Coated Sand

Abstract

To provide coated sand that suppresses moisture formation and improves storage stability. [Solution] A coated sand comprising fire-resistant aggregate, a first coating layer formed on the fire-resistant aggregate, and a second coating layer formed on the first coating layer, The first coating layer contains a water-soluble organic compound that is solid at 25°C. Coated sand wherein the second coating layer contains metasilicate hydrate.

Description

Technical Field

[0001] The present invention relates to coated sand.

Background Art

[0002] As a mold used for casting of castings, for example, there is known one obtained by molding into a desired shape using coated sand having a refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate.

[0003] As the inorganic binder, it is known to use metasilicate hydrate or water glass mainly composed of sodium silicate.

[0004] Examples of the technology related to such coated sand include those described in Patent Document 1 and Patent Document 2.

[0005] Patent Document 1 describes an inorganic coated sand in a dry state having a refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate, wherein the inorganic binder layer contains crystallized metasilicate hydrate.

[0006] Patent Document 2 describes a dry inorganic coated sand in which the surface of a refractory aggregate is coated with a solid first coating layer containing an organic compound selected from a thermoplastic resin and a crosslinkable curable resin, and a solid second coating layer made of a binder composition containing an alkaline water-soluble inorganic binder is formed so as to cover the first coating layer. Further, it is disclosed that water glass is used as the alkaline water-soluble inorganic binder.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

[0008] Molds manufactured using coated sand are typically destroyed (crushed) and recovered after being used for casting, and then recycled through various methods to be reused 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.

[0009] However, it has been found that when dry coated sand is produced by using coated sand as described in Patent Document 1, recovering it, and then processing the recycled sand to form an inorganic binder layer containing metasilicate hydrate, the coated sand, which was dry immediately after production, may gradually become wet. When coated sand becomes wet, its fluidity at room temperature decreases, reducing its ability to fill molds during mold manufacturing, which may result in a decrease in the strength and quality of the mold.

[0010] Furthermore, it was found that even when dry coated sand is produced by forming an inorganic binder layer containing metasilicate hydrate on refractory aggregate with a relatively high degree of amorphousness, instead of recycled sand derived from coated sand as described in Patent Document 1, the coated sand, which is dry immediately after production, may gradually become wet.

[0011] Furthermore, since the coated sand described in Patent Document 2 uses water glass as an inorganic binder, the problem of the coated sand becoming wet does not arise in the first place.

[0012] The present invention aims to provide coated sand in which moisture formation is suppressed and storage stability is improved. [Means for solving the problem]

[0013] The present invention A coated sand comprising fire-resistant aggregate, a first coating layer formed on the fire-resistant aggregate, and a second coating layer formed on the first coating layer, The first coating layer contains a water-soluble organic compound that is solid at 25°C. The second coating layer is a coated sand containing metasilicate hydrate. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide coated sand that suppresses moisture formation and has excellent storage stability. [Modes for carrying out the invention]

[0015] <Coated Sand> The coated sand of this embodiment comprises a refractory aggregate, a first coating layer formed on the refractory aggregate, and a second coating layer formed on the first coating layer, wherein the first coating layer contains a water-soluble organic compound that is solid at 25°C, and the second coating layer contains a metasilicate hydrate. The coated sand of this embodiment has suppressed wetting and excellent storage stability.

[0016] The coated sand of this embodiment is preferably in a dry state that is fluid at room temperature. Dry coated sand refers to 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.

[0017] The dynamic angle of repose of coated sand can be measured by the following method. (Method for measuring dynamic angle of repose) Put coated sand equal to half of the volume into a cylindrical transparent plastic bottle (diameter: 7.7 cm, height: 16 cm), and using a bottle stirrer, hold the axis of the cylindrical transparent plastic bottle horizontally and rotate it around the horizontal axis at a rotational speed of 60 rpm. The slope of the coated sand layer flowing in the cylindrical transparent plastic bottle becomes a flat surface. Measure the angle formed between such a slope and the horizontal plane. In addition, when the coated sand does not flow in the cylindrical transparent plastic bottle or even if it flows, the slope of the coated sand layer is not formed as a flat surface, and as a result, the dynamic angle of repose cannot be measured, it is in a wet state.

[0018] The coated sand of this embodiment is preferably spherical from the viewpoint of improving fluidity and further enhancing the filling property into a molding die. Here, the coated sand being spherical means having a round shape like a ball.

[0019] The sphericity of the coated sand is preferably 0.75 or more, more preferably 0.80 or more, and even more preferably 0.82 or more from the viewpoints of improving fluidity, mold quality, and mold strength, and the ease of molding of the mold. Also, specifically, the upper limit value of the sphericity is 1.00.

[0020] Specifically, the sphericity of the coated sand coincides with the sphericity of the refractory aggregate described later.

[0021] The sphericity of the coated sand is obtained by image analysis of the image (photo) of the particles obtained by an optical microscope or a digital scope (for example, VH-8000 type manufactured by Keyence Corporation), obtaining the area of the particle projection cross-section of the particles and the perimeter of the cross-section, and then, sphericity = [circumference (mm) of a perfect circle with the same area as the area (mm 2 ) of the particle projection cross-section] / [perimeter (mm) of the particle projection cross-section], and for any 50 particles, the values obtained respectively can be averaged to obtain it.

[0022] 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.

[0023] The average particle size of the coated sand can be measured specifically by the following method. (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.

[0024] The following describes the various components of the coated sand according to this embodiment.

[0025] [Fire-resistant aggregate] The refractory aggregate is preferably recycled sand (A) having one or more silicates and silicate reactants selected from the surface, and / or refractory aggregate (B) having an amorphous degree of 20% or more. When coated sand is manufactured from such recycled sand (A) and / or refractory aggregate (B), the coated sand may gradually become wet. However, the wetting of the coated sand can be suppressed by incorporating a water-soluble compound that is solid at 25°C into the first coating layer formed on the recycled sand (A) and / or refractory aggregate (B). Therefore, using recycled sand and / or refractory aggregate (B) as the refractory aggregate is preferable in terms of demonstrating the effect of using a water-soluble compound that is solid at 25°C as the first coating layer. Furthermore, using recycled sand (A) is preferable from the viewpoint of reducing the amount of mold waste sand that is discarded, and using refractory aggregate (B) is preferable from the viewpoint of improving mold strength by making the surface of the aggregate smoother and obtaining low thermal expansion.

[0026] The aforementioned fire-resistant aggregate (B) may be one or more selected from the group consisting of natural sand and artificial sand.

[0027] Examples of the aforementioned natural sand include one or more types selected from the group consisting of silica sand, chromite sand, zircon sand, olivine sand, and alumina sand.

[0028] Examples of the aforementioned artificial sand include one or more types selected from the group consisting of synthetic mullite sand, SiO2-based sand with SiO2 as the main component, Al2O3-based sand with Al2O3 as the main component, SiO2 / Al2O3-based sand, SiO2 / MgO-based sand, SiO2 / Al2O3 / Al2O3-based ZrO2-based sand, SiO2 / Al2O3 / Fe2O3-based sand, and slag-derived sand. Here, the main component refers to the component that is most abundant by mass among the components contained in the sand. The aforementioned artificial sand refers to sand that is not naturally occurring sand, but rather sand that has been artificially prepared by preparing metal oxide components and then melting or sintering them.

[0029] The content of each component, such as SiO2, Al2O3, and Fe2O3, in the aforementioned fire-resistant aggregate can be measured using the following X-ray fluorescence method. [Method for measuring the components of the aforementioned refractory aggregate using fluorescent X-ray method] The refractory aggregate is adjusted to a size of approximately 0.1 μm or less using a vibratory mill and heated at 1050°C for 1 hour. Then, 5 g of lithium tetraborate and 0.5 g of refractory aggregate are mixed and heated at 1200°C for 10 minutes to melt, and then cooled to prepare a glassy sample (glass bead method). The sample can be analyzed using a ZSX Primus II X-ray fluorescence analyzer (manufactured by Rigaku Corporation) by X-ray fluorescence analysis using the fundamental parameter (FP) method to measure the components of the refractory aggregate.

[0030] The recycled sand (A) can be obtained by recycling a used casting mold or core formed from refractory aggregate and an inorganic binder containing silicate. 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 one or more selected from silicates and silicate reactants. Silicate reactants refer to dimers, trimers, polysilicates, and reactants formed by the reaction of silicates with metal oxides. Examples of cations constituting silicates include monovalent cations such as sodium, potassium, lithium, and ammonium, and divalent cations such as magnesium, calcium, and zinc.

[0031] The recycled sand (A) can be manufactured, for example, by the following method. [Method for manufacturing recycled sand (A)] Methods for recycling mold waste sand after casting using coated sand can be based on known methods (e.g., "Mold Making Method," 4th edition, Japan Foundry Technology Association, November 18, 1996, pp. 327-330). For example, methods such as dry polishing (mechanical wear), wet polishing, roasting, and combinations of these processes are known.

[0032] 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.

[0033] 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.

[0034] The aforementioned roasting process includes, for example, a method in which sand is continuously fed into a roasting furnace such as a fluidized bed furnace or a rotary kiln, and roasted at a temperature in the range of 200 to 1000°C.

[0035] Any method can be used for regeneration, but since wet processing and roasting processes are complicated and energy-intensive, dry polishing is preferred.

[0036] The sphericity of the refractory aggregate is the same as that of the coated sand. Specifically, 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 fluidity, mold quality, improved mold strength, and ease of mold formation. The upper limit of the sphericity is specifically 1.00. The method for measuring the sphericity of the refractory aggregate is the same as the method for measuring the sphericity of the coated sand.

[0037] The average particle size 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. Furthermore, if the average particle size of the refractory aggregate is above the above lower limit, it is preferable that the amount of the second coating layer used as a coating layer can be reduced during mold manufacturing, thus making it easier to regenerate the coated sand. The average particle size 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. Furthermore, if the average particle size of the refractory aggregate is below the above upper limit, it is preferable that the porosity is reduced during mold manufacturing, thereby increasing the mold strength. The method for measuring the average particle size of the refractory aggregate can be the same as the method for measuring the average particle size of the coated sand.

[0038] The degree of amorphousness of the refractory aggregate is preferably 20% or more, more preferably 30% or more, and even more preferably 40% or more, from the viewpoint of effectively improving storage stability, making the aggregate surface smoother and further improving mold strength, and obtaining low thermal expansion. There is no upper limit to the degree of amorphousness of the refractory aggregate, but for example it may be 100% or less, or 99% or less.

[0039] The degree of amorphousness of refractory aggregate can be measured by the following X-ray diffraction method. (X-ray diffraction method) Refractory aggregate is crushed in a mortar and pressed onto the X-ray glass holder of a powder X-ray diffractometer for measurement. The powder X-ray diffractometer used is a MultiFlex manufactured by Rigaku Denki Co., Ltd. (light source: CuKα rays, tube voltage: 40kV, tube current: 40mA), and measurements are performed in the range of 2θ = 5 to 90° with a scanning interval of 0.01°, a scanning speed of 2° / min, and slits DS1, SS1, and RS 0.3mm. In the range of 2θ = 10° to 50°, the X-ray intensities on the low and high angle sides are connected by straight lines, and the area below the line is defined as the background. The degree of crystallinity is determined using the software attached to the instrument, and subtracted from 100 to obtain the degree of amorphousness. Specifically, for the area above the background, amorphous peaks (halos) and each crystalline component are separated by curve fitting, the area of ​​each is determined, and the degree of amorphousness (%) is calculated using the following formula. Amorphization (%) = Area of ​​halo / (Area of ​​crystalline components + Area of ​​halo) × 100

[0040] There are various methods for controlling the degree of amorphousness of refractory aggregates, but generally, it is preferable to use a manufacturing method that rapidly cools the molten material. For example, there are methods such as melting the raw material and rapidly cooling it by blowing air through it, or processing it in a flame and then rapidly cooling it. In any case, the cooling method can be appropriately selected at various rates depending on the material and particle size. It is also conceivable to use a method of amorphousizing a material that has already crystallized through heat treatment and cooling treatment.

[0041] [First coating layer] The first coating layer is a layer formed on the refractory aggregate, preferably formed to cover the surface of the refractory aggregate. The first coating layer has the function of maintaining the crystalline structure of the metasilicate hydrate in the second coating layer while suppressing contact between the refractory aggregate and the second coating layer. The first coating layer is not limited to being continuous, and may have discontinuous regions in part. The first coating layer may be formed directly on the refractory aggregate, or there may be other layers between the refractory aggregate and the first coating layer.

[0042] The first coating layer contains a water-soluble organic compound that is solid at 25°C, from the viewpoint of maintaining the crystalline structure of the metasilicate hydrate in the second coating layer. A solid is defined as a substance that does not have fluidity. Water solubility means having a solubility of 2 g / 100 mL or more in water (20°C).

[0043] The aforementioned water-soluble organic compound preferably satisfies the following condition a. Condition a: Under conditions of 25°C and 55% RH, a water-soluble organic compound sieved through a 28-mesh sieve and sodium metasilicate nonahydrate are uniformly mixed in a weight ratio of 1:1. The resulting mixture is immediately poured into a 50 ml glass graduated cylinder (with markings) up to the 10 ml mark, and the opening of the graduated cylinder is then sealed with a glass lid and stored for 24 hours. The volume of the mixture before 24 hours of storage is V1 (cm³). 3 ) and the volume of the mixture after 24 hours of storage is V2(cm³). 3 When this is the case, the rate of change in volume calculated from the following formula (1) is preferably 10% or less. [(V1-V2) / V1] × 100 (1) (Volume change rate) The volume change rate is preferably 10.0% or less, more preferably 7.0% or less, even more preferably 5.0% or less, even more preferably 3.0% or less, even more preferably 1.0% or less, and even more preferably 0.1% or less, from the viewpoint of further improving storage stability. (Regarding condition a) Under conditions of 25°C and 55% RH, both the water-soluble organic compound and sodium metasilicate nonahydrate are solid. Under condition a, the shape of the water-soluble organic compound and sodium metasilicate nonahydrate is not particularly limited, but is granular or powdery. The size of the organic compound and sodium metasilicate nonahydrate is 28 mesh or less.

[0044] In condition a, the mixing of the water-soluble organic compound and sodium metasilicate nonahydrate can be done using known methods, and to ensure uniformity, for example, the organic compound and sodium metasilicate nonahydrate in a sealed container may be shaken in a vortex mixer for 30 seconds or more.

[0045] In condition a above, the volumes V1 and V2 of the mixture shall be determined by using the markings on a 50 ml capacity glass graduated cylinder, and the volume obtained from the height of the top surface of the mixture shall be considered the volume of the mixture. If the top surface of the mixture is not flat, the highest point shall be considered the height of the mixture.

[0046] Furthermore, under condition a, each operation is carried out smoothly so that the sodium metasilicate nonahydrate and the water-soluble organic compound do not react.

[0047] From the viewpoint of availability and handling, the aforementioned water-soluble organic compound may be one or more selected from glycols, celluloses, polycarboxylic acids and their salts, with glycols being preferred.

[0048] Examples of the aforementioned glycols include polyethylene glycol, polypropylene glycol, polyoxyethylene glycol monoether, polypropylene glycol monoether, and polyoxyethylene propylene glycol monoether.

[0049] Examples of the aforementioned celluloses include hydroxyalkyl cellulose such as hydroxymethylcellulose, hydroxyethylcellulose, and hydroxypropylcellulose; and carboxyalkyl cellulose such as carboxymethylcellulose, carboxyethylcellulose, and carboxypropylcellulose.

[0050] Examples of polycarboxylic acids or their salts include polyacrylic acid, which may be either linear polyacrylic acid or crosslinked polyacrylic acid obtained by crosslinking linear polyacrylic acid. Examples of polyacrylate salts include metal salts of polyacrylic acid such as sodium polyacrylate and potassium polyacrylate; amine salts of polyacrylate such as polyacrylate monoethanolamine, polyacrylate diethanolamine, and polyacrylate triethanolamine; and ammonium polyacrylate salts.

[0051] The weight-average molecular weight (Mw) of the water-soluble organic compound is preferably 1,000 or more, more preferably 2,000 or more, and even more preferably 5,000 or more, from the viewpoint of improving storage stability. The weight-average molecular weight (Mw) of the water-soluble organic compound is preferably 5,000,000 or less, more preferably 1,000,000 or less, and even more preferably 800,000 or less, from the viewpoint of improving storage stability while also ensuring good handling. The weight-average molecular weight of the water-soluble organic compound is measured by gel permeation chromatography (GPC) analysis.

[0052] The content of the first coating layer is preferably 0.05 parts by mass or more, more preferably 0.07 parts by mass or more, even more preferably 0.10 parts by mass or more, and even more preferably 0.20 parts by mass or more, per 100.00 parts by mass of refractory aggregate, in order to suppress moisture formation and improve storage stability. The content of the first coating layer is preferably 5.00 parts by mass or less, more preferably 2.00 parts by mass or less, even more preferably 1.50 parts by mass or less, even more preferably 1.20% by mass or less, and even more preferably 1.00 part by mass or less, per 100.00 parts by mass of refractory aggregate, in order to maintain good storage stability while improving productivity and mold strength.

[0053] [Second coating layer (inorganic binder layer)] The second coating layer is a layer formed on the first coating layer, and is preferably formed to cover the surface of the first coating layer in order to effectively suppress moisture formation. The second coating layer is also called an inorganic binder 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.

[0054] 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.

[0055] 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.

[0056] The cations constituting the metasilicate salt contained in the metasilicate hydrate include monovalent cations such as sodium, potassium, lithium, and ammonium, and divalent cations such as magnesium, calcium, and zinc. Specific examples of the metasilicate include sodium metasilicate and potassium metasilicate, with sodium metasilicate being preferred among these.

[0057] The aforementioned metasilicate hydrate can be produced using a mixture of water glass, caustic alkali, and water in specific ratios. Furthermore, the SiO2 / Na2O molar ratio of the metasilicate hydrate is 0.9 to 1.1.

[0058] The water glass used in the production of the aforementioned metasilicate hydrate can be specifically one or more types selected from the group consisting of sodium silicate no. 1 to 5. Here, sodium silicate is classified into no. 1 to 5 according to the molar ratio of SiO2 / Na2O, and sodium silicate no. 1 to 3 are specified in JIS-K-1408. The molar ratios of SiO2 / Na2O for each no. are specifically as follows. Sodium silicate No. 1: Molar ratio of SiO2 / Na2O = 2.0~2.3 Sodium silicate No. 2: Molar ratio of SiO2 / Na2O = 2.4~2.6 Sodium silicate No. 3: Molar ratio of SiO2 / Na2O = 2.8~3.3 Sodium silicate No. 4: Molar ratio of SiO2 / Na2O = 3.3~3.5 Sodium silicate No. 5: Molar ratio of SiO2 / Na2O = 3.6~3.8

[0059] Furthermore, the molar ratio of SiO2 / Na2O may be adjusted to a desired extent by mixing two or more types of sodium silicate. The water glass used in the production of the metasilicate hydrate is preferably at least one selected from sodium silicate No. 1 and sodium silicate No. 2.

[0060] 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.

[0061] 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.

[0062] 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 method described below to confirm that it is metasilicate hydrate.

[0063] [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 of hydration of metasilicate hydrate = [(A) / molecular weight of water] / [(B) / molecular weight of anhydrous metasilicate]

[0064] (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, moisture resistance improvers, coupling agents that strengthen the bond between the refractory aggregate and the inorganic binder composition, lubricants, surfactants, mold release agents, etc.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] The coupling agent is not limited to these, but examples include silane coupling agents, zircon coupling agents, and titanium coupling agents.

[0069] Examples of moisture-resistant agents include metal oxides (excluding those listed above), carbonates, borates, sulfates, and phosphates.

[0070] 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.

[0071] 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.

[0072] <Method for manufacturing coated sand> The manufacturing method of this embodiment is a method for manufacturing coated sand, comprising the steps of: (1) mixing the refractory aggregate with the water-soluble organic compound to form a first coating layer containing the water-soluble organic compound on the refractory aggregate; and (2) mixing the refractory aggregate on which the first coating layer has been formed with a metasilicate hydrate to form a second coating layer containing the metasilicate hydrate on the first coating layer.

[0073] [Step (1)] In step (1) described above, the method for mixing the refractory aggregate and the water-soluble organic compound to form a first coating layer containing the water-soluble organic compound on the refractory aggregate is not particularly limited, and known methods can be applied depending on the type of water-soluble organic compound. For example, a first coating layer containing the water-soluble organic compound can be formed on the refractory aggregate by mixing the heated and melted liquid water-soluble organic compound with the refractory aggregate in a known manner. Alternatively, for example, a first coating layer containing the water-soluble organic compound can be formed on the refractory aggregate by mixing a water-soluble organic compound solution, obtained by dissolving the water-soluble organic compound in a solvent such as water, with the refractory aggregate in a known manner to obtain a mixture, and then drying the mixture.

[0074] In step (1) above, the mixing conditions for the refractory aggregate and the water-soluble organic compound or the water-soluble organic compound solution can be, for example, a temperature of 15 to 150°C, a time of 1 to 10 minutes, and a rotation speed of the stirring blades of the mixer used for mixing of 30 to 3000 rpm. [Step (2)] In step (2) above, the method for mixing the refractory aggregate on which the first coating layer has been formed with the metasilicate hydrate to form a second coating layer containing the metasilicate hydrate on the first coating layer is not particularly limited. For example, the refractory aggregate on which the first coating layer has been formed with the heated and melted metasilicate hydrate can be mixed in a known manner to obtain a mixture, and then the mixture can be cooled to a temperature below the melting point of the metasilicate hydrate to form a second coating layer containing the metasilicate hydrate on the first coating layer.

[0075] In step (2) above, the mixing temperature is preferably 80°C or lower, more preferably 70°C or lower, and even more preferably 60°C or lower, from the viewpoint of increasing the fluidity of the coated sand, and even more preferably 40°C or lower, from the viewpoint of being able to mix at room temperature. Also, in step (2) above, the mixing temperature is preferably above the melting point of the metasilicate hydrate, from the viewpoint of supplying metasilicate to the refractory aggregate and increasing the fluidity of the coated sand. Note that the mixing temperature may be measured as the temperature of the mixture of the refractory aggregate and the metasilicate hydrate.

[0076] In step (2) above, the amount of metasilicate hydrate to be mixed is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, even 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 the refractory aggregate, from the viewpoint of obtaining a high-strength casting mold. In step (2) above, the amount of metasilicate hydrate to be mixed 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 the refractory aggregate, from the viewpoint of obtaining a high-strength casting mold.

[0077] <Casting molds> The casting mold of this embodiment is formed using the coated sand as the material.

[0078] <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, and a molding method in which steam is further passed through a heated molding die and then hot air is passed through it. [Examples]

[0079] The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited thereto.

[0080] <Evaluation Method> [Method for measuring the degree of amorphousness of fire-resistant aggregates] [X-ray diffraction method] Refractory aggregate was crushed in a mortar and pestle, pressed onto the X-ray glass holder of a powder X-ray diffractometer, and measured. A MultiFlex powder X-ray diffractometer manufactured by Rigaku Denki Co., Ltd. (light source: CuKα rays, tube voltage: 40kV, tube current: 40mA) was used, and measurements were performed in the range of 2θ = 5 to 90° with a scanning interval of 0.01°, a scanning speed of 2° / min, and slits DS1, SS1, and RS 0.3mm. In the range of 2θ = 10° to 50°, the X-ray intensities on the low and high angle sides were connected by straight lines, and the area below the straight line was defined as the background. The degree of crystallinity was determined using the software attached to the instrument, and the degree of amorphousness was obtained by subtracting it from 100. Specifically, for the area above the background, amorphous peaks (halos) and each crystalline component were separated by curve fitting, the area of ​​each was determined, and the degree of amorphousness (%) was calculated using the following formula. Amorphization (%) = Area of ​​halo / (Area of ​​crystalline components + Area of ​​halo) × 100

[0081] [Evaluation of water-soluble organic compounds (calculation of volume change rate)] In a constant temperature and humidity chamber at 25°C and 55% RH, 10 g of an organic compound, whose particle size was adjusted using a mortar and pestle to pass through a 28-mesh sieve, and 10 g of sodium metasilicate noctahydrate were filled into a 100 ml polypropylene (PP) screw bottle. The bottle was then sealed and uniformly mixed using a vortex mixer (Touch Mixer (MT-31), manufactured by Yamato Scientific Co., Ltd.) for 1 minute. The resulting mixture was then immediately poured into a 50 ml glass graduated cylinder (with markings) to the 10 ml mark. The graduated cylinder was tapped five times during pouring to ensure the mixture was densely packed. The graduated cylinder was then sealed with a glass lid and stored for 24 hours. The volume of the mixture before it is placed in a graduated cylinder and sealed for 24 hours is V1(cm³). 3 )(10cm 3 ), the volume of the mixture after 24 hours of sealed storage is V2(cm³). 3 The volume change rate was calculated using the following formula (1) to evaluate the water-soluble organic compounds. [(V1-V2) / V1] × 100 (1) The volume of the mixture was calculated from the height of the top surface of the mixture. If the top surface of the mixture was not flat, the highest point was measured and the volume was calculated from that.

[0082] [Evaluation of storage stability (measurement of time until moisture occurs)] Immediately after preparing the coated sand, the dynamic angle of repose of the coated sand was measured using the following procedure (i). Separately, immediately after preparing the coated sand, 2 kg of the coated sand was placed in a sealed plastic bag and left in a constant temperature room at 25°C / 55%RH. The dynamic angle of repose of the coated sand was measured every 24 hours using the following procedure (i), and the state of the coated sand (dry or wet) was confirmed using the following procedure (ii). If the coated sand was wet, the time from when it was placed in the plastic bag until it became wet was defined as "time to become wet" (days). (i) Procedure (Measurement of dynamic angle of repose) Half of 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. The bottle was held with its axis horizontal and rotated around the horizontal axis at room temperature (25°C) and a speed of 60 rpm. The angle (dynamic angle of repose) formed between the slope of the flowing coated sand layer inside the cylinder and the horizontal plane was measured once the slope became flat. (ii) Confirmation (determination of whether it is dry or wet) In the procedure described above, the case where the angle could be measured was defined as "dry state," and the case where the coated sand did not flow within the cylinder, or even if it did flow, 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 was defined as "wet state."

[0083] <Material> [Fire-resistant aggregate] • Recycled sand (A1): Prepared using the following method. [Method for producing recycled sand (A1)] (1) Preparation of coated sand 100 parts by mass of refractory aggregate (Espearl #60L, manufactured by Yamakawa Sangyo Co., Ltd., average particle size: 241 μm) was added to a stirrer as a refractory aggregate. Next, 2.00 parts by mass of sodium metasilicate nonahydrate, which had been heated to 80°C and melted, was added to the stirrer and kneaded for 4 minutes. Then, amorphous silica fine particles (0.6 parts by mass) were added and kneaded for 2 minutes to obtain dry coated sand to be used in the production of recycled sand (A1). (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 180°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 After casting, the casting was removed from the test mold, the test mold was crushed using a hammer or similar tool, and the recovered sand was obtained by further crushing it using a mini crusher (manufactured by Kiyota Casting Co., Ltd.). (5) Production of recycled sand 100 kg of recovered sand 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 batch processed at a rotor speed of 2400 rpm for 60 minutes to obtain recycled sand (A1). • Refractory aggregate (B1): Spherical fused silica (produced by spheroidizing natural silica sand using a flame melting method; average particle size: 200 μm; degree of amorphism: >95%) • Refractory aggregate (B2): Naigai Cerabeads 60 #650 (Mullite-based sintered artificial sand manufactured by Itochu Ceratec Co., Ltd., average particle size: 200 μm, amorphity: 30%)

[0084] [Organic compounds] • Organic compound 1: Polyethylene glycol ("Polyethylene Glycol 6,000," manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., weight-average molecular weight 7,300-9,300, solid at 25°C, water-soluble organic compound with a solubility of 2 g / 100 mL or more in water (20°C)). • Organic compound 2: Polyethylene glycol ("Polyethylene glycol 500,000," manufactured by Fujifilm & Wako Pure Chemical Industries, Ltd., weight-average molecular weight approximately 500,000, solid at 25°C, water-soluble organic compound with a solubility of 2 g / 100 mL or more in water (20°C)) • Organic compound 3: Polyacrylic acid ("Polyacrylic acid 5,000," manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., weight-average molecular weight approximately 5,000, solid at 25°C, a water-soluble organic compound with a solubility of 2 g / 100 mL or more in water (20°C)). • Organic compound 4: Hydroxypropylcellulose ("NISSO HPC-SSL", manufactured by Nippon Soda Co., Ltd., weight-average molecular weight 40,000, solid at 25°C, water-soluble organic compound with a solubility of 2g / 100mL or more in water (20°C)) • Organic compound 5: Novolac-type phenolic resin ("TD-2090," manufactured by DIC Corporation), solid at 25°C, a water-insoluble organic compound with a solubility of less than 2 g / 100 mL in water (20°C).

[0085] Organic compounds 1-4 and water were mixed using a magnetic stirrer in the proportions (parts by mass) shown in Table 1 to prepare coating solutions 1-4.

[0086] [Table 1]

[0087] [Inorganic binders] • Sodium metasilicate nonahydrate: Sodium metasilicate (nonahydrate) Na2SiO3·9H2O (manufactured by Nippon Chemical Industrial Co., Ltd., Na2SiO3·9H2O, melting point: 47℃, SiO2 / Na2O ratio = 0.9~1.1)

[0088] <Examples> [Example 1] 100.00 parts by mass of recycled sand (A1) at room temperature was placed in a stirrer. Next, 0.25 parts by mass of coating liquid 1 was added to the stirrer and mixed for 5 minutes to obtain dry refractory aggregate coated with a first coating layer containing organic compound 1. Next, 2.00 parts by mass of sodium metasilicate nonahydrate, which had been heated to 80°C and melted, was placed in the stirrer and mixed for 4 minutes to obtain dry coated sand that was fluid at room temperature.

[0089] [Example 2] Coated sand was prepared in the same manner as in Example 1, except that the amount of coating solution 1 added was 1.25 parts by mass.

[0090] [Example 3] Coated sand was prepared in the same manner as in Example 1, except that the amount of coating solution 1 added was 2.50 parts by mass.

[0091] [Example 4] 100.00 parts by mass of recycled sand (A1) heated to 105°C were placed in a stirrer. Next, 0.25 parts by mass of coating liquid 2 were added to the stirrer and mixed for 5 minutes to obtain dry refractory aggregate coated with a first coating layer containing organic compound 2. After that, the refractory aggregate was allowed to cool naturally in the stirrer until it reached room temperature. Then, 2.00 parts by mass of sodium metasilicate nonahydrate, which had been heated to 80°C and melted, was added to the stirrer and mixed for 4 minutes to obtain dry coated sand that was fluid at room temperature.

[0092] [Example 5] Coated sand was prepared in the same manner as in Example 1, except that coating solution 3 was used instead of coating solution 1.

[0093] [Example 6] Coated sand was prepared in the same manner as in Example 1, except that coating solution 4 was used instead of coating solution 1.

[0094] [Example 7] Coated sand was prepared in the same manner as in Example 1, except that fire-resistant aggregate (B1) was used as the fire-resistant aggregate in Table 2.

[0095] [Example 8] Coated sand was prepared in the same manner as in Example 1, except that fire-resistant aggregate (B2) was used as the fire-resistant aggregate shown in Table 2.

[0096] <Comparative Example> [Comparative Examples 1-3] Coated sand was obtained in the same manner as in Example 1, except that the fire-resistant aggregates shown in Table 2 were used and a first coating layer made of organic compounds was not formed.

[0097] [Comparative Example 4] 100.00 parts by mass of recycled sand (A1) heated to 200°C were placed in a stirrer. Next, 0.10 parts by mass of organic compound 5 were added to the stirrer and mixed for 10 minutes to obtain dry refractory aggregate coated with a first coating layer containing organic compound 5. After that, the refractory aggregate was allowed to cool naturally in the stirrer until it reached room temperature. Then, 2.00 parts by mass of sodium metasilicate nonahydrate, which had been heated to 80°C and melted, was added to the stirrer and mixed for 4 minutes to obtain dry coated sand that was fluid at room temperature.

[0098] The evaluation results are shown in Table 2.

[0099] [Table 2]

Claims

1. A coated sand comprising fire-resistant aggregate, a first coating layer formed on the fire-resistant aggregate, and a second coating layer formed on the first coating layer, The first coating layer contains a water-soluble organic compound that is solid at 25°C. Coated sand wherein the second coating layer contains metasilicate hydrate.

2. The coated sand according to claim 1, wherein the refractory aggregate is recycled sand (A) having one or more selected from silicates and silicate reactants on its surface, and / or refractory aggregate (B) having an amorphous degree of 20% or more.

3. The coated sand according to claim 1, wherein the water-soluble organic compound is one or more selected from glycols, celluloses, polycarboxylic acids, and salts of polycarboxylic acids.

4. The coated sand according to claim 1, wherein the weight-average molecular weight (Mw) of the water-soluble organic compound is 1,000 or more and 5,000,000 or less.

5. The coated sand according to claim 1, wherein the content of the first coating layer in the coated sand is 0.05 parts by mass or more and 5.00 parts by mass or less with respect to 100.00 parts by mass of the fire-resistant aggregate.

6. The coated sand according to claim 1, wherein the content of the second coating layer in the coated sand is 0.10 parts by mass or more and 15.00 parts by mass or less per 100.00 parts by mass of the fire-resistant aggregate.

7. A method for producing coated sand according to any one of claims 1 to 6, Step (1) involves mixing the fire-resistant aggregate with the water-soluble organic compound to form a first coating layer containing the water-soluble organic compound on the fire-resistant aggregate, Step (2) is to mix the fire-resistant aggregate on which the first coating layer is formed with a metasilicate hydrate to form a second coating layer containing the metasilicate hydrate on the first coating layer, A method for manufacturing coated sandwiches, including [the specified ingredient].

8. A casting mold formed using coated sand as a material according to any one of claims 1 to 6.

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