U.S. patent application number 11/810403 was filed with the patent office on 2008-12-11 for method of hardening titanium and titanium alloys.
Invention is credited to Christopher R. Goodman.
Application Number | 20080304998 11/810403 |
Document ID | / |
Family ID | 40096060 |
Filed Date | 2008-12-11 |
United States Patent
Application |
20080304998 |
Kind Code |
A1 |
Goodman; Christopher R. |
December 11, 2008 |
Method of hardening titanium and titanium alloys
Abstract
A method of hardening the outer surface of a titanium or
titanium alloy substrate under standard atmospheric conditions. The
method comprises focusing an electromagnetic beam from a laser
generating apparatus, absent the disposition of a chemical
compound, onto at least a portion of the substrate to heat it to a
point below the melting point of the substrate. The treated
substrate has a substantial increased harness and durability
compared to an untreated surface of titanium or titanium alloy.
Inventors: |
Goodman; Christopher R.;
(Tequesta, FL) |
Correspondence
Address: |
MCHALE & SLAVIN, P.A.
2855 PGA BLVD
PALM BEACH GARDENS
FL
33410
US
|
Family ID: |
40096060 |
Appl. No.: |
11/810403 |
Filed: |
June 5, 2007 |
Current U.S.
Class: |
420/420 ;
219/121.66 |
Current CPC
Class: |
C22F 1/183 20130101;
C22C 14/00 20130101 |
Class at
Publication: |
420/420 ;
219/121.66 |
International
Class: |
C22C 14/00 20060101
C22C014/00; C22F 1/18 20060101 C22F001/18 |
Claims
1. A method of hardening an outer surface of a metallic substrate
in open atmospheric conditions comprising the steps of: providing a
substrate of titanium or titanium alloys; focusing an
electromagnetic radiation beam formed by a laser generating
apparatus onto at least a portion of said substrate surface at
sufficiently high power densities to cause an incandescent reaction
above the substrate melting temperature with the substrate; and
limiting the incandescent reaction at any given area of the
substrate to a sufficiently short period of time to prevent any
substantial melting of the substrate, whereby said laser treated
surface of said substrate has a substantial increased hardness and
durability compared to an untreated surface of said substrate.
2. The method as set forth in claim 1, wherein said laser
generating apparatus is operated at a frequency between about 25 to
about 50 kHz.
3. The method as set forth in claim 1, wherein said laser
generating apparatus operates at a power density of about 606,664
watts/mm.sup.2.
4. The method as set forth in claim 1, wherein said laser
generating apparatus operates at a scanning speed between about
0.01 to about 5.0 inches/sec.
5. A method of hardening an outer surface of a metallic substrate
in open atmospheric conditions consisting of the steps of:
providing a substrate of titanium or titanium alloys; focusing an
electromagnetic radiation beam formed by a laser generating
apparatus onto at least a portion of said substrate surface at
sufficiently high power densities to cause an incandescent reaction
above the substrate melting temperature with the substrate; and
limiting the incandescent reaction at any given area of the
substrate to a sufficiently short period of time to prevent any
substantial melting of the substrate, whereby said laser treated
surface of said substrate has a substantial increased hardness and
durability compared to an untreated surface of said substrate.
6. The method as set forth in claim 5, wherein said laser
generating apparatus is operated at a frequency between about 25 to
about 50 kHz.
7. The method as set forth in claim 5, wherein said laser
generating apparatus operates at a power density of about 606,664
watts/mm.sup.2.
8. The method as set forth in claim 5, wherein said laser
generating apparatus operates at a scanning speed between about
0.01 to about 5.0 inches/sec.
9. A titanium containing composition having a hardness in the range
of 965 to 1200 Koops hardness number produced by the process of
claim 1.
10. A titanium containing composition having a hardness in the
range of 965 to 1200 Koops hardness number produced by the process
of claim 5.
Description
FIELD OF THE INVENTION
[0001] The invention generally relates to a method for hardening
the surface of metals or alloys; particularly, a method for
hardening titanium and titanium alloys using a laser for reducing
wear and improving corrosion resistance of items made from the
hardened titanium or titanium alloy.
BACKGROUND OF THE INVENTION
[0002] Titanium is an excellent lightweight material, whose
strength, chemical resistance, and biocompatibility make it
particularly suitable for various applications in the aerospace,
medical and chemical industries. However, titanium's low resistance
to wear caused by sliding friction and its low surface hardness
often precludes its use in the above noted applications. Numerous
techniques have been developed to increase the surface hardness of
titanium so that it will not gall or chip off when used in abrasive
mechanical and environmental conditions (saltwater, acid, autoclave
ovens, etc.)
[0003] The term "hardness" refers to the resistance of a material
to localized deformation. Deformation includes, albeit not limited
to, indentation, scratching, cutting or bending. In metals, the
deformation occurs mainly at the surface of the workpiece. There
are a large variety of testing methods used for determining the
hardness of a substance, some of which include the Brinell hardness
test, Rockwell Hardness test, Vickers hardness test and Knoop
hardness test. The methodology for each of these aforementioned
tests is well known and will not be described herein for the sake
of brevity. Metallic parts exposed to abrasive and/or corrosive
conditions should be resistant to corrosion and have a surface
Rockwell Hardness of at least 40 HRC to 55 HRC (Rockwell Hardness
on the "C" scale) to prevent galling, seizing, and wear when the
substrate is in rubbing and sliding contact with other materials
(e.g., metal). The approximate surface hardness values for common
materials are given below in both Rockwell Hardness C (HRC) numbers
and Knoop hardness numbers (KHN).
TABLE-US-00001 Material Surface Hardness 303 stainless steel 19
HRC; 180 KHN Commercially Pure titanium 16 HRC; 175 KHN Titanium
alloy (Ti--6Al--4V) 34 HRC; 363 KHN
[0004] Standard 303 stainless steel is prone to corrosion, whereas,
the commercially pure titanium (about 98% to about 99.5% Ti) and
titanium alloy are both resistant to corrosion. However, the low
surface hardness makes titanium containing workpieces generally
unsuitable for use in conditions where the unhardened titanium
workpiece is in physical contact with other materials.
[0005] Surface hardening of metals is a process that includes a
wide variety of techniques designed to improve the wear resistance
of parts without affecting the tough interior of the part.
Presently available techniques of hardening the surface of titanium
and it alloys include nitriding, anodizing, surface alloying,
metallic and ceramic coatings. However, these techniques are
elaborate and often require expensive equipment, such as a furnace,
vacuum chamber, heat source, or other means for supplying a
specific atmosphere environment (nitrogen, argon, etc.).
[0006] Heat treating using a laser to focus onto and harden a
metallic substrate has been utilized. Prior to using the laser,
these substrates are coated or preconditioned in a manner to form a
uniform layer of oxides and/or phosphates, often referred to as
"black oxidizing" to make it more absorbent to the light of the
laser. It is critical that this coating is uniform and
substantially thick. Otherwise, a substantial portion of the
laser's light energy may be reflected away from the surface of the
object. As a result of laser treating, the coating creates a
textured layer on the workpiece with a high coefficient of friction
so that the surface must be smoothed or polished, thereby adding an
additional step to the process.
[0007] What has been heretofore lacking in the art is a simple and
inexpensive method of hardening titanium and titanium alloy
materials. Desirably, a hard coating is formed on the titanium
which does not gall or chip off when in moving contact with other
metal parts. It has been discovered by the present inventor that
substantial hardening of titanium and titanium alloys is achieved
with a combination of parameters on a laser. It is theorized that
these specific parameters can be harmonized to create the hard
surface of varying depth. The present invention could be used in
various applications, such as hardening cutting tools, hardening
working areas on hand tools, strengthening stressed areas of
existing titanium tools, etc.
DESCRIPTION OF THE PRIOR ART
[0008] Numerous patents have been directed to hardening substrates
composed of titanium and titanium alloys, however, none of the
known prior art discloses a method of focusing a beam from a laser
generating apparatus onto at least a portion of the substrate
surface to harden the substrate in the open, uncontrolled
atmosphere.
[0009] For example, U.S. Pat. No. 5,145,530, to Cassady discloses a
method of hardening the surface of titanium and its alloys to form
hard carbides, by treating the surface thereof with a moving and
continuously energized carbon arc. A carbon arc is created by an
electrical lead connected to both an electrode, formed of carbon in
any of its allotropic forms, and the workpiece and passing an
electrical current between them. The carbon arc liquefies the
workpiece surface and creates craters on the workpiece surface. The
regions of the creators on workpiece are hardened.
[0010] U.S. Pat. No. 4,304,978 to Saunders is drawn to a method and
apparatus utilizing a laser for heat treating a transformation
hardenable workpiece. The workpiece is initially coated with oxides
or phosphates to absorb the wavelength of the laser. Sufficiently
high laser power densities are provided at the workpiece surface to
cause an incandescent reaction with the workpiece. The incandescent
reaction only occurs at temperatures above the melting point of the
workpiece. In the areas where work-hardening has occurred a
textured surface of oxide results. This must be removed by wire
brushing. In the areas where work-hardening has not occurred
hydrochloric acid must be employed to remove the oxide layer. This
in direct contrast with the present invention where the laser heats
the workpiece to point lower than the melting points of the
titanium or titanium alloy so as to avoid possible deformation of
the workpiece.
[0011] U.S. Pat. No. 4,434,189, to Zaplatynsky, is directed to
coating metal substrates, preferably titanium and titanium alloys,
by forming TiN on the substrate surface. A laser beam strikes the
surface of a moving substrate. Unlike the present invention, this
process is performed in a purified nitrogen gas atmosphere. This
heated area reacts with the nitrogen gas to form a solid solution.
The alloying or formation of TiN occurs by diffusion of nitrogen
into the titanium.
[0012] U.S. Pat. No. 6,231,956 to Brenner et al., discloses a
process for creating a wear-resistant edge layer for titanium and
its alloys which can be subjected to high loads and has a low
coefficient of friction. Unlike the present invention, this process
involves melting the surface of the substrate in a controlled
atmosphere.
[0013] Therefore, there remains a need in the art for a simple and
cost-effective process by which a titanium or titanium alloy
workpiece may be substantially hardened, without the need for
special environments or pretreatments, so that the workpiece may be
used in abrasive mechanical and environmental conditions.
SUMMARY OF THE INVENTION
[0014] Accordingly, the instant invention is related to a method of
hardening an outer surface of a metallic substrate under standard
atmospheric conditions and without the use of inert gases or a
vacuum. The method comprises the steps of providing a substrate of
titanium or titanium alloys and focusing an electromagnetic
radiation beam formed by a laser generating apparatus onto at least
a portion of the substrate surface to heat the substrate surface to
a point below the melting point of the substrate and then cooling
the substrate surface. The laser intensity and duration is limited
such that a disposition of a chemical compound of the surface of
the substrate does not occur. The laser treated surface of the
metallic substrate has increased hardness and durability compared
to the untreated surface of the substrate.
[0015] It is an objective of the instant invention to provide
method of treating a metallic substrate with a laser having a high
power density and a short exposure time such that selected areas of
the substrate may be hardened as desired under normal atmospheric
conditions.
[0016] It is a further objective of the instant invention to
provide a method for hardening a metallic substrate which does not
require preconditioning, pretreatment, or coating prior to
treatment.
[0017] Yet another objective of the instant invention to provide a
method of hardening a metallic substrate where minimum distortion
and/or selective hardening of the workpiece are achieved.
[0018] Still another objective of the invention to teach a method
of hardening a metallic substrate where the contact time of the
laser on the substrate is sufficiently short so that no significant
melting of the substrate occurs.
[0019] Other objects and advantages of this invention will become
apparent from the following description taken in conjunction with
any accompanying drawings wherein are set forth, by way of
illustration and example, certain embodiments of this invention.
Any drawings contained herein constitute a part of this
specification and include exemplary embodiments of the present
invention and illustrate various objects and features thereof.
BRIEF DESCRIPTION OF THE FIGURES
[0020] The patent or application file contains at least one drawing
executed in color. Copies of this patent or patent application
publication with color drawing(s) will be provided by the Office
upon request and payment of the necessary fee.
[0021] FIG. 1 is a scanning electron micrograph (SEM) image of a
cross section of a titanium alloy (Ti-6Al-4V) substrate magnified
200.times., treated by the method of the present invention;
[0022] FIG. 2 is a scanning electron micrograph image, at low
magnification, of the titanium substrate of FIG. 1 mounted on a
specimen stub with wire (scale bar is 1000 microns);
[0023] FIG. 3 is a detail of the surface of the titanium substrate
seen in FIG. 2 at a higher magnification (scale bar is 200
microns);
[0024] FIG. 4 is another SEM micrograph of the center of the
titanium substrate of FIG. 1 in cross-section (scale bar is 100
microns);
[0025] FIG. 5 is an Energy Dispersive Spectrum (EDS) collected from
the central region of the titanium substrate's cross-section
illustrated in FIG. 4;
[0026] FIG. 6 is another EDS spectrum representative of fractured
surfaces of the outer layer of the titanium substrate;
[0027] FIG. 7 is an EDS spectrum representative of surface
elemental composition of the outer layer of the titanium
substrate;
[0028] FIG. 8 is a SEM image of the area from which the spectrum
presented in FIG. 6 was collected (scale bar is 5 microns);
[0029] FIG. 9 is a SEM image representative of the scan area from
which the FIG. 7 surface spectrum was collected (scale bar is 20
microns)
[0030] FIG. 10 illustrates the test results for titanium alloy
(Ti-6Al-4V) treated by the method of the present invention at
various laser parameters, such as frequency and current;
[0031] FIG. 11 is a photograph of a bar of 303 stainless steel with
a helical groove cut into it by a titanium cutter hardened by the
present inventive method;
[0032] FIG. 12 is a photograph of a bar of 303 stainless steel
which was attempted to be cut by a titanium cutter which was not
hardened by the present inventive method; and
[0033] FIG. 13 is a photograph of the untreated titanium cutter
used in the FIG. 12 photograph.
DETAILED DESCRIPTION OF THE INVENTION
[0034] Detailed embodiments of the instant invention are disclosed
herein, however, it is to be understood that the disclosed
embodiments are merely exemplary of the invention, which may be
embodied in various forms. Therefore, specific functional and
structural details disclosed herein are not to be interpreted as
limiting, but merely as a basis for the claims and as a
representation basis for teaching one skilled in the art to
variously employ the present invention in virtually any
appropriately detailed structure.
[0035] It has been discovered by the present inventor that
hardening of titanium and titanium alloys is achieved using a laser
generating apparatus operating under a specific set of parameters.
These parameters result in a surface hardness that does not gall or
chip off when in moving contact with other metal parts. This makes
the treated substrate particularly desirable when used in implant
or medical applications. The hardening process is performed under
open atmospheric conditions, e.g. normal air and at room
temperature. Thus, no specialized equipment (vacuum chamber, gas
chamber, supply of inert gas, etc.) is required. This makes the
present process easier and inexpensive to perform than the methods
taught by the prior art. Moreover, the use of a laser generating
apparatus for hardening titanium and titanium alloys allows for
selective treatment of the workpiece wherein only certain areas on
the surface of a workpiece can be hardened without affecting the
other surface areas thereby reducing the cost of the process.
[0036] According to a preferred, albeit non-limiting, embodiment of
the invention, surface hardening was accomplished with a Nd--YAG
laser used under the following range of parameters. Other lasers
can be used such as a carbon dioxide laser without departing from
the scope of the invention. Utilizing a Q-switch on the laser the
frequency (KHz) of the pulsed laser was from about 25 to about 50
KHz; the power or current (Amps) was from about 8 to about 25
amperes; and the speed at which the laser beam traveled across the
treated surface was from about 0.01 to about 5.0 inches/sec (IPS).
Also, the number of laser cycles, repeats of beam travel across the
treated surface, was variable. The focal length of the laser was
variable and dependent on the type of lens used in the laser.
Further, the use of a continuous wave (CW) or non-pulsed laser beam
also resulted in hardening of the substrate surface.
EXAMPLE 1
[0037] This is an illustrative example in which an alloy of
titanium has been treated. It is within the purview of the present
invention that pure titanium or any titanium alloy could be
similarly treated.
[0038] A substrate made of the Alpha-Beta alloy of titanium
comprising about 6 wt. % of aluminum and about 4 wt. % of vanadium
(also referred to as Ti-6Al-4V) with the dimensions of
10.times.40.times.60 mm3 which was cleaned by a solvent to removal
all residues. The substrate was positioned on the work table under
standard atmospheric conditions (temperature and pressure). A
Q-switched Nd:YAG laser having a power density of
60.6664.times.10.sup.4 watts/mm.sup.2 at the surface of the
substrate was employed. The laser was pulsed in the frequency range
of 10-50 KHz. It was also operated in a continuous wave mode. The
current applied was 10-20 apms. The laser beam was in constant
motion so there was no "dwell time" of the beam on the substrate.
The electromagnetic radiation beam formed by the laser generating
apparatus was focused onto a portion of the surface of the
Ti-6Al-4V substrate. The surface was heated to a point below the
melting point of the substrate. The substrate was then cooled. The
cooling could be performed by any means of cooling deemed suitable,
e.g., water, air, etc. The laser-treated surface of the cooled
substrate exhibited increased hardness and durability than the
untreated surface of the substrate as evidenced by the results
illustrated in the table of FIG. 11.
[0039] In addition a sample of the titanium alloy hardened by the
method described above was sent to Matco Associates, Inc.
(Pittsburgh, Pa.) to perform a Knoop microhardness test to
determine its surface hardness. The Knoop microhardness test was
conducted at room temperature (RT). A transverse cross-section
through the coating and substrate was prepared for subsequent
metallographic inspection. In the polished condition a Knoop
microhardness inspection, using a 200 gram load, was performed in
the outer 0.0015 inches of the coating as is known in the art.
[0040] Table 1 below provides the results of this Knoop
microhardness test and includes one approximate value for Rockwell
Hardness C scale (HRC). The ten individual tests results shown in
TABLE 1 for Rockwell Hardness C scale (HRC) are approximate values.
The resultant average Knoop hardness number (KHN) of the ten tests
is about 1080 and Rockwell hardness is above about 69.7, which, as
discussed above, is well above that needed to prevent galling,
seizing, and wear (about 40-C to about 55-C Rockwell hardness) in
the substrate when in rubbing and sliding contact with other
materials.
TABLE-US-00002 TABLE 1 Microhardness Test KHN Approx. HRC 965 69.7
980 -- 980 -- 1160 -- 1040 -- 1040 -- 1190 -- 1230 -- 1020 -- 1200
--
Analysis of Elemental Composition of Outer Coating on the Treated
Titanium of Example I.
[0041] A sample rod of the titanium alloy hardened by the
aforementioned inventive procedure was submitted to Impact
Analytical (Midland, Mich.) for identification of the composition
of the hard surface layer. Energy dispersive spectroscopy (EDS) of
the central and outer areas of the rod was performed in the
scanning electron microscope (SEM), to compare the elemental
composition of the surface layer (FIGS. 6 & 7) with the inner
rod (FIG. 5). It was discovered that the surface layer contains
significant oxygen which is not present in the bulk rod.
[0042] The treated sample of titanium was first rinsed with acetone
and methanol, blown dry with filtered nitrogen, and tied to a SEM
sample stub with wire to avoid contamination, as illustrated in
FIG. 2. The resulting specimen was inserted in the SEM at the
accelerating voltage of approximately 20 keV. The EDS spectra and
digital images were collected from the outer layer and the center
of the sample. Additional spectra and images were collected from
fractured surfaces of the outer layer produced by the Knoop
microhardness test. Spectra were deconvoluted to determine
elemental composition. The surface layer and bulk spectra were
compared and the results are presented in TABLE 2.
[0043] FIG. 1 presents an overview of the titanium sample as
mounted in the scanning electron micrograph (SEM). The photograph
of the sample is magnified at 200.times., showing the coating on
the titanium substrate sample and one of the Knoop hardness
indentations, after etching with Kroll's reagent.
[0044] FIG. 2 provides further detail of the sample surface
morphology. This figure is a low magnification scanning electron
micrograph (SEM) of the sample of titanium Ti-6Al-4V treated by the
present inventive hardening process. As described above, the sample
is mounted on a specimen stub (not shown) with wire. Note the
distinctive surface morphology of the surface, characterized by
parallel band domains with overlapping orientations.
[0045] FIG. 3 is an image detail of the surface seen in FIG. 2, at
a higher magnification.
[0046] FIG. 4 is a SEM micrograph of the center of the sample bar
in cross-section. This is the surface area scanned for x-ray
collection comprising the spectrum seen in FIG. 5.
[0047] FIG. 5 is the spectrum derived from an EDS collected from
the central region of the rod cross-section shown in FIG. 4, and is
representative of the bulk rod material. SEM is used in conjunction
with EDS to perform elemental analysis on the microscopic section
of the material being test or contaminants that may be present as
is well known in the art. The EDS spectrum of FIG. 5 illustrates
the x-ray energy (keV) seen along the abscissa versus the relative
of counts of the detected x-rays (y-axis). The energy of the x-ray
is characteristic of the element from which the x-ray was emitted.
This spectrum provides both the qualitative and quantitative values
for the elements present in the sample.
[0048] As seen in FIG. 5, the dominant titanium peak has been
truncated, such that the other peaks can be scaled for visibility.
Note that an overlap with a secondary feature of Ti (K beta peak or
second peak) exaggerates the apparent signal from vanadium. The
presence of small V beta peak supports the conclusion that vanadium
is present at greater than trace levels. The asterisk indicated a
peak artifact, associated with the large Ti signal.
[0049] FIG. 6 is another EDS spectrum representative of fracture
surfaces of the outer layer, providing evidence of the composition
of the outer layer without surface contamination or other
variations associated with the extreme outer surface of the
coating. Comparison with the bulk spectrum in FIG. 5 reveals that
oxygen is now significantly detected. This element is not present
in the bulk material. The vanadium signal is again exaggerated by
overlap with Ti as noted in the FIG. 5 caption. The Ti peak
artifact is again noted by an asterisk.
[0050] FIG. 7 is EDS spectrum representative of the surface
elemental composition of the outer layer. Although the sample was
cleaned with solvents as noted above (acetone, methanol), due to
the rough surface microstructure some difference with the FIG. 6
spectrum may be due to trapped contamination. Aluminum (Al), Carbon
(C), and Oxygen (O) are significantly more prevalent than in
previous regions, as are several other elements as summarized in
TABLE 2 above. The vanadium signal is again exaggerated by overlap
with Ti as noted in the FIG. 5 caption. The Ti peak artifact is
again noted by an asterisk.
TABLE-US-00003 TABLE 2 Elements detected by Energy Dispersive
Spectroscopy (EDS). Sample Position Major elements Minor elements
Trace elements Center (bulk) Ti Al, C, V Si Surface layer Ti Al, C,
O, V Ca, Fe, Si fracture site Surface Ti, Al, C, O Ca, Fe, Si, V
Cl, K, Na, S
[0051] FIG. 8 is another SEM image of the area of the sample from
which the EDS spectrum presented in FIG. 6 was collected. These
regions of micro-fracture in the surface coating enabled the
generation of the x-rays from the internal structure of the surface
layer of interest.
[0052] FIG. 9 is a SEM image which is representative of the area of
the sample from which the FIG. 7 spectrum was collected.
[0053] Observation of the sample in the stereomicroscope revealed
chipped, fractured areas in the surface coating on one cross-cut
end of the rod sample. These regions afforded the opportunity to
gain an approximate measure of the layer thickness of about 60 to
about 100 microns. Additionally, these fractured surfaces enables
elemental analysis of the internal composition of the outer layer.
Again, significant differences between the internal and surface
composition of the outer layer of interest are noted in Table 2.
Although some of the differences may be due to contamination,
trapped by the rough morphology of the external surface (see FIG.
2), it is unlikely that the significant increase in the signal for
aluminum, carbon and oxygen, relative to titanium content, is
attributable solely to contamination. The different elemental
composition at the surface of the outer layer is more likely to
originate from the layer forming process.
EXAMPLE 2
[0054] In this example, the ability of a cutting tool made from the
untreated Ti-6Al-4V substrate and a cutting tool made from the same
Ti-6Al-4V substrate but treated by the inventive process to cut
into 303 stainless steel were compared. FIG. 11 is a photograph of
a bar of 303 stainless steel with a helical groove cut into it by a
titanium cutter treated by the method of the present invention. The
resultant groove is about 1/16 of an inch deep. FIG. 12 is a
photograph of a bar of 303 stainless steel which was attempted to
be cut by a titanium cutter which was not treated by the method of
the present invention. It can be seen that there are only minimal
abrasions on the surface of the bar. There is no penetration into
the bar as shown in FIG. 11. FIG. 13 is a photograph illustrating
the damage done to the untreated titanium cutter which was used to
attempt to cut the bar of 303 stainless steel shown in FIG. 12.
[0055] All patents and publications mentioned in this specification
are indicative of the levels of those skilled in the art to which
the invention pertains. All patents and publications are herein
incorporated by reference to the same extent as if each individual
publication was specifically and individually indicated to be
incorporated by reference.
[0056] It is to be understood that while a certain form of the
invention is illustrated, it is not to be limited to the specific
form or arrangement herein described and shown. It will be apparent
to those skilled in the art that various changes may be made
without departing from the scope of the invention and the invention
is not to be considered limited to what is shown and described in
the specification and any drawings/figures included herein.
[0057] One skilled in the art will readily appreciate that the
present invention is well adapted to carry out the objectives and
obtain the ends and advantages mentioned, as well as those inherent
therein. The embodiments, methods, procedures and techniques
described herein are presently representative of the preferred
embodiments, are intended to be exemplary and are not intended as
limitations on the scope. Changes therein and other uses will occur
to those skilled in the art which are encompassed within the spirit
of the invention and are defined by the scope of the appended
claims. Although the invention has been described in connection
with specific preferred embodiments, it should be understood that
the invention as claimed should not be unduly limited to such
specific embodiments. Indeed, various modifications of the
described modes for carrying out the invention which are obvious to
those skilled in the art are intended to be within the scope of the
following claims.
* * * * *