Plastic and nonmetallic article shaping or treating: processes – Forming articles by uniting randomly associated particles – Projecting particles in a moving gas stream
Reexamination Certificate
2000-03-16
2003-02-18
Theisen, Mary Lynn (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Forming articles by uniting randomly associated particles
Projecting particles in a moving gas stream
C264S029100, C264S122000
Reexamination Certificate
active
06521152
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for forming fiber reinforced composite parts.
2. Description of the Related Art
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.
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 was prepared by a non-woven process that involved needle-punching layers of carbon fibers to form a preform, 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 fiber 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.
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 fabric, and thereupon dipped into a liquid bath to impregnate the fabric with a liquid resin. The resin-impregnated fabric was then pulled between rollers to form a sheet of pre-impregnated carbon-fiber fabric. After impregnation, the fabric was dried and b-staged under low heat. 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. In order to produce a carbon-carbon component, the composite part is carbonized which creates internal porosity. Multiple infiltration cycles using CVD or resin were required to achieve final density of the composite part. 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.
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, dried, and then chopped to a desired length. The resin coated chopped fibers are then placed into a mold and cured using heat and pressure. However, the steps of impregnating 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.
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.
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 ¼ to ½ 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 (1-1½ 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 into a composite part).
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.
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
101
. 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
.
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
.
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.
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 th
Gonsowski Thaddeus W.
Hudalla Vernon R.
Kriskovich Dean S.
LaForest Mark L.
Murdie Neil
Honeywell International , Inc.
Palguta Larry J.
Theisen Mary Lynn
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