Inorganic coated sand

Abstract

To provide inorganic coated sand which is excellent in the property of filling to a mold, which enables achievement of a casting mold excellent in strength and which can be manufactured without the need for use of an aqueous solution of an inorganic binder and a step for removal of water, and inorganic coated sand which dispenses with water vapor ventilation in the manufacture of the casting mold.SOLUTION: Dry inorganic coated sand comprises refractory aggregate, and an inorganic binder layer that is formed on a surface of the refractory aggregate. The inorganic binder layer includes a metasilicate hydrate in the dry inorganic coated sand.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to inorganic coated sand. [Background technology]

[0002] Known molds used for casting castings include those obtained by molding a desired shape using inorganic coated sand having a refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate. Examples of technologies relating to such inorganic coated sand include those described in Patent Document 1 (JP 53-025803 B), Patent Document 2 (WO 2014 / 098129), and Patent Document 3 (WO 2018 / 097180).

[0003] Patent Document 1 describes a method for producing a mold, which involves adding an alkali metasilicate solution, prepared by adding a caustic alkali to water glass, to refractory particles such as silica sand and kneading them together, or alternatively adding an alcohol during kneading to precipitate and adhere a crystalline alkali silicate to the surfaces of the refractory particles such as silica sand, and then adding and mixing fine dust, mainly composed of SiO2, generated during Fe-Si refining, to form a powder-and-granular mixed sand, which is then heated to at least the melting point of the crystalline alkali silicate and hardened.

[0004] Patent Document 2 describes coated sand characterized in that it is obtained by mixing heated refractory aggregate with a water glass aqueous solution as a binder, and then evaporating the water to form a coating layer of the binder on the surface of the refractory aggregate, thereby producing dry coated sand that has fluidity at room temperature, and the moisture content of the coated sand is adjusted to 0.5 mass % or less.

[0005] Furthermore, Patent Document 3 describes a technology relating to coated sand, in which the surface of a fire-resistant aggregate is covered with a coating layer containing water glass, resulting in a dry coated sand having fluidity at room temperature, and the coating layer contains spherical particles. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 53-025803 [Patent Document 2] International Publication No. 2014 / 098129 [Patent Document 3] International Publication No. 2018 / 097180 Summary of the Invention [Problem to be solved by the invention]

[0007] The inventors' investigations have revealed that conventional inorganic-coated sand leaves room for improvement in terms of mold filling and mold strength. Furthermore, conventional inorganic-coated sand requires the passage of water vapor during hardening, which necessitates the use of equipment for venting water vapor when producing a mold. Furthermore, when producing dry inorganic-coated sand, a water glass aqueous solution is used as a binder, and the water must be evaporated. The present invention was made in consideration of the above circumstances and relates to inorganic-coated sand that can realize a mold with excellent mold filling ability and strength, and does not require the passage of water vapor during mold production. The present invention also relates to a method for producing a mold that does not require the passage of water vapor during hardening of the inorganic-coated sand. The present invention also relates to a method for producing inorganic-coated sand that does not require the use of an aqueous solution of an inorganic binder and does not require a water removal step. [Means for solving the problem]

[0008] The present inventors conducted extensive research to develop inorganic-coated sand that can provide molds with excellent mold filling properties and strength. As a result, they found that inorganic-coated sand containing metasilicate hydrate in an inorganic binder layer can provide molds with excellent mold filling properties and strength. They also found that when producing inorganic-coated sand containing metasilicate hydrate in an inorganic binder layer, it is not necessary to use an aqueous solution of metasilicate hydrate, thereby eliminating the need for a water removal step. They also found that there is no need to pass water vapor through the sand when producing a mold, thereby simplifying the equipment required.

[0009] That is, according to the present invention, A dry inorganic coated sand having a refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate, The inorganic coated sand is provided, in which the inorganic binder layer contains metasilicate hydrate.

[0010] Further, according to the present invention, A manufacturing method for manufacturing dry inorganic coated sand having a refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate, comprising: the inorganic binder layer contains metasilicate hydrate, (1) a step of mixing the refractory aggregate and the metasilicate hydrate at a temperature equal to or higher than the melting point of the metasilicate hydrate to obtain a mixture; and (2) cooling the mixture to a temperature below the melting point of the metasilicate hydrate.

[0011] Further, according to the present invention, A casting mold formed from the inorganic coated sand is provided.

[0012] Further, according to the present invention, Step (3) of filling the inorganic coated sand into a mold to provide the desired casting mold; and (4) heating the mold filled with the inorganic coated sand without passing water vapor through it to harden the inorganic coated sand. [Effects of the Invention]

[0013] According to the present invention, a casting mold having excellent mold filling properties and excellent strength can be realized. When producing the inorganic-coated sand, it is not necessary to use an aqueous solution of an inorganic binder, so the step of removing water can be omitted. Furthermore, it is not necessary to ventilate water vapor when producing the casting mold, so inorganic-coated sand can be provided, which allows for simplification of the equipment. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, embodiments of the present invention will be described. Furthermore, in this specification, "A to B" indicating a numerical range means a range from A to B unless otherwise specified. Furthermore, the components and elements described in each embodiment can be combined as appropriate as long as the effects of the invention are not impaired.

[0015] [Inorganic coated sand (C)] First, the inorganic coated sand (C) according to this embodiment will be described. The inorganic coated sand (C) according to this embodiment is a dry inorganic coated sand having a refractory aggregate (A) and an inorganic binder layer (B) formed on the surface of the refractory aggregate (A), and the inorganic binder layer (B) contains metasilicate hydrate. The reason why the above-mentioned effect is exhibited when metasilicate hydrate is used as the inorganic binder constituting the inorganic binder layer (B) is not clear, but is thought to be as follows. If the inorganic binder layer (B) is metasilicate hydrate, the crystallinity of the inorganic binder layer (B) can be improved, and the inorganic coated sand (C) will be in a dry state, which will provide excellent room temperature fluidity and improved mold strength. Furthermore, because metasilicate hydrate has a low melting point, there is no need to use an aqueous solution of metasilicate hydrate when producing the inorganic coated sand (C), which eliminates the need for a water removal step. Furthermore, because the inorganic binder is metasilicate hydrate, there is no need to ventilate with water vapor when producing the mold, which simplifies the equipment.

[0016] In this embodiment, the inorganic coated sand (C) is composed of a group of inorganic coated sand particles, and the refractory aggregate (A) is composed of a group of refractory particles.

[0017] The inorganic coated sand (C) is in a dry state. Dry coated sand means coated sand for which a measurement value can be obtained when measuring the dynamic angle of repose regardless of the moisture content. The dynamic angle of repose can be measured by the following method. A cylindrical transparent plastic bottle is filled with coated sand up to half its volume, and the bottle is held with its axis horizontal and rotated at a constant speed around the horizontal axis. The inclined surface of the coated sand layer flowing inside the cylinder becomes flat. The angle formed between this inclined surface and the horizontal plane is measured. The dynamic angle of repose is preferably 80° or less, more preferably 45° or less, and even more preferably 30° or less. If the coated sand does not flow in the cylinder, or if it does flow, the slope of the coated sand layer does not form a flat surface, and as a result the dynamic angle of repose cannot be measured, it is in a wet state.

[0018] The slump loss value of the inorganic coated sand (C) is preferably 90 mm or more, more preferably 100 mm or more, even more preferably 105 mm or more, and even more preferably 108 mm or more, from the viewpoint of further improving mold filling properties and mold strength. This is thought to improve the room temperature fluidity of the inorganic coated sand (C), thereby improving mold filling properties. Furthermore, it is thought that the improved mold filling properties and improved bonding between the inorganic coated sands (C) can increase mold strength. The slump loss value of the inorganic coated sand (C) is preferably 140 mm or less, more preferably 130 mm or less, and even more preferably 120 mm or less, from the viewpoint of improving mold strength and handleability.

[0019] The slump flow value of the inorganic coated sand (C) is preferably 150 mm or more, more preferably 200 mm or more, even more preferably 230 mm or more, and still more preferably 240 mm or more, from the viewpoint of further improving the mold filling property and mold strength. The slump flow value of the inorganic coated sand (C) is preferably 500 mm or less, more preferably 400 mm or less, even more preferably 350 mm or less, and even more preferably 320 mm or less, from the viewpoint of improving mold strength and handleability.

[0020] In this embodiment, in order to adjust the slump loss value and slump flow value of the inorganic coated sand (C) to fall within the above ranges, it is necessary to highly control, for example, the types and contents of the refractory aggregate (A) and the inorganic binder constituting the inorganic binder layer (B), the manufacturing method of the inorganic coated sand (C), etc. In particular, in this embodiment, factors for controlling the slump loss value and slump flow value of the inorganic coated sand (C) within the above ranges include using spherical aggregate as the refractory aggregate (A), using metasilicate hydrate as the inorganic binder constituting the inorganic binder layer (B), and producing the inorganic coated sand (C) by a method in which the inorganic binder is coated on the refractory aggregate (A) and then the fluidity of the inorganic binder is reduced to fix the inorganic binder to the surface of the refractory aggregate (A).

[0021] The slump loss value and slump flow value of the inorganic coated sand (C) can be measured in an environment of 25°C and relative humidity 55% by a slump test in accordance with JIS A 1101:2014 using a slump cone with an upper inner diameter of 50 mm, a lower inner diameter of 100 mm, and a height of 150 mm. Here, a slump cone is formed in a shape such that a cone is cut at a predetermined height along a plane parallel to the bottom, with the portion above the cut plane removed. Although the dimensions of this slump cone are different from those of the slump cone used in the slump test in JIS A 1101:2014, they have the same shape. Furthermore, the upper and lower inner diameters refer to the diameters of only the open spaces at the upper and lower openings, respectively, and do not include the thickness of the rim of the slump cone. More specifically, the slump loss value and the slump flow value of the inorganic coated sand (C) can be measured by the following procedure. (1) First, the slump cone is placed on a horizontal and smooth table, for example, a flat table, with the lower opening facing downward and the upper opening facing upward. (2) Next, inorganic coated sand (C) is poured into the hollow portion of the slump cone from the upper opening so that the hollow inside the slump cone is filled with inorganic coated sand (C). In this case, if the inorganic coated sand (C) is poured in while being stirred with a metal rod or the like, the inorganic coated sand (C) can be filled into the hollow without entraining air. Furthermore, rather than pouring the inorganic coated sand (C) all at once, it is preferable to pour the inorganic coated sand (C) in several batches so that the inorganic coated sand (C) is gradually filled. (3) After the inorganic coated sand (C) is filled into the slump cone, the upper surface of the inorganic coated sand (C) is smoothed to match the upper end of the slump cone. In other words, the upper opening is made to coincide with the upper end surface of the inorganic coated sand (C) filled into the slump cone. (4) After filling with inorganic coated sand (C), the slump cone is pulled up vertically so that at least the lower end opening is positioned above the height of the slump cone. (5) When the slump cone is pulled up, the shape formed by the inorganic coated sand (C) begins to collapse under its own weight, and eventually the collapse stops. The height from the top to the bottom of the inorganic coated sand (C) when this collapse stops is H2, and the difference between the height H1 of the original shape and H2, i.e., the value H1 - H2, is the slump loss value. The diameter of the expanded inorganic coated sand (C) when the collapse stops is L2, and the difference between L2 and the diameter L1 in the original shape, i.e., L2-L1, is the slump flow value.

[0022] From the viewpoint of improving the flowability and further improving the mold filling property, the inorganic coated sand (C) is preferably spherical. Here, the inorganic coated sand (C) according to this embodiment is spherical means that it has a round shape like a ball, and more specifically, the sphericity is preferably 0.80 or more, more preferably 0.85 or more, even more preferably 0.90 or more, still more preferably 0.95 or more, and even more preferably 0.97 or more. It is preferable that the sphericity of the inorganic coated sand (C) according to this embodiment is equal to or greater than the above lower limit from the viewpoints of improving the flowability, mold quality, and mold strength, and from the viewpoint of ease of mold making. The upper limit of the sphericity is specifically 1 or less.

[0023] The sphericity of the inorganic coated sand (C) is determined by analyzing the image (photograph) of the particle obtained by an optical microscope or a digital scope (for example, Keyence VH-8000 model) to determine the area of ​​the projected cross section of the particle and the perimeter of the cross section, and then calculating the projected cross section area (mm 2 The particle diameter can be calculated by dividing the circumference (mm) of a perfect circle with the same area as the particle by the circumference (mm) of the particle's projected cross section, and then averaging the values ​​obtained for any 50 particles.

[0024] The average particle size of the inorganic-coated sand (C) is preferably 0.05 mm or more, more preferably 0.1 mm or more, from the viewpoints of improving mold quality and mold strength and facilitating mold production. Furthermore, when the average particle size of the inorganic-coated sand (C) is equal to or greater than the above-mentioned lower limit, the amount of inorganic binder layer (B) used during mold production can be reduced, which is preferable because it makes it easier to regenerate the inorganic-coated sand (C). From the viewpoints of improving mold quality and mold strength, and of ease of mold production, the average particle size of the inorganic coated sand (C) is preferably 2 mm or less, more preferably 1 mm or less, and even more preferably 0.5 mm or less. Furthermore, when the average particle size of the inorganic coated sand (C) is equal to or less than the above upper limit, the porosity is reduced during mold production, which is preferable because the mold strength can be increased. In this embodiment, the average particle size of the inorganic coated sand (C) can be measured by the following method.

[0025] (Method for measuring average particle size) If the sphericity of the particle's projected cross section is 1, the diameter (mm) is measured; on the other hand, if the sphericity is less than 1, the major axis diameter (mm) and minor axis diameter (mm) of randomly oriented particles are measured and (major axis diameter + minor axis diameter) / 2 is calculated, and the average value obtained for 100 randomly selected particles is used as the average particle size (mm). The major axis diameter and minor axis diameter are defined as follows: When a particle is stabilized on a flat surface and the projected image of the particle on the flat surface is sandwiched between two parallel lines, the width of the particle at the smallest distance between the parallel lines is called the minor axis diameter, and the distance when the particle is sandwiched between two parallel lines perpendicular to the parallel lines is called the major axis diameter. The major axis diameter and minor axis diameter of a particle can be determined by taking an image (photograph) of the particle using an optical microscope or a digital scope (for example, Keyence VH-8000 model) and analyzing the obtained image.

[0026] [Refractory aggregate (A)] The refractory aggregate (A) according to this embodiment may be natural sand or artificial sand. Examples of natural sand include silica sand, which is mainly composed of quartz, chromite sand, zircon sand, olivine sand, and alumina sand. Examples of artificial sand include synthetic mullite sand, SiO2-based foundry sand whose main component is SiO2, Al2O3-based foundry sand whose main component is Al2O3, SiO2 / Al2O3-based foundry sand, SiO2 / MgO-based foundry sand, SiO2 / Al2O3 / ZrO2-based foundry sand, SiO2 / Al2O3 / Fe2O3-based foundry sand, and slag-derived foundry sand. Here, the term "main component" refers to the component that is most abundant among the components contained in the sand. Artificial sand is not found in nature, but is found in sand that has been artificially prepared from metal oxide components and melted or sintered. Reclaimed sand made from used refractory aggregate and recycled sand made from recycled sand can also be used. These may be used alone or in combination of two or more. From the viewpoint of improving mold strength, the refractory aggregate (A) according to this embodiment preferably contains at least one selected from the group consisting of SiO2 and Al2O3. From the viewpoint of improving mold strength, the refractory aggregate (A) according to this embodiment is preferably artificial sand, and among the artificial sands, at least one selected from the group consisting of synthetic mullite sand, SiO2-based foundry sand, Al2O3-based foundry sand, SiO2 / Al2O3-based foundry sand, SiO2 / Al2O3 / ZrO2-based foundry sand, and SiO2 / Al2O3 / Fe2O3-based foundry sand is preferred.

[0027] From the viewpoints of improving mold strength and fire resistance, and of low thermal expansion, the refractory aggregate (A) preferably contains 30 mass % or more of SiO2, more preferably 60 mass % or more, even more preferably 80 mass % or more, and still more preferably 90 mass % or more, when the total of all components contained in the refractory aggregate (A) is taken as 100 mass %. The upper limit of the SiO2 content in the refractory aggregate (A) is not limited, but may be, for example, 100 mass % or less, or 99 mass % or less.

[0028] From the viewpoints of improving mold strength and fire resistance, and of low thermal expansion, the refractory aggregate (A) preferably contains 20 mass % or more of Al2O3, more preferably 30 mass % or more, even more preferably 40 mass % or more, and still more preferably 50 mass % or more, when the total of all components contained in the refractory aggregate (A) is taken as 100 mass %. There is no upper limit to the content of Al2O3 contained in the refractory aggregate (A), but it is, for example, 95 mass % or less, and preferably 85 mass % or less.

[0029] The content of each component such as SiO2, Al2O3, Fe2O3, etc. in the refractory aggregate (A) can be measured by a known analytical method, for example, a wet gravimetric method or a fluorescent X-ray method.

[0030] The degree of amorphization of the refractory aggregate (A) is preferably 30% or more, more preferably 50% or more, even more preferably 65% ​​or more, and even more preferably 80% or more, from the viewpoint of achieving a smoother surface of the aggregate and thus improved mold strength, and from the viewpoint of obtaining low thermal expansion. The upper limit of the degree of amorphization of the refractory aggregate (A) is not limited, but may be, for example, 100% or less, or 99% or less.

[0031] There are various methods for controlling the degree of amorphization of the refractory aggregate (A), but it is generally preferable to use a manufacturing method that rapidly cools a molten material. For example, there is a method in which the raw material is melted and rapidly cooled by air-crushing, or a method in which it is treated in a flame and rapidly cooled. In either case, the cooling method may be selected appropriately at various speeds depending on the material and particle size. Another possible method is to amorphize a material that has been once crystallized by heat treatment and cooling treatment. Among these, the flame fusion method, which allows easy control of heating and cooling, is preferred.

[0032] The degree of amorphization of the refractory aggregate (A) can be determined by the X-ray diffraction method shown below. (X-ray diffraction method) The refractory aggregate (A) was crushed in a mortar and pressed onto an X-ray glass holder of a powder X-ray diffractometer. The powder X-ray diffractometer used was a Rigaku MultiFlex (CuKα radiation source, 40 kV tube voltage, 40 mA tube current) with a scan interval of 0.01°, a scan rate of 2° / min, and slits DS1, SS1, and RS0.3 mm, in the 2θ range of 5° to 90°. A straight line was drawn connecting the X-ray intensities at low and high angles in the 2θ range of 10° to 50°. The area under the line was used as the background. The crystallinity was calculated using the instrument's software and subtracted from 100 to obtain the amorphousness. Specifically, the amorphous peak (halo) and each crystalline component were separated by curve fitting for the area above the background, and their respective areas were determined. The amorphousness (%) was calculated using the following formula: Amorphous ratio (%) = halo area / (crystalline component area + halo area) × 100

[0033] The refractory aggregate (A) is preferably spherical from the viewpoint of improving the fluidity of the inorganic-coated sand (C) and further improving its fillability into a mold. Here, the refractory aggregate (A) according to this embodiment is spherical, meaning a round, ball-like shape. More specifically, the sphericity is preferably 0.80 or more, more preferably 0.85 or more, even more preferably 0.90 or more, even more preferably 0.95 or more, and even more preferably 0.97 or more. The sphericity of the refractory aggregate (A) according to this embodiment is preferably at least the above-mentioned lower limit, from the viewpoints of improving fluidity, mold quality, and mold strength, as well as ease of mold formation. Furthermore, the sphericity of the refractory aggregate (A) according to this embodiment is preferably at least the above-mentioned lower limit, because the aggregate surface becomes smoother, resulting in a better coating state of the inorganic binder layer (B) and a mold with even greater strength. The upper limit of the sphericity is specifically 1 or less. The sphericity of the refractory aggregate (A) can be measured in the same manner as the sphericity of the inorganic coated sand (C).

[0034] The average particle size of the refractory aggregate (A) is preferably 0.05 mm or more, more preferably 0.1 mm or more, from the viewpoints of improving mold quality and mold strength and facilitating mold production. Furthermore, when the average particle size of the refractory aggregate (A) is equal to or greater than the above-mentioned lower limit, the amount of inorganic binder layer (B) used in mold production can be reduced, which is preferable because it makes it easier to regenerate the inorganic-coated sand (C). The average particle size of the refractory aggregate (A) 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 ease of mold production. Furthermore, when the average particle size of the refractory aggregate (A) is equal to or less than the above upper limit, the porosity is reduced during mold production, which is preferable because the mold strength can be increased. The average particle size of the refractory aggregate (A) can be measured in the same manner as the average particle size of the inorganic coated sand (C).

[0035] [Inorganic binder layer (B)] The inorganic binder constituting the inorganic binder layer (B) is metasilicate hydrate. The use of metasilicate hydrate is preferable because it improves the crystallinity of the inorganic binder layer (B) and furthermore, the inorganic coated sand (C) becomes a dry state, resulting in excellent room temperature fluidity. Furthermore, by using a metasilicate hydrate with a low melting point, the inorganic binder layer (B) can be formed on the surface of the refractory aggregate (A) without being dissolved in water. In other words, since there is no need to use an aqueous solution of metasilicate hydrate in the process of producing the inorganic coated sand (C), the water removal step can be omitted, simplifying the production method. Furthermore, since the inorganic binder is metasilicate hydrate, there is no need to ventilate with water vapor when producing a mold, simplifying the equipment.

[0036] From the above viewpoints, the metasilicate hydrate is preferably at least one selected from sodium metasilicate pentahydrate, sodium metasilicate nonahydrate, potassium metasilicate pentahydrate, and potassium metasilicate nonahydrate, and more preferably at least one selected from sodium metasilicate pentahydrate and sodium metasilicate nonahydrate. The melting point of sodium metasilicate pentahydrate is 72°C, and the melting point of sodium metasilicate nonahydrate is 47°C.

[0037] From the viewpoint of obtaining a high-strength casting mold, the coating amount of the inorganic binder layer (B) contained in the inorganic coated sand (C) is, for example, 0.05 parts by mass or more, preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, even more preferably 1 part by mass or more, and still more preferably 2 parts by mass or more, relative to 100 parts by mass of the refractory aggregate (A). The coating amount of the inorganic binder layer (B) contained in the foundry sand composition (C) is, from the viewpoint of obtaining a high-strength casting mold, for example, 10 parts by mass or less, preferably 8 parts by mass or less, and more preferably 6 parts by mass or less, per 100 parts by mass of the refractory aggregate (A).

[0038] The content of water in the inorganic binder layer (B) contained in the inorganic-coated sand (C) is preferably 60 parts by mass or more, more preferably 65 parts by mass or more, even more preferably 90 parts by mass or more, and still more preferably 110 parts by mass or more, per 100 parts by mass of metasilicate, from the viewpoints of obtaining a high-strength casting mold and easily producing the mold; and from the viewpoints of improving fluidity and further improving mold fillability, is preferably 180 parts by mass or less, more preferably 160 parts by mass or less, even more preferably 150 parts by mass or less, and still more preferably 140 parts by mass or less. For example, when the inorganic binder constituting the inorganic binder layer (B) is composed only of sodium metasilicate pentahydrate, the water content is 74 parts by mass, and when the inorganic binder is composed only of sodium metasilicate nonahydrate, the water content is 133 parts by mass.

[0039] The inorganic coated sand (C) according to this embodiment can be molded using a desired casting mold, either alone or in combination with other known refractory aggregates or other additives.

[0040] The inorganic coated sand (C) according to this embodiment may be used in combination with other additives such as a coupling agent, a lubricant, a mold release agent, and the like. The coupling agent is not limited, but examples thereof include silane coupling agents, zirconium coupling agents, and titanium coupling agents. Lubricants include, but are not limited to, waxes such as paraffin wax, synthetic polyethylene wax, and montanic acid wax; fatty acid amides such as stearic acid amide, oleic acid amide, and erucic acid amide; alkylene fatty acid amides such as methylene bis-stearic acid amide and ethylene bis-stearic acid amide; stearic acid; stearyl alcohol; metal stearates such as lead stearate, zinc stearate, calcium stearate, and magnesium stearate; stearic acid monoglyceride; stearyl stearate; and hydrogenated oils. The release agent is not limited to, but examples thereof include paraffin, wax, light oil, machine oil, spindle oil, insulating oil, waste oil, vegetable oil, fatty acid ester, organic acid, graphite fine particles, mica, vermiculite, fluorine-based release agents, and silicone-based release agents.

[0041] The inorganic-coated sand (C) according to this embodiment preferably further contains inorganic fine particles on or in the inorganic binder layer (B), and more preferably further contains inorganic fine particles on the inorganic binder layer (B). The inorganic-coated sand (C) according to this embodiment may be contained both on and in the inorganic binder layer (B). By doing so, the particles of the inorganic coated sand (C) are more firmly bound together via the inorganic fine particles, and as a result, the strength of the resulting mold can be further improved. Here, the inorganic fine particles on the inorganic binder layer (B) may be partly embedded in the inorganic binder layer (B).

[0042] The inorganic particles are not limited to, but include, for example, silica particles, silicon particles, etc. From the viewpoint of improving the strength of the mold, silica particles are preferred, and amorphous silica particles are more preferred. These inorganic particles may be used alone or in combination of two or more. When silica particles are used as inorganic fine particles, from the viewpoint of improving the fusion property of the inorganic-coated sand (C), when the total of all components contained in the refractory aggregate (A) is taken as 100 mass%, the refractory aggregate (A) preferably contains 30 mass% or more of SiO2, more preferably 60 mass% or more, even more preferably 80 mass% or more, and even more preferably 90 mass% or more of SiO2. The upper limit of the SiO2 content in the refractory aggregate (A) is 100 mass% or less.

[0043] The degree of amorphization of the amorphous silica particles is preferably 80% or more, more preferably 90% or more, even more preferably 93% or more, and even more preferably 95% or more, from the viewpoint of more firmly binding the particles of the inorganic-coated sand (C) to each other via the inorganic fine particles. The upper limit of the degree of amorphization of the amorphous silica particles is not limited, but may be, for example, 100% or less, or 99% or less.

[0044] In addition, the average particle diameter d of the inorganic fine particles in the weight-based particle size distribution measured by a laser diffraction scattering particle size distribution measurement method 50 From the viewpoint of improving mold strength per unit mass and ease of handling, the thickness is preferably 0.1 μm or more, more preferably 0.3 μm or more, even more preferably 0.4 μm or more, and even more preferably 0.5 μm or more, and from the viewpoint of improving mold strength per unit mass, the thickness is preferably 2.0 μm or less, more preferably 1.0 μm or less, and even more preferably 0.8 μm or less. Here, the average particle diameter d of the inorganic fine particles in the weight-based particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method is 50 can be obtained, for example, by removing the inorganic binder layer from the coated sand by dissolving it in water, extracting the inorganic fine particles, and then measuring the particle size of the obtained inorganic fine particles by a laser diffraction / scattering particle size distribution measuring method. In addition, the average particle diameter d of the inorganic fine particles in the weight-based particle size distribution measured by a laser diffraction scattering particle size distribution measurement method 50 can also be obtained by measuring the particle size of the inorganic fine particles that are the raw material by a laser diffraction scattering particle size distribution measurement method.

[0045] Furthermore, the average particle size of the inorganic microparticles, as determined from an image observed with a scanning electron microscope, is preferably 0.1 μm or more, more preferably 0.3 μm or more, and even more preferably 0.4 μm or more, from the viewpoint of improving mold strength per unit mass and ease of handling, and is preferably 2.0 μm or less, more preferably 1.0 μm or less, and even more preferably 0.8 μm or less, from the viewpoint of improving mold strength per unit mass. Here, the average particle diameter of the inorganic fine particles can be determined from the image observed with a scanning electron microscope using various image analysis methods. Irregular particle selection may also be performed as a pretreatment. For example, after determining the inorganic binder layer and the inorganic fine particles based on elements, 100 inorganic fine particles are arbitrarily selected and their particle diameters are measured. The average particle diameter of the remaining 80 inorganic fine particles, excluding the 10 largest and 10 smallest inorganic fine particles (a total of 20 inorganic fine particles), can be determined as the average particle diameter of the inorganic fine particles.

[0046] Furthermore, from the viewpoint of improving mold strength and handling, the content of inorganic fine particles contained in the inorganic coated sand (C) is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, and preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 3 parts by mass or less, per 100 parts by mass of the refractory aggregate (A).

[0047] [Method for manufacturing inorganic coated sand (C)] Next, a method for producing the inorganic coated sand (C) according to this embodiment will be described. The method for producing the inorganic coated sand (C) is different from conventional methods for producing inorganic coated sand.

[0048] The method for producing inorganic coated sand (C) is a method for producing dry inorganic coated sand having refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate. The inorganic binder layer contains metasilicate hydrate. The inorganic coated sand (C) according to this embodiment can be obtained, for example, by a production method including the following steps (1) and (2). Step (1): A step of mixing a refractory aggregate (A) and a metasilicate hydrate (B) at a temperature equal to or higher than the melting point of the metasilicate hydrate to obtain a mixture. Step (2): Cooling the mixture to a temperature below the melting point of the metasilicate hydrate.

[0049] According to the method for producing inorganic-coated sand (C) of this embodiment, the inorganic binder layer (B) can be crystallized, thereby making it possible to obtain inorganic-coated sand (C) with superior fluidity compared to conventional production methods. Furthermore, since it is not necessary to use an aqueous solution of metasilicate hydrate, a dehydration step is not required, and the method for producing inorganic-coated sand (C) can be simplified.

[0050] Specifically, in the step (1), the surface of the refractory aggregate (A) is coated with fluidized metasilicate hydrate at a temperature equal to or higher than the melting point of the metasilicate hydrate. Examples of the method for mixing the refractory aggregate (A) with the metasilicate hydrate at a temperature equal to or higher than the melting point of the metasilicate hydrate include a method in which the metasilicate hydrate is added to the refractory aggregate (A) that has been heated to a temperature equal to or higher than the melting point of the metasilicate hydrate, and the refractory aggregate (A) and the metasilicate hydrate are mixed while melting the metasilicate hydrate [step (1A)], and a method in which the heated and melted metasilicate hydrate is added to the refractory aggregate (A) and mixed [step (1B)]. Among these, the step (1B) is preferred from the viewpoint of shortening the coating time. From the same viewpoint, it is preferable that the metasilicate hydrate is mixed in step (1) without being previously converted into an aqueous solution, and it is also preferable that step (1) does not include a step of intentionally adding water. The mixing conditions such as the stirring speed and treatment time when mixing the refractory aggregate (A) and the metasilicate hydrate can be appropriately determined depending on the amount of the mixture to be treated.

[0051] In step (2), the mixture obtained in step (1) is cooled to a temperature below the melting point of the metasilicate hydrate to reduce the fluidity of the metasilicate hydrate and fix the metasilicate hydrate to the surface of the refractory aggregate (A), thereby forming a metasilicate hydrate layer, i.e., an inorganic binder layer (B).

[0052] The method for producing the inorganic-coated sand (C) may further comprise the step of mixing the inorganic-coated sand obtained in step (2) with the inorganic fine particles.

[0053] By the above method, the inorganic coated sand (C) according to this embodiment can be obtained.

[0054] [Casting mold] Next, the casting mold according to this embodiment will be described. The casting mold according to this embodiment is formed from inorganic coated sand (C). The method for producing a casting mold includes the following steps (3) and (4). Step (3): A step of filling the inorganic coated sand (C) into a mold to give the desired casting mold. Step (4): A step of heating the mold filled with the inorganic coated sand (C) without passing water vapor through it to harden the inorganic coated sand.

[0055] In step (3), the mold is preferably preheated to maintain its temperature, from the viewpoint of improving mold productivity and mold strength. The heating temperature is preferably 100°C or higher, more preferably 150°C or higher, and is preferably 300°C or lower, more preferably 250°C or lower, from the viewpoint of improving mold productivity and mold strength.

[0056] In step (4), the mold filled with the inorganic coated sand (C) is heated without passing water vapor through it. By using the inorganic coated sand (C) of this embodiment, the inorganic coated sand (C) can be hardened without passing water vapor through it, and equipment for passing water vapor through it is not necessary. The heating temperature is preferably 100° C. or higher, more preferably 150° C. or higher, and preferably 300° C. or lower, more preferably 250° C. or lower, from the viewpoint of improving mold productivity and mold strength. The heating time is preferably 30 seconds or higher, more preferably 60 seconds or higher, and preferably 600 seconds or lower, from the viewpoint of obtaining stable mold strength.

[0057] Although the embodiments of the present invention have been described above, these are merely examples of the present invention, and various other configurations can also be adopted. The present invention is not limited to the above-described embodiment, and modifications and improvements within the scope of achieving the object of the present invention are included in the present invention.

[0058] In relation to 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. <1> A dry inorganic coated sand having a refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate, the inorganic binder layer contains metasilicate hydrate, and the amount of water contained in the inorganic binder layer is 60 parts by mass or more and 140 parts by mass or less per 100 parts by mass of the metasilicate, The refractory aggregate contains one or more selected from the group consisting of SiO2 and Al2O3, The inorganic coated sand has an average particle size of 0.05 mm or more and 2 mm or less. <2> A dry inorganic coated sand having a refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate, the inorganic binder layer contains one or more selected from sodium metasilicate pentahydrate and sodium metasilicate nonahydrate, the amount of water contained in the inorganic binder layer is 60 parts by mass or more and 140 parts by mass or less per 100 parts by mass of the metasilicate, The refractory aggregate contains one or more selected from the group consisting of SiO2 and Al2O3, The inorganic coated sand has an average particle size of 0.05 mm or more and 2 mm or less, and a sphericity of 0.80 or more. <3> A dry inorganic coated sand having a refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate, the inorganic binder layer contains one or more selected from sodium metasilicate pentahydrate and sodium metasilicate nonahydrate, the amount of water contained in the inorganic binder layer is 60 parts by mass or more and 140 parts by mass or less per 100 parts by mass of the metasilicate, The refractory aggregate contains one or more selected from the group consisting of SiO2 and Al2O3, and the degree of amorphization of the refractory aggregate is 30% or more; The coating amount of the inorganic binder layer is 0.5 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the refractory aggregate. The inorganic coated sand has an average particle size of 0.05 mm or more and 2 mm or less, and a sphericity of 0.80 or more. <4> the inorganic binder layer and / or the inorganic binder layer further contain inorganic fine particles having an average particle diameter of 0.1 μm or more and 2.0 μm or less in an amount of 0.2 parts by mass or more and 3 parts by mass or less per 100 parts by mass of the refractory aggregate; <1> ~ <3> 10. The inorganic coated sand according to any one of the preceding items. <5> the inorganic binder layer and / or the inorganic binder layer further contain silica having an average particle size of 0.1 μm or more and 2.0 μm or less in an amount of 0.2 parts by mass or more and 3 parts by mass or less relative to 100 parts by mass of the refractory aggregate; <1> ~ <3> 10. The inorganic coated sand according to any one of the preceding items. <6> A manufacturing method for manufacturing dry inorganic coated sand having refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate, comprising: the inorganic binder layer contains metasilicate hydrate, (1) a step of mixing the refractory aggregate and the metasilicate hydrate at a temperature equal to or higher than the melting point of the metasilicate hydrate without previously dissolving the metasilicate hydrate in an aqueous solution to obtain a mixture; and (2) cooling the mixture to a temperature below the melting point of the metasilicate hydrate. <7> A manufacturing method for manufacturing dry inorganic coated sand having refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate, comprising: the inorganic binder layer contains metasilicate hydrate, the metasilicate hydrate is one or more selected from sodium metasilicate pentahydrate and sodium metasilicate nonahydrate, The refractory aggregate contains one or more selected from the group consisting of SiO2 and Al2O3, The average particle size of the refractory aggregate is 0.05 mm or more and 2 mm or less, and the sphericity is 0.80 or more, a step (1) of mixing the refractory aggregate and the metasilicate hydrate at a temperature equal to or higher than the melting point of the metasilicate hydrate without previously dissolving the metasilicate hydrate in an aqueous solution to obtain a mixture; and (2) cooling the mixture to a temperature below the melting point of the metasilicate hydrate. <8> A manufacturing method for manufacturing dry inorganic coated sand having refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate, comprising: the inorganic binder layer contains metasilicate hydrate, the metasilicate hydrate is one or more selected from sodium metasilicate pentahydrate and sodium metasilicate nonahydrate, The refractory aggregate contains one or more selected from the group consisting of SiO2 and Al2O3, The average particle size of the refractory aggregate is 0.05 mm or more and 2 mm or less, and the sphericity is 0.80 or more, a step (1) of mixing the refractory aggregate with 0.5 parts by mass or more and 10 parts by mass or less of the metasilicate hydrate per 100 parts by mass of the refractory aggregate at a temperature equal to or higher than the melting point of the metasilicate hydrate, without previously dissolving the metasilicate hydrate in an aqueous solution, to obtain a mixture; and (2) cooling the mixture to a temperature below the melting point of the metasilicate hydrate. <9> The method further comprises a step of mixing the inorganic coated sand obtained in step (2) with inorganic fine particles having an average particle size of 0.1 μm or more and 2.0 μm or less in an amount of 0.2 parts by mass or more and 3 parts by mass or less per 100 parts by mass of the refractory aggregate. <6> ~ <8> 10. The method for producing the inorganic coated sand according to claim 9, wherein the inorganic coated sand is a crystalline or crystalline silicon dioxide. <10> The method further comprises a step of mixing the inorganic coated sand obtained in step (2) with silica having an average particle size of 0.1 μm or more and 2.0 μm or less in an amount of 0.2 parts by mass or more and 3 parts by mass or less per 100 parts by mass of the refractory aggregate. <6> ~ <8> 10. The method for producing the inorganic coated sand according to claim 9, wherein the inorganic coated sand is a crystalline or crystalline silicon dioxide. <11> The aforementioned <1> ~ <5> Step (3) of filling the inorganic coated sand according to any one of the above into a mold to provide the desired mold; and (4) heating the mold filled with the inorganic coated sand without passing water vapor through it to harden the inorganic coated sand. [Example]

[0059] EXAMPLES The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these.

[0060] [1]Measurement method First, the measurement methods used in the following examples and comparative examples will be described.

[0061] (1) Average particle size of refractory aggregate and inorganic coated sand (or mixed sand) If the sphericity of the particle from the projected cross section was 1, the diameter (mm) was measured. On the other hand, if the sphericity was <1, the long axis diameter (mm) and short axis diameter (mm) of randomly oriented particles were measured to calculate (long axis diameter + short axis diameter) / 2, and the values ​​obtained for 100 randomly selected particles were averaged to obtain the average particle size (mm). The major axis diameter and minor axis diameter of the particles were determined by taking an image (photograph) of the particles using a digital scope (Keyence Corporation, VH-8000 model) and analyzing the obtained image.

[0062] (2) Average particle size of inorganic fine particles The particle size distribution of inorganic fine particles was measured by a laser diffraction method using a laser diffraction scattering particle size distribution analyzer. From the measurement results, the particle size (d 50, average particle size) were calculated.

[0063] (3) Chemical composition ratio of refractory aggregate The composition ratio of each component in the refractory aggregate was measured by X-ray fluorescence spectroscopy.

[0064] (4) Amorphousness of refractory aggregate The refractory aggregate was crushed in a mortar and compressed into an X-ray glass holder for powder X-ray diffractometry. The powder X-ray diffractometer used was a Rigaku MultiFlex (CuKα radiation source, 40 kV tube voltage, 40 mA tube current) with a scan interval of 0.01°, a scan rate of 2° / min, and slits DS1, SS1, and RS0.3 mm. X-ray intensities at low and high angles were connected by a straight line over the 2θ range of 10° to 50°. The area under the line was used as the background. The crystallinity was calculated using the instrument's software and subtracted from 100 to obtain the amorphousness. Specifically, the amorphous peak (halo) and each crystalline component were separated by curve fitting for the area above the background, and the respective areas were determined. The amorphousness (%) was calculated using the following formula: Amorphous ratio (%) = halo area / (crystalline component area + halo area) × 100

[0065] (5) Sphericity of inorganic coated sand (or mixed sand) The sphericity of the refractory aggregate and inorganic coated sand (or mixed sand) was determined by analyzing the particle images (photographs) taken with a digital scope (Keyence, VH-8000) to determine the area of ​​the projected cross section of the particle and the perimeter of the cross section, and then calculating the projected cross section area (mm 2 The particle diameter was calculated by dividing the circumference (mm) of a circle having the same area as the particle diameter by the circumference (mm) of the particle projected cross section, and the average value was calculated for 50 randomly selected particles.

[0066] (6) Slump loss value and slump flow value of inorganic coated sand (or mixed sand) The slump loss value and slump flow value of inorganic coated sand (or mixed sand) were measured in an environment of 25°C and relative humidity 55% by a slump test in accordance with JIS A 1101:2014 using a slump cone with an upper inner diameter of 50 mm, a lower inner diameter of 100 mm, and a height of 150 mm.

[0067] (7) Inorganic coated sand or mixed sand, dry or wet Half the volume of coated sand is placed in a cylindrical transparent plastic bottle 76 mm in diameter and 125 mm in height, and the bottle is rotated around the horizontal axis at room temperature (25°C) and 25 rpm. The condition is considered dry when the slope of the coated sand or mixed sand layer flowing inside the cylinder becomes flat and the angle formed between this slope and the horizontal plane (dynamic angle of repose) can be measured. The condition is considered wet when the coated sand or mixed sand does not flow inside the cylinder, or when the slope of the coated sand or mixed sand layer does not form a flat surface even if it flows, making it impossible to measure the dynamic angle of repose.

[0068] [2] Evaluation method Next, the evaluation methods used in the following Examples and Comparative Examples will be described.

[0069] (1) Preparation of the mold Using the inorganic coated sand (or mixed sand) obtained in the Examples and Comparative Examples, molds were produced by the following methods, all of which were carried out under conditions that did not allow water vapor to pass through. Small mold (pressure) Coated sand (or mixed sand) was packed into a horizontal five-cavity mold heated to 200°C, which was capable of molding 10 x 10 x 60 mm test pieces, and the mixture was pressed with a trowel. After that, the mixture was heated for 10 minutes to harden, and test pieces were obtained. Small mold (pouring) Coated sand (or mixed sand) was poured into a horizontal five-cavity mold measuring 10 x 10 x 60 mm heated to 200°C, and then heated for 10 minutes to harden, after which test specimens were obtained. ·blow Using a CSR-43 blow molding machine, the resin was blown vertically into a 22.3 x 22.3 x 180 mm test piece (5-cavity) mold heated to 200°C at a blow pressure of 0.45 MPa, and then heated for 10 minutes to harden the mold, yielding test pieces.

[0070] (2) Mold density The mold density was calculated by measuring the weight of the test piece and dividing it by the volume calculated by measuring the dimensions.

[0071] (3) Bending strength of the mold For test pieces using small molds, a digital force gauge ZTS-500N was attached to a vertical electric measuring stand manufactured by Imada Co., Ltd., and measurements were taken in accordance with the JACT test method SM-1. The test pieces obtained by blow molding were measured using a universal strength testing machine, PFG type, manufactured by George Fischer, equipped with a PBV flexural attachment.

[0072] (4) Filling rate The density of the obtained test piece was divided by the bulk density of the coated sand (or mixed sand) and multiplied by 100 to obtain the packing ratio.

[0073] [3] Material Next, the materials used in the following examples and comparative examples will be described.

[0074] (1) Fire-resistant aggregate ·Refractory aggregate 1: Silica sand (manufactured by Mikawa Siliceki Co., Ltd., No. R6) Refractory aggregate 2: Electrofused artificial sand (Yamakawa Sangyo Co., Ltd., Espearl 60L) Refractory aggregate 3: Spherical fused silica (made by spheroidizing natural silica sand using the flame fusion method) Refractory aggregate 4: Mullite-based artificial sand (Lunamos MS#60, manufactured by Kao Corporation)

[0075] The physical properties of refractory aggregates 1 to 4 are shown in Table 1.

[0076] [Table 1]

[0077] (2) Inorganic binders Inorganic binder 1: Sodium metasilicate nonahydrate (Na2SiO3·9H2O), melting point 47°C Inorganic binder 2: Water glass aqueous solution A (a water glass aqueous solution obtained by diluting sodium silicate (SiO2 / Na2O=2.1) with water to a solids concentration (water glass aqueous solution excluding water) of 35% by mass)

[0078] (3) Inorganic fine particles Inorganic particles 1: amorphous silica particles (average particle diameter d 50 :0.4μm) Inorganic particles 2: amorphous silica particles (average particle diameter d 50 :0.6μm)

[0079] Example 1 Refractory aggregate 1 heated to 105°C was placed in a mixer and then cooled to 65°C. Next, inorganic binder 1 was added in a ratio of 5 parts by mass per 100 parts by mass of refractory aggregate 1, and the mixture was kneaded while being cooled to room temperature (25°C), thereby crystallizing and pulverizing inorganic binder 1 to obtain dry coated sand 1. The obtained coated sand 1 was evaluated as described above. The results are shown in Table 2.

[0080] <Examples 2 to 4> Dry coated sands 2 to 4 were obtained in the same manner as in Example 1, except that refractory aggregates 2 to 4 were used instead of refractory aggregate 1. The obtained coated sands 2 to 4 were each evaluated as described above. The obtained results are shown in Table 2.

[0081] <Example 5> Coated sand 2 (105 parts by mass) obtained in Example 2 and inorganic fine particles 1 (1 part by mass) were placed in a mixer and mixed by stirring at a temperature of 25°C, thereby coating the inorganic binder layer of coated sand 2 with inorganic fine particles 1, thereby obtaining dry coated sand 5. The obtained coated sand 5 was evaluated as described above. The obtained results are shown in Table 2.

[0082] <Examples 6 and 7> Dry coated sands 6 to 7 were obtained in the same manner as in Example 5, except that coated sands 3 and 4 were used instead of coated sand 2. The obtained coated sands 6 to 7 were each evaluated as described above. The obtained results are shown in Table 2.

[0083] Example 8 Dry coated sand 8 was obtained in the same manner as in Example 6, except that inorganic fine particles 2 were used instead of inorganic fine particles 1. The obtained coated sand 8 was evaluated as described above. The obtained results are shown in Table 2.

[0084] <Comparative Example 1> Refractory aggregate 1 heated to 25°C was placed in a mixer, and inorganic binder 2 was added in a ratio of 1.2 parts by mass per 100 parts by mass of refractory aggregate 1, followed by mixing for 1 minute to obtain wet mixed sand 1. The obtained mixed sand 1 was evaluated as described above. The results are shown in Table 2.

[0085] <Comparative Example 2> Wet mixed sand 2 was obtained in the same manner as in Comparative Example 1, except that Refractory Aggregate 2 was used instead of Refractory Aggregate 1. The obtained mixed sand 2 was evaluated as described above. The obtained results are shown in Table 2.

[0086] <Comparative Example 3> Refractory aggregate 2 heated to 120°C was charged into a mixer, and inorganic binder 2 was added in a ratio of 1.2 parts by mass per 100 parts by mass of refractory aggregate 2, followed by kneading. The inorganic binder 2 was dried and pulverized while removing moisture, to obtain dry coated sand 9. The obtained coated sand 9 was subjected to the above evaluations. The results are shown in Table 2.

[0087] [Table 2]

[0088] The dry inorganic coated sands of Examples 1 to 8 had higher filling rates and superior mold filling properties than the wet mixed sands of Comparative Examples 1 and 2. Furthermore, the molds obtained using the dry inorganic coated sands of Examples 1 to 8 had higher bending strength and superior strength compared to the molds obtained using the wet mixed sands of Comparative Examples 1 and 2. The dry coated sand of Comparative Example 3 did not harden under conditions where water vapor was not allowed to pass through. From the above, it was confirmed that the inorganic coated sand according to this embodiment has excellent mold filling properties and can realize a mold with excellent strength. It was also confirmed that the inorganic coated sand according to this embodiment hardens even under conditions that do not allow water vapor to pass through, which shows that equipment, etc. can be simplified. It was also found that the inorganic coated sand according to this embodiment can be produced without using an aqueous solution of an inorganic binder, and that the production of the inorganic coated sand does not require a step of removing water.

Claims

1. A dry inorganic coated sand having a refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate, The inorganic coated sand, wherein the inorganic binder layer contains metasilicate hydrate.

2. 2. The inorganic coated sand according to claim 1, wherein the amount of water contained in the inorganic binder layer is 60 parts by mass or more and 140 parts by mass or less per 100 parts by mass of the metasilicate.

3. 3. The inorganic coated sand according to claim 1, wherein the metasilicate hydrate is at least one selected from the group consisting of sodium metasilicate pentahydrate and sodium metasilicate nonahydrate.

4. The inorganic coated sand according to any one of claims 1 to 3, wherein the refractory aggregate has an amorphization rate of 30% or more.

5. 5. The inorganic coated sand according to claim 1, wherein the sphericity of the inorganic coated sand is 0.80 or more.

6. The inorganic coated sand according to any one of claims 1 to 5, wherein the average particle size of the inorganic coated sand is 0.05 mm or more and 2 mm or less.

7. The refractory aggregate is SiO ２ and Al ２ O ３ The inorganic coated sand according to any one of claims 1 to 6, comprising one or more selected from the group consisting of:

8. 8. The inorganic-coated sand according to claim 1, further comprising inorganic fine particles on or within the inorganic binder layer.

9. 9. The inorganic coated sand according to claim 8, wherein the inorganic fine particles have an average particle size of 0.1 μm or more and 2.0 μm or less.

10. 10. The inorganic coated sand according to claim 1, wherein the slump loss value measured in an environment of 25°C and 55% relative humidity in a slump test conforming to JIS A 1101:2014 using a slump cone having an upper inner diameter of 50 mm, a lower inner diameter of 100 mm, and a height of 150 mm is 90 mm or more.

11. A manufacturing method for manufacturing dry inorganic coated sand having a refractory aggregate and an inorganic binder layer formed on a surface of the refractory aggregate, comprising: the inorganic binder layer contains metasilicate hydrate, (1) a step of mixing the refractory aggregate and the metasilicate hydrate at a temperature equal to or higher than the melting point of the metasilicate hydrate to obtain a mixture; and (2) cooling the mixture to a temperature below the melting point of the metasilicate hydrate.

12. The method for producing inorganic coated sand according to claim 11, wherein in the step (1), the metasilicate hydrate is mixed without being previously prepared as an aqueous solution.

13. A casting mold formed from the inorganic coated sand according to any one of claims 1 to 10.

14. Step (3) of filling the inorganic coated sand according to any one of claims 1 to 10 into a mold to provide the desired casting mold; and (4) heating the mold filled with the inorganic coated sand without passing water vapor through it to harden the inorganic coated sand.

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