U.S. patent application number 12/327288 was filed with the patent office on 2010-06-03 for method of casting a metal article.
Invention is credited to LAWRENCE D. GRAHAM.
Application Number | 20100132906 12/327288 |
Document ID | / |
Family ID | 42221727 |
Filed Date | 2010-06-03 |
United States Patent
Application |
20100132906 |
Kind Code |
A1 |
GRAHAM; LAWRENCE D. |
June 3, 2010 |
METHOD OF CASTING A METAL ARTICLE
Abstract
During the casting of the metal article, a mold is lowered from
a furnace assembly into a body of an inert gas. A stream having a
thermal conductivity greater than the thermal conductivity of the
inert gas is directed against a first portion of the mold to
initiate solidification of molten metal in the first portion of the
mold. The stream is subsequently directed against portions of the
mold disposed in the body of inert gas and disposed above the first
portion of the mold to initiate solidification of molten metal and
portions of the mold above the first portion of the mold. The
stream may be formed of a molten metal. Alternatively, the stream
may be formed of an inert gas in which particulate is
entrained.
Inventors: |
GRAHAM; LAWRENCE D.;
(Chagrin Falls, OH) |
Correspondence
Address: |
TAROLLI, SUNDHEIM, COVELL & TUMMINO L.L.P.
1300 EAST NINTH STREET, SUITE 1700
CLEVEVLAND
OH
44114
US
|
Family ID: |
42221727 |
Appl. No.: |
12/327288 |
Filed: |
December 3, 2008 |
Current U.S.
Class: |
164/66.1 |
Current CPC
Class: |
B22D 27/045
20130101 |
Class at
Publication: |
164/66.1 |
International
Class: |
B22D 27/04 20060101
B22D027/04 |
Claims
1. A method of casting a metal article, said method comprising the
steps of filling a mold with molten metal while the mold is
disposed in a furnace, lowering the mold from the furnace in a body
of inert gas, directing a stream having a thermal conductivity
greater than the thermal conductivity of the inert gas against a
first portion of the mold disposed in the body of inert gas to
initiate solidification of molten metal in the first portion of the
mold, and directing the stream having a thermal conductivity
greater than the thermal conductivity of the inert gas against
portions of the mold disposed in the body of gas and disposed above
the first portion of the mold to initiate solidification of molten
metal in portions of the mold above the first portion of the
mold.
2. A mold as set forth in claim 1 wherein said step of directing a
stream having a thermal conductivity greater than the thermal
conductivity of the inert gas against a first portion of the mold
includes directing a stream of molten metal against the first
portion of the mold.
3. A method as set forth in claim 1 wherein said step of directing
a stream having a thermal conductivity greater than the thermal
conductivity of the inert gas against a first portion of the mold
includes directing a stream of the inert gas in which a particulate
is entrained against the first portion of the mold.
4. A method as set forth in claim 1 further including the steps of
collecting material from the stream and returning the collected
material to the stream.
5. A method as set forth in claim 1 wherein said step of directing
a stream having a thermal conductivity greater than the thermal
conductivity of the inert gas against the first portion of the mold
includes directing a stream of liquid against the first portion of
the mold and allowing at least a portion of the liquid from the
stream of liquid to move downwardly in the body of inert gas under
the influence of gravity.
6. A method as set forth in claim 1 wherein said step of directing
a stream having a thermal conductivity greater than the thermal
conductivity of the inert gas against portions of the mold disposed
above the first portion of the mold includes directing a stream of
liquid against the portions of the mold disposed above the first
portion of the mold and allowing liquid from the stream of liquid
to move downwardly along portions of the mold disposed below a
portion of the mold against which the stream of liquid is directed
and to move downwardly in the body of inert gas under the influence
of gravity.
7. A method as set forth in claim 1 wherein said step of directing
a stream having a thermal conductivity greater than the thermal
conductivity of the inert gas against the first portion of the mold
includes directing a stream of liquid against the first portion of
the mold at a first location in the body of inert gas, said step of
directing a stream having a thermal conductivity greater than the
thermal conductivity of the inert gas against portions of the mold
disposed in the body of gas and disposed above the first portion of
the mold includes directing a stream of liquid against the portions
of the mold above the first portion of the mold at the first
location in the body of inert gas.
8. A method as set forth in claim 7 wherein said step of directing
a stream of liquid against the portions of the mold above the first
portion of the mold is performed with the first portion of the mold
at least partially exposed to the inert gas in the body of inert
gas.
9. A method as set forth in claim 7 further including the step of
collecting a body of the liquid which contains liquid which was
directed against the mold in a stream of liquid, said step of
collecting the body of liquid includes collecting the body of
liquid at a location disposed at a level below the mold and with an
upper surface of the body of liquid exposed to gas in the body of
inert gas.
10. A method as set forth in claim 9 further including the step of
pumping liquid from the body of liquid and at least partially
forming the stream having a thermal conductivity greater than the
thermal conductivity of the inert gas and which is directed against
portions of the mold disposed above the first portion of the mold.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a new and improved method
of casting a metal article.
[0002] It has previously been suggested that a casting apparatus
may employ a body of molten metal or a fluidized bed as a cooling
bath to promote directional solidification of an article in a mold.
Apparatus for doing this is disclosed in U.S. Pat. No. 6,308,767
and U.S. Pat. No. 6,695,034. When a mold is immersed in a bath of
molten metal, in the manner disclosed in U.S. Pat. No. 6,308,767,
there is a tendency for stress to develop in the cast metal article
due to differential thermal contraction.
[0003] It has also been suggested that a flow of inert gas be
directed against a mold to promote directional solidification of
metal in the mold. An apparatus for doing this is disclosed in U.S.
Pat. No. 7,017,646. However, an inert gas has a relatively low
thermal conductivity. The low thermal conductivity of an inert gas
does not promote heat transfer to initiate solidification of molten
metal in the mold.
SUMMARY OF THE INVENTION
[0004] The present invention relates to a new and improved method
of casting a metal article. A mold is filled with molten metal
while the mold is disposed in a furnace assembly. The mold is
lowered from the furnace assembly in a body of inert gas.
[0005] In accordance with one of the features of the present
inventions a stream of coolant having a thermal conductivity
greater than the thermal conductivity of the inert gas, is directed
against a first portion of the mold to initiate solidification of
molten metal in the first portion of the mold. The stream is
directed against portions of the mold disposed in the body of gas
and disposed above the first portion of the mold to initiate
solidification of molten metal in portions of the mold above the
first portion of the mold.
[0006] The stream which is directed against the mold may be formed
of a molten metal. Alternatively, the stream which is directed
against the mold may be formed of an inert gas in which particulate
is entrained.
[0007] The present invention has a plurality of different features
which are advantageously utilized together in the manner described
herein. However, it is contemplated that the features may be
utilized separately and/or in combination with features from the
prior art.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The foregoing and other features of the invention will
become more apparent upon a consideration of the following
description taken in connection with the accompanying drawings
wherein:
[0009] FIG. 1 is a schematic illustration depicting the manner in
which a mold is lowered from a furnace assembly and a stream of
molten metal is directed against the mold; and
[0010] FIG. 2 is a schematic illustration depicting the manner in
which a mold is lowered from a furnace assembly and a stream of
inert gas with particulate entrained therein is directed against
the mold.
DESCRIPTION OF SPECIFIC PREFERRED EMBODIMENTS OF THE INVENTION
[0011] An improved casting apparatus 10 is illustrated
schematically in FIG. 1 and is utilized in an improved method of
casting metal articles in a mold structure 12. The casting
apparatus 10 includes a furnace assembly 16 in which a molten metal
is poured into the ceramic mold structure 12 in a known manner.
Directly beneath the furnace assembly 16 is a container 20 into
which the mold structure 12 is lowered from the furnace assembly
16. The furnace assembly 16 and container 20 are enclosed by a
suitable housing 24 which is connected with a source of vacuum or
low pressure by a conduit 26. The housing 24 is connected with a
source of an inert gas, such as argon, by a conduit 27.
[0012] The housing 24 enables the body 28 of inert gas to be
maintained in the container 20. The housing 24 may have any one of
many known constructions, including the construction disclosed in
U.S. Pat. No. 3,841,384 and/or the construction shown in U.S. Pat.
No. 6,308,767. Of course, the housing 24 may have a construction
which is different than the known constructions illustrated in the
aforementioned patents.
[0013] The-framework 36 is provided to support the mold 12 for
movement to and from the furnace assembly 16 and for movement to
and from the container 20. The metal framework 36 includes a
plurality of parallel support rods 38 and a mold support structure
42. The mold support structure 42 has a vertical central axis which
coincident with central axes of the furnace assembly 16 and
container 20. The mold support structure 42 functions as, and may
be referred to as, a chill plate.
[0014] The support rods 38 are connected with an upper drive
assembly 44. The upper drive assembly 44 is operable to raise and
lower the framework 36 relative to the furnace assembly 16 and
container 20. If desired, the support rods 38 may be disposed
outside the furnace assembly 16. A lower drive assembly 48 is
connected with the container 20. The lower drive assembly 48 is
operable to raise and lower the container 20 relative to the
furnace assembly 16. The upper and lower drive assemblies 44 and 48
may be operated simultaneously and/or sequentially to raise and/or
lower the framework 36 and/or container 20.
[0015] During operation of the casting apparatus 10, the housing 24
is evacuated through the conduit 26. Inert gas is then conducted
into the housing 24 through the conduit 27. In the illustrated
embodiment of the invention, the housing 24 encloses both the
furnace assembly 16 and the container 20. It is contemplated that
an upper housing may be associated with the furnace assembly 16 and
a separate lower housing may be associated with the container 20 if
desired.
[0016] After the housing 24 has been filled with an inert gas, the
mold structure 12 is filled with molten metal while the mold
structure is in the cylindrical furnace assembly 16. The molten
metal with which the mold structure is filled is a nickel-chrome
super alloy which melts at a temperature which is greater than
3,000 degrees Fahrenheit. Of course, the mold structure 12 may be
filled with a different molten metal which melts at a different
temperature. For example, the mold structure 12 may be filled with
molten titanium or a titanium alloy.
[0017] Once the mold structure 12 has been filled with the molten
nickel-chrome super alloy or other metal, the upper drive assembly
44 is operated to lower the framework 36 and mold structure 12 into
the cylindrical container 20. While the upper drive assembly 44 is
operated to lower the mold structure 12, the lower drive assembly
48 may be operated to raise the container 20. It should be
understood that the mold structure 12 may be lowered without
raising the container 20. In the illustrated embodiment of the
invention, the container 20 is raised to the position illustrated
schematically in FIG. 1 relative to the furnace assembly 16 before
the mold structure 12 is lowered into the container by operation of
the upper drive assembly 44.
[0018] In accordance with one of the features of the present
invention, as the mold structure 12 is lowered into the body 28 of
inert gas in the container 20, a plurality of streams 54 of coolant
are directed toward the mold structure from nozzles 56 disposed in
a circular array around the mold structure 12. Although only two
nozzles 56 are illustrated in FIG. 1, it is contemplated that a
greater number of nozzles may be provided if desired. For example,
ten nozzles 56 may be provided in the array of nozzles. The
circular array of nozzles 56 is disposed in a coaxial relationship
with the furnace 16 and container 20.
[0019] The array of nozzles 56 may have any desired configuration.
The illustrated array of nozzles 56 has a circular configuration.
This results in an annular array of streams 54 of coolant being
directed from the nozzles 56 radially inwardly toward the mold
structure 12 as the mold structure is lowered into the body 28 of
inert gas. The streams 54 of coolant are effective to cool the mold
structure and initiate solidification of molten metal in a portion
of the mold structure against which the streams impinge.
[0020] Although a single array of nozzles 56 has been illustrated
in FIG. 1 as being on one level, the nozzles 56 may be located on
different levels. For example, a plurality of circular arrays of
nozzles may be provided. Each array of the plurality of arrays of
nozzles 56 may be located on a different level. Thus, an array of
nozzles 56 may be disposed below the array of nozzles illustrated
schematically in FIG. 1.
[0021] In the illustrated embodiment of the invention, coolant
flows at the same rate from each of the nozzles 56. However, the
nozzles 56 may be constructed so as to have different flow rates
from different nozzles. For example, a nozzle 56 having a
relatively small flow rate may direct a flow of coolant toward a
portion of a mold structure 12 which is to be cooled at a
relatively low rate. At the same time, another nozzle 56 having a
greater flow rate may direct a flow of coolant toward a portion of
the mold structure 12 which is to be cooled at a higher rate. If
arrays of nozzles 56 are provided at different levels in the
container 20 in the manner set forth above, the nozzles 56 in an
array at one level may direct a flow of coolant toward a mold
structure 12 at a first flow rate and nozzles in an array at
another level may direct a flow of coolant toward a mold structure
12 at a second flow rate. For example, an array of nozzles 56 at a
relatively high level in the container 20 may direct a flow of
coolant toward a mold structure 12 at a greater flow rate than
nozzles at a relatively low level in the container 20.
[0022] In accordance with one of the features of the present
invention, the streams 54 of coolant from the nozzles 56 are formed
of a material having a thermal conductivity which is greater than
the thermal conductivity of the inert gas forming the body 28 of
inert gas into which the mold structure 12 is lowered. In one
embodiment of the invention, the streams 54 of coolant are formed
of liquid (molten) metal.
[0023] The molten metal in the streams 54 are formed of tin and are
at a temperature of approximately 500 degrees Fahrenheit. However,
the streams 54 of molten metal may be formed of lead or aluminum if
desired. The streams 54 of molten metal may be at any desired
temperature which is sufficient to maintain the metal forming
streams in a molten condition. Since the molten metal in the mold
structure 12 is a nickel-chrome super alloy with a melting
temperature of approximately 3,700 degrees Fahrenheit, the streams
54 of molten metal are effective to cool the mold structure 12 and
the molten metal (nickel-chrome super alloy) contained within the
mold structure 12.
[0024] As the upper drive assembly 44 is operated to begin lowering
the framework 36 and mold structure 12 from the furnace assembly
16, the mold support structure 42 moves through an opening 60
formed in a baffle 62. The baffle 62 is mounted on the upper end
portion of the container 20 and is effective to block splashing of
molten metal upwardly toward the furnace assembly 16. Although the
opening 60 has a circular configuration, corresponding to the
generally circular configuration of the upper end portion of the
container 20 and the lower end portion of the furnace assembly 16,
it is contemplated that the opening in the baffle 62 may have a
different configuration if desired. For example, the baffle opening
60 may have a configuration which is a function of the overall
configuration of the mold structure 12 and mold support structure
42.
[0025] It is contemplated that the baffle 62 may have any one of
many known constructions. If desired, the baffle 62 may have
relatively movable sections in the manner disclosed in U.S. Pat.
No. 6,698,493. Alternatively, the baffle 62 may have flexible
projections which extend from a support portion and engage the mold
structure 12 in the manner disclosed in U.S. Pat. No.
4,969,501.
[0026] The mold structure 12 and mold support framework 36 may have
a construction which is the same as disclosed in co-pending U.S.
patent application Ser. No. 12/145,033 filed Jun. 24, 2008 by
Robert M. Garlock and entitled Method of Casting Metal Articles.
The disclosure in the aforementioned U.S. patent application Ser.
No. 12/145,033 is hereby incorporated herein, in its entirety by
this reference thereto. Of course, the framework 36 may have a
different construction if desired. For example, the mold support
framework 36 and associated drive assembly 44 may have any one of
the constructions disclosed in U.S. Pat. No. 6,776,213.
[0027] When the upper drive assembly 44 is operated to lower the
framework 36, the mold support structure 42 passes through the
opening 60 in the baffle 62. Continued lowering of the framework 36
results in a lower portion 66 of the mold structure 12 being
exposed to the streams 54 of coolant. The streams 54 of coolant
impinge against the lower portion 66 of the mold structure 12. As
this occurs, solidification of the molten metal in the lower
portion 66 of the mold structure is initiated.
[0028] After impinging, against the lower portion 66 of the mold
structure 12, the coolant falls downward under the influence of
gravity into a body 70 of coolant. Pumps 72 are provided to pump
coolant from the body 70 of coolant upward through conduits 74 to
the nozzles 56. Although only a singe nozzle 56 has been
illustrated in FIG. 1 in association with each of the pumps 72, it
should be understood that a plurality of nozzles may be connected
with each of the pumps by a manifold so that each pump 72 may
supply more than one nozzle 56 with coolant. Although only two
nozzles 56 have been illustrated schematically in FIG. 1, it should
be understood that a greater number of nozzles may be provided.
Similarly, although only two pumps 72 have been illustrated
schematically in FIG. 1, it should be understood that a greater
number of pumps may be provided.
[0029] As operation of the upper drive assembly 44 continues to
slowly lower the mold structure 12 into the body 28 of inert gas in
the container 20, the streams 54 of coolant are directed against,
portions of the mold structure disposed above the lower portion 66
of the mold structure. Heat is transferred from the portions of the
mold structure 12 above the lower portion 66 of the mold structure
as the streams 54 of coolant impinge against the mold structure.
This results in initiation of solidification of molten metal in
portions of the mold structure disposed above the lower portion 66
of the mold structure. As the mold structure 12 continues to be
lowered into the container 20, the streams 54 of coolant are
directed against progressively upper portions of the mold structure
until the entire mold structure has been engaged by the streams 54
of coolant.
[0030] The portion of the mold structure 12 below the nozzles 56 is
exposed to the body 28 of inert gas in the container 20. Since the
thermal conductivity of the body 28 of inert gas is less than the
thermal conductivity of the coolant in the streams 54, the rate of
transfer of heat from portions of the mold structure disposed below
the streams 54 of coolant is less than the rate of transfer of heat
from portions of the mold structure engaged by the streams 54 of
coolant. Due, to the reduced rate at which heat is transferred from
the mold structure at, locations below the nozzles 56, the inducing
of stresses in the portion of a casting disposed in the mold
structure below the nozzles 56 is reduced. Any tendency for the
occurrence of differential thermal contraction of the casting in
the mold structure 12 is reduced with a resulting reduction in any
tendency for the establishment of stresses in the casting.
[0031] The mold support structure 42 remains above an upper surface
76 of the body 70 of coolant. Therefore, all of the mold structure
12 which is disposed at a level below the nozzles 56 is exposed to
the body 28 of inert gas and is cooled at a rate which is less than
the rate at which a portion of the mold structure engaged by the
streams 54 of coolant is cooled. The relatively low rate of cooling
of the, portion of the mold structure 12 below the streams 54 of
coolant tends to minimize any tendency for differential thermal
contraction of the casting in the mold structure.
[0032] In the embodiment of the invention illustrated in FIG. 1,
the streams 54 of coolant are streams of molten (liquid) metal. The
molten metal in the streams 54 of coolant is at a temperature below
1,000 degrees Fahrenheit. The molten super alloy in the mold
structure 12 is at a temperature above 3,000 degrees Fahrenheit.
Since there is a substantial temperature differential between the
molten metal in the mold structure 12 and the molten metal in the
stream 54 of coolant, there is a relatively high rate of heat
transfer from the mold structure 12 to the liquid metal in the
streams 54 of coolant. This results in relatively rapid cooling of
the area of the mold structure 12 against which the streams 54 of
coolant impinge. The portion of the mold structure 12 which is at a
lower level than the streams 54 of coolant is exposed to the body
28 of inert gas which has a thermal conductivity which is
substantially less than the thermal conductivity of the molten
metal in the streams 54. Therefore, there is a reduced rate of
cooling of the mold structure after it moves below the nozzles
56.
[0033] The positions of the nozzles 56 relative to the container 20
and furnace assembly 16 remains constant as the mold structure 12
is slowly lowered by operation of the upper drive assembly 44.
Therefore, solidification of the molten metal in the mold structure
12 is initiated at the level where the streams 54 of coolant
impinge against the mold structure. The solidified or at least
partially solidified metal in the portion of the mold structure 12
beneath the level of the nozzles 56 is exposed to the body of inert
gas 28. The portion of the body 28 of inert gas which is closely
adjacent to the mold structure 12 quickly heats to a relatively
high temperature. However, since the thermal conductivity of the
body 28 of inert gas is relatively low, compared to the thermal
conductivity of the molten metal in the streams 54 of coolant, the
rate of cooling the portion of the mold structure below the nozzles
56 is less than the rate of cooling of the portion of the mold
structure against which the streams 54 of coolant are directed.
[0034] Heating coils 80 extend around the lower portion of the
container 20 to maintain the body 70 of coolant in a molten or
liquid condition. Of course, heating coils may also be provided
around the upper portion of the container 20 if desired. Suitable
heating coils may also be provided in association with the conduits
74 and/or nozzles 56 to maintain the flow of molten metal through
the conduits and/or nozzles at a desired temperature.
[0035] In the embodiment of the invention illustrated in FIG. 1,
the streams 54 of coolant are formed of liquid, that is, molten
metal. In the embodiment of the invention illustrated in FIG. 2,
the streams of coolant are formed of particulate entrained in a
flow of inert gas. Since the embodiment of the invention
illustrated in FIG. 2 is generally similar to the embodiment of the
invention illustrated in FIG. 1, similar numerals will be utilized
to designate similar components, the suffix letter "a" being
associated with the numerals of FIG. 2 to avoid confusion.
[0036] A casting apparatus 10a includes a furnace assembly 16a
(FIG. 2) in which a mold structure 12a is preheated and filled with
molten metal. The mold structure 12a is disposed on a framework 36a
which includes a mold support structure 42a. The mold support
structure 42a is connected with an upper drive assembly 44a by
support rods 38a.
[0037] A housing 24a encloses the furnace assembly 16a and a
container 20a. The housing 24a is connected with a source of low
pressure (vacuum) by a conduit 26a. The housing 24a is connected
with a source of inert gas by a conduit 27a.
[0038] The housing 24a is evacuated by connecting the conduit 26a
with a source of low pressure (vacuum). A valve in the conduit 26a
is then closed and a valve in a conduit 27a opened to connect the
conduit with a source of inert gas. Although any one of many
different inert gases may be utilized, in the illustrated
embodiment of the invention, the housing 24a is filled with argon.
The container 20a holds a body 28a of the inert gas (argon).
[0039] In accordance with one of the features of the present
invention, a fluidized bed 70a is provided in the lower portion of
the container 20a. The fluidized bed contains particles suspended
in gas. In the embodiment of the invention illustrated in FIG. 2,
the particulate is alumina particles of 325 to 90 mesh size. The
alumina particles are suspended in the inert gas (argon) to form
the fluidized bed 70a.
[0040] To maintain the fluidized bed 70a, inert gas is conducted to
a cylindrical plenum chamber 90 through a conduit 92. The inert gas
flows from the plenum chamber 90 through a porous layer 96 into the
fluidized bed 70a to maintain the particulate suspended in the
fluidized bed. If desired, a stirrer assembly may be provided
adjacent to the upper side of the porous layer 96.
[0041] A flow of particulate suspended in inert gas is conducted
from the fluidized bed 70a through conduits 74a to nozzles 56a.
Streams 54a of particulate entrained in inert gas are directed by
the nozzles 56a against the mold structure 12. Pumps 72a are
provided to maintain the flow of inert gas with particulate
entrained therein from the fluidized bed 70a to the nozzles
56a.
[0042] In the embodiment of the invention illustrated in FIG. 2,
the pumps 72a are of the fluid ejector type. Of course, other types
of pumps may be used if desired. The pumps 72a are effective
aspirate a flow of particulate suspended in gas from the fluidized
bed to the conduits 74a. The pumps 72a are effective to force the
flow of inert gas with particulate entrained therein to flow upward
to the nozzles 56a and radially inward through the nozzles in the
streams 54a which are directed against the mold structure 12a.
[0043] Each of the pumps 72a include a convergent-divergent venture
nozzle or diffuser to which a flow of transport gas under pressure
is directed from a conduit 100. The manner in which the fluidized
bed is established and which the pumps 72a direct streams of
particulate entrained in inert gas is the same as is disclosed in
U.S. Pat. No. 6,695,034. The disclosure in the aforementioned U.S.
Pat. No. 6,695,034 is hereby incorporated herein in its entirety by
this reference thereto.
[0044] When articles are to be cast in the mold structure 12a, the
mold structure is heated to a desired temperature in the furnace
assembly 16a. Molten metal, which may be a nickel-chrome super
alloy is poured into the mold structure 12a while the mold
structure is in the furnace assembly 16a.
[0045] After the mold structure 12a has been filled with molten
metal, the upper drive assembly 44a is operated to lower the
framework 36a. As the framework 36a is lowered, a lower portion 66a
of the mold structure 12a moves into alignment with the streams 54a
of coolant. The streams 54a of coolant are, in the embodiment of
the invention illustrated in FIG. 2, particulate entrained in inert
gas. Since the particulate is entrained in the inert gas, the
streams 54 have a thermal conductivity which is greater than the
thermal conductivity of the inert gas by itself. As the streams 54a
of particulate entrained in inert gas are directed against the
lower portion 66a of the mold structure 12a, solidification of the
molten metal in the lower portion 66a of the mold structure 12 is
initiated.
[0046] As the upper drive assembly 44a continues to be operated to
slowly lower the framework 36a and mold structure 12a, the streams
54a of coolant, that is, of particulate entrained in inert gas, is
directed against portions of the mold disposed above the lower
portion 66a. As this occurs, solidification of the molten in
portions of the mold structure 12 above the lower portion 66a of
the mold structure is initiated.
Conclusion
[0047] In view of the foregoing description, it is apparent that
the present invention provides a new and improved method of casting
a metal article. A mold 12 is filled with molten metal while the
mold is disposed in a furnace assembly 16. The mold 12 is lowered
from the furnace assembly 16 into a body 28 of inert gas.
[0048] In accordance with one of the features of the present
invention, a stream 54 of coolant having a thermal conductivity
greater than the thermal conductivity of the inert gas, is directed
against a first portion 66 of the mold 12 to initiate
solidification of molten metal in the first portion of the mold.
The stream 54 is directed against portions of the mold 12 disposed
in the body 28 of gas and disposed above the first portion 66 of
the mold to initiate solidification of molten metal in portions of
the mold above the first portion of the mold.
[0049] The stream 54 which is directed against the mold 12 may be
formed of a molten metal. Alternatively, the stream 54 which is
directed against the mold 12 may be formed of an inert gas in which
particulate is entrained.
[0050] The present invention has a plurality of different features
which are advantageously utilized together in the manner described
herein. However, it is contemplated that the features may be
utilized separately and/or in combination with features from the
prior art.
* * * * *