U.S. patent application number 10/020490 was filed with the patent office on 2002-07-04 for reinforced ceramic shell mold and method of making same.
This patent application is currently assigned to Howmet Research Corporation. Invention is credited to Corrigan, John, Naik, Rajeev V..
Application Number | 20020084057 10/020490 |
Document ID | / |
Family ID | 25467774 |
Filed Date | 2002-07-04 |
United States Patent
Application |
20020084057 |
Kind Code |
A1 |
Naik, Rajeev V. ; et
al. |
July 4, 2002 |
Reinforced ceramic shell mold and method of making same
Abstract
A ceramic investment shell mold is reinforced with a carbon
based fibrous reinforcement having an extremely high tensile
strength that increases as the mold temperature is increased
especially within the range of casting temperatures employed for
casting large directionally solidified industrial gas turbine
components. The carbon based fibrous reinforcement is wrapped or
otherwise positioned around the repeating ceramic slurry/stucco
layers forming the intermediate thickness of the shell mold wall.
The reinforced shell mold can be used to cast large directionally
solidified industrial gas turbine components with accurate
dimensional control.
Inventors: |
Naik, Rajeev V.; (Yorktown,
VA) ; Corrigan, John; (Yorktown, VA) |
Correspondence
Address: |
Edward J. Timmer
Walnut Woods Centre
5955 W. Main Street
Kalamazoo
MI
49009
US
|
Assignee: |
Howmet Research Corporation
|
Family ID: |
25467774 |
Appl. No.: |
10/020490 |
Filed: |
October 30, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10020490 |
Oct 30, 2001 |
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08935846 |
Sep 23, 1997 |
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6364000 |
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Current U.S.
Class: |
164/516 ;
164/361; 164/411; 264/221; 264/225 |
Current CPC
Class: |
B22C 9/04 20130101; B22C
1/00 20130101; B22C 1/165 20130101; Y10T 29/49988 20150115 |
Class at
Publication: |
164/516 ;
264/225; 264/221; 164/361; 164/411 |
International
Class: |
B22C 009/04 |
Claims
We claim:
1. A ceramic investment shell mold having a mold wall reinforced
with a carbon based fibrous reinforcement having sufficent tensile
strength at casting temperature to reduce creep deformation of the
shell mold and having a coefficient of thermal expansion that is
less than the average coefficient of thermal expansion of shell
mold to provide compressive loading at casting temperature.
2. The mold of claim 1 wherein the carbon based fibrous
reinforcement is comprised of a plurality of carbon fibers or
filaments having a tensile strength of at least about 250,000 psi
at room temperature.
3. The mold of claim 2 wherein the carbon fibers or filaments have
a coefficient of thermal expansion that is about 1/4 the average
coefficient of thermal expansion of the shell mold at room
temperature.
4. The mold of claim 1 wherein the carbon based fibrous
reinforcement comprises carbon fiber cordage having a cordage
breaking strength of about 90 to about 165 pound force.
5. The mold of claim 4 wheren the carbon fiber cordage comprises
woven carbon fiber yarn.
6. The mold of claim 1 wherein the carbon based fibrous
reinforcement comprises woven or braided carbon fiber net-like
cloth.
7. The mold of claim 1 wherein the carbon based fibrous
reinforcement is disposed at the repeating ceramic slurry/stucco
layers forming the intermediate thickness of the shell mold
wall.
8. The mold of claim wherein the carbon based fibrous reinforcement
is disposed around the 6th to the 9th shell mold layers forming an
intermdiate thickness of the shell mold wall.
9. The mold of claim 1 wherein the carbon based fibrous
reinforcement is wrapped in a sprial configuration around the shell
mold with a space between successive wraps.
10. The mold of claim of 9 wherein the sprial carbon based fibrous
reinforcement has a space between successive wraps of said
reinforcement of about 0.2 to 1 inch.
11. In a method of making a ceramic investment shell mold by
coating a pattern having the desired shape of the cast component
with cermaic slurry and then ceramic stucco with the sequence
repeated to build up of a shell mold wall, the improvement for
increasing mold creep resistance at elevated casting temperature
comprising positioning in the mold wall a carbon based fibrous
reinforcement having a high tensile strength sufficient to reduce
creep deformation of the shell mold at the casting temperature and
having a coefficient of thermal expansion that is less than the
average coefficient of thermal expansion of shell mold to provide
compressive loading of the mold wall at the casting
temperature.
12. The method of claim 11 including positioning the carbon based
fibrous reinforcement at an intermediate mold wall thickness.
13. The method of claim 12 wherein the carbon based fibrous
reinforcement is positioned around 6th to the 9th shell mold layers
forming said intermdiate thickness of the shell mold wall.
14. The method of claim 12 wherein the carbon based fibrous
reinforcement is wrapped in a sprial configuration on the shell
mold intermediate thickness with a space between successive
wraps.
15. The method of claim of 14 wherein the sprial carbon based
fibrous reinforcement has a space between successive wraps of said
reinforcement of about 0.2 to 1 inch.
16. The method of claim 12 wherein the carbon based fibrous
reinforcement is comprised of carbon fibers or filaments having a
tensile strength of at least about 250,000 psi at room
temperature.
17. The methd of claim 16 wherein the carbon fibers or filaments
have a coefficient of thermal expansion that is about 1/4 the
average coefficient of thermal expansion of the shell mold at room
temperature.
18. The mold of claim 12 wherein the carbon based fibrous
reinforcement comprises carbon fiber cordage having a cordage
breaking strength of about 120 to about 165 pound force.
19. The method of claim 18 wheren the carbon fiber cordage
comprises woven carbon fiber yarn.
20. The method of claim 12 wherein the carbon based fibrous
reinforcement comprises woven or braided carbon fiber net-like
cloth.
21. A method of casting a large directionally solidified component
with dimensional control, comprising preheating a ceramic
investment shell mold having a mold wall reinforced with a carbon
based fibrous reinforcement to an elevated casting temperature of
about 2800 degrees F. and above, introducing molten metal into the
preheated shell mold, and directionally solidifying the molten
metal residing in the shell mold by propagating a soldification
front through the molten metal over an extended time to form a
columnar grain or single crystal microstructure.
22. The method of claim 21 wherein a molten nickel base or cobalt
superalloy is introduced into the shell mold.
23. The method of claim 21 wherein about 40 to 300 pounds of molten
metal are introduced into the mold.
24. The method of claim 21 wherein the molten metal is
directionally solidified over a time period of about 2 to about 6
hours.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a reinforced ceramic
investment casting shell mold especially useful in the casting of
large industrial gas turbine and aerospace components and a method
of making same such that the shell mold exhibits increased strength
and creep resistance at elevated casting temperatures to maintain
casting dimensional control.
BACKGROUND OF THE INVENTION
[0002] Ceramic investment shell molds are widely used in the
investment casting of superalloys and other metals/alloys to
produce gas turbine engine components, such as turbine blades, and
aerospace components, such as structural airframe components, to
near net shape where dimensional control of the casting is provided
by the shell mold cavity dimensions.
[0003] The need for industrial gas turbines (IGT's) with improved
operating performance has increased the demand for large IGT
components with directionally solidified (DS) microstructures, such
as columnar grain and single crystal cast microstructures. However,
production of DS components subjects the ceramic investment shell
mold to casting parameters, such as elevated temperature,
metallostatic pressure and time, beyond the capability of present
ceramic investment shell molds. In particular, present ceramic
investment shell molds are susceptible to bulging and cracking
during DS casting processes, especially when the shell mold is
filled with a large quantity of molten metal/alloy at higher
casting temperature and longer times needed, for example, to effect
directional soldification of the IGT components.
[0004] When the investment shell mold bulges or sags during the DS
casting process, dimensional control is lost and inaccurately
dimensioned cast components are produced. Moreover, a significant
cracking of the shell mold can occur and result in runout of molten
metal/alloy and a scrap casting.
[0005] The most common ceramic mold materials, such as alumina and
zirconia, used to produce ceramic shell molds exhibit creep
deformation at about 2700 degrees F. with the creep deformation
increasing with increasing temperature and hold time at
temperature. Hold times in excess of 3 hours and temperature in
excess of 2800 degrees F. are common in the casting of large
directionally solidified IGT components. These casting parameters
together with increased metallostatic pressure involved are severe
enough that conventional ceramic shell molds have not been suitable
for the casting of large directionally solidified IGT components.
In particular, use of conventional ceramic shell molds for the
casting of large directionally solidified IGT blades has resulted
in changes in the blade chord width or changes to blade bow and
displacment indicative of mold bulging or sagging during DS
casting.
[0006] Therefore, there is an acute need for more robust ceramic
shell molds that can withstand these severe casting parameters and
resist creep deformation, such as bulging and sagging, as well as
cracking to enable casting of large directionally solidified IGT
components with dimensional control.
[0007] Several attempts have been investigated to raise the
capability of ceramic shell molds manufactured using conventional
ceramic materials. For example, one attempt has involved use of
composite shell molds made of combinations of ceramic materials to
minmize grain growth and hence reduce creep deformation of the
mold. U.S. Reissue 34,702 describes another attempt wherein
alumina-based or mullite-based ceramic fibrous reinforcement is
wrapped about the mold. These techniques, although having further
pushed the limit of conventional shell molds, have been found not
to be sufficient to meet the stringent casting parameters imposed
in the casting of large directionally solidified IGT components
with dimensional control.
[0008] An object of the present invention is to provide a ceramic
investment shell mold reinforced in a manner to exhibit improved
resistance to creep deformation and cracking at elevated casting
temperatures, especially under the aforementioned severe casting
parameters demanded by casting of large directionally solidified
IGT components with dimensional control.
[0009] Another object of the present invention is to provide a
method of making a ceramic investment shell mold reinforced in a
manner to exhibit improved resistance to creep deformation and
cracking at elevated casting temperatures.
[0010] Still another object of the present invention is to provide
a method of casting large directionally solidified IGT components
with dimensional control.
SUMMARY OF THE INVENTION
[0011] To achieve the foregoing objects and in accordance with the
purpose of the invention, as embodied and broadly described herein,
a ceramic investment shell mold is reinforced with a carbon based
fibrous reinforcement having an extremely high tensile strength
sufficient to reduce creep deformation of the mold, such as bulging
or sagging, at high casting temperature, especially at temperatures
experienced during casting of large directionally solidified IGT
components. Preferably, the carbon based fibrous reinforcement is
made of carbon fibers or filaments having a tensile strength of at
least about 250,000 psi at room temperature (70 degrees F.) and a
coefficient of thermal expansion that is less than the average
coefficient of thermal expansion of shell mold to provide
compressive loading of the mold.
[0012] Carbon fiber cordage (comprising a large number of carbon
fibers or filaments) having a cordage breaking strength of 90 to
165 pound force, preferably 120 to 165 pound force, at room
temperature is especially preferred as the reinforcement.
[0013] The carbon based fibrous reinforcement preferably is
disposed at the ceramic slurry/stucco layers forming the
intermediate thickness of the shell mold wall. For example only,
the carbon based fibrous reinforcement can be disposed around the
6th to the 9th shell mold layers forming an intermediate thickness
of the shell mold wall.
[0014] In a method embodiment of the present invention, a pattern
having the desired shape of the cast component to be produced is
dipped in ceramic slurry and then stuccoed with relatively coarse
ceramic stucco with the sequence repeated to build up a shell mold
wall comprising repeating ceramic slurry/stucco layers on the
pattern. At intermediate ceramic slurry/stucco layers defining an
intermediate shell mold wall thickness, the carbon based fibrous
reinforcement is applied around the shell mold wall, preferably by
wrapping in a sprial configuration about the intermediate shell
mold wall, followed by continuation of the dipping and stuccoing
steps to build up the overall shell mold wall thickness over the
reinforcement. When used, the sprial wrapped carbon based fibrous
reinforcement can have a space between successive wraps of about
0.2 to 1 inch.
[0015] A carbon based woven or braided fiber cloth like
reinforcement can be used to reinforce regions of the shell mold
which render difficult or prohibit wrapping of the reinforement
around the shell mold.
[0016] A method of casting large directionally solidified IGT
components with dimensional control in accordance with an
embodiment of the present invention involves preheating a ceramic
investment shell mold reinforced as decribed above to an elevated
casting temperature above about 2800 degrees F. introducing molten
metal into the preheated shell mold, and directionally solidifying
the molten metal residing in the shell mold by propagating a
solidification front through the molten metal over an extended time
period to form a columnar grain or single crystal microstructure.
Large IGT components typically involve introduction of molten metal
in the range of about 40 to about 300 pounds molten metal into the
preheated shell mold and solidified over a time period of about 3
to about 6 hours therein.
[0017] The above objects and advantages of the present invention
will be better understood with reference to the following drawings
taken with the following detailed description.
DESCRPITION OF THE DRAWIGS
[0018] FIG. 1 is schematic side elevational view, partially broken
way, of a ceramic investment mold in accordance with an embodiment
of the invention reinforced with a carbon based fiber reinforcement
cordage wrapped thereon.
[0019] FIG. 2 is a graph showing the percent strength retention of
ceramic mold, Nextel 440 fiber, and carbon fiber as temperature
increases.
[0020] FIG. 3 is a perspective view of a ceramic investment mold in
accordance with another embodiment of the invention reinforced with
a carbon based fiber reinforcement cordage wrapped thereon.
DETAILED DESCRPITION OF THE INVENTION
[0021] Reference will now be made in detail to an illustrative
embodiment of the present invention especially useful for the
casting of large directionally solidified IGT components with
accurate dimensional control, although the present invention can be
practiced cast other myriad components using casting techniques
other than directional solidification.
[0022] A fugitive pattern having the shape of the desired cast
component to be made is provided. The pattern may be made of wax,
plastic, foam or other suitable pattern material for use in the
so-called "lost wax" process. The "lost wax" process is well known
and involves dipping the pattern into a ceramic slurry comprising
cermaic powders or flour in a binder to form a slurry layer on the
pattern, draining excess slurry, and then applying a stucco layer
of relatively coarse dry, ceramic stucco particles (e.g. 120 mesh
or coarser alumina particles). After drying the slurry/stucco
layers, the dipping/draining/stuccoing sequence is repeated to
build up the desired shell mold wall thickness. The initial slurry
coating or layer applied to the pattern forms a so-called facecoat
that contacts the molten metal and comprises a highly refractory
ceramic material and a binder. To this end, the ceramic slurry may
be comprised of silcia, alumina, zirconia or other suitable ceramic
powders or flours in a suitable binder (e.g. colloidal silica)
depending upon the metal to be cast in the shell mold.
[0023] In practicing an illustrative embodiment of the invention,
the dipping/stuccoing steps typically are repeated over the
facecoat to build up an intermediate thickness of the shell mold
wall that is less the final overall mold wall thickness. The
intermediate wall thickness used can be varied depending upon the
final mold wall thickness desired. Typically, the intermediate
shell mold thickness can be built up by repeating the dipping step
and stuccoing step 6 to 9 times. Any sharp edges and corners formed
on the shell mold are rounded at the intermediate stage of the
shell build up.
[0024] In accordance with an embodiment of the invention, a carbon
based fibrous reinforcement 12 is disposed around the intermediate
shell mold thickness of the shell mold at a region requiring
reinforcement. For example, in FIG. 1, the reinforcement 12 is
disposed around the intermediate shell mold thickness at an airfoil
tip region R1 of the mold 11 for making a large industrial gas
turbine blade. The airfoil tip region of the shell mold 11 is
connected to a mold base B that in turn rests on a chill plate (not
shown) of DS casting apparatus as is well known. The reinforcement
12 can be disposed around the entire shell mold or a region thereof
requiring reinforcement. The carbon based fibrous reinforcement has
an extremely high tensile strength that increases with mold
temperature in the range of DS casting temperatures where
conventional ceramic materials are weak and further has a
coefficient of thermal expansion that is less than the average
coefficient of thermal expansion of shell mold to provide
compressive loading of the mold wall at casting temperature. The
average coefficient of thermal expansion of shell mold is based on
the coefficients of thermal expansion of the ceramic materials
comprising the ceramic slurry powders and the ceramic stucco.
[0025] The carbon based fibrous reinforcement 12 preferably
comprises a pan-based material from polyacrylonitrile, rather than
a pitch-based material from tar-based material. To this end, the
reinforcement 12 preferably comprises pan-based carbon fibers or
filaments having a tensile strength of at least about 250,000 psi
at room temperature and a coefficient of thermal expansion at 2700
degrees F. that is about 1/4 the average coefficient of thermal
expansion of the shell mold. Such carbon fibers and filaments are
available commercially form Amoco Coporation, Greenville, S.C., and
Hecules Corporation, Wilmington, Del. The carbon based fibrous
reinforcement typically will have a continuous length sufficient to
be wound or wrapped around the intermediate shell mold wall
thickness as needed, for example, as illustrated in FIG. 1 for an
IGT airfoil.
[0026] A preferred elongated carbon based fibrous reinforcement
comprises carbon fiber cordage having a cordage breaking strength
of 90 to 165 pound force, preferably 120 to 165 pound force. Such
carbon fiber cordage typically comprises from 12,000 to 24,000
braided fibers or filaments forming the cordage. Twisted fiber
cordage is advantageous in terms of convenience of handling and
winding around the intermediate mold wall thickness. The fibers or
filaments typically will have individual diameters in the range of
10 microns to 20 microns.
[0027] The breaking strength of the carbon fiber cordage will
depend on its overall diameter which, in turn, depends on the
number of carbon fibers or filaments in the cordage as well as
individual fiber diameters. A representative breaking strength of a
carbon fiber cordage having a diameter of 0.034 inch and containing
12,000 filaments of 12 microns diameter is about 90 pound-force,
whereas that for a 0.072 inch diameter cordage containing 24,000
filaments of the same diameter is about 165 pound-force. Carbon
fiber cordage of this type is available commercially from Fiber
Materials Inc., Biddeford, Me.
[0028] FIG. 2 illustrates the percent retention of room temperature
tensile strength at elevated temperatures for a carbon reinforcing
fiber of the polyacrylonitrile type useful in practicing the
invention, Nextel 440 mullite based ceramic fibers, and ceramic
(alumina-based slurry/stucco layers) shell mold material.
[0029] Unlike the other materials shown in FIG. 2, the carbon
reinforcing fiber does not lose its tensile strength with
increasing temperatures in the range of typical casting temperature
2750 to 2850 degrees F. for DS casting processes. The carbon
reinforcing fiber increases in tensile strength with increasing
temperature in the DS casting tempreature range of 2750 to 2850
degrees F. and, more generally, from 2500 up to 4000 degrees F.
[0030] Although a Nextel 440 reinforced shell mold pursuant to U.S.
Reissue 34,702 functions relatively well up to temperatures of 2750
degrees F. as long as hold time is short (e.g. 2 hours) and the
metallostatic pressure is low, an increase in casting temperature
beyond 2800 degrees F. results in the Nextel 440 fiber reinforced
shell mold exhibiting creep deformation because of the softening of
the Nextel fibers illustrated in FIG. 2.
[0031] A carbon fibrous reinforced shell mold pursuant of the
present invention will reduce or avoid such creep as a result of
the increasing tensile strength and creep resistance of the carbon
fibers with temperature illustrated in FIG. 2. Such increased
tensile strength and creep resistance of the shell mold is needed
for the large ceramic shell molds used for casting large
directionally solidified IGT components with dimensional
accuracy.
[0032] The reinforcement 12 is disposed around the intermediate
shell mold thickness with sufficient tension that it remains fixed
during subsequent handling, dipping and stuccoing required to build
up the shell mold to its overall thickness. If desired, ceramic
adhesive or dip coat may be used to locally fasten the free ends
and intermediate sections of the fibrous reinforcement to the shell
mold for convenience in handling.
[0033] The reinforcement 12 typically is wrapped in a substantially
continuous sprial configuration around the intermediate thickness
of the shell mold with a space 13 between successive wraps or
spirals. The space between successive sprial wraps is provided to
allow for adequate shell build up around the reinforcement 12 to
structurally join the reinforcement to the shell mold. The space
between successive spiral wraps of the reinforcement 12 can be
about 0.2 to 1 inch to this end for carbon fiber reinforcement
12.
[0034] After the reinforcement 12 is disposed around the
intermediate mold wall thickness, the remaining ceramic slurry and
stucco layers are applied to build up the mold wall W to the final
overall thickness desired. The green shell mold then is dried,
subjected to a pattern removal operation, such as conventional
dewaxing operation for a wax pattern, and conventionally fired at
elevated temperature (e.g. 1800 degrees F.) to develop adequate
mold strength for casting.
[0035] Altenately, a carbon based fiber loosely woven or braided
fiber fabric or cloth 14 can be used to locally reinforce regions
of the shell mold which are not amenable to spiral wrapping of the
reinforcement 12. For example, in FIG. 1, a loosely woven or
braided carbon fiber cloth 14 is positioned around a region R2 of
the intermediate mold wall thickness defining a platform of the
shell mold 11 for making a large industrial gas turbine blade.
[0036] In lieu of the sprial wrap described above, the
reinforcement can be applied about the mold in other patterns, for
example only, as shown in FIG. 3 where the reinforcement 12' is
crisscrossed about an airfoil region R1' of a mold having enlarged
platform type end regions R2'.
[0037] The invention can be practiced to provide virtually any
reinforced ceramic investment shell mold, and is especially useful
and advantageous for reinforced ceramic investment shell molds for
casting large directionally solidified IGT components (e.g. about
40 to about 300 pounds per casting) with accurate dimensional
control as a result of the reduction, or elimination, of creep
deformation, such as mold bulging or sagging, under DS
solidification processing conditions. DS solidification processing
can be effected by the well known mold withdrawal technique where
the shell mold residing on chill plate in a casting furnace is
preheated to a selected elevated casting temperature, melt is
introduced into the preheated mold, and the melt-filled mold
residing on the chill plate is gradually withdrawn from a casting
furnace over an extended time period to form a columnar grain or
single crystal microstrucutre in the casting. The well known power
down technique as well as other DS casting techniques that
establish undirectional heat removal from the molten metal in the
shell mold also may be used.
[0038] As a result of the carbon fibrous reinforcement having a
coefficent of thermal expansion less than the average coefficient
of thermal expansion of the ceramic materials comprising the shell
mold, the reinforcement 12 imparts a compressive load on the
regions of the shell mold on which it is disposed. This compressive
load serves to increase the green (unfired) strength, fired
strength, and hot casting strength of the shell mold. The
compressive load exerted by the reinforcement increases with
increasing temperature and helps in minimizing the growth and
expansion of any cracks that may have formed by prior dewaxing
operations.
[0039] The following Examples are offered for purposes of
illustrating the invention and not limiting it.
EXAMPLE 1
[0040] A 16 inch long and 10 inch wide single crystal shell mold
was spirally wound with carbon cordage reinforcement at the 7th
slurry dip coat or layer. The mold cavity was shaped to make a gas
turbine vane. The carbon cordage was available from Fiber
Materials, Inc. and had a diameter of 0.075 inch and 24,000 carbon
filaments of individual filament diameter of 12 microns. A total of
7 turns of the cordage were made around the shell mold intermediate
wall thickness in spiral fashion as illustrated in FIG. 1 with a
space between successive spiral wraps of 1/2 inch. After the
reinforcement was wrapped, the shell mold was further dipped and
stuccoed to apply 7 additional layers to bring the shell mold wall
thickness to a final wall thickness of 1/2 inch. The ceramic slurry
for the dip coats comprised alumina slurry, while the ceramic
stucco comprised alumina stucco.
[0041] A total of 5 such shell molds were made. Each mold was
preheated to 2800 degrees F. and cast with 45 pounds of N5 nickel
base superalloy, at a melt temperature of 2820 degrees F. followed
by directional soildification using the well known mold withdrawal
techique for a period of 4 hours to propagate a soldification front
through the molten alloy and form a single crystal casting in the
shell molds. The shell molds held the molten metal and produced
dimensionally acceptable castings.
EXAMPLE 2
[0042] A 20 inch long and 6 inch wide IGT blade shell mold was
spirally wound with carbon cordage reinforcement at the 8th dip
slurry coat or layer. The carbon cordage was available from Fiber
Materials, Inc. and had a dimaeter of 0.075 inch and 24,000 carbon
filaments of individual filament diameter of 12 microns. A total of
8 turns of the cordage were made around the shell mold intermdiate
wall in spiral fashion as illustrated in FIG. 1 with a space
between successive spiral wraps of 5/8 inch. After the
reinforcement was wrapped, the shell mold was further dipped and
stuccoed to apply 7 additional layers to bring the shell mold wall
thickness to a final wall thickness of 1/2 inch. The ceramic slurry
for the dip coats comprised alumina slurry, while the ceramic
stucco comprised alumina stucco.
[0043] The shell mold was preheated to 2750 degrees F. and cast
with 40 pounds of GTD 111 nickel base superalloy at a melt
temperature of 2750 degrees F. followed by directional
solidification using the well known mold withdrawal technique for 4
hours to propagate a soldification front through the molten alloy
and form a single crystal casting. The shell mold held the molten
metal without mold leakage. The blade casting was dimensionally
evaluated and found to be acceptable to blue print specifications
and showed no increase in the blade chord width or changes to blade
bow and displacment, indicating the absence of mold bulging or
sagging.
[0044] Although the present invention has been described in terms
of illustrative embodiments thereof, it is not intended to be
limited thereto but rather only as set forth in the appended
claims.
* * * * *