U.S. patent application number 13/299823 was filed with the patent office on 2013-05-23 for cast nickel-iron-base alloy component and process of forming a cast nickel-iron-base alloy component.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. The applicant listed for this patent is Ganjiang FENG, George Albert GOLLER, Matthew LAYLOCK, Joseph C. RAZUM. Invention is credited to Ganjiang FENG, George Albert GOLLER, Matthew LAYLOCK, Joseph C. RAZUM.
Application Number | 20130126056 13/299823 |
Document ID | / |
Family ID | 47216106 |
Filed Date | 2013-05-23 |
United States Patent
Application |
20130126056 |
Kind Code |
A1 |
FENG; Ganjiang ; et
al. |
May 23, 2013 |
CAST NICKEL-IRON-BASE ALLOY COMPONENT AND PROCESS OF FORMING A CAST
NICKEL-IRON-BASE ALLOY COMPONENT
Abstract
A cast nickel-iron-base alloy component having by weight about
12.0% to about 16.5% Cr, about 1.0% to about 2.0% Al, about 2.0% to
about 3.0% Ti, about 2.0% to about 3.0% W, about 3.0 to about 5.0%
Mo, up to about 0.1% Nb, up to about 0.2% Mn, up to about 0.1% Si,
about 0.05% to about 0.10% C, about 0.003 to about 0.010% B, about
35% to about 37% Fe, and balance essentially Ni and inevitable
impurities. The nickel-iron-base alloy component has a creep
rupture life greater than about 1000 hours at about 25 ksi to about
30 ksi at about 1400.degree. F. A method for forming the cast
nickel-iron-base alloy component is also disclosed.
Inventors: |
FENG; Ganjiang; (Greenville,
SC) ; GOLLER; George Albert; (Greenville, SC)
; RAZUM; Joseph C.; (Greenville, SC) ; LAYLOCK;
Matthew; (Mauldin, SC) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FENG; Ganjiang
GOLLER; George Albert
RAZUM; Joseph C.
LAYLOCK; Matthew |
Greenville
Greenville
Greenville
Mauldin |
SC
SC
SC
SC |
US
US
US
US |
|
|
Assignee: |
GENERAL ELECTRIC COMPANY
Schenectady
NY
|
Family ID: |
47216106 |
Appl. No.: |
13/299823 |
Filed: |
November 18, 2011 |
Current U.S.
Class: |
148/707 ;
420/586.1 |
Current CPC
Class: |
C22F 1/10 20130101; F05D
2300/111 20130101; F05D 2240/12 20130101; C22C 19/056 20130101;
C21D 1/00 20130101 |
Class at
Publication: |
148/707 ;
420/586.1 |
International
Class: |
C21D 1/00 20060101
C21D001/00; C22C 30/00 20060101 C22C030/00 |
Claims
1. A cast nickel-iron-base alloy component comprising by weight:
about 12.0% to about 16.5% Cr; about 1.0% to about 2.0% Al; about
2.0% to about 3.0% Ti; about 2.0% to about 3.0% W; about 3.0 to
about 5.0% Mo; up to about 0.1% Nb; up to about 0.2% Mn; up to
about 0.1% Si; about 0.05% to about 0.10% C; about 0.003 to about
0.010% B; about 35% to about 37% Fe; and balance essentially Ni and
inevitable impurities; wherein the component has a creep rupture
life greater about 1000 hours at about 25 ksi to about 30 ksi at
about 1400.degree. F.
2. The cast nickel-iron-base alloy component of claim 1, comprising
about 12.0% to about 14% Cr, about 1.35% to about 1.65% Al, about
2.25% to about 2.75% Ti, about 2.0% to about 2.7% W, about 3.2 to
about 4.0% Mo, up to about 0.1% Nb, up to about 0.2% Mn, up to
about 0.1% Si, about 0.07% to about 0.09% C, about 0.005 to about
0.008% B, about 35% to about 37% Fe, and balance essentially Ni and
inevitable impurities.
3. The cast nickel-iron-base alloy component of claim 1, comprising
about 12.5% Cr, about 1.5% Al, about 2.5% Ti, about 2.5% W, about
3.5% Mo, up to about 0.1% Nb, up to about 0.2% Mn, up to about 0.1%
Si, about 0.08% C, about 0.006% B, about 36% Fe, and balance
essentially Ni and inevitable impurities.
4. The cast nickel-iron-base alloy component of claim 1, wherein
the composition is devoid of Co.
5. The cast nickel-iron-base alloy component of claim 1, wherein
the nickel-iron-base alloy component has a creep rupture life of
greater than about 1400 hours at about 25 ksi to about 30 ksi at
about 1400.degree. F.
6. The cast nickel-iron-base alloy component of claim 1, wherein
the nickel-iron-base alloy component has a creep rupture life of
greater than about 1800 hours at about 25 ksi to about 30 ksi at
about 1400.degree. F.
7. The cast nickel-iron-base alloy component of claim 1, wherein
the nickel-iron-base alloy component has a resistance to oxidation
of greater than about 48,000 hours.
8. The cast nickel-iron-base alloy component of claim 1, wherein
the nickel-iron-base alloy component is a nozzle.
9. The cast nickel-iron-base alloy component of claim 1, wherein
the nickel-iron-base alloy component is a shroud.
10. A process of forming a cast nickel-iron-base alloy component,
the process comprising: casting an alloy comprising by weight:
about 12.0% to about 16.5% Cr; about 1.0% to about 2.0% Al; about
2.0% to about 3.0% Ti; about 2.0% to about 3.0% W; about 3.0 to
about 5.0% Mo; up to about 0.1% Nb; up to about 0.2% Mn; up to
about 0.1% Si; about 0.05% to about 0.10% C; about 0.003 to about
0.010% B; about 35% to about 37% Fe; and balance essentially Ni and
inevitable impurities to form a cast ingot; homogenizing the cast
ingot at a temperature from about 2000.degree. F. to about
2200.degree. F. to form a homogenized ingot; heat treating the
homogenized ingot at a temperature from about 1700.degree. F. to
about 1850.degree. F. to form a heat treated ingot; and aging the
heat treated ingot at a first aging temperature from about
1200.degree. F. to about 1500.degree. F. and then at a second aging
temperature from about 1000.degree. F. to about 1200.degree. F. to
form an aged ingot; wherein the aged ingot has a creep rupture life
greater than about 1000 hours at about 25 ksi to about 30 ksi at
about 1400.degree. F.
11. The process of claim 10, wherein the alloy comprises about
12.0% to about 14% Cr, about 1.35% to about 1.65% Al, about 2.25%
to about 2.75% Ti, about 2.0% to about 2.7% W, about 3.2 to about
4.0% Mo, up to about 0.1% Nb, up to about 0.2% Mn, up to about 0.1%
Si, about 0.07% to about 0.09% C, about 0.005 to about 0.008% B,
about 35% to about 37% Fe, and balance essentially Ni and
inevitable impurities.
12. The process of claim 10, wherein the alloy comprises about
12.5% Cr, about 1.5% Al, about 2.5% Ti, about 2.5% W, about 3.5%
Mo, up to about 0.1% Nb, up to about 0.2% Mn, up to about 0.1% Si,
about 0.08% C, about 0.006% B, about 36% Fe, and balance
essentially Ni and inevitable impurities.
13. The process of claim 10, wherein the alloy is devoid of Co.
14. The process of claim 10, wherein the homogenizing includes
heating the cast ingot to a temperature of from about 2050.degree.
F. to about 2150.degree. F.
15. The process of claim 10, wherein the heat treating includes
heating the homogenized ingot to a temperature of from about
1750.degree. F. to about 1800.degree. F.
16. The process of claim 10, wherein the aging includes heating the
heat-treated ingot to a first temperature of from about
1300.degree. F. to about 1400.degree. F. and a second temperature
of from about 1050.degree. F. to about 1150.degree. F.
17. The process of claim 10, wherein the aged ingot has a creep
rupture life greater than about 1400 hours at about 25 ksi to about
30 ksi at about 1400.degree. F.
18. The process of claim 10, wherein the aged ingot has a creep
rupture life greater than about 1800 hours at about 25 ksi to about
30 ksi at about 1400.degree. F.
19. The process of claim 10, wherein the nickel-iron-base alloy
component is a nozzle.
20. The process of claim 10, wherein the nickel-iron-base alloy
component is a shroud.
Description
FIELD OF THE INVENTION
[0001] The present invention is directed to alloys, articles
including alloys, and processes of forming alloys. More
specifically, the present invention is directed to a
nickel-iron-base alloy and a process of forming a nickel-iron-base
alloy.
BACKGROUND OF THE INVENTION
[0002] The operating temperature within a gas turbine engine is
both thermally and chemically hostile. Significant advances in high
temperature capabilities have been achieved through the development
of iron, nickel and cobalt-based superalloys and the use of
environmental coatings capable of protecting superalloys from
oxidation, hot corrosion, etc., but coating systems continue to be
developed to improve the performance of the materials.
[0003] In the compressor portion of a gas turbine engine,
atmospheric air is compressed to 10-25 times atmospheric pressure,
and adiabatically heated to 800.degree.-1250.degree. F.
(427.degree. C.-677.degree. C.) in the process. This heated and
compressed air is directed into a combustor, where it is mixed with
fuel. The fuel is ignited, and the combustion process heats the
gases to very high temperatures, in excess of 3000.degree. F.
(1650.degree. C.). These hot gases pass through the turbine, where
airfoils fixed to rotating turbine disks extract energy to drive
the fan and compressor of the engine, and the exhaust system, where
the gases provide sufficient thrust to propel the aircraft. To
improve the efficiency of operation of the engine, combustion
temperatures have been raised. Of course, as the combustion
temperature is raised, steps must be taken to prevent thermal
degradation of the materials forming the flow path for these hot
gases of combustion.
[0004] Demand for enhanced performance continues to increase. This
demand for enhanced performance applies for newer engines and
modifications of proven designs. Specifically, higher thrusts and
better fuel economy are among the performance demands. To improve
the performance of engines, the combustion temperatures have been
raised to very high temperatures. This can result in higher thrusts
and/or better fuel economy.
[0005] Stator components (nozzles and shrouds) are hot gas path
components for gas turbines. It is desirable for the stator
components to have oxidation resistance, thermal-mechanical fatigue
capability and high temperature creep strength. Traditionally, the
stator components are made of Ni-based or Co-based cast
superalloys. These superalloys suffer from the drawback that they
can have very high costs.
[0006] Known attempts to use different materials have been
unsuccessful. For example, advanced stainless steels (for example
Alumina-Forming Austenitic (AFA) alloys, developed by Oak Ridge
National Laboratory) contain nano-precipitates and oxide-forming
elements and demonstrate an outstanding heat-resistance. However,
these advanced stainless steels have undesirably low creep strength
for nozzles. Particularly, the creep strength of these advanced
stainless steels only reaches about one half of design requirement
for gas turbine nozzles.
[0007] Another group of low cost alternative materials,
nickel-iron-base superalloys including A286, INCOLOY.RTM. 901,
INCOLOY.RTM. 903 and INCONEL.RTM. 706, have been regarded as
suffering from several drawbacks. "INCOLOY" and "INCONEL" are
federally registered trademarks of alloy produced by Inco Alloys
International, Inc., Huntington, W. Va. For example, INCOLOY.RTM.
901 has been regarded as lacking gamma prime phases (resulting in
low creep strength), containing significant amounts of eta, sigma,
and laves phases (resulting in low ductility and/or poor long-term
mechanical properties), and having a wide solidification range and
poor castability. The composition of INCOLOY.RTM. 901 is well-known
and includes a composition of 40.0-45.0% Ni, up to 0.35% Al,
2.35-3.10% Ti, 11.0-14.0% Cr, 5.0-7.0% Mo, up to about 1.0% Co, up
to 1.0% Mn, up to 0.03% S, up to 0.10% C, up to 0.60% Si, up to
0.03% P, up to 0.50% Cu, from 0.01 to 0.02% B, balance Fe. The
composition of INCONEL.RTM. 706 is well-known and includes a
composition of 39.0-44.0% Ni, 14.5-17.5% Cr, up to 0.40% Al,
1.5-2.0% Ti, 2.5-3.3% Nb+Ta, up to about 1.0% Co, up to 0.35% Mn,
up to 0.015% S, up to 0.06% C, up to 0.35% Si, up to 0.020% P, up
to 0.30% Cu, from up to 0.006% B, balance Fe.
[0008] Nickel-iron-base alloy components and processes of forming
nickel-iron-base alloy components that do not suffer from the above
drawbacks are desirable in the art.
SUMMARY OF THE INVENTION
[0009] According to an exemplary embodiment of the present
disclosure, a cast nickel-iron-base alloy component having by
weight:
[0010] about 12.0% to about 16.5% Cr;
[0011] about 1.0% to about 2.0% Al;
[0012] about 2.0% to about 3.0% Ti;
[0013] about 2.0% to about 3.0% W;
[0014] about 3.0 to about 5.0% Mo;
[0015] up to about 0.1% Nb;
[0016] up to about 0.2% Mn;
[0017] up to about 0.1% Si;
[0018] about 0.05% to about 0.10% C;
[0019] about 0.003 to about 0.010% B;
[0020] about 35% to about 37% Fe; and
[0021] balance essentially Ni and inevitable impurities;
The nickel-iron-base alloy component has a creep rupture life
greater about 1000 hours at about 25 ksi to about 30 ksi at about
1400.degree. F.
[0022] Another exemplary embodiment of the present disclosure
includes a process of forming a cast nickel-iron-base alloy
component. The process includes casting an alloy having by
weight:
[0023] about 12.0% to about 16.5% Cr;
[0024] about 1.0% to about 2.0% Al;
[0025] about 2.0% to about 3.0% Ti;
[0026] about 2.0% to about 3.0% W;
[0027] about 3.0 to about 5.0% Mo;
[0028] up to about 0.1% Nb;
[0029] up to about 0.2% Mn;
[0030] up to about 0.1% Si;
[0031] about 0.05% to about 0.10% C;
[0032] about 0.003 to about 0.010% B;
[0033] about 35% to about 37% Fe; and
[0034] balance essentially Ni and inevitable impurities;
The cast ingot is homogenized at a temperature from about
2000.degree. F. to about 2200.degree. F. to form a homogenized
ingot. The homogenized ingot is heat treated at a temperature from
about 1700.degree. F. to about 1850.degree. F. to form a
heat-treated ingot. The heat-treated ingot is then aged at a first
aging temperature from about 1200.degree. F. to about 1500.degree.
F. and then aged at a second aging temperature from about
1000.degree. F. to about 1200.degree. F. to form an aged ingot. The
aged ingot has a creep rupture life greater than about 1000 hours
at about 25 ksi to about 30 ksi at about 1400.degree. F.
[0035] Other features and advantages of the present invention will
be apparent from the following more detailed description of the
preferred embodiment, taken in conjunction with the accompanying
drawings which illustrate, by way of example, the principles of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] FIG. 1 is a photomicrograph of an alloy according to the
present disclosure.
[0037] FIG. 2 is a photomicrograph of an alloy according to the
present disclosure.
[0038] FIG. 3 is a graph showing creep rupture time data for Alloys
1-6.
[0039] FIG. 4 is a graph showing tensile property data for Alloys
1-6.
[0040] FIG. 5 is a graph showing low cycle fatigue (LCF) data for
Alloys 1-6.
DETAILED DESCRIPTION OF THE INVENTION
[0041] Provided is a cast nickel-iron-base alloy component having a
plurality of predetermined properties and a process of forming a
nickel-iron-base alloy component having a plurality of
predetermined properties. Embodiments of the present disclosure
involve a nickel-iron-base alloy formed from one or more low-cost
alloys previously regarded as unsuitable for hot gas path
components such as engine turbine stators.
[0042] An embodiment of the present disclosure includes a
high-temperature component, such as a turbine nozzle or shroud,
having a desirable creep strength through casting and heat
treatment according to the present disclosure. In addition, the
nickel-iron-base alloy components, according to the present
disclosure, having desirable long-term mechanical properties, are
suitable for use in power generation systems.
[0043] One or more specific embodiments of the present invention
will be described below. In an effort to provide a concise
description of these embodiments, all features of an actual
implementation may not be described in the specification. It should
be appreciated that in the development of any such actual
implementation, as in any engineering or design project, numerous
implementation-specific decisions must be made to achieve the
developers' specific goals, such as compliance with system-related
and business-related constraints, which may vary from one
implementation to another. Moreover, it should be appreciated that
such a development effort might be complex and time consuming, but
would nevertheless be a routine undertaking of design, fabrication,
and manufacture for those of ordinary skill having the benefit of
this disclosure. Specific structural and functional details
disclosed herein are not to be interpreted as limiting, but merely
as a basis for the claims as a representative basis for teaching
one skilled in the art to variously employ the present invention.
Any modifications or variations in the depicted systems and
methods, and such further applications of the principles of the
invention as illustrated herein, as would normally occur to one
skilled in the art, are considered to be within the spirit of this
invention.
[0044] When introducing elements of various embodiments of the
present invention, the articles "a," "an," "the," and "said" are
intended to mean that there are one or more of the elements. The
terms "comprising," "including," and "having" are intended to be
inclusive and mean that there may be additional elements other than
the listed elements.
[0045] Power generation systems include, but are not limited to,
gas turbines, steam turbines, and other turbine assemblies. In
certain applications, power generation systems, including the
turbomachinery therein (e.g., turbines, compressors, and pumps) and
other machinery may include components that are exposed to extreme
environments and heavy wear conditions. For example, certain power
generation system components, such as blades, casings, rotor
wheels, shafts, nozzles, and so forth, may operate in high heat and
high revolution environments. As a result of the extreme
environmental operating conditions, cracks, gouges, cavities, or
gaps may develop on the surface of the components.
[0046] Embodiments of the present disclosure include
nickel-iron-base alloys having the following broad, preferred and
nominal compositions:
TABLE-US-00001 TABLE 1 Preferred wt % Broad Range Range Nominal
Chromium 12.0-16.5 12.0-14.0 12.5 Aluminum 1.0-2.0 1.35-1.65 1.5
Titanium 2.0-3.0 2.25-2.75 2.5 Tungsten 2.0-3.0 2.0-2.7 2.5
Molybdenum 3.0-5.0 3.2-4.0 3.5 Niobium <0.1 <0.1 <0.1
Manganese <0.2 <0.2 <0.2 Silicon <0.1 <0.1 <0.1
Carbon 0.05-0.10 0.07-0.09 0.08 Boron 0.003-0.010 0.005-0.008 0.006
Iron 35-37 35-37 36 Nickel Balance Balance Balance
[0047] In one embodiment, the nickel-iron-base alloy has a creep
rupture life of greater than about 1000 hours, or greater than
about 1400 hours, or greater than about 1800 hours at about
1400.degree. F. and at about 25 ksi to about 30 ksi of loading. In
one embodiment, the nickel-iron-base alloy is resistant to
oxidation for 48,000 hours or more. In one embodiment, hold time
low cycle fatigue of the nickel-iron-base alloy at 1400.degree. F.
is substantially the same or exceeds typical cobalt-base or
nickel-base alloys for gas turbine nozzle castings, such as FSX414
alloy or GTD-222 alloy, respectively. For example, the
nickel-iron-base alloy hold time (2 minutes) low cycle fatigue life
at 1400.degree. F. and 5% total strain may reach 2000 cycles or
more.
[0048] In one embodiment, the component according to the present
disclosure can be formed using a casting method, such as, but not
limited to, investment casting. Investment casting or lost wax
casting can prepare articles or components having intricate shapes
while maintaining accuracy of features. Generally, investment
casting comprises the following steps: forming a wax form of the
part to be cast; building a shell around the wax form; de-waxing to
leave a shell; filling the shell with molten metal; and removing
the shell around the cast part. One important characteristic of
casting alloy is the solidification range. It is the temperature
range between the liquidus and solidus, which is often used to
evaluate the castability of an alloy. The greater the
solidification range is, the easier the shrinkage formation is. In
one embodiment, the nickel-iron-base alloy has a solidification
range less than about 110.degree. F. This solidification range
provides good castability of the alloy. Other steps and processing
may also be utilized to provide the cast ingot or component. In
addition subsequent machining or other processes may be utilized to
form the ingot or component into its final form.
[0049] Once the ingot or component has been cast, the ingot or
component is subjected to heat treatment. The heat treatment
includes homogenization, heat treatment and aging at temperatures
and conditions that provide fine precipitates allowing the alloy to
have strength and creep rupture resistance greater than known
nickel-iron-base alloys, such as INCOLOY.RTM. 903 and INCONEL.RTM.
706. In one embodiment, the homogenizing includes homogenizing the
cast ingot at a temperature from about 2000.degree. F. to about
2200.degree. F. or 2050.degree. F. to about 2150.degree. F. or
about 2100.degree. F. to form a homogenized ingot where the
precipitates are put into solution and essentially only MC
precipitates remain. The heat treating includes heat treating the
homogenized ingot to a temperature from about 1700.degree. F. to
about 1850.degree. F. for 2 hours or 1750.degree. F. to about
1800.degree. F. for 2 hours or about 1775.degree. F. for 2 hours to
form fine discrete carbides and an eta-phase microstructure along
the grain boundaries (see, for example, FIG. 1). After the heat
treatment, an aging process is provided. In one exemplary aging
process, a multi-step aging is utilized, including aging the heat
treated ingot at a first aging temperature from about 1200.degree.
F. to about 1500.degree. F. for 8 hours or about 1300.degree. F. to
about 1400.degree. F. for 8 hours or about 1350.degree. F. for 8
hours and then at a second aging temperature from about
1000.degree. F. to about 1200.degree. F. for 8 hours or
1050.degree. F. to about 1150.degree. F. for 8 hours or about
1100.degree. F. for 8 hours to form an aged ingot having fine
precipitates in matrix of the alloy (see, for example, FIG. 2).
Depending on the application and the desired mechanical properties,
a 3.sup.rd step of age may be applied.
[0050] In one embodiment, the component is a power generation
system component. For example, the component may be a turbine
stator component including, but not limited to, a nozzle, a shroud,
other suitable portions, or combinations thereof.
EXAMPLES
TABLE-US-00002 [0051] TABLE 2 Wt % EXAMPLES Alloy 1 Alloy 2 Alloy 3
Chromium 16.0 14.0 12.5 Aluminum 1.5 1.5 1.5 Titanium 2.5 2.5 2.5
Tungsten 2.0 2.0 2.5 Molybdenum 1.0 4.0 3.5 Niobium <0.1 <0.1
<0.1 Manganese <0.2 <0.2 <0.2 Silicon <0.1 <0.1
<0.1 Carbon 0.08 0.08 0.08 Boron 0.006 0.006 0.006 Iron 36 36 36
Nickel Balance Balance Balance Wt % COMPARATIVE EXAMPLES Alloy 4
Alloy 5 Alloy 6 Chromium 12.5 16.0 16.0 Aluminum 0.2 1.50 0.20
Titanium 2.8 1.75 1.75 Tungsten 0.1 2.00 <0.12 Molybdenum 5.7
<0.12 <0.12 Niobium <0.1 0.50 2.90 Manganese <0.2
<0.2 <0.2 Silicon <0.1 <0.1 <0.1 Carbon 0.05 0.070
0.020 Boron 0.01 <0.006 0.006 Iron 36 37 37 Nickel Balance
Balance Balance
[0052] Alloys 1-3, as shown in Table 2, are alloys according to the
present disclosure. Comparative Alloy 4 is an INCONEL.RTM. 706
alloy and Comparative Alloy 6 is an INCOLOY.RTM. 901 alloy. All of
the alloys shown in Table 2 are investment cast alloys according to
the indicated composition. In addition, the alloys in Table 2 were
heat treated by homogenization, heat treatment and double
aging.
[0053] FIG. 3 shows the creep rupture time for Alloys 1-6. FIG. 4
shows the tensile properties, including the % elongation, tensile
strength and 0.2% yield strength of Alloys 1-6. FIG. 5 shows low
cycle fatigue (LCF) values at 1400.degree. F. with 0.5% strain and
2 min hold for Alloys 1-6. Alloys 1-3 according to the present
disclosure showed about 5-10 times improvement in 1400.degree. F.
creep over the Alloy 6, INCOLOY.RTM. 901 alloy and the Alloy 4,
INCONEL.RTM. 706 alloy baseline. LCF capability at the given
condition (1400.degree. F., 0.5% total strain, 2 minutes hold time)
reached 2000 cycles, which is substantially the same as that of a
nickel-base alloy, GTD-222. Alloys 1-3, according to the present
disclosure, showed excellent castability, and heat treatment
feasibility, which is evidenced by microstructure and mechanical
properties.
[0054] While the invention has been described with reference to a
preferred embodiment, it will be understood by those skilled in the
art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the invention. In addition, many modifications may be made to
adapt a particular situation or material to the teachings of the
invention without departing from the essential scope thereof.
Therefore, it is intended that the invention not be limited to the
particular embodiment disclosed as the best mode contemplated for
carrying out this invention, but that the invention will include
all embodiments falling within the scope of the appended
claims.
* * * * *