JP6978366B2 - Method of manufacturing coated sand and mold using it, and method of recycling cast sand - Google Patents

Description

The present invention relates to a coated sand, a method for producing a mold using the coated sand, and a method for regenerating cast sand.

Conventionally, as one of the molds used for casting molten metal, coated sand made of refractory aggregate and coated with a predetermined binder is used to form a mold into a desired shape. The obtained one is used. Specifically, in "Casting Engineering Handbook" edited by the Japan Foundry Engineering Society, pages 78-90, as a binder in such coated sand, in addition to an inorganic binder such as water glass, a phenol resin and the like are used. Organic binders using resins such as furan resin and urethane resin have been clarified, and various methods for molding self-hardening molds using these binders have been conventionally proposed.

For example, in Patent Document 1 (Japanese Unexamined Patent Publication No. 2012-76115), a solid coating layer containing a predetermined water-soluble inorganic compound such as water glass as a binder on the surface of a refractory aggregate (casting sand). A highly fluid binder coated refractory (coated sand), which is coated with, has been clarified. Further, in the same document, such a binder coated refractory (coated sand) having good fluidity is filled in a molding cavity of a molding mold for molding, and then steam is introduced into the molding mold. The method of solidifying the binder coated refractory (coated sand) by aeration and obtaining the desired mold has also been clarified.

Here, the coated sand composed of an inorganic binder such as water glass has a lower organic content than the coated sand using an organic binder, so that it is used during molding or casting. It has been conventionally known that the generation of various gases due to the heat of time is advantageously suppressed, and problems such as odor are unlikely to occur. However, in the case of coated sand constructed by using a conventional inorganic binder, such as those disclosed in Patent Document 1, the cast sand (fire-resistant aggregate) is recovered from the mold after casting. When the recovered sand is regenerated by roasting, the inorganic binder remaining on the surface of the recovered sand does not burn, but is sintered on the contrary, and the surface of the cast sand (fire-resistant aggregate) There is an inherent problem that it is difficult to regenerate because it sticks hard to the sand. In particular, in coated sand using water glass as an inorganic binder, the water glass is vitrified by the heat during casting, and the cast sand recovered after casting is roasted and polished. However, 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 does not have sufficient disintegration property of the template obtained by using it, and there is still room for improvement in this respect as well. ..

Further, in Patent Document 2 (Patent No. 5717242), the surface of the refractory aggregate is coated with a solid coating layer containing a water-soluble inorganic compound and a thermosetting resin as a binder. The characteristic binder coated refractory (coated sand) has been clarified. In this conventional binder coated refractory (coated sand), a water-soluble inorganic compound and a thermosetting resin may be mixed to form a coating layer, or individual coating layers may be formed. It has been clarified that a two-layer coated sand may be used.

However, in the coated sand as in Patent Document 2, the alkaline component of the water-soluble inorganic compound causes the thermosetting resin to be alkaline-deteriorated. Therefore, especially when a highly alkaline water-soluble inorganic compound is used, In the case of a mixture of a water-soluble inorganic compound and a thermosetting resin or a two-layer structure without considering the characteristics of the material, the thermosetting resin is deteriorated by the alkali of the water-soluble inorganic compound, and the coating layer is used. There was a risk that the mold strength would decrease due to the decrease in the binding force.

Japanese Unexamined Patent Publication No. 2012-76115 Japanese Patent No. 5717242

Here, the present invention has been made against the background of such circumstances, and the problem to be solved thereof is to suppress deterioration of the coating layer due to the alkaline component of the water-soluble inorganic binder and to have high mold strength. It is an object of the present invention to provide a coated sand which is excellent in the disintegration property of the mold, has a good casting surface, and is easy to regenerate the casting sand while maintaining the above. Further, the present invention has a method capable of advantageously producing coated sand having such excellent properties, a method for producing a mold using such coated sand, and further, a method for producing cast sand from such a mold. Providing a reproduction method is also a solution.

The present invention can be suitably carried out in various embodiments listed below in order to solve the above-mentioned problems, and each of the embodiments described below is adopted in any combination. It is possible. It should be noted that the aspects or technical features of the present invention are not limited to those described below, and can be recognized based on the invention 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 cover the surface of cast sand made of fire-resistant aggregate, and further, the first coating layer is to be coated. In addition, a dry coated sand having a coating structure of at least two layers in which a solid second coating layer made of a binder composition containing an alkaline water-soluble inorganic binder is formed is prepared as described above. When the casting sand coated with one coating layer is mixed with 50 g of the 3.0% concentration solution of the water-soluble inorganic binder and held at a temperature of 20 ° C. for 24 hours. , A coated sand characterized by having a characteristic of an elution amount of 30% by mass or less of the solid content in the first coating layer of the casting sand.
(2) The coated sand according to the above aspect (1), wherein the organic compound is selected from the group consisting of a thermoplastic resin and a crosslink curable resin.
(3) The coated sand according to the above aspect (2), wherein the crosslinkable curable resin has a gelation time of 110 seconds or less.
(4) The coated sand according to any one of the above aspects (1) to (3), wherein the organic compound is a cured product of a crosslink curable resin.
(5) The coated sand according to the above aspect (4), wherein the cured product of the crosslinkable curable resin is a cured product of a phenol resin or a phenol urethane resin.
(6) The embodiment in which the water content in the coated sand is 1.5% by mass or less (6).
The coated sand according to any one of 1) to (5) above.
(7) The coated sand according to any one of the embodiments (1) to (6), wherein the thickness of the first coating layer is 0.1 to 6 μm.
(8) The coated sandwich according to any one of the above-mentioned embodiments (1) and (7), wherein the binder composition contains inorganic oxide particles.
(9) The coated sand according to the above aspect (8), wherein the inorganic oxide particles are at least one selected from the group consisting of silicon dioxide particles, aluminum oxide particles and titanium oxide particles.
(10) The embodiment (1) to the embodiment (9), wherein the water-soluble inorganic binder is at least one selected from the group consisting of water glass, sodium phosphate, sodium carbonate, sodium aluminum acid and potassium carbonate. ) Is described in any one of the coated sands.
(11) The coated sand according to any one of the above-mentioned embodiments (1) to (10) is filled in a molding cavity of a predetermined molding mold, and then steam is aerated in the molding mold. A method for producing a mold, which comprises obtaining a desired mold by holding, solidifying or hardening.
(12) The method for producing a mold according to the above aspect (11), wherein the molding die is heated to a temperature of 80 ° C. to 200 ° C.
(13) Water is added to the coated sand according to any one of the embodiments (1) to (10) to moisten the coated sand, and the wet coated sand is placed in a molding die. A method for producing a mold, which comprises obtaining a desired mold by holding it in such a molding mold after filling and solidifying or curing it.
(14) The method for producing a mold according to the above aspect (13), wherein the molding die is heated to a temperature of 80 ° C. to 300 ° C.
(15) The method for producing a mold according to any one of the above embodiments (11) to (14), wherein hot air or superheated steam is aerated in the mold while the mold is being held.
(16) Casting is performed using a mold made of the solidified or cured product of the coated sand according to any one of the above-mentioned aspects (1) to (10), and then the casting sand is removed from the mold. A method for regenerating cast sand, which is characterized in that it is collected and subjected to a dry regeneration process to obtain recycled sand.

According to the dry coated sand according to the present invention, various effects as listed below can be achieved.
(A) A second coating layer made of a solid binder composition containing an alkaline water-soluble inorganic binder is formed and applied on the solid first coating layer containing the organic compound. The second coating layer is configured so that the first coating layer has an elution amount or less specified with respect to the water-soluble inorganic binder used for forming the second coating layer. It effectively prevents the organic compound of the first coating layer from being modified by the alkaline component of the water-soluble inorganic binder constituting the coating layer and causing deterioration of the coating layer. High mold strength can be maintained in molds molded from coated sands having such two coating layers.
(B) When casting is carried out using a mold made of dry coated sand according to the present invention, the organic compound contained in the solid first coating layer on the surface of the cast sand is effective due to the heat generated by the molten metal. The second coating layer is easily peeled off from the casting sand, and the disintegration property of the mold after casting becomes good. Further, in the casting sand recovered from the mold after casting, the solidified or cured product of the water-soluble inorganic binder is in a state of being easily peeled off from the surface of the casting sand due to the thermal decomposition of the organic compound described above. Therefore, the recovered sand can be easily and easily regenerated by subjecting it to a dry regeneration process including a polishing step.
(C) During casting using a mold, the heat of the molten metal causes the organic compounds contained in the first coating layer to be thermally decomposed to generate gas. Therefore, the molten metal constitutes a casting. A gas layer that suppresses the intrusion between sand particles (sand particles) is advantageously formed between the mold surface and the cast product, and the cast surface of the finally obtained cast product is good. Become.
(D) By using a cured product of a crosslink-curable resin as the organic compound contained in the first coating layer, a coating layer having good surface stability can be advantageously formed and water-soluble. Since the deterioration of the first coating layer due to the alkaline component of the inorganic binder can be prevented more advantageously, higher mold strength can be maintained.

It is a vertical cross-sectional explanatory view of the sand mold for a casting test used in the disintegration test in an Example. Obtained in disintegration test in Examples is a longitudinal sectional illustration of a cast product containing therein the waste core.

By the way, in the dry coated sand according to the present invention, the cast sand coated with the solid first coating layer containing an organic compound is formed by a solid binder composition containing a water-soluble inorganic binder. It is configured in a two-layer structure further coated with a second coating layer to be formed. In short, a solid first coating layer containing an organic compound and a solid binder containing a water-soluble inorganic binder are bound to a fire-resistant granular or powdery material (casting sand) as a base material. It has a two-layer structure in which a second coating layer of the agent composition is laminated. As described above, in the coated sand of the present invention, in addition to the solid first coating layer, the second coating layer, which is a coating layer located on the outer surface of the cast sand particles, is formed by alkaline water-soluble inorganic bonding. Since it is composed of a solid binder composition containing an agent, it exhibits a dry state (appearance) having room temperature fluidity as a whole, that is, a dry state.

Here, the "dry coated sand having normal temperature fluidity" in the present invention means a coated sand from which a measured value can be obtained when the dynamic angle of repose is measured regardless of the water content. Is. This dynamic angle of repose is the volume of the coated sand contained in a cylinder whose one end in the axial direction is closed with a transparent plate (for example, in a container having a diameter of 7.2 cm and a height of 10 cm). (Put the coated sand up to half of the), hold the axis in the horizontal direction, and rotate it around the horizontal axis at a constant speed (for example, 25 rpm), so that the coated sand is flowing in the cylinder. It refers to the angle formed between the slope and the horizontal plane when the slope of the layer is flat. The dynamic angle of repose is preferably 80 ° or less, more preferably 45 ° or less, and even more preferably 30 ° or less. In particular, when the refractory aggregate is spherical, a dynamic angle of repose of 45 ° or less can be easily realized. When the coated sand is moist, it does not flow in the cylinder, the slope of the coated sand layer is not formed as a flat surface, and as a result, the dynamic angle of repose cannot be measured. It will be classified as a coated sandwich.

The cast sand constituting the dry coated sand according to the present invention is made of a refractory aggregate (particles) that functions as a base material of the mold, and is various types of refractory conventionally used for the mold. Any of the granular or powdery materials of the nature can be used. Slag-based particles such as ferronickel-based slag and converter slag; artificial particles such as alumina-based particles and murite-based particles and their regenerated particles; alumina balls, magnesia clinker and the like can be mentioned. It should be noted that these casting sands may be new sand, or recycled sand or recovered sand that has been used once or multiple times for molding the mold, and further, such recycled sand or recovered sand. There is no problem even if the mixed sand is made by adding fresh sand to the sand and mixing it. Then, such cast sand is generally used as having a particle size of about 40 to 130 in AFS index, preferably about 60 to 110.

Further, the surface of the cast sand constituting the coated sand of the present invention is first coated with a first coating layer in a solid state containing an organic compound. As described above, since the predetermined first coating layer is present on the surface of the casting sand, the water-soluble inorganic binder described later does not come into direct contact with the casting sand. Further, since the first coating layer in the solid state contains an organic compound, when a molten metal is poured into a mold (hereinafter, simply referred to as a mold) made of the coated sand of the present invention, the first The organic compound contained in the coating layer of the above is thermally decomposed and gasified, and the generated gas advantageously destroys the solidified or cured product of the water-soluble inorganic binder at the joint portion between the casting sand particles. As a result, the disintegration property of the mold becomes excellent. Further, when the organic compound contained in the first coating layer is thermally decomposed and gasified, the internal pressure of the gas causes the solidified or cured product of the water-soluble inorganic binder present on the outer surface of the casting sand particles to be formed. Since it is destroyed from the inside (from the casting sand particle side), for example, in the polishing process when regenerating the casting sand recovered from the casting mold, the solidified or hardened water-soluble inorganic binder is used as the casting sand particles. It becomes easy to peel off from the surface, and it becomes easy to regenerate the casting sand. In addition, during casting using a mold, gas is generated by the thermal decomposition of the organic compound contained in the first coating layer, so that the gas that suppresses the intrusion of molten metal into the casting sand particles that make up the mold. The layer is advantageously formed between the mold surface and the cast product, thus resulting in a good cast surface of the final cast product.

However, the solid first coating layer containing such an organic compound is always in contact with the alkaline water-soluble inorganic binder contained in the binder composition constituting the second coating layer formed on the solid first coating layer. Therefore, depending on the material of the organic compound, the coated sand may be deteriorated by the alkaline component of the water-soluble inorganic binder during the period from the time of manufacture to the time of use. The alkaline deterioration of the organic compound in the solid first coating layer makes the contact area between the first coating layer and the second coating layer brittle, resulting in molding using coated sand. The strength of the mold will be reduced.

Therefore, in the present invention, 50 g of the cast sand coated with the solid first coating layer containing the organic compound is used as a solution of the water-soluble inorganic binder at a concentration of 3.0%. When mixed with 50 g and held at a temperature of 20 ° C. for 24 hours, the solid content in the first coating layer of the cast sand is 30% by mass or less, preferably 20% by mass or less, more preferably 10% by mass. The first coating layer is configured so as to exhibit the following elution amount, whereby the solid first coating layer is formed by the alkaline component of the water-soluble inorganic binder. Deterioration is effectively prevented, and high mold strength can be maintained. The solid content in the coating layer is calculated by subtracting the mass of the casting sand particles from the mass of the casting sand coated with the solid coating layer. In practice, when measuring from casting sand coated with a solid coating layer, the casting sand coated with such a coating layer is exposed to heat at 900 ° C. for 1 hour to burn the coating layer. The calculated value is used by subtracting the mass of the foundry sand from the mass of the foundled sand coated with the coating layer before the heat exposure.

In the present invention, the organic compound that is difficult to be eluted with such an aqueous solution of a water-soluble inorganic binder can form a solid coating layer on the surface of the cast sand particles, and is in such a solid state. The coating layer is not particularly limited as long as it is difficult to elute into a liquid water-soluble inorganic binder having a concentration of 3.0% and the elution amount is less than the specified amount, but is generally a thermoplastic resin. At least one selected from the group consisting of a crosslinkable curable resin or a cured product thereof is preferably used. Among them, the crosslinkable curable resin is, for example, heated or heated in the presence or absence of a curing agent such as hexamethylenetetramine, an organic ester, an organic acid, a carbon dioxide gas, a peroxide, a metal ion, an amine, or a curing catalyst. It exhibits crosslink curability under non-heating (normal temperature). Further, as such a crosslinkable curable resin, in order to increase the curing rate and further suppress the elution amount with respect to alkali, the gelation time is 110 seconds or less, preferably 30 to 30 at a measurement temperature of 150 ° C. 110 seconds, more preferably 50 to 105 seconds, still more preferably 60 to 100 seconds will be advantageously used. The gelation time is measured according to the JACT test method RS-5 “Gelification time test method”.

Specific examples of the thermoplastic resin include polyvinyl alcohol, polyvinyl acetate, polystyrene, styrene acrylonitrile copolymer, styrene / butadiene / acrylonitrile copolymer, ethylene vinyl acetate copolymer, polyvinyl chloride, and polymethyl. Resins such as methacrylate, paraffin, polyethylene, polypropylene can be mentioned. Among them, polyvinyl alcohol, polyvinyl acetate, and polystyrene are particularly preferably used from the viewpoint of ease of production of coated sand and low elution amount with respect to the aqueous solution of the water-soluble inorganic binder.

Furthermore, in the present invention, it is recommended to use a cured product of a crosslink curable resin as the organic compound. Here, the cured product of the crosslinkable curable resin is a product in which the molecular weight is increased to a high molecular weight compound by subjecting a low molecular weight material to a curing reaction. After coating the surface of cast sand particles with a low-molecular-weight material with low melt viscosity, the cross-linking curable resin is cured by heating or adding a curing agent to form a solid coating layer. As a result, the amount of elution of the formed coating layer can be effectively suppressed to a specified value or less, and in particular, in a highly cured product of a crosslink curable resin, elution is substantially eliminated. Further, the cured product of the cross-linking curable resin can form a high molecular weight coating layer having good surface stability, and both coating property and surface stability can be achieved. When the crosslinkable curable resin is cured, it does not elute into the aqueous solution of the water-soluble inorganic binder, so that deterioration due to alkali is prevented and high mold strength can be maintained. Further, the cured product of the cross-curable resin has 1) suppressed softening of the coating layer due to heat, improved mold strength, and 2) required for pre-curing, as compared with the uncured cross-curable resin. Since a large amount of heat is consumed, the supplied heat is effectively used for thermal decomposition, and the thermal decomposition is accelerated, so that the disintegration property of the mold is further improved, and 3) the gas accompanying the curing is released in advance. Therefore, there is an advantage that the amount of gas generated during casting can be suppressed. In the present invention, the cured product of the crosslinkable resin means that the ratio (c) 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. It is most preferably 100% by mass.

Specific examples of the crosslinkable curable resin used as such a cured product include a phenol-based resin, a phenol-urethane-based resin, an epoxy resin, a melamine resin, an unsaturated polyester resin, and a polyfunctional acrylamide-based resin (particularly). (Refer to Kohei 7-106421), unsaturated alkyd resins, unsaturated fatty acid-modified alkyd resins, diallyl phthalate resins, and resin mixtures in which these resins are combined, if necessary, and the like can be mentioned. Among them, from the viewpoint of more advantageously enjoying the effects of the present invention, a novolak-type or resol-type phenol-based resin or a phenol-urethane-based resin formed by combining a phenol-based resin with a polyisocyanate compound is particularly preferable. Will be adopted.

Further, in the present invention, the organic compound which is a constituent component of the coating layer (first) formed on the surface of the casting sand is a polymer compound (polymer, multimer) from the viewpoint of coating property to the casting sand particles. Is desirable. Specifically, a polymer compound (weight) having a weight average molecular weight of 300 or more, preferably 300 to 100,000,000, more preferably 500 to 50,000,000, and even more preferably 800 to 20,000,000. Combined, multimer) will be used advantageously. Even organic compounds that are not included in the category of polymer compounds (polymers, multimers) are preferably those having a molecular weight of 300 or more from the viewpoint of surface stability of the solid coating layer, and are cast sand. From the viewpoint of coating property on particles, those having 100,000,000 or less are preferably used.

Further, in the dry coated sand according to the present invention, it is effective to include the coupling agent in the first coating layer provided on the surface of the cast sand. By impregnating the first coating layer with a coupling agent, the wettability and adhesiveness of the first coating layer can be improved, and the bond between the casting sand and the first coating layer can be strengthened. There is an advantage that can be done. As the coupling agent contained in the first coating layer, for example, known ones such as a silane coupling agent, a zircon coupling agent, and a titanium coupling agent can be mentioned as suitable ones. 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, and more preferably 1 to 3 parts by mass with respect to 100 parts by mass of the organic compound. It is said to be the ratio of.

In the present invention, as described above, the film thickness of the solid first coating layer formed on the surface of the cast sand is generally 0.1 to 6 μm, preferably 0.2 to 5 μm, more preferably. Is 0.3 to 3 μm, more preferably 0.5 to 2 μm. When this film thickness is thinner than 0.1 μm, it becomes difficult to form it as a coating layer, and it is effectively gasified inside a second coating layer made of a binder composition containing a water-soluble inorganic binder. On the other hand, if it is thicker than 6 μm, the amount of organic compounds may be too large and an odor may be generated. As a method for measuring the thickness of such a coating layer, a cross section of the casting sand particles in which the casting sand particles on which the coating layer is formed is embedded in an epoxy resin or the like and cut using a cutting device such as an ion cutter is used. Examples thereof include a method in which observation is performed using an optical machine such as an optical microscope or an electronic microscope, 10 cross-sectional particles are randomly selected, and the film thickness of the coating layer is measured. Further, this film thickness can be calculated from the average particle size of the cast sand particles and the amount of the cast sand particles and the organic compound added when the cast sand particles are spherical.

In the dry coated sand according to the present invention, the cast sand coated with the above-mentioned first coating layer is a solid binder composition further containing an alkaline water-soluble inorganic binder. It is covered and configured by a second coating layer formed in. As the alkaline water-soluble inorganic binder contained in this solid binder composition, any one conventionally used in coated sand can be used. For example, water glass, sodium phosphate, sodium carbonate, sodium aluminum oxide, potassium carbonate, sodium vanadate, sodium borate, etc. may be used alone or in combination of two or more selected from them. Is possible. Among them, water glass, sodium phosphate, sodium carbonate, sodium aluminum oxide and potassium carbonate are preferably used because the effect of the present invention can be advantageously exerted in a water-soluble inorganic binder having a strong alkalinity. From the viewpoint of ease of handling and the strength of the mold finally obtained, water glass or one containing water glass as a main component is more preferably used.

The water glass used here is an aqueous solution of a soluble silicic acid compound, and examples of such a silicic acid compound include sodium silicate, potassium silicate, sodium metasilicate, potassium metasilicate, and lithium silicate. , Ammonium silicate and the like can be mentioned, but in particular, in the present invention, sodium silicate (soda silicate) will be advantageously used. Further, it does not matter if water glass is used as a main component and a water-soluble binder such as a thermosetting resin, a saccharide, a protein, a synthetic polymer, a salt or an inorganic polymer is blended. When water glass is used in combination with another water-soluble binder, the proportion of water glass in 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. ..

As described above, sodium silicate, which is a water glass, which is advantageously used in the present invention, is usually classified into the types of Nos. 1 to 5 according to the molar ratio of _{SiO 2} / Na _{2 O and used.} Specifically, sodium silicate No. 1 has _{a molar ratio of SiO 2} / Na ₂ O of 2.0 to 2.3, and sodium silicate No. 2 has a molar ratio of SiO ₂ / Na ₂ O. The molar ratio is 2.4 to 2.6, and sodium silicate No. 3 has _{a molar ratio of SiO 2} / Na ₂ O of 2.8 to 3.3. In addition, sodium silicate No. 4 has _{a molar ratio of SiO 2} / Na ₂ O of 3.3 to 3.5, and sodium silicate No. 5 has a molar ratio of _{SiO 2} / Na _{2 O.} Is 3.6 to 3.8. Among these, sodium silicate Nos. 1 to 3 are also specified in JIS-K-1408. Then, these sodium silicates may be used alone or in a mixed manner, or two or more kinds of sodium silicates may be mixed to prepare a molar ratio of _{SiO 2} / Na _{2 O.} Is also possible.

In order to advantageously obtain a dry coated sand according to the present invention, _{the molar ratio of SiO 2} / Na ₂ O is generally 1.9 or more as the sodium silicate constituting the water glass used as a binder. , It is preferably 2.0 or more, more preferably 2.1 or more, and in the above-mentioned classification of sodium silicate, sodium silicate corresponding to No. 1 and No. 2 is used particularly advantageously. Become. Such sodium silicate No. 1 and No. 2 respectively provide a coated sand having good characteristics and being stable even in a wide range of sodium silicate concentration in water glass. _{Further, the upper limit of the molar ratio of SiO 2} / Na ₂ O in such sodium silicate is appropriately selected according to the characteristics of 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 becomes smaller than 1.9, a large amount of alkali is present in the water glass, so that the solubility of the water glass in water increases and the coated sand deteriorates due to moisture absorption. It may be easier to do. On the other hand, _{sodium silicate having a molar ratio of SiO 2} / Na ₂ O of more than 3.5 has low solubility in water, so that the adhesion area between the casting sand particles cannot be obtained in the finally obtained mold. 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 in a state of being dissolved in water, and when the coated sand of the present invention is produced, it is in the state of a stock solution as purchased on the market. In addition to being used, it will be used in a diluted state by adding water to such a stock solution. The non-volatile content (water glass component) obtained by removing volatile substances such as water and solvent from such water glass is called a solid content, which corresponds to the above-mentioned soluble silicic acid compound such as sodium silicate. It is a thing. Further, the higher the proportion of such solid content, the higher the concentration of the silicic acid compound in the water glass. Therefore, the solid content of the water glass used in the present invention corresponds to the ratio excluding the water content in the undiluted solution when it is composed only of the undiluted solution, while the undiluted solution is made into water. When a diluted solution obtained by diluting is used, the ratio excluding the amount of water in the stock solution and the amount of water used for dilution corresponds to the solid content of the water glass used. Will be.

By the way, the solid content in such water glass is set to an appropriate ratio depending on the type of the water glass component (soluble silicic acid compound) and the like, but is advantageously 20 to 50% by mass. It is desirable that it is contained in a proportion. Using water glass in which the water glass component corresponding to the solid content is appropriately present in the aqueous solution, the casting sand is formed by kneading or mixing with the casting sand coated with the first coating layer. On the other hand, it is possible to prepare an admixture in which the water glass component is evenly and uniformly dispersed, whereby the target mold can be advantageously molded according to the present invention. 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 performed for the production of the coated sand. It is necessary to raise the temperature and lengthen the heating time. On the other hand, if the proportion of solid content in the water glass becomes too high, it becomes difficult to prepare an admixture in which the water glass component is evenly dispersed with respect to the cast sand, and the target mold can be used. It is desirable to prepare the water glass in the form of an aqueous solution so that the solid content is 50% by mass or less, and therefore the water content is 50% by mass or more, because it may cause a problem in the characteristics.

Further, as sodium phosphate which is one of the water-soluble inorganic binders used in the present invention, monosodium phosphate hydrate (NaH ₂ PO ₄ · xH ₂ O; x is a known integer) and phosphoric acid. Disodium hydrate (Na ₂ HPO ₄ · x'H ₂ O; x'is a known integer), trisodium phosphate hydrate (Na ₃ PO ₄ · x "H ₂ O; x" is a known integer) ) Etc. can be mentioned. Sodium phosphate is soluble in water, as represented by the dissolved amount of trisodium phosphate hydrate in 100 g of water being 25.8 g (20 ° C.), and disodium phosphate water. The melting point of sodium phosphate is relatively high, as typified by the melting point of Japanese products being 1340 ° C. Therefore, the coated sand formed by forming the second coating layer using sodium phosphate as a water-soluble inorganic binder can be easily disintegrated with water to produce a mold having high heat resistance. .. Similarly, sodium carbonate, sodium aluminum oxide, or potassium carbonate, which are water-soluble inorganic binders, also exert the same effect as the above sodium phosphate, and they are used to form a second coating layer. The coated sand is easily disintegrated with water and exhibits the characteristic that it is possible to produce a mold having high heat resistance.

Further, in the coated sand according to the present invention, the above-mentioned water-soluble inorganic binder has a mass equivalent to that of a solid, and a solid content equivalent to that of a liquid, which is converted into solid content. It is desirable to use it in an amount of 0.1 to 2.5 parts by mass with respect to 100 parts by mass of the material), and in particular, an amount of 0.2 to 2.0 parts by mass. Adopted in an advantageous way. Here, when the amount of the water-soluble inorganic binder used becomes too small, a sufficient amount of the water-soluble inorganic binder is contained on the solid first coating layer provided on the surface of the casting sand. It becomes difficult to form a second coating layer made of a solid binder composition, which may cause a problem that it becomes difficult to sufficiently solidify or cure the coated sand. Further, even if the amount of the water-soluble inorganic binder used is too large, an excessive amount of the water-soluble inorganic binder is present on the solid first coating layer provided on the surface of the casting sand. As a result, the casting sand particles may stick to each other and form agglomerates (composite particles), which adversely affects the physical characteristics of the mold and makes it difficult to remove the sand from the core after casting the metal. It also causes problems.

Then, the solid second coating layer formed of the binder composition containing such a water-soluble inorganic binder is allowed to exist on the first coating layer at an appropriate thickness. However, the thickness is generally 0.1 to 6 μm, preferably 0.2 to 5 μm, more preferably 0.3 to 3 μm, still more preferably about 0.5 to 2 μm, and it is advantageous. The thickness will be thicker than that of the first coating layer.

The solid content of the water-soluble inorganic binder is measured as follows. That is, 10 g of the sample was weighed and contained in an aluminum foil dish (length: 9 cm, width: 9 cm, height: 1.5 cm), placed on a heating plate maintained at 180 ± 1 ° C., and left for 20 minutes. After that, the sample dish is inverted and left on the heating plate for another 20 minutes. Next, the sample dish dried by heating is taken out from the heating plate, allowed to cool in a desiccator, weighed, and the solid content (% by mass) is calculated by the following formula.
Solid content (% by mass) = {[Mass of sample dish after drying (g) -Mass of sample dish (g)]
/ [Mass of sample dish before drying (g) -Mass of sample dish (g)]} x 100

Further, the coupling agent can be contained in the second coating layer made of the solid binder composition containing the water-soluble inorganic binder described above. By including the coupling agent in the binder composition, the wettability and the adhesiveness are improved, and the bond between the first coating layer and the second coating layer formed on the surface of the cast sand is strengthened. Can be done. It should be noted that such an effect can be enjoyed by incorporating the coupling agent in either the first coating layer or the second coating layer, but the first coating layer and the second coating can be enjoyed. Since both of the layers contain a coupling agent, the binding force between the two layers is further improved, and the strength of the finally obtained mold is further improved, which is more preferable. I can say. Examples of the coupling agent to be contained in the binder composition include those listed above as the coupling agents that can be contained in the first coating layer. The content of the coupling agent in the binder composition is generally 0.5 to 10 parts by mass, preferably 1 part by mass with respect to 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.

Further, the solid binder composition containing the water-soluble inorganic binder is advantageously contained with the inorganic oxide particles. Since the binder composition contains the inorganic oxide particles, it is effective in improving the fluidity and filling property of the coated sand, and further improving the moisture resistance of the finally obtained mold. The size of the inorganic oxide particles used in the present invention is preferably smaller than that of the cast sand particles constituting the coated sand, and specifically, the average particle size is 0.01 μm or more and 300 μm or less. Inorganic oxide particles having a size of 0.3 μm or more and 200 μm or less, and particularly preferably 0.5 μm or more and 100 μm or less are used. The average particle size can be obtained from the particle size distribution measured by a laser diffraction type particle size distribution measuring device or the like. The content of the inorganic oxide particles in the binder composition is generally 5 to 200 parts by mass, preferably 10 to 10 parts by mass with respect to 100 parts by mass of the solid content of the water-soluble inorganic binder contained therein. The ratio is 100 parts by mass.

The inorganic oxide particles used above may be spherical particles or non-spherical particles, but the spherical particles are more advantageous in the effect of the present invention and have a better casting surface in particular. It is preferable in that it makes it possible to obtain a cast product. The spherical particles may have a spherical shape that is generally recognized, and are not necessarily required to have a true spherical shape, but usually have a sphericity of 0.5 or more. Those having a value of 0.7 or more, and more preferably those having a value of 0.9 or more are advantageously used. Here, the sphericity is the aspect ratio (minor axis / major axis ratio) obtained from the projected shape of 10 single particles randomly selected in observation using a scanning electron microscope. It means the average value. When non-spherical inorganic oxide particles are used, since protrusions and dents are present on the surface of such inorganic oxide particles, for example, the inorganic oxide particles are dissolved by the supplied water. When trying to flow between the cast sand particles together with the water-soluble inorganic binder in the form, the protrusions on the surface of the inorganic oxide particles collide with the cast sand particles and other inorganic oxide particles, and have an anti-slip effect. Will occur, and the flow of the water-soluble inorganic binder and the inorganic oxide particles between the cast sand particles will be hindered, and as a result, the filling property of the finally obtained mold and its strength may be deteriorated. ..

The material constituting the inorganic oxide particles is not particularly limited, but is preferably an inorganic metal oxide. As the particles made of the inorganic metal oxide, particles made of silicon dioxide, aluminum oxide, titanium oxide or the like are advantageously used. Among them, the silicon dioxide particles are particularly strong alkaline water glass or the like. The water-soluble inorganic binder can react with the silanol groups formed on the surface of silicon dioxide, and when water evaporates, it is strong between the silicon dioxide and the solid water-soluble inorganic binder. It can be said that it is preferable in that a bond is formed and the template strength can be improved. There are two types of silicon dioxide, crystalline and amorphous, but amorphous is preferable, and the amorphous silicon dioxide is precipitated silica, calcined silica produced in an electric arc or by flame hydrolysis. , _{Silica produced by thermal decomposition of ZrSiO 4} , silicon dioxide produced by oxidizing metallic silicon with a gas containing oxygen, quartz glass powder which is a spherical particle produced from crystalline quartz by melting and subsequent quenching, and the like. It can be illustrated. These can be used alone or in combination of two or more. In the present invention, silicon dioxide is treated as an inorganic metal oxide. Further, the silicone resin particles may be added instead of or in combination with the inorganic oxide particles.

Further, in the present invention, it is also effective to include a known moisture resistance improving agent in the solid binder composition constituting the second coating layer. By incorporating the moisture resistance improving agent into the binder composition, it is possible to improve the moisture resistance of the finally obtained mold. In addition, the binder composition may contain a surfactant. The dry coated sand according to the present invention is prepared (manufactured) by 1) the presence of the surfactant because the surfactant is contained in the binder composition containing the water-soluble inorganic binder. ), The amount of water added at the time of) can be suppressed to the minimum necessary, 2) the surface tension of water is suppressed, the fluidity of the coated sand is improved, and 3) molding is performed. In addition to being excellent in mold releasability from the molding mold, the mold can also advantageously enjoy the effects of exhibiting excellent strength and the like. As such a surfactant, any of a cationic surfactant, an anionic surfactant, an amphoteric surfactant, a nonionic surfactant, a silicone-based surfactant and a fluorine-based surfactant can be used. , Can be used. Further, the solid 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 swelling property of the coated sandwich that has been moistened during molding is solidified or cured by heating. It will be possible to maintain it stably until it is done.

Furthermore, in the dry coated sand according to the present invention, if necessary, a lubricant or a mold release agent is contained in the binder composition constituting the solid second coating layer that surrounds the cast sand particles. It is also possible to appropriately contain various other known additives such as. In particular, the lubricant may be formed as a layer on the outer peripheral surface of the solid second coating layer. In order to include such an additive in the binder composition, when the solid binder composition is prepared, it is added to the composition together with a water-soluble inorganic binder and the like, and the preparation thereof is performed. The method of kneading or mixing the binder composition containing the additive with the casting sand, or adding a predetermined additive to the casting sand separately from the binder composition, as a whole. A method of uniformly kneading or mixing is adopted.

By the way, in the dry coated sand according to the present invention, 1) first, a solid first coating layer containing an organic compound is formed on the surface of the casting sand, and then 2) the casting in which such a coating layer is formed. An aqueous solution-like binder composition containing a water-soluble inorganic binder is added to sand, and the mixture is kneaded or mixed, and the water is evaporated to form a solid binder composition. The second coating layer (coating layer) can be advantageously produced according to the method of obtaining the coated sand formed on the first coating layer.

When producing the dry coated sand according to the present invention according to such a production method, first, in order to form a solid first coating layer containing an organic compound on the surface of the cast sand, it is known. From various methods, those according to the characteristics of the organic compound and the like are appropriately selected and adopted. For example, as a method for forming a first coating layer, which is a solid coating layer containing an organic compound, on the surface of cast sand, known methods such as a dry hot coat method and a cold coat method can be exemplified. However, the method is not particularly limited as long as a solid coating layer can be formed.

In the dry hot coat method, a solid organic compound is added to and mixed with casting sand heated to 120 to 180 ° C., and the solid organic compound is melted by the heat of the casting sand to melt the solid organic compound. This is a method of forming a solid coating layer on the surface of the casting sand by covering the surface of the casting sand with the obtained organic compound and then cooling while maintaining the mixed state. The cold coat method is a method in which an organic compound is dissolved in a solvent such as methanol to make it liquid, and the liquid material is added to the casting sand and mixed to volatilize the solvent to volatilize the surface of the casting sand. It is a method of forming a solid coating layer.

When a crosslinkable curable resin is used as the organic compound, for example, after forming a solid coating layer according to the above-mentioned coating method, further heating and / or adding a curing agent or a curing catalyst is added. As a result, a method of curing the crosslinkable curable resin and increasing the molecular weight of the crosslinkable curable resin contained in the coating layer will be adopted. When the crosslinkable 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 5 to 60 minutes for reaction curing, or preheated to 150 ° C. to 300 ° C. There is a method of kneading the cast sand for about 5 to 60 minutes in a kneader heated to 120 ° C. to 300 ° C. for reaction curing. In addition, when the crosslink curable resin contained in the first coating layer is cured, there is a possibility that the cast sand particles (sand particles) may be bonded to each other to form an integral lump or a composite particle. In order to improve the surface condition of the cast sand coated with the first coating layer, it is preferable to perform reaction curing while kneading with a kneader (speed muller) having a high rotation speed. Further, since peeling may occur and fine powder may be generated when kneaded for a long time, it is preferable to adopt a method of reacting at a high temperature and in a short time. When the crosslinkable curable resin is a phenol urethane resin, a method of curing by mixing a phenol resin and a known polyisocyanate compound is adopted. Further, even when the crosslinkable curable resin is cured by using a curing agent, it is desirable to adopt a method of reaction curing while kneading with a kneader.

Next, the cast sand having the first solid coating layer containing the organic compound provided on the surface thereof is further coated with the solid binder composition containing the water-soluble inorganic binder to obtain the first coating. In forming the second coating layer, generally, an aqueous solution-like water-soluble inorganic binder as a binder composition is kneaded or mixed with an additive used as necessary with respect to the casting sand. At the very least, prepare an admixture in which the surface of the cast sand is uniformly covered with a water-soluble inorganic binder, and then evaporate (evaporate) the water contained in the prepared admixture. , A method of obtaining a dry coated sand having a target room temperature fluidity by forming a second coating layer in a solid state on the first coating layer is adopted. In such a method, the evaporation of water in the admixture needs to be carried out rapidly before the solidification or hardening of the water-soluble inorganic binder is promoted. Therefore, in the present invention, the first step is made. Moisture content within 5 minutes, more preferably within 3 minutes, after the water-soluble inorganic binder in the form of an aqueous solution is added (mixed) to the foundry sand on which one coating layer is formed. It is desirable to skip the to make a dry coated sand. If the evaporation time is long, the kneading (mixing) cycle becomes long, the productivity is lowered, and the water-soluble inorganic binder is _{exposed to CO 2} in the air for a long time, resulting in deactivation. This is because there is a high risk of causing.

The water content of the dry coated sand thus obtained is 1.5% by mass or less, preferably 0.1 to 1.2% by mass, and more preferably 0.2 to 1 with respect to the coated sand. It is adjusted to be 0.0% by mass. When water glass is used as the water-soluble inorganic binder, the content is 5 to 55% by mass, preferably 10 to 50% by mass, and more preferably 20 to 50% by mass with respect to the solid content of the water glass. So prepared. The water content of the coated sand can be measured by the Karl Fischer method or the mass change when heated by a dryer or the like.

Further, in the manufacturing process of such a dry coated sand, as one of the effective means for rapidly evaporating the water content in the above-mentioned admixture, the cast sand on which the first coating layer is formed is previously provided. A method of preparing an admixture by heating and kneading or mixing a water-soluble inorganic binder (caking agent composition) in the form of an aqueous solution is adopted. By kneading or mixing the water-soluble inorganic binder in the form of an aqueous solution with the preheated casting sand, the water derived from the water-soluble inorganic binder in the form of an aqueous solution can be removed. It is possible to evaporate very quickly by the heat of such casting sand, and thus the moisture content of the obtained coated sand can be effectively reduced, and the dry coated sand having room temperature fluidity can be obtained. , Will be obtained in an advantageous manner. The preheating temperature of the cast sand is appropriately selected according to the type and blending amount of the water-soluble inorganic binder used, the amount of water in the aqueous solution of the water-soluble inorganic binder, and the like. By the way, for example, in the case of water glass, it is desirable to heat the cast sand to a temperature of generally about 100 to 160 ° C, preferably about 110 to 140 ° C. If this preheating temperature becomes too low, it will not be possible to effectively evaporate the water, and it will take time to dry the admixture. Therefore, it is desirable to adopt a temperature of 100 ° C. or higher. If the preheating temperature becomes too high, the water-soluble inorganic binder component will be solidified (cured) when the obtained coated sand is cooled, and in addition, composite particles will be formed. There is a risk of problems with its function, especially its physical properties such as strength. Further, in the production of the dry coated sand according to the present invention, the aqueous water-soluble inorganic binder as the binder composition is used when the water-soluble inorganic binder used is a solid. Is used in a state of being previously dissolved in water. On the other hand, even in the case of a liquid water-soluble inorganic binder, it is possible to use one diluted with water in order to adjust its viscosity. Further, it is also possible to individually add a solid or liquid water-soluble inorganic binder and water to the casting sand at the time of kneading or mixing with the casting sand or the like.

Various conventionally known methods can be adopted when molding a target mold by using the dry coated sand according to the present invention thus obtained. For example, the following two methods can be adopted. That is, as a first method, a dry coated sand is moistened by kneading with water at a molding site, and the wet coated sand is given a target mold. While filling into the molding cavity of, the mold is heated to a temperature of 80-300 ° C. and held in the mold until the filled coated sand dries. In addition, as a second method, after filling a dry coated sand in a molding cavity of a molding mold that gives a target mold, steam is blown into the molding cavity, and steam is generated in a packed phase made of the coated sand. It is aerated, and by this aeration of water vapor, moisture is supplied to the dry coated sand to become moist (moistened), and until such wet coated sand dries. , 80-200 ° C., held in a mold heated to 80-200 ° C.

At the time of such molding, it is desirable that the molding dies such as dies and wooden dies, which are filled with dry coated sand having normal temperature fluidity, are kept warm by heating in advance, thereby kneading with water and steam. Drying of the coated sand moistened with water vapor can be promoted in an advantageous manner. As the heat retention temperature by the preheating, generally, the temperature of 80 to 300 ° C., preferably 90 to 250 ° C., more preferably about 100 to 200 ° C. is desirable in the first method, and 80 in the second method. A temperature of about 200 ° C., preferably 90 to 150 ° C., more preferably about 100 to 140 ° C. is desirable. If the heat retention temperature is too high, it becomes difficult for steam to pass to the surface of the mold, while if the temperature is too low, it takes time to dry the molded mold.

By the way, in the first method, when the dry coated sand and water are kneaded (mixed), the dry coated sand is transported to the molding site, which is the manufacturing site of the mold, and then at the molding site. After adding water to moisten the mold, the obtained moist coated sand is filled in a molding mold to form a target mold, and the dry state is used there. In the process of adding water to the coated sand to moisten it, it is sufficient to moisten the coated sand by simply adding a predetermined amount of water and the dry coated sand to an appropriate mixer and mixing them. From a certain point, it can be carried out by an extremely simple work, and it can be carried out extremely easily and easily even in a molding site where the working environment is bad. Further, the coated sand may be preheated at 40 ° C. to 100 ° C. before use by adding water. When water is added, one or more selected from other additives, a curing accelerator, and a water-soluble inorganic binder for readjusting the mold strength may be added together. When the other additive or the like is a liquid, water contained in the solution may be used as the water in the liquid.

Further, in the second method, when steam is blown into the coated sand (filled phase) filled in the molding cavity of the molding mold, the temperature of the steam is generally about 80 to 150 ° C., more preferably 95 to. It is about 120 ° C. When high-temperature steam is used, a large amount of energy is required for its production, so that a steam temperature of around 100 ° C. is particularly advantageous. Further, 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. Further, as the ventilation time, a ventilation time of about 2 seconds to about 60 seconds is generally adopted. This is because if the aeration time of the water vapor is too short, it becomes difficult to sufficiently moisten the surface of the coated sand in a dry state, and if the aeration time is too long, it constitutes a coating layer on the surface of the coated sand. This is because there is a risk that the water-soluble inorganic binder may dissolve or flow out.

Here, in the above-mentioned first method and the second method, hot air or superheated steam is blown into the mold to positively dry the packed phase made of moist coated sand, and the packed phase is aerated. Such a method is preferably adopted. By such aeration of hot air or superheated steam (hot air, etc.), the inside of the packed phase of the coated sand is quickly dried, and the solidification or hardening of the packed phase is promoted more advantageously, and thus the hardening is performed. In addition to advantageously increasing the speed, it is possible to advantageously enhance the properties such as the bending strength of the obtained mold, and it is also possible to advantageously contribute to shortening the molding time of the mold. Further, in the first method, for example, before the aeration of hot air or the like, in the second method, for example, between the aeration of steam and the aeration of hot air or the like, the solidification or curing of the packed phase is more advantageous. In order to promote it, the curing agent may be aerated in the form of gas or mist, and by neutralizing the water-soluble inorganic binder with this curing agent, it is possible to further promote the solidification or curing. be. It should be noted that the curing agent may be aerated at the same time as the aeration of hot air or the like in the first method, and at the same time as the aeration of steam or the aeration of the hot air in the second method. Further, as another method for positively drying the packed phase, the pressure inside the molding die may be reduced. By such a reduced pressure, the coated sand filled in the cavity of the molding die is dried and solidified. Examples of the depressurizing method include depressurizing the inside of the molding die by a known suction means. Further, when the pressure inside the mold is reduced, hot air or superheated steam may be blown into the mold in order to promote evaporation of water.

The curing agent used during the above molding includes organic acids such as carbon dioxide (carbonated water), sulfuric acid, hydrochloric acid, nitrate, phosphoric acid, oxalic acid, carboxylic acid, and paratoluenesulfonic acid, methyl formate, and ethyl formate. , Esters such as propyl formate, γ-butyrolactone, γ-propion lactone, ethylene glycol diacetate, diethylene glycol diacetate, glycerin diacetate, triacetin, propylene carbonate, and monohydric alcohols such as methanol, ethanol, butanol, hexanol, octanol, etc. Etc. can be exemplified. These curing agents can be used alone, or can be used by mixing two or more kinds of them.

Then, using the dry coated sand according to the present invention, the excellent effects described below can be advantageously enjoyed in any of the molds obtained according to the above-mentioned manufacturing method and the molds obtained according to other manufacturing methods. It is possible to do. That is, the solid first coating layer containing the organic compound is effectively prevented from being deteriorated by the alkaline component of the water-soluble inorganic binder constituting the second coating layer, and the high strength of the mold is increased. It will be possible to maintain. Further, when casting is carried out using such a mold, the heat generated by the molten metal effectively decomposes the organic compound contained in the solid first coating layer on the surface of the casting sand, and the heat decomposition causes gas. From the place where the above occurs, the disintegration property of the mold after casting becomes good.

Further, casting is performed using a mold made of dry coated sand according to the present invention, and in the casting sand (recovered sand) recovered from the mold after casting, an organic compound present on the surface of the casting sand is used. Since the solidified or cured product of the water-soluble inorganic binder is in a state where it is easily peeled off from the surface of the casting sand due to the gas generated by the thermal decomposition of the sand, such recovered sand should be subjected to dry regeneration treatment. Therefore, it can be easily regenerated.

Here, the dry regeneration treatment for the recovered sand can be adopted by any method as long as it is a conventionally known dry regeneration treatment method as a method for regenerating the recovered sand. Generally, a method for treating recovered sand, which includes at least a polishing treatment and, if necessary, a firing treatment, a classification treatment, and the like, is called a dry regeneration treatment.

Further, in the polishing treatment in the dry regeneration treatment, the deposits remaining on the particle surface of the recovered sand are scraped off. Specifically, by putting the recovered sand into a rotating rotor and polishing it, the recovered sand is crushed into individual casting sand particles, and further, deposits on the surface of the casting sand particles (adhesion on the surface of the casting sand particles). The solidified or cured product of the water-soluble inorganic binder will be scraped off. The polishing method is not particularly limited, and examples thereof include polishing using a rotary reclaimer, a sand fresher, a sand shiner, and the like. Further, various polishing conditions such as polishing time in the polishing treatment are appropriately determined according to the state of adhesion of deposits on the surface of the recovered sand.

Further, the firing treatment is carried out for the purpose of burning and removing organic compounds, dust, impurities and the like in the coating layer adhering to the recovered sand. For such a firing process, for example, a roasting furnace such as a rotary kiln or a tunnel kiln is used, and the recovered sand is fired in the furnace while the recovered sand is thrown into the roasting furnace at any time. The firing temperature in the roasting furnace is 200 to 700 ° C, preferably 300 to 700 ° C, more preferably 350 to 650 ° C, and even more preferably 400 to 600 ° C. If the firing temperature is lower than 200 ° C., there is a risk that dust and the like adhering to the recovered sand will not be sufficiently burned. On the other hand, if the firing temperature exceeds 700 ° C., the water-soluble inorganic binder remaining on the surface of the recovered sand may be sintered and it may be difficult to peel off from the surface of the sand particles. Such a firing process may be performed before or after the above-mentioned polishing process, or may be performed before or after the polishing process.

Further, the classification treatment is generally carried out after the above-mentioned polishing treatment or, when the baking treatment is carried out after the polishing treatment, after such a baking treatment, and is taken out from the above-mentioned treatment step. The dust collection process of removing the fine powder contained in such a cast sand treated product by the dust collecting device by flowing the cast sand treated product with an air flow, and the foreign matter contained in the cast sand treated product by sieving. It has a sieving process to remove. Specifically, in the dust collection process, the cast sand treated product is made to flow by an air flow, and fine particles such as shavings, dust, and fine powder contained in the cast sand treated product, which could not be removed by the previous steps, are made to flow. The inclusions are removed by a driven state dust collector, which effectively removes minute residues from the cast sand treatment. Further, in the sieving step, by classifying the particle size of the cast sand treated product using a sieve, foreign substances contained in such the cast sand treated product, which could not be removed by the previous steps, are removed. As a result, sand having an appropriate particle size can be selectively taken out.

The classification process adopted in the present invention is not limited to the one having the dust collecting step and the sieving step as described above, and is, for example, one having only one of the dust collecting step and the sieving step. However, there is no problem even if the dust collection process is performed after the sieving process is performed. Further, as the classification step, any other known method can be adopted as long as the casting sand can be classified to a predetermined size.

Then, as described above, the foundry sand regenerated by the method for regenerating the recovered cast sand according to the present invention is again provided to the coated sand manufacturing process and the mold molding process to give a mold having excellent characteristics. As a result, it will be used advantageously.

Hereinafter, the present invention will be clarified more specifically by using some examples, but the present invention shall not be construed in any way by the description of such examples. Should be understood. In the following examples and comparative examples, "%" and "part" are both shown on a mass basis unless otherwise specified. Further, measurement of the curing rate of the coating layer, measurement of the elution amount of the casting sand coated with the coating layer, measurement of the water content, the mold strength of the mold made of coated sand (CS) obtained in Examples and Comparative Examples, The casting surface, disintegration property and abrasion peelability were evaluated as follows, respectively.

-Measurement of cure rate of the first coating layer-
10 g of cast sand coated with a solid first coating layer containing an organic compound is precisely weighed and immersed in 50 g of methanol. After stirring with a stirrer for 10 minutes, filter with filter paper and separate into methanol and sand. After the sand is air-dried at room temperature to remove the methanol, the sand is dried in a hot air dryer at 110 ° C. for 30 minutes, and the mass of the cast sand after being soaked in methanol is weighed. The curing rate is calculated based on the following equation.
Curing rate (% by mass) = [[Mass of solid first coating layer- (Mass of cast sand coated with solid first coating layer before immersion-First solid after immersion Mass of cast sand coated with the coating layer of)} / Mass of the solid first coating layer] × 100

The mass of the solid first coating layer may be calculated by subtracting the weight loss at the time of curing (calculated by TG or the like) from the amount of the resin added to the coated sand, and the solid first coating layer containing an organic compound may be calculated. The cast sand (A) coated with the coating layer of No. 1 may be calcined at 900 ° C. for 1 hour, and the mass of the cast sand after calcining may be subtracted from the mass of the cast sand (A) before calcining.

-Measurement of elution of foundry sand coated with the first coating layer-
First, 50 g of cast sand coated with a solid first coating layer containing an organic compound is precisely weighed. This is referred to as casting sand A (before immersion).
This casting sand A is added to a solution of a water-soluble inorganic binder used for coated sand at a concentration of 3.0% (adjusted by diluting a water glass aqueous solution or a potassium carbonate aqueous solution with water) and stirred for 1 minute. The immersion treatment was carried out by allowing the mixture to stand for 24 hours in an atmosphere at room temperature of 20 ° C. Next, the surface of the extracted casting sand was washed with pure water to remove alkaline components, and then dried at 100 ° C. for 1 hour with a hot air dryer, and then the mass was precisely weighed. This is referred to as casting sand B (after immersion).
Next, the casting sand A (before immersion) and the casting sand B (after immersion) obtained above are each fired under the conditions of 900 ° C. × 1 hour, and the casting sand A (before immersion) after the firing is performed. ) And the mass of the cast sand B (after immersion) after firing are precisely weighed.
The elution amount is calculated by the following formula.
Elution amount (mass%) = [{(mass of casting sand A-mass of casting sand A after firing)-(mass of casting sand B-mass of casting sand B after firing)} / (mass of casting sand A) -Mass of cast sand A after firing)] x 100

-Measurement of water content-
Weigh 20 g of coated sand (CS). It is heated in a hot air dryer at 110 ° C. for 30 minutes to remove water in the coated sand, and the mass of the coated sand (CS) after drying is measured. The water content in the coated sand is calculated by the following formula.
Moisture content (% / CS) = {(mass of CS before drying-mass of CS after drying) / mass of CS before drying} x 100

-Measurement of mold strength-
For the strength test pieces obtained using each CS, the breaking load was measured using a measuring instrument (manufactured by Takachiho Seiki Co., Ltd .: digital casting sand strength tester), and based on the breaking load, the following formula was used. The bending strength is calculated and used as the mold strength. Here, the obtained bending strength (kgf / cm ² ) is multiplied by the gravitational acceleration of 9.8 and displayed in SI units expressed ^{in N / cm 2.}
Anti-folding strength = 1.5 x LW / ab ²
[However, L: distance between fulcrums (cm), w: breaking load (kgf), a: width of test piece (cm), b: thickness of test piece (cm)]

-Collapse test-
First, as shown in FIG. 1, a semi-cracked hollow main mold 6 (cavity diameter:: A circular aerial core 10 (diameter: 5 cm, height: 5 cm) having a skirting board portion 8 produced by using each CS is bonded and fixed by the skirting board fixing portion 4 within 6 cm (diameter: 5 cm, height: 6 cm). After that, the half-cracked hollow main molds 6 are further adhered and fixed to each other to prepare a sand mold 12 for a casting test. In addition, in order to prevent hot water leakage during casting, clamp the bonded main mold with a vise or wrap it with a wire to firmly fix it. Next, molten iron FC150 (temperature 1350 ± 50 ° C.) was poured from the pouring injection port 2 of the sand mold 12 for casting test to solidify it, and then the main mold 6 was broken to form a cylindrical casting shown in FIG. The circular non-aerial core 10 is discharged by taking out the 16 and hitting the casting 16 at room temperature with an air hammer. At the time of 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 ease of discharging the CS (hereinafter referred to as core CS) constituting the circular airless core 16 from the casting 16 is evaluated on a five-point scale according to the criteria shown below. In the present invention, A to C are accepted.
A: All core CSs are discharged within 10 hits.
B: All core CSs are discharged within 30 hits.
C: All core CSs are discharged within 60 hits.
D: With 60 hits, 50% or more and less than 100% of core CS is discharged.
E: With 60 hits, less than 0 to 50% of the core CS is discharged.

-Evaluation of casting surface-
The casting obtained in the above-mentioned disintegration test is cut in half, and the condition of the casting surface (casting surface) is visually and touched, and evaluated in four stages according to the following criteria. In the present invention, ⊚ and ◯ are acceptable.
⊚: No seizure is observed and the surface is smooth.
◯: Burn-in is not observed, but roughness is observed on the surface.
Δ: Burn-in is observed on a part of the cast surface, and roughness is also observed on the surface.
X: Burn-in is observed on the entire surface of the cast surface, and roughness is also observed on the surface.

-Abrasion peelability test-
100 g of the sand (recovered sand) constituting the circular aerial core, which was taken out in the above-mentioned disintegration test, was placed in a ball mill and polished for 1 hour. After that, sieving is performed for 1 minute with 200 mesh, separated into cast sand and exfoliated fine powder, the amount of fine powder obtained is measured, and the ease of exfoliation in the recovered sand is determined in 5 steps according to the criteria shown below. Evaluate with. In the present invention, A to C are accepted.
A: The amount of fine powder is 3% by mass or more with respect to the mass of the cast sand.
B: The amount of fine powder is 2% by mass or more and less than 3% by mass with respect to the mass of the cast sand.
C: The amount of fine powder is 1% by mass or more and less than 2% by mass with respect to the mass of the cast sand.
D: The amount of fine powder is 0.5% by mass or more and less than 1% by mass with respect to the mass of the cast sand.
E: The amount of fine powder is less than 0.5% by mass with respect to the mass of the foundry sand.

As for the resole-type phenol resin and the like used in manufacturing each CS, those manufactured according to the following procedure or commercially available products were prepared.

(1) Preparation of resol-type phenol resin A 940 g of phenol, 766 g of 47% formaldehyde aqueous solution, and 23.5 g of 20% caustic soda aqueous solution were added, and the temperature was raised and maintained at 70 ° C., and after 20 minutes, 34 g of hexamethylenetetramine was added. After 40 minutes of addition, 79 g of hexamethylenetetramine was added and reacted at 70 ° C., and when the viscosity (30 ° C.) reached 1000 cP, 47 g of methylene bisstearic acid amide, 28.2 g of salicylic acid, 20 94 g of a% Arabic rubber aqueous solution was added to form granules to form a suspension, which was further reacted at 70 ° C. for 3 hours, cooled to 50 ° C. or lower, and drained by filtration to form a water-containing resin. Granules (moisture content: 15%) were obtained. Next, air at room temperature was sent by an air-type flow device, and then the temperature of the air was gradually raised to 70 ° C. and dried for 1 hour as it was, with a weight average molecular weight (Mw) of 3200 and a gelation time of 90 seconds. A resol type phenol resin A was obtained.

(2) Preparation of Resol-type Phenol Resin B As the resol-type phenol resin B, a commercially available liquid HP3000A (weight average molecular weight (Mw) 600, non-volatile content 70%) manufactured by Asahi Organic Materials Co., Ltd. was prepared.

(3) Preparation of novolak-type phenol resin Using 940 parts of phenol and 447 parts of 47% formalin aqueous solution, 2.8 parts of oxalic acid was added thereto, and the mixture was reacted at 100 ° C. for 5 hours, and then 180 under a reduced pressure of 50 tolls. After heating to ° C., dehydration and dephenolization were carried out to obtain a novolak-type phenol formaldehyde having a weight average molecular weight (Mw) of 2690.

(4) Preparation of phenol urethane resin Bengilik ether type phenol resin (manufactured by Asahi Organic Materials Co., Ltd., trade name: CBP-160EH, Mw: 1220) and polyvinyl MDI (manufactured by Asahi Organic Materials Co., Ltd.) as a polyisocyanate compound; CB-MT3) was prepared, and when the coating layer was formed on the surface of the cast sand, the two resins were mixed at a ratio of 1: 1 (mass ratio) to prepare as a mixture.

(5) Preparation of polyvinyl acetate As polyvinyl acetate, a polyvinyl acetate solution of Gosenil M35-X6 (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., 35% methanol solution) (weight average molecular weight (Mw) 220,000, concentration 65%) ) Was prepared.

− Production example of dry CS 1-
Recycled sand (recycled sand A5 manufactured by Asahi Organic Materials Co., Ltd.) was prepared as casting sand, and resole-type phenol resin A was prepared as an organic compound. Then, after heating the regenerated sand to a temperature of about 130 ° C., the regenerated sand is put into a whirl mixer (manufactured by Enshu Iron Works), and the above-prepared resole-type phenol resin A is further added to 0.5 with respect to 100 parts of the regenerated sand. Resol is added to the surface of the cast sand particles by adding them in proportions of parts and kneading for 3 minutes to melt the resole-type phenol formaldehyde A, while stirring and mixing until the sand granules collapse and then taking them out. A solid first coating layer made of the type phenol resin A was formed. The thickness of the formed solid first coating layer is 0.4 μm based on the average particle diameter of the cast sand particles as a spherical shape and the amount of the cast sand and the organic compound (resole-type phenol resin A) added. Calculated. Then, the curing rate of the first coating layer thus formed and the elution amount of the casting sand coated with this coating layer were measured, and the results are shown in Table 1 below.

Next, as a water glass as a water-soluble inorganic binder, a commercially available product: sodium silicate No. 2 (trade name: manufactured by Fuji Chemical Co., Ltd., _{molar ratio of SiO 2} / Na ₂ O: 2.4) was prepared. Was used to prepare a water glass aqueous solution having a solid component (concentration) of 41%. Then, the previously prepared casting sand provided with the first solid coating layer on the surface is heated to a temperature of about 130 ° C., and then put into a whirl mixer (manufactured by Enshu Iron Works) to further prepare the above. The water glass aqueous solution was added at a ratio of 3.5 parts (solid component: 1.4 parts) to 100 parts of the regenerated sand, kneaded for 3 minutes, and stirred and mixed until uniform. In a dry state, it is composed of a first coating layer formed on the surface of cast sand by taking it out after squeezing, and a second coating layer in a solid state formed by an aqueous solution of water glass. Obtained coated sand (CS1). The water content of the obtained CS1 was 0.2% by mass.

− Production example of dry CS 2-4-
In the production example 1 of the dry state CS, the above production examples except that the amounts of the resol type phenol resin used at the time of forming the first coating layer were 1.0 part, 2.0 part, and 5.5 parts, respectively. A dry coated sand (CS2-CS4) was obtained according to the same procedure as in 1. The water contents of the obtained CS2 to CS4 were 0.2% by mass, 0.2% by mass, and 0.5% by mass, respectively. Further, the curing rate of the first coating layer in CS2 to CS4 and the elution amount of the casting sand on which such a coating layer was formed were also measured in the same manner, and the results are shown in Table 1 below.

-Production example of dry CS 5-
In Production Example 1 of dry CS, the resol-type phenol resin A was replaced with the polyvinyl acetate resin solution, and the polyvinyl acetate resin solution was added at a ratio of 1.5 parts to 100 parts of the regenerated sand. A dry coated sand (CS5) was obtained in the same procedure as in Production Example 1 except for the above. The water content of the obtained CS5 was 0.3% by mass. Further, the curing rate of the first coating layer in CS5 and the elution amount of the casting sand on which such a coating layer was formed were also measured in the same manner, and the results are shown in Table 1 below.

-Production example of dry CS 6-
In Production Example 2 of Dry CS, after obtaining the casting sand coated with the first coating layer, the casting sand on which the coating layer is formed is placed in a constant temperature bath at 180 ° C. for 30 minutes to obtain a resole-type phenol resin. Dry coated according to the same procedure as in Production Example 2 above, except that the resole-type phenol resin A in the first coating layer was cured to a curing rate of 100% by adding a step of promoting the curing of A. Sand (CS6) was obtained. The water content of the obtained CS6 was 0.3% by mass. Further, the curing rate of the first coating layer in CS6 and the elution amount of the casting sand on which such a coating layer was formed were also measured in the same manner, and the results are shown in Table 1 below.

-Production example of dry CS 7-
In Production Example 1 of the dry state CS, the resol-type phenol resin A was replaced with the resol-type phenol resin B, and the resol-type phenol resin B was added at a ratio of 1.4 parts to 100 parts of the regenerated sand. After obtaining the casting sand coated with one coating layer, toluenesulfonic acid is added at a ratio of 35% / resin to the casting sand on which the coating layer is formed, and the mixture is mixed at room temperature to form a resol type. A dry coated sand (CS7) was obtained according to the same procedure as in Production Example 1 except that the phenol resin B was cured to a curing rate of 100%. The water content of the obtained CS7 was 0.2% by mass. Further, the curing rate of the first coating layer in CS7 and the elution amount of the casting sand on which such a coating layer was formed were also measured in the same manner, and the results are shown in Table 1 below.

-Production example of dry CS 8-
In Production Example 1 of dry CS, the resol-type phenol resin A is replaced with the novolak-type phenol resin, and the novolak-type phenol resin is added at a ratio of 1.0 part to 100 parts of the regenerated sand and kneaded. Occasionally, 0.15 parts of hexamethylenetetramine was added to obtain cast sand coated with a coating layer, and then the cast sand on which the coating layer was formed was placed in a constant temperature bath at 180 ° C. for 30 minutes to form a novolak-type phenol resin. A dry coated sand (CS8) was prepared according to the same procedure as in Production Example 1 above, except that the novolak-type phenol formaldehyde in the first coating layer was cured to a curing rate of 100% by adding a step of promoting curing. ) Was obtained. The water content of the obtained CS8 was 0.3% by mass. Further, the curing rate of the first coating layer in CS8 and the elution amount of the casting sand on which such a coating layer was formed were also measured in the same manner, and the results are shown in Table 1 below.

-Production example of dry CS 9-
In Production Example 1 of Dry CS, except that the first coating layer was formed according to the following procedure in order to replace the organic compound forming the first coating layer with the phenol urethane resin from the resole type phenol resin A. Obtained a dry coated sand (CS9) according to the same procedure as in Production Example 1. That is, the regenerated sand is put into a whirl mixer (manufactured by Enshu Iron Works) at a temperature of 130 ° C., and a benzic ether type phenol resin for forming a phenol urethane resin and a polyisocyanate compound are further mixed at a mass ratio of 1: 1. , Add in an amount such that the total amount thereof is 1.3 parts, knead in a mixer, and the benzylic ether type phenol resin and the polyisocyanate compound react with each other to form a phenol urethane resin (solid content: 1. 0 parts), stirred and mixed until 100% cured, and then taken out. The water content of the obtained CS9 was 0.2% by mass. Further, the curing rate of the first coating layer in CS9 and the elution amount of the casting sand on which such a coating layer was formed were also measured in the same manner, and the results are shown in Table 1 below.

-Production example of dry CS 10-
In Production Example 6 of Dry CS, a part of silicon dioxide particles: Elchem microsilica (trade name, manufactured by Elchem Japan Co., Ltd., average particle diameter: 0.15 μm) was added to an aqueous solution of water glass as inorganic oxide particles. A dry coated sand (CS10) was obtained according to the same procedure as in Production Example 6 except that the particles were added. The water content of the obtained CS10 was 0.3% by mass. Further, the curing rate of the first coating layer in CS10 and the elution amount of the casting sand on which such a coating layer was formed were also measured in the same manner, and the results are shown in Table 2 below.

-Production example of dry CS 11-
In Production Example 6 of Dry CS, a part of silicon dioxide particles: HS312 (trade name, manufactured by Nippon Steel & Sumikin Materials Co., Ltd., average particle diameter: 9.5 μm) was added to the water glass aqueous solution as inorganic oxide particles. A dry coated sand (CS11) was obtained according to the same procedure as in Production Example 6 above. The water content of the obtained CS11 was 0.3% by mass. Further, the curing rate of the first coating layer in CS11 and the elution amount of the casting sand on which such a coating layer was formed were also measured in the same manner, and the results are shown in Table 2 below.

-Production example of dry CS 12-
In Production Example 6 of Dry CS, a part of aluminum oxide particles: AZ-75 (trade name, manufactured by Nippon Steel & Sumikin Materials Co., Ltd., average particle diameter: 2.5 μm) was used as an aqueous solution of water glass as inorganic oxide particles. A dry coated sand (CS12) was obtained according to the same procedure as in Production Example 6 except that the particles were added to the above-mentioned production example 6. The water content of the obtained CS12 was 0.3% by mass. Further, the curing rate of the first coating layer in CS12 and the elution amount of the casting sand on which such a coating layer was formed were also measured in the same manner, and the results are shown in Table 2 below.

-Production example of dry CS 13-
In Production Example 2 of Dry CS, after obtaining the casting sand coated with the first coating layer, the casting sand on which the coating layer is formed is placed in a constant temperature bath at 180 ° C. for 5 minutes to obtain a resole-type phenol resin. Dry coated according to the same procedure as in Production Example 2 above, except that the resole-type phenol resin A in the first coating layer was cured to a curing rate of 85% by adding a step of promoting the curing of A. Sand (CS13) was obtained. The water content of the obtained CS13 was 0.2% by mass. Further, the curing rate of the first coating layer in CS13 and the elution amount of the casting sand on which such a coating layer was formed were also measured in the same manner, and the results are shown in Table 2 below.

-Production example of dry CS 14-
In the production example 6 of the dry state CS, the above production example except that the potassium carbonate aqueous solution having a solid component (concentration) of potassium carbonate of 50% was used instead of the water glass aqueous solution and the amount used was 3 parts. A dry coated sand (CS14) was obtained according to the same procedure as in 6. The water content of the obtained CS14 was 0.3% by mass. Further, the curing rate of the first coating layer in CS14 and the elution amount of the casting sand on which such a coating layer was formed were also measured in the same manner, and the results are shown in Table 2 below.

-Production example of dry CS 15-
This dry coated sandwich (CS15) was obtained in the same procedure as in Production Example 1 above, except that the step of forming the solid coating layer was not carried out in Production Example 1 of dry CS. The water content of the obtained CS15 was 0.2% by mass. Further, the curing rate of the first coating layer in CS15 and the elution amount of the casting sand on which such a coating layer was formed were also measured in the same manner, and the results are shown in Table 2 below.

-Production example of dry CS 16-
In Production Example 15 of Dry CS, a part of silicon dioxide particles: Elchem microsilica (trade name, manufactured by Elchem Japan Co., Ltd., average particle diameter: 0.15 μm) was added to an aqueous solution of water glass as inorganic oxide particles. A dry coated sand (CS16) was obtained according to the same procedure as in Production Example 15 except that the particles were added. The water content of the obtained CS16 was 0.3% by mass. Further, the curing rate of the first coating layer in CS16 and the elution amount of the casting sand on which such a coating layer was formed were also measured in the same manner, and the results are shown in Table 2 below.

-Production example of dry CS 17-
Except for the fact that the resol-type phenol resin A was replaced with the novolak-type phenol resin in Production Example 1 of the dry CS, and this novolak-type phenol resin was added at a ratio of 1.0 part to 100 parts of the regenerated sand. A dry coated sand (CS17) was obtained according to the same procedure as in Production Example 1. The water content of the obtained CS17 was 0.3% by mass. Further, the curing rate of the first coating layer in CS17 and the elution amount of the casting sand on which such a coating layer was formed were also measured in the same manner, and the results are shown in Table 2 below.

-Production example of dry CS 18-
In Production Example 1 of Dry CS, instead of the aqueous glass solution, an aqueous solution of potassium carbonate having a solid component (concentration) of potassium carbonate of 50% was used, and the amount used was 3 parts, and the solid first coating was used. A dry coated sand (CS18) was obtained according to the same procedure as in Production Example 1 except that the step of forming the layer was not carried out. The water content of the obtained CS18 was 0.4% by mass. Further, the curing rate of the first coating layer in CS18 and the elution amount of the casting sand on which such a coating layer was formed were also measured in the same manner, and the results are shown in Table 2 below.

-Molding Example I (Examples 1 to 14, Comparative Examples 1 to 4)-
CS1 to CS18 (temperature: 20 ° C.) manufactured according to the above procedures were put into a Shinagawa universal stirrer (5DM-r type, manufactured by Dalton Corporation) at room temperature, and water was further added. CS (coated sand) moistened was prepared by adding the mixture in a stirrer at a ratio of 2.0 parts to 100 parts of CS and stirring the mixture. Next, the wet-state CS taken out from the stirrer was blown into a molding die heated to 150 ° C. with a blow pressure of 0.3 MPa to fill it, and then held in the molding die for 1 minute and 30 seconds. Then, under a gauge pressure of 0.03 MPa, hot air at 300 ° C. was blown for 1 minute and 30 seconds to solidify (cure) each of the CS filled in the molding die, and to measure the mold strength. Molds used as a test piece (2.54 × 2.54 × 20 cm) and a test piece (φ5 × 5 cm) of a circular aerial core were prepared. Then, the mold strength, casting surface, disintegration property, and polishing peelability were measured using the molds corresponding to each of the obtained CSs, and the results are also shown in Tables 1 and 2 below. The CS used when preparing the templates (test specimens) according to each of Examples 1 to 14 and Comparative Examples 1 to 4 are as shown in Tables 1 and 2 below.

As is clear from the results of Tables 1 and 2, in each of CS1 to 14 used in Examples 1 to 14, the first coating layer is an aqueous solution of a water-soluble inorganic binder having a second coating layer. Since the elution amount is configured to be less than or equal to the specified value, the molds obtained from these CSs have excellent mold strength and give a casting with a good casting surface. It is recognized that it is excellent in disintegration property and polishing peelability.

On the other hand, Comparative Examples 1 to 18 using CS15-18 provided with the first coating layer in which the first coating layer does not exist, or even if it exists, the elution by the water-soluble inorganic binder aqueous solution is remarkable. In No. 4, it is recognized that the results are inferior in all of the mold strength, the casting surface, the disintegration property, and the polishing peelability.

-Molding Example II (Examples 15 to 28, Comparative Examples 5 to 8)-
CS1 to CS18 (temperature: 20 ° C.) manufactured according to each of the above procedures are blown into a molding die heated to 100 ° C. at a blow pressure of 0.3 MPa to fill them, and then further. 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 and aerated through the coated sand (CS) phase filled in the molding die. I made it. Then, after the aeration of such steam is completed, hot air having a temperature of 300 ° C. is blown for 2 minutes and 40 seconds under a gauge pressure of 0.03 MPa to solidify (cure) the CS filled in the molding die. As a result, a mold used as a test piece of mold strength (2.54 × 2.54 × 20 cm) and a test piece of a circular aerial core (φ5 × 5 cm) was prepared. Then, the mold strength, casting surface, disintegration property, and polishing peelability were measured using the molds corresponding to each of the obtained CSs, and the results are also shown in Tables 3 and 4 below. The CS used when preparing the templates (test specimens) according to each of Examples 15 to 28 and Comparative Examples 5 to 8 are as shown in Tables 3 and 4 below.

As is clear from the results of Tables 3 and 4, unlike the above-mentioned mold molding example I, even when the mold molding method by steam aeration is adopted, the same result as that of the mold molding example I is obtained. Obtained. That is, excellent results were obtained in Examples 15 to 28 corresponding to Examples 1 to 14, whereas the present invention was obtained in Comparative Examples 5 to 8 corresponding to Comparative Examples 1 to 4 above. It is acknowledged that the purpose of is not fully achieved.

Claims (14)

A solid first coating layer containing a crosslinkable curable resin or a cured product thereof is formed so as to cover the surface of cast sand made of a fire-resistant aggregate, and the first coating layer is further formed. A dry coated sand having at least two coating structures formed by forming a solid second coating layer consisting of a binder composition containing an alkaline water-soluble inorganic binder so as to be coated. ,
50 g of the cast sand coated with the first coating layer was mixed with 50 g of a 3.0% concentration solution of the water-soluble inorganic binder and kept at a temperature of 20 ° C. for 24 hours. The coated sand is characterized in that it is configured to have a characteristic of an elution amount of 30% by mass or less of the solid content in the first coating layer of the cast sand. The coated sand according to claim 1 , wherein the crosslinkable curable resin has a gelation time of 110 seconds or less. The cross-linked cured resins are coated sand according to claim 1 or claim 2 which is a phenolic resin or a phenolic urethane resins. The coated sand according to any one of claims 1 to 3 , wherein the water content in the coated sand is 1.5% by mass or less. The coated sand according to any one of claims 1 to 4 , wherein the thickness of the first coating layer is 0.1 to 6 μm. The coated sandwich according to any one of claims 1 to 5 , wherein the binder composition contains inorganic oxide particles. The coated sand according to claim 6 , wherein the inorganic oxide particles are at least one selected from the group consisting of silicon dioxide particles, aluminum oxide particles, and titanium oxide particles. The invention according to any one of claims 1 to 7 , wherein 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. The coated sand according to any one of claims 1 to 8 is filled in a molding cavity of a predetermined molding mold, and then water vapor is aerated to hold the coated sand in the molding mold to solidify or cure the coated sand. A method for manufacturing a mold, which comprises obtaining a desired mold by casting. The method for producing a mold according to claim 9 , wherein the molding die is heated to a temperature of 80 ° C. to 200 ° C. Water is added to the coated sand according to any one of claims 1 to 8 to moisten the coated sand, and the wet-state coated sand is filled in the molding die, and then the molding die is used. A method for producing a mold, which comprises obtaining a desired mold by holding it inside and solidifying or hardening it. The method for manufacturing a mold according to claim 11 , wherein the molding die is heated to a temperature of 80 ° C. to 300 ° C. The method for producing a mold according to any one of claims 9 to 12 , wherein hot air or superheated steam is aerated in the mold while the mold is being held. After casting using the mold made of the solidified or cured product of the coated sand according to any one of claims 1 to 8, the cast sand is recovered from the mold and subjected to a dry regeneration treatment. A method for regenerating cast sand, which is characterized by applying and obtaining regenerated sand.

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