Inorganic coated sand and method for producing the same

Abstract

To provide an inorganic coated sand in a dry state, capable of achieving high productivity.SOLUTION: An inorganic coated sand in a dry state has: a refractory aggregate; and an inorganic binder layer formed on a surface of the refractory aggregate. The inorganic binder layer comprises silicate and the amount (A) of Ca ion eluted into 100 g of water at 20°C per 100 g of the refractory aggregate is 10 mg / L or more.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to inorganic coated sand and a method for manufacturing the same.

Background Art

[0002] As a mold used for casting a casting, for example, a dry inorganic coated sand having a refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate is used to mold into a desired shape. What is obtained is known. Dry inorganic coated sand is obtained by solidifying a liquid inorganic binder composition on the surface of a refractory aggregate to form a layer. Then, molten metal is poured into the mold, cooled and solidified, and then the mold is broken down to obtain a desired casting.

[0003] As a technology related to conventional inorganic coated sand, for example, in Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2022-9343), an aqueous binder composition containing an alkaline water-soluble inorganic binder is added to casting sand, kneaded or mixed, and the moisture is evaporated. Thus, an inorganic coated sand in which a second coating layer made of a solid binder composition is formed on a first coating layer is described.

[0004] Further, in Patent Document 2 (International Publication No. 2021 / 140725), from the viewpoint of suppressing deformation of the mold during casting, an inorganic coated sand having a refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate is used. In the mold thus produced, an inorganic coated sand having a Ca content in the inorganic binder layer of 3% by mass or more and 45% by mass or less is described.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

[0006] The inventor has found that there is room for improvement in shortening the time until the inorganic binder composition solidifies and forms a layer on the surface of the refractory aggregate in the process of forming an inorganic bonding layer covering the refractory aggregate, as described in Patent Documents 1 and 2. Means for Solving the Problems

[0007] Therefore, as a result of intensive studies to shorten the drying time during the production of inorganic coated sand, the inventor has found that it is effective to use a refractory aggregate with a controlled elution amount of calcium ions, and has completed the present invention.

[0008] According to the present invention, there is provided a dry inorganic coated sand having a refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate, wherein the inorganic binder layer contains a silicate, and there is provided an inorganic coated sand in which the elution amount (A) of Ca ions into 100 g of water at 20°C per 100 g of the refractory aggregate is 10 mg / L or more.

[0009] Also, according to the present invention, there is provided a casting mold formed of the above inorganic coated sand.

[0010] Also, according to the present invention, there is provided a method for producing a dry inorganic coated sand having a refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate, including a step of forming the inorganic binder layer on the surface of the refractory aggregate using an inorganic binder composition containing a silicate, and there is provided a method for producing an inorganic coated sand in which the elution amount (A) of Ca ions into 100 g of water at 20°C per 100 g of the refractory aggregate is 10 mg / L or more. Advantages of the Invention

[0011] According to the present invention, a dry inorganic-coated sand capable of improving productivity can be provided.

Mode for Carrying Out the Invention

[0012] In this specification, "a~b" indicating a numerical range represents a range of a or more and b or less unless otherwise specified. Also, the configurations and elements described in each embodiment can be appropriately combined as long as the effects of the invention are not impaired. Further, in this specification, "coating" is not limited to being continuous, and may have partially discontinuous portions. Hereinafter, embodiments of the present invention will be described.

[0013] <Inorganic-coated sand> The inorganic-coated sand of this embodiment is a dry inorganic-coated sand having a refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate, wherein the inorganic binder layer contains a silicate, and the Ca ion elution amount (A) into 100 g of water at 20°C per 100 g of the refractory aggregate is 10 mg / L or more.

[0014] Thereby, the drying time during the production of the inorganic-coated sand can be shortened. Although the details of the reason are not clear, it is presumed as follows. First, when forming an inorganic binder layer on the surface of the refractory aggregate, it is necessary to solidify the inorganic binder composition on the surface of the refractory aggregate. It is considered that the Ca-containing compound present on the surface of the refractory aggregate serves as a crystal nucleus and can promote the crystallization of the inorganic binder. Therefore, it is considered that by setting the Ca ion elution amount (A) of the refractory aggregate to 10 mg / L or more, the crystallization of the inorganic binder can be promoted by an appropriate amount of the Ca-containing compound, and as a result, the drying time can be shortened and the productivity can be improved.

[0015] Hereinafter, the details will be described.

[0016] [Ca ion elution amount (A)] The amount of Ca ion elution (A) is the amount of Ca ions (mg / L) eluted from the refractory aggregate when the refractory aggregate is immersed in water at 20°C. From the refractory aggregate, metal ion species other than Ca ions such as Na, K, Mg, and Zn may be detected. However, as a result of investigations by the present inventors, the amount most correlated with the dry state of the inorganic coated sand was the amount of Ca ions.

[0017] In terms of shortening the dry state time while maintaining good initial strength of the mold, the refractory aggregate has a Ca ion elution amount (A) of 10 mg / L or more, preferably 15 mg / L or more, more preferably 20 mg / L or more, still more preferably 30 mg / L or more, still more preferably 40 mg / L or more, and still more preferably 50 mg / L or more.

[0018] On the other hand, the upper limit value of the Ca ion elution amount (A) is not particularly limited. However, if the amount of the Ca-containing compound is too large, it may hinder the improvement of the mold strength during mold making. Therefore, in terms of improving the initial strength and collapsibility of the mold while maintaining a good dry state time, the refractory aggregate preferably has a Ca ion elution amount (A) of 100 mg / L or less, more preferably 80 mg / L or less, still more preferably 60 mg / L or less, and still more preferably 55 mg / L or less.

[0019] The amount of Ca ion elution (A) can be measured by stirring the refractory aggregate in water, filtering the supernatant, pretreating it by a method conforming to JIS K 0102-5.5, and then using an ICP emission spectroscopic analyzer (for example, ICPS-8100 type manufactured by Shimadzu Corporation) by a method conforming to JIS K 0102-50.3. Note that 20°C is intended to be the temperature of water.

[0020] Also, the Ca ions may be those contained in the refractory aggregate as a calcium-containing compound. The calcium-containing compound may be either an inorganic compound or an organic compound. Examples of the calcium-containing inorganic compound include one or more selected from the group consisting of calcium oxide, calcium carbonate, calcium silicate, calcium sulfate, calcium nitrate, and calcium phosphate. Examples of the calcium-containing organic compound include fatty acid metal salts such as calcium stearate, calcium oleate, and calcium palmitate.

[0021] [Loss on Ignition (B)] Furthermore, it is preferable to control the loss on ignition (B) of the refractory aggregate by the following formula. Loss on ignition (B) (mass%) = {[mass (g) of the refractory aggregate dried at 105°C for 1 hour] - [mass (g) of the refractory aggregate heat-treated at 1000°C for 1 hour after drying at 105°C for 1 hour]} / [mass (g) of the refractory aggregate dried at 105°C for 1 hour] × 100

[0022] Specifically, from the viewpoint of improving the collapsibility while maintaining good initial strength of the mold, the loss on ignition (B) of the refractory aggregate is preferably 0.03 mass% or more, more preferably 0.05 mass% or more, still more preferably 0.07 mass% or more, and even more preferably 0.1 mass% or more. On the other hand, from the viewpoint of improving the initial strength of the mold while obtaining good collapsibility, the loss on ignition (B) is preferably 0.35 mass% or less, more preferably 0.30 mass% or less, still more preferably 0.28 mass% or less, and even more preferably 0.25 mass% or less.

[0023] The ignition loss (B) refers to the amount of reduction (mass %) of the refractory aggregate that decreases by heat-treating the refractory aggregate at 1000 °C for 1 hour under the atmosphere. The reason for such reduction is that the organic matter contained in the refractory aggregate is thermally decomposed and vaporized by heat. Therefore, by setting the ignition loss (B) of the refractory aggregate to be equal to or higher than the above lower limit value, it is considered that the organic matter on the surface of the refractory aggregate can be easily thermally decomposed by the heat during casting, moderately reducing the strength of the mold, and improving the collapsibility of the mold after casting. On the other hand, by setting the ignition loss (B) to be equal to or lower than the above upper limit value, it is considered that the initial mold strength of the inorganic-coated sand using the refractory aggregate can be maintained.

[0024] Here, the Ca ion elution amount (A) and ignition loss (B) of the above-mentioned refractory aggregate can be appropriately adjusted, for example, by selecting recycled sand, adding organic compounds and Ca-containing compounds to artificial sand or natural sand used as raw materials for the refractory aggregate, and roasting. Specifically, for example, recycled sand of resin-coated sand can be used as the refractory aggregate, or calcium stearate can be added as a lubricant to the refractory aggregate.

[0025] In addition, in the inorganic-coated sand, the Ca ion elution amount (A) and ignition loss (B) of the refractory aggregate can be confirmed, for example, as follows. The Ca ion elution amount (A) can be measured, for example, by immersing the inorganic-coated sand in water and stirring for a certain period of time to elute the metal ions in the inorganic binder layer component and on the surface of the refractory aggregate, and then analyzing the eluate with an ICP emission spectrometer to measure the Ca ion concentration. Also, for the ignition residue (B), methods such as confirming the ignition loss after heat-treating the filter residue of the inorganic-coated sand (i.e., the refractory aggregate) after eluting the metal ions in the inorganic binder layer component and on the surface of the refractory aggregate, drying it, and then heat-treating it at 1000 °C can be mentioned.

[0026] Hereinafter, the inorganic-coated sand will be described more specifically.

[0027] The inorganic coated sand is in a dry state. The dry coated sand means a coated sand for which a measured value can be obtained when measuring the dynamic angle of repose regardless of the moisture content. The dynamic angle of repose is preferably 80° or less, more preferably 45° or less, and still more preferably 30° or less.

[0028] The dynamic angle of repose of the inorganic coated sand can be measured by the following method. (Method for measuring the dynamic angle of repose) Put half of the volume of the coated sand into a cylindrical transparent plastic bottle, hold it so that the axis is horizontal, and rotate it around the horizontal axis at a rotational speed of 60 rpm for 10 minutes. The slope of the flowing coated sand layer in the cylinder becomes flat. Measure the angle formed between such a slope and the horizontal plane. In addition, when the coated sand does not flow in the cylinder, or even if it flows, the slope of the coated sand layer is not formed as a flat surface, and as a result, the dynamic angle of repose cannot be measured, it is in a wet state.

[0029] Specifically, the inorganic coated sand is composed of a group of particles of the inorganic coated sand.

[0030] From the viewpoint of improving fluidity and further improving the filling property into the molding die, the inorganic coated sand is preferably spherical. Here, the inorganic coated sand being spherical means having a round shape like a ball.

[0031] The sphericity of the inorganic coated sand is preferably 0.75 or more, more preferably 0.80 or more, and still more preferably 0.82 or more from the viewpoints of improving fluidity, mold quality and mold strength, and the ease of molding the mold. Also, specifically, the upper limit value of the sphericity is 1. In the present embodiment, specifically, the sphericity of the inorganic coated sand coincides with the sphericity of the refractory aggregate described later.

[0032] The sphericity of the inorganic-coated sand can be determined by image analysis of the images (photographs) of the particles obtained by an optical microscope or a digital microscope (e.g., VH-8000 type manufactured by Keyence Corporation). The area of the particle projection cross-section and the perimeter of the cross-section of the particles are obtained. Then, sphericity = [circumference (mm) of a perfect circle with the same area as the area (mm 2 ) of the particle projection cross-section] / [perimeter (mm) of the particle projection cross-section] is calculated, and for any 50 particles, the values obtained can be averaged.

[0033] From the viewpoints of improving the mold quality and mold strength, as well as the ease of molding the mold and storage stability, the average particle diameter of the inorganic-coated sand is preferably 0.05 mm or more, more preferably 0.1 mm or more. Also, when the average particle diameter of the inorganic-coated sand is at or above the above lower limit value, the amount of use of the coating layer, etc. can be reduced during the manufacture of the mold, which is also preferable in terms of making the regeneration of the inorganic-coated sand easier. From the viewpoints of improving the mold quality and mold strength, and the ease of molding the mold, 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. Also, when the average particle diameter of the inorganic-coated sand is at or below the above upper limit value, the porosity becomes smaller during the manufacture of the mold, which is also preferable in terms of enhancing the mold strength.

[0034] In this embodiment, the average particle diameter of the inorganic-coated sand can be specifically measured by the following method. (Method for measuring the average particle diameter) When the sphericity from the particle projection cross-section of the particle is 1, measure the diameter (mm), while when the sphericity < 1, measure the major axis diameter (mm) and minor axis diameter (mm) of the randomly oriented particles, and obtain (major axis diameter + minor axis diameter) / 2. For any 100 particles, average the values obtained respectively to obtain the average particle diameter (mm). The major axis diameter and minor axis diameter are defined as follows. When the particle is stabilized on a plane and the projection image of the particle on the plane is sandwiched between two parallel lines, the width of the particle when the distance between the parallel lines is minimized is called the minor axis diameter, while the distance when the particle is sandwiched between two parallel lines in a direction perpendicular to these parallel lines is called the major axis diameter. The major axis diameter and minor axis diameter of the particle can be obtained by photographing an image (photo) of the particle with an optical microscope or a digital microscope (for example, manufactured by Keyence Corporation, VH-8000 type) and performing image analysis on the obtained image.

[0035] Also, in order to obtain good disintegration properties, the inorganic-coated sand preferably contains an organic substance. The organic substance is not particularly limited and may be those contained in the following refractory aggregates.

[0036] Hereinafter, each component of the inorganic-coated sand will be described.

[0037] [Refractory Aggregate] Specifically, the refractory aggregate is composed of a particle group of refractory aggregates. The material of the refractory aggregate is one or more selected from the group consisting of natural sand and artificial sand.

[0038] Examples of the natural sand include one or more selected from the group consisting of silica sand mainly composed of quartz, chromite sand, zircon sand, olivine sand, and alumina sand.

[0039] Examples of artificial sand include one or more selected from the group consisting of synthetic mullite sand, SiO2-based foundry sand mainly composed of SiO2, Al2O3-based foundry sand mainly composed of Al2O3, SiO2 / Al2O3-based foundry sand, SiO2 / MgO-based foundry sand, SiO2 / Al2O3 / ZrO2-based foundry sand, SiO2 / Al2O3 / Fe2O3-based foundry sand, and slag-derived foundry sand. Here, the main component refers to the component with the highest content among the components contained in the sand. Artificial sand refers to foundry sand that is not produced naturally but is artificially prepared by adjusting the components of metal oxides and melting or sintering.

[0040] In addition, recovered sand obtained by recovering used refractory aggregates and recycled sand obtained by subjecting the recovered sand to a recycling process can also be used. Among them, recycled sand of resin-coated sand (RCS) is preferable in terms of being easy to control the ignition loss (B) and being easy to improve the collapsibility. Note that resin-coated sand is obtained by coating refractory aggregates using natural sand and / or artificial sand with resin. Therefore, the recycled sand of resin-coated sand may contain organic substances such as the base resin and curing agent. The resin-coated sand is not particularly limited, and known ones can be used. Also, the resin may be either a thermoplastic resin or a thermosetting resin, or may contain both. Specifically, for example, one or more thermosetting resins selected from among phenol resin, epoxy resin, unsaturated polyester resin, melamine resin, and polyurethane resin; one or more thermoplastic resins selected from among polyamide resins such as nylon 6 and nylon 66, polyolefin resins such as polyester and polypropylene, polyphenylene sulfide resin, polyacetal resin, polyether ether imide resin, polybutylene terephthalate resin, polyether imide resin, polyamide imide resin, and polyether sulfone resin can be mentioned.

[0041] The content of each component such as SiO2, Al2O3, and Fe2O3 in the refractory aggregate can be measured using the following fluorescent X-ray method. Adjust the refractory aggregate to a size of about 0.1 μm or less with a vibration mill and heat it at 1050 °C for 1 hour. Then, mix 5 g of lithium tetraborate and 0.5 g of the refractory aggregate, heat and melt them at 1200 °C for 10 minutes, and then cool to prepare a sample in a glassy state (glass bead method). The sample is subjected to fluorescent X-ray analysis by the Fundamental Parameter (FP) method using a fluorescent X-ray analyzer ZSX Primus II (manufactured by Rigaku Corporation).

[0042] The sphericity of the refractory aggregate is the same as that of the above-mentioned inorganic-coated sand. Specifically, from the viewpoints of fluidity, mold quality, and improvement of mold strength, and from the viewpoint of ease of mold making, the sphericity of the refractory aggregate is preferably 0.75 or more, more preferably 0.80 or more, and even more preferably 0.82 or more. Also, specifically, the upper limit value of the sphericity is 1.

[0043] The measurement method of the sphericity of the refractory aggregate can use the same measurement method as that of the above-mentioned inorganic-coated sand.

[0044] From the viewpoints of improving mold quality and mold strength and from the viewpoint of ease of mold making, the average particle size of the refractory aggregate is preferably 0.05 mm or more, more preferably 0.1 mm or more. Also, when the average particle size of the refractory aggregate is equal to or greater than the above lower limit value, the amount of the inorganic binder layer used as the second coating layer can be reduced during the manufacture of the mold, which is also preferable in terms of making the regeneration of the inorganic-coated sand easier. From the viewpoints of improving mold quality and mold strength and from the viewpoint of ease of mold making, the average particle size 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. Also, when the average particle size of the refractory aggregate is equal to or less than the above upper limit value, the porosity becomes small during the manufacture of the mold, which is also preferable in terms of increasing the mold strength.

[0045] The measurement method of the average particle diameter of the refractory aggregate can use the same measurement method as the above inorganic-coated sand.

[0046] From the viewpoints that the surface of the aggregate becomes smoother and the mold strength is further improved, and that low thermal expansion is obtained, the degree of amorphization of the refractory aggregate is preferably 20% or more, more preferably 30% or more, and still more preferably 40% or more. The upper limit of the degree of amorphization of the refractory aggregate is not limited, but for example, it may be 100% or less, or may be 99% or less.

[0047] The degree of amorphization of the refractory aggregate can be measured by the following X-ray diffraction method. (X-ray diffraction method) The refractory aggregate is pulverized in a mortar, pressed onto the X-ray glass holder of a powder X-ray diffractometer, and measured. The powder X-ray diffractometer uses Rigaku Corporation's MultiFlex (light source CuKα ray, tube voltage 40 kV, tube current 40 mA), and is performed at a scanning interval of 0.01°, a scanning speed of 2° / min, and slits DS1, SS1, and RS 0.3 mm in the range of 2θ = 5 to 90°. In the 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 under the straight line is taken as the background, the crystallinity is obtained using the software attached to the instrument, and 100 is subtracted to obtain the degree of amorphization. Specifically, for the area above the background, the amorphous peak (halo) and each crystalline component are separated by curve fitting, the area of each is obtained, and the degree of amorphization (%) is calculated by the following formula. Degree of amorphization (%) = Area of halo / (Area of crystalline component + Area of halo) × 100

[0048] There are various methods for controlling the degree of amorphization of the refractory aggregate, but generally, it is preferable to use a manufacturing method such as rapidly cooling the melt. For example, there are a method of melting the raw material, pulverizing it with air and rapidly cooling it, and a method of treating it in a flame and rapidly cooling it. In any case, the cooling method may be appropriately selected at various speeds depending on the material and particle size. Also, a method of amorphizing a once-crystallized material by heat treatment and cooling treatment is also conceivable.

[0049] [Inorganic binder layer] The inorganic binder layer is formed on the surface of the refractory aggregate. In other words, the inorganic binder layer covers the surface of the refractory aggregate. Note that the covering is not limited to being continuous, and there may be partially discontinuous portions. From the inorganic binder layer, a mold can be formed as inorganic-coated sand.

[0050] From the viewpoint of obtaining a high-strength casting mold, the coating amount of the inorganic binder layer contained in the inorganic-coated sand is, for example, 0.1 part by mass or more, preferably 0.2 part by mass or more, more preferably 0.5 part by mass or more, still more preferably 1 part by mass or more, and even more preferably 2 parts by mass or more with respect to 100 parts by mass of the refractory aggregate. Also, from the viewpoint of obtaining a high-strength casting mold, the coating amount of the inorganic binder layer contained in the inorganic-coated sand is, for example, 15 parts by mass or less, preferably 10 parts by mass or less, and more preferably 8 parts by mass or less with respect to 100 parts by mass of the refractory aggregate.

[0051] Also, the inorganic binder layer only needs to have a layer containing at least a silicate, and may be a single layer or a multilayer. Further, the layer containing at least the silicate is formed by an inorganic binder composition containing a silicate. For example, the inorganic binder layer may be a layer coated with a mixture of a silicate hydrate and the amorphous SiO2-containing fine particles described later; a layer further coated with amorphous SiO2-containing fine particles on a layer coated with a silicate hydrate; or a layer further coated with amorphous SiO2-containing fine particles on a layer coated with a mixture of a silicate hydrate and amorphous silica.

[0052] (Silicate) The inorganic binder layer contains a silicate as an inorganic binder. Specifically, examples of the silicate include silicate and metasilicate. Further, 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. Specifically, for example, one or more selected from sodium silicate, sodium metasilicate, potassium silicate, potassium metasilicate, lithium silicate, and ammonium silicate may be mentioned. Among them, sodium metasilicate and potassium metasilicate are preferable, and sodium metasilicate is more preferable. Also, the silicate may be a hydrate.

[0053] Specific examples of the above-mentioned sodium silicate include one or more selected from the group consisting of sodium silicate No. 1 to No. 5. Here, sodium silicate is classified into No. 1 to No. 5 according to the molar ratio of SiO2 / Na2O, and sodium silicate No. 1 to No. 3 are defined in JIS-K-1408. The molar ratio of SiO2 / Na2O in each grade is specifically as follows. Sodium silicate No. 1: Molar ratio of SiO2 / Na2O = 2.0 to 2.3 Sodium silicate No. 2: Molar ratio of SiO2 / Na2O = 2.4 to 2.6 Sodium silicate No. 3: Molar ratio of SiO2 / Na2O = 2.8 to 3.3 Sodium silicate No. 4: Molar ratio of SiO2 / Na2O = 3.3 to 3.5 Sodium silicate No. 5: Molar ratio of SiO2 / Na2O = 3.6 to 3.8 Also, by mixing two or more sodium silicates, the molar ratio of SiO2 / Na2O may be adjusted to a desired level. Sodium silicate is preferably water glass No. 2.

[0054] From the viewpoints of improving the mold strength, excellent productivity, and easy availability, the content of the silicate in the inorganic binder is preferably 80% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, even more preferably 98% by mass or more, and even more preferably substantially 100% by mass. The content of the silicate in the inorganic binder refers to the content of the silicate with respect to the total components other than water in the inorganic binder layer.

[0055] Also, from the viewpoint of improving the storage stability and the mold strength while increasing the content of silicate in the inorganic-coated sand, it 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 more preferably 0.7 parts by mass or more with respect to 100 parts by mass of the refractory aggregate. Also, from the viewpoint of maintaining the storage stability and improving the filling property into the molding die, the content of silicate in the inorganic-coated sand is preferably 5 parts by mass or less, more preferably 4 parts by mass or less, and still more preferably 3 parts by mass or less with respect to 100 parts by mass of the refractory aggregate.

[0056] As a method for confirming that the inorganic binder layer contains silicate, for example, a method of analyzing the components eluted by stirring the inorganic-coated sand in an aqueous hydrochloric acid solution with an ICP emission spectrometer to obtain the concentrations of silicate ions, sodium ions, etc., a method of performing elemental analysis on the surface of the inorganic-coated sand by scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDX) to confirm the presence of ions such as silicon and sodium, or 23 Na, 29 a method of confirming the structure derived from silicate by solid-state NMR of Si can be mentioned.

[0057] (Fine particles containing amorphous SiO2) The inorganic binder layer preferably further contains fine particles containing amorphous SiO2. The fine particles containing amorphous SiO2 are used from the viewpoint of high reactivity with the metasilicate hydrate. This makes it easier to improve the mechanical strength of the mold.

[0058] Examples of the fine particles containing amorphous SiO2 include precipitated silica, calcined silica produced by electric arc or flame hydrolysis, silica produced by thermal decomposition of ZrSiO4, silicon dioxide produced by oxidation of metallic silicon with a gas containing oxygen, and quartz glass powder of spherical particles produced from crystalline quartz by melting and subsequent rapid cooling. These can be used alone, and of course, two or more of them can be mixed and used.

[0059] From the perspective of more firmly binding the particles of the inorganic-coated sand via the amorphous SiO₂-containing fine particles, the degree of amorphization of the amorphous SiO₂-containing fine particles is preferably 80% or more, more preferably 90% or more, still more preferably 93% or more, even more preferably 95% or more, and particularly preferably 98% or more. The upper limit of the degree of amorphization of the amorphous SiO₂-containing fine particles is not limited, but for example, it may be 100% or less, may be 99.8% or less, or may be 99% or less.

[0060] The degree of amorphization of the amorphous SiO₂-containing fine particles can be determined by the same X-ray diffraction method as that for refractory aggregates.

[0061] The amorphous SiO₂-containing fine particles are preferably in particle form. From the perspective of improving the mold strength per unit mass and the handleability, the average particle diameter of the amorphous SiO₂-containing fine particles is preferably 0.1 μm or more, more preferably 0.3 μm or more. Also, from the perspective of improving the mold strength per unit mass, the average particle diameter of the amorphous SiO₂-containing fine particles is preferably 2.0 μm or less, more preferably 1.0 μm or less, still more preferably 0.8 μm or less, and even more preferably 0.6 μm or less.

[0062] The average particle diameter of the amorphous SiO₂-containing fine particles is determined from the observation images of a scanning electron microscope, and in this case, various image analysis methods can be used. Irregular particle selection may be performed as a pretreatment. For example, after determining the amorphous SiO₂-containing fine particles relying on elements, 100 arbitrary amorphous SiO₂-containing fine particles are selected, their particle diameters are measured, and the average value of the particle diameters of 80 amorphous SiO₂-containing fine particles excluding a total of 20 amorphous SiO₂-containing fine particles, which are 10 counted from the maximum particle diameter and 10 counted from the minimum particle diameter, can be taken as the average particle diameter of the amorphous SiO₂-containing fine particles.

[0063] The SiO₂ content (mass %) in the amorphous SiO₂-containing fine particles is preferably 50 mass % or more, more preferably 70 mass % or more, still more preferably 80 mass % or more, particularly preferably 85 mass % or more, and even more preferably 90 mass % or more from the viewpoint of improving the mold strength. The SiO₂ content (mass %) in the amorphous SiO₂-containing fine particles can be measured by the fluorescent X-ray method in the same manner as for refractory aggregates.

[0064] The content of the amorphous SiO₂-containing fine particles is preferably 0.1 part by mass or more, more preferably 0.2 part by mass or more, and preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and still more preferably 3 parts by mass or less with respect to 100 parts by mass of the refractory aggregate from the viewpoints of improving the mold strength and the mold surface shape while obtaining storage stability and suppressing dust scattering.

[0065] Also, the content of the amorphous SiO₂-containing fine particles is preferably 25 parts by mass or more, more preferably 30 parts by mass or more, and preferably 200 parts by mass or less, more preferably 150 parts by mass or less, and still more preferably 145 parts by mass or less with respect to 100 parts by mass of the silicate (anhydride conversion).

[0066] The inorganic binder layer may further contain components other than the silicate, for example, inorganic fine particles other than the amorphous SiO₂-containing fine particles, a humectant, a moisture resistance improver, a coupling agent for strengthening the bond between the refractory aggregate and the inorganic binder composition, a lubricant, a surfactant, a mold release agent, etc. However, it is preferably that none of them contains calcium.

[0067] The above-mentioned inorganic fine particles are not particularly limited. For example, crystalline silica, silicon; carbonates such as zinc carbonate, basic zinc carbonate, iron carbonate, manganese carbonate, copper carbonate, aluminum carbonate, barium carbonate, magnesium carbonate, lithium carbonate, potassium carbonate, sodium carbonate, etc.; borates such as sodium tetraborate, potassium tetraborate, lithium tetraborate, ammonium tetraborate, strontium tetraborate, silver tetraborate, sodium metaborate, lithium metaborate, ammonium metaborate, silver metaborate, copper metaborate, lead metaborate, magnesium metaborate, etc.; sulfates such as sodium sulfate, potassium sulfate, lithium sulfate, magnesium sulfate, strontium sulfate, barium sulfate, titanium sulfate, aluminum sulfate, zinc sulfate, copper sulfate, etc.; phosphates such as sodium phosphate, sodium hydrogen phosphate, potassium phosphate, potassium hydrogen phosphate, lithium phosphate, lithium hydrogen phosphate, magnesium phosphate, titanium phosphate, aluminum phosphate, zinc phosphate, etc.; hydroxides such as lithium hydroxide, magnesium hydroxide, strontium hydroxide, barium hydroxide, aluminum hydroxide, zinc hydroxide, etc.; oxides such as silicon, zinc, magnesium, aluminum, lithium, copper, iron, boron, zirconium, etc. One or more fine particles selected from the above can be mentioned.

[0068] The coupling agent is not limited, and examples thereof include silane coupling agents, zirconium coupling agents, titanium coupling agents, etc. Examples of the humectant include polyhydric alcohols, water-soluble polymers, hydrocarbons, saccharides, proteins, and inorganic compounds other than those described above. Examples of the moisture resistance improver include metal oxides (excluding those mentioned above), carbonates, borates, sulfates, phosphates, etc. Examples of the lubricant include waxes; fatty acid amides; alkylene fatty acid amides; stearic acid; stearyl alcohol; metal stearates such as lead stearate, zinc stearate, magnesium stearate, etc.; monoglyceryl stearate; stearyl stearate; hydrogenated oils, etc. Examples of the release 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, fluorine-based release agent, silicone-based release agent, and the like.

[0069] <Method for manufacturing inorganic-coated sand> Next, the method for manufacturing the inorganic-coated sand of the present embodiment will be described. The method for manufacturing the inorganic-coated sand of the present embodiment is a method for manufacturing dry inorganic-coated sand having a refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate, and includes a step of forming the inorganic binder layer on the surface of the refractory aggregate using an inorganic binder composition containing a silicate. The refractory aggregate has a metal ion elution amount (A) in water at 20°C of 10 mg / L or more. Thereby, the drying time can be shortened.

[0070] Hereinafter, an example of the method for manufacturing the inorganic-coated sand will be described in detail.

[0071] First, a refractory aggregate having a metal ion elution amount (A) in water at 20°C of 10 mg / L or more is prepared. The details of the refractory aggregate are as described above.

[0072] Next, an inorganic binder layer is formed on the surface of the refractory aggregate. Specifically, first, an inorganic binder composition containing a silicate and a refractory aggregate are mixed to prepare a mixture. Examples of the mixing method include a method of charging the inorganic binder composition into a refractory aggregate heated to about 50°C to 100°C and mixing the refractory aggregate and the inorganic binder composition while melting the silicate; a method of charging the heat-melted inorganic binder composition into the refractory aggregate and mixing; a method of charging the refractory aggregate into the inorganic binder composition dissolved in a liquid such as water and mixing; a method of mixing the refractory aggregate with an inorganic binder composition obtained by mixing water glass, caustic alkali, and water, and the like. Among these, from the viewpoint that it is easy to control the moisture content in the obtained inorganic binder layer and it is easy to obtain inorganic coated sand with excellent fluidity, a method of charging and mixing the heat-melted silicate into the refractory aggregate; a method of mixing an inorganic binder composition in which a refractory aggregate, water glass, caustic alkali, and water are mixed is preferable. Mixing conditions such as the stirring speed and treatment time when mixing each raw material can be appropriately determined according to the treatment amount of the mixture.

[0073] <Mold> The casting mold of the present embodiment is formed of the inorganic coated sand in the above-described present embodiment. Examples of the molding method of the casting mold include a molding method using a heated mold, a molding method in which steam is further passed through the heated mold and then hot air is passed through.

[0074] As described above, the embodiments of the present invention have been described, but these are examples of the present invention, and various configurations other than the above can also be adopted.

[0075] Regarding the above-described embodiments, the present invention further discloses the following inorganic coated sand, a method for manufacturing inorganic coated sand, and a method for manufacturing a casting mold.

Examples

[0076] Hereinafter, the present invention will be described with reference to examples and comparative examples, but the present invention is not limited thereto.

[0077] (1) Preparation of refractory aggregate The refractory aggregate shown in Table 1 was prepared by the following procedure. [Refractory aggregate (x1)] Mikawa R6 (manufactured by Mikawa Silica Co., average particle diameter: 200 μm, 100 parts by mass) pre-heated to 200 °C in advance was put into a stirrer. Next, 1.5 parts by mass of a novolak-type phenol resin ("SP610" manufactured by Asahi Organic Materials Co., Ltd.) was added and kneaded uniformly for 3 minutes. While continuing the stirring, 1.25 parts by mass of a curing agent (18% hexamethylenetetramine aqueous solution) was added and kneaded for 2 minutes until the formed lump disintegrated into granules. After adding 0.1 part by mass of calcium stearate, it was kneaded for 1 minute to obtain resin-coated sand (RCS). Subsequently, the resin-coated sand (RCS) was heated at 500 °C in the atmosphere for 120 minutes to obtain a refractory aggregate (x1).

[0078] [Refractory aggregates (x2) to (x4)] Refractory aggregates (x2) to (x4) were obtained respectively in the same procedure as the refractory aggregate (x1), except that the addition amounts of calcium stearate were changed to 0.4 part by mass for x2, 0.5 part by mass for x3, and 1.0 part by mass for x4.

[0079] [Refractory aggregate (y1)] A refractory aggregate (y1) was obtained in the same procedure as the refractory aggregate (x1), except that calcium stearate was not added.

[0080] [Measurement of Ca ion elution amount (A)] 50 g each of the refractory aggregates (x1) to (x4) and (y1) were used, stirred with 50 g of water (about 20 °C) and a magnetic stirrer for 15 minutes (speed 1350 rpm), and then only the supernatant was collected. Thereafter, the filtered supernatant was pretreated by a method conforming to JIS K 0102-5.5, and then the Ca ion concentration in the filtrate was measured using an ICP emission spectroscopic analyzer (ICPS-8100 type, manufactured by Shimadzu Corporation) by a method conforming to JIS K 0102-50.3. The results are shown in Table 1.

[0081]

Table 1

[0082] (2) Preparation and Evaluation of Inorganic Coated Sand Inorganic coated sand was prepared using the following materials. · Refractory aggregates (x1) to (x4), (y1): Those prepared in the above (1) were used. · Metasilicate: Sodium metasilicate (nonahydrate) (manufactured by Nippon Chemical Industry Co., Ltd., sodium metasilicate nonahydrate, melting point 47°C, SiO2 / Na2O ratio = 0.9 - 1.1) · Fine particles containing amorphous SiO2: Denka fused silica SFP-20M (manufactured by Denka Co., Ltd., average particle diameter: 0.4 μm, degree of amorphization: 99.5% or more)

[0083] [Experiment 1; Verification of Evaluation of Drying Time] Each inorganic coated sand having the composition shown in Table 1 was prepared. [Example 1-1] Refractory aggregate (x1) (100 parts by mass) was put into a stirrer. Next, metasilicate (3.0 parts by mass) heated to 80°C and melted so as to be at or above the melting point was further added while stirring with the above stirrer, and uniform kneading was started. Stirring was continued, and after confirming that drying occurred in the drying time (seconds) shown in Table 1 from the start of kneading, stirring was stopped to obtain an inorganic coated sand having room temperature fluidity. The time until drying of the refractory aggregate (x1) was measured with the time when the addition of metasilicate was completed as 0. The results are shown in Table 1.

[0084] [Example 2-1, Example 3-1, Example 4-1, Comparative Example 1-1] Except that the refractory aggregate was changed to those shown in Table 1, inorganic coated sand was obtained using each of the refractory aggregates (x2) to (x4), (y1) in the same manner as in Example 1. Also, the time until drying was measured with the time when the addition of metasilicate was completed as 0 (seconds). The results are shown in Table 1.

[0085] [Experiment 2; Verification of Initial Mold Strength and Disintegration] Each inorganic coated sand having the composition shown in Table 2 was prepared.

[0086] <Example 1-2> Inorganic-coated sand having room temperature fluidity was prepared in the same manner as in Example 1-1, and further, amorphous SiO2-containing fine particles in the amounts (parts by mass) shown in Table 2 were added and kneaded for 2 minutes to form an inorganic binder layer. Table 2 shows the compounding composition of the obtained inorganic-coated sand.

[0087] <Examples 2-2, 3-2, 4-2, 5-2, Comparative Example 1-2> Inorganic-coated sand was obtained in the same manner as in Example 1-2, except that the refractory aggregate described in Table 2 was used instead of the refractory aggregate (x1).

[0088] [Evaluation and Measurement] Using the obtained inorganic-coated sand, the following evaluations and measurements were carried out. The results are shown in Table 2.

[0089] ·Initial mold strength Using each inorganic-coated sand, a mold was prepared by the following procedure, and the mold strength was measured. The evaluation results are shown in Table 2. (Procedure) A mold for 22.3 mm × 22.3 mm × 180 mm test pieces (5 pieces) was heated to 180°C. Each inorganic-coated sand of the above examples and comparative examples was filled into the mold heated to 180°C with a CSR-43 blow molding machine at a blow pressure of 0.3 MPa, and the inorganic-coated sand was allowed to stand in the mold for 150 seconds to be cured, obtaining a mold test piece. (Measurement) Using a PFG-type universal strength testing machine manufactured by Georg Fischer Co., Ltd. with a PBV flexure attachment attached in advance, the mold strength of the mold test piece immediately after being taken out of the above mold was measured as the initial mold strength (MPa) of the mold.

[0090] ·Collapsibility: Strength reduction rate Using the obtained mold test pieces, the following test was carried out to measure the strength reduction rate. The mold test piece left in a thermo-hygrostat chamber at 25°C / 55%RH for 24 hours was heated at 500°C for 10 minutes, then left in a thermo-hygrostat chamber at 25°C / 55%RH for 1 hour, and then the mold strength (MPa) was measured. The strength reduction rate obtained by the following formula was measured and used as an index of collapsibility. Strength reduction rate (%) = 100 - 〔Mold strength (MPa) of the mold test piece left in a thermo-hygrostat chamber at 25°C / 55%RH for 24 hours, heated at 500°C for 10 minutes, and then left in a thermo-hygrostat chamber at 25°C / 55%RH for 1 hour〕 / 〔Mold strength (MPa) of the mold test piece left in a thermo-hygrostat chamber at 25°C / 55%RH for 24 hours〕 × 100

[0091]

Table 2

Claims

Claim 1 A dry inorganic coated sand having a refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate, wherein the inorganic binder layer contains a silicate, and the inorganic coated sand has a Ca ion elution amount (A) of 10 mg / L or more in 100 g of water at 20°C per 100 g of the refractory aggregate. Claim 2 The inorganic coated sand according to Claim 1, wherein the inorganic binder layer contains a metasilicate hydrate. Claim 3 The inorganic coated sand according to Claim 1 or 2, The inorganic binder layer contains amorphous SiO ２ -containing fine particles, and is an inorganic-coated sand. Claim 4 A casting mold formed of the inorganic coated sand according to any one of Claims 1 to 3. Claim 5 A method for producing a dry inorganic coated sand having a refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate, the method including a step of forming the inorganic binder layer on the surface of the refractory aggregate using an inorganic binder composition containing a silicate, wherein the Ca ion elution amount (A) in 100 g of water at 20°C per 100 g of the refractory aggregate is 10 mg / L or more.

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