Coated Sand

Abstract

To provide a coated sand containing refractory aggregate having an inorganic binder layer and amorphous silica particles, which can be used to manufacture molds with excellent surface strength. [Solution] A coated sand containing a refractory aggregate having an inorganic binder layer formed on its surface containing an inorganic binder containing a metasilicate hydrate, wherein the inorganic binder layer contains inorganic fine particles containing amorphous silica particles and a fatty acid amide.

Description

Technical Field

[0001] The present invention relates to coated sand.

Background Art

[0002] As a mold used for casting of a casting, Patent Document 1 discloses an inorganic coated sand having a refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate, wherein the inorganic binder layer contains a metasilicate hydrate.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Patent Document 1 describes that in order to improve the strength of a mold, inorganic fine particles such as amorphous silica particles are contained in inorganic coated sand. However, it has been found that a mold manufactured using inorganic coated sand containing a refractory aggregate having an inorganic binder layer and amorphous silica particles has room for improvement in surface strength.

[0005] An object of the present invention is to provide a coated sand containing a refractory aggregate having an inorganic binder layer and amorphous silica particles, which can produce a mold having excellent surface strength.

Means for Solving the Problems

[0006] The present invention is a coated sand containing a refractory aggregate having an inorganic binder layer formed on the surface thereof, the inorganic binder layer containing an inorganic binder containing a metasilicate hydrate, wherein an inorganic fine particle containing amorphous silica particles and a fatty acid amide are contained on the inorganic binder layer. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide coated sand containing refractory aggregate having an inorganic binder layer and amorphous silica particles, which can be used to manufacture molds with excellent surface strength. [Modes for carrying out the invention]

[0008] <Coated Sand> The coated sand of this embodiment is a coated sand containing a refractory aggregate having an inorganic binder layer formed on its surface containing an inorganic binder containing a metasilicate hydrate, wherein the inorganic binder layer contains inorganic fine particles including amorphous silica particles and a fatty acid amide. In the coated sand of this embodiment, the inorganic fine particles and the fatty acid amide may be partially embedded in the inorganic binder layer. Furthermore, in the coated sand of this embodiment, it is preferable that a portion of the inorganic fine particles are present on the fatty acid amide. According to the coated sand of this embodiment, it is possible to manufacture a mold with excellent surface strength. The reason why the coated sand of this embodiment exhibits such an effect is not clear, but it is presumed to be as follows.

[0009] It is presumed that when amorphous silica particles are added to coated sand containing refractory aggregate with an inorganic binder layer formed on its surface, the amorphous silica particles will aggregate at the adhesion points between the refractory aggregates, inhibiting adhesion and reducing the surface strength of the mold. In this embodiment, the coated sand is thought to be able to produce a mold with excellent surface strength by suppressing the aggregation of amorphous silica particles at the adhesion points between the refractory aggregates and inhibiting adhesion between the refractory aggregates themselves, thanks to the fatty acid amide.

[0010] [Fire-resistant aggregate] The aforementioned fire-resistant aggregate may be one or more selected from the group consisting of natural sand and artificial sand.

[0011] Examples of the aforementioned natural sand include one or more types selected from the group consisting of silica sand, chromite sand, zircon sand, olivine sand, and alumina sand.

[0012] Examples of the aforementioned artificial sand include one or more types selected from the group consisting of synthetic mullite sand, SiO2-based sand with SiO2 as the main component, Al2O3-based sand with Al2O3 as the main component, SiO2 / Al2O3-based sand, SiO2 / MgO-based sand, SiO2 / Al2O3 / Al2O3-based ZrO2-based sand, SiO2 / Al2O3 / Fe2O3-based sand, and slag-derived sand. Here, the main component refers to the component that is most abundant by mass among the components contained in the sand. The aforementioned artificial sand refers to sand that is not naturally occurring sand, but rather sand that has been artificially prepared by preparing metal oxide components and then melting or sintering them.

[0013] The aforementioned refractory aggregate may be recovered sand collected from used molds, or recycled sand obtained by recycling recovered sand.

[0014] The refractory aggregate is preferably granular in order to improve the fluidity of the coated sand according to this embodiment and to improve its ability to fill into the molding die. Furthermore, the average particle size of the refractory aggregate is preferably 0.05 mm or more, more preferably 0.10 mm or more, and similarly preferably 2.00 mm or less, more preferably 1.00 mm or less, and even more preferably 0.50 mm or less, from the viewpoint of improving mold quality and strength, and ease of molding the mold. The average particle size of the coated sand and the refractory aggregate according to this embodiment can be measured, for example, by the following method.

[0015] [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 diameter (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 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 digital microscope (for example, Keyence VH-8000) and performing image analysis on the obtained image.

[0016] The degree of amorphousness of the refractory aggregate is preferably 10% or more, more preferably 20% or more, even more preferably 30% or more, and even more preferably 40% or more, from the viewpoint of improving the strength of the mold and obtaining low thermal expansion. There is no upper limit to the degree of amorphousness of the refractory aggregate, but for example, it is 100% or less, and preferably 99% or less. There are various methods for controlling the degree of amorphousness of the refractory aggregate, but generally it is preferable to use a manufacturing method that rapidly cools the molten material. For example, there is a method of melting the raw material and rapidly cooling it by blowing it with air, or a method of processing it in a flame and rapidly cooling it. In any case, the cooling method can be appropriately selected at various speeds depending on the material and particle size. It is also conceivable to amorphous a material that has already crystallized by heat treatment and cooling treatment. Among these, the flame melting method, in which heating and cooling can be easily controlled, is preferred. The degree of amorphousness of the refractory aggregate and the amorphous silica particles can be determined, for example, by the X-ray diffraction method shown below.

[0017] [X-ray diffraction method] The particles are ground 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-angle 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 attached to the instrument, and subtracted from 100 to obtain the degree of amorphousness. Specifically, for the area above the background, amorphous peaks (halos) 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

[0018] [Inorganic binder layer] The inorganic binder layer is formed on the surface of the refractory aggregate. Preferably, the refractory aggregate is completely covered by the inorganic binder layer, but there may be some uncovered portions. The inorganic binder layer contains an inorganic binder including a metasilicate hydrate.

[0019] As for the metasilicate hydrate, from the viewpoint of using the coated sand in a dry state and improving its fluidity at room temperature, at least one selected from sodium metasilicate pentahydrate, sodium metasilicate notahydrate, potassium metasilicate pentahydrate, and potassium metasilicate notahydrate is preferred, and at least one selected from sodium metasilicate pentahydrate and sodium metasilicate notahydrate is more preferred.

[0020] In this specification, the content of the inorganic binder refers to the content of components other than water in the inorganic binder. For example, when sodium metasilicate hydrate is used as the inorganic binder, the content is determined in terms of sodium metasilicate. In this specification, the components other than water in the inorganic binder may also be referred to as "inorganic binder excluding water". Further, in this specification, "metasilicate" means the components other than water in metasilicate hydrate.

[0021] From the viewpoints of improving the strength of the mold, improving productivity, and ease of availability, the content of metasilicate in the inorganic binder excluding water is preferably 80% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, even more preferably 98% by mass or more, and even more preferably substantially 100% by mass. In this specification, "substantially" means that it may contain trace amounts of components included unintentionally.

[0022] From the viewpoints of improving the strength of the mold and improving the surface stability of the mold, the content of the inorganic binder excluding water in the inorganic binder layer is preferably 30% by mass or more, more preferably 35% by mass or more, still more preferably 40% by mass or more, and even more preferably 45% by mass or more with respect to the total components other than water in the inorganic binder layer. From the viewpoint of favorably suppressing sand sticking to the casting, the content of the inorganic binder excluding water in the inorganic binder layer is preferably 93% by mass or less, more preferably 91% by mass or less, and still more preferably 90% by mass or less with respect to the total components other than water in the inorganic binder layer.

[0023] From the perspective of improving the strength of the mold and the surface shape of the mold, the content of the moisture removed from the inorganic binder in the coated sand according to this embodiment is preferably 0.03 parts by mass or more, more preferably 0.10 parts by mass or more, still more preferably 0.50 parts by mass or more with respect to 100.00 parts by mass of the refractory aggregate. From the perspective of improving the filling property into the molding die, the content of the moisture removed from the inorganic binder in the coated sand according to this embodiment is preferably 5.00 parts by mass or less, more preferably 4.00 parts by mass or less, still more preferably 3.00 parts by mass or less, and even more preferably 2.00 parts by mass or less with respect to 100.00 parts by mass of the refractory aggregate.

[0024] 〔Inorganic fine particles〕 The coated sand according to this embodiment contains inorganic fine particles from the perspective of improving the strength of the mold, and the inorganic fine particles contain amorphous silica particles from the same perspective. The coated sand according to this embodiment has the inorganic fine particles on the inorganic binder layer from the perspective of improving the strength of the mold. The inorganic fine particles on the inorganic binder layer may be partially embedded in the inorganic binder layer. From the perspective of manufacturing a mold with excellent surface strength, it is preferable that at least a part of the inorganic fine particles is present on the fatty acid amide.

[0025] From the perspective of more firmly binding the particles of the coated sand according to this embodiment to each other through the amorphous silica particles, the degree of amorphization of the amorphous silica particles is preferably 80% or more, more preferably 90% or more, still more preferably 93% or more, even more preferably 95% or more, and even more preferably 98% or more. The upper limit of the degree of amorphization of the amorphous silica particles is not limited, but for example, it may be 100% or less, or 99.8% or less.

[0026] From the perspective of improving the strength of the mold, the content of the amorphous silica particles in the inorganic fine particles is preferably 10% by mass or more, more preferably 30% by mass or more, still more preferably 50% by mass or more, still more preferably 70% by mass or more, still more preferably 90% by mass or more, and may be 100% by mass.

[0027] The average particle diameter d in the weight-based particle size distribution of the inorganic fine particles as measured by laser diffraction scattering particle size distribution analysis. 50 From the viewpoint of improving the strength of the mold and improving handling, the particle size is preferably 0.1 μm or larger, more preferably 0.3 μm or larger. The average particle diameter d in the weight-based particle size distribution of the inorganic fine particles measured by laser diffraction scattering particle size distribution measurement method. 50 From the viewpoint of improving the strength of the mold, the thickness 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.

[0028] The average particle diameter of the inorganic fine particles, as determined from the scanning electron microscope observation images, is preferably 0.1 μm or more, more preferably 0.3 μm or more, from the viewpoint of improving mold strength per unit mass and handling properties. The average particle diameter of the inorganic fine particles, as determined from the 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, from the viewpoint of improving mold strength per unit mass. The average particle diameter of the inorganic fine particles can be determined from the scanning electron microscope observation images using various image analysis methods. Irregular particle sorting may also be performed as a pretreatment. For example, after determining the inorganic fine particles in the coated sand based on elements, 100 arbitrary inorganic fine particles can be selected, their particle diameters measured, and the average particle diameter of the 80 inorganic fine particles remaining after excluding 20 inorganic fine particles (10 from the largest particle diameter and 10 from the smallest particle diameter) can be taken as the average particle diameter of the inorganic fine particles.

[0029] From the viewpoint of improving the strength of the mold, the content of the inorganic fine particles in the coated sand according to this embodiment is preferably 20 parts by mass or more, more preferably 40 parts by mass or more, and even more preferably 50 parts by mass or more, per 100 parts by mass of the inorganic binder with water removed. From the viewpoint of improving the surface shape of the mold and suppressing dust scattering, the content of the inorganic fine particles in the coated sand according to this embodiment 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, and even more preferably 80 parts by mass or less, per 100 parts by mass of the inorganic binder with water removed.

[0030] [Fatty acid amide] The coated sand according to this embodiment contains a fatty acid amide from the viewpoint of producing a mold with excellent surface strength. The coated sand according to this embodiment has the fatty acid amide on the inorganic binder layer from the viewpoint of improving the strength of the mold. The fatty acid amide on the inorganic binder layer may be partially embedded in the inorganic binder layer.

[0031] The fatty acid amide may contain monoamides or bisamides. Examples of monoamides include N-stearylamide, oleic acid amide, erucic acid amide, and stearylamide. Examples of bisamides include ethylenebisstearylamide, ethylenebispalmitylamide, ethylenebismyristylamide, ethylenebislaurylamide, ethylenebisoleylamide, propylenebisstearylamide, propylenebispalmitylamide, propylenebismyristylamide, propylenebislaurylamide, propylenebisoleylamide, butylenebisstearylamide, butylenebispalmitylamide, butylenebismyristylamide, butylenebislaurylamide, butylenebisoleylamide, methylenebislaurylamide, methylenebisstearylamide, and hexamethylenebisstearylamide. Of these, from the viewpoint of producing molds with excellent surface strength, ethylenebisstearylamide, ethylenebispalmitylamide, ethylenebislaurylamide, butylenebisstearylamide and butylenebispalmitylamide are preferred, ethylenebisstearylamide, ethylenebispalmitylamide and ethylenebismyristylamide are more preferred, ethylenebisstearylamide and ethylenebislaurylamide are even more preferred, and ethylenebisstearylamide is even more preferred. These fatty acid amides can be used individually or in combination of two or more.

[0032] From the viewpoint of producing a mold with excellent surface strength, the content of the fatty acid amide in the coated sand according to this embodiment is preferably 0.6 parts by mass or more, more preferably 0.8 parts by mass or more, even more preferably 1.0 part by mass or more, even more preferably 1.5 parts by mass or more, and even more preferably 2.0 parts by mass or more, per 100.0 parts by mass of the inorganic fine particles. From the viewpoint of improving the strength of the mold, the content of the fatty acid amide in the coated sand according to this embodiment is preferably 20.0 parts by mass or less, more preferably 15.0 parts by mass or less, even more preferably 10.0 parts by mass or less, and even more preferably 8.0 parts by mass or less, per 100.0 parts by mass of the inorganic fine particles.

[0033] The total content of the inorganic fine particles and the fatty acid amide in the coated sand according to this embodiment is preferably 25 parts by mass or more, more preferably 45 parts by mass or more, and even more preferably 55 parts by mass or more, per 100 parts by mass of the inorganic binder after removing water, from the viewpoint of improving the strength of the mold and producing a mold with excellent surface strength. The total content of the inorganic fine particles and the fatty acid amide in the coated sand according to this embodiment is preferably 180 parts by mass or less, more preferably 150 parts by mass or less, even more preferably 120 parts by mass or less, and even more preferably 100 parts by mass or less, per 100 parts by mass of the inorganic binder after removing water.

[0034] [Other ingredients] The binder-coated sand may contain other additives as needed, in addition to the components described above. Examples of other additives include humectants, moisture-resistant agents, coupling agents that strengthen the bond between the refractory aggregate and the inorganic binder, lubricants, surfactants, and release agents.

[0035] Examples of the aforementioned humectants include polyhydric alcohols, water-soluble polymers, hydrocarbons, sugars, proteins, and inorganic compounds such as sodium chloride, calcium chloride, and magnesium chloride.

[0036] Examples of moisture-resistant improvers include carbonates, borates, sulfates, and phosphates. Specific examples of carbonates include zinc carbonate, basic zinc carbonate, iron carbonate, manganese carbonate, copper carbonate, aluminum carbonate, barium carbonate, magnesium carbonate, calcium carbonate, lithium carbonate, potassium carbonate, and sodium carbonate. Specific examples of borates include sodium tetraborate, potassium tetraborate, lithium tetraborate, ammonium tetraborate, calcium tetraborate, strontium tetraborate, silver tetraborate, sodium metaborate, potassium metaborate, lithium metaborate, ammonium metaborate, calcium metaborate, silver metaborate, copper metaborate, lead metaborate, and magnesium metaborate. Specific examples of sulfates include sodium sulfate, potassium sulfate, lithium sulfate, magnesium sulfate, calcium sulfate, strontium sulfate, barium sulfate, titanium sulfate, aluminum sulfate, zinc sulfate, and copper sulfate. Specific examples of phosphates include sodium phosphate, sodium hydrogen phosphate, potassium phosphate, potassium hydrogen phosphate, lithium phosphate, lithium hydrogen phosphate, magnesium phosphate, calcium phosphate, titanium phosphate, aluminum phosphate, and zinc phosphate.

[0037] Examples of the coupling agents include silane coupling agents, zircon coupling agents, and titanium coupling agents.

[0038] Examples of the lubricants include waxes; 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.

[0039] Examples of the aforementioned surfactants include cationic surfactants, anionic surfactants, amphoteric surfactants, nonionic surfactants, and silicone-based surfactants.

[0040] Examples of the aforementioned release agents include paraffin, wax, fatty acid ester, organic acid, graphite fine particles, mica, vermiculite, fluorine-based release agents, silicone-based release agents, and the like.

[0041] The sphericity of the coated sand according to this embodiment is preferably 0.75 or higher, more preferably 0.80 or higher, and even more preferably 0.82 or higher, from the viewpoint of improving the quality of the mold, improving the strength of the mold, and improving the moldability of the mold. The sphericity of the coated sand according to this embodiment is 1 or less.

[0042] The sphericity of the coated sand according to this embodiment can be determined by performing image analysis on images (photographs) of the particles obtained with an optical microscope or digital scope (for example, a VH-8000 model from Keyence Corporation) to determine the area of ​​the particle projection cross-section and the perimeter of said cross-section, and then calculating [circumference of a perfect circle with the same area as the area of ​​the particle projection cross-section (mm2) (mm)] / [perimeter of the particle projection cross-section (mm)], and averaging the obtained values ​​for any 50 particles.

[0043] The average particle size of the coated sand according to this embodiment is preferably 0.05 mm or more, more preferably 0.10 mm or more, from the viewpoint of improving the quality of the mold, improving the strength of the mold, and improving the moldability of the mold. The average particle size of the coated sand according to this embodiment is preferably 2.00 mm or less, more preferably 1.00 mm or less, and even more preferably 0.50 mm or less, from the viewpoint of improving the quality of the mold, improving the strength of the mold, and improving the moldability of the mold.

[0044] <Method for manufacturing coated sand> The manufacturing method of this embodiment is a method for manufacturing coated sand, comprising the steps of (1) forming the inorganic binder layer on the surface of the refractory aggregate, (2) A step of mixing the refractory aggregate having the inorganic binder layer formed on its surface with the fatty acid amide, and The process includes a step (3) of mixing the refractory aggregate having the inorganic binder layer formed on its surface with the amorphous silica particles.

[0045] In step (1) described above, the method for forming the inorganic binder layer on the surface of the refractory aggregate is not particularly limited, and known methods can be applied depending on the type of inorganic binder. For example, the refractory aggregate and a heated and melted metasilicate hydrate can be mixed by a known method to obtain a mixture, and then the mixture can be cooled to a temperature below the melting point of the metasilicate hydrate to form an inorganic binder layer containing metasilicate hydrate on the surface of the refractory aggregate.

[0046] In step (2) above, the method of mixing the refractory aggregate on which the inorganic binder layer is formed on its surface with the fatty acid amide is not particularly limited and can be done by known methods.

[0047] In step (3) above, the method for mixing the refractory aggregate on which the inorganic binder layer is formed on its surface with the amorphous silica particles is not particularly limited and can be done by known methods.

[0048] Step (2) and step (3) may be performed either first or simultaneously, but from the viewpoint of allowing a portion of the inorganic fine particles to be present on the fatty acid amide and producing a mold with excellent surface strength, it is preferable to perform step (3) after step (2).

[0049] <Method for manufacturing molds> The mold manufacturing method according to this embodiment is a mold manufacturing method using the coated sand. The mold manufacturing method according to this embodiment can be manufactured by applying known methods other than using the coated sand. The mold manufacturing method using coated sand is not particularly limited, but examples include a molding method using a heated molding die, a molding method in which steam is further passed through a heated molding die and then hot air is passed through it, and so on. [Examples]

[0050] The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited thereto.

[0051] <Material> The materials used in the following examples and comparative examples will be described below. [Fire-resistant aggregate] • Fire-resistant aggregate 1: Espal #60L (manufactured by Yamakawa Sangyo Co., Ltd., average particle size: 241 μm, amorphity 45%, sphericity 0.97) [Inorganic binders] • Metasilicate hydrate 1: Sodium metasilicate 9-hydrate (Na2SiO3·9H2O), manufactured by Nippon Chemical Industrial Co., Ltd., melting point 47℃ [Inorganic fine particles] • Amorphous silica particles 1: Denka Co., Ltd. Denka Fused Silica SFP-20M (average particle size: 0.4 μm, amorphization degree 99.5% or higher, silica content: 99% by mass or higher) [Fatty acid amide] • Fatty acid amide 1: Kao Corporation Kao Wax EB-FF (ethylene bisstearyl amide, powder)

[0052] <Making Coated Sand> [Examples 1-3] 100.00 parts by mass of the refractory aggregate 1 and 2.00 parts by mass of metasilicate hydrate 1 (equivalent to 0.86 parts by mass of metasilicate) heated to 80°C and melted were added to a stirrer and kneaded for 4 minutes to obtain coated sand with fluidity at room temperature. Next, the amount of fatty acid amide 1 shown in Table 1 was added and kneaded for a further 1 minute. Then, amorphous silica particles 1 (0.60 parts by mass) were added and kneaded for a further 1 minute to obtain coated sand according to each example.

[0053] [Comparative Example 1] A coated sand according to Comparative Example 1 was obtained in the same manner as in Examples 1 to 3, except that the fatty acid amide 1 was not added.

[0054] <Rating> [Measurement of tape peeling amount on mold surface] Using the coated sand according to each example and comparative example, molds were prepared according to the following procedure, and the surface strength of the molds was evaluated by measuring the amount of tape peeling from the mold surface according to the following procedure.

[0055] [Mold making] A mold for 22.3 mm x 22.3 mm x 180 mm test specimens (5 cavities) was heated to 180°C. The coated sand for each example and comparative example was filled into the mold heated to 180°C using a CSR-43 blow molding machine at a blow pressure of 0.3 MPa, and then left to harden in the mold for 150 seconds to produce molds for evaluation.

[0056] [Measurement of tape peeling amount on the mold surface (evaluation of mold surface strength)] The obtained evaluation molds were left in an environment of 25°C / 55%RH for 24 hours. Then, in the same environment, a piece of double-sided tape (Nichiban Nicetack NW-15 (adhesion strength 02)) with its release paper still attached, cut to 8 cm and with its mass measured, was placed on the top surface of a 22.3 mm × 180 mm mold test piece, and a 1 kg metal plate was placed on top. After 1 minute, the metal plate was removed, and the double-sided tape with the release paper still attached was peeled off and its mass was measured. The amount of tape peeled off the mold surface (mg) was calculated by subtracting the mass of the double-sided tape before it was attached to the mold test piece. A smaller amount of tape peeled off the mold surface indicates higher surface strength of the mold. The results are shown in Table 1.

[0057] [Table 1]

Claims

1. A coated sand containing a refractory aggregate having an inorganic binder layer formed on its surface containing an inorganic binder containing a metasilicate hydrate, A coated sand comprising inorganic fine particles containing amorphous silica particles and a fatty acid amide on the inorganic binder layer.

2. The coated sand according to claim 1, wherein the amount of inorganic binder water, which is a component of the inorganic binder other than water in the inorganic binder, in the coated sand is 0.03 parts by mass or more and 5.00 parts by mass or less per 100.00 parts by mass of the refractory aggregate.

3. The coated sand according to claim 2, wherein the amount of inorganic fine particles in the coated sand is 20 parts by mass or more and 150 parts by mass or less, based on 100 parts by mass of the inorganic binder, which is the inorganic binder's water-free component other than water in the inorganic binder.

4. The coated sand according to claim 2, wherein the total content of the inorganic fine particles and the fatty acid amide in the coated sand is 25 parts by mass or more and 180 parts by mass or less per 100 parts by mass of the inorganic binder water removed.

5. The coated sand according to claim 1, wherein the content of the fatty acid amide is 0.6 parts by mass or more and 20.0 parts by mass or less per 100.0 parts by mass of the inorganic fine particles.

6. A method for producing coated sand according to any one of claims 1 to 5, (1) A step of forming the inorganic binder layer on the surface of the fire-resistant aggregate, Step (2) of mixing the refractory aggregate having the inorganic binder layer formed on its surface with the fatty acid amide, and A method for producing coated sand, comprising the step (3) of mixing a refractory aggregate having an inorganic binder layer formed on its surface with amorphous silica particles.

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