CN109982786B

CN109982786B - Precoated sand, method for producing same, and method for producing mold using same

Info

Publication number: CN109982786B
Application number: CN201780072064.4A
Authority: CN
Inventors: 高间智宏; 浦哲也
Original assignee: Asahi Yukizai Corp
Current assignee: Asahi Yukizai Corp
Priority date: 2016-11-22
Filing date: 2017-11-22
Publication date: 2021-04-20
Anticipated expiration: 2037-11-22
Also published as: JPWO2018097180A1; JP7055753B2; WO2018097180A1; CN109982786A

Abstract

The present invention provides: the coated sand is dry and has room temperature fluidity, and the mold obtained by using the coated sand exerts excellent strength and excellent disintegration. A coated sand which is a dry coated sand having room-temperature fluidity and obtained by covering the surface of a refractory aggregate with a coating layer containing water glass as a binder, wherein the coating layer contains spherical particles, preferably spherical particles having an average particle diameter of 0.1 to20 [ mu ] m.

Description

Precoated sand, method for producing same, and method for producing mold using same

Technical Field

The present invention relates to a coated sand, a method for producing the same, and a method for producing a mold using the same, and particularly to: the finally obtained mold exhibits excellent strength and excellent disintegration properties, and is a dry precoated sand having room-temperature fluidity.

Background

Conventionally, as one of the molds used for casting molten metal, a mold obtained by: and molding the casting sand into a desired shape by using precoated sand obtained by covering casting sand made of a refractory aggregate with a predetermined binder. Specifically, on pages 78 to 90 of "casting engineering review" edited by japan foundry society, as a binder in such coated sand, in addition to an inorganic binder such as water glass, an organic binder using a resin such as a phenol resin, a furan resin, or a urethane resin is described, and a method of molding a self-hardening mold using such a binder is also described.

For example, jp 2012-076115 a (patent document 1) discloses a binder-coated refractory (coated sand) having good fluidity, in which a coating layer containing a solid water glass is coated on the surface of a refractory aggregate, as a binder-coated refractory using water glass as a binder. Therein, the following methods are elucidated: after filling the refractory material coated with the binder (precoated sand) having such good fluidity into the cavity of a mold for molding a mold, the binder-coated refractory material (precoated sand) is cured by introducing steam, thereby obtaining a target mold.

However, as disclosed in patent document 1, when molding conventional dry precoated sand according to the method disclosed herein, specifically, according to a method of filling the precoated sand into a mold cavity and then ventilating water vapor into a filling phase of the precoated sand, there are problems as follows: when the mold is temporarily filled with the precoated sand, there is no room for improvement in the filling property of the precoated sand in the mold. On the other hand, the disintegration properties of the resulting mold are still insufficient, leaving room for improvement.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 2012-76115

Non-patent document

Non-patent document 1: pages 78-90 of casting engineering

Disclosure of Invention

Problems to be solved by the invention

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide: the finally obtained mold exhibits excellent strength and excellent disintegration properties, and is a dry precoated sand having room-temperature fluidity. Further, another object of the present invention is to provide: a method for producing a mold using such excellent precoated sand.

Means for solving the problems

In order to solve the above-described problems, the present invention may be suitably implemented in various embodiments described below, and any combination of the various embodiments described below may be adopted. It should be noted that the aspects and technical features of the present invention are not limited to the following description, and are understood to be technical means that can be recognized based on the inventive idea that can be grasped from the entire description of the specification.

(1) A precoated sand which is a dry precoated sand having room-temperature fluidity, the precoated sand being obtained by covering the surface of a refractory aggregate with a covering layer containing water glass,

the coating layer contains spherical particles.

(2) The coated sand according to the aspect (1), wherein the water content is 5 to 55 mass% of the solid content of the water glass in the coating layer.

(3) The coated sand according to the mode (1) or the mode (2), wherein the content of the spherical particles is 0.1 to 500 parts by mass with respect to 100 parts by mass of the solid content of the water glass in the coating layer.

(4) The coated sand according to any one of the above aspects (1) to (3), wherein the spherical particles have an average particle diameter of 0.1 to 20.0 μm.

(5) The coated sand according to any one of the above aspects (1) to (4), wherein the spherical particles are one or two or more selected from spherical particles formed of silica, alumina, or titanium oxide.

(6) The coated sand according to any one of the above aspects (1) to (5), wherein the average particle diameter d1 of the spherical particles and the average particle diameter d2 of the refractory aggregate satisfy the following formula (1).

4×d1≤d2≤5000×d1···(1)

(7) The precoated sand according to any one of aspects (1) to (6), wherein the refractory aggregate is spherical.

(8) A method for producing precoated sand, characterized in that it is a method for producing dry precoated sand having room-temperature fluidity, in which the surface of a refractory aggregate is covered with a coating layer containing water glass,

a binder mainly composed of water glass and spherical particles are mixed with the heated refractory aggregate, and the surface of the refractory aggregate is covered with a covering layer composed of water glass and spherical particles by evaporating water, thereby producing coated sand having a water content of 5 to 55 mass% of the solid content of water glass in the covering layer.

(9) A method for producing a mold, characterized in that the precoated sand according to any one of the above aspects (1) to (7) is used, and after being filled into a cavity of a mold for providing a target mold, the precoated sand is allowed to ventilate with water vapor, held in the mold, and cured or hardened to obtain the target mold.

(10) A method for producing a mold, characterized in that the precoated sand according to any one of the above aspects (1) to (7) is added with water to be wet, and after the wet precoated sand is filled into a mold, the mold is held in the mold and cured or hardened, thereby obtaining a target mold.

(11) The method of manufacturing a mold according to the above aspect (9) or (10), wherein, during the holding of the mold, dry air, heated dry air, or nitrogen gas is further introduced into a mold cavity of the mold.

ADVANTAGEOUS EFFECTS OF INVENTION

As described above, the dry coated sand having room-temperature fluidity according to the present invention is configured as follows: the covering layer covering the surface of the refractory aggregate contains both water glass as a binder and spherical particles. When the precoated sand of the present invention is filled into a mold (more specifically, into a mold cavity of a mold), and water is supplied to the filled precoated sand (filler phase) by the aeration of water vapor or the like, the spherical particles efficiently flow between the refractory aggregates together with the water glass that is in a solution state by the supplied water, and as a result, the filling property of the precoated sand in the mold (in the mold cavity) can be advantageously improved. In addition, in the mold obtained by curing or hardening the water glass in a state in which the filling property is further improved, the spherical particles are effectively interposed in the gaps between the adjacent refractory aggregates, and thereby excellent strength is exhibited.

In addition, the mold obtained using the dry precoated sand having room temperature fluidity of the present invention has a structure similar to a stone wall due to the refractory aggregate, the spherical particles, and the cured or hardened water glass, and thus exhibits strength capable of withstanding high pressure at the time of melt injection. Further, when a high-temperature molten liquid is poured into a mold, water glass that bonds the refractory aggregates in the mold is decomposed, and as a result, spherical particles exist between the refractory aggregates, so that in the mold obtained using the coated sand of the present invention, the bonding effect between the refractory aggregates by the water glass is lost earlier than before after the molten liquid is poured, and the disintegration property becomes excellent.

Drawings

FIG. 1 is a vertical cross-sectional explanatory view of a sand mold for casting test used in the examples for measuring the disintegratability of the core.

FIG. 2 is a longitudinal sectional view of an aluminum alloy casting containing a waste core in the example.

Detailed Description

Thus, the precoated sand of the present invention is generally produced as follows: the coated sand is a dry coated sand in which a dried coating layer formed of a solid component of water glass as a binder is formed on the surface of the refractory aggregate in a predetermined thickness, and has good room-temperature fluidity.

Here, the term "dry coated sand having room temperature fluidity" in the present invention means a coated sand that can obtain a measured value when the dynamic repose angle is measured, regardless of the moisture content. The dynamic repose angle is an angle formed between a slope of a precoated sand layer flowing in a cylinder and a horizontal plane by accommodating precoated sand in the cylinder whose one axial end is closed by a transparent plate (for example, by putting the precoated sand in a container having a diameter of 7.2cm × a height of 10cm to a half of the volume of the container), holding the cylinder with the axis in the horizontal direction, and rotating the cylinder around the horizontal axis at a constant speed (for example, 25 rpm). The dynamic repose angle of the precoated sand of the present invention is preferably 80 ° or less, more preferably 45 ° or less, and further preferably 30 ° or less. In the present invention, by using the spherical refractory aggregate, coated sand having a dynamic repose angle of 45 ° or less can be advantageously obtained. For example, when the coated sand does not flow in the cylinder and the slope of the coated sand layer is not formed as a flat surface in a wet state, and as a result, the dynamic repose angle cannot be measured, the coated sand is referred to as wet coated sand.

The dry precoated sand having room temperature fluidity according to the present invention preferably has a water content corresponding to a ratio of 5 to 55 mass%, more preferably 10 to 50 mass%, most preferably 20 to 50 mass%, relative to the solid content of the water glass contained in the coating layer covering the surface of the refractory aggregate. When the water content in the coated sand is less than an amount corresponding to 5 mass% of the solid content of the water glass in the coating layer, the water glass is vitrified, and there is a possibility that the coated sand cannot be restored to a solution state even by adding water again at the time of mold formation, while when the water content is more than an amount corresponding to 55 mass%, the coated sand is not in a dry state. The method for measuring the moisture content in the coated sand is not particularly limited, and a method conforming to the type of water glass or the like can be suitably used. Specifically, the measurement method described in the column of the example described later can be exemplified. In addition, when the coating layer of the coated sand contains an organic component (for example, a surfactant, a humectant, or the like) containing moisture as an additive, it is necessary to measure (calculate) the moisture content in consideration of the moisture in the organic component.

As the refractory aggregate constituting the precoated sand of the present invention, any of various refractory granular or powdery materials conventionally used for casting use can be used as the refractory material functioning as a base material of a mold, and specifically, specific examples include silica sand, regenerated silica sand, special sand such as alumina sand, olivine sand, zircon sand, and chromite sand, and slag-based particles such as ferrochrome-based slag, ferronickel-based slag, and converter slag; artificial particles such as alumina-based particles and mullite-based particles, and regenerated particles thereof; alumina spheres, magnesium frit, and the like. The refractory aggregate may be fresh sand, reclaimed sand or reclaimed sand used once or more times as foundry sand in the molding of a mold, or mixed sand obtained by adding fresh sand to the reclaimed sand or reclaimed sand and mixing the same, without limitation. The refractory aggregate is generally an aggregate having a particle size of about 40 to 130 in terms of AFS index, and preferably an aggregate having a particle size of about 50 to 110.

The refractory aggregate is preferably spherical, and specifically, a refractory aggregate having a coefficient of angularity (coefficient of angularity) of 1.2 or less, more preferably 1.0 to 1.1 is desirable. By using a refractory aggregate having an angle coefficient of 1.2 or less, fluidity and filling property during mold molding are improved, the number of joints between aggregates is increased, and as a result, the amount of binder and additive required for exhibiting the same strength can be reduced. The angular coefficient of the aggregate used herein is generally used as one of the dimensions showing the shape of the particle, and is also referred to as angular factor, and the closer the value is to 1, the closer the value is to a sphere (spherical sphere). The angular coefficient is expressed by a value calculated using the surface area of the aggregate (sand surface area) measured by various known methods, and is, for example, a value obtained by measuring the surface area of actual aggregate particles (sand grains) per 1g using a sand surface area measuring instrument (manufactured by Georg Fischer ltd., ltd.) and dividing the surface area by the theoretical surface area. The theoretical surface area is a surface area when all the aggregate particles (sand grains) are assumed to be spherical.

In the precoated sand of the present invention, as the binder for covering the refractory aggregate, a binder mainly composed of water glass is used. The water glass is a water-soluble silicate compound, and examples of such silicate compounds include sodium silicate, potassium silicate, sodium metasilicate, potassium metasilicate, lithium silicate, and ammonium silicate, and among these, sodium silicate (sodium silicate) can be used favorably in the present invention. The binder may be any of various water-soluble binders, such as thermosetting resins, saccharides, proteins, synthetic polymers, salts, and inorganic polymers, as long as the binder contains water glass as a main component. When another water-soluble binder is used in combination with water glass, the ratio of water glass in the entire binder is preferably 60% by mass or more, more preferably 80% by mass or more, and most preferably 90% by mass or more.

Here, sodium silicate is generally based on SiO₂/Na₂The molar ratio of O is used in the range of 1 to 5. Specifically, sodium silicate No. 1 is SiO₂/Na₂Sodium silicate with a molar ratio of O of 2.0-2.3, and sodium silicate No. 2 being SiO₂/Na₂Sodium silicate having a molar ratio of O of 2.4 to 2.6, and further sodium silicate No. 3 is SiO₂/Na₂Sodium silicate having a molar ratio of O of 2.8 to 3.3. In addition, sodium silicate No. 4 is SiO₂/Na₂Sodium silicate with the molar ratio of O being 3.3-3.5, and the sodium silicate No. 5 is SiO₂/Na₂Sodium silicate having a molar ratio of O of 3.6 to 3.8. Among these, sodium silicate Nos. 1 to 3 are also defined in JIS-K-1408. In the present invention, these various sodium silicates may be used alone or in combination, or SiO may be adjusted by mixing₂/Na₂Molar ratio of O.

In the present invention, in order to advantageously obtain dry precoated sand, SiO, a sodium silicate constituting water glass used as a binder, is used₂/Na₂The molar ratio of O is preferably 1.9 or more, preferably 2.0 or more, and more preferably 2.1 or more, and sodium silicates corresponding to nos. 1 and 2 are particularly advantageously used in the above classification of sodium silicates. The sodium silicate nos. 1 and 2 stably obtained coated sand in a dry state with good characteristics even in a wide range of the concentration of sodium silicate in water glass. In addition, SiO of the sodium silicate₂/Na₂The upper limit of the molar ratio of O is appropriately selected depending on the characteristics of the water glass in the form of an aqueous solution, and is usually 3.5 or less, preferably 3.2 or less, and more preferably 2.7 or less. Here, if SiO₂/Na₂Of OWhen the molar ratio is less than 1.9, the viscosity of the water glass is low, and if the water content is not reduced to a large extent, the coated sand may be difficult to be dried, while when the molar ratio is more than 3.5, the solubility to water is reduced, and the bonding area is not obtained, so that the strength of the finally obtained mold may be reduced.

The water glass used in the present invention is a solution of a silicic acid compound dissolved in water, and may be used in a state of being diluted by adding water to a stock solution as it is, in addition to the stock solution as it is purchased in the market. The nonvolatile component (water glass component) obtained by removing volatile substances such as water and solvents from such water glass is referred to as a solid component, and corresponds to a soluble silicate compound such as sodium silicate. Further, the higher the ratio of such solid components (nonvolatile components), the higher the silicate compound concentration in the water glass becomes. Therefore, when the solid content of the water glass used in the present invention is constituted only by the stock solution, the amount obtained by subtracting the amount of water in the stock solution corresponds to the solid content of the water glass used, and when a diluted solution obtained by diluting the stock solution with water is used, the amount obtained by subtracting the amount of water in the stock solution and the amount of water used for dilution corresponds to the solid content of the water glass used.

The solid content (nonvolatile content) in the water glass is preferably contained in an appropriate ratio depending on the kind of the water glass component (soluble silicic acid compound), and is preferably 20 to 50 mass%. By appropriately making the water glass component corresponding to the solid component exist in the aqueous solution, the water glass component can be uniformly and uniformly coated on the refractory aggregate at the time of mixing (kneading) with the refractory aggregate, and thus the target mold can be favorably molded. When the concentration of the water glass component in the water glass is too low and the total amount of solid components is less than 20 mass%, the heating temperature needs to be increased or the heating time needs to be prolonged for drying the coated sand, which causes problems such as energy loss. In addition, when the proportion of the solid component in the water glass is too high, it is difficult to uniformly coat the surface of the refractory aggregate with the water glass component, which causes a problem in improving the characteristics of the intended mold, and it is desirable to prepare the water glass in the form of an aqueous solution so that the solid component becomes 50 mass% or less and the water content becomes 50 mass% or more.

The water glass is preferably used in a ratio of 0.1 to 5.0 parts by mass, preferably 0.1 to 2.5 parts by mass, particularly preferably 0.2 to 2.0 parts by mass, based on 100 parts by mass of the refractory aggregate in terms of solid content considering only nonvolatile components, and a predetermined coating layer is formed on the surface of the refractory aggregate. Here, the solid content was measured as follows. That is, 10g of a sample was weighed and stored in an aluminum foil dish (vertical: 9cm, horizontal: 9cm, height: 1.5cm), placed on a hot plate maintained at 180. + -. 1 ℃ for 20 minutes, the dish was inverted, and further placed on the hot plate for 20 minutes. Thereafter, the sample dish was taken out from the hot plate, cooled naturally in a desiccator, and weighed, and the solid content (% by mass) was calculated by the following equation.

Solid content (% by mass) ([ mass (g) after drying)/mass (g) before drying) ] × 100

In the present invention, when the amount of water glass used is too small, it becomes difficult to form a coating layer on the surface of the refractory aggregate, and there is a fear that the coated sand is not sufficiently cured or hardened during the molding of the mold. Further, even if the amount of water glass used becomes excessive, an excessive amount of water glass adheres to the surface of the refractory aggregate, it is difficult to form a uniform coating layer, and there is a fear that coated sand sticks to each other and agglomerates (composite particles), and therefore, there is a fear that: this has a problem that the physical properties of the finally obtained mold are adversely affected and the mold core after metal casting is difficult to be shaked.

In addition, the precoated sand of the present invention is characterized in that spherical particles are contained in a coating layer made of water glass and covering the surface of the refractory aggregate. When the coated sand containing spherical particles in the coating layer containing the water glass is filled into a mold (in a cavity of a mold), and water is supplied to the filled coated sand (filler phase) by the aeration of water vapor or the like, the spherical particles in the coating layer flow efficiently between the refractory aggregates together with the water glass that has been brought into a solution state by the supplied water, and as a result, the filling property of the coated sand in the mold (in the cavity) can be advantageously improved. In addition, in a state where such filling properties are further improved, the spherical particles are effectively interposed between the gaps between the adjacent refractory aggregates in the mold obtained by curing or hardening the water glass, and thereby excellent strength is exhibited.

In addition, the mold obtained using the dry precoated sand having room temperature fluidity of the present invention has a structure similar to a stone wall due to the refractory aggregate, the spherical particles, and the cured or hardened water glass, and thus exhibits strength capable of withstanding high pressure at the time of melt injection. Further, when a high-temperature molten liquid is poured into the mold, the water glass for binding the refractory aggregates in the mold is decomposed, and as a result, spherical particles exist between the refractory aggregates, so that in the mold obtained using the coated sand of the present invention, the binding action between the refractory aggregates by the water glass is lost earlier than before after the molten liquid is poured, and the disintegration property is also excellent.

In the dry precoated sand having room temperature fluidity according to the present invention, the spherical particles contained in the coating layer are preferably spherical particles having an average particle diameter of 0.1 to 20.0. mu.m, more preferably 0.1 to 10 μm, and most preferably 0.5 to 5.0. mu.m. In the present invention, the content of the spherical particles is 0.1 to 500 parts by mass, preferably 0.3 to 300 parts by mass, more preferably 0.5 to200 parts by mass, further preferably 0.75 to 100 parts by mass, and most preferably 1.0 to 50 parts by mass, based on 100 parts by mass of the solid content of the water glass in the coating layer. In this way, by containing spherical particles having a predetermined average particle diameter at a predetermined ratio in the coating layer, the above-described effects can be more advantageously enjoyed. The average particle diameter of the spherical particles can be determined from a particle size distribution measured by a laser diffraction particle size distribution measuring apparatus or the like.

In the present invention, when water is supplied during mold formation, the spherical particles are effectively interposed between the refractory aggregates so that the spherical particles favorably flow together with the water glass in a solution state through the gaps between the adjacent refractory aggregates, and the average particle diameter of the spherical particles is: d1 and average particle diameter of refractory aggregate: d2 preferably satisfies the following formula (1), more preferably satisfies the following formula (2), and still more preferably satisfies the following formula (3). The average particle diameter of the refractory aggregate may be determined from a particle size distribution measured by a laser diffraction particle size distribution measuring apparatus or the like.

4×d1≤d2≤5000×d1···(1)

6×d1≤d2≤3000×d1···(2)

7×d1≤d2≤2500×d1···(3)

In the present invention, the spherical particles used need only be spherical, and need not be spherical, and as a result, a spherical particle having a sphericity of usually 0.5 or more, preferably 0.7 or more, and more preferably 0.9 or more is advantageously used. Here, the sphericity is an average value of aspect ratios (ratio of short diameter/long diameter) obtained by randomly selecting 10 single particles and projecting the particles on a scanning electron microscope. Since projections and depressions are present on the surface of particles that are not spherical (non-spherical particles), for example, when the non-spherical particles are intended to flow between the particles of the refractory aggregate together with the water glass that is in a solution state by the supplied water, the projections and the like on the surface of the non-spherical particles collide with the refractory aggregate particles and other non-spherical particles, thereby causing a slip-preventing action and preventing the flow of the water glass and the non-spherical particles between the refractory aggregate particles. Therefore, in the present invention, when non-spherical particles are used, there is a fear that the filling property of the finally obtained mold and the strength thereof are lowered.

In the present invention, the material constituting the spherical particles to be used is not particularly limited, and an inorganic metal oxide is preferable. As the particles formed of an inorganic metal oxide, particles formed of silica, alumina, titania or the like are favorably used, among which, particularly, for dioxygenSilicon particles, strongly basic water glass, can react with silanol groups formed on the surface of silica, and when water evaporates, strong bonds are formed between silica and water glass which becomes solid, which is preferable in that the mold strength can be improved. The silica includes crystalline and amorphous states, desirably amorphous states, and examples of the amorphous silica include precipitated silica, calcined silica produced in an arc or by flame hydrolysis, and ZrSiO₄Silica produced by thermal decomposition of (a), silica produced by oxidation of metallic silicon in a gas containing oxygen, silica glass powder of spherical particles produced from crystalline quartz by melting and then quenching, and the like. These may be used alone or in combination of 2 or more. In the present invention, silica is treated as an inorganic metal oxide.

Further, in the coated sand of the present invention, the coating layer may contain various additives as needed in addition to the spherical particles.

One of such additives is a surfactant. When the surfactant is contained in the coating layer of the coated sand of the present invention, the permeability of water in the coated sand, in other words, the wettability of the coated sand with water is effectively improved, and therefore, even when a smaller amount of water than in the conventional case is supplied to the coated sand filled into the molding cavity of the molding die, the entire coated sand in the molding cavity is favorably wet and is in a wet state. In this way, the amount of water added to the precoated sand can be suppressed to a small amount, and therefore, the mold releasability of the mold obtained by molding from the mold is further improved, and the obtained mold exhibits more excellent strength.

In the present invention, any of various conventionally known surfactants, for example, cationic surfactants, anionic surfactants, amphoteric surfactants, nonionic surfactants, silicone surfactants, fluorine surfactants, and the like can be used as long as the object of the present invention is not impaired. The silicone surfactant is a surfactant having a siloxane structure as a nonpolar portion, and the fluorine surfactant is a surfactant having a perfluoroalkyl group. The content of the surfactant in the present invention is desirably 0.1 to 20.0 parts by mass, preferably 0.5 to 15.0 parts by mass, and particularly preferably 0.75 to 12.5 parts by mass, based on 100 parts by mass of the solid content of the water glass in the coating layer. When the amount of the surfactant contained is too small, the above-mentioned effects may not be favorably enjoyed, while when the amount of the surfactant is too large, improvement of the effect corresponding to the amount of the surfactant may not be observed, and depending on the boiling point of the surfactant, the following may occur: when the water glass is dried, the surfactant is not solidified, and the coated sand in a dry state cannot be obtained, and further, it is not a good measure from the viewpoint of cost performance.

The coating layer in the coated sand of the present invention may further contain a humectant. By including the humectant in the covering layer containing water glass, the wettability of the coated sand wetted with moisture and made wet can be stably maintained until the coated sand is cured or hardened by heating at the time of mold forming. The content of the humectant in the present invention is preferably 0.1 to 20.0 parts by mass, more preferably 0.5 to 15.0 parts by mass, and most preferably 0.75 to 12.5 parts by mass, based on 100 parts by mass of the solid content of the water glass in the coating layer. As such a humectant, polyhydric alcohols, water-soluble polymers, hydrocarbons, saccharides, proteins, inorganic compounds, and the like can be used.

Specific examples of the polyhydric alcohol include ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, dipropylene glycol, propylene glycol, butylene glycol, 1, 2-pentanediol, 1, 5-pentanediol, 1, 2-hexanediol, 2-ethyl-1, 3-hexanediol, 1, 6-hexanediol, 1, 2-heptanediol, 1, 2-octanediol, 1,2, 6-hexanetriol, thioglycol, hexanediol, glycerin, trimethylolethane, and trimethylolpropane. The water-soluble polymer compound is particularly a compound having 5 to 25 alcoholic hydroxyl groups per 1000 molecular weight. Examples of the water-soluble polymer compound include polyvinyl alcohol and polyvinyl alcohol polymers such as various modified products thereof; cellulose derivatives such as alkyl cellulose, hydroxyalkyl cellulose, alkylhydroxyalkyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, and hydroxypropyl methyl cellulose; starch derivatives such as alkyl starch, carboxymethyl starch, and oxidized starch; water-absorbing polymers such as sodium polyacrylate. Examples of the hydrocarbon include aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, petroleum ether, petroleum benzyl, tetrahydronaphthalene, decahydronaphthalene, tert-amylbenzene, and dimethylnaphthalene. Examples of the saccharide include polysaccharides such as monosaccharides, oligosaccharides, and dextrins, among which monosaccharides are those that cannot be further decomposed into simple saccharides by hydrolysis, and preferably three-carbon saccharides (monosaccharides having 3 carbon atoms) to ten-carbon saccharides (monosaccharides having 10 carbon atoms), and more preferably six-carbon saccharides (monosaccharides having 6 carbon atoms). In addition, examples of the protein include gelatin and the like. Examples of the inorganic compound include common salt, sodium sulfate, calcium chloride, magnesium chloride, and silicate. These various humectants may be used alone or in combination of 2 or more.

In the present invention, it is preferable to use a humectant having a low viscosity increase when charged with water at normal temperature (25 ℃). Specifically, in the case of a water-soluble humectant, the following are advantageously used: a humectant is added to water at normal temperature in an amount of 20% by mass of the water, and the mixture is stirred for 1 hour, whereby the viscosity of the stirred solution is 0.8 to 10cP, preferably 0.8 to 5 cP. On the other hand, a sparingly water-soluble humectant, if dispersed in water, exerts an effect as a humectant, and as a result, even a sparingly water-soluble humectant, the following humectants are advantageously used: a humectant in an amount of 20% by mass of water was added to water at normal temperature, and the mixture was stirred for 1 hour, and the stirred solution (mixture of water and humectant) was filtered to obtain a filtrate having a viscosity within the above range. As described above, examples of the humectant to be favorably used in the present invention include cellulose derivatives such as glycerin and hydroxypropylmethylcellulose, water-absorbing polymers such as sodium polyacrylate, vinyl alcohol polymers such as polyvinyl alcohol, and polyethylene glycol (polyethylene oxide) having a weight average molecular weight of 50000 or more.

Further, in the present invention, the cover layer may contain a moisture resistance improver. By including the moisture resistance improver in the covering layer, the moisture resistance of the finally obtained mold can be improved. In the present invention, any moisture resistance improver that has been conventionally used in coated sand and does not impair the effects of the present invention can be used. Specific examples thereof include carbonates such as zinc carbonate, basic zinc carbonate, iron carbonate, manganese carbonate, copper carbonate, aluminum carbonate, barium carbonate, magnesium carbonate, calcium carbonate, lithium carbonate, potassium carbonate, and sodium carbonate, borates such as sodium tetraborate, potassium tetraborate, lithium tetraborate, ammonium tetraborate, calcium tetraborate, strontium tetraborate, silver tetraborate, sodium metaborate, potassium metaborate, lithium metaborate, ammonium metaborate, calcium metaborate, silver metaborate, copper metaborate, lead metaborate, and magnesium metaborate, borates such as sodium sulfate, potassium sulfate, lithium sulfate, magnesium sulfate, calcium sulfate, strontium sulfate, barium sulfate, titanium sulfate, zinc sulfate, copper sulfate, sodium phosphate, sodium hydrogen phosphate, potassium hydrogen phosphate, lithium hydrogen phosphate, magnesium phosphate, calcium phosphate, titanium phosphate, aluminum phosphate, zinc phosphate, and zinc phosphate, phosphates such as lithium hydroxide, magnesium hydroxide, calcium hydroxide, magnesium carbonate, calcium carbonate, and sodium phosphate, Hydroxides such as strontium hydroxide, barium hydroxide, aluminum hydroxide and zinc hydroxide, and oxides such as silicon, zinc, magnesium, aluminum, calcium, lithium, copper, iron, boron and zirconium. Among them, alkaline zinc carbonate, sodium tetraborate, potassium metaborate, lithium sulfate, and lithium hydroxide are particularly preferable for improving the moisture resistance. The moisture resistance improving agents represented by the above-mentioned substances may be used alone or in combination of 2 or more.

The amount of the moisture resistance improver to be used is generally preferably about 0.5 to 50 parts by mass, more preferably 1 to20 parts by mass, particularly preferably 2 to 15 parts by mass, based on 100 parts by mass of the solid content of the water glass. The amount of the moisture resistance improver to be added is preferably 0.5 parts by mass or more in order to obtain a favorable effect of adding the moisture resistance improver, and on the other hand, if the amount is too large, the bonding of water glass may be inhibited, and the strength of the finally obtained mold may be lowered, and therefore, 50 parts by mass or less is desirable.

In addition, it is also effective to contain, as another additive, a coupling agent for reinforcing the bond between the refractory aggregate and the water glass, and for example, a silane coupling agent, a zirconium coupling agent, a titanium coupling agent, or the like can be used. In addition, it is also effective to contain a lubricant which is advantageous for improving the fluidity of the coated sand, and for example, waxes such as paraffin wax, synthetic polyethylene wax, and montan wax; fatty acid amides such as stearic acid amide, oleic acid amide and erucic acid amide; alkylene fatty acid amides such as methylene bis stearamide and ethylene bis stearamide; stearic acid, stearyl alcohol; metal stearates such as lead stearate, zinc stearate, calcium stearate, and magnesium stearate; stearic acid monoglyceride, stearic acid stearyl ester, hydrogenated oil, etc. Further, as the release agent, paraffin wax, light oil, engine 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, and the like can be used. These other additives are contained in the coating layer of the coated sand in such an amount that the solid content of the water glass in the coating layer is generally 5 mass% or less, preferably 3 mass% or less.

Therefore, in producing the dry coated sand having room-temperature fluidity according to the present invention, the following method is generally employed: the surface of the refractory aggregate is covered with water glass containing spherical particles, and the water content of the water glass is evaporated, thereby forming a coating layer containing the water glass and the spherical particles on the surface of the refractory aggregate. In such a method, since it is necessary to quickly evaporate the water in the coating layer before the water glass is cured or hardened, it is desirable that the water glass in the form of an aqueous solution is charged (mixed) into the refractory aggregate, and then the mixture is generally within 5 minutes, more preferably within 5 minutesThe contained water was scattered within 3 minutes to form dry powdery precoated sand. This is because, when the above-mentioned time period for the evaporation becomes long, the mixing (kneading) cycle becomes long, the productivity of the precoated sand is lowered, and further, water glass and CO in the air are generated₂The contact time becomes long and there is a high possibility that problems such as deactivation occur.

In addition, in the production process of the coated sand, as one of effective means for rapidly evaporating water in the water glass, the following method is adopted: the refractory aggregate is previously heated, and water glass and spherical particles in the form of an aqueous solution are kneaded or mixed therein and mixed. By kneading or mixing water glass and spherical particles with the refractory aggregate heated in advance, the water in the water glass can be evaporated extremely rapidly by the heat of the refractory aggregate, and thus the water content of the resulting coated sand can be reduced effectively, and a dry powder having room-temperature fluidity can be obtained advantageously. The preheating temperature of the refractory aggregate can be suitably selected depending on the water content of the water glass, the amount of the water glass to be blended, and the like, and generally a temperature of about 100 to 160 ℃, preferably a temperature of about 100 to 140 ℃ is used. When the preheating temperature is too low, the moisture is not efficiently evaporated, and it takes time to dry, so that it is desirable to use a temperature of 100 ℃ or higher, and when the preheating temperature is too high, the hardening of the water glass component proceeds when the obtained coated sand is cooled, and further, the composite granulation proceeds, so that there arises a problem in the function as the coated sand, particularly in the physical properties such as the strength of the finally obtained mold.

In the coated sand of the present invention, the spherical particles contained in the coating layer containing water glass, and other additives used as needed, for example, a surfactant, a humectant, and the like may be added to the refractory aggregate in a state in which water glass is mixed in advance and kneaded, or may be added separately from water glass and kneaded during kneading, or may be added and kneaded with a time difference from the input of water glass during kneading. Therefore, the coating layer in the coated sand of the present invention is, for example, in a state where the water glass and the spherical particles are integrated; or in a state where the concentration of the solid content (nonvolatile content) of the water glass is sequentially decreased or increased and the concentration of the spherical particles or the like is sequentially increased or decreased from the surface of the refractory aggregate to the outside. In kneading or the like, it is desirable that, as the timing of charging the water glass and the spherical particles to the refractory aggregate, the water glass is charged first and kneaded, and then the spherical particles are charged (with a time difference). By following such a procedure, spherical particles are present on the surface of the obtained coated sand near the coating layer, and as a result, a mold obtained by molding using such a coated sand exhibits more excellent filling properties. Further, when water glass is charged into a mixer (mixer), the viscosity of the kneaded product increases as the water contained in the water glass evaporates, and the motor load of the mixer increases, and as a result, by charging the spherical particles before the motor load of the mixer becomes maximum, the spherical particles can be effectively attached to the softened water glass covering the surface of the refractory aggregate, and the following effects can be obtained: the falling off of spherical particles in the finally obtained precoated sand is favorably prevented, and precoated sand in which spherical particles are uniformly distributed on the surface can be favorably obtained. In the production of the precoated sand of the present invention, water glass diluted with water for adjusting the viscosity may be used as the water glass as the binder, and water glass and water may be separately added in kneading or mixing with the refractory aggregate.

According to the above-mentioned method, the dry precoated sand having room-temperature fluidity according to the present invention is produced by: the water content is preferably produced so as to be in a proportion of 5 to 55 mass%, more preferably in a proportion of 10 to 50 mass%, and most preferably in a proportion of 20 to 50 mass% with respect to the solid content of the water glass contained in the coating layer covering the surface of the refractory aggregate.

Therefore, the following two methods can be used as a method for molding a mold using the dry precoated sand of the present invention. In the first method, dry precoated sand is kneaded with water at a molding site, which is a manufacturing site of a mold, to wet the precoated sand and fill the wet precoated sand into a mold cavity of a mold for providing a target mold, while heating the mold to a temperature of 90 to200 ℃, and the filled precoated sand is held in the mold until it is dry. In the second method, after filling precoated sand into a cavity of a mold for providing a target mold, steam is blown, and the filling phase of the precoated sand is wetted to a wet state by the ventilation of the steam, and then, the mold is kept in a mold heated to 90 to200 ℃ until dried.

In this case, it is desirable that the mold such as a metal mold or a wood mold, which is filled with the dry precoated sand having room temperature fluidity, is heated and kept warm in advance, whereby the precoated sand that is wet by the steam can be favorably dried. The temperature for the heat retention by the preheating is generally preferably about 90 to200 ℃, particularly about 100 to 140 ℃. When the holding temperature is too high, it is difficult for steam to pass through to the surface of the mold, while when the temperature is too low, it takes time to dry the mold. Further, it is desirable that the precoated sand in a dry state filled into the above-mentioned mold is also favorably preheated. Generally, the mold is filled with precoated sand heated to a temperature of 30 ℃ or higher, whereby the flexural strength of the resulting mold can be more favorably improved. The heating temperature of the coated sand is preferably about 30 to 100 ℃, and particularly, coated sand heated to a temperature of about 40 to 80 ℃ is favorably used.

In the first method, the step of adding water to the dry precoated sand and making it wet can be simply performed as follows: since the dry precoated sand and a predetermined amount of water are put into a suitable mixer and mixed, the method has the following advantages: can be carried out by a very simple operation, and can be carried out very simply and easily even in a molding site having a poor working environment. When water is added, other additives may be added. In the first method, instead of heating the mold, the coated sand filled in the mold in a wet state may be dried, cured, or hardened by blowing dry air, dry heated air, nitrogen gas, or the like into the coated sand.

In the second method, on the other hand, in the heated mold, specifically, after the dry precoated sand of the present invention is filled in the cavity of the mold, steam is introduced under pressure through an air vent provided in the mold in the filling phase formed therein to wet (wet) the precoated sand constituting the filling phase, and the precoated sand is bonded and connected to each other by water glass contained in the coating layer of the precoated sand, thereby forming an integrated aggregate (joint) of the precoated sand in the shape of a mold. The water glass is usually solidified by evaporation and solidification of water without adding any additive, and is hardened by adding an oxide or a salt as a hardening agent. In practice, the filler phase is hardened by adding a hardening agent, but may be simply hardened without limitation.

Here, the temperature of the steam blown through the vent of the mold to ventilate the filled phase of the coated sand is generally about 80 to 150 ℃, and more preferably about 95 to 120 ℃. When high steam temperatures are used, a large amount of energy is required for their production, so that steam temperatures in the vicinity of 100 ℃ are particularly advantageously used. Further, the pressure of the steam to be ventilated is favorably about 0.01 to 0.3MPa, more preferably about 0.01 to 0.1MPa in terms of gauge pressure. When the precoated sand has good air permeability, the precoated sand has the following characteristics: the pressure for ventilating the steam is only required to be about the gauge pressure, the steam can be ventilated in the mold formed in the mold without leakage, and the ventilation time of the steam and the drying time of the mold can be completed in a short time, thereby shortening the molding speed. In addition, if the gauge pressure is such, there are the following advantages: the molding can be performed even when the precoated sand has poor air permeability. When the gauge pressure is too high, there is a fear that sticking occurs in the vicinity of the vent hole, whereas when the gauge pressure is too low, there is a fear that ventilation is not performed in the entire packed phase of the precoated sand, and the precoated sand cannot be sufficiently wetted.

As a method for ventilating the water vapor in this manner, the following method is employed: the time for which the precoated sand can be bonded (joined) to each other can be appropriately selected depending on the size of the mold, the number of vents, and the like, and generally, a venting time of about 2 seconds to about 60 seconds is employed. This is because, if the aeration time of the steam is too short, it is difficult to sufficiently wet the surface of the coated sand, and if the aeration time is too long, there is a fear that the binder (water glass) on the surface of the coated sand dissolves or flows out. Further, the air permeability of the water vapor in the precoated sand filled in the mold can be further improved by sucking the atmosphere in the mold from the exhaust port of the mold and ventilating the water vapor.

Furthermore, when a mold is produced using the coated sand of the present invention, in the first and second methods, in order to actively dry the filling phase of the wet coated sand, the following method is suitably employed: the filling phase is ventilated by blowing dry air, heated dry air or nitrogen gas. By the ventilation with such dry air, heated dry air, or nitrogen gas, the filling phase of the coated sand is sufficiently and rapidly dried to the inside thereof, and the solidification and hardening of the filling phase can be further advantageously promoted, whereby the solidification rate can be advantageously increased, the properties such as the flexural strength of the obtained mold can be advantageously improved, and the molding time of the mold can be advantageously shortened.

In addition, in holding the mold, a hardening agent may be added to the mold as an additive for accelerating hardening of the water glass. The binder (water glass) is neutralized with a hardener, so that its curing can be further promoted. The aeration of the curing agent may be performed at any time as long as it is held in the mold, and may be performed simultaneously with the aeration of water vapor or the aeration of dry air or the like, without limitation.

Examples of the hardening agent include carbon dioxide (carbonated water), sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, oxalic acid, carboxylic acid, organic acids such as p-toluenesulfonic acid, esters such as methyl formate, ethyl formate, propyl formate, γ -butyrolactone, γ -propiolactone, ethylene glycol diacetate, diethylene glycol diacetate, glycerol triacetate, and propylene carbonate, and monohydric alcohols such as methanol, ethanol, butanol, hexanol, and octanol. These curing agents may be used alone, or 2 or more kinds may be mixed and used. In addition, as for these hardening agents, the hardening agents in a gas or mist form may be introduced into the mold while the mold is being held, or when water is added to the dry coated sand to be wet, the hardening agents may be added together with the water.

Further, when a sand mold is produced using the coating of the present invention, it is needless to say that various known molding methods can be suitably employed in addition to the above-described method of filling the coating sand into the mold and molding.

Examples

The present invention will be described more specifically with reference to the following examples, but it should be understood that the present invention is not to be construed as being limited thereto. In the following examples and comparative examples, "%" and "part(s)" are expressed on a mass basis unless otherwise specified. The Coated Sand (CS) obtained in examples and comparative examples was evaluated for moisture content, filling property, filling flowability, and strength as follows.

Determination of the amount of water relative to the solid content of the water glass

In the empty-fired and weighed crucible, 10g of each CS was weighed and stored, and the amount of water in CS (W1) was calculated from the following formula (4) using the mass reduction (%) after 1 hour of heat exposure at 900 ℃. Note that the weighing was measured to the 4 th digit after the decimal point. Then, the solid content (B1) of the water glass with respect to the CS was calculated by the following formula (5), and then, the water content with respect to the solid content of the water glass (water content of the CS with respect to the solid content of the water glass in the cover layer: W2) was calculated by the following formula (6) based on the water content (W1) in the CS and the solid content (B1) of the water glass with respect to the CS. The W2 calculated as described above is represented as "moisture content" in the following tables 1 and 2.

W1＝[(M1-M2)/M3]×100···(4)

[ W1: moisture content (%) in CS, M1: total mass (g) of crucible before firing and CS, M2: total mass (g) of crucible after firing and CS, M3: mass (g) of CS before firing

B1＝[B2/(100+B2)]×(100-W1)···(5)

[ B1: solid content (%) of water glass to CS, B2: amount of solid components (parts) of water glass added to 100 parts of sand, W1: moisture content (%) in CS

W2＝(W1/B1)×100···(6)

[ W2: moisture content (%) of CS with respect to solid content of water glass in the coating layer, W1: moisture content (%) in CS, B1: amount of solid component (%) of water glass relative to CS

Determination of the bending Strength

For the width obtained using each CS: 2.54cm × height: 2.54cm × Length: a20.0 cm-sized test piece was subjected to a breaking load measurement using a measuring instrument (Takachiho Seiki Co., Ltd., manufactured by Digital Sand Strength testing machine). Then, using the measured breaking load, the bending strength was calculated from the following formula (7).

Flexural strength (N/cm)²)＝1.5×(L×W)/(a×b²)

···(7)

[ L: distance between fulcrums (cm), W: breaking load (N), a: width (cm) of test piece, b: thickness (cm) of test piece

Determination of the filling Rate (%)

The width obtained by molding in each example or each comparative example was used: 2.54cm × height: 2.54cm × Length: the ratio of the specific gravity (calculated by dividing the mass by the volume of the test piece) of each test piece to the true specific gravity of the aggregate was calculated as a percentage using a mold having a size of 20cm as a test piece.

Filling ratio (%) { [ each test { [ solution ]Mass (g)/volume (cm) of the tablet³)]

True specific gravity (g/cm) of aggregate³)}×100

Core disintegration test

First, as shown in fig. 1, a circular hollow core 10 (diameter: 5cm, height: 5cm) having a core portion 8, which is manufactured using each CS, is bonded and fixed by a core fixing portion 4 in a half-cut hollow master mold 6 (cavity diameter: 6cm, height: 6cm) which is previously manufactured from normal temperature self-hardening sand and has a melt inlet 2 at the upper portion and a core fixing portion 4 (this portion becomes a discharge port for discharging a waste core from a casting) having a core at the lower portion, and then the opposing hollow master mold 6 is further bonded and fixed to manufacture a sand mold 12 for a casting test. Next, an aluminum alloy melt was poured from the melt inlet 2 of the sand mold 12 for casting test (temperature: 710. + -.5 ℃ C.), solidified, and then the master mold 6 was broken to take out a casting 16 having a circular waste core outlet 14 (diameter: 1.6cm) shown in FIG. 2. Then, after the temperature reached the predetermined temperature, the casting 16 obtained as described above was heated under a pressure: 0.2MPa, 1 time and 3 seconds of impact was applied by an air hammer, and the mixture was discharged from the discharge port 14. The impact from the air hammer was repeated until 100% of the core sand was discharged, and the number of times was recorded.

Average particle size-

The average particle diameter (D) was determined by measuring the particle diameter at a cumulative value of 50% from the particle size distribution using a Microtrac particle size distribution measuring apparatus (product name: MT3200II, manufactured by Nikkiso K.K.)₅₀). In the following, the average particle diameters of the spherical particles and the non-spherical particles used in the examples and comparative examples are measured by the above-mentioned measuring apparatus, and as a result, the error between the notice values of the respective manufacturers is within 10%, and therefore, the average particle diameters of the spherical particles and the non-spherical particles are shown as the notice values of the manufacturers.

Production example 1 of dry CS

LUNAMOS #50 (trade name, Kao-Quaker Co., Ltd., average particle diameter: 292.1 μm, particle diameter coefficient: 1.01) which is a commercially available artificial sand for casting was prepared as a refractory aggregate, and sodium silicate No. 2 (trade name, Fuji Kagaku Co., Ltd.) which is a commercially available product was prepared as a water glass which is a binderrp., PREPARATION OF SiO₂/Na₂Molar ratio of O: 2.5, solid content: 41.3%). Then, the LUNAMOS #50 was heated to a temperature of about 120 ℃, and then put into a kawa universal mixer (5DM-r type) (DALTON co., ltd., manufactured), the water glass was further added at a ratio of 1.21 parts (solid content: 0.50 parts) to the LUNAMOS # 50100 parts, and as spherical particles, Elkem Micro Silica (trade name, manufactured by Elkem Japan corporation, average particle size: 0.15 μm, sphericity: 0.96) was added at a ratio of 0.05 parts (10 parts to the solid content 100 parts of the water glass) to knead for 3 minutes to evaporate water, and on the other hand, the mixture was stirred until the sand grains were disintegrated, and further, 0.01 parts of calcium stearate (2 parts to the solid content 100 parts of the water glass) was added and stirred and mixed, thereby obtaining dry-state coated sand having normal temperature fluidity: CS 1. The water content of CS1 after the kneading was measured, and it was found that the amount corresponded to 40 mass% of the solid content of the water glass in the coating layer.

Production example 2 of dry CS

CS2 in a dry state having room-temperature fluidity was obtained in the same manner as in production example 1, except that the added spherical particles were HS311 (product name, manufactured by Nippon Steel & Sumikin Materials Corporation, average particle diameter: 2.2 μm, sphericity: 0.98). The water content of CS2 thus obtained was calculated and found to be an amount corresponding to 40 mass% of the solid content of the water glass in the coating layer.

Production example 3 of dry CS

CS3 in a dry state having room-temperature fluidity was obtained in the same manner as in production example 1, except that the added spherical particles were HS312 (trade name, manufactured by Nippon Steel & Sumikin Materials Corporation, average particle diameter: 9.5 μm, sphericity: 0.96). The water content of CS3 thus obtained was calculated and found to be an amount corresponding to 40 mass% of the solid content of the water glass in the coating layer.

Preparation example 4 of dry CS

CS4 in a dry state having room-temperature fluidity was obtained in the same manner as in production example 1, except that the added spherical particles were HS206 (trade name, manufactured by Nippon Steel & Sumikin Materials Corporation, average particle diameter: 12.0 μm, sphericity: 0.97). The water content of CS4 thus obtained was calculated and found to be an amount corresponding to 40 mass% of the solid content of the water glass in the coating layer.

Production example 5 of dry CS

CS5 in a dry state having room-temperature fluidity was obtained in the same manner as in production example 1, except that the spherical particles to be added were Sunsphere NP-200 (trade name, AGC Si-Tech Co., Ltd., manufactured by Ltd., average particle diameter: 18.2 μm, sphericity: 0.97). The water content of CS5 thus obtained was calculated and found to be an amount corresponding to 40 mass% of the solid content of the water glass in the coating layer.

Preparation example 6 of dry CS

CS6 in a dry state having room-temperature fluidity was obtained in the same manner as in production example 1, except that the added spherical particles were AZ2-75 (trade name, manufactured by Nippon Steel & Sumikin Materials Corporation, average particle diameter: 2.5 μm, sphericity: 0.95). The water content of CS6 thus obtained was calculated and found to be an amount corresponding to 40 mass% of the solid content of the water glass in the coating layer.

Preparation example 7 of dry CS

CS7 in a dry state having room-temperature fluidity was obtained in the same manner as in production example 1, except that the added spherical particles were AZ4-75 (trade name, manufactured by Nippon Steel & Sumikin Materials Corporation, average particle diameter: 4.5 μm, sphericity: 0.96). The water content of CS7 thus obtained was calculated and found to be an amount corresponding to 40 mass% of the solid content of the water glass in the coating layer.

Production example 8 of dry CS

CS8 in a dry state having room-temperature fluidity was obtained in the same manner as in production example 1, except that the added spherical particles were AZ10-75 (trade name, manufactured by Nippon Steel & Sumikin Materials Corporation, average particle diameter: 10.5 μm, sphericity: 0.94). The water content of CS8 thus obtained was calculated and found to be an amount corresponding to 40 mass% of the solid content of the water glass in the coating layer.

Preparation example 9 of dry CS

CS9 in a dry state having room-temperature fluidity was obtained in the same manner as in production example 1, except that the added spherical particles were SG-TO200 (trade name, Sukgyung AT Co., Ltd., average particle diameter: 0.2 μm, manufactured by Ltd., sphericity: 0.93). The water content of CS9 thus obtained was calculated and found to be an amount corresponding to 40 mass% of the solid content of the water glass in the coating layer.

Preparation example 10 of dry CS

As the water glass as a binder, commercially available sodium silicate No. 1 (trade name, Fuji Kagaku Corp., manufactured by Kogyo Kagaku corporation, SiO) was used₂/Na₂Molar ratio of O: 2.1, solid content: 48.5%) was added in an amount of 1.03 parts (0.50 parts as a solid content) based on 100 parts of a refractory aggregate (LUNAMOS #50), and CS10 in a dry state having room-temperature fluidity was obtained by following the same procedure as in production example 2. The water content of CS10 thus obtained was calculated and found to be an amount corresponding to 40 mass% of the solid content of the water glass in the coating layer.

Preparation example 11 of dry CS

As the water glass as a binder, commercially available sodium silicate No. 3 (trade name, Fuji Kagaku Corp., manufactured by Nicotiana Kogyo Co., Ltd.) was used₂/Na₂Molar ratio of O: 3.2, solid content: 38%) was added in the same manner as in production example 2 except that the amount of the additive was changed to 1.32 parts (0.50 part as a solid content) based on 100 parts of a refractory aggregate (LUNAMOS #50), thereby obtaining CS11 in a dry state having room-temperature fluidity. The water content of CS11 thus obtained was calculated and found to be an amount corresponding to 40 mass% of the solid content of the water glass in the coating layer.

Preparation example 12 of dry CS

CS12 in a dry state having room-temperature fluidity was obtained in the same manner as in production example 2, except that the amount of the spherical particles added was changed to 0.5 part. The water content of CS12 thus obtained was calculated and found to be an amount corresponding to 40 mass% of the solid content of the water glass in the coating layer.

Preparation example 13 of dry CS

CS13 in a dry state having room-temperature fluidity was obtained in the same manner as in production example 2, except that the amount of the spherical particles added was changed to 1.0 part. The water content of CS13 thus obtained was calculated and found to be an amount corresponding to 40 mass% of the solid content of the water glass in the coating layer.

Preparation example 14 of dry CS

CS14 was obtained in a dry state having room-temperature fluidity in the same manner as in production example 1, except that no spherical particles were added. The water content of CS14 thus obtained was calculated and found to be an amount corresponding to 40 mass% of the solid content of the water glass in the coating layer.

Preparation example 15 of dry CS

CS15 in a dry state having room-temperature fluidity was obtained in the same manner as in production example 1, except that Sunlovely (trade name, AGC Si-Tech Co., Ltd., average particle diameter: 4.1 μm) which is a non-spherical silica particle was used in place of the spherical particles. The water content of CS15 thus obtained was calculated and found to be an amount corresponding to 40 mass% of the solid content of the water glass in the coating layer.

Preparation example 16 of dry CS

CS16 in a dry state having room-temperature fluidity was obtained in the same manner as in production example 1, except that KA-10 (product name, manufactured by titanium industries, Ltd., average particle diameter: 0.4 μm) which is non-spherical titanium oxide particles was used in place of the spherical particles. The water content of CS16 thus obtained was calculated and found to be an amount corresponding to 40 mass% of the solid content of the water glass in the coating layer.

Production example 17 of dry CS

CS17 in a dry state having room-temperature fluidity was obtained in the same manner as in production example 1, except that STT-65C-S (trade name, manufactured by titanium industries, Ltd., average particle diameter: 0.04 μm) which is non-spherical titanium oxide particles was used in place of the spherical particles. The water content of CS17 thus obtained was calculated and found to be an amount corresponding to 40 mass% of the solid content of the water glass in the coating layer.

Mold-making examples (examples 1 to 13, comparative examples 1 to 4) -

Under the conditions of pressure: CS (temperature: 20 ℃) prepared in the above steps was blown into a molding die heated to 110 ℃ under a gauge pressure of 0.3MPa and filled, and then the blow temperature was further controlled under a gauge pressure of 0.05 MPa: steam at 99 ℃ for 5 seconds was introduced into the precoated sand phase filled in the molding die. After the completion of the steam aeration, hot air at a temperature of 150 ℃ was blown at a gauge pressure of 0.03MPa for 2 minutes to cure CS filled in the molding dies, thereby producing molds used as test pieces [2.54 cm. times.2.54 cm. times.20.0 cm ]. The CS used for producing each of the molds (test pieces) of the examples and comparative examples is shown in tables 1 to 3 below.

The respective molds (test pieces) obtained in examples 1 to 13 and comparative examples 1 to 4 were subjected to the measurement of filling properties and the measurement of strength according to the test methods described above. Furthermore, a sand mold for casting test shown in FIG. 1 was prepared using CS 1-17, and the disintegration of the core was evaluated according to the test method described above. These results are shown in tables 1 to 3 below.

[ Table 1]

[ Table 2]

[ Table 3]

As is clear from the results in tables 1 to 3, it was confirmed that the mold obtained using the dry coated sand having room temperature fluidity of the present invention exhibited excellent strength (flexural strength) and also had excellent disintegration properties.

Next, CS2, CS6, CS9, and CS14 (temperature: 20 ℃) produced in the above steps were directly put into a "kawa" type universal mixer (5DM-r type, DALTON co., ltd., etc.) at normal temperature, and water was added to the mixer at a ratio of 2.0 parts per 100 parts of CS, followed by stirring to prepare a wet CS. After the wet CS taken out from the stirrer was filled in a molding die heated to 150 ℃, the molding die was held in the molding die, and hot air at a temperature of 150 ℃ was blown at a gauge pressure of 0.03MPa for 90 seconds to solidify (harden) the CS filled in the molding die, thereby producing a mold used as a test piece [2.54cm × 2.54cm × 20.0cm ]. The CS used for producing each of the molds (test pieces) of examples 14 to 16 and comparative example 5 is shown in Table 4 below.

Further, a circular blank core shown in fig. 1 was produced using CS that was made wet by adding a predetermined amount of water as described above, and the disintegration of the core was evaluated according to the test method described above. The conditions for producing the core (such as the heating temperature of the mold) are the same as those for producing the mold (test piece). The test results are shown in table 4 below.

[ Table 4]

From the results of table 4, it was clearly confirmed that when a mold was molded using a mold made by adding water to the coated sand of the present invention to be wet, the mold obtained therefrom exhibited higher strength and exhibited comparable filling properties and disintegration properties to those of the mold obtained by aeration with water vapor.

Description of the reference numerals

2 molten metal pouring inlet 4 core print fixing part

6 head of 8 cores of master die

10-core 12-sand mold

14 waste core discharge port 16 casting

Claims

1. A precoated sand which is a dry precoated sand having room-temperature fluidity, the precoated sand being obtained by covering the surface of a refractory aggregate with a covering layer containing water glass,

the covering layer contains spherical particles, and the spherical particles,

wherein the water content is 5 to 55 mass% of the solid content of the water glass in the coating layer,

the refractory aggregate is a spherical refractory aggregate having an angle coefficient of 1.2 or less.

2. The precoated sand according to claim 1, wherein the content of the spherical particles is 0.1 to 500 parts by mass relative to 100 parts by mass of the solid content of the water glass in the coating layer.

3. The precoated sand according to claim 1 or claim 2, wherein the spherical particles have an average particle diameter of 0.1 to 20.0 μm.

4. The precoated sand according to claim 1 or claim 2, wherein the spherical particles are one or more selected from spherical particles formed of silica, alumina, or titanium oxide.

5. The precoated sand according to claim 1 or claim 2, wherein the average particle diameter d1 of the spherical particles and the average particle diameter d2 of the refractory aggregate satisfy the following formula (1),

4×d1≤d2≤5000×d1···(1)。

6. a method for producing precoated sand, characterized in that it is a method for producing dry precoated sand having room-temperature fluidity, in which the surface of a refractory aggregate is covered with a coating layer containing water glass,

mixing a binder containing water glass as a main component with spherical particles to the heated refractory aggregate, and evaporating water to coat the surface of the refractory aggregate with a coating layer containing water glass and spherical particles, thereby producing coated sand having a water content of 5 to 55 mass% based on the solid content of water glass in the coating layer,

7. A method for producing a mold, characterized in that the precoated sand according to any one of claims 1 to 5 is used, and after being filled into a cavity of a mold for providing a target mold, the target mold is obtained by allowing water vapor to pass therethrough, being held in the mold, and being cured or hardened.

8. The method for manufacturing a casting mold according to claim 7, wherein, in the holding of the molding die, dry air or nitrogen gas is further ventilated in a molding cavity of the molding die.

9. The method for manufacturing a mold according to claim 7, wherein the heated dry air is further ventilated in a molding cavity of the molding die while the molding die is being held.

10. A method for producing a casting mold, characterized in that the precoated sand according to any one of claims 1 to 5 is moistened by adding water, and the moistened precoated sand is filled into a mold, and then held in the mold, and solidified or hardened, thereby obtaining a target casting mold.

11. The method for manufacturing a casting mold according to claim 10, wherein in the holding of the molding die, dry air or nitrogen gas is further ventilated in a molding cavity of the molding die.

12. The method for manufacturing a mold according to claim 10, wherein the holding of the molding die further comprises ventilating heated dry air into a molding cavity of the molding die.