Foundry sand

Abstract

To provide foundry sand that is less prone to blocking even in environments with relatively high humidity. [Solution] Foundry sand having a first coating layer containing aluminosilicate on a refractory aggregate, wherein the surface roughness Sa1 of the particles constituting the foundry sand is 20 nm or more and 250 nm or less.

Description

Technical Field

[0001] The present invention relates to foundry sand.

Background Art

[0002] As a mold used for casting of castings, a coated sand having a refractory aggregate and an inorganic binder layer containing a metasilicate hydrate formed on the surface of the refractory aggregate is filled into a mold, and the coated sand filled into the mold is cured. What is obtained by making it is known.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] A mold manufactured using coated sand is usually broken (crushed) and recovered after being used for casting, and is subjected to a regeneration process by various methods and reused as recycled sand. From the viewpoints of economy and waste reduction, it is common in foundry factories to manufacture molds using recycled sand as a refractory aggregate.

[0005] However, it has been revealed that recycled sand (foundry sand) obtained by recovering and subjecting to a regeneration process after using coated sand as described in Patent Document 1 is likely to aggregate and block in an environment with a relatively high humidity. When the recycled sand (foundry sand) blocks, it becomes difficult to uniformly form an inorganic binder layer on the surface, which is not preferable from the viewpoint of the strength of the mold.

[0006] Furthermore, it has become clear that when coated sand, such as that described in Patent Document 1, is used, then recovered and subjected to a recycling process to obtain recycled sand (foundry sand), and a layer of inorganic binder containing metasilicate hydrate is formed on the recycled sand, a mold with the desired strength can be obtained if it is used immediately after production. However, as time passes after the production of the coated sand, the strength of the resulting mold tends to decrease.

[0007] The present invention aims to provide foundry sand that is less prone to blocking even in environments with relatively high humidity.

[0008] The present invention aims to provide coated sand that can suppress the decrease in the strength of a mold even when used in the manufacture of a mold a long time after its production. [Means for solving the problem]

[0009] The present invention relates to foundry sand having a first coating layer containing aluminosilicate on a refractory aggregate, wherein the surface roughness Sa1 of the particles constituting the foundry sand is 20 nm or more and 250 nm or less.

[0010] The present invention relates to a coated sand containing the foundry sand, wherein the first coating layer has a second coating layer containing metasilicate hydrate. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide foundry sand that is less prone to blocking even in environments with relatively high humidity.

[0012] According to the present invention, it is possible to provide coated sand that can suppress the decrease in the strength of a mold even when used in the manufacture of a mold a long time after its manufacture. [Modes for carrying out the invention]

[0013] <Foundry sand> The foundry sand of this embodiment is a foundry sand having a first coating layer containing aluminosilicate on a refractory aggregate, and the surface roughness Sa1 of the particles constituting the foundry sand is 20 nm to 250 nm. The foundry sand of this embodiment is less prone to blocking even in environments with relatively high humidity. The reason why the foundry sand of this embodiment exhibits such an effect is not entirely clear, but it is thought to be as follows.

[0014] The blocking of recycled sand in relatively high humidity environments is thought to be due to the absorption of moisture by residues derived from metasilicate hydrate, which is used as an inorganic binder. Metasilicate hydrate becomes silicate during the casting process and remains on the surface of recycled sand (refractory aggregate). Because silicate has silanol groups, it readily adsorbs water molecules, adsorbing moisture from the environment, and blocking occurs due to the formation of liquid crosslinks between refractory aggregates. Therefore, blocking is further promoted when humidity is high. Since the cause of blocking is the formation of liquid crosslinks between refractory aggregates, it is expected that reducing the surface roughness Sa1 of the refractory aggregate, i.e., making the surface of the refractory aggregate smooth, will reduce the number of adhesion points and suppress the formation of liquid crosslinks. However, it has been found that reducing the surface roughness Sa1 of the refractory aggregate alone is ineffective because silicate inherently readily adsorbs water molecules. Therefore, by co-condensing the silanol groups of silicates with aluminates and forming a first coating layer containing aluminosilicate on the refractory aggregate, it is believed that the silanol groups were protected from moisture, thereby suppressing the blocking of recycled sand in relatively humid environments. Furthermore, it was found that blocking could be further suppressed by combining this with a method for reducing the surface roughness Sa1 of the aggregate, which had not been effective in the past.

[0015] The foundry sand in this embodiment is a group of particles. The sphericity of the foundry sand 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 fluidity and further enhancing the ability to fill into the molding die. Specifically, the upper limit of the sphericity is 1.

[0016] The sphericity of the foundry sand is consistent with that of the refractory aggregate described later. The method for measuring the sphericity of the foundry sand involves analyzing images (photographs) of the particles obtained using an optical microscope or digital scope (for example, Keyence VH-8000 model) to determine the area of ​​the particle projection cross-section and the perimeter of the cross-section, and then calculating the sphericity = [Area of ​​particle projection cross-section (mm²)]. 2 The value can be calculated by dividing the circumference of a perfect circle with the same area as the particle by the circumference of the particle projection cross-section (mm), and then averaging the obtained values ​​for any 50 particles.

[0017] The average particle size of the foundry sand is preferably 0.05 mm or more, and more preferably 0.10 mm or more, from the viewpoint of improving mold quality and mold strength, ease of mold making, and storage stability. The average particle size of the foundry sand 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 mold quality and mold strength, and ease of mold making.

[0018] The average particle size of the foundry sand can be measured by the following method for measuring average particle size. (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. 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 scope (for example, Keyence VH-8000) and performing image analysis on the obtained image.

[0019] [Fire-resistant aggregate] The refractory aggregate includes one or more selected from the group consisting of natural sand and artificial sand.

[0020] Examples of the natural sand include one or more selected from the group consisting of silica sand, chromite sand, zircon sand, olivine sand, and alumina sand.

[0021] Examples of the artificial sand include one or more 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 / ZrO2-based sand, SiO2 / Al2O3 / Fe2O3-based sand, and slag-derived sand. Here, the main component refers to the component with the largest content on a mass basis among the components contained in the sand. The artificial sand refers to sand that is not naturally produced, but is sand prepared by artificially adjusting the components of metal oxides and melting or sintering them.

[0022] Note that the content of each component such as SiO2, Al2O3, Fe2O3, etc. in the refractory aggregate can be measured using the following X-ray fluorescence method. [Method for Measuring the Components of the Refractory Aggregate by X-ray Fluorescence Method] The refractory aggregate is adjusted to a size of about 0.1 μm or less with a vibration mill and heated at 1050 °C for 1 hour. Then, 5 g of lithium tetraborate and 0.5 g of the refractory aggregate are mixed and heated at 1200 °C for 10 minutes to be melted, and then cooled to prepare a sample in a glassy state (glass bead method). The components of the refractory aggregate can be measured by performing X-ray fluorescence analysis on the sample using a fundamental parameter (FP) method with a ZSX Primus II X-ray fluorescence analyzer (manufactured by Rigaku Corporation).

[0023] The refractory aggregate is generally recycled sand. The recycled sand is obtained by recycling a used casting mold or core formed from a refractory aggregate and an inorganic binder containing metasilicate. The recycled sand contains the refractory aggregate and has a residue of the inorganic binder after use on the refractory aggregate. The residue of the inorganic binder after use contains silicate. Examples of the cation constituting the silicate include monovalent cations such as sodium, potassium, lithium, and ammonium, and divalent cations such as magnesium, calcium, and zinc.

[0024] The recycled sand can be produced, for example, by the following method. [Method for producing recycled sand] As a method for recycling the mold waste sand after casting using coated sand, it can conform to a known method (for example, "Casting Molding Method", 4th edition, Japan Foundry Technology Association, November 18, 1996, pages 327 - 330). For example, methods such as dry grinding treatment (mechanical abrasion), wet grinding treatment, roasting treatment, and methods combining these treatments are known.

[0025] In the dry grinding treatment, for example, a rotary reclaimer that grinds ore by the collision and friction between the projected sand generated by the centrifugal force and the input sand that falls when the sand is input onto a rotor rotating at high speed, a hybrid sand master which is a composite type of recycling machine integrating a rotary reclaimer and a fluid classifier, a sand fresher using the grinding and polishing force of a grindstone, etc. can be used.

[0026] Examples of the wet grinding treatment include a method using a trough attrition mill that grinds ore by the friction between sand grains in a trough where feathers are rotated.

[0027] Examples of the roasting treatment include a method of using a roasting furnace such as a fluid roasting furnace or a rotary kiln, inputting sand into the roasting furnace at any time, and firing in the range of 200 - 1000°C.

[0028] Any method can be used for regeneration, but since wet processing and roasting processes are complicated and energy-intensive, dry polishing is preferred.

[0029] The sphericity of the refractory aggregate 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 fluidity, mold quality, and mold strength, as well as ease of mold formation. Specifically, the upper limit of sphericity is 1.00. The method for measuring the sphericity of the refractory aggregate is the same as the method for measuring the sphericity of the foundry sand.

[0030] The average particle diameter of the refractory aggregate is preferably 0.05 mm or more, more preferably 0.10 mm or more, from the viewpoint of improving mold quality and strength, and ease of mold formation. The average particle diameter of the refractory aggregate 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 mold quality and strength, and ease of mold formation. The method for measuring the average particle diameter of the refractory aggregate is the same as the method for measuring the average particle diameter of the foundry sand.

[0031] [First coating layer] The foundry sand of this embodiment has a first coating layer containing aluminosilicate on the refractory aggregate. The first coating layer covers the refractory aggregate. Note that the coating is not limited to being continuous, and may have discontinuous portions. Furthermore, if the foundry sand of this embodiment contains the refractory aggregate as recycled sand, the foundry sand of this embodiment has the first coating layer on the residue of the used inorganic binder that the recycled sand has. If the foundry sand of this embodiment contains the refractory aggregate as recycled sand, the foundry sand of this embodiment has silicate between the refractory aggregate and the first coating layer.

[0032] Aluminosilicates preferably contain at least one of a silicate and a reaction product of aluminate or aluminum hydroxide, as this facilitates improved storage stability. Examples of cations constituting aluminates include monovalent cations such as sodium, potassium, and lithium, and divalent cations such as magnesium, calcium, and zinc.

[0033] Methods for confirming the presence of aluminosilicate in the first coating layer include, for example, a method of grinding foundry sand in a mill or other pulverizer to remove the components of the first coating layer, analyzing the components of the first coating layer by infrared spectroscopy to confirm absorption originating from aluminosilicate, or analyzing the components by solid-state nuclear magnetic resonance spectroscopy (ssNMR) to confirm signals originating from aluminosilicate.

[0034] The aluminosilicate content in the first coating layer can be determined in terms of Al2O3. From the viewpoint of storage stability, the aluminosilicate content in the first coating layer is preferably 0.005 parts by mass or more, more preferably 0.010 parts by mass or more, per 100 parts by mass of the refractory aggregate, and from the viewpoint of obtaining a high-strength mold, it is preferably 1.000 parts by mass or less, more preferably 0.500 parts by mass or less, and even more preferably 0.300 parts by mass or less, per 100 parts by mass of the refractory aggregate.

[0035] The Al2O3 content of aluminosilicate in the first coating layer can be determined by the following method. The following formula is used, based on the analytical values ​​of the aggregate obtained by the aforementioned X-ray fluorescence method and the analytical values ​​of the foundry sand containing the first coating layer using those values. Aluminosilicate content of the first coating layer (in terms of Al2O3) [parts by mass] ={Al2O3 [parts by mass] of foundry sand}-{Al2O3 [parts by mass] of refractory aggregate}

[0036] The content of the first coating layer is preferably 0.005 parts by mass or more, more preferably 0.010 parts by mass or more, and even more preferably 0.020 parts by mass or more, per 100 parts by mass of the refractory aggregate, from the viewpoint of improving storage stability and obtaining a high-strength casting mold, and preferably 1.000 parts by mass or less, and more preferably 0.500 parts by mass or less, per 100 parts by mass of the refractory aggregate, from the viewpoint of achieving both storage stability and strength.

[0037] The first coating layer is preferably solid at room temperature, from the viewpoint of improving fluidity and further enhancing its ability to fill into the molding die. Here, room temperature refers to 25°C.

[0038] The surface roughness Sa1 of the particles constituting the foundry sand (hereinafter sometimes referred to as foundry sand particles) is 20 nm or more, preferably 30 nm or more, more preferably 40 nm or more, even more preferably 50 nm or more, and even more preferably 53 nm or more, from the viewpoint of obtaining a high-strength mold, and 250 nm or less, preferably 150 nm or less, more preferably 120 nm or less, even more preferably 90 nm or less, and even more preferably 70 nm or less, from the viewpoint of improving storage stability. In this specification, the surface roughness Sa1 of the foundry sand particles is measured by the method described in the examples.

[0039] The ratio of the surface roughness Sa1 to the surface roughness Sa2 of the foundry sand particles (surface roughness Sa1 / surface roughness Sa2) is preferably 0.5 or more, more preferably 1.0 or more, from the viewpoint of obtaining a high-strength mold, and preferably 5.0 or less, more preferably 3.0 or less, even more preferably 2.0 or less, and even more preferably 1.5 or less, from the viewpoint of improving storage stability. In this specification, the surface roughness Sa2 of the foundry sand particles and the ratio of the surface roughness Sa1 to the surface roughness Sa2 of the foundry sand particles (surface roughness Sa1 / surface roughness Sa2) are determined by the method described in the examples. Note that the surface roughness Sa2 of the foundry sand particles refers to the surface roughness of particles equivalent to new sand from which the residual binder layer of the foundry sand particles (recycled sand) has been removed.

[0040] <Method for manufacturing foundry sand> The method for producing foundry sand according to this embodiment is a method for producing foundry sand, comprising the steps of (1) mixing a refractory aggregate having silicate on its surface (hereinafter sometimes also referred to as refractory aggregate (A)) with an aluminate, and (2) stirring the refractory aggregate obtained in step (1). The first coating layer containing aluminosilicate is formed by the reaction of silicate and aluminate. The refractory aggregate (A) is generally recycled sand. The mixing in step (1) and the stirring in step (2) may be performed intermittently with time intervals in between, or continuously.

[0041] The method for mixing the refractory aggregate (A) and the aluminate in step (1) and the method for stirring the refractory aggregate in step (2) are not particularly limited, and examples include a method of mixing / stirring by rotating the stirring part using a known mixing device having a stirring part. Examples of the mixing device include a kneader, ribbon mixer, Nauter mixer, Proscher mixer, Lödige mixer, high-speed mixer, etc. From the viewpoint of forming a uniform first coating layer, a Lödige mixer and a kneader are preferred, and a Lödige mixer is more preferred. Furthermore, a device that can heat and stir while rolling and sliding the material to be processed by rotating the container or rotating the internal paddle can also be used, and examples include a heatable rotary container type mixing device (rotary drum, rotary kiln, rotary dryer), a paddle dryer, a paddle mixer, and an intensive mixer. All of these are devices that can form a first coating layer by stirring (kneading) under heating.

[0042] In step (1) above, if a Redigeg mixer is used, a chopper may also be used in addition to the main wing from the viewpoint of forming a uniform first coating layer.

[0043] In step (1) above, when the mixing of the refractory aggregate (A) and the aluminate is carried out using a Redigge mixer, the rotation speed of the main blade of the Redigge mixer is preferably 40 rpm or more, more preferably 60 rpm or more, even more preferably 80 rpm or more, and even more preferably 100 rpm or more, from the viewpoint of forming a uniform first coating layer, and preferably 500 rpm or less, more preferably 400 rpm or less, and even more preferably 300 rpm or less, from the viewpoint of reducing the surface roughness of the foundry sand.

[0044] In step (1) above, when the mixing of the refractory aggregate (A) and the aluminate is carried out using a Redigge mixer, the tip peripheral speed of the stirring section of the main blade of the Redigge mixer is preferably 0.62 m / sec or more, more preferably 1.54 m / sec or more, from the viewpoint of forming a uniform first coating layer, and preferably 7.70 m / sec or less, more preferably 4.62 m / sec or less, from the viewpoint of reducing the surface roughness of the foundry sand.

[0045] In step (1) above, when the refractory aggregate (A) and aluminate are mixed in a kneader, the rotation speed of the main blade of the kneader is preferably 20 rpm or more, more preferably 30 rpm or more, and even more preferably 40 rpm or more, from the viewpoint of forming a uniform first coating layer, and preferably 80 rpm or less, more preferably 70 rpm or less, and even more preferably 60 rpm or less, from the viewpoint of reducing the surface roughness of the foundry sand.

[0046] In step (1) above, the temperature at which the refractory aggregate (A) and the aluminate are mixed is preferably 15°C or higher, more preferably 30°C or higher, and even more preferably 50°C or higher, from the viewpoint of forming a uniform first coating layer, and from the viewpoint of reducing energy consumption, it is preferably 200°C or lower, more preferably 150°C or lower, even more preferably 120°C or lower, even more preferably 100°C or lower, even more preferably 80°C or lower, even more preferably 60°C or lower, and even more preferably less than 60°C.

[0047] In step (1) above, the mixing of the refractory aggregate (A) and the aluminate may be done by heating the refractory aggregate (A) to 15°C or 200°C or below, and then adding the aluminate or aluminum hydroxide and mixing, or by adding the aluminate or aluminum hydroxide to the refractory aggregate (A) and then heating to 15°C or 200°C or below and mixing.

[0048] In step (1) above, the mixing time of the refractory aggregate (A) and the aluminate is 10 seconds or more, preferably 20 seconds or more, more preferably 40 seconds or more, and even more preferably 60 seconds or more, from the viewpoint of forming a uniform first coating layer, and from the viewpoint of reducing energy consumption, it is preferably 600 seconds or less, more preferably 300 seconds or less, and even more preferably 150 seconds or less.

[0049] In step (2) above, when stirring is performed with a Redigge mixer, the rotation speed of the main blades of the Redigge mixer is preferably 40 rpm or more, more preferably 60 rpm or more, even more preferably 80 rpm or more, and even more preferably 100 rpm or more, from the viewpoint of improving storage stability, and preferably 500 rpm or less, more preferably 400 rpm or less, and even more preferably 300 rpm or less, from the viewpoint of reducing the surface roughness of the foundry sand.

[0050] In step (2) above, when stirring is performed with a Redigge mixer, the peripheral speed of the tip of the stirring section of the main blade of the Redigge mixer is preferably 0.62 m / sec or more, more preferably 1.54 m / sec or more, from the viewpoint of improving storage stability, and preferably 7.70 m / sec or less, more preferably 4.62 m / sec or less, from the viewpoint of reducing the surface roughness of the foundry sand.

[0051] In step (2) above, when stirring is performed with a kneader, the rotation speed of the main blade of the kneader is preferably 20 rpm or more, more preferably 30 rpm or more, and even more preferably 40 rpm or more, from the viewpoint of storage stability, and preferably 80 rpm or less, more preferably 70 rpm or less, and even more preferably 65 rpm or less, from the viewpoint of reducing the surface roughness of the foundry sand.

[0052] In step (2) above, the temperature during stirring is preferably 15°C or higher, more preferably 30°C or higher, even more preferably 50°C or higher, even more preferably 60°C or higher, and even more preferably 80°C or higher, from the viewpoint of improving storage stability, and preferably 200°C or lower, more preferably 150°C or lower, and even more preferably 120°C or lower, from the viewpoint of reducing energy consumption.

[0053] In step (2) above, the stirring time is preferably 5 minutes or more, more preferably 15 minutes or more, more preferably 35 minutes or more, and even more preferably 50 minutes or more, from the viewpoint of improving storage stability, and preferably 120 minutes or less, more preferably 80 minutes or less, and even more preferably 60 minutes or less, from the viewpoint of reducing energy consumption.

[0054] <Coated Sand> The coated sand of this embodiment is a coated sand having a second coating layer containing metasilicate hydrate on a first coating layer of foundry sand. The coated sand of this embodiment can suppress the decrease in the strength of the mold even when used in the manufacture of a mold a long time after its manufacture.

[0055] The coated sand of this embodiment is a group of particles. The coated sand of this embodiment is preferably in a dry state that is fluid at room temperature. Dry coated sand means coated sand from which a measurement can be obtained when measuring the dynamic angle of repose regardless of the moisture content. The dynamic angle of repose is preferably 80° or less, more preferably 45° or less, and even more preferably 30° or less. Here, room temperature refers to 25°C.

[0056] The dynamic angle of repose of coated sand can be measured by the following method. (Method for measuring dynamic angle of repose) Half the volume of coated sand is placed in a cylindrical transparent plastic bottle (diameter: 7.7 cm, height: 16 cm). Using a bottle agitator, the bottle is held so that its axis is horizontal and rotated at a speed of 60 rpm around the horizontal axis. The slope of the flowing coated sand layer inside the plastic bottle becomes flat. The angle formed between this slope and the horizontal plane is measured. If the coated sand does not flow inside the cylindrical transparent plastic bottle, or if it flows but the slope of the coated sand layer does not form a flat surface, and as a result the dynamic angle of repose cannot be measured, the bottle is in a wet state.

[0057] In this embodiment, the coated sand is preferably spherical in shape, from the viewpoint of improving fluidity and further enhancing its ability to fill into molding dies. Here, "spherical" in the context of coated sand refers to a round shape, like a ball.

[0058] The sphericity of the coated sand 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 fluidity, mold quality, and mold strength, as well as the ease of mold formation. Specifically, the upper limit of the sphericity is 1.00. The sphericity of the coated sand is the same as that of the refractory aggregate. The method for measuring the sphericity of the coated sand is the same as the method for measuring the sphericity of the foundry sand.

[0059] The average particle size of the coated sand is preferably 0.05 mm or more, and more preferably 0.10 mm or more, from the viewpoint of improving mold quality and strength, ease of mold making, and storage stability. Furthermore, if the average particle size of the coated sand is above the lower limit, it is preferable that the amount of coating layer etc. used during mold manufacturing can be reduced, making it easier to regenerate the inorganic coated sand. The average particle size of the coated sand 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 mold quality and strength, and ease of mold making. Furthermore, if the average particle size of the coated sand is below the upper limit, it is preferable that the porosity is reduced during mold manufacturing, thereby increasing mold strength. The method for measuring the average particle size of the coated sand can be the same as the method for measuring the average particle size of the foundry sand.

[0060] [Second coating layer] The second coating layer is a layer formed on the first coating layer, and from the viewpoint of improving mold strength, it is preferably formed to cover the surface of the first coating layer. The second coating layer is a layer obtained by the crystallization of metasilicate hydrate and is intended to function as coated sand. The second coating layer is not limited to being continuous, and may have discontinuous regions in part. The second coating layer may be formed directly on the first coating layer, or there may be other layers between the first and second coating layers.

[0061] From the viewpoint of obtaining a high-strength casting mold, the content of the second coating layer is, for example, 0.1 parts by mass or more, preferably 0.2 parts by mass or more, more preferably 0.5 parts by mass or more, even more preferably 1.0 part by mass or more, and even more preferably 1.5 parts by mass or more, per 100.0 parts by mass of refractory aggregate. From the viewpoint of obtaining a high-strength casting mold, the content of the second coating layer is, for example, 15.0 parts by mass or less, preferably 10.0 parts by mass or less, more preferably 8.0 parts by mass or less, even more preferably 6.0 parts by mass or less, even more preferably 4.0 parts by mass or less, and even more preferably 3.0 parts by mass or less, per 100.0 parts by mass of refractory aggregate.

[0062] The second coating layer may have at least a layer containing metasilicate hydrate, and may be a single layer or a multilayer. Furthermore, the layer containing at least metasilicate hydrate is formed by an inorganic binder composition containing metasilicate hydrate. The use of metasilicate hydrate is preferable because it can improve the crystallinity of the second coating layer and the coated sand exhibits excellent room-temperature fluidity. In addition, by using metasilicate hydrate, the second coating layer can be formed on the surface of the refractory aggregate without dissolving it in water.

[0063] Examples of cations constituting metasilicate hydrate salts include monovalent cations such as sodium, potassium, lithium, and ammonium, as well as divalent cations such as magnesium, calcium, and zinc.

[0064] The content of metasilicate in the second coating layer 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. In this specification, "substantially" means that it may include components that are included unintentionally. In this specification, the content of metasilicate in the second coating layer refers to the content of metasilicate relative to the total components other than water in the second coating layer.

[0065] From the viewpoint of obtaining a high-strength casting mold, the content of metasilicate in the second coating layer is, for example, 0.03 parts by mass or more, preferably 0.10 parts by mass or more, and more preferably 0.50 parts by mass or more, per 100.00 parts by mass of refractory aggregate. From the viewpoint of obtaining a high-strength casting mold, the content of metasilicate in the second coating layer is, for example, 5.00 parts by mass or less, preferably 4.00 parts by mass or less, more preferably 3.00 parts by mass or less, even more preferably 2.00 parts by mass or less, and even more preferably 1.00 part by mass or less, per 100.00 parts by mass of refractory aggregate.

[0066] Methods for confirming that the second coating layer contains metasilicate include, for example, a method of grinding the coated sand in a mill or other grinder to remove only the second coating layer component, analyzing the second coating layer component by XRD, and confirming the peak indicating the crystalline structure of metasilicate hydrate; a method of immersing the coated sand in water and stirring for a certain period of time to dissolve the second coating layer component, drying the dissolved component, analyzing the dried solid content by XRD, confirming the peak indicating the crystalline structure of metasilicate, and analyzing the amount of hydration water by the following method to confirm that it is metasilicate hydrate.

[0067] [Measurement of hydration water volume] (1) A crucible that has been preheated and weighed is filled with 10 g of coated sand before the addition of additives such as amorphous SiO2 fine particles, and after heating at 900°C for 1 hour, the amount of mass loss (%) is used to calculate the moisture content (%) in the coated sand (A). A = [(M1 - M2) / M3] × 100 (M1: Total mass of crucible and coated sand before firing (g), M2: Total mass of crucible and coated sand after firing (g), M3: Mass of coated sand before firing (g)) (2) Weigh 100 g of coated sand before adding additives such as amorphous SiO2 fine particles, immerse it in 200 mL or more of water or hot water and stir for at least 1 hour to extract metasilicate hydrate. Filter the refractory aggregate from the obtained extract, and then remove water by vacuum distillation using a rotary evaporator at 40°C and an internal pressure of 15 mmHg or less. After that, heat dry at a temperature of 120°C to 180°C for 1 to 3 hours and weigh the dry product. Calculate the dry solid content (%) of metasilicate hydrate in the coated sand (B). B = (M12 / M11) × 100 (M11: Mass of coated sand (g), M12: Dry weight (g)) (3) Amount of water to hydrate metasilicate hydrate = [(A) / molecular weight of water] / [(B) / molecular weight of anhydrous metasilicate]

[0068] (others) The second coating layer may further contain components other than metasilicate, such as amorphous SiO2-containing fine particles, inorganic fine particles other than amorphous SiO2-containing fine particles, humectants, moisture-resistant agents, coupling agents that strengthen the bond between the refractory aggregate and the inorganic binder composition, lubricants, surfactants, mold release agents, etc.

[0069] Amorphous SiO2-containing fine particles may be used due to their high reactivity with metasilicate hydrates. This makes it easier to improve the mechanical strength of the mold.

[0070] Examples of amorphous SiO2-containing fine particles include precipitated silica, calcined silica produced in an electric arc or by flame hydrolysis, silica produced during the manufacture of Fe-Si, silica produced by the thermal decomposition of ZrSiO4, silicon dioxide produced by the oxidation of metallic silicon with an oxygen-containing gas, and spherical particles of quartz glass powder produced from crystalline quartz by melting and subsequent rapid cooling. These can be used individually, or two or more can be mixed and used together.

[0071] Inorganic fine particles are not particularly limited as long as they are not amorphous SiO2-containing fine particles as described above, but examples include crystalline silica, silicon; carbonates such as zinc carbonate, basic zinc carbonate, iron carbonate, manganese carbonate, copper carbonate, aluminum carbonate, barium carbonate, magnesium carbonate, calcium carbonate, lithium carbonate, potassium carbonate, and sodium carbonate; borates such as sodium tetraborate, potassium tetraborate, lithium tetraborate, ammonium tetraborate, calcium tetraborate, strontium tetraborate, silver tetraborate, sodium metaborate, potassium metaborate, lithium metaborate, ammonium metaborate, calcium metaborate, silver metaborate, copper metaborate, lead metaborate, and magnesium metaborate; sodium sulfate, potassium sulfate, and sulfuric acid. Examples of fine particles include one or more types of fine particles selected from among sulfates such as lithium, magnesium sulfate, calcium sulfate, strontium sulfate, barium sulfate, titanium sulfate, aluminum sulfate, zinc sulfate, and copper sulfate; phosphates such as sodium phosphate, sodium hydrogen phosphate, potassium phosphate, potassium hydrogen phosphate, lithium phosphate, lithium hydrogen phosphate, magnesium phosphate, calcium phosphate, titanium phosphate, aluminum phosphate, and zinc phosphate; hydroxides such as lithium hydroxide, magnesium hydroxide, calcium hydroxide, strontium hydroxide, barium hydroxide, aluminum hydroxide, and zinc hydroxide; and oxides such as silicon, zinc, magnesium, aluminum, calcium, lithium, copper, iron, boron, and zirconium.

[0072] The coupling agent is not limited to these, but examples include silane coupling agents, zircon coupling agents, and titanium coupling agents.

[0073] Examples of humectants include polyhydric alcohols, water-soluble polymers, hydrocarbons, sugars, proteins, and inorganic compounds other than those mentioned above.

[0074] Examples of moisture-resistant agents include metal oxides (excluding those listed above), carbonates, borates, sulfates, and phosphates.

[0075] 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.

[0076] 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.

[0077] <Method for manufacturing coated sand> The manufacturing method of this embodiment is a method for manufacturing coated sand, comprising the step (3) of forming a second coating layer containing an inorganic binder containing metasilicate hydrate on the first coating layer of the foundry sand.

[0078] [Step (3)] In step (3) above, the method of mixing the foundry sand and the inorganic binder to form a second coating layer containing the inorganic binder on the first coating layer is not particularly limited. Examples include a method of mixing the foundry sand and the inorganic binder containing heated and melted metasilicate hydrate in a known manner to obtain a mixture, and then cooling the mixture to a temperature below the melting point of the inorganic binder to form the second coating layer on the first coating layer of the foundry sand, or a method of mixing the foundry sand with a solution containing water glass, caustic alkali, and water in a known manner to obtain a mixture, and then drying the mixture to form the second coating layer on the first coating layer of the foundry sand.

[0079] When a mixture is obtained by mixing the foundry sand and the inorganic binder containing heated and melted metasilicate hydrate in a known method, and then the mixture is cooled to a temperature below the melting point of the inorganic binder to form the second coating layer on the foundry sand, step (3) includes step (3-1) of mixing the foundry sand and the inorganic binder containing metasilicate hydrate.

[0080] When forming the second coating layer on the first coating layer of the foundry sand by mixing the foundry sand with a solution containing water glass, caustic alkali, and water in a known manner to obtain a mixture, and then drying the mixture, step (3) includes step (3-2) of mixing the foundry sand with a solution containing water glass, caustic alkali, and water.

[0081] <Casting molds> The casting mold of this embodiment includes coated sand having a second coating layer containing metasilicate hydrate on the first coating layer of the foundry sand. The casting mold of this embodiment is formed using the coated sand as the material.

[0082] <Method for manufacturing casting molds> The method for manufacturing a casting mold according to this embodiment is a method for manufacturing a mold using the coated sand. The method for manufacturing a casting mold according to this embodiment can be manufactured by applying known methods other than using the coated sand. The method for manufacturing a casting mold 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, a gas hardening method (CO2 method), a room temperature self-hardening method (ester hardening method), or a combination thereof. The selection of these molding methods is determined appropriately within the scope that does not impair the effects of the present invention.

[0083] In the gas curing method described above, the coated sand filled in the molding die may be treated with carbon dioxide (CO2) gas to gel and harden the inorganic binder through a decrease in pH caused by dissolved carbon dioxide.

[0084] In the above-mentioned room-temperature self-hardening method, after mixing the inorganic binder with the foundry sand, an organic ester as a hardening agent may be added, and the inorganic binder may be hardened by the saponification of the ester and the resulting decrease in pH. The organic ester is not particularly limited, and examples include ethylene glycol diacetate, diacetin, triacetin, propylene carbonate, and γ-butyrolactone.

[0085] With respect to the embodiments described above, the present invention further includes the following embodiments. <1> Foundry sand having a first coating layer containing aluminosilicate on fire-resistant aggregate, Foundry sand having a surface roughness Sa1 of 20 nm or more and 250 nm or less of the particles constituting the foundry sand. <2> The surface roughness Sa1 of the particles constituting the foundry sand is preferably 30 nm to 150 nm, more preferably 40 nm to 120 nm, even more preferably 50 nm to 90 nm, and even more preferably 53 nm to 70 nm. <1> The foundry sand described above. <3> The first coating layer is solid at room temperature, <1> or <2> The foundry sand described above. <4> The fire-resistant aggregate and the first coating layer have a silicate between them, <1> ~ <3> Foundry sand as described in any of the following. <5> The content of the aluminosilicate in the first coating layer is preferably 0.005 parts by mass or more and 1.000 parts by mass or less, more preferably 0.010 parts by mass or more and 0.500 parts by mass or less, and even more preferably 0.010 parts by mass or more and 0.300 parts by mass or less, based on Al2O3 equivalent, per 100 parts by mass of the refractory aggregate. <1> ~ <4> Foundry sand as described in any of the following. <6> The aforementioned <1> ~ <5> Coated sand having a second coating layer containing metasilicate hydrate on the first coating layer of the foundry sand described in any of the above. <7> The content of the second coating layer is preferably 0.1 parts by mass or more and 15.0 parts by mass or less, more preferably 0.2 parts by mass or more and 10.0 parts by mass or less, even more preferably 0.5 parts by mass or more and 8.0 parts by mass or less, even more preferably 1.0 parts by mass or more and 6.0 parts by mass or less, even more preferably 1.5 parts by mass or more and 4.0 parts by mass or less, and even more preferably 1.5 parts by mass or more and 3.0 parts by mass or less, per 100.0 parts by mass of the fire-resistant aggregate. <6> Coated sand as described. <8> The above is in a dry state. <6> or <7> Coated sand as described. <9> The aforementioned <1> ~ <5> A casting mold containing coated sand, wherein the first coating layer of the foundry sand described in any of the above has a second coating layer containing metasilicate hydrate. <10> A method for producing foundry sand having a first coating layer containing aluminosilicate on a refractory aggregate, A method for producing foundry sand, comprising the steps of (1) mixing a refractory aggregate having silicate on its surface with an aluminate, and (2) stirring the refractory aggregate obtained in step (1). <11> In step (1) above, the mixture is preferably mixed at a temperature of 15°C to 200°C, more preferably 15°C to 150°C, even more preferably 15°C to 120°C, even more preferably 15°C to 100°C, even more preferably 15°C to 80°C, even more preferably 15°C to 60°C, and even more preferably 15°C to less than 60°C. <10> A method for producing foundry sand as described above. <12> In step (2) above, the refractory aggregate obtained in step (1) above is stirred using a Lödige mixer or kneader. <11> A method for producing foundry sand as described above. <13> In step (2) above, the rotational speed of the main blade of the Redigeg mixer is preferably 40 rpm or more and 500 rpm or less, more preferably 60 rpm or more and 400 rpm or less, even more preferably 80 rpm or more and 300 rpm or less, and even more preferably 100 rpm or more and 300 rpm or less. <12> A method for producing foundry sand as described above. <14> In step (2) above, the tip peripheral speed of the stirring section of the main blade of the Redigge mixer is preferably 0.62 m / sec or more and 7.70 m / sec or less, more preferably 1.54 m / sec or more and 4.62 m / sec or less. <13> A method for producing foundry sand as described above. <15> In step (2) above, the rotational speed of the main blade of the kneader is preferably 20 rpm or more and 80 rpm or less, more preferably 30 rpm or more and 70 rpm or less, and even more preferably 40 rpm or more and 65 rpm or less. <12> A method for producing foundry sand as described above. <16> In step (2) above, the mixture is stirred preferably at 15°C to 200°C, more preferably at 30°C to 150°C, even more preferably at 50°C to 150°C, and even more preferably at 60°C to 150°C. <10> ~ <15> A method for manufacturing foundry sand as described in any of the following. <17> In step (2) above, the stirring time is preferably 15 minutes or more and 120 minutes or less, more preferably 35 minutes or more and 80 minutes or less, and even more preferably 50 minutes or more and 60 minutes or less. <10> ~ <16> A method for manufacturing foundry sand as described in any of the following. <18> The surface roughness Sa1 of the particles constituting the foundry sand is 20 nm or more and 250 nm or less. <10> ~ <17> A method for manufacturing foundry sand as described in any of the following. <19> The aforementioned <1> ~ <5> A method for producing coated sand, comprising the step (3) of forming a second coating layer containing metasilicate hydrate on the first coating layer of the foundry sand described in any of the above. <20> The above step (3) includes a step (3-1) of mixing the foundry sand with an inorganic binder containing metasilicate hydrate, <19> A method for manufacturing coated sand as described above. <21> The above step (3) includes step (3-2) of mixing the foundry sand with a solution containing water glass, caustic alkali, and water. <19> or <20> A method for manufacturing coated sand as described above. [Examples]

[0086] The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited thereto.

[0087] <Evaluation Method> [Method for preparing samples for measuring the surface roughness Sa1 of foundry sand particles] 20g of foundry sand particles were collected and placed in a 100mL poly bottle, then mixed for 1 minute using a vortex mixer. After that, a piece of double-sided tape (1.5cm x 1.5cm) was placed on a glass plate, and 0.1g of the mixed foundry sand particles was placed on top of it. Then, particles that did not adhere to the double-sided tape were removed with compressed air to obtain a sample for surface roughness Sa1 measurement.

[0088] [Method for preparing samples for measuring the surface roughness (Sa2) of foundry sand particles] 20g of foundry sand particles were taken and placed in a 100mL poly bottle, then mixed for 1 minute using a vortex mixer. Next, the residual binder layer of the recycled sand was removed to obtain a sample equivalent to new sand, and the following procedure was performed to calculate the ratio of the surface roughness Sa1 of the original sand to the surface roughness Sa2 of the new sand equivalent. 0.5g of foundry sand particles (original sand) were taken and placed in a 100mL poly bottle, then 50g of a 1mol / L sodium hydroxide aqueous solution was mixed and stirred for 12 hours. The solution was removed from the resulting mixture, washed three times with 50g of water, and then dried at 105°C for 1 hour. After that, double-sided tape (1.5cm × 1.5cm) was placed on a glass plate, 0.1g of the dried particles were placed on top of it, and then particles that were not attached to the double-sided tape were removed with compressed air to obtain a sample for measuring the surface roughness Sa2 of the new sand equivalent.

[0089] [Method for measuring the surface roughness Sa1 or Sa2 of foundry sand particles] Surface roughness Sa1 was measured by placing a sample for surface roughness Sa1 measurement in a laser microscope (Lasertec Corporation, OPTELICS® HYBRID+), randomly selecting one particle from the sample, and performing image analysis of the particle surface obtained at an optical magnification of 150x and a working distance (WD) of 350 μm. For the image analysis, surface roughness measurement was performed, and waviness correction was carried out using an S filter of 0.1 μm and an L filter of 50 μm to obtain the surface roughness Sa. This measurement was performed on a total of 10 particles randomly selected from the sample (10 measurements), and the average value of the 10 measurements was taken as the surface roughness Sa1. Surface roughness Sa2 was measured in the same manner as surface roughness Sa1, and the average value of 10 measurements using a sample for surface roughness Sa2 was taken as the surface roughness Sa2.

[0090] [Method for calculating the surface roughness ratio (Sa1 / Sa2)] The surface roughness ratio Sa1 / Sa2 was calculated by dividing the surface roughness value Sa1 by the surface roughness value Sa2. A higher value for this parameter indicates greater surface roughness of the foundry sand particles.

[0091] [Method for evaluating the storage stability of foundry sand] 100g of each foundry sand from the examples and comparative examples were placed in a poly bottle, and stored open without a lid at a temperature of 25°C and a relative humidity of 90% for 12 hours. Afterward, the contents of the poly bottle were placed on a sieve with a mesh size of 1.7mm, and the blocking rate was calculated from the mass of the foundry sand remaining on the sieve using the following formula. A lower blocking rate indicates better storage stability. Blocking rate (%) = (Mass of foundry sand remaining on the sieve [g] / 100 [g]) × 100

[0092] [Method for evaluating mold strength] 1. Storage of coated sand Immediately after preparing the coated sands for Examples 6-8 and Comparative Examples 3-5, 3 kg of each coated sand was placed in a poly bag (0.05 mm thick, 500 mm wide, 600 mm long). The air inside the poly bag was squeezed out by hand, the bag was sealed, and stored at 35°C for 10 days. 2. Method for determining whether coated sand is dry or wet. Half the volume of coated sand was placed in a cylindrical transparent plastic bottle with a diameter of 76 mm and a height of 125 mm. Using a bottle agitator, the plastic bottle was held so that its axis was horizontal, and rotated around the horizontal axis at room temperature (25°C) and a speed of 60 rpm. The dry state was defined as when the slope of the flowing coated sand layer inside the plastic bottle became a flat surface, and the angle formed between this slope and the horizontal surface (dynamic angle of repose) could be measured. The wet state was defined as when the coated sand did not flow inside the plastic bottle, or when it flowed but the slope of the coated sand layer did not form a flat surface, and as a result the dynamic angle of repose could not be measured. In the wet state, the fluidity was low, making it difficult to prepare the mold test piece in the next step, so evaluation was not possible, and the value for mold strength evaluation was set to 0 MPa. 3. Preparation of mold test specimens 100 parts by mass of each coated sand after storage were placed in a stirrer (Taiyo Machinery Co., Ltd., Mini Mini Super Mixer type B), 0.70 parts by mass of amorphous silica fine particles were added, and the mixture was stirred for 1 minute. The resulting mixture was filled into a mold (for 5 test specimens, 22.3 mm × 22.3 mm × 180 mm) heated to 180°C at a blow pressure of 0.3 MPa using a CSR-43 blow molding machine, and the coated sand was left to harden in the mold for 150 seconds to obtain a molded test specimen. 4. Evaluation of mold strength The bending strength (MPa) of each molded test specimen was measured using a tensile and compression testing machine SVZ-201F (manufactured by Imada Seisakusho Co., Ltd.) under conditions of a span of 150 mm and a speed of 300 mm / min. The molded test specimens were left for 24 hours in a constant temperature and humidity chamber at 25°C and 55% relative humidity after being removed from the mold. The evaluation results are shown in Table 2.

[0093] <Material> [Fire-resistant aggregate] Aggregate 1: Espal #60L (artificially produced Al2O3-based spherical aggregate: manufactured by Yamakawa Sangyo Co., Ltd., average particle size: 241 μm, degree of amorphism: 45%) • Recycled sand (A): Prepared using the following method. [Method for producing recycled sand (A)] (1) Preparation of coated sand Aggregate 1 (100 parts by mass) was added to a stirrer as a refractory aggregate. Next, sodium metasilicate heptahydrate (2.00 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 (0.70 parts by mass) were added and kneaded for 2 minutes to obtain dry coated sand. (2) Preparation of the mold Ten kg of the obtained coated sand was poured into a mold for test mold production, and a test mold was obtained by heating it in a heating furnace at 230°C for 20 minutes. (3) Casting Ten kg of aluminum alloy AC4C material (720°C) was poured into the resulting test mold. (4) Preparation of recovered sand (B) After casting, the casting was removed from the test mold, the test mold was crushed using a hammer or similar tool, and further crushed using a mini crusher (manufactured by Taiyo Machinery Co., Ltd.) to obtain recovered sand (B). (5) Production of recycled sand 100 kg of recovered sand (B) was fed into a dry-type foundry sand recycling device (Hybrid Sand Master, manufactured by Nippon Chuzo Co., Ltd.) equipped with a fluidized bed, and recycled sand (A) was obtained by batch processing at a rotor speed of 2400 rpm for 60 minutes. [Material for first coating layer] • 50% sodium aluminate aqueous solution: Sodium aluminate #2019 (50% sodium aluminate aqueous solution manufactured by Asada Chemical Industries Co., Ltd.) • Water: Ion-exchanged water [Inorganic binders] • Sodium metasilicate nonahydrate: Sodium metasilicate nonahydrate (manufactured by Nippon Chemical Industrial Co., Ltd., Si / Na molar ratio 1.0, solids content 42.9% by weight) • Sodium metasilicate pentahydrate: Sodium metasilicate pentahydrate (manufactured by Nippon Chemical Industrial Co., Ltd., Si / Na molar ratio 1.0, solids content 57.5% by weight) • Sodium metasilicate heptahydrate: A mixture of 50 parts by mass of sodium metasilicate 9hydrate and 50 parts by mass of sodium metasilicate pentahydrate (Si / Na molar ratio 1.0, solid content 50.2% by weight). [Inorganic particles] • Amorphous silica particles: Denka Fused Silica SFP-20M (manufactured by Denka Co., Ltd., average particle size: 0.4 μm, degree of amorphization: 99.5% or higher)

[0094] <Manufacturing of foundry sand> [Example 1] Process (1): 100 parts by mass of recycled sand (A) was put into a mixing device (Chuo Kiko Co., Ltd., Redigge mixer M20 type), and while mixing at a main blade rotation speed of 230 rpm (circumferential speed 3.55 m / s) and a chopper at 3000 rpm, a liquid mixture of 0.07 parts by mass of 50% sodium aluminate aqueous solution and 1.2 parts by mass of water was sprayed for 1 minute, after which mixing was stopped. Step (2): The obtained refractory aggregate was heated to 120°C, and the chopper was kept stopped while the main blade rotation speed was 230 rpm (peripheral speed 3.55 m / s) and stirred for 60 minutes from the start of heating. After that, the contents were discharged from the apparatus and then cooled to room temperature to obtain refractory aggregate (foundry sand 1) on which the first coating layer containing the aluminosilicate of Example 1 was formed. The surface roughness Sa1 of the obtained foundry sand 1 was 56.4 nm, and the surface roughness ratio Sa1 / Sa2 was 1.16.

[0095] [Example 2] Except for changing the stirring time in step (2) from 60 minutes to 45 minutes, the foundry sand 2 of Example 2 described in Table 1 was obtained in the same manner as in Example 1. The surface roughness Sa1 of the obtained foundry sand 2 was 76.4 nm, and the surface roughness ratio Sa1 / Sa2 was 1.77.

[0096] [Example 3] Except for changing the stirring time in step (2) from 60 minutes to 30 minutes, the foundry sand 3 of Example 3 described in Table 1 was obtained in the same manner as in Example 1. The surface roughness Sa1 of the obtained foundry sand 3 was 92.2 nm, and the surface roughness ratio Sa1 / Sa2 was 2.13.

[0097] [Example 4] Except for changing the main blade rotation speed in steps (1) and (2) from 230 rpm to 90 rpm, the foundry sand 4 of Example 4 described in Table 1 was obtained in the same manner as in Example 1. The surface roughness Sa1 of the obtained foundry sand 4 was 82.2 nm, and the surface roughness ratio Sa1 / Sa2 was 1.79.

[0098] [Example 5] Process (1): 100 parts by mass of recycled sand (A) was put into a mixing device (Irie Shoji Co., Ltd., tabletop kneader PNV-1), and while mixing at a main blade rotation speed of 60 rpm, a liquid mixture of 0.07 parts by mass of 50% sodium aluminate aqueous solution and 1.2 parts by mass of water was added, and mixing was stopped 1 minute after the start of addition. Step (2): The obtained refractory aggregate was heated to 120°C and stirred for 60 minutes from the start of heating at a main blade rotation speed of 60 rpm. After that, the contents were discharged from the apparatus and then cooled to room temperature to obtain refractory aggregate (foundry sand 5) on which the first coating layer containing the aluminosilicate of Example 5 was formed. The surface roughness Sa1 of the obtained foundry sand 5 was 82.3 nm, and the surface roughness ratio Sa1 / Sa2 was 2.06.

[0099] [Comparative Example 1] Recycled sand (A) was used without any treatment. This was designated as foundry sand 6, and its surface roughness Sa1 was 136 nm, with a surface roughness ratio Sa1 / Sa2 of 3.40.

[0100] [Comparative Example 2] The foundry sand 7 of Comparative Example 2, as shown in Table 1, was obtained in the same manner as in Example 1, except that 0.07 parts by mass of a 50% sodium aluminate aqueous solution was not added. The surface roughness Sa1 of the obtained foundry sand 7 was 50.0 nm, and the surface roughness ratio Sa1 / Sa2 was 1.22.

[0101] Table 1 shows the evaluation results of the foundry sand for Examples 1-5 and Comparative Examples 1 and 2.

[0102] [Table 1]

[0103] <Manufacturing of coated sand> [Example 6] 100 parts by mass of the foundry sand 1 from Example 1 were left to stand for 12 hours in an environment of 35°C to adjust the temperature. Then, the sand was placed in a stirrer (Kenmix Aiko Chef PRO, manufactured by Aikosha Seisakusho Co., Ltd.) installed in an environment of 25°C. Sodium metasilicate heptahydrate (2 parts by mass), which had been heated to 80°C and melted, was added to the stirrer and kneaded for 4 minutes to obtain the coated sand 1 from Example 6.

[0104] [Example 7] Foundry sand 8 of Example 7, as shown in Table 2, was obtained in the same manner as in Example 1, except that recycled sand (A) was replaced with recovered sand (B). The surface roughness Sa1 of the obtained foundry sand 8 was 189 nm, and the surface roughness ratio Sa1 / Sa2 was 3.79. Coated sand 2 of Example 7, as shown in Table 2, was obtained in the same manner as in Example 6, except that foundry sand 1 was replaced with foundry sand 8.

[0105] [Example 8] Except for changing foundry sand 1 to foundry sand 5, the coated sand 3 of Example 8 described in Table 2 was obtained in the same manner as in Example 6.

[0106] [Comparative Example 3] Except for changing foundry sand 1 to foundry sand 6, the coated sand 4 of Comparative Example 3 shown in Table 2 was obtained in the same manner as in Example 6.

[0107] [Comparative Example 4] Coated sand 5 of Comparative Example 4, as shown in Table 2, was obtained in the same manner as in Example 6, except that foundry sand 1 was changed to foundry sand 7.

[0108] [Comparative Example 5] The recovered sand (B) was used as is without any treatment. This was designated as foundry sand 9, and its surface roughness Sa1 was 270 nm, with a surface roughness ratio Sa1 / Sa2 of 6.59. Coated sand 6 of Comparative Example 5, shown in Table 2, was obtained in the same manner as in Example 6, except that foundry sand 1 was changed to foundry sand 9.

[0109] [Table 2]

[0110] Table 3 shows the evaluation results of the coated sands for Examples 6-8 and Comparative Examples 3-5.

[0111] [Table 3]

Claims

1. Foundry sand having a first coating layer containing aluminosilicate on fire-resistant aggregate, Foundry sand having a surface roughness Sa1 of 20 nm or more and 250 nm or less of the particles constituting the foundry sand.

2. The foundry sand according to claim 1, wherein the first coating layer is solid at room temperature.

3. The foundry sand according to claim 1, wherein a silicate is provided between the refractory aggregate and the first coating layer.

4. The content of the aluminosilicate in the first coating layer is Al ２ O ３ The foundry sand according to claim 1, wherein the amount is 0.005 parts by mass or more and 1.000 parts by mass or less per 100 parts by mass of the refractory aggregate.

5. Coated sand having a second coating layer containing metasilicate hydrate on the first coating layer of the foundry sand according to any one of claims 1 to 4.

6. The coated sand according to claim 5, which is in a dry state.

7. A casting mold comprising coated sand, wherein the first coating layer of the foundry sand according to any one of claims 1 to 4 has a second coating layer containing metasilicate hydrate.

8. A method for producing foundry sand having a first coating layer containing aluminosilicate on a refractory aggregate, A method for producing foundry sand, comprising the steps of (1) mixing a refractory aggregate having silicate on its surface with an aluminate, and (2) stirring the refractory aggregate obtained in step (1).

9. The method for producing foundry sand according to claim 8, wherein in step (2), the refractory aggregate obtained in step (1) is stirred using a Lödige mixer.

10. The method for producing foundry sand according to claim 9, wherein in step (2), the rotational speed of the main blade of the Redigeg mixer is 40 rpm or more and 500 rpm or less.

11. The method for producing foundry sand according to claim 8, wherein in step (2) above, the sand is stirred at a temperature of 15°C or higher and 200°C or lower.

12. A method for producing foundry sand according to any one of claims 8 to 11, wherein the surface roughness Sa1 of the particles constituting the foundry sand is 20 nm or more and 250 nm or less.

13. A method for producing coated sand, comprising the step (3) of forming a second coating layer containing metasilicate hydrate on the first coating layer of the foundry sand according to any one of claims 1 to 4.

14. The method for producing coated sand according to claim 13, wherein step (3) is a step (3-1) of mixing the foundry sand with an inorganic binder containing metasilicate hydrate.

15. The method for producing coated sand according to claim 13, wherein step (3) is a step (3-2) of mixing the foundry sand with a solution containing water glass, caustic alkali, and water.

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