Mold manufacturing method

Abstract

To provide a method capable of manufacturing industrially advantageously a mold having improved mold characteristics such as strength, moisture resistance or scratch hardness, which is an improved manufacturing method of a mold.SOLUTION: Wet coated sand obtained by heating a fire-resistant aggregate and then kneading it together with a water-soluble binder, to thereby coat the surface of the fire-resistant aggregate with the water-soluble binder, is formed in the warmed state, and the wet coated sand in the warmed state is filled into a preheated prescribed form block, to thereby perform molding.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a mold, and more particularly to a method for advantageously manufacturing a mold having excellent mold characteristics. [Background technology]

[0002] Conventionally, one type of mold used for casting molten metal is obtained by molding a desired shape using coated sand (mold material), which is a structure in which the surface of refractory aggregate (molding sand) is coated with a specific binder (binding agent). The binder used in such coated sand includes inorganic binders such as water glass, as well as organic binders made of resins such as phenolic resins, furan resins, and urethane resins. Techniques for molding self-hardening molds using these binders have also been put to practical use.

[0003] Among these binders, water-soluble binders are used in the form of an aqueous solution, which is mixed with a predetermined refractory aggregate to form coated sand, in which the surface of the refractory aggregate is coated with the water-soluble binder.Various methods have been proposed for forming a mold using this coated sand.In general, when forming a mold using such coated sand, the mold into which the coated sand is filled is preheated to a predetermined temperature in order to rapidly solidify and harden the coated sand and obtain the desired properties such as strength.

[0004] For example, Japanese Patent Laid-Open Publication No. 2012-76115 and Japanese Patent Laid-Open Publication No. 2012-501850 propose a method of molding a mold of a desired shape by filling coated sand, which is made by coating a specified refractory aggregate (molding sand) with water glass, which is one such water-soluble binder, into a molding die preheated to a temperature of 20°C to 250°C, and it is said that this method can shorten the molding time, etc.

[0005] Furthermore, JP2010-506731A also discloses that by adding and incorporating predetermined metal oxide particles and phosphates into a wet molding material mixture, so-called wet coated sand, obtained by mixing a fire-resistant molding base material (fire-resistant aggregate) with water glass, which is a water-soluble binder, it is possible to manufacture a mold including thin-walled portions and to prevent deformation of the thin-walled portions of such a mold during metal casting.

[0006] However, in such molding techniques, the coated sand filled into the mold is generally provided at room temperature. When such room-temperature coated sand is filled into a preheated mold and molding is carried out, heat is likely to be transferred unevenly to the filled coated sand. This causes uneven solidification or hardening of the coated sand, which leads to problems such as a decrease in mold strength and makes it difficult to stably achieve the physical properties of the mold. Furthermore, when the formed wet coated sand is left at room temperature, the moisture contained therein partially escapes, causing the problem of uneven moisture content in the coated sand mass. In addition, when such wet coated sand at room temperature is filled into a preheated mold and heated, the adhesive area of ​​the coated sand decreases, particularly when the binder, a component of the coated sand, has high viscosity. This not only makes it difficult for the mold to develop its strength, but also inherently leads to a deterioration in moisture resistance because the remaining moisture cannot be sufficiently removed. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-76115 [Patent Document 2] Special Publication No. 2012-501850 [Patent Document 3] Special Publication No. 2010-506731 Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been made in light of the above circumstances, and aims to provide an improved method for manufacturing casting molds. Another aim is to provide a method for industrially advantageously manufacturing casting molds with improved mold properties such as strength, moisture resistance, and scratch hardness. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems, the present invention can be suitably implemented in various aspects as listed below, and the aspects described below can be adopted in any combination. It should be understood that the aspects and technical features of the present invention are not limited to those described below, but can be recognized based on the inventive idea grasped from the description of the entire specification.

[0010] To solve the above-mentioned problems, one of the basic aspects of the present invention is a method for producing a casting mold, which comprises heating refractory aggregate and then kneading it with a water-soluble binder to form wet coated sand in a heated state, with the surface of the refractory aggregate being coated with the water-soluble binder, and then filling the wet coated sand in a preheated mold to produce a mold.

[0011] In one desirable embodiment of the mold manufacturing method according to the present invention, the heated wet coated sand is at a temperature of 30°C to 100°C, and the refractory aggregate is heated to a temperature of 32°C to 150°C.

[0012] As another basic aspect of the present invention for solving the above-mentioned problems, the present invention provides a method for manufacturing a casting mold, which comprises heating refractory aggregate at room temperature while kneading it, adding a water-soluble binder, and kneading the mixture with the heated refractory aggregate to form wet coated sand in a heated state, in which the surface of the refractory aggregate is coated with the water-soluble binder, and then filling the wet coated sand in a heated state into a predetermined preheated mold to form a mold.

[0013] In another such basic embodiment, the refractory aggregate is preferably heated in the mixer to a temperature of 30°C to 100°C as the wet coated sand, and to a temperature of 32°C to 150°C prior to the addition of the water-soluble binder, and in addition, it is preferable that the mixer for kneading the refractory aggregate is preheated prior to kneading the refractory aggregate.

[0014] Furthermore, in the present invention, it is generally desirable that the mold be preheated to a temperature of 40°C to 250°C.

[0015] According to another preferred embodiment of the method for manufacturing a mold according to the present invention, the water-soluble binder is preferably preheated to a temperature below its boiling point, and the preheating temperature of the water-soluble binder is preferably 30°C to 100°C.

[0016] Furthermore, in another desirable embodiment of the method for producing a mold according to the present invention, a packing improver is further added when the refractory aggregate and the water-soluble binder are mixed together, and the packing improver is contained in the resulting wet coated sand.

[0017] Furthermore, in another preferred embodiment of the method for producing a mold according to the present invention, a moisture resistance improving agent is further added when the refractory aggregate and the water-soluble binder are mixed together, so that the moisture resistance improving agent is contained in the resulting wet coated sand.

[0018] According to yet another preferred embodiment of the method for producing a mold according to the present invention, the wet coated sand has a moisture content of more than 55 mass % relative to the solid content of the water-soluble binder.

[0019] Additionally, in the present invention, a soluble silicate compound is preferably used as the water-soluble binder. [Effects of the Invention]

[0020] As described above, in the method for manufacturing a mold according to the present invention, wet coated sand is obtained by mixing a water-soluble binder such as water glass as a binder with refractory aggregate, and is formed in a heated state.The wet coated sand is then filled into a predetermined preheated mold under such heated conditions, and molding is carried out.This makes it possible to mold while maintaining a stable humidity, which not only advantageously ensures the uniformity of the wet coated sand, but also effectively reduces the viscosity of the binder present on the surface of the refractory aggregate, thereby advantageously enhancing its effectiveness as a binder.In particular, since the heat capacity of the refractory aggregate is high, it is possible to mold while minimizing temperature drops in the coated sand, thereby advantageously achieving the desired effects. Thus, according to the present invention, not only can the bending strength and moisture resistance of the resulting mold be effectively improved, but also the scratch hardness of the mold can be advantageously improved, making it possible to industrially advantageously produce molds with excellent mold characteristics. DETAILED DESCRIPTION OF THE INVENTION

[0021] Coated sand (mold material) obtained by mixing refractory aggregate and a water-soluble binder is classified into dry coated sand and wet coated sand depending on its state after preparation. The present invention focuses on wet coated sand, in which the water-soluble binder has developed adhesive properties and the overall appearance is wet. This wet coated sand is then filled into a mold (molding cavity), for example, and heated and dried there, causing a solidification or hardening reaction to occur, thereby forming the desired mold. Whether coated sand is dry or wet depends on the moisture content relative to the solid content of the water-soluble binder in the coated sand. However, the moisture content at which the coated sand is dry or wet varies depending on the type of water-soluble binder. However, in general, coated sand containing moisture in an amount equivalent to 5 to 55 mass % of the solid content of the water-soluble binder will be in a dry state, while coated sand containing moisture in an amount equivalent to more than 55 mass % of the solid content of the water-soluble binder will be in a wet state.

[0022] Wet coated sand according to the present invention is coated sand that does not have flowability at room temperature and for which the dynamic angle of repose cannot be measured, regardless of its moisture content. Here, the dynamic angle of repose is measured by placing coated sand in a cylinder whose axial end is closed with a transparent plate (for example, a container 7.2 cm in diameter x 10 cm in height is filled with coated sand up to half its volume), holding the axis horizontal, and rotating the cylinder at a constant speed (for example, 25 rpm) around the horizontal axis. The angle formed between the slope of the coated sand layer flowing in the cylinder and the horizontal plane is measured. Therefore, coated sand that does not flow in the cylinder in a wet state, and the slope of the coated sand layer does not form a flat surface, and therefore the dynamic angle of repose cannot be measured, is wet coated sand.

[0023] The refractory aggregate constituting the coated sand described above is a refractory substance that functions as a base material for a mold and can be any of the various granular or powdery refractory materials conventionally used for molds, including silica sand, recycled silica sand, specialty sands such as alumina sand, olivine sand, zircon sand, and chromite sand, slag particles such as ferrochrome slag, ferronickel slag, and converter slag, artificial particles such as alumina particles and mullite particles, and recycled particles thereof, alumina balls, magnesia clinker, etc. Furthermore, these refractory aggregates may be new sand, recycled sand or reclaimed sand that has been used once or multiple times as foundry sand for molding a mold, or a mixed sand obtained by mixing such recycled sand or reclaimed sand with new sand. Such refractory aggregates are generally used with a particle size of about 40 to 130, preferably about 60 to 110, in terms of AFS index.

[0024] Such refractory aggregate is preferably spherical, with a particle shape coefficient of 1.2 or less, more preferably 1.0 to 1.1. Using refractory aggregate with a particle shape coefficient of 1.2 or less improves fluidity and packing, increasing the number of contact points between aggregate particles, thereby reducing the amount of binder and additives required to achieve the same strength. The particle shape coefficient of aggregate used here is generally used as a measure of the external shape of particles and is also called the particle shape index. The closer the value is to 1, the closer the particle is to a spherical shape (perfect sphere). The particle shape coefficient is expressed as a value calculated using sand surface area measured by various known methods. For example, it is calculated by measuring the surface area of ​​actual sand particles per gram using a sand surface area measuring device (manufactured by George Fischer) and dividing this value by the theoretical surface area. The theoretical surface area is the surface area assuming all sand particles are spherical.

[0025] The binder that coats the refractory aggregate as described above is also called a binder, and in the present invention, a water-soluble binder is used. As the water-soluble binder, any known binder, such as inorganic polymers, thermosetting resins, sugars, synthetic polymers, salts, or proteins, can be used, as long as it is water-soluble. These binders may be used alone or in combination of two or more, with inorganic polymers being particularly preferred. These water-soluble binders may also be diluted with water or a solvent before use.

[0026] Examples of inorganic polymers used as such water-soluble binders include water glass, colloidal silica, alkyl silicates, bentonite, cement, etc., with water glass being preferred among these. Water glass is a solution of a soluble silicate compound, and examples of such silicate compounds include sodium silicate, potassium silicate, sodium metasilicate, potassium metasilicate, lithium silicate, ammonium silicate, and their hydrates, such as sodium metasilicate nonahydrate and sodium metasilicate pentahydrate. In particular, sodium silicate (sodium silicate) is advantageously used in the present invention.

[0027] Furthermore, such sodium silicates are usually classified into types 1 to 5 according to the SiO2 / Na2O molar ratio and used. Specifically, sodium silicate No. 1 has a SiO2 / Na2O molar ratio of 2.0 to 2.3, sodium silicate No. 2 has a SiO2 / Na2O molar ratio of 2.4 to 2.6, and sodium silicate No. 3 has a SiO2 / Na2O molar ratio of 2.8 to 3.3. In addition, sodium silicate No. 4 has a SiO2 / Na2O molar ratio of 3.3 to 3.5, and sodium silicate No. 5 has a SiO2 / Na2O molar ratio of 3.6 to 3.8. Of these, sodium silicates No. 1 to No. 3 are also specified in JIS-K-1408. These sodium silicates may be used alone or in combination, and the SiO2 / Na2O molar ratio can be adjusted by mixing. The molar ratio of SiO2 / Na2O is not limited to the range specified by the above-mentioned sodium silicate No. 1 to No. 5, but may be in the range of 0.8 to 4.0, for example.

[0028] To obtain the wet coated sand advantageously used in the present invention, the sodium silicate constituting the water glass used as a binder should have an SiO2 / Na2O molar ratio of generally 1.9 or higher, preferably 2.0 or higher, and more preferably 2.1 or higher. Sodium silicates corresponding to No. 1 and No. 2 in the above-mentioned classification of sodium silicates are particularly advantageously used. These sodium silicates No. 1 and No. 2, respectively, provide stable wet coated sand with good properties even over a wide range of sodium silicate concentrations in the water glass. The upper limit of the SiO2 / Na2O molar ratio in such sodium silicates is appropriately selected depending on the properties of the water glass in the form of an aqueous solution, but is generally 3.5 or lower, preferably 3.2 or lower, and more preferably 2.7 or lower.

[0029] The water glass used in the present invention refers to a solution of a silicate compound dissolved in water, and may be used in the form of a stock solution purchased on the market, or in a diluted form obtained by adding water to the stock solution. The solid content (water glass component) remaining after excluding volatile substances such as water and solvents from the water glass is called the non-volatile content, and this corresponds to the soluble silicate compounds such as sodium silicate described above. The higher the proportion of the non-volatile content (solid content), the higher the concentration of silicate compounds in the water glass. Therefore, when the water glass is composed solely of the stock solution, the non-volatile content of the water glass used in the present invention corresponds to the proportion excluding the water content of the stock solution. On the other hand, when a diluted solution obtained by diluting the stock solution with water is used, the non-volatile content of the water glass used corresponds to the amount remaining after excluding the water content of the stock solution and the amount of water used for dilution.

[0030] The non-volatile content in the water glass is determined in an appropriate proportion depending on the type of water glass component (soluble silicate compound), etc., but is preferably contained in a proportion of 20 to 50 mass %. By allowing an appropriate amount of water glass component corresponding to this non-volatile content to be present in the aqueous solution, the water glass component can be evenly and uniformly coated on the refractory aggregate when mixed (kneaded) with the refractory aggregate, thereby making it possible to advantageously mold the desired mold according to the present invention.

[0031] Thermosetting resins, which are water-soluble binders other than the inorganic polymers mentioned above, include resol-type phenolic resins, furan resins, water-soluble epoxy resins, water-soluble melamine resins, water-soluble urea resins, water-soluble unsaturated polyester resins, and water-soluble alkyd resins. It is also advantageous to incorporate curing agents such as acids or esters into these thermosetting resins to improve their thermosetting properties. Among these thermosetting resins, resol-type phenolic resins are preferred, and such phenolic resins can be prepared by reacting phenols with formaldehyde in the presence of a reaction catalyst. In the present invention, water-soluble alkaline resol resins are preferred as such phenolic resins. The use of such alkaline resol resins can provide molds that can be used in a wide range of fields, including cast iron and cast steel.

[0032] Other types of sugars, such as water-soluble binders, can include known monosaccharides, oligosaccharides, and polysaccharides. These can be used alone or in combination. Examples of monosaccharides include glucose, fructose, and galactose. Examples of oligosaccharides include disaccharides such as maltose, sucrose, lactose, and cellobiose. Examples of polysaccharides include starch sugar, dextrin, xanthan gum, curdlan, pullulan, cycloamylose, chitin, cellulose, and starch. Other examples include gums derived from plant mucilages, such as gum arabic. Carboxylic acids can also be used as hardeners for sugars, particularly polysaccharides.

[0033] Furthermore, examples of synthetic polymers that can be used as water-soluble binders include polyethylene oxide, poly-α-hydroxyacrylic acid, acrylic acid copolymers, acrylic acid ester copolymers, methacrylic acid ester copolymers, polyacrylamide, anionic polyacrylamide, cationized polyacrylamide, polyaminoalkyl methacrylate, acrylamide / acrylic acid copolymers, polyvinyl sulfonic acid, polystyrene sulfonic acid, sulfonated maleic acid polymers, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene glycol, polyvinyl methyl ether, polyether-modified silicone, polyvinyl acetate, and modified products thereof. These can be used alone or in combination.

[0034] Furthermore, the salts used are those that solidify when added with water and then dried, and examples thereof include sulfates such as magnesium sulfate and sodium sulfate, bromides such as sodium bromide and potassium bromide, carbonates such as sodium carbonate and potassium carbonate, chlorides such as barium chloride, sodium chloride, potassium chloride, etc. In addition, examples of proteins include gelatin, glue, etc.

[0035] The water-soluble binder is preferably used in an amount of 0.1 to 5 parts by mass, calculated as solids content (considering only nonvolatile content), per 100 parts by mass of refractory aggregate. A ratio of 0.2 to 2.5 parts by mass is particularly advantageous, forming a desired coating layer on the surface of the refractory aggregate. The solids content is measured as follows: 10 g of sample is weighed and placed in an aluminum foil sample dish (length: 90 mm, width: 90 mm, height: 15 mm). The dish is placed on a heating plate maintained at 180±1°C and left for 20 minutes. The dish is then inverted and left on the heating plate for another 20 minutes. The sample dish is then removed from the heating plate, allowed to cool in a desiccator, and weighed. The solids content (% by mass) is calculated using the following formula: Solid content (mass%) = {[mass of sample dish after drying (g) - mass of sample dish only (g)] / [Weight of sample dish before drying (g) - Weight of sample dish only (g)]} × 100

[0036] If the amount of water-soluble binder used is too small, it becomes difficult to form a coating layer on the surface of the refractory aggregate, which makes it difficult to solidify or harden the coated sand sufficiently. On the other hand, if the amount of water-soluble binder used is too large, excess water-soluble binder will adhere to the surface of the refractory aggregate, making it difficult to form a uniform coating layer, and there is also the risk that the coated sand will stick to each other and form agglomerates (composite particles), which will have an adverse effect on the mold properties and make it difficult to remove the sand from the core after the metal has been cast.

[0037] The present invention is directed to wet coated sand, which is formed by using the above-mentioned water-soluble binder to form a coating layer on the surface of refractory aggregate. Such a coating layer can contain known additives as needed. To incorporate such additives into the coating layer, various methods can be used, such as blending the additives with the water-soluble binder beforehand and then kneading or mixing them with the refractory aggregate, or adding the additives separately from the water-soluble binder to the refractory aggregate and then kneading or mixing the whole together with the water-soluble binder. The water-soluble binder and additives can be kneaded or mixed simultaneously or with a time lag.

[0038] In the present invention, a filler improver is advantageously used as one such additive. Such a filler improver is particulate, and when present on the particle surfaces of the resulting coated sand—in other words, on the surface of the water-soluble binder layer that coats the refractory aggregate—when the coated sand is fluidized to fill a mold (die), particles of the coated sand come into contact with each other via the filler improver. This effectively reduces friction between the coated sand particles, advantageously improving the fluidity of the coated sand. This also advantageously improves the packing of the coated sand into the mold and prevents the coated sand from adhering to molding equipment such as the mold. Examples of filler improvers include spherical silicone resin powders (particles) and inorganic oxide particles, with spherical silicone resin powders (particles) being particularly advantageously used.

[0039] The term "spherical" in this spherical silicone resin powder refers to a generally recognized spherical shape, and does not necessarily require a perfect sphere, but particles with a sphericity of 0.5 or more are usually used, preferably 0.7 or more, and more preferably 0.9 or more are advantageously used. Here, the sphericity refers to the average value of the aspect ratio (ratio of minor axis / major axis) obtained from the projected shape of 10 randomly selected single particles observed using a scanning electron microscope.

[0040] Furthermore, such spherical silicone resin powder has a particle size smaller than that of the refractory aggregate, and its average particle size is generally 0.01 μm to 50 μm, preferably 0.05 μm to 25 μm, more preferably 0.1 μm to 10 μm, and even more preferably 0.2 μm to 3 μm. Because spherical silicone resin powder with such an average particle size has a smaller particle size than the refractory aggregate to be mixed with, it can easily penetrate between the refractory aggregate, be uniformly dispersed, and be uniformly distributed on the particle surfaces of the coated sand.

[0041] Furthermore, the amount of such spherical silicone resin powder used is 0.1 to 500 parts by mass, preferably 0.3 to 300 parts by mass, more preferably 0.5 to 200 parts by mass, even more preferably 0.75 to 100 parts by mass, and most preferably 1 to 50 parts by mass, per 100 parts by mass of the solid content of the water-soluble binder constituting the coating layer on the surface of the refractory aggregate. Thus, by incorporating a predetermined proportion of spherical silicone resin powder having a predetermined average particle size into the water-soluble binder coating layer on the surface of the refractory aggregate, the effects of the present invention can be more effectively achieved. The average particle size of the silicone resin powder can be determined from the particle size distribution measured using a laser diffraction particle size distribution analyzer or the like.

[0042] The spherical silicone resin powder described above is not particularly limited as long as it is spherical and has binder repellency, and various known silicone resin particles may be appropriately selected and used. Preferably, the silicone resin is primarily composed of an organopolysiloxane, and more preferably, the organopolysiloxane is silsesquioxane. Furthermore, it is particularly desirable that the silsesquioxane is polymethylsilsesquioxane. By using a silsesquioxane as the organopolysiloxane constituting the spherical silicone resin powder, and by using a polymethylsilsesquioxane as the silsesquioxane, spherical particles having effective binder repellency, a high silicon content, and excellent heat resistance can be obtained. By imparting such properties, thermal decomposition or melting due to the heat generated during mold making is unlikely to occur, and the spherical shape can be advantageously maintained even during molding and casting, thereby advantageously maintaining the effects of improved packing properties and strength. In addition, odors and smoke generated during molding can be suppressed, so that the effects of preventing sand adhesion and improving the casting surface can be even more advantageously exerted during casting.

[0043] The inorganic oxide particles may be spherical or non-spherical, but spherical particles are preferred because they enable the production of cast products with a better casting surface. The material constituting the inorganic oxide particles is not particularly limited, but inorganic metal oxides are preferred. Particles made of such inorganic metal oxides are advantageously made of silicon dioxide, aluminum oxide, titanium oxide, or the like. Silicon dioxide can be crystalline or amorphous, with amorphous being preferred. Examples of amorphous silicon dioxide include precipitated silica, calcined silica produced in an electric arc or by flame hydrolysis, silica produced by thermal decomposition of ZrSiO4, silicon dioxide produced by oxidizing metallic silicon with an oxygen-containing gas, and quartz glass powder, which is spherical particles produced from crystalline quartz by melting and subsequent rapid cooling. The spherical shape, average particle size, and range of use of such inorganic oxide particles are similar to those of the spherical silicone resin powder described above.

[0044] Furthermore, in the present invention, it is preferable that a moisture resistance improver be used as an additive together with or separately from the fillability improver as described above. By incorporating a moisture resistance improver into the coated sand in this way, it is possible to further improve the moisture resistance of the final mold obtained.

[0045] Here, any of the moisture resistance improvers conventionally used in coated sand can be used as long as they do not impair the effects of the present invention. Specifically, carbonates such as zinc carbonate, basic zinc carbonate, iron carbonate, manganese carbonate, copper carbonate, aluminum carbonate, barium carbonate, magnesium carbonate, calcium carbonate, lithium carbonate, potassium carbonate, and sodium carbonate; borates such as sodium tetraborate, potassium tetraborate, lithium tetraborate, ammonium tetraborate, calcium tetraborate, strontium tetraborate, silver tetraborate, sodium metaborate, potassium metaborate, lithium metaborate, ammonium metaborate, calcium metaborate, silver metaborate, copper metaborate, lead metaborate, and magnesium metaborate; sodium sulfate, potassium sulfate, lithium sulfate, magnesium sulfate; sulfuric acid; Examples of suitable additives include sulfates such as calcium, strontium sulfate, barium sulfate, titanium sulfate, aluminum sulfate, zinc sulfate, and copper sulfate; phosphates such as sodium phosphate, sodium hydrogen phosphate, potassium phosphate, potassium hydrogen phosphate, lithium phosphate, lithium hydrogen phosphate, magnesium phosphate, calcium phosphate, titanium phosphate, aluminum phosphate, and zinc phosphate; hydroxides such as lithium hydroxide, magnesium hydroxide, calcium hydroxide, strontium hydroxide, barium hydroxide, aluminum hydroxide, and zinc hydroxide; and oxides of silicon, zinc, magnesium, aluminum, calcium, lithium, copper, iron, boron, and zirconium. Among these, basic zinc carbonate, sodium tetraborate, potassium metaborate, lithium sulfate, and lithium hydroxide can more effectively improve moisture resistance when water glass is used as the water-soluble binder. The moisture resistance improvers described above can be used alone, or two or more can be used in combination. The moisture resistance improving agents listed above include compounds that can be used as water-soluble binders, and such compounds can act as moisture resistance improving agents when a different water-soluble binder is used.

[0046] The amount of the moisture resistance improving agent used is generally preferably about 0.5 to 50 parts by mass, more preferably 1 to 20 parts by mass, and even more preferably 2 to 15 parts by mass, relative to 100 parts by mass of the solid content of the liquid water-soluble binder. To obtain the full effect of adding the moisture resistance improving agent, it is desirable to use an amount of 0.5 parts by mass or more. However, if the amount added is too large, it may hinder the bonding of the water-soluble binder and cause problems such as a decrease in the strength of the final mold obtained, so it is desirable to use an amount of 50 parts by mass or less.

[0047] It is also effective to add a coupling agent to strengthen the bond between the refractory aggregate and the water-soluble binder, such as a silane coupling agent, a zirconium coupling agent, or a titanium coupling agent. It is also effective to add a lubricant to improve the fluidity of the coated sand, such as waxes (e.g., paraffin wax, synthetic polyethylene wax, or montanic acid wax); fatty acid amides (e.g., stearic acid amide, oleic acid amide, or erucic acid amide); alkylene fatty acid amides (e.g., methylene bis-stearic acid amide or ethylene bis-stearic acid amide); stearic acid, stearyl alcohol; metal stearates (e.g., lead stearate, zinc stearate, calcium stearate, or magnesium stearate); stearic acid monoglyceride, stearyl stearate, or hydrogenated oil. Furthermore, release agents that can be used include paraffin, wax, light oil, machine oil, spindle oil, insulating oil, waste oil, vegetable oil, fatty acid ester, organic acid, graphite fine particles, mica, vermiculite, fluorine-based release agents, silicone-based release agents, etc. These other additives are generally contained in an amount of 5% by mass or less, and preferably 3% by mass or less, based on the non-volatile components in the water-soluble binder.

[0048] In the present invention, when producing wet coated sand that does not have room temperature fluidity using the above-mentioned refractory aggregate, water-soluble binder, and optionally added additives, either of the following methods (a) or (b) is adopted. That is, method (a) is a method in which the refractory aggregate is heated, then charged into a mixer, which is a mixing device, and kneaded with the water-soluble binder to coat the surface of the refractory aggregate with the water-soluble binder. Method (b) is a method in which the refractory aggregate at room temperature is charged into a mixer, heated while being kneaded in the mixer, and then a water-soluble binder is added and kneaded with the heated refractory aggregate to coat the surface of the refractory aggregate with the water-soluble binder.

[0049] Specifically, in the above method (a), the refractory aggregate is heated and then charged into a suitable mixer (mixing device), and the water-soluble binder is added to the mixer together with optional additives, and the mixture is kneaded or mixed in the same manner as in the conventional method to achieve a uniform mixture and to coat the surface of the refractory aggregate with the water-soluble binder. The heating temperature of the refractory aggregate is appropriately selected so as to avoid evaporation of the water in the water-soluble binder and to obtain wet coated sand with the desired moisture content, but it is generally desirable to heat the refractory aggregate to a temperature of 32°C to 150°C, preferably 35°C to 120°C, and more preferably 40°C to 110°C. Furthermore, any method can be used to heat the refractory aggregate as long as it can heat the refractory aggregate to a predetermined temperature. However, preferred methods include a heating method using a thermostatic chamber and a heating method using a temperature control unit as described in JP 2001-321886 A, JP 2009-142830 A, and International Publication No. WO2010 / 143746 A.

[0050] In the above-mentioned method (b), room-temperature refractory aggregate is introduced into a mixer, and the refractory aggregate is heated while being mixed (stirred) in the mixer. Then, a water-soluble binder is added to the mixer and mixed with the heated refractory aggregate, thereby coating the surface of the refractory aggregate with the water-soluble binder. The heating temperature of the refractory aggregate in the mixer prior to the addition of the water-soluble binder is appropriately selected, as in the above-mentioned method (a), to avoid excessive evaporation of the water in the water-soluble binder and to obtain wet coated sand with the desired moisture content. Generally, a temperature of 32°C to 150°C is desirable. If the heating temperature is too low, it becomes difficult to obtain effectively wet coated sand. If the heating temperature is too high, the coated sand may dry out, and uniform wetting may become difficult.

[0051] The mixer used to mix the refractory aggregate and water-soluble binder as described above is one that can sufficiently agitate and mix (knead) the refractory aggregate to be fed and, if necessary, is equipped with a heating means such as a heater or a circulating heat medium, or a means for blowing hot air, etc., to heat the refractory aggregate being mixed. Heating the refractory aggregate to a predetermined temperature in such a mixer generally takes about 0.5 to 30 minutes, preferably about 1 to 15 minutes, and more preferably about 3 to 10 minutes. Mixing the refractory aggregate heated to the predetermined temperature with the water-soluble binder to form wet coated sand generally takes about 0.5 to 15 minutes, preferably about 1 to 10 minutes, and more preferably about 1.5 to 5 minutes.

[0052] Furthermore, in the above-mentioned mixing and heating operation of the refractory aggregate or the mixing operation of the refractory aggregate with the water-soluble binder, it is desirable that the mixer (mixing device) be preheated before the refractory aggregate is charged. Any configuration is acceptable as long as it is capable of preheating to the predetermined temperature. Specifically, the mixer is heated using a heating means such as a heater or a circulating heat medium provided in the mixer or a blowing means such as hot air, so that the preheat temperature of the wall surface that comes into contact with the coated sand being mixed in the mixer is about 32°C to 150°C, preferably about 35°C to 120°C, and more preferably about 40°C to 110°C in the case of the above-mentioned method (a), or about 50°C to 200°C, preferably about 55°C to 180°C, and more preferably about 60°C to 150°C in the case of method (b). This allows the added refractory aggregate to be heated and the heated refractory aggregate to be mixed with the water-soluble binder efficiently and quickly, thereby advantageously achieving the object of the present invention.In the above-mentioned method (a), it is also effective to preheat the wall surface of the mixer that comes into contact with the coated sand when mixing the heated refractory aggregate in the mixer.

[0053] Furthermore, it is desirable that the water-soluble binder added to the mixer for mixing with the refractory aggregate be preheated to a temperature below its boiling point, generally within the range of 30°C to 100°C, preferably 35°C to 90°C, and more preferably 40°C to 80°C. By incorporating such a preheated water-soluble binder into the heated refractory aggregate, a coating layer made of the water-soluble binder can be effectively formed on the surface of the refractory aggregate, thereby more effectively achieving the effects of the present invention. By adopting such a mixing method, the viscosity of the water-soluble binder can be maintained low, and when the spherical silicone resin powder used as an additive is mixed, it is easily exposed to the surface of the wet coated sand, thereby more effectively achieving the effects of adding the silicone resin powder.

[0054] The wet coated sand thus obtained, which does not have room-temperature fluidity, can have its moisture content adjusted appropriately to the extent that it remains wet. Generally, the moisture content is adjusted to more than 55% by mass, preferably 70 to 900% by mass, and more preferably 95 to 500% by mass, relative to the solid content of the water-soluble binder. Wet coated sand adjusted to such a moisture content effectively prevents drying and obstruction of filling into the mold when blown air is used to fill the mold during molding, while maintaining the wetness of the wet coated sand. In addition, molds molded using such coated sand are endowed with excellent properties.

[0055] In the manufacturing process of wet coated sand according to the present invention, various additives used as needed can be added simultaneously with the refractory aggregate and water-soluble binder and kneaded or mixed, or they can be added separately during the kneading process, or they can be kneaded at different times during the kneading process. The water-soluble binder used as a binder is kneaded with the refractory aggregate in the form of an aqueous solution. However, if the water-soluble binder itself is normally solid, it is used in a water-dissolved state. Liquid water-soluble binders can also be diluted with water to adjust their viscosity. The water can be mixed with the water-soluble binder in advance, or the water and water can be added separately during the kneading or mixing process with the refractory aggregate.

[0056] In the present invention, the wet coated sand formed as described above is removed from the mixer and heated, specifically at a temperature of about 30°C to 100°C, preferably 35°C to 90°C, and more preferably 40°C to 80°C. While maintaining this heated state, the wet coated sand is filled into a preheated mold, specifically the molding cavity of the mold, and the wet coated sand is dried and solidified or hardened, thereby effectively improving the properties of the resulting mold. That is, the wet coated sand removed from the mixer in a heated state, particularly at a temperature of 30°C to 100°C, is filled into a preheated mold while still heated to that temperature, so that heat can be effectively transferred to the filled wet coated sand, which advantageously promotes uniform heat transfer and achieves stable mold strength. In addition, the moisture resistance of the mold and the scratch hardness can also be advantageously improved.

[0057] Here, filling a mold with wet coated sand while maintaining its heated state means that the wet coated sand removed from the mixer is in a heated state, particularly at a temperature of 30°C to 100°C, and the wet coated sand is maintained at a temperature within this range, in other words, is filled into a predetermined mold while maintaining a temperature of 30°C or higher. If the temperature of the wet coated sand removed from the mixer falls below 30°C, it becomes difficult to prevent uneven heat transfer in the mold. On the other hand, if the temperature exceeds 100°C, a large amount of water will evaporate from the wet coated sand, and this evaporation will increase the viscosity of the water-soluble binder, resulting in problems such as an insufficient adhesive surface area for the binder and a decrease in strength.

[0058] Furthermore, when the wet coated sand filled in the mold is dried and solidified or cured to form the desired mold, a preheated mold is advantageously used to facilitate drying of the wet coated sand. By using this preheated mold, the drying of the filled wet coated sand can be effectively promoted, thereby advantageously shortening the molding time. The heating temperature for such a mold is generally within the range of 40°C to 250°C, preferably 70°C to 200°C, and more preferably 100°C to 175°C. If the heating temperature is less than 40°C, it is difficult to fully utilize the drying-accelerating effect of heating, resulting in a problem of a longer molding time. On the other hand, if the temperature is higher than 250°C, the wet coated sand filled into the mold will solidify or harden too quickly, resulting in a deterioration in its filling properties. In addition, the wet coated sand will dry out too much, losing its stickiness and reducing its adhesive effect, which will result in a decrease in the strength of the resulting mold.

[0059] In order to accelerate the drying of the wet coated sand filled in the mold, it is also effective to directly heat the filled wet coated sand with microwaves, and this is particularly suitable when the casting mold is a resin mold. Furthermore, it is also effective to pass heated or dry air through the mold filled with wet coated sand, thereby accelerating the drying and more rapidly solidifying or hardening the filled wet coated sand. In addition, vacuum drying of the mold filled with wet coated sand by vacuum suction is also an effective drying method, and this is particularly advantageous when the mold is made of a material that is easily affected by heat, such as a resin mold.

[0060] Furthermore, in the present invention, as described above, the desired mold is produced by removing the water content of the aqueous medium used to wet the coated sand packed into the mold. In this process, the water glass that forms the coating layer on the surface of the coated sand usually solidifies by evaporating the water to dryness if no additives are added, and hardens if an oxide, salt, or other hardening agent is added. To harden the water glass, it is also effective to pass carbon dioxide gas or an organic ester gas through the mold packed with the wet coated sand. This allows the water glass to harden rapidly, as in the conventional method, and advantageously increases the molding speed. As the organic ester gas, for example, methyl formate, ethyl formate, propyl formate, γ-butyrolactone, β-propiolactone, ethylene glycol diacetate, diethylene glycol diacetate, glycerin diacetate, triacetin, propylene carbonate, or the like may be used in a gaseous or atomized form.

[0061] In accordance with the present invention, a refractory aggregate and a water-soluble binder are heated and kneaded to form a coated sand in a predetermined wet state, which is then filled into a preheated mold under heated conditions to form a mold. Any of a variety of known molding techniques may be suitably employed, and the desired mold can be produced industrially advantageously.

[0062] Although the embodiments of the present invention have been described in detail above, they are merely examples, and the present invention should not be construed as being limited in any way by the specific descriptions of such embodiments. The present invention can be embodied in various forms, with various changes, modifications, improvements, etc. added based on the knowledge of those skilled in the art, and it goes without saying that all such embodiments belong to the scope of the present invention as long as they do not deviate from the spirit of the present invention. [Example]

[0063] The present invention will be further clarified using several examples below, but it should be understood that the present invention is not to be construed in any way as being limited by the description of such examples. In the following examples and comparative examples, "%" and "parts" are all expressed on a mass basis unless otherwise specified. The bending strength and scratch hardness of the molds obtained in the examples and comparative examples were measured as follows.

[0064] - Bending strength (kgf / cm 2 ) Measurement - The breaking load of a test piece measuring 25.4 mm in width x 25.4 mm in height x 200 mm in length, which was molded using the wet coated sand obtained in the Examples and Comparative Examples, was measured using a measuring device (a digital foundry sand strength tester manufactured by Takachiho Seiki Co., Ltd.), and the bending strength (transverse strength) was calculated using the breaking load obtained by the measurement according to the following formula. Bending strength = 1.5 x LW / ab 2 [where L: distance between supports (cm), W: breaking load (kgf), a: width of test piece (cm), b: thickness of test piece (cm)] The bending strength was measured on the molds immediately after molding, and also on molds that had been kept in an environment of 23°C x 60% RH for 1 hour or 24 hours after molding. The strength retention rate was calculated using the ratio of the bending strength obtained 24 hours after molding to the bending strength obtained 1 hour after molding, and the moisture resistance of the resulting molds was evaluated.

[0065] -Scratch hardness (mm) measurement- Test pieces measuring 25.4 mm wide x 25.4 mm high x 200 mm long were molded using the wet coated sand obtained in the Examples and Comparative Examples. The test pieces were then stored in an environment of 23°C and 60% RH for one hour after molding. The scratch hardness was measured using a GF-type scratch hardness tester (n=3, average value). Specifically, the scratch hardness was measured by first pressing the tip of the scratch hardness tester against the surface of the test piece, then rotating the black lever on the top clockwise once, then counterclockwise once, and repeating this rotation five times until the teeth gradually sink into the surface. The depth of the teeth sinking into the surface was then read from the scale (mm) on the side. A smaller measured value indicates a higher scratch hardness, while a larger measured value indicates a lower scratch hardness.

[0066] -Example of mold making- Example 1 The refractory aggregate was prepared using Espearl #60L (Yamakawa Sangyo Co., Ltd.), a commercially available artificial sand for casting. The binder (water-soluble binder) was also prepared using commercially available No. 2 sodium silicate (Fuji Chemical Co., Ltd., SiO / NaO molar ratio: 2.5, solids content: 35%). One hundred parts of the Espearl #60L was heated to approximately 58°C and then placed in a Shinagawa-type universal mixer (Model 5DM-r, Dalton Co., Ltd.). 1.0 part of the water glass was added and mixed to obtain wet coated sand (WCS), which does not have free flow at room temperature. The moisture content of the WCS was measured and found to be 180% of the water glass solids content in the WCS.

[0067] The wet coated sand obtained was then removed from the Shinagawa-type universal mixer at a temperature of about 50°C, and while still heated, was immediately blown into a molding die preheated to 150°C at a gauge pressure of 0.3 MPa to fill the space. After holding for 30 seconds, hot air at about 150°C was blown into the sand for 30 seconds to dry and solidify it. After that, the sand was removed from the molding die to obtain a mold as a test piece.

[0068] Example 2 A WCS with a moisture content of 182% was obtained in the same manner as in Example 1, except that 0.05 parts of Tospearl 120 (trade name: manufactured by Momentive Performance Materials Japan, LLC), which is a spherical silicone resin particle, was added and kneaded together with the water glass as a filler improver, which is an additive used if necessary, the heating temperature of the refractory aggregate was set to about 35°C, and the temperature at which it was removed from the Shinagawa-type universal mixer was set to about 30°C. Then, using this WCS, molding was carried out in the same manner as in Example 1 while maintaining the removal temperature, and molds were obtained as test pieces.

[0069] Example 3 In Example 2, a WCS with a moisture content of 180% was formed in the same manner as in Example 2, except that the heating temperature of the refractory aggregate fed into the Shinagawa-type universal mixer was set to about 58°C and the temperature at which it was removed from the mixer was set to about 50°C.After removing it from the mixer, molding was carried out in the same manner as in Example 2 while it was still heated, without cooling, to obtain a mold as a test piece.

[0070] Example 4 In Example 2, a WCS with a moisture content of 177% was obtained in the same manner as in Example 2, except that the heating temperature of the refractory aggregate was set to about 80°C and the temperature at which the wet coated sand was removed from the mixer was set to about 70°C. Then, using this WCS, molding was carried out in the same manner as in Example 2 while maintaining the removal temperature, and a mold was obtained as a test piece.

[0071] Example 5 In Example 2, a WCS with a moisture content of 175% was obtained in the same manner as in Example 2, except that the heating temperature of the refractory aggregate was set to about 100°C and the temperature at which the wet coated sand was removed from the mixer was set to about 90°C. Then, using this WCS, a mold was obtained as a test piece in the same manner as in Example 2, while maintaining the removal temperature.

[0072] Example 6 A WCS with a moisture content of 180% was prepared in the same manner as in Example 3, except that the water glass was preheated to a temperature of about 50°C before being added to the Shinagawa-type universal mixer. After removing the WCS from the mixer, molding was carried out in the same manner as in Example 3 without cooling it, while still in the heated state, to obtain a mold as a test piece.

[0073] Example 7 In Example 3, a WCS having a moisture content of 181% was obtained in the same manner as in Example 3, except that 0.10 parts of zinc carbonate, a moisture resistance improving agent, was added as an additive. Then, using this WCS, a mold as a test piece was obtained in the same manner as in Example 3, while maintaining the removal temperature.

[0074] (Comparative Example 1) In Example 1, wet coated sand with a moisture content of 184% was formed in the same manner as in Example 1, except that the fire-resistant aggregate, Espearl #60L, was not heated but was instead placed in a Shinagawa-type universal mixer at room temperature.Then, the resulting WCS was filled into a molding die at room temperature in the same manner as in Example 1 to prepare a mold as a test piece.

[0075] (Comparative Example 2) In Example 2, molding was carried out in the same manner as in Example 2, except that the Espearl #60L refractory aggregate was not heated, and therefore the wet coated sand (moisture content: 184%) taken out of the Shinagawa-type universal mixer was at room temperature, and molds were produced as test pieces.

[0076] -Evaluation of mold properties- The bending strength and scratch hardness of each of the molds (test pieces) obtained in Examples 1 to 7 and Comparative Examples 1 and 2 were measured according to the methods described above, and the results are shown in Tables 1 and 2 below.

[0077] [Table 1]

[0078] [Table 2]

[0079] As is clear from the results in Tables 1 and 2, the molds (test pieces) of Examples 1 to 7, which were obtained by heating refractory aggregate (Espearl #60L) to form wet coated sand (WCS) in a heated state using a preheated molding die, have excellent bending strength and scratch hardness, and are also excellent in moisture resistance and strength retention over time.

[0080] In contrast, as shown in Comparative Examples 1 and 2, in the case of molds made using wet coated sand obtained by using a refractory aggregate (Espearl #60L) without preheating, or using wet coated sand that was subsequently heated, the bending strength immediately after molding was low, and the bending strength was insufficient even 1 hour and 24 hours after molding, and the strength retention rate after moisture absorption was also poor.Furthermore, it was found that the scratch hardness of the molds 1 hour after molding was also insufficient.

[0081] Example 8 A Shinagawa-type universal mixer (5DM-r type) had been previously blasted with hot air at 200°C until the wall temperature (average of measurements taken at five points on the inner wall) reached approximately 50°C. One hundred parts of Espearl #60L, a refractory aggregate, was then added at room temperature. While continuing to blast with hot air, the mixer was mixed for five minutes to heat the Espearl #60L. After this, 1.0 part of commercially available No. 2 sodium silicate (SiO2 / Na2O molar ratio: 2.5, solid content: 35%) was added as water glass to be used as a binder (water-soluble binder). The mixture was then blasted for another two minutes to obtain wet coated sand (WCS) with a moisture content of 182% and no room-temperature fluidity.

[0082] Next, the WCS was removed from the Shinagawa-type universal mixer at a temperature of approximately 30°C, and while still heated, it was immediately blown into a mold preheated to 150°C at a gauge pressure of 0.3 MPa to fill it, and after holding for 30 seconds, hot air at approximately 120°C was blown into it for 30 seconds to dry and solidify it.After that, it was removed from the mold to obtain a mold as a test piece.

[0083] Example 9 In Example 8, a WCS with a moisture content of 180% was formed in the same manner as in Example 1, except that the preheating temperature of the inner wall surface of the Shinagawa-type universal mixer was set to approximately 70°C, the heating and kneading time was set to 6 minutes (an additional 2 minutes after adding water glass), and the temperature at which it was removed from the mixer was set to approximately 50°C.After removing it from the mixer, molding was carried out in the same manner as in Example 1 without cooling it, while still in the heated state, to obtain a mold as a test piece.

[0084] Example 10 In Example 1, a WCS with a moisture content of 177% was formed in the same manner as in Example 1, except that the preheating temperature of the inner wall surface of the Shinagawa-type universal mixer was set to approximately 90°C, the heating and kneading time was set to 7 minutes (an additional 2 minutes after adding water glass), and the temperature at which it was removed from the mixer was set to approximately 70°C.After removing it from the mixer, it was molded in the same manner as in Example 1 without being cooled, while still in the heated state, to obtain a mold as a test piece.

[0085] Example 11 In Example 8, instead of preheating the inner wall surface of the Shinagawa-type universal mixer by blowing hot air, a heat medium at 100°C was circulated through a temperature control device installed in the mixer to heat it, thereby preheating the temperature of the inner wall surface of the mixer to approximately 70°C, and the kneading time was set to 6 minutes (an additional 2 minutes after adding water glass). Except for this, a WCS with a moisture content of 179% was formed in the same manner as in Example 8, and then removed from the mixer while heated to approximately 50°C. Molding was then performed in the same manner as in Example 8 to produce a mold as a test piece.

[0086] (Comparative Example 3) In Example 8, hot air was not blown in (heated), and therefore the inner wall surface of the Shinagawa-type universal mixer was kept at room temperature (20°C), and a WCS with a moisture content of 185% was formed for a mixing time of 2 minutes.The obtained WCS was then filled into a molding die at room temperature in the same manner as in Example 8 to prepare a mold as a test piece.

[0087] -Evaluation of mold properties- The bending strength and scratch hardness of each of the molds (test pieces) obtained in Examples 8 and 9 and Comparative Example 3 were measured according to the methods described above, and the results are shown in Table 3 below.

[0088] [Table 3]

[0089] As is clear from the results in Table 3, the molds (test pieces) of Examples 8 to 11, which were obtained by heating and stirring room-temperature refractory aggregate in a Shinagawa-type universal mixer, adding water glass as a water-soluble binder, and kneading the mixture to obtain wet coated sand (WCS), were molded in a preheated molding die while still heated, and were found to have excellent properties in terms of bending strength and scratch hardness.

[0090] In contrast, as shown in Comparative Example 3, in the case of a mold made from wet coated sand (WCS) formed by kneading refractory aggregate with water glass as a binder at room temperature without preheating, both bending strength and scratch hardness were found to be insufficient.

Claims

1. A method for producing a mold, comprising heating refractory aggregate to a temperature of 32°C to 150°C, kneading the refractory aggregate with a water-soluble binder comprising an aqueous solution of a soluble silicate compound, thereby forming wet coated sand in which the surface of the refractory aggregate is coated with the water-soluble binder, and heating the sand to a temperature of 30°C to 100°C. The wet coated sand in the heated state is then filled into a predetermined preheated mold to produce a mold.

2. A method for producing a mold, comprising the steps of: kneading refractory aggregate at room temperature while heating it to a temperature of 32°C to 150°C; adding a water-soluble binder consisting of an aqueous solution of a soluble silicate compound; kneading the mixture with the heated refractory aggregate; and forming wet coated sand in which the surface of the refractory aggregate is coated with the water-soluble binder under heating at 30°C to 100°C; and then filling the wet coated sand in the heated state into a predetermined preheated mold to produce a mold.

3. 3. The method for manufacturing a mold according to claim 1, wherein a filler improver is further added when the refractory aggregate and the water-soluble binder are kneaded together, so that the filler improver is contained in the resulting wet coated sand.

4. 4. The method for manufacturing a mold according to claim 1, wherein a moisture resistance improving agent is further added when the refractory aggregate and the water-soluble binder are mixed together, so that the moisture resistance improving agent is contained in the resulting wet coated sand.

5. 5. The method for manufacturing a mold according to claim 1, wherein the wet coated sand has a moisture content exceeding 55% by mass relative to the solid content of the water-soluble binder.

6. 6. The method for manufacturing a casting mold according to claim 1, wherein the mold is heated to a temperature of 40°C to 250°C.

7. 7. The method for producing a mold according to claim 1, wherein the aqueous solution of the soluble silicate compound is water glass.

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