Inorganic coated sand in dry state, method for manufacturing inorganic coated sand in dry state, and method for manufacturing mold

Abstract

To provide a method for manufacturing inorganic coated sand, capable of shortening a time required for drying during manufacturing of the inorganic coated sand.SOLUTION: A method for manufacturing dry inorganic coated sand in a dry state having a fire-resistant aggregate and an inorganic binder layer formed on a surface of the fire-resistant aggregate, includes a step of mixing the fire-resistant aggregate, inorganic coated sand for crystallization, and liquid metasilicate hydrate, wherein a blended amount of the inorganic coated sand for crystallization is 0.1 mass% or more and 15 mass% or less of the total amount of the inorganic coated sand in the dry state.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a dry inorganic coated sand, a method for producing the dry inorganic coated sand, and a method for producing a casting mold. [Background technology]

[0002] As a mold used for casting of castings, for example, one obtained by molding into a desired shape using inorganic coated sand having refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate is known. Examples of technologies relating to such inorganic coated sand include those described in Patent Document 1 (JP 2020-11296 A) and Patent Document 2 (JP 53-025803 B).

[0003] Patent Document 1 discloses a dry inorganic coated sand having a refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate, in which the inorganic binder layer contains one or more metasilicate hydrates selected from sodium metasilicate pentahydrate and sodium metasilicate nonahydrate.

[0004] Patent Document 2 describes a method for producing a mold, which comprises adding an alkali metasilicate solution prepared by adding a caustic alkali to water glass to refractory particles such as silica sand and kneading the solution with the refractory particles, or further adding an alcohol during kneading, thereby precipitating and coating a crystalline alkali silicate on the surfaces of the refractory particles such as silica sand, and then adding and mixing fine dust generated during Fe-Si refining and mainly composed of SiO2 to produce a powder-and-granular mixed sand, which is then heated to at least the melting temperature of the crystalline alkali silicate and hardened. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2020-11296 A [Patent Document 2] Special Publication No. 53-025803 Summary of the Invention [Problem to be solved by the invention]

[0006] According to the inventors' investigations, it has been found that the conventional inorganic coated sands disclosed in Patent Documents 1 and 2 have room for improvement in terms of shortening the time required for the inorganic binder to solidify on the surface of the refractory aggregate and for the inorganic coated sand to become dry in the process of forming an inorganic binder layer on the refractory aggregate. [Means for solving the problem]

[0007] Therefore, the present inventors have conducted extensive research to shorten the drying time during the production of inorganic coated sand, and have come up with the idea of ​​using inorganic coated sand, on which an inorganic binder layer has already been formed on the surface of a refractory aggregate, as a crystallization promoter for the inorganic binder (for crystallizing the inorganic binder). As a result of further research, the inventors have found that, when forming an inorganic binder layer on a refractory aggregate, mixing a specific amount of inorganic coated sand for crystallization can effectively promote the crystallization of the inorganic binder, and can form an inorganic binder layer on the surface of the refractory aggregate in a short time, thereby completing the present invention.

[0008] According to the present invention, there is provided a method for producing dry inorganic coated sand having a refractory aggregate and an inorganic binder layer formed on a surface of the refractory aggregate, comprising the steps of: The method includes a step of mixing a refractory aggregate, an inorganic coated sand for crystallization, and a liquid metasilicate hydrate, The method for producing dry coated inorganic sand is provided, in which the amount of the inorganic coated sand for crystallization is 0.1 mass % or more and 15 mass % or less based on the total amount of the dry coated inorganic sand.

[0009] The present invention also provides a method for producing a mold using the dry inorganic coated sand obtained by the above-mentioned method for producing dry inorganic coated sand.

[0010] According to the present invention, there is also provided a dry inorganic coated sand having a refractory aggregate and an inorganic binder layer formed on a surface of the refractory aggregate, There is provided a dry inorganic coated sand, in which the particles of the dry inorganic coated sand contain particles in which the inorganic binder layer has a multi-layer structure. Effect of the Invention

[0011] According to the present invention, a method for producing dry inorganic coated sand can be provided, which can shorten the drying time during the production of the inorganic coated sand. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, the embodiments of the present invention will be described. In addition, in this specification, "A to B" indicating a numerical range means a range from A to B, including both ends, unless otherwise specified. In addition, the components and elements described in each embodiment can be appropriately combined as long as the effect of the invention is not impaired. In the present application, the term "dry inorganic coated sand" refers to inorganic coated sand that has fluidity at room temperature, and more specifically, refers to coated sand that provides a measured value when measuring the dynamic angle of repose regardless of the moisture content.

[0013] <Manufacturing method of dry inorganic coated sand> The method for producing dry inorganic coated sand of the present embodiment is a method for producing dry inorganic coated sand having a refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate, The method includes a step of mixing a fire-resistant aggregate, inorganic coated sand for crystallization, and liquid metasilicate hydrate, and the amount of the inorganic coated sand for crystallization is 0.1 mass % or more and 15 mass % or less based on the total amount of the dry inorganic coated sand (the amount of inorganic coated sand obtained after the final step).

[0014] This makes it possible to shorten the drying time when producing dry inorganic coated sand. Although the details of the reason for this are not clear, it is speculated as follows. First, when forming an inorganic binder layer on the surface of the refractory aggregate, it is necessary to solidify the inorganic binder on the surface of the refractory aggregate. Therefore, in this embodiment, it is considered that by mixing an appropriate amount of inorganic coated sand for crystallization into the particle group of the refractory aggregate, the inorganic coated sand for crystallization functions as a crystal nucleus and can promote the crystallization of metasilicate hydrate (inorganic binder). In addition, it is predicted that the strength of a mold using dry inorganic coated sand will decrease if particles other than the inorganic coated sand are mixed in with the particle group of the dry inorganic coated sand. However, in this embodiment, the inorganic coated sand itself is mixed in as a crystallization promoter, so that good mold strength can be maintained. Furthermore, a method of adding metasilicate hydrate crystals themselves as crystal nuclei can also be considered, but the use of inorganic coated sand for crystallization allows the addition of finer crystals formed on the sand surface as crystal nuclei rather than adding metasilicate hydrate crystals, thereby further promoting the crystallization of metasilicate hydrate.

[0015] Details are explained below.

[0016] (Mixing process) First, an inorganic coated sand for crystallization is prepared. Any known inorganic coated sand can be used as the inorganic coated sand for crystallization, but it is preferable that the inorganic coated sand contains metasilicate hydrate in order to facilitate the promotion of crystallization. More specifically, the inorganic coated sand for crystallization may be a known inorganic coated sand, and is a refractory aggregate having a surface covered with an inorganic binder layer. The inorganic binder layer is obtained from an inorganic binder containing metasilicate hydrate. Details of the refractory aggregate and the inorganic binder layer are the same as those of the refractory aggregate and the inorganic binder layer for the dry inorganic coated sand described later. In addition, inorganic coated sand that has been produced in advance and remains in the mixer can be used as the inorganic coated sand for crystallization as it is, allowing the same mixer to be used as is and increasing continuous productivity.

[0017] Next, the refractory aggregate, the inorganic coated sand for crystallization, and the liquid metasilicate hydrate are mixed to obtain a mixture. The amount of inorganic coated sand for crystallization is 0.1 mass% or more, and preferably 0.2 mass% or more, based on the total amount of dry inorganic coated sand finally obtained, from the viewpoint of facilitating crystallization, and more preferably 0.4 mass% or more from the viewpoint of reducing the amount of lumps (large clumps of inorganic coated sand aggregated together). On the other hand, from the viewpoint of facilitating crystallization, the amount of inorganic coated sand for crystallization is 15 mass % or less, preferably 12 mass % or less, and more preferably 10 mass % or less, based on the total amount of dry inorganic coated sand finally obtained.

[0018] In order to facilitate the promotion of crystallization, the amount of the inorganic coated sand for crystallization is preferably 0.2 mass % or more, more preferably 0.3 mass % or more, and even more preferably 0.4 mass % or more, relative to the refractory aggregate mixed in this mixing step. On the other hand, from the viewpoint of facilitating crystallization, the amount of the inorganic coated sand for crystallization is preferably 15 mass % or less, and more preferably 12 mass % or less, relative to the refractory aggregate mixed together in this mixing step.

[0019] This step of obtaining a mixture may include the following steps (i) or (ii). In either case, the crystallization is promoted by the use of inorganic coated sand for crystallization. (i) The method includes a step of mixing a fire-resistant aggregate with an inorganic coated sand for crystallization to obtain a mixture (hereinafter also referred to as a "sand mixture"), and a step of further mixing the obtained mixture with liquid metasilicate hydrate, in this order. (ii) The method includes, in this order, a step of mixing a refractory aggregate with a liquid metasilicate hydrate to obtain a mixture, and a step (post-mixing step) of further mixing the obtained mixture with inorganic coated sand for crystallization.

[0020] In the above case of (i), the mixing conditions such as the stirring speed and processing time when mixing the refractory aggregate and the inorganic coated sand for crystallization can be appropriately determined depending on the processing amount of the mixture, and can be, for example, the following conditions. The mixing time may be, for example, 5 seconds or more from the viewpoint of sufficient mixing, and 180 seconds or less from the viewpoint of shortening the production time.

[0021] In the above case (i), the temperature of the refractory aggregate and the temperature of the inorganic coated sand for crystallization are preferably set to be lower than the melting temperature of the inorganic binder layer of the inorganic coated sand for crystallization from the viewpoint of shortening the drying time. That is, in order for the inorganic binder layer of the inorganic coated sand for crystallization to function as a crystallization promoter, it is important that the inorganic binder layer is not melted. For example, when the inorganic binder layer of the inorganic coated sand for crystallization is formed of sodium metasilicate nonahydrate, the temperature of the refractory aggregate and the temperature of the inorganic coated sand for crystallization are preferably lower than the melting temperature of the sodium metasilicate nonahydrate, 47°C.

[0022] In the above case of (i), the particles of the refractory aggregate and the particles of the inorganic coated sand for crystallization may be mixed together at once, or the particles of the inorganic coated sand for crystallization may be added to the particles of the refractory aggregate in several batches.

[0023] In the above case of (ii), the mixing conditions such as the stirring speed and processing time when mixing the refractory aggregate and the liquid metasilicate hydrate can be appropriately determined depending on the processing amount of the mixture, as in the above case of (i).

[0024] In the above case of (ii), the particle group of the inorganic coated sand for crystallization may be mixed all at once, or the particle group of the inorganic coated sand for crystallization may be added in several batches. The mixing conditions when and after adding the inorganic coated sand for crystallization may be appropriately determined according to the amount of the mixture to be processed, as in the above case of (i).

[0025] In both of the above (i) and (ii), when the average particle size (μm) of the refractory aggregate in the finally obtained dry inorganic coated sand is SA1 and the average particle size (μm) of the refractory aggregate in the inorganic coated sand for crystallization is SA2, the average particle size ratio (SA2 / SA1) is, from the viewpoint of shortening the drying time, preferably 1.6 or less, more preferably 1.4 or less, even more preferably 1.0 or less, and even more preferably 0.9 or less. Similarly, from the viewpoint of shortening the drying time, it is preferably 0.3 or more, more preferably 0.4 or more. In other words, a small average particle size ratio (SA2 / SA1) means that the average particle size of the inorganic coated sand for crystallization is smaller than the average particle size of the fire-resistant aggregate of the finally obtained dry inorganic coated sand. It is believed that by making the average particle size ratio (SA2 / SA1) small, the inorganic coated sand for crystallization can more easily function as a crystallization accelerator.

[0026] Furthermore, when the average particle size (μm) of the finally obtained dry inorganic coated sand is CS1 and the average particle size (μm) of the inorganic coated sand for crystallization is CS2, for the same reasons as for the refractory aggregate, the average particle size ratio (CS2 / CS1) is preferably 1.6 or less, more preferably 1.4 or less, even more preferably 1.0 or less, still more preferably 0.9 or less, and on the other hand, is preferably 0.3 or more, more preferably 0.4 or more.

[0027] The average particle size of the refractory aggregate is measured by the same method as that for measuring the average particle size of the inorganic coated sand described below.

[0028] By using the liquid metasilicate hydrate, the surface of the refractory aggregate can be coated with the liquid metasilicate hydrate, and an inorganic binder layer can be formed to coat the surface of the refractory aggregate. The term "liquid" means that the liquid has flowability and viscosity.

[0029] The liquid metasilicate hydrate may be (a) a molten metasilicate hydrate obtained by heating to a temperature equal to or higher than the melting temperature of metasilicate hydrate, or (b) a mixed liquid obtained by mixing water glass, caustic alkali, and water in a specific ratio. (a) The temperature equal to or higher than the melting temperature of metasilicate hydrate can be specifically, for example, 47°C to 100°C. Also, (b) a mixture of water glass, caustic alkali, and water in a specific ratio refers to a mixture that remains in a liquid state even at or below the melting point of the metasilicate hydrate obtained from the mixture.

[0030] (Metasilicate hydrate) The metasilicate hydrate is one of the components of the inorganic binder layer and is also one of the components of the inorganic binder. The use of the metasilicate hydrate is preferable because it can improve the crystallinity of the inorganic binder layer, and furthermore, the inorganic coated sand becomes a dry state and has excellent fluidity at room temperature. In addition, the use of the metasilicate hydrate allows the inorganic binder layer to be formed on the surface of the refractory aggregate without being dissolved in water. That is, in the process of producing the inorganic coated sand, since it is not necessary to use an aqueous solution of the metasilicate hydrate, the process of removing water can be omitted, and the production method can be simplified. In addition, since the metasilicate of the inorganic binder layer is a hydrate, it is not necessary to ventilate the mold with water vapor to harden the mold, and the equipment can be simplified. The metasilicate hydrate can also be produced by using a mixed liquid in which water glass, caustic alkali, and water are mixed in a specific ratio. The SiO2 / Na2O molar ratio of the metasilicate hydrate in this embodiment is 0.9 to 1.1.

[0031] Specific examples of water glass include one or more types selected from the group consisting of sodium silicate No. 1 to No. 5. Sodium silicate is classified into No. 1 to No. 5 based on the molar ratio of SiO2 / Na2O, and sodium silicate No. 1 to No. 3 are specified in JIS-K-1408. The molar ratio of SiO2 / Na2O for each type is specifically as follows: Sodium silicate No. 1: SiO2 / Na2O molar ratio = 2.0-2.3 Sodium silicate No. 2: SiO2 / Na2O molar ratio = 2.4-2.6 Sodium silicate No. 3: SiO2 / Na2O molar ratio = 2.8-3.3 Sodium silicate No. 4: SiO2 / Na2O molar ratio = 3.3-3.5 Sodium silicate No. 5: SiO2 / Na2O molar ratio = 3.6-3.8 Moreover, two or more kinds of sodium silicate may be mixed to adjust the molar ratio of SiO2 / Na2O to a desired level. The water glass is preferably at least one selected from sodium silicate No. 1 and sodium silicate No. 2.

[0032] The salt of metasilicate hydrate is preferably an alkali metal, more preferably one or more selected from lithium, sodium, and potassium, more preferably at least one of sodium and potassium, and even more preferably sodium.

[0033] In the case of (i) above, examples of the method for mixing the sand mixture (a mixture of refractory aggregate and inorganic coated sand for crystallization) with liquid metasilicate hydrate include, from the viewpoint of making it easy to control the moisture content in the resulting inorganic binder layer and to obtain dry inorganic coated sand with excellent fluidity, (i)-1: a method in which liquid metasilicate hydrate is poured into a sand mixture whose temperature has been lowered below the melting point of the metasilicate hydrate and mixed; and (i)-2: a method in which a sand mixture whose temperature has been lowered below the melting point of the metasilicate hydrate is poured into liquid metasilicate hydrate and mixed.

[0034] The temperature of the liquid metasilicate hydrate to be mixed is preferably 47° C. or higher, and from the viewpoint of preventing evaporation of water, is preferably 100° C. or lower, more preferably 90° C. or lower, and even more preferably 80° C. or lower.

[0035] In addition, in the post-mixing step carried out after mixing the sand mixture with the liquid metasilicate hydrate, it is preferable to continue stirring the refractory aggregate, the inorganic coated sand for crystallization and the obtained dry inorganic coated sand so that the particles do not fuse to each other.

[0036] From the viewpoint of obtaining a high-strength casting mold, the amount of liquid metasilicate hydrate to be mixed is, for example, 0.1 parts by mass or more, preferably 0.2 parts by mass or more, more preferably 0.5 parts by mass or more, even more preferably 1 part by mass or more, and even more preferably 2 parts by mass or more, per 100 parts by mass of the refractory aggregate. In addition, from the viewpoint of obtaining a high-strength casting mold, the amount of liquid metasilicate hydrate to be mixed is, for example, 15 parts by mass or less, preferably 10 parts by mass or less, more preferably 8 parts by mass or less, even more preferably 6 parts by mass or less, and even more preferably 5 parts by mass or less, per 100 parts by mass of the refractory aggregate.

[0037] In the manner described above, an inorganic binder layer is formed on the surface of the refractory aggregate, and dry inorganic coated sand having room temperature fluidity can be obtained. The dry inorganic coated sand can contain particles having a multi-layered inorganic binder layer among the particle groups.

[0038] In the above post-mixing step, the mixture may be cooled to a temperature below the melting temperature of the metasilicate hydrate in order to reduce the fluidity of the metasilicate hydrate and fix the metasilicate hydrate to the surface of the refractory aggregate.

[0039] In order to improve the strength of the mold, it is preferable to sieve the recovered inorganic coated sand to remove aggregates (lumps). Examples of aggregates (lumps) include aggregates of inorganic coated sand. The sieve used is preferably 10 to 80 mesh. In this embodiment, the dry inorganic coated sand before the lumps are removed is also referred to as untreated dry inorganic coated sand.

[0040] <Dry inorganic coated sand> The dry inorganic coated sand of the present embodiment is a particle group made of dry inorganic coated sand having a refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate. In this embodiment, the dry inorganic coated sand contains particles in which the inorganic binder layer has a multi-layer structure. The multi-layer structure is formed by crystallizing the inorganic binder in multiple steps, and can be confirmed by observing the different crystal orientations or the interface in the cross section of the inorganic binder layer.

[0041] The content of the particles having a multilayer structure of the inorganic binder layer is preferably 0.1 mass % or more, more preferably 0.2 mass % or more, and even more preferably 0.3 mass % or more, based on the total amount of the dry inorganic coated sand. On the other hand, the content of particles having a multilayer structure of the inorganic binder layer is preferably 15 mass % or less, more preferably 12 mass % or less, and even more preferably 10 mass % or less, based on the total amount of the dry inorganic coated sand.

[0042] The dry inorganic coated sand will be described in more detail below.

[0043] The dry inorganic coated sand in this embodiment means coated sand for which a measurement value can be obtained when measuring the dynamic angle of repose. The dynamic angle of repose is preferably 80° or less, more preferably 45° or less, and even more preferably 30° or less.

[0044] The dynamic angle of repose of the dry inorganic coated sand can be measured by the following method. (Method of measuring dynamic angle of repose) Put half the volume of inorganic coated sand into a cylindrical transparent plastic bottle (diameter: 7.7 cm, height: 16 cm). Using a bottle agitator, hold the cylindrical transparent plastic bottle so that its axis is horizontal and rotate it around the horizontal axis at a rotation speed of 60 rpm for 10 seconds. The inclined surface of the inorganic coated sand layer flowing inside the cylindrical transparent plastic bottle becomes flat. Measure the angle formed between this inclined surface and the horizontal plane. Note that if the inorganic coated sand does not flow inside the cylindrical transparent plastic bottle, or if it does flow but the inclined surface of the inorganic coated sand layer does not form a flat surface, and as a result the dynamic angle of repose cannot be measured, it is in a wet state.

[0045] Specifically, the dry inorganic coated sand is composed of a group of inorganic coated sand particles.

[0046] From the viewpoint of improving the flowability and further improving the filling property into a molding die, the inorganic coated sand in a dry state is preferably spherical. Here, the spherical shape of the inorganic coated sand in a dry state means a round shape like a ball.

[0047] The sphericity of the dry inorganic coated sand is preferably 0.75 or more, more preferably 0.80 or more, and even more preferably 0.82 or more, from the viewpoints of improving fluidity, mold quality, and mold strength, and of ease of mold making. The upper limit of the sphericity is specifically 1. In this embodiment, the sphericity of the dry inorganic coated sand specifically coincides with the sphericity of the refractory aggregate described below.

[0048] The sphericity of dry inorganic coated sand is determined by analyzing the image (photograph) of the particle taken with an optical microscope or a digital scope (e.g., Keyence VH-8000) to determine the area of ​​the projected cross section of the particle and the perimeter of the cross section, and then calculating the sphericity = [area of ​​the projected cross section of the particle (mm 2 The particle diameter can be calculated by dividing the circumference (mm) of a perfect circle with the same area as the particle diameter by the circumference (mm) of the projected cross section of the particle, and then averaging the values ​​obtained for any 50 particles.

[0049] The average particle size of the dry inorganic coated sand is preferably 0.05 mm or more, more preferably 0.1 mm or more, from the viewpoints of mold quality and mold strength improvement, ease of mold making, and storage stability. In addition, if the average particle size of the dry inorganic coated sand is equal to or more than the above lower limit, the amount of coating layer, etc. used during mold production can be reduced, which is also preferable in that the dry inorganic coated sand can be easily regenerated. The average particle size of the dry inorganic coated sand is preferably 2 mm or less, more preferably 1 mm or less, and even more preferably 0.5 mm or less, from the viewpoints of improving mold quality and mold strength, and of ease of mold making. In addition, if the average particle size of the dry inorganic coated sand is equal to or less than the above upper limit, it is also preferable in that the porosity is reduced during mold production, and the mold strength can be increased.

[0050] In this embodiment, the average particle size of the dry inorganic coated sand and the inorganic coated sand for crystallization can be specifically measured by the following method. (Method of measuring average particle size) If the sphericity of the particle from the projected cross section is 1, the diameter (mm) is measured, whereas if the sphericity is <1, the long axis diameter (mm) and short axis diameter (mm) of the randomly oriented particles are measured to calculate (long axis diameter + short axis diameter) / 2, and the values ​​obtained for any 100 particles are averaged to determine the average particle size (mm). The long axis diameter and short axis diameter are defined as follows: A particle is stabilized on a flat surface, and when the projected image of the particle on the flat surface is sandwiched between two parallel lines, the width of the particle at which the distance between the parallel lines is the smallest is called the short axis diameter, whereas the distance when the particle is sandwiched between two parallel lines perpendicular to the parallel lines is called the long axis diameter. The major axis diameter and minor axis diameter of a particle can be determined by taking an image (photograph) of the particle using an optical microscope or a digital scope (for example, VH-8000 model, manufactured by Keyence Corporation) and subjecting the obtained image to image analysis.

[0051] Each component of the dry inorganic coated sand will be described below.

[0052] [Fire-resistant aggregate] The refractory aggregate is specifically composed of a group of refractory aggregate particles. The material of the fire-resistant aggregate is at least one selected from the group consisting of natural sand and artificial sand.

[0053] Examples of natural sand include one or more types selected from the group consisting of silica sand, which is mainly composed of quartz, chromite sand, zircon sand, olivine sand, and alumina sand.

[0054] Examples of artificial sand include one or more types 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 term "major component" refers to the component contained in the sand in the greatest amount. Artificial sand is not found in nature, but is found in sand that has been artificially prepared from metal oxide components and then melted or sintered.

[0055] In addition, recycled sand made from recovered refractory aggregate and recycled sand made from recycled sand that has been regenerated can also be used.

[0056] The content of each component such as SiO2, Al2O3, and Fe2O3 in the refractory aggregate can be measured using the following X-ray fluorescence method. The refractory aggregate is adjusted to a size of approximately 0.1 μm or less using a vibration mill and heated at 1050°C for 1 hour. Then, 5 g of lithium tetraborate and 0.5 g of refractory aggregate are mixed and heated at 1200°C for 10 minutes to melt, and then cooled to prepare a glassy sample (glass bead method). The sample is subjected to X-ray fluorescence analysis using the Fundamental Parameter (FP) method using an X-ray fluorescence analyzer ZSX Primus II (manufactured by Rigaku Corporation).

[0057] The sphericity of the refractory aggregate is equal to that of the dry inorganic coated sand. Specifically, 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, from the viewpoints of improving fluidity, mold quality, and mold strength, and from the viewpoints of ease of mold making. The upper limit of the sphericity is specifically 1.

[0058] The sphericity of the refractory aggregate can be measured by the same measuring method as that for the dry inorganic coated sand described above.

[0059] The average particle size of the refractory aggregate is preferably 0.05 mm or more, more preferably 0.1 mm or more, from the viewpoints of improving the quality and strength of the mold and of ease of molding the mold. In addition, when the average particle size of the refractory aggregate is equal to or more than the above lower limit, the amount of inorganic binder layer used as a coating layer during mold production can be reduced, which is also preferable in that it makes it easier to regenerate the dry inorganic coated sand. 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, from the viewpoints of improving the quality and strength of the mold and of ease of molding the mold. In addition, if the average particle size of the refractory aggregate is equal to or less than the above upper limit, it is also preferable in that the porosity is reduced during mold production and the mold strength can be increased.

[0060] The average particle size of the refractory aggregate can be measured by the same method as that for the dry inorganic coated sand described above.

[0061] The degree of amorphization of the refractory aggregate is preferably 20% or more, more preferably 30% or more, and even more preferably 40% or more, from the viewpoint of obtaining a smoother surface of the aggregate and thus improving mold strength, and from the viewpoint of obtaining low thermal expansion. The upper limit of the degree of amorphization of the refractory aggregate is not limited, but may be, for example, 100% or less, and may be 99% or less.

[0062] 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 crushed in a mortar and pressed against an X-ray glass holder of a powder X-ray diffractometer for measurement. The powder X-ray diffractometer is a Rigaku MultiFlex (CuKα light source, tube voltage 40 kV, tube current 40 mA), and the measurement is performed in the range of 2θ = 5 to 90° with a scan interval of 0.01°, a scan speed of 2° / min, and slits DS1, SS1, and RS0.3 mm. In the range of 2θ = 10° to 50°, the X-ray intensities on the low angle side and the high angle side are connected with a straight line, the area under the straight line is taken as the background, the crystallinity is calculated using the software attached to the device, and the degree of amorphousness is calculated by subtracting it from 100. 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 calculated, and the degree of amorphousness (%) is calculated using the following formula. Amorphous content (%) = halo area / (crystalline component area + halo area) x 100

[0063] There are various methods for controlling the degree of amorphization of refractory aggregate, but it is generally preferable to use a manufacturing method that rapidly cools the molten material. For example, there is a method in which the raw material is melted and rapidly cooled by crushing it with air, or a method in which it is treated in a flame and rapidly cooled. In either case, the cooling method may be appropriately selected at various speeds depending on the material and particle size. In addition, a method in which a crystallized material is once made amorphic by heat treatment and cooling treatment may also be considered.

[0064] [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 a continuous covering, and may have a discontinuous portion. The inorganic binder layer allows the mold to be formed as dry inorganic coated sand.

[0065] From the viewpoint of obtaining a high-strength casting mold, the coating amount of the inorganic binder layer contained in the dry inorganic coated sand is, for example, 0.1 parts by mass or more relative to 100 parts by mass of the refractory aggregate, preferably 0.2 parts by mass or more, more preferably 0.5 parts by mass or more, even more preferably 1 part by mass or more, and even more preferably 2 parts by mass or more. In addition, the coating amount of the inorganic binder layer contained in the dry inorganic coated sand is, for example, 15 parts by mass or less, preferably 10 parts by mass or less, more preferably 8 parts by mass or less, even more preferably 6 parts by mass or less, and even more preferably 5 parts by mass or less, relative to 100 parts by mass of the refractory aggregate, from the viewpoint of obtaining a high-strength casting mold.

[0066] The inorganic binder layer may be a single layer or multiple layers as long as it has a layer containing a metasilicate hydrate. The layer containing a metasilicate hydrate is formed from an inorganic binder composition containing a metasilicate hydrate.

[0067] From the viewpoints of improving mold strength, excellent productivity, and ease of availability, the content of metasilicate in the inorganic binder layer is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, still more preferably 98% by mass or more, and even more preferably substantially 100% by mass. The content of metasilicate in the inorganic binder refers to the content of metasilicate relative to the total components other than water in the inorganic binder layer.

[0068] The content of metasilicate (anhydride equivalent) in the inorganic binder is preferably 11% by mass or more, more preferably 40% by mass or more, from the viewpoint of improving the storage stability of the dry inorganic coated sand, while it is preferably 58% by mass or less, more preferably 50% by mass or less, from the viewpoint of improving the mold strength.

[0069] Methods for confirming that the inorganic binder layer contains metasilicate hydrate include, for example, a method in which inorganic coated sand is subjected to a grinding machine such as a mill to separate only the inorganic binder layer components, the inorganic binder layer components are analyzed by XRD, and a peak showing the crystal structure of metasilicate hydrate is confirmed; a method in which inorganic coated sand is immersed in water and stirred for a certain period of time to elute the inorganic binder layer components, the eluted components are dried, and the dried solid content is analyzed by XRD to confirm the peak showing the crystal structure of metasilicate while also analyzing the amount of water of hydration by the following method to confirm that it is metasilicate hydrate.

[0070] <Measurement of the amount of water of hydration> (1) 10 g of inorganic coated sand to which additives such as amorphous SiO2-containing fine particles have not yet been added is weighed and placed in a pre-baked and weighed crucible, and the moisture content (%) in the inorganic coated sand (A) is calculated using the mass loss (%) after heating at 900°C for 1 hour. A = [(M1-M2) / M3] x 100 (M1: total mass (g) of the crucible and inorganic coated sand before firing, M2: total mass (g) of the crucible and inorganic coated sand after firing, M3: mass (g) of the inorganic coated sand before firing) (2) Weigh out 100 g of inorganic coated sand before adding additives such as amorphous SiO2-containing fine particles, immerse in 200 mL or more of water or hot water, and stir for 1 hour or more to extract metasilicate hydrate. Filter the resulting extract to remove the refractory aggregate, and then use a rotary evaporator to remove moisture by vacuum distillation at 40°C and an internal pressure of 15 mmHg or less. Then heat and dry at a temperature of 120°C to 180°C for 1 to 3 hours, and weigh the weight of the dried material. Calculate the dry solid content (%) (B) of metasilicate hydrate in the inorganic coated sand. B = (M12 / M11) x 100 (M11: mass of inorganic coated sand (g), M12: dry weight (g)) (3) Amount of water of hydration of metasilicate hydrate = [(A) / molecular weight of water] / [(B) / molecular weight of metasilicate anhydrate]

[0071] (others) The inorganic binder layer may further contain components other than metasilicate, such as amorphous SiO2-containing fine particles, inorganic fine particles other than amorphous SiO2-containing fine particles, a humectant, a moisture resistance improver, a coupling agent that strengthens the bond between the fire-resistant aggregate and the inorganic binder composition, a lubricant, a surfactant, a release agent, etc.

[0072] Amorphous SiO2-containing fine particles may be used because of their high reactivity with metasilicate hydrate, which makes it easier to improve the mechanical strength of the mold. Examples of amorphous SiO2-containing fine particles include precipitated silica, calcined silica produced in an electric arc or by flame hydrolysis, silica produced by thermal decomposition of ZrSiO4, silicon dioxide produced by oxidation of metallic silicon with an oxygen-containing gas, and spherical particles of quartz glass powder produced from crystalline quartz by melting and subsequent rapid cooling. These can be used alone, or two or more of them can be mixed together.

[0073] The inorganic fine particles are not particularly limited as long as they are not the amorphous SiO2-containing fine particles, and examples thereof include crystalline silica, silicon; carbonates such as zinc carbonate, basic zinc carbonate, iron carbonate, manganese carbonate, copper carbonate, aluminum carbonate, barium carbonate, magnesium carbonate, calcium carbonate, lithium carbonate, potassium carbonate, and sodium carbonate; borates such as sodium tetraborate, potassium tetraborate, lithium tetraborate, ammonium tetraborate, calcium tetraborate, strontium tetraborate, silver tetraborate, sodium metaborate, potassium metaborate, lithium metaborate, ammonium metaborate, calcium metaborate, silver metaborate, copper metaborate, lead metaborate, and magnesium metaborate; sodium sulfate, potassium sulfate. Examples of fine particles include one or more types selected from sulfates such as lithium sulfate, magnesium sulfate, calcium sulfate, strontium sulfate, barium sulfate, titanium sulfate, aluminum sulfate, zinc sulfate, and copper sulfate; phosphates such as sodium phosphate, sodium hydrogen phosphate, potassium phosphate, potassium hydrogen phosphate, lithium phosphate, lithium hydrogen phosphate, magnesium phosphate, calcium phosphate, titanium phosphate, aluminum phosphate, and zinc phosphate; hydroxides such as lithium hydroxide, magnesium hydroxide, calcium hydroxide, strontium hydroxide, barium hydroxide, aluminum hydroxide, and zinc hydroxide; and oxides such as silicon, zinc, magnesium, aluminum, calcium, lithium, copper, iron, boron, and zirconium.

[0074] The coupling agent is not limited, but examples thereof include silane coupling agents, zircon coupling agents, and titanium coupling agents. Examples of the moisturizing agent include polyhydric alcohols, water-soluble polymers, hydrocarbons, sugars, proteins, and inorganic compounds other than those mentioned above. Examples of the moisture resistance improver include metal oxides (other than those listed above), carbonates, borates, sulfates, phosphates, and the like. Examples of lubricants include waxes; fatty acid amides; alkylene fatty acid amides; stearic acid; stearyl alcohol; metal stearates such as lead stearate, zinc stearate, calcium stearate, and magnesium stearate; stearic acid monoglyceride; stearyl stearate; and hardened oils. 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 particles, mica, vermiculite, fluorine-based release agents, and silicone-based release agents.

[0075] <Casting mold> Next, the casting mold according to this embodiment will be described. The casting mold according to this embodiment is manufactured using dry inorganic coated sand obtained by the manufacturing method of dry inorganic coated sand. The method for manufacturing the casting mold from dry inorganic coated sand is not particularly limited, but an example of the method is to fill a molding die with dry inorganic coated sand and, if necessary, other components, and heat and harden them. In addition, various known molding methods can be applied.

[0076] Although the embodiments of the present invention have been described above, these are merely examples of the present invention, and various configurations other than those described above may also be adopted. Furthermore, modifications and improvements within the scope of the present invention that can achieve the object of the present invention are also included in the present invention.

[0077] In relation to the above-mentioned embodiments, the present invention further discloses the following dry inorganic coated sand, a method for manufacturing the dry inorganic coated sand, and a method for manufacturing a casting mold. <1> A method for producing dry inorganic coated sand having a refractory aggregate and an inorganic binder layer formed on a surface of the refractory aggregate, comprising: The method includes a step of mixing a refractory aggregate, an inorganic coated sand for crystallization, and a liquid metasilicate hydrate, A method for producing dry inorganic coated sand, wherein the amount of the inorganic coated sand for crystallization is 0.1 mass% or more and 15 mass% or less, preferably 0.2 mass% or more, more preferably 0.4 mass% or more, preferably 12 mass% or less, and more preferably 10 mass% or less, based on the total amount of the dry inorganic coated sand. <2> <1> A method for producing the dry inorganic coated sand according to claim 1, The mixing step comprises: A step of mixing the refractory aggregate and the inorganic coated sand for crystallization to obtain a mixture; Further mixing the obtained mixture with the liquid metasilicate hydrate; A method for producing dry inorganic coated sand, comprising: <3> <1> or <2> A method for producing the dry inorganic coated sand according to claim 1, The method for producing dry inorganic coated sand, wherein the inorganic coated sand for crystallization has a refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate. <4> <3> A method for producing the dry inorganic coated sand according to claim 1, A method for producing dry inorganic coated sand, wherein the inorganic binder layer of the inorganic coated sand for crystallization contains metasilicate hydrate. <5> <1> ~ <4> A method for producing the dry inorganic coated sand according to any one of the following: A method for producing dry inorganic coated sand, wherein in the step of mixing the refractory aggregate and the inorganic coated sand for crystallization, the mixing is performed at a temperature lower than the melting temperature of the inorganic binder layer of the inorganic coated sand for crystallization. <6> <1> ~ <5> A method for producing the inorganic coated sand according to any one of the following: A method for producing dry inorganic coated sand, in which the ratio of the average particle size of the inorganic coated sand for crystallization to the average particle size of the dry inorganic coated sand (average particle size of the inorganic coated sand for crystallization / average particle size of the dry inorganic coated sand) is 0.3 or more and 0.9 or less, more preferably 0.4 or more, more preferably 1.4 or less, even more preferably 1.0 or less, and still more preferably 0.9 or less. <7> <1> ~ <6> A method for producing the inorganic coated sand according to any one of the following: The liquid metasilicate hydrate is a metasilicate hydrate melted by heating. <8> <1> ~ <7> A method for producing the dry inorganic coated sand according to any one of the following: A method for producing dry inorganic coated sand, wherein the liquid metasilicate hydrate is a mixture of water glass, caustic alkali and water. <9> <1> ~ <8> A method for producing the dry inorganic coated sand according to any one of the following: In the step of mixing the refractory aggregate, the inorganic coated sand for crystallization, and the liquid metasilicate hydrate, A method for producing dry inorganic coated sand, wherein the amount of the inorganic coated sand for crystallization is preferably 0.2 mass% or more, more preferably 0.3 mass% or more, even more preferably 0.4 mass% or more, and is preferably 15 mass% or less, more preferably 12 mass% or less, relative to the refractory aggregate. <10> <1> ~ <9> A method for producing a mold, comprising producing a mold using the dry inorganic coated sand obtained by any one of the methods for producing dry inorganic coated sand. <11> A dry inorganic coated sand having a refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate, A dry inorganic coated sand, comprising particles in which the inorganic binder layer has a multi-layer structure, the particles being included in the dry inorganic coated sand. <12> <11> The dry inorganic coated sand according to claim 1, The content of the particles having a multilayer structure of the inorganic binder layer is preferably 0.1 mass % or more, more preferably 0.2 mass % or more, even more preferably 0.3 mass % or more, and is preferably 15 mass % or less, more preferably 12 mass % or less, and even more preferably 10 mass % or less, based on the total amount of the dry inorganic coated sand. EXAMPLES

[0078] EXAMPLES Hereinafter, the present invention will be described with reference to examples and comparative examples, but the present invention is not limited to these.

[0079] (1) Material [Fire-resistant aggregate] Espearl 35L: Espearl #35L (manufactured by Yamakawa Sangyo Co., Ltd., average particle size: 574 μm, amorphous degree 40%, sphericity 0.97) Espearl 50L: Espearl #50L (manufactured by Yamakawa Sangyo Co., Ltd., average particle size: 417 μm, amorphous degree 40%, sphericity 0.97) Espearl 60L: Espearl #60L (manufactured by Yamakawa Sangyo Co., Ltd., average particle size: 305 μm, amorphous degree 45%, sphericity 0.97) Espearl 75L: Espearl #75L (manufactured by Yamakawa Sangyo Co., Ltd., average particle size: 269 μm, amorphous degree 50%, sphericity 0.97) Espearl 100L: Espearl #100L (manufactured by Yamakawa Sangyo Co., Ltd., average particle size: 121 μm, amorphous degree 72%, sphericity 0.98) ·Mikawa Silica Sand R6: Mikawa Silica Sand R6 (manufactured by Mikawa Silica Co., Ltd., average particle size: 200 μm, amorphousness 0.2%, sphericity 0.85) Mikawa Silica Sand R8: Mikawa Silica Sand R8 (Mikawa Silica Co., Ltd., average particle size: 127 μm, amorphousness 0.2%, sphericity 0.85) [Inorganic binder: metasilicate hydrate] Metasilicate 1: A mixture of sodium metasilicate nonahydrate (Na2SiO3·9H2O, Nippon Chemical Industry Co., Ltd., melting point 47°C, SiO2 / Na2O ratio = 0.9-1.1) and sodium metasilicate pentahydrate (Na2SiO3·5H2O, Nippon Chemical Industry Co., Ltd., melting point 72°C, SiO2 / Na2O ratio = 0.9-1.1) in a weight ratio of 4:3 Metasilicate 2: Aqueous solution containing water glass prepared by the following procedure

[0080] (procedure) Water glass, caustic soda (NaOH), and water were mixed in a mixer for 10 minutes in the ratio (parts by mass) shown in Table 1 below, to obtain metasilicate 2 shown in Table 1.

[0081] [Table 1]

[0082] No. 1 50 water glass: Fuji Chemical Co., Ltd., SiO2 (%) = 30.0, Na2O (%) = 14.7, solid content 44.7% by mass NaOH: Caustic soda, Fujifilm Wako Pure Chemical NaOH, granular

[0083] (2) Preparation of inorganic coated sand for crystallization Using the above-mentioned materials (1), inorganic coated sand for crystallization was prepared so that the refractory aggregate and inorganic binder were as shown in Table 2 (type, parts by mass). Specifically, the fire-resistant aggregate shown in Table 2 was placed in a mixer, and then the inorganic binder that had been heated to 80°C and melted was added to the mixer and kneaded for 4 minutes to obtain dry sand with room temperature fluidity, which was used as inorganic coated sand for crystallization.

[0084] (3) Preparation of dry inorganic coated sand Dry inorganic coated sand was prepared using the material of (1) above and the inorganic coated sand for crystallization obtained in (2) above, so that the refractory aggregate and inorganic binder were as shown in Table 2 (type, mass parts). That is, as shown in Table 2, the total amount of the refractory aggregate used in (3) and the refractory aggregate in the inorganic coated sand for crystallization was 100 parts by mass, and the total amount of the sodium metasilicate nonahydrate used in (3) and the metasilicate 1 in the inorganic coated sand for crystallization was 2 parts by mass or 3 parts by mass. Each example and comparative example will be described below.

[0085] <Example 1> The amounts of refractory aggregate (Espearl 60L: 99.70 parts by mass) and inorganic coated sand for crystallization (Espearl 60L: 0.30 parts by mass, metasilicate 1: 0.006 parts by mass) adjusted to 35°C shown in Table 2 were charged into a mixer. Next, liquid metasilicate 1 (1.994 parts by mass) that had been heated to 80 ° C. and melted was further added while stirring with the above stirrer, and uniform kneading was started. Stirring was continued, and it was confirmed that the mixture had been dried within the drying time shown in Table 2 from the start of kneading, and stirring was stopped to obtain 102 parts by mass of untreated dry inorganic coated sand having room temperature fluidity. Then, the untreated dry inorganic coated sand was sieved (20 mesh) to remove aggregates (lumps), and 101 parts by mass of dry inorganic coated sand was obtained. Therefore, the amount of inorganic coated sand for crystallization added was 0.3% by mass (0.306 parts by mass of inorganic coated sand for crystallization ÷ 101 parts by mass of total amount of dry inorganic coated sand × 100) relative to the total amount of dry inorganic coated sand. The ratio of the amount of removed lumps to the amount of untreated dry inorganic coated sand was calculated as 0.6 (mass%) of lumps (0.6 parts by mass of removed lumps ÷ 102 parts by mass of untreated dry inorganic coated sand × 100). The results are shown in Table 2.

[0086] <Examples 2 to 9 and Comparative Examples 1 to 3> The dry inorganic coated sands shown in Table 2 were obtained in the same manner as in Example 1, except that the refractory aggregate and inorganic binder were changed to those shown in Table 2 (types, parts by mass).

[0087] [Table 2]

[0088] The following notations in Table 2 have the following meanings: SA1: Average particle size (μm) of refractory aggregate used as raw material for dry inorganic coated sand SA2: Average particle size of refractory aggregate of inorganic coated sand for crystallization (μm) CS1: Average particle size of dry inorganic coated sand (μm) CS2: Average particle size of inorganic coated sand for crystallization (μm)

Claims

1. A method for producing dry inorganic coated sand comprising fire-resistant aggregate and an inorganic binder layer formed on the surface of the fire-resistant aggregate, The process includes mixing refractory aggregate, inorganic coated sand for crystallization, and liquid metasilicate hydrate. A method for producing dry inorganic coated sand, wherein the amount of the inorganic coated sand for crystallization is 0.1% by mass or more and 15% by mass or less relative to the total amount of the dry inorganic coated sand.

2. A method for producing dry inorganic coated sand according to claim 1, The mixing step described above is A step of mixing the aforementioned fire-resistant aggregate with the aforementioned inorganic coated sand for crystallization to obtain a mixture, The obtained mixture and the liquid metasilicate hydrate are further mixed. A method for producing dry inorganic coated sand, including [the specified substance].

3. A method for producing dry inorganic coated sand according to claim 1 or 2, A method for producing dry inorganic coated sand, wherein the amount of the inorganic coated sand for crystallization is 0.2% by mass or more and 15% by mass or less relative to the refractory aggregate.

4. A method for producing dry inorganic coated sand according to claim 1 or 2, A method for producing a dry inorganic coated sand, wherein the inorganic coated sand for crystallization comprises a refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate.

5. A method for producing dry inorganic coated sand according to claim 4, A method for producing dry inorganic coated sand, wherein the inorganic binder layer of the inorganic coated sand for crystallization contains metasilicate hydrate.

6. A method for producing dry inorganic coated sand according to claim 4, A method for producing dry inorganic coated sand, comprising the step of mixing the refractory aggregate and the inorganic coated sand for crystallization, wherein the mixing is performed at a temperature below the melting temperature of the inorganic binder layer of the inorganic coated sand for crystallization.

7. A method for producing inorganic coated sand according to claim 1 or 2, A method for producing dry inorganic coated sand, wherein the ratio of the average particle size of the inorganic coated sand for crystallization to the average particle size of the dry inorganic coated sand (average particle size of the inorganic coated sand for crystallization / average particle size of the dry inorganic coated sand) is 0.3 or more and 0.9 or less.

8. A method for producing inorganic coated sand according to claim 1 or 2, A method for producing dry inorganic coated sand, wherein the liquid metasilicate hydrate is a metasilicate hydrate that has been melted by heating.

9. A method for producing inorganic coated sand according to claim 1 or 2, A method for producing dry inorganic coated sand, wherein the SiO₂ / Na₂O molar ratio of the metasilicate hydrate is 0.9 to 1.

1.

10. A method for producing inorganic coated sand according to claim 1 or 2, A method for producing dry inorganic coated sand, wherein the amount of metasilicate hydrate added is 0.1 parts by mass or more and 15 parts by mass or less per 100 parts by mass of the refractory aggregate.

11. A method for producing dry inorganic coated sand according to claim 1 or 2, The liquid metasilicate hydrate is a mixture of water glass, caustic alkali, and water, in a method for producing dry inorganic coated sand.

12. A method for manufacturing a mold, comprising manufacturing a mold using dry inorganic coated sand obtained by the method for manufacturing dry inorganic coated sand according to claim 1 or 2.