U.S. patent application number 11/942198 was filed with the patent office on 2009-05-21 for liquid metal directional casting apparatus.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. Invention is credited to Andrew John Elliott, Michael Francis Gigliotti, Shyh-Chin Huang, Adegboyega Masud Makinde, Roger J. Petterson, Stephen Francis Rutkowski.
Application Number | 20090126894 11/942198 |
Document ID | / |
Family ID | 40640707 |
Filed Date | 2009-05-21 |
United States Patent
Application |
20090126894 |
Kind Code |
A1 |
Elliott; Andrew John ; et
al. |
May 21, 2009 |
LIQUID METAL DIRECTIONAL CASTING APPARATUS
Abstract
An apparatus for directionally casting articles generally
includes a seal between a mold assembly and chill plate. In one
embodiment, the mold assembly includes a skirt laterally extending
from at least one shell mold, wherein the skirt includes a channel
disposed in a bottom surface that is configured to surround the at
least one shell mold. A chill plate fastened to a bottom of the
mold assembly and includes a boss having a shape complementary to
the channel, wherein the boss of the chill plate is seated within
the channel of the mold assembly to define the seal about the at
least one shell mold.
Inventors: |
Elliott; Andrew John;
(Greer, SC) ; Gigliotti; Michael Francis; (Scotia,
NY) ; Huang; Shyh-Chin; (Latham, NY) ;
Makinde; Adegboyega Masud; (Niskayuna, NY) ;
Petterson; Roger J.; (Fultonville, NY) ; Rutkowski;
Stephen Francis; (Duanesburg, NY) |
Correspondence
Address: |
CANTOR COLBURN, LLP
20 Church Street, 22nd Floor
Hartford
CT
06103
US
|
Assignee: |
GENERAL ELECTRIC COMPANY
Schenectady
NY
|
Family ID: |
40640707 |
Appl. No.: |
11/942198 |
Filed: |
November 19, 2007 |
Current U.S.
Class: |
164/371 |
Current CPC
Class: |
B22D 27/045
20130101 |
Class at
Publication: |
164/371 |
International
Class: |
B22D 15/04 20060101
B22D015/04 |
Claims
1. An apparatus for directionally casting an article, the apparatus
comprising: a mold assembly comprising an opening for receiving
molten metal, at least one shell mold in fluid communication with
the opening, and a skirt laterally extending from the at least one
shell mold, wherein the skirt comprises a selected one of a channel
and a boss disposed in a bottom surface that is configured to
surround the at least one shell mold; and a chill plate comprising
the other of the selected one of the channel and the boss having a
complementary shape such that the boss is seated within the channel
to define a seal about the at least one shell mold when the mold
assembly is attached to the chill plate.
2. The apparatus of claim 1, further comprising a ring abutting an
interior side of the boss and seated within the channel when the
chill plate and mold assembly are fastened together.
3. The apparatus of claim 1, further comprising a ring abutting an
exterior side of the boss and seated within the channel when the
chill plate and mold assembly are fastened together.
4. The apparatus of claim 1, further comprising two rings abutting
each sidewall of the boss and seated within the channel when the
chill plate and mold assembly are fastened together.
5. The apparatus of claim 1, wherein the ring is dimensioned such
that the ring compresses upon fastening of the mold assembly and
the chill plate.
6. The apparatus of claim 2, further comprising a paste disposed on
the ring.
7. The apparatus of claim 2, wherein the ring is formed of a
metal.
8. The apparatus of claim 2, wherein the ring is formed of a
cloth.
9. The apparatus of claim 2, wherein the ring is formed of alumina,
alumina-silica, alumina-boria-silica, graphite, silicon carbide,
carbon, copper, aluminum, and combinations thereof.
10. The apparatus of claim 2, wherein the ring is formed of a
ceramic.
11. An apparatus for directionally casting an article, the
apparatus comprising: a mold assembly comprising an opening for
receiving molten metal, at least one shell mold in fluid
communication with the opening, and a skirt laterally extending
from the at least one shell mold, wherein the skirt comprises a
channel disposed in a bottom surface that is configured to surround
the at least one shell mold; a chill plate fastened to the mold
assembly, the chill plate comprising a channel complementary to the
channel of the mold assembly; and a sealing member disposed within
the channels of the chill plate and the mold assembly to define a
seal between the mold assembly and the chill plate.
12. The apparatus of claim 11, wherein the seal member is
dimensioned such that the sealing member compresses upon fastening
of the mold assembly and the chill plate.
13. The apparatus of claim 11, wherein the sealing member is
disposed about the at least one shell mold.
14. The apparatus of claim 11, wherein the sealing member is formed
of a metal.
15. The apparatus of claim 11, wherein the sealing member is formed
of a cloth.
16. The apparatus of claim 11, wherein the seal member is formed of
a ceramic.
17. An apparatus for directionally casting an article, comprising:
a mold assembly comprising at least one shell mold in fluid
communication with an opening for receiving molten metal, and a
skirt laterally extending from the at least one shell mold, wherein
the skirt comprises a channel disposed in a bottom surface that is
configured to surround the at least one shell mold; a chill plate
fastened to the mold assembly, the chill plate comprising a
substantially planar surface, and a support post configured to
effect lowering of the mold assembly; a sealing member disposed
within the channel between the mold assembly and the chill plate;
and a liquid metal cooling bath positioned below the chill plate
maintained at a temperature below a solidus temperature of the
molten metal.
18. The apparatus of claim 17, further comprising a paste disposed
on the sealing member.
19. The apparatus of claim 18, wherein the sealing member is
dimensioned such that the sealing member compresses upon fastening
of the mold assembly and the chill plate.
20. The apparatus of claim 18, wherein the sealing member is formed
of a ceramic or a metal.
Description
BACKGROUND OF THE INVENTION
[0001] The present disclosure generally relates to apparatuses for
casting an article, and more specifically, to apparatuses for
directionally casting an article.
[0002] Certain components, such as turbine blades and stator vanes
for gas turbine engines, are often manufactured using a directional
solidification casting. In this process, a shell mold is
specifically configured for the particular component being cast,
such as the turbine engine blade or vane.
[0003] Directional solidification casting can enhance the strength
of these components by obtaining single crystal or columnar grain
components. Here, a mold assembly generally includes a shell mold
and a chill plate, wherein the chill plate is at the lowest
position of the mold assembly. The entire mold assembly is then
raised into a heating chamber where it is preheated, and
subsequently filled with a desired superalloy in a superheated
liquid melt condition. Thereafter, the bottom of the mold assembly
is then subjected to preferential cooling, immersed into a liquid
metal cooling bath, such as molten tin or aluminum, to create a
large temperature gradient in the casting and commence the
unidirectional solidification process necessary for a desired
crystal formation, which travels upwardly through the mold
assembly. In other words, after the mold is filled with molten
metal, the mold is lowered into the liquid metal cooling bath at a
controlled rate to translate the thermal gradient across the part,
thus resulting in directional solidification. Upon completion of
melt solidification inside the shell mold, the mold assembly is
removed from the bath, furnace, and housing.
[0004] To obtain unidirectional crystal growth vertically upward, a
uniform high thermal gradient in the axial (vertical) direction is
established, so that there is a horizontal liquid-solid interface
within the shell mold, with the interface moving vertically upwards
as the metal cools. The cooling occurs unidirectionally in the
vertical (axial) direction. Any heat loss or a thermal gradient in
the radial direction (i.e., radially outwards of the mold assembly)
can result in uncontrolled crystal growth. This happens when
exterior portions of the shell mold cool prior to interior
portions, and resulting in a non-planar liquid-solid interface.
[0005] A typical mold assembly has at its bottom a chill plate
adapted to effect cooling of the shell mold by conducting heat from
the shell mold to the liquid metal bath. However, one of the
problems with current designs is the effectiveness of the seal
between the chill plate and the shell mold. Current designs are
prone to leakage, i.e., ingress of liquid metal from the bath into
the mold assembly and egress of the casting metal from the mold
assembly into the liquid metal cooling bath. Without an effective
seal, the casting metal is oftentimes subject to surface attack,
e.g., erosion and chemical interaction, by the liquid metal
coolant. In addition, the liquid metal coolant will also get
contaminated from the escaped cast metal and vice versa. Therefore,
without an effective seal, the reliability of the casting process
and apparatus is compromised.
[0006] Accordingly, it would be desirable to provide an effective
seal between the shell mold and the chill plate.
BRIEF DESCRIPTION OF THE INVENTION
[0007] Disclosed herein are apparatuses for directionally casting
an article using liquid metal. In one embodiment, the apparatus for
directionally casting an article comprises a mold assembly
comprising an opening for receiving molten metal, at least one
shell mold in fluid communication with the opening, and a skirt
laterally extending from the at least one shell mold, wherein the
skirt comprises a selected one of a channel and a boss disposed in
a bottom surface that is configured to surround the at least one
shell mold; and a chill plate comprising the other of the selected
one of the channel and the boss having a complementary shape such
that the boss is seated within the channel to define a seal about
the at least one shell mold when the mold assembly is attached to
the chill plate.
[0008] In another embodiment, the apparatus comprises a mold
assembly comprising an opening for receiving molten metal, at least
one shell mold in fluid communication with the opening, and a skirt
laterally extending from the at least one shell mold, wherein the
skirt comprises a channel disposed in a bottom surface that is
configured to surround the at least one shell mold; a chill plate
fastened to the mold assembly, the chill plate comprising a channel
complementary to the channel of the mold assembly; and a seal
member disposed within the channels of the chill plate and the mold
assembly to define a seal between the mold assembly and the chill
plate.
[0009] In yet another embodiment, an apparatus for directionally
casting an article comprises a mold assembly comprising at least
one shell mold in fluid communication with an opening for receiving
molten metal, and a skirt laterally extending from the at least one
shell mold having an opening, wherein the skirt comprises a channel
disposed in a bottom surface that is configured to surround the at
least one shell mold opening; a chill plate fastened to the mold
assembly, the chill plate comprising a planar surface, and a
support post configured to effect lowering of the mold assembly; a
seal member disposed within the channel to define a sealing member
between the mold assembly and the chill plate; and a liquid metal
cooling bath positioned below the chill plate maintained at a
temperature below a solidus temperature of the molten metal.
[0010] The above described and other features are exemplified by
the following figures and detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Referring now to the figures, which are exemplary
embodiments, and wherein the like elements are numbered alike:
[0012] FIG. 1 is a sectional view of a cluster mold assembly
apparatus;
[0013] FIG. 2 is a partial perspective sectional view illustrating
the cluster mold assembly apparatus in accordance with one
embodiment;
[0014] FIG. 3 is a partial perspective sectional view illustrating
the cluster mold assembly apparatus in accordance with another
embodiment;
[0015] FIG. 4 is a partial perspective sectional view illustrating
the cluster mold assembly apparatus in accordance with still
another embodiment;
[0016] FIG. 5 is a partial perspective sectional view illustrating
the cluster mold assembly apparatus in accordance with still
another embodiment;
[0017] FIG. 6 is a partial perspective sectional view illustrating
the cluster mold assembly apparatus in accordance with another
embodiment; and
[0018] FIG. 7 depicts a sectional view of FIG. 1 taken along line
7-7 illustrating individual seal configurations about each mold
opening.
DETAILED DESCRIPTION OF THE INVENTION
[0019] Disclosed herein is an apparatus and process for effectively
sealing an interface between a shell mold and a chill plate in a
casting assembly. FIG. 1 shows a cutaway perspective view of a mold
assembly 10 sitting on a chill plate 12. The mold assembly 10
generally includes an opening 14, e.g., a funnel in fluid
communication with runners 16 that are in fluid communication with
one or more shell molds 18. The shell molds, i.e., cavities, define
the shape of the part to be cast. A mold assembly having more than
one shell mold is often referred to as a cluster mold assembly. A
skirt 20 extends laterally across a bottommost portion of the mold
assembly. A groove (i.e., channel) 22 is formed in a bottom surface
of the skirt such that the shell molds 18 are contained within a
perimeter defined by the groove.
[0020] The chill plate 12 includes a substantially planar surface
24 and a boss 26 circumscribed about a perimeter of the surface 24.
The boss 26 has a shape complementary to the groove 22 such that
the mold assembly 10 is seated on the boss 26 prior to mechanical
fastening, e.g., by a mechanical connector such as but not limited
to tie rods, cords, clamps, or any other fixture that can
mechanically perform the clamping function required while
sustaining the high temperatures of the furnace and melt. The shape
of the boss 26 or the channel 22 is not intended to be limited and
is generally configured to surround the shell mold 18 or one or
more shell molds in the case of a cluster mold assembly. Surface 24
also serves to enclose an opening of the shell mold that faces the
chill plate, i.e., at a bottom surface of the mold assembly (shown
more clearly in FIG. 7). A support shaft 28 is coupled to the chill
plate 12 to effect lowering of the mold assembly 10 into a liquid
metal cooling bath.
[0021] Optionally, a reverse arrangement can be made to occur. In
this embodiment, the groove is formed in a top surface of the chill
plate and a boss is formed in a bottom surface of the mold
assembly, wherein the groove and boss have complementary shapes
such that the boss seats within the groove when the mold assembly
and the chill plate are fastened together. Still further, multiple
grooves and bosses can be formed in an opposing relationship e.g.,
a labyrinth type seal.
[0022] Although the mold assembly may be utilized to cast many
different articles, it is believed that it will be particularly
advantageous to cast turbine engine blades or vanes formed of a
nickel-based, iron-based, and/or cobalt-based superalloys. However,
it should be understood that the method and apparatus is not to be
limited to the casting of any particular article or metal. For
example, the apparatus and method can be used during the casting of
articles formed of titanium and/or other metals having any desired
configuration. In cluster mold assemblies, such as the one shown,
multiple parts such as blades or vanes can be simultaneously cast.
The parts can be the same or different. Prior to use, the mold
assembly 10 is mechanically fastened to the chill plate 12.
[0023] A furnace 30 encapsulates the mold assembly 10 and is of a
conventional design. The furnace is not intended to be limited to
any particular type and the illustrated furnace is exemplary. For
example, the furnace can include coils 32 that are energized to
provide heat within an evacuated space of the furnace in which the
mold assembly is seated. Once the mold assembly 10 has been heated
to a desired temperature, molten metal is poured into the mold
through the funnel 14 to fill the mold cavities 18. The illustrated
furnace can include an additional funnel 34 or opening that is in
coaxial alignment with the funnel 14. The space around the
additional funnel or opening is often evacuated to prevent
contamination of the molten metal as it is poured into the mold
assembly 10.
[0024] A liquid metal cooling bath 36 is disposed beneath the mold
assembly and chill plate. The liquid metal cooling bath is
maintained at a temperature below the solidus temperature of the
metal in the mold. As such, as the mold assembly 10 moves into the
liquid metal cooling bath, the metal in the shell mold
directionally solidifies from the lower end portion of the shell
mold to the upper end portion of the mold. The chill plate 12
ensures the directional solidification of the casting as it cools.
The directional solidification of the molten metal in the shell
mold is particularly advantageous when it is desired to cast a
metal article with a columnar grain or to cast the metal article as
a single crystal. Cast material can also solidify in the runners
16. In some instances, the solidified runner castings are intended
to be part of the final cast part; the rest of the time they are
discarded or recycled.
[0025] In another embodiment, the mold assembly and chill plate
further includes a ring formed of a metal or ceramic material. The
ring can be configured to have a smaller diameter than the boss
such that it abuts an interior surface of the boss. Alternatively,
the ring can have a larger diameter than the boss such that it
abuts the exterior surface of the boss. Still further, inner and
outer rings relative to the boss can be utilized. FIGS. 2-4
illustrate the various arrangements of the ring 40. Although
reference is made specifically to a ring, it should be noted that
the shape can vary and is not intended to be limited. Suitable
shapes include circular, elliptical, and/or any polygonal shape
[0026] FIG. 5 illustrates an alternative embodiment for providing a
seal between the mold assembly 10 and the chill plate 12. The chill
plate includes an annular shaped channel 42 into which the ring 40
is disposed. In this embodiment, the ring 40 is dimensioned to
protrude from the planar surface 24 of the chill plate and extend
into the groove 22 of the skirt 20 upon attachment of the mold
assembly 10 to the chill plate 12. The channel 42 can be chamfered
as may be desired for some applications.
[0027] In yet another embodiment as shown in FIG. 6, the planar
surface 24 of the chill plate 12 is free from the boss or the
channel as described above. The ring 40 is disposed within the
channel 22 in the skirt 20 of the mold assembly 10 such that upon
attachment of the mold assembly 10 to the chill plate 12, the ring
40 compresses against the planar surface to provide an effective
seal. In this embodiment, the diameter of the ring is slightly
oversized so as to provide a compressive force against the planar
surface when the mold assembly and the chill plate are mechanically
fastened. Optionally, the ring can be coated with a material
effective to prevent relatively small leaks in this or any of the
other embodiments where applicable. For example, the ring can be
coated with a ceramic-based paste.
[0028] As previously noted, the ring can be formed of ceramics,
metals and the like. Suitable materials include, without
limitation, silicon carbide, carbon, graphite, alumina, aluminum,
copper, and the like. The ring can be formed of a number of
filaments, which may be wound together into a single unit or left
separately in a bunch. The ring can be configured to have a solid
cross section or may be configured to have a hollow cross-sectional
structure. By way of example, the rope can be made of ceramic-fiber
filaments, for example, alumina-boria-silica fibers with high
strength and low shrinkage up to 2200 degrees Fahrenheit (1204
degrees Celsius). These fibers are sold commercially as Nextel 312,
Nextel 440, and the like, a trademark of 3M Ceramic Materials
Department, 3M Center, St. Paul, Minn., 55144, United States.
Between rope ends, the rope can be overlapped or twisted together
to make a seamless connection to ensure a continuous seal.
[0029] In addition, a cloth made of metal or ceramic fibers can be
used. Some specific materials for the cloth are alumina,
alumina-silica fibers, or alumina-boria-silica fibers. The cloth
can be specifically layered, rolled, or twisted. A specific example
of a commercially available ceramic cloth, also sold by 3M, is a
cloth trademarked under the name "Nextel."
[0030] Alternatively, the ring can be formed of ductile metals such
as aluminum, copper, and the like, that can be compressed as may be
desired for some applications so as to provide conformality when
compressed between the mold and the chill plate. In one embodiment,
the metal is selected to have a melting point higher than that
exposed to during the liquid metal casting process.
[0031] Although reference has been made to a single channel, boss,
and/or ring, to define a seal assembly that circumscribes the shell
molds, in other embodiments, the seal assembly is configured for
each individual shell mold 18, i.e., each individual shell mold,
such as may be beneficial in cluster mold assemblies for
simultaneous casting multiple parts. FIG. 7 illustrates a sectional
view of an exemplary cluster mold assembly that includes four shell
molds for directionally casting four parts. The seal as described
in the embodiments shown in relation to FIGS. 1-6 is disposed
around each of the mold openings provided by each shell mold 18. In
this manner, each individual shell mold will be sealed and prevent
egress of metal within the mold or ingress of metal from the liquid
metal cooling bath. Alternatively, selected ones of the mold
openings provided by the individual shell mold 18 in a cluster mold
assembly apparatus can be sealed in this manner. For example, two
of the shell molds in a four shell mold cluster assembly apparatus
can be sealed with one of the seal embodiments as defined above and
the remaining shell molds can be individually or collectively
sealed. The various combinations of seal arrangements are not
intended to be limited. The sealing arrangement is created by
mechanically compressing the ring, if present, or by aligning the
boss in the chill plate with the correspondingly shaped channel of
the mold assembly as previously described.
[0032] When an article is to be cast in the mold assembly 10, the
mold assembly, including the shell molds 18, is placed on the chill
plate 12 and moved into the furnace 30. The exemplary furnace
includes coils 32 that can be energized to heat the mold assembly
10. Molten metal is then poured though opening 34 into the
preheated mold assembly through the funnel 14 in a known manner.
The furnace maintains the molten metal at a temperature above the
solidus temperature of the metal. The mold assembly is then lowered
at a controlled rate into the liquid metal cooling bath 36. To
lower the mold from the furnace, the support shaft 28 coupled to
the chill plate 12 is moved downward. This causes the chill plate
to move into the liquid metal cooling bath. As the lower end of the
mold assembly is cooled, the molten metal solidifies upward from
the lower end portion often mold assembly to the upper end portion
of the mold assembly.
[0033] Advantageously, the seal configurations as described herein
prevent molten metal from running out of the shell mold or the
liquid-metal cooling agent from flowing inside of the shell mold
before solidification of the cast metal. An exemplary embodiment
can provide a tight seal between a shell mold and its supporting
chill plate. The tight seal is necessary to prevent molten metal
from leaking out of the mold before the completion of
solidification, or, conversely, the cooling medium from ingression
into the molds and reaction with the casting. This embodiment of
this seal has several aspects including surface features in the
shell and chill plate, a gasket, and a configuration of seals
around mold openings.
[0034] Still further, productivity of a liquid-metal-cooled
directional solidification process is beneficially increased.
Better sealing decreases the ingress and egress of undesired metal
into the shell mold 18 and melt bath resulting in less leaking and
fewer corrupted castings. As such, the casting yield of a liquid
metal cooled casting process will be improved and more efficient by
minimizing shell mold run-out and producing castings with minimal
surface attack by the cooling medium. The increased yield provided
by the embodiments mentioned above will make liquid metal casting
cost competitive with conventional casting processes, a critical
step in the commercialization of the liquid metal casting process.
Moreover, each shell mold will have increased protection because of
the individual seal configurations and possible redundancy.
[0035] As used herein, the term "comprising" means various
compositions, compounds, components, layers, steps and the like can
be conjointly employed in the present invention. Accordingly, the
term "comprising" encompasses the more restrictive terms
"consisting essentially of" and "consisting of."
[0036] Unless defined otherwise, technical and scientific terms
used herein have the same meaning as is commonly understood by one
of skill in the art to which this invention belongs. The terms "a"
and "an" do not denote a limitation of quantity, but rather denote
the presence of the referenced item.
[0037] Reference throughout the specification to "one embodiment",
"another embodiment", "an embodiment", and so forth, means that a
particular element (e.g., feature, structure, and/or
characteristic) described in connection with the embodiment is
included in at least one embodiment described herein, and may or
may not be present in other embodiments. In addition, it is to be
understood that the described elements may be combined in any
suitable manner in the various embodiments.
[0038] All cited patents, patent applications, and other references
are incorporated herein by reference in their entirety. However, if
a term in the present application contradicts or conflicts with a
term in the incorporated reference, the term from the present
application takes precedence over the conflicting term from the
incorporated reference.
[0039] This written description uses examples to disclose the
invention, including the best mode, and also to enable practice of
the invention, including making and using any devices or systems
and performing any incorporated methods. The patentable scope of
the invention is defined by the claims, and may include other
examples. Such other examples are intended to be within the scope
of the claims if they have structural elements that do not differ
from the literal language of the claims, or if they include
equivalent structural elements with insubstantial differences from
the literal languages of the claims.
* * * * *