Inorganic coated sand

Abstract

To provide inorganic coated sand that can suppress a deformation of a casting mold that is caused during casting.SOLUTION: In a method for suppressing a deformation of a casting mold during casting, an inorganic caking agent layer contains one or more kinds selected from zinc oxides and magnesium oxides and total contents of the zinc oxides and the magnesium oxides are set to be 6 mass parts or more and 70 mass parts or less with respect to 100 mass parts of the inorganic caking agent, in a casting mold prepared using an inorganic coated sand having a fire-resistant aggregate and the inorganic caking agent layer formed on a surface of the fire-resistant aggregate.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] As a mold used for casting of a casting, for example, there is known one obtained by molding into 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 related to such inorganic coated sand include those described in Patent Document 1 (Japanese Patent Application Laid-Open No. 2014-117740) and Patent Document 2 (International Publication No. 2015 / 194550).

[0003] Patent Document 1 describes a production method for a dry coated sand having room temperature fluidity, in which a specific water glass aqueous solution is mixed with a heated refractory aggregate and the water is evaporated to form a coating layer of the binder on the surface of the refractory aggregate.

[0004] Patent Document 2 describes a production method for a mold, in which a molding material mixture containing at least a refractory aggregate, a binder having water glass as an essential component, and a carbonate and / or borate is used, filled into a molding die heated to a specific temperature, and hardened by holding.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] Through our research, we have newly discovered that with conventional inorganic coated sand, for example, when manufacturing molds with complex and thin-walled shapes, the mold is exposed to high-temperature molten metal during casting and deforms, leaving room for improvement in terms of dimensional accuracy. The present invention provides a method for suppressing deformation of a mold made using inorganic coated sand during casting. Furthermore, the present invention provides inorganic coated sand that suppresses mold deformation that occurs during casting. [Means for solving the problem]

[0007] The present inventors have found that in a mold made using inorganic coated sand having refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate, the deformation of the mold during casting can be suppressed by including zinc oxide or magnesium oxide in the inorganic binder layer.

[0008] According to the present invention, A method is provided for suppressing deformation of a mold during casting in a mold made using inorganic coated sand having refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate, wherein the inorganic binder layer contains one or more selected from zinc oxide and magnesium oxide, and the total content of zinc oxide and magnesium oxide is 6 parts by mass or more and 70 parts by mass or less per 100 parts by mass of the inorganic binder.

[0009] According to the present invention, An inorganic coated sand having fire-resistant aggregate and an inorganic binder layer formed on the surface of the fire-resistant aggregate, The inorganic binder layer contains one or more selected from zinc oxide and magnesium oxide. An inorganic coated sand is provided, wherein the total content of zinc oxide and magnesium oxide is 6 parts by mass or more and 70 parts by mass or less per 100 parts by mass of inorganic binder. [Effects of the Invention]

[0010] According to the present invention, a method for suppressing deformation of a mold made using inorganic coated sand during casting can be provided. Furthermore, according to the present invention, inorganic coated sand that suppresses mold deformation during casting can be provided. [Brief explanation of the drawing]

[0011] [Figure 1] This is a cross-sectional view illustrating the method for measuring mold deformation in the embodiment. [Modes for carrying out the invention]

[0012] Embodiments of the present invention will be described below. In this specification, unless otherwise specified, "A to B" indicating a numerical range represents a range of A or greater and B or less, including both values ​​at both ends. 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.

[0013] <Method for suppressing deformation of the mold during casting> In this embodiment, the method for suppressing mold deformation during casting is to use an inorganic coated sand mold having refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate, wherein the inorganic binder layer contains one or more selected from zinc oxide and magnesium oxide, and the total content of zinc oxide and magnesium oxide is 6 parts by mass or more and 70 parts by mass or less per 100 parts by mass of the inorganic binder, specifically per 100 parts by mass of the solid content of the inorganic binder.

[0014] (Mechanism for suppressing deformation) In this embodiment, although the reason for the effect of suppressing the deformation of the mold is not clear, it is considered as follows. Taking the configuration in which the inorganic binder contains alkali silicate or metasilicate as an example, specifically, by incorporating a specific amount of zinc oxide or magnesium oxide into the inorganic binder layer of the inorganic coated sand, zinc oxide or magnesium oxide forms a salt with the alkali metal ions of alkali silicate or metasilicate, etc., releasing the alkali metal ions that inhibit the cross-linking of the silicate chain out of the system to promote the cross-linking of the silicate chain and strengthen the silicate network. As a result, the softening point of the inorganic binder rises, and it is considered that even when the mold is exposed to the heat of the molten metal, it is difficult to cause deformation due to the softening of the inorganic binder. Hereinafter, the manufacturing method of the inorganic coated sand and the mold will be described more specifically.

[0015] <Inorganic Coated Sand> The inorganic coated sand has 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 zinc oxide and magnesium oxide. The total content of zinc oxide and magnesium oxide is 6 parts by mass or more and 70 parts by mass or less with respect to 100 parts by mass of the inorganic binder, specifically, with respect to 100 parts by mass of the solid content of the inorganic binder. Specifically, the inorganic coated sand is composed of a group of particles of the inorganic coated sand, and the refractory aggregate is specifically composed of a group of particles of the refractory aggregate.

[0016] 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. More specifically, from the viewpoints of improving fluidity, mold quality, and mold strength, and the ease of molding the mold, the sphericity of the inorganic coated sand is preferably 0.75 or more, more preferably 0.80 or more, and even more preferably 0.82 or more. Also, specifically, the upper limit value of the sphericity is 1 or less.

[0017] Here, the sphericity of the inorganic-coated sand can be obtained by image analysis of the image (photo) of the particles obtained by an optical microscope or a digital scope (for example, VH-8000 type manufactured by Keyence Corporation), determining the area of the particle projection cross-section of the particle and the perimeter of the cross-section, and then calculating [circumference (mm) of a perfect circle with the same area as the area of the particle projection cross-section (mm 2 )] / [perimeter (mm) of the particle projection cross-section], and for any 50 particles, the obtained values can be averaged and determined respectively.

[0018] From the viewpoints of improving the mold quality and mold strength and the ease of molding the mold, the average particle size of the inorganic-coated sand is preferably 0.05 mm or more, more preferably 0.1 mm or more. Also, when the average particle size of the inorganic-coated sand is at or above the above lower limit value, the amount of the inorganic binder layer used can be reduced during the production of the mold, which is also preferable in terms of making the regeneration of the inorganic-coated sand easier. From the viewpoints of improving the mold quality and mold strength and the ease of molding the mold, the average particle size of the inorganic-coated sand is preferably 2 mm or less, more preferably 1 mm or less, and even more preferably 0.5 mm or less. Also, when the average particle size of the inorganic-coated sand is at or below the above upper limit value, the porosity becomes smaller during the production of the mold, which is also preferable in terms of increasing the mold strength. In this embodiment, the average particle sizes of the inorganic-coated sand and the refractory aggregate described later can be specifically measured by the following method.

[0019] (Method for measuring average particle size) If the sphericity of the particle from the particle projection cross section is 1, the diameter (mm) is measured. On the other hand, if the sphericity is < 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. For any 100 particles, the obtained values ​​are averaged to obtain the average particle size (mm). The major axis diameter and minor axis diameter are defined as follows: When a particle is stabilized on a plane and its projection image onto the plane is sandwiched between two parallel lines, the width of the particle at which the distance between the parallel lines is minimized is called the minor axis diameter. On the other hand, the distance when the particle is sandwiched between two parallel lines perpendicular to these parallel lines is called the major axis diameter. The major and minor axis diameters of a particle can be determined by taking an image (photograph) of the particle using an optical microscope or digital scope (for example, the VH-8000 model from Keyence Corporation) and performing image analysis on the obtained image.

[0020] (Fireproof aggregate) The materials for the fire-resistant aggregate include one or more selected from the group consisting of natural sand and artificial sand.

[0021] Examples of natural sand include one or more types selected from the group consisting of silica sand (primarily composed of quartz), chromite sand, zircon sand, olivine sand, and alumina sand.

[0022] Examples of artificial sand include one or more types selected from the group consisting of synthetic mullite sand, SiO2-based foundry sand with SiO2 as the main component, Al2O3-based foundry sand with Al2O3 as the main component, 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 main component refers to the most abundant component in the sand. Artificial sand refers to foundry sand that is not naturally occurring, but rather sand that has been artificially prepared by adjusting the metal oxide components and then melting or sintering it. Recycled sand, obtained by recovering used refractory aggregate, and recycled sand, obtained by treating recycled sand, can also be used.

[0023] The refractory aggregate is preferably in particulate form, from the viewpoint of improving the fluidity of the inorganic coated sand and further enhancing its ability to fill into the molding die. Furthermore, the average particle size of the refractory aggregate is preferably 0.05 mm or larger, and more preferably 0.1 mm or larger, from the viewpoint of improving mold quality and strength, as well as ease of mold formation. In addition, if the average particle size of the refractory aggregate is above the above lower limit, the amount of inorganic binder layer used during mold manufacturing can be reduced, which is also preferable because it makes it easier to regenerate the inorganic coated sand. 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 viewpoint of improving mold quality and mold strength, and from the viewpoint of ease of mold formation. Furthermore, when the average particle size of the refractory aggregate is below the above upper limit, it is also preferable that the porosity is reduced during mold manufacturing, thereby increasing the mold strength.

[0024] (Inorganic binder layer) The inorganic binder layer specifically contains an inorganic binder and one or more selected from zinc oxide and magnesium oxide. The inorganic binder layer is, specifically, a coating layer formed on the surface of the refractory aggregate. The inorganic binder layer can be, for example, a layer coated with a mixture of one or more selected from an inorganic binder, zinc oxide, and magnesium oxide; a layer coated with one or more selected from zinc oxide and magnesium oxide on top of the inorganic binder coating; or a layer coated with one or more selected from zinc oxide and magnesium oxide on top of a layer coated with a mixture of an inorganic binder and one or more selected from zinc oxide and magnesium oxide.

[0025] From the viewpoint of improving mold strength, the content of the inorganic binder layer in the inorganic coated sand is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, even more preferably 0.5% by mass or more, even more preferably 1.0% by mass or more, and especially preferably 1.5% by mass or more, relative to the total amount of components other than water in the inorganic coated sand. Furthermore, from the viewpoint of improving the fillability into the molding die and improving the strength of the mold, the content of the inorganic binder layer in the inorganic coated sand is preferably 10% by mass or less, more preferably 8% by mass or less, even more preferably 6% by mass or less, even more preferably 4.5% by mass or less, and even more preferably 4% by mass or less, relative to the total amount of components other than water in the inorganic coated sand. Here, the inorganic binder layer content refers to the content excluding water contained in the inorganic binder layer. For example, when sodium metasilicate hydrate, which will be described later, is used as the inorganic binder, the content is calculated by converting it to sodium metasilicate.

[0026] From the viewpoint of improving mold strength, the amount of inorganic binder layer in the inorganic coated sand relative to 100 parts by mass of refractory aggregate is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, even more preferably 0.5 parts by mass or more, even more preferably 1 part by mass or more, and especially preferably 1.5 parts by mass or more. Furthermore, from the viewpoint of improving the ability to fill the molding die and improving the strength of the mold, the amount of inorganic binder layer per 100 parts by mass of refractory aggregate in the inorganic coated sand is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, even more preferably 6 parts by mass or less, even more preferably 4.5 parts by mass or less, and even more preferably 4 parts by mass or less.

[0027] Next, we will explain the components contained in the inorganic binder layer. (Inorganic binder) In this embodiment, from the viewpoint of excellent productivity and ease of availability, the inorganic binder includes, for example, a silicate compound, and preferably includes at least one selected from sodium silicate and sodium metasilicate. Furthermore, the inorganic binder may also contain other water-soluble silicate compounds as its main component. Specific examples of silicate compounds other than sodium silicate and sodium metasilicate include potassium silicate, potassium metasilicate, lithium silicate, and ammonium silicate.

[0028] Specifically, sodium silicate refers to one or more types 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 specified in JIS-K-1408. The molar ratios of SiO2 / Na2O for each no. are as follows: Sodium silicate No. 1: Molar ratio of SiO2 / Na2O = 2.0~2.3 Sodium silicate No. 2: Molar ratio of SiO2 / Na2O = 2.4~2.6 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 Alternatively, the molar ratio of SiO2 / Na2O may be adjusted to a desired degree by mixing two or more types of sodium silicate. Sodium silicate is preferably at least one selected from No. 1 water glass and No. 3 water glass.

[0029] Sodium metasilicate is preferably in hydrate form from the viewpoint of improving the productivity of inorganic coated sand and the productivity of molds. From the above viewpoint, at least one selected from sodium metasilicate pentahydrate and sodium metasilicate nonahydrate is preferred as the sodium metasilicate hydrate, and sodium metasilicate nonahydrate is more preferred.

[0030] From the viewpoint of improving mold strength and improving the surface shape of the mold, the inorganic binder content in the inorganic binder layer is preferably 25% by mass or more, more preferably 30% by mass or more, even more preferably 35% by mass or more, and even more preferably 40% by mass or more, relative to the entire inorganic binder layer. Furthermore, from the viewpoint of suppressing deformation of the mold at high temperatures, the inorganic binder content in the inorganic binder layer is preferably 94% by mass or less, and more preferably 93% by mass or less, relative to the entire inorganic binder layer. Here, the inorganic binder content in the inorganic binder layer refers to the inorganic binder content excluding water, relative to the total amount of components other than water in the inorganic binder layer.

[0031] The total content of sodium silicate and sodium metasilicate in the inorganic binder is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, and even more preferably substantially 100% by mass, from the viewpoint of improving mold strength, excellent productivity, and availability. Here, "substantially" means that it may include components that are included unintentionally, for example, components other than sodium silicate and sodium metasilicate that are contained in the raw materials sodium silicate and sodium metasilicate. The total content of sodium silicate and sodium metasilicate in an inorganic binder refers to the total content of sodium silicate and sodium metasilicate relative to the total content of all components other than water in the inorganic binder.

[0032] Furthermore, from the viewpoint of improving mold strength and improving the surface shape of the mold, the inorganic binder content in the inorganic coated sand is preferably 0.03 parts by mass or more, more preferably 0.1 parts by mass or more, even more preferably 0.5 parts by mass or more, even more preferably 0.8 parts by mass or more, and especially preferably 1 part by mass or more, per 100 parts by mass of refractory aggregate. Furthermore, from the viewpoint of improving the ability to fill into the molding die, the amount of inorganic binder in the inorganic coated sand is preferably 5 parts by mass or less, more preferably 4 parts by mass or less, even more preferably 3 parts by mass or less, and even more preferably 2 parts by mass or less, per 100 parts by mass of refractory aggregate.

[0033] (Zinc oxide, magnesium oxide) The properties of zinc oxide (ZnO) and magnesium oxide (MgO) are preferably in the form of fine particles from the viewpoint of enhancing their reactivity with inorganic binders. From the viewpoint of enhancing reactivity with the inorganic binder, the average particle size of zinc oxide and magnesium oxide is preferably 100 μm or less, more preferably 50 μm or less, even more preferably 30 μm or less, even more preferably 20 μm or less, and even more preferably 15 μm or less. Furthermore, the average particle size of zinc oxide and magnesium oxide is preferably 0.1 μm or larger, more preferably 0.3 μm or larger, even more preferably 0.5 μm or larger, and even more preferably 1 μm or larger, from the viewpoint of ease of handling and availability.

[0034] The average particle size of zinc oxide and magnesium oxide can be determined specifically using the following measurement method. (Method for measuring average particle size) This is the average particle diameter at 50% volume cumulative, measured using a laser diffraction particle size distribution analyzer LA-960V2 (manufactured by Horiba, Ltd.). The analysis conditions are as follows: • Measurement method: Flow method ·Dispersion medium: water • Dispersion method: stirring, built-in ultrasonic for 3 minutes • Sample concentration: 2 mg / 100 mL • Refractive index: Refractive index of each oxide (zinc oxide: 2.00, magnesium oxide: 1.76)

[0035] From the viewpoint of suppressing deformation of the mold at high temperatures, the total content of zinc oxide and magnesium oxide in the inorganic binder layer is preferably 2% by mass or more, and more preferably 3% by mass or more, relative to the total amount of components other than water in the inorganic binder layer. Furthermore, from the viewpoint of improving mold strength, the total content of zinc oxide and magnesium oxide in the inorganic binder layer is preferably 45% by mass or less, more preferably 40% by mass or less, and even more preferably 35% by mass or less, relative to the total content of the inorganic binder layer other than water.

[0036] The total content of zinc oxide and magnesium oxide per 100 parts by mass of inorganic binder is preferably 6 parts by mass or more, more preferably 7 parts by mass or more, even more preferably 10 parts by mass or more, even more preferably 15 parts by mass or more, and especially preferably 20 parts by mass or more, from the viewpoint of suppressing deformation of the mold at high temperatures. Furthermore, from the viewpoint of improving mold strength and suppressing dust scattering when zinc oxide and magnesium oxide are added (externally) after coating the refractory aggregate with an inorganic binder during the production of inorganic coated sand, the total content of zinc oxide and magnesium oxide per 100 parts by mass of inorganic binder is preferably 70 parts by mass or less, more preferably 60 parts by mass or less, even more preferably 55 parts by mass or less, and even more preferably 50 parts by mass or less.

[0037] (Other additives) In addition to the components mentioned above, the inorganic binder layer may contain various additives as needed. Other additives include humectants, moisture resistance enhancers, coupling agents to strengthen the bond between the refractory aggregate and the inorganic binder, lubricants, surfactants, and release agents. Examples of humectants include polyhydric alcohols, water-soluble polymers, hydrocarbons, sugars, proteins, and inorganic compounds other than those mentioned above. Examples of moisture-resistant agents include metal oxides (excluding zinc oxide and magnesium oxide), carbonates, borates, sulfates, and phosphates. Examples of lubricants include waxes; fatty acid amides; alkylene fatty acid amides; stearic acid; stearyl alcohol; metal stearate salts such as lead stearate, zinc stearate, calcium stearate, and magnesium stearate; monoglyceride stearate; stearyl stearate; and hydrogenated oils. Examples of mold release agents include paraffin, wax, diesel fuel, machine oil, spindle oil, insulating oil, waste oil, vegetable oil, fatty acid esters, organic acids, graphite fine particles, mica, vermiculite, fluorine-based mold release agents, silicone-based mold release agents, and the like.

[0038] (Inorganic fine particles) In this embodiment, the inorganic coated sand may further contain inorganic fine particles other than zinc oxide and magnesium oxide. Preferably, the inorganic fine particles form part of the inorganic binder layer. In this case, it is preferable that the inorganic binder layer further contains inorganic fine particles on and within the layer, and more preferably that it further contains inorganic fine particles on the layer. The inorganic fine particles may be contained both on and within the inorganic binder layer. By doing so, the inorganic coated sand particles bond more strongly to each other via inorganic microparticles, and as a result, the strength of the resulting mold can be further improved. Here, the inorganic fine particles on the inorganic binder layer may be partially embedded in the inorganic binder layer.

[0039] While the inorganic fine particles are not limited to those mentioned above, examples include silica particles and silicon particles. From the viewpoint of improving the strength of the mold, silica particles are preferred, and amorphous silica particles are more preferred from the viewpoint of having a large specific surface area and high reactivity with sodium silicate and sodium metasilicate. These inorganic fine particles may be used individually or in combination of two or more types.

[0040] (Amorphous silica particles) In this embodiment, the inorganic coated sand may further contain amorphous silica particles. The amorphous silica particles preferably form part of the inorganic binder layer.

[0041] The degree of amorphousness of the amorphous silica particles is preferably 80% or more, more preferably 90% or more, even more preferably 93% or more, even more preferably 95% or more, and especially preferably 98% or more, from the viewpoint of more firmly bonding the inorganic coated sand particles together via the amorphous silica particles. The upper limit of the degree of amorphousness of the amorphous silica particles is not limited, but for example it may be 100% or less, 99.8% or less, or 99% or less.

[0042] The degree of amorphousness of amorphous silica particles can be determined by the X-ray diffraction method shown below. (X-ray diffraction method) Amorphous silica particles are crushed in a mortar and pressed onto the X-ray glass holder of a powder X-ray diffractometer for measurement. The powder X-ray diffractometer used is a MultiFlex manufactured by Rigaku Denki Co., Ltd. (light source: CuKα rays, tube voltage: 40kV, tube current: 40mA), and measurements are 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, RS0.3mm. In the range of 2θ = 10° to 50°, the X-ray intensities on the low and high angle sides are connected by straight lines, and the area below the line is defined as the background. The degree of crystallinity is determined using the software provided with the instrument, and subtracted from 100 to obtain the degree of amorphousness. Specifically, for the area above the background, the amorphous peak (halo) and each crystalline component are separated by curve fitting, the area of ​​each is determined, and the degree of amorphousness (%) is calculated using the following formula. Amorphization (%) = Area of ​​halo / (Area of ​​crystalline components + Area of ​​halo) × 100

[0043] Average particle diameter d in the weight-based particle size distribution of amorphous silica particles by laser diffraction scattering particle size distribution measurement method 50 From the viewpoint of improving mold strength and handling performance, the average particle diameter d of amorphous silica particles is preferably 0.1 μm or larger, and more preferably 0.3 μm or larger. Furthermore, from the viewpoint of improving mold strength, the average particle diameter d of amorphous silica particles is also 50 The particle size is preferably 2.0 μm or less, more preferably 1.0 μm or less, even more preferably 0.8 μm or less, and even more preferably 0.6 μm or less. Here, the average particle diameter d in the weight-based particle size distribution of amorphous silica particles measured by laser diffraction scattering particle size distribution analysis is defined as 50 This can be obtained, for example, by dissolving and removing the inorganic binder layer from inorganic coated sand with water, extracting amorphous silica particles, and then measuring the particle size distribution of the obtained amorphous silica particles using a laser diffraction scattering particle size distribution analysis method. Furthermore, the average particle diameter d in the weight-based particle size distribution of amorphous silica particles measured by laser diffraction scattering particle size distribution analysis. 50This can also be obtained by measuring the particle size of the amorphous silica particles used as raw material using a laser diffraction scattering particle size distribution analysis method.

[0044] Furthermore, the average particle size of amorphous silica particles, as determined from scanning electron microscope observation images, is preferably 0.1 μm or more, and more preferably 0.3 μm or more, from the viewpoint of improving mold strength per unit mass and handling properties. Also, from the viewpoint of improving mold strength per unit mass, the average particle size of amorphous silica particles, as determined from scanning electron microscope observation images, is preferably 2.0 μm or less, more preferably 1.0 μm or less, even more preferably 0.8 μm or less, and even more preferably 0.6 μm or less. Here, the average particle size of amorphous silica particles, obtained from scanning electron microscope observation images, can be determined using various image analysis techniques. Irregular particle sorting may be performed as a pretreatment. For example, after determining the inorganic binder layer and amorphous silica particles based on their elements, 100 arbitrary amorphous silica particles can be selected, their particle sizes measured, and the average particle size of the remaining 80 amorphous silica particles (10 from the largest particle size and 10 from the smallest particle size) can be taken as the average particle size of the amorphous silica particles.

[0045] From the viewpoint of improving mold strength, the content of amorphous silica particles in the inorganic binder layer is specifically 0% by mass or more, preferably 20% by mass or more, more preferably 25% by mass or more, and even more preferably 30% by mass or more, relative to the total components of the inorganic binder layer other than water. Furthermore, from the viewpoint of improving the surface shape of the mold and suppressing dust scattering, the content of amorphous silica particles in the inorganic binder layer is preferably 55% by mass or less, more preferably 50% by mass or less, and even more preferably 45% by mass or less, relative to the total components of the inorganic binder layer other than water.

[0046] Furthermore, from the viewpoint of improving mold strength, the content of amorphous silica particles is specifically 0 parts by mass or more, preferably 20 parts by mass or more, more preferably 40 parts by mass or more, even more preferably 50 parts by mass or more, and even more preferably 60 parts by mass or more, per 100 parts by mass of inorganic binder. Furthermore, from the viewpoint of improving the surface shape of the mold and suppressing dust scattering, the content of amorphous silica particles is preferably 150 parts by mass or less, more preferably 120 parts by mass or less, even more preferably 100 parts by mass or less, even more preferably 90 parts by mass or less, and even more preferably 80 parts by mass or less, per 100 parts by mass of inorganic binder.

[0047] From the viewpoint of obtaining a high-strength mold, the water content in the inorganic binder layer contained in the inorganic coated sand is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 20 parts by mass or more, per 100 parts by mass of the inorganic binder. Furthermore, from the viewpoint of filling into the molding die and obtaining a high-strength mold, the water content in the inorganic binder layer contained in the inorganic coated sand 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 even more preferably 140 parts by mass or less, per 100 parts by mass of inorganic binder.

[0048] The water content in the inorganic binder layer of inorganic coated sand can be adjusted according to the type of inorganic binder used. When the inorganic binder is sodium silicate, the water content in the inorganic binder layer is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 20 parts by mass or more, per 100 parts by mass of sodium silicate, from the viewpoint of obtaining a high-strength mold. Furthermore, from the viewpoint of filling into the molding die and obtaining a high-strength mold, the water content in the inorganic binder layer contained in the inorganic coated sand is preferably 55 parts by mass or less, and more preferably 50 parts by mass or less, per 100 parts by mass of sodium silicate.

[0049] When the inorganic binder is sodium metasilicate, from the viewpoint of obtaining a high-strength mold and manufacturing the mold easily, the water content in the inorganic binder layer 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 even more preferably 110 parts by mass or more, per 100 parts by mass of sodium metasilicate. Furthermore, from the viewpoint of improving fluidity and further enhancing the ability to fill into the molding die, the water content 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 even more preferably 140 parts by mass or less. For example, when the inorganic binder layer consists only of sodium metasilicate pentahydrate, the water content is 74 parts by mass per 100 parts by mass of sodium metasilicate, and when it consists only of sodium metasilicate nonahydrate, the water content is 133 parts by mass per 100 parts by mass of sodium metasilicate.

[0050] <Method for manufacturing inorganic coated sand> The method for producing inorganic coated sand can be selected, for example, depending on the type of inorganic binder used.

[0051] When the inorganic binder contains sodium silicate, for example, by kneading or mixing an aqueous solution of water glass as an inorganic binder with heated refractory aggregate, along with any additives as needed, to ensure uniform mixing, and by coating the surface of the refractory aggregate with the aqueous solution of water glass while allowing the water in the aqueous solution to evaporate, a dry inorganic coated sand with fluidity at room temperature can be obtained.

[0052] When the inorganic binder contains sodium metasilicate hydrate, for example, a manufacturing method can be used to obtain dry inorganic coated sand by a method comprising the steps of: mixing refractory aggregate and sodium metasilicate hydrate at a temperature above the melting point of sodium metasilicate hydrate to obtain a mixture; and cooling the mixture to a temperature below the melting point of sodium metasilicate hydrate. According to this manufacturing method, the inorganic binder layer can be crystallized, resulting in inorganic coated sand with superior fluidity compared to conventional manufacturing methods. Furthermore, since it does not require the use of an aqueous solution of sodium metasilicate hydrate, a dehydration step is unnecessary, simplifying the manufacturing process for inorganic coated sand.

[0053] In the process of obtaining the mixture, specifically, the surface of the refractory aggregate is coated with fluidized sodium metasilicate hydrate at a temperature above the melting point of sodium metasilicate hydrate. Methods for mixing refractory aggregate and sodium metasilicate hydrate at a temperature above the melting point of sodium metasilicate hydrate include, for example, adding sodium metasilicate hydrate to refractory aggregate heated to a temperature above the melting point of sodium metasilicate hydrate and mixing the refractory aggregate and sodium metasilicate hydrate while melting the sodium metasilicate hydrate; or adding heated and melted sodium metasilicate hydrate to refractory aggregate and mixing them. Among these methods, the preferred method is to add heated and melted sodium metasilicate hydrate to the refractory aggregate and mix it, from the viewpoint of shortening the coating time. From a similar viewpoint, it is preferable that the sodium metasilicate hydrate is not pre-dissolved in an aqueous solution before mixing in the process of obtaining the mixture. It is also preferable that the process of obtaining the mixture does not include a step of intentionally adding water. The mixing conditions, such as the stirring speed and processing time, when mixing refractory aggregate and sodium metasilicate hydrate can be appropriately determined depending on the amount of mixture being processed.

[0054] In the step of cooling the mixture, the mixture obtained in the step of obtaining the mixture is cooled to a temperature below the melting point of sodium metasilicate hydrate, thereby reducing the fluidity of the sodium metasilicate hydrate and fixing the sodium metasilicate hydrate to the surface of the refractory aggregate, thereby forming a sodium metasilicate hydrate layer, or inorganic binder layer.

[0055] Furthermore, there are no restrictions on the method of adding zinc oxide or magnesium oxide in the production of inorganic coated sand. For example, refractory aggregate may be coated with an inorganic binder, amorphous silica particles if necessary, and other additives as described above, and then coated with one or more selected from zinc oxide and magnesium oxide, amorphous silica particles if necessary, and other additives. Alternatively, one or more inorganic binders, zinc oxide, and magnesium oxide, along with amorphous silica particles and other additives as needed, may be coated onto the refractory aggregate. Alternatively, the refractory aggregate may be coated with one or more inorganic binders, zinc oxide, and magnesium oxide, and optionally amorphous silica particles or other additives, and then coated with one or more zinc oxide and magnesium oxide, and optionally amorphous silica particles or other additives. From the viewpoint of suppressing deformation of the mold, it is preferable to coat the refractory aggregate with an inorganic binder, and then coat it with one or more selected from zinc oxide and magnesium oxide.

[0056] Zinc oxide or magnesium oxide can be mixed with refractory aggregates, inorganic binders, etc., in solid or aqueous dispersion form. Furthermore, the addition of zinc oxide or magnesium oxide may be done all at once or in multiple steps.

[0057] By the above method, the inorganic coated sand of this embodiment can be obtained. Furthermore, the resulting inorganic coated sand can be used alone or in combination with other known refractory aggregates or other additives to form desired molds.

[0058] <Mold> In this embodiment, the mold is made using the inorganic coated sand described in the above embodiment. Examples of mold forming methods include a forming method using a heated molding die, and a forming method in which steam is further passed through a heated molding die, followed by the passage of hot air. If the inorganic binder layer contains sodium metasilicate hydrate, a method of molding by filling an inorganic coated sand into a heated molding die is preferred. If the inorganic binder layer contains sodium silicate, a method of molding by adding water to the inorganic coated sand, kneading it, and then filling it into a heated molding die is preferred, or a method of molding by filling an inorganic coated sand into a heated molding die, then passing steam through it, and then passing hot air through it is preferred.

[0059] When the inorganic binder layer contains sodium metasilicate hydrate, in a molding method using a heated mold, for example, first, the inorganic coated sand is filled into the mold to give the desired mold. Here, from the viewpoint of improving mold productivity, the molding die is preferably preheated before filling with inorganic coated sand. The heating temperature at this time is preferably 100°C or higher, more preferably 150°C or higher, and preferably 300°C or lower, and more preferably 250°C or lower, from the viewpoint of improving mold productivity and mold strength.

[0060] After filling with inorganic coated sand, the molding die is heated without allowing steam to pass through, thereby curing the inorganic coated sand. When the inorganic binder layer contains sodium metasilicate hydrate, the inorganic coated sand can be cured without the need for steps of adding water to the inorganic coated sand and kneading it, or steps of allowing steam to pass through, thus eliminating the need for equipment to allow steam to pass through. 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 preferably 300°C or lower, and more preferably 250°C or lower. Furthermore, from the viewpoint of obtaining stable mold strength, the heating time is preferably 30 seconds or higher, more preferably 60 seconds or higher, and preferably 600 seconds or lower.

[0061] Furthermore, when the inorganic binder layer contains sodium silicate, water is added to the inorganic coated sand and kneaded before filling it into a heated molding die. In addition, in molding methods that use steam, for example, after filling the molding die that will give the desired mold with inorganic coated sand, steam is blown in. The filling phase of the inorganic coated sand is moistened by the steam, making it wet. Then, hot air is blown into the molding die heated to 90-200°C to dry and harden the inorganic coated sand.

[0062] Furthermore, the inorganic coated sand in this embodiment can also be used in additive manufacturing.

[0063] With respect to the embodiments described above, the present invention further discloses a method for suppressing mold deformation and an inorganic coated sand. <1> A method for suppressing deformation of a mold during casting, in a mold made using inorganic coated sand having refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate, wherein the inorganic binder layer contains one or more selected from zinc oxide and magnesium oxide, and the total content of zinc oxide and magnesium oxide is 6 parts by mass or more and 70 parts by mass or less per 100 parts by mass of the inorganic binder.

[0064] <2> In a mold made using inorganic coated sand having 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 zinc oxide and magnesium oxide. The total content of the aforementioned zinc oxide and magnesium oxide shall be 6 parts by mass or more and 70 parts by mass or less per 100 parts by mass of the inorganic binder. The inorganic binder contains at least one selected from the group consisting of sodium silicate and sodium metasilicate, in a total amount of 80% by mass or more of sodium silicate and sodium metasilicate. The amount of the inorganic binder layer in the inorganic coated sand relative to 100 parts by mass of the refractory aggregate is set to 0.05 parts by mass or more and 10 parts by mass or less. <1> A method for suppressing deformation of the mold during casting as described above. <3> In a mold made using inorganic coated sand having 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 zinc oxide and magnesium oxide. The total content of the aforementioned zinc oxide and magnesium oxide shall be 6 parts by mass or more and 55 parts by mass or less per 100 parts by mass of the inorganic binder. The inorganic binder contains at least one selected from the group consisting of sodium silicate and sodium metasilicate, in a total amount of 98% by mass or more of sodium silicate and sodium metasilicate. The amount of the inorganic binder layer in the inorganic coated sand relative to 100 parts by mass of the refractory aggregate is set to 1 part by mass or more and 4.5 parts by mass or less. <1> or <2> A method for suppressing deformation of the mold during casting as described above. <4> The average particle size of the inorganic coated sand is 0.05 mm or more and 2 mm or less. <1> ~ <3> A method for suppressing deformation of the mold during casting, as described in any of the following. <5> The average particle size of the aforementioned fire-resistant aggregate is 0.05 mm or more and 2 mm or less. <1> ~ <4> A method for suppressing deformation of the mold during casting, as described in any of the following. <6> The inorganic binder layer content in the inorganic coated sand is 1.0% by mass or more and 4.5% by mass or less. <1> ~ <5> A method for suppressing deformation of the mold during casting, as described in any of the following. <7> The inorganic binder content in the inorganic binder layer is 35% by mass or more and 94% by mass or less. <1> ~ <6> A method for suppressing deformation of the mold during casting, as described in any of the following. <8> The total content of sodium silicate and sodium metasilicate in the inorganic binder is substantially 100% by mass. <1> ~ <7> A method for suppressing deformation of the mold during casting, as described in any of the following. <9> The inorganic binder content in the inorganic coated sand is 0.5 parts by mass or more and 3 parts by mass or less per 100 parts by mass of refractory aggregate. <1> ~ <8> A method for suppressing deformation of the mold during casting, as described in any of the following. <10> The average particle size of the zinc oxide and magnesium oxide is 0.5 μm or more and 30 μm or less. <1> ~ <9> A method for suppressing deformation of the mold during casting, as described in any of the following. <11> The total content of zinc oxide and magnesium oxide in the inorganic binder layer is 2% by mass or more and 40% by mass or less. <1> ~ <10> A method for suppressing deformation of the mold during casting, as described in any of the following. <12> The total content of the aforementioned zinc oxide and magnesium oxide is 20 parts by mass or more and 55 parts by mass or less per 100 parts by mass of the inorganic binder. <1> ~ <11> A method for suppressing deformation of the mold during casting, as described in any of the following. <13> The water content in the inorganic binder layer is 20 parts by mass or more and 150 parts by mass or less per 100 parts by mass of the inorganic binder. <1> ~ <12> A method for suppressing deformation of the mold during casting, as described in any of the following. <14> An inorganic coated sand having fire-resistant aggregate and an inorganic binder layer formed on the surface of the fire-resistant aggregate, The inorganic binder layer contains one or more selected from zinc oxide and magnesium oxide. An inorganic coated sand in which the total content of zinc oxide and magnesium oxide is 6 parts by mass or more and 70 parts by mass or less per 100 parts by mass of inorganic binder. <15> An inorganic coated sand having fire-resistant aggregate and an inorganic binder layer formed on the surface of the fire-resistant aggregate, The inorganic binder layer contains one or more selected from zinc oxide and magnesium oxide. The total content of the aforementioned zinc oxide and magnesium oxide is 6 parts by mass or more and 70 parts by mass or less per 100 parts by mass of the inorganic binder. The inorganic binder contains at least one selected from the group consisting of sodium silicate and sodium metasilicate, in a total amount of 80% by mass or more of sodium silicate and sodium metasilicate. The amount of the inorganic binder layer in the inorganic coated sand relative to 100 parts by mass of the refractory aggregate is 0.05 parts by mass or more and 10 parts by mass or less. <14> The inorganic coated sand described above. <16> An inorganic coated sand having fire-resistant aggregate and an inorganic binder layer formed on the surface of the fire-resistant aggregate, The inorganic binder layer contains one or more selected from zinc oxide and magnesium oxide. The total content of the aforementioned zinc oxide and magnesium oxide is 6 parts by mass or more and 55 parts by mass or less per 100 parts by mass of the inorganic binder. The inorganic binder contains at least one selected from the group consisting of sodium silicate and sodium metasilicate, in a total amount of 98% by mass or more of sodium silicate and sodium metasilicate. The amount of the inorganic binder layer in the inorganic coated sand relative to 100 parts by mass of the refractory aggregate is 1 part by mass or more and 4.5 parts by mass or less. <14> or <15> The inorganic coated sand described above. <17> The average particle size of the inorganic coated sand is 0.05 mm or more and 2 mm or less. <14> ~ <16> Inorganic coated sand as described in one of the following. <18> The average particle size of the aforementioned fire-resistant aggregate is 0.05 mm or more and 2 mm or less. <14> ~ <17> Inorganic coated sand as described in one of the following. <19> The inorganic binder layer content in the inorganic coated sand is 1.0% by mass or more and 4.5% by mass or less. <14> ~ <18> Inorganic coated sand as described in one of the following. <20> The inorganic binder content in the inorganic binder layer is 35% by mass or more and 94% by mass or less. <14> ~ <19> Inorganic coated sand as described in one of the following. <21> The total content of sodium silicate and sodium metasilicate in the inorganic binder is substantially 100% by mass. <14> ~ <20> Inorganic coated sand as described in one of the following. <22> The inorganic binder content in the inorganic coated sand is 0.5 parts by mass or more and 3 parts by mass or less per 100 parts by mass of refractory aggregate. <14> ~ <21> Inorganic coated sand as described in one of the following. <23> The average particle size of the zinc oxide and magnesium oxide is 0.5 μm or more and 30 μm or less. <14> ~ <22> Inorganic coated sand as described in one of the following. <24> The total content of zinc oxide and magnesium oxide in the inorganic binder layer is 2% by mass or more and 40% by mass or less. <14> ~ <23> Inorganic coated sand as described in one of the following. <25> The total content of the aforementioned zinc oxide and magnesium oxide is 20 parts by mass or more and 55 parts by mass or less per 100 parts by mass of the inorganic binder. <14> ~ <24> Inorganic coated sand as described in one of the following. <26> The water content in the inorganic binder layer is 20 parts by mass or more and 150 parts by mass or less per 100 parts by mass of the inorganic binder. <14> ~ <25> Inorganic coated sand as described in one of the following. <27> The inorganic coated sand contains amorphous silica particles, and the amount of amorphous silica particles is 50 parts by mass or more and 90 parts by mass or less per 100 parts by mass of inorganic binder. <14> ~ <26> Inorganic coated sand as described in one of the following. <28> The content of amorphous silica particles in the inorganic binder layer is 20% by mass or more and 45% by mass or less. <27> The inorganic coated sand described above. <29> The amorphous silica particles have a degree of amorphousness of 90% or more, and the average particle size of the amorphous silica particles is 0.1 μm or more and 2.0 μm or less. <27> or <28> The inorganic coated sand described above. <30> The process includes a step of coating the refractory aggregate with an inorganic binder, and a step of coating the refractory aggregate coated with the inorganic binder with at least one selected from zinc oxide and magnesium oxide. <14> ~ <29> A method for producing inorganic coated sand as described in any of the above. [Examples]

[0065] The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited thereto. First, the raw materials used in the following example are listed.

[0066] (Raw materials used in the manufacture of inorganic coated sand) ·Refractory aggregate Mikawa Silica Sand R6 (manufactured by Mikawa Siliceki Co., Ltd., average particle size: 200μm) Lunamos MS#60 (artificial sand for casting, manufactured by Kao Quaker Company, average particle size: 200 μm) • Inorganic binder Sodium metasilicate nonahydrate (Na2SiO3·9H2O) (manufactured by Nippon Chemical Industrial Co., Ltd.) No. 1 50 water glass (SiO2 / Na2O=2.1) (manufactured by Fuji Chemical Co., Ltd.: 45% by mass aqueous solution) No. 3 water glass (SiO2 / Na2O=3.1) (manufactured by Fuji Chemical Co., Ltd.: 40% by mass aqueous solution) · Amorphous microparticles Denka Fused Silica SFP-20M (Average particle size d 50 (0.4 μm, Amorphization: 99.5% or higher) (Manufactured by Denka Co., Ltd.) • Zinc oxide (ZnO) Zinc oxide: Manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., in powder form, average particle size 1.37 μm Magnesium oxide (MgO) Magnesium oxide: Manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., in powder form, average particle size 12.2 μm

[0067] <Examples 1-4> Mikawa silica sand R6 (100 parts by mass) was added to a stirrer as a refractory aggregate. Next, sodium metasilicate nonahydrate (4.00 parts by mass), which had been heated to 80°C and melted, was added to the stirrer and kneaded for 4 minutes. Then, amorphous silica fine particles (1.20 parts by mass) were added and kneaded for 2 minutes. Next, zinc oxide or magnesium oxide in the amounts shown in Table 1 was added and kneaded for 2 minutes to obtain the inorganic coated sands of Examples 1 to 4. Table 1 shows the composition of the inorganic coated sands.

[0068] <Examples 5-12> As a refractory aggregate, 100 parts by mass of Mikawa silica sand R6, heated to approximately 120°C, was added to a stirrer. Next, 4.00 parts by mass of No. 1 50 water glass was added to the stirrer and kneaded to evaporate the water, stirring for approximately 3 minutes until the sand particles broke down. Furthermore, zinc oxide or magnesium oxide (in the amounts shown in Table 2) was added and kneaded for 2 minutes to obtain the inorganic coated sands of Examples 5 to 12. Table 2 shows the composition of the inorganic coated sands.

[0069] <Example 13> Lunamos MS#60 (100 parts by mass), heated to approximately 120°C, was added to a stirrer as a refractory aggregate. Next, No. 1 50 water glass (2.00 parts by mass) was added to the stirrer and kneaded to evaporate the water, stirring for approximately 3 minutes until the sand particles broke down. Furthermore, zinc oxide (0.19 parts by mass) was added and kneaded for 2 minutes to obtain the inorganic coated sand of Example 13. Table 2 shows the composition of the inorganic coated sand.

[0070] <Examples 14, 16> As a refractory aggregate, 100 parts by mass of Mikawa silica sand R6, heated to approximately 120°C, was added to a stirrer. Next, 4.00 parts by mass of No. 3 water glass and 0.41 parts by mass of zinc oxide or magnesium oxide were added to the stirrer and kneaded to evaporate the water. The mixture was stirred for approximately 3 minutes until the sand particles broke down, yielding the inorganic coated sands of Examples 14 and 16. Table 3 shows the composition of the inorganic coated sands.

[0071] <Examples 15, 17> As a refractory aggregate, 100 parts by mass of Mikawa silica sand R6, heated to approximately 120°C, was added to a stirrer. Next, 4.00 parts by mass of No. 3 water glass was added to the stirrer and kneaded to evaporate the water, stirring for approximately 3 minutes until the sand particles broke down. Furthermore, 0.41 parts by mass of zinc oxide or magnesium oxide was added and kneaded for 2 minutes to obtain the inorganic coated sand of Examples 15 and 17.

[0072] <Comparative Example 1> Comparative Example 1, an inorganic coated sand, was obtained in the same manner as in Examples 1 to 4, except that neither zinc oxide nor magnesium oxide was added. Table 1 shows the composition of the inorganic coated sand.

[0073] <Comparative Example 2> Comparative Example 2's inorganic coated sand was obtained in the same manner as in Examples 5 to 12, except that neither zinc oxide nor magnesium oxide was added. Table 2 shows the composition of the inorganic coated sand.

[0074] <Comparative Example 3> The inorganic coated sand of Comparative Example 3 was obtained in the same manner as in Example 13, except that zinc oxide was not added. Table 2 shows the composition of the inorganic coated sand.

[0075] <Comparative Example 4> Comparative Example 4's inorganic coated sand was obtained in the same manner as in Examples 14-17, except that neither zinc oxide nor magnesium oxide was added. Table 3 shows the composition of the inorganic coated sand.

[0076] (Evaluation method) Using the inorganic coated sand obtained in each example, molds were prepared using the following method, and their deformation was evaluated. The evaluation results are shown in the respective tables.

[0077] (Mold making) <Examples 1-4, Comparative Example 1> A mold measuring 22.3 × 22.3 × 180 mm (5 cavities) was heated to 180°C. For each example of inorganic coated sand, a CSR-43 blow molding machine was used to fill the mold with the inorganic coated sand at a blow pressure of 0.3 MPa. The inorganic coated sand was then allowed to harden in the mold for 150 seconds to obtain a mold test piece.

[0078] <Examples 5-17, Comparative Examples 2-4> After adding water (2 parts by mass) to inorganic coated sand (100 parts by mass) and kneading for 2 minutes, the inorganic coated sand was filled into a molding die using the same procedure as in Examples 1-4 and Comparative Example 1 to obtain a mold test piece.

[0079] (Deformation of the mold) Figures 1(a) and 1(b) are cross-sectional views illustrating the method for measuring mold deformation. After leaving the mold test specimens obtained by the method described above in a constant temperature room at 25°C / 55%RH for 1 hour, they were cut into 5 × 22.3 × 90 mm plate-shaped test specimens 10. Metal bases 11a and 11b (13 mm × 13 mm, height 13 mm) were placed on an iron plate of appropriate size with a distance of 90 mm between their centers, and the plate-shaped test specimen 10 was placed on top of them so that both ends were centered on the respective bases (Figure 1(a)). A weight 13 (4.7 g) was then placed in the center of the plate-shaped test specimen 10. Subsequently, the iron plate on which the plate-shaped test specimen 10 was placed was heated in a muffle furnace heated under the conditions described later. After a predetermined time had elapsed, the plate-shaped test specimen 10 was removed from the muffle furnace and left to cool for 1 hour. After that, the amount of deformation of the plate-shaped test specimen 10 was measured. The deformation was defined as the maximum vertical distance from the straight line connecting both ends of the plate-shaped test specimen 10 to the curved portion (Figure 1(b)). The heating conditions for all of Examples 1-17 and Comparative Examples 1-4 were 500°C for 10 minutes. [Table 1]

[0080] [Table 2]

[0081] [Table 3]

[0082] Tables 1 to 3 show that when comparing Examples 1 to 4 with Comparative Example 1, Examples 5 to 12 with Comparative Example 2, Example 13 with Comparative Example 3, and Examples 14 to 17 with Comparative Example 4, each example showed superior mold deformation suppression compared to the comparative examples. [Explanation of Symbols]

[0083] 10 Plate-shaped test specimens 11a, 11b Pedestal 13 weights

Claims

1. It comprises a fire-resistant aggregate and an inorganic binder layer formed on the surface of the fire-resistant aggregate. The inorganic binder layer contains an inorganic binder containing sodium metasilicate and one or more selected from zinc oxide and magnesium oxide. A method for suppressing deformation of a mold during casting by preparing a mold using inorganic coated sand in which the total content of zinc oxide and magnesium oxide is 6 parts by mass or more and 70 parts by mass or less per 100 parts by mass of the inorganic binder excluding water.

2. A method for suppressing deformation of a mold according to claim 1, wherein the amount of the inorganic binder layer, excluding water, relative to 100 parts by mass of the refractory aggregate in the inorganic coated sand is 0.05 parts by mass or more and 10 parts by mass or less.

3. A method for suppressing mold deformation according to claim 1 or 2, wherein the average particle size of the zinc oxide and magnesium oxide in the inorganic binder layer is 0.1 μm or more and 100 μm or less.

4. A method for suppressing deformation of a mold according to any one of claims 1 to 3, wherein the total content of sodium metasilicate in the inorganic binder, excluding water, is 80% by mass or more.

5. An inorganic coated sand comprising a fire-resistant aggregate and an inorganic binder layer formed on the surface of the fire-resistant aggregate, The inorganic binder layer contains an inorganic binder containing sodium metasilicate and one or more selected from zinc oxide and magnesium oxide. An inorganic coated sand in which the total content of zinc oxide and magnesium oxide is 6 parts by mass or more and 70 parts by mass or less per 100 parts by mass of the inorganic binder excluding water.

6. The inorganic coated sand according to claim 5, wherein the amount of the inorganic binder layer, excluding water, relative to 100 parts by mass of the refractory aggregate in the inorganic coated sand is 0.05 parts by mass or more and 10 parts by mass or less.

7. The inorganic coated sand according to claim 5 or 6, wherein the average particle size of the zinc oxide and magnesium oxide is 0.1 μm or more and 100 μm or less.

8. The inorganic coated sand according to any one of claims 5 to 7, wherein the total content of sodium metasilicate in the inorganic binder, excluding water, is 80% by mass or more.

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