Method for producing coated sand

Abstract

To provide a method for producing coated sand by which a mold having high strength can be obtained in spite of being derived from reclaimed sand.SOLUTION: A method for producing coated sand includes a step (1) of mixing aggregates (A) having an acid consumption of 25mL or more and 100mL or less with a metasilicate (B).SELECTED DRAWING: None

Description

[Technical Field]

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

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

[0003] Patent Document 2 discloses a method for producing coated sand, which comprises mixing a water glass aqueous solution as a binder with heated refractory aggregate, using an aqueous solution of sodium silicate with an SiO2 / Na2O molar ratio of 3.0 to 4.0 as the water glass aqueous solution, and adjusting the viscosity of the aqueous solution at 25°C to fall within the range of 10 to 50 cP before mixing it with the refractory aggregate. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-11296 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-117740 Summary of the Invention [Problem to be solved by the invention]

[0005] Coated sand as described in Patent Documents 1 and 2 is generally used in a casting mold, and then the mold is broken (disassembled) to produce single particles of recovered sand, which is then further recycled by various methods to produce recycled sand, which is then mixed with a 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. [Means for solving the problem]

[0008] The present invention is a method for producing coated sand used in producing molds, which includes a step (1) of mixing aggregate (A) having an acid consumption V measured by the following method of 25 mL or more and 100 mL or less with metasilicate (B). <Method for measuring acid consumption V> [Step (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 (Toyo Roshi Kaisha, Ltd., No. 3 φ70). 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 of 0.1 M NaOH aqueous solution (A [mL]) used to change the pH to 7 was measured. [Step (2)] Let B [mL] be the volume of 0.1M NaOH aqueous solution obtained by performing the same procedure as in step (1) without using 25 g of aggregate (A). [Step (3)] The acid consumption amount V is calculated by the following formula. V=4(BA) Here, V is the amount of acid consumed V [mL], A is the amount A [mL] of 0.1M NaOH in step (1), and B is the amount B [mL] of 0.1M NaOH in step (2). [Effects of the Invention]

[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 particulate matter that is one of the components that make up a mold, and more specifically, refers to sand. 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. Reclaimed sand refers to sand that has been used after casting work has been completed and its fluidity restored (dismantled), and reclaimed sand refers to sand obtained by subjecting the reclaimed sand to a regeneration process. DETAILED DESCRIPTION OF THE INVENTION

[0011] <Coated sand manufacturing method> The method for producing coated sand of this embodiment is a method for producing coated sand used in producing molds, and includes a step (1) of mixing aggregate (A) having an acid consumption V measured by the following method of 25 mL to 100 mL and metasilicate (B). <Method for measuring acid consumption V> [Step (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 (Toyo Roshi Kaisha, Ltd., No. 3 φ70). 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 of 0.1 M NaOH aqueous solution (A [mL]) used to change the pH to 7 was measured. [Step (2)] Let B [mL] be the volume of 0.1M NaOH aqueous solution obtained by performing the same procedure as in step (1) without using 25 g of aggregate (A). [Step (3)] The acid consumption amount V is calculated by the following formula. V=4(BA) Here, V is the amount of acid consumed V [mL], A is the amount A [mL] of 0.1M NaOH in step (1), and B is the amount B [mL] of 0.1M NaOH in step (2).

[0012] 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.

[0013] Residues of the binder used in mold production adhere to the surface of the recycled sand. If the binder is an inorganic binder, silicates and silicate reaction products adhere to the surface of the aggregate. When coated sand is produced using such recycled sand and water glass (sodium silicate hydrate, Na2O·nSiO2xH2O: n≧2, where x is the molecular hydration number) as an inorganic binder, the water glass reacts with the inorganic binder residues on the surface of the recycled sand even at room temperature. This reaction is particularly rapid when the residue contains silicates and / or silicate reaction products, forming a gel-like substance. This gel-like substance lacks adhesive strength to bind aggregates together and is therefore difficult to function as a binder. As a result, when recycled sand is used, the water glass fails to function as a binder, 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 an inorganic binder, the metasilicate reacts mildly with the silicate and / or its reactants at room temperature, which may prevent the formation of a gel-like substance, and thus may enable the production of coated sand that can produce molds with high mold strength. On the other hand, if the amount of silicate and / or its reactants present on the aggregate is too high, the reaction with the metasilicate is accelerated, resulting in the formation of a gel-like substance. Therefore, by setting the amount of silicate and its reactants present within an appropriate range using the acid consumption amount V, it is thought that a decrease in mold strength can be prevented.

[0014] Aggregate In the method for producing coated sand of this embodiment, the aggregate (A) has an acid consumption V measured by the following method of 25 mL or more and 100 mL or less. <Method for measuring acid consumption V> [Step (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 (Toyo Roshi Kaisha, Ltd., No. 3 φ70). 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 of 0.1 M NaOH aqueous solution (A [mL]) used to change the pH to 7 was measured. [Step (2)] Let B [mL] be the volume of 0.1M NaOH aqueous solution obtained by performing the same procedure as in step (1) without using 25 g of aggregate (A). [Step (3)] The acid consumption amount V is calculated by the following formula. V=4(BA) Here, V is the amount of acid consumed V [mL], A is the amount A [mL] of 0.1M NaOH in step (1), and B is the amount B [mL] of 0.1M NaOH in step (2).

[0015] 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 obtain 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 obtain recycled sand before step (1). In the coated sand manufacturing method of this embodiment, the number of steps of treating recycled sand to obtain 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.

[0016] The aggregate (A) used in step (1) in the method for producing coated sand of this embodiment is preferably one selected from the group consisting of natural sand and artificial sand, and may be a combination of these.

[0017] 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.

[0018] 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 / Al2O3-based ZrO2-based sand, SiO2 / Al2O3 / Fe2O3-based sand, and slag-derived sand. Here, the term "major component" refers to the component that is most abundant by mass among the components contained in the sand. The artificial sand does not refer to naturally occurring sand, but refers to sand obtained by artificially preparing metal oxide components and then 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 more preferably Al2O3-based artificial sand.

[0019] (Average particle size of aggregate (A)) From the viewpoints of improving mold quality and mold strength, and 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 viewpoints, 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 viewpoints, 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.

[0020] In the method for producing coated sand of this embodiment, the average particle size of the aggregate (A) can be measured, for example, by the following method. (Method for measuring the average particle size of aggregate (A)) If the sphericity of the aggregate (A) particle projected cross section is 1, the diameter (mm) is measured. On the other hand, if the sphericity is less than 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. 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: A particle is stabilized on a flat surface, and when the projected image of the particle on the flat surface 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. The distance between the particle and two parallel lines perpendicular to the parallel lines is called the major axis diameter. The major and minor axis diameters of a particle can be determined by taking an image (photograph) of the particle using an optical microscope or a digital microscope (e.g., Keyence VH-8000) and analyzing the resulting image.

[0021] (Amorphous degree of aggregate (A)) From the viewpoint of improving mold strength and obtaining low thermal expansion, the degree of amorphization 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 degree of amorphization 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 degree of amorphization 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 raw materials are treated in a flame and rapidly cooled. In either case, the cooling method may be selected appropriately at various rates depending on the material and particle size. Another possible method is to amorphize a material that has been crystallized by heat treatment and cooling treatment. Among these, the flame fusion method, in which heating and cooling can be easily controlled, is preferred.

[0022] 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) was crushed in a mortar and pressed onto an X-ray glass holder of a powder X-ray diffractometer. The powder X-ray diffractometer used was a Rigaku MultiFlex (CuKα radiation source, 40 kV tube voltage, 40 mA tube current) with a scan interval of 0.01°, a scan rate of 2° / min, and slits DS1, SS1, and RS0.3 mm, in the 2θ range of 5° to 90°. A straight line was drawn connecting the X-ray intensities at low and high angles in the 2θ range of 10° to 50°. 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, the amorphous peak (halo) and each crystalline component were separated by curve fitting for the area above the background, and their respective areas were determined. The amorphousness (%) was calculated using the following formula: Amorphous ratio (%) = halo area / (crystalline component area + halo area) × 100

[0023] (Components derived from the binder contained in aggregate (A)) When the aggregate (A) is recycled sand, the components derived from the binder contained in the aggregate (A), i.e., the residue of the binder used in producing the mold, may be organic or inorganic. 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 the aggregate (A) contains a component derived from an inorganic binder.

[0024] (Components derived from inorganic binders 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. More specifically, aggregate (A') is preferably silica (SiO2), sodium silicate (Na2O·nSiO2:n≧2), potassium silicate (KO·nSiO2:n≧2), sodium metasilicate (Na2O·nSiO2:n≧2), or the like. More preferably, the silicate is treated with one or more selected from the group consisting of potassium metasilicate (K2O·nSiO2:n=0.9-1.1), potassium orthosilicate (Na2O·nSiO2:n=0.49-0.59), and potassium orthosilicate (K2O·nSiO2:n=0.49-0.59), and even more preferably, it is treated with one or more selected from silica, sodium silicate, and sodium metasilicate. The silicate may be anhydrous or hydrated.

[0025] The aggregate (A) containing a component derived from an inorganic binder preferably means 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.

[0026] [Acid consumption V] 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> [Step (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 (Toyo Roshi Kaisha, Ltd., No. 3 φ70). 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 of 0.1 M NaOH aqueous solution (A [mL]) used to change the pH to 7 was measured. [Step (2)] Let B [mL] be the volume of 0.1M NaOH aqueous solution obtained by performing the same procedure as in step (1) without using 25 g of aggregate (A). [Step (3)] The acid consumption amount V is calculated by the following formula. V=4(BA) Here, V is the amount of acid consumed V [mL], A is the amount A [mL] of 0.1M NaOH in step (1), and B is the amount B [mL] of 0.1M NaOH in step (2).

[0027] The acid consumption V is an indicator of the amount of components contained in aggregate (A) that originate from the binder used to mold the aggregate, i.e., the amount of residue. When the binder used to mold the aggregate is an inorganic binder, silicic acid and / or silicate compounds, which are components originating from the binder used to mold the aggregate, react with hydrochloric acid and are consumed. The remaining hydrochloric acid is then back-titrated with sodium hydroxide to calculate the amount of inorganic binder remaining in aggregate (A) that was used to mold the aggregate. When the binder used to mold the aggregate is an inorganic binder, the acid consumption V is an indicator of the amount of components originating 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 coated sand production method 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.

[0028] 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 high, 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.

[0029] [Metasilicate (B)] (Type of metasilicate (B)) The metasilicate (B) mixed with the aggregate (A) in step (1) of the coated sand production method of this embodiment is preferably an alkali metal metasilicate (MO·nSiO: M = alkali metal, n = 0.9 to 1.1) from the viewpoint of improving the strength of a mold produced using the coated sand obtained by the coated sand production method of this embodiment. Among these, one or more selected from sodium metasilicate and potassium metasilicate are more preferred, and sodium metasilicate is even more preferred.

[0030] 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.

[0031] In step (1) of the method for producing coated sand of this embodiment, an inorganic binder other than metasilicate (B) may be added and mixed in addition to metasilicate (B). In the method for producing coated sand of this embodiment, the inorganic binder other than metasilicate (B) is preferably one or more selected from sodium silicate (NaO·nSiO2: n≧2), potassium silicate (KO·nSiO2: n≧2), sodium orthosilicate (NaO·nSiO2: n=0.49-0.59), and potassium orthosilicate (KO·nSiO2: n=0.49-0.59). In step (1) of the method for producing coated sand of this embodiment, the amount of inorganic binder other than metasilicate (B) added relative to 100 parts by mass of 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 even more preferably 0 part by mass.

[0032] (Ratio of aggregate (A) and metasilicate (B)) In the method for producing coated sand of this embodiment, the mixing ratio of aggregate (A) to metasilicate (B) is 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 even more preferably 0.8 part by mass or more, per 100 parts by mass 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. From the same viewpoint, the mixing ratio 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 even more preferably 2 parts by mass or less.

[0033] (Inorganic particles) In the method for producing coated sand of this 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 this embodiment.

[0034] 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.

[0035] 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 into the mixture of the aggregate (A) and the metasilicate (B), the metasilicate (B) may be further mixed into the mixture of the aggregate (A) and the inorganic particles, or the aggregate (A) may be further mixed into the mixture of the metasilicate (B) and the inorganic particles (C).

[0036] 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.

[0037] (Average particle size of inorganic particles (C)) The average particle size of the inorganic particles (C) is preferably 0.1 μm or more, more preferably 0.3 μm or more, from the viewpoints of improving mold quality and mold strength, and of ease of mold production, and from the same viewpoints, 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.

[0038] (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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] Examples of the surfactant include cationic surfactants, anionic surfactants, amphoteric surfactants, nonionic surfactants, and silicone surfactants.

[0044] 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.

[0045] 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.

[0046] [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).

[0047] 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 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 mixed with aggregate (A), and the mixture is cooled to a temperature below the melting point of metasilicate (B).

[0048] Furthermore, by adjusting the molar ratio of SiO2 / MO (M represents an alkali metal) / HO in a solution containing water glass, caustic alkali, and water 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 from 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.

[0049] 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. [Example]

[0050] EXAMPLES The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these.

[0051] <Material> The materials used in the following examples and comparative examples will be described. 〔aggregate〕 Aggregate 1: Espearl #60L (artificially produced Al2O3-based spherical aggregate: manufactured by Yamakawa Sangyo Co., Ltd., average particle size: 194 μm, amorphousness: 45%) The average particle size of Aggregate 1 was determined by measuring the long axis diameter (μm) and short axis diameter (μm) of randomly oriented particles using a digital microscope (Keyence VH-8000) to calculate (long axis diameter + short axis diameter) / 2, and then averaging the values ​​obtained for 100 randomly selected particles. The long axis diameter and short axis diameter were defined as follows: A particle was stabilized on a flat surface, and when the particle's projection onto 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 short axis diameter, and the distance when the particle was sandwiched between two parallel lines perpendicular to the parallel lines was defined as the long axis diameter. The degree of amorphousness of Aggregate 1 was measured by crushing Aggregate 1 in a mortar and pressing it into an X-ray glass holder of a powder X-ray diffractometer. The powder X-ray diffractometer used was a Rigaku MultiFlex (CuKα radiation source, 40 kV tube voltage, 40 mA tube current) with a scan interval of 0.01°, a scan rate of 2° / min, and slits DS1, SS1, and RS0.3 mm in the 2θ range of 5° to 90°. A straight line was drawn connecting the X-ray intensities at low and high angles in the 2θ range of 10° to 50°. The area under the line was used as the background. The degree of crystallinity was calculated using the software provided with the instrument and subtracted from 100 to obtain the degree of amorphousness. Specifically, the amorphous peak (halo) and each crystalline component were separated by curve fitting for the area above the background, and the respective areas were determined. The degree of amorphousness (%) was calculated using the following formula: Amorphous ratio (%) = halo area / (crystalline component area + halo area) × 100 [Inorganic particles (C)] Inorganic particle 1: Denka fused silica SFP-20M (manufactured by Denka Co., Ltd., average particle size: 0.4 μm, amorphous silica particles, amorphous content: 99.5% or more) The average particle size of the 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 3 minutes Sample concentration: 2mg / 100mL Refractive index: 1.43 The degree of amorphism of inorganic particles 1 was determined in the same manner as in the measurement of the degree of amorphism of aggregate 1. [Inorganic binder] 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)

[0052] <Preparation of recycled sand (A)> [Preparation of recycled 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 mass of Aggregate 1 (Espearl #60L) was placed in a mixer. Next, sodium metasilicate nonahydrate (2 parts by mass) that had been heated to 80°C and melted was added to the mixer and mixed for 4 minutes to obtain dry sand with room temperature fluidity. Then, inorganic particles 1 (0.6 parts by mass) were added and mixed for 2 minutes to obtain aggregate containing an inorganic binder. (ii) Preparation of the template The resulting aggregate containing inorganic binder was poured into the center of a truncated conical mold (top diameter 298 mm, bottom diameter 205 mm, height 265 mm) for preparing a test mold, up to a height of 50 mm. Next, a truncated conical metal core (top diameter 280 mm, bottom diameter 200 mm, height 220 mm) heated to 180°C was placed in the mold. The remaining aggregate containing 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 material (pouring temperature 720°C) was poured into the obtained test mold. After pouring, it was left to cool at room temperature. (iv) Preparation of recycled sand After casting, the casting was removed from the test mold, and the test mold was crushed with a hammer or the like, and further crushed in a mini crusher (manufactured by Taiyo Machinery Co., Ltd.) until the mold became single particles, and recovered sand was obtained. (v) Preparation of recycled sand The reclaimed 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 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.

[0053] [Production of recycled sand (A2)] The same procedures (i) to (v) were repeated to obtain reclaimed sand (A2) that had undergone two regeneration operations, except that the reclaimed sand (A1) was used instead of the aggregate 1 in the reclaimed sand (A1) production procedure (i). The average particle size of the 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.

[0054] [Production of recycled sand (A3)] The same procedures (i) to (v) were repeated to obtain reclaimed sand (A3), which had undergone three regeneration operations, except that the reclaimed sand (A2) was used instead of the aggregate 1 in the reclaimed sand (A1) production procedure (i). The average particle size of the reclaimed sand (A3) was measured using the same procedure as for the aggregate 1, and was found to be 199 μm.

[0055] [Production of recycled sand (A4)] The same procedures (i) to (v) were repeated to obtain reclaimed sand (A4), which had undergone four regeneration operations, except that the reclaimed sand (A3) was used instead of the aggregate 1 in the reclaimed sand (A1) production procedure (i). The average particle size of the 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.

[0056] [Production of recycled sand (A5)] The same procedures (i) to (v) were repeated to obtain reclaimed sand (A5), which had undergone five regeneration operations, except that the reclaimed sand (A4) was used instead of the aggregate 1 in the reclaimed sand (A1) production procedure (i). The average particle size of the reclaimed sand (A5) was measured using the same procedure as for the aggregate 1, and was found to be 199 μm.

[0057] [Production of recycled sand (A5')] The same operations as in the above-mentioned reclaimed sand preparation procedures (i) to (v) 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 changed to sodium metasilicate nonahydrate (4 parts by mass), and further, inorganic particle 1 (0.6 parts by mass) was changed to inorganic particle 1 (1.2 parts by mass). The reclaimed sand obtained in the above-mentioned reclaimed sand preparation procedures (i') to (v') was designated as reclaimed sand (A1'). Further, the reclaimed sands (A2) to (A4) were also prepared. In the production of the recycled sand (A4'), steps (i) to (v) were replaced with steps (i') to (v'), and recycled sand (A1') to (A3') were used instead of steps (i) to (v), respectively, to obtain recycled sand (A4').Furthermore, in the production of the recycled sand (A5), recycled sand (A4') was used instead of recycled sand (A4), and steps (i') to (v') were replaced with steps (i) to (v) to obtain recycled sand (A5'), which underwent five recycling operations.The average particle size of the resulting recycled 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.

[0058] [Measurement of acid consumption V] The acid consumption V of each of the reclaimed sands (A1) to (A5) and (A5') was measured by the following procedure. The measurement results of the acid consumption V are shown in Table 1. 1. Step (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 (rotation speed: 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 taken and titrated with 0.1 M NaOH aqueous solution (manufactured by Isekyu Co., Ltd.) at 20°C using a potentiometric titrator. The amount of 0.1 M NaOH aqueous solution used to change the pH to 7 was defined as A mL. 2. Step (2) The amount of 0.1 M NaOH aqueous solution obtained by performing the same treatment as in step (1) without using 25 g of each of the reclaimed sands (A1) to (A5) and (A5') was designated as B mL. 3. Calculation of acid consumption V The acid consumption amount V was calculated by the following formula. V=4(BA) The symbols in the formula are as follows: V: Acid consumption [mL] A: Amount of 0.1M NaOH in step (1) [mL] B: Amount of 0.1M NaOH in step (2) [mL]

[0059] <Production of coated sand> [Preparation of Coated Sand 1 (Example 1)] 100 parts by mass of reclaimed sand (A2) used as aggregate (A) was left to stand in an environment of 25°C for 12 hours to adjust the temperature to that temperature, and then placed in a mixer placed in an environment adjusted to a temperature of 20 to 28°C. Sodium metasilicate nonahydrate (2 parts by mass) that had been heated to 80°C and melted was then added to the mixer and kneaded for 4 minutes to obtain coated sand 1 of Example 1.

[0060] [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).

[0061] [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).

[0062] [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).

[0063] [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').

[0064] [Preparation of Coated Sand 6 (Example 6)] Coated sand 1 obtained in Example 1 was left 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 mixed with inorganic particles 1 (0.6 parts by mass) for 2 minutes in a mixer placed in an environment adjusted to a temperature of 20 to 28°C to obtain coated sand 6 of Example 5 listed in Table 1.

[0065] [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.

[0066] [Preparation of Coated Sand 8 (Comparative Example 2)] Coated sand 8 of Comparative Example 2 listed in Table 1 was obtained in the same manner as in Example 2, except that in Example 2, sodium metasilicate nonahydrate (2 parts by mass) was replaced with No. 2 water glass (2.1 parts by mass) that had been left to stand in an environment of 25°C and 55% RH for 12 hours and adjusted to that temperature and humidity.

[0067] <Evaluation method> [Mold strength] 1. Preparation of Mold Specimens A mold for 22.3 mm × 22.3 mm × 180 mm test pieces (5 pieces) 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 at a blow pressure of 0.3 MPa using a CSR-43 blow molding machine, and the coated sand was left to harden in the mold for 150 seconds to obtain a molded test piece. 2. Evaluation The mold strength (MPa) of each mold specimen was measured using a George Fischer PFG universal strength testing machine equipped with a PBV flexural attachment. The mold specimens 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.

[0068] [Table 1]

Claims

1. A method for producing coated sand used in the production of casting molds, comprising: A method for producing coated sand, comprising the step (1) of mixing aggregate (A) having an acid consumption V of 25 mL or more and 100 mL or less, as measured by the following method, with metasilicate (B). <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 (rotational speed: 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.), and 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 treatment as in procedure (1) without using 25 g of aggregate (A) is defined as B [mL]. [Procedure (3)] The acid consumption amount V is calculated by the following formula. V = 4 (B - A) Here, V means the amount of acid consumed V [mL], A means the amount A [mL] of 0.1 M NaOH in step (1), and B means the amount B [mL] of 0.1 M NaOH in step (2).

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

5. 2. The method for producing coated sand according to claim 1, further comprising, before the 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. 2. The method for producing coated sand according to claim 1, wherein the metasilicate (B) is at least one selected from the group consisting of anhydrous sodium metasilicate, sodium metasilicate pentahydrate, and sodium metasilicate nonahydrate.

7. 2. The method for producing coated sand according to claim 1, wherein a 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 with respect to 100 parts by mass of the aggregate (A).

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

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