Coated Sand Manufacturing Method

Abstract

To provide a method for producing dry coated sand that can manufacture molds with excellent mold strength and surface strength. [Solution] A method for producing dry coated sand, comprising the step (1) of mixing water with refractory aggregate A having an inorganic binder layer formed on its surface containing an inorganic binder containing a metasilicate hydrate, A method for producing coated sand, wherein the mass ratio of the inorganic binder water (a component of the inorganic binder other than water) to the water in the coated sand (mass of water in the coated sand / mass of the inorganic binder water) is 1.00 to 1.60.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing coated sand.

Background Art

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

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When casting is performed using a mold manufactured using conventional dry inorganic coated sand, sand derived from the mold may adhere to the surface of the casting, which is the casting product, and may adversely affect the quality of the casting. Therefore, it has been found that there is room for improvement in the strength and surface strength of molds manufactured using conventional dry inorganic coated sand.

[0005] An object of the present invention is to provide a method for manufacturing dry coated sand that can produce a mold excellent in mold strength and surface strength.

Means for Solving the Problems

[0006] The present invention is a method for manufacturing dry coated sand having a step (1) of mixing a refractory aggregate A having an inorganic binder layer containing a metasilicate hydrate formed on the surface thereof with water. The ratio of the amount of water removed from the inorganic binder (a component of the inorganic binder other than water) to the amount of water in the coated sand (mass of water in the coated sand / mass of the amount of water removed from the inorganic binder) is between 1.00 and 1.60. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a method for producing dry coated sand that can manufacture molds with excellent mold strength and surface strength. [Brief explanation of the drawing]

[0008] [Figure 1] A photograph serving as a drawing, showing one cross-section of the mold used for evaluating sand-filling properties. [Modes for carrying out the invention]

[0009] <Method for manufacturing coated sand> The method for manufacturing coated sand according to this embodiment is: A method for producing dry coated sand, comprising the step (1) of mixing water with refractory aggregate A having an inorganic binder layer formed on its surface containing an inorganic binder containing a metasilicate hydrate, The mass ratio of the inorganic binder's water content (a component of the inorganic binder other than water) to the water content in the coated sand (mass of water in the coated sand / mass of the inorganic binder's water content) is 1.00 to 1.60. According to the method for manufacturing coated sand of this embodiment, it is possible to manufacture a dry coated sand that produces a mold with excellent mold strength and surface strength. The reason why the coated sand of this embodiment exhibits such effects is not clear, but it is presumed to be as follows.

[0010] When coated sand is filled into a mold, the mold is heated and hardened. However, because the heating rate is high near the mold, the inorganic binder hardens quickly. Condensation water generated during the hardening of the inorganic binder remains as bubbles in the hardened inorganic binder, which is thought to reduce the mold strength and surface strength. The dry coated sand produced by the manufacturing method of this embodiment contains a certain amount of water, which reduces the viscosity of the heated inorganic binder and lowers the hardening rate of the inorganic binder. This suppresses the generation of bubbles in the hardened inorganic binder due to the condensation water, and is thought to enable the production of molds with excellent mold strength and surface strength.

[0011] [Coated Sandwich] The coated sand produced by the manufacturing method of this embodiment is in a dry state. Dry coated sand refers to coated sand from which a measurement value can be obtained when measuring the dynamic angle of repose regardless of the moisture content. The dynamic angle of repose of coated sand can be measured by the method described in the examples.

[0012] [Fire-resistant aggregate A] The aforementioned fire-resistant aggregate A is a fire-resistant aggregate having an inorganic binder layer formed on its surface containing an inorganic binder containing a metasilicate hydrate. In this specification, "fire-resistant aggregate having an inorganic binder layer formed on its surface containing an inorganic binder containing a metasilicate hydrate" is referred to as "fire-resistant aggregate A," and "fire-resistant aggregate" means fire-resistant aggregate that does not have the inorganic binder on its surface, that is, the fire-resistant aggregate itself.

[0013] (Fireproof aggregate) The aforementioned fire-resistant aggregate may be one or more selected from the group consisting of natural sand and artificial sand.

[0014] 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.

[0015] Examples of the artificial sand include one or more selected from the group consisting of synthetic mullite sand, SiO2-based sand mainly composed of SiO2, Al2O3-based sand mainly composed of Al2O3, SiO2 / Al2O3-based sand, SiO2 / MgO-based sand, SiO2 / Al2O3 / ZrO2-based sand, SiO2 / Al2O3 / Fe2O3-based sand, and slag-derived sand. Here, the main component refers to the component with the largest mass among the components contained in the sand. The artificial sand refers to sand that is not naturally produced but is artificially prepared with metal oxide components and melted or sintered.

[0016] The refractory aggregate may be recovered sand recovered from a used mold, recycled sand obtained by subjecting the recovered sand to a recycling process, or the like.

[0017] From the viewpoint of improving the fluidity of the coated sand according to the present embodiment and enhancing the filling property into the molding die, the refractory aggregate is preferably particulate. From the viewpoint of further improving the fluidity of the coated sand according to the present embodiment and enhancing the filling property into the die, the sphericity of the refractory aggregate is preferably 0.80 or more, more preferably 0.85 or more. The sphericity of the coated sand and the refractory aggregate according to the present embodiment can be measured, for example, by the following method.

[0018] (Method for Measuring Sphericity of Coated Sand and Refractory Aggregate) The sphericity of the coated sand and the refractory aggregate 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) to determine the area of the particle projection cross-section of the particle and the perimeter of the cross-section. Then, [circumference (mm) of a perfect circle with the same area as the area of the particle projection cross-section (mm 2 )] / [perimeter (mm) of the particle projection cross-section] is calculated, and for any 50 particles, the obtained values can be averaged and determined.

[0019] From the viewpoints of improving the mold quality and the strength of the mold, and the ease of molding the mold, the average particle diameter of the refractory aggregate is preferably 0.05 mm or more, more preferably 0.10 mm or more, and from the same viewpoints, it is preferably 2.00 mm or less, more preferably 1.00 mm or less, and even more preferably 0.50 mm or less. The coated sand according to the present embodiment and the average particle diameter of the refractory aggregate can be measured, for example, by the following method.

[0020] (Method for Measuring the Average Particle Diameter of Coated Sand and Refractory Aggregate) 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 long-axis diameter (mm) and the short-axis diameter (mm) of the randomly oriented particles are measured, and (long-axis diameter + short-axis diameter) / 2 is obtained. For any 100 particles, the values obtained are averaged to obtain the average particle diameter (mm). The long-axis diameter and the short-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 at which the distance between the parallel lines is minimized is called the short-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 long-axis diameter. The long-axis diameter and the short-axis diameter of the particle can be obtained by taking a photograph (image) of the particle with an optical microscope or a digital microscope (for example, VH-8000 type manufactured by Keyence Corporation) and performing image analysis on the obtained image.

[0021] (Inorganic Binder Layer) The inorganic binder layer is formed on the surface of the refractory aggregate. It is preferable that the entire refractory aggregate is covered by the inorganic binder layer, but there may be a portion that is not covered. The inorganic binder layer contains an inorganic binder containing metasilicate hydrate.

[0022] As for the metasilicate hydrate, from the viewpoint of using the coated sand in a dry state and improving fluidity at room temperature, at least one selected from metasilicate pentahydrate and metasilicate notahydrate is preferred, a mixture of metasilicate notahydrate and metasilicate pentahydrate is more preferred, and metasilicate pentahydrate is even more preferred.

[0023] 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.

[0024] The method for forming the inorganic binder layer on the surface of the refractory aggregate is not particularly limited, and known methods can be applied depending on the type of inorganic binder. For example, the refractory aggregate and a heated and melted metasilicate hydrate can be mixed by a known method to obtain a mixture, and then the mixture can be cooled to a temperature below the melting point of the metasilicate hydrate to form an inorganic binder layer containing metasilicate hydrate on the surface of the refractory aggregate.

[0025] [Other ingredients] The refractory aggregate A may contain other additives as needed, in addition to the components described above. Examples of other additives include humectants, moisture-resistant agents, coupling agents that strengthen the bond between the refractory aggregate and the inorganic binder, lubricants, surfactants, and release agents.

[0026] Examples of the aforementioned humectants include polyhydric alcohols, water-soluble polymers, hydrocarbons, sugars, proteins, and inorganic compounds such as sodium chloride, calcium chloride, and magnesium chloride.

[0027] Examples of moisture-resistant improvers include carbonates, borates, sulfates, and phosphates. Specific examples of carbonates include zinc carbonate, basic zinc carbonate, iron carbonate, manganese carbonate, copper carbonate, aluminum carbonate, barium carbonate, magnesium carbonate, calcium carbonate, lithium carbonate, potassium carbonate, and sodium carbonate. Specific examples of borates include sodium tetraborate, potassium tetraborate, lithium tetraborate, ammonium tetraborate, calcium tetraborate, strontium tetraborate, silver tetraborate, sodium metaborate, potassium metaborate, lithium metaborate, ammonium metaborate, calcium metaborate, silver metaborate, copper metaborate, lead metaborate, and magnesium metaborate. Specific examples of sulfates include sodium sulfate, potassium sulfate, lithium sulfate, magnesium sulfate, calcium sulfate, strontium sulfate, barium sulfate, titanium sulfate, aluminum sulfate, zinc sulfate, and copper sulfate. Specific examples of phosphates include sodium phosphate, sodium hydrogen phosphate, potassium phosphate, potassium hydrogen phosphate, lithium phosphate, lithium hydrogen phosphate, magnesium phosphate, calcium phosphate, titanium phosphate, aluminum phosphate, and zinc phosphate.

[0028] Examples of the coupling agents include silane coupling agents, zircon coupling agents, and titanium coupling agents.

[0029] Examples of the lubricants include waxes; fatty acid amides such as ethylenebisstearate amide; 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.

[0030] Examples of the aforementioned surfactants include cationic surfactants, anionic surfactants, amphoteric surfactants, nonionic surfactants, and silicone-based surfactants.

[0031] Examples of the mold release agent include paraffin, wax, fatty acid ester, organic acid, graphite fine particles, mica, vermiculite, fluorine-based mold release agents, silicone-based mold release agents, and the like.

[0032] The sphericity of the refractory aggregate A is preferably 0.75 or higher, more preferably 0.80 or higher, and even more preferably 0.82 or higher, from the viewpoint of improving the quality of the mold, improving the strength of the mold, and improving the moldability of the mold. The sphericity of the refractory aggregate A is 1 or less.

[0033] The sphericity of the aforementioned fire-resistant aggregate A can be determined by performing image analysis on 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 said cross-section. Then, the formula [circumference of a perfect circle with the same area as the area of ​​the particle projection cross-section (mm2) (mm)] / [perimeter of the particle projection cross-section (mm)] is calculated, and the average of the obtained values ​​for any 50 particles is used to determine the sphericity.

[0034] The average particle size of the refractory aggregate A is preferably 0.05 mm or more, more preferably 0.10 mm or more, from the viewpoint of improving the quality of the mold, improving the strength of the mold, and improving the moldability of the mold. The average particle size of the refractory aggregate A is preferably 2.00 mm or less, more preferably 1.00 mm or less, and even more preferably 0.50 mm or less, from the viewpoint of improving the quality of the mold, improving the strength of the mold, and improving the moldability of the mold.

[0035] In this specification, the content of the inorganic binder refers to the content of components other than water in the inorganic binder. For example, when sodium metasilicate hydrate is used as the inorganic binder, the content is determined by converting it to sodium metasilicate. In this specification, the components other than water in the inorganic binder may also be referred to as "inorganic binder water". In this specification, "metasilicate" refers to the components other than water in metasilicate hydrate.

[0036] The content of metasilicate in the inorganic binder water remover 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 the strength of the mold, improving productivity, and availability. In this specification, "substantially" means that it may contain trace amounts of components that are unintentionally present.

[0037] The content of the inorganic binder water removed in the inorganic binder layer is preferably 30% by mass or more, more preferably 35% by mass or more, even more preferably 40% by mass or more, and even more preferably 45% by mass or more, relative to the total components other than water in the inorganic binder layer, from the viewpoint of improving the strength of the mold and improving the surface stability of the mold. The content of the inorganic binder water removed in the inorganic binder layer is preferably 90% by mass or less, more preferably 85% by mass or less, even more preferably 80% by mass or less, even more preferably 75% by mass or less, and even more preferably 70% by mass or less, relative to the total components other than water in the inorganic binder layer, from the viewpoint of effectively suppressing sand adhesion to the casting.

[0038] The content of the inorganic binder water removed in the coated sand is preferably 0.03% by mass or more, more preferably 0.10% by mass or more, even more preferably 0.50% by mass or more, even more preferably 0.80% by mass or more, and even more preferably 1.00% by mass or more, from the viewpoint of improving the strength of the mold and improving the surface shape of the mold. The content of the inorganic binder water removed in the coated sand is preferably 5.00% by mass or less, more preferably 4.00% by mass or less, even more preferably 3.00% by mass or less, and even more preferably 2.00% by mass or less, from the viewpoint of improving the fillability into the molding die.

[0039] The content of the metasilicate in the coated sand is preferably 0.03% by mass or more, more preferably 0.10% by mass or more, even more preferably 0.50% by mass or more, even more preferably 0.80% by mass or more, and even more preferably 1.00% by mass or more, from the viewpoint of improving the strength of the mold and improving the surface shape of the mold. The content of the metasilicate in the coated sand according to this embodiment is preferably 5.00% by mass or less, more preferably 4.00% by mass or less, even more preferably 3.00% by mass or less, and even more preferably 2.00% by mass or less, from the viewpoint of improving the fillability into the molding die.

[0040] The water content in the coated sand is preferably 0.50% by mass or more, more preferably 0.80% by mass or more, even more preferably 0.10% by mass or more, even more preferably 1.20% by mass or more, and even more preferably 1.40% by mass or more, from the viewpoint of improving the strength of the mold and improving the surface shape of the mold. The metasilicate content in the coated sand according to this embodiment is preferably 5.00% by mass or less, more preferably 4.00% by mass or less, even more preferably 3.00% by mass or less, even more preferably 2.50% by mass or less, and even more preferably 2.30% by mass or less, from the viewpoint of improving the fillability into the molding die.

[0041] The mass ratio of the amount of water removed from the inorganic binder in the coated sand to the mass of water in the coated sand (mass of water in the coated sand / mass of water removed from the inorganic binder) is 1.00 or more, preferably 1.05 or more, more preferably 1.10 or more, even more preferably 1.15 or more, even more preferably 1.20 or more, and even more preferably 1.25 or more, from the viewpoint of improving the strength of the mold and improving the surface shape of the mold, and 1.60 or less, preferably 1.55 or less, more preferably 1.50 or less, even more preferably 1.45 or less, and even more preferably 1.40 or less, from the viewpoint of improving the fillability into the molding die.

[0042] [Inorganic fine particles] The coated sand preferably contains inorganic fine particles from the viewpoint of improving the strength of the mold, and the inorganic fine particles preferably contain amorphous silica particles from the same viewpoint. The coated sand preferably has the inorganic fine particles on the inorganic binder layer from the viewpoint of improving the strength of the mold. The inorganic fine particles on the inorganic binder layer may be partially embedded in the inorganic binder layer.

[0043] The degree of amorphousness of the amorphous silica particles is preferably 80% or more, more preferably 90% or more, even more preferably 93% or more, even more preferably 95% or more, and even more preferably 98% or more, from the viewpoint of more firmly bonding the particles of the coated sand together via the amorphous silica particles. The upper limit of the degree of amorphousness of the amorphous silica particles is not limited, but for example, it may be 100% or less, or 99.8% or less.

[0044] The content of amorphous silica particles in the inorganic fine particles is preferably 10% by mass or more, more preferably 30% by mass or more, even more preferably 50% by mass or more, even more preferably 70% by mass or more, and even more preferably 90% by mass or more, and may be 100% by mass, from the viewpoint of improving the strength of the mold.

[0045] The inorganic fine particles other than the amorphous silica particles are not particularly limited, but include, for example, crystalline silica, silicon, zinc carbonate, basic zinc carbonate, iron carbonate, manganese carbonate, copper carbonate, aluminum carbonate, barium carbonate, magnesium carbonate, calcium carbonate, lithium carbonate, potassium carbonate, sodium carbonate and other carbonates; 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, magnesium metaborate and other borates; sodium sulfate, potassium sulfate Examples of inorganic fine particles other than amorphous silica particles can be used alone, but it is preferable to use them in combination with amorphous silica particles.

[0046] The average particle diameter d in the weight-based particle size distribution of the inorganic fine particles as measured by laser diffraction scattering particle size distribution analysis. 50 From the viewpoint of improving the strength of the mold and improving handling, the particle size is preferably 0.1 μm or larger, more preferably 0.3 μm or larger. The average particle diameter d in the weight-based particle size distribution of the inorganic fine particles measured by laser diffraction scattering particle size distribution measurement method. 50 From the viewpoint of improving the strength of the mold, the thickness is preferably 2.0 μm or less, more preferably 1.0 μm or less, even more preferably 0.8 μm or less, and even more preferably 0.6 μm or less.

[0047] The average particle diameter of the inorganic fine particles, as determined from the scanning electron microscope observation images, is preferably 0.1 μm or more, more preferably 0.3 μm or more, from the viewpoint of improving mold strength per unit mass and handling properties. The average particle diameter of the inorganic fine particles, as determined from the scanning electron microscope observation images, is preferably 2.0 μm or less, more preferably 1.0 μm or less, even more preferably 0.8 μm or less, and even more preferably 0.6 μm or less, from the viewpoint of improving mold strength per unit mass. The average particle diameter of the inorganic fine particles can be determined from the scanning electron microscope observation images using various image analysis methods. Irregular particle sorting may also be performed as a pretreatment. For example, after determining the inorganic fine particles in the coated sand based on elements, 100 arbitrary inorganic fine particles can be selected, their particle diameters measured, and the average particle diameter of the 80 inorganic fine particles remaining after excluding 20 inorganic fine particles (10 from the largest particle diameter and 10 from the smallest particle diameter) can be taken as the average particle diameter of the inorganic fine particles.

[0048] From the viewpoint of improving the strength of the mold, the content of the inorganic fine particles in the coated sand is preferably 20 parts by mass or more, more preferably 40 parts by mass or more, and even more preferably 50 parts by mass or more, per 100 parts by mass of the inorganic binder with water removed. From the viewpoint of improving the surface shape of the mold and suppressing dust scattering, the content of the inorganic fine particles in the coated sand is preferably 150 parts by mass or less, more preferably 120 parts by mass or less, even more preferably 100 parts by mass or less, and even more preferably 80 parts by mass or less, per 100 parts by mass of the inorganic binder with water removed.

[0049] [Step (1)] Step (1) is a step of mixing water with refractory aggregate A, which has an inorganic binder layer formed on its surface containing an inorganic binder containing metasilicate hydrate. The method of mixing the refractory aggregate A and water in step (1) is not particularly limited and can be done by known methods. The coated sand can be obtained by adjusting the amount of water added in step (1) according to the amount of water removed from the inorganic binder in the refractory aggregate A and the amount of water contained in the refractory aggregate A.

[0050] [Step (2)] If the coated sand contains the inorganic fine particles, the manufacturing method of this embodiment includes a step (2) of mixing the refractory aggregate A and the inorganic fine particles before or simultaneously with step (1), or a step (2') of mixing the coated sand and the inorganic fine particles after step (1). In step (2), the method of mixing the refractory aggregate A and the inorganic fine particles is not particularly limited and can be done by known methods. Also, in step (2'), the method of mixing the coated sand and the inorganic fine particles is not particularly limited and can be done by known methods. In step (2), when mixing the refractory aggregate A and the inorganic fine particles simultaneously with step (1), water and the inorganic fine particles may be added separately to the refractory aggregate A and then mixed, or water and the inorganic fine particles may be mixed to prepare a mixture of water and the inorganic fine particles, which may then be added to the refractory aggregate A and mixed.

[0051] <Method for manufacturing molds> The method for manufacturing a mold according to this embodiment includes the steps of (3) filling a mold with the coated sand produced by the manufacturing method, and (4) hardening the coated sand filled in the mold. The method for manufacturing a mold according to this embodiment can be manufactured by applying known methods other than using the coated sand produced by the manufacturing method. The method for manufacturing a mold using the coated sand produced by the manufacturing method is not particularly limited, but examples include a molding method using a heated molding die, a molding method in which steam is further passed through a heated molding die and then hot air is passed through it, and so on. [Examples]

[0052] The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited thereto.

[0053] <Material> The materials used in the following examples and comparative examples will be described below. [Fire-resistant aggregate] ·Mikawa Silica Sand R6 (manufactured by Mikawa Siliceki Co., Ltd., average particle size: 200 μm, amorphousness 0.2%, sphericity 0.85) [Inorganic binders] Sodium metasilicate pentahydrate (Na2SiO3·5H2O, SiO2 / Na2O molar ratio = 0.9~1.1), manufactured by Nippon Chemical Industrial Co., Ltd., melting point 72℃ Sodium metasilicate nonahydrate (Na2SiO3·9H2O, SiO2 / Na2O molar ratio = 0.9~1.1), manufactured by Nippon Chemical Industrial Co., Ltd., melting point 47℃ • No. 2 water glass: Manufactured by Fuji Chemical Co., Ltd., SiO2 (mass%) = 28.6, Na2O (mass%) = 12.0, solids content 40.6% by mass [Inorganic fine particles] • Amorphous silica particles 1: Denka Co., Ltd.'s Denka Fused Silica SFP-20M (average particle size: 0.4 μm, amorphity 99.5% or higher, SiO2 mass%: 99% or higher)

[0054] <Making Coated Sand> [Examples 1-7, Comparative Examples 1-6] Refractory aggregate (100 parts by mass) was placed in a stirrer. Next, the amount (parts by mass) of sodium metasilicate pentahydrate, or a mixture of sodium metasilicate pentahydrate and sodium metasilicate nonahydrate shown in Table 1, was heated to 80°C to melt and obtain a molten liquid. Then, the molten liquid was placed in the stirrer and mixed uniformly with the refractory aggregate. While continuing to stir, the mixture was allowed to cool naturally until the temperature was below the melting point of the sodium metasilicate pentahydrate, or the mixture of sodium metasilicate pentahydrate and sodium metasilicate nonahydrate. Stirring was stopped 7 minutes after the start of mixing to obtain dry refractory aggregate A that is fluid at room temperature. To this refractory aggregate A, the amount (parts by mass) of inorganic fine particles and water shown in Table 1 was added and mixed for 2 minutes.

[0055] [Comparative Example 7] Refractory aggregate (100 parts by mass) was heated to approximately 120°C and then added to a stirrer. Next, the amounts (parts by mass) of No. 2 silicate water glass and inorganic fine particles shown in Table 1 were added and kneading with the refractory aggregate began uniformly. While continuing to stir, the water in No. 2 sodium silicate was evaporated, and stirring was stopped 10 minutes after the start of kneading to obtain dry sand with fluidity at room temperature. Furthermore, the amount (parts by mass) of water shown in Table 1 was added and kneading was carried out for 2 minutes.

[0056] [Table 1]

[0057] <Rating> [Method for measuring moisture content (mass%) [α] in coated sand] A crucible that had been preheated and weighed was filled with 10g of coated sand, and after being exposed to heat at 900°C for 1 hour, the amount of mass loss (mass%) was used to calculate the moisture content (mass%) in the coated sand [α]. [α] = [(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))

[0058] [Method for measuring the amount of water removed from inorganic binders (%)[β] in coated sand] 30 g of coated sand was placed in a 200 ml tall beaker, 100 ml of pure water was added, and the mixture was stirred with a magnetic stirrer for 25 minutes to prepare an extract. The supernatant of the extract was then filtered through a membrane filter (pore size: 0.45 μm), and 10 ml of the filtrate was collected in a 100 ml beaker. [Titration] After adding 20 ml of 0.1 mol / l HCl aqueous solution to a 100 ml beaker containing 10 ml of the filtrate described above, the 0.1 mol / l NaOH aqueous solution was titrated using an automatic titrator (e.g., Eco Titrator (Metrohm)) while stirring with a magnetic stirrer. The titration volume X (ml) at which the pH reached 7 was measured using a pH meter, and the amount of water removed by the inorganic binder in the coated sand (mass%) [β] was calculated using the following two formulas. Acid consumption Y (mol) = ([Amount of HCl aqueous solution (ml)] - [Titer amount X (ml)]) / 1000 x [HCl aqueous solution concentration (mol / l)] = (20-X) / 1000 x 0.1 [β] = ([Acid consumption Y (mol)] × 10 × [Molecular weight of inorganic binder] / [Na valency]) / (Amount of coated sand (g)) × 100 = (Y × 10 × Molecular weight of inorganic binder / 2) / 30 × 100

[0059] [Method for distinguishing between dry and wet coated sand (Method for measuring dynamic angle of repose)] Half the volume of coated sand was placed in a cylindrical transparent plastic bottle (diameter: 7.7 cm, height: 16 cm). Using a bottle agitator, the cylindrical transparent plastic bottle was held so that its axis was horizontal and rotated around the horizontal axis at a rotation speed of 60 rpm. It was confirmed that the slope of the flowing coated sand layer inside the cylindrical transparent plastic bottle became a flat surface, and the angle formed between this slope and the horizontal surface was measured. If the coated sand did not flow inside the cylindrical transparent plastic bottle, or if the slope of the coated sand layer did not form a flat surface even if it flowed, and as a result it was not possible to measure the dynamic angle of repose, the sample was considered wet.

[0060] [Evaluation of sand filling capabilities for complex-shaped molds] Using each coated sand, blow filling was performed into the mold according to the following procedure, and the feasibility of filling was evaluated. [procedure] The mold for the T-shaped test specimen shown in Figure 1 was heated to 180°C. Each of the coated sands from the above examples and comparative examples was filled into the mold heated to 180°C using a CSR-43 blow molding machine at a blow pressure of 0.2 MPa. The coated sand was then left to harden in the mold for 90 seconds to obtain a mold test specimen. The mold test specimens were visually inspected, and those in which the entire mold was filled with coated sand were marked with ○, and those in which there was insufficient filling were marked with ×.

[0061] [Method for measuring mold strength, and method for measuring mold surface strength] [Preparation of mold test specimens] A mold for 22.3 mm × 22.3 mm × 180 mm test specimens (5 cavities) was heated to 180°C. Each of the coated sands from the above examples and comparative examples was filled into the mold heated to 180°C using a CSR-43 blow molding machine at a blow pressure of 0.3 MPa. The coated sand was then left to harden in the mold for 150 seconds to obtain the mold test specimens for each example and comparative example. [Measuring mold strength] The flexural strength (MPa) of each mold specimen was measured using an SVZ-201F tensile and compression testing machine manufactured by Imada Manufacturing Co., Ltd., under conditions of a span of 150 mm and a speed of 300 mm / min. The mold specimens were left for 1 hour in a constant temperature and humidity chamber at 25°C / 55%RH after being removed from the mold. [Measuring the surface strength of the mold] A DIETERT 674-A scratch hardness tester was pressed against the surface of each mold specimen, and the scratch strength after one rotation was measured to evaluate the surface strength of the mold. The mold specimens used were left in a constant temperature and humidity chamber at 25°C / 55%RH for one hour after being removed from the mold.

[0062] The results of each evaluation are shown in Table 2.

[0063] Table 2

Claims

1. A method for producing dry coated sand, comprising the step (1) of mixing water with refractory aggregate A having an inorganic binder layer formed on its surface containing an inorganic binder containing a metasilicate hydrate, A method for producing coated sand, wherein the mass ratio of the inorganic binder water (a component of the inorganic binder other than water) to the water in the coated sand (mass of water in the coated sand / mass of the inorganic binder water) is 1.00 to 1.

60.

2. The method for producing coated sand according to claim 1, wherein the metasilicate hydrate contains metasilicate pentahydrate.

3. The method for producing coated sand according to claim 2, wherein the metasilicate hydrate contains metasilicate notahydrate.

4. A method for producing coated sand according to any one of claims 1 to 3, comprising a step (2) of mixing the refractory aggregate A with inorganic fine particles before or simultaneously with step (1).

5. A method for producing coated sand according to any one of claims 1 to 3, further comprising the step (2') of mixing the coated sand with inorganic fine particles after the step (1).

6. A dry coated sand containing a refractory aggregate A having an inorganic binder layer formed on its surface containing an inorganic binder containing a metasilicate hydrate, A coated sand in which the mass ratio of the inorganic binder water (a component other than water in the inorganic binder) to the water in the coated sand (mass of water in the coated sand / mass of the inorganic binder water) is 1.00 to 1.

60.

7. The coated sand according to claim 6, wherein the metasilicate hydrate contains metasilicate pentahydrate.

8. The coated sand according to claim 7, wherein the metasilicate hydrate contains metasilicate notahydrate.

9. The coated sand according to claim 6, wherein inorganic fine particles are contained on the inorganic binder layer.

10. Step (3) of filling a mold with the coated sand according to any one of claims 6 to 9, and A method for manufacturing a mold, comprising the step (4) of hardening the coated sand filled in the mold.

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