U.S. patent application number 14/429081 was filed with the patent office on 2015-08-13 for precision casting mold and method of producing the same.
This patent application is currently assigned to MITSUBISHI HITACHI POWER SYSTEMS, LTD.. The applicant listed for this patent is MITSUBISHI HITACHI POWER SYSTEMS, LTD.. Invention is credited to Kazutaka Mori, Hidetaka Oguma, Ikuo Okada, Sachio Shimohata.
Application Number | 20150224569 14/429081 |
Document ID | / |
Family ID | 50477380 |
Filed Date | 2015-08-13 |
United States Patent
Application |
20150224569 |
Kind Code |
A1 |
Oguma; Hidetaka ; et
al. |
August 13, 2015 |
PRECISION CASTING MOLD AND METHOD OF PRODUCING THE SAME
Abstract
Provided is a precision casting mold including a core having a
shape corresponding to an internal hollow portion of a cast product
and an outer mold corresponding to a shape of an outer peripheral
surface of the cast product, and the outer mold is made up of: a
prime layer which is formed on an inner peripheral surface and is a
slurry film obtained by drying slurry for the precision casting
mold which includes mono-dispersed ultrafine alumina particles and
silica sol having a particle size of 1.0 .mu.m or smaller and
functions as mullite during firing; and a multi-layered backup
layer which is formed on the outside of the prime layer by
repeatedly forming a first backup layer obtained by forming and
drying a slurry layer formed from the slurry for the precision
casting mold and a stucco layer in which a stucco material is
adhered to the slurry layer.
Inventors: |
Oguma; Hidetaka; (Tokyo,
JP) ; Mori; Kazutaka; (Tokyo, JP) ; Okada;
Ikuo; (Tokyo, JP) ; Shimohata; Sachio; (Tokyo,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MITSUBISHI HITACHI POWER SYSTEMS, LTD. |
Yokohama-shi, Kanagawa |
|
JP |
|
|
Assignee: |
MITSUBISHI HITACHI POWER SYSTEMS,
LTD.
Yokohama-shi, Kanagawa
JP
|
Family ID: |
50477380 |
Appl. No.: |
14/429081 |
Filed: |
October 7, 2013 |
PCT Filed: |
October 7, 2013 |
PCT NO: |
PCT/JP2013/077275 |
371 Date: |
March 18, 2015 |
Current U.S.
Class: |
164/23 ;
164/365 |
Current CPC
Class: |
B22C 9/10 20130101; B22C
1/00 20130101; B22C 9/04 20130101; B22C 9/043 20130101 |
International
Class: |
B22C 9/04 20060101
B22C009/04; B22C 9/10 20060101 B22C009/10; B22C 1/00 20060101
B22C001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 9, 2012 |
JP |
2012-224614 |
Claims
1. A precision casting mold which is used to produce a cast
product, comprising: a core having a shape corresponding to an
internal hollow portion of the cast product; and an outer mold
corresponding to a shape of an outer peripheral surface of the cast
product, wherein the outer mold is made up of: a prime layer which
is formed on an inner peripheral surface and is formed from a
slurry film obtained by drying slurry for the precision casting
mold which includes mono-dispersed ultrafine alumina particles and
silica sol having a particle size of 0.3 .mu.m to 0.6 .mu.m and
functions as mullite during firing; and a multi-layered backup
layer which is formed on the outside of the prime layer by
repeatedly forming a backup layer obtained by forming and drying a
slurry layer formed from the slurry for the precision casting mold
and a stucco layer in which a stucco material is adhered to the
slurry layer.
2. The precision casting mold according to claim 1, wherein the
slurry for the precision casting mold contains either of zircon
powders or alumina powders having an average particle size of 50
.mu.m or smaller, and the stucco material is either of zircon
stucco particles or alumina stucco particles having an average
particle size of 0.5 mm or larger.
3. The precision casting mold according to claim 1, wherein the
prime layer has the stucco layer in which the stucco material is
adhered to the slurry layer formed from the slurry for the
precision casting mold.
4. A method of producing a precision casting mold which is used to
produce a cast product, the method comprising: a first film forming
process in which a precision casting wax pattern is immersed and
pulled up into/from slurry for the precision casting mold which
includes mono-dispersed ultrafine alumina particles and silica sol
having a particle size of 0.3 .mu.m to 0.6 .mu.m and functions as
mullite during firing and then a drying treatment is performed,
thereby forming a prime layer, which is formed from a slurry film,
on a surface of the wax pattern; a second film forming process in
which a stucco material is sprinkled on a surface of the slurry
after the wax pattern formed with the prime layer is immersed and
pulled up into/from the slurry for the precision casting mold and
then a drying treatment is performed, thereby forming a backup
layer; a molded body forming process in which the second film
forming process of forming the backup layer is repeated more than
once, thereby obtaining a molded body formed with a multi-layered
backup layer; a wax removing process in which wax of the wax
pattern is melted and removed from the obtained molded body; and a
mold firing process in which the molded body obtained after the wax
removal is subjected to a firing treatment, thereby obtaining a
mold.
5. The method of producing the precision casting mold according to
claim 4, wherein a stucco material is adhered to the slurry layer
formed from the slurry for the precision casting mold to form a
stucco layer and the stucco layer is dried during the first film
forming process.
6. The method of producing the precision casting mold according to
claim 4, wherein a dispersing agent of the slurry for the precision
casting mold is polycarboxylic acid salts.
7. The precision casting mold according to claim 1, wherein a
mixing ratio of the alumina particles and the silica sol
(Al.sub.2O.sub.3/SiO.sub.2) is equal to 1.5 (molar ratio).
8. The precision casting mold according to claim 4, wherein a
mixing ratio of the alumina particles and the silica sol
(Al.sub.2O.sub.3/SiO.sub.2) is equal to 1.5 (molar ratio).
Description
FIELD
[0001] The present invention relates to a precision casting mold
and a method of producing the same.
BACKGROUND
[0002] There is a precision casting method used in the case of
producing a cast product with high precision as a casting method of
producing a cast product. In the precision casting method, as
disclosed in Patent Literature 1, slurry is applied around a lost
foam pattern (wax pattern) having the same shape as a molded
component and then a first stucco (flour) layer is adhered to it
and is then subjected to a drying treatment. Thereafter, three
operations of the application of the slurry, the adhesion of the
stucco, the drying are repeatedly performed, thereby producing a
pattern for covering the outside (outer mold) of the cast
product.
[0003] Here, the precision casting mold is formed in such a manner
that the wax pattern is placed in slurry mainly including a silica
sol, the slurry is adhered to the surface of the wax pattern, and
then the slurry is dried.
[0004] Since the slurry adhered by single operation is only less
and thin, the operation is repeatedly performed from several to ten
times to obtain the thickness. In addition, coarse particles called
a stucco material are sprinkled and adhered to the surface of the
slurry to fast perform the drying, quickly ensure the thickness, or
prevent dry cracks. Therefore, a dense layer and a coarse particle
layer are repeated in the cross-sectional structure of the
mold.
[0005] For example, the silica sol is a solution in which spherical
silica particles having a particle size of about 20 nm are
dispersed. When the ultrafine silica particles are adhered to the
surface of relatively fine particles (from several microns to
scores of microns) and coarse particles (stucco) (hundreds of
microns to several millimeters) such as zircon or alumina contained
in the slurry during the drying and are tightly bonded to each
other by drying and heat treatment, the shape of the mold is
maintained and strength is also held, so that it is possible to use
as a mold.
CITATION LIST
Patent Literature
[0006] Patent Literature 1: Japanese Patent Application Laid-open
No. 2001-18033
SUMMARY
Technical Problem
[0007] However, in general, it is sufficient to produce a mold
using the above-described silica sol (solution in which ultrafine
silica particles are dispersed), but it is necessary to hold a
molten metal to control a crystal precipitation direction in, for
example, a production of a unidirectional solidified blade. As a
result, holding time at a high temperature (for example, about
1550.degree. C.) becomes longer. In this case, there is a problem
that the silica serving as a binder is softened due to the
high-temperature holding, resulting in occurring deformation of the
mold.
[0008] In such a production of the unidirectional solidified blade
referred herein, the blade is generally produced in such a manner
that the mold is placed in a vacuum heater and is heated and held
at a temperature equal to or higher than a melting point of the
molten metal, and thus the molten metal is poured into the mold and
the mold is taken out from the heater while being controlled for
the pulling toward a lower side, so that the molten metal is cooled
and solidified from the lower side.
[0009] Accordingly, for example, in the production of the
unidirectional solidified blade, a mold is required which is not
deformed even in the case of being held at the high temperature
(for example, about 1550.degree. C.) over a long period.
[0010] The present invention has been achieved in consideration of
the above problem and an object thereof is to provide a precision
casting mold which is not deformed even in the case of being held
at the high temperature for a long period and a method of producing
the same.
Solution to Problem
[0011] According to a first aspect of the present invention in
order to solve the above-mentioned problems, there is provided a
precision casting mold which is used to produce a cast product,
including: a core having a shape corresponding to an internal
hollow portion of the cast product; and an outer mold corresponding
to a shape of an outer peripheral surface of the cast product,
wherein the outer mold is made up of: a prime layer which is formed
on an inner peripheral surface and is formed from a slurry film
obtained by drying slurry for the precision casting mold which
includes mono-dispersed ultrafine alumina particles and silica sol
having a particle size of 1.0 .mu.m or smaller and functions as
mullite during firing; and a multi-layered backup layer which is
formed on the outside of the prime layer by repeatedly forming a
backup layer obtained by forming and drying a slurry layer formed
from the slurry for the precision casting mold and a stucco layer
in which a stucco material is adhered to the slurry layer.
[0012] According to a second aspect of the present invention, there
is provided the precision casting mold according to the first
aspect, wherein the slurry for the precision casting mold contains
either of zircon powders or alumina powders having an average
particle size of 50 .mu.m or smaller, and the stucco material is
either of zircon stucco particles or alumina stucco particles
having an average particle size of 0.5 mm or larger.
[0013] According to a third aspect of the present invention, there
is provided the precision casting mold according to the first or
second aspect, wherein the prime layer has the stucco layer in
which the stucco material is adhered to the slurry layer formed
from the slurry for the precision casting mold.
[0014] According to a fourth aspect of the present invention, there
is provided a method of producing a precision casting mold which is
used to produce a cast product, the method including: a first film
forming process in which a precision casting wax pattern is
immersed and pulled up into/from slurry for the precision casting
mold which includes mono-dispersed ultrafine alumina particles and
silica sol having a particle size of 1.0 .mu.m or smaller and
functions as mullite during firing and then a drying treatment is
performed, thereby forming a prime layer, which is formed from a
slurry film, on a surface of the wax pattern; a second film forming
process in which a stucco material is sprinkled on a surface of the
slurry after the wax pattern formed with the prime layer is
immersed and pulled up into/from the slurry for the precision
casting mold and then a drying treatment is performed, thereby
forming a backup layer; a molded body forming process in which the
second film forming process of forming the backup layer is repeated
more than once, thereby obtaining a molded body formed with a
multi-layered backup layer; a wax removing process in which wax of
the wax pattern is melted and removed from the obtained molded
body; and a mold firing process in which the molded body obtained
after the wax removal is subjected to a firing treatment, thereby
obtaining a mold.
[0015] According to a fifth aspect of the present invention, there
is provided the method of producing the precision casting mold
according to the fourth aspect, wherein a stucco material is
adhered to the slurry layer formed from the slurry for the
precision casting mold to form a stucco layer and the stucco layer
is dried during the first film forming process.
[0016] According to a sixth aspect of the present invention, there
is provided the method of producing the precision casting mold
according to the fourth or fifth aspect, wherein a dispersing agent
of the slurry for the precision casting mold is polycarboxylic acid
salts.
Advantageous Effects of Invention
[0017] According to the present invention, fine alumina particles
and silica sol, which have high heat resistant and function as
mullite, are used as slurry, and thus it is possible to obtain an
effect that a mold is obtained which is increased in a heat
resistant temperature and is not deformed in the case of being held
at a high temperature (for example, 1550.degree. C.) over a long
period in, for example, a production of a unidirectional solidified
blade, as compared to the case of using the conventional silica
sol.
BRIEF DESCRIPTION OF DRAWINGS
[0018] FIG. 1 is a configuration diagram of a dried molded body
which is an outer mold.
[0019] FIG. 2 is a configuration diagram of another dried molded
body which is an outer mold.
[0020] FIG. 3 is a flowchart illustrating an example of processes
in a casting method.
[0021] FIG. 4 is a flowchart illustrating an example of processes
in a method of producing a mold.
[0022] FIG. 5 is an explanatory diagram schematically illustrating
a process of producing a core.
[0023] FIG. 6 is a perspective view schematically illustrating a
part of a metal mold.
[0024] FIG. 7 is an explanatory diagram schematically illustrating
a process of producing a wax pattern.
[0025] FIG. 8 is an explanatory diagram schematically illustrating
a configuration in which slurry is applied on the wax pattern.
[0026] FIG. 9 is an explanatory diagram schematically illustrating
a process of producing the outer mold.
[0027] FIG. 10 is an explanatory diagram schematically illustrating
some processes in the method of producing the mold.
[0028] FIG. 11 is an explanatory diagram schematically illustrating
some processes in a casting method.
DESCRIPTION OF EMBODIMENTS
[0029] Hereinafter, the present invention will be described in
detail with reference to the drawings. Furthermore, the present
invention is not limited to the following description. Further,
components in the following description include those which are
easily conceived by persons skilled in the art, those which are
substantially identical thereto, and those in a scope of so-called
equivalents.
[0030] FIG. 1 is a configuration diagram of a dried molded body of
an outer mold. FIG. 2 is a configuration diagram of another dried
molded body of an outer mold.
[0031] As illustrated in FIG. 1, a precision casting mold is a
precision casting mold to be used to produce a cast product and
includes a core having a shape corresponding to an internal hollow
portion of the cast product and an outer mold corresponding to a
shape of an outer peripheral surface of the cast product, and the
outer mold is made up of: a prime layer (first dried film) 101A
which is formed on an inner peripheral surface and is formed from a
slurry film obtained by drying slurry for the precision casting
mold which includes mono-dispersed ultrafine alumina particles and
silica sol having a particle size of 1.0 .mu.m or smaller
(preferably, 0.3 to 0.5 .mu.m, disclosed in Examples) and functions
as mullite during firing; and a multi-layered backup layer 105A
which is formed on the outside of the prime layer (first dried
film) 101A by repeatedly forming a first backup layer (second dried
film) 104-1 obtained by forming and drying a slurry layer 102
formed from the slurry for the precision casting mold and a stucco
layer 103 in which a stucco material is adhered to the slurry layer
102.
[0032] Here, the fine alumina particles (ultrafine alumina
particles) of high purity ultrafine particles, which are subjected
to mono-dispersion using, for example, a ball mill as a dispersion
means, are used as a binder forming the slurry in the present
invention.
[0033] The term "mono-dispersion" used herein refers to a state of
being mono-dispersed into 0.5 .mu.m even in a result of a
dispersion treatment when the slurry is formed using, for example,
fine alumina particles having a particle size of about 0.5
.mu.m.
[0034] Here, the particle size of the fine alumina particles is 1.0
.mu.m or smaller and more preferably may be in the range of 0.3 to
0.6 .mu.m.
[0035] In the present invention, the reason why the fine alumina
particles are preferably 1.0 .mu.m or smaller in size is that
results of a bending strength test are undesirable when the fine
alumina particles exceed 1.0 .mu.m in size.
[0036] Here, polycarboxylic acid salts (for example, ammonium
salts) are used to be mono-dispersed as a dispersing agent.
[0037] In addition, a ball mill using, for example, balls having a
diameter of 10 to 20 mm can be exemplified as the dispersion means,
but the dispersion means is not limited thereto as long as being a
means that mono-disperses.
[0038] In the present invention, it is important to obtain good
slurry by mono-dispersing the fine alumina particles serving as the
binder.
[0039] Furthermore, in the present invention, since it is important
that mullite is uniformly formed during firing, for example, it is
preferable that the mixing ratio of fine alumina particles
mono-dispersed into 0.5 .mu.m be high.
[0040] Here, the particle size of alumina may be 1.0 .mu.m or
smaller and preferably in the range of 0.3 to 0.6 .mu.m.
[0041] Preferably, such a mixing ratio is in the following
range.
Al.sub.2O.sub.3/SiO.sub.2=1.5 (molar ratio)
[0042] The silica sol is a uniform dispersion material of silica of
0.02 .mu.m and is uniformly dispersed in the alumina slurry.
[0043] In the present invention, since the fine alumina particles
having a predetermined particle size act as a uniform dispersion
material, the fine alumina particles excellently react with the
silica sol in a firing operation and thus mullite can be formed at
a temperature (for example, 1,000.degree. C.) lower than a general
temperature.
[0044] In the case where the fine alumina particles are solely used
as the slurry for the precision casting mold, since the fine
alumina particles are expensive, the production cost becomes
higher. Therefore, when the mullite is formed during the firing by
adding the silica sol to the fine alumina particles as in the
present invention, it is possible to reduce the production
cost.
[0045] Zircon powders (for example, having a size of 350-mesh) as
flour are added to the mixed slurry obtained by adding the silica
sol to the slurry of the mono-dispersed fine alumina particles,
thereby obtaining the slurry for the precision casting mold.
[0046] Further, the present invention may be also acceptable a case
where the flour is not added.
[0047] Next, a method of producing the precision casting mold will
be described with reference to FIGS. 1 and 2.
[0048] (First Film Forming Process)
[0049] First, in the first film forming process, a wax pattern 30
is immersed and then pulled up into/from the slurry (hereinafter,
referred to as "slurry") for the precision casting mold which
includes the mono-dispersed ultrafine alumina particles and the
silica sol having a particle size of 1.0 .mu.m or smaller and
functions as the mullite during firing, and excess slurry is
dropped. Thereafter, a slurry film (first dried film) is obtained
on the surface of the wax pattern 30 by a drying treatment.
[0050] In FIG. 1, the slurry film is the prime layer 101A which
comes in contact with the surface of the wax pattern 30.
[0051] (Second Film Forming Process)
[0052] Next, the wax pattern 30 having the prime layer 101A is
immersed and is then pulled up into/from the slurry, and the excess
slurry is dropped, thereby forming the slurry layer (second layer)
102. Zircon stucco particles (having an average particle size of
0.8 mm) are sprinkled (stuccoed) on the wet slurry layer (second
layer) 102 as a stucco material, thereby forming the stucco layer
(first layer) 103 adhered with the stucco material. A laminated
structure of the slurry layer (second layer) 102 and the stucco
layer (first layer) 103 is dried, so that the first backup layer
(second dried film) 104-1 is formed on the prime layer (first dried
film) 101A.
[0053] (Molded Body Forming Process)
[0054] The similar operation as the second film forming process of
forming the first backup layer 104-1 is repeated more than once
(for example, 6 to 10 times), thereby obtaining a dried molded body
106A which is the outer mold having a predetermined thickness of
the multi-layered backup layer 105A in which the slurry layer
((n+1)-th layer) 102 and the stucco layer (n-th layer) 103 are
alternately laminated.
[0055] The dried molded body is put in, for example, an autoclave
of 150.degree. C., so that wax constituting the wax pattern 30 is
melted and then is discharged.
[0056] Thereafter, the pattern is subjected to a heat treatment at
1,000.degree. C., thereby obtaining the precision casting mold
configured by mullite slurry.
[0057] The obtained precision casting mold was not deformed even in
a strength test at 1500.degree. C. as indicated in a test example
to be described below, which had high strength. In contrast, a
softening behavior was confirmed in the case of using the
conventional silica sol.
[0058] In addition, as illustrated in FIG. 2, a prime stucco layer
101b adhered with the stucco material may be formed on a prime
slurry layer 101a in a prime layer 101B and may be then dried,
thereby forming the prime layer 101B.
[0059] Further, as in the prime layer 101B, when the stucco
material is adhered, it is possible to obtain a dried molded body
106B of an outer mold having a multi-layered backup layer 105B in
which the slurry layer and the stucco layer 103 of the
multi-layered backup layer 105B have the same laminated number (n
layers).
[0060] In the present invention, although zircon powders were used
as flour, it is possible to obtain the similar precision casting
mold even when alumina powders other than the zircon powders are
used as the flour and alumina stucco particles are used instead of
the zircon stucco particles as a stucco material.
[0061] Further, the relation between the flour and the stucco
material is not limited, but either of the zircon powders or the
alumina powders may be used as the flour and either of the zircon
stucco particles or the alumina stucco particles may be used as the
stucco material.
[0062] Although the particle size of the flour is 350-mesh, the
present invention is not limited thereto, but preferably uses
particles of, for example, about 5 to 80 .mu.m and particles having
an average particle size of, for example, 50 .mu.m or smaller.
[0063] Although the particle size of the stucco particles is 0.8
mm, the present invention is not limited thereto, but preferably
uses particles of, for example, about 0.4 mm to 2 mm and particles
having an average particle size of, for example, 0.5 mm or
larger.
[0064] A casting method using the precision casting mold according
to the present invention will be described below.
[0065] FIG. 3 is a flowchart illustrating an example of processes
in the casting method. The casting method will be described below
with reference to FIG. 3. Here, the processes illustrated in FIG.
3, may be fully automatically executed or may be executed in such a
manner that an operator operates each of apparatuses for executing
each of the processes. In the casting method of the present
embodiment, a mold is produced (step S1). The mold may be
previously produced or may be produced every time a casting process
is executed.
[0066] The method of producing the mold of the present embodiment
to be executed in step S1 will be described below with reference to
FIGS. 4 to 10. FIG. 4 is a flowchart illustrating an example of
processes in the method of producing the mold. Here, processes
illustrated in FIG. 4, may be fully automatically executed or may
be executed in such a manner that an operator operates each of
apparatuses for executing each of the processes.
[0067] In the method of producing the mold, a core is produced
(step S12). The core has a shape corresponding to an internal
hollow of a cast product to be produced with the mold. That is, the
core is disposed at a portion corresponding to the internal hollow
of the cast product and prevents inflow of a metal, which is a
material for the cast product, during casting. Hereinafter, a
process of producing the core will be described with reference to
FIG. 5. FIG. 5 is an explanatory diagram schematically illustrating
the process of producing the core. In the method of producing the
mold, as illustrated in FIG. 5, a metal mold 12 is prepared (step
S101). The metal mold 12 has a hollow region corresponding to the
core. The hollow portion of the core is a convex portion 12a.
Further, in FIG. 5, the metal mold 12 is illustrated in cross
section, but the metal mold 12 becomes basically the hollow for
covering an entire periphery of the region corresponding to the
core, except for an opening through which a material is poured into
a space and a hole through which air is discharged. In the method
of casting the mold, as indicated by an allow 14, ceramic slurry 16
is poured into the inside of the metal mold 12 from the opening
through the material is poured into the space of the metal mold 12.
Specifically, a core 18 is produced by so-called injection molding
which sprays the ceramic slurry 16 into the inside of the metal
mold 12. In the method of producing the mold, after the core 18 is
produced inside the metal mold 12, the core 18 is detached from the
metal mold 12 and the detached core 18 is placed in a firing
furnace 20, thereby being fired. Thus, the core 18 formed of a
ceramic is fired and hardened (step S102). In the method of casting
the mold, the core 18 is produced in the manner described above.
Further, the core 18 is formed of a material capable of being
removed with a core removing treatment such as a chemical treatment
after the cast product is hardened.
[0068] In the method of producing the mold, after the core 18 is
produced, an external metal mold is produced (step S14). The
external metal mold has a shape in which an inner peripheral
surface thereof corresponds to the outer peripheral surface of the
cast product. The metal mold may be formed of a metal or may be
formed of a ceramic. FIG. 6 is a perspective view schematically
illustrating a part of the metal mold. A metal mold 22a illustrated
in FIG. 6 is configured such that a concave portion formed on the
inner peripheral surface corresponds to the outer peripheral
surface of the cast product. Further, in FIG. 6, only the metal
mold 22a is illustrated, but corresponding to the metal mold 22a, a
metal mold corresponding to the metal mold 22a is also produced in
a direction to close the concave portion formed on the inner
peripheral surface. The method of producing the mold is a type in
which the inner peripheral surface corresponds to the outer
peripheral surface of the cast product when two metal molds are
fitted to each other.
[0069] In the method of producing the mold, after the external
metal mold is produced, a wax pattern is produced (step S16). The
description will be made below with reference to FIG. 7. FIG. 7 is
an explanatory diagram schematically illustrating a process of
producing the wax pattern. In the method of producing the mold, the
core 18 is installed at a predetermined position of the metal mold
22a (step S110). Thereafter, a metal mold 22b corresponding to the
metal mold 22a covers a surface on which the concave portion of the
metal mold 22a is formed, so that the metal molds 22a and 22b
surround the periphery of the core 18 and a space 24 is formed
between the core 18 and the metal molds 22a and 22b. In the method
of producing the mold, as indicated by an arrow 26, a pouring of a
WAX 28 starts to be poured from a pipe connected to the space 24
into the inside of the space 24 (step S112). The WAX 28 is, for
example, wax of a relatively low-melting point material which is
melted when being heated to a predetermined temperature or higher.
In the method of producing the mold, the entire region of the space
24 is filled with the WAX 28 (step S113). Thereafter, the WAX 28
encloses around the core 18 by solidifying the WAX 28, thereby
forming the wax pattern 30. The wax pattern 30 is a wax pattern in
which a portion formed of the WAX 28 has basically the same shape
as the cast product of the production object. Thereafter, in the
method of producing the cast product, the wax pattern 30 is
separated from the metal molds 22a and 22b and then a sprue 32 is
attached to the wax pattern (step S114). The sprue 32 is a mouth
into which a molten metal, which is a metal melted during casting,
is introduced. In the method of producing the mold, the wax pattern
30 formed of the WAX 28 is produced in the manner described above
so as to have the same shape as the cast product and include the
core 18 therein.
[0070] In the method of producing the mold, after the wax pattern
30 is produced, slurry is applied (dipped) (step S18). FIG. 8 is an
explanatory diagram schematically illustrating a configuration in
which the slurry is applied on the wax pattern. In the method of
producing the mold, as illustrated in FIG. 8, the wax pattern 30 is
immersed into a storage portion 41, in which slurry 40 is stored,
and then is dried after being taken out therefrom (step S19). Thus,
the prime layer 101A can be formed on the surface of the wax
pattern 30.
[0071] Here, the applied slurry in step S18 is slurry which is
directly applied on the wax pattern 30. The slurry 40 including the
ultrafine alumina particles and the silica sol functions as the
mullite during the firing and is used for the mold for the
precision casting mold. In the slurry 40, for example, zirconia
having refractory fine particles of about 350-mesh is preferably
used as flour. In addition, polycarboxylic acid salts are
preferably used as a dispersing agent. In addition, a trace of an
antifoaming agent (silicon-based substance) or a wettability
improving agent of, for example, 0.01% is preferably added to the
slurry 40. By the addition of the wettability improving agent,
adhesive property of the slurry 40 can be improved with respect to
the wax pattern 30.
[0072] In the method of producing the mold, as illustrated in FIG.
8, a slurry application is performed with the slurry 40, and the
applied slurry is dried, so that the wax pattern having the prime
layer (first dried film) 101A is further applied (dipped) with the
slurry (step S20). As illustrated in FIG. 9, stuccoing process of
sprinkling the zircon stucco particles (having an average particle
size of 0.8 mm) as a stucco material 54 is performed on the surface
of the wet slurry (step S21). Thereafter, the stucco material
adhered to the surface of the slurry layer is dried, thereby
forming the first backup layer (second dried film) 104-1 on the
prime layer (first dried film) 101A (step S22).
[0073] A process of determining whether the similar operation as
the forming process of the first backup layer (second dried film)
104-1 is repeated more than once (for example, n: six to ten times)
is performed (step S23). An n-th backup layer 104-n is laminated by
a predetermined number of times (n) (step S23: Yes), thereby
obtaining the dried molded body 106A which is the outer mold formed
with the multi-layered backup layer 105A having the thickness of,
for example, 10 mm.
[0074] In the method of producing the mold, after the dried molded
body 106A having the multilayer structure is obtained which is
formed with the prime layer 101A and the multi-layered backup layer
105A, the dried molded body 106A is 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 further fired.
The description will be made below with reference to FIG. 10. FIG.
10 is an explanatory diagram schematically illustrating some
processes of the method of producing the mold. In the method of
producing the mold, as illustrated in step S130, the dried molded
body 106A which is the outer mold having the multilayer structure
formed with the prime layer 101A and the multi-layered backup layer
105A is put in an autoclave 60 and then is heated. The inside of
the autoclave 60 is filled with pressurized steam, and thus the wax
pattern 30 inside the dried molded body 106A is heated by the
pressurized steam. Thus, the WAX constituting the wax pattern 30 is
melted and a melted WAX 62 is discharged from a space 64 surrounded
by the dried molded body 106A.
[0075] In the method of producing the mold, when the melted WAX 62
is discharged from the space 64, as illustrated in step S131, a
mold 72 is produced in which the space 64 is formed in a region
filled with the WAX between the dried molded body 106A which is the
outer mold and the core 18. Thereafter, in the method of producing
the mold, as illustrated in step S132, the mold 72 having the space
64 formed between the dried molded body 106A which is the outer
mold and the core 18 is heated by a firing furnace 70. Thus, in the
mold 72, a water component or an unnecessary component contained in
the dried molded body 106A which is the outer mold is removed and
an outer mold 61 is formed by being further fired and cured. In the
method of producing the cast product, the mold 72 is produced in
the manner described above.
[0076] The casting method will be continuously described with
reference to FIGS. 3 and 11. FIG. 11 is an explanatory diagram
schematically illustrating some processes of the casting method. In
the casting method, after the mold is produced in step S1, the mold
is pre heated (step S2). For example, the mold is disposed in a
furnace (vacuum furnace, firing furnace) and is heated to
800.degree. C. or higher and 900.degree. C. or lower. By the
pre-heating, it is possible to suppress the damage of the mold when
the molten metal (melted metal) is poured into the mold at the time
of producing the cast product.
[0077] In the casting method, after the mold is pre-heated, the
molten metal is poured (step S3). That is, as illustrated in step
S140 of FIG. 11, a molten metal 80, that is, a dissolved raw
material (for example, steel) of the cast product is poured between
the outer mold 61 and the core 18 from the opening of the mold
72.
[0078] 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 illustrated in step S141 of FIG. 11, after the molten
metal 80 is hardened inside the mold 72 and becomes a cast product
90, the outer mold 61 is crushed and is then removed from the cast
product 90 as a fragment 61a.
[0079] In the casting method, after the outer mold 61 is removed
from the cast product 90, a core removing treatment is performed
(step S5). That is, as illustrated in step S142 of FIG. 11, the
cast product 90 is put in an autoclave 92 and is subjected to the
core removing treatment, so that the core 18 inside the cast
product 90 is dissolved and a dissolved core 94 is discharged from
the inside of the cast product 90. Specifically, the cast product
90 charged into an alkaline solution inside the autoclave 92 is
repeatedly pressurized and depressurized, so that the dissolved
core 94 is discharged from the cast product 90.
[0080] In the casting method, after the core removing treatment is
performed, a finishing treatment is performed (step S6). That is,
the finishing treatment is performed on the surface or the interior
of the cast product 90. Furthermore, in the casting method,
inspection of the cast product is performed along with the
finishing treatment. Thus, as illustrated in step S143 of FIG. 11,
a cast product 100 can be produced.
[0081] In the casting method of the present embodiment, as
described above, the mold is produced by a lost-wax casting method
using WAX (wax), thereby producing the cast product. Here, in the
method of producing the mold, the casting method, and the mold of
the present embodiment, the outer mold having the multilayer
structure which is the outside of the mold is formed in such a
manner that the prime layer (first dried film as a first layer)
101A serving as the inner peripheral surface is formed using the
ultrafine zirconia particles as the slurry and the multi-layered
backup layer 105A is formed on the outside of the prime layer
101A.
[0082] In addition, as described above, the prime layer may be the
prime layer 101B including the prime slurry layer 101a added with
the stucco material and the prime stucco layer 101b (see FIG.
2).
Example 1
[0083] The method of producing the mold and the casting method of
the present embodiment will be described below using Examples.
Further, in the following Examples, a front wax pattern formed with
an outer mold was a member having a width of 30 mm, a thickness of
8 mm, and a length of 300 mm, and a prime layer (first dried film)
formed from a slurry layer and a multi-layered backup layer made of
slurry and a stucco material are formed in the wax pattern, thereby
producing a mold.
[0084] High-purity ultrafine alumina particles (Al.sub.2O.sub.3,
having a specific surface area of 10 m.sup.2/g and a particle size
of about 0.5 .mu.m) were kneaded with a ball mill for 24 hours
using polycarboxylate ammonium as a dispersing agent and thus were
formed in a slurry form. A solid content concentration of the
obtained alumina slurry is 30 wt %.
[0085] It was confirmed that the resulting alumina particles of a
dispersion treatment was mono-dispersed into 0.5 .mu.m in the
alumina slurry.
[0086] In addition, the silica sol (SiO.sub.2, having the particle
size of 0.02 .mu.m and a solid content concentration of 30%) was
prepared.
[0087] In order to achieve the mixing of the mullite
(3Al.sub.2O.sub.3.2SiO.sub.2) during the firing, slurry was
previously prepared in which the alumina slurry and the silica sol
satisfied the following relation:
Alumina slurry:silica sol=306:120 (a molecular weight of
3Al.sub.2O.sub.3 is 306 (3.times.102) and a molecular weight of
2SiO.sub.2 is 120 (2.times.60)).
[0088] At this time, occurrence of precipitation was not observed
even in the case of being mixed.
[0089] Zircon powders of 350-mesh were added to the slurry thus
prepared as flour, thereby forming slurry for a precision casting
mold.
[0090] Further, at the same time, a silicon-based substance as an
antifoaming agent of 0.01% and a wettability improving agent of
0.01% were added to make as in-use slurry.
[0091] A wax body having a width of 30 mm, a thickness of 8 mm, and
a length of 300 mm was prepared, after the wax body was immersed
and then pulled up into/from the obtained slurry, thereby adhering
the in-use slurry to the surface of the wax, excess in-use slurry
was dropped and a prime layer (first dried film) of the slurry was
obtained on the surface of the wax body by a drying treatment.
[0092] Next, in order to obtain a second dried film, the wax body
having the prime layer was immersed and then pulled up into/from
the slurry and excess in-use slurry was dropped.
[0093] Zircon stucco particles having an average particle size of
0.8 mm were adhered to wet slurry and then were dried, so that a
second dried film (first backup layer) was formed.
[0094] The similar operation as the second dried film (first backup
layer) forming process was repeated six times, so that a molded
body having a multi-layered backup layer was obtained to have a
thickness of about 10 mm.
[0095] The obtained dried molded body was put in an autoclave of
150.degree. C., so that the wax was melted and then was
discharged.
[0096] Thereafter, the wax pattern was subjected to a heat
treatment at 1000.degree. C., thereby obtaining the mold of Example
1.
Comparative Example
[0097] For comparison, a trial production of a mold of Comparative
Example was simultaneously performed using slurry of the
conventional silica sol (solution in which spherical silica
particles having a particle size of about 20 nm were dispersed) in
the similar operation as in Example.
[0098] [Test]
[0099] A test piece for strength having a size 10 mm.times.50 mm
and a thickness of 5 mm was worked from the obtained mold of
Example 1 and the mold of Comparative Example was subjected to a
high-temperature strength test.
[0100] In a strength test at 1500.degree. C., a softening behavior
was confirmed in the case of using the conventional silica sol.
[0101] In addition, as a result, cutting of the test piece
according to Comparative Example was not clear and was bent.
[0102] In contrast, the test piece using the mixed slurry (zircon
particles as a stucco material), which functions as the mullite
(3Al.sub.2O.sub.3.2SiO.sub.2), according to the present Example was
broken at 100 MPa without being deformed.
[0103] Here, the strength test was performed based on "bending
strength of ceramics (1981) by JIS R 1601.
[0104] From this test result, when a binder was the slurry of the
mullite (melting point: 1,885.degree. C.) having high heat
resistant during the firing and a stucco material was zircon
particles (melting point: 2,715.degree. C.), as compared to the
case using the conventional silica sol, it was possible to obtain
the mold which is increased in a heat resistant temperature and is
not deformed even in the case of being held at a high temperature
(1,550.degree. C.) for a long period in the production of a
unidirectional solidified blade.
Example 2
[0105] Slurry obtained by adding alumina powders of 350-mesh as
flour instead of the zircon powders in Example 1 was used for
slurry for a precision casting mold.
[0106] In addition, a mold of Example 2 was obtained by the similar
operation as in Example 1 except for using alumina stucco particles
having an average particle size of 0.8 mm as a stucco material.
[0107] [Test]
[0108] A test piece for strength having a size 10 mm.times.50 mm
and a thickness of 5 mm was worked from the obtained mold of
Example 2 and the mold of Comparative Example was subjected to the
similar high-temperature strength test as in Example 1.
[0109] The test piece using slurry functioning as mullite (alumina
particles as a stucco material) according to the present Example
was broken at 100 MPa without being deformed.
[0110] From this test result, when a binder was slurry of the
mullite (melting point: 1,885.degree. C.) having high heat
resistant during the firing and a stucco material was alumina
particles (melting point: 2,070.degree. C.), as compared to the
case using the conventional silica sol, it was possible to obtain
the mold which was increased in a heat resistant temperature and
was not deformed even in the case of being held at a high
temperature (1,550.degree. C.) for a long period in the production
of a unidirectional solidified blade.
[0111] From the above, when the binder is the slurry for the
precision casting mold which includes the mono-dispersed ultrafine
alumina particles and the silica sol having a particle size of 1.0
.mu.m or smaller and functions as the mullite during the firing and
the stucco material is the zircon powders or the alumina powders,
as compared to the case using the conventional silica sol, it was
possible to obtain the mold which was increased in the heat
resistant temperature of the obtained mold and was not deformed
even in the case of being held at a high temperature (1,550.degree.
C.) for a long period in the production of a unidirectional
solidified blade.
REFERENCE SIGNS LIST
[0112] 12, 22a, 22b METAL MOLD [0113] 12a CONVEX PORTION [0114] 14,
26 ARROW [0115] 16 CERAMIC SLURRY [0116] 18 CORE [0117] 20, 70
FIRING FURNACE [0118] 24, 64 SPACE [0119] 28 WAX [0120] 30 WAX
PATTERN [0121] 32 SPRUE [0122] 40 SLURRY [0123] 60, 92 AUTOCLAVE
[0124] 61 OUTER MOLD [0125] 61a FRAGMENT [0126] 62 DISSOLVED WAX
[0127] 72 MOLD [0128] 80 MOLTEN METAL [0129] 90, 100 CAST PRODUCT
[0130] 94 DISSOLVED CORE [0131] 101A, 101B PRIME LAYER [0132] 102
SLURRY LAYER [0133] 103 STUCCO LAYER [0134] 104-1 FIRST BACKUP
LAYER [0135] 104-n n-TH BACKUP LAYER [0136] 105A, 105B
MULTI-LAYERED BACKUP LAYER
* * * * *