U.S. patent application number 11/972124 was filed with the patent office on 2008-10-23 for mold assembly for use in a liquid metal cooled directional solidification furnace.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. Invention is credited to Andrew John ELLIOTT, Michael Francis Xavier GIGLIOTTI, Shyh-Chin HUANG, Adegboyega Masud MAKINDE, Roger PETTERSON.
Application Number | 20080257517 11/972124 |
Document ID | / |
Family ID | 52354632 |
Filed Date | 2008-10-23 |
United States Patent
Application |
20080257517 |
Kind Code |
A1 |
ELLIOTT; Andrew John ; et
al. |
October 23, 2008 |
MOLD ASSEMBLY FOR USE IN A LIQUID METAL COOLED DIRECTIONAL
SOLIDIFICATION FURNACE
Abstract
A mold assembly for a liquid metal cooled directional
solidification furnace having a cooling chamber provided with
liquid metal and a heating chamber includes a mold member having a
main body portion that defines an interior mold cavity. The mold
member is adapted to be positioned in the heating chamber. The mold
assembly also includes a chill-plate formed from a material having
a thermal diffusivity a 600.degree. K greater than approximately 10
E-6 m2/s, inert to at least one of molten tin and molten aluminum
and adapted to be at least partially immersed in the liquid metal.
The chill-plate includes a main body portion having a first surface
extending to a second surface through an intermediate portion. The
chill-plate is adapted to establish a thermal gradient between the
mold member and the heating chamber.
Inventors: |
ELLIOTT; Andrew John;
(Greer, SC) ; GIGLIOTTI; Michael Francis Xavier;
(Scotia, NY) ; HUANG; Shyh-Chin; (Latham, NY)
; MAKINDE; Adegboyega Masud; (Niskayuna, NY) ;
PETTERSON; Roger; (Fultonville, NY) |
Correspondence
Address: |
CANTOR COLBURN, LLP
20 Church Street, 22nd Floor
Hartford
CT
06103
US
|
Assignee: |
GENERAL ELECTRIC COMPANY
Schenectady
NY
|
Family ID: |
52354632 |
Appl. No.: |
11/972124 |
Filed: |
January 10, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11305247 |
Dec 16, 2005 |
7357609 |
|
|
11972124 |
|
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|
Current U.S.
Class: |
164/122.1 ;
164/352 |
Current CPC
Class: |
B22D 27/04 20130101 |
Class at
Publication: |
164/122.1 ;
164/352 |
International
Class: |
B22D 27/04 20060101
B22D027/04; B22D 15/00 20060101 B22D015/00 |
Claims
1. A mold assembly for a liquid metal cooled directional
solidification furnace having a cooling chamber provided with
liquid metal and a heating chamber, the mold assembly comprising: a
mold member having a main body portion that defines an interior
mold cavity, the mold member being adapted to be positioned in the
heating chamber; and a chill-plate formed from a material having a
thermal diffusivity at 600 K greater than approximately 10 E-6
m2/s, inert to at least one of molten tin and molten aluminum and
adapted to be at least partially immersed in the liquid metal, the
chill-plate including a main body portion having a first surface
extending to a second surface through an intermediate portion,
wherein the chill-plate is adapted to establish a thermal gradient
between the mold member and the heating chamber.
2. The mold assembly according to claim 1, wherein the chill-plate
is formed from a material having a thermal diffusivity at
600.degree. K greater than approximately 20 E-6 m 2/s.
3. The mold assembly according to claim 2, wherein the chill-plate
is formed from a material having a thermal diffusivity at
600.degree. K greater than approximately 30 E-6 m 2/s.
4. The mold assembly according to claim 1, wherein the chill-plate
is formed from one of molybdenum, a molybdenum alloy, graphite, a
graphite alloy, tungsten, a tungsten alloy and combinations
thereof.
5. The mold assembly according to claim 1, wherein the main body
portion of the chill-plate has a thickness of up to approximately
12 inches (30.48 cm)
6. The mold assembly according to claim 5, wherein the main body
portion of the chill-plate has a thickness of between approximately
3 inches (7.62 cm) and approximately 5 inches (12.7 cm).
7. The mold assembly according to claim 6, wherein the main body
portion of the chill-plate has a thickness of approximately 4
inches (10.16 cm).
8. A liquid metal cooled directional solidification furnace
comprising: a heating portion including a heating chamber having a
first temperature; a cooling portion including a cooling chamber
provided with liquid metal having a second temperature, the second
temperature being less than the first temperature; and a mold
assembly positioned in each of the heating portion and cooling
portion, the mold assembly including: a mold member having a main
body portion that defines an interior mold cavity, the mold member
being positioned in the heating chamber; and a chill-plate formed
from a material having a thermal diffusivity at 600.degree. K
greater than approximately 10 E-6 m2/s and at least partially
immersed in the liquid metal, the chill-plate including a main body
portion having a first extending to a second surface through an
intermediate portion, wherein the chill-plate, partially immersed
in the liquid metal, establishes a thermal gradient between the
mold member and the heating chamber.
9. The mold assembly according to claim 8, wherein the chill-plate
is plate is formed from a material having a thermal diffusivity at
600.degree. K greater than approximately 20 E-6 m 2/s.
10. The mold assembly according to claim 9, wherein the chill-plate
plate is formed from a material having a thermal diffusivity at
600.degree. K greater than approximately 30 E-6 m 2/s.
11. The mold assembly according to claim 8, wherein the chill-plate
is formed from one of molybdenum, a molybdenum alloy, graphite, a
graphite alloy, tungsten, a tungsten alloy, and combinations
thereof.
12. The liquid cooled directional solidification furnace according
to claim 8, wherein the main body portion of the chill-plate has a
thickness of up to approximately 12 inches (30.48 cm).
13. The liquid cooled directional solidification furnace according
to claim 12, wherein the main body portion of the chill-plate has a
thickness of between 3 inches (7.62 cm) and approximately 5 inches
(12.7 cm).
14. The liquid cooled directional solidification furnace according
to claim 13, wherein the main body portion of the chill-plate has a
thickness of approximately 4 inches (10.16 cm).
15. The liquid cooled directional solidification furnace according
to claim 8, wherein the liquid metal includes tin.
16. The liquid cooled directional solidification furnace according
to claim 8, wherein the liquid metal is aluminum.
17. A method of forming a cast component in a liquid metal cooled
directional solidification furnace comprising: supporting a portion
of a mold assembly upon a chill-plate formed from a material having
a thermal diffusivity at 600.degree. K greater than approximately
10 E-6 m2/s into a liquid cooled directional solidification
furnace; positioning a the mold member in a heating chamber having
a first temperature and a portion of the chill-plate into a liquid
metal bath having a second temperature, the second temperature
being higher than the first temperature; raising the temperature in
the heating chamber from the first temperature to a third
temperature, the third temperature being substantially higher than
the second temperature; and maintaining the portion of the mold
member supported upon the chill-plate at a fourth temperature, the
fourth temperature being substantially less than the third
temperature.
18. The method of claim 17, wherein support a portion of the mold
member upon a chill-plate formed from a material having a thermal
diffusivity at 600.degree. K greater than approximately 10 E-6 m2/s
includes supporting a portion of the mold member on a chill-plate
formed from at least one of molybdenum, a molybdenum alloy,
graphite, a graphite alloy, tungsten, a tungsten alloy and
combinations thereof.
19. The method of claim 17, further comprising: maintaining a
temperature variation within the chill-plate between approximately
482.degree. F. (250.degree. C.) and 1022.degree. F. (550.degree.
C.).
Description
BACKGROUND OF THE INVENTION
[0001] The present invention pertains to the art of mold assemblies
and, more particularly, to a mold assembly having molybdenum
chill-plate employed in a liquid metal cooled solidification
furnace.
[0002] Certain components for gas turbine engines are typically
cast from superalloys, for example cobalt, iron and nickel-based
alloys. Superalloys have high strength and typically very high
melting temperatures. Thus, superalloys well suited for gas turbine
engine components such as rotor blades and stator vanes that have
complex shapes and are exposed to harsh operating environments. The
strength of such components is further enhanced using a directional
solidification process.
[0003] In a typical directional solidification process, a
superalloy charge is placed in a melting crucible surrounded by a
heater. The heater melts the charge to form a molten metal. A mold
is initially positioned inside a heating chamber located within a
directional solidification furnace. The heating chamber preheats
the mold to a suitable temperature. Once the mold is preheated, the
molten metal is poured from the crucible into the mold. At this
point the mold is withdrawn or immersed into a cooling bath filled
with a cooling liquid. The cooling liquid is typically a liquid
metal such as tin or aluminum. As the mold is withdrawn into the
cooling liquid, the liquid metal directionally solidifies inside
the mold.
[0004] In order to control the directional solidification and
establish a desired grain structure, the mold is positioned upon a
chill-plate. The chill-plate acts as a thermal interface between
the mold and the heating chamber during preheat. That is, during
preheat, a portion of the chill-plate extends into the liquid
metal. The liquid metal establishes a thermal gradient within the
chill-plate. In this manner, an upper, exposed, surface of the
chill-plate remains at a temperature that is lower than the preheat
temperature. With this arrangement, a bottom portion of the mold
that rests upon the chill-plate also remains at a temperature that
is below the preheat temperature. This temperature differential is
particularly desirable during an initial stage of the directional
solidification process.
[0005] Chill-plates are typically formed from copper or copper
alloys and are often provided with an internal water cooling
scheme. Unfortunately, copper and copper alloys react negatively to
tin and aluminum. Thus, copper chill-plates have a very short
service life and, due to the poor interaction with aluminum and
tin, may also detrimentally affect the directional solidification
process. Stainless steel is also used as a material for forming
chill-plates. However, while more durable than copper, stainless
steel has a relatively low thermal diffusivity and exhibits a
reaction with, for example, liquid aluminum. The low thermal
diffusivity allows heat from the heating chamber to rapidly
transfer into the cooling liquid and raise surface temperatures of
the chill-plate to approximately the preheat temperature.
Therefore, stainless steel chill-plates, at best, provide only a
minimal benefit for the directional solidification process.
BRIEF DESCRIPTION OF THE INVENTION
[0006] In accordance with one aspect of the invention, a mold
assembly for a liquid metal cooled directional solidification
furnace having a cooling chamber provided with liquid metal and a
heating chamber includes a mold member having a main body portion
that defines an interior mold cavity. The mold member is adapted to
be positioned in the heating chamber. The mold assembly also
includes a chill-plate formed from a material having a thermal
diffusivity at 600.degree. K greater than 10 E-6 m 2/sec, inert
with at least one of molten tin and molten aluminum and adapted to
be at least partially immersed in the liquid metal. The chill-plate
includes a main body portion having a first surface extending to a
second surface through an intermediate portion. The chill-plate is
adapted to establish a thermal gradient between the mold member and
the heating chamber.
[0007] In accordance with another aspect of the present invention,
a liquid metal cooled directional solidification furnace is
provided. The furnace includes a heating portion including a
heating chamber having a first temperature and a cooling portion
including a cooling chamber provided with a liquid metal having a
second temperature with the second temperature being less than the
first temperature. The furnace also includes a mold assembly that
is positioned at least in part in each of the heating portion and
cooling portion. The mold assembly includes a mold member having a
main body portion that defines an interior mold cavity positioned
in the heating chamber, a support yoke including at least one
support member connected to the mold member, and a chill-plate. The
chill-plate is formed from a material having a thermal diffusivity
at 600.degree. K greater than 10 E-6 m 2/sec, inert with at least
one of molten tin and molten aluminum, and is positioned, at least
in part, in the liquid metal. The chill-plate includes a main body
portion having a first surface that extends to a second surface
through an intermediate portion. The chill-plate establishes a
thermal gradient between the mold member and the heating
chamber.
[0008] In accordance with yet another aspect of the present
invention, a method of forming a cast component in a liquid metal
cooled directional solidification furnace is provided. The method
includes placing a mold assembly having a mold member including a
bottom portion supported directly upon a chill-plate formed from a
material having a thermal diffusivity at 600.degree. K greater than
10 E-6 m 2/sec and inert with at least one of molten tin and molten
aluminum into the liquid cooled directional solidification furnace.
The method further requires positioning the mold member in a
heating chamber having a first temperature and a portion of the
chill-plate into a liquid metal bath having a second temperature
with the second temperature being higher than the first temperature
and raising the temperature in the heating chamber from the first
temperature to a third temperature, with the third temperature
being substantially higher than the second temperature. Finally,
the method requires maintaining the bottom portion of the mold
member at a fourth temperature, the fourth temperature being
substantially less than the third temperature.
[0009] Additional objects, features and advantages of various
aspects of the present invention will become more readily apparent
from the following detailed description of illustrated aspects when
taken in conjunction with the drawings wherein like reference
numerals refer to corresponding parts in the several views.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a schematic view of a liquid metal cooled
directional solidification furnace including a mold cluster
assembly including a chill-plate constructed in accordance with an
aspect of the present invention;
[0011] FIG. 2 is a left perspective view of a portion of the mold
cluster assembly of FIG. 1; and
[0012] FIG. 3 is a detailed view of the chill-plate portion of the
portion of the mold cluster assembly of FIG. 2.
DETAILED DESCRIPTION OF THE INVENTION
[0013] With initial reference to FIG. 1, a liquid metal cooled
(LMC) solidification furnace is generally indicated at 2. Furnace 2
includes a heating portion 4 having a heating chamber 8 provided
with an opening 10. Opening 10 is positioned to receive a flow of
molten metal, such as a superalloy, from a crucible 11. Crucible 11
is in operable communication with a heater 12 that melts a volume
of superalloy such as an ingot 13 of superalloy to form molten
metal for producing various component parts. Furnace 2 further
includes a cooling portion 14 having a cooling chamber 16
positioned adjacent heating portion 4. In the embodiment shown,
cooling chamber 16 is filled with a liquid metal 19 such as tin or
aluminum. Cooling chamber 16 is separated from heating chamber 8 by
a baffle 23 that is in contact with the liquid metal 19. Tin and
aluminum are desirable liquid metals for use in LMC furnace 2 given
their relatively low melting point temperatures and low vapor
pressures at elevated temperatures. However it should be understood
that other liquid metals, including alloys of tin and aluminum
could also be employed. In any event, furnace 2 is also shown to
include a mold cluster assembly 40 supported by a moveable platform
41.
[0014] As best shown in FIG. 1 and 2, mold cluster assembly 40
includes a pair of mold members one of which is indicated at 43. At
this point it should be understood that mold cluster assembly 40
includes an additional mold member (not shown) such that FIG. 2
illustrates only a portion of mold cluster assembly 40. In any
event, mold member 43 includes a main body portion 46 configured,
in the embodiment shown, to produce a turbine bucket. Main body
portion 46 includes a first portion 47 that extends to a second
portion 48 through an intermediate portion 49 which collectively
define an interior mold cavity 50. Mold member 43 also includes a
pair of vent openings 51 and 52 provided at first portion 47. Mold
cluster assembly 40 is further shown to include a support yoke 54.
Support yoke 54 includes a first end section 57, which defines an
inlet, which extends to a second end section 58 through an
intermediate zone 59. First end section 57 is connected to mold
member 43 through a pair of connecting members 62 and 63 while
second end section 58 is joined to a chill-plate 70.
[0015] Chill-plate 70 is preferably formed from a material having a
thermal diffusivity at 600.degree. K greater than approximately 10
E-6 m 2/sec, more preferably, the material has a thermal
diffusivity at 600.degree. K greater than approximately 20 E-6 m
2/sec, and most preferably the material has a thermal diffusivity
at 600.degree. K greater than approximately 30 E-6 m 2/sec. In
addition, the material is neutral, i.e., does not react in at least
one of molten tin and molten aluminum. In accordance with one
exemplary embodiment the material is molybdenum and/or alloys
thereof. In accordance with another exemplary embodiment the
material is tungsten and/or alloys thereof. In accordance with yet
another exemplary embodiment, the material is graphite and/or
alloys thereof.
[0016] As shown, chill-plate 70 includes a main body portion 74
having a first surface 80 that extends to a second surface 81
through an intermediate portion 82 which collectively define a
thickness "w". As will be discussed more fully below, second
portion 48 of mold member 43 is directly supported by first surface
80 of chill-plate 70. In accordance with one aspect of the
invention, thickness "w" ranges up to about 12-inches (30.48 cm).
In accordance with another aspect of the invention, thickness "w"
ranges between approximately 3 inches (7.62 cm) and approximately 5
inches (12.7 cm). In accordance with yet another aspect of the
invention, thickness "w" is approximately 4 inches (10.16 cm).
[0017] In operation, mold cluster assembly 40 is positioned within
heating chamber 8 with lower portion 48 of mold member 43 resting
directly upon chill-plate 70 which, in turn, is partially immersed
in liquid metal 19. (See FIG. 1) At this point heating chamber 8
and mold cluster assembly 40 are at a uniform temperature, for
example 158.degree. F. (70.degree. C.) and liquid metal 19 is at a
temperature of approximately 250.degree. C. for a tin coolant and
approximately 700.degree. C. for an aluminum coolant. Once mold
cluster assembly 40 is properly in position, a plurality of heaters
110-113 are activated create a heating zone within heating chamber
8 and a preheat stage initiated. Of course, depending upon the
particular configuration a single heater may be employed. With the
activation of heaters 110-113, the temperature in heating chamber 8
rises to approximately 2822.degree. F. (1550.degree. C.) to preheat
mold member 43 in preparation for receiving molten metal from
crucible 11. As the temperature within heating chamber 8 rises, the
lower temperature of liquid metal 19 establishes a thermal gradient
within chill-plate 70 such that first surface 80 remains at a
temperature that is lower than the temperature in heating chamber
8. As a consequence, second portion 48 of mold member 43 also
remains at a temperature that is lower than the temperature in
heating chamber 8.
[0018] That is, evidence has shown, immersing chill-plate 70 two
(2) inches into liquid metal 19, and raising the temperature in
heating chamber 8 to approximately 2822.degree. F. (1550.degree.
C.), results in first surface 80 remaining at approximately
824.degree. F. (450.degree. C.). Moreover, an overall temperature
variation within chill-plate 70 is only between approximately
482.degree. F. (250.degree. C.) and approximately 1022.degree. F.
(550.degree. C.). In any event, following the preheat stage, molten
metal is dispensed into interior mold cavity 50 and mold cluster
assembly 40 is withdrawn into cooling portion 14 so as to form a
directionally solidified casting. At this point it should be
understood that forming chill-plate 70 from molybdenum and/or
molybdenum alloy advantageously provides for an enhanced cooling or
quenching process that creates durable microstructures in resultant
castings. Moreover, the use of molybdenum and/or a molybdenum alloy
extends an overall service life of the mold assembly. That is, as
molybdenum is compatible with tin and aluminum, no reaction will
occur between the chill-plate and the liquid metal that could
otherwise impact service life and possibly the resultant castings.
Of course, it should be understood that while the above described
mold member is configured to form a turbine bucket, the present
invention can be employed to produce various components, such as
turbine nozzles, blades, and vanes for turbine engines as well as
other articles that would benefit from directionally solidified
grain structure.
[0019] At this point it should be appreciated that the present
invention provides a mold assembly for a liquid metal cooled
directional solidification process having a chill-plate that
possesses a high thermal diffusivity. Thus, during preheat, the
bottom portion of the mold member is maintained at a temperature
that is substantially lower than the temperature in the heating
chamber. In this manner, the present invention achieves a desired
directional solidification while providing a mold assembly having a
long service period as compared to a chill-plate formed from
copper. Moreover, the present invention provides a mold assembly
having an extended service life without requiring the use of
additional cooling circuits.
[0020] In general, this written description uses examples to
disclose the invention, including the best mode, and also to enable
any person skilled in the art to practice 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 that occur to
those skilled in the art. Such other examples are intended to be
within the scope of the present invention 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 language of the
claims.
* * * * *