JP7312883B2 - Mold material and method for manufacturing same, method for manufacturing mold, and method for recycling recovered refractory aggregate - Google Patents

Description

The present invention relates to a mold material, a method for manufacturing the same, a method for manufacturing a mold, and a method for regenerating recovered refractory aggregate. More particularly, the present invention relates to a mold material that prevents adhesion of the mold material and/or solidified products thereof to the casting product in the finally obtained mold, and exhibits excellent mold strength and mold filling properties.

Conventionally, as one of the molds used for casting molten metal, a coated sand obtained by coating mold sand made of a refractory aggregate with a predetermined binding agent is used as a mold material, and the desired shape is obtained by molding. Specifically, in "Casting Engineering Handbook" edited by the Japan Foundry Engineering Society, pp. 78-90, organic binders using resins such as phenolic resin, furan resin, urethane resin, etc. are clarified as binders in such coated sand, in addition to inorganic binders such as water glass, and methods for forming self-hardening molds using these binders are also clarified.

For example, in Patent Document 1 (Japanese Patent Application Laid-Open No. 2012-76115), the surface of a refractory aggregate is coated with a solid coating layer containing a water-soluble inorganic compound such as water glass as a binder, and a binder-coated refractory (coated sand) having good fluidity is disclosed. There, such a binder-coated refractory (coated sand) with good fluidity is filled into a molding cavity of a mold for making a mold, and then steam is allowed to pass through, thereby solidifying the binder-coated refractory (coated sand) and obtaining a desired mold.

However, in the conventional coated sand made by using an inorganic binder such as water glass as disclosed in Patent Document 1, since it contains only a small amount of organic matter, the amount of gas generated by heating accompanying pouring of the molten metal is small. Organic binders generally lose their adhesiveness when heated, but inorganic binders do not lose their adhesiveness by heating alone. Therefore, the coated sand (and/or its solidified product) adhering to the surface of the casting product often remains on the surface of the casting product even after heating in the casting process and subsequent heat treatment processes. For this reason, after these processing steps, a step of removing the coated sand (and/or its solidified substance) adhering to the surface of the casting product is required, which is a problem of great labor. In addition, conventional coated sand using an inorganic binder such as water glass is still insufficient in collapsibility of the mold obtained using it, and in this respect, there is still room for improvement.

JP 2012-76115 A

"Casting Engineering Handbook" pp.78-90

Here, the present invention has been made against the background of such circumstances, and the problem to be solved is to provide a mold material that prevents adhesion of the mold material and/or its solidified product to the casting product in the finally obtained mold, and exhibits excellent mold strength and mold filling properties. In addition, another object of the present invention is to provide a method for advantageously producing such an excellent mold material, a method for producing a mold using such an excellent mold material, and a method for recycling recovered refractory aggregate.

In order to solve the above problems, the present invention can be suitably implemented in various aspects as listed below, and each aspect described below can be employed in any combination. It should be understood that the aspects and technical features of the present invention are not limited to those described below, but can be recognized based on the inventive idea that can be grasped from the description of the entire specification.

(1) A mold material composed of a wet coated sand having no normal temperature fluidity, characterized by containing at least (a) a refractory aggregate, (b) a water-soluble inorganic binder, and (c) a powdery substance of an iron-containing compound (excluding Fe—Si alloys) having an average particle size of 0.01 μm or more and less than 50 μm, but not containing any powdery substance of a metal-containing compound other than the powdery substance of the iron-containing compound.
(2) The mold material according to aspect (1), wherein the iron-containing compound is iron oxide.
(3) The mold material according to aspect (2), wherein the iron oxide is selected from the group consisting of magnetite, maghemite, ferrite, and mixtures of two or more thereof.
(4) The mold material according to any one of the aspects (1) to (3), wherein the iron-containing compound powder is contained in a proportion of 1 to 500 parts by mass with respect to 100 parts by mass of the solid content of the water-soluble inorganic binder.
(5) The mold material according to any one of the aspects (1) to (4), wherein an average value of light transmittance at a wavelength of 660 nm of a dispersion obtained by mixing 5 parts by mass of the iron-containing compound powder with respect to 100 parts by mass of the blank solution is 20% or less when an aqueous solution containing 30% by mass of the water-soluble inorganic binder as a solid content is used as a blank solution, and the light transmittance of the blank solution at a wavelength of 660 nm is 100%.
(6) The mold material according to any one of the aspects (1) to (5), wherein the iron-containing compound powder is spherical.
(7) The mold material according to any one of the aspects (1) to (6), further comprising a surfactant.
(8) The mold material according to any one of the aspects (1) to (7), wherein the water-soluble inorganic binder is water glass.
(9) A method for producing a mold, characterized in that the mold material according to any one of the above aspects (1) to (8) is filled in a heated mold, held in the mold, and solidified or hardened to obtain a desired mold.
(10) The mold manufacturing method according to the aspect (9) , wherein the mold is heated to a temperature of 80°C to 300°C.
(11) The mold manufacturing method according to the aspect (9) or the aspect (10) , wherein hot air or superheated steam is passed through the mold while the mold is being held.
(12) A method for regenerating a recovered refractory aggregate containing a refractory aggregate to which the water-soluble inorganic binder containing the powder of the iron-containing compound adheres, which is obtained after casting using a mold made of the mold material according to any one of the aspects (1) to (8),
After the refractory aggregate is recovered, the recovered refractory aggregate is polished to scrape off the water-soluble inorganic binder adhering to the surface thereof, and then the solid matter of the water-soluble inorganic binder scraped off from the refractory aggregate is separated from the refractory aggregate by utilizing the action of attracting the powder of the iron-containing compound contained in the solid matter to a magnet. how to play.
(13) The method for regenerating recovered refractory aggregate according to the aspect (12) , wherein the magnetic separation treatment is performed by a magnetic separator having a magnetic flux density within the range of 500 to 10000 Gauss.
(14) The method for regenerating recovered refractory aggregates according to aspect (12) or aspect (13) , wherein the firing treatment of the refractory aggregate is performed prior to the polishing treatment, between the polishing treatment and the magnetic separation treatment, and/or after the magnetic separation treatment.

According to the mold material, the manufacturing method thereof, and the mold manufacturing method according to the present invention, various effects as listed below can be achieved.
(A) In the mold made of the mold material according to the present invention (hereinafter simply referred to as mold in this paragraph), adhesion of the mold material and/or its solidified product to the casting product manufactured using the mold is effectively suppressed. That is, since the iron-containing compound powder having an average particle size within a predetermined range exhibits excellent dispersibility in the water-soluble inorganic binder (and the mixture with water), it is present in a well-dispersed state even in the mold made of the mold material of the present invention, and thus the adhesion of the mold material and/or its solidified substance to the casting product is evenly suppressed on the outer surface of the casting product.
(B) The surface roughness of the cast product manufactured using the mold is improved.
(C) The mold exhibits excellent strength.
(D) Excellent fillability in the mold.

Further, according to the method for recycling recovered refractory aggregate according to the present invention, various effects described below can be achieved.
(E) The solid matter of the water-soluble inorganic binder scraped off by the grinding treatment can be easily separated from the refractory aggregate using magnetic force.
(F) It is possible to easily separate scraped water-soluble inorganic binder solids adhering to static electricity, etc., which cannot be completely removed by ordinary dust collection operations.
(G) Powdered iron-containing compounds are advantageously present in the solid matter of the water-soluble inorganic binder scraped off by the polishing treatment, and even fine powdered solid matter can be efficiently removed by the subsequent magnetic separation treatment. Therefore, when a mold is made again using the regenerated refractory aggregate, it is possible to advantageously suppress a decrease in strength.

FIG. 2 is an explanatory longitudinal cross-sectional view of a casting test sand mold used to evaluate the state of adhesion of coated sand to castings in Examples. FIG. 2 is a vertical cross-sectional explanatory view of an aluminum alloy casting containing a waste core in an example.

By the way, the mold material containing the refractory aggregate and the water-soluble inorganic binder is classified into a dry mold material and a wet mold material depending on the state after preparation. First, the dry mold material has a form in which a coating layer made of a water-soluble inorganic binder is formed on the surface of a refractory aggregate. In the dry state, the material does not have adhesiveness (does not exhibit adhesiveness), but when moisture is supplied by ventilation of water vapor, the coating layer (water-soluble inorganic binder) covering the surface of the refractory aggregate dissolves and exhibits adhesiveness. Such a dry mold material is, for example, filled into a mold in a state in which moisture is added to develop adhesive force, and then heated and dried, or filled into a mold in a dry state, supplied with water vapor by passing water vapor into the mold, and then heated and dried to proceed with a solidification or curing reaction, thereby forming a desired mold. On the other hand, the wet mold material exhibits a wet state (appearance) as a whole, in which the water-soluble inorganic binder exhibits stickiness. Such a wet mold material is, for example, filled in a mold, heated and dried in the mold to proceed with a solidification or hardening reaction, thereby forming a desired mold. Whether the mold material exhibits a dry state or a wet state is determined by the water content relative to the solid content of the water-soluble inorganic binder in the mold material. For example, when the water-soluble inorganic binder is water glass, a mold material containing water in an amount corresponding to 5 to 55% by mass of the solid content exhibits a dry state, while a mold material containing a water content corresponding to more than 55% by mass of the solid content of water glass exhibits a wet state.

The dry mold material (coated sand) having normal temperature fluidity in the present invention refers to a mold material (coated sand) that gives a measured value of the dynamic angle of repose when the dynamic angle of repose is measured, regardless of the water content. Here, the dynamic angle of repose is obtained by placing a mold material (coated sand) in a cylinder having a transparent flat surface on one side (for example, putting the mold material into a container with a diameter of 7.2 cm and a height of 10 cm to half the volume), rotating the mold material at a constant speed (for example, 25 rpm), and measuring the angle formed between the slope and the horizontal plane when the slope of the layer of the mold material flowing in the cylinder becomes flat. The dynamic angle of repose is preferably 80° or less, more preferably 45° or less, and even more preferably 30° or less. Especially when the refractory aggregate is spherical, a dynamic angle of repose of 45° or less can be easily achieved. On the other hand, when the mold material (coated sand) does not flow in the cylinder in a wet state, the slope of the mold material (coated sand) layer is not formed as a plane, and therefore the dynamic repose angle cannot be measured, the wet mold material (coated sand) is used.

The refractory aggregate constituting the mold material according to the present invention is a refractory substance that functions as a base material of the mold, and any of various refractory granular or powder materials that have been conventionally used for molds can be used. Specifically, silica sand, recycled silica sand, special sand such as alumina sand, olivine sand, zircon sand, chromite sand, slag particles such as ferrochrome slag, ferronickel slag, and converter slag, and alumina. artificial particles such as mullite particles, artificial particles such as mullite particles, regenerated particles thereof, alumina balls, magnesia clinker, and the like. These refractory aggregates may be fresh sand, reclaimed sand or recovered sand that has been used once or more than once for making molds as foundry sand, or mixed sand obtained by adding new sand to such reclaimed sand or recovered sand and mixing them. Such refractory aggregates are generally used with a particle size of about 40 to 130, preferably about 60 to 110, in terms of AFS index. Further, the refractory aggregate used in the present invention is preferably spherical, and specifically, it is desirable that 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 factor of 1.2 or less, the flowability and filling properties during mold production are improved, and the number of contact points between the refractory aggregates increases, so the amount of water-soluble inorganic binder and additives required to achieve the same strength can be reduced. The particle shape index of the refractory aggregate used here is generally adopted as one measure of the outer shape of the particles, and is also called the particle shape index. Such a grain shape factor is represented by a value calculated using the surface area (sand surface area) of the refractory aggregate measured by various known methods. The theoretical surface area is the surface area when all the refractory aggregate particles (sand grains) are assumed to be spherical.

As the water-soluble inorganic binder in the mold material according to the present invention, one or more selected from water glass, sodium chloride, sodium phosphate, sodium vanadate, sodium aluminum oxide, potassium chloride, potassium carbonate, etc., is advantageously used as a main component. Among these, water glass and those containing water glass as a main component are particularly preferable from the viewpoint of ease of handling, moisture resistance, and strength of the finally obtained mold. Here, water glass is an aqueous solution of a soluble silicate compound, and examples of such a silicate compound include sodium silicate, potassium silicate, sodium metasilicate, potassium metasilicate, lithium silicate, and ammonium silicate. In particular, sodium silicate (sodium silicate) is advantageously used in the present invention. In the present invention, as long as water glass is used as the main component, it is also possible to use other water-soluble binders such as thermosetting resins, sugars, proteins, synthetic polymers, salts and inorganic polymers. When water glass is used in combination with another water-soluble binder, the proportion of water glass in the total amount of the binder is 60% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more.

Here, sodium silicate is usually classified into types 1 to 5 according to the molar ratio of SiO ₂ /Na ₂ O and used. Specifically, sodium silicate No. 1 has a SiO ₂ /Na ₂ O molar ratio of 2.0 to 2.3, sodium silicate No. 2 has a SiO ₂ /Na ₂ O molar ratio of 2.4 to 2.6, and sodium silicate No. 3 has a SiO ₂ /Na ₂ O molar ratio of 2.8 to 3.3. In addition, sodium silicate No. 4 has a SiO ₂ /Na ₂ O molar ratio of 3.3 to 3.5, and sodium silicate No. 5 has a SiO ₂ /Na ₂ O molar ratio of 3.6 to 3.8. Among these, sodium silicate Nos. 1 to 3 are also defined in JIS-K-1408. These sodium silicates may be used singly or in combination, and by mixing two or more kinds, it is possible to adjust the SiO ₂ /Na ₂ O molar ratio.

In order to advantageously obtain the mold material according to the present invention, the sodium silicate constituting the water glass used as the binding agent preferably has a SiO ₂ /Na ₂ O molar ratio of generally 1.9 or more, preferably 2.0 or more, more preferably 2.1 or more, and sodium silicates corresponding to Nos. 1 and 2 in the above sodium silicate classification are particularly advantageously used. Such sodium silicate Nos. 1 and 2 provide mold materials that are stable and have good properties even over a wide range of sodium silicate concentrations in water glass. Further, the upper limit of the molar ratio of SiO ₂ /Na ₂ O in such sodium silicate is appropriately selected according to the properties of water glass in the form of an aqueous solution, but is generally 3.5 or less, preferably 3.2 or less, more preferably 2.7 or less. Here, if the molar ratio of SiO ₂ /Na ₂ O is less than 1.9, a large amount of alkali will be present in the water glass, so the solubility of the water glass in water increases, and the mold material may easily deteriorate due to moisture absorption. On the other hand, sodium silicate with a molar ratio of SiO ₂ /Na ₂ O greater than 3.5 has low solubility in water, so that the final mold cannot increase the adhesion area between the refractory aggregates, and there is a possibility that the strength of the mold will decrease.

Further, the water glass used in the present invention means a solution of a silicic acid compound dissolved in water, and when producing the mold material of the present invention, it is used in the undiluted state as it is purchased in the market, or in a diluted state by adding water to such a undiluted liquid. The non-volatile content (water glass component) obtained by removing volatile substances such as water and solvents from such water glass is called solid content, and this corresponds to the above-mentioned soluble silicate compound such as sodium silicate. Also, the higher the proportion of such solids, the higher the silicic acid compound concentration in the water glass. Therefore, the solid content of the water glass used in the present invention corresponds to the ratio of the water glass excluding the water content in the stock solution when the water glass is composed only of the stock solution. On the other hand, when a diluted solution obtained by diluting the stock solution with water is used, the ratio excluding the water content in the stock solution and the amount of water used for dilution corresponds to the solid content of the water glass used.

The solid content in such water glass is set at an appropriate ratio depending on the type of the water glass component (soluble silicic acid compound), etc., but is preferably contained at a ratio of 20 to 50% by mass. By using the water glass in which the water glass component corresponding to the solid content is appropriately present in the aqueous solution is kneaded or mixed with the refractory aggregate, it is possible to prepare a mixture in which the water glass component is evenly and uniformly dispersed in the refractory aggregate. If the concentration of the water glass component (soluble silicate compound) in the water glass becomes too low and the total amount of the water glass component (solid content) becomes less than 20% by mass, for example, when producing a dry mold material, it is necessary to raise the heating temperature or lengthen the heating time in order to dry the mixture of the refractory aggregate, the powder of the iron-containing compound, and the water glass. occurs, which causes problems such as energy loss. On the other hand, if the proportion of solids in the water glass is too high, it becomes difficult to prepare a mixture in which the water glass components are evenly and uniformly dispersed in the refractory aggregate, and this may cause problems in terms of the properties of the desired mold.

In the present invention, sodium chloride (NaCl), which can be used as a water-soluble inorganic binder, is edible, harmless to the human body, and can be used at a low cost. Further, since it is easily dissolved in water, a mold material using sodium chloride as a binding agent can be used to manufacture molds that are easily disintegrated by water. In particular, the solubility of sodium chloride in water in the temperature range of 0 to 100° C. is 35.7 to 39.1 g with respect to 100 g of water, and the change due to water temperature is small, so workability is good. Furthermore, since the melting point of sodium chloride is 1413° C., which is relatively high, a mold with high heat resistance can be produced.

As sodium phosphate, monosodium phosphate hydrate ( _NaH2PO4.xH2O ; x is a known integer ₎ , disodium phosphate _hydrate ( _{Na2HPO4.x'H2O} ; x' is a known integer), _{trisodium phosphate hydrate (Na3PO4.x " H2O} ; x" is a known integer ₎ , and the like can be _used . Sodium phosphate is soluble in water, as typified by the fact that the amount of trisodium phosphate hydrate dissolved in 100 g of water is 1.5 g (0°C), and the melting point of sodium phosphate is relatively high, as typified by the melting point of disodium phosphate hydrate being 1340°C. Therefore, a mold material using sodium phosphate as a water-soluble inorganic binder is easily disintegrated by water, and a mold with high heat resistance can be produced.

Furthermore, sodium vanadate (Na ₃ VO ₄ ) is soluble in water and has a relatively high melting point of 866°C. Therefore, a mold material using sodium vanadate as a water-soluble inorganic binder is easily disintegrated by water, and a mold with high heat resistance can be produced.

In addition, sodium aluminum oxide (NaAlO ₂ ) is soluble in water and has a high melting point of 1700° C. or higher. Therefore, a mold material using sodium aluminum oxide as a water-soluble inorganic binder is easily disintegrated by water, and a mold having high heat resistance can be produced.

Potassium chloride (KCl) dissolves easily in water, and is inexpensive, with a solubility of 28.1 g (0° C.) in 100 g of water. Also, the melting point is relatively high at 776°C. Therefore, a mold material using potassium chloride as a water-soluble inorganic binder is easily disintegrated by water, and a mold having high heat resistance can be produced.

Furthermore, potassium carbonate (K ₂ CO ₃ ) is easily dissolved in water, with a solubility of 129.4 g (0° C.) per 100 g of water, and has a relatively high melting point of 891° C. Therefore, a mold material using potassium carbonate as a water-soluble inorganic binder is easily disintegrated by water, and a mold having high heat resistance can be produced.

The above-described various water-soluble inorganic binders are used in the mold material according to the present invention in an amount that is 0.1 to 5 parts by mass, preferably 0.1 to 2.5 parts by mass, with respect to 100 parts by mass of the refractory aggregate. Among them, an amount of 0.2 to 2.0 parts by mass is particularly advantageously employed. Here, the measurement of solid content is carried out as follows. That is, 10 g of a sample is placed in a sample plate made of aluminum foil (length: 9 cm, width: 9 cm, height: 1.5 cm), weighed, placed on a heating plate maintained at 180 ± 1 ° C., and left for 20 minutes. Next, the sample dish is taken out from the heating plate, allowed to cool in a desiccator, weighed, and the solid content (% by mass) is calculated according to the following equation.
Solid content (% by mass) = {[mass of sample dish after drying (g) - mass of sample dish (g)]
/ [mass of sample dish before drying (g) - mass of sample dish (g)]}
×100

In the present invention, if the amount of the water-soluble inorganic binder used is too small, it becomes difficult to form a coating layer on the surface of the refractory aggregate in the case of a dry mold material, which may cause a problem that the solidification or hardening of the mold material may not be sufficiently performed. On the other hand, even if the amount of the water-soluble inorganic binder used is too large, in the dry mold material, an excessive amount of the water-soluble inorganic binder adheres to the surface of the refractory aggregate, making it difficult to form a uniform coating layer. In addition, problems such as difficulty in sand removal (removal of solidified mold material) from the core after casting the metal also arise.

The mold material according to the present invention contains a powdery iron-containing compound having an average particle size of 0.01 μm or more and less than 50 μm, preferably 0.05 μm or more and 25 μm or less, more preferably 0.1 μm or more and 10 μm or less, further preferably 0.2 μm or more and 3 μm or less, together with the above water-soluble inorganic binder such as water glass. As described above, since the mold material of the present invention contains a powder of an iron-containing compound having an average particle size within a predetermined range, when a mold made with such a mold material is used for casting, a suitable gap is formed between the casting product and the mold, more specifically between the casting product and the solidified (hardened) caking agent, due to the powder of the iron-containing compound. It will be stopped. In addition, the iron-containing compound powder having an average particle size within a predetermined range, which is used in the present invention, exhibits excellent dispersibility in the water-soluble inorganic binder (and the mixture with water). Such powder is present in a well-dispersed state even in the mold made of the mold material of the present invention. Therefore, the adhesion of the mold material and/or its solidified product to the cast product is suppressed without causing unevenness on the outer surface of the cast product. In addition, by containing such a powdery iron-containing compound, a mold made with the mold material of the present invention has a high thermal conductivity and exhibits excellent collapsibility during casting. Furthermore, iron-containing compounds are inexpensive compared to other metal-containing compounds, have a small impact on the manufacturing cost of the mold material, and have excellent thermal conductivity and high specific heat, so there is very little risk of adversely affecting the physical properties of the finally obtained mold.

Here, the iron-containing compound used in the present invention means a compound having an iron atom, in other words, all compounds having Fe in the chemical formula. Specifically, iron, iron alloys, iron oxide, iron oxyhydroxide, iron hydroxide, mixed crystal ferrite in which a part of iron oxide is replaced with another metal, etc. can be exemplified. In addition, in the present invention, iron oxide is advantageously used in consideration of the risk of fire and explosion because the iron-containing compound powder is used. Examples of iron oxide include ferrous oxide, ferric oxide, triiron tetroxide (magnetite), iron oxyhydroxide, iron hydroxide, maghemite, and ferrite. Of these iron oxides, those having magnetism, specifically magnetite, maghemite, ferrite, and mixtures of two or more of these are particularly preferred. Since the magnetic iron oxide powder exhibits excellent dispersibility in the water-soluble inorganic binder (and the mixture with water), it is possible to more effectively suppress the occurrence of surface roughness in the casting product produced using the finally obtained mold. It should be noted that having magnetism means having a magnetizing ability.

The mold material according to the invention also has the advantage that the regeneration of the refractory aggregate recovered after casting with molds made of such mold material can be advantageously carried out. That is, after casting using a mold made of the mold material of the present invention, the refractory aggregate to which the water-soluble inorganic binder containing the powder of the iron-containing compound adheres is recovered, and then the recovered refractory aggregate is polished to scrape off the water-soluble inorganic binder adhering to the surface thereof. The iron-containing compound powder is dispersed in the scraped solid matter of the water-soluble inorganic binding agent, and by performing magnetic separation treatment to separate the iron-containing compound powder matter from the refractory aggregate by utilizing the action of the iron-containing compound powder being attracted to the magnet, the solid matter of the water-soluble inorganic binding agent scraped off by the polishing treatment can be more easily separated from the refractory aggregate using a magnetic force, and even the fine powder of the solid matter of the water-soluble inorganic binding agent can be removed more efficiently. There is. When regenerating the refractory aggregate according to such a regenerating method, magnetic materials such as magnetite, maghemite, ferrite, and mixtures of two or more of these are more preferable as the iron-containing compound contained in the mold material.

In addition, the shape of the iron-containing compound powder is not particularly limited, and it is possible to use a spherical, polyhedral (hexahedron, octahedron, etc.), acicular, columnar, etc. powder, but a spherical powder is preferably used. Among iron-containing compound powders having a spherical shape, those having a sphericity of 0.7 or more, preferably 0.8 or more, more preferably 0.9 or more in terms of aspect ratio (minor axis/major axis) are used. Spherical powders are easy to loosen and hard to aggregate, so they are easy to disperse in a water-soluble inorganic binder (and a mixture with water), and the fluidity of the mixture when manufacturing (preparing) the mold material is good. The sphericity of a powdery substance having a spherical shape means the average value of the aspect ratios (ratio of short diameter/long diameter) obtained from the projected shape of 10 single particles randomly selected in observation with a scanning electron microscope.

Further, the powdery iron-containing compound used in the present invention desirably has the following properties between it and the water-soluble inorganic binder which together constitutes the mold material, in other words, between it and the water-soluble inorganic binder used together when producing the mold material. That is, when an aqueous solution containing 30% by mass of a solid content of a water-soluble inorganic binder is used as a blank solution, and the transmittance of light at a wavelength of 660 nm is assumed to be 100%, the dispersion obtained by mixing 5 parts by mass of the iron-containing compound powder with 100 parts by mass of the blank solution preferably has an average light transmittance of 20% or less at a wavelength of 660 nm. More specifically, the transmittance of light with a wavelength of 660 nm in a blank solution (aqueous solution containing 30% by mass of a water-soluble inorganic binder as a solid content) is assumed to be 100%, 5 parts by mass of a powder of an iron-containing compound is added to 100 parts by mass of the blank solution, and mixed and stirred to prepare a dispersion. , to measure. In the present invention, a powdery iron-containing compound having an average transmittance of 20% or less, preferably 10% or less, for light having a wavelength of 660 nm in the dispersion calculated from the three measurements is advantageously used. The fact that the average transmittance of light having a wavelength of 660 nm in the dispersion is 20% or less means that the powder of the iron-containing compound contained in the dispersion is present in the dispersion in a well-dispersed state. Therefore, the powder of such an iron-containing compound exhibits high dispersibility even in the water-soluble inorganic binder (and/or its aqueous solution).

As a method for directly confirming the dispersed state of the iron-containing compound powder in the mold, a method of measuring the color difference: ΔE using a color difference meter can be exemplified. That is, when the powder of the iron-containing compound is poorly dispersed in the mold, the color difference ΔE between the mold and the mold which does not contain the powder of the iron-containing compound is low. On the other hand, when the powder is well dispersed, the color difference ΔE tends to increase. Accordingly, when the color difference ΔE is 1.0 or more, preferably 2.0 or more, it can be determined that the iron-containing compound powder is well dispersed in the mold. A mold in which the iron-containing compound powder is dispersed in a good state has the advantage that a more uniform gap is formed between the mold surface and the cast product, and adhesion of the mold material and/or its solidified product to the cast product is more effectively suppressed, and a decrease in mold strength due to aggregation of the iron-containing compound powder is advantageously suppressed.

The powdery iron-containing compound described in detail above should be contained in the mold material of the present invention in an amount of 1 to 500 parts by mass, preferably 10 to 300 parts by mass, more preferably 20 to 200 parts by mass, with respect to 100 parts by mass of the solid content of the water-soluble inorganic binder, in order to advantageously enjoy the effects of its blending.

Further, in the casting mold material according to the present invention, it is preferable that a surface active agent is further contained together with the above powdery iron-containing compound. By incorporating a surfactant, there is an advantage that the water permeability of the mold material of the present invention, in other words, the wettability with water is improved. More specifically, when water is supplied to the dry mold material containing a surfactant according to the present invention, the surfactant mediates between the supplied water and the water-soluble inorganic binder, so that even a small amount of water effectively wets the entire mold material. 1) It is possible to minimize the supply time of water to the mold material (for example, when water is supplied by water vapor, the water vapor ventilation time), and 2) As a result of suppressing the amount of water supplied to the mold (molding cavity) to a small amount, it is possible to advantageously enjoy effects such as excellent releasability from the mold and excellent strength in the molded mold. Furthermore, the moist mold material containing a surfactant according to the present invention can advantageously enjoy the following effects: 1) the presence of the surfactant makes it possible to minimize the amount of water added during its preparation (manufacturing), 2) the surface tension of water is suppressed and the fluidity of the mold material is improved, and 3) the molded mold exhibits excellent strength in addition to excellent releasability from the mold.

Here, the amount of the surfactant contained in the mold material of the present invention is desirably 0.1 to 20.0 parts by mass, preferably 0.5 to 15.0 parts by mass, particularly preferably 0.75 to 12.5 parts by mass, based on 100 parts by mass of the solid content of the water-soluble inorganic binder. If the amount of the surfactant contained is too small, the above-mentioned effects may not be advantageously obtained. On the other hand, if the amount of the surfactant is too large, the improvement of the effect according to the amount used may not be observed, and depending on the surfactant, the water-soluble inorganic binder may not solidify when dried, and even if an attempt is made to obtain a dry mold material, it may not be possible. In the present invention, any of cationic surfactants, anionic surfactants, amphoteric surfactants, nonionic surfactants, silicone surfactants and fluorine surfactants can be used as surfactants.

Specific examples of cationic surfactants include aliphatic amine salts, aliphatic quaternary ammonium salts, benzalkonium salts, benzethonium chloride, pyridinium salts, and imidazolinium salts. Examples of anionic surfactants include fatty acid soaps, N-acyl-N-methylglycinates, N-acyl-N-methyl-β-alanine salts, N-acylglutamates, alkyl ether carboxylates, acylated peptides, alkylsulfonates, alkylbenzenesulfonates, alkylnaphthalenesulfonates, dialkylsulfosuccinates, alkylsulfoacetates, α-olefinsulfonates, N-acylmethyltaurine, sulfated oils, higher alcohol sulfates, and secondary higher alcohol sulfates. salts, alkyl ether sulfates, secondary higher alcohol ethoxy sulfates, polyoxyethylene alkylphenyl ether sulfates, monoglysulfates, fatty acid alkylolamide sulfates, alkyl ether phosphates, alkyl phosphates and the like. Furthermore, amphoteric surfactants include carboxybetaine type, sulfobetaine type, aminocarboxylate, imidazolinium betaine, and the like. In addition, nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene secondary alcohol ethers, polyoxyethylene alkylphenyl 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 acids. 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 alkylamines, alkylamine oxides, acetylene glycol, acetylene alcohol and the like.

Among various surfactants, those having a siloxane structure as a non-polar site are called silicone-based surfactants, and those having a perfluoroalkyl group are called fluorine-based surfactants. Examples of silicone-based surfactants include polyester-modified silicones, acrylic-terminated polyester-modified silicones, polyether-modified silicones, acrylic-terminated polyether-modified silicones, polyglycerin-modified silicones, aminopropyl-modified silicones, and the like. Fluorinated surfactants include perfluoroalkyl sulfonates, perfluoroalkyl carboxylates, perfluoroalkyl phosphates, perfluoroalkyltrimethylammonium salts, perfluoroalkylethylene oxide adducts, perfluoroalkyl group-containing oligomers, and the like.

In the present invention, various surfactants as described above can be used alone or in combination of two or more. However, some surfactants may react with the water-soluble inorganic binder and may lose or lose their surfactant activity over time. Therefore, for example, when water glass is used as the water-soluble inorganic binder, anionic surfactants, nonionic surfactants and silicone-based surfactants that do not react with water glass are advantageously used.

Furthermore, the casting mold material according to the present invention may contain various known additives, if necessary, in addition to the surfactants described above. In order to incorporate such an additive into the mold material, a method of preliminarily blending a predetermined additive with the water-soluble inorganic binder and then kneading or mixing it with the refractory aggregate, or a method of adding a predetermined additive to the refractory aggregate separately from the water-soluble inorganic binder and kneading or mixing the whole uniformly, etc. are employed.

Moisture resistance improvers can be exemplified as additives that can be used in the present invention. In the present invention, any moisture resistance improver conventionally used in mold materials can be used as long as it does not impair the effects of the present invention. Specifically, zinc carbonate, basic zinc carbonate, iron carbonate, manganese carbonate, copper carbonate, aluminum carbonate, barium carbonate, magnesium carbonate, calcium carbonate, lithium carbonate, potassium carbonate, carbonates such as sodium carbonate, 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, metaborate Borate salts such as lead borate and magnesium metaborate; sulfates such as sodium sulfate, potassium sulfate, lithium sulfate, magnesium sulfate, calcium sulfate, strontium sulfate, barium sulfate, titanium sulfate, aluminum sulfate, zinc sulfate, copper sulfate; , hydroxides such as aluminum hydroxide and zinc hydroxide, and oxides such as silicon, zinc, magnesium, aluminum, calcium, lithium, copper, iron, boron and zirconium. Among them, basic zinc carbonate, sodium tetraborate, potassium metaborate, lithium sulfate, and lithium hydroxide can more advantageously improve moisture resistance when water glass is used as the water-soluble inorganic binder. Moisture resistance improvers such as those mentioned above may be used alone, or may be used in combination of two or more. Among the compounds listed above as moisture resistance improvers, there are also compounds that can be used as water-soluble inorganic binders. However, such compounds can act as moisture resistance improvers when a different water-soluble inorganic binder is used, and when water glass is used as the water-soluble inorganic binder, they act more effectively as moisture resistance improvers.

The amount of such a moisture resistance improver used is generally 0.5 to 10% by mass, preferably 1 to 8% by mass, based on the solid content in the water-soluble inorganic binder. In order to advantageously enjoy the effect of adding the moisture resistance improver, the amount used is preferably 0.5% by mass or more. On the other hand, if the amount added is too large, the binding of the water-soluble inorganic binder may be hindered, and problems such as a decrease in the strength of the finally obtained mold may occur.

Nitrates such as alkali metal nitrates and alkaline earth metal nitrates may be added in order to improve disintegration properties of the mold. Furthermore, polyhydric alcohols, water-soluble polymer compounds, carbohydrates, sugars, proteins, inorganic compounds, and the like may be added in order to improve the mold releasability by increasing the moisture retention of the mold and increasing the viscosity of the water-soluble inorganic binder. The total amount of such additives used is generally preferably about 0.5 to 30 parts by mass, more preferably 1 to 20 parts by mass, and even more preferably 2 to 15 parts by mass, based on 100 parts by mass of the solid content of the water glass.

Furthermore, as other additives, it is effective to include a coupling agent that strengthens the bond between the refractory aggregate and the water-soluble inorganic binder. For example, silane coupling agents, zircon coupling agents, titanium coupling agents, etc. can be used. In addition, it is also effective to contain a lubricant that contributes to improving the fluidity of the mold material. For example, waxes such as paraffin wax, synthetic polyethylene wax and montanic acid wax; fatty acid amides such as stearamide, oleic acid amide and erucamide; alkylene fatty acid amides such as methylenebisstearic acid amide and ethylenebisstearic acid amide; stearic acid, stearyl alcohol; stearic acid metal salts such as lead stearate, zinc stearate, calcium stearate and magnesium stearate. stearic acid monoglyceride, stearyl stearate, hydrogenated oils and the like can be used. Furthermore, as a release agent, paraffin, wax, light oil, machine oil, spindle oil, insulating oil, waste oil, vegetable oil, fatty acid ester, organic acid, graphite fine particles, mica, vermiculite, fluorine-based release agent, silicone-based release agent, etc. can be used. These other additives are generally contained in a proportion of 5% by mass or less, preferably 3% by mass or less, relative to the solid content in the water-soluble inorganic binder.

By the way, when producing a dry mold material having room-temperature fluidity according to the present invention, generally, an aqueous water-soluble inorganic binding agent as a binding agent is kneaded or mixed with a refractory aggregate together with additives used as necessary to prepare a mixture in which the surface of the refractory aggregate is uniformly covered with the water-soluble inorganic binding agent, and then water contained in the prepared mixture is evaporated. Thus, a method of obtaining the desired dry powdery mold material (dry coated sand) having normal temperature fluidity is adopted. In such a method, it is necessary that the water in the mixture evaporate quickly before the water-soluble inorganic binder solidifies or hardens. Therefore, in the present invention, it is desirable to evaporate the contained water within 5 minutes, more preferably within 3 minutes, after adding (mixing) the water-soluble inorganic binder in the form of an aqueous solution to the refractory aggregate to form a dry coated sand. This is because if the evaporation time becomes longer, the kneading (mixing) cycle becomes longer, the productivity decreases, and the water-soluble inorganic binder becomes more likely to come into contact with CO ₂ in the air, resulting in problems such as deactivation. The water content of the dry coated sand thus obtained is, for example, when water glass is used as the water-soluble inorganic binder, it is adjusted to be 5 to 55% by mass, preferably 10 to 50% by mass, and more preferably 20 to 50% by mass based on the solid content of the water glass.

In the process of producing such a dry coated sand (mold material), as one of the effective means for rapidly evaporating the water content in the mixture, a method of preheating refractory aggregates and kneading or mixing a water-soluble inorganic binder in the form of an aqueous solution with them to prepare a mixture is adopted. By kneading or mixing the water-soluble inorganic binder in the form of an aqueous solution with the preheated refractory aggregate, the water originating from the water-soluble inorganic binder in the form of the aqueous solution can be evaporated very quickly by the heat of the refractory aggregate, thereby effectively reducing the water content of the resulting mold material, and the dry coated sand having room temperature fluidity can be advantageously obtained. . The temperature for preheating the refractory aggregate is appropriately selected according to the type and amount of the water-soluble inorganic binder used, and the amount of water in the water-soluble inorganic binder aqueous solution. If the preheating temperature is too low, the moisture cannot be evaporated effectively, and it takes time to dry the mixture. Therefore, it is desirable to adopt a temperature of 100° C. or higher. If the preheating temperature is too high, the solidification (hardening) of the water-soluble inorganic binder component proceeds during cooling of the resulting coated sand (mold material), and in addition, the formation of composite particles proceeds, which causes problems in the function as a mold material, particularly physical properties such as strength. There is fear.

On the other hand, when producing a wet mold material that does not have normal temperature fluidity, a wet mold material that does not have normal temperature fluidity (coated sand) is generally obtained by kneading or mixing an aqueous water-soluble inorganic binder as a binder with a room temperature refractory aggregate, together with additives as necessary. method is adopted. The moisture content of the mold material (coated sand) in a wet state that does not have normal temperature fluidity is adjusted as necessary to the extent that it exhibits a wet state. For example, when water glass is used as the water-soluble inorganic binder, the moisture content of the mold material (coated sand) is adjusted to be more than 55% by mass, preferably 70 to 900% by mass, more preferably 95 to 500% by mass of the solid content of the water glass. be done. The wet mold material (coated sand) having the moisture content adjusted in this way is dried by the blown air when the mold is filled in the molding process, effectively preventing the filling of the mold from being obstructed, and keeping the wet mold material (coated sand) moist. In addition, the mold made using such a mold material (coated sand) is also endowed with excellent properties. In the present invention, a mold material in a wet state that does not have normal temperature fluidity refers to a mold material whose dynamic angle of repose cannot be measured regardless of the water content.

The mold material according to the present invention may be used in either a dry state or a wet state, but a dry state with room temperature fluidity is more desirable because it has room temperature fluidity and is easy to handle.

In the process of producing a dry or wet mold material, the iron-containing compound powder may be added to the refractory aggregate in a state of being pre-mixed with an aqueous water-soluble inorganic binder and kneaded or mixed, may be added separately during kneading and kneaded, or may be kneaded with a time lag during kneading. Therefore, in the case of the dry mold material according to the present invention, the coating layer covering the surface of the refractory aggregate may be composed of a layer containing a mixture of the water-soluble inorganic binder and the powdery substance of the iron-containing compound, or may have a structure in which a layer containing the powdery substance of the water-soluble inorganic binder and the powdery substance of the iron-containing compound is formed around the outer periphery of the layer of the water-soluble inorganic binder. It is desirable that the layer is a mixture of the water-soluble inorganic binder and the iron-containing compound powder. In addition, without using the powdered iron-containing compound, a dry aggregate in which the surface of the refractory aggregate is covered with a coating layer made of a water-soluble inorganic binder may be produced, and water and powdered iron-containing compound, if necessary, other additives may be added to the dry aggregate, and other additives may be added and kneaded, and the resulting mixture may be used as the mold material. In the production of the dry or wet mold material according to the present invention, the water-soluble inorganic binding agent in the form of an aqueous solution as a binding agent is dissolved in water in advance when the water-soluble inorganic binding agent used is solid. Even a liquid water-soluble inorganic binder can be diluted with water to adjust its viscosity. It is also possible to separately add a solid or liquid water-soluble inorganic binder and water to the refractory aggregate or the like during kneading or mixing with the refractory aggregate or the like.

Techniques for molding a desired mold using the mold material (coated sand) thus obtained according to the present invention are roughly classified as follows, depending on the state of the mold material (coated sand) used, that is, whether it exhibits a wet state with no fluidity at room temperature or a dry state with fluidity at room temperature.

When a mold is molded using a wet mold material (coated sand) that does not have room temperature fluidity, the mold material is filled into the molding cavity of the mold that provides the desired mold, while the mold is heated to a temperature of 80 to 300° C., preferably 100 to 200° C., and held in the mold until the mold material filled therein is dried. The solidification or hardening of the filled mold material progresses by heating and holding in such a mold.

That is, by filling and holding a mold material in a wet state (coated sand) that does not have normal temperature fluidity in the cavity of the heated mold, the mold material that constitutes the filling phase in the cavity is in a wet state, so that the refractory aggregates are mutually bonded and connected via the water-soluble inorganic binder to form an assembly (bond) of the mold material that exhibits an integral mold shape. A water-soluble inorganic binder usually solidifies by evaporation of water to dryness if no additives are added, and it hardens if an oxide or salt is added as a hardening agent. In the present invention, the assembly (bond) of the mold material includes both those that are simply solidified and those that are cured with a curing agent. In addition, it should be understood that the expression "solidified material" in this specification is used in a sense including "cured material".

In addition, the wet mold material (coated sand) that does not have normal temperature fluidity is heated in advance to 80 to 300° C. and held for a certain period of time in the mold that is kept at that temperature, so that the water evaporates to dryness and is dried and solidified or hardened. The heat retention temperature for this preheating is 80 to 300.degree. C., preferably 100 to 200.degree. C., more preferably 120 to 180.degree. The temperature is preferably 80°C or higher from the viewpoint of accelerating drying and shortening the molding time, and from the viewpoint of improving moisture resistance strength by additives, and preferably 300°C or lower from the viewpoint of preventing the occurrence of the problem that moisture evaporates before the bond between the refractory aggregates is sufficiently formed and the mold strength does not develop. By heating the mold at a temperature within such a temperature range, the moisture resistance strength of the finally obtained mold can be improved and the drying of the mold material can be advantageously promoted. In addition, while the mold material is held in the mold, hot air or superheated steam may be blown into the mold to promote drying, and in order to further accelerate the solidification or curing of the mold material (filling phase), carbon dioxide (CO ₂ gas) or ester as a curing accelerator may be gaseous or misted and ventilated into the mold.

On the other hand, when a mold is made using a dry mold material (coated sand) having room temperature fluidity, the first method is to knead the dry mold material with water at the mold making site to make it wet, and the wet mold material is heated in advance to 80 to 300 ° C. and held in the molding cavity of the mold heated at that temperature for a certain period of time until the mold material dries. In the first method, a temperature of 80 to 300.degree. C., preferably 90 to 250.degree. C., more preferably 100 to 200.degree. In the second method, the mold is preheated to 80 to 200° C. and is kept at that temperature, and then filled with a dry mold material into the mold cavity, and then steam is blown into the mold cavity to allow the steam to pass through the filling phase composed of the mold material. In the second method, the heat retention temperature of the mold by preheating is 80 to 200.degree. C., preferably 90 to 150.degree. C., more preferably 100 to 140.degree.

In the first method, when a dry mold material (coated sand) and water are kneaded (mixed), the dry mold material is transported to a mold manufacturing site, where the mold is manufactured, and then water is added to make it wet at the mold manufacturing site, and then the resulting wet mold material is filled into a mold to form the desired mold. Since it is sufficient to moisten the mold material by simply putting the dry mold material and a predetermined amount of water into a suitable mixer and mixing them, the work can be carried out in an extremely simple manner, and can be carried out very simply and easily even at a molding site where the work environment is poor. When water is added, one or more substances selected from other additives, curing accelerators, and water-soluble inorganic binders for readjusting mold strength may be added together. Moreover, water may be used in which water is contained in a solution.

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

Here, in the first method and the second method described above, in order to actively dry the filled phase composed of the wet mold material, hot air or superheated steam is blown into the mold to allow the filled phase to ventilate. By passing such hot air or superheated steam (hot air, etc.), the inside of the filled phase of the mold material is dried quickly, and the solidification or hardening of the filled phase is more advantageously accelerated, thereby advantageously increasing the curing rate and improving the characteristics such as the bending strength of the obtained mold, and also advantageously contributing to shortening the molding time of the mold. In the first method, for example, before the passage of hot air, for example, in the second method, for example, between the passage of water vapor and the passage of hot air, for example, carbon dioxide (CO ₂ gas), ester, etc. may be gaseous or misted and aerated as a curing accelerator in order to promote the solidification or curing of the filling phase. The aeration of carbon dioxide, ester, etc. may be carried out simultaneously with the aeration of hot air or the like in the first method, or at the same time as the aeration of water vapor or with the aeration of hot air or the like in the second method.

Examples of the curing accelerator include carbon dioxide (carbonated water), esters such as methyl formate, ethyl formate, propyl formate, γ-butyrolactone, γ-propionlactone, ethylene glycol diacetate, diethylene glycol diacetate, glycerin diacetate, triacetin, and propylene carbonate; organic acids such as sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, oxalic acid, carboxylic acid, and p-toluenesulfonic acid; can be exemplified. These curing accelerators may be used alone or in combination of two or more. It should be noted that these hardening accelerators should be gaseous or misted while the mold is being held, and should be passed through the mold. When water is added to the dry mold material to wet it, the hardening accelerator may be added to the mold material together with water.

In addition to the methods described above, various known molding techniques can be appropriately adopted as the method for manufacturing a mold using the mold material according to the present invention. For example, it is also possible to employ a layered manufacturing method in which layers of the mold material are sequentially laminated while a portion corresponding to the desired mold is cured to directly mold a three-dimensional mold.

As described above, a predetermined molten metal is cast using a mold manufactured according to various manufacturing methods, and a desired metal part (cast product) is manufactured. However, the casting method is not particularly limited, and various known casting methods can be adopted.

Since the mold material according to the present invention contains a powder of an iron-containing compound, the refractory aggregate can be advantageously regenerated, for example, by following the regeneration method detailed below. When carrying out the recycling method described below, after the casting using the mold made of the mold material of the present invention is completed, the used mold is pulverized or crushed according to a known technique using a crusher or the like, and collected into small pieces, preferably to a size of about several millimeters or less, more preferably to a size close to each grain of refractory aggregate.

The recycling method for recovered refractory aggregates, which will be described in detail below, is mainly intended for refractory aggregates recovered from used molds after casting as described above. However, recovered refractory aggregates in the form of mold materials discharged in the molding process of the molds, and refractory aggregates recovered from unused molds that have not been subjected to casting, can also be targeted. A powdery iron-containing compound is contained in a water-soluble inorganic binder. The refractory aggregate contained in the water-soluble inorganic binder to which the iron-containing compound powder is adhered generally constitutes the whole of the recovered refractory aggregate to which the recycling method of the present invention is applied. Needless to say, the higher the ratio of the refractory aggregate containing the iron-containing compound in the recovered refractory aggregate, the more advantageous the characteristics of the present invention can be exhibited. As other refractory aggregates to be used together with such iron-containing compound-containing refractory aggregates, any refractory aggregate recovered from a mold making process or a casting process can be used regardless of the presence or absence of an iron-containing compound and regardless of the type of clay component.

In the method for regenerating recovered refractory aggregates according to the present invention, in order to regenerate the recovered refractory aggregates as described above, a polishing treatment is first carried out to scrape off the solids of the water-soluble inorganic binder adhering to the surface of the recovered refractory aggregates, and then the scraped solids are separated from the refractory aggregates by utilizing the force (action) that the iron-containing compound powders contained in the solids are attracted to the magnets by the magnetic force. Processing will be carried out.

In the grinding process, the collected refractory aggregate is ground to scrape off the solid matter of the water-soluble inorganic binder, which is a solid substance remaining on the surface of the aggregate, and separate it from the aggregate. Specifically, the recovered refractory aggregate is put into a conventionally known polishing apparatus, and the solid binder containing water-soluble inorganic binder such as water glass as a binding component that coats or adheres to the surface of the aggregate is scraped off. At this time, if the refractory aggregate to be charged is in a nodule state, it is crushed into particles one by one by the rotating rotor of the polishing apparatus, and then the surface is further polished. The polishing method in this polishing process is not particularly limited, but for example, a polishing method using a rotary reclaimer, a sand fresher, a sand shiner, or the like is appropriately adopted. In addition, the polishing conditions such as the polishing time in the polishing process are appropriately selected according to the state of solid matter adhered to the surface of the recovered refractory aggregate.

In addition, the refractory aggregate taken out from the grinding process contains a mixture of solid powders of the water-soluble inorganic binder scraped off in the grinding process, and the powder of the binder or its dust cannot be sufficiently or reliably removed by a dust collector or the like usually provided in the grinding apparatus, and is physically adhered to the surface of the refractory aggregate. A magnetic separation treatment using an appropriate magnetic separator is applied, and the iron-containing compound powder dispersed and contained in the solid water-soluble inorganic binder powder is attracted to the magnet, whereby the powder or dust of the binder is separated from the refractory aggregate. That is, magnetic separation is performed on the ground material in which the refractory aggregate and the solid binder powder are mixed, so that the refractory aggregate to which the binder is not adhered is collected in the refractory aggregate collecting section provided below the magnetic separator, while the solid binder powder containing the iron-containing compound is collected in the iron-containing compound collecting section provided below the magnetic separator.

As magnetic separators used in the above-mentioned magnetic separation process, various systems such as a semi-magnetic outer ring system, a suspension system, and a magnet pulley system are known. However, as long as the solid binder powder containing the iron-containing compound can be separated from the polished product of the recovered refractory aggregate by the magnetic force, the structure and form thereof are not particularly limited, and known machines are appropriately employed. In addition, the magnetic force in such a magnetic separator preferably has a magnetic flux density of 500 to 10,000 gauss, preferably 1,000 to 8,000 gauss, and more preferably 1,500 to 6,000 gauss for good separation of the refractory aggregate and the solid binder powder containing the iron-containing compound. If the magnetic flux density is lower than 500 gauss, the binder powder cannot be effectively separated by magnetic separation treatment, and if the magnetic flux density is higher than 10000 gauss, the solid binder powder containing the iron-containing compound is strongly attracted to the magnetic separator and magnetically attached, causing problems such as difficulty in recovery.

As described above, since the molding material according to the present invention contains the powdered material of the iron -containing compound, the solid object of the water -soluble inorganic sticker stuck to the recovery -resistant aggregate is inevitably contains the powdered material of the iron -containing compound, and the grinding and magnetization of such a recovery -resistant aggregate. By applying, a solid water -soluble inorganic sticker (powder), which has been shaved by polishing, can be easily separated from the fire -resistant aggregate using magnetic force. Moreover, the scraped solid binder powder adhering to the surface of the refractory aggregate due to static electricity or the like, which cannot be completely removed by ordinary dust collection or the like, can be easily separated from the aggregate. As described above, according to the method for recycling recovered refractory aggregates according to the present invention, it is possible to advantageously provide recycled refractory aggregates of good quality. Furthermore, since the refractory aggregate thus regenerated has the solid water-soluble inorganic binder powder scraped off sufficiently and reliably removed, when the refractory aggregate is used again for making a mold, the decrease in strength of the obtained mold can be effectively suppressed, and a mold having excellent strength can be provided.

By the way, in the recycling method of the present invention, it is also possible to advantageously employ a calcining treatment for calcining the recovered refractory aggregate to be recycled. This firing treatment can be performed before the polishing treatment according to the present invention, and can also be performed between such polishing treatment and magnetic separation treatment, further after magnetic separation treatment, and further before, between, and after two or more of these polishing and magnetic separation treatments. In addition, for the firing treatment of such recovered refractory aggregate, for example, a roasting furnace such as a rotary kiln or a tunnel kiln is used, and the recovered refractory aggregate is continuously charged into the roasting furnace while firing. A method is adopted.

By carrying out such a calcination treatment prior to the polishing treatment or the magnetic separation treatment according to the present invention, it becomes possible to burn and remove deposits, dust, and impurities on the refractory aggregate. The firing temperature in the roasting furnace in such firing treatment is generally about 200 to 700°C, preferably about 300 to 700°C, more preferably about 350 to 650°C, and still more preferably about 400 to 600°C. If the firing temperature is lower than 200°C, there is a risk that the deposits, dust, and impurities of the refractory aggregate will not burn sufficiently. If the firing temperature exceeds 700°C, the iron-containing compound will be oxidized, and the attraction of the iron-containing compound to the magnet will decrease, and the water-soluble inorganic binder will sinter, causing problems such as difficulty in peeling off from the refractory aggregate.

Further, in the case where such a calcination treatment is performed after the magnetic separation treatment according to the present invention, even if the binder adheres to the recovered refractory aggregate, the water-soluble inorganic binder can be deactivated by heating due to calcination. The firing temperature in the roasting furnace in such firing treatment is generally about 200 to 1000°C, preferably about 300 to 900°C, more preferably about 350 to 850°C, and still more preferably about 400 to 800°C. If the firing temperature is lower than 200°C, the water-soluble inorganic binder adhering to the refractory aggregate may not be sufficiently deactivated. Further, if the baking temperature exceeds 1000° C., problems such as an increased load on the roasting furnace and an increase in heating cost may be caused.

Furthermore, in the method for regenerating recovered refractory aggregate according to the present invention, it is also effective to classify the treated refractory aggregate taken out from the grinding treatment or magnetic separation treatment. If firing treatment is performed after polishing treatment or magnetic separation treatment according to the present invention, this classification treatment is performed after such firing treatment. The classification process includes a dust collection step in which fine powder contained in the treated refractory aggregate is removed by a dust collector by causing the treated refractory aggregate to flow with an air flow, and a sieving step in which foreign matter contained in the treated refractory aggregate is removed by a sieve. Specifically, in the dust collection step, the treated refractory aggregate is made to flow by an air flow, and fine powder such as shavings, dust, and fine powder contained in the treated refractory aggregate that could not be removed in the previous steps is removed by the dust collector in a driven state. In addition, in the sieving step, a sieve is used to classify the particle size of the treated refractory aggregate, thereby removing foreign matter contained in such treated refractory aggregate that could not be removed in the previous steps. This removes large residues from the refractory aggregate after magnetic separation and selectively extracts aggregates of appropriate particle size.

The classification process employed here is not limited to one having the dust collection process and the sieving process as described above. For example, it may have either one of the dust collection process and the sieving process, or the dust collection process may be performed after the sieving process. Furthermore, the classification step can employ any other known technique as long as it is a technique capable of classifying the refractory aggregate into predetermined sizes.

Then, as described above, the refractory aggregate regenerated by the method for regenerating recovered refractory aggregate according to the present invention is again supplied to the molding process of the mold, and is advantageously used as an aggregate (foundry sand) capable of providing a mold with excellent properties.

It should be noted that the mold material and its manufacturing method, mold manufacturing method, and recovered refractory aggregate regeneration method according to the present invention described above should not be construed in any limiting way by the specific descriptions of the above-described exemplary embodiments, and the present invention can be implemented in aspects with various changes, modifications, improvements, etc., based on the knowledge of those skilled in the art, and such aspects of implementation do not deviate from the gist of the present invention, so long as they all fall within the scope of the present invention. , should be understood.

For example, in each step of the polishing treatment and the magnetic separation treatment in the above-described method for regenerating the recovered refractory aggregate, fine powder is dispersed in the air during the treatment. Therefore, in addition to the above-described dust collection step, an operation of sucking the atmosphere so as to remove the fine powder is appropriately adopted in each step.

Some examples of the present invention will be shown below to clarify the present invention more specifically, but it goes without saying that the present invention is not subject to any restrictions by the description of such examples. Note that "%" and "parts" shown in the following description are based on mass unless otherwise specified. In the following examples and comparative examples, the average particle size of the powder, the light transmittance of the dispersion of the powder, the water content of the coated sand (CS) as the mold material, the magnetic adhesion rate of CS, the adhesion of sand (adherence of CS) when casting using each CS, and the surface roughness of the casting surface were measured and evaluated as follows.

(1) Average particle size of the powdery material Regarding the average particle size of the powdery material, the particle size at an integrated value of 50% is measured as the average particle size (D ₅₀ ) from the particle size distribution using a Microtrac particle size distribution analyzer (product name: MT3200II) manufactured by Nikkiso Co., Ltd. In addition, when the average particle size of the powder used in Examples and Comparative Examples was measured using the above-mentioned measuring device, the error between the published value of each manufacturer was within 10%.

(2) Light transmittance of dispersion liquid of powder First, for a blank liquid made of an aqueous solution containing 30% by mass of a solid content of a water-soluble inorganic binder (water glass No. 2 or sodium chloride), the transmittance of light at a wavelength of 660 nm is measured using a spectrophotometer (manufactured by Hitachi High-Tech Science Co., Ltd., trade name: U-2800), and the transmittance is adjusted to 100%. Next, 5 parts by mass of the powdery material is added to 100 parts by mass of the blank liquid and stirred for 1 minute to prepare a dispersion liquid. After 15 minutes have passed since the dispersion liquid is placed in a measurement container and allowed to stand still, the transmittance of light having a wavelength of 660 nm is measured. This measurement was performed three times, and the average value of the light transmittance calculated from the three measurements is shown in Tables 1 to 6 below as "light transmittance of dispersion".

(3) Water content of CS When water glass is used as a water-soluble inorganic binder, the water content in CS (water content relative to the solid content of water glass contained in CS) was measured and calculated according to the following procedure. 10 g of each CS is weighed and placed in a crucible that has been air-fired and weighed, and the amount of water content (W1) in CS is calculated from the following formula (1) using the mass reduction amount (%) after exposure to heat at 900 ° C. for 1 hour. In addition, the weighing amount is measured to the fourth decimal place. Next, the solid content (B1) of water glass relative to CS is calculated using the following formula (2), and then the water content relative to the solid content of water glass (the water content of CS relative to the solid content of water glass in the coating layer: W2) is calculated using the following formula (3) from the water content (W1) in CS and the solid content (B1) of water glass relative to CS. W2 calculated as described above is shown as "moisture content" in Tables 1 to 6 below.
W1=[(M1−M2)/M3]×100 (1)
[W1: water content in CS (%), M1: total mass of crucible and CS before firing (g),
M2: total mass of crucible and CS after firing (g), M3: mass of CS before firing (g
)]
B1=[B2/(100+B2)]×(100−W1) (2)
[B1: solid content (%) of water glass relative to CS, B2: solid content (parts) of water glass added to 100 parts of sand, W1: water content in CS (%)]
W2=(W1/B1)×100 (3)
[W2: Water content (%) of CS with respect to the solid content of water glass in the coating layer, W1:
Moisture content (%) in CS, B1: Solid content (%) of water glass relative to CS]

(4) Magnetization Percentage of CS As for the dry CS, 100 g was taken out from the dry CS and used as a sample. On the other hand, as for the wet CS, after holding the CS in a dryer at 110° C. for 30 minutes, the dried CS was thawed, and 100 g of the thawed CS was taken out and used as a sample. The removed sample was attached to a magnet of 5000 gauss, and the magnetic attachment rate of the sample (CS) was calculated from the amount of the sample attached to the magnet using the following formula.
Magnetic adhesion rate (%) = [attached mass (g)] / [sample amount (g)] × 100

(5) Evaluation of adhesion state of CS First, as shown in Fig. 1 , in a half-split hollow main mold 6 (cavity diameter: 6 cm, height: 6 cm) made in advance with room-temperature self-hardening sand and having a core baseboard fixing part 4 at the bottom (cavity diameter: 6 cm, height: 6 cm), a circular hollow core 10 (diameter: 5 cm, height: 5 cm) having a base board part 8 made using each CS is adhesively cracked and fixed with the base board fixing part 4, and then further semi-hollow. The main molds 6 are adhered and fixed to each other to produce a sand mold 12 for casting test. Next, molten aluminum alloy (temperature: 710±5° C.) is poured from the pouring port 2 of the casting test sand mold 12 and allowed to solidify, then the main mold 6 is broken to remove the cylindrical casting 16 shown in FIG. After that, the core part was removed, and the adhesion of core sand (CS) to the casting was visually confirmed. In addition, in the present invention, evaluations of Δ and ◯ are regarded as acceptable. The evaluation results for each CS are shown in Tables 1 to 4 as "state of sand adhesion after casting".
◯: Adhesion of sand was not observed at all.
Δ: Adhesion of sand was observed on part of the casting surface.
x: Adhesion of sand was observed over the entire casting surface.

(6) Evaluation of Surface Roughness of Casting Surface For castings for which the state of adhesion of sand was confirmed according to the above "(5) Evaluation of CS adhesion state", the surface roughness was evaluated visually and by the feel when touched with a finger according to the following criteria. When sand (CS) adhered to the surface of the casting, the surface of the casting was evaluated after removing the adhering sand (CS) with a brass brush or the like. In the present invention, evaluations of Δ and ◯ are regarded as acceptable.
◯: There is almost no unevenness that can be visually recognized, and fingertips do not feel caught.
Δ: Some unevenness is visually observed, but fingertips are not caught.
x: Large unevenness is visually recognized and the fingertip is caught.

-Production example 1 of wet CS-
Lunamos #60 (trade name, manufactured by Kao-Quaker Co., Ltd.), which is a commercially available artificial sand for casting, is used as a refractory aggregate, and as water glass, which is a water-soluble inorganic binder, commercially available sodium silicate No. 2 (trade name, manufactured by Fuji Chemical Co., Ltd., molar ratio of SiO ₂ /Na ₂ O: 2.5, solid content: 41.3%), and magnetite powder (spherical, average particle diameter: 0.25 μm), which is an iron-containing compound. and prepared. Magnetite powder in an amount corresponding to 0.125 parts per 100 parts of aggregate (Lunamos #60) was added to water glass in an amount corresponding to 1.0 parts (solid content: 0.41 parts) per 100 parts of aggregate (Lunamos #60), and mixed to form a liquid mixture. Ton), and the previously prepared liquid mixture (water glass + magnetite powder) was put into a stirrer, kneaded for 3 minutes, and stirred and mixed until uniform. After that, the mixed material was taken out from the stirrer to obtain a wet mold material (coated sand): CS1 consisting of a mixed material of aggregate, water glass and magnetite powder. When the water content of CS1 obtained was calculated, it was an amount corresponding to 140% by mass of the solid content of water glass.

-Production example 2 of wet CS-
A wet mold material: CS2 was obtained in the same manner as in Production Example 1 above, except that the amount of magnetite powder added was 0.25 parts. When the water content of CS2 obtained was calculated, it was an amount corresponding to 140% by mass of the solid content of water glass.

-Production example 3 of wet CS-
A mold material in a wet state: CS3 was obtained in the same manner as in Production Example 1 above, except that the amount of magnetite powder added was 0.50 parts. When the water content of CS3 obtained was calculated, it was an amount corresponding to 140% by mass of the solid content of water glass.

-Production example 4 of wet CS-
A wet mold material: CS4 was obtained in the same manner as in Production Example 1 above, except that the amount of magnetite powder added was 1.00 parts. When the water content of the obtained CS4 was calculated, it was an amount corresponding to 140% by mass of the solid content of the water glass.

-Production example 5 of wet CS-
A wet mold material CS5 was obtained in the same manner as in Production Example 3, except that magnetite powder having a spherical shape and an average particle size of 0.10 μm was used. When the water content of CS5 obtained was calculated, it was an amount corresponding to 140% by mass of the solid content of water glass.

-Production example 6 of wet CS-
A wet mold material CS6 was obtained in the same manner as in Production Example 3, except that magnetite powder having a spherical shape and an average particle size of 3.0 μm was used. When the water content of the obtained CS6 was calculated, it was an amount corresponding to 140% by mass of the solid content of the water glass.

-Production example 7 of wet CS-
A wet mold material: CS7 was obtained in the same manner as in Production Example 3, except that magnetite powder having an octahedral shape and an average particle size of 0.30 μm was used. When the water content of CS7 obtained was calculated, it was an amount corresponding to 140% by mass of the solid content of water glass.

-Production example 8 of wet CS-
A wet mold material: CS8 was obtained in the same manner as in Production Example 3, except that ferrite powder (acicular, average particle size: φ0.2 × 1.0 µm) was used instead of magnetite powder. When the water content of the obtained CS8 was calculated, it was an amount corresponding to 140% by mass of the solid content of the water glass.

-Production example 9 of wet CS-
A wet mold material: CS9 was obtained in the same manner as in Production Example 3, except that instead of the magnetite powder, iron oxide powder (needle-shaped, average particle size: φ0.08 × 0.8 µm), which is neither magnetite nor ferrite, was used. When the water content of the obtained CS9 was calculated, it was an amount corresponding to 140% by mass of the solid content of the water glass.

-Production example 10 of wet CS-
In Production Example 3, a wet mold material: CS10 was obtained in the same manner as in Production Example 3, except that a commercially available anionic surfactant (trade name: Olphine PD-301, manufactured by Nissin Chemical Industry Co., Ltd.) was added in the proportion shown in Table 2 below. When the water content of CS10 obtained was calculated, it was an amount corresponding to 140% by mass of the solid content of water glass.

-Production example 11 of wet CS-
In Production Example 3, a wet mold material: CS11 was obtained in the same manner as in Production Example 3, except that a commercially available nonionic surfactant (trade name: Olphine E1004, manufactured by Nissin Chemical Industry Co., Ltd.) was added in the proportion shown in Table 2 below. When the water content of CS11 obtained was measured, it was found to be an amount corresponding to 140% by mass of the solid content of water glass.

-Production example 12 of wet CS-
Lunamos #60 (trade name, manufactured by Kao-Quaker Co., Ltd.), which is commercially available artificial sand for casting, as a refractory aggregate, magnetite powder (spherical, average particle size: 0.25 μm), which is an iron-containing compound, and sodium chloride (Na chloride), which is a water-soluble inorganic binder, were dissolved in water to prepare an aqueous sodium chloride solution having a solid content (concentration) of 20% by mass. Then, the aggregate (Lunamos #60) was put into a Shinagawa-type universal stirrer (5DM-r type, manufactured by Dalton Co., Ltd.) at room temperature, and further, sodium chloride aqueous solution was added to 100 parts of the aggregate (Lunamos #60) at a rate of 3.0 parts (solid component: 0.6 parts), and magnetite powder was added at a rate of 0.50 parts to 100 parts of the aggregate (Lunamos #60). Here, the magnetite powder was added in a state in which it was previously mixed with an aqueous sodium chloride solution. After this addition, kneading was performed for 3 minutes in a stirrer, and stirring and mixing were performed until uniform. After that, the mixed material was taken out from the stirrer to obtain a wet mold material: CS12 consisting of a mixed material of aggregate, sodium chloride and magnetite powder. The water content of the obtained CS12 was calculated and found to be 79% by mass of the solid content of the aqueous sodium chloride solution, in other words, an amount corresponding to 79% by mass of the sodium chloride (solid content) contained in CS.

-Production example 13 of wet CS-
A mold material in a wet state: CS13 was obtained according to the same procedure as in Production Example 1 above, except that no magnetite powder was used in Production Example 1 above. When the water content of the obtained CS13 was calculated, it was an amount corresponding to 140% by mass of the solid content of the water glass.

-Production example 14 of wet CS-
A wet mold material: CS14 was obtained in the same manner as in Production Example 3, except that magnetite powder having a spherical shape and an average particle size of 160.2 μm was used. When the water content of CS14 obtained was calculated, it was an amount corresponding to 140% by mass of the solid content of water glass.

-Production example 15 of wet CS-
A wet mold material CS15 was obtained in the same manner as in Production Example 3, except that magnetite powder having a spherical shape and an average particle size of 106.5 μm was used. The water content of the obtained CS15 was calculated and found to be an amount corresponding to 140% by mass of the solid content of the water glass.

-Production example 16 of wet CS-
A wet mold material: CS16 was obtained in the same manner as in Production Example 3, except that copper oxide powder (amorphous, average particle size: 32.1 μm) was used instead of magnetite powder. When the water content of CS16 obtained was calculated, it was an amount corresponding to 140% by mass of the solid content of water glass.

-Molding Example I (Examples 1 to 12, Comparative Examples 1 to 4)-
CS1 to CS16 (temperature: 20° C.) produced according to each of the procedures described above were filled in a mold heated to 150° C., held in the mold, and each CS filled in the mold was solidified (cured) to prepare a mold for use as a test piece (φ50×50 cm) of a circular non-aerial element. Tables 1 and 2 below show the CS used in producing the molds (test specimens) for Examples 1 to 12 and Comparative Examples 1 to 4.

As is clear from the results in Tables 1 and 2, in the mold obtained using the wet mold material (CS: coated sand) according to the present invention, the adhesion of the mold material (CS: coated sand) to the casting (cast product) produced using the mold is effectively suppressed.

Next, a dry coated sand (CS) according to the present invention was produced and tested in the same manner as the wet CS.

-Production Example 17 of Dry CS-
Lunamos #60 (trade name, manufactured by Kao-Quaker Co., Ltd.), which is a commercially available artificial sand for casting, is used as a refractory aggregate, and as water glass, which is a water-soluble inorganic binder, commercially available sodium silicate No. 2 (trade name, manufactured by Fuji Chemical Co., Ltd., molar ratio of SiO ₂ /Na ₂ O: 2.5, solid content: 41.3%), and magnetite powder (spherical, average particle diameter: 0.25 μm), which is an iron-containing compound. and prepared. To water glass in an amount equivalent to 1.0 parts (solid content: 0.41 parts) per 100 parts of the aggregate (Lunamos #60), magnetite powder in an amount equivalent to 0.50 parts per 100 parts of the aggregate (Lunamos #60) is added and mixed to form a liquid mixture. Then, the previously prepared liquid mixture (water glass + magnetite powder) was put into the mixer and kneaded for 3 minutes to evaporate the water contained in the water glass and stirred and mixed until the sand grains collapsed. After that, sand grains were taken out from the mixer to obtain a dry mold material (coated sand): CS17 in which a coating layer containing water glass and a powder of an iron-containing compound was formed on the surface of the aggregate. The water content of the obtained CS17 was calculated and found to be an amount corresponding to 32% by mass of the solid content of the water glass in the coating layer.

-Production Example 18 of Dry CS-
In Production Example 17, a dry mold material: CS18 was obtained in the same manner as in Production Example 17, except that a commercially available anionic surfactant (trade name: Olphine PD-301, manufactured by Nissin Chemical Industry Co., Ltd.) was added in the proportion shown in Table 3 below. The water content of the obtained CS18 was calculated and found to be an amount corresponding to 34% by mass of the solid content of the water glass in the coating layer.

-Production Example 19 of Dry CS-
A dry mold material: CS19 was obtained in the same manner as in Production Example 17, except that the powdered magnetite was not used. The water content of the obtained CS19 was calculated and found to be an amount corresponding to 32% by mass of the solid content of the water glass in the coating layer.

-Production example 20 of dry CS-
A dry mold material: CS20 was obtained in the same manner as in Production Example 17, except that magnetite powder having a spherical shape and an average particle size of 106.5 μm was used. The water content of the obtained CS20 was calculated and found to be an amount corresponding to 34% by mass of the solid content of the water glass in the coating layer.

-Molding Example II (Examples 13-14, Comparative Examples 5-6)-
CS17 to 20 (temperature: 20°C) produced according to each of the procedures described above was blown into a molding die heated to 110°C at a gauge pressure of 0.3 MPa to fill the mold, and then under a gauge pressure of 0.05 MPa, water vapor at a temperature of 99°C was blown for 4 seconds to allow the coated sand (CS) phase filled in the molding die to pass through. Next, after such aeration of water vapor 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 (φ50 × 50 cm) of a circular non-aerial element. Table 3 below shows the CS used to prepare the molds (test specimens) for Examples 13 and 14 and Comparative Examples 5 and 6.

-Molding Example III (Examples 15-16, Comparative Examples 7-8)-
CS17 to 20 (temperature: 20° C.) produced according to each of the procedures described above was charged into a Shinagawa universal stirrer (type 5DM-r, manufactured by Dalton Co., Ltd.) at room temperature, and then water was added to 100 parts of CS at a rate of 1.0 part, and stirred to prepare a moistened CS (molding material). After filling the wet CS taken out from the stirrer into a molding die heated to 150° C., the CS was held in the molding die, and each CS filled in the molding die was solidified (cured) to prepare a mold used as a test piece (φ50×50 cm) of a circular no-aerial element. Table 4 below shows the CS used to prepare the molds (test specimens) of Examples 15-16 and Comparative Examples 7-8.

As is clear from the results in Tables 3 and 4 above, the dry mold material (CS: coated sand) according to the present invention is also found to effectively suppress adhesion of the mold material (CS) to the casting (cast product) when casting is performed in a mold obtained using the same. In particular, the molds (test specimens) according to Examples 13 and 14 were molded with a mold material (CS) that was made wet by aeration of water vapor, and the molds (test specimens) according to Examples 15 and 16 were molded with a mold material that was made wet by adding water. It is recognized that the adhesion of the mold material (CS) to the casting (cast product) is effectively suppressed even in the body).

-Molding Example IV (Examples 17-18, Comparative Examples 9-10)-
Using each of CS3, CS7, CS10, CS11, CS13 and CS15, according to the procedure of "Molding Example I" described above, a mold (width: 2.54 cm × height: 2.54 cm × length: 20 cm) serving as a test body was produced, and the bending strength and filling rate (%) of the resulting mold (test body) were measured according to the methods described below. The measurement results are shown in Table 5 below.

(7) Bending strength The breaking load of the mold (test piece) obtained using each CS is measured using a measuring device (manufactured by Takachiho Seiki Co., Ltd.; digital casting sand strength tester). Then, using this measured breaking load, the bending strength is calculated from the following formula.
Bending strength (N/cm ² )=1.5×(L×W)/(a×b ² )
[L: distance between fulcrums (cm), W: breaking load (N), a: width of test piece (cm),
b: Thickness of specimen (cm)]

(8) Filling rate For the mold (specimen) obtained using each CS, the ratio of the specific gravity of each mold (specimen) to the true specific gravity of the aggregate (calculated by dividing the mass by the volume of the test piece) is calculated as a percentage.
Filling rate (mass%) = {[mass of specimen (g)/volume of specimen (cm ³ )]
/ true specific gravity of aggregate (g/cm ³ )}×100

As is clear from the results in Table 5, the mold obtained using the mold material according to the present invention exhibits excellent mold strength and is also excellent in fillability.

-Production Example of Recycled CS and Mold Forming Example V (Examples 21 and 22, Comparative Example 11)-
After bonding and fixing a circular coreless core 10 (5 cm in diameter x 5 cm in height) having a baseboard 8 made using each of the above three mold materials (CS3, CS10, CS13) with a baseboard fixing part 4, inside a half-split hollow main mold 6 (cavity: 6 cm in diameter x 6 cm in height), which is shown in FIG. Furthermore, the half-split hollow main molds 6 were bonded and fixed to each other to prepare a sand mold 12 for casting test. In addition, in order to prevent molten metal from leaking during casting, the bonded main mold was firmly fixed by clamping it with a vise or the like, or by wrapping the circumference of the main mold with a wire. Molten aluminum alloy (temperature: 710±5° C.) was poured from the pouring port 2 of the casting test sand mold 12 and allowed to solidify, then the main mold 6 was broken to remove the cylindrical casting 16 shown in FIG. Then, the recovered mold pieces were pulverized until the size (maximum length) thereof became 3 mm or less.

500 parts of the crushed mold pieces (refractory aggregate to which water glass adheres) were placed in a ball mill as a grinder and subjected to grinding treatment for 30 minutes. Then, as magnetic separation treatment, a 5000 gauss magnet was used to remove powders and particulates attracted to the magnet from the refractory aggregate after the grinding treatment. After that, as a dust collection step, a dust collector was provided above a 280-mesh sieve, and fine particles were removed by blowing air from below during sieving to obtain a regenerated refractory aggregate. Hereinafter, 1) the above casting is performed using a core made of CS3, and then the recycled aggregate a is a refractory aggregate regenerated from the recovered core piece, 2) the above casting is performed using the CS10 core, and then the recycled aggregate b is a refractory aggregate regenerated from the recovered core piece, and 3) the above casting is performed using a core made of CS13, and then the above-described refractory aggregate is regenerated from the recovered core piece. The flammable aggregate is denoted as recycled aggregate c, respectively. Then, 1) using the recycled aggregate a, a wet mold material: recycled CS3′ was obtained according to the same manufacturing method as CS3, 2) using the recycled aggregate b, a wet mold material: recycled CS10′ was obtained according to the same manufacturing method as CS10, and 3) using the recycled aggregate c, a wet mold material: recycled CS13′ was obtained according to the same manufacturing method as CS13.

Using the obtained regenerated CS3′, regenerated CS10′, and regenerated CS13′, a mold (width: 2.54 cm×height: 2.54 cm×length: 20 cm) serving as a specimen was prepared according to the procedure of “Casting Example I” described above, and the bending strength of the resulting mold (test specimen) was measured according to the method shown in “(7) Measurement of bending strength” described above. Then, from 1) the bending strength of CS3 (the bending strength of Example 17) and the bending strength of the recycled CS3′ obtained using the recycled aggregate of CS3 (the recycled aggregate a), 2) the bending strength of CS10 (the bending strength of Example 19) and the bending strength of the recycled CS10′ obtained using the recycled aggregate of CS10 (the recycled aggregate b), 3) the bending strength of CS13 (the bending strength of Comparative Example 9) and CS. Based on the bending strength of the recycled CS13' obtained using the recycled aggregate (recycled aggregate c) of No. 13, the strength expression rate (%) was calculated based on the following formula. The results are shown in Table 6 below.
Strength expression rate (%)
=[Bending strength of CS (N/cm ² )/Bending strength of recycled CS (N/cm ² )]×100

As is clear from the results in Table 6, the mold materials (recycled CS3' and recycled CS10') using refractory aggregates recycled from the mold materials according to the present invention were found to have a high strength development rate (Examples 21 and 22). On the other hand, in the casting mold material (recycled CS13') using the refractory aggregate recycled from the casting mold material in which the powder of the iron-containing compound is not used, the strength development rate is low, and it has been confirmed that it is difficult to efficiently recycle the recovered refractory aggregate.

2 Molten metal injection port 4 Baseboard fixing part 6 Main mold 8 Baseboard part 10 Circular airless element 12 Casting test mold 14 Waste core discharge port 16 Casting

Claims (14)

(a) a refractory aggregate;
(b) a water-soluble inorganic binder;
(c) A mold material composed of a wet coated sand having no normal temperature fluidity, characterized by containing at least a powdery substance of an iron-containing compound (excluding Fe—Si alloys) having an average particle size of 0.01 μm or more and less than 50 µm, but not containing powdery substance of a metal-containing compound other than the powdery substance of the iron-containing compound. The mold material of claim 1, wherein said iron-containing compound is iron oxide. 3. The mold material of claim 2, wherein said iron oxide is selected from the group consisting of magnetite, maghemite, ferrite, and mixtures of two or more thereof. The mold material according to any one of claims 1 to 3, wherein the iron-containing compound powder is contained in a proportion of 1 to 500 parts by mass with respect to 100 parts by mass of the solid content of the water-soluble inorganic binder. 5. The mold material according to any one of claims 1 to 4, wherein an aqueous solution containing 30% by mass of the water-soluble inorganic binder as a solid content is used as a blank solution, and the light transmittance of the blank solution at a wavelength of 660 nm is 100%. 6. The mold material according to any one of claims 1 to 5, wherein the iron-containing compound powder is spherical. 7. The mold material according to any one of claims 1 to 6, further comprising a surfactant. The mold material according to any one of claims 1 to 7, wherein the water-soluble inorganic binder is water glass. A method of manufacturing a mold, comprising filling the mold material according to any one of claims 1 to 8 into a heated mold, holding the mold material in the mold, and solidifying or hardening the material to obtain a desired mold. The mold manufacturing method according to claim 9 , wherein the mold is heated to a temperature of 80°C to 300°C. 11. The mold manufacturing method according to claim 9 or 10 , wherein hot air or superheated steam is passed through the mold while the mold is being held. A method for regenerating recovered refractory aggregate containing refractory aggregate to which the water-soluble inorganic binder containing the powder of the iron-containing compound adheres, which is obtained after casting using a mold made of the mold material according to any one of claims 1 to 8,
After the refractory aggregate is recovered, the recovered refractory aggregate is polished to scrape off the water-soluble inorganic binder adhering to the surface thereof, and then the solid matter of the water-soluble inorganic binder scraped off from the refractory aggregate is separated from the refractory aggregate by utilizing the action of attracting the powder of the iron-containing compound contained in the solid matter to a magnet. how to play. 13. The method for regenerating recovered refractory aggregate according to claim 12, wherein the magnetic separation treatment is performed by a magnetic separator having a magnetic flux density within the range of 500 to 10000 gauss. 14. The method for regenerating recovered refractory aggregates according to claim 12 or 13 , wherein the sintering treatment of the refractory aggregate is performed prior to the polishing treatment, between the polishing treatment and the magnetic separation treatment, and/or after the magnetic separation treatment.

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