EP3060362B1 - Multi-component system for producing molds and cores and methods form making molds and cores - Google Patents

Description

The invention relates to a multi-component system for obtaining molding material mixtures for the foundry industry, comprising one or more powdery oxidic boron compounds in combination with refractory molding raw materials, a water glass-based binder system and amorphous particulate silicon dioxide, in particular for the production of castings from aluminum, and a process for the production thereof of molds and cores from the molding material mixtures, which easily disintegrate after metal casting.

State of the art

Casting molds essentially consist of cores and molds, which represent the negative molds of the casting to be produced. These cores and molds consist of a refractory material, for example quartz sand, and a suitable binder, which gives the casting mold sufficient mechanical strength after removal from the mold. For the production of casting molds, a refractory base material is used, which is coated with a suitable binder. The refractory mold raw material is preferably in a free-flowing form, so that it can be filled into a suitable hollow mold and compacted there. The binder creates a firm bond between the particles of the base material, so that the casting mold is given the required mechanical stability.

Casting molds have to meet various requirements. During the casting process itself, they must first have sufficient strength and temperature resistance in order to be able to absorb the liquid metal into the cavity formed from one or more casting (partial) molds. After the solidification process begins, the mechanical stability of the casting is ensured by a solidified metal layer that forms along the walls of the casting mold. The material of the casting mold must now decompose under the influence of the heat given off by the metal in such a way that it loses its mechanical strength, that is to say the cohesion between individual particles of the refractory material is broken. Ideally, the mold disintegrates into fine sand that can be easily removed from the casting.

In recent times, more and more, it has been increasingly demanded that, during the manufacture of the casting molds and during the production of the casting and cooling, there are as few emissions as possible in the form of CO ₂ or hydrocarbons, in order to protect the environment and mainly to reduce the odor of the environment by hydrocarbons with aromatic hydrocarbons. In order to meet these requirements, inorganic binding systems have been developed or developed in recent years, the use of which means that emissions of CO ₂ and hydrocarbons in the production of metal molds can be avoided or at least significantly minimized. However, the use of inorganic binding systems is often associated with other disadvantages, which are described in detail in the explanations below.

Compared to organic binders, inorganic binders have the disadvantage that the casting molds produced therefrom have relatively low strengths. This is particularly evident immediately after the mold is removed from the tool. Good strengths at this point are particularly important for the production of complicated and / or thin-walled molded parts and their safe handling. The resistance to air humidity is also significantly reduced compared to organic binders.

EP 1802409 B1 discloses that higher instant strengths and greater resistance to atmospheric moisture can be achieved by using a refractory molding base, a water glass-based binder and addition of particulate amorphous silicon dioxide. This addition ensures safe handling of even complicated molds.

Inorganic binder systems have the disadvantage over organic binder systems that the coring behavior, i.e. the ability of the casting mold to disintegrate quickly (under mechanical stress) into a free-flowing form after casting, in purely inorganic casting molds (e.g. those that use water glass as a binder ) is often worse than in molds made with an organic binder.

This last-mentioned property, poor de-coring behavior, is particularly disadvantageous if thin-walled or filigree or complex casting molds are used, which in principle are difficult to remove after casting. As an example, so-called water jacket cores can be attached here, which are necessary in the production of certain areas of an internal combustion engine.

Attempts have already been made to add organic components to the molding material mixture, which pyrolyze / react under the influence of the hot metal and thereby facilitate the disintegration of the casting mold after casting through pore formation. An example of this is the DE 2059538 (= GB 1299779 A ). However, the amounts of glucose syrup added here are very large and are also associated with a considerable emission of CO ₂ and other pyrolysis products.

Problems of the state of the art and task

1. (a) keine oder zumindest eine deutlich reduzierte Menge an Emissionen von CO₂ und organischen Pyrolyseprodukten (gasförmig und/oder aerosolförmig, z.B. aromatische Kohlenwasserstoffe, Qualm) während des Metallgießens entstehen lässt,
2. (b) ein entsprechendes Festigkeitsniveau erreicht, welches im automatisierten Fertigungsprozess nötig ist (insbesondere Heißfestigkeiten und Festigkeiten nach Lagerung),
3. (c) eine sehr gute Oberflächengüte des betreffenden Gussstücks ermöglicht, so dass keine oder zumindest nur eine geringe Nachbearbeitung nötig ist, und
4. (d) zu einer sehr guten Zerfallseigenschaft der Gießform nach dem Metallguss führt, so dass das betreffende Gussstück leicht und rückstandsfrei von der Gießform getrennt werden kann.

The previously known inorganic binder systems for foundry purposes still have room for improvement. Above all, it is desirable to develop an inorganic binder system that:

1. (a) causes no or at least a significantly reduced amount of emissions of CO ₂ and organic pyrolysis products (gaseous and / or aerosol-like, for example aromatic hydrocarbons, smoke) during metal casting,
2. (b) a corresponding strength level is reached, which is necessary in the automated manufacturing process (in particular hot strengths and strengths after storage),
3. (c) enables a very good surface quality of the casting in question, so that no or at least only slight reworking is necessary, and
4. (d) leads to a very good disintegration property of the casting mold after the metal casting, so that the casting in question can be separated from the casting mold easily and without residue.

The invention was therefore based on the object of providing a multicomponent system for obtaining a molding material mixture for producing casting molds for metal processing, which particularly effectively improves the disintegration properties of the casting mold after metal casting and at the same time achieves a level of strength which is necessary in the automated production process is.

Furthermore, the production of casting molds with a complex geometry should be made possible, which can also include thin-walled sections, for example. The casting mold should also have a high storage stability and remain stable even at higher temperatures and air humidity.

Summary of the invention

The above tasks are solved by the multi-component system and the method with the features of the independent claims. Advantageous developments of the multi-component system according to the invention are the subject of the dependent claims or described below.

Surprisingly, it was found that by adding at least one powdery, oxidic boron compound to the molding material mixture, which is obtained from the multi-component system according to the invention, casting molds based on inorganic binders can be produced, which have high strength both immediately after production and even with long storage.

A key advantage is that the addition of powdered borates leads to significantly improved disintegration properties of the casting mold after metal casting. This advantage is associated with significantly lower costs for the production of a casting, in particular for castings which have a complex geometry with very small cavities from which the casting mold has to be removed.

According to one embodiment of the invention, the multi-component system contains organic components with a proportion of up to a maximum of 0.49% by weight, in particular up to a maximum of 0.19% by weight, so that only very small amounts of emissions of CO ₂ and other pyrolysis products are produced ,

For this reason, the exposure at the workplace for the employees employed there and for people living in the vicinity can be restricted by emissions that are harmful to health. The use of the molding material mixture also contributes to the reduction of climate-damaging emissions from CO ₂ and other organic pyrolysis products.

• einen feuerfesten Formgrundstoff; sowie
• ein auf Wasserglas basierendes Bindemittel und
• partikuläres amorphes Siliziumdioxid; und
• eine oder mehrere pulverförmige, oxidische Bor-Verbindung(en).

The molding material mixture for the production of casting molds for metal processing comprises at least:

• a refractory mold base; such as
• a water glass based binder and
• particulate amorphous silicon dioxide; and
• one or more powdery, oxidic boron compound (s).

Detailed description of the invention

Common and known materials can be used as the refractory mold base material for the production of casting molds. Suitable are, for example, quartz, zircon or chrome ore sand, olivine, vermiculite, bauxite, chamotte as well as artificial mold raw materials, in particular more than 50% by weight quartz sand based on the refractory mold raw material. It is not necessary to use only new sands. In terms of conserving resources and avoiding landfill costs, it is even advantageous to use the highest possible proportion of regenerated old sand, as can be obtained from used forms by recycling.

A refractory molded raw material is understood to mean substances that have a high melting point (melting temperature). The melting point of the refractory mold base material is preferably greater than 600 ° C., preferably greater than 900 ° C., particularly preferably greater than 1200 ° C. and particularly preferably greater than 1500 ° C.

The refractory molding base material preferably makes up greater than 80% by weight, in particular greater than 90% by weight, particularly preferably greater than 95% by weight, of the molding material mixture obtained from the multicomponent system according to the invention.

A suitable sand is eg in the WO 2008/101668 A1 (= US 2010/173767 A1 ) described. Regenerates can also be used, which can be obtained by washing and then drying shredded used molds. As a rule, the regenerates can make up at least about 70% by weight of the refractory base material, preferably at least about 80% by weight and particularly preferably greater than 90% by weight.

The average diameter of the refractory mold raw materials is generally between 100 μm and 600 μm, preferably between 120 μm and 550 μm and particularly preferably between 150 μm and 500 μm. The particle size can e.g. determine by sieving according to DIN ISO 3310. Particle shapes with the greatest linear expansion to the smallest linear expansion (perpendicular to one another and in each case for all spatial directions) from 1: 1 to 1: 5 or 1: 1 to 1: 3, i.e. those that e.g. are not fibrous.

The refractory molding base material preferably has a free-flowing state, in particular in order to be able to process the molding material mixture obtained from the multi-component system according to the invention in conventional core shooters.

The water glasses contain dissolved alkali silicates and can be prepared by dissolving glass-like lithium, sodium and potassium silicates in water. The water glass preferably has a molar module SiO ₂ / M ₂ O (cumulative for different M's, ie in total) in the range from 1.6 to 4.0, in particular 2.0 to less than 3.5, where M is Lithium, sodium and / or potassium is available. The binders can also be based on water glasses which contain more than one of the alkali ions mentioned, for example those from DE 2652421 A1 (= GB1532847 A ) well-known lithium-modified water glasses. Furthermore, the water glasses can also contain polyvalent ions, such as those in EP 2305603 A1 (= WO 2011/042132 A1 ) described aluminum-modified water glasses. According to a particular embodiment, a proportion of lithium ions, in particular amorphous lithium silicates, lithium oxides and lithium hydroxide, or a ratio [Li ₂ O] / [M ₂ O] or [Li ₂ O _active ] / [M ₂ O] as in FIG DE 102013106276 A1 described used.

The water glasses have a solids content in the range from 25 to 65% by weight, preferably from 30 to 55% by weight, in particular from 30 to 50% by weight and very particularly preferably from 30 to 45% by weight.

The solids content relates to the amount of SiO ₂ and M ₂ O contained in the water glass. Depending on the application and the desired level of strength, between 0.5% and 5% by weight of the binder based on water glass is used, preferably between 0.75% by weight % and 4% by weight, particularly preferably between 1% by weight and 3.5% by weight and particularly preferably 1 to 3% by weight, in each case based on the molding base. The information relates to the total amount of water glass binder, including the (in particular aqueous) solvent or diluent and the (any) solids content (together = 100% by weight). For the purposes of calculating the preferred total amount of water glass, the above values are based on a solids content of 35% by weight (see examples), regardless of which solids content is actually used.

Powdery or particulate in each case means solid powder (including dusts) or also granules which can be poured and thus can also be sieved.

The molding material mixture contains one or more powdery, oxidic boron compounds. The average particle size of the oxidic boron compounds is preferably less than 1 mm, preferably less than 0.5 mm, particularly preferably less than 0.25 mm. The particle size of the oxidic boron compounds is preferably greater than 0.1 μm, preferably greater than 1 μm and particularly preferably greater than 5 μm.

The average particle size can be determined using a sieve analysis. The screen residue on a screen with a mesh size of 1.00 mm is preferably less than 5% by weight, particularly preferably less than 2.0% by weight and particularly preferably less than 1.0% by weight. Particularly preferably, the screen residue is less than 20% by weight, preferably less than 15% by weight, particularly preferably less than 10% by weight and particularly preferably less, regardless of the information given above on a screen with a mesh size of 0.5 mm than 5% by weight. Particularly preferably, the sieve residue is preferably less than 50% by weight, preferably less than 25% by weight and particularly preferably less than 15% by weight, independently of the preceding information on a sieve with a mesh size of 0.25 mm. The screening residue is determined using the machine screening method described in DIN 66165 (Part 2), with a chain ring also being used as a screening aid.

Oxidic boron compounds are understood to mean compounds in which the boron is in the oxidation state +3. Furthermore, the boron is coordinated with oxygen atoms (in the first coordination sphere, i.e. as the closest neighbor) - either 3 or 4 oxygen atoms.

The oxidic boron compound is preferably selected from the group of borates, boric acids, boric anhydrides, borosilicates, borophosphates, borophosphosilicates and mixtures thereof, the oxidic boron compound preferably not containing any organic groups.

Boric acids are understood to mean orthoboric acid (empirical formula H ₃ BO ₃ ) and meta or polyboric acids (empirical formula (HBO ₂ ) _n ). Orthoboric acid occurs, for example, in water vapor sources and as a mineral sassolin. It can also be produced from borates (eg borax) by acid hydrolysis. For example, meta or polyboric acids can be produced from orthoboric acid by intermolocular condensation by heating.

Boric anhydride (empirical formula B ₂ O ₃ ) can be produced by annealing boric acids. Boric anhydride is obtained as a mostly glassy, hygroscopic mass that can then be crushed.

In principle, borates are derived from boric acids. They can be of both natural and synthetic origin. Borates are made up, among other things, of borate structural units in which the boron atom is surrounded by either 3 or 4 oxygen atoms as the closest neighbors. The individual structural units are mostly anionic and can either be isolated within a substance, for example in the case of orthoborate [BO ₃ ] ^3- , or linked together, such as Metaborate [BO ₂ ] ^n- _n , whose units are linked to form rings or chains can be - if you look at such a linked structure with corresponding BOB bonds, it is anionic in the overall view.

Borates which contain linked BOB units are preferably used. Orthoborates are suitable, but not preferred. Counterions to the anionic borate units are, for example, alkali and / or alkaline earth cations, but also, for example, zinc cations.

In the case of mono- or divalent cations, the molar molar ratio between cation and boron can be described in the following manner: M _x O: B ₂ O ₃ , where M stands for the cation and x for divalent cations 1 and for monovalent cations 2 is. The molar molar ratio of M _x O (x = 2 for M = alkali metals and x = 1 for M = alkaline earth metals): B ₂ O ₃ can vary within wide limits, but is preferably less than 10: 1, preferably less than 5 : 1 and particularly preferably less than 2: 1. The lower limit is preferably greater than 1:20, preferably greater than 1:10 and particularly preferably greater than 1: 5.

Borates in which trivalent cations serve as counterions to the anionic borate units are also suitable, for example aluminum cations in the case of aluminum borates.

Natural borates are mostly hydrated, ie water is contained as structural water (as OH groups) and / or as water of crystallization (H ₂ O molecules). Borax or borax decahydrate (di-sodium tetraborate decahydrate) can be regarded as an example, the empirical formula in the literature either as [Na (H ₂ O) ₄ ] ₂ [B ₄ O ₅ (OH) ₄ ] or for the sake of simplicity is given as Na ₂ B ₄ O ₇ ^∗ 10H ₂ O. Both hydrated and non-hydrated borates can be used, but the hydrated borates are preferred.

Both amorphous and crystalline borates can be used. Amorphous borates are understood to mean, for example, alkali or alkaline earth borate glasses.

Perborates are not preferred due to their oxidative properties. In principle, the use of fluoroborates is also conceivable, but due to the fluorine content not particularly preferred in aluminum casting. Since the use of ammonium borate with an alkaline water glass solution produces significant amounts of ammonia, which endangers the health of the people working in the foundry, such a substance is not preferred.

Borosilicates, borophosphates and borophosphosilicates are understood to mean compounds which are usually amorphous / glass-like.

The structure of these compounds contains not only neutral and / or anionic boron-oxygen coordinates (eg neutral BO ₃ units or anionic BO ₄ ^- units), but also neutral and / or anionic silicon-oxygen and / or phosphorus - Oxygen coordinations - the silicon is in the oxidation level +4 and the phosphorus is in the oxidation level +5. The coordinations can be linked to one another via bridging oxygen atoms, such as for Si-OB or POB. Metal oxides, in particular alkali and alkaline earth metal oxides, which serve as so-called network modifiers, can be built into the structure of the borosilicates, borophosphates and borophosphosilicates. The proportion of boron (calculated as B ₂ O ₃ ) in the borosilicates, borophosphates and borophosphosilicates is preferably greater than 15% by weight, preferably greater than 30% by weight, particularly preferably greater than 40% by weight, based on the total mass of the corresponding borosilicate, borophosphate or borophosphosilicate.

From the group of borates, boric acids, boric anhydride, borosilicates, borophosphates and / or borophosphosilicates, however, the borates, borophosphates and borophosphosilicates, and in particular the alkali and alkaline earth borates, are clearly preferred. One reason for this selection is the strong hygroscopicity of the boric anhydride, which impairs its possible use as a powder additive when it is stored for a long time. In casting experiments with an aluminum melt, it was also shown that borates lead to significantly better casting surfaces than boric acids, which is why the latter are less preferred. Borates are particularly preferably used. Alkali and / or alkaline earth borates are particularly preferred, of which sodium borates and / or calcium borates are preferred.

Surprisingly, it was found that even very small additions to the molding material mixture significantly improve the disintegration ability of the casting mold after exposure to temperature, ie after metal casting, in particular after aluminum casting. The proportion of the oxidic boron compound, based on the refractory mold raw material, is preferably less than 1.0% by weight, preferably less than 0.4% by weight, particularly preferably less than 0.2% by weight, particularly preferably less than 0.1% by weight and particularly preferably less than 0.075% by weight. The lower limit is preferably greater than 0.002% by weight, preferably greater than 0.005% by weight, particularly preferably greater than 0.01% by weight and particularly preferably greater than 0.02% by weight.

It has also surprisingly been found that alkaline earth borates, in particular calcium metaborate, increase the strength of molds and / or cores which have been cured with acidic gases such as CO ₂ . It has also surprisingly been found that the moisture resistance of the molds and / or cores is improved by the addition of oxidic boron compounds according to the invention.

The molding material mixture contains a portion of a particulate amorphous silicon dioxide in order to increase the strength level of the casting molds produced with such molding material mixtures. An increase in the strengths of the casting molds, in particular the increase in the hot strengths, can be advantageous in the automated production process. Synthetically produced amorphous silicon dioxide is particularly preferred.

The particle size of the amorphous silicon dioxide is preferably less than 300 μm, preferably less than 200 μm, particularly preferably less than 100 μm and has, for example, an average primary particle size between 0.05 μm and 10 μm. The sieve residue of the particulate amorphous SiO ₂ when passing through a sieve with a mesh size of 125 μm (120 mesh) is preferably not more than 10% by weight, particularly preferably not more than 5% by weight and very particularly preferably not more than 2% by weight. %. Independently of this, the sieve residue on a sieve with a mesh size of 63 μm is less than 10% by weight, preferably less than 8% by weight. The screening residue is determined using the machine screening method described in DIN 66165 (Part 2), with a chain ring also being used as a screening aid.

The particulate amorphous silicon dioxide which is preferably used according to the present invention has a water content of less than 15% by weight, in particular less than 5% by weight and particularly preferably less than 1% by weight.

The particulate amorphous SiO ₂ is used as a powder (including dusts).

Both synthetically produced and naturally occurring silicas can be used as amorphous SiO ₂ . The latter are out, for example DE 102007045649 are known, but are not preferred since they generally contain not insignificant crystalline components and are therefore classified as carcinogenic. Synthetic is not understood to mean naturally occurring amorphous SiO ₂ , that is to say the production thereof comprises a deliberately carried out chemical reaction, as is caused by a human, For example, the production of silica sols by ion exchange processes from alkali silicate solutions, the precipitation from alkali silicate solutions, the flame hydrolysis of silicon tetrachloride, the reduction of quartz sand with coke in an electric arc furnace in the production of ferrosilicon and silicon. The amorphous SiO ₂ produced by the latter two processes is also referred to as pyrogenic SiO ₂ .

Occasionally, synthetic amorphous silicon dioxide means only precipitated silica (CAS No. 112926-00-8) and flame-hydrolytically produced SiO ₂ (pyrogenic silica, fumed silica, CAS No. 112945-52-5), while that in the case of ferrosilicon or Silicon production product is only referred to as amorphous silicon dioxide (Silica Fume, Microsilica, CAS No. 69012-64-12). For the purposes of the present invention, the product formed in the manufacture of ferrosilicon or silicon is also understood to be amorphous SiO ₂ .

Precipitated silicas and pyrogenic, ie flame hydrolytic or arc-produced silicon dioxide are preferably used. Amorphous silicon dioxide produced by thermal decomposition of ZrSiO ₄ (described in US Pat DE 102012020509 ) and SiO ₂ produced by oxidation of metallic Si using an oxygen-containing gas (described in US Pat DE 102012020510 ). Also preferred is quartz glass powder (mainly amorphous silicon dioxide), which was produced from crystalline quartz by melting and rapid cooling again, so that the particles are spherical and not splintered (described in US Pat DE 102012020511 ). The average primary particle size of the particulate 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 can be determined, for example, with the aid of dynamic light scattering (for example Horiba LA 950) and checked by scanning electron microscope images (SEM images with, for example, Nova Nano-SEM 230 from FEI). Furthermore, with the help of the SEM images, details of the primary particle shape down to the order of 0.01 µm could be made visible. For the SEM measurements, the silicon dioxide samples were dispersed in distilled water and then applied to an aluminum holder stuck with copper tape before the water was evaporated.

Furthermore, the specific surface area of the particulate amorphous silicon dioxide was determined using gas adsorption measurements (BET method) in accordance with DIN 66131. The specific surface area of the particulate 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. If necessary. the products can also be mixed, for example to obtain specific mixtures with specific particle size distributions.

Depending on the type of manufacture and the producer, the purity of the amorphous SiO _{2 can} vary widely. Types with a content of at least 85% by weight of silicon dioxide have proven suitable, preferably of at least 90% by weight and particularly preferably of at least 95% by weight. Depending on the application and the desired level of strength, between 0.1% and 2% by weight of the particulate amorphous SiO ₂ are used, preferably between 0.1% and 1.8%, particularly preferably between 0.1%. % and 1.5% by weight, based in each case on the basic molding material.

The ratio of water glass binder to particulate amorphous silicon dioxide can be varied within wide limits. This offers the advantage that the initial strengths of the cores, i.e. improve the strength immediately after removal from the tool without significantly affecting the final strength. This is of particular interest in light metal casting. On the one hand, high initial strengths are desired so that the cores can be easily transported after assembly or assembled into whole core packages; on the other hand, the final strengths should not be too high to avoid difficulties in the core disintegration after casting, i.e. the base material of the mold should be able to be easily removed from the cavities of the mold after casting.

Based on the total weight of the water glass binder (including diluent or solvent), the amorphous SiO _{2 is} preferably present in a proportion of 1 to 80% by weight, preferably 2 to 60% by weight, particularly preferably 3 to 55% by weight. % and particularly preferably between 4 to 50% by weight. Or independently of this, based on the ratio of solids content of the water glass (based on the oxides, ie total mass of alkali metal oxide and silicon dioxide) to amorphous SiO _2, from 10: 1 to 1: 1.2 (parts by weight) is preferred.

The addition of the amorphous silicon dioxide can according to EP 1802409 B1 both before and after adding the binder directly to the refractory, but it can also, as in EP 1884300 A1 (= US 2008/029240 A1 ) first prepared a premix of the SiO ₂ with at least part of the binder or sodium hydroxide solution and then mixed with the refractory. Any binder or binder fraction that is still present and not used for the premixing can be added to the refractory before or after the addition of the premix or together with it. The amorphous SiO _{2 is} preferably added to the refractory before the binder is added.

In a further embodiment, barium sulfate can be added to the molding material mixture in order to further improve the surface of the casting, in particular made of aluminum.

The barium sulfate can be synthetically produced as well as natural barium sulfate, ie added in the form of minerals that contain barium sulfate, such as heavy spar or barite. This, as well as other features of the suitable barium sulfate and the molding mixture produced with it, are described in the DE 102012104934 described in more detail and their disclosure content is thus made by reference to the disclosure of the present property right. The barium sulfate is preferably used in an amount of 0.02 to 5.0% by weight, particularly preferably 0.05 to 3.0% by weight, particularly preferably 0.1 to 2.0% by weight or 0.3 to 0 , 99% by weight, based in each case on the entire molding mixture, added.

In a further embodiment, at least aluminum oxides and / or aluminum / silicon mixed oxides in particulate form or metal oxides of aluminum and zirconium in particulate form in concentrations between 0.05 wt.% And 4.0 wt.%, Preferably between 0.1 % By weight and 2.0% by weight, particularly preferably between 0.1% by weight and 1.5% by weight and particularly preferably between 0.2% by weight and 1.2% by weight, in each case based on the basic molding material , to be added to the molding material mixture, in particular via the additive component (A), as in the DE 102012113073 or the DE 102012113074 described in more detail.

In this respect, these writings are also used as a disclosure for the present property right by reference. Such additives can be used to obtain castings, in particular made of iron or steel, with a very high surface quality after the metal casting, so that after the removal of the casting mold, little or no post-processing of the surface of the casting is required.

In a further embodiment, the molding material mixture can comprise a phosphorus-containing compound . This addition is preferred for very thin-walled sections of a casting mold. These are preferably inorganic phosphorus compounds in which the phosphorus is preferably in the +5 oxidation state.

The phosphorus-containing compound is preferably in the form of a phosphate or phosphorus oxide. The phosphate can be present as an alkali metal or as an alkaline earth metal phosphate, alkali metal phosphates and in particular the sodium salts being particularly preferred.

Both orthophosphates and polyphosphates, pyrophophates or metaphosphates can be used as phosphates. The phosphates can be prepared, for example, by neutralizing the corresponding acids with an appropriate base, for example an alkali metal base, such as NaOH, or optionally also an alkaline earth metal base, it not necessarily being necessary for all the negative charges of the phosphate to be saturated by metal ions. Both the metal phosphates and the metal hydrogen phosphates and the metal dihydrogen phosphates can be used, such as Na ₃ PO ₄ , Na ₂ HPO ₄ , and NaH ₂ PO ₄ . The anhydrous phosphates and hydrates of the phosphates can also be used. The phosphates can be introduced into the molding material mixture both in crystalline and in amorphous form.

Polyphosphates are understood to mean, in particular, linear phosphates which comprise more than one phosphorus atom, the phosphorus atoms in each case being connected to one another via oxygen bridges.

Polyphosphates are obtained by the condensation of orthophosphate ions with elimination of water, so that a linear chain of PO ₄ tetrahedra is obtained, which are each connected via corners. Polyphosphates have the general formula (O (PO ₃ ) n) ^{(n + 2) -} , where n corresponds to the chain length. A polyphosphate can comprise up to several hundred PO ₄ tetrahedra. However, polyphosphates with shorter chain lengths are preferably used. N preferably has values from 2 to 100, particularly preferably 5 to 50. Highly condensed polyphosphates can also be used, ie polyphosphates in which the PO ₄ tetrahedra are connected to one another via more than two corners and therefore show polymerization in two or three dimensions.

Metaphosphates are understood to be cyclic structures which are made up of PO ₄ tetrahedra which are connected to one another via corners. Metaphosphates have the general formula ((PO ₃ ) n) ^n- , where n is at least 3. N preferably has values from 3 to 10.

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

The preferred proportion of the phosphorus-containing compound, based on the refractory base material, is between 0.05 and 1.0% by weight. The proportion of the phosphorus-containing compound is preferably chosen to be between 0.1 and 0.5% by weight. The phosphorus-containing, inorganic compound preferably contains between 40 and 90% by weight, particularly preferably between 50 and 80% by weight, phosphorus, calculated as P ₂ O ₅ . The phosphorus-containing compound can in itself be added to the molding material mixture in solid or dissolved form. The phosphorus-containing compound is preferably added to the molding material mixture as a solid.

According to an advantageous embodiment, the molding material mixture according to the invention contains a proportion of platelet-shaped lubricants, in particular graphite or MoS ₂ . The amount of the platelet-shaped lubricant, in particular graphite, added is preferably 0.05 to 1% by weight, particularly preferably 0.05 to 0.5% by weight, based on the basic molding material.

According to a further advantageous embodiment, surface-active substances, in particular surfactants, can also be used which improve the flowability of the molding material mixture . Suitable representatives of these compounds are, for example, in WO 2009/056320 (= US 2010/0326620 A1 ) described. Anionic surfactants are preferably used for the molding material mixture. Surfactants with sulfuric acid or sulfonic acid groups should be mentioned here in particular. The pure surface-active substance, in particular the surfactant, based on the weight of the refractory base material, is preferably present in the molding material mixture in a proportion of 0.001 to 1% by weight, particularly preferably 0.01 to 0.2% by weight.

The molding material mixture is an intensive mixture of at least the above-mentioned components of the multi-component system. The particles of the refractory molding material are preferably coated with a layer of the binder. By evaporating the water present in the binder (approx. 40-70% by weight, based on the weight of the binder), a firm cohesion can then be achieved between the particles of the refractory base material.

Despite the high strengths that can be achieved with the binder system, the casting molds produced with the molding material mixture surprisingly show very good disintegration after casting, in particular when casting aluminum. As already explained, it was also found that the molding material mixture can be used to produce casting molds which also show very good disintegration when cast iron, so that the molding material mixture can be poured out again from narrow and angled sections of the casting mold after the casting. The use of the moldings produced from the molding material mixture is therefore not only restricted to light metal casting and / or non-ferrous metal casting. The casting molds are generally suitable for casting metals, such as non-ferrous metals or ferrous metals. However, the molding material mixture is particularly preferably suitable for the casting of aluminum.

• Bereitstellen der oben beschriebenen Formstoffmischung durch Zusammenbringen und Mischen zumindest der oben genannten obligatorischen Komponenten;
• Formen der Formstoffmischung;
• Aushärten der geformten Formstoffmischung, wobei die ausgehärtete Gießform erhalten wird.

The invention further relates to a method for producing casting molds for metal processing, the molding material mixture being used. The method according to the invention comprises the steps:

• Providing the above-described molding material mixture by bringing together and mixing at least the above-mentioned mandatory components;
• Forming the mixture of molding materials;
• Curing the molded molding material mixture, whereby the hardened casting mold is obtained.

In the production of the molding material mixture from the multi-component system according to the invention, the procedure is generally such that the refractory molding raw material (component (F)) is initially introduced and then the binder or component (B) and the additive or component (A) are stirred is added. The additives described above can be added in any form to the molding material mixture. They can be added individually or as a mixture. According to a preferred embodiment, the binder is provided as a two-component system, a first liquid component containing the water glass and possibly a surfactant (see above) (components (B)) and a second but solid component containing one or more oxidic boron Compounds and the particulate silicon dioxide (components (A)) and all other solid additives mentioned above, with the exception of the basic molding materials, in particular the particulate amorphous silicon dioxide and possibly a phosphate and possibly a preferably platelet-shaped lubricant and possibly barium sulfate or possibly other components such as described include.

In the production of the molding material mixture, the refractory molding raw material is placed in a mixer and then preferably the solid component (s) of the binder is first added and mixed with the refractory molding material. The mixing time is chosen so that the refractory base material and solid binder component are thoroughly mixed. The mixing time depends on the amount of the molding material mixture to be produced and on the mixing unit used. The mixing time is preferably chosen between 1 and 5 minutes.

The liquid component of the binder is then added, preferably with further movement of the mixture, and the mixture is then mixed further until a uniform layer of the binder has formed on the grains of the refractory base molding material.

Here too, the mixing time depends on the amount of molding material mixture to be produced and on the mixing unit used. The duration for the mixing process is preferably chosen between 1 and 5 minutes. A liquid component is understood to mean both a mixture of different liquid components and the entirety of all liquid individual components, the latter also being able to be added individually. Likewise, a solid component is understood to mean both the mixture of individual or all of the solid components described above and the entirety of all solid individual components, the latter being able to be added to the molding material mixture together or in succession. According to another embodiment, the liquid component of the binder can first be added to the refractory base material and only then can the solid component be added to the mixture. According to a further embodiment, 0.05 to 0.3% by weight of water, based on the weight of the mold base, is first added to the refractory mold base and only then are the solid and liquid components of the binder added.

In this embodiment, a surprising positive effect on the processing time of the molding material mixture can be achieved. The inventors believe that the dehydrating effect of the solid components of the binder is reduced in this way and the curing process is thereby delayed. The molding material mixture is then brought into the desired shape. The usual methods for shaping are used. For example, the molding material mixture can be shot into the molding tool by means of a core shooting machine with the aid of compressed air. The molding material mixture is then cured, it being possible to use all processes which are known for binders based on water glass, for example hot curing, gassing with CO ₂ or air or a combination of both, and curing by means of liquid or solid catalysts. Hot curing is preferred.

Water is removed from the molding material mixture during hot curing. This presumably also initiates condensation reactions between silanol groups, so that the water glass crosslinks.

The heating can take place, for example, in a mold which preferably has a temperature of 100 to 300 ° C., particularly preferably a temperature of 120 to 250 ° C. It is possible to fully harden the casting mold in the mold. However, it is also possible to harden the casting mold only in its edge region, so that it has sufficient strength to be able to be removed from the molding tool. The mold can then be fully cured by removing more water from it. This can be done in an oven, for example. The water can also be removed, for example, by evaporating the water under reduced pressure.

The hardening of the casting molds can be accelerated by blowing heated air into the mold. In this embodiment of the method, the water contained in the binder is rapidly removed, as a result of which the casting mold is solidified in periods of time suitable for industrial use. The temperature of the air blown in is preferably 100 ° C. to 180 ° C., particularly preferably 120 ° C. to 150 ° C. The flow rate of the heated air is preferably set so that the casting mold is cured in time periods suitable for industrial use. The time periods depend on the size of the molds produced. The aim is to cure in a period of less than 5 minutes, preferably less than 2 minutes. For very large molds, however, longer periods of time may be required.

The water can also be removed from the molding material mixture in such a way that the heating of the molding material mixture is effected or assisted by irradiation with microwaves. It would be conceivable, for example, to mix the basic molding material with the solid, powdery component (s), to apply this mixture in layers on a surface and to print the individual layers with the aid of a liquid binder component, in particular with the aid of water glass, the layer-by-layer application of the Solid mixture, one printing process with the help of the liquid binder follows.

At the end of this process, i.e. at the end of the last printing process, the entire mixture can be heated in a microwave oven.

The methods according to the invention are suitable per se for the production of all casting molds customary for metal casting, that is to say for example of cores and molds. Casting molds which comprise very thin-walled sections can also be produced particularly advantageously.

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

Furthermore, the invention is explained in more detail by means of examples without being limited to these. The fact that only the hardening process is described as the hardening process is not a limitation.

Examples 1) Influence of various powdery oxidic boron compounds on the bending strength

• Die in Tabelle 1 aufgeführten Komponenten wurden in einem Laborflügelmischer (Firma Vogel & Schemmann AG, Hagen, DE) gemischt. Dazu wurde zunächst der Quarzsand vorgelegt und unter Rühren das Wasserglas zugegeben. Als Wasserglas wurde ein Natriumwasserglas verwendet, das Anteile von Kalium aufwies. In den nachfolgenden Tabellen ist das Modul daher mit SiO₂:M₂O angegeben, wobei M die Summe aus Natrium und Kalium angibt. Nachdem die Mischung für eine Minute gerührt worden war, wurden amorphes SiO₂ und ggfs. pulverförmige oxidische Borverbindungen unter weiterem Rühren hinzugegeben. Die Mischung wurde anschließend noch für eine weitere Minute gerührt;
• Die Formstoffmischungen wurden in den Vorratsbunker einer H 2,5 Hot-Box-Kernschießmaschine der Firma Röperwerk - Gießereimaschinen GmbH, Viersen, DE, überführt, deren Formwerkzeug auf 180 °C erwärmt war;
• Die Formstoffmischungen wurden mittels Druckluft (5 bar) in das Formwerkzeug eingebracht und verblieben für weitere 35 Sekunden im Formwerkzeug;
• Zur Beschleunigung der Aushärtung der Mischungen wurde während der letzten 20 Sekunden Heißluft (2 bar, 100 °C beim Eintritt in das Werkzeug) durch das Formwerkzeug geleitet;
• Das Formwerkzeug wurde geöffnet und die Prüfriegel entnommen.

So-called Georg Fischer test bars were produced for testing a molding material mixture. Georg Fischer test bars are square-shaped test bars with the dimensions 150 mm x 22.36 mm x 22.36 mm. The compositions of the molding material mixtures are given in Table 1. The procedure for producing the Georg Fischer test bars was as follows:

• The components listed in Table 1 were mixed in a laboratory wing mixer (Vogel & Schemmann AG, Hagen, DE). For this purpose, the quartz sand was first placed and the water glass was added with stirring. Sodium water glass containing potassium was used as the water glass. In the tables below, the module is therefore given as SiO ₂ : M ₂ O, where M is the sum of sodium and potassium. After the mixture had been stirred for one minute, amorphous SiO ₂ and, if appropriate, powdery oxidic boron compounds were added with further stirring. The mixture was then stirred for a further minute;
• The molding material mixtures were transferred to the storage bunker of an H 2.5 hot box core shooter from Röperwerk - Gießereimaschinen GmbH, Viersen, DE, whose mold was heated to 180 ° C;
• The molding material mixtures were introduced into the mold using compressed air (5 bar) and remained in the mold for a further 35 seconds;
• To accelerate the curing of the mixtures, hot air (2 bar, 100 ° C. when entering the mold) was passed through the mold during the last 20 seconds;
• The mold was opened and the test bar removed.

• 10 Sekunden nach der Entnahme (Heißfestigkeiten)
• 1 Stunde nach Entnahme (Kaltfestigkeiten)
• 24 Stunden nach Lagerung der Kerne im Klimaschrank bei 30°C und 60% relativer Luftfeuchte, wobei die Kerne erst nach dem Erkalten (1 Stunde nach der Entnahme) in den Klimaschrank platziert wurden.

Tabelle 1 Zusammensetzungen der Formstoffmischungen Quarzsand H32 Alkaliwasserglas Amorphes SiO₂ Pulverförmige(s) Borsäure oder Borat 1.01 100 GT 2,0 GT ^a) - - Vergleich 1.02 100 GT 2,0 GT ^a) 0,5 GT ^b) - Vergleich 1.03 100 GT 2,0 GT ^a) 0,5 GT ^b) 0,05 GT ^c) erfindungsgem. 1.04 100 GT 2,0 GT ^a) 0,5 GT ^b) 0,05 GT ^d) erfindungsgem. 1.05 100 GT 2,0 GT ^a) 0,5 GT ^b) 0,05 GT ^e) erfindungsgem. 1.06 100 GT 2,0 GT ^a) 0,5 GT ^b) 0,05 GT ^f) erfindungsgem. 1.07 100 GT 2,0 GT ^a) 0,5 GT ^b) 0,05 GT ^g) erfindungsgem. 1.08 100 GT 2,0 GT ^a) 0,5 GT ^b) 0,05 GT ^h) erfindungsgem. 1.09 100 GT 2,0 GT ^a) 0,5 GT ^b) 0,05 GT ⁱ⁾ erfindungsgem. 1.10 100 GT 2,05 GT ^k) 0,5 GT ^b) - Vergleich 1.11 100 GT 2,0 GT ^a) 0,5 GT ^b) 0,01 GT ^f) erfindungsgem. 1.12 100 GT 2,0 GT ^a) 0,5 GT ^b) 0,02 GT ^f) erfindungsgem. 1.13 100 GT 2,0 GT ^a) 0,5 GT ^b) 0,1 GT ^f) erfindungsgem. 1.14 100 GT 2,0 GT ^a) 0,5 GT ^b) 0,2 GT ^f) erfindungsgem. 1.15 100 GT 2,0 GT ^a) - 0,05 GT ^f) Vergleich 1.16 100 GT 2,0 GT ^a) - 0,05 GT ⁱ⁾ Vergleich Vergleich = nicht erfindungsgemäß
Die Indizes in Tabelle 1 haben jeweils folgende Bedeutung:
^a) Alkaliwasserglas mit einem molaren Modul SiO₂:M₂O von ca. 2,2; bezogen auf das gesamte Wasserglas. Feststoffgehalt von ca. 35%
^b) Microsilica POS B-W 90 LD (amorphes SiO2, Fa. Possehl Erzkontor; Entstehung bei der thermischen Zersetzung von ZrSiO₄)
^b) Microsilica POS B-W 90 LD (amorphes SiO2, Fa. Possehl Erzkontor; Entstehung bei der thermischen Zersetzung von ZrSiO₄)
^c) Borsäure technisch (99,9% H₃BO₃, Fa. Cofermin Chemicals GmbH & Co. KG)
^d) Etibor 48 (Borax-Pentahydrat, Na₂B₄O₇ ^∗5H₂O, Fa. Eti Maden Isletmeleri)
^e) Sodium Metaborate 8Mol (Na₂O∗B₂O₃ ^∗8H₂O, Fa. Borax Europe Limited)
^f) Borax Decahydrat SP (Na₂B₄O₇ ^∗10H₂O - Pulver, Fa. Borax Europe Limited)
^g) Borax Decahydrat (Na₂B₄O₇ ^∗10H₂O - granuliert, Fa. Eti Maden Isletmeleri)
^h) Lithiumtetraborat (99,998% Li₂B₄O₇, Fa. Alfa Aesar)
ⁱ⁾ Calciummetaborat (Fa. Sigma Aldrich)
^k) Alkaliwasserglas mit einem molaren Modul SiO₂:M₂O von ca. 2,2; bezogen auf das gesamte Wasserglas. Feststoffgehalt von ca. 35% - in dieses Wasserglas werden 0,05 GT Borax Decahydrat ^g) vor der Verwendung vorgelöst, sodass eine klare Lösung entsteht. To determine the bending strengths, the test bars were placed in a Georg Fischer strength tester equipped with a 3-point bending device (DISA Industrie AG, Schaffhausen, CH) and the force measured which caused the test bars to break. The bending strengths were measured according to the following scheme:

• 10 seconds after removal (heat resistance)
• 1 hour after removal (cold strength)
• 24 hours after storing the cores in a climatic cabinet at 30 ° C and 60% relative humidity, whereby the cores were only placed in the climatic cabinet after cooling (1 hour after removal).

<i> Table 1 </i> Compositions of the molding material mixtures Quartz sand H32 Alkali water glass Amorphous SiO ₂ Powdered boric acid or borate 1:01 100 GT 2.0 GT ^a) - - comparison 1:02 100 GT 2.0 GT ^a) 0.5 GT ^b) - comparison 1:03 100 GT 2.0 GT ^a) 0.5 GT ^b) 0.05 GT ^c) invention. 1:04 100 GT 2.0 GT ^a) 0.5 GT ^b) 0.05 GT ^d) invention. 1:05 100 GT 2.0 GT ^a) 0.5 GT ^b) 0.05 GT ^e) invention. 1:06 100 GT 2.0 GT ^a) 0.5 GT ^b) 0.05 GT ^f) invention. 1:07 100 GT 2.0 GT ^a) 0.5 GT ^b) 0.05 GT ^g) invention. 1:08 100 GT 2.0 GT ^a) 0.5 GT ^b) 0.05 GT ^h) invention. 1:09 100 GT 2.0 GT ^a) 0.5 GT ^b) 0.05 GT ⁱ⁾ invention. 1.10 100 GT 2.05 GT ^k) 0.5 GT ^b) - comparison 1.11 100 GT 2.0 GT ^a) 0.5 GT ^b) 0.01 GT ^f) invention. 1.12 100 GT 2.0 GT ^a) 0.5 GT ^b) 0.02 GT ^f) invention. 1.13 100 GT 2.0 GT ^a) 0.5 GT ^b) 0.1 GT ^f) invention. 1.14 100 GT 2.0 GT ^a) 0.5 GT ^b) 0.2 GT ^f) invention. 1.15 100 GT 2.0 GT ^a) - 0.05 GT ^f) comparison 1.16 100 GT 2.0 GT ^a) - 0.05 GT ⁱ⁾ comparison Comparison = not according to the invention
The indices in Table 1 each have the following meaning:
^a) alkali water glass with a molar module SiO ₂ : M ₂ O of approx. 2.2; based on the entire water glass. Solids content of approx. 35%
^b) Microsilica POS BW 90 LD (amorphous SiO2, Possehl Erzkontor; formation during the thermal decomposition of ZrSiO ₄ )
^b) Microsilica POS BW 90 LD (amorphous SiO2, from Possehl Erzkontor; formation during the thermal decomposition of ZrSiO ₄ )
^c) Technical boric acid (99.9% H ₃ BO ₃ , Cofermin Chemicals GmbH & Co. KG)
^d) Etibor 48 (borax pentahydrate, Na ₂ B ₄ O ₇ ^∗ 5H ₂ O, from Eti Maden Isletmeleri)
^e) Sodium Metaborate 8 mol (Na ₂ O ∗ B ₂ O ₃ ^∗ 8H ₂ O, Borax Europe Limited)
^f) Borax decahydrate SP (Na ₂ B ₄ O ₇ ^∗ 10H ₂ O powder, Borax Europe Limited)
^g) Borax decahydrate (Na ₂ B ₄ O ₇ ^∗ 10H ₂ O - granulated, from Eti Maden Isletmeleri)
^h) lithium tetraborate (99.998% Li ₂ B ₄ O ₇ , Alfa Aesar)
ⁱ⁾ Calcium metaborate (Sigma Aldrich)
^k) alkali water glass with a molar module SiO ₂ : M ₂ O of approx. 2.2; based on the entire water glass. Solids content of approx. 35% - 0.05 pbw of borax decahydrate ^g) are pre-dissolved in this water glass before use, so that a clear solution is formed.

The measured bending strengths are summarized in Table 2.

Examples 1.01 and 1.02 illustrate that the addition of amorphous SiO ₂ can achieve a significantly improved strength level (according to EP 1802409 B1 and DE 102012020509 A1 ). A comparison of Examples 1.02 to 1.14 shows that the strength level is not noticeably influenced by the addition of powdery oxidic boron compounds.

Examples 1.06 and 1.11 to 1.14 show a slight deterioration in the strength levels with an increasing proportion of the additive according to the invention. However, the effect is very weak.

The comparison of Examples 1.01, 1.15 and 1.16 shows that the addition of boron compounds according to the invention alone, i.e. without the addition of the amorphous silicon dioxide, has a negative influence on the strengths, in particular hot strengths and cold strengths. The hot strengths are also too low for automated series production.

A comparison of Examples 1.02, 1.06 and 1.09 shows that the addition of boron compounds according to the invention has little influence on the hot and cold strengths if the molding material mixture contains amorphous silicon dioxide as a powdery additive. Surprisingly, the addition of the boron compound according to the invention to the molding material mixture improves the moisture stability of the cores produced therewith. <i> Table 2 </i> flexural strengths Heat resistance [N / cm ² ] Strength after 1 h [N / cm ² ] Strengths after 24h storage in a climatic cabinet [N / cm ² ] 1:01 90 380 10 comparison 1:02 165 530 170 comparison 1:03 160 520 not determined inventively 1:04 170 540 not determined inventively 1:05 160 510 not determined inventively 1:06 160 520 290 inventively 1:07 170 545 not determined inventively 1:08 160 535 not determined inventively 1:09 165 520 400 inventively 1.10 170 515 not determined comparison 1.11 170 550 not determined inventively 1.12 160 530 not determined inventively 1.13 160 515 not determined inventively 1.14 155 510 not determined inventively 1.15 75 360 10 comparison 1.16 85 350 not determined comparison Comparison = not according to the invention

2) Improvement of the decay behavior

• Georg-Fischer-Prüfriegel der Formstoffmischungen 1.01 bis 1.14 in Tabelle 1 wurden hinsichtlich der Biegefestigkeiten untersucht (analog zum Beispiel 1 - es haben sich keine Unterschiede zu den in Tabelle 2 zusammengefassten Werten ergeben).
• Anschließend wurden die in zwei Teile etwa hälftig quer zur größten Längenausdehnung gebrochene Georg-Fischer-Prüfriegel in einem Muffelofen (Fa. Naber Industrieofenbau) bei einer Temperatur von 650 °C für 45 Minuten thermisch belastet.
• Nach Entnahme der Riegel aus dem Muffelofen und nach einem darauf folgenden Abkühlprozess auf Raumtemperatur wurden die Riegel auf einem sogenannten Rüttelsieb (Sieb platziert auf der Vibrationssiebmaschine AS 200 digit, Fa. Retsch GmbH) mit einer Maschenweite von 1,25 mm platziert.
• Anschließend wurden die Riegel bei einer festgelegten Amplitude (70% der maximal möglichen Einstellung (100 Einheiten)) für 60 Sekunden gerüttelt.
• Es wurden sowohl der Rückstand auf dem Sieb als auch die zerkleinerte Menge in der Auffangwanne (entkernter Anteil) mit Hilfe einer Waage bestimmt. In Tabelle 3 ist der entkernte Anteil in Prozent angegeben.

The influence of various powdery oxidic boron compounds on the coring behavior was investigated. The procedure for this was as follows:

• Georg Fischer test bars of the molding material mixtures 1.01 to 1.14 in Table 1 were examined with regard to their bending strengths (analogously to Example 1 - there were no differences from the values summarized in Table 2).
• Subsequently, the Georg Fischer test bar, which was broken in half transversely to the greatest length, was subjected to thermal stress in a muffle furnace (from Naber Industrieofenbau) at a temperature of 650 ° C for 45 minutes.
• After removing the bars from the muffle furnace and after a subsequent cooling process to room temperature, the bars were placed on a so-called vibrating screen (screen placed on the vibrating screening machine AS 200 digit, from Retsch GmbH) with a mesh size of 1.25 mm.
• The bars were then shaken at a fixed amplitude (70% of the maximum possible setting (100 units)) for 60 seconds.
• Both the residue on the sieve and the shredded amount in the drip pan (cored portion) were determined using a balance. Table 3 shows the percentage of the core removed.

The respective values, which each reflect mean values of a quadruple determination, are summarized in Table 3.

A comparison of Examples 1.01 and 1.02 shows that adding a particulate, amorphous silicon dioxide to the molding material mixture significantly deteriorates the disintegration behavior of the molds produced with it. A comparison of Examples 1.02 to 1.09, on the other hand, clearly shows that the use of powdery oxidic boron compounds leads to significantly improved disintegration properties of the forms bonded with water glass. A comparison of Examples 1.07 and 1.10 shows that it makes a difference whether the borate (in this case) was pre-dissolved in the binder before use in the molding mixture or whether the borate was added to the molding mixture as a solid powder. Such an effect is surprising.

Examples 1.06 and 1.11 to 1.14 illustrate that the disintegration behavior can be increased significantly with an increasing proportion of the additive according to the invention. It also becomes clear that even small additions are sufficient to significantly increase the disintegration ability of the hardened molding material mixture after thermal stress. <i> Table 3 </i> Entkernverhalten Cored portion [%] 1:01 58 comparison 1:02 37 comparison 1:03 57 inventively 1:04 63 inventively 1:05 56 inventively 1:06 70 inventively 1:07 60 inventively 1:08 55 inventively 1:09 59 inventively 1.10 38 comparison 1.11 52 inventively 1.12 57 inventively 1.13 79 inventively 1.14 89 inventively Comparison = not according to the invention

Claims (19)

1. A multi-component system for producing molds or cores comprising at least the following components (A), (B) and (F) being present in a spatially separated manner:

   (A) a pulverulent additive component comprising at least

   - one or more pulverulent oxidic boron compounds and

   - particulate amorphous silica, and

   - no water glass containing alkali silicate solutes,

   (B) a liquid binder component (B) comprising at least

   - water glass containing water and alkali silicate solutes, and

   (F) a free-flowing refractory component (F) comprising

   - a refractory molding base material and

   - no water glass containing alkali silicate solutes,

   to obtain a molding material mixture following contacting.
2. The multi-component system according to at least one of the preceding claims, wherein the oxidic boron compound is selected from the group consisting of borates, borophosphates, borophosphosilicates and mixtures thereof and in particular is a borate, preferably an alkali and/or alkaline earth borate such as sodium borate and/or calcium borate, wherein the oxidic boron compound still preferably contains no organic groups.
3. The multi-component system according to at least one of the preceding claims, wherein the oxidic boron compound is composed of B-O-B structural elements.
4. The multi-component system according to at least one of the preceding claims, wherein the oxidic boron compound has an average particle size of greater than 0.1 µm and smaller than 1 mm, preferably greater than 1 µm and less than 0.5 mm, and particularly preferably greater than 5 µm and less than 0.25 mm.
5. The multi-component system according to at least one of the preceding claims, wherein more than 0.002 wt.% and less than 1.0 wt.%, preferably more than 0.005 wt.% and less than 0.4 wt.%, particularly preferably more than 0.01 wt.% and less than 0.1 wt.% and more particularly preferably more than 0.02 wt.% and less than 0.075 wt.% of the oxidic boron compound is added or contained, relative to the refractory molding base material.
6. The multi-component system according to at least one of the preceding claims, wherein the refractory molding material comprises silica sand, zircon sand or chromium ore sand, olivine, vermiculite, bauxite, chamotte, glass beads, glass granules, hollow aluminum silicate microspheres and mixtures thereof and preferably more than 50% by weight of silica sand, relative to the refractory molding material.
7. The multi-component system according to at least one of the preceding claims, wherein more than 80 wt.%, preferably more than 90 wt.%, and particularly preferably more than 95 wt.% of the multi-component system is refractory molding material.
8. The multi-component system according to at least one of the preceding claims, wherein said amorphous particulate silica is synthetically produced amorphous particulate silica.
9. The multi-component system according to at least one of the preceding claims, wherein the multi-component system is furthermore characterized by one or more of the following features:

   (a) in the water glass (including the water) there are soluble alkali silicates in an amount of 0.75 wt.% to 4 wt.%, particularly preferably between 1 wt.% and 3.5 wt.%., relative to the molding base material, in the molding mixture, and still preferably independently, but preferably in combination with the above values, the solids content of water glass being from 0.2625 to 1.4 wt.%, preferably from 0.35 to 1.225 wt.%, relative to the molding base material in the molding mixture;

   (b) the water glass has a molar modulus SiO₂/M₂O in the range of from 1.6 to 4.0, in particular from 2.0 to less than 3.5, with M = lithium, sodium and potassium.
10. The multi-component system according to at least one of the preceding claims, the multi-component system, besides particulate amorphous SiO₂, containing other particulate metal oxides, preferably aluminum oxides, in particular selected from one or more members of groups a) to d):

    a) corundum plus zirconium dioxide,

    (b) zirconia mullite,

    (c) zirconia corundum and

    (d) aluminum silicates plus zirconium dioxide,

    preferably as a component of component (A).
11. The multi-component system according to at least one of the preceding claims, wherein the multi-component system furthermore contains at least one phosphorus-containing compound, preferably from 0.05 to 1.0 wt.%, particularly preferably from 0.1 to 0.5 wt.%, relative to the weight of the refractory molding base, preferably as a component of component (A) and also, independently thereof, the phosphorus-containing compound is preferably added as a solid and not in the dissolved state.
12. The multi-component system according to at least one of the preceding claims, wherein a hardener is added, in particular at least one ester or phosphate compound, preferably as a component of component (A) or as further component.
13. A method for the preparation of molds or cores comprising:

    providing a molding material mixture by contacting and mixing at least the components (A), (B) and (F) of the multi-component system according to at least one of the claims 1 to 12;

    introducing the molding material mixture into a mold; and

    curing the molding material mixture by hot-curing while heating and removing water, the oxidic boron compound being added to the molding material mixture as a solid powder.
14. The method according to claim 13, wherein the molding material mixture is introduced into the mound by means of a core shooting machine using compressed air and the mould is a molding tool and is passed through by one or more gases, in particular CO₂, or gases containing CO₂, preferably CO₂ heated to above 60°C and/or air heated to above 60°C.
15. The method according to claim 13 or 14, wherein the molding material mixture is subjected to a temperature of 100 to 300°C, preferably 120 to 250°C, preferably for less than 5 min, for curing, wherein further preferably the temperature is produced at least partially by blowing heated air into a molding tool.
16. The method according to at least one of claims 13 to 15, wherein heating is performed by heating and removal of water by exposing the molding material to a temperature of 100 to 300°C.
17. The method according to at least one of claims 13 to 16,
    wherein the oxidic boron compound is composed of B-O-B structural elements, and/or
    wherein the amorphous particulate silica is synthetically produced amorphous particulate silica.
18. A method of layerwise building bodies, comprising:

    - mixing at least the pulverulent additive component (A) and the pourable refractory component (F) according to claims 1 to 12, besides any other possible optional components according to said claims to form a mixture,

    - layerwise applying the mixture to a surface in the form of layers and

    - printing the layers using the liquid binder component (B),

    wherein said layerwise application of the mixture, in each case, is followed by a printing method using the liquid binder component (B).
19. The method according to claim 18 wherein curing is performed by the action of microwaves.