Inorganic coated sand and method for manufacturing inorganic coated sand

Abstract

To provide a dried inorganic coated sand capable of shortening the drying time of the inorganic coated sand in manufacturing while maintaining the strength of a mold.SOLUTION: A dried inorganic coated sand comprises: a refractory aggregate; and an inorganic binder layer formed on a surface of the refractory aggregate. The inorganic binder layer contains a silicate and a particulate compound, and the particulate compound has an aspect ratio of 3 or more and 10 or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to inorganic coated sand and a method for manufacturing the same.

Background Art

[0002] As a mold used for casting a casting, for example, a dry inorganic coated sand having a refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate is used to mold it into a desired shape. The dry inorganic coated sand is obtained by solidifying a liquid inorganic binder composition on the surface of the refractory aggregate to form a layer.

[0003] As a technology related to conventional inorganic coated sand, for example, Patent Document 1 (Japanese Patent Application Laid-Open No. 2022-001384) describes casting sand having fluidity at room temperature, which is obtained by coating the surface of silica sand with at least one of sodium silicate and sodium metasilicate and hydrated calcined kaolin.

[0004] Further, Patent Document 2 (Japanese Patent Application Laid-Open No. 2022-179288) describes that, from the viewpoint of suppressing the sintering of sand derived from a mold to a casting, in a dry inorganic coated sand having an inorganic binder layer, the binder layer contains one or more selected from the group consisting of graphite, mica, and zirconium silicate, and the total content of graphite, mica, and zirconium silicate is 7 parts by mass or more and 70 parts by mass or less with respect to 100 parts by mass of the inorganic binder.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] The inventor has found that there is room for improvement in shortening the time required for the inorganic binder composition to solidify on the surface of the refractory aggregate until a layer is obtained in the process of forming an inorganic binder layer on the refractory aggregate while maintaining the strength of the mold by the inorganic coated sand, as described in Patent Documents 1 and 2.

Means for Solving the Problems

[0007] Therefore, the inventor conducted intensive studies to shorten the drying time during the production of inorganic coated sand while maintaining the strength of the mold by the inorganic coated sand. As a result, it was found that there are cases where the drying time can be effectively shortened and cases where it cannot, and it was found that controlling the aspect ratio of the particulate compound is effective, and the present invention was completed.

[0008] According to the present invention, there is provided a dry inorganic coated sand having a refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate, wherein the inorganic binder layer contains a metasilicate hydrate and a particulate compound, and the particulate compound has an aspect ratio of 3 or more and 10 or less.

[0009] Further, according to the present invention, there is provided a casting mold formed of the above inorganic coated sand.

[0010] Further, according to the present invention, there is provided a method for producing a dry inorganic coated sand having a refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate, the method including a step of mixing a refractory aggregate, a metasilicate hydrate, and a particulate compound to form an inorganic binder layer on the surface of the refractory aggregate, wherein the particulate compound has an aspect ratio of 3 or more and 10 or less.

Advantages of the Invention

[0011] According to the present invention, an inorganic coated sand capable of shortening the drying time during the production of the inorganic coated sand while maintaining the strength of the mold made of the inorganic coated sand can be provided.

Embodiments for Carrying Out the Invention

[0012] In this specification, "a~b" indicating a numerical range represents a range of a or more and b or less unless otherwise specified. Also, the configurations and elements described in each embodiment can be appropriately combined as long as the effects of the invention are not impaired. Further, in this specification, "coating" is not limited to being continuous, and may have partially discontinuous portions. Hereinafter, embodiments of the present invention will be described.

[0013] <Inorganic Coated Sand> The inorganic coated sand of this embodiment is a dry inorganic coated sand having a refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate, wherein the inorganic binder layer contains a metasilicate hydrate and a particulate compound, and the aspect ratio of the particulate compound is 3 or more and 10 or less.

[0014] Thereby, the drying time during the production of the inorganic coated sand can be shortened while maintaining the strength of the mold made of the inorganic coated sand. Although the details of such a reason are not clear, it is presumed as follows. First, when forming the inorganic binder layer on the surface of the refractory aggregate, it is necessary to solidify the inorganic binder composition on the surface of the refractory aggregate. Therefore, by making the particulate compound into an appropriate shape, the contact area between the particulate compound and the inorganic binder and the contact probability with the crystallization starting point on the particulate compound can be effectively increased, and crystallization can be promoted. As a result, it is considered that the drying time during the production of the inorganic coated sand can be effectively shortened.

[0015] Hereinafter, details will be described.

[0016] [Particulate compound] It is presumed that the particulate compound can promote the crystallization of the metasilicate hydrate by functioning as a crystal nucleus of the metasilicate hydrate.

[0017] The particulate compound in this embodiment means small particles, and includes various shapes such as needle-like and plate-like as long as a predetermined aspect ratio is satisfied. The particulate compound may be either an organic particulate compound or an inorganic particulate compound, and may also be a mixture of one or more kinds, or a single compound.

[0018] Examples of the organic particulate compound include polymer powders; aliphatic powders having a total of two or more of one or more groups selected from the group consisting of an ester group, a hydroxyl group, and an amide group. Examples of the above polymer powders include, for example, polyamide, polyester, polyethylene, polypropylene, polyisopropylene, polybutene, polystyrene, polyurethane, polytetrafluoroethylene, polymethyl methacrylate, polymethylsilsesquioxane, styrene-acrylic acid copolymer, divinylbenzene-styrene copolymer, vinyl resin, urea resin, phenol resin, fluororesin, acrylic resin, melamine resin, epoxy resin, polycarbonate resin, cellulose, starch, cellulose acetate, nylon, silicone resin, polyethylene glycol, polypropylene glycol, organic phosphate metal salt, silk, etc. One or more selected from the above are mentioned. Examples of the aliphatic powder include one or more selected from carboxylic acid amides, aliphatic carboxylates, aliphatic alcohols, carboxylic acid esters, phosphate esters salts, etc. More specifically, for example, lauroyl lysine, lauroyl sarcosine, lauroyl alanine, lauroyl methyl alanine, erucic acid amide, stearic acid amide, ethylene bis lauric acid amide, palmitic acid amide, hydroxystearic acid amide, sodium laurate, potassium laurate, zinc laurate, magnesium stearate, calcium stearate, barium stearate, zinc stearate, aluminum stearate, sodium myristate, potassium myristate, magnesium myristate, calcium myristate, barium myristate, zinc myristate, calcium oxalate, lauryl alcohol, myristyl alcohol, palmityl alcohol, stearyl alcohol, benzylidene sorbitol, dibenzylidene sorbitol, sucrose stearate, sucrose palmitate, sodium phenylphosphonate, potassium phenylphosphonate, zinc phenylphosphonate, etc.

[0019] Examples of the inorganic particulate compound include, specifically, minerals such as talc, mica, halloysite, kaolin, illite, montmorillonite, vermiculite, palygorskite, pyrophyllite, beidellite, nontronite, saponite, hectorite, sauconite, calcium silicate, aluminum silicate, wollastonite, glass flakes, molybdenum sulfide, carbon nanotubes, graphite, and carbon black; metal oxides such as titanium oxide, magnesium oxide, aluminum oxide, neodymium oxide, and zinc oxide; nitrates such as potassium nitrate and sodium nitrate; sulfates such as potassium sulfate, aluminum sulfate, sodium sulfite, and calcium sulfate; carbonates such as strontium carbonate, magnesium carbonate, and calcium carbonate; metal foils, boron nitride, glass fibers, carbon fibers, graphite fibers, metal fibers, gypsum fibers, silica fibers, silica-alumina fibers, and zirconia fibers; reinforcing fibers such as cellulose nanofibers and derivatives thereof. Among them, talc, kaolin, and mica are preferred.

[0020] (Aspect ratio) From the viewpoint of improving the mold strength while having a good dry state time, the aspect ratio of the particulate compound is 3 or more, preferably 4 or more, and more preferably 6 or more. On the other hand, from the viewpoint of shortening the dry state time while obtaining a good mold strength, the aspect ratio of the particulate compound is 10 or less, preferably 9 or less, and more preferably 8 or less.

[0021] The aspect ratio of the particulate compound is defined as follows. The particulate compound is observed with a scanning electron microscope (SEM) at 500 to 10,000 times magnification, and 10 particles capable of observing the cross section are arbitrarily selected. The longest diameter (major axis) (μm) and the longest diameter (minor axis) (μm) perpendicular to the major axis of the particle are measured. The aspect ratio (major axis (μm) / minor axis (μm)) can be calculated from the obtained measurement values, and further, the arithmetic mean value thereof can be calculated.

[0022] (Particle size) The particle size of the particulate compound is preferably 0.1 μm or more, more preferably 0.3 μm or more, and still more preferably 0.5 μm or more, from the viewpoint of shortening the drying time while maintaining good mold strength. On the other hand, the particle size of the particulate compound is preferably 15 μm or less, more preferably 12 μm or less, and still more preferably 6 μm or less, from the viewpoint of improving the mold strength while maintaining a good drying time.

[0023] The particle size of the particulate compound is specifically measured by the following method.

[0024] (Particle size measurement method) The measurement method using a laser diffraction particle size distribution analyzer LA-960V2 (manufactured by Horiba, Ltd.) is as follows. ·Measurement method: Flow method ·Dispersion medium Regarding the selection of the dispersion medium, follow the following procedure. First, add 0.1 g of the measurement sample to a beaker containing 50 ml of water, stir with a stirring rod for 1 minute, and let it stand for 5 minutes. After that, if no phenomenon such as the sample floating in water, adhering to the beaker, sedimenting, or dissolving occurs, use water as the dispersion medium. If the sample floats in water, adheres to the beaker, or sediments, consider adding a surfactant (such as polyoxyethylene, sorbitan monolaurate), adding a dispersant (such as 0.2% sodium hexametaphosphate solution), or changing the dispersion medium to an organic solvent (such as methanol), and use a dispersion medium in which no phenomenon such as the sample floating in water, adhering to the beaker, or sedimenting occurs. Also, for the case where the sample dissolves, consider an organic solvent. ·Dispersion method: Stirring, built-in ultrasonic wave for 3 minutes ·Sample concentration: 2 mg / 100 mL ·Refractive index Regarding the selection of the refractive index, follow the following procedure. First, search for the refractive index of the corresponding substance using the software attached to the device. If the refractive index is not in the list, search for the literature value in a chemical handbook or other reference book. If the refractive index cannot be found even after searching, use the refractive index of an approximate composition or chemical formula (for organic substances: around 1.60, for inorganic substances: 1.70 - 3.00). In the case of a mixture, use the refractive index of the substance with the highest content or the substance that constitutes the fine particles.

[0025] For the particle size (μm) of the particulate compound, in the above laser diffraction particle size distribution, when it has a single peak, use the value (μm) at 50% volume cumulative, and when it has multiple peaks, use the value (μm) of the peak with the highest volume frequency.

[0026] The particulate compound preferably has a single peak in the above laser diffraction particle size distribution.

[0027] Also, the particulate compound may be pre-screened to remove at least one of the ultrafine particles and coarse particles, or it may be a pulverized product of coarse particles using a mortar or the like.

[0028] The content of the particulate compound is preferably 0.01 part by mass or more, more preferably 0.02 part by mass or more, and even more preferably 0.05 part by mass or more with respect to 100 parts by mass of the refractory aggregate, from the viewpoint of shortening the drying time while maintaining the strength of the mold well. On the other hand, the content of the particulate compound is preferably 4.0 parts by mass or less, more preferably 3.0 parts by mass or less, and even more preferably 2.0 parts by mass or less with respect to 100 parts by mass of the refractory aggregate, from the viewpoint of improving the strength of the mold while maintaining a good drying time.

[0029] When the particulate compound contains one or more selected from talc, kaolin, and mica, the content of one or more selected from talc, kaolin, and mica is preferably 80% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, even more preferably 98% by mass or more, and even more preferably 99.9% by mass or more, based on the total amount of the particulate compound.

[0030] Hereinafter, the inorganic coated sand will be described more specifically.

[0031] The inorganic coated sand is in a dry state. The dry coated sand means a coated sand for which a measured value can be obtained when measuring the dynamic angle of repose regardless of the moisture content. The dynamic angle of repose is preferably 80° or less, more preferably 45° or less, and still more preferably 30° or less.

[0032] The dynamic angle of repose of the inorganic coated sand can be measured by the following method. (Method for measuring the dynamic angle of repose) Put half of the volume of the coated sand into a cylindrical transparent plastic bottle, hold it so that the axis is in the horizontal direction, and rotate it around the horizontal axis at a rotational speed of 60 rpm. The slope of the flowing coated sand layer in the cylinder becomes a flat surface. Measure the angle formed between such a slope and the horizontal plane. In addition, when the coated sand does not flow in the cylinder, or even if it flows, the slope of the coated sand layer is not formed as a flat surface, and as a result, the dynamic angle of repose cannot be measured, it is in a wet state.

[0033] Specifically, the inorganic coated sand is composed of a group of particles of the inorganic coated sand.

[0034] From the viewpoint of improving fluidity and further enhancing the filling property into the molding die, the inorganic coated sand is preferably spherical. Here, the inorganic coated sand being spherical means having a round shape like a ball.

[0035] The sphericity of the inorganic-coated sand is preferably 0.80 or more, more preferably 0.82 or more, and still more preferably 0.85 or more, from the viewpoints of fluidity, mold quality, and improvement of mold strength, and from the viewpoint of ease of molding of the mold. Also, specifically, the upper limit value of the sphericity is 1. In the present embodiment, the sphericity of the inorganic-coated sand specifically coincides with the sphericity of the refractory aggregate described later.

[0036] The sphericity of the inorganic-coated sand is obtained by image analysis of an image (photo) of particles obtained by an optical microscope or a digital scope (for example, VH-8000 type manufactured by Keyence Corporation), to obtain the area of the particle projection cross-section of the particle and the perimeter of the cross-section. Then, sphericity = [circumference of a perfect circle (mm) with the same area as the area of the particle projection cross-section (mm 2 )] / [perimeter of the particle projection cross-section (mm)] is calculated, and for any 50 particles, the values obtained can be averaged.

[0037] The average particle diameter of the inorganic-coated sand is preferably 0.05 mm or more, more preferably 0.1 mm or more, from the viewpoints of improving mold quality and mold strength, ease of molding of the mold, and storage stability. Also, when the average particle diameter of the inorganic-coated sand is equal to or greater than the above lower limit value, the amount of use of the coating layer or the like can be reduced during the manufacture of the mold, which is also preferable in terms of making the regeneration of the inorganic-coated sand easier. The average particle diameter of the inorganic-coated sand is preferably 2 mm or less, more preferably 1 mm or less, and still more preferably 0.5 mm or less, from the viewpoints of improving mold quality and mold strength, and ease of molding of the mold. Also, when the average particle diameter of the inorganic-coated sand is equal to or less than the above upper limit value, the porosity becomes small during the manufacture of the mold, which is also preferable in terms of increasing the mold strength.

[0038] In the present embodiment, the average particle diameter of the inorganic-coated sand can be specifically measured by the following method. (Method for measuring average particle diameter) When the sphericity from the particle projection cross-section of the particle is 1, measure the diameter (mm). On the other hand, when the sphericity < 1, measure the major axis diameter (mm) and minor axis diameter (mm) of the randomly oriented particles, and obtain (major axis diameter + minor axis diameter) / 2. For any 100 particles, average the values obtained respectively to obtain the average particle diameter (mm). The major axis diameter and minor axis diameter are defined as follows. When the particle is stabilized on a plane and the projection image of the particle on the plane is sandwiched between two parallel lines, the width of the particle when the distance between the parallel lines is minimized is called the minor axis diameter. On the other hand, when the particle is sandwiched between two parallel lines in a direction perpendicular to these parallel lines, the distance is called the major axis diameter. The major axis diameter and minor axis diameter of the particle can be obtained by photographing an image (photo) of the particle with an optical microscope or a digital scope (for example, VH-8000 type manufactured by Keyence Corporation) and performing image analysis on the obtained image.

[0039] Hereinafter, each component of the inorganic coated sand will be described.

[0040] [Refractory aggregate] Specifically, the refractory aggregate is composed of a particle group of refractory aggregate. The material of the refractory aggregate is one or more selected from the group consisting of natural sand and artificial sand.

[0041] Examples of natural sand include one or more selected from the group consisting of silica sand mainly composed of quartz, chromite sand, zircon sand, olivine sand, and alumina sand.

[0042] Examples of artificial sand include one or more selected from the group consisting of synthetic mullite sand, SiO2-based casting sand mainly composed of SiO2, Al2O3-based casting sand mainly composed of Al2O3, SiO2 / Al2O3-based casting sand, SiO2 / MgO-based casting sand, SiO2 / Al2O3 / ZrO2-based casting sand, SiO2 / Al2O3 / Fe2O3-based casting sand, and casting sand derived from slag. Here, the main component refers to the most abundant component among the components contained in the sand. Artificial sand refers to foundry sand that is not produced naturally, but rather is artificially prepared from metal oxide components and melted or sintered.

[0043] In addition, recycled sand obtained by recovering used refractory aggregates or recycled sand obtained by subjecting the recycled sand to a recycling process can also be used as artificial sand.

[0044] The content of each component such as SiO2, Al2O3, and Fe2O3 in the refractory aggregate can be measured using the following X-ray fluorescence method. The refractory aggregate is adjusted to a size of about 0.1 μm or less using a vibration mill and heated at 1050 °C for 1 hour. Thereafter, 5 g of lithium tetraborate and 0.5 g of the refractory aggregate are mixed and heated at 1200 °C for 10 minutes to be melted, and then cooled to prepare a sample in a glassy state (glass bead method). The sample is subjected to X-ray fluorescence analysis by the fundamental parameter (FP) method using an X-ray fluorescence analyzer ZSX Primus II (manufactured by Rigaku Corporation).

[0045] The sphericity of the refractory aggregate is the same as that of the above-mentioned inorganic-coated sand. Specifically, from the viewpoints of fluidity, mold quality, and improvement of mold strength, and the ease of molding of the mold, the sphericity of the refractory aggregate is preferably 0.80 or more, more preferably 0.82 or more, and even more preferably 0.85 or more. Also, specifically, the upper limit value of the sphericity is 1.

[0046] The measurement method of the sphericity of the refractory aggregate can use the same measurement method as that of the above-mentioned inorganic-coated sand.

[0047] From the viewpoints of improving mold quality and mold strength and the ease of molding of the mold, the average particle size of the refractory aggregate is preferably 0.05 mm or more, more preferably 0.1 mm or more. Also, when the average particle size of the refractory aggregate is equal to or greater than the above lower limit value, the amount of the inorganic binder layer used can be reduced during the manufacture of the mold, which is also preferable in terms of making the recycling of the inorganic-coated sand easier. The average particle size of the refractory aggregate is preferably 2 mm or less, more preferably 1 mm or less, and even more preferably 0.5 mm or less, from the viewpoints of improving mold quality and mold strength and the ease of molding the mold. Also, when the average particle size of the refractory aggregate is below the above upper limit value, it is also preferable in that the porosity becomes small and the mold strength can be increased during the production of the mold.

[0048] As the measurement method of the average particle size of the refractory aggregate, the same measurement method as that of the above inorganic-coated sand can be used.

[0049] The degree of amorphization of the refractory aggregate is preferably 20% or more, more preferably 30% or more, and even more preferably 40% or more, from the viewpoints of the surface of the aggregate becoming smoother and the mold strength being further improved and obtaining low thermal expansibility. The upper limit of the degree of amorphization of the refractory aggregate is not limited, but for example, it may be 100% or less, or may be 99% or less.

[0050] The degree of amorphization of the refractory aggregate can be measured by the following X-ray diffraction method. (X-ray diffraction method) The refractory aggregate is pulverized in a mortar and pressed onto the X-ray glass holder of a powder X-ray diffractometer for measurement. As the powder X-ray diffractometer, MultiFlex manufactured by Rigaku Corporation (light source CuKα ray, tube voltage 40 kV, tube current 40 mA) is used, and scanning is performed in the range of 2θ = 5 to 90° with a scanning interval of 0.01°, a scanning speed of 2° / min, and slits DS1, SS1, and RS 0.3 mm. In the range of 2θ = 10° to 50°, the X-ray intensities on the low-angle side and the high-angle side are connected by a straight line, the area under the straight line is taken as the background, and the crystallinity is obtained using the software attached to the instrument, and 100 is subtracted to obtain the degree of amorphization. Specifically, for the area above the background, the amorphous peak (halo) and each crystalline component are separated by curve fitting, and the area of each is obtained, and the degree of amorphization (%) is calculated by the following formula. Degree of amorphization (%) = Area of halo / (Area of crystalline component + Area of halo) × 100

[0051] There are various methods for controlling the degree of amorphization of refractory aggregates. Generally, it is preferable to use a manufacturing method such as rapidly cooling a melt. For example, there are methods of melting raw materials, pulverizing them with air and rapidly cooling them, or treating them in a flame and rapidly cooling them. In any case, the cooling method may be appropriately selected at various speeds depending on the material and particle size. Also, a method of amorphizing a once-crystallized material by heat treatment and cooling treatment is also conceivable.

[0052] [Inorganic binder layer] The inorganic binder layer is formed on the surface of the refractory aggregate. In other words, the inorganic binder layer covers the surface of the refractory aggregate. Note that the covering is not limited to being continuous, and there may be some discontinuous parts. From the inorganic binder layer, a mold can be formed as inorganic coated sand.

[0053] From the viewpoint of obtaining a high-strength casting mold, the coating amount of the inorganic binder layer contained in the inorganic coated sand is, for example, 0.1 part by mass or more, preferably 0.2 part by mass or more, more preferably 0.5 part by mass or more, still more preferably 1 part by mass or more, and even more preferably 2 parts by mass or more with respect to 100 parts by mass of the refractory aggregate. Also, from the viewpoint of obtaining a high-strength casting mold, the coating amount of the inorganic binder layer contained in the inorganic coated sand is, for example, 15 parts by mass or less, preferably 10 parts by mass or less, and more preferably 8 parts by mass or less with respect to 100 parts by mass of the refractory aggregate.

[0054] Also, the inorganic binder layer may have a layer containing at least a metasilicate hydrate, and may be a single layer or a multi-layer. Also, the layer containing at least the metasilicate hydrate is formed by an inorganic binder composition containing the metasilicate hydrate. For example, the inorganic binder layer may be a layer coated with a mixture of a metasilicate hydrate and the amorphous SiO2-containing fine particles described later; a layer further coated with the amorphous SiO2-containing fine particles on the layer coated with the metasilicate hydrate; or a layer further coated with the amorphous SiO2-containing fine particles on the layer coated with a mixture of the metasilicate hydrate and the amorphous SiO2-containing fine particles.

[0055] (Metasilicate hydrate) The metasilicate hydrate is one of the components of the inorganic binder layer and is also one of the components constituting the above inorganic binder. When the metasilicate hydrate is used, the crystallinity of the inorganic binder layer can be improved, and furthermore, the inorganic coated sand becomes dry and has excellent normal temperature fluidity, which is preferable. In addition, by using the metasilicate hydrate, an inorganic binder layer can be formed on the surface of the refractory aggregate in a state where it is not dissolved in water. That is, in the process of manufacturing the inorganic coated sand, since it is not necessary to use an aqueous solution of the metasilicate hydrate, the step of removing water can be omitted, and the manufacturing method can be simplified. In addition, since the metasilicate of the inorganic binder layer is a hydrate, it is not necessary to ventilate steam to cure the mold, and the equipment can be simplified. In addition, the metasilicate hydrate can also be produced by using a mixed solution obtained by mixing water glass, caustic alkali, and water in a specific ratio. In addition, the SiO2 / Na2O molar ratio of the metasilicate hydrate in the present embodiment is 0.9 to 1.1.

[0056] Specific examples of the above water glass include one or more selected from the group consisting of sodium silicate No. 1 to No. 5. Here, sodium silicate is classified into No. 1 to No. 5 according to the molar ratio of SiO2 / Na2O, and sodium silicate No. 1 to No. 3 are defined in JIS-K-1408. The molar ratio of SiO2 / Na2O in each number is specifically as follows. Sodium silicate No. 1: Molar ratio of SiO2 / Na2O = 2.0 to 2.3 Sodium silicate No. 2: Molar ratio of SiO2 / Na2O = 2.4 to 2.6 Sodium silicate No. 3: molar ratio of SiO2 / Na2O = 2.8 - 3.3 Sodium silicate No. 4: molar ratio of SiO2 / Na2O = 3.3 - 3.5 Sodium silicate No. 5: molar ratio of SiO2 / Na2O = 3.6 - 3.8 Moreover, by mixing two or more kinds of sodium silicate, the molar ratio of SiO2 / Na2O may be adjusted to a desired level. The water glass is preferably at least one selected from sodium silicate No. 1 and sodium silicate No. 2.

[0057] The salts of metasilicate hydrate include alkali metals, and specifically, it is preferably one or more selected from lithium, sodium, and potassium, more preferably at least one of sodium and potassium, and even more preferably sodium.

[0058] From the viewpoints of improving the mold strength, excellent productivity, and easy availability, the content of metasilicate in the inorganic binder is preferably 80% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, even more preferably 98% by mass or more, and even more preferably substantially 100% by mass. The content of metasilicate in the inorganic binder refers to the content of metasilicate with respect to the total components other than water in the inorganic binder layer.

[0059] Moreover, from the viewpoint of improving the mold strength while improving the storage stability, the content of metasilicate in the inorganic coated sand is preferably 0.03 part by mass or more, more preferably 0.1 part by mass or more, still more preferably 0.5 part by mass or more, and even more preferably 0.7 part by mass or more with respect to 100 parts by mass of the refractory aggregate. Also, from the viewpoint of maintaining the storage stability and improving the filling property into the molding die, the content of metasilicate in the inorganic coated sand is preferably 5 parts by mass or less, more preferably 4 parts by mass or less, still more preferably 3 parts by mass or less with respect to 100 parts by mass of the refractory aggregate.

[0060] As a method for confirming that the inorganic binder layer contains metasilicate hydrate, for example, the inorganic coated sand is put into a crusher such as a mill to peel off only the inorganic binder layer components, and the inorganic binder layer components are analyzed by XRD to confirm the peak indicating the crystal structure of metasilicate hydrate; the inorganic coated sand is immersed in water and stirred for a certain period of time to elute the inorganic binder layer components, and the eluted components are dried and the dry solid content is analyzed by XRD to confirm the peak indicating the crystal structure of metasilicate, and the water content is analyzed by the following method to confirm that it is metasilicate hydrate.

[0061] <Measurement of water content of hydrate> (1) Weigh 10 g of the inorganic coated sand before adding additives such as amorphous SiO2-containing fine particles into a crucible that has been air-baked and weighed, and calculate the water content (%) (A) in the inorganic coated sand using the mass reduction rate (%) after heating at 900 °C for 1 hour. A = [(M1 - M2) / M3] × 100 (M1: Total mass of the crucible and the inorganic coated sand before firing (g), M2: Total mass of the crucible and the inorganic coated sand after firing (g), M3: Mass of the inorganic coated sand before firing (g)) (2) Weigh 100 g of the inorganic coated sand before adding additives such as amorphous SiO2-containing fine particles, immerse it in 200 mL or more of water or hot water and stir for 1 hour or more to extract metasilicate hydrate. Filter and remove the refractory aggregate from the obtained extract, and then remove the water by vacuum distillation at 40 °C and an internal air pressure of 15 mmHg or less using a rotary evaporator, and then heat and dry at a temperature of 120 °C to 180 °C for 1 to 3 hours, and weigh the dry matter weight. Calculate the dry solid content (%) (B) of metasilicate hydrate in the inorganic coated sand. B = (M12 / M11) × 100 (M11: Mass of the inorganic coated sand (g), M12: Dry matter weight (g)) (3) Water content of metasilicate hydrate = [(A) / molecular weight of water] / [(B) / molecular weight of metasilicate anhydride]

[0062] The inorganic binder layer may further contain components other than the metasilicate hydrate and the particulate compound. For example, it may contain inorganic fine particles (excluding the above particulate compound with an aspect ratio of 2 or more and 10 or less), a humectant, a moisture resistance improver, a coupling agent that strengthens the bond between the refractory aggregate and the inorganic binder composition, a lubricant, a surfactant, a mold release agent, etc.

[0063] (Inorganic fine particles) The inorganic binder layer may contain inorganic fine particles other than the inorganic particulate compound of the present embodiment. Among them, from the viewpoint of high reactivity with the metasilicate hydrate, it is preferable to use amorphous SiO2-containing fine particles having an aspect ratio of less than 3.

[0064] Examples of the amorphous SiO2-containing fine particles include precipitated silica, calcined silica produced by electric arc or flame hydrolysis, silica produced by thermal decomposition of ZrSiO4, silicon dioxide produced by oxidation of metallic silicon with a gas containing oxygen, and quartz glass powder of spherical particles produced from crystalline quartz by melting and subsequent rapid cooling. These can be used alone, and it is also possible to mix and use two or more of them.

[0065] The degree of amorphization of the amorphous SiO2-containing fine particles is preferably 98% or more from the viewpoint of more firmly binding the particles of the inorganic-coated sand via the amorphous SiO2-containing fine particles.

[0066] The degree of amorphization of the amorphous SiO2-containing fine particles can be determined by the same X-ray diffraction method as that for the refractory aggregate.

[0067] The amorphous SiO2-containing fine particles are preferably in a particulate state. The average particle diameter of the amorphous SiO2-containing fine particles is 0.1 μm or more and 2.0 μm or less from the viewpoints of improving the mold strength per unit mass and the handleability.

[0068] The average particle diameter of the amorphous SiO2-containing fine particles is determined from the observation images of a scanning electron microscope. In this case, various image analysis methods can be used.

[0069] From the viewpoint of improving the mold strength, the SiO2 content (mass %) in the amorphous SiO2-containing fine particles is preferably 90 mass % or more. The SiO2 content (mass %) in the amorphous SiO2-containing fine particles can be measured by the fluorescent X-ray method in the same manner as for refractory aggregates.

[0070] From the viewpoints of improving the mold strength and the mold surface shape and suppressing dust scattering while obtaining storage stability, the content of the amorphous SiO2-containing fine particles is preferably 0.1 part by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the refractory aggregate.

[0071] Furthermore, as the inorganic fine particles, for example, crystalline silica, silicon; 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, magnesium metaborate; 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, zinc phosphate; hydroxides such as lithium hydroxide, magnesium hydroxide, calcium hydroxide, strontium hydroxide, barium hydroxide, aluminum hydroxide, zinc hydroxide, etc., one or more kinds of fine particles selected therefrom may be used.

[0072] The coupling agent is not limited, and examples thereof include silane coupling agents, zircon coupling agents, titanium coupling agents, etc. Examples of the humectant include polyhydric alcohols, water-soluble polymers, hydrocarbons, saccharides, proteins, and inorganic compounds other than those described above. Examples of the moisture resistance improver include carbonates, borates, sulfates, phosphates, and the like. Examples of the lubricant include waxes; fatty acid amides; alkylene fatty acid amides; stearic acid; stearyl alcohol; metal stearates such as lead stearate, zinc stearate, calcium stearate, and magnesium stearate; monoglyceryl stearate; stearyl stearate; hydrogenated oils, and the like. Examples of the mold release agent include paraffin, wax, light oil, machine oil, spindle oil, insulating oil, waste oil, vegetable oil, fatty acid ester, organic acid, fluorine-based mold release agent, silicone-based mold release agent, and the like.

[0073] <Method for manufacturing inorganic coated sand> Next, the method for manufacturing the inorganic coated sand of the present embodiment will be described. The method for manufacturing the inorganic coated sand of the present embodiment is a method for manufacturing dry inorganic coated sand having a refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate, and includes a step of mixing a refractory aggregate, a metasilicate hydrate, and a particulate compound to form an inorganic binder layer on the surface of the refractory aggregate. The particulate compound has an aspect ratio of 3 or more and 10 or less. Thereby, it is possible to improve the strength of the mold using the inorganic coated sand while shortening the drying time.

[0074] Hereinafter, an example of the method for manufacturing the inorganic coated sand will be described in detail.

[0075] First, a particulate compound having an aspect ratio of 3 or more and 10 or less is prepared. The details of the particulate compound are as described above.

[0076] Next, an inorganic binder layer is formed on the surface of the refractory aggregate. Specifically, first, a particulate compound, an inorganic binder composition containing metasilicate hydrate, and a refractory aggregate are mixed to prepare a mixture. Examples of the mixing method include: a method of charging the particulate compound and the inorganic binder composition into the refractory aggregate heated to about 50°C to 100°C and mixing the refractory aggregate, the particulate compound, and the inorganic binder composition while melting the metasilicate hydrate; a method of charging the heat-melted inorganic binder composition and the particulate compound into the refractory aggregate and mixing them; a method of charging the refractory aggregate and the particulate compound into the inorganic binder composition dissolved in a liquid such as water and mixing them; a method of charging a mixed liquid obtained by mixing water glass, caustic alkali, and water in a specific ratio and the particulate compound into the refractory aggregate and mixing them, etc. Among these, from the viewpoint of easily controlling the moisture content in the obtained inorganic binder layer and easily obtaining inorganic coated sand with excellent fluidity, a method of charging the particulate compound and the heat-melted metasilicate hydrate into the refractory aggregate and mixing them; a method of charging a mixed liquid obtained by mixing water glass, caustic alkali, and water in a specific ratio and the particulate compound into the refractory aggregate and mixing them are preferable. Mixing conditions such as the stirring speed and treatment time when mixing each raw material can be appropriately determined according to the processing amount of the mixture.

[0077] In addition, in the above mixing step, from the viewpoint of reducing the fluidity of the metasilicate hydrate and fixing the metasilicate hydrate on the surface of the refractory aggregate, it may be cooled to a temperature below the melting temperature of the metasilicate hydrate. Thereby, the inorganic coated sand according to the present embodiment can be obtained.

[0078] <Mold> The casting mold of the present embodiment is formed of the inorganic coated sand in the above-described present embodiment. Examples of the molding method of the casting mold include a molding method using a heated molding die, a molding method in which steam is further passed through the heated molding die and then hot air is passed through.

[0079] As described above, the embodiments of the present invention have been described, but these are examples of the present invention, and various configurations other than the above can also be adopted.

[0080] Regarding the above-described embodiments, the present invention further discloses the following inorganic-coated sand, a method for manufacturing the inorganic-coated sand, and a method for manufacturing a casting mold for casting.

Example

[0081] Hereinafter, the present invention will be described by way of examples and comparative examples, but the present invention is not limited thereto.

[0082] (1) Materials [Refractory aggregate] · Refractory aggregate 1: Espar #60L (manufactured by Yamakawa Sangyo Co., Ltd., particle size: 241 μm, degree of amorphization 45%, sphericity 0.97)

[0083] [Inorganic binder] · Metasilicate 1: A mixture of sodium metasilicate (nonahydrate) (manufactured by Nippon Chemical Industry Co., Ltd., sodium metasilicate nonahydrate, melting point 47 °C, SiO2 / Na2O ratio = 0.9 - 1.1) and sodium metasilicate (pentahydrate) (manufactured by Nippon Chemical Industry Co., Ltd., sodium metasilicate pentahydrate, melting point 72 °C, SiO2 / Na2O ratio = 0.9 - 1.1) in a weight ratio of 4:3

[0084] [Particulate compound] · Particulate compound 1: Nano Ace D600 (manufactured by Nippon Talc Co., Ltd., talc, aspect ratio 8, particle size 0.6 μm) · Particulate compound 2: Micro Ace P-8 (manufactured by Nippon Talc Co., Ltd., talc, aspect ratio 9, particle size 2.9 μm) · Particulate compound 3: Talc (manufactured by Fujifilm Wako Pure Chemical Corporation, talc, aspect ratio 10, particle size 9.6 μm) · Particulate compound 4: General-purpose mica powder A-11 (manufactured by Yamaguchi Mica Co., Ltd., mica, aspect ratio 7, particle size 5.2 μm) · Particulate compound 5: Kaolin (manufactured by Sigma-Aldrich Co., Ltd., kaolin, aspect ratio 5, particle size 3.1 μm) · Particulate compound 6: Amihope LL (manufactured by Ajinomoto Co., Inc., lauroyl lysine, aspect ratio 8, particle size 10 μm) · Particulate compound 7: Muscovite 200M (manufactured by KIRARA, mica, aspect ratio 12, particle size 16.5 μm)

[0085] (2) Preparation of Inorganic Coated Sand <Example 1> The normal-temperature refractory aggregate 1 (100 parts by mass) shown in Table 1 was put into a stirrer and stirred. Next, the liquid metasilicate 1 (3.0 parts by mass) melted by heating to 80°C and the particulate compound 1 (0.02 parts by mass) were further put into the above stirrer. Furthermore, the stirring and mixing were continued, and after confirming that drying was achieved in the drying time shown in Table 1 from the start of stirring and mixing, the stirring and mixing were stopped to obtain an inorganic coated sand having normal-temperature fluidity.

[0086] <Examples 2 to 9, Comparative Examples 1 to 2> Inorganic coated sand was produced in the same manner as in Example 1 except that the particulate compound was changed to those shown in Table 1 and the blending amount was adjusted, and the drying time (seconds) of each was measured. The results are shown in Table 1. However, the particulate compound 6 was used after being pulverized in a mortar for 5 minutes in advance.

[0087] (3) Evaluation and Measurement Using the obtained inorganic coated sand, the following evaluation and measurement were performed. The results are shown in Table 1. <Mold Strength> Using each inorganic coated sand, a mold was produced by the following procedure and the mold strength was measured. The evaluation results are shown in Table 1. (Procedure) A mold for 22.3 mm × 22.3 mm × 180 mm test pieces (5 pieces) was heated to 180°C. Each inorganic coated sand of the above examples and comparative examples was filled into the mold heated to 180°C at a blow pressure of 0.3 MPa using a CSR-43 blow molding machine, and left to stand in the mold for 150 seconds to cure, thereby obtaining a mold test piece. (Measurement) Using a universal strength tester PFG type manufactured by Georg Fischer, with a PBV flexural attachment pre-installed, the mold strength (MPa) of each obtained mold test piece was measured. The mold test pieces used were those left in a thermo-hygrostat chamber at 25°C / 55%RH for 1 hour after being taken out of the mold.

[0088]

Table 1

Claims

1. A dry inorganic coated sand having a refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate, wherein the inorganic binder layer contains a metasilicate hydrate and a particulate compound, and the particulate compound has an aspect ratio of 3 or more and 10 or less. The inorganic coated sand.

2. The inorganic coated sand according to Claim 1, wherein the particulate compound contains one or more selected from an organic particulate compound and an inorganic particulate compound. The inorganic coated sand.

3. A casting mold formed of the inorganic coated sand according to Claim 1 or 2.

4. A method for producing a dry inorganic coated sand having a refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate, the method including a step of mixing a refractory aggregate, a metasilicate hydrate, and a particulate compound to form an inorganic binder layer on the surface of the refractory aggregate, wherein the particulate compound has an aspect ratio of 3 or more and 10 or less. The method for producing an inorganic coated sand.

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