EP2209572B1 - Mould material mixture having improved flowability - Google Patents

Description

The invention relates to a molding material mixture for the production of casting molds for metal processing, which comprises at least one refractory molding material, a water glass based binder, and a proportion of a particulate metal oxide, which is selected from the group of silica, alumina, titania and zinc oxide. Furthermore, the invention relates to a method for the production of molds for metal processing using the molding material mixture as well as a mold obtained by the method.

Molds for the production of metal bodies are essentially produced in two versions. A first group form the so-called cores or forms. From these, the casting mold is assembled, which essentially represents the negative mold of the casting to be produced. A second group form hollow bodies, so-called feeders, which act as a compensation reservoir. These take up liquid metal, by taking appropriate measures to ensure that the metal remains in the liquid phase longer than the metal that is in the the negative mold forming mold is located. If the metal solidifies in the negative mold, liquid metal can flow out of the compensation reservoir to compensate for the volume contraction that occurs when the metal solidifies.

Casting molds are made of a refractory material, such as quartz sand, whose grains are connected after molding of the mold by a suitable binder to ensure sufficient mechanical strength of the mold. For the production of molds so you use a refractory molding material, which has been treated with a suitable binder. The refractory molding base material is preferably present in a free-flowing form, so that it can be filled into a suitable mold and compacted there. The binder produces a firm cohesion between the particles of the molding base material, so that the casting mold obtains the required mechanical stability.

Molds must meet various requirements. During the casting process itself, they must first of all have sufficient stability and temperature resistance in order to receive the liquid metal in the mold formed from one or more casting molds. After the start of the solidification process, the mechanical stability of the mold is ensured by a solidified metal layer, which forms along the walls of the mold. The material of the casting mold must now decompose under the influence of the heat given off by the metal in such a way that it loses its mechanical strength, that is to say the cohesion between individual particles of the refractory material is removed. This is achieved, for example, by decomposing the binder under heat. After cooling, the solidified casting is shaken, ideally, the material of the casting molds again to a fine Sand breaks down, which can be poured out of the cavities of the metal mold.

For the production of casting molds both organic and inorganic binders can be used, the curing of which can be carried out in each case by cold or hot processes. Cold processes are processes which are carried out essentially at room temperature without heating the casting mold. The curing is usually carried out by a chemical reaction, which is triggered for example by the fact that a gas is passed as a catalyst through the mold to be cured. In hot processes, the molding material mixture is heated to a sufficiently high temperature after molding to expel, for example, the solvent contained in the binder or to initiate a chemical reaction by which the binder is cured, for example, by crosslinking.

At present, such organic binders are often used for the production of casting molds, in which the curing reaction is accelerated by a gaseous catalyst or cured by reaction with a gaseous hardener. These methods are referred to as "cold-box" methods.

An example of the production of molds using organic binders is the so-called Ashland cold box process. It is a two-component system. The first component consists of the solution of a polyol, usually a phenolic resin. The second component is the solution of a polyisocyanate. Thus, according to the US 3,409,579 A reacting the two components of the polyurethane binder by passing a gaseous tertiary amine through the mixture of molding base and binder after shaping. The curing reaction of polyurethane binders is a polyaddition, ie a reaction without elimination of By-products, such as water. Other advantages of this cold-box process include good productivity, dimensional accuracy of the molds, and good engineering properties such as the strength of the molds, the processing time of the mixture of mold base and binder, etc.

Hot-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 phenolic novolac resins. In the hot-box and warm-box processes, liquid resins are processed with a latent curing agent which is only effective at elevated temperatures to form a molding material mixture. In the croning process mold base materials, such as quartz, chrome ore, zirconium, etc., are coated at a temperature of about 100 to 160 ° C with a liquid at this temperature phenol novolac resin. Hexamethylenetetramine is added as a reaction partner for the subsequent curing. In the above-mentioned hot-curing technologies, the shaping and curing take place in heatable tools, which are heated to a temperature of up to 300 ° C.

Regardless of the curing mechanism, all organic systems have in common that they thermally decompose when the liquid metal is poured into the mold, releasing pollutants such as benzene, toluene, xylenes, phenol, formaldehyde and higher, sometimes unidentified cracking products. Although various measures have succeeded in minimizing these emissions, they can not be completely avoided with organic binders. Also in inorganic-organic hybrid systems which, as for example, when resole binder CO ₂ method used, contain a proportion of organic compounds, such undesirable emissions occur during casting of the metals.

In order to avoid the emission of decomposition products during the casting process, it is necessary to use binders which are based on inorganic materials or contain at most a very small proportion of organic compounds. Such binder systems have been known for some time.

A first group of inorganic binders are based on the use of water glass. For these binders, water glass forms the essential binder component. The water glass is mixed with a molding base material, for example sand, to form a molding material mixture and the molding material mixture is shaped into a shaped body. After shaping the molding material mixture, the water glass is cured to give the molded body the desired mechanical stability. Essentially, three methods have been developed.

According to a first method, water is removed from the water glass by heating the shaped body produced from the molding mixture after molding. This increases the viscosity of the water glass and it forms on the surface of the grains of sand, a hard, vitreous film, which ensures a stable connection of the grains of sand. This process is also referred to as a "thermosetting" process.

After a second process, carbon dioxide is passed through the molded body after molding. Due to the carbon dioxide, the sodium ions contained in the water glass are precipitated as sodium carbonate, which causes an immediate solidification of the molding. In the course of a post-curing, a further crosslinking of the highly hydrated silicon dioxide can take place. This process is also referred to as a "gas-curing" process.

Finally, according to a third method, an ester can be added to the water glass as hardener. Suitable esters are, for example, acetates of polyhydric alcohols, carbonates, such as propylene or butylene carbonate, or lactones such as butyrolactone. In the alkaline environment of the water glass, the esters are hydrolyzed, liberating the corresponding acid and causing gelling of the water glass. This variant is also referred to as a "self-curing" method.

Thus, binder systems have been developed which can be cured by the introduction of gases. Such a system is for example in the GB 782,205 described in which an alkali water glass is used as a binder, which can be cured by the introduction of CO ₂ . In the DE 199 25 167 describes an exothermic feeder composition containing an alkali metal silicate as a binder.

In the DE 10 2004 057 669 B3 describes the use of water glass as a binder for the production of molds and cores for metal casting. One or more sparingly soluble metal salts are added to the water glass, these metal salts being said to be so sparingly soluble that they do not react to any appreciable extent with the water glass at room temperature. The sparingly soluble metal salts may by themselves have a low solubility. But it is also possible to provide these metal salts with a coating to obtain the desired low solubility. In the examples, calcium fluoride, a mixture of aluminum fluoride and aluminum hydroxide, and a mixture of magnesium hydroxide and aluminum hydroxide are used as sparingly soluble metal salts. Surfactants or wetting agents may also be added to improve the flowability of a molding mixture made from sand and the binder composition.

Furthermore, binder systems have been developed which are self-curing at room temperature. Such, based on phosphoric acid and metal oxides system is eg in the US 5,582,232 described.

In the WO 97/049646 describes a binder composition which is suitable for the production of molding material mixtures for the production of molds and cores. This binder composition contains a silicate, a phosphate and a catalyst selected from the group consisting of aliphatic carbonates, cyclic alkylene carbonates, aliphatic carboxylic acid esters, cyclic carboxylic acid esters, phosphate esters and mixtures thereof. The phosphate used is a polyphosphate having an ionic unit of the formula ((PO ₃ ) _n O), where n corresponds to the average chain length and is between 3 and 45. The ratio silicate: phosphate can, based on the solids, be chosen between 97.5: 2.5 and 40: 60. Further, a surfactant may be added to the composition.

In the US 6,139,619 Another binder system based on a combination of water glass and a water-soluble amorphous inorganic phosphate glass will be described. The molar ratio SiO ₂ to M ₂ O of the water glass is between 0.6 and 2.0, wherein M is selected from the group of sodium, potassium, lithium and ammonium. In one embodiment, the binder system may also include a surfactant.

Finally, inorganic binder systems are known which are cured at higher temperatures, for example in a hot tool. Such thermosetting binder systems are for example from US 5,474,606 in which a binder system consisting of alkali water glass and aluminum silicate is described.

However, inorganic binders also have disadvantages compared to organic binders. For example, the casting molds made with water glass as a binder have a relatively low strength. This results in particular in the removal of the mold from the tool to problems because the mold can break. Good strengths at this time are especially important for the production of complicated, thin-walled molded parts and their safe handling. The reason for the low strength is primarily that the molds still contain residual water from the binder. Longer dwell times in the hot, closed tool only help to a limited extent because the water vapor can not escape sufficiently. In order to achieve a complete drying of the molds, is in the WO 98/06522 proposed to leave the molding material mixture after molding only in a tempered core box so long that forms a dimensionally stable and sustainable edge shell. After opening the core box, the mold is removed and then completely dried under the action of microwaves. However, the additional drying is complex, prolongs the production time of the molds and contributes, not least by the energy costs, significantly to the increase in the cost of the manufacturing process.

In order to ensure the flowability of a based on a water glass binder refractory molding mixture, relatively high amounts of water glass are required. However, this leads to a reduction in the refractoriness of the mold and a poor disintegration after the casting process. Thus, only a small proportion of the used molding sand can be attributed to the production of casting molds.

In the DE 29 09 107 A describes a process for the production of molds from granular and / or fibrous material with sodium or potassium silicate as a binder, wherein the surfactant mixture, preferably a surfactant, silicone oil or a silicone emulsion is added to the mixture.

In the WO 95/15229 For example, a binder composition for binding, for example, sand is described. Such a binder composition can be used in the manufacture of cores and molds. The binder composition comprises a mixture of an aqueous solution of an alkali metal silicate, ie water glass, and a water-soluble surface-active compound. When using the binder composition, an improvement in the yield strength of the molding material mixture is achieved.

In the EP 1 095 719 A2 a water-based binder system is described. The binder system contains water glass and a hygroscopic base and further an emulsion solution with 8 to 10% silicone oil, based on the amount of binder, wherein the silicone oil has a boiling point ≤ 250 ° C. The silicone emulsion is added to control the hygroscopic properties and to improve the flowability of the molding material mixture.

In the US 5,711,792 there is described a binder composition for making molds which comprises an inorganic binder consisting of an aqueous solution containing polyphosphate chains and / or borate ions as well as a water-soluble surface-active compound. The addition of the water-soluble surface-active compound increases the flowability of the molding material mixture.

Another weak point of the previously known inorganic binders is the low stability of the casting molds produced therewith against high humidity. For a storage of the molded body over a longer period, as usual with organic binders, not secured possible.

Molds made with water glass as a binder often show poor disintegration after metal casting. In particular, when the water glass has been cured by treatment with carbon dioxide, the binder can be vitrified under the influence of the hot metal, so that the mold is very hard and can be removed only with great effort from the casting. you has therefore tried to add to the molding material mixture of organic components which burn under the influence of the hot metal and facilitate the pore formation, a decay of the mold after casting.

In the DE 2 059 538 are described core and molding sand mixtures containing sodium silicate as a binder. To obtain improved disintegration of the mold after 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 metal silicate and a sufficient amount of a core or molding sand. In the examples it has been found that forms and nuclei containing glucose syrup have much better disintegration properties than forms and nuclei containing sucrose or pure dextrose.

In the WO 2006/024540 A2 A description is given of a molding material mixture for the production of casting molds for metal processing, which comprises at least one refractory molding base material and a water glass-based binder. Added to the binder is a portion of a particulate metal oxide selected from the group of silica, alumina, titania and zinc oxide. Particular preference is given to using precipitated silica or pyrogenic silica as the particulate metal oxide. Due to the particulate metal oxide, in particular silicon dioxide, a very easy disintegration of the mold after the metal casting is achieved, so that little effort to remove the mold is required.

By adding the particulate metal oxide to the molding material mixture, however, the flow properties of the molding mixture deteriorate significantly, so that there are difficulties in the production of the mold, a uniform degree of filling of the mold Model and thus to achieve a uniform density of the mold. In the worst case, therefore, can arise within the mold areas in which the molding material mixture is not compressed at all. These faulty areas are transferred to the casting so that it is unusable. As a further problem, uneven densification of the molding material mixture causes increased mold fragility. This complicates automation of the casting process, since the casting molds can only be transported badly without damage. It is therefore preferred to the refractory molding mixture to a proportion of a flake-form lubricant, such as graphite, mica or talc, which are intended to reduce the friction between individual grains of sand, so that more complex molds can be made without much difficulty.

With increasing complexity of the core geometries, however, constantly higher demands are placed on the flowability of the molding material mixture. If these problems were previously solved by the use of organic binders, so after the successful introduction of inorganic binders in the large-scale production of foundries also expressed the desire to make even for very complex molds suitable inorganic binder or refractory molding mixtures available. It must be ensured that cores with such a complex geometry can also be mass-produced industrially. Thus, it must be possible to comply with short process cycles during the production of the core, wherein the core must have a sufficiently high strength in all phases of its production, so that, for example, an automatic production is possible without the thin-walled areas of the core in particular suffer damage. The strength of the cores in all steps of the manufacturing process must be ensured even with fluctuating properties of the molding sand used. For the production of cores is not necessarily New sand used. Rather, the molding sand is worked up again after the casting and that Regenerat then used again for the production of molds and cores. During the regeneration of the molding sand, the majority of the binder remaining on the surface of the sand grains is removed again. This can be done mechanically, for example, by moving the sand so that the grains of sand rub against each other. The sand is then dedusted and reused. However, it is usually not possible to completely remove the binder layer. As a result of the mechanical action, the grain of sand can also be damaged, so that ultimately a compromise is made between the requirement to remove the binder as completely as possible and the requirement not to damage the grain of sand. It is therefore usually not possible to restore the properties of a new sand in the regeneration of used molding sand. In most cases, the regenerate has a rougher surface compared to new sand. This has an influence on the production or also on the flow properties of a molding material mixture produced from the regenerate.

The invention therefore an object of the invention to provide a molding material mixture for the production of molds for metal processing, which comprises at least one refractory molding material and a water glass based binder system, wherein the molding material mixture contains a proportion of a particulate metal oxide, which is selected from Group of silica, alumina, titania and zinc oxide, which allows the production of molds with very complex geometry and which may include, for example, thin-walled sections.

This object is achieved with a molding material mixture having the features of patent claim 1. Advantageous developments of Molding material mixture according to the invention are the subject of the dependent claims.

By adding at least one surface-active substance, the flowability of the molding material mixture can be significantly improved. In the manufacture of molds, a significantly higher density is achieved, i. the packing of the particles of the refractory base molding material is packed significantly denser. This increases the stability of the casting mold and even in geometrically demanding sections of the casting mold imperfections that cause deterioration of the casting pattern can be significantly reduced. As a further advantage, when using the molding material mixture according to the invention for the production of casting molds, the mechanical stress on the molding tools is substantially reduced. The abrasive action of the sand on the tools is minimized, reducing the need for maintenance. The increased flowability of the molding material mixture also makes it possible to reduce the shooting pressures at the core shooting machines, without having to accept a lower core compaction for this purpose.

Surprisingly, the addition of the surfactant also increased the hot strength of the core. After the production of a core, this can therefore be quickly removed from the mold, so that short production cycles are possible. This is also possible for cores comprising thin-walled sections, which are thus sensitive to mechanical stress.

The molding material mixture according to the invention is preferably cured after the shaping by removal of water and by initiation of a polycondensation. The surfactant surprisingly does not exert a negative effect on the hot strength of a molded article made from the molding compound mixture, although it was actually expected that the surfactant Material would interfere with the formation of the structure in the glassy film and thus rather leads to a decrease in the hot strength.

• einen feuerfesten Formgrundstoff;
• ein auf Wasserglas basierendes Bindemittel;
• einen Anteil eines teilchenförmigen Metalloxids, welches ausgewählt ist aus der Gruppe von Siliciumdioxid, Aluminiumoxid, Titanoxid und Zinkoxid;

erfindungsgemäß ist der Formstoffmischung ein Anteil zumindest eines oberflächenaktiven Stoffs zugesetzt.The molding material mixture according to the invention for the production of casting molds for metalworking comprises at least:

• a refractory molding base;
• a water glass based binder;
• a proportion of a particulate metal oxide selected from the group of silica, alumina, titania and zinc oxide;

According to the invention, a proportion of at least one surface-active substance is added to the molding material mixture.

As a refractory molding base material can be used for the production of molds usual materials. Suitable examples are quartz or zircon sand. Furthermore, fibrous refractory mold bases are suitable, such as chamotte fibers. Other suitable refractory mold bases are, for example, olivine, chrome ore sand, vermiculite.

Next synthetic molding materials, glass beads, glass granules or known under the name "Cerabeads ^®" or "Carboaccucast ^®" spherical ceramic mold raw materials can be used as refractory mold raw materials such as aluminum silicate hollow spheres (microspheres called.). These spherical ceramic mold bases contain as minerals, for example mullite, corundum, β-cristobalite in different proportions. They contain as essential proportions alumina and silica. Typical compositions contain, for example, Al ₂ O ₃ and SiO ₂ in approximately equal proportions. In addition, further constituents may be present in proportions of <10%, such as TiO ₂ , Fe ₂ O ₃ . The diameter of the spherical mold base materials is preferably less than 1000 μm, in particular less than 600 μm. Also suitable are synthetically prepared refractory mold base materials, such as, for example, mullite (xAl ₂ O ₃ .yI SiO ₂ , where x = 2 to 3, y = 1 to 2; ideal formula: Al ₂ SiO ₅ ). These artificial molding bases are not of natural origin and may have been subjected to a special molding process, such as in the production of aluminum silicate microbubbles, glass beads or spherical ceramic molding bases.

According to one embodiment, glass materials are used as refractory artificial mold bases. These are used in particular either as glass beads or as glass granules. Conventional glasses can be used as the glass, with glasses showing a high melting point being preferred. Suitable examples are glass beads and / or glass granules, which is made of glass breakage. Also suitable are borate glasses. The composition of such glasses is exemplified in the table below. Table: Composition of glasses component glass breakage borate glass SiO ₂ 50 - 80% 50 - 80% Al ₂ O ₃ 0 -15% 0 - 15% Fe ₂ O ₃ <2% <2% M ^II O 0 - 25% 0 - 25% M ^I ₂ O 5 - 25% 1 - 10% B ₂ O ₃ <15% Otherwise. <10% <10% M ^II : alkaline earth metal, eg Mg, Ca, Ba
M ^I : alkali metal, eg Na, K

In addition to the glasses listed in the table, however, it is also possible to use other glasses whose content of the abovementioned compounds lies outside the ranges mentioned. Likewise, it is also possible to use special glasses which, in addition to the oxides mentioned, also contain other elements or their oxides.

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

In casting experiments with aluminum, it has been found that, when using artificial mold raw 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 artificial mold base materials therefore makes it possible to produce smoother cast surfaces, wherein a complicated post-treatment by blasting is not required or at least to a considerably lesser extent.

It is not necessary to form the entire mold base from the artificial mold bases. The preferred level of artificial shaped bases is at least about 3 Wt .-%, particularly preferably at least 5 wt .-%, particularly preferably at least 10 wt .-%, preferably at least about 15 wt .-%, particularly preferably at least about 20 wt .-%, based on the total amount of refractory base molding material. The refractory molding base material preferably has a free-flowing state, so that the molding material mixture according to the invention can be processed in conventional core shooting machines.

As a further component, the molding material mixture according to the invention comprises a water glass-based binder. As a water glass while standard water glasses can be used, as they are already used as binders in molding material mixtures. These water glasses contain dissolved sodium or potassium silicates and can be prepared by dissolving glassy potassium and sodium silicates in water. The water glass preferably has a modulus SiO ₂ / M ₂ O in the range of 1.6 to 4.0, in particular 2.0 to 3.5, wherein M is sodium and / or potassium. The water glasses preferably have a solids content in the range of 30 to 60 wt .-%. The solids content refers to the amount of SiO ₂ and M ₂ O present in the water glass. The water glass-based binder may contain, in addition to water glass, other components acting as binders. However, pure water glass is preferably used as the binder. The solids content of the waterglass is preferably formed to be more than 80% by weight, more preferably at least 90% by weight, more preferably at least 95% by weight and according to another embodiment at least 98% by weight as alkali metal silicates. If the binder contains phosphates, then their proportion, calculated as P ₂ O ₅ and based on the solids content of the water glass, preferably less than 10 wt .-%, more preferably less than 5 wt .-% and according to another embodiment less than 2% by weight. In one embodiment, the binder does not contain phosphate.

Further, the molding material mixture contains a proportion of a particulate metal oxide selected from the group of silica, alumina, titania and zinc oxide. The average primary particle size of the particulate metal oxide may preferably be between 0.10 μm and 1 μm. However, because of the agglomeration of the primary particles, the particle size of the metal oxides is preferably less than 300 μm, preferably less than 200 μm, particularly preferably less than 100 μm. According to one embodiment, the particle size is more than 5 μm, according to a further embodiment more than 10 μm, according to a further embodiment more than 15 μm. The average particle size is preferably in the range from 5 to 90 .mu.m, particularly preferably from 10 to 80 .mu.m, and very particularly preferably in the range from 15 to 50 .mu.m. The particle size can be determined, for example, by sieve analysis. Particularly preferably, the sieve residue on a sieve with a mesh width of 63 μm is less than 10% by weight, preferably less than 8% by weight.

Particularly preferred as the particulate metal oxide silica is used, in which case synthetically produced amorphous silica is particularly preferred.

The particulate silica is not equivalent to the refractory molding base. For example, if quartz sand is used as a refractory base molding material, the silica sand can not simultaneously act as particulate silica. Quartz sand shows a very sharp reflex in the X-ray diffractogram, while amorphous silicon dioxide has a low degree of crystallization and therefore shows a much broader reflection in the X-ray diffractogram.

As the particulate silica, precipitated silica or fumed silica is preferably used. These silicas can be used both individually and in a mixture. Precipitated silica is obtained by reaction of an aqueous alkali metal silicate solution with mineral acids. The resulting precipitate is then separated, dried and ground. Fumed silicas are understood to mean silicic acids which are obtained by coagulation from the gas phase at high temperatures. The production of fumed silica can be carried out, for example, by flame hydrolysis of silicon tetrachloride or in an electric arc furnace by reduction of quartz sand with coke or anthracite to silicon monoxide gas with subsequent oxidation to silica. The pyrogenic silicas produced by the arc furnace process may still contain carbon. Precipitated silica and fumed silica are equally well suited for the molding material mixture according to the invention. These silicas are hereinafter referred to as "synthetic amorphous silica".

Pyrogenic silica is characterized by a very high specific surface area. Preferably, therefore, the particulate silica has a specific surface area of more than 10 m ² / g, according to another embodiment more than 15 m ² / g. In one embodiment, the particulate silica has a specific surface area of less than 40 m ² / g, in another embodiment less than 30 m ² / g. The specific surface area can be determined by nitrogen adsorption according to DIN 66131.

According to one embodiment, the amorphous uncompacted particulate silica has a bulk density of more than 100 m ³ / kg, according to another embodiment of more than 150 m ³ / kg. According to one embodiment, the amorphous uncompacted particulate silica has a bulk density of less than 500 m ² / g, in another embodiment a bulk density of less than 400 m ² / g.

The inventors believe that the strong alkaline water glass can react with the silanol groups located on the surface of the synthetic amorphous silica and that upon evaporation of the water, an intense bond between the silica and the then solid water glass is produced.

As an essential further component, the molding material mixture according to the invention contains a surface-active substance. A surface-active substance is understood as meaning a substance which can form a monomolecular layer on an aqueous surface, that is, for example, is capable of forming a membrane. Furthermore, the surface tension of water is lowered by a surfactant. Suitable surface-active substances are, for example, silicone oils.

Most preferably, the surfactant is a surfactant. Surfactants include a hydrophilic part and a hydrophobic part, which are so balanced in their properties that the surfactants in an aqueous phase, for example, form micelles or accumulate at the interface.

All classes of surfactants can be used per se in the molding material mixture according to the invention. In addition to anionic surfactants, nonionic surfactants, cationic surfactants and amphoteric surfactants are also suitable. Examples of nonionic surfactants are, for example, ethoxylated or propoxylated long-chain alcohols, amines or acids, such as fatty alcohol ethoxylates, alkylphenol ethoxylates, fatty amine ethoxylates, fatty acid ethoxylates, the corresponding propoxylates or else sugar surfactants, such as, for example, fatty alcohol-based polyglycosides. The fatty alcohols preferably comprise 8 to 20 carbon atoms. Suitable cationic surfactants are alkyl ammonium compounds and imidazolinium compounds.

Anionic surfactants are preferably used for the molding material mixture according to the invention. The anionic surfactant comprises as polar, hydrophilic group preferably a sulfate, sulfonate, phosphate or carboxylate group, with sulfate and phosphate groups being particularly preferred. If sulfate-containing anionic surfactants are used, preference is given to using the monoesters of sulfuric acid. If phosphate groups are used as the polar group of the anionic surfactant, the mono- and diesters of orthophosphoric acid are particularly preferred.

A common feature of the surfactants used in the molding material mixture according to the invention is that the non-polar hydrophobic portion is preferably formed by alkyl, aryl and / or aralkyl groups which preferably comprise more than 6 carbon atoms, particularly preferably 8 to 20 carbon atoms. The hydrophobic portion can have both linear chains and branched structures. Likewise, mixtures of different surfactants can be used.

Particularly preferred anionic surfactants are selected from the group of oleyl sulfate, stearyl sulfate, palmitylsulfate, myristyl sulfate, lauryl sulfate, decyl sulfate, octyl sulfate, 2-ethylhexyl sulfate, 2-ethyloctyl sulfate, 2-ethyldecyl sulfate, palmitoleylsulfate, linolylsulfate 2-Ethyl stearyl sulfonate, linolyl sulfonate, hexyl phosphate, 2-ethylhexyl phosphate, capryl phosphate, lauryl phosphate, myristyl phosphate, palmityl phosphate, palmitoleyl phosphate, oleyl phosphate, stearyl phosphate, poly (1,2-ethanediyl) phenol hydroxyphosphate, poly (1,2-ethanediyl) - Stearyl phosphate, and poly (1,2-ethanediyl) oleyl phosphate.

In the novel molding material mixture, the pure surface-active substance is preferably present in a proportion of 0.001 to 1% by weight, particularly preferably 0.01 to 0.5% by weight, based on the weight of the refractory molding base material. Often Such surfactants are commercially available as a 20 to 80% solution. In this case, especially the aqueous solutions of the surfactants are preferred.

In principle, the surface-active substance can be added both in dissolved form, for example in the binder, as a separate component or via a solid component which acts as a carrier material, for example in an additive, to the molding material mixture. Particularly preferably, the surface-active substance is dissolved in the binder.

According to a preferred embodiment, the refractory molding base material is at least partially formed by a regenerated refractory molding material. A regenerated refractory base molding material is understood to mean a refractory molding material that has already been used at least once for the production of casting molds and has subsequently been worked up again in order to be returned to the process of producing casting molds.

The improved flowability observed with the molding material mixture according to the invention is particularly important if the molding material mixture contains, instead of a pure refractory molding base material, for example a pure quartz sand, fractions of a regenerated refractory molding base material, for example a regenerated quartz sand. Regardless of the type of regeneration, regenerated refractory mold raw materials still contain residues of the binder which can not readily be removed from the surface of the grain. These residues give the regenerate a "dull character" and reduce the flowability of the molding material mixture. Because of this, in practice, complicated shapes can often be made only with new sand. However, the molding material mixture according to the invention has such a good flowability that even if the molding material mixture shares of regenerated refractory Form base material, the production of cores is possible with very complicated geometry. Surprisingly, it has been found that molds made of regenerated refractory molding base material also have a very high dimensional stability, in particular high resistance. This strength is significantly higher than in the case of molds which have been produced from a molding material mixture which contains, in addition to the refractory molding base material, water glass as binder and a finely divided amorphous silicon dioxide, but no surfactant, in particular no surfactant.

For the regeneration, all refractory mold base materials can be used per se, for example the abovementioned refractory molding base materials. Also, the binder with which the refractory molding base is contaminated prior to regeneration is not limited in itself. Both organic and inorganic binders may have been used in the prior use of the refractory mold base. So it can be used for regeneration both mixtures of different used refractory molding materials so pure varieties of used refractory mold bases. Preference is given to using regenerated refractory molding base materials which have been produced from only one type of used refractory molding base material, wherein the used refractory base molding material still contains residues of a preferably inorganic binder, particularly preferably a binder based on water glass, in particular a binder, which consists essentially of Water glass is constructed.

For the regeneration of the refractory molding base material, any desired methods can be used. Thus, the used refractory base molding material, for example, be mechanically regenerated, which after the casting on the used refractory mold base remaining binder residues or decomposition products are removed by rubbing. For this purpose, the sand can be moved, for example, so that the adhering binder residues are detached by collision of adjacent grains. The binder residues can then be separated by sieving and dedusting the regenerated refractory base molding material. Possibly. The used refractory base molding material can also be thermally pretreated to embrittle the binder film on the grains of the refractory base molding material, so that it can be easily abraded. In particular, if the used refractory base molding material still contains residues of water glass as a binder, the workup can also be done in such a way that the used refractory molding base material is washed with water.

The used refractory mold raw materials may also have been thermally regenerated. Such regeneration is common, for example, with used refractory mold bases that are contaminated with organic binder residues. When air enters, these organic binder residues burn. Possibly. a mechanical pre-cleaning can be carried out, so that already a proportion of the binder residues is removed.

It is particularly preferred to use a regenerated refractory molding base material obtained from a used water-glass contaminated refractory base molding material, whereby the used refractory molding base material has been thermally regenerated. In such a regeneration process, a used refractory molding base is provided which has a water glass based binder. The used foundry sand is then subjected to a thermal treatment, wherein the used refractory base molding material is heated to a temperature of at least 200 ° C.

Such a method is used, for example, in WO 2008/101668 A1 described.

The proportion of the regenerated refractory base molding material contained in the refractory base molding material in the molding material mixture can be chosen arbitrarily per se. The refractory base molding material may consist entirely of regenerated refractory base molding material. But it is also possible that the refractory base molding material contains only small amounts of regenerated refractory molding material. For example, the proportion of regenerated refractory molding base material between 10 and 90 wt .-%, according to another embodiment, between 20 and 80 wt .-%, based on the refractory molding material contained in the molding material mixture. But there are also larger or smaller shares possible.

According to one embodiment, at least one carbohydrate is added to the molding material mixture according to the invention. The addition of carbohydrates to the molding material mixture can be used to produce casting molds based on inorganic binders which have high strength both immediately after production and during prolonged storage. Further, after the casting of the metal, a casting having a very high surface quality is obtained, so that after the removal of the casting mold, only a slight finishing of the surface of the casting is required. As carbohydrates both mono- or disaccharides and higher molecular oligo- or polysaccharides can be used. The carbohydrates can be used both as a single compound and as a mixture of different carbohydrates. The purity of the carbohydrates used are not excessive requirements. It is sufficient if the carbohydrates, based on the dry weight, are present in a purity of more than 80% by weight, more preferably more than 90% by weight, especially preferably more than 95% by weight, in each case based on the dry weight. The monosaccharide units of the carbohydrates can be linked as desired. The carbohydrates preferably have a linear structure, for example an α- or β-glycosidic 1,4-linkage. The carbohydrates may also be wholly or partially 1,6-linked, such as. As the amylopectin, which has up to 6% α-1,6 bonds.

The amount of carbohydrate can be chosen relatively small in order to already observe a significant effect on the strength of the molds before casting or a significant improvement in the quality of the surface. The proportion of the carbohydrate, based on the refractory molding base material, in the range from 0.01 to 10 wt.%, Particularly preferably 0.02 to 5 wt.%, Particularly preferably 0.05 to 2.5 wt. % and most preferably selected in the range of 0.1 to 0.5 wt .-%. Even small amounts of carbohydrates in the range of about 0.1 wt .-% lead to significant effects.

According to a further embodiment, the carbohydrate may be present in underivatized form in the molding material mixture. Such carbohydrates can be favorably obtained from natural sources, such as plants, for example, cereals or potatoes. The molecular weight of such carbohydrates obtained from natural sources can be lowered for example by chemical or enzymatic hydrolysis, for example to improve the solubility in water. In addition to underivatized carbohydrates, which are thus composed only of carbon, oxygen and hydrogen, but also derivatized carbohydrates can be used in which, for example, a part or all hydroxy groups are etherified with, for example, alkyl groups. Suitable derivatized carbohydrates are, for example, ethyl cellulose or carboxymethyl cellulose.

In itself, even low molecular weight hydrocarbons, such as mono- or disaccharides can be used. Examples are glucose or sucrose. However, the advantageous effects are observed in particular when using oligosaccharides or polysaccharides. It is therefore particularly preferred to use an oligosaccharide or polysaccharide as the carbohydrate.

In this case, it is preferred that the oligosaccharide or polysaccharide have a molecular weight in the range from 1000 to 100,000 g / mol, preferably 2,000 and 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 mold is observed, so that the mold can be easily removed from the mold during manufacture and transported. Even with prolonged storage, the mold shows a very good strength, so that even for a series production of castings required storage of the molds, even over several days in the event of access of humidity, readily possible. Also, the resistance to exposure to water, such as is inevitable when applying a size to the casting mold, is very good.

Preferably, the polysaccharide is composed of glucose units, these being particularly preferably linked to α- or β-glycosidic 1,4. However, it is also possible to use carbohydrate compounds which contain other monosaccharides in addition to glucose, such as galactose or fructose, as an inventive additive. Examples of suitable carbohydrates are lactose (α- or β-1,4-linked disaccharide of galactose and glucose) and sucrose (disaccharide of α-glucose and β-fructose).

The carbohydrate is particularly preferably selected from the group of cellulose, starch and dextrins and derivatives of these carbohydrates. Suitable derivatives are, for example, derivatives completely or partially etherified with alkyl groups. It can but also other derivatizations are carried out, for example esterifications with inorganic or organic acids.

A further optimization of the stability of the casting mold and the surface of the casting can be achieved if special carbohydrates and in this case particularly preferred starches, dextrins (hydrolyzate product of the starches) and their derivatives are used as additive for the molding material mixture. As starches, especially the naturally occurring starches, such as potato, corn, rice, peas, banana, horse chestnut or wheat starch can be used. But it is also possible to use modified starches, such as swelling starch, low-boiling starch, oxidized starch, citrate starch, acetate starch, starch ethers, starch esters or starch phosphates. There is no limit to the choice of strength per se. The starch may, 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 of potato dextrin, maize dextrin, yellow dextrin, white dextrin, borax dextrin, cyclodextrin and maltodextrin.

In particular, in the production of molds with very thin-walled sections, the molding material mixture preferably additionally comprises a phosphorus-containing compound. In this case, both organic and inorganic phosphorus compounds can be used per se. In order to trigger any unwanted side reactions during metal casting is also preferred that the phosphorus in the phosphorus-containing compounds is preferably present in the oxidation state V. The addition of phosphorus-containing compounds, the stability of the mold can be further increased. This is particularly important when the metal casting the liquid metal meets on an inclined surface and because of the high metallostatic pressure exerts a high erosion effect or can lead to deformations in particular of thin-walled sections of the casting mold.

The phosphorus-containing compound is preferably present in the form of a phosphate or phosphorus oxide. The phosphate can be present as alkali metal or as alkaline earth metal phosphate, with the sodium salts being particularly preferred. As such, ammonium phosphates or phosphates of other metal ions can also be used. However, the alkali metal or alkaline earth metal phosphates mentioned as being preferred are readily available and are available inexpensively in amounts which are in themselves arbitrary.

If the phosphorus-containing compound is added to the molding material mixture in the form of a phosphorus oxide, the phosphorus oxide is preferably present in the form of phosphorus pentoxide. However, it can also find Phosphortri- and Phosphortetroxid use.

According to a further embodiment, the phosphorus-containing compound in the form of the salts of the fluorophosphoric acids may be added to the molding material mixture. Particularly preferred in this case are the salts of monofluorophosphoric acid. Especially preferred is the sodium salt.

According to a preferred embodiment, organic phosphates are added to the molding material mixture as the phosphorus-containing compound. Preference is given here to alkyl or aryl phosphates. The alkyl groups preferably comprise 1 to 10 carbon atoms and may be straight-chain or branched. The aryl groups preferably comprise 6 to 18 carbon atoms, wherein the aryl groups may also be substituted by alkyl groups. Particularly preferred are phosphate compounds derived from monomeric or polymeric carbohydrates such as glucose, cellulose or starch. The use of a phosphorus-containing organic component as an additive is advantageous in two respects. To the One can be achieved by the phosphorus content, the necessary thermal stability of the mold and on the other hand, the surface quality of the corresponding casting is positively influenced by the organic content.

As phosphates, both orthophosphates and polyphosphates, pyrophosphates or metaphosphates can be used. The phosphates can be prepared, for example, by neutralization of the corresponding acids with a corresponding base, for example an alkali metal or an alkaline earth metal base, such as NaOH, whereby not necessarily all negative charges of the phosphate ion must be saturated by metal ions. Both the metal phosphates and the metal hydrogen phosphates and the metal dihydrogen phosphates can be used, such as Na ₃ PO ₄ , Na ₂ HPO ₄ and NaH ₂ PO ₄ . Likewise, the anhydrous phosphates as well as hydrates of the phosphates can be used. The phosphates can be introduced into the molding material mixture both in crystalline and in amorphous form.

Polyphosphates are understood in particular to be linear phosphates which comprise more than one phosphorus atom, the phosphorus atoms being connected in each case via oxygen bridges. Polyphosphates are obtained by condensation of orthophosphate ions with elimination of water, so that a linear chain of PO ₄ tetrahedra is attached, which are each connected via corners. Polyphosphates have the general formula (O (PO ₃ ) _n ) ^{(n + 2) -} , where n corresponds to the chain length. A polyphosphate may comprise up to several hundred PO ₄ tetrahedra. However, polyphosphates with shorter chain lengths are preferably used. N preferably has values of 2 to 100, particularly preferably 5 to 50. It is also possible to use higher-condensed polyphosphates, ie polyphosphates in which the PO ₄ tetrahedra is over more than two corners are connected together and therefore show a polymerization in two or three dimensions.

Metaphosphates are understood to mean cyclic structures composed of PO ₄ tetrahedra connected by vertices. Metaphosphates have the general formula ((PO ₃ ) _n ) ^n- , where n is at least 3. Preferably, n has values of 3 to 10.

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

The preferred proportion of the phosphorus-containing compound, based on the refractory molding material, is between 0.05 and 1.0 wt .-%. With a proportion of less than 0.05 wt .-%, no significant influence on the dimensional stability of the mold to determine. If the proportion of the phosphate exceeds 1.0% by weight, the hot strength of the casting mold sharply decreases. Preferably, the proportion of phosphorus-containing compound is selected between 0.10 and 0.5 wt .-%. The phosphorus-containing compound preferably contains between 0.5 and 90% by weight of phosphorus, calculated as P ₂ O ₅ . If inorganic phosphorus compounds are used, they preferably contain from 40 to 90% by weight, particularly preferably from 50 to 80% by weight, of phosphorus, calculated as P ₂ O ₅ . If organic phosphorus compounds are used, these preferably contain from 0.5 to 30% by weight, particularly preferably from 1 to 20% by weight, of phosphorus, calculated as P ₂ O ₅ .

The phosphorus-containing compound may be added per se in solid or dissolved form of the molding material mixture. The phosphorus-containing compound is preferably added to the molding material mixture as a solid. If the phosphorus-containing compound is added in dissolved form, water is preferred as the solvent.

The molding material mixture according to the invention represents an intensive mixture of at least the constituents mentioned. In this case, the particles of the refractory molding material are preferably coated with a layer of the binder. By evaporation of the water present in the binder (about 40-70 wt .-%, based on the weight of the binder), a firm cohesion between the particles of the refractory base molding material can then be achieved.

The binder, i. the water glass as well as the particulate metal oxide, in particular synthetic amorphous silica, and the surface-active substance are preferably present in the molding material mixture in an amount of less than 20% by weight, particularly preferably less than 15% by weight. The proportion of the binder refers to the solids content of the binder. If massive molding base 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 .-%, more preferably less than 5 wt .-%. If refractory mold bases are used which have a low density, such as the hollow microspheres described above, the proportion of binder increases accordingly. In order to obtain a cohesion of the grains of the refractory base molding material, the proportion of the binder according to an embodiment greater than 1 wt .-%, according to a further embodiment, greater than 1.5 wt .-% is selected.

The ratio of water glass to particulate metal oxide, especially synthetic amorphous silica, can be varied within wide ranges. This offers the advantage of improving the initial strength of the casting mold, ie the strength immediately after removal from the hot mold, and the moisture resistance, without the final strengths, ie the strengths after cooling of the casting mold, over one Water glass binders without amorphous silicon dioxide to influence significantly. 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 easily transport these after the production of the casting mold or to assemble them with other casting molds. On the other hand, the final strength after curing should not be too high to avoid difficulties in binder decay after casting, ie the molding base should be easily removed from mold cavities after casting.

The particulate metal oxide, in particular the synthetic amorphous silicon dioxide, based on the total weight of the binder, preferably in a proportion of 2 to 80 wt .-% in the binder, preferably between 3 and 60 wt .-%, particularly preferably between 4 and 50% by weight.

The molding material contained in the molding material mixture according to the invention may contain at least a proportion of hollow microspheres in one embodiment of the invention. The diameter of the hollow microspheres is usually in the range of 5 to 500 μm, preferably in the range of 10 to 350 μm, and the thickness of the shell is usually in the range of 5 to 15% of the diameter of the microspheres. These microspheres have a very low specific gravity, so that the molds produced using hollow microspheres have a low weight. Particularly advantageous is the insulating effect of the hollow microspheres. The hollow microspheres are therefore used in particular for the production of molds, if they are to have an increased insulating effect. Such casting molds are, for example, the feeders already described in the introduction, which act as a compensation reservoir and contain liquid metal, wherein the metal should be kept in a liquid state until the metal filled into the mold cavity is frozen. Another application of casting molds containing hollow microspheres are, for example, sections of a casting mold which 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 prematurely solidify and thus clog the paths within the casting mold.

If hollow microspheres are used, the binder, due to the low density of these hollow microspheres, is preferably used in a proportion in the range of preferably less than 20% by weight, particularly preferably in the range from 10 to 18% by weight. The values relate to the solids content of the binder.

The hollow microspheres are preferably made of an aluminum silicate. These aluminum silicate microbubbles preferably have an aluminum oxide content of more than 20% by weight, but may also have a content of more than 40% by weight. Such hollow microspheres are obtained, for example, from Omega Minerals Germany GmbH, Norderstedt, under the designations 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 about 43% in the trade. Corresponding products are available from the PQ Corporation (USA) under the name "Extendospheres ^®".

According to a further embodiment, hollow microspheres are used as the refractory molding base, which are made of glass.

According to a particularly preferred embodiment, the hollow microspheres consist of a borosilicate glass. The borosilicate glass has a proportion of boron, calculated as B ₂ O ₃ , of more as 3% by weight. The proportion of hollow microspheres is preferably chosen to be less than 20% by weight, based on the molding material mixture. When using borosilicate glass microballoons, a small proportion is preferably selected. This is preferably less than 5 wt .-%, preferably less than 3 wt .-%, and is more preferably in the range of 0.01 to 2 wt .-%.

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

It is also possible to form the molding material mixture as an exothermic molding material mixture, which is 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 form 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 are, for example, aluminum or magnesium. Suitable oxidizing agents are, for example, iron oxide or potassium nitrate.

According to a further embodiment, the molding material mixture according to the invention may contain, in addition to the surface-active substance, a proportion of lubricants, for example platelet-shaped lubricants, in particular graphite, MoS ₂ , talc and / or pyrophillite. The amount of added lubricant, such as graphite, is preferably 0.05 wt .-% to 1 wt .-%, based on the molding material.

In addition to the constituents mentioned, the molding material mixture according to the invention may also comprise further additives. For example, internal release agents may be added which enhance the release facilitate the molds from the mold. Suitable internal release agents are, for example, 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.

Thus, in one embodiment, the molding material mixture according to the invention contains an organic additive which has a melting point in the range from 40 to 180.degree. C., preferably from 50 to 175.degree. C., ie is solid at room temperature. Organic additives are understood to be compounds whose molecular skeleton is composed predominantly of carbon atoms, that is, for example, organic polymers. By adding the organic additives, the quality of the surface of the casting can be further improved. The mechanism of action of the organic additives has not been clarified. Without wishing to be bound by this theory, however, the inventors assume that at least some of the organic additives are burned during the casting process, thereby creating a thin gas cushion between liquid metal and the molding base material forming the wall of the casting mold and thus a reaction between liquid metal and water Mold base is prevented. Further, the inventors believe that some of the organic additives under the reducing atmosphere of the casting form a thin layer of so-called lustrous carbon, which also prevents reaction between metal and mold base. As a further advantageous effect, an increase in the strength of the casting mold after curing can be achieved by adding the organic additives.

The organic additives are preferably used in an amount of 0.01 to 1.5% by weight, more preferably 0.05 to 1.3% by weight, particularly preferably 0.1 to 1.0% by weight, respectively based on the molding material added.

It has been found that an improvement of the surface of the casting is achieved with very different organic additives can be. Suitable organic additives are, for example, phenol-formaldehyde resins, such as novolaks, epoxy resins such as bisphenol A epoxy resins, bisphenol F epoxy resins or epoxidized novolacs, polyols such as polyethylene glycols or polypropylene glycols, polyolefins such as polyethylene or polypropylene, copolymers 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 gum rosin, 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 mono- to trivalent metals. The organic additives can be contained both as a pure substance, as well as a mixture of different organic compounds.

According to a further embodiment, the molding material mixture according to the invention contains a proportion of at least one silane. Suitable silanes are, 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-amino propyltrimethoxysilane.

Based on the particulate metal oxide typically about 5 to 50% silane are used, preferably about 7 to 45%, more preferably about 10 to 40%.

Despite the achievable with the binder according to the invention high strengths show the casting molds according to the invention, in particular cores and Forms, after casting surprisingly good decay, especially in aluminum casting. However, the use of the moldings produced from the molding material mixture according to the invention is not limited to light metal casting. The molds are generally suitable for casting metals. Such metals are, for example, non-ferrous metals, such as brass or bronze, and ferrous metals.

• Herstellen der oben beschriebenen Formstoffmischung;
• Formen der Formstoffmischung;
• Aushärten der geformten Formstoffmischung, indem die Formstoffmischung erwärmt wird, wobei die ausgehärtete Gießform erhalten wird.

The invention further relates to a method for the production of molds for metal processing, wherein the molding material mixture according to the invention is used. The method according to the invention comprises the steps:

• Producing the above-described molding material mixture;
• Forms of the molding material mixture;
• Curing the molded molding material mixture by heating the molding material mixture to obtain the cured mold.

In the production of the molding material mixture according to the invention, the procedure is generally such that initially the refractory molding base material is introduced and then the binder is added with stirring.

As already stated in the explanation of the molding material mixture according to the invention, the refractory molding base material can be formed at least partially from a regenerated used refractory molding material.

It is particularly preferred to use a regenerated refractory molding base made from a used refractory molding base to which residuals of water glass adhesive are attached. More preferably, a regenerated refractory molding material is used, which consists of a used refractory molding material has been prepared, the binder residues of water glass adhere and which has been thermally regenerated, wherein for the regeneration preferably a method is used, as in the WO 2008/101668 A1 is described. For this purpose, a used refractory molding base material is thermally regenerated, which is associated with a water glass based binder to which a particulate metal oxide is added, in particular an amorphous silica, for example fumed silica.

With the method according to the invention, it is thus possible to circulate the refractory base molding material during the production of casting molds and the subsequent casting, wherein only portions of the refractory molding base material which are separated by sieving during regeneration are replaced by new refractory base molding material.

To the refractory mold base may be added the water glass as well as the particulate metal oxide, especially the synthetic amorphous silica, and the surfactant per se in any order. The surfactant can be added in bulk or as a solution or emulsion, preferably water being used as the solvent. Preference is given to aqueous emulsions or solutions of the surfactant. In the production of the molding material mixture, the procedure is preferably such that no excessive foaming occurs. This can be achieved on the one hand by the selection of the surfactant. On the other hand, the addition of defoamers is possible, if necessary.

The other additives described above may be added per se in any form of the molding material mixture. They can be added individually or as a mixture. They can be added in the form of a solid, but also in the form of solutions, pastes or dispersions. If the addition occurs 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 solvent or dispersion medium for the additives.

According to a preferred embodiment, 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. The solid component may further contain, for example, the phosphate and optionally a carbohydrate. The surfactant is preferably added to the liquid component.

In the preparation of the molding material mixture, the refractory molding base material is placed in a mixer and then preferably first the solid component (s) of the binder is added and mixed with the refractory molding base material. The mixing time is chosen so that an intimate mixing of refractory base molding material and solid binder component takes place. The mixing time depends on the amount of the molding material mixture to be produced and on the mixing unit used. Preferably, the mixing time is selected between 1 and 5 minutes. Preferably, with further agitation of the mixture, the liquid component of the binder is then added and then the mixture is further mixed until a uniform layer of the binder has formed on the grains of the refractory base molding material. Again, the mixing time of the amount of the molding mixture to be produced as well as the mixing unit used depends. Preferably, the duration for the mixing process is selected between 1 and 5 minutes. A liquid component is understood to mean both a mixture of different liquid components and the totality of all liquid individual components, the latter also being able to be added individually. Likewise, under a solid component, both the mixture single or all of the solid components described above as well as the totality of all solid individual components understood, the latter can be added together or even successively to the molding material mixture.

According to another embodiment, the liquid component of the binder may also first be added to the refractory base molding material and only then be fed to the solid component of the mixture. According to a further embodiment, first 0.05 to 0.3% of water, based on the weight of the molding material, is added to the refractory molding material and only then the solid and liquid components of the binder are added. In this embodiment, a surprising positive effect on the processing time of the molding material mixture can be achieved. The inventors believe that the dehydrating effect of the solid components of the binder is thus reduced and the curing process is thereby delayed.

The molding material mixture is then brought into the desired shape. In this case, customary methods are used for the shaping. For example, the molding material mixture can be shot by means of a core shooting machine with the aid of compressed air into the mold. The molding material mixture is then cured by supplying heat in order to evaporate the water contained in the binder. The heating can be done for example in the mold. It is possible to fully cure the mold already in the mold. But it is also possible to cure the mold only in its edge region, so that it has sufficient strength to be removed from the mold can. The casting mold can then be completely cured by removing further water. This can be done for example in an oven. The dehydration For example, can be done by the water is evaporated at reduced pressure.

The curing of the molds can be accelerated by blowing heated air into the mold. In this embodiment of the method, a rapid removal of the water contained in the binder is achieved, whereby the mold is solidified in suitable periods for industrial use. The temperature of the injected 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 to cure the mold in periods suitable for industrial use. The periods depend on the size of the molds produced. It is desirable to cure in less than 5 minutes, preferably less than 2 minutes. For very large molds, however, longer periods may be required.

The removal of the water from the molding material mixture can also be carried out in such a way that the heating of the molding material mixture is effected by irradiation of microwaves. However, the irradiation of the microwaves is preferably carried out after the casting mold has been removed from the molding tool. For this purpose, however, the casting mold must already have sufficient strength. As already explained, this can be achieved, for example, by curing at least one outer shell of the casting mold already in the molding tool.

As already described, the molding material mixture may also comprise further organic additives. The addition of these other organic additives can be done per se at any time during the preparation of the molding material mixture. The addition of the organic additive can be carried out in bulk or in the form of a solution.

Water-soluble organic additives can be used in the form of an aqueous solution. If the organic additives are soluble in the binder and are stable in storage over several months in the binder, they can also be dissolved in the binder and thus added to the mold base together with it. Water-insoluble additives may be used in the form of a dispersion or a paste. The dispersions or pastes preferably contain water as the dispersing medium. As such, 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 preferably used.

Preferably, the addition of the organic additives is carried out as a powder or as a short fiber, wherein the average particle size or the fiber length is preferably selected so that it does not exceed the size of the refractory molding base particles. Particularly preferably, the organic additives can be sieved through a sieve with the mesh size of about 0.3 mm. In order to reduce the number of components added to the refractory molding base, the particulate metal oxide and the organic additive (s) are preferably not added separately to the molding sand but are premixed.

Contains the molding material silanes or siloxanes, they are usually added in the form that they are incorporated in advance in the binder. The silanes or siloxanes may also be added to the molding base as a separate component. However, it is particularly advantageous to silanize the particulate metal oxide, ie to mix the metal oxide with the silane or siloxane, so that its surface is provided with a thin silane or siloxane layer. If the particulate metal oxide pretreated in this way is used, increased strengths are found compared with the untreated metal oxide and improved resistance to high humidity. If, as described, an organic additive is added to the molding material mixture or the particulate metal oxide, it is expedient to do so before the silanization.

The inventive method is in itself suitable for the production of all casting molds customary for metal casting, that is to say, for example, of cores and molds. It is also particularly advantageous to produce casting molds which comprise very thin-walled sections or complex deflections. In particular, when adding insulating refractory molding base material or when adding exothermic materials to the molding material mixture according to the invention, the inventive method for the production of feeders is.

The molds produced from the molding material mixture according to the invention or with the inventive method have a high strength immediately after the production, without the strength of the molds after curing is so high that difficulties after the production of the casting occur during removal of the mold. Furthermore, these molds have a high stability at elevated humidity, i. Surprisingly, the casting molds can also be stored without problems for a long time. As a particular advantage, the mold has a very high stability under mechanical stress, so that even thin-walled sections of the mold or sections with very complex geometry can be realized without these being deformed by the metallostatic pressure during the casting process. Another object of the invention is therefore a mold, which was obtained by the inventive method described above.

The casting mold according to the invention is generally suitable for metal casting, in particular light metal casting. Particularly advantageous results are obtained in aluminum casting. According to a preferred Embodiment while the refractory mold base material is recycled by a mold prepared from the molding material mixture according to the invention is worked up again after the casting, whereby a regenerated refractory molding material is obtained, which can then be used again for the production of a molding material mixture, from which then produced again casting molds become.

Particular preference is given to the regeneration of the used refractory molding base material by a thermal process.

According to one embodiment, there is provided a used refractory molding base material having a water glass based binder to which a particulate metal oxide, in particular amorphous silica, is added. The used refractory base molding material is subjected to a thermal treatment, wherein the used refractory base molding material is heated to a temperature of at least 200 ° C.

The entire volume of the used refractory base molding material should reach this temperature. The duration for which the used refractory base molding material is subjected to a thermal treatment depends, for example, on the amount of the used refractory base molding material or also on the amount of the water glass-containing binder which adheres to the used refractory base molding material. The duration of treatment also depends on whether the mold used in the previously performed casting has already largely crumbled to a sand or even larger fragments or aggregates includes. The progress of the thermal regeneration can be determined for example by sampling. The sample removed should disintegrate to loose sand with slight mechanical impact, as occurs, for example, when shaking the mold. The cohesion between the grains of the refractory base molding material should be weakened so far that the thermally treated refractory base molding material can be sieving sieve easily to separate larger aggregates or impurities. The duration of the thermal treatment can be selected, for example, between 5 minutes and 8 hours. However, longer or shorter treatment times are also possible. The progress of the thermal regeneration can be followed, for example, by determining the acid consumption on samples of the thermally treated foundry sand. Foundry sands, such as chromite sand, can even have basic properties, so that foundry sand influences acid consumption. However, the relative acid consumption can be used as a parameter for the progress of the regeneration. For this purpose, first the acid consumption of the intended for the reprocessing used refractory molding base material is determined. To observe the regeneration, the acid consumption of the regenerated refractory base molding material is determined and related to the acid consumption of the used refractory base molding material. As a result of the thermal treatment carried out in the method according to the invention, the acid consumption for the regenerated refractory molding material preferably decreases by at least 10%. The thermal treatment is preferably continued until the acid consumption has decreased by at least 20%, in particular at least 40%, particularly preferably at least 60% and especially preferably at least 80%, compared to the acid consumption of the used refractory molding material. The acid consumption is given in ml of acid consumed per 50 g of the refractory base molding material, the determination with 0.1 N hydrochloric acid being determined analogously to the method specified in VDG Merkblatt P 28 (May 1979). The method for determining the acid consumption is detailed in the examples. More details of the process for the regeneration of used refractory molding materials are in WO 2008/101668 A1 disclosed.

Fig. 1:

eine Darstellung des zur Prüfung der Eigenschaften von Formstoffmischungen verwendete Einlasskanalkerns.

The invention will be explained in more detail below with reference to examples and with reference to the accompanying figures. Showing:

Fig. 1:

a representation of the inlet channel core used to test the properties of molding material mixtures.

Measurement methods used:

AFS number: The AFS number was determined in accordance with the VDG leaflet P 27 (Verein Deutscher Gießereifachleute, Düsseldorf, October 1999).

Average grain size: The mean grain size was determined in accordance with VDG leaflet P 27 (Verein Deutscher Gießereifachleute, Düsseldorf, October 1999).

Acid consumption: Acid consumption was determined analogously to the instructions in the VDG leaflet P 28 (Association of German Foundry Experts, Düsseldorf, May 1979).

• Salzsäure 0,1 n
• Natronlauge 0,1 n
• Methylorange 0,1 %
• 250 ml Kunststoffflaschen (Polyethylen)
• geeichte Vollpipetten

Reagents and devices:

• Hydrochloric acid 0.1 n
• Sodium hydroxide solution 0.1 n
• Methyl orange 0.1%
• 250 ml plastic bottles (polyethylene)
• calibrated volumetric pipettes

• Sofern der Gießereisand noch größere Aggregate von gebundenem Gießereisand enthält, werden diese Aggregate beispielsweise mit Hilfe eines Hammers zerkleinert und der Gießereisand durch ein Sieb mit einer Maschenweite von 1 mm gesiebt.

Implementation of the provision:

• If the foundry sand contains even larger aggregates of bonded foundry sand, these aggregates are crushed, for example by means of a hammer and the foundry sand is sieved through a sieve with a mesh size of 1 mm.

50 ml of distilled water and 50 ml of 0.1 N hydrochloric acid are pipetted into the plastic bottle. Subsequently, using a funnel, 50.0 g of the foundry sand to be examined are added to the bottle and sealed. For the first 5 minutes, shake vigorously for 5 seconds per minute, then every 30 minutes for 5 seconds. After each shaking, the sand is allowed to settle for a few seconds and rinsed by briefly swiveling the sand adhering to the bottle wall. During the breaks, the bottle stops at room temperature. After 3 hours, filter through a medium filter (white tape, diameter 12.5 cm). The funnel and the beaker used for collection must be dry. The first ml of the filtrate are discarded. Pipette 50 ml of the filtrate into a 300 ml titration flask and add 3 drops of methyl orange as indicator. It is then titrated from red to yellow with a 0.1 N sodium hydroxide solution.

Calculation: $$\left(\mathrm{25}.\mathrm{0}\mathrm{ml\; of\; salt}\ddot{\mathrm{a}}\mathrm{ure}\mathrm{0}.\mathrm{1}\mathrm{n}-\mathrm{consumed\; ml\; of\; sodium\; hydroxide\; solution}\mathrm{0}.\mathrm{1}\mathrm{n}\right)\times \mathrm{2}=\mathrm{ml\; S}\ddot{\mathrm{a}}\mathrm{ureverbrauch}/\mathrm{50}\mathrm{g\; foundry\; sand}$$

Determination of bulk density

A graduated cylinder cut off at the 1000 ml mark is weighed. Then, the sample to be examined is filled by means of a Pulvertrichters so in a train in the measuring cylinder that forms above the end of the measuring cylinder, a pour cone. The pour cone is removed by means of a ruler, which is led over the opening of the measuring cylinder, and the filled measuring cylinder is weighed again. The difference corresponds to the bulk density

example 1

Influence of surfactants on the strength and density of molds.

1. Preparation and testing of the molding material mixture

For the examination of the molding material mixture were in Fig. 1 shown inlet channel cores made.

• Die in Tabelle 1 aufgeführten Komponenten wurden in einem Mischer gemischt. Dazu wurde zunächst der Quarzsand vorgelegt und unter Rühren das Wasserglas und ggf. der oberflächenaktive Stoff zugegeben. Als Wasserglas wurde ein Natriumwasserglas verwendet, das Anteile an Kalium aufwies. Das Modul SiO₂ : M₂O des Wasserglases betrug ca. 2,2, wobei M die Summe aus Natrium und Kalium angibt. Nachdem die Mischung für eine Minute gerührt worden war, wurde ggf. das amorphe Siliciumdioxid unter weiterem Rühren zugegeben. Die Mischung wurde anschließend noch für eine weitere Minute gerührt.

The composition of the molding material mixture is given in Table 1. The inlet channel cores were produced as follows:

• The components listed in Table 1 were mixed in a mixer. For this purpose, initially the quartz sand was introduced and added with stirring, the water glass and optionally the surfactant. As a water glass, a sodium water glass was used, which had proportions of potassium. The modulus SiO ₂ : M ₂ O of the water glass was about 2.2, where M is the sum of sodium and potassium. After stirring the mixture for one minute, the amorphous silica was added, if necessary, with further stirring. The mixture was then stirred for an additional 1 minute.

The molding material mixtures were transferred to the storage bin of a core shooter 6.5 L from Röperwerk - Gießereimaschinen GmbH, Viersen, DE, whose mold was heated to 180.degree.

The molding material mixtures were introduced into the mold by means of compressed air (2 bar) and remained in the mold for a further 50 seconds.

To accelerate the curing of the mixtures, hot air (3 bar, 150 ° C on entering the mold) was passed through the mold during the last 20 seconds.

The mold was opened and the inlet channel removed.

To determine the bending strengths, the test specimens were placed in a Georg Fischer strength tester equipped with a 3-point bending device (DISA Industrie AG, Schaffhausen, CH) and the force was measured, which led to the breakage of the test bars.

The flexural strengths were measured according to the following scheme:
- 10 seconds after removal (hot strength)
- 1 hour after removal (cold strength)
- 3 hours storage of the cooled cores in the climatic chamber at 30 ° C and 75% relative humidity. <u> Table 1 </ u> Composition of the molding material mixtures Quartz sand H32 Alkali water glass Amorphous silica Oberflächenakt. material 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) inventively 1.5 100 GT 2.0 ^a) 0.5 ^b) 0.05 ^d) inventively 1.6 100 GT 2.0 ^a) 0.5 ^b) 0.05 ^e) erfingdungsgemäß 1.7 100 GT 2.0 ^a) 0.5 ^b) 0.05 ^f) inventively 1.8 100 GT 2.0 ^a) 0.5 ^b) 0.05 ^g) inventively 1.9 100 GT 2.0 ^a) 0.5 ^b) 0.10 ^h) inventively 1.10 100 GT Regenerat ⁱ⁾ 2.0 ^a) 0.5 ^b) Comparison, not according to the invention 1.11 100 GT Regenerat ⁱ⁾ 2.0 ^a) 0.5 ^b) 0.05 ^e) inventively ^a ) alkali water glass with modulus SiO ₂ : M ₂ O of approx. 2.2; based on the entire water glass
^b) Elkem Microsilica 971 ^® (fumed silica; production in an arc furnace); Bulk density 300 - 450 kg / m ³ (manufacturer)
^c) Melpers ^® 0030 (polycarboxylate in water, Fa. BASF)
^d) Melpers ^® VP 4547/240 L (modified polyacrylate in water, Fa. BASF)
^e) Texapon ^® EHS (2-ethylhexyl sulfate in water, Fa. Cognis)
^f) Glukopon ^® 225 DK (polyglucoside in water, Fa. Cognis)
^g) Texapon ^® 842 (sodium octyl sulfate in water, Fa. Lakeland)
^h) Castament ^® FS 60 (modified Carboxylatether, solid, Fa. BASF)
ⁱ ) thermally processed used sand of the mixture 1.6 (90 minutes, 650 ° C)

The results of the strength tests are summarized in Table 2. <u> Table 2 </ u> flexural strengths Hot Strengths [N / cm ² ] Cold Strength [N / cm ² ] After storage in a climatic 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 inventively 1.5 170 450 180 1315 inventively 1.6 180 440 200 1310 erfingdungsgemäß 1.7 160 430 150 1319 inventively 1.8 170 440 200 1321 inventively 1.9 150 400 210 1280 inventively 1.10 140 350 110 1201 Comparison, not according to the invention 1.11 160 410 160 1299 inventively

Result

Molding compounds containing neither amorphous silica nor a surfactant (Mixture 1.1) have a hot strength that is insufficient for an automated core manufacturing process. Cores the with this molding material mixture are produced at low shooting pressures structural loosening, which can lead to rejection of the core (low mechanical stability, transmission of defects on the cast pattern). By increasing the shooting pressure up to 5 bar this error pattern can be counteracted.

Addition of the amorphous silicon dioxide to the molding material mixture (mixture 1.2) shows a significant increase in the hot strength. The core weight, which gives information about the compaction and flowability, is comparable to that of mixture 1.1. Also, the compaction on the core surface is comparable to mixture 1.1 and shows at 2 bar rough microstructural loosening.

When using surface-active substances without the addition of amorphous silicon dioxide (mixture 1.3), it is possible to increase the core weight, but there is no positive effect on the hot strength. The densification of the core is improved, so that in comparison to the mixtures 1.1 and 1.2 little structural loosening can be seen.

Only by combining both molding material components, i. By adding both amorphous silica and surfactants (blends 1.4 to 1.9), increases in hot strength and core weight can be observed simultaneously. The cold strengths and the moisture stability of the mixtures 1.4 to 1.9 also have higher values than the shaped bodies of the mixtures 1.1 to 1.3. The compaction of the cores is improved by an increased flowability of the molding material mixture, resulting in an increase in the mechanical stability. Microstructural loosening, as shown by the nuclei of mixtures 1.1 and 1.2, is minimal.

The comparison of mixtures 1.10 and 1.11 shows that, especially when using Regeneratsanden (in this case, a thermal Regenerates), the addition of surfactants is of particular advantage. This results in an even clearer increase in the strengths and the core weight than, for example, when using new quartz sand is the case.

Claims (15)

1. A mould material mixture for producing casting moulds for metalworking comprising at least:

   - a refractory base moulding material;

   - a binder based on water glass;

   - a proportion of a particulate metal oxide selected from the group consisting of silicon dioxide, aluminium oxide, titanium oxide, and zinc oxide;

   characterized in that a proportion of at least one surfactant is added to the mould material mixture.
2. The mould material mixture according to claim 1, characterized in that the surfactant is dissolved in the binder.
3. The mould material mixture according to claim 1 or 2, characterized in that the surfactant is an anionic surfactant.
4. The mould material according to any of claims 1 to 3, characterized in that the surfactant includes a sulphate, sulphonate, or phosphate group.
5. The mould material mixture according to any of claims 2 to 4, characterized in that the surfactant is selected from the group consisting of oleyl sulphate, stearyl sulphate, palmityl sulphate, myristyl sulphate, lauryl sulphate, decyl sulphate, octyl sulphate, 2-ethylhexyl sulphate, 2-ethyloctyl sulphate, 2-ethyldecyl sulphate, palmitoleyl sulphate, linolyl sulphate, lauryl sulphonate, 2-ethyldecyl sulphonate, palmityl sulphonate, stearyl sulphonate, 2-ethylstearyl sulphonate, linolyl sulphonate, hexyl phosphate, 2-ethylhexyl phosphate, capryl phosphate, lauryl phosphate, myristyl phosphate, palmityl phosphate, palmitoleyl phosphate, oleyl phosphate, stearyl phosphate, poly-(1,2- ethanediyl-)-phenol hydroxyphosphate, poly-(1, 2-ethanediyl-)-stearyl phosphate, and poly-(1, 2-ethanediyl-)-oleyl phosphate.
6. The mould material mixture according to any of the preceding claims, characterized in that the surfactant is included in the mould material mixture in a proportion from 0.001 to 1% by weight relative to the weight of the refractory base moulding material.
7. The mould material mixture according to any of the preceding claims, characterized in that the refractory base moulding material is at least in part a regenerated refractory base moulding material.
8. The mould material mixture according to any of the preceding claims, further characterized by one or more of the following features:

   a) at least one carbohydrate is added to the mould material mixture;

   b) a phosphorous-containing compound is added to the mould material mixture;

   c) the particulate metal oxide is selected from the group consisting of precipitated silicic acid and pyrogenic silicic acid;

   d) the water glass has an SiO₂/M₂O ratio in the range from 1.6 to 4.0, particularly from 2.0 to 3.5, wherein M stands for sodium ions and/or potassium ions;

   e) the inorganic binder is contained in the mould material mixture in a proportion of less than 20% by weight;

   f) the particulate metal oxide is contained in a proportion from 2 to 80% by weight relative to the binder;

   g) the refractory base moulding material contains at least a proportion of hollow microspheres;

   h) the base moulding material contains at least a proportion of glass granules, glass beads, and/or spherical ceramic moulding materials;

   i) an oxidisable metal and an oxidant are added to the mould material mixture;

   j) the mould material mixture contains at least a proportion of an inorganic additive that is solid at room temperature.
9. The mould material mixture according to any of the preceding claims, characterized in that the mould material mixture contains at least one silane or siloxane.
10. A process for producing casting moulds for metal processing having at least the following steps:

    - obtaining a mould material mixture according to any of claims 1 to 9;

    - moulding of the mould material mixture;

    - curing of the moulded mould material mixture by heating the mould material mixture to obtain the casting mould.
11. The method according to claim 10, characterized in that the mould material mixture is heated to a temperature in the range from 100 to 300 °C.
12. The method according to either of claims 10 or 11, characterized in that heated air is blown into the moulded mould material mixture in order to cure it.
13. The method according to any of claims 10 to 12, characterized in that heating of the moulded mould material mixture is effected by the action of microwaves.
14. A casting mould obtained from the mould material mixture according to any of claims 1 to 9 and/or by a method according to any of claims 10 to 13.
15. Use of a casting mould according to claim 14 for casting metal, particularly casting light metal.

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