Method for producing coated sand

Abstract

The present invention relates to a method for producing coated sand, the method comprising a step (1) of mixing an aggregate (A) having an acid consumption of 25 to 100 mL with a metasilicate (B). According to the present invention, it is possible to provide a method for producing coated sand that enables production of a mold having high strength, even when derived from recycled sand.

Description

Coated sand manufacturing method

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

[0002] As a mold used for casting, Japanese Patent Application Laid-Open No. 2020-11296 discloses 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 metasilicate hydrate.

[0003] In Japanese Patent Laid-Open No. 2014-117740, a water glass aqueous solution is mixed as a binder with heated refractory aggregate, and the water glass aqueous solution contains SiO ２ / Na ２ The present invention discloses a method for producing coated sand, which is characterized by using an aqueous solution of sodium silicate having a molar ratio of 0 to 3.0 to 4.0, adjusting the viscosity of the aqueous solution at 25°C to within the range of 10 to 50 cP, and mixing the aqueous solution with the refractory aggregate.

[0004] The present invention provides a method for producing coated sand for use in producing molds, comprising the step (1) of mixing aggregate (A) and metasilicate (B), the acid consumption V of which, as measured by the following method, is 25 mL to 100 mL. <Method for Measuring Acid Consumption V> [Procedure (1)]: 25 g of aggregate that had been dried at 105°C for 1 hour and 50 mL of 0.1 M HCl aqueous solution were placed in a 100 mL beaker and stirred with a magnetic stirrer (800 rpm) at 20°C for 60 minutes. The resulting mixture was filtered through pleated filter paper (No. 3, φ70, manufactured by Toyo Roshi Kaisha, Ltd.). 25 mL of the resulting filtrate was then titrated with 0.1 M NaOH aqueous solution at 20°C using a potentiometric titrator. The amount (A [mL]) of 0.1 M NaOH aqueous solution used to change the pH to 7 was measured. [Procedure (2)] The amount of 0.1 M NaOH aqueous solution obtained by performing the same process as in Procedure (1) without using 25 g of aggregate (A) is defined as B [mL]. [Procedure (3)] The amount of acid consumed V is calculated using the following formula: V = 4(B - A) where V is the amount of acid consumed V [mL], A is the amount of 0.1 M NaOH A [mL] in Procedure (1), and B is the amount of 0.1 M NaOH B [mL] in Procedure (2). Detailed Description of the Invention

[0005] Coated sand such as that described in JP 2020-11296 A and JP 2014-117740 A is generally used in a casting mold, and then the mold is destroyed (disassembled) to produce recovered sand as single particles, which is then further regenerated by various methods to produce regenerated sand, which is then mixed with new binder and used again as coated sand.

[0006] However, molds made using coated sand obtained by mixing the reclaimed sand with an inorganic binder again tend to have low strength.

[0007] An object of the present invention is to provide a method for producing coated sand that can obtain a mold having high strength even when the aggregate used is derived from recycled sand.

[0008] The present invention provides a method for producing coated sand for use in producing molds, comprising the step (1) of mixing aggregate (A) and metasilicate (B), the acid consumption V of which, as measured by the following method, is 25 mL to 100 mL. <Method for Measuring Acid Consumption V> [Procedure (1)]: 25 g of aggregate that had been dried at 105°C for 1 hour and 50 mL of 0.1 M HCl aqueous solution were placed in a 100 mL beaker and stirred with a magnetic stirrer (800 rpm) at 20°C for 60 minutes. The resulting mixture was filtered through pleated filter paper (No. 3, φ70, manufactured by Toyo Roshi Kaisha, Ltd.). 25 mL of the resulting filtrate was then titrated with 0.1 M NaOH aqueous solution at 20°C using a potentiometric titrator. The amount (A [mL]) of 0.1 M NaOH aqueous solution used to change the pH to 7 was measured. [Procedure (2)] The amount of 0.1 M NaOH aqueous solution obtained by performing the same process as in Procedure (1) without using 25 g of aggregate (A) is defined as B [mL]. [Procedure (3)] The amount of acid consumed V is calculated using the following formula: V = 4(B - A) where V is the amount of acid consumed V [mL], A is the amount of 0.1 M NaOH A [mL] in Procedure (1), and B is the amount of 0.1 M NaOH B [mL] in Procedure (2).

[0009] According to the present invention, it is possible to provide a method for producing coated sand that can obtain a mold having high strength even when the aggregate used is derived from recycled sand.

[0010] In this specification, "mold" refers to a sand mold. In this specification, "aggregate" refers to a particulate material that is one of the components that make up a mold, and more specifically, refers to sand. In addition, "coated sand" refers to sand that has a binder component on all or part of its surface, and the binder refers to a substance that bonds aggregate particles together in order to maintain the shape of the mold before, during, and after the molten metal is poured into it. In addition, "reclaimed sand" refers to sand that has been used after casting work has been completed, and its fluidity has been restored by destroying (disassembling) the mold. In addition, "reclaimed sand" refers to sand obtained by subjecting the reclaimed sand to a regeneration process.

[0011] An embodiment of the present invention will be described below.

[0012] <Method for Manufacturing Coated Sand> The method for manufacturing coated sand of this embodiment is a method for manufacturing coated sand used in manufacturing molds, and includes step (1) of mixing aggregate (A) and metasilicate (B), the acid consumption V of which, as measured by the following method, is 25 mL or more and 100 mL or less. <Method for Measuring Acid Consumption V> [Procedure (1)] 25 g of aggregate that had been dried at 105°C for 1 hour and 50 mL of 0.1 M HCl aqueous solution were placed in a 100 mL beaker and stirred with a magnetic stirrer (800 rpm) at 20°C for 60 minutes. The resulting mixture was filtered through pleated filter paper (No. 3, φ70, manufactured by Toyo Roshi Kaisha, Ltd.). 25 mL of the resulting filtrate was sampled and titrated with 0.1 M NaOH aqueous solution at 20°C using a potentiometric titrator. The amount (A [mL]) of 0.1 M NaOH aqueous solution used to change the pH to 7 was measured. [Procedure (2)] The amount of 0.1 M NaOH aqueous solution obtained by performing the same process as in Procedure (1) without using 25 g of aggregate (A) is defined as B [mL]. [Procedure (3)] The amount of acid consumed V is calculated using the following formula: V = 4(B - A) where V is the amount of acid consumed V [mL], A is the amount of 0.1 M NaOH A [mL] in Procedure (1), and B is the amount of 0.1 M NaOH B [mL] in Procedure (2).

[0013] According to the method for producing coated sand of this embodiment, it is possible to produce coated sand that can be used to obtain molds with high strength, even if the aggregate used is derived from recycled sand. The reason why the method for producing coated sand of this embodiment has such an effect is not clear, but it is presumed to be as follows.

[0014] Residues of the binder used in the production of the mold are attached to the surface of the recycled sand. If the binder is an inorganic binder, silicates and their reaction products will be attached to the surface of the aggregate. When this recycled sand is used with water glass (sodium silicate hydrate) as an inorganic binder, ２ O.nSiO ２ xH ２When coated sand is produced using a binder such as PEG (n≧2, x is the number of hydration molecules), water glass reacts with the inorganic binder residue on the surface of the reclaimed sand even at room temperature, and the reaction is particularly rapid when the residue contains silicate and / or silicate reaction products, forming a gel-like substance. This gel-like substance has poor adhesive strength to bind aggregates together and is therefore unlikely to function as a binder. As a result, when reclaimed sand is used, water glass is unable to exhibit its binding properties, and the strength of the mold obtained using the coated sand is reduced. On the other hand, when coated sand is produced using metasilicate as the inorganic binder, the metasilicate reacts mildly with the silicate and / or silicate reaction products at room temperature, suppressing the formation of a gel-like substance and presumably enabling the production of coated sand that can produce molds with high mold strength. On the other hand, if the amount of silicate and / or silicate reactant present on the aggregate is too large, the reaction with metasilicate is promoted and a gel-like substance is formed. Therefore, it is thought that by setting the amount of silicate and silicate reactant present within an appropriate range using the acid consumption amount V, it is possible to suppress a decrease in mold strength.

[0015] [Aggregate (A)] In the method for producing coated sand of this embodiment, the aggregate (A) has an acid consumption V of 25 mL or more and 100 mL or less, as measured by the following method. <Method for measuring acid consumption V> [Procedure (1)] 25 g of aggregate that had been dried at 105°C for 1 hour and 50 mL of 0.1 M HCl aqueous solution were placed in a 100 mL beaker and stirred with a magnetic stirrer (800 rpm) in an environment of 20°C for 60 minutes. The resulting mixture was filtered through pleated filter paper (No. 3 φ70, manufactured by Toyo Roshi Kaisha, Ltd.). 25 mL of the resulting filtrate was taken and titrated with 0.1 M NaOH aqueous solution at 20°C using a potentiometric titrator. The amount (A [mL]) of 0.1 M NaOH aqueous solution used to change the pH to 7 was measured. [Procedure (2)] The amount of 0.1 M NaOH aqueous solution obtained by performing the same process as in Procedure (1) without using 25 g of aggregate (A) is defined as B [mL]. [Procedure (3)] The amount of acid consumed V is calculated using the following formula: V = 4(B - A) where V is the amount of acid consumed V [mL], A is the amount of 0.1 M NaOH A [mL] in Procedure (1), and B is the amount of 0.1 M NaOH B [mL] in Procedure (2).

[0016] In the coated sand manufacturing method of this embodiment, the aggregate (A) is preferably recycled sand. In the coated sand manufacturing method of this embodiment, an example of a method for recycling recycled sand to produce recycled sand is the method described in "Mold Molding Method," 4th Edition (Japan Foundry Technology Association, November 18, 1996, pp. 327-330). That is, the coated sand manufacturing method of this embodiment preferably includes a step of treating recycled sand to produce recycled sand before step (1). In the coated sand manufacturing method of this embodiment, the number of steps of treating recycled sand to produce recycled sand before step (1) is preferably one or more. That is, in this specification, recycled sand means sand obtained by subjecting recycled sand to recycling treatment as described above, which contains components derived from the binder in addition to components derived from the aggregate.

[0017] The aggregate (A) used in step (1) in the method for producing coated sand of this embodiment is preferably derived from one type selected from the group consisting of natural sand and artificial sand, and these may also be combined.

[0018] Examples of the natural sand include one or more types selected from the group consisting of silica sand, chromite sand, zircon sand, olivine sand, and alumina sand.

[0019] Examples of the artificial sand include synthetic mullite sand, SiO ２ SiO ２ Sand, Al ２ O ３ Al, the main component of which is ２ O ３ System sand, SiO ２ / Al ２ O ３ System sand, SiO ２ / MgO-based sand, SiO ２ / Al ２ O ３ / Al ２ O ３ ZrO ２ System sand, SiO ２ / Al ２ O ３ / Fe ２ O ３ The aggregate (A) used in step (1) of the coated sand manufacturing method of this embodiment is preferably one or more selected from the group consisting of sand derived from slag and sand derived from slag. Here, the term "main component" refers to the component that is most abundant by mass among the components contained in the sand. The artificial sand is not naturally occurring sand, but refers to sand obtained by artificially preparing metal oxide components and melting or sintering them. The aggregate (A) used in step (1) of the coated sand manufacturing method of this embodiment is preferably derived from artificial sand, and is preferably Al. ２ O ３ Artificial sand of this type is more preferred.

[0020] (Average particle size of aggregate (A)) From the viewpoint of improving mold quality and mold strength, and from the viewpoint of ease of mold production, the average particle size of aggregate (A) is preferably 0.05 mm (50 μm) or more, more preferably 0.1 mm (100 μm) or more, and from the same viewpoint, it is preferably 2 mm (2000 μm) or less, more preferably 1 mm (1000 μm) or less, and even more preferably 0.5 mm (500 μm) or less. From the same viewpoint, the average particle size of aggregate (A) is preferably 50 μm or more and 2000 μm or less, more preferably 50 μm or more and 1000 μm or less, even more preferably 50 μm or more and 500 μm or less, even more preferably 100 μm or more and 300 μm or less, and even more preferably 150 μm or more and 250 μm or less.

[0021] In the method for producing coated sand of this embodiment, the average particle diameter of aggregate (A) can be measured, for example, by the following method. (Method for Measuring the Average Particle Diameter of Aggregate (A)) When the sphericity of the aggregate (A) particle projected from its cross section is 1, the diameter (mm) is measured. On the other hand, when the sphericity is <1, the major axis diameter (mm) and minor axis diameter (mm) of randomly oriented particles are measured to calculate (major axis diameter + minor axis diameter) / 2, and the average value obtained for 100 randomly selected particles is used as 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 projected image on the plane is sandwiched between two parallel lines, the width of the particle at the smallest distance between the parallel lines is called the minor axis diameter, and the distance between two parallel lines perpendicular to the parallel lines when the particle is sandwiched between the 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 a digital microscope (for example, VH-8000 model, manufactured by Keyence Corporation) and analyzing the obtained image.

[0022] (Amorphous Degree of Aggregate (A)) From the viewpoint of improving mold strength and obtaining low thermal expansion, the amorphous degree of the aggregate (A) is preferably 20% or more, more preferably 30% or more, even more preferably 50% or more, and even more preferably 80% or more. The upper limit of the amorphous degree of the aggregate (A) is not limited, but is, for example, 100% or less, preferably 99% or less. There are various methods for controlling the amorphous degree of the aggregate (A), but it is generally preferable to use a manufacturing method that rapidly cools a molten material. For example, there is a method in which raw materials are melted and rapidly cooled by air-crushing, or a method in which they are treated in a flame and rapidly cooled. In either case, the cooling method may be appropriately selected at various rates depending on the material and particle size. In addition, a method in which a crystallized material is amorphized by heat treatment and cooling treatment is also considered. Among these, a flame fusion method is preferred, in which heating and cooling can be easily controlled.

[0023] The degree of amorphization of the aggregate (A) can be determined, for example, by the X-ray diffraction method shown below. (X-ray Diffraction Method) The aggregate (A) is pulverized in a mortar and then compressed onto an X-ray glass holder of a powder X-ray diffractometer for measurement. The powder X-ray diffractometer is a MultiFlex (CuKα radiation source, 40 kV tube voltage, 40 mA tube current) manufactured by Rigaku Corporation, and the diffractometer is operated at a scanning interval of 0.01°, a scanning speed of 2° / min, and slits DS1, SS1, and RS0.3 mm in the range of 2θ = 5° to 90°. A straight line is drawn between the X-ray intensities on the low-angle and high-angle sides in the range of 2θ = 10° to 50°, and the area under the line is used as the background. The degree of crystallinity is calculated using the software provided with the instrument, and this is subtracted from 100 to obtain the degree of amorphization. Specifically, for the area above the background, the amorphous peak (halo) and each crystalline component are separated by curve fitting, the area of ​​each is determined, and the amorphous degree (%) is calculated using the following formula: Amorphous degree (%) = halo area / (crystalline component area + halo area) × 100

[0024] (Components derived from the binder contained in aggregate (A)) When aggregate (A) is recycled sand, the components derived from the binder contained in aggregate (A), i.e., residues of the binder used in producing the mold, may be organic or inorganic components. From the viewpoint of improving the strength of the mold produced using the coated sand obtained by the method for producing coated sand of this embodiment, it is preferable that aggregate (A) contain components derived from an inorganic binder.

[0025] (Components derived from inorganic binder contained in aggregate (A)) Specific examples of components derived from the inorganic binder contained in the aggregate (A) include silicates. Suitable examples of silicates include sodium silicate, potassium silicate, sodium orthosilicate, potassium orthosilicate, sodium metasilicate, and potassium metasilicate. That is, in the method for producing coated sand of this embodiment, when the aggregate (A) is recycled sand, and the aggregate used to form a mold before the aggregate (A) was recycled is referred to as aggregate (A'), it is preferable that aggregate (A') is treated with a binder consisting of an inorganic component, and more specifically, aggregate (A') is silica (SiO ２ ), sodium silicate (Na ２ O.nSiO ２ : n≧2), potassium silicate (K ２ O.nSiO ２ : n≧2), sodium metasilicate (Na ２ O.nSiO ２ : n = 0.9 to 1.1), potassium metasilicate (K ２ O.nSiO ２ : n = 0.9 to 1.1), sodium orthosilicate (Na ２ O.nSiO ２ : n = 0.49 to 0.59), and potassium orthosilicate (K ２ O.nSiO ２ : n = 0.49 to 0.59), and more preferably, treated with one or more selected from silica, sodium silicate, and sodium metasilicate. The silicate may be anhydrous or hydrated.

[0026] The aggregate (A) containing a component derived from an inorganic binder preferably means a state selected from a state in which the aggregate (A) is entirely coated with a component derived from a binder made of an inorganic component contained in the aggregate (A'), a state in which the aggregate (A) is partially coated with the component, or both of these states.

[0027] [Acid Consumption V] In the coated sand manufacturing method of this embodiment, the aggregate (A) has an acid consumption V of 25 mL or more and 100 mL or less, as measured by the following method. <Method for Measuring Acid Consumption V> [Procedure (1)] 25 g of aggregate that had been dried at 105°C for 1 hour and 50 mL of 0.1 M HCl aqueous solution were placed in a 100 mL beaker and stirred with a magnetic stirrer (800 rpm) in an environment of 20°C for 60 minutes. The resulting mixture was filtered through pleated filter paper (No. 3 φ70, manufactured by Toyo Roshi Kaisha, Ltd.). 25 mL of the resulting filtrate was taken and titrated with 0.1 M NaOH aqueous solution at 20°C using a potentiometric titrator. The amount (A [mL]) of 0.1 M NaOH aqueous solution used to change the pH to 7 was measured. [Procedure (2)] The amount of 0.1 M NaOH aqueous solution obtained by performing the same process as in Procedure (1) without using 25 g of aggregate (A) is defined as B [mL]. [Procedure (3)] The amount of acid consumed V is calculated using the following formula: V = 4(B - A) where V is the amount of acid consumed V [mL], A is the amount of 0.1 M NaOH A [mL] in Procedure (1), and B is the amount of 0.1 M NaOH B [mL] in Procedure (2).

[0028] The acid consumption V is an index of the amount of components contained in aggregate (A) that are derived from the binder used to form the aggregate into a mold, i.e., the amount of residue. When the binder used to form the aggregate into a mold is an inorganic binder, silicic acid and / or silicate compounds, which are components derived from the binder used to form the aggregate into a mold, react with hydrochloric acid and are consumed, and the remaining hydrochloric acid is back-titrated with sodium hydroxide to calculate the amount of inorganic binder used to form the aggregate into a mold remaining in aggregate (A). When the binder used to form the aggregate into a mold is an inorganic binder, the acid consumption V is an index of the amount of components derived from the inorganic binder, i.e., the amount of residue, contained per 50 g of aggregate (A). From the viewpoint of improving the strength of a mold produced using the coated sand obtained by the method for producing coated sand of this embodiment, the acid consumption V is 25 mL or more, preferably 30 mL or more, more preferably 33 mL or more, even more preferably 35 mL or more, and 100 mL or less, preferably 85 mL or less, more preferably 70 mL or less, even more preferably 60 mL or less, still more preferably 50 mL or less, still more preferably 45 mL or less, and still more preferably 40 mL or less. From the same viewpoint, the acid consumption V is preferably 30 mL or more and 70 mL or less, more preferably 30 mL or more and 60 mL or less, still more preferably 30 mL or more and 50 mL or less, still more preferably 33 mL or more and 45 mL or less, and still more preferably 35 mL or more and 40 mL or less. The acid consumption V is measured by the method described in the Examples.

[0029] The method for producing coated sand of this embodiment preferably includes, before step (1), step (0) of confirming that the acid consumption V of the aggregate is 25 mL or more and 100 mL or less by the method for measuring the acid consumption V. Step (0) makes it possible to indirectly quantify the amounts of silicate and silicate reaction products present in the aggregate via the acid consumption V. When the amounts of silicate and silicate reaction products present are large, it may be possible to carry out a treatment to adjust the amounts present, for example, by roasting. However, for aggregates whose acid consumption V is within a specific range, it is possible to determine that molds with high mold strength can be obtained without such treatment, thereby significantly improving production efficiency.

[0030] [Metasilicate (B)] (Type of metasilicate (B)) The metasilicate (B) mixed with the aggregate (A) in step (1) of the method for producing coated sand of this embodiment is selected from the group consisting of alkali metal metasilicate (M) and alkali metal metasilicate (M). ２ O.nSiO ２ (M=alkali metal, n=0.9 to 1.1) is preferred. Among these, one or more selected from sodium metasilicate and potassium metasilicate is more preferred, with sodium metasilicate being even more preferred.

[0031] An example of the metasilicate (B) is anhydrous sodium metasilicate. In the method for producing coated sand of this embodiment, the metasilicate (B) is preferably used in a hydrated state. As the hydrate of metasilicate (B), one or more selected from sodium metasilicate pentahydrate and sodium metasilicate nonahydrate are preferred, and from the viewpoint of improving the strength of a mold produced using the coated sand obtained by the method for producing coated sand of this embodiment, sodium metasilicate nonahydrate is more preferred.

[0032] In step (1) of the method for producing coated sand of this embodiment, an inorganic binder other than the metasilicate (B) may be added and mixed in addition to the metasilicate (B). In the method for producing coated sand of this embodiment, examples of the inorganic binder other than the metasilicate (B) include sodium silicate (Na ２ O.nSiO ２ : n≧2), potassium silicate (K ２ O.nSiO ２ : n≧2), sodium orthosilicate (Na ２ O.nSiO ２ : n = 0.49 to 0.59), and potassium orthosilicate (K ２ O.nSiO ２ In step (1) of the method for producing coated sand of this embodiment, the amount of inorganic binder other than the metasilicate (B) added relative to the metasilicate (B) is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, even more preferably 1 part by mass or less, and still more preferably 0 part by mass, per 100 parts by mass of the metasilicate (B).

[0033] (Ratio of Aggregate (A) to Metasilicate (B)) In the method for producing coated sand of this embodiment, the mixing ratio of aggregate (A) to metasilicate (B) is, from the viewpoint of improving the strength of a mold produced using the coated sand obtained by the method for producing coated sand of this embodiment, preferably 0.01 part by mass or more, more preferably 0.03 part by mass or more, even more preferably 0.1 part by mass or more, still more preferably 0.5 part by mass or more, and still more preferably 0.8 part by mass or more, per 100 parts by mass of aggregate (A). From the same viewpoint, it is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, even more preferably 4 parts by mass or less, still more preferably 3 parts by mass or less, and still more preferably 2 parts by mass or less.

[0034] (Inorganic Particles) In the method for producing coated sand of the present embodiment, in step (1), inorganic particles (C) are preferably mixed in addition to the aggregate (A) and the metasilicate (B), from the viewpoint of improving the strength of a mold produced using the coated sand obtained by the method for producing coated sand of the present embodiment.

[0035] Examples of the inorganic particles (C) include silica particles, silicon particles, etc., and silica particles are preferred, and among silica particles, amorphous silica particles are more preferred. These inorganic particles (C) may be used alone or in combination of two or more.

[0036] When step (1) is a step of mixing the inorganic particles (C) in addition to the aggregate (A) and the metasilicate (B), the inorganic particles (C) may be further mixed with the mixture of the aggregate (A) and the metasilicate (B), the metasilicate (B) may be further mixed with the mixture of the aggregate (A) and the inorganic particles, or the aggregate (A) may be further mixed with the mixture of the metasilicate (B) and the inorganic particles (C).

[0037] When step (1) is a step of mixing inorganic particles (C) in addition to aggregate (A) and metasilicate (B), the ratio of inorganic particles (C) relative to 100 parts by mass of aggregate (A) is preferably 0.01 parts by mass or more, more preferably 0.03 parts by mass or more, even more preferably 0.1 parts by mass or more, and still more preferably 0.5 parts by mass or more, from the viewpoint of improving the strength of a mold produced using the coated sand obtained by the method for producing coated sand of this embodiment. From the same viewpoint, the ratio is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, even more preferably 2 parts by mass or less, and still more preferably 1 part by mass or less.

[0038] (Average particle size of inorganic particles (C)) From the viewpoints of improving mold quality and mold strength, and of ease of mold production, the average particle size of the inorganic particles (C) is preferably 0.1 μm or more, more preferably 0.3 μm or more, and from the same viewpoints, it is preferably 2.0 μm or less, more preferably 1.0 μm or less, and even more preferably 0.8 μm or less. In the method for producing coated sand of this embodiment, the average particle size of the inorganic particles (C) can be measured by the laser diffraction / scattering particle size distribution measurement method described in the Examples.

[0039] (Other Additives) In the method for producing coated sand of this embodiment, other additives may be further mixed in addition to the aggregate (A), metasilicate (B), and inorganic particles (C). Examples of other additives include humectants, moisture resistance improvers, coupling agents that strengthen the bond between the aggregate (A) and metasilicate (B), lubricants, surfactants, and mold release agents.

[0040] Examples of the moisturizing agent include polyhydric alcohols, water-soluble polymers, hydrocarbons, sugars, proteins, and inorganic compounds such as sodium chloride, calcium chloride, and magnesium chloride.

[0041] Examples of the moisture resistance improver 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.

[0042] Examples of the coupling agent that strengthens the bond between the aggregate (A) and the metasilicate (B) include a silane coupling agent, a zirconium coupling agent, and a titanium coupling agent.

[0043] Examples of the lubricant include waxes; fatty acid amides; alkylene fatty acid amides; stearic acid; stearyl alcohol; metal stearates such as lead stearate, zinc stearate, calcium stearate, and magnesium stearate; stearic acid monoglyceride; stearyl stearate; and hydrogenated oils.

[0044] Examples of the surfactant include cationic surfactants, anionic surfactants, amphoteric surfactants, nonionic surfactants, and silicone surfactants.

[0045] Examples of the release agent include paraffin, wax, fatty acid ester, organic acid, graphite fine particles, mica, vermiculite, fluorine-based release agents, and silicone-based release agents.

[0046] In step (1), when additives such as the humectant, moisture resistance improver, coupling agent for strengthening the bond between the aggregate (A) and the metasilicate (B), lubricant, surfactant, and release agent are mixed in addition to the aggregate (A) and the metasilicate (B), the additives may be further mixed into the mixture of the aggregate (A) and the metasilicate (B), or the metasilicate (B) may be further mixed into the mixture of the aggregate (A) and the additives.

[0047] [Step (1)] In the step (1), a commercially available kneader can be used to mix the aggregate (A) and the metasilicate (B). In the step (1), the aggregate (A) and the metasilicate (B) can be mixed by mixing the aggregate (A) and the metasilicate (B) that has been heated and melted at 25°C to obtain a mixture, and then maintaining the mixture at a temperature below the melting point of the metasilicate (B).

[0048] Other examples include a method in which metasilicate (B) maintained at 25°C is added to aggregate (A) heated to a temperature equal to or higher than the melting point of metasilicate (B), and the aggregate (A) and metasilicate (B) are mixed while melting the metasilicate; and a method in which metasilicate (B) is added to aggregate (A) heated to a temperature equal to or higher than the melting point of metasilicate (B), and the metasilicate (B) is heated and melted, and the aggregate (A) and metasilicate (B) are mixed, and the mixture is cooled to a temperature below the melting point of metasilicate (B).

[0049] Also, SiO in a solution containing water glass, caustic alkali, and water ２ / M ２ O (M represents an alkali metal) / H ２By adjusting the molar ratio of O to 1:1:n (5≦n≦9), metasilicate hydrate with the desired amount of water of hydration can be formed. Furthermore, by mixing the above solution containing water glass, caustic alkali, and water with the molding sand, the surface of the molding sand can be coated with metasilicate hydrate, forming a second coating layer. The conditions for mixing the water glass, caustic alkali, and water are not particularly limited, and known methods can be used. For example, mixing can be performed at ambient temperature. Alternatively, if heat is generated in the molten liquid, mixing can be continued and then allowed to cool to ambient temperature. This allows the coated sand of this embodiment to be obtained.

[0050] The coated sand produced by the coated sand producing method of this embodiment can be used alone or in combination with other known aggregates or other additives to form a desired mold.

[0051] EXAMPLES The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these.

[0052] <Materials> The materials used in the following examples and comparative examples are described below. [Aggregate] Aggregate 1: Espar #60L (artificially produced Al ２ O ３Spherical aggregate: Yamakawa Sangyo Co., Ltd., average particle size: 194 μm, degree of amorphization: 45%). The average particle size of Aggregate 1 was determined by measuring the major axis diameter (μm) and minor axis diameter (μm) of randomly oriented particles using a digital microscope (Keyence Corporation, VH-8000 model) to calculate (major axis diameter + minor axis diameter) / 2, and then averaging the values ​​obtained for 100 randomly selected particles. The major axis diameter and minor axis diameter were defined as follows: A particle was stabilized on a flat surface, and when the projection of the particle on the flat surface was sandwiched between two parallel lines, the width of the particle at the smallest distance between the parallel lines was defined as the minor axis diameter, and the distance when the particle was sandwiched between two parallel lines perpendicular to the parallel lines was defined as the major axis diameter. The degree of amorphization of Aggregate 1 was measured by pulverizing Aggregate 1 in a mortar and pressing it against an X-ray glass holder of a powder X-ray diffractometer. The powder X-ray diffraction was performed using a Rigaku MultiFlex (CuKα radiation source, tube voltage 40 kV, tube current 40 mA) with a scan interval of 0.01°, a scan rate of 2° / min, and slits DS1, SS1, and RS 0.3 mm in the range of 2θ = 5 to 90°. The X-ray intensities at the low and high angles were connected by a straight line in the range of 2θ = 10 to 50°, and the area under the line was used as the background. The crystallinity was calculated using the software provided with the instrument, and this was subtracted from 100 to obtain the amorphousness. Specifically, for the area above the background, the amorphous peak (halo) and each crystalline component were separated by curve fitting, and their respective areas were determined. The amorphousness (%) was calculated using the following formula: Amorphous degree (%) = halo area / (crystalline component area + halo area) × 100 [Inorganic particles (C)] Inorganic particles 1: Denka fused silica SFP-20M (manufactured by Denka Corporation, average particle size: 0.4 μm, amorphous silica particles, amorphous degree: 99.5% or more) The average particle size of inorganic particles 1 is the average particle size (d50) at 50% cumulative volume measured using a laser diffraction / scattering particle size distribution analyzer (LA-960V2 manufactured by Horiba, Ltd.). The analysis conditions are as follows: Measurement method: flow method Dispersion medium: water Dispersion method: stirring, built-in ultrasonic for 3 minutes Sample concentration: 2 mg / 100 mL Refractive index: 1.43 The amorphous degree of inorganic particles 1 was determined in the same manner as in the measurement of the amorphous degree of aggregate 1.[Inorganic binders] Sodium metasilicate nonahydrate: sodium metasilicate nonahydrate (manufactured by Nippon Chemical Industry Co., Ltd., Si / Na molar ratio 1.0, solid content 42.9% by weight) No. 2 water glass: No. 2 sodium silicate (manufactured by Fuji Chemical Co., Ltd., Si / Na molar ratio 2.4, solid content 40.6% by weight).

[0053] <Preparation of Reclaimed Sand (A)> [Preparation of Reclaimed Sand (A1)] The reclaimed sand (A1) was prepared according to the following reclaimed sand preparation procedures (i) to (v). (i) Preparation of Aggregate Containing Inorganic Binder: 100 parts by weight of Aggregate 1 (Espearl #60L) was placed in a mixer. Next, 2 parts by weight of sodium metasilicate nonahydrate, which had been heated to 80°C and melted, was added to the mixer and kneaded for 4 minutes to obtain dry sand with room temperature fluidity. Then, 0.6 parts by weight of Inorganic Particles 1 were added and kneaded for 2 minutes to obtain an aggregate containing an inorganic binder. (ii) Preparation of Mold: The obtained aggregate containing inorganic binder was poured into the center of a truncated cone mold for preparing a test mold, measuring 298 mm in upper diameter, 205 mm in lower diameter, and 265 mm in height, to a height of 50 mm. Next, a metal core with a truncated cone shape, measuring 280 mm in upper diameter, 200 mm in lower diameter, and 220 mm in height, heated to 180°C, was placed in the mold. The remaining aggregate containing the inorganic binder was poured into the space between the mold and the metal core, and the mold was heated in a heating furnace at 180°C for 20 minutes to obtain a test mold. (iii) Casting: 10 kg of aluminum alloy AC4C (pouring temperature: 720°C) was poured into the obtained test mold. After pouring, the mold was left to cool at room temperature. (iv) Preparation of Reclaimed Sand: After casting, the casting was removed from the test mold, crushed with a hammer, etc., and further crushed in a mini crusher (manufactured by Taiyo Machinery Co., Ltd.) until the mold was reduced to single particles, obtaining recovered sand. (v) Preparation of Reclaimed Sand: The recovered sand was placed in a dry foundry sand reclamation device (Hybrid Sand Master, manufactured by Nippon Chuzo Co., Ltd.) equipped with a fluidized bed, and batch-processed for 60 minutes at a rotor speed of 2400 rpm to obtain reclaimed sand (A1). Fine powder derived from the inorganic binder generated during processing was removed using a dust collector. The average particle size of the resulting reclaimed sand (A1) was measured using the same procedure as for measuring the average particle size of Aggregate 1, and was found to be 195 μm.

[0054] [Preparation of Reclaimed Sand (A2)] Reclaimed sand (A2) that had undergone two regeneration operations was obtained by carrying out the procedures (i) to (v) for preparing the reclaimed sand (A1), except that in the procedure (i) for preparing the reclaimed sand (A1), the reclaimed sand (A1) was used instead of the aggregate 1. The average particle size of the obtained reclaimed sand (A2) was measured using the same procedure as for measuring the average particle size of aggregate 1, and was found to be 198 μm.

[0055] [Preparation of Reclaimed Sand (A3)] Reclaimed sand (A3) was obtained by repeating the procedures (i) to (v) for preparing the reclaimed sand (A1), except that the reclaimed sand (A2) was used instead of the aggregate 1 in the procedure (i) for preparing the reclaimed sand (A1). The average particle size of the obtained reclaimed sand (A3) was measured using the same procedure as for measuring the average particle size of aggregate 1, and was found to be 199 μm.

[0056] [Preparation of Reclaimed Sand (A4)] Reclaimed sand (A4) was obtained by repeating the procedures (i) to (v) for preparing the reclaimed sand (A1), except that the reclaimed sand (A3) was used instead of the aggregate 1 in the procedure (i) for preparing the reclaimed sand (A1). The average particle size of the obtained reclaimed sand (A4) was measured using the same procedure as for measuring the average particle size of aggregate 1, and was found to be 200 μm.

[0057] [Preparation of Reclaimed Sand (A5)] Reclaimed sand (A5) was obtained by repeating the procedures (i) to (v) for preparing the reclaimed sand (A1), except that the reclaimed sand (A4) was used instead of the aggregate 1 in the procedure (i) for preparing the reclaimed sand (A1). The average particle size of the obtained reclaimed sand (A5) was measured using the same procedure as for measuring the average particle size of aggregate 1, and was found to be 199 μm.

[0058] [Preparation of Reclaimed Sand (A5')] The same operations as in the preparation procedures (i) to (v) of the reclaimed sand were carried out except that in the preparation procedure (i) of the reclaimed sand (A1), the sodium metasilicate nonahydrate (2 parts by mass) in the procedure (i) was replaced with sodium metasilicate nonahydrate (4 parts by mass), and further, inorganic particles 1 (0.6 parts by mass) was replaced with inorganic particles 1 (1.2 parts by mass). The reclaimed sand obtained in the preparation procedures (i') to (v') of the reclaimed sand was designated as reclaimed sand (A1'), and further used to prepare the reclaimed sands (A2) to (A4). In the production of the reclaimed sand (A4'), production procedures (i') to (v') were performed instead of production procedures (i) to (v), and reclaimed sand (A1') to (A3') were used instead of reclaimed sand (A1) to (A3), respectively, to obtain reclaimed sand (A4'). Furthermore, in the production of the reclaimed sand (A5), reclaimed sand (A4') was used instead of reclaimed sand (A4), and reclaimed sand production procedures (i') to (v') were performed instead of reclaimed sand production procedures (i) to (v), to obtain reclaimed sand (A5') that had undergone five reclaiming operations. The average particle size of the obtained reclaimed sand (A5') was measured using the same procedure as for measuring the average particle size of aggregate 1, and was found to be 200 μm.

[0059] [Measurement of Acid Consumption V] The acid consumption V of each of the reclaimed sands (A1) to (A5) and (A5') was measured using the following procedure. The measurement results of the acid consumption V are shown in Table 1. 1. Procedure (1) 25 g of reclaimed sand (A1) to (A5) and (A5') that had been dried at 105°C for 1 hour and 50 mL of 0.1 M HCl aqueous solution (manufactured by Isekyu Co., Ltd.) were placed in a 100 mL beaker and stirred for 60 minutes with a magnetic stirrer (800 rpm) in an environment of 20°C. The resulting mixture was filtered through pleated filter paper (No. 3 φ70, manufactured by Toyo Roshi Kaisha, Ltd.), and 25 mL of the filtrate was titrated with 0.1 M NaOH aqueous solution (manufactured by Isekyu Co., Ltd.) using a potentiometric titrator at 20°C. The amount of 0.1 M NaOH aqueous solution used to change the pH to 7 was designated as A mL. 2. Procedure (2) The same treatment as in Procedure (1) was carried out without using 25 g of each of the reclaimed sands (A1) to (A5) and (A5'), and the amount of 0.1 M NaOH aqueous solution was defined as B mL. 3. Calculation of acid consumption V The acid consumption V was calculated using the following formula: V = 4(B - A) where the symbols in the formula are as follows: V: Acid consumption [mL] A: Amount A of 0.1 M NaOH in Procedure (1) [mL] B: Amount B of 0.1 M NaOH in Procedure (2) [mL]

[0060] <Preparation of Coated Sand> [Preparation of Coated Sand 1 (Example 1)] 100 parts by mass of reclaimed sand (A2) used as aggregate (A) that had been left to stand in an environment of 25°C for 12 hours and adjusted to that temperature was charged into a mixer placed in an environment adjusted to a temperature of 20 to 28°C, and sodium metasilicate nonahydrate (2 parts by mass) that had been heated to 80°C and melted was charged into the mixer and kneaded for 4 minutes to obtain coated sand 1 of Example 1.

[0061] [Preparation of Coated Sand 2 (Example 2)] Coated sand 2 of Example 2 shown in Table 1 was obtained in the same manner as in Example 1, except that the aggregate (A2) was changed to recycled sand (A3).

[0062] [Preparation of Coated Sand 3 (Example 3)] Coated sand 3 of Example 3 shown in Table 1 was obtained in the same manner as in Example 1, except that the aggregate (A2) was changed to recycled sand (A4).

[0063] [Preparation of Coated Sand 4 (Example 4)] Coated sand 4 of Example 4 shown in Table 1 was obtained in the same manner as in Example 1, except that the aggregate (A2) was changed to recycled sand (A5).

[0064] [Preparation of Coated Sand 5 (Example 5)] Coated sand 5 of Example 5 shown in Table 1 was obtained in the same manner as in Example 1, except that the aggregate (A2) was changed to recycled sand (A5').

[0065] [Preparation of Coated Sand 6 (Example 6)] Coated Sand 1 obtained in Example 1 was allowed to stand in an environment of 25°C and 55% RH for 12 hours to adjust the temperature and humidity to that temperature, and then kneaded with Inorganic Particles 1 (0.6 parts by mass) for 2 minutes using a mixer placed in an environment adjusted to a temperature of 20 to 28°C to obtain Coated Sand 6 of Example 5 shown in Table 1.

[0066] [Preparation of Coated Sand 7 (Comparative Example 1)] Coated sand 7 of Comparative Example 1 shown in Table 1 was obtained in the same manner as in Example 1, except that the recycled sand (A2) was changed to recycled sand (A1) as the aggregate.

[0067] [Preparation of Coated Sand 8 (Comparative Example 2)] Coated sand 8 of Comparative Example 2 shown in Table 1 was obtained in the same manner as in Example 2, except that the sodium metasilicate nonahydrate (2 parts by mass) in Example 2 was changed to No. 2 water glass (2.1 parts by mass) that had been left to stand for 12 hours in an environment of 25°C and 55% RH to adjust to that temperature and humidity.

[0068] <Evaluation Method> [Mold Strength] 1. Preparation of Mold Test Pieces A mold for 22.3 mm x 22.3 mm x 180 mm test pieces (5 pieces) was heated to 180°C. Each coated sand from the above Examples and Comparative Examples was filled into the mold heated to 180°C at a blow pressure of 0.3 MPa using a CSR-43 blow molding machine. The coated sand was then left to harden in the mold for 150 seconds to obtain a mold test piece. 2. Evaluation The mold strength (MPa) of each obtained mold test piece was measured using a George Fischer PFG universal strength testing machine equipped with a PBV transverse attachment. The mold test pieces were removed from the mold and left in a constant temperature and humidity chamber at 25°C / 55% RH for 1 hour. The evaluation results are shown in Table 1.

[0069]

Claims

1. A method for producing coated sand used in the manufacture of molds, comprising step (1) mixing aggregate (A) and metasilicate (B), the acid consumption V of which, as measured by the following method, is 25 mL or more and 100 mL or less: <Method for measuring acid consumption V> [Procedure (1)] 25 g of aggregate that had been dried at 105°C for 1 hour and 50 mL of 0.1 M HCl aqueous solution were placed in a 100 mL beaker and stirred with a magnetic stirrer (800 rpm) at 20°C for 60 minutes. The resulting mixture was filtered through pleated filter paper (Toyo Roshi Kaisha, Ltd., No. 3, φ70). 25 mL of the resulting filtrate was then titrated with 0.1 M NaOH aqueous solution at 20°C using a potentiometric titrator, and the amount (A [mL]) of 0.1 M NaOH aqueous solution used to change the pH to 7 was measured. [Procedure (2)] The amount of 0.1 M NaOH aqueous solution obtained by performing the same process as in Procedure (1) without using 25 g of aggregate (A) is defined as B [mL]. [Procedure (3)] The amount of acid consumed V is calculated using the following formula: V = 4(B - A) where V is the amount of acid consumed V [mL], A is the amount of 0.1 M NaOH A [mL] in Procedure (1), and B is the amount of 0.1 M NaOH B [mL] in Procedure (2).

2. The method for producing coated sand according to claim 1, wherein the aggregate (A) is recycled sand.

3. The method for producing coated sand according to claim 2, wherein the aggregate (A) contains a component derived from an inorganic binder.

4. A method for producing coated sand according to any one of claims 1 to 3, wherein the average particle size of the aggregate (A) is 50 μm or more and 500 μm or less.

5. A method for producing coated sand according to any one of claims 1 to 4, which includes, before step (1), a step (0) of confirming that the acid consumption V of the aggregate (A) is 25 mL or more and 100 mL or less.

6. A method for producing coated sand according to any one of claims 1 to 5, wherein the metasilicate (B) is one or more selected from the group consisting of anhydrous sodium metasilicate, sodium metasilicate pentahydrate, and sodium metasilicate nonahydrate.

7. A method for producing coated sand according to any one of claims 1 to 6, wherein the mixing ratio of the aggregate (A) and the metasilicate (B) is 0.01 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the aggregate (A).

8. A method for producing coated sand according to any one of claims 1 to 7, wherein step (1) is a step of mixing inorganic particles (C) in addition to the aggregate (A) and metasilicate (B).

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