Inorganic coated sand

Abstract

Provided is a method for reducing sand burning in a cast by a casting mold, which is manufactured using inorganic coated sand including a refractory aggregate and an inorganic binder layer formed on a surface of the refractory aggregate, in which the inorganic binder layer contains one or more selected from the group consisting of graphite, mica, and zirconium silicate, and a total content of the graphite, the mica, and the zirconium silicate is 7 parts by mass or greater and 70 parts by mass or less with respect to 100 parts by mass of an inorganic binder.

Description

TECHNICAL FIELD

[0001] The present invention relates to inorganic coated sand.BACKGROUND ART

[0002] As a casting mold used for casting a cast, for example, a mold obtained by molding into a desired shape using inorganic coated sand that includes a refractory aggregate and an inorganic binder layer formed on a surface of the refractory aggregate has been known.

[0003] Examples of technology related to such inorganic coated sand include those described in Patent Document 1 (Pamphlet of International Publication No. WO2018 / 097180) and Patent Document 2 (Japanese Unexamined Patent Publication No. 2018-86661).

[0004] Patent Document 1 discloses a technology for dried coated sand having fluidity at ordinary temperature, in which a surface of refractory aggregate is coated with a coating layer containing water glass, and spherical particles are contained in the coating layer (Claim 1).

[0005] Patent Document 2 discloses a binder-coated refractory in which a surface of a refractory aggregate is coated with a binder layer composed of a binding material for a casting mold, which contains a binder and silicon carbide (Claims 1 and 2).RELATED DOCUMENTPATENT DOCUMENT

[0006] [Patent Document 1] Pamphlet of International Publication No. WO2018 / 097180 [Patent Document 2] Japanese Unexamined Patent Publication No. 2018-86661 SUMMARY OF THE INVENTION

[0007] According to the present invention, there is provided a method for reducing sand burning in a cast by a casting mold, which is manufactured using inorganic coated sand including a refractory aggregate and an inorganic binder layer formed on a surface of the refractory aggregate, in which the inorganic binder layer contains one or more selected from the group consisting of graphite, mica, and zirconium silicate, and a total content of the graphite, the mica, and the zirconium silicate is 7 parts by mass or greater and 70 parts by mass or less with respect to 100 parts by mass of an inorganic binder.

[0008] According to the present invention, there is provided inorganic coated sand including: a refractory aggregate; and an inorganic binder layer formed on a surface of the refractory aggregate, in which the inorganic binder layer contains one or more selected from the group consisting of graphite, mica, and zirconium silicate, and a total content of the graphite, the mica, and the zirconium silicate is 7 parts by mass or greater and 70 parts by mass or less with respect to 100 parts by mass of an inorganic binder.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] [Fig. 1] A sectional view for illustrating a schematic configuration of a casting test mold in Example.DESCRIPTION OF EMBODIMENTS

[0010] According to the studies of the present inventors, when casting is performed using a casting mold molded with conventional inorganic coated sand, the sand, which is derived from the molded casting mold, may be burned on a surface of a cast, which is a casting product, and it is newly found that there is room for improvement in the quality of the cast.

[0011] The present invention provides a technology for reducing burning of the casting mold-derived sand in the cast.

[0012] The present inventors have found that sand burning of the cast can be reduced by containing a specific component in the inorganic binder layer of a casting mold, which is manufactured by using inorganic coated sand that includes a refractory aggregate and an inorganic binder layer formed on a surface of the refractory aggregate.

[0013] According to the present invention, it is possible to provide a technology for reducing burning of the casting mold-derived sand in the cast. In addition, according to the present invention, it is possible to provide inorganic coated sand that reduces sand burning of a cast.

[0014] Hereinafter, embodiments of the present invention will be described in detail. In the present specification, "A to B" indicating a numerical range indicates a range of A or greater and B or less unless otherwise specified, and includes both values. The configurations and elements described in the embodiments can be appropriately combined as long as the effects of the invention are not impaired.<Method for reducing Sand Burning of Cast>

[0015] In the present embodiment, there is provided a method for reducing sand burning in a cast by a casting mold, which is manufactured using inorganic coated sand including a refractory aggregate and an inorganic binder layer formed on a surface of the refractory aggregate, in which the inorganic binder layer contains one or more selected from the group consisting of graphite, mica, and zirconium silicate, and a total content of the graphite, the mica, and the zirconium silicate is 7 parts by mass or greater and 70 parts by mass or less with respect to 100 parts by mass of an inorganic binder.

[0016] For example, the method in the present embodiment may be a method for preventing sand burning in a cast by a casting mold that is manufactured using inorganic coated sand.(Mechanism for reducing Sand Burning in Cast)

[0017] In the present embodiment, the reason why it is not clear that the effects of reducing sand burning in a cast by using the inorganic coated sand are exhibited, and is presumed as follows. It is presumed that the reason why the sand is burned in the cast is that the inorganic binder reacts with a molten metal during casting and adheres the sand to the surface of the cast. On the other hand, since graphite, mica, and zirconium silicate all have low reactivity with the molten metal, and these substances exist in an outermost layer of the casting mold that is molded with the inorganic coated sand which contains these substances in the inorganic binder layer, it is presumed that the reaction between the inorganic binder and the molten metal is reduced.

[0018] In this case, the reduction of sand burning in the present embodiment specifically means reduction of adhering the sand in the casting mold to the cast, and it is different from improving releasability, which improves the ease of removing the casting mold from the die.

[0019] Hereinafter, the inorganic coated sand and the method for manufacturing a casting mold will be described in more detail.<Inorganic Coated Sand>

[0020] The inorganic coated sand includes a refractory aggregate and an inorganic binder layer formed on a surface of the refractory aggregate. The inorganic binder layer contains one or more selected from the group consisting of graphite, mica, and zirconium silicate. The total content of graphite, mica, and zirconium silicate is 7 parts by mass or greater and 70 parts by mass or less with respect to 100 parts by mass of the inorganic binder, specifically, with respect to 100 parts by mass of the solid content of the inorganic binder.

[0021] The inorganic coated sand is specifically composed of particle groups of the inorganic coated sand, and the refractory aggregate is specifically composed of particle groups of the refractory aggregate.

[0022] The inorganic coated sand preferably has a spherical shape in terms of improving fluidity and further improving a filling property into a molding die. Here, the spherical shape of the inorganic coated sand means a ball-like round shape.

[0023] More specifically, sphericity of the inorganic coated sand is preferably 0.75 or greater, more preferably 0.80 or greater, and still more preferably 0.82 or greater, in terms of improvement in fluidity, quality of the casting mold, and strength of the casting mold, or easiness of molding the casting mold. In addition, an upper limit of the sphericity is specifically 1 or less. In the present embodiment, the sphericity of the inorganic coated sand specifically matches the sphericity of the refractory aggregate.

[0024] 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.

[0025] An average particle diameter of the inorganic coated sand is preferably 0.05 mm or greater, and more preferably 0.1 mm or greater, in terms of improvement in quality of the casting mold and strength of the casting mold, or easiness of molding the casting mold. Further, when the average particle diameter of the inorganic coated sand is the lower limit or greater described above, an amount of the inorganic binder 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.

[0026] 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.

[0027] 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)

[0028] 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.

[0029] 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.(Refractory Aggregate)

[0030] Examples of materials of the refractory aggregate include one or more selected from the group consisting of natural sand and artificial sand.

[0031] Examples of the natural sand include one or two or greater selected from the group consisting of silica sand containing quartz as a main component, chromate sand, zircon sand, olivine sand, and alumina sand.

[0032] Examples of artificial sand include one or two or greater 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 slag-derived casting sand. Here, the main component means the most abundant component among the components contained in the sand.

[0033] 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, recycled sand obtained by reproducing the recovered sand, and the like can also be used.

[0034] The refractory aggregate is preferably in a form of particles in terms of improvement in fluidity of the inorganic coated sand and further improvement in filling property into the molding die.

[0035] Further, an average particle diameter of the refractory aggregate is preferably 0.05 mm or greater, and more preferably 0.1 mm or greater, 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 greater described above, an amount of the inorganic binder 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.

[0036] 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 is reduced during the manufacture of the casting mold, which is preferable in terms of increasing the strength of the casting mold.(Inorganic Binder Layer)

[0037] The inorganic binder layer specifically contains an inorganic binder and one or more selected from the group consisting of graphite, mica, and zirconium silicate.

[0038] Specifically, the inorganic binder layer is a coating layer formed on the surface of the refractory aggregate. The inorganic binder layer can be, for example, a layer that is coated with a mixture of an inorganic binder and one or more selected from the group consisting of graphite, mica, and zirconium silicate; a layer that is further coated with one or more selected from the group consisting of graphite, mica, and zirconium silicate on the layer coated with the inorganic binder; or a layer that is further coated with one or greater compounds selected from the group consisting of graphite, mica, and zirconium silicate on the layer which is coated with a mixture of the inorganic binder and one or more compounds selected from the group consisting of graphite, mica, and zirconium silicate.

[0039] A content of the inorganic binder layer in the inorganic coated sand is preferably 0.05% by mass or greater, more preferably 0.1% by mass or greater, even more preferably 0.5% by mass or greater, still more preferably 1.0% by mass or greater, and yet more preferably 1.5% by mass or greater with respect to all components other than water in the inorganic coated sand, in terms of improving a strength of the casting mold.

[0040] In addition, the content of the inorganic binder layer in the inorganic coated sand is preferably 10% by mass or less, more preferably 8% by mass or less, even more preferably 6% by mass or less, still more preferably 4.5% by mass or less, yet more preferably 4% by mass or less, and further more preferably 3.5% by mass or less with respect to all components other than water in the inorganic coated sand, in terms of improving a filling property into the molding die and improving a strength of the casting mold.

[0041] In this case, the content of the inorganic binder layer means a content of the inorganic binder layer excluding water. For example, when sodium metasilicate hydrate, which will be described later, is used as the inorganic binder, the content thereof is obtained in terms of sodium metasilicate.

[0042] The content of the inorganic binder layer in the inorganic coated sand with respect to 100 parts by mass of the refractory aggregate is preferably 0.05 parts by mass or greater, more preferably 0.1 part by mass or greater, even more preferably 0.5 parts by mass or greater, still more preferably 1 part by mass or greater, and yet more preferably 1.5 parts by mass or greater, in terms of improving a strength of the casting mold. In addition, the content of the inorganic binder layer in the inorganic coated sand with respect to 100 parts by mass of the refractory aggregate is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, even more preferably 6 parts by mass or less, still more preferably 4.5 parts by mass or less, yet more preferably 4 parts by mass or less, and further more preferably 3.5 parts by mass or less, in terms of improving a filling property into the molding die and improving a strength of the casting mold.

[0043] Next, components contained in the inorganic binder layer will be described.(Inorganic Binder)

[0044] In the present embodiment, the inorganic binder includes, for example, a silicic acid compound, and preferably at least one selected from the group consisting of sodium silicate and sodium metasilicate in terms of excellent productivity and availability.

[0045] The inorganic binder may further contain a water-soluble silicic acid compound other than the above as a main component. Specific examples of the silicic acid compound other than sodium silicate and sodium metasilicate include potassium silicate, potassium metasilicate, lithium silicate, and ammonium silicate.

[0046] Specific examples of the sodium silicate include one or two or greater selected from the group consisting of sodium silicate Nos. 1 to 5. Here, the sodium silicate is classified into Nos. 1 to 5 according to a molar ratio of SiO 2 / Na 2 O, and sodium silicates Nos. 1 to 3 are defined in JIS-K-1408. Specific molar ratio of SiO 2 / Na 2 O in each No. is as follows. Sodium silicate No. 1: molar ratio of SiO 2 / Na 2 O = 2.0 to 2.3 Sodium silicate No. 2: molar ratio of SiO 2 / Na 2 O = 2.4 to 2.6 Sodium silicate No. 3: molar ratio of SiO 2 / Na 2 O = 2.8 to 3.3 Sodium silicate No. 4: molar ratio of SiO 2 / Na 2 O = 3.3 to 3.5 Sodium silicate No. 5: molar ratio of SiO 2 / Na 2 O = 3.6 to 3.8

[0047] Further, the molar ratio of SiO 2 / Na 2 O may be adjusted to a desired degree by mixing two or more kinds of sodium silicate.

[0048] The sodium silicate is preferably No. 1 water glass.

[0049] Sodium metasilicate is preferably a hydrate in terms of improving productivity of the inorganic coated sand and improving productivity of the casting mold.

[0050] From the point described above, the sodium metasilicate hydrate is preferably at least one selected from sodium metasilicate pentahydrate and sodium metasilicate nonahydrate, and more preferably sodium metasilicate nonahydrate.

[0051] The content of the inorganic binder in the inorganic binder layer is preferably 30% by mass or greater, more preferably 35% by mass or greater, even more preferably 40% by mass or greater, and still more preferably 45% by mass or greater with respect to the entire inorganic binder layer, in terms of improving a strength of the casting mold and improving a surface stability of the casting mold.

[0052] In addition, the content of the inorganic binder in the inorganic binder layer may be, for example, 96% by mass or less, and is preferably 93% by mass or less, more preferably 91% by mass or less, and even more preferably 90% by mass or less with respect to the entire inorganic binder layer, in terms of efficiently reducing sand burning in the cast.

[0053] In this case, the content of the inorganic binder in the inorganic binder layer refers to a content of the inorganic binder excluding water with respect to a total amount of components other than water in the inorganic binder layer.

[0054] A total content of sodium silicate and sodium metasilicate in the inorganic binder is preferably 80% by mass or greater, more preferably 90% by mass or greater, even more preferably 95% by mass or greater, still more preferably 98% by mass or greater, and yet still more preferably substantially 100% by mass, in terms of improvement in strength of the casting mold, excellent productivity, and availability. The "substantially" as used herein means that unintentionally contained components, for example, components other than sodium silicate and sodium metasilicate, contained in sodium silicate and sodium metasilicate which are raw materials may be included.

[0055] The total content of sodium silicate and sodium metasilicate in the inorganic binder refers to a total content of sodium silicate and sodium metasilicate with respect to a total amount of components other than water in the inorganic binder.

[0056] Further, the content of the inorganic binder in the inorganic coated sand is preferably 0.03 parts by mass or greater, more preferably 0.1 part by mass or greater, even more preferably 0.5 parts by mass or greater, and still more preferably 1 part by mass or greater with respect to 100 parts by mass of the refractory aggregate, in terms of improving a strength of the casting mold and forming a good surface of the casting mold.

[0057] In addition, the content of the inorganic binder in the inorganic coated sand is preferably 5 parts by mass or less, more preferably 4 parts by mass or less, even more preferably 3 parts by mass or less, and still more preferably 2 parts by mass or less with respect to 100 parts by mass of the refractory aggregate, in terms of improving a filling property into the molding die.(Graphite, Mica, And Zirconium Silicate)

[0058] As graphite, mica, and zirconium silicate, for example, various commercially available materials can be used.

[0059] Specific examples of graphite include natural graphite such as earthy graphite, vein graphite, and flake graphite; and artificial graphite (synthetic graphite).

[0060] In addition, specific examples of mica include muscovite and biotite.

[0061] The properties of graphite, mica, and zirconium silicate are preferably fine particles in terms of improving dispersibility in the inorganic binder layer.

[0062] The average particle diameter of graphite, mica, and zirconium silicate is preferably 100 um or less, more preferably 80 um or less, even more preferably 50 um or less, still more preferably 30 um or less, and yet still more preferably 20 um or less in terms of improving dispersibility into the inorganic binder layer.

[0063] In addition, the average particle diameter of graphite, mica, and zirconium silicate is preferably 0.1 um or greater, more preferably 0.5 um or greater, even more preferably 1.0 um or greater, and still more preferably 3.0 um or greater in terms of ease of handling and availability.

[0064] Specifically, the average particle diameter of graphite, mica, and zirconium silicate can be measured using the following measuring method.(Method for Measuring Average Particle Diameter)

[0065] The average particle diameter of 50% cumulative volume is measured by using a laser diffraction type particle diameter distribution measuring device LA-960V2 (manufactured by HORIBA, Ltd.). The analysis conditions are as follows. · Measurement method flow method · Dispersion medium graphite: methanol, mica and zirconium silicate: water · Dispersion method stirring, built-in ultrasonic waves 3 minutes · Sample concentration 2 mg / 100 mL · Refractive index graphite: 1.92, mica: 1.59, zirconium silicate: 1.97

[0066] The total content of graphite, mica, and zirconium silicate in the inorganic binder layer is preferably 4% by mass or greater, more preferably 5% by mass, and even more preferably 6% by mass or greater with respect to the total amount of components other than water in the inorganic binder layer, in terms of reducing sand burning in the cast.

[0067] In addition, the total content of graphite, mica, and zirconium silicate in the inorganic binder layer is preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 32% by mass or less with respect to the total amount of components other than water in the inorganic binder layer, in terms of improving a strength of the casting mold.

[0068] The total content of graphite, mica, and zirconium silicate is preferably 7 parts by mass or greater, more preferably 9 parts by mass or greater, and even more preferably 10 parts by mass or greater with respect to the 100 parts by mass of the inorganic binder, in terms of reducing sand burning in the cast.

[0069] In addition, the total content of graphite, mica, and zirconium silicate is preferably 70 parts by mass or less, more preferably 60 parts by mass or less, even more preferably 55 parts by mass or less, and still more preferably 50 parts by mass or less with respect to 100 parts by mass of the inorganic binder, in terms of improving a strength of the casting mold.(Other Additives)

[0070] In addition to the above-mentioned components, various additives may be contained in the inorganic binder layer, if necessary. Examples of other additives include a moisturizing agent, a moisture resistance improving agent, a coupling agent that strengthens the bond between the refractory aggregate and the inorganic binder, a lubricant, a surfactant, and a releasing agent.

[0071] Among them, 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.

[0072] Examples of the moisture resistance improving agent include metal oxide, carbonate, borate, sulfate, phosphate, and the like.

[0073] 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.

[0074] 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, vermiculite, a fluorine-based mold releasing agent, and silicone-based mold releasing agent.(Inorganic Fine Particles)

[0075] In the present embodiment, the inorganic coated sand may further include inorganic fine particles other than graphite, mica, and zirconium silicate. The inorganic fine particles preferably form a part of the inorganic binder layer. In this case, the inorganic binder layer preferably further includes inorganic fine particles at least one of on the layer and in the layer, and more preferably further includes inorganic fine particles on the layer. The inorganic fine particles may be included both on the inorganic binder layer and in the inorganic binder layer.

[0076] Therefore, the particles of the inorganic coated sand are strongly bound to each other through the inorganic fine particles, and as a result, the strength of a casting mold to be obtained can be further improved.

[0077] In this case, the inorganic fine particles on the inorganic binder layer may be partially embedded in the inorganic binder layer.

[0078] The inorganic fine particles are not limited, and examples thereof include silica particles and silicon particles, and in terms of improving a strength of a casting mold, silica particles are preferable, and amorphous silica particles are more preferable. The inorganic fine particles may be used alone or in combination of two or more kinds thereof.(Amorphous Silica)

[0079] In the present embodiment, the inorganic coated sand may further include amorphous silica. Amorphous silica preferably forms a part of the inorganic binder layer.

[0080] The amorphous silica is preferably amorphous silica particles described above in terms of a large specific surface area and high reactivity with sodium silicate and sodium metasilicate.

[0081] The content of amorphous silica particles in the amorphous silica is preferably 80% by mass or greater, more preferably 90% by mass or greater, even more preferably 95% by mass or greater, still more preferably 98% by mass or greater, and yet still more preferably substantially 100% by mass, in terms of improvement in strength of the casting mold and availability. The term "substantially" herein means that unintentionally included components, for example, amorphous silica other than the amorphous silica particles included in the amorphous silica particles may be included.

[0082] A degree of amorphization of the amorphous silica particles is preferably 80% or greater, more preferably 90% or greater, even more preferably 93% or greater, still more preferably 95% or greater, and yet more preferably 98% or greater, in terms of firmly binding particles of the inorganic coated sand through the amorphous silica particles. An upper limit of the degree of amorphization of the amorphous silica particles is not limited, but may be, for example, 100% or less, 99.8% or less, or 99% or less.

[0083] The degree of amorphization of the amorphous silica particles can be obtained by an X-ray diffraction method shown below.(X-Ray Diffraction Method)

[0084] The amorphous silica particles are measured by pulverizing in a mortar, and pressure-bonding the pulverized amorphous silica particles to an X-ray glass holder of a powder X-ray diffraction apparatus. The powder X-ray diffraction apparatus performs measurement by using MultiFlex (light source: CuKα ray, tube voltage: 40 kV, tube current: 40 mA) manufactured by Rigaku Corporation in a range of 20 = 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 20 = 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 degree of amorphization. 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 degree of amorphization (%) by the following formula. Degree of Amorphization % = Area of Halo / Area of Crystalline Component + Area of Halo × 100

[0085] An average particle diameter d 50 in a weight-standard particle diameter distribution of the amorphous silica particles measured by a laser diffraction / scattering type particle diameter distribution measurement method is preferably 0.1 µm or greater, and more preferably 0.3 µm or greater, in terms of improvement in strength of the casting mold or improvement in handling property. In addition, the average particle diameter d 50 of the amorphous silica particles is preferably 2.0 um or less, more preferably 1.0 µm or less, even more preferably 0.8 µm or less, and still more preferably 0.6 µm or less, in terms of improvement in strength of the casting mold.

[0086] In this case, the average particle diameter d 50 in the weight-standard particle diameter distribution of the amorphous silica particles measured by the laser diffraction / scattering type particle diameter distribution measurement method can be obtained by, for example, dissolving the inorganic binder layer in water and removing the inorganic binder layer from the inorganic coated sand, taking the amorphous silica particles out, and then measuring particle diameters of the obtained amorphous silica particles by the laser diffraction / scattering type particle diameter distribution measurement method.

[0087] In addition, the average particle diameter d 50 in the weight-standard particle diameter distribution of the amorphous silica particles measured by the laser diffraction / scattering type particle diameter distribution measurement method can be obtained by measuring particle diameters of the amorphous silica particles, which are raw materials, by the laser diffraction / scattering type particle diameter distribution measurement method.

[0088] Further, an average particle diameter of the amorphous silica particles, determined from an image observed with a scanning electron microscope, is preferably 0.1 µm or greater, and more preferably 0.3 µm or greater, in terms of improvement in strength of the casting mold per unit mass or improvement in handling property. In addition, the average particle diameter of the amorphous silica particles, obtained from the image observed with the scanning electron microscope, is preferably 2.0 µm or less, more preferably 1.0 µm or less, even more preferably 0.8 µm or less, and still more preferably 0.6 µm or less, in terms of improvement in strength of the casting mold per unit mass.

[0089] In this case, various image analysis methods can be used to determine the average particle diameter of the amorphous silica particles from the image observed with the scanning electron microscope. Irregular particle sorting may be performed as a pretreatment. For example, after the inorganic binder layer and the amorphous silica particles are determined on the basis of the elements, any 100 amorphous silica particles are selected, and the particle diameters thereof are measured. An average value of particle diameters of 80 amorphous silica particles, excluding 10 particles counted in order of decreasing diameter from the maximum particle diameter and 10 particles counted in order of increasing diameter from the minimum particle diameter, that is, total 20 amorphous silica particles, can be defined as the average particle diameter of the amorphous silica particles.

[0090] The content of amorphous silica in the inorganic binder layer is specifically 0% by mass or greater, preferably 20% by mass or greater, more preferably 25% by mass or greater, and even more preferably 30% by mass or greater with respect to the total amount of components other than water in the inorganic binder layer, in terms of improvement in strength of the casting mold.

[0091] In addition, the content of amorphous silica in the inorganic binder layer is preferably 55% by mass or less, more preferably 50% by mass or less, and even more preferably 45% by mass or less with respect to the total amount of components other than water in the inorganic binder layer, in terms of forming a good surface shape of the casting mold and in terms of reducing dust scattering.

[0092] Further, the content of amorphous silica is specifically 0 parts by mass or greater, preferably 20 parts by mass or greater, more preferably 40 parts by mass or greater, even more preferably 50 parts by mass or greater, and still more preferably 60 parts by mass or greater with respect to 100 parts by mass of the inorganic binder, in terms of improvement in strength of the casting mold.

[0093] In addition, the content of amorphous silica is preferably 150 parts by mass or less, more preferably 120 parts by mass or less, even more preferably 100 parts by mass or less, still more preferably 90 parts by mass or less, and yet still more preferably 80 parts by mass or less with respect to 100 parts by mass of the inorganic binder, in terms of forming a good surface shape of the casting mold and in terms of reducing dust scattering.

[0094] A content of water in the inorganic binder layer contained in the inorganic coated sand is preferably 5 parts by mass or greater, more preferably 10 parts by mass or greater, and even more preferably 20 parts by mass or greater with respect to 100 parts by mass of the inorganic binder, in terms of obtaining a high-strength casting mold.

[0095] Further, the content of water in the inorganic binder layer contained in the inorganic coated sand 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 of the inorganic binder, in terms of improving a filling property into the molding die and obtaining a high-strength casting mold.

[0096] The content of water in the inorganic binder layer contained in the inorganic coated sand can be adjusted according to a type of the inorganic binder.

[0097] When the inorganic binder is sodium silicate, the content of water in the inorganic binder layer is preferably 5 parts by mass or greater, more preferably 10 parts by mass or greater, and even more preferably 20 parts by mass or greater with respect to 100 parts by mass of sodium silicate, in terms of obtaining a high-strength casting mold.

[0098] In addition, the content of water in the inorganic binder layer contained in the inorganic coated sand is preferably 55 parts by mass or less, and more preferably 50 parts by mass or less with respect to 100 parts by mass of sodium silicate, in terms of improving a filling property into the molding die and obtaining a high-strength casting mold.

[0099] When the inorganic binder is sodium metasilicate, the content of water in the inorganic binder layer is preferably 60 parts by mass or greater, more preferably 65 parts by mass or greater, even more preferably 90 parts by mass or greater, and still more preferably 110 parts by mass or greater with respect to 100 parts by mass of sodium metasilicate, in terms of obtaining a high-strength casting mold and easily manufacturing a casting mold. In addition, the content of water in the inorganic binder layer 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, in terms of improving fluidity and further improving a filling property into the molding die.

[0100] For example, when the inorganic binder constituting the inorganic binder 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 when the inorganic binder constituting the inorganic binder 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 Inorganic Coated Sand>

[0101] A method for producing the inorganic coated sand can be selected, for example, according to a type of the inorganic binder.

[0102] When the inorganic binder contains sodium silicate, a dried inorganic coated sand having fluidity at ordinary temperature can be obtained by, for example, adding a water glass aqueous solution as an inorganic binder to the heated refractory aggregate, if necessary, with an additive, kneading and uniformly mixing the resultant, coating the water glass aqueous solution to the surface of the refractory aggregate, and evaporating moisture of the water glass aqueous solution.

[0103] When the inorganic binder contains a sodium metasilicate hydrate, for example, a dried inorganic coated sand can be obtained by a producing method including: mixing the refractory aggregate and sodium metasilicate hydrate at a temperature of equal to or higher than a melting point of the sodium metasilicate hydrate to obtain a mixture; and cooling the mixture at a temperature of lower than the melting point of the sodium metasilicate hydrate.

[0104] According to such a producing method, since the inorganic binder layer can be crystallized, it is possible to obtain inorganic coated sand having excellent fluidity as compared with the conventional producing method. In addition, since it is not necessary to use an aqueous solution of the sodium metasilicate hydrate, there is no need for a dehydration step, which can simplify the method for producing the inorganic coated sand.

[0105] In the obtaining the mixture, specifically, the surface of the refractory aggregate is coated with the fluidized sodium metasilicate hydrate at a temperature equal to or higher than the melting point of the sodium metasilicate hydrate.

[0106] Examples of the method for mixing the refractory aggregate and the sodium metasilicate hydrate at a temperature equal to or higher than the melting point of the sodium metasilicate hydrate include: a method for putting the sodium metasilicate hydrate into the refractory aggregate that is heated to a temperature equal to or higher than the melting point of the sodium metasilicate hydrate and mixing the refractory aggregate and the sodium metasilicate hydrate while melting the sodium metasilicate hydrate; and a method for putting the heated and melted sodium metasilicate hydrate into the refractory aggregate and mixing them.

[0107] Among them, the method for putting the heated and melted sodium metasilicate hydrate into the refractory aggregate and mixing them is preferable in terms of shortening a coating time. In the same terms thereof, in the obtaining the mixture, mixing the mixture without using the sodium metasilicate hydrate as an aqueous solution in advance is preferable. In addition, the obtaining the mixture does not include intentionally adding water, which is preferable.

[0108] When the refractory aggregate and the sodium metasilicate hydrate are mixed, mixing conditions such as a stirring speed, a treatment time, and the like can be appropriately determined depending on a treatment amount of the mixture.

[0109] In the cooling the mixture, the mixture obtained in the obtaining the mixture is cooled to a temperature lower than the melting point of the sodium metasilicate hydrate to reduce fluidity of the sodium metasilicate hydrate, and the sodium metasilicate hydrate is fixed to the surface of the refractory aggregate to form a sodium metasilicate hydrate layer, that is, an inorganic binder layer.

[0110] In the production of the inorganic coated sand, the method for adding graphite, mica, and zirconium silicate is not limited, and for example, the refractory aggregate may be coated with the inorganic binder, if necessary, amorphous silica and other additives thereof, and then may be coated with graphite, mica, and zirconium silicate or if necessary, amorphous silica and other additives thereof.

[0111] Alternatively, the inorganic binder and graphite, mica and zirconium silicate, if necessary, amorphous silica and other additives may be coated together on the refractory aggregate.

[0112] Alternatively, an inorganic binder and graphite, mica, and zirconium silicate, optionally amorphous silica and other additives are coated together on a refractory aggregate, and then graphite, mica, zirconium silicate and optionally amorphous silica and other additives may be coated.

[0113] In terms of reducing dust scattering during molding, it is preferable to coat (internally added) the inorganic binder and graphite, mica, and zirconium silicate together on the refractory aggregate.

[0114] Graphite, mica, and zirconium silicate can be in solid form or in aqueous dispersion and mixed with the refractory aggregate, the inorganic binder, and the like.

[0115] In addition, graphite, mica, and zirconium silicate may be added all at once or in a plurality of times.

[0116] By the above method, the inorganic coated sand in the present embodiment can be obtained.

[0117] In addition, the obtained inorganic coated sand can be used alone or in combination with other known refractory aggregates or other additives to mold a desired casting mold.<Casting Mold>

[0118] In the present embodiment, a casting mold is manufactured by using the inorganic coated sand in the present embodiment described above. 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.

[0119] When the inorganic binder layer contains sodium metasilicate hydrate, a method for molding a casting mold by filling the inorganic coated sand into the heated molding die is preferable. When the inorganic binder layer contains sodium silicate, a method for molding a casting mold by adding water to the inorganic coated sand, kneading, and then filling the resultant into the heated molding die, or a method for molding a casting mold by filling the inorganic coated sand into the heated molding die, aerating the steam, and then aerating the hot air is preferable.

[0120] When the inorganic binder layer contains sodium metasilicate hydrate, in the molding method using the heated molding die, for example, first, the inorganic coated sand is filled in a molding die for providing a desired casting mold.

[0121] Here, preferably, the molding die is kept warm by heating in advance before filling the inorganic coated sand thereinto, in terms of improving productivity of the casting mold. In this case, a heating temperature of the molding die is preferably 100°C or higher, more preferably 150°C or higher, and preferably 300°C or lower, and more preferably 250°C or lower, in terms of improvement in productivity of the casting mold and improvement in strength of the casting mold.

[0122] After filling the inorganic coated sand, the molding die is heated without aeration of the steam to cure the inorganic coated sand. When the inorganic binder layer contains sodium metasilicate hydrate, the inorganic coated sand can be cured without using adding water to the inorganic coated sand and kneading the resultant, or aerating the steam, such that there is no need for equipment to aerate the steam.

[0123] The heating temperature of the molding die is preferably 100°C or higher, more preferably 150°C or higher, and preferably 300°C or lower, and more preferably 250°C or lower, in terms of improving productivity of the casting mold and improving a strength of the casting mold. In addition, a heating time of the molding die is preferably 30 seconds or longer, and more preferably 60 seconds or longer, and preferably 600 seconds or shorter, in terms of obtaining the stable strength of the casting mold.

[0124] Further, when the inorganic binder layer contains sodium silicate, water is added to the inorganic coated sand, kneaded, and then filled the resultant into a heated molding die. Moreover, in the molding method for aerating the steam, for example, the inorganic coated sand is filled into the molding die for providing a desired casting mold, and the steam is then blown into the casting mold. A filling phase of the inorganic coated sand is moistened by aeration of the steam and becomes a wet state. The hot air is then blown into the molding die heated to 90°C to 200°C to dry and cure the inorganic coated sand.

[0125] Further, the inorganic coated sand in the present embodiment can also be used in an additive manufacturing method.

[0126] Regarding the above embodiment, the present invention further discloses the following method for reducing sand burning in a cast and inorganic coated sand. <1> A method for reducing sand burning in a cast by a casting mold, which is manufactured using inorganic coated sand including a refractory aggregate and an inorganic binder layer formed on a surface of the refractory aggregate, in which the inorganic binder layer contains one or more selected from the group consisting of graphite, mica, and zirconium silicate, and a total content of the graphite, the mica, and the zirconium silicate is 7 parts by mass or greater and 70 parts by mass or less with respect to 100 parts by mass of an inorganic binder. <2> The method for reducing sand burning in a cast by a casting mold according to <1>, which is manufactured using inorganic coated sand including a refractory aggregate and an inorganic binder layer formed on a surface of the refractory aggregate, in which the inorganic binder layer contains one or more selected from the group consisting of graphite, mica, and zirconium silicate, a total content of the graphite, the mica, and the zirconium silicate is 7 parts by mass or greater and 70 parts by mass or less with respect to 100 parts by mass of the inorganic binder, the inorganic binder contains at least one selected from the group consisting of sodium silicate and sodium metasilicate in a total content of sodium silicate and sodium metasilicate in the inorganic binder of 80% by mass or greater, and a content of the inorganic binder layer in the inorganic coated sand with respect to 100 parts by mass of the refractory aggregate is 0.05 parts by mass or greater and 10 parts by mass or less. <3> The method for reducing sand burning in a cast by a casting mold according to <1> or <2>, which is manufactured using inorganic coated sand including a refractory aggregate and an inorganic binder layer formed on a surface of the refractory aggregate, in which the inorganic binder layer contains one or more selected from the group consisting of graphite, mica, and zirconium silicate, a total content of the graphite, the mica, and the zirconium silicate is 9 parts by mass or greater and 55 parts by mass or less with respect to 100 parts by mass of the inorganic binder, the inorganic binder contains at least one selected from the group consisting of sodium silicate and sodium metasilicate in a total content of sodium silicate and sodium metasilicate in the inorganic binder of 98% by mass or greater, and a content of the inorganic binder layer in the inorganic coated sand with respect to 100 parts by mass of the refractory aggregate is 1 part by mass or greater and 4 parts by mass or less. <4> The method for reducing sand burning in a cast according to any one of <1> to <3>, in which an average particle diameter of the inorganic coated sand is 0.05 mm or greater and 2 mm or less. <5> The method for reducing sand burning in a cast according to any one of <1> to <4>, in which an average particle diameter of the refractory aggregate is 0.05 mm or greater and 2 mm or less. <6> The method for reducing sand burning in a cast according to any one of <1> to <5>, in which a content of the inorganic binder layer in the inorganic coated sand is 1.0% by mass or greater and 4% by mass or less. <7> The method for reducing sand burning in a cast according to any one of <1> to <6>, in which the content of the inorganic binder in the inorganic binder layer is 35% by mass or greater and 93% by mass or less. <8> The method for reducing sand burning in a cast according to any one of <1> to <7>, in which the inorganic binder contains at least one selected from the group consisting of sodium silicate and sodium metasilicate, and a total content of the sodium silicate and the sodium metasilicate in the inorganic binder is 80% by mass or greater, and preferably substantially 100% by mass. <9> The method for reducing sand burning in a cast according to any one of <1> to <8>, in which a content of the inorganic binder in the inorganic coated sand is 0.5 parts by mass or greater and 3 parts by mass or less with respect to 100 parts by mass of the refractory aggregate. <10> The method for reducing sand burning in a cast according to any one of <1> to <9>, in which the graphite, the mica, and the zirconium silicate have an average particle diameter of 3.0 µm or greater and 80 µm or less. <11> The method for reducing sand burning in a cast according to any one of <1> to <10>, in which a total content of the graphite, the mica, and the zirconium silicate in the inorganic binder layer is 4% by mass or greater and 35% by mass or less. <12> The method for reducing sand burning in a cast according to any one of <1> to <11>, in which the content of water in the inorganic binder layer is 20 parts by mass or greater and 150 parts by mass or less. <13> Inorganic coated sand including: a refractory aggregate; and an inorganic binder layer formed on a surface of the refractory aggregate, in which the inorganic binder layer contains one or more selected from the group consisting of graphite, mica, and zirconium silicate, and a total content of the graphite, the mica, and the zirconium silicate is 7 parts by mass or greater and 70 parts by mass or less with respect to 100 parts by mass of an inorganic binder. <14> The inorganic coated sand according to <13>, including: a refractory aggregate; and an inorganic binder layer formed on a surface of the refractory aggregate, in which the inorganic binder layer contains one or more selected from the group consisting of graphite, mica, and zirconium silicate, a total content of the graphite, the mica, and the zirconium silicate is 7 parts by mass or greater and 70 parts by mass or less with respect to 100 parts by mass of the inorganic binder, the inorganic binder contains at least one selected from the group consisting of sodium silicate and sodium metasilicate in a total content of sodium silicate and sodium metasilicate in the inorganic binder of 80% by mass or greater, and a content of the inorganic binder layer in the inorganic coated sand with respect to 100 parts by mass of the refractory aggregate is 0.05 parts by mass or greater and 10 parts by mass or less. <15> The inorganic coated sand according to <13> or <14>, including: a refractory aggregate; and an inorganic binder layer formed on a surface of the refractory aggregate, in which the inorganic binder layer contains one or more selected from the group consisting of graphite, mica, and zirconium silicate, a total content of the graphite, the mica, and the zirconium silicate is 9 parts by mass or greater and 55 parts by mass or less with respect to 100 parts by mass of the inorganic binder, the inorganic binder contains at least one selected from the group consisting of sodium silicate and sodium metasilicate in a total content of sodium silicate and sodium metasilicate in the inorganic binder of 98% by mass or greater, and a content of the inorganic binder layer in the inorganic coated sand with respect to 100 parts by mass of the refractory aggregate is 1 part by mass or greater and 4 parts by mass or less. <16> The inorganic coated sand according to any one of <13> to <15>, in which an average particle diameter of the inorganic coated sand is 0.05 mm or greater and 2 mm or less. <17> The inorganic coated sand according to any one of <13> to <16>, in which an average particle diameter of the refractory aggregate is 0.05 mm or greater and 2 mm or less. <18> The inorganic coated sand according to any one of <13> to <17>, in which a content of the inorganic binder layer in the inorganic coated sand is 1.0% by mass or greater and 4% by mass or less. <19> The inorganic coated sand according to any one of <13> to <18>, in which a content of the inorganic binder in the inorganic binder layer is 35% by mass or greater and 93% by mass or less. <20> The inorganic coated sand according to any one of <13> to <19>, in which the inorganic binder contains at least one selected from the group consisting of sodium silicate and sodium metasilicate, and a total content of the sodium silicate and the sodium metasilicate in the inorganic binder is 80% by mass or greater, and preferably substantially 100% by mass. <21> The inorganic coated sand according to any one of <13> to <20>, in which a content of the inorganic binder in the inorganic coated sand is 0.5 parts by mass or greater and 3 parts by mass or less with respect to 100 parts by mass of the refractory aggregate. <22> The inorganic coated sand according to any one of <13> to <21>, in which the graphite, the mica, and the zirconium silicate have an average particle diameter of 3.0 µm or greater and 80 µm or less. <23> The inorganic coated sand according to any one of <13> to <22>, in which the total content of the graphite, the mica, and the zirconium silicate in the inorganic binder layer is 4% by mass or greater and 35% by mass or less. <24> The inorganic coated sand according to any one of <13> to <23>, in which the content of water in the inorganic binder layer is 20 parts by mass or greater and 150 parts by mass or less. <25> The inorganic coated sand according to any one of <13> to <24>, in which the inorganic coated sand contains amorphous silica, and a content of the amorphous silica is 50 parts by mass or greater and 90 parts by mass or less with respect to 100 parts by mass of the inorganic binder. <26> The inorganic coated sand according to any one of <13> to <25>, in which the inorganic coated sand contains amorphous silica, and the content of the amorphous silica in the inorganic binder layer is 20% by mass or greater and 45% by mass or less. <27> The inorganic coated sand according to <25> or <26>, in which the amorphous silica contains 80% by mass or greater of amorphous silica particles. <28> The inorganic coated sand according to any one of <25> to <27>, in which the amorphous silica contains substantially 100% by mass of amorphous silica particles. <29> The inorganic coated sand according to any one of <25> to <28>, in which the amorphous silica particles have a degree of amorphization of 90% or greater, and an average particle diameter of the amorphous silica particles is 0.1 µm or greater and 2.0 µm or less. Examples

[0127] Hereinafter, the present invention will be described with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

[0128] First, raw materials used in the following examples are shown.(Raw Materials Used to Produce Inorganic Coated Sand)

[0129] · Refractory Aggregate Mikawa silica sand R6 (manufactured by Mikawa Silica Sand Kabushiki Kaisha, average particle diameter: 200 µm, sphericity: 0.85) · Inorganic Binder Sodium metasilicate nonahydrate (Na 2 SiO 3 ·9H 2 O) (manufactured by Nippon Chemical Industrial CO., LTD.) No. 1-50 water glass (SiO 2 / Na 2 O = 2.1) (manufactured by FUJI CHEMICAL CO., LTD.: 45% by mass of aqueous solution) · Amorphous Silica Fine Particles Denka molten silica SFP-20M (average particle diameter d 50 : 0.4 µm, degree of amorphization: 99.5% or greater) (manufactured by Denka Company Limited) · Vein graphite Vein graphite -280 (manufactured by Mihara Carbon Co., Ltd., average particle diameter: 62.0 µm) · Earthy Graphite Earthy graphite G3 (manufactured by Mihara Carbon Co., Ltd., average particle diameter: 16.5 µm) · Mica Muscovite 200M (manufactured by Kirara Corporation, average particle diameter: 16.5 µm) · Zirconium Silicate Zircosil No. 2K (manufactured by HAKUSUI TECH, average particle diameter: 7.0 µm) (Raw Material Used for Casting Test)

[0130] · Refractory Aggregate Mikawa silica sand R6 (manufactured by Mikawa Silica Sand Kabushiki Kaisha, average particle diameter: 200 µm) · Binder Kao Step SH-8010 (manufactured by Kao-Quaker Company, Limited) Kao Step DH-25 (manufactured by Kao-Quaker Company, Limited) <Examples 1 to 7>

[0131] In Examples 1 to 6, Mikawa silica sand R6 (100 parts by mass) was put into a mixer as a refractory aggregate. Next, the additive in the amount shown in Table 1 was put into a mixer and then kneaded for 30 seconds, and sodium metasilicate nonahydrate (3.50 parts by mass), which was heated to 80°C and melted, was then put into the mixer. After kneading the mixture for 4 minutes, amorphous silica fine particles (1.05 parts by mass) were further put and kneaded for 2 minutes to obtain inorganic coated sands of Examples 1 to 6.

[0132] In Example 7, inorganic coated sand of Example 7 was obtained in the same manner as in Examples 1 to 6, except that the amorphous silica fine particles were not put.

[0133] Table 1 shows a blending composition of the inorganic coated sand.<Examples 8 to 13>

[0134] Mikawa silica sand R6 (100 parts by mass) obtained by heating to about 120°C as a refractory aggregate was put into the mixer. Next, the additive in the amount shown in Table 2 was put into the mixer and kneaded for 30 seconds, and then No. 1-50 water glass (3.50 parts by mass) was put into the mixer and kneaded to evaporate the water, and the mixture was stirred for about 3 minutes until the sand grain clumps collapsed to obtain inorganic coated sands of Examples 8 to 13. Table 2 shows a blending composition of the inorganic coated sand.<Comparative Example 1>

[0135] Inorganic coated sand of Comparative Example 1 was obtained in the same manner as in Examples 1 to 7 except that the additive was not added. Table 1 shows a blending composition of the inorganic coated sand.<Comparative Example 2>

[0136] Inorganic coated sand of Comparative Example 2 was obtained in the same manner as in Examples 8 to 13 except that the additive was not added. Table 2 shows a blending composition of the inorganic coated sand.(Evaluation Method)

[0137] A casting mold was manufactured by using the inorganic coated sand obtained in each Example by the following method, and the casting was evaluated. The evaluation results are shown in each table.(Manufacture of Casting Mold)<Examples 1 to 7 And Comparative Example 1>

[0138] A die of test pieces (5 pieces) of 22.3 × 22.3 × 180 mm was heated to 180°C. As for the inorganic coated sand of each example, the inorganic coated sand was filled into the die at a blow pressure of 0.3 MPa using a CSR-43 blow molding machine. The inorganic coated sand was then left for 150 seconds in the molding die to be cured to obtain a casting mold test piece.<Examples 8 to 13 And Comparative Example 2>

[0139] Water (1.75 part by mass) was added to the inorganic coated sand (100 parts by mass) in advance and kneaded for 2 minutes, and the inorganic coated sand was then filled into the molding die by the same operation as in Examples 1 to 7 and Comparative Example 1 to obtain a casting mold test piece.(Casting Evaluation)

[0140] A casting test was performed using the casting mold test pieces prepared in Examples 1 to 13 and Comparative Examples 1 and 2. Fig. 1 is a sectional view for illustrating a schematic configuration of a casting test mold.

[0141] That is, a main mold shown in Fig. 1 was produced using kneaded sand that is prepared by kneading, with the mixer, Mikawa silica sand R6 (100 parts by mass), Kao step SH-8010 (1.2 parts by mass), and Kao step DH-25 (0.24 parts by mass). The main mold was composed of an upper mold 103a and a lower mold 103b, and had a width (in a horizontal direction in Fig. 1) of 340 mm, a depth (perpendicular to the sheet of Fig. 1) of 250 mm, and a height, which is from a bottom of the lower mold 103b to a top of the upper mold 103a, of 200 mm.

[0142] The casting mold test pieces prepared in Examples 1 to 13 and Comparative Examples 1 and 2 were set as a core 101 in the main mold, and an aluminum alloy (corresponding to AC7A) (8.5 kg) having a casting temperature of 720°C was poured from a sprue 105. After cooling, the casting mold test piece (core 101) was removed from the cast, the cast was cut, and a portion where the casting mold test piece (core 101) is in contact with the cast was visually observed.

[0143] A case where an area where sand is burned in a portion, in which the casting mold test piece (core 101) is in contact with the cast, is less than 1% of the entire portion, in which the casting mold (core 101) is in contact with the cast, was evaluated as "4", a case where the area is 1% or greater and less than 5% was evaluated as "3", a case where the area is 5% or greater and less than 10% was evaluated as "2", and a case where the area is 10% or greater was evaluated as "1".[Table 1]

[0144] Table 1Inorganic coated sandContent of additive in inorganic binder layer (% by mass)Content of additive with respect to 100 parts by mass of solid content of inorganic binder (parts by mass)Content of inorganic binder layer with respect to 100 parts by mass of refractory aggregate (parts by mass)Content of inorganic binder in inorganic binder layer (% by mass)Sand burning on surface of castRefractory aggregateInorganic binder layerInorganic binderAdditivesAmorphous silicaTypeParts by massTypeParts by massSodium metasilicate (parts by mass)TypeParts by massparts by massExample 1Mikawa silica sand R6100Sodium metasilicate nonahvdrate3.501.50Earthy graphite0.351.0512.123.32.9051.74Example 2Mikawa silica sand R6100Sodium metasilicate nonahvdrate3.501.50Vein graphite0.181.056.411.72.7355.03Example 3Mikawa silica sand R6100Sodium metasilicate nonahvdrate3.501.50Vein graphite0.351.0512.123.32.9051.74Example 4Mikawa silica sand R6100Sodium metasilicate nonahvdrate3.501.50Vein graphite0.701.0521.546.73.2546.24Example 5Mikawa silica sand R6100Sodium metasilicate nonahvdrate3.501.50Mica0.351.0512.123.32.9051.74Example 6Mikawa silica sand R6100Sodium metasilicate nonahvdrate3.501.50Zirconium silicate0.701.0521.546.73.2546.24Example 7Mikawa silica sand R6100Sodium metasilicate nonahvdrate3.501.50Vein graphite0.350.0018.923.31.8581.14Comparative Example 1Mikawa silica sand R6100Sodium metasilicate nonahvdrate3.501.50-0.001.05002.5558.81 [Table 2]

[0145] Table 2Inorganic coated sandContent of additive in inorganic binder layer (% by mass)Content of additive with respect to 100 parts by mass of solid content of inorganic binder (parts by mass)Content of inorganic binder layer with respect to 100 parts by mass of refractory aggregate (parts by mass)Content of inorganic binder in inorganic binder layer (% by mass)Sand burning on surface of castRefractory aggregateInorganic binder layerInorganic binderAdditivesTypeParts by massTypeParts by massSolid content (Parts by mass)TypeParts by massExample 8Mikawa silica sand R6100No. 1-50 water glass3.501.60Earthy graphite0.3718.823.11.9781.24Example 9Mikawa silica sand R6100No. 1-50 water glass3.501.60Vein graphite0.1910.611.91.7989.43Example 10Mikawa silica sand R6100No. 1-50 water glass3.501.60Vein graphite0.3718.823.11.9781.24Example 11Mikawa silica sand R6100No. 1-50 water glass3.501.60Vein graphite0.7531.946.92.3568.14Example 12Mikawa silica sand R6100No. 1-50 water glass3.501.60Mica0.3718.823.11.9781.24Example 13Mikawa silica sand R6100No. 1-50 water glass3.501.60Zirconium silicate0.7531.946.92.3568.14Comparative Example 2Mikawa silica sand R6100No. 1-50 water glass3.501.60-0.00001.60100.01

[0146] It can be seen from Tables 1 and 2 that in Examples 1 to 13, sand burning on a surface of the cast is reduced compared to Comparative Examples 1 and 2.REFERENCE SIGNS LIST

[0147] 101 core 103a upper mold 103b lower mold 105 sprue

Claims

1. A method for reducing sand burning in a cast by a casting mold, which is manufactured using inorganic coated sand including a refractory aggregate and an inorganic binder layer formed on a surface of the refractory aggregate, wherein the inorganic binder layer contains one or more selected from the group consisting of graphite, mica, and zirconium silicate, and a total content of the graphite, the mica, and the zirconium silicate is 7 parts by mass or greater and 70 parts by mass or less with respect to 100 parts by mass of an inorganic binder.

2. The method for reducing sand burning in a cast according to Claim 1, wherein a content of the inorganic binder layer in the inorganic coated sand with respect to 100 parts by mass of the refractory aggregate is 0.05 parts by mass or greater and 10 parts by mass or less.

3. The method for reducing sand burning in a cast according to Claim 1 or 2, wherein the inorganic binder contains at least one selected from the group consisting of sodium silicate and sodium metasilicate.

4. The method for reducing sand burning in a cast according to Claim 3, wherein a total content of the sodium silicate and the sodium metasilicate in the inorganic binder is 80% by mass or greater.

5. The method for reducing sand burning in a cast according to any one of Claims 1 to 4, wherein a content of the inorganic binder in the inorganic binder layer is 35% by mass or greater and 93% by mass or less.

6. The method for reducing sand burning in a cast according to any one of Claims 1 to 5, wherein the graphite, the mica, and the zirconium silicate have an average particle diameter of 3.0 µm or greater and 80 pm or less.

7. The method for reducing sand burning in a cast according to any one of Claims 1 to 6, wherein the total content of the graphite, the mica, and the zirconium silicate in the inorganic binder layer is 4% by mass or greater and 35% by mass or less.

8. Inorganic coated sand comprising: a refractory aggregate; and an inorganic binder layer formed on a surface of the refractory aggregate, wherein the inorganic binder layer contains one or more selected from the group consisting of graphite, mica, and zirconium silicate, and a total content of the graphite, the mica, and the zirconium silicate is 7 parts by mass or greater and 70 parts by mass or less with respect to 100 parts by mass of an inorganic binder.

9. The inorganic coated sand according to Claim 8, wherein a content of the inorganic binder layer in the inorganic coated sand with respect to 100 parts by mass of the refractory aggregate is 0.05 parts by mass or greater and 10 parts by mass or less.

10. The inorganic coated sand according to Claim 8 or 9, wherein the inorganic binder contains at least one selected from the group consisting of sodium silicate and sodium metasilicate.

11. The inorganic coated sand according to Claim 10, wherein a total content of the sodium silicate and the sodium metasilicate in the inorganic binder is 80% by mass or greater.

12. The inorganic coated sand according to any one of Claims 8 to 11, wherein a content of the inorganic binder in the inorganic binder layer is 35% by mass or greater and 93% by mass or less.

13. The inorganic coated sand according to any one of Claims 8 to 12, wherein the graphite, the mica, and the zirconium silicate have an average particle diameter of 3.0 µm or greater and 80 pm or less.

14. The inorganic coated sand according to any one of Claims 8 to 13, wherein the total content of the graphite, the mica, and the zirconium silicate in the inorganic binder layer is 4% by mass or greater and 35% by mass or less.

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