Molding sand

Abstract

The present invention is molding sand having, on a refractory aggregate, a first coating layer containing aluminosilicate, wherein the surface roughness Sa1 of particles constituting the molding sand is 20-250 nm. According to the present invention, it is possible to provide molding sand that is not susceptible to blocking even in an environment having a relatively high humidity.

Description

Foundry sand

[0001] This invention relates to foundry sand.

[0002] A known type of mold used in casting is obtained by filling a mold with coated sand, which has refractory aggregate and an inorganic binder layer containing metasilicate hydrate formed on the surface of the refractory aggregate, and then hardening the coated sand filled in the mold.

[0003] The present invention relates to a 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.

[0004] 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. Detailed description of the invention

[0005] Molds manufactured using coated sand are typically destroyed (crushed) and recovered after being used for casting, and then recycled through various methods for reuse as recycled sand. From an economic and waste reduction perspective, it is common practice in foundries to manufacture molds using recycled sand as refractory aggregate.

[0006] However, it has become clear that recycled sand (foundry sand) obtained by using coated sand as described in Japanese Patent Publication No. 2020-11296, then recovering and recycling it, tends to agglomerate and block in relatively humid environments. When recycled sand (foundry sand) blocks, it becomes difficult to uniformly form an inorganic binder layer on the surface, which is undesirable from the viewpoint of mold strength.

[0007] Furthermore, it has become clear that when coated sand, such as that described in Japanese Patent Publication No. 2020-11296, is used, then recovered and subjected to a recycling process to obtain recycled sand (foundry sand), and then an inorganic binder layer containing metasilicate hydrate is formed on the recycled sand, a mold with the desired strength can be obtained when used immediately after production. However, as time passes after the production of the coated sand, the strength of the resulting mold tends to decrease.

[0008] The present invention aims to provide foundry sand that is less prone to blocking even in environments with relatively high humidity.

[0009] 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.

[0010] The present invention relates to a 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.

[0011] 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.

[0012] 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.

[0013] 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.

[0014] The following describes one embodiment of the present invention.

[0015] <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 or more and 250 nm or less. 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 clear, but it is thought to be as follows.

[0016] 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 not effective because silicate inherently readily adsorbs water molecules. Therefore, by co-condensing the silanol groups of silicates with aluminates to form 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.

[0017] 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 improving the ability to fill into the molding die. Specifically, the upper limit of the sphericity is 1.

[0018] 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, a VH-8000 model from Keyence Corporation) 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 determining the circumference of a perfect circle with the same area (mm) / (perimeter of the particle projection cross-section (mm)) and averaging the obtained values ​​for any 50 particles.

[0019] From the viewpoints of improving the mold quality and mold strength, as well as the ease of molding and storage stability of the mold, the average particle diameter of the foundry sand is preferably 0.05 mm or more, more preferably 0.10 mm or more. From the viewpoints of improving the mold quality and mold strength, and the ease of molding of the mold, the average particle diameter 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.

[0020] The average particle diameter of the foundry sand can be measured by the following method for measuring the average particle diameter. (Method for measuring the average particle diameter) When the sphericity from the particle projection cross-section of the particle is 1, the diameter (mm) is measured. On the other hand, when the sphericity < 1, the major axis diameter (mm) and minor axis diameter (mm) of the randomly oriented particles are measured, and (major axis diameter + minor axis diameter) / 2 is obtained. For any 100 particles, the values obtained are averaged to obtain the average particle diameter (mm). The major axis diameter and minor axis diameter are defined as follows. The particle is stabilized on a plane, and when the projection image of the particle on the plane is sandwiched between two parallel lines, the width of the particle when the distance between the parallel lines is minimized is called the minor axis diameter. On the other hand, when the particle is sandwiched between two parallel lines in a direction perpendicular to these parallel lines, the distance is called the major axis diameter. The major axis diameter and minor axis diameter of the particle can be obtained by photographing an image (photo) of the particle with an optical microscope or a digital scope (for example, manufactured by Keyence Corporation, VH-8000 type) and performing image analysis on the obtained image.

[0021] [Refractory aggregate] The refractory aggregate contains one or more selected from the group consisting of natural sand and artificial sand.

[0022] 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.

[0023] Examples of the artificial sand include, for example, synthetic mullite sand, SiO ２ sand with SiO ２ as the main component, Al ２ O ３ sand with Al ２ O ３ as the main component, SiO ２ / Al２ O ３ -based sand, SiO ２ / MgO-based sand, SiO ２ / Al ２ O ３ / ZrO ２ -based sand, SiO ２ / Al ２ O ３ / Fe ２ O ３ -based sand, and one or more selected from the group consisting of slag-derived sand. Here, the main component refers to the component with the largest content based on mass among the components contained in the sand. The artificial sand refers to sand that is not naturally produced, but rather sand prepared by artificially adjusting the components of metal oxides and melting or sintering them.

[0024] Incidentally, the content of each component such as SiO ２ , Al ２ O ３ , Fe ２ O ３ in the refractory aggregate can be measured using the following fluorescent X-ray method. [Method for Measuring Components of the Refractory Aggregate by Fluorescent X-ray 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 and melted at 1200 °C for 10 minutes, and then cooled to prepare a sample in a glassy state (glass bead method). The sample can be used to measure the components of the refractory aggregate by performing fluorescent X-ray analysis by the fundamental parameter (Fundamental Parameter: FP) method using a fluorescent X-ray analyzer ZSX Primus II (manufactured by Rigaku Corporation).

[0025] The aforementioned refractory aggregate is generally recycled sand. This recycled sand is obtained by recycling used casting molds or cores formed from refractory aggregate and an inorganic binder containing metasilicate. The recycled sand contains the refractory aggregate and has residue of the used inorganic binder on the refractory aggregate. The residue of the used inorganic binder contains silicate. Examples of cations constituting silicate include monovalent cations such as sodium, potassium, lithium, and ammonium, and divalent cations such as magnesium, calcium, and zinc.

[0026] The recycled sand can be manufactured, for example, by the following method. [Method for manufacturing recycled sand] As a method for recycling mold waste sand after casting using coated sand, known methods (for example, "Mold Making Method", 4th edition, Japan Foundry Technology Association, November 18, 1996, pp. 327-330) can be followed. For example, methods such as dry polishing (mechanical wear), wet polishing, roasting, and combinations thereof are known.

[0027] In the aforementioned dry polishing process, for example, a rotary reclaimer can be used, which polishes the sand by the collision and friction that occurs between the projected sand generated by centrifugal force and the falling input sand when sand is fed onto a high-speed rotating rotor; a hybrid sand master, which is a composite type of reclaimer that integrates a rotary reclaimer and a fluid classifier; and a sand freshener that utilizes the grinding and polishing force of a grinding wheel.

[0028] One example of the wet polishing treatment is a method using a trough polishing machine that polishes the sand by friction between sand grains in a trough with rotating blades.

[0029] The aforementioned roasting process includes, for example, a method in which sand is continuously added to a roasting furnace such as a fluidized bed furnace or a rotary kiln, and the material is roasted in a temperature range of 200 to 1000°C.

[0030] Any method can be used for regeneration, but since wet processing and roasting processes are complicated and energy-intensive, dry polishing is preferred.

[0031] 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.

[0032] 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 same measurement method as the measurement method for the average particle diameter of the foundry sand can be used to measure the average particle diameter of the refractory aggregate.

[0033] [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 there may be discontinuous parts. 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.

[0034] Aluminosilicates preferably contain at least one of a silicate and a reaction product of aluminate or aluminum hydroxide, as this improves 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.

[0035] 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 crushing machine 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 a method of analyzing by solid-state nuclear magnetic resonance spectroscopy (ssNMR) to confirm signals originating from aluminosilicate.

[0036] Furthermore, the aluminosilicate content in the first coating layer is Al ２ O ３ It can be calculated by conversion. The aluminosilicate content in the first coating layer is Al ２ O ３ In terms of conversion, from the viewpoint of storage stability, the amount 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, the amount 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.

[0037] Furthermore, the Al of the aluminosilicate in the first coating layer ２ O ３ The content obtained by conversion is determined by the following method. Using the analytical values ​​of the aggregate by the fluorescent X-ray method and the analytical values ​​of the foundry sand containing the first coating layer using those values, it is calculated from the following formula: Aluminosilicate content of the first coating layer (Al ２ O ３ (Conversion) [Parts by mass] = {Al of foundry sand} ２ O ３ [Mass portion] - {Al of fire-resistant aggregate} ２ O ３ [Parts by mass]}

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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. 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.

[0042] <Method for Manufacturing Foundry Sand> The method for manufacturing foundry sand according to this embodiment is a method for manufacturing foundry sand, comprising a step (1) of mixing a refractory aggregate having silicate on its surface (hereinafter sometimes also referred to as refractory aggregate (A)) with an aluminate, and a step (2) of 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 they may be performed continuously.

[0043] 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. For example, a known mixing device having a stirring section can be used, and the mixing / stirring can be performed by rotating the stirring section. Examples of such mixing devices include kneaders, ribbon mixers, Nauter mixers, Proscher mixers, Lödige mixers, and high-speed mixers. From the viewpoint of forming a uniform first coating layer, Lödige mixers and kneaders are preferred, and Lödige mixers are more preferred. Furthermore, devices that can heat and stir the material to be processed while rolling and sliding it by rotating the container or rotating the internal paddles can also be used. Examples include heated rotary container type mixing devices (rotary drums, rotary kilns, rotary dryers), paddle dryers, paddle mixers, and intensive mixers. All of these devices can form a first coating layer by stirring (kneading) under heating.

[0044] 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.

[0045] In step (1) above, when the mixing of the refractory aggregate (A) and aluminate is carried out in 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.

[0046] 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.

[0047] In step (1) above, when the mixing of the refractory aggregate (A) and the aluminate is performed 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.

[0048] 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.

[0049] 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, 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] <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 the 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.

[0057] 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.

[0058] The dynamic angle of repose of coated sand can be measured by the following method: (Method for measuring the 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 rotation 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, then the sand is in a wet state.

[0059] 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 the molding die. Here, "spherical" in the context of coated sand refers to a round shape, like a ball.

[0060] 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 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.

[0061] 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.

[0062] [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 coating layer and the second coating layer.

[0063] 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 parts 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.

[0064] 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.

[0065] 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.

[0066] 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 components may be 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.

[0067] 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 parts by mass or less, per 100.00 parts by mass of refractory aggregate.

[0068] 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.

[0069] [Measurement of hydration water content] (1) In a crucible that has been heated and weighed, amorphous SiO ２ 10 g of coated sand before the addition of additives such as fine particles is weighed and placed in the crucible, and the amount of mass loss (%) after heating at 900°C for 1 hour 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) Amorphous SiO ２100 g of coated sand before adding additives such as fine particles is weighed and immersed in 200 mL or more of water or hot water and stirred for 1 hour or more to extract metasilicate hydrate. The refractory aggregate is filtered out of the obtained extract, and water is removed by vacuum distillation using a rotary evaporator at 40°C and an internal pressure of 15 mmHg or less. Then, it is heated and dried at a temperature of 120°C to 180°C for 1 to 3 hours, and the weight of the dried product is weighed. The dry solid content (%) (B) of metasilicate hydrate in the coated sand is calculated. B = (M12 / M11) × 100 (M11: mass of coated sand (g), M12: weight of dried product (g)) (3) Amount of water in the hydration of metasilicate hydrate = [(A) / molecular weight of water] / [(B) / molecular weight of anhydrous metasilicate]

[0070] (Other) The second coating layer may further contain components other than metasilicate, for example amorphous SiO ２ Contains fine particles, amorphous SiO ２ The composition may also contain inorganic fine particles other than the contained fine particles, humectants, moisture-resistant agents, coupling agents that strengthen the bond between the refractory aggregate and the inorganic binder composition, lubricants, surfactants, release agents, etc.

[0071] Amorphous SiO ２ The contained fine particles may be used because of their high reactivity with metasilicate hydrate. This makes it easier to improve the mechanical strength of the mold.

[0072] Amorphous SiO ２ The contained fine particles include precipitated silica, calcined silica produced in an electric arc or by flame hydrolysis, silica produced during the manufacture of Fe-Si, and ZrSiO ４ Examples include silica produced by thermal decomposition, silicon dioxide produced by oxidation of metallic silicon with an oxygen-containing gas, and spherical quartz glass powder produced from crystalline quartz by melting and subsequent rapid cooling. These can be used individually, or two or more can be used in combination.

[0073] Inorganic nanoparticles are amorphous SiO as described above. ２While not particularly limited to those containing fine particles, 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, lithium sulfate, magnesium sulfate Examples of fine particles include sulfates such as 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 of silicon, zinc, magnesium, aluminum, calcium, lithium, copper, iron, boron, zirconium, etc., selected from one or more types of fine particles.

[0074] The coupling agent is not limited to these, but examples include silane coupling agents, zircon coupling agents, and titanium coupling agents.

[0075] Examples of humectants include polyhydric alcohols, water-soluble polymers, hydrocarbons, sugars, proteins, and inorganic compounds other than those mentioned above.

[0076] Examples of moisture-resistant agents include metal oxides (excluding those listed above), carbonates, borates, sulfates, and phosphates.

[0077] 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.

[0078] 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.

[0079] <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.

[0080] [Step (3)] In step (3), 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 and 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.

[0081] 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.

[0082] 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.

[0083] <Casting mold> 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.

[0084] <Method for Manufacturing Casting Molds> The method for manufacturing casting molds according to this embodiment is a method for manufacturing molds using the coated sand. The method for manufacturing casting molds according to this embodiment can be manufactured by applying known methods other than using the coated sand. The method for manufacturing molds using coated sand is not particularly limited, but for example, 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, and a gas hardening method (CO2) ２ Methods for manufacturing molds include the following: the molding method, the 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.

[0085] In the aforementioned gas hardening method, the coated sand filled in the molding die is heated to carbon dioxide (CO2). ２ The inorganic binder may be gelled and hardened by treatment with gas, via a decrease in pH caused by dissolved carbon dioxide.

[0086] 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.

[0087] 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 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. <2> The foundry sand according to <1>, wherein the surface roughness Sa1 of the particles constituting the foundry sand is preferably 30 nm or more and 150 nm or less, more preferably 40 nm or more and 120 nm or less, even more preferably 50 nm or more and 90 nm or less, and even more preferably 53 nm or more and 70 nm or less. <3> The foundry sand according to <1> or <2>, wherein the first coating layer is solid at room temperature. <4> The foundry sand according to any one of <1> to <3>, wherein there is silicate between the refractory aggregate and the first coating layer. <5> The content of the aluminosilicate in the first coating layer is Al ２ O ３The foundry sand according to any one of <1> to <4> above, wherein the amount 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, per 100 parts by mass of the refractory aggregate. <6> Coated sand having a second coating layer containing metasilicate hydrate on the first coating layer of the foundry sand according to any one of <1> to <5> above. <7> The coated sand according to <6>, wherein 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 refractory aggregate. <8> The coated sand according to <6> or <7>, in a dry state. <9> A casting mold comprising coated sand having a second coating layer containing metasilicate hydrate on the first coating layer of the foundry sand according to any one of <1> to <5>. <10> A method for producing foundry sand having a first coating layer containing aluminosilicate on a refractory aggregate, 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> The method for producing foundry sand according to <10>, wherein in step (1), the mixing is preferably carried out 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. <12> The method for producing foundry sand according to <11>, wherein in step (2), the stirring of the refractory aggregate obtained in step (1) is carried out using a Lödige mixer or a kneader.<13> The method for producing foundry sand according to <12>, wherein in step (2), the rotational speed of the main blade of the Lödige 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. <14> The method for producing foundry sand according to <13>, wherein in step (2), the peripheral speed of the tip of the stirring section of the main blade of the Lödige 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. <15> The method for producing foundry sand according to <12>, wherein in step (2), the rotation 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. <16> The method for producing foundry sand according to any one of <10> to <15>, wherein in step (2), the mixture is preferably stirred at 15°C or more and 200°C or less, more preferably 30°C or more and 150°C or less, even more preferably 50°C or more and 150°C or less. <17> The method for producing foundry sand according to any one of <10> to <16>, wherein in step (2), 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. <18> A method for producing foundry sand according to any one of <10> to <17>, wherein the surface roughness Sa1 of the particles constituting the foundry sand is 20 nm or more and 250 nm or less. <19> A method for producing coated sand, comprising step (3) of forming a second coating layer containing metasilicate hydrate on the first coating layer of foundry sand according to any one of <1> to <5>. <20> A method for producing coated sand according to <19>, wherein step (3) comprises step (3-1) of mixing the foundry sand with an inorganic binder containing metasilicate hydrate. <21> A method for producing coated sand according to <19> or <20>, wherein step (3) comprises step (3-2) of mixing the foundry sand with a solution containing water glass, caustic alkali, and water.

[0088] The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited thereto.

[0089] <Evaluation Method> [Preparation Method for Samples for Surface Roughness Sa1 Measurement of Foundry Sand Particles] 20 g of foundry sand particles were taken and placed in a 100 mL poly bottle, and mixed for 1 minute using a vortex mixer. Then, a piece of double-sided tape (1.5 cm x 1.5 cm) was placed on a glass plate, and 0.1 g of the mixed foundry sand particles was placed on top of it. Next, particles that were not attached to the double-sided tape were removed with compressed air to obtain a sample for surface roughness Sa1 measurement.

[0090] [Method for preparing a sample for measuring the surface roughness Sa2 of foundry sand particles] 20 g of foundry sand particles were taken and placed in a 100 mL poly bottle, and mixed for 1 minute using a vortex mixer. Next, the residual binder layer of recycled sand was removed to obtain a product 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 product equivalent to new sand. 0.5 g of foundry sand particles (original sand) were taken and placed in a 100 mL poly bottle, and then 50 g of a 1 mol / L sodium hydroxide aqueous solution was mixed and stirred for 12 hours. The solution was removed from the resulting mixture, washed three times with 50 g of water, and then dried at 105°C for 1 hour. After that, double-sided tape (1.5 cm x 1.5 cm) was placed on a glass plate, 0.1 g of the dried particles were placed on it, and then particles that were not attached to the double-sided tape were removed with compressed air to obtain a sample equivalent to new sand for measuring surface roughness Sa2.

[0091] [Method for measuring the surface roughness Sa1 or Sa2 of foundry sand particles] Surface roughness Sa1 was measured by placing a sample for measuring surface roughness Sa1 in a laser microscope (Lasertec Corporation, OPTELICS® HYBRID+), randomly selecting one particle from the sample, and determining the surface roughness Sa1 by 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 (10 measurements) randomly selected from the sample, 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 measuring surface roughness Sa2 was taken as the surface roughness Sa2.

[0092] [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 that the surface roughness of the foundry sand particles is greater.

[0093] [Method for Evaluating the Storage Stability of Foundry Sand] 100 g 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. After that, the contents of the poly bottle were placed on a sieve with a mesh size of 1.7 mm, 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

[0094] [Method for Evaluating Mold Strength] 1. Storage of Coated Sand Immediately after preparing each coated sand according to Examples 6-8 and Comparative Examples 3-5, 3 kg of the 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, and the bag was sealed and stored for 10 days at 35°C. 2. Method for Determining the Dry or Wet State of Coated Sand 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) at a speed of 60 rpm. The dry state was defined as the case where the slope of the coated sand layer flowing inside the plastic bottle became a flat surface, and the angle formed between this slope and the horizontal plane (dynamic angle of repose) could be measured. The wet state was defined as the case where the coated sand did not flow inside the plastic bottle, or even if it flowed, 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 case of 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, meaning the value for evaluating the mold strength was set to 0 MPa. 3. 100 parts by mass of each coated sand after the preparation and storage of the mold test piece was 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 obtained 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. The coated sand was then left to harden in the mold for 150 seconds to obtain mold test specimens. 4. Evaluation of mold strength The bending strength (MPa) of each obtained mold 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 mold 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.

[0095] <Materials> [Fire-resistant aggregate] Aggregate 1: Espal #60L (artificially manufactured aluminum) ２ O ３Spherical aggregate: Manufactured by Yamakawa Sangyo Co., Ltd., average particle size: 241 μm, degree of amorphousness: 45% Recycled sand (A): Prepared by the following method. [Method for preparing recycled sand (A)] (1) Preparation of coated sand Aggregate 1 (100 parts by mass) was put into a mixer as a refractory aggregate. Next, sodium metasilicate heptahydrate (2.00 parts by mass), which had been heated to 80°C and melted, was put into the mixer 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 mold 10 kg of the obtained coated sand was poured into a mold for test mold preparation and heated in a heating furnace at 230°C for 20 minutes to obtain a test mold. (3) Casting 10 kg of aluminum alloy AC4C material (720°C) was poured into the obtained test mold. (4) Preparation of recovered sand (B) The casting was removed from the test mold after casting, the test mold was crushed with a hammer or the like, and further crushed using a mini crusher (manufactured by Taiyo Machinery Co., Ltd.) to obtain recovered sand (B). (5) Preparation of recycled sand 100 kg of recovered sand (B) was put into a dry-type foundry sand recycling device (Hybrid Sand Master manufactured by Nippon Chuzo Co., Ltd.) equipped with a fluidized bed, and batch processed for 60 minutes at a rotor speed of 2400 rpm to obtain recycled sand (A). [Materials for the 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 9-hydrate: Sodium metasilicate 9-hydrate (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 9-hydrate and 50 parts by mass of sodium metasilicate pentahydrate (Si / Na molar ratio 1.0, solids content 50.2% by weight). [Inorganic Particles] ・Amorphous silica particles: Denka fused silica SFP-20M (Denka Corporation, average particle size: 0.4 μm, degree of amorphization: 99.5% or higher)

[0096] <Manufacturing of Foundry Sand> [Example 1] Step (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 (peripheral 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, and then mixing was stopped. Step (2): The obtained refractory aggregate was heated to 120°C, and with the chopper stopped, it was stirred at a main blade rotation speed of 230 rpm (peripheral speed 3.55 m / s) for 60 minutes from the start of heating. After that, the contents were discharged from the device, and then cooled to room temperature to obtain refractory aggregate (foundry sand 1) in which the first coating layer containing 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.

[0097] [Example 2] Except for changing the stirring time in step (2) from 60 minutes to 45 minutes, the same procedure as in Example 1 was used to obtain the foundry sand 2 of Example 2 shown in Table 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.

[0098] [Example 3] The foundry sand 3 of Example 3, as shown in Table 1, was obtained in the same manner as in Example 1, except that the stirring time in step (2) was changed from 60 minutes to 30 minutes. The surface roughness Sa1 of the obtained foundry sand 3 was 92.2 nm, and the surface roughness ratio Sa1 / Sa2 was 2.13.

[0099] [Example 4] The foundry sand 4 of Example 4 described in Table 1 was obtained in the same manner as in Example 1, except that the main blade rotation speed in steps (1) and (2) was changed from 230 rpm to 90 rpm. The surface roughness Sa1 of the obtained foundry sand 4 was 82.2 nm, and the surface roughness ratio Sa1 / Sa2 was 1.79.

[0100] [Example 5] Step (1): 100 parts by mass of recycled sand (A) was put into a mixing device (tabletop kneader PNV-1, manufactured by Irie Shoji Co., Ltd.), 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 at a main blade rotation speed of 60 rpm for 60 minutes from the start of heating. After that, the contents were discharged from the device and then cooled to room temperature to obtain refractory aggregate (foundry sand 5) with a first coating layer containing aluminosilicate of Example 5. The surface roughness Sa1 of the obtained foundry sand 5 was 82.3 nm, and the surface roughness ratio Sa1 / Sa2 was 2.06.

[0101] [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.

[0102] [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.

[0103] Table 1 shows the evaluation results of the foundry sand for Examples 1 to 5 and Comparative Examples 1 and 2.

[0104]

[0105] <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 of Example 6.

[0106] [Example 7] The 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. The 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.

[0107] [Example 8] Coated sand 3 of Example 8, 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 5.

[0108] [Comparative Example 3] Coated sand 4 of Comparative Example 3, 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 6.

[0109] [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.

[0110] [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.

[0111]

[0112] Table 3 shows the evaluation results of the coated sands for Examples 6-8 and Comparative Examples 3-5.

[0113]

Claims

1. 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.

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 or 2, wherein a silicate is present 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 any one of claims 1 to 3, 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, comprising: (1) a step of mixing a refractory aggregate having silicate on its surface with an aluminate; and (2) a step of 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. A method for producing foundry sand according to any one of claims 8 to 10, wherein in step (2) above, the material 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) comprises 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 or 14, wherein step (3) comprises step (3-2) of mixing the foundry sand with a solution containing water glass, caustic alkali, and water.

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