JP5986498B2 - Coated sand manufacturing method and mold manufacturing method - Google Patents

Description

  The present invention relates to a method for producing a coated sand, a coated sand obtained thereby, and a method for producing a mold, and in particular, a method for advantageously producing dry coated sand having fluidity at room temperature, and thereby The present invention relates to a coated sand having excellent characteristics obtained, and a method for producing a casting mold having good characteristics using such coated sand.

  Conventionally, as one of the molds used for casting molten metal, using a coated sand formed by coating mold sand made of refractory aggregate with a predetermined caking additive, the desired shape can be obtained with a molding die. What is obtained by molding into a shape has been used. For example, "Casting Engineering Handbook" edited by the Japan Foundry Engineering Society, pages 78-90, as such a binder, in addition to inorganic binders such as water glass, phenol resins, furan resins, urethane resins. Organic caking materials using resins such as these have been clarified, and a method for forming a self-hardening mold using these caking materials has also been clarified.

  One of the methods for producing a mold using resin-coated sand obtained by coating mold sand with a thermosetting resin such as phenol resin, which is an organic binder among these binders, is disclosed in JP It is clarified in the 2009-90334 gazette. According to the manufacturing method disclosed therein, after the resin-coated sand is filled in the mold, water vapor is blown into the mold to raise the temperature of the resin-coated sand, and then the heated gas is injected into the mold. The target mold is manufactured by blowing into the mold to evaporate the condensed water in the mold and heating the resin-coated sand binder to a temperature at which it solidifies or cures. However, since resin such as phenolic resin is used as a binder for resin-coated sand, when high heat acts when casting a mold or casting a molten metal, There is a problem that the resin binder is decomposed to generate decomposition gases such as phenol and aldehyde, and the odor and irritation cannot be completely removed. Not suitable for.

On the other hand, when water glass is used as the inorganic binder, a curing agent such as CO ₂ gas is generally used for curing the water glass. In the conventional method relating to the glass / CO ₂ gas process, a material obtained by kneading mold sand (fire-resistant aggregate) and a water glass aqueous solution as a binder has been used for molding a mold. Yes. And since it is used in a wet form (wet condition) in which wet water glass adheres to the surface of the mold sand, it is coated by coating the mold sand with such a binder. Sand has poor fluidity, which makes it difficult to fill the mold, and causes problems such as poor filling and poor productivity.

  Therefore, in JP 2012-76115 A, as a binder, water glass, sodium chloride, sodium phosphate, sodium carbonate, vanadium are used to obtain a binder-coated refractory (coated sand) having good fluidity. Using a water-soluble inorganic compound selected from the group consisting of sodium oxide, sodium borate, sodium aluminum oxide, potassium chloride, and potassium carbonate, a solid coating layer containing this water-soluble inorganic compound is used to form a refractory aggregate. A binder-coated refractory with a surface coating has been proposed. In addition, after filling such a binder coated refractory into a mold, steam is blown into the mold to heat the binder coated refractory and moisten the binder in the coating layer, and then solidify. Thus, a method for producing a mold has also been clarified.

  However, in such a binder-coated refractory, a coating layer made of a water-soluble inorganic compound such as water glass or sodium chloride is formed on the surface of the refractory aggregate as a solid coating layer. However, in some cases, the fluidity may not be sufficiently ensured, the change over time due to moisture absorption of the mold obtained using the same is large, and the properties such as strength are not sufficient. It became clear. Further, when the fire-resistant aggregate is coated with such a water-soluble inorganic compound (binder), the water-soluble inorganic compound is applied as an aqueous solution in a state dissolved in water. However, it became clear that the state of the coating became different depending on the amount of water contained in the aqueous solution, and therefore the physical properties of the binder-coated refractory also changed. That is, if the amount of moisture is small, uniform coating cannot be performed, and if the amount of moisture is large, it cannot be sufficiently dried. Therefore, when using a binder-coated refractory in such a state, moldability and It causes problems such as deterioration in physical properties and non-uniformity, and the properties of the binder-coated refractory formed according to the water-soluble inorganic compound are greatly different, and the binder-coated refractory under the same conditions. However, there is a problem in that it is difficult to optimize manufacturing conditions due to variations in physical properties.

JP 2009-90334 A JP 2012-76115 A

"Casting Engineering Handbook" pages 78-90

  Here, the present invention has been made in the background of such circumstances, and the problem to be solved is a method for producing dry coated sand having excellent room temperature fluidity and obtained by the method. The object of the present invention is to provide a coated sand and a method for producing a mold having excellent characteristics by using such a coated sand. Another object is to provide a mold used for mold making. Fillability into the mold cavity can be remarkably improved, and deterioration due to moisture absorption of the resulting mold can be suppressed or prevented, and the problem of change over time due to long-term storage can be advantageously eliminated. Method for producing coated sand, coated sand having excellent properties obtained thereby, and casting using such coated sand It is to provide a method of manufacturing a mold.

  And, in order to solve the above-mentioned problems, the present invention can be suitably implemented in various aspects as listed below, and each aspect described below is adopted in any combination. Is possible. It should be noted that aspects or technical features of the present invention are not limited to those described below, and can be recognized based on the inventive concept that can be grasped from the description of the entire specification. Should be understood.

(1) A water-glass aqueous solution is mixed as a binder to a heated refractory aggregate, and moisture is evaporated to form a binder coating layer on the surface of the refractory aggregate. In preparing a dry coated sand having room temperature fluidity, an aqueous solution of sodium silicate having a SiO ₂ / Na ₂ O molar ratio of 3.0 to 4.0 is used as the water glass aqueous solution. A method for producing coated sand, characterized in that the viscosity at 25 ° C. of the aqueous solution is adjusted within a range of 10 to 50 cP and mixed with the refractory aggregate.
(2) The above aspect (100), wherein the aqueous solution of sodium silicate is used at a ratio of 0.1 to 2.5 parts by mass in terms of solid content with respect to 100 parts by mass of the refractory aggregate. The manufacturing method of the coated sand as described in 1).
(3) A heated water-resistant aggregate is mixed with a water glass aqueous solution as a binder, and water is evaporated to form a binder coating layer on the surface of the fire-resistant aggregate. In the production of dry coated sand having room temperature fluidity, as the water glass aqueous solution, an aqueous solution of sodium silicate having a SiO ₂ / Na ₂ O molar ratio of 3.0 to 4.0, In addition, a sodium silicate aqueous solution having a viscosity at 25 ° C. of 30 cP or more is used, and the sodium silicate aqueous solution and water are mixed with the refractory aggregate simultaneously or with a time difference within 10 seconds. The manufacturing method of the coated sand characterized by these.
(4) The sodium silicate aqueous solution is used in a proportion of 0.1 to 2.5 parts by mass in terms of solid content with respect to 100 parts by mass of the refractory aggregate, and water is 0.1 It is used in the ratio of -3.0 mass part, The manufacturing method of the coated sand as described in the said aspect (3) characterized by the above-mentioned.
(5) In any one of the above aspects (1) to (4), the molar ratio of SiO ₂ / Na ₂ O of the sodium silicate is 3.0 to 3.5. The manufacturing method of the coated sand of description.
(6) The method for producing coated sand according to any one of the above aspects (1) to (5), wherein water is evaporated within 5 minutes from the start of mixing of the aqueous sodium silicate solution. .
(7) Upon mixing of the aqueous sodium silicate solution, at least one of silicon dioxide, zinc oxide, aluminum oxide, boron oxide, zinc carbonate, potassium metaborate, sodium tetraborate, and potassium tetraborate, The method for producing coated sand according to any one of the aspects (1) to (6), further comprising addition.
(8) Coated sand obtained by the production method according to any one of aspects (1) to (7), wherein the moisture content is 0.5% by mass or less, and the amount of lumps is Coated sand characterized by being 3% by mass or less.
(9) After using the coated sand described in the above aspect (8) and filling it into a molding cavity of a molding mold that gives a target mold, water vapor is passed through to solidify in the molding mold. A method for producing a mold, comprising obtaining a target mold by curing.
(10) The mold production according to the aspect (9), wherein after the water vapor is ventilated, further, dry air, heated dry air, or nitrogen gas is vented into the molding cavity of the mold. Method.
(11) The method for producing a mold according to the aspect (9) or the aspect (10), wherein the coated sand is preheated to 30 ° C. or more and then filled into a molding cavity of the mold.
(12) The mold manufacturing method according to any one of the aspects (9) to (11), wherein the mold is preheated and kept warm.
(13) A method for producing a mold, wherein the target mold is formed by layering using the coated sand according to the aspect (8).

Thus, in the present invention, an aqueous solution of sodium silicate having a specific SiO ₂ / Na ₂ O molar ratio is used as a binder, and the viscosity of such an aqueous solution is adjusted to provide fire resistance. By covering the surface of the aggregate, a coating layer made of specific sodium silicate can be efficiently and uniformly formed on such a fire-resistant aggregate. The fluidity of the coated sand obtained can be further improved, and the filling property of the coated sand into the mold cavity of the mold for mold molding can be remarkably improved, thereby increasing the mold strength. In addition to being able to advantageously produce excellent and healthy molds, the molds made using such coated sand are less susceptible to moisture absorption, which Aging of the mold is obtained is effectively blocked by the storage, it's also has characteristics that can be maintained over a good mold properties for long-term.

  In addition, according to the present invention, an aqueous solution of a specific sodium silicate used as a binder can be adjusted to a predetermined viscosity so that the concentration of the non-volatile content (solid content) in such an aqueous solution can be reduced. By doing so, a coated sand with a small amount of lumps can be advantageously obtained, and properties such as strength of a mold obtained by using such a coated sand can be further advantageously enhanced.

  In the coated sand obtained according to the present invention, since sodium silicate is used as the binder, it is obtained using a conventional organic binder such as phenol resin or furan resin. Unlike resin-coated sand, it is possible to suppress or prevent the generation of odorous low-molecular gas components when casting molds or casting molten metal. One of the features is that it does not cause problems that worsen the work environment.

  By the way, in the manufacturing method of the coated sand according to the present invention, the refractory aggregate used is a refractory substance that functions as a base material of a mold, and various refractory granules conventionally used for molds. Any material can be used, specifically, silica sand, recycled silica sand, special sand such as alumina sand, olivine sand, zircon sand, chromite sand, ferrochrome slag, ferronickel slag, converter Examples include slag-based particles such as slag, porous particles such as alumina-based particles and mullite-based particles, and regenerated particles thereof; alumina balls, magnesia clinker, and the like. These refractory aggregates may be fresh sand, or reclaimed sand or recovered sand that has been used once or a plurality of times as a casting sand for casting molds. Even mixed sand made by adding new sand to sand or recovered sand and mixing them can be used. Such a refractory aggregate generally has a particle size of about 40 to 80 in terms of AFS index, and preferably has a particle size of about 60 or less in order to facilitate the ventilation and drying of water vapor during mold molding. As a thing, it will be used.

  Such a refractory aggregate is heated in advance and used for mixing with a predetermined aqueous sodium silicate solution. By mixing or mixing a predetermined sodium silicate aqueous solution with the preheated refractory aggregate, the water in the sodium silicate aqueous solution is heated by the heat of the refractory aggregate. Thus, the moisture content of the coated sand obtained can be effectively reduced, and a dry powder having room temperature fluidity can be advantageously obtained. It will be done. In addition, the preheating temperature of the refractory aggregate is appropriately selected according to the water content of the sodium silicate aqueous solution and the blending amount thereof, but is generally about 100 to 150 ° C, more preferably. It is desirable to heat the refractory aggregate to a temperature of about 100 to 120 ° C. If the preheating temperature is too low, it is not possible to effectively evaporate moisture, and it takes time to dry. Therefore, it is desirable to set the temperature to 100 ° C. or higher. If the temperature is higher than 150 ° C., the hardening of the sodium silicate proceeds during cooling of the resulting coated sand, and in addition, the formation of composite particles proceeds. It will cause problems with physical properties.

Further, in the present invention, a water glass aqueous solution is used as a binder for covering the surface of the above-mentioned refractory aggregate, and among them, particularly, the obtained coated sand is difficult to block, and the moldability is high. From a good point, an aqueous solution of sodium silicate (sodium silicate) is targeted. In addition, such sodium silicate is normally classified into the types of No. 1 to No. 5 and used according to the SiO ₂ / Na ₂ O molar ratio. Specifically, sodium silicate No. 1 has a SiO ₂ / Na ₂ O molar ratio of 2.0 to 2.3, and sodium silicate No. 2 is SiO ₂ / Na ₂ O The molar ratio is 2.4 to 2.5, and the sodium silicate No. 3 has a SiO ₂ / Na ₂ O molar ratio of 3.1 to 3.3. In addition, sodium silicate No. 4 has a SiO ₂ / Na ₂ O molar ratio of 3.3 to 3.5, and sodium silicate No. 5 has a SiO ₂ / Na ₂ O molar ratio. Is 3.6 to 3.8. Among these, sodium silicate Nos. 1 to 3 are also defined in JIS K1408. And it is possible to adjust the molar ratio by mixing these sodium silicates.

In the present invention, among these sodium silicates, a mold having excellent moisture resistance is provided, and by suppressing or preventing the moisture absorption deterioration of the mold, the mold can be stored for a long period of time. In order to obtain a coated sand that can provide a mold having excellent properties such as folding strength and achieve a high packing density, a SiO ₂ / Na ₂ O molar ratio in the range of 3.0 or more and 4.0 or less. Sodium acid is used. Therefore, sodium silicate corresponding to No. 3 to No. 5 is advantageously used in the above-mentioned classification of sodium silicate. Among them, those having a SiO ₂ / Na ₂ O molar ratio in the range of 3.0 to 3.5 are more preferable, and this includes sodium silicate Nos. 3 to 4, in particular, silicic acid. Sodium 3 will be used advantageously.

  Furthermore, when producing the target coated sand according to the present invention, (A) as the sodium silicate aqueous solution described above, the sodium silicate aqueous solution (stock solution) as purchased on the market is further diluted with water, Using a sodium silicate aqueous solution whose viscosity at 25 ° C. is adjusted to 10 to 50 cP (centipoise), this is mixed with a refractory aggregate, or (B) a sodium silicate aqueous solution having a viscosity of 30 cP or more and A method is employed in which the water for dilution is individually added to mixing means such as a mixer, kneaded and mixed, and mixed. However, if the viscosity of a sodium silicate aqueous solution (stock solution) obtained in the market is within the above specified range, the addition of water for dilution is optional. In addition, diluting water can be added to make a sodium silicate aqueous solution with lower viscosity within the above specified range, and it can be used as it is without adding such diluting water. It is also possible to do. Here, the sodium silicate aqueous solution (stock solution) is composed of a volatile substance such as water and solvent and a solid content excluding the volatile substance, and the viscosity of each of the various sodium silicate aqueous solutions is the water relative to the solid content (water content of the stock solution + It is determined by the ratio of water for dilution). When the ratio of the solid content is high, the viscosity becomes high, and when it is low, the viscosity becomes low.

  Accordingly, by adjusting the viscosity of the aqueous sodium silicate solution at 25 ° C. within the range of 10 to 50 cP, and particularly within the range of 10 to 40 cP, according to the method (A), the fire resistance is improved in the mixing operation such as kneading. When the aggregate is coated with sodium silicate, the aqueous solution of sodium silicate is not sticky, and by maintaining an appropriate sliminess, the fire-resistant aggregate can be coated uniformly and uniformly with sodium silicate. At the same time, since the coated sand particles can be made difficult to stick to each other, it is possible to effectively suppress the occurrence of lumps during the mixing operation. And by reducing the amount of lumps in the coated sand, problems such as a significant decrease in the bending strength and scratch hardness of the mold obtained from such coated sand can be effectively prevented. It is. In addition, by dispersing sodium silicate in an aqueous solution appropriately, an aqueous solution of sodium silicate is provided so that the refractory aggregate can be uniformly and uniformly coated with sodium silicate when mixed. The viscosity of the resin must be 50 cP or less. In addition, the lower the viscosity of the aqueous sodium silicate solution, the less the occurrence of lumps can be suppressed. However, if the proportion of water is too large to reduce the viscosity, the coated sand is difficult to dry. Therefore, also in improving the drying efficiency, the viscosity of the aqueous sodium silicate solution is adjusted to be 10 cP or more.

Moreover, such a sodium silicate aqueous solution having a viscosity of 10 to 50 cP may be used at a ratio of 0.1 to 2.5 parts by mass in terms of solid content with respect to 100 parts by mass of the refractory aggregate. Desirably, the ratio of 0.2 to 2.0 parts by mass is particularly advantageously adopted, and a coating layer of sodium silicate is formed on the surface of the refractory aggregate. Here, the solid content was measured on a heating plate that weighed and contained 10 g of a sample in an aluminum foil dish (length: 90 mm, width: 90 mm, height: 15 mm) and held at 180 ± 1 ° C. After placing and leaving for 20 minutes, the sample pan was inverted and left on the heating plate for an additional 20 minutes. Then, the sample dish was taken out from the heating plate, allowed to cool in a desiccator, weighed, and obtained by the following formula.
Solid content (%) = [weight after drying (g) / weight before drying (g)] × 100
If the amount of the sodium silicate aqueous solution used is too small, it becomes difficult to form an effective coating layer of sodium silicate on the surface of the refractory aggregate, and the coated sand is sufficiently solidified or hardened. It is because it becomes difficult, and even if the amount of sodium silicate aqueous solution used is excessive, excess sodium silicate aqueous solution adheres to the surface of the refractory aggregate, making it difficult to form a uniform coating layer, This is because there is a possibility that the generation amount of lumps may increase, which in turn adversely affects the physical properties of the mold and makes it difficult to remove the sand from the core after casting the metal.

On the other hand, in the case where a sodium silicate aqueous solution having a viscosity at 25 ° C. of 30 cP or more is used together with water according to the method (B) described above, the viscosity at 25 ° C. of the sodium silicate aqueous solution should be 30 cP or more. The upper limit is not particularly limited, but is generally about 2000 cP. The desirable viscosity range is 30 to 250 cP in sodium silicate having a SiO ₂ / Na ₂ O molar ratio of 3.0 to 4.0. A sodium silicate aqueous solution having such a viscosity range can be used as it is even in the state of a stock solution available on the market.

  In addition, the amount of water for dilution used together with an aqueous solution of sodium silicate having a viscosity of 30 cP or more is such that the aqueous solution of sodium silicate (mixed solution) obtained by directly mixing the aqueous solution of sodium silicate and the water for dilution The viscosity is such that the viscosity becomes 10 to 30 cP at 25 ° C. Thus, even if a high-viscosity sodium silicate aqueous solution is used together with the corresponding water, the above-mentioned viscosity of 10 to 50 cP It is possible to obtain a coated sand having the same characteristics as when an aqueous sodium acid solution is used. In addition, when the viscosity of the sodium silicate aqueous solution used there is about 30 to 50 cP, it may be added as it is or may be added together with water as described above. Since it is preferable that the viscosity of the aqueous solution is low, it is desirable to use a sodium silicate aqueous solution having a viscosity of 30 to 50 cP in a form to be added together with water.

  Further, when the aqueous solution of sodium silicate having a viscosity of 30 cP or more and water are kneaded and mixed together with the refractory aggregate, the timing of adding these two components is as follows: When the time difference between the additions becomes large, the evaporation of moisture proceeds and it becomes difficult to uniformly cover the surface of the refractory aggregate with sodium silicate. Therefore, the time difference is within 10 seconds, preferably within 5 seconds. In particular, simultaneous addition is advantageously employed. In addition, when mixing the sodium silicate aqueous solution and water with a time difference, the order of addition of the sodium silicate aqueous solution and water is not limited, and any of them may be added and blended first.

  In this way, when the sodium silicate aqueous solution having a viscosity of 30 cP or more and water are added together and mixed with the refractory aggregate, the addition ratio thereof is 100% of the refractory aggregate. Such sodium silicate aqueous solution is used in a proportion of 0.1 to 2.5 parts by mass in terms of solid content, and water is used in a proportion of 0.1 to 3.0 parts by mass with respect to parts by mass. Is desirable. And by adopting the addition amount within such a range, it is possible to advantageously cure it as coated sand formed by effectively covering the surface of the refractory aggregate with sodium silicate, A uniform coating layer having no unevenness can be advantageously formed by preventing extra sodium silicate from adhering to the aggregate to form a coating layer.

The ratio of the sodium silicate aqueous solution and water to be added together varies depending on the viscosity of the stock solution of the sodium silicate aqueous solution. The viscosity of the stock solution of sodium silicate aqueous solution, although different by the molar ratio of SiO ₂ / Na ₂ O of sodium silicate, the molar ratio of SiO ₂ / Na ₂ O at 3.0 to 4.0 For a certain aqueous solution (stock solution) of sodium silicate, a ratio such that sodium silicate aqueous solution: water = 1: 1 to 40: 1 is advantageously employed on a mass basis. .

  And in the present invention, the coated sand in which the coating layer is formed on the surface of the refractory aggregate using the above-mentioned sodium silicate aqueous solution is the target. The coating layer may contain a predetermined additive as required. In order to incorporate such an additive into the coating layer, a method of kneading or mixing with a refractory aggregate after mixing a predetermined additive in a sodium silicate aqueous solution in advance, and a sodium silicate aqueous solution Separately, a method of adding a predetermined additive to the refractory aggregate and uniformly kneading or mixing the whole is adopted.

  Here, solid oxides and salts are advantageously used as one of such additives. By containing these solid oxides and salts, the moisture resistance of the coated sand can be advantageously improved. Of these, as the solid oxide, it is effective to use oxides of silicon, zinc, magnesium, aluminum, calcium, lead, and boron, for example. In particular, among these, use of silicon dioxide, zinc oxide, aluminum oxide, and boron oxide is desirable. Of silicon dioxide, precipitated silicic acid and exothermic silicic acid are preferably used. On the other hand, as the salt, there are silicofluoride, silicate, phosphate, borate, tetraborate, carbonate, etc. Among them, zinc carbonate, potassium metaborate, sodium tetraborate, tetraborate The use of potassium acid is desirable. And these solid oxides and salts will be used in the ratio of 100 mass% or less with respect to the non volatile matter in sodium silicate aqueous solution, Preferably about 0.5-5 mass%.

  As other additives, it is also effective to include a coupling agent that reinforces the bond between the refractory aggregate and sodium silicate (binder). For example, silane coupling agents, zircon coupling agents, titanium A coupling agent or the like can be used. It is also effective to contain a lubricant that contributes to improving the flowability of the coated sand. For example, waxes such as paraffin wax, synthetic polyethylene wax, montanic acid wax; stearic acid amide, oleic acid amide, erucic acid amide, etc. Fatty acid amides; alkylene fatty acid amides such as methylene bis stearic acid amide and ethylene bis stearic acid amide; stearic acid metal salts such as lead stearate, zinc stearate, calcium stearate, magnesium stearate; stearic acid, stearyl alcohol; It is possible to use stearic acid monoglyceride, stearyl stearate, hydrogenated oil and the like. Furthermore, as release agents, paraffin, wax, light oil, machine oil, spindle oil, insulating oil, waste oil, vegetable oil, fatty acid ester, organic acid, fine graphite particles, mica, meteorite, fluorine release agent, silicone release agent An agent or the like can also be used. Each of these other additives is generally contained in a proportion of 5% by mass or less, preferably 3% by mass or less, based on the nonvolatile content in the aqueous sodium silicate solution.

By the way, when manufacturing the coated sand according to the present invention as described above, a predetermined sodium silicate aqueous solution as a binder is further required alone or together with water for the heated refractory aggregate. Depending on the additive, it is kneaded or mixed and mixed uniformly so that the surface of the refractory aggregate is coated with an aqueous sodium silicate solution, and the water of the aqueous sodium silicate solution is evaporated. By letting it squeeze, a technique for obtaining a dry powdered coated sand having room temperature fluidity is adopted. In this case, the transpiration of the aqueous solution of the sodium silicate (coating layer) needs to be performed quickly before the solidification or hardening of the sodium silicate proceeds. It is desirable to dry the powdered coated sand in 5 minutes, more preferably within 3 minutes after the sodium silicate aqueous solution is added (mixed) to the synthetic aggregate. . If the transpiration time becomes longer, the mixing (kneading) cycle becomes longer, the productivity is lowered, and the time during which the sodium silicate aqueous solution is in contact with CO ₂ in the air becomes longer, causing problems such as deactivation. This is because fear increases.

  In addition, in the coated sand obtained according to such a process, the presence of so-called lumps, which are composite particles in which a plurality of particles are combined, is effectively reduced, and is screened with a 20 mesh sieve. When the coated sand having a particle size larger than 20 mesh remaining on the sieve is 3% by mass or less, preferably 1% by mass or less, based on the total amount of the coated sand is advantageously obtained. It becomes. In addition to such a reduction in the amount of lumps, in addition to being able to effectively improve the filling property of the mold for forming the mold into the mold cavity, it is advantageous to further improve the mold strength. Can be realized.

  The coated sand thus obtained has a moisture content of 0.5% by mass or less, preferably 0.3% by mass or less. The filling property into the molding cavity is further improved, and excellent characteristics are imparted even in a mold formed using such coated sand.

  Further, when molding a mold using the coated sand according to the present invention thus obtained, first, the coated sand is filled into a molding cavity of a mold that gives a target mold, and then steam is blown. The filled coated sand is solidified or cured by passing through the filled phase of the coated sand and holding in the mold until it is dry.

  At that time, it is desirable that a mold such as a mold or a wooden mold to be filled with dry coated sand is preliminarily kept warm by heating, so that drying of the coated sand moistened with water vapor is advantageous. It can be made to progress. In general, a temperature of about 90 to 140 ° C., particularly about 100 to 130 ° C. is desirable as the temperature for preheating. When this heat retention temperature is high, it becomes difficult for steam to pass to the surface of the mold, and when the temperature is too low, it takes time to dry the molded mold. In addition, the dry coated sand to be filled in such a mold is also preferably preheated. Generally, the bending strength of the obtained mold can be increased more advantageously by filling the molding die with the coated sand heated to a temperature of 30 ° C. or higher. The heating temperature of such a coated sand is preferably about 30 to 100 ° C., and particularly, the coated sand heated to a temperature of about 40 to 80 ° C. is advantageously used.

  The mold is heated as described above. Specifically, after the dry coated sand is filled into the mold cavity, the mold is provided in the filling phase formed there. Through the vents, water vapor is passed under pressure to wet the coated sand that constitutes the filling phase, and they are bonded and joined together to form an integral mold-shaped coated sand aggregate (bonded product). It is formed. Sodium silicate is usually solidified by evaporation to dryness of water if no additives are added, and it is cured when oxides or salts are added as curing agents. It becomes. In the present invention, practically, since the curing agent is added, the filling phase is cured, but it may be simply solidified.

  The temperature of water vapor that is blown through the vent of such a mold and allows the filled phase of the coated sand to be vented is generally about 80 to 150 ° C., more preferably about 95 to 120 ° C. . When a high steam temperature is employed, a large amount of energy is required for production, and therefore, a steam temperature around 100 ° C. is advantageously employed. Moreover, as the pressure of the water vapor vented according to the present invention, a value of about 0.01 to 0.3 MPa, more preferably about 0.01 to 0.1 MPa is advantageously employed as a gauge pressure. In the case where the breathability of the coated sand is good, if the pressure for venting water vapor is about the above-mentioned gauge pressure, the water vapor can be evenly vented to the mold formed in the mold, In addition, the water vapor passage time and the mold drying time are short, and the molding speed can be reduced. In addition, such a gauge pressure has an advantage that molding is possible even when the breathability of the coated sand is poor. If the gauge pressure is too high, a squeezing occurs near the vent, and if it is too low, the whole may not be ventilated and the coated sand may not be sufficiently moistened.

  In addition, as a method of venting water vapor as described above, a method is adopted in which water vapor is blown from a vent provided in the mold, and the coated sand (phase) filled in the molding cavity of the mold is vented. As the ventilation time, water vapor is supplied to the surface of the filled coated sand so that the sodium silicate as the binding material on the surface is sufficiently moistened so that the coated sand can be bonded (joined) to each other. The appropriate time is appropriately selected depending on the size of the mold, the number of ventilation holes, and the like, but generally, the ventilation time from about 2 seconds to about 60 seconds is adopted. If the water vapor passage time is too short, it will be difficult to sufficiently wet the coated sand surface. If the air passage time is too long, the binder on the coated sand surface may dissolve and flow out. This is because of the above. The improvement in water vapor permeability in the coated sand filled in the mold can be further enhanced by performing water vapor ventilation while sucking the atmosphere in the mold from the exhaust port of the mold. Is possible. In addition, in the present invention, the method is not particularly limited as long as the coated sand can be moistened in addition to aeration of water vapor, but since the molding time and the molding process are simple, the above water vapor is used. A venting technique is advantageously employed.

  Furthermore, in the present invention, after aeration with water vapor, in order to actively dry the filling phase of the coated sand wet with the water vapor, dry air, heated dry air or nitrogen gas is blown into the aeration phase. A technique for causing the caulking is preferably employed. By such aeration of dry air, heated dry air or nitrogen gas, the inside of the coated sand filling phase is quickly dried, and the solidification or hardening of the filling phase is further advantageously promoted. In addition to advantageously increasing the curing rate, properties such as the bending strength of the resulting mold can be advantageously enhanced, and it can also advantageously contribute to shortening the molding time of the mold.

Further, as described above, carbon dioxide (CO ₂ gas), ester, or carbonate gas may be passed between the water vapor and the dry air. By neutralizing the binder, the solidification can be further promoted. It should be noted that the aeration of carbon dioxide, ester and carbonate gas may be performed simultaneously with the aeration of water vapor or the aeration of dry air.

  Furthermore, the mold formed as described above can be heated by microwaves. Thereby, there exists an advantage which can evaporate only a water | moisture content selectively. If water is present inside the mold, the caking material (binder) may be dissolved again by the moisture in the mold, causing a decrease in bending strength. There are inherent problems such as the generation of hydrogen gas that is decomposed by heat during pouring and causing gas defects in the resulting casting. For this reason, in order to remove the moisture in the mold, the method of heating the molded mold with microwaves can be considered as an effective means for the preservation of the mold and the improvement of the casting quality.

  In addition, as a method for forming a mold using the coated sand according to the present invention, as described above, various known forming methods can be appropriately employed in addition to the method of filling the forming die with the coated sand and forming the mold. By the way, for example, a layered modeling technique as disclosed in Japanese Patent Application Laid-Open No. 7-507508, Japanese Patent Laid-Open No. 9-141386, etc., specifically, while sequentially laminating a layer of coated sand, It is also possible to employ a method in which a portion corresponding to the mold to be cured is cured and a three-dimensional mold is directly formed.

  Hereinafter, the present invention will be more specifically clarified by using some examples, but the present invention is not construed as being limited in any way by the description of such examples. It should be understood. In the following examples and comparative examples, all parts and percentages are shown on a mass basis unless otherwise specified. Further, in the examples and comparative examples, the viscosity of the sodium silicate aqueous solution at 25 ° C., the moisture content of the coated sand (CS) obtained in these examples and comparative examples, the amount of lumps, the bulk density, the filling rate, The measurement of the sand condition and the bending strength, scratch hardness, strength after moisture absorption deterioration of the mold obtained by using each CS, and observation of the adhesion state of the kettle during kneading are as follows. went.

-Measurement of viscosity (cP) at 25 ° C-
In accordance with “9. Viscosity measurement method using a single cylindrical rotary viscometer” defined in “Measurement method of viscosity of liquid” in JIS Z 8803 (2011), an apparatus having the same principle as that described therein was used. The viscosity (cP) at a temperature of 25 ° C. of the sodium silicate aqueous solution used in Examples and Comparative Examples is measured.

-Measurement of moisture content (%)-
Karl Fischer moisture measuring machine (manufactured by Hiranuma Sangyo Co., Ltd .; AQV-7 HIRANUMA) containing 2.0 g of the obtained coated sand (CS) and 100 mL of Aquamicron ML (manufactured by Mitsubishi Chemical Corporation) as a dehydrating solvent AQUACOUNTER) flask [Previously add Karl Fischer reagent (Sigma-Aldrich Laborchemikalien Gmbh, Hydranal Composite 5) dropwise to keep moisture to 0], then use a magnetic stirrer for several minutes. After stirring, the hydranal composite 5 is dropped, the moisture content of the charged CS is quantified, and the moisture content is calculated from the obtained value.

-Measurement of the amount of lumps (%)-
The CS obtained in each production example is sieved with a 20-mesh sieve, and composite particles (dama) having a particle size of 20 mesh or more on the sieve are taken out. The amount of lumps is calculated as mass% of the mass of lumps relative to the mass of sand used for kneading.
Dama amount (%) = Dama mass / (Dama mass + Mass of sand below 20 mesh) × 100

-Measurement of bulk density-
Using CS obtained in each of the production examples, measurement is performed according to JACT test method S-10: foundry sand filling property (bulk density) test method.

−Measurement of bending strength (kgf / cm ² ) −
About the test piece of width: 25.4mmxheight: 25.4mmxlength: 200mm obtained using each CS, the breaking load was measured with a measuring instrument (Takachiho Seiki Co., Ltd .: Digital foundry sand. Measure using a strength tester. Then, the bending strength is calculated by the following formula using the measured breaking load.
Bending strength = 1.5 × LW / ab ²
[However, L: distance between fulcrums (cm), W: breaking load (kgf), a: width of test piece (cm), b: thickness of test piece (cm)]

-Measurement of scratch hardness (mm)-
About the test piece of width: 25.4mmxheight: 25.4mmxlength: 200mm obtained using each CS, the scratch hardness is measured using a scratch hardness meter (GF type). To do. For the scratch hardness, first, the tip of the scratch hardness tester is pressed against the surface of the test piece, and the upper black lever is rotated once in a clockwise direction and once in a counterclockwise direction, and the rotation is repeated five times. Thus, from the point where the tooth gradually sinks, the depth of the tooth penetration is read from the scale on the side (mm). The scratch hardness is stronger as the value is smaller and weaker as the value is larger.

-Measurement of filling rate (%)-
The ratio of the specific gravity of each test piece used above (calculated by dividing the mass by the volume of the test piece) with respect to the true specific gravity of the aggregate is calculated as a percentage.
Filling rate (%) = {mass (g) / volume (cm ³ ) of each test piece}
/ True specific gravity of aggregate (g / cm ³ ) × 100

-Measurement of strength after moisture absorption deterioration-
Put humidity-adjusting water / glycerol mixed solution and wire mesh in a container, float each test piece obtained above with a wire mesh, keep it in contact with water / glycerol mixed solution, store in such container for a predetermined time, Each specimen is subjected to moisture absorption deterioration. The strength of each test piece after the moisture absorption deterioration is measured according to the bending strength measurement method.

-Calculation of strength deterioration rate-
About each test piece obtained above, the bending strength and the strength after moisture absorption deterioration obtained in accordance with the measurement method, respectively, as the normal strength and the deterioration strength, respectively, the strength deterioration rate (%) based on the following formula, calculate.
Strength deterioration rate = (normal strength−deterioration strength) / normal strength × 100

−Observation of pot sand during kneading−
After kneading, the state of the sand adhering to the kettle is confirmed by visual observation and rubbing. And, when sand is not attached, ◯, when sand is attached, but when sand can be easily dropped by rubbing, △, when sand is attached and sand cannot be easily dropped ,evaluate.

-CS Production Example 1 (Example 1)-
Lunamos # 50 (trade name: manufactured by Kao Corporation), a commercially available spherical artificial sand for casting, is prepared as a fireproof aggregate, and a commercially available sodium silicate No. 3 (trade name: Fuji Chemical) is used as a caking additive. Co., Ltd.) was diluted with water to prepare an aqueous sodium silicate solution having a viscosity at 25 ° C. of 46.1 cP.

  Next, the above-mentioned Lunamos # 50 heated to a temperature of about 120 ° C. was put into a Shinagawa universal stirrer (5DM-r type) (Dalton Co., Ltd.), and the sodium silicate aqueous solution was further added to Lunamos # 50. In terms of solid content when considered as only the non-volatile content, 100 parts of is added at a rate of 0.5 part, kneaded for 3 minutes to evaporate the water, while the sand lump collapses After being stirred and mixed until it was taken out, dry coated sand (CS) 1 having free flow at room temperature was obtained. Then, the amount of lumps generated in the CS obtained by kneading, the moisture content of the CS, and the state of adhesion of the kettle during kneading were observed. The results are shown in the table below.

-Production Examples 2 to 4 of CS (Examples 2 to 4)-
As a binder, commercially available sodium silicate No. 3 (trade name: manufactured by Fuji Chemical Co., Ltd.) is diluted with water, and the viscosity at 25 ° C. is 36.3 cP, 17.3 cP, or 11.1 cP, respectively. CS2-4 were obtained according to the same procedure as in Production Example 1 except that the prepared sodium silicate aqueous solution was prepared.

-CS Production Examples 5 to 7 (Examples 5 to 7)-
As a binder, commercially available sodium silicate No. 5 (trade name: manufactured by Fuji Chemical Co., Ltd.) was diluted with water, and the viscosity at 25 ° C. was 36.3 cP, 17.3 cP, or 11.1 cP, respectively. CS5 to 7 were obtained according to the same procedure as in Production Example 1 except that the prepared sodium silicate aqueous solution was prepared.

-CS Production Example 8 (Example 8)-
As a fireproof aggregate, a commercially available alumina-based spherical artificial aggregate ESPAL # 60 (trade name: manufactured by Yamakawa Sangyo Co., Ltd.) was used, and an aqueous sodium silicate solution having a viscosity at 25 ° C. of 11.1 cP was prepared. Except for the above, CS8 was obtained according to the same procedure as in Production Example 1.

-CS Production Example 9 (Example 9)-
100 parts of Mikawa Sanda No. 7 using Mikawa Sanda No. 7 (trade name: manufactured by Mikawa Silica Co., Ltd.) as a fireproof aggregate and an aqueous sodium silicate solution having a viscosity of 11.1 cP at 25 ° C. On the other hand, CS9 was obtained according to the same procedure as in Production Example 1 except that it was added at a ratio of 1.0 part in terms of solid content when considered as only the nonvolatile content.

-CS Production Examples 10 to 13 (Comparative Examples 1 to 4)-
As a binder, commercially available sodium silicate No. 3 (trade name: manufactured by Fuji Chemical Co., Ltd.) was diluted with water, and the viscosities at 25 ° C. were respectively 72.5 cP, 55.8 cP, 6.9 cP, Or CS10-13 were obtained according to the procedure similar to manufacture example 1 except having prepared sodium silicate aqueous solution which was 6.0 cP.

-Production Examples 14-15 of CS (Comparative Examples 5-6)-
A sodium silicate aqueous solution in which a commercially available sodium silicate No. 5 (trade name: manufactured by Fuji Chemical Co., Ltd.) is diluted with water as a binder, and the viscosity at 25 ° C. is 6.9 cP or 6.0 cP. CS14-15 were obtained according to the procedure similar to manufacture example 1 except having prepared.

-Production Examples 16 to 19 of CS (Comparative Examples 7 to 10)-
As a binder, commercially available sodium silicate No. 1 (trade name: manufactured by Fuji Chemical Co., Ltd.) was diluted with water, and the viscosities at 25 ° C. were 121 cP, 36.3 cP, 11.1 cP, or 6, respectively. CS16-19 were obtained according to the procedure similar to manufacture example 1 except having prepared the sodium silicate aqueous solution which is 0.0 cP.

-Production Examples 20-23 of CS (Comparative Examples 11-14)-
As a binder, commercially available sodium silicate No. 2 (trade name: manufactured by Fuji Chemical Co., Ltd.) was diluted with water, and the viscosities at 25 ° C. were 121 cP, 36.3 cP, 11.1 cP, or 6, respectively. CS20 to 23 were obtained according to the same procedure as in Production Example 1 except that a sodium silicate aqueous solution of 0.0 cP was prepared.

-Production Example 24 of CS (Comparative Example 15)-
Production Example, except that commercially available potassium silicate No. 1 (trade name: manufactured by Fuji Chemical Co., Ltd.) was diluted with water as a water glass to prepare a potassium silicate aqueous solution having a viscosity at 25 ° C. of 8 cP. Following the same procedure as 1, CS24 was obtained.

-CS Production Example 25 (Comparative Example 16)-
Manufactured except that a commercially available potassium silicate No. 2 (trade name: manufactured by Fuji Chemical Co., Ltd.) was diluted with water as a water glass to prepare an aqueous potassium silicate solution having a viscosity at 25 ° C. of 10 cP. Following the same procedure as Example 1, CS25 was obtained.

-Examples of mold making-
The CS 1 to 25 having a temperature of 20 ° C. obtained in each of the CS production examples were blown into a molding die heated to 110 ° C. at a pressure of 0.3 MPa and filled. Thereafter, steam at a temperature of 99 ° C. was further blown for 5 seconds under a gauge pressure of 0.05 MPa, and the coated sand phase filled in the molding die was aerated. Then, after such aeration of water vapor is completed, hot air at a temperature of 150 ° C. is blown for 2 minutes under a gauge pressure of 0.03 MPa, and CS1 to 25 filled in the molding die are cured, respectively. Each mold used as a test piece [25.4 mm × 25.4 mm × 200 mm] was produced.

-Measurement of mold-
For each test piece corresponding to CS1-25 obtained above, according to the test method described above, the bulk density, filling rate, bending strength, strength after moisture absorption deterioration, strength deterioration rate, scratch hardness, respectively, The results are shown in Tables 1 to 4 below.

As is clear from the results of Tables 1 to 4, the sodium silicate aqueous solution used as the binder is sodium silicate having a SiO ₂ / Na ₂ O molar ratio in the range of 3.0 to 4.0. In the case of Examples 1 to 9 using No. 3 or No. 5 and an aqueous solution having a viscosity at 25 ° C. in the range of 10 to 50 cP, the filling rate and bending strength are good, and further, moisture absorption It is recognized that the strength after deterioration and the strength deterioration rate are excellent. Also, CS1～4 obtained in Examples 1 to 4, than CS5~7 obtained in Example 5-7, scratch hardness is better, in particular, the molar ratio of SiO ₂ / Na ₂ O It can be seen that the use of sodium silicate No. 3 in the range of 3.0 to 3.5 is effective. Here, the upper limit of the viscosity of commercially available sodium silicate No. 3 (stock solution) is about 70 to 75 cP, and the upper limit of the viscosity of commercially available sodium silicate No. 5 (stock solution) is about 35 to 40 cP. Thus, no experiments were conducted on sodium silicate aqueous solutions having a viscosity higher than their viscosity, and examples of low-viscosity sodium silicate aqueous solutions obtained by adding water to these stock solutions are shown. .

  Further, as is apparent from the results of Comparative Examples 4, 6, 10, and 14, CS in a wet state corresponding to CS 13, 15, 19, and 23 having a moisture content of 0.5% or more is a filling property. CS1-9 according to Examples 1-9, in which the moisture density is 0.5% or less, while the bulk density is in a blocked state and is incapable of being measured. It is recognized that it has sex. In Comparative Examples 15 and 16, CS24 and 25 obtained using potassium silicate Nos. 1 and 2 did not have sufficient fluidity even when the moisture content was lowered. It is recognized that the mold characteristics are inferior to those of CS1-9 obtained using sodium silicate No. 3 or No. 5 according to the present invention.

  Next, in the production of the coated sand, in order to contrast with the case of Example 4 (internal addition) in which a sodium silicate stock solution was diluted with water to form a sodium silicate aqueous solution as a binder, An experiment in the case of using a sodium acid stock solution and water added at the same time (external addition) was conducted, and the obtained coated sand was evaluated.

-CS Production Example 26 (Example 10)-
Lunamos # 50 (trade name: manufactured by Kao Corporation), a commercially available spherical artificial sand for casting, is prepared as a fireproof aggregate, and a commercially available sodium silicate No. 3 (trade name: Fuji Chemical) is used as a caking additive. A stock solution (manufactured by Kogyo Co., Ltd.) was prepared, and further, a dilution water equivalent to an aqueous sodium silicate solution having a viscosity of 11.1 cP at 25 ° C. was prepared by diluting the sodium silicate stock solution.

  Next, after the above-mentioned Lunamos # 50 heated to a temperature of about 120 ° C. was put into a Shinagawa universal stirrer (5DM-r type) (manufactured by Dalton Co., Ltd.), the stock sodium silicate stock solution was further added. To 100 parts of Lunamos # 50, in terms of solid content when considered only as a non-volatile content, at the same time as adding at a ratio of 0.5 part, the prepared dilution water was added and kneaded for 3 minutes, While evaporating the water, the mixture was stirred and mixed until the lump of sand collapsed, and then taken out to obtain dry CS26 having free flow at room temperature. Then, the amount of lumps generated in the CS obtained by kneading and the moisture content in the CS were measured, and further, the state of sticking to the kettle during kneading was observed. In addition, using the obtained CS26, the mold was molded in the same manner as described above, and the obtained mold test piece was subjected to the measurement methods described above according to the measurement method described above, bulk density, filling rate, bending strength, strength after moisture absorption deterioration, The strength deterioration rate and scratch hardness were measured, and the obtained results were shown together with the evaluation of CS4 obtained in Example 4 above in Table 5 below.

  As is clear from the results of Table 5, in Example 10 above, the sodium silicate stock solution was diluted with water and used as an aqueous sodium silicate solution (internal addition). When the sodium silicate stock solution and the dilution water are added simultaneously (external addition), it is recognized that the obtained CS4 and CS26 have substantially the same performance. Therefore, when kneading with the refractory aggregate, if the sodium silicate stock solution and the dilution water can be kneaded before evaporation, the sodium silicate stock solution and the dilution water can be added internally or externally, It will be appreciated that a coated sand having substantially similar properties can be formed.

  In addition, when the sodium silicate aqueous solution as a binder is kneaded with the refractory aggregate, the coated sand obtained by simultaneously kneading the solid oxide and salt as a curing agent is evaluated as follows. did.

-Production Examples 27 to 29 of CS (Examples 11 to 13)-
Lunamos # 50 (trade name: manufactured by Kao Corporation), a commercially available spherical artificial sand for casting, is prepared as a fireproof aggregate, and a commercially available sodium silicate No. 3 (trade name: Fuji Chemical) is used as a caking additive. A stock solution of (manufactured by Co., Ltd.) was diluted with water to prepare an aqueous sodium silicate solution having a viscosity of 17.3 cP at 25 ° C. Moreover, zinc carbonate (made by Kishida Chemical Co., Ltd.) was prepared as an additive which is a curing agent.

  And the manufacturing example 1 except having added zinc carbonate which is this additive in the ratio of 0.005, 0.015, or 0.025 mass part with respect to 100 mass parts of above-mentioned Lunamos # 50. According to the same procedure as above, CS27 to 29 were obtained. Further, measurement of the amount of lumps generated in the CS obtained by kneading and measurement of the moisture content of the CS were carried out, and further, the state of adhesion of the CS to the kettle during kneading was observed. In addition, using the obtained CS27-29, molds were formed in the same manner as described above, and for each of the obtained test pieces (molds), according to the measurement method described above, the bulk density, filling rate, bending resistance The strength, strength after moisture absorption degradation, and strength degradation rate were measured, and the results are also shown in Table 6 below.

-Production Examples 30 to 32 of CS (Examples 14 to 16)-
As an additive (curing agent), sodium tetraborate, potassium metaborate, or zinc oxide is used in place of zinc carbonate, and each additive is added in an amount of 0.015 with respect to 100 parts by mass of Lunamos # 50. CS30-32 were obtained according to the procedure similar to said manufacture example 27-29 except having added in the ratio of the mass part. And about these obtained CS30-32, the characteristic evaluation was performed similarly to the said manufacture examples 27-29, and the result was combined with following Table 6, and was shown.

As is apparent from the results of Table 6, the CS3 obtained in Example 3 was obtained by adding a solid oxide or salt as an additive (curing agent) as in Examples 11 to 16. As for CS27-32, all have the result that the strength after the moisture absorption deterioration is improved and the strength deterioration rate is reduced, and accordingly, in CS27-32, the moisture absorption deterioration is more effectively suppressed or prevented. It is recognized that it can be done.

Claims (13)

Mixing a water glass aqueous solution as a binder to the heated refractory aggregate and evaporating the water to form a coating layer of the binder on the surface of the refractory aggregate. When producing dry coated sand having properties,
As the water glass aqueous solution, an aqueous solution of sodium silicate having a SiO ₂ / Na ₂ O molar ratio of 3.0 to 4.0 is used, and the viscosity at 25 ° C. of the aqueous solution is within a range of 10 to 50 cP. A method for producing coated sand, which is adjusted and mixed with the refractory aggregate.   The aqueous solution of sodium silicate is used at a ratio of 0.1 to 2.5 parts by mass in terms of solid content with respect to 100 parts by mass of the refractory aggregate. Manufacturing method of coated sand. Mixing a water glass aqueous solution as a binder to the heated refractory aggregate and evaporating the water to form a coating layer of the binder on the surface of the refractory aggregate. When producing dry coated sand having properties,
As the water glass aqueous solution, a sodium silicate aqueous solution having an SiO ₂ / Na ₂ O molar ratio of 3.0 to 4.0 and a viscosity at 25 ° C. of 30 cP or more is used. Using the aqueous sodium silicate solution and an amount of water with a viscosity at 25 ° C. of the aqueous sodium silicate solution in the range of 10 to 30 cP simultaneously or with a time difference within 10 seconds, the fireproof aggregate is used. A method for producing coated sand, characterized by being mixed.   The aqueous solution of sodium silicate is used at a ratio of 0.1 to 2.5 parts by mass in terms of solid content with respect to 100 parts by mass of the refractory aggregate, and water is 0.1 to 3. The method for producing coated sand according to claim 3, wherein the coated sand is used at a ratio of 0 part by mass. 5. The coated sand production method according to claim 1, wherein the sodium silicate has a SiO ₂ / Na ₂ O molar ratio of 3.0 to 3.5. .   The method for producing coated sand according to any one of claims 1 to 5, wherein water is evaporated within 5 minutes from the start of mixing of the aqueous sodium silicate solution.   In mixing the sodium silicate aqueous solution, at least one of silicon dioxide, zinc oxide, aluminum oxide, boron oxide, zinc carbonate, potassium metaborate, sodium tetraborate, and potassium tetraborate is further added. The method for producing coated sand according to any one of claims 1 to 6, wherein the coated sand is produced. 8. A coated sand having a moisture content of 0.5% by mass or less and a dama amount of composite particles in which a plurality of particles are combined is 3% by mass or less . The manufacturing method of the coated sand of any one of Claims 1 . The coated sand obtained by the manufacturing method according to any one of claims 1 to 8 is filled into a molding cavity of a mold that gives a target mold, and then water vapor is passed through the coated sand. A method for producing a mold, wherein a target mold is obtained by solidifying or curing in the mold.   The method for producing a mold according to claim 9, wherein after the water vapor is passed, dry air, heated dry air, or nitrogen gas is further passed through the molding cavity of the mold.   The mold manufacturing method according to claim 9 or 10, wherein the coated sand is preheated to 30 ° C or higher and then filled into a molding cavity of the mold.   The method for producing a mold according to any one of claims 9 to 11, wherein the mold is preheated and kept warm. A method for producing a mold, comprising forming a target mold by laminating using the coated sand obtained by the production method according to any one of claims 1 to 8.