MX2008002893A - Borosilicate glass-containing molding material mixtures - Google Patents

Abstract

The invention relates to a molding material for producing cast moldings for the foundry industry, at least comprising:a fire-proof molding material, a binding agent for hardening the molding material, and;a proportion of a borosilicate glass. The invention also relates to a method for producing a molded body from the inventive molding material, to the corresponding casting mold or the corresponding molded body, and to its use during metal casting.

Description

MIXING MATERIALS FOR MOLDS CONTAINING BOROSILICATE GLASS DESCRIPTION OF THE INVENTION The invention relates to a molding compound for the production of moldings for the foundry industry, to a method for the production of these moldings for the foundry industry, to moldings for the industry of casting. the melting, and the use of these molded bodies for the foundry industry in a method for casting a casting. In the production of molten metal parts, a model is first produced whose shape substantially corresponds to the piece of molten metal to be produced. Supply and feeder elements are applied to this model. For the production of a casting mold the model is surrounded in a mold box with a mixture of material for molds. The mixture of mold material consists essentially of a material for refractory molds, for example, quartz sand, and a binder with which the grains of the mold material are united in a solid molded body upon curing. The mixture of mold material is compressed and then cured. For curing it is possible, for example, that the molded body is heated to evaporate solvent contained in the binder or to initiate a crosslinking reaction in the binder. But it is also possible to add a catalyst, or already REF. : 190760 during the production of the mold material mixture or by circulating a gaseous catalyst through the compressed molded body. After curing, the molded body is removed from the mold box or model. The casting molds are made up of molds and cores. The outer contour of the cast part is defined by the molds. The internal contour of the cast part, or the restriction of a gap provided in the cast part, is formed by the cores. In the finished casting mold, a mold cavity is formed between the mold and the core, which is filled with liquid metal when casting. In addition to cores and molds there are also hollow bodies, the so-called feeders that serve as a compensation deposit. During the emptying, they initially receive liquid metal, and by corresponding measures care is taken that the metal is stored for a longer time in the liquid phase than the metal found in the mold cavity. When the metal solidifies in the mold cavity it is possible for liquid metal to flow additionally from the compensation tank to compensate for the contraction of the volume that occurs when the metal solidifies. After the casting mold was assembled, optionally from several molded bodies, liquid metal is filled into the cavity of the casting mold. The liquid metal that flows into the interior displaces the air that found in the mold cavity. The air escapes through openings that are provided in the casting mold or through porous sections of the casting mold, for example through the wall of a feeder. After the molten metal part has solidified, it is removed from the casting mold. For this purpose it is possible, for example, to shake the casting mold, so that it again disintegrates into grains. The cast part is released by additional shaking of the males that are inside. The surface of the molten metal parts frequently still has defects, so that further processing by machining is necessary to obtain the desired surface quality. The reason for these defects is the heat that influences the casting mold when casting the molten metal, heat that generates stresses in the material of the casting mold. This leads to the formation of cracks in the surface of the mold and of the cores. The molten metal penetrates these fissures and thus leaves laminar structures in the casting that are also generally designated as leaf ribs. This casting defect occurs in particular when using quartz sand as a material for molds, since the quartz sand undergoes a transformation of its crystalline structure and with it, for example, also of its density under the thermal influence of the liquid metal. In addition to this, there are other foundry defects such as spills, penetration and mineralization. To contain considerably the melting defects, to the mixture of material for molds are added various additives in addition to the quartz sand, which must compensate the variation of volume of the material for molds. To the quartz sand is added, for example, iron oxide in amounts of about 1 to 3% by weight. Fayalite can be formed from quartz and iron oxide, thereby reducing the stresses that occur in the casting mold and thereby reducing the tendency to form leaf ribs. However, the lower mechanical stability of the casting mold observed with the addition of iron oxide is a disadvantage. In addition, the formation of fayalite causes a greater risk of metal penetration into the casting mold, which causes irregularities on the castings which in turn must be subjected to further processing. In order to reduce the formation of leaf ribs, it is also possible to add organic material to the mixture of mold material, such as wood dust or coal dust in amounts of approximately 1 to 3% by weight. The organic material is burned during the emptying process. With this produces gaps in the entire volume of the casting mold through which the volume growth of the quartz sand is compensated, so that there is no variation in the size of the casting mold towards the outside. The disadvantage of these additives is the amount of gas that is produced during combustion. If the gas can not escape from the casting mold, bubbles form in the liquid metal by the penetration of gas, which form gaps in the solidified casting. In addition, by the addition of the organic additives described above, the stability of the casting mold is reduced, so that it can not support the mechanical loads that occur during the casting process as well. The formation of leaf ribs can be further contained by the addition of 0.5 to 5% by weight of titanium oxide to the mold sand, as described, for example, in US 4,735,973. By means of titanium oxide, the thermal expansion of the mold material is reduced and, in this way, the formation of leaf ribs is considerably avoided. Titanium dioxide also does not impair the mechanical stability of the casting mold, and the formation of additional gases does not occur through the additive either. However, in the case of mixtures of material for molds containing titanium oxide as an additive, a greater tendency to penetration of the liquid metal into the wall areas of the casting mold, so that it is necessary to treat the surface of the casting mold with a conditioner or other materials prior to casting. As an additional possibility to improve the quality of the casting, it is also possible to use materials for molds with a lower thermal expansion index, such as, for example, chromite, zirconium or olivine sand. The molds of casting of these materials for mold only cause to a lesser extent the formation of leaf ribs. However, these mold materials are relatively expensive. Finally it is also possible to treat the sand so that it is first melted in an oven to obtain a kind of paste and it is ground after solidification. The sand obtained is mixed with approximately 50% quartz sand. The material for molds obtained in this way no longer expands during emptying, so that the formation of leaf ribs is almost no longer observed. In this method the disadvantage consists of the expense for the production of the material for molds, and the high costs that are caused thereby. EP 0 891 954 A1 discloses blends of material for molds containing a proportion of hollow microspheres of aluminum silicate. By means of the addition of the hollow microspheres of aluminum silicate it is possible to markedly contain the formation of cracks on the surface of the casting mold. The thermal expansion of the material for molds is compensated by the holes of the spheres. The additive does not diminish the mechanical loading capacity of the casting molds nor causes a greater gas formation. However, in order to obtain an optimum result in the emptying it is necessary that the proportion of the hollow spheres in relation to the total of the mixture of material for molds be chosen in the range of approximately 10-20%. Through this, the costs for the manufacture of the casting mold increases again. In DE 196 09 539 it is proposed to add cryolite as an additive to the mixtures of material for molds for the foundry industry. It is possible to obtain a free surface of leaf ribs by adding 0.1-10% by weight of cryolite relative to the sand. The cryolite can be used both as a single additive or in combination with other components, such as wood powders, mica, iron oxide, etc. However, with the use of cryolite there are other foundry defects that, among other things, are manifested in an extreme hatching of the casting surface. Another technique that is used in the foundry industry to improve the casting surface constitutes the coating of the casting molds with suspensions of inorganic (highly) refractory materials. This mold coating, which is generally referred to as a smoothing agent, must protect the casting mold against the thermal load caused by the molten metal, in this way obtaining an improvement of the casting surface, allowing a clean separation of liquid metal and casting mold. and reduce the defects of the casting surface. The straighteners are constituted in the simplest case of a carrier liquid in which a refractory material is suspended in fine particles. The smoothing agent can be applied, for example, by painting, spraying, pouring or immersion on at least the surfaces of the casting mold that come into contact with the liquid metal. The binders contained in the carrier liquid cause a fixation of the inorganic basic materials to the surface of the casting mold after drying. The typical inorganic basic materials that are used in the smoothing agents are mineral oxides such as corundum, magnesite, mullite, quartz or chromite, silicates such as zirconium silicate, olivine or refractory ceramic mass (chamotte), as well as carbon or graphite. As a carrier liquid it is possible to use water and organic solvents such as, for example, ethanol or isopropanol. The typical binders are starch derivatives, lignin derivatives, natural resins, synthetic resins or plastics. Frequently the straighteners also contain suspending agents which prevent the solid components from sinking into the carrier liquid. As suspending agents, foamed sheet silicates or cellulose derivatives capable of inclusion in water are used. A disadvantage that often occurs with straighteners is the very dense structure of the mold coatings, so that sufficient gas permeability can not be guaranteed. However, this is necessary to be able to evacuate in a controlled manner the gases that are produced during the melting process by the thermal decomposition of the binders. Otherwise, the internal gas pressure of the core can overcome the metallostatic back pressure and cause the boiling of the metal and consequently the inclusion of gas bubbles in the casting. It is also possible to observe a partial detachment of the coating and subsequent inclusion of the fragment in the casting. In DE-C 42 03 904 it is proposed that in order to increase the gas permeability, organic fibers are introduced into the smoothing agent. However, the fibers tend to form tangles, so that neither a uniform distribution nor an application can be guaranteed. smooth of the straightener. In O 94/26440 a cast iron strainer is described for producing mold coatings which includes a content of inorganic hollow spheres in an amount of 1-40% by weight relative to the ready-to-use polisher. The straightener may additionally comprise an inorganic or organic fiber content in an amount of 0.1-10% by weight relative to the ready-to-use straightener. The hollow spheres are preferably filled with an inert gas. They may consist of oxides, such as aluminum oxide, quartz, magnesite, mullite, chromite, zirconium oxide and / or titanium oxide, borides, carbides and nitrides such as silicon carbide, titanium carbide, titanium boride, nitride, boron and / or boron carbide, carbon, glass or metals or mixtures of these materials. In the examples hollow spheres of aluminum silicate are used, of which up to 80% of the particles have a size between 250-90 μp ?. Its proportion is 5 and 10% by weight in water straighteners, as well as 4 and 10% in weight in alcohol straighteners. In the examples no hollow spheres of other materials are used. No more detailed indications are given about the properties and composition of the hollow glass spheres. In the following the mixtures of material for molds and straighteners are grouped under the concept "molding mass".

By a "mixture of for molds" are meant mixtures that are used to manufacture casting molds or shaped bodies by molding and curing. The object of the invention is to provide a molding compound for the production of casting molds for the foundry industry which allows the production of casting molds which, in the casting, produce a smooth surface substantially free of casting defects. This problem is solved with a molding compound for the production of foundry molds for the foundry industry having the features of claim 1. Favorable improvements of the molding compound are subject of the dependent claims. The molding compound according to the invention contains borosilicate glass as an essential component. It was unexpectedly found that by adding glass to the borosilicate it is possible to obtain a remarkable improvement of the surface of the castings, that is, that the number and intensity of the casting defects can be markedly contained. By means of the proportion of glass to the borosilicate in the molding mass it is almost possible to eliminate the formation of leaf ribs and the tendency to penetration. Another advantage of adding borosilicate glass to the molding mass is the surface particularly smooth of the casting that is obtained when emptying in the mold. The molded bodies or casting molds produced with the molding compound according to the invention have a high mechanical stability compared to casting molds known up to now, so that it is possible to significantly reduce the risk of a breakage of the body molding or casting mold when removing it from the molding tool or erosion of the casting mold when filling it with the liquid metal. The molding compound according to the invention can be configured both as a mixture of material for molds for the production of casting molds and also as a smoothing agent. The molding compound according to the invention contains, in addition to the borosilicate glass, a material for molds and a binder with which it is possible to cure the molding compound. A material for refractory molds is preferably used as mold material. As the material for refractory molds, for example, aluminum silicates, for example, refractory materials in the form of fibers or also quartz sand, zirconium oxide or chromium ore can be used. It is also possible to use materials for refractory molds that are produced synthetically, such as, for example, bullita (x Al203 · and Si02, with x = 2 to 3 e y = l a 2; ideal Al2Si05). It is also possible to use reconditioned foundry sand as mold material. In an embodiment for smoothing the molding compound according to the invention, it is possible to use the customary inorganic mold materials for smoothers as mold material. Suitable material for molds are, for example, mineral oxides such as corundum, magnesite, mullite, quartz or chromite, silicates, such as zirconium silicate, olivine or chamotte, as well as carbon or graphite. As far as the choice of the mold materials themselves is concerned, there are no restrictions. It is possible to use all the usual mold materials for mixtures of material for molds and straighteners. As an additional component, the molding compound according to the invention contains a binder for curing the molding compound. In this case, too, the binders customary in the field of casting are used. If the molding compound according to the invention is made as a mixture of material for molds for the production of moldings or casting molds it is possible to use binders such as those used, for example in the cold box process, hot box or tempered box. It is also possible, for example, to use water glass as a binder. Preferably organic binders are used.

If water glass is used as a binder, then in one embodiment, in particular in one embodiment as a mixture of mold material for the production of moldings or casting molds, the molding compound according to the invention does not contain oxide metal in the form of particles, in particular no metal oxide in the form of particles selected from the group of silicon dioxide, aluminum oxide, titanium oxide and zinc oxide. If the molding compound according to the invention is designed as a smoothing agent, it is possible to use as binders, for example, starch derivatives, lignin derivatives, natural resins, synthetic resins or plastics. The proportion of material for molds and of the binder is chosen within the usual ranges. In one embodiment as a mixture of mold material for the production of moldings or casting molds, the mold material is usually included in a proportion of 50-99.7% by weight, preferably 80 to 99.5% by weight, and the binder in a proportion of 0.3 to 20% by weight, preferably 0.5 to 10% by weight, in each case in relation to the weight of the molding mass. In an embodiment of the molding compound according to the invention as a smoothing agent the material for molds is included in a proportion of 50 to 98% by weight, preferably 60 to 90% by weight and the binder in a proportion of 2 to 10% by weight, preferably 3 to 5% in weight, in each case in relation to the solid content of the smoothing agent, that is, without solvent. In addition to the aforementioned components, the molding compound according to the invention can still include additional customary components, such as, for example, clay minerals, graphite, dextrins, mineral oils, etc. The favorable properties of the molding compound according to the invention can already be observed with very small proportions of borosilicate glass. Preferably the borosilicate glass is included in a proportion of at least 0.001% by weight, preferably at least 0.005% by weight, in particular at least 0.01% by weight relative to the material for molds, and in the case of the smoothing agent in relation to to the proportion of solids in the molding mass. The proportion of the glass to the borosilicate is preferably chosen to be less than 2% by weight, and very particularly preferably within a range of 0.01 to 1% by weight, in each case in relation to the material for molds, and in the case of the smoothing agent in relation to the proportion of solids. The borosilicate glass can be included in the form of a granulate in a powder in the molding compound according to the invention. The diameter of the particles of the granulate or of the powder is preferably selected such that the average diameter D50 is in the range of 5-500 μ, particularly preferably 10-250 μt ?. The average diameter D50 can be determined by conventional methods, for example by screening analysis or laser granulometry. The fineness of the granulate or powder is preferably chosen so that the residue on a sieve with a mesh size of 350 μp? is 10% by weight maximum, and the residue on a sieve of 200 μp mesh size? of 20% by weight maximum. According to a particularly preferred embodiment borosilicate glass is included in the form of hollow microspheres in the molding compound. Hollow microspheres are hollow spheres with a diameter in the order of preferably 5-500 μp ?, particularly preferably 10-250 μp ?, whose shell is made of borosilicate glass. The hollow microspheres are preferably filled with hydrogen, air or an inert gas, for example, nitrogen or mixtures of nitrogen and carbon dioxide. The hollow microspheres preferably have a diameter of less than 200 μt ?. The size of the microspheres can be determined, for example, by screening analysis. The hollow microspheres preferably have a wall thickness of 5-30%, in particular of 6-20% of their external diameter. The hollow microspheres preferably have a bulk density of less than 1.2 g / ml, preferably in particular less than 0.5 g / ml. The hollow microspheres containing the molding compound according to the invention can be made of conventional borosilicate glass. The borosilicate glass preferably contains 2 to 10% by weight of sodium oxide and potassium oxide, 1 to 10% by weight of aluminum oxide, 0 to 10% by weight of alkaline earth metal oxides and 60 to 90% by weight by weight of silicon dioxide. The borosilicate glass preferably has a boron content greater than 3% by weight calculated as B203, particularly preferably from 5 to 15% by weight. Other components may be organic silanes or siloxanes, such as, for example, methyltrimethoxysilane or dimethylpolysiloxane. The inventors assume that borosilicate glass, in particular if it is included in the molding mass in the form of hollow microspheres, melts under the influence of the temperature of the liquid metal and thereby hollow spaces are released which can compensate for the increase in Volume of the material for molds due to the increase in temperature. Preferably the softening point of the glass to the borosilicate is adjusted in the range of less than 1500 ° C, particularly preferably in the range of 500 to 1000 ° C.

As already explained above, the molding compound according to the invention can be configured as a mixture of material for molds for the production of molded bodies and casting molds, in particular molds and cores. To solidify the molding compound, it contains a usual binder for the solidification of molding compositions. Preferably this binder is selected from cold box binders, hot box binders, self-hardening binders and water glass (silicate binders). The tendency to the formation of leaf ribs is very particularly marked in cold box binders. Therefore, the use of hollow borosilicate glass microspheres is particularly preferred in those molding compositions containing a cold box binder. The cold box binder is preferably selected from the group of phenol-urethane resins, which can be cured by amines, epoxy-acryl resins, which can be cured by SiO2 / alkaline phenolic resins, which can be cured. They can be cured by C02 or by methyl formate. It is also possible to use water glass as a binder, which among other things can be cured by C02, as well as self-hardening resins. As a binder, phenol-urethane resins are particularly preferred. cure by amines. These binders are known to the person skilled in the art. Such binders are described, for example, in US 3,409,579 or US 4,526,219. In accordance with another preferred embodiment, water glass is used as the binder. As a water glass it is possible to use the usual soluble glasses as they are already used as a binder in mixtures of material for molds for the foundry industry. These soluble glasses contain dissolved sodium or potassium silicates and can be produced by dissolving potassium silicate vitreous silicate in water. The water glass preferably has a SiO2 / M20 module in the range of 2.0 to 3.5, where M represents sodium and / or potassium. Soluble glasses preferably have a solids content in the range of 20 to 50% by weight. The molding compound according to the invention can also contain solid water glass. For the proportion in the molding mass, in each case only the solid fractions of the water glass are taken into account. If water glass is used as a binder, it can also be cured, for example, by dehydration. A particular advantage of the addition of borosilicate glass according to the invention to a molding compound, in particular in the form of hollow borosilicate glass microspheres, is that the addition of borosilicate glass according to the invention does not it negatively influences the properties of other additives. Therefore, in addition to the borosilicate glass, according to a preferred embodiment, the molding compound according to the invention can also comprise at least one additional additive to reduce the formation of leaf ribs. The minimum of an additional additive is preferably chosen from combustible organic compounds, mica and iron oxide. According to a further preferred embodiment, the molding compound according to the invention comprises an addition of at least one organic and / or inorganic acid and / or an acid source. The processing time of a molding compound often depends on its pH value. Thus, for example, alkalis can accelerate the curing process of the molding compound, in particular in the cold box process. Because the addition of the hollow microspheres to the molding compositions can have the effect of varying the pH value, this pH variation and the shortening of the processing time of the molding composition optionally associated with it can be counteracted by the addition of suitable substances. This can occur, for example, by the addition of organic or inorganic acids, but the addition of commonly used regulators is also possible. The examples of these acids are, among others, formic acid, acetic acid, maleic acid, malonic acid, fumaric acid, adipic acid, benzoic acid, various fatty acids such as oleic acid, lauric acid or stearic acid, lactic acid, citric acid, oxalic acid , boric acid, phenolsulfonic acid, para-toluenesulfonic acid, salicylic acid, glycolic acid, glyoxylic acid, phosphoric acid, sulfuric acid, hydrofluoric acid or also substances which are available as sources of the aforementioned acids, such as, for example, phosphorus oxychloride. In the production of the molding mass these substances can be added in substance to the molding compound, or also as a mixture with the molding compound and / or the binder, or also as a mixture with other additives. According to another preferred embodiment, the molding compound according to the invention is designed as a smoother. The straightener can be configured both as a water straightener and also, for example, as an alcohol straightener. The amalgamants according to the invention are substantially similar to the known ones, although the smoothing agent additionally contains hollow borosilicate glass microspheres. The proportion of water or alcohol is preferably from about 20 to 80% by weight, particularly preferably 40-70% by weight. The Straighteners according to the invention contain the usual components, such as, for example, bentonites for the adjustment of flow properties, fibers, graphite, crosslinking agents and preservatives. With the use of the straighteners according to the invention, if at any time a detachment of the protective coating is observed under the influence of the liquid metal, then only in extremely rare cases. In addition to the hollow borosilicate microspheres, the molding compound according to the invention can also contain hollow microspheres of other materials, for example, of aluminum silicates. However, preferably the molding compound according to the invention only contains hollow borosilicate glass microspheres and no microspheres of other materials. Another object of the invention relates to a method for the production of a molded body for the foundry industry, wherein - a model corresponding to at least one section of a cast part is provided; - a mixture of mold material is introduced into the model; - the mixture of mold material is cured to give a molded body; and - the molded body is removed from the model.

The method according to the invention is characterized in that at least surfaces of the molded body which come into contact with the liquid metal when casting the metal are constituted by a molding compound as described above. By molded body for the foundry industry is generally meant a molded body as used to shape a cast part with metal casting. This type of molded bodies are, for example, molds and cores, and also hollow bodies such as feeders and supply elements. Casting molds are understood as molds that are used directly for casting metals. These casting molds can be composed of several molded bodies. An essential characteristic of the method according to the invention is that the production of the molded body is carried out in such a way that at least the surfaces that come into contact with the liquid metal during casting comprise a proportion of borosilicate glass, in particular of hollow borosilicate glass microspheres. This can be achieved in different ways. According to a first embodiment of the method, the mixture of material for molds for the production of the molded body is constituted completely of a mass of molding as described in the foregoing and comprising a proportion of borosilicate glass. As already explained above, borosilicate glass is preferably introduced in the form of hollow microspheres into the molding compound. In the production of the dough to mold the hollow glass microspheres to the borosilicate can be added to the mass of molding in substance, but also as a mixture with the material for molds and / or the binder, or also as a mixture with other additives. By virtue of the relatively low mechanical loading capacity of the hollow microspheres, during the production of the molding compound, high cutting forces should not influence the molding mass to prevent premature destruction of the hollow microspheres. The molding compound can be introduced into the model so that only parts of the model are filled with the molding compound containing borosilicate glass, while the rest of the volume is filled with a mixture of glass-free mold material. borosilicate. However, preferably the entire molded body is produced from a molding compound containing borosilicate glass, in particular in the form of hollow microspheres. In this embodiment, a molded body is obtained in which the borosilicate glass is homogeneously distributed over the entire volume, for example, in the form of hollow microspheres. The model for the production of the molded body corresponds to a model as already described above in the introductory part, being that the model optionally also includes the molding box. According to another embodiment of the method according to the invention, the molding compound described in the foregoing is applied in the form of a smoothing agent as a mold coating. The molded body for the foundry industry can be produced from a mixture of mold material which also contains borosilicate hollow glass microspheres or which is free of hollow borosilicate glass microspheres. The straightener is applied by conventional methods on the cured or uncured molding, for example, by spraying, painting or immersing the casting mold in the straightener. Another object of the invention relates to a molded body for the foundry industry composed of a material for refractory molds, characterized in that at least the sections of the molded body that come into contact with the liquid metal during the casting process contain glass at borosilicate. In the method according to the invention it was already explained that it is possible that the borosilicate glass is only contained in the outer sections of the casting mold or the molded body, for example inform of a coating of material for molds produced with a straightener, or it can be present distributed evenly over the entire molded body or especially the casting mold. As already explained above, preferably the borosilicate glass in the form of hollow borosilicate glass microspheres is contained in the molded body or in the mold coating produced from a straightener. More details regarding the properties of the hollow microspheres have already been discussed in the foregoing. Another object of the invention relates to the use of a casting mold for the foundry industry as described above and which can optionally be composed of several molded bodies, in a process for casting a casting. The method is carried out in the conventional manner. First, a casting mold is produced in which at least the surfaces coming into contact with the liquid metal are constituted by a molding compound containing borosilicate glass, in particular in the form of hollow microspheres. The liquid metal is then poured into this casting mold. As metals, it is possible to use all the metals that are usual for metal casting. As metals it is possible to use light metals, such as aluminum or magnesium having a relatively low melting point, or metals with a melting point. higher, such as cast iron or steel. The use of hollow microspheres in casting molds and straighteners is not limited to a certain type of cast iron, but comprises all types of cast iron from light cast iron to steel cast iron. Particularly preferably, the casting mold according to the invention or the molded body according to the invention for the foundry industry is used for the casting of iron, since it achieves higher temperatures than cast iron of light metal. The invention is explained below in more detail by way of examples and with reference to the appended figures. They show: Figure 1 a photographic reproduction of the surface of test bodies (called dome cores) obtained by melting iron, being that a molded body without smoothing agent was used, which contained additives that were partially supplemented with hollow glass microspheres borosilicate; Figure 2 a photographic reproduction of the surface of test bodies (called dome cores) obtained by melting iron, when a molded body with smoother was used. The lining of the mold was made once with and once without hollow borosilicate glass microspheres.

Methods of analysis: Determination of bulk density: A graduated glass cylinder cut at the 1000 ml mark is weighed in vacuum. The substance to be measured is then filled with the aid of a powder funnel at a stroke, so that a slope cone is formed above the upper edge of the graduated cylinder. The cone of the slope is flush with the aid of a ruler and the material adhered to the outside of the cylinder is eliminated. The cylinder is reweighed, the difference in weight corresponds to the bulk density. Average particle size (d50) The average particle size is determined by laser diffraction on a Mastersizer S of the company. Malvern Intruments GmbH, Herrenberg, DE according to the manufacturer's instructions. For the following tests, hollow glass microspheres were used to the borosilicate Q-Cel type 5020FPS of the company. MEGA Minerals Germany GmbH. The microspheres have a white color, a particle size in the range of 100-200 μP ?, an effective density of 0.14-0.70 g / cm3, a coefficient of thermal expansion of 9 x 10"6 / ° C and a hardness ( Mohs) from 3.5 to 4.0 The average grain size of the hollow microspheres is 40 μp. The pressure resistance is 4 MPa.

In order to determine the molding masses, a dome male casting is produced in each case. For this purposeAs a binder, consisting of 20 kg of quartz sand 100 T H25 as well as 160 g of Novathen® 155 and 160 g of Novathen® 260 (ASK GmbH, Hilden, DE) as a binder, a male is produced main round with plug male and pouring male that enclose a cylindrical hollow space with a diameter of 310 mm and a height of 157 mm. At the bottom of the cylindrical hollow space, 5 dome-shaped domes are fixed, having a height of 50 mm and a diameter of 50 mm. These dome cores are produced in each case from the molding mass to be analyzed. The mold is assembled by first gluing the dome cores on the base of the hollow space and closing the hollow space with the cap male. A circular opening with a diameter of 20 mm is provided in the cap male. On the cap male, the pouring plug is then fixed in the form of a wall so that the funnel leads towards the opening opening of the cap male. The emptying process is carried out by gravity emptying. The melting temperature is approximately 1410-1430 ° C. The casting time is approximately 10 seconds, the weight of the casting approximately 15 kg. Examples 1 to 3 and comparative example 1: Use of hollow borosilicate glass microspheres in sands for For the test series, quartz sand (Quarzwerke GmbH, Frechen), type H 32 was mixed, first with the additives to be analyzed and then with a cold box binder (Isocure® 366 (part I) and Isocure® 666 ( part II) of the company Ashland-Südchemie-Kernfest GmbH (ASK) The mixing time per component was one minute The addition amounts of the additives were 0-2.0% in relation to the total weight of the sand. The binder system was added in fractions of 0.8-0.9% per part.The curing process was carried out by gassing with amine For this purpose the catalyst 700 of the ASK company was passed through the box of males. a scavenging pressure of 2 bar For the comparative example 1, a mixture without additive was produced For the examples 1 to 3 the additives based on starch (example 1), mica (example 2) and granulate were used in each case hardwood (example 3) obtained from ASK Company, Hilden, DE. they were in each case pure (example (a)), as well as modified with 2.5% of Q-Cel® (example (b)). Iron (GG 25) was used as the casting metal. The melting temperature between 1420 and 1430 ° C. The emptying time was 10 seconds. The test data are compiled in table 1.

The test bodies that are obtained are reproduced photographically in Figure 1. Figure 1 shows in each case two shots of the test body, being that different directions of illumination were used. In the comparative example, that is, without the addition of an additive only a poor penetration was observed, which can be recognized on the smooth surface of the test body. However, there was a very strong formation of leaf ribs that in the photographic shots is recognized as remarkable fillets on the surface of the test body. In Example 1A, in which only pure starch was added as an additive, no leaf rib formation was observed. No fillets on the test body surface are recognized in the photograph. The surface is curved uniformly. However, a medium thickness penetration of the iron appears in the casting mold. This can be recognized in the photographic shot by the rough surface of the test body, which intensely disperses the light that falls on it. In example IB in which Q-Cel® is added with a 2.5% by weight fraction of starch as an additive, no leaf rib formation is observed. The surface is curved uniformly and has no sharp-edged elevations. The test body a casting surface clean that can be recognized in uniform reflection slightly reflective of light. If, as in Example 2A, mica is used as an additive, it is true that leaf rib formation is not observed. However, the test body shows strong erosions that are recognized in the irregular shape of the test body. If, in addition to the mica, Q-Cel® hollow microspheres are added as in Example 2B as an additional additive, no leaf rib formation is observed. A clean casting surface of the test body is observed. This can be recognized in the photographic shot by the slightly reflecting surface of the test body. In test 3A, a hardwood granulate is used as an additive. Foliar rib formation is not observed. However, as shown by the photographic shot, there is a strong penetration of the liquid iron in the casting mold. The surface of the test body is very rough and strongly scatters the incident light. If, as in Example 3B, hollow Q-Cel microspheres are added to the hardwood granulate, no leaf rib formation is observed as an additional additive. The surface of the test body is smooth, which can be recognized in the reflection of the incident light. In all the types of additive a remarkable improvement of the casting surface was obtained with a very scarce of hollow raicrospheres of Q-Cel. Here it is even possible to do without the smoothing in thin-walled castings or in males with thin straightening. Example 4 and 5: Use of hollow microspheres in straighteners To a smoother that already acts well against the formation of leaf ribs, hollow microspheres of Q-Cel® were added. For this purpose, dome cores, additive and cold box resin were produced according to the following description. As a smoothing agent, the commercial Kerntop® WV 021010B of the Company was used. Ashland-Südchemie-Kernfest GmbH. In Example 4, the pure straightener was used, while in Example 5 0.3% by weight of Q-Cel® hollow microspheres were added to the straightener. The straighteners were adjusted in the viscosity so that the same layer thicknesses were obtained with the immersion. The conditions of the test as well as the results are compiled in table 2.

Table 2: Casting tests with molded bodies that have smoothing The molded bodies obtained are reproduced photographically in figure 2. In example 4 a slight inclination towards the formation of leaf ribs is observed. The molded body surface is slightly matt. There is little penetration of liquid iron into the molded body. With the addition of few amounts of hollow glass microspheres to the borosilicate, leaf rib formation is no longer observed. The surface of the casting is smooth, which can be recognized in the reflection of light on the surface of the test body.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (20)

1. CLAIMS Having described the invention as above, the content of the following claims is claimed as property: 1. Molding compound for the production of foundry molds for the foundry industry, characterized in that it comprises at least: - a material for refractory molds; - a binder for curing the molding compound; - a proportion of borosilicate glass in the form of a granulate or powder.
2. 2. Molding compound according to claim 1, characterized in that the molding compound contains the borosilicate glass in a proportion of at least 0.001% by weight with respect to the material for refractory molds.
3. Shaping mass according to claim 1 or 2, characterized in that the molding compound contains the borosilicate glass in the form of hollow microspheres.
4. Molding compound according to claim 3, characterized in that the hollow microspheres have a mean diameter of less than 200 μp ?.
5. 5. Molding mass according to any of claims 3 or 4, characterized in that a wall thickness of the hollow microspheres is 5-30% of its external diameter.
6. Molding compound according to any of claims 3 to 5, characterized in that the hollow microspheres have a bulk density of less than 1.2 g / ml.
7. Molding compound according to any one of the preceding claims, characterized in that the borosilicate glass has a boron content of more than 3% by weight, calculated as B203.
8. 8. Molding compound according to any of the preceding claims, characterized in that the borosilicate glass has a softening point of less than 1500 ° C.
9. 9. Molding compound according to any of the preceding claims, characterized in that the binder is selected from cold box binders, hot box binders, silicate binders, in particular water glass and self-hardening binders.
10. 10. Molding compound according to claim 9, characterized in that the cold box binder is selected from the group of phenol-urethane resins, epoxy-acrylic resins, alkaline phenol resins, glass soluble and self-healing resins.
11. Molding compound according to any of the preceding claims, characterized in addition to borosilicate glass, the molding compound comprises at least one additional additive to reduce the formation of leaf ribs.
12. 12. Molding compound according to claim 11, characterized in that the minimum of an additional additive is selected from combustible organic compounds, mica and iron oxide.
13. 13. Molding compound according to any of the preceding claims, characterized in that the molding compound comprises an additive of at least one organic or inorganic acid and / or an acid source.
14. The molding compound according to any one of claims 1 to 8, characterized in that the molding compound is formed as a smoother.
15. 15. Method for producing a molded body for the foundry industry, where a model corresponding to at least one section of the casting is provided, in the model a mixture of mold material including at least one material is introduced for refractory molds and a binder, the mixture of mold material is cured to obtain a molded body, and the molded body is removed from the model, characterized in that the method is carried out so that at least the sections of the molded body that come into contact with the liquid metal during the casting of the metal are constituted by a molding compound according to any of claims 1 to 14.
16. 16. Method according to claim 15, characterized in that the mixture of material for molds that is introduced in the model is constituted by a molding compound according to any of claims 1 to 13.
17. 17. Method according to claim 15, characterized in that after removing the molded body from the model, they are covered with a molding compound according to any of claims 1 to 14, at least the surfaces of the molded body that come into contact with the liquid metal during the emptying process.
18. 18. Molded body for the foundry industry which is composed of a material for refractory molds, characterized in that at least the sections of the molded body that come into contact with the liquid metal during the emptying process they contain borosilicate glass.
19. 19. Molded body according to claim 18, characterized in that the borosilicate glass is contained in the form of hollow microspheres.
20. 20. Use of a molded body for the foundry industry according to any of claims 18 or 19 in a method for emptying a cast part of a metal.