EP3986634A1

EP3986634A1 - Sized molds obtainable from a molding material mixture containing an inorganic bonding agent and phosphatic compounds and oxidic boron compounds and method for production and use thereof

Info

Publication number: EP3986634A1
Application number: EP20740224.9A
Authority: EP
Inventors: Felix MÜCK; Tamara Jacqueline HOLTHAUSEN; Ronja Resch
Original assignee: ASK Chemicals GmbH
Current assignee: ASK Chemicals GmbH
Priority date: 2019-06-19
Filing date: 2020-06-18
Publication date: 2022-04-27
Also published as: BR112021025517A2; DE102019116702A1; US20220355365A1; MX2021015621A; CN114080283A; JP2022539004A; WO2020253917A1; KR20220029667A

Abstract

The invention relates to sized molds for metal casting, obtainable from molding material mixtures on the basis of inorganic bonding agents containing at least one phosphatic compound and at least one oxidic boron compound, in particular sized, water glass-bound forms and cores, comprising at least one fireproof basic molding material, water glass as inorganic bonding agent and amorphous particulate silicon dioxide and one or more powdery oxidic boron compounds and one or more phosphatic compounds. The invention furthermore relates to a method for producing sized foundry mold bodies and use thereof, in particular for producing cast parts from iron alloys. The size is a water-based size.

Description

FINISHED CASTING FORMS AVAILABLE FROM ONE

MOLDING MATERIAL MIXTURE CONTAINING AN INORGANIC BINDING AGENT AND PHOSPHIC COMPOUNDS AND OXIDE BORON COMPOUNDS AND PROCESS FOR THEIR PRODUCTION AND

THEIR USE

The invention relates to sized casting molds for metal casting obtainable from molding material mixtures based on inorganic binders, containing at least one phosphate-containing compound and at least one oxidic boron compound, namely sized, water-glass-bound molds and cores comprising at least one refractory basic molding material, water glass as an inorganic binder and amorphous particulate Silicon dioxide, as well as one or more oxidic boron compounds and one or more phosphate-containing compounds, in particular for the production of castings from iron alloys. Furthermore, the invention relates to a method for the production of sized foundry moldings and their use, in particular for the production of castings from iron alloys. The size is a water-based size.

Technical environment

Casting molds are essentially composed of cores and molds that represent the negative molds of the casting to be produced. In the following, the casting mold (including the plural) is used as a synonym for cores, forms (each individually) and for cores and forms (together). Cores and molds are based on a refractory material, for example quartz sand, and a suitable binding agent, which gives the casting mold sufficient mechanical strength after it has been removed from the mold. For the production of casting molds, a refractory basic molding material is used, which is coated with a suitable binding agent. The refractory basic molding material is preferably in a free-flowing form so that it can be filled into a suitable hollow mold and compacted there. The binding agent creates a firm bond between the particles of the basic mold material so that the casting mold has 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 in the cavity formed from one or more casting molds. After the start of the solidification process, 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, i.e. the cohesion of the individual particles of the refractory material is broken. Ideally, the mold disintegrates again into fine sand that can be easily removed from the casting.

Since casting molds are exposed to very high thermal and mechanical loads during the casting process, defects can arise at the contact surface between the liquid metal and the casting mold, for example if the casting mold tears or if liquid metal penetrates into the structure of the casting mold

If necessary, especially in steel and iron casting, the surfaces of the foundry mold body, especially of molds and cores, are coated with a finishing layer, especially those surfaces that come into contact with the cast metal. Finishes form a boundary or barrier layer between the form / core and metal, including for the targeted suppression of failure mechanisms at these points or for the use of metallurgical effects. In general, coatings in foundry technology should primarily fulfill the following functions:

- Improvement of the smoothness of the casting surface;

- As complete as possible separation of liquid metal and form or core;

- Avoidance of chemical reactions between components of the mold / core and melt, thereby facilitating the separation between the mold / core and the casting and / or

- Avoidance of surface defects on the casting such as Gas bubbles, penetrations, veins and / or scabs.

If the errors described above occur, the surface of the casting must be reworked in a complex manner in order to achieve the desired surface properties. This requires additional work steps and thus a decrease in productivity and an increase in costs. If the defects occur on surfaces of the casting that are poorly or not at all accessible, this can also lead to a loss of the casting.

Furthermore, the size can have a metallurgical influence on the casting, for example by selectively transferring additives into the casting on the surface of the casting, which additions improve the surface properties of the casting. Furthermore, the coatings form a layer which chemically isolates the casting mold from the liquid metal. This reduces the adhesion between the casting and the casting mold, so that the casting can be removed from the casting mold without difficulty. The size can also be used to control the heat transfer between the liquid metal and the casting mold in a targeted manner, for example to bring about the formation of a certain metal structure through the cooling rate.

A size usually consists of an inorganic refractory substance and a binder, the sizes being dissolved or slurried in a suitable carrier liquid, for example water or alcohol. If possible, one would like to forego the use of alcohol-containing coatings and instead use aqueous systems, since the organic solvents cause emissions in the course of the drying process.

In recent times in particular, there has been increasing demand that no emissions in the form of CO ₂ or hydrocarbons occur during the production of the casting molds, as well as during casting and cooling, in order to protect the environment and the odor nuisance of the environment from hydrocarbons, mainly aromatic Hydrocarbons. In order to meet these requirements, inorganic binder systems have been developed or further 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 binder systems is often associated with other disadvantages, which are described in detail in the following explanations.

Compared to organic binders, inorganic binders have the disadvantage that the casting molds made from them have relatively low strengths. This is particularly evident immediately after the casting mold has been removed from the tool. However, good strengths at this point are particularly important for the production of complex and / or thin-walled molded parts and for safe handling. Molds and cores produced with inorganic binders such as water glass also have a comparatively low resistance to atmospheric moisture or to water or aqueous moisture. This means that it is often not possible to apply a water-based or water-containing size or to store such foundry molds or cores for a longer period of time, as is customary with organic molding material binders.

Inorganic binder systems have the disadvantage compared to organic binder systems that the seeding behavior, i.e. the ability of the casting mold to quickly degenerate into a light, pourable form after metal casting (under mechanical stress) is often worse in the case of purely inorganically manufactured casting molds (e.g. those that use water glasses as a binder) than for casting molds made with an organic binder . This is especially true for cast iron applications.

This last named property, a poorer coring behavior, is particularly disadvantageous when thin-walled or filigree or complex casting molds are used, which in principle are difficult to remove after casting. So-called water jacket cores, which are necessary in the manufacture of certain areas of an internal combustion engine, can be attached here as an example.

EP 1802409 B1 discloses that higher instant strengths and higher resistance to atmospheric moisture can be achieved through the use of a fireproof molding base material, a binder based on water glass and the addition of particulate amorphous silicon dioxide.

DE 102013106276 A1 discloses that a higher resistance to humidity and to water-based sizes can be achieved by using a lithium-containing molding material mixture based on an inorganic binder, in particular in combination with amorphous silicon dioxide. This ensures safe handling of even complicated casting molds.

EP 2097192 B1 discloses that by using one or more phosphorus-containing compounds in combination with amorphous silicon dioxide, a significantly higher heat resistance can be achieved. In addition, test specimens produced from phosphate-containing molding material mixtures show significantly improved thermal stability with a time delay or reduction in “hot deformation”. It is also disclosed that, despite the high strengths, casting molds produced from the molding material mixtures according to the invention, in particular in the case of aluminum casting, show very good disintegration.

WO 2015058737 A 2 discloses that higher flexural strengths can be achieved after storage in atmospheric humidity by using one or more boron oxide compounds. This addition ensures improved handling of even complicated casting molds. Furthermore, it is disclosed that, despite the high strength of the casting molds produced from the molding material mixtures, they show very good disintegration, in particular in the case of aluminum casting.

Problems of the prior art and the task at hand

In order to be able to meet the increasing requirements in the area of environmental and emission protection, inorganic molding material binders, in particular water-containing molding material binders, should also gain in importance in the production of molds and cores in the future in the field of steel and iron casting. In order to achieve the desired or necessary casts, it is usually necessary or advantageous, as stated above, to cover inorganically bound molds and cores with a coating. In terms of environmental and emission protection, it is therefore also worthwhile when selecting the size to avoid the use of organic carrier liquids as far as possible or, preferably, water-based sizes, i.e. Sizing with water as the sole carrier liquid or as at least a predominant proportion (in terms of weight) of the carrier liquid.

As indicated above, foundry moldings, in particular molds and cores made with inorganic molding material binders, in particular with water-containing molding material binders, have a low stability to the action of water or aqueous moisture. The water contained in water-based sizing compositions can consequently damage the inorganically bound forms and cores treated (sized) with it. In particular, this can disadvantageously reduce the strength of the shapes and cores that have been finished in this way. This problem, known in foundry technology, can be solved with the means used up to now, including, for example, particularly intensive hardening of the molds and cores, Complex methods for drying the applied size or adapting the molding material mixture or adapting the size composition (DE 102017107655 A1 / DE 102017107657 A1 / DE 102017107658 A1) have so far only been inadequately met.

The previously known inorganic binder systems for foundry purposes, especially in iron and steel casting, still have room for improvement. Above all, it is desirable to develop an inorganic binder system for iron and steel casting, which:

Achieve a corresponding strength level, which is necessary in the automated production process (especially strengths in the sizing-drying process and strengths after storage),

has a particularly high moisture resistance and thus enables compatibility with water-based coatings so that even particularly thin-walled or filigree or complex inorganic casting molds can be coated reliably without shape and / or core breakage;

the application of a water-based size to molds and / or cores (ie in particular to those molds and / or cores which, for example, due to incomplete cooling after thermal setting, still temperatures of more than 50 ° C., preferably temperatures in the range from 50 to 100 ° C) made possible or at least improved;

allows a very good surface of the cast piece produced, so that no or at least only a little post-processing is necessary.

The invention was therefore based on the object of providing an inorganic molding material mixture for the production of casting molds for metal processing, in particular of iron and iron alloys, which is particularly effective in improving the stability towards environmentally friendly water-based coatings and at the same time has a high level of strength in the coating-drying Process guarantees that is necessary in the automated manufacturing process for the production of particularly thin-walled or filigree or complex, smooth casting molds.

Furthermore, the casting mold should have high storage stability and very good disintegration properties. Summary of the invention

The above objects are achieved by forms and / or cores, the use or the method with the features of the independent patent claims. Advantageous developments of the molding material mixture according to the invention are the subject matter of the dependent claims or are described below.

Surprisingly, it has been found that the presence of at least one oxidic boron compound (i) and at least one phosphate-containing compound (ii) in inorganic molding mixtures contains a binder based on water glass and amorphous silicon dioxide in casting molds, i.e. Forms and / or cores are accessible that solve the problems described above in a settled manner.

A decisive unique selling point is that the inorganic molding material mixtures used according to the invention can also be used to produce complex component geometries with reduced emissions or emission-free in cast iron.

The casting molds according to the invention, namely molds or cores, for metal processing are obtainable from at least one molding material mixture

- a refractory molding base material;

- a binding agent comprising at least water glass,

- Particulate amorphous silldum oxide,

- An oxidic boron compound, in particular in powder form; and

- a phosphate-containing compound, in particular in powder form or dissolved, e.g. dissolved in water

and will

after molding and setting to obtain a finished casting mold with a coating, at least partially and in particular completely, provided at least on those surfaces of the casting mold that come into contact with the cast metal.

Part of the binder are the water glass, the particulate amorphous silicon dioxide, the oxidic boron compound and the phosphate-containing compound.

Customary and known materials can be used as the refractory base molding material for the production of casting molds. For example, quartz sand, zirconium sand or chrome ore sand, olivine, vermiculite, bauxite, chamotte, and artificial mold base materials, in particular those with more than 50% by weight of quartz sand based on the refractory mold base material, are suitable. It is not necessary to only use new sand. In order to conserve resources and avoid landfill costs, it is even advantageous to use as high a proportion as possible of regenerated used sand, as can be obtained from used molds by recycling.

A refractory base molding material is understood to mean substances that have a high melting point (melting temperature). The melting point of the refractory base molding 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 basic molding material preferably makes up more than 80% by weight, in particular more than 90% by weight, particularly preferably more than 95% by weight, of the molding material mixture.

A suitable sand is e.g. described in WO 2008/101668 A1 (= US 2010/173767 A1). Regenerated materials that can be obtained by washing and then drying comminuted, used molds can also be replaced. As a rule, the regrind can make up at least about 70% by weight of the refractory base molding material, preferably at least about 80% by weight and particularly preferably greater than 90% by weight.

The mean diameter of the refractory base molding materials is generally between 120 mm and 600 mm and preferably between 150 mm and 500 mm. The particle size can be z. B. determined by sieving according to DIN ISO 3310. Particle geometries with the greatest length expansion to the smallest length expansion (at right angles to one another and in each case for all spatial directions) of 1: 1 to 1: 5 or 1: 1 to 1: 3, i.e. those, e.g. are not fibrous.

The refractory basic molding material has a free-flowing state, in particular in order to be able to process the molding material mixture according to the invention in conventional core shooting machines. The water glasses contain dissolved alkali silicates and can be produced by dissolving vitreous lithium, sodium and / or potassium silicates in water. The water glass preferably has a molar module SiO ₂ / M ₂ O (cumulative with 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. The binders can also be based on water glasses that contain more than one of the alkali ions mentioned, such as. B. the lithium-modified water glasses known from DE 2652421 A1 (= GB 1532847 A). Furthermore, the water glasses can also contain polyvalent ions such as, for example, the aluminum-modified water glasses described in EP 2305603 A1 (= WO 2011/042132 A1). Particularly preferred is a water glass which has a proportion of lithium ions, in particular amorphous lithium silicates, lithium oxides and lithium hydroxides, or a ratio as described in DE 102013106276 A1.

The water glasses have a solids content in the range from 25 to 65% by weight, preferably from 33 to 55% by weight, in particular from 30 to 50% 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 strength level, between 0.5% by weight and 5% by weight of the waterglass-based binder is used, preferably between 0.75% by weight and 4% by weight, particularly preferably between 1% by weight. -% and 3.5% by weight, each based on the basic molding material. The data relate to the total amount of water glass binder, including the (in particular aqueous) solvent or diluent, the dissolved water glass and the (any) solids content (together = 100% by weight).

In each case, powdery or particulate is understood to mean a solid powder (including dusts) or granules that are pourable and thus screenable.

The molding mixture according to the invention contains a portion of a particulate amorphous silicon dioxide in order to increase the strength level of the casting molds produced with such molding mixtures. An increase in the strength of the casting mold, in particular an increase in the heat strength, can be advantageous in the automated production process. Synthetically produced amorphous silica is particularly preferred. The particulate amorphous silicon dioxide 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 dust). Both synthetically produced and naturally occurring silicas can be used as amorphous SiO ₂ . The latter are z. B. from DE 102007045649, but are not preferred, since they usually contain not inconsiderable crystalline components and are therefore classified as carcinogenic. Understood by synthetically and not naturally occurring amorphous SiO ₂ , ie the synthetic production comprises a deliberately carried out chemical reaction, as it is initiated by a person, e.g. B. the production of silica sols by ion exchange processes as alkali silicate solutions, the distribution from alkali metal silicate solutions, the flame hydrolysis of silicon tetrachloride, the reaction of quartz sand with coke in the electric arc furnace in the production of ferrosilicate and silicon. The amorphous SiO ₂ produced by the two last-mentioned processes is also referred to as pyrogenic SiO ₂ .

Occasionally, synthetic amorphous silicon dioxide is understood to mean only precipitated silica (CAS No. 112926-00-8) and SiO ₂ produced by flame hydrolysis (Pyrogenic Slica, Fumed Silica, CAS No. 112945-52-5), while that in the product resulting from the manufacture of ferrosilicon or silicide is referred to merely as amorphous silicon dioxide (silica fume, microsilica, CAS No. 69012-64-12). For the purposes of the present invention, the product resulting from femosilicon or silicon production is also understood to be amorphous SiO ₂ .

Preference is given to using precipitated silicas and pyrogenic silicon dioxide, ie silicon dioxide produced by flame hydrolysis or an electric arc. Amorphous silicon dioxide produced by thermal decomposition of ZrSi04 (described in DE 102012020509 A1) and SiO ₂ produced by oxidation of metallic Si by means of an oxygen-containing gas (described in DE 102012020510 A1) are particularly preferred. Quartz glass powder is also preferred (mainly amorphous silicon dioxide), which was produced from crystalline quartz by melting and rapid cooling again, so that the particles are spherical and not splintery (described in DE 102012020511 A1). The mean particle size of the amorphous silicon dioxide is preferably less than 100 mm, in particular less than 70 mm. The sieve residue of the particulate amorphous SiO ₂ when passing through a sieve with 125 mm mesh size (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 Wt%. Irrespective of this, the sieve residue on a sieve with a mesh size of 63 ml is less than 10% by weight, preferably less than 8% by weight. This sieving residue is determined using the machine sieving method described in DIN 66165 (Part 2), a chain ring being used as a sieving aid.

The mean primary particle size of the particulate amorphous silicon dioxide can be between 0.05 mm and 10 mm, in particular between 0.1 mm and 5 mm and preferably between 0.1 mm and 2 mm. The primary particle size can e.g. can be determined with the help of dynamic light scattering (e.g. Horiba LA 959) and checked by scanning electron microscope images (SEM images with e.g. Nova NanoSEM 230 from FEI). Furthermore, with the aid of the SEM images, details of the primary particle shape down to the order of 0.01 mm could be made visible. For the SEM measurements, the silicon dioxide samples were dispersed in distilled water and then placed on an aluminum holder covered with copper tape before the water was evaporated.

Furthermore, the specific surface area of the particulate amorphous silicon dioxide was determined with the aid of gas adsorption measurements (BET method) according to DIN 66131. The specific surface of the particulate amorphous SiO ₂ is between 1 and 200 m ² / g, in particular between 1 and 50 nWg, particularly preferably between 1 and 19 m ² / g. Possibly. the products can also be mixed, for example in order to obtain mixtures with specific particle size distributions in a targeted manner.

The purity of the amorphous SiO _{2 can} vary greatly depending on the production method and producer. Types having a silicon dioxide content of at least 85% by weight, preferably at least 90% by weight and particularly preferably at least 95% by weight, have proven to be suitable.

Depending on the application and the desired strength level, between 0.1% by weight and 2% by weight of the particulate amorphous SiO ₂ are used, preferably between 0.1% by weight and 1.8% by weight, particularly preferably between 0 , 1% by weight and 1, 5% by weight, each based 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 of greatly improving the initial strength of the molds and / or cores, ie the strength immediately after removal from the tool, without significantly affecting the final strength. On the one hand, high initial strengths are desired in order to be able to transport the molds and / or cores without any problems after production or to be able to assemble them into whole core packages, on the other hand, the final strengths should not be too high to avoid difficulties with the core disintegrating after casting to avoid, ie the basic mold material should be able to be easily removed from cavities of the casting mold after casting.

Based on the total weight of the water glass (including diluents or solvents), the amorphous SiO _{2 is} preferably contained in a proportion of 1 to 80% by weight, preferably 2 to 60% by weight, particularly preferably from 3 to 55% by weight. % and particularly preferably between 4 to 50% by weight. Or regardless 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 of 10: 1 to 1: 1.2 (parts by weight) preferred.

According to EP 1802409 B1, the amorphous silicon dioxide can be added directly to the refractory material both before and after the addition of the water glass, including any substances dissolved or suspended therein, but it can also be done, as in EP 1884300 A1 (= US 2008/029240 A1) described, a mixture of the SiO ₂ with at least part of the water glass and / or the sodium hydroxide solution is first produced and these are then mixed with the refractory material. Any water glass that is still present and not used for the premix can be added to the refractory material before or after the premix is added or together with it. The amorphous SiO ₂ is preferably added to the refractory material before the addition of waterglass.

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 wt.%, Preferably between 0.1 wt % and 2% by weight, particularly preferably between 0.1% by weight and 1.5% by weight and particularly preferably 0.1% by weight to 2.0% by weight or 0.3 up to 0.99% by weight, based in each case on the total molding material mixture, can be added. The solid mixture according to the invention contains one or more oxidic boron compounds, in particular in particulate form in powder form. The mean particle size of the oxidic boron compound is preferably less than 1 mm, more preferably less than 0.5 mm, particularly preferably less than 0.25 mm. The particle size of the oxidic boron compound is preferably greater than 0.1 mm, preferably greater than 1 μm and particularly preferably greater than 5 mm.

The residue on a sieve with a mesh size of 1.00 mm is less than 5% by weight, particularly preferably less than 2.0% by weight and particularly preferably less than 1.0% by weight. Particularly preferably, regardless of the above information, the sieve residue on a sieve with a mesh size of 0.5 mm is preferably less than 20% by weight, preferably less than 15% by weight, particularly preferably less than 10% by weight and in particular preferably less than 5% by weight. Particularly preferably, regardless of the above information on the sieve with a mesh size of 0.25 mm, the sieve residue is preferably less than 50% by weight, more preferably less than 25% by weight and particularly preferably less than 15% by weight. The sieve residue is determined using the machine sieving method described in DIN 66165 (Part 2), a chain ring being used as a sieving aid.

Oxidic boron compounds are understood to mean compounds in which the boron is in the +3 oxidation state. Furthermore, the boron is coordinated with oxygen atoms (in the first coordination sphere, i.e. as the closest neighbors) - either by 3 or 4 of 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 H3BO3) and meta or polyboric acids (empirical formula (HBQz) n). Orthoboric acid occurs, for example, in water vapor sources and as the mineral sassolin. Orthoboric acid can also be produced from borates (e.g. borax) by acid hydrolysis. Meta- or polyboric acids can be produced, for example, from orthoboric acid by intermolecular 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 vitreous, hygroscopic mass, which can then be turned into small pieces.

Borates are principally derived from boric acids. They can be of both natural and synthetic origin. Borates are composed 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, e.g. in the case of orthoborate or with one another be linked, such as metaborate of

Units can be linked to form rings or chains - if one considers such a linked structure with corresponding B-O-B bonds, then it is anionic in the overall view.

Preference is given to using borates which contain linked B-O-B units. Orthorates are suitable, but not preferred. Alkali and / or alkaline earth cations, for example, but also, for example, zinc cations, in particular sodium or calcium cations, particularly preferably calcium, serve as counterions to the anionic borate units.

In the case of monovalent or divalent cations, the molar molar ratio between cation and boron can be described in the following way: where M stands for the cation and x for divalent cations 1 and for monovalent cations 2. The molar molar ratio of MxO (x = 2 for M = alkali metals and x = 1 for M = alkaline earth metals): B ₂ O ₃ can vary within wide limits, but it 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.

Also suitable are borates in which trivalent cations serve as counterions to the anionic borate units, 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 crystal water (H ₂ O molecules). As an example, borax or borax decahydrate (disodium tetraborate decahydrate) can be considered, whose molecular formula in the literature is either

or for simplicity as is specified. Both hydrated and non-hydrated borates can be used, but the hydrated borates are preferably used.

Both amorphous and crystalline borates can be used. Alkali or alkaline earth borate glasses are understood as amorphous borates, for example.

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

In the structure of these compounds there are not only neutral and / or anionic boron-oxygen coordinations (for example neutral BO ₃ units and anionic BCV units), but also neutral and / or anionic silicon-oxygen and / or Phos - phosphorus-oxygen coordination - the silicon is in the +4 oxidation state and the phosphorus is in the +5 oxidation state. The coordinations can be linked to one another via bridging oxygen atoms, such as Si-OB or P-OB. In the structure of the borosilicates, borophosphates and borophosphosilicates, metal oxides, in particular alkali and earth metal oxides, which serve as so-called network modifiers, can be incorporated. 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, bonophosphate or borophosphosilicate.

From the group of borates, boric acids, boric anhydrides, 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 boric anhydride, which impairs its possible use as a powder additive in the event of prolonged storage. Casting tests with an aluminum melt have also shown that borates lead to significantly better cast surfaces than boric acids, which is why the latter are less preferred. Borates are particularly preferably used. Particular preference is given to using alkali and / or terminal alkali borates, of which sodium borates and / or calcium borates are preferred. Calcium borate is particularly preferred.

The proportion of the oxidic boron compound, based in each case on the refractory base molding material, is preferably less than 1.0% by weight, preferably less than 0.4% by weight, particularly preferably less than 0.2% by weight and particularly preferred less than 0.1% 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.

The molding material mixture used according to the invention also contains a phosphate-containing compound. These are inorganic phosphate compounds in which the phosphorus is in the +5 oxidation state and is surrounded by oxygen atoms in the immediate vicinity.

The phosphate can be in the form of an alkali metal phosphate or an alkaline earth metal phosphate, with alkali metal phosphates and in particular the sodium salts being preferred.

Both orthophosphates and also polyphosphates, pyrophosphates or metaphosphates can be used as phosphates, polyphosphates and metaphosphates being preferred, sodium polyphosphates and sodium metaphosphates being very particularly preferred. The phosphates can be produced, for example, by neutralizing the corresponding acids with a corresponding base, for example an alkali metal base such as NaOH, or possibly also an alkaline earth metal base, although not all of the negative charges on the phosphate necessarily have to be replaced by metal ions. The phosphates can be introduced into the molding material mixture either in crystalline or in amorphous form.

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

Polyphosphates are obtained by condensation of orthophosphate ions with elimination of water, so that a linear chain of PO4 tetrahedra is obtained, each of which is connected by corners. Polyphosphates have the general formula, where n> = 2 corresponds to the chain length. A polyphosphate can comprise up to several hundred PO ₄ tetrahedra. However, preference is given to using polyphosphates with shorter chain lengths. N preferably has values from 3 to 100, particularly preferably 5 to 50. It is also possible to use more highly condensed polyphosphates, ie polyphosphates in which the PO ₄ tetrahedra are connected to one another via more than two corners and therefore exhibit polymerization in two or three dimensions.

Metaphosphate is understood to mean cyclic structures that are built up from PO4 tetrahedra that are each connected to one another via corners. Metaphosphates have the general formula where n is at least 3. Preferably, n has values from 3 to 10.

Both individual phosphates and mixtures of different phosphates can be used as the phosphate-containing compound.

The phosphate-containing compound independently preferably contains between 40% by weight and 90% by weight, particularly preferably between 50% and 80% by weight phosphorus, that is to say calculated on P2O5. The phosphate-containing compound can itself be added to the molding material mixture in solid or dissolved form. The phosphate-containing compound is preferably added to the molding material mixture as a solid.

Surprisingly, it has been shown that the combination of very small additions of one or more powdery oxidic boron compounds and one or more phosphate-containing compounds significantly improve the stability of the casting mold with respect to water-based sizes in the size-drying process.

The weight ratio of the oxidic boron compound to the phosphate-containing compound can vary over wide ranges and is preferably from 1:30 to 1: 1, preferably from 1:25 to 1: 2, particularly preferably from 1:20 to 1: 3.

If compounds are used that contain both boron oxide and phosphate groups, the stoichiometric ratio of P: B is considered. If the stoichiometric ratio of P: B is £ 1, the compound is assigned to the phosphate-containing compounds, all other compounds are counted as an oxidic boron compound Surprisingly, it has also been shown that the moisture resistance of the sized molds and / or cores is improved by adding combinations according to the invention of oxidic boron compounds and phosphate-containing compounds to the molding material mixture, and thus their strength and storage stability are increased.

According to an advantageous embodiment, the molding material mixture according to the invention contains a proportion of platelet-shaped lubricants, in particular graphite or MoS2. The amount of flake-form lubricant added, in particular graphite, is preferably 0.05% by weight to 1% by weight, particularly preferably 0.05% by weight 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 and the strength in a water-containing atmosphere. Suitable representatives of these compounds are e.g. described in WO 2009/056320 A1 (= US 2010/0326620 A1). Anionic surfactants are preferably used for the molding material mixture according to the invention. In particular, surfactants with sulfuric acid or sulfonic acid groups or their salts may be mentioned here. In the molding material mixture according to the invention, the pure surface-active substance, in particular the surfactant, based on the weight of the refractory base molding material, is preferably in a proportion of 0.001% by weight to 1% by weight, particularly preferably 0.01% by weight to 0, 2% by weight.

The molding material mixture according to the invention represents an intensive mixture of at least the mentioned constituents. The particles of the refractory molding base material are preferably coated with a layer of the binder. By evaporating the water present in the binding agent (e.g. approx. 40-70% by weight, based on the weight of the binding agent), firm cohesion between the particles of the refractory basic molding material can then be achieved.

Despite the high strengths that can be achieved with the binder system according to the invention, the casting molds produced with the molding material mixture according to the invention surprisingly show very good disintegration even after casting, even with iron and steel casting, so that the casting mold can easily be removed from narrow and angled sections of the casting after casting leaves. The casting molds are generally suitable for casting metals such as light metals, non-ferrous metals or ferrous metals. However, the molding material mixture according to the invention is particularly preferably suitable for the casting of iron and iron alloys.

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

- Provision of the above-mentioned molding material mixtures by bringing together and mixing at least the above-mentioned mandatory components;

- Shapes of the molding material mixture;

- Curing of the shaped molding material mixture, the cured casting mold being obtained.

- Application of a water-based coating to the hardened casting mold and subsequent drying.

In the production of the molding material mixture used according to the invention, the procedure is generally such that first the refractory molding base material is initially introduced and then the binder and the additive are added with stirring. The additives described above can be added to the molding material mixture in any form. They can be dosed individually or as a mixture. According to a preferred embodiment, the binder is provided as a two-component n-system, a first liquid component containing the water glass and optionally a surfactant (see above), and a second, but solid component containing the particulate silicon dioxide and one or more oxidic ones Boron compounds and one or more phosphate-containing compounds and possibly other old solid additives mentioned above, with the exception of the basic molding materials.

During the production of the molding material mixture, the refractory basic molding material is preferably placed in a mixer and then preferably the solid component (s) of the binder are first added and mixed with the refractory basic molding material. The mixing time is chosen so that the refractory molding base material and solid binder component are thoroughly mixed. The mixing time depends on the amount of molding material mixture to be produced and on the mixing unit used. The mixing time is preferably between 1 and 5 minutes. The liquid component of the binding agent is then added, preferably with further agitation of the mixture, and the mixture is then preferably further mixed until a uniform layer of the binding agent has formed on the grains of the refractory molding base 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 selected from 1 to 5 minutes. A liquid component is understood to mean both a mixture of various liquid components and the entirety of all liquid individual components, the latter being able to be added to the molding material mixture together or one after the other. A solid component is also 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 one after the other.

According to a further embodiment, the liquid component of the binder can also first be added to the refractory base molding material and only then the solid component can be added to the mixture. According to a further embodiment, 0.05% by weight to 0.3% by weight of water, based on the weight of the molding material, is added to the refractory base molding material and only then are the solid and liquid components of the binder added.

The mold material mixture is then brought into the desired shape. For example, the mold material mixture can be shot into the mold by means of a core shooter with the help of compressed air. The molding material mixture is then cured, whereby all methods can be used which are known for binders based on water glass, eg hot curing, gassing with CO ₂ or air or a combination of both and curing by liquid or solid catalysts. Heat curing is preferred.

During hot curing, water is removed from the molding material mixture. This presumably also initiates condensation reactions between silanol groups, so that crosslinking of the water glass occurs. The heating can take place, for example, in a mold which preferably has a temperature of 100.degree. C. to 300.degree. C., particularly preferably a temperature of 120.degree. C. to 250.degree. It is possible to cure the casting mold completely in the molding tool. However, it is also possible to cure the casting mold only in its edge area, so that it has sufficient strength to be able to be removed from the molding tool. The casting mold can then be completely cured by removing other 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 mold can be accelerated by blowing heated air into the mold. In this embodiment of the method, the water contained in the binding agent is quickly transported away, so that the casting mold is solidified in periods of time suitable for industrial use. The temperature of the air blown in is preferably 100.degree. C. to 180.degree. C., particularly preferably 120.degree. C. to 150.degree. The flow rate of the heated air is preferably adjusted in such a way that the casting mold is cured in periods of time suitable for industrial use. The time periods depend on the size of the molds made. The aim is to cure in less than 5 minutes, preferably less than 2 minutes. However, longer periods of time may also be required for very large molds.

The removal of water from the molding material mixture can also take place in such a way that the heating of the molding material mixture is brought about or supported by irradiating 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 to a surface and to print the individual layers with the help of a liquid binder component, in particular with the help of a water glass, the layer-by-layer application the solid mixture is followed by a printing process with the aid of the liquid binder

At the end of this process, i.e. After the final print is finished, the entire mixture can be heated in a microwave oven.

The at least partially cured cores and molds produced in this way are then provided, at least on partial areas, with the size composition according to the invention in the form of a coating or a coating. The sizing composition can be brought into contact with the core or the mold by spraying, brushing, dipping or flooding. The sizing composition is a liquid in use, with solids suspended in it. To remove the carrier liquid in the size, namely water or possibly also low-boiling alcohols, this is in air or at an elevated temperature of 60 ° C to 220 ° C, in particular 100 to 200 ° C, preferably 120 to 180 ° C, for example in a continuous or batch oven, e.g. dried using an IR heater or microwave. The carrier liquid is the constituent that can be evaporated at 160 ° C. and normal pressure (1013 mbar) and, in this sense, by definition, that which is not solid.

The carrier liquid can be partially or completely formed by water. The carrier liquid contains more than 50% by weight, preferably 75% by weight, in particular more than 80% by weight, possibly more than 95% by weight, of water. The other components in the carrier liquid can be organic solvents. Suitable solvents are alcohols, including polyalcohols and polyether alcohols. Exemplary alcohols are ethanol, n-propanol, isopropanol, n-butanol, glycols, glycol monoethers and glycol monoesters.

The solids content of the ready-to-use size composition is preferably set in the range from 10 to 60% by weight, or in the sales form (before dilution, in particular with water), in particular 30 to 80% by weight.

The size composition comprises at least 20% by weight of carrier liquid, preferably greater than 40% by weight.

Thus, the sizing composition comprises at least one refractory base material in powder form before being added to the sizing composition. The refractory base material is used to close the pores in a casting mold against the penetration of the liquid metal. The refractory base material also provides thermal insulation between the casting mold and the liquid metal. Particularly suitable refractory base materials are materials which have a melting point which is at least 200 ° C. above the temperature of the liquid metal to be cast (at least greater than 900 ° C.) and independently of this does not react with the metal as much as possible. Pyrophyllite, mica, zirconium silicate, andalusite, chamotte, iron oxide, kyanite, bauxite, olivine, aluminum oxide, quartz, talc, calcined kaolins (metakaolin) and / or graphite alone or as mixtures thereof can be used as refractory raw materials (for the size) .

With clay as the adjusting agent, the passage portion D10 can preferably be from 0.01 mm to 5 mm, more preferably from 0.01 mm to 1 mm, particularly preferably from 0.01 mm to 0.2 mm for the grain size. The clay can preferably have a passage fraction D01 of 0.001 mm to 0.2 mm, more preferably from 0.001 mm to 0.1 mm, particularly preferably from 0.001 mm to 0.05 mm for the particle size.

For mica, the passage portion D90 is preferably from 100 mm to 300 mm, more preferably from 150 mm to 250 mm, particularly preferably from 200 mm to 250 mm. The passage portion D50 of the mica can preferably be from 45 mm to 125 mm, more preferably from 63 mm to 125 mm, particularly preferably from 75 mm to 125 mm. The passage portion D10 can preferably have a grain size from 1 mm to 63 mm, more preferably from 5 mm to 45 mm, particularly preferably from 10 mm to 45 mm. The passage portion D01 can preferably be from 0.1 mm to 10 mm, more preferably from 0.5 mm to 10 mm, particularly preferably from 1 mm to 5 mm.

Furthermore, the particle diameter of the refractory base materials of the size is not particularly restricted; any customary grain sizes from 1 mm to 300 mm, particularly preferably from 1 mm to 280 mm, can be used.

The grain size distribution of the individual solid constituents of the size composition can be determined using the passage proportions D90, D50, D10 and D01. These are a measure of the particle size distribution. Here the passage proportions D90, D50, D10 or D01 denote the proportions in 90%,

50%, 10% and 1% of the particles which are smaller than the specified diameter. With a D10 value of 5 mm, for example, 10% of the particles have a diameter of less than 5 μm. The grain size and the passage proportions D90, D50, D10 and D01 can be determined using laser diffraction granulometry in accordance with ISO 13320. The percentage of passage is given on a volume basis. In the case of non-spherical particles, a hypothetical spherical grain size is calculated and the corresponding diameter is used as a basis. The grain size is therefore to be equated with the calculated diameter.

The particle diameter and its distribution is determined by laser diffraction in a water / isopropanol mixture, the suspension being obtained (only) by stirring, with a Horiba LA-960 laser light scattering spectrometer from Retsch based on static light scattering (according to DIN / ISO 13320) and by evaluation using the Fraunhofer model.

The grain size is selected so that a stable structure is created in the coating and that the size composition e.g. can easily be distributed on the wall of the mold with a spray device.

According to one embodiment, the size composition according to the invention can comprise at least one adjusting agent. The adjusting agent causes an increase in the viscosity of the size, so that the solid constituents of the size composition do not sink in the suspension or only sink to a small extent. Both organic and inorganic materials or mixtures of these materials can be used to increase the viscosity.

Swellable sheet silicates, which are capable of storing water between the layers, can be contained as adjusting agents; The swellable sheet silicate can preferably be selected from attapulgite (palygorskite), serpentines, kaolins, smectites (such as saponite, montmorillonite, beidellite and nontronite), vermiculite, IIIite, spiolite, synthetic lithium-magnesium sheet silicate, Laponite RD and mixtures thereof Attapulgite (palygorskite), serpentines, smectites (such as saponite, beidellite and nontronite), vermiculite, lllite, spiolite, synthetic lithium-magnesium phyllosilicate, Laponite RD and mixtures thereof are preferred; the swellable phyllosilicate can particularly preferably be attapulgite.

As an alternative or in addition, organic thickeners can also be selected as thickening agents, since these can be dried to such an extent after the protective coating has been applied that they hardly give off any water when they come into contact with the liquid metal. For example, swellable polymers such as carboxymethyl, methyl, ethyl, hydroxyethyl and hydroxypropyl cellulose, plant mucilages, polyvinyl alcohols, polyvinyl pyrrolidone, pectin, gelatin, agar agar, polypeptides and / or alginates can be used as organic setting materials.

The proportion of inorganic adjusting agents, based on the total size composition, is preferably selected to be 0.1 to 5% by weight, preferably 0.5 to 3% by weight, particularly preferably 1 to 2% by weight.

The proportion of organic adjusting agents, based on the total size composition, is preferably 0.01 to 1% by weight, preferably 0.01 to 0.5% by weight, particularly preferably 0.01 to 0.1% by weight. % chosen.

The size composition can e.g. the combination of certain clays as ingredients of the sizes, which also function as adjusting agents. A combination of is particularly suitable as clay materials

a) 1 to 4 parts by weight, in particular 1 to 2.2 parts by weight of palygorskite, b) 1 to 4 parts by weight, in particular 1 to 2.2 parts by weight, hectorite and c) 1 to 4 parts by weight, in particular 1 to 2.2 parts by weight, sodium bentonite, (in each case relative to one another), in particular in a weight ratio of palygorskite to hectorite of 1: 0.8 to 1.2 and a ratio of palygorskite to hectorite together to sodium bentonite of 1: 0.8 to 1.2.

According to another definition, the size (especially as a concentrate) contains

(A) at least the following tones

(A1) 1 to 10 parts by weight of palygorskite,

(A2) 1 to 10 parts by weight of hectorite and

(A3) 1 to 20 parts by weight of sodium bentonite, based on the ratio of components (A1), (A2) and (A3) relative to one another, and

(B) a carrier liquid containing water, which at up to 160 ° C and 1013

mbar is completely evaporable, and

(C) refractory raw materials different from (A).

The total clay content of the above clays in the size composition is 0.1 to 4.0% by weight, preferably 0.5 to 3.0% by weight and particularly preferably 1.0 to 2.0% by weight, based on the solids content of the size composition. According to a preferred embodiment, the size composition comprises at least one binder as a further component. The binder enables better fixation of the size composition or the protective coating produced from the size composition on the surface of the casting mold. In addition, the binding agent increases the mechanical stability of the size coating, so that less erosion is observed under the action of the liquid metal. The binder preferably hardens irreversibly, so that an abrasion-resistant coating is obtained. Particularly preferred are binders that do not re-soften on contact with atmospheric moisture. Clays, for example, especially bentonite and / or kaolin, can be used as binders. Further suitable binders are, for example, starch, dextrin, peptides, polyvinyl alcohol, polyvinyl acetate copolymers, polyacrylic acid, polystyrene, polyvinyl acetate-polyacrylate dispersions and mixtures thereof.

The proportion of the binder is preferably in the range from 0.1 to 20% by weight, particularly preferably 0.5 to 5% by weight and particularly preferably 0.2 to 2% by weight, based on the solids content of the size composition, elected.

According to a further preferred embodiment, the size composition contains a proportion of graphite. This supports the formation of lamellar carbon at the interface between the casting and the casting mold. The proportion of graphite is preferably selected in the range from 0 to 30% by weight, preferably 1 to 25% by weight, and particularly preferably from 1 to 20% by weight, based on the solids content of the size composition. In iron casting, graphite has a beneficial effect on the surface quality of the casting.

Anionic and non-anionic surfactants, in particular those with an HLB value of at least 7, can be used as wetting agents for the size. An example of such a wetting agent is disodium dioctyl sulfosucinate. The wetting agent is preferably used in an amount of 0.01 to 1% by weight, preferably 0.05 to 0.3% by weight, based on the ready-to-use size composition.

Defoamers, also called antifoam agents, can be used to prevent foam formation during the production of the sizing composition or when the same is applied. Foam formation when the sizing composition is applied can lead to an uneven layer thickness and holes in the coating. Silicone or mineral oil, for example, can be used as defoamers. The defoamer is preferably present in an amount from 0.01 to 1% by weight, preferably from 0.05 to 0.3% by weight, based on the ready-to-use size composition.

Customary pigments and dyes can optionally be used in the size composition. These are added to provide a different contrast, e.g. between different layers, or to bring about a stronger separation effect of the coating from the casting. Examples of pigments are red and yellow iron oxide and graphite. Examples of dyes are commercially available dyes such as the Luconyl® color range from BASF SE. The dyes and pigments are preferably present in an amount from 0.01 to 10% by weight, preferably from 0.1 to 5% by weight, based on the solids content of the size composition.

According to a further embodiment, the size composition contains a biocide in order to prevent bacterial infestation and thus to avoid a negative influence on the rheology of the size and the binding force of the binding agent.

This is particularly preferred when the carrier liquid contained in the sizing composition is essentially formed from water in relation to its weight, that is to say the sizing composition according to the invention is provided in the form of a so-called water sizing agent.

Examples of suitable biocides are formaldehyde, formaldehyde releasers, 2-methyi-4-isothiazolin-3-one (MIT), 5-chloro-2-methyl-4-iosthiazolin-3-one (CIT), 1, 2-Ben - zisothiazolin-3-one (BIT) and biocidal substances that contain bromine and nitrile groups. The biocides are usually used in an amount from 10 to 1000 ppm, preferably from 50 to 500 ppm, based on the weight of the ready-to-use size composition.

The size composition can be prepared by adding water and breaking up a clay that acts as an adjusting agent using a high-shear stirrer. Then the refractory base material, pigments (if available) and dyes (if available) are stirred in until a homogeneous mixture is obtained. Finally, wetting agents (if any), anti-foam agents (if any), biocides (if any) and binding agents (if any) are stirred in.

The size composition can be produced and sold as a ready-to-use formulated size composition. The size composition can, however, also be produced and marketed in concentrated form. In this case, in order to provide a ready-to-use size composition, the amount of (further) carrier liquid is added which is necessary to set the desired viscosity and density of the size composition.

It is also possible to apply several layers of size, either in multiple layers, each with the same size, in order to produce a desired layer thickness, or using different sizes.

The dry layer thickness of the cover layer is, for example, 0.01 mm to 1 mm, preferably 0.05 mm to 0.8 mm, more preferably 0.1 mm to 0.6 mm and most preferably 0.2 mm to 0.3 mm .

The dry layer thickness of the coating is determined either by dimensioning bending bars before and after finishing (dried) with a micrometer screw (preferred) or by measuring with the wet layer thickness comb. For example, you can use a comb to determine the layer thickness by scratching away the coating at the end marks of the comb until the substrate appears. The layer thickness can then be read from the markings on the teeth. Instead, you can also measure the wet layer thickness in the matted state in accordance with DIN EN ISO 2808.

The methods according to the invention are suitable per se for the production of all casting molds customary for metal casting, that is for example for cores and molds. Casting molds which comprise very thin-walled sections can also be produced particularly advantageously. The casting molds produced with the molding material mixture or with the method according to the invention have a high level of strength immediately after production and in the entire production process, in particular the sizing-drying process, without the strength of the casting mold being impaired after curing or after sizing. Drying is so high that demolding difficulties occur after the production of the casting when removing the casting mold. Furthermore, these casting molds in the unsized and sized state have a high level of stability with increased air humidity, ie the casting molds can surprisingly also be stored for a long time without problems and without any loss of quality. As an advantage, the casting mold has a very high stability under mechanical stress, so that even thin-walled sections of the casting mold can be realized without them being deformed by the metallostatic pressure during casting. In addition, the casting mold has the advantage that after metal casting, in particular iron casting, it has significantly improved disintegration properties, which also enable thin-walled sections of the casting mold to be cored. The invention therefore also relates to a casting mold which was obtained by the method according to the invention described above.

The invention is explained in more detail below using examples, without being restricted to these. For example, the fact that only heat curing is described as the curing process is not a limitation.

Examples

The following example is intended to describe and explain the invention without limiting its scope.

Example: Influence of powdery oxidic boron compounds and / or compounds containing phosphates on the flexural strengths in the sizing-drying process

So-called Georg Fischer test bars were produced for testing a molding material mixture. Georg Fischer test bars are to be understood as rectangular test bars with dimensions of 180 mm x 22.36 mm x 22.36 mm. The compositions of the molding mixtures are given in Table 1. The following procedure was used to manufacture the Georg Fischer test bars: • The components listed in Table 1 were mixed in a laboratory paddle mixer HSM10 (HOBART GmbH, Hürth, DE). First the quartz sand was initially introduced and particulate amorphous SiO ₂ and possibly powdery oxidic boron compounds and / or powdery phosphate-containing compounds were added to it. The mixture was mixed for one minute. A sodium water glass that contained 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. In a second step, the water glass was added to the mixture of sand and the powdery components mentioned, and the mixture was then stirred for a further minute.

• The molding material mixtures were transferred to the storage bunker of an L1 laboratory hot box core shooting machine from Lämpe & Mösner GmbH (Schopfheim, DE), the mold of which was heated to 180 ° C.

• The molding material niches were introduced into the mold using compressed air (3 bar) and remained in the mold for a further 35 seconds.

• To accelerate the hardening of the mixtures, hot air (2 bar, 100 ° C when entering the tool) was passed through the mold for the last 25 seconds.

• The molding tool was opened and the test bolt removed.

To determine the flexural strengths, the test bars (180 mm x 22.36 mm x 22.36 mm) were measured in a standard bending bar device of the “Multiserw-Morek LRu-2e” type, each with a standard measuring program “Rg1v_B 870 N / cm” ² “(3-point bending device) from Multiserw-Morek (Bresnrtz, PL). The flexural strengths were measured according to the following scheme:

• 10 seconds after removal (heat strength)

• 1 hour after removal (cold strengths)

• After storage for 24 hours at room temperature, followed by a further 24 hours at 30 ° C and 60% relative humidity in a climatic cabinet.

As can be seen from Table 3, the parameters of the size composition used were set for the purpose provided here, the application to test cores by means of an immersion application or an immersion bath. The density of the ready-to-use size composition given in Table 3 was measured in accordance with the standard test method DIN EN ISO 2811-2: 2011.

The flow time of the ready-to-use size composition given in Table 3 was measured in accordance with the standard test method DIN 53211 (1974) by determination with the DIN cup 4.

Table 1: Composition of the molding material mixture.

Table 2: Strengths of the molding material mixtures

The strength tests of mixture 1.1 - 1.4 show that the climatic stability of inorganically bound cores is not improved by the addition of a phosphate-containing component alone; the percentage retention of strength after KJimalagerung is almost identical for mixture 1.1 (45%) and 1.2 (44%). However, a positive effect is achieved by adding an oxidic boron compound, in this case calcium metaborate. The addition gives 84% (mixture 1.3) or 83% (mixture 1.4) of the cold strength after climatic storage, the phosphate-containing component again shows no additional influence in a comparison of mixture 1.3 and 1.4,

Table 3: Parameters of the ready-to-use size KERNTOP® V 302/88 used. KERNTOP® V 302/88 is a water-based coating based on aluminum silicate and graphite, solid approx. 49% by weight. Viscosity 12 Pa-s (at 25 ° C).

To determine the softening of foundry core (i.e. the maximum decrease in flexural strength), the test cores were immersed one hour after core production with the size composition according to Table 3 at room temperature (25 ° C) by dipping (1 s immersion, 3 s holding time in the size composition, 1 s immersion) coated (finished). The wet layer thickness of the size was adjusted to about 250 mm.

The sized test cores were then dried under the conditions specified below (20 min, 140 ° C.) in a forced-air oven and the changes in their flexural strength under the drying conditions were examined in each case.

The sized test cores were each dried over a period of 20 minutes, their flexural strengths (In N / cm ² , according to the definition as given in the leaflet R202 of the Association of German Foundry Experts, October 1987 edition) at various times during the drying, and then again one hour after the end of the drying process, measurements were taken with a standard bending device of the type “MultiservwMorek LRu-2e”, evaluated in accordance with the standard measurement program (3-point flexural strength).

Table 4 shows the strength values for the investigated sized test cores, produced with the molding compounds 1.1-1.4. and the sizing according to Table 3. The cold strength of the unsized cores, the minimum strength during the sizing drying process (absolute value) and the relatively largest drop in strength during the sizing drying process are compared. In addition, the cold strengths of the sized test cores are listed.

Table 4: Absolute flexural strengths before and after the size-drying process as well as the minimum flexural strengths (based on the cold strengths, unsized) during the size-drying process (20 min, 140 ° C).

The comparison of the minimum strengths during the drying of the size shows first of all a strong drop in strength for the mixture 1.1, here up to 88% are lost compared to the cold strength of the unsized cores.

With the mixtures 1.2 - 1.4 this maximum loss of strength is reduced to 77 - 38%.

The application of a water-based size to an inorganic core suggests a drop in strength, as water is introduced into a moisture-sensitive system. The experiments described in this application show that the addition of an oxidic boron compound has a positive effect on maintaining the strength of a sized inorganic core (cf. Table 4, mixture 1.3). For the mixtures 1.2. and 1.4 the results in Table 2 show no effect on the climatic stability due to the addition of a phosphate-containing component. In contrast to this, a positive effect can be seen from the results in Table 4 when comparing mixture 1.1 and 1.2; the phosphate-containing component increases the retention of strength during the drying of the size.

It can also be seen from Table 4 when comparing mixtures 1.2, 1.3 and 1.4 that the combined addition of a phosphate-containing component and an oxidic boron compound has a stronger effect than the individual addition of both components and, with the combined addition, surprisingly the highest retention of strength during the size drying is achieved.

Claims

1. Molds or cores obtainable by providing a shaped and hardened molding material mixture with a size to obtain sized shapes and sized cores, the molding material mixture comprising at least:

- a refractory molding base material;

- water glass;

- Particulate amorphous silica;

- At least one oxidic boron compound; and

- at least one phosphate-containing compound,

characterized in that the mold or the core is coated with a water-containing size.

2. Molds or cores according to at least one of the preceding claims, wherein the size contains clays, water and refractory raw materials, in particular

(A) at least the following tones

(A1) 1 to 10 parts by weight palygorskite,

(A2) 1 to 10 parts by weight of hectorite and

(B) a carrier liquid containing water, which at up to 160 ° C and 1013

mbar is completely evaporable, and

(C) refractory raw materials different from (A).

3. Molds or cores according to at least one of the preceding claims, wherein the size is characterized by one or more of the following features:

(i) a total clay content A1, A2 and A3 of the size of together 0, 1

Up to 4.0% by weight, preferably 0.5 to 3.0% by weight and particularly preferably 1.0 to 2.0% by weight, based on the solids content of the size;

(ii) the carrier liquid comprises more than 50% by weight water and furthermore, if necessary, softens alcohols, including polyalcohols and polyether alcohols;

(III) the solids content of the size composition is from 20% by weight to 90% by weight, in particular from 30% by weight to 80% by weight;

(iv) the size composition contains 10 to 85% by weight of refractory base materials, based on the solids content of the size composition.

4. Molds or cores according to at least one of the preceding claims, wherein the oxidic boron compound is selected from the group comprising borates, bon> phosphates, borophosphosilicates and mixtures thereof and the oxidic boron compound is in particular a borate, preferably an alkali and / or final alkali borate such as sodium borate and / or calcium borate.

5. Molds or cores according to at least one of the preceding claims, wherein the oxidic boron compound is built up from B-O-B structural elements and, independently thereof, does not contain any organic groups.

6. Molds or cores according to at least one of the preceding claims, wherein the oxidic boron compound is added as a solid in powder form, in particular with an average particle size of greater than 0.1 mm and less than 1 mm, preferably greater than 1 mm and less than 0.5 mm, and particularly preferably greater than 5 mm and less than 0.25 mm.

7. Molds or cores according to at least one of the preceding claims, wherein the oxidic boron compound, based on the refractory base material, is greater than 0.002% by weight and less than 1.0% by weight, preferably greater than 0.005% by weight % and less than 0.4% by weight, particularly preferably greater than 0.01% by weight and Weiner than 0.1% by weight and particularly preferably greater than 0.02% by weight. and added to Weiner as 0.075 wt%.

8. Molds or cores according to at least one of the preceding claims, wherein the refractory basic mold material comprises quartz sand, 23rconsand, chrome ore sand, olivine, vermiculite, bauxite, fireclay, glass beads, glass granules, aluminum silicate microspheres and mixtures thereof and preferably more than 50% by weight Quartz sand based on the refractory mold base material

9. Molds or cores according to at least one of the preceding claims, wherein greater than 80% by weight, preferably greater than 90% by weight, and particularly preferably greater than 95% by weight, of the molding material mixture are refractory basic molding material.

10. Molds or cores according to at least one of the preceding claims, wherein the refractory basic molding material has mean particle diameters of 100 mm to 600 mm, preferably between 120 mm and 550 mm.

11. molds or cores according to at least one of the preceding claims, wherein the particulate amorphous silicon dioxide has a BET surface area between 1 and 200 m ² / g, preferably greater than or equal to 1 m ² / g and less than or equal to 30 m ² / g, particularly preferred from 1 to less than or equal to 19 m ² / g. indicates.

12. Molds or cores according to at least one of the preceding claims, wherein the particulate amorphous silicon dioxide, based on the total weight of the binder, is used in a proportion of 1 to 80% by weight, preferably between 2 and 60% by weight.

13. Molds or cores according to at least one of the preceding claims, wherein the particulate amorphous silicon dioxide has an average primary particle diameter determined by dynamic light scattering between 0.05 mm and 10 mm, in particular between 0.1 mm and 5 mm and particularly preferably between 0, 1 mm and 2 mm.

14. Molds or cores according to at least one of the preceding claims, wherein the particulate amorphous silicon dioxide is selected from the group consisting of: precipitated silica, fumed silicon dioxide produced by flame hydrolysis or in an electric arc, amorphous silicon dioxide produced by thermal decomposition of ZrSi04, by oxidation of metallic silicon by means of an oxygen-containing one Gases produced silicon dioxide, quartz glass powder with spherical particles, which was produced by melting and rapid cooling again from crystalline quartz, and mixtures of which is selected.

15. Molds or cores according to at least one of the preceding claims, wherein the mold mixture contains the particulate amorphous silicon dioxide in amounts of 0.1 to 2% by weight, preferably 0.1 to 1.5% by weight, in each case based on the basic molding material contains, and independent of it

the molding material mixture contains the particulate amorphous silicon dioxide in amounts of 2 to 60% by weight, particularly preferably 4 to 50% by weight, based on the weight of the binder including water, the solids part of the binder being 20 to 55% by weight, preferably from 25 to 50% by weight

16. Molds or cores according to at least one of the preceding claims, wherein the particulate amorphous silicon dioxide used has a water content of less than 5% by weight and particularly preferably less than 1% by weight.

17. Molds or cores according to at least one of the preceding claims, wherein the water glass including the water 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, is contained in the molding material mixture and further preferably also independently, but preferably in combination with the above values, the solids content of waterglass of 0.2625 to 1.4% by weight, preferably 0.35 is up to 1.225 wt .-%, relative to the base molding material in the molding material mixture.

18. Molds or cores according to at least one of the preceding claims, wherein the water glass has a molar module SiO ₂ / M ₂ O in the range from 1.6 to 4.0, in particular 2.0 to less than 3.5, with M = lithium , Sodium and potassium or M = sodium and potassium.

19. Molds or cores according to at least one of the preceding claims, wherein the phosphate-containing compound is an inorganic phosphate compound with phosphorus in the oxidation state +5, metaphosphates and / or polyphosphates being preferred, in particular in each case as alkali or alkaline earth metal phosphate, special the alkaline earth metal sodium is preferred.

20. Molds or cores according to at least one of the preceding claims, wherein the molding material mixture is based on the phosphate-containing compound in an amount of 0.05 and 1.0 wt.%, Particularly preferably 0.1 and 0.5 wt contains the weight of the refractory base molding material.

21. A method of making sized shapes or sized cores comprising:

- Provision of the molding material mixture by bringing together and mixing the substances or components according to claims 1 to 20,

- Introducing the molding material mixture into a mold, and

Curing of the molding material mixture by hot curing with heating and removal of water, preferably by exposing the molding material mixture to a temperature of 100 ° to 300 ° C. to obtain molds or cores, and

- Finishing the molds or cores with a water-based coating.

22. The method according to claim 21, wherein the molding material mixture is introduced into the mold by means of a core shooting machine with the help of compressed air and the mold is a molding tool and one or more gases flow through the molding tool, in particular CO ₂ , or gases containing CO ₂ , preferably CO ₂ heated to over 60 ° C and / or air heated to over 60 ° C.

23. The method according to claim 21 or 22, wherein the molding material mixture for curing is exposed to a temperature of 100 to 300 ° C, preferably from 120 to 250 ° C, preferably for less than 5 min, more preferably the temperature is at least partially heated by blowing in Air is stiffened in a mold.

24. Use of the mold or the cores according to at least one of claims 1 to 20 for metal casting, in particular iron casting.