JP2014534075A - COATING COMPOSITION FOR INORGANIC MOLD AND CORE CONTAINING FORUMATE AND METHOD OF USING THE SAME - Google Patents

Abstract

The object of the present invention is to provide a coating composition comprising a formate ester, an aqueous carrier fluid and a powdered refractory material, and to use the coating composition in a mold produced in particular using water glass as a binder. Is to provide a method. [Selection figure] None

Description

  The present invention relates to a sizing composition as a template coating composition containing a formate ester. Sizing compositions are particularly suitable for cores and molds produced using water glass as a binder.

  The mold is manufactured by molding a refractory material such as silica sand into a mold and caking using a suitable binder, thereby ensuring sufficient mechanical strength of the mold. For this reason, a refractory mold material and a suitable binder are used for the production of the mold. The refractory mold material is preferably present in an injectable form, which allows for injection into a suitable hollow mold and molding in situ. The binder forms a strong bond between the mold material particles and achieves the mechanical stability required for the mold.

  An organic or inorganic binder can be used for the production of the mold, and curing thereof is carried out by a high temperature method or a low temperature method, respectively. The low temperature method is a method which is carried out substantially at room temperature without heating the mold. In this case, curing is mainly performed by a chemical reaction, and the chemical reaction is started, for example, by passing a gas serving as a catalyst through a mold to be cured. In the high temperature method, the molding material mixture after molding is heated to a sufficiently high temperature, for example, for the purpose of removing the solvent contained in the binder or initiating a chemical reaction. In this chemical reaction, the binder is cured, for example, by crosslinking. .

  Common to all organic systems regardless of the curing mechanism, but the organics in the mold thermally decompose during liquid metal injection, for example benzene, toluene, xylene, phenol, formaldehyde and other partially unspecified decomposition products Hazardous substances such as are released.

  Although it has been successfully minimized by various methods, it has not been possible to completely avoid this in organic binders.

In order to minimize or avoid the release of decomposition products in the casting process, binders based on inorganic materials or with a very low content of organic compounds can be used. Such binders are already known for some time. Binder systems that cure by allowing gas to pass through have been developed. Such a system is described in Patent Document 1, for example, and alkaline water glass is used as a binder, and curing is performed by allowing CO ₂ to pass through. Patent Document 2 describes an exothermic hot water containing alkali silicate as a binder. In addition, binder systems that self cure at room temperature have been developed. An example is the phosphoric acid and metal oxide based binder system described in US Pat. In addition, inorganic binder systems are also known which cure at high temperatures, for example in high temperature equipment. Such a high-temperature curing binder system is disclosed in, for example, Patent Document 4, which describes a binder system containing alkaline water glass and aluminum silicate.

Patent Document 5 discloses a binder system for foundry sand for core production. The water glass based binder system contains an aqueous sodium silicate solution and a hygroscopic base such as sodium hydroxide added thereto in a ratio of 1: 4 to 1: 6. Water glass contains 2.5 to 3.5 SiO ₂ / M ₂ O module and 20 to 40% solid part. In order to produce an injectable mold mix that can be filled into complex core shapes and to control hygroscopicity, the binder system includes a surfactant such as silicone oil with a boiling point ≧ 250 ° C. The binder system is mixed with a suitable refractory material such as silica sand and injected into the core using a molding machine. Curing of the molding material mixture is achieved by draining the remaining water. Mold drying or curing is also achieved by microwave irradiation.

  However, inorganic binders also have drawbacks compared to organic binders. For example, molds produced using conventional inorganic binders are less stable against high humidity and water. For this reason, the shaped body cannot be reliably stored for a long time as in the case of the organic binder. In order to increase the initial hardness, improve the durability of the mold against humidity, and obtain good results on the casting surface during casting, Patent Document 6 discloses a mold containing a water glass-based binder in addition to a refractory molding material. A material mixture is disclosed. Particulate metal oxide is partially added to the molding material mixture. Preferably, precipitated silica or calcined silica is used as the particulate metal oxide.

  The described mold and core manufacturing method further mainly includes the application of a refractory mold coating, also referred to as a sizing agent, applied at least to the surface of the base mold and in contact with the injected metal. To do. Mold coating, on the other hand, aims to control the mold part surface, improve the appearance of the casting, control the casting metallurgically and / or avoid casting errors.

  Commonly used sizing agents include, for example, clay, quartz, diatomaceous earth, cristobalite, tridymite, aluminum silicate, zirconium silicate, mica, and / or chamotte, coke and graphite. These substrates are the active component of the sizing agent, coating the mold surface and closing the holes so that the cast metal does not enter.

  By this coating, the surface of the mold can be deformed or adjusted according to the properties of the metal to be processed. Since irregularity due to the particle size of the molding material is smoothed by the sizing agent, a smooth surface is formed, and the appearance of the casting is improved by the sizing agent. The sizing agent can further have a metallurgical effect on the casting, for example, the sizing agent selectively moves additives into the casting on the casting surface, thereby improving the surface performance of the casting. Furthermore, the sizing agent forms a layer that chemically isolates the mold from the liquid metal during casting.

  Thereby, adhesion with a casting and a casting_mold | template is avoided, and a casting can be taken out from a casting_mold | template comfortably. The sizing agent may also be used to control the heat transfer between the liquid metal and the mold, for example to create a structure in the metal through the cooling rate.

  In recent years, the curing of inorganic binders that have been used is often caused by a condensation reaction that starts at a high temperature, and involves the formation of crosslinks by dehydration. As with many other chemical reactions, the reverse reaction is also a problem here, i.e. contact with water and the reaction can break down the crosslinks again, and the extent of this reverse reaction is a manufacturing process parameter for core production. Strongly depends on. Under typical process parameters (high production cycle, high temperature) in mass production, contact with water and with some alcohol reduces mold hardness, weakens the surface and impairs the shape of the mold.

British Patent No. 782205 US Pat. No. 6,972,059 US Pat. No. 5,582,232 US Pat. No. 5,474,606 US Pat. No. 7,022,178 U.S. Pat. No. 7,770,629

  The present invention provides a sizing agent that does not impair the stability of the core or mold, thereby negatively affecting processing and storage, and that can reliably produce defects-free coatings, particularly inorganic cores and molds. Based on the task of doing.

  This problem is solved by a sizing composition having the features of claim 1 and preferred embodiments constitute the subject of protection of the dependent claims and are detailed below.

  The sizing composition of the present invention is provided in the form of a paste or suspension according to a preferred embodiment. In this embodiment, the sizing composition includes a carrier fluid.

  Surprisingly, by adding certain additives to the aqueous sizing composition, the quality of the sized inorganic core and mold can be continuously improved, and the core and mold can be stably stored for several days. Can be done without problems.

  An ester of formic acid (methanoic acid) is used as an additive component of the sizing composition, and the chain length of the alcohol or alcohol mixture used for esterification is lower than 6 on average, and particularly preferably lower than 3 carbon atoms. Particularly preferred are methyl formate (methyl formate) and ethyl formate (ethyl formate). If the alcohol group or some of the alcohol groups have one or two further substituents, for example ether, hydroxyl, ester or carboxyl groups, or formic acid is cross-linked by a second or third hydroxyl group, for example by condensation It is also possible to be done.

  The total content of the above additives with respect to the sizing composition is 1 to 8% by weight, preferably 2 to 8% by weight, particularly preferably 3 to 6% by weight.

  As an additive, for example, “methyl pure formate” manufactured by BASF may be used. This CAS number is 107-31-3.

  Depending on the desired use of the sizing composition, e.g. as a base coating or as a top coating, and depending on the desired layer thickness of the coating produced from the sizing composition, the characteristic parameters of the sizing composition Can be prepared.

  The carrier fluid may consist partly or entirely of water. The carrier fluid is a component that volatilizes at a normal pressure of 160 ° C., and in this sense, the carrier fluid does not contain a solid according to the above definition. The water content of the carrier fluid is more than 50% by weight, preferably 75% by weight, in particular more than 80% by weight and in some cases more than 95% by weight.

  An additional component of the carrier fluid may be an organic solvent. Suitable solvents are alcohols including polyhydric alcohols and polyether alcohols. Examples of alcohols are ethanol, n-propanol, isopropanol, butanol and glycol.

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

  The sizing agent may contain, for example, a certain kind of clay as a constituent material of the sizing agent in combination. As clay constituents, a) 1-10 parts by weight, in particular 1-5 parts by weight of palygorskite, b) 1-10 parts by weight, in particular 1-5 parts by weight of hectorite, and c) 1-20 parts by weight, in particular A combination of 1 to 5 parts by weight of sodium bentonite (each constituent material is relative to each other) is used. In particular, the weight ratio of palygorskite to hectorite is 1: 0.8 to 1.2, and each of palygorskite and hectorite is The weight ratio with sodium bentonite is 1: 0.8 to 1.2. The total clay content of the sizing agent in the case of the above clay is 0.1 to 4.0% by weight, preferably 0.5 to 3.0% by weight, particularly preferably the solid content of the sizing composition. 1.0 to 2.0% by weight. When these clays are used, the storage stability of the core and the mold is further increased.

  The sizing composition may further comprise metallic magnesium and / or a metallic manganese salt, the concentration or optionally the combination of which is greater than 1% by weight relative to the sizing composition. As for the anion of the salt, it is particularly preferable to use a sulfate ion and / or a chloride ion. Particularly, the oxidation state of magnesium is +2 or +4, and / or the oxidation state of manganese is +2, and The concentration relative to the sizing composition is in particular greater than 3% by weight, in particular greater than 5% by weight. In certain embodiments, the salt concentration is at most the saturation concentration of the carrier fluid used, but the salt concentration is still less than 10% by weight relative to the sizing composition.

  The sizing composition of the present invention contains at least one powdered refractory material. This refractory material plays a role of closing the hole of the mold so that the liquid metal does not enter. Furthermore, heat insulation between the mold and the liquid metal is achieved by the refractory material. As the refractory material, a refractory material usually used in metal casting may be used. Examples of suitable refractory materials are quartz, aluminum oxide, zirconium oxide, aluminum silicate, such as granite, kyanite, columbite or chamotte, zircon sand, zirconium silicate, olivine, talc, mica, coke Feldspar, feldspar, diatomite, kaolin, calcined kaolin, kaolinite, metakaolinite, iron oxide and / or bauxite.

  The refractory material is provided in powder form. A stable structure is formed in the coating and the particle size is distributed so that the sizing agent can be applied to the mold wall without problems, preferably using a spray device. The average particle size of the refractory material (measured using light scattering according to DIN / ISO 13320) is preferably in the range of 0.1 to 500 μm, particularly preferably in the range of 1 to 200 μm. In particular, a material that has a melting point that is at least 200 ° C. higher than that of the liquid metal and that does not cause a chemical reaction with the metal is suitable as the refractory material.

  The content of refractory material (which in any case contributes only to the solid content) is preferably more than 70% by weight, preferably more than 80% by weight, preferably for the solid part of the sizing composition in the commercial paste state, Particularly preferred is more than 85% by weight.

  In certain embodiments (each relating only to the solid content), the content of the refractory is selected to be lower than 70% by weight, in further embodiments lower than 60% by weight and in further embodiments lower than 50% by weight. Is done.

  The sizing agent of the present invention contains at least one suspending agent in certain embodiments. The suspending agent increases the viscosity of the sizing agent so that there is no or only a small sedimentation in the suspension of the solid component of the sizing agent. Organic or inorganic materials or mixtures of these materials may be used to increase the viscosity. Suitable inorganic suspending agents are strong swellable clays such as sodium bentonite.

  As an alternative or further component of the suspending agent, an organic thickener may also be used, since it can be dried to the extent that little water is released upon contact with the liquid metal after application of the protective coating. It is. Examples of organic suspending agents are swellable polymers, examples of which include carboxymethylcellulose, methylcellulose, ethylcellulose, hydroxyethylcellulose and hydroxypropylcellulose, plant mucus, polyvinyl alcohol, polyvinylpyrrolidone, pectin, gelatin, agar, polypeptides and / Or alginate.

  The content of the suspending agent is preferably 0.1 to 5% by weight, preferably 0.5 to 3% by weight, particularly preferably 1 to 2% by weight, based on the whole sizing composition. .

  In a preferred embodiment, the sizing agent of the present invention contains at least one binder as a further component. The binder improves the fixing of the protective coating on the mold wall produced from the sizing agent or sizing agent. Furthermore, the binder increases the mechanical stability of the protective coating and erosion due to the influence of the liquid metal is not observed. The binder is preferably irreversibly cured to provide an abrasion resistant coating. Particularly preferably, the binder does not re-soften due to contact with atmospheric humidity. Any binder used in sizing agents can be included. For this reason, inorganic and organic binders may be used. As the binder, for example, a clay such as bentonite and / or kaolin may be used.

  The binder content is preferably in the range from 0.1 to 20% by weight, particularly preferably in the range from 0.5 to 5% by weight, based on the solids content of the sizing composition.

  In other preferred embodiments, the sizing agent partially contains graphite. This facilitates the formation of layered carbon at the interface between the casting and the mold. The graphite content is preferably in the range from 1 to 30% by weight, particularly preferably in the range from 5 to 15% by weight, based on the solids content of the sizing composition. Graphite has a positive effect on surface quality in iron casting.

  The sizing composition of the present invention may contain additional components common as sizing agents, such as wetting agents, antifoaming agents, pigments, dyes or biocides. The content of these further components is preferably less than 10% by weight, preferably less than 5% by weight, particularly preferably less than 1% by weight in the ready-to-use coating composition.

  For example, anionic and non-anionic surfactants having an HSB value of at least 7 can be used as the wetting agent. An example of such a wetting agent is disodium dioctyl sulfosuccinate. The content of the wetting agent is preferably 0.01 to 1% by weight, preferably 0.05 to 0.3% by weight, based on the ready-to-use sizing composition.

  Antifoaming agents are also called antifoaming agents and may be used to avoid foam formation during the manufacture of the sizing composition or its application. If bubbles are formed during application of the sizing composition, the layer thickness may not be constant or pores may be formed in the coating. As the antifoaming agent, for example, silicone oil or mineral oil may be used. The content of the antifoaming agent is 0.01 to 1% by weight, preferably 0.05 to 0.3% by weight, based on the sizing composition ready for use.

  In the sizing composition of the present invention, conventional pigments and dyes may be used as necessary. This is used, for example, to differentiate between different sizing agents, for example to enhance the separation of the sizing agent from the casting. Examples of pigments are red and yellow iron oxide and graphite. Examples of dyes are commercially available dyes, for example the Luconyl® dye series (BASF AG, Ludwigshafen, Germany). The amount of dye and pigment is preferably 0.01 to 10% by weight, preferably 0.1 to 5% by weight, based on the solids content of the sizing composition.

  In a further embodiment, the sizing composition contains a biocide, which serves to avoid attack from bacteria and consequently avoid adverse effects on the rheology and binding performance of the binder.

  It is particularly preferred if the carrier fluid contained in the sizing composition consists essentially of water on a weight basis, in which case the sizing agent according to the invention is provided in the form of a so-called aqueous sizing agent. Examples of suitable biocides are formaldehyde, 2-methyl-4-isothiazolin-3-one (MIT), 5-chloro-2-methyl-4-isothiazolin-3-one (CIT), 1,2-benzisothiazoline. -3-ON (BIT). Preferably MIT, BIT or mixtures thereof are used. The amount of biocide used is usually 10 to 1000 ppm, preferably 50 to 500 ppm, based on the weight of the ready-to-use sizing composition.

  In addition to the above components, the sizing composition of the present invention may further contain components usually used for sizing agents.

  The sizing composition of the present invention can be produced by conventional methods. The sizing composition of the present invention may be produced, for example, by dispersing clay serving as a suspending agent in water using a high shear mixer. Next, the refractory component, pigment, dye and metal additive are mixed until a uniform mixture is obtained. Finally, wetting agents, antifoaming agents, biocides and binders are mixed.

  The sizing composition of the present invention may be manufactured and sold as a sizing agent prepared to be ready for use. The sizing agent of the present invention may also be manufactured and sold in a concentrated state. In this case, in order to obtain a ready-to-use sizing agent, it is necessary to add a certain amount of carrier fluid and adjust the viscosity and density of the sizing agent to the desired values. The sizing composition of the present invention may further be provided and sold in the form of a kit, where, for example, the solid component and the solvent component are stored in separate containers. The solid component may be provided in a separate container as a powdered solid mixture. Additional liquid components, such as binders, surfactants, wetting / antifoaming agents, pigments, dyes and biocides, used as needed may be stored in separate containers within the kit. The solvent component may contain further use components as necessary, for example, in the same container, or may be contained in a separate container in which further necessary components are separated.

  A suitable amount of solid components, additional components as needed and solvent components may be mixed for the production of a ready-to-use sizing agent.

The sizing composition of the present invention is suitable for coating a mold. As used herein, the expression “mold” includes all types of structures necessary for the production of castings, such as cores, molds and dies. The method of using the sizing composition of the present invention involves partially coating the mold. The sizing agent is used in a mold for metal processing obtained from an inorganic mold material mixture, and includes at least one refractory mold material, a water glass binder, and preferably a metal oxide component. Is selected from the group consisting of silicon dioxide, in particular amorphous silicon dioxide, aluminum oxide, titanium oxide, zinc oxide and mixtures thereof, which are preferably present in particulate form, with a particle size of particularly less than 300 μm (sieving analysis) is there. Amorphous silicon dioxide can be produced, for example, by a precipitation process from water glass obtained by dissolving silica sand with sodium carbonate or potassium carbonate. The SiO ₂ thus produced is called precipitated silica depending on the production conditions. Another important production mode is so-called calcined SiO ₂ produced in an oxyhydrogen flame, which is produced from liquid chlorosilane, eg silicon tetrachloride.

  A method for producing a mold for metal processing using a mold material mixture and a cured mold material mixture is described in WO 2006/024540 (= US Pat. No. 7,770,629), the disclosure of which Included in this application as a reference. Suitable molding material mixtures are the subject of protection in the claims of WO 2006/024540. The mold to be coated is typically a) more than 80% by weight of refractory molding material (including additives that behave similarly to refractory molding material), b) 0.01-5% as binder % Hardened water glass, c) 0 to 5% by weight of the one or more metal oxides as required.

  The invention further relates to a method for producing a sized mold for metalworking, which includes the application of a sizing agent to the partially or fully cured inorganic mold material mixture as described above. Application or preparation of a sizing agent is performed as follows.

  When immersing as an application means, a basic coating is applied to the hollow portion of the mold as necessary, and the mold is placed in a container filled with the sizing agent of the present invention ready for use for about 2 seconds to 2 minutes. Soaked. The mold is then removed from the sizing composition and excess sizing composition is removed from the mold. The time required to remove excess sizing composition after soaking depends on the removal capacity of the sizing composition used.

  When spray is used as the application means, a commercially available pressure tank spray device is used. In this case, the sizing composition is filled into the pressure tank in a diluted state. Due to the regulated high pressure, the sizing agent is introduced into the spray gun and sprayed with the aid of a separately controlled atomizing air. When spraying, the pressure of the sizing composition and the atomizing air is adjusted in the spray gun, so that the sprayed sizing composition reaches the mold and the core in a wet state, and a smooth application is achieved.

  When flow coating is performed as an application means, a basic coating is applied to the hollow portion of the mold as necessary, and a ready-to-use sizing composition is flow-coated using a tube, a lance or the like. The mold is completely covered by the sizing composition and excess sizing composition is removed from the mold. The time required to remove excess sizing composition in the flow coating depends on the removal capacity of the sizing composition used.

  Further, the sizing agent may be applied with a brush.

  The carrier fluid contained in the sizing agent is then volatilized to obtain a dry sizing agent layer. Any conventional drying means may be used as the drying means, such as air drying, drying with dehumidified air, drying by microwave or infrared irradiation, drying with a convection oven, and similar means.

  In a preferred embodiment of the invention, the coated mold is dried in a convection oven at 20-250 ° C, preferably 50-180 ° C.

  When an alcohol-based sizing agent is used, the sizing composition of the present invention is dried by burning the alcohol or alcohol mixture. In this case, the coated mold is further heated by the combustion heat. In further preferred embodiments, the coated mold is air-dried without further processing or dried by use of microwaves.

  The sizing agent is applied in the form of a single layer or in the form of a plurality of layers stacked one above the other. In this case, the individual layers may have the same or different composition. For example, a base coating may first be formed with a commercially available coating that does not contain the metal additive of the present invention. For example, an aqueous sizing agent or an alcohol-based sizing agent may be used as the base coating. It is also possible to make all layers using the sizing composition of the present invention. All layers that will later come into contact with the liquid metal are produced by the sizing agent of the present invention. In multi-layer application, individual single layers may be fully or partially dried after application.

  The dry layer thickness of the coating with the sizing composition according to the invention is preferably at least 0.1 mm, preferably at least 0.2 mm, more preferably at least 0.45 mm, particularly preferably at least 0.55 mm. According to certain embodiments, the thickness of the coating is selected to be less than 1.5 mm. Dry layer strength is herein the layer strength of the dried coating and is obtained by substantially complete removal of the solvent component and subsequent curing as required by drying the sizing composition. The dry layer strength of the base coating (undercoat) and topcoat is preferably measured using a wet layer thickness comb.

  The mold may then be fully assembled as needed. Casting is preferably performed for the production of iron or steel castings.

Example 1
In this example, the effect of adding various water glass hardeners to the sizing agent on the strength of the sized core is tested. The core sizing 1 to 3 used contains the components listed in Tables 1 to 3.

  The mold sizing agent was prepared as follows: using high shear agglomeration and chopper discs, water was added to the vessel and the clay was allowed to dissolve for at least 15 minutes. Next, the refractory components, pigments and dyes were mixed and stirred for at least 15 minutes until a uniform mixture was obtained. Along with the solid material, in the sizing agents 1 and 2, methyl formate or ethyl formate as an additive was added. Finally, additives such as wetting agents, antifoaming agents, preservatives and binders were mixed and stirred for 5 minutes.

  The sizing agent is adjusted to a range of 0.6 Pas, which is a suitable viscosity during application, for the following tests. Adjustment is made by adding an appropriate amount of water to the original composition to homogenize. The main parameter is the viscosity at 20 ° C. and was measured using a Brookfield viscometer (DIN EN ISO 2555) and a DIN 4 mm viscosity flow cup (DIN EN ISO 2431).

  In addition to other properties, methyl formate contained in sizing agent 1 can react with an inorganic binder that is partially dissolved during the sizing process. This cures the dissolved inorganic binder and thus improves the stability of the sized core. Conversely, a decrease in content in the sizing agent results in a reduction in core strength. The same applies to ethyl formate used in sizing 2. In the following, the handling of the corresponding series of experiments, which form the basis for the described aspects, will be detailed.

  Similarly, equivalent results can be obtained by using esters that are chemically similar.

(Manufacture and testing of mold material specimens)
For testing, two different structural cores are tested. One structure is a so-called George Fisher test bar, which illustrates the behavior of a sized specimen with a thick core structure, and the other structure is a so-called long core, the behavior of a sized specimen with a thin structure. Is illustrated. The George Fisher test bar is a square test bar having a size of 150 mm × 22.36 mm × 22.36 mm. The size of the long core is 13 mm × 20 mm × 235 mm.

The composition of the mold material mixture is listed in Table 3. The Georg Fischer test bar was prepared as follows: The ingredients shown in Table 3 were mixed using a laboratory bladed mixer (Vogel & Chemmann, Hagen, Germany). First, silica sand was added, and water glass was added while stirring. Sodium water glass partially containing potassium was used as the water glass. The SiO ₂ : M ₂ O module of water glass is about 2.2, where M is the sum of sodium and potassium contained. After the mixture has been stirred for 1 minute, amorphous silicon dioxide is optionally added with further stirring. As the amorphous silicon dioxide, baked silica manufactured by RW Silicium is used. The mixture is then stirred for a further time.

  The mold material mixture was transferred to a storage container of an H2,5 hot box core shooting machine (Roeperwerk Giesseleimaschinen GmbH, Vierzen, Germany) and the mold was warmed to 180 ° C. The mold material mixture was introduced into the mold using compressed air (5 bar) and left in the mold for a further 35 seconds. In order to accelerate the curing of the mixture, hot air (2 bar, 150 ° C. when entering the mold) is passed through the mold for the last 20 seconds. Open the mold and remove the test bar.

  The coating composition was applied by immersing the test bar and the application parameters used are listed in Table 2. The test bars were coated immediately after removal from the mold or after a 30 minute cooling time. The coating test bar was left on a drying shelf for 30 minutes at 150 ° C. after application of the coating.

  In order to determine the bending strength, the test bar was attached to a three-point bending apparatus (DISA Industry AG, Schaffhausen, Switzerland) in a George Fisher strength test apparatus, and the force with which the test bar breaks was measured.

The bending strength of uncoated test bars was measured by the following method:
-10 seconds after removal (high temperature strength)
-1 hour after removal (low temperature strength)

The test bars were coated in the following way:
-Coating 1 minute after removal (high temperature coating)
-Coating 30 minutes after removal (low temperature coating)

The bending strength of the coated test bars was measured by the following method-10 seconds after removal from the drying shelf (high temperature strength, high temperature coating)
-30 minutes after removal coating (low temperature strength, high temperature coating, immediately after removal from the furnace)
-10 seconds after removal from drying shelf (high temperature strength, low temperature coating, room temperature 20 ° C)
-30 minutes after coating (low temperature strength, low temperature coating)

(result)
It is not desirable to use an alcohol-containing coating due to the disadvantage of emissions occurring in the casting process. When a water-based standard coating material is used, the strength of the test piece made of a water glass-containing molding material is greatly reduced (sizing agent 4).

Surprisingly, in the search for the possibility of suppressing the reaction between water from the coating and the binder of the molding material, it has been found that the addition of formate to the coating significantly suppresses this effect. Here, the strength is maintained. For example, as seen in sizing agents 1 and 2 of Example 1, esters of various chain lengths and structures can be used. The positive effect is proved by the fact that the strength is higher than that of the core sized by the sizing agent 3.

Claims (12)

(A) formic acid ester;
(B) a carrier fluid containing or consisting of water;
(C) a refractory material;
A sizing composition comprising: The alcohol group of the formate ester has less than 10 carbon atoms, preferably less than 6 and particularly preferably less than 3;
The sizing composition according to claim 1. The concentration of the formic acid ester in the sizing composition is 1 to 8% by weight, preferably 2 to 8% by weight, particularly preferably 3 to 6% by weight;
A sizing composition according to claim 1 or 2. The carrier fluid contains more than 50% by weight of water, preferably further containing alcohols including polyhydric alcohols and polyether alcohols, in particular it can be completely volatilized below 160 ° C. and below 1013 bar;
The sizing composition according to any one of claims 1 to 3, wherein: The solid content of the sizing composition is 30 to 70% by weight;
The sizing composition according to any one of claims 1 to 4, wherein: The sizing composition contains 10 to 85% by weight of a refractory material based on the solid content of the sizing composition;
The sizing composition according to any one of claims 1 to 5, wherein: The refractory material is quartz, aluminum oxide, zirconium dioxide, aluminum silicate, zircon sand, zirconium silicate, olivine, talc, mica, coke, feldspar, diatomite, calcined kaolin, kaolinite, metakaolinite, oxidation Being iron, bauxite and / or mixtures thereof,
The sizing composition according to any one of claims 1 to 6, wherein: The refractory material has a particle size measured using light scattering according to DIN / ISO 13320 of 0.1 to 500 μm, in particular 1 to 200 μm,
The sizing composition according to any one of claims 1 to 7, wherein: The sizing composition contains from 0.1 to 20% by weight, in particular from 0.5 to 5% by weight, of at least one binder, based on the solids content of the sizing composition;
A sizing composition according to any one of claims 1 to 8. The sizing composition contains a bright coal former or graphite, in particular 0.1 to 10% by weight, in particular 0.5 to 3% by weight,
The sizing composition according to any one of claims 1 to 9, wherein:   A method of using the sizing composition according to any one of claims 1 to 10 for coating a molding material mixture which is diluted with water at least in advance as desired and cured with water glass as a binder. The molding material mixture contains silicon dioxide, aluminum oxide, titanium oxide or zinc oxide and / or mixtures thereof, and in particular amorphous silicon dioxide,
The method according to claim 11.