KR20200057880A - Water-soluble core material and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a water-soluble core material and to a manufacturing method thereof. According to the present invention, the manufacturing method of the water-soluble core material comprises the steps of: (a) manufacturing a water-soluble inorganic binder; (B) manufacturing a mixture by mixing the water-soluble inorganic binder with an inorganic metal oxide; (c) manufacturing a core material by injecting or pressure-molding the mixture; (d) manufacturing a sealant; and (e) coating the sealant on a surface of the core material.

Description

Water-soluble core material and manufacturing method thereof

The present invention relates to a water-soluble core material and a method for manufacturing the same, and more specifically, serves as a core material for molding a mold or a hollow shape inside a product for molding a product, and is easily separated from the product after product molding and It relates to a water-soluble core material that can be removed and a method for manufacturing the same.

Since there are many hollow structures among the fiber-reinforced composite parts used in the aviation, automobile, leisure, and sports fields, in order to realize this shape, a core material must be inserted into the inside and then pressurized from the outside to form or blow. It must be molded by pressing from inside to outside using a ladder.

As such, a water soluble core material is installed inside the mold and is used to form a space to match the shape of the water soluble core inside the mold. That is, after the water-soluble core is installed inside the mold, a molten metal is injected into the mold to form a space to match the shape of the water-soluble core.

Conventional core materials are only partially satisfied, not satisfying all due to the properties of the material in the required characteristics such as heat resistance, dimensional stability, collapse and strength.

Among them, the CO ₂ type is excellent in heat resistance and strength, but its disintegration property is extremely poor, and the green sand type has insufficient heat resistance and strength, and the resin type has problems in heat resistance, causing problems such as seizure.

In addition, the core material produced using NaCl is used for die casting and gravity casting, but if the core is thin or the structure is complicated, the pores of the core shrink and cracks occur during casting. And the core could be destroyed, especially during pressure die casting.

In order to compensate for this, by forming a coating film on the surface with a heat-resistant coating material, seizure is prevented, and by molding by mixing pitch or sawdust, the collapse property after casting is improved.

However, when the heat resistance is improved by application, the air permeability often decreases, and when the coating film is insufficient, seizure occurs, and when the pitch or sawdust is mixed and formed, there is a problem that the amount of gas generated in the core increases rapidly.

Accordingly, problems such as sintering are improved without deteriorating air permeability, and there is a need to develop a core material having improved strength.

In order to solve the above problems, the present invention serves as a core material so as to form a product having a hollow shape or a product that cannot be molded with a general mold among the fiber-reinforced plastic composite materials, and after product molding, the product is easily It is to provide a water-soluble core material that can be separated and removed from and a method for manufacturing the same.

In order to solve the above problems, a method of manufacturing a water-soluble core material according to an embodiment of the present invention includes: (a) preparing a water-soluble inorganic binder; (b) mixing the water-soluble inorganic binder with an inorganic metal oxide to prepare a mixture; (c) preparing a core material by injecting or pressure-molding the mixture; (d) manufacturing a sealant and (e) coating the sealant on the surface of the core material.

Here, the step (a) is characterized in that to prepare a water-soluble inorganic binder by mixing two or more of sodium phosphate, sodium tetraborate and magnesium sulfate with water.

In addition, the step (a) is characterized in that to prepare a water-soluble inorganic binder by mixing 400 parts by weight of water with 340 to 360 parts by weight of sodium phosphate, 18 to 28 parts by weight of sodium tetraborate and 138 to 158 parts by weight of magnesium sulfate. do.

In addition, in the step (a), the temperature of the water is 45 to 55 ° C., and is characterized by being prepared by mixing for 8 to 12 minutes.

In addition, the step (b) is characterized in that when the injection molding in the step (c), 30 to 35 parts by weight of the water-soluble inorganic binder is mixed with 100 parts by weight of the inorganic metal oxide.

In addition, the step (b) is characterized in that the mixture is prepared by mixing 10 to 15 parts by weight of the water-soluble inorganic binder in 100 parts by weight of the inorganic metal oxide when pressure-molding in the step (c).

In addition, step (c) is characterized in that the mixture is press-molded to produce a core material having a molding density of 1.8 to 2.2 g / cm ³ .

In addition, the step (d) is a polyvinyl alcohol (PVA) slowly added to water and dissolved to prepare a solution; Cooling the solution and mixing the ethyl alcohol with the solution may include preparing a sealant.

In addition, it is possible to provide a water-soluble core material produced by a method for manufacturing a water-soluble core material according to an embodiment of the present invention.

The water-soluble core material according to the embodiment of the present invention as described above and a method of manufacturing the water-soluble core material using an inorganic binder and a ceramic-based powder, and the surface of the water-soluble sealant or the like to prevent the resin from penetrating the material during molding. By being manufactured by coating, it functions as a mold for molding a product or a core material for molding a hollow shape inside the product, and can be easily separated and removed from the product after product molding.

When a composite material is manufactured using such a water-soluble core material, the manufacturing cost is relatively low compared to a conventional molding method such as RIM, RTM, Autoclave, etc., which is commercialized for manufacturing the composite material.

In addition, manufacturing and shape can be changed in a variety of ways compared to the conventional general core material, mandrel, so that a desired shape can be realized and weight reduction can be maximized.

In addition, since it is water-soluble, it is an eco-friendly material, and may not cost extra when removing the core material.

Furthermore, the water-soluble core material manufactured according to the present invention is expected to have an effect that can be usefully used in the production of hollow composite products having a shape in which it is difficult to remove the fuel tank and the inner mandrel.

1 is a flowchart sequentially showing a method of manufacturing a water-soluble core material according to an embodiment of the present invention.
Figure 2 is a flow chart sequentially showing the step S40 of Figure 1;
3 is a graph showing the average results of compressive strength of Examples 1 to 5 and Comparative Example 1 of the present invention.
4 is a graph showing the average result of compressive strength of Examples 6 to 10 and Comparative Example 2 of the present invention.
Figure 5 is a graph of the average results of the flexural strength of Examples 1 to 5 and Comparative Example 1 of the present invention.
Figure 6 is a graph of the average results of the flexural strength of Examples 6 to 10 and Comparative Example 2 of the present invention.

The present invention can be variously modified and may have various forms, and specific embodiments will be described in detail in the text. However, this is not intended to limit the present invention to a specific disclosure form, it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

The terms used in this application are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, the terms "include" or "have" are intended to indicate that a combination of features, numbers, steps, components, etc., described in the specification exists, one or more other features or numbers, It should be understood that the presence or addition possibility of those combining steps, components, and the like is not excluded in advance.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person skilled in the art to which the present invention pertains. Terms such as those defined in a commonly used dictionary should be interpreted as having meanings consistent with meanings in the context of related technologies, and should not be interpreted as ideal or excessively formal meanings unless explicitly defined in the present application. Does not.

Here, repeated descriptions, well-known functions that may unnecessarily obscure the subject matter of the present invention, and detailed description of the configuration will be omitted. Embodiments of the present invention are provided to more fully describe the present invention to those skilled in the art.

The present invention relates to a water-soluble core material and a method for manufacturing the same, and more specifically, to prepare a water-soluble core material using an inorganic binder and a ceramic-based powder, and to coat the surface with a water-soluble sealant or the like so that the resin does not penetrate the material during molding. The main content is a water-soluble core material that can be used as a mold for molding a product or a core material for molding a hollow shape inside the product, and can be easily separated and removed from the product after product molding.

Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS. 1 to 6.

1 is a flowchart sequentially showing a method of manufacturing a water-soluble core material according to an embodiment of the present invention, and FIG. 2 is a flowchart sequentially showing steps S40 of FIG. 1.

Referring to Figure 1, the method of manufacturing a water-soluble core material according to an embodiment of the present invention comprises the steps of preparing a water-soluble inorganic binder (S10), mixing a water-soluble inorganic binder with an inorganic metal oxide to prepare a mixture (S20), a mixture It may include a step (S30) for preparing a core material by injecting or pressure-molding, a step for producing a sealant (S40), and a step for coating the sealant on the surface of the core material (S50).

First, the step of preparing a water-soluble inorganic binder (S10) is a step of preparing a water-soluble inorganic binder by mixing a water-soluble metal salt with water, and mixing two or more of sodium phosphate, sodium tetraborate, and magnesium sulfate with water to form a water-soluble inorganic Binders can be prepared.

Here, sodium phosphate is sodium hydrogen phosphate, the formula NaH ₂ PO ₄ · nH ₂ O (n = 0, 1, 2), the aqueous solution (1 → 20) is weakly acidic, pH is 4.1. From the aqueous solution, dihydrate at 41 ° C or lower, monohydrate at 41 to 58 ° C, and anhydrous salt at 100 ° C can be obtained. In addition, it is easily soluble in water, but not soluble in alcohol and ether. When heated, it becomes metaphosphate, has a slightly deliquescent effect and has a buffering effect.

The sodium phosphate may be used in 340 to 360 parts by weight based on 400 parts by weight of water in step S10, and preferably 350 parts by weight.

This is because when the sodium phosphate is less than 340 parts by weight, the physical properties of the core material may be deteriorated, and when it exceeds 360 parts by weight, it may be eluted because it does not dissolve in water.

Sodium tetraborate is of the formula Na ₂ B ₄ O ₇ , sometimes called sodium diborate (in this case, sodium tetraborate refers to Na ₂ O · 4B ₂ O ₃ ), and the 10-hydrate salt is called borax. , It is one of the components of the buffer.

The sodium tetraborate may be used in an amount of 18 to 28 parts by weight based on 400 parts by weight of water in step S10, and 23 parts by weight is preferably used.

This is because when the sodium tetraborate is less than 18 parts by weight, the physical properties of the core material may be deteriorated, and when it exceeds 28 parts by weight, it may be eluted because it does not dissolve in water.

Magnesium sulfate has many hydrous salts in addition to anhydrous salts, and when it is usually called magnesium sulfate, it refers to a hexahydrate salt, and this is called an epsom salt, and a natural one is particularly called sari salt. The chemical formula is MgSO ₄ and the anhydrous salt is a white crystalline powder with a melting point of 1,185 ° C and a specific gravity of 2.66. 26.9g at 0 ℃ and 68.3g at 100 ℃ in 100g of water, and slightly soluble in alcohol. The state of the hydrous salt varies depending on the temperature at which the crystal is precipitated from the saturated aqueous solution.

As for the magnesium sulfate, 138 to 158 parts by weight may be used based on 400 parts by weight of water in step S10, and 148 parts by weight is preferably used.

This is because when magnesium sulfate is less than 138 parts by weight, the physical properties may be deteriorated, and when it exceeds 158 parts by weight, it may be eluted because it does not dissolve in water.

In addition, in step S10, it is preferable to prepare a water-soluble inorganic binder by mixing sodium phosphate, sodium tetraborate, magnesium sulfate and water, that is, 400 parts by weight of water, 350 parts by weight of sodium phosphate and 23 parts by weight of sodium tetraborate. And it is more preferable to prepare a water-soluble inorganic binder by mixing 148 parts by weight of magnesium sulfate.

In addition, the temperature of the water in step S10 may be 45 to 55 ° C, and it is more preferable to use water at 50 ° C. This is because sodium phosphate, sodium tetraborate, and magnesium sulfate are most efficiently dissolved within the temperature range of the water.

In addition, the step S10 can be mechanically stirred for 8 to 12 minutes by mixing each composition in the above mixing ratio, and it is preferable to stir for 10 minutes.

At this time, if the stirring time is less than 8 minutes, sodium phosphate, sodium tetraborate, and magnesium sulfate may not all be melted, and when it exceeds 12 minutes, further stirring is already inactive and further stirring is inefficient.

The step of preparing a mixture by mixing a water-soluble inorganic binder with an inorganic metal oxide (S20) is a step of preparing a mixture by mixing a water-soluble inorganic binder with a ceramic-based inorganic metal oxide according to a method of forming a core material in step S30.

Here, the inorganic metal oxide preferably includes at least one of aluminum oxide powder, magnesium oxide powder, and titanium dioxide powder, but is not limited thereto, and may further include various inorganic metal oxides.

First, when the core material is injection-molded in step S30, the mixture may be prepared by mixing 30 to 35 parts by weight of a water-soluble inorganic binder in 100 parts by weight of an inorganic metal oxide, and water-soluble inorganic binder 35 in 100 parts by weight of an inorganic metal oxide It is more preferable to mix parts by weight.

At this time, when the content of the water-soluble inorganic binder is less than 30 parts by weight, curability may be reduced during molding, and when it exceeds 35 parts by weight, the water-soluble inorganic binder may be eluted during molding.

In addition, when the core material is pressure-molded in step S30, the mixture may be prepared by mixing 10 to 15 parts by weight of a water-soluble inorganic binder in 100 parts by weight of an inorganic metal oxide, and water-soluble inorganic binder in 100 parts by weight of an inorganic metal oxide 15 It is more preferable to mix parts by weight.

At this time, when the content of the water-soluble inorganic binder is less than 10 parts by weight, curability may be deteriorated during molding, and when it exceeds 15 parts by weight, the water-soluble inorganic binder may be eluted during molding.

The step of preparing the core material by injecting or pressure-molding the mixture (S30) is a step of manufacturing the core material by injecting the mixture into an injection-molding mold, or molding it by injecting it into an injection-molding mold and pressing it with a press.

When the press-molding take place in step S30, the molded density can be produced with the core material from 1.8 to 2.2g / cm ^3, the molding density is preferably made of a core material 2.0 g / cm ^3.

This means that if the molding density of the core material is less than 1.8 g / cm ³ , the shape of the specimen is not well maintained, and if it exceeds 2.2 g / cm ³ , the molding mold may be deformed due to high pressure.

In addition, in step S30, after the molding, the prepared core material may be dried.

At this time, the drying may be first dried at room temperature (20 ± 5 ° C) for 24 hours, followed by hot air drying at 60 ° C for 48 hours.

In this way, drying at room temperature and then hot air drying is preferably divided into primary and secondary drying as described above because only the surface of the core material is dried and the inside is not dried when hot air drying is performed immediately.

The step of preparing the sealant (S40) is a step of preparing the sealant to coat the surface of the core material. Referring to FIG. 2, the step of slowly adding and dissolving polyvinyl alcohol (PVA) in water to prepare a dissolving solution ( S41), a step of cooling the solution (S42) and a step of preparing a sealant by mixing ethyl alcohol with the solution (S43).

First, in step S41, polyvinyl alcohol (PVA) is slowly added and dissolved to prepare a solution. Here, the polyvinyl alcohol can be dissolved in 10 to 12 parts by weight of water, preferably 12 parts by weight of water.

At this time, when the polyvinyl alcohol is dissolved in less than 10 parts by weight, the sealant function may be deteriorated, and when it is dissolved in excess of 12 parts by weight, the viscosity of the sealant may be increased, and coating for coating the core material may be difficult.

Here, the temperature of water is preferably 80 to 85 ° C to dissolve the polyvinyl alcohol, and more preferably 80 ° C.

In step S42, the solution prepared in step S41 may be cooled to room temperature. This is to prevent the vaporization of ethyl alcohol to be mixed later.

In step S43, a sealant may be prepared by mixing ethyl alcohol with the dissolved solution cooled in step S42. Mixing ethyl alcohol in this way is to allow the sealant to dry quickly when the sealant is coated on the core material.

In step S43, 25 to 35 parts by weight of ethyl alcohol may be further added to the solution and mixed to prepare a sealant, and it is preferable to prepare a sealant by adding 30 parts by weight.

At this time, if the ethyl alcohol is less than 25 parts by weight, the effect of shortening the sealant drying time is negligible, and when it exceeds 35 parts by weight, it may react with PVA to cause gelation of the sealant.

In the step (S50) of coating the sealant on the surface of the core material, the final water-soluble core material may be prepared by coating the sealant prepared on the S40 step on the surface of the core material prepared on step S30.

In step S50, a sealant may be coated on the surface of the core material using spraying and brushing as a coating method.

Specifically, in step S50, the sealant may be coated by first applying the sealant to the surface of the core material and drying it for 3 hours or more, followed by drying by applying the sealant a second time.

Through the above-described manufacturing method, a water-soluble core material according to an embodiment of the present invention can be provided.

The water-soluble core material thus manufactured has a compressive strength of 4 MPa or more, a water solubility of 50 g / min · m ² or more, and a thermal expansion coefficient of 5 × 10 ⁻⁶ mm / mm · ° C. or less.

As described above, the water-soluble core material according to an embodiment of the present invention and a method for manufacturing the same are prepared using an inorganic binder and a ceramic-based powder to prepare a water-soluble core material, and the surface is water-soluble so that the resin does not penetrate the material during molding. It is manufactured by coating with a sealant or the like, and serves as a mold for molding a product or a core material for molding a hollow shape inside the product, and can be easily separated and removed from the product after product molding.

When a composite material is manufactured using such a water-soluble core material, the manufacturing cost is relatively low compared to a conventional molding method such as RIM, RTM, Autoclave, etc., which is commercialized for manufacturing the composite material.

In addition, manufacturing and shape can be changed in a variety of ways compared to the conventional general core material, mandrel, so that a desired shape can be realized and weight reduction can be maximized.

In addition, since it is water-soluble, it is an eco-friendly material, and may not cost extra when removing the core material.

Furthermore, the water-soluble core material manufactured according to the present invention is expected to have an effect that can be usefully used in the production of hollow composite products having a shape in which it is difficult to remove the fuel tank and the inner mandrel.

Hereinafter, the present invention will be described in more detail by way of example.

However, the following examples are merely illustrative of the present invention, and the contents of the present invention are not limited by the following examples.

In addition, the embodiments of the present invention described below can be implemented by various substitutions, modifications, and changes without departing from the technical spirit of the present invention, and such implementations are described in the technical field to which the present invention pertains from the description of the above-described embodiments. If you are an expert, you can easily implement it.

[ Example ]

[Example 1]

After mixing 350 parts by weight of sodium phosphate and 23 parts by weight of sodium tetraborate to 400 parts by weight of water at 50 ° C to prepare a water-soluble inorganic binder, and mixing 15 parts by weight of water-soluble inorganic binder to 100 parts by weight of an inorganic metal oxide to prepare a mixture. , Injecting the mixture into the injection molding mold and press molding to prepare a core material having a molding density of 2.0 g / cm ³ .

[Example 2]

It was prepared in the same manner as in Example 1, except that 400 parts by weight of sodium phosphate 350 parts by weight and 148 parts by weight of magnesium sulfate were mixed to prepare a water-soluble inorganic binder.

[Example 3]

It was prepared in the same manner as in Example 1, except that 148 parts by weight of magnesium sulfate and 23 parts by weight of sodium tetraborate were mixed with 400 parts by weight of water to prepare a water-soluble inorganic binder.

[Example 4]

It was prepared in the same manner as in Example 1, except that 400 parts by weight of sodium phosphate 350 parts by weight, 148 parts by weight of magnesium sulfate and 23 parts by weight of sodium tetraborate were mixed to prepare a water-soluble inorganic binder.

[Example 5]

It was prepared in the same manner as in Example 1, except that the mixture was injected and molded into the injection molding mold.

[Example 6]

It was prepared in the same manner as in Example 2 except that the mixture was injected and molded into the injection molding mold.

[Example 7]

It was prepared in the same manner as in Example 3 except that the mixture was injected and molded into the injection molding mold.

[Example 8]

It was prepared in the same manner as in Example 4, except that the mixture was injected and molded into the injection molding mold.

[Comparative Example 1]

Water-soluble inorganic binders are prepared by mixing 350 parts by weight of sodium phosphate at 400 parts by weight of water at 50 ° C, and 15 parts by weight of water-soluble inorganic binder is mixed at 100 parts by weight of the inorganic metal oxide, and then the mixture is added to an injection molding mold. By injection and pressure molding, a core material having a molding density of 2.0 g / cm ³ was prepared.

[Comparative Example 2]

It was prepared in the same manner as in Comparative Example 1, except that 148 parts by weight of magnesium sulfate was mixed with 400 parts by weight of water to prepare a water-soluble inorganic binder.

[Comparative Example 3]

It was prepared in the same manner as in Comparative Example 1 except that the mixture was injected and molded into the injection molding mold.

[Comparative Example 4]

It was prepared in the same manner as in Comparative Example 2, except that the mixture was injected and molded into the injection molding mold.

[ Experimental Example  One] Core material  Compressive strength analysis

Compressive strength was measured to compare the core materials of Examples 1 to 4 and Comparative Examples 1 and 2 and Examples 5 to 8 and Comparative Examples 3 and 4.

At this time, the compressive strength (MPa) was measured twice, first and second, and the average was derived.

The results are shown in Table 1, Figure 3, Table 2, and Figure 4 below.

Comparative Example 1 Comparative Example 2 Example 1 Example 2 Example 3 Example 4 One 1.27 2.23 3.50 7.64 2.87 8.91 2 1.91 2.23 3.18 7.96 3.18 8.91 Average 1.59 2.23 3.34 7.80 3.03 8.91 Standard Deviation 0.45 0.00 0.23 0.23 0.22 0.00

Comparative Example 3 Comparative Example 4 Example 5 Example 6 Example 7 Example 8 One 1.74 2.24 5.66 7.26 2.70 13.88 2 1.58 2.05 5.30 8.22 3.01 11.97 Average 1.64 2.15 5.48 7.73 2.86 12.93 Standard Deviation 0.09 0.13 0.25 0.69 0.22 1.35

As can be seen from Table 1 and FIG. 3, it was confirmed that the compressive strengths of Examples 1 to 4 were higher than those of Comparative Examples 1 and 2, and it was confirmed that the compressive strengths of Example 4 were the highest. And as can be seen in Figure 4, it can be seen that the compressive strength of Examples 5 to 8 was higher than Comparative Examples 3 and 4, and the compressive strength of Example 8 was the highest.

[ Experimental Example  2] Core material  Flexural strength analysis

Flexural strength was measured to compare the core materials of Examples 1 to 4 and Comparative Examples 1 and 2 and Examples 5 to 8 and Comparative Examples 3 and 4.

At this time, the flexural strength (MPa) was measured twice in the first and second order in the case of pressure molding, and three times in the first, second, and third times in the case of injection molding, and an average was derived.

The results are shown in Tables 3, 5, 4, and 6 below.

At this time,-is too low to measure the intensity value.

To comparison 1 Comparative Example 2 Example 1 Example 2 Example 3 Example 4 One 4.19 - 5.27 10.15 5.54 15.96 2 4.58 3.69 5.27 8.74 5.60 14.51 Average 4.39 3.69 5.27 9.45 5.57 15.24 Standard Deviation 0.28 0.00 1.00 0.04 1.03

Comparative Example 3 Comparative Example 4 Example 5 Example 6 Example 7 Example 8 One 2.06 3.52 6.02 9.39 7.51 11.87 2 1.86 3.84 6.20 7.91 7.77 11.87 3 1.80 3.73 5.93 7.77 7.77 12.27 Average 1.91 3.70 6.05 8.36 7.68 12.00 Standard Deviation 0.14 0.16 0.14 0.90 0.15 0.23

As can be seen from Table 3 and FIG. 5, it was confirmed that the flexural strengths of Examples 1 to 4 were higher than those of Comparative Examples 1 and 2, and it was confirmed that the flexural strengths of Example 4 were the highest. In addition, as can be seen by looking at Tables 4 and 6, it was confirmed that the flexural strengths of Examples 5 to 8 were higher than those of Comparative Examples 3 and 4, and that the flexural strengths of Example 8 were the highest.

Therefore, the water-soluble core material of the present invention has excellent compressive strength and flexural strength, and is considered to have improved strength.

As described above, since a specific part of the contents of the present invention has been described in detail, for those skilled in the art, this specific technology is only a preferred embodiment, and the scope of the present invention is not limited thereby. It will be obvious. Therefore, the substantial scope of the present invention will be defined by the appended claims and their equivalents.

Claims (9)

(A) preparing a water-soluble inorganic binder;
(b) preparing a mixture by mixing the water-soluble inorganic binder with an inorganic metal oxide;
(c) preparing a core material by injecting or pressure-molding the mixture;
(d) preparing a sealant and
(e) A method of manufacturing a water-soluble core material comprising the step of coating the sealant on the surface of the core material.
According to claim 1,
Step (a) is,
A method of manufacturing a core material, characterized in that two or more of sodium phosphate, sodium tetraborate and magnesium sulfate are mixed with water to prepare a water-soluble inorganic binder.
According to claim 2,
Step (a) is,
A method of manufacturing a core material, characterized in that 400 parts by weight of water is mixed with 340 to 360 parts by weight of sodium phosphate, 18 to 28 parts by weight of sodium tetraborate and 138 to 158 parts by weight of magnesium sulfate to prepare a water-soluble inorganic binder.
According to claim 2,
Step (a) is,
The temperature of the water is 45 to 55 ℃, the method of manufacturing a core material characterized in that it is prepared by mixing for 8 to 12 minutes.
According to claim 1,
Step (b) is,
When the injection molding in step (c), the method of manufacturing a core material, characterized in that the mixture of 30 to 35 parts by weight of the water-soluble inorganic binder is mixed with 100 parts by weight of the inorganic metal oxide.
According to claim 1,
Step (b) is,
A method of manufacturing a core material, characterized in that, when pressure-molding in the step (c), 10 to 15 parts by weight of the water-soluble inorganic binder is mixed with 100 parts by weight of the inorganic metal oxide.
According to claim 1,
Step (c) is,
A method of manufacturing a core material, characterized in that the mixture is press-molded to produce a core material having a molding density of 1.8 to 2.2 g / cm ³ .
According to claim 1,
Step (d) is,
Preparing a solution by slowly dissolving and adding polyvinyl alcohol (PVA) to water;
Cooling the solution and
Method of manufacturing a core material comprising the step of preparing a sealant by mixing ethyl alcohol in the solution.
A water-soluble core material produced by the method of any one of claims 1 to 8.

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