DE112014002622T5 - Investment casting core, method for producing a investment casting core, and investment casting tool - Google Patents

Abstract

By mixing and sintering silica particles and silica dust, a investment casting core body is produced. The resistance of the silica dust mixture lowers during the injection molding performed under heating, and therefore the flowability improves by the addition of silica dust. Accordingly, as the flowability improves, it is possible to reduce the injection pressure used in the production of a core. In addition, the mixture with improved flowability can be applied to a thin compact and to a complex compact.

Description

area

The present invention relates to a precision casting core, a method for producing a investment casting core, and a precision casting tool.

State of the art

As a precision cast product, for example, a turbine blade used in a gas turbine is known. In the gas turbine, a working fluid is heated by a burner to provide a high temperature / high pressure working fluid, and the working fluid rotates the turbine. That is, the working fluid compressed using a compressor is heated by the burner to increase the energy of the working fluid, the turbine recovers the energy to generate a rotational force, and the rotational force generates electrical energy. The turbine is provided with a turbine runner, and the outer edge region of the turbine runner is provided with at least one gas turbine blade.

Since a turbine blade of a jet engine or a gas turbine located at the bottom is exposed to high temperatures, it is provided with a complex cooling structure (an air hole), through which (s) a cooling medium (air) flows. In order to form such an inner cooling structure, a core (formed of silicon dioxide) having the same shape as a flow channel guiding the cooling medium is disposed inside a molding tool to thereby perform a casting process and a cooling process. Accordingly, a metal casting product can be obtained. At this time, an external shape can be obtained by breaking the mold. However, since the core remains therein, the core is usually removed by dissolution and removal by means of a base (eg, NaOH or KOH).

Accordingly, since the core has to be dissolved by means of a base, a silicon dioxide material (SiO ₂ ) is used (Patent Literature 1).

An investment casting core may be obtained by molding a silica material such as molten silica (SiO ₂ ) by injection molding or slip casting, and heat treating the same.

The injection molding method is a method in which a compact is obtained by kneading ceramic powder and wax, injecting a material obtained by heating and melting the wax into a metal mold, and cooling and curing the material.

The slip casting method further provides a method in which slurry is prepared by mixing ceramic powder with water or the like, the slurry is poured into a mold made of a solution absorbing material such as gypsum, and the slurry is dried to obtain a desired shaped body.

Bibliography

patent literature

• Patent Literature 1: Disclosed Japanese Patent Publication 6-340467

Summary

Technical problem

Incidentally, since the silica material is usually obtained by grinding a block formed by melting quartz, the problem arises that the material is comparatively coarse-grained. Such a material is formed into a core by, for example, an injection molding process, and then subjected to a heat treatment (sintering). However, since the particles are coarse-grained, the strength of the sintered body is low.

Since the flowability of the material during injection molding is low, there is still the problem that a high injection pressure is needed.

Moreover, since the existing core is mainly produced from the aspect of alkali solubility, there arises a problem that the core has low strength at high temperatures.

Furthermore, in the injection molding process, a plurality of holes are formed in the surface of the core, which is sintered following the molding. This results in the problem of low strength, which is why the core breaks from the holes as origin points during casting.

Accordingly, there has been a demand for an investment casting core having improved strength at high temperatures.

The invention has been made in consideration of the circumstances described above and has set itself the task of a investment casting with improved flowability and high temperature strength, a method of making a investment casting core, and a precision casting tool.

the solution of the problem

According to a first aspect of the invention for solving the problems described above, there is provided an investment casting core in which an investment casting core body obtained by mixing and sintering silica particles and silica dust is formed.

According to a second aspect, in the first aspect, there is provided an investment casting core in which a covering layer is formed on the surface of the sintered investment casting core body.

According to a third aspect, there is provided a precision casting tool used for producing a metal casting which comprises the investment casting core according to the first or second aspect in a shape corresponding to a cavity inside the metal casting and an outer molding corresponding to the shape of the outer boundary surface of the metal casting , includes.

According to a fourth aspect, there is provided a method of manufacturing a precision casting core which comprises immersing a sintered body of a fine casting core body mainly containing silica particles in a coating material containing a silica material and an alumina material, drying the sintered body, and heating the sintered body Sintered body for forming a cover layer on the surface of the investment casting core body comprises.

According to a fifth aspect, in the fourth aspect, there is provided a method of manufacturing an investment casting core in which the silica material is silica sol and the alumina material is alumina sol.

Advantageous Effects of the Invention

According to the present invention, it is possible to improve the fluidity of a composite formed by adding a spherical ultrafine particulate silica dust to coarse silica particles. Accordingly, it is possible to reduce the injection pressure used in the production of a core.

Moreover, since the cover layer of two kinds of silica materials having different particle diameters is formed on the surface of the sintered investment core body, the holes formed in the surface during sintering are sealed. Accordingly, there is an effect that core breakage during casting is avoided by improving the strength of the core and closing the holes.

Brief description of the drawings

1 Fig. 16 is a graph illustrating the relationship between the strength and the amount of added silica dust in Example 2.

2 Fig. 16 is a graph illustrating the relationship between the strength and the amount of added silica dust in Example 3.

3 FIG. 10 is a flowchart exemplifying the flow of a casting method. FIG.

4 FIG. 4 is a flowchart exemplifying the flow of a method of manufacturing a molding tool. FIG.

5 FIG. 12 is a schematic diagram illustrating a method of manufacturing a core. FIG.

6 FIG. 12 is a schematic perspective view illustrating a part of a metal mold. FIG.

7 Fig. 12 is a schematic diagram illustrating a method of producing a wax model.

8th Figure 3 is a schematic diagram illustrating one embodiment of the application of slurry to a wax model.

9 FIG. 12 is a schematic diagram illustrating a method of manufacturing an outer mold. FIG.

10 is a schematic diagram illustrating a sub-process of the method for producing a mold.

11 is a schematic representation illustrating a sub-process of the casting process.

12 is a schematic diagram illustrating a method for producing a core according to Example 2.

13 is a cross-sectional structure diagram of a investment casting core.

Description of embodiments

In the following the invention will be described in more detail with reference to the drawings. Moreover, the invention is not limited to the following description. Furthermore, the components to be described below may comprise a component readily derivable by a person skilled in the art, a component having a substantially identical configuration, and a so-called equivalent component.

example 1

The investment casting core of the present invention is obtained by mixing and sintering silica particles and silica dust (having a particle diameter of 0.15 μm) to form the investment casting core body.

The silica particles are formed here, for example, from fused silica (SiO ₂ ), such as quartz sand and quartz powder.

The core body is produced by a known method, whereby silica dust (having a particle diameter of 0.15 μm) silica particles such as quartz sand (220 mesh (20 to 70 μm) or 350 mesh (20 to 40 μm)) or by mixing Quartz flour (eg, 800 mesh (10 to 20 μm)) and quartz sand (for example, 220 mesh or 350 mesh) in a 1: 1 weight ratio mixture is added, wax is added, and the resulting product is heated and kneaded to this way to get a composite body.

Here, it is desirable that the silica dust has a particle diameter of 0.05 to 0.5 μm.

As illustrated in the examples described below, it is desirable that the silica dust mixed with silica particles be used in an amount of 5% by weight or more, preferably 10% by weight or more, and more preferably 20% by weight. % or more is present. This is because the strength of the core does not improve so much at less than 5% by weight.

By injection molding of the obtained composite body, a core compact is obtained.

By performing a degreasing treatment at, for example, 600 ° C and a sintering treatment at, for example, 1200 ° C, a core body is subsequently obtained.

It is possible to improve the fluidity of a composite formed by adding a spherical ultrafine particulate silica dust to coarse silica particles. Accordingly, it is possible to reduce the injection pressure used in the production of the core.

<Test Example 1>

A test example is described which verifies the flowability of the invention on which it is based.

In order to check the improved injection moldability, a comparative test was conducted on the flowability of the composite.

10 wt% (thermoplastic) wax was added to and kneaded with silica particles (for example, 220 mesh) to thereby obtain a composite body functioning as a comparative composite.

Silica dust was mixed with silica particles (for example, 220 mesh) in a weight ratio of 9: 1, and then added with 10 wt% (thermoplastic) wax and kneaded, to thereby obtain a composite body functioning as a sample composite.

The comparative composite body containing no silica dust according to the prior art and the silica dust-containing sample composite were each injected into an injection molding apparatus so as to be heated and injected. At that time their pressures were compared.

When the pressure of the prior art only comparative silica composite particle-containing body is set to 100, the pressure of the sample compound body containing 10% by weight of silica dust is 85 , which verifies that the addition of silica dust reduces the resistance in the sample composite and improves the flowability.

Accordingly, since the flowability of the sample composite improves, it is possible to reduce the injection pressure used in the production of the core. In addition, the composite body with improved flowability can be applied to a thin compact and to a complex compact.

<Test Example 2>

A test example is described, which shows the effect of the invention on which the strength is based.

In the test example, by adding wax to mixtures in which quartz sand (220 mesh: 20 to 70 μm) each having 10 wt%, 20 wt%, 30 wt%, and 40 wt%, respectively Silica dust was added, and heating and kneading of the mixtures obtained sample composite. Herein, "RD-120" (product name) manufactured by Tatsumori Ltd. was used as quartz sand.

By injection molding of the sample composite bodies obtained, one compact each was obtained.

As the test sample, a sample each having a width of 30 mm, a length of 200 mm and a thickness of 5 mm was obtained.

By performing a degreasing treatment at 600 ° C and a sintering treatment at 1200 ° C, a test sample for a core body was subsequently obtained for each of the sample composite bodies.

The strength of the obtained test samples was measured.

The strength test was conducted on the basis of "Bending strength of ceramic compositions (1981)" in accordance with JIS R 1601.

The test result for Test Example 2 is in 1 illustrated. 1 Fig. 16 is a graph illustrating the relationship between the strength and the amount of added silica dust in Test Example 2.

As in 1 When the amount of silica dust added is increased to 20% by weight, flexural strength increased. Moreover, when adding 20% by weight or more of silica dust, the improvement of the strength level was poor.

Accordingly, because of concerns that the time required to dissolve the core in an alkali solution may increase due to the use of a mixed fine particle silica fume which would further densify in the case of use, it has been verified that there is an improvement the strength of the core, the amount of added silica dust must be 5 wt% to 30 wt%, and preferably 10 wt% to 30 wt%.

As the composite is made into coarse-grained silica particles by adding a silica-dust spherical particles of ultrafine particles, the core structure is densified to improve the bending strength.

<Test Example 3>

Following Test Example 2, a bending test was conducted using silica mesh particles having a size of 350 mesh (20 to 40 μm) instead.

The test result for Test Example 3 is in 2 illustrated. 2 Fig. 16 is a graph illustrating the relationship between the strength and the amount of added silica dust in Test Example 3.

Since the quartz sand was finer than that of Test Example 2, the initial value for flexural strength was high as in 2 is illustrated. Moreover, when the amount of added silica dust was increased to 20% by weight, the bending strength increased. However, when adding 30% by weight or more of silica dust, the improvement in the degree of strength was poor. Accordingly, in 2 verifies that in order to improve the strength of the core, the amount of added silica dust must be 5 wt% to 30 wt%, and preferably 10 wt% to 30 wt%.

Hereinafter, a casting method will be described, which uses a molding tool with an investment casting core of the invention arranged therein.

3 FIG. 10 is a flowchart exemplifying a flow of the casting method. FIG. The casting method will be described below with reference to 3 described. The in 3 In this case, the process illustrated can be carried out completely automatically, or it can be performed by the the individual devices operating persons are performed process adapted. In the casting method of the embodiment, a molding tool is manufactured (step S1). The molding tool can be prepared in advance, or it can be made at every molding.

With reference to the 4 to 10 For example, the method of manufacturing a mold of the embodiment described by the process of step S1 will be described below. 4 FIG. 10 is a flowchart exemplifying the flow of the method of manufacturing a molding tool. FIG. The in 4 In this case, the illustrated process can be carried out completely automatically, or it can be performed by the persons operating the individual devices in a process-adapted manner.

In the method of manufacturing a molding tool, a core is manufactured (step S12). The core has a shape corresponding to the cavity inside the metal casting produced using the mold. Thus, since the core is disposed in a region corresponding to the cavity inside the metal casting, it is possible to prevent inflow of the metal functioning as casting metal during casting. Hereinafter, the method of manufacturing a core will be described with reference to FIG 5 described.

5 Fig. 12 is a schematic diagram illustrating the method of producing a core. As in 5 In the method of manufacturing a core, a metal mold is illustrated 12 manufactured (step S101). The metal mold 12 is formed such that an area corresponding to the core is formed as a cavity. A cavity-formed portion of the core becomes a convex portion 12a , Although it is in the cross-section of the metal mold 12 according to 5 is illustrated is the metal mold 12 moreover, shaped such that, in addition to an opening for injecting a material into a space or a hole for releasing air, basically another area, which includes the entire boundary surface of a region corresponding to the core, is formed as a cavity. In the method of casting a mold, over the opening for injecting a material into the gap of the metal mold 12 a ceramic slip 16 into the metal mold 12 injected, as with an arrow 14 is indicated. In particular, it becomes a core 18 produced by so-called injection molding, by the ceramic slip 16 into the metal mold 12 is injected. Following the production of the core 18 inside the metal mold 12 becomes the core 18 in the method of manufacturing a mold from the metal mold 12 separated, and the severed core 18 is in a combustion furnace 20 sintered. In this way, the core formed of ceramic 18 sintered and hardened (step S102).

Following the production of the core 18 For example, in the method of manufacturing a mold, an outer metal mold is produced (step S14). The outer metal mold has a shape whose inner boundary surface corresponds to the outer boundary surface of the metal casting. The metal mold may be formed of metal or ceramic. 6 is a schematic perspective view illustrating a part of the metal mold. In the in 6 illustrated metal mold 22a corresponds to a formed on the inner boundary surface recess of the outer boundary surface of the metal casting. In addition, in 6 only the metal mold 22a illustrated; however, in addition, another, the metal mold 22a corresponding metal mold made in an orientation in which the recess formed on the inner boundary surface is covered so that it with the metal mold 22a matches.

In the method of manufacturing a mold, when two metal molds are combined together, a mold is obtained whose inner boundary surface corresponds to the outer boundary surface of the metal mold.

Subsequent to the production of the outer metal mold, in the method of manufacturing a mold, a wax model (a wax mold) is prepared (step S16). Hereinafter, this method will be described with reference to 7 described. 7 Fig. 12 is a schematic diagram illustrating a method of producing a wax model. In the method of manufacturing a molding tool, the core becomes 18 at a predetermined location in the metal mold 22a arranged (step S110). After that, one covers the metal mold 22a corresponding metal mold 22b the recessed surface of the metal mold 22a while at the same time the boundary surface of the core 18 from metal mold tools 22a and 22b is enclosed, so the core 18 and the metal molds 22a and 22b a gap 24 form. In the process of making a mold, wax is then started 28 from one with the gap 24 connected line in the interspace 24 to inject, as with an arrow 26 is indicated (step S112). The wax 28 Here, a material, such as a wax, whose melting point is comparatively low, and which is heated and melted at a predetermined temperature or higher. In the method of manufacturing a mold, the wax becomes 28 in the entire area of the gap 24 filled (step S113). By curing the wax 28 then becomes a wax model 30 produced, in which the wax 28 the boundary surface of the core 18 encloses. The wax model 30 is shaped so that it is essentially made of wax 28 formed region which has the same shape as the metal casting to be produced is formed. In the process of making a metal casting, the wax model becomes 30 then from the metal molds 22a and 22b separated, and it becomes a sprue 32 attached thereto (step S114). The sprue 32 represents an opening through which molten metal functioning as a molten metal is introduced during casting. In the method of manufacturing a mold, the wax model becomes 30 which is the core 18 includes and from the same shape as the metal casting having wax 28 is formed as described above.

Following the production of the wax model 30 In the method of manufacturing a molding tool, slurry application (dipping) is performed (step S18). 8th Figure 3 is a schematic diagram illustrating one embodiment of the application of slurry to a wax model. 9 FIG. 12 is a schematic diagram illustrating a method of manufacturing an outer mold. FIG. As in 8th is illustrated, the wax model 30 in the process of making a mold into a slurry 40 filled storage area 41 dipped, and is withdrawn therefrom for drying (step S19). In this way, a primary layer 101A on the surface of the wax model 30 be formed.

The slip applied in step S18 is in this case a slip which directly onto the wax model 30 is applied. As a slip 40 a slip obtained by dispersing exclusively ultrafine alumina particles is used. In the slip 40 For example, it is desirable to use refractory microparticles, such as about 350 mesh zirconia, as flour. Further, it is desirable to use a polycarboxylic acid as a dispersant. Further, it is desirable to the slurry 40 Add a small amount, for example 0.01%, of defoamer (a silicon material) or of a wettability enhancing agent. If the wettability enhancing agent is added to the slip, it is possible to increase the adhesive property of the slip 40 to the wax model 30 to improve.

As in 8th is illustrated, the application of slurry (dipping) is carried out on the primary layer (the first dried film) 101A wax model in the process of making a mold by applying and drying the slurry 40 (Step S20). As in 9 is then stuccoed, consisting of zirconia stucco grains (with a mean particle diameter of 0.8 mm) as stucco material 54 are sprinkled on the surface of the wet slurry (step S21). Following this is a layer of moist slurry, on the surface of which is the stucco material 54 adheres, dried, to thereby form a first backing layer (a second dried film) 104-1 on the primary layer (the first dried film) 101A form (step S22).

It is determined whether or not to form the first supporting layer (the second dried film) 104-1 used process is repeated several times (for example, n: 6 to 10 times) (step S23). The nth support layer 104-n is laminated in a predetermined number (n) (step S23: Yes), so that a dried compact acting as an outer mold becomes 106A which is the thickness of a multilayer backing layer 105A of for example 10 mm.

Following the preparation of one with a plurality of layers consisting of the primary layer 101A and the multilayer support layer 105A provided dried compact 106A becomes the dried compact 106A in the process for producing a molding tool, subjected to a heat treatment (step S24). Specifically, the wax between the outer mold and the core is removed, and the outer mold and the core are sintered. This will be explained below with reference to 10 described. 10 is a schematic diagram illustrating a sub-process of the method for producing a mold. As illustrated in step S130, the one acting as an outer mold becomes a plurality of layers consisting of the primary layer 101A and the multilayer support layer 105A provided dried compact 106A in the process of making a mold in an autoclave 60 heated. The autoclave 60 heats the wax model 30 inside the dried compact 106A by introducing pressurized steam into the latter. In this way, this becomes the wax model 30 forming wax melted, leaving molten wax 62 from one of the dried compact 106A enclosed space 64 is dissipated.

Because the melted wax 62 from the gap 64 is discharged, is in the process for producing a mold, a molding tool 72 generated, in which the gap 64 in a wax filled area between the core 18 and the dried molding acting as the outer mold 106A is formed as illustrated in step S131. As illustrated in step S132, in the method of manufacturing a molding tool, the space is subsequently used 64 between the core 18 and as an outer mold acting dried compact 106A provided mold 72 by means of a combustion furnace 70 heated. This way, out of the mold 72 one in the acting as an outer mold dried compact 106A removed superfluous component or moisture component, and the mold is used to form the outer mold 61 sintered and hardened. In the method of producing a metal casting, the molding tool becomes 72 prepared as described above.

The casting method is described with reference to 3 to 11 described throughout. 11 is a schematic representation illustrating a sub-process of the casting process. Following the manufacture of the mold in step S1, the mold is preheated in the casting process (step S2). Here, the mold is placed, for example, in a furnace (a vacuum furnace and a combustion furnace) and heated to a range of 800 ° C to 900 ° C. Due to the preheating treatment, it is possible to avoid breaking of the mold when molten metal (molten metal) is injected into the mold to make a metal mold.

Following the preheating of the molding tool, potting is performed in the casting process (step S3). As in step S140 of FIG 11 is illustrated, this means that molten metal 80 ie, a raw material (eg steel) of a molten cast metal, from the opening of the mold 72 in a gap between the outer mold 61 and the core 18 is injected.

Following the solidification of the in the mold 72 poured molten metal 80 In the casting process, the outer mold becomes 61 removed (step S4). As in step S141 of FIG 11 is illustrated, this means that the outer mold 61 after the metal casting 90 by solidifying the molten metal inside the mold 72 was obtained, is crushed, as a fragment 61a from metal casting 90 to be disconnected.

Following the separation of the outer mold 61 from metal casting 90 In the casting method, the core removal process is performed (step S5). As in step S142 of FIG 11 is illustrated, this means that by introducing the metal casting 90 in an autoclave 92 a core removal process is performed. The core 18 inside the metal casting 90 is then melted, and a molten core 94 is from inside the metal casting 90 dissipated. This is the metal casting 90 inside the autoclave 92 immersed in an alkali solution and repeatedly subjected to pressure increase and pressure lowering around the molten core 94 from the metal casting 90 dissipate.

Subsequent to performing the core removal process, a post-treatment is performed in the casting process (step S6). This means that an aftertreatment of the surface or the interior of the metal casting 90 he follows. Furthermore, in the casting process during the aftertreatment, the quality of the metal casting is checked. As in step S143 of FIG 11 can be illustrated in this way a metal casting 100 getting produced.

In the casting method of the embodiment, the metal casting is produced by producing the molding tool by the above-described lost wax casting method using a wax. In the method of manufacturing a mold, the casting method, and the mold of the embodiment, the outer mold functioning as the outer portion of the mold is hereby formed as a multi-layered structure in which the primary layer (the first dried film functioning as the primary layer) 101A formed as an inner boundary surface due to the use of a slurry of ultrafine alumina particles and the multilayer support layer 105A on the outside of the primary layer 101A is trained.

As the investment casting product according to the invention, besides the gas turbine blade, there may be exemplified a gas turbine nozzle, a gas turbine combustor, a gas turbine pipe ring, or the like.

Example 2

Next, a second investment casting core will be described. 13 is a cross-sectional structure diagram of a investment casting core.

An investment casting core according to the invention is obtained by forming a covering layer of two kinds of silica materials having different particle diameters on a surface of a sintered main casting core body mainly containing silica particles (hereinafter referred to as "core body").

As in the upper part of the cross-sectional representation of acting as a sintered body, in 13 illustrated core body becomes, during sintering, a plurality of holes 18c in a surface 18b a core body 18a educated.

As in the lower part of 13 Illustrated are those in the surface 18b trained holes 18c in the context of the invention by coating the holes 18c with a cover layer 19a locked.

In this example, the cover layer becomes 19a on the surface 18b of the core body functioning as a sintered body 18a formed by mixing and sintering the obtained in Example 1 silica particles with silica dust (with a particle diameter of 0.15 microns).

In the top layer 19a For example, two types of silica materials having different particle diameters are used.

In the two types of silica materials having different particle diameters, silica sol (30 wt% SiO ₂ ) is used as the first material, and silica dust (having a particle diameter of 0.15 μm) is used as the second material.

In the invention, a slurry consisting of silica sol and silica dust is prepared by adding silica dust and dispersing the silica dust in silica sol.

Silica sol and silica dust are mixed together in a weight ratio of 1: 1 to 4: 1. In the amount of silica microparticles in the silica sol contained in the slurry consisting of silica sol and silica dust kneaded in a weight ratio of 2: 1, the ratio of solid content of the sol to silica dust was 30 : 50 set.

The sintered core body 18a is dipped in the slurry of silica sol and silica dust and withdrawn therefrom at a later time, around the cover layer formed of silica sol and silica dust 19a on the surface of the core body 18a train. As part of the training of the top layer 19a penetrates the slip component also in the holes 18c on the surface of the core, therefore, after the drying of the core body, a component formed of silica sol and silica dust also deposits in the holes of the core.

After the drying process, a heat treatment at, for example, 1000 ° C is performed. If the surface with the topcoat 19a is provided, the heat treatment at, for example, 1000 ° C or less can be performed.

Since voids within the large particle diameter silica dust are filled up with the silica particle sol having a small particle diameter in the silicon dioxide material functioning as a constituent material, in the obtained cover layer 19a due to the fine filling state creates a dense layer.

Further, since silica dust is spherical, the silica particle sol having a small particle diameter easily penetrates into gaps between the silica particle particles having a large particle diameter, and therefore the silica material is additionally filled with fines. In addition, since silica sol containing microparticles improves the interparticle adhesion, they contribute to improved strength.

In this way, the high-temperature strength of the investment casting core is improved according to the invention.

In addition, a silica material and an alumina material are used as a second cover layer forming material.

The silica material is silica sol (30 wt% SiO ₂ ), and the alumina material is alumina sol (Al ₂ O ₃ ).

To prepare a mixed sol (silica-alumina sol), silica sol (SiO ₂ ) and alumina sol (Al ₂ O ₃ ) are mixed in a molar ratio of 2: 3.

A sample of the core is dipped into and pulled out of the generated silica-alumina sol to form a layer of silica-alumina sol on the surface 18b of the core body 18a and depositing the silica-alumina sol even in the hole 18c to effect the core surface.

After the drying process, for example, a heat treatment at 1000 ° C is performed. If the surface with the topcoat 19a is provided, the heat treatment at, for example, 1000 ° C or less can be performed.

In the course of the heat treatment, the silica-alumina sol transforms into mullite (3Al ₂ O ₃ × 2SiO ₂ ) which has a high melting point due to a reaction. That way, it's possible to get the core 18 to get in which the core body 18a with a mullite topcoat 19a is covered.

Since the melting point of mullite is 1900 ° C and is therefore higher than the melting point of silicon dioxide (1600 ° C), this high casting temperatures can be handled.

Further, an alkoxide material is used as a third material forming the cover layer.

The alkoxide material herein comprises solely silicon alkoxide, or comprises a mixed alkoxide of silicon alkoxide and aluminum alkoxide.

As the silicon alkoxide, silicon ethoxide or silicon butoxide is used, and ethanol or butanol is used as the solvent.

In addition, when two kinds of alkoxides are mixed together, a mixed alkoxide material obtained by mixing silicon alkoxide and aluminum alkoxide is used, for example, using an alcoholic solvent such as butanol as a solvent.

When a mixed alkoxide is prepared, a mixed alkoxide consisting of silicon ethoxide and aluminum isopropoxide is dissolved in a butanolic solution.

The mixed alkoxide (silicon ethoxide + aluminum isopropoxide) is mixed in a molar ratio of 2: 3 to thereby produce an organic mixed alkoxide.

The sample of the core is dipped in and withdrawn from the single alkoxide or mixed alkoxide product to form a silicon layer or silicon aluminum alkoxide layer on the surface 18b of the core body 18a and a silicon component or silicon-aluminum alkoxide component even in the hole 18c to deposit the core surface.

Since the sole alkoxide or the mixed alkoxide dissolves in an alcoholic solution during dipping, the sole alkoxide or the mixed alkoxide easily penetrates into the core body, for which reason a good covering layer is formed thereon.

After the drying process, a heat treatment at, for example, 1000 ° C is performed. If the surface with the topcoat 19a is provided, the heat treatment at, for example, 1000 ° C or less can be performed.

In the case of a mixed alkoxide, the silicon-aluminum alkoxide layer undergoes heat-treatment transformation into inorganic mullite (3Al ₂ O ₃ .2SiO ₂ ) which has a high melting point. That way, it's possible to get the core 18 in which the core body 18a with the mullite topcoat 19a is covered.

Since the melting point of mullite is 1900 ° C and is therefore higher than the melting point of silicon dioxide (1600 ° C), this high casting temperatures can be handled.

Further, an alkoxide-silica dust material containing an alkoxide material and silica dust is used as a fourth material forming the cover layer.

The alkoxide material herein comprises solely silicon alkoxide, or comprises a mixed alkoxide of silicon alkoxide and aluminum alkoxide.

In inorganic silica dust, for example, a spherical material having a particle diameter of 0.15 μm is used.

Here, it is desirable that the silica dust has a particle diameter of 0.05 to 0.5 μm.

The dispersion content of silica dust is adjusted to 5 to 40% by weight, and is approximately 20% by weight.

As the silicon alkoxide, silicon ethoxide or silicon butoxide is used, and ethanol or butanol is used as the solvent.

When two kinds of alkoxides are mixed together, a mixed alkoxide material obtained by mixing silicon alkoxide and aluminum alkoxide is used, for example, using an alcoholic solvent such as butanol as a solvent.

When a mixed alkoxide is prepared, a mixed alkoxide consisting of silicon ethoxide and aluminum isopropoxide is dissolved in a butanolic solution.

The mixed alkoxide (silicon ethoxide + aluminum isopropoxide) is mixed in a molar ratio of 2: 3 to thereby produce an organic mixed alkoxide.

The sample of the core is incorporated in the sole alkoxide or mixed alkoxide and silica dust dispersed therein Dipped and pulled out of this product to a silicon dioxide dust-containing silicon layer or Siliziumaluminiumalkoxidschicht on the surface 18b of the core body 18a and a silicon dioxide-containing silicon layer or silicon-aluminum alkoxide component even in the hole 18c to deposit the core surface.

Since the sole alkoxide or the mixed alkoxide dissolves in an alcoholic solution during dipping, the sole alkoxide or the mixed alkoxide easily penetrates into the core body, for which reason a good covering layer is formed thereon.

After the drying process, for example, a heat treatment at 1000 ° C is performed. If the surface with the topcoat 19a is provided, the heat treatment at, for example, 1000 ° C or less can be performed.

Following the drying process has a deposition of the alkoxide and silica dust components even in the hole 18c the surface 18b of the core body 18a occurred. At that time, a mixed layer is formed from a large particle size silica dust layer and a fine and dense alkoxide layer.

Since an inorganic ceramic material is generated in the alkoxide layer due to the heat treatment at 1000 ° C., voids in the large particle size silica dust layer are filled by means of a dense ceramic layer, and therefore, the adhesion strength between the particles improves.

In the case of a mixed alkoxide, the silicon dioxide dust-containing silicon aluminum alkoxide layer undergoes heat-treatment transformation into inorganic mullite (3Al ₂ O ₃ .2SiO ₂ ) which has a high melting point. Since the voids in the large particle size silica dust layer are filled with a dense mullite layer, it is possible to fill the core 18 to get in which the core body 18a with the improved adhesion between the particles effecting cover layer 19a is covered.

Since the melting point of mullite is 1900 ° C and is therefore higher than the melting point of silicon dioxide (1600 ° C), this high casting temperatures can be handled.

In this way, since the plurality of holes formed in the surface are closed, it is possible to avoid the problem described in the prior art, according to which the core breaks from the holes as origin points during casting. Accordingly, the high-temperature strength of the investment casting core is improved.

Moreover, since silica dust has a large particle size, even a heat treatment at 1000 ° C. is associated with a low heat shrinkage.

Further, a silica material, an alumina material, and silica dust are used as a fifth capping-forming material.

The silica material is silica sol (30 wt% SiO ₂ ), and the alumina material is alumina sol (Al ₂ O ₃ ).

The proportion of dispersion of silica dust dispersed in the silica material and the alumina material is set to be 5 to 40% by weight, and is approximately 20% by weight.

It is desirable that the silica dust has a particle diameter of 0.05 to 0.5 μm.

For preparing a mixed sol (silica-alumina sol) (in which the particle diameter of the dispersed particles is from 1 to several hundreds of nanometers), silica sol (SiO ₂ ) and alumina sol (Al ₂ O ₃ ) are incorporated therein a molar ratio of 2: 3 mixed.

Silica dust is added to and dispersed in the produced silica-alumina sol to produce a slip composed of silica-alumina sol and silica dust.

The sample of the core is dipped in and pulled out of the slurry of silica-alumina sol and silica dust to form a layer of silica-alumina sol and silica dust on the surface 18b of the core body 18a and depositing the component formed of silica-alumina sol and silica dust even in the hole 18c to effect the core surface.

After the drying process, a heat treatment at, for example, 1000 ° C is performed. If the surface with the topcoat 19a is provided, the Heat treatment, for example, be carried out at 1000 ° C or less.

In the course of the heat treatment, silica-alumina sol transforms into mullite (3Al ₂ O ₃ .2SiO ₂ ), which has a high melting point, due to a reaction. Since voids in the large particle size silica dust layer are filled with the dense mullite layer, it is possible to fill the core 18 to get in which the core body 18a with the improved adhesion between the particles effecting cover layer 19a is covered.

Since the melting point of mullite is 1900 ° C and is therefore higher than the melting point of silicon dioxide (1600 ° C), this high casting temperatures can be handled.

In this way, since the plurality of holes formed in the surface are closed, it is possible according to the invention to avoid the problem described in the prior art, according to which the core breaks from the holes as origin points during casting. Accordingly, the high-temperature strength of the investment casting core is improved.

Moreover, since silica dust has a large particle size, even a heat treatment at 1000 ° C. is associated with a low heat shrinkage.

<Test Example 4>

For verification of the effect underlying the invention, a test example is described below.

In the test example, a composite was obtained by adding wax to a mixture in which silica sand (220 mesh) was added with 20% by weight of silica dust, and heating and kneading the mixture.

Injection molding of the obtained composite obtained a compact.

As a test sample, a sample having a width of 30 mm, a length of 200 mm, and a thickness of 5 mm was obtained.

By carrying out a degreasing treatment at 600 ° C and a sintering treatment at 1200 ° C, a sample for a core body was subsequently obtained.

Next, a slurry consisting of silica sol and silica dust was prepared by adding silica dust (spherical, having a particle diameter of 0.15 μm) and dispersing the silica dust in silica sol (30 wt% SiO ₂ ) (silica sol and Silica dust was kneaded together in a weight ratio of 2: 1). With this amount of silica microparticles in the silica sol, the ratio of solid content of the sol to silica dust was thus set to a value of 30:50.

The sample of the core body was dipped in and pulled out of the obtained slurry of silica sol and silica dust around the cover layer formed of silica sol and silica dust 19a to train on the surface. Following the drying process, a heat treatment was carried out at 1000 ° C, around the cover layer made of silica sol and silica dust 19a on the surface 18b of the core body 18a train.

As a comparative example, a core body without a cover layer was prepared as a comparative sample.

The strength of each test sample was measured.

The strength test was conducted on the basis of "Bending strength of ceramic compositions (1981)" in accordance with JIS R 1601.

The strength of the comparative sample without the overcoat according to the conventional method was 23 MPa, whereas the strength of the sample of the core body according to the method of the present invention was 29 MPa. As a result, it was found that the strength in the sample of the core body of the invention was increased by 25%.

Hereinafter, a casting method will be described, which uses a molding tool with an investment casting core of the invention arranged therein.

Incidentally, an explanation of processes which are identical to those of the casting method according to Example 1 is omitted, and only the "process for producing a core" with reference to 12 described.

12 is a schematic diagram illustrating the process for producing a core according to Example 2. As in 12 is illustrated, in the method of manufacturing a mold, a metal mold becomes 12 manufactured (step S101). The metal mold 12 is formed such that an area corresponding to the core is formed as a cavity. A cavity-formed portion of the core corresponds to the convex portion 12a , Although it is in the cross-section of the metal mold 12 according to 12 is illustrated is the metal mold 12 moreover, shaped such that, in addition to an opening for injecting a material into a space or a hole for releasing air, basically another area, which includes the entire boundary surface of a region corresponding to the core, is formed as a cavity. In the method of casting a mold, over the opening for injecting a material into the gap of the metal mold 12 a ceramic slip 16 into the metal mold 12 injected, as with an arrow 14 is indicated. In particular, it becomes a core 18 produced by so-called injection molding, by the ceramic slip 16 into the metal mold 12 is injected. Following the production of the core 18 inside the metal mold 12 becomes the core 18 in the method of manufacturing a mold from the metal mold 12 separated, and the severed core 18 is in a combustion furnace 20 sintered. In this way, the core formed of ceramic 18 sintered and hardened (step S102).

The processes described so far are identical to those of Example 1.

To make a topcoat on the surface of the core 18 form the sintered core 18 , as in 12 is illustrated, then in a with slip 19 filled storage area 17 dipped, and is withdrawn therefrom for drying (step S103). After that, the dipped core becomes 18 taken and in the incinerator 20 sintered. In this way, the cover layer becomes 19a on the surface of the ceramic core 18 formed (step S104).

In the method of casting a mold, the one with the cover layer becomes 19a provided core 18 prepared as described above. In addition, the core becomes 18 made of a material that can be removed after curing of the metal casting using a core removal process, such as a chemical treatment.

In the molding method of the embodiment, since the cover layer is formed on the surface of the core, the dimensional accuracy improves, thus improving the durability even at high molding temperatures.

Moreover, since a core having high strength is provided, the freedom of potting design (for example, a low pull-down speed or the like) increases even with a long casting time.

Moreover, it is possible to provide a precision cast product, such as a turbine blade, which is thin and has good thermal efficiency.

LIST OF REFERENCE NUMBERS

12, 22a, 22b

Metal mold

12a

Convex area

14, 26

arrow

16

Ceramic slip

18

core

18a

core body

18b

surface

18c

hole

19

Schlicker

19a

topcoat

20, 70

incinerator

24, 64

gap

28

wax

30

wax model

32

sprue

40

Schlicker

60, 92

autoclave

61

outer mold

61a

fragment

62

melted wax

72

mold

80

molten metal

90, 100

metal casting

94

melted core

101A

primary layer

Claims (5)

Investment casting core in which an investment casting obtained by mixing and sintering of silica particles and silica dust is formed. Investment casting core according to claim 1, wherein a cover layer is formed on the surface of the sintered investment casting core body. Precision casting tool used to make a metal casting comprising: the investment casting core according to claim 1 or 2, which has a shape corresponding to a cavity in the interior of the metal casting; and an outer mold which corresponds to the shape of the outer boundary surface of the metal casting. A method of manufacturing a precision casting core, comprising: immersing a sintered body of a silica particle mainly containing Investment casting core body in a coating material containing a silica material and an alumina material; Drying the sintered body; and heating the sintered body to form a cover layer on the surface of the investment casting core body. The method of manufacturing a investment casting core according to claim 4, wherein the silica material is silica sol and the alumina material is alumina sol.

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