JP7202237B2 - Coated sand and mold manufacturing method using the same - Google Patents

Description

The present invention relates to a coated sand and a mold manufacturing method using the same, and in particular, a coated sand that can provide a mold that is excellent in disintegration and is easy to regenerate, and a mold that is excellent in disintegration and is easy to regenerate. It relates to a manufacturing method.

Conventionally, as one of the molds used for casting molten metal such as iron and aluminum, coated sand made by coating a refractory aggregate with a predetermined binder is used as foundry sand to obtain the desired shape. is known. Binders used to form the coating layer in such coated sand include water-soluble inorganic binders such as water glass and sodium phosphate, as well as phenol resins, furan resins, urethane resins, and the like. Organic binders using resins have been clarified, and various techniques for forming self-hardening molds using these binders have been proposed.

By the way, coated sand composed of an inorganic binder such as water glass has a lower organic content than a coated sand using an organic binder, so it is difficult to use during molding or casting. It is known that the generation of various gases due to the heat of time is advantageously suppressed, and problems such as odor are less likely to occur. However, in the case of coated sand (mold material or foundry sand) constructed using a conventional inorganic binder, refractory aggregate (sand) is recovered from the mold after casting, and the recovered sand is roasted. When trying to regenerate by burning, the inorganic binder remaining on the surface of the collected sand cannot be burned, and instead it is sintered and sticks firmly to the surface of the refractory aggregate (sand). As a result, there is an inherent problem that reproduction is difficult. In particular, coated sand using water glass as an inorganic binder causes the water glass to vitrify due to the heat during casting. Also, there is a problem that it is very difficult to remove the vitrified water glass on the sand surface. In addition, the conventional coated sand using an inorganic binder has an inherent problem that the mold obtained using the sand does not have sufficient collapsibility.

For this reason, in a mold molded using a coated sand coated with an inorganic binder such as water glass, in order to improve the collapsibility after casting and the reclaimability of recovered sand, various methods have been developed. For example, in Japanese Patent Laid-Open No. 50-128620, the surface of sand particles is coated with a thermoplastic resin to form a resin film, and a water glass layer is formed on the resin film. Formed laminated foundry sand (coated sand) is disclosed in which the thermoplastic resin that provides the resin coating in such coated sand is heated to soften, gasify, or It has been clarified that the formation of carbon particles destroys the water glass coating of the coated sand, thereby improving the collapsibility of the mold.

Further, in Japanese Patent Application Laid-Open No. 54-35821, by forming a hydrophobic resin film on the surface of sand particles and further forming a film of an inorganic binder thereon to form a coated sand with a layered structure, It has been revealed that the post-cast disintegration properties of molds obtained from such coated sand are improved, while the binder adhering to the sand surface can be easily removed by mechanical treatment. ing. Furthermore, in JP-A-2012-76114, a binder-coated refractory is formed by forming a solid coating layer containing a water-soluble inorganic compound and a thermosetting resin as a binder on the surface of a refractory aggregate. It is said that it is possible to provide a mold with good disintegration property, excellent heat resistance and strength.

However, the conventionally proposed molds made using coated sand having a laminated structure exhibit a predetermined collapsibility improvement effect only in the casting of a part of molten metal. Therefore, it was not possible to exhibit an excellent effect of improving the collapsibility against the molten metal. That is, the effect of improving the collapsibility of the mold obtained by using each coated sand of the laminated structure described above is the so-called high-temperature casting such as casting of molten iron at a casting temperature or pouring temperature of 1300 to 1500 ° C. However, in so-called low-temperature casting such as casting of molten aluminum in which the casting temperature or pouring temperature is around 700 ° C., the desired crumbling property cannot be sufficiently exhibited. As a matter of course, the problem of reclaiming recovered sand has not been satisfactorily resolved either.

JP-A-50-128620 JP-A-54-35821 JP 2012-76114 A

Here, the present invention has been made against the background of such circumstances, and the problem to be solved is a mold that has good collapsibility not only in high-temperature casting but also in low-temperature casting. Another object of the present invention is to provide a coated sand that can be advantageously formed, and another object is to provide a coated sand that facilitates recycling of recovered sand. A further object of the present invention is to provide a method for advantageously producing useful molds using coated sand having such excellent properties.

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 can be used in any combination Adoptable. It should be noted that the aspects and technical features of the present invention are not limited to those described below, and can be recognized based on the inventive idea that can be grasped from the description of the entire specification. should be understood.

(1) A solid first coating layer containing an organic compound is formed so as to coat the surface of the refractory aggregate, and a water-soluble coating layer is further formed so as to coat the first coating layer. In the coated sand having a laminated structure in which the second coating layer made of the binder composition containing the organic inorganic binder is formed, the first coating layer contains an oxate, an organic carboxylate and an organic phosphor. A coated sand characterized by containing at least one or more compounds selected from the group consisting of acid esters.
(2) The coated sand according to the aspect (1), wherein the organic compound is selected from the group consisting of a crosslinked curable resin and its cured product, a thermoplastic resin, and a carbohydrate.
(3) The water-soluble inorganic binder is at least one selected from the group consisting of water glass, sodium phosphate, sodium carbonate, sodium aluminum oxide and potassium carbonate. The coated sand according to the aspect (2).
(4) The above aspects (1) to 300, wherein the oxyacid salt or the organic carboxylate is contained at a ratio of 1 to 300 parts by mass with respect to 100 parts by mass of the organic compound. The coated sand according to any one of the aspects (3).
(5) Aspects (1) to (1), wherein the organic phosphate ester is contained in a proportion of 0.5 to 100 parts by mass with respect to 100 parts by mass of the organic compound. 4) Coated sand according to any one of items.
(6) The coated sand according to any one of the aspects (1) to (5), wherein the first coating layer further contains a metal oxide.
(7) The coated sand according to the aspect (6), wherein the metal oxide is contained in a proportion of 1 to 300 parts by mass with respect to 100 parts by mass of the organic compound.
(8) The coated sand according to any one of the above aspects (1) to (7), which is formed as a wet coated sand having no normal temperature fluidity.
(9) The coated sand according to any one of the above aspects (1) to (7), which is formed as a dry coated sand having normal temperature fluidity.
(10) Molding a mold by using the wet coated sand according to the aspect (8), filling it into the molding cavity of the mold, and holding it in the mold. 1. A mold manufacturing method comprising the step of solidifying or hardening coated sand filled in a cavity to obtain a desired mold.
(11) Using the dry coated sand according to the aspect (9), filling it into the molding cavity of a predetermined molding die, allowing water vapor to pass through, and then holding it in the molding die. A mold manufacturing method characterized by solidifying or hardening the coated sand filled in the molding cavity of the mold by a process to obtain the desired mold. (12) Using the dry coated sand according to the aspect (9), adding water to it to make it moist, and then placing the wet coated sand in the molding cavity of the mold. A mold manufacturing method characterized by solidifying or hardening the coated sand filled in the molding cavity by filling and holding it in the mold to obtain the desired mold.

Thus, in the coated sand according to the present invention, of the two types of coating layers laminated on the surface of the refractory aggregate, the first coating layer containing an organic compound, which is the lower layer, The contained oxysalt, organic carboxylate, or organic phosphate accelerates the thermal decomposition of the first coating layer, or accelerates the carbonization of the first coating layer. The second coating layer becomes brittle, which makes the second coating layer located thereover easier to peel off, thereby further improving the collapsibility of the mold obtained from such coated sand. As a result, even in casting using molten aluminum with a low casting temperature or low pouring temperature, the collapsibility of the mold used therein can be advantageously enhanced.

Moreover, in the coated sand according to the present invention, the layered coating layer formed on the surface of the refractory aggregate is easily peeled off by the action of heat applied during casting. It is possible to advantageously perform the reclaiming operation of recovered sand recovered from the casting process of molten metal with a low hot water temperature. Recycled sand (refractory aggregate) that can be effectively recycled by a mild polishing process that applies a physical impact to the extent that the collected sand collides with each other, and is therefore reusable. can be advantageously obtained.

Further, in the coated sand according to the present invention, since the first coating layer containing the organic compound is formed in a solid state, the problem of odor due to volatilization of the organic compound or the like is unlikely to occur. In addition, due to the heat of the molten metal applied in the casting process using the mold molded from such coated sand, the gas generated by the thermal decomposition of the organic compound contained in the coating layer causes the molten metal to move the mold. A gas layer that suppresses intrusion between particles of the constituent coated sand (refractory aggregate) is effectively formed between the mold surface and the cast product, and the finally obtained cast product The casting surface of the steel can be improved satisfactorily.

FIG. 2 is a vertical cross-sectional explanatory view of a sand mold for casting test used in a collapsibility test in Examples. FIG. 2 is a vertical cross-sectional explanatory view of a casting containing a waste core in an example.

First, the coated sand (foundry sand) targeted in the present invention has a laminated structure of two layers, in which a refractory aggregate coated with a first coating layer is further coated with a second coating layer. In, it is configured. In short, a two-layer structure in which a predetermined first coating layer and a predetermined second coating layer are sequentially laminated on a refractory granular or powder aggregate (particles). There is. Depending on the state of the second coating layer, which is the coating layer located on the outer surface of the coated sand, the coated sand as a whole is in a dry state (appearance) having fluidity at room temperature, that is, in a dry state. (dry coated sand), or as a wet state (appearance) that does not have normal temperature fluidity as a whole, that is, as a wet state (wet coated sand). It will be done.

Here, the term "dry coated sand having normal temperature fluidity" in the present invention means coated sand that gives a measured value when the dynamic angle of repose is measured, regardless of the water content. is. Specifically, the dynamic repose angle here means that a coated sand for measurement is accommodated in a cylinder (for example, diameter 7 .2 cm x 10 cm high container filled with coated sand to half its volume), held so that the axis is horizontal, and rotated about the horizontal axis at a constant speed (e.g., 25 rpm). Thus, when the surface of the coated sand flowing in the cylinder has a flat inclined surface shape, it refers to the angle formed between the inclined surface and the horizontal surface. The dynamic angle of repose is preferably 80° or less, more preferably 45° or less, and even more preferably 30° or less. Especially when the refractory aggregate is spherical, a dynamic angle of repose of 45° or less can be easily achieved. On the other hand, when the coated sand is wet, it does not flow in the cylinder, the surface of the coated sand is not formed as a flat inclined surface, and as a result, the dynamic angle of repose cannot be measured. It is classified as a "wet coated sand that does not have normal temperature fluidity" in the invention.

The refractory aggregate that constitutes the dry or wet coated sand described above is made of refractory particles that function as the base material of the mold. Any of refractory granular or powdery materials can be used. Specifically, silica sand, recycled silica sand, special sand such as alumina sand, olivine sand, zircon sand, chromite sand, ferrochrome slag, Slag-based particles such as ferronickel-based slag and converter slag; 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, reclaimed sand or reclaimed sand that has been used once or several times to form a mold. Mixed sand obtained by adding new sand to recovered sand and mixing them may be used without any problem. Furthermore, such refractory aggregates are generally used with a particle size of about 40 to 130, preferably about 60 to 110, in terms of AFS index.

Also, in order to obtain the coated sand according to the present invention, a solid state first coating layer containing an organic compound is formed so as to cover the surface of such refractory aggregate. As the organic compound used there, it is possible to form a solid coating layer on the surface of the refractory aggregate (particles), and it is possible to include it in the solid coating layer. Although it is not particularly limited as long as it is possible, in the present invention, at least one or more compounds selected from the group consisting of crosslinked curable resins and cured products thereof, thermoplastic resins, and carbohydrates , will be preferably used.

The cross-linkable curable resin suitably used for forming such a first coating layer includes, for example, hexamethylenetetramine, organic esters, organic acids, carbon dioxide gas, peroxides, metal ions, curing agents such as amines, or In the presence or absence of a curing catalyst, a cross-linking curing reaction is expressed under heating or non-heating (normal temperature). Specifically, in addition to phenol-based resins and phenol-urethane-based resins, epoxy resins, melamine resins, unsaturated polyester resins, polyfunctional acrylamide-based resins (see JP-B-7-106421), unsaturated alkyd resins, unsaturated Examples include saturated fatty acid-modified alkyd resins, diallyl phthalate resins, and, if necessary, mixed resins obtained by combining these resins. Among them, from the viewpoint of being able to enjoy the effects of the present invention more advantageously, in particular, in addition to phenolic resins such as novolak type and resol type, phenol urethane-based mixtures of such phenolic resins and polyisocyanate compounds A resin-forming material will preferably be used.

Here, in the present invention, the cured product of the cross-linking curable resin recommended as the material for forming the first coating layer is a high molecular weight compound obtained by subjecting a low-molecular-weight cross-linking curable resin to a curing reaction. It is what I let you do. Specifically, after coating the surface of the refractory aggregate particles with a low-molecular-weight material with a low melt viscosity, the crosslinking curable resin is cured by heating or adding a curing agent to form a solid coating. It forms a layer, and as a result, the elution amount of the formed coating layer can be effectively suppressed. Gone. In addition, the cured product of the crosslinked curable resin can form a high-molecular-weight coating layer with good surface stability, making it possible to achieve both coverage and surface stability. When the crosslinked curable resin is cured, it is no longer eluted into the water-soluble inorganic binder, which prevents deterioration due to the water-soluble inorganic binder and maintains high mold strength. I can. Furthermore, the cured product of the crosslinked curable resin has the properties that 1) the softening of the coating layer due to heat is suppressed and the strength of the mold is improved, and 2) the mold strength is improved as compared with the uncured crosslinked curable resin. Since a large amount of heat is consumed, the supplied heat is effectively used for thermal decomposition, and thermal decomposition is accelerated, so that the collapsibility of the mold is further improved. This also has the advantage of suppressing the amount of gas generated during casting. In the present invention, the cured product of the crosslinked curable resin means that the proportion of the cured resin in the coating layer is generally 80% by mass or more, preferably 90% by mass or more, and more preferably 95% by mass or more. Yes, especially 100% by weight (completely cured) is most preferred.

Examples of thermoplastic resins, which are organic compounds, include polyvinyl alcohol, polyvinyl acetate, polystyrene, styrene-acrylonitrile copolymer, styrene-butadiene-acrylonitrile copolymer, ethylene-vinyl acetate copolymer, Synthetic resins such as polyvinyl chloride and polymethyl methacrylate, cellulose acetate, paraffin and the like can be mentioned. Among them, polyvinyl alcohol, polyvinyl acetate, polystyrene, ethylene/vinyl acetate copolymer, polymethyl methacrylate, cellulose acetate, and polycarbonate are particularly preferably used from the viewpoint of solvent solubility (film formability).

Carbohydrates include, for example, glucose, fructose, galactose, lactose, sucrose, maltose, trehalose, starch, glycogen and cellulose. Among them, trehalose, starch, and glycogen are particularly preferred from the viewpoint of film-forming properties.

In addition, other organic compounds such as acrylamide, N-methylolacrylamide, diacrylamide dimethyl ether, methylenebisacrylamide, ethylenebisacrylamide, and ethyleneglycol diacrylamide can be used.

Moreover, the organic compound, which is a constituent component of such a first coating layer, is desirably a high-molecular compound (polymer, multimer) from the viewpoint of covering the refractory aggregate. Specifically, a polymer compound (heavy coalescence, multimers) will be used to advantage. Even organic compounds that are not included in the category of high-molecular compounds (polymers, multimers) preferably have a molecular weight of 300 or more from the viewpoint of surface stability of the solid coating layer.

Furthermore, in the present invention, a poorly water-soluble or water-insoluble organic compound can be advantageously used, and a water-insoluble organic compound is particularly suitable as the organic compound contained in the solid coating layer. Because the easily water-soluble organic compound is used to form the second coating layer on the first coating layer, it is included in the binder composition containing the water-soluble inorganic binder. This is because there is a possibility that it will dissolve in water and the solid coating layer cannot be maintained. In the present invention, the solubility in 100 g of water at 25° C. is 1% by mass or less, preferably 0.5% by mass or less, more preferably 0.3% by mass or less, and still more preferably 0.1% by mass or less. An organic compound is advantageously employed as the organic compound contained in the solid first coating layer. Here, the solubility means the amount of the organic compound dissolved in the solvent (water) when 10 g of the organic compound is added to 100 g of water at 25° C., stirred for 1 hour, and allowed to stand still for 1 hour. It is. A water-insoluble organic compound is an organic compound that does not dissolve in water.

Therefore, as described above, the solid-state first coating layer containing the organic compound is present on the surface of the refractory aggregate, so that the water-soluble inorganic binder constituting the second coating layer is Advantageously, direct contact with the refractory aggregate can be avoided. Since the solid-state first coating layer contains an organic compound, a mold (hereinafter simply referred to as mold ), the organic compound contained in the first coating layer is thermally decomposed and gasified, and the generated gas acts as a water-soluble inorganic binder at the joints between the refractory aggregate particles. Advantageously, the solidified or hardened product of the mold is destroyed, thereby making the mold excellent in collapsibility. When the organic compound contained in the first coating layer is thermally decomposed and gasified, the internal pressure of the gas causes the water-soluble inorganic binder present on the outer surface of the refractory aggregate particles to solidify or harden. However, since it is destroyed from the inside (from the refractory aggregate particle side), for example, in the polishing process when regenerating the refractory aggregate recovered from the casting mold, solidified or hardened water-soluble inorganic clay It becomes easier to separate the binder from the surface of the refractory aggregate particles, and the regeneration of the refractory aggregate becomes easier.

However, the excellent characteristics of mold collapsibility and recovery of recovered sand obtained by providing such a first coating layer are due to the casting temperature or pouring temperature of molten iron of 1300 to 1500 ° C. However, in low-temperature casting such as casting using molten aluminum in which the casting temperature or pouring temperature is around 700 ° C., the characteristics cannot be fully exhibited. , was clarified as a result of further studies by the present inventors.

Therefore, according to the present invention, it is possible to advantageously improve the collapsibility even in the mold subjected to the above-described low-temperature casting, and the water-soluble sand recovered from the mold after such low-temperature casting. In order to facilitate the removal of the solidified or cured inorganic binder (second coating layer) and facilitate the recycling process, the organic compound as described above is used. The first coating layer further contains at least one or more compounds selected from the group consisting of oxates, organic carboxylates and organic phosphates.

As described above, according to the present invention, the presence of the oxysalt and the organic carboxylate in the first coating layer causes the oxysalt and the organic carboxylate to react with the heating action during pouring of the molten metal. This is because the acid salt is thermally decomposed to generate oxygen, which provides oxygen to the organic compound of the coating layer and promotes its combustion, thereby promoting thermal decomposition. , the organic phosphate ester present in the first coating layer promotes the carbonization of the organic compound by depriving the organic compound of the coating layer of hydrogen, thereby coating the refractory aggregate with The first coating layer of organic compound becomes more brittle and the second coating layer of water-soluble inorganic binder is more likely to peel off the refractory aggregate. As a result, even in low-temperature casting at a casting temperature or pouring temperature of about 700° C., the disintegration property of the mold is improved, and sufficient disintegration property is obtained even in casting of molten aluminum. In addition, there is no need to adopt general polishing by grinding (high-level polishing or hard polishing), and a light physical impact (soft polishing or light polishing) that causes collected sand to collide with each other is performed. This makes it possible to easily reclaim the recovered sand, and also advantageously avoids the possibility that the surface of the refractory aggregate will be scraped off by grinding.

In the present invention, examples of oxyacid salts contained in the first coating layer include nitrates of various metals such as alkali metals such as Li, Na and K and alkaline earth metals such as Mg and Ca; Manganates, molybdates, tungstates, carbonates and the like can be exemplified, and organic carboxylates include oxalates and tartrates of various metals.

These oxyacid salts and organic carboxylates are generally 1 to 300 parts by mass, preferably 20 to 250 parts by mass, more preferably 40 to 300 parts by mass with respect to 100 parts by mass of the organic compound in the first coating layer. It will be contained at a rate of 220 parts by mass. Incidentally, the second coating layer containing the water-soluble inorganic binder contains a large amount of additives, for example, at a rate of 30% by mass or more with respect to the solid content of the water-soluble inorganic binder. If the oxyacid salt or the organic Since the carboxylate is contained in the first coating layer, it is possible to increase the content of the carboxylate, thereby exhibiting the effect of addition of the oxyacid salt and the organic carboxylate more effectively. It will be possible to do so. However, if the content of these oxyacid salts and organic carboxylates is too high, the strength of the mold is adversely affected. On the other hand, if the content of these oxoacid salts and organic carboxylates is too low, it becomes difficult to fully enjoy the effects of their addition.

Further, according to the present invention, the organic phosphate to be contained in the first coating layer covering the surface of the refractory aggregate is not particularly limited, and known monophosphates, condensed phosphates, etc. can be used alone or in combination, among which monophosphates include, for example, trimethyl phosphate, triethyl phosphate, tributyl phosphate, tri(2-ethylhexyl) phosphate, tributoxyethyl phosphate, tri phenyl phosphate, tricresyl phosphate, trixylenyl phosphate, tris(isopropylphenyl) phosphate, tris(phenylphenyl) phosphate, trinaphthyl phosphate, cresyl diphenyl phosphate, xylenyl diphenyl phosphate, diphenyl(2-ethylhexyl) phosphate, di(isopropylphenyl)phenyl phosphate, monoisodecyl phosphate, 2-acryloyloxyethyl acid phosphate, 2-methacryloyloxyethyl acid phosphate, diphenyl-2-acryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, melamine phosphate, Dimelamine phosphate, melamine pyrophosphate, triphenylphosphine oxide, tricresylphosphine oxide, diphenyl methanephosphonate, diethyl phenylphosphonate, resylcinol bis(diphenyl phosphate), bisphenol A bis(diphenyl phosphate), phosphaphenanthrene, tris (1-chloro-2-propyl) phosphate, tris(chloroethyl) phosphate, tris(dichloropropyl) phosphate, tetrakis(2-chloroethyl) dichloroisopentyl diphosphate, 2,2-bis(chloromethyl)-1,3- Propanebis(chloroethyl)phosphate, Tris(2,3-dibromopropyl)phosphate, Tris(tribromoneopentyl)phosphate, 2,2-bis(chloromethyl)trimethylenebis(bis(2-chloroethyl)phosphate), Poly Oxyalkylenebisdichloroalkyl phosphate and the like can be mentioned.

Furthermore, the condensed phosphate is not particularly limited, and examples thereof include trialkyl polyphosphate, resorcinol polyphenyl phosphate, resorcinol poly(di-2,6-xylyl) phosphate (PX -200), hydroquinone poly(2,6-xylyl) phosphate, and condensed phosphates such as these condensates.

Such condensed phosphate esters can also be selected from commercially available ones, such as resorcinol polyphenyl phosphate (CR-733S manufactured by Daihachi Chemical Industry Co., Ltd.), bisphenol A poly Cresyl phosphate (CR-741 manufactured by Daihachi Chemical Industry Co., Ltd.), aromatic condensed phosphate ester (CR-747 manufactured by Daihachi Chemical Industry Co., Ltd.), resorcinol polyphenyl phosphate (ADEKA STAB PFR manufactured by ADEKA Co., Ltd.), bisphenol A Polycresyl phosphate (ADEKA Co., Ltd. ADEKA STAB FP-600, ADEKA STAB FP-700), non-halogen condensed phosphate (DAIGURD-580, DAIGURD-610 manufactured by Daihachi Chemical Industry Co., Ltd.), halogen-containing condensed phosphate (CR-504L, CR-570, and DAIGURD-540 manufactured by Daihachi Chemical Industry Co., Ltd.) and the like are selected as appropriate.

Such an organic phosphate ester is generally 0.5 to 100 parts by weight, preferably 1 to 60 parts by weight, more preferably 5 to 35 parts by weight with respect to 100 parts by weight of the organic compound in the first coating layer. will be included in the ratio of parts. This is because if the content of the organic phosphate ester becomes too small, it becomes difficult to achieve the effect of adding it sufficiently. It exudes to the surface of the coating layer, and when forming the second coating layer, it is mixed in the binder composition containing the water-soluble inorganic binder to reduce the binding strength of the coated sand, thereby There is a risk of causing problems such as lowering the strength of a mold molded from such coated sand.

In the present invention, at least one or more selected from the group consisting of oxyacid salts, organic carboxylates and organic phosphate esters as described above is applied to the first coating layer containing an organic compound. Along with the compound, a metal oxide will also advantageously be included. This metal oxide oxidizes the active hydrogen and CO in the gas generated by the thermal decomposition of the organic compound that constitutes the first coating layer due to heating during pouring of the molten metal, to form an inert H By changing to ₂ O or CO ₂ , gas defects during casting can be prevented, and the mold molded using coated sand can be given more flexibility (flexibility) to prevent veining during casting. In addition, the generated CO ₂ forms an effective gas film layer on the mold surface during casting, so it suppresses the intrusion of molten iron, aluminum, etc. Or it prevents it, and exhibits characteristics such as giving a good casting surface to the cast product to be formed.

Examples of such metal oxides include ferrous oxide, ferric oxide, triiron tetraoxide, cobaltous oxide, cobaltic oxide, nickelous oxide, nickelic oxide, and cuprous oxide. , cupric oxide, zinc oxide, etc., but it should be understood that they are not, of course, limited to these. In addition, such a metal oxide is generally 1 to 300 parts by mass, preferably 20 to 250 parts by mass, more preferably 40 to 200 parts by mass with respect to 100 parts by mass of the organic compound in the first coating layer. will be contained at a rate of If the content of this metal oxide is too small, the effect of addition cannot be fully enjoyed, and if the content is too large, the surface of the first coating layer becomes uneven, It comes to have an adverse effect on the mold strength.

Furthermore, in the coated sand according to the present invention, it is effective to incorporate a coupling agent into the first coating layer provided on the surface of the refractory aggregate. By including a coupling agent in the first coating layer, the wettability and adhesion of such first coating layer can be improved to enhance the bond between the refractory aggregate and the first coating layer. There are advantages to being able to As the coupling agent contained in the first coating layer, for example, known ones such as silane coupling agents, zircon coupling agents, titanium coupling agents, etc. can be mentioned as suitable ones. Further, the content of the coupling agent in the coating layer is generally 0.5 to 10 parts by mass, preferably 1 to 5 parts by mass, more preferably 1 to 3 parts by mass with respect to 100 parts by mass of the organic compound. Percentage.

In the present invention, the film thickness of the solid first coating layer formed on the surface of the refractory aggregate as described above is generally 0.1 to 6 μm, preferably 0.2 to 5 μm, and more It is preferably 0.3 to 3 μm, more preferably 0.5 to 2 μm. If the film thickness is less than 0.1 μm, it becomes difficult to form the coating layer, and the inside of the second coating layer made of the binder composition containing the water-soluble inorganic binder is effectively gaseous. On the other hand, if the thickness is more than 6 μm, the amount of organic compounds may be too much and odor may be generated. Here, as a method for measuring the film thickness of such a coating layer, refractory aggregate particles having a coating layer formed thereon are embedded in epoxy resin or the like, and the refractory aggregate is cut using a cutting device such as an ion cutter. A method of observing the cross section of a particle using an optical instrument such as an optical microscope or an electron microscope, randomly selecting 10 points on the cross section of the particle, and measuring the film thickness of the coating layer can be mentioned. In addition, such a film thickness can be calculated from the average particle diameter of the refractory aggregate particles and the amount of addition of the refractory aggregate particles and the organic compound, etc., assuming that the refractory aggregate particles are spherical. is also possible.

In the coated sand according to the present invention, the refractory aggregate coated with the first coating layer is further formed with a binder composition containing a water-soluble inorganic binder. It is covered by a second coating layer. That is, it is configured as a coated sand having a coating of a laminated structure in which a second coating layer is further formed on the first coating layer. As the water-soluble inorganic binder contained in such a binder composition, any one conventionally used in coated sand can be used. Water glass, sodium phosphate, sodium carbonate, sodium aluminum oxide, potassium carbonate, sodium vanadate, sodium borate, etc. can be used alone or in combination of two or more selected from them. is. Among them, water glass, sodium phosphate, sodium carbonate, sodium aluminum oxide and potassium carbonate are preferably used in the present invention. For example, water glass or one containing water glass as a main component is more preferably used.

Water glass as used herein is an aqueous solution of a soluble silicate compound such as sodium silicate, potassium silicate, sodium metasilicate, potassium metasilicate, lithium silicate. , ammonium silicate, etc., but in particular, sodium silicate (sodium silicate) is advantageously used in the present invention. In addition, water glass may be used as a main component, and water-soluble binders such as thermosetting resins, sugars, proteins, synthetic polymers, salts and inorganic polymers may be blended without any problem. When water glass is used in combination with another water-soluble binder, the ratio of water glass to the total amount of the binder is 60% by mass or more, preferably 80% by mass or more, and more preferably 90% by mass or more. .

Thus, sodium silicate, which is water glass, which is advantageously used in the present invention, is usually classified into types 1 to 5 according to the molar ratio of SiO ₂ /Na ₂ O and used. 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 has a SiO ₂ /Na ₂ O molar ratio of 2.0 to 2.3. 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 of is 3.6 to 3.8. Among these, sodium silicate Nos. 1 to 3 are also defined in JIS-K-1408. These sodium silicates may be used singly or in combination, and two or more of them may be mixed to adjust the SiO ₂ /Na ₂ O molar ratio. is also possible.

In order to advantageously obtain the desired coated sand according to the present invention, 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 2.0 or more, more preferably 2.1 or more, and in the above classification of sodium silicates, sodium silicates corresponding to Nos. 1 and 2 are particularly advantageously used. Such sodium silicate Nos. 1 and 2 provide coated sand stably with good properties even in a wide range of sodium silicate concentrations in water glass. Also, the upper limit of the molar ratio of SiO ₂ /Na ₂ O in such sodium silicate is appropriately selected according to the properties of the water glass in the form of an aqueous solution, but is 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 less than 1.9, a large amount of alkali is present in the water glass, so the solubility of the water glass in water increases, and the coated sand deteriorates due to moisture absorption. It may become easier. On the other hand, sodium silicate with a molar ratio of SiO ₂ /Na ₂ O greater than 3.5 has low solubility in water, so that in the finally obtained mold, the adhesion area between the refractory aggregate particles increases. However, there is a risk that the mold strength will decrease.

Further, the water glass used in the present invention means a solution of a silicic acid compound dissolved in water. In addition to being used, water is added to such a stock solution to be used in a diluted state. The non-volatile content (water glass component) obtained by removing volatile substances such as water and solvents from such water glass is called solid content, which corresponds to the soluble silicate compound such as sodium silicate described above. It is. Also, the higher the proportion of such solids, the higher the silicic acid compound concentration in the water glass. Therefore, the solid content of the water glass used in the present invention, when it is composed only of the undiluted solution, corresponds to the ratio excluding the water content in the undiluted solution. When a diluted solution obtained by diluting with become.

By the way, the solid content in such water glass is set to an appropriate ratio depending on the type of water glass component (soluble silicic acid compound), etc., but is preferably 20 to 50% by mass. It is desirable that the water glass component is included in proportion. Water glass in which a water glass component corresponding to the solid content is appropriately present in an aqueous solution is kneaded or mixed with the refractory aggregate coated with the first coating layer to obtain the second It is possible to prepare a mixture in which the water glass component is evenly and uniformly dispersed on the surface of one coating layer, thereby advantageously molding the desired mold according to the present invention. becomes possible. If the concentration of the water glass component (soluble silicic acid compound) in the water glass becomes too low and the total amount of the water glass component (solid content) is less than 20% by mass, heating is required to produce the coated sand. It becomes necessary to raise the temperature or lengthen the heating time. On the other hand, when the proportion of solids in the water glass becomes too high, a mixture is prepared in which the water glass component is evenly and uniformly dispersed in the refractory aggregate provided with the first coating layer. Since this may cause problems in the properties of the desired mold, the solid content is 50% by mass or less, and the water content is 50% by mass or more. It is desirable to prepare a certain water glass.

Further, sodium phosphate, which is one of the water-soluble inorganic binders used in the present invention, includes monosodium phosphate hydrate (NaH ₂ PO ₄ ·xH ₂ O; x is a known integer), phosphoric acid Disodium hydrate ( _{Na2HPO4.x'H2O} ; x' is a known integer), _Trisodium phosphate hydrate _{( Na3PO4.x} "_H2O; _x " is a known integer ), etc. can be mentioned. Sodium phosphate is soluble in water, as typified by the fact that the amount of trisodium phosphate hydrate dissolved in 100 g of water is 25.8 g (20° C.). The melting point of sodium phosphate is relatively high, as typified by the melting point of 1340° C. of the hydrate. For this reason, the coated sand formed by forming the second coating layer using sodium phosphate as a water-soluble inorganic binder is easily disintegrated by water, and it is possible to manufacture a mold with high heat resistance. be. Similarly, sodium carbonate, sodium aluminum oxide, or potassium carbonate, which are water-soluble inorganic binders, exhibit the same effect as the above sodium phosphate, and are used to form the second coating layer. The coated sand is easily disintegrated by water, and exhibits the characteristic that it is possible to manufacture a mold having high heat resistance.

Furthermore, in the coated sand according to the present invention, the above-mentioned water-soluble inorganic binder has a solid content conversion of 100% of the refractory aggregate when the mass is considered as a solid content, and when the liquid content is considered as a solid content only. It is preferably used in an amount of 0.1 to 2.5 parts by mass with respect to parts by mass, and among them, an amount of 0.2 to 2.0 parts by mass is particularly advantageously employed. be. Here, if the amount of the water-soluble inorganic binder used becomes too small, a sufficient amount of the water-soluble inorganic binder is deposited on the first solid coating layer provided on the surface of the refractory aggregate. It becomes difficult to form the second coating layer made of the binder composition containing the above, and there is a possibility that the solidification or curing of the coated sand may be difficult to be performed sufficiently. Also, even if the amount of the water-soluble inorganic binder used is too large, an excessive amount of the water-soluble inorganic binder is formed on the solid first coating layer provided on the surface of the refractory aggregate. There is a risk that the refractory aggregate particles will adhere to each other and form agglomerates (composite particles), which will adversely affect the physical properties of the mold, and the core after casting the molten metal. It also causes problems such as making it difficult to remove the sand.

Then, the second coating layer formed of the binder composition containing such a water-soluble inorganic binder is present on the first coating layer with an appropriate thickness. , Its thickness is generally 0.1 to 6 μm, preferably 0.2 to 5 μm, more preferably 0.3 to 3 μm, and still more preferably 0.5 to 2 μm. It will be thicker than the coating layer.

In addition, the measurement of solid content in a water-soluble inorganic binder will be implemented as follows. That is, after placing 10 g of the sample in an aluminum foil dish (length: 9 cm, width: 9 cm, height: 1.5 cm) and weighing it, place it on a heating plate maintained at 180 ± 1 ° C. for 20 minutes. After that, the sample-accommodating dish is inverted and left on the heating plate for 20 minutes. Next, the sample storage dish that has been dried by heating is removed from the heating plate, allowed to cool in a desiccator, weighed, and the solid content (% by mass) is calculated by the following equation.
Solid content (% by mass) = {[mass of sample storage dish after drying (g) - mass of dish itself (g)]
/ [mass of sample storage dish before drying (g) - mass of dish itself (g)]} x 100

In addition, the second coating layer made of the binder composition containing the water-soluble inorganic binder described above can contain the same coupling agent as the first coating layer. By including a coupling agent in such a binder composition, wettability and adhesiveness are improved, and bonding between the first coating layer and the second coating layer formed on the surface of the refractory aggregate is facilitated. can be strengthened. This effect is further enhanced by containing a coupling agent in both the first coating layer and the second coating layer, and the strength of the finally obtained mold is further increased. It will improve. The content of the coupling agent in the binder composition is generally 0.5 to 10 parts by mass, preferably 1 to 10 parts by mass, per 100 parts by mass of the solid content of the water-soluble inorganic binder contained therein. The ratio is 5 parts by mass, more preferably 1 to 3 parts by mass.

Furthermore, in the present invention, it is effective to incorporate a known moisture resistance improver into the binder composition constituting the second coating layer. By including a moisture resistance improver in the binder composition, the moisture resistance of the finally obtained mold can be improved. In addition, such binder compositions may contain surfactants. By including a surfactant in the binder composition containing the water-soluble inorganic binder, the dry coated sand according to the present invention can: 1) be prepared (manufactured) due to the presence of the surfactant; 2) the surface tension of water is suppressed and the fluidity of the coated sand is improved; It is possible to advantageously enjoy effects such as that the mold exhibits excellent strength in addition to excellent releasability from the mold. Examples of such surfactants include cationic surfactants, anionic surfactants, amphoteric surfactants, nonionic surfactants, silicone surfactants and fluorosurfactants. , can be used. Also, the binder composition constituting the second coating layer may contain a polyhydric alcohol. Since the polyhydric alcohol is contained in the binder composition containing the water-soluble inorganic binder, the swellability of the coated sand in a wet state is solidified or hardened by heating. It can be maintained stably until

Furthermore, in the wet or dry coated sand according to the present invention, the binder composition constituting the second coating layer covering the outer surface of the refractory aggregate particles on which the first coating layer is formed In addition, if necessary, other known additives such as lubricants and release agents can be added as appropriate. In particular, the lubricant can be present as a separate layer on the outer surface of the second coating layer. In addition, in order to include such an additive in the binder composition, the binder composition is prepared by mixing with a water-soluble inorganic binder or the like, and the prepared binder containing the additive is prepared. A method of kneading or mixing the binder composition with the refractory aggregate forming the first coating layer, or a method of using a predetermined additive separately without mixing the binder composition into the second A method of adding to the refractory aggregate on which the coating layer is formed and uniformly kneading or mixing the whole is adopted.

By the way, the coated sand according to the present invention is prepared by: 1) first forming a solid first coating layer containing the organic compound on the surface of the refractory aggregate, and then 2-1) forming such a coating layer. The liquid binder composition containing the water-soluble inorganic binder is added to the refractory aggregate obtained above, and kneaded or mixed to remove the wet binder composition. as a wet coated sand in which a second coating layer (coating layer) is formed on the first coating layer, or 2-2) kneading or mixing with the liquid binder composition together with, by evaporating the moisture, a second coating layer (coating layer) made of a solid binder composition is formed on the first coating layer as a dry coated sand, respectively It is possible to manufacture advantageously.

When producing the wet or dry coated sand according to the present invention according to such a production method, first, a solid first coating layer containing an organic compound is formed on the surface of the refractory aggregate. Furthermore, from among various known methods, a method suitable for the characteristics of the organic compound is appropriately selected and employed. For example, as a method of forming the first coating layer, which is a solid coating layer containing an organic compound, on the surface of the refractory aggregate, known methods such as a dry hot coating method and a cold coating method are exemplified. However, the method is not particularly limited as long as a solid coating layer can be formed.

The dry hot coating method is a method in which a solid organic compound is added to and mixed with a refractory aggregate heated to 120 to 180° C., and the solid organic compound is melted by the heat of the refractory aggregate. by coating the surface of the refractory aggregate with the molten organic compound, and then cooling while maintaining the mixed state to form a solid coating layer on the surface of the refractory aggregate. is. In the cold coating method, an organic compound is used as it is or dissolved in a solvent such as methanol to form a liquid, and the liquid is added to the refractory aggregate and mixed. This is a method of forming a solid coating layer on the surface of elastic aggregate.

In the case of using a crosslinked curable resin as an organic compound, for example, after forming a solid coating layer according to the above-described coating method, further heating and/or a known curing agent or curing catalyst is added. A method of curing the cross-linking curable resin by adding it and increasing the molecular weight of the cross-linking curable resin contained in the coating layer is adopted. When the cross-linking curable resin is cured by heating, for example, it is placed in a constant temperature bath at 120°C to 300°C and held for about 5 to 60 minutes for reactive curing, or preheated to 150°C to 300°C. There is a method of kneading the obtained refractory aggregate together with a cross-linkable curable resin in a kneader heated to 120° C. to 300° C. for about 5 to 60 minutes for reaction hardening. In the case of curing the cross-linked curable resin contained in the first coating layer, the refractory aggregate particles (sand grains) may bond with each other to form an integral mass or form composite particles. Therefore, in order to improve the surface condition of the refractory aggregate coated with the first coating layer, it is preferable to react and harden the aggregate while kneading it with a kneader having a high rotation speed (speed muller). Further, if kneaded for a long time, peeling may occur and fine powder may be generated. Therefore, it is preferable to adopt a method of reacting at high temperature in a short time. When the cross-linkable curable resin is a phenol urethane resin, a method of curing by mixing the phenol resin and a known polyisocyanate compound is employed. In addition, even when curing a cross-linking curable resin using a curing agent such as hexamethylenetetramine or triethylamine, a method of reaction curing while kneading them with a refractory aggregate in a kneader is adopted. It is desirable to

Next, the refractory aggregate having a surface provided with a solid first coating layer containing an organic compound is further coated with a binder composition containing a water-soluble inorganic binder to obtain a wet state. In forming the second coating layer in a state or solid state (dry state), generally, the refractory aggregate provided with such a first coating layer is coated with an aqueous solution as a binder composition. is kneaded or mixed with additives used as necessary, and mixed uniformly to form a wet or dry state on the first coating layer Thus, the coated sand according to the present invention having the second coating layer formed thereon can be obtained in a wet or dry state. The conditions for such mixing are appropriately determined according to the type and amount of water of the water-soluble inorganic binder in the form of an aqueous solution. In some cases, the temperature is generally about room temperature to 40°C.

Specifically, when producing the wet coated sand described above, the water content is adjusted so that the resulting coated sand exhibits an appropriate wet state. When water glass is used as the binder, the water content in the coated sand is preferably 70 to 900% by mass, more preferably 95 to 500% by mass so that the solid content of the water glass is greater than 55% by mass. %. In this way, the wet coated sand with the adjusted moisture content prevents the wet coated sand from drying out and blocking due to the blow air when filling the mold during mold making. In addition to being able to advantageously secure the wettability of the coated sand, excellent properties are imparted to the mold molded using such coated sand. The water content of the coated sand can be measured by the Karl Fischer method or by weight change when heated with a dryer or the like.

On the other hand, in the production of the dry coated sand, as described above, a uniform mixture of the refractory aggregate provided with the first coating layer and the binder composition containing the water-soluble inorganic binder is prepared. After obtaining, the desired room temperature fluidity is obtained by evaporating (transpiration) the water contained in the prepared mixture to form a second coating layer in a solid state on the first coating layer. A technique for obtaining a dry coated sand having properties is adopted. In such a method, it is necessary that the water in the mixture evaporate rapidly before the solidification or hardening of the water-soluble inorganic binder proceeds. , within 5 minutes, more preferably within 3 minutes, after adding (mixing) the water-soluble inorganic binder in the form of an aqueous solution to the refractory aggregate on which the first coating layer is formed. In addition, it is desirable to evaporate the contained water to obtain a dry coated sand. If the transpiration time becomes longer, the kneading (mixing) cycle becomes longer, productivity decreases, and the water-soluble inorganic binder becomes inactive due to longer contact time with CO ₂ in the air. This is because the risk of causing

The moisture content of the dry coated sand thus obtained is 1.5% by mass or less, preferably 0.1 to 1.2% by mass, more preferably 0.2 to 1%, based on the coated sand. 0% by mass. Further, when water glass is used as the water-soluble inorganic binder, it is 5 to 55% by mass, preferably 10 to 50% by mass, more preferably 15 to 50% by mass based on the solid content of water glass. so that it is adjusted. The moisture content of such coated sand can be measured by the Karl Fischer method or by mass change when heated with a dryer or the like, as described above.

In the manufacturing process of such a dry coated sand, as one of the effective means for rapidly evaporating the moisture in the mixture, the refractory aggregate on which the first coating layer is formed is preheated and kneaded or mixed with a water-soluble inorganic binder (binder composition) in the form of an aqueous solution to prepare a mixture. By kneading or mixing the water-soluble inorganic binder in the form of an aqueous solution with the preheated refractory aggregate, the water derived from the water-soluble inorganic binder in the form of the aqueous solution is The heat of such refractory aggregates can evaporate very quickly, thereby effectively reducing the water content of the resulting coated sand and providing a dry coated sand having normal temperature fluidity. is advantageously obtained. In addition, as another means for rapidly evaporating water in the mixture, kneading or mixing may be performed while blowing hot air at 120°C or higher, and the refractory aggregate is preheated to 40°C to 80°C. After that, the water-soluble inorganic binder may be kneaded or mixed while reducing the pressure.

Therefore, the preheating temperature of the refractory aggregate on which the first coating layer is formed depends on the type and amount of the water-soluble inorganic binder used, and the water content in the aqueous solution of the water-soluble inorganic binder. Although it is appropriately selected depending on the amount etc., for example, in the case of water glass, generally about 100 to 160 ° C., preferably about 110 to 140 ° C. It is desirable to heat the material and knead it with the water-soluble inorganic binder. If the preheating temperature is too low, the water cannot evaporate effectively and it takes a long time to dry the mixture. On the other hand, if the preheating temperature is too high, solidification (hardening) of the water-soluble inorganic binder component proceeds during cooling of the resulting coated sand, and in addition, formation of composite particles also proceeds. There is a risk of causing problems in physical properties such as the function as a material, especially strength.

Further, when producing the dry coated sand according to the present invention, the water-soluble inorganic binder in the form of an aqueous solution as the binder composition is used when the water-soluble inorganic binder used is solid is used in a pre-dissolved state in water. On the other hand, even a liquid water-soluble inorganic binder can be diluted with water to adjust its viscosity. Further, when kneading or mixing with the refractory aggregate, the solid or liquid water-soluble inorganic binder and water can be separately added to the refractory aggregate.

The wet or dry coated sand according to the present invention thus obtained can be used to form the desired mold using various conventionally known techniques. For example, while filling the wet coated sand described above into the molding cavity of a mold that provides the desired mold, the mold is heated to a temperature of 80 to 300° C., preferably 100 to 200° C. and maintained. and hold it in the mold until the filled coated sand dries. By holding the heat in the mold, solidification or hardening of the filled wet coated sand progresses, and the desired mold can be obtained.

That is, a binder composition in which refractory aggregate particles constituting the coated sand are present in the surroundings by filling and holding wet coated sand in the cavity of the mold heated to the above temperature. Through the water-soluble inorganic binder contained in the coated sand, an aggregate (combination) of the coated sand is formed, which is connected to each other and presents an integral template shape. At this time, as an additive for accelerating the curing of the water-soluble inorganic binder, a predetermined curing agent may be introduced into the cavity in the form of liquid or gas. Incidentally, the water-soluble inorganic binder is generally solidified by evaporation of water to dryness if no additives are added, and is hardened if a hardening agent is added. In the present invention, the mold composed of an aggregate (bonded body) of coated sand may be either simply solidified coated sand (solidified product) or cured with a curing agent (cured product). includes.

In addition, when heating the wet coated sand in the cavity of the mold, it is advantageous to heat (preheat) to a predetermined temperature in advance and prepare the mold held at that temperature. Preferably, the cavity of the mold is filled with the coated sand and the coated sand is heated. By preheating the molding die in this manner, the coated sand can be dried quickly, and the molding time can be shortened. The holding temperature for this preheating is 80 to 300.degree. C., preferably 100 to 200.degree. C., more preferably 120 to 180.degree. The holding temperature is preferably 80° C. or higher from the viewpoint of accelerating the drying, shortening the molding time, and improving the moisture resistance strength by the additive, and the bonding between the refractory aggregate particles is sufficient. The temperature is preferably 300° C. or less from the viewpoint of preventing the occurrence of the problem that the mold strength does not develop due to the evaporation of water before the mold is formed. By heating the mold at a temperature within such a temperature range, the moisture resistance strength of the finally obtained mold can be improved and the drying of the coated sand can be advantageously advanced.

Furthermore, while the coated sand is held in the mold, hot air or superheated steam is blown into the mold to promote the evaporation of water so that the filled phase (coated sand) in the mold is aerated. method is preferably employed. Such ventilation of hot air or superheated steam quickly dries even the inside of the filled phase composed of the coated sand, and further advantageously accelerates the solidification or curing of the filled phase, thereby solidifying (hardening). In addition to advantageously increasing the speed, the properties of the resulting mold such as bending strength can be advantageously improved, and the molding time of the mold can be advantageously shortened. In addition, in order to promote solidification or hardening of the coated sand more favorably while the coated sand is held in the mold, a carrier gas comprising at least one of carbon dioxide, argon, nitrogen and helium is introduced into the mold. A technique of blowing into and aerating the packed phase is preferably employed. Carbon dioxide then acts as a curing agent, and argon, nitrogen and helium as solidification accelerators. By allowing such a carrier gas to act on the water-soluble inorganic binder, it is possible to further accelerate the solidification or hardening of the coated sand. Only one of the ventilation of hot air or superheated steam and the ventilation of carrier gas may be performed, but it is also possible to perform both of them. Techniques such as performing aeration and carrier gas aeration at the same time, aeration of hot air or superheated steam followed by aeration of carrier gas, or aeration of carrier gas followed by aeration of hot air or superheated steam are adopted. be. In short, after the cavity of the mold is filled with the wet coated sand, as long as it is held in the mold, hot air and/or carrier gas can be ventilated at any timing, It doesn't matter.

In addition to the method of heating in the mold as described above, the molding of the mold using the wet coated sand according to the present invention can be performed by introducing the above-described curing agent into the mold. A method of solidifying or hardening the sand or a method of solidifying or hardening the coated sand by reducing the pressure in the mold filled with the coated sand can also be employed.

Here, introduction of the curing agent into the mold is to promote curing through reaction between the water-soluble inorganic binder and the curing agent. As a method of introducing the curing agent, a method of adding the curing agent to the coated sand before filling the mold and filling the coated sand to which the curing agent has been added into the mold, and a method of filling the mold with the coated sand. It is possible to adopt any method of introducing the hardening agent as a carrier gas into the filled coated sand by aeration. Curing by the curing agent progresses while it is held in the mold. At this time, it is also effective to blow hot air or superheated steam into the mold in order to accelerate the evaporation of water. be. Furthermore, in order to promote solidification or hardening of the coated sand more advantageously, a carrier gas comprising at least one of carbon dioxide, argon, nitrogen and helium can be blown into the mold. When the curing agent is added, heating of the mold is not necessarily required, but it is preferable to heat the mold in order to promote solidification or curing more advantageously.

Examples of curing agents used there include organic acids such as carbon dioxide (carbonated water), sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, oxalic acid, carboxylic acid, paratoluenesulfonic acid, methyl formate, ethyl formate, propyl formate, Esters such as γ-butyrolactone, β-propiolactone, ethylene glycol diacetate, diethylene glycol diacetate, glycerin diacetate, triacetin, propylene carbonate, and monohydric alcohols such as methanol, ethanol, butanol, hexanol, octanol, etc. I can give an example. These curing agents can be used alone, and can also be used in combination of two or more.

Further, the method of depressurizing the inside of the mold is to dry and solidify the coated sand filled in the cavity of the mold by such decompression. Examples of the decompression method include a method of decompressing the inside of the mold by a known suction means. When the mold is depressurized, it is not always necessary to heat the mold, but it is preferable to heat the mold in order to promote solidification or curing more advantageously.

On the other hand, the following two methods, for example, can be used to mold the desired mold using the dry coated sand. That is, in the first method, the dry coated sand is kneaded with water at the mold making site to make it wet, and the wet coated sand is used in a mold to give the desired mold. It is a water addition method in which the mold is heated to a temperature of 80 to 300° C. and held in the mold until the filled coated sand is dried. In the second method, after filling the molding cavity of the mold that provides the desired mold with dry coated sand, water vapor is blown into the molding cavity to ventilate the water vapor into the filled phase composed of the coated sand. In the method, the aeration of the water vapor supplies moisture to the dry coated sand to bring it into a wet state (moistened state), and then, after such a wet state, It is a water vapor ventilation system in which the coated sand is held in a mold heated to 80 to 200° C. until it is dried.

In such molding, it is desirable that the mold, such as a metal mold or a wooden mold, into which the dry coated sand having room-temperature fluidity is filled is preheated, so that kneading with water or steam is performed. Drying of the coated sand moistened by can be allowed to proceed advantageously. The preheating temperature is generally 80 to 300° C., preferably 90 to 250° C., more preferably 100 to 200° C. in the first method, and 80 to 200° C. in the second method. C., preferably 90-150.degree. C., more preferably about 100-140.degree. If the heat retention temperature is too high, it will be difficult for the steam to pass through the surface of the mold, while if the temperature is too low, it will take time to dry the molded mold.

By the way, in the above first method, when the dry coated sand and water are kneaded (mixed), the dry coated sand is transported to the molding site where the mold is manufactured, and then kneaded at the molding site. , After adding water to make it wet, the resulting wet coated sand is filled in a mold, and the desired product is obtained in the same manner as in the case of molding the wet coated sand. The process of adding water to the dry coated sand to make it wet is simply putting the dry coated sand and a predetermined amount of water into a suitable mixer. Since it is sufficient to moisten the coated sand by mixing and mixing, it can be carried out with extremely simple work, and can be carried out very simply and easily even at a molding site where the work environment is poor. be. Also, the coated sand may be preheated to 40° C. to 100° C. before adding water. At the time of adding water, one or more substances selected from other additives, curing accelerators, and water-soluble inorganic binders for readjusting mold strength may be added together. Moreover, when other additives are liquid, the liquid containing water may be used.

In the second method, when steam is blown into the coated sand (filling phase) filled in the molding cavity of the mold, the temperature of the steam is generally about 80 to 150°C, more preferably 95 to 120°C. °C. If high-temperature steam is used, a large amount of energy is required for its production, so a steam temperature of around 100° C. is particularly advantageous. Moreover, as the pressure of the water vapor to be ventilated, a gauge pressure of about 0.01 to 0.3 MPa, more preferably about 0.02 to 0.1 MPa is advantageously adopted. Furthermore, as the ventilation time, generally, a ventilation time of about 2 seconds to about 60 seconds is adopted. This is because if the aeration time of this water vapor is too short, it will be difficult to sufficiently wet the surface of the dry coated sand, and if the aeration time is too long, it will form a coating layer on the surface of the coated sand. This is because problems such as dissolution and outflow of the water-soluble inorganic binder may occur.

Here, in the first method and the second method described above, hot air or superheated steam is blown into the mold to actively dry the filled phase composed of the wet coated sand, and the filled phase is made to aerate. A method to make it so is preferably adopted. Such ventilation of hot air or superheated steam (hot air, etc.) quickly dries even the inside of the filled phase of the coated sand, thereby promoting the solidification or curing of the filled phase more advantageously, thereby curing. In addition to advantageously increasing the speed, the properties of the resulting mold such as bending strength can be advantageously improved, and the molding time of the mold can be advantageously shortened. In the first method, the solidification or hardening of the filling phase is more advantageously performed, for example, before the aeration of hot air or the like, and in the second method, for example, between the aeration of water vapor and the aeration of hot air or the like. In order to accelerate the curing, the above curing agent may be gaseous or misted and aerated. By neutralizing the water-soluble inorganic binder with this curing agent, the solidification or curing can be further accelerated. It is possible. The curing agent may be aerated simultaneously with hot air in the first method, or at the same time with water vapor or hot air in the second method. Also, as another method for actively drying the filled phase, the inside of the mold may be decompressed. Such reduced pressure dries and solidifies the coated sand filled in the cavity of the mold. As a decompression method, for example, there is a method of decompressing the inside of the mold by a known suction means. In addition, when depressurizing the inside of the mold, hot air or superheated steam may be blown into the mold in order to promote the evaporation of water.

Then, using the wet or dry coated sand according to the present invention, the following excellent effects can be obtained in both the mold obtained by the above-described manufacturing method and the mold obtained by other manufacturing methods. It becomes possible to enjoy That is, among the coating layers of the laminated structure of the coated sand, the first coating layer containing the organic compound located below the second coating layer made of the binder composition containing the water-soluble inorganic binder. , an oxate, an organic carboxylate and an organic phosphate, the heat generated by the molten metal during casting reduces the casting temperature or Even when the pouring temperature is low, the action of heat during casting makes it easier for the coating layer of the laminated structure of the coated sand to separate from the surface of the refractory aggregate, and as a result, the collapse of the mold after casting. becomes even better.

In addition, using a mold molded from wet or dry coated sand according to the present invention, casting of a predetermined molten metal is performed, and the coated sand (recovered sand) recovered from the mold after casting In this case, by promoting effective thermal decomposition and carbonization of the organic compounds present on the surface of the coated sand (refractory aggregate), the water-soluble inorganic binder constituting the second coating layer is solidified or hardened. However, since it is in a state where it is easier to separate from the surface of the refractory aggregate, it is possible to easily reclaim such recovered sand by subjecting it to dry reclaiming treatment.

Here, for the dry regeneration treatment of the recovered sand, any dry regeneration treatment method conventionally known as a method for reclaiming recovered sand can be employed, and generally includes at least polishing treatment, If necessary, a method for treating recovered sand that includes firing treatment, classification treatment, etc. is adopted. Or even in the casting of molten aluminum with a low pouring temperature, since it is easy to separate, it is possible to collide the collected sand without adopting the generally adopted advanced polishing by grinding (hard polishing). It has the characteristic that it can be regenerated only by light polishing (soft polishing) by physical impact. In particular, by adopting such soft polishing, it is possible to eliminate the possibility that the surface of the refractory aggregate constituting the coated sand will be scraped off. Needless to say, according to the present invention, not only soft sanding but also ordinary hard sanding can be used for reclaiming recovered sand.

Then, as described above, the refractory aggregate obtained by regenerating the recovered sand is again provided to the coated sand manufacturing process, and the obtained coated sand is further provided to the mold molding process. As a result, it can be advantageously used to form a mold with excellent properties.

The present invention will be clarified more specifically below using some examples according to the present invention, but the present invention should not be construed in any limited way by the description of such examples. It should be understood that the In the following examples and comparative examples, "%" and "parts" are expressed on a mass basis unless otherwise specified. In addition, the measurement of the water content of the coated sand (CS, CE-CS) obtained in Examples and Comparative Examples, the mold obtained using such CS (including CE-CS; hereinafter the same) The collapsibility test, evaluation of reclaimability of recovered sand, and evaluation of gas defects and veining of casting products obtained by casting were carried out as follows.

-Measurement of moisture content of CS-
A predetermined amount of CS as a sample is placed on a magnetic dish and accurately weighed with an electronic balance to determine the mass (M1) of the CS sample before heating. Next, the CS sample placed on the magnetic dish is heated to 130° C. with an electric heater, held for 30 minutes, cooled to room temperature, and the mass (M2) of the heated CS sample is accurately weighed. Then, using the obtained mass of the CS sample before heating (M1) and the mass of the CS sample after heating (M2), the water content (W1) in the CS is calculated from the following formula (1). do. Next, the solid content (B1) of the water-soluble inorganic binder with respect to CS is calculated using the following formula (2), and then the water content (W1) in CS and the water-soluble inorganic binder with respect to CS From the solid content (B1), the water content relative to the solid content of the water-soluble inorganic binder (the water content of CS relative to the solid content of the water-soluble inorganic binder in the second coating layer: W2) is calculated by the following formula ( 3) is used for calculation. In these formulas, B2 is the solid content (g) of the water-soluble inorganic binder added to 100 g of the CS sample.
W1=[(M1−M2)/M1]×100 (1)
B1=[B2/(100+B2)]×(100−W1) (2)
W2=(W1/B1)×100 (3)

-Disintegration test-
First, as shown in FIG. 1, one of the hollow main halves was prepared in advance using a predetermined room temperature self-hardening sand, and had a molten metal inlet 2 at its upper portion and a core baseboard fixing portion 4 at its lower portion. Inside the mold 6 (cavity diameter: 6 cm, height: 6 cm), a circular airless element 10 (diameter: 5 cm, height: 5 cm) having a skirting part 8 made using each CS is placed. After adhesively fixing with the wooden fixing part 4, the other half hollow main mold 6 is assembled, and the two half hollow main molds 6, 6 are adhesively fixed to each other to produce the casting test sand mold 12. . In addition, in order to prevent molten metal from leaking during casting, the bonded main mold is clamped with a vise or the like, or tightly fixed by wrapping it with a wire. Next, molten iron FC150 (temperature: 1350±50° C.) or molten aluminum AC4C (temperature: 700±50° C.) is poured from the molten metal injection port 2 of the casting test sand mold 12 and solidified. The mold 6 is broken and a cylindrical casting 16 shown in FIG. 2 is taken out. Then, the casting 16 that has reached room temperature is hit repeatedly with an air hammer to eject the circular airless element 10 . During such discharge, the chipping pressure is set to 0.3 MPa, and the casting 16 is hit with an air hammer every 3 seconds. Then, the easiness of discharging the CS (hereinafter referred to as core CS) forming the circular non-aerial element 10 from the casting 16 is evaluated on a scale of 5 according to the following criteria. In the present invention, in the evaluation criteria, A to C are accepted.
A: All cores CS are discharged within 10 hits.
B: All the cores CS are discharged within 30 hits.
C: All cores CS are discharged within 60 hits.
D: 50% or more and less than 100% of the core CS is ejected by hitting 60 times.
E: 0 to less than 50% of the core CS is discharged at 60 impacts.

-Evaluation of reproducibility-
The sand (recovered sand) that had formed the circular aneurons taken out in the above-mentioned collapsibility test was roasted at a temperature of 400° C. for 60 minutes, and then hard-polished or soft-polished. That is, as the hard polishing, 300 g of the roasted recovered sand is placed in an alumina ball mill with an inner diameter of 180 mm and a length of 190 mm (desktop ball mill manufactured by Eisin Co., Ltd.: type BM10) together with 500 g of spherical alumina balls having a diameter of 20 mm. , and polished for 10 minutes at a rotational speed of 120 rpm. Further, as soft polishing, 5000 g of the roasted recovered sand was placed in a whirl mixer manufactured by Enshu Iron Works Co., Ltd., and stirred and mixed for 10 minutes at a rotation speed of 60 rpm to cause the sands to collide with each other. A polishing method was adopted. Then, the polished recovered sand is sieved with a 200-mesh sieve for 1 minute to separate the sand and the exfoliated fine powder (water-soluble inorganic binder). The amount of fine powder is measured, and the easiness of peeling of the recovered sand is evaluated on a scale of 5 according to the following criteria. In the present invention, in the evaluation criteria, A to C are accepted.
A: The amount of fine powder is 1.0% by mass or more with respect to the mass of recovered sand.
B: The amount of fine powder is 0.8% by mass or more and less than 1.0% by mass with respect to the mass of recovered sand.
C: The amount of fine powder is 0.5% by mass or more and less than 0.8% by mass with respect to the mass of recovered sand.
D: The amount of fine powder is 0.3% by mass or more and less than 0.5% by mass with respect to the mass of recovered sand.
E: The amount of fine powder is less than 0.3% by mass with respect to the mass of recovered sand.

-Evaluation of gas defects and veining-
After forming a cylinder head casting mold using each CS, 20 cylinder heads are cast by pouring molten aluminum AC4C (temperature: 700±50° C.) by a low pressure casting method. Then, all of the obtained cylinder heads (castings) are cut, the inside is observed, the presence of gas defects and the presence of veining (casting burrs) are observed, and gas defects and veining are determined according to the following criteria. Evaluation is done on a 5-point scale. In these evaluations, A to C are all considered acceptable.
・Number of cylinder heads with gas defects A: 0 to 1, B: 2 to 3, C: 4 to 5, D: 6 to 7, E: 8 or more ・Cylinder heads with veining Number of A: 0 to 1, B: 2 to 3, C: 4 to 5, D: 6 to 7, E: 8 or more

In addition, novolak type phenolic resins and the like, which are organic compounds used in producing each CS, were prepared according to the following procedures or commercially available products.

(1) Preparation of novolac-type phenolic resin Into a reaction vessel equipped with a thermometer, a stirrer and a condenser were charged 940 parts of phenol, 479 parts of 47% formalin and 2.8 parts of oxalic acid. Next, while stirring, the temperature inside the reaction vessel is gradually raised to reach the reflux temperature, and then the mixture is refluxed for 90 minutes for reaction, and further heated and concentrated under reduced pressure until the temperature of the reaction solution reaches 170°C. Thus, a novolak-type phenol resin having a weight average molecular weight (Mw) of 2,900 was obtained.

(2) Preparation of resol-type phenolic resin As a resol-type phenolic resin, SP400 (trade name, Mw: 2100) manufactured by Asahi Yukizai Co., Ltd., which is an ammonia resol-type phenolic resin, was prepared.

(3) Preparation of materials for forming phenol urethane resin Benzylic ether type phenol resin (manufactured by Asahi Yukizai Co., Ltd., trade name: CBP-160EH, Mw: 1200) and polymeric MDI (Asahi Yukizai Co., Ltd.) as a polyisocyanate compound Company; It was used as a resin forming material.

(4) Preparation of polyvinyl acetate Polyvinyl acetate solution [weight average molecular weight (Mw) 220000, concentration 65%] made of Gohsenyl M35-X6 (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., methanol 35% solution) as polyvinyl acetate prepared.

-Production example 1 of wet CS-
Commercially available Flutary silica sand (#60) was prepared as the refractory aggregate, and the previously prepared novolak-type phenolic resin was prepared as the organic compound. Then, after heating the fluttery silica sand to a temperature of about 130° C., it is put into a whirl mixer (manufactured by Enshu Iron Works Co., Ltd.). 0.1 part of potassium nitrate as one of the oxysalts is added to each and kneaded for 3 minutes to evaporate the moisture while the sand grains are stirred and mixed until the lumps of sand grains collapse, and then taken out. As a result, a solid first coating layer (first layer) made of a novolac-type phenolic resin containing potassium nitrate was formed on the surface of the fluttery silica sand (particles).

Next, commercial product: No. 2 sodium silicate (trade name: manufactured by Fuji Chemical Co., Ltd., SiO ₂ /Na ₂ O molar ratio: 2.5) was used as water glass as a water-soluble inorganic binder, and solidified. A water glass aqueous solution with a component (concentration) of 41% was prepared. Then, the previously prepared Flutary silica sand having a solid first coating layer on its surface is put into a Shinagawa-type universal stirrer (5DM-r type, manufactured by Dalton Co., Ltd.) at room temperature, and further, 3.0 parts of the water glass aqueous solution is added to 100 parts of Flutary silica sand, kneaded for 3 minutes, stirred until uniform, mixed, and taken out to form the first coating. A wet coated sand (CS1) was obtained in which a second coating layer (second layer) made of water glass was provided on the layer. The water content of the obtained CS1 was an amount corresponding to 144% of the solid content of the water glass.

-Production Examples 2 to 5 of Wet CS-
Except that in Production Example 1 of Wet CS, the amount of potassium nitrate used in forming the first coating layer was set to 0.3 parts, 0.5 parts, 1.0 parts, or 2.0 parts, respectively. , Various wet coated sands (CS2 to CS5) were obtained according to the same procedure as in Production Example 1 above. Each of the obtained CS2 to CS5 had a water content corresponding to 144% of the solid content of the water glass.

-Production Examples 6 to 12 of Wet CS-
In wet CS production example 3, the above production was performed except that sodium nitrate, magnesium nitrate, calcium nitrate, potassium permanganate, calcium permanganate, sodium molybdate, or potassium tungstate was used instead of potassium nitrate. Following the same procedure as in Example 3, various wet coated sands (CS6-CS12) were obtained respectively. Each of the obtained CS6 to CS12 had a water content corresponding to 144% of the solid content of the water glass.

-Production example 13 of wet CS-
In wet state CS production example 3, the same procedure as in production example 3 above, except that the first coating layer was formed using the previously prepared resol-type phenolic resin instead of the novolac-type phenolic resin. A wet coated sand (CS13) was obtained according to The water content of the obtained CS13 was an amount corresponding to 144% of the solid content of the water glass.

-Production example 14 of wet CS-
In Wet CS Production Example 3, phenol A moist coated sand (CS14) was obtained in the same manner as in Production Example 3 above, except that a first coating layer made of urethane resin was formed. In forming the first coating layer, the stirring and mixing operation of the fluttery silica sand and the phenol urethane resin-forming material is carried out by mixing the benzylic ether type phenol resin and the polyisocyanate compound that constitute the phenol urethane resin-forming material. reacted to form a phenol urethane resin, which was cured and solidified. The water content of CS14 thus obtained was equivalent to 144% of the solid content of water glass.

-Production example 15 of wet CS-
In wet CS production example 3, 3.08 parts of the previously prepared polyvinyl acetate solution was used in place of the novolak-type phenolic resin, and the solvent was evaporated during the formation of the coating layer to form the first coating layer. A wet coated sand (CS15) was obtained according to the same procedure as in Production Example 3 above, except that the was formed. The water content of the obtained CS15 was an amount corresponding to 144% of the solid content of the water glass.

-Production example 16 of wet CS-
In wet CS production example 3, instead of the water glass aqueous solution, a potassium carbonate aqueous solution having a potassium carbonate solid content (concentration) of 50% and having a viscosity at 25° C. of 8 cP was used, A moist coated sand (CS16) was obtained in the same manner as in Production Example 3, except that the amount used was 3.5 parts. The water content of the obtained CS16 was an amount corresponding to 100% of the solid content of potassium carbonate.

-Production Examples 17 to 19 of Wet CS-
In wet CS production example 1, the above production was performed except that 0.1 part, 0.2 part, or 0.3 part of triethyl phosphate, which is one of organic phosphoric acid esters, was used instead of potassium nitrate. Following the same procedure as in Example 1, various wet coated sands (CS17-CS19) were obtained respectively. The water contents of CS17 to CS19 thus obtained corresponded to 144% of the solid content of the water glass.

-Production Examples 20 to 22 of Wet CS-
In wet CS production example 18, the same as production example 18 above except that tributyl phosphate, tricresyl phosphate, or triphenyl phosphate was used instead of triethyl phosphate to form the first coating layer. According to the procedure, various wet coated sands (CS20-CS22) were obtained respectively. The water contents of CS20 to CS22 thus obtained corresponded to 144% of the solid content of water glass.

-Production Examples 23 to 25 of Wet CS-
The same procedure as in Production Examples 13 to 15 above, except that 0.2 parts of triethyl phosphate was used in place of potassium nitrate to form the first coating layer in Production Examples 13 to 15 of wet CS. Various coated sands (CS23-CS25) in wet state were obtained respectively according to. Each of the obtained CS23 to CS25 had a water content corresponding to 144% of the solid content of the water glass.

-Wet CS Production Example 26-
In wet CS production example 18, instead of the aqueous solution of water glass, an aqueous potassium carbonate solution having a potassium carbonate solid content (concentration) of 50% and having a viscosity of 8 cP at 25°C was used. A wet coated sand (CS26) was obtained in the same manner as in Production Example 18 except that the amount used was changed to 3.5 parts. The water content of the obtained CS26 was an amount corresponding to 100% of the solid content of potassium carbonate.

-Production Examples 27 and 28 of wet CS-
Except that in wet CS production example 3, in addition to 0.5 parts of potassium nitrate, 0.2 parts of triethyl phosphate or 0.2 parts of tributyl phosphate were used to form the first coating layer. obtained two wet coated sands (CS27 and CS28), respectively, according to the same procedure as in Production Example 3 above. The water contents of CS27 and CS28 obtained respectively corresponded to 144% of the solids content of the water glass.

-Production Examples 29 and 30 of wet CS-
In wet CS production example 3, together with 0.5 parts of potassium nitrate, 1.0 parts of ferric oxide or 1.0 parts of cupric oxide, which are metal oxides, are used to prepare the first Two wet coated sands (CS29, CS30) were obtained in the same manner as in Production Example 3 except that the coating layer was formed. The water contents of CS29 and CS30 obtained respectively corresponded to 144% of the solid content of water glass.

-Production Examples 31 and 32 of Wet CS-
In Production Example 27 of Wet CS, except that 1.0 part of each of ferric oxide or cupric oxide, which is a metal oxide, was further used to form the first coating layer, the above production example Two wet coated sands (CS31, CS32) were obtained respectively following the same procedure as in 27. The water contents of the obtained CS31 and CS32 were each equivalent to 144% of the solids content of the water glass.

-Production Examples 33 and 34 of Wet CS-
In Production Example 9 of wet CS, the same as Production Example 9 above, except that 0.2 parts of triethyl phosphate or 1.0 part of ferric oxide was further used to form the first coating layer. Two wet coated sands (CS33, CS34) were obtained respectively according to the procedure of . The water contents of the obtained CS33 and CS34 respectively corresponded to 144% of the solid content of the water glass.

-Production Examples 35 and 36 of Wet CS-
In Wet CS Production Example 18, except that 1.0 part of ferric oxide or cupric oxide was further used to form the first coating layer, following the same procedure as in Production Example 18 above, Two wet coated sands (CS35, CS36) were obtained respectively. The water contents of the obtained CS35 and CS36 respectively corresponded to 144% of the solids content of the water glass.

-Wet CS Production Example 37-
In Production Example 18 of wet CS, 0.7 parts of ferric oxide and 0.3 parts of cupric oxide were further used to form the first coating layer, as in Production Example 18 above. A wet coated sand (CS37) was obtained following a similar procedure. The water content of the obtained CS37 was an amount corresponding to 144% of the solid content of the water glass.

-Wet CS Production Example 38-
In Wet CS Production Example 26, following the same procedure as in Production Example 26 above, except that 0.5 parts of potassium nitrate, which is one of the oxates, was further used to form the first coating layer, A wet coated sand (CS38) was obtained. The water content of the obtained CS38 was an amount corresponding to 100% of the solid content of potassium carbonate.

-Wet CS Production Example 39-
In Production Example 16 of wet CS, the same procedure as in Production Example 16 above was performed, except that 1.0 part of ferric oxide, which is one of the metal oxides, was further used to form the first coating layer. A wet coated sand (CS39) was obtained according to the procedure. The water content of the obtained CS39 was an amount corresponding to 100% of the solid content of potassium carbonate.

-Production example 40 of wet CS-
In wet CS Production Example 39, the same procedure as in Production Example 39 above, except that 0.2 parts of triethyl phosphate, which is one of organic phosphoric acid esters, was used instead of 0.5 parts of potassium nitrate. A wet coated sand (CS40) was obtained according to The water content of the obtained CS40 was an amount corresponding to 100% of the solid content of potassium carbonate.

-Production Examples 1 and 2 of Wet CE-CS-
In wet state CS production examples 1 and 16, respectively, except that the step of forming a solid first coating layer was not performed, according to the same procedure as in production examples 1 and 16, wet two Two coated sands (CE-CS1, CE-CS2) were obtained, respectively. The water contents of the obtained CE-CS1 and CE-CS2 corresponded to 144% of the solids content of water glass and 100% of the solids content of potassium carbonate, respectively.

-Production Examples 3 to 7 of Wet CE-CS-
In Production Examples 1 and 13 to 16 of wet state CS, each wet state coating was prepared according to the same procedure as in Production Examples 1 and 13 to 16, except that potassium nitrate was not added to the first coating layer. Sands (CE-CS3 to CE-CS7) were obtained respectively. The water contents of CE-CS3 to CE-CS7 obtained were respectively 144% of the solid content of water glass and 100% of the solid content of potassium carbonate.

- Molding Example I (Examples 1 to 40, Comparative Examples 1 to 7) -
The wet CS1 to 40 and CE-CS1 to 7 produced according to the procedures described above are respectively filled in a mold heated to 150° C., then held in the mold and heated. By doing so, each CS and CE-CS filled in the mold is cured and used as a circular test piece (diameter: 5 cm × height: 5 cm) and a mold for casting a cylinder head. Various templates were made. Next, using the molds corresponding to each of the CS and CE-CS thus obtained, evaluation of disintegration and reproducibility was performed, and the presence or absence of gas defects and veining was examined and evaluated. The results are also shown in Tables 1 to 6 below. Tables 1 to 6 below show the CS and CE-CS used to prepare the molds (test specimens) of Examples 1 to 40 and Comparative Examples 1 to 7.

As is clear from the results in Tables 1 to 5, the molds (Examples 1 to 40) obtained by using the wet coated sands CS1 to CS40 according to the present invention had a high pouring temperature of Fe. It is recognized that the collapse property of the mold after casting is excellent not only in the case of casting using molten metal, but also in the case of casting molten Al with a low pouring temperature. Regarding the sand recovered after the casting of molten Al, when removing the solidified or hardened material of the water-soluble inorganic binder adhering thereto, it is necessary not only in the case of hard polishing but also in soft polishing. , it is easy to remove the wet coated sand according to the present invention. Furthermore, since the first coating layer of the coated sand contains a metal oxide in addition to the oxysalt and the organic phosphate, casting defects such as gas defects and veining are advantageously improved. You can also accept that you get it.

On the other hand, as is clear from Table 6, the molds obtained using CE-CS1 and CE-CS2, which are wet-state coated sands not provided with the first coating layer containing an organic compound (comparative In Examples 1 and 2), the collapsibility after casting of both the molten Fe and the molten Al is not sufficient, and the sand recovered after the casting is subjected to hard polishing as well as soft polishing. Even in , it was difficult to reproduce it. Furthermore, even when a first coating layer containing an organic compound is provided, the wet coated sand does not contain an oxate, an organic phosphate, or the like in the first coating layer. In the molds obtained using CE-CS3 to CE-CS7 (Comparative Examples 3 to 7), in casting molten Fe at a high pouring temperature, the mold collapse property after casting is excellent. However, the collapsibility of the mold after casting molten Al with a low pouring temperature is not sufficient. Also, it is recognized that the cured product is difficult to remove easily.

-Production example 1 of dry CS-
Flutary silica sand (#60) was prepared as a refractory aggregate, and the previously prepared novolak-type phenolic resin was prepared as an organic compound. After heating the fluttery silica sand to a temperature of about 130° C., it is put into a whirl mixer (manufactured by Enshu Iron Works Co., Ltd.), and 2 parts of the novolak type phenol resin prepared above is added to 100 parts of the fluttery silica sand. Further, 0.5 part of potassium nitrate is added and kneaded for 3 minutes to evaporate the water content, while stirring and mixing until the sand grain lumps collapse and then taken out to obtain fluttery silica sand. A solid first coating layer (first layer) made of a novolak-type phenolic resin was formed on the particle surface.

Next, commercial product: No. 2 sodium silicate (trade name: manufactured by Fuji Chemical Co., Ltd., SiO ₂ /Na ₂ O molar ratio: 2.5) was used as water glass as a water-soluble inorganic binder, and solidified. A water glass aqueous solution with a component (concentration) of 41% was prepared. Then, the previously prepared flattery silica sand having a surface provided with a solid first coating layer is heated to a temperature of about 50° C., then put into a whirl mixer (manufactured by Enshu Iron Works Co., Ltd.), and further 3.0 parts of the water glass aqueous solution prepared above was added to 100 parts of Flutary silica sand, and kneaded in a whirl mixer for 5 minutes while blowing hot air at 120°C to obtain a uniform mixture. By stirring and mixing until it becomes A dry coated sand (CS41) was obtained, consisting of a layer). The water content of the obtained CS41 was an amount corresponding to 18% of the solid content of the water glass.

-Production example 2 of dry CS-
A dry coated sand (CS42) was obtained in the same manner as in Dry CS Production Example 1, except that potassium permanganate was used in place of potassium nitrate in Dry CS Production Example 1. . The water content of the obtained CS42 was an amount corresponding to 20% of the solid content of the water glass.

-Production example 3 of dry CS-
A dry coated sand was prepared in the same manner as in Dry CS Production Example 1, except that 2 parts of a resol-type phenolic resin was used in place of the novolac-type phenolic resin in Dry CS Production Example 1. (CS43) was obtained. The water content of the obtained CS43 was an amount corresponding to 19% of the solid content of the water glass.

-Production Example 4 of Dry CS-
In Dry CS Production Example 1, phenol A dry coated sand (CS44) was obtained in the same manner as in Dry CS Production Example 1, except that a first coating layer made of a urethane resin was formed. The stirring and mixing of the fluttery silica sand and the phenol urethane resin forming material causes the reaction between the benzylic ether type phenol resin and the polyisocyanate compound that constitute the phenol urethane resin forming material to form the phenol urethane resin. , hardened and solidified. The water content of the obtained CS44 was equivalent to 16% of the solid content of the water glass.

-Production Example 5 of Dry CS-
In Dry CS Production Example 1, 3.08 parts of the previously prepared polyvinyl acetate solution was used in place of the novolak-type phenolic resin, and the solvent was evaporated during the formation of the coating layer to form the first coating. A dry coated sand (CS45) was obtained in the same manner as in Dry CS Production Example 1 except that a layer was formed. The water content of the obtained CS45 was an amount corresponding to 19% of the solid content of the water glass.

-Production Example 6 of Dry CS-
In Dry CS Production Example 1, instead of the aqueous solution of water glass, an aqueous potassium carbonate solution having a solid component (concentration) of potassium carbonate of 50% and adjusted to have a viscosity of 8 cP at 25° C. was used. A dry coated sand (CS46) was obtained in the same manner as in Dry CS Production Example 1, except that the amount used was 3.5 parts. The water content of the obtained CS46 was an amount corresponding to 26% of the solid content of the water glass.

-Production Examples 7 and 8 of Dry CS-
In Dry CS Production Example 1, except that 0.2 parts of triethyl phosphate or tributyl phosphate was used instead of potassium nitrate, following the same procedure as in Dry CS Production Example 1, two dry CS Coated sands (CS47, CS48) were obtained respectively. The water contents of the obtained CS47 and CS48 corresponded to 18% and 17%, respectively, of the solid content of the water glass.

-Production Examples 9 to 11 of Dry CS-
In Dry CS Production Examples 3 to 5, dry CS was prepared according to the same procedure as in Dry CS Production Examples 3 to 5, except that 0.2 parts of triethyl phosphate was used instead of potassium nitrate. of various coated sands (CS49 to CS51) were obtained, respectively. The water contents of CS49 to CS51 thus obtained corresponded to 21%, 19% and 18% of the solid content of the water glass, respectively.

-Production Example 12 of Dry CS-
A dry coated sand (CS52) was prepared in the same manner as in Dry CS Production Example 6, except that 0.2 parts of triethyl phosphate was used instead of potassium nitrate in Dry CS Production Example 6. got The water content of the obtained CS52 was an amount corresponding to 27% of the solid content of the water glass.

-Production Examples 13 and 14 of dry CS-
In Dry CS Production Example 1, 0.2 part of triethyl phosphate as a phosphoric acid ester or 1.0 part of ferric oxide as a metal oxide was further used together with potassium nitrate as an oxate. Except for this, two dry coated sands (CS53 and CS54) were obtained in the same manner as in Dry CS Production Example 1 above. The water contents of CS53 and CS54 obtained corresponded to 20% and 17%, respectively, of the solid content of the water glass.

-Production Example 15 of Dry CS-
In Dry CS Production Example 14, dry CS was prepared according to the same procedure as in Dry CS Production Example 14, except that 0.2 parts of triethyl phosphate was further added to form a first coating layer. of coated sand (CS55) was obtained. The water content of the obtained CS55 was an amount corresponding to 19% of the solid content of the water glass.

- Dry CS Production Examples 16 and 17 -
In Dry CS Production Example 2, 0.2 part of triethyl phosphate or 1.0 part of ferric oxide was further added to form the first coating layer, but the above dry CS was Two dry coated sands (CS56, CS57) were respectively obtained according to the same procedure as in Production Example 2. The water contents of the obtained CS56 and CS57 corresponded to 18% and 17%, respectively, of the solid content of the water glass.

-Production Example 18 of Dry CS-
In Dry CS Production Example 7, the same as Dry CS Production Example 7 above, except that 1.0 parts of ferric oxide, which is a metal oxide, was further added to form the first coating layer. A dry coated sand (CS58) was obtained according to the procedure of . The water content of the obtained CS58 was an amount corresponding to 19% of the solid content of the water glass.

-Production Examples 19 and 20 of dry CS-
In Dry CS Production Example 6, 0.2 part of triethyl phosphate or 1.0 part of ferric oxide was further added to form the first coating layer, but the above dry CS was Two dry coated sands (CS59, CS60) were respectively obtained according to the same procedure as in Production Example 6. The water contents of CS59 and CS60 obtained corresponded to 27% and 28%, respectively, of the solid content of the water glass.

-Production Example 21 of Dry CS-
Dry CS Production Example 12 is the same as Dry CS Production Example 12, except that 1.0 part of ferric oxide, which is a metal oxide, is further added to form the first coating layer. A dry coated sand (CS61) was obtained following a similar procedure. The water content of the obtained CS61 was an amount corresponding to 28% of the solid content of the water glass.

-Production Examples 8 and 9 of dry CE-CS-
Dry CS production example 1 or 6, except that the step of forming a solid first coating layer was not carried out, followed by the same procedures as in dry CS production example 1 or 6 above. were obtained respectively (CE-CS8, CE-CS9). The water contents of the obtained CE-CS8 and CE-CS9 corresponded to 17% and 28%, respectively, of the solid content of the water glass.

-Production Examples 10 to 13 of Dry CE-CS-
In Dry CS Production Examples 1, 3 to 5, except that potassium nitrate was not added to the first coating layer, dry CS was produced in the same manner as in Dry CS Production Examples 1, 3 to 5. Various coated sands (CE-CS10 to CE-CS13) were obtained respectively. The water contents of CE-CS10 to CE-CS13 thus obtained corresponded to 18%, 20%, 19% and 18% of the solid content of the water glass, respectively.

-Production Example 14 of Dry CE-CS-
In Dry CS Production Example 6, a dry coated sand (CE-CS14) was prepared according to the same procedure as in Dry CS Production Example 6 above, except that potassium nitrate was not added to the first coating layer. Obtained. The water content of the obtained CE-CS14 was equivalent to 27% of the solid content of the water glass.

- Molding example of mold (water addition method) II (Examples 41 to 61, Comparative Examples 8 to 14) -
The dry CS41 to CS61 or CE-CS8 to CE-CS14 produced according to the above procedures are each charged into a Shinagawa universal stirrer (type 5DM-r, manufactured by Dalton Co., Ltd.) at room temperature, Furthermore, water was added in a stirrer at a ratio of 2.0 parts to 100 parts of CS or CE-CS, and stirred to prepare moistened CS or CE-CS, respectively. . Next, the wet CS or CE-CS taken out from the stirrer is blown into a molding die heated to 150° C. at a blow pressure of 0.3 MPa, and then left in the molding die for 1 minute. Hold for 30 seconds, then blow hot air at 300 ° C. for 1 minute and 30 seconds under a gauge pressure of 0.03 MPa to solidify (harden) the CS or CE-CS filled in the mold. ) to prepare a mold for use as a circular no-aerial test body (diameter: 5 cm×height: 5 cm) and a mold for casting a cylinder head. Next, using the molds corresponding to each CS or each CE-CS thus obtained, a pouring test is performed to evaluate the collapsibility of the mold and the reproducibility of the recovered sand. The presence or absence of was investigated and evaluated, and the results are also shown in Tables 7 to 10 below. Tables 7 to 10 below show the CS and CE-CS used to prepare the molds (test specimens) of Examples 41 to 61 and Comparative Examples 8 to 14.

As is clear from the results of Tables 7 to 9, CS41 to 61 used in Examples 41 to 61 all show excellent results similar to those of Examples 1 to 40. was recognized. That is, in each mold obtained using CS41 to 61 in a dry state, not only in the casting of molten Fe with a high pouring temperature, but also in the casting of molten Al with a low pouring temperature. However, it was found that the mold after casting was excellent in collapsibility, and the sand recovered after casting the molten Al was found to be a solidified or hardened water-soluble inorganic binder adhering to it. When removing objects, it is easy to remove not only hard sand but also soft sand. It is understood that the operation is extremely easy. Furthermore, casting defects such as gas defects and veining can be advantageously improved by including a predetermined metal oxide in addition to the oxysalt and the organic phosphoric acid ester in the first coating layer of the coated sand. can also be recognized.

On the other hand, as is clear from Table 10, CE-CS8 and CE-CS9, which are dry coated sands with no first coating layer, were used (Comparative Examples 8 and 9 ), the collapsibility after casting of either molten Fe or molten Al is not sufficient, and even in the sand recovered after casting, not only soft polishing but also hard polishing , was difficult to play. Furthermore, even when the first coating layer is provided, the dry coated sand CE- In the molds obtained using CS10 to CE-CS14 (Comparative Examples 10 to 14), it was found that the mold collapse property after casting molten Fe with a high pouring temperature was excellent. The collapsibility of the mold after casting molten aluminum with a low hot water temperature is not sufficient. It can be admitted that it is difficult to remove easily.

- Molding example of mold (water vapor ventilation method) III (Examples 62 to 65, Comparative Examples 15 to 18) -
Using the dry CS41, 47, 49, 50 or CE-CS8, 10-12 produced above, each of them is placed in a mold heated to 100 ° C. at a blow pressure of 0.3 MPa. After blowing and filling, steam at a temperature of 100° C. under a gauge pressure of 0.04 MPa and nitrogen gas under a gauge pressure of 0.2 MPa are simultaneously blown for 20 seconds into the mold. The packed coated sand (CS/CE-CS) phase was aerated. Then, after such ventilation of water vapor is completed, hot air at a temperature of 300°C is blown for 2 minutes and 40 seconds under a gauge pressure of 0.03 MPa to solidify the CS and CE-CS filled in the mold. By (curing), a mold used as a test body of a circular aneuron (diameter: 5 cm×height 5 cm) was produced, respectively. Then, using the molds corresponding to each CS and CE-CS thus obtained, evaluations of collapsibility and reclaimability of recovered sand were carried out, and the results are also shown in Table 11 below. The CS and CE-CS used to prepare the molds (test specimens) of Examples 62-65 and Comparative Examples 15-18 are shown in Table 11 below.

As is clear from the results in Table 11, a mold making method was adopted in which the desired mold (core) was made by blowing water vapor into the mold to solidify or harden the dry coated sand. In any case, in Examples 62 to 65 using CS according to the present invention, excellent results similar to those in Tables 7 to 9 above could be obtained. On the other hand, CE-CS8, which is a dry coated sand that is not provided with the first coating layer, and dry state that does not contain an oxate or an organic phosphate in the first coating layer. All of the molds obtained using CE-CS10 to 12, which are coated sands, have the same results as in Table 10 above, indicating that the object of the present invention cannot be sufficiently achieved. Is recognized.

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

Claims (10)

A solid first coating layer containing an organic compound is formed so as to cover the surface of the refractory aggregate, and a water-soluble inorganic caking layer is further coated so as to cover the first coating layer. In a coated sand having a laminated structure in which a second coating layer made of a binder composition containing an agent is formed,
The first coating layer contains at least one or more compounds selected from the group consisting of oxysalts and organic phosphates, and the oxysalt is 100 parts by mass of the organic compound. 1 to 300 parts by mass of the organic compound, while the organic phosphate ester is contained in a ratio of 0.5 to 100 parts by mass with respect to 100 parts by mass of the organic compound. coated sand. 2. The coated sand according to claim 1, wherein the organic compound is selected from the group consisting of crosslinked curable resins and cured products thereof, thermoplastic resins, and carbohydrates. 3. The water-soluble inorganic binder is at least one selected from the group consisting of water glass, sodium phosphate, sodium carbonate, sodium aluminum oxide and potassium carbonate. coated sand. 4. The coated sand according to any one of claims 1 to 3 , wherein said first coating layer further contains a metal oxide. 5. The coated sand according to claim 4 , wherein the metal oxide is contained in a proportion of 1 to 300 parts by mass with respect to 100 parts by mass of the organic compound. 6. The coated sand according to any one of claims 1 to 5 , which is formed as a wet coated sand having no fluidity at normal temperature. 6. The coated sand according to any one of claims 1 to 5 , which is formed as a dry coated sand having normal temperature fluidity. The wet coated sand of claim 6 is used, filled into the mold cavity of the mold and held in the mold to obtain the coated material filled in the mold cavity of the mold. 1. A mold manufacturing method characterized by solidifying or hardening sand to obtain a desired mold. By using the dry coated sand according to claim 7 , filling it into the molding cavity of a predetermined mold, and holding it in the mold after passing water vapor, such a mold A mold manufacturing method characterized by solidifying or hardening the coated sand filled in the molding cavity of (1) to obtain the desired mold. Using the dry coated sand of claim 7 , add water to it to make it wet, fill the wet coated sand into the molding cavity of the mold, and A mold manufacturing method comprising the step of solidifying or hardening the coated sand filled in the mold cavity by holding it in the mold to obtain the intended mold.

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