JP2015514591A - Method for producing mold and core for metal casting, and mold and core produced based on this method - Google Patents

Abstract

The present invention relates to a method for manufacturing a mold and a core. In the mold and core, a cast base material comprising at least one refractory material and preferably a binder curable by CO2 based on water glass is cured by gas filling with CO2 and jetting with a second gas. . The invention further relates to a mold and a core produced according to this method.

Description

The present invention relates to a method for manufacturing a mold and a core. In said method, the mold mixture comprising at least one refractory material and a binder curable with CO ₂ , preferably comprising water glass or consisting of water glass, is a CO ₂ or CO ₂ containing gas And is cured by purging with a second gas that does not contain CO ₂ or contains at least a small amount of CO ₂ . Furthermore, the invention relates to a mold and a core manufactured according to this method.

  The mold and core are typically manufactured using a refractory mold base material, such as quartz sand, and a suitable binder. The refractory mold base material in such a method is preferably such that a mixture of the mold base material and a binder, the so-called mold mixture, can be filled into a hollow mold where it can be compressed and cured. Exists in a free-flowing state. The binder causes solid adhesion between the particles of the mold base material so that the mold and core are of the required mechanical stability.

  During casting, the mold forms the outer wall for the casting. A core is used when a cavity is required in the casting. A mold and core made of the same material are not absolutely necessary. For example, the outer shape of the casting is formed using a durable metal mold. Combinations of molds and cores manufactured by various methods are also possible. As described on the basis of the core, the same description applies to molds (molds) manufactured according to the same method, and vice versa.

  Both organic and inorganic binders that can be cured by low or high temperature methods can be used to produce the core. The low temperature method is a method that is essentially performed at room temperature without heating the mold used for core manufacture. In this method, curing is usually performed by a chemical reaction induced, for example, by the fact that gas passes through the mold mixture to be cured. In a high temperature process, after molding, the mold mixture is heated, for example, to remove the solvent contained in the binder and / or to initiate a chemical reaction by curing the binder, for example by crosslinking. The mold is heated to a sufficiently high temperature.

Curing the water glass-binder with CO ₂ is known, for example, from DE 6554817 (Patent Document 1). In the 1950s and 1960s, water glass -CO ₂ method was widely used. One weakness of this method is that the core produced therefrom has a relatively low strength, particularly immediately after production. Longer gas filling times with CO ₂ ensure a higher initial intensity, but at the same time the intensity after 1 or 2 days of storage decreases. In addition to the relatively low initial and final strength, the water glass-CO ₂ process only allows low to moderate production rates.

For this reason, Y.C. A. As explained by Owu, it has been proposed to combine standard CO ₂ curing with the later so-called “hot air method” (YA Owusu, Ph.D. Dissertation “Sodium Silicate Bonding in Foundry”. Sands ", Pennsylvania State University, May 1, 1980, p. 88, 102-103 (Non-Patent Document 1) and AFS Transactions, vol. 89, 1981, pp. 47-54 (Non-Patent Document 2)). The hot air method is defined as oven curing after CO ₂ gas filling. This is because Y.C. A. Also confirmed by Owu's academic papers. In the case of at least some water glass binders, this method gives better strength in the case of pure CO ₂ curing, but has the disadvantage that the production time for the core is increased from seconds to minutes.

German Offenlegungsschrift 10 2011010548 (Patent Document 2) describes a method for curing a mold mixture bonded with water glass. In the method, a combination of air and carbon dioxide flows is used. In this example, the mold mixture must first be gas filled with air and then gas filled with CO ₂ or an air-carbon dioxide mixture. Furthermore, it is of great importance for the present invention that the alkali silicate solution used has a weight ratio of SiO _{2 to} metal oxide in the range of 1.5: 1 to 2.0: 1.

A further patent describing this type of method is WO 80/01254 (Patent Document 3). This discloses a method for curing a water glass-containing mold mixture that is heated at a temperature of 110 to 180 ° C. while simultaneously passing a CO ₂ or CO ₂ -air mixture.

Polish Patent No. 129359 (Patent Document 4) describes a binder for producing a mold for a metal casting produced from water glass and urea resin. In this case, curing the mold mixture, CO 2 _- it is carried out by jet air mixture. This method is advantageous for gases heated to a temperature of 60-200 ° C. CO ₂ - Additional publications describing the use of the air mixture is Chinese Patent Application Publication No. 94111187 Pat (Patent Document 5).

From EP 201414392 (Patent Document 6) it is known to use amorphous spherical SiO ₂ available in more than one particle size classification. However, EP 2014392 does not disclose the use of a second gas stream and introduces said SiO ₂ in an aqueous suspension. In this case, as a result of the increased introduction of water, it is disadvantageous for the (initial) strength of the mold produced according to the method of the invention provided herein.

Good strength, even after short curing times, is required more and more today, and at the same time is required to reliably manage increasingly complex and thin-walled molds that guarantee high productivity. For this reason, it is not surprising that the water glass-CO ₂ method has rapidly lost its importance due to the advent of organic binder-based methods, in particular the so-called Ashland polyurethane cold box method.

  However, all organic binders have the disadvantage that they can undergo thermal decomposition during casting and release harmful substances such as benzene, toluene or xylene. Furthermore, organic binder systems have already released solvents into the environment during core manufacture and storage, or unpleasant odorous gases are used as curing catalysts. As a result of the various measurements, it has certainly become possible to avoid all these emissions, but they cannot be avoided in the case of organic binders.

  For this reason, attempts have been increasing for years to develop binders that are entirely based on inorganic materials or that contain at most small amounts of organic compounds. In order to achieve high strength in a short time, for example, the pathway is cured in a hot instrument and, if necessary, into the mold mixture to remove the water present as completely as possible. Follow passing hot air. One such system is described, for example, in EP 1802409 (US Pat. No. 7,770,629 (US Pat. No. 7,770,629)). However, these methods have the disadvantage that the instruments must be designed such that they can be heated and consume more energy by heating. The energy consumption represents a significant cost burden for the method.

German Patent Invention No. 654817 German Patent Application Publication No. 10201110548 International Publication No. 80/01254 Pamphlet Polish Patent No. 129359 Chinese Patent Application No. 94111187 EP 20143922 specification European Patent No. 1802409 U.S. Pat. No. 7,770,629

Y. A. Owusu, Ph. D. Dissertation “Sodium Silicate Bonding in Foundry Sands”, Pennsylvania State University, May 1, 1980, p. 88,102-103 AFS Transactions, vol. 89, 1981, pp. 47-54

The inventors have therefore raised the challenge of developing a process that would allow the production of molds and cores in non-heated appliances using inorganic CO ₂ curable binders. In said method, the strength should already be substantially higher without removing the same binder and the same binder content and subsequent heat treatment than in the already known curing with CO ₂ , especially immediately after removal from the appliance. It is.

  This object will be achieved using a method having the features of claim 1. Advantageous further embodiments of the method according to the invention are the subject matter of the dependent claims or will be described below.

Surprisingly, it has been found that a core with good strength can be achieved by a combination of CO ₂ curing with a first gas and a jet of a mold mixture with a second gas (hereinafter also referred to as a jet gas). It was done. In this method, the first gas and the second gas are not set such that the first gas is applied before the second gas. Conversely, the order can be as desired, and the first and / or the second gas can be applied multiple times. However, the second gas is preferably introduced last, and independently of this, the first gas is preferably introduced into the mold first.

During the filling of the first gas (hereinafter also referred to as CO ₂ gas) between 15 ° C. and 120 ° C., preferably between 15 ° C. and 100 ° C., particularly preferably between 25 ° C. and 80 ° C. Is advantageous. In addition, when used in the further description of the method according to the present invention, the gas temperature means the temperature of the gas to the entrance in the mold. The second gas also preferably has a gas temperature between 15 ° C. and 120 ° C., preferably between 15 ° C. and 100 ° C., particularly preferably between 25 ° C. and 80 ° C., but in many cases higher temperatures This makes it possible to shorten the jet flow time. There is no upper limit to this based on the cure mechanism. In practice, depending on the shape and size of the core or the mold, the temperature will be between 40 ° C and 250 ° C, preferably between 50 ° C and 200 ° C. First and foremost, financial considerations are against the use of very high temperatures. This is because the cost of the heater necessary for this purpose is greatly increased by improving the output, and the cost for effectively insulating the wiring becomes very high. For example, the temperature of the first gas is approximately the same as the temperature of the second gas. However, preferably, the temperature of the second gas is higher than the temperature of the first gas.

  As a result of the above measurements, it is advantageous to control the cooling of the mold mixture seen during gas filling by controlling the temperature of the two gas streams.

  The use of heatable appliances available can be cooled, ie, atmospheric or room temperature of 15 to 30 ° C. or lower than normal, ie less than 200 ° C. or less than 120 ° C. It is by no means excluded in the methods described throughout the method of the present invention, which discloses the possibility of operating the instrument at any temperature below 100 ° C. Instruments that are not particularly heatable can be used advantageously. Such a device is not heatable. That is, they do not have a heating device, for example an electric heater, but can be heated by the gas introduced at a controlled temperature. The method according to the invention does not exclude the possibility of subsequently subjecting the core or mold to further heat treatment.

The method according to the invention comprises the following steps:
Producing a mold mixture from at least one refractory mold base material and preferably a CO ₂ curable binder based on water glass, forming the mold mixture, jetting the mold mixture with CO ₂ gas A step of jetting the mold mixture with CO ₂ gas and the jet gas, or
A step of jetting the mold mixture with a second gas (jet gas)

  The approach commonly involved in producing the mold mixture is that the refractory mold base material is used first and the binder is added under shaking. The shaking is continued until a homogeneous distribution of the binder in the mold base material is ensured.

The mold mixture is then placed in the desired mold. In this method, a method useful for casting is used. For example, the mold mixture is injected into the core molding machine using compressed air. Subsequently, curing is performed. That is, (especially) first, the CO ₂ gas passes through a mold filled with the mold mixture and is subsequently jetted by the second gas. One skilled in the art can readily appreciate that various designs are possible for this method.

For example, it is not necessary (although in many cases advantageous) to use pure CO ₂ (eg, industrial grade) as the CO ₂ gas. However, in order to achieve a cure time as possible in the shortest, the CO ₂ gas is at least 50 vol% of CO _2, preferably, it is advantageous to include a CO ₂ of at least 80 vol%.

On the other hand, the second gas need not be completely CO ₂ , for example, synthetic air or nitrogen. Air is preferred for cost reasons. CO ₂ may be added to the jet gas, but it is 10 vol% or less, particularly preferably 5 vol% or less, particularly 2 vol% or less or 1 vol% or less.

The transition from the CO ₂ gas to the second gas does not have to be performed in one step, and a stepwise or fluid transition is possible as well. Furthermore, both gases or one of the two can be pulsed into the template mixture.

A further modification is that a part of the water present in the mold mixture is first removed by simply gas filling with a low CO ₂ content gas as a jet gas, and then the binder is converted into the CO _2. It consists of the fact that it is hardened with gas and optionally is treated again with the low CO ₂ gas for further drying.

The addition of the CO ₂ may be performed by establishing any particular CO ₂ flow rate or a particular gas filling pressure for CO ₂ gas. Either of the two possibilities is due to many factors in practice, such as the shape and size of the core, the tightness of the mold, the ratio of gas inflow to gas exhaust, the gas permeability of the mold base material, the gas It is selected according to the diameter of the line, the content of the binder, the desired gas filling time and the like. In order to optimize the properties, the gas filling parameters are adjusted according to requirements in the shape of the selected core or mold within the framework of the present disclosure and the knowledge routinely processed by those skilled in the art. obtain. Generally between 0.5 L / min and 600 L / min (in each case standard liters), preferably between 0.5 L / min and 300 L / min, particularly preferably between 0.5 L / min and 100 L / min. would CO ₂ flow rate between the minute is selected. According to another embodiment, the CO ₂ flow rate is between 0.5 L / min and 30 L / min, preferably between 0.5 L / min and 25 L / min, particularly preferably 0.5 L / min. And 20 L / min. This embodiment is particularly advantageous at low gas temperatures for CO ₂ or CO ₂ containing gases, between 15 and 40 ° C.

In the case of pressure regulation, the pressure of the CO ₂ gas is usually between 0.5 bar and 10 bar, preferably between 0.5 bar and 8 bar, particularly preferably between 0.5 bar and 6 bar. Fluctuates.

  In the case of air as the jet gas, this can be taken from the pressure line normally available in casting so that for purely practical reasons the pressure above it represents an upper limit for gas filling . The lower limit for effective gas filling with air is about 0.5 bar. At lower pressures, the gas filling time will be very long. This will be related to lost productivity.

  Unless otherwise noted, all pressure descriptions relate to gauge pressure, ie, pressure higher than atmospheric pressure.

The ratio of the gas filling times of the first gas (CO ₂ gas) and the second gas (jet gas) is, for example, between 2:98 and 90:10, preferably 2:98 to 20:80. Between, particularly preferably between 5:95 and 30:70. However, since maintaining CO ₂ consumption as low as possible is also the purpose of this application, the gas filling time with the CO ₂ gas is preferably 60% or less, particularly preferably 50% of the total gas filling time. % Or less should be achieved.

  By proper selection of gas filling parameters and the layout of the instrument, it is possible to secure even that for larger cores and corresponding production times with organic binders, eg less than 3 minutes, preferably less than 2.5 minutes. Particularly preferably, less than 2 minutes are possible. In some cases, such optimization can be performed with the aid of computer simulation.

  The curing of the mold material can be easily modified by a known method, for example, by applying a vacuum. Furthermore, other known processes, such as microwave treatment or oven heating, may be followed by the actual curing procedure.

  Conventional materials may be used to manufacture the mold as the mold base material. Suitable materials are, for example, quartz, zirconium or chrome ore sand, meteorite, vermiculite, bauxite and refractory clay. In such cases, it is not necessary to use fresh sand exclusively. It is even advantageous to use the highest possible amount of recycled old sand for resource saving purposes and to avoid waste disposal costs.

  For example, suitable sands are described in WO 2008/101668 (= US 2010/173767). Recycled products obtained by washing and then drying are also suitable. Recycled products obtained by purely mechanical processing are useful but less preferred. The reclaimed product can generally replace at least about 70 wt%, preferably at least about 80 wt%, particularly preferably at least about 90 wt% of fresh sand.

  Synthetic mold materials, such as glass beads, glass granules, spherical ceramic construction base materials known under the name “Cerabaads” or “Carboaccucast” or aluminum silicate hollow microspheres (so-called microspheres) are refractory molds. It is also useful as a base material. Such aluminum silicate hollow microspheres are marketed in various qualities with different aluminum oxide contents under the name “Omega-Spheres”, for example by Omega Minerals Germany GmbH, Norderstedt. A corresponding product is available from PQ Corporation (USA) under the name “Extendspheres”.

  The average diameter of the mold base material is generally between 100 μm and 600 μm, preferably between 120 μm and 550 μm, particularly preferably between 150 μm and 500 μm. The particle size can be measured, for example, by screening based on DIN ISO 3310.

In casting experiments with aluminum, when a synthetic mold base material is used, for example in the case of glass beads, glass granules or microspheres, there is almost no mold sand adhering to the metal surface than when pure quartz sand is used. Did not remain. Thus, the use of an artificial mold base material allows for the achievement of a smoother casting surface so that expensive post-processing by blasting is not required, or at least to a much lesser extent.
In such an example, not all of the template base material comprising the synthetic template base material is required.

  A preferred ratio of the synthetic mold base material is at least about 3 wt%, particularly preferably at least 5 wt%, particularly preferably at least 10 wt%, advantageously at least about 15 wt%, based on the total amount of the refractory mold base material, Particularly preferred is at least about 20 wt%. Said refractory mold base material is preferably in a free-flowing state so that the mold mixture according to the invention can be processed in a conventional core injection machine.

  As a further component, the mold mixture according to the invention comprises a binder based on water glass. The water glass that can be used includes conventional water glass, such as those already used as binders in mold mixtures.

  Water glass is an aqueous solution of alkali silicates, especially lithium, sodium and potassium silicates, and is also used as a binder in other fields, such as construction. The water glass is produced on a large industrial scale by, for example, melting quartz sand and alkali carbonate at 1350 ° C. to 1500 ° C. In this method, the water glass is first obtained in the form of a block-like solid glass. The solid glass is dissolved in water under the application of temperature and pressure. A further method for producing water glass is the direct decomposition of quartz sand with sodium hydroxide.

The obtained alkali silicate solution can then be adjusted to the desired SiO ₂ / M ₂ O molar ratio by adding alkali hydroxides and / or alkali oxides or hydrates thereof. Furthermore, the composition of the alkali silicate solution can be adjusted by dissolving various components and alkali silicate. In addition to alkali silicate solutions, alkali silicates containing solid water, such as Kasolv, Britesil or Pyramide products from PQ Corporation are available.

The binder is a water glass containing two or more of the above alkali ions, for example, a lithium-modified water glass known from DE 2652421 (= DE 1532847). It can also be based on. Furthermore, the water glass may also contain multivalent ions, such as boron or aluminum (corresponding compounds are described in EP 2305603 (= WO 2011/042132). .)
The water glass preferably has a SiO ₂ / M ₂ O molar ratio in the range of 1.6 to 4.0, especially 2.0 to less than 3.5. M represents lithium, sodium or potassium.

  The water glass preferably has a solid content of 30 wt% or more, particularly preferably 33 wt% or more, and particularly preferably 36 wt% or more. The upper limit for the solid content of the preferable water glass is 65 wt% or less, particularly preferably 60 wt% or less, and particularly preferably 55 wt% or less. The solids are measured in a Sartorius MA30 humidity analyzer. In this analyzer, about 3-4 g of binder is heated to a constant weight at a temperature of 140 ° C. on an aluminum pan (diameter = 10 cm, height = 0.7 cm).

Further, the water glass has a solid content calculated as M ₂ O and SiO ₂ in the range of 25 to 65 wt%, preferably 30 to 60 wt%. The solid content is based on the amount of alkali silicate calculated as SiO ₂ and M ₂ O contained in the water glass.

  Depending on the application and the desired liquid level, in each case based on the mold base material, it is between 0.5 wt% and 5 wt%, preferably between 0.75 wt% and 4 wt%, particularly preferably 1 wt%. A binder based on water glass between 3.5 wt% is used. The information herein is based on water glass having the given solid content and includes water as a diluent.

Based on the amount of alkali silicate calculated as M ₂ O and SiO ₂ , the alkali silicate is added to the mold base containing the inorganic binder according to the present invention without considering the diluent. The amount of binder used is 0.2 to 2.5 wt%, preferably 0.3 to 2 wt%, based on the mold base material. M ₂ O has the above meaning.

  Said mold mixture is preferably a particulate metal oxide selected from the group of silicon dioxide, aluminum dioxide, titanium dioxide and zinc oxide and mixtures or mixed oxides thereof, in particular silicon dioxide, aluminum dioxide and / or aluminosilicate. Including the amount of goods. The particle size of these metal oxides is preferably less than 300 μm, preferably less than 200 μm, particularly preferably less than 100 μm, for example having an average primary particle size between 0.05 μm and 10 μm.

  The particle size can be measured by screen analysis. Particularly preferably, the screen residue on a screen having a mesh size of 63 μm will be less than 10 wt%, preferably less than 8 wt%. Particularly preferably, silicon dioxide is used as the particulate metal oxide. In this case, synthetically produced amorphous silicon dioxide is particularly preferred.

  Preferably, precipitated silica and / or calcined silica is used as the particulate silicon dioxide.

Optionally, the template mixture may comprise amorphous SiO _2. Surprisingly, the addition of amorphous SiO ₂ to the mold mixture has only a positive effect in the thermosetting described in EP 1802409 (= US Pat. No. 7,770,629). It was also found to have a positive effect in curing with CO ₂ gas and jet gas. In terms of initial strength, the strength enhancement appears much greater than that of increasing the binder content to the same amount. On the other hand, in terms of ultimate strength, a higher binder content becomes more advantageous so that alternative means can be utilized based on the desired effect.

Said amorphous SiO ₂ used according to the invention preferably has a water content of less than 15 wt%, in particular less than 5 wt%, particularly preferably less than 1 wt%. In particular, the amorphous SiO ₂ is used as a powder.

Both synthetically produced silica and naturally derived silica can be used as the amorphous SiO ₂ . However, the latter is not preferred, as is known, for example, from DE 102007045649. This is because they are generally classified as carcinogenic because they contain significant crystalline portions.

By synthesis is meant non-naturally-derived amorphous SiO ₂ . That is, it can be produced by chemical reaction, for example, production of silica sol by ion exchange treatment from alkali silicate solution, precipitation from alkali silicate solution, flame hydrolysis method of silicon tetrachloride or ferrosilicon And reduction of quartz sand by coke in an electric furnace during the production of silicon. Amorphous SiO ₂ produced according to the two last named methods is also called calcined SiO ₂ .

In some cases, synthetic amorphous SiO ₂ is exclusively composed of precipitated silica (CAS No. 112926-00-8) and SiO ₂ (fired silica, fumed silica, CAS No. 112945-) produced by flame hydrolysis. 52-5). On the other hand, the product produced in ferrosilicon or silicon production is hardly known as amorphous SiO ₂ (silica fume, microsilica, CAS No. 69012-64-12). For the purposes of the present invention, the product produced in ferrosilicon or silicon manufacturing will also be defined as amorphous SiO ₂ synthesis.

Precipitated silica and calcined, ie flame hydrolyzed SiO ₂ or electric arc produced SiO ₂ are preferably used. Particular preference is given to amorphous SiO ₂ produced by thermal decomposition of ZrSiO ₄ (see DE 102012020509) and SiO produced by oxidation of metallic Si with an oxygen-containing gas. ₂ (see German Offenlegungsschrift 102012020510). Also preferred is a quartz glass powder (mainly amorphous SiO ₂ ) produced from crystalline quartz by melting and rapid cooling so that the particles are spherical and free of debris (DE 102012020511). checking.). The average primary particle size of the synthetic amorphous silicon dioxide can be between 0.05 μm and 10 μm, in particular between 0.1 μm and 5 μm, particularly preferably between 0.1 μm and 2 μm. . The primary particle size is measured by dynamic light scattering in a Horiba LA 950 and is confirmed by scanning electron microscopy (SEM microscopy) in a Nova NanoSEM 230 from a farm of FEI. Furthermore, with the aid of SEM images, the details of the primary particle size can be visualized to the order of 0.01 μm. The SiO ₂ sample is dispersed in distilled water for SEM measurements and then applied to an aluminum holder bonded to a copper strip before the water evaporates.

Furthermore, the specific surface area of the synthetic amorphous silicon dioxide was measured with the aid of gas adsorption measurement (BET method) based on DIN 66131. The specific surface area of the synthetic amorphous SiO ₂ is between 1 and 200 m ² / g, in particular between 1 and 50 m ² / g, particularly preferably between 1 and 30 m ² / g. In some cases, the products can be mixed, for example, to synthetically obtain a mixture having a specific particle size distribution.

The aforementioned amorphous SiO ₂ species readily form larger aggregates by aggregation. Due to the homogeneous distribution of amorphous SiO ₂ in the mold material mixture, it is important that the agglomerates are broken again into smaller units by mixing or do not exceed a certain size from the start. Preferably, the screen residue used to describe the degree of agglomeration is about 10 wt% or less, especially about 5 wt% or less, most particularly preferred, based on passage through a screen having a mesh size of 45 μm (325 mesh). Is about 2 wt% or less.

Depending on the manufacturing method and the manufacturer, the purity of the amorphous SiO ₂ can vary greatly. A variety comprising at least 85 wt%, preferably at least 90 wt%, particularly preferably at least 95 wt% SiO ₂ has proven suitable.

Depending on the application and the desired strength level, in each case based on the mold base mixture, it is between 0.1 wt% and 2 wt%, preferably between 0.1 wt% and 1.8 wt%, particularly preferably 0. The fine particulate amorphous SiO ₂ between 1 wt% and 1.5 wt% is used.

The ratio of water glass binder to amorphous SiO ₂ can vary within wide limits. This offers the advantage of significantly improving the initial strength of the core, i.e. the strength immediately after removal from the instrument, without substantially affecting the final strength. This is particularly significant for light metal casting. On the one hand, a high initial strength is desirable for transporting the cores without problems after they are manufactured, and for creating the entire core package. However, on the one hand, the final strength should not be too high to avoid problems due to core collapse after casting.

Based on the weight of the binder, the amorphous SiO ₂ is preferably present in a quantity of 2 to 60 wt%, preferably 3 to 55 wt%, particularly preferably between 4 and 50 wt%, or in particular Preferably, it is based on the solids ratio of water glass to amorphous SiO ₂ of 10: 1 to 1: 1.2 (parts by weight).

According to EP 1802409, the addition of amorphous SiO ₂ can be performed directly on the refractory material both before and after the addition of the binder, although EP 1 844 300. First, a SiO ₂ premix containing at least a portion of the binder is prepared, and then mixed with the refractory material as described in US Patent Application Publication No. 2008/029240. It is also possible. Binders or binder portions that are present but not used for the premix can be added to the refractory material before or after the addition of the premix or with it. Preferably, the amorphous SiO ₂ is added directly to the refractory material before the addition of the binder.

  Without being bound by theory, the inventors have shown that alkaline water glass can be highly reactive with silanol groups located on the surface of amorphous silicon dioxide and that the water has evaporated. In this case, a strong bond occurs between the silicon dioxide and the water glass and is assumed to be solid at that time.

  In a further embodiment, barium sulfate may be added to the casting mixture in order to further improve the surface of castings, in particular light metal castings, for example aluminum castings. Said barium sulphate may be produced synthetically or may be added as natural barium sulphate, ie in the form of minerals containing barium sulphate, for example barite or barite. This and other features of suitable barium sulphate and the solid mixtures produced thereby will be described in more detail in German Offenlegungsschrift DE 102 01 210 4934. Accordingly, the disclosure content thereof is incorporated into the disclosure of this patent by reference.

  Said barium sulfate is preferably 0.02 to 5.0 wt%, in particular 0.05 to 3.0 wt%, particularly preferably 0.1 to 2.0 wt% or in each case based on the total mold mixture or It is added in an amount of 0.3 to 0.99 wt%.

  Based on further embodiments, other materials may also be added to the casting mixture and are characterized by low wetting by molten aluminum, for example boron nitrite.

  Such a mixture of barium sulphate as a material that is hardly wettable, for example, along with others, as well as other materials can likewise result in a smooth casting surface without sand adhesion. Based on the total amount of non-wetting / substantially wettable material, the barium sulfate content should be greater than 5 wt%, preferably greater than 10 wt%, particularly preferably greater than 20 wt% or greater than 60 wt%. It is.

  The upper limit represents pure barium sulfate-in this case the amount of non-wetting substance in the barium sulfate is 100 wt%. Non-wettable / nearly wettable substances, in particular barium sulphate mixtures, are preferably 0.02 to 5.0 wt.%, Particularly preferably 0.05 to 3.0 wt.% In each case based on said mold mixture, Particularly preferably, it is added in an amount of 0.1 to 2.0 wt% or 0.3 to 0.99 wt%.

  In a further embodiment, the additive component of the mold mixture according to the invention is at least one particulate form, as described in DE 10 2012 121 13073 or DE 10 20 121 13074. Or a single particulate aluminum or mixed metal oxide of aluminum and zirconium. By means of such additives, especially iron or steel castings with very high surface quality, the removal of the mold requires little or no post-cast surface treatment. In addition, it can be obtained after metal casting.

  The particulate metal oxide or the particulate mixed metal oxide tends to hardly react with an inorganic binder, particularly alkaline water glass, or does not react with the water glass at room temperature.

  The particulate metal oxide in this case is in particular at least one aluminum / silicon mixed oxide excluding aluminum oxide in the alpha phase and / or an aluminum-silicon mixed oxide having a phyllosilicate structure. Or may be made of the same oxide. At least one particulate metal oxide comprising at least one aluminum / silicon mixed oxide, excluding aluminum oxide in the alpha phase and / or aluminum / silicon mixed oxide having a phyllosilicate structure, is purely oxidized. Not only fine metal oxides made of aluminum or pure alumosilicates or aluminosilicates, but also metal oxides and other oxides such as zirconium, mixed oxides of zirconium contained in aluminum / silicon or different types It is also defined as a mixture of substances, ie consisting of a plurality of thicknesses. Said mixture of dissimilar materials comprises, together with others, at least two of the above solids or substrates: alumina oxide-containing and / or aluminum / silicon oxide-containing solids or phases.

  Fine metal oxides selected from the group of corundum and zirconium dioxide, zirconium mullite, zirconium corundum and aluminum silicate (excluding those having a phyllosilicate structure) and zirconium dioxide are preferred, and in some cases other metal oxides are also included. Including.

  As additives for the binder, aluminum / silicon mixed oxides having a layer structure, such as metakaolin, kaolin and kaolinite are unsuitable. A calcined amorphous aluminum oxide is also inappropriate.

  Said particulate mixed metal oxide is at least one particulate mixed oxide or a particulate mixture of at least two oxides, or particulate with at least one further particulate oxide. It exists at least as a mixed oxide. In this case, the particulate mixed oxide contains at least one aluminum oxide and at least one zirconium oxide.

In addition to aluminum oxide, zirconium oxide, the particulate mixed metal oxides included in each case include not only pure zirconium oxide and zirconium dioxide, but also mixed oxides such as aluminum silicate and zirconium oxide or foreign substances A mixture of a plurality of phases. Said mixture of different substances comprises, together with others, at least one or more aluminum oxide-containing and / or zirconium oxide-containing solids or phases.
Preferred are particulate mixed metal oxides according to the invention selected from one or more members of the group of a) corundum and zirconium dioxide, b) zirconium mullite, c) zirconium corundum and d) aluminum silicate and zirconium dioxide, Additional metal oxides may also be included.

  Aluminum silicate is defined herein as both an alumosilicate and an aluminosilicate.

Both the aluminum / silicon mixed oxide and the aluminum silicate are preferably island-like silicates as long as they are not amorphous (ie, there is crystallinity or partial crystallinity). In the island-like silicate, the SiO ₄ units (tetrahedrons) present in the structure do not directly bond to each other (there is no Si—O—Si bond), but the tetrahedral SiO ₄ units to one or more Al atoms There is an alternative bond (Si-O-Al). The Al atoms are coordinated by 4, 5 and / or 6 oxygen atoms in this way.
(Systematik der Minerale after Strunz [Strunz'Classification of Minerals], based on the 9 th edition) Typical representatives of these islands silicates, for example, mullite (herein, fusion and calcined mullite and ZrO ₂ Containing mullite) and sillimanite and other members of the sillimanite group (eg, kyanite or andalusite). The kyanite is particularly preferably used from the sillimanite group. Particularly preferred are amorphous aluminum silicates (excluding those having a silicate structure) containing more than 50 atom% aluminum atoms based on the sum of all silicon and aluminum. Optionally, zirconium / zirconium oxide or an aluminum oxide-containing powder formed as a by-product in the production of zirconium corundum is also included, so that zirconium oxide in a finely divided state can also be included. This and other features of suitable particulate metal oxides or particulate mixed metal oxides of aluminum or aluminum and zirconium are described in DE 10 2012 121 13073 or DE 10 20 121 130 74. It is described in more detail in the description. Thus, these are also incorporated by reference into the disclosure of this patent.

The particulate amorphous silicon dioxide added to the template mixture to improve strength can be added as part of or separately from the particulate mixed metal oxide.
In any case, the statements made herein in the concentration of the particulate mixed metal oxide and the particulate amorphous silicon dioxide are in each case understood to be free of other components. is there. In case of doubt, the ingredients must be calculated on this basis.

  In a further embodiment, the additive component of the template mixture according to the present invention may comprise a phosphorus-containing compound. Such additives are preferred in the case of very thin walls of the mold and especially the core. This is because, in this method, the thermal stability of the core or the thin wall portion of the mold can be improved. This is particularly true when the liquid metal on the counter and tilted surfaces during casting can exert a strong erosion action there due to metal static pressure, or in particular can cause the thin walls of the mold to collapse. is important. Suitable phosphorus compounds have little or no significant effect on the processing time of the template mixture according to the invention. Suitable representative examples of this group and their addition amounts are described in detail in WO 2008/046653. For this reason, this is also incorporated by reference into the disclosure of this patent.

Aqueous binders that are binders generally have poor flow performance compared to binders based on organic solvents. This means that a mold having a narrow flow path and a plurality of directional changes cannot be satisfied. As a result, the core may have poorly cured parts. This can also lead to casting failures in the finished casting. According to an advantageous embodiment, the mold material according to the invention comprises a quantity of a lubricant that is easily peeled off, in particular graphite or MoS ₂ . Surprisingly, the addition of such lubricants, especially graphite, can also produce complex shapes with thin walls. In this case, the mold has always a homogeneously high density and strength so that essentially no casting failure is observed during casting. The amount of lubricant, particularly graphite, that is easy to peel off, is preferably 0.05 wt% to 1 wt%, based on the mold base material.

  Instead of lubricants that are easy to peel, surfactants, in particular surfactants, can be used to improve the flowability of the mold mixture. Suitable representative examples of these compounds are described in, for example, International Publication No. 2009/056320 (= US Patent Application Publication No. 2010/0326620). Surfactants containing sulfuric acid or sulfate groups can be specifically mentioned herein.

  In addition to the components mentioned, the mold mixture according to the invention may also contain other additives. For example, an internal mold release agent may be added. The internal mold release agent facilitates removal of the mold from the mold. Suitable internal lubricants are, for example, calcium stearate, fatty acid esters, waxes, natural resins or special alkyd resins.

  Surprisingly, it has been found that the addition of organic additives leads to an improvement in the surface quality of castings, in particular aluminum castings. The mechanism of action of the organic additive is not clear. While not being bound by this theory, the inventors have found that at least some organic additive burns during the casting process between the liquid metal and the mold material that forms the mold walls. It is presumed that a thin gas cushion is formed, thereby preventing a reaction between the liquid metal and the mold material. In addition, the inventors have found that some of the organic additives form a thin layer of so-called glossy carbon in a reducing atmosphere that persists during casting, which is also the same between the metal and the mold material. It is estimated that the reaction between will be prevented. As a further advantageous effect, the addition of the organic additive can improve the strength of the mold after curing.

  It was surprising that the casting surface improvement could be achieved with many different organic additives. 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 glycol, polypropylene glycol Glycerol or polyglycerol; polyolefins such as polyethylene or polypropylene, olefins such as ethylene or propylene and further comonomers such as vinyl acetate or styrene and / or diene monomers; polyamides such as polyamide-6, polyamide- 12 or polyamide-6,6; natural resins such as balsam resins: fatty acid esters such as palmitic acid Chill; fatty amides, such as ethylene - diamine - bis - stearamide; carbohydrates such as dextrin; and metal soaps, for example, oleic acid salt or a divalent or trivalent metal oleate of. The organic additive may be present as either a pure material or a mixture of various organic compounds.

  The organic additive is preferably 0.01 to 1 wt% or 0.1 to 1.0 wt%, particularly preferably 0.05 to 0.5 wt%, particularly preferably 0 in each case based on the mold material. 0.1-0.2 wt% is added.

  In addition, silane may be added to the mold mixture according to the present invention to improve the mold and core resistance to high atmospheric humidity and / or water-based mold material coating. According to a further preferred embodiment, the template mixture comprises an amount of at least one silane. Suitable silanes are, for example, amino silanes, epoxy silanes, mercapto silanes, hydroxy silanes and ureido silanes. 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. Typically, 0.1 to 2 wt%, preferably 0.1 to 1 wt% silane is used, based on the binder.

  Further suitable additives are alkali metal siliconates, such as potassium methyl siliconate, used at 0.5 to 15 wt%, preferably 1 to 10 wt%, particularly preferably 1 to 5 wt%, based on the binder. Is done. If the mold mixture includes an organic additive, this addition can be made at any time in the manufacture of the mold mixture. The addition of the organic solvent can be performed in bulk or in solution. Water-soluble organic additives can be used in the form of an aqueous solution. So long as the additives are soluble in the binder and stable to it for several months without degrading, they can also be dissolved in the binder and thus added to the mold material. Water-insoluble additives can be used in the form of a dispersion or paste. This dispersion or paste preferably contains water as a liquid medium.

  If the template mixture contains silane and / or alkali methyl siliconate, they are usually added in the state that they have been previously included in the binder. However, they can also be added to the mold material as separate components.

  Organic additives can also have a positive effect on the characteristics of the core produced according to the method of the invention. For example, AFS Transactions, vol. 88, pp. 601-608 (1980) and vol. 89, pp. 47-54 (1981) improves the moisture resistance of the core during storage. On the other hand, a phosphorus compound known from International Publication No. 2008/046653 pamphlet (= Canadian Patent Application Publication No. 2666760) improves the thermal stability of the core.

  In the manufacture of the mold mixture, the refractory mold base material is placed in the mixture, and then preferably a liquid component is added first, and the refractory mold base material and the homogeneous layer of the binder are added to the mixture. Mix until formed on granules of refractory mold base material. The mixing time is selected so that intimate mixing of the refractory mold base material and the liquid component occurs. The duration of the mixing depends on the amount of mold mixture produced and the mixing equipment used. Preferably, the duration of the mixing is selected between 1 and 5 minutes. Then, preferably by further shaking of the mixture, a solid component is added in the form of the particulate mixed metal oxide, optionally in the form of amorphous silicon dioxide, barium sulphate or further powdered. Solids are added and then the mixture is further mixed. Herein, the duration of the mixing is also determined by the quantity of the mold mixture produced and the mixing unit used. Preferably, the mixing time is selected between 1 and 5 minutes. The liquid component may be either a mixture of various liquid components or the sum of all individual liquid components. In this case, the latter can be added together or continuously to the mold mixture. According to another embodiment, first the solid component can be added to the refractory mold material, and then only the liquid component is added to the mixture.

  The mold material mixture is then brought into the desired mold. In this method, a normal molding method is used. For example, the mold mixture can be injected into the mold with compressed air using a core injector. A further possibility consists of allowing the mold mixture to flow freely from the mixture into the mold and shaping it by shaking, die forging or compression.

  The method according to the invention itself is suitable for producing all molds suitable for metal casting, for example cores and molds.

  Despite the high strength that can be achieved by the method according to the invention, the cores produced by the mold mixture according to the invention show good disintegration after casting, in particular after casting aluminum. However, the use of the molded product produced from the mold mixture according to the present invention is not limited to light metal casting. The mold is generally suitable for cast metal. Examples of such metals include non-ferrous metals such as brass or copper and iron alloys.

  The invention will be explained in more detail on the basis of the following non-limiting examples.

1. Preparation of mold mixture 1.1 No addition of amorphous SiO _{2 In} each case, 5 kg of quartz sand H32 from Quarzwerke Frechen GmbH was placed in the bowl of a Hobart mixer (model HSM10). The binder was then added under shaking and mixed thoroughly with the sand. Each amount added is indicated in an individual experiment.
1.2 Addition of amorphous SiO ₂ Before adding the binder, 0.5 PW of amorphous SiO ₂ calculated based on sand was added and mixed with this for 1 minute. , 1 was followed. The mode of addition is listed in each experiment.

2. Specimen Production and Part of the mold mixture produced according to tests 1.1 and 1.2 was placed in the reservoir of the H1 core injection machine Roperwerke AG. Wherein each of the remaining template mixture, prior to refilling the core injection machine, carefully stored in a sealed container and protect them from premature reaction with CO ₂ present in dry and air. The mold mixture was injected from the reservoir by compressed air (4 bar) into a non-temperature controlled mold with two engraved grooves for a 50 mm diameter and 50 mm high round core. The test core was then cured. This detail is presented in individual experiments. After curing, the test specimen was removed from the mold and its compressive strength was measured with a Zwick Universal tester (Model Z 010) immediately, ie up to 15 seconds after removal and after storage for 24 hours. The values listed in each table represent the average from 8 cores in each case. In order to eliminate most of the effects of climate change, all specimens used to measure the 24 hour intensity were stored in a climate controlled chamber at 23 ° C. and 50% relative humidity.
In the case of Examples 4.01 to 4.07, the experiment was carried out on an L1 core injector from farm of Laempe & Mossner GmbH. The injector was equipped with a heated tube (model HT42-13) from Hillesheim GmbH. In order to test the mold mixture, a rectangular test bar with dimensions of 150 mm × 22.36 mm × 22.36 mm was produced (so-called Georg-Fischer bar). The three-part mold used was capable of producing four rectangular test bars simultaneously. A part of the mold mixture produced according to 1.2 was moved into the storage part of the core injector. The mold was not heated electrically. The remainder of each mold material mixture is carefully stored in a sealed container until used to refill the core injector, protecting it from drying and premature reaction with CO ₂ present in the air. Prevented. The mold mixture was introduced from the storage container into the mold by compressed air (4 bar) and jetted with hot CO ₂ or hot air. More information about jetting time and gas temperature with compressed air or CO ₂ is given in [Section] 6. After curing, the mold was opened and the test bar was removed.
In order to measure the bending strength, the test bar was placed in a Georg-Fischer strength testing device equipped with a three-point bending device. The force to break the test bar was measured. The bending strength was measured immediately, that is, both up to 15 seconds after removal (initial strength) and about 24 hours after production (final strength).
The results of the strength test are shown in Table 4. The values presented here are averages from multiple measurements on at least 4 cores.

3. _3. Curing with CO ₂ 3.1 To produce the specimen, quartz sand H32 with a molar ratio of about 2.33 and a solids content of about 40 wt%, each 2.0 PW (PW = parts by weight), 2 A mold mixture consisting of .5 PW and 3.25 PW sodium water glass was used. For curing, CO ₂ (supplier and purity in each case: Linde AG, at least 99.5 vol% CO ₂ ) was passed through the mold mixture. The temperature of the gas at the inlet in the mold was between 22 and 25 ° C. Table 1 represents the gas filling time, CO ₂ flow rate, and compressive strength measured under these conditions (see Examples 1.01 to 1.21 and 1.29 to 1.42).
3.2 Some experiments based on 3.1 were repeated with the difference that 0.5 PW of powdered amorphous silicon dioxide was mixed into the mold mixture prior to the addition of the binder. The results are also shown in Table 1 (Examples 1.22 to 1.28).

The following is evident from Table 1 (see attached document):
No addition of amorphous SiO ₂ :
The strength is determined by the amount of CO ₂ used for curing. In this case, the initial intensity increases as the amount of CO ₂ increases. On the other hand, the strength after a storage time of 24 hours decreases due to the effects of known overgas filling (see Examples 1.01 to 1.21). In this case, the overgas filling effect occurs in the latter with a higher binder content, as expected.
With the same absolute amount of CO ₂ , a low flow rate CO ₂ has a predominantly positive effect on the initial intensity. On the other hand, high flow rate CO ₂ has a positive effect on the final strength (Examples 1.03 / 1.08, 1.04 / 1.09 / 1.15, 1.05 / 1.16). /1.06/1.11/1.17, 1.07 / 1.12 / 1.18, 1.14 / 1.20).

Addition of amorphous SiO ₂ :
Addition of amorphous SiO ₂ cured with the same gas filling parameters, but resulted in improved strength compared to the core containing amorphous SiO ₂ (compared to Examples 1.08-1.14). (See 1.22-1.28).
The strength loss after 24 hours storage due to overgas filling is reduced by the amorphous SiO ₂ (see 1.22-1.28 compared to Examples 1.08-1.14).
Besides the long gas filling time, the addition of amorphous SiO ₂ results in a higher improvement in the initial strength than increasing the binder content to the same amount. On the other hand, the final strength improves substantially higher with increased binder content, but drops again higher at longer gas filling times due to the effect of overgas filling (Example 1.29-1). (See 1.22-1.28 compared to .35.)
Even with the same solid content, the mixture of water glass binder and amorphous SiO ₂ can be used for the increased amount of binder that does not contain amorphous SiO ₂ , except for the long gas filling time. Provides advantages in terms of strength. On the other hand, in the case of the final strength, the increased binder content has a higher effect. In this case, the decrease in strength with a long gas filling time is again evident due to overgas filling (see 1.22-1.28 compared to Examples 1.36-1.42). .

4). 4.1 Hardening with air 4.1 PW, 2.5 PW or 3.25 PW sodium with quartz sand H32 and a molar ratio of about 2.33 and a solids content of about 40 wt% to produce the specimen. A mold mixture consisting of water glass was used. Compressed air was applied to the mold mixture for curing.
The temperature of the compressed air at the inlet to the mold was between 22 and 25 ° C. Table 2 shows the gas filling time, gas filling pressure, and compressive strength measured under these conditions (see Examples 2.01-2.03 and 2.07-2.12).
4.2 Some experiments based on 4.1 were repeated with the difference that 0.5 PW of powdered amorphous silicon dioxide was mixed into the mold mixture prior to the addition of the binder. These results are similarly presented in Table 2 (see Examples 2.04-2.06).

From Table 2, we can see that:
No addition of amorphous SiO ₂ :
The strength is determined by the amount of air passed through. In this case, the initial strength increases considerably with respect to the final strength with increasing air volume (see Examples 2.01-2.03 and 2.07-2.12). .
Higher binder content is not necessary to provide better strength. This may possibly be explained by a poorer compression capacity and higher moisture content in the mold mixture (see 2.01-2.03 compared to Examples 2.07-2.12).

Addition of amorphous SiO ₂ :
Addition of amorphous SiO ₂ results in an improvement in strength over a core that is cured with the same gas filling parameters but does not contain amorphous SiO ₂ . In this case, a higher effect is seen in the initial intensity than in the final intensity (see 2.04-2.06 compared to Examples 2.01-1.03).
The improvement in strength due to the amorphous SiO ₂ is higher than that obtained by increasing the binder content to the same amount (see 2.07-2.09 compared to Examples 2.04-2.06). ).
The improvement in strength caused by the amorphous SiO ₂ is higher than that of increasing the binder content for the same solids (2.10-2.12 compared to Examples 2.04-2.06). checking.).

5. Hardening with a combination of CO ₂ and air 5.1 To produce the specimen, 2.0 PW, 2.5 PW, and quartz sand H32 with a molar ratio of about 2.33 and a solids content of about 40 wt% A mixture of solids consisting of 3.25 PW water glass was used. For curing, first CO ₂ and then compressed air were passed through the mold mixture. The temperature of both gases before entering the mold was between 22 and 25 ° C.
Table 3 shows the gas filling time for CO ₂ and air, the CO ₂ flow rate, the gas filling pressure (air), and the compressive strengths found under these conditions (Examples 3.01-3.09, 3 19-3.27, 3.37-3.45).
5.2 Some experiments corresponding to 5.1 were repeated with the difference that 0.5 PW of powdered amorphous silicon dioxide was mixed with the mold mixture prior to the addition of the binder. . These results are also shown in Table 3 (see Examples 3.10-3.18, 3.28-3.36 and 3.46-3.48).
5.3 Some experiments based on 5.1 were repeated with the difference that the compressed air passing through the mold mixture was heated to about 100 ° C. measured at the entrance to the mold. The results are also shown in Table 3 (see Examples 3.49-3.51).
5.4 Some experiments based on 5.2 were repeated with the difference that the compressed air passing through the mold mixture was heated to about 100 ° C. measured at the inlet in the mold. The results are also shown in Table 3 (see Examples 3.52-3.54).
The following is clear from Table 3.

No addition of amorphous SiO ₂ :
As a result of the combined gas filling of CO ₂ / air, substantially better strength is achieved than by gas filling with CO ₂ or air alone (Examples 1.01-1.21 and 2.01 respectively). (See 3.01-3.09 and 3.19-3.27 compared to -2.03.)
Increasing the pressure during gas filling with air results in a further increase in strength (see 3.43-3.45 compared to Examples 3.04-3.06).
Heating the air used for gas filling improves the final strength (see 3.49-3.51 compared to Examples 3.04-3.06). The fact that the initial strength does not show the same effect can probably be explained by the fact that they remained hot during the strength test.
The extension of the gas filling time with CO ₂ does not always have a positive effect on the intensity due to the effect of the overgas filling (see Examples 3.01-3.09 and 3.19-3.27). See
The increase in CO ₂ flow rate, wherein at improving the initial strength is effected, which were compared for the final strength is disadvantageous (Example 3.19-3.27 3.01-3 .09)).
A higher binder content results in a higher final strength but is not necessary for a higher initial strength. The latter can probably be explained by an increase in the amount of moisture in the template mixture (see 3.37-3.42 compared to Examples 3.04-3.06).

Addition of amorphous SiO ₂ :
The addition of amorphous SiO ₂ results in improved strength compared to a core that is cured with the same parameters but does not contain amorphous SiO ₂ . In this case, the effect on the initial intensity is higher than that on the final intensity. At higher CO ₂ flow rates and / or longer CO ₂ gas filling times, the final strength was somewhat reduced due to the effect of the overgas filling (compared to Examples 3.01-3.09). (See 3.10-3.18 and 3.28-3.36 compared to Examples 3.19-3.27).
The addition of the amorphous SiO ₂ results in a higher improvement in the initial strength than increasing the binder content to the same amount. However, in the case of the final strength, the effect of the improved binder strength is higher (see 3.13-3.15 compared to Examples 3.37-3.39). .
Even at the same solids, a mixture of water glass binder and amorphous SiO ₂ offers advantages in initial strength over the corresponding increased amount of binder without amorphous SiO ₂ . On the other hand, in the case of the final strength, the effect of the higher binder content is stronger (see 3.13-3.15 compared to Examples 3.40-3.42).
An increase in pressure in the case of gas filling with air results in a further increase in strength (see 3.46-3.48 compared to Examples 3.13-3.15).

6. Curing with CO ₂ , air or a combination of CO ₂ and air at a gas filling temperature of 115 to 90 ° C. 6.1 To produce the specimen, quartz sand H32 and a molar ratio of about 2.33 and A mold material mixture consisting of 2.0 PW water glass with a solids content of about 40 wt% was used. Further, 0.5 PW of powdered amorphous silicon dioxide was added to the mold mixture before the binder was added. For curing, first CO ₂ and then compressed air were passed through the mold mixture. Both gases were heated to temperatures up to 120 ° C. using heating tubes. The temperature of both gases at the inlet in the mold first reached 115 ° C. and then dropped to 90 ° C. during 35 seconds of gas filling. This temperature drop is due to the fact that the heating tube cannot maintain a constant gas temperature during gas filling.
Just before starting the experiment, experiment 4.04 was first repeated about 80 times over a period of 50 minutes so that the mold reached the required operating temperature of about 60 ° C.
Table 4 represents the gas filling time for CO ₂ and air, the CO ₂ flow rate, the gas filling pressure (air), and the bending strength found under these conditions (see Examples 4.01-3.07). Of that.)

Table 4 shows the following.
The values for the strength clearly confirm that the combined gas filling of CO ₂ and air is clearly superior to gas filling with either air or CO ₂ alone. In particular, Examples 4.01 to 4.03, in which the curing was performed exclusively with CO ₂ , showed a clearly lower initial value, with the exception of Example 4.01, an example of the method according to the invention. It also shows a lower final intensity compared to 4.05-4.07.
Strength of Example 4.04 indicating the value of the gas filling with air alone, likewise, according to the present invention CO 2 _- significantly lower than the intensity of the combined gas-filled air. On the other hand, the final strength for Examples 4.05-4.07 is 10-60 N / cm ^2, which is higher than the value for Example 4.04. The first of the intensity is higher than 50-60N / cm ^2. Thus, the apparently higher initial intensity of Examples 4.05 to 4.07 positively explains the effect of the present invention, even with an improved gas temperature of 115 to 90 ° C. for CO ₂ and air. To do. Examples 4.05 to 4.07 show only slight differences from each other, but these are not significant.

Claims (19)

Preparing a mold mixture comprising at least one refractory mold base material and an inorganic binder;
Introducing the mold mixture into a mold, and
While the mold mixture is jetted with a) a gas containing gaseous CO ₂ or CO ₂ as the first gas, and b) a second gas containing less carbon dioxide than the first gas, the mold Curing the mold mixture in
A method for producing molds and cores.   The mold material mixture is introduced into the air with the aid of compressed air using a core launcher, the mold is a mold, and the mold is jetted with the first and second gases. The method of claim 1.   3. At least one of claims 1-2, wherein the mold is either not superheatable or is heated to a temperature of less than 70 ° C, preferably less than 60 ° C, particularly preferably less than 40 ° C. The method described. The binder has a SiO ₂ / M ₂ O molar ratio of 1.6 to 4.0, preferably 2.0 to less than 3.5, having M equal to water glass, in particular lithium, sodium and / or potassium. The method according to at least one of claims 1 to 3, wherein the method is water glass.   5. The method according to claim 1, wherein the mold material mixture comprises at most 1 wt%, preferably at most 0.5 wt%, particularly preferably at most 0.2 wt% of organic compounds. Said second gas, CO ₂ of less than 10 vol%, in particular comprises a CO ₂ of less than 2 vol%, particularly, mixtures thereof of air or nitrogen, the method according to at least one of the claims 1 5. The first gas is at least 25 mol% of CO _2, in particular at least 50 mol% of CO _2, preferably at least 80 mol% of CO _2, The method according to at least one of the claims 1 6.   The gas flow rate of the first and / or the second gas is 0.5 to 600 L / min (standard liter), preferably 0.5 to 300 L / min, particularly preferably 0.5 L / min to 100 L / min. The method according to claim 1, wherein the method is reached.   The gas flow rate of the first and / or second gas is preferably 0.5 to 30 L when the first gas and / or the second gas is used at a temperature of 15 to 40 ° C. 9. A process according to at least one of claims 1 to 8, wherein it reaches 1 / min (standard liters), preferably 0.5 to 25 L / min, particularly preferably 0.5 L / min to 20 L / min.   The filling pressure of the first and / or the second gas with respect to the mold is between 0.5 bar and 10 bar, preferably between 0.5 bar and 8 bar, particularly preferably between 0.5 and 6 bar. 10. The method according to at least one of claims 1 to 9, wherein   The ratio of the gas filling time with the first gas to the gas filling time with the second gas is from 2:98 to 90:10, preferably from 2:98 to 20:80, particularly preferably from 5:95 to 30: The gas filling time with the first gas is 70, in particular reaching at most 60% of the sum of the gas filling times with the first and second gases. Method.   Quartz-, zirconia- or chromium-ore ore sand, meteorite, vermiculite, bauxite and / or refractory clay, in which the refractory mold base material has in particular an average particle size of 100 to 600 μm, preferably 150 to 500 μm 12. The method according to at least one of claims 1 to 11, wherein   If the binder, in particular water glass, is water glass, based on the mold base material, preferably 0.5 to 5 wt%, preferably 25 to 65 wt%, preferably 30 to 60 wt% based on the solids content. 13. A method according to at least one of claims 1 to 12, wherein the method is 1 to 3.5 wt%. Furthermore, it preferably has an average particle size of between 0.05 and 10 μm, in particular between 0.1 and 5 μm, particularly preferably between 0.1 and 2 μm, independently of surface area reaches 200 meters ² / g from 1, particularly 1 to ^{50 m} 2 / g, particularly from preferably 1 to ^{30 m} 2 / g, amorphous SiO _2, in particular amorphous SiO ₂ synthesis is used, claims 14. The method according to at least one of 1 to 13. The amorphous SiO ₂ is used in an amount of 0.1 to 2 wt%, preferably 0.1 to 1.5 wt% in each case based on the mold base material, independently of the binder. 15. A method according to at least one of the preceding claims, used at 2 to 60 wt%, particularly preferably 4 to 50 wt%, based on weight.   The first gas is introduced into the mold at a temperature of 15 to 120 ° C., preferably 15 to 100 ° C., particularly preferably 25 to 80 ° C., independently of the second gas, The temperature of the second gas introduced into the mold at a temperature within the same temperature interval or at a temperature of 40 to 250 ° C., preferably the temperature of the second gas introduced into the mold is that of the first gas. 16. A method according to at least one of claims 1 to 15, which is higher. The amorphous SiO ₂ used has a water content of less than 15 wt%, in particular less than 5 wt%, particularly preferably less than 1 wt%, independently of this, in particular used as a powder. The method according to at least one of 1 to 16.   The first gas and the second gas are introduced into the mold in any order and number of introduction processes, but at least temporally separated from each other, preferably the second gas is 18. Lastly, through the mold, in particular, the first and only once first gas and then the second gas are performed through the mold. Method.   A mold or core that can be manufactured according to at least one of claims 1-18.