U.S. patent application number 11/128703 was filed with the patent office on 2006-11-16 for bare metal laser shock peening.
Invention is credited to Roger Owen Barbe, Seetha Ramaiah Mannava, Todd Jay Rockstroh.
Application Number | 20060254681 11/128703 |
Document ID | / |
Family ID | 37417960 |
Filed Date | 2006-11-16 |
United States Patent
Application |
20060254681 |
Kind Code |
A1 |
Mannava; Seetha Ramaiah ; et
al. |
November 16, 2006 |
Bare metal laser shock peening
Abstract
A method of making a laser shock peened article includes bare
laser shock peening a bare metallic surface of a substrate of the
article without using an ablative coating and forming a
pre-stressed region having deep compressive residual stresses
extending into the article and a recast layer above the
pre-stressed region. Removing just the recast layer with an
abrasive vibratory process with an abrasive media. The vibratory
process may include one or more of the following: abrasive tumbling
including packing the article within a bed of abrasive particles
and shaking the article within the bed during a tumbling cycle,
mechanical peening including peening the article with small
particles which either abrade and/or shatter a brittle surface of
the recast layer, and abrasive polishing including loading the
article into a bed of paste including abrasive particles and
oscillating the bed across and around the article.
Inventors: |
Mannava; Seetha Ramaiah;
(Cincinnati, OH) ; Rockstroh; Todd Jay;
(Maineville, OH) ; Barbe; Roger Owen; (Cincinnati,
OH) |
Correspondence
Address: |
Steven J. Rosen;Patent Attorney
4729 Cornell Rd.
Cincinnati
OH
45241
US
|
Family ID: |
37417960 |
Appl. No.: |
11/128703 |
Filed: |
May 13, 2005 |
Current U.S.
Class: |
148/565 |
Current CPC
Class: |
C22F 3/00 20130101; B23K
26/356 20151001 |
Class at
Publication: |
148/565 |
International
Class: |
C22F 3/00 20060101
C22F003/00 |
Claims
1. A method of making a laser shock peened article comprising the
following steps: (a) bare laser shock peening a bare metallic laser
shock peening surface of a substrate of the article without using
an ablative coating on the metallic surface and forming a
pre-stressed region having deep compressive residual stresses
imparted by laser shock peening extending into the article from a
laser shock peened surface and a recast layer above the laser shock
peened surface and the pre-stressed region, and (b) removing just
the recast layer with an abrasive vibratory process with an
abrasive media.
2. A method as claimed in claim 1 further comprising the vibratory
process including an abrasive tumbling process including packing
the article within a bed of abrasive particles and shaking the
article within the bed during a tumbling cycle for a period of
time.
3. A method as claimed in claim 2 further comprising the period of
time of the tumbling cycle being in a range of several minutes to
several hours.
4. A method as claimed in claim 3 further comprising the tumbling
cycle being run at vibratory frequencies in a range from a few Hz
to several hundred Hz.
5. A method as claimed in claim 2 wherein the abrasive media
includes stones characterized as having a size range from about 0.2
inches to 1.0 inches.
6. A method as claimed in claim 1 further comprising the vibratory
process including mechanical peening of the article with small
particles which either abrade and/or shatter a brittle surface of
the recast layer.
7. A method as claimed in claim 6 further wherein the small
particles are glass beads.
8. A method as claimed in claim 1 further comprising the vibratory
process being an abrasive polishing process including loading the
article into a bed of paste including abrasive particles and
oscillating the bed across and around the article.
9. A method as claimed in claim 1 further comprising the vibratory
process including a combination of two or more of the following
processes: an abrasive tumbling process including packing the
article within a bed of abrasive particles and shaking the article
within the bed during a tumbling cycle for a period of time, a
mechanical peening process including peening the article with small
particles which either abrade and/or shatter a brittle surface of
the recast layer, and an abrasive polishing process including
loading the article into a bed of paste including abrasive
particles and oscillating the bed across and around the
article.
10. A method as claimed in claim 1 further comprising the bare
laser shock peening including providing a confining medium over the
bare metallic surface and firing a laser beam through the confining
medium onto the bare surface with sufficient power to vaporize
material of the substrate to form the pre-stressed region having
deep compressive residual stresses imparted by laser shock peening
extending into the article and the recast layer above the
pre-stressed region.
11. A method as claimed in claim 1 wherein the article is a gas
turbine engine airfoil having a leading edge and pressure and
suction sides and the bare laser shock peening is performed at
least on a portion of the bare metallic surface along the leading
edge on both the pressure and suction sides of the airfoil
simultaneously.
12. A method as claimed in claim 11 further comprising the
vibratory process being an abrasive tumbling process including
packing the article within a bed of abrasive particles and shaking
the article within the bed during a tumbling cycle for a period of
time.
13. A method as claimed in claim 12 further comprising the period
of time of the tumbling cycle being in a range of several minutes
to several hours.
14. A method as claimed in claim 13 further comprising the tumbling
cycle being run at vibratory frequencies in a range from a few Hz
to several hundred Hz.
15. A method as claimed in claim 12 wherein the abrasive media
includes stones characterized as having a size range from about 0.2
inches to 1.0 inches.
16. A method as claimed in claim 11 further comprising the
vibratory process being a mechanical peening including peening the
article with small particles which either abrade and/or shatter a
brittle surface of the recast layer.
17. A method as claimed in claim 16 further wherein the small
particles are glass beads.
18. A method as claimed in claim 11 further comprising the
vibratory process being an abrasive polishing process including
loading the article into a bed of paste including abrasive
particles and oscillating the bed across and around the
article.
19. A method as claimed in claim 11 further comprising the bare
laser shock peening including providing a confining medium over the
bare metallic surface and firing a laser beam through the confining
medium onto the bare surface with sufficient power to vaporize
material of the substrate to form the pre-stressed region having
deep compressive residual stresses imparted by laser shock peening
extending into the article and the recast layer above the
pre-stressed region.
20. A method as claimed in claim 1 further comprising a preliminary
abrasive grinding process to pre-clean the laser shock peened
surface of the article after the bare laser shock peening and prior
to the removing just the recast layer with an abrasive vibratory
process.
21. A method as claimed in claim 20 wherein the preliminary
abrasive grinding process includes using a flexible abrasive wheel
to pre-clean the laser shock peened surface.
22. A method as claimed in claim 11 further comprising: a
preliminary abrasive grinding process to pre-clean the laser shock
peened surface of the airfoil after the bare laser shock peening
and prior to the removing just the recast layer with an abrasive
vibratory process, the preliminary abrasive grinding process
including running the laser shock peened surface along the leading
edge of the airfoil between two slightly spaced apart and spinning
flexible abrasives wheels to pre-clean the laser shock peened
surface on both the pressure and suction sides of the airfoil.
23. A laser shock peened article comprising: a laser shock peened
surface of a substrate of the article, a pre-stressed region having
deep compressive residual stresses imparted by laser shock peening
extending into the article from the laser shock peened surface, the
laser shock peened surface and the pre-stressed region having been
formed using bare laser shock peening, the bare laser shock peening
a bare metallic surface of a substrate of the article without using
an ablative coating on the metallic surface and forming a
pre-stressed region having deep compressive residual stresses
imparted by laser shock peening extending into the article and a
recast layer above the pre-stressed region, and removing just the
recast layer with an abrasive vibratory process with an abrasive
media.
24. An article as claimed in claim 23 wherein the vibratory process
includes one or more of the following processes: an abrasive
tumbling process including packing the article within a bed of
abrasive particles and shaking the article within the bed during a
tumbling cycle for a period of time, a mechanical peening process
including peening the article is with small particles which either
abrade and/or shatter a brittle surface of the recast layer, and an
abrasive polishing process including loading the article into a bed
of paste including abrasive particles and oscillating the bed
across and around the article.
25. An article as claimed in claim 23 further comprising the laser
shock peened surface being located along a leading edge of a gas
turbine engine airfoil.
26. An article as claimed in claim 25 wherein the vibratory process
includes one or more of the following processes: an abrasive
tumbling process including packing the article within a bed of
abrasive particles and shaking the article within the bed during a
tumbling cycle for a period of time, a mechanical peening process
including peening the article with small particles which either
abrade and/or shatter a brittle surface of the recast layer, and an
abrasive polishing process including loading the article into a bed
of paste including abrasive particles and oscillating the bed
across and around the article.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to laser shock peening and, more
particularly, to methods for laser shock peening uncoated
surfaces.
[0002] Laser shock peening (LSP) or laser shock processing, as it
is also referred to, is a process for producing a region of deep
compressive residual stresses imparted by laser shock peening a
surface area of an article. Laser shock peening typically uses one
or more radiation pulses from high and low power pulsed lasers to
produce an intense shock wave at the surface of an article similar
to methods disclosed in U.S. Pat. No. 3,850,698 entitled "Altering
Material Properties"; U.S. Pat. No. 4,401,477 entitled "Laser Shock
Processing"; and U.S. Pat. No. 5,131,957 entitled "Material
Properties". Laser shock peening, as understood in the art and as
used herein, means utilizing a pulsed laser beam from a laser beam
source to produce a strong localized compressive force on a portion
of the surface. The portion of the surface may have an ablative
coating or be bare meaning having no ablative coating. An explosive
force is produced at the impingement point of the laser beam by an
instantaneous ablation or vaporization of a thin layer of the
material surface or of a coating (such as tape or paint) on the
surface which forms a plasma.
[0003] Laser shock peening is being developed for many applications
in the gas turbine engine field, some of which are disclosed in the
following U.S. Pat. No. 5,736,965 entitled "On The Fly Laser Shock
Peening"; U.S. Pat. No. 5,591,009 entitled "Laser shock peened gas
turbine engine fan blade edges"; U.S. Pat. No. 5,531,570 entitled
"Distortion control for laser shock peened gas turbine engine
compressor blade edges"; U.S. Pat. No. 5,492,447 entitled "Laser
shock peened rotor components for turbomachinery"; U.S. Pat. No.
5,674,329 entitled "Adhesive tape covered laser shock peening"; and
U.S. Pat. No. 5,674,328 entitled "Dry tape covered laser shock
peening", all of which are assigned to the present Assignee.
[0004] High energy laser beams, from about 20 to about 50 Joules,
or low energy laser beams, from about 3 to about 10 Joules, have
been used and other levels are contemplated. See, for example, U.S.
Pat. No. 5,674,329 (Mannava et al.) issued Oct. 7, 1997 (LSP
process using high energy lasers) and U.S. Pat. No. 5,932,120
(Mannava et al.) issued Aug. 3, 1999 (LSP process using low energy
lasers). Low energy laser beams can be produced using different
laser materials such as neodymium doped yttrium aluminum garnet (Nd
YAG), Nd:YLF, and others. Laser shock peening processes typically
employ a curtain of water or other confinement liquid medium flowed
over the article or some other method to provide a plasma confining
medium. This medium enables the plasma to rapidly achieve shockwave
pressures that produce the plastic deformation and associated
residual stress patterns that constitute the LSP effect. The
curtain of water provides a confining medium, to confine and
redirect the process generated shockwaves into the bulk of the
material of a component being LSP'D, to create the beneficial
compressive residual stresses.
[0005] The LSP process generates deep compressive stresses in the
article resulting in improved fatigue strength under foreign object
damage (FOD) conditions. LSP improves material properties such as
high cycle fatigue, low cycle fatigue, corrosion & erosion
resistance. However, this process also generates residual tensile
stresses which can cause the loss of fatigue strength and HCF and
LCF capability. It is desirable to LSP articles such as rotating
gas turbine engine components without using an ablative coating
because of the extra cost and time associated with coating and
recoating surfaces of the components that are laser shock peened.
Laser shock peening of leading and/or trailing edges of fan,
compressor, and turbine blade airfoils may require several coatings
and recoatings of the surfaces that are laser shock peened. Devices
used to coat the components are expensive and/or difficult to
maintain in the noisy and dirty environment of the LSP process.
[0006] The benefit of coating surfaces during the LSP process
include lower ignition thresholds and enhancing the magnitude of
the LSP effect. If the coating is eliminated, then the surface of
the component will typically be burned either from the laser
radiation directly or the broadband radiation from the expanding
blast wave (plasma) above the surface of the component, or both.
Surface burning is of a concern because the component is
cosmetically "scarred" and will appear different from similar
components that are non-LSP'd or LSP'd with a surface coating. The
scarring is melted and resolidified component material termed
"recast" or "remelt". Surface burning may also cause the component
to exhibit a lower LSP effect as compared to an LSP process using
ablative coating. The component can potentially fail (circumvent
the LSP deep compressive stress) if cracks or defects can initiate
in the burned surface layer and propagate around the LSP effected
area.
[0007] Thus, it is highly desirable to provide a laser shock
peening process on bare metal without the use of ablative coatings
and avoid and counter the detrimental effects of surface burning
typically associated with bare laser shock peening. It also highly
desirable to provide such a process in an inexpensive manner. It is
also desirable to remove the recast formed during bare surface
laser shock peening.
BRIEF DESCRIPTION OF THE INVENTION
[0008] A method of making a laser shock peened article includes
bare laser shock peening a bare metallic surface of a substrate of
the article without using an ablative coating and forming a
pre-stressed region. The pre-stressed region has deep compressive
residual stresses extending into the article. The bare laser shock
peening causes a recast layer to form above the pre-stressed
region. A next step of the method is removing just the recast layer
with an abrasive vibratory process with an abrasive media. The
vibratory process may include one or more of the following:
abrasive tumbling including packing the article within a bed of
abrasive particles and shaking the article within the bed during a
tumbling cycle, mechanical peening including peening the article
with small particles which either abrade and/or shatter a brittle
surface of the recast layer, and abrasive polishing process
including loading the article into a bed of paste including
abrasive particles, and oscillating the bed across and around the
article.
[0009] One embodiment of the abrasive tumbling process includes
packing the article within a bed of abrasive particles and shaking
the article within the bed during a tumbling cycle for a period of
time in a range of several minutes to several hours and using
vibratory frequencies in a range from a few Hz to several hundred
Hz. One abrasive media includes stones characterized as having a
size range from about 0.2 inches to 1.0 inches.
[0010] The method of making a laser shock peened article by bare
laser shock peening without the use of ablative coatings and
removing just the recast layer with an abrasive vibratory process
is less expensive than using coatings and avoids and counters the
detrimental effects of surface burning associated with bare laser
shock peening.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a perspective view of an exemplary aircraft gas
turbine engine fan blade.
[0012] FIG. 2 is a cross-sectional view illustration of the fan
blade in FIG. 1 after it has been bare laser shock peened.
[0013] FIG. 3 is a schematic perspective view illustration of a fan
blade, similar to the blade in FIG. 1, mounted in a laser shock
peening system illustrating an exemplary bare laser shock peening
step of the method of the present invention.
[0014] FIG. 4 is a partial cross-sectional and a partial schematic
view of the setup in FIG. 3.
[0015] FIG. 5 is an enlarged view illustration of a bare laser
shock peened leading edge of the blade illustrated in FIG. 2.
[0016] FIG. 6 is an enlarged view illustration of a bare laser
shock peened surface of the blade illustrated in FIG. 5.
DETAILED DESCRIPTION OF THE INVENTION
[0017] Illustrated in FIGS. 1, 2, and 3, is a fan blade 8 having an
airfoil 34 made of a Titanium alloy extending radially outward from
a blade platform 36 to a blade tip 38. The fan blade 8 exemplifies
an article 12 having a bare (uncoated) laser shock peening surface
54 of a hard metallic substrate 10 a portion of which is laser
shock peened bare meaning without an ablative coating. The fan
blade 8 includes a root section 40 extending radially inward from
the platform 36 to a radially inward end 37 of the root section 40.
At the radially inward end 37 of the root section 40 is a blade
root 42 which is connected to the platform 36 by a blade shank 44.
The airfoil 34 extends in the chordwise direction between a leading
edge LE and a trailing edge TE of the airfoil. A chord C of the
airfoil 34 is the line between the leading edge LE and trailing
edge TE at each cross-section of the blade as illustrated in FIG.
2. A pressure side 46 of the airfoil 34 faces in the general
direction of rotation as indicated by an arrow V and a suction side
48 is on the other side of the airfoil and a mean-line ML is
generally disposed midway between the two faces in the chordwise
direction.
[0018] The fan blade 8 has leading and trailing edge sections 50
and 70 that extend along the leading and trailing edges LE and TE,
respectively, of the airfoil 34 from the blade platform 36 to the
blade tip 38. The leading and trailing edge sections 50 and 70
includes first and second widths W1 and W2, respectively, such that
the leading and trailing edge sections 50 and 70 encompass nicks 52
and tears that may occur along the leading and trailing edges of
the airfoil 34. The airfoil 34 is subject to a significant tensile
stress field due to centrifugal forces generated by the fan blade 8
rotating during engine operation. The airfoil 34 is also subject to
vibrations generated during engine operation and the nicks 52 and
tears operate as high cycle fatigue stress risers producing
additional stress concentrations around them.
[0019] To counter fatigue failure of portions of the blade along
possible crack lines that can develop and emanate from the nicks
and tears, one or both of the pressure side 46 and the suction side
48 are bare laser shock peened forming laser shock peened surfaces
55 with a pre-stressed region 56 having deep compressive residual
stresses imparted by laser shock peening (LSP) extending into the
airfoil 34 from the laser shock peened surfaces 55 as seen in FIG.
2. The pre-stressed regions 56 are illustrated as being
co-extensive with the leading and trailing edge sections 50 and 70
in the chordwise direction to the full extent of widths W1 and W2
and are deep enough into the airfoil 34 to coalesce for at least a
part of the widths. The pre-stressed regions 56 are shown
co-extensive with the leading edge section 50 in the radial
direction along the leading edge LE but may be shorter.
[0020] Illustrated in FIG. 4 is a laser shock peening apparatus 1
including a laser beam apparatus having a generator 31 with an
oscillator and a pre-amplifier and a beam splitter which feeds the
pre-amplified laser beam into two beam optical transmission
circuits each having a first and second amplifier 30 and 32,
respectively, and optics 35 which include optical elements that
transmit and focus the laser beam 2 on the bare or uncoated laser
shock peening surfaces 54. The controller 24 may be used to
modulate and fire the laser beam apparatus to fire the laser beam 2
on the laser shock peening surface 54 in a controlled manner.
[0021] A clear confining medium 68 to cover the laser shock peening
surface 54 is provided by a curtain of clear fluid such as water 21
supplied by a water nozzle 20 at the end of a water supply tube 19.
The curtain of water 21 is particular to the exemplary embodiment
illustrated herein, however, other types of confining mediums may
be used. The laser shock peening apparatus 1 illustrated herein
includes a laser beam apparatus including a generator 31 having an
oscillator and a pre-amplifier and a beam splitter which feeds the
pre-amplified laser beam into two beam optical transmission
circuits each having a first and second amplifier 30 and 32,
respectively, and optics 35 which include optical elements that
transmit and focus the laser beam 2 on the laser shock peening
surface 54. The controller 24 may be used to modulate and fire the
laser beam apparatus to fire the laser beam 2 on the bare laser
shock peening surface 54 in a controlled manner.
[0022] The laser beam shock induced deep compressive residual
stresses in the compressive pre-stressed regions 56 are generally
about 50-150 KPSI (Kilo Pounds per Square Inch) extending from the
bare laser shock peened surfaces 55 to a depth of about 20-50 mils
into the compressive pre-stressed regions 56. The laser beam shock
induced deep compressive residual stresses are produced by
repetitively firing a high energy laser beam 2 that is defocused+a
few mils with respect to the laser shock peening surface 54. The
laser beam 2 typically has a peak power density on the order of
magnitude of a gigawatt/cm.sup.2 and is fired with a curtain of
flowing water or other fluid that is flowed over the laser shock
peening surface 54 or some other clear confining medium.
[0023] Bare metal of the metallic substrate 10 is ablated
generating plasma which results in shock waves on the surface of
the material. These shock waves are redirected towards the laser
shock peening surface 54 by the clear liquid confining medium 68,
illustrated herein as the curtain of water 21, or confining layer
to generate travelling shock waves (pressure waves) in the material
below the laser shock peening surface 54. The amplitude and
quantity of these shockwave determine the depth and intensity of
compressive stresses.
[0024] Referring to FIGS. 5 and 6, during the bare laser shock
peening process described above a recast layer 11 of melted and
resolidified material of the metallic substrate 10 is formed
directly above the compressive pre-stressed regions 56 which extend
inward into the article from the bare laser shock peened surfaces
55. The recast layer 11 may cause article to exhibit a lower LSP
effect as compared to an article laser shock peened using an
ablative coating. The article may also fail, by circumventing the
LSP deep compressive stress, if cracks or defects can initiate in
the recast layer and propagate around the LSP area or compressive
pre-stressed region. The recast layer 11 is typically brittle.
[0025] The recast layer 11 reduces HCF strength of the fan blade 8
which was laser shock peened along the leading edge of the airfoil
34. The same is true for compressor and turbine blade airfoils. To
that end, as part of a method of making a laser shock peened
article 12, just the recast layer 11 above the pre-stressed region
56 is removed using a vibratory process with an abrasive media.
Several vibratory processes are suitable. One suitable vibratory
process is an abrasive tumbling process with the article being
packed within a bed of abrasive particles and shaken during a
tumbling cycle for a period of time. The period of time of the
tumbling cycle may be in a range of several minutes to several
hours and the tumbling cycle may incorporate vibratory frequencies
in a range from a few Hz to several hundred Hz. The abrasive media
may include stones characterized as having a size range from about
0.2 inches to 1.0 inches.
[0026] Another suitable vibratory process is mechanical peening of
the article with small particles which either abrade and/or shatter
a brittle surface of the recast layer. In a more particular
embodiment the small particles are glass beads. Another suitable
vibratory process is abrasive polishing which includes loading the
article into a bed of paste including abrasive particles and
oscillating the bed across and around the article. Another suitable
process is a combination of two or more of the above mentioned
processes. All three of the above mentioned vibratory processes may
be used and particularly in the following order: the abrasive
tumbling, the mechanical peening, and the abrasive polishing.
[0027] Vibratory finishing processes well known in the art for
removing burrs from castings include barrelling, tumbling,
rotating, agitating, spinning, shaking or centrifugal processes,
where one or more workpieces are placed in a container or similar
device with an abrasive medial or abrading elements that displace
portions of the workpiece during the vibratory finishing process.
The vibratory finishing process can be performed with or without a
solution in the container. Tumbling processes have been used for
many years during the manufacture of a wide variety of articles for
surface preparation or treatment. For example, tumbling has been
used for abrading, polishing, rough cutting, deburring, edge
radiusing, descaling, surface texture or property improvement,
cleaning, and destressing, among others. Various types of tumbling
systems used include barrel, vibratory, and centrifugal, alone or
in combinations, with or without liquid. Certain components for gas
turbine engines, for example blades, vanes and nozzles, are complex
in shape and have precision requirements for surface finish,
including edges. The tumbling process has been used for surface
treatment or preparation including removal of burrs and for the
rounding of sharp edges produced during manufacture, as well as to
achieve required surface finish.
[0028] One embodiment of the method of making a laser shock peened
article 12 includes a preliminary abrasive grinding process to
remove some level of recast prior to the tumbling or other
vibratory processes with an abrasive media and other subsequent
surface finishing operations or processes. The purpose is to insure
that all recast and only recast is removed and eliminate the need
for final inspections such as blue etch anodizing. An abrasive
wheel, a simple commercially available abrasive media such as
Scotch-Brite "Bristle Disks", "Flap Brush" or "Combi Wheel"
products from 3M, may be used in an automated abrasive wheel
grinding process to pre-clean the airfoils prior to the abrasive
tumbling, the mechanical peening, and/or the abrasive polishing
processes. The abrasive such as the Scotch-Brite (TM) material
which can also be impregnated with more aggressive abrasives such
as alumina and garnet. These wheels are typically over 1 inch in
diameter and over one inch in height and attached to the shaft of a
small motor, electric or pneumatically driven. A pair of
motors/abrasive wheel assemblies may be placed in a vertical
spinning orientation such that their outer diameters are a few mils
apart when spinning.
[0029] After the laser shock peening process the airfoil is passed
between the two spinning abrasive wheels, which are flexible, such
that surface imperfections such as LSP induced recast is abrasively
removed. These abrasive wheel finishing processes already are used
at various stages in the manufacture of a compressor airfoil and
the use for the method of making a laser shock peened article 12
with the bare laser shock peening process would simply involve
moving one of these processes immediately after the LSP
process.
[0030] While there have been described herein what are considered
to be preferred and exemplary embodiments of the present invention,
other modifications of the invention shall be apparent to those
skilled in the art from the teachings herein and, it is therefore,
desired to be secured in the appended claims all such modifications
as fall within the true spirit and scope of the invention.
Accordingly, what is desired to be secured by Letters Patent of the
United States is the invention as defined and differentiated in the
following claims.
* * * * *