U.S. patent application number 09/826535 was filed with the patent office on 2001-09-13 for resin transfer molding process.
This patent application is currently assigned to The Boeing Company. Invention is credited to Bennett, Henry H., Cundiff, Thomas R., Lund, Brad G., Renz, Robert S., Wright, Donald E..
Application Number | 20010021427 09/826535 |
Document ID | / |
Family ID | 22362184 |
Filed Date | 2001-09-13 |
United States Patent
Application |
20010021427 |
Kind Code |
A1 |
Cundiff, Thomas R. ; et
al. |
September 13, 2001 |
Resin transfer molding process
Abstract
A wind tunnel blade (30) connected to a base (32) and held in
position by a two-piece cuff (34). The wind tunnel blade (30) is
formed in a resin transfer molding process in which central, fore,
and aft foam core sections (70, 72, 74) are placed together to form
the wind tunnel blade (30). Radius fillers (120) are used to fill
the gaps between the outer edge of the foam core sections. The
radius fillers (120) used in the wind tunnel blade (30) are formed
by a braided sleeve (122) surrounding a number of unidirectional
tows (124). A tip (68) is formed separately from the rest of the
wind tunnel blade (30) and is glued to the top thereof. Stacked
layers of braided fibers (100) are used to reinforce the central
core section (70).
Inventors: |
Cundiff, Thomas R.;
(Edgewood, WA) ; Bennett, Henry H.; (Redmond,
WA) ; Lund, Brad G.; (Auburn, WA) ; Renz,
Robert S.; (Seattle, WA) ; Wright, Donald E.;
(Seattle, WA) |
Correspondence
Address: |
CHRISTENSEN, O'CONNOR, JOHNSON, KINDNESS, PLLC
1420 FIFTH AVENUE
SUITE 2800
SEATTLE
WA
98101-2347
US
|
Assignee: |
The Boeing Company
|
Family ID: |
22362184 |
Appl. No.: |
09/826535 |
Filed: |
April 4, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09826535 |
Apr 4, 2001 |
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09115568 |
Jul 14, 1998 |
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6231941 |
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Current U.S.
Class: |
428/36.3 ;
264/103; 264/137; 264/161; 264/257; 264/279; 264/313; 403/365;
411/378; 87/1; 87/6; 87/9 |
Current CPC
Class: |
Y10T 428/1348 20150115;
Y10T 428/2457 20150115; Y10T 428/249986 20150401; B29C 70/086
20130101; Y10T 428/1369 20150115; B29C 70/443 20130101; Y10T
428/24504 20150115; Y10T 428/24496 20150115; B29L 2031/08 20130101;
B29C 70/083 20130101; B29D 99/0025 20130101; B29D 99/0005 20210501;
Y10T 403/7047 20150115; Y10T 428/24008 20150115 |
Class at
Publication: |
428/36.3 ;
264/161; 403/365; 264/103; 264/137; 264/257; 264/279; 264/313;
87/1; 87/6; 87/9; 411/378 |
International
Class: |
B29D 023/00; B29C
037/04; F16D 001/033; B25G 003/02; F16B 033/00; F16B 035/00 |
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. A plug comprising: (a) a flexible outer bushing having first and
second ends; (b) a connector attached to the first end of the
bushing; and (c) a fastener extending along the flexible outer
bushing and attached to the connector, the fastener being
configured such that actuation of the fastener causes the flexible
outer bushing to expand outward, whereby the flexible outer bushing
can be inserted into a hollow opening and can expand against the
sides of the opening by actuation of the fastener.
2. The plug of claim 1, wherein the connector is a female-threaded
insert.
3. The plug of claim 2, wherein the fastener extends along the
bushing and comprises (1) an abutment surface for engaging the
second end of the bushing and (2) male threads that are received in
the female-threaded insert, and wherein actuation of the fastener
comprises rotating the fastener to move the connector towards the
second end.
4. The plug of claim 1, wherein the fastener extends along the
bushing and comprises an abutment surface for engaging the second
end of the bushing and actuation of the fastener comprises causing
the fastener to pull the connector toward the abutment surface.
5. A method of resin transfer molding a product having a hollow
tube therein, the method comprising: (a) placing an expandable plug
into a hollow tube so that a portion of the plug extends along or
beyond the intended finished line of the product being formed; (b)
expanding the expandable plug so that the expandable plug is
pressed against the outer sides of the hollow tube; (c) injecting
resin about the hollow tube and around the plug in a resin transfer
molding process such that excess resin is formed beyond the
intended finish line; and (d) cutting the excess resin along the
intended finish line so that the plug is removed from the final
finished part.
6. The method of claim 5, wherein the plug comprises: (a) a
flexible outer bushing having first and second ends; (b) a
connector attached to the first end of the bushing; and (c) a
fastener extending along the flexible outer bushing and attached to
the connector, the fastener being configured such that actuation of
the fastener causes the flexible outer bushing to expand outward,
whereby the flexible outer bushing can be inserted into a hollow
opening and can expand by actuation of the fastener against the
sides of the opening.
7. The method of claim 6, wherein the cutting step comprises
cutting the fastener so that the outer bushing no longer expands
outward and is free to fall out of the hollow tube.
8. The method of claim 6, wherein the fastener extends along the
bushing and comprises an abutment surface for engaging the second
end of the bushing and actuation of the fastener comprises causing
the fastener to pull the connector toward the abutment surface.
9. The method of claim 5, wherein the expandable plug is cut during
the cutting process so that the plug is no longer expanded against
the sides of the hollow tube and falls out of the hollow tube.
10. A reinforced core structure for use in a resin transfer molding
process comprising: (a) an expanded core having a longitudinal
axis; (b) a first set of braided fibers extending from a first end
of the expanded core to a first location and reversing from the
first groove over itself and back towards the first end; and (c) a
second set of braided fibers extending from the first end over the
first set of braided fibers and to a second location beyond the
first location and reversing from the second location, back over
itself and rearward to the first end.
11. The reinforced core structure of claim 10, wherein the expanded
core comprises a plurality of grooves extending transverse to the
longitudinal axis;
12. The reinforced core structure of claim 11, wherein a first
groove is located at the first location, and further comprising: a
first cord tying off the first set of braided fibers and extending
between the overlapped layers of the first set of braided fibers
and opposite the first groove so that the first cord presses the
first set of braided fibers into the first groove.
13. The reinforced core structure of claim 12, wherein a second
groove is located at the second location and further comprising: a
second cord tying off the second set of braided fibers and
extending between the overlapped layers of the second set of
braided fibers and opposite the second groove so that the second
cord presses the second set of braided fibers into the second
groove.
14. The reinforced core structure of claim 13, wherein the
perimeter of the expanded core between the first and second grooves
is substantially the same as the perimeter of the expanded core in
the region between the first groove and the end and the overlapped
layers of the first set of braided fibers extending over this
latter area.
15. The reinforced core structure of claim 14, further comprising:
a third set of braided fibers extending from the first end, past
the first and second grooves, to a third groove beyond the second
groove and reversing at the third groove over itself and back to
the first end.
16. The reinforced core structure of claim 15, further comprising:
a third cord tying off the third set of braided fibers and
extending between the overlapped layers of the third set of braided
fibers and opposite the third groove so that the third cord presses
the third set of braided fibers into the third groove.
17. The reinforced core structure of claim 15, wherein the
perimeter of the expanded core between the first and second grooves
and the overlapped layers of the second set of braided fibers
extending thereover is substantially the same as the perimeter of
the expanded core in the region between the second and third
grooves.
18. The reinforced core structure of claim 13, further comprising:
a third set of braided fibers extending from the first end, past
the first and second locations, to a third location beyond the
second location and reversing at the third location over itself and
back to the first end.
19. A method of forming a reinforced core structure for use in a
resin transfer molding process comprising: (a) providing an
expanded core having a longitudinal axis; (b) braiding a first set
of fibers from a first end of the expanded core to a first location
on the expanded core; (c) reversing the direction of the braiding
of the first set of fibers at the first location and continuing
braiding back to the first end so that the first set of braided
fibers is braided back upon itself to form a first dual layer fiber
structure; (d) braiding a second set of fibers over the first set
of braided fibers from the first end beyond the first location to a
second location; and (e) reversing the braiding direction of the
second set of fibers at the second location back toward the first
end so that the second set of braided fibers is braided back upon
itself to form a second dual layer fiber structure.
20. The method of claim 19, further comprising the step of tying
the first set of braided fibers at the first location with a cord
before reversing direction of the braided fibers.
21. The method of claim 20, further comprising the step of tying
the second set of braided fibers at the second location with a cord
before reversing direction of the braided fibers.
22. The method of claim 19, wherein the expanded core comprises a
plurality of grooves extending transverse to the longitudinal
axis;
23. The method of claim 22, wherein a first groove is located at
the first location, and further comprising: tying the first set of
braided fibers with a cord before reversing direction of the first
set of braided fibers, the cord being arranged opposite the first
groove such as to pull the first set of braided fibers into the
first groove.
24. The method of claim 23, wherein a second groove is located at
the second location, and further comprising: tying the second set
of braided fibers with a cord before reversing direction of the
second set of braided fibers, the cord being arranged opposite the
groove such as to pull the second set of braided fibers into the
second groove.
25. The method of claim 24, wherein the perimeter of the expanded
core between the first and second grooves is substantially the same
as the perimeter of the expanded core in the region between the
first groove and the end and the overlapped layers of the first set
of braided fibers extending over this latter area.
26. The method of claim 25, further comprising: braiding a third
set of fibers from the first end over the first and second sets of
braided fibers to beyond the second groove to a third groove; and
reversing the braiding direction of the third set of fibers at the
third groove back toward the first end so that the third set of
braided fibers is braided back upon itself to form a third dual
layer fiber structure.
27. The method of claim 26 further comprising: tying the third set
of braided fibers with a cord before reversing direction of the
third set of braided fibers, the cord being arranged opposite the
groove such as to pull the third set of braided fibers into the
third groove.
28. The method of claim 26, wherein the perimeter of the expanded
core between the first and second grooves and the overlapped layers
of the second set of braided fibers extending thereover is
substantially the same as the perimeter of the expanded core in the
region between the second and third grooves.
29. The method of claim 19, further comprising: braiding a third
set of fibers from the first end over the first and second sets of
braided fibers to beyond the second location to a third location;
and reversing the braiding direction of the third set of fibers at
the third location back toward the first end so that the third set
of braided fibers is braided back upon itself to form a third dual
layer fiber structure.
30. A method of preparing a reinforced core structure for a product
to be formed in a resin transfer molding process utilizing a resin,
the method comprising: (a) applying fibers over a core beyond the
final finished line for the product to be formed; (b) applying a
tackifier solution to the fibers located at the final finish line,
the tackifier solution comprising a reduced resin concentration
from the final resin concentration of the product to be formed in
the resin transfer molding process; (c) locally consolidating the
tackifier solution; and (d) cutting along the final finish
line.
31. The method of claim 30, wherein the tackifier solution
comprises resin to be used for the resin transfer molding process
diluted by a solvent.
32. A radius filler for use in a resin transfer molding system, the
radius filler comprising: (a) unidirectional tows; and (b) a
braided sleeve of fibers extending around the unidirectional
tows.
33. The radius filler of claim 32, further comprising a tackifier
solution added to the braided sleeve, the tackifier solution
comprising a diluted mixture of the resin to be used in the resin
transfer molding system.
34. The radius filler of claim 33, wherein the tackifier solution
comprises resin to be used for the resin transfer molding process
diluted by a solvent.
35. A method of forming a radius filler for use in forming a
preform to be used in a resin transfer molding process, the method
comprising: (a) providing unidirectional tows; and (b) braiding a
sleeve of fibers around the unidirectional tows.
36. The method of claim 35, further comprising: (a) applying a
tackifier to the braided sleeve, the tackifier comprising a diluted
solution including the resin to be used in the final resin transfer
molding process; and (b) consolidating the tackifier so as to lend
rigidity to the radius filler.
37. The method of claim 36, further comprising: (a) adjoining the
radius filler with a preform; and (b) resin transfer molding the
radius filler and the preform.
38. A method of forming a core structure comprising: (a) providing
a mold having an internal cavity; (b) arranging a prepreg along the
inside of the internal cavity, the prepreg being of a size such
that the prepreg can extend around a circumference of the mold; (c)
placing an expandable foam material in the cavity of the mold and
within the prepreg material; (d) heating the expandable foam
material so as to expand the foam material within the prepreg
material so to press the prepreg material against the walls of the
cavity of the mold; and (e) curing the expandable foam material and
the prepreg material so as to form the core structure.
Description
FIELD OF THE INVENTION
[0001] This invention relates to a process of resin transfer
molding lightweight, foam-filled products and the strong,
lightweight products made thereby. More particularly, the present
invention is directed to a process of resin transfer molding a wind
tunnel blade and the structure of the wind tunnel blade.
BACKGROUND OF THE INVENTION
[0002] Resin transfer molding has been around for many decades, and
its use has grown considerably in recent years. The process allows
the economical manufacture of high quality composites. In
accordance with the process, a resin system is transferred at low
viscosities and low pressures into a closed mold die containing a
preform of dry fibers. The dry fibers, which may have the form of
continuous strand mat, unidirectional, woven, or knitted preforms,
are placed in a closed mold and resin is introduced into the mold
under external pressure or vacuum. The resin cures under the action
of its own exotherm, or heat can be applied to the mold to complete
the curing process.
[0003] The resin transfer molding process can be used to produce
low-cost composite parts that are complex in shape. These parts
typically provide continuous fiber reinforcement, along with inside
mold line and outside mold line controlled surfaces. It is the
placement of the continuous fiber reinforcements in large
structures that sets resin transfer molding apart from other liquid
molding processes.
[0004] In the past, resin transfer molding was used for
applications suitable to consumer product markets. However, in the
last few years, through the development of high-strength resin
systems and more advanced pumping systems, resin transfer molding
has advanced to new levels. These recent developments have promoted
resin transfer molding technology as a practical manufacturing
option for high-strength composite designs, particularly in the
aerospace industry.
[0005] In the aerospace industry, the most visible advantage to the
resin transfer molding process lies in resin transfer molding's
ability to combine multiple, detailed components into one
configuration. For example, many traditional designs consist of
many individual details that are combined as a subassembly. These
subassemblies usually require labor-intensive shimming, bonding,
mechanical fastening, and sealing. Consequently, these
subassemblies demonstrate high part-to-part variability due to
tolerance build-up.
[0006] Resin transfer molding produces an aerodynamic, decorative
finish, with controlled fit-up surfaces. Being a product of the
mold makes the surface quality of the part produced within the mold
comparable to that of the tool's surface.
[0007] Resin transfer molding also provides control of the
fiber/resin ratio in the completed product. This advantage produces
parts that are lightweight and high in strength.
[0008] Unlike conventional composite systems that use lay-up of
prepreg materials, resin transfer molding does not require an
autoclave. Therefore, no autoclave costs are incurred, no size
limitations are inherent, and no staging issues occur.
[0009] In terms of raw material cost, resin transfer molding offers
cost savings by using bulk materials like broad goods. Because dry
goods are less expensive than preimpregnated materials, savings can
be associated with the cost of the wasted material during the
ply-knitting operation. Also, bulk materials do not require special
handling requirements such as freezer storage.
[0010] The basic injection operation of resin transfer molding is
straightforward and easily learned. Hence, minimal training is
required to bring operators on line. On the other hand, in making
preforms, the level of operator skill and training is dependent
upon the method of preforming that is used. Preform fabrication
methods include braiding, knitting, weaving, filament winding, and
stitching. Each of these methods is quite different and must be
individually evaluated for specific design characteristics.
[0011] The initial capital investment costs of resin transfer
molding are low when compared with many other molding processes. An
elementary form of resin transfer molding can be achieved using a
pressure pot, an oven, and a vacuum source. A variety of
commercially available equipment can be used to enhance the process
in many areas.
[0012] In most cases, resin transfer molded materials can be formed
with minimal chemical exposure to workers and their environment.
Many high-performance resin systems are stable and release low
volatiles. Since resin transfer molding is processed within a
closed system, workers are exposed to the resin only when loading
the dispensing equipment.
[0013] One of the problems encountered when using resin transfer
molding is that complex cavities that extend into the surface of
the part must be formed in the mold cavity surface, or the complex
cavity will be filled by resin during the resin injection process.
If the complex cavity is designed to receive a bushing or an
insert, the bushing or insert can be incorporated into the preform
and injected in place to eliminate some higher level assembly and
to avoid the need for a complex tooling surface. If the part
includes an internal hollow tube, proper design of the tool to take
this into account may be difficult and expensive, or may produce a
tooling configuration from which removal of the finished part would
be difficult.
[0014] Other problems are encountered in laying up or arranging
preforms of fibers prior to placing the preform into the mold. If
braided or woven fabric is used, cutting of that fabric often
results in frayed edges, which is undesirable. Arranging stacks, or
tapered-off sections of the preforms on a substrate so that ply
drops are aligned correctly is also difficult.
[0015] The present invention solves many of the above problems by
providing a series of unique processes for the fabrication of a
wind tunnel blade. The processes result in a new structure for a
wind tunnel blade.
[0016] It has become conventional practice in the aircraft industry
to manufacture helicopter and other blades having a molded
fiber-reinforced resin body formed by resin transfer molding. The
fiber-reinforced resin bodies were often formed about an internal,
metallic, load-bearing spar. Such fiber-reinforced resin bodies
exhibited high strength and low weight characteristics. With the
exception of the internal metal spar, however, prior art resin
transfer molded rotor blades did not include structural
reinforcements along their length.
[0017] Prior art wind tunnel blades were formed from a lay-up of
prepreg composite material that was shaped into a unitary structure
including a base attached to the blade. The housing and the hub for
the wind tunnel blades required that a technician lay on his back
and install the unitary base and blade structure into the wind
tunnel's hub, which was difficult.
[0018] Because prior art wind tunnel blades were subjected to high
speed wind conditions, the wind tunnel blades were often damaged as
a result of fatigue and wind erosion. To counter this wind erosion,
the prior art wind tunnel blades included frangible foam tips at
their distal ends. The frangible foam tips were often formed of a
foam material having a uniform density. The frangible foam tip was
wrapped in plies of fiberglass to protect the foam from wind
erosion and to improve impact resistance. This wrapped fiber piece
was difficult to form, and required a large amount of labor to
produce.
[0019] Prior art wind tunnel blades were difficult to balance
because the wind tunnel blades were not of uniform weight and did
not have consistent centers of gravity. The prior art wind tunnel
blades were balanced by adding lead weights to the blade butt to
adjust the center of gravity. After the center of gravity was
adjusted, the blade must be matched to another blade of
approximately the same weight. This matching process can be
difficult because of the large blade-to-blade variation in
weight.
[0020] The present invention solves the above problems by providing
a novel wind tunnel blade design incorporating a variety of
different features that permit easier installation, service, and
replacement of the wind tunnel blades. The process of forming the
unique wind tunnel blade incorporates a number of new composites
forming techniques. These techniques are applicable to a number of
parts or products, and can be used to form parts having a number of
different configurations or complex shapes.
SUMMARY OF THE INVENTION
[0021] The present invention provides a plug including a flexible
outer bushing having first and second ends, a connector attached to
the first end of the bushing, and a fastener extending along the
flexible outer bushing and attached to the connector. The fastener
is configured such that actuation of the fastener causes the
flexible outer bushing to expand outward, whereby the flexible
outer bushing can be inserted into a hollow opening and can expand
against the sides of the opening by actuation of the fastener.
[0022] In one embodiment, the connector is a female-threaded
insert. The fastener can extend along the bushing and includes (1)
an abutment surface for engaging the second end of the bushing and
(2) male threads that are received in the female-threaded insert.
Actuation of the fastener involves rotating the fastener to move
the connector towards the second end.
[0023] In accordance with another aspect of the plug, the fastener
extends along the bushing and comprises an abutment surface for
engaging the second end of the bushing and actuation of the
fastener comprises causing the fastener to pull the connector
toward the abutment surface.
[0024] The present invention also provides a method of resin
transfer molding a product having a hollow tube therein. The method
includes placing an expandable plug into a hollow tube so that a
portion of the plug extends along the intended finished line of the
product being formed, and expanding the expandable plug so that the
expandable plug is pressed against the outer sides of the hollow
tube. Resin is injected about the hollow tube and around the plug
in a resin transfer molding process such that excess resin is
formed beyond the intended finish line. The excess resin and the
expandable plug are cut along the intended finish line so that the
plug is no longer expanded and falls out of the hollow tube.
[0025] The present invention further provides a reinforced core
structure for use in a resin transfer molding process. The
reinforced core structure includes an expanded core having a
longitudinal axis, a first set of braided fibers extending from a
first end of the expanded core to a first location and reversing
from the first groove over itself and back towards the first end,
and a second set of braided fibers extending from the first end
over the first set of braided fibers and to a second location
beyond the first location and reversing from the second location,
back over itself and rearward to the first end.
[0026] In one embodiment, the expanded core includes a plurality of
grooves extending transverse to the longitudinal axis.
[0027] In accordance with another aspect of the invention, a first
groove is located at the first location, and a first cord ties off
the first set of braided fibers and extends between the overlapped
layers of the first set of braided fibers and opposite the first
groove so that the first cord presses the first set of braided
fibers into the first groove. A second groove can be provided that
is located at the second location. A second cord ties off the
second set of braided fibers and extending between the overlapped
layers of the second set of braided fibers and opposite the second
groove so that the second cord presses the second set of braided
fibers into the second groove.
[0028] Preferably, the perimeter of the expanded core between the
first and second grooves is substantially the same as the perimeter
of the expanded core in the region between the first groove and the
end and the overlapped layers of the first set of braided fibers
extending over this latter area.
[0029] A third set of braided fibers can be provided that extends
from the first end, past the first and second grooves, to a third
groove beyond the second groove and reversing at the third groove
over itself and back to the first end. A third cord can be provided
that ties off the third set of braided fibers and extends between
the overlapped layers of the third set of braided fibers and
opposite the third groove so that the third cord presses the third
set of braided fibers into the third groove.
[0030] Preferably, the perimeter of the expanded core between the
first and second grooves and the overlapped layers of the second
set of braided fibers extending thereover is substantially the same
as the perimeter of the expanded core in the region between the
second and third grooves.
[0031] The present invention further provides a method of forming a
reinforced core structure for use in a resin transfer molding
process. The method includes providing an expanded core having a
longitudinal axis, braiding a first set of fibers from a first end
of the expanded core to a first location on the expanded core, and
reversing the direction of the braiding of the first set of fibers
at the first location and continuing braiding back to the first end
so that the first set of braided fibers is braided back upon itself
to form a first dual layer fiber structure. A second set of fibers
is braided over the first set of braided fibers from the first end
beyond the first location to a second location. The braiding
direction of the second set of fibers is reversed at the second
location back toward the first end so that the second set of
braided fibers is braided back upon itself to form a second dual
layer fiber structure.
[0032] In accordance with one aspect of the method, the first set
of braided fibers are tied at the first location with a cord before
reversing direction of the braided fibers. The second set of
braided fibers are tied at the second location with a cord before
reversing direction of the braided fibers.
[0033] The expanded core can be provided with a plurality of
grooves extending transverse to the longitudinal axis. A first
groove is located at the first location, and the first set of
braided fibers is tied with a cord before reversing direction of
the first set of braided fibers. The cord is arranged opposite the
first groove such as to pull the first set of braided fibers into
the first groove. A second groove is located at the second
location, and the second set of braided fibers is tied with a cord
before reversing direction of the second set of braided fibers. The
cord is arranged opposite the groove such as to pull the second set
of braided fibers into the second groove.
[0034] The method further provides braiding a third set of fibers
from the first end over the first and second sets of braided fibers
to beyond the second groove to a third groove and reversing the
braiding direction of the third set of fibers at the third groove
back toward the first end so that the third set of braided fibers
is braided back upon itself to form a third dual layer fiber
structure.
[0035] In accordance with another aspect of the present invention,
a method of preparing a reinforced core structure for a product to
be formed in a resin transfer molding process utilizing a resin is
provided. The method includes applying fibers over a core beyond
the final finished line for the product to be formed, applying a
tackifier solution to the fibers located at the final finish line,
the tackifier solution comprising a reduced resin concentration
from the final resin concentration of the product to be formed in
the resin transfer molding process, locally consolidating the
tackifier solution, and cutting along the final finish line.
[0036] Preferably, the tackifier solution includes resin to be used
for the resin transfer molding process diluted by a solvent.
[0037] The present invention further provides a radius filler for
use in a resin transfer molding system. The radius filler includes
unidirectional tows and a braided sleeve of fibers extending around
the unidirectional tows. A tackifier solution can be added to the
braided sleeve, the tackifier solution comprising a diluted mixture
of the resin to be used in the resin transfer molding system. The
tackifier solution can include resin to be used for the resin
transfer molding process diluted by a solvent.
[0038] The present invention further provides a method of forming a
radius filler for use in forming a preform to be used in a resin
transfer molding process, the method including providing
unidirectional tows, and braiding a sleeve of fibers around the
unidirectional tows. A tackifier can be applied to the braided
sleeve, the tackifier including a diluted solution including the
resin to be used in the final resin transfer molding process. The
tackifier is consolidated so as to lend rigidity to the radius
filler.
[0039] The present invention further provides a method of forming a
core structure including providing a mold having an internal
cavity, arranging a prepreg along the inside of the internal
cavity, the prepreg being of a size such that the prepreg can
extend around a circumference of the mold, placing an expandable
foam material in the cavity of the mold and within the prepreg
material, heating the expandable foam material so as to expand the
foam material within the prepreg material so to press the prepreg
material against the walls of the cavity of the mold, and curing
the expandable foam material and the prepreg material so as to form
the core structure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] The foregoing aspects and many of the attendant advantages
of this invention will become more readily appreciated as the same
becomes better understood by reference to the following detailed
description, when taken in conjunction with the accompanying
drawings, wherein:
[0041] FIG. 1 shows a side perspective view of a wind tunnel blade
made in accordance with the process of the present invention, the
wind tunnel blade shown as mounted on a base that attaches to a
wind tunnel fan hub;
[0042] FIG. 2 is an exploded side perspective view of the wind
tunnel blade and base of FIG. 1;
[0043] FIG. 3 is a sectional view taken along the section lines 3-3
of FIG. 1;
[0044] FIG. 4 is a side perspective view of adjacent cuffs for
adjacent wind tunnel blades such as is shown in FIG. 1;
[0045] FIG. 5 is a sectional view taken along the section lines 5-5
of FIG. 4;
[0046] FIG. 6 is a top view of three foam core sections used to
make the wind tunnel blade of FIG. 1;
[0047] FIG. 7 is a perspective view of the wind tunnel blade of
FIG. 1, with the core sections of FIG. 6 shown in phantom;
[0048] FIG. 8 shows a top plan view of the bottom mold for making
the central core section of FIG. 6;
[0049] FIG. 9 shows the core for the central core section of FIG.
6;
[0050] FIG. 10 shows a diagrammatic cutaway view of an expandable
plug for use in formation of the core of FIG. 9;
[0051] FIG. 11 shows the expandable plug of FIG. 10 in an expanded
position and positioned within a metal tube;
[0052] FIG. 12 shows a diagrammatic side view of the core of FIG.
9, with braided fibers being applied around one end;
[0053] FIG. 13 is a diagrammatic side view similar to FIG. 12, with
a portion of the braided fibers being tied off within a groove on
the core;
[0054] FIG. 14 is a diagrammatic side view similar to FIGS. 12 and
13, showing the braided fibers being braided onto the core in an
opposite direction over the first layer of braided fibers;
[0055] FIG. 15 is a diagrammatic side view similar to FIG. 14,
showing additional braided fibers extending over the first braided
fibers;
[0056] FIG. 16 is a diagrammatic side view similar to FIG. 15, with
the second braided fibers in position;
[0057] FIG. 17 is a diagrammatic side view similar to FIG. 16, with
five braided fibers in place on the outside of the core;
[0058] FIG. 18 is a diagrammatic side view similar to FIG. 7, with
additional braided fibers over the outside of the core;
[0059] FIG. 19 is a side perspective view of the finished braided
central core section shown in FIGS. 9-18;
[0060] FIG. 20 shows the application of a tackifier to the end of
the central core section of FIG. 19;
[0061] FIG. 21 shows shrink tape being applied over the tackifier
that is applied in FIG. 20;
[0062] FIG. 22 shows the central core section of FIGS. 19-21 placed
in a frame prior to cutting;
[0063] FIG. 23 is a sectional view of the central core section of
FIG. 22, taken along the sectional lines 23-23;
[0064] FIG. 24 is a sectional view of the wind tunnel blade of FIG.
7, taken along the sectional lines 24-24;
[0065] FIG. 25 is a detailed view of a radius filler formed in
accordance with the present invention, taken in the detail section
25 of FIG. 24;
[0066] FIG. 26 shows a mandrel for formation of the radius filler
of FIG. 25;
[0067] FIG. 27 is a sectional view of the mandrel of FIG. 26, taken
along the sectional lines 27-27 and showing a vacuum bag in place
over the mandrel;
[0068] FIG. 28 shows the cut core sections of FIG. 6 in place and
being wrapped by a prepreg sheet;
[0069] FIG. 29 shows a mold in which the fan tunnel blade of FIG. 6
is formed;
[0070] FIG. 30 is a diagrammatic view of the wind tunnel blade of
FIG. 6, as removed from the mold of FIG. 29, and displaying a cut
line along which the wind tunnel blade is cut before finishing;
[0071] FIG. 31 shows a mold in which the tip for the wind tunnel
blade of FIG. 1 is formed, the mold having foam material and an
outer skin therein;
[0072] FIG. 32 is a diagrammatic view of the mold of FIG. 31, with
the foam material expanded and the outer skins pressed against the
inner mold line of the mold;
[0073] FIG. 33 is a top view of the wind tunnel blade tip formed in
the mold of FIGS. 31 and 32; and
[0074] FIG. 34 is a side perspective view of a balance mechanism
that is fitted within the wind tunnel blade of FIG. 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0075] Referring now to the drawing, in which like reference
numerals represent like parts throughout the several views, FIG. 1
shows a wind tunnel blade 30 made in accordance with the present
invention. The wind tunnel blade 30 is connected to a base 32 and
is held in position by a two-piece cuff 34.
[0076] Briefly described, the present invention is directed to the
separate wind tunnel blade 30, base 32 and cuff 34 system, and the
unique configuration and structure of the wind tunnel blade 30. In
addition, the present invention is directed to resin molding
transfer processes for forming the wind tunnel blade 30.
[0077] The base 32 is designed to be attached to a hub of a wind
tunnel fan (not shown). A plurality of the wind tunnel blades 30
project radially outward from the hub and are supported therefrom
in a conventional fashion at the base 32. Any number of wind tunnel
blades 30 can be used with the wind tunnel fan. As a nonlimiting
example, the wind tunnel blade 30 shown in FIG. 1 is for use with a
wind tunnel fan having seventy-two (72) wind tunnel blades spaced
circumferentially about the hub for the wind tunnel fan. Since each
wind tunnel blade 30 is identical, only a single wind tunnel blade
will be described in this disclosure.
[0078] The base 32 is preferably cast aluminum, and includes a
pedestal 36 (best shown in FIG. 2) that is configured to be
attached to a rotating wind tunnel fan hub (not shown, but well
known in the art). The pedestal 36 includes two legs 38 and five
elongate bores 40 extending therethrough. The elongate bores 40
receive bolts (not shown) that are attached to the rotary wind
tunnel fan hub in a manner known in the art.
[0079] A series of flanges 42 extend orthogonally from top comers
of the sidewalls of the pedestal 36. The flanges 42 include
downwardly extending mounting holes 44 that are configured to
receive bolts (not shown) that extend through the cuff 34.
[0080] The cuff 34 includes a fore cuff piece 45 and an aft cuff
piece 46 (best shown in FIG. 2). The fore and aft cuff pieces 45,
46 include holes 48 through which mounting bolts extend into the
mounting holes 44 on the base 32. The fore cuff piece 45 and the
aft cuff piece 46 include angled cuts 50, 52 (FIG. 3) that are
configured to extend along and underneath the bottom edges of the
wind tunnel blade 30. The angled cuts 50, 52 are preferably cut,
one at an acute angle, the other at an obtuse angle, to the top
plane of the fore cuff piece 45 and the aft cuff piece 46, and are
arranged so that they fit together to form a smooth transition
between the fore cuff piece 45 and the aft cuff piece 46. The
angled cuts 50, 52 are shaped so that the surfaces of the two cuts
extend forwardly and downwardly from the top surface of the fore
and aft cuff pieces 45, 46. In this manner, air flow (see FIG. 3)
over the top surface of the cuff pieces 45, 46 is not directed into
the joint between the cuff pieces.
[0081] The fore cuff piece 45 and the aft cuff piece 46 are
preferably compression molded using fiberglass in an epoxy resin.
As can be seen in FIG. 5, the forward portion of the fore cuff
piece 45 is formed with a stepped-downward section 54. A trailing,
flat section 56 of the aft cuff piece 46 fits over the
stepped-downward section 54 of the fore cuff piece 45. The
stepped-down section 54 and the flat section 56 form an
interconnected lap joint that is attached by nutplates (not shown,
but of a typical model designed for composites) so that a series of
the cuffs 34 creates a passive p-seal between the cuffs 34 (FIG. 4)
that extend over the wind tunnel fan hub (not shown).
[0082] In summary, the cuff 34 includes three design features that
contribute to preventing airflow leakage downward through the cuffs
into the wind tunnel fan hub. First, the angled cuts 50, 52 form a
split line that is angled away from air flow over the cuff 34 and
is covered by the bottom edge of the wind tunnel blade 30. Second,
the cuffs 34 are linked together so as to form a passive p-seal
over the wind tunnel fan hub. Finally, the interconnected lap joint
between the stepped-down section 54 of the fore cuff piece 45 and
the flat section 56 of the aft cuff piece 46 prevents further
leakage.
[0083] Referring back to FIG. 1, the wind tunnel blade 30 includes
a rearward edge 62 and a rounded, leading edge 64. The wind tunnel
blade 30 includes a tang root 66 (FIG. 2) that extends into a slot
within the base 32 and attaches to the base 32 by bolts (not shown)
through holes 65 in the tang root. The tang root 66 includes a
protrusion 67 at the intersection of the tang root and the wind
tunnel blade 30 that extends perpendicular to the longitudinal axis
of the wind tunnel blade and along the aft, right top portion of
the tang root 66. The aft cuff piece 46 fits over the protrusion
67, to add further stability and to help fix the wind tunnel blade
30 in position.
[0084] The wind tunnel blade 30 includes a separate tip 68 attached
along the distal end of the wind tunnel blade. The function and the
structure of the tip 68 are described in detail below.
[0085] The method of forming the wind tunnel blade 30 will now be
described. Describing the process broadly with reference to FIG. 6,
the wind tunnel blade 30 is formed from a central foam core section
70, a fore foam core section 72, and an aft foam core section 74,
each of which extends longitudinally the length of the blade. The
central, fore, and aft core sections 70, 72, 74 are attached along
their surfaces to form the body of the blade (FIG. 7). The central
foam core section 70 extends downward beyond the bottom ends of the
fore and aft core sections 72, 74 to form the tang root 66. The tip
68 is attached along the distal end of the foam core sections 70,
72, 74.
[0086] A bottom mold 76 for forming a foam core 83 (FIG. 9) for the
central foam core section 70 is shown in FIG. 8. The cavity 77 for
the bottom mold 76 substantially matches the outer contour of the
desired finished product; i.e., the foam core 83. The mold cavity
77 includes protrusions 78a-e that extend transverse to the
longitudinal axis of the bottom mold 76, and extend around the
perimeter of the cavity, including a top for the mold (not shown)
that is closed over the bottom mold 76 to form a closed cavity for
formation of the foam core 83. A metal tube 80 is suspended by a
wire 81 within the cavity 77 of the mold 76. Preferably, the wire
81 extends upward from the bottom of the cavity 77 (not shown). In
the embodiment shown, the wire 81 is welded to the end of the metal
tube 80, and extends into a small hole 82 at the end of the mold
cavity 77. Many other arrangements for suspending the metal tube 80
with a wire can be used.
[0087] As is described in detail below, the foam core 83 is formed
around the metal tube 80 so that the metal tube and the wire 81
become a part of the foam core and later a part of the central foam
core section 70. The top portion of the metal tube 80 is plugged so
as to prevent the flow of core therein. The bottom of the metal
tube fits against a protrusion (not shown) in the mold cavity 77 to
prevent flow in that end. The metal tube 80 is arranged so as to
extend from the bottom portion of the foam core 83 (i.e., the end
that forms the tang root 66) to a location approximately two-thirds
of the length up the central foam core section 70. The metal tube
80 is designed to receive a balance mechanism 82 (FIG. 34), the
function and structure of which are described in detail below. The
metal tube 80 is preferably cylindrically shaped and formed from
aluminum, but any appropriately shaped metal or other suitable
material can be used.
[0088] After the metal tube 80 is in place, a polyurethane foam
mixture (not shown) is poured into the mold cavity 77 and
encapsulates the metal tube 80. The top mold (not shown) is placed
over the bottom mold 7-6 to seal the cavity 77. The polyurethane
foam mixture is heated until expanded to fill the mold and is held
at a curing temperature until hardened. The polyurethane foam
mixture and the metal tube 80 thus form a unitary structure of the
foam core 83 for use in forming the central foam core section 70.
The length of the foam core 83 after it is removed from the mold 76
is slightly longer than the final central foam core section 70 used
to form the wind tunnel blade 30. The excess length represents
excess foam at each end of the foam core 83 that is removed after a
braided fiber shell has been placed around the foam core 83, as is
described in detail below.
[0089] As can be seen in FIG. 9, the final foam core 83 includes
indentations, or grooves 85a-e that extend around the circumference
of the foam core 83. The grooves 85a-e are formed by the
protrusions 78a-e in the mold cavity 77. The foam core 83 also
tapers in circumference (i.e., decreases in perimeter) as the foam
core approaches the bottom end (i.e., the tang root end). The
decreases in perimeter occur in steps, and each of the steps begins
at one of the grooves 85a-e. The functions of the stepped decreases
in perimeter and the grooves are described in detail below.
[0090] An expandable plug 87 (FIG. 10) is placed in the open end of
the metal tube 80. The expandable plug 87 includes a threaded
fastener 88 that extends through a rubber-faced metal washer 89 and
into a rubber bushing 90. The rubber bushing 90 has an internal
diameter that substantially matches the outside diameter of the
threaded fastener 88. The outer diameter of the bushing 90 is
slightly smaller than the inner diameter of the metal tube 80. A
flange 92 extends around the circumference of the top end of the
rubber bushing 90. A threaded insert 94 is located within the
internal circumference of the bore for the rubber bushing 90. A
tool-receiving pattern 95 is located at the top end of the threaded
fastener 88.
[0091] The expandable plug 87 is placed in the end of the metal
tube so that the flange 92 fits over the outer circumference of the
metal tube. A tool, such as a screwdriver, is placed in the
tool-receiving pattern 95 of the threaded fastener 88. The threaded
fastener 88 is then rotated into the threaded insert 94 until the
rubber face metal washer 89 is pressed against the flange 92 on the
rubber bushing 90. Continued rotation of the threaded fastener 88
causes the rubber bushing to buckle (FIG. 11), and press outward on
the sides of the metal tube 80, thus sealing the end of the metal
tube 80.
[0092] After the expandable plug 87 is in place, fibers 99 (FIG.
12) are braided around the foam core 83, beginning at the bottom
end so as to form a fiber sock 100a. The braided fiber sock 100a is
preferably formed from fiberglass fibers, but can be graphite,
aramid, ceramics, or any other suitable material. The fibers 99 are
preferably braided onto the foam core 83, but can be knitted,
woven, filament-wound, or stitched onto the foam core. Braiding
results in the fibers being in an oriented pattern around the
entire circumference of the foam core 83. The braided fibers 99
also form a snug-fitting preform around the foam core 83.
[0093] The fibers 99 are continually braided up the circumference
of the foam core 83 until the braided fiber sock 100a extends
beyond the first groove 85a (FIG. 12). A cord 102a (FIG. 13) is
then placed around the braided fiber sock 100a opposite the first
groove 85a. The cord 102a is preferably made of fiberglass; but any
other suitable material can be used. The cord 102a is tensioned and
tied off such that the braided fiber sock 100a extends downward
into the groove 85a (FIG. 13). The braiding direction of the fibers
is then reversed such that the braided fiber sock 100a overlaps
itself (FIG. 14) and extends back to and beyond the bottom end of
the foam core 83. The braided fiber sock 100a is then cut, and the
free ends are permitted to dangle beyond the end of the foam core
83.
[0094] Preferably, the groove 85a is of a depth and size so that
the fold in the braided fiber sock 100a where the braided fiber
sock reverses direction is contained within the groove 85a, and
thus a smooth surface is maintained at the transition (FIG. 14).
Moreover, the perimeter of the foam core 83 between the groove 85a
and the end of the foam core is a sufficient amount less than the
perimeter between the grooves 85a and 85b such that, once the
braided fiber sock 100a has been put in place, the outer surface of
the return layer of the braided fiber sock is level with the outer
circumference of the foam core 83 between the grooves 85a and 85b
(FIG. 14).
[0095] After the braided fiber sock 100a is extended beyond the
bottom of the foam core 83, the fibers are cut and a second
braiding process begins from the bottom of the core over the
initial braided fiber sock 100a. Instead of cutting the initial
braided fiber sock 100a, the direction of braiding of the fibers
can be reversed, and the A second braided fiber sock 100b (FIG. 15)
is formed over the initial braided fiber sock 100a and over the
outer circumference of the foam core 83 between the grooves 85a and
85b. Instead of cutting the initial braided fiber sock 100a, the
direction of braiding of the fibers can be reversed, and the second
braided fiber sock 100b can be formed by continued braiding of the
first fiber sock. This method is preferred to cutting, because it
does not produce frayed edges that must be kept in order.
[0096] The second braided fiber sock 100b is extended beyond the
groove 85b (FIG. 15) and a second cord 102b is tensioned and tied
over the second braided fiber sock 100b and pulled downward into
the groove 85b. The direction of the braid for the braided fiber
sock 100b is then reversed, and the braided fiber sock 100b extends
rearward beyond the bottom of the foam core 83 (FIG. 16). The
second fiber sock 100b is then cut, and a third fiber sock 100c is
formed over the second fiber sock 100b (alternatively braiding is
reversed, as described above). This process is continued until all
of the grooves 85a-e have been filled, and five braided fiber socks
100a-e extend to the respective grooves 85a-e (FIG. 17), and extend
rearward beyond the bottom end of the foam core 83. A final braided
fiber sock 103 (FIG. 16) is then formed along the length of the
foam core 83 over the braided fiber socks 100a-e and the exposed
portion of the foam core 83. The final braided fiber sock 103
extends beyond both ends of the foam core 83.
[0097] The fore and aft foam core sections 72, 74 include foam
cores 104, 105 (FIG. 24) formed in a manner similar to the foam
core 83. That is, the foam cores 104, 105 are covered by braided
fiber socks 106, 107. The braided fiber socks 106, 107 are placed
on the foam cores 104, 105 so that the braided fiber socks extend
beyond both ends of the foam cores. Unlike the foam core 83 for the
central foam core section 70, the foam cores 104, 105 do not
include step sections. Instead, only a single layer of fibers (the
braided fiber socks 106, 107) extend the entire length of the fore
and aft foam core sections 72, 74. Any number of layers of the
braided fiber socks 106, 107 may be used over the foam cores 104,
105, but in the preferred embodiment, only one layer of the braided
fiber sock is used on each of the foam cores.
[0098] After the central, fore, and aft foam core sections 70, 72,
74 are formed, the ends of the foam core sections are cut so as to
remove excess material from the ends of the foam cores 83, 104, 105
and the excess braided fiber socks 100a-e, 103, 106, and 107. To
cleanly cut the braided fiber socks 100a-e, 103, 106, and. 107, a
unique process has been developed. Because each of the foam core
sections 70, 72, 74 are preferably cut in the same manner, the
cutting process for only the central foam core section 70 will be
described.
[0099] A tackifier 112 is applied by a brush 109 (FIG. 20) to the
ends of the central foam core section 70. The tackifier 112 is
preferably the base resin that will be used in the final resin
transfer molding process of the wind tunnel blade 30, diluted in a
solvent such as acetone. The tackifier 112 is applied at the
location of the cuts, and overlaps the cuts in both directions by
approximately half an inch. The tackifier 112 is applied in
sufficient quantities to saturate through each of the braided fiber
socks 100a-e, 103.
[0100] The tackifier 112 is locally consolidated by such methods as
vacuum bag, shrink tape, or hard tooling until the polymer material
is stable due to cooling of the hot melt or by flashing of the
solvent from the solution. In the embodiment shown, shrink tape 113
(FIG. 21) is applied around and over the portion of the braided
fiber socks 100a-e, 103 that has been saturated with the tackifier
112. The shrink tape 113 is heated to apply pressure and heat to
the tackifier 112, causing the shrink tape 113 to constrict around
the central foam core section 70 and apply pressure until the
tackifier 112 precures (i.e., semi-hardens).
[0101] The central foam core section 70 is then removed from the
oven and placed in a frame 108 (FIG. 22). The frame 108 is designed
as a four-sided box having sides 109 and ends 110. The sides 109
extend beyond the side edge of the central core section. The ends
110 of the frame 108 are spaced apart a length that is the same as
the length of the finished central foam core section 70. The top
surface of the ends 110 include indentations 111 (FIG. 23) that are
designed to receive and support the ends of the central foam core
section 70.
[0102] The uncut central foam core section 70 is placed on the
frame 108 such that the excess materials for the foam core 83 and
braided fiber socks 100a-e and 103 extend beyond the ends 110 of
the frame. The portions of the central foam core section 70 upon
which the tackifier 112 was applied align with the ends 110 of the
frame.
[0103] After the central foam core section 70 is placed on the
frame 108, brackets 114 are placed over opposite ends of the
central foam core section opposite the ends 110 of the frame. The
brackets 114 include indentations 115 (FIG. 23) that substantially
match the contour of the upper side of the central foam core
section 70. Thus, the brackets 114 and the ends 110 of the frame
108 work together to encase the central foam core section 70 at
opposite ends of the central foam core section. The brackets 114
and the ends are then attached so as to hold the central foam core
section 70.
[0104] The central foam core section 70 is then cut just along the
outer edges of the ends 110 and brackets 114. The fact that the
central foam core section 70 is clamped between the indentations
111, 115 on the ends 110 and the brackets 114 ensures that the
central foam core section 70 is stable during the cutting process.
In this manner, the braided fiber socks 100a-e, 103 are not pulled
away from the foam core 83, and damage to the foam core 83 during
the cutting process is minimized.
[0105] The tackifier 112 seals the braided fiber socks 100a-e, 103
against the outer surface of the foam core 83 and prevent fraying
of the fiberglass within the braided fiber socks upon cutting of
the socks. In this manner, smooth cuts are formed at the ends of
the central foam core section 70.
[0106] The fore and aft foam core sections 72, 74 are prepared and
cut in the same manner as the central foam core section 70. The
central, fore, and aft foam core sections 70, 72, 74 are now ready
for assembly.
[0107] As stated above, the central, fore, and aft foam core
sections 70, 72, 74 are placed together to form the wind tunnel
blade 30. Because the edges of the central, fore, and aft foam core
sections 70, 72, 74 are rounded, radius fillers 120 (FIG. 24) are
used to fill the gaps between the outer edge of the foam core
sections. The radius fillers 120 used in the wind tunnel blade 30
are formed using a novel process. In accordance with the process, a
braided sleeve 122 surrounds a number of unidirectional tows 124
(FIG. 25). The unidirectional tows 124 can be inserted into the
bi-axial braided sleeve 122, or the braided sleeve can be formed
around the unidirectional tows.
[0108] The core of the unidirectional tows 124 can be of uniform
cross section, or can be varied in cross-section along its length
so as to fit a particular gap. The radius fillers 120 of the wind
tunnel blade 30 have a substantially uniform triangular
cross-section, with two radiused, or curved sides 125. The curved
sides 125 correspond to the sides that abut against adjacent foam
core sections.
[0109] The radius filler 120 is formed on a mandrel 127 (FIG. 26)
that includes a contoured surface that is substantially the same as
the juncture of the two foam core sections 70, 72 or 70, 74,
between which the radius filler will be placed. In the present
invention, the mandrel 127 includes a first radiused mandrel
surface 126 adjacent to a second radiused mandrel surface 128. The
first radiused mandrel surface 126 in the example shown in the
drawings is a pipe that has a radius that is substantially the same
as the outer radius of the fore foam core section 72. The second
radiused mandrel surface 128 is a machined metal that has a radius
that is substantially the same as the outer radius of the central
foam core section 70.
[0110] The braided sleeve 122 is braided around the unidirectional
tows 124, and is then soaked with a tackifier that is similar in
composition to the tackifier 112 described in detail above. The
braided sleeve 122 with the unidirectional tows 124 therein is then
placed between the two radiused mandrel surfaces 126, 128, and is
vacuum bagged under a bladder 130 (FIG. 27). The bagged radius
filler 120 is then placed in an autoclave (not shown) and heat is
applied while vacuum is applied to the bladder 130. The bagged
radius filler 120 is heated until the tackifier on the braided
sleeve 122 is precured, or semi-hardened.
[0111] The tackifier solution that is placed on the braided sleeve
122 places a resin coating over the braided sleeve so that the
resin equals approximately 6% of the weight of the fibers in the
resin. In contrast, in the final resin transfer molding process,
the resin is approximately 50% of the weight of the resin and fiber
composite. The amount of resin in the tackifier is preferably
sufficient to maintain or hold the shape of the radius filler 120
after precuring, but is not sufficient to harden it into a rigid,
cured state. Thus, the tackifier works as a binding agent to
maintain consolidation and configuration of the braided sleeve 122
until the final resin transfer molding of the wind tunnel blade
30.
[0112] Each of the radius fillers 120 for the wind tunnel blade 30
are formed in a manner similar to the process described above.
However, the radiused mandrel surfaces 126, 128 may have a
different contour so as to produce radius fillers that fit between
the respective foam core sections 70, 72, and 74.
[0113] The formed central, fore, and aft foam core sections 70, 72,
74 and the radius fillers 120 are then consolidated into the shape
of the wind tunnel blade 30. The entire assembly is laid over a
tackified sheet 131 (FIG. 28) on a lay-up mandrel (not shown). The
tackified sheet 131 is wrapped over the top of the assembly and is
trimmed to fit the assembly. The assembly and the tackified sheet
131 are then vacuum bagged and precured. The consolidated assembly,
called a "preform," is then ready for resin transfer molding.
[0114] The preform is removed from the lay-up mandrel and is placed
within a bottom mold 133 (FIG. 29) for the resin transfer molding
process. The bottom mold 133 is contoured to the tang 60, leading
edge 62, rearward edge 64, tang root 66, and the protrusion 67 of
the wind tunnel blade 30. The bottom mold 133 includes an inlet 134
adjacent to the tang root 66, but is spaced approximately two
inches therefrom. An outlet 135 is located at the top end of the
bottom mold 133 for the outflow of resin. The bottom mold 133
includes inner and outer O-rings 136, 137, which provide a primary
and secondary seal between the bottom mold and a top mold (not
shown). The two O-rings improve seal performance to maintain vacuum
during the resin transfer molding process, and the second seal 137
provides a backup to the primary seal 136 in case of primary seal
failure.
[0115] The preform is carefully positioned in the bottom mold 133
with index locators. Once the preform has been set in place, the
parting planes are inspected for possible ply mislocation or
obstruction that will cause ply pinch and mold closure
interference.
[0116] After the tool has been closed and the plumbing attached,
the system is checked for vacuum integrity. This is commonly done
with the vacuum source and a vacuum gauge at the resin trap.
Shutoff valves can isolate the plumping for the entire system.
After applying high vacuum, the system is allowed to stand static
for up to five minutes to verify the level of vacuum stability. The
vacuum assists the resin flow through the complex shapes with
minimal porosity.
[0117] The bottom mold 133 and the upper mold are then heated to
the resin system injection temperature, and the resin system is
injected into the mold through the inlet port 134. The expandable
plug 87 in the metal tube 80 prevents the resin system from flowing
into the metal tube. The resin fills the void at the bottom end of
the bottom mold 133 between the inlet 134 and the tang root 66. In
addition, the resin penetrates all of the preforms within the
system, including the braided fiber socks 100a-e, 103, 106, 107 and
the tackified sheet 131. The inlet 134 and the outlet 135 are used
to deliver the resin to and from the mold.
[0118] The resin for the wind tunnel blade 30 is preferably Epon
dpl 862 RTM liquid resin with the Epon curing agent W added as a
curing additive, available from Shell Chemical Company, but other
resins or other resin systems can be used. When selecting a resin
for a transfer molding resin design, the first step is to clearly
define the performance conditions. Some of the performance criteria
include the range of operating temperatures, thermal cycles, and
mechanical properties. To insure the proper resin selection, the
resin properties must be evaluated based on the performance
conditions. A wide variety of resin systems are available for use
in the present invention, along with many others that are in the
development stage. Some of the generic resin transfer molding resin
systems that can be used include: epoxy resin systems; cyanate
ester resin systems; vinyl ester resin systems; phenolic resin
systems; polyester resin systems; and bismaleimide resin
systems.
[0119] Ideally, the resin injection procedure creates a
constant-flow front, with complete fiber wet-out on a microscopic
level, and achieves total mold cavity fill. The recommended way to
create a constant-flow front is to use an injection system that
maintains positive displacement at low pressure. Sustaining a low
resin viscosity through the injection cycle helps to control the
pumping pressure. Another aid to achieving total fiber wet-out and
mold fill is to conclude the injection cycle with an appropriate
hydrostatic pressure. The hydrostatic pressure should be maintained
until the resin matrix is well within its gel phase. The level of
hydrostatic pressure is governed by the type of resin system, mold
design, and supporting equipment.
[0120] After the resin is completely injected into the preform, the
temperature of the mold is increased to the cure temperature for
the resin system. The mold is held at this temperature for a
sufficient time to cure the resin. After curing is complete, the
wind tunnel blade 30 is removed from the mold and the excess resin
66a at the tang root 66 is sheared off along the line 66b shown in
FIG. 30. When the excess resin 66a is cut off the tang root 66, the
metal tube 80 and the expandable plug 87 are also cut, generally
along the dotted line 66b shown in FIG. 30. After the excess resin
66a and the portions of the metal tube 80 and expandable plug 87
are removed, the threaded fastener 88 is cut in half, releasing the
rubber bushing 90 of the expandable plug 87 so that the rubber
bushing 90 is no longer forced against the sides of the metal tube
80, and simply falls out. Alternatively and preferably, a cut can
be made so that the entire expandable plug 87 is cut out and falls
out, and the tube and the expandable plug 87 (still fully expanded)
are separated from the final product.
[0121] The tip 68 is formed separately from the rest of the wind
tunnel blade 30. To form the tip 68, a teardrop-shaped mold 142
having a mold cavity that substantially matches the shape of the
tip is used. An outer skin 144, preferably a prepreg sheet of
material (fibers impregnated with a resin), is placed within the
mold 142. The outer skin 144 wraps substantially around the inside
mold cavity 143 of the mold 142.
[0122] Foam material 150 is placed inside the outer skin 144. The
mold 142 is then placed in an oven and heated so that the foam
material 150 expands. During this expansion process, the outer skin
144 is pressed outward against the mold cavity 143. The resin in
the outer skin 144 cures during the same process, and a tip 68 is
formed (FIG. 33) that has a foam core with a hard, outer skin 144.
The tip 68 is then glued to the top end of the molded wind tunnel
blade 30.
[0123] The balance mechanism 82 is shown in FIG. 34. The balance
mechanism 82 is inserted into the metal tube 80 after the resin
transfer molding process. The balance mechanism 82 includes a
threaded rod 154 that extends the length of the metal tube 80.
Ballast weights 156 are located along the length of the threaded
rod 154. A metal plate 158 is secured to the end of the threaded
rod 154 by a jam nut 162. An end cap 160, that is sized and shaped
to fit against the end of the tang root 66, is bonded to the end of
the tang root. The plate 158 is held against the end cap 160 by
bolts 164. The bolts 164 extend upward into the end cap 160.
[0124] The distal end of the threaded rod 154 includes a tube cap
166 that is sized so as to receive the end of the threaded rod and
to position the threaded rod laterally within the metal tube 80.
Each of the ballast weights 156 include grooves on the outer
surface thereof for receiving O-rings 168. The O-rings 168 bear
against the inner surface of the metal tube 80 to minimize
vibration of the ballast weights 156. Thus, the O-rings 168 are
located along the length of the threaded rod 154 and position the
threaded rod within the metal tube 80. The ballast weights 156 and
O-rings 168 are held between pairs of jam nuts 157.
[0125] In practice, the wind tunnel blade 30 is balanced by the
balance mechanism 82. The balance mechanism allows both the weight
and the center of gravity of the wind tunnel blade 30 to be
adjusted. The number of ballast weights 156 can be varied by
removing or adding ballast weights 156 to the threaded rod 154. The
position of the ballast weights 156 along the threaded rod 154 can
be varied by moving the jam nuts 157 up and down the length of the
threaded rod 154, which in turn moves the ballast weights 156 up
and down the threaded rod. In this manner, both the weight and the
center of gravity of the wind tunnel blade 30 can be adjusted.
[0126] As can be understood from the foregoing, the present
invention provides numerous advantages in the structure of the wind
tunnel blade 30 over wind tunnel blades of the prior art. The
separate wind tunnel blade 30, base 32, and cuff 34 provide ease of
maintenance. If damage to the wind tunnel blade 30 occurs, the wind
tunnel blade can be released from the base 32 and the cuff 34, and
a new wind tunnel blade can be installed. In contrast, in prior art
wind tunnel blades, the blade, base and cuff were a single
structure, and had to be replaced upon damage to the wind tunnel
blade.
[0127] The two-piece cuff 34 allows access to the wind tunnel blade
30 by removing only one of the fore cuff piece 45 or the aft cuff
piece 46. In addition, the cuff 34 minimizes air flow leakage
downward through the cuffs into the wind tunnel fan by providing
the angled cuts 50, 52 that form a split line that is angled away
from air flow over the cuff 34 and is covered by the bottom edge of
the wind tunnel blade 30. In addition, adjacent cuffs 34 are linked
together so as to form a passive p-seal over the wind tunnel fan
hub. The interconnected lap joint between adjacent cuffs 34 is also
designed to prevent leakage.
[0128] Resin transfer molding provides smooth finished surfaces on
both sides of the wind tunnel blade 30. In contrast, prior art
prepreg lay-up methods provided a single surface that was formed
against a tool and that was smooth. The smooth surfaces provided by
resin transfer molding provide an aerodynamic, decorative finish,
with controlled fit-up surfaces.
[0129] The new construction of a tip 68 for the wind tunnel blade
30 provides an improved structure and ease of construction not
provided by the prior art.
[0130] The radius filler 120 provides several advantages over prior
art radius fillers. In the prior art, radius fillers were most
often formed by prepreg materials that were formed into the shape
of the radius fillers. In contrast, the radius filler 120 of the
present invention provides unidirectional tows 122 within a
bi-axial braided sleeve 124. The unidirectional tows 122 can be
tailored to accommodate various cross-sectional areas. In addition,
the core of the unidirectional tows 122 can be of uniform
cross-section or can be tailored to provide varying cross-sectional
areas along the length.
[0131] The three-piece core construction of the wind tunnel blade
30 provides structural, longitudinal support along the length of
the wind tunnel blade. Adjacent foam core sections provide I-beams
at their intersections.
[0132] The balance mechanism 82 provides an easy manner in which to
match the centers of gravity and weight of a large number of wind
tunnel blades 30. The balance mechanism 82 is easily adjustable,
and is easily accessed by removal of the wind tunnel blade 30.
[0133] The stepped braided fibers on the central foam core section
70 provide increased strength adjacent to the base 32, and lighter
weight near the tip 38 of the wind tunnel blade 30. The stepped
construction therefore provides the optimal strength and weight
characteristics for the wind tunnel blade 30.
[0134] The methods of construction of the wind tunnel blade 30
disclosed herein are not only convenient for formation of the wind
tunnel blade 30, but can also be used for additional parts. For
example, the expandable plug 87 provides an easy manner of plugging
a tube within a preform. The expandable plug 87 prevents the flow
of resin into the metal tube 80 during the resin transfer molding
process, but after being cut, releases the sides of the metal tube
80 and falls out of the metal tube.
[0135] The tackifier 112 provides a convenient way of stabilizing
the edges of reinforced preforms prior to trimming the edges. A
tackifier 112 is applied to edges to be cut, and is locally
consolidated so that the fiber preforms are held together during
the cutting process. In this way, the fraying, lofting, and
distortion caused by trimming can be avoided.
[0136] The method for providing multiple ply drop off of braided
fabric disclosed herein provides a convenient and efficient manner
of providing a reinforced core structure for a composite part.
Grooves are provided on the core, and the braided fibers are tied
off in the grooves. The tied off, braided fibers provide a smooth
transition on reverse of direction of the braiding of the fibers,
and permits an additional fiber layer to be braided over the
transition.
[0137] While the preferred embodiment of the invention has been
illustrated and described with reference to preferred embodiments
thereof, it will be appreciated that various changes can be made
therein without departing from the spirit and scope of the
invention as defined in the appended claims.
* * * * *