U.S. patent application number 11/942199 was filed with the patent office on 2008-06-26 for densification of formed composite parts.
Invention is credited to Thaddeus W. Gonsowski, Vernon R. Hudalla, Dean S. Kriskovich, Mark L. LaForest, Neil Murdie, Michael D. Wood.
Application Number | 20080150183 11/942199 |
Document ID | / |
Family ID | 24101009 |
Filed Date | 2008-06-26 |
United States Patent
Application |
20080150183 |
Kind Code |
A1 |
Wood; Michael D. ; et
al. |
June 26, 2008 |
DENSIFICATION OF FORMED COMPOSITE PARTS
Abstract
Methods and apparatuses for combining raw fibrous and binding
materials in single mixing step (Step S3), followed by
consolidation (Step S5) to greatly shorten overall cycle time to
finished fiber-reinforced composite part. Chopped fibrous materials
and binder materials are deposited sequentially onto belt conveyor
(Step S2) so that materials are successively layered on top of one
another in predetermined ratio and subsequently mixed (Step S3) to
achieve uniform dispersion throughout. Mixed materials are
deposited into rotating mold (Step S4), which further ensures
uniform dispersion of fibrous and binder materials. Impregnation of
fibrous materials with the binder material occurs in situ as
uniformly mixed materials are heated and subsequently compacted in
mold (Step S5) to obtain desired shape of fiber-reinforced
composite part. Rotation device including: turntable for rotating
mold; and actuator for supporting turntable and providing
reciprocating motion to mold.
Inventors: |
Wood; Michael D.; (South
Bend, IN) ; LaForest; Mark L.; (Granger, IN) ;
Murdie; Neil; (South Bend, IN) ; Kriskovich; Dean
S.; (Avon, IN) ; Hudalla; Vernon R.;
(Charlotte, NC) ; Gonsowski; Thaddeus W.;
(Osceola, WI) |
Correspondence
Address: |
HONEYWELL INTERNATIONAL INC.
Law Dept. AB2, P.O. Box 2245
Morristown
NJ
07962-9806
US
|
Family ID: |
24101009 |
Appl. No.: |
11/942199 |
Filed: |
November 19, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10315464 |
Dec 10, 2002 |
7318717 |
|
|
11942199 |
|
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|
|
09527322 |
Mar 16, 2000 |
6521152 |
|
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10315464 |
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Current U.S.
Class: |
264/71 ;
425/576 |
Current CPC
Class: |
B29B 11/16 20130101;
C04B 2235/526 20130101; F16D 69/023 20130101; Y10S 425/108
20130101; C04B 35/83 20130101; Y10T 428/30 20150115; C04B 2235/5272
20130101 |
Class at
Publication: |
264/71 ;
425/576 |
International
Class: |
B29C 67/00 20060101
B29C067/00 |
Claims
1. A rotation device adapted for use in forming fiber-reinforced
composite parts, said rotation device comprising: a turntable for
rotating a mold thereon; and an actuator for supporting said
turntable, and for providing reciprocating motion to said mold,
wherein said turntable and actuator simultaneously rotate and
reciprocate said mold during a deposition of materials therein to
provide improved densification of the final formed composite
part.
2. The rotation device of claim 1, wherein said actuator is a
linear actuator.
3. The rotation device of claim 2, further comprising air cylinders
for reciprocating said mold in a +X and -X direction.
4. A method of improving densification of a formed composite part
employing a rotation device adapted for use in forming
fiber-reinforced composite parts, said method comprising the steps
of: rotating a mold on a turntable; and providing reciprocating
motion to said mold with an actuator for supporting said turntable,
whereby said turntable and actuator simultaneously rotate and
reciprocate said mold during a deposition of materials therein to
provide improved densification of the final formed composite
part.
5. The method of claim 4, wherein said materials are mixed fibrous
and binder materials and wherein said simultaneous rotation and
reciprocation provide substantially uniform dispersion of said
fibrous and binder materials.
6. The method of claim 4, wherein said actuator is a linear
actuator and wherein said rotation device further comprises air
cylinders for reciprocating said mold in a +X and -X direction.
7. The method of claim 4, further comprising the step of: adjusting
said linear actuator to move said mold up to four inches to a side
of a centerline of a cyclone dust collector.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of application Ser. No.
10/315,464, filed Dec. 10, 2002. Ser. No. 10/315,464 is in turn a
divisional of application Ser. No. 09/527,322, filed Mar. 16, 2000,
now U.S. Pat. No. 6,521,152. Benefit of the filing dates of these
two parent applications is claimed under 35 U.S.C. .sctn. 120. The
entire disclosure of each of the parent applications is
incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to a method and apparatus for
forming fiber reinforced composite parts.
BACKGROUND OF INVENTION
[0003] Fiber-reinforced composite structures, such as carbon-carbon
composites for example, are widely used as friction materials for
heavy-duty brakes in automobiles, trucks, and aircraft. This is
because they exhibit high thermal conductivity, large heat
capacity, and excellent friction and wear characteristics and thus
can provide excellent performance.
[0004] However, past manufacturing processes for producing these
fiber-reinforced composite structures were often lengthy
undertakings, requiring months to fabricate a single part. In one
example, a typical fiber-reinforced composite part such as a
preform was prepared by a non-woven process that involved
needle-punching layers of carbon fibers, a slow, time-consuming
process. When two or more layers of fibers are needle punched
together by metal needles having barbs on one end, the barbs
commingle fibers from a particular layer into successive layers.
The commingled fibers essentially stitch the layers of fabric
together. This non-woven technology achieved preform densities on
the order of about 0.5 g/cc. To obtain a final composite part, the
preform was subsequently infiltrated with a matrix binder material
via a chemical vapor deposition ("CVD") or chemical vapor
infiltration ("CVI") process, for example. CVD and CVI are used
interchangeably for the purposes of the present application.
[0005] In another process, a preform was prepared by building up
successive layers of pre-impregnated carbon fiber fabric. Tows (the
term "tow" is used hereinafter to refer to a strand of continuous
filaments) of carbon fiber were woven into a two-dimensional weave,
and thereupon dipped into a liquid batch to impregnate the weave
with a liquid resin. The resin-impregnated weave was then pulled
between rollers to form a sheet of pre-impregnated carbon-fiber
fabric. A plurality of desired shapes were then cut out of the
sheet material and stacked within a mold, and subsequently cured
using heat and pressure to obtain the desired composite part.
However, the procedure for impregnating a binder into the pores of
the fibrous material was often repeated many times, which
cumulatively decreased porosity of the resultant composite. For
this reason, it often took a term of several months to obtain a
final product, causing the product to be extremely expensive.
Further, much material was wasted in order to obtain the final
product.
[0006] Several processes have been developed in order to reduce
overall processing time needed to manufacture a fiber reinforced
composite part. One process, a "random-fiber process", uses
entirely tow material. Somewhat similar to the pre-impregnating
method described above, in the random-fiber process a continuous
tow of fiber is dipped through a resin bath and then chopped up,
whereupon the resin coated chopped fibers are placed into a mold
for curing by heat and pressure. However, the steps of dipping the
continuous tow are performed separately from the molding and curing
required to create the composite part, thereby extending the
"process cycle" of manufacturing the composite part.
[0007] Another method involves a molding compound process whereby
chopped fibrous material are mixed with a resin so as to form a
continuous sheet of mixed material. A plurality of desired shapes
are then cut out of the sheet material and stacked within a mold,
and subsequently cured using heat and pressure to obtain the
desired composite part. Again, this process requires extensive time
and wastes material in order to obtain the final product.
[0008] A further process developed to shorten the manufacturing
time involves using a liquid slurry to mix the fibrous material
with a resin powder, as illustrated in U.S. Pat. No. 5,744,075 to
Klett et al. However, the fibrous material needs to be chopped into
small pieces (on the order of 1/4 to 1/2 inch (about 0.6-1.3 cm))
so as to attain a uniform mix with the resin powder in the slurry.
Thus, longer chopped fibers (1-11/2 inches (about 2.5-3.8 cm)) do
not work well in this liquid slurry method, since a uniform
dispersion of fibrous material and resin powder in the slurry
cannot be attained with the longer chopped fiber lengths. The
longer fibers tended to "ball-up" during mixing with the powdered
resin and during deposition into the mold, making it difficult to
obtain a uniform end product. Moreover, this "balling effect"
directly contributed to the "loftiness" of the preform, a
disadvantageous result of the water slurry method since a lofty
preform was difficult to control within the mold. Additionally, an
excess step of drying the preform was required (i.e., removing the
water from the preform in the heating step is required before
pressing the materials in the mold into a composite part). Further,
and similar to the above methods, a continuous tow of fibrous
material needs to be chopped before mixing the fibrous chop with
the resin binder.
[0009] Recent developments have introduced a method and apparatus
that combines chopped fibers and a powdered resin utilizing a
dry-blending process. Such a dry-blending process and apparatus 100
is illustrated in the rough schematic diagram of FIG. 1. Apparatus
100 includes a first lower enclosure 101 connected to a second
upper enclosure 102 via a neck portion 119. First enclosure 101 has
an adjuster 120 connected thereto which houses compressed air lines
121 and 124 for feeding air jets 122. Second enclosure 102 houses a
screen 126, and has a funnel 132 and vacuum line 135 connected
thereto.
[0010] In FIG. 1, chopped tow 115 is loaded into first enclosure
101, where air jets 122 feed compressed air into the chopped tow
115 within first enclosure 110. The compressed air fed via
compressed air lines 121 and air jets 122 enters below the level of
chopped tow in first enclosure 101. This compressed air forces the
chopped tow 115 into upper portion 117 of first enclosure 101 such
that the individual fibers of the chopped tow 115 are entrained in
air and further broken-up (defibrillated) into smaller strands or
filaments 118. Adjuster 120 maintains the compressed air jets 122
at a level equal to or below the chopped tow 115 within first
enclosure 101.
[0011] The broken-up fibers 118 entrained in air in the upper
section 117 are then forced through neck portion 119 into a second
enclosure 102, whereby they are mixed with a powdered resin 130 fed
through at funnel 132 of second enclosure 102. The powder resin 130
mixes with the broken-up fibers in a powder and fiber mixing region
140, whereupon the "mixed materials" settle at the bottom of second
enclosure 102 to form a layer which constitutes the building-up of
a preform 125. The mixed materials fall due to a vacuum 135 being
applied to the bottom of second enclosure 102 which removes the
bulk of the air volume in second enclosure 102, thereby allowing
the mixed materials to fall and condense at the bottom of second
enclosure 102 on top of screen 126.
[0012] The "dry-blending" apparatus of FIG. 1 provides a medium for
mixing the powder 130 with the fibrous material (chopped tow 115)
to attain a uniform mixture of the binder material with the fibrous
material. However, in the apparatus 100 of FIG. 1, the proportions
of chopped fiber and binder material have to be first individually
weighed out to obtain the proper proportions, before being loaded
in enclosures 101 and 102 to be mixed in mixing region 140.
Further, apparatus 100 of FIG. 1 is limited to a single-batch
process, i.e., to make one final fiber-reinforced composite part,
the individual proportions for each fibrous material and binder
material have to be weighed and added individually for each preform
made.
[0013] Yet a further process to shorten the manufacturing cycle
time of a composite part is illustrated in U.S. Pat. No. 5,236,639
to Sakagami et al. The objective of this process is to provide
excess carbon material to fill pores in the matrix material during
subsequent curing and carbonization steps, thus producing a
carbon-carbon composite material that requires no repetition of
production steps including any further densification of the
composite material. This involves mechanically mixing a matrix
carbon material and carbon fibers in proportions that are
determined on the basis of the carbonization ratio of the matrix
material and on the basis of the desired ratio of fibers to be
contained in a resultant end product. However, such a process
requires the use of excess carbon matrix material, a curing step
under pressure after formation of an intermediate-formed part such
as a preform or mold, and also requires subsequent carbonization
and graphitization of the cured intermediate part, both under
pressure, to obtain the final fully-densified composite part. Of
course, no further production steps are required or repeated,
including densification of the composite material. However, it is
costly and time consuming to perform the curing, carbonization and
graphitization all under pressure.
[0014] Therefore, what is desired is a method and apparatus which
would feed, blend, and deposit various lengths of chopped fibrous
and binder materials into a mold of a desired final shape, wherein
the raw fibrous materials and binder materials are combined in a
single step, followed by consolidation of the materials. The
resultant preform would not require any curing or carbonization
under pressure during the follow-on heating processes to
manufacture the final composite part. Such a method and apparatus
would provide fiber-reinforced composite parts with densities that
are higher than achieved with current technologies, and would
decrease overall cycle time to a finished composite part. The
method can be used to provide an intermediate preform product that
is subsequently stabilized, carbonized, optionally heat treated,
densified, and final heat treated to provide a carbon-carbon
composite material.
SUMMARY OF THE INVENTION
[0015] The present invention provides a method and apparatus for
combining raw fibrous and binding materials in a single mixing
step, followed by consolidation so as to greatly shorten the
overall cycle time to a finished fiber-reinforced composite part.
In the method, chopped fibers, which can include single length or
multiple lengths of fibrous material, and a powdered resin binder
material are combined in a continuous process at predetermined
ratios, mixed together, and deposited into a mold having the shape
of the final product. Specifically, the chopped fibrous materials
and binder materials are deposited sequentially onto a belt
conveyor so that the materials are successively layered in a
predetermined ratio, and subsequently mixed to achieve uniform
dispersion throughout. The "mixed materials" are then deposited
into a rotating mold to further ensure uniform dispersion of
fibrous and binder materials, wherein impregnation of the fibrous
materials with the binder material occurs in-situ as the uniformly
mixed materials are heated in the mold, and subsequently compacted
to obtain the final desired shape of the preform. The resultant
preform requires no excess use of matrix material, no curing or
carbonization under pressure in the follow-on heating processes
required to obtain the intermediate fiber-reinforced composite
part.
[0016] Objectives of the present invention will become more
apparent from the detailed description given hereinafter. However,
it should be understood that the detailed description and specific
examples, while indicating preferred embodiments of the invention,
are given by way of illustration only, since various changes and
modifications within the spirit and scope of the invention will
become apparent to those skilled in the art from this detailed
description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The present invention will become more fully understood from
the detailed description given hereinbelow and the accompanying
drawings, wherein like elements are represented by like reference
numerals, which are given by way of illustration only, and thus are
not limitative of the present invention and wherein:
[0018] FIG. 1 illustrates a conventional dry-blending
apparatus;
[0019] FIG. 2 is a schematic diagram of the equipment and major
components used in accordance with the preferred embodiment of the
present invention;
[0020] FIG. 3 illustrates a device to rotate the mold in accordance
with the preferred embodiment of the present invention;
[0021] FIG. 4 illustrates general processing steps performed in
accordance with the preferred embodiment of the present
invention;
[0022] FIG. 5 illustrates the feeding system in accordance with the
present invention,
[0023] FIG. 6 illustrates the layer deposition step of FIG. 4 in
more detail;
[0024] FIG. 7 illustrates the mixing step of FIG. 4 in more
detail;
[0025] FIG. 8 illustrates the mold deposition step of FIG. 4 in
more detail;
[0026] FIG. 9 illustrates the consolidation step of in more detail;
and
[0027] FIG. 10 illustrates the follow-on heating and densification
step of FIG. 4 in more detail.
DETAILED DESCRIPTION OF THE INVENTION
[0028] The method and apparatus in accordance with the preferred
embodiment enables the production of fiber-reinforced composite
parts suitable for use in manufacturing various components and
high-friction applications such as automobile, truck, and aircraft
brakes. By combining fibrous materials with a binder material in a
single apparatus, a fiber-reinforced composite part with improved
friction and wear performance can be produced in fewer processing
steps as compared to the current techniques of the related art used
to fabricate fiber-reinforced composite materials, thereby
providing increased reliability and reduced process cycle times.
Additionally, the preferred embodiment allows for more complete
control over defibrillation of carbon fibers so as to obtain a
sufficient balance between strength/wear properties with adequate
dispersion of mixed carbon fiber and matrix resin materials, as
compared to other manufacturing processes such as using a liquid
slurry, for example.
[0029] FIG. 2 illustrates a schematic diagram of the equipment used
in accordance with the preferred embodiment. Referring to FIG. 2,
the fiber-reinforced composite apparatus 200 includes a series of
feeders 210, 220, and 230, and a constituent transport arrangement,
preferably a conveyer belt 205, which is situated below the feeders
and adjacently mounted to a first inlet 241 of a material handling
fan 240. An outlet 242 of the material handling fan 240 connects to
inlet 249 of a cyclone dust collector 260 via line 245. A return
air fan 250 takes a suction off the cyclone dust collector 260 at
point 251. Additionally, the return air fan 250 includes an outlet
252 which is connected to a second inlet 243 of material handling
fan 240 via a line 255. The cyclone dust collector 260 is arranged
above a mold 270 that rests on a rotational device 271. Further,
fiber-reinforced composite apparatus 200 includes a dust filter fan
280 that takes a suction from mold 270 at 275.
[0030] Feeder 210 may feed reinforcing fibers between about 0.5-1.5
inches (about 1.3-3.8 cm) in length at a first predetermined rate.
Preferably, feeder 210 feeds 1-inch (2.54 cm) fibers (hereinafter
"reinforcing fiber"); however, reinforcing fibers longer than 1.5
inches (3.8 cm) may be used. Feeder 220 may feed milled and short
fibers between about 100 .mu.m and 1/2'' (1.27 cm) in length, and
preferably feeds 100 .mu.m (0.1 mm) length fiber (hereinafter
"milled fiber") at a second predetermined rate. The milled fiber
acts as a "filler" fiber to fill in gaps between the longer
reinforcing fibers. Feeder 230 can be a resin feeder which feeds a
resin binder material at a third predetermined rate. Alternatively,
the fibrous materials from feeders 210 and 220 can be the same size
(for example, equal length fibers up to about 1.5 inches (3.8 cm)
in length). It is advantageous to use a mixture of longer and
shorter fibers to obtain better friction and wear properties while
still maintaining adequate strength in the finished component. The
longer fibers provide the strength, while the shorter fibers fill
in gaps between the longer fibers and the matrix material to help
increase the final density of the intermediate-formed part/preform,
and/or of the final composite part.
[0031] The chopped reinforcing and milled fibrous materials can be
polyacrylonitrile (PAN) based carbon fibers, preferably to be used
for fabrication of carbon-carbon composite parts. However, glass
fibrous material or other reinforcing fibrous material such as
metal fibers and synthetic fibers, for example may be used,
depending on the resultant composite part to be fabricated. The
binder material can be a high-carbon yielding mesophase pitch resin
matrix (i.e., in powdered form; however, phenolic resins and other
thermoplastic or thermosetting resin materials in powdered form may
be used as the binder material, depending on the resultant
composite part to be fabricated.
[0032] The fibrous chop and resin binder fed from feeders 210, 220,
and 230 are deposited onto a belt conveyor 205 as a series of
continuous, stacked layers. This provides for a semi-continous
process whereby the feeders contain a sufficient amount of
materials to produce many composite parts. The stacked layers
travel along belt conveyor 205 to be dispensed into a material
handling fan 240. Material handling fan 240 mixes the fibrous and
binder materials, while partially or fully defibrillating the
chopped fiber materials from feeders 210 and 220. Alternatively,
the fibrous chop and resin from the feeders may be fed directly
into the material handling fan without a belt conveyer.
[0033] Material handling fan 240 further provides a volume of air
flow to convey the "mixed materials" via a line 245 to cyclone dust
collector 260. The cyclone dust collector 260 receives the
air-entrained mixed materials and separates the solid particles of
the materials from the air used to convey them. Return air fan 250
takes a suction of cyclone dust collector 260 to circulate the bulk
of the air volume coming from line 245 back to the material
handling fan 240 via line 255, allowing the remaining mixed
materials to exit the bottom of the cyclone dust collector 260 into
mold 270. Dust filter fan 280 removes any residual dust created by
the deposition of the mixed materials into the mold 270, and
deposits dust particles into dust collector 285. To further ensure
uniform deposition of the mixed materials from cyclone dust
collector 260 into mold 270, the mold can be arranged on a rotation
device 271.
[0034] FIG. 3 illustrates a rotation device 271 to rotate mold 270
in accordance with the preferred embodiment of the present
invention. Rotation device 271 includes a turntable 272 mounted
upon a support 274 and connected to an electric motor 276 by a
rotating spindle 273. Support 274 (along with turntable 272 and
electric motor 276) can be jogged back and forth via air cylinders
277, and rests on a linear actuator 278. The entire assembly is
supported by a table lift 279.
[0035] Turntable 272 and the combination of the air cylinders 277
and linear actuator 278 provide rotational and linear motion for
mold 270 during the deposition process. In operation, turntable 272
is powered by electric motor 276 via the spindle 273 to rotate the
mold. Simultaneously with this rotation, mold 270 may be
reciprocated in a +X and -X direction for the duration of the
deposition process by air cylinders 277, the cylinders essentially
jogging the support 274 supporting the turntable 272. The mold 270
is aligned to the outlet of the cyclone dust collector 260 such
that it can be moved up to four (4) inches to either side of the
centerline of the cyclone dust collector 260 by adjusting linear
actuator 278 (for example, the linear actuator "distance" can be
set at positions such as -1.0'' (-2.54 cm) or +2.5'' (+6.35 cm)
from the centerline of the cyclone dust collector 260). The jogging
action imparted by air cylinders 277, together with the rotation
imparted by turntable 272, ensures that the mixed material falling
from the bottom of the cyclone dust collector 260 is uniformly
dispersed in the mold 270 as the mold 270 fills to a desired level,
in preparation for a subsequent consolidation step to be discussed
later below.
[0036] FIG. 4 illustrates a process by which fibrous material and
binder materials are combined to manufacture a fiber-reinforced
composite part in accordance with the preferred embodiment. All
parameters for operation are initialized prior to operating the
fiber-reinforced composite apparatus 200 (Step S1). This includes
determining the rates at which the fibrous and binder materials
will be gravimetrically fed from feeders 210, 220, and 230,
respectively, onto conveyor belt 205. These rates are determined by
a programmed processor (not depicted) running a software
application, and are based on the desired ratios of these materials
in the final formed fiber-reinforced composite part. Additionally,
fan speeds are pre-set for each of the material handling fan 240,
return fan 250, and dust filter fan 280, and preferably do not
change throughout the entire manufacturing operation. Further, the
belt conveyor speed for belt conveyor 205 and the turntable
rotational speed and linear actuator distance for rotation device
271 are set, and preferably do not change throughout the entire
manufacturing operation.
[0037] FIG. 5 illustrates a feeding system in accordance with the
present invention. Once the predetermined ratios are set, the
gravimetrical feeding of the chopped fiber and resin binder
material is controlled by a feeding system 290. For example, as
illustrated in FIG. 5, the feeding system 290 comprises the
individual feeders 210, 220 and 230, a common feeder controller 235
and a set of load cells 211, 221 and 231 for each feeder. Each
feeder has an electric motor 213, 223, 233 which drives a
corresponding feeding mechanism or feed screw 212, 222 and 232
(such as an auger or roller with pins) to propel fibrous material
from a storage hopper to a desired location (i.e., the belt
conveyor 205). The respective motors are driven by an electrical
signal received via input lines 236 by feeder controller 235, the
signal ranging from 0-100% motor speed.
[0038] As shown in FIG. 5, each feeder 210, 220 and 230 rests on a
corresponding sensitive load cell 211, 221 and 231. These load
cells measure the weight of the feeder in small time increments
(several times per second) and sends a signal to feeder controller
235 via one of the input lines 236 as the feeder is operating in
the gravimetric mode. The feeder controller 235 calculates a feed
rate over several of these time increments, and adaptively adjusts
the motor speed of the feeder to compensate by sending a signal via
output lines 237 to the respective motors 213, 223 and 233. Thus,
the average feed rate required to obtain the desired ratio can be
achieved over the operating period to convey and mix materials for
the resultant preform. Although in the preferred embodiment, a
single feeder controller 235 preferably monitors all feeders
simultaneously during operation, each feeder can have its own
individual feeder controller.
[0039] Once all parameters have been initialized, the operation
proceeds with sequential deposition of chopped fibrous materials
and resin binder material onto conveyor belt 205 (Step S2). The
layers are then mixed in a mixing step by material handling fan 240
(Step S3) and conveyed in an air volume to cyclone dust collector
260. There, the mixture of chopped fibrous materials and resin
binder is separated from the air volume and deposited into the
rotating mold 270 (Step S4). Once the mold is filled to a desired
level, a drag chain conveyor (not shown in FIG. 2 but similar to
belt 205) is provided to transport the constrained mold of mixed
material to be consolidated. This provides a semi-continous process
of part fabrication, since the feeders contain sufficient material
to make many individual parts. Thus, when one "filled" mold is
conveyed away from underneath cyclone dust collector 260, another
"empty" mold moves in and the filling cycle is repeated.
[0040] Once a mold 270 is filled to a desired level and removed
from underneath the cyclone dust collector 260, a consolidation
process is performed by heating for in-situ impregnation of the
fibrous material with the now softened binder resin, and
subsequently compacting the ingredients in mold 270 to obtain an
intermediate fiber-reinforced composite part of a desired shape
(Step S5). Thereafter, the intermediate composite part or preform
is ejected from the mold and subjected to follow-on heating and
densification treatments so as to obtain a final, fully-densified
composite part (Step S6).
[0041] FIGS. 6-10 illustrate the steps of FIG. 4 in more detail. In
FIG. 6, Steps S11-S14 correspond to Step S2 of FIG. 4. In FIG. 7,
Steps S15-S17 correspond to Step S3 of FIG. 4. In FIG. 8, Steps
S18-S20 correspond to Step S4 of FIG. 4. In FIG. 9, Steps S21 and
S22 correspond to Step S5 in the process outlined in FIG. 4; and in
FIG. 10, Steps S23-S28 correspond to Step S6 of FIG. 4.
[0042] Referring to FIG. 6, once all parameters have been
initialized (completion of Step S1 in FIG. 4), the operation begins
with the first feeder 210 gravimetrically depositing the
reinforcing fibers at a first predetermined rate onto belt conveyor
205 (Step S11). The milled fibers and resin binder material from
feeders 220 and 230 each have a staggered start such that the
milled fiber chop and resin binder materials are successively and
gravimetrically deposited on top of the reinforcing fiber chop as
the conveyor belt 205 passes underneath (Steps S12-S13). This forms
a continuous tri-layer of materials on conveyor belt 205, which is
subsequently dispensed into a material handling fan 240 (Step
S14).
[0043] Referring to FIG. 7, the mixing step S3 carried out by
material handling fan 240 has several purposes: it provides the air
flow which will convey the combination of fibrous chop and resin
binder material to the mold 270. More importantly, it mixes
together the layered materials (Step S15) while simultaneously
defibrillating the reinforcing and milled fibrous chop materials
into smaller fiber strands (Steps S16). The defibrillation step
further breaks up the reinforcing fibers and milled fibers into
smaller strands to promote even better mixing with the resin binder
material in material handling fan 240.
[0044] The use of material handling fan 240 allows control over the
amount of desired defibrillation. Particularly, and unlike
conventional liquid slurry processes for example, where
defibrillation is complete in breaking up a fiber tow into
individual filaments, material handling fan 240 allows for a wide
range of defibrillation, breaking up the chopped fibrous material
into smaller filament bundles ranging from hundreds of filaments to
almost 10,000 filaments, thereby preserving strength while
providing improved wear properties for the resultant finished
composite part. After mixing and defibrillation, the "mixed
materials" are conveyed via line 245 to a cyclone dust collector
260 (Step S17).
[0045] Referring to FIG. 8, the cyclone dust collector 260 acts as
a separator, in conjunction with a return air fan 250.
Specifically, the "fluid" entering cyclone dust collector 260 is a
mix of the defibrillated fibrous chopped materials and resin binder
materials entrained in a bulk volume of air. The return air fan 250
acts as a vacuum to circulate the bulk of this air volume back to
the material handling fan 240 via a line 255. This air removal
process allows the mixed materials to gently exit the bottom of the
cyclone dust collector 260 so that they are deposited into the
rotating mold 270 (Step S18).
[0046] To further promote uniform dispersion of the mixed materials
in to the mold 270, the mold is rotated during deposition by
turntable 272 (Step S19). As the mold fills with the mixed
materials, a dust filter fan 285 simultaneously creates a suction
on mold 270 that removes any entrained dust that is present when
the mixed materials fill the mold 270 (Step S20).
[0047] Referring to FIG. 9, once the mold 270 is filled to a
desired level, it is placed in an oven and heated to a temperature
sufficient to soften and/or melt the resin binder material,
preferably at about 300.degree. C. and 1 ATM (Step S21). After
heating is completed, the mixed material is compacted using a
suitable method such as a hydraulic press, for example, to
impregnate the fiber tows and to obtain the desired final shape of
the intermediate composite part/preform (Step 22).
[0048] Referring to FIG. 10, the preform is cooled in the mold 270
until the resin binder material solidifies, and is then ejected
from the mold 270. (Step S23). The preform then undergoes oxygen
stabilization (Step S24) whereby it is heated in circulating air
(preferably about 170.degree. C.) for an extended period.
Alternatively, this step could be performed in a cyclic pressure
device (sometimes called an iron lung), by thermally shocking the
preform to develop cracks, or by subjecting the preform to a high
pressure oxygen treatment at about 40 psi. Following oxygen
stabilization, the preform is subjected to carbonization, where it
is slowly heated (preferably between 1.degree./min to 1.degree./hr)
to about 600-900.degree. C. in nitrogen at atmospheric pressure
(Step S25). Following carbonization, the preform undergoes a
chemical vapor deposition (CVD)/chemical vapor infiltration (CVI)
process for up to about 600 hours to achieve full density (Step
S26). CVD/CVI includes approximately 50-200 hours of CVD/CVI
infiltration followed by at least 400 hours or more of CVD/CVI
cycles, or densification can be performed by resin transfer molding
(RTM) cycles, to fully densify the preform. A final heat treat is
performed in a standard temperature range of 1600-2200.degree. C.
thereafter to obtain a near final (machining is also typically
required) fiber-reinforced composite part such as a carbon-carbon
composite aircraft brake disc (Step S27).
EXAMPLE
[0049] Several test parts were fabricated using the above method
and apparatus, specifically nine (9) stator and six (6) rotor-size
parts for 767 aircraft made by the BOEING Corporation. For a
stator, 3.976 pounds (1807 g) of 1-inch (2.54 cm) chop length
carbon fiber (grade X9755) and 1.454 pounds (661 g) of milled
carbon fiber (grade 341, each grade of fibers marketed by
FORTAFIL), and 7.176 pounds (3262 g) of AR mesophase pitch resin
(pellets ground into powder) marketed by the MITSUBISHI Corporation
were dispensed onto a belt conveyer over approximately a thirteen
(13) minute period (a total of 12.606 pounds or 5723 g of "mixed
material" was deposited in the mold over the time period to form a
preform). The material handling fan was operating at 80% of the
maximum motor speed, the return air fan at 37% of maximum motor
speed and dust collector fan at 60% of maximum motor speed. The
mold was located at a 2.5 inch (6.35 cm) linear position from the
centerline of the cyclone dust collector and was turning 6 rpm
during deposition.
[0050] For this example, the stator part was built up in two equal
batches, due only to the current limitation of the 1-inch chopped
fiber feeder's hopper capacity. After the fibrous and binder
materials were mixed and dispensed in the mold, the mold was placed
into an air circulating oven and heated to a temperature of
315.degree. C. for four hours. After heating, the preform was
compacted with 30 tons of force until mechanical stops were met.
The preform thickness was maintained at 1.405'' (3.569 cm) until
cool, and then was removed from the mold. The density of the 5490 g
weight preform was measured at 1.35 g/ cc.
[0051] Therefore the method and apparatus in accordance with the
preferred embodiment enables the production of fiber-reinforced
composite parts suitable for use in manufacturing various
high-friction components for applications such as automobile,
truck, and aircraft brakes. The density of the envisioned composite
parts are between 1.2 and 1.5 g/cc. By combining low-cost chopped
PAN-based carbon fibers with a high carbon yielding mesophase pitch
matrix resin, a carbon/carbon composite material with improved
friction and wear performance can be produced in fewer processing
steps as compared to current techniques used to fabricate
fiber-reinforced composite materials, thereby providing increased
reliability and reduced process cycle times. Such friction
materials would typically have a density of at least 1.7 g/cc.
[0052] The invention being thus described, it will be obvious that
the same may be varied in many ways. For example, the constituent
transport arrangement below feeders 210, 220 and 230 of FIG. 2 may
be a plurality of belt conveyors, each feeder having their own
designated belt conveyer to transport the respective materials to a
common mixing point. In another embodiment, a fourth feeder may be
added to the apparatus in FIG. 2 to deposit other performance
modifying additives which might be necessary in forming the
resultant composite part. These additives can include materials
such as metals, ceramic particles, graphite, cokes, curing agents,
mica, carbon oxidation inhibitors, glass or polymer films, or any
other agents or materials which improve friction and wear
characteristics of a composite part and/or to further strengthen
the fibrous/binder materials used to fabricate the composite part.
Alternatively, these additives may be mixed in with the resin
binder material at feeder 230 to conserve space.
[0053] Additionally, in lieu of or in addition to performing oxygen
stabilization (Step 24) of the intermediate part (FIG. 9), a
support fixture may be utilized during carbonization (Step S25) to
prevent bloating and maintain part shape. Further regarding FIG. 9,
an optional heat treat (HTT--High Temperature Treatment) may be
performed between carbonization (Step S25) and CVD/CVI (Step S26),
heating the preform at about 1.degree./min to about 1800.degree. C.
Such variations are not to be regarded as a departure from the
spirit and scope of the invention, and all such modifications as
would be obvious to one skilled in the art, are intended to be
included within the scope of the following claims.
* * * * *