KR20150123470A - Ceramic core and method of manufacturing thereof - Google Patents

Abstract

The present invention relates to a ceramic core and a method for producing the same and, more specifically, to a ceramic core having high molding strength and calcining strength and a method for producing the same. The method comprises: a first step of producing a mixed solution by mixing metal alkoxide, a silica precursor, a start ceramic powder particle, and a solvent; a second step of producing a ceramic powder particle coated with the metal alkoxide and the silica precursor by drying the mixed solution; a third step of mixing a polymer precursor with a ceramic powder particle coated with an inorganic coating agent; a fourth step of performing gel-casting on a mixture of the coated ceramic particle and the polymer precursor; and a fifth step of heating a molded product molded through the gel-casting.

Description

TECHNICAL FIELD [0001] The present invention relates to a ceramic core and a method of manufacturing the same.

The present invention relates to a ceramic core and a manufacturing method thereof, and more particularly, to a ceramic core having a high molding strength and a plastic strength and a manufacturing method thereof.

As the global temperature policy increases the inlet temperature of the gas turbine, the shape of the cooling channel inside the gas turbine becomes more complex. Accordingly, there is a demand for a ceramic core having a thinner thickness and a high strength. That is, not only is it necessary to have a high temperature strength which is in direct contact with a high-temperature molten metal at the time of casting and can withstand the weight of the molten metal, but also with the pressure at the time of wax injection necessary for producing a shell mold for producing the external shape of a casting, The above-mentioned room temperature and high-temperature strength are required.

Conventional ceramic cores are composed of ceramic particles such as zirconia and silica and a mixture of organic compounds such as a polymer material (wax, etc.) or a surfactant to improve the compatibility with the ceramic particles or the molded body. Therefore, the molding strength of the core is caused by the entanglement or twist between the long chains of the wax composed of the carbon compound, so that the strength of the core is insufficient for manufacturing a ceramic core having a complicated shape of the thin film. In addition, the plastic strength in injection molding may be expressed by sintering between starting particles during heat treatment.

Therefore, the thermal and mechanical properties of the ceramic core are highly dependent on the size, distribution, composition ratio, and process parameters of the starting powder, and it is difficult to obtain accurate data for fabricating the ceramic core according to the required characteristics. In addition, there is a problem that during sintering, the shape of the ceramic core is shrunk due to shrinkage and pores in the core are formed due to vaporization of the organic material. These problems lead to the breakage of the ceramic core during casting or directly to the failure of the casting product, and the provision of more than necessary strength results in a degradation of the collapsibility after casting.

Furthermore, a conventional ceramic core manufacturing method in which a mixture of an organic compound such as a starting ceramic particle, a wax, or a surfactant is prepared as a slurry at a high temperature and then molded into a metal mold, This changes sensitively. In addition, there has been a problem in that shape and dimensional change by sintering of starting particles for the strength development at high temperature are necessarily accompanied.

Accordingly, in the present invention, a new ceramic core manufacturing process has been developed in order to manufacture a ceramic core having no change in properties according to the combination ratio of starting materials, manufacturing process parameters, heat treatment conditions, and the like, .

SUMMARY OF THE INVENTION It is an object of the present invention to provide a ceramic core and a method of manufacturing the ceramic core in which the thermal and mechanical characteristics of the ceramic core are not dependent on the composition ratio of the starting material and the process parameters.

It is still another object of the present invention to provide a ceramic core having high molding strength and plasticity strength and a method for producing the same.

In order to achieve the above object, the present invention provides a ceramic core comprising a ceramic particle and a silicate, which is a glassy metal coating the ceramic particle.

Specifically, the ceramic particles are selected from the group consisting of zirconia, silica, and alumina.

Preferably, the ceramic core is produced by a gel-casting process.

The present invention also relates to a process for preparing a mixed solution by mixing a metal alkoxide (MOR) with a silica precursor, starting ceramic powder particles, and a solvent; A second step of drying the mixed solution to prepare ceramic powder particles coated with the metal alkoxide and the silica precursor; A third step of mixing the coated ceramic powder particles and the polymer precursor; A fourth step of gel-casting a mixture of the coated ceramic powder particles and the polymer precursor; And a fifth step of heat-treating the formed body formed by the gel-casting.

In detail, the metal (M) of the metal alkoxide (MOR) is an alkali metal or an alkaline earth metal, and R of the metal alkoxide (MOR) is hydrogen or an alkyl group, and the alkyl group is a methyl group (-CH3) ), A propyl group (-CH2CH2CH3), a butyl group (-CH2CH2CH2CH3), a pentyl group (-CH2CH2CH2CH3), an isopropyl group (-CHCH3CH3), a hexyl group (-CH2CH2CH2CH2CH3), and a cyclohexyl group (-CHCH2CH2CH2CH2CH2) By weight based on the total weight of the ceramic core.

In one embodiment of the present invention, the content of the metal alkoxide is 1 to 60 parts by weight based on 100 parts by weight of the solvent.

The content of the silica precursor is 1 to 50 parts by weight based on 100 parts by weight of the solvent.

In one embodiment of the present invention, the silica precursor is selected from the group consisting of tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, tetraisopropoxy silane tetraisopropoxysilane, methoxytriethoxysilane, demethoxydiethoxysilane, ethoxytrimethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, methyltriethoxysilane, methyltriethoxysilane, , Ethyltriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, diethyldiethoxysilane, tetramethoxymethylsilane, tetramethoxyethylsilane (tetramethoxyethylsilane), tetramethoxysilane tetramethoxyethylsilane) and tetraethoxymethylsilane. In the group consisting of < RTI ID = 0.0 > It is characterized.

In one embodiment of the present invention, the solvent is selected from the group consisting of methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, butyl alcohol, isobutyl alcohol isobutyl alcohol, hexyl alcohol, and cyclohexyl alcohol. The present invention also provides a method for producing a ceramic core.

Specifically, the phase polymer precursor of the present invention is characterized by having a liquid phase. Further, the polymer precursor is characterized by having a network structure due to a polymerization reaction. More specifically, the present invention provides a method for manufacturing a ceramic core, wherein the polymer precursor has 1 to 4 functional groups, and one functional group is used alone or in combination.

In one embodiment of the present invention, the third step provides a method for manufacturing a ceramic core further comprising at least one of a solvent, a dispersant, an initiator, and a catalyst.

In one embodiment of the present invention, the content of the polymer precursor is 1 to 10 parts by weight based on 100 parts by weight of the mixture prepared in the third step.

The drying step in one embodiment of the present invention is characterized in that it is carried out at 80 ° C to 120 ° C.

Also, in the embodiment of the present invention, the heat treatment step is performed at 900 ° C to 1,000 ° C.

The present invention also provides a ceramic core produced by the above-described method for manufacturing a ceramic core.

The ceramic core provided in the present invention provides a ceramic core capable of producing a ceramic core having high strength without dimensional deformation.

Unlike a conventional manufacturing process, a ceramic core using a polymer precursor is manufactured by applying a gel-casting process to provide a core having a complicated shape.

Further, there is provided a ceramic core and a manufacturing method which do not require a pressurized high temperature process, and which are not susceptible to the composition ratio of the starting material and the process parameters due to the manifestation of strength by the inorganic binder.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a process flow chart schematically showing a process flow of the ceramic core manufacturing method of the present invention. FIG.
2 is a graph showing the results of measurement of fracture strength for Example 1 and Comparative Example 1 in Test Example 1 of the present invention.
3 is a photograph before and after the experiment of dissolution of the ceramic core according to Example 1 in Test Example 2 of the present invention.

Best Mode for Carrying Out the Invention Hereinafter, preferred embodiments are described to facilitate understanding of the present invention. However, the following examples are provided to further understand the present invention, and the present invention is not limited by the examples.

The present invention provides a ceramic core comprising ceramic particles and a glassy metal silicate coating the ceramic particles. Preferably, the ceramic particles are selected from the group consisting of zirconia, silica or alumina. More preferably, the ceramic core is manufactured by a gel-casting process.

BACKGROUND OF THE INVENTION [0002] Generally, a ceramic core is a molded product used in a process of precisely casting a hollow component of a complicated inner cooling channel used in a gas turbine or a complicated component such as an impeller in a vacuum state, Molding or gel-casting method.

The gel-casting method used in one embodiment of the present invention is a technique applying injection molding, which is a ceramics molding technique, and polymerization, which is a polymer manufacturing process. And it is relatively easy to remove various process additive. Therefore, it has many advantages over other molding methods when forming a large-sized member having a complicated shape.

Silicate refers to a compound formed by the combination of one or more metal oxides with silica (SiO2), and in one embodiment of the present invention, the metal alkoxide and the silica precursor are reacted with each other by a sol- After being converted to the side and silica, it is subjected to a heat treatment process to form a vitreous substance called a metal silicate. This is called a vitreous metal silicate.

The present invention also provides a method for producing a mixed solution comprising: a first step of mixing a metal alkoxide (MOR) with a silica precursor, a starting ceramic powder and a solvent to prepare a mixed solution; A second step of drying the mixed solution to prepare ceramic powder particles coated with the metal alkoxide and the silica precursor; A third step of mixing the ceramic precursor coated with the inorganic coating material and the polymer precursor; A fourth step of gel-casting a mixture comprising the coated ceramic particles and the polymer precursor; And a fifth step of heat treating the formed body formed by gall-casting. This is illustrated in FIG.

Specifically, the first step in one embodiment of the present invention is the step of mixing the metal alkoxide (MOR) and the silica precursor with the starting ceramic particles. More specifically, the metal alkoxide and the silica precursor may be referred to as an inorganic alkali metal compound.

The starting ceramic particles include at least one selected from the group consisting of various sizes of zirconia, silica, alumina and the like. Preferably, the inorganic alkali metal compound and the starting ceramic particles are mixed for 1 minute to 60 minutes.

The metal alkoxide is represented by a general formula MOR, wherein M represents an alkali metal or an alkaline earth metal, and R represents hydrogen or an alkyl group. Specifically, the alkyl group may be selected from the group consisting of sodium (Na), magnesium (Mg), potassium (K), calcium (Ca), lithium (Li) and beryllium (Be) (-CH2CH2CH2CH2CH3), an ethyl group (-CH2CH3), a propyl group (-CH2CH2CH3), a butyl group (-CH2CH2CH2CH3), a pentyl group (-CH2CH2CH2CH3), an isopropyl group (-CHCH3CH3), a hexyl group But the present invention is not limited thereto.

Preferably, the content of the metal alkoxide is 1 to 60 parts by weight based on 100 parts by weight of the first stage solvent.

When the amount of the metal alkoxide is less than 1 part by weight based on 100 parts by weight of the solvent, the role as a network modifier is reduced to increase the glass transition temperature of the silica. When the amount of the metal alkoxide exceeds 60 parts by weight, And the mechanical strength of the ceramic core is not sufficiently developed due to the whitening phenomenon, which is not preferable.

The silica precursor may be selected from the group consisting of tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, tetraisopropoxysilane, methoxytriethoxy But are not limited to, methoxytriethoxysilane, demethoxydiethoxysilane, ethoxytrimethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, ethyltriethoxysilane, ), Dimethyldimethoxysilane, dimethyldiethoxysilane, diethyldiethoxysilane, tetramethoxymethylsilane, tetramethoxyethylsilane, and tetraethoxymethylsilane (hereinafter referred to as " tetramethoxyethylsilane " (tetraethoxymethylsilane). < RTI ID = 0.0 > But is not limited thereto.

Preferably, the silica precursor is 1 to 50 parts by weight based on 100 parts by weight of the solvent. When the amount of the silica precursor is less than 1 part by weight based on 100 parts by weight of the solvent, the vitrification reaction by silica hardly occurs. When the amount of the silica precursor is more than 50 parts by weight, the glass transition temperature of the silica is increased to deteriorate the mechanical strength of the ceramic core Problems can arise.

The solvent is selected from the group consisting of methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, butyl alcohol, isobutyl alcohol, hexyl alcohol, and cyclohexyl alcohol. However, the present invention is not limited thereto.

Next, in the second step, the starting material of the ceramic core mixed with the metal alkoxide and the silica precursor prepared in the first step is filtered and dried to prepare a starting material coated with an inorganic metal alkaline compound.

In detail, the drying step is characterized in that the starting material is dried at 80 ° C to 120 ° C. More specifically, the drying step is performed for 30 minutes to 3 hours. Preferably, the drying step may include a step of drying the alcohol solvent or the alcohol produced during the hydrolysis reaction.

The drying step may include a step of drying the solvent or the alcohol produced during the hydrolysis reaction. When the ceramic particles are dried at a temperature of less than 80 ° C, there is a problem that the alcohol does not sufficiently volatilize and the drying time becomes longer than necessary. When drying at a temperature of more than 120 ° C, the metal alkoxide and the silica precursor There is a problem that the vitrification reaction efficiency is reduced due to vaporization or decomposition. Further, when the drying step is conducted for less than 30 minutes, sufficient drying is not performed, and the sol-gel reaction of the metal alkoxide and the silica precursor is completed within 3 hours, so that the drying does not proceed for more than 3 hours .

The third step is a step of mixing the ceramic precursor coated with the inorganic coating agent and the polymer precursor. Preferably, one or more of a dispersant and an initiator catalyst may be further added and mixed.

Specifically, the inorganic coating agent is an inorganic alkali metal mixture used for imparting plasticity strength and dimensional stability, and is synthesized as a silica precursor and a metal alkoxide. The inorganic coating agent is synthesized through hydrolysis reaction and condensation reaction as follows, Coated on the surface.

(1) Hydrolysis and condensation reaction

[Reaction Scheme 1]

MOR + H ₂ O → ROH + MOH

[Reaction Scheme 2]

_{nSi (OR) 4 + 4nH 2} O → nSiO 2 + 4nROH

In the above reaction formula, MOR, ROH, MOH, Si (OR) ₄ and SiO ₂ are respectively named metal alkoxide, alcohol, metal hydroxide, alkyl silicate and silica.

The metal alkoxide and alkyl silicate are hydrolyzed by water to metal hydroxide, silica and alcohol. In particular, the alkyl silicate is subjected to a condensation reaction in which silanol (SiOH) molecules generated through hydrolysis and reaction simultaneously react with each other, Gel reaction to produce silica.

The resulting silica and hydroxide metal are formed on the surface of the ceramic core particles by the vitreous of the metal silicate through heat treatment at a high temperature (> 900 ^o C), and the plastic strength of the ceramic core is expressed through the following vitrification process.

(2) vitrification reaction

SiO ₂ + 2MOH? SiO ₂ M ₂ O + H ₂ O

In addition, the polymer precursor may be used alone or in combination with one or more monomers capable of forming a network structure by a polymerization reaction. More specifically, the content of the polymer precursor is 1 to 10 parts by weight based on 100 parts by weight of the mixture prepared in the third step.

Preferably, the polymer precursor is in liquid form for uniform mixing with the ceramic core powder particles.

The fourth step is a step of forming a molded body by gel-casting the mixture of the coated ceramic powder particles and the polymer precursor in the third step.

The fifth step is a step of heat-treating the molded body formed by gel-casting, specifically, the heat treatment is performed at a temperature of 900 ° C to 1000 ° C. The heat treatment step is a step for forming a vitreous metal silicate on the surface of the ceramic particles, and the plastic strength of the ceramic core is expressed through vitrification. Wherein the glassy metal silicate is the product obtained through the vitrification of the metal alkoxide and the silica precursor. When the heat treatment temperature is less than 900 ° C, there is a problem in that the conversion of the glassy metal silicate to glassy is reduced. In the case of heat treatment exceeding 1000 ° C, vaporization and decomposition of the glassy metal silicate are promoted, Therefore, it is not preferable.

The metal of the vitreous metal silicate can be used as an alkali metal or an alkaline earth metal and more specifically can be selected from the group consisting of sodium (Na), magnesium (Mg), potassium (K), calcium (Ca), lithium (Li) Be), but the present invention is not limited thereto.

Hereinafter, the present invention will be described in more detail with reference to Examples. It is to be understood by those skilled in the art that these embodiments are only for describing the present invention in more detail and that the scope of the present invention is not limited by these embodiments in accordance with the gist of the present invention .

Example 1

The starting ceramic particles were mixed with the composition shown in Table 1 below and mixed with an alkali metal compound composed of a silica precursor (tetraethylorthosilicate) and a metal alkoxide (sodium methoxide) as shown in Table 3 .

The mixture was dried at 100 ° C for 1 hour to prepare ceramic powder coated with an inorganic alkali metal compound.

Then, the ceramic particles coated on the surface were mixed with the compound containing the polymer precursor of [Table 2] and subjected to a gel-casting process to prepare a ceramic core compact.

The formed body was heat-treated at 1000 ° C for 1 hour to prepare a ceramic core test piece.

Composition table according to starting ceramic particle size Starting ceramic particles Content (wt%) Zircon Flour 2 10 Zircon Flour 3 10 Fused silica 10 Silica powder (25 탆) 10 Silica powder (45 탆) 25 Silica powder (149 탆) 25 Silica powder (100 ~ 200㎛) 10

Composition ratio for gel-casting Starting Ceramic Particles (Vol%) menstruum
(Vol%) Dispersant
(wt%) Monofunctional precursor
(wt%) This functional group precursor
(wt%) Initiator
(g) catalyst
(g) 60 40 1.1 3.3 0.7 0.15 0.15

Composition ratio of inorganic coating Tetraethylorthosilicate
(wt% (mol%)) Sodium methoxide
(wt% (mol%)) Isobutyl alcohol
(wt% (mol%)) 38 (0.18) 56 (1.5) 6 (0.08)

Comparative Example 1

A mixture of the starting ceramic particles blended with the composition of Table 1 and the organic compound shown in Table 4 below was uniaxially pressed and then subjected to a cold isostatic press (CIP) to form a compact. And the ceramic core specimens were prepared.

Organic Compound Composition Ratio for Making Conventional Ceramic Core Conventional binder Ratio (wt.%) Paraffin wax (Paraffin Wax, solid) 80 ~ 85 Micro Crystal Wax (solid) 7 ~ 9 Oleic acid (Oleic Acid, liquid) 5 ~ 7 Stearic acid (solid) 1-3 Total 100

Test Example 1: Fracture Strength Measurement Test

The fracture strength of the ceramic core specimens prepared in Example 1 and Comparative Example 1 was measured and shown in Fig. Fig. 2 shows the respective fracture strengths before and after the heat treatment.

The fracture strength is a mean value of five measurements at room temperature at a rate of 0.5 mm / min in a 4-point bending mode using a universal testing machine.

Referring to FIG. 2, it is confirmed that the ceramic core test piece manufactured by Example 1 exhibits higher molding strength than the ceramic core produced by press molding of Comparative Example 1 due to the network structure of the polymer precursor by gel-casting .

Further, by coating the starting inorganic particles with the inorganic alkali metal compound, the high coating efficiency on the surface of the starting particles and the glass phase formed well at the particle interface caused the calcination of the ceramic core of Comparative Example 1 And the strength value of 10 MPa was obtained.

Test Example 2: Elution test

A photograph of a dissolution test (concentration of 40 wt%) in a sodium hydroxide solution of the ceramic core test piece of Example 1 prepared according to one embodiment of the present invention is shown in FIG. Here, it means (a) before the elution test and (b) after 10 hours of the elution test.

As a result of the decomposition of the ceramic cores made of the inorganic alkali metal compounds in the sodium hydroxide solution, it was found that the glassy substance of the sodium silicate produced by drying and heat treatment was completely decomposed in the sodium hydroxide solution.

In the ceramic core of the present invention, the inorganic coating material is coated on the starting particles, and the strength is expressed by the vitreous formed between the particles. The ceramic cores are impregnated with a sodium hydroxide solution after casting to decompose them, and hollow cavities can be made using the space of the disassembled ceramic core. From the above results, it was found that a ceramic core having high mechanical strength and excellent elution property was produced.

As described above, preferred embodiments of the present invention have been disclosed in the present specification and drawings, and although specific terms have been used, they have been used only in a general sense to easily describe the technical contents of the present invention and to facilitate understanding of the invention , And are not intended to limit the scope of the present invention.

It is to be understood by those skilled in the art that other modifications based on the technical idea of the present invention are possible in addition to the embodiments disclosed herein.

Claims (18)

Ceramic particles; And
And a glassy metal silicate coating said ceramic particles. The method according to claim 1,
Wherein the ceramic particles are selected from the group consisting of zirconia, silica and alumina. 3. The method according to claim 1 or 2,
Wherein the ceramic core is made by a gel-casting process. A first step of mixing a metal alkoxide (MOR) with a silica precursor, starting ceramic powder particles and a solvent to prepare a mixed solution;
A second step of drying the mixed solution to prepare ceramic powder particles coated with the metal alkoxide and the silica precursor;
A third step of mixing the coated ceramic powder particles and the polymer precursor;
A fourth step of gel-casting the mixture comprising the coated ceramic powder particles and the polymer precursor; And
And a fifth step of heat-treating the formed body formed by the gel-casting. 5. The method of claim 4,
The silica precursor may be at least one selected from the group consisting of tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, tetraisopropoxysilane, But are not limited to, methoxytriethoxysilane, demethoxydiethoxysilane, ethoxytrimethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, but are not limited to, ethyltriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, diethyldiethoxysilane, tetramethoxymethylsilane, tetramethoxyethylsilane, and tetraethoxymethyl Wherein the ceramic core is selected from the group consisting of tetraethoxymethylsilane, Article methods. 6. The method of claim 5,
Wherein the content of the silica precursor is 1 to 50 parts by weight based on 100 parts by weight of the solvent of the first step. 5. The method of claim 4,
The solvent is selected from the group consisting of methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, butyl alcohol, isobutyl alcohol, hexyl alcohol, and cyclohexyl alcohol. < Desc / Clms Page number 18 >
5. The method of claim 4,
Wherein the content of the metal alkoxide is 1 to 60 parts by weight based on 100 parts by weight of the solvent of the first step. 5. The method of claim 4,
R of the metal alkoxide (MOR) is hydrogen or an alkyl group,
The alkyl group is preferably a methyl group (-CH3), an ethyl group (-CH2CH3), a propyl group (-CH2CH2CH3), a butyl group (-CH2CH2CH2CH3), a pentyl group (-CH2CH2CH2CH3), an isopropyl group (-CHCH3CH3) And a cyclohexyl group (-CHCH2CH2CH2CH2CH2). ≪ / RTI > 5. The method of claim 4,
Wherein the metal (M) of the metal alkoxide (MOR) is an alkali metal or an alkaline earth metal. 5. The method of claim 4,
Wherein the polymer precursor is a liquid phase. 12. The method of claim 11,
Wherein the polymer precursor has a network structure. 12. The method of claim 11,
Wherein the polymer precursor has 1 to 4 functional groups and one functional group is used alone or in combination. 5. The method of claim 4,
Wherein the polymer precursor content is 1 to 10 parts by weight based on 100 parts by weight of the mixture prepared in the third step. 5. The method of claim 4,
Wherein the third step further comprises mixing at least one of a dispersant, an initiator, and a catalyst. 5. The method of claim 4,
Wherein the drying step is performed at 80 ° C to 120 ° C. 5. The method of claim 4,
Wherein the heat treatment step is performed at 900 ° C to 1,000 ° C. 18. A ceramic core produced by the method of any one of claims 4 to 17.

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