Method for manufacturing a casting mold

Abstract

Provided is a method for industrially advantageously producing a mold having improved mold characteristics such as strength, moisture resistance, and scratch hardness. A dry coated sand obtained by covering the surface of a refractory aggregate with a water-soluble binder is added with an aqueous medium, whereby a wet coated sand is formed in a heated state. The wet coated sand is then filled into a prescribed molding mold that has been preheated while maintaining the heated state of the wet coated sand, and molding is performed.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing molds, and in particular to a method for advantageously manufacturing molds with excellent mold properties. Background Technology

[0002] Traditionally, one type of mold used in casting molten metal employs coated sand (mold material) with a structure in which a specified binder is applied to the surface of refractory aggregate (molding sand), and the mold is shaped into the desired form. Furthermore, in addition to inorganic binders such as water glass, organic binders containing resins such as phenolic resin, furan resin, and urethane resin have been used as binders in this coated sand. Moreover, methods for creating self-hardening molds using these binders have also been put into practical use.

[0003] Furthermore, various methods have been proposed for molding these adhesives, where water-soluble adhesives are used in the form of an aqueous solution and mixed with specified refractory aggregates to form coated sand that covers the surface of the refractory aggregates with the water-soluble adhesive. Additionally, in molding with this type of coated sand, the mold filled with the coated sand is typically preheated to a specified temperature to rapidly cure and harden the coated sand to obtain the desired strength and other properties.

[0004] For example, Japanese Patent Application Publication No. 2012-76115 discloses a method in which dry coated sand with good flowability, made by covering a specified refractory aggregate with water glass as one of the water-soluble binders, is filled into a molding die. Water vapor is blown into the die or water is supplied to wet the binder layer on the surface of the coated sand. Then, it is heated to solidify the sand and a mold of the desired shape is produced. This provides a mold with good flowability, heat resistance and excellent strength.

[0005] However, this method of manufacturing molds has the following potential problems: Since the coated sand is moistened by supplying water vapor or moisture to the mold, the entire coated sand is difficult to moisten uniformly. Therefore, the physical properties of the molded mold vary depending on the location within the mold, becoming uneven. Furthermore, if the dissolution of the water-soluble binder covering the coated sand is insufficient due to the supply of moisture, a concentration difference (binder component concentration difference) arises between the aggregate side of the adhesive layer and the middle part between the aggregates at the bonding portions of the coated sand, thus deteriorating moisture resistance. In particular, this concentration difference is easily caused when using water glass as a binder. Therefore, a large amount of water-soluble sodium is present on the surface of the binder layer, resulting in undissolved silica components remaining on the aggregate side, further worsening moisture resistance. Furthermore, if water vapor or moisture is supplied excessively or unevenly in order to wet the coated sand filling the molding mold, resulting in excessive moisture in certain areas, it will take time to heat and dry and solidify these areas, potentially leading to a longer molding cycle. In addition, if the mold is removed while the coated sand filling layer in the molding mold is not sufficiently dry, the moisture resistance of the mold will deteriorate due to residual moisture.

[0006] In addition, Japanese Patent Publication No. 2012-501850 proposes the following method: using dry coated sand formed by forming a water glass layer on the surface of mineral sand or synthetic sand as refractory aggregate, filling it into a molding die preheated to a temperature of 20°C to 160°C, and then hardening the filled coated sand by blowing in water vapor, thereby shaping the target mold.

[0007] Furthermore, the molding method described above has the following potential problems: Since the coated sand filled into the mold is usually provided at room temperature, if this room-temperature coated sand is filled into a preheated mold for molding, the heat transfer to the filled coated sand can easily become uneven. This leads to uneven curing and / or hardening of the coated sand, resulting in reduced mold strength and difficulty in achieving stable mold properties. Moreover, this room-temperature coated sand also has the following potential problems: Since its temperature is difficult to rise immediately even when filled into a preheated mold, there is a concern about insufficient dissolution of water glass. Consequently, the adhesion between the coated sand particles weakens, making it impossible to fully utilize the mold strength.

[0008] Existing technical documents

[0009] Patent documents

[0010] Patent Document 1: Japanese Patent Application Publication No. 2012-76115

[0011] Patent Document 2: Japanese Patent Publication No. 2012-501850 Summary of the Invention

[0012] The problem the invention aims to solve

[0013] The present invention was made in light of the above-mentioned actual situation. The problem to be solved is to provide a manufacturing method for improving the mold. Another problem is to provide a method for industrially manufacturing molds that can advantageously improve the mold properties such as strength, moisture resistance, and scratch hardness.

[0014] Solution for solving the problem

[0015] Furthermore, in order to solve the above problems, the present invention can be suitably implemented in various ways listed below, and the various ways described below can be combined in any way. It should be noted that the methods and technical features of the present invention are not limited in any way by the following description, and can be understood as technical solutions that can be understood based on the inventive concept that can be grasped from the description as a whole.

[0016] Therefore, in order to solve the aforementioned problems, the first approach adopted by the present invention is a method for manufacturing a casting mold, characterized in that a dry coated sand obtained by covering the surface of refractory aggregate with a water-soluble adhesive is prepared, an aqueous medium is added to it, and it is mixed to form a wet coated sand under heating. The wet coated sand is then filled into a preheated mold while maintaining its heated state for molding.

[0017] It should be noted that, according to the second aspect of the method for manufacturing the mold of this invention, the aforementioned dry coated sand is preheated, and then the aforementioned aqueous medium is added and mixed, thereby wetting the dry coated sand and forming the aforementioned wet coated sand in a heated state.

[0018] In addition, in the third aspect of the present invention, the preheating temperature of the aforementioned dry coated sand is 32°C to 150°C.

[0019] Furthermore, in the fourth aspect of the present invention, the aforementioned dry coated sand at room temperature is mixed and heated while an aqueous medium is added, thereby forming the aforementioned wet coated sand in a heated state.

[0020] In addition, in the fifth aspect of the present invention, the mixing and heating of the aforementioned dry coated sand is carried out in a mixing device, and the mixing device is preheated before the aforementioned dry coated sand is added.

[0021] Furthermore, in the sixth aspect of the present invention, the wall surface of the aforementioned mixing device that is in contact with the aforementioned dry coated sand is heated to a temperature of 50°C to 200°C.

[0022] In the seventh aspect of the present invention, the aforementioned dry coated sand is mixed and heated, and the aforementioned aqueous medium is added just before the mixing is about to end.

[0023] In addition, in the eighth aspect of the present invention, the addition of the aforementioned aqueous medium begins 30 seconds to 2 minutes before the end of the aforementioned mixing time.

[0024] Furthermore, in the ninth aspect of the present invention, the aforementioned aqueous medium is characterized in that it is in a liquid state or a vapor state.

[0025] Furthermore, in the tenth aspect of the present invention, the aforementioned wet coated sand in a heated state is characterized by a temperature of 30°C to 100°C.

[0026] In addition, in the eleventh aspect of the present invention, the aforementioned aqueous medium is preheated to a temperature below its boiling point.

[0027] Furthermore, in the twelfth aspect of the method for manufacturing the mold according to the present invention, the preheating temperature of the aforementioned aqueous medium is 30°C to 100°C.

[0028] Furthermore, in the thirteenth aspect of the present invention, the aforementioned aqueous medium is added at a ratio of 0.3 to 6 parts by mass relative to 100 parts by mass of the aforementioned dry coated sand.

[0029] In the fourteenth aspect of the present invention, the aforementioned molding die is heated to a temperature of 40°C to 250°C.

[0030] Furthermore, in the fifteenth aspect of the present invention, the aforementioned water-soluble adhesive is characterized by being a soluble silica compound.

[0031] Furthermore, in the sixteenth aspect of the present invention, the aforementioned dry coated sand contains a filler improver.

[0032] Furthermore, in a seventeenth aspect of the method for manufacturing a mold according to the present invention, the aforementioned dry coated sand contains a moisture resistance improver.

[0033] Furthermore, according to the eighteenth aspect of the present invention, the dry coated sand prepared above is transported to the molding site, which serves as the manufacturing site for the mold, and the aforementioned aqueous medium is added to the dry coated sand at the molding site for mixing, thereby forming the aforementioned wet coated sand in a heated state.

[0034] The effects of the invention

[0035] Thus, in the method for manufacturing the mold of the present invention, dry coated sand obtained by using water-soluble adhesives such as water glass as binders is heated to form wet coated sand, which is then kept in the heated state during the wetting process and molded using a preheated molding die. Therefore, the effect of the coating layer formed by the water-soluble adhesive in the coated sand as an adhesive can be advantageously improved, the bending strength and moisture resistance of the obtained mold can be effectively improved, and the scratch hardness of the mold can also be advantageously improved. Furthermore, it is advantageous to manufacture molds with excellent mold properties in the industry. Detailed Implementation

[0036] Furthermore, in the method for manufacturing the mold of the present invention, the pre-prepared dry coated sand is typically manufactured by mixing refractory aggregate with a water-soluble binder in an aqueous solution as a binder, and then evaporating the water from the mixture; in other words, by evaporating the water from the water-soluble binder in an aqueous solution. Moreover, the resulting coated sand is a dry coated sand formed by a dried coating layer of a predetermined thickness formed from the solid components of the water-soluble binder as a binder on the surface of the refractory aggregate, exhibiting good room temperature fluidity.

[0037] Furthermore, the range of water content used to obtain the dry state in the coated sand varies depending on the properties of the water-soluble binder. Therefore, the dry state in this invention refers to the state in which the dynamic angle of repose can be measured regardless of the amount of water. Here, the dynamic angle of repose refers to the angle formed between the coated sand and the horizontal plane when the slope of the coated sand layer flowing inside the cylinder becomes a flat surface, after the cylinder is sealed at one end of the axial direction with a transparent plate. It should be noted that when the coated sand does not flow inside the cylinder in a wet state, the slope of the coated sand layer cannot form a flat surface, and the dynamic angle of repose cannot be measured, this type of coated sand is called wet coated sand.

[0038] Furthermore, in this invention, by using the dry coated sand as described above as the molding material, its service life is long, which can advantageously improve storage stability. Therefore, a large amount of this dry coated sand can be prepared in advance in places such as work sites different from the molding site, and a portion of it can be transported to the molding site and used for molding the target mold. This can also greatly contribute to the efficiency of the molding operation.

[0039] Here, the refractory aggregate constituting the coated sand as described above is any refractory material that serves as the base material for the mold, and can be any refractory granular or powdered material conventionally used for mold applications. Specifically, it includes silica sand and recycled silica sand, as well as special sands such as alumina sand, olivine sand, zircon sand, and chromite sand; slag-based particles such as ferrochrome slag, ferronickel slag, and converter slag; artificial particles such as alumina particles and mullite particles, and their recycled particles; alumina balls, magnesium frit, etc. Furthermore, these refractory aggregates can be virgin sand, or recycled or recovered sand that has been used once or multiple times as casting sand in mold making, or even mixed sand formed by adding virgin sand to such recycled or recovered sand; there are no limitations. Moreover, these refractory aggregates typically use aggregates with a particle size of approximately 40 to 130 based on the AFS index, preferably aggregates with a particle size of approximately 60 to 110.

[0040] This refractory aggregate is preferably spherical, and ideally, its coefficient of angularity is 1.2 or less, more preferably 1.0 to 1.1. By using refractory aggregates with a coefficient of angularity of 1.2 or less, good flowability and filling properties are achieved, resulting in a greater number of contact points between the aggregates. This reduces the amount of binder and additives required to achieve the same strength. It should be noted that the aggregate coefficient used here is generally used as a standard to describe the shape of the particles, also known as the particle shape index. A value closer to 1 indicates a shape closer to spherical (perfectly spherical). Furthermore, this particle shape coefficient is expressed as a value calculated using the surface area of ​​sand measured by various known methods. For example, it is the value obtained by dividing the surface area of ​​1g of actual sand particles measured using a sand surface area meter (manufactured by Georg Fischer Ltd) by the theoretical surface area. It should be noted that the theoretical surface area is the surface area assuming all sand particles are spherical.

[0041] Furthermore, the adhesive covering the refractory aggregate as described above is also called a binder, and in this invention, a water-soluble adhesive is used. As this water-soluble adhesive, any of the following can be used, as long as it is water-soluble: inorganic polymers, thermosetting resins, sugars, synthetic polymers, salts, and proteins. Moreover, these can be used alone, or two or more can be used; inorganic polymers are particularly preferred. Furthermore, these water-soluble adhesives can be diluted with water or a solvent before use.

[0042] Furthermore, examples of inorganic polymers used as such water-soluble adhesives include water glass, colloidal silica, alkyl silicates, bentonite, and cement, among which water glass is preferred. Additionally, the water glass is a solution of a soluble silicate compound. 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 is advantageously used in this invention.

[0043] Furthermore, sodium silicate is typically used in grades 1 through 5 based on its SiO2 / Na2O molar ratio. Specifically, sodium silicate grade 1 has a SiO2 / Na2O molar ratio of 2.0 to 2.3; sodium silicate grade 2 has a SiO2 / Na2O molar ratio of 2.4 to 2.6; sodium silicate grade 3 has a SiO2 / Na2O molar ratio of 2.8 to 3.3; sodium silicate grade 4 has a SiO2 / Na2O molar ratio of 3.3 to 3.5; and sodium silicate grade 5 has a SiO2 / Na2O molar ratio of 3.6 to 3.8. JIS-K-1408 also specifies sodium silicate grades 1 through 3. Moreover, these sodium silicates can be used alone or in mixtures, and the SiO2 / Na2O molar ratio can be adjusted arbitrarily through mixing. It should be noted that the molar ratio of SiO2 / Na2O is not limited to the range specified in sodium silicate No. 1 to No. 5 above; for example, it can be in the range of 0.8 to 4.0.

[0044] It should be noted that, in order to advantageously obtain the dry coated sand used in this invention, the molar ratio of SiO2 / Na2O for the sodium silicate constituting the water glass used as a binder is ideally 1.9 or more, preferably 2.0 or more, and more preferably 2.1 or more. Among the aforementioned classifications of sodium silicate, sodium silicate corresponding to No. 1 and No. 2 is particularly advantageous. Both No. 1 and No. 2 sodium silicates can stably produce dry coated sand with good properties even with a wide range of sodium silicate concentrations in the water glass. Furthermore, the upper limit of this SiO2 / Na2O molar ratio of the sodium silicate is appropriately selected based on the characteristics of the water glass in its aqueous solution form, and is typically 3.5 or less, preferably 3.2 or less, and more preferably 2.7 or less. Here, if the molar ratio of SiO2 / Na2O is less than 1.9, the viscosity of water glass will be lower, and it will be difficult to dry without significantly reducing the water content. On the other hand, if it is greater than 3.5, the solubility in water will be reduced, resulting in insufficient adhesion to the surface of refractory aggregates. Therefore, there are problems such as insufficient bonding area and reduced mold strength.

[0045] Furthermore, the water glass used in this invention refers to a solution of silicate compounds dissolved in water. Besides being used directly as a commercially available stock solution, it can also be used diluted by adding water to this stock solution. Moreover, the solid component (water glass component) from which volatile substances such as water and solvents have been removed is called the non-volatile component, which corresponds to the aforementioned soluble silicate compounds such as sodium silicate. Furthermore, the higher the proportion of this non-volatile component (solid component), the higher the concentration of silicate compounds in the water glass. Therefore, regarding the non-volatile component of the water glass used in this invention, when it consists solely of the stock solution, it corresponds to the proportion of water removed from the stock solution. On the other hand, when using a diluted solution obtained by diluting the stock solution with water, the amount remaining after removing the water from the stock solution and the amount of water used for dilution corresponds to the non-volatile component of the water glass used.

[0046] Furthermore, the non-volatile components in this water glass are present in an appropriate proportion depending on the type of water glass component (soluble silicate compound), ideally at a proportion of 20-50% by mass. By moderately containing water glass components equivalent to this non-volatile component in the aqueous solution, the refractory aggregate can be uniformly and without deviation coated with water glass components during mixing (blending). This allows for the advantageous molding of the target mold using the present invention. It should be noted that if the concentration of water glass components in the water glass is too low, resulting in a total non-volatile component content of less than 20% by mass, the heating temperature or heating time needs to be increased to dry the coated sand, thus causing problems such as energy loss. Additionally, if the proportion of non-volatile components in the water glass is too high, it is difficult to uniformly coat the surface of the refractory aggregate with water glass components, also causing problems in improving the characteristics of the target mold. Ideally, the water glass in the aqueous solution form should be prepared in a proportion of non-volatile components of 50% by mass or less and water content of 50% by mass or more.

[0047] In addition, examples of thermosetting resins that are water-soluble adhesives other than the aforementioned inorganic polymers include methyl 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. Furthermore, it is advantageous to improve the thermosetting properties of these thermosetting resins by mixing them with hardeners such as acids and esters. It should be noted that among these thermosetting resins, methyl phenolic resins are preferred, as they are prepared by reacting phenols and formaldehydes in the presence of a reaction catalyst. Furthermore, in this invention, water-soluble basic methyl phenolic resins are suitable examples of such phenolic resins. Using such basic methyl phenolic resins provides molds that can be used in a wide range of applications, including cast iron and cast steel.

[0048] Furthermore, for sugars as another example of water-soluble binders, known sugars such as monosaccharides, oligosaccharides, and polysaccharides can be used. One type of monosaccharide, oligosaccharide, or polysaccharide can be selected for use alone, or multiple types can be used in combination; there are no limitations. Examples of monosaccharides include glucose, fructose, and galactose. Examples of oligosaccharides include maltose, sucrose, lactose, and disaccharides such as cellulobiose. Examples of polysaccharides include starch sugars, dextrin, xanthan gum, gelling polysaccharides, amylopectin, cyclodextrin, chitin, cellulose, and starch. Additionally, gums from plant mucilages such as gum arabic can be used as hardening agents for sugars, especially polysaccharides, and carboxylic acids can also be used.

[0049] Furthermore, examples of synthetic polymers used as water-soluble adhesives include polyethylene oxide, poly-α-hydroxyacrylic acid, acrylic copolymers, acrylate copolymers, methacrylate copolymers, polyacrylamide, anionic polyacrylamide, cationic 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, or modified forms thereof. Moreover, they can be used individually or in combination.

[0050] Furthermore, as salts, substances that solidify upon drying after being added to water can be used, such as sulfates like magnesium sulfate and sodium sulfate, bromides like sodium bromide and potassium bromide, carbonates like sodium carbonate and potassium carbonate, and chlorides like barium chloride, sodium chloride, and potassium chloride. Additionally, as proteins, gelatin and animal glue can be used.

[0051] Furthermore, the water-soluble binder described above is ideally used at a ratio of 0.1 to 5 parts by weight relative to 100 parts by weight of the refractory aggregate, calculated by considering only the non-volatile components, with a particularly advantageous ratio of 0.2 to 2.5 parts by weight, to form a prescribed coating layer on the surface of the refractory aggregate. Here, the determination of the solid content is performed in the same manner as before, for example, according to the method described in International Publication No. WO2019 / 132006.

[0052] It should be noted that if the amount of water-soluble binder is too small, it will be difficult to form a coating layer on the surface of the refractory aggregate, resulting in insufficient curing and / or hardening of the coated sand. Conversely, if the amount of water-soluble binder is too large, not only will the excess binder adhere to the surface of the refractory aggregate, making it difficult to form a uniform coating layer, but there is also a risk that the coated sand will adhere to each other and clump together (composite granulation), thus adversely affecting the mold properties and causing difficulty in removing the core sand after the molten metal is poured.

[0053] Furthermore, the object of the present invention is a dry coated sand formed by using the aforementioned water-soluble binder to form a coating layer on the surface of refractory aggregate. This coating layer may also contain various additives as needed. It should be noted that, in order to include such additives in the coating layer, methods such as: pre-mixing a specified additive into the water-soluble binder and then kneading or mixing it with the refractory aggregate; or adding the specified additive separately from the water-soluble binder to the refractory aggregate and then uniformly kneading and / or mixing it together with the water-soluble binder. It should be noted that the water-soluble binder and additives can be kneaded and / or mixed simultaneously, or kneaded and / or mixed with a time difference.

[0054] As one such additive, a filler modifier is advantageously used in this invention. The filler modifier is a granular substance that exists partially exposed on the surface of the resulting coated sand particles—in other words, on the surface of the water-soluble binder layer covering the refractory aggregate. Therefore, when the coated sand flows to fill the molding die, the coated sand particles come into contact with each other through the filler modifier, thereby effectively reducing friction between the coated sand particles and advantageously improving its flowability. Furthermore, it advantageously improves the filling performance of the coated sand into the molding die and prevents the coated sand from adhering to the molding die or other molding devices. Examples of such filler modifiers include spherical silicone resin powder (particles) and inorganic oxide particles; spherical silicone resin powder (particles) are particularly advantageous.

[0055] It should be noted that the "spherical" in the context of the spherical silicone resin powder refers to a generally understood degree of sphericity, not necessarily perfect sphericity. Silicone resin powder with a sphericity of 0.5 or higher is typically used, preferably 0.7 or higher, and more preferably 0.9 or higher. Here, sphericity refers to the average aspect ratio (ratio of minor axis to major axis) obtained from the projected shape of 10 randomly selected individual particles observed using a scanning electron microscope.

[0056] Furthermore, it is advantageous to use silicone resin powder with a particle size smaller than that of the refractory aggregate, and whose average particle size is typically 0.01 μm or more and 50 μm or less, preferably 0.05 μm or more and 25 μm or less, more preferably 0.1 μm or more and 10 μm or less, and even more preferably 0.2 μm or more and 3 μm or less. Because the particle size of this spherical silicone resin powder is smaller than that of the mixed refractory aggregate, it easily penetrates between the refractory aggregates and can be uniformly dispersed, existing evenly on the surface of the coated sand particles.

[0057] Furthermore, the amount of the spherical silicone resin powder used is typically 0.1 to 500 parts by mass, preferably 0.3 to 300 parts by mass, more preferably 0.5 to 200 parts by mass, further preferably 0.75 to 100 parts by mass, and most preferably 1 to 50 parts by mass, relative to 100 parts by mass of the solid component of the water-soluble binder constituting the surface coating of the refractory aggregate. In this way, by containing spherical silicone resin powder with a specified average particle size in a specified proportion in the water-soluble binder coating of the refractory aggregate surface, the effects of the present invention can be more advantageously enjoyed. It should be noted that the average particle size of the silicone resin powder can be determined by measuring the particle size distribution using a laser diffraction-type particle size distribution measuring device or the like.

[0058] Furthermore, as described above, the spherical silicone resin powder is not particularly limited as long as it is spherical and has anti-adhesion properties; various known silicone resin particles can be used. It should be noted that, as the silicone resin, an organopolysiloxane is preferably used as the main component, and more preferably, the organopolysiloxane is formed from 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 further by using a polymethylsilsesquioxane, spherical particles with effective anti-adhesion properties, high silicon content, and excellent heat resistance can be obtained. Moreover, by imparting such properties, thermal decomposition and melting caused by the heat during molding are less likely, thus maintaining the spherical shape advantageously during molding and casting. This advantageously maintains the effects of filling and strength improvement, and suppresses odors and fumes during molding. Therefore, during casting, it can further advantageously prevent sand adhesion and improve the surface of the casting.

[0059] Furthermore, the inorganic oxide particles can be spherical or non-spherical, but spherical particles are preferred in order to obtain castings with a better surface finish. There are no particular limitations on the material constituting the inorganic oxide particles, but inorganic metal oxides are preferred. Particles formed from such inorganic metal oxides are advantageously made of silicon dioxide, alumina, titanium dioxide, etc. It should be noted that silicon dioxide can be crystalline or amorphous; amorphous silicon dioxide is ideal. Examples of amorphous silicon dioxide include precipitated silicon dioxide, sintered silicon dioxide generated in an electric arc or flame hydrolysis, silicon dioxide generated by the thermal decomposition of ZrSiO4, silicon dioxide generated by oxidizing metallic silicon using an oxygen-containing gas, and quartz glass powder with spherical particles formed from crystalline quartz through melting and subsequent quenching. The spherical shape, average particle size, and dosage range of the inorganic oxide particles are the same as those of the spherical organosilicon resin powder.

[0060] Furthermore, in this invention, it is preferable to use a moisture resistance improver as an additive, either together with or separately from the filler improver described above. In this way, by including the moisture resistance improver in the coated sand, the moisture resistance of the final mold can be further improved.

[0061] Here, as a moisture resistance improver, any moisture resistance improver conventionally used in coated sand can be used as long as it does not hinder the effect of the present invention. Specifically, examples include 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, and silver tetraborate; borates such as sodium metaborate, potassium metaborate, lithium metaborate, ammonium metaborate, calcium metaborate, silver metaborate, copper metaborate, lead metaborate, and magnesium metaborate; sulfates such as sodium sulfate, potassium sulfate, lithium sulfate, magnesium sulfate, calcium sulfate, strontium sulfate, barium sulfate, titanium sulfate, aluminum sulfate, zinc sulfate, and copper sulfate; and sulfates such as sodium phosphate, sodium hydrogen phosphate, potassium phosphate, potassium hydrogen phosphate, lithium phosphate, and lithium hydrogen phosphate. Phosphates such as 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, in particular, can significantly improve moisture resistance when using water glass as a water-soluble binder. These moisture resistance improvers can be used alone or in combination of two or more. It should be noted that the moisture resistance improvers listed above also include compounds that can be used as water-soluble binders; these compounds function as moisture resistance improvers when used with different water-soluble binders.

[0062] Furthermore, the amount of this moisture resistance improver, relative to 100 parts by weight of the solid component of the liquid water-soluble adhesive, is generally preferably about 0.5 to 50 parts by weight, more preferably 1 to 20 parts by weight, and particularly preferably 2 to 15 parts by weight. To advantageously enjoy the effect of adding this moisture resistance improver, an amount of 0.5 parts by weight or more is ideal. On the other hand, if the amount added is too large, there is a risk of hindering the bonding of the water-soluble adhesive and causing a decrease in the strength of the final mold; therefore, it is ideally set to 50 parts by weight or less.

[0063] In addition, coupling agents that strengthen the bond between refractory aggregates and water-soluble binders are also effective additives. Examples include silane coupling agents, zirconium coupling agents, and titanium coupling agents. Lubricants that improve the flowability of coated sand are also effective. Examples include solid paraffin wax, synthetic polyethylene wax, lignite wax, and other waxes; fatty acid amides such as stearamide, oleamide, and erucamide; alkylene fatty acid amides such as methylene bis-stearamide and ethylene bis-stearamide; stearic acid and stearyl alcohol; metal stearate salts such as lead stearate, zinc stearate, calcium stearate, and magnesium stearate; glyceryl monostearate, stearyl alcohol stearate, and hydrogenated oil. Furthermore, as release agents, paraffin wax, waxes, light oils, machine oils, spindle oils, insulating oils, waste oils, vegetable oils, fatty acid esters, organic acids, graphite particles, mica, vermiculite, fluorinated release agents, and silicone release agents can also be used. Furthermore, the other additives are typically contained in proportions of 5% by mass or less, preferably 3% by mass or less, relative to the non-volatile components in the water-soluble adhesive.

[0064] Furthermore, in this invention, when manufacturing the pre-prepared dry coated sand, the following method is typically employed: For refractory aggregates, a water-soluble binder, acting as a binder, is mixed and / or blended with additives as needed using conventional methods, resulting in uniform mixing. The surface of the refractory aggregates is then covered with the water-soluble binder, and the moisture in this binder evaporates, thereby obtaining a dry, powdery coated sand with room-temperature fluidity. However, the evaporation of moisture from the coating layer must occur rapidly before the curing and / or hardening of the water-soluble binder progresses. Therefore, in this invention, it is ideal to allow the moisture-containing material to evaporate within 5 minutes, more preferably within 3 minutes, after adding (mixing) the water-soluble binder (in aqueous solution) to the refractory aggregates, thereby producing a dry, powdery coated sand. This is because a longer evaporation time increases the risk of problems such as: a longer mixing (blending) cycle, reduced productivity, and prolonged exposure of the water-soluble binder to CO2 in the air, leading to deactivation.

[0065] It should be noted that, in the manufacturing process of this dry coated sand, one effective means of rapidly evaporating the moisture in the water-soluble binder is to appropriately employ the following method: preheating the refractory aggregate, and then mixing and / or blending the water-soluble binder in an aqueous solution within it. By mixing and / or blending the water-soluble binder in the preheated refractory aggregate, the moisture in the water-soluble binder can be evaporated extremely rapidly due to the heat of the refractory aggregate. Therefore, the moisture content of the resulting coated sand can be effectively reduced, advantageously yielding a dry powder with room-temperature flowability. It should be noted that the preheating temperature of the refractory aggregate is appropriately selected based on the moisture content of the water-soluble binder, its mixing ratio, etc. Ideally, the refractory aggregate is typically heated to approximately 100°C to 160°C, preferably approximately 100°C to 140°C. If the preheating temperature is too low, the moisture cannot be effectively evaporated, and drying takes a long time. Therefore, it is ideal to use a temperature above 100°C. In addition, if the preheating temperature is too high, the hardening of the water-soluble binder components will be accelerated during the cooling of the resulting coated sand, and composite granulation will also occur. Therefore, problems will arise in the function of the coated sand, especially in terms of physical properties such as strength.

[0066] The resulting dry, powdered coated sand typically has a moisture content of approximately 5-55% by mass relative to the solid content of the water-soluble binder, ideally 10-50% by mass. Particularly when the water-soluble binder is water glass, the coated sand is formed by adjusting the moisture content to 20-50% by mass. Conversely, if the moisture content is less than 5% by mass, the water-soluble binder, such as water glass, vitrifies, preventing it from returning to a solution state even with the addition of water. On the other hand, if it is more than 55% by mass, it becomes a wet state rather than a dry state and lacks fluidity at room temperature. It should be noted that, depending on the type of water-soluble binder, there are cases where the moisture content in the dry coated sand exceeds 55% by mass relative to the solid content of the water-soluble binder, yet it still appears to be in a dry state. Whether it is dry or not is determined by the presence of a dynamic angle of repose.

[0067] Furthermore, in this invention, after the dry coated sand obtained as described above is transported to the molding site, which serves as the manufacturing location for the mold, an aqueous medium is added to the dry coated sand at the molding site and the mixture is kneaded, thereby forming the target wet coated sand under heating. As a method, either of the following two methods is advantageously employed.

[0068] First, in an advantageous method (I) for obtaining the target wet coated sand under heating, the dry coated sand is heated (preheated) to a predetermined temperature and then placed into a suitable mixer (mixing device) for mixing / blending with an aqueous medium added later, thereby wetting the dry coated sand and forming the target wet coated sand. Therefore, as a method for heating the dry coated sand, any known method can be used as long as the dry coated sand can be heated to a predetermined temperature. For example, a heating method using a constant temperature bath, a heating method using a temperature regulating unit as described in Japanese Patent Application Publication No. 2001-321886, Japanese Patent Application Publication No. 2009-142830, and International Publication No. WO2010 / 143746, etc., may be appropriately employed.

[0069] Furthermore, for the mixer used here as a mixing / blending method, a known mixing device can be appropriately selected that can thoroughly stir / mix (blend) the added coated sand and, as needed, has a heating means such as a heater, a blowing means such as hot air, so as to achieve heating of the blended coated sand. In addition, it is ideal that such a mixer preheats the dry coated sand before it is added. Specifically, using a heater installed in the mixer, a heating means such as a circulating hot medium, a blowing means such as hot air, the preheating temperature of the coated sand in contact with the wall of the mixer is usually heated to about 32°C to 150°C, preferably about 35°C to 120°C, more preferably about 40°C to 110°C, so as to advantageously maintain or further heat the temperature of the added dry coated sand.

[0070] Next, the dry coated sand fed into the mixer is humidified by adding a prescribed aqueous medium during the mixing process. It should be noted that this mixing of the dry coated sand and the aqueous medium in the mixer typically takes about 0.5 to 30 minutes, preferably 1 to 15 minutes, and more preferably 3 to 10 minutes. This allows for effective humidification of the dry coated sand using the added aqueous medium, and the humidified coated sand can be removed from the mixer while still hot, at a temperature effective for molding. Furthermore, during the humidification of the dry coated sand, a water-soluble binder can be added as a further additive to readjust the mold strength. By adding a water-soluble binder during mold molding, strength can be increased when the shape and size of the mold to be manufactured require different strengths.

[0071] Furthermore, for the humidification of the dry coated sand as described above, the aqueous medium added to the mixer can be water itself, or an aqueous solution and / or aqueous dispersion prepared by adding various known additives to water as needed. It should be noted that, as additives used as needed, there are various surfactants such as cationic, anionic, amphoteric, nonionic, silicone-based, and fluorine-based surfactants, as well as polyols such as ethylene glycol, polyethylene glycol, and glycerin. The addition of these additives can improve the fluidity and moisture retention of the humidified coated sand. Ideally, the amount of such additive added is 1% to 30% by mass of the aqueous medium, preferably 3% to 20% by mass. Additionally, as is known, it is also advantageous to add hardeners such as acids and esters, and hardening accelerators such as metal salts and metal powders. Furthermore, the addition of spherical particles, such as inorganic oxide particles like silica, alumina, and titanium dioxide, and resin particles like spherical organosilicon particles, is also effective. The addition of these spherical particles can beneficially improve the filling properties of the coated sand during molding. It should be noted that filling property improvers such as inorganic oxide particles and spherical organosilicon particles can be added to dry coated sand, or they can be added together with an aqueous medium.

[0072] Furthermore, the amount of aqueous medium used in the aforementioned wetting process should be appropriately set according to the degree of wetting of the dry coated sand in the mixer. Typically, it is appropriately determined within a ratio of 0.3 to 6 parts by mass, preferably 0.5 to 4 parts by mass, and more preferably 0.75 to 3.5 parts by mass relative to 100 parts by mass of the dry coated sand. It should be noted that if the amount of aqueous medium added is too small, the dry coated sand cannot be sufficiently wetted, resulting in weaker adhesion between the coated sand particles and deterioration of the fluidity of the coated sand, leading to poor filling performance into the mold and consequently, reduced strength of the resulting mold. On the other hand, if the amount of aqueous medium added is too large, it not only makes filling the mold difficult but also requires more time for drying after filling, resulting in longer molding times.

[0073] Furthermore, for mixing with preheated refractory aggregate, the aqueous medium added to the mixer is ideally heated to a temperature below its boiling point, typically within the range of 30°C to 100°C, preferably 35°C to 95°C, and more preferably 40°C to 90°C. This mixing of the preheated aqueous medium with the heated, dry coated sand advantageously enhances the adhesive effect of the coating layer formed by the water-soluble binder on the surface of the coated sand, thereby more effectively achieving the effects of the invention. In particular, by employing this mixing method, the viscosity of the water-soluble binder can be maintained at a low level, thus allowing the spherical silicone resin powder used as an additive to easily expose on the surface of the formed wet coated sand if present in the coating layer, thereby more advantageously maximizing the effect of the silicone resin powder addition.

[0074] On the other hand, in another advantageous method (II) for obtaining the target wet coated sand under heating, the aforementioned dry coated sand is placed at room temperature into a suitable mixer (mixing device) having a heating means such as a heater, a circulating hot medium, and a hot air blowing means. While mixing and heating in the mixer (mixing device), a prescribed aqueous medium is added, and then mixing / kneading is carried out, thereby wetting the dry coated sand and forming the target wet coated sand.

[0075] It should be noted that, as with the aforementioned method (I), the mixer used here as a mixing / blending means can be of any structure as long as it is capable of being preheated to a specified temperature. It is appropriate to select a known mixing device that can thoroughly stir / mix (blend) the added coated sand and has heating means such as heaters, circulating heat media, or hot air blowing means to heat the blended coated sand.

[0076] Furthermore, the mixing of dry coated sand in this mixer typically requires approximately 0.5 to 30 minutes, preferably 1 to 15 minutes, and more preferably 1.5 to 10 minutes, to achieve uniform heating. Through this heating during mixing, the dry coated sand is typically heated to approximately 32°C to 150°C, preferably 35°C to 120°C, and more preferably 40°C to 110°C. Additionally, during this mixing / heating of the dry coated sand, the mixer is ideally preheated before the dry coated sand is added. Specifically, using heating methods such as heaters installed in the mixer, circulating heat media, or hot air blowing, the preheating temperature of the walls of the mixer in contact with the coated sand is typically heated to approximately 50°C to 200°C, preferably 70°C to 150°C, thereby effectively and rapidly heating the added dry coated sand.

[0077] Next, a prescribed aqueous medium is added to the heated, dry coated sand as described above to wet it. It should be noted that the timing of adding this wetted aqueous medium should be appropriately selected based on its amount and form. Ideally, the prescribed aqueous medium, in liquid or vapor form, should be introduced (added) into the mixer just before the end of the mixing time described above, mixing with the mixed and heated coated sand to wet it, thus effectively utilizing the added aqueous medium for wetting the coated sand. It should be noted that for this addition of the aqueous medium just before the end of the mixing process, it is advantageous to begin adding it 30 seconds to 2 minutes before the end of the aforementioned mixing time, thereby removing the wetted coated sand from the mixer at a temperature effective for molding.

[0078] Furthermore, in order to wet the dry coated sand as described above, an aqueous medium is added to the mixer. Similar to method (I), in addition to water itself, an aqueous solution and / or aqueous dispersion containing various known additives can be used. It should be noted that, as additives used as needed, examples include surfactants and polyols, as exemplified above. Their addition can improve the fluidity and moisture retention of the wetted coated sand. Additionally, the addition of known hardeners and hardening accelerators is also advantageous. Furthermore, similar to method (I), the addition of spherical particles, such as inorganic oxide particles and spherical organosilicon particles, is also effective. The addition of these spherical particles can advantageously improve the filling properties of the coated sand during molding. It should be noted that, as mentioned above, the inorganic oxide particles and spherical organosilicon particles can be added not only as filling improvers and contained in the dry coated sand, but also together with the aqueous medium and present on the surface of the coated sand. Furthermore, the amount of aqueous medium used in the above-mentioned wetting process is the same as in method (I). In addition, the aqueous medium added to the mixer for mixing with the preheated refractory aggregate is ideally preheated to a temperature below its boiling point, and the preferred preheating temperature used is the same as in method (I).

[0079] It should be noted that the moisture content of the wet coated sand, which does not have room temperature fluidity, can be appropriately adjusted to a wet state. Typically, the moisture content relative to the solid content of the water-soluble binder is adjusted to more than 55% by mass, preferably 70-900% by mass, and more preferably 95-500% by mass. This moisture content effectively prevents the coated sand from drying out during molding due to air blowing into the mold, thus preventing it from hindering filling. It also maintains the wetness of the coated sand, and molds made using this coated sand exhibit excellent properties.

[0080] Furthermore, in this invention, the wet coated sand, typically at around 30°C to 100°C, preferably around 35°C to 90°C, and more preferably around 40°C to 80°C, obtained by taking the wetted dry coated sand formed as described above from the mixer, is directly filled into a preheated mold, specifically into the molding cavity of the mold, without cooling, while maintaining its heated state. This process dries, cures, and / or hardens the wet coated sand, thereby effectively improving the characteristics of the resulting mold. That is, by directly filling the preheated mold with the wet coated sand taken from the mixer at a still-hot temperature of around 30°C to 100°C, heat transfer to the filled wet coated sand can be effectively achieved, and the coating sand can be advantageously bonded together, thereby stably achieving mold strength. Furthermore, it is also advantageous to improve the mold's moisture resistance and, consequently, its scratch hardness.

[0081] Here, filling the molding die with wet coated sand while maintaining its heated state means that the wet coated sand taken from the mixer is at a temperature of 30°C to 100°C. Therefore, the wet coated sand is maintained at this temperature range; in other words, it is filled into the specified molding die while maintaining a temperature above 30°C. Thus, as long as this temperature range is maintained, the distance between the mixer and the molding die is not particularly limited. It should be noted that if the temperature of the wet coated sand taken from the mixer is below 30°C, it is difficult to suppress uneven heat transfer in the molding die. On the other hand, if the temperature is above 100°C, more moisture evaporates from the wet coated sand, and the viscosity of the water-soluble adhesive increases due to this moisture evaporation. Therefore, insufficient adhesive-based bonding area is not obtained, leading to problems such as reduced strength.

[0082] Furthermore, when drying and curing the wet coated sand filled into the mold to form the target mold, a preheated mold can be used to facilitate the drying of the wet coated sand. Using a preheated mold allows for efficient drying of the filled wet coated sand, thereby advantageously shortening the molding time. It should be noted that the heating temperature for this mold is typically 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 below 40°C, the drying-promoting effect based on heating is not fully utilized, and the molding time becomes longer. Furthermore, if the temperature is above 250°C, the wet coated sand in the mold cures and / or hardens too quickly, resulting in poor filling properties. Additionally, excessive drying of the wet coated sand leads to loss of adhesion and reduced bonding effect, which in turn reduces the strength of the resulting mold.

[0083] Furthermore, to promote the drying of the wet coated sand filled into the mold, directly heating the wet coated sand with microwaves is also effective, especially when the mold is a resin mold. Even more effective is introducing heated or dry air into the mold filled with wet coated sand, allowing it to pass through the filling layer of the wet coated sand, thereby promoting drying and achieving more rapid curing and / or hardening of the filled wet coated sand. In addition, depressurized suction drying within the mold filled with wet coated sand is also an effective drying method, particularly advantageous for molds made of heat-sensitive materials such as resin molds.

[0084] Furthermore, in this invention, as described above, the water used in the wetting process of the aqueous medium is removed from the wet coated sand filled into the molding die, thereby molding the target mold. At this time, the water glass constituting the surface coating of the coated sand typically hardens due to water evaporation and drying without any additives. However, if oxides, salts, or the like are added as hardening agents, hardening occurs. Moreover, for this hardening of the water glass, it is effective to circulate carbon dioxide or organic ester gas within the molding die filled with wet coated sand. This allows the water glass to harden rapidly, as in the past, thereby advantageously increasing the molding speed. It should be noted that, as organic ester gas, for example, methyl formate, ethyl formate, propyl formate, γ-butyrolactone, β-propiolactone, ethylene glycol diacetate, diethylene glycol diacetate, glyceryl diacetate, glyceryl triacetate, propylene carbonate, etc., can be used in gaseous or mist form.

[0085] It should be noted that, according to the present invention, after the dry coated sand is humidified under mixing / heating, it is filled into a preheated molding mold under a specific heating state as a molding method. Various known molding methods can be used appropriately, thereby industrially advantageously manufacturing target molds.

[0086] The above detailed description of the embodiments of the present invention is merely illustrative, and the present invention is not to be construed as limiting due to the specific description of these embodiments. Moreover, the present invention can be implemented in various ways based on the understanding of those skilled in the art, including but not limited to, any modifications, alterations, and improvements made thereto. Such implementations, as long as they do not depart from the spirit of the present invention, are of course within the scope of the present invention.

[0087] Example

[0088] The present invention will now be described in more detail with reference to some embodiments, but it should be understood that the invention is not to be limited by these embodiments. It should be noted that in the following embodiments and comparative examples, "%" and "parts" are expressed on a mass basis unless otherwise specified. Furthermore, the bending strength and scratch hardness of the molds obtained in the embodiments and comparative examples were measured as follows.

[0089] - Bending strength (kgf / cm) 2 Determination of )

[0090] For the test pieces with a width of 25.4 mm × height of 25.4 mm × length of 200 mm obtained from the examples and comparative examples, which were molded using wet coated sand, the failure load was measured using a measuring instrument (manufactured by Takachiho Seiki Co., Ltd.: digital molding sand strength tester). Using the failure load obtained by the measurement, the flexural strength (flexural strength) was calculated as follows.

[0091] Bending strength = 1.5 × LW / ab 2

[0092] [Where, L: distance between support points (cm), W: failure load (kgf), a: width of the test piece (cm), b: thickness of the test piece (cm)]

[0093] Then, the bending strength of the mold after molding, and the mold after molding kept at 3°C ​​× 60% RH for 1 hour or 24 hours, is measured. The strength retention rate is calculated by using the ratio of the bending strength after 24 hours to the bending strength after 1 hour, and the moisture resistance of the mold is evaluated.

[0094] -Determination of scratch hardness (mm)-

[0095] For test pieces with dimensions of 25.4 mm width × 25.4 mm height × 200 mm obtained from the examples and comparative examples, which were molded using wet coated sand, the scratch hardness (n=3, average value) of the test pieces after molding and maintenance at 23°C × 60% RH for 1 hour was measured using a scratch hardness tester (GF type). Specifically, the scratch hardness was measured as follows: First, the front teeth of the scratch hardness tester were pressed against the surface of the test piece, and the upper black rod was rotated clockwise once and then counterclockwise once, and this rotation operation was repeated 5 times, so that the teeth slowly penetrated, and the penetration depth of the teeth was read using the scale (mm) on the side. For scratch hardness, the smaller the measured value, the higher the scratch hardness, and the larger the measured value, the lower the scratch hardness.

[0096] -Example 1 of manufacturing dry coated sand (DCS)-

[0097] As a refractory aggregate, commercially available foundry sand ESPEARL#60L (trade name: Yamakawa Sangyo Co., Ltd.) was prepared, and as a binder (water-soluble adhesive), commercially available sodium silicate No. 2 (trade name: Fuji Chemical Co., Ltd., SiO2 / Na2O molar ratio: 2.5, solid content: 35%) was prepared. Then, 100 parts of the above-mentioned ESPEARL#60L were heated to approximately 120°C and added to a Shinagawa-type universal mixer (5DM-r type) (manufactured by DALTON CORPORATION). Next, 1.0 part of the aforementioned water glass was added, and the mixture was kneaded to obtain a dry coated sand (DCS1) that is free-flowing at room temperature. The water content of the DCS1 was measured, and the result showed that the solid content relative to the water glass in the DCS was 32%.

[0098] -Example 2 of manufacturing dry coated sand-

[0099] Furthermore, 0.05 parts of spherical silicone resin particles Tospearl 120 (trade name: MOMENTIVE PERFORMANCE MATERIALS JAPAN LLC, particle size: 2.0 μm) were added as an additive to improve filler properties. Otherwise, the process was carried out in the same manner as in "Example 1 of Manufacturing Dry Coated Sand" described above, resulting in dry coated sand (DCS2) that is free-flowing at room temperature. The resulting DCS2 had a water content relative to the solid content of water glass in the DCS of 33%.

[0100] -Example 3 of manufacturing dry coated sand-

[0101] In "Example 2 of manufacturing dry coated sand", 0.1 parts of zinc carbonate, as a moisture resistance improver, were further added as an additive. Otherwise, the process was the same as in "Example 2 of manufacturing dry coated sand" to obtain dry coated sand (DCS3) that is free-flowing at room temperature. The water content of the DCS3 was measured, and the result showed that the solid content relative to the water glass in the DCS was 33%.

[0102] -Example 1 of mold design-

[0103] (Example 1)

[0104] First, 100 parts of DCS1 obtained in the aforementioned "Example 1 of manufacturing dry coated sand" were preheated to approximately 50°C and then added to a mixer. Next, room-temperature water was added to the preheated DCS1 at a ratio of 1.0%, and the mixture was kneaded to wet the DCS1, resulting in wet coated sand (WCS) that does not have room-temperature flowability. It should be noted that the water content of the obtained WCS was measured, and the result showed that the solid content relative to water glass in the WCS was 317%.

[0105] Next, the wet coated sand (WCS) obtained by wetting through the DCS1, which does not have room temperature fluidity, is taken out from the mixer. Without cooling, it is directly blown into and filled into a molding die preheated to 150°C at a gauge pressure of 0.3 MPa while it is still hot. After holding for 30 seconds, hot air at about 120°C is blown in for 30 seconds to dry and solidify it. Then, it is taken out of the molding die to obtain a mold for the test piece.

[0106] (Example 2)

[0107] Using the DCS2 obtained in "Example 2 of manufacturing dry coated sand", and setting the preheating temperature of the DCS2 to about 30°C, the same procedure as in Example 1 was followed to form a WCS with a water content of 318% relative to the solid content of water glass in the WCS. The hot WCS taken out of the mixer was molded directly in the same manner as in Example 1 without cooling to obtain a mold for the test piece.

[0108] (Examples 3-6)

[0109] The DCS2 was preheated to approximately 40°C, 50°C, 70°C, or 90°C. Otherwise, it was operated in the same manner as in Example 2 to perform humidification, forming WCS with a water content of 316%, 310%, 305%, or 293% relative to the solid content of water glass in the WCS. The WCS taken from the mixer was then molded directly in the hot state in the same manner as in Example 2, thereby producing molds as test pieces.

[0110] (Example 7)

[0111] The temperature of the water added to DCS2 was set to about 50°C. Otherwise, the DCS2 was humidified in the same manner as in Example 4 to form a WCS with a water content of 305% relative to the solid content of water glass in the WCS. The hot WCS taken out of the mixer was then molded directly in the same manner as in Example 4 to produce a mold for the test piece.

[0112] (Example 8)

[0113] The temperature of the water added to DCS2 was set to about 80°C. Otherwise, the DCS2 was humidified in the same manner as in Example 4 to form a WCS with a water content of 304% relative to the solid content of water glass in the WCS. The hot WCS taken out of the mixer was then molded directly in the same manner as in Example 4 to produce a mold for the test piece.

[0114] (Example 9)

[0115] Using the DCS3 obtained in "Example 3 of manufacturing dry coated sand", except that, the same procedure as in Example 4 was followed to form a WCS with a water content of 302% relative to the solid content of water glass in the WCS. Then, after removing it from the mixer, without cooling, it was molded directly in the hot state in the same manner as in Example 4 to obtain a mold as a test piece.

[0116] (Comparative Example 1)

[0117] In Example 1, DCS1 was not preheated and was used at room temperature. Otherwise, the process was the same as in Example 1. DCS1 was humidified and the resulting WCS (moisture content: 319%) was filled into a molding die and shaped to make a mold for the test piece.

[0118] (Comparative Example 2)

[0119] In Example 2, the DCS2 was not preheated but used at room temperature. Otherwise, the same procedure as in Example 2 was followed to wet the DCS2. The resulting WCS (moisture content: 320%) was filled into a molding die and shaped to create a mold for the test piece.

[0120] -Evaluation of casting properties 1-

[0121] Using the molds (test pieces) obtained in Examples 1 to 9 and Comparative Examples 1 to 2 above, their bending strength and scratch hardness were measured according to the aforementioned method, and the results are shown in Tables 1 and 2 below.

[0122] [Table 1]

[0123]

[0124] [Table 2]

[0125]

[0126] According to the results in Tables 1 and 2, it is clear that the molds (test pieces) of Examples 1 to 9, which are formed by directly using wet coated sand (WCS) obtained by preheating dry coated sand (DCS1-3), adding water, and mixing, and molding with a preheated molding die, have excellent flexural strength, scratch hardness, and also excellent moisture resistance and strength retention over time.

[0127] In contrast, it can be seen that for molds made by molding wet coated sand (WCS) obtained by wetting dry coated sand (DCS1-2) at room temperature without preheating, as shown in Comparative Examples 1-2, the bending strength immediately after molding is low. In addition, the bending strength is insufficient after 1 hour and 24 hours of molding, and the strength retention rate after moisture absorption is also poor. Furthermore, the scraping hardness of the mold is also insufficient after 1 hour of molding.

[0128] -Example 2 of mold design-

[0129] (Example 10)

[0130] First, hot air at 200°C was blown into 100 parts of DCS2 at room temperature obtained in the aforementioned dry coated sand manufacturing example 2, and then introduced into a Shinagawa-type universal mixer (5DM-r type) with a wall surface temperature (average of the measured values ​​of 5 parts of the inner wall) of about 50°C. The mixture was kneaded for 5 minutes while the hot air was continuously blown in. After heating the mixed DCS2, room temperature water was added at a ratio of 1.0% relative to the DCS2, and then kneaded for 1 minute. The mixed DCS2 was thus moistened in the mixer to obtain wet coated sand (WCS) with a water content of 182% relative to the solid content of water glass in WCS.

[0131] Next, the wet coated sand (WCS) obtained by wetting through the DCS2, which does not have room temperature fluidity, is taken out from the Shinagawa-type universal mixer at a temperature of about 30°C. Under this heated state, it is immediately blown into and filled into a molding die preheated to 150°C with a gauge pressure of 0.3 MPa. After holding for 30 seconds, hot air at about 120°C is blown in for 30 seconds to dry and cure. Afterward, it is taken out of the molding die to obtain a mold for the test piece.

[0132] (Example 11)

[0133] The preheating temperature of the inner wall of the Shinagawa-type universal mixer, caused by the influx of hot air, was set to approximately 70°C. The heating and mixing time of the added DCS2 was set to 6 minutes (plus room temperature water, then 1 minute). The temperature at which the mixer was removed was set to approximately 50°C. Otherwise, the process was repeated as in Example 10. After obtaining a WCS with a water content of 180% relative to the solid content of water glass in the WCS, the WCS was used, and the aforementioned removal temperature was maintained. The process was repeated as in Example 10 to obtain a mold for the test piece.

[0134] (Example 12)

[0135] In Example 10, the preheating temperature of the inner wall of the Shinagawa-type universal mixer was set to approximately 90°C, the heating and mixing time was set to 7 minutes (adding room temperature water, then 1 minute), and the temperature at which it was removed from the mixer was set to approximately 70°C. Otherwise, the process was the same as in Example 10, to form a WCS with a water content of 177% relative to the solid content of water glass in the WCS. After removing it from the mixer, it was not cooled, but directly molded while heated, just like in Example 10, to obtain a mold for the test piece.

[0136] (Example 13)

[0137] For the heating of DCS2 mixed in the Shinagawa-type universal mixer, instead of blowing in hot air, a 100°C heat medium is circulated through the temperature control device provided in the mixer for heating. Otherwise, the process is the same as in Example 11. After forming WCS with a water content of 179% relative to the solid content of water glass in the WCS, it is removed from the mixer at approximately 50°C and molded directly in the same manner as in Example 11 to create a mold for the test piece. It should be noted that the preheating temperature of the mixer's inner wall is approximately 70°C, and the heating and mixing time is 6 minutes.

[0138] (Example 14)

[0139] In Example 10, the preheating temperature of the inner wall of the Shinagawa-type universal mixer, caused by the introduction of hot air, was set to approximately 70°C. After 6 minutes of heating and mixing, water vapor was blown into the DCS2 while mixing for another 2 minutes. This resulted in a WCS with a water content of 182% relative to the solid content of water glass in the WCS. The WCS was then removed from the mixer at approximately 50°C and molded directly in the same manner as in Example 10 to create a mold for the test piece. It should be noted that, regarding the amount of water added based on the steam aeration, since the water content of the extracted WCS was consistent with that in Example 10, water was added at a ratio of 1.0% relative to the DCS2.

[0140] (Example 15)

[0141] The heating and mixing time of the DCS2 was set to 6 minutes, water at 50°C was added, and then the process was repeated for 1 minute. Otherwise, the process was repeated in the same way as in Example 11. After obtaining WCS with a water content of 182% relative to the solid content of water glass in the WCS, the WCS was used to obtain a mold as a test piece while maintaining the aforementioned extraction temperature.

[0142] (Example 16)

[0143] The heating and mixing time of the DCS2 was set to 6 minutes, water at 80°C was added, and then the process was repeated for 1 minute. Otherwise, the process was repeated as in Example 11. After obtaining WCS with a water content of 181% relative to the solid content of water glass in the WCS, the WCS was used to obtain a mold as a test piece while maintaining the aforementioned extraction temperature.

[0144] (Comparative Example 3)

[0145] In Example 10, no hot air was blown in (no heating was performed), and DCS2 was directly humidified on the inner wall of the Shinagawa-type universal mixer at room temperature (20°C) for a mixing time of 1 minute. The resulting WCS (moisture content: 185%) was then filled into a molding die at room temperature in the same manner as in Example 10 to create a mold for test pieces.

[0146] -Evaluation of casting properties 2-

[0147] Using the molds (test pieces) obtained in Examples 10-16 and Comparative Example 3 above, their bending strength and scratch hardness were measured according to the aforementioned method, and the results are shown in Table 3 below.

[0148] [Table 3]

[0149]

[0150] As can be clearly seen from the results in Table 3, the molds (test pieces) of Examples 10-16, which are formed by simultaneously mixing and heating dry coated sand (DCS2) to wet coated sand (WCS) and molding it using a preheated molding die under the heated state, have excellent flexural strength, scratch hardness, wet strength, and thus excellent strength retention over time.

[0151] In contrast, it can be seen that for the mold shown in Comparative Example 3, which is made by molding wet coated sand (WCS) obtained by wetting dry coated sand (DCS2) at room temperature without preheating, the bending strength immediately after molding is low. In addition, the bending strength after 1 hour and 24 hours of molding is insufficient, and the strength retention rate after moisture absorption is also poor. Furthermore, the scraping hardness of the mold after 1 hour of molding is also insufficient.

Claims

1. A method for manufacturing a casting mold, characterized in that, A dry coated sand is prepared by coating the surface of refractory aggregate with a water-soluble binder. An aqueous medium is added to the sand, and the mixture is kneaded to form a wet coated sand under heating. The wet coated sand is then filled into a preheated mold while maintaining its heating state for molding. The temperature of the wet coated sand under heating is 30°C to 100°C.

2. The method for manufacturing a casting mold according to claim 1, characterized in that, After preheating the dry coated sand, the aqueous medium is added and the mixture is kneaded, thereby wetting the dry coated sand and forming the wet coated sand under heating.

3. The method for manufacturing a casting mold according to claim 2, characterized in that, The preheating temperature of the dry coated sand is 32℃~150℃.

4. The method for manufacturing a casting mold according to claim 1, characterized in that, The dry coated sand at room temperature is mixed and heated while an aqueous medium is added, thereby forming the wet coated sand under heating.

5. The method for manufacturing a casting mold according to claim 4, characterized in that, The mixing and heating of the dry coated sand are carried out in a mixing device, and the mixing device is preheated before the dry coated sand is added.

6. The method for manufacturing a casting mold according to claim 5, characterized in that, The wall surface of the mixing device that comes into contact with the dry coated sand is preheated to a temperature of 50°C to 200°C.

7. The method for manufacturing a casting mold according to any one of claims 4 to 6, characterized in that, The dry coated sand is mixed and heated, and the aqueous medium is added just before the mixing is finished.

8. The method for manufacturing a casting mold according to claim 7, characterized in that, The addition of the aqueous medium begins 30 seconds to 2 minutes before the end of the mixing time.

9. The method for manufacturing a casting mold according to any one of claims 4 to 6 and 8, characterized in that, The aqueous medium is in a liquid or vapor state.

10. The method for manufacturing a casting mold according to claim 7, characterized in that, The aqueous medium is in a liquid or vapor state.

11. The method for manufacturing a casting mold according to any one of claims 1 to 6, 8, and 10, characterized in that, The aqueous medium is preheated to a temperature below its boiling point.

12. The method for manufacturing a casting mold according to claim 7, characterized in that, The aqueous medium is preheated to a temperature below its boiling point.

13. The method for manufacturing a casting mold according to claim 9, characterized in that, The aqueous medium is preheated to a temperature below its boiling point.

14. The method for manufacturing a casting mold according to claim 11, characterized in that, The preheating temperature of the aqueous medium is 30℃~100℃.

15. The method for manufacturing a casting mold according to claim 12 or 13, characterized in that, The preheating temperature of the aqueous medium is 30℃~100℃.

16. The method for manufacturing a casting mold according to any one of claims 1 to 6, 8, 10, and 12 to 14, characterized in that, The aqueous medium is added at a ratio of 0.3 to 6 parts by mass relative to 100 parts by mass of the dry coated sand.

17. The method for manufacturing a casting mold according to claim 7, characterized in that, The aqueous medium is added at a ratio of 0.3 to 6 parts by mass relative to 100 parts by mass of the dry coated sand.

18. The method for manufacturing a casting mold according to claim 9, characterized in that, The aqueous medium is added at a ratio of 0.3 to 6 parts by mass relative to 100 parts by mass of the dry coated sand.

19. The method for manufacturing a casting mold according to claim 11, characterized in that, The aqueous medium is added at a ratio of 0.3 to 6 parts by mass relative to 100 parts by mass of the dry coated sand.

20. The method for manufacturing a casting mold according to claim 15, characterized in that, The aqueous medium is added at a ratio of 0.3 to 6 parts by mass relative to 100 parts by mass of the dry coated sand.

21. The method for manufacturing a casting mold according to any one of claims 1-6, 8, 10, 12-14, 17-20, characterized in that, The molding die is preheated to a temperature of 40°C to 250°C.

22. The method for manufacturing a casting mold according to claim 7, characterized in that, The molding die is preheated to a temperature of 40°C to 250°C.

23. The method for manufacturing a casting mold according to claim 9, characterized in that, The molding die is preheated to a temperature of 40°C to 250°C.

24. The method for manufacturing a casting mold according to claim 11, characterized in that, The molding die is preheated to a temperature of 40°C to 250°C.

25. The method for manufacturing a casting mold according to claim 15, characterized in that, The molding die is preheated to a temperature of 40°C to 250°C.

26. The method for manufacturing a casting mold according to claim 16, characterized in that, The molding die is preheated to a temperature of 40°C to 250°C.

27. The method for manufacturing a casting mold according to any one of claims 1-6, 8, 10, 12-14, 17-20, and 22-26, characterized in that, The water-soluble adhesive is a soluble silica compound.

28. The method for manufacturing a casting mold according to claim 7, characterized in that, The water-soluble adhesive is a soluble silica compound.

29. The method for manufacturing a casting mold according to claim 9, characterized in that, The water-soluble adhesive is a soluble silica compound.

30. The method for manufacturing a casting mold according to claim 11, characterized in that, The water-soluble adhesive is a soluble silica compound.

31. The method for manufacturing a casting mold according to claim 15, characterized in that, The water-soluble adhesive is a soluble silica compound.

32. The method for manufacturing a casting mold according to claim 16, characterized in that, The water-soluble adhesive is a soluble silica compound.

33. The method for manufacturing a casting mold according to claim 21, characterized in that, The water-soluble adhesive is a soluble silica compound.

34. The method for manufacturing a mold according to any one of claims 1-6, 8, 10, 12-14, 17-20, 22-26, 28-33, characterized in that, The dry coated sand contains a filler improver.

35. The method for manufacturing a casting mold according to claim 7, characterized in that, The dry coated sand contains a filler improver.

36. The method for manufacturing a casting mold according to claim 9, characterized in that, The dry coated sand contains a filler improver.

37. The method for manufacturing a casting mold according to claim 11, characterized in that, The dry coated sand contains a filler improver.

38. The method for manufacturing a casting mold according to claim 15, characterized in that, The dry coated sand contains a filler improver.

39. The method for manufacturing a casting mold according to claim 16, characterized in that, The dry coated sand contains a filler improver.

40. The method for manufacturing a casting mold according to claim 21, characterized in that, The dry coated sand contains a filler improver.

41. The method for manufacturing a casting mold according to claim 27, characterized in that, The dry coated sand contains a filler improver.

42. The method for manufacturing a mold according to any one of claims 1-6, 8, 10, 12-14, 17-20, 22-26, 28-33, 35-41, characterized in that, The dry coated sand contains a moisture resistance improver.

43. The method for manufacturing a casting mold according to claim 7, characterized in that, The dry coated sand contains a moisture resistance improver.

44. The method for manufacturing a casting mold according to claim 9, characterized in that, The dry coated sand contains a moisture resistance improver.

45. The method for manufacturing a casting mold according to claim 11, characterized in that, The dry coated sand contains a moisture resistance improver.

46. ​​The method for manufacturing a casting mold according to claim 15, characterized in that, The dry coated sand contains a moisture resistance improver.

47. The method for manufacturing a casting mold according to claim 16, characterized in that, The dry coated sand contains a moisture resistance improver.

48. The method for manufacturing a casting mold according to claim 21, characterized in that, The dry coated sand contains a moisture resistance improver.

49. The method for manufacturing a casting mold according to claim 27, characterized in that, The dry coated sand contains a moisture resistance improver.

50. The method for manufacturing a casting mold according to claim 34, characterized in that, The dry coated sand contains a moisture resistance improver.

51. The method for manufacturing a mold according to any one of claims 1-6, 8, 10, 12-14, 17-20, 22-26, 28-33, 35-41, 43-50, characterized in that, After the prepared dry coated sand is transported to the molding site, which serves as the manufacturing location for the mold, the aqueous medium is added to the dry coated sand and mixed to form the wet coated sand under heating.

52. The method for manufacturing a casting mold according to claim 7, characterized in that, After the prepared dry coated sand is transported to the molding site, which serves as the manufacturing location for the mold, the aqueous medium is added to the dry coated sand and mixed to form the wet coated sand under heating.

53. The method for manufacturing a casting mold according to claim 9, characterized in that, After the prepared dry coated sand is transported to the molding site, which serves as the manufacturing location for the mold, the aqueous medium is added to the dry coated sand and mixed to form the wet coated sand under heating.

54. The method for manufacturing a casting mold according to claim 11, characterized in that, After the prepared dry coated sand is transported to the molding site, which serves as the manufacturing location for the mold, the aqueous medium is added to the dry coated sand and mixed to form the wet coated sand under heating.

55. The method for manufacturing a casting mold according to claim 15, characterized in that, After the prepared dry coated sand is transported to the molding site, which serves as the manufacturing location for the mold, the aqueous medium is added to the dry coated sand and mixed to form the wet coated sand under heating.

56. The method for manufacturing a casting mold according to claim 16, characterized in that, After the prepared dry coated sand is transported to the molding site, which serves as the manufacturing location for the mold, the aqueous medium is added to the dry coated sand and mixed to form the wet coated sand under heating.

57. The method for manufacturing a casting mold according to claim 21, characterized in that, After the prepared dry coated sand is transported to the molding site, which serves as the manufacturing location for the mold, the aqueous medium is added to the dry coated sand and mixed to form the wet coated sand under heating.

58. The method for manufacturing a casting mold according to claim 27, characterized in that, After the prepared dry coated sand is transported to the molding site, which serves as the manufacturing location for the mold, the aqueous medium is added to the dry coated sand and mixed to form the wet coated sand under heating.

59. The method for manufacturing a casting mold according to claim 34, characterized in that, After the prepared dry coated sand is transported to the molding site, which serves as the manufacturing location for the mold, the aqueous medium is added to the dry coated sand and mixed to form the wet coated sand under heating.

60. The method for manufacturing a casting mold according to claim 42, characterized in that, After the prepared dry coated sand is transported to the molding site, which serves as the manufacturing location for the mold, the aqueous medium is added to the dry coated sand and mixed to form the wet coated sand under heating.

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