JP2020093299A - Casting mold and production method thereof - Google Patents

Abstract

To provide a casting mold which keeps gas from being generated during teeming while maintaining strength, and a production method thereof.SOLUTION: There is provided a casting mold comprising a fireproof granular material, a water soluble sulfuric acid compound, and a water soluble phosphate compound or alcohol having a boiling point of 105°C or greater. When the phosphate compound is contained, a heating loss (α) at 300°C is 1.0% or smaller, and when the alcohol is contained, a heating loss (β) at 700°C is 0.5 to 3.5%.SELECTED DRAWING: None

Description

The present invention relates to a mold and a method for manufacturing the mold.

Conventionally, casting molds (hereinafter, also simply referred to as “molds”) include ordinary molds and special molds, and ordinary molds include a raw mold and a dry mold. On the other hand, special molds include thermosetting molds, self-hardening molds, and gas curing molds.
A refractory granular material such as silica sand is used as the material for the mold, but a refractory granular material alone tends to collapse when dried, so a binder is added to prevent it from collapsing.
Usually, clay such as bentonite is used as a binder in the mold. On the other hand, an organic binder such as phenol resin, furan resin, urethane resin or an inorganic binder such as water glass is used for the special mold.

A liquid produced by melting a metal such as iron, copper, or aluminum at a high temperature is poured into a mold manufactured by various methods to obtain a casting. The casting is taken out by disassembling the mold. Further, it is general that the refractory granular material is regenerated from the disassembled mold and reused in the manufacture of the mold.
The mold using the organic binder is excellent in disintegration upon dismantling. However, when the molten metal is poured, the organic binder is easily decomposed by heat to generate a gas (pyrolysis gas), which easily causes defects in the casting and deteriorates the working environment.
On the other hand, in the mold using the inorganic binder, the inorganic binder is less likely to be thermally decomposed, and thus the thermally decomposed gas of the binder is less likely to be generated during pouring. However, the mold using water glass as the inorganic binder is less likely to deteriorate in strength after pouring and is less likely to disintegrate (inferior in disintegrating property), and thus is more difficult to disassemble than the mold using the organic binder. ..

As a template using an inorganic binding agent instead of water glass, for example, Patent Document 1 contains a refractory granular material and a water-soluble binding agent containing a sulfuric acid compound such as magnesium sulfate, and a sulfuric acid compound in a dry state. Discloses a mold containing water of crystallization.

Japanese Patent No. 4223830

Like the template described in Patent Document 1, a template using a sulfuric acid compound as a binder can exhibit high strength because the binder contains water of crystallization.
However, when the binder contains water of crystallization, the water of crystallization of the binder evaporates during pouring to generate gas, which may cause gas defects.
If the water of crystallization of the binder is removed, the amount of gas generated during pouring can be reduced and gas defects can be suppressed, but the strength of the mold will be reduced.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a mold in which gas is less likely to be generated during pouring while maintaining strength, and a manufacturing method thereof.

The present invention has the following aspects.
[1] contains a refractory granular material, a water-soluble sulfuric acid compound, and a water-soluble phosphoric acid compound,
A mold whose loss on heating (α) determined by the following measuring method is 1.0% or less.
(Measuring method)
The mold is weighed and heated in an electric furnace preliminarily kept at 300°C for 2 hours, then allowed to cool to 25°C, the mass of the mold after cooling is measured, and the heating loss (α) is calculated from the following formula (1). Ask for.
Heating loss (α)={(mass of mold before heating-mass of mold after cooling)/mass of mold before heating}×100 (1)
[2] The template according to [1], wherein the content of the sulfuric acid compound is 0.5 to 15 parts by mass with respect to 100 parts by mass of the refractory granular material.
[3] The template according to [1] or [2], wherein the content of the phosphoric acid compound is 0.1 to 5 parts by mass with respect to 100 parts by mass of the refractory granular material.
[4] After the sand composition containing the refractory granular material, the water-soluble sulfuric acid compound, and the water-soluble phosphoric acid compound is molded, the heating loss (α) determined by the following measuring method is 1.0%. A method for producing a mold, which comprises heating until:
(Measuring method)
The mold is weighed and heated in an electric furnace preliminarily kept at 300°C for 2 hours, then allowed to cool to 25°C, the mass of the mold after cooling is measured, and the heating loss (α) is calculated from the following formula (1). Ask for.
Heating loss (α)={(mass of mold before heating-mass of mold after cooling)/mass of mold before heating}×100 (1)

[5] contains a refractory granular material, a water-soluble sulfuric acid compound, and an alcohol having a boiling point of 105° C. or higher,
A mold whose loss on heating (β) determined by the following measuring method is 0.5 to 3.5%.
(Measuring method)
The mold is weighed and heated in an electric furnace previously held at 700° C. for 2 hours, then allowed to cool to 25° C., the mass of the mold after cooling is measured, and the heating loss (β) is calculated from the following formula (2). Ask for.
Heating loss (β)={(mass of mold before heating-mass of mold after cooling)/mass of mold before heating}×100 (2)
[6] The template according to [5], wherein the content of the sulfuric acid compound is 0.5 to 15 parts by mass with respect to 100 parts by mass of the refractory granular material.
[7] The template according to [5] or [6], wherein the content of the alcohol is 0.1 to 5 parts by mass with respect to 100 parts by mass of the refractory granular material.
[8] After molding a sand composition containing a refractory granular material, a water-soluble sulfuric acid compound, and an alcohol having a boiling point of 105° C. or more, the heating loss (β) determined by the following measurement method is 0.5. A method for producing a mold, which comprises heating to ~3.5%.
(Measuring method)
The mold is weighed and heated in an electric furnace previously held at 700° C. for 2 hours, then allowed to cool to 25° C., the mass of the mold after cooling is measured, and the heating loss (β) is calculated from the following formula (2). Ask for.
Heating loss (β)={(mass of mold before heating-mass of mold after cooling)/mass of mold before heating}×100 (2)

According to the present invention, it is possible to provide a mold in which gas is hardly generated during pouring while maintaining strength and a method for manufacturing the mold.

It is a perspective view showing one embodiment of a mold for mold making used by the present invention. It is a figure which shows the casting mold for making the test piece used in the Example and the comparative example, (a) is a perspective view, (b) is a top view.

[template]
<First aspect>
The mold according to the first aspect of the present invention includes a refractory granular material, a water-soluble sulfuric acid compound, and a water-soluble phosphoric acid compound.
The term “water-soluble” as used in the present invention means that the solubility in water at 20° C. is 2 g/100 mL or more.

As the refractory granular material, natural sand such as silica sand, chromite sand, zircon sand, olivine sand, amorphous silica, alumina sand and mullite sand; conventionally known materials such as artificial sand can be used. Further, it is also possible to use a product obtained by collecting used refractory granular material (recovered sand) or a product subjected to a recycling treatment (reclaimed sand). These refractory granular materials may be used alone or in combination of two or more.
From the viewpoint of production cost, natural sand is preferable, and silica sand is more preferable. Artificial sand is preferable from the viewpoint of being less likely to expand due to heat. Natural sand and artificial sand may be mixed and used in consideration of the balance between production cost and heat resistance.

The particle size of the refractory granular material is preferably 50 to 600 μm, more preferably 60 to 500 μm, further preferably 70 to 300 μm, and particularly preferably 75 to 150 μm. When the particle diameter of the refractory granular material is not less than the above lower limit value, handling is excellent and workability can be favorably maintained. When the particle size of the refractory granular material is not more than the above upper limit value, a mold having high strength can be obtained. In addition, the surface properties of a casting that is cast using the mold are also excellent.
The particle diameter of the refractory granular material is the median diameter of the cumulative volume of 50% of the refractory granular material measured by the dynamic light scattering method.

The water-soluble sulfuric acid compound functions as a binder.
Examples of water-soluble sulfuric acid compounds include magnesium sulfate, aluminum sulfate, zinc sulfate, copper sulfate, sodium sulfate, nickel sulfate, manganese sulfate, iron sulfate and the like. These sulfuric acid compounds may be used alone or in combination of two or more.

The content of the sulfuric acid compound is preferably 0.5 to 15 parts by mass, more preferably 1 to 13 parts by mass, and even more preferably 2 to 12 parts by mass with respect to 100 parts by mass of the refractory granular material. When the content of the sulfuric acid compound is at least the above lower limit value, the strength of the mold is further increased. The effect of improving the mold strength tends to be more easily obtained as the content of the sulfuric acid compound increases, but the effect only reaches the ceiling when the content is increased too much.

The water-soluble phosphate compound acts as a binder.
As the water-soluble phosphate compound, for example, trisodium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, tripotassium phosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, potassium monohydrogen phosphate, Examples thereof include magnesium phosphate. These phosphoric acid compounds may be used alone or in combination of two or more.

The content of the phosphoric acid compound is preferably 0.1 to 5 parts by mass, more preferably 0.2 to 3 parts by mass, and still more preferably 0.3 to 1 part by mass with respect to 100 parts by mass of the refractory granular material. . When the content of the phosphoric acid compound is at least the above lower limit value, the strength of the mold is further increased. The effect of improving the mold strength tends to be more easily obtained as the content of the phosphate compound increases, but if the amount is too large, the effect only reaches the ceiling.

The mold of the first aspect may include components (other components) other than the refractory granular material, the sulfuric acid compound and the phosphoric acid compound described above.
Other components include water-soluble binders other than sulfuric acid compounds and phosphoric acid compounds (other water-soluble binders).

Examples of other water-soluble binders include chlorides, carbonate compounds, water glass and the like. These other water-soluble binders may be used alone or in combination of two or more.
Examples of the chloride include sodium chloride, potassium chloride, calcium chloride, magnesium chloride and the like. These chlorides may be used alone or in combination of two or more.
Examples of the carbonic acid compound include sodium carbonate and potassium carbonate. These carbonate compounds may be used alone or in combination of two or more.
Examples of the water glass include sodium silicate (specifically, Nos. 1, 2 and 3 described in JIS K 1408: 1966 and sodium metasilicate (1 type, 2 types)), potassium silicate, and these. A mixture etc. are mentioned. These water glasses may be used alone or in combination of two or more.

The mold of the first aspect has a heating loss (α) of 1.0% or less, which is determined by the following measuring method.
(Measuring method)
The mold is weighed and heated in an electric furnace preliminarily kept at 300°C for 2 hours, then allowed to cool to 25°C, the mass of the mold after cooling is measured, and the heating loss (α) is calculated from the following formula (1). Ask for.
Heating loss (α)={(mass of mold before heating-mass of mold after cooling)/mass of mold before heating}×100 (1)

The heating temperature of the mold when measuring the heating loss (α) is 300°C. The reason for setting the heating temperature of the mold to 300° C. is that it is a temperature at which the water of hydration of the hydrate is almost removed and is below the temperature at which the inorganic salt decomposes.
A heating loss (α) (hereinafter, also referred to as “heating loss (α) at 300° C.”) of 1.0% or less means that the content of components contained in the mold that evaporate at 300° C. It means 1.0% by mass or less based on the mass. That is, it means that the binder contained in the template, specifically, the water of crystallization such as the sulfuric acid compound and the phosphoric acid compound has been substantially removed.

If the loss on heating (α) of the mold is less than or equal to the above upper limit value, the crystallization water of the binder such as a sulfuric acid compound and a phosphoric acid compound is almost removed, so the gas generated by the crystallization water evaporating during pouring. The amount of gas (gas generation amount) can be reduced, and gas defects can be suppressed.
The loss on heating (α) of the mold is preferably 0.5% or less, more preferably 0.3% or less, further preferably 0.2% or less, particularly preferably 0.1% or less. The smaller the value of the heating loss (α) is, the more preferable, and the most preferable value is 0%. That is, the lower limit of the heating loss (α) is preferably 0%.

(Production method)
The mold of the first aspect has a heating loss (α) of 1 after molding a sand composition containing the above-mentioned refractory granular material, a sulfuric acid compound, a phosphoric acid compound, and optionally other components. It is obtained by heating until it becomes 0.0% or less.

<< molding process >>
The molding step is a step of molding the sand composition to obtain a molded article.
The molding method of the sand composition is not particularly limited, for example, a refractory granular material, a sulfuric acid compound, a phosphoric acid compound, water, and kneading the other components as necessary to prepare kneaded sand, A method of filling the obtained kneading sand in a mold for molding is mentioned.
By using water together, the binder such as the sulfuric acid compound and the phosphoric acid compound is dissolved, and the refractory granular material is uniformly impregnated. The melted binder is solidified in the heating step described later, so that the refractory granular material is solidified into the shape of the mold for molding, and the mold is removed to obtain a mold having a desired shape.
The amount of water added is preferably 5 to 35 parts by mass, and more preferably 10 to 25 parts by mass with respect to 100 parts by mass of the refractory granular material.

The binder such as the sulfuric acid compound and the phosphoric acid compound may be dissolved in water in advance and used as an aqueous solution. These binders may be separately dissolved in water, or may be dissolved in water in a mixed state. Hereinafter, an aqueous solution in which a binder is dissolved in water is also referred to as “binder aqueous solution”.
The binder such as the sulfuric acid compound and the phosphoric acid compound used for producing the template may be an anhydride or a hydrate.

When the mold contains water glass, the water glass may be mixed with the refractory granular material at the timing of preparing the kneading sand, but the refractory granular material is previously coated with a silicate such as sodium silicate or potassium silicate. You may keep it.
The silicate-coated refractory granular material is obtained, for example, by adding water glass to the refractory granular material heated to 100 to 120° C. and mixing. By adding water glass to the heated refractory particulate material, the water evaporates and the silicate remains on the refractory granular material, coating the surface of the refractory granular material.

The mold for molding is a mold for molding a mold.
The material for the mold for molding is not particularly limited, and examples thereof include resin, metal, and wood.
When the mold for molding is irradiated with microwaves in the heating step described below, the mold for molding is preferably made of a material that transmits microwaves.
The transmission of microwaves means that at least a part of the microwaves passes through the mold for molding to the extent that the heat required to heat the molded product is generated, and specifically, the relative permittivity of the material. It means that (ε _r ) is 7 or less. The relative permittivity is preferably 6 or less, more preferably 5 or less. The lower limit of the relative dielectric constant is not particularly limited.
The relative permittivity is obtained by the cavity resonance perturbation method. Specifically, for example, at room temperature, a material is molded into a size of width 50.0 mm×length 50.0 mm×thickness 1.5 mm, and the obtained molded product is subjected to a cavity resonance perturbation method to obtain a relative dielectric constant (ε _r ) is measured.

Examples of materials that transmit microwaves include glass, preferably soda-lime glass (ε _r =6.0 to 8.0), polyamide (ε _r =3.5 to 5.0), epoxy resin (ε _r =). 2.5-6.0), polystyrene (ε _r =2.4-2.6), silicone resin (ε _r =3.5-5.0), polyurethane (ε _r =5.0-5.3). ), polylactic acid (ε _r =about 3), polyphenylene sulfide (ε _r =3 to 4) and the like. These materials may be used alone or in combination of two or more.

The method for manufacturing the mold for molding is not particularly limited, but the mold has a high degree of freedom in shape and can be easily manufactured even in a complicated shape by an additional manufacturing method (additive manufacturing) such as three-dimensional additive manufacturing. It is preferable to manufacture a molding die. Among the three-dimensional additive manufacturing, the selective laser sintering method (SLS method: Selective Laser Sintering method) is preferable.
Hereinafter, an example of a method for manufacturing a mold for molding by the selective laser sintering method will be described.

First, three-dimensional data of the cross-sectional shape of a target mold for molding at regular intervals is created in advance, and based on this three-dimensional data, a thin layer of powdery material is laminated on a workbench. Examples of powdery materials that can be used include glass, polyamide, polyphenylene sulfide, polystyrene, polypropylene, polybutylene terephthalate, polyether ether ketone, polyallyl ether ketone, and fluororesin. Among these, a mixture of glass (preferably soda-lime glass) and polyamide is preferable because it can transmit microwaves.
Next, the powdery material is sintered by scanning and irradiating the obtained thin layer with laser. Then, another thin layer made of the powdery material is laminated on the sintered thin layer, and the operation of scanning and irradiating with a laser is repeated to form a mold made of the powdery material melt-bonded. A molding die is obtained.

The mold for molding may be manufactured by a method other than the additive manufacturing method. For example, a molding die having a desired shape may be manufactured by injection molding or cutting.

<< heating process >>
The heating step is a step of heating the molded article obtained in the molding step.
As described above, the refractory granular material is impregnated with the binder such as the dissolved sulfuric acid compound and phosphoric acid compound. By heating the molded object, the water impregnated in the refractory granular material evaporates and the dissolved binder solidifies, the refractory granular material solidifies into the shape of the mold for molding, and the mold is removed. By doing so, a mold having a desired shape can be obtained.

In the heating step, the molded product is heated until the loss on heating (α) of the obtained mold is 1.0% or less, and the mold is obtained. By heating the molded product until the heating loss (α) becomes 1.0% or less, the crystal water of the binder such as the sulfuric acid compound and the phosphoric acid compound is almost removed.
In order to reduce the heating loss (α) to 1.0% or less, it is preferable to heat the molded article at a heating temperature of 100 to 700° C. under normal pressure. The heating temperature of the molded product under normal pressure is more preferably 250 to 700°C. The heating time at this time is not particularly limited as long as the heating loss (α) is 1.0% or less, and may be adjusted according to the size of the mold for molding.

The heating step may be performed once or may be performed in plural times. However, since the molded product before heating is not solidified, normally, the molded product is heated while being filled in the mold for molding. If the mold for mold making has heat resistance that can withstand the heating temperature during the heating step, the molded object may be heated while being filled in the mold for mold making until the end of the heating step without removing the mold.
When the heat-resistant temperature of the mold for molding is low, the molded product may be heated under the heat-resistant temperature of the mold for molding while being filled in the mold for molding under reduced pressure. Alternatively, under normal pressure, the molded product is heated at a temperature not higher than the heat-resistant temperature of the mold for molding while it is still filled in the mold for molding, and when the molded product is hardened to some extent, it is demolded, and only the molded product is further heated at 100 to 700°C. You may.

As a heating method for the molded article, a method of irradiating the molded article with microwaves, a method of heating the molded article in a dryer or an electric furnace, a method of directly applying hot air to the molded article to heat, and a burner directly to the molded article There is a method of hitting. These methods may be carried out under normal pressure or under reduced pressure. These methods may be used alone or in combination of two or more. In particular, from the viewpoint that the heating loss (α) can be easily controlled to a desired value while shortening the heating time, it is possible to heat the molded article by combining heating by irradiation with microwaves and heating in an electric furnace. preferable. Specifically, the mold for molding is irradiated with microwaves under normal pressure or under reduced pressure to heat the mold while the mold is filled with the molded product (first heating step), and then the molded product in an electric furnace. It is preferable to heat (2nd heating process) while it is filled in the mold for molding, or it is removed from the mold for molding.

When the mold for molding is irradiated with microwaves and heated, the mold for molding is made of a material that transmits microwaves.
The microwave irradiation conditions may be controlled by the output and irradiation time according to the size of the obtained mold, the type and content of the binder.
If the output is too high, the mold for molding may melt. Therefore, the output is preferably 1000 W or less, more preferably 900 W or less. Further, from the viewpoint of being able to shorten the irradiation time, it is preferably 200 W or higher, more preferably 300 W or higher.
If the irradiation time is too long, the mold for molding may melt. Therefore, it is preferable to set the irradiation time according to the output.
Further, at least one of the output and the irradiation time may be changed and the microwave may be irradiated in plural times.

The pressure (vacuum degree) for depressurization is preferably 50 kPa or less, and more preferably 20 kPa or less, from the viewpoint of shortening the heating time. The lower limit of the degree of vacuum is not particularly limited, but is usually 5 kPa or more.

<< Other manufacturing method >>
By the way, the kneading sand used in the above-mentioned molding step is in a wet state because it contains water. Therefore, when a mold having a complicated shape is manufactured, the shape of the mold for molding the mold may be complicated, and it may be difficult to fill the kneading sand. In such a case, it is preferable to mold the sand composition as follows.

First, for example, as shown in FIG. 1, a mold 10 is prepared in which a plurality of holes 14 are formed.
FIG. 1 is a perspective view showing a mold for molding for molding a core as an embodiment of the mold for molding. The core is a mold that is fitted into a mold that serves as a main mold as a part corresponding to the hollow part when manufacturing a casting having a hollow part.
The casting mold 10 shown in FIG. 1 includes an upper die 11 and a lower die 12.
The upper mold 11 and the lower mold 12 have a recess 13 corresponding to the shape of the mold. Among the depressions 13, 13a is a depression in a portion corresponding to the core body, and 13b is a depression in a portion corresponding to a skirting board. The upper mold 11 and the lower mold 12 are overlapped so that these recesses 13 are on the inside, and specifically, the first convex portion 15a and the first concave portion 16a, the second convex portion 15b and the second concave portion 16b, The refractory granular material is filled in the space inside the mold 10 for molding, which is formed by superposing the third convex portion 15c and the third concave portion 16c, and the fourth convex portion 15d and the fourth concave portion 16d, respectively.

A plurality of holes 14 are formed in the mold 10 for mold making. The holes 14 do not prevent water from penetrating into the inside of the mold 10 for molding the refractory granular material when immersed in water, and the refractory granular material flows out from the inside. Is formed so as to inhibit the.
Examples of the shape of the hole 14 include, but are not limited to, a circle, an ellipse, a polygon (for example, a triangle, a quadrangle, a pentagon, a hexagon, a rhombus, a trapezoid, etc.) and a slit shape.
Although water easily penetrates into the slit-shaped holes, there is a tendency that linear protrusions along the slit-shaped holes are formed in the mold. A convex portion tends to be formed in the mold corresponding to the circular, elliptical, or polygonal hole, but is less noticeable than the linear convex portion along the slit-shaped hole. Therefore, for example, as shown in FIG. 1, it is preferable that a circular hole 14a in which a pattern is less noticeable when transferred to the mold is formed in the recess 13a in the portion corresponding to the core body. Instead of the circular hole 14a, an oval or polygonal hole may be formed in the recess 13a in the portion corresponding to the core body. On the other hand, it is preferable that a slit-like hole 14b is formed in the recess 13b in the portion corresponding to the skirting board so that water easily permeates.

The size of the holes 14 is preferably equal to or smaller than the particle diameter of the refractory granular material filled in the mold 10 for molding. However, if the so-called stone wall effect is obtained, in which a refractory granular material with a small particle size is filled into the gap between the refractory granular materials with a large particle size, and a dense packing state is obtained, the outflow of the refractory granular material is The size of the holes 14 may be larger than the particle size of the refractory granular material, as it can inhibit.
Specifically, the size of the hole 14 is preferably 0.05 to 1 mm, more preferably 0.1 to 1 mm. When the size of the hole 14 is equal to or larger than the above lower limit value, the hole 14 can be easily formed and water can easily permeate. If the size of the holes 14 is equal to or smaller than the above upper limit value, the outflow of the refractory granular material is likely to be hindered.
In the present specification, the size of the hole 14 means the diameter of a circle when the shape is circular, the minor diameter of the ellipse when the shape is elliptical, and the diameter of the inscribed circle when the shape is polygonal, and the slit. In case of the shape, it is the slit width.

0.1-10% is preferable and, as for the opening rate of the mold 10 for mold making, 1-5% is more preferable. If the opening ratio is equal to or more than the above lower limit value, water easily penetrates. If the opening ratio is not more than the above upper limit, the surface of the mold will be smooth.
In the present specification, the opening ratio refers to the area ratio of the holes 14 on the surface of the recess 13 portion of the mold 10 for molding.

The mold 10 for mold making can be easily manufactured by using an additional manufacturing method. For example, a molded product having a desired shape is manufactured by injection molding or cutting, and a desired size is obtained at a desired position of the resulting molded product. The holes 10 may be formed to manufacture the mold 10 for molding.

Next, the refractory granular material is filled in the mold for molding in which the above-described specific holes are formed (filling step).
Since the refractory granular material is dry as compared with the above-mentioned kneading sand, it has excellent fluidity. Therefore, even if the shape of the mold for molding is complicated, the mold can be uniformly and quickly filled.
The refractory particulate material may be silicate coated.

Next, the mold for molding, which is filled with the refractory granular material, is immersed in an aqueous binder solution containing a sulfuric acid compound and a phosphoric acid compound, and optionally another water-soluble binder (immersing step).
By immersing the casting mold in the binder aqueous solution, the binder aqueous solution permeates through the holes formed in the casting mold and dissolves in the entire refractory granular material filled in the casting mold. The binder is impregnated to obtain a molded article.
The molded article thus obtained is heated in the above-mentioned heating step to obtain a mold.

0.5-15 mass parts is preferable, as for the ratio of the sulfuric acid compound with respect to 100 mass parts of refractory granular materials with which the mold for mold making is filled, 1-13 mass parts is more preferable, 2-12 mass parts is further more preferable. .. Moreover, 0.1-5 mass parts is preferable, as for the ratio of the phosphoric acid compound with respect to 100 mass parts of refractory granular materials with which the mold for mold making is filled, 0.2-3 mass parts is more preferable, and 0.3. Is more preferably 1 part by mass.

In order to set the ratio of the sulfuric acid compound and the phosphoric acid compound to 100 parts by mass of the refractory granular material within the above ranges, respectively, the content of the sulfuric acid compound and the phosphoric acid compound in the binder aqueous solution and the viscosity of the mold for molding. The permeation amount of the binder aqueous solution may be adjusted.
The content of the sulfuric acid compound with respect to the total mass of the binder aqueous solution is preferably 5 to 35% by mass, more preferably 10 to 25% by mass.
1-15 mass% is preferable and, as for content of the phosphoric acid compound with respect to the total mass of the binder aqueous solution, 2-10 mass% is more preferable.
The permeation amount of the binder aqueous solution into the mold for molding is preferably 10 to 40 parts by mass, and more preferably 15 to 30 parts by mass, relative to 100 parts by mass of the refractory granular material filled in the mold for molding. ..
The permeation amount of the binder aqueous solution into the mold for molding can be adjusted by the immersion time and the opening ratio of the mold for molding.

The time for immersing the mold for molding in the binder aqueous solution is not particularly limited, and may be adjusted depending on the size of the mold for molding.

The refractory granular material used in the filling step may be mixed with a sulfuric acid compound and a phosphoric acid compound and, if necessary, other water-soluble binder. In this case, in the dipping step, the casting mold filled with the refractory granular material is dipped in water or an aqueous binder solution. By immersing the casting mold in water or the binder aqueous solution, the water or the binder aqueous solution permeates through the holes formed in the casting mold, and the binder mixed in the refractory granular material is removed. Dissolve and impregnate the entire refractory particulate material.

(Effect)
The mold of the first aspect of the present invention described above has a heating loss (α) of 1.0% or less, and the binder contained in the mold, specifically, water of crystallization such as a sulfuric acid compound and a phosphoric acid compound. Almost removed. Therefore, according to the mold of the first aspect of the present invention, it is possible to reduce the amount of gas (gas generation amount) generated by evaporation of crystal water during pouring, and suppress gas defects.

By the way, as described above, if the water of crystallization of the binder is removed, the strength of the mold is reduced.
However, the template of the first aspect of the present invention contains a phosphate compound in addition to the sulfate compound. The phosphoric acid compound exhibits a sufficient caking action when treated at a high temperature, and forms a salt with a sulfuric acid compound, so that even if the water of crystallization is removed, the decrease in template strength can be suppressed.

Thus, with the mold according to the first aspect of the present invention, gas is less likely to be generated during pouring while maintaining strength.
Further, since the template of the first aspect of the present invention contains a sulfuric acid compound and a phosphoric acid compound which are inorganic binders as a binder, a thermal decomposition gas of the sulfuric acid compound or the phosphoric acid compound is generated during pouring. Hard to do. In addition, the mold maintains its shape and its strength is maintained by the sulfuric acid compound and phosphoric acid compound, but since the sulfuric acid compound and phosphoric acid compound are easily dissolved in water, it is easy to apply water to the mold after casting. The mold collapses. Further, since the sulfuric acid compound and the phosphoric acid compound are dissolved in water, the refractory granular material can be easily regenerated from the disassembled mold by solid-liquid separation. Further, the sulfuric acid compound and the phosphoric acid compound can be reused by removing water from the liquid obtained by solid-liquid separation.

<Second mode>
The mold of the second aspect of the present invention contains a refractory granular material, a water-soluble sulfuric acid compound, and an alcohol having a boiling point of 105°C or higher.
Examples of the refractory granular material and the sulfuric acid compound include the refractory granular material and the sulfuric acid compound exemplified above in the description of the mold of the first embodiment.

The content of the sulfuric acid compound is preferably 0.5 to 15 parts by mass, more preferably 1 to 13 parts by mass, and even more preferably 2 to 12 parts by mass with respect to 100 parts by mass of the refractory granular material. When the content of the sulfuric acid compound is at least the above lower limit value, the strength of the mold is further increased. The effect of improving the mold strength tends to be more easily obtained as the content of the sulfuric acid compound increases, but the effect only reaches the ceiling when the content is increased too much.

The boiling point of alcohol is 105° C. or higher, preferably 150° C. or higher, more preferably 200° C. or higher, still more preferably 250° C. or higher. If the boiling point of the alcohol is equal to or higher than the above lower limit, the water of crystallization of the binder will evaporate first when the molded product is heated in the heating step described below, so that even if the water of crystallization is removed to some extent, the alcohol tends to remain in the mold. .. This alcohol substitutes for the water of crystallization and can maintain the strength of the mold.

The alcohol having a boiling point of 105° C. or higher may be a monohydric alcohol or a polyhydric alcohol.
Examples of monohydric alcohols include pentanol, hexanol, heptanol, octanol, nonanol and decanol. These monohydric alcohols may be used alone or in combination of two or more.
Examples of the polyhydric alcohol include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,3-butylene glycol, 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol. And dihydric alcohols such as glycerin, trimethylolethane, trimethylolpropane, diglycerin, erythritol, pentaerythritol, xylitol, sorbitol, dipentaerythritol and mannitol. These polyhydric alcohols may be used alone or in combination of two or more.
Among these, water-soluble alcohols are preferable from the viewpoint that the mold can be easily disassembled by applying water to the mold after casting, and among them, glycerin and sorbitol are particularly preferable from the viewpoint of mold strength and addition amount.

The content of alcohol is preferably 0.1 to 5 parts by mass, more preferably 0.2 to 3 parts by mass, and still more preferably 0.5 to 1.5 parts by mass with respect to 100 parts by mass of the refractory granular material. .. When the alcohol content is at least the above lower limit, the strength of the mold will be further increased. When the content of alcohol is not more than the above upper limit, the amount of gas generated from alcohol can be minimized.

The mold of the second aspect may contain components (other components) other than the above-mentioned refractory granular material, sulfuric acid compound and alcohol.
Other components include water-soluble binders other than sulfuric acid compounds (other water-soluble binders).
Other water-soluble binders include the other water-soluble binders exemplified above in the description of the template of the first embodiment.

The mold of the second aspect has a loss on heating (β) of 0.5 to 3.5%, which is determined by the following measurement method.
(Measuring method)
The mold is weighed and heated in an electric furnace previously held at 700° C. for 2 hours, then allowed to cool to 25° C., the mass of the mold after cooling is measured, and the heating loss (β) is calculated from the following formula (2). Ask for.
Heating loss (β)={(mass of mold before heating-mass of mold after cooling)/mass of mold before heating}×100 (2)

The heating temperature of the mold when measuring the heating loss (β) is 700°C. The reason why the heating temperature of the mold is set to 700° C. is that the temperature is higher than the boiling point of the high boiling point alcohol and lower than the decomposition temperature of the inorganic salt.
The heating loss (β) (hereinafter, also referred to as “heating loss at 700° C. (β)”) of 0.5 to 3.5% means that the content of the component which is contained in the mold and evaporates at 700° C. It means 0.5 to 3.5 mass% or less based on the total mass of the mold. That is, it means that the binder contained in the template, specifically, water of crystallization such as a sulfuric acid compound, and alcohol are appropriately removed.

When the loss on heating (β) of the mold is at least the above lower limit value, the strength of the mold can be maintained well. If the loss on heating (β) of the mold is less than or equal to the above upper limit value, the crystallization water of the binder such as a sulfuric acid compound and the alcohol have been appropriately removed. The amount of gas (gas generation amount) can be reduced, and gas defects can be suppressed.
The loss on heating (β) of the mold is preferably 1.0 to 3.0%.

(Production method)
The mold of the second aspect has a heating loss (β) of 0.5 after molding a sand composition containing the above-mentioned refractory granular material, a sulfuric acid compound, alcohol, and optionally other components. Obtained by heating to ~3.5%.

<< molding process >>
The molding step is a step of molding the sand composition to obtain a molded article.
The molding step in the second aspect is the same as the molding step in the first aspect, except that the phosphate compound is replaced with alcohol.

<< heating process >>
The heating step is a step of heating the molded article obtained in the molding step.
The refractory granular material is impregnated with a binder such as a dissolved sulfuric acid compound. By heating the molded object, the water impregnated in the refractory granular material evaporates and the dissolved binder solidifies, the refractory granular material solidifies into the shape of the mold for molding, and the mold is removed. By doing so, a mold having a desired shape can be obtained.

In the heating step, the molded object is heated until the loss on heating (β) of the obtained mold is 0.5 to 3.5% to obtain the mold. By heating the molded product until the heating loss (β) becomes 0.5 to 3.5%, the water of crystallization of the binder such as a sulfuric acid compound and the alcohol are appropriately removed.
In order to reduce the heating loss (β) to 0.5 to 3.5%, it is preferable to heat the molded article under atmospheric pressure at 105° C. or higher and below the boiling point of the alcohol contained in the molded article. The heating time at this time is not particularly limited as long as the heating loss (β) is 0.5 to 3.5%, and may be adjusted according to the size of the mold for molding.

The heating step may be performed once or may be performed in plural times. However, since the molded product before heating is not solidified, normally, the molded product is heated while being filled in the mold for molding. If the mold for mold making has heat resistance that can withstand the heating temperature during the heating step, the molded object may be heated while being filled in the mold for mold making until the end of the heating step without removing the mold.
When the heat-resistant temperature of the mold for molding is low, the molded product may be heated under the heat-resistant temperature of the mold for molding while being filled in the mold for molding under reduced pressure. Alternatively, under normal pressure, the molded product is heated at a temperature not higher than the heat-resistant temperature of the mold for molding while being filled in the mold for molding, and when the molded product is hardened to some extent, the molded product is demolded, and the molded product alone is 105° C. or higher, alcohol. You may heat further below the boiling point of.

Examples of the heating method for the molded article include the heating methods exemplified above in the heating step in the first aspect. In particular, from the viewpoint of easily controlling the heating loss (β) to a desired value while shortening the heating time, it is possible to heat the molded article by combining heating by microwave irradiation and heating in an electric furnace. preferable. Specifically, the mold for molding is irradiated with microwaves under normal pressure or under reduced pressure to heat the mold while the mold is filled with the molded product (first heating step), and then the molded product in an electric furnace. It is preferable to heat (2nd heating process) while it is filled in the mold for molding, or it is removed from the mold for molding.

(Effect)
The mold of the second aspect of the present invention described above has a loss on heating (β) of 0.5 to 3.5%, a binder contained in the mold, specifically, water of crystallization such as a sulfuric acid compound, and Alcohol is moderately removed. Therefore, according to the mold of the second aspect of the present invention, it is possible to reduce the amount of gas generated by the evaporation of crystallization water during pouring (gas generation amount) and suppress gas defects. Since the alcohol contained in the mold of the second aspect has a higher boiling point than water, the volume of gas generated during pouring is small and the gas generation timing is late. Therefore, even if the template of the second aspect contains alcohol, gas defects can be suppressed.
Moreover, the template of the second aspect of the present invention contains an alcohol having a boiling point of 105° C. or higher in addition to the sulfuric acid compound. Since this alcohol substitutes for the water of crystallization, it is considered that the decrease in the mold strength can be suppressed even if the water of crystallization is removed to some extent.

Thus, with the mold of the second aspect of the present invention, gas is unlikely to be generated during pouring while maintaining strength.
Moreover, since the template of the second aspect of the present invention contains a sulfuric acid compound which is an inorganic binder as a binder, a thermal decomposition gas of the sulfuric acid compound is unlikely to be generated during pouring. In addition, the mold maintains its shape by a sulfuric acid compound that is a binder, and the strength is maintained, but since the sulfuric acid compound is easily dissolved in water, the mold can be easily formed by sprinkling water on the mold after casting. Collapse. Further, since the sulfuric acid compound dissolves in water, the refractory granular material can be easily regenerated from the disassembled mold by solid-liquid separation. Further, the sulfuric acid compound can be reused by removing water and alcohol from the liquid obtained by solid-liquid separation.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. The refractory granular materials, sulfuric acid compounds, phosphoric acid compounds and alcohols used in each example are shown below. Further, various measuring methods and evaluation methods, and a method for manufacturing a mold for molding are as follows.

<Fireproof granular material>
As the refractory granular material, _(containing 95 wt% of Al ₂ O 3 -SiO _2, Itochu Ceratec K.K. "CB-X # 1450") artificial sand obtained by sintering method, the particle size 53 ˜150 μm) was used.

<Sulfate compound>
The following were used as the sulfuric acid compound.
· MgSO _4: magnesium sulfate anhydride _{· Al 2 (SO 4) 3} : Aluminum sulfate 16-hydrate · ZnSO _4: zinc sulfate heptahydrate · CuSO _4: copper sulfate pentahydrate

<Phosphate compound>
The following compounds were used as phosphoric acid compounds.
· _Na 3 PO _4: trisodium phosphate 12-hydrate _· K 3 PO _4: tripotassium phosphate anhydride · _KH 2 PO _4: Potassium dihydrogen phosphate anhydride · _NaH 2 PO _4: Sodium dihydrogen phosphate Anhydrous/K ₂ HPO ₄ : Dipotassium hydrogen phosphate anhydrous/Na ₂ HPO ₄ : Disodium hydrogen phosphate anhydrous

<Alcohol>
As the alcohol, the following ones were used.
-Glycerin: Boiling point 290°C, water-soluble-Sorbitol: Boiling point 296°C, water-soluble-Methanol: Boiling point 64.7°C, water-soluble

<Measurement and evaluation>
(Measurement of heating loss (α))
20 g of mold (test piece) was weighed in a crucible, heated for 2 hours in an electric furnace kept at 300° C. in advance, taken out of the crucible, allowed to cool to 25° C. in a desiccator, and allowed to cool. Was measured, and the heating loss (α) was determined from the following formula (1).
Heating loss (α)={(mass of mold before heating-mass of mold after cooling)/mass of mold before heating}×100 (1)

(Measurement of heating loss (β))
20 g of mold (test piece) was weighed in a crucible and heated for 2 hours in an electric furnace kept at 700° C. in advance, then the crucible was taken out of the electric furnace, allowed to cool to 25° C. in a desiccator, and allowed to cool. Was measured, and the heating loss (β) was calculated from the following formula (2).
Heating loss (β)={(mass of mold before heating-mass of mold after cooling)/mass of mold before heating}×100 (2)

(Measurement of bending strength)
The bending strength of the test pieces obtained in each of the examples and comparative examples was measured using the measuring method described in JACT test method SM-1.

<Manufacture of mold for mold making (1)>
Soda lime glass (product name "Glass beads" manufactured by Potters Ballotini Co., Ltd., average particle size 50 μm, ε _r =6.0) 7.5 kg, and polyamide 11 (product name "RILSAN INVENT NATURAL manufactured by Arkema Co., Ltd." , Average particle diameter 50 μm, and ε _r =4.3) 7.5 kg were mixed for 5 minutes with a screw type mixer to obtain a material for an additional production method.
Based on the SLS method, the additive manufacturing material was selectively laser-sintered with a laser sintering machine ("EOSINT P380" manufactured by EOS Co., Ltd.) to fabricate a mold 10 for molding as shown in FIG. A circular hole 14a having a diameter of 0.8 mm is formed in the recess 13a in the portion corresponding to the core body, and a slit-like hole 14b having a length of 75 to 81 mm is formed in the recess 13b in the portion corresponding to the skirting board. It is formed and the aperture ratio is 3.1%.

<Manufacture of mold for mold making (2)>
A material for an additional production method was obtained in the same manner as in the production (1) of the mold for molding.
Based on the SLS method, a plurality of parts were manufactured by selectively laser-sintering the additive manufacturing material with a laser sintering machine ("EOSINT P380" manufactured by EOS Co., Ltd.). As shown in FIG. 2, a plurality of parts thus obtained are combined to form a mold 20 for forming a test piece, in which five parallelepiped-shaped depressions 13 each having a length of 60 mm, a width of 10 mm, and a depth of 10 mm are formed. did. A slit-shaped hole 14b having a width of 0.3 mm and a length of 8 to 30 mm is formed on the side surface and the bottom surface of the depression 13, and the aperture ratio is 7.9%.

[Example 1]
16 parts by mass of magnesium sulfate anhydrous as a sulfuric acid compound and 2 parts by mass of anhydrous potassium dihydrogen phosphate as a phosphoric acid compound were dissolved in 82 parts by mass of water to prepare a binder aqueous solution.
The refractory granular material was filled in the depression 13 of the mold 10 for molding shown in FIG. Next, the casting mold 10 filled with the refractory granular material was dipped in the binder aqueous solution for 30 seconds. Then, the mold 10 for mold making is pulled up from the binder aqueous solution, put in a microwave vacuum dryer (manufactured by Saikou Engineering Co., Ltd.), and dried for 5 minutes under the conditions of a microwave output of 1000 W and a vacuum degree of 10 kPa, and then a mold. A mold weighing 250 g was taken out of the molding die 10.

According to Example 1, when the refractory granular material was filled in the casting mold 10 shown in FIG. 1, it was possible to sufficiently fill it. Furthermore, a mold could be produced by allowing the binder aqueous solution to permeate and then drying.
Therefore, it has been shown that even if the shape of the mold for molding is complicated, the refractory granular material can be uniformly and quickly filled, and defective filling and reduction in mold strength can be suppressed.

[Example 2]
To 100 parts by mass of the refractory granular material, 4 parts by mass of magnesium sulfate anhydride as a sulfuric acid compound, 0.5 parts by mass of trisodium phosphate dodecahydrate as a phosphoric acid compound, and 18 parts by mass of water were added, and 1 It kneaded for a minute to obtain kneaded sand.
The obtained kneading sand was filled in the depression 13 of the mold 20 for molding shown in FIG. 2 (molding step). Then, the mold for molding 20 filled with the kneading sand was put into a microwave vacuum dryer (manufactured by Saikou Engineering Co., Ltd.) and heated for 1.5 minutes under the conditions of a microwave output of 800 W and a vacuum degree of 10 kPa (the first). One heating step), five test pieces were taken out from the mold 20 for molding. By performing the same operation, a total of 20 test pieces were manufactured.
Of the 20 test pieces obtained, the heat loss (α) of 5 test pieces was measured, and the average value thereof was obtained. The results are shown in Table 1.
Further, of the remaining 15 test pieces, the bending strength of 5 test pieces was measured and the average value thereof was calculated. The results are shown in Table 1.

Furthermore, after heating the remaining 10 test pieces for 1 hour in an electric furnace previously held at 300°C (second heating step), the test pieces were taken out of the electric furnace and allowed to cool to 25°C in a desiccator. did.
The heating loss (α) of 5 test pieces out of the 10 test pieces after being left to cool was measured, and the average value thereof was obtained. The results are shown in Table 1.
Further, the bending strength of the remaining five test pieces was measured, and the average value thereof was calculated. The results are shown in Table 1.

[Examples 3 to 7]
A test piece was manufactured in the same manner as in Example 2 except that the type of the phosphoric acid compound was changed to that shown in Table 1, and the heating loss (α) and the bending strength were measured. The results are shown in Table 1.

[Comparative Example 1]
A test piece was produced in the same manner as in Example 2 except that the phosphoric acid compound was not used, and the heating loss (α) and the bending strength were measured. The results are shown in Table 1.

From the results in Table 1, in each of the examples, the strength of the test piece after the first heating step was high, but the heating loss (α) was more than 1.0%, and gas was likely to be generated during pouring. .. However, the amount of gas generated during pouring could be reduced by performing the second heating step, that is, by performing the heat treatment until the loss on heating (α) was 1.0% or less. Moreover, it was possible to suppress the decrease in strength of the test piece after the second heating step.
On the other hand, in the case of Comparative Example 1 in which no phosphoric acid compound was used, the test piece after the first heating step had high strength, but the loss on heating (α) was more than 1.0%, and gas was generated during pouring. It was easy. By performing the second heating step, the amount of gas generated could be reduced, but the strength of the test piece was extremely reduced.

[Examples 8 to 10]
A test piece was manufactured in the same manner as in Example 2 except that the types of the sulfuric acid compound and the phosphoric acid compound were changed to those shown in Table 2, and the heating loss (α) and the bending strength were measured. The results are shown in Table 2. The results of Example 4 are also shown in Table 2.

From the results in Table 2, in each of the examples, the strength of the test piece after the first heating step was high, but the heating loss (α) was more than 1.0%, and gas was likely to be generated during pouring. . However, the amount of gas generated during pouring could be reduced by performing the second heating step, that is, by performing the heat treatment until the loss on heating (α) was 1.0% or less. Moreover, it was possible to suppress the decrease in strength of the test piece after the second heating step.

[Example 11]
To 100 parts by mass of the refractory granular material, 5 parts by mass of magnesium sulfate insoluble as a sulfuric acid compound, 1 part by mass of glycerin as an alcohol, and 18 parts by mass of water were added and kneaded for 1 minute to obtain kneaded sand.
The obtained kneading sand was filled in the depression 13 of the mold 20 for molding shown in FIG. 2 (molding step). Then, the mold for molding 20 filled with the kneading sand was put into a microwave vacuum dryer (manufactured by Saikou Engineering Co., Ltd.) and heated for 1.5 minutes under the conditions of a microwave output of 800 W and a vacuum degree of 10 kPa (the first). One heating step), five test pieces were taken out from the mold 20 for molding. The same operation was performed to manufacture a total of 30 test pieces.
Of the 30 test pieces obtained, the heat loss (β) of 5 test pieces was measured, and the average value thereof was obtained. The results are shown in Table 3.
In addition, of the remaining 25 test pieces, the bending strength of 5 test pieces was measured, and the average value thereof was obtained. The results are shown in Table 3.

Further, the remaining 20 test pieces were divided into 10 pieces, respectively, and after heating for 1 hour in an electric furnace previously held at 105°C or 200°C (second heating step), the test pieces were taken out from the electric furnace. , And allowed to cool to 25°C in a desiccator.
Of 10 test pieces after being left to cool, 5 test pieces were subjected to heating loss (β) measurement, and an average value thereof was obtained. The results are shown in Table 3.
Further, the bending strength of the remaining five test pieces was measured, and the average value thereof was calculated. The results are shown in Table 3.

[Example 12]
A test piece was produced in the same manner as in Example 11 except that glycerin was changed to sorbitol, and the heating loss (β) and bending strength were measured. The results are shown in Table 3.

[Comparative example 2]
A test piece was produced in the same manner as in Example 11 except that alcohol was not used, and the heating loss (β) and the bending strength were measured. The results are shown in Table 3.

[Comparative Example 3]
A test piece was produced in the same manner as in Example 11 except that glycerin was changed to methanol, and the heating loss (β) and the bending strength were measured. The results are shown in Table 3.

From the results in Table 3, in each of the examples, the strength of the test piece after the first heating step was high, but the heating loss (β) was more than 3.5%, and gas was likely to be generated during pouring. .. However, the amount of gas generated during pouring could be reduced by performing the second heating step, that is, by performing the heat treatment until the loss on heating (β) was 0.5 to 3.5%. Moreover, it was possible to suppress the decrease in strength of the test piece after the second heating step.
On the other hand, in Comparative Example 2 in which alcohol was not used and Comparative Example 3 in which methanol was used as alcohol, the strength of the test piece after the first heating step was high, but the heating loss (β) was more than 3.5%. Yes, gas was likely to be generated when pouring. By performing the second heating step, the amount of gas generated could be reduced, but the strength of the test piece was extremely reduced.

10 Mold for mold making 11 Upper mold 12 Lower mold 13 Cavity 13a Cavity in the part corresponding to the core body 13b Cavity in the part corresponding to a skirting board 14 Hole 14a Circular hole 14b Slit-like hole 15a First convex part 15b No. Two convex portions 15c Third convex portion 15d Fourth convex portion 16a First concave portion 16b Second concave portion 16c Third concave portion 16d Fourth concave portion 20 Mold for molding

Claims (8)

Containing a refractory granular material, a water-soluble sulfuric acid compound, and a water-soluble phosphoric acid compound,
A mold whose loss on heating (α) determined by the following measuring method is 1.0% or less.
(Measuring method)
The mold is weighed and heated in an electric furnace preliminarily kept at 300°C for 2 hours, then allowed to cool to 25°C, the mass of the mold after cooling is measured, and the heating loss (α) is calculated from the following formula (1). Ask for.
Heating loss (α)={(mass of mold before heating-mass of mold after cooling)/mass of mold before heating}×100 (1) The mold according to claim 1, wherein the content of the sulfuric acid compound is 0.5 to 15 parts by mass with respect to 100 parts by mass of the refractory granular material. The mold according to claim 1 or 2, wherein the content of the phosphoric acid compound is 0.1 to 5 parts by mass based on 100 parts by mass of the refractory granular material. After molding a sand composition containing a refractory granular material, a water-soluble sulfuric acid compound, and a water-soluble phosphoric acid compound, the heating loss (α) obtained by the following measuring method becomes 1.0% or less. A method of manufacturing a mold, which is heated to.
(Measuring method)
The mold is weighed and heated in an electric furnace preliminarily kept at 300°C for 2 hours, then allowed to cool to 25°C, the mass of the mold after cooling is measured, and the heating loss (α) is calculated from the following formula (1). Ask for.
Heating loss (α)={(mass of mold before heating-mass of mold after cooling)/mass of mold before heating}×100 (1) Contains a refractory granular material, a water-soluble sulfuric acid compound, and an alcohol having a boiling point of 105° C. or higher,
A mold whose loss on heating (β) determined by the following measuring method is 0.5 to 3.5%.
(Measuring method)
The mold is weighed and heated in an electric furnace previously held at 700° C. for 2 hours, then allowed to cool to 25° C., the mass of the mold after cooling is measured, and the heating loss (β) is calculated from the following formula (2). Ask for.
Heating loss (β)={(mass of mold before heating-mass of mold after cooling)/mass of mold before heating}×100 (2) The mold according to claim 5, wherein the content of the sulfuric acid compound is 0.5 to 15 parts by mass with respect to 100 parts by mass of the refractory granular material. The mold according to claim 5 or 6, wherein the content of the alcohol is 0.1 to 5 parts by mass with respect to 100 parts by mass of the refractory granular material. After molding a sand composition containing a refractory granular material, a water-soluble sulfuric acid compound, and an alcohol having a boiling point of 105° C. or more, the heating loss (β) obtained by the following measuring method is 0.5 to 3. A method for producing a mold, which comprises heating to 5%.
(Measuring method)
The mold is weighed and heated in an electric furnace previously held at 700° C. for 2 hours, then allowed to cool to 25° C., the mass of the mold after cooling is measured, and the heating loss (β) is calculated from the following formula (2). Ask for.
Heating loss (β)={(mass of mold before heating-mass of mold after cooling)/mass of mold before heating}×100 (2)

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