JP2014231081A - Core for precision casting, production method therefor, and mold for precision casting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a core for precision casting with improved high-temperature strength, a production method therefor, and a mold for precision casting.SOLUTION: A core for precision casting comprises a coating layer (19a) formed on the surface of a core main body (18a) for precision casting that is sintered using silica particles as the main component thereof, the coating layer composed of silica materials, alumina materials and silica fume. As a result, holes (18c) formed on the surface are sealed. Therefore, core breakage during casting can be prevented.

Description

  The present invention relates to a core for precision casting, a manufacturing method thereof, and a mold for precision casting.

  Examples of precision castings include moving blades used in gas turbines. In a gas turbine, a working fluid is burned in a combustor to form a high-temperature and high-pressure working fluid, and the turbine is rotated by the working fluid. That is, the working fluid compressed by the compressor is burned by the combustor, energy is increased, and the energy is recovered by the turbine to generate a rotational force, thereby generating electric power. The turbine section is provided with a turbine rotor, and at least one gas turbine rotor blade is provided on the outer periphery of the turbine rotor.

  Here, the gas turbine rotor blade is exposed to a high temperature. As a countermeasure, a cooling medium for cooling is supplied to the gas turbine rotor blade. For this reason, the gas turbine rotor blade is provided with an internal cooling structure. In order to configure such an internal cooling structure, a core (core) having the same shape as the flow path of the cooling medium is disposed, and the core is removed after casting. The core is removed by dissolving and removing the core in an alkali (for example, NaOH or KOH) solution, thereby forming an internal cooling structure of the turbine rotor blade, for example.

  As the core, a ceramic core using ceramic particles is conventionally used (Patent Document 1).

Here, the core for precision casting is obtained by molding a siliceous material such as fused silica (SiO ₂ ) by a method such as injection molding or slip casting, and then performing a heat treatment.
The injection molding method is a method of obtaining a molded product by kneading ceramic powder and wax, then injecting and injecting a material obtained by heating and melting the wax into a mold, and cooling and solidifying the material.
Slip cast molding is a method in which ceramic powder is mixed with water or the like to form a slurry, which is poured into a mold made of a material that absorbs a solution such as gypsum, dried, and molded.

JP-A-6-340467

By the way, since the present core is manufactured mainly for alkali solubility, there are problems such as low high-temperature strength. In addition, in the injection molding method, after the molding, the sintered core has a large number of holes on its surface, so the strength is low. There is a problem that there is a concern about the possibility of breaking.
Therefore, the appearance of a core for precision casting with improved high temperature strength is eagerly desired.

  This invention is made | formed in view of the above, Comprising: It aims at providing the core for precision casting which the high temperature strength improved, its manufacturing method, and the mold for precision casting.

  The first invention of the present invention for solving the above-described problem is that a siliceous material, an alumina material, and a silica fume are formed on the surface of a sintered precision casting core body that is mainly composed of siliceous particles. In the core for precision casting, the coating layer is formed.

  A second invention is the precision casting core according to the first invention, wherein the siliceous material is silica sol and the alumina material is alumina sol.

  According to a third aspect of the present invention, there is provided a precision casting mold for use in manufacturing a casting, the core for precision casting according to claim 1 or 2 having a shape corresponding to a hollow portion inside the casting, and an outer peripheral surface of the casting. A precision casting mold characterized by having an outer mold corresponding to the shape.

  In a fourth invention, the sintered body of the core body for precision casting mainly composed of siliceous particles is immersed in a coating material composed of siliceous material, alumina material and silica fume, and then dried, and thereafter A method for producing a core for precision casting, characterized in that a coating layer is formed on the surface of the core body for precision casting by heat treatment.

  According to a fifth aspect of the present invention, there is provided the method for producing a core for precision casting according to the fourth aspect, wherein the siliceous material is silica sol, and the alumina material is alumina sol.

  In the present invention, by forming a coating layer of two types of siliceous materials and alumina materials having different particle diameters on the surface of the sintered core body for precision casting, pores generated on the surface during sintering are formed. Since the core is sealed and the strength of the core is improved, the hole is sealed, so that the core can be prevented from being broken during casting.

FIG. 1 is a cross-sectional configuration diagram of a precision casting core. FIG. 2 is a flowchart showing an example of the steps of the casting method. FIG. 3 is a flowchart showing an example of the steps of the mold manufacturing method. FIG. 4 is an explanatory view schematically showing a manufacturing process of the core. FIG. 5 is a perspective view schematically showing a part of the mold. FIG. 6 is an explanatory view schematically showing a wax mold manufacturing process. FIG. 7 is an explanatory diagram schematically showing a configuration in which slurry is applied to a wax mold. FIG. 8 is an explanatory view schematically showing a manufacturing process of the outer mold. FIG. 9 is an explanatory view schematically showing a part of the mold manufacturing method. FIG. 10 is an explanatory view schematically showing a part of the casting method.

  Hereinafter, the present invention will be described in detail with reference to the drawings. The present invention is not limited to the following description. In addition, constituent elements in the following description include those that can be easily assumed by those skilled in the art, those that are substantially the same, and those in a so-called equivalent range.

FIG. 1 is a cross-sectional configuration diagram of a precision casting core.
The core for precision casting according to the present invention has two types of different particle diameters on the surface of a sintered core body for precision casting (hereinafter referred to as “core body”) mainly composed of siliceous particles. A coating layer of a siliceous material and an alumina material is formed.

As shown in the upper section of the cross-sectional view of the core body of the sintered body shown in FIG. 1, a large number of holes 18c are generated in the surface 18b of the core body 18a during sintering.
In the present invention, as shown in the lower part of FIG. 1, the hole 18c is sealed by covering the hole 18c formed on the surface with the coating layer 19a.

Here, the core body 18a contains siliceous particles as a main component, and is formed of fused silica (SiO ₂ ) such as silica sand or silica flour.
The core body 18a is manufactured by a known method, and for example, silica flour (for example, 800 mesh (10 to 20 μm)) and silica sand (for example, 220 mesh (20 to 70 μm)) are used as siliceous particles. A wax is added to the mixture at a weight ratio of 1: 1 and heated and kneaded to obtain a compound.

The obtained compound is molded by injection molding to obtain a core molded body.
Thereafter, a degreasing process up to, for example, 600 ° C. is performed, and then a sintering process is performed at, for example, 1,200 ° C. to obtain the core body 18a.

In the present invention, the coating layer 19a is formed on the surface of the core body 18a of the obtained sintered body.
The covering layer 19a uses a siliceous material, an alumina material, and silica fume.

Here, the siliceous material is silica sol (SiO ₂ is 30 wt%), and the alumina material is alumina sol (Al ₂ O ₃ ).
Here, the dispersion ratio of the silica fume dispersed in the siliceous material and the alumina material is 5 to 40% by weight, preferably about 20% by weight.
Silica fume preferably has a particle size of 0.05 to 0.5 μm.

Here, the mixing of the silica sol (SiO ₂ ) and the alumina sol (Al ₂ O ₃ ) is prepared so that the molar ratio = 2: 3, and the mixed sol (silica-alumina sol) is prepared (the particle diameter of the dispersed particles). : 1 to several 100 nm).
Silica fume is added and dispersed in the prepared silica-alumina sol to prepare a silica-alumina sol-silica fume slurry.
After immersing the core specimen in this prepared silica-alumina sol-silica fume slurry, it is pulled up to form a layer of silica-alumina sol-silica fume on the surface 18b of the core body 18a, and in the holes 18c on the core surface. Also, silica-alumina sol-silica fume components are deposited.
Thereafter, drying is performed, and then heat treatment is performed at 1,000 ° C., for example. This heat treatment may be, for example, 1,000 ° C. or less as long as the coating layer 19a is formed on the surface.
In this heat treatment, the silica-alumina sol is converted into a high melting point mullite (3Al ₂ O ₃ .2SiO ₂ ) by the reaction. The core 18 in which the core body 18a is covered with the coating layer 19a in which the voids of the silica fume layer having a large particle diameter are filled with a dense mullite layer and the adhesion between the particles is improved is obtained.
Here, since the melting point of mullite is 1,900 ° C., which is considerably higher than the melting point of silica (1,600 ° C.), it is possible to cope with a high casting temperature.
As described above, according to the present invention, since a large number of holes formed on the surface are sealed, it is possible to prevent the core from being broken at the time of casting by using such a hole as a starting point. Therefore, the high temperature strength of the core for precision casting is improved.

  In addition, since silica fume has a large particle size, thermal contraction is small even in heat treatment at 1,000 ° C.

<Test example>
Hereinafter, test examples for confirming the effects of the present invention will be described.
In this test example, first, a wax is added to a mixture of silica flour (800 mesh) and silica sand (220 mesh) at a weight ratio of 1: 1, and heated and kneaded to obtain a compound. Here, silica flower is “MCF-200C” (trade name) manufactured by Tatsumori, silica sand is “RD-120” (trade name) manufactured by Tatsumori, and wax is “Cerita Wax F30-” manufactured by Paramelt. 75 "(trade name) was used.
A molded body is obtained by injection molding of the obtained compound.
As an evaluation test body, width 30 × length 200 × thickness 5 mm was obtained.

  Next, a degreasing process up to 600 ° C. and a sintering process at 1,200 ° C. were performed to obtain a test body for a core body.

Next, silica sol (SiO ₂ ) and alumina sol (Al ₂ O ₃ ) are used to prepare a mixed sol (silica-alumina sol) with a blending ratio (molar ratio = 2: 3) that results in mullite. To do.
A silica-alumina sol-silica fume slurry containing 20% by weight of silica fume (for example, a particle size of 0.15 μm; spherical body) and 20% by weight of silica fume is prepared in the silica-alumina sol thus obtained.
The core body specimen was immersed in the prepared silica-alumina sol-silica fume slurry, and then pulled up to form a silica-alumina sol coating layer 19a on the surface. Next, after drying, heat treatment was performed at 1,000 ° C., and a coating layer 19a made of mullite formed by reaction of silica-alumina sol containing silica fume was formed on the core body surface 18b.

As a comparative example, a comparative test body was formed without a coating layer.
The strength of these evaluation specimens was measured.
Here, the strength test was performed according to “Bending strength of ceramics (1981)” according to JIS R 1601.

The strength of the comparative test body in which the coating layer of the conventional method was not formed was 20 MPa, whereas the strength of the test body for the core body according to the method of the present invention was 27 MPa. As a result, the strength improvement of 35% was confirmed in the test body for the core body of the present invention.
According to the present invention, since the high temperature durability of the core is improved by mullite formation, for example, a mold that does not deform even when held at a high temperature (for example, 1,550 ° C.) for a long time in unidirectionally solidified blade manufacturing is obtained. Can do.

  Hereinafter, a casting method using a mold having the precision casting core of the present invention will be described.

  FIG. 2 is a flowchart showing an example of the steps of the casting method. Hereinafter, the casting method will be described with reference to FIG. Here, the processing shown in FIG. 2 may be executed fully automatically, or may be executed by an operator operating an apparatus that executes each process. The casting method of this embodiment produces a casting mold (step S1). The mold may be produced in advance or may be produced each time casting is performed.

  Hereinafter, the mold manufacturing method of the present embodiment executed in the step S1 will be described with reference to FIGS. FIG. 3 is a flowchart showing an example of the steps of the mold manufacturing method. Here, the processing shown in FIG. 3 may be executed fully automatically, or may be executed by an operator operating an apparatus that executes each process.

  The mold manufacturing method produces a core (core) (step S12). The core has a shape corresponding to a cavity inside a casting made of a mold. That is, the core is arranged in a portion corresponding to the cavity inside the casting, thereby suppressing the metal that becomes the casting from flowing in at the time of casting. Hereinafter, the manufacturing process of the core will be described with reference to FIG.

  FIG. 4 is an explanatory view schematically showing a manufacturing process of the core. In the mold manufacturing method, a mold 12 is prepared as shown in FIG. 4 (step S101). The mold 12 has a hollow area corresponding to the core. The portion that becomes the cavity of the core becomes the convex portion 12a. In FIG. 4, the cross section of the mold 12 is shown. However, the mold 12 basically has an entire circumference corresponding to the core except for an opening for injecting material into the space and a hole for extracting air. It is a covering cavity. In the mold casting method, the ceramic slurry 16 is injected into the mold 12 through an opening for injecting material into the space of the mold 12 as indicated by an arrow 14. Specifically, the core 18 is produced by so-called injection molding in which the ceramic slurry 16 is injected into the mold 12. In the mold manufacturing method, when the core 18 is produced inside the mold 12, the core 18 is removed from the mold 12, and the removed core 18 is placed in the firing furnace 20 and fired. Thereby, the core 18 formed of ceramics is baked and hardened (step S102).

Next, in order to form a coating layer on the surface of the core 18, the sintered core 18 is immersed in the storage portion 17 in which the slurry 19 is stored, and is taken out and then dried (step 103). Next, the immersed core 18 is taken out, placed in the firing furnace 20, and fired. Thereby, the coating layer 19a is formed on the surface of the core 18 made of ceramics (step S104).
The mold casting method produces the core 18 on which the coating layer 19a is formed as described above. The core 18 is formed of a material that can be removed by a core removal process such as a chemical process after the casting is solidified.

  In the mold manufacturing method, when the core 18 is manufactured, an external mold is manufactured (step S14). The outer mold has a shape in which the inner peripheral surface corresponds to the outer peripheral surface of the casting. The mold may be made of metal or ceramics. FIG. 5 is a perspective view schematically showing a part of the mold. As for the metal mold | die 22a shown in FIG. 5, the recessed part formed in the internal peripheral surface respond | corresponds to the outer peripheral surface of casting. In FIG. 5, only the mold 22a is shown, but a mold corresponding to the mold 22a and corresponding to the mold 22a is also produced so as to close the recess formed on the inner peripheral surface. In the mold manufacturing method, two molds are combined to form a mold whose inner peripheral surface corresponds to the outer peripheral surface of the casting.

  After producing the external mold, the mold manufacturing method produces a wax mold (wax mold) (step S16). Hereinafter, a description will be given with reference to FIG. FIG. 6 is an explanatory view schematically showing a wax mold manufacturing process. In the mold manufacturing method, the core 18 is installed at a predetermined position of the mold 22a (step S110). Thereafter, a mold 22b corresponding to the mold 22a is placed on the surface of the mold 22a where the recess is formed, and the core 18 is surrounded by the molds 22a and 22b, and the core 18 and the molds 22a and 22b are surrounded. A space 24 is formed between the two. The mold manufacturing method starts injection of WAX 28 from the pipe connected to the space 24 toward the inside of the space 24 as indicated by an arrow 26 (step S112). WAX 28 is a substance having a relatively low melting point, such as wax, which melts when heated above a predetermined temperature. In the mold manufacturing method, the entire space 24 is filled with the WAX 28 (step S113). Thereafter, the wax 28 is solidified to form the wax mold 30 in which the core 18 is surrounded by the wax 28. The wax mold 30 basically has the same shape as the casting for which the part formed by the WAX 28 is manufactured. Thereafter, in the casting manufacturing method, the wax mold 30 is separated from the molds 22a and 22b, and the gate 32 is attached (step S114). The gate 32 is a port into which molten metal, which is a metal melted during casting, is charged. As described above, the mold manufacturing method produces the solder mold 30 including the core 18 inside and formed of the WAX 28 having the same shape as the casting.

In the mold manufacturing method, when the wax mold 30 is produced, slurry application (dipping) is performed (step S18). FIG. 7 is an explanatory diagram schematically showing a configuration in which slurry is applied to a wax mold. FIG. 8 is an explanatory view schematically showing a manufacturing process of the outer mold. In the mold manufacturing method, as shown in FIG. 7, the wax mold 30 is immersed in the storage part 41 in which the slurry 40 is stored, and is taken out and then dried (step S19). Thereby, the prime layer 101 </ b> A can be formed on the surface of the wax mold 30.
Here, the slurry applied in step S <b> 18 is a slurry applied directly to the wax mold 30. As the slurry 40, a slurry in which alumina ultrafine particles are monodispersed is used. In the slurry 40, it is preferable to use refractory fine particles of about 350 mesh, such as zirconia, as flour. Moreover, it is preferable to use polycarboxylic acid as a dispersing agent. Further, it is preferable to add a small amount, for example, 0.01%, of an antifoaming agent (silicon-based substance) or a wettability improving agent to the slurry 40. By adding the wettability improving agent, the adhesion of the slurry 40 to the wax mold 30 can be improved.

In the mold manufacturing method, as shown in FIG. 7, slurry application is performed with the slurry 40, and then the wax mold having the prime layer (first dry film) 101A is further applied with slurry (dipping) (step S20). . Next, as shown in FIG. 8, stuccoing is performed by sprinkling zircon stucco grains (average particle size 0.8 mm) as the stucco material 54 on the surface of the wet slurry (step S21). After that, the surface of the slurry layer with the stucco material 54 attached is dried, and the first backup layer (second dry film) 104-1 is formed on the prime layer (first dry film) 101A (step S22). .
A determination is made to repeat the same operation as that for forming the first backup layer (second dry film) 104-1 a plurality of times (for example, n: 6 to 10 times) (step S23). A predetermined number (n) of the n-th backup layers 104-n are stacked (step S23: Yes) to obtain a dry molded body 106A which is an outer mold having a thickness of, for example, 10 mm on which the multilayer backup layer 105A is formed.

In the mold manufacturing method, after obtaining the dry molded body 106A on which a plurality of layers of the prime layer 101A and the multilayer backup layer 105A are obtained, the dry molded body 106A is subjected to heat treatment (step S24). Specifically, WAX between the outer mold and the core is removed, and the outer mold and the core are further fired. Hereinafter, a description will be given with reference to FIG. FIG. 9 is an explanatory view schematically showing a part of the mold manufacturing method. In the mold manufacturing method, as shown in step S130, a dry molded body 106 serving as an outer mold in which a plurality of layers of a prime layer 101A and a multilayer backup layer 105A is formed is placed in the autoclave 60 and heated. The autoclave 60 heats the wax mold 30 in the dry molded body 106 by filling the interior with pressurized steam. As a result, the wax forming the wax mold 30 is melted and the molten wax 62 is discharged from the space 64 surrounded by the dry molded body 106.
In the mold manufacturing method, the melted WAX 62 is discharged from the space 64, so that the space between the dry molded body 106 serving as the outer mold and the core 18 is filled with space as shown in step S131. A mold 72 in which 64 is formed is produced. Thereafter, in the mold manufacturing method, as shown in step S <b> 132, the mold 72 in which the space 64 is formed between the dry molded body 106 serving as the outer mold and the core 18 is heated in the firing furnace 70. As a result, the mold 72 is cured by firing by removing water components and unnecessary components contained in the dry molded body 106 serving as the outer mold, and the outer mold 61 is formed. In the casting manufacturing method, the mold 72 is produced as described above.

  The description of the casting method will be continued with reference to FIGS. FIG. 10 is an explanatory view schematically showing a part of the casting method. In the casting method, when the mold is produced in step S1, the mold is preheated (step S2). For example, the mold is placed in a furnace (vacuum furnace, firing furnace) and heated to 800 ° C. or higher and 900 ° C. or lower. By performing preheating, it is possible to prevent the mold from being damaged when molten metal (melted metal) is injected into the mold at the time of casting production.

  In the casting method, when the mold is preheated, pouring is performed (step S3). That is, as shown in step S <b> 140 of FIG. 10, a molten metal 80, that is, a molten casting material (for example, steel) is injected between the outer mold 61 and the core 18 from the opening of the mold 72.

  In the casting method, after the molten metal 80 poured into the mold 72 is solidified, the outer mold 61 is removed (step S4). That is, as shown in step S141 of FIG. 10, when the molten metal hardens into the casting 90 inside the mold 72, the outer mold 61 is crushed and removed from the casting 90 as a broken piece 61a.

  In the casting method, when the outer mold 61 is removed from the casting 90, the core removal process is performed (step S5). That is, as shown in step S142 of FIG. 10, the casting 90 is put into the autoclave 92 and the core removal process is performed to melt the core 18 inside the casting 90, and the melted melting core 94 is removed. It discharges from the inside of the casting 90. Specifically, the casting 90 is put into an alkaline solution inside the autoclave 92, and the melting core 94 is discharged from the casting 90 by repeating pressurization and decompression.

  In the casting method, after the core removal process is performed, a finishing process is performed (step S6). That is, a finishing process is performed on the surface and inside of the casting 90. In the casting method, the casting is inspected together with the finishing process. Thereby, as shown to step S143 of FIG. 10, the casting 100 can be manufactured.

  As described above, the casting method of the present embodiment produces a casting by using a lost wax casting method using WAX (wax) to produce a casting. Here, the mold manufacturing method, the casting method, and the mold according to the present embodiment include an outer mold that is an outer portion of the mold, and a prime layer (first layer that is the first layer) that forms an inner peripheral surface using alumina ultrafine particles as a slurry. (Dry film) 101A is formed, and a plurality of backup layers 105A are formed outside the prime layer 101A to form a multilayer structure.

In the casting method of this embodiment, since the coating layer is formed on the surface of the core, the dimensional accuracy is improved, and the durability is improved even when the casting temperature is high.
Even when the casting process takes a long time, since it is a high-strength core, the degree of freedom in casting design (for example, setting the pulling speed low) is improved.
Furthermore, it is possible to reduce the thickness of the product and manufacture a precision casting such as a turbine rotor blade having good thermal efficiency.

  Examples of precision castings according to the present invention include gas turbine stationary blades, gas turbine combustors, gas turbine split rings, and the like in addition to gas turbine rotor blades.

12, 22a, 22b Mold 12a Convex 14, 26 Arrow 16 Ceramic slurry 18 Core (core)
18a Core body 18b Surface 18c Hole 19 Slurry 19a Coating layer 20, 70 Firing furnace 24, 64 Space 28 WAX (Wax)
30 Wax mold 32 Gate 40 Slurry 60, 92 Autoclave 61 Outer mold 61a Debris 62 Molten WAX
72 Mold 80 Molten metal 90, 100 Casting 94 Melting core 101A, 101B Prime layer

Claims (5)

On the surface of a sintered precision casting core body mainly composed of siliceous particles,
A precision casting core comprising a coating layer comprising a siliceous material, an alumina material and silica fume. In claim 1,
The core for precision casting, wherein the siliceous material is silica sol and the alumina material is alumina sol. A mold for precision casting used in the manufacture of castings,
The core for precision casting according to claim 1 or 2 having a shape corresponding to a hollow portion inside the casting,
A precision casting mold comprising: an outer mold corresponding to a shape of an outer peripheral surface of the casting. A sintered body of a core body for precision casting mainly composed of siliceous particles,
Immerse in a coating material consisting of siliceous material, alumina material and silica fume,
A method for producing a core for precision casting, which is then dried and then heat-treated to form a coating layer on the surface of the core body for precision casting. In claim 4,
A method for producing a core for precision casting, wherein the siliceous material is silica sol and the alumina material is alumina sol.

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