Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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CUTTER ASSEMBLY AND PROCESS
BACKGROUND OF THE INVENTION
This invention pertains to repairing the blades
(vanes) of a gas turbine and, more particularly, to a
cutter assembly and process for removing and restoring the
blades or vanes of a gas turbine.
Gas turbines are extensively used in oil refineries,
such as with catalytic cracking units, ultracracking
units, power houses, and cogeneration plants, as well as
in chemical plants, power plants, and other industrial
sites to generate power.
In gas turbines, the moving rotor blades and the sta-
tionary stator blades experience considerable wear over
time due to erosion from dust, metal chips, and other
solid particulates and chemical corrosion from corrosive
gases, such as sulfur oxides and nitrogen oxides, in the
surrounding environment. Gas turbines with worn blades
are inefficient and often ineffective and must be
periodically repaired.
The repair and restoration of gas turbine blades
(vanesJ is not an easy job. It usually requires a team of
at least four or five people working 7 to 10, 24-hour,
days to fix and restore the gas turbine blades. During
such repair, the associated refinery equipment and operat-
ing unit are often required to be shut down, thereby caus-
ing loss of revenue ranging from about 1.75 to 10 milliondollars. Not only is such repair expensive from a stand-
point of loss of revenue, but it is tedious, cumbersome,
time-consuming, and difficult.
Over the years a variety of methods have been sug-
gested for overhauling, repairing, and replacing wornstator blades of a gas turbine. Such prior art methods
include heating, hammering, acetylene torching, chemical
dissolution, plasma deposition, machining, and punching.
In one common prior art method, the stator blades are
heated to a temperature of 600F to 800F and the blades,
base ring sections (shrouds), and/or the compressor case
of the gas turbine are hammered. Heating to such high
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temperatures followed by hammering can cause considerable
damage to the compressor case, thereby requiring replace-
ment, further downtime, and considerable expense.
Typifying, some of the different prior art methods,
techniques, and equipment for repairing turbine blades, as
well as other machines and machining operations, are those
shown in U.S. Patents 1,795,262; 1,798,224; 3,099,902;
3,421,265; 3,641,709; 4,141,124; 4,291,448; 4,291,973;
4,376,356; and 4,464,865. The above prior art methods,
techniques, and equipment have met with varying degrees of
success.
It is, therefore, desirable to provide an improved
cutter assembly and process for revamping gas turbine
blades.
SUMMARY OF THE INVENTION
An improved cutter assembly and process are provided
to revamp, overhaul, repair, and restore turbine blades
(vanes) and especially the stationary stator blades of an
axial compressor case of a gas turbine. Advantageously,
the novel cutter assembly and process are efficient, easy
to use, and effective. They are also safe, simple, eco-
nomical, and save considerable time and manpower.
To this end, the novel cutter assembly has a power-
driven grinding wheel, one or more counterweights, at
least one and preferably two control arms (swing arms)
which extend between and connect the grinding wheel and
counterweight, and a steering wheel assembly or other
rotation equipment to arcuately move and rotate the swing
arms and grinding wheel about the stator blades of a gas
turbine. In the preferred form, an adjustment assembly is
provided to adjust the length ~diameter) of the arms and
the depth of cut of the grinding wheel. Preferably, the
cutter assembly is equipped with a safety shield, a
reduction gear unit (gear box), and a special straddle
assembly to support the reduction gear unit and associated
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equipment as well as to facilitate setup and cutting of
the encased portions (dovetail stubs) of the turbine
blades.
In order to revamp, overhaul, and restore the stator
blades of a gas turbine, the encased dovetail stub por-
tions of the stator blades and the base ring section
(shroudJ of the compressor to which the stator blades are
attached, are arcuately cut in two or more pieces with the
grinding wheel of the cutter assembly. The cut stub por-
tions of the stator blade and base ring section can be
optionally heated such as with an oxy-acetylene torch, and
are knocked out of the compressor case with a hammer.
After the worn stator blades have been removed, new blades
are inserted into the grooved channels (tails) of the com-
pressor case, preferably at uniform intervals, and the gas
turbine is reassembled.
A more detailed explanation of the invention is pro-
vided in the following description and appended claims
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a perspective view of an axial flow com-
pressor case of a gas turbine;
Figure 2 illustrates the upper portions of the stator
blade being removed by an arc air torch;
Figure 3 is a perspective view of a cutter assembly
in accordance with principles of the present invention;
Figure 4 is a front view of the cutter assembly;
Figure 5 is a front view of the grinding wheel and
swing arms of the cutter assembly;
Figure 6 is a top view of a portion of the cutter
assembly;
Fiqure 7 is a perspective view of the cutter assembly
acruately cutting the lower encased stub portions of the
stator blades;
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Figure 8 is a perspective view of the cut lower stub
portions of the stator blades being jarred loose and
knocked out by a hammer; and
Figure 9 is a perspective view of new stator blades
being inserted into the grooved channels (tails) of the
axial flow compressor case.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
As shown in Figure 1, a typical gas turbine 20, such
as a frame 5, 6, or ~ gas turbine, has an axial flow com-
pressor 22 which is connected along a common shaft to a
power recovery section. The gas turbine can have as many
as 16 stages or more to stage the pressure within the gas
turbine, such as from atmospheric pressure to 990 psi.
Gas turbines are used for generating power in oil refin-
eries, such as for catalytic cracking units, ultra crack-
ing units, or cogeneration plants, as well as in
petrochemical plants, power plants, and other industrial
sites.
The gas turbine has stationary stator blades or vanes
24 and rotating rotor blades or vanes. The stator and
rotor blades wear out from use and prolonged exposure to
particulates and corrosive gases and have to be period-
ically repaired, replaced, or restored. In order to
repair the blades, the axial flow compressor and the rotor
assembly is removed from the gas turbine and disassembled.
The stator blades of the axial flow compressor are mounted
and encased in the base ring sections, shrouds, root sec-
tions, or holders 26 of the axial flow compressor case 28.
The base ring sections are typically mounted in undercut
dovetail sections or grooved channels 30 (Figure 2) of the
axial flow compressor case. The base ring sections and
axial flow compressor case are typically split into quad-
rants or semicircular portions 32.
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In order to remove the stator blades of the axial
flow compressor case, the upper elongated portions 34 of
the stator blades, which extend radially inwardly of the
base ring section, are removed, severed, and cut by a
torch, such as an arc air torch 36, as shown in Figure 2.
Thereafter, the lower stub portions 37, which are encased
in a tight interference fit in the base ring sections, are
arcuately cut in half by the rotating abrasive grinding
wheel 38 of a stator blade cutter assembly 40, as shown in
Figure 7. The grinding wheel has to have sufficient
structural and abrasive strength to cut the carbon steel
base ring sections (root sections or holders) of the steel
blades (vanes).
The cut stub portions of the stator blades and root
sections can then be heated to a temperature less than
425F before being repetitively struck and loosened with
the hammer. The cut stub portions and root sections are
repetitively struck with a hammer as shown in Figure 8, to
jar loose, vibrate,~and knock-out the remaining portions
of the stator blades and base ring sections from the com-
pressor case. If desired, the cast iron, axial flow com-
pressor case can also be repetitively struck with a hammer
H to facilitate removal of the root sections and the cut
stator blades, but care must be taken not to use excessive
force which might crack or otherwise damage the compressor
case.
The knocked-out portions of the root sections and
stator blades are emptied into a bin or other receptacle
and new stator blades and new root sections are inserted
into the grooved channels (recessed, dovetailed portions)
of the compressor case as shown in Figure 9.
The cutter assembly ~ of Figures 3-7 provides an
effective and safe stator blade holder cutter for effi-
ciently cutting the encased lower stub portions of thestator blades and base ring sections of a gas turbine.
The cutter assembly has a power-driven, abrasive grinding
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wheel 38 mounted on a grinding wheel shaft 42 (Figure 6).
A substantial portion of the grinding wheel is covered,
shielded, and protected by an arcuate grinding wheel cover
44. In the illustrative embodiment the grinding wheel
cover extends and covers about 30~ degrees of the grinding
wheel. The grinding wheel cover can cover a greater or
lesser amount of the wheel, if desired. The grinding
wheel cover is substantially rigid and has a generally
flat or planar upper arm-engaging, base portion 46 which
faces and abuts against an upper control, swing arm 48.
An electric motor 50 with an electric power cord 52 is
mounted and positioned in coaxial alignment with the
grinding wheel. The electric motor is operatively con-
nected to and rotates the grinding wheel shaft to rotateand drive the grinding wheel. In one test unit, a fifteen
horsepower electric motor was used and operated at 360
rpm.
The upper control, swing arm or plate 48 is posi-
tioned between the motor and the grinding wheel cover.
The upper arm has an upper, outer end portion 54 with an
outer upper opening or hole 56 (Figure 6) which rotatably
receives the grinding wheel shaft. The upper, inner end
portion 58 (Figure 5) of the upper arm has an inward,
upper pair of parallel elongated slots 60 and 62 which
receive the bolts 64 of an adjustment fastenin~ assembly
66. The upper outer end portion has a semicircular,
convex, arcuate outer edge 68. The upper arm has paral-
lel, upper, flat or planar, inwardly and outwardly facing
surfaces 70 and 72 (Figure 6) which extend between and
connect the upper, inner, and outer end portions. The
inwardly facing surface of the upper arm has a cover-en-
gaging portion 74, which is positioned adjacent to the
upper outer end portion and abuts against and engages the
base portion of the grinding wheel cover. The upper out-
wardly facing surface of the upper arm has a motor-engag-
ing portion 76, which is positioned adjacent to the upper
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end portion and abuts against and engages the electric
motor.
A lower control, swing arm or plate 78 is securely
connected to the upper arm by the bolts of the adjustment
fastening assembly. The lower arm has a lower outer end
portion 80 (Figure 6) with an outer lower opening or hole
82 which is positioned diametrically opposite of the
upper grinding wheel shaft-hole 56 of the upper arm. The
lower opening receives the counterweight shaft 84. The
lower, inner end portion of the lower arm has an inward,
lower pair of tapped internally threaded holes or openings
86 and 87 which are aligned in registration with the slots
of the upper arm. The bottom intermediate portion of the
lower arm can have an outwardly extending key 88 which
securely engages a keyway 89 in the upper arm to further
securely connect and maintain the parallel relationship of
the arms. The lower end portion of the lower arm has a
semicircular, convex arcuate edge 90 positioned diametri-
cally opposite of the curved upper end portion 68 of theupper arm. The lower arm has parallel, lower, flat or
planar, inwardly and outwardly facing surfaces 92 and 94
which extend between and connect the lower, inner and
outer end portions of the lower arm. The inwardly facing
surface of the lower arm has a central, coupling-engaging
portion 96 which is positioned in proximity to the lower
outer end portion of the lower arm. The inwardly-facing
surface of the lower arm also has an inner counterweight-
engaging portion 98 which is positioned adjacent to the
lower end portion of the lower arm. The outwardly-facing
surface of the lower arm has an outer counterweight-engag-
ing surface 100 which is positioned adjacent to the lower
end portion of the lower arm and has a yoke-supporting
surface 102 ~Figure 3).
The counterweight shaft extends through the lower
opening of the lower arm. The counterweight shaft has an
inner portion and an outer portion. A pair of inner cir-
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cular counterweights 104 and 106 are securely mounted on
the inner portion of the counterweight shaft. The inner
counterweights abut against and engage the inner counter-
weight-engaging portion of the lower arm to substantially
counterbalance the grinding wheel and cover to allow for
smooth rotation and swing of the arms. A pair of outer
circular counterweights 108 and 110 are securely mounted
to the outer portion of the counterweight shaft. The
outer counterweights are smaller than the inner counter-
weights. The outer counterweights abut against and engage
the outer counterweight-engaging portion of the lower arm
to substantially counterbalance the electric motor to help
enhance the smooth rotation and swing of the swing arms.
As shown in Figure 3, the adjustment fastening assem-
bly 66 is connected to the swing arms to adjust the over-
all length and the diameter of rotation of the swing arms.
The adjustment fastening assembly includes washers 112 and
a set of bolts 64 or other fasteners which extend through
the slots of the upper arms and are threadedly connected
to tapped holes of the lower arms. The adjustment fasten-
ing assembly also includes the key 88 (Figures 5 and 6)
and keyway 89 which help secure and maintain parallel
alignment of the arms. The adjustment fastener assembly
further includes a yoke or turnbuckle assembly 114 with a
lower yoke 116 which is connected to the yoke-engaging
surface of the lower arm, an upper, internally threaded,
yoke 118 which is connected to the inner end portion of
the upper arm, and a threaded rod or bolt 120. The lower
yoke has an internal thrust bearing 119 which receives and
engages the upper portion of the bolt (threaded) rod. The
head 121 of the bolt abuts against the lower face of the
lower yoke. The threaded end of the bolt threadedly
engages the upper yoke to permit selective adjustment,
expansion, and contraction of the overall span (length)
and diameter of swing of the swing arms to control the
depth of cut of the grinding wheel. The grinding wheel
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cover can have a recessed cutaway portion 123 with an
abutment wall 125 to facilitate expansion and movement of
the lower arm. While the illustrated arrangement is pre-
ferred, in some circumstances it may be desirable that thebolt or threaded rod also threadedly engage the lower
yoke.
As shown in Figures 3 and 6, a coupling or bearing
mount 122 is connected to the central coupling-engaging
portion of the lower arm. A driven gear shaft 124 is
securely connected to the coupling and positioned perpen-
dicular to the inwardly facing surface of the lower arm.
A wheel-actuated drive shaft 126 (Figure 6) is posi-
tioned in coaxial alignment with the gear shaft. A manu-
ally operable, steering wheel 128 has a hub 130 connectedto the drive shaft to rotate the swing arms, grinding
wheel, motor, and counterweights about the coupling and
gear shaft. The steering wheel controls the angular speed
and cutting of the grinding wheel. In the preferred
embodiment the steering wheel is in the form of a spoked
helmsman wheel with a set of manually grippable, outwardly
extending, radial spokes or handles 132.
In order to lock the wheel in place, a locking arm
134 can be pivotally connected to a gear box 136. The
locking arm has an upright locking arm portion 137 con-
nected to and extending upwardly from the gear box and a
pivotable, horizontal, locking arm portion 138 which is
pivotally connected to the upright locking arm portions by
a hinge or pivot pin 139. The horizontal locking arm has
an elongated slot 140 which slides over and lockably
receives the dead center, upwardly extending spoke or
handle of the wheel.
The gear box houses a reduction gear assembly 141
with a set of intermeshing reduction gears. The gear box
is positioned between and operatively connected to the
wheel-actuated drive shaft and the gear-driven shaft
(driven gear shaftJ to substantially reduce the angular
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speed of rotation of the driven shaft and swing arms rela-
tive to the drive shaft and wheel. In one test unit, the
gear box had a gear reduction ratio of 25:1.
A switch box and control panel 140 has a manually
operable toggle switch 142 to remotely activate (turn on)
and stop tshut off) the electric motor. The electric
motor power cord 52 is connected to the outwardly facing
side of the switch box. An outlet electric power cord 144
is connected to the outer end of the switch box.
A saddle assembly 146 provides a housing, support
platform, and cradle to support the weight of the gear box
and switch box. The saddle also provides a template and
setup assembly to facilitate setup and cutting (grinding)
of the base ring sections (root sections) and encased
lower stub portions of the stator blades of the axial flow
compressor case. The saddle assembly has a U-shaped sup-
port portion 148 which supports, receives and engages the
gear box. The U-shaped support portion has parallel,
upwardly extending legs lS0 and 152 with upper and lower
portions and a horizontal gear box and assembly-supporting
strut member 154 which extends laterally between and con-
nects the lower portions of the legs. Extending horizon-
tally outwardly in opposite directions from the tops of
the legs are horizontal, elongated, cantilevered support
arms 156 and 158. The left arm provides a support plat-
form to support and carry the switch box. The other arm
can support other equipment. Each of the arms are about
the same size and have a lateral guide member 160 or 162
at the unattached free end of the arm with flat or planar,
downwardly facing portions 164 and 166 which provide guide
plates that seat upon corresponding sections of the com-
pressor case to facilitate setup and efficiency of cutting
with the grinding wheel. Extending upwardly from each of
the guide members is an outriqger, stiffener and stabi-
lizer member 168 and 169 to enhance the stability of the
saddle assembly and prevent rocking during use of the
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cutter assembly. The stiffener members can also serve as
auxiliary guide members. One or more braces or gussets
171 can connect the legs and arms and brace their inter-
secting corners to rigidify and strenqthen the saddleassembly. The gear box and switch box can be mounted to
the saddle assembly by bolts or other suitable fasteners.
As shown in Figures 3, 4, and 7, an upright barrier
wall 170 extends vertically between the: (lJ saddle
assembly, gear box, and wheel: and (2) the coupling, swing
arms, grinding wheel, motor, and counterweights. The bar-
rier wall has a generally rectangular, transparent upper
portion 172 and a lower arcuate portion 174. The upper
portion extends laterally between the outrigger stiffening
members and upwardly from the ends (guide members) of the
saddle assembly. The uppor portion of the barrier wall
provides an upper, vertical, transparent safety shield 172
which per~its viewing of the grinding wheel by an operator
stahding behind the steering wheel while protecting the
operator's upper body, arms, face and eyes from sparks,
metal chips and debris from the grinder and workpiece
during grinding and cutting operations of the cutter
assembly. The lower arcuate membèr of the barrier wall
provides a semicircular, arcuate, convex guard plate 174
which is positioned against the outwardly facing sides of
the arms and U-shaped portions of the saddle assembly and
extends vertically downwardly from the safety shield. The
semicircular guard plate protects the operator's legs and
feet from sparks, flying metal chips and other debris from
the grinder and workpiece during cutting and grinding
operations of the cutter assembly. The lower semicircular
guard plate has a circular, gear shaft-receiving opening
or hole 176 (Figure 3) in its upper middle portion,
through which the gear shaft extends and rotates. The top
central portion of the upper safety shield has a down-
wardly extending U-shaped notch, groove, or opening 178 to
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receive and support the electric motor power cord which
connects the motor to the switch box.
A flat metal bar or finger 180 has an opening or hole
at one end to slide upon the outer portion of the counter-
weight shaft. The finger is secured to the counterweight
shaft by a nut 182. Desirably, the finger extends radi-
ally from the outer portion of the counterweight shaft to
provide a power cord-guard member to abut against, engage,
and hold the electric motor power cord which connects the
motor to the switch box to prevent the power cord from
contacting the rotating arms, grinding wheel, and gear
shaft of the cutter assembly during cutting and/or rota-
tion of the arms.
The axial flow compressor casing can be supported by
an inverted U-shaped frame assembly 184 (Figures 1 and 4).
The frame assembly has vertical support legs 186 and 188,
a horizontal base 190, and corner braces or gussets 192
and 194.
In use, the axial flow compressor case of the gas
turbine is partially disassembled and removed from the
other portions of the gas turbine. Thereafter, the upper
portions of the stator blades in the base ring sections of
the axial flow compressor case are severed (cut off) with
an arc air torch as shown in Figure 2. The guide members
of the saddle assembly are then placed and seated upon the
flanges or flat sections 184 (Figures 4 and 7) of the
axial flow compressor case. The guide members can be
mounted or otherwise secured to the flanges or flat sec-
tions of the compressor case by bolts 186. The fasteners64 and bolt 120 ~threaded rod) of the adjustment fastener
and yoke assembly can be adjusted to attain the desired
radius of rotation of the swing arms and depth and cut of
the grinding wheel. The power switch 142 in the switch
box can be turned on to activate the motor and grinding
wheel. The operator can then turn the wheel to rotate and
arcuately move the swing arms so that the grinding wheel
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engages, grinds, and cuts the lower encased, dovetailed,
stub portions of the stator blades and the base ring (root
section) in two or more pieces as shown in Figure 7. This
procedure is continued for each of the base rings and
lower encased stub portions of the stator blades, before
the cutter assembly is removed.
The cut stub portions of the stator blades can then
be heated to a temperature less than about 425F with an
oxy-acetylene torch. The heated cut, lower stub portions
of the stator blades are then jarred loose, vibrated, and
knocked out of the base ring (root) sections by repet-
itively striking the cut stub portions of the stator
blades and the base ring sections with a hammer H as shown
in Figure 8. Any loosened and knocked-out stub portions
and base ring sections can be dumped or emptied into a bin
or other receptacle. New stator blades 34 and base ring
sections 26 are then inserted into the groove channels 30
of the axial flow compressor case 22 at uniform intervals
as shown in Figùre 9. The axial flow compressor case can
then be reassembled and mounted to the gas turbine for
startup and use.
The cutter assembly and stator blade-removal and
revamping process were extensively tested at the Amoco Oil
Company Refinery at Texas City, Texas. It was unexpect-
edly and surprisingly found that the novel cutter assembly
and revamping process were very effective in overhauling,
revamping, repairing, and restoring the stator blades of a
gas turbine and resulted in substantial savings of turn-
around time of the gas turbine and downtime of the associ-
ated operating units. Previous conventional techniques
and [prior art equipment required a team of at least four
or five people working seven to ten 24-hour man-days to
fix and restore the gas turbine blades. With the novel
cutter assembly and revamping process described above, it
took a team of only two or three people about one and one-
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half to two 24-hour days to fix and restore the gas tur-
bine blades.
Among the many advantages of the preceding cutter
assembly and stator blade-revamping and repair process
are:
1. Substantially reduced downtime of the gas
turbine and associated operating units.
2. Significantly less turnaround time.
3. Reduced labor and manpower requirements.
4. Decreasing the probability of cracking or other-
wise damaging the compressor case by heating the cut stub
portions of the stator blades to much lower temperatures
than prior art techniques.
5. Enhanced efficiency.
6. Greater reliability.
7. Safer.
8. Economical.
9. More effective.
Although embodiments of this invention have been
shown and described, it is to be understood that various
modifications and substitutions, as well as rearrangements
and combinations of parts, equipment, or process steps,
can be made by those skilled in the art without departing
from the novel spirit and scope of this invention.
