U.S. patent application number 10/064896 was filed with the patent office on 2004-03-04 for apparatus and method of removing abradable material from a turbomachine fan containment case.
This patent application is currently assigned to General Electric Company. Invention is credited to Bruner, Terry Joe, Ford, Robert Thomas, Fox, Michael Dean.
Application Number | 20040043703 10/064896 |
Document ID | / |
Family ID | 31713852 |
Filed Date | 2004-03-04 |
United States Patent
Application |
20040043703 |
Kind Code |
A1 |
Fox, Michael Dean ; et
al. |
March 4, 2004 |
APPARATUS AND METHOD OF REMOVING ABRADABLE MATERIAL FROM A
TURBOMACHINE FAN CONTAINMENT CASE
Abstract
An apparatus (10) and method for removing an abradable material
from an interior surface (16) of a fan containment case (14),
without requiring removal of the fan containment case (14) from its
engine (12). The apparatus (10) and method generally involve
adjusting the elevation of a blast head (40) and centering a
horizontal axis of rotation thereof with the fan containment case
(14) to position the blast head (40) adjacent the abradable
material on the case surface (16). An erosion media is then sprayed
with the blast head (40) in a substantially radial direction
relative to the horizontal axis of rotation of the blast head (40),
such that the erosion media impacts and erodes the abradable
material. The blast head (40) is rotated about the horizontal axis
of rotation thereof so that the erosion media is sprayed at the
abradable material along the entire circumference of the fan
containment case (14). The erosion media is preferably retrieved
after being sprayed and impacted against
Inventors: |
Fox, Michael Dean; (Liberty
Township, OH) ; Bruner, Terry Joe; (Geuda Springs,
KS) ; Ford, Robert Thomas; (Abilene, KS) |
Correspondence
Address: |
HARTMAN AND HARTMAN, P.C.
552 EAST 700 NORTH
VAIPARAISO
IN
46383
US
|
Assignee: |
General Electric Company
Schenectady
NY
|
Family ID: |
31713852 |
Appl. No.: |
10/064896 |
Filed: |
August 27, 2002 |
Current U.S.
Class: |
451/38 ;
451/91 |
Current CPC
Class: |
B24C 3/325 20130101;
B24C 3/32 20130101 |
Class at
Publication: |
451/038 ;
451/091 |
International
Class: |
B24B 001/00; B24C
001/00; B24C 003/06 |
Claims
1. An apparatus (10) capable of removing abradable material from an
interior surface (16) of a fan containment case (14) while the fan
containment case (14) remains mounted to an engine (12), the
apparatus (10) comprising: a frame (20); means (40,66) rotatably
mounted to the frame (20) for spraying an erosion media in a radial
direction relative to a horizontal axis of rotation of the spraying
means (40,66) such that the erosion media impacts the abradable
material on the interior surface (16) of the fan containment case
(14) when the spraying means (40,66) is positioned within the fan
containment case (14); means (40,64) rotatably mounted to the frame
(20) with the spraying means (40,66) for retrieving the erosion
media after the erosion media is sprayed from the spraying means
(40,66) and has impacted the abradable material; means (48) mounted
to the frame (20) for centering the horizontal axis of rotation of
the spraying means (40,66) relative to the interior surface (16) of
the fan containment case (14), the centering means (48) having a
horizontal central axis that substantially coincides with the
horizontal axis of rotation of the spraying means (40,66); means
(28) for adjusting together the elevation of the horizontal central
axis of the centering means (48) and the horizontal axis of
rotation of the spraying means (40,66) relative to the frame (20);
and means (42,44,46) for positioning a portion (66) of the spraying
means (40,66) adjacent the interior surface (16) of the fan
containment case (14).
2. An apparatus (10) according to claim 1, wherein the frame (20)
is supported on wheels (29).
3. An apparatus (10) according to claim 1, wherein the centering
means (48) comprises three arms (50) coupled together for movement
in unison toward and away from the horizontal central axis of the
centering means (48).
4. An apparatus (10) according to claim 3, wherein each arm (50) of
the centering means (48) has a distal end (58) for engaging the
interior surface (16) of the fan containment case (14) and a clamp
(60) for gripping the fan containment case (14).
5. An apparatus (10) according to claim 1, further comprising means
(62) for moving the spraying means (40, 66) in an axial direction
along the horizontal axis of rotation thereof.
6. An apparatus (10) according to claim 1, wherein the portion (66)
of the spraying means (40,66) positioned adjacent the interior
surface (16) of the fan containment case (14) is a spray head (66)
comprising multiple nozzles that rotate together about an axis
substantially parallel to the radial direction in which the erosion
media is sprayed.
7. An apparatus (10) according to claim 1, wherein the portion (66)
of the spraying means (40,66) positioned adjacent the interior
surface (16) of the fan containment case (14) is a spray head (66),
the spraying means (40,66) further comprising a containment
enclosure (64) to which the spray head (66) is mounted, the
containment enclosure (64) having means for sealing against the
interior surface (16) of the fan containment case (14).
8. An apparatus (10) according to claim 7, wherein the retrieving
means (40,64) is coupled to the containment enclosure (64), the
spray head (66) sprays the erosion media at a first volumetric
flowrate, and the retrieving means (40, 64) draws the erosion media
from the containment enclosure (64) at a second volumetric flowrate
that is higher than the first volumetric flowrate.
9. An apparatus (10) according to claim 1, wherein the apparatus
(10) is operable to substantially remove the abradable material
from the interior surface (16) of the fan containment case (14) in
a single rotation of the spraying means (40,66) about the
horizontal axis of rotation.
10. An apparatus (10) for removing abradable material from an
interior surface (16) of a fan containment case (14) while the fan
containment case (14) remains mounted to a high bypass turbofan
engine (12), the apparatus (10) comprising: a frame assembly (20)
having a base structure (22) and a platform structure (24); a shaft
(30) rotatably mounted to the platform structure (24); a radial arm
(38) mounted to the shaft (30); a spray head (66) mounted to the
radial arm (38) for spraying an erosion media in a radial direction
relative to a horizontal axis of rotation of the shaft (30) such
that the erosion media impacts the abradable material on the
interior surface (16) of the fan containment case (14) when the
spray head (66) is positioned within the fan containment case (14);
a containment enclosure (64) mounted to the radial arm (38) for
containing the erosion media sprayed by the spray head (66), the
containment enclosure (64) having means for sealing against the
interior surface (16) of the fan containment case (14); means (72)
coupled to the containment enclosure (64) for retrieving the
erosion media from the containment enclosure (64) after the erosion
media is sprayed from the spray head (66) and has impacted the
abradable material; chucking means (48) mounted to the platform
structure (24) for centering the horizontal axis of rotation of the
shaft (30) relative to the interior surface (16) of the fan
containment case (14), the chucking means (48) comprising arms (50)
coupled together for movement in unison toward and away from a
horizontal central axis of the chucking means (48), the horizontal
central axis substantially coinciding with the horizontal axis of
rotation of the shaft (30); means (28) for adjusting the elevation
of the platform structure (24) relative to the base structure (22)
so as to adjust together the elevation of the horizontal central
axis of the chucking means (48) and the horizontal axis of rotation
of the shaft (30) relative to the base structure (22); means
(42,44) for adjusting the spray head (66) on the radial arm (38) in
the radial direction from the shaft (30); and means (74) for
controlling the spraying and rotating steps so as not to require
manual control and to continue the spraying and rotating steps
while the shaft (30) makes about one complete rotation about the
horizontal axis thereof, during which time the abradable material
is substantially removed from the interior surface (16) of the fan
containment case (14).
11. An apparatus (10) according to claim 10, wherein the frame
assembly (20) is supported on wheels (29).
12. An apparatus (10) according to claim 10, wherein each arm (50)
of the chucking means (48) has a distal end (58) for engaging the
interior surface (16) of the fan containment case (14) and a clamp
(60) for gripping the fan containment case (14).
13. An apparatus (10) according to claim 10, further comprising
means (62) for moving the radial arm (38) in an axial direction
along the horizontal axis of rotation of the shaft (30).
14. An apparatus (10) according to claim 10, wherein the spray head
(66) comprises multiple nozzles that rotate together about an axis
substantially parallel to the radial direction in which the erosion
media is sprayed.
15. A method of removing abradable material from an interior
surface (16) of a fan containment case (14), the method comprising
the steps of: providing a spraying means (40,66) rotatably mounted
to a frame (20); adjusting the elevation of the spraying means (40,
66) and centering a horizontal axis of rotation of the spraying
means (40,66) with the fan containment case (14) to position the
spraying means (40,66) adjacent the interior surface (16) of the
fan containment case (14); spraying an erosion media with the
spraying means (40,66) in a radial direction relative to the
horizontal axis of rotation of the spraying means (40,66) such that
the erosion media-impacts and erodes the abradable material on the
interior surface (16) of the fan containment case (14); rotating
the spraying means (40,66) about the horizontal axis of rotation
thereof so that the erosion media is sprayed at the interior
surface (16) of the fan containment case (14) along a
circumferential direction thereof; and retrieving the erosion media
after the erosion media is sprayed from the spraying means (40, 66)
and has impacted the abradable material on the interior surface
(16) of the fan containment case (14).
16. A method according to claim 15, wherein the step of centering
the spraying means (40,66) comprises moving three arms (50) coupled
together in unison away from the horizontal axis of rotation of the
spraying means (40,66).
17. A method according to claim 16, further comprising the steps of
engaging the interior surface (16) of the fan containment case (14)
with a distal end (58) of each arm (50) and clamping the distal end
(58) of each arm (50) to the fan containment case (14).
18. A method according to claim 15, further comprising the step of
moving the spraying means (40,66) in an axial direction along the
horizontal axis of rotation thereof to position the spraying means
(40,66) within the fan containment case (14).
19. A method according to claim 15, wherein the spraying means
(40,66) comprises a spray head (66) comprising multiple nozzles
that rotate together about an axis substantially parallel to the
radial direction in which the erosion media is sprayed.
20. A method according to claim 15, wherein the spraying means
(40,66) comprises a spray head (66) and a containment enclosure
(64) to which the spray head (66) is mounted, the containment
enclosure (64) being sealed against the interior surface (16) of
the fan containment case (14) and containing the erosion media
sprayed from the spray head (66) as the spraying means (40,66) is
rotated about the horizontal axis of rotation thereof.
21. A method according to claim 20, wherein the erosion media is
retrieved from the containment enclosure (64), the spray head (66)
sprays the erosion media at a first volumetric flowrate, and the
erosion media is retrieved from the containment enclosure (64) at a
second volumetric flowrate that is higher than the first volumetric
flowrate.
22. A method according to claim 15, wherein the abradable material
is substantially removed from the interior surface (16) of the fan
containment case (14) in a single rotation of the spraying means
(40, 66) about the horizontal axis of rotation.
23. A method of removing abradable material from an interior
surface (16) of a fan containment case (14) while the fan
containment case (14) remains mounted to a high bypass turbofan
engine (12), the method comprising the steps of: providing an
apparatus (10) comprising a frame assembly (20) having a base
structure (22) and a platform structure (24), a shaft (30)
rotatably mounted to the platform structure (24), a radial arm (38)
mounted to the shaft (30), a containment enclosure (64) mounted to
the radial arm (38) and having means for sealing against the
interior surface (16) of the fan containment case (14), a spray
head (66) mounted to the containment enclosure (64), and chucking
means (48) mounted to the platform structure (24) for centering the
horizontal axis of rotation of the shaft (30) relative to the
interior surface (16) of the fan containment case (14), the
chucking means (48) comprising arms (50) coupled together for
movement in unison toward and away from a horizontal central axis
of the chucking means (48), the horizontal central axis
substantially coinciding with the horizontal axis of rotation of
the shaft (30); removing fan blades from the engine (12);
positioning the apparatus (10) in front of the fan containment case
(14); raising the platform structure (24) to adjust the elevation
of the platform structure (24) relative to the base structure (22)
and thereby adjust together the elevation of the horizontal central
axis of the chucking means (48) and the horizontal axis of rotation
of the shaft (30) relative to the base structure (22); operating
the apparatus (10) to position the spray head (66) and the arms
(50) within the fan containment case (14); engaging the arms (50)
with the fan containment case (14) to center the horizontal axis of
rotation of the shaft (30) relative to the interior surface (16) of
the fan containment case (14); moving the containment enclosure
(64) on the radial arm (38) in a radial direction relative to the
horizontal axis of rotation of the shaft (30) to seal the
containment enclosure (64) against the interior surface (16) of the
fan containment case (14) and position the spray head (66) adjacent
the abradable material on the interior surface (16) of the fan
containment case (14); spraying an erosion media with the spray
head (66) in the radial direction of the shaft (30) such that the
erosion media impacts and erodes the abradable material; rotating
the shaft (30) about the horizontal axis of rotation thereof so
that the erosion media is sprayed at the abradable material along a
circumferential direction of the fan containment case (14); and
retrieving the erosion media from the containment enclosure (64)
after the erosion media is sprayed from the spray head (66) and has
impacted the abradable material on the interior surface (16) of the
fan containment case (14); wherein the spraying and rotating steps
are automated so as not to require manual control and continue
while the shaft (30) makes about one complete rotation about the
horizontal axis thereof, during which time the abradable material
is substantially removed from the interior surface (16) of the fan
containment case (14).
24. A method according to claim 23, wherein the step of engaging
the arms (50) with the fan containment case (14) comprises engaging
the interior surface (16) of the fan containment case (14) with a
distal end (58) of each arm (50) of the chucking means (48) and
gripping the fan containment case (14) with a clamp (60) associated
with the distal end (58) of each arm (50).
25. A method according to claim 23, wherein the step of positioning
the spray head (66) within the fan containment case (14) comprises
moving the radial arm (38) in an axial direction along the
horizontal axis of rotation of the shaft (30).
26. A method according to claim 23, wherein the spray head (66)
comprises multiple nozzles that rotate together about an axis
substantially parallel to the radial direction of the shaft (30).
Description
BACKGROUND OF INVENTION
[0001] 1. Field of the Invention
[0002] The present invention generally relates to fan containment
assemblies for turbomachinery, such as gas turbine engines. More
particularly, this invention relates to an automated apparatus and
method for removing an abradable material for a fan containment
assembly.
[0003] 2. Description of the Related Art
[0004] Gas turbine engines generally operate on the principle of
compressing air within a compressor section of the engine, and then
delivering the compressed air to the combustion section of the
engine where fuel is added to the air and ignited. Afterwards, the
resulting combustion mixture is delivered to the turbine section of
the engine, where a portion of the energy generated by the
combustion process is extracted by a turbine to drive the engine
compressor. High bypass turbofan engines, widely used for high
performance aircraft which operate at subsonic speeds, have a large
fan placed at the front of the engine to produce greater thrust and
reduce specific fuel consumption. The fan compresses the incoming
air, a portion of which is then delivered to the combustion
chamber, though a larger portion is bypassed to the rear of the
engine to generate additional engine thrust.
[0005] The fan is circumscribed by a fan containment case such that
the case is immediately adjacent the tips of the fan blades. The
containment case serves to channel incoming air through the fan so
as to ensure that the bulk of the air entering the engine will be
compressed by the fan. However, a small portion of the air is able
to bypass the fan blades through a radial gap present between the
fan blade tips and the containment case. Because the air compressed
by the fan blades is used to generate thrust and feed the turbine
section of the engine, engine efficiency can be increased by
limiting the amount of air which is able to bypass the fan blades
through this gap. Accordingly, the fan and containment case are
manufactured to close tolerances in order to minimize the gap.
However, manufacturing tolerances, differing rates of thermal
expansion and dynamic effects limit the extent to which this gap
can be reduced. Furthermore, during the normal operation of an
aircraft turbofan engine, the fan blades may rub the containment
case as a result of a hard landing or a hard maneuver of the
aircraft. Any rubbing contact between the fan blade tips and the
containment case will abrade the tips of the rotors, tending to
further increase the gap between the containment case and blade
tips, thereby reducing engine efficiency. The fan is circumscribed
by a fan containment case such that the case is immediately
adjacent the tips of the fan blades. The containment case serves to
channel incoming air through the fan so as to ensure that the bulk
of the air entering the engine will be compressed by the fan.
However, a small portion of the air is able to bypass the fan
blades through a radial gap present between the fan blade tips and
the containment case. Because the air compressed by the fan blades
is used to generate thrust and feed the turbine section of the
engine, engine efficiency can be increased by limiting the amount
of air which is able to bypass the fan blades through this gap.
Accordingly, the fan and containment case are manufactured to close
tolerances in order to minimize the gap. However, manufacturing
tolerances, differing rates of thermal expansion and dynamic
effects limit the extent to which this gap can be reduced.
Furthermore, during the normal operation of an aircraft turbofan
engine, the fan blades may rub the containment case as a result of
a hard landing or a hard maneuver of the aircraft. Any rubbing
contact between the fan blade tips and the containment case will
abrade the tips of the rotors, tending to further increase the gap
between the containment case and blade tips, thereby reducing
engine efficiency.
[0006] In view of the above, it is well known in the art to cover
the portion of the containment case adjacent the blade tips with an
abradable material, such that the abradable material will
sacrificially abrade away when rubbed by the fan blades.
Inherently, as the abradable material is removed, the gap between
the blade tips and the surface of the abradable material will
increase, necessitating removal and replacement of the abradable
material to maintain desirable aerodynamic efficiencies associated
with a smooth abradable surface and a small gap between the
abradable surface and the fan blade tips. Restoration of the
abradable material also becomes necessary if damage has occurred
from impacts with foreign objects.
[0007] A common technique for removing the abradable material is
performed with handheld tools, such as an air chisel, after which
sandpaper is used to achieve a smooth surface finish. While
suitable for use on steel fan cases, air chisels are too aggressive
for use on engines with aluminum cases. Aluminum fan cases must be
removed from the fan frame, stripped of gearboxes, wire harnesses,
controls, etc., and then centered on a turning machine to remove
the old abradable material. Any damage that may occur to the base
metal must be repaired before applying and bonding the new
abradable material. The removal process can be time consuming and
expensive, and requires a large maintenance facility to which at
least the front of the engine must be transported for disassembly.
Due to the special equipment required to perform the machining
operation, a limited number of facilities are available for
removing fan case abradable material. As a result, additional
costs, scheduling and transport problems are common.
[0008] Accordingly, it would be desirable if an improved technique
were available by which the abradable material of a fan containment
case could be removed without requiring removal of the fan case
from the engine, such that restoration can be performed in the
field.
SUMMARY OF INVENTION
[0009] The present invention provides an apparatus and method for
removing an abradable material from an interior surface of a fan
containment case, without requiring removal of the fan containment
case from its engine, e.g., a high-bypass gas turbine engine. The
apparatus of this invention generally includes a frame, and means
rotatably mounted to the frame for spraying an erosion media in a
substantially radial direction relative to a horizontal axis of
rotation of the spraying means. The erosion media impacts the
abradable material on the interior surface of the fan containment
case while the spraying means is positioned within the fan
containment case adjacent the abradable material. The apparatus
further includes means rotatably mounted to the frame with the
spraying means for retrieving the erosion media after impacting the
abradable material. Also provided is means mounted to the frame for
centering the horizontal axis of rotation of the spraying means
relative to the interior surface of the fan containment case, means
for adjusting together the elevation of a horizontal central axis
of the centering means and the horizontal axis of rotation of the
spraying means relative to the frame, and means for positioning the
spraying means adjacent the interior surface of the fan containment
case.
[0010] A method made possible with the apparatus of this invention
generally comprises the steps of adjusting the elevation of the
spraying means and centering the horizontal axis of rotation
thereof with the fan containment case to position the spraying
means adjacent the abradable material on the interior surface of
the fan containment case. The erosion media is then sprayed with
the spraying means in a substantially radial direction relative to
the horizontal axis of rotation of the spraying means, such that
the erosion media impacts and erodes the abradable material on the
interior surface of the fan containment case. In addition, the
spraying means is rotated about the horizontal axis of rotation
thereof so that the erosion media is sprayed at the abradable
material along the entire circumference of the fan containment
case. At the same time, the erosion media is retrieved after being
sprayed and impacted against the abradable material.
[0011] In view of the above, it can be seen that a significant
advantage of this invention is that the apparatus is capable of
removing the abradable material from a fan containment case without
requiring removal of the case from an engine. Instead, only the fan
blades need be removed to gain access to the interior surface of
the case. Another advantage of the invention is that the apparatus
provides a means by which the spraying means is self-centered with
respect to the interior surface of the fan containment case, and
the operation of the spraying means can be controlled to follow a
specific path along the inner diameter of the fan containment case.
As such, the apparatus requires minimal setup, and can be operated
in an automated mode without further human supervision. In a
preferred embodiment, the apparatus is capable of removing
substantially all of the abradable material in roughly a single
rotation of the spraying means about its horizontal axis of
rotation. With the use of appropriate abradable material and spray
pressures, this operation can be completed in about one hour
without damaging the substrate beneath the abradable material.
[0012] Other objects and advantages of this invention will be
better appreciated from the following detailed description.
BRIEF DESCRIPTION OF DRAWINGS
[0013] FIG. 1 is a side view of an apparatus for removing abradable
material from a fan containment case in accordance with a preferred
embodiment of this invention.
[0014] FIGS. 2, 3, 4 and 5 are a top view, front end view, back end
view, and perspective view, respectively, of the apparatus of FIG.
1.
[0015] FIG. 6 is a perspective view of a blast head shown mounted
to the apparatus of FIG. 1.
DETAILED DESCRIPTION
[0016] FIGS. 1 through 5 represent an apparatus 10 for removing an
abradable material in accordance with a preferred embodiment of the
invention. The apparatus 10 is particularly adapted for removing an
abradable material from the blade containment case of a
turbomachine, such as the fan containment case of a high bypass
turbofan engine. As known in the art, high bypass turbofan engines
have a fan section within which a fan formed by a number of fan
blades is mounted to a hub. A fan section 12 is represented in
phantom in FIG. 1, and includes a fan containment case 14 that
circumscribes the fan (shown removed), and whose radially inward
surface has a channel 16 containing an abradable material. Suitable
materials for the abradable material include various lightweight
materials known and used in the prior art, including composite
materials such as an epoxy filled with hollow glass beads. The
apparatus 10 of this invention is adapted to remove the abradable
material from the case 14 to permit the application of a new layer
of abradable material. While the invention can be used to remove
abradable material from containment cases formed of a variety of
materials, including steel, the invention is particularly well
suited for use on aluminum cases that are more prone to damage
during removal of the abradable material by conventional
methods.
[0017] As represented in FIGS. 1 through 5, the apparatus 10 is
able to remove the abradable material while the fan containment
case 14 remains mounted to the engine. The apparatus 10 is shown as
comprising a frame assembly 20 having a base 22, platform 24 and
legs 26 pivotably connected to both the base 22 and platform 24. A
vertical actuator 28 is mounted to the base 22 and connected to the
platform 24 to raise and lower the platform 24 relative to the base
22. The base 22 is shown as being equipped with wheels 29 that
enable the apparatus 10 to be moved and positioned in front of the
fan section 12. The wheels 29 are preferably equipped with wheel
locks (not shown) of any conventional design to prevent movement of
the apparatus 10 once positioned.
[0018] A shaft assembly 30 is rotatably mounted to the platform 24
in any suitable manner. An electric motor 34 and reduction gear
assembly 36 is mounted to the platform 24 for rotating the shaft
assembly 30 at an adjustable controlled speed, such as about one
rotation per hour, though faster and slower speeds are foreseeable.
A radial arm 38 is mounted to the end of the shaft assembly 30
opposite the motor 34, and extends in a radial direction relative
to the axis of rotation of the shaft assembly 30. At the distal end
of the radial arm 38, a blast head 40 is mounted by a pair of
articulating arms 42 whose movement and position, and therefore the
radial position of the blast head 40, are controlled with a radial
adjustor 44 mounted to the arm 38. As will be discussed in greater
detail with respect to FIG. 6, the blast head 40 delivers an
erosion media (not shown) for the purpose of removing the abradable
material from the fan containment case 14. Finally, the orientation
(tilt) of the blast head 40 is adjusted with a tilt adjustor 46,
also mounted to the articulating arms 42. With the electric motor
34, the entire assembly--comprising the shaft assembly 30, radial
arm 38, arms 42 and blast head 40, etc.--can be caused to rotate
about the axis of the shaft assembly 30, which is oriented
horizontally in view of the orientation of the engine fan section
12. In this manner, the blast head 40 can be caused to follow the
inner circumference of the fan case 14 while spraying the erosion
media in a generally radial direction, such that the erosion media
impacts the abradable material located on the interior surface of
the fan containment case 14, as represented in FIG. 1.
[0019] Also shown in FIGS. 1 through 5 is a chuck assembly 48
mounted to a housing 32 that supports the shaft assembly 30. The
chuck assembly 48 is shown as comprising three two-bar arm
assemblies 50, which as shown in FIG. 1 are adapted to engage the
fan containment case 14 and center the shaft assembly 30 with the
centerline of the fan section 12. For this purpose, three
equiangularly-spaced arm assemblies 50 are preferred, though it is
foreseeable that a different number of arms could be used. The arm
assemblies 50 are articulated in unison through rods 52 connected
to a collar 54 mounted with bearings to the shaft assembly 30. As
such, the chuck assembly 48 has a horizontal central axis that
substantially coincides with the axis of rotation of the shaft
assembly 30. An actuator 56 is coupled to the collar 54 to move the
collar 54 axially along a given length of the shaft assembly 30,
causing the arm assemblies 50 to pivot in unison toward or away
from the axis of rotation of the shaft assembly 30. The distal end
58 of each arm assembly 50 is adapted to engage the interior
surface of the fan containment case 14, and is equipped with a
clamp 60 for gripping the case 14 with the distal end 58.
[0020] In FIGS. 1 and 2, an actuator 62 is shown with which the
shaft assembly 30--and therefore simultaneously the blast head 40
and chuck assembly 48--can be moved axially, i.e., parallel to the
axis of rotation of the shaft assembly 30. Consequently, the blast
head 40 can be introduced into the fan section 12, positioned in
the cross-sectional plane of the case 14 containing the abradable
material to perform the removal operation, and later retracted from
the fan section 12 at the completion of the operation.
Simultaneously with the introduction of the blast head 40 in the
fan section 12, the arm assemblies 50 are moved toward the fan
section 12. Once the blast head 40 is properly axially positioned
within the fan section 12, the arm assemblies 50 can be pivoted
radially outward with the actuator 56 to engage the rim of the fan
containment case 14 and thereby center the shaft assembly 30 within
the fan section 12. Finally, finer adjustments can be made to place
the blast head 40 immediately adjacent the abradable material
through the radial adjustor 44 and the tilt adjustor 46.
[0021] The blast head 40 represented in FIGS. 1 through 5 is shown
in greater detail in FIG. 6. The blast head 40 can be seen to
comprise a containment enclosure 64 for containing the erosion
media sprayed through a spray head 66 disposed in a wall of the
enclosure 64. The outer surface 68 of the containment enclosure 64
is contoured to correspond to the radius of the fan containment
case 14, and is equipped with a rubber or brush seal (not shown) to
provide a sealing action with the interior surface of the fan
containment case 14. The erosion media is delivered to the spray
head 66 through a supply hose 70, and retrieved from the enclosure
64 through a pair of hoses 72 attached to opposite sides of the
enclosure 64. As such, the erosion media is retrieved from the
containment enclosure 64 after the erosion media is sprayed from
the spray head 66 and has impacted the abradable material on the
interior surface of the fan containment case 14. Thereafter, the
spent erosion media containing particles of the abradable material
may be discarded, though in a preferred embodiment the erosion
media is separated from particles of the abradable material and
reused.
[0022] While spray heads 66 of various designs may be used, a
preferred spray head 66 is equipped with multiple nozzles,
preferably three as shown, that rotate together about the axis
along which the media is sprayed. A blast head 40 equipped with the
preferred spray head 66 and media retrieval and reclamation system
particularly suitable for use with this invention is the MPC Series
of machines available from Abrasive Blast Systems, Inc., of
Abilene, Kans. An erosion material found to be suitable for use
with the apparatus 10 of this invention is a plastic bead material
formed of Type II urea formaldehyde thermoset per Mil-P-85291, and
therefore commercially available from a number of sources. In
practice, a suitable particle size for the Mil-P-85291 media is
about twenty to about thirty mesh, though smaller and larger
particle sizes could be used. When using this plastic erosion media
within the stated particle size range, suitable operating
parameters for the blast head 40 include an adjustable supply
pressure of about 50 to about 80 psi (about 3.5 to about 5.5 bar),
such as about 65 psi (about 4.5 bar). The volumetric airflow rate
from the enclosure 64 is preferably slightly higher than the
flowrate to the enclosure 64 to promote a vacuuming effect for
reclaiming the media from the enclosure 64. With these parameters,
abradable material has essentially been completely removed from a
fan containment casing with a single complete rotation of the blast
assembly 40. Some overlap (e.g., about 370 degrees rotation) is
generally desirable to ensure that the entire circumference of the
case 14 has been thoroughly treated during the operation.
[0023] In the preferred embodiment, the apparatus 10 is capable of
being operated within minimal supervision by an operator. For this
purpose, the apparatus 10 is preferably equipped with controls that
cause the shaft assembly 30 to rotate and the blast head 40 to
spray the media according to predetermined settings. Automatic
safety stops are preferably provided to stop the operation of the
blast head 40 if the shaft assembly 30 stops rotating. In FIG. 2, a
control unit 74 is seen mounted to the platform 24 by which the
rotational speed of the blast head 40 (through the shaft assembly
30) is controlled. Connected to this unit 74 is a pendant control
76 with switches, etc., for controlling the operation of the chuck
assembly 48 and actuators 28, 56 and 62.
[0024] In view of the above, the apparatus 10 of this invention can
be used to remove abradable material from an interior surface of a
fan containment case 14 while the case 14 remains mounted to a high
bypass turbofan engine. Prior to the operation, the fan blades are
removed from the engine, the platform 24 is raised with the
vertical actuator 28 to align the axis of the shaft assembly 30
(and therefore the axis of the chuck assembly 48) with the
centerline of the fan section 12. The blast head 40 and arm
assemblies 50 can then be introduced into the case 14 by extending
the actuator 62. As a result of actuating the actuator 56 to engage
the arm assemblies 50 with the rim of the fan containment case 14,
the axis of rotation of the shaft assembly 30 is accurately
centered with the centerline of the fan containment case 14. The
blast head 40 can then be moved in the radial direction with the
arms 42 and adjustor 44 until the containment enclosure 64 contacts
the interior surface of the case 14 and the spray head 66 is
positioned over the abradable material. Thereafter, the spraying
operation is commenced, with the blast head 40 closely following
the entire inner circumferential surface of the case 14 covered by
the abradable material as a result of the operation of the motor
34, controlled with the control unit 74 to rotate the blast head 40
at a predetermined speed. The control unit 74 can also be employed
to terminate the flow of erosion media to and from the blast head
40.
[0025] While the invention has been described in terms of a
preferred embodiment, it is apparent that other forms could be
adopted by one skilled in the art. For example, the physical
configuration of the apparatus 10 could differ from that shown.
Therefore, the scope of the invention is to be limited only by the
following claims.
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