Inorganic coated sand and method for producing same, casting mould, and method for improving storage stability of inorganic coated sand

Abstract

An inorganic coated sand is a dry inorganic coated sand including one or two kinds of aggregates selected from a regenerated sand (A) and a refractory aggregate (B), and a first coating layer covering the aggregate and disposed on a surface thereof; and a second coating layer containing a metasilicate on the first coating layer of the casting sand, in which the refractory aggregate (B) contains SiO2, and a cation exchange capacity (CEC) of the casting sand is 3 mmol (+) / kg or more and 40 mmol (+) / kg or less.

Description

TECHNICAL FIELD

[0001] The present invention relates to an inorganic coated sand, a method for producing the same, a casting mold, and a method for improving storage stability of the inorganic coated sand.BACKGROUND ART

[0002] In recent years, the importance of product design that takes into consideration people and the environment has increased from the viewpoint of sustainable development goals (SDGs), and the technical development of an environmentally friendly casting process in which CO 2 emissions and VOCs are reduced has been accelerated.

[0003] As the environmentally friendly casting process, for example, an inorganic binder process of wet sand using a refractory aggregate and an inorganic binding agent consisting of liquid water glass is known. Examples thereof include those described in Patent Document 1 (PCT Japanese Translation Patent Publication No 2010-519042)

[0004] Patent Document 2 (Published Japanese Translation No. 2021-536367) describes that a mixture is obtained by mixing regenerated sand with a particulate amorphous oxide containing silicon dioxide, and the mixture is heat-treated at a temperature of 400°C or higher, whereby the usable time is improved, the surface quality of a casting is improved, and a significant energy saving can be realized.

[0005] Patent Document 3 (Japanese Unexamined Patent Publication No. 2014-117740) discloses a method for producing dry coated sand having normal temperature fluidity, in which a specific water glass aqueous solution is mixed with a heated refractory aggregate as a bonding material, and moisture is evaporated to form a coating layer of the bonding material on a surface of the refractory aggregate.RELATED DOCUMENTPATENT DOCUMENT

[0006] Patent Document 1: PCT Japanese Translation Patent Publication No 2010-519042 Patent Document 2: Published Japanese Translation No. 2021-536367 Patent Document 3: Japanese Unexamined Patent Publication No. 2014-117740 SUMMARY OF THE INVENTIONTECHNICAL PROBLEM

[0007] By the way, after casting, the coated sand used for the mold is usually reused as regenerated sand obtained by performing a regeneration treatment on regenerated sand obtained by breaking (crushing) the mold to obtain single particles by various methods. From the viewpoint of economy and the viewpoint of waste reduction, it has become essential to manufacture a mold using regenerated sand in a foundry.

[0008] The present inventors have found that, in a case where a new metasilicate hydrate layer is formed to produce inorganic coated sand with casting sand formed of regenerated sand in an inorganic binder process using an inorganic binding agent in the related art as described in Patent Document 2 and 3, the sand may be quickly moistened during storage, and a desired mold may not be modeled. In addition, even in a case where a refractory aggregate having a relatively high degree of crystallization is used, the same tendency of being moistened during storage is observed in a case where the inorganic coated sand is produced by forming a layer of a metasilicate hydrate.

[0009] Examples of a regeneration method for the inorganic binder process in the related art include the baking regeneration described in Patent Document 1. However, it is not possible to sufficiently suppress the wetting, and since a high-temperature treatment at 600°C to 800°C is performed, there is a problem in terms of energy consumption and CO 2 emission. In addition, Patent Document 1 relates to an inorganic binder process of wet sand using an inorganic binding agent consisting of liquid water glass.

[0010] That is, an object of the present invention is to suppress the wetting of the inorganic coated sand during the storage of the regenerated sand and the like, and to reduce the environmental load during the production of the casting sand for the inorganic coated sand using the regenerated sand and the like.SOLUTION TO PROBLEM

[0011] Therefore, the inventors of the present invention found that applying a coating layer to the regenerated sand or the refractory aggregate containing SiO 2 and setting the cation exchange capacity (CEC) of the casting sand to a specific value is effective for solving the above-described problems, and completed the present invention.

[0012] According to the present invention, there is provided an inorganic coated sand in a dry state including: a casting sand in which a first coating layer is disposed on a surface of one or two kinds of aggregates selected from a regenerated sand (A) and a refractory aggregate (B); and a second coating layer containing a metasilicate on the first coating layer of the casting sand, in which the refractory aggregate (B) contains SiO 2 , and a cation exchange capacity (CEC) of the casting sand is 3 mmol (+) / kg or more and 40 mmol (+) / kg or less.

[0013] In addition, according to the present invention, there is provided a casting mold consisting of the above-described inorganic coated sand.

[0014] In addition, according to the present invention, there is provided a method for producing an inorganic coated sand, the method including: a step (1) of mixing one or two kinds of aggregates selected from a regenerated sand (A) and a refractory aggregate (B), and an aluminate or aluminum hydroxide, and forming a first coating layer on a surface of the aggregate to obtain a casting sand; a step (2) of mixing the obtained casting sand with a molten solution of a metasilicate hydrate to obtain a mixture; and a step (3) of cooling the mixture to a temperature lower than a melting point of the metasilicate hydrate, in which the refractory aggregate (B) contains SiO 2 .

[0015] In addition, according to the present invention, there is provided a method for producing an inorganic coated sand, the method including: a step (4) of mixing one or two kinds of aggregates selected from a regenerated sand (A) and a refractory aggregate (B), and an aluminate or aluminum hydroxide, forming a first coating layer on a surface of the aggregate to a obtain casting sand; a step (5) of mixing the obtained casting sand with a solution including water glass, caustic alkali, and water to obtain a mixture including a metasilicate hydrate, in which the refractory aggregate (B) contains SiO 2 .

[0016] In addition, according to the present invention, there is provided a method for improving storage stability of an inorganic coated sand, in which the inorganic coated sand includes a casting sand containing one or two kinds of aggregates selected from a regenerated sand (A) and a refractory aggregate (B); and a second coating layer containing a metasilicate coating the casting sand, the refractory aggregate (B) contains SiO 2 , and the inorganic coated sand in a dry state is prepared such that a cation exchange capacity (CEC) of the casting sand is 3 mmol (+) / kg or more and 40 mmol (+) / kg or less. ADVANTAGEOUS EFFECTS OF INVENTION

[0017] According to the present invention, it is possible to improve the storage stability of the inorganic coated sand while reducing the environmental load during the production of the casting sand for inorganic coated sand.DESCRIPTION OF EMBODIMENTS

[0018] Hereinafter, embodiments of the present invention will be described. In this specification, "A to B" indicating a numerical range represents a range of A or greater and B or less unless otherwise specified. The configurations and elements described in the embodiments can be appropriately combined as long as the effects of the invention are not impaired.

[0019] In addition, the "coating" and the "coating layer" are not limited to being continuous, and may have a discontinuous portion in a part thereof.<Inorganic Coated Sand>

[0020] The inorganic coated sand of the present embodiment is an inorganic coated sand in a dry state including a casting sand that includes one or two kinds of the aggregate selected from the regenerated sand (A) and the refractory aggregate (B), and a first coating layer that covers the aggregate and is located on the surface thereof, and a second coating layer that includes a metasilicate and is provided on the first coating layer of the casting sand. The refractory aggregate (B) contains SiO 2 , and a cation exchange capacity (CEC) of the casting sand is 3 mmol (+) / kg or more and 40 mmol (+) / kg or less.

[0021] That is, in a case of producing the inorganic coated sand by using one or two kinds of the aggregates selected from the regenerated sand (A) and the refractory aggregate (B), the inorganic coated sand of the present embodiment can improve the storage stability of the inorganic coated sand using one or two kinds of the aggregates selected from the regenerated sand (A) and the refractory aggregate (B) by laminating the first coating layer and the second coating layer containing a silicate in this order on the surface of the aggregate and controlling the cation exchange capacity (CEC) of the casting sand.

[0022] The details of the reason for this are not clear, but are presumed to be as follows. (i) A residue of an inorganic binding agent that has been used once for casting may be attached to the surface of the regenerated sand (A). In a case where a surface of regenerated sand (A) having a residue of an inorganic binding agent is coated with a metasilicate hydrate to produce inorganic coated sand, the component in the residue reacts with the metasilicate hydrate, the metasilicate hydrate crystal is melted, and the inorganic coated sand is wet. (ii) On the other hand, in a case where a silicate hydrate is coated on a surface of a refractory aggregate (B) containing SiO 2 to produce an inorganic coated sand, as in the case of (i), the SiO 2 component of the refractory aggregate (B) and the silicate hydrate may react with each other, and thus the silicate hydrate crystal may be melted and the inorganic coated sand may be wet. (iii) Therefore, it is presumed that, by forming the first coating layer to cover the surface of the regenerated sand (A) or the refractory aggregate (B) and forming a casting sand having a specific CEC, the reaction with the residue can be suppressed, and even in a case where the second coating layer containing a metasilicate is laminated, the melting of the metasilicate hydrate in the second coating layer can be suppressed, and as a result, the wetting of the inorganic coated sand can be suppressed and the storage stability can be improved.

[0023] In addition, in a case where the first coating layer that coats the surface of the regenerated sand (A) or the refractory aggregate (B) is formed of an aluminosilicate-containing substance, the first coating layer can be formed at a relatively low temperature. Therefore, in the regeneration of the inorganic binder process in the related art, a baking step at 600°C to 800°C is taken, but this can be omitted, and it is possible to suppress the consumption of thermal energy and the emission of CO 2 , and to reduce the environmental load.

[0024] Hereinafter, the inorganic coated sand of the present embodiment will be described in more detail.

[0025] The inorganic coated sand is dry. The coated sand in a dry state means coated sand in which regardless of the water content, a measured value is obtained in the measurement of a dynamic angle of repose. The dynamic angle of repose is preferably 80° or less, more preferably 45° or less, and even more preferably 30° or less.

[0026] Here, the dynamic angle of repose can be measured by the following method.(Measurement Method for Dynamic Repose Angle)

[0027] Coated sand of half the volume of the cylindrical transparent plastic bottle is put into the cylindrical transparent plastic bottle, the cylindrical transparent plastic bottle is held such that the axial center is horizontal, and the cylindrical transparent plastic bottle is rotated around the horizontal axial center at a rotation speed of 60 rpm. A slope of the coated sand layer flowing in the cylinder becomes flat. An angle formed between the slope and the horizontal plane is measured. In a case where the coated sand does not flow in the cylinder, or the slope of the coated sand layer is not formed as a flat plane even when the coated sand flows, and as a result, the dynamic angle of repose cannot be measured, the sand is in a wet state.

[0028] The inorganic coated sand is specifically composed of a particle group of the inorganic coated sand.

[0029] The inorganic coated sand preferably has a spherical shape in terms of improving fluidity further improving a filling property into a molding die. Here, the spherical shape of the inorganic coated sand means a ball-like round shape. More specifically, from the viewpoint of improving fluidity, mold quality, and mold strength, and from the viewpoint of ease of modeling the mold, the sphericity of the inorganic coated sand is preferably 0.75 or more, more preferably 0.80 or more, and still more preferably 0.82 or more. In addition, the upper limit value of the sphericity is specifically 1.

[0030] In the present embodiment, the sphericity of the inorganic coated sand specifically coincides with the sphericity of the refractory aggregate described later.

[0031] Here, the sphericity of the inorganic coated sand can be determined by analyzing an image (photograph) of particles obtained by using an optical microscope or a digital microscope (for example, VH-8000 manufactured by KEYENCE CORPORATION), determining an area of a cross section of projected particles and a perimeter of the cross section, and calculating [perimeter (mm) of perfect circle with the same area as the area (mm 2< ) of cross section of projected particles] / [perimeter (mm) of cross section of projected particles], and then averaging values each obtained for any 50 particles.

[0032] An average particle diameter of the inorganic coated sand is preferably 0.05 mm or more, and more preferably 0.1 mm or more, in terms of improvement in quality of the casting mold and strength of the casting mold, or easiness of molding the casting mold, and the storage stability. Further, when the average particle diameter of the inorganic coated sand is the lower limit or more described above, an amount of the second coating layer used can be reduced during the manufacture of the casting mold, which is preferable in terms of easiness of reproduction of the inorganic coated sand.

[0033] The average particle diameter of the inorganic coated sand is preferably 2 mm or less, more preferably 1 mm or less, and even more preferably 0.5 mm or less in terms of improvement in quality of the casting mold and strength of the casting mold, or easiness of molding the casting mold. In addition, when the average particle diameter of the inorganic coated sand is the upper limit or less described above, a porosity of the inorganic coated sand is reduced during the manufacture of the casting mold, which is preferable in terms of increasing the strength of the casting mold.

[0034] In the present embodiment, the average particle diameter of the inorganic coated sand and an average particle diameter of the refractory aggregate to be described later can be specifically measured by the following method.(Method for Measuring Average Particle Diameter)

[0035] When the sphericity = 1, a diameter (mm) of the particles is measured from the cross section of the projected particles. On the other hand, when the sphericity < 1, a major axis diameter (mm) and a minor axis diameter (mm) of particles randomly oriented are measured to determine (major axis diameter + minor axis diameter) / 2, and values each obtained for any 100 particles are averaged to obtain an average particle diameter (mm). The major axis diameter and the minor axis diameter are defined as follows. When the particles are stabilized on a plane and a projected image of the particles on the plane is sandwiched between two parallel lines, a width of the particles as a minimum distance between the parallel lines is referred to as the minor axis diameter, whereas a distance when the particles are sandwiched between the two parallel lines in a direction perpendicular to the parallel lines is referred to as the major axis diameter.

[0036] The major axis diameter and the minor axis diameter of the particles can be determined by capturing an image (photograph) of the particles with an optical microscope or a digital microscope (for example, VH-8000 manufactured by KEYENCE CORPORATION), and analyzing the obtained image.

[0037] Hereinafter, each configuration of the inorganic coated sand will be described.[Regenerated Sand (A)]

[0038] The regenerated sand (A) is a refractory material that is reused from a used casting mold or core formed of a refractory aggregate and a binding agent. Preferably, the regenerated sand (A) has a refractory aggregate and an inorganic binding agent layer which is formed on a surface of the refractory aggregate and contains one or more selected from a silicate and a reactant of the silicate.

[0039] The regenerated sand (A) is obtained, for example, by a production method described later.(Refractory Aggregate)

[0040] Examples of the material of the refractory aggregate constituting the regenerated sand (A) include one or more selected from the group consisting of natural sand and artificial sand. The refractory aggregate is specifically composed of the particle group of the refractory aggregate.

[0041] Examples of the natural sand include one or two or more selected from the group consisting of silica sand containing quartz as a main component, chromate sand, zircon sand, olivine sand, and alumina sand.

[0042] Examples of the artificial sand include one or two or more selected from the group consisting of synthetic mullite sand, SiO 2 -based casting sand containing SiO 2 as a main component, Al 2 O 3 -based casting sand containing Al 2 O 3 as a main component, SiO 2 / Al 2 O 3 -based casting sand, SiO 2 / MgO-based casting sand, SiO 2 / Al 2 O 3 / ZrO 2 -based casting sand, SiO 2 / Al 2 O 3 / Fe 2 O 3 -based casting sand, and casting sand derived from slag. Here, the main component means the most abundant component among the components contained in the sand.

[0043] The artificial sand refers to casting sand in which a metal oxide component is artificially prepared and melted or sintered, not casting sand produced from nature. In addition, recovered sand obtained by recovering the used refractory aggregate, regenerated sand obtained by reproducing the recovered sand, and the like can also be used as the artificial sand.

[0044] The content of each component such as SiO 2 , Al 2 O 3 , and Fe 2 O 3 in the refractory aggregate can be measured using the following fluorescence X-ray method. The refractory aggregate is adjusted to a size of about 0.1 µm or less with a vibration mill, and heated at 1,050°C for 1 hour. Then, 5 g of lithium tetraborate and 0.5 g of a refractory aggregate are mixed, and the mixture is heated at 1,200°C for 10 minutes to be melted and then cooled to prepare a sample in a glassy state (glass bead method). The sample is subjected to fluorescence X-ray analysis by a fundamental parameter (FP) method using a fluorescence X-ray analyzer ZSX Primus II (manufactured by Rigaku Corporation).

[0045] In the present embodiment, since the sphericity of the refractory aggregate matches the sphericity of the inorganic coated sand, the same preferred conditions are applied.

[0046] Further, an average particle diameter of the refractory aggregate is preferably 0.05 mm or more, and more preferably 0.1 mm or more, in terms of improvement in quality of the casting mold and a strength of the casting mold, or easiness of molding the casting mold. Further, when the average particle diameter of the refractory aggregate is the lower limit or more described above, an amount of the second coating layer used can be reduced during the manufacture of the casting mold, which is preferable in terms of easiness of reproduction of the inorganic coated sand.

[0047] The average particle diameter of the refractory aggregate is preferably 2 mm or less, more preferably 1 mm or less, and even more preferably 0.5 mm or less, in terms of improvement in quality of the casting mold and a strength of the casting mold, or easiness of molding the casting mold. In addition, when the average particle diameter of refractory aggregate is the upper limit or less described above, a porosity of the inorganic coated sand{b> <b}is reduced during the manufacture of the casting mold, which is preferable in terms of increasing the strength of the casting mold.

[0048] From the viewpoint of obtaining a smoother surface of the aggregate and further improving the strength of the mold, and from the viewpoint of obtaining low thermal expansion properties, the degree of amorphousness of the refractory aggregate is preferably 20% or more, more preferably 30% or more, and still more preferably 40% or more.

[0049] The upper limit of the amorphous degree of the refractory aggregate (A) is not limited, but is, for example, 100% or less, and may be 99% or less.

[0050] The degree of amorphousness of the refractory aggregate can be measured by the following X-ray diffraction method.(X-Ray Diffraction Method)

[0051] The refractory aggregate was pulverized in a mortar, and pressure-bonded to an X-ray glass holder of a powder X-ray diffraction apparatus for measurement. As the powder X-ray diffraction apparatus, MultiFlex (light source: CuKα ray, tube voltage: 40 kV, tube current: 40 mA) manufactured by Rigaku Corporation was used, and the measurement was performed in a range of 2θ = 5° to 90° at a scanning interval of 0.01° and a scanning speed of 2° / min with slits DS 1, SS 1, RS 0.3 mm. Within a range of 2θ = 10° to 50°, the X-ray intensities on the low-angle side and the high-angle side are connected by a straight line, the area below the straight line is set as a background, the crystallinity is obtained using the software attached to the apparatus and subtracted from 100, and the result is defined as the amorphous degree. Specifically, with respect to the area above the background, the amorphous peak (halo) and each crystalline component are separated by curve fitting, and areas thereof are obtained to calculate the amorphous degree (%) by the following formula.

[0052] Various methods are used as a method for controlling the amorphous degree of the refractory aggregate (A), and in general, a manufacturing method in which a melted material is rapidly cooled is preferably used. For example, a method including: melting a raw material; air-granulating the melted material; and rapidly cooling the air-granulated material, or a method including: treating a raw material in the flame; and rapidly cooling the raw material. In any case, the cooling method may be appropriately selected at various rates according to the material and the particle diameter. A method for making a crystallized material amorphous through a heat treatment and a cooling treatment is also considered. Among these, those using a flame melting method, in which heating and cooling can be easily controlled, are preferable.(Inorganic Binder Layer)

[0053] It is preferable that the regenerated sand (A) has an inorganic binding agent layer. Specifically, the inorganic binding agent layer includes one or more selected from a silicate and a reactant of a silicate, and covers the surface of the refractory aggregate. The coating is not limited to a continuous coating, and may have a discontinuous portion in a part thereof.

[0054] The inorganic binding agent layer is intended to be a layer in which, in a case where an inorganic coated sand having a refractory aggregate and an inorganic binding agent formed on a surface of the refractory aggregate is molded into a casting mold for casting, used as the casting mold, and then reproduced to be a regenerated sand, the inorganic binding agent is present on the surface of the refractory aggregate as a residual inorganic binding agent.

[0055] That is, the silicate and the reactant of the silicate, which are contained in the inorganic binding agent layer, are intended to be present on the surface of the refractory aggregate as the residual inorganic binding agent.

[0056] Specifically, examples of the reactant of the silicate and the silicate include a silicate and a metasilicate, a reactant of a silicate and an amorphous silica, a reactant of a silicate and an amorphous silica, and the like, and one kind or two or more kinds are mixed. In addition, examples of the cation constituting the salt include monovalent cations such as sodium, potassium, lithium, and ammonium, and divalent cations such as magnesium, calcium, and zinc.

[0057] Examples of the method for confirming that the inorganic binding agent layer contains a silicate or a reactant of a silicate include a method for analyzing a component eluted by stirring regenerated sand in an aqueous hydrochloric acid solution with an ICP emission spectrometer and obtaining a concentration of a silicate ion, a sodium ion, or the like, a method for performing element analysis of a regenerated sand surface with a scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDX) to confirm the presence of silicon, sodium, or the like, and a method for confirming a structure derived from a silicate by 23< Na and 29< Si solid NMR.[Refractory Aggregate (B)]

[0058] The degree of crystallization of the refractory aggregate (B) is at least 20% or more, preferably 30% or more, preferably 99% or less, more preferably 80% or less, even more preferably 70% or less, and still more preferably 60% or less, from the viewpoint of improving the mold strength due to a smoother surface of the aggregate and obtaining low thermal expansion properties, and from the viewpoint of improving the storage stability.

[0059] In addition, from the viewpoint of storage stability, the content of SiO 2 in the refractory aggregate (B) is preferably 10% or more, more preferably 20% or more, and still more preferably 30% or more, and from the viewpoint of further improving the mold hardness, the content of SiO 2 is preferably 99% or less, more preferably 80% or less, and still more preferably 70% or less. In addition, from the viewpoint of improving storage stability, the content of SiO 2 in the refractory aggregate (B) is preferably 50% or less and more preferably 40% or less.

[0060] The degree of amorphicity of the refractory aggregate (B) is obtained by the same X-ray diffraction method as that for the refractory aggregate of the regenerated sand (A).

[0061] In addition, the content of SiO 2 in the refractory aggregate (B) can be measured using the same fluorescence X-ray method as that of the refractory aggregate of the regenerated sand (A).[casting sand]

[0062] The casting sand has, as an outermost layer, a first coating layer formed on a surface of one or two kinds of aggregates selected from regenerated sand (A) and refractory aggregate (B). The casting sand can function as inorganic coated sand by further forming a second coating layer on the first coating layer.

[0063] The cation exchange capacity (CEC) of the casting sand needs to be controlled to a specific value from the viewpoint of suppressing the wet state of the inorganic coated sand. The control of the cation exchange capacity (CEC) can be performed by combining known methods, but can be performed, for example, by selecting the material of the coating layer, adjusting the content, and adjusting the baking temperature and time.

[0064] Specifically, the casting sand is composed of a particle group of the casting sand.

[0065] The CEC of the casting sand is obtained by the ammonium acetate method (fertilizer analysis method (Ministry of Agriculture, Forestry and Fisheries Agricultural Environmental Technology Research Institute Law) 5.31.1) shown below.

[0066] First, small pieces of absorbent cotton are placed as a support layer in the lower part of the permeation tube, and the paper pulp obtained by finely cutting filter paper and stirring the paper in hot water is packed to a thickness of about 5 mm to form a flat filtration surface. Next, a stopper is placed at a lower end of the permeation tube, a few mL of a 1 M ammonium acetate solution is put therein, 2 to 4 g of an analysis sample (casting sand) is weighed and allowed to fall and settle down little by little to fill the permeation tube, the stopper is removed, the device is assembled, and washing with an ammonium acetate solution is started. 100 mL of a 1 M ammonium acetate solution is used, and the dropping rate is adjusted so that the permeation is completed in 4 to 20 hours. After the permeation is completed, the upper part inside the permeation tube is washed with a small amount of an alcohol solution, and the sample layer is further washed with 50 mL of an 80% alcohol solution to remove the excess ammonium acetate solution. The analysis sample saturated with NH 4 +< obtained in this way is washed with 100 mL of a 10% sodium chloride solution to exchange and leach NH 4 +< . Ammoniacal nitrogen in the leachate is quantified by steam distillation and alkali titration, and is expressed as millimole equivalent per 1 kg of the analysis sample to obtain a cation exchange capacity.

[0067] From the viewpoint of improving the storage stability, the cation exchange capacity (CEC) is 3 mmol (+) / kg or more, and preferably 6 mmol (+) / kg or more.

[0068] On the other hand, from the viewpoint of improving the storage stability, the cation exchange capacity (CEC) is 40 mmol (+) / kg or less, preferably 20 mmol (+) / kg or less, and more preferably 10 mmol (+) / kg or less.(First Coating Layer)

[0069] The first coating layer constituting the casting sand is a layer for coating the surface of one or two kinds of aggregates selected from the regenerated sand (A) and the refractory aggregate (B). In addition, the first coating layer constitutes the outermost layer of the casting sand, and in the inorganic coated sand, the first coating layer is located between the second coating layer described later and the surface of the aggregate.

[0070] The first coating layer is preferably a coating layer formed of a constituent material different from that of the second coating layer and more preferably a layer formed of an aluminosilicate, and it is preferable that the first coating layer does not contain at least a metasilicate. As a result, it is possible to efficiently prevent the silicate in the second coating layer from acting on the aggregate to promote the wetting of the inorganic coated sand.

[0071] Examples of the aluminosilicate include one or more selected from silicates and reactants of silicates, and a reactant of aluminate or aluminum hydroxide. Here, the silicate refers to a substance containing, in a composition, an anion group having a structure in which one or several silicon atoms are centered and an electronegative ligand surrounds the one or several silicon atoms. Specifically, the term "the residual inorganic binder" or "the refractory aggregate (B)" indicates any one or both of the residual inorganic binder or the refractory aggregate (B) present on the surface of the refractory aggregate.

[0072] From the viewpoint of easily improving the storage stability, it is preferable that the above-described aluminosilicate includes at least one among one or more selected from a reactant of a silicate and a reactant of a silicate, and sodium aluminate or aluminum hydroxide.

[0073] The form of sodium aluminate is not particularly limited, and may be any of a powder or an aqueous solution.

[0074] From the viewpoint of improving storage stability, the content of aluminum in the first coating layer is preferably 0.1 parts by mass or more and more preferably 0.4 parts by mass or more with respect to 100 parts by mass of the aggregate, in terms of Al 2 O 3 .

[0075] On the other hand, the content of aluminum in the first coating layer is preferably 20 parts by mass or less and more preferably 10 parts by mass or less with respect to 100 parts by mass of the aggregate in terms of Al 2 O 3 in order to improve the mold strength and obtain good storage stability.

[0076] The content of aluminum in the first coating layer is obtained by the following method.

[0077] The Al 2 O 3 content in the first coating layer is calculated from the following expression using the analytical values of the aggregate and of the casting sand containing the first coating layer.

[0078] Al 2 O 3 [parts by mass] of first coating layer = {Al 2 O 3 [parts by mass] of casting sand} - {Al 2 O 3 [parts by mass] of aggregate}

[0079] From the viewpoint of improving storage stability and obtaining a casting mold with high strength, the content of the first coating layer is preferably 0.02 parts by mass or more, preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, still more preferably 1 part by mass or more, and even still more preferably 2 parts by mass or more with respect to 100 parts by mass of the aggregate.

[0080] From the viewpoint of achieving both storage stability and strength, the content of the first coating layer is preferably 10 parts by mass or less and more preferably 9.5 parts by mass or less with respect to 100 parts by mass of the aggregate.[Second Coating Layer]

[0081] The second coating layer is a layer formed on the first coating layer, and is a layer that serves as an outermost layer of the inorganic coated sand.

[0082] The second coating layer contains a metasilicate and is used to impart a function as a bonding agent to the aggregate. The crystallinity of the second coating layer can be improved, and the inorganic coated sand is dried and has excellent fluidity at room temperature, which is preferable.

[0083] Examples of the metasilicate include one or two or more selected from sodium metasilicate, potassium metasilicate, lithium metasilicate, ammonium metasilicate, and the like, and hydrates thereof. Among these, sodium metasilicate and potassium metasilicate are preferable. In addition, the amount of water of hydration of the metasilicate hydrate is not particularly limited, but is preferably 5 or more and 9 or less. Specifically, at least one selected from sodium metasilicate pentahydrate or sodium metasilicate nonahydrate is preferable, and sodium metasilicate nonahydrate is more preferable.

[0084] From the viewpoint of improving storage stability and obtaining a casting mold with high strength, the content of the second coating layer is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, still more preferably 0.5 parts by mass or more, even more preferably 1 part by mass or more, and even still more preferably 2 parts by mass or more with respect to 100 parts by mass of the aggregate.

[0085] On the other hand, from the viewpoint of achieving both storage stability and strength, the content of the second coating layer is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and still more preferably 6 parts by mass or less with respect to 100 parts by mass of the aggregate.

[0086] From the viewpoint of improving mold strength, the viewpoint of excellent productivity, and the viewpoint of availability, the content of the metasilicate in the second coating layer is preferably 80% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, even still more preferably 98% by mass or more, and even still more preferably substantially 100% by mass.

[0087] Here, the term "substantially" means that a component other than the metasilicate contained in the metasilicate which is a raw material may be unintentionally contained.

[0088] The total content of the metasilicate in the second coating layer refers to the total content of the metasilicate with respect to all components other than water in the second coating layer.

[0089] From the viewpoint of improving storage stability and obtaining a casting mold with high strength, the content (in terms of anhydride) of the metasilicate in the second coating layer is preferably 0.03 parts by mass or more, more preferably 0.1 parts by mass or more, still more preferably 0.5 parts by mass or more, and even still more preferably 0.9 parts by mass or more with respect to 100 parts by mass of the aggregate.

[0090] On the other hand, from the viewpoint of achieving both storage stability and strength, the content of the metasilicate is preferably 5 parts by mass or less, more preferably 4 parts by mass or less, still more preferably 3 parts by mass or less, and even still more preferably 2 parts by mass or less with respect to 100 parts by mass of the aggregate.(Inorganic Fine Particles)

[0091] In the present embodiment, the inorganic coated sand may further contain inorganic fine particles.

[0092] In a case where the inorganic fine particles are contained, the inorganic fine particles preferably form a part of the second coating layer. Specifically, the second coating layer preferably further contains inorganic fine particles on at least one of the layer or in the layer, and more preferably further contains inorganic fine particles on the layer. The inorganic fine particles may be included in both the second coating layer and the second coating layer. Thanks to this, the particles of the inorganic coated sand (C) are strongly bound to each other via the inorganic fine particles, and as a result, the strength of a mold to be obtained can be further improved. The inorganic fine particles on the second coating layer may be partially embedded in the second coating layer.

[0093] The inorganic fine particles are not limited, and examples thereof include one or two or more kinds of fine particles selected from silica, silicon, zinc oxide, aluminum hydroxide, tin oxide, and the like. Among these, from the viewpoint of improving the strength of the mold, silica particles are preferable, and from the viewpoint of having a large specific surface area and high reactivity with silicates, amorphous silica particles are more preferable. The inorganic fine particles may be used alone or in combination of two or more kinds thereof.(Other Additives)

[0094] The second coating layer may contain various additives as necessary, in addition to the above-described components. Examples of the other additives include a coupling agent, a moisturizing agent, a moisture improvement agent, a lubricant, a surfactant, and a mold release agent.

[0095] The coupling agent is not limited, and examples thereof include a silane coupling agent, a zircon coupling agent, and a titanium coupling agent.

[0096] Examples of the moisturizing agent include a polyhydric alcohol, a water-soluble polymer, hydrocarbons, sugars, protein, and an inorganic compound other than those described above.

[0097] Examples of the moisture resistance improving agent include a metal oxide (other than those described above), a carbonate, a borate, a sulfate, and a phosphate.

[0098] Examples of the lubricant include waxes; fatty acid amides; alkylene fatty acid amides; stearic acids; stearyl alcohol; metal stearic acid salts such as lead stearate, zinc stearate, calcium stearate, and magnesium stearate; stearic acid monoglyceride; stearyl stearate; and hydrogenated oil.

[0099] Examples of a mold releasing agent include paraffin, wax, light oil, machine oil, spindle oil, insulating oil, waste oil, vegetable oil, fatty acid ester, organic acid, graphite fine particles, mica, vermiculite, a fluorine-based mold releasing agent, and silicone-based mold releasing agent.(Moisture Content)

[0100] From the viewpoint of obtaining a mold with high strength, the content of water including the crystal water in the second coating layer is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and still more preferably 20 parts by mass or more with respect to 100 parts by mass (in terms of anhydride) of the silicate.

[0101] In addition, from the viewpoint of filling property into the molding mold and viewpoint of obtaining a casting mold having a high strength, the content of water in the second coating layer is preferably 180 parts by mass or less, more preferably 160 parts by mass or less, still more preferably 150 parts by mass or less, and even still more preferably 140 parts by mass or less with respect to 100 parts by mass of the silicate.

[0102] The content of water including the crystal water in the second coating layer included in the inorganic coated sand can be adjusted according to the type of silicate.

[0103] In a case where the metasilicate is sodium metasilicate, from the viewpoint of obtaining a high-strength mold and the viewpoint of easily producing a mold, the content of water including the crystal water in the second coating layer is preferably 60 parts by mass or more, more preferably 65 parts by mass or more, still more preferably 90 parts by mass or more, and even still more preferably 110 parts by mass or more with respect to 100 parts by mass (in terms of anhydride) of sodium metasilicate, and from the viewpoint of improving fluidity and further improving the moldability into a molding die, the content of water is preferably 180 parts by mass or less, more preferably 160 parts by mass or less, even still more preferably 150 parts by mass or less, and even still more preferably 140 parts by mass or less.

[0104] For example, in a case where the silicate constituting the second coating layer is only sodium metasilicate pentahydrate, the content of water is 74 parts by mass with respect to 100 parts by mass of sodium metasilicate, and in a case where the silicate constituting the second coating layer is only sodium metasilicate nonahydrate, the content of water is 133 parts by mass with respect to 100 parts by mass of sodium metasilicate.<Method for Producing Regenerated Sand (A) / method for Regenerating Used casting sand>

[0105] As a method for reproducing the waste sand of the mold after casting, a known method (for example, "Mold Modeling Method", 4th edition, Japan Foundry Engineering Society, November 18, 1996, pp. 327 to 330) can be followed. For example, methods such as a dry polishing treatment (mechanical abrasion), a wet polishing treatment, and a baking treatment, and methods in which these treatments are combined are known.

[0106] In the dry polishing treatment, a part of the residue of the inorganic binding agent layer present on the surface of the refractory aggregate can be removed. For the removal, for example, a method using a sand reclaimer that performs a polishing treatment by collision and friction between sand grains by causing sand to rise in a device by a high-speed air flow and causing the sand to collide with a collision plate, a rotary reclaimer that performs a polishing treatment by collision and friction between projection sand generated by centrifugal force and falling sand to be input by inputting sand onto a high-speed rotating rotor, or an agitator mill that performs a polishing treatment by using friction between sand grains can be used.

[0107] In addition, examples of the wet polishing treatment include a method using a trough polishing machine that performs a polishing treatment by friction between sand grains in a trough in which blades are rotated.

[0108] Examples of the baking treatment include a method in which a baking furnace such as a fluid baking furnace or a rotary kiln is used, sand is added to the baking furnace, and baking is carried out in a range of 200°C to 1,000°C. In addition, it is known that the baking is carried out at 600°C to 800°C in order to further improve the accuracy.

[0109] Although any method may be used for the reproduction, the wet treatment or the baking treatment is complicated in terms of steps and has a large energy load. Therefore, among these, the dry polishing treatment is preferable.<Method for Producing Inorganic Coated Sand>

[0110] Next, a method for producing the inorganic coated sand of the present embodiment will be described.

[0111] The method for producing an inorganic coated sand of the present embodiment is a method for producing an inorganic coated sand in a dry state, the method including: a casting sand that includes one or two kinds of aggregates selected from a regenerated sand (A) and a refractory aggregate (B), and a first coating layer that covers the aggregate and is located on a surface of the aggregate; and a second coating layer that includes a metasilicate and is provided on the first coating layer of the casting sand, in which the refractory aggregate (B) includes SiO 2 , and a cation exchange capacity (CEC) of the casting sand satisfies 3 mmol (+) / kg or more and 40 mmol (+) / kg or less.

[0112] According to the production method for the present embodiment, since the first coating layer is formed on the surface of the aggregate material and the cation exchange capacity (CEC) of the casting sand is controlled, it is possible to omit the baking step of the aggregate material while improving the storage stability, and thus it is possible to reduce the consumption of thermal energy and to reduce the environmental load.

[0113] First, as an example of the method for producing the inorganic coated sand of the present embodiment, a method including the following steps (1) to (3) in which the refractory aggregate (B) contains SiO 2 may be mentioned. · Step (1): a step of mixing one or two kinds of aggregates selected from regenerated sand (A) and refractory aggregate (B) with an aluminates or aluminum hydroxide to form the first coating layer on the surface of the aggregate, thereby obtaining casting sand · Step (2): step of mixing the obtained casting sand with a molten solution of a metasilicate hydrate to obtain a mixture · Step (3): step of cooling the obtained mixture to a temperature lower than a melting point of the metasilicate hydrate to form the second coating layer on the first coating layer

[0114] In the step (1), the aluminate or aluminum hydroxide and the aggregate are mixed together to form the first coating layer to cover the surface of the aggregate. Among these, it is preferable to heat the first coating layer to 25°C or higher and lower than 400°C to form the first coating layer.

[0115] Examples of the method for forming the first coating layer by heating the mixture to 25°C or higher and lower than 400°C in the step (1) include a method for putting an aluminate into the aggregate heated to 25°C or higher and lower than 400°C, and a method for putting an aluminate or aluminum hydroxide into the aggregate and then heating the aggregate to 25°C or higher and lower than 400°C.

[0116] Among these, the latter method is preferable from the viewpoint of forming a uniform coating layer.

[0117] In addition, from the viewpoint of improving storage stability, the heating temperature is preferably 40°C or higher and 300°C or lower, and more preferably 70°C or higher and 200°C or lower.

[0118] Examples of the method for heating the coating film to 25°C or higher and lower than 400°C in the step (1) to form the first coating layer include a method for putting an aluminate or aluminum hydroxide into the aggregate heated to 25°C or higher and lower than 400°C, and a method for putting an aluminate or aluminum hydroxide into the aggregate and then heating the aggregate to 25°C or higher and lower than 400°C.

[0119] Among these, the latter method is preferable from the viewpoint of forming a uniform coating layer.

[0120] In addition, from the viewpoint of improving storage stability, the heating temperature is preferably 40°C or higher and 300°C or lower, and more preferably 70°C or higher and 200°C or lower.

[0121] The mixing conditions such as a stirring speed and a treatment time in a case of mixing the aggregate with the aluminates or the aluminum hydroxide can be appropriately determined depending on the treatment amount of the mixture.

[0122] As a result, a casting sand in which a cation exchange capacity (CEC) is 3 mmol (+) / kg or more and 40 mmol (+) / kg or less is obtained. in the step (2), the casting sand and a molten solution of a metasilicate hydrate are mixed to obtain a mixture.

[0123] Examples of the method for mixing the molten solution of the metasilicate hydrate with the casting sand in the step (2) include a method for charging the metasilicate into the casting sand heated to a temperature equal to or higher than the melting point of the metasilicate hydrate, and a method for charging the metasilicate heated to a temperature equal to or higher than the melting point of the metasilicate hydrate into the casting sand.

[0124] Among these, the latter method is preferable from the viewpoint of shortening the coating time.

[0125] The mixing conditions such as a stirring speed and a treatment time in a case of mixing the casting sand and the metasilicate hydrate can be appropriately determined depending on the treatment amount of the mixture.

[0126] In the step (3), the mixture obtained in the step (2) is cooled to a temperature lower than the melting point of the metasilicate hydrate to reduce the fluidity of the metasilicate hydrate, and the metasilicate hydrate is fixed to the surface of the casting sand to form a metasilicate hydrate layer, that is, a second coating layer.

[0127] In this manner, the inorganic coated sand according to the present embodiment can be obtained.

[0128] Next, as another example of the method for producing the inorganic coated sand of the present embodiment, a method for producing the inorganic coated sand, in which the refractory aggregate (B) contains SiO 2 and includes the following steps (4) and (5), is exemplified.

[0129] Step (4): a step of mixing one or two kinds of the aggregates selected from the regenerated sand (A) and the refractory aggregate (B) with an aluminates or aluminum hydroxide to form the first coating layer on the surface of the aggregate, thereby obtaining casting sand

[0130] Step (5): a step of mixing the casting sand with a solution containing water glass, caustic alkali, and water to obtain a mixture containing a sodium metasilicate hydrate

[0131] The step (4) can be carried out by the same method as in the step (1).

[0132] In the step (5), by setting the molar ratio of SiO 2 / M 2 O (M represents an alkali metal) / H 2 O in the solution containing water glass, caustic alkali, and water to 1:1:n (5 ≤ n ≤ 9), a desired amount of hydrated metasilicate hydrate can be formed.

[0133] Further, the second coating layer can be formed by mixing the above-described solution containing water glass, caustic alkali, and water with the casting sand to coat the surface of the casting sand with a metasilicate hydrate.

[0134] The mixing conditions of water glass, caustic alkali, and water are not particularly limited, and a known method can be used. For example, the mixing may be carried out at an environmental temperature, and in a case where the molten solution generates heat, the mixing may be continued as it is, and then the mixture may be allowed to stand until the environmental temperature is reached.

[0135] In this manner, the inorganic coated sand according to the present embodiment can be obtained.<Casting Mold>

[0136] The casting mold for casting according to the present embodiment comprises the inorganic coated sand in the present embodiment described above, and is formed of the inorganic coated sand. Examples of a method for molding a casting mold include a molding method using a heated molding die, a molding method in which steam is further aerated in the heated molding die, and then hot air is aerated.<Method for Improving Storage Stability>

[0137] The method for improving the storage stability of the inorganic coated sand of the present embodiment is a method for improving the storage stability of the inorganic coated sand, the method including: a casting sand containing one or two kinds of the sands selected from the regenerated sand (A) and the refractory aggregate (B); and a second coating layer containing a metasilicate that coats the casting sand, in which the refractory aggregate (B) contains SiO 2 , and a step of preparing an inorganic coated sand in a dry state is prepared such that a cation exchange capacity (CEC) of the casting sand satisfies 3 mmol (+) / kg or more and 40 mmol (+) / kg or less.

[0138] In this manner, the storage stability of the inorganic coated sand can be improved. The step of preparing the cation exchange capacity (CEC) of the casting sand to be 3 mmol (+) / kg or more and 40 mmol (+) / kg or less is performed by adjusting the method for producing the inorganic coated sand and the casting sand. The details are the same as those described in the method for producing the inorganic coated sand described above. In addition, the details of the configuration and the like of the inorganic coated sand and the casting sand are also the same as those described above.

[0139] Although the embodiments of the present invention have been described above, these are examples of the present invention, and various configurations other than the above can be adopted.

[0140] Regarding the above-described embodiments, the present invention further discloses the following inorganic coated sand, inorganic coated sand manufacturing method, and casting mold manufacturing method.

[0141] <1> An inorganic coated sand in a dry state includes: a casting sand including one or two kinds of aggregates selected from a regenerated sand (A) and a refractory aggregate (B), and a first coating layer covering the aggregate and disposed on a surface thereof; and a second coating layer containing a metasilicate on the first coating layer of the casting sand, in which the refractory aggregate (B) contains SiO 2 , and a cation exchange capacity (CEC) of the casting sand is 3 mmol (+) / kg or more, preferably 6 mmol (+) / kg or more, 40 mmol (+) / kg or less, preferably 20 mmol (+) / kg or less, and more preferably 10 mmol (+) / kg or less. <2> The inorganic coated sand according to <1>, in which a content of the first coating layer is 0.02 parts by mass or more, preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, still more preferably 1 part by mass or more, and even still more preferably 2 parts by mass or more, and is 10 parts by mass or less, preferably 9.5 parts by mass or less, with respect to 100 parts by mass of the aggregate. <3> The inorganic coated sand according to <1> or <2>, in which a content of the second coating layer is 0.05 parts by mass or more, preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, still more preferably 1 part by mass or more, and even still more preferably 2 parts by mass or more, and is 10 parts by mass or less, preferably 8 parts by mass or less, and more preferably 6 parts by mass or less, with respect to 100 parts by mass of the aggregate. <4> The inorganic coated sand according to any one of <1> to <3>, in which the first coating layer of the casting sand contains an aluminosilicate, and the aluminosilicate contains a reactant of one or more selected from a silicate and a reactant of a silicate, and an aluminate or aluminum hydroxide. <5> The inorganic coated sand according to any one of <1> to <4>, in which the aluminosilicate includes at least one reactant of one or more selected from a silicate or a reactant of a silicate, and sodium aluminate or aluminum hydroxide. <6> The inorganic coated sand according to any one of <1> to <5>, in which a dynamic rest angle of the inorganic coated sand is preferably 80° or less, more preferably 45° or less, and still more preferably 30° or less. <7> The inorganic coated sand according to any one of <1> to <6>, in which a degree of noncrystallization of the refractory aggregate (B) is preferably 30% or more, more preferably 50% or more, still more preferably 65% or more, and even still more preferably 80% or more, and is preferably 100% or less and more preferably 99% or less. <8> The inorganic coated sand according to any one of <1> to <7>, in which a content of SiO 2 in the refractory aggregate (B) is preferably 10% or more, preferably 20% or more, and more preferably 30% or more, and is preferably 99% or less, more preferably 80% or less, still more preferably 70% or less, even still more preferably 50% or less, and even still more preferably 40% or less. <9> The inorganic coated sand according to any one of <1> to <8>, in which a content of aluminum in the first coating layer is preferably 0.1 parts by mass or more and more preferably 0.4 parts by mass or more, and is preferably 20 parts by mass or less and more preferably 10 parts by mass or less, with respect to 100 parts by mass of the aggregate, in terms of Al 2 O 3 . <10> The inorganic coated sand according to any one of <1> to <9>, in which a content of the metasilicate in the second coating layer is preferably 80% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, even still more preferably 98% by mass or more, and even still more preferably substantially 100% by mass. <11> The inorganic coated sand according to any one of <1> to <10>, in which a content of water including water of crystallization in the second coating layer is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and still more preferably 20 parts by mass or more, and is preferably 180 parts by mass or less, more preferably 160 parts by mass or less, even more preferably 150 parts by mass or less, and still more preferably 140 parts by mass or less, with respect to 100 parts by mass (in terms of anhydride) of a silicate. <12> A casting mold consisting of the inorganic coated sand according to any one of any one of <1> to <11>. <13> A method for producing an inorganic coated sand, the method including: a step (1) of mixing one or two kinds of aggregates selected from a regenerated sand (A) and a refractory aggregate (B), and an aluminate or aluminum hydroxide, and forming a first coating layer on a surface of the aggregate to obtain a casting sand; a step (2) of mixing the obtained casting sand with a molten solution of a metasilicate hydrate to obtain a mixture; and a step (3) of cooling the mixture to a temperature lower than a melting point of the metasilicate hydrate, in which the refractory aggregate (B) contains SiO 2 . <14> A method for producing an inorganic coated sand, the method including: a step (4) of mixing one or two kinds of aggregates selected from a regenerated sand (A) and a refractory aggregate (B), and an aluminate or aluminum hydroxide, forming a first coating layer on a surface of the aggregate to a obtain casting sand; a step (5) of mixing the obtained casting sand with a solution including water glass, caustic alkali, and water to obtain a mixture including a metasilicate hydrate, in which the refractory aggregate (B) contains SiO 2 . <15> The method for producing an inorganic coated sand according to <13> or <14>, in the step (1) or the step (4), the first coating layer is formed by heating at 25°C or higher and lower than 400°C, preferably 40°C or higher and 300°C or lower, and more preferably 70°C or higher and 200°C or lower. <16> The method for producing an inorganic coated sand according to <14>, in which in the step (5), a molar ratio of SiO 2 / M 2 O (M represents an alkali metal) / H 2 O in a solution containing water glass, caustic alkali, and water is 1:1:n (5 ≤ n ≤ 9). <17> A method for improving storage stability of an inorganic coated sand, in which the inorganic coated sand includes a casting sand containing one or two kinds of aggregates selected from a regenerated sand (A) and a refractory aggregate (B); and a second coating layer containing a metasilicate coating the casting sand, the refractory aggregate (B) contains SiO 2 , and the inorganic coated sand in a dry state is prepared such that a cation exchange capacity (CEC) of the casting sand is 3 mmol (+) / kg or more and 40 mmol (+) / kg or less. Examples

[0142] Hereinafter, the present invention will be described with reference to Examples and Comparative Examples, but the present invention is not limited thereto.(1) Materials

[0143] Materials used in the following Examples and Comparative Examples will be described.[Refractory Aggregate]

[0144] · Refractory aggregate 1: ESPEARL #60L (manufactured by Yamakawa Sangyo Co., Ltd., average particle diameter: 241 µm, degree of amorphization: 45%) · Refractory aggregate (B1): spherical fused silica (natural silica sand is spheroidized by flame fusion method, average particle diameter: 200 µm, degree of amorphization: 95% or more) · Refractory aggregate (B2): NIGAI CERABEADS 60#650 (manufactured by Itochu Ceratec Co., Ltd., average particle diameter: 200 µm, degree of amorphization: 30%) [Inorganic Fine Particles]

[0145] · Amorphous silica fine particles: Denka molten silica SFP-20M (manufactured by Denka Company Limited., average particle diameter: 0.4 µm, degree of amorphality: 99.5% or more) · Calcined kaolin: Satinon W (manufactured by BASF SE, average particle diameter: 0.4 µm) [Regenerated Sand (A)]

[0146] · Regenerated sand (A1) was produced according to the following procedure. (i) Production of inorganic coated sand

[0147] 100 parts by mass of a refractory aggregate 1 (ESPEARL #60L) as a refractory aggregate was put into a stirrer. Next, a sodium metasilicate nonahydrate (2.00 parts by mass) that had been heated and melted at 80°C was put into a stirrer and kneaded for 4 minutes to obtain dry sand having fluidity at normal temperature, and then fine amorphous silica particles (0.6 parts by mass) were further put thereinto and kneaded for 2 minutes to obtain an inorganic coated sand in a dry state used for the production of the regenerated sand (A1).(ii) Preparation of Mold

[0148] A part of 10 kg of the obtained inorganic coated sand was poured into the center of a conical mold having an upper diameter of 298 mm, a lower diameter of 205 mm, and a height of 265 mm for producing a test casting mold, up to a height of 50 mm. Subsequently, a metal core of a truncated cone having an upper diameter of 280 mm, a lower diameter of 200 mm, and a height of 220 mm, which had been heated to 180°C, was installed. The remaining inorganic coated sand was poured into a space between the mold and the metal core, and heated in a heating furnace at 180°C for 20 minutes to obtain a test casting mold.(iii) Casting

[0149] 10 kg of an aluminum alloy AC4C material (720°C) was poured into the obtained test casting mold. After the injection of the solution, the solution was allowed to stand at room temperature and cooled.(iv) Production of Recovered Sand

[0150] The casting was taken out from the test casting mold after casting, the test casting mold was crushed with a hammer or the like, and the test casting mold was further crushed with a mini crusher (manufactured by Taiyo Kogyo Co., Ltd.) until the test casting mold was a single particle, thereby obtaining recovered sand.(v) Production of Regenerated Sand

[0151] 100 kg of regenerated sand was put into a dry-type casting sand recycling device (Hybrid Sand Master manufactured by Nippon Casting Co., Ltd.) equipped with a fluidized layer, and batch treatment was performed at a rotor rotation speed of 2,400 rpm for 60 minutes to obtain regenerated sand (A1). Fine powder derived from the binder generated during the treatment was removed by a dust collector.[Material for First Coating Layer]

[0152] · 50% sodium aluminate: sodium aluminate #2019 (50% sodium aluminate aqueous solution manufactured by Asada Chemical Co., Ltd.) · Aluminum hydroxide (Al(OH) 3 ): aluminum hydroxide (manufactured by FUJIFILM Wako Pure Chemical Corporation, powder form, average particle diameter: 2.01 µm) · No. 2 water glass: No. 2 sodium silicate (manufactured by FUJI CHEMICAL INDUSTRY CO., LTD., Si / Na molar ratio: 2.4) [Material for Second Coating Layer]

[0153] · Sodium metasilicate nonahydrate: sodium metasilicate nonahydrate (manufactured by Nippon Chemical Industrial Co., Ltd.) (2) Production of Inorganic Coated Sand

[0154] Each inorganic coated sand of the formulation compositions shown in Table 1 was produced by the following procedure.<Example 1>

[0155] 100 parts by mass of regenerated sand (A1) as a refractory aggregate was put into a stirrer. Next, 2.3 parts by mass of a 50% sodium aluminate aqueous solution was added thereto, and the mixture was stirred for 2 minutes to obtain a mixture. Thereafter, the obtained mixture was heat-treated in a baking furnace at a baking temperature of 80°C for 12 hours, cooled to room temperature, and then aggregates in the mixture were removed through a sieve (20 mesh) to obtain casting sand in which a first coating layer consisting of an aluminosilicate was formed on the surface of the regenerated sand (A1).

[0156] Next, the casting sand and a sodium metasilicate nonahydrate (3.50 parts by mass) heated and melted at 80°C were put into a stirrer and kneaded for 4 minutes to form a second coating layer on the first coating layer, thereby obtaining inorganic coated sand of Example 1. Table 1 shows a blending composition of the inorganic coated sand.<Examples 2 and 3>

[0157] In the same manner as in Example 1, except that the adding amount of the 50% sodium aluminate aqueous solution in a case of forming the first coating layer consisting of an aluminosilicate on the surface of the regenerated sand (A1) was changed to the parts by mass shown in Table 1, inorganic coated sands of Examples 2 and 3 described in Table 1 were obtained.<Example 4>

[0158] In a case where the first coating layer consisting of an aluminosilicate was formed on the surface of the regenerated sand (A1), 0.1 parts by mass of No. 2 water glass was additionally added at the time of adding a 50% sodium aluminate aqueous solution, thereby obtaining the inorganic coated sand of Example 4 shown in Table 1 in the same manner as in Example 1.<Examples 5 to 8>

[0159] inorganic coated sand was obtained in the same manner as in Example 1, except that the baking temperature at which the first coating layer consisting of an aluminosilicate was formed on the surface of the regenerated sand (A1) was changed to the temperature shown in Table 1. Table 1 shows the formulation compositions of the inorganic coated sands of Examples 5 to 8.<Example 9>

[0160] inorganic coated sand was obtained in the same manner as in Example 1, except that a suspension in which aluminum hydroxide was suspended in water in advance (aluminum hydroxide:water = 1:1 by mass ratio) was used instead of the 50% sodium aluminate aqueous solution. Table 1 shows the formulation composition of the inorganic coated sand of Example 9.<Examples 10 and 12>

[0161] Inorganic coated sand was obtained in the same manner as in Example 2, except that the regenerated sand (A1) as the refractory aggregate was changed to the refractory aggregate shown in Table 2. Table 2 shows the formulation compositions of the inorganic coated sands of Examples 10 and 12.<Example 11>

[0162] Inorganic coated sand was obtained in the same manner as in Example 3, except that the regenerated sand (A1) as the refractory aggregate was changed to the refractory aggregate shown in Table 2. Table 2 shows the formulation composition of the inorganic coated sand of Example 11.<Example 13>

[0163] Using the inorganic coated sand obtained in Example 2, regenerated sand (A2) was obtained in the same manner as in the procedure (ii) to (v) of the regenerated sand (A1) described above. The inorganic coated sand was produced in the same manner as in Example 2 using the regenerated sand (A2), and the procedure (ii) to (v) of the regenerated sand (A1) was repeated again to obtain regenerated sand (A3). Further, the step of obtaining regenerated sand (A3) from the regenerated sand (A2) was repeated twice using the regenerated sand (A3), and regenerated sand (A5) was obtained.

[0164] In the same manner as in Example 2, inorganic coated sand was obtained using regenerated sand (A5). The results of the storage stability are shown in Table 3.<Comparative Example 1>

[0165] In the same manner as in Example 1, except that the addition of 50% sodium aluminates and the heating treatment were not performed, an inorganic coated sand containing the inorganic binding agent of Comparative Example 1 and not containing the first coating layer consisting of an aluminosilicate was obtained. Table 1 shows the formulation composition of the inorganic coated sand of Comparative Example 1.<Comparative Examples 2 and 3>

[0166] inorganic coated sands of Comparative Examples 2 and 3 were obtained in the same manner as in Example 1, except that the heating treatment was performed at the temperature shown in Table 1 without adding 50% sodium aluminate. Table 1 shows the formulation compositions of the inorganic coated sands of Comparative Examples 2 and 3.<Comparative Example 4>

[0167] 100 parts by mass of regenerated sand (A1) was prepared as a refractory aggregate and put into a stirrer. Next, 0.25 parts by mass of calcined kaolin, 0.25 parts by mass of noncrystalline silica fine particles, and 0.50 parts by mass of water were put into the container and stirred for 2 minutes. Thereafter, the obtained mixture was heat-treated in an electric furnace at 730°C for 1 hour, the heating of the electric furnace was stopped, the mixture was left as it was in the electric furnace for 4 hours, the mixture was taken out from the electric furnace, and the mixture was cooled to room temperature at room temperature, and then an aggregate was removed from the mixture through a sieve (20 mesh). The obtained mixture and a sodium metasilicate nonahydrate (3.50 parts by mass) heated to 80°C and melted were put into a stirrer and kneaded for 4 minutes to obtain inorganic coated sand of Comparative Example 4. Table 1 shows a blending composition of the inorganic coated sand.<Comparative Examples 5 and 6>

[0168] Inorganic coated sands of Comparative Examples 5 and 6 were obtained in the same manner as in Comparative Example 1, except that the regenerated sand (A1) as the refractory aggregate was changed to the type of the refractory aggregate shown in Table 2. Table 2 shows the formulation compositions of the inorganic coated sands of Comparative Examples 5 and 6.(3) Evaluation and Measurement

[0169] The following evaluations and measurements were performed using the obtained inorganic coated sand. The results are shown in Tables 1 and 2.<Storage Stability; Measurement of Time until Wetting>

[0170] Immediately after the production of the inorganic coated sand, the dynamic rest angle of the inorganic coated sand was measured by the following procedure.

[0171] Separately, immediately after the production of the inorganic coated sand, 2 kg of the inorganic coated sand was put into a polybag, sealed, and left in a constant temperature / humidity chamber of 25°C / 55% RH, and the dynamic rest angle of the inorganic coated sand was measured according to the following procedure every 24 hr, and the following confirmation was performed regarding the state (dry state or wet state) of the inorganic coated sand. In a case where the inorganic coated sand was wet, the time taken from the placement in the plastic bag to the wetting was defined as "time taken to wet" (days).(i) Procedure (Measurement of Dynamic Repose Angle)

[0172] A cylindrical transparent plastic bottle having a diameter of 76 mm and a height of 125 mm was filled with the inorganic coated sand in an amount half the volume of the bottle, held such that an axis was kept horizontal, and rotated at room temperature (25°C) and a speed of 60 rpm around the horizontal axis. The inclined surface of the inorganic coated sand layer flowing in the cylinder was formed in a flat surface state, and an angle (dynamic repose angle) formed between the inclined surface and the horizontal surface was measured.(ii) Confirmation (Determination of Dry State or Wet State)

[0173] In the above procedure, a case where the angle could be measured was defined as "dry state", and a case where the inorganic coated sand did not flow in the cylinder or the inclined surface of the inorganic coated sand layer was not formed as a flat surface even in a case where the inorganic coated sand flowed, and as a result, the dynamic repose angle could not be measured was defined as "wet state".[Table 1]

[0174] Table 1Inorganic coated sandCasting sandRefractory aggregateFirst coating layerEnvironmen tal loadProperti esTypesPart s by massCompoun d 1Part s by massCompound 2Part s by massBaking temperatur e [°C]Cation exchange capacity [mmol (+) ·kg -1< ]Example 1Regenerat ed sand (A1)10050% Alumina te Na2.3--809Example 2Regenerat ed sand (A1)10050% Alumina te Na4.6--808Example 3Regenerat ed sand (A1)10050% Alumina te Na9.1--807Example 4Regenerat ed sand (A1)10050% Alumina te Na4.6No. 2 water glass0.1808Example 5Regenerat ed sand (A1)10050% Alumina te Na4.6--403Example 6Regenerat ed sand (A1)10050% Alumina te Na4.6--1208Example 7Regenerat ed sand (A1)10050% Alumina te Na4.6--2008Example 8Regenerat ed sand (A1)10050% Alumina te Na4.6--3508Example 9Regenerat ed sand (A1)10050% Aluminu m hydroxi de4.6--808Comparati ve example 1Regenerat ed sand (A1)100None0---1Comparati ve example 2Regenerat ed sand (A1)100None0--801Comparati ve example 3Regenerat ed sand (A1)100None0--6001Comparati ve example 4Regenerat ed sand (A1)100Calcine d kaolin0.25Noncrystall ine silica fine particles0.257301 [Table 1(Continued)]

[0175] Table 1Inorganic coated sandSecond coating laverCompound 3Parts by massSodium metasilicate [Parts by mass]StateDynamic rest angle [°]Storage stabilityTime until wetting [Dav]Example 1Sodium metasilicate nonahydrate3.501.51Dry sand2286Example 2Sodium metasilicate nonahydrate3.501.51Dry sand20226Example 3Sodium metasilicate nonahydrate3.501.51Dry sand20226Example 4Sodium metasilicate nonahydrate3.501.51Dry sand20226Example 5Sodium metasilicate nonahydrate3.501.51Dry sand2030Example 6Sodium metasilicate nonahydrate3.501.51Dry sand25203Example 7Sodium metasilicate nonahydrate3.501.51Dry sand20183Example 8Sodium metasilicate nonahydrate3.501.51Dry sand20164Example 9Sodium metasilicate nonahydrate3.501.51Dry sand20158Comparative example 1Sodium metasilicate nonahydrate3.501.51Dry sand251Comparative example 2Sodium metasilicate nonahydrate3.501.51Dry sand251Comparative example 3Sodium metasilicate nonahydrate3.501.51Dry sand2030Comparative example 4Sodium metasilicate nonahydrate3.501.51Dry sand2530 [Table 2]

[0176] Table 2Inorganic coated sandCasting sandRefractory aggregateFirst coating layerEnvironment al loadProperti esTypesPart s by massDegree of amorphici ty [%]SiO 2 [%]Compound 1Part s by massBaking temperature [°C]Cation exchange capacity [mmol (+) ·kg -1< ]Example 10Refracto ry aggregat e (B1): spherica 1 fused silica100More than 959950% Aluminat e Na4.6808Example 11Refracto ry aggregat e (B1): spherica 1 fused silica100More than 959950% Aluminat e Na9.1807Example 12Refracto ry aggregat e (B2): NIGAI CEPABEAD S 60#650100303650% Aluminat e Na4.6808Comparati ve example 5Refracto ry aggregat e (B1): spherica 1 fused silica100> 9599None0-Less than 1Comparati ve example 6Refracto ry aggregat e (B2): NIGAI CEPABEAD S 60#6501003036None0-Less than 1 [Table 2(Continued)]

[0177] Table 2Inorganic coated sandSecond coating layerCompound 3Parts by massSodium metasilicate [Parts by mass]StateDynamic rest angle [°]Storage stabilityTime until wetting [Dav]Example 10Sodium metasilicate nonahydrate3.501.51Dry sand228Example 11Sodium metasilicate nonahydrate3.501.51Dry sand2220Example 12Sodium metasilicate nonahydrate3.501.51Dry sand20121Comparative example 5Sodium metasilicate nonahydrate3.501.51Dry sand201Comparative example 6Sodium metasilicate nonahydrate3.501.51Dry sand2014 [Table 3]

[0178] Table 3Inorganic coated sandCasting sandRefractory aggregateStorage stabilityTypesNumber of times of regeneration [Number]Time until wetting [Day]Example 2Regenerated sand (Al)1226Comparative example 13Regenerated sand (A5)5181

Examples

examples

[0142]Hereinafter, the present invention will be described with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

(1) Materials

[0143]Materials used in the following Examples and Comparative Examples will be described.

[Refractory Aggregate]

[0144] · Refractory aggregate 1: ESPEARL #60L (manufactured by Yamakawa Sangyo Co., Ltd., average particle diameter: 241 µm, degree of amorphization: 45%) · Refractory aggregate (B1): spherical fused silica (natural silica sand is spheroidized by flame fusion method, average particle diameter: 200 µm, degree of amorphization: 95% or more) · Refractory aggregate (B2): NIGAI CERABEADS 60#650 (manufactured by Itochu Ceratec Co., Ltd., average particle diameter: 200 µm, degree of amorphization: 30%)

[Inorganic Fine Particles]

[0145] · Amorphous silica fine particles: Denka molten silica SFP-20M (manufactured by Denka Company Limited., average particle diameter: 0.4 µm, degree of amorphality: 99.5% or more) ...

TECHNICAL FIELD

[0001] The present invention relates to an inorganic coated sand, a method for producing the same, a casting mold, and a method for improving storage stability of the inorganic coated sand.BACKGROUND ART

[0002] In recent years, the importance of product design that takes into consideration people and the environment has increased from the viewpoint of sustainable development goals (SDGs), and the technical development of an environmentally friendly casting process in which CO 2 emissions and VOCs are reduced has been accelerated.

[0003] As the environmentally friendly casting process, for example, an inorganic binder process of wet sand using a refractory aggregate and an inorganic binding agent consisting of liquid water glass is known. Examples thereof include those described in Patent Document 1 (PCT Japanese Translation Patent Publication No 2010-519042)

[0004] Patent Document 2 (Published Japanese Translation No. 2021-536367) describes that a mixture is obtained by mixing regenerated sand with a particulate amorphous oxide containing silicon dioxide, and the mixture is heat-treated at a temperature of 400°C or higher, whereby the usable time is improved, the surface quality of a casting is improved, and a significant energy saving can be realized.

[0005] Patent Document 3 (Japanese Unexamined Patent Publication No. 2014-117740) discloses a method for producing dry coated sand having normal temperature fluidity, in which a specific water glass aqueous solution is mixed with a heated refractory aggregate as a bonding material, and moisture is evaporated to form a coating layer of the bonding material on a surface of the refractory aggregate.RELATED DOCUMENTPATENT DOCUMENT

[0006] Patent Document 1: PCT Japanese Translation Patent Publication No 2010-519042 Patent Document 2: Published Japanese Translation No. 2021-536367 Patent Document 3: Japanese Unexamined Patent Publication No. 2014-117740 SUMMARY OF THE INVENTIONTECHNICAL PROBLEM

[0007] By the way, after casting, the coated sand used for the mold is usually reused as regenerated sand obtained by performing a regeneration treatment on regenerated sand obtained by breaking (crushing) the mold to obtain single particles by various methods. From the viewpoint of economy and the viewpoint of waste reduction, it has become essential to manufacture a mold using regenerated sand in a foundry.

[0008] The present inventors have found that, in a case where a new metasilicate hydrate layer is formed to produce inorganic coated sand with casting sand formed of regenerated sand in an inorganic binder process using an inorganic binding agent in the related art as described in Patent Document 2 and 3, the sand may be quickly moistened during storage, and a desired mold may not be modeled. In addition, even in a case where a refractory aggregate having a relatively high degree of crystallization is used, the same tendency of being moistened during storage is observed in a case where the inorganic coated sand is produced by forming a layer of a metasilicate hydrate.

[0009] Examples of a regeneration method for the inorganic binder process in the related art include the baking regeneration described in Patent Document 1. However, it is not possible to sufficiently suppress the wetting, and since a high-temperature treatment at 600°C to 800°C is performed, there is a problem in terms of energy consumption and CO 2 emission. In addition, Patent Document 1 relates to an inorganic binder process of wet sand using an inorganic binding agent consisting of liquid water glass.

[0010] That is, an object of the present invention is to suppress the wetting of the inorganic coated sand during the storage of the regenerated sand and the like, and to reduce the environmental load during the production of the casting sand for the inorganic coated sand using the regenerated sand and the like.SOLUTION TO PROBLEM

[0011] Therefore, the inventors of the present invention found that applying a coating layer to the regenerated sand or the refractory aggregate containing SiO 2 and setting the cation exchange capacity (CEC) of the casting sand to a specific value is effective for solving the above-described problems, and completed the present invention.

[0012] According to the present invention, there is provided an inorganic coated sand in a dry state including: a casting sand in which a first coating layer is disposed on a surface of one or two kinds of aggregates selected from a regenerated sand (A) and a refractory aggregate (B); and a second coating layer containing a metasilicate on the first coating layer of the casting sand, in which the refractory aggregate (B) contains SiO 2 , and a cation exchange capacity (CEC) of the casting sand is 3 mmol (+) / kg or more and 40 mmol (+) / kg or less.

[0013] In addition, according to the present invention, there is provided a casting mold consisting of the above-described inorganic coated sand.

[0014] In addition, according to the present invention, there is provided a method for producing an inorganic coated sand, the method including: a step (1) of mixing one or two kinds of aggregates selected from a regenerated sand (A) and a refractory aggregate (B), and an aluminate or aluminum hydroxide, and forming a first coating layer on a surface of the aggregate to obtain a casting sand; a step (2) of mixing the obtained casting sand with a molten solution of a metasilicate hydrate to obtain a mixture; and a step (3) of cooling the mixture to a temperature lower than a melting point of the metasilicate hydrate, in which the refractory aggregate (B) contains SiO 2 .

[0015] In addition, according to the present invention, there is provided a method for producing an inorganic coated sand, the method including: a step (4) of mixing one or two kinds of aggregates selected from a regenerated sand (A) and a refractory aggregate (B), and an aluminate or aluminum hydroxide, forming a first coating layer on a surface of the aggregate to a obtain casting sand; a step (5) of mixing the obtained casting sand with a solution including water glass, caustic alkali, and water to obtain a mixture including a metasilicate hydrate, in which the refractory aggregate (B) contains SiO 2 .

[0016] In addition, according to the present invention, there is provided a method for improving storage stability of an inorganic coated sand, in which the inorganic coated sand includes a casting sand containing one or two kinds of aggregates selected from a regenerated sand (A) and a refractory aggregate (B); and a second coating layer containing a metasilicate coating the casting sand, the refractory aggregate (B) contains SiO 2 , and the inorganic coated sand in a dry state is prepared such that a cation exchange capacity (CEC) of the casting sand is 3 mmol (+) / kg or more and 40 mmol (+) / kg or less. ADVANTAGEOUS EFFECTS OF INVENTION

[0017] According to the present invention, it is possible to improve the storage stability of the inorganic coated sand while reducing the environmental load during the production of the casting sand for inorganic coated sand.DESCRIPTION OF EMBODIMENTS

[0018] Hereinafter, embodiments of the present invention will be described. In this specification, "A to B" indicating a numerical range represents a range of A or greater and B or less unless otherwise specified. The configurations and elements described in the embodiments can be appropriately combined as long as the effects of the invention are not impaired.

[0019] In addition, the "coating" and the "coating layer" are not limited to being continuous, and may have a discontinuous portion in a part thereof.<Inorganic Coated Sand>

[0020] The inorganic coated sand of the present embodiment is an inorganic coated sand in a dry state including a casting sand that includes one or two kinds of the aggregate selected from the regenerated sand (A) and the refractory aggregate (B), and a first coating layer that covers the aggregate and is located on the surface thereof, and a second coating layer that includes a metasilicate and is provided on the first coating layer of the casting sand. The refractory aggregate (B) contains SiO 2 , and a cation exchange capacity (CEC) of the casting sand is 3 mmol (+) / kg or more and 40 mmol (+) / kg or less.

[0021] That is, in a case of producing the inorganic coated sand by using one or two kinds of the aggregates selected from the regenerated sand (A) and the refractory aggregate (B), the inorganic coated sand of the present embodiment can improve the storage stability of the inorganic coated sand using one or two kinds of the aggregates selected from the regenerated sand (A) and the refractory aggregate (B) by laminating the first coating layer and the second coating layer containing a silicate in this order on the surface of the aggregate and controlling the cation exchange capacity (CEC) of the casting sand.

[0022] The details of the reason for this are not clear, but are presumed to be as follows. (i) A residue of an inorganic binding agent that has been used once for casting may be attached to the surface of the regenerated sand (A). In a case where a surface of regenerated sand (A) having a residue of an inorganic binding agent is coated with a metasilicate hydrate to produce inorganic coated sand, the component in the residue reacts with the metasilicate hydrate, the metasilicate hydrate crystal is melted, and the inorganic coated sand is wet. (ii) On the other hand, in a case where a silicate hydrate is coated on a surface of a refractory aggregate (B) containing SiO 2 to produce an inorganic coated sand, as in the case of (i), the SiO 2 component of the refractory aggregate (B) and the silicate hydrate may react with each other, and thus the silicate hydrate crystal may be melted and the inorganic coated sand may be wet. (iii) Therefore, it is presumed that, by forming the first coating layer to cover the surface of the regenerated sand (A) or the refractory aggregate (B) and forming a casting sand having a specific CEC, the reaction with the residue can be suppressed, and even in a case where the second coating layer containing a metasilicate is laminated, the melting of the metasilicate hydrate in the second coating layer can be suppressed, and as a result, the wetting of the inorganic coated sand can be suppressed and the storage stability can be improved.

[0023] In addition, in a case where the first coating layer that coats the surface of the regenerated sand (A) or the refractory aggregate (B) is formed of an aluminosilicate-containing substance, the first coating layer can be formed at a relatively low temperature. Therefore, in the regeneration of the inorganic binder process in the related art, a baking step at 600°C to 800°C is taken, but this can be omitted, and it is possible to suppress the consumption of thermal energy and the emission of CO 2 , and to reduce the environmental load.

[0024] Hereinafter, the inorganic coated sand of the present embodiment will be described in more detail.

[0025] The inorganic coated sand is dry. The coated sand in a dry state means coated sand in which regardless of the water content, a measured value is obtained in the measurement of a dynamic angle of repose. The dynamic angle of repose is preferably 80° or less, more preferably 45° or less, and even more preferably 30° or less.

[0026] Here, the dynamic angle of repose can be measured by the following method.(Measurement Method for Dynamic Repose Angle)

[0027] Coated sand of half the volume of the cylindrical transparent plastic bottle is put into the cylindrical transparent plastic bottle, the cylindrical transparent plastic bottle is held such that the axial center is horizontal, and the cylindrical transparent plastic bottle is rotated around the horizontal axial center at a rotation speed of 60 rpm. A slope of the coated sand layer flowing in the cylinder becomes flat. An angle formed between the slope and the horizontal plane is measured. In a case where the coated sand does not flow in the cylinder, or the slope of the coated sand layer is not formed as a flat plane even when the coated sand flows, and as a result, the dynamic angle of repose cannot be measured, the sand is in a wet state.

[0028] The inorganic coated sand is specifically composed of a particle group of the inorganic coated sand.

[0029] The inorganic coated sand preferably has a spherical shape in terms of improving fluidity further improving a filling property into a molding die. Here, the spherical shape of the inorganic coated sand means a ball-like round shape. More specifically, from the viewpoint of improving fluidity, mold quality, and mold strength, and from the viewpoint of ease of modeling the mold, the sphericity of the inorganic coated sand is preferably 0.75 or more, more preferably 0.80 or more, and still more preferably 0.82 or more. In addition, the upper limit value of the sphericity is specifically 1.

[0030] In the present embodiment, the sphericity of the inorganic coated sand specifically coincides with the sphericity of the refractory aggregate described later.

[0031] Here, the sphericity of the inorganic coated sand can be determined by analyzing an image (photograph) of particles obtained by using an optical microscope or a digital microscope (for example, VH-8000 manufactured by KEYENCE CORPORATION), determining an area of a cross section of projected particles and a perimeter of the cross section, and calculating [perimeter (mm) of perfect circle with the same area as the area (mm 2< ) of cross section of projected particles] / [perimeter (mm) of cross section of projected particles], and then averaging values each obtained for any 50 particles.

[0032] An average particle diameter of the inorganic coated sand is preferably 0.05 mm or more, and more preferably 0.1 mm or more, in terms of improvement in quality of the casting mold and strength of the casting mold, or easiness of molding the casting mold, and the storage stability. Further, when the average particle diameter of the inorganic coated sand is the lower limit or more described above, an amount of the second coating layer used can be reduced during the manufacture of the casting mold, which is preferable in terms of easiness of reproduction of the inorganic coated sand.

[0033] The average particle diameter of the inorganic coated sand is preferably 2 mm or less, more preferably 1 mm or less, and even more preferably 0.5 mm or less in terms of improvement in quality of the casting mold and strength of the casting mold, or easiness of molding the casting mold. In addition, when the average particle diameter of the inorganic coated sand is the upper limit or less described above, a porosity of the inorganic coated sand is reduced during the manufacture of the casting mold, which is preferable in terms of increasing the strength of the casting mold.

[0034] In the present embodiment, the average particle diameter of the inorganic coated sand and an average particle diameter of the refractory aggregate to be described later can be specifically measured by the following method.(Method for Measuring Average Particle Diameter)

[0035] When the sphericity = 1, a diameter (mm) of the particles is measured from the cross section of the projected particles. On the other hand, when the sphericity < 1, a major axis diameter (mm) and a minor axis diameter (mm) of particles randomly oriented are measured to determine (major axis diameter + minor axis diameter) / 2, and values each obtained for any 100 particles are averaged to obtain an average particle diameter (mm). The major axis diameter and the minor axis diameter are defined as follows. When the particles are stabilized on a plane and a projected image of the particles on the plane is sandwiched between two parallel lines, a width of the particles as a minimum distance between the parallel lines is referred to as the minor axis diameter, whereas a distance when the particles are sandwiched between the two parallel lines in a direction perpendicular to the parallel lines is referred to as the major axis diameter.

[0036] The major axis diameter and the minor axis diameter of the particles can be determined by capturing an image (photograph) of the particles with an optical microscope or a digital microscope (for example, VH-8000 manufactured by KEYENCE CORPORATION), and analyzing the obtained image.

[0037] Hereinafter, each configuration of the inorganic coated sand will be described.[Regenerated Sand (A)]

[0038] The regenerated sand (A) is a refractory material that is reused from a used casting mold or core formed of a refractory aggregate and a binding agent. Preferably, the regenerated sand (A) has a refractory aggregate and an inorganic binding agent layer which is formed on a surface of the refractory aggregate and contains one or more selected from a silicate and a reactant of the silicate.

[0039] The regenerated sand (A) is obtained, for example, by a production method described later.(Refractory Aggregate)

[0040] Examples of the material of the refractory aggregate constituting the regenerated sand (A) include one or more selected from the group consisting of natural sand and artificial sand. The refractory aggregate is specifically composed of the particle group of the refractory aggregate.

[0041] Examples of the natural sand include one or two or more selected from the group consisting of silica sand containing quartz as a main component, chromate sand, zircon sand, olivine sand, and alumina sand.

[0042] Examples of the artificial sand include one or two or more selected from the group consisting of synthetic mullite sand, SiO 2 -based casting sand containing SiO 2 as a main component, Al 2 O 3 -based casting sand containing Al 2 O 3 as a main component, SiO 2 / Al 2 O 3 -based casting sand, SiO 2 / MgO-based casting sand, SiO 2 / Al 2 O 3 / ZrO 2 -based casting sand, SiO 2 / Al 2 O 3 / Fe 2 O 3 -based casting sand, and casting sand derived from slag. Here, the main component means the most abundant component among the components contained in the sand.

[0043] The artificial sand refers to casting sand in which a metal oxide component is artificially prepared and melted or sintered, not casting sand produced from nature. In addition, recovered sand obtained by recovering the used refractory aggregate, regenerated sand obtained by reproducing the recovered sand, and the like can also be used as the artificial sand.

[0044] The content of each component such as SiO 2 , Al 2 O 3 , and Fe 2 O 3 in the refractory aggregate can be measured using the following fluorescence X-ray method. The refractory aggregate is adjusted to a size of about 0.1 µm or less with a vibration mill, and heated at 1,050°C for 1 hour. Then, 5 g of lithium tetraborate and 0.5 g of a refractory aggregate are mixed, and the mixture is heated at 1,200°C for 10 minutes to be melted and then cooled to prepare a sample in a glassy state (glass bead method). The sample is subjected to fluorescence X-ray analysis by a fundamental parameter (FP) method using a fluorescence X-ray analyzer ZSX Primus II (manufactured by Rigaku Corporation).

[0045] In the present embodiment, since the sphericity of the refractory aggregate matches the sphericity of the inorganic coated sand, the same preferred conditions are applied.

[0046] Further, an average particle diameter of the refractory aggregate is preferably 0.05 mm or more, and more preferably 0.1 mm or more, in terms of improvement in quality of the casting mold and a strength of the casting mold, or easiness of molding the casting mold. Further, when the average particle diameter of the refractory aggregate is the lower limit or more described above, an amount of the second coating layer used can be reduced during the manufacture of the casting mold, which is preferable in terms of easiness of reproduction of the inorganic coated sand.

[0047] The average particle diameter of the refractory aggregate is preferably 2 mm or less, more preferably 1 mm or less, and even more preferably 0.5 mm or less, in terms of improvement in quality of the casting mold and a strength of the casting mold, or easiness of molding the casting mold. In addition, when the average particle diameter of refractory aggregate is the upper limit or less described above, a porosity of the inorganic coated sand{b> <b}is reduced during the manufacture of the casting mold, which is preferable in terms of increasing the strength of the casting mold.

[0048] From the viewpoint of obtaining a smoother surface of the aggregate and further improving the strength of the mold, and from the viewpoint of obtaining low thermal expansion properties, the degree of amorphousness of the refractory aggregate is preferably 20% or more, more preferably 30% or more, and still more preferably 40% or more.

[0049] The upper limit of the amorphous degree of the refractory aggregate (A) is not limited, but is, for example, 100% or less, and may be 99% or less.

[0050] The degree of amorphousness of the refractory aggregate can be measured by the following X-ray diffraction method.(X-Ray Diffraction Method)

[0051] The refractory aggregate was pulverized in a mortar, and pressure-bonded to an X-ray glass holder of a powder X-ray diffraction apparatus for measurement. As the powder X-ray diffraction apparatus, MultiFlex (light source: CuKα ray, tube voltage: 40 kV, tube current: 40 mA) manufactured by Rigaku Corporation was used, and the measurement was performed in a range of 2θ = 5° to 90° at a scanning interval of 0.01° and a scanning speed of 2° / min with slits DS 1, SS 1, RS 0.3 mm. Within a range of 2θ = 10° to 50°, the X-ray intensities on the low-angle side and the high-angle side are connected by a straight line, the area below the straight line is set as a background, the crystallinity is obtained using the software attached to the apparatus and subtracted from 100, and the result is defined as the amorphous degree. Specifically, with respect to the area above the background, the amorphous peak (halo) and each crystalline component are separated by curve fitting, and areas thereof are obtained to calculate the amorphous degree (%) by the following formula.

[0052] Various methods are used as a method for controlling the amorphous degree of the refractory aggregate (A), and in general, a manufacturing method in which a melted material is rapidly cooled is preferably used. For example, a method including: melting a raw material; air-granulating the melted material; and rapidly cooling the air-granulated material, or a method including: treating a raw material in the flame; and rapidly cooling the raw material. In any case, the cooling method may be appropriately selected at various rates according to the material and the particle diameter. A method for making a crystallized material amorphous through a heat treatment and a cooling treatment is also considered. Among these, those using a flame melting method, in which heating and cooling can be easily controlled, are preferable.(Inorganic Binder Layer)

[0053] It is preferable that the regenerated sand (A) has an inorganic binding agent layer. Specifically, the inorganic binding agent layer includes one or more selected from a silicate and a reactant of a silicate, and covers the surface of the refractory aggregate. The coating is not limited to a continuous coating, and may have a discontinuous portion in a part thereof.

[0054] The inorganic binding agent layer is intended to be a layer in which, in a case where an inorganic coated sand having a refractory aggregate and an inorganic binding agent formed on a surface of the refractory aggregate is molded into a casting mold for casting, used as the casting mold, and then reproduced to be a regenerated sand, the inorganic binding agent is present on the surface of the refractory aggregate as a residual inorganic binding agent.

[0055] That is, the silicate and the reactant of the silicate, which are contained in the inorganic binding agent layer, are intended to be present on the surface of the refractory aggregate as the residual inorganic binding agent.

[0056] Specifically, examples of the reactant of the silicate and the silicate include a silicate and a metasilicate, a reactant of a silicate and an amorphous silica, a reactant of a silicate and an amorphous silica, and the like, and one kind or two or more kinds are mixed. In addition, examples of the cation constituting the salt include monovalent cations such as sodium, potassium, lithium, and ammonium, and divalent cations such as magnesium, calcium, and zinc.

[0057] Examples of the method for confirming that the inorganic binding agent layer contains a silicate or a reactant of a silicate include a method for analyzing a component eluted by stirring regenerated sand in an aqueous hydrochloric acid solution with an ICP emission spectrometer and obtaining a concentration of a silicate ion, a sodium ion, or the like, a method for performing element analysis of a regenerated sand surface with a scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDX) to confirm the presence of silicon, sodium, or the like, and a method for confirming a structure derived from a silicate by 23< Na and 29< Si solid NMR.[Refractory Aggregate (B)]

[0058] The degree of crystallization of the refractory aggregate (B) is at least 20% or more, preferably 30% or more, preferably 99% or less, more preferably 80% or less, even more preferably 70% or less, and still more preferably 60% or less, from the viewpoint of improving the mold strength due to a smoother surface of the aggregate and obtaining low thermal expansion properties, and from the viewpoint of improving the storage stability.

[0059] In addition, from the viewpoint of storage stability, the content of SiO 2 in the refractory aggregate (B) is preferably 10% or more, more preferably 20% or more, and still more preferably 30% or more, and from the viewpoint of further improving the mold hardness, the content of SiO 2 is preferably 99% or less, more preferably 80% or less, and still more preferably 70% or less. In addition, from the viewpoint of improving storage stability, the content of SiO 2 in the refractory aggregate (B) is preferably 50% or less and more preferably 40% or less.

[0060] The degree of amorphicity of the refractory aggregate (B) is obtained by the same X-ray diffraction method as that for the refractory aggregate of the regenerated sand (A).

[0061] In addition, the content of SiO 2 in the refractory aggregate (B) can be measured using the same fluorescence X-ray method as that of the refractory aggregate of the regenerated sand (A).[casting sand]

[0062] The casting sand has, as an outermost layer, a first coating layer formed on a surface of one or two kinds of aggregates selected from regenerated sand (A) and refractory aggregate (B). The casting sand can function as inorganic coated sand by further forming a second coating layer on the first coating layer.

[0063] The cation exchange capacity (CEC) of the casting sand needs to be controlled to a specific value from the viewpoint of suppressing the wet state of the inorganic coated sand. The control of the cation exchange capacity (CEC) can be performed by combining known methods, but can be performed, for example, by selecting the material of the coating layer, adjusting the content, and adjusting the baking temperature and time.

[0064] Specifically, the casting sand is composed of a particle group of the casting sand.

[0065] The CEC of the casting sand is obtained by the ammonium acetate method (fertilizer analysis method (Ministry of Agriculture, Forestry and Fisheries Agricultural Environmental Technology Research Institute Law) 5.31.1) shown below.

[0066] First, small pieces of absorbent cotton are placed as a support layer in the lower part of the permeation tube, and the paper pulp obtained by finely cutting filter paper and stirring the paper in hot water is packed to a thickness of about 5 mm to form a flat filtration surface. Next, a stopper is placed at a lower end of the permeation tube, a few mL of a 1 M ammonium acetate solution is put therein, 2 to 4 g of an analysis sample (casting sand) is weighed and allowed to fall and settle down little by little to fill the permeation tube, the stopper is removed, the device is assembled, and washing with an ammonium acetate solution is started. 100 mL of a 1 M ammonium acetate solution is used, and the dropping rate is adjusted so that the permeation is completed in 4 to 20 hours. After the permeation is completed, the upper part inside the permeation tube is washed with a small amount of an alcohol solution, and the sample layer is further washed with 50 mL of an 80% alcohol solution to remove the excess ammonium acetate solution. The analysis sample saturated with NH 4 +< obtained in this way is washed with 100 mL of a 10% sodium chloride solution to exchange and leach NH 4 +< . Ammoniacal nitrogen in the leachate is quantified by steam distillation and alkali titration, and is expressed as millimole equivalent per 1 kg of the analysis sample to obtain a cation exchange capacity.

[0067] From the viewpoint of improving the storage stability, the cation exchange capacity (CEC) is 3 mmol (+) / kg or more, and preferably 6 mmol (+) / kg or more.

[0068] On the other hand, from the viewpoint of improving the storage stability, the cation exchange capacity (CEC) is 40 mmol (+) / kg or less, preferably 20 mmol (+) / kg or less, and more preferably 10 mmol (+) / kg or less.(First Coating Layer)

[0069] The first coating layer constituting the casting sand is a layer for coating the surface of one or two kinds of aggregates selected from the regenerated sand (A) and the refractory aggregate (B). In addition, the first coating layer constitutes the outermost layer of the casting sand, and in the inorganic coated sand, the first coating layer is located between the second coating layer described later and the surface of the aggregate.

[0070] The first coating layer is preferably a coating layer formed of a constituent material different from that of the second coating layer and more preferably a layer formed of an aluminosilicate, and it is preferable that the first coating layer does not contain at least a metasilicate. As a result, it is possible to efficiently prevent the silicate in the second coating layer from acting on the aggregate to promote the wetting of the inorganic coated sand.

[0071] Examples of the aluminosilicate include one or more selected from silicates and reactants of silicates, and a reactant of aluminate or aluminum hydroxide. Here, the silicate refers to a substance containing, in a composition, an anion group having a structure in which one or several silicon atoms are centered and an electronegative ligand surrounds the one or several silicon atoms. Specifically, the term "the residual inorganic binder" or "the refractory aggregate (B)" indicates any one or both of the residual inorganic binder or the refractory aggregate (B) present on the surface of the refractory aggregate.

[0072] From the viewpoint of easily improving the storage stability, it is preferable that the above-described aluminosilicate includes at least one among one or more selected from a reactant of a silicate and a reactant of a silicate, and sodium aluminate or aluminum hydroxide.

[0073] The form of sodium aluminate is not particularly limited, and may be any of a powder or an aqueous solution.

[0074] From the viewpoint of improving storage stability, the content of aluminum in the first coating layer is preferably 0.1 parts by mass or more and more preferably 0.4 parts by mass or more with respect to 100 parts by mass of the aggregate, in terms of Al 2 O 3 .

[0075] On the other hand, the content of aluminum in the first coating layer is preferably 20 parts by mass or less and more preferably 10 parts by mass or less with respect to 100 parts by mass of the aggregate in terms of Al 2 O 3 in order to improve the mold strength and obtain good storage stability.

[0076] The content of aluminum in the first coating layer is obtained by the following method.

[0077] The Al 2 O 3 content in the first coating layer is calculated from the following expression using the analytical values of the aggregate and of the casting sand containing the first coating layer.

[0078] Al 2 O 3 [parts by mass] of first coating layer = {Al 2 O 3 [parts by mass] of casting sand} - {Al 2 O 3 [parts by mass] of aggregate}

[0079] From the viewpoint of improving storage stability and obtaining a casting mold with high strength, the content of the first coating layer is preferably 0.02 parts by mass or more, preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, still more preferably 1 part by mass or more, and even still more preferably 2 parts by mass or more with respect to 100 parts by mass of the aggregate.

[0080] From the viewpoint of achieving both storage stability and strength, the content of the first coating layer is preferably 10 parts by mass or less and more preferably 9.5 parts by mass or less with respect to 100 parts by mass of the aggregate.[Second Coating Layer]

[0081] The second coating layer is a layer formed on the first coating layer, and is a layer that serves as an outermost layer of the inorganic coated sand.

[0082] The second coating layer contains a metasilicate and is used to impart a function as a bonding agent to the aggregate. The crystallinity of the second coating layer can be improved, and the inorganic coated sand is dried and has excellent fluidity at room temperature, which is preferable.

[0083] Examples of the metasilicate include one or two or more selected from sodium metasilicate, potassium metasilicate, lithium metasilicate, ammonium metasilicate, and the like, and hydrates thereof. Among these, sodium metasilicate and potassium metasilicate are preferable. In addition, the amount of water of hydration of the metasilicate hydrate is not particularly limited, but is preferably 5 or more and 9 or less. Specifically, at least one selected from sodium metasilicate pentahydrate or sodium metasilicate nonahydrate is preferable, and sodium metasilicate nonahydrate is more preferable.

[0084] From the viewpoint of improving storage stability and obtaining a casting mold with high strength, the content of the second coating layer is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, still more preferably 0.5 parts by mass or more, even more preferably 1 part by mass or more, and even still more preferably 2 parts by mass or more with respect to 100 parts by mass of the aggregate.

[0085] On the other hand, from the viewpoint of achieving both storage stability and strength, the content of the second coating layer is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and still more preferably 6 parts by mass or less with respect to 100 parts by mass of the aggregate.

[0086] From the viewpoint of improving mold strength, the viewpoint of excellent productivity, and the viewpoint of availability, the content of the metasilicate in the second coating layer is preferably 80% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, even still more preferably 98% by mass or more, and even still more preferably substantially 100% by mass.

[0087] Here, the term "substantially" means that a component other than the metasilicate contained in the metasilicate which is a raw material may be unintentionally contained.

[0088] The total content of the metasilicate in the second coating layer refers to the total content of the metasilicate with respect to all components other than water in the second coating layer.

[0089] From the viewpoint of improving storage stability and obtaining a casting mold with high strength, the content (in terms of anhydride) of the metasilicate in the second coating layer is preferably 0.03 parts by mass or more, more preferably 0.1 parts by mass or more, still more preferably 0.5 parts by mass or more, and even still more preferably 0.9 parts by mass or more with respect to 100 parts by mass of the aggregate.

[0090] On the other hand, from the viewpoint of achieving both storage stability and strength, the content of the metasilicate is preferably 5 parts by mass or less, more preferably 4 parts by mass or less, still more preferably 3 parts by mass or less, and even still more preferably 2 parts by mass or less with respect to 100 parts by mass of the aggregate.(Inorganic Fine Particles)

[0091] In the present embodiment, the inorganic coated sand may further contain inorganic fine particles.

[0092] In a case where the inorganic fine particles are contained, the inorganic fine particles preferably form a part of the second coating layer. Specifically, the second coating layer preferably further contains inorganic fine particles on at least one of the layer or in the layer, and more preferably further contains inorganic fine particles on the layer. The inorganic fine particles may be included in both the second coating layer and the second coating layer. Thanks to this, the particles of the inorganic coated sand (C) are strongly bound to each other via the inorganic fine particles, and as a result, the strength of a mold to be obtained can be further improved. The inorganic fine particles on the second coating layer may be partially embedded in the second coating layer.

[0093] The inorganic fine particles are not limited, and examples thereof include one or two or more kinds of fine particles selected from silica, silicon, zinc oxide, aluminum hydroxide, tin oxide, and the like. Among these, from the viewpoint of improving the strength of the mold, silica particles are preferable, and from the viewpoint of having a large specific surface area and high reactivity with silicates, amorphous silica particles are more preferable. The inorganic fine particles may be used alone or in combination of two or more kinds thereof.(Other Additives)

[0094] The second coating layer may contain various additives as necessary, in addition to the above-described components. Examples of the other additives include a coupling agent, a moisturizing agent, a moisture improvement agent, a lubricant, a surfactant, and a mold release agent.

[0095] The coupling agent is not limited, and examples thereof include a silane coupling agent, a zircon coupling agent, and a titanium coupling agent.

[0096] Examples of the moisturizing agent include a polyhydric alcohol, a water-soluble polymer, hydrocarbons, sugars, protein, and an inorganic compound other than those described above.

[0097] Examples of the moisture resistance improving agent include a metal oxide (other than those described above), a carbonate, a borate, a sulfate, and a phosphate.

[0098] Examples of the lubricant include waxes; fatty acid amides; alkylene fatty acid amides; stearic acids; stearyl alcohol; metal stearic acid salts such as lead stearate, zinc stearate, calcium stearate, and magnesium stearate; stearic acid monoglyceride; stearyl stearate; and hydrogenated oil.

[0099] Examples of a mold releasing agent include paraffin, wax, light oil, machine oil, spindle oil, insulating oil, waste oil, vegetable oil, fatty acid ester, organic acid, graphite fine particles, mica, vermiculite, a fluorine-based mold releasing agent, and silicone-based mold releasing agent.(Moisture Content)

[0100] From the viewpoint of obtaining a mold with high strength, the content of water including the crystal water in the second coating layer is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and still more preferably 20 parts by mass or more with respect to 100 parts by mass (in terms of anhydride) of the silicate.

[0101] In addition, from the viewpoint of filling property into the molding mold and viewpoint of obtaining a casting mold having a high strength, the content of water in the second coating layer is preferably 180 parts by mass or less, more preferably 160 parts by mass or less, still more preferably 150 parts by mass or less, and even still more preferably 140 parts by mass or less with respect to 100 parts by mass of the silicate.

[0102] The content of water including the crystal water in the second coating layer included in the inorganic coated sand can be adjusted according to the type of silicate.

[0103] In a case where the metasilicate is sodium metasilicate, from the viewpoint of obtaining a high-strength mold and the viewpoint of easily producing a mold, the content of water including the crystal water in the second coating layer is preferably 60 parts by mass or more, more preferably 65 parts by mass or more, still more preferably 90 parts by mass or more, and even still more preferably 110 parts by mass or more with respect to 100 parts by mass (in terms of anhydride) of sodium metasilicate, and from the viewpoint of improving fluidity and further improving the moldability into a molding die, the content of water is preferably 180 parts by mass or less, more preferably 160 parts by mass or less, even still more preferably 150 parts by mass or less, and even still more preferably 140 parts by mass or less.

[0104] For example, in a case where the silicate constituting the second coating layer is only sodium metasilicate pentahydrate, the content of water is 74 parts by mass with respect to 100 parts by mass of sodium metasilicate, and in a case where the silicate constituting the second coating layer is only sodium metasilicate nonahydrate, the content of water is 133 parts by mass with respect to 100 parts by mass of sodium metasilicate.<Method for Producing Regenerated Sand (A) / method for Regenerating Used casting sand>

[0105] As a method for reproducing the waste sand of the mold after casting, a known method (for example, "Mold Modeling Method", 4th edition, Japan Foundry Engineering Society, November 18, 1996, pp. 327 to 330) can be followed. For example, methods such as a dry polishing treatment (mechanical abrasion), a wet polishing treatment, and a baking treatment, and methods in which these treatments are combined are known.

[0106] In the dry polishing treatment, a part of the residue of the inorganic binding agent layer present on the surface of the refractory aggregate can be removed. For the removal, for example, a method using a sand reclaimer that performs a polishing treatment by collision and friction between sand grains by causing sand to rise in a device by a high-speed air flow and causing the sand to collide with a collision plate, a rotary reclaimer that performs a polishing treatment by collision and friction between projection sand generated by centrifugal force and falling sand to be input by inputting sand onto a high-speed rotating rotor, or an agitator mill that performs a polishing treatment by using friction between sand grains can be used.

[0107] In addition, examples of the wet polishing treatment include a method using a trough polishing machine that performs a polishing treatment by friction between sand grains in a trough in which blades are rotated.

[0108] Examples of the baking treatment include a method in which a baking furnace such as a fluid baking furnace or a rotary kiln is used, sand is added to the baking furnace, and baking is carried out in a range of 200°C to 1,000°C. In addition, it is known that the baking is carried out at 600°C to 800°C in order to further improve the accuracy.

[0109] Although any method may be used for the reproduction, the wet treatment or the baking treatment is complicated in terms of steps and has a large energy load. Therefore, among these, the dry polishing treatment is preferable.<Method for Producing Inorganic Coated Sand>

[0110] Next, a method for producing the inorganic coated sand of the present embodiment will be described.

[0111] The method for producing an inorganic coated sand of the present embodiment is a method for producing an inorganic coated sand in a dry state, the method including: a casting sand that includes one or two kinds of aggregates selected from a regenerated sand (A) and a refractory aggregate (B), and a first coating layer that covers the aggregate and is located on a surface of the aggregate; and a second coating layer that includes a metasilicate and is provided on the first coating layer of the casting sand, in which the refractory aggregate (B) includes SiO 2 , and a cation exchange capacity (CEC) of the casting sand satisfies 3 mmol (+) / kg or more and 40 mmol (+) / kg or less.

[0112] According to the production method for the present embodiment, since the first coating layer is formed on the surface of the aggregate material and the cation exchange capacity (CEC) of the casting sand is controlled, it is possible to omit the baking step of the aggregate material while improving the storage stability, and thus it is possible to reduce the consumption of thermal energy and to reduce the environmental load.

[0113] First, as an example of the method for producing the inorganic coated sand of the present embodiment, a method including the following steps (1) to (3) in which the refractory aggregate (B) contains SiO 2 may be mentioned. · Step (1): a step of mixing one or two kinds of aggregates selected from regenerated sand (A) and refractory aggregate (B) with an aluminates or aluminum hydroxide to form the first coating layer on the surface of the aggregate, thereby obtaining casting sand · Step (2): step of mixing the obtained casting sand with a molten solution of a metasilicate hydrate to obtain a mixture · Step (3): step of cooling the obtained mixture to a temperature lower than a melting point of the metasilicate hydrate to form the second coating layer on the first coating layer

[0114] In the step (1), the aluminate or aluminum hydroxide and the aggregate are mixed together to form the first coating layer to cover the surface of the aggregate. Among these, it is preferable to heat the first coating layer to 25°C or higher and lower than 400°C to form the first coating layer.

[0115] Examples of the method for forming the first coating layer by heating the mixture to 25°C or higher and lower than 400°C in the step (1) include a method for putting an aluminate into the aggregate heated to 25°C or higher and lower than 400°C, and a method for putting an aluminate or aluminum hydroxide into the aggregate and then heating the aggregate to 25°C or higher and lower than 400°C.

[0116] Among these, the latter method is preferable from the viewpoint of forming a uniform coating layer.

[0117] In addition, from the viewpoint of improving storage stability, the heating temperature is preferably 40°C or higher and 300°C or lower, and more preferably 70°C or higher and 200°C or lower.

[0118] Examples of the method for heating the coating film to 25°C or higher and lower than 400°C in the step (1) to form the first coating layer include a method for putting an aluminate or aluminum hydroxide into the aggregate heated to 25°C or higher and lower than 400°C, and a method for putting an aluminate or aluminum hydroxide into the aggregate and then heating the aggregate to 25°C or higher and lower than 400°C.

[0119] Among these, the latter method is preferable from the viewpoint of forming a uniform coating layer.

[0120] In addition, from the viewpoint of improving storage stability, the heating temperature is preferably 40°C or higher and 300°C or lower, and more preferably 70°C or higher and 200°C or lower.

[0121] The mixing conditions such as a stirring speed and a treatment time in a case of mixing the aggregate with the aluminates or the aluminum hydroxide can be appropriately determined depending on the treatment amount of the mixture.

[0122] As a result, a casting sand in which a cation exchange capacity (CEC) is 3 mmol (+) / kg or more and 40 mmol (+) / kg or less is obtained. in the step (2), the casting sand and a molten solution of a metasilicate hydrate are mixed to obtain a mixture.

[0123] Examples of the method for mixing the molten solution of the metasilicate hydrate with the casting sand in the step (2) include a method for charging the metasilicate into the casting sand heated to a temperature equal to or higher than the melting point of the metasilicate hydrate, and a method for charging the metasilicate heated to a temperature equal to or higher than the melting point of the metasilicate hydrate into the casting sand.

[0124] Among these, the latter method is preferable from the viewpoint of shortening the coating time.

[0125] The mixing conditions such as a stirring speed and a treatment time in a case of mixing the casting sand and the metasilicate hydrate can be appropriately determined depending on the treatment amount of the mixture.

[0126] In the step (3), the mixture obtained in the step (2) is cooled to a temperature lower than the melting point of the metasilicate hydrate to reduce the fluidity of the metasilicate hydrate, and the metasilicate hydrate is fixed to the surface of the casting sand to form a metasilicate hydrate layer, that is, a second coating layer.

[0127] In this manner, the inorganic coated sand according to the present embodiment can be obtained.

[0128] Next, as another example of the method for producing the inorganic coated sand of the present embodiment, a method for producing the inorganic coated sand, in which the refractory aggregate (B) contains SiO 2 and includes the following steps (4) and (5), is exemplified.

[0129] Step (4): a step of mixing one or two kinds of the aggregates selected from the regenerated sand (A) and the refractory aggregate (B) with an aluminates or aluminum hydroxide to form the first coating layer on the surface of the aggregate, thereby obtaining casting sand

[0130] Step (5): a step of mixing the casting sand with a solution containing water glass, caustic alkali, and water to obtain a mixture containing a sodium metasilicate hydrate

[0131] The step (4) can be carried out by the same method as in the step (1).

[0132] In the step (5), by setting the molar ratio of SiO 2 / M 2 O (M represents an alkali metal) / H 2 O in the solution containing water glass, caustic alkali, and water to 1:1:n (5 ≤ n ≤ 9), a desired amount of hydrated metasilicate hydrate can be formed.

[0133] Further, the second coating layer can be formed by mixing the above-described solution containing water glass, caustic alkali, and water with the casting sand to coat the surface of the casting sand with a metasilicate hydrate.

[0134] The mixing conditions of water glass, caustic alkali, and water are not particularly limited, and a known method can be used. For example, the mixing may be carried out at an environmental temperature, and in a case where the molten solution generates heat, the mixing may be continued as it is, and then the mixture may be allowed to stand until the environmental temperature is reached.

[0135] In this manner, the inorganic coated sand according to the present embodiment can be obtained.<Casting Mold>

[0136] The casting mold for casting according to the present embodiment comprises the inorganic coated sand in the present embodiment described above, and is formed of the inorganic coated sand. Examples of a method for molding a casting mold include a molding method using a heated molding die, a molding method in which steam is further aerated in the heated molding die, and then hot air is aerated.<Method for Improving Storage Stability>

[0137] The method for improving the storage stability of the inorganic coated sand of the present embodiment is a method for improving the storage stability of the inorganic coated sand, the method including: a casting sand containing one or two kinds of the sands selected from the regenerated sand (A) and the refractory aggregate (B); and a second coating layer containing a metasilicate that coats the casting sand, in which the refractory aggregate (B) contains SiO 2 , and a step of preparing an inorganic coated sand in a dry state is prepared such that a cation exchange capacity (CEC) of the casting sand satisfies 3 mmol (+) / kg or more and 40 mmol (+) / kg or less.

[0138] In this manner, the storage stability of the inorganic coated sand can be improved. The step of preparing the cation exchange capacity (CEC) of the casting sand to be 3 mmol (+) / kg or more and 40 mmol (+) / kg or less is performed by adjusting the method for producing the inorganic coated sand and the casting sand. The details are the same as those described in the method for producing the inorganic coated sand described above. In addition, the details of the configuration and the like of the inorganic coated sand and the casting sand are also the same as those described above.

[0139] Although the embodiments of the present invention have been described above, these are examples of the present invention, and various configurations other than the above can be adopted.

[0140] Regarding the above-described embodiments, the present invention further discloses the following inorganic coated sand, inorganic coated sand manufacturing method, and casting mold manufacturing method.

[0141] <1> An inorganic coated sand in a dry state includes: a casting sand including one or two kinds of aggregates selected from a regenerated sand (A) and a refractory aggregate (B), and a first coating layer covering the aggregate and disposed on a surface thereof; and a second coating layer containing a metasilicate on the first coating layer of the casting sand, in which the refractory aggregate (B) contains SiO 2 , and a cation exchange capacity (CEC) of the casting sand is 3 mmol (+) / kg or more, preferably 6 mmol (+) / kg or more, 40 mmol (+) / kg or less, preferably 20 mmol (+) / kg or less, and more preferably 10 mmol (+) / kg or less. <2> The inorganic coated sand according to <1>, in which a content of the first coating layer is 0.02 parts by mass or more, preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, still more preferably 1 part by mass or more, and even still more preferably 2 parts by mass or more, and is 10 parts by mass or less, preferably 9.5 parts by mass or less, with respect to 100 parts by mass of the aggregate. <3> The inorganic coated sand according to <1> or <2>, in which a content of the second coating layer is 0.05 parts by mass or more, preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, still more preferably 1 part by mass or more, and even still more preferably 2 parts by mass or more, and is 10 parts by mass or less, preferably 8 parts by mass or less, and more preferably 6 parts by mass or less, with respect to 100 parts by mass of the aggregate. <4> The inorganic coated sand according to any one of <1> to <3>, in which the first coating layer of the casting sand contains an aluminosilicate, and the aluminosilicate contains a reactant of one or more selected from a silicate and a reactant of a silicate, and an aluminate or aluminum hydroxide. <5> The inorganic coated sand according to any one of <1> to <4>, in which the aluminosilicate includes at least one reactant of one or more selected from a silicate or a reactant of a silicate, and sodium aluminate or aluminum hydroxide. <6> The inorganic coated sand according to any one of <1> to <5>, in which a dynamic rest angle of the inorganic coated sand is preferably 80° or less, more preferably 45° or less, and still more preferably 30° or less. <7> The inorganic coated sand according to any one of <1> to <6>, in which a degree of noncrystallization of the refractory aggregate (B) is preferably 30% or more, more preferably 50% or more, still more preferably 65% or more, and even still more preferably 80% or more, and is preferably 100% or less and more preferably 99% or less. <8> The inorganic coated sand according to any one of <1> to <7>, in which a content of SiO 2 in the refractory aggregate (B) is preferably 10% or more, preferably 20% or more, and more preferably 30% or more, and is preferably 99% or less, more preferably 80% or less, still more preferably 70% or less, even still more preferably 50% or less, and even still more preferably 40% or less. <9> The inorganic coated sand according to any one of <1> to <8>, in which a content of aluminum in the first coating layer is preferably 0.1 parts by mass or more and more preferably 0.4 parts by mass or more, and is preferably 20 parts by mass or less and more preferably 10 parts by mass or less, with respect to 100 parts by mass of the aggregate, in terms of Al 2 O 3 . <10> The inorganic coated sand according to any one of <1> to <9>, in which a content of the metasilicate in the second coating layer is preferably 80% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, even still more preferably 98% by mass or more, and even still more preferably substantially 100% by mass. <11> The inorganic coated sand according to any one of <1> to <10>, in which a content of water including water of crystallization in the second coating layer is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and still more preferably 20 parts by mass or more, and is preferably 180 parts by mass or less, more preferably 160 parts by mass or less, even more preferably 150 parts by mass or less, and still more preferably 140 parts by mass or less, with respect to 100 parts by mass (in terms of anhydride) of a silicate. <12> A casting mold consisting of the inorganic coated sand according to any one of any one of <1> to <11>. <13> A method for producing an inorganic coated sand, the method including: a step (1) of mixing one or two kinds of aggregates selected from a regenerated sand (A) and a refractory aggregate (B), and an aluminate or aluminum hydroxide, and forming a first coating layer on a surface of the aggregate to obtain a casting sand; a step (2) of mixing the obtained casting sand with a molten solution of a metasilicate hydrate to obtain a mixture; and a step (3) of cooling the mixture to a temperature lower than a melting point of the metasilicate hydrate, in which the refractory aggregate (B) contains SiO 2 . <14> A method for producing an inorganic coated sand, the method including: a step (4) of mixing one or two kinds of aggregates selected from a regenerated sand (A) and a refractory aggregate (B), and an aluminate or aluminum hydroxide, forming a first coating layer on a surface of the aggregate to a obtain casting sand; a step (5) of mixing the obtained casting sand with a solution including water glass, caustic alkali, and water to obtain a mixture including a metasilicate hydrate, in which the refractory aggregate (B) contains SiO 2 . <15> The method for producing an inorganic coated sand according to <13> or <14>, in the step (1) or the step (4), the first coating layer is formed by heating at 25°C or higher and lower than 400°C, preferably 40°C or higher and 300°C or lower, and more preferably 70°C or higher and 200°C or lower. <16> The method for producing an inorganic coated sand according to <14>, in which in the step (5), a molar ratio of SiO 2 / M 2 O (M represents an alkali metal) / H 2 O in a solution containing water glass, caustic alkali, and water is 1:1:n (5 ≤ n ≤ 9). <17> A method for improving storage stability of an inorganic coated sand, in which the inorganic coated sand includes a casting sand containing one or two kinds of aggregates selected from a regenerated sand (A) and a refractory aggregate (B); and a second coating layer containing a metasilicate coating the casting sand, the refractory aggregate (B) contains SiO 2 , and the inorganic coated sand in a dry state is prepared such that a cation exchange capacity (CEC) of the casting sand is 3 mmol (+) / kg or more and 40 mmol (+) / kg or less. Examples

[0142] Hereinafter, the present invention will be described with reference to Examples and Comparative Examples, but the present invention is not limited thereto.(1) Materials

[0143] Materials used in the following Examples and Comparative Examples will be described.[Refractory Aggregate]

[0144] · Refractory aggregate 1: ESPEARL #60L (manufactured by Yamakawa Sangyo Co., Ltd., average particle diameter: 241 µm, degree of amorphization: 45%) · Refractory aggregate (B1): spherical fused silica (natural silica sand is spheroidized by flame fusion method, average particle diameter: 200 µm, degree of amorphization: 95% or more) · Refractory aggregate (B2): NIGAI CERABEADS 60#650 (manufactured by Itochu Ceratec Co., Ltd., average particle diameter: 200 µm, degree of amorphization: 30%) [Inorganic Fine Particles]

[0145] · Amorphous silica fine particles: Denka molten silica SFP-20M (manufactured by Denka Company Limited., average particle diameter: 0.4 µm, degree of amorphality: 99.5% or more) · Calcined kaolin: Satinon W (manufactured by BASF SE, average particle diameter: 0.4 µm) [Regenerated Sand (A)]

[0146] · Regenerated sand (A1) was produced according to the following procedure. (i) Production of inorganic coated sand

[0147] 100 parts by mass of a refractory aggregate 1 (ESPEARL #60L) as a refractory aggregate was put into a stirrer. Next, a sodium metasilicate nonahydrate (2.00 parts by mass) that had been heated and melted at 80°C was put into a stirrer and kneaded for 4 minutes to obtain dry sand having fluidity at normal temperature, and then fine amorphous silica particles (0.6 parts by mass) were further put thereinto and kneaded for 2 minutes to obtain an inorganic coated sand in a dry state used for the production of the regenerated sand (A1).(ii) Preparation of Mold

[0148] A part of 10 kg of the obtained inorganic coated sand was poured into the center of a conical mold having an upper diameter of 298 mm, a lower diameter of 205 mm, and a height of 265 mm for producing a test casting mold, up to a height of 50 mm. Subsequently, a metal core of a truncated cone having an upper diameter of 280 mm, a lower diameter of 200 mm, and a height of 220 mm, which had been heated to 180°C, was installed. The remaining inorganic coated sand was poured into a space between the mold and the metal core, and heated in a heating furnace at 180°C for 20 minutes to obtain a test casting mold.(iii) Casting

[0149] 10 kg of an aluminum alloy AC4C material (720°C) was poured into the obtained test casting mold. After the injection of the solution, the solution was allowed to stand at room temperature and cooled.(iv) Production of Recovered Sand

[0150] The casting was taken out from the test casting mold after casting, the test casting mold was crushed with a hammer or the like, and the test casting mold was further crushed with a mini crusher (manufactured by Taiyo Kogyo Co., Ltd.) until the test casting mold was a single particle, thereby obtaining recovered sand.(v) Production of Regenerated Sand

[0151] 100 kg of regenerated sand was put into a dry-type casting sand recycling device (Hybrid Sand Master manufactured by Nippon Casting Co., Ltd.) equipped with a fluidized layer, and batch treatment was performed at a rotor rotation speed of 2,400 rpm for 60 minutes to obtain regenerated sand (A1). Fine powder derived from the binder generated during the treatment was removed by a dust collector.[Material for First Coating Layer]

[0152] · 50% sodium aluminate: sodium aluminate #2019 (50% sodium aluminate aqueous solution manufactured by Asada Chemical Co., Ltd.) · Aluminum hydroxide (Al(OH) 3 ): aluminum hydroxide (manufactured by FUJIFILM Wako Pure Chemical Corporation, powder form, average particle diameter: 2.01 µm) · No. 2 water glass: No. 2 sodium silicate (manufactured by FUJI CHEMICAL INDUSTRY CO., LTD., Si / Na molar ratio: 2.4) [Material for Second Coating Layer]

[0153] · Sodium metasilicate nonahydrate: sodium metasilicate nonahydrate (manufactured by Nippon Chemical Industrial Co., Ltd.) (2) Production of Inorganic Coated Sand

[0154] Each inorganic coated sand of the formulation compositions shown in Table 1 was produced by the following procedure.<Example 1>

[0155] 100 parts by mass of regenerated sand (A1) as a refractory aggregate was put into a stirrer. Next, 2.3 parts by mass of a 50% sodium aluminate aqueous solution was added thereto, and the mixture was stirred for 2 minutes to obtain a mixture. Thereafter, the obtained mixture was heat-treated in a baking furnace at a baking temperature of 80°C for 12 hours, cooled to room temperature, and then aggregates in the mixture were removed through a sieve (20 mesh) to obtain casting sand in which a first coating layer consisting of an aluminosilicate was formed on the surface of the regenerated sand (A1).

[0156] Next, the casting sand and a sodium metasilicate nonahydrate (3.50 parts by mass) heated and melted at 80°C were put into a stirrer and kneaded for 4 minutes to form a second coating layer on the first coating layer, thereby obtaining inorganic coated sand of Example 1. Table 1 shows a blending composition of the inorganic coated sand.<Examples 2 and 3>

[0157] In the same manner as in Example 1, except that the adding amount of the 50% sodium aluminate aqueous solution in a case of forming the first coating layer consisting of an aluminosilicate on the surface of the regenerated sand (A1) was changed to the parts by mass shown in Table 1, inorganic coated sands of Examples 2 and 3 described in Table 1 were obtained.<Example 4>

[0158] In a case where the first coating layer consisting of an aluminosilicate was formed on the surface of the regenerated sand (A1), 0.1 parts by mass of No. 2 water glass was additionally added at the time of adding a 50% sodium aluminate aqueous solution, thereby obtaining the inorganic coated sand of Example 4 shown in Table 1 in the same manner as in Example 1.<Examples 5 to 8>

[0159] inorganic coated sand was obtained in the same manner as in Example 1, except that the baking temperature at which the first coating layer consisting of an aluminosilicate was formed on the surface of the regenerated sand (A1) was changed to the temperature shown in Table 1. Table 1 shows the formulation compositions of the inorganic coated sands of Examples 5 to 8.<Example 9>

[0160] inorganic coated sand was obtained in the same manner as in Example 1, except that a suspension in which aluminum hydroxide was suspended in water in advance (aluminum hydroxide:water = 1:1 by mass ratio) was used instead of the 50% sodium aluminate aqueous solution. Table 1 shows the formulation composition of the inorganic coated sand of Example 9.<Examples 10 and 12>

[0161] Inorganic coated sand was obtained in the same manner as in Example 2, except that the regenerated sand (A1) as the refractory aggregate was changed to the refractory aggregate shown in Table 2. Table 2 shows the formulation compositions of the inorganic coated sands of Examples 10 and 12.<Example 11>

[0162] Inorganic coated sand was obtained in the same manner as in Example 3, except that the regenerated sand (A1) as the refractory aggregate was changed to the refractory aggregate shown in Table 2. Table 2 shows the formulation composition of the inorganic coated sand of Example 11.<Example 13>

[0163] Using the inorganic coated sand obtained in Example 2, regenerated sand (A2) was obtained in the same manner as in the procedure (ii) to (v) of the regenerated sand (A1) described above. The inorganic coated sand was produced in the same manner as in Example 2 using the regenerated sand (A2), and the procedure (ii) to (v) of the regenerated sand (A1) was repeated again to obtain regenerated sand (A3). Further, the step of obtaining regenerated sand (A3) from the regenerated sand (A2) was repeated twice using the regenerated sand (A3), and regenerated sand (A5) was obtained.

[0164] In the same manner as in Example 2, inorganic coated sand was obtained using regenerated sand (A5). The results of the storage stability are shown in Table 3.<Comparative Example 1>

[0165] In the same manner as in Example 1, except that the addition of 50% sodium aluminates and the heating treatment were not performed, an inorganic coated sand containing the inorganic binding agent of Comparative Example 1 and not containing the first coating layer consisting of an aluminosilicate was obtained. Table 1 shows the formulation composition of the inorganic coated sand of Comparative Example 1.<Comparative Examples 2 and 3>

[0166] inorganic coated sands of Comparative Examples 2 and 3 were obtained in the same manner as in Example 1, except that the heating treatment was performed at the temperature shown in Table 1 without adding 50% sodium aluminate. Table 1 shows the formulation compositions of the inorganic coated sands of Comparative Examples 2 and 3.<Comparative Example 4>

[0167] 100 parts by mass of regenerated sand (A1) was prepared as a refractory aggregate and put into a stirrer. Next, 0.25 parts by mass of calcined kaolin, 0.25 parts by mass of noncrystalline silica fine particles, and 0.50 parts by mass of water were put into the container and stirred for 2 minutes. Thereafter, the obtained mixture was heat-treated in an electric furnace at 730°C for 1 hour, the heating of the electric furnace was stopped, the mixture was left as it was in the electric furnace for 4 hours, the mixture was taken out from the electric furnace, and the mixture was cooled to room temperature at room temperature, and then an aggregate was removed from the mixture through a sieve (20 mesh). The obtained mixture and a sodium metasilicate nonahydrate (3.50 parts by mass) heated to 80°C and melted were put into a stirrer and kneaded for 4 minutes to obtain inorganic coated sand of Comparative Example 4. Table 1 shows a blending composition of the inorganic coated sand.<Comparative Examples 5 and 6>

[0168] Inorganic coated sands of Comparative Examples 5 and 6 were obtained in the same manner as in Comparative Example 1, except that the regenerated sand (A1) as the refractory aggregate was changed to the type of the refractory aggregate shown in Table 2. Table 2 shows the formulation compositions of the inorganic coated sands of Comparative Examples 5 and 6.(3) Evaluation and Measurement

[0169] The following evaluations and measurements were performed using the obtained inorganic coated sand. The results are shown in Tables 1 and 2.<Storage Stability; Measurement of Time until Wetting>

[0170] Immediately after the production of the inorganic coated sand, the dynamic rest angle of the inorganic coated sand was measured by the following procedure.

[0171] Separately, immediately after the production of the inorganic coated sand, 2 kg of the inorganic coated sand was put into a polybag, sealed, and left in a constant temperature / humidity chamber of 25°C / 55% RH, and the dynamic rest angle of the inorganic coated sand was measured according to the following procedure every 24 hr, and the following confirmation was performed regarding the state (dry state or wet state) of the inorganic coated sand. In a case where the inorganic coated sand was wet, the time taken from the placement in the plastic bag to the wetting was defined as "time taken to wet" (days).(i) Procedure (Measurement of Dynamic Repose Angle)

[0172] A cylindrical transparent plastic bottle having a diameter of 76 mm and a height of 125 mm was filled with the inorganic coated sand in an amount half the volume of the bottle, held such that an axis was kept horizontal, and rotated at room temperature (25°C) and a speed of 60 rpm around the horizontal axis. The inclined surface of the inorganic coated sand layer flowing in the cylinder was formed in a flat surface state, and an angle (dynamic repose angle) formed between the inclined surface and the horizontal surface was measured.(ii) Confirmation (Determination of Dry State or Wet State)

[0173] In the above procedure, a case where the angle could be measured was defined as "dry state", and a case where the inorganic coated sand did not flow in the cylinder or the inclined surface of the inorganic coated sand layer was not formed as a flat surface even in a case where the inorganic coated sand flowed, and as a result, the dynamic repose angle could not be measured was defined as "wet state".[Table 1]

[0174] Table 1Inorganic coated sandCasting sandRefractory aggregateFirst coating layerEnvironmen tal loadProperti esTypesPart s by massCompoun d 1Part s by massCompound 2Part s by massBaking temperatur e [°C]Cation exchange capacity [mmol (+) ·kg -1< ]Example 1Regenerat ed sand (A1)10050% Alumina te Na2.3--809Example 2Regenerat ed sand (A1)10050% Alumina te Na4.6--808Example 3Regenerat ed sand (A1)10050% Alumina te Na9.1--807Example 4Regenerat ed sand (A1)10050% Alumina te Na4.6No. 2 water glass0.1808Example 5Regenerat ed sand (A1)10050% Alumina te Na4.6--403Example 6Regenerat ed sand (A1)10050% Alumina te Na4.6--1208Example 7Regenerat ed sand (A1)10050% Alumina te Na4.6--2008Example 8Regenerat ed sand (A1)10050% Alumina te Na4.6--3508Example 9Regenerat ed sand (A1)10050% Aluminu m hydroxi de4.6--808Comparati ve example 1Regenerat ed sand (A1)100None0---1Comparati ve example 2Regenerat ed sand (A1)100None0--801Comparati ve example 3Regenerat ed sand (A1)100None0--6001Comparati ve example 4Regenerat ed sand (A1)100Calcine d kaolin0.25Noncrystall ine silica fine particles0.257301 [Table 1(Continued)]

[0175] Table 1Inorganic coated sandSecond coating laverCompound 3Parts by massSodium metasilicate [Parts by mass]StateDynamic rest angle [°]Storage stabilityTime until wetting [Dav]Example 1Sodium metasilicate nonahydrate3.501.51Dry sand2286Example 2Sodium metasilicate nonahydrate3.501.51Dry sand20226Example 3Sodium metasilicate nonahydrate3.501.51Dry sand20226Example 4Sodium metasilicate nonahydrate3.501.51Dry sand20226Example 5Sodium metasilicate nonahydrate3.501.51Dry sand2030Example 6Sodium metasilicate nonahydrate3.501.51Dry sand25203Example 7Sodium metasilicate nonahydrate3.501.51Dry sand20183Example 8Sodium metasilicate nonahydrate3.501.51Dry sand20164Example 9Sodium metasilicate nonahydrate3.501.51Dry sand20158Comparative example 1Sodium metasilicate nonahydrate3.501.51Dry sand251Comparative example 2Sodium metasilicate nonahydrate3.501.51Dry sand251Comparative example 3Sodium metasilicate nonahydrate3.501.51Dry sand2030Comparative example 4Sodium metasilicate nonahydrate3.501.51Dry sand2530 [Table 2]

[0176] Table 2Inorganic coated sandCasting sandRefractory aggregateFirst coating layerEnvironment al loadProperti esTypesPart s by massDegree of amorphici ty [%]SiO 2 [%]Compound 1Part s by massBaking temperature [°C]Cation exchange capacity [mmol (+) ·kg -1< ]Example 10Refracto ry aggregat e (B1): spherica 1 fused silica100More than 959950% Aluminat e Na4.6808Example 11Refracto ry aggregat e (B1): spherica 1 fused silica100More than 959950% Aluminat e Na9.1807Example 12Refracto ry aggregat e (B2): NIGAI CEPABEAD S 60#650100303650% Aluminat e Na4.6808Comparati ve example 5Refracto ry aggregat e (B1): spherica 1 fused silica100> 9599None0-Less than 1Comparati ve example 6Refracto ry aggregat e (B2): NIGAI CEPABEAD S 60#6501003036None0-Less than 1 [Table 2(Continued)]

[0177] Table 2Inorganic coated sandSecond coating layerCompound 3Parts by massSodium metasilicate [Parts by mass]StateDynamic rest angle [°]Storage stabilityTime until wetting [Dav]Example 10Sodium metasilicate nonahydrate3.501.51Dry sand228Example 11Sodium metasilicate nonahydrate3.501.51Dry sand2220Example 12Sodium metasilicate nonahydrate3.501.51Dry sand20121Comparative example 5Sodium metasilicate nonahydrate3.501.51Dry sand201Comparative example 6Sodium metasilicate nonahydrate3.501.51Dry sand2014 [Table 3]

[0178] Table 3Inorganic coated sandCasting sandRefractory aggregateStorage stabilityTypesNumber of times of regeneration [Number]Time until wetting [Day]Example 2Regenerated sand (Al)1226Comparative example 13Regenerated sand (A5)5181

Examples

examples

[0142]Hereinafter, the present invention will be described with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

(1) Materials

[0143]Materials used in the following Examples and Comparative Examples will be described.

[Refractory Aggregate]

[0144] · Refractory aggregate 1: ESPEARL #60L (manufactured by Yamakawa Sangyo Co., Ltd., average particle diameter: 241 µm, degree of amorphization: 45%) · Refractory aggregate (B1): spherical fused silica (natural silica sand is spheroidized by flame fusion method, average particle diameter: 200 µm, degree of amorphization: 95% or more) · Refractory aggregate (B2): NIGAI CERABEADS 60#650 (manufactured by Itochu Ceratec Co., Ltd., average particle diameter: 200 µm, degree of amorphization: 30%)

[Inorganic Fine Particles]

[0145] · Amorphous silica fine particles: Denka molten silica SFP-20M (manufactured by Denka Company Limited., average particle diameter: 0.4 µm, degree of amorphality: 99.5% or more) ...

Claims

1. An inorganic coated sand in a dry state comprising: a casting sand in which a first coating layer is disposed over a surface of one or two kinds of aggregates selected from a regenerated sand (A) and a refractory aggregate (B); and a second coating layer containing a metasilicate over the first coating layer of the casting sand, wherein the refractory aggregate (B) contains SiO2, and a cation exchange capacity (CEC) of the casting sand is 3 mmol (+) / kg or more and 40 mmol (+) / kg or less.

2. The inorganic coated sand according to Claim 1, wherein a content of the first coating layer is 0.02 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the aggregate.

3. The inorganic coated sand according to Claim 1 or 2, wherein a content of the second coating layer is 0.05 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the aggregate.

4. The inorganic coated sand according to any one of Claims 1 to 3, wherein the first coating layer contains an aluminosilicate, and the aluminosilicate contains a reactant of one or more selected from a silicate and a reactant of a silicate, and an aluminate or aluminum hydroxide.

5. The inorganic coated sand according to Claim 4, wherein the aluminosilicate includes at least one reactant of one or more selected from a silicate or a reactant of a silicate, and sodium aluminate or aluminum hydroxide.

6. A casting mold consisting of the inorganic coated sand according to any one of Claims 1 to 5.

7. A method for producing an inorganic coated sand, the method comprising: a step (1) of mixing one or two kinds of aggregates selected from a regenerated sand (A) and a refractory aggregate (B), and an aluminate or aluminum hydroxide, and forming a first coating layer over a surface of the aggregate to obtain a casting sand; a step (2) of mixing the obtained casting sand with a molten solution of a metasilicate hydrate to obtain a mixture; and a step (3) of cooling the mixture to a temperature lower than a melting point of the metasilicate hydrate, wherein the refractory aggregate (B) contains SiO2.

8. A method for producing an inorganic coated sand, the method comprising: a step (4) of mixing one or two kinds of aggregates selected from a regenerated sand (A) and a refractory aggregate (B), and an aluminate or aluminum hydroxide, forming a first coating layer over a surface of the aggregate to a obtain casting sand; a step (5) of mixing the obtained casting sand with a solution including water glass, caustic alkali, and water to obtain a mixture including a metasilicate hydrate, wherein the refractory aggregate (B) contains SiO2.

9. The method for producing an inorganic coated sand according to Claim 7 or 8, wherein in the step (1) or the step (4), the first coating layer is formed by heating at 25°C or higher and lower than 400°C.

10. A method for improving storage stability of an inorganic coated sand, wherein the inorganic coated sand includes a casting sand containing one or two kinds of aggregates selected from a regenerated sand (A) and a refractory aggregate (B); and a second coating layer containing a metasilicate coating the casting sand, the refractory aggregate (B) contains SiO2, and the inorganic coated sand in a dry state is prepared such that a cation exchange capacity (CEC) of the casting sand is 3 mmol (+) / kg or more and 40 mmol (+) / kg or less.

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