Dry-form inorganic coated sand, dry-form inorganic coated sand production method, and method for producing mold

Abstract

This inorganic coated sand production method is for producing a dry-form inorganic coated sand that has a refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate, the method comprising a step for mixing a refractory aggregate, an inorganic coated sand for crystallization, and a liquid metasilicate hydrate. The blended amount of the inorganic coated sand for crystallization is 0.1-15 mass% of the total amount of the dry-form inorganic coated sand.

Description

Dry inorganic coated sand, method for manufacturing dry inorganic coated sand, and method for manufacturing mold

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

[0002] Known molds used in casting include those obtained by molding a desired shape using inorganic coated sand having a refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate. Examples of techniques related 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 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 at least one metasilicate hydrate selected from sodium metasilicate pentahydrate and sodium metasilicate nonahydrate.

[0004] In Patent Document 2, an alkali metasilicate solution prepared by adding a caustic alkali to water glass is added to refractory particles such as silica sand and kneaded together, or an alcohol is further added during kneading, so that crystalline alkali silicate is deposited and adhered to the surface of the refractory particles such as silica sand, and then SiO generated during Fe-Si refining is added to the surface of the refractory particles. ２ The document describes a method for producing a mold, which comprises heating a powder-mixed sand prepared by adding and mixing fine dust mainly composed of the above-mentioned crystalline alkali silicate to a temperature at least equal to or higher than the melting point of the above-mentioned crystalline alkali silicate, and hardening the mixture.

[0005] JP 2020-11296 A JP 53-025803 A

[0006] According to the investigations of the present inventors, it has been found that the conventional inorganic coated sand disclosed in Patent Documents 1 and 2 has 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.

[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 the surface of which an inorganic binder layer has already been formed, as a crystallization accelerator for the inorganic binder (for crystallizing the inorganic binder). As a result of further research, they have found that by mixing a specific amount of inorganic-coated sand for crystallization when forming an inorganic binder layer on a refractory aggregate, the crystallization of the inorganic binder can be effectively accelerated, and an inorganic binder layer can be formed on the surface of the refractory aggregate in a short period of time, and have completed 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 the surface of the refractory aggregate, the method comprising the step of mixing the refractory aggregate, inorganic-coated sand for crystallization, and liquid metasilicate hydrate, wherein 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.

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

[0010] The present invention also provides dry inorganic-coated sand having a refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate, wherein the particles of the dry inorganic-coated sand contain particles in which the inorganic binder layer has a multilayer structure.

[0011] According to the present invention, a method for producing dry inorganic-coated sand can be provided that can shorten the drying time during the production of inorganic-coated sand.

[0012] Hereinafter, embodiments of the present invention will be described. Furthermore, in this specification, unless otherwise specified, "A to B" indicating a numerical range represents a range from A to B inclusive, and includes both end values. Furthermore, the components and elements described in each embodiment can be combined as appropriate as long as the effects of the invention are not impaired. Furthermore, the term "dry inorganic coated sand" in this application refers to inorganic coated sand that has room temperature fluidity. More specifically, it refers to coated sand for which a measurement value can be obtained when measuring the dynamic angle of repose regardless of the moisture content.

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

[0014] This shortens the drying time required for producing dry inorganic-coated sand. While the details of the reason for this are unclear, 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, by mixing an appropriate amount of inorganic-coated sand for crystallization with the refractory aggregate particles, the inorganic-coated sand for crystallization functions as a crystal nucleus, presumably promoting the crystallization of metasilicate hydrate (the inorganic binder). Furthermore, the presence of particles other than inorganic-coated sand in the dry inorganic-coated sand particles is expected to reduce the strength of the mold used. However, in this embodiment, the inorganic-coated sand itself is mixed in as a crystallization accelerator, thereby maintaining good mold strength. 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 for 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 Step) First, inorganic-coated sand for crystallization is prepared. Known inorganic-coated sand can be used as the inorganic-coated sand for crystallization, but it preferably contains metasilicate hydrate to facilitate crystallization. More specifically, known inorganic-coated sand can be used as the inorganic-coated sand for crystallization, and the surface of the refractory aggregate is coated with an inorganic binder layer. The inorganic binder layer is obtained using an inorganic binder containing metasilicate hydrate. Details of the refractory aggregate and inorganic binder layer are the same as those for the dry inorganic-coated sand described below. Furthermore, inorganic-coated sand that has been previously produced and remains in the mixer can be used as the inorganic-coated sand for crystallization. This allows the same mixer to be used as is, improving 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 the inorganic coated sand for crystallization is 0.1% by mass or more, preferably 0.2% by mass or more, based on the total amount of the dry inorganic coated sand obtained in order to facilitate crystallization. From the viewpoint of reducing the amount of lumps (large clumps of inorganic coated sand aggregated together), the amount is more preferably 0.4% by mass or more. On the other hand, from the viewpoint of facilitating crystallization, the amount of the inorganic coated sand for crystallization is 15% by mass or less, preferably 12% by mass or less, more preferably 10% by mass or less, based on the total amount of the dry inorganic coated sand obtained in order to facilitate crystallization.

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

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

[0020] In the case of (i) above, 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 case of (i) above, the temperatures of the refractory aggregate and the inorganic-coated sand for crystallization during mixing are preferably set below 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 accelerator, 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 temperatures of the refractory aggregate and the inorganic-coated sand for crystallization are preferably set below 47°C, the melting temperature of sodium metasilicate nonahydrate.

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

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

[0024] In the case of (ii) above, the particle groups of the inorganic-coated sand for crystallization may be mixed all at once, or the particle groups 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 can be determined appropriately depending on the amount of the mixture to be processed, as in the case of (i) above.

[0025] In both of (i) and (ii) above, 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 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, from the viewpoint of shortening the drying time. 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 refractory aggregate in the finally obtained dry inorganic-coated sand. It is believed that a small average particle size ratio (SA2 / SA1) makes it easier for the inorganic-coated sand for crystallization to 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, and 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, which will be described later.

[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 that coats the surface of the refractory aggregate. The term "liquid" means that the liquid has fluidity 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) A temperature equal to or higher than the melting temperature of metasilicate hydrate may specifically be, for example, 47°C to 100°C. Furthermore, (b) a mixed liquid obtained by mixing water glass, caustic alkali, and water in a specific ratio refers to a liquid that remains in a liquid state even at a temperature equal to or lower than the melting temperature of the metasilicate hydrate obtained from the mixed liquid.

[0030] (Metasilicate hydrate) Metasilicate hydrate is one of the components constituting the inorganic binder layer and also one of the components constituting the inorganic binder. The use of 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, resulting in excellent room temperature fluidity. Furthermore, the use of metasilicate hydrate allows the inorganic binder layer to be formed on the surface of the refractory aggregate without being dissolved in water. In other words, since there is no need to use an aqueous solution of metasilicate hydrate in the process of producing inorganic coated sand, the water removal step can be omitted, thereby simplifying the production method. Furthermore, since the metasilicate of the inorganic binder layer is a hydrate, there is no need to ventilate the mold with water vapor to harden it, thereby simplifying the equipment. Furthermore, metasilicate hydrate can also be produced by using a mixed solution of water glass, caustic alkali, and water in a specific ratio. Furthermore, the SiO of metasilicate hydrate in this embodiment ２ / Na ２ The O molar ratio is 0.9 to 1.1.

[0031] Specific examples of water glass include one or more types selected from the group consisting of sodium silicates No. 1 to No. 5. Here, sodium silicate is SiO ２ / Na ２ Sodium silicates are classified into No. 1 to No. 5 according to the molar ratio of SiO to O, and sodium silicates No. 1 to No. 3 are specified in JIS-K-1408. ２ / Na ２ The molar ratio of sodium silicate No. 1 to SiO is specifically as follows:２ / Na ２ Molar ratio of Sodium silicate No. 2:SiO ２ / Na ２ Molar ratio of sodium silicate No. 3 to SiO ２ / Na ２ Molar ratio of Sodium silicate No. 4:SiO ２ / Na ２ Molar ratio of Sodium silicate No. 5:SiO ２ / Na ２ Molar ratio of SiO = 3.6 to 3.8. Also, by mixing two or more types of sodium silicate, ２ / Na ２ The molar ratio of O may be adjusted 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, and 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 viewpoints of making it easy to control the water 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 introduced into a sand mixture whose temperature has been lowered to a temperature lower than the melting point of the metasilicate hydrate, and they are mixed; and (i)-2: a method in which a sand mixture whose temperature has been lowered to a temperature lower than the melting point of the metasilicate hydrate is introduced into liquid metasilicate hydrate, and they are 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 together.

[0036] The amount of liquid metasilicate hydrate blended 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, relative to 100 parts by mass of the refractory aggregate, from the viewpoint of obtaining a high-strength casting mold. Also, the amount of liquid metasilicate hydrate blended 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.

[0037] In this manner, 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 with a multilayered inorganic binder layer among the particles.

[0038] In the post-mixing step, the mixture may be cooled to a temperature below the melting point 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] Furthermore, from the viewpoint of improving mold strength, it is preferable to sieve the recovered inorganic coated sand to remove agglomerates (lumps). Examples of agglomerates (lumps) include aggregates of inorganic coated sand. A sieve with a mesh size of 10 to 80 is preferable. 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 this embodiment is a particle group consisting 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 multilayer structure. The multilayer structure is formed by crystallizing the inorganic binder in multiple stages, and can be confirmed by different crystal orientations or by observing the interface in the cross section of the inorganic binder layer.

[0041] The content of the particles having a multilayered inorganic binder layer is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and even more preferably 0.3% by mass or more, based on the total amount of the dry inorganic-coated sand. On the other hand, the content of the particles having a multilayered inorganic binder layer is preferably 15% by mass or less, more preferably 12% by mass or less, and even more preferably 10% by 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 refers to 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 dry inorganic-coated sand can be measured by the following method. (Method for measuring the dynamic angle of repose) Half the volume of inorganic-coated sand is placed in a cylindrical transparent plastic bottle (diameter: 7.7 cm, height: 16 cm). Using a bottle agitator, the cylindrical transparent plastic bottle is held so that its axis is horizontal and rotated around the horizontal axis at a rotation speed of 60 rpm for 10 seconds. The inclined surface of the inorganic-coated sand layer flowing in the cylindrical transparent plastic bottle becomes flat. The angle formed between this inclined surface and the horizontal plane is measured. Note that if the inorganic-coated sand does not flow in the cylindrical transparent plastic bottle, or if it flows 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, the inorganic-coated sand 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 fillability into a molding die, the inorganic coated sand in a dry state is preferably spherical. Here, spherical inorganic coated sand in a dry state refers to a round shape like a ball.

[0047] From the viewpoints of improving fluidity, mold quality, and mold strength, and of ease of mold formation, 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. 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 obtained by an optical microscope or a digital scope (for example, Keyence VH-8000 model) 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 ２The particle diameter can be determined by calculating the perimeter (mm) of a circle having the same area as the particle diameter (mm) / the perimeter (mm) of the projected cross section of the particle, and 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 improving mold quality and mold strength, ease of mold production, and storage stability. Furthermore, if the average particle size of the dry inorganic-coated sand is equal to or greater than the above-mentioned lower limit, the amount of coating layer, etc. used during mold production can be reduced, making it easier to regenerate the dry inorganic-coated sand. From the viewpoints of improving mold quality and mold strength and ease of mold production, 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. Furthermore, if the average particle size of the dry inorganic-coated sand is equal to or less than the above-mentioned upper limit, the porosity during mold production is reduced, thereby increasing mold strength.

[0050] In this embodiment, the average particle size of the dry inorganic-coated sand and the inorganic-coated sand for crystallization can be measured specifically by the following method. (Method for Measuring Average Particle Size) If the sphericity of the particle from the projected cross section is 1, the diameter (mm) is measured. On the other hand, if the sphericity is <1, the major axis diameter (mm) and minor axis diameter (mm) of randomly oriented particles are measured to calculate (major axis diameter + minor axis diameter) / 2, and the average value obtained for 100 randomly selected particles is used as the average particle size (mm). The major axis diameter and minor axis diameter are defined as follows: When a particle is stabilized on a plane and its projected image on the plane is sandwiched between two parallel lines, the width of the particle at the smallest distance between the parallel lines is called the minor axis diameter, and the distance between two parallel lines perpendicular to the parallel lines when the particle is sandwiched between the parallel lines is called the major 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 analyzing the obtained image.

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

[0052] [Refractory Aggregate] The refractory aggregate is specifically composed of a group of refractory aggregate particles. The material of the refractory aggregate is one or more kinds 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 synthetic mullite sand, SiO ２ SiO ２ Al-based foundry sand ２ O ３ The main component is Al ２ O ３ Foundry sand of the SiO ２ / Al ２ O ３ Foundry sand of the SiO ２ / MgO-based foundry sand, SiO ２ / Al ２ O ３ / ZrO ２ Foundry sand of the SiO ２ / Al ２ O ３ / Fe ２ O ３ The term "main component" refers to the component that is most abundant among the components contained in the sand. Artificial sand refers to foundry sand that is not naturally occurring, but is made by artificially preparing metal oxide components and melting or sintering them.

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

[0056] In addition, SiO in the refractory aggregate ２ , Al ２ O ３ , Fe ２ O ３The content of each component, such as ammonium nitrate, ammonium nitrate, and ammonium hydroxide, can be measured using the following X-ray fluorescence method. 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, 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 a ZSX Primus II X-ray fluorescence analyzer (manufactured by Rigaku Corporation) using the fundamental parameter (FP) method.

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

[0058] The sphericity of the refractory aggregate can be measured by the same 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 mold quality and mold strength, and ease of mold production. Furthermore, when the average particle size of the refractory aggregate is equal to or greater than the above-mentioned lower limit, the amount of inorganic binder layer used as a coating layer during mold production can be reduced, making it easier to regenerate the dry inorganic-coated sand. From the viewpoints of improving mold quality and mold strength, and ease of mold production, 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. Furthermore, when the average particle size of the refractory aggregate is equal to or less than the above-mentioned upper limit, the porosity during mold production is reduced, thereby increasing mold strength.

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

[0061] The amorphization degree 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 improving mold strength by making the surface of the aggregate smoother and obtaining low thermal expansion. The upper limit of the amorphization degree of the refractory aggregate is not limited, but may be, for example, 100% or less, or may be 99% or less.

[0062] The degree of amorphization of a 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 then pressed onto an X-ray glass holder of a powder X-ray diffractometer for measurement. The powder X-ray diffractometer is a MultiFlex (CuKα radiation source, 40 kV tube voltage, 40 mA tube current) manufactured by Rigaku Denki Co., Ltd., and is measured at a scanning interval of 0.01°, a scanning speed of 2° / min, and slits DS1, SS1, and RS0.3 mm in the range of 2θ = 5° to 90°. A straight line is drawn between the low-angle and high-angle X-ray intensities in the range of 2θ = 10° to 50°, and the area under the line is used as the background. The degree of crystallinity is calculated using the software provided with the instrument and subtracted from 100 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 determined, and the amorphous degree (%) is calculated using the following formula: Amorphous degree (%) = halo area / (crystalline component area + halo area) × 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 air crushing, or a method in which it is treated in a flame and rapidly cooled. In either case, the cooling method may be selected appropriately at various speeds depending on the material and particle size. Another possible method is to amorphize a material that has been crystallized by heat treatment and cooling treatment.

[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. The coating is not limited to a continuous layer, and may have discontinuous portions. The inorganic binder layer allows the dry inorganic coated sand to be used to form a mold.

[0065] The coating amount of the inorganic binder layer contained in the dry inorganic-coated sand is, from the viewpoint of obtaining a high-strength casting mold, 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 still more preferably 2 parts by mass or more, relative to 100 parts by mass of the refractory aggregate. Furthermore, 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, from the viewpoint of obtaining a high-strength casting mold, 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 still more preferably 5 parts by mass or less, relative to 100 parts by mass of the refractory aggregate.

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

[0067] From the viewpoints of improving mold strength, excellent productivity, and easy 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 still more preferably substantially 100% by mass. The content of metasilicate in the inorganic binder refers to the content of metasilicate relative to all 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] Possible 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, and the inorganic binder layer components are analyzed by XRD to confirm peaks indicating the crystal structure of metasilicate hydrate; 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 peaks indicating the crystal structure of metasilicate, and the amount of water of hydration is analyzed by the following method to confirm that the inorganic binder layer is metasilicate hydrate.

[0070] <Measurement of the amount of water of hydration> (1) Amount of amorphous SiO ２ 10 g of inorganic coated sand before adding additives such as fine particles is weighed and placed in a container, and the amount of mass loss (%) after heating at 900°C for 1 hour is used to calculate the moisture content (%) (A) in the inorganic coated sand. 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) Amorphous SiO ２ 100 g of inorganic coated sand before the addition of additives such as fine particles is weighed, immersed in 200 mL or more of water or hot water, and stirred for at least 1 hour to extract metasilicate hydrate. The refractory aggregate is removed from the resulting extract by filtration, and the water is removed by vacuum distillation using a rotary evaporator at 40°C and an internal pressure of 15 mmHg or less. The resulting mixture is then dried by heating at a temperature of 120°C to 180°C for 1 to 3 hours, and the weight of the dried product is weighed. The dry solid content (%) (B) of metasilicate hydrate in the inorganic coated sand is calculated: B = (M12 / M11) x 100 (M11: mass (g) of inorganic coated sand, M12: weight (g) of the dried product). (3) Amount of water of hydration of metasilicate hydrate = [(A) / molecular weight of water] / [(B) / molecular weight of metasilicate anhydride]

[0071] (Others) The inorganic binder layer may further contain components other than metasilicate, for example, amorphous SiO ２ Containing fine particles, amorphous SiO２ The composition may contain inorganic fine particles other than the contained fine particles, a humectant, a moisture resistance improver, a coupling agent that strengthens the bond between the refractory aggregate and the inorganic binder composition, a lubricant, a surfactant, a mold release agent, and the like.

[0072] Amorphous SiO ２ The contained fine particles may be used from the viewpoint of high reactivity with metasilicate hydrate. This makes it easier to improve the mechanical strength of the mold. Amorphous SiO ２ The particulates contained include precipitated silica, pyrogenic silica produced in an electric arc or by flame hydrolysis, ZrSiO ４ Examples of suitable silica include silica produced by thermal decomposition of silicon dioxide, 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 may be used alone or in combination of two or more.

[0073] The inorganic fine particles are the amorphous SiO ２The additive is not particularly limited as long as it excludes the contained 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, lithium sulfate, and sulfuric acid. Examples of fine particles include one or more types selected from sulfates such as magnesium, 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] Coupling agents include, but are not limited to, silane coupling agents, zirconium coupling agents, titanium coupling agents, etc. Moisturizing agents include, for example, polyhydric alcohols, water-soluble polymers, hydrocarbons, sugars, proteins, and inorganic compounds other than those mentioned above. Moisture resistance improvers include metal oxides (excluding those listed above), carbonates, borates, sulfates, phosphates, etc. Lubricants include, for example, 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 hydrogenated oils. Mold release agents include, for example, paraffin, wax, light oil, machine oil, spindle oil, insulating oil, waste oil, vegetable oil, fatty acid esters, organic acids, graphite particles, mica, vermiculite, fluorine-based mold release agents, and silicone-based mold 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 a method for manufacturing dry inorganic-coated sand. There are no particular limitations on the method for manufacturing a casting mold from dry inorganic-coated sand, but examples include a method in which the dry inorganic-coated sand and, if necessary, other components are filled into a molding die, and then heated and hardened. Various known molding techniques can also be used.

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

[0077] In addition to the above-described embodiments, the present invention further discloses the following dry inorganic-coated sand, a method for producing dry inorganic-coated sand, and a method for producing a casting mold: <1> 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 comprising the step of mixing the refractory aggregate, inorganic-coated sand for crystallization, and liquid metasilicate hydrate, wherein the amount of the inorganic-coated sand for crystallization is 0.1% by mass or more and 15% by mass or less, preferably 0.2% by mass or more, more preferably 0.4% by mass or more, preferably 12% by mass or less, and more preferably 10% by mass or less, based on the total amount of the dry inorganic-coated sand. <2> The method for producing dry inorganic coated sand according to <1>, wherein the mixing step includes: mixing the refractory aggregate and the inorganic coated sand for crystallization to obtain a mixture; and further mixing the obtained mixture with the liquid metasilicate hydrate. <3> The method for producing dry inorganic coated sand according to <1> or <2>, 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> The method for producing dry inorganic coated sand according to <3>, wherein the inorganic binder layer of the inorganic coated sand for crystallization contains metasilicate hydrate. <5> A method for producing the dry inorganic coated sand according to any one of <1> to <4>, 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> A method for producing dry inorganic-coated sand according to any one of <1> to <5>, 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, 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> A method for producing dry inorganic-coated sand according to any one of <1> to <6>, wherein the liquid metasilicate hydrate is metasilicate hydrate melted by heating. <8> A method for producing dry inorganic-coated sand according to any one of <1> to <7>, wherein the liquid metasilicate hydrate is a mixed liquid of water glass, caustic alkali, and water. <9> The method for producing dry inorganic-coated sand according to any one of <1> to <8>, wherein in the step of mixing the refractory aggregate, the inorganic-coated sand for crystallization, and liquid metasilicate hydrate, the amount of the inorganic-coated sand for crystallization relative to the refractory aggregate is preferably 0.2% by mass or more, more preferably 0.3% by mass or more, even more preferably 0.4% by mass or more, and preferably 15% by mass or less, and more preferably 12% by mass or less. <10> A method for producing a mold using the dry inorganic-coated sand obtained by the method for producing dry inorganic-coated sand according to any one of <1> to <9>. <11> Dry inorganic-coated sand having a refractory aggregate and an inorganic binder layer formed on the surface of the refractory aggregate, wherein the particle groups of the dry inorganic-coated sand contain particles in which the inorganic binder layer has a multilayer structure.<12> The dry inorganic coated sand according to <11>, wherein the content of the particles having a multilayer inorganic binder layer is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, even more preferably 0.3% by mass or more, and is preferably 15% by mass or less, more preferably 12% by mass or less, even more preferably 10% by mass or less, relative to the total amount of the dry inorganic coated sand.

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

[0079] (1) Materials [Refractory 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, amorphization degree 0.2%, sphericity 0.85) Mikawa silica sand R8: Mikawa silica sand R8 (manufactured by Mikawa Silica Co., Ltd., average particle size: 127 μm, amorphization degree 0.2%, sphericity 0.85) [Inorganic binder: metasilicate hydrate] Metasilicate 1: Sodium metasilicate nonahydrate (Na ２ SiO ３ ・9H ２ O, manufactured by Nippon Chemical Industry Co., Ltd., melting point 47°C, SiO ２ / Na ２ O ratio = 0.9 to 1.1) and sodium metasilicate pentahydrate (Na ２ SiO ３ ・5H ２ O, manufactured by Nippon Chemical Industry Co., Ltd., melting point 72°C, SiO ２ / Na ２0 ratio = 0.9 to 1.1) in a weight ratio of 4:3. Metasilicate 2: A water glass-containing aqueous solution 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]

[0082] No. 1 50 water glass: manufactured by Fuji Chemical Co., Ltd., SiO ２ (%)=30.0, Na ２ O (%) = 14.7, solid content 44.7 mass% NaOH: caustic soda, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., granular

[0083] (2) Preparation of inorganic coated sand for crystallization Inorganic coated sand for crystallization was prepared using the materials described in (1) above, with the refractory aggregate and inorganic binder (type, parts by mass) shown in Table 2. Specifically, the refractory aggregate shown in Table 2 was placed in a mixer, and then the inorganic binder, which 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 Using the materials of (1) above and the inorganic coated sand for crystallization obtained in (2) above, dry inorganic coated sand was prepared so that the refractory aggregate and inorganic binder were as shown in Table 2 (type, parts by mass). 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 shown in Table 2 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 were added to a mixer. Next, liquid metasilicate 1 (1.994 parts by mass) heated to 80°C and melted was further added while stirring with the mixer, and uniform kneading was initiated. Stirring was continued, and once drying was confirmed within the drying time shown in Table 2 from the start of kneading, stirring was stopped, yielding 102 parts by mass of untreated, dry inorganic-coated sand with room temperature fluidity. The untreated, dry inorganic-coated sand was then sieved (20 mesh) to remove aggregates (lumps), yielding 101 parts by mass of dry inorganic-coated sand. Therefore, the amount of inorganic-coated sand for crystallization added was 0.3% by mass relative to the total amount of dry inorganic-coated sand (0.306 parts by mass of inorganic-coated sand for crystallization ÷ 101 parts by mass of total amount of dry inorganic-coated sand × 100). The ratio of the amount of removed lumps to the amount of untreated dry inorganic-coated sand was calculated as a lump amount of 0.6 (mass%) (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, Comparative Examples 1 to 3> Each dry inorganic coated sand shown in Table 2 was 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]

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

Claims

1. A method for producing dry inorganic coated sand having a fire-resistant aggregate and an inorganic binder layer formed on the surface of the fire-resistant aggregate, comprising a step of mixing the fire-resistant aggregate, inorganic coated sand for crystallization, and liquid metasilicate hydrate, wherein 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.

2. A method for producing dry inorganic coated sand as described in claim 1, wherein the mixing step includes the steps of: mixing the refractory aggregate and the inorganic coated sand for crystallization to obtain a mixture; and further mixing the obtained mixture with the liquid metasilicate hydrate.

3. A method for producing dry inorganic coated sand as described in claim 1 or 2, 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. A method for producing dry inorganic coated sand according to any one of claims 1 to 3, wherein the inorganic binder layer of the inorganic coated sand for crystallization contains metasilicate hydrate.

5. A method for producing dry inorganic coated sand as described in any one of claims 1 to 4, 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. A method for producing inorganic coated sand according to any one of claims 1 to 5, 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.

7. A method for producing dry inorganic coated sand according to any one of claims 1 to 6, wherein the liquid metasilicate hydrate is a metasilicate hydrate melted by heating.

8. A method for producing dry inorganic coated sand according to any one of claims 1 to 6, wherein the liquid metasilicate hydrate is a mixture of water glass, caustic alkali and water.

9. A method for producing a mold, comprising producing a mold using the dry inorganic coated sand obtained by the method for producing dry inorganic coated sand according to any one of claims 1 to 8.

10. Dry inorganic coated sand having a fire-resistant aggregate and an inorganic binder layer formed on the surface of the fire-resistant aggregate, wherein the particle group of the dry inorganic coated sand contains particles in which the inorganic binder layer has a multi-layer structure.

Images