especially preferably at least 10 wt. %, preferably at least about 15 wt. %, particularly preferably at least about 20 wt. %, based on the total amount of the refractory mold base material. The refractory mold base material preferably has a free-flowing state, so that the mold material mixture according to the invention can be processed in conventional core shooting machines.

[0036] As a further component, the molding material mixture according to the invention comprises a binder based on water glass. Conventional water glasses, such as those already used as binders in molding material mixtures, can be used as the water glass. These water glasses contain dissolved sodium or potassium silicates and can be produced by dissolving glassy potassium and sodium silicates in water. The water glass preferably has an SiO2 / M2O modulus in the range from 1.6 to 4.0, in particular 2.0 to 3.5, where M stands for sodium and / or potassium. The water glasses preferably have a solids content in the range from 30 to 60 wt.%. The solids content refers to the amount of SiO2 and M2O contained in the water glass.

[0037] The molding material mixture further contains a portion of a particulate metal oxide, wherein the particulate metal oxide is synthetically produced amorphous silicon dioxide. The average primary particle size of the particulate metal oxide can be between 0.10 µm and 1 µm. However, due to the agglomeration of the primary particles, the particle size of the metal oxides is preferably less than 300 µm, more preferably less than 200 µm, and most preferably less than 100 µm.

[0038] It is preferably in the range from 5 to 90 µm, particularly preferably from 10 to 80 µm, and most preferably from 15 to 50 µm. The particle size can be determined, for example, by sieve analysis. The sieve residue on a sieve with a mesh size of 63 µm is particularly preferably less than 10 wt.%, preferably less than 8 wt.%.

[0039] Precipitated silica and / or fumed silica are preferably used as particulate silicon dioxide. Precipitated silica is obtained by reacting an aqueous alkali silicate solution with mineral acids. The resulting precipitate is then separated, dried, and ground.

[0040] Fumed silicas are silicas obtained from the gas phase by coagulation at high temperatures. Fumed silica can be produced, for example, by flame hydrolysis of silicon tetrachloride or in an electric arc furnace by reducing quartz sand with coke or anthracite to silicon monoxide gas, followed by oxidation to silicon dioxide. Fumed silicas produced by the electric arc furnace process may still contain carbon. Precipitated silica and fumed silica are equally suitable for the molding material mixture according to the invention. These silicas are referred to below as "synthetic amorphous silicon dioxide."

[0041] The inventors assume that the strongly alkaline water glass can react with the silanol groups arranged on the surface of the synthetically produced amorphous silicon dioxide and that when the water evaporates, an intensive bond is formed between the silicon dioxide and the then solid water glass.

[0042] As an essential additional component, the molding material mixture according to the invention contains a surfactant. A surfactant is understood to be a substance that can form a monomolecular layer on an aqueous surface, for example, capable of forming a membrane. Furthermore, a surfactant reduces the surface tension of water. Suitable surfactants include silicone oils.

[0043] The surface-active substance is a surfactant. Surfactants consist of a hydrophilic and a hydrophobic part, whose properties are balanced so that the surfactants can, for example, form micelles in an aqueous phase or accumulate at the interface.

[0044] The anionic surfactants are selected from the group of octyl sulfate and 2-ethylhexyl sulfate.

[0045] In the molding material mixture according to the invention, the pure surfactant is preferably present in a proportion of 0.001 to 1 wt.%, particularly preferably 0.01 to 0.5 wt.%, based on the weight of the refractory mold base material. Such surfactants are often offered commercially as 20 to 80% solutions. In this case, aqueous solutions of the surfactants are particularly preferred.

[0046] The surfactant is dissolved in the binder.

[0047] According to one embodiment, at least one carbohydrate is added to the molding material mixture according to the invention. By adding carbohydrates to the molding material mixture, casting molds based on inorganic binders can be produced that exhibit high strength both immediately after production and during prolonged storage. Furthermore, after metal casting, a casting with a very high surface quality is obtained, so that only minimal post-processing of the surface of the casting is required after removal of the mold. Mono- or disaccharides as well as higher molecular weight oligo- or polysaccharides can be used as carbohydrates. The carbohydrates can be used both as a single compound and as a mixture of different carbohydrates. There are no excessive requirements regarding the purity of the carbohydrates used.It is sufficient if the carbohydrates, based on dry weight, are present in a purity of more than 80 wt.%, particularly preferably more than 90 wt.%, particularly preferably more than 95 wt.%, in each case based on dry weight. The monosaccharide units of the carbohydrates can be linked in any way.

[0048] The carbohydrates preferably have a linear structure, for example, an α- or β-glycosidic 1,4-linkage. However, the carbohydrates can also be fully or partially 1,6-linked, such as amylopectin, which has up to 6% α1,6-linkages.

[0049] The amount of carbohydrate can be chosen relatively low in order to observe a significant effect on the strength of the casting molds prior to casting or a significant improvement in the surface quality. The proportion of carbohydrate, based on the refractory mold base material, is preferably selected in the range of 0.01 to 10 wt.%, particularly preferably 0.02 to 5 wt.%, especially preferably 0.05 to 2.5 wt.%, and most preferably in the range of 0.1 to 0.5 wt.%.

[0050] Even small amounts of carbohydrates in the range of about 0.1% by weight lead to significant effects.

[0051] According to a further embodiment, the carbohydrate can be contained in the molding material mixture in underivatized form. Such carbohydrates can be inexpensively obtained from natural sources, such as plants, for example grains or potatoes. The molecular weight of such carbohydrates obtained from natural sources can be reduced, for example, by chemical or enzymatic hydrolysis, in order to improve solubility in water. In addition to underivatized carbohydrates, which are therefore composed only of carbon, oxygen, and hydrogen, derivatized carbohydrates can also be used, in which, for example, some or all of the hydroxyl groups are etherified with, for example, alkyl groups. Suitable derivatized carbohydrates include, for example, ethylcellulose or carboxymethylcellulose.

[0052] Low-molecular-weight hydrocarbons such as mono- or disaccharides can be used. Examples include glucose or sucrose. However, the beneficial effects are particularly observed with the use of oligo- or polysaccharides. Therefore, an oligo- or polysaccharide is particularly preferred as the carbohydrate.

[0053] It is preferred that the oligosaccharide or polysaccharide has a molecular weight in the range of 1,000 to 100,000 g / mol, preferably 2,000 to 30,000 g / mol. In particular, when the carbohydrate has a molecular weight in the range of 5,000 to 20,000 g / mol, a significant increase in the strength of the casting mold is observed, so that the casting mold can be easily removed from the mold and transported during production. Even during extended storage, the casting mold displays very good strength, so that storage of the casting molds, as required for series production of castings, even for several days in the presence of atmospheric moisture, is easily possible. Resistance to the effects of water, as is unavoidable, for example, when applying a coating to the casting mold, is also very good.

[0054] The polysaccharide is preferably composed of glucose units, which are particularly preferably linked via α- or β-glycosidic 1,4-bonds. However, it is also possible to use carbohydrate compounds containing other monosaccharides in addition to glucose, such as galactose or fructose, as the additive according to the invention. Examples of suitable carbohydrates are lactose (α- or β-1,4-bonded disaccharide of galactose and glucose) and sucrose (disaccharide of α-glucose and β-fructose).

[0055] The carbohydrate is particularly preferably selected from the group of cellulose, starch, and dextrins, as well as derivatives of these carbohydrates. Suitable derivatives include, for example, derivatives that are fully or partially etherified with alkyl groups. However, other derivatizations can also be carried out, for example, esterifications with inorganic or organic acids.

[0056] Further optimization of the stability of the mold and the surface of the casting can be achieved by using special carbohydrates, particularly starches, dextrins (hydrolyzate products of starches), and their derivatives as additives to the molding material mixture. Naturally occurring starches such as potato, corn, rice, pea, banana, horse chestnut, or wheat starch can be used as starches. However, modified starches such as pregelatinized starch, thin-boiling starch, oxidized starch, citrate starch, acetate starch, starch ethers, starch esters, or even starch phosphates can also be used. There are no limitations to the choice of starch.

[0057] The starch can, for example, be low-viscosity, medium-viscosity, or high-viscosity, cationic or anionic, cold-water-soluble or hot-water-soluble. The dextrin is particularly preferably selected from the group consisting of potato dextrin, corn dextrin, yellow dextrin, white dextrin, borax dextrin, cyclodextrin, and maltodextrin.

[0058] Particularly when producing casting molds with very thin-walled sections, the molding material mixture preferably also comprises a phosphorus-containing compound. Both organic and inorganic phosphorus compounds can be used. To avoid triggering undesirable side reactions during metal casting, it is also preferred that the phosphorus in the phosphorus-containing compounds is preferably in oxidation state V. The addition of phosphorus-containing compounds can further increase the stability of the casting mold. This is particularly important when, during metal casting, the liquid metal strikes an inclined surface and, due to the high metallostatic pressure, exerts a strong erosive effect or can lead to deformation, particularly of thin-walled sections of the casting mold.

[0059] The phosphorus-containing compound is preferably in the form of a phosphate or phosphorus oxide. The phosphate can be in the form of an alkali metal phosphate or an alkaline earth metal phosphate, with sodium salts being particularly preferred. Ammonium phosphates or phosphates of other metal ions can also be used. However, the alkali metal phosphates and alkaline earth metal phosphates mentioned as preferred are readily available and inexpensively in any desired quantities.

[0060] If the phosphorus-containing compound is added to the molding material mixture in the form of a phosphorus oxide, the phosphorus oxide is preferably in the form of phosphorus pentoxide. However, phosphorus trioxide and phosphorus tetroxide can also be used.

[0061] According to a further embodiment, the phosphorus-containing compound can be added to the molding material mixture in the form of salts of fluorophosphoric acids. Particularly preferred are the salts of monofluorophosphoric acid. The sodium salt is especially preferred.

[0062] According to a preferred embodiment, organic phosphates are added to the molding material mixture as a phosphorus-containing compound. Alkyl or aryl phosphates are preferred. The alkyl groups preferably comprise 1 to 10 carbon atoms and can be straight-chain or branched. The aryl groups preferably comprise 6 to 18 carbon atoms, whereby the aryl groups can also be substituted by alkyl groups. Phosphate compounds derived from monomeric or polymeric carbohydrates such as glucose, cellulose, or starch are particularly preferred. The use of a phosphorus-containing organic component as an additive is advantageous in two respects. Firstly, the phosphorus content can achieve the necessary thermal stability of the casting mold, and secondly, the organic content has a positive influence on the surface quality of the corresponding casting.

[0063] Orthophosphates, polyphosphates, pyrophosphates, or metaphosphates can be used as phosphates. Phosphates can be produced, for example, by neutralizing the corresponding acids with a corresponding base, such as an alkali metal or alkaline earth metal base such as NaOH. Not all of the negative charges of the phosphate ion necessarily have to be saturated by metal ions. Metal phosphates, metal hydrogen phosphates, and metal dihydrogen phosphates, such as Na3PO4, Na2HPO4, and NaH2PO4, can be used. Anhydrous phosphates and phosphate hydrates can also be used. The phosphates can be incorporated into the molding mixture in either crystalline or amorphous form.

[0064] Polyphosphates are understood to be linear phosphates that contain more than one phosphorus atom, with the phosphorus atoms each connected via oxygen bridges. Polyphosphates are obtained by condensation of orthophosphate ions with elimination of water, resulting in a linear chain of PO4 tetrahedra, each connected via vertices. Polyphosphates have the general formula (O(PO3) n ) (n+2)- where n corresponds to the chain length. A polyphosphate can comprise up to several hundred PO4 tetrahedra. However, preference is given to using polyphosphates with shorter chain lengths. n preferably has values ​​from 2 to 100, particularly preferably from 5 to 50. Higher-condensed polyphosphates can also be used, i.e., polyphosphates in which the PO4 tetrahedra are connected to one another via more than two vertices and therefore exhibit polymerization in two or three dimensions.

[0065] Metaphosphates are cyclic structures composed of PO4 tetrahedra, each connected by vertices. Metaphosphates have the general formula ((PO3) n ) n- where n is at least 3. Preferably, n has values ​​from 3 to 10.

[0066] Both individual phosphates and mixtures of different phosphates and / or phosphorus oxides can be used.

[0067] The preferred proportion of the phosphorus-containing compound, based on the refractory mold base material, is between 0.05 and 1.0 wt.%. At a proportion of less than 0.05 wt.%, no significant influence on the dimensional stability of the casting mold can be observed. If the phosphate proportion exceeds 1.0 wt.%, the hot strength of the casting mold decreases significantly. The proportion of the phosphorus-containing compound is preferably selected between 0.10 and 0.5 wt.%. The phosphorus-containing compound preferably contains between 0.5 and 90 wt.% phosphorus, calculated as P2O5. If inorganic phosphorus compounds are used, these preferably contain 40 to 90 wt.%, particularly preferably 50 to 80 wt.% phosphorus, calculated as P2O5. If organic phosphorus compounds are used, these preferably contain 0.5 to 30 wt.%, particularly preferably 1 to 20 wt.% phosphorus, calculated as P2O5.

[0068] The phosphorus-containing compound can be added to the molding material mixture in solid or dissolved form. Preferably, the phosphorus-containing compound is added to the molding material mixture as a solid. If the phosphorus-containing compound is added in dissolved form, water is the preferred solvent.

[0069] The molding material mixture according to the invention represents an intensive mixture of at least the aforementioned components. The particles of the refractory molding base material are preferably coated with a layer of the binder. By evaporating the water present in the binder (approximately 40-70% by weight, based on the weight of the binder), a strong bond between the particles of the refractory molding base material can be achieved.

[0070] The binder, i.e. the water glass and the particulate metal oxide, in particular synthetic amorphous silicon dioxide, and the surfactant, is preferably present in the molding material mixture in a proportion of less than 20 wt.%, particularly preferably in a range from 1 to 15 wt.%. The proportion of binder refers to the solid content of the binder. If solid molding materials are used, such as quartz sand, the binder is preferably present in a proportion of less than 10 wt.%, preferably less than 8 wt.%, particularly preferably less than 5 wt. If refractory molding materials with a low density are used, such as the hollow microspheres described above, the proportion of binder increases accordingly.

[0071] The synthetic amorphous silicon dioxide is preferably present in a proportion of 2 to 80 wt.%, preferably between 3 and 60 wt.%, particularly preferably between 4 and 50 wt.%, based on the total weight of the binder.

[0072] The ratio of water glass to particulate metal oxide, particularly synthetic amorphous silicon dioxide, can be varied within wide ranges. This offers the advantage of improving the initial strength of the casting mold, i.e. the strength immediately after removal from the hot tool, and the moisture resistance, without significantly influencing the final strengths, i.e. the strengths after the casting mold has cooled, compared to a water glass binder without amorphous silicon dioxide. This is of great interest, especially in light metal casting. On the one hand, high initial strengths are desired in order to be able to transport the casting mold easily after it has been manufactured or to combine it with other casting molds. On the other hand, the final strength after hardening should not be too high in order to avoid difficulties with binder decomposition after casting, i.e.The mold base material should be able to be easily removed from the mold cavities after casting.

[0073] In one embodiment of the invention, the molding base material contained in the molding material mixture according to the invention can contain at least a proportion of hollow microspheres. The diameter of the hollow microspheres is normally in the range from 5 to 500 µm, preferably in the range from 10 to 350 µm, and the thickness of the shell is usually in the range from 5 to 15% of the diameter of the microspheres. These microspheres have a very low specific gravity, so that the casting molds produced using hollow microspheres are lightweight. The insulating effect of the hollow microspheres is particularly advantageous. The hollow microspheres are therefore used in particular for the production of casting molds when they are required to have an increased insulating effect.Such casting molds include, for example, the risers described in the introduction, which act as compensating reservoirs and contain liquid metal. The metal is intended to be kept in a liquid state until the metal poured into the hollow mold has solidified. Another application for casting molds containing hollow microspheres is, for example, sections of a casting mold that correspond to particularly thin-walled sections of the finished casting mold. The insulating effect of the hollow microspheres ensures that the metal in the thin-walled sections does not solidify prematurely and thus block the paths within the casting mold.

[0074] If hollow microspheres are used, the binder is preferably used in a proportion of less than 20 wt.%, particularly preferably in the range of 10 to 18 wt.%, due to the low density of these hollow microspheres. These values ​​refer to the solids content of the binder.

[0075] The hollow microspheres preferably consist of an aluminum silicate. These hollow aluminum silicate microspheres preferably have an aluminum oxide content of more than 20 wt.%, but can also have a content of more than 40 wt.%. Such hollow microspheres are marketed, for example, by Omega Minerals Germany GmbH, Norderstedt, under the names Omega-Spheres® SG with an aluminum oxide content of approximately 28-33%, Omega-Spheres® WSG with an aluminum oxide content of approximately 35-39%, and E-Spheres® with an aluminum oxide content of approximately 43%. Corresponding products are available from PQ Corporation (USA) under the name "Extendospheres®."

[0076] According to a further embodiment, hollow microspheres made of glass are used as the refractory molding material.

[0077] According to a particularly preferred embodiment, the hollow microspheres consist of a borosilicate glass. The borosilicate glass has a boron content, calculated as B2O3, of more than 3 wt.%. The proportion of hollow microspheres is preferably less than 20 wt.%, based on the molding material mixture. When using hollow borosilicate glass microspheres, a lower proportion is preferably selected. This is preferably less than 5 wt.%, more preferably less than 3 wt.%, and particularly preferably in the range of 0.01 to 2 wt.%.

[0078] As already explained, in a preferred embodiment the molding material mixture according to the invention contains at least a proportion of glass granulate and / or glass beads as a refractory molding base material.

[0079] It is also possible to form the molding material mixture as an exothermic molding material mixture, suitable, for example, for the production of exothermic feeders. For this purpose, the molding material mixture contains an oxidizable metal and a suitable oxidizing agent. Based on the total mass of the molding material mixture, the oxidizable metals preferably constitute a proportion of 15 to 35 wt.%. The oxidizing agent is preferably added in a proportion of 20 to 30 wt.%, based on the molding material mixture. Suitable oxidizable metals include, for example, aluminum or magnesium. Suitable oxidizing agents include, for example, iron oxide or potassium nitrate.

[0080] According to a further embodiment, the molding material mixture according to the invention can also contain, in addition to the surfactant, a proportion of platelet-shaped lubricants, in particular graphite, MoS2, talc, and / or pyrophillite. The amount of added platelet-shaped lubricant, in particular graphite, is preferably 0.05 wt.% to 1 wt.%, based on the mold base material. However, it is preferred that no further platelet-shaped lubricant besides the surfactant be contained in the molding material mixture according to the invention.

[0081] In addition to the aforementioned components, the molding material mixture according to the invention may also comprise other additives. For example, internal release agents can be added to facilitate the removal of the casting molds from the molding tool. Suitable internal release agents include calcium stearate, fatty acid esters, waxes, natural resins, or special alkyd resins. Furthermore, silanes can also be added to the molding material mixture according to the invention.

[0082] Thus, in one embodiment, the molding material mixture according to the invention contains an organic additive which has a melting point in the range of 40 to 180 °C, preferably 50 to 175 °C, i.e. is solid at room temperature. Organic additives are understood to be compounds whose molecular framework is predominantly made up of carbon atoms, for example organic polymers. The addition of the organic additives can further improve the quality of the surface of the casting. The mechanism of action of the organic additives has not been clarified. Without wishing to be bound to this theory, the inventors assume that at least some of the organic additives burns during the casting process, creating a thin gas cushion between the liquid metal and the mold base material forming the wall of the casting mold, thus preventing a reaction between the liquid metal and the mold base material.The inventors further assume that some of the organic additives form a thin layer of so-called lustrous carbon under the reducing atmosphere prevailing during casting, which also prevents a reaction between the metal and the mold base material. Another beneficial effect achieved by adding the organic additives is an increase in the strength of the casting mold after curing.

[0083] The organic additives are preferably added in an amount of 0.01 to 1.5 wt.%, particularly preferably 0.05 to 1.3 wt.%, particularly preferably 0.1 to 1.0 wt.%, in each case based on the molding material.

[0084] It has been found that an improvement in the surface of the casting can be achieved with very different organic additives. Suitable organic additives include, for example, phenol-formaldehyde resins, such as novolaks, epoxy resins, such as bisphenol A epoxy resins, bisphenol F epoxy resins or epoxidized novolaks, polyols, such as polyethylene glycols or polypropylene glycols, polyolefins, such as polyethylene or polypropylene, copolymers of olefins, such as ethylene or propylene, and other comonomers, such as vinyl acetate, polyamides, such as polyamide 6, polyamide 12 or polyamide 6,6, natural resins, such as balsam resin, fatty acids, such as stearic acid, fatty acid esters, such as cetyl palmitate, fatty acid amides, such as ethylenediamine bisstearamide, and metal soaps, such as stearates or oleates of monovalent to trivalent metals.The organic additives can be present either as a pure substance or as a mixture of various organic compounds.

[0085] According to a further embodiment, the molding material mixture according to the invention contains a proportion of at least one silane. Suitable silanes include, for example, aminosilanes, epoxysilanes, mercaptosilanes, hydroxysilanes, methacrylsilanes, ureidosilanes, and polysiloxanes. Examples of suitable silanes are γ-aminopropyltrimethoxysilane, γ-hydroxypropyltrimethoxysilane, 3-ureidopropyltriethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, β-(3,4-epoxycyclohexyl)trimethoxysilane, 3-methacryloxypropyltrimethoxysilane, and N-β(aminoethyl)-γ-aminopropyltrimethoxysilane.

[0086] Based on the particulate metal oxide, typically about 5 - 50% silane is used, preferably about 7 - 45%, particularly preferably about 10 - 40%.

[0087] Despite the high strengths achievable with the binder according to the invention, the casting molds, especially cores and molds, produced with the molding material mixture according to the invention surprisingly exhibit good disintegration after casting, especially in aluminum casting. However, the use of the molded bodies produced from the molding material mixture according to the invention is not limited to light metal casting. The casting molds are generally suitable for casting metals. Such metals include, for example, non-ferrous metals such as brass or bronze, as well as ferrous metals.

[0088] The invention relates to a method for producing casting molds for metal processing, using the molding material mixture according to the invention. The method according to the invention comprises the following steps: Producing the molding material mixture described above; molding the molding material mixture; curing the molded molding material mixture by heating the molding material mixture, whereby the cured casting mold is obtained.

[0089] The molding material mixture according to the invention is generally produced by first adding the refractory mold base material and then adding the binder while stirring. The water glass, the particulate metal oxide, in particular synthetic amorphous silicon dioxide, and the surfactant itself can be added in any order. The surfactant can be added in bulk or as a solution or emulsion, with water being the preferred solvent. Aqueous emulsions or solutions of the surfactant are preferred. The molding material mixture is preferably produced in such a way that excessive foaming does not occur. This can be achieved, on the one hand, by selecting the surfactant. On the other hand, the addition of defoamers is also possible if necessary.

[0090] The additional additives described above can be added to the molding material mixture in any form. They can be added individually or as a mixture. They can be added as a solid, but also in the form of solutions, pastes, or dispersions. If added as a solution, paste, or dispersion, water is preferred as the solvent. It is also possible to use the water glass used as a binder as a dissolving or dispersing medium for the additives.

[0091] According to a preferred embodiment, the binder is provided as a two-component system, with a first liquid component containing the water glass and a second solid component containing the particulate metal oxide. The solid component may further contain, for example, the phosphate and optionally a carbohydrate. The surfactant is added to the liquid component.

[0092] When producing the molding material mixture, the refractory mold base material is placed in a mixer and then preferably the solid component(s) of the binder are added and mixed with the refractory mold base material. The mixing time is selected so that the refractory mold base material and the solid binder component are thoroughly mixed. The mixing time depends on the amount of molding material mixture to be produced and the mixing unit used. The mixing time is preferably between 1 and 5 minutes. The liquid component of the binder is then added, preferably while continuing to agitate the mixture, and the mixture is then mixed further until an even layer of the binder has formed on the grains of the refractory mold base material. Here, too, the mixing time depends on the amount of molding material mixture to be produced and the mixing unit used.The mixing process preferably lasts between 1 and 5 minutes. A liquid component is understood to mean both a mixture of various liquid components and the totality of all individual liquid components, whereby the latter can also be added individually. Likewise, a solid component is understood to mean both a mixture of individual or all of the solid components described above and the totality of all individual solid components, whereby the latter can be added to the molding material mixture together or sequentially.

[0093] According to another embodiment, the liquid component of the binder can also be added to the refractory mold base material first, and only then is the solid component added to the mixture. According to a further embodiment, 0.05 to 0.3% water, based on the weight of the mold base material, is first added to the refractory mold base material, and only then are the solid and liquid components of the binder added. This embodiment can have a surprisingly positive effect on the processing time of the mold material mixture. The inventors assume that the dehydrating effect of the solid components of the binder is reduced in this way, thereby delaying the curing process.

[0094] The molding material mixture is then formed into the desired shape. Conventional molding processes are used. The molding material mixture is shot into the mold using a core shooter with compressed air. The molding material mixture is then cured by applying heat to evaporate the water contained in the binder. This heating can take place, for example, in the mold. It is possible to completely cure the mold while it is still in the mold. However, it is also possible to only cure the mold's edges so that it has sufficient strength to be removed from the mold. The mold can then be completely cured by removing more water. This can be done, for example, in an oven. The water can also be removed, for example, by evaporating the water under reduced pressure.

[0095] The curing of the casting molds can be accelerated by blowing heated air into the mold. This embodiment of the process achieves rapid removal of the water contained in the binder, whereby the casting mold is solidified within a time period suitable for industrial application. The temperature of the blown-in air is preferably 100°C to 180°C, particularly preferably 120°C to 150°C. The flow rate of the heated air is preferably adjusted so that curing of the casting mold occurs within a time period suitable for industrial application. The time periods depend on the size of the casting molds produced. The aim is to cure within a time period of less than 5 minutes, preferably less than 2 minutes. However, longer times may be necessary for very large casting molds.

[0096] The water can also be removed from the molding material mixture by heating it with microwaves. However, microwaves are preferably applied after the mold has been removed from the molding tool. For this to happen, however, the mold must already have sufficient strength. As already explained, this can be achieved, for example, by curing at least one outer shell of the mold while it is still in the molding tool.

[0097] As already described, the molding material mixture may also contain additional organic additives. These additional organic additives can be added at any time during the production of the molding material mixture. The organic additive can be added in bulk or in the form of a solution.

[0098] Water-soluble organic additives can be used in the form of an aqueous solution. If the organic additives are soluble in the binder and can be stored undecomposed for several months, they can also be dissolved in the binder and added together with it to the molding material. Water-insoluble additives can be used in the form of a dispersion or paste. The dispersions or pastes preferably contain water as the dispersing medium. Solutions or pastes of the organic additives can also be prepared in organic solvents. However, if a solvent is used for the addition of the organic additives, water is preferred.

[0099] The organic additives are preferably added as a powder or as short fibers, with the average particle size or fiber length preferably being selected so that it does not exceed the size of the refractory mold base material particles. The organic additives can particularly preferably be sieved through a sieve with a mesh size of approximately 0.3 mm. To reduce the number of components added to the refractory mold base material, the particulate metal oxide and the organic additive(s) are preferably not added separately to the molding sand, but are mixed beforehand.

[0100] If the molding material mixture contains silanes or siloxanes, they are usually added by first incorporating them into the binder. The silanes or siloxanes can also be added to the molding material as a separate component. However, it is particularly advantageous to silanize the particulate metal oxide, i.e. to mix the metal oxide with the silane or siloxane so that its surface is covered with a thin silane or siloxane layer. If the particulate metal oxide pretreated in this way is used, increased strength and improved resistance to high humidity are found compared to the untreated metal oxide. If an organic additive is added to the molding material mixture or the particulate metal oxide, as described, it is advisable to do this before silanization.

[0101] The process according to the invention is suitable for the production of all casting molds commonly used in metal casting, such as cores and molds. It is particularly advantageous for producing casting molds that include very thin-walled sections or complex deflections. The process according to the invention is particularly suitable for the production of risers when insulating refractory mold base material or exothermic materials are added to the mold material mixture according to the invention.

[0102] The casting molds produced from the molding material mixture according to the invention or using the method according to the invention have a high level of strength immediately after production, without the strength of the casting molds being so high after curing that difficulties arise when removing the casting mold after the casting has been produced. Furthermore, these casting molds have a high level of stability at elevated air humidity, i.e. the casting molds can surprisingly be stored for extended periods of time without any problems. As a particular advantage, the casting mold has a very high level of stability under mechanical stress, so that even thin-walled sections of the casting mold or sections with a very complex geometry can be realized without them being deformed by the metallostatic pressure during the casting process. The invention therefore further relates to a casting mold which was obtained by the method according to the invention described above.

[0103] The casting mold according to the invention is generally suitable for metal casting, especially light metal casting. Particularly advantageous results are obtained with aluminum casting.

[0104] The invention will be explained in more detail below using examples and with reference to the accompanying figures. Fig. 1: a representation of the inlet channel core used to test the properties of molding compounds. Example 1

[0105] Influence of surfactants on the strength and density of casting molds. 1. Production and testing of the molding material mixture

[0106] For testing the molding material mixture, Fig. 1 shown inlet channel cores were manufactured.

[0107] The composition of the molding material mixture is given in Table 1. The following procedure was used to manufacture the inlet channel cores: The components listed in Table 1 were mixed in a mixer. First, the quartz sand was added, and the water glass and, if applicable, the surfactant were added while stirring. The water glass used was sodium water glass containing potassium. The SiO2:M2O modulus of the water glass was approximately 2.2, where M is the sum of sodium and potassium. After the mixture had been stirred for one minute, the amorphous silicon dioxide, if applicable, was added while stirring. The mixture was then stirred for another minute.

[0108] The molding material mixtures were transferred into the storage hopper of a 6.5 L core shooter manufactured by Röperwerk - Gießereimaschinen GmbH, Viersen, Germany, whose mold was heated to 180 °C.

[0109] The molding material mixtures were introduced into the mold using compressed air (2 bar) and remained in the mold for a further 50 seconds.

[0110] To accelerate the curing of the mixtures, hot air (3 bar, 150 °C at the entry into the tool) was passed through the mold during the last 20 seconds.

[0111] The mold was opened and the inlet channel was removed.

[0112] To determine the flexural strength, the test specimens were placed in a Georg Fischer strength testing machine equipped with a 3-point bending device (DISA Industrie AG, Schaffhausen, CH) and the force leading to the fracture of the test bars was measured.

[0113] The flexural strengths were measured according to the following scheme: - 10 seconds after removal (hot strength) - 1 hour after removal (cold strength) - Storage of the cooled kernels for 3 hours in a climate cabinet at 30 °C and 75% relative humidity. Table I

[0114] Composition of the molding material mixtures Quartz sand H32 Alkali water glass Amorphous silicon dioxide Surface active substance 1.1 100 GT 2,0 a) Comparison, not according to the invention 1.2 100 GT 2,0 a) 0,5 b) Comparison, not according to the invention 1.3 100 GT 2,0 a) 0,05 c) Comparison, not according to the invention 1.4 100 GT 2,0 a) 0,5 b) 0,05 c) Comparison, not according to the invention 1.5 100 GT 2,0 a) 0,5 b) 0,05 d) Comparison, nichterfindunasaemäß 1.6 100 GT 2,0 a) 0,5 b) 0,05 e) according to the invention 1.7 100 GT 2,0 a) 0,5 b) 0,05 f) Comparison, not according to the invention 1.8 100 GT 2,0 a) 0,5 b) 0,05 g) according to the invention 1.9 100 GT 2,0 a) 0,5 b) 0,1 h) Comparison, not according to the invention a) Alkali water glass with SiO2:M2O modulus of approx. 2.2 b) Elkem Microsilica 971 (fumed silica; produced in an electric arc furnace) c) Melpers 0030 (polycarboxylate ether in water, BASF) d) Melpers VP 4547 / 240L (modified polyacrylate in water, BASF) e) Texapon EHS (2-Ethylhexylsulfat in Wasser, Fa. Cognis) f) Glukopon 225 DK (Polyglucosid in Wasser, Fa. Cognis) g) Texapon 842 (sodium octyl sulfate in water, Lakeland) h) Castament FS 60 (modified carboxylate ether, solid, BASF)

[0115] The results of the strength tests are summarized in Table 2. Table 2

[0116] Flexural strengths Hot strength [N / cm 2 ] Cold strength[N / cm 2 ] After storage in a climate chamber [N / cm 2 ] Core weight [g]* 1.1 80 400 10 1255 Comparison, not according to the invention 1.2 170 410 150 1256 Comparison, not according to the invention 1.3 80 420 10 1310 Comparison, not according to the invention 1.4 180 460 210 1317 Comparison, not according to the invention 1.5 170 450 180 1315 Comparison, not according to the invention 1.6 180 440 200 1310 according to the invention 1.7 160 430 150 1319 Comparison, not according to the invention 1.8 170 440 200 1321 according to the invention 1.9 150 400 210 1280 Comparison, not according to the invention Result

[0117] Molding material mixtures that contain neither amorphous silicon dioxide nor a surfactant (mixture 1.1) have a high-temperature strength that is insufficient for an automated core production process. Cores produced with this molding material mixture exhibit structural loosening at low shooting pressures, which can lead to core rejection (low mechanical stability, transfer of defects to the casting pattern). This defect pattern can be counteracted by increasing the shooting pressure up to 5 bar.

[0118] The addition of amorphous silicon dioxide to the molding material mixture (Mixture 1.2) results in a significant increase in hot strength. The core weight, which provides information about compaction and flowability, is comparable to that of Mixture 1.1. Compaction at the core surface is also comparable to Mixture 1.1, showing coarse structural loosening at 2 bar.

[0119] When using surfactants without the addition of amorphous silicon dioxide (mixture 1.3), the core weight can be increased, but there is no positive effect on hot strength. Core compaction is improved, resulting in less structural loosening compared to mixtures 1.1 and 1.2.

[0120] Only by combining both molding material components, i.e., by adding both amorphous silicon dioxide and the surfactants used according to the invention (mixtures 1.6 and 1.8), can increases in hot strength and core weight be observed simultaneously. The cold strength and moisture stability of mixtures 1.6 and 1.8 also exhibit higher values ​​than the molded bodies of mixtures 1.1 to 1.3. Core compaction is improved by the increased flowability of the molding material mixture, resulting in an increase in mechanical stability. Structural loosening, such as that exhibited by the cores of mixtures 1.1 and 1.2, is minimal.

Claims

[1] A method for producing casting moulds for metalworking comprising at least the following steps: - Production of a moulding material mixture comprising at least: - a refractory molding material; - a water glass-based binder; - a proportion of a particulate metal oxide, wherein the particulate metal oxide is synthetically produced amorphous silicon dioxide; and - a proportion of at least one surfactant; wherein the binder is provided as a two-component system, wherein a first liquid component contains the water glass and a second solid component contains the particulate metal oxide, wherein the surfactant is an octyl sulfate or a 2-ethylhexyl sulfate as a surfactant and the surfactant is added to the liquid component and the surfactant is dissolved in the binder; - molding the molding material mixture, whereby the molding material mixture is shot into a mold by means of a core shooter with the aid of compressed air; and - Curing the molded molding mixture by heating the molded molding mixture to evaporate the water contained in the binder, thereby obtaining the casting mold. [2] Method according to claim 1, characterized by that the surfactant is sodium 2-ethylhexyl sulfate. [3] Method according to one of the preceding claims, characterized by that the surface-active substance is contained in the molding material mixture in a proportion of 0.001 to 1 wt.% based on the weight of the refractory molding base material. [4] Method according to one of the preceding claims, characterized by that at least one carbohydrate is added to the molding material mixture. [5] Method according to one of the preceding claims, characterized bythat a phosphorus-containing compound is added to the molding material mixture. [6] Method according to one of the preceding claims, characterized by that the particulate metal oxide is selected from the group of precipitated silica and pyrogenic silica. [7] Method according to one of the preceding claims, characterized by that the water glass has a modulus SiO2 / M2O in the range of 1.6 to 4.0, in particular 2.0 to 3.5, where M represents sodium ions and potassium ions. [8] Method according to one of the preceding claims, characterized by that the inorganic binder is contained in the moulding material mixture in a proportion of less than 20% by weight. [9] Method according to one of the preceding claims, characterized by that the particulate metal oxide is present in a proportion of 2 to 80 wt.% based on the binder. [10] Method according to one of the preceding claims, characterized bythat the refractory molding material contains at least a proportion of hollow microspheres. [11] Method according to one of the preceding claims, characterized by that the molding material contains at least a proportion of glass granules, glass beads and / or spherical ceramic moldings. [12] Method according to one of the preceding claims, characterized by that an oxidizable metal and an oxidizing agent are added to the molding material mixture. [13] Method according to one of the preceding claims, characterized by that the molding material mixture contains a proportion of at least one organic additive which is solid at room temperature. [14] Method according to one of the preceding claims, characterized by that the molding material mixture contains at least one silane or siloxane. [15] Method according to claim 1, characterized by that the molding material mixture is heated to a temperature in the range of 100 to 300 °C. [16] Method according to one of claims 1 or 15, characterized by that heated air is blown into the molded molding mixture to cure it. [17] Method according to one of claims 1, 15 or 16, characterized by that the heating of the molded molding material mixture is effected by the action of microwaves.

Images