U.S. patent application number 10/671193 was filed with the patent office on 2004-04-01 for gas distributor for vapor coating method and container.
Invention is credited to Brown, Terri K., Cove, Edward J., Schmidt, Richard L., Wheat, Gary E..
Application Number | 20040062865 10/671193 |
Document ID | / |
Family ID | 21848374 |
Filed Date | 2004-04-01 |
United States Patent
Application |
20040062865 |
Kind Code |
A1 |
Wheat, Gary E. ; et
al. |
April 1, 2004 |
Gas distributor for vapor coating method and container
Abstract
A gas distributor suitable for introducing a carrier gas at the
top of a coating container used to provide a metallic coating on
articles. The gas distributor includes a gas inlet and a gas outlet
head in communication with the gas inlet for receiving a flow of
gas from the gas inlet. A plurality of gas outlets through which
the gas flow exits as a gas stream are spaced along the peripheral
surface of the gas outlet head. A plurality of gas deflectors, each
proximate to one of the gas outlets, at least initially direct the
gas stream exiting the gas outlet in at least a generally
centripetal path. This gas distributor can be used in vapor coating
apparatus having a coating container, at least one holder for each
article to be coated positioned within the coating container and
below the gas outlet head of the gas distributor and at least one
holder for the source of the metallic coating positioned within the
coating container and below the gas outlet head of the gas
distributor. A method is also provided for introducing the carrier
gas as a plurality of carrier gas streams proximate the top of the
coating container so that each carrier gas stream flows at least
initially in at least a generally centripetal path, as well as a
method for coating the articles with a metallic coating in the
coating container.
Inventors: |
Wheat, Gary E.;
(Madisonville, KY) ; Brown, Terri K.; (Central
City, KY) ; Schmidt, Richard L.; (Marblehead, MA)
; Cove, Edward J.; (Middleton, MA) |
Correspondence
Address: |
HASSE GUTTAG & NESBITT LLC
7550 CENTRAL PARK BLVD.
MASON
OH
45040
US
|
Family ID: |
21848374 |
Appl. No.: |
10/671193 |
Filed: |
September 25, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10671193 |
Sep 25, 2003 |
|
|
|
10029311 |
Dec 20, 2001 |
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Current U.S.
Class: |
427/252 ;
118/715; 427/253 |
Current CPC
Class: |
C23C 16/455 20130101;
C23C 16/12 20130101; C23C 16/45563 20130101; C23C 16/45508
20130101; C23C 10/06 20130101; C23C 16/45591 20130101; C23C 16/4488
20130101 |
Class at
Publication: |
427/252 ;
427/253; 118/715 |
International
Class: |
C23C 016/06 |
Claims
What is claimed is:
1. A gas distributor, which comprises: (a) a gas inlet; (b) a gas
outlet head in communication with the gas inlet for receiving a
flow of gas from the gas inlet and having a peripheral surface; (c)
a plurality of gas outlets spaced along the peripheral surface, the
gas flow exiting as a gas stream from each gas outlet; (d) a
plurality of gas deflectors, each deflector being proximate to one
of the gas outlets and at least initially directing the gas stream
exiting each gas outlet in at least a generally centripetal
path.
2. The distributor of claim 1 wherein each deflector is an angular
deflector comprising an aft component having a generally forward
deflecting surface and an upper component having a generally
downward deflecting surface such that the gas stream exiting each
gas outlet is directed by each deflector into a curved generally
centripetal, downward path.
3. The distributor of claim 2 wherein each deflector has an open
generally trapezoidal shape.
4. The distributor of claim 3 wherein the aft component has a
generally triangular shape and wherein the upper component has a
generally triangular shape and wherein the forward deflecting
surface and the downward deflecting surface intersect at an
edge.
5. The distributor of claim 1 wherein the gas outlet head is
generally cylindrical and wherein the peripheral surface is
generally circular.
6. The distributor of claim 5 wherein the gas outlets are in the
form of holes spaced along the peripheral surface and wherein the
number of holes is at least 4.
7. The distributor of claim 6 wherein the number of holes is in the
range of from 4 to 20.
8. The distributor of claim 7 wherein the number of holes is in the
range from 6 to 12.
9. An apparatus for vapor coating of articles with a metallic
coating, which comprises: (1) a coating container having a base, a
top spaced from the base, and a side wall connecting the top and
the base; (2) a gas distributor comprising: (a) a gas inlet; (b) a
gas outlet head in communication with the gas inlet for receiving a
flow of gas from the gas inlet and having a peripheral surface; (c)
a plurality of gas outlets spaced along the peripheral surface, the
gas flow exiting as a gas stream from each gas outlet; (d) a
plurality of gas deflectors, each deflector being proximate to one
of the gas outlets and at least initially directing the gas stream
exiting the gas outlet in at least a generally centripetal path (3)
at least one holder for each article to be coated positioned within
the coating container and below the gas outlet head of the gas
distributor; (4) at least one holder for a source of the metallic
coating positioned within the coating container and below the gas
outlet head of the gas distributor.
10. The apparatus of claim 9 wherein the container and the side
wall are generally cylindrical.
11. The apparatus of claim 10 wherein each deflector is an angular
deflector comprising an aft component having a generally forward
deflecting surface and an upper component having a generally
downward deflecting surface such that the gas stream exiting each
gas outlet is directed by each deflector into a curved generally
centripetal, downward path.
12. The apparatus of claim 11 wherein each deflector has an open
generally trapezoidal shape.
13. The apparatus of claim 12 wherein the aft component has a
generally triangular shape and wherein the upper component has a
generally triangular shape and wherein the forward deflecting
surface and the downward deflecting surface intersect at an
edge.
14. The apparatus of claim 13 wherein the gas outlet head is
generally cylindrical and wherein the peripheral surface is
generally circular.
15. The apparatus of claim 13 wherein the gas outlets are in the
form of holes spaced along the peripheral surface and wherein the
number of holes is in the range from 4 to 20.
16. A method for introducing an inert carrier gas into a coating
container for vapor coating of articles with a metallic coating,
the container having a base, a top spaced from the base, and a side
wall connecting the top and the base, the method comprising the
step of introducing the carrier gas as a plurality of carrier gas
streams proximate the top of the coating container, each carrier
gas stream flowing at least initially in at least a generally
centripetal path.
17. The method of claim 16 wherein each carrier gas stream is
flowing at least initially in a curved generally centripetal,
downward path.
18. The method of claim 17 wherein the carrier gas is introduced at
a gas flow rate of at least about 15 ft.sup.3/hour (about 425
liters.sup.3/hour).
19. The method of claim 18 wherein the gas flow rate is in the
range of from about 15 to about 120 ft.sup.3/hour (from about 425
to about 3,398 liters.sup.3/hour).
20. The method of claim 19 wherein the gas flow rate is in the
range of from about 40 to about 70 ft.sup.3/hour (from about 1133
to about 1982 liters.sup.3/hour).
21. The method of claim 18 wherein the carrier gas is argon.
22. A method for coating articles with a metallic coating in a
vapor coating container having a base, a top spaced from the base,
and a side wall connecting the top and the base, the base, top and
side wall defining a coating chamber, the method comprising the
steps of: (a) loading the coating chamber of the container with
articles to be coated; (b) loading the coating chamber of the
container with a source of a metallic coating; (c) introducing an
inert carrier gas as a plurality of inert carrier gas streams
proximate the top of the loaded coating container, each carrier gas
stream flowing at least initially in a curved generally
centripetal, downward path to provide an inert gas atmosphere in
the coating chamber of the loaded container; (d) after the inert
gas atmosphere is provided in the coating chamber of the loaded
container, heating the loaded container to a temperature sufficient
to form a metallic coating gas from the metallic coating source;
(e) continuing the flow of the carrier gas into the coating chamber
of the loaded container to move the metallic coating gas within the
coating chamber of the loaded container so as to deposit a coating
on the articles.
23. The method of claim 22 wherein the articles are airfoil turbine
blades, wherein the metallic coating source is an aluminum source
and wherein the metallic coating gas is an aluminide-bearing
gas.
24. The method of claim 23 which comprises the further step of
loading the coating chamber of the container with a halide
activator prior to step (d) and wherein the halide activator forms
a reactive halide gas after heating during step (d) that reacts
with the aluminum source to form the aluminide-bearing gas.
25. The method of claim 23 wherein the halide activator is selected
from the group consisting of aluminum chloride, aluminum fluoride,
ammonium fluoride and mixtures thereof.
26. The method of claim 24 wherein the carrier gas is introduced
during step (e) into the coating chamber of the loaded container at
a gas flow rate of at least about 15 ft.sup.3/hour (about 425
liters.sup.3/hour).
27. The method of claim 26 wherein the gas flow rate during step
(e) is in the range of from about 15 to about 120 ft.sup.3/hour
(from about 425 to about 3,398 liters.sup.3/hour).
28. The method of claim 27 wherein the gas flow rate during step
(e) is in the range of from about 40 to about 70 ft.sup.3/hour
(from about 1133 to about 1982 liters.sup.3/hour).
29. The method of claim 26 wherein the carrier gas is argon.
30. The method of claim 26 wherein the loaded container is heated
during step (c) to a temperature of at least about 1000.degree. F.
(about 538.degree. C.).
31. The method of claim 30 wherein the loaded container is heated
during step (c) to a temperature in the range from about
1000.degree. to about 2200.degree. F. (from about 538.degree. to
about 1204.degree. C.) 32. The method of claim 31 wherein the
loaded container is heated during step (c) to a temperature in the
range of from about 1900.degree. to about 2000.degree. F. (from
about 1038.degree. to about 1093.degree. C.).
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates generally to a gas distributor
useful for a vapor coating method and container. The present
invention particularly relates to a gas distributor for introducing
nonoxidizing or inert carrier gases for vapor coating of articles
such as gas turbine engine blades with a metallic coating,
especially an aluminide coating.
[0002] Certain articles operating at elevated temperatures in an
oxidizing atmosphere have been provided with environmental
protection in the form of coatings of various types. For example,
components such as gas turbine engine turbine blades, vanes and
other airfoils operating at high temperatures typically experienced
in the turbine section of the engine frequently include metallic
surface coatings alone or in various combinations with other
materials. Such coatings are capable of resisting the oxidation,
corrosion and sulfidation conditions generated during high
temperature operation.
[0003] Application methods for such metallic coatings include
depositing a vapor of one or more protective metals, for example
aluminum or alloys of aluminum, to provide a form of aluminide
coating, on an article surface at high temperatures. Such vapor
coating methods are typically conducted in a nonoxidizing or inert
atmosphere (e.g. hydrogen, nitrogen, helium or argon) within a
coating container or chamber commonly referred to as a "retort".
Generally, the article or more typically articles(e.g., airfoils
such as turbine blades) to be coated are placed within the
container, along with a source of the aluminide coating, typically
in the form of metallic pellets or powder, and is often retained in
perforated baskets that can be arranged in rows to surround the
articles. The container is then placed within a heater such as a
furnace to generate a coating vapor. Generation of the coating
vapor typically includes the use of halide "activators" such as
fluorides, chlorides or bromides. This halide activator can be in
the form of a gas that is introduced into the container to react
with the source of the aluminide coating to form the
aluminide-bearing gas or can be generated from a halide activator
source within the container that forms the reactive halide gas upon
heating.
[0004] The aluminide-bearing gas is typically transported or moved
within the coating container by a nonoxidizing or inert carrier gas
(e.g., hydrogen, nitrogen, helium or argon). In some vapor coating
systems, this carrier gas is introduced through the bottom of the
container and carries the aluminide-bearing gas upwardly to coat
the articles. See, for example, U.S. Pat. No. 4,148,275 (Benden et
al), issued Apr. 10, 1979; U.S. Pat. No. 5,928,725 (Howard et al),
issued Jul. 27, 1999. In other vapor coating systems, the carrier
gas is introduced through the top of the coating container and then
diffuses throughout the container to carry the aluminide-bearing
gas and coat the articles. See U.S. Pat. No. 6,039,810 (Mantkowski
et al), issued Mar. 21, 2000. The advantage in introducing a
carrier gas, such as argon, at the top (versus the bottom) of the
container is that argon, being denser and heavier than air, will
naturally flow downwardly through the container to commingle with
the metallic (aluminide) coating vapor and will also act as a
"plunger" to aid in the internal coating of the articles.
[0005] In one such system where the carrier gas is introduced
through the top of the container, a gas distributor is used to
disperse the carrier gas. One such gas distributor has a
configuration similar to that of a "shower head" in that it is
provided with a plurality of gas outlet holes spaced along the
periphery of the cylindrical or disk-shaped head through which the
carrier gas exits. This "shower head" distributor is typically
positioned at the top of the container and above the aluminide
generating pellets and articles to be coated.
[0006] It has been found that when a carrier gas such as argon is
introduced through such a "shower head" distributor at the top of
the container, the aluminide-bearing gas is not consistently moved
or mixed within the coating container. This is particularly true as
the argon gas moves and diffuses through the rows of aluminide
generating pellets and through the rows of articles (e.g.,
airfoils) to be coated. Because the rows of pellets and articles
impede or resist the gas flow, regions having varying densities of
aluminide-bearing gas can be formed, thus creating a nonhomogeneous
environment of the aluminide-bearing gas surrounding the articles
to be coated. This nonhomogeneous environment of the
aluminide-bearing gas usually results in an inconsistent
distribution of the aluminide coating on the exterior of the
article, as well as inconsistent internal gas flow and coating of
the interior surface of the article (e.g. hollow airfoils such as
hollow gas turbine blades).
[0007] Accordingly, it would be desirable to be able to provide a
gas distributor that can introduce the carrier gas in a manner such
that the aluminide-bearing gas is consistently moved and mixed
within the coating container such that a more uniform and
consistent aluminide coating is provided on the exterior of the
articles, as well as on the interior of hollow articles.
SUMMARY OF THE INVENTION
[0008] The present invention relates to a gas distributor suitable
for introducing a carrier gas at the top of a coating container
used to provide a metallic coating on articles. This gas
distributor comprises:
[0009] (a) a gas inlet;
[0010] (b) a gas outlet head in communication with the gas inlet
for receiving a flow of gas from the gas inlet and having a
peripheral surface;
[0011] (c) a plurality of gas outlets spaced along the peripheral
surface, the gas flow exiting as a gas stream from each gas
outlet;
[0012] (d) a plurality of gas deflectors, each deflector being
proximate to one of the gas outlets and at least initially
directing the gas stream exiting each gas outlet in at least a
generally centripetal path.
[0013] The present invention also relates to an apparatus for vapor
coating of articles with a metallic coating. This apparatus
comprises;
[0014] (1) a coating container having a base, a top spaced from the
base, and a side wall connecting the top and the base;
[0015] (2) the gas distributor previously described for introducing
a carrier gas into the coating container positioned such that the
gas outlet head is proximate the top of the coating container;
[0016] (3) at least one holder for each article to be coated
positioned within the coating container and below the gas outlet
head of the gas distributor;
[0017] (4) at least one holder for the source of the metallic
coating positioned within the coating container and below the gas
outlet head of the gas distributor.
[0018] The present invention also relates to a method for
introducing the carrier gas into the coating container for vapor
coating of articles with a metallic coating. This method comprises
the step of introducing the carrier gas as a plurality of carrier
gas streams proximate the top of the coating container, each
carrier gas stream flowing at least initially in at least a
generally centripetal path.
[0019] The present invention further relates to a method for
coating the articles with a metallic coating in the coating
container. This method comprises the steps of:
[0020] (a) loading the coating chamber of the container with
articles to be coated;
[0021] (b) loading the coating chamber of the container with a
source of a metallic coating;
[0022] (c) introducing an inert carrier gas as a plurality of inert
carrier gas streams proximate the top of the coating chamber of the
loaded coating container, each carrier gas stream flowing at least
initially in a curved generally centripetal, downward path to
provide an inert gas atmosphere in the coating chamber of the
loaded container;
[0023] (d) after the inert gas atmosphere is provided in the
coating chamber, heating the loaded coating container to a
temperature sufficient to form a metallic coating gas from the
metallic coating source;
[0024] (e) continuing the flow of the carrier gas into the coating
chamber of the loaded container to move the metallic coating gas
within the coating chamber of the loaded container so as to deposit
a coating on the articles.
[0025] The gas distributor and vapor coating apparatus, as well as
the method for introducing the carrier gas, and method for coating
the articles, of the present invention provides a number of
significant benefits, especially when introducing the carrier gas
at or proximate the top of a coating container for vapor coating of
articles with a metallic coating. Because the carrier gas (e.g.,
argon) is introduced into the top of the coating container at least
initially in at least a generally centripetal path, this carrier
gas tends to move in circular or swirling fashion and thus keeps
the environment above the articles to be coated more uniform and
homogeneous. As a result, the environment of the metallic coating
(e.g., aluminide)-bearing gas surrounding the articles tends to be
more uniform and homogeneous, thus leading to a more uniform
metallic coating on the exterior surface of the articles. In
addition, in the case of hollow articles, such as airfoils, there
will be a more uniform distribution of gas flow internally,
resulting in a more uniform metallic coating on the interior
surface of the articles.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is perspective view of an embodiment of the gas
distributor of the present invention is useful.
[0027] FIG. 2 is bottom view of the distributor of FIG. 1
[0028] FIG. 3 is sectional side view of an embodiment of a vapor
coating apparatus using the distributor of FIG. 1.
[0029] FIG. 4 is a sectional view taken along line 4-4 of FIG.
3.
DETAILED DESCRIPTION OF THE INVENTION
[0030] Referring to the drawings, FIGS. 1 and 2 show an embodiment
of the gas distributor indicated generally as 10. Distributor 10
comprises a generally cylindrical hollow gas inlet tube or pipe 14
for receiving the gas from a source of supply (not shown) and a
generally cylindrical or disk-shaped gas outlet head or manifold
indicated as 18 connected to pipe 14. As shown in FIG. 1, pipe 14
is provided with a hole indicated as 20 for securing the source of
the gas to pipe 14. Although not shown, manifold 18 is also hollow
so that as gas is fed into pipe 14, this gas is then delivered to
manifold 18, i.e., pipe 14 is in fluid communication with manifold
18.
[0031] Referring especially to FIG. 1, manifold 18 comprises a
bottom surface indicated as 22 and is shown as having a generally
circular peripheral surface indicated as 26. However, peripheral
surface 26 can have other shapes or configurations, including
polygonal shapes or configurations (e.g., hexagonal, octagonal,
decagonal, dodecagonal, etc.) A plurality of gas outlets in the
form of apertures or holes 30 are formed in and spaced along
peripheral surface 26. The number of holes 30 can vary depending on
the size of the holes and the size of peripheral surface 26.
Usually, the number of holes 30 along peripheral surface 26 is at
least 4, and is typically in the range of from 4 to 20, and more
typically in the range of from 6 to 12.
[0032] Proximate each of the holes 30 is an angular gas baffle or
deflector 34 which is shown in FIG. 1 as having an open generally
trapezoidal or "hooded" configuration or shape. However, deflectors
34 can also be formed to have other configurations or shapes (e.g.,
rounded). Each deflector 34 is shown as comprising a generally
triangular aft deflector component 36 having a generally forward
deflecting inner surface 38 and a generally triangular upper
deflector component 40 having a generally downward deflecting inner
surface 42. Surfaces 38 and 42 of components 36 and 40 intersect
along a seam or edge 46. As shown in FIG. 1, as the gas flow or
stream exits each hole 30, it is at least initially deflected by
inner surface of 38 (of component 36) into a generally centripetal
path (i.e., along or parallel to surface 26) and by inner surface
42 (of components 40) into a slightly downward path (i.e.,
eventually away from bottom surface 22). As a result, the gas
stream exiting from holes 30 moves into a curved generally
centripetal, slightly downward path, as indicated by arrows 50.
[0033] As shown in FIG. 3, gas distributor 10 is typically used
with a vapor coating apparatus indicated generally as 100 that
includes a generally cylindrical coating container indicated as
110. As shown in FIG. 3, distributor 10 (including pipe and
manifold 18) is sized to fit within container 110. Container 110
has a top or lid indicated as 114, a base indicated as 118 spaced
from lid 114, and a generally cylindrical circumferential side wall
indicated as 122 that connects lid 110 and base 118 and extends
downwardly beyond base 118. Lid 114, base 118 and side wall 122 of
container 110 define an interior coating chamber indicated as 124.
As also shown in FIG. 3, pipe 14 of distributor 10 is inserted
partially through a hole or aperture 126 at or proximate the center
of lid 114; manifold 18 is positioned within chamber 124 at or
proximate the top thereof, i.e., proximate lid 114.
[0034] Apparatus 100 also has an article support or holder 128
attached to or otherwise associated with base 118 of container 110
that is provided with apertures, typically in the form of slots
(not shown) or other suitable devices, for receiving and holding
articles such as airfoils (e.g., turbine blades) 132 to be coated.
Apparatus 100 also has holders in the form of perforated baskets
indicated as 140 positioned within container 110 for receiving or
holding pellets of the metallic coating. As shown in FIG. 3,
baskets 140 and articles 132 are below manifold 18 of distributor
10. The number and spacing of baskets 140 and articles 132 can be
varied depending upon the internal dimensions and configuration of
container 110, the size of articles 132 to be coated and like
factors known to those skilled in the art. A representative
arrangement is shown in FIG. 4, where articles 132 and baskets 140
are arranged in alternating concentric rows or circles. The spacing
of the rows of articles 132 and baskets 140 should be such as to
allow the free flow of gas therebetween. Between each row of
articles 132 and baskets 140 is typically placed discrete portions
of a powdered halide activator indicated generally as 146. This
powdered halide activator is typically placed so as not to touch or
be in contact with articles 132 or baskets 140.
[0035] In order to coat hollow articles 132 (e.g., airfoils such as
turbine blades), having internal surfaces and passageways in
predetermined locations with the aluminide coating, it may be
necessary to mask those areas not requiring any coating. After
loading holder 128 with the articles 132, the container 110 and its
contents, which also contains a metallic coating source (e.g.,
aluminum pellets) loaded into baskets 140, is sealed and then
loaded into a furnace or other heating device. Gas inlet pipe 14 is
then connected to as source of a nonoxidizing or inert carrier gas
such as hydrogen, nitrogen, helium, or argon.
[0036] After loading the container 110 into a furnace or other
heating device, interior chamber 124 is purged of air by
introducing the nonoxidizing or inert carrier gas through gas inlet
pipe 14 which then flows into manifold 18 and exits through gas
outlets 30 as gas streams 50 so as to provide an inert gas
atmosphere. The rate at which the carrier gas flows into pipe 14
(and out of holes 30 as gas streams 50) of manifold 18 is usually
at least about 15 ft.sup.3/hour (about 425 liters.sup.3/hour), and
is typically in the range of from about 15 to about 120
ft.sup.3/hour (from about 425 to about 3,398 liters.sup.3/hour),
and more typically from about 40 to about 70 ft.sup.3/hour (from
about 1133 to about 1982 liters.sup.3/hour). As the gas exits
outlets 30, each of gas streams 50 are directed by deflectors 34
into a curved generally centripetal, slightly downward path so that
the inert carrier gas swirls above the concentric rows of baskets
140 and articles 132, thus creating a relatively uniform and
homogeneous atmosphere in chamber 124. In addition, the pressure of
the gas flow forces the streams 50 of the carrier gas downwardly
from distributor 10 and around and through the rows of baskets 140
and articles 132.
[0037] When this inert gas atmosphere is provided or established,
container 110 is usually heated to an elevated, preselected
temperature, of at least about 1000.degree. F. (about 538.degree.
C.), typically in the range from about 1000.degree. to about
2200.degree. F. (from about 538.degree. to about 1204.degree. C.),
and more typically in the range of from about 1900.degree. to about
2000.degree. F. (from about 1038.degree. to about 1093.degree. C.).
The particular elevated temperature selected will depend on the
coating application parameters desired (including the source of
metallic coating used) and other factors that would be understood
by those skilled in the art. Upon reaching this preselected
temperature, the powdered activator 146 will form a reactive halide
gas. Suitable halide activators can be selected from aluminum
chloride, aluminum fluoride, ammonium fluoride and mixtures
thereof. This reactive halide gas flows through the pellets in
baskets 140 containing the metallic coating source (e.g., aluminum
source) and reacts with the aluminum source to provide the metallic
coating gas in the form of an aluminum halide or aluminide-bearing
gas. The aluminum source can be any aluminum or aluminum alloy, for
example, cobalt aluminum alloys (CoAl), iron aluminum alloys
(FeAl), or chromium aluminum alloys (CrAl), typically in powder or
pelletized form,. As would be understood by those skilled in the
art, the reaction kinetics controlling the rate of formation of the
aluminide-bearing gas will be dependent on the temperature, as well
as the rate at which the carrier gas is introduced into chamber 124
by distributor 10 which is the driving force (i.e., "plunger") for
moving the aluminide-bearing gas within chamber 124, as well as
amongst, around and through articles 132. This, in turn controls
the rate of deposition of the coating upon articles 132 and hence
the coating thickness.
[0038] As the aluminide-bearing gas flows over the surfaces of
articles 132, as well as through the holes in articles 132, such
air cooling holes (not shown) in the case of a hollow airfoil, the
aluminide-bearing gas is reduced to aluminum, thereby coating the
exterior surfaces of articles 132, as well as the interior surfaces
of hollow articles 132. Of course, the rate and uniformity of
deposition is greatly influenced by the uniformity of the
aluminide-bearing gas environment in proximity to articles 132,
which is in turn controlled by the rate at which the carrier gas is
introduced into chamber 124 and mixes with the aluminide-bearing
gas, as previously discussed.
[0039] In order to force the aluminide-bearing gas through the rows
of articles 132, a certain minimum pressure of the carrier gas is
required. This is typically achieved by having the carrier gas
continue to flow into chamber 124 at the previously indicated flow
rates through pipe 14. Thus, the carrier gas can not only be used
to control the uniformity of the aluminide-bearing gas environment,
and hence reduction of the aluminide-bearing gas at the surface
(exterior and interior), but it can also be balanced to provide the
necessary pressure to move and force the aluminide-bearing gas
through the rows of articles 132 (and into the interior when
articles 132 are hollow), thereby coating them. In particular, the
inert carrier gas commingles and mixes with the aluminide-bearing
gas and acts, in essence, as a "plunger" to aid in the coating of
external (and internal) surfaces of articles 132. After passing
through articles 132, the remaining aluminide-bearing gas is
exhausted from chamber 124 through gas exhaust outlet indicated as
152 and into an open evacuation chamber or area indicated as 160
defined by the extension of side wall 122 beyond base 118. Upon
completion of the coating operation to the desired coating
thickness, container 110 can be removed from the furnace and cooled
or optionally furnace cooled, while maintaining an inert gas
atmosphere if desired.
[0040] While specific embodiments of the method of the present
invention have been described, it will be apparent to those skilled
in the art that various modifications thereto can be made without
departing from the spirit and scope of the present invention as
defined in the appended claims.
* * * * *