Casting sand for casting mould and method for producing same, casting mould, and method for improving storage stability of casting sand for casting mould

Abstract

A casting sand for a mold includes 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 silicate on the first coating layer of the casting sand, in which 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 a casting sand for a mold, a method for producing the casting sand for a mold, a casting mold, and a method for improving storage stability of the casting sand for a mold.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.RELATED DOCUMENTPATENT DOCUMENT

[0005] Patent Document 1: PCT Japanese Translation Patent Publication No 2010-519042 Patent Document 2: PCT Japanese Translation Patent Publication No. 2021-536367 SUMMARY OF THE INVENTIONTECHNICAL PROBLEM

[0006] However, in a case where a casting sand for a mold is produced by applying an inorganic binding agent to the regenerated sand as disclosed in Patent Document 1 and 2, and a mold is cast, casting may not be performed appropriately due to insufficient liquid crosslinking by heating. That is, there was room for improvement in terms of extending the usable time of the casting sand for a mold.

[0007] In addition, since the regenerated sand obtained by the method for the related art is subjected to a high-temperature treatment at 600°C to 800°C in the regeneration treatment, it is insufficient from the viewpoint of suppressing energy consumption and CO 2 emission.

[0008] That is, the present invention relates to extending the usable time of the casting sand for a mold using regenerated sand or the like and reducing the environmental load during the formation of the casting sand for a mold.SOLUTION TO PROBLEM

[0009] The present inventors have found that it is effective to use a casting sand in which a coating layer is applied to a regenerated sand or a refractory aggregate containing SiO 2 in a casting sand for a mold using casting sand to control a cation exchange capacity (CEC) to a specific value, and have completed the present invention.

[0010] According to the present invention, there is provided a casting sand for a mold, the sand comprising: 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 silicate 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.

[0011] In addition, according to the present invention, there is provided a casting mold consisting of the above-described casting sand for a mold.

[0012] In addition, according to the present invention, there is provided a method for producing a casting sand for a mold, the method comprising: a step of forming a first coating layer on a surface of one or two kinds of aggregates selected from a regenerated sand (A) and a refractory aggregate (B) to obtain a casting sand having a cation exchange capacity (CEC) of 3 mmol (+) / kg or more and 40 mmol (+) / kg or less; and a step of mixing the casting sand with a silicate and forming a second coating layer including the silicate on the first coating layer of the casting sand, in which the refractory aggregate (B) contains SiO 2 .

[0013] In addition, according to the present invention, there is provided a method for improving storage stability of a casting sand for a mold, the method comprising: a step of forming a first coating layer on a surface of one or two kinds of aggregates selected from a regenerated sand (A) and a refractory aggregate (B) containing SiO 2 to obtain a casting sand having a cation exchange capacity (CEC) of 3 mmol (+) / kg or more and 40 mmol (+) / kg or less; and a step of mixing the casting sand with a silicate and forming a second coating layer including the silicate on the first coating layer of the casting sand, in which the refractory aggregate (B) contains SiO 2 . ADVANTAGEOUS EFFECTS OF INVENTION

[0014] According to the present invention, it is possible to provide a casting sand for a mold, which can improve storage stability while reducing an environmental load during the production of the casting sand for a mold.DESCRIPTION OF EMBODIMENTS

[0015] 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.

[0016] In addition, the "coating" and the "coating layer" are not limited to being continuous, and may have a discontinuous portion in a part thereof.<Casting Sand for Mold>

[0017] The casting sand for a mold according to the present embodiment has 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 silicate is disposed 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.

[0018] That is, in a case of producing the casting sand for a mold using an inorganic binding agent containing a silicate and an aggregate, the casting sand for a mold of the present embodiment is obtained by covering the aggregate with the first coating film to obtain the casting sand having a predetermined cation exchange capacity (CEC), and thus the storage stability of the casting sand for a mold in which the second coating layer containing a silicate is formed using the casting sand for a mold can be improved.

[0019] 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 the regenerated sand (A) having a residue of the inorganic binder is kneaded with the inorganic binder to produce the casting sand for a mold, a reaction between the silicate in the residue or a reactant of the silicate and the silicate in the inorganic binder proceeds, and the usable time of the casting sand for a mold is shortened. (ii) On the other hand, in a case where the refractory aggregate (B) containing SiO 2 is kneaded with the inorganic binding agent to produce the casting sand for a mold, the reaction between the SiO 2 component of the refractory aggregate (B) and the silicate in the inorganic binding agent can proceed as in the case of (i), and thus the usable time can be shortened. (iii) Therefore, by forming the first coating layer to cover the surface of the aggregate and using the casting sand having a specific CEC, it is possible to suppress the reaction with the residue. As a result, it is considered that even in a case where the casting sand is used and the inorganic binding agent is applied to produce the casting sand for a mold, a favorable usable time can be maintained and the storage stability can be improved.

[0020] In addition, in a case where the first coating layer covering the surface of the aggregate 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.[Casting Sand]

[0021] The casting sand is obtained by disposing a first coating layer on a surface of a predetermined aggregate, and has a cation exchange capacity (CEC) of 3 mmol (+) / kg or more and 40 mmol (+) / kg or less. By covering the casting sand with the inorganic binding agent layer which is the second coating layer, the casting sand for a mold is obtained.[Cation Exchange Capacity]

[0022] The cation exchange capacity (CEC) of the casting sand needs to be controlled to a specific value from the viewpoint of obtaining good storage stability.

[0023] From the viewpoint of improving storage stability, the cation exchange capacity (CEC) is 3 mmol (+) / kg or more, preferably 5 mmol (+) / kg or more, and more preferably 6 mmol (+) / kg or more.

[0024] On the other hand, from the viewpoint of maintaining good storage stability, the cation exchange capacity (CEC) is 40 mmol (+) / kg or less, preferably 20 mmol (+) / kg or less, more preferably 10 mmol (+) / kg or less, and still more preferably 8 mmol (+) / kg or less.

[0025] In addition, the control of the cation exchange capacity (CEC) can be performed by combining known methods, and examples thereof include a method for selecting a material of the first coating layer, adjusting the content, and adjusting the baking temperature and time.

[0026] 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.

[0027] 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.

[0028] Hereinafter, the casting sand of the present embodiment will be described in more detail.

[0029] The casting sand of the present embodiment is a particle group. From the viewpoint of improving fluidity and further improving the filling property into the molding die, the casting sand is preferably spherical. Here, the casting sand having a spherical shape refers to a casting sand having a round shape like a ball. 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 casting 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 casting sand specifically coincides with the sphericity of the refractory aggregate described later.

[0031] The sphericity of the casting sand can be obtained as follows: a particle image (photograph) obtained by an optical microscope or a digital scope (for example, model VH-8000 manufactured by KEYENCE CORPORATION) is analyzed to obtain an area of a projected cross-section of the particle and a circumferential length of the cross-section, [circumferential length (mm) of true circle having area same as that (mm 2< ) of projected cross-section of particle] / [circumferential length (mm) of projected cross-section of particle] is calculated, and values obtained for each of optional 50 particles are averaged.(Mean Particle Diameter)

[0032] From the viewpoint of improving mold quality and mold strength, and from the viewpoint of ease of modeling and storage stability of the mold, the average particle diameter of the casting sand is preferably 0.05 mm or more and more preferably 0.1 mm or more. In addition, in a case where the average particle diameter of the casting sand is equal to or larger than the above-described lower limit value, the amount of the inorganic binding agent or the like used in the production of the mold can be reduced, and thus it is also preferable from the viewpoint that the regeneration into the regenerated sand is further facilitated.

[0033] From the viewpoint of improving mold quality and mold strength and the viewpoint of ease of molding of the mold, the average particle diameter of the casting sand is preferably 2 mm or less, more preferably 1 mm or less, and still more preferably 0.5 mm or less. In addition, in a case where the average particle diameter of the casting sand is equal to or smaller than the above-described upper limit value, it is preferable from the viewpoint of reducing the void ratio and increasing the mold strength in a case of manufacturing a mold.

[0034] The average particle diameter of the casting sand can be measured by the following method.

[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.[Regenerated Sand (A)]

[0037] The regenerated sand (A) is a refractory material that is reused from a used casting mold or core, which is 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.

[0038] The regenerated sand (A) is obtained, for example, by a production method described later.(Refractory Aggregate)

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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).

[0044] From the viewpoint of improving the fluidity of the casting sand for a mold and further improving the filling property into a forming mold, the shape of the refractory aggregate is the same as that of the casting sand described above.(Mean Particle Diameter)

[0045] 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. In addition, it is preferable that the average particle diameter of the refractory aggregate is equal to or greater than the above-described lower limit value, because then the amount of the inorganic binding agent used in the case of manufacturing a mold can be reduced, and thus it is easier to regenerate the casting sand for a mold.

[0046] 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.

[0047] A method for measuring the average particle diameter of the refractory aggregate is the same as the method for measuring the average particle diameter of the casting sand.(Degree of Crystallization)

[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.(X-Ray Diffraction Method)

[0050] The degree of amorphousness of the refractory aggregate can be measured by the following 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 a casting sand for a mold containing a refractory aggregate having an inorganic binding agent formed on its surface is formed into a casting mold for casting, used as the casting mold, and then regenerated 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] Specific examples of the silicate and the silicate reactant include a silicate, and a reactant of a silicate and an amorphous silica, and a reactant of a silicate and an amorphous silica, and the like, and one kind or two or more kinds thereof 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] 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 (B) is preferably 20% or more and more preferably 30% or more, and from the viewpoint of improving storage stability, the degree of crystallization of the refractory aggregate (B) is preferably 99% or less, more preferably 80% or less, even more preferably 70% or less, and still more preferably 60% or less.

[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).

[0062] In addition, the average particle diameter of the refractory aggregate (B) can be measured by the same image analysis as that for the refractory aggregate of the regenerated sand (A).[First Coating Layer]

[0063] 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), and is a layer which is an outermost layer of the casting sand. In addition, the refractory aggregate (B) contains SiO 2 .

[0064] The first coating layer suppresses the inorganic binding agent from acting on the aggregate (casting sand), and thus the usable time of the casting sand for a mold can be maintained. In particular, by forming the first coating layer as a layer formed of an aluminosilicate, the first coating layer can be formed at a relatively low temperature, and thus the environmental load due to the heat treatment can be further reduced.

[0065] In the present embodiment, the aluminosilicate specifically indicates either or both of the residual inorganic binder present on the surface of the refractory aggregate (B) or the refractory aggregate (B).

[0066] Examples of the aluminosilicate include one or more selected from silicates and reactants of silicates, and reaction products with an aluminate or aluminum hydroxide.

[0067] From the viewpoint of easily improving the storage stability, it is preferable that the above-described aluminosilicate includes at least one of a reaction product of one or more selected from silicates and reactants of silicates, and sodium aluminate or aluminum hydroxide.

[0068] The form of sodium aluminate is not particularly limited, and may be any of a powder or an aqueous solution.

[0069] The silicate refers to a substance having a silicate in the composition, that is, a substance containing 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 in the composition. Examples of the silicate include aluminosilicate and metasilicate.

[0070] 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 .

[0071] 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.

[0072] The content of aluminum in the first coating layer is obtained by the following method.

[0073] 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.

[0074] 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.

[0075] 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.[Method for Producing casting sand]

[0076] Next, a method for producing the casting sand of the present embodiment will be described.

[0077] The method for producing a casting sand of the present embodiment is a method for producing a casting sand having one or two kinds of aggregates selected from regenerated sand (A) and a refractory aggregate (B), and a first coating layer covering a surface of the aggregate, in which the casting sand has a cation exchange capacity (CEC) of 3 mmol (+) / kg or more and 40 mmol (+) / kg or less. In addition, the refractory aggregate (B) contains SiO 2 .

[0078] The casting sand is then covered with the second coating layer to be used as casting sand for a mold having an inorganic binding agent layer.

[0079] According to the production method for the present embodiment, since the cation exchange capacity (CEC) of the casting sand obtained by forming the first coating layer on the surface of the aggregate material is controlled, it is possible to omit the baking step of the aggregate material at a high temperature while improving the storage stability, and thus it is possible to reduce the consumption of thermal energy and to reduce the environmental load.

[0080] First, as an example of the method for producing the casting sand according to the present embodiment, a production method including the following step (1) is exemplified. · 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 a first coating layer on a surface of the aggregate, thereby obtaining casting sand

[0081] However, the refractory aggregate (B) contains SiO 2 .

[0082] In the step (1), the aluminate or aluminum hydroxide is mixed with the aggregate 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.

[0083] 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.

[0084] Among these, the latter method is preferable from the viewpoint of forming a uniform first coating layer.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] As described above, the casting sand according to the present embodiment can be obtained.

[0089] Next, the casting sand for a mold using the casting sand of the present embodiment will be described.<Casting Sand for Mold and Producing Method thereof>

[0090] The casting sand for a mold includes the above-described casting sand and a second coating layer containing a silicate on the first coating layer of the casting sand. That is, the second coating layer is formed by kneading the casting sand and the silicate as the inorganic binding agent to adhere the inorganic binding agent to the surface of the casting sand. In the casting sand for a mold, liquid crosslinking proceeds by heating in a case of casting a mold thereafter, and a mold having a desired shape and mechanical strength can be cast.

[0091] The kneading conditions are not particularly limited, but for example, the temperature is preferably 5°C or higher and more preferably 10°C or higher from the viewpoint of uniform kneading. On the other hand, from the viewpoint of the use time, the temperature is preferably 40°C or lower and more preferably 35°C or lower. In addition, the kneading time is preferably 0.5 minutes or more and more preferably 1 minute or more from the viewpoint of uniform kneading. On the other hand, the time is preferably 10 minutes or less and more preferably 5 minutes or less from the viewpoint of the use time. In addition, the rotation speed of the kneading is preferably 100 rpm or more and more preferably 200 rpm or more from the viewpoint of uniform kneading. On the other hand, from the viewpoint of suppressing material breakage of the casting sand for a mold, the stirring speed is preferably 700 rpm or less and more preferably 500 rpm or less.

[0092] The casting sand for a mold according to the present embodiment is in a wet state having no fluidity at normal temperature. In addition, the wet state is a state in which the inorganic binding agent exhibits pressure-sensitive adhesiveness, and for example, in a case of casting a mold, a solidification and hardening reaction proceeds by heating and drying, and a desired mold can be obtained.

[0093] Specifically, those that cannot measure the following dynamic wetting angle are "wet states".

[0094] (Measurement Method for Dynamic Repose Angle) casting sand for a mold is put into a cylindrical transparent plastic bottle in an amount of half of the volume of the bottle, the bottle is held such that the axis is horizontal, and the bottle is rotated around the horizontal axis at 60 rpm. In a case where the casting sand for a mold does not flow in the cylinder or the inclined surface of the layer of the casting sand for a mold is not formed as a flat surface even in a case where the casting sand for a mold flows, and as a result, the dynamic repose angle cannot be measured, the state is a wet state.[Second Coating Layer]

[0095] The second coating layer coats the surface of the casting sand, and is obtained by using a silicate as an inorganic binding agent.(Inorganic Binder)

[0096] The inorganic binding agent has a function of firmly binding the mold sand to each other so that a desired mold is obtained in a case of casting the mold. The state in which the inorganic binding agent is added in a case of being mixed with the above-described casting sand is a liquid.

[0097] The inorganic binding agent contains a silicate, preferably contains sodium silicate, more preferably contains sodium silicate having a SiO 2 / Na 2 O molar ratio of 1.0 or more and 4.0 or less, and still more preferably contains sodium silicate having a SiO 2 / Na 2 O molar ratio of more than 1.1 and 4.0 or less. The inorganic binding agent may further include a silicate other than the above-described silicates as a main component. Specific examples of the silicate other than sodium silicate include potassium silicate, lithium silicate, and ammonium silicate.

[0098] In a case of a monovalent cation, the silicate of the present embodiment refers to a compound represented by General Formula: xM 2 O·ySiO 2 (where x and y are any positive numerical values).

[0099] In addition, the inorganic binding agent may be a solution containing water glass, caustic alkali, and water. The mixing conditions of water glass, caustic alkali, and water are not particularly limited, and a known method can be used.

[0100] The content of the inorganic binding agent 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.

[0101] On the other hand, from the viewpoint of achieving both storage stability and strength, the content of the inorganic binding agent 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.(Others)

[0102] The casting sand for a mold may contain, in addition to the inorganic binding agent, additives such as inorganic fine particles, a coupling agent, a moisturizing agent, a moisture improvement agent, a lubricant, a surfactant, and a mold release agent in the second coating layer.

[0103] 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 fine particles are preferable, and from the viewpoint of having a large specific surface area and high reactivity with silicates, amorphous silica fine particles are more preferable. The inorganic fine particles may be used alone or in combination of two or more kinds thereof.

[0104] The content of the amorphous silica fine particles is preferably 0.03 parts by mass or more, more preferably 0.1 parts by mass or more, and still more preferably 0.5 parts by mass or more with respect to 100 parts by mass of the aggregate.

[0105] On the other hand, from the viewpoint of achieving both storage stability and strength, the content of the amorphous silica fine particles is preferably 4 parts by mass or less, more preferably 3 parts by mass or less, still more preferably 2 parts by mass or less, and even still more preferably 1 part by mass or less with respect to 100 parts by mass of the aggregate.

[0106] The coupling agent is not limited, and examples thereof include a silane coupling agent, a zircon coupling agent, and a titanium coupling agent.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] 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.<Method for Improving Storage Stability of casting sand for Mold>

[0111] The method for improving the storage stability of the casting sand for a mold according to the present embodiment includes a step of mixing the casting sand for a mold with an inorganic binding agent to prepare the casting sand for a mold. That is, by using the specific casting sand, the usable time of the casting sand for a mold can be extended, and the storage stability can be improved.

[0112] Specifically, the inorganic binding agent is attached to the surface of the casting sand by kneading the casting sand in which the first coating layer is disposed on the surface of one or two kinds of the aggregates selected from the regenerated sand (A) and the refractory aggregate (B) and having a cation exchange capacity (CEC) of 3 mmol (+) / kg or more and 40 mmol (+) / kg or less, and the inorganic binding agent (silicate). In addition, the refractory aggregate (B) contains SiO 2 . The kneading method can be the same as the method for producing the casting sand for a mold described above.

[0113] The configuration, the method for producing, and the like of the casting sand and the casting sand for a mold in the method for preserving the casting sand for a mold are the same as those described above.<Method for Producing Regenerated Sand (A) / method for Regenerating Used casting sand>

[0114] As a method for reproducing the waste mold sand 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.

[0115] 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.

[0116] 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.

[0117] 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.

[0118] 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.<Casting Mold>

[0119] The casting mold for casting of the present embodiment is formed of the above-described casting sand for a mold in the present embodiment. 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.

[0120] 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.

[0121] Hereinafter, the present invention further discloses the following casting sand for a mold, a method for producing casting sand for a mold, and a method for producing a casting mold. <1> A casting sand for a mold, the sand 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 silicate 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, preferably 5 mmol (+) / kg or more, more preferably 6 mmol (+) / kg or more, preferably 20 mmol (+) / kg or less, more preferably 10 mmol (+) / kg or less, and still more preferably 8 mmol (+) / kg or less. <2> The casting sand for a mold according to <1>, in which 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 casting sand for a mold according to <1> or <2>, in which the first coating layer contains an aluminosilicate, and the aluminosilicate is a mixture of one or more selected from a silicate and a reactant of the silicate, an aluminate, and one or more selected from zeolite. <4> The casting sand for a mold according to <3>, in which the aluminate is at least one of sodium aluminate and aluminum hydroxide. <5> A casting mold consisting of the casting sand for a mold according to any one of <1> to <4>. <6> A method for producing a casting sand for a mold, the method including: a step of forming a first coating layer on a surface of one or two kinds of aggregates selected from a regenerated sand (A) and a refractory aggregate (B) containing SiO 2 to obtain a casting sand having a cation exchange capacity (CEC) of 3 mmol (+) / kg or more and 40 mmol (+) / kg or less; and a step of mixing the casting sand with a silicate and forming a second coating layer including the silicate on the first coating layer of the casting sand, in which the refractory aggregate (B) contains SiO 2 . <7> The method for producing a casting sand for a mold according to <6>, in which in the step of obtaining the casting sand, the aggregate and an aluminate or aluminum hydroxide are mixed to form the first coating layer on the surface of the aggregate. <8> The method for producing a casting sand for a mold according to <6> or <7>, in which in the step of obtaining the casting sand, the first coating layer is formed on the surface of the aggregate by heating the casting sand to 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. <9> A method for improving storage stability of a casting sand for a mold, the method including: a step of forming a first coating layer on a surface of one or two kinds of aggregates selected from a regenerated sand (A) and a refractory aggregate (B) containing SiO 2 to obtain a casting sand having a cation exchange capacity (CEC) of 3 mmol (+) / kg or more and 40 mmol (+) / kg or less, preferably 5 mmol (+) / kg or more, more preferably 6 mmol (+) / kg or more, preferably 20 mmol (+) / kg or less, more preferably 10 mmol (+) / kg or less, and still more preferably 8 mmol (+) / kg or less; and a step of mixing the casting sand with a silicate and forming a second coating layer including the silicate on the first coating layer of the casting sand, in which the refractory aggregate (B) contains SiO 2 . <10> The casting sand for a mold according to any one of <1> to <4>, in which the casting sand for a mold is a particle group. <11> The casting sand for a mold according to any one of <1> to <4> and <10>, in which an average particle diameter of the refractory aggregate is preferably 0.05 mm or more, more preferably 0.1 mm or more, preferably 2 mm or less, more preferably 1 mm or less, and still more preferably 0.5 mm or less. <12> The casting sand for a mold according to any one of <1> to <4>, <10>, and <11>, in which a degree of amorphization of the refractory aggregate (B) is preferably 20% or more, more preferably 30% or more, preferably 99% or less, more preferably 80% or less, still more preferably 70% or less, and even more preferably 60% or less. <12> The casting sand for a mold according to any one of <1> to <4>, <10>, and <11>, in which a 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, even still more preferably 2 parts by mass or more, 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. <13> The casting sand for a mold according to any one of <1> to <4>, and <10> to <12>, in which the second coating layer contains a silicate, preferably contains sodium silicate, and more preferably contains a silicate having a SiO 2 / Na 2 O molar ratio of 1.0 or more and 4.0 or less. <14> The casting sand for a mold according to any one of <1> to <4> and <10> to <13>, in which in the second coating layer, a content of the inorganic binding agent including a silicate 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, and 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. <15> The casting sand for a mold according to any one of <1> to <4> and <10> to <14>, in which the second coating film layer further contains noncrystalline silica fine particles. <16> The casting sand for a mold according to any one of <1> to <4> and <10> to <15>, in which the casting sand for a mold is in a wet state that does not have fluidity at normal temperature. Examples

[0122] Hereinafter, the present invention will be described with reference to Examples and Comparative Examples, but the present invention is not limited thereto.(1) Materials

[0123] Materials used in the following Examples and Comparative Examples will be described.[Refractory Aggregate]

[0124] · 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]

[0125] · 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)]

[0126] · Regenerated sand (A1) was produced according to the following procedure. (i) Production of Casting Sand for Mold containing Inorganic Binding Agent

[0127] 100 parts by mass of a refractory aggregate 1 (ESPEARL #60L) as a refractory aggregate was put into a stirrer. Next, as an inorganic binding agent, No. 2 water glass (0.90 parts by mass) and noncrystalline silica fine particles (0.60 parts by mass) were put into a stirrer and kneaded for 2 minutes to obtain a casting sand for a mold containing an inorganic binding agent in a wet state, which is used for producing regenerated sand (A1).(ii) Preparation of Mold

[0128] A part of 10 kg of the casting sand for a mold containing the obtained inorganic binding agent was poured into the center of a mold of a truncated cone 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 casting sand for a mold, which contained the remaining inorganic binding agent, 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 mold.(iii) Casting

[0129] 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

[0130] 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

[0131] 100 kg of recovered 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]

[0132] · 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) [Material for Second Coating Layer: Inorganic Binding Agent]

[0133] · No. 2 water glass: No. 2 sodium silicate (manufactured by FUJI CHEMICAL INDUSTRY CO., LTD., Si / Na molar ratio: 2.4) (2) Production of Casting Sand and Casting Sand for Mold

[0134] Each casting sand and casting sand for a mold shown in Table 1 was produced according to the following procedure.<Example 1>

[0135] 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).

[0136] Next, the regenerated sand (A1) having the first coating layer formed on the surface, and as the inorganic binding agent, No. 2 water glass (0.90 parts by mass) and amorphous silica fine particles (0.60 parts by mass) were put into a stirrer, and kneaded for 2 minutes to further coat the regenerated sand (A1) coated with the first coating layer with a second coating layer containing the inorganic binding agent shown in Table 1, thereby obtaining a casting sand for a mold.

[0137] Table 1 shows the formulation compositions of the casting sand and the obtained casting sand for a mold.<Examples 2 and 3>

[0138] Each cast sand and casting sand for a mold of Examples 2 and 3 shown in Table 1 was obtained 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. Table 1 shows the formulation compositions of the casting sand and the obtained casting sand for a mold.<Example 4>

[0139] Each casting sand and casting sand for a mold of Example 4 shown in Table 1 was obtained in the same manner as in Example 1, except that, at the time of adding a 50% sodium aluminate aqueous solution, 0.1 parts by mass of No. 2 water glass was additionally added to the surface of the regenerated sand (A1) in a case of forming the first coating layer consisting of an aluminosilicate. Table 1 shows the formulation compositions of the casting sand and the obtained casting sand for a mold.<Examples 5 to 8>

[0140] Each of the casting sands and the casting sand for a mold of Examples 5 to 8 shown in Table 1 was obtained in the same manner as in Example 1, except that the baking temperature for forming the first coating layer consisting of an aluminosilicate 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 casting sand and the obtained casting sand for a mold.<Example 9>

[0141] Each casting sand and the casting sand for a mold were 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 compositions of the casting sand and the obtained casting sand for a mold.<Examples 10 and 12>

[0142] Each casting sand and casting sand for a mold were 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 casting sands of Examples 10 and 12 and the casting sands for molds.<Example 11>

[0143] Each casting sand and each casting sand for a mold were 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 compositions of each casting sand and the casting sand for a mold of Example 11.<Example 13>

[0144] Using the casting sand for a mold obtained in Example 2, the regenerated sand (A2) was obtained in the same manner as in the procedure (ii) to (v) of the above-described regenerated sand (A1). The same procedure as in Example 2 was carried out to produce a casting sand for a mold using the regenerated sand (A2), and the procedure (ii) to (v) of the regenerated sand (A1) was repeated again to obtain a 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.

[0145] Each casting sand and casting sand for a mold were obtained in the same manner as in Example 2 using the regenerated sand (A5). The results of the storage stability are shown in Table 3.<Comparative Example 1>

[0146] The casting sand for a mold, which contained the inorganic binding agent of Comparative Example 1 and did not contain the first coating layer consisting of an aluminosilicate, was obtained in the same manner as in Example 1, except that the addition of 50% sodium aluminate and the heating treatment were not performed. Table 1 shows the formulation compositions of each casting sand and the casting sand for a mold of Comparative Example 1.<Comparative Examples 2 and 3>

[0147] The casting sands for molds 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 casting sands of Comparative Examples 2 and 3 and the casting sands for molds.<Comparative Example 4>

[0148] 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 subsequently taken out from the electric furnace, cooled to room temperature at room temperature, and then the aggregates were removed from the mixture through a sieve (20 mesh) to obtain regenerated sand (A1) (casting sand) in which a coating layer was formed.

[0149] Next, the obtained casting sand, No. 2 water glass (0.90 parts by mass), and noncrystalline silica fine particles (0.60 parts by mass) were put into a stirrer and kneaded for 2 minutes to obtain casting sand for a mold of Comparative Example 4. Table 1 shows the formulation compositions of each casting sand and casting sand for a mold.<Comparative Example 5>

[0150] The casting sand for a mold of Comparative Example 5 was 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 refractory aggregate shown in Table 2. Table 2 shows the formulation compositions of the casting sand and the casting sand for a mold of Comparative Example 5.(3) Evaluation and Measurement

[0151] The following evaluations and measurements were performed on each of the obtained casting sands and the obtained casting sand for a mold.<Storage stability; Measurement of Time to Reach Certain State>

[0152] A mold test piece is produced using the casting sand for a mold immediately after kneading obtained as described above, and the strength in a case where the mold strength is measured after 24 hours is defined as S1. On the other hand, the strength in a case where the casting sand for a mold is stored in an environment of 25°C and 55% RH, a mold test piece is produced under the same conditions, and the strength is measured after 24 hours is defined as S2. In a case where S1 was 100%, the time taken until S2 was 80% was defined as the usable time.

[0153] The mold test piece was created and the mold strength of the mold test piece was measured as follows.(Production of Mold Test Piece)

[0154] A mold for a 22.3 × 22.3 × 180 mm test piece (5 pieces) was heated to 180°C. For the casting sand for a mold of each example, the mold was filled with the casting sand for a mold using a CSR-43 blow molding machine at a blow pressure of 0.45 MPa. Thereafter, the casting sand for a mold was allowed to stand in the mold for 150 seconds to be cured, thereby obtaining a casting mold test piece.(Measurement of Mold Strength)

[0155] Using a universal strength tester PFG type manufactured by Georg Fischer Ltd. to which the PBV anti-reflection attachment was attached in advance, the casting mold bending strength (MPa) of each casting mold test piece obtained above was measured.[Table 1]

[0156] Table 1Casting sand for mold containing inorganic binderCasting 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)] Table 1Casting sand for mold containing inorganic binderInorganic binder (second coating layer)Compound 3Parts by massCompound 4PartsStateStorageby massUsable time * 1Example 1No. 2 water0.90Noncrystalline0.60Wet1.3Example 2No. 2 water0.90Noncrystalline0.60Wet2.7Example 3No. 2 water0.90Noncrystalline0.60Wet2.6Example 4No. 2 water0.90Noncrystalline0.60Wet2.7Example 5No. 2 water0.90Noncrystalline0.60Wet1.0Example 6No. 2 water0.90Noncrystalline0.60Wet2.5Example 7No. 2 water0.90Noncrystalline0.60Wet2.4Example 8No. 2 water0.90Noncrystalline0.60Wet2.3Example 9No. 2 water0.90Noncrystalline0.60Wet2.0Comparative example 1No. 2 water glass0.90Noncrystalline silica fine0.60Wet sand0.8Comparative example 2No. 2 water glass0.90Noncrystalline silica fine0.60Wet sand0.8Comparative example 3No. 2 water glass0.90Noncrystalline silica fine0.60Wet sand1.5Comparative example 4No. 2 water glass0.90Noncrystalline silica fine0.60Wet sand1.6 * 1 The time in a case where the mold strength obtained using the casting sand for a mold immediately after kneading after 24 hours is regarded as 100%, the casting sand for a mold is stored in an environment of 25°C and 55% RH, the mold strength obtained using the casting sand for a mold after 24 hours is 80%. [Table 2]

[0157] Table 2Casting sand for mold containing inorganic binderCasting sandInorganic binder (second coating layer)Refractory aggregateFirst coating layerEnvironme ntal loadPropert iesCompo und 3Par ts by mas sCompound 4Par ts by mas sSta teStorag e stabil ityTypesPar ts by mas sCompo und 1Par ts by mas sCompou nd 2Par ts by mas sBaking temperatu re [°C]Cation exchang e capacit y [mmol (+) ·kg -1< ]Usable time * 1 [h]Example 10Refract ory aggrega te (B1) : spheric al fused silica100> 959950% Alumin ate Na4.6808No. 2 water glass0.9 0Noncrysta lline silica fine particles0.6 0Wet san d2.3Example 11Refract ory aggrega te (B1) : spheric al fused silica100> 959950% Alumin ate Na9.1807No. 2 water glass0.9 0Noncrysta lline silica fine particles0.6 0Wet san d2.5Example 12Refract ory aggrega te (B2) : NIGAI CERABEA DS 60#650100303650% Alumin ate Na4.6808No. 2 water glass0.9 0Noncrysta lline silica fine particles0.6 0Wet san d2.5Compara tive example 5Refract ory aggrega te (B1): spheric al fused silica100> 9599None0-< 1No. 2 water glass0.9 0Noncrysta lline silica fine particles0.6 0Wet san d0.5* 1 The time in a case where the mold strength obtained using the casting sand for a mold immediately after kneading after 24 hours is regarded as 100%, the casting sand for a mold is stored in an environment of 25°C and 55% RH, the mold strength obtained using the casting sand for a mold after 24 hours is 80%. [Table 3]

[0158] Table 3Casting sand for mold containing inorganic binderCasting sandRefractory aggregateStorage stabilityTypesNumber of times of regeneration [Number]Usable time * 1 [h]Example 2Regenerated sand (Al)12.7Comparative example 13Regenerated sand (A5)52.6* 1 The time in a case where the mold strength obtained using the casting sand for a mold immediately after kneading after 24 hours is regarded as 100%, the casting sand for a mold is stored in an environment of 25°C and 55% RH, the mold strength obtained using the casting sand for a mold after 24 hours is 80%.

Claims

1. A casting sand for a mold, the sand comprising: 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 silicate on 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 casting sand for a mold 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 casting sand for a mold according to Claim 1 or 2, wherein the first coating layer contains an aluminosilicate, and the aluminosilicate is a mixture of one or more selected from a silicate and a reactant of the silicate, an aluminate, and one or more selected from zeolite.

4. The casting sand for a mold according to Claim 3, wherein the aluminate is at least one of sodium aluminate and aluminum hydroxide.

5. A casting mold consisting of the casting sand for a mold according to any one of Claims 1 to 4.

6. A method for producing a casting sand for a mold, the method comprising: a step of forming a first coating layer on a surface of one or two kinds of aggregates selected from a regenerated sand (A) and a refractory aggregate (B) containing SiO2 to obtain a casting sand having a cation exchange capacity (CEC) of 3 mmol (+) / kg or more and 40 mmol (+) / kg or less; and a step of mixing the casting sand with a silicate and forming a second coating layer including the silicate on the first coating layer of the casting sand, wherein the refractory aggregate (B) contains SiO2.

7. The method for producing a casting sand for a mold according to Claim 6, wherein in the step of obtaining the casting sand, the aggregate and an aluminate or aluminum hydroxide are mixed to form the first coating layer on the surface of the aggregate.

8. The method for producing a casting sand for a mold according to Claim 6 or 7, wherein in the step of obtaining the casting sand, the first coating layer is formed on the surface of the aggregate by heating the casting sand at 25°C or higher and lower than 400°C.

9. A method for improving storage stability of a casting sand for a mold, the method comprising: a step of forming a first coating layer on a surface of one or two kinds of aggregates selected from a regenerated sand (A) and a refractory aggregate (B) to obtain a casting sand having a cation exchange capacity (CEC) of 3 mmol (+) / kg or more and 40 mmol (+) / kg or less; and a step of mixing the casting sand with a silicate and forming a second coating layer including the silicate on the first coating layer of the casting sand, wherein the refractory aggregate (B) contains SiO2.

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