EA023525B1 - Coating composition for casting moulds and cores, casting mould for casting metals and method for producing the same - Google Patents

Abstract

The invention relates to a coating composition for casting moulds and cores, comprising at least one metallic additive which contains a metal or a compound of a metal, wherein the metal is selected from one of groups 7 or 9 to 12 of the Periodic Table of the Elements. The invention also relates to a process for producing a casting mould, which comprises a mould coating of the size according to the invention, and to the use of said mould for the casting of metals.

Description

The invention relates to a coating composition, which, in particular, is suitable for large castings, to a method for manufacturing castings and to a coated casting mold.

Most of the products of ferrous metallurgy and the steel industry, as well as metallurgy of non-ferrous metals, as a first stage of molding pass through casting processes. In this case, molten liquid materials - ferrous or non-ferrous metals - are placed in geometrically limited objects that reflect the properties of the manufactured product. For molding castings, molds must first be made, sometimes very complex, into which the melts are poured. The molds are divided into temporary (single) molds, which are destroyed after each casting, and permanent molds, using which a large number of castings can be made.

Single forms consist mainly of mineral refractory granular molding material, which is often mixed with various additives, for example, to obtain high-quality surfaces of castings and which is reinforced with a binder. As refractory granular molding material, washed and sorted quartz sand is most often used. For certain applications, in which special requirements must be fulfilled, chromite, zircon and olivine sand are also used. In addition, molding materials based on chamotte, magnesite, sillimanite or corundum are also used. The binders used to strengthen molding materials may be inorganic or organic in nature. Small one-time molds are made mainly from molding materials, which are reinforced with bentonite as a binder, whereas for larger molds, organic polymers are mainly used as binders. The manufacture of molds is usually carried out in such a way that the molding material is first mixed with a binder, so that the grains of the molding material are coated with a thin film of binder. This moldable mixture is then placed in the appropriate mold and, if necessary, compacted to obtain sufficient mold resistance. The mold is then cured, for example, by heating it or by adding a catalyst that causes a curing reaction. After the mold has reached at least a certain initial strength, it can be removed from the mold and transferred to complete cure, for example, in a furnace, so that it is heated to a certain temperature for a predetermined time.

Permanent forms are used for the manufacture of a large number of castings. Therefore, they must, without being damaged, withstand the casting process and associated loads. As the material for the manufacture of permanent forms, depending on the area of their application, cast iron or unalloyed and alloyed steels, as well as copper, aluminum, graphite, cermets and ceramic materials, are most often used. Permanent casting methods include chill casting, pressing, centrifugal casting and continuous casting.

Molds during the casting process are subject to very high thermal and mechanical stresses. Therefore, defects can occur on the contact surface between the liquid metal and the mold, for example, if the mold breaks or if the liquid metal penetrates the structure of the mold. Therefore, mold surfaces that come into contact with molten metal are usually provided with a protective coating, which is also called molding paint. Such a coating composition consists essentially of an inorganic refractory material and a binder that are dissolved or suspended in a suitable carrier liquid, for example, water or alcohol.

Due to such coatings, the surface of the mold can be modified and adapted to the properties of the metal being processed. So, using the coating composition, you can improve the appearance of the casting, namely, to obtain a smooth surface, since using the coating composition it is possible to even out irregularities due to the granularity of the mold material. In addition, the coating composition may affect the casting metallurgically, for example, additives improving the surface properties of the casting can be selectively transferred from the coating composition to the surface of the casting. In addition, the coating compositions form a coating that chemically isolates the mold from the molten metal during filling. This prevents adhesion between the casting and the mold, so that the casting can be easily removed from the mold. In addition, the coating composition should provide thermal separation of the mold and casting. This is of particular importance in the case of permanent forms. If this function is not fulfilled, then, for example, a metal mold during subsequent casting processes experiences such high thermal loads that it prematurely breaks. Therefore, the coating composition can also be used to purposefully control the heat transfer between the liquid metal and the mold, for example, in order to contribute to the formation of a certain metal structure due to the cooling rate.

Commonly used coating compositions contain, as base materials, for example, clay, quartz, kieselguhr, cristobalite, tridymite, aluminum silicate, zirconium silicate, mica, chamotte, coke or graphite. These basic materials cover the surface of the mold and clog the pores, preventing the penetration of liquid metals into the mold. Owing to their good insulating properties, coating compositions are often used that contain silica or kieselguhr as main materials, since such coating compositions can be prepared at low cost and can be used in large quantities.

Attempts have already been made using the coating composition to purposefully introduce alloying components into the surface of the casting, for example, to increase the surface hardness. So, K. NsrGnPy and 8. P | pcx1. Tssytksys ΖαΙδΟιπΠ Gig 4a§ S1s55sgs1 \ us5sp. 19, 1973, 365-400, and K. NsgGshGy, 8. R1pksg1. K. Yo ^ ak, Ocr £ 1 acsi1ddypdsp νοη 81ai1di55 w 4sg Oyuzkogt, Rgrzsgdsg Roshchsiipdkspsyk V. 184, 1975, 203-215, describe pastes containing large amounts of transition metals such as chromium, nickel or manganese, for example ferromanganese. The content of these metals or alloys in the paste significantly exceeds 50 wt.%. In addition, the paste also contains a binder, usually water glass. These pastes are applied to those surfaces of the mold that come into contact with liquid metal material during casting, usually with steel. During casting, the metals contained in the paste melt due to the heat of the liquid metal material and locally form an alloy with it on the surface of the casting, which then solidifies in the form of an outer shell. Depending on the mode in which the method is carried out, external shells with a thickness of up to 10 mm can be formed. These outer shells can then exhibit very high hardness. In order to make a mold, for example for a mechanical shovel, when using this method, it is no longer necessary to produce the entire cast from the corresponding alloy. On the contrary, it is enough with the help of the alloy components contained in the paste purposefully during the casting process to produce from the alloy, which provides a particularly high surface hardness, only those parts of the casting that experience a particularly high load, for example, the teeth of a mechanical shovel. However, in this method, a different shrinkage coefficient of various materials is problematic. Because of this, the cured surface layer does not everywhere have the same thickness, or surface irregularities such as cracks, peeling or pits are observed.

When casting from cast iron and steel, defects sometimes form on the surface of the casting, such as a pitted, rough or mineralized surface, peeling, sinks, holes or pores, or white or black deposits are formed. The causes of these defects are still not well understood. They try to fight them, for this, for example, they change the casting parameters, modify the binder system in the mold or add various additives to the coating composition. However, the result of these measures is usually unsatisfactory. Although the defect initially disappears, after a while it reappears, and the point in time when it appears, the intensity and volume of the defect cannot be predicted.

If the above-described defects have arisen, a laborious additional surface treatment of the casting is necessary to ensure the desired surface properties. This requires additional work operations, and therefore productivity is reduced and costs are increased. If defects occur on the surface of the casting that are difficult to access or not accessible at all, this can also lead to rejection of the casting.

Therefore, the present invention was based on the task of proposing measures by which in the process of casting metals, it is possible to achieve such an improvement in the quality of the surface of the casting so that the amount of surface treatment of the casting after casting can be reduced.

This problem is solved due to the coating composition with the characteristics of paragraph 1 of the claims. Preferred embodiments of the coating composition according to the present invention are the subject of the dependent claims.

It has been unexpectedly found that by adding a certain metal-containing additive to the coating composition, it is possible to stably improve the surface quality of the casting and, for example, significantly or completely suppress the formation of irregularities on the surface of the casting. In this case, there was no transition of significant amounts of metal-containing additives or its components into the casting. Therefore, there are no difficulties associated with various coefficients of expansion or shrinkage of the casting and its outer shell.

The metal-containing additive contained in the coating composition according to the present invention contains at least one metal or one metal compound, which metal is selected from one of groups 7 or 9 to 12 of the Periodic Table of the Elements.

The numbering of the groups is based on the applicable regulations of the International Union of Pure and Applied Chemistry (SRAS). According to the old requirements of the SRAS, group 7 corresponds to the group νΐΙΑ. Groups 9 and 10 correspond to the elements Co, Ky, 1d, as well as Νί, P4 and P1 of the old USHA group, and groups 11 and 12 correspond to the groups ΙΒ and ΙΙΒ of the old classification.

The metal-containing additive may contain the metal itself, that is, a metal with a zero oxidation state, and the metal can be used both in pure form or in the form of an alloy with other metals. The metal-containing additive may also be in the form of an oxidized metal, that is, in the form of an oxide or salt, for example carbonate, nitrate or chloride, with the oxide being preferred.

It is preferable to use the metal in reduced form, that is, with an oxidation state of zero.

- 2 023525

A metal-containing additive may contain several of the above metals or compounds of these metals. However, it is preferable that the metal-containing additive contains only one metal in reduced or oxidized form.

Preferably, the metal-containing additive uses metals or their compounds selected from groups 7, 10 or 11 of the Periodic system of elements, with manganese, nickel and copper being particularly preferred.

The metal-containing additive may consist solely of the above metals or their compounds. However, it is also possible that in addition to these metals or their compounds, other metals or their compounds are present in the metal-containing additive.

According to a preferred embodiment of the present invention, the metal or metal compound is contained in the metal-containing additive in an amount of at least 10 wt.%, Preferably at least 20 wt.%, Preferably in an amount of at least 30 wt.%, Particularly preferably in an amount of at least at least 40 wt.%, even more preferably in an amount of at least 50 wt.% in terms of metal and by weight of the metal-containing additive.

According to one of the embodiments of the present invention, the metal-containing additive contains only at least one of the above metals, in particular manganese, nickel or copper. However, according to another embodiment of the present invention, it is sufficient if the metal or its compound is contained in the metal-containing additive in an amount of less than 90 wt.%, According to the following embodiment of the present invention in an amount of less than 80 wt.%, According to another embodiment of the present invention in an amount less than 70 wt.%.

The coating composition may contain, in addition to the metal-containing additive, other components common to molding inks. In order to achieve a lasting effect on the surface of the casting, according to a preferred embodiment of the present invention, it is provided that the metal-containing additive is contained in the coating composition in an amount of at least 10%, preferably at least 15%, particularly preferably at least 20% of the solids content in covering composition.

As already explained, the coating composition should preferably not provide alloying of the surface layer of the casting, but the surface or outer shell should have essentially the same composition as those sections of the casting that are located at a distance from the surface of the casting, i.e. in the volume of the casting.

Therefore, it is preferably contemplated that the content of the metal-containing additive in the coating composition is less than 50 wt.%, Preferably less than 40 wt.%, Particularly preferably less than 35 wt.% Of the solids content in the coating composition.

As already explained above, the metal-containing additive may contain only at least one of the aforementioned metals, preferably at least one of the manganese, nickel and copper metals. However, according to one embodiment of the present invention, it is also possible that at least one metal is contained in the metal-containing additive in the form of an alloy. According to one embodiment of the present invention, the metal is contained in a metal-containing additive in the form of an alloy with iron. The proportion of iron in the metal-containing additive in terms of elemental iron is preferably selected in the range from 20 to 80 wt.%, More preferably in the range from 30 to 70 wt.%.

In addition to metal and iron, the alloy may also contain other components.

According to a further embodiment of the present invention, the metal-containing additive as a constituent contains aluminum, wherein the aluminum content of the metal-containing additive in terms of elemental aluminum is preferably less than 10 wt.%, More preferably less than 8 wt.%. According to one of the embodiments of the present invention, the metal-containing additive contains aluminum in an amount exceeding 2 wt.%. According to a further embodiment of the coating composition according to the present invention, the metal-containing additive comprises an aluminum fraction in the range of from 2 to 8 wt.%, Preferably from 3 to 6 wt.%, Particularly preferably from 3 to 5 wt.%.

According to one embodiment of the present invention, the metal-containing additive can be used in the form of an alloy with silicon. Moreover, the silicon content in such an alloy with silicon is preferably in the range from 20 to 80 wt.%, Particularly preferably from 50 to 70 wt.%.

The metal-containing additive may also contain other components, in particular metals, moreover, their content is preferably less than 2 wt.%, More preferably less than 1 wt.%.

These other components are preferably selected from the group consisting of cerium, magnesium, chromium, molybdenum.

The content of these alloying components preferably lies in the range from 0.01 to 2 wt.%, More preferably from 0.1 to 1 wt.% By weight of the metal-containing additive. As another dopant, the metal-containing additive may contain calcium. Calcium content at

- 3 023525 this preferably lies in the range from 0.2 to 2 wt.%, Particularly preferably in the range from 0.5 to 1.5 wt.%.

The particle size of the metal-containing additive should preferably not be too small, in particular if the metals, preferably manganese, nickel and copper, are contained in the metal-containing additive in elemental form, since there is a danger that the metal-containing additive will react with other components of the coating composition and, for example, will be oxidized. On the other hand, the particle size should preferably not be too large, since otherwise the metal-containing additive may, for example, settle in the coating composition, and due to this, the metal-containing additive will be unevenly applied on the surface of the mold.

The metal-containing additive preferably has an average particle size (E ₅₀ ) of less than 0.5 mm, preferably less than 0.4 mm, particularly preferably less than 0.3 mm. The average particle size (Ό ₅₀ ) can be determined, for example, by sieve analysis or laser granulometry. The metal-containing additive contained in the coating composition according to the present invention typically has a relatively high density and therefore rapidly settles in the coating composition. However, this subsidence can be slowed down by adding a thickener. By reducing the particle size, it is also possible to further slow down the settling of the seed material, so that the seed material remains homogeneously distributed in the coating composition. Another advantage is that if a spray device is used to apply the coating composition, when using a fine-grained metal-containing additive, the nozzle of the spray device is less clogged. It is particularly preferred if the seed material has an average particle size of less than 0.3 mm. However, with a decrease in particle size, the specific surface area of the metal-containing additive increases, and hence the ability to react with the liquid contained in the coating composition, for example with water. During the reaction of the metal-containing additive, for example, with water, gas formation is observed, which leads to the appearance of foam. In this case, the coating composition is difficult to pump or spray. Therefore, preferably, the average particle size should be greater than 50 microns, particularly preferably greater than 80 microns. It is particularly preferable to use a metal-containing additive with a grain size in the range of 20 to 1000 microns, more preferably in the range of 80 to 300 microns.

The coating composition according to the present invention is preferably prepared in the form of a paste or suspension. In this embodiment of the present invention, the coating composition comprises a carrier fluid. This carrier fluid should be selected so that it can completely evaporate under the conditions common in metal bottling. Therefore, the carrier fluid should preferably have a boiling point at normal pressure below 130 ° C, more preferably below 110 ° C.

The carrier fluid may be wholly or partially composed of water. In particular, if the metal-containing additive contains elemental metals or an alloy of elemental metals, then oxidation of the metal-containing additive is sometimes observed. Therefore, according to a preferred embodiment of the present invention, the coating composition comprises a solvent, which at least partially consists of an organic solvent.

The oxidation of the metal-containing additive can be suppressed due to the high content of an organic solvent, for example alcohol, in the carrier fluid. A second advantage is that after application, such a coating composition is very easy to dry by burning off an organic solvent.

If an organic solvent is contained in the coating composition, its content in the carrier fluid is preferably greater than 20 wt.%, More preferably greater than 30 wt.%, Particularly preferably greater than 40 wt.%.

The carrier fluid may consist entirely of an organic solvent. However, according to one embodiment of the present invention, the content of the organic solvent in the carrier fluid is chosen lower. According to one embodiment of the present invention, the content of the organic solvent in the carrier liquid is less than 90 wt.%, According to the following embodiment, less than 80 wt.% And according to another embodiment less than 70 wt.%.

Suitable solvents are, for example, aliphatic, cycloaliphatic or aromatic hydrocarbons, which preferably contain from 5 to 15 carbon atoms, esters of aliphatic carboxylic acids, the carboxylic acids preferably containing from 2 to 20 carbon atoms, and the alcohol components of the esters preferably containing from 1 up to 4 carbon atoms. Other preferred organic solvents are, for example, ketones, preferably containing from 4 to 20 carbon atoms. Also, ethers can be used as solvents, in which case polyglycols can also be used.

According to one preferred embodiment of the present invention, the solvent at least partially or completely consists of an alcohol, which preferably contains from 1 to 10 25525 carbon atoms. Examples of such alcohols are ethanol, n-propanol, isopropanol and butanol.

If alcohol is used as a solvent component of the carrier fluid, its content is preferably more than 50 wt.%, More preferably more than 60 wt.% Of the weight of the carrier fluid.

Along with the components already indicated, the coating composition according to the present invention may contain other components that are common to molding paints.

Thus, a coating composition according to the present invention in one of the preferred embodiments of the present invention contains at least one powdery refractory material. This refractory material serves to plug the pores in the mold to prevent liquid metal from entering. As the refractory material, standard refractory materials used in casting metals can be used. Examples of suitable refractory materials are quartz, alumina, zirconia, aluminum silicate, for example pyrolyllite, kyanite, andalusite or chamotte, zircon sand, zirconium silicate, olivine, talc, mica, graphite, coke, feldspar, diatomite, kaolin, calcined kaolin , kaolinite, metakaolinite, iron oxide, bauxite.

The refractory material is in powder form. In this case, the particle size is chosen so that a stable structure appears in the coating and that the coating composition can be distributed without problems along the mold wall, preferably using a spray device. A suitable particle size of the refractory material is in the range of 0.1 to 500 microns, particularly preferably in the range of 1 to 200 microns. Suitable materials for use as refractory materials are those which have a melting point at least 200 ° C higher than the temperature of the liquid metal and do not react with the metal.

The content of the refractory material is preferably greater than 10 wt.%, More preferably greater than 20 wt.%, Particularly preferably greater than 30 wt.% Of the solids content of the coating composition. According to one embodiment of the present invention, the content of the refractory material is less than 80 wt.%, According to the following embodiment, less than 70 wt.% And according to another embodiment less than 60 wt.%.

The coating composition according to the present invention may also contain at least one thickener. The thickener provides an increase in the viscosity of the coating composition, so that the solid components of the coating composition do not settle in suspension or settle to a small extent. To increase the viscosity, both organic and inorganic materials or mixtures of these materials can be used. Suitable inorganic thickeners are, for example, highly swellable clays.

In order to avoid settling of the solid components of the coating composition and at the same time to ensure that it can be applied uniformly to the mold, the viscosity of the coating composition is preferably selected in the range from 1000 to 3000 mPa-s, particularly preferably from 1200 to 2000 mPa-s.

In this case, the metal-containing additive can be distributed almost evenly in the coating composition and therefore can be uniformly applied to the mold wall. Due to this, it is possible to very precisely control the amount of metal-containing additives applied to the surface of the mold.

Both bilayer silicates and trilayer silicates, for example attapulgite, serpentines, kaolins, smectites, for example saponite, montmorillonite, beidellite and nontronite, vermiculite, illite, hectorite and mica can be used as a highly swelling layered silicate. Hectorite also gives the coating composition thixotropic properties, thereby facilitating the formation of a protective coating on the mold, since the coating composition does not spread after application. Since the layered silicates in the intermediate layers contain water that does not evaporate after applying the coating composition to a hot mold having a temperature in the range of about 250 to 350 ° C., it is preferable to select as little clay as possible.

The amount of highly swellable layered silicate is preferably selected in the range from 0.01 to 5.0 wt.%, Particularly preferably in the range from 0.1 to 1.0 wt.% Of the solids content in the coating composition.

It is preferable to use organic thickeners as thickeners, since they dry out after applying a protective coating and almost do not give water when in contact with liquid metal. As an organic thickener, for example, swellable polymers such as carboxymethyl, methyl, ethyl, hydroxyethyl and hydroxypropyl cellulose, plant mucus, polyvinyl alcohols, polyvinyl pyrrolidone, pectin, gelatins, agar-agar, polypeptides and alginates can be used.

According to a preferred embodiment of the present invention, the coating composition according to the present invention contains at least one binder as an additional component. A binder provides better fixation of the coating composition or

- 5,023,525 made from the composition of the protective coating on the wall of the mold. In addition, due to the binder, the mechanical stability of the protective coating is increased, so that less erosion is observed under mechanical stress or when exposed to liquid metal. Preferably, the binder cures irreversibly to provide an abrasion resistant coating. Particularly preferred are binders that do not re-soften under the influence of moisture contained in the air. As a binder, any binders that are used in molding inks can be used. In this case, both inorganic and organic binders can be used. As a binder, for example, clays, in particular bentonite, can be used.

Curable binders are preferably used. For example, in the case of acrylate systems, curing can be achieved by radical formers that decompose upon exposure to high-energy radiation, such as ultraviolet radiation, to form free radicals.

Other examples of binders are starch, dextrin, peptides, polyvinyl alcohol, copolymers of polyvinyl acetate, polyacrylic acid, dispersions of polystyrene and / or polyvinyl acetate and polyacrylate. In general, polymers are preferably used that can be used in aqueous, alcoholic or hydroalcoholic systems and which, after curing, do not soften repeatedly under the influence of moisture contained in the air.

According to a preferred embodiment of the present invention, an alkyd resin is used as a binder, preferably a resin which is soluble in both water and lower alcohols, which preferably contain from 2 to 4 carbon atoms, such as ethanol, n-propanol and isopropanol.

According to a further embodiment of the present invention, the coating composition of the present invention contains kieselzol as a binder. Kieselgol is preferably obtained by neutralizing liquid glass. The obtained amorphous silicic acid preferably has a specific surface area in the range from 10 to 1000 m ² / g, particularly preferably in the range from 30 to 300 m ² / g.

The binder content is preferably selected in the range from 0.1 to 20 wt.%, Particularly preferably in the range from 0.5 to 5 wt.% Of the solids content in the coating composition.

According to a further preferred embodiment of the present invention, the coating composition comprises an amount of graphite. Graphite promotes the formation of lamellar carbon at the interface between the casting and the mold. The graphite content is preferably selected in the range from 1 to 30 wt.%, Particularly preferably in the range from 5 to 15 wt.% By weight of the coating composition.

The coating composition according to the present invention may optionally contain other components common to molding inks, for example wetting agents, anti-foaming agents, pigments, dyes or biocides. The content of these components in the ready-to-use coating composition is preferably less than 1 wt.%.

As wetting agents, for example, anionic and nonionic surfactants of medium or high polarity, which have an H8B value of at least 7, can be used. Disodium dioctyl sulfosuccinate is an example of this type of wetting agent. The wetting agent is preferably used in an amount of from 0.01 to 1 wt.%, Preferably from 0.05 to 0.3 wt.%, By weight of the ready-to-use coating composition.

Defoamers, or anti-foaming agents, can be used to prevent the formation of foam when preparing the coating composition or when applying it. The formation of foam during application of the coating composition can lead to uneven coating thickness and the formation of holes in the coating. As antifoaming agents, for example, silicone or mineral oil can be used. Preferably, the antifoam is used in an amount of from 0.01 to 1% by weight, more preferably from 0.05 to 0.3% by weight of the ready-to-use coating composition.

In the coating composition according to the present invention, conventionally used pigments and dyes can be used if necessary. They are added in order to provide contrast, for example, between different layers or to enhance the effect of separating the coating composition from the casting. Examples of pigments are red and yellow iron oxides and graphite. Examples of dyes are commercially available dyes, such as dyes of the Lsopu1® series manufactured by BA8P AC, Ludwigshafen, Germany. Dyes and pigments are preferably used in an amount of from 0.01 to 10 wt.%, More preferably from 0.1 to 5 wt.% Of the solids content in the coating composition.

According to a further embodiment of the present invention, the coating composition comprises a biocide in order to prevent damage to the coating by bacteria and to avoid negative effects on the rheology and adhesive strength of the binder. The use of a biocide is particularly preferred if the carrier fluid contained in the coating composition essentially consists of water, i.e. the coating composition according to the present invention is prepared in the form of the so-called

- 6,023,525 aqueous composition. Examples of suitable biocides are formaldehyde, 2-methyl-4-isothiazolin-3-one (ΜΙΤ), 5-chloro-2-methyl-4-isothiazolin-3-one (C1T) and 1,2-benzisothiazolin-3-one ( ΒΙΤ). Preferably, ΜΙΤ, ΒΙΤ or a mixture thereof is used. Biocides are typically used in an amount of from 10 to 1000 parts per million (ppm), preferably from 50 to 500 parts per million by weight of a ready-to-use coating composition.

The solids content of the ready-to-use coating composition is preferably selected in the range from 10 to 60 wt.%, More preferably from 20 to 50 wt.%.

The coating composition according to the present invention can be prepared by conventional methods. For example, it is possible to prepare a coating composition according to the present invention so that first pour water and mix clay acting as a thickener with it using a high shear mixer. Then refractory components, pigments and dyes are mixed into the mixture. In conclusion, a wetting agent, antifoam, biocides and a binder are mixed in.

A coating composition according to the present invention can be prepared and marketed as a ready-to-use composition with a specific composition. In addition, the coating composition according to the present invention can be prepared and marketed in concentrated form. In this case, to obtain a ready-to-use coating composition, a certain amount of carrier fluid is added, which is necessary to obtain the desired viscosity and density of the coating composition. In addition, the coating composition according to the present invention can be prepared and marketed in the form of a kit in which, for example, solid components and solvents are contained in separate containers. The solid components may be in a separate container in the form of a powdered mixture of solids. Liquid components used if necessary, such as a binder, wetting agent, wetting / anti-foaming agent, pigments, dyes and biocides, may be in this kit in a separate container. Solvents can be added to the components used, that is, they can be in a common container with them, or they can be in a separate container separately from other possible components. To prepare a ready-to-use coating composition, the required amounts of solid components, other possible components and solvents are mixed. The solids content of the coating composition according to the present invention in the ready-to-use state is preferably from 20 to 80% by weight, more preferably from 30 to 70% by weight of the ready-to-use coating composition. It is also possible to prepare a coating composition according to the present invention, in which the solvent component initially consists solely of water. By adding, for example, a volatile alcohol or a mixture of alcohols, preferably ethanol, propanol, isopropanol and mixtures thereof, preferably in amounts of from 40 to 200% by weight of the weight of the aqueous composition, a ready-to-use alcohol coating composition can be obtained from this aqueous composition. The solids content of such an alcohol coating composition is preferably from 20 to 60 wt.%, More preferably from 30 to 40 wt.%.

Depending on the desired application of the coating composition, for example in the form of a base coating or surface coating, and the desired thickness of the coating obtained from the coating composition, other characteristic parameters of the coating composition can be adjusted. Thus, the coating compositions according to the present invention, used for coating molds and cores in the foundry industry, in a preferred embodiment of the present invention have a viscosity in the range from 11 to 25 s, more preferably from 12 to 15 s (viscosity is determined according to ΌΙΝ 53211 ; funnel hole diameter 4 mm, Ford funnel). Preferred densities of the ready-to-use coating composition range from 0 to 120 ° Bome, significantly more preferably from 30 to 50 ° Bome (density determined by hydrostatic weighing according to Bome; ΌΙΝ 12791).

Coating compositions according to the present invention are suitable for coating molds. Used in this context, the expression casting mold covers all types of objects necessary for the manufacture of castings, for example casting cores, half-molds and chill molds. The use of a coating composition according to the present invention also includes partial coating of the molds.

Therefore, another object of the present invention is a method for manufacturing a mold in which at least one cavity provided in the mold is coated with a coating composition according to the present invention.

The method includes operations in which a molding material composition is prepared which comprises at least one refractory molding material and a binder;

from the composition of the molding material, a basic mold is formed which has a cavity;

the coating composition described above is applied at least on the surface of the cavity of the base mold.

- 7 023525

Initially, in a known manner, a base mold is made from a molding material composition. To obtain a composition of the molding material, the refractory molding material is mixed with a binder, after which it is formed into a base mold or part of a base mold. The base mold in its form essentially corresponds to the mold or part of the mold. However, it does not yet have a coating consisting of a coating composition.

As a refractory molding material, in principle, all refractory materials that are usually used for the manufacture of molded products for the foundry industry can be used. Examples of suitable refractory molding materials are silica sand, zircon sand, olivine sand, aluminosilicate sand and chrome sand, or mixtures thereof. Quartz sand is preferably used. The refractory molding material must have a particle size sufficient for the molded product made from the molding material composition to have a sufficiently high porosity so that volatile compounds can be released during the casting process. Preferably, at least 70 wt.%, More preferably at least 80 wt.% Of the refractory molding material has a particle size of <290 μm. The average particle size of the refractory molding material should preferably lie in the range from 100 to 350 microns. Particle size can be determined, for example, by sieve analysis. The refractory molding material must be loose in shape so that a binder or liquid catalyst can easily be applied to the grains of the refractory molding material, for example in a mixer.

According to one embodiment of the present invention, regenerated spent molding sands may be used as the refractory molding material. Large aggregates are removed from the used foundry sand and, if necessary, the used sand is separated into separate grains. After mechanical or heat treatment, dust is removed from the used foundry sands, after which they can be reused. Prior to reuse, the acid balance in the regenerated spent foundry sand is preferably checked. In particular, during thermal regeneration, by-products contained in sand, such as carbonates, can be converted to the corresponding oxides, which then give an alkaline reaction. If binders are used that cure during acid catalysis, then acids added as a catalyst can be neutralized by the alkaline components of the regenerated spent foundry sand. In the same way, for example, during mechanical regeneration of used sand, acids may remain in the used sand, which must be taken into account when preparing the binder, since otherwise, for example, the processing time of the molding material composition may be reduced.

Refractory molding material must be dry. Preferably, the refractory molding material contains less than 1 wt.% Water. In order to avoid premature curing of the binder under the influence of heat, the refractory molding material should not be too warm. Preferably, the refractory molding material should have a temperature in the range of 20 to 35 ° C. If necessary, the refractory molding material may be cooled or heated.

As a binder, in principle, all binders that are commonly used for the manufacture of foundry molds for metal casting can be used. Both inorganic and organic binders can be used. As an inorganic binder, for example, liquid glass can be used, which can be thermally cured or by passing carbon dioxide. Examples of organic binders are уретο-Vake and Co1bVake polyurethane binders (cold curing binders), binders based on furan or phenolic resins or epoxy acrylate binders.

Polyurethane-based binders usually consist of two components, the first component containing a phenolic resin and the second component a polyisocyanate. Both of these components are mixed with the refractory molding material and the molding composition by packing, injection, injection, or otherwise placed in the mold, compacted and then cured. Depending on the method by which the catalyst is added to the molding sand composition, the polyurethane Νο-Wake method and the polyurethane CoM-Voh method are distinguished.

In the Νο-Wake method, a liquid catalyst, typically a liquid tertiary amine, is added to the molding material composition before it is placed in the mold and cured. To prepare the composition of the molding material, a phenolic resin, a polyisocyanate, and a curing catalyst are mixed with a refractory molding material. In this case, it is possible, for example, to first envelop the particles of the refractory molding material with one component of the binder, and then add another component. The curing catalyst is then added to one of the components. The finished composition of the molding material must have a sufficiently long processing time so that the composition of the molding material can undergo plastic deformation for a sufficiently long time and it is possible to make a molded product from it. Therefore, polymerization, respectively, should take place slowly enough so that the composition of the molding material does not already cure in the storage bins or in the supply pipelines. On the other hand, curing should not occur too slowly in order to ensure a sufficiently high throughput in the manufacture of molds. Processing time can be influenced, for example, by the addition of inhibitors that slow down the curing of the sand composition. A suitable inhibitor is, for example, phosphoroxychloride.

In the case of the Co1b-Bocch method, the composition of the molding material is first placed in the mold without a catalyst. A gaseous tertiary amine is then passed through the molding material composition, which, if necessary, can be mixed with an inert carrier gas. Upon contact with the gaseous catalyst, the binder sets very quickly, so that high productivity can be achieved in the manufacture of molds.

Polyurethane-based binder systems comprise a polyol component and a polyisocyanate component, wherein known components can be used.

The polyisocyanate component of the binder system may contain an aliphatic, cycloaliphatic or aromatic isocyanate. The polyisocyanate preferably contains at least 2 isocyanate groups, preferably from 2 to 5 isocyanate groups in one molecule. Mixtures of isocyanates may also be used, depending on the desired properties. The isocyanates used may consist of mixtures of monomers, oligomers and polymers and therefore will hereinafter be referred to as polyisocyanates.

As a polyisocyanate component, in principle, any polyisocyanate that is commonly used in polyurethane-based binders for the production of molding compositions for the foundry industry can be used. Suitable isocyanates are aliphatic polyisocyanates, for example hexamethylenediisocyanate, alicyclic polyisocyanates, for example 4,4'-dicyclohexylmethanediisocyanate, and their dimethyl derivatives. Examples of suitable aromatic polyisocyanates are toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, 1,5-naphthalene diisocyanate, xylylene diisocyanate and its methyl derivatives, diphenylmethane-4,4'-diisocyanate and polymethylene polyphenyl polyisocyanate.

Although essentially all common polyisocyanates react with a phenolic resin to form a network polymer structure, it is preferable to use aromatic polyisocyanates, particularly preferably polymethylene polyphenyl polyisocyanate, for example, commercially available mixtures of diphenylmethane-4,4'-diisocyanate, its isomers and higher homologs.

Polyisocyanates can be used both as a substance and as a solution in an inert or chemically active solvent. A chemically active solvent is understood to mean a solvent which has a reactive group, so that when the binder is cured, it is integrated into the structure of the binder. It is preferable to use the polyisocyanates in dilute form so that due to the reduced viscosity it is possible to better coat the particles of the refractory molding material with a thin film of a binder.

Polyisocyanates or their solutions in organic solvents are used in concentrations sufficient to allow the curing of the polyol as one component, usually in the range from 10 to 500 wt.% By weight of the polyol as one component. Preferably, 20 to 300% by weight of the polyol as one component is used. Liquid polyisocyanates can be used in undiluted form, while solid or viscous polyisocyanates are dissolved in organic solvents. Solvents may constitute up to 80 wt.%, Preferably up to 60 wt.%, Particularly preferably up to 40 wt.% Of the isocyanate component.

Preferably, the polyisocyanate is used in such an amount that the number of isocyanate groups is from 80 to 120% of the number of free hydroxyl groups of the polyol component.

As a polyol as one component, in principle all polyols used in binders based on polyurethanes can be used. The polyol component contains at least 2 hydroxyl groups which can react with the isocyanate groups of the polyisocyanate component so that crosslinking of the binder during curing can be ensured and thereby the strength of the cured molded article is greater.

Phenolic resins are preferably used as polyols, which are obtained by condensation of phenols with aldehydes, preferably formaldehyde, in the liquid phase at temperatures up to about 180 ° C in the presence of catalytic amounts of metal. Methods for producing such phenolic resins are known to those skilled in the art.

The polyol component is preferably used in liquid form or in the form of a solution in organic solvents to ensure uniform distribution of the binder over the refractory molding material. The polyol component is preferably used in anhydrous form, since the reaction of the isocyanate component with water is an undesirable side reaction. Non-aqueous or anhydrous in the context of the present invention means the water content in the polyol as one component, which is preferably less than 5 wt.%, More preferably less than 2 wt.%.

Phenolic resin is understood to mean the reaction product of phenol, phenol derivatives, bisphenols, and higher condensation products of phenol with an aldehyde. The composition of the phenolic resin is specific.

- 9 023525 selected starting materials, the ratio of starting materials and the reaction conditions. For example, the type of catalyst, the reaction time and temperature, as well as the presence of solvents and other substances play an important role.

Phenolic resin is usually a mixture of various compounds and may contain in various ratios addition products, condensation products and unreformed starting compounds, such as phenols, bisphenol and / or aldehyde.

Addition products are understood to mean reaction products in which the organic component replaces at least one hydrogen atom on a previously unsubstituted phenol or condensation product. By a condensation product is meant reaction products with two or more phenolic rings.

As a result of the condensation reactions of phenols with aldehydes, phenolic resins are formed, which, depending on the quantitative ratios of the educts, the reaction conditions, and the catalysts used, can be divided into two classes of products — novolaks and resols.

Novolacs are soluble, fusible, non-self-curing and storage-stable oligomers with a molar mass in the range of about 500 to 5,000 g / mol. They are formed during the condensation of aldehydes and phenols in a molar ratio of 1:> 1 in the presence of acid catalysts. Novolacs are phenolic resins that do not contain methylol groups in which the phenyl nuclei are joined by methylene bridges. They can be cured after the addition of hardeners, for example, formaldehyde donors, preferably hexamethylenetetramine, at elevated temperatures due to the formation of a network structure.

Resoles are mixtures of hydroxymethylphenols, which are connected by methylene and methylene ether bridges, and which can be obtained as a result of the reaction between aldehydes and phenols in a molar ratio of 1: <1, if necessary, in the presence of a catalyst, for example, a basic catalyst. They have a molar mass of Μ _ν <10000 g / mol.

Particularly suitable for use as polyol as one component, phenolic resins are known as o-o'-novolacs, or novolacs with a high content of ortho bonds, or benzyl ester resins. They can be obtained by condensation of phenols with aldehydes in a slightly acidic environment using suitable catalysts.

Catalysts suitable for the preparation of benzyl ester resins are salts containing divalent metal ions, for example Μη, Ζη, Cb, MD, Co, Νί, Pe, Pb, Ca and Ba. Zinc acetate is preferred. The amount used is not critical. Typical amounts of metal catalyst are from 0.02 to 0.3 wt.%, Preferably from 0.02 to 0.15 wt.% Of the total weight of phenol and aldehyde.

All conventionally used phenols are suitable for the production of phenolic resins. Along with unsubstituted phenols, substituted phenols or mixtures thereof can be used. In order for polymerization to be possible, the phenolic compounds must not be substituted either in both ortho positions or in the same ortho and para position. The remaining carbon atoms in the ring may be substituted. The choice of substituents is not particularly limited if the substituent does not adversely affect the polymerization of phenol or aldehyde. Examples of substituted phenols are alkyl substituted phenols, alkoxy substituted phenols and aryloxy substituted phenols.

Substituents, which should be mentioned in the first place, contain, for example, from 1 to 26, preferably from 1 to 15 carbon atoms. Examples of suitable phenols are o-cresol, m-cresol, pcresol, 3,5-xylene, 3,4-xylene, 3,4,5-trimethylphenol, 3-ethylphenol, 3,5-diethylphenol, p-butylphenol, 3, 5dibutylphenol, p-amylphenol, cyclohexylphenol, p-octylphenol, p-nonylphenol, 3,5-dicyclohexylphenol, p-crotylphenol, p-phenylphenol, 3,5-dimethoxyphenol and p-phenoxyphenol.

Phenol itself is particularly preferred. More highly condensed phenols such as bisphenol A are also suitable. In addition, polybasic phenols which contain more than one phenolic hydroxyl group are also suitable. Preferred polybasic phenols contain from 2 to 4 phenolic hydroxyl groups. Specific examples of suitable polybasic phenols are pyrocatechol, resorcinol, hydroquinone, pyrogallol, fluoroglycine, 2,5-dimethylresorcinol, 4,5dimethylresorcinol, 5-methylresorcinol and 5-ethylresorcinol.

Mixtures of various monobasic and polybasic and / or substituted and / or condensed phenolic components can also be used to produce the polyol as one component.

In one embodiment of the present invention, phenols of the general formula I are used to prepare the phenolic resin component

Formula I

- 10 023525 where A, B and C are independently selected from a hydrogen atom, a branched or unbranched alkyl radical, which may contain, for example, from 1 to 26, preferably from 1 to 15 carbon atoms, a branched or unbranched alkoxy radical, which may contain, for example, from 1 to 26, preferably from 1 to 15, carbon atoms, a branched or unbranched alkenoxyl radical, which may contain, for example, from 1 to 26, preferably from 1 to 15 carbon atoms, an aryl or alkylaryl radical ical, for example bisphenyl.

Suitable aldehydes for preparing the phenolic resin component are aldehydes having the formula

where K is a hydrogen atom or a radical consisting of carbon atoms, which preferably contains from 1 to 8 carbon atoms, particularly preferably from 1 to 3 carbon atoms. Specific examples are formaldehyde, acetaldehyde, propionic aldehyde, furfuryl aldehyde and benzaldehyde. It is particularly preferred to use formaldehyde either in aqueous form, i.e. in the form of paraformaldehyde, or in the form of trioxane.

To obtain phenolic resins, at least an equivalent number of moles of aldehyde, based on the number of moles of the phenolic component, should be used. The molar ratio of aldehyde to phenol is preferably from 1: 1.0 to 2.5: 1, particularly preferably from 1.1: 1 to 2.2: 1, even more preferably from 1.2: 1 to 2.0: 1 .

Obtaining a phenolic resin component is carried out by a method known to a person skilled in the art. In this case, phenol and aldehyde react essentially under anhydrous conditions in the presence of divalent metal ions at temperatures that are preferably below 130 ° C. The resulting water is distilled off. For this, a suitable resolving agent, for example toluene or xylene, can be added to the reaction mixture, or distillation under reduced pressure can be carried out.

To obtain a binder composition for the molding sand, the phenolic component preferably reacts with the aldehyde to form a benzyl ester resin. It is also possible to react with primary or secondary aliphatic alcohol to produce an alkoxy-modified phenolic resin in a one-step or two-step method (EP-B-0177871 and EP 1137500). In a one-step process, phenol, aldehyde and alcohol are reacted in the presence of a suitable catalyst. In a two-step process, an unmodified resin is first obtained, which is then converted into a reaction with alcohol. When using alkoxy-modified phenolic resins, there are basically no restrictions on the molar ratios of the components, however, the alcohol component is preferably used with a molar ratio of alcohol: phenol of less than 0.25 so that less than 25% of hydroxymethyl groups are esterified. Suitable alcohols are primary and secondary aliphatic alcohols with one hydroxyl group and 1-10 carbon atoms. Suitable primary and secondary alcohols are, for example, methanol, ethanol, propanol, n-butanol and n-hexanol. Particularly preferred are methanol and n-butanol.

The phenolic resin is preferably selected so that crosslinking with the polyisocyanate component is possible. Phenolic resins that contain molecules with at least two hydroxyl groups in each molecule are particularly suitable for building a network structure. The phenolic resin component or the isocyanate component of the binder system is preferably used as a solution in an organic solvent or in a combination of organic solvents. Solvents may be necessary in order to maintain a sufficiently low viscosity state of the binder components. This, among other things, is necessary in order to ensure uniform crosslinking of the refractory molding material and preservation of its flowability.

As a solvent for the polyisocyanate or polyol as one component of the polyurethane-based binder system, in principle any solvent conventionally used in such kind of binder systems for the foundry industry can be used. Suitable solvents are, for example, oxygen-rich polar organic solvents. Especially suitable are dicarboxylic acid esters, glycol ether, glycol diester, glycol diester, cyclic ketones, cyclic esters or cyclic carbonates. Preferably, dicarboxylic acid esters, cyclic ketones or cyclic carbonates are used. Esters of dicarboxylic acids having the formula K ^and DUS K ^L COOK ^and where the radicals K ^and independently represent an alkyl group containing from 1 to 12, preferably from 1 to 6 carbon atoms, a and ^b - alkylene group, there is an alkyl group with a double bond containing from 1 to 12, preferably from 1 to 6 carbon atoms. K ^b may also contain one or more double bonds between carbon atoms. Examples are dimethyl esters of carboxylic acids containing from 4 to 10 carbon atoms, which can be purchased, for example, under the name dibasic esters (EVE) from the company ΙηνίδΙα 1p1egia1uia1 8.a.g. 1., Geneva, Switzerland. Glycol ether esters are compounds having the formula K ^with OK + OOSKD where K ^c is an alkyl group containing from 1 to 4 carbon atoms, K. ' ¹ is an ethylene group, a propylene group or oligomeric ethylene oxide or propylene oxide, and K ^e is an alkyl 11 023525 group containing from 1 to 3 carbon atoms. Glycol ether acetates are preferred, for example, butyl glycol acetate. Complex glycol diesters, respectively, have the general formula K ^e COO-K ⁴ OOSK ^e , where K ⁴ and K ^e are the same as defined above, and the radicals K ^e are selected independently of each other. Glycol diacetates, for example propylene glycol diacetate, are preferred. Simple glycol diesters can be characterized by the formula K ^c —O — K ⁴ —O — K ^c , where K ^c and K ⁴ are the same as defined above and the radicals K ^c are independently selected. A suitable glycol diester is, for example, dipropylene glycol dimethyl ether. Also suitable are cyclic ketones, cyclic esters and cyclic carbonates containing from 4 to 5 carbon atoms. A suitable cyclic carbonate is, for example, propylene carbonate. Alkyl and alkylene groups may be branched and unbranched, respectively.

The proportion of solvent in the binder system is preferably not chosen too large, since the solvent evaporates during the manufacture and use of the molded product made from the composition of the molding mixture, which can lead, for example, to the formation of an unpleasant odor or to the formation of smoke during metal filling. Preferably, the proportion of solvent in the binder system is selected so that it is less than 50 wt.%, Particularly preferably less than 40 wt.%, Even more preferably less than 35 wt.%.

In the manufacture of a molded product at first, as already described above, the binder is mixed with a refractory molding material to obtain a molding composition. If the molding is to be manufactured using the Ρυ-Νο-Wake method, then a suitable catalyst can also be added to the molding composition. Preferably, liquid amines are added to the molding composition for this purpose. These amines preferably have a pKb value of from 4 to 11. Examples of suitable catalysts are 4-alkyl pyridines in which the alkyl group contains from 1 to 4 carbon atoms, isoquinoline, aryl pyridines such as phenyl pyridine, pyridine, acryline, 2-methoxypyridine, pyridazine, 3 -chloropyridine, quinoline, n-methylimidazole, 4,4'-dipyridine, phenylpropylpyridine, 1-methylbenzimidazole, 1,4-thiazine, Ν, д-dimethylbenzylamine, triethylamine, tribenzylamine, H ^ dimethyl-1.3-propanediamine. Ν, Ν-dimethylethanolamine and triethanolamine. If necessary, the catalyst can be diluted with an inert solvent, for example 2,2,4-trimethyl-1,3-pentanediol diisobutyrate or a fatty acid ester. The amount of added catalyst is selected in the range from 0.1 to 15 wt.% By weight of the polyol as one component.

Then the composition of the molding sand using standard means is placed in the mold and compacted there. After that, the composition of the moldable mixture is cured to obtain a molded product. When cured, the molded product should preferably maintain its external shape.

If curing is to be carried out in accordance with the Pu-Co14-Boh method, a gaseous catalyst is passed through the molded composition of the moldable mixture. As the catalyst, standard catalysts from the region of the Co14-Box method can be used. Particularly preferably, amines are used as catalysts, most preferably dimethylethylamine, dimethyl-n-propylamine, dimethylisopropylamine, dimethyl-n-butylamine, triethylamine and trimethylamine in gaseous form or in the form of an aerosol.

According to a further preferred embodiment of the present invention, a furan resin or phenolic resin is used as a binder; the composition of the moldable mixture is cured according to the furan Νο-Vake method using strong acid catalysis.

Furan and phenolic resins exhibit very good degradability during casting. Under the influence of heat from a liquid metal, the furan or phenolic resin decomposes, and the strength of the mold is significantly reduced. Therefore, after casting, the casting cores can be very easily removed from the cavities, for example after preliminary shaking of the casting.

Reactive furan resins contained in furan Νο-Wake binders as first components contain furfuryl alcohol as an important component. In acid catalysis, furfuryl alcohol can react with itself to form a polymer. Pure furfuryl alcohol is usually not used to obtain furan Νο-Vake binders, but other compounds that are polymerized together with the resin are added to furfuryl alcohol. Examples of such compounds are aldehydes such as formaldehyde or furfural, ketones such as acetone, phenols, urea or polyols such as sugar alcohols or ethylene glycol.

Other additional components can be added to the resins that affect the properties of the resin, for example, their elasticity. For example, melamine can be added to bind free formaldehyde.

Furan Νο-Wake binders are usually prepared by a process in which furfuryl-containing precondensates, for example, consisting of urea, formaldehyde and furfuryl alcohol, are first prepared under acidic conditions. In this case, the reaction conditions are chosen such that only slight polymerization of furfuryl alcohol occurs. These precondensates are then diluted with furfuryl alcohol. To obtain furan Νο-vake-binders, you can also use resole. Resoles are obtained by polymerization of mixtures of phenol and formaldehyde. These resoles are then diluted with furfuryl alcohol.

The second component of furan Νο-Wake-binders is acid. This acid, firstly, neutralizes the alkaline components contained in the refractory molding material, and secondly, catalyzes the crosslinking of reactive furan resin.

Aromatic sulfonic acids and, in some special cases, phosphoric or sulfuric acid are usually used as acids. Phosphoric acid is used in concentrated form, that is, in concentrations of over 75%. However, it is only suitable for the catalytic curing of furan resins with a relatively high urea content. The nitrogen content in such resins is more than 2.0 wt.%. Sulfuric acid, as a relatively strong acid, can be used as a starter to cure furan resins with weaker acids. However, during the casting, a smell typical of sulfur compounds is released. In addition, there is a danger that sulfur will be absorbed by the material used for casting, which will affect its properties. Aromatic sulfonic acids are commonly used as catalysts. Due to their availability and high strength as acids, toluene sulfonic acid, xylene sulfonic acid and benzenesulfonic acid are primarily used.

Phenolic resins as the second large group of acid-catalyzed ΝοBake binders contain resoles, that is, phenolic resins obtained under conditions of excess formaldehyde, as reactive resin components. Phenolic resins, in comparison with furan resins, exhibit noticeably lower chemical activity and require the use of strong sulfonic acids as catalysts. Phenolic resins have a relatively high viscosity, which increases even more with long-term storage of the resin. In particular, the viscosity increases sharply at temperatures below 20 ° C, so you have to heat the sand in order to evenly apply a binder to the surface of the sand grains. After applying the phenolic Вο-Wake-binder to the refractory molding base material, the molding composition should be processed as quickly as possible so that the quality of the molding composition does not decrease due to premature curing, which can lead to a decrease in the strength of foundry molds made from the molding composition . When using phenolic Νο-Wake binders, the fluidity of the molding composition is usually very poor. Therefore, in the manufacture of the mold, it is necessary to very carefully compact the composition of the molding material in order to ensure high strength of the mold.

Preparation and processing of the composition of the molding material should be carried out at temperatures in the range from 15 to 35 ° C. At lower temperatures, the composition of the molding material is poorly processed due to the high viscosity of the phenolic Νο-Wake resin. At temperatures above 35 ° C, the processing time is reduced due to premature curing of the binder.

After casting, the composition of the molding material based on phenolic Νο-Vake-resins can also be reused, and mechanical, thermal or combined mechanothermal methods can also be used for regeneration in this case.

Then, acid is applied to the bulk solid refractory material, whereby an acid coated refractory molding material is obtained. The acid is applied to the refractory molding material by conventional methods, for example, by spraying the acid onto the refractory molding material. The amount of acid is preferably selected in the range of 5 to 45% by weight, particularly preferably in the range of 20 to 30% by weight, based on the weight of the binder, calculated on the basis of pure acid, excluding the solvent used if necessary. If the acid is not in liquid form and does not have a sufficiently low viscosity so that it can be applied as a thin film to the grains of the refractory molding material, then the acid is diluted with a suitable solvent. Examples of solvents are water, alcohols, or mixtures of water and alcohol. In particular, when using water, it is necessary to obtain the most concentrated solution possible, in order to keep the amount of water falling into the binder or molding composition as low as possible. For a uniform distribution of acid over the surface of the grains, the mixture of the refractory core molding material and the acid is thoroughly homogenized.

Then, an acid-curing binder is applied to the refractory core molding material with an acid coating. The amount of binder is preferably selected in the range from 0.25 to 5 wt.%, Particularly preferably in the range from 1 to 3 wt.% By weight of the refractory molding material, calculated on the resin component. As the acid-curing binder, in principle any acid-curable binders can be used, in particular, such acid-cured binders that are commonly used to prepare molding compositions for the foundry industry in the state of the art. In addition to the crosslinkable resin, the binder may also contain other standard components, for example, a viscosity adjusting solvent or fillers, which replace part of the crosslinkable resin.

The binder is applied to a refractory molding material coated with an acid and, by mixing the mixture, it is evenly distributed on the surface of the grains of the refractory molding

- 13,023,525 material in the form of a thin film.

The amounts of binder and acid are selected so as to ensure, on the one hand, sufficient mold strength and, on the other hand, sufficient processing time for the molding composition. Suitable, for example, processing times are in the range of 5 to 45 minutes.

Then, a molded article is molded from a refractory molding material coated with a binder by standard methods. For this, the molding composition can be placed in a suitable mold and sealed there. The molded product thus obtained is left to cure.

As a furan Νο-Wake binder, in principle, any furan resins that are already used in furan Νο-Wake binder systems can be used.

Furan resins used in industrial furan Νο-Wake binders are usually precondensates or mixtures of furfuryl alcohol with other monomers or precondensates. The precondensates contained in furan Νο-Vake-binders are prepared by methods already known.

According to a preferred embodiment of the present invention, furfuryl alcohol is used in combination with urea and / or formaldehyde or urea / formaldehyde precondensates. Formaldehyde can be used both in monomeric form, for example in the form of a solution of formalin, and in the form of its polymers, such as trioxane or paraformaldehyde. Other aldehydes or ketones can also be used with formaldehyde or instead of formaldehyde. Suitable aldehydes are, for example, acetaldehyde, propionic aldehyde, butyric aldehyde, acrolein, crotonaldehyde, benzaldehyde, salicylic aldehyde, cinnamaldehyde, glyoxal and mixtures of these aldehydes. Formaldehyde is preferred, and it is preferably used in the form of paraformaldehyde.

As ketone components can be used any ketones with a sufficiently high chemical activity. Examples of ketones are methyl ethyl ketone, methyl propyl ketone and acetone, with acetone being preferred.

These aldehydes and ketones can be used as separate compounds or in a mixture with each other.

The molar ratio of aldehyde, in particular formaldehyde, or ketone and furfuryl alcohol can be selected in a wide range. In the preparation of furan resins per mole of aldehyde, it is preferable to use from 0.4 to 4 moles of furfuryl alcohol, more preferably from 0.5 to 2 moles of furfuryl alcohol.

For the preparation of precondensates, furfuryl alcohol, formaldehyde and urea, after adjusting the pH to a value in excess of 4.5, can be brought to a boil, while water will continuously be distilled off from the reaction mixture. The reaction time can be up to several hours, for example, 2 hours. Under such reaction conditions, almost no polymerization of furfuryl alcohol occurs. However, furfuryl alcohol, together with formaldehyde and urea, condenses to resin.

According to an alternative method, a reaction is carried out between furfuryl alcohol, formaldehyde and urea at a pH value that is significantly lower than 4.5, for example, at a pH value of 2.0, and when heated, while the water formed by condensation is distilled off under reduced pressure. The reaction product has a relatively high viscosity and in the preparation of the binder it is diluted with furfuryl alcohol to obtain the desired viscosity.

Combinations of the described cooking methods may also be used.

There is also the possibility of adding phenol to the precondensate. To do this, you can first carry out the reaction of phenol under alkaline conditions with formaldehyde to obtain a resol resin. You can then react or mix this resole with furfuryl alcohol or with a resin containing furan groups. Such resins containing furan groups can be prepared, for example, by the methods described above. Higher phenols, for example, resorcinol, cresol and bisphenol A, can also be used to produce the precondensate. The proportion of phenol or higher phenols in the binder is preferably selected in the range of up to 45 wt.%, More preferably up to 20 wt.%, Particularly preferably up to 10 wt.% . According to one embodiment of the present invention, the proportion of phenol or higher phenols may exceed 2 wt.%, According to another embodiment of the present invention, it may exceed 4 wt.%.

You can also use condensates consisting of aldehydes and ketones, which are subsequently mixed with furfuryl alcohol in the preparation of the binder. Such condensates can be obtained by converting aldehydes and ketones under alkaline conditions. Formaldehyde is preferably used as the aldehyde, in particular in the form of paraformaldehyde. Acetone is preferably used as the ketone. Other aldehydes and ketones may also be used. The relative molar ratio of aldehyde to ketone is preferably selected in the range from 7: 1 to 1: 1, preferably from 1.2: 1 to 3.0: 1. The condensation is preferably carried out under alkaline conditions at a pH in the range from 8 to 11.5, preferably from 9 to 11. A suitable base is,

- 14,023,525, for example, sodium carbonate.

The amount of furfuryl alcohol contained in the furan Νο-Wake binder, on the one hand, is determined by the need to keep its content as low as possible from economic considerations. On the other hand, due to the high proportion of furfuryl alcohol, an increase in the strength of the mold is achieved. However, with a very high content of furfuryl alcohol in the binder, very brittle foundry molds are obtained, which are very difficult to work with. Preferably, the content of furfuryl alcohol in the binder is selected in the range from 30 to 95 wt.%, More preferably from 50 to 90 wt.%, Particularly preferably from 60 to 85 wt.%. The content of urea and / or formaldehyde in the binder is preferably selected in the range from 2 to 70 wt.%, More preferably in the range from 5 to 45 wt.%, Particularly preferably from 15 to 30 wt.%. These values include both the unbound amounts of these compounds contained in the binder and those that are bound in the resin.

Other additives may be added to the furan resins, for example ethylene glycol or similar aliphatic polyols, for example sugar alcohols, which serve as fillers and replace part of furfuryl alcohol. Too high a content of such fillers can in an adverse case lead to a decrease in the strength of the mold and a decrease in reactivity. Therefore, the content of such fillers in the binder is preferably less than 25 wt.%, More preferably less than 15 wt.% And particularly preferably less than 10 wt.%. In order to provide cost savings without having to take into account the excessive influence on the strength of the mold, the filler content according to one embodiment of the present invention exceeds 5 wt.%.

Furan Νο-Wake binders may also contain water. Since water slows down the curing of the molding composition, and when cured, water is formed as a by-product, the proportion of water is preferably chosen as small as possible. Preferably, the water content in the binder is less than 20 wt.%, More preferably less than 15 wt.%. From an economic point of view, a binder water content in excess of 5 wt.% May be acceptable.

Resoles are used as phenolic resins in the process of the present invention. Resoles are mixtures of hydroxymethylphenols that are crosslinked by methylene and methylene ether bridges and which can be obtained in the reaction between aldehydes and phenols in a molar ratio of 1: <1, if necessary in the presence of a catalyst, for example, a basic catalyst. They have a molar mass of <10,000 g / mol.

All commonly used phenols are suitable for the production of phenolic resins, with phenol being particularly preferred. Formaldehyde is preferably used as the aldehyde component, in particular in the form of paraformaldehyde. Alternative phenols and aldehydes are already described in the context of polyurethane binders. Here we make a link to the relevant paragraphs.

Binders may contain other standard additives, for example silanes, as adhesion promoters. Suitable silanes are, for example, aminosilanes, epoxysilanes, mercaptosilanes, hydroxysilanes and ureidosilanes, e.g. - (aminoethyl) ^ - aminopropyltrimethoxysilane.

If such a silane is used, it is added to the binder in an amount of from 0.1 to 3 wt.%, Preferably from 0.1 to 1 wt.%.

Binders may also contain other standard components, such as activators or plasticizers.

The composition of the molding material, in addition to the refractory molding material, binder and, if necessary, the catalyst may also contain other standard ingredients. Examples of other ingredients are iron oxide, crushed special fibers, wood flour granules, ground coal or clay.

Then, from the composition of the molding material, the basic casting mold or part of the basic casting mold is molded by conventional methods and, if necessary, cured. Then, the base mold is fully or partially assembled and the surface of the cavity provided inside the base mold covering the composition described above is completely or partially covered. At the same time, any standard methods can be used to apply the coating composition. The coating composition can be applied, for example, by immersion, spraying, brushing or spraying.

When using immersion as a method of applying a casting mold, on the surface of the cavity of which, if necessary, a primer coating has already been applied, for a period of about 2 seconds to 2 minutes, it is immersed in a tank that is filled with a ready-to-use coating composition according to the present invention. Then the mold is removed from the coating composition and the excess coating composition is allowed to drain from the mold. Time required to drain excess

- 15,023,525 of the coating composition after immersion, depending on the fluidity of the coating composition used.

When using spraying as a method of application, standard spraying devices with a pressure tank are used. In this case, the coating composition in a diluted state is poured into a pressure tank. Due to the established overpressure, the coating composition can be squeezed into the spray gun, from which it is sprayed using a separately regulated spray air. When spraying, it is preferable to select such conditions that the pressure of the coating composition and the spraying air is set in the spray gun so that the spraying coating composition is wet on the surface of the mold or casting core, but the application is uniform.

Then, the carrier fluid contained in the coating composition is vaporized and a dry layer of coating composition is formed. As drying methods, any conventional drying methods can be used, for example, air drying, drying using dehydrated air, drying using microwave or infrared radiation, drying in convection ovens and similar methods.

In a preferred embodiment of the present invention, the coated mold is dried in a convection oven at a temperature of from 100 to 250 ° C, preferably from 120 to 180 ° C. When using alcohol compositions, the coating composition according to the present invention is preferably dried by burning alcohols or alcohol mixtures. For this, the coated casting mold is additionally heated due to the heat released during combustion. In a further preferred embodiment of the present invention, the coated mold is dried in air without further processing.

If necessary, the layer of the coating composition can then be further cured, for example, by irradiation with ultraviolet radiation, if the coating composition contains a binder, cured in an appropriate way.

The coating composition can be applied in the form of a single layer or in the form of several layers located one above the other. In this case, the individual layers may have the same or different composition. For example, a primer may first be applied from a commercially available molding paint that does not contain a metal-containing additive according to the present invention. As a primer coating, for example, aqueous coating compositions or alcohol coating compositions can be used. It is also possible to obtain all layers from a coating composition according to the present invention. However, a layer that will subsequently come into contact with the molten metal is necessarily made from the coating composition according to the present invention. When applying several layers, each individual layer after application can be completely or partially dried.

A coating made from a coating composition preferably has a dry layer thickness of at least 0.1 mm, more preferably at least 0.2 mm, particularly preferably at least 0.45 mm, even more preferably at least 0, 55 mm.

According to one embodiment of the present invention, the coating thickness is less than 1.5 mm. In this context, the dry layer thickness is the thickness of the dried coating layer, which was obtained by drying the coating composition by essentially completely removing the solvent component and, if necessary, additional curing. The thickness of the dry layer of the primer coating and the outer coating is preferably determined by means of a measuring comb to determine the thickness of the wet coatings.

Then the mold can be finally assembled if necessary.

The next subject of the present invention is the use of the above-described mold for producing castings.

For this, a mold is first made. It can be a single mold, which, as described above, is made of refractory material, such as silica sand, and a binder, or a permanent mold, which is usually used to make pipes, bearings or bushings, the surface of the mold cavity being coated with the coating composition described above. The mold, at least on those surfaces that come into contact with the molten metal, has a protective coating that insulates the molten metal from the mold and which can positively affect the surface properties of the casting. A molten metal, preferably cast iron or an alloy of iron, is then poured into the prepared mold. Then the liquid metal is allowed to cool to obtain a casting, after which the casting is separated from the mold. To do this, use standard methods. In the case of single molds, the mold is mechanically destroyed, for example by shaking. In the case of permanent molds, the casting is removed from the mold using standard methods.

A further subject of the present invention is a mold containing a coating obtained from the coating composition described above. Such a mold preferably contains an insulating layer between the molten metal and the mold, thereby reducing the thermal load on the mold during the casting process, thereby increasing the service life of the mold. As another advantage, the mold coating contains a metal-containing additive that can positively affect the surface properties of the casting, in particular preventing the formation of an uneven surface of the casting.

Molds having an outer coating obtained from a coating composition according to the present invention are used, inter alia, for the manufacture of bearings for wind power plants, runner bowls, motors and motor parts, machine stands and turbines, machine parts and molds.

The invention will now be described in more detail based on an example of its implementation.

The coating composition for casting cores used in the following examples had the composition shown in the table.

The composition of the coating composition

The coating composition for the molds was prepared as follows: isopropanol was prepared and clay was mixed with it for 15 minutes using a high shear mixer. Then, refractory components, pigments, manganese and dyes were mixed in for the next 15 minutes until a homogeneous mixture was obtained. In conclusion, ethanol, rheological additives and a binder were added.

Claims (12)

CLAIM 1. The coating composition for molds and cores for casting metals, containing at least one carrier fluid and a metal-containing additive that contains a metal or metal compound, the metal being manganese, where the content of the metal-containing additive in the coating composition is from 15 to less than 50 wt.% Of the solids content in the coating composition, where the content of the metal or metal compound in the metal-containing additive is at least 20 wt.%, And the carrier fluid consists of and and comprises at least partially, at least one alcohol. 2. The coating composition according to claim 1, characterized in that the metal-containing additive is a metal compound, which is manganese oxide or a manganese salt. 3. The coating composition according to claim 1, characterized in that the metal is used in pure form or in the form of an alloy with other metals. 4. The coating composition according to claim 1, characterized in that the content of the metal or metal compound in the metal-containing additive is in terms of metal at least 40 wt.% By weight of the metal-containing additive. 5. The coating composition according to claim 1, characterized in that the content of the metal-containing additive in the coating composition is at least 20 wt.% Of the solids content in the coating composition. 6. The coating composition according to claim 1, characterized in that the metal-containing additive has an average particle size of Ό ₅₀ in the range from 20 to 1000 microns. 7. The coating composition according to claim 1, characterized in that it further comprises a refractory material, the content of which is less than 80 wt.% Of the solids content in the coating composition. 8. The coating composition according to claim 1, characterized in that the content of at least one alcohol in the carrier fluid is at least 50 wt.% By weight of the carrier fluid. 9. The coating composition according to claim 1, characterized in that the content of the metal-containing additive is less than 35 wt.% Of the solids content in the coating composition. 10. A coating composition according to any one of claims 1 to 9, characterized in that it further comprises a binder. 11. A method of manufacturing a mold for casting metals, which prepare a composition of a molding material, which contains at least one refractory molding material and a binder; from the composition of the molding material, a basic mold is formed which has a cavity; and a coating composition according to any one of claims 1 to 8 is applied at least on the surface of the cavity of the base mold. 12. A mold for casting metals with an internal cavity having surfaces, where at least one surface of the internal cavity of the mold is coated with a composition according to any one of claims 1 to 8. Eurasian Patent Organization, EAPO