Mold material composition and method for manufacturing a mold using the same

Abstract

To provide a mold material composition which is capable of advantageously forming a mold having satisfactory collapsibility and easily regenerating a refractory aggregate (sand) which is recovered after casting.SOLUTION: A mold material composition is prepared using (a) a refractory aggregate, (b) a binder with water glass as an essential component and (c) phosphate ester as a neutralizer with which a decomposition product produced by heating upon casting causes neutralization reaction with an alkali component of the water glass as essential structural components.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a mold material composition and a method for manufacturing a mold using the same, and particularly to a mold material composition capable of providing a mold that is excellent in collapsibility after casting and is also easy to recycle the recovered refractory aggregate, and a method capable of advantageously manufacturing a mold exhibiting such excellent characteristics.

Background Art

[0002] Conventionally, as one of the molds used for casting molten metal such as iron and aluminum, a coated sand (mold material composition) obtained by coating a refractory aggregate with a predetermined binder and shaped into a desired shape is known. And as the binder used for forming the coating layer in such a mold material composition, in addition to water-soluble inorganic binders such as water glass and sodium phosphate, organic binders using resins such as phenol resin, furan resin, and urethane resin have been clarified, and various methods for shaping self-hardening molds using these binders have been proposed.

[0003] Incidentally, it is known that a mold material composition composed of an inorganic binder such as water glass has a lower organic content compared to a mold material composition using an organic binder, so that the generation of various gases due to heat during molding or casting is advantageously suppressed, and it is difficult to cause problems such as odors. However, in a conventional mold material composition composed of an inorganic binder, when attempting to recover refractory aggregates (sand) from the mold after casting and regenerate the recovered sand by baking treatment, the inorganic binder remaining on the surface of the recovered sand cannot be burned, but instead sinters and adheres firmly to the surface of the refractory aggregates (sand), thus inherently having the problem of being difficult to regenerate. In particular, in a mold material composition using water glass as an inorganic binder, due to the heat during casting, the water glass is vitrified, and even if baking treatment and polishing treatment are performed on the sand recovered after casting, it is very difficult to remove the vitrified water glass on the sand surface. In addition, conventional mold material compositions using inorganic binders also inherently have the problem that the collapsibility of the molds obtained using them is not sufficient.

[0004] Under such circumstances, various measures for improving the collapsibility of the mold after casting and techniques related to the regeneration of the recovered refractory aggregates (sand) have been proposed conventionally. For example, in Patent Document 1 (Japanese Patent Application Laid-Open No. 2016-64422), a mold disintegrant composition composed of an acidic solution has been proposed as a composition for disintegrating a water glass mold, and a method of contacting such a mold disintegrant composition with a water glass mold after pouring molten metal to disintegrate the mold has been proposed. However, even if the water glass mold is disintegrated using the mold disintegrant composition disclosed in the same patent document, there is a possibility that water glass remains on the surface of the recovered refractory aggregates (sand), and if a baking treatment is performed on such recovered sand, re-welding may occur between the particles of the recovered sand, making regeneration difficult. In addition, since the mold disintegrant composition disclosed in the same patent document is an acidic solution, there is a risk of corroding the metal casting apparatus and the obtained castings.

[0005] In Patent Document 2 (Japanese Patent Application Laid-Open No. 2015-51446), as a method for recycling foundry sand, a method including a mixing step of mixing and stirring pulverized foundry sand in water at 5°C to 70°C to separate the binder attached to the foundry sand from the foundry sand has been proposed. However, for example, when the recycling treatment method disclosed in the patent document is applied to a foundry sand mold using water glass as a binder, treated water containing a large amount of alkali components due to water glass is generated, and there is a problem that further labor is required for handling and disposal (treatment) of the treated water.

[0006] Furthermore, in Patent Document 3 (Japanese Patent Application Laid-Open No. 2017-77570) and Patent Document 4 (Japanese Patent Application Laid-Open No. 2010-519042), as a method for recycling foundry sand recovered from a mold formed of foundry sand using an inorganic binder (water glass), it is disclosed that the recovered foundry sand is fired at a high temperature to vitrify and deactivate the water glass. However, in order to vitrify the water glass, it is necessary to fire at a high temperature of 900°C or higher, and from the viewpoint of energy efficiency during recycling, it is difficult to say that it is an efficient method.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0008] Here, the present invention has been made against such a background, and the problem to be solved is to advantageously form a mold with good collapsibility and to provide a mold material composition capable of easily regenerating the refractory aggregate (sand) recovered after casting. Further, the present invention also aims to provide a method capable of advantageously manufacturing a useful mold using such a mold material composition having such excellent characteristics.

Means for Solving the Problem

[0009] And the present invention can be preferably implemented in various aspects listed below in order to solve the above-described problems, and each aspect described below can also be adopted in any combination. It should be understood that the aspects or technical features of the present invention are not limited to those described below, and can be recognized based on the inventive concept grasped from the description of the entire specification.

[0010] (1) (a) A refractory aggregate, (b) a binder having water glass as an essential component, and (c) a phosphate ester as a neutralizing agent in which the decomposition product generated by heating during casting causes a neutralization reaction with the alkali component of the water glass, at least containing See, the phosphate ester is contained in such an amount that the decomposition products generated by heating during casting neutralize the alkali component of the water glass, so that the proportion of the alkali component of the water glass after casting becomes 15% by mass or less. A mold material composition characterized by the above. (2) The above aspect in which a coating layer containing the binder and the phosphate ester is formed so as to cover the surface of the refractory aggregate (1) to The mold material composition described. (3) The above aspect in which a solid first coating layer containing the phosphate ester is formed so as to cover the surface of the refractory aggregate, and a second coating layer made of a binder composition containing the binder is formed so as to cover the first coating layer (1) to The mold material composition described. (4) The first coating layer is , i) it is possible to form the solid first coating layer on the surface of the refractory aggregate, and ii) it thermally decomposes by heating during casting to generate gas One containing an organic compound Aspect (3) The mold material composition described in (5) The mold material composition according to any one of the above aspects (1) to Aspect (4) wherein the refractory aggregate is spherical. (6) The mold material composition according to any one of the above aspects (1) to Aspect (5) which does not have room temperature fluidity and exhibits a wet state. (7) The mold material composition according to any one of the above aspects (1) to Aspect (5) which has room temperature fluidity and exhibits a dry state. (8) The Aspect (6) A method for manufacturing a mold, characterized in that the mold material composition exhibiting a wet state described in (9) is used, filled into a mold, held in the mold, and solidified or cured to obtain a target mold. Aspect (7) A method for manufacturing a mold, characterized in that the mold material composition exhibiting a dry state described in (10) is used, filled into a mold, steam is passed through, held in the mold, and solidified or cured to obtain a target mold. Aspect (7) A method for manufacturing a mold, characterized in that the mold material composition exhibiting a dry state described in is used, water is added thereto to make it wet, the wet mold material composition is filled into a mold, held in the mold, and solidified or cured to obtain a target mold.

[0011] Thus, in the mold material composition according to the present invention, (a) a refractory aggregate, (b) a binder having water glass as an essential component, and (c) a phosphate ester as a neutralizing agent that causes a decomposition product generated by heating during casting to undergo a neutralization reaction with the alkali component of water glass are also essential components. Therefore, when casting is carried out using a mold formed of such a mold material composition, the mold is heated by the molten metal (generally heated to a temperature exceeding 300°C), and the decomposition product generated from the neutralizing agent (phosphate ester) by such heating undergoes a neutralization reaction with the alkali component of water glass, whereby the water glass becomes physically fragile, so that the collapsibility of the mold after casting becomes good. Further, due to the heating accompanying the pouring of the molten metal, some or all of the alkali components of the water glass are neutralized. Therefore, in the mold material composition composed of refractory aggregates (coated sand) covered with a coating layer, dissolution of the coating layer on the surface of the coated sand due to the high-temperature alkali components is effectively prevented. As a result, re-welding (sintering) between the coated sand particles due to heating during pouring is advantageously suppressed.

[0012] Furthermore, in the refractory aggregate (sand) recovered after casting is carried out using a mold composed of the mold material composition of the present invention, all or part of the alkali component of the water glass is neutralized and deactivated. Therefore, when regenerating the recovered sand, high-temperature firing treatment for removing the alkali component or neutralization treatment using an acid is unnecessary. In addition, since the alkali component of the water glass is neutralized, the recovered refractory aggregate lumps are brittle, so that the advantage of being easily regenerated by polishing can also be enjoyed.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Mode for Carrying Out the Invention

[0014] Incidentally, the mold material composition according to the present invention is roughly classified into a mold material composition in a wet state and a mold material composition in a dry state depending on the state of a layer (coating layer) containing a binder having water glass as an essential component. The mold material composition in a dry state has good normal-temperature fluidity, whereas the mold material composition in a wet state does not have such normal-temperature fluidity.

[0015] Here, the "mold material composition having normal-temperature fluidity and presenting a dry state" in the present invention means a mold material composition for which a measured value is obtained when measuring the dynamic angle of repose, regardless of the water content. This dynamic angle of repose refers to a case where the mold material composition is accommodated in a cylinder whose one end in the axial direction is closed with a transparent plate material (for example, a container with a diameter of 7.2 cm × a height of 10 cm is filled with the mold material composition up to half of its volume), held so that the axial center is in the horizontal direction, and rotated around the horizontal axial center at a constant speed (for example, 25 rpm), whereby the slope of the layer of the mold material composition flowing in the cylinder becomes a flat surface shape, and it refers to the angle formed between such a slope and the horizontal plane. This dynamic angle of repose is preferably 80° or less, more preferably 45° or less, and still 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 achieved. In addition, those in which the mold material composition is in a wet state, does not flow in the cylinder, the slope of the layer of the mold material composition is not formed as a flat surface, and as a result, the dynamic angle of repose cannot be measured shall be classified as a mold material composition in a wet state.

[0016] The mold material composition according to the present invention, which has normal temperature fluidity and exhibits a dry state, desirably has a moisture content corresponding to an amount in the range of 5 to 55% by mass, more desirably 10 to 50% by mass, and most desirably 20 to 50% by mass, based on the solid content of the water glass that constitutes the binder contained in the coating layer covering the surface of the refractory aggregate. When the moisture content in this mold material composition is less than the amount corresponding to 5% by mass based on the solid content of the water glass in the coating layer, the water glass may vitrify and may not return to a solution state even if water is added again during mold shaping. On the other hand, if it exceeds the amount corresponding to 55% by mass, the mold material composition may not be in a dry state. However, even a mold material composition with a moisture content exceeding 55% by mass based on the solid content of the water glass may exhibit a dry state depending on the type of water glass. Whether it corresponds to a mold material composition in a dry state or a wet state is determined by the presence or absence of the above-described normal temperature fluidity. Note that the method for measuring the moisture content in the mold material composition is not particularly limited, and known methods can be appropriately adopted.

[0017] On the other hand, in the case of a mold material composition according to the present invention that does not have normal temperature fluidity and exhibits a wet state, the moisture content desirably corresponds to an amount in the range of 70 to 400% by mass, more desirably 80 to 300% by mass, and most desirably 90 to 200% by mass, based on the solid content of the water glass as the binder. When the moisture content in this mold material composition is less than the amount corresponding to 70% by mass based on the solid content of the water glass, the viscosity of the water glass increases, making it difficult to mix uniformly during kneading and resulting in an inability to obtain a uniform mold. On the other hand, if it exceeds the amount corresponding to 400% by mass, the mold material composition may become slurry-like, and as a result, it may be impossible to fill the molding die. Also, even if it can be filled, there is a risk that it will take a long time to dry in the molding die.

[0018] Here, as the refractory aggregate constituting the mold material composition of the present invention, any of various refractory granular or powdery materials that function as the base material of the mold and have been conventionally used for molds can be used. Specifically, silica sand, recycled silica sand, and special sands such as alumina sand, olivine sand, zircon sand, and chromite sand, as well as slag-based particles such as ferrochrome slag, ferronickel slag, and converter slag; artificial particles such as alumina-based particles and mullite-based particles and their recycled particles; alumina balls, magnesia clinker, etc. can be mentioned. These refractory aggregates can be new sand, or recycled sand or recovered sand that has been used once or multiple times for molding the mold as foundry sand, or even a mixed sand obtained by adding new sand to such recycled sand or recovered sand and mixing them. And such refractory aggregates are generally used with a particle size of about 40 to 200 in terms of the AFS index, preferably about 50 to 150. Also, the refractory aggregate is preferably spherical, specifically, the particle shape coefficient is 1.2 or less, more preferably 1.0 to 1.1. By using a refractory aggregate with a particle shape coefficient of 1.2 or less, the fluidity and filling property are improved, and the number of contact points between the aggregates increases, so that the amount of binder and additives required to exhibit the same strength can be reduced. The particle shape coefficient of the aggregate used here is generally adopted as a measure indicating the outer shape of the particles and is also called the particle shape index. The closer its value is to 1, the closer it means to a spherical (true sphere) shape. And such a particle shape coefficient is represented by a value calculated using the sand surface area measured by various known methods. For example, using a sand surface area measuring instrument (manufactured by Georg Fischer), the actual surface area of the sand grains per 1 g is measured, and the value obtained by dividing it by the theoretical surface area is meant. The theoretical surface area is the surface area assuming that all the sand grains are spherical.

[0019] In addition, in the mold material composition according to the present invention, as the binder to be blended with the refractory aggregate as described above, one containing water glass as an essential component will be used. Here, water glass is a water-soluble silicate compound. Examples of such silicate compounds include sodium silicate, potassium silicate, sodium metasilicate, potassium metasilicate, lithium silicate, ammonium silicate, etc. Among them, sodium silicate (sodium silicate) is particularly preferably used in the present invention. Further, as the binder, as long as water glass is used as an essential component, various water-soluble binders such as thermosetting resins, saccharides, proteins, synthetic polymers, salts, and inorganic polymers can be used in combination. When other water-soluble binders are used in combination with water glass, the proportion of water glass in the total binder is preferably 60% by mass or more, more preferably 80% by mass or more, and most preferably 90% by mass or more on a solid content basis. Also, water glass can be used in a hydrated state.

[0020] Furthermore, the above-mentioned sodium silicate usually has a molar ratio of SiO 2 / Na 2 O and is classified into five types, namely No. 1 to No. 5, and is 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 of 2.4 to 2.6. Furthermore, 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 2The molar ratio of O is 3.6 to 3.8. Among these, sodium silicates No. 1 to No. 3 are also specified in JIS-K-1408. And these various sodium silicates may be used alone or in combination in the present invention. Also, by mixing them, it is possible to adjust the molar ratio of SiO 2 / Na 2 O. Note that the molar ratio of SiO 2 / Na 2 O is not limited to the range specified by the above-mentioned sodium silicates No. 1 to No. 5, and for example, a range of 0.8 to 4.0 may be sufficient.

[0021] And in the present invention, in order to advantageously obtain the target mold material composition, the sodium silicate constituting the water glass used as a binder has a molar ratio of SiO 2 / Na 2 O generally of 1.9 or more, preferably 2.0 or more, more preferably 2.1 or more. Among the above classifications of sodium silicates, the sodium silicates corresponding to No. 1 and No. 2 are particularly advantageously used. Such sodium silicates No. 1 and No. 2 each give a mold material composition with stable and good characteristics even in a wide range of sodium silicate concentrations in water glass. Also, the upper limit of the molar ratio of SiO 2 / Na 2 O in such sodium silicate will be appropriately selected according to the characteristics of the water glass in aqueous solution form, but generally it is 3.5 or less, preferably 3.2 or less, more preferably 2.7 or less. Here, when the molar ratio of SiO 2 / Na 2 O becomes less than 1.9, especially in the dry state, the viscosity of the water glass becomes low, and it may be difficult to make the mold material composition in a dry state unless the moisture content is made quite low. On the other hand, when it becomes more than 3.5, the solubility in water decreases, the adhesion area cannot be obtained, and the strength of the finally obtained mold may decrease.

[0022] In addition, the water glass used in the present invention means a solution of a silicic acid compound in a state dissolved in water. It is used not only in the state of the stock solution purchased in the market but also in a diluted state by adding water to such a stock solution. And from such water glass, the non-volatile component (water glass component) excluding volatile substances such as water and solvents is referred to as the solid content, which corresponds to the soluble silicic acid compound such as sodium silicate described above. Also, the higher the ratio of such a solid content (non-volatile component), 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, when it is composed only of the stock solution, corresponds to the amount excluding the amount of water in such a stock solution. On the other hand, when a diluted solution obtained by diluting the stock solution with water is used, the amount excluding the amount of water in the stock solution and the amount of water used for dilution corresponds to the solid content of the water glass used.

[0023] Furthermore, the solid content in such water glass will be in an appropriate ratio according to the type of water glass component (soluble silicate compound) and the like. Advantageously, it is preferably contained in a ratio of 20 to 50% by mass. By appropriately allowing the water glass component corresponding to this solid content to be present in the aqueous solution, when mixing (kneading) with refractory aggregates, a coating of the water glass component can be formed uniformly and without unevenness on such refractory aggregates in the dry state, and in the wet state, the aggregates and water glass can be mixed uniformly and without unevenness, thereby enabling the advantageous molding of the target mold. When the concentration of the water glass component in the water glass becomes too low and the total amount of the solid content is less than 20% by mass, in the dry state, it is necessary to increase the heating temperature or the heating time for drying the mold material composition, thus causing problems such as energy loss. In the wet state, the time for heating in the molding die becomes longer, causing the problem of lengthening the mold molding cycle. Also, when the ratio of the solid content in the water glass becomes too high, it becomes difficult to uniformly coat the surface of the refractory aggregates with the water glass component in the dry state, and in the wet state, the viscosity of the water glass becomes too high, making it difficult to uniformly mix the aggregates and water glass without unevenness, which also causes problems in improving the characteristics of the target mold. Therefore, it is desirable to prepare water glass in the form of an aqueous solution such that the solid content is 50% by mass or less and thus the water content is 50% by mass or more.

[0024] And such water glass is desirably used at a ratio of 0.1 to 5.0 parts by mass in terms of solid content when considering only the non-volatile content with respect to 100 parts by mass of the refractory aggregate. Among them, a ratio of 0.3 to 4.0 parts by mass is particularly advantageously employed. Here, the measurement of the solid content in the water glass is carried out as follows. That is, 10 g of the sample is placed in a sample dish made of aluminum foil (length: 9 cm, width: 9 cm, height: 1.5 cm) and weighed, then placed on a hot plate maintained at 180 ± 1 °C, left for 20 minutes, after which the sample dish is inverted and further left on the hot plate for 20 minutes. Then, the sample dish is taken out from the hot plate, cooled in a desiccator, and weighed, and the solid content (mass %) is calculated by the following formula. Solid content (mass %) = {[Mass of the sample dish after drying (g) - Mass of the sample dish (g)] / [Mass of the sample dish before drying (g) - Mass of the sample dish (g)]} × 100

[0025] In the present invention, if the amount of water glass used is too small, it becomes difficult to form a coating layer on the surface of the refractory aggregate in the mold material composition in the dry state. On the other hand, in the mold material composition in the wet state, it becomes impossible to cover the aggregate with the aqueous water glass, and there is a risk that the solidification or hardening of the mold material composition during mold shaping does not proceed sufficiently. Also, if the amount of water glass used is too large, in the dry state, an excessive amount of water glass adheres to the surface of the refractory aggregate, making it difficult to form a uniform coating layer, and there is also a risk that the mold material compositions adhere to each other and agglomerate (composite particle formation). In the wet state, an excessive amount of water glass may become uneven during mold shaping, interfering with the uniform physical properties of the mold. Therefore, it has an adverse effect on the physical properties of the finally obtained mold, and in addition, there is a risk of causing problems such as making it difficult to remove the sand from the core after casting the metal.

[0026] And in the mold material composition according to the present invention, a predetermined neutralizing agent is used as an essential component together with the above-described refractory aggregate and the binder containing water glass as an essential component, and there is a great technical feature in this constitution.

[0027] That is, when casting is carried out using a mold formed of the mold material composition of the present invention, in which a predetermined neutralizing agent (a neutralizing agent whose decomposition product generated by heating causes a neutralization reaction with the alkali component of water glass) is blended, the mold is heated by the molten metal (generally heated to a temperature exceeding 300°C), and the decomposition product generated from the neutralizing agent by such heating during casting neutralizes part or all of the alkali component of water glass. Since part or all of the alkali component of water glass is neutralized, water glass becomes physically fragile. Therefore, in the mold material composition according to the present invention, the mold formed using it has good collapsibility after being subjected to casting. Further, due to the heating (heating during casting) accompanying the pouring of the molten metal, the alkali component of water glass is neutralized. Therefore, in the mold material composition composed of refractory aggregates (coated sand) covered with a coating layer, dissolution of the coating layer on the surface of the coated sand due to the high-temperature alkali component is effectively prevented, and thus, re-welding (sintering) between the coated sand particles due to heating during pouring is advantageously suppressed. Furthermore, in the refractory aggregates (sand) recovered after casting is carried out using the mold composed of the mold material composition of the present invention, since part or all of the alkali component of water glass is neutralized and in an inactivated state, when recycling the recovered sand, high-temperature firing treatment for removing the alkali component or neutralization treatment using an acid, etc. become unnecessary. Moreover, since the alkali component of water glass is neutralized and the coating layer on the surface of the coated sand becomes brittle, the grain mass of the recovered refractory aggregates becomes brittle and can enjoy the advantage that regeneration by polishing is easy. Note that the alkali component of water glass is contained in the solid content of water glass, dissolves in the moisture contained in water glass, and the alkali metal ions generated therein cause a neutralization reaction with the decomposition product of the neutralizing agent. Also, in the dry-state mold material composition, the fact that moisture remains in the water glass contained therein is obvious from the above-mentioned "mold material composition presenting a dry state".

[0028] Here, the neutralizing agent used in the present invention is one in which the decomposition product generated by heating during casting undergoes a neutralization reaction with the alkali component of water glass. More specifically, it does not decompose during the preparation (manufacture) of the mold material composition or heating during mold shaping (generally heating below 300°C), but decomposes by heating with the molten metal during casting (heating at a temperature exceeding 300°C), and the generated decomposition product neutralizes the alkali component of water glass (for example, in the case of sodium silicate, Na 2 O). A compound that neutralizes is used as the neutralizing agent in the present invention. Here, the decomposition mentioned means complete decomposition. Even a compound that starts to decompose partially during heating below 300°C, as long as the temperature at which it completely decomposes exceeds 300°C and the decomposition product undergoes a neutralization reaction with the alkali component of water glass, it can be used as the neutralizing agent of the present invention. Any compound having such characteristics can be used as the neutralizing agent in the present invention without particular limitation, but preferably an organic halogen compound or a phosphate ester is used, and particularly preferably an organic halogen compound is used. The organic halogen compound decomposes upon heating with the molten metal during casting (heating at a temperature exceeding 300°C) to release halogen, and this released halogen reacts with the sodium of water glass, whereby the alkali component of water glass is neutralized. From the viewpoints of the neutralization effect and cost, in the present invention, organic chlorine compounds and organic bromine compounds are most preferably used as the neutralizing agent. In the present invention, when the neutralizing agent is manufactured according to the manufacturing method described later, it will be present in a uniformly dispersed state in the coating layer. Therefore, for example, uneven distribution of the neutralizing agent, which is a problem when an acid is blended as the neutralizing agent, does not occur in the present invention.

[0029] In the present invention, examples of the organic halogen compounds used as neutralizing agents include organic chlorine compounds such as chlorinated paraffin, chlorinated diphenyl, chlorinated ethane, chlorinated polyethylene, chlorinated polyphenyl, chlorinated diphenyl, vinyl chloride, perchlorocyclopentadecanone, tetrachlorobisphenol A, tris(chloroethyl) phosphate, tris(dichloropropyl) phosphate, tris(β-chloropropyl) phosphate, etc.; organic bromine compounds such as brominated paraffin, brominated polyphenyl, tetrabromoethane, tetrabromobenzene, decabromodiphenyl oxide, octabromodiphenyl oxide, hexabromocyclododecane, bis(tribromophenoxy) ethane, ethylenebistetrabromophthalimide, hexabromobenzene, polydibromophenylene oxide, tetrabromobisphenol A, tris(2,3-dibromopropyl-1) isocyanurate, tribromophenol allyl ether, brominated polystyrene, tribromoneopentyl alcohol, dibromodichloropropane, dibromotetrafluoroethane, tris(tribromophenyl) phosphate, tris(tribromoneopentyl) phosphate, etc.; and organic fluorine compounds such as polytetrafluoroethylene, perfluoroalkoxyalkane, perfluoroethylene propene copolymer, ethylene tetrafluoroethylene copolymer, ethylene chlorotrifluoroethylene copolymer, polyvinylidene fluoride, polychlorotrifluoroethylene, etc. Further, in the present invention, examples of the phosphate esters used as neutralizing agents include triphenyl phosphate (TPP), tricresyl phosphate (TCP), trixylenyl phosphate (TXP), cresyl diphenyl phosphate (CDP), xylenyl diphenyl phosphate (XDP), resorcinol-bis-(diphenyl phosphate), 2-ethylhexyl diphenyl phosphate, dimethyl methyl phosphate, triallyl phosphate (Reophos), alkyl phosphate, etc.

[0030] In the mold material composition of the present invention, if the amount (blending amount) of the neutralizing agent as described above is too small, the amount of the alkali component in the water glass neutralized by heating during casting will inevitably be small, and there is a risk that the effects of the present invention cannot be advantageously enjoyed. Therefore, in the present invention, a predetermined neutralizing agent is preferably contained in the mold material composition in such an amount ratio that the decomposition product generated by heating during casting neutralizes the alkali component of the water glass, so that the ratio of the alkali component of the water glass after casting is 15% by mass or less. Particularly when sodium silicate is used as the water glass, by using a neutralizing agent in the above-described amount ratio, the ratio of the alkali component (Na 2 +Na 2 O) in the solid content (SiO 2 O) of the refractory aggregate (sand) recovered after casting in the water glass is 15% by mass or less, the water glass solidifies, and the alkali component (Na 2 O) is no longer eluted from the solidified water glass, making it possible to more advantageously enjoy the effects of the present invention. Regarding the solidification of the water glass (sodium silicate), those skilled in the art can technically understand it in view of the conventionally known Na 2 O - SiO 2 phase diagram. The Na 2 O - SiO 2 phase diagram can be confirmed on the homepage of Tosoh Sangyo Co., Ltd. (URL: http: / / www.toso-sangyo.com / products / keisansoda2#2.html. However, "#" indicates a half-width underscore.) and in a plurality of papers (for example, Kracek F.C., "The System Sodium Oxide - Silica", J. Phys. Chem., 34, p. 1583 - 1598 (1930)). Further, in the present invention, it is desirable that the neutralizing agent is not added in an amount exceeding the amount ratio such that the ratio of the alkali component in the water glass becomes 0% by mass by heating during casting.

[0031] Incidentally, in the mold material composition of the present invention, in addition to the above-described predetermined neutralizing agent, various known additives can be appropriately contained in the mold material composition as needed. Examples of such additives include surfactants, lubricants, inorganic oxide particles, carbonates and / or borates, and moisture resistance improvers.

[0032] By adding a surfactant to the mold material composition of the present invention, the water permeability, in other words, the wettability of the mold material composition to water, can be improved. Particularly for a mold material composition in a dry state, when moisture is supplied during mold shaping, the surfactant mediates between the supplied moisture and water glass, so that even a small amount of moisture can effectively wet the entire mold material composition. Thus, 1) it becomes possible to suppress the water supply time to the mold material composition (for example, when supplying moisture by water vapor, the ventilation time of the water vapor) to the minimum necessary, and 2) as a result of suppressing the amount of moisture supplied to the mold (molding cavity) to a small amount, in the case of the molded mold, in addition to excellent mold release property from the mold, effects such as exhibiting excellent strength can be advantageously enjoyed.

[0033] In the present invention, the amount of the surfactant contained in the mold material composition is desirably 0.1 to 20.0 parts by mass, preferably 0.5 to 15.0 parts by mass, and particularly preferably 0.75 to 12.5 parts by mass with respect to 100 parts by mass of the solid content of water glass. If the amount of the contained surfactant is too small, there is a risk that the above-described effects cannot be advantageously enjoyed. On the other hand, even if the amount of the surfactant is too large, no improvement in the effect corresponding to the usage amount is recognized, and furthermore, it is not a good measure from the viewpoint of cost effectiveness.

[0034] 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. Specifically, examples of the cationic surfactant include aliphatic amine salts, aliphatic quaternary ammonium salts, benzalkonium salts, benzethonium chloride, and the like. Examples of the anionic surfactant include fatty acid soaps, N-acyl-N-methylglycine salts, N-acyl-N-methyl-β-alanine salts, N-acylglutamic acid salts, alkyl ether carboxylates, acylated peptides, alkyl sulfonates, alkylbenzene sulfonates, alkylnaphthalene sulfonates, dialkyl sulfosuccinate ester salts, alkyl sulfacetates, α-olefin sulfonates, N-acylmethyl taurine, sulfated oils, higher alcohol sulfate ester salts, secondary higher alcohol sulfate ester salts, alkyl ether sulfates, secondary higher alcohol ethoxysulfates, polyoxyethylene alkyl phenyl ether sulfate salts, monoglyceride sulfates, fatty acid alkanolamide sulfate ester salts, alkyl ether phosphate ester salts, alkyl phosphate ester salts, and the like. Further, examples of the amphoteric surfactant include carboxy betaine type, sulfo betaine type, aminocarboxylates, imidazolinium betaine, and the like.In addition, examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene secondary alcohol ethers, polyoxyethylene alkyl phenyl ethers (e.g., Emulgen 911), polyoxyethylene sterol ethers, polyoxyethylene lanolin derivatives, polyoxyethylene polyoxypropylene alkyl ethers (e.g., Newpol PE-62), polyoxyethylene glycerin fatty acid esters, polyoxyethylene castor oil, hydrogenated castor oil, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, polyethylene glycol fatty acid esters, fatty acid monoglycerides, polyglycerin fatty acid esters, sorbitan fatty acid esters, propylene glycol fatty acid esters, sucrose fatty acid esters, fatty acid alkanolamides, polyoxyethylene fatty acid amides, polyoxyethylene alkyl amines, alkyl amine oxides, acetylene glycol, acetylene alcohol, and the like.

[0035] Among various surfactants, those having a siloxane structure as a nonpolar part are particularly called silicone-based surfactants, and those having a perfluoroalkyl group are called fluorine-based surfactants. Among them, examples of silicone-based surfactants include polyester-modified silicone, acrylic-terminated polyester-modified silicone, polyether-modified silicone, acrylic-terminated polyether-modified silicone, polyglycerin-modified silicone, aminopropyl-modified silicone, and the like. Examples of fluorine-based surfactants include perfluoroalkyl sulfonates, perfluoroalkyl carboxylates, perfluoroalkyl phosphates, perfluoroalkyl trimethylammonium salts, perfluoroalkyl ethylene oxide adducts, perfluoroalkyl group-containing oligomers, and the like.

[0036] In the present invention, various surfactants as described above can be used alone or in combination of two or more. However, depending on the surfactant, there are some that may react with water glass and may cause a decrease or even disappearance of the surfactant performance over time. Therefore, anionic surfactants, nonionic surfactants, and silicone-based surfactants that do not react with water glass are particularly advantageously used in the mold material composition of the present invention.

[0037] In the present invention, it is preferable to add a lubricant as an additive and make it present on the surface of the refractory aggregate of the mold material composition. Due to the presence of such a lubricant, the fluidity of the mold material composition can be advantageously improved.

[0038] Here, the amount of the lubricant contained in the mold material composition according to the present invention is desirably 0.1 to 10 parts by mass, preferably 0.3 to 8 parts by mass, and particularly preferably 0.5 to 5 parts by mass with respect to 100 parts by mass of the solid content of water glass. If the amount of the contained lubricant is too small, there is a risk that the above-described effects cannot be advantageously enjoyed. On the other hand, if the amount of the lubricant is too large, the mold strength will decrease, and furthermore, it is not a good measure from the viewpoint of cost-effectiveness.

[0039] Examples of the lubricant used in the present invention include waxes such as paraffin wax, synthetic polyethylene wax, and montan wax; fatty acid amides such as stearic acid amide, oleic acid amide, and erucic acid amide; alkylene fatty acid amides such as methylene bisstearic acid amide and ethylene bisstearic acid amide; stearic acid and stearyl alcohol; metal stearates such as lead stearate, zinc stearate, calcium stearate, and magnesium stearate; and stearic acid monoglyceride, stearyl stearate, and hydrogenated oil. Among these, calcium stearate and the like are particularly advantageously used.

[0040] In addition, the mold material composition of the present invention can also contain inorganic oxide particles. By containing inorganic oxide particles in the mold material composition, it is possible to improve the fluidity and filling properties of the mold material composition, and furthermore, 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 refractory aggregate constituting the mold material composition. Specifically, inorganic oxide particles having an average particle diameter of 0.01 μm or more and 300 μm or less, more preferably 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. This average particle diameter can be determined from the particle size distribution measured by a laser diffraction type particle size distribution measuring device or the like. In addition, the content of the inorganic oxide particles in the mold material composition is generally in the range of 5 to 200 parts by mass, preferably 10 to 100 parts by mass, based on 100 parts by mass of the solid content of the binder containing water glass as an essential component therein.

[0041] In addition, the inorganic oxide particles used in the present invention may be spherical particles or non-spherical particles. However, using spherical particles allows for more advantageously enjoying the compounding effects of the above-described inorganic oxide particles. In addition, it is preferable in that it enables obtaining a casting product having a better casting surface. Such spherical particles only need to exhibit sphericity to a generally recognized degree and do not necessarily need to exhibit a perfect spherical shape. Usually, those with a sphericity of 0.5 or more, preferably 0.7 or more, and more preferably 0.9 or more are advantageously used. Here, the sphericity means the average value of the aspect ratio (the ratio of the minor axis to the major axis) obtained from the projected shape by randomly selecting 10 single particles and observing them using a scanning electron microscope. When inorganic oxide particles that are not spherical are used, since there are protrusions and depressions on the surface of such inorganic oxide particles, for example, when the inorganic oxide particles attempt to flow between refractory aggregates together with a binder containing water glass that has become a solution due to the supplied moisture, the protrusions on the surface of the inorganic oxide particles collide with the refractory aggregates or other inorganic oxide particles, resulting in an anti-slip effect, which hinders the flow of the binder and the inorganic oxide particles between the refractory aggregates. As a result, there is a risk of reducing the filling property and strength of the finally obtained mold.

[0042] Also, the material constituting such inorganic oxide particles is not particularly limited, but it is preferably an inorganic metal oxide. As particles composed of this inorganic metal oxide, particles composed of silicon dioxide, aluminum oxide, titanium oxide, etc. are advantageously used. Among them, in particular, silicon dioxide particles are preferable in that a binder containing strongly alkaline water glass can react with silanol groups formed on the surface of silicon dioxide, and a strong bond is formed between the silicon dioxide and the solidified binder during the evaporation of water, which can improve the mold strength. Note that silicon dioxide has crystalline and amorphous forms, and the amorphous form is more desirable. As amorphous silicon dioxide, precipitated silica, calcined silica produced by electric arc or flame hydrolysis in an electric arc, ZrSiO4 Examples thereof include silica produced by thermal decomposition, silicon dioxide produced by oxidizing metallic silicon with a gas containing oxygen, and quartz glass powder which is spherical particles produced from crystalline quartz by melting and subsequent rapid cooling. Needless to say, these can be used alone, and it is also possible to use a mixture of two or more of them. In the present invention, silicon dioxide shall be treated as an inorganic metal oxide. Further, silicone resin particles may be added instead of or in combination with the inorganic oxide particles.

[0043] In the mold material composition of the present invention, it is preferable to use at least one of carbonate and borate. The carbonate releases carbon dioxide due to the heat generated by molding and casting, generates cracks in the bonding film of water glass, and breaks the bonding film of water glass, thereby making it easier to collapse the mold. At the same time, the generated carbon dioxide becomes carbonic acid, a weak acid, due to the moisture in the water glass, and can promote the neutralization of the alkaline component of the water glass. On the other hand, the borate reacts with the hydroxyl group (-OH) in the water glass and the tetraborate ion or metaborate ion generated from the borate due to the heat generated by molding and casting, and blocks the hydroxyl group (-OH) in the water glass, making it difficult to redissolve, and thus can prevent the softening of the bonding film of the water glass. From these facts, the collapsibility of the mold molded using the mold material composition can be further improved, and the moisture resistance of the mold can be improved, and the strength deterioration due to moisture absorption can be suppressed.

[0044] In the present invention, the amount of the carbonate and / or borate as described above contained in the mold material composition is desirably 0.5 to 50 parts by mass, preferably 1 to 20 parts by mass, and particularly preferably 2 to 15 parts by mass with respect to 100 parts by mass of the solid content of the water glass. If the amount of the carbonate and / or borate contained is too small, there is a risk that the above-described effects cannot be advantageously enjoyed. On the other hand, even if the amount of the carbonate and / or borate is too large, no improvement in the effect corresponding to the amount used is recognized, and further, from the viewpoint of cost effectiveness, it is not a good measure. The carbonate and the borate may be used in combination.

[0045] Here, examples of such carbonates include zinc carbonate, basic zinc carbonate, iron carbonate, manganese carbonate, copper carbonate, aluminum carbonate, barium carbonate, magnesium carbonate, calcium carbonate, lithium carbonate, potassium carbonate, sodium carbonate, and the like. Examples of such borates include sodium tetraborate, potassium tetraborate, lithium tetraborate, ammonium tetraborate, calcium tetraborate, strontium tetraborate, silver tetraborate, sodium metaborate, potassium metaborate, lithium metaborate, ammonium metaborate, calcium metaborate, silver metaborate, copper metaborate, lead metaborate, magnesium metaborate, and the like. Among them, basic zinc carbonate, sodium tetraborate, and potassium metaborate are preferably used.

[0046] In the present invention, as other additives, a moisture resistance improver may be further contained. By incorporating a moisture resistance improver into the water glass, it is possible to improve the moisture resistance of the finally obtained mold. As the moisture resistance improver used in the present invention, any material can be used as long as it has been conventionally used in mold material compositions such as coated sand and does not inhibit the effects of the present invention. Specifically, sulfates such as sodium sulfate, potassium sulfate, lithium sulfate, magnesium sulfate, calcium sulfate, strontium sulfate, barium sulfate, titanium sulfate, aluminum sulfate, zinc sulfate, and copper sulfate; phosphates such as sodium phosphate, sodium hydrogen phosphate, potassium phosphate, potassium hydrogen phosphate, lithium phosphate, lithium hydrogen phosphate, magnesium phosphate, calcium phosphate, titanium phosphate, aluminum phosphate, and zinc phosphate; hydroxides such as lithium hydroxide, magnesium hydroxide, calcium hydroxide, strontium hydroxide, barium hydroxide, aluminum hydroxide, and zinc hydroxide; oxides such as silicon, zinc, magnesium, aluminum, calcium, lithium, copper, iron, boron, and zirconium can be exemplified. Among them, lithium sulfate and lithium hydroxide are particularly advantageous in improving moisture resistance. The moisture resistance improvers including those described above can of course be used alone, and it is also possible to use two or more of them in combination.

[0047] In addition, as the amount of such a moisture resistance improver used, generally, in the total amount, it is preferably about 0.5 to 50 parts by mass with respect to 100 parts by mass of the solid content of the water glass. Among them, 1 to 20 parts by mass is more preferable, and particularly, 2 to 15 parts by mass is even more preferable. In order to favorably enjoy the addition effect of the moisture resistance improver, it is desirable to use an amount of 0.5 part by mass or more. On the other hand, if the addition amount is too large, it may inhibit the bonding of the aggregate by the water glass and cause problems such as a decrease in the strength of the finally obtained mold. Therefore, it is desirable that the amount be 50 parts by mass or less.

[0048] In addition, as other additives, it is also effective to contain a coupling agent that strengthens the bond between the refractory aggregate and water glass. For example, silane coupling agents, zircon coupling agents, titanium coupling agents, etc. can be used. Furthermore, as mold release agents, paraffin, wax, light oil, machine oil, spindle oil, insulating oil, waste oil, vegetable oil, fatty acid esters, organic acids, graphite fine particles, mica, vermiculite, fluorine-based mold release agents, silicone-based mold release agents, etc. can also be used. And these other additives are each contained in an amount such that, generally, the ratio is 5% by mass or less, preferably 3% by mass or less, based on the solid content of water glass.

[0049] By the way, when manufacturing the mold material composition according to the present invention, for example, according to the method described in detail below, 1) a coated sand (CS) in which a coating layer containing a binder having water glass as an essential component and a predetermined neutralizing agent is formed on the surface of a refractory aggregate (sand), which constitutes a mold material composition (hereinafter referred to as "CS (mold material composition) with a one-layer structure"), or 2) a solid first coating layer containing a predetermined neutralizing agent is formed on the surface of a refractory aggregate (sand), and a second coating layer containing a binder having water glass as an essential component is formed on such a first coating layer, and a coated sand (CS) is used to form a mold material composition (hereinafter referred to as "CS (mold material composition) with a two-layer structure").

[0050] (1) Manufacture of "CS (mold material composition) with a one-layer structure" a) When manufacturing a "CS (mold material composition) with a one-layer structure" that does not have room temperature fluidity and exhibits a wet state, generally, water glass as a binder and a predetermined neutralizing agent are kneaded or mixed at room temperature together with additives used as necessary with respect to the refractory aggregate, and uniformly mixed, whereby a film layer of a water glass composition with a high water content (a coating layer containing a binder having water glass as an essential component and a predetermined neutralizing agent) is formed on the surface of the refractory aggregate. This method will be adopted.

[0051] b) On the other hand, when manufacturing a one-layer structured CS (mold material composition) that has room temperature fluidity and exhibits a dry state, generally, for refractory aggregates, water glass as a binder and a predetermined neutralizing agent are kneaded or mixed together with additives used as necessary to be uniformly mixed. Then, the surface of such refractory aggregates is coated with a water glass composition containing a neutralizing agent, etc., and by evaporating the moisture of such a water glass composition, a coating layer of the water glass composition (a coating layer containing a binder having water glass as an essential component and a predetermined neutralizing agent) is formed on the surface of the refractory aggregates. Such a method will be adopted. In such a method, since the evaporation of the moisture in the coating layer needs to be carried out rapidly before the solidification or hardening of the water glass progresses, after charging (mixing) water glass in the form of an aqueous solution to the refractory aggregates, generally within 5 minutes, more preferably within 3 minutes, it is desirable to remove the contained moisture to obtain a dry powdery mold material composition. If the time for such evaporation becomes long, the mixing (kneading) cycle becomes long, and in addition to the productivity of the mold material composition decreasing, the problem that the water glass comes into contact with CO 2 in the air for a long time and may cause problems such as deactivation becomes highly likely.

[0052] c) Further, in the manufacturing process of the one-layer CS (mold material composition) having a dry state as described above, as one of the effective means for rapidly evaporating the moisture in the water glass, a method is preferably adopted in which refractory aggregates are pre-heated in advance, and then water glass or a predetermined neutralizing agent, etc. in the form of an aqueous solution is kneaded or mixed and blended therewith. By kneading or mixing water glass with such pre-heated refractory aggregates, the moisture in the water glass can be evaporated extremely rapidly by the heat of such refractory aggregates. Thus, the moisture content of the obtained mold material composition can be effectively reduced, and a dry powder having normal-temperature fluidity can be advantageously obtained. Here, the pre-heating temperature of the refractory aggregates will be appropriately selected according to the moisture content and blending amount of the water glass, etc. Generally, a temperature of about 100 to 160°C, preferably about 100 to 140°C, is adopted. If this pre-heating temperature is too low, moisture evaporation cannot be effectively carried out, and drying will take a long time. Therefore, it is desirable to adopt a temperature of 100°C or higher. On the other hand, if the pre-heating temperature is too high, when the obtained mold material composition is cooled, solidification or hardening of the water glass component will progress, and in addition, composite granulation will proceed, which will cause problems in the functions of the mold material composition, especially the physical properties such as the strength of the finally obtained mold.

[0053] d) In the method for manufacturing the mold material composition described above, neutralizing agents contained in the coating layer together with water glass, and other additives used as necessary, such as surfactants and lubricants, etc., may be added to the refractory aggregate in a state of being previously mixed with water glass and kneaded, or may be added separately from water glass during kneading and kneaded, or further, during kneading, a time difference may be provided with respect to the introduction of water glass and added and kneaded. Therefore, the coating layer in the dry mold material composition of the present invention is, for example, in a state where water glass and a neutralizing agent, etc. are mixed, or in a state where, from the surface of the refractory aggregate outward, while the concentration of the solid content (non-volatile content) of water glass gradually decreases or increases, the concentration of the neutralizing agent, etc. gradually increases or decreases, and is formed in such a form. Further, water glass as a binder may be diluted with water in order to adjust its viscosity. Also, there is no problem even if water glass and water are added separately during kneading or mixing.

[0054] (2) Manufacture of "CS (mold material composition) with a two-layer structure" - a-1) When manufacturing the "CS (mold material composition) with a two-layer structure", first, a solid first coating layer containing a predetermined neutralizing agent is formed on the surface of the refractory aggregate. Such a first coating layer may be composed only of a predetermined neutralizing agent, or from the perspective of the dispersion of the neutralizing agent and the isolation from water glass, it is also possible to configure the first coating layer to contain a predetermined neutralizing agent and an organic compound. When the molten metal is poured into a mold made of such a mold material composition in which an organic compound is contained in the first coating layer located directly above the refractory aggregate, the organic compound contained in the first coating layer thermally decomposes and gasifies, and the generated gas advantageously breaks the solidified or cured product of water glass at the joint portion between the refractory aggregate particles, and the collapsibility of the mold becomes excellent. Further, when the organic compound contained in the first coating layer thermally decomposes and gasifies, due to the internal pressure of the gas, the solidified or cured product of water glass present on the refractory aggregate particles is broken from the inside (from the refractory aggregate side). Therefore, for example, in the polishing process when regenerating the refractory aggregate (sand) recovered from the mold after casting, it becomes easier to peel off the solidified or cured water glass from the surface of the casting sand particles, and the regeneration of the sand becomes easy. Furthermore, during casting using the mold, since gas is generated by the thermal decomposition of the organic compound contained in the first coating layer, a gas layer that suppresses the molten metal from entering between the refractory aggregate particles constituting the mold is advantageously formed between the mold surface and the casting product, and thus, there is an advantage that the surface of the finally obtained casting product is good. When using a neutralizing agent such as a phosphate ester that reacts with water glass to promote curing, it is preferable to form a first coating layer containing such a neutralizing agent and an organic compound. In the CS (mold material composition) with a two-layer structure in which such a neutralizing agent and water glass are present in different layers, it is possible to prevent the curing from proceeding more than necessary due to the reaction between the neutralizing agent and water glass.

[0055] a-2) In the present invention, the film thickness of the solid first coating layer formed on the surface of the refractory aggregate is 0.1 to 6 μm, preferably 0.2 to 5 μm, more preferably 0.3 to 3 μm, and still more preferably 0.5 to 2 μm. If the film thickness is less than 0.1 μm, it is difficult to form as a coating layer, and there is a possibility that it may be difficult to gasify inside the second coating layer made of a binder composition containing water glass. On the other hand, if it is more than 6 μm, there is a possibility that odor may be generated by the organic compound. As a method for measuring the film thickness of the first coating layer, refractory aggregate particles on which the first coating layer is formed are embedded in an epoxy resin or the like, and the cross-section of the cast sand particles cut using a cutting device such as an ion cutter is observed using an optical instrument such as an optical microscope or an electron microscope. Ten points of cross-section particles are randomly selected, and methods such as measuring the film thickness of the coating layer can be mentioned. Regarding the film thickness, when the refractory aggregate particles are spherical, it may be calculated from the average particle diameter of the refractory aggregate particles and the addition amounts of the refractory aggregate particles and the organic compound.

[0056] a-3) Further, the organic compound used in the present invention is not particularly limited as long as it can form a solid coating layer on the surface of the refractory aggregate particles, and can form a solid coating layer together with a predetermined neutralizing agent. However, it is preferably at least one selected from the group consisting of crosslinkable curable resins and their cured products, thermoplastic resins, and carbohydrates. Among these organic compounds, crosslinkable curable resins and their cured products are advantageously used from the viewpoint of maintaining the strength of the coated sand (CS).

[0057] a-4) The crosslinkable and curable resin is a resin that exhibits crosslinkable and curable properties under heating or non-heating (room temperature) conditions, with or without the presence of a curing agent or curing catalyst such as hexamethylenetetramine, organic ester, organic acid, carbon dioxide gas, peroxide, metal ion, amine, etc., and binds refractory aggregate particles to each other to form a mold. Specific examples of such crosslinkable and curable resins include phenolic resins, phenol urethane resins, epoxy resins, melamine resins, unsaturated polyester resins, polyfunctional acrylamide resins (see Japanese Patent Publication No. 7-106421), unsaturated alkyd resins, unsaturated fatty acid-modified alkyd resins, diallyl phthalate resins, and resins obtained by combining these resins as necessary. Among these, from the viewpoint of more advantageously enjoying the effects of the present invention, novolak-type or resol-type phenolic resins and phenol urethane resins used in combination with polyisocyanate compounds are particularly preferred.

[0058] a-5) In addition, the cured product of the crosslinkable and curable resin is obtained by increasing the molecular weight to a high molecular compound by subjecting a low molecular weight crosslinkable and curable resin to a curing reaction. After coating the surface of casting sand particles with a low molecular weight material having a low melt viscosity, it is cured by heating or adding a curing agent, thereby preventing alkali deterioration and forming a high molecular weight coating layer with good surface stability, enabling both coating properties and surface stability. Further, compared with the uncured crosslinkable and curable resin, the cured product of the crosslinkable and curable resin has the following advantages: 1) softening of the coating layer due to heat is suppressed, improving the mold strength; 2) since the heat required for curing is consumed in advance, heat is effectively used for thermal decomposition, accelerating the thermal decomposition, and further improving the collapsibility of the mold; and 3) since the gas generated during curing is released in advance, the amount of gas generated during casting can be suppressed.

[0059] a-6) Further, specific examples of the thermoplastic resin include resins such as polyvinyl alcohol, polyvinyl acetate, polystyrene, styrene acrylonitrile copolymer, styrene-butadiene-acrylonitrile copolymer, ethylene vinyl acetate copolymer, polymethyl methacrylate, methacryl-styrene copolymer, cellulose acetate, polycarbonate, and polyvinyl chloride. Among them, from the viewpoint of solvent solubility (film-forming property), polyvinyl alcohol, polyvinyl acetate, polystyrene, ethylene vinyl acetate copolymer, polymethyl methacrylate, cellulose acetate, and polycarbonate are particularly preferred.

[0060] a-7) Furthermore, specific examples of the carbohydrate include those composed of glucose, fructose, galactose, lactose, sucrose, maltose, trehalose, starch, glycogen, cellulose, etc. Among them, from the viewpoint of film-forming property, trehalose, starch, and glycogen are particularly preferred. In addition, examples of other organic compounds include acrylamide, N-methylolacrylamide, diacrylamidodimethyl ether, methylenebisacrylamide, ethylenebisacrylamide, ethylene glycol diacrylamide, etc.

[0061] a-8) In the present invention, the organic compound contained in the first coating layer on the surface of the refractory aggregate particles is preferably a high molecular compound (polymer, multimer) from the viewpoint of the coating property on the refractory aggregate particles. Specifically, a high molecular compound (polymer, multimer) having a weight average molecular weight of 300 or more, preferably 300 to 100000000, more preferably 500 to 50000000, and still more preferably 800 to 20000000 is advantageously used. Even an organic compound not included in the category of high molecular compounds (polymers, multimers) is preferably one having a molecular weight of 300 or more from the viewpoint of the surface stability of the solid coating layer, and preferably one having a molecular weight of 100000000 or less from the viewpoint of the coating property on the refractory aggregate particles.

[0062] a-9) Further, in the present invention, water-insoluble or even water-insoluble organic compounds are preferably used. In particular, water-insoluble organic compounds are suitable as the organic compounds contained in the solid first coating layer. This is because if a water-soluble organic compound is used, the organic compound may dissolve into the moisture contained in the second coating layer composed of a liquid binder composition containing water glass, which is coated on the surface of the first coating layer, and there is a risk that the first coating layer may not be maintained in a solid state. Specifically, in the present invention, an organic compound having a solubility of 1% by mass or less, preferably 0.5% by mass or less, more preferably 0.3% by mass or less, and still more preferably 0.1% by mass or less in 100 g of water at 25°C is used as the organic compound contained in the solid coating layer. The solubility means the amount of the organic compound dissolved in the solvent (water) when 10 g of the organic compound is added to 100 g of water at 25°C, stirred for 1 hour, and then allowed to stand for 1 hour. A water-insoluble organic compound is an organic compound that does not dissolve in water.

[0063] b) In the present invention, when forming a solid layer composed of only a predetermined neutralizing agent as the first coating layer on the surface of the refractory aggregate, as the method, from among various conventionally known methods, one corresponding to the form and characteristics of the neutralizing agent, etc. is appropriately selected and adopted. For example, when the neutralizing agent has the property of melting without decomposing at a temperature lower than the temperature at which it is heated during casting (hereinafter referred to as the said temperature in this paragraph), the refractory aggregate and the neutralizing agent are mixed in a state heated to the said temperature, and a layer of the melted neutralizing agent is formed on the surface of the refractory aggregate. Then, by cooling, it is possible to form a solid first coating layer composed of the neutralizing agent on the surface of the refractory aggregate.

[0064] c-1) On the other hand, even when forming a solid layer containing a predetermined neutralizing agent and an organic compound as the first coating layer on the surface of the refractory aggregate, among various conventionally known methods, those suitable according to the form, properties, etc. of the neutralizing agent and the organic compound are appropriately selected and adopted. Specifically, the dry hot coat method, the cold coat method, etc. can be exemplified, but as long as it is a method capable of forming a solid coating layer, the method is not particularly limited.

[0065] c-2) The dry hot coat method is a method in which a solid organic compound and a predetermined neutralizing agent are added to and mixed with a refractory aggregate heated to 130 to 180°C, the solid organic compound is melted by the heat of the refractory aggregate, the surface of the refractory aggregate is coated with the melted organic compound, and then the mixture is cooled while maintaining this mixing to form a solid coating layer containing the organic compound and the predetermined neutralizing agent on the surface of the refractory aggregate. The cold coat method is a method in which the organic compound is used as it is or dissolved in a solvent such as methanol to make it liquid, a predetermined neutralizing agent is contained in the liquid, added to and mixed with the refractory aggregate, and the solvent is volatilized, etc. to form a solid coating layer containing the organic compound and the predetermined neutralizing agent on the surface of the refractory aggregate.

[0066] c-3) Further, when using a crosslinkable curable resin as the organic compound, for example, after forming a solid first coating layer according to the coating method described above, the crosslinkable curable resin may be cured by further heating and / or by adding a curing agent or a curing catalyst to increase the molecular weight of the crosslinkable curable resin contained in the first coating layer. When curing the crosslinkable curable resin by heating, for example, it can be put into a constant temperature bath at 120°C to 300°C and reaction-cured for about 5 to 60 minutes, or the casting sand can be heated to 150°C to 300°C and kneaded for about 5 to 60 minutes with a kneader heated to 120°C to 300°C for reaction curing. In addition, since the cured mold material composition containing the crosslinkable curable resin in the coating layer has a strong neck between refractory aggregate particles (sand grains) and may form a single mass or composite particles, in order to make the surface state of the refractory aggregate coated with the first coating layer good, it is preferable to react and cure with a high-speed kneader (speed muller) with kneading and a high rotation speed. Also, since peeling may occur and fine powder may be generated when kneading for a long time, it is preferable to react at a high temperature for a short time. On the other hand, when curing the crosslinkable curable resin using a curing agent or a curing catalyst, as such a curing agent or curing catalyst, for example, hexamethylenetetramine, organic ester, organic acid, carbon dioxide gas, peroxide, metal ion, amine, etc. are used. Also, when the crosslinkable curable resin is a phenol urethane-based resin, it is also possible to cure it by mixing a phenol resin and a polyisocyanate resin. Even when curing the crosslinkable curable resin using a curing agent, it is desirable to react and cure while kneading with a kneader.

[0067] d) When manufacturing a "two-layer CS (mold material composition)" that has no normal-temperature fluidity and exhibits a wet state, using either refractory aggregate formed on a surface where a solid first coating layer consisting of only a predetermined neutralizing agent is formed, or refractory aggregate formed on a surface where a solid first coating layer containing a predetermined neutralizing agent and an organic compound is formed, according to the method described above, it is manufactured, for example, according to the following procedure. That is, water glass as a binder is kneaded or mixed, together with additives as necessary, uniformly with the refractory aggregate provided with the first coating layer, so that a mold material composition is obtained, which is a mixture of a refractory aggregate provided with a solid first coating layer containing a predetermined neutralizing agent and a liquid binder composition containing water glass. In other words, a mold material composition is obtained in which a second coating layer consisting of a binder composition containing water glass is formed so as to cover the first coating layer on the surface of the refractory aggregate. Various conditions during mixing are appropriately determined according to the type and moisture content of the water-soluble inorganic binder in aqueous solution. Also, the temperature during mixing is generally about normal temperature to 40 °C. When manufacturing a mold material composition that exhibits a wet state according to the present invention, the water content thereof is adjusted so that the obtained mold material composition exhibits an appropriate wet state. Specifically, it is adjusted to be more than 55% by mass of the solid content of water glass, preferably 70 to 900% by mass, more preferably 95 to 500% by mass. In the mold material composition that exhibits a wet state according to the present invention and has the water content adjusted in this way, when filling the mold during mold shaping, the blow air prevents the mold material composition that exhibits a wet state from drying and blocking, and enables the wetness of the mold material composition to be maintained. In addition, excellent properties are imparted to the mold shaped using such a mold material composition. The water content of the mold material composition can be measured by the Karl Fischer method or by the change in weight when heated in a dryer or the like.

[0068] e) On the other hand, when manufacturing a "CS (mold material composition) with a two-layer structure" that has normal-temperature fluidity and exhibits a dry state using refractory aggregates with a solid first coating layer, it can be manufactured according to the same method as detailed in item 'b)' in the column of '(1) Manufacturing of "CS (mold material composition) with a one-layer structure)". Specifically, water glass as a binder is kneaded or mixed with refractory aggregates having a first coating layer formed thereon, together with additives used as necessary, to be uniformly mixed, and the surface of the first coating layer in such refractory aggregates is coated with a water glass composition, and by evaporating the moisture in such a water glass composition, a coating layer of the water glass composition (a second coating layer containing a binder having water glass as an essential component) is formed as the outermost layer on the surface of the refractory aggregates. In such a method, since the evaporation of the moisture in the second coating layer needs to be carried out rapidly before the solidification or hardening of the water glass progresses, after introducing (mixing) water glass in the form of an aqueous solution into the refractory aggregates, generally within 5 minutes, more preferably within 3 minutes, it is desirable to remove the contained moisture to obtain a dry powdery mold material composition. If the time for such evaporation becomes long, the mixing (kneading) cycle becomes long, and in addition to the productivity of the mold material composition decreasing, there is a high risk of problems such as the water glass being in contact with CO 2 in the air for a long time and deactivating.

[0069] f) In addition, in the above-mentioned '(2) Manufacturing of "CS (mold material composition) with a two-layer structure)", various additives such as surfactants used as necessary can be contained in the first coating layer or the second coating layer according to the purpose of use of each additive, and depending on the type of additive, it is also possible to contain it in both the first coating layer and the second coating layer.

[0070] By the way, as a method of molding a mold using the mold material composition exhibiting a wet state according to the present invention, for example, first, such a mold material composition is filled into the molding cavity of a molding die that gives the target mold, and the molding die is heated and held at a temperature of 80 to 300 ° C, preferably 100 to 200 ° C, and held in the molding die until the filled mold material composition dries. By such heating and holding in the molding die, solidification or hardening of the filled mold material composition in a wet state proceeds, and the target mold can be obtained.

[0071] That is, by filling and holding a mold material composition in a wet state in the cavity of the molding die heated to the above temperature, the refractory aggregate particles constituting the mold material composition are mutually bonded and connected via the water glass contained in the binder composition existing around, and an aggregate (bond) of refractory aggregates exhibiting an integral mold shape is formed. At this time, as an additive for accelerating the hardening of water glass, a predetermined hardening agent may be introduced into the cavity in a liquid state or a gaseous state. Note that water glass usually solidifies by evaporation and drying of water if no additive is added, and hardens when a hardening agent is added. In the present invention, the mold composed of an aggregate (bond) of coated sand includes both such coated sand that is simply solidified (solidified product) and that hardened by a hardening agent (hardened product).

[0072] When heating a mold material composition in a wet state within the cavity of a mold, it is preferably done by first preparing a mold that has been preheated to a predetermined temperature and maintained at that temperature, and then filling the cavity of such a mold with the mold material composition to heat the mold material composition. In this way, by preheating the mold, it is possible to accelerate the drying of the mold material composition and shorten the molding time. The holding temperature for this preheating is 80 to 300°C, preferably 100 to 200°C, more preferably 120 to 180°C. From the viewpoints of accelerating drying and shortening the molding time, and improving the moisture resistance strength with additives, it is preferable that such a holding temperature is 80°C or higher. Also, from the viewpoint of preventing the problem that moisture evaporates before sufficient bonding is formed between refractory aggregate particles and the mold strength cannot be developed, it is preferable that it is 300°C or lower. By heating the mold at a temperature within such a temperature range, it is possible to improve the moisture resistance strength of the finally obtained mold, and the drying of the mold material composition can be advantageously advanced.

[0073] Furthermore, in order to promote the evaporation of water during the retention of the mold material composition in the mold, a method of blowing hot air or superheated steam into the mold and ventilating the filled phase (mold material composition) in the mold is preferably employed. By such ventilation of hot air or superheated steam, the interior of the filled phase composed of the mold material composition can be rapidly dried, and the solidification or hardening of such a filled phase can be promoted more advantageously, thereby advantageously increasing the solidification (hardening) rate and also advantageously enhancing the properties such as the flexural strength of the obtained mold. In addition, it can also contribute advantageously to shortening the molding time of the mold. Also, during the retention of the mold material composition in the mold, in order to more advantageously promote the solidification or hardening of the mold material composition, a method of blowing a carrier gas composed of at least one of carbon dioxide, argon, nitrogen, and helium into the mold and ventilating the filled phase is preferably employed. At that time, carbon dioxide acts as a hardening agent, and argon, nitrogen, and helium act as solidification accelerators, respectively. By allowing such a carrier gas to act on the water-soluble inorganic binder, it is possible to further promote the solidification or hardening of the mold material composition. It should be noted that either only one of the ventilation of hot air or superheated steam and the ventilation of the carrier gas may be carried out, but it is also possible to carry out both of them. In that case, methods such as simultaneously carrying out the ventilation of hot air or superheated steam and the ventilation of the carrier gas, ventilating the carrier gas after the ventilation of hot air or superheated steam, or ventilating hot air or superheated steam after the ventilation of the carrier gas are employed. In short, after filling the cavity of the mold with the mold material composition in a wet state, during the retention in the mold, ventilation of hot air, etc. and / or the carrier gas can be carried out at any timing without any problem.

[0074] Also, regarding the molding of a mold using the wet mold material composition according to the present invention, in addition to the method of heating in the mold as described above, a method of solidifying or hardening the mold material composition by introducing the hardening agent described above into the mold, or a method of solidifying or hardening the mold material composition by reducing the pressure in the mold filled with the mold material composition can also be employed.

[0075] Here, the introduction of the curing agent into the mold is to cause the curing to proceed by the reaction between the curing agent and another binder (for example, a water-soluble inorganic binder) used in combination with water glass. As a method for introducing the curing agent, a method of adding the curing agent to the mold material composition before filling it into the mold and filling the mold material composition to which such a curing agent is added into the mold, and a method of introducing the curing agent by ventilating it as a carrier gas to the mold material composition filled into the mold can both be adopted. Also, while being held in the mold, the curing by the curing agent proceeds. At that time, in order to promote the evaporation of water, it is also effective to blow hot air or superheated steam into the mold. Furthermore, in order to more advantageously promote the solidification or curing of the mold material composition, it is also possible to blow a carrier gas composed of at least one of carbon dioxide, argon, nitrogen, and helium into the mold. When adding the curing agent, heating of the mold is not necessarily required, but in order to more advantageously promote the solidification or curing, it is preferable to heat the mold.

[0076]

[0077] ​In addition, the method of reducing the pressure inside the mold aims to dry and solidify the coated sand filled in the cavity of the mold by such pressure reduction. Examples of this pressure reduction method include the method of reducing the pressure inside the mold by known suction means. When reducing the pressure of the mold, heating of the mold is not necessarily required, but in order to more advantageously promote solidification or hardening, it is preferable to heat the mold.

[0078] On the other hand, when molding the target mold using a mold material composition in a dry state, for example, the following two methods can be adopted. That is, the first method is to wet the mold material composition in a dry state by kneading it with water at the mold molding site, and fill the wet mold material composition into the molding cavity of the mold that gives the target mold. At the same time, the mold is heated to a temperature of 80 to 300 °C and held in the mold until the filled mold material composition dries. This is the water addition method. The second method is a method in which after filling the molding cavity of the mold that gives the target mold with the mold material composition in a dry state, steam is blown into the molding cavity to allow the steam to pass through the filling phase composed of the mold material composition. By this ventilation of steam, moisture is supplied to the mold material composition in a dry state to make it in a wet state (moistened state), and then it is held in the mold heated to 80 to 200 °C until such a wet mold material composition dries. This is the steam ventilation method.

[0079] When making a mold in this way, it is desirable that a mold such as a metal mold or a wooden mold filled with a mold material composition having normal-temperature fluidity and presenting a dry state be preheated. By doing so, the kneading with water and the drying of the mold material composition moistened by water vapor can proceed advantageously. In general, as the preheating temperature, in the first method, a temperature of 80 to 300 °C, preferably 90 to 250 °C, more preferably about 100 to 200 °C is desirable. In the second method, a temperature of 80 to 200 °C, preferably 90 to 150 °C, more preferably about 100 to 140 °C is desirable. If this heat preservation temperature is too high, it becomes difficult for steam to pass through to the surface of the mold. On the other hand, if the temperature is too low, it takes time to dry the molded mold.

[0080] By the way, in the above first method, when kneading (mixing) a mold material composition presenting a dry state and water, after transporting the mold material composition presenting a dry state to the molding site, which is the place for manufacturing the mold, at that molding site, after adding water to make it moist, the obtained mold material composition presenting a wet state is filled into the mold, and in the same way as in the case of molding the previous mold material composition presenting a wet state, the target mold is molded. However, in this case, the step of adding water to the mold material composition presenting a dry state to make it moist is simply to put the mold material composition presenting a dry state and a predetermined amount of water into an appropriate mixer and mix them to moisten the mold material composition, so it can be carried out with extremely simple operations. Even at a molding site with a poor working environment, it can be carried out extremely simply and easily. Also, before adding water, the mold material composition may be preheated to 40 °C to 100 °C in advance and then used. In addition, when adding water, 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. Also, when other additives, etc. are in liquid form, those containing water in the liquid may be used.

[0081] In addition, in the above-described second method, when blowing steam into the mold material composition (filled phase) filled in the molding cavity of the mold, the temperature of the steam is generally about 80 to 150°C, more preferably about 95 to 120°C. When high-temperature steam is used, a large amount of energy is required for its production. Therefore, a steam temperature near 100°C is particularly advantageously adopted. Further, as the pressure of the steam to be vented, a gauge pressure of about 0.01 to 0.3 MPa, more preferably about 0.02 to 0.1 MPa, is advantageously adopted. Furthermore, as the venting time, generally, a venting time from about 2 seconds to about 60 seconds is adopted. This is because if the venting time of the steam is too short, it becomes difficult to sufficiently moisten the surface of the mold material composition in a dry state. Also, if the venting time is too long, there is a risk of problems such as dissolution and outflow of the water glass constituting the coating layer on the surface of the mold material composition (coating layer on the surface of the refractory aggregate).

[0082] Here, in the above-described first method and second method, in order to actively dry the filling phase composed of the wet mold material composition, a technique of blowing hot air or superheated steam into the mold and allowing ventilation through such a filling phase is preferably employed. By such ventilation of hot air or superheated steam (such as hot air), the inside of the filling phase of the mold material composition can be quickly dried, and the solidification or hardening of such a filling phase can be promoted more advantageously, thereby advantageously increasing the hardening speed and also advantageously enhancing the properties such as the flexural strength of the obtained mold. In addition, it can also advantageously contribute to shortening the molding time of the mold. Further, in the first method, for example, before ventilation of hot air or the like, and in the second method, for example, between ventilation of steam and ventilation of hot air or the like, in order to more advantageously promote the solidification or hardening of the filling phase, the above-described hardening agent may be made gaseous or atomized and ventilated, and by neutralizing water glass (and other water-soluble inorganic binders) with this hardening agent, it is possible to further promote its solidification or hardening. It should be noted that the ventilation of the hardening agent may be carried out simultaneously with the ventilation of hot air or the like in the first method, simultaneously with the ventilation of steam in the second method, or simultaneously with the ventilation of hot air or the like without any problem. Also, as another method of actively drying the filling phase, the inside of the mold may be depressurized. By such depressurization, the mold material composition filled in the cavity of the mold is dried and solidified. Examples of the depressurization method include techniques such as depressurizing the inside of the mold by known suction means. Also, when depressurizing the inside of the mold, hot air or superheated steam may be blown into the mold to promote the evaporation of water without any problem.

[0083] Moreover, regardless of whether the mold is obtained by the above-described manufacturing method or other manufacturing methods using a mold material composition in a wet or dry state according to the present invention, it is possible to advantageously enjoy the excellent effects described below. That is, when such a mold is used for casting, the mold is heated by the molten metal (generally heated to a temperature exceeding 300°C), and the decomposition products generated from the neutralizing agent by such heating cause a neutralization reaction with the alkali component of the water glass, whereby the water glass becomes physically fragile and the collapsibility of the mold after casting becomes good. Further, in the refractory aggregate (sand) recovered after casting, since all or part of the alkali component of the water glass has been neutralized and deactivated, when regenerating the recovered sand, high-temperature firing treatment for removing the alkali component, neutralization treatment using an acid, etc. become unnecessary.

Examples

[0084] Hereinafter, the present invention will be further specifically clarified using some examples according to the present invention. However, it should be understood that the present invention is not to be construed in any limiting way by such descriptions of the examples. In the following examples and comparative examples, “%” and “parts” are both shown on a mass basis unless otherwise specified. Also, the collapsibility test of the mold obtained using each mold material composition (coated sand: CS) according to the examples and comparative examples, the evaluation of the recovered refractory aggregate (recovered sand), the calculation of the alkali reduction rate, the measurement of pH, and the polishing and peeling test were each performed as follows.

[0085] -Collapsibility test of mold- First, as shown in Fig. 1, a semi-cracked hollow main mold 6 (cavity diameter: 6 cm, height: 6 cm) that has been pre-made from room-temperature self-hardening sand and has a molten metal inlet 2 at the top and a core width-wood fixing part 4 at the bottom (this part serves as the discharge port for waste cores from the casting) is prepared. A circular solid core 10 (diameter: 5 cm, height: 5 cm) with a width-wood part 8 made using each CS is adhesively fixed at the width-wood fixing part 4. Then, the semi-cracked hollow main molds 6 are adhesively fixed to each other to produce a sand mold 12 for casting tests. Next, molten aluminum alloy (temperature: 710 ± 5 °C) is poured from the molten metal inlet 2 of this sand mold 12 for casting tests, allowed to solidify, and then the main mold 6 is broken to take out a casting 16 having a circular waste core discharge port 14 (diameter: 1.6 cm) shown in Fig. 2. And when it reaches a predetermined temperature, an impact (strike) of 3 seconds per time is applied to such obtained casting 16 with an air hammer at a pressure of 0.2 MPa and discharged from the discharge port 14. The number of strikes until 100% of the sand is discharged from the core is counted and evaluated according to the criteria shown below. ○: The sand discharge rate reached 100% with 1 to 5 strikes. △: The sand discharge rate reached 100% with 6 to 10 strikes. ×: Even with 10 strikes, the sand discharge rate did not reach 100%.

[0086] -Evaluation of the recovered refractory aggregate (recovered sand)- 100 g of the refractory aggregate (recovered sand) recovered in the above collapsibility test was heated in a constant temperature bath at 500 °C for 1 hour. The state of the recovered sand (heat-exposed sand) after such heating was visually observed and evaluated according to the criteria shown below. ○: No lumps are observed in the heat-exposed sand. △: Slight lumps are observed in the heat-exposed sand. ×: The heat-exposed sand is in a lump state, and re-welding is clearly observed.

[0087] -Calculation of the alkali reduction rate- The above heat-exposed sand was put into water, and the amount of alkali eluted into the water (the amount of alkali remaining in the heat-exposed sand) was measured. The alkali reduction rate (%) was calculated by subtracting the measured alkali residue amount from 100% of the alkali amount in the mold material composition.

[0088] -Measurement of pH- 50 g of the heat-exposed sand was put into distilled water, stirred for 30 minutes, filtered through filter paper, and the pH of the filtrate was measured.

[0089] -Abrasion and peeling test- 100 g of the refractory aggregate (recovered sand) that had formed circular void neutrons and was taken out in the above-mentioned collapsibility test was put into a ball mill and ground for 1 hour. Then, sieving was performed through a 200-mesh sieve for 1 minute to separate it into refractory aggregate and fine powder peeled off from the refractory aggregate. The amount of the obtained fine powder was measured, and the ease of peeling of the recovered sand was evaluated in three levels according to the following criteria. ○: The amount of fine powder is 0.3 mass% or more based on the mass of the refractory aggregate. △: The amount of fine powder is 0.1 mass% or more and less than 0.3 mass% based on the mass of the refractory aggregate. ×: The amount of fine powder is less than 0.1 mass% based on the mass of the refractory aggregate.

[0090] Also, the raw materials used in manufacturing each coated sand (CS) are as follows. · Refractory aggregate: Alumina-based spherical aggregate (Product name: Espal #60, manufactured by Yamakawa Sangyo Co., Ltd.) · Refractory aggregate: Flattery silica sand (Flattery No. 6) · Sodium silicate: Sodium silicate No. 1 (Product name, manufactured by Fuji Chemical Co., Ltd., molar ratio of SiO 2 / Na 2 O: 2.1, Solid content: 45 mass%) · Sodium silicate: Sodium silicate No. 2 (Product name, manufactured by Fuji Chemical Co., Ltd., SiO 2 / Na 2 O molar ratio: 2.5, Solid content: 41 mass%) · Sodium silicate: Sodium silicate No. 3 (Product name, manufactured by Fuji Chemical Co., Ltd., SiO 2 / Na 2 O molar ratio: 3.0, Solid content: 35% by mass · Neutralizing agent: chlorinated paraffin (Product name: Empara 70, manufactured by Ajinomoto Fine-Techno Co., Ltd.) · Neutralizing agent: chlorinated paraffin (Product name: Toyoparax 40S, manufactured by Tosoh Corporation) · Neutralizing agent: vinyl chloride (Product name: Luron Paste, manufactured by Tosoh Corporation) · Neutralizing agent: tetrabromobisphenol A (Product name: Frame Cut 120G, manufactured by Tosoh Corporation) · Neutralizing agent: brominated aliphatic and aromatic compounds (Product name: Pyrogard SR130, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) · Neutralizing agent: brominated aliphatic and aromatic compounds (Product name: SR720N, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) · Neutralizing agent: polytetrafluoroethylene (Product name: Fluon L169J, manufactured by AGC Inc.) · Neutralizing agent: phosphate ester [Triphenyl phosphate (TPP), manufactured by Daihachi Chemical Industry Co., Ltd.]

[0091] - Manufacturing Example 1 of Wet CS- Using sodium silicate (sodium metasilicate No. 2), an aqueous sodium silicate solution with a solid content (concentration) of 41% was prepared. Refractory aggregate (Espal #60) was charged into a Shinagawa-type universal stirrer (5DM-r type, manufactured by Dalton Co., Ltd.) at room temperature, and the above aqueous sodium silicate solution was added at a ratio of 1.0 part per 100 parts of the refractory aggregate. At the same time, chlorinated paraffin (Empara 70) as a neutralizing agent was added at a ratio of 0.10 part per 100 parts of the refractory aggregate, and kneading was carried out for 3 minutes. After stirring and mixing until uniform, it was taken out, and a coating layer containing sodium silicate and a neutralizing agent (chlorinated paraffin) was provided on the surface of the refractory aggregate, obtaining a mold material composition (Wet CS: CS1a) in a wet state.

[0092] - Manufacturing Examples 2 to 4 of Wet CS- In Production Example 1 of wet CS, except that the amounts of the neutralizing agent (Empala 70) used were 0.20 part, 0.30 part, and 0.05 part, respectively, mold material compositions (CS2a to CS4a) exhibiting a wet state were obtained according to the same procedure as in Production Example 1 above.

[0093] -Production Example 5 of wet CS- In Production Example 1 of wet CS, except that the amount of the water glass aqueous solution used was 2.0 parts and the amount of the neutralizing agent (Empala 70) used was 0.20 part, a mold material composition (CS5a) exhibiting a wet state was obtained according to the same procedure as in Production Example 1 above.

[0094] -Production Example 6 of wet CS- In Production Example 1 of wet CS, except that a water glass aqueous solution having a solid content (concentration) of 45% obtained using water glass (sodium silicate No. 1) was used as the water glass aqueous solution and the amount of the neutralizing agent (Empala 70) used was 0.14 part, a mold material composition (CS6a) exhibiting a wet state was obtained according to the same procedure as in Production Example 1 above.

[0095] -Production Example 7 of wet CS- In Production Example 1 of wet CS, except that a water glass aqueous solution having a solid content (concentration) of 35% obtained using water glass (sodium silicate No. 3) was used as the water glass aqueous solution and the amount of the neutralizing agent (chlorinated paraffin: Empala 70) used was 0.07 part, a mold material composition (CS7a) exhibiting a wet state was obtained according to the same procedure as in Production Example 1 above.

[0096] -Production Example 8 of wet CS- In Production Example 1 of wet CS, except that Flattery No. 6 was used as the refractory aggregate, the amount of the water glass aqueous solution used was 3.0 parts, and the amount of the neutralizing agent (Empala 70) used was 0.30 part, a mold material composition (CS8a) exhibiting a wet state was obtained according to the same procedure as in Production Example 1 above.

[0097] -Production Example 9 of wet CS- In Production Example 1 of wet CS, a mold material composition (CS9a) exhibiting a wet state was obtained according to the same procedure as in Production Example 1 above, except that 0.18 part of chlorinated paraffin (Toyoparax 40S) was used as the neutralizing agent.

[0098] -Production Example 10 of wet CS- In Production Example 1 of wet CS, a mold material composition (CS10a) exhibiting a wet state was obtained according to the same procedure as in Production Example 1 above, except that 0.13 part of vinyl chloride (Luron Paste) was used as the neutralizing agent.

[0099] -Production Example 11 of wet CS- In Production Example 1 of wet CS, a mold material composition (CS11a) exhibiting a wet state was obtained according to the same procedure as in Production Example 1 above, except that 0.27 part of tetrabromobisphenol A (Frame Cut 120G) was used as the neutralizing agent.

[0100] -Production Example 12 of wet CS- In Production Example 1 of wet CS, a mold material composition (CS12a) exhibiting a wet state was obtained according to the same procedure as in Production Example 1 above, except that 0.25 part of brominated aliphatic-aromatic compound (Pirogard SR130) was used as the neutralizing agent.

[0101] -Production Example 13 of wet CS- In Production Example 1 of wet CS, a mold material composition (CS13a) exhibiting a wet state was obtained according to the same procedure as in Production Example 1 above, except that 0.46 part of brominated aliphatic-aromatic compound (Pirogard SR130) was used as the neutralizing agent.

[0102] -Production Example 14 of wet CS- In Production Example 1 of wet CS, a mold material composition (CS14a) exhibiting a wet state was obtained according to the same procedure as in Production Example 1 above, except that 0.24 part of brominated aliphatic-aromatic compound (SR720N) was used as the neutralizing agent.

[0103] -Production Example 15 of wet CS- In Production Example 1 of wet CS, a mold material composition (CS15a) in a wet state was obtained according to the same procedure as in Production Example 1 above, except that 0.05 part of polytetrafluoroethylene (Fluon L169J) was used as the neutralizing agent.

[0104] -Production Example 16 of wet CS- After heating the refractory aggregate (Espal #60) to a temperature of about 130°C, it was put into a Turbula mixer (manufactured by Enshu Iron Works Co., Ltd.). Further, 0.10 part of a neutralizing agent (chlorinated paraffin: Empala 70) was added at a ratio of 0.10 part per 100 parts of the refractory aggregate, and kneading was carried out for 3 minutes. After stirring and mixing until the sand grain mass disintegrated and then taken out, a solid first coating layer (lower layer) composed of the neutralizing agent (Empala 70) was formed on the surface of the refractory aggregate.

[0105] Next, an aqueous sodium silicate solution with a solid content (concentration) of 41% was prepared using sodium silicate (sodium metasilicate No. 2). Then, the refractory aggregate provided with the solid first coating layer on the surface prepared above was put into a Shinagawa type universal stirrer (5DM-r type, manufactured by Dalton Co., Ltd.) at room temperature, and the above aqueous sodium silicate solution was added at a ratio of 1.0 part per 100 parts of the refractory aggregate, and kneading was carried out for 3 minutes. After stirring and mixing until it became uniform and then taken out, a mold material composition (CS16a) in a wet state was obtained, in which a second coating layer (upper layer) made of sodium silicate was provided on the solid first coating layer (lower layer).

[0106] -Production Example 17 of wet CS- After heating refractory aggregate (Espal #60) to a temperature of about 60°C, it was put into a Wal mixer (manufactured by Enshu Iron Works Co., Ltd.). Further, 0.10 part of a neutralizing agent (Empala 70) was added at a ratio of 0.10 part per 100 parts of the refractory aggregate. Also, 0.20 part of an aromatic polyester polyol (manufactured by Kawasaki Kasei Co., Ltd., trade name: MAXIMOL RDK-133) and 0.15 part of a polyisocyanate (MDI, manufactured by Mitsui Chemicals SKC Polyurethane Co., Ltd., trade name: Cosmonate M-200) were added. They were mixed until the aromatic polyester polyol and the polyisocyanate reacted and cured as a phenol urethane resin, and then taken out. Thus, a solid first coating layer (lower layer) composed of a neutralizing agent (Empala 70) and a phenol urethane resin was formed on the surface of the refractory aggregate.

[0107] Next, an aqueous sodium silicate solution with a solid content (concentration) of 41% was prepared using water glass (sodium silicate No. 2). Then, the refractory aggregate prepared previously and provided with a solid first coating layer on its surface was put into a Shinagawa type universal stirrer (5DM-r type, manufactured by Dalton Co., Ltd.) at room temperature. The above aqueous sodium silicate solution was added at a ratio of 1.0 part per 100 parts of the refractory aggregate, and kneading was carried out for 3 minutes. After stirring and mixing until it became uniform and then taken out, a mold material composition (CS17a) in a wet state was obtained, in which a second coating layer (upper layer) made of water glass was provided on the solid first coating layer (lower layer).

[0108] -Manufacturing Example 18 of Wet CS- In Manufacturing Example 16 of Wet CS, a mold material composition (CS18a) in a wet state was obtained according to the same procedure as in the above Manufacturing Example 16, except that 0.25 part of a brominated aliphatic and aromatic compound (Piroguard SR130) was used instead of 0.10 part of chlorinated paraffin (Empala 70) as the neutralizing agent.

[0109] -Manufacturing Example 19 of Wet CS- In Production Example 17 of wet CS, a mold material composition (CS19a) in a wet state was obtained according to the same procedure as in Production Example 17 above, except that 0.25 part of a brominated aliphatic-aromatic compound (Pirogard SR130) was used instead of 0.10 part of chlorinated paraffin (Empal 70) as the neutralizing agent.

[0110] -Production Example 20 of wet CS- In Production Example 17 of wet CS, a mold material composition (CS19a) in a wet state was obtained according to the same procedure as in Production Example 17 above, except that 0.22 part of a phosphate ester (TPP) was used instead of 0.10 part of chlorinated paraffin (Empal 70) as the neutralizing agent.

[0111] -Production Example 21 of wet CS- In Production Example 1 of wet CS, a mold material composition (CS21a) in a wet state was obtained according to the same procedure as in Production Example 1 above, except that no neutralizing agent (Empal 70) was used.

[0112] -Production Example 22 of wet CS- In Production Example 6 of wet CS, a mold material composition (CS22a) in a wet state was obtained according to the same procedure as in Production Example 6 above, except that no neutralizing agent (Empal 70) was used.

[0113] -Production Example 23 of wet CS- In Production Example 7 of wet CS, a mold material composition (CS23a) in a wet state was obtained according to the same procedure as in Production Example 7 above, except that no neutralizing agent (Empal 70) was used.

[0114] -Production Example 24 of wet CS- In Production Example 8 of wet CS, a mold material composition (CS24a) in a wet state was obtained according to the same procedure as in Production Example 8 above, except that no neutralizing agent (Empal 70) was used.

[0115] -Production Example 25 of wet CS- In Production Example 1 of the wet CS, a mold material composition (CS25a) in a wet state was obtained according to the same procedure as in Production Example 1 above, except that 0.21 part of 35% hydrochloric acid was used instead of 0.10 part of chlorinated paraffin (Empara 70) as the neutralizing agent.

[0116] - Molding Example I of the mold (Examples 1 to 20, Comparative Examples 1 to 5)- CS1a to CS25a (temperature: 20°C) produced according to the above-described respective procedures were filled into a molding die heated to 150°C, then held in the molding die, and the CS filled in such a molding die was each solidified (cured) to produce a mold used as a test piece of a circular void neutron (diameter: 5 cm, height: 5 cm). The CS used when producing the molds (test pieces) according to each of Examples 1 to 20 and Comparative Examples 1 to 5 is as shown in Tables 1 to 4 below.

[0117] [Table 1]

[0118] [Table 2]

[0119] [Table 3]

[0120] [Table 4]

[0121] As is clear from the results in Tables 1 to 3 above, in the case of the mold material compositions (wet CS: CS1a to CS20a) exhibiting a wet state according to the present invention, by containing a predetermined neutralizing agent, the molds obtained using them are excellent in collapsibility, and it is also recognized that the amount of alkali remaining in the refractory aggregate (reclaimed sand) recovered after casting is sufficiently low. Furthermore, the evaluation in the polishing and peeling test is also good, and it is also confirmed that the polishing treatment of the reclaimed sand is easy.

[0122] On the other hand, as is clear from Table 4 above, for the mold material compositions exhibiting a wet state and not containing a predetermined neutralizing agent (wet CS: CS21a to CS25a), 1) in the case of CS21a to CS24a, it is recognized that the collapsibility of the molds obtained using them is poor and the amount of alkali remaining in the reclaimed sand is also large, and 2) in the case of CS25a, it is confirmed that the mold cannot be formed in the first place.

[0123] - Manufacturing Example 1 of Dry CS - Using water glass (sodium metasilicate No. 2), an aqueous water glass solution with a solid content (concentration) of 41% was prepared. After heating the refractory aggregate (Espal #60) to a temperature of about 130°C, it was put into a Turbula mixer (manufactured by Enshu Iron Works Co., Ltd.), and the above aqueous water glass solution was added at a ratio of 1.0 part per 100 parts of the refractory aggregate, and chlorinated paraffin (Enpara 70) as a neutralizing agent was added at a ratio of 0.10 part per 100 parts of the refractory aggregate, followed by kneading for 3 minutes, stirring and mixing until uniform, and then taking it out. Thus, a mold material composition (dry CS: CS1b) exhibiting a dry state and provided with a coating layer containing water glass and a neutralizing agent (chlorinated paraffin) on the surface of the refractory aggregate was obtained.

[0124] - Manufacturing Example 2 of Dry CS - A mold material composition (CS2b) exhibiting a dry state was obtained according to the same procedure as in Manufacturing Example 1 above, except that the amount of the aqueous water glass solution used was 2.0 parts and the amount of the neutralizing agent (Enpara 70) used was 0.20 parts in Manufacturing Example 1 of Dry CS.

[0125] -Production Example 3 of Dry CS In Production Example 1 of dry CS, except that an aqueous water glass solution having a solid content (concentration) of 45% obtained using water glass (sodium silicate No. 1) as the aqueous water glass solution and the amount of the neutralizing agent (Empara 70) used was 0.14 part, a mold material composition (CS3b) exhibiting a dry state was obtained according to the same procedure as in Production Example 1 above.

[0126] -Production Example 4 of Dry CS In Production Example 1 of dry CS, except that an aqueous water glass solution having a solid content (concentration) of 35% obtained using water glass (sodium silicate No. 3) as the aqueous water glass solution and the amount of the neutralizing agent (chlorinated paraffin: Empara 70) used was 0.07 part, a mold material composition (CS4b) exhibiting a dry state was obtained according to the same procedure as in Production Example 1 above.

[0127] -Production Example 5 of Dry CS In Production Example 1 of dry CS, except that 0.13 part of vinyl chloride (Rulon paste) was used as the neutralizing agent, a mold material composition (CS5b) exhibiting a dry state was obtained according to the same procedure as in Production Example 1 above.

[0128] -Production Example 6 of Dry CS In Production Example 1 of dry CS, except that 0.25 part of a brominated aliphatic-aromatic compound (Pirogard SR130) was used as the neutralizing agent, a mold material composition (CS6b) exhibiting a dry state was obtained according to the same procedure as in Production Example 1 above.

[0129] -Production Example 7 of Dry CS In Production Example 1 of dry CS, except that 0.24 part of a brominated aliphatic-aromatic compound (SR720N) was used as the neutralizing agent, a mold material composition (CS7b) exhibiting a dry state was obtained according to the same procedure as in Production Example 1 above.

[0130] -Production Example 8 of Dry CS In Production Example 1 of dry CS, a mold material composition (CS8b) presenting a dry state was obtained according to the same procedure as in Production Example 1, except that 0.05 part of polytetrafluoroethylene (Fluon L169J) was used as the neutralizing agent.

[0131] -Production Example 9 of dry CS- After heating refractory aggregate (Espal #60) to a temperature of about 60°C, it was put into a Turbula mixer (manufactured by Enshu Iron Works Co., Ltd.). Further, 0.10 part of a neutralizing agent (Empala 70) was added at a ratio of 0.10 part per 100 parts of the refractory aggregate. Also, 0.20 part of an aromatic polyester polyol (manufactured by Kawasaki Chemical Co., Ltd., trade name: MAXIMOL RDK-133) and 0.15 part of a polyisocyanate (MDI, manufactured by Mitsui Chemicals SKC Polyurethane Co., Ltd., trade name: Cosmonate M-200) were added. They were mixed until the aromatic polyester polyol and the polyisocyanate reacted and cured as a phenol urethane resin, and then taken out. Thus, a solid first coating layer (lower layer) composed of the neutralizing agent (Empala 70) and the phenol urethane resin was formed on the surface of the refractory aggregate.

[0132] Next, an aqueous sodium silicate solution with a solid content (concentration) of 41% was prepared using sodium silicate (No. 2 sodium silicate). Then, the refractory aggregate prepared previously and provided with the solid first coating layer on its surface was heated to a temperature of about 50°C, put into a Turbula mixer (manufactured by Enshu Iron Works Co., Ltd.), and the above aqueous sodium silicate solution was added at a ratio of 1.0 part per 100 parts of the refractory aggregate. Kneading was carried out for 5 minutes while passing hot air at 120°C through the Turbula mixer, and after stirring and mixing until it became uniform, it was taken out. Thus, a mold material composition (CS9b) presenting a dry state was obtained, in which a second coating layer (upper layer) made of sodium silicate was provided on the solid first coating layer (lower layer).

[0133] -Production Example 10 of dry CS- In Production Example 9 of dry CS, a mold material composition (CS10b) in a dry state was obtained according to the same procedure as in Production Example 9 above, except that 0.25 part of a brominated aliphatic-aromatic compound (Pirogard SR130) was used instead of 0.10 part of chlorinated paraffin (Enpara 70) as the neutralizing agent.

[0134] -Production Example 11 of dry CS- In Production Example 9 of dry CS, a mold material composition (CS11b) in a dry state was obtained according to the same procedure as in Production Example 17 above, except that 0.22 part of a phosphate ester (TPP) was used instead of 0.10 part of chlorinated paraffin (Enpara 70) as the neutralizing agent.

[0135] -Production Example 12 of dry CS- In Production Example 1 of dry CS, a mold material composition (CS12b) in a dry state was obtained according to the same procedure as in Production Example 1 above, except that no neutralizing agent (Enpara 70) was used.

[0136] -Production Example 13 of dry CS- In Production Example 3 of dry CS, a mold material composition (CS13b) in a dry state was obtained according to the same procedure as in Production Example 3 above, except that no neutralizing agent (Enpara 70) was used.

[0137] -Production Example 14 of dry CS- In Production Example 4 of dry CS, a mold material composition (CS14b) in a dry state was obtained according to the same procedure as in Production Example 4 above, except that no neutralizing agent (Enpara 70) was used.

[0138] -Production Example 15 of dry CS- In Production Example 1 of dry CS, a mold material composition (CS15b) in a dry state was obtained according to the same procedure as in Production Example 1 above, except that 0.21 part of 35% hydrochloric acid was used instead of 0.10 part of chlorinated paraffin (Enpara 70) as the neutralizing agent.

[0139] -Molding Example II of mold (Examples 21 to 31, Comparative Examples 6 to 9)- CS1b to CS15b (temperature: 20°C) manufactured according to the above-described respective procedures were put into a Shinagawa-type universal stirrer (5DM-r type, manufactured by Dalton Co., Ltd.) at room temperature, and further, water was added to the stirrer at a ratio of 1.0 part per 100 parts of CS and stirred to prepare wetted CS (molding material). After the wetted CS taken out from the stirrer was filled into a molding die heated to 150°C, it was held in the molding die, and the CS filled in such a molding die was each solidified (cured) to produce a mold used as a test piece of circular void neutrons (diameter: 5 cm, height: 5 cm). Note that the CS used when producing the molds (test pieces) according to each of Examples 21 to 31 and Comparative Examples 6 to 9 is as shown in Tables 5 to 7 below.

[0140]

Table 5

[0141]

Table 6

[0142]

Table 7

[0143] As is clear from the results of Tables 5 and 6, even when water is added to the mold material composition (dry-state CS: CS1b to CS11b) in a dry state according to the present invention to make it wetted, like the mold material composition (wetted CS: CS1a to CS20a) in a wetted state according to the present invention, since they contain a predetermined neutralizing agent, it is recognized that the molds obtained using them are excellent in collapsibility, and the amount of alkali remaining in the refractory aggregate (recovered sand) recovered after casting is also sufficiently low. Furthermore, the evaluation in the polishing and peeling test is also good, and it is also confirmed that the polishing treatment of the recovered sand is easy.

[0144] On the other hand, as is clear from Table 7 above, for dry CS (CS12b to CS15b) which is a mold material composition in a dry state and does not contain a predetermined neutralizing agent, 1) in the case of CS12b to CS14b, the collapsibility of the mold obtained using them is poor, and it is also recognized that the amount of alkali remaining in the recovered sand is large. 2) In addition, in the case of CS15b, it is confirmed that the mold cannot be molded in the first place.

[0145] - Mold Molding Example III (Examples 32 to 36, Comparative Examples 10 to 11)- CS1b, CS6b, CS9b to CS12b, CS15b (temperature: 20°C) manufactured according to the above-described respective procedures were blown into a molding die heated to 110°C at a gauge pressure of 0.3 MPa and filled. Then, under a gauge pressure of 0.05 MPa, steam at a temperature of 99°C was blown in for 4 seconds, and ventilation was performed on the coated sand (CS) phase filled in the molding die. Next, after such steam ventilation was completed, hot air at a temperature of 150°C was blown in for 2 minutes under a gauge pressure of 0.03 MPa to solidify (harden) the CS filled in the molding die, thereby producing a mold used as a test piece of a circular void neutron (diameter: 5 cm, height: 5 cm). The CS used when producing the molds (test pieces) according to each of Examples 32 to 36 and Comparative Examples 10 to 11 is as shown in Tables 8 and 9 below.

[0146]

Table 8

[0147]

Table 9

[0148] As is clear from the results of Table 8 and Table 9 above, even when steam is passed through the mold for the mold material compositions in the dry state according to the present invention (dry state CS: CS1b, CS6b, CS9b to CS11b), similar to the mold material compositions in the wet state according to the present invention (wet state CS: CS1a to CS20a), since they contain a predetermined neutralizing agent, it is recognized that the molds obtained using them are excellent in collapsibility, and the amount of alkali remaining in the refractory aggregate (recovered sand) recovered after casting is also sufficiently low. Furthermore, the evaluation in the polishing and peeling test is also good, and it is also confirmed that the polishing treatment of the recovered sand is easy.

[0149] On the other hand, as is clear from Table 9 above, for the dry-state mold material compositions that do not contain a predetermined neutralizing agent, namely dry-state CS (CS12b, CS15b), 1) in the case of CS12b, it is recognized that the collapsibility of the molds obtained using them is poor and the amount of alkali remaining in the recovered sand is also large, and 2) in the case of CS15b, it is confirmed that the mold cannot be formed in the first place.

Explanation of Reference Signs

[0150] 2 Molten metal inlet 4 Lath fixing part 6 Main mold 8 Lath part 10 Core 12 Sand mold 14 Waste core discharge port 16 Casting

Claims

1. (a) a refractory aggregate; (b) a binder having water glass as an essential component; (c) at least including a phosphate ester as a neutralizing agent, wherein a decomposition product generated by heating during casting causes a neutralization reaction with an alkali component of the water glass; The phosphate ester is contained in an amount such that a decomposition product generated by heating during casting neutralizes the alkali component of the water glass, and the proportion of the alkali component of the water glass after casting becomes 15% by mass or less. A mold material composition characterized by this.

2. The mold material composition according to claim 1, wherein a coating layer containing the binder and the phosphate ester is formed so as to cover the surface of the refractory aggregate.

3. A solid first coating layer containing the phosphate ester is formed so as to cover the surface of the refractory aggregate, and a second coating layer made of a binder composition containing the binder is formed so as to cover the first coating layer. The mold material composition according to claim 1.

4. The first coating layer is capable of forming the solid first coating layer on the surface of the refractory aggregate, and ii) contains an organic compound that thermally decomposes and generates gas by heating during casting. The mold material composition according to claim 3.

5. The mold material composition according to any one of claims 1 to 4, wherein the refractory aggregate is spherical.

6. The mold material composition according to any one of claims 1 to 5, which does not have fluidity at room temperature and exhibits a wet state.

7. The mold material composition according to any one of claims 1 to 5, which has fluidity at room temperature and exhibits a dry state.

8. A method for manufacturing a mold, characterized in that the mold material composition exhibiting a wet state according to claim 6 is used, filled into a molding die, held in the molding die, and solidified or cured to obtain a target mold.

9. A method for manufacturing a mold, characterized in that the mold material composition exhibiting a dry state according to claim 7 is used, filled into a molding die, passed through steam, held in the molding die, and solidified or cured to obtain a target mold.

10. A method for manufacturing a mold, characterized in that a mold material composition in a dry state according to Claim 7 is used, water is added thereto to make it wet, the wet mold material composition is filled into a mold, and then held in the mold and solidified or cured to obtain a target mold.

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