U.S. patent application number 10/897738 was filed with the patent office on 2006-01-26 for steel-shelled ceramic spacer block.
Invention is credited to Calvin Bates, Bradley D. Greve, Joseph P. Harenski, Stephan C. Jones, Roger W. Kaufold, Roger D. Miller, Daniel W. Severa, Patricia A. Stewart, Larry F. Wieserman.
Application Number | 20060017204 10/897738 |
Document ID | / |
Family ID | 35656306 |
Filed Date | 2006-01-26 |
United States Patent
Application |
20060017204 |
Kind Code |
A1 |
Kaufold; Roger W. ; et
al. |
January 26, 2006 |
Steel-shelled ceramic spacer block
Abstract
A spacer member for supporting a metallic alloy product during
heat treatment comprising a ceramic core and a tubular housing is
disclosed. The tubular housing, which encloses the ceramic core,
comprises a bore, a wall portion, and two end portions. In order to
resist deformation during usage, the tubular housing is made from
high temperature steel, a high temperature steel alloy, or cold
rolled steel. The wall portion has at least two substantially flat
surfaces having corner edges that have a radius of at least 3/8
inch and ends that are tapered at least 1/4 inch. In addition, the
flat surfaces also have a coating that reduces the sticking of a
metallic alloy product. The end portions each have at least one
aperture to allow the inside to adjust itself to ambient
atmospheric pressure. A method of making a spacer member is also
disclosed.
Inventors: |
Kaufold; Roger W.;
(Pittsburgh, PA) ; Miller; Roger D.; (Bettendorf,
IA) ; Greve; Bradley D.; (Donahue, IA) ;
Jones; Stephan C.; (Bettendorf, IA) ; Stewart;
Patricia A.; (Pittsburgh, PA) ; Severa; Daniel
W.; (Brackenridge, PA) ; Harenski; Joseph P.;
(Export, PA) ; Bates; Calvin; (Monroeville,
PA) ; Wieserman; Larry F.; (Apollo, PA) |
Correspondence
Address: |
ECKERT SEAMANS CHERIN & MELLOTT, LLC;ALCOA TECHNICAL CENTER
100 TECHNICAL DRIVE
ALCOA CENTER
PA
15069-0001
US
|
Family ID: |
35656306 |
Appl. No.: |
10/897738 |
Filed: |
July 23, 2004 |
Current U.S.
Class: |
266/275 |
Current CPC
Class: |
F27D 5/00 20130101 |
Class at
Publication: |
266/275 |
International
Class: |
C21C 5/46 20060101
C21C005/46 |
Claims
1. A spacer member for supporting a metallic alloy product during
heat treatment, said spacer member comprising: a ceramic core; and
a tubular housing comprising a wall portion, a bore defined by said
wall portion that is structured to receive said ceramic core, and
two end portions, said housing enclosing said ceramic core, said
housing wall portion having at least two substantially flat
surfaces in parallel with each other, said flat surfaces having
corner edges having a radius of at least 3/8 inch and ends being
tapered at least 1/4 inch inward toward said bore of said tubular
housing, said end portions each having at least one aperture.
2. A spacer member of claim 1 wherein said flat surfaces have a
non-stick coating comprising a thermal oxide of nickel.
3. A spacer member of claim 2 wherein said non-stick coating
consists of nickel aluminide.
4. A spacer member of claim 2 wherein said non-stick coating has a
thickness of from about 5 nm to about 50 microns.
5. A spacer member as in claim 1 wherein said tubular housing
comprises a metal selected from the group consisting of a high
temperature steel, a high temperature steel alloy, or a cold rolled
steel.
6. A spacer member as in claim 1 wherein said aperture of said end
portion is from about 1/64 inch to about 1/16 inch in diameter.
7. A spacer member for supporting a metallic alloy product during
heat treatment, said spacer member comprising: a ceramic core; and
a tubular housing comprising a wall portion, a bore defined by said
wall portion that is structured to receive said ceramic core, and
two end portions, said housing enclosing said ceramic core, said
housing wall portion having at least two substantially flat
surfaces in parallel with each other, said flat surfaces having
corner edges having a radius of at least 3/8 inch and ends being
tapered at least 1/4 inch inward toward said bore of said tubular
housing, said end portions each having at least one aperture, said
flat surfaces having a non-stick coating comprising a thermal oxide
of nickel.
8. A spacer member of claim 7 wherein said non-stick coating
consists of nickel aluminide.
9. A spacer member of claim 7 wherein said non-stick coating has a
thickness of from about 5 nm to about 50 microns.
10. A spacer member as in claim 7 wherein said tubular housing
comprises a metal selected from the group consisting of a high
temperature steel, a high temperature steel alloy, or a cold rolled
steel.
11. A spacer member as in claim 7 wherein said aperture of said end
portion is from about 1/64 inch to about 1/16 inch in diameter.
12. A method of making a spacer member for supporting a metallic
alloy product during heat treatment, said method comprising the
steps of: providing a tubular housing comprising a bore and a wall
portion having at least two substantially flat surfaces in parallel
with each other, said flat surfaces having corner edges and ends;
tapering said ends at least 1/4 inch inward toward said bore of
said tubular housing; attaching an end portion comprising at least
one aperture to one of said ends of said flat surfaces; filling the
tubular housing with a ceramic material; attaching another of said
end portions comprising at least one aperture to another of said
ends of said flat surfaces; and applying to said flat surfaces of
said wall portion a non-stick coating for preventing sticking of a
heat treated metallic alloy product to said spacer member.
13. The method of claim 12 further comprising subjecting said
tubular housing to a high temperature heating step after applying
said non-stick coating wherein said tubular housing is held at an
elevated temperature of from about 800 degrees F. to about 1200
degrees F. (427.degree.-649.degree. C.).
14. The method of claim 12 wherein tapering said ends comprises
cutting said ends along said corner edges and tapering said ends
via the use of a tapering means.
15. The method of claim 14 wherein said tapering means comprises a
break or radius forming jig.
16. The method of claim 12 wherein said tubular housing comprises a
metal selected from the group consisting of a high temperature
steel or steel alloy or cold rolled steel.
17. The method of claim 12 wherein said non-stick coating comprises
a thermal oxide of nickel.
18. The method of claim 12 wherein said non-stick coating consists
of nickel aluminide.
19. The method of claim 12 wherein said non-stick coating has a
thickness of from about 5 nm to about 50 microns.
20. The method of claim 12 wherein said aperture of said end
portion is from about 1/64 inch to about 1/16 inch in diameter.
21. The method of claim 12 wherein said flat surfaces have corner
edges having a radius of at least 3/8 inch.
22. A method of making a spacer member for supporting a metallic
alloy product during heat treatment, said method comprising the
steps of: providing a tubular housing comprising a bore and a wall
portion having at least two substantially flat surfaces in parallel
with each other, said flat surfaces having corner edges and ends;
tapering said ends at least 1/4 inch inward toward said bore of
said tubular housing, wherein said ends are cut along said corner
edges and tapered via the use of a tapering means; attaching an end
portion having at least one aperture to one of said ends of said
flat surfaces; filling the tubular housing with a ceramic material;
attaching another of said end portions comprising at least one
aperture to another of said ends of said flat surfaces; and
applying to said flat surfaces of said wall portion of said tubular
housing a non-stick coating for preventing sticking of a heat
treated metallic alloy product to said spacer member, wherein said
tubular housing is held at an elevated temperature of from about
800 degrees F. to about 1200 degrees F. (427.degree. C.-649.degree.
C.) after applying said non-stick coating.
23. The method of claim 22 wherein said tapering means comprises a
break or radius forming jig.
24. The method of claim 22 wherein said tubular housing comprises a
metal selected from the group consisting of a high temperature
steel or steel alloy or cold rolled steel.
25. The method of claim 22 wherein said non-stick coating comprises
a thermal oxide of nickel.
26. The method of claim 22 wherein said non-stick coating consists
of nickel aluminide.
27. The method of claim 22 wherein said non-stick coating has a
thickness of from about 5 nm to about 50 microns.
28. The method of claim 22 wherein said aperture of said end
portion is from about 1/64 inch to about 1/16 inch in diameter.
29. The method of claim 22 wherein said flat surfaces have corner
edges having a radius of at least 3/8 inch.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to spacer blocks positioned
between aluminum ingots in preheat furnaces and, more particularly,
to an improved spacer block that is more robust and has a longer
useful life.
BACKGROUND OF THE INVENTION
[0002] Heating of aluminum ingots is a well-established practice
for achieving desired properties in the ingot and to render the
ingot sufficiently malleable for reduction in thermo-mechanical
processes. During a preheating step, aluminum ingots are heated to
temperatures below the melting point of the aluminum alloy.
Preheating serves to control the metallurgical properties of the
ingot, reduce cracking, and reduce the forces needed to further
process the ingot. Up to six ingots can typically be vertically
stacked in a preheat furnace at one time. Spacer blocks are
typically positioned between the stacked ingots to maintain a gap
between the ingots and prevent them from sticking to one another,
allow hot gases to circulate between the ingots for faster heat-up,
and provide uniform exposure to the furnace atmosphere.
[0003] Conventional blocks are solid blocks of an aluminum alloy,
which may be the same as or different from the alloy of the ingot
supported thereby and have a size of about 1 to 4 inches.times.2 to
6 inches.times.6 to 24 inches. Each of these spacer blocks weighs
over ten pounds. A single operator may handle 400 to 500 spacer
blocks per shift.
[0004] Additional drawbacks to conventional spacer blocks relate to
their composition. When heated in a furnace, the metal of the ingot
as well as the metal of the spacer blocks soften. When aluminum
alloy spacer blocks are subjected to the weight of a conventional
ingot load in a preheat furnace and temperatures of about
600.degree. F. (316.degree. C.) and higher, the strength of the
spacer block begins to decrease. When subjected to higher preheat
furnace temperature conditions of about 800.degree. F. (427.degree.
C.) and higher, aluminum alloy spacer blocks exhibit a diminished
strength capacity that is typically unsatisfactory for providing
adequate ingot support.
[0005] In addition, oxide layers grow and volatile metals, such as
magnesium and lithium, migrate to the surfaces of the spacer blocks
and the ingots. The migrated metals cause the spacer blocks and the
ingots to adhere to one another. Deformation and adhesion of the
spacer blocks to the ingots is particularly problematic for the
ingots at the bottom of the stack where the load is the greatest.
When the preheat cycle is complete, a crane is used to remove an
ingot from the stack and position the ingot at the beginning of a
hot line rolling mill, reversing mill, or the like. An operator
must remove any spacer blocks stuck to the ingot prior to any ingot
processing. Occasionally, the spacer block can be removed from the
ingot by simple hand pressure. However, often the spacer block is
so tightly adhered to the ingot that it must be knocked off with a
large hammer or an axe. Occasionally, a forklift or the like must
be used to loosen the adhered spacer block from the surface of the
ingot.
[0006] An additional problem associated with sticking of
conventional spacer blocks to the ingot is the formation of marks,
which are typically left on an ingot upon removal of the spacer
block. Spacer blocks often produce defects in the surface of the
ingot. When an ingot having such a defect is subsequently rolled,
the defect becomes a surface imperfection in the rolled product.
For many applications of rolled product, such defects are
unacceptable in the marketplace.
[0007] Another drawback to the aluminum spacer blocks is the
tendency of various aluminum alloys used for conventional spacer
blocks to creep at high temperatures. At temperatures of about
900-1140.degree. F. (482-616.degree. C.), conventional spacer
blocks having initial dimensions of 3 inch.times.3 inch'12 inch can
become deformed into dimensions of about 2.5 inch.times.3.5
inch.times.12.5 inch. Not all spacer blocks in a stack of ingots
are always deformed similarly. Hence, in a set of spacer blocks
used with a stack of ingots, the individual spacer blocks may have
differing dimensions. Variable dimensions in the spacer blocks can
aggravate sticking of the spacer blocks to the ingots. For example,
when six spacer blocks are used for an ingot and two of the spacer
blocks do not touch the ingot because they have been deformed, only
four of the spacer blocks contact the ingot, thereby supporting the
entire load. In this situation, the load per unit area borne by the
four spacer blocks contacting the ingot increases by about 33%. At
such higher loads, the adhesion between the spacer blocks and the
ingots is aggravated.
[0008] High temperature creep of aluminum spacer blocks is also a
problem in preheat furnaces operated at higher temperatures, e.g.,
at or above about 1120.degree. F. (604.degree. C.). It has become
common practice in those circumstances to position the spacer
blocks between the ingots so that a portion of the spacer block
extends out between the ingots. During the preheat cycle, the
portion of the spacer block which is sandwiched between the ingots
becomes flattened to a thickness of about 1/2 inch while the
remaining portion of the spacer block which did not support the
ingot retains its original width and height of 3 inch.times.3 inch.
In order to reuse spacer blocks that have been partially flattened,
operators turn the spacer blocks between ingots. This often results
in the entire spacer block being flattened into a thickness of
about 1/2. When the spacer block between the ingots is greatly
reduced to about 1/2 inch, airflow between the ingots is greatly
reduced which results in uneven heating, extended cycle times, and
insufficient exposure of the ingot surfaces to the furnace
atmosphere.
[0009] Accordingly, a need exists for a spacer block for use in
aluminum ingot preheat furnaces which is lightweight, does not
stick to the ingot surfaces, and retains its shape when subjected
to high temperature furnace conditions.
SUMMARY OF THE INVENTION
[0010] This need is met by the spacer member of the present
invention, which may be used for supporting a metallic alloy
product subject to heat treatment. The spacer block comprises a
tubular housing with a core of a ceramic material. The tubular
housing, which encloses the ceramic core, comprises a wall portion,
two end portions, and a bore. The wall portion has at least two
substantially flat surfaces in parallel with each other, with the
flat surfaces having corner edges that have a radius of at least
3/8 inch and ends that are tapered at least 1/4 inch inward toward
the bore of the tubular housing. In addition, the flat surfaces
also have a coating that reduces the sticking of a metallic alloy
product. The end portions each have at least one aperture to allow
the internal portions of the block to adjust to ambient atmospheric
pressure.
[0011] The spacer member of the present invention may be produced
by providing a tubular housing comprising a bore and a wall portion
having at least two substantially flat surfaces in parallel with
each other wherein the flat surfaces have corner edges and ends,
tapering the ends at least 1/4 inch inward toward the bore of the
tubular housing, attaching an end portion having at least one
aperture to an end of the tubular housing, filling the tubular
housing with a ceramic material, and attaching another end portion
having at least one aperture to the other end of the tubular
housing. The flat surfaces may then be coated with a non-stick
coating for preventing sticking of a heat-treated metallic alloy
product to the spacer member.
[0012] A complete understanding of the invention will be obtained
from the following description when taken in connection with the
accompanying drawing figures wherein like reference characters
identify like parts throughout.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1a is a perspective view of a tubular housing of a
spacer member of the present invention.
[0014] FIG. 1b is a cross-sectional view of a housing of the spacer
member of the present invention filled with a ceramic material.
[0015] FIG. 2 is a graph showing the average cold crushing strength
for various preferred castable ceramic core materials.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0016] As shown in FIGS. 1a and 1b, the spacer member of the
present invention includes a housing 20 with core 30 of a ceramic
material. The housing 20 is preferably in the form of a tube having
a wall portion with at least two substantially flat surfaces 40 in
parallel with each other and a bore 90 defined by the wall portion
that is structured to receive the ceramic core. As shown in FIG.
1a, housing 20 can have any functional dimensions, however, typical
spacer members have a width (W) of from about 1 to about 4 inches,
a height (H) of from about 2 to 6 inches, and a length (L) of from
about 6 to 24 inches.
[0017] The thickness of the flat surfaces 40 of the housing 20 can
be from about 1/64 inch to about 1/2 inch, preferably from about
1/16 inch to about 1/8 inch. While thicker walls can be employed,
relatively thin walls are typically desirable due to the
considerable weight savings. Thinner walls allow for a lower weight
for the spacer member, however, if the walls are too thin (e.g.,
less than about 1/64 inch), the spacer member may be prone to
crushing and tearing under the ingot load.
[0018] The exterior of the flat surfaces 40 of the housing 20 are
preferably smooth to minimize any mechanical interlocking with
ingot surface during a heat treatment. A suitable maximum roughness
is an Ra of about 10 to about 10,000 microinches. The smoothness of
the flat surface exterior 40 may be controlled by the extrusion
process or rolling process used to manufacture the housing 20. In
one embodiment of the present invention, the surfaces 40 may be
machined or polished as needed.
[0019] The exterior of the flat surfaces 40 of the housing 20 also
may be coated with a material to further prevent ingot sticking in
the preheat furnace. The preferred material used is the metal oxide
coating nickel aluminide, but other metal oxide coatings such as
nickel oxide, nickel aluminide, cobalt oxide, chromium oxide,
molybdenum oxide, zirconium oxide, aluminum oxide, and magnesium
oxide could also be used.
[0020] In one embodiment of the present invention, the thermal
oxide of nickel formed on the exterior of the flat surfaces 40 of
the housing 20 has a thickness of from about 5 nm to about 50
microns. In another embodiment, the thermal oxide of nickel formed
on the exterior of the flat surfaces 40 has a thickness of from
about 10 nm to about 2 microns.
[0021] While the exterior of only two opposing flat surfaces 40
need to be smoothed and/or coated as described above when used to
support ingots in a preheat furnace, it is preferred that the
exterior of all of the flat surfaces 40 are similarly treated. In
this manner, a user need not be concerned which of the exterior
surfaces 40 contact an ingot in a preheat furnace.
[0022] The flat surfaces 40 have corner edges 50 that have an
outside radius of curvature R.sub.0 of at least 3/8 inch and ends
80 that are tapered at least 1/4 inch inward toward a bore 90
defined by the wall portion that is structured to receive the
ceramic core. This reduces high stress risers that contribute to
premature failure at the corner edges 50 and reduces the potential
for sticking of the ingot to the spacer member. The rounded corner
edges 50 may be any suitable shape having some degree of curvature,
such as circular, elliptical, or ovular. In the preferred
embodiment, the rounded corner edge 50 extends longitudinally along
the length of the spacer member. By rounding the interior of the
corner edges 50, the load of the ingots applied to the housing 20
is partially shifted away from the edges 50 to reduce stress at the
edges 50. Furthermore, when spacer blocks have pointed or sharply
angled corner edges 50, sharp divots or deep deformations can form
in the ingot at the point of contact between the spacer block
corner edge 50 and the soft ingot. The sharper and/or deeper the
resulting ingot deformation is, the more remedial processing is
required to remove the defect from the ingot for subsequent use.
Additional remedial processing contributes greatly to the expense
of the resulting product. Accordingly, by rounding the corner edges
50 of the spacer members, the subsequent remedial ingot processing
is reduced and the lifespan of the spacer member is prolonged.
[0023] The tubular housing 20 comprises a metal selected from the
group consisting of high temperature steel, high temperature steel
alloy, or cold rolled steel. High temperature steel or steel alloys
are preferred because the solidus temperature of steel is
significantly higher than the temperature of the preheat furnace
conditions. Steel and steel alloys also exhibit tensile compressive
yield strengths that are sufficient to support the weight of ingot
loads at the preheat furnace temperatures. Preferred high
temperature steel or steel alloys are 1018 and 1020. High
temperature steel and steel alloys are particularly well suited for
use in relatively high temperature furnaces employing temperatures
of from about 800.degree. F. to about 1,200.degree. F. (427.degree.
C.-649.degree. C.).
[0024] In one embodiment, the spacer member has a thickness of from
about 0.5 to about 4 inches. Spacer members less than about 0.5
inch thick do not typically allow for adequate circulation of the
furnace atmosphere between ingots, and spacer members sized larger
than about 4 inches thick result in an ingot stack that is too tall
for conventional preheat furnaces and may destabilize the ingot
stack. In one embodiment of the present invention, housing 20 has a
square cross-sectional configuration and dimensions of about 3
inch.times.3 inch.times.12 inch. In another embodiment, the housing
20 has a rectangular cross-sectional configuration and dimensions
of about 2 inches.times.5 inches.times.16 inches. Each of these
preferred embodiments are sized and configured to conform with the
conventional spacer blocks presently used in the ingot processing
industry, however, other cross-sectional configurations of the
housing 20 are encompassed by the present invention.
[0025] Housing 20 is designed to enclose at least a part of the
ceramic core 30. The core 30 is preferably manufactured from a
curable ceramic material. Ceramic materials typically have a
relatively low density (compared to aluminum) and high strength.
However, most ceramic materials are brittle and tend to crumble
under impact loads, therefore spacer member includes housing 20 to
retain the ceramic core 30. The housing 20 also serves to prevent
the ceramic material from contacting and damaging ingots during
use. Accordingly, the ends 80 of the housing 20 should be
substantially closed off to prevent escape of the ceramic core 30
during use as shown in FIGS. 1a and 1b.
[0026] The ceramic core 30 may comprise a castable material, such
as calcium aluminates. The ceramic material preferably has a cold
crushing strength of from about 500 psi to about 20,000 psi. Cold
crushing strength is a measure of the static load the spacer member
can withstand until failure occurs. The density of the ceramic
material preferably is less than the density of conventional solid
aluminum spacer blocks (about 173 lbs/ft.sup.3 or 2.8 g/cc) to
achieve significant weight savings for the spacer member of the
present invention. Typically, the density of the ceramic material
is not greater than about 150 lbs/ft.sup.3 or 2.4 g/cc. Preferably,
the density of the ceramic material is not greater than about 125
lbs/ft.sup.3 or 2.0 g/cc. The properties of the ceramic material of
cold crushing strength and density are balanced to obtain a
suitable material for the core 30.
[0027] Particularly preferred castable materials include Greenlite
Express 24, CW108 Castable, HPV Castable, Reno Cast FSLC/A1, and
Metroflo SR. These preferred castable materials are available from
RHI Refractories (Greenlite & CW108), Chicago Fire Brick
Division (HPV), Renofractories, Inc. (Reno Cast), and Matrix
Refractories, Inc. (Metroflo). These ceramic materials were
evaluated for suitability for use in the core 30 of the spacer
member of the present invention. FIG. 2 illustrates the average
cold crushing strength of each of these preferred castable
materials. From the figure, Reno Cast FSLC/A1 and Metroflo SR have
the greatest cold crushing strength and therefore would be the most
preferred castable material.
[0028] At least one end portion 60 of the housing 20 comprises at
least one aperture 70 having a diameter of from about 1/64 inch to
about 1/16 inch sized to allow the inside of the spacer member to
adjust to the ambient atmospheric pressure of the furnace while
substantially retaining the ceramic core 30. In another embodiment,
a plurality of end portions 60 of housing 20 contains a plurality
of apertures 70. The end portions 60 are attached to the ends 80 of
the housing 20.
[0029] The method of making a spacer member includes: providing a
tubular housing 20 comprising a wall portion having at least two
substantially flat surfaces 40 in parallel with each other and a
bore 90 wherein the flat surfaces 40 have corner edges 50 and ends
80; tapering the ends 80 at least 1/4 inch inward toward the bore
90 of the tubular housing 20; attaching an end portion 60 having at
least one aperture 70 to an end 80 of the tubular housing 20;
filling the tubular housing 20 with a ceramic material; attaching
an end portion 60 having at least one aperture 70 to the other end
80 of the tubular housing 20; and applying to the flat surfaces 40
of the wall portion a non-stick coating for preventing sticking of
a heat treated metallic alloy product to the spacer member.
[0030] The housing 20 may be formed by extruding the steel into a
tube of the desired shape or by providing a sheet of steel, shaping
the sheet of steel into the desired configuration, and welding the
edges of the sheet together to form a tube. In a preferred
embodiment of the present invention, a low cost housing 20 is made
from cold rolled steel and robotically welded. In another
embodiment, the housing 20 is roll form welded in the same flow
path.
[0031] After the housing 20 is formed, one end of the housing 20
may be closed off by attaching an end portion 60 comprising at
least one aperture 70 having a diameter of from about 1/64 inch to
about 1/16 inch sized to allow the inside of the spacer member to
adjust to the ambient atmospheric pressure of the furnace while
substantially retaining the ceramic core 30. After an end 80 of the
housing 20 is closed off, the uncured ceramic material is then
poured into the housing 20 and allowed to cure. The other end 80 of
the housing 20 may then be closed off. In this manner, the housing
20 acts as a shell surrounding the ceramic core 30.
[0032] In a preferred embodiment, tapering would occur by first
cutting the ends 80 along the corner edges 50 and then tapering the
ends 80 inward toward the bore 90 of the tubular housing 20 via the
use of a tapering means. However, one skilled in the art would know
that tapering the ends could occur via the use of other methods.
The length of the cut along the corner edges 50 can be from 1/4
inch to 1 inch. A preferable means for cutting the corner edges 50
is milling, but could include sawing, shearing, or grinding.
Tapering means includes anything that would be strong enough to
bend the metal including a break or a radius forming jig. An end
portion 60 is then attached to the housing 20 preferably by welding
the end portion 60 to the ends 80 of the housing 20. However, the
end portion 60 could also be attached via the use of fasteners or
any means that would properly attached the end portion 60 to the
ends 80 of the housing 20.
[0033] A coating comprising a thermal oxide of nickel, specifically
nickel aluminide, is then formed on the exterior of the flat
surfaces 40 of the housing 20. Nickel or nickel alloys can be
applied to the flat surfaces 40 of the housing 20 prior to forming
the housing 20 or after the housing 20 is manufactured via
conventional coating techniques, such as brushing, plasma spraying,
thermal spraying, cold spraying, electroplating, electroless
plating, cladding, plasma vapor deposition, sputtering, and
electron beam evaporation.
[0034] After applying a nickel aluminide coating to the flat
surfaces 40 of the wall portion, the housing 20 is preferably
subjected to an oxidizing step. The oxidizing step comprises
subjecting the housing 20 to a heating period in an oxidizing
atmosphere, in which the housing 20 is held to an elevated
temperature of from about 800.degree. F. to about 1200.degree. F.
(427.degree.-649.degree. C.) for greater than 2 hours. The high
temperature heating step is beneficial in forming a thick
non-reactive oxide on the surface of the coating and to form a
diffusion layer between the coating and the housing 20. In another
embodiment of the present invention, housing 20 can be subjected to
a standard plasma spray process. In yet another embodiment of the
present invention, housing 20 can be subjected to ozone or another
oxidizing atmosphere for a period of time sufficient to allow a
nickel oxide to form on housing 20.
[0035] It will be readily appreciated by those skilled in the art
that modifications may be made to the invention without departing
from the concepts disclosed in the forgoing description. Such
modifications are to be considered as included within the following
claims unless the claims, by their language, expressly state
otherwise. Accordingly, the particular embodiments described in
detail herein are illustrative only and are not limiting to the
scope of the invention which is to be given the full breadth of the
appended claims and any and all equivalents thereof.
* * * * *