JP6865715B2 - Fire resistant aggregate - Google Patents

Description

The present invention relates to refractory aggregates.

As a mold used for casting a casting, for example, a mold obtained by molding into a desired shape using casting sand containing a refractory aggregate and an inorganic binder is known.
Examples of techniques related to foundry sand containing a refractory aggregate and an inorganic binder are described in Patent Document 1 (Japanese Patent Publication No. 53-025803) and Patent Document 2 (International Publication No. 2014/098129). Things can be mentioned.

In Patent Document 1, crystalline silicic acid is obtained by adding and kneading an alkali metasilicate solution prepared by adding a chemical alkali to water glass in advance to refractory particles such as silica sand, or by further adding alcohols during kneading. Alkali is deposited and adhered to the surface of refractory particles such as silicic acid, and then _{fine-grained dust generated during Fe-Si refining and mixed with fine-grained dust containing SiO 2} as the main component is added and mixed. A method for producing a mold is described, which comprises heating and curing above the melting point of an alkali silicate.

In Patent Document 2, a water glass aqueous solution is mixed with a heated refractory aggregate as a binder, and water is evaporated to form a coating layer of the binder on the surface of the refractory aggregate. Described is a coated sand that is formed and has a normal temperature fluidity and is in a dry state, and the moisture content of the coated sand is adjusted to 0.5% by mass or less.

Special Publication No. 53-025803 International Publication No. 2014/098129

From the viewpoint of improving the handleability of the mold, the mold is required to have high strength and weight reduction.
The present invention has been made in view of the above circumstances, and relates to a refractory aggregate capable of realizing a mold having an excellent balance between light weight and strength.

The present inventors have diligently studied to realize a mold having an excellent balance between light weight and strength. As a result, the present inventors have an excellent balance between lightness and strength when a fire-resistant aggregate having a true specific gravity of 2.50 g / cm ³ or less and a spherical shape is used together with an inorganic binder. It was found that a mold was obtained.

According to the present invention
A refractory aggregate used as casting sand for molding molds using inorganic binders.
Provided is a refractory aggregate having a true specific gravity of 2.50 g / cm ³ or less and a spherical shape.

Further, according to the present invention
A cast sand composition containing the refractory aggregate and an inorganic binder is provided.

Further, according to the present invention
A casting mold composed of the above-mentioned casting sand composition is provided.

According to the present invention, it is possible to provide a refractory aggregate capable of realizing a mold having an excellent balance between light weight and strength.

Hereinafter, embodiments of the present invention will be described. Further, in the present specification, "A to B" indicating a numerical range represents a range of A or more and B or less unless otherwise specified. In addition, the components and elements described in each embodiment can be appropriately combined as long as the effects of the invention are not impaired.

[Fireproof aggregate (A)]
First, the refractory aggregate (A) according to the present embodiment will be described.
The refractory aggregate (A) according to the present embodiment is a refractory aggregate used as casting sand for molding a mold using an inorganic binder, and has a true specific gravity of 2.50 g / cm ³ or less. And it is spherical. Here, in the present embodiment, the refractory aggregate (A) is composed of a group of particles of refractory particles.

As described above, the present inventors have diligently studied to realize a mold having an excellent balance between light weight and strength. As a result, it was found that a mold having an excellent balance of light weight and strength can be obtained when a fire-resistant aggregate having a true specific gravity of 2.50 g / cm ^{3 or less and being spherical is used.}
Here, it is not always clear why a mold having an excellent balance of light weight and strength can be obtained when a fire-resistant aggregate having a true specific gravity of 2.50 g / cm ^{3 or less and being spherical is used.} , The true specific gravity is not more than the above upper limit value, and the spherical shape improves the filling property of the refractory aggregate in the mold, and as a result, the strength of the mold can be increased, and the true specific gravity is further the above upper limit value. It is considered that this is because the mold can be made lighter by the following.

The true specific gravity of the refractory aggregate (A) is 2.50 g / cm ³ or less, but from the viewpoint of further reducing the weight while maintaining the strength of the obtained mold, 2.30 g / cm ³ or less is used. more preferably from 2.20 g / cm ³ or less, more preferably 2.15 g / cm ³ or less.
Further, the true specific gravity of the refractory aggregate (A), from the viewpoint of mold strength improvement, 1.50 g / cm ³ or more, more preferably 1.80 g / cm ³ or more, 2.00 g / cm ³ or higher More preferred.

Here, in the present embodiment, for example, _{the content of SiO 2} contained in the refractory aggregate (A) is increased, the degree of amorphous is increased, or the refractory aggregate is manufactured by a method of spheroidizing by a flame melting method. By doing so, it is possible to adjust the true specific gravity of the refractory aggregate (A) to be equal to or less than the above upper limit value.

The true specific gravity of the refractory aggregate (A) according to the present embodiment can be measured by using the specific gravity bin method according to JIS R2205.

Artificial sand is preferable as the refractory aggregate (A) according to the present embodiment. Artificial sand refers to foundry sand that is not naturally produced foundry sand, but artificially prepared metal oxide components and melted or sintered. In addition, recovered sand obtained by recovering used refractory aggregate, recycled sand obtained by regenerating the recovered sand, and the like can also be used.

_{The fire-resistant aggregate (A) is SiO 2} when the total of all the components contained in the fire-resistant aggregate (A) is 100% by mass from the viewpoint of improving the mold strength and fire resistance and from the viewpoint of low thermal expansion. Is preferably contained in an amount of 90% by mass or more and 100% by mass or less, more preferably 95% by mass or more and 100% by mass or less, and further preferably 97% by mass or more and 100% by mass or less.
_{The content of SiO 2 in} the refractory aggregate (A) can be measured by using a known analysis method, for example, a wet gravimetric method, a fluorescent X-ray method, or the like.
If refractory aggregate according to the present embodiment (A) comprises SiO _2, as the ones that may be included as components other than SiO _2, for _{example, Al 2 O 3, CaO,} MgO, Fe 2 O 3, TiO 2 , _K 2 O, and metal oxides Na ₂ O and the like. From the viewpoint of improving fire resistance, the total amount of these is preferably 10% by mass or less, and more preferably 5% by mass or less in the refractory aggregate (A).

The degree of amorphousness of the refractory aggregate (A) is preferably 80% or more, preferably 90% or more, from the viewpoint of smoothing the surface of the aggregate to further improve the mold strength and obtaining low thermal expansion. Is more preferable, 93% or more is further preferable, and 95% or more is further preferable.
The upper limit of the degree of amorphousness of the refractory aggregate (A) is not particularly limited, but may be, for example, 100% or less and 99% or less.

There are various methods for controlling the degree of amorphousness of the refractory aggregate (A), but it is generally preferable to use a manufacturing method that quenches the melt. For example, there are a method of melting a raw material and air-crushing it to quench it, and a method of treating it in a flame and quenching it. In either case, the cooling method may be appropriately selected at various speeds depending on the material and particle size. Further, a method of decrystallizing the once crystallized product by heat treatment and cooling treatment is also conceivable. Among these, those using a flame melting method in which heating and cooling can be easily controlled are preferable.

The degree of amorphousness of the refractory aggregate (A) can be determined by the X-ray diffraction method shown below.
(X-ray diffraction method)
The refractory aggregate (A) is crushed in a mortar and pressure-bonded to an X-ray glass holder of a powder X-ray diffractometer for measurement. The powder X-ray diffractometer uses a MultiFlex (light source CuKα ray, tube voltage 40 kV, tube current 40 mA) manufactured by Rigaku Denki Co., Ltd., with a scanning interval of 0.01 ° and a scanning speed of 2 ° / min in the range of 2θ = 5 to 90 °. , Slit DS1, SS1, RS 0.3mm. In the range of 2θ = 10 ° to 50 °, connect the X-ray intensity on the low angle side and the high angle side with a straight line, use the area under the straight line as the background, and determine the crystallinity using the software attached to the device, 100 Is subtracted from to obtain the degree of amorphousness. Specifically, for the area above the background, the amorphous peak (halo) and each crystalline component are separated by curve fitting, the area of each is calculated, and the degree of crystallinity (%) is calculated by the following formula. calculate.
Amorphousity (%) = halo area / (crystalline component area + halo area) x 100

The refractory aggregate (A) is spherical. Here, the refractory aggregate (A) according to the present embodiment means a ball-like round shape, and more specifically, the sphericity is preferably 0.80 or more, more preferably 0.80 or more. It means 0.83 or more, more preferably 0.86 or more, and even more preferably 0.88 or more. When the sphericity of the refractory aggregate (A) according to the present embodiment is at least the above lower limit, it is preferable from the viewpoint of improving fluidity, mold quality and mold strength, and easiness of molding the mold.
In the present embodiment, the sphericality of the fire-resistant aggregate (A) is obtained by image-analyzing an image (photograph) of fire-resistant particles obtained by an optical microscope or a digital scope (for example, VH-8000 type manufactured by Keyence). By doing so, the area of the particle projection cross section of the fire-resistant particle and the peripheral length of the cross section are obtained, and then [the circumference length (mm) of a perfect circle having the same area as the area of the ^{particle projection cross section (mm 2)] / [particle} Perimeter of the projected cross section (mm)] can be calculated, and the values obtained for each of the 50 fire-resistant particles can be averaged.

The average particle size of the refractory aggregate (A) is preferably 0.05 mm or more, more preferably 0.1 mm or more, from the viewpoint of improving the mold quality and strength of the mold and the ease of molding the mold. Further, when the average particle size of the refractory aggregate (A) is at least the above lower limit value, the amount of the inorganic binder used in the production of the mold can be reduced, so that the refractory aggregate (A) can be used. ) Is preferable because it is easier to regenerate.
The average particle size of the refractory aggregate (A) according to the present embodiment is preferably 2 mm or less, more preferably 1 mm or less, and 0, from the viewpoint of improving mold quality and mold strength and easiness of molding the mold. 5.5 mm or less is more preferable. Further, when the average particle size of the refractory aggregate (A) is not more than the above upper limit value, the porosity is reduced and the mold strength can be increased during the production of the mold, which is preferable.
In the present embodiment, the average particle size of the refractory aggregate (A) can be measured by the following method.

(Measuring method of average particle size)
When the sphericality from the projected cross section of the fire-resistant particles = 1, the diameter (mm) is measured, while when the sphericalness <1, the major axis diameter (mm) and short of the randomly oriented fire-resistant particles are measured. Measure the shaft diameter (mm) to obtain (major shaft diameter + minor shaft diameter) / 2, and average the obtained values for any 100 fire-resistant particles to obtain the average particle size (mm). .. The major axis diameter and the minor axis diameter are defined as follows. When a particle is stabilized on a plane and the projected image of the particle on the plane is sandwiched between two parallel lines, the width of the particle that minimizes the distance between the parallel lines is called the minor axis diameter, while this parallel The distance when particles are sandwiched between two parallel lines in the direction perpendicular to the line is called the major axis diameter.
For the major axis diameter and minor axis diameter of the fire resistant particles, an image (photograph) of the particles is taken with an optical microscope or a digital scope (for example, VH-8000 type manufactured by KEYENCE CORPORATION), and the obtained image is image-analyzed. It can be obtained by

[Manufacturing method of refractory aggregate (A)]
The refractory aggregate (A) according to the present embodiment can be produced, for example, by a method (for example, a flame melting method) including a step of melting powder particles as a raw material in a flame to form spheroids.
Hereinafter, an example of a method for producing the refractory aggregate (A) using the flame melting method will be described.

When the powder particles as a starting material are melted, if the particles contain water, the water evaporates, resulting in a decrease in the sphericity of the obtained refractory aggregate (A). Therefore, the water content (% by weight) of the starting material is preferably 10% by weight or less, more preferably 3% by weight or less, from the viewpoint of adjusting the sphericity of the obtained refractory aggregate (A) to an appropriate range. 1% by weight or less is more preferable. The water content can be determined by weight loss when 10 g of powder particles are heated at 800 ° C. for 1 hour.

The starting material can be selected from, for example, refractory mining raw materials and synthetic raw materials. Examples of the raw material as the SiO ₂ source include silica stone, silica sand, quartz, cristobalite, and amorphous silica. Each of these raw materials can be used alone or in combination of two or more. The selected starting material is preferably used by calcining in order to reduce its water content or facilitate its melting.

In the step of melting powder particles as a starting material in a flame and spheroidizing them, the starting materials as described above are dispersed in a carrier gas such as oxygen, and the particles are melted and spheroidized by being put into the flame ( Flame melting method). In a preferred embodiment, it is put into the following flame.
The flame used can be generated by burning fuels such as propane, butane, methane, natural liquefied gas, LPG, heavy oil, kerosene, light oil, and pulverized coal with oxygen. The fuel to oxygen ratio is preferably 1.01 to 1.3 in terms of volume ratio from the viewpoint of complete combustion. From the viewpoint of generating a high-temperature flame, an oxygen-added air burner and an oxygen / gas burner are preferable. Further, an oxygen / gas burner is preferable.

The powder particles are put into the flame by being dispersed in the carrier gas. Oxygen is preferably used as the carrier gas. In this case, the oxygen of the carrier gas has an advantage that it can be consumed for fuel combustion. The powder concentration in the gas is preferably 0.1 to 20 kg / Nm ³ , more preferably ^{0.2 to 10 kg / Nm 3} from the viewpoint of ensuring sufficient dispersibility of the powder particles.

It is preferable to select the shape and composition of the raw material powder particles from the viewpoint of rapidly spheroidizing in a flame and obtaining a monodisperse refractory aggregate (A). As for the shape, the major axis diameter / minor axis diameter ratio of the raw material powder particles is preferably 9 or less, more preferably 4 or less, from the viewpoint of securing the residence time in the flame, melting, and spheroidizing quickly. More preferably, it is 2 or less.
Also, the powder particles are suitably melted even plasma jet flame generated by ionizing an N ₂ inert gas or the like, it spheroidized.
The temperature of the flame is appropriately about 1800 to 3000 ° C.

By the above method, the refractory aggregate (A) according to the present embodiment can be obtained.

The refractory aggregate (A) according to the present embodiment is mixed with an inorganic binder such as clay, alkali metal silicate, or silica sol alone or in combination with other known refractory aggregates such as silica sand. Then, it can be molded according to a known method using a desired casting mold.
Hereinafter, the cast sand composition obtained by mixing the refractory aggregate (A) according to the present embodiment with an inorganic binder will be described.

[Casted sand composition (C)]
The cast sand composition (C) according to the present embodiment contains a refractory aggregate (A) and an inorganic binder (B). The cast sand composition (C) according to the present embodiment is formed on the surface of the refractory aggregate (A) and the refractory aggregate (A), and is composed of the inorganic binder (B). It may be a so-called coated sand containing an inorganic binder layer.

The content of the inorganic binder (B) contained in the foundry sand composition (C) is, for example, 0 with respect to 100 parts by mass of the refractory aggregate (A) from the viewpoint of obtaining a high-strength casting mold. It is 0.05 parts by mass or more, preferably 0.1 parts by mass or more, and more preferably 0.5 parts by mass or more.
Further, the content of the inorganic binder (B) contained in the casting sand composition (C) is based on 100 parts by mass of the refractory aggregate (A) from the viewpoint of obtaining a high-strength casting mold. For example, it is 10 parts by mass or less, preferably 8 parts by mass or less, and more preferably 6 parts by mass or less.

Examples of the inorganic binder (B) include clay, alkali metal silicate, silica sol, ethyl silicate, sulfate, phosphate, nitrate and the like.
Of these, alkali metal silicates are preferred. The alkali metal silicate can be used in the state of water glass by dissolving it in water. Further, the alkali metal silicate can be used even in a state of being insoluble in water by making it a hydrate.

Examples of the alkali metal silicate include sodium silicate, potassium silicate, sodium metasilicate, potassium metasilicate, lithium silicate, ammonium silicate, colloidal silica, alkyl silicate and the like. Further, a plurality of alkali metal silicates may be mixed and used.
When sodium silicate is used, _{the molar ratio of SiO 2} / Na ₂ O is preferably 2.0 to 3.3, and more preferably 2.1 to 3.1 from the viewpoint of handling.
Among the alkali metal silicates, at least one compound selected from sodium silicate, potassium silicate, sodium metasilicate and potassium metasilicate is preferable, and at least one compound selected from sodium metasilicate and potassium metasilicate is preferable. More preferred.
Here, the alkali metal silicate may be a hydrate.

The cast sand composition (C) according to the present embodiment may contain other additives such as a coupling agent, a lubricant, and a mold release agent.
The coupling agent is not particularly limited, and examples thereof include a silane coupling agent, a zircon coupling agent, and a titanium coupling agent.
The lubricant is not particularly limited, but for example, waxes such as paraffin wax, synthetic polyethylene wax, and montanic acid wax; fatty acid amides such as stearic acid amide, oleic acid amide, and erucate amide; methylenebis stearic acid amide, ethylenebis Alkylene fatty acid amides such as stearic acid amide; stearic acid; stearyl alcohol; stearic acid metal salts such as lead stearate, zinc stearate, calcium stearate, magnesium stearate; stearic acid monoglyceride; stearyl stearate; cured oil and the like. Be done.
The release agent is not particularly limited, but for example, paraffin, wax, light oil, machine oil, spindle oil, insulating oil, waste oil, vegetable oil, fatty acid ester, organic acid, graphite fine particles, mica, sardine, and fluorine-based release agent. , Silicone-based mold release agent and the like.

The cast sand composition (C) according to the present embodiment is formed on the surface of the refractory aggregate (A) and the refractory aggregate (A), and is composed of the inorganic binder (B). In the case of coated sand containing an inorganic binder layer, for example, it can be produced by the following method.
For example, an aqueous solution of the inorganic binder (B) or a melt of the inorganic binder (B) is kneaded or kneaded with an additive to the heated refractory aggregate (A), if necessary. It can be produced by mixing and uniformly mixing, and coating the surface of the refractory aggregate (A) with the inorganic binder (B).

The cast sand composition (C) according to the present embodiment is formed on the surface of the fire-resistant aggregate (A) and the fire-resistant aggregate (A), and is composed of the inorganic binder (B). In the case of a coated sand containing an inorganic binder layer, it is preferable that at least one of the inorganic binder layer and the inorganic binder layer further contains inorganic fine particles, and the inorganic fine particles are further contained on the inorganic binder layer. It is more preferable to further contain inorganic fine particles. The inorganic fine particles according to the present embodiment may be contained both on the inorganic binder layer and in the inorganic binder layer.
By doing so, the particles of the coated sand are more firmly bonded to each other via the inorganic fine particles, and as a result, the strength per unit mass of the obtained mold can be further improved.
Here, the inorganic fine particles on the inorganic binder layer may be partially embedded in the inorganic binder layer.

The inorganic fine particles are not particularly limited, and examples thereof include silica particles and silicon particles. Silica particles are preferable, and amorphous silica particles are more preferable. These inorganic fine particles may be used alone or in combination of two or more.
When silica particles are used as the inorganic fine particles, when the total of all the components contained in the fire-resistant aggregate (A) is 100% by mass, from the viewpoint of improving the fusion property between the cast sand compositions (C). The fire-resistant aggregate (A) _{preferably contains SiO 2} in an amount of 90% by mass or more and 100% by mass or less, more preferably 92% by mass or more and 100% by mass or less, and preferably 95% by mass or more and 100% by mass or less. More preferred.

The degree of amorphousness of the amorphous silica particles is preferably 80% or more, more preferably 90% or more, still more preferably 93% or more, from the viewpoint of binding the coated sand particles to each other more firmly via the inorganic fine particles. Preferably, 95% or more is even more preferable.
The upper limit of the degree of amorphousness of the amorphous silica particles is not particularly limited, but may be, for example, 100% or less and 99% or less.

_{Further, the average particle size d 50} in the weight-based particle size distribution measured by the laser diffraction / scattering type particle size distribution measurement method for the inorganic fine particles is preferably 0.1 μm or more, more preferably 0.1 μm or more, from the viewpoint of improving the mold strength per unit mass and handling. Is 0.3 μm or more, more preferably 0.4 μm or more, preferably 2.0 μm or less, more preferably 1.0 μm or less, still more preferably 0.8 μm from the viewpoint of improving the template strength per unit mass. It is as follows.
_{Here, the average particle size d 50} in the weight-based particle size distribution measured by the laser diffraction / scattering type particle size distribution measurement method for the inorganic fine particles is obtained by, for example, dissolving the inorganic binder layer in water to remove the inorganic fine particles from the coated sand. It can be obtained by taking it out and then measuring the particle size of the obtained inorganic fine particles by a laser diffraction / scattering type particle size distribution measuring method.
_{Further, the average particle size d 50} in the weight-based particle size distribution by the laser diffraction scattering type particle size distribution measurement method of the inorganic fine particles can be obtained by measuring the particle size of the inorganic fine particles as a raw material by the laser diffraction scattering type particle size distribution measurement method. You can also.

The average particle size of the inorganic fine particles obtained from the observation image of the scanning electron microscope is preferably 0.1 μm or more, more preferably 0.3 μm or more, from the viewpoint of improving the template strength per unit mass and handling. It is more preferably 0.4 μm or more, preferably 2.0 μm or less, more preferably 1.0 μm or less, still more preferably 0.8 μm or less from the viewpoint of improving the template strength per unit mass.
Here, various image analysis methods can be used for the average particle size of the inorganic fine particles obtained from the observation image of the scanning electron microscope. Irregular particle sorting may be performed as a pretreatment. For example, after determining the inorganic binder layer and the inorganic fine particles by relying on the elements, 100 arbitrary inorganic fine particles are selected, their particle diameters are measured, and 10 particles are counted from the maximum particle diameter, which is the minimum particle diameter. The average particle size of the 80 inorganic fine particles excluding the 10 total 20 inorganic fine particles counted from the above can be used as the average particle size of the inorganic fine particles.

Further, the content of the inorganic fine particles contained in the cast sand composition (C) according to the present embodiment is based on 100 parts by mass of the fire-resistant aggregate (A) from the viewpoint of improving the mold strength per unit mass and handling. The amount is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, preferably 10 parts by mass or less, more preferably 5 parts by mass or less, still more preferably 3 parts by mass or less.

[Casting mold]
Next, the casting mold according to the present embodiment will be described.
The casting mold according to the present embodiment is composed of a casting sand composition (P).
The method for producing a casting mold according to the present embodiment is not particularly limited, and examples thereof include a method in which a casting sand composition (P) is filled in a molding die and heat-cured. Further, it is possible to apply various known molding methods.

Although the embodiments of the present invention have been described above, these are examples of the present invention, and various configurations other than the above can be adopted.
The present invention is not limited to the above-described embodiment, and modifications, improvements, and the like within the range in which the object of the present invention can be achieved are included in the present invention.

With respect to the embodiments described above, the present invention further discloses the following refractory aggregates, cast sand compositions and casting molds.
<1>
A refractory aggregate used as casting sand for molding molds using inorganic binders.
A refractory aggregate having a true specific gravity of 2.50 g / cm ³ or less and a spherical shape.
<2>
The true specific gravity is preferably 2.30 g / cm ³ or less, more preferably 2.20 g / cm ³ or less, more preferably 2.15 g / cm ³ or less, and preferably 1.50 g / cm ³ or more, more preferably The fire-resistant aggregate according to <1> above, wherein is 1.80 g / cm ³ or more, more preferably 2.00 g / cm ^{3 or more.}
<3>
SiO ₂ is preferably contained in an amount of 90% by mass or more, more preferably 90% by mass or more and 100% by mass or less, further preferably 92% by mass or more and 100% by mass or less, and further preferably 95% by mass or more and 100% by mass or less. , The refractory aggregate according to the above <1> or <2>.
<4>
The degree of amorphousness is preferably 80% or more, more preferably 90% or more, further preferably 93% or more, still more preferably 95% or more, and may be, for example, 100% or less, 99% or less. , The refractory aggregate according to any one of <1> to <3>.
<5>
Any one of <1> to <4>, wherein the sphericity is preferably 0.80 or more, more preferably 0.83 or more, still more preferably 0.86 or more, still more preferably 0.88 or more. The fire-resistant aggregate described in 1.
<6>
The average particle size is preferably 0.05 mm or more, more preferably 0.1 mm or more, and preferably 2 mm or less, more preferably 1 mm or less, still more preferably 0.5 mm or less. The fire-resistant aggregate according to any one of 5>.
<7>
The fire-resistant aggregate according to any one of <1> to <6>, wherein the fire-resistant aggregate contains artificial sand.
<8>
A cast sand composition containing the refractory aggregate according to any one of <1> to <7> and an inorganic binder.
<9>
The inorganic binder preferably contains an alkali metal silicate, more preferably contains at least one compound selected from sodium silicate, potassium silicate, sodium metasilicate and potassium metasilicate, and even more preferably. The casting sand composition according to <8> above, which comprises at least one compound selected from sodium metasilicate and potassium metasilicate.
<10>
The inorganic binder preferably contains a metasilicate hydrate, more preferably contains at least one compound selected from metasilicate pentahydrate and metasilicate 9hydrate, and more preferably. It contains at least one compound selected from sodium metasilicate hydrate and potassium metasilicate hydrate, and even more preferably sodium metasilicate pentahydrate, sodium metasilicate 9 hydrate, potassium metasilicate pentahydrate. Containing at least one compound selected from the product and potassium metasilicate nine hydrate, and even more preferably containing at least one compound selected from sodium metasilicate pentahydrate and sodium metasilicate nine hydrate. The casting sand composition according to <8> or <9>.
<11>
The content of the inorganic binder contained in the cast sand composition is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, based on 100 parts by mass of the fire-resistant aggregate. More preferably 0.5 parts by mass or more, and for example, 10 parts by mass or less, preferably 8 parts by mass or less, more preferably 6 parts by mass or less, any one of the above <8> to <10>. The cast sand composition of the description.
<12>
The refractory aggregate according to any one of <1> to <7>, and an inorganic binder formed on the surface of the refractory aggregate and composed of the inorganic binder. The cast sand composition according to any one of <8> to <11>, which is a coated sand containing a layer.
<13>
The casting sand composition according to <12>, wherein the inorganic fine particles are further contained on at least one of the inorganic binder layer and the inorganic binder layer.
<14>
The casting according to <13>, wherein the inorganic fine particles preferably contain at least one particle selected from silica particles and silicon particles, more preferably contain silica particles, and still more preferably contain amorphous silica particles. Sand composition.
<15>
The inorganic fine particles contain amorphous silica particles, and the inorganic fine particles contain amorphous silica particles.
The degree of amorphousness of the amorphous silica particles is preferably 80% or more, more preferably 90% or more, still more preferably 93% or more, still more preferably 95% or more, and for example, 100% or less, 99. % Or less, the cast sand composition according to <13> or <14>.
<16>
The average particle size of the inorganic fine particles is preferably 0.1 μm or more, more preferably 0.3 μm or more, still more preferably 0.4 μm or more, and preferably 2.0 μm or less, more preferably 1.0 μm. Hereinafter, the cast sand composition according to any one of <13> to <15>, which is more preferably 0.8 μm or less.
<17>
The content of the inorganic fine particles contained in the cast sand composition is preferably 0.1 part by mass or more, more preferably 0.2 part by mass or more, and preferably 0.2 parts by mass or more with respect to 100 parts by mass of the fire-resistant aggregate. The cast sand composition according to any one of <13> to <16>, which is 10 parts by mass or less, more preferably 5 parts by mass or less, and further preferably 3 parts by mass or less.
<18>
A casting mold made of the foundry sand composition according to any one of <8> to <17>.

Hereinafter, the present invention will be described with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

[1] Measurement method First, the measurement methods in the following Examples and Comparative Examples will be described.

(1) Average particle diameter of fire-resistant aggregate The diameter (mm) is measured when the sphericality of the fire-resistant particles is 1 from the projected cross section of the particles, while the diameter (mm) is measured when the sphericality is <1, and the fire resistance is randomly oriented. Measure the major axis diameter (mm) and minor axis diameter (mm) of the sex particles to obtain (major axis diameter + minor axis diameter) / 2, and obtain the values for each of the 100 arbitrary fire-resistant particles. The average particle size (mm) was taken as an average.
The major axis diameter and the minor axis diameter of the refractory particles were determined by taking an image (photograph) of the particles with a digital scope (manufactured by Keyence Corporation, VH-8000 type) and analyzing the obtained images.

(2) Average Particle Size of Inorganic Fine Particles The particle size distribution of the inorganic fine particles was measured by a laser diffraction method using a laser diffraction scattering type particle size distribution measuring device. _{From the measurement results, the particle size (d 50} , average particle size) at 50% cumulative in the weight-based cumulative distribution was determined for the inorganic fine particles.

(3) Chemical composition ratio of refractory aggregate The composition ratio of each component in the refractory aggregate was measured by the fluorescent X-ray method.

(4) Amorphousity of fire-resistant aggregate The fire-resistant aggregate was crushed in a mortar and pressure-bonded to an X-ray glass holder of a powder X-ray diffractometer for measurement. The powder X-ray diffractometer uses a MultiFlex (light source CuKα ray, tube voltage 40 kV, tube current 40 mA) manufactured by Rigaku Denki Co., Ltd., with a scanning interval of 0.01 ° and a scanning speed of 2 ° / min in the range of 2θ = 5 to 90 °. , Slit DS1, SS1, RS 0.3 mm. In the range of 2θ = 10 ° to 50 °, connect the X-ray intensity on the low angle side and the high angle side with a straight line, use the area under the straight line as the background, and determine the crystallinity using the software attached to the device, 100 Was subtracted from to obtain the degree of amorphousness. Specifically, for the area above the background, the amorphous peak (halo) and each crystalline component are separated by curve fitting, the area of each is calculated, and the degree of crystallinity (%) is calculated by the following formula. Calculated.
Amorphousity (%) = halo area / (crystalline component area + halo area) x 100

(5) True Specific Gravity of Refractory Aggregate The true specific gravity of the refractory aggregate was measured by the specific gravity bin method according to JIS R2205.

(6) Spherical degree of fire-resistant aggregate The sphericalness of fire-resistant aggregate is determined by image analysis (photograph) of images (photographs) of fire-resistant particles obtained by a digital scope (Keence, VH-8000 type). The area of the particle projected cross section of the fire-resistant particle and the peripheral length of the cross section are obtained, and then [the circumference of a perfect circle (mm) having the same area as the area of the ^{particle projected cross section (mm 2)] / [the particle projected cross section.} Perimeter (mm)] was calculated, and the values obtained for each of the 50 arbitrary fire-resistant particles were averaged.

[2] Evaluation Method Next, the evaluation methods in the following Examples and Comparative Examples will be described.

(1) Preparation of molds Using the cast sand compositions obtained in Examples and Comparative Examples, molds were prepared by the following methods.
・ Small mold (pressurized)
A 10 × 10 × 60 mm test piece heated to a predetermined temperature can be molded into a horizontal 5-piece die, which is filled with a casting sand composition under pressure and filled with a trowel, and then cured by heating for a predetermined time before testing. I got a piece.

(2) Mold density The mold density was calculated by measuring the weight of the test piece and dividing by the volume calculated by the dimensional measurement.

(3) Bending strength of mold Regarding the test piece using a small mold, a digital force gauge ZTS-500N was attached to a vertical electric measuring stand manufactured by Imada Co., Ltd., and the test piece was measured by a method compliant with the JACT test method SM-1.

[3] Materials Next, the materials used in the following examples and comparative examples will be described.

(1) Refractory aggregate / refractory aggregate 1: Spherical fused silica (made by spheroidizing natural silica sand by the flame melting method)
-Refractory aggregate 2: Silica sand (manufactured by Mikawa Silica, R6)
-Fire-resistant aggregate 3: Spherical fused silica (made by spheroidizing natural silica sand by the flame melting method)

Table 1 shows the physical characteristics of the refractory aggregates 1 to 3.

(2) an inorganic binder, an inorganic binder 1: sodium metasilicate nonahydrate _{(Na 2} SiO 3 · _9H 2 O)
-Inorganic binder 2: Water glass aqueous solution A (sodium silicate (SiO ₂ / Na ₂ O = 2.1) diluted with water and solid content (water glass aqueous solution minus water content) concentration) Water glass aqueous solution with 35% by mass)
-Inorganic binder 3: Water glass aqueous solution B (sodium silicate (SiO ₂ / Na ₂ O = 2.1) diluted with water and solid content (water glass aqueous solution minus water content) concentration) Water glass aqueous solution with 45% by mass)
-Inorganic binder 4: Water glass aqueous solution C (sodium silicate (SiO ₂ / Na ₂ O = 3.1) diluted with water and solid content (water glass aqueous solution minus water content) concentration) Water glass aqueous solution with 35% by mass)

(3) Inorganic fine particles / inorganic fine particles 1: Amorphous silica particles (uniform particle size d ₅₀ : 0.4 μm)
-Inorganic fine particles 2: Amorphous silica particles (average particle size d ₅₀ : 0.6 μm)

<Example 1>
The refractory aggregate 1 heated to a temperature of 105 ° C. was put into a stirrer and then cooled to 65 ° C. Next, the inorganic binder 1 is added to the refractory aggregate 1 (100 parts by mass) at a ratio of 3 parts by mass, and kneading is performed while cooling to obtain the inorganic binder 1. It was pulverized while crystallizing to obtain a cast sand composition 1. The above evaluation was performed on the obtained cast sand composition 1. The results obtained are shown in Table 2.

<Example 2>
The cast sand composition 1 (103 parts by mass) and the inorganic fine particles 1 (0.6 parts by mass) obtained in Example 1 are put into a stirrer and then stirred and mixed at a temperature of 25 ° C. to form a cast sand composition. Inorganic fine particles 1 were coated on the inorganic binder layer of the product 1 to obtain a cast sand composition 2. The above evaluation was performed on the obtained cast sand composition 2. The results obtained are shown in Table 2.

<Example 3>
After the refractory aggregate 1 heated to a temperature of 25 ° C. is put into a stirrer, the inorganic binder 2 is added at a ratio of 1.2 parts by mass to the refractory aggregate 1 (100 parts by mass). Then, kneading was carried out for 1 minute to obtain a cast sand composition 3. The above evaluation was performed on the obtained cast sand composition 3. The results obtained are shown in Table 2.

<Example 4>
The cast sand composition 3 (101.2 parts by mass) and the inorganic fine particles 1 (0.6 parts by mass) obtained in Example 3 were put into a stirrer and then stirred and mixed at a temperature of 25 ° C. to form a casting. Inorganic fine particles 1 were coated on the inorganic binder layer of the sand composition 3 to obtain a cast sand composition 4. The above evaluation was performed on the obtained cast sand composition 4. The results obtained are shown in Table 2.

<Example 5>
A cast sand composition 5 was obtained by the same method as in Example 3 except that the inorganic binder 3 was used instead of the inorganic binder 2 as the inorganic binder. The above evaluation was performed on the obtained cast sand composition 5. The results obtained are shown in Table 2.

<Example 6>
A cast sand composition 6 was obtained by the same method as in Example 1 except that the inorganic binder 1 was added to the refractory aggregate 1 (100 parts by mass) at a ratio of 5 parts by mass. The above evaluation was performed on the obtained cast sand composition 6. The results obtained are shown in Table 2.

<Comparative example 1>
A cast sand composition 7 was obtained by the same method as in Example 1 except that the refractory aggregate 2 was used instead of the refractory aggregate 1 as the refractory aggregate. The above evaluation was performed on the obtained cast sand composition 7. The results obtained are shown in Table 2.

<Comparative example 2>
A cast sand composition 8 was obtained by the same method as in Example 3 except that the refractory aggregate 2 was used instead of the refractory aggregate 1 as the refractory aggregate. The above evaluation was performed on the obtained cast sand composition 8. The results obtained are shown in Table 2.

<Comparative example 3>
A cast sand composition 9 was obtained by the same method as in Example 5 except that the refractory aggregate 2 was used instead of the refractory aggregate 1 as the refractory aggregate. The above evaluation was performed on the obtained cast sand composition 9. The results obtained are shown in Table 2.

<Example 7>
A cast sand composition 10 was obtained by the same method as in Example 1 except that the refractory aggregate 3 was used instead of the refractory aggregate 1 as the refractory aggregate. The above evaluation was performed on the obtained cast sand composition 10. The results obtained are shown in Table 2.

<Example 8>
A cast sand composition 11 was obtained by the same method as in Example 3 except that the inorganic binder 4 was used instead of the inorganic binder 2 as the inorganic binder. The above evaluation was performed on the obtained cast sand composition 11. The results obtained are shown in Table 2.

<Example 9>
A cast sand composition 12 was obtained by the same method as in Example 2 except that the inorganic fine particles 2 were used instead of the inorganic fine particles 1 as the inorganic fine particles. The above evaluation was performed on the obtained cast sand composition part 12. The results obtained are shown in Table 2.

The molds obtained by using the cast sand compositions of Examples 1 to 9 have higher bending strength per unit mass and are lighter than the molds obtained by using the cast sand compositions of Comparative Examples 1 to 3. It had an excellent balance of sex and strength.
From the above, it was confirmed that the refractory aggregate and the cast sand composition according to the present embodiment can realize a mold having an excellent balance between light weight and strength.

Claims (9)

A refractory aggregate used as casting sand for molding molds using inorganic binders.
And a true specific gravity of 2.50 g / cm ³ or less, spherical der is, including SiO ₂ more than 97 wt%, refractory aggregate. The refractory aggregate according to claim 1, which has an amorphous degree of 80% or more. The refractory aggregate according to claim 1 or 2 , which has a sphericity of 0.80 or more. The refractory aggregate according to any one of claims 1 to 3 , wherein the average particle size is 0.05 mm or more and 2 mm or less. A cast sand composition containing the refractory aggregate according to any one of claims 1 to 4 and an inorganic binder. The cast sand composition according to claim 5 , wherein the inorganic binder contains an alkali metal silicate. The refractory aggregate according to any one of claims 1 to 4 , and an inorganic binder layer formed on the surface of the refractory aggregate and composed of the inorganic binder. The cast sand composition according to claim 5 or 6 , which is a coated sand containing the above. The cast sand composition according to claim 7 , further comprising inorganic fine particles on at least one of the inorganic binder layer and the inorganic binder layer. A casting mold made of the foundry sand composition according to any one of claims 5 to 8.