WO2018097180A1 - Coated sand, method for producing same, and method for producing casting mold using same - Google Patents

Abstract

The present invention provides coated sand that is in a dry state, that is fluid at room temperature, and that makes it possible to obtain excellent strength and excellent disintegration properties in a casting mold obtained using the coated sand. The coated sand is in a dry state, is fluid at room temperature, and is coated by a coating layer in which the surface of a fire-resistant aggregate contains water glass as a binder. The coating layer includes spherical particles that are preferably spherical particles having an average particle size of 0.1-20 µm.

Description

Coated sand, method for producing the same, and method for producing a mold using the same

The present invention relates to a coated sand, a method for producing the same, and a method for producing a mold using the same, and in particular, a mold finally obtained exhibits excellent strength and is excellent in disintegration. The present invention relates to a dry coated sand having fluidity.

Conventionally, as one of the molds used for casting molten metal, using a coated sand made of refractory aggregate coated with a predetermined caking additive, it is molded into the desired shape. What is obtained is used. Specifically, “Casting Engineering Handbook”, pages 78-90, edited by the Japan Foundry Engineering Society, as a binder in such coated sand, in addition to inorganic binders such as water glass, phenolic resins, Organic binders using resins such as furan resins and urethane resins have been clarified, and methods for molding self-hardening molds using these binders have also been clarified.

For example, in Japanese Patent Application Laid-Open No. 2012-076115 (Patent Document 1), a solid coating layer containing water glass on the surface of a refractory aggregate is used as a binder coated refractory using water glass as a binder. A binder coated refractory with good flowability (coated sand) is disclosed. Therefore, such a binder-coated refractory having good fluidity (coated sand) is filled in a molding cavity of a mold for mold making, and then, when water vapor is allowed to pass therethrough, it is applied. The method of obtaining the target mold has been clarified as the binder coated refractory (coated sand) is solidified.

However, in the conventional dry-type coated sand as disclosed in Patent Document 1, the method disclosed therein, specifically, after filling the molding cavity, water vapor is contained in the filled phase of the coated sand. In the case of molding according to the method of ventilating, there is a problem that once the coated sand is filled in the mold, there is no room for improving the filling property of the coated sand in the mold. On the other hand, even the disintegration property of the obtained mold is still insufficient, leaving room for improvement.

JP 2012-76115 A

Here, the present invention has been made against the background of such circumstances, and the problem to be solved is that the finally obtained mold exhibits excellent strength and excellent disintegration. Another object of the present invention is to provide a dry coated sand having room temperature fluidity. Another object of the present invention is to provide a mold manufacturing method using such excellent coated sand.

In order to solve the above-described problems, the present invention can be suitably implemented in various aspects as listed below, and each aspect described below is employed 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) The surface of the refractory aggregate is covered with a coating layer containing water glass, which is a dry coated sand having room temperature fluidity, and spherical particles are contained in the coating layer. A characteristic coated sand.
(2) The coated sand according to the aspect (1), wherein the moisture content is 5 to 55% by mass of the solid content of water glass in the coating layer.
(3) The aspect (1), wherein the content of the spherical particles is 0.1 to 500 parts by mass with respect to 100 parts by mass of the solid content of water glass in the coating layer.
Or the coated sand as described in said aspect (2).
(4) The coated sand according to any one of aspects (1) to (3), wherein the spherical particles have an average particle diameter of 0.1 to 20.0 μm.
(5) In any one of the above aspects (1) to (4), the spherical particles are one or more selected from spherical particles made of silicon dioxide, aluminum oxide, or titanium oxide. The described coated sand.
(6) The average particle diameter d1 of the spherical particles and the average particle diameter d2 of the refractory aggregate
The coated sand according to any one of the aspects (1) to (5) satisfying the following formula (1).
4 × d1 ≦ d2 ≦ 5000 × d1 (1)
(7) The coated sand according to any one of the aspects (1) to (6), wherein the refractory aggregate is spherical.
(8) A method for producing dry coated sand having room temperature fluidity, in which the surface of the refractory aggregate is covered with a coating layer containing water glass. By mixing a binder mainly composed of glass and spherical particles and evaporating water, the surface of the refractory aggregate is covered with a coating layer containing water glass and spherical particles, and the moisture content is increased. A method for producing a coated sand, comprising producing a coated sand having a content of 5 to 55 mass% of the solid content of water glass in the covering layer.
(9) After using the coated sand according to any one of the above aspects (1) to (7) and filling it into a mold cavity of a mold that gives a target mold, water vapor is added. A method for producing a mold, characterized in that a target mold is obtained by aeration, holding in such a mold, and solidifying or curing.
(10) Water is added to the coated sand according to any one of the above aspects (1) to (7) to make it wet, and the wet coated sand is filled in a mold. A method for producing a mold, which is characterized in that a target mold is obtained by holding in the mold and then solidifying or curing.
(11) According to the aspect (9) or the aspect (10), during the holding of the mold, further, dry air, heated dry air, or nitrogen gas is vented into the molding cavity of the mold. Mold manufacturing method.

Thus, in the dry coated sand having room temperature fluidity according to the present invention, the coating layer covering the surface of the refractory aggregate contains spherical particles together with water glass as a binder, It is composed. Such coated sand of the present invention is filled in the mold (more specifically, in the molding cavity of the mold), and moisture is supplied to the filled coated sand (filled phase) by aeration of water vapor or the like. Then, the spherical particles effectively flow between the refractory aggregates together with the water glass made into a solution by the supplied moisture, and as a result, the filling property of the coated sand in the molding die (in the molding cavity) is improved. It is advantageously improved. In a mold obtained by solidifying or hardening the water glass with such improved filling properties, spherical particles are effectively interposed in the gaps between adjacent refractory aggregates. As a result, excellent strength is exhibited.

Further, in the mold obtained using the dry coated sand having room temperature fluidity of the present invention, a structure similar to a stone wall is formed by refractory aggregate, spherical particles, and solidified or hardened water glass. As a result, a strength that can withstand the high pressure at the time of pouring the molten metal is exhibited. Furthermore, when high-temperature molten metal is poured into the mold, the water glass that bonds between the refractory aggregates in the mold is decomposed, and spherical particles exist between the refractory aggregates. In the mold obtained using the coated sand of the present invention, the bonding action between the refractory aggregates by water glass is lost early after the injection of the molten metal compared to the conventional one, and therefore, the collapsibility It will be excellent.

It is a longitudinal cross-sectional explanatory drawing of the sand mold for casting tests used in order to measure the collapsibility of a core in an Example. It is a longitudinal cross-sectional explanatory drawing of the aluminum alloy casting which included the waste core in the Example.

By the way, the coated sand according to the present invention is generally prepared by mixing water glass in the state of an aqueous solution as a binder with the refractory aggregate and evaporating water from the mixture, in other words, an aqueous solution. The surface of the refractory aggregate is produced by evaporating the water of the water glass in the state of It is formed in a dry state and has good room temperature fluidity.

Here, the “dry coated sand having room temperature fluidity” in the present invention means a coated sand from which a measured value is obtained when the dynamic angle of repose is measured regardless of the moisture content. This dynamic angle of repose means that the coated sand is accommodated in a cylinder whose one end in the axial direction is closed with a transparent plate (for example, in a container having a diameter of 7.2 cm and a height of 10 cm, its volume The coated sand is flowing in the cylinder by holding the shaft center in the horizontal direction and rotating it around the horizontal axis at a constant speed (for example, 25 rpm). The slope of the layer is flat and refers to the angle formed between the slope and the horizontal plane. The dynamic repose angle of the coated sand according to the present invention is preferably 80 ° or less, more preferably 45 ° or less, and still more preferably 30 ° or less. In the present invention, a coated sand having a dynamic angle of repose of 45 ° or less can be advantageously obtained by using a spherical refractory aggregate. In addition, for example, when the coated sand is moist, it does not flow in the cylinder, the slope of the coated sand layer is not formed as a flat surface, and as a result, the dynamic angle of repose cannot be measured, It will be referred to as wet coated sand.

The dry coated sand having room temperature fluidity according to the present invention has a moisture content of 5 to 55% by mass with respect to the solid content of water glass contained in the coating layer covering the surface of the refractory aggregate. The corresponding amount is desirable, more desirably 10 to 50% by mass, and most desirably 20 to 50% by mass. When the moisture content in the coated sand is less than the amount corresponding to 5% by mass with respect to the solid content of the water glass in the coating layer, the water glass is vitrified and water is added again during the mold making. There is a possibility that it does not return to a solution state. On the other hand, if the amount exceeds 55% by mass, the coated sand may not be in a dry state. In addition, it does not specifically limit as a measuring method of the moisture content in a coated sand, The method according to types, such as water glass, is employable suitably. Specifically, the measuring method described in the column of Examples described later can be exemplified. In addition, when an organic component containing moisture (for example, a surfactant or a humectant) is added as an additive to the coated layer of the coated sand, the moisture content is also taken into account with the moisture in the organic component. Must be measured (calculated).

The refractory aggregate constituting the coated sand of the present invention is a refractory substance that functions as a base material of a mold, and any of various refractory granular or powder materials conventionally used for molds. Specifically, silica sand, recycled silica sand, special sand such as alumina sand, olivine sand, zircon sand, chromite sand, ferrochrome slag, ferronickel slag, converter slag, etc. Slag-based particles; artificial 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 casting sand for casting molds. Even mixed sand made by adding fresh sand to sand or recovered sand and mixing them can be used. Such a refractory aggregate is generally used with a particle size of about 40 to 130, preferably about 50 to 110 in terms of AFS index.

Also, the refractory aggregate is preferably spherical, and specifically, a refractory aggregate having a particle shape factor of 1.2 or less, more preferably 1.0 to 1.1 is desirable. By using a fireproof aggregate with a particle shape factor of 1.2 or less, the fluidity and filling properties during mold making are improved, and the number of contacts between aggregates increases, so that the same strength is expressed. It is possible to reduce the amount of binders and additives necessary for the treatment. In addition, the particle size coefficient of the aggregate used here is generally adopted as one scale indicating the outer shape of the particle, and is also referred to as a particle shape index, and as the value approaches 1, This means approaching a sphere (true sphere). And such a particle shape factor is represented by the value calculated using the surface area (sand surface area) of the aggregate measured by various well-known methods, for example, a sand surface area measuring device ( This means a value obtained by measuring the surface area of actual aggregate particles (granular sand) per gram using George Fischer) and dividing it by the theoretical surface area. In addition, a theoretical surface area is a surface area when it is assumed that aggregate particles (sand particles) are all spherical.

In the coated sand according to the present invention, a binder mainly composed of water glass is used as a binder for covering the fireproof aggregate as described above. Water glass is a water-soluble silicate compound. Examples of such a silicate compound include sodium silicate, potassium silicate, sodium metasilicate, potassium metasilicate, lithium silicate, and ammonium silicate. Among them, sodium silicate (sodium silicate) is particularly advantageously used in the present invention. As a binder, various water-soluble binders such as thermosetting resins, saccharides, proteins, synthetic polymers, salts and inorganic polymers may be used in combination as long as water glass is used as a main component. Is possible. When other water-soluble binder is used in combination with water glass, the ratio of water glass in the whole binder is preferably 60% by mass or more, more preferably 80% by mass or more, and most preferably 90% by mass. That's it.

Here, sodium silicate is usually classified and used as No. 1 to No. 5 depending on the molar ratio of SiO ₂ / Na ₂ O ₂ . 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 ₂ The molar ratio is 2.4 to 2.6, and sodium silicate No. 3 has a SiO ₂ / Na ₂ O molar ratio of 2.8 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-K-1408. In the present invention, these various sodium silicates may be used alone or in combination, and the molar ratio of SiO ₂ / Na ₂ O may be adjusted by mixing. Is possible.

In the present invention, in order to advantageously obtain a dry coated sand, the sodium silicate constituting the water glass used as the binder generally has a SiO ₂ / Na ₂ O molar ratio of 1.9 or more, preferably Is preferably 2.0 or more, more preferably 2.1 or more, and sodium silicate corresponding to No. 1 and No. 2 in the above-mentioned classification of sodium silicate is particularly advantageously used. Such sodium silicates No. 1 and No. 2 provide dry coated sand having stable and good characteristics even when the sodium silicate concentration in the water glass is wide. Further, the upper limit of the SiO ₂ / Na ₂ O molar ratio in such sodium silicate is appropriately selected according to the characteristics of the water glass in the form of an aqueous solution, but generally 3.5 or less, It is preferably 3.2 or less, more preferably 2.7 or less. Here, when the molar ratio of SiO ₂ / Na ₂ O is smaller than 1.9, the viscosity of the water glass is lowered, and it becomes difficult to make the coated sand dry unless the water content is considerably reduced. On the other hand, if it exceeds 3.5, the solubility in water decreases, the adhesion area cannot be gained, and the strength of the mold finally obtained may decrease.

The water glass used in the present invention means a solution of a silicate compound in a state dissolved in water. In addition to being used in a stock solution as purchased in the market, water is added to such a stock solution. It is added and used in a diluted state. And, from such water glass, the non-volatile content (water glass component) excluding volatile substances such as water and solvent is called solid content, which corresponds to the above-described soluble silicate compound such as sodium silicate. To do. Moreover, the higher the proportion of such solid content (nonvolatile content), the higher the concentration of the silicate compound in the water glass. Therefore, the solid content of the water glass used in the present invention corresponds to the amount excluding the amount of water in the stock solution when it is composed only of the stock solution, while the stock solution is converted into water. When the diluted solution obtained by dilution is used, the amount excluding the amount of water in the stock solution and the amount of water used for dilution corresponds to the solid content of the water glass used. It becomes.

The solid content (nonvolatile content) in such water glass is set to an appropriate ratio depending on the type of the water glass component (soluble silicate compound), etc., but is preferably 20 to 50. It is desirable that it is contained in a proportion by mass. By making the water glass component corresponding to the solid content appropriately present in the aqueous solution, the water glass component can be uniformly and uniformly applied to the fire resistant aggregate during mixing (kneading) with the fire resistant aggregate. So that the target mold can be advantageously formed. If the concentration of the water glass component in the water glass is too low and the total amount of solids is less than 20% by mass, the heating temperature is increased or the heating time is increased for drying the coated sand. For this reason, problems such as energy loss are caused. In addition, if the ratio of the solid content in the water glass becomes too high, it becomes difficult to uniformly coat the surface of the refractory aggregate with the water glass component, which causes a problem in improving the properties of the target mold. Therefore, it is desirable to prepare water glass in the form of an aqueous solution so that the solid content is 50% by mass or less, and thus the water content is 50% by mass or more.

Such water glass is preferably in a proportion of 0.1 to 5.0 parts by mass in terms of solid content when considered as only non-volatile content with respect to 100 parts by mass of the refractory aggregate. It is desirable to use at a ratio of 2.5 parts by mass, and among them, a ratio of 0.2 to 2.0 parts by mass is particularly advantageously employed to form a predetermined coating layer on the surface of the refractory aggregate. The Rukoto. Here, the measurement of solid content is implemented as follows. That is, 10 g of a sample was weighed and stored in an aluminum foil dish (length: 9 cm, width: 9 cm, height: 1.5 cm), placed on a heating plate maintained at 180 ± 1 ° C., and left for 20 minutes. After that, the sample pan is inverted and left on the heating plate for another 20 minutes. Thereafter, the sample dish is taken out from the heating plate, allowed to cool in a desiccator, weighed, and the solid content (% by mass) is calculated by the following formula.
Solid content (mass%) = [mass after drying (g) / mass before drying (g)]
× 100

In the present invention, if the amount of water glass used is too small, it is difficult to form a coating layer on the surface of the refractory aggregate, and the solidification or hardening of the coated sand at the time of mold making may not proceed sufficiently. There is. In addition, even if the amount of water glass used is excessive, an excessive amount of water glass adheres to the surface of the refractory aggregate, making it difficult to form a uniform coating layer, and the coated sand adheres to each other. There is also a risk of agglomeration (composite particle formation), which adversely affects the physical properties of the final mold, and also makes it difficult to remove the sand from the core after casting the metal. There is a risk of triggering.

And, in the coated sand according to the present invention, there is a great technical feature in that spherical particles are contained in the coating layer containing water glass that covers the surface of the refractory aggregate. . Coated sand containing spherical particles in such a coating layer containing water glass is filled in the molding die (in the molding cavity of the molding die), and water vapor is added to the filled coated sand (filled phase). When moisture is supplied by ventilation or the like, the spherical particles in the coating layer effectively flow between the refractory aggregates together with the water glass that has become a solution by the supplied moisture, and as a result, in the mold ( The filling property of the coated sand in the molding cavity) is advantageously improved. In a mold obtained by solidifying or hardening the water glass with such improved filling properties, spherical particles are effectively interposed in the gaps between adjacent refractory aggregates. As a result, excellent strength is exhibited.

Further, in the mold obtained using the dry coated sand having room temperature fluidity of the present invention, a structure similar to a stone wall is formed by refractory aggregate, spherical particles, and solidified or hardened water glass. As a result, a strength that can withstand the high pressure at the time of pouring the molten metal is exhibited. Furthermore, when high-temperature molten metal is poured into the mold, the water glass that bonds between the refractory aggregates in the mold is decomposed, and spherical particles exist between the refractory aggregates. In the mold obtained by using the coated sand of the present invention, the bonding action between the refractory aggregates by water glass is lost early after the molten metal is injected as compared with the conventional one. It will be excellent.

Here, in the dry coated sand having room temperature fluidity of the present invention, the spherical particles contained in the coating layer have an average particle diameter of preferably 0.1 to 20.0 μm, more preferably. Those having a thickness of 0.1 to 10 μm, most preferably 0.5 to 5.0 μm are used. In the present invention, the content of the spherical particles is 0.1 to 500 parts by mass, preferably 0.3 to 300 parts by mass with respect to 100 parts by mass of the solid content of water glass in the coating layer. More preferably, it is 0.5 to 200 parts by mass, still more preferably 0.75 to 100 parts by mass, and most preferably 1.0 to 50 parts by mass. As described above, it is possible to more advantageously enjoy the above-described effect by including spherical particles having a predetermined average particle diameter in the coating layer in a predetermined ratio. The average particle diameter of the spherical particles can be obtained from the particle size distribution measured by a laser diffraction type particle size distribution measuring device or the like.

Further, in the present invention, when moisture is supplied to mold making, spherical particles advantageously flow together with water glass in a solution state in the gap between adjacent refractory aggregates, and the refractory bone In order to effectively interpose between the materials, the average particle diameter of the spherical particles: d1 and the average particle diameter of the refractory aggregate: d2 preferably satisfy the following formula (1), and the following formula ( It is more preferable to satisfy 2), and it is most preferable to satisfy the following formula (3). The average particle size of the refractory aggregate can also be obtained from the particle size distribution measured by a laser diffraction type particle size distribution measuring device or the like.
4 × d1 ≦ d2 ≦ 5000 × d1 (1)
6 × d1 ≦ d2 ≦ 3000 × d1 (2)
7 × d1 ≦ d2 ≦ 2500 × d1 (3)

The spherical particles used in the present invention are not particularly limited as long as they have a spherical shape, and are not necessarily required to have a true spherical shape. Usually, those having a sphericity of 0.5 or more are preferably 0. Those of 0.7 or more, more preferably 0.9 or more, are advantageously used. Here, the sphericity is the average value of the aspect ratio (minor axis / major axis ratio) obtained from the projection shape of 10 single particles randomly selected in scanning electron microscope observation. I mean. In addition, since there are protrusions and depressions on the surface of non-spherical particles (non-spherical particles), for example, the non-spherical particles are refractory aggregate together with water glass that has become a solution by the supplied moisture. When trying to flow between the particles, non-slip action occurs due to the collision between the projections on the surface of the non-spherical particles and the refractory aggregate particles or other non-spherical particles, and water between the refractory aggregate particles The flow of glass and non-spherical particles is impeded. For this reason, when non-spherical particles are used in the present invention, there is a risk of reducing the filling properties and strength of the finally obtained mold.

The material constituting the spherical particles used in the present invention is not particularly limited, but is preferably an inorganic metal oxide. As particles composed of inorganic metal oxides, particles composed of silicon dioxide, aluminum oxide, titanium oxide, etc. are advantageously used. Among them, particularly, silicon dioxide particles are strongly alkaline water glass composed of silicon dioxide. It can react with silanol groups formed on the surface, and when water is evaporated, a strong bond is formed between silicon dioxide and solid water glass, which can improve the mold strength. ,preferable. Silicon dioxide has crystallinity and amorphousness, but amorphous is desirable. Amorphous silicon dioxide includes precipitated silica, calcined silica produced in an electric arc or by flame hydrolysis, ZrSiO Examples include silica produced by pyrolysis of ₄ , silicon dioxide produced by oxidation of metallic silicon with a gas containing oxygen, and quartz glass powder of spherical particles produced from crystalline quartz by melting and subsequent rapid cooling. . Of course, these can be used alone or in combination of two or more. In the present invention, silicon dioxide is treated as an inorganic metal oxide.

Furthermore, in the coated sand of the present invention, in addition to the spherical particles described above, various additives can be appropriately contained in the coating layer as necessary.

A surfactant can be exemplified as one of such additives. When a surfactant is contained in the coating layer of the coated sand of the present invention, the water permeability in the coated sand, in other words, the wettability of the coated sand with respect to water is effectively improved. Even when a small amount of moisture is supplied to the coated sand filled therein, the entire coated sand in the molding cavity is advantageously wetted and becomes wet. As described above, since the amount of moisture added to the coated sand can be suppressed to a small amount, the mold release property of the molded mold is further improved, and the obtained mold exhibits more excellent strength. It will be.

In the present invention, conventionally known various surfactants, for example, cationic surfactants, anionic surfactants, amphoteric surfactants, nonionic surfactants, silicone surfactants and fluorine-based surfactants. Any surfactant or the like can be used as long as the object of the present invention is not impaired. The silicone-based surfactant specifically indicates a surfactant having a siloxane structure as a nonpolar site, and the fluorine-based surfactant particularly indicates a surfactant having a perfluoroalkyl group. In addition, the content of the surfactant in the present invention is desirably 0.1 to 20.0 parts by mass with respect to 100 parts by mass of the solid content of water glass in the coating layer, and more preferably 0.5 to 15 parts by mass. 0.0 parts by mass is preferable, and 0.75 to 12.5 parts by mass is particularly preferable. If the amount of the surfactant to be contained is too small, the above-mentioned effects may not be enjoyed advantageously. On the other hand, even if the amount of the surfactant is too large, the effect according to the amount used may be reduced. There is no improvement, and depending on the boiling point of the surfactant, the surfactant may not be solidified when the water glass is dried, and it may not be obtained even when trying to obtain a dry coated sand. Moreover, it is not a good idea from the viewpoint of cost effectiveness.

Further, the coating layer of the coated sand of the present invention may further contain a moisturizing agent. By incorporating a moisturizing agent into the coating layer containing water glass, the wettability of the coated sand wetted by moisture during mold casting is stably maintained until solidified or cured by heating. It becomes possible. The content of the humectant in the present invention is preferably 0.1 to 20.0 parts by mass with respect to 100 parts by mass of the solid content of water glass in the coating layer, and more preferably 0.5 to 15.0 parts by mass. Part is more desirable, and most preferably 0.75 to 12.5 parts by mass. Moreover, as such a humectant, polyhydric alcohol, water-soluble polymer, hydrocarbons, saccharides, protein, inorganic compounds, and the like can be used.

Specific examples of the polyhydric alcohol include ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, dipropylene glycol, propylene glycol, butylene glycol, 1,2-butanediol, 1,2-pentanediol, 1,5-pentanediol, 1,2-hexanediol, 2-ethyl-1,3-hexanediol, 1,6-hexanediol, 1,2-heptanediol, 1,2-octanediol, 1,2, Examples include 6-hexanetriol, thioglycol, hexylene glycol, glycerin, trimethylolethane, and trimethylolpropane. The water-soluble polymer compound particularly refers to a compound having 5 to 25 alcoholic hydroxyl groups per 1000 molecular weight. Examples of such water-soluble polymer compounds include vinyl alcohol polymers such as polyvinyl alcohol and various modified products thereof; celluloses such as alkyl cellulose, hydroxyalkyl cellulose, alkyl hydroxyalkyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, and hydroxypropyl methyl cellulose. Derivatives; starch derivatives such as alkyl starch, carboxymethyl starch, and oxidized starch; and water-absorbing polymers such as sodium polyacrylate. Examples of the hydrocarbons include aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, petroleum ether, petroleum benzyl, tetralin, decalin, tertiary amylbenzene, dimethylnaphthalene and the like. Examples of the saccharide include monosaccharides, oligosaccharides, polysaccharides such as dextrin, among which monosaccharides are saccharides that cannot be decomposed into simpler saccharides by hydrolysis, preferably Tricarbon sugar (monosaccharide having 3 carbon atoms) to decacarbon sugar (monosaccharide having 10 carbon atoms), more preferably hexose sugar (monosaccharide having 6 carbon atoms). Moreover, gelatin etc. are mentioned as protein. In addition, examples of inorganic compounds include sodium chloride, sodium sulfate, calcium chloride, magnesium chloride, and silicate. These various humectants can be used alone or in admixture of two or more.

In addition, various conventionally known moisturizers include those that are water-soluble to those that are sparingly water-soluble. In the present invention, the viscosity increases when poured into water at room temperature (25 ° C.). A moisturizing agent with a low is advantageously used. Specifically, in the case of a water-soluble humectant, an amount of humectant corresponding to 20% of the mass of water is added to water at room temperature, and the mixture is stirred for 1 hour. A humectant of 8 to 10 cP, preferably 0.8 to 5 cP, is advantageously used. On the other hand, a poorly water-soluble humectant exhibits an effect as a humectant when dispersed in water. Even if it is a poorly water-soluble humectant, it is 20% of the mass of water in normal temperature water. It is preferable that a moisturizing agent in an amount corresponding to 1 is added, stirred for 1 hour, the solution after stirring (a mixture of water and moisturizing agent) is filtered, and the viscosity of the obtained filtrate is within the above range. Used. As described above, the humectant advantageously used in the present invention includes cellulose derivatives such as glycerin and hydroxypropylmethylcellulose, water-absorbing polymers such as sodium polyacrylate, vinyl alcohol polymers such as polyvinyl alcohol, and weight average molecular weight. 50,000 or more polyethylene glycol (polyethylene oxide) etc. can be mentioned.

Furthermore, in the present invention, a moisture resistance improver may be included in the coating layer. Inclusion of a moisture resistance improver in the coating layer can improve the moisture resistance of the final mold. As the moisture resistance improver used in the present invention, any agent can be used as long as it is conventionally used in the coated sand as long as it does not impair the effects of the present invention. Specifically, 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, sodium carbonate, tetraboric acid Sodium, potassium tetraborate, lithium tetraborate, ammonium tetraborate, calcium tetraborate, strontium tetraborate, silver tetraborate, sodium metaborate, potassium metaborate, lithium metaborate, ammonium metaborate, metaborate Calcium, silver metaborate, borate salts such as copper metaborate, lead metaborate, magnesium metaborate, sodium sulfate, potassium sulfate, lithium sulfate, magnesium sulfate, calcium sulfate, strontium sulfate, barium sulfate, titanium sulfate, aluminum sulfate, sulfuric acid Zinc, copper sulfate Sulfate, sodium phosphate, sodium hydrogen phosphate, potassium phosphate, potassium hydrogen phosphate, lithium phosphate, lithium hydrogen phosphate, magnesium phosphate, calcium phosphate, titanium phosphate, aluminum phosphate, zinc phosphate, etc. Phosphate, lithium hydroxide, magnesium hydroxide, calcium hydroxide, strontium hydroxide, barium hydroxide, aluminum hydroxide, zinc hydroxide and other hydroxides, silicon, zinc, magnesium, aluminum, calcium, lithium, copper Examples thereof include oxides such as iron, boron and zirconium. Among these, basic zinc carbonate, sodium tetraborate, potassium metaborate, lithium sulfate, and lithium hydroxide can improve moisture resistance more advantageously. The moisture resistance improvers including those described above can be used alone, and two or more kinds can be used in combination.

In general, the amount of such moisture resistance improver used is preferably about 0.5 to 50 parts by mass with respect to 100 parts by mass of the solid content of water glass. Is more preferably 20 parts by mass, and particularly preferably 2-15 parts by mass. In order to advantageously enjoy the effect of adding the moisture resistance improver, it is desirable that the amount used is 0.5 parts by mass or more. On the other hand, if the amount added is too large, binding of water glass is inhibited, It is desirable that the amount be 50 parts by mass or less because there is a possibility of causing problems such as a decrease in the strength of the finally obtained mold.

In addition, as another additive, it is also effective to include a coupling agent that strengthens the bond between the refractory aggregate and water glass. For example, a silane coupling agent, a zircon coupling agent, a titanium coupling agent Etc. 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, and 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, stearyl alcohol; stearic acid metal salts such as lead stearate, zinc stearate, calcium stearate, magnesium stearate; stearin Acid monoglycerides, stearyl stearate, hydrogenated oils and the like can be used. 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 5% by mass or less, preferably 3% by mass or less with respect to the solid content of the water glass in the coated sand coating layer. It is contained in

By the way, when producing a dry coated sand having room temperature fluidity according to the present invention, generally, water glass as a binder, spherical particles, and as necessary, are used for a refractory aggregate. Additives are added, kneaded or mixed and mixed uniformly to cover the surface of the refractory aggregate with water glass containing spherical particles, and the water of such water glass is evaporated. A technique of forming a coating layer containing water glass and spherical particles on the surface of the refractory aggregate is used. In such a technique, water vaporization of the coating layer needs to be performed quickly before the water glass solidifies or hardens, so that the water glass in the form of an aqueous solution is used against the refractory aggregate. In general, it is desirable to remove the water content within 5 minutes, and more preferably within 3 minutes, after the addition (mixing) of the powder to obtain a dry powdered coated sand. If the transpiration time becomes longer, the mixing (kneading) cycle becomes longer, the productivity of the coated sand is lowered, and the time that the water glass is in contact with CO ₂ in the air becomes longer, resulting in inactivation. This is because there is a high risk of occurrence.

Moreover, in the manufacturing process of the above-mentioned coated sand, as one of effective means for rapidly evaporating the water in the water glass, the refractory aggregate is preheated and water in the form of an aqueous solution is added. A technique is adopted in which glass and spherical particles are kneaded or mixed to be mixed. By mixing or mixing water glass and spherical particles with this preheated refractory aggregate, the water in the water glass is very quickly heated by the heat of such refractory aggregate. This means that the moisture content of the resulting coated sand can be effectively reduced, and a dry powder having room temperature fluidity can be advantageously obtained. . Here, the preheating temperature of the refractory aggregate is appropriately selected depending on the water content of the water glass and the blending amount thereof, but generally a temperature of about 100 to 160 ° C. is preferable. A temperature of about 100 to 140 ° C. is employed. If this preheating temperature is too low, it is not possible to effectively evaporate water, and it takes time to dry. Therefore, it is desirable to employ a temperature of 100 ° C. or higher. If it is too high, hardening of the water glass component will proceed while cooling of the resulting coated sand, and in addition, the formation of composite particles will proceed, so the function as the coated sand, especially the strength of the final mold obtained. This causes problems in physical properties.

In the coated sand of the present invention, spherical particles to be contained in the coating layer containing water glass and other additives used as necessary, for example, surfactants and moisturizers, were previously mixed with water glass. It may be added to the refractory aggregate in a state and kneaded, or it may be added separately from the water glass at the time of kneading and further kneaded. It may be provided and charged and kneaded. Therefore, the coating layer in the coated sand of the present invention is, for example, in a state where water glass and spherical particles are integrally integrated, or from the surface of the refractory aggregate to the outside, While the concentration of (nonvolatile content) gradually decreases or increases, the concentration of spherical particles or the like is configured to increase or decrease gradually. In kneading and the like, it is desirable that the water glass and the spherical particles are added to the refractory aggregate first by adding the water glass and kneading, and then adding the spherical particles (with a time difference). . By following such an order, spherical particles are present near the surface of the coating layer on the surface of the obtained coated sand, so that a mold formed using such a coated sand has better filling properties. Will be demonstrated. In addition, when water glass is introduced into the kneader (mixer), the viscosity of the kneaded product increases as the water contained in the water glass evaporates, and the motor load of the mixer increases. The spherical particles can be effectively adhered to the soft water glass that covers the surface of the refractory aggregate by introducing the spherical particles before becoming, and the spherical particles fall off in the finally obtained coated sand. Is advantageously prevented, and it is also possible to enjoy the effect that a coated sand in which spherical particles are uniformly distributed on the surface is advantageously obtained. In the production of the coated sand of the present invention, the water glass as a binder can be used even if it is diluted with water in order to adjust the viscosity. It is also possible to add water glass and water separately during kneading or mixing with the material.

According to the production method as described above, the dry coated sand having room temperature fluidity according to the present invention preferably has a moisture content of 5 with respect to the solid content of the water glass contained in the coating layer covering the surface of the refractory aggregate. An amount corresponding to a proportion of ˜55 mass%, more preferably an amount corresponding to a proportion of 10 to 50 mass%, most preferably an amount corresponding to a proportion of 20 to 50 mass%. Thus, it is manufactured.

Incidentally, the following two methods can be exemplified as a method for forming a mold using the dry coated sand according to the present invention. In the first method, dry coated sand and water are kneaded at the molding site where the mold is manufactured to make the coated sand wet, and the wet coated While filling the sand into the mold cavity of the mold that gives the target mold, the mold is heated to a temperature of 90-200 ° C. until the filled coated sand is dried in the mold, Will be held. In the second method, after the coated sand is filled into the mold cavity of the mold that gives the target mold, water vapor is blown, and the flow phase of the water vapor wets the filled phase of the coated sand, Thereafter, it is held in a mold heated to 90 to 200 ° C. until it is dried.

At that time, molds such as molds and wooden molds, which are filled with dry coated sand having room temperature fluidity, are preferably preliminarily kept warm by heating, thereby being wetted by water vapor. The drying of the coated sand can proceed advantageously. In general, a temperature of about 90 to 200.degree. C., particularly about 100 to 140.degree. C. is desirable as the temperature for preheating. If the temperature is too high, it becomes difficult for steam to pass to the surface of the mold, while if 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 coated sand is preferably about 30 to 100 ° C., and particularly, coated sand heated to a temperature of about 40 to 80 ° C. is advantageously used.

In the first method described above, the step of adding water to the wet coated sand to make it wet simply puts the dry coated sand and a predetermined amount of water into an appropriate mixer and mixes them. Therefore, there is an advantage that it can be carried out by a very simple work and can be carried out very easily and easily even in a molding site where the working environment is bad. In addition, it is also possible to add another additive at the time of addition of water. Further, in the first method, instead of heating the mold, the coated sand is blown into the wet coated sand filled in the mold by blowing dry air, dry heated air, nitrogen gas, or the like. It is also possible to dry and solidify or harden the sand.

On the other hand, in the second method described above, the mold is heated as described above, specifically, the mold cavity is filled with the dry coated sand according to the present invention, and then formed therein. In the filled phase, water vapor is passed under pressure through a vent provided in the mold, so that the coated sand constituting the filled phase is moistened (moistened) to coat the coated sand. The coated sand is bonded and connected to each other by the water glass contained in the layer to form an integral mold-shaped coated sand aggregate (bonded product). Water glass is usually solidified by evaporation to dryness of water if no additives are added, and is cured when oxides or salts as curing agents are added. It becomes. Practically, since the curing agent is added, the filling phase is hardened, but it can be simply solidified.

Here, 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. The When a high steam temperature is employed, a large amount of energy is required for production thereof, and therefore, a steam temperature around 100 ° C. is particularly advantageously employed. As the pressure of the water vapor to be aerated, a gauge pressure value of about 0.01 to 0.3 MPa, more preferably about 0.01 to 0.1 MPa is advantageously employed. 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. In addition, if the gauge pressure is too high, there is a risk of squeezing near the vent, while if the gauge pressure is too low, the entire coated phase of the coated sand is not vented and the coated sand is sufficiently moistened. There is a fear that it cannot be done.

In addition, as a method for 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 water glass as a binder contained in the coating layer on the surface is sufficiently moistened, and the coated sand is bonded (bonded) to each other. The possible time is appropriately selected depending on the size of the mold, the number of vents, and the like. Generally, a ventilation time of about 2 seconds to about 60 seconds is adopted. . This is because if the water vapor passage time is too short, it becomes difficult to sufficiently wet the surface of the coated sand. If the air passage time is too long, the binder (water glass) on the coated sand surface dissolves or flows out. This is because there is a fear of doing so. The breathability of water vapor in the coated sand filled in the mold can be further improved by venting the water vapor while sucking the atmosphere in the mold from the exhaust port of the mold. It is.

Furthermore, when producing a mold using the coated sand of the present invention, in the first method and the second method described above, in order to actively dry the filling phase of the wet coated sand, dry air, heat drying A method in which air or nitrogen gas is blown into the filling phase is preferably employed. By aeration of such dry air, heated dry air or nitrogen gas, it is possible to sufficiently and quickly dry the inside of the coated sand filling phase, thereby further advantageously promoting the solidification or curing of the filling phase. Thus, the curing rate can be advantageously increased, and the properties such as the bending strength of the obtained mold can be advantageously enhanced, and it can also contribute to shortening the molding time of the mold.

Further, a curing agent may be added in the mold as an additive for promoting the hardening of the water glass during holding of the mold. It is possible to further promote the solidification by neutralizing the binder (water glass) with a curing agent. It should be noted that the curing agent may be vented at any timing as long as it is being held in the mold, and there is no problem even if it is performed simultaneously with the vaporization of water vapor or the ventilation of dry air or the like.

Curing agents include carbon dioxide (carbonated water), sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, oxalic acid, carboxylic acid, paratoluenesulfonic acid and other organic acids, methyl formate, ethyl formate, propyl formate, γ-butyrolactone, Examples include γ-propionlactone, ethylene glycol diacetate, diethylene glycol diacetate, glycerol diacetate, triacetin, propylene carbonate, and other monovalent alcohols such as methanol, ethanol, butanol, hexanol, and octanol. . These curing agents can be used alone, or two or more of them can be mixed and used. In addition, these hardeners are good to ventilate the gas mold or mist while holding the mold, into the mold, and when wetted by adding water to the dry coated sand, A curing agent may be added together with water.

Furthermore, when producing a mold using the coated sand of the present invention, various known molding techniques can be appropriately employed in addition to the above-described technique of filling the molded mold with the coated sand. Needless to say.

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. Should be understood. In the following examples and comparative examples, “%” and “parts” are shown on a mass basis unless otherwise specified. Moreover, the water content, filling property, filling fluidity, and strength of the coated sand (CS) obtained in Examples and Comparative Examples were evaluated as follows.

-Measurement of water content relative to solid content of water glass-
Each CS is weighed and accommodated in a crucible that has been baked and weighed, and the amount of moisture (W1) in the CS is calculated using the mass loss (%) after heating at 900 ° C. for 1 hour. It calculates from the following formula (4). The weighing is measured to the fourth decimal place. Next, the solid content (B1) of the water glass with respect to CS is calculated using the following formula (5), and then the water content (W1) in CS and the solid content (B1) of the water glass with respect to CS, The water content relative to the solid content of water glass (CS water content relative to the solid content of water glass in the coating layer: W2) is calculated using the following equation (6). W2 calculated as described above is shown as “moisture content” in Tables 1 and 2 below.
W1 = [(M1-M2) / M3] × 100 (4)
[W1: Moisture content (%) in CS, M1: Total mass (g) of crucible and CS before firing, M2: Total mass (g) of crucible and CS after firing, M3
: Mass of CS before firing (g)]
B1 = [B2 / (100 + B2)] × (100−W1) (5)
[B1: Solid content (%) of water glass with respect to CS, B2: 100 of sand
Solid amount of water glass added to parts (part), W1: amount of water in CS (%)]
W2 = (W1 / B1) × 100 (6)
[W2: Moisture content of CS with respect to solid content of water glass in coating layer (
%), W1: moisture content in CS (%), B1: solid content of water glass with respect to CS (%)]

-Measurement of bending strength-
About the test piece of width: 2.54cmxheight: 2.54cmxlength: 20cm obtained using each CS, the breaking load was measured with a measuring instrument (manufactured by Takachiho Seiki Co., Ltd .: digital casting Measure using a sand strength tester). Then, the bending strength is calculated by the following formula (7) using the measured breaking load.
Bending strength (N / cm ² ) = 1.5 × (L × W) / (a × b ² )
... (7)
[L: distance between fulcrums (cm), W: breaking load (N), a: width of test piece (
cm), b: thickness of specimen (cm)]

-Measurement of filling rate (%)-
The molds of width: 2.54 cm × height: 2.54 cm × length: 20 cm obtained by molding in each example or each comparative example were used as test pieces, respectively. The ratio of the specific gravity of each test piece to the specific gravity (calculated by dividing the mass by the volume of the test piece) 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

-Core disintegration test-
First, as shown in FIG. 1, a molten metal injection port 2 formed in advance at room temperature self-hardening sand and a core base fixing portion 4 at a lower portion (this portion is a discharge port for a waste core from a casting). In the half-cracked hollow main mold 6 (cavity diameter: 6 cm, height: 6 cm) having circular baseless cores 10 (diameter: 5 cm, high 5 cm) is bonded and fixed by the skirting board fixing portion 4, and the opposite hollow main mold 6 is further bonded and fixed to produce a sand mold 12 for casting test. Next, molten aluminum alloy (temperature: 710 ± 5 ° C.) is poured from the molten metal inlet 2 of the casting test sand mold 12 and solidified, and then the main mold 6 is broken to form a circular waste as shown in FIG. A casting 16 having a core outlet 14 (diameter: 1.6 cm) is taken out. When the temperature reaches a predetermined temperature, an impact is applied to the obtained casting 16 at a pressure of 0.2 MPa for 3 seconds at a time by an air hammer and discharged from the discharge port 14. The impact by the air hammer was repeated until 100% of the core sand was discharged, and the number of times was indicated.

-Average particle size-
Using a Microtrac particle size distribution measuring device (product name: MT3200II) manufactured by Nikkiso Co., Ltd., the particle size at an integrated value of 50% was measured as an average particle size (D ₅₀ ) from the particle size distribution. In addition, for the spherical particles and non-spherical particles used in the examples and comparative examples, the average particle diameter was measured using the above measuring apparatus, and the error between the published values of each manufacturer was within 10%. Below, the average particle diameter of a spherical particle and a non-spherical particle shows a manufacturer's published value.

-Production example 1 of dry CS
As refractory aggregate, Lunamos # 50 (trade name, manufactured by Kao Quaker Co., Ltd., average particle size: 292.1 μm, particle size coefficient: 1.01), which is a commercially available artificial sand for casting, is prepared and caking is performed. No. 2 sodium silicate (trade name, manufactured by Fuji Chemical Co., Ltd., SiO ₂ / Na ₂ O molar ratio: 2.5, solid component: 41.3%) was prepared as the water glass as the agent. . Then, the lunamos # 50 is heated to a temperature of about 120 ° C. and then put into a Shinagawa universal stirrer (5DM-r type) (manufactured by Dalton Co., Ltd.). The ratio is 1.21 parts (solid component: 0.50 parts) with respect to parts, and as spherical particles, Elchem microsilica (trade name, manufactured by Elchem Japan Ltd., average particle diameter) which is spherical silicon dioxide particles. : 0.15 μm, sphericity: 0.96) at a ratio of 0.05 parts (10 parts with respect to 100 parts of the solid content of water glass) and kneading for 3 minutes to evaporate the water On the other hand, the mixture is stirred and mixed until the sand lump breaks down, and 0.01 parts of calcium stearate (2 parts with respect to 100 parts of the solid content of water glass) is added and stirred and mixed. Coated of Inuitai with sand: Got a CS1. When the moisture content of CS1 after such kneading was measured, it was an amount corresponding to 40% by mass of the solid content of water glass in the coating layer.

-Production example 2- of dry CS
The above production example 1 except that the spherical particles to be added are HS311 (trade name, manufactured by Nippon Steel & Sumikin Materials Co., Ltd., average particle size: 2.2 μm, sphericity: 0.98) which is spherical silicon dioxide particles. According to the same procedure as above, dry CS2 having room temperature fluidity was obtained. When the moisture content of the obtained CS2 was calculated, it was an amount corresponding to 40% by mass of the solid content of water glass in the coating layer.

-Production example of dry CS 3-
The above production example 1 except that the spherical particles to be added are HS312 (trade name, manufactured by Nippon Steel & Sumikin Materials Co., Ltd., average particle size: 9.5 μm, sphericity: 0.96) which are spherical silicon dioxide particles. According to the same procedure as above, dry CS3 having room temperature fluidity was obtained. When the moisture content of the obtained CS3 was calculated, it was an amount corresponding to 40% by mass of the solid content of water glass in the coating layer.

-Production example 4 of dry CS
The above production example 1 except that spherical particles to be added are HS206 which is spherical silicon dioxide particles (trade name, manufactured by Nippon Steel & Sumikin Materials Co., Ltd., average particle size: 12.0 μm, sphericity: 0.97). According to the same procedure as above, dry CS4 having room temperature fluidity was obtained. When the moisture content of the obtained CS4 was calculated, it was an amount corresponding to 40% by mass of the solid content of water glass in the coating layer.

-Production example of dry CS 5-
Except that the spherical particles to be added were Sunsphere NP-200 (trade name, manufactured by AGC S-Tech Co., Ltd., average particle size: 18.2 μm, sphericity: 0.97), which are spherical silicon dioxide particles. According to the same procedure as in Production Example 1, dry CS5 having room temperature fluidity was obtained. When the moisture content of the obtained CS5 was calculated, it was an amount corresponding to 40% by mass of the solid content of water glass in the coating layer.

-Production example 6 of dry CS-
Except that the spherical particles to be added are AZ2-75 (trade name, manufactured by Nippon Steel & Sumikin Materials Co., Ltd., average particle size: 2.5 μm, sphericity: 0.95) which are spherical aluminum oxide particles. According to the same procedure as in Example 1, dry CS6 having room temperature fluidity was obtained. When the moisture content of the obtained CS6 was calculated, it was an amount corresponding to 40% by mass of the solid content of water glass in the coating layer.

-Production example 7 of dry CS-
Except that the spherical particles to be added were AZ4-75 (trade name, manufactured by Nippon Steel & Sumikin Materials Co., Ltd., average particle size: 4.5 μm, sphericity: 0.96), which are spherical aluminum oxide particles. According to the same procedure as in Example 1, dry CS7 having room temperature fluidity was obtained. When the moisture content of the obtained CS7 was calculated, it was an amount corresponding to 40% by mass of the solid content of water glass in the coating layer.

-Production example 8 of dry CS-
Except that the spherical particles to be added are AZ10-75 (trade name, manufactured by Nippon Steel & Sumikin Materials Co., Ltd., average particle size: 10.5 μm, sphericity: 0.94) which are spherical aluminum oxide particles. According to the same procedure as in Example 1, dry CS8 having room temperature fluidity was obtained. When the moisture content of the obtained CS8 was calculated, it was an amount corresponding to 40% by mass of the solid content of water glass in the coating layer.

-Production example 9 of dry CS-
Except that the spherical particles to be added were SG-TO200 (trade name, manufactured by Sukkyung AT Co., Ltd., average particle size: 0.2 μm, sphericity: 0.93) which are spherical titanium oxide particles. According to the same procedure as in Production Example 1, dry CS9 having room temperature fluidity was obtained. When the moisture content of the obtained CS9 was calculated, it was an amount corresponding to 40% by mass of the solid content of water glass in the coating layer.

-Production example 10 of dry CS-
As water glass as a binder, commercially available No. 1 sodium silicate (trade name, manufactured by Fuji Chemical Co., Ltd., molar ratio of SiO ₂ / Na ₂ O: 2.1, solid component: 48.5%) was used. The addition amount was 1.03 parts (solid component 0.50 part) with respect to 100 parts of the refractory aggregate (Lunamos # 50) according to the same procedure as in Production Example 2 above. A dry CS10 having fluidity was obtained. When the moisture content of the obtained CS10 was calculated, it was an amount corresponding to 40% by mass of the solid content of water glass in the coating layer.

-Production example 11 of dry CS-
As binder serving water glass No. 3 sodium silicate commercially available (trade name, manufactured by Fuji Chemical Co., Ltd., SiO ₂ / Na ₂ O molar ratio of: 3.2, solid content: 38%) was used, its According to the same procedure as in Production Example 2, except that the addition amount was 1.32 parts (0.50 parts of solid component) with respect to 100 parts of the refractory aggregate (Lunamos # 50), room temperature fluidity A dry CS11 was obtained. When the moisture content of the obtained CS11 was calculated, it was an amount corresponding to 40% by mass of the solid content of water glass in the coating layer.

-Production example 12 of dry CS-
A dry CS12 having room temperature fluidity was obtained according to the same procedure as in Production Example 2 except that the amount of spherical particles added was 0.5 parts. When the moisture content of the obtained CS12 was calculated, it was an amount corresponding to 40% by mass of the solid content of water glass in the coating layer.

-Production example 13 of dry CS-
A dry CS13 having room temperature fluidity was obtained according to the same procedure as in Production Example 2 except that the amount of spherical particles added was 1.0 part. When the moisture content of the obtained CS13 was calculated, it was an amount corresponding to 40% by mass of the solid content of water glass in the coating layer.

-Production example 14 of dry CS-
A dry CS14 having room temperature fluidity was obtained according to the same procedure as in Production Example 1 except that spherical particles were not added. When the moisture content of the obtained CS14 was calculated, it was an amount corresponding to 40% by mass of the solid content of water glass in the coating layer.

-Production example 15 of dry CS-
Instead of spherical particles, Sunlably (trade name, manufactured by AGC S-Tech Co., Ltd., average particle size: 4.1 μm), which is non-spherical silicon dioxide particles, was used according to the same procedure as in Production Example 1 above. A dry CS15 having room temperature fluidity was obtained. When the moisture content of the obtained CS15 was calculated, it was an amount corresponding to 40% by mass of the solid content of water glass in the coating layer.

-Production example 16 of dry CS-
Instead of spherical particles, KA-10 (trade name, manufactured by Titanium Industry Co., Ltd., average particle size: 0.4 μm), which is non-spherical titanium oxide particles, was used, and the same procedure as in Production Example 1 was followed. A dry CS16 having room temperature fluidity was obtained. When the moisture content of the obtained CS16 was calculated, it was an amount corresponding to 40% by mass of the solid content of water glass in the coating layer.

-Production example 17 of dry CS-
A procedure similar to that in Production Example 1 except that STT-65C-S (trade name, manufactured by Titanium Industry Co., Ltd., average particle size: 0.04 μm), which is a non-spherical titanium oxide particle, was used in place of the spherical particles. As a result, dry CS17 having room temperature fluidity was obtained. When the moisture content of the obtained CS17 was calculated, it was an amount corresponding to 40% by mass of the solid content of water glass in the coating layer.

-Examples of mold making (Examples 1 to 13, Comparative Examples 1 to 4)-
CS (temperature: 20 ° C.) produced according to each of the above procedures is blown into a molding die heated to 110 ° C. at a gauge pressure of 0.3 MPa, and further filled with 0.05 MPa. Under the gauge pressure, steam at a temperature of 99 ° C. was blown for 5 seconds, and the coated sand phase filled in the molding die was aerated. Then, after such a water vapor ventilation is completed, under a gauge pressure of 0.03 MPa, hot air at a temperature of 150 ° C. is blown for 2 minutes, and the CS filled in the molding die is cured, respectively. Each mold used as a piece [2.54 cm × 2.54 cm × 20.0 cm] was prepared. In addition, CS used when producing the casting_mold | template (test piece) which concerns on each of an Example and a comparative example is as showing in following Table 1 thru | or Table 3. FIG.

For each of the molds (test pieces) obtained in Examples 1 to 13 and Comparative Examples 1 to 4, the filling property and the strength were measured according to the test method described above. Further, a casting test sand mold shown in FIG. 1 was prepared using CS1 to 17, and the core disintegration property was evaluated according to the test method described above. The results are shown in Tables 1 to 3 below.

As is apparent from the results of Tables 1 to 3, in the dry coated sand having room temperature fluidity according to the present invention, the mold obtained using the dry coated sand has excellent strength (bending strength). And exhibiting excellent disintegration property.

Next, CS2, CS6, CS9, and CS14 (temperature: 20 ° C.) manufactured according to the above-described procedures are charged at a normal temperature into a Shinagawa universal agitator (5DM-r type, manufactured by Dalton Co., Ltd.). Water was added into the stirrer at a ratio of 2.0 parts with respect to 100 parts of CS, and the wet CS was prepared by stirring. The wet CS taken out from the stirrer is filled in a molding die heated to 150 ° C., then held in the molding die, and hot air at a temperature of 150 ° C. under a gauge pressure of 0.03 MPa. Were blown for 90 seconds, and each CS filled in the mold was solidified (cured), thereby producing respective molds used as test pieces [2.54 cm × 2.54 cm × 20.0 cm]. The CS used in producing the mold (test piece) according to each of Examples 14 to 16 and Comparative Example 5 is as shown in Table 4 below.

Further, using the CS moistened by adding a predetermined amount of water as described above, the circular non-empty core shown in FIG. 1 is produced, and the collapsibility of the core is evaluated according to the test method described above. did. Various conditions (such as the heating temperature of the mold) during core production were the same as those for the above-described mold (test piece) production. The test results are shown in Table 4 below.

As is apparent from the results in Table 4, when a mold is formed using a wet-coated material obtained by adding water to the coated sand according to the present invention, the resulting mold is obtained by aeration of water vapor. It is recognized that it exhibits higher strength and exhibits the same degree of filling and disintegrating properties as compared with the obtained mold.

2 Molten metal injection port 4 Baseboard fixing part 6 Main mold 8 Baseboard part 10 Core 12 Sand mold 14 Waste core outlet 16 Casting

Claims (11)

1. It is characterized in that the surface of the refractory aggregate is covered with a coating layer containing water glass, is a dry coated sand having room temperature fluidity, and spherical particles are contained in the coating layer. Coated sand.
2. The coated sand according to claim 1, wherein the moisture content is 5 to 55 mass% of the solid content of water glass in the coating layer.
3. The coated sand according to claim 1 or 2, wherein the content of the spherical particles is 0.1 to 500 parts by mass with respect to 100 parts by mass of the solid content of water glass in the coating layer.
4. The coated sand according to any one of claims 1 to 3, wherein the spherical particles have an average particle size of 0.1 to 20.0 µm.
5. The coated sand according to any one of claims 1 to 4, wherein the spherical particles are one or more selected from spherical particles made of silicon dioxide, aluminum oxide, or titanium oxide.
6. The coated sand according to any one of claims 1 to 5, wherein an average particle diameter d1 of the spherical particles and an average particle diameter d2 of the refractory aggregate satisfy the following formula (1).
   4 × d1 ≦ d2 ≦ 5000 × d1 (1)
7. The coated sand according to any one of claims 1 to 6, wherein the refractory aggregate is spherical.
8. In the method for producing dry coated sand having room temperature fluidity, the surface of the refractory aggregate is covered with a coating layer containing water glass,
   The heated refractory aggregate is mixed with a binder mainly composed of water glass and spherical particles, and the water is evaporated to coat the surface of the refractory aggregate containing water glass and spherical particles. A method for producing a coated sand, characterized by producing a coated sand having a moisture content of 5 to 55% by mass of the solid content of water glass in the coating layer.
9. The coated sand according to any one of claims 1 to 7, wherein the coated sand is filled into a molding cavity of a molding mold that gives a target mold, and then water is passed through the mold to provide the inside of the molding mold. A method for producing a mold, characterized in that a target mold is obtained by holding and solidifying or curing.
10. A water is added to the coated sand according to any one of claims 1 to 7 to make it wet, and the wet coated sand is filled in the mold and then held in the mold. And obtaining a target mold by solidifying or curing the mold.
11. The method for producing a mold according to claim 9 or 10, wherein during the holding of the mold, dry air, heated dry air, or nitrogen gas is further aerated in the molding cavity of the mold.

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