EP1802409B1 - Material mixture for producing casting moulds for machining metal - Google Patents

Abstract

Material mixture comprises a refractory molding base material, a binder based on water glass and a particulate metal oxide selected from silicon dioxide, aluminum oxide, titanium oxide and zinc oxide. An independent claim is also included for a process for the production of casting molds using the above material mixture.

Description

The invention relates to a molding material mixture for the production of casting molds for metal processing, which comprises at least one free-flowing refractory molding base material and a water glass-based binder. 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, whereby appropriate measures are taken to ensure that the metal lasts longer the liquid phase remains as the metal which is in the mold forming the negative mold. 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 different 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. Even in the case of inorganic-organic hybrid systems which, like the binders used, for example, in the resol CO ₂ process, contain a proportion of organic compounds, such unwanted emissions occur during the 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. 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 will describe an exothermic feeder mass containing an alkali silicate as a binder. 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. 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.

Inorganic binders have the disadvantage, in comparison to organic binders, that the casting molds produced therefrom have relatively low strengths. This is especially evident immediately after the removal of the mold from the tool. Good strength at this time, however, are particularly important for the production of complicated, thin-walled moldings 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 will only be of help, as the water vapor can not escape sufficiently. To complete the drying of the molds as complete as possible will reach 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.

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.

In the EP 1 122 002 describes a method that is suitable for the production of molds for metal casting. For the preparation of the binder, an alkali metal hydroxide, in particular sodium hydroxide solution, is mixed with a particulate metal oxide, which can form a metalate in the presence of the alkali metal hydroxide solution. The particles are dried after a layer of the metal has formed at the edge of the particles. At the core of the particles remains a section in which the metal oxide was not reacted. As the metal oxide, a dispersed silica or finely divided titanium oxide or zinc oxide is preferably used.

In the WO 94/14555 describes a molding material mixture, which is also suitable for the production of molds and which contains a binder in addition to a refractory molding material, which consists of a phosphate or borate glass, wherein the mixture further contains a finely divided refractory material. For example, silicon dioxide can also be used as the refractory material.

A molding material mixture for producing metal working molds comprising a refractory molding base, a water glass based binder and a proportion of a particulate metal oxide is known from the JP 52-138434 A which discloses titanium oxide, zinc oxide, iron oxide and aluminosilicates as metal oxides. However, the use of synthetic amorphous silica as the particulate metal oxide is not known in the art.

In the EP 1 095 719 A2 describes a binder system for molding sands for the production of cores. The waterglass-based binder system consists of an aqueous alkali silicate solution and a hygroscopic base, such as sodium hydroxide, added in a ratio of 1: 4 to 1: 6. The water glass has a modulus SiO ₂ / M ₂ O of 2.5 to 3.5 and a solids content of 20 to 40%. In order to obtain a free-flowing molding material mixture, which can also be filled into complicated core molds, and for controlling the hygroscopic properties, the binder system also contains a surface-active substance, such as silicone oil, which has a boiling point ≥ 250 ° C. The binder system is mixed with a suitable refractory material, such as quartz sand, and then injected into a core box with a core shooter. The hardening of the molding material mixture takes place by removal of the water still contained. The drying or hardening of the casting mold can also take place under the action of microwaves.

The previously known molding material mixtures for the production of casting molds still have room for an improvement in the properties, for example, in terms of the strength of the molds produced and in terms of their resistance to atmospheric moisture during storage for a long period. Furthermore, the goal is to achieve a high quality of the surface of the casting after the casting, so that the finishing of the surface can be carried out with little effort.

The object of the invention was therefore to provide a molding material mixture for the production of casting molds for metalworking, which comprises at least one refractory molding base material and a water glass-based binder system which enables the production of casting molds. which have high strength both immediately after shaping and during prolonged storage.

Furthermore, the molding material mixture should allow the production of casting molds, with which castings can be produced, which have a high quality of the surface, so that only a small finishing of the surfaces is required.

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

Surprisingly, it has been found that the use of a binder containing an alkali water glass as well as a particulate metal oxide which is a particulate synthetic amorphous silica demonstrates the strength of molds both immediately after molding and curing and when stored under elevated humidity can be improved.

• einen feuerfesten Formgrundstoff; sowie
• ein auf Wasserglas basierendes Bindemittel.

The molding material mixture according to the invention for the production of casting molds for metalworking comprises at least:

• a refractory molding base; such as
• a water glass based binder.

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.

Furthermore, artificial molding materials can also be used as refractory molding base materials, for example aluminum silicate hollow spheres (so-called microspheres), glass beads, glass granules or spherical ceramic molding base materials known under the name "Cerabeads" or "Carboaccucast". 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, other constituents may be present in proportions of <10%, such as TiO ₂ Fe ₂ O ₃ . The diameter of the microspheres 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.

Glass materials are particularly preferably used as refractory artificial mold base materials. 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, special glasses can be used which contain other elements or their oxides in addition to the aforementioned oxides.

The diameter of the glass beads is preferably less than 1000 μm, in particular less than 600 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 complex after-treatment by blasting is not required or at least to a significantly lesser extent.

It is not necessary to form the entire mold base from the artificial mold bases. The preferred proportion of the artificial molding base materials is at least about 3 wt .-%, more 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 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 contained in the water glass.

According to the invention, the molding material mixture contains a proportion of a particulate metal oxide which is a particulate synthetic amorphous silica. The particle size of these metal oxides is preferably less than 300 microns, preferably less than 200 microns, more preferably less than 100 microns. The particle size can be determined 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.

As the particulate silica, precipitated silica and / or fumed silica is preferably used. 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".

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.

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 evaporating the water present in the binder (about 40 to 70 wt .-%, based on the weight of the binder) can then be a solid cohesion between the particles of the refractory base molding material can be achieved.

The binder, i. the water glass as well as the particulate synthetic amorphous silica is preferably contained in the molding material mixture in a proportion of less than 20% by weight. If massive molding base materials are used, such as quartz sand, the binder is preferably present in a proportion of less than 10% by weight, preferably less than 8% by weight, more preferably less than 5% by weight. If refractory mold bases are used which have a low density, such as the hollow microspheres described above, the proportion of binder increases accordingly.

The particulate synthetic amorphous silica, based on the weight of the binder, is preferably contained in a proportion of 2 to 60% by weight, preferably between 3 and 50% by weight, especially preferably between 4 and 40% by weight.

The ratio of water glass to particulate 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 tool and the moisture resistance, without significantly affecting the final strengths, ie the strengths after cooling of the casting mold, compared to a waterglass binder without amorphous silica. 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 hardness after curing should not be too high to cause difficulties Binder decomposition after casting to avoid, ie the molding material should be able to be easily removed from the cavities of the mold after casting.

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 has solidified. 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 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 for example from Omega Minerals Germany GmbH, Norderstedt, under the names OmegaSpheres ^® SG with an alumina content of about 28 - 33%, Omega-Spheres ^® WSG with an alumina content of about 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 than 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. This contains the molding material mixture 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.

Binders containing water have inferior flowability compared to organic solvent based binders. This means that molds with narrow passages and multiple deflections can fill poorer. As a result, the molds have portions with insufficient compaction, which in turn can lead to casting defects during casting. According to an advantageous embodiment, the molding material mixture according to the invention contains a proportion of platelet-shaped lubricants, in particular graphite or MoS _2. Surprisingly, it has been found that with addition of such lubricants, in particular graphite, even complex shapes can be produced with thin-walled sections, the casting molds being continuous have a consistently high density and strength so that essentially no casting defects were observed during casting. The amount of added platelet-shaped lubricant, in particular graphite, is preferably 0.1 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 can be added which facilitate the separation of 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 a preferred 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 ° C., preferably from 50 to 175 ° 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 burnt during the casting process, thereby creating a thin gas cushion between the liquid metal and the molding material forming the wall of the casting mold and thus a reaction between the liquid metal and the molding material 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 molding material. 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.

Surprisingly, it has been found that an improvement of the surface of the casting with very different organic additives can be achieved. Suitable organic additives are, for example, phenol-formaldehyde resins, such as novolacs, 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 of olefins such as ethylene or propylene, and other comonomers such as vinyl acetate, polyamides such as polyamide-6, polyamide-12 or polyamide-6,6, natural resins such for example, gum rosin, fatty acid esters such as cetyl palmitate, fatty acid amides such as ethylenediamine bisstearamide, and metal soaps such as stearates or oleates of di- or tri-valent 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 preferred 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 and ureidosilanes. Examples of suitable silanes are γ-aminopropyltrimethoxysilane, γ-hydroxypropyltrimethoxysilane, 3-ureidopropyltriethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, β- (3,4-epoxycyclohexyl) trimethoxysilane and N-β (aminoethyl) -γ-aminopropyltrimethoxysilane.

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%.

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

Despite the high strengths which can be achieved with the binder according to the invention, the casting molds produced with the molding material mixture according to the invention, in particular cores and molds, show a good disintegration after the casting, in particular during 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. The invention further relates to a process for the production of casting molds, for metal processing, wherein the novel molding compound mixture is used. The process according to the invention comprises the steps:

• Producing the above-described molding material mixture;
• Forms of the molding material mixture;
• Curing the molding material mixture by heating the molding material mixture, wherein the cured mold is obtained.

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. In this case, the water glass and the particulate synthetic amorphous silica can be added per se in any order. However, it is advantageous to add the liquid component first. The addition is carried out with vigorous stirring, so that the binder is evenly distributed in the refractory molding material and this coated.

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 aushäzten 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 finished be cured by their further water is withdrawn. This can be done for example in an oven. The dehydration can for example also 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 explained above, the flowability of the molding material mixture according to the invention can be improved by the addition of platelet-shaped lubricants, in particular graphite and / or MoS ₂ . In the production, the platy Lubricant, in particular graphite thereby be added separately from the two binder components of the molding material mixture. However, it is equally possible to premix the platelet-shaped lubricant, in particular graphite, with the particulate synthetic amorphous silica and only then to mix with the water glass and the refractory base molding material.

If the molding material mixture comprises an organic additive, the addition of the organic additive per se can be carried out 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 molding material 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 solvent. 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 molding material 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 molding material, the particulate Metal oxide and the organic or the additives preferably not separately added to the molding sand, but mixed in advance.

If the molding material mixture contains silanes, the silanes are usually added in the form that they are incorporated into the binder in advance. However, the silanes can also be added to the molding material as a separate component. However, it is particularly advantageous to silanize the particulate metal oxide, i. To mix the metal oxide with the silane, so that its surface is provided with a thin silane layer. If one uses the thus pretreated particulate metal oxide, one finds compared to the untreated metal oxide increased strengths and an 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. 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, ie the molds can be stored easily for a long time. Another object of the invention is therefore a casting mold which has been obtained by the process according to the invention 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.

Fig. 1:

einen Querschnitt durch ein zur Prüfung der Fließfähigkeit verwendetes Formwerkzeug;

Fig. 2:

einen Querschnitt durch eine Gießform, welche zur Prüfung der erfindungsgemäßen Formstoffmischung verwendet wurde.

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

Fig. 1:

a cross section through a mold used for testing the flowability;

Fig. 2:

a cross section through a mold, which was used to test the molding material mixture according to the invention.

example 1 Influence of synthetically produced amorphous silicon dioxide on the strength of shaped articles with quartz sand as molding material 1. Preparation and testing of the molding material mixture

For the testing of the molding material mixture so-called Georg Fischer test bars were produced. Georg Fischer test bars are cuboid test bars measuring 150 mm x 22.36 mm x 22.36 mm.

• Die in Tabelle 1 aufgeführten Komponenten wurden in einem Laborflügelmischer (Firma Vogel & Schemmann AG, Hagen, DE) gemischt. Dazu wurde zunächst der Quarzsand vorgelegt und unter Rühren das Wasserglas zugegeben. Als Wasserglas wurde ein Natriumwasserglas verwendet, das Anteile von Kalium aufwies. In den nachfolgenden Tabellen ist das Modul daher mit SiO₂ : M₂O angegeben, wobei M die Summe aus Natrium und Kalium angibt. Nachdem die Mischung für eine Minute gerührt worden war, wurde ggf. das amorphe Siliciumdioxid (erfindungsgemäße Beispiele) unter weiterem Rühren zugegeben. Die Mischung wurde anschließend noch für eine weitere Minute gerührt;
• Die Formstoffmischungen wurden in den Vorratsbunker einer H 2,5 Hot-Box-Kernschießmaschine der Firma Röperwerk - Gießereimaschinen GmbH, Viersen, DE, überführt, deren Formwerkzeug auf 200°C erwärmt war;
• Die Formstoffmischungen wurden mittels Druckluft (5 bar) in das Formwerkzeug eingebracht und verblieben für weitere 35 Sekunden im Formwerkzeug;
• Zur Beschleunigung der Aushärtung der Mischungen wurde während der letzten 20 Sekunden Heißluft (2 bar, 120°C beim Eintritt in das Werkzeug) durch das Formwerkzeug geleitet;
• Das Formwerkzeug wurde geöffnet und die Prüfriegel entnommen.

The composition of the molding material mixture is given in Table 1. The Georg Fischer test bars were prepared as follows:

• The components listed in Table 1 were mixed in a laboratory blade mixer (Vogel & Schemann AG, Hagen, DE). For this purpose, initially the quartz sand was introduced and added with stirring the water glass. As a water glass, a sodium water glass was used, which had proportions of potassium. In the tables below, the modulus is therefore given as SiO ₂ : M ₂ O, where M is the sum of sodium and potassium. After stirring the mixture for one minute, the amorphous silica (examples of the present invention) was optionally added with further stirring. The mixture was then stirred for an additional 1 minute;
• The molding material mixtures were transferred to the storage bunker of a H 2.5 hot-box core shooting machine from Röperwerk-Gießereimaschinen GmbH, Viersen, DE, whose mold had been heated to 200 ° C.;
• The molding material mixtures were introduced into the mold by means of compressed air (5 bar) and remained in the mold for a further 35 seconds;
• To accelerate the curing of the mixtures, hot air (2 bar, 120 ° C on entering the mold) was passed through the mold during the last 20 seconds;
• The mold was opened and the test bars removed.

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

• 10 Sekunden nach der Entnahme (Heißfestigkeiten) ;
• ca. 1 Stunde nach der Entnahme (Kaltfestigkeiten);
• Nach 3 Stunden Lagerung der erkalteten Kerne im Klimaschrank bei 25°C und 75 % relativer Luftfeuchte.

The flexural strengths were measured according to the following scheme:

• 10 seconds after removal (hot strengths);
• about 1 hour after removal (cold strength);
• After 3 hours storage of the cooled cores in a climatic chamber at 25 ° C and 75% relative humidity.

The measured flexural strengths are summarized in Table 2. <u> Table 1 </ u> Composition of the molding material mixtures Quartz sand H 32 Alkali water glass amorphous silica 1.1 100 GT 2, 5 GT ^a) - Comparison, not according to the invention 1.2 100 GT 2, 5 GT ^b) - Comparison, not according to the invention 1.3 100 GT 2, 5 GT ^c) - Comparison, not according to the invention 1.4 100 GT 2, 5 GT ^a) 0.2 GT ^d) inventively 1.5 100 GT 2, 5 GT ^a) 0.6 GT ^d) inventively 1.6 100 GT 2, 5 GT ^a) 1, 0 GT ^d) inventively 1.7 100 GT 2, 5 GT ^a) 1.5 GT ^d) inventively 1.8 100 GT 2, 5 GT ^b) 0.2 GT ^d) inventively 1.9 100 GT 2, 5 GT ^c) 0.2 GT ^d) inventively 1.10 100 GT 2, 5 GT ^a) 0.2 GT ^e) inventively 1.11 100 GT 2, 5 GT ^a) 0.2 GT ^f) inventively ^a) Alkali water glass with modulus SiO ₂ : M ₂ O of approx. 2.3
^b) Alkali water glass with modulus SiO ₂ : M ₂ O of approx. 3.35
^c) Alkali water glass with modulus SiO ₂ : M ₂ O of approx. 2.03
^d) Elkem Microsilica 971 (pyrogenic silica, production in an electric arc furnace)
^e) Degussa Sipernat 360 (precipitated silica)
^f) Wacker HDK N 20 (fumed silica, production by flame hydrolysis) flexural strengths Hot Strengths [N / cm ² ] Cold Strength [N / cm ² ] After storage in a climatic chamber [N / cm ² ] 1.1 80 490 30 Comparison, not according to the invention 1.2 110 220 210 Comparison, not according to the invention 1.3 60 400 110 Comparison, not according to the invention 1.4 105 570 250 inventively 1.5 185 670 515 inventively 1.6 250 735 690 inventively 1.7 315 810 700 inventively 1.8 140 280 270 inventively 1.9 90 510 170 inventively 1.10 95 550 280 inventively 1.11 110 540 290 inventively

2nd result a) Influence of the added amount of amorphous silica

In Examples 1.4 to 1.7, increasing amounts of amorphous silica, which had been produced in the electric arc furnace, were added to the molding material mixtures. The amount of mold base and water glass was kept constant. In Comparative Example 1.1, a molding material mixture was prepared, which had the same composition as the molding material mixtures of Examples 1.4 to 1.7, but no amorphous silica was added.

The results from Table 2 show that the addition of amorphous, arc-prepared silica markedly increases the flexural strength of the test bars. The flexural strength of the test bars increases particularly strongly in the case of a measurement after storage in the climatic cabinet at elevated air humidity. This means that the test bars produced with the molding material mixture according to the invention substantially retain their strength even after prolonged storage. Increasing amounts of added amorphous silica lead to increasing flexural strengths. In the case of the flexural strengths, measured after storage in the climatic chamber, a strong increase in the flexural strengths is observed initially, which flattens out as the amount of added amorphous silicon dioxide increases.

b) Influence of the ratio SiO ₂ : M ₂ O of the alkali water glass

In Examples 1.4, 1.8 and 1.9, equal amounts of mold base, water glass and amorphous silicon dioxide (produced in the arc) were processed, but the ratio SiO ₂ : M ₂ O of the alkali water glass was changed. In the comparative examples 1.1, 1.2 and 1.3, in each case equal amounts of mold base material and water glass were processed, but also the ratio SiO ₂ : M ₂ O of the alkali water glass was varied. As shown by the bending strengths shown in Table 2, the amorphous silica produced in the arc furnace is effective regardless of the ratio SiO ₂ : M ₂ O of the alkali water glass.

c) Influence of the type of synthetic amorphous silica

In Examples 1.4, 1.10 and 1.11, equal amounts of mold base, water glass and amorphous silica were processed respectively, but the nature of the synthetic amorphous silica was varied. The flexural strengths listed in Table 2 show that precipitated and pyrogenic, by Flame hydrolysis produced silicas are as effective as in the arc furnace produced amorphous silica.

Example 2

Influence of the ratio of alkali water glass: amorphous silica on the strengths of moldings at a constant total binder amount with quartz sand as molding material.

1. Preparation and testing of the molding material mixture

The preparation of the molding material mixtures and their testing was carried out analogously to Example 1. The compositions of the molding material mixtures used for the preparation of the test bars are listed in Table 3. The values found in the flexural strength tests are summarized in Table 4. <u> Table 3 </ u> Composition of the molding material mixtures Quartz sand H 32 Alkali water glass ^b) amorphous silicon dioxide ^c) 2.1 ^a) 100 GT 2.5 GT - Comparison, not according to the invention 2.2 100 GT 2.3 GT 0.2 GT inventively 2.3 100 GT 1.9 GT 0.6 GT inventively 2.4 100 GT 1.5 GT 1.0 GT inventively ^a) corresponds to experiment 1.1
^b) Alkali water glass with modulus SiO ₂ : M ₂ O of approx. 2.3
^c) Elkem Microsilica 971 flexural strengths Hot Strengths [N / cm ² ] Cold Strength [N / cm ² ] After storage in a climatic chamber [N / cm ² ] 2.1 80 490 30 Comparison, not according to the invention 2.2 90 505 220 inventively 2.3 160 505 390 inventively 2.4 185 470 380 inventively

2nd result

By varying the ratio of water glass: amorphous silica while retaining the total amount of water glass and amorphous silica, the hot strengths and high humidity resistance can be improved without simultaneously increasing the cold strengths.

Example 3 Influence of silanes on the strength of the moldings 1. Production and testing of the molding material mixtures

The preparation of the molding material mixtures and their testing was carried out as in Ex. The composition of the molding material mixtures used for the preparation of the test bars are listed in Table 5. The values found in the flexural strength tests are summarized in Tab. <u> Table 5 </ u> Composition of the molding material mixtures Quartz sand H 32 Alkali water glass ^c) amorphous silica ^d) silane 3.1 ^a) 100 GT 2, 5 GT --- --- Comparison, not according to the invention 3.2 ^b) 100 GT 2, 5 GT 0.2 GT --- inventively 3.3 100 GT 2, 5 GT 0.2 GT 0.02 GT ^e) inventively 3.4 100 GT 2, 5 GT 0.2 GT 0.08 GT ^e) inventively 3.5 100 GT 2, 5 GT 0.2 GT 0.02 GT ^f) inventively ^a) corresponds to experiment 1.1
^b) corresponds to experiment 1.4
^c) Alkali water glass with modulus SiO ₂ : M ₂ O of approx. 2.3
^d) Elkem Microsilica 971
^e) Dynasilan Glymo (Degussa AG), mixed with the amorphous silica before the experiment
^f) Dynasilan Ameo T (Degussa AG), mixed with the amorphous silica before the experiment flexural strengths hot strengths cold strengths After storage in the climatic chamber [N / cm ² ] [N / cm ² ] [N / cm ² ] 3.1 80 490 30 Comparison, not according to the invention 3.2 105 570 250 inventively 3.3 120 620 300 inventively 3.4 140 670 400 inventively 3.5 125 650 380 inventively

2nd result

Examples 3.3-3.5 show that the addition of silane has a positive effect on the strengths, especially with respect to the resistance to high humidity.

Example 4 Influence of the amorphous silica on the strengths of moldings with artificial mold bases 1. Preparation and testing of the molding material mixture

The preparation of the molding material mixtures and their testing was carried out analogously to Example 1. The compositions of the molding material mixtures used for the preparation of the test bars are listed in Table 7. The values found in the flexural strength tests are summarized in Table 8. <u> Table 7 </ u> Composition of the molding material mixtures Mold base material Alkali water glass ^d) amorphous silica ^e) 4.1 Aluminum silicate microbubbles ^a) 100 GT 14 GT - Comparison, not according to the invention 4.2 Aluminum silicate microbubbles ^a) 100 GT 14 GT 1.5 GT inventively 4.3 Aluminum silicate microbubbles ^a) 100 GT 14 GT 3, 0 GT inventively 4.4 Ceramic balls ^b) 100 GT 2, 5 GT - Comparison, not according to the invention 4.5 Ceramic balls ^b) 100 GT 2, 5 GT 0, 2 GT inventively 4.6 Glass beads ^c) 100 GT 2, 5 GT - Comparison, not according to the invention 4.7 Glass beads ^c) 100 GT 2, 5 GT 0.2 GT inventively ^a) Omegaspheres WSG from Omega Minerals Germany GmbH
^b) Carbo Accucast LD 50 from Carbo Ceramics Inc.
^c) glass beads 100-200 μm from Reidt GmbH & Co.KG
^d) Alkali water glass with modulus SiO ₂ : M ₂ O of approx. 2.3
^e) Elkem Microsilica 971 Bending strength Hot Strengths [N / cm ² ] Cold Strength [N / cm ² ] After storage in a climatic chamber [N / cm ² ] 4.1 120 230 decay Comparison, not according to the invention 4.2 160 290 130 inventively 4.3 200 340 180 inventively 4.4 70 370 20 Comparison, not according to the invention 4.5 100 470 100 inventively 4.6 170 650 30 Comparison, not according to the invention 4.7 260 770 100 inventively

2nd result

It can be seen that the positive effect of the amorphous silica is not limited to quartz sand as a molding material, but that it also increases the strength of other molding materials, e.g. Microspheres, ceramic balls and glass beads.

Example 5

Influence of amorphous silica on the strengths of exothermic mass molded articles.

The following composition was used as exothermic composition: Aluminum (0.063 - 0.5 mm grain size) 25% potassium nitrate 22% Micro hollow spheres (Omegaspheres ^® WSG der 44% Company Omega Minerals Germany GmbH) Refractory surcharge (fireclay) 9%

1. Production and testing of molding material-binder mixtures

The preparation of the molding material-binder mixtures and their testing was carried out analogously to Example 1. The compositions of the molding material mixtures used for the preparation of the test bars are listed in Table 9. The values found in the flexural strength tests are summarized in Table 10. <u> Table 9 </ u> Exothermic mass Alkali water glass ^a) amorphous silicon dioxide ^b) 5.1 100 GT 14 GT - Comparison, not according to the invention 5.2 100 GT 14 GT 1.5 GT inventively 5.3 100 GT 14 GT 3, 0 GT inventively ^a) Alkali water glass with modulus SiO ₂ : M ₂ O of approx. 2.3
^b) Elkem Microsilica 971 flexural strengths Hot strength [N / cm ² ] Cold strength [N / cm ² ] After storage in a climate cabinet [N / cm ² ] 5.1 50 180 decay Comparison, not according to the invention 5.2 70 225 70 inventively 5.3 95 280 110 inventively

2nd result

The amorphous silica also increases strength in the case of exothermic compositions as a molding material.

Example 6 Improvement of the flowability of the molding material mixture 1. Preparation and testing of the molding material mixture

The components listed in Table 11 were mixed in a laboratory paddle mixer (Vogel & Schemann AG, Hagen, DE). For this purpose, initially the quartz sand was introduced and added with stirring the water glass. After the mixture was stirred for one minute, the amorphous silica was added with further stirring. The mixture was then stirred for an additional 1 minute. Finally, in Examples 6.2 to 6.4, graphite was added and the mixture was finally stirred for a further minute.

The flowability of the molding material mixtures was determined by means of the degree of filling of the in Fig. 1 determined mold 1 determined. The mold 1 consists of two halves, which can be connected to each other, so that a cavity 2 is formed. The cavity 2 comprises three chambers 2a, 2b and 2c of circular cross-section having a diameter of 100 mm and a height of 30 mm. The chambers 2a, 2b and 2c are each connected by circular openings 3a, 3b having a diameter of 15 mm. The circular openings are made in partitions 4a, 4b, which have a thickness of 8 mm. The openings 3a, 3b are each 37.5 mm to the central axis 6 offset at a maximum distance from each other. In the chamber 2a also leads along the central axis 6, an access 5 through which the molding material mixture can be filled. The access 5 has a circular cross section with a diameter of 15 mm. In the chamber 2c, a vent opening 7 is further provided, which has a circular cross-section with a diameter of 9 mm and which is provided with a so-called slot nozzle. The mold 1 is used for filling in a core shooting machine.

• Mischen der in Tabelle 11 aufgeführten Komponenten;
• Überführung der Mischungen in den Vorratsbunker einer H 1-Cold-Box-Kernschießmaschine der Firma Röperwerke - Gießereimaschinen GmbH, Viersen, DE;
• Einbringen der Mischungen in das nicht erwärmte Formwerkzeug 1 mittels Druckluft (5 bar);
• Aushärtung der Mischungen durch Einleiten von CO₂;
• Entnahme der gehärteten Formkörper aus dem Werkzeug und Registrierung ihres Gewichts.

More specifically, the procedure was as follows:

• Mixing the components listed in Table 11;
• Transfer of the mixtures into the storage bunker of an H 1 cold box core shooter from Röperwerke - Gießereimaschinen GmbH, Viersen, DE;
• Introducing the mixtures into the unheated mold 1 by means of compressed air (5 bar);
• Curing the mixtures by introducing CO ₂ ;
• Removal of the hardened moldings from the tool and registration of their weight.

The determined weights of the moldings are summarized in Table 12. <u> Table 11 </ u> Composition of the molding material mixtures Quartz sand H 32 Alkaline water glass ^a) amorphous silica ^b) graphite 6.1 100 GT 2.5 GT 0.2 GT - Comparison, not according to the invention 6.2 100 GT 2.5 GT 0.2 GT 0.2 GT inventively 6.3 100 GT 2.5 GT 0.2 GT 0.2 GT inventively 6.4 100 GT 2.5 GT 0.2 GT 1.0 GT inventively ^a) Alkali water glass with modulus SiO ₂ : M ₂ O of approx. 2.3
^b) Elkem Microsilica 971 Weight of the moldings Weight [g] 6.1 512 Comparison, not according to the invention 6.2 534 inventively 6.3 564 inventively 6.4 588 inventively

2nd result

The addition of graphite improves the flowability of the molding material mixtures, ie the tool is filled better.

Example 7 Casting tests 1. Preparation and testing of the molding material mixture

To carry out the pouring tests, four of the Georg Fischer test bars 8 produced in Examples 1 to 6 were each offset by 90 ° into the lower part 9 of the Georg Fischer test bars 8 Fig. 2 Glued sample reproduced. Subsequently, the funnel-shaped upper part 10 of the sample mold was glued to the lower part 9. Lower part 9 and upper part 10 of the sample mold were produced by a conventional polyurethane cold box process. Thereafter, the sample mold was filled with liquid aluminum (740 ° C). After the metal had cooled, the outer sample mold was removed and the sample casts in the sections of the four test specimens were examined for their surface finish (sand deposits, smoothness). The rating was 1 (very good) to 10 (very bad). The results are summarized in Table 13. <u> Table 13 </ u> Composition of the molding material mixtures and casting result Composition see Ex. Surface quality 7.1 1.1 (Tab. 1) 5 Comparison, not according to the invention 7.2 1.4 (Tab. 1) 5 inventively 7.3 4.1 (Tab. 7) 2 not according to the invention 7.4 4.2 (Tab. 7) 2 inventively 7.5 4.4 (Tab. 7) 4 not according to the invention 7.6 4.5 (Tab. 7) 4 inventively 7.7 4.6 (Tab. 7) 1 not according to the invention 7.8 4.7 (Tab. 7) 1 inventively

2nd result

The results from Table 13 show that the use of artificial molding bases such as e.g. Aluminiumilikatmikrohohlkugeln, ceramic balls or glass beads the surface quality of the castings z.T. significantly improved.

Example 8 Effect of organic additives on the casting result 1. Production and testing of the molding material mixtures

The composition of the investigated molding material mixtures is listed in Table 14.

The casting experiments and their evaluation took place analogously to Example 7. The result of the pouring tests can also be found in Table 14. <u> Table 14 </ u> Composition of the molding material mixtures and casting result Quartz sand H 32 Alkali water glass ^b) amorphous silicon dioxide ^c) organic additive Casting result 8.1 ^a) 100 GT 2.5 GT 0.2 GT --- 5 8.2 100 GT 2.5 GT 0.2 GT 0.2 GT ^d) 3 8.3 100 GT 2, 5 GT 0.2 GT 0.2 GT ^e) 1 8.4 100 GT 2.5 GT 0.2 GT 0.2 GT ^f) 3 8.5 100 GT 2.5 GT 0, 2 GT 0.2 GT ^g) 2 8.6 100 GT 2.5 GT 0, 2 GT 1.0 GT ^h) 2 8.7 100 GT 2.5 GT 0.2 GT 1.0 GT ⁱ⁾ 2 8.8 100 GT 2.5 GT 0.2 GT 0.2 GT ^j) 1 8.9 100 GT 2.5 GT 0.2 GT 0, 2 GT ^k) 3 8.10 100 GT 2.5 GT 0.2 GT 0.2 GT ^l) 1 8.11 100 GT 2.5 GT 0.2 GT 0.2 GT ^m) 1 ^a) corresponds to experiment 1.4
^b) Alkali water glass with modulus SiO ₂ : M ₂ O of approx. 2.3
^c) Elkem Microsilica 971
^d) Novolak Bakelite 0235 DP (Bakelite AG)
^e) polyethylene glycol PEG 6000 (BASF AG)
^f) Polyol PX (Peratorp AB)
^g) PE fiber Stewathix 500 (Schwarzwälder Textilwerke GmbH)
^h) vinyl acetate-ethylene copolymer Vinnex C 50 (Wacker Chemie GmbH)
ⁱ⁾ polyamide 12 Vestosint 1111 (Degussa AG)
^j) Balsam resin WW (Bassermann & Co)
^k) zinc gluconate (Merck KGaA)
^l) zinc oleate (Peter Greven Fettchemie GmbH & Co. KG)
^m) aluminum stearate (Peter Greven Fettchemie GmbH & Co. KG)

2nd result

Table 14 shows that the addition of organic additives improves the casting surface.

Claims (22)

1. Moulding mixture for producing casting moulds for metalworking, comprising at least:

   • a refractory mould raw material;

   • a binder based on water glass;

   characterized in that to the moulding mixture a proportion of a particulate synthetic amorphous silicon dioxide is added.
2. Moulding mixture according to claim 1, characterized in that the synthetic amorphous silicon dioxide is selected from the group consisting of precipitated silica and pyrogenic silica.
3. Moulding mixture according to claim 1 or 2, characterized in that the water glass has an SiO₂/M₂O ratio in the range from 1.6 to 4.0, in particular 2.0 to 3.5, where M represents sodium ions and/or potassium ions.
4. Moulding mixture according to any one of the preceding claims, characterized in that the water glass comprises a solids content of SiO₂ and M₂O in the range from 30 to 60% by weight.
5. Moulding mixture according to any one of the preceding claims, characterized in that the binder is present in a proportion of less than 20% by weight in the moulding mixture.
6. Moulding mixture according to any one of the preceding claims, characterized in that the particulate synthetic amorphous silicon dioxide is present in a proportion of from 2 to 60% by weight, based on the binder.
7. Moulding mixture according to any one of the preceding claims, characterized in that the mould raw material contains at least a proportion of hollow microspheres.
8. Moulding mixture according to Claim 7, characterized in that the hollow microspheres are hollow aluminium silicate microspheres and/or hollow glass microspheres.
9. Moulding mixture according to any one of the preceding claims, characterized in that the mould raw material contains at least a proportion of glass granules, glass beads and/or spherical ceramic bodies.
10. Moulding mixture according to any one of the preceding claims, characterized in that the mould raw material contains at least a proportion of mullite, chromium ore sand and/or olivine.
11. Moulding mixture according to any one of the preceding claims, characterized in that an oxidizable metal and an oxidant have been added to the moulding mixture.
12. Moulding mixture according to any one of the preceding claims, characterized in that the moulding mixture contains a proportion of a platelet-shaped lubricant.
13. Moulding mixture according to Claim 12, characterized in that the platelet-shaped lubricant is selected from among graphite and molybdenum sulphide.
14. Moulding mixture according to any one of the preceding claims, characterized in that the moulding mixture contains a proportion of at least one organic additive which is solid at room temperature.
15. Moulding mixture according to any one of the preceding claims, characterized in that the moulding mixture contains at least one silane.
16. Process for producing moulds for casting metalworking, which comprises the steps:

    • production of a moulding mixture according to any one of Claims 1 to 15;

    • moulding of the moulding mixture;

    • curing of the moulding mixture by heating the moulding mixture to give the cured casting mould.
17. Process according to Claim 16, characterized in that the moulding mixture is heated to a temperature in the range from 100 to 300°C.
18. Process according to either Claim 16 or 17, characterized in that heated air is blown into the moulding mixture for curing.
19. Process according to either Claim 16 or 17, characterized in that the heating of the moulding mixture is effected by the action of microwaves.
20. Process according to any one of Claims 16 to 19, characterized in that the casting mould is a feeder.
21. Casting mould obtained by a process according to any one of Claims 16 to 20.
22. Use of the casting mould according to Claim 21 for metal casting, in particular light metal casting.

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