EP2763807B1 - Coating compositions for inorganic casting molds and cores, containing salts, and use thereof - Google Patents

Description

The invention relates to slip molds having a sizing composition as a coating composition. the production of such molds and the use of the size compositions. The sizing composition is suitable for cores and molds made using waterglass as a binder under thermal cure. The sizing composition contains certain salts.

State of the art

Molds are available from a refractory material, such as quartz sand, to form into a casting mold and set by a suitable binder to ensure sufficient mechanical strength of the mold. For the production of molds is thus used a refractory molding material and a suitable binder. The refractory molding base material is preferably present in a free-flowing form, so that it can be filled into a suitable mold and compacted there. The binder produces a firm cohesion between the particles of the molding base material, so that the casting mold obtains the required mechanical stability.

For the production of casting molds both organic and inorganic binders can be used, the curing of which can be carried out in each case by cold or hot processes. Cold processes are processes which are carried out essentially at room temperature without heating the casting mold. The curing is usually carried out by a chemical reaction, which is triggered for example by the fact that a gas is passed as a catalyst through the mold to be cured. In hot processes, the molding material mixture is heated to a sufficiently high temperature after molding to expel, for example, the solvent contained in the binder or to initiate a chemical reaction by which the binder is cured, for example, by crosslinking. Regardless of the curing mechanism, all organic systems have in common that they thermally decompose when the liquid metal is poured into the mold, releasing pollutants such as benzene, toluene, xylenes, phenol, formaldehyde, and other partially unidentified cracking products.

Although various measures have succeeded in minimizing these emissions, they can not be completely avoided with organic binders.

In order to minimize or avoid the emission of decomposition products during the casting process, it is possible to use binders which are based on inorganic materials or contain a very low proportion of organic compounds. Such binder systems have been known for some time.

Binder systems have been developed which can be cured by the introduction of gases. Such a system is for example in the GB 782205 described in which an alkali water glass is used as a binder, which can be cured by the introduction of CO ₂ . In the US 6972059 B1 describes an exothermic feeder composition containing an alkali metal silicate as a binder. Furthermore, binder systems have been developed which are self-curing at room temperature. Such, based on phosphoric acid and metal oxides system is eg in the US 5582232A described. Finally, inorganic binder systems are known which are cured at higher temperatures, for example in a hot tool. Such thermosetting binder systems are for example from US 5474606 A in which a binder system consisting of alkali water glass and aluminum silicate is described.

In the US 7022178 B1 describes a binder system for molding sands for the production of cores. The waterglass-based binder system consists of an aqueous alkali silicate solution and a hygroscopic base, such as sodium hydroxide, added in a ratio of 1: 4 to 1: 6. The water glass has a modulus SiO ₂ / M ₂ O of 2.5 to 3.5 and a solids content of 20 to 40%. In order to obtain a free-flowing molding material mixture, which can also be filled into complicated core molds, as well as to control the hygroscopic properties, the binder system still contains a surface-active substance, such as silicone oil, which has a boiling point ≥ 250 ° C. The binder system is mixed with a suitable refractory material, such as quartz sand, and then injected into a core box with a core shooter.

The use of metal salts, such as magnesium or manganese salts. as part of sizing is known, for example from the WO 2004/071738 A1 , of the US 3501320 of the DD 63853 A1 , of the US 3211560 A , of the US 2,426,987 A or the JP 2005211983 A , However, the influence of magnesium or manganese salts on the stability of water-glass-thermally cured molding mixtures of, inter alia, powdery refractory materials does not disclose these because forms and cores of other materials are used there.

The hardening of the molding material mixture takes place by removal of the water or condensation still contained. The drying or hardening of the casting mold can also take place under the action of microwaves.

However, inorganic binders also have disadvantages compared to organic binders, for example the known inorganic binders have a low stability of the casting molds produced therewith against high humidity or against water. For a storage of the molded body over a longer period, as usual with organic binders, not secured possible. In order to obtain higher initial strengths, a better resistance of the mold against atmospheric moisture and a better result on the surface of the casting during casting, the US 7770629 B2 proposed a molding material mixture containing a water-based binder in addition to a refractory molding material. A proportion of a particulate metal oxide is added to the molding material mixture. Precipitated silica or fumed silica is preferably used as the particulate metal oxide.

The methods described for the production of molds and cores usually also include the application of a refractory mold coating, which is also called sizing, at least on those surfaces of the basic shape, which come into contact with the cast metal. The purpose of the mold coatings is to influence the molding surface, to improve the casting appearance, to metallurgically influence the casting and / or to avoid casting defects.

The commonly used sizing agents contain as base materials e.g. Clays, quartz, kieselguhr, cristobalite, tridymite, aluminum silicate, zirconium silicate, mica, chamotte and also coke and graphite. These bases are the purportive portion of the sizings which cover the mold surface and close the pores against the penetration of the cast metal.

By means of these coatings, therefore, the surface of the casting mold can be modified and matched to the properties of the metal to be processed. Thus, the size can be used to improve the appearance of the casting by creating a smooth surface because the size compensates for irregularities caused by the size of the grains of the molding material.

Further, the size may metallurgically influence the casting by, for example, selectively transferring additives to the casting at the surface of the casting over the size which enhance the surface properties of the casting. Further, the sizings form a layer which chemically isolates the casting mold from the liquid metal during casting. This prevents any adhesion between the casting and the casting mold so that the casting can be removed from the casting mold without difficulty. However, the sizing can also be used to selectively control the heat transfer between the liquid metal and the casting mold in order, for example, to effect the formation of a specific metal structure by the cooling rate.

The curing of the inorganic binder used is nowadays increasingly via a condensation reaction initiated by elevated temperatures, in which the formation of the binder bridges takes place via the splitting off of water. As with many chemical reactions, this is a reversible reaction, i. by contact and reaction with water, the bonds can be split again, the extent of this back-reaction is highly dependent on the process parameters for core production. Among the process parameters typically used in series production (fast tents, high temperatures), the molds lose their strength through contact with water and sometimes also through contact with alcohol, the surface softens and the mold loses its shape.

task

The invention had the object of proposing a sizing, by which the most error-free coating for water glass hardened inorganic cores and molds can be ensured without negatively affecting the stability of the cores or molds and thus the processing and storage.

Summary of the invention

This object is achieved with molds provided with a sizing composition having the features of claim 1, advantageous embodiments form the subject of the dependent claims or are described below.

The sizing composition used is, according to a preferred embodiment, provided in the form of a paste or a suspension. Also in this embodiment, the sizing composition contains a carrier liquid.

Surprisingly, it has been found that the addition of certain salts in a certain concentration range to an aqueous size composition, the quality of the sized inorganic cores and molds can be sustainably improved and, for example, a shelf life of the cores and forms of several days can be achieved easily.

Detailed description of the invention

It has surprisingly been found that salts of the metals magnesium and / or manganese can be used to achieve the above object. The amount salts are preferably used in the oxidation state +2 or +4. Particular preference is given to using magnesium salts in the oxidation state +2 and the manganese salts in the oxidation state +2. The concentration of the salts is greater than 1% by weight, preferably greater than 3% by weight and particularly preferably greater than 5% by weight, based on the size composition. According to one embodiment, the concentration is limited upwards by the saturation concentration of the respective amount used and type of carrier liquid. According to another embodiment, the maximum concentration is less than 10 wt.%, Based on the Schllchtezusammensetzung. As anions, preference is given to using sulfate ion and / or particularly preferably the monovalent chloride ion as countercurrent ion.

Depending on the desired use of the sizing composition, e.g. as a basecoat or as a topcoat, and desired layer thickness of the coating made from the sizing composition, other characteristic parameters of the sizing composition may be adjusted.

As a further additive component of the sizing composition, it is possible to use esters of formic acid (methanoic acid), the chain length of the alcohol or alcohol mixture used in the esterification in particular being on average less than 6 and particularly preferably less than 3 carbon atoms. Methyl formate (methyl formate) and ethyl formate (ethyl formate) are particularly preferably used. It is also possible for the alcohol group (s) or some of the alcohol groups to carry one or two further groups, such as ether, hydroxy groups, ester groups or carboxyl groups, or the formic acid through the second or third hydroxyl group is crosslinked, eg by condensation.

The total content of the above additives, based on the size composition, is from 1 to 8% by weight, preferably from 2 to 8% by weight and more preferably from 3 to 6% by weight. As an additive, e.g. "Methyl formate purely" of BASF can be used. It has the CAS number 107-31-3.

1. a) 1 bis 10 Gewichtsteilen, insbesondere 1 bis 5 Gewichtsteilen Palygorskit,
2. b) 1 bis 10 Gewichtsteilen, insbesondere 1 bis 5 Gewichtsteilen, Hectorit und
3. c) 1 bis 20 Gewichtsteilen, insbesondere 1 bis 5 Gewichtsteilen, Natriumbentonit

(jeweils relativ zueinander) verwendet, insbesondere in einem Gewichtsverhältnis Palygorskit zu Hectorit von 1 zu 0,8 bis 1,2 und einem Verhältnis von Palygorskit zu Hectorit gemeinsam zu Natriumbentonit von 1 zu 0,8 bis 1,2. Der Gesamttongehalt der Schlichte an obigen Tonen beträgt dabei 0,1 bis 4,0 Gew.%, bevorzugt 0,5 bis 3,0 % Gew. und besonders bevorzugt 1,0 bis 2,0 Gew.%, bezogen auf den Feststoffgehalt der Schlichtezusammensetzung. Unter Verwendung dieser Tone kann man die Lagerstabilität der Kerne und Formen weiter steigern.The sizing may include, for example, the combination of certain clays as ingredients of the sizings. As clay materials was a combination of

1. a) 1 to 10 parts by weight, in particular 1 to 5 parts by weight of Palygorskit,
2. b) 1 to 10 parts by weight, in particular 1 to 5 parts by weight, hectorite and
3. c) 1 to 20 parts by weight, especially 1 to 5 parts by weight, sodium bentonite

(in each case relative to each other) used, in particular in a weight ratio Palygorskit to hectorite of 1 to 0.8 to 1.2 and a ratio of Palygorskit to hectorite together to sodium bentonite of 1 to 0.8 to 1.2. The total clay content of the size of the above clays is 0.1 to 4.0% by weight, preferably 0.5 to 3.0% by weight and more preferably 1.0 to 2.0% by weight, based on the solids content of size composition. By using these clays, one can further increase the storage stability of the cores and molds.

The carrier liquid can be proportionately or completely formed by water. The carrier liquid is the constituent which is vaporizable at 160 ° C and atmospheric pressure and in this sense, by definition, that which is not solids content. The carrier liquid contains greater than 50% by weight, preferably 75% by weight, in particular greater than 80% by weight, if appropriate greater than 95% by weight of water.

The other ingredients in the carrier liquid may be organic solvents. Suitable solvents are alcohols, including polyhydric alcohols and polyether alcohols. Exemplary alcohols are ethanol, n-propanol, isopropanol, butanol and glycol.

The solids content of the ready-to-use sizing composition is preferably set in the range from 10 to 85% by weight, or in the sold form (before dilution), in particular from 30 to 70% by weight.

Thus, the sizing composition comprises at least one powdered refractory material . This refractory material serves to close the pores in a mold against the penetration of the liquid metal. Next is achieved by the refractory thermal insulation between the mold and liquid metal. As refractory material, conventional refractory materials can be used in metal casting. Examples of suitable refractory materials are quartz, aluminum oxide, zirconium oxide, aluminum silicates, such as pyropyllite, kyanite, andalusite or chamotte, zirconium, ciconsilicates, olivine, talc, mica, coke, feldspar, diatomite, calcined kaolins, kaolinite, metakaolinite, iron oxide and / or bauxite ,

The refractory material is provided in powder form. The grain size is chosen so that a stable structure is produced in the coating and that the sizing can preferably be distributed without problem on the wall of the casting mold with a spray device. Suitably, the refractory material has an average particle size (measured by means of light scattering in accordance with DIN / ISO 13320) in the range from 0.1 to 500 μm, particularly preferably in the range from 1 to 200 μm. In particular, materials which have a melting point which is at least 200 ° C. above the temperature of the liquid metal and, independently of this, do not react with the metal are suitable as the refractory material.

The fraction of the refractory material (in each case contributing only to the solids content), based on the solids content of the sizing composition, is preferably greater than 70% by weight, preferably greater than 80% by weight, particularly preferably greater than 85% by weight.

According to one embodiment (in each case contributing only to the solids content), the fraction of the refractory material is chosen to be less than 70% by weight, according to a further embodiment less than 60% by weight and according to a further embodiment less than 50% by weight.

The sizing may comprise at least one adjusting means according to one embodiment. The adjusting agent causes an increase in the viscosity of the size, so that the solid components of the size in the suspension do not or only to a small extent decrease. To increase the viscosity, both organic and inorganic materials or mixtures of these materials can be used. Suitable inorganic adjusting agents are, for example, strongly swellable clays, such as sodium bentonite.

As an adjusting agent, organic thickening agents may alternatively or additionally be selected, since these can be dried to the extent that they hardly give off any more water upon contact with the liquid metal after application of the protective coating. Suitable organic solvents are, for example, swellable polymers, such as carboxymethyl, methyl, ethyl, hydroxyethyl and hydroxypropyl cellulose, mucilages, polyvinyl alcohols, Polyvlnylpyrrolldon, pectin, gelatin, agar agar, polypeptides and / or alginates. The proportion of the adjusting agent, based on the total size composition, is preferably selected to be from 0.1 to 5% by weight, preferably from 0.5 to 3% by weight, particularly preferably from 1 to 2% by weight.

According to a preferred embodiment, the size comprises as further constituent at least one binder . The binder allows a better fixation of the size or of the protective coating produced from the size on the wall of the mold. In addition, the binder increases the mechanical stability of the protective coating so that less erosion is observed under the action of the liquid metal. Vorzugswelse cures the binder irreversibly, so that an abrasion-resistant coating is obtained. Particular preference is given to binders which do not soften on contact with atmospheric moisture. All binders which are used in sizing can be contained per se. In this case, both inorganic and organic binders can be used. For example, clays can be used as binders, in particular bentonite and / or kaolin.

The proportion of the binder is preferably selected in the range of 0.1 to 20 wt .-%, particularly preferably 0.5 to 5 wt .-%, based on the solids content of the sizing composition.

According to a further preferred embodiment, the size contains a proportion of graphite . This supports the formation of lamellar carbon at the interface between casting and mold. The proportion of graphite is preferably selected in the range of 1 to 30 wt .-%, particularly preferably 5 to 15 wt .-%, based on the solids content of the size composition. Graphite has a favorable effect on the surface quality of castings during iron casting.

If appropriate, the sizing composition may also comprise further components customary for sizing, for example wetting agents, defoamers, pigments, dyes or biocides. The proportion of these further constituents in the ready-to-use coating composition is preferably less than 10% by weight, preferably less than 5% by weight and more preferably less than 1% by weight.

Suitable wetting agents are , for example, anionic and non-anionic surfactants, in particular those having an HSB value of at least 7. An example of such a wetting agent is disodium dioctyl sulfosuccinate. The wetting agent is preferably used in an amount of 0.01 to 1 wt .-%, preferably 0.05 to 0.3 wt .-%, based on the ready-to-use sizing composition.

Defoamers , or anti-foaming agents, can be used to prevent foaming in the preparation of the sizing composition or in applying it. Foaming on application of the sizing composition can result in uneven layer thickness and voids in the coating. As defoamers, for example, silicone or mineral oil can be used. The defoamer is preferably present in an amount of from 0.01 to 1% by weight, preferably from 0.05 to 0.3% by weight, based on the ready-to-use sizing composition.

in the sizing composition, if necessary, usual pigments and dyes may be used. These are added in order to achieve a different contrast, for example between different sizes, or to bring about a greater separation effect of the size of 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 series of BASF AG, Ludwigshafen, DE. The dyes and pigments are preferably contained in an amount of 0.01 to 10 wt .-%, preferably from 0.1 to 5 wt .-%, based on the solids content of the sizing composition.

In another embodiment, the sizing composition contains a biocide to prevent bacterial attack, thereby avoiding a negative impact on the rheology and binding power of the binding agents. This is particularly preferred when the carrier liquid contained in the sizing composition is formed substantially in water with respect to the weight, that is, the sizing composition is provided in the form of a so-called water sizing. Examples of elicited biocides are formaldehyde, 2-methyl-4-isothiazolin-3-one (MIT), 5-chloro-2-methyl-4-iosthiazolin-3-one (CIT) and 1,2-benzisothiazolin-3-one (BIT). Preferably, MIT, BIT or a mixture thereof are used. The biocides are usually used in an amount of from 10 to 1000 ppm, preferably from 50 to 500 ppm, based on the weight of the ready-to-use sizing composition.

In addition to the constituents already mentioned, the sizing composition may contain further constituents customary for sizing.

The heat composition can be prepared by conventional methods. For example, the sizing composition may be prepared by initially introducing water and breaking up a clay acting as a sizing agent using a high shear stirrer. Subsequently, the refractory components, pigments and dyes and the metallic additive are stirred until a homogeneous mixture is formed. Finally, wetting agents, antifoams, biocides and binders are added.

The sizing composition may be prepared and sold as a ready-to-use sizing. However, the size can also be produced and sold in concentrated form. In this case, to provide a ready-to-use size, the amount of carrier liquid necessary to adjust the desired viscosity and density of the size is added. In addition, the sizing composition may also be provided and sold in the form of a kit, for example where the solid components and the solvent component are present side by side in separate containers. The solid components can be provided as a powdery solid mixture in a separate container.

Optionally, further liquid components to be used, e.g. Binders, wetting agents, wetting agents / defoamers, pigments, dyes and biocides, may in this kit again be present in a separate container. The solvent component may comprise either the optionally additional components to be used, e.g. in a common container, or it may be separate from other optional components in a separate container. To prepare a ready-to-use size, the appropriate amounts of the solid component, the optional further components and the solvent component are mixed together.

The sizing compositions are useful for coating slip forms . As used herein, the term "mold" includes all types of bodies necessary to make a casting, such as cores, molds and molds. The use of the size compositions according to the invention also includes partial coating of casting molds. The sizings are used for metal working molds obtainable from inorganic molding material mixtures comprising at least one refractory molding base, a water glass based binder, and preferably a portion of a metal oxide selected from the group of silica, especially amorphous silica, alumina, titania or zinc oxide and mixtures thereof, this preferably being in the form of a wafer and in particular having particle sizes of less than 300 μm (sieve analysis). Amorphous silica is available, for example, via precipitation processes starting from water glass, which is obtainable by digesting quartz sand with sodium carbonate or potassium carbonate. Depending on the process conditions, so-called SIO _{2 is} called precipitated silica. Another important production variant is the production of so-called pyrogenic SiO ₂ in a blast gas flame, starting from liquid chlorosilanes such as silicon tetrachloride. The molding material mixtures and a method for the production of casting molds for metal processing using the cured molding material mixtures are in WO 2006/024540 (= US 7770629 B2 ) and the publication is insofar made by reference to the content of this application. Preferred molding material mixtures are the subject of the claims of WO 2006/024540 ,

1. a) größer 80 Gew.% einen feuerfesten Formgrundstoff (einschließlich Additive, die sich wie feuerfeste Formgrundstoffe verhalten),
2. b) 0,01 bis 5 Gew.% ausgehärtetes Wasserglas als Bindemittel
3. c) 0 bis 5 Gew.% ggf. obiges Metalloxid bzw. Metalloxide.

The molds to be coated thus typically include

1. a) greater than 80% by weight of a refractory base molding material (including additives which behave like refractory molding materials),
2. b) 0.01 to 5 wt.% Tempered water glass as a binder
3. c) 0 to 5% by weight, if appropriate, of the above metal oxide or metal oxides.

Furthermore, the invention relates to a process for the preparation of glazed molds for metal processing with application of the sizes to the above partially or completely cured inorganic molding material mixtures. The application or provision of the sizes can be carried out as follows:
When dipping as an application method, the mold, in the mold cavity of which optionally a primer coating has been applied, is immersed for about 2 seconds to 2 minutes in a container filled with a ready-to-use, sizing composition. The slip mold is then removed from the sizing composition and excess sizing composition drained from the casting mold. The tent, which takes the expiration of the excess sizing composition after dipping, depends on the flow behavior of the sizing composition used.

In spraying as the application method commercial pressure sprayers are used. Here, the sizing composition is filled in a dilute state in a pressure pot. The sizing can be pressed into a spray gun via the overpressure to be set, where it is sprayed with the aid of separately adjustable atomizing air. In spraying, the conditions are preferably selected so that the pressure for sizing composition and atomizing air is adjusted at the gun such that the sprayed sizing composition still wet on the mold or the core, but gives a uniform application.

In the case of flooding as the application method, the casting mold, in the mold cavity of which a base coat has optionally been applied, is poured over with the aid of a hose, a lance or similar instruments with a ready-to-use sizing composition. The mold is completely covered with the sizing composition, the excess sizing composition drains from the mold. The tent, which takes advantage of the drainage of the excess size composition after flooding, depends on the flow behavior of the sizing composition used.

In addition, the sizing can also be applied by brushing .

The carrier liquid contained in the size is then evaporated, so that a dry size coat is obtained. As the drying method, any conventional drying method can be used, such as air drying, dehumidified air drying, microwave or infrared radiation drying, convection oven drying, and similar methods. In a preferred embodiment of the invention, the coated casting mold is dried at 20 to 250 ° C, preferably at 50 to 180 ° C, in a convection oven.

When using alcohol sizes, the sizing composition is preferably dried by burning off the alcohol or alcohol mixture. In this case, the coated casting mold is additionally heated by the heat of combustion. In a further preferred embodiment, the coated casting mold is dried in the air without further treatment or using microwaves.

The size can be applied in the form of a single layer or else in the form of a plurality of layers arranged one above the other. The individual layers in their composition can be the same or different. For example, a base coat can first be prepared from a commercially available size which does not contain any metallic additive used according to the invention. As a primer coating, for example, water-based or alcohol-based sizing can be used. But it is also possible to produce all layers of the sizing composition. However, the layer which later comes into contact with the liquid metal is always made from the size used according to the invention. When applying several layers, each individual layer can be completely or partially dried after application.

The coating prepared from the sizing composition preferably has a dry film thickness of at least 0.1 mm, preferably at least 0.2 mm, more preferably at least 0.45 mm, most preferably at least 0.55 mm. According to one embodiment, the thickness of the coating is chosen to be less than 1.5 mm. The dry layer thickness here is the layer thickness of the dried coating, which was obtained by drying the sizing composition by substantially complete removal of the solvent component and optionally subsequent curing. The dry layer thickness of the base coat and the top coat are preferably determined by measurement with the wet film thickness comb.

If necessary, the casting mold can then be completely assembled. The casting is preferably carried out for the production of iron and cast steel bodies.

Example 1:

In this example, the influence of salts in sizings on the strengths of the sized cores was examined. The core sizes 1 to 3 used have the compositions given in Table 1 to 3. Table 1: Composition of the sizes Simple 1 Simple 2 Simple 3 component % By weight % By weight % By weight water 31 31 31.0 MnCl2 5.0 - MgSO4 - 5.0 0.5 Zirconium flour 45 μm 19.5 19.5 21.0 Actigel 208 1.0 1.0 1.0 PVA solution (25%) 1.5 1.5 1.5 Satintone W® 17 17 18 Surfynol® SEF (wetting agent 1) 0.2 0.2 0.2 Dynol® 604 (wetting agent 2) 0.05 0.05 0.05 Foamstar® MF324 (defoamer) 0.2 0.2 0.2 Pyrax RG 140 12 12 13 Gloss Powder Graphite 85% C 12 12 13 Acticide® F (N) (preservative 1 0.4 0.4 0.4 Acticide® MBS, (Preservative 2) 0.15 0.15 0.15

The mold casting size was prepared as follows: Water is introduced and the salts are dissolved therein. The clay is then disrupted by using a high shear stirrer for at least 15 minutes.

Subsequently, the refractory components, pigments and dyes are stirred for at least 15 minutes until a homogeneous mixture is formed. Finally, additives such as wetting agents, defoamers and preservatives and the binder are stirred.

The sizes were adjusted to a viscosity suitable for the application in the range of 0.6 Pas for the following tests. The adjustment was carried out by adding appropriate amounts of water to the original composition and subsequent homogenization. The main parameters are the viscosity at 20 ° C, measured with a Brookfield viscometer (DIN EN ISO 2555) and with a DIN 4 mm flow cup (DIN EN ISO 2431). Table 2: Application parameters Simple 1 Simple 2 Simple 3 Brookfield [Pas] 0.6 0.6 0.6 Flow time [s] 15.5 15.5 15.5 Solids content [%] 57.5 57.5 62.5 Penetration depth [mm] 2 2 2 According to the patent According to the patent Not according to patent

The manganese chloride contained in the size 1 or the magnesium sulfate contained in size 2, when used on inorganic cores and molds, significantly reduces the dissolution or softening of the inorganic binder in the surface. Thus, a higher stability of the sized cores compared to conventional sizes can be determined.
The effect is based on the fact that the water contained in the sizing upon contact with the cured inorganic binder must absorb the ions formed during the dissolution process. However, if the water already contains an unusually high ion content, the solubility product increases and the uptake of further ions is impeded or prevented. Thus, the solubilized salts in the sizing contribute to the prevention of destabilization of the inorganic cores and molds during the sizing process.

A comparable behavior can also be achieved with chemically related salts of the metals magnesium and manganese.

Production and Testing of the Formstoffprüfkörper

Two different core geometries were tested for experimental purposes. One geometry, the so-called Georg Fischer test strip, illustrates the behavior of the sized test specimens on thicker core geometries, the other geometry, so-called long cores, illustrates the behavior of the sized test specimens on thin geometries. Georg Fischer test bars are cuboid test bars measuring 150 mm x 22.36 mm x 22.36 mm. The long cores have dimensions of 13 mm x 20 mm x 235 mm.

The composition of the molding material mixture is given in Table 3. The Georg Fischer test bars were prepared as follows: The components listed in Table 3 were mixed in a laboratory paddle mixer (Vogel & Schemmann AG, Hagen, DE). For this purpose, initially the quartz sand was introduced and added with stirring the water glass. As a water glass, a sodium water glass was used, which had proportions of potassium. The modulus SiO ₂ : M ₂ O of the water glass was about 2.2, where M is the sum of sodium and potassium. After stirring the mixture for one minute, amorphous silica was added, if necessary, with further stirring. The amorphous silica is pyrogenic silica from RW silicon. The mixture was then stirred for an additional 1 minute.

The molding material mixture was transferred to the storage bunker of an H 2.5 hot-box core shooter from Röperwerk-Gießereimaschinen GmbH, Viersen, DE, whose mold had been heated to 180.degree. The molding material mixture was introduced into the mold by means of compressed air (5 bar) and remained in the mold for a further 35 seconds. To accelerate the curing of the mixture, hot air (2 bar, 150 ° C on entering the mold) was passed through the mold during the last 20 seconds. The mold was opened and the test bars removed.

The coating compositions were applied to the test bars by dipping, the application parameters are listed in Table 2. The test bars were coated either immediately after removal from the mold or after a 30 minute cooling time. The coated test bars were stored after application of the coating in a drying oven for 30 minutes at 150 ° C.

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 was measured, which leads to the breakage of the test bars.

• 10 Sekunden nach der Entnahme (Heißfestigkeiten)
• 1 Stunde nach der Entnahme (Kaltfestigkeiten).

The flexural strengths of the uncoated test bars were measured according to the following scheme:

• 10 seconds after removal (hot strength)
• 1 hour after removal (cold strength).

• 1 Minute nach der Entnahme beschichtet (Heißbeschichtung)
• 30 Minuten nach der Entnahme beschichtet (Kaltbeschichtung)

The test bars were coated according to the following scheme:

• 1 minute after removal coated (hot coating)
• Coated 30 minutes after removal (cold coating)

• 10 Sekunden nach der Entnahme aus dem Trockenschrank (Heißfestigkeiten, heißbeschichtet)
• 30 Minuten nach der Entnahme beschichtet (Kaltfestigkeiten, heißbeschichtet, direkt nach Ofenentnahme)
• 10 Sekunden nach der Entnahme aus dem Trockenschrank (Heißfestigkeiten, kaltbeschichtet, Raumtemperatur 20°C)
• 30 Minuten nach der Entnahme beschichtet (Kaltfestigkeiten, kaltbeschichtet)

Tabelle 3: Zusammensetzung der Formstoffmischungen Quarzsand H32 Alkaliwasserglas Amorphes Siliciumdioxid Beschichtung 1 100 GT 2,0 0,5 - Vergleich, nicht erfindungsgemäß 2 100 GT 2,0 0,5 Schlichte 1 erfindungsgemäß 3 100 GT 2,0 0,5 Schlichte 2 erfindungsgemäß 4 100 GT 2,0 0,5 Schlichte 3 Nicht erfindungsgemäß Tabelle 4: Festigkeiten an Georg-Fischer Prüfriegeln Heißfestigkeit, heißbeschichtet [N/cm2] Kaltfestigkeit, heißbeschichtet [N/cm2] Heißfestigkeit, kaltbeschichtet [N/cm2] Kaltfestigkeit, kaltbeschichtet [N/cm2] 1 400 450 400 450 Vergleich, nicht erfindungsgemäß 2 290 390 330 460 Erfindungsgemäß 3 290 350 300 450 Erfindungsgemäß 4 220 - (zerbrochen) - (zerbrochen) 300 Nicht erfindungsgemäß Tabelle 5: Festigkeiten an Langkernen Heißfestigkeit, heißbeschichtet [N/cm2] Kaltfestigkeit, heißbeschichtet [N/cm2] Heißfestigkeit, kaltbeschichtet [N/cm2] Kaltfestigkeit, kaltbeschichtet |N/cm2] 1 250 280 250 280 Vergleich, nicht erfindungsgemäß 2 220 240 270 270 Erfindungsgemäß 3 200 250 260 250 Erfindungsgemäß 4 - (zerbrochen) - (zerbrochen) - (zerbrochen) - (zerbrochen) Nicht erfindungsgemäß The flexural strengths of the coated test bars were measured according to the following scheme

• 10 seconds after removal from the oven (hot-strength, hot-coated)
• Coated 30 minutes after removal (cold strength, hot-coated, directly after removal of the furnace)
• 10 seconds after removal from the drying cabinet (hot strength, cold-coated, room temperature 20 ° C)
• Coated 30 minutes after removal (cold strength, cold-coated)

Table 3: Composition of the molding material mixtures Quartz sand H32 Alkali water glass Amorphous silica coating 1 100 GT 2.0 0.5 - Comparison, not according to the invention 2 100 GT 2.0 0.5 Simple 1 inventively 3 100 GT 2.0 0.5 Simple 2 inventively 4 100 GT 2.0 0.5 Simple 3 Not according to the invention Hot strength, hot-coated [N / cm2] Cold strength, hot-coated [N / cm 2] Hot-strength, cold-coated [N / cm2] Cold strength, cold-coated [N / cm2] 1 400 450 400 450 Comparison, not according to the invention 2 290 390 330 460 According to the invention 3 290 350 300 450 According to the invention 4 220 - (broken) - (broken) 300 Not according to the invention Hot strength, hot-coated [N / cm2] Cold strength, hot-coated [N / cm 2] Hot-strength, cold-coated [N / cm2] Cold strength, cold-coated | N / cm2] 1 250 280 250 280 Comparison, not according to the invention 2 220 240 270 270 According to the invention 3 200 250 260 250 According to the invention 4 - (broken) - (broken) - (broken) - (broken) Not according to the invention

The use of an alcoholic coating is undesirable because of the disadvantage of emissions generation during the casting process. Using standardized water-based coating compositions, the test specimens of water-glass-containing molding material lose much strength (size 4).

Surprisingly, it was found in the search for ways to suppress the reaction between the water from the coating with the binder of the molding material that the addition of certain salts in a certain concentration range to an aqueous sizing composition, the quality of the sized inorganic cores and molds can be sustainably improved, and For example, a storage stability of the cores and forms of several days can be achieved easily. For this purpose, salts of the metals magnesium or manganese can be used. Preferably, the manganese salts are used with a valency of +4. Particularly preferred are magnesium salts having a valency of +2 and the manganese salts having a valency of +2.

Sulfate ion is preferably used as anions, particularly preferably the monovalent chloride ion is used as anions.

The concentration of the salts is in particular between 1% and the respective saturation concentration, preferably between 3% and the respective saturation concentration, particularly preferably between 5% and the respective saturation concentration.

Claims (19)

1. Casting mould for metal processing, obtainable from moulding material mixtures comprising at least one refractory moulding base material and a binder based on water glass which is cured at elevated temperature by means of a condensation reaction, the casting mould being at least partially coated with a sizing composition comprising

   (A) salts of the metals magnesium and/or manganese in a concentration, optionally in combination, of greater than 1 % by weight, based on the sizing composition,

   (B) a carrier fluid comprising or consisting of water, and

   (C) refractory materials.
2. Casting mould according to claim 1, wherein sulfate ions and/or chloride ions are used as the anions of the salts.
3. Casting mould according to claim 1 or 2, characterised in that manganese in the oxidation state +2 or +4 and/or magnesium in the oxidation state +2 is/are used.
4. Casting mould according to one or more of the preceding claims, wherein the concentration of the salts amounts to greater than 3 % by weight and especially to greater than 5 % by weight, based on the sizing agent composition.
5. Casting mould according to one or more of the preceding claims, wherein the salt concentration corresponds, at maximum, to the saturation concentration of the carrier fluid used.
6. Casting mould according to one or more of the claims 1 to 4, wherein the concentration of the salts amounts to less than 10 % by weight, based on the sizing composition.
7. Casting mould according to one or more of the preceding claims, wherein the carrier liquid comprises more than 50% water and in addition, preferably contains alcohols, including polyalcohols and polyether alcohols, and especially can be evaporated completely at up to 160°C and 1013 mbar.
8. Casting mould according to one or more of the preceding claims, wherein the solids content of the sizing composition amounts to 30 to 70 % by weight.
9. Casting mould according to one or more of the preceding claims, wherein the sizing composition comprises 10 to 85 % by weight of refractory materials, based on the solids content of the sizing composition.
10. Casting mould according to one or more of the preceding claims, wherein the refractory materials are quartz, aluminum oxide, zirconium dioxide, aluminum silicates, zirconium sands, zirconium silicates, olivine, talc, mica, coke, feldspar, diatomite, calcined kaolins, kaolinite, metakaolinite, iron oxide, bauxite and/or mixtures thereof.
11. Casting mould according to one or more of the preceding claims, in which the refractory materials have particle sizes of 0.1 to 500 µm, especially 1 to 200 µm, measured by light scattering according to DIN/ISO 13320.
12. Casting mould according to one or more of the preceding claims, wherein the sizing composition comprises 0.1 to 20% by weight, especially 0.5 to 5 % by weight, of at least one binder, based on the solids content of the sizing composition.
13. Casting mould according to one or more of the preceding claims, wherein the sizing composition comprises a lustrous coal forming agent or graphite, especially in the quantity of 0.1 to 10 % by weight, especially 0.5 to 3 % by weight.
14. Use of the sizing composition according to one or more of the preceding claims for at least partially coating moulding material mixtures which are cured with water glass as binder at elevated temperature by means of a condensation reaction, the sizing composition comprising:

    (A) salts of the metals magnesium and/or manganese in a concentration, optionally in combination, of greater than 1 % by weight, based on the sizing composition,

    (B) a carrier fluid comprising or consisting of water, and

    (C) refractory materials.
15. Use according to claim 14, wherein the moulding material mixtures comprise silicon dioxide, aluminium oxide, titanium oxide or zinc oxide and/or mixtures thereof, especially amorphous silicon dioxide.
16. Method for manufacturing a casting mould which has been provided with a size for metal processing comprising
    providing a moulding material mixture comprising at least one refractory moulding base material and a binder based on water glass,
    curing the moulding material mixture at elevated temperature by means of a condensation reaction to obtain a cured casting mould,
    coating the cured mould at least partially with a sizing composition comprising:

    (A) salts of the metals magnesium and/or manganese in a concentration, optionally in combination, of greater than 1 % by weight, based on the sizing composition,

    (B) a carrier fluid comprising or consisting of water, and

    (C) refractory materials.
17. Method according to claim 16, wherein the carrier liquid comprises more than 50% water and in addition, preferably contains alcohols, including polyalcohols and polyether alcohols, and especially can be evaporated completely at up to 160°C and 1013 mbar.
18. Method according to claim 16 or 17, wherein the solids content of the sizing composition amounts to 30 to 70 % by weight.
19. Method according to claim 16, 17 or 18, wherein the moulding material mixture further comprises silicon dioxide, aluminium oxide, titanium oxide or zinc oxide and/or mixtures thereof, especially amorphous silicon dioxide.